text:
\section{Introduction}

IMDs are the particular type of medical devices that are implanted in the patient's body, to diagnose, monitor, or treat a variety of conditions, diseases and injuries.
For example, insulin pump can monitor and deliver insulin to treat diabetes, pacemaker regulate the beating of the heart using electrical impulses, neurostimulator sends electrical signals to the spine to treat chronic pains.
According to a recent report published by Allied Market Research \cite{market}, the global IMD market is projected to reach \$116.3 billion by 2022.
However, IMDs are threatened by both external cyber attacks and internal flaws in software or firmware design. These security vulnerabilities allow an adversary to steal sensitive medical data, reset the configuration parameters, and issue unauthorized commands to an IMD, which could cause fatal consequences.

IMDs are equipped with a radio transceiver to communicate with the external IMD programmer. The IMD programmer is the specific device used to collect the medical data from IMDs and issue operation/configuration commands to deliver drug, change dosage, etc. With the wireless interface enabled, IMDs can be accessed by an authorized operator in physical proximity via the IMD programmer  (e.g., an eligible medical staff or the patient himself/herself).
However, the wireless communication and networking capabilities of IMDs turn out to be the major sources of security vulnerabilities.
Due to the broadcast nature of wireless channels, all messages exchanged between the IMD and the programmer can be captured by eavesdroppers. This would not only expose the patient privacy like he/she is carrying an IMD to treat a certain disease, but also lead to other classic wireless attacks such as the forging, tampering, and replying of the messages.
Existing research works have presented the breaches in a number of commercial IMDs \cite{SP2008, HealthCom2011, hack2011, hack2016, Jack}, including the implantable cardioverter defibrillator (ICD), insulin pump and pacemaker. It has been demonstrated how an adversary can reverse-engineer the communication protocol and take full control of the IMD using a software radio.

Intuitively, to secure the communications between the IMD and the IMD programmer, a pair of symmetric keys must be shared between the two parties to encrypt their wireless communications.
Unlike traditional electronic devices, the power supply of IMDs is highly constrained. The wireless charging technologies for IMDs still need lots of practical testing and clinical trials to ensure that no negative effect will be caused to human organs and tissues. Additionally, the replacement of an IMD or its battery requires invasive surgery. Hence, commercial IMD products are designed to last for 5 to 10 years. The energy consumption of IMDs should be minimized, by avoiding complicated cryptographic computations and long-range wireless communications.
Currently, only symmetric cryptography is considered for the data encryption in IMDs.

In this paper, we propose a novel proxy-based access control scheme for IMDs, in which the communications between the IMD programmer and the proxy are conducted through an audio cable rather than the conventional wireless channels. The proposed scheme employs the attribute-based access control model, which grants access based on the attributes (i.e., qualifications) that the access requestor owns. Meanwhile, the access requestor is authenticated in our scheme, mainly to provide accountability in case of a medical dispute.

Our major contributions can be summarized as follows:

\begin{enumerate}[leftmargin=*]
\item We first comprehensively studied and analyzed various existing IMD access control schemes in terms of the access control architecture and access control model. We also took a full consideration of the special use cases that a good IMD control scheme should be able to handle.
\item Our proxy-based IMD access control scheme can greatly alleviate the computational overhead and power consumption of IMDs. The proxy communicates with the IMD programmer via the audio cable, which can defend against the wireless passive and active attacks. Unlike USB connection, communications through headphone jack does not require the patient to unlock the device for manual approval, which is a practical concern especially for patients who are unconscious.
\item Our scheme adopts the ciphertext-policy attribute-based encryption (CP-ABE) to provide a fine-grained access control over the qualifications of the programmer operator. Specifically, the proxy encrypts the temporary session key with a specific access policy and sends the ciphertext to the IMD programmer. If the programmer operator owns the set of required attributes (qualifications), the temporary session key can be correctly retrieved.
\item We implemented our scheme on real emulator devices: the IMD is emulated by TelosB mote, the proxy is emulated by smartphone, and the IMD programmer is emulated by Rasberry Pi 3. The evaluation results show that the proposed scheme is lightweight and effective.
\end{enumerate}

\section{Background}

IMD manufacturers are supposed to give equal attentions to the security of their products, as to their functionalities. However, when facing security vulnerabilities, the manufacturers that should take full responsibility seem to be numb towards the potential security problems.
In May 2014, an independent security researcher Billy Rios discovered 100 vulnerabilities in the communications system software of several different versions of infusion pumps made by the medical device company Hospira (HSP), which can be exploited by an attacker to hack into the pumps and change the dosage of medication to be delivered \cite{CNN}.
Rios immediately notified Hospira, but Hospira stayed silent on the issue until another researcher Jeremy Richards publicly disclosed the vulnerability in April 2015. Then, the U.S. Food and Drug Administration (FDA) and the Department of Homeland Security's Industrial Control Systems Cyber Emergency Response Team followed up the issue, and sent out advisories notifying hospitals of the danger of Hospira pumps and encouraging the transition to alternative infusion systems \cite{Hospira}.
Although the governmental agency FDA is obliged to supervise and regulate the IMD industry, it only provides guidelines and recommendations for IMD security which are not legally binding \cite{premarket, postmarket}. There is no checking or verification of new IMD products (software and hardware) and their cybersecurity documentations by a trusted agency.

The security and robustness of IMDs still rely on the research and development team of each individual manufacturers, who design access control schemes only specific to their own products.

\begin{figure*}[t]
\centerline{
\subfigure[Two-party Access Control]{\includegraphics[width=3in,height=1.4in]{architecturetwoparty.pdf}%
\label{fig:two}} %
\hspace{7mm}
\subfigure[Proxy-based Access Control]{\includegraphics[width=3.8in,height=1.5in]{architectureproxy.pdf}%
\label{fig:proxy}} %
}

\caption{IMD Access Control Architecture}
\label{fig:random}

\end{figure*}

\section{Motivation}

The security researchers have been seeking generalized and effective access control schemes for IMDs.
A variety of access control schemes have been proposed with different access control models and architectures. In addition, various assumptions have been made on the environmental settings and human factors.
In this section, we conduct a thorough analysis on all these aspects, and present how we are motivated to design our novel IMD access control scheme.

\subsection{Special Use Cases}
IMD access control is not a difficult problem under regular situations such as when the patient uses his/her own IMD programmer to access the IMD or when an acquainted doctor wants to access the IMD. However, it becomes much more complicated in some special but practical situations.

\subsubsection{\textbf{Medical Emergency}}
In medical emergency conditions such as when the patient falls sick while travelling out of town and needs immediate treatment, the patient has to verify the authenticity and qualification of the stranger who attempts to access the IMD (e.g., emergency medical technician). In a worse case, the patient may have been unconscious and is not able to manually verify the programmer operator. Hence, to deal with the emergency cases, an effective IMD access control scheme requires:

\begin{enumerate}[leftmargin=*]
\item All eligible medical personnels should have access to the IMD, regardless of whether they have been granted access before or if the patient is acquainted with them.
\item The access decision can be made autonomously by the IMD, without the patient's involvement.
\item If the access is permitted, the IMD must first be paired up with the programmer so that a pair of symmetric keys are shared between them, to encrypt their communications.
\end{enumerate}

\subsubsection{\textbf{Internet Connection}}

Online authentication has been widely used in IT applications. Intuitively, offloading authentication to a dedicated server of a governmental health agency or hospital can greatly reduce the complexity of the access control computations running on IMDs \cite{online1, family}. This requires either the IMD (may be assisted by an external proxy) or the programmer to be able to connect to the Internet. However, Internet connection may not be always available, especially when the patient is located in a depopulated area with poor infrastructure.
Hence, a robust IMD access control scheme should not rely on online authentication.

\subsection{Adversary Model}

The common assumptions agreed by existing works regarding the capabilities of the attackers in IMD context include:

\begin{itemize}[leftmargin=*]
\item The adversary may be equipped with powerful software radio transmitter, hence is able to interact with the IMD in a long distance.
\item The adversary may obtain legitimate IMD programmer to access the IMD. Since IMD programmers are specialized devices running closed-source software programs, they are considered secure and cannot be hacked by the attacker.
\item The adversary cannot approach the patient within a security range (typically 10 cm), nor can the adversary make physical contact with the patient or the patient's personal belongings, deterred from leaving criminal evidence such as fingerprint or video taken by surveillance cameras.
\end{itemize}

Generally, two types of adversaries may exist depending on the attack tactics: passive adversary and active adversary. A passive adversary will only eavesdrop on the wireless channel and listen to the packets exchanged between the IMD and the IMD programmer. Given an unencrypted radio channel, a passive attack can break the confidentiality of the data being transmitted. Almost all existing access control schemes require encrytions over the wireless channel, hence are resistant to passive attackers. An active adversary, however, can replay or tamper the packets. If the communication protocol between the IMD and the programmer is reverse-engineered, the active attacker is able to send unauthorized commands to the IMD (e.g. changing the configurations and parameters).
Based on the purposes of the attacks launched by an active adversary, we can classify active attacks into three categories:

\begin{itemize}[leftmargin=*]
\item \textbf{Unauthorized access.} The goal of this type of attacks is to bypass the access control scheme and gain access to the IMD without authorization.
\item \textbf{Resource depletion.} This type of attacks repeatedly requests for access to the IMD, causing the IMD to continuously running the access control computations, while its actual intention is to drain the battery power and reduce the lifetime of the IMD.
\item \textbf{Denial-of-service (DoS).} DoS attacks aim to disrupt the authorized access to the IMD, by interfering the communications between the IMD and the programmer. As the result, the IMD is unable to serve the incoming requests.
\end{itemize}

The resource depletion attacks and DoS attacks are not the focus of this paper.
Many previous works have proposed effective schemes to solve the resource depletion attacks on IMDs. Liu \emph{et al.} \cite{Liu} suggested to add an extra wake-up circuit before the main circuit of the IMD, which employs the passive RFID technology so as to harvest energy from the incoming signal to perform the verification of the wake-up code. The main circuit is waked up only if the wake-up code is correct. Gollakota \emph{et al.} \cite{SIGCOMM} presented \emph{Shield} to protect the confidentiality of the IMD, which utilizes a novel full-duplex radio design with a jamming antenna and a receive antenna, allowing it to  simultaneously receive the IMD's signal and jam the IMD's messages. Consequently, the programmer cannot receive IMD's packets or directly interact with it. Hei \emph{et al.} \cite{Hei2010} proposed to train the normal IMD access patterns and detect unusual access requests using the support vector machine (SVM).
The DoS attacks, however, have been evaded in existing works. Since the IMD is installed inside human body and has to interact with the programmer over a wireless channel, an attacker can just block/interfere its communications by jamming the wireless channel. Although the DoS attacks can be easily detected, there is no effective and low-cost solution to prevent it.

