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# Thread: trig word problem; sinusoidal function

1. ## trig word problem; sinusoidal function

A piston in an engine moves up and down in a cylinder. The height, h centimetres, of the piston a t seconds is given by the formula h= 120 sin Pi t+ 200.
-State amplitude & period
-State max & min. heights of piston
-How many complete cycles does the piston make in 30 min.

I have no idea where to start. Is this the same as y=a sin k(x+c)? Should I graph the equation as is and go from there?

Thanks in advance for any suggestions!

W.

2. Originally Posted by sux@math
A piston in an engine moves up and down in a cylinder. The height, h centimetres, of the piston a t seconds is given by the formula h= 120 sin Pi t+ 200.
-State amplitude & period
-State max & min. heights of piston
-How many complete cycles does the piston make in 30 min.

I have no idea where to start. Is this the same as y=a sin k(x+c)? Should I graph the equation as is and go from there?

Thanks in advance for any suggestions!

W.
Well for starters is this equation:
$h = 120 ~ sin(\pi t) + 200$
or
$h = 120 ~ sin(\pi t + 200)$

-Dan

3. Thanks for the quick reply! Um . . . I'm sorry, but the equation in my book has no parentheses! (it's kind of a crap correspondence course I am taking for Grade 11 Math)....

It reads exactly how I typed it in my first post.

4. Originally Posted by sux@math
A piston in an engine moves up and down in a cylinder. The height, h centimetres, of the piston a t seconds is given by the formula h= 120 sin Pi t+ 200.
-State amplitude & period
-State max & min. heights of piston
-How many complete cycles does the piston make in 30 min.
All right then, we read it almost without any parenthesis. The $\pi t$ is obviously meant to be in the argument of the sine function; I will take the 200 as outside.
$h = 120 ~sin(\pi t) + 200$

The amplitude should be obvious, its 120 cm.

The period of a function is how much time it takes for one oscillation. One oscillation of the sine function is $2\pi$. So find when $\pi t$ is $2 \pi$:
$\pi T = 2 \pi \implies T = 2~s$

I'll leave it to you to determine the max and min heights.

As to how many complete cycles are in a time period of 30 minutes, how many periods are in 30 minutes? (Remember that the period is in seconds, not minutes!)

-Dan

5. Thank you, Dan!!!


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Register now and save up to $200 Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code ## Percentile and Raw Score This topic has 4 expert replies and 2 member replies camtip Senior | Next Rank: 100 Posts Joined 17 Aug 2010 Posted: 30 messages Followed by: 2 members #### Percentile and Raw Score Mon Jul 30, 2012 8:37 am Hi, I have just taken a Practice test, and scored a 600 (Q37/V32). My target is to have an almost balanced score i.e. Q37/V37. But is there a way to know which score a Q37/V37 would give? Thank you camtip Senior | Next Rank: 100 Posts Joined 17 Aug 2010 Posted: 30 messages Followed by: 2 members Wed Aug 22, 2012 4:12 am David@VeritasPrep wrote: Camtip - Two things - if you look at the percentiles a score of 37 and 37 is pretty unbalanced actually. The Verbal percentile would be much higher at 81%-ile while the Quant is only the 46th-tile. Even your current score of Quant 37 and Verbal 32 is still weighted toward the verbal with a 64th percentile in Verbal equaling a scaled score of 32. Second, while it is true that different percentiles are represented by the scaled score "37" (i.e. a "high 37" and a "low 37.") It is just not possible that the same score would give you a 610 and someone else a 650. Rebecca said that two students with the same scaled score "could receive different total scores" but that would mean 610 and 620 but not 610 and 650. The variation in scaled scores is simply not that great as to take you from the 67th %ile (a 610) to the 79th %ile (a 650). GMAC is always very careful in what they say and so I thought I would make that clarification for you. Thank you david, That was exactly my point. So, I understant that a balanced score means "balanced percentile" a Q45 V36 is actually a balanced score since both are ine the 72-73rd percentile. ### GMAT/MBA Expert David@VeritasPrep GMAT Instructor Joined 22 Feb 2010 Posted: 2193 messages Followed by: 508 members Upvotes: 1186 GMAT Score: 770 Wed Aug 22, 2012 6:12 am I agree with you! That is how I would define a balanced score - balanced percentages. It is very interesting that the room in the scale is all on the top end of the verbal, I mean everything from a 45 to a 51 is all just within the 99th percentile band, and the room is all on the lower end of the Quant, with just 12 scaled score points above the 50th percentile (40 to 51) and over 20 points of scaled score below the 50th percentile. _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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Hi, Camtip.
The short answer to your question is “it depends.” Your total score is based on raw performance on both the Verbal and Quantitative sections. A range of raw scores will map onto a single scaled score, but since the Total score is based on the raw performance, greater differentiation is possible. That means the same Quant and Verbal scores can map to different Total scores. A 37 score in Quant would put you at Mean, and a 37 in Verbal would be above Mean, but it would be difficult to estimate your Total Score.