Instead, our paper focuses on enhancing the IMD access control in terms of lower complexity and better granularity.

\subsection{Access Control Architecture}

\subsubsection{\textbf{Two-party Access Control}} The basic IMD access control architecture is composed of two parties. As illustrated in Figure~\ref{fig:two}, the access object is the IMD and the subject is the programmer and its operator.

\subsubsection{\textbf{Proxy-based Access Control}}
To reduce the energy consumption of the IMD, the proxy-based access control architecture has been proposed \cite{Hei2010,IMDGuard,Cloaker,MedMon}, which take advantage of a proxy device to delegate the heavy computations for the IMD. As shown in Figure~\ref{fig:proxy}, the proxy can be a smartphone or other wearable device (e.g., smart watch, smart bracelet) with more sufficient computational resources and battery capacity.
The communications between the IMD and the proxy are protected by the lightweight symmetric encryption, which can be considered safe given that a pair of symmetric keys have been distributed and shared securely during the initial setup. This is reasonable since the initial setup is conducted either by the doctor when the IMD is implanted or by the patient when the proxy is used for the first time. It is very difficult for a malicious eavesdropper to overhear the key being transmitted to IMD at these specific moments. After pair-up, the proxy device will perform the access control on behalf of the IMD.

The proxy-based access control depends on the presence of the proxy device. In the particular case that the proxy is not detected in vicinity, the commonly used solution is that the IMD will enter the open-access mode, in which it only verifies the physical proximity of the programmer and permits the incoming access requests from any programmer nearby. This allows eligible physicians to be still able to access the IMD when the proxy is damaged or lost. Later, patient can pair up the IMD with a new proxy using its unique master key. A copy of this master key is provided to the patient by the IMD manufacturer along with the product manual. Meanwhile, the IMD manufacturer or the hospital should keep a backup copy of the master key for the patient to retrieve from.

However, we are aware that the usage of a proxy device may increase the attack surface of the IMD access control. Two types of attacks targeted at the proxy may exist:
\begin{itemize}[leftmargin=*]

\item \textbf{Jamming attacks.} The adversary may attempt to bypass the access control performed by the proxy, by selectively jamming the messages of the proxy to spoof the IMD about the absence of  the proxy.
\item \textbf{Malware-based attacks.} If the proxy is a general-purpose device like smartphone, the adversary can attack through a pre-installed malware. However, since Android OS and iOS both use sandboxing to isolate applications from each other, the malware cannot compromise the client application running the access control program. Instead, it can only eavesdrop or disrupt the communications between the proxy and the IMD/programmer.
\end{itemize}

\begin{figure*}[t]
\centering
\includegraphics[width=6.1in,height=1.3in]{wiredconnectionnew.pdf}
\vspace{-2mm}
\caption{Architecture of Access Control with Wired Connection}
\label{fig:wired}
\vspace{-4.5mm}
\end{figure*}

Our scheme employs the proxy-based access control architecture. Note that we do not specifically address the jamming-based spoofing attack - our access control scheme can nicely integrate with existing solution \cite{IMDGuard}. Additionally, we do not propose new access control method for the particular case in which the proxy is indeed absent. The existing coarse-grained proximity-based access control schemes \cite{CCS2013, HealthSec2012, Vibration, RasmussenCCS2009, hei2014, NFC2} can be adopted to protect the IMD under such circumstances.

\subsection{Access Control Model}

There are three types of traditional access control models that may be applied in IMD context.

\begin{itemize}[leftmargin=*]
\item \textbf{Identity-based access control (IBAC):} a user is permitted or denied access based on whether the user appears in the access control list that contains all of the authorized users.
\item \textbf{Role-based access control (RBAC):} the access permission is granted to a group of people who have a common role.
\item \textbf{Attribute-based access control (ABAC):} a set of attributes are created and assigned to subjects to enforce the access control. The access rule is defined as a mixing of attributes, and the decision is made by matching the attributes required.
\end{itemize}

In fact, most existing access control schemes are not designed under traditional models, but instead are simplified to accommodate the resource-limited IMD:
\begin{itemize}[leftmargin=*]
\item \textbf{Pre-shared secret based access control:} Some works assume that the IMD and the programmer have pre-shared secret like a master key \cite{SP2008} or rolling code \cite{HealthCom2011}. However, considering that the IMD may be accessed by any doctor in emergency situations, the pre-distribution of the secret of each IMD to all possible doctors is not practical.
\item \textbf{Proximity-based access control:} Some existing schemes manage access control solely based on physical proximity \cite{Hei2011, DenningCHI2010, CCS2013, HealthSec2012, Vibration, RasmussenCCS2009, hei2014, NFC2}. Although proximity is sufficient under the adversary model that the attacker will not approach the patient or make physical contact, it can only provide coarse-grained access control in which the identity of the requesting programmer operator is not authenticated.
\end{itemize}

To enable the authentication of the programmer operator, public-key cryptography must be used, which is feasible in the proxy-based access control architecture. However, considering that online authentication is unavailable and it is not practical to store the information of the huge number of eligible medical personnel into a local ACL on the proxy, IBAC model is not a viable option in IMD context.
Instead, ABAC allows the multi-dimensional rules/policies (not just based on the identity or a simple role) to be enforced for fine-grained access control, e.g., the specialty and affiliation of the physician, the certificate of the eligibility to operate a certain model of IMD, etc.

Therefore, our scheme employs the ABAC model to verify the qualifications of the access requestor. Meanwhile, to provide accountability in medical disputes, the proxy also authenticates the programmer operator and (if authorized) will record the access details (i.e., start time, end time) into a log as the evidence.

\subsection{Communications through Audio Cable}

\vspace{-1mm}
In the proxy-based access control architecture, the proxy needs to first build a secured connection with the IMD programmer. However, for general-purpose proxy device like smartphone, setting up a local connection with an external device (e.g. IMD programmer) via Bluetooth, NFC, or USB requires either the phone to be in the unlocked mode or the manual approval on the smartphone (also when the phone is unlocked).
This means such types of connections will be unavailable when the smartphone is locked and the patient has gone unconscious, as the programmer operator does not know the password to unlock the patient's phone.
According to the recent data from Duo Labs, 34\% Android smartphones are not secured with a lock-screen passcode \cite{lock}. In another word, about 2/3 of phone users have enabled the screen-locking function.
Therefore, we must choose a connection channel that is secure and available regardless of the patient's involvement.

We found that most modern smartphones have a headphone jack/port and most commercial IMD programmers have a USB port. A smartphone serving as the proxy can be connected with an IMD programmer through an audio cable. As shown in Figure~\ref{fig:wired}, the one end of the audio cable is plugged into the smartphone's headphone port while the other end links to an audio-to-USB adapter, which is then plugged into the USB port of the programmer. The audio-to-USB adapter is actually an external sound card with digital-to-analog converter (DAC) and analog-to-digital converter (ADC), hence the analog signal transmitting over the audio cable can be converted into digital data, or vice versa. The access control mobile application is always running in the background, ready to process the incoming requests from the audio cable.
The advantages of using the audio cable for communications include:
\begin{itemize}[leftmargin=*]
\item \textbf{No patient involvement required.} The data can be transmitted through audio cable in a plug-and-play manner, even if the phone is in the lock-up mode.
\item \textbf{Reduce the attack surface.} The packets exchanged are no longer exposed in the air. The remote adversary cannot overhear or jam the communications.
\item \textbf{Reduce the energy consumption.} Wireless transmissions consume at least 10 times more power than wired transmissions when providing comparable access rates and traffic volumes \cite{consumption}. Although both proxy and programmer are assumed to have sufficient power, energy saving becomes a critical concern when the phone battery is low.
\item \textbf{Proof of proximity.} The programmer operator needs to plug the audio cable into the headphone port of the smartphone, which proves the proximity of the operator to the patient.
\item \textbf{Low cost.} The audio cable connection does not require extra hardware. An audio-to-USB adapter only costs around \$10.
\end{itemize}

\section{Attribute-based Encryption}

Our scheme achieves attribute-based access control using the attribute-based encryption (ABE) technique. ABE is a one-to-many encryption method, which allows data to be encrypted based on a set of attributes, so that only those users who own the specified attributes are able to correctly decrypt. ABE is collusion-resistant, which can prevent colluding users to gain access by combining their associated attributes, if none of them possesses the full set of required attributes.

There are two major types of ABE schemes: Key-Policy Attribute-Based Encryption (KP-ABE) \cite{KPABE} and Ciphertext-Policy Attribute-Based Encryption (CP-ABE) \cite{CPABE}. In KP-ABE, users' secret keys are generated based on an access tree (i.e. access policy) whose leaves are associated with attributes, and the data are encrypted over a set of attributes. Since the access policy is embedded in the decryptor's secret keys, the data encryptor has no control over who can access the data. However, in the IMD access control context, the proxy must check the programmer operator's qualifications, which are formed as a policy composed of a specific set of attributes. This requirement can be satisfied by CP-ABE, in which the users' secret keys are generated over a set of attributes and the ciphertext specifies the access policy.