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camtip Senior | Next Rank: 100 Posts
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Mon Jul 30, 2012 1:04 pm
Let me rephrase:

If I understand well, a student can score Q37/V37 and a total of 610 and another student can score

Q37/V37 and score 650?

Thank you

### GMAT/MBA Expert

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Mon Aug 06, 2012 12:31 pm
Hello, Catnip. Two students with a balanced score of Q37/V37 could receive different total scores, yes.

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Wed Aug 22, 2012 4:03 am
Camtip -

Two things - if you look at the percentiles a score of 37 and 37 is pretty unbalanced actually. The Verbal percentile would be much higher at 81%-ile while the Quant is only the 46th-tile. Even your current score of Quant 37 and Verbal 32 is still weighted toward the verbal with a 64th percentile in Verbal equaling a scaled score of 32.

Second, while it is true that different percentiles are represented by the scaled score "37" (i.e. a "high 37" and a "low 37.") It is just not possible that the same score would give you a 610 and someone else a 650. Rebecca said that two students with the same scaled score "could receive different total scores" but that would mean 610 and 620 but not 610 and 650. The variation in scaled scores is simply not that great as to take you from the 67th %ile (a 610) to the 79th %ile (a 650). GMAC is always very careful in what they say and so I thought I would make that clarification for you.

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The Korean Physical Society 06130 22, Teheran-ro 7-gil, Gangnam-gu, Seoul, Republic of Korea 610 Representation : Tae Won NOH TEL: 02-556-4737 FAX: 02-554-1643 E-mail : webmaster@kps.or.kr Copyright(C) KPS, All rights reserved.

# The XXX International Conference on Neutrino Physics and Astrophysics (Neutrino 2022)

30 May 2022 to 4 June 2022
Virtual Seoul
Asia/Seoul timezone

## Neutrino mass and the early universe

Not scheduled
5m
Virtual Seoul

#### Virtual Seoul

Poster Neutrinos and cosmology

### Speaker

Bowen Fu (University of Southampton)

### Description

The long-existing problem of neutrino mass and mixing can be connected to cosmological phenomena, such as the leptogenesis and the existence of dark matter (DM). In the extension of the type I seesaw model with two right-handed (RH) neutrinos, the seesaw Yukawa can drive the DM production, even with the competition from gravitational effect and constraints from leptogenesis. However, the DM production driven by the seesaw Yukawa is not compatible with the testability of the traditional type I seesaw model, which motivates us to seek a variation. By considering two Higgs doublets, a new type Ib seesaw model is proposed, which can explain the neutrino mass, dark matter and leptogenesis simultaneously while keeping its testability. Moreover, the type Ib seesaw model allows a different approach to dark matter production and stability through a $U(1)'$ extension.

### Primary author

Bowen Fu (University of Southampton)


text:
# Tag Info

8

The flickered orders are postonly bid at 15.16. The exchange slides it back to 15.15 to avoid a locked market. Submitting firm sees the slideback and cancels. Then tries again. When the 15.16 offer is executed or cancelled out, the offer moves to 15.17 then the postonly bid at 15.16 goes through at the targeted price and gains good queue position.

6

Re the first part of the question: Quants play no role whatsoever in the actual execution tasks of trading regardless of frequency or whether we talk systematic trading or not. Its done by traders/execution traders (especially on the discretionary side) and not by quants. As your title suggests your focus is on hft, I still would claim quants do not really ...

6

There is a wide literature on optimal execution, among others: Rigorous Strategic Trading: Balanced Portfolio and Mean-Reversion, by Lehalle, 2009, Vol. 4, No. 3: pp. 40-46 Optimal Control of Trading Algorithms: A General Impulse Control Approach, by Bouchard, Dang, Lehalle, in SIAM J. Finan. Math., 2(1), 404–438 Optimal starting times, stopping times and ...

6

For reference, note that execution strategies for some types of futures contracts can be very different from equities. An example are Interest Rate Futures, e.g. here. The main reason lies in microstructure differences. For some more details see the white paper "US Treasury Futures Roll Microstructure Basics" by Quantitative Brokers (I have no affiliation ...

6

You are correct that large orders should be algorithmically broken-up. Perhaps the most straightforward algo is the VWAP (volume-weighted average price), which most brokers offer. Since a VWAP is easy to compute, the trading details are often transparent to the user. There are more sophisticated algos, like Arrival Price, though not every broker offers ...

6

The shops I've worked for have had access to multiple brokers, but not for redundancy as your question implies. It's often because no one broker can handle every task. For example, I might need a floor broker, a dark-pool broker, an algo broker, and a separate prime broker. Each agency handles a different requirement. Even if one broker could handle all of ...

5

This isn't exclusive to VWAP; any assumed trade price (NBBO, Arrival Price, etc) has the same vulnerabilities. Many shops often lump market impact with slippage and transaction costs when modeling the difference between the ideal price and the realized price. To model the impact during a backtest for a given trade price, assess a penalty: This penalty can ...

5

It depends if the large incoming sell order is a market order or a limit order. If it is a market order, it will immediately "sweep" through as many levels of the bid book as neccessary to get the required volume. There is no chance for someone to add more bids to execute against the market order. A limit order will execute against all the bid volume ...

5

Most exchanges will cross a large order with numerous smaller orders so long as the large order sufficiently crosses the book to cause a fill. This is obviously dependent on specific instructions on the large order causing the cross as well as the orders on the other side of the book. As for the second part a new order coming in should only cross with the ...

5

If your original algo's goal was the follow the top-of-book quote, then it should have had some minimums before it would join a new quote. For example, the reference quote must have a minimum size shown and must be live for a minimum amount of time before you'll join. Also, it helps to "stack the book" by breaking your quote into smaller orders at worse ...

4

If you want to be more aggressive without revealing your hand, place your orders as hidden orders inside the bid/ask. Algos on the other side will fish with small size orders to see what is hidden however. The fishing will not reveal the size of your order, but reveal that something is there. Can get some size done this way. The advice above regarding ...

4

If you look at the ladder, you might have some insight, but it's mainly speculation. The only way to be really "sure" in my opinion would be to have some insight from a broker. Otherwise, what I'd try to look for is to recognize execution schemes, but again you have to know the algorithms of all the participants in order to determine "who" it was. In my ...

4

Everyone can do what HFTs do, if they spend the necessary time and money to build and run the infrastructure required. This may involve becoming a regulated broker/dealer, but it is in no way an invite-only club. Now, to your specific question, you'll find some information on Haim Bodek's site. Bodek does content that ISO's and Day ISOs are used to gain ...

4

I have heard of several allegations in the recent days, but they are mostly baseless. However, there are a rare, few trading venues whose matching rules are most often accused of giving unfair order execution advantages to certain firms. These usually arise from violations of the standard price-time priority: IEX's broker priority rule. "All orders will ...

4

Think of it like a forward trade on the settlement price. If you are buying with a TAS you are agreeing to go long the futures contract at the settlement price (+/- the offset), and whoever you trade with is agreeing to go short at the same price. It is guaranteed because the exchange becomes the counterparty for both traders and there is a margin deposit. ...

3

With respect to what you need, you have to consider different aspects of optimal trading: the Almgren-Chriss framework (cited by Anna, since Jim and Alex -amongst others- extended it) focus on obtaining an optimal trading rate, it is nice but not really what you need. You can nevertheless use it to plan / schedule your trading during the day. but what you ...