Therefore, we adopt CP-ABE to implement the IMD access control. Specifically, the proxy encrypts the verification message with CP-ABE and sends the ciphertext to the programmer. The programmer can successfully decrypt the message only if the operator's attributes satisfy the access policy specified in the ciphertext. In contrast, the adversaries cannot decrypt the ciphertext, even if they collude. The CP-ABE scheme consists of the following four fundamental algorithms:
\begin{itemize}[leftmargin=*]
\item \textbf{Setup$(k)$}. The Setup algorithm takes a security parameter $k$ as input and randomly picks two exponents, to calculate the public parameters $PK$ and the master key $MK$. $PK$ will be used for encryption, while $MK$ will be used to generate users' secret keys and is known only to the central authority.
\item \textbf{Encryption$(PK, M, T)$}. The encryption algorithm takes as input the public parameters $PK$, a plaintext message $M$, and an access tree structure $T$ over the universe of attributes. This algorithm will encrypt $M$, and produce a ciphertext $CT$ which only users who possess a set of attributes that satisfies the access structure $T$ are able to decrypt.
\item \textbf{Key Generation$(MK, S)$}. The secret key generation algorithm takes as input the set of attributes $S$ that user $U$ owns, the master key $MK$, and randomly selects a set of $|S|+1$ numbers specific to user $U$. It outputs a secret key $SK$.
\item \textbf{Decrypt$(PK, CT, SK)$}. The decryption algorithm takes as input the public parameters $PK$, a ciphertext $CT$ which contains the access policy $T$, and a secret key $SK$ generated from attribute set $S$. If the set $S$ of attributes satisfies the access policy $T$, the algorithm will successfully decrypt the ciphertext and return the plaintext message $M$.
\end{itemize}

\begin{figure*}[t]
\centering
\includegraphics[width=6in,height=2.8in]{mine.pdf}
\vspace{-2.5mm}
\caption{Access Control Procedure}
\vspace{-5mm}
\label{fig:workflow}
\end{figure*}

\section{Protocol Design}

\subsection{System Overview}
\begin{itemize}[leftmargin=*]
\item \textbf{IMD.} Each IMD has a unique identification $ID_{i}$ and a master key $K^{M}_{i}$. Note that the master key is only used for pairing up the IMD with a proxy device, and will not directly participate the access control procedure.
\item \textbf{Programmer.} The programmer can be simply viewed as the terminal device used by its operator to interact with the IMD or proxy. It obtains all information required for access control (e.g., secret keys, certificates) from the operator, by manual input or reading in from a smart card.
\item \textbf{Operator.} The programmer operator is the actual subject to be verified. All legitimate operators must first be registered at a Central Health Authority (CHA), which manages the qualifications of operators and issues digital certificates for them. Each operator has a unique identification $ID_{o}$, a pair of public/private keys $KU$ and $KR$, and a public key certificate $Cert$. The qualifications that an operator owns correspond to a set of attributes $S$. CHA will generate the secret key $SK$ for the operator based on the set of attributes $S$. $SK$ can be used to decrypt the ciphertext produced by CP-ABE if the access policy is satisfied. Besides, all operators know the public parameters $PK$ used in CP-ABE.
\item \textbf{Proxy.} The proxy device has the identification $ID_{p}$. There is a client program running on the proxy to perform the access control for the IMD. The proxy has been paired up with the IMD through initial setup.
The client program has a copy of the public parameters $PK$ used to run CP-ABE, and is able to generate the access tree (policy) $T$ that describes the qualifications required for access.
\end{itemize}

\subsection{Access Control Protocol Design}

The access control procedure includes two separate processes: the authentication of the programmer operator and the authorization for access.

Although the IBAC model is not suitable in IMD context and we utilize attributes to control access instead, it is still necessary to authenticate the identity of the programmer operator. One reason for that is to provide non-repudiation guarantee in case of medical disputes. For example, a programmer operator cannot deny his/her access if the start time and end time of the access have been signed by his/her own private key. The other reason is that the ciphertext $CT$ generated by CP-ABE contains the access policy in plaintext. The access policy specifies the expected qualifications of the authorized physicians (e.g., speciality) and the information related to the IMD model (e.g., the certifications required to operate), which are all very sensitive with regard to the patient's privacy and should not be publicly accessible to anyone who requests for access. Therefore, our scheme authenticates the programmer operator before the authorization stage, so that only a legitimate operator who has registered at CHA (not necessarily authorized to access) can continue to the authorization process and view the access policy.

In the authorization stage, the proxy encrypts a randomly generated temporary session key $K_{t}$ with CP-ABE and sends the ciphertext to the programmer. If the operator is an eligible physician whose qualifications (attributes) satisfy the access policy, the session key $K_{t}$ can be correctly retrieved and used to establish a secured communication channel with the IMD.

The access control procedure is presented in Figure~\ref{fig:workflow}.
We assume that the proxy device has already been paired up with the IMD, and a pair of symmetric keys $K_{s}$ have been shared between them for encrypted communications.
The detailed procedure is described as follows:
\begin{enumerate}[leftmargin=*]
\item The programmer initializes the access control protocol by connecting with the proxy via audio cable, and sending an access request which is composed of a unique action sequence ``$access\_req$'', the operator's digital certificate $Cert$, a random selected session number $SN$, timestamp $t_{1}$, and a signature $Sig_{1}$ signed by the operator's private key $KR$. The certificate contains the operator's public key $KP$ and identification $ID_{o}$. The signature $Sig_{1}=Sign_{KR}(ID_{o}|SN|t_{1})$ is attached to prove that the current access requestor is indeed $ID_{o}$.
\item The access control mobile application has registered a receiver of the headset connection state changes. When this program is notified of the plug-in event, it will read in and demodulate the audio data. If the action sequence ``$access\_req$'' can be found in the demodulated data, it indicates that the data is for IMD access request instead of regular audio (e.g., music). Then it extracts and verifies the received $Sig_{1}$ using the requestor's certified public key $KP$ embedded in $Cert$. If the signature is valid, the programmer operator is successfully authenticated. The proxy will next check if that operator is authorized to access. Specifically, it randomly generates a temporary session key $K_{t}$ and encrypts $K_{t}$ using CP-ABE. Then, the produced ciphertext $CT = \hat{E}_{PK, T}(K_{t})$ is sent back to the programmer.
\item The programmer decrypts $CT$ with the operator's secret key $SK$ (generated and assigned by the CHA). If the operator's qualifications (attributes) satisfy the access policy, the secret key $SK$ will be able to retrieve the temporary session key $K_{t}$. Then, it calculates the hash value of $K_{t}$ and sends the hash value to the proxy.
\item The proxy also calculates the hash value of $K_{t}$ with the same hash function. If the two hash values are equal, it indicates that the programmer operator is eligible for access. The proxy will inform the IMD that the programmer $ID_{o}$ has been authenticated and is authorized to access, and sends a copy of the session key $K_{t}$ to IMD. Note that all communications to/from the IMD are conducted in the wireless channel, which may suffer eavesdropping, replay, and tampering attacks. Hence, the session key is encrypted by the shared key $K_{s}$ to prevent eavesdropping. A timestamp $t_{2}$ is added to defend replay attacks. The keyed-hash message authentication code (HMAC) of the message is calculated using $K_{s}$ to ensure the authenticity and integrity of the message.
\item After receiving the authorization notification from the proxy, the IMD retrieves the $K_{t}$ and sends ``ready'' message to the programmer.
\item In the mutual communications between the IMD and the programmer, the operation commands $C$ sent by the programmer and the data/result $D$ returned by the IMD are all encrypted using the temporary session key $K_{t}$. Each authorization permits multiple operations (e.g., data reading, drug delivery). We only draw one round of operation in Figure~\ref{fig:workflow} for illustration. The timestamps and HMACs are also adopted in the communications between the IMD and the programmer to defeat various active wireless attacks.
\item After the programmer has completed the access, it sends a ``logout'' notification message to the proxy. Another signature $Sig_{2}=Sign_{KR}(ID_{o}|SN|t_{5})$ is generated in which the access end time $t_{5}$ is signed.
\item Finally, the proxy will notify the IMD that the current session has ended so that the session key $K_{t}$ will be removed. Timestamp $t_{6}$ and $HMAC_{4}$ are included in the this message.
\end{enumerate}

Our scheme asks the programmer to explicitly log out the session, and requires it to sign the time that session ends. Therefore, $Sig_{1}$ and $Sig_{2}$ together can prove that the operator has accessed the IMD in that period of time. Any wrong operations performed in this period will be attributed to that specific operator. The programmer should maintain the wired connection with the proxy during interacting with the IMD, to eliminate the possibility that a second programmer is connected with the proxy while the first one is still interacting with the IMD.
However, it may happen that the programmer does not sign out by the end of its session for certain reasons, a time-out mechanism is used to tackle this situation. Specifically, if there is no interaction made by the programmer for a fixed amount of time $T_{out}$, the session will be closed and the session key $K_{t}$ will be disabled.

\begin{figure}[t]
\centering
\includegraphics[width=3.4in,height=1.8in]{implementation.jpg}
\caption{Prototype Setup}
\vspace{-1mm}
\label{fig:implement}
\vspace{-1mm}
\end{figure}

\begin{figure}[t]
\centering
\includegraphics[width=3.45in,height=1.8in]{dft.pdf}
\caption{Illustration of Signal Modulated by BFSK}
\label{fig:dft}
\vspace{-1mm}
\vspace{-4mm}
\end{figure}

\section{Security Analysis}

\vspace{-1.5 mm}
\subsection{Resistance to Passive Attacks}

In the wireless channel, the adversary is able to eavesdrop the communications between the proxy and the IMD, as well as between the programmer and the IMD, to obtain the data, operation commands, or keys being transmitted. To defend against such passive wireless attack, all sensitive information is protected with symmetric encryptions. Specifically, a pair of keys $K_{s}$ have been pre-shared by IMD and the proxy (during initial setup), and another pair of keys $K_{t}$ are securely distributed to IMD and the programmer. The adversary cannot decrypt the ciphertexts without the cryptographic keys.

Over the audio cable, even if the proxy has been infected by malware which will overhear the audio data received by the proxy, our scheme can ensure that it cannot obtain any sensitive information. The temporary session key $K_{t}$ is encrypted by CP-ABE. The malware cannot correctly derive the plaintexts without the required qualifications (attributes). Additionally, it cannot infer $K_{t}$ from its hash value $H(K_{t})$.

\subsection{Resistance to Active Attacks}

In the wireless channel, all messages containing sensitive information are timestamped to prevent replay attacks. In addition, a HMAC is calculated using the corresponding shared keys ($K_{s}$ between the proxy and the IMD, or $K_{t}$ between the programmer and the IMD), to defeat the tampering attacks.

Over the audio cable, the malware on the proxy can send arbitrary messages to the programmer or tamper the messages sent by the application running the access control. In our scheme, the only outgoing message to the programmer via the wired audio channel is $CT$. However, either the replay or manipulation of this message cannot help an unauthorized programmer operator to gain access, since only eligible operators can successfully decrypt $CT$ and retrieve the session key $K_{t}$.

\subsection{Other Attacks}

Over the audio cable, the mobile malware can add noise to the audio data sent by the access control application, but this sort of attacks can only disrupt the access of legitimate operators (e.g. causing the failure of authentication or authorization). As we have mentioned before, DoS attacks are not the focus of this work.
Besides, our scheme is well-compatible with existing solutions to the proxy-absence spoofing attacks \cite{IMDGuard} and the resource depletion attacks \cite{Liu,SIGCOMM,Hei2010}.