3

In the paper Optimal split of orders across liquidity pools: a stochastic algorithm approach (2011) we present the theoretical aspect of liquidity seeking, thus you will learn how they work. There is a seminal (once again) white paper by Robert Almgren on iceberg chasing that is very informative too.

3

Look into OLF's Findur http://www.olf.com/software/financial-capital.html highly customizable trading platform, will not give you everything you mentioned out of the gate but has capability to get there with some development effort

3

To get a feel for it think about an extreme scenario. Suppose I have an order to buy $100bln VWAP in IBM over the course of one day. My "cost" relative to VWAP will be near zero, b/c I will be on the buy side of every trade that day. However, my market impact will be extremely high b/c IBM will fall like a rock the next day, leaving me with huge losses. ... 3 Can't speak to the cash equity space, but at futures shops I think it is common to have the phone number of a give-up broker in case the power goes out or something, but it is uncommon to ever use them. 3 This could be very difficult to determine in practice, because the axe (who controls the supply and demand) wants to hide his tracks. Also consider the axe's aliases. I mention this because you would need to take into account the axe disguising his trades through another market maker (for example, Goldman trading through ARCA, or even showing sales between ... 2 Here is a good mental model. The exchange's matching engine processes incoming orders one at a time: all effects of an order on the book are settled before any further incoming orders for the same instrument are looked at. So, when a marketable order comes in, it is matched against resting orders "atomically", producing one or more fills. If this completely ... 2 In addition to @madilyn's answer, there is one point that needs to be addressed and that is often called an unfair advantage although it is merely a competitive advantage. Take the US Equities market. There are now several venues on which the same symbols are traded. If one HFT acquires information about one symbol in one venue - e.g. due to a limit order ... 2 So to summarize the comments given, dark pools seem to do the following: banning of specific firms by the dark pool requiring a minimum order size banning of firms by the participants flow analysis to separate different types of players To me it seems that this covers most of the reasonable actions they could possibly take and whether this is done seems ... 2 Here is how I would approach such a calibration. Assuming we have the necessary market data one can easily construct the emprical distribution of the arrival rate. Let$\lambda_{emp}(\delta)\$ be the empirical distribution. Then one can define a metric by $$m(k,A,N)=\sum_{i=1}^N |\lambda_{emp}(i)-\lambda^a(i)|$$ After you have decided upon a suitable ...

1

I guess this remark refers mainly to "penny stocks". In the US (it is not true in Europe where crossing is far more regulated) it may be possible to choose to cross at any point inside the bid-ask spread. It means that if it is closer to the bid than to the ask, it will advantage the buyer. In Sub Penny Trading in US Equity Markets (by Romain Delassus, ...

1

Based on the conditions you set forth this would be relatively simple in the CQG API. You can, for example, set up condition triggers in the IC. All you're really asking is for an API action following one of the triggers. Pseudo code would be something like this: Handles event trigger: If (additional conditions) then execute trade. Are you just shopping ...

Only top voted, non community-wiki answers of a minimum length are eligible


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# 2013 DEF CON CTF qualifying - musicman writeup

This writeup explains how we (Andreas Straub, rep and myself as part of 0ldEr0pe) ended up pwning the musicman service during the 2013 DEF CON CTF qualifying (for which we did’t qualify this year. meh!).

## Overview

The service listens on port TCP port 7890. As soon as you connect it starts throwing binary data at you. After dumping that data into a file, we recognized that this is a WAV audio file. After fucking everybody up by playing the high-pitch noise contained in that file a few times for the lulz we opened it up in audacity and saw some obvious structures:

That doesn’t look or sound like normal music.

## The binary

So, let’s have a look at the binary.

This is the main function:

void __cdecl main()
{
signed int v0; // [sp+2Ch] [bp-424h]@10
signed int v1; // [sp+30h] [bp-420h]@7
FILE *v2; // [sp+34h] [bp-41Ch]@1
int v3; // [sp+38h] [bp-418h]@4
int v4; // [sp+3Ch] [bp-414h]@11
__pid_t v5; // [sp+40h] [bp-410h]@14
int v6; // [sp+44h] [bp-40Ch]@4
int v7; // [sp+42Ch] [bp-24h]@7
int v8; // [sp+430h] [bp-20h]@7
int v9; // [sp+434h] [bp-1Ch]@7
int v10; // [sp+438h] [bp-18h]@7
int v11; // [sp+43Ch] [bp-14h]@11
int v12; // [sp+44Ch] [bp-4h]@1

v12 = *MK_FP(__GS__, 20);
signal(17, (__sighandler_t)1);
v2 = fopen("/home/musicman/key", "r");
if ( !v2 )
{
puts("Unable to open key file");
exit(-1);
}
fgets((char *)&v6, 999, v2);
fclose(v2);
SendString(0, (const char *)&v6, key);
v3 = socket(2, 1, 0);
if ( v3 < 0 )
{
perror("ERROR opening socket");
exit(1);
}
v1 = 1;
setsockopt(v3, 1, 2, &v1, 4u);
v7 = 0;
v9 = 0;
v10 = 0;
LOWORD(v7) = 2;
v8 = 0;
HIWORD(v7) = htons(0x1ED2u);
if ( bind(v3, (const struct sockaddr *)&v7, 0x10u) < 0 )
{
perror("ERROR on binding");
exit(1);
}
listen(v3, 5);
v0 = 16;
while ( 1 )
{
v4 = accept(v3, (struct sockaddr *)&v11, (socklen_t *)&v0);
if ( v4 < 0 )
break;
v5 = fork();
if ( v5 < 0 )
{
perror("ERROR on fork");
exit(1);
}
if ( !v5 )
{
close(v3);
drop_privs("musicman");
handle_client(v4);
}
close(v4);
}
perror("ERROR on accept");
exit(1);
}

The first important thing that it does is opening the keyfile and giving it to a function SendString(). After that the program does the usual socket bind-listen-accept-fork-dropprivs-dance until we land in handle_client where our connection is finally handled.

handle_client looks like this:

void __cdecl handle_client(int fd)
{
int v1; // [sp+1Ch] [bp-7DCh]@2
char s; // [sp+404h] [bp-3F4h]@2
int v3; // [sp+7ECh] [bp-Ch]@1

v3 = *MK_FP(__GS__, 20);
puts("Sending string");
SendString(fd, "Hello there...send me something\n", 0);
while ( 1 )
{
RecvString(fd, &v1, 1000u);
sleep(1u);
snprintf(&s, 0x3E8u, "You said: %s", &v1);
SendString(fd, &s, 0);
}
}

So, the only thing it seems to do is first sending a greeting and then receiving some data and echo it back to you. But the communication isn’t just done via normal ASCII characters. All the data is encoded in WAV-files.

## Sending Text

This is the core of the SendString() function:

for ( i = 0; i <= 7; ++i )
{
GenerateWave(v10, 0xFFu);
v10 += 4410;
}
for ( j = 0; j < (signed int)(v3 - 1); ++j )
{
GenerateWave(v10, a2[j]);
v10 += 4410;
}
for ( k = 0; k <= 7; ++k )
{
GenerateWave(v10, 0xFFu);
v10 += 4410;
}
if ( dest )
{
result = memcpy(dest, wav, *(_DWORD *)&wav[4] + 8);
}
else
{
v6 = send(fd, wav, *(_DWORD *)&wav[4] + 8, 0);
result = (void *)(*(_DWORD *)&wav[4] + 8);
if ( (void *)v6 != result )
exit(-1);
}

This function is responsible for taking an ASCII string and converting that into a WAV-file.

After some setup it calls the GenerateWave()-function 8 times with 0xFF, then it does the same for each byte in the passed string again and in a last step it again appends 8 bytes with a value of 0xFF. After that the resulting waveforms are either copied into a destination buffer or send out to a filedescriptor. The destination buffer was used for the key data and the filedescriptor is usually the socket of the client connection.