\section{Evaluation}

In this section, we implement our schemes on real devices and evaluate the overheads of our scheme with experiments.

\subsection{Prototype Implementation}

The key challenge of the implementation of our scheme is the difficulty in obtaining open-source commercial IMD products. Alternatively, in our prototype system, we use TelosB Mote TPR2420 sensor node with 8 MHz TI MSP430 microcontroller, 10kB RAM, and 48kB Flash Memory as the replacement of IMD. We choose the Rasberry Pi Version 3 Model B, a small single-board device with 1.2GHz 64-bit quad-core CPU and 1GB RAM, to emulate the programmer. A Nexus 4 smartphone powered by a 1.5 GHz quad-core processor with 2 GB of RAM, is used to emulate the proxy.

In our scheme, symmetric encryption and public-key cryptography are implemented using the Advanced Encryption Standard (AES) algorithm and RSA algorithm, respectively. We use 128 bits key for AES encryption and 1024 bit keys for RSA encryption. SHA-1 is chosen for HMAC generation.

\begin{table}[t]
  \caption{Parameters used for modulation and demodulation}
  \footnotesize
  \centering
  \begin{tabular}{|m{1.3in}<{\centering}|m{1in}<{\centering}|}
    \hline
    Parameter    &   Value  \\
    \hline
    Sampling rate   &  44100Hz  \\
    \hline
    Pulse-code modulation (PCM) bit depth   &  16 \\
    \hline
    $f_{0}$   &  1575Hz  \\
    \hline
    $f_{1}$   & 3150Hz\\
    \hline
    Baud rate   &  315 \\
    \hline
  \end{tabular}
  \label{table:modu}
\vspace{-3.5 mm}
\end{table}

\subsection{Testbed Specification}

We developed an Android application to delegate the access control on the Nexus 4 smartphone. This mobile application is able to perform CP-ABE and modulate/demodulate the audio signals. Correspondingly, we developed a client program running on the Raspberry Pi, which can decrypt the ciphertext encrypted using CP-ABE if the programmer operator's attributes satisfy the access policy embedded in the ciphertext. This client program is also capable of modulating/demodulating audio signals.
The smartphone and the programmer is connected via an audio cable and a SYBA external USB Sound Adapter (audio-to-USB convertor). A screenshot of the prototype is shown in Figure~\ref{fig:implement}.

We adopted the Binary Frequency-Shift Keying (BFSK) frequency modulation scheme for modulation, in which the digital data are converted into the analog signals at two different frequencies for transmissions over the audio cable. For example, the binary ``0'' bit is represented by the audio signal at frequency $f_{0}$ while the binary ``1'' bit is represented by the audio signal at frequency $f_{1}$.  Figure~\ref{fig:dft} displays the results of the signal modulation and spectrum analysis.
The red signal (upper sine waves) in Figure~\ref{fig:dft} is the analog signal after modulated by BFSK.
At the receiver end, the analog signal is sampled to a sequence of discrete-time signal (samples). Then, we use the Discrete Fourier Transform (DFT) algorithm to convert the sampled analog signal from time domain into the frequency domain representation, which is illustrated in Figure~\ref{fig:dft} as the blue pulse-like signal. Specifically, the analog signal to be demodulated can be viewed as an addition of multiple sine signals in different frequencies. With Fourier transform, the magnitudes of the modulated signal on various frequencies within the spectrum range are calculated.
The frequency with the highest amplitude (i.e., maximum power) is called the peak frequency. If the peak frequency equals $f_{0}$, then the current signal sample represents a ``0'' bit; while if the peak frequency equals $f_{0}$, then the signal sample represents a ``1'' bit.
The parameters we used for modulation and demodulation are listed in Table~\ref{table:modu}:

\begin{figure}[t]
\centering
\begin{minipage}{1.65in}
  \centering
  \includegraphics[width=1.65in,height=1.55in]{modulation.pdf}
	\vspace{-7mm}
  \caption{Time - Modulation
  \label{fig:modulation}
\end{minipage}%
\hspace{2mm}
\begin{minipage}{1.65in}
  \centering
  \includegraphics[width=1.65in,height=1.55in]{demodulation.pdf}
	\vspace{-7mm}
  \caption{Time - Demodulation
  \label{fig:demodulation}
\end{minipage}
\vspace{-2.5 mm}
\end{figure}

\begin{figure}[t]
\centering
\begin{minipage}{1.65in}
  \centering
  \includegraphics[width=1.65in,height=1.5in]{encryption.pdf}
	\vspace{-6.5mm}
  \caption{Time - CP-ABE Encryption
  \label{fig:E}
\end{minipage}%
\hspace{2mm}
\begin{minipage}{1.65in}
  \centering
  \includegraphics[width=1.65in,height=1.5in]{decryption.pdf}
	\vspace{-6.5mm}
  \caption{Time - CP-ABE Decryption
  \label{fig:D}
\end{minipage}
\vspace{-4.5 mm}
\end{figure}

\subsection{Experimental Results}

To evaluate the efficiency of our scheme, we measure the computational overheads of the protocols running on the IMD (TelosB Mote), the proxy (Nexus 4 smartphone), and the  IMD programmer (Rasberry Pi), respectively. All the run-time overheads are the average of 50 measurements.

\subsubsection{IMD} The major cryptographic computations performed on the IMD are the symmetric encryption and HMAC. On TelosB node, the 128-bit AES encryption takes 2ms. For HMAC, we estimate the length of the plaintext message $(``operate\_rep\textquotedblright, SN, ID_{i}, ID_{o}, E_{K_{t}(D)}, t_{4})$ to be 78 bytes in total, including a 4-byte command, a 2-byte sequence number, two 4-byte IDs, and a 64-byte data/result returned). The HMAC computation over a 78-byte massage takes 47ms.

\subsubsection{IMD programmer and proxy} The IMD programmer (Rasberry Pi) and proxy (smartphone) both need to conduct modulation/demodulation for their wired communications through the audio cable. Figure~\ref{fig:modulation} and Figure ~\ref{fig:demodulation} show the time consumption for modulation and demodulation on smartphone and Rasberry Pi, respectively. As we can see, the Rasberry Pi has a better performance than the smartphone, and the demodulation takes longer times than the modulation process.

Additionally, the proxy (smartphone) needs to encrypt the temporary session key with CP-ABE encryption algorithm, and he IMD programmer (Rasberry Pi) will run the decryption algorithm to retrieve the key. Figure~\ref{fig:E} and Figure~\ref{fig:D} show the time consumption for CP-ABE encryption on smartphone and decryption on Rasberry Pi, respectively. The run-time overheads for CP-ABE encryption and decryption both increase with the number of leaf nodes (attributes). Our experiments tested a maximum of 20 attributes, which should be sufficient to specify the qualifications of the programmer operator. The decryption is found to be the most time-consuming step in the whole scheme, which takes about twice the time used for encryption. Since the CP-ABE encryption/decryption is required only once, their execution time are considered acceptable.

\section{Related Work}

Most existing works employ the two-party access control architecture, in which the IMD with constrained computational power, battery capacity and storage must perform the access control by itself, resulting in a relatively weak access control and shorter IMD lifetime. Some works proposed that the IMD should be accessible only to a group of trusted people (e.g., doctors, relatives) who have been added into the IMD's access control list (ACL) \cite{ACL1}\cite{ACL2}. The limited storage of IMD will greatly restrict the scalability of such schemes. In addition, the authentication of the requestor requires the verification of the certificate/signature. The computing power and battery can hardly afford the public-key cryptographic computations.

Some other two-party based access control schemes only check whether the programmer is in proximity. Specifically, IMD and the programmer need to extract certain features from the same source simultaneously, and generate the temporary keys based on the extracted feature, respectively. The source is usually the signal in an out-of-band channel, such as electrocardiography (ECG) signal \cite{CCS2013}, body-coupled electric signal \cite{HealthSec2012}, vibration \cite{Vibration}, ultrasound \cite{RasmussenCCS2009}, etc. If the programmer is close enough to the IMD, they will derive the same (symmetric) temporary key for the encryption of future communications. The real-time signal measurement and key extraction computations both bring in an extra burden to the resource-constrained IMD.
Other works proposed to pre-load the patient's biometric information (e.g., fingerprint) or a password into the IMD. During access, the programmer operator can manually collect the biometric features from the patient \cite{Hei2011} or the password from a physical object carrying it \cite{DenningCHI2010}, respectively. However, the bio-features and the password engraved on an object can be stole by the adversary. Besides, a common disadvantage of these two types of schemes is that they only provide a coarse-grained access control. No information about the access requestor is acquired and validated.

By contrast, in the proxy-based architecture, the powerful proxy device handles those resource-consuming tasks. It can support more complicated and robust access control schemes. However, previous proxy-based access control schemes either depend on anomaly detection of the access pattern \cite{Hei2010,MedMon} or only verify the authenticity of the programmer \cite{IMDGuard,Cloaker}. The former method does not check the access requestor and require a training process for each patient. The second method is vulnerable considering that an attacker could also purchase or steal a legitimate programmer. Our scheme views the programmer and its operator together as one subject, and the access decision is made based on the programmer operator. We not only authenticate the operator, but also employ the CP-ABE algorithm to verify the qualifications of the operator.

Key management \cite{management1, management2, management3} is essential for security. Several papers \cite{Hei2011,other2,GuanIoTJ,other3,other4,GuanCommMaga,other5} have studied related security issues.

\section{Conclusion}

In this paper, we proposed a novel fine-grained IMD access control scheme based on a proxy device like the patient's smartphone, which will delegate the heavy access control computations for the IMDs. To mitigate the potential wireless attacks, the communications between the proxy and the IMD programmer are conducted through an audio cable. The ciphertext-policy attribute-based encryption is employed to enforce the fine-grained access control over the qualifications of the programmer operator. We built a prototype to evaluate our scheme. The experimental results demonstrated its feasibility and effectiveness.

\bibliographystyle{abbrv}

redpajama_set_name: RedPajamaArXiv


text:
Who the heck is Rod Zimmer?
With Senator Zimmer currently in the headlines, Aaron Wherry considers one obvious question (there are others, of course)
By Aaron Wherry August 27, 2012
With Rod Zimmer currently in the headlines, Aaron Wherry considers his journey to the Senate:
In 1999, Rod Zimmer, a prominent Winnipeg businessman and fundraiser, was reportedly among the final two candidates for the posting of Lieutenant Governor in Manitoba. Jean Chrétien chose the other finalist, Peter Liba.
Six years later, Zimmer received a decent consolation prize—an appointment to the Senate. Zimmer was among five senators selected in August of that year by Paul Martin.
From 1968 to 1971, Zimmer was an assistant to Cyril MacDonald, the Liberal minister of welfare in Saskatchewan, and for most of the rest of the 1970s he was an assistant to James Richardson, the federal minister of defence. He was the Manitoba chair for the federal Liberal campaign in 1980 and while then building a career in business—including prominent positions with CanWest and the Manitoba Lotteries Foundation—Zimmer continued to work within and around the Liberal party. He was a member of the fundraising committee for Paul Martin's leadership campaign in 2003 and revenue chair for the federal Liberals in Manitoba from 2004 to 2006.
"People will comment on the fundraising that he's done for the Liberal party, but what is overlooked is the incredible amount of work he's done for all sorts of other causes in Manitoba," Manitoba Liberal leader Jon Gerrard told the Winnipeg Free Press when Zimmer's Senate appointment was announced. "That kind of commitment is a positive thing. He has a lot of public spirit."
After Martin's resignation, Zimmer helped raise funds for Ken Dryden's leadership campaign.
From 1989 to 1991, he was president of the Royal Winnipeg Ballet and from 1981 to 1993 he was a member of the board of directors for the Winnipeg Blue Bombers. And according to Zimmer's official biography, he is a "champion swimmer, diver, and water-skier" and "he has actively participated in hockey, baseball, football, basketball, volleyball, curling, tennis, golf, soccer, squash, handball, badminton and downhill skiing."
FILED UNDER: CanWest Cyril MacDonald James Richardson Jean Chretien Ken Dryden Manitoba Paul Martin Peter Liba Rod Zimmer Royal Winnipeg Ballet Senate Winnipeg Blue Bombers

redpajama_set_name: RedPajamaCommonCrawl


text:
Did You Know That Pigs Don't Sweat?
"Sweat like a pig" is a common phrase. But did you know that pigs don't sweat? Learn more in the following article.
Last update: 26 December, 2021
Around the animals considered "farm animals" orbit a series of sayings and beliefs that often don't fit with reality, such as the phrase "sweat like a pig". Today, we're going to reveal a little know secret: The truth is, pigs don't sweat.
In fact, in this article, we'll disprove 2 popular beliefs about swine. Are you curious to learn more? Here, you'll learn something more about pigs, which are incredible but underrated animals. Keep reading!
Do pigs sweat?
The answer is simple: no, pigs don't sweat. To sweat, you need sweat glands that secrete water and mineral salts through the dermis. This substance (sweat) evaporates with the ambient heat, thus lowering the skin temperature.
However, pigs have very few sweat glands, so it's impossible for them to sweat. In fact, these mammals are very sensitive to high temperatures precisely because of this reality, as their dissipation of body heat is more limited.
Because humans are so accustomed to this thermoregulation mechanism -in fact, we're among the animals that sweat the most-, sometimes we don't realize that it's not very common among other species. Dogs, for example, only sweat through the pads of their feet. To dissipate excess heat, they help themselves by panting.
If pigs don't sweat, then where does the saying "sweating like a pig" come from?
How did it occur to anyone to say that someone else "sweats like a pig" if they've never seen one sweat? Actually, the origin of this phrase is due to a misunderstanding of the origin of this common saying.
Centuries ago, in the United Kingdom, the word pig was used to refer to the molds into which cast iron was poured, as it was shaped like the breasts of these animals. The molten iron in the mold was called pig iron.
To know if the iron had solidified, blacksmiths needed to check if there was a layer of liquid on its surface, that is, the "pig's sweat". For this reason (and because of the high temperatures in the foundries), "sweating like a pig" became established as a catchphrase. Therefore, the actual meaning of the phrase has nothing to do with the sweating of an actual live pig.
How do pigs regulate their temperature?
So, this brings us to the next question. If pigs don't sweat, then how do they not die of heat? And this is where the second myth about pigs comes in–the idea that they wallow in their own feces because they're filthy.
Like other animals that don't sweat, pigs choose to protect their skin from the sun by taking mud baths. Elephants, hippopotamuses, and other mammals also do this, as the earth creates a protective barrier that shields them from the sun.
The problem comes when you keep pigs in poor conditions: If they live surrounded by their own feces, they'll have no choice but to wallow in it to protect themselves from the heat. This obviously makes them smell bad and develop skin problems, so it's not a natural behavior for them.
In reality, swine are very clean animals; if you have the opportunity to see them living in optimal conditions, you'll notice that they keep themselves clean and tidy.
How to help pigs thermoregulate
If you live with these cute animals, you know that too much sun exposure can cause them problems. Although they know how to regulate themselves through bathing, it's important to prepare their space so that they don't suffer from any of these imbalances:
Heat stroke: Pigs go out of their optimal thermal zone at 26°C. Heat stroke can be as deadly as in any other species.
Sunburn: Crossbred farm pigs have whiter skin and less hair than wild pigs, which makes them much more prone to sunburn. The burns are very painful for the animal.
Squamous cell carcinoma: A sunburn can lead to this type of cancer, which is very common due to exposure to ultraviolet rays.
So what do you do to ensure the health of your pigs in this regard? Most of the information comes from the experience of sanctuaries that rescue pigs from farms. Over many years, they've sought the best care for them, which allows us to give you this general advice:
Your space should have shelter and plenty of shade so that your pig can take refuge from unfavorable weather conditions.
Provide a pond: It's as easy as digging a hole in the ground with a ramp on one side and just allow the rain to fall in. Pigs will really enjoy bathing and wallowing in the mud. However, the space should be kept as clean as possible to avoid infection and other ailments.
Provide clean, cool water throughout the day: Drinking is also a way to lower body temperature.
Use sunscreen: Using sunscreen specifically for pigs is a great help in preventing them from getting sunburned – they love to nap in the sun – as well as preventing skin cancer. The mixture should be spread over the ears, back, belly, and shoulders.
Pigs are one of the most punished animals in popular culture. Always seen as food or interchangeable goods, they're rarely given an identity of their own despite being incredibly smart and loving animals. That's why debunking the myths surrounding them is one more step towards recognizing their true nature and fostering empathy towards them.
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Reproduction in Pigs
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The Open Sanctuary Project, Inc. (2021, 21 septiembre). Pigs and Mud: Let them Wallow! The Open Sanctuary Project. https://opensanctuary.org/article/pigs-and-mud/
The Open Sanctuary Project, Inc. (2020, 4 agosto). The Importance Of Sun Protection For Pigs. The Open Sanctuary Project. https://opensanctuary.org/article/the-importance-of-sun-protection-for-pigs/
Schifferli, C., González, H., & Yaciuk, R. (1995). Neoplasias en el cerdo. Descripción patológica de los casos diagnosticados durante 10 años. Arch. Med. Vet., 27.
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MARBLE FALLS — Kim Boni defied the mold, even that of her distance coach Anthony Torns.
The Marble Falls High School senior signed her letter of intent to run for the University of Arkansas-Little Rock on April 18 after Torns, who is the Lady Mustangs head cross-country and track-and-field coach, talked about Boni's journey.
"… It's been real crazy for her," he said, noting she only had one collegiate offer during the cross-country season. So the two went back to work, and Torns made her promise. If she ran the times college coaches sought, they would find her.
That's just what happened as she had a personal best of 5 minutes 18 seconds in the 1,600 meters. Shortly after that time posted, Arkansas-Little Rock called Torns for Boni's phone number. After visiting the campus and ensuring the scholarship was a full ride and not a partial, Boni committed to running for the Division I member of the Sun Belt Conference.
Boni will run in any distance event beginning with the 800 meters to 5 kilometers as a cross-country and track runner.
Still, Torns couldn't talk about the end of the journey without reflecting on Boni's beginning.
As a freshman, she came to him as a triple jumper and 400-meter runner, and Torns admitted he wasn't that impressed by her.
He isn't a fan of what he calls the "pity clap," when fans see a runner who is lapped and struggling to finish and encourage that athlete to keep going to the finish line.
So he put her in the 400 meters knowing she would run as fast as she could for one lap. While she may not win, at least she wouldn't receive the pity clap.
But Boni kept asking Torns how she could get better. So he encouraged her to participate in cross country as a sophomore, emphasizing the longer distance would be good for her 400 meters in the spring.
So he switched her to longer distances and watched as she excelled.
He credited her for being self-driven, noting she reaches out to him almost every day to ask what kind of workout she needs to do or what kind of time she needs to post. He noted that she has felt disappointment at regional and state meets that has simply fueled her desire to get better. And it also helped that a group of talented freshmen were at the high school campus this year, he added.
The daughter of Chris Boni and Joni Boni will major in kinesiology.


text:
Q: Form of a 2-form if and only if wedge is zero. Let $\{\alpha^1,...,\alpha^p\}$ be a collection of linearly independent 1-forms. Show a 2-form $\beta$ is of the form
\begin{align*}
\beta=\gamma^1\wedge\alpha^1+\cdots+\gamma^p\wedge\alpha^p
\end{align*}
for 1-forms $\gamma^i$ if and only if
\begin{align*}
\beta\wedge\alpha^1\wedge\cdots\wedge\alpha^p=0.
\end{align*}
I'm pretty new to wedge products. I really have not been able to come up with a strategy on how to connect the wedge product being zero with some sort of computation for the $\gamma^i$ with that said the forward direction of this proof I believe is straightforward.
If $\beta=\gamma^1\wedge\alpha^1+\cdots+\gamma^p\wedge\alpha^p$ then
\begin{align*}
\beta\wedge\alpha^1\wedge\cdots\wedge\alpha^p&=(\gamma^1\wedge\alpha^1+\cdots+\gamma^p\wedge\alpha^p)\wedge\alpha^1\cdots\wedge\alpha^p\\
&=\sum_{i=1}^p\gamma^i\wedge\alpha^i\wedge\alpha^1\wedge\cdots\wedge\alpha^p\\
&=\sum_{i=1}^p\gamma^i\wedge0\\
&=0.
\end{align*}
Assuming this is correct I am very stuck on the reverse direction. I'm sure that I need to extend the linearly independent collection of 1-forms to a basis but beyond that I've just been spinning my wheels for quite some time. Any help would be greatly appreciated.

A: Extend your $\alpha_i$ to a basis in the dual space $\{\alpha_1,\alpha_2,\dots \alpha_p,\alpha_{p+1},\dots\alpha_n\}$. Then, your $2$-form $\beta$ can be written as
$$
\beta=\sum\limits_{1\le i<j\le n}A_{ij}\alpha_i\wedge\alpha_j.
$$
Now we can split the sum into two pieces, the first will contain all wedge products containing at least one of the $\alpha_i$ with $1\le i\le p$ and the second, all wedge products of the form $\alpha_k\wedge\alpha_r$ with $k,r>p$:
$$
\beta={\rm{First\ \ piece}}+\sum\limits_{k,r}A_{k,r>p, k<r}\alpha_k\wedge \alpha_r
$$
Next, right-wedge-multiply by $\alpha_1\wedge\alpha_2\dots\wedge\alpha_p$. Then the first piece disappears since at least two factors in the wedge products coincide, and you get
$$
0=\sum\limits_{k,r>p, k<r}A_{k,r}\alpha_k\wedge \alpha_r\wedge\alpha_1\dots\wedge\alpha_p.
$$
On the right hand side, all the $p+2$-forms are linearly independent in the exterior $p+2$-power space and therefore $A_{k,r}=0$ for all $k,r>p$. This implies that $\beta$ is equal to the first piece, where all the addends contain some $\alpha_i$ with $i=1,2,\dots p$,
$$
\beta =\sum\limits_{1\le i<j\le p}A_{ij}\alpha_i\wedge\alpha_j=\sum\limits_{j=2}^p\gamma_j\wedge\alpha_j
$$
where $\gamma_j=\sum_i A_{ij}\alpha_i$.

redpajama_set_name: RedPajamaStackExchange


text:
10 Best XTC Songs
Dave Swanson
What's the best XTC song? It's kind of like asking if you prefer air to water. Their catalog is an endlessly fascinating musical adventure that has not paled one shade since they first burst onto an unsuspecting music scene in late 1977 with their debut single, 'Science Friction.' Always looking to the future with a knowing glance at the past, XTC remain one of the most loved bands to have emerged from the spirited days of the late '70s and early '80s. We decided not to include any tracks from their alter ego, the Dukes of the Stratosphere, because hey, it was hard enough to whittle it down to this list of the 10 Best XTC Songs.
' The Ballad of Peter Pumpkinhead'
From: 'Nonesuch' (1992)
The opening track and one of the highlights from the band's 'Nonesuch' LP, 'The Ballad of Peter Pumpkinhead' kicks off with the sound of a guitar being plugged in, followed by a classic, almost Pete Townshend-style, riff. Another in a career-long trail of wonderful melodies can be found here. Andy Partridge wrote the song in an attempt to do a Dylan-style tune, which explains the sharp harmonica on this one. "I just came up with some Harrison-esque guitar, and we added some Hammond organ to give it that 'Blonde On Blonde' feel," said guitarist Dave Gregory in the book 'XTC Song Stories,' "It might have been a hit if it had been chopped down."
'The Mayor Of Simpleton'
From: 'Oranges And Lemons' (1989)
Jangling guitars ring out loud and proud on this perfect little pop gem, No. 9 on our list of the 10 Best XTC Songs. One of many highlights from the band's 1989 LP 'Oranges And Lemons,' The Mayor Of Simpleton' is pop perfection in four minutes flat. From it's Byrdsian guitars to the very "modern" production, it balanced the worlds of looking back and looking straight ahead that XTC often straddled. It's one of the few records made with glaring '80s production techniques that has not suffered long term the way most have. Though it was never a big mainstream chart hit, it proved to be a huge hit for the band on College Radio and the ever popular Modern Rock format of the times.
'This Is Pop'
UK single (1978)
With a whispered, "Yes," we're off and running. 'This Is Pop' first appeared on the band's debut LP, 'White Music,' and was then re-recorded for single release. The single (featured here) wins hands down. It's far more emphatic and immediate in its approach as it grabs and molests your ears, leaving them in, well, ecstasy. Andy Partridge spews out one of his fiercest vocals amid the over-the-top Pop, with a capital "P."
'No Thugs In Our House'
From: 'English Settlement' (1982)
'No Thugs In Our House' is one of the most revved-up tunes on their classic 1982 LP, 'English Settlement.' Amid the LP's variety of styles, 'Thugs' is as good an example of XTC rocking it out as there is. The song packs a sweet punch that never lets up, while Andy Partridge sings a tale about a misguided buffoon of sorts, who has pledged his allegiance to the National Front. In the book, 'XTC Song Stories,' Partidge referred to the song as "violent Tamla-Motown meets Johnny Winter," adding, "I get to do my best rebel yell in this."
'Making Plans For Nigel'
From: 'Drums And Wires' (1979)
Another of many pearls from the pen of bassist Colin Moulding, 'Making Plans For Nigel' is a genuine pop classic and one of XTC's best loved songs. Though nowhere near as prolific as band leader Andy Partridge, Moulding's contributions were undeniable. His style was, in many ways, much more direct and traditional than Partridge's. Despite a mutual admiration, this did leave Partridge a bit out of sorts. "I was incredibly jealous that everything Colin did was getting all the attention," Partidge said in the book 'XTC Song Stories.' He felt that Virgin Records was grooming him to be the 'star' of the band. "He was the handsome dos and I was the egghead," continued Partridge, "You could see Virgin's reasoning." The song would, however, not be without significant contribution from Partridge, who came up with the distinct drum pattern, which gave the song an undeniably unique kick. Released as a single in their homeland, 'Making Plans For Nigel' hit the Top 20 and stayed on the charts for 11 weeks.
'Respectable Street'
From: 'Black Sea' (1980)
The first song on the band's 1980 classic 'Black Sea,' No. 5 on our list of the 10 Best XTC Songs is a full-on stomping rock 'n' roller. As the song begins, it sound like it's coming out of an old Victrola before the jagged guitar riff announces itself loudly. Walking a somewhat similar terrain to that of many a mid-'60s Ray Davies song in terms of its observations on everyday life, the tune includes such great lines as "as they speak of contraception and immaculate reception on their portable Sony entertainment centers." The combination of '60s pop sensibility and the energy of punk made for a perfect recipe for the band at this junction. The punch of the song never lets up, and it may be one of the defining moments in this era of XTC.
'Dear God'
From: 'Skylarking' (1986)
Inspired by the 'Dear God' children's books, Andy Partridge lets loose his thoughts on this larger than life topic. The song was originally issued as the b-side of the song 'Grass' and was, in the mind of Partridge, never meant to be anything more than a b-side. The song, however, took on a life of it's own, particularly in America, when college radio began playing it repeatedly. The song is undeniably striking, both musically and lyrically. The addition of the child's voice for the first verse is brilliant. 'Dear God' was added to the second pressing of the 'Skylarking' LP and went on to become a genuine hit for the band in the States. "It did us a lot of good," recalled Partridge to author Neville Farmer in the book 'XTC Song Stories,' "although it upset as many people as it pleased."
'Generals and Majors'
From its first beat, 'Generals and Majors' leaps right out of the speakers. Released in September 1980 as a single, the song jumped into the Top 30 in the U.K. and was a key track from the band's album released that fall, the ever-wonderful 'Black Sea.' Musically frantic and charged, the song is irresistibly catchy. At the same time, the lyrics are both satirical and thought provoking. "It was definitely going to be a song about the military," said writer Colin Moulding in the book 'XTC Song Stories,' " but from the pompous, slightly humorous side rather than an antiwar song."
'Senses Working Overtime'
On their 1982 LP 'English Settlement,' XTC really began to expand their approach, including a wider variety of styles and instrumentation. The pop perfection XTC was capable of shines brighter than ever on that LP's first single. 'Senses Working Overtime' has it all and then some. From the percussive picking on the acoustic guitar set to a sauntering rhythm, the band kick into high gear as the ultra-catchy chorus bursts in. The single hit the U.K. Top 10 and became a regular on U.S. college radio.
'Life Begins at the Hop'
From: UK single (1979)
Stomping out of the gates, 'Life Begins at the Hop,' first on our list of the 10 Best XTC Songs, is one of the group's most infectious and irresistible songs. The lyrics are a clever take on teen drama, while the urgency and the melody are invigorating and life affirming. Written by Colin Mouding, the song was released as single in the spring of 1979, preceding the 'Drums and Wires' LP. The single just missed the U.K. Top 50 but has remained a fan favorite since its release. To borrow a phrase from Nick Lowe, this is "pure pop for now people!" Turn it up ... LOUD!
The Sheer Ecstasy Of XTC!!
Is our list of the 10 Best XTC Songs missing your punky, psychedelic favorite? Life begins at the comments section, so drop us a line there and let us know.
Next: 10 Best Kinks Songs
Filed Under: XTC


text:
Students design beautiful homes for mass-production at just $20,000 each
by Lucy Wang
High-quality design and affordability don't have to be mutually exclusive—just ask the architecture students at Auburn University's Rural Studio, a "social justice architecture" program that has been designing sustainable and low-cost homes for the rural poor in an initiative called the 20K Project. Now, after a decade of design/build experience, Rural Studio is hoping to take their affordable designs to mass production, starting with its first two dwellings built out-of-state at the bucolic New Urban village of Serenbe in Chattahoochee Hills, Georgia.
While the partnership between Rural Studio and the high-end Serenbe community may seem odd at first glance, the mutually beneficial collaboration provides a valuable field testing opportunity for the 20K Project and gives students their first chance to work with a commercial contractor and take the project through all stages of construction, including zoning and code compliance. In return, Serenbe's Art Farm has gained two live/work studios that will serve as housing for the community's artists residency program.
Rural Studio began the 20K Project in 2005 as a research project that aimed to create a mass-market affordable house that could be built for $20,000, a cost considered affordable for potential homeowners living on Social Security who are unable to qualify for commercial credit. To date, students have designed and built 17 low-cost prototypes, which include one-bedroom and two-bedroom models.
The two one-bedroom, one-bath homes installed at Serenbe measure under 550 square feet each. The materials, which were priced at Home Depot and include corrugated metal cladding and timber, cost about $13,000. Elevated on piers, the homes are designed with passive heating and cooling principles to keep utility costs low. The two cottages at Serenbe are beautifully furnished and finished—as expected from two prototypes built to show what the 20K Project can accomplish given a generous partnership.
Related: Affordable, colorful and humane housing for London's homeless pop ups in just five months
"Once these field tests have been deemed successful it is the ultimate goal to develop a set of construction documents and specifications complete enough for construction in a climate similar to our local region, and easily adjusted to meet the building requirements of other areas beyond," says a statement in the press release. Though these student-designed prototype homes at Serenbe are admirable and beautiful, they also have a long way to go. According to ArtsATL, the two cottages and the connecting deck cost $135,000 to build, not to mention the challenges of hiring contractors for low-cost homes and zoning ordinances that regulate building size.
+ Rural Studio 20K Project
Images via Sunshine Sachs, © Serenbe
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8 thoughts on "Students design beautiful homes for mass-production at just $20,000 each"
Luis Adolfo Gomez Espinoza July 23, 2017 at 1:32 am
http://www.goodshomedesign.com/the-hunter-log-cabin-for-only-5885/
Anonymous August 21, 2016 at 5:53 am
Yes Yes YES! Housing is fast becoming the crisis issue all around the country, and the New Economy us not exactly showering us with opportunities that would pay the mortgage on a traditional mid-six-figure home. If you make less than $25 an hour, or $50k a year, it's just not feasible. HOWEVER... $20k? Or even $25k, $30k, heck let's just shoot for the moon, $40k? Yes, that becomes achievable! I can have a HOME! A home that's MINE! On the societal level, the homeless crisis here in Portland for example is, inarguably, the single largest, most pressing problem faced by our city. Just 6 or 7 years ago, our city built a brand new apartment building designed for career homeless people to move into for long term, permanent housing. That's all well and good, but the small, stark and very, very utilitarian housing units ultimately cost the taxpayers over $250,000 PER UNIT! THAT'S OVER A,QUARTER MILLION DOLLARS FOR EACH ROOM! THAT'S ASININE, UNSUSTAINABLE AND JUST PLAIN STUPID. We can do better. The 20k Project demonstrates this admirably well. Thank you!
Anonymous February 8, 2016 at 1:16 am
You be lucky if you can just live without paying cut throat property taxes. Even though it cost 20k, you will be taxed according to market rate, because F up tax clerk will tax you at what it's worth usually 150k+ which is the market rate for a new house anywhere in USA. so your new property tax bill will be 2k+ a year easily. Won't pay, well the county will just auction it off from beneath you. Welcome to america where banks and gov. are the pirates.
Davidg February 1, 2016 at 9:01 am
This is a great initiative. With the way the economy is going more and more people might be needing cheap housing alternatives like this. It's an added bonus that they are beautiful!
timallard January 25, 2016 at 11:14 am
The black walls absorb thermal energy, most colors also do this. From heat-transfer studies I'd suggest insulating outside the sheathing with furring to allow condensation to drip off, and, reduces radiative gain-loss to wind & sun. If you do this it triples the R-factor, hemp-mortar also does this and is fireproof, won't allow fungus to grow against it and transpires moisture so allows walls to dry out.
Anonymous January 24, 2016 at 6:59 am
I think they are great. Great job!
Anonymous January 22, 2016 at 8:02 pm
They are pretty nice. But if they are passive design, why is one of them black?
So the goal was to spend $20,000 / House... but the article ends and says the 2 houses cost $135,000 (minus labor). What was the point of this article then??? to prove that a mark like $20,000 is just a gross underestimation??
Rural Studio 20K House Project
20K project by Rural Studio at Art Farm Serenbe
Rural Studio began the 20K Project in 2005 as a research project that aimed to create a mass-market affordable house that could be built for $20,000, a cost considered affordable for potential homeowners living on Social Security who are unable to qualify for commercial credit.
To date, students have designed and built 17 low-cost prototypes, which include one-bedroom and two-bedroom models.
The two one-bedroom, one-bath homes installed at Serenbe measure under 550 square feet each.
The two cottages at Serenbe are beautifully furnished and finished—as expected from two prototypes built to show what the 20K Project can accomplish given a generous partnership.
"Once these field tests have been deemed successful it is the ultimate goal to develop a set of construction documents and specifications complete enough for construction in a climate similar to our local region, and easily adjusted to meet the building requirements of other areas beyond," says a statement in the press release.


text:
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Jia Ni (Jarnie) Zhu
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Dr Jia Ni Zhu, 'Jarnie' to her patients and friends, is an experienced doctor with a wide range of skills. Originally from New Zealand, Jarnie completed her Bachelor of Medicine, Bachelor of Surgery and Bachelor of Medical Science in 2009 at the University of Melbourne. She also took up the opportunity in her final year of studies to go to The School of Medicine at the University of Cambridge in the UK and her research has been previously published in the Medical Journal of Australia.
Jarnie gained invaluable experience in paediatrics, gynaecology, obstetrics, cardiology, endocrinology, psychiatry and surgery while working in hospitals within the Southern Health Network (including Monash Medical Centre). She is a supervisor for General Practice registrars and an Examiner for the Royal Australasian College of General Practitioners. Since 2015, Jarnie has been providing quality and dedicated care for her patients in and around Elwood.
Jarnie's special interests are:
Gynaecology and sexual health, including Implanon insertions and removals
Spending time with her friends and family, Jarnie also enjoys travelling and the simple things in life; walking along the beach with her husband and their dog Olli, a golden retriever.
Bahman Mansourzadeh
MD, FRACGP
Dr Bahman completed his doctorate of medicine in 2004 and gained experience in general and emergency medicine in Iran before moving to Australia in 2010. He obtained his Fellowship from the Royal Australian College of General Practitioners in 2014.
Having worked in both urban and rural settings in Queensland, Western Australia, Tasmania and Victoria, Dr Bahman is a passionate doctor who enjoys all aspects of general practice. He has a particular focus on:
Musculoskeletal conditions (joint pains and sport injuries)
Women and children's health
Sexual and mental health
Skin checks and skin cancer management (special interest)
Outside his office, he enjoys playing sports (especially soccer) and loves to travel.
Sepideh Rouhi
Dr Sepideh graduated with a Degree of Medicine in 2004 and worked as a general practitioner for few years in Iran. She then completed her masters in the UK on "Nanotechnology & Regenerative Medicine," specifically focussing on breast cancer. After a few years of working in Australia, Dr Sepideh obtained her Fellowship from the Royal Australian College of General Practitioners in 2017.
Dr Sepideh has worked in QLD, WA, TAS and now in Victoria. She really enjoys general practice and has experience in:
Women and children's health
She enjoys travelling the most, which is one of the reasons she chose to move to and travel around Australia.
Fatima Zahora
MBBS, FRACGP
Dr Zahora received her MBBS degree in 2002 from Dhaka University, Bangladesh. She started her medical career in Australia in 2006. She worked in regional Victoria for 3 years and moved to Central Queensland in 2010 to complete her general practice training. Fatima obtained the fellowship of Royal College of General Practitioners in 2012. She has worked in GP settings across Australia for last 9 years.
Fatima has broad experience in obstetrics and gynaecology, antenatal care, post natal care, Implanon insertion and removal, Mirena removal, family planning. Furthermore, she is a shared maternity care affiliate with multiple hospitals.
Fatima's special interests are:
Fertility and Family Planning
Skin checks
Patients will find her approachable and caring, so please feel free to book an appointment to discuss any health concerns you have.
Magdalena Simonis
MBBS (Melb), FRACGP, DRANZCOG
Magdalena Simonis is an examiner with the Royal Australian College of General Practitioners, teaches University of Melbourne Medical Students and is on the Royal Australian College of General Practitioners Expert Committee for Quality Care. Magdalena is Honorary Research Fellow with the department of General Practice at the University of Melbourne, and has spearheaded research that has been published achieving international recognition.
Magdalena is a GP with interests in:
Shared antenatal care
Furthermore, she is on the board of Women's Health Victoria, is President of the Victorian Medical Women's Society, on the strategy and policy committee for Breast Cancer Network Australia and is on the board of National Hearing Heath Advisory board Australia. Her articles are regularly published in Yours magazine, Girlfriend, Women's Health, Medical Republic and she is has been an RACGP representative to senate enquiries.
Despina Pytharoulios
MBBS, FRACGP, Cert Allergy (RCH), Cert Eczema (RCH), Cert Clinical Occupational Medicine
Dr Despina Pytharoulios joined the practice in 2007. She completed her Bachelor degree in Medicine at the University of Monash and gained her Fellowship of the Royal Australian College of General Practitioners in 1996. She undertook further training at the Royal Children's Hospital, completing certificates in both Allergy and Eczema. She has a particular interest in the diagnosis and management of asthma, women's health and paediatrics.
Despina enjoys working in Occupational Medicine, and furthered her knowledge in this area by completing a certificate in Occupational Medicine in 2012. A calm and approachable person, Despina enjoys the broad variety of presentations in general practice.
EC Wong
Dr EC Wong joined the team at St Kilda Road in 2006 and has been working in general practice for over 30 years in the South Yarra area and enjoys all the activities undertaken by practitioners working in a busy general practice.
As well as general practice, he continues to regularly assist in plastic surgery. In over 30 years working in this field he has gained useful skills and experience in minor surgical procedures including skin cancer excision.


Start small if you want to keep a New Year's resolution. The top reason people abandon their goals for self-improvement is that they set their expectations too high—targeting a pie-in-the-sky figure of 20 pounds lost, for example, or $1, 000 saved. Instead, "Start with very, very small steps, " Dr. Lina Shihabuddin, a psychiatrist and chief medical officer at RWJBarnabas Health in West Orange, N.J., told USA Today. Otherwise, you can get frustrated and give up on your goals altogether.


Everyone has their own characters to root for in Game of Thrones. There's no shortage of heroes and social climbers to pick for a favorite, but, as the blood-soaked seasons have wound on, I've been sorry to see my favorites killed off one by one. In Westeros, direwolves are the real underdogs, facing down the same extinction that they suffered in the real world.
George R.R. Martin's canids are a curious breed. The beasts are enormous, with some rumored to reach the size of ponies, and they're also part of the novelist's Pleistocene pastiche. Along with woolly mammoths, direwolves are creatures that really lived on Earth not so very long ago. And while Game of Thrones has largely neglected these poor pups, paleontologists have been able to dig up quite a bit about the lives of the Ice Age pack hunters that used to pad around North America.
If you were able to wander around the Ice Age Americas between 125,000 and 10,000 years ago, you would have been able to hear the howls of dire wolves almost everywhere you went. Their bones have been found from southern Alberta, Canada all the way down to Bolivia at elevations from sea level up to 7,400 feet. In the what would become the United States, they loped from coast to coast, although the hundreds upon hundreds of specimens drawn from the La Brea asphalt seeps in southern California puts all other collections to shame.
All these remains reassemble into an animal that wouldn't have been quite so imposing as Lady, Ghost and the other fictional canids in George R.R. Martin's world. Canis dirus were larger and more burly than the gray wolves that were also slinking around during the Pleistocene, with an estimated average weight of 130 pounds compared to 88 for gray wolves. That's hefty, but nowhere near horse size. In fact, telling a living dire wolf apart from a gray wolf might have been difficult without looking them both in the mouth. Among other dental differences, dire wolf jaws have a very large first molar shaped to give them a better shearing bite than their relatives.
A small sample of the many dire wolves found at the La Brea asphalt seeps. Photo by Brian Switek.
Still, despite the anatomical points that mark them as a different species, dire wolves probably lived much like the gray wolves that still lope around parts of North America. The sheer number of remains found at the La Brea asphalt seeps, outnumbering any other large vertebrate by far, only make sense if dire wolves were pack hunters, which falls into accord with evidence that these carnivores were chasing mid-sized herbivores such as horses. Wolves lack the grappling abilities of cats, relying instead on their running endurance and jaws, and so the dire wolf has almost always been envisioned as roving through prehistoric habitats in packs. More than that, some dire wolf remains at La Brea show painful injuries that would have crippled the animals and yet show signs of healing. This hints that these dogs had some sort of social support structure that allowed them to survive.
Dire wolf teeth and jaws do more than just fill in details about their hunting lives, though. Male and female dire wolves have similarly-sized canine teeth, for example, suggesting that dire wolves formed pair bonds with mates instead of males vying for dominance. And teeth also record tough times for dire wolves. About 15,000 years ago, the dire wolves of La Brea were chewing bone more often. Fractured teeth suggest that dire wolves really had to make the most of every carcass. Better times came back by about 12,000 years ago, although the very last of these carnivores disappeared just after 10,000 years ago. Exactly why we can't find them still loping around the Americas today is a mystery.
"There's not been a direwolf sighted south of the Wall in two hundred years." This is what Theon Greyjoy says when Robb Stark discovers a litter of six pups, helpless after the death of their mother, at the very beginning of Game of Thrones. It seems that the series is moving towards extirpating them all over again, repeating the slip of extinction that their real counterparts suffered. But, according to the lore, there are wolves still north of the Wall, and winter is coming. I hope the direwolves come with it.
Harris, J. 2010. Rancho La Brea: Death Trap and Treasure Trove. Los Angeles: Natural History Museum of Los Angeles County.


Deore XT upgraded with Di2 and wireless capabilities for instant shifting with extreme accuracy under all conditions.
Between the top professional racers and the weekend warriors are a group of very skilled, highly competitive mountain bikers. These are the privateers of the sport; self-supported, motivated riders who put in the hours to keep race-fit and are always on the look out for that race-winning advantage. If you're one of this select group, then Shimano had you in mind when it created the game-changing Deore XT Di2.
With the Shimano Deore XT Di2, at the touch of a button you can instantly shift gears with extreme accuracy under all conditions. Fly through a sea of switchbacks, attack those rollers, shift gears on very steep trails with the confidence that you'll always have the ideal gearing even when your hands are aching or frozen.
Combined with the built-in trim function, which automatically adjusts the front derailleur, you always have access to that perfect gear instantly for the ultimate pure-adrenaline racing experience.
The most groundbreaking upgrade to Deore XT Di2 is its Bluetooth connection to Shimano's E-tube program. Now you can wirelessly set up the Di2 shifting behaviour using your computer or tablet, or even via your smartphone while out on the trail.
With its customisable shift map, you can program the next best gear at which Di2 shifts when going through the gears. You also have the option to simply use one shifter to take care of your front and rear gear changes thanks to the Synchro Shift technology.
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Deore XT Di2 comes equipped with front and rear FIREBOLT shifters, for easy operation and accurate shifting with an ergonomic rotary action, short single-click action as well as effortless custom multi-shift possibilities. The FIREBOLT shift button placement is flexible and can be positioned exactly where your thumbs naturally rest. This allows you to shift faster to seamlessly match your efforts.
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Front shifting boasts 25% increase in power over the mechanical Deore XT, while shifting in the rear remains smooth – even under high loads, on steep climbs or when the cassette is riddled with mud. This is also thanks to its Shadow RD+ technology that eliminates chain bounce to keep the chain on the sprockets under all conditions.
Shimano Deore XT Di2 components will be available in July, so get ready to triumph on the trail!
Deore XT: Over 2000 components of adventure!


text:
Baltimore: The Plague Ships #2
Baltimore: The Plague Ships
Lord Baltimore sets sail from a harbor choked with sunken ships, where plague victims are burned in great furnaces. Lord Baltimore finally reveals a terrible incident that took place during the war, where his men fell victim to creatures that feast on the freshly dead, and where Baltimore himself first met the vampire who has become his obsession. Praise for the novel Baltimore; or, The Steadfast Tin Soldier and the Vampire: "Mythic adventure, midway between Lovecraft and the Brothers Grimm. The book burns with black inspiration."Sci Fi Magazine
Christopher Golden Mike Mignola
Ben Stenbeck
Supernatural/Occult Horror Action/Adventure
Baltimore Big Bundle
Vol. 1: The Plague Ships
After a devastating plague ends World War I, Europe is suddenly flooded with vampires. Lord Henry Baltimore, a soldier determined to wipe out the monsters, fights his way through bloody battlefields, ruined plague ships, exploding zeppelins, and submarine graveyards on the hunt for the creature who's become his obsession.
Witchfinder
Mike Mignola teams up with artist Ben Stenbeck (B.P.R.D.: The Ectoplasmic Man) for a look into one of the Hellboy universe's greatest enigmas: nineteenth-century occult investigator Edward Grey!
Rise of the Black Flame
The bizarre origin of the BPRD's greatest foe. Young girls are going missing from the cities of Siam, and the trail leads to the jungle hideout of a bloodthirsty cult wielding an ancient evil power, the Cult of the Black Flame. Christopher Mitten joins the Mignolaverse!
Lobster Johnson
After years of captivating fans from the pages of Hellboy and B.P.R.D., the pulp-style adventures of Lobster Johnson take the limelight in this collection of the Lobster's first solo series.
Rasputin: The Voice of the Dragon
With the World War II raging, Hellboy's future guardian Trevor Bruttenholm enlists with Britain's Military Intelligence, where he uncovers a collection of strange messages. Believing it to be an occult language, he follows his hunch and is thrown into a world of animated corpses, deadly mystics, and Nazi agents. The treacherous journey leads him face to face with the man who will bring Hellboy to


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It was hard for us not to lose it during that song. We praise Him in all things. How much sweeter and more blessed an occasion it was knowing that He could have just as easily allowed him to lose those fingers, yet He graciously spared him that. My husband is once again able to play guitar, one of his passions. God blessed him with a gift that he so enjoys using to worship Him, and my heart overflows with thanksgiving that he is able to play and rejoice in God's goodness. I didn't know if that day would come. It did. To God be the glory!
3. CHEERS to a Target date with my Princess!! ... I L-O-V-E their Mango Smoothies! Y U M!!
4. Princess modeling the cute new outfit she got during our shopping trip. I noticed a clearance price on the pretty pink, sparkly skirt she was eyeing. She never wants us to spend a dime on her, and never asks for anything, so it's such a joy to bless her with things when we go out for mom/daughter shopping trips every so often!
5. Pad Thai & egg rolls from our favorite restaurant. They totally hit the spot.
So great to here your husband is doing well and able to play again!
OMGosh gave me chills about his hand. God was watching over him that day.
God definitely was watching over him that day!! Can't take for granted His protection. I had a friend who literally finished the Boston marathon and was already on the subway just minutes before the explosion happened. Never would have fathomed when I prayed for her protection that morning that it would be for such a thing! And that song brings me to tears every time! Thanks again for always linking up with me, I love getting to share our weeks with each other!! Hope you have a fabulous weekend friend!
I am so glad your husband is on the mend and able to play the guitar again. So glad he wore the right gloves that day...wow!
I was super happy to get to feature you! I hope you have a great week this week with many more than 5 loves for your next 5 on Friday.


text:
var expect = require('chai').expect,
  through = require('through2'),
  ReadableStream = require('readable-stream/readable'),
  multistreamMerge = require('./');

describe('multistream-merge', function() {

  it('should merge 2 readable streams (buffer)', function(done) {
    var stream1 = new ReadableStream();
    stream1._read = function() {
      var self = this;
      setTimeout(function() {
        self.push('astring1');
      }, 50);
      setTimeout(function() {
        self.push(null);
      }, 100);
      this._read = function(){};
    };
    var stream2 = new ReadableStream();
    stream2._read = function() {
      var self = this;
      setTimeout(function() {
        self.push('astring2');
      }, 30);
      setTimeout(function() {
        self.push(null);
      }, 70);
      this._read = function(){};
    };

    var buffer = [];
    multistreamMerge(stream1, stream2)
      .pipe(through(function(chunk, enc, cb) {
        buffer.push(String(chunk));
        cb();
      }))
      .on('finish', function() {
        expect(buffer).to.have.length(2);
        expect(buffer).to.contain('astring1');
        expect(buffer).to.contain('astring2');
        done();
      });
  });

  it('should merge 2 readable streams (objectMode)', function(done) {
    var stream1 = new ReadableStream({objectMode: true});
    stream1._read = function() {
      var self = this;
      setTimeout(function() {
        self.push({obj1: true});
      }, 50);
      setTimeout(function() {
        self.push(null);
      }, 100);
      this._read = function(){};
    };
    var stream2 = new ReadableStream({objectMode: true});
    stream2._read = function() {
      var self = this;
      setTimeout(function() {
        self.push({obj2: true});
      }, 30);
      setTimeout(function() {
        self.push(null);
      }, 70);
      this._read = function(){};
    };

    var buffer = [];
    multistreamMerge.obj(stream1, stream2)
      .pipe(through.obj(function(chunk, enc, cb) {
        buffer.push(chunk);
        cb();
      }))
      .on('finish', function() {
        expect(buffer).to.have.length(2);
        expect(buffer[0].obj1 || buffer[0].obj2).to.be.true;
        expect(buffer[1].obj1 || buffer[1].obj2).to.be.true;
        done();
      });
  });
});

redpajama_set_name: RedPajamaGithub