Now to get finally to the part where the actual ASCII-data is transformed into waveforms: The GenerateWave() function called repeatedly by SendString():

int __cdecl GenerateWave(int a1, unsigned __int8 a2)
{
double v3; // [sp+28h] [bp-20h]@2
signed int i; // [sp+34h] [bp-14h]@1
signed int j; // [sp+38h] [bp-10h]@2

for ( i = 0; i <= 2104; ++i )
{
v3 = sin((long double)f[0] * 6.283185307179586 * (long double)i / 44100.0);
for ( j = 1; j <= 8; ++j ) {
if ( ((signed int)a2 >> (j - 1)) & 1 )
v3 = sin((long double)f[j] * 6.283185307179586 * (long double)i / 44100.0) + v3;
}
*(_WORD *)(a1 + 2 * i) = (signed __int16)(double)(v3 * 3000.0);
}
return GenerateSilence(a1 + 4210);
}

The function looks complicated, but is actually pretty simple: It iterates over 2105 values, each representing a point in time. Audio data consists of a different values for different points in time to resemble a waveform. One second of this audio data in this example consists of 44100 samples. So what this code essentially does is iterating over 2105 of those samples, generate a sine wave with a frequency of f[0] and at the same time loop over all 8 bits of the byte to be processed and add other sine waves successively. The frequencies generated are coming from the array f:

.data:0804C0B8                 public f
.data:0804C0B8 ; __int16 f[]
.data:0804C0B8 f               dw 15000 ; DATA XREF: ReadChar+86r
.data:0804C0B8                          ; GenerateWave:loc_80499E8r ...
.data:0804C0BA                 dw 15250
.data:0804C0BC                 dw 15500
.data:0804C0BE                 dw 15750
.data:0804C0C0                 dw 16000
.data:0804C0C2                 dw 16250
.data:0804C0C4                 dw 16500
.data:0804C0C6                 dw 16750
.data:0804C0C8                 dw 17000

All these values are frequencies in HZ. So the first sine wave which is always present has a frequency of 15kHz, the lowermost bit of the to be processed byte has a frequency of 15.25kHz and so on.

So, for each byte to be transmitted a complex waveform consisting of up to 9 sine waves of different frequencies is generated followed by some silence. We obviously need to decode that stuff somehow, because the key is stored in this format, too. Let’s do it!

## Decoding

Actually, decoding is pretty easy: We need to process each transmitted symbol one after another and somehow extract all present frequencies for that duration. We can do that by transforming the signal from the time domain into the frequency domain using a fourier transformation. This display format shows us the spectrum of the signal or in other words which frequencies of a sine wave are contained in this complex signal consisting of several frequencies mixed together. We did this in python and plotted the spectrum a few times during development to see if we got everything right.

This is one of the 0xFF bytes at the beginning:

And this is how an H-character looks like:

You can perfectly see which frequencies are present and which are absent.

Now the last step we need to do is set all bits which have a peak at their frequency in the frequency domain and convert it to ASCII.

## Getting the key

Before we actually got the key we also implemented the encoding of ASCII characters into a waveform which turned out to be unnecessary, but it wasn’t that much work as we already knew how the algorithm worked. You can find all the routines in the exploit.

Now, how do we get the key? The buffer of the key wav-file is only used in the main-function. Stack canaries are everywhere and all the strings are properly bounds checked. So there is nothing we can do here to exploit that service. Mark then, after looking at the code for about five minutes, finally found the one bit we needed in the receive-path of the code. RecvString() reads a whole WAV-file from the socket and puts it into the „wav“-buffer somewhere in RAM. Then it verifies a few values from the header in the WAV-file to make sure the format is correct and then successively calls ReadChar with a pointer to the wav-buffer and the number of the sample where the symbol that should be decoded starts in the WAV-file:

if ( *(_DWORD *)wav == 1179011410
&& *(_DWORD *)&wav[8] == 1163280727
&& *(_DWORD *)&wav[12] == 544501094
&& *(_DWORD *)&wav[36] == 1635017060
&& *(_DWORD *)&wav[16] == 16
&& *(_WORD *)&wav[20] == 1
&& *(_WORD *)&wav[22] == 1
&& *(_WORD *)&wav[34] == 16
&& *(_DWORD *)&wav[24] == 44100 )
{
v7 = 0x44E8u;
v8 = 0x4D85u;
v6 = 0;
do
{
if ( 2 * v8 >= (unsigned int)(*(_DWORD *)&wav[4] - 35272) )
break;
*((_BYTE *)a2 + v6++) = ReadChar(v7, v8);
v7 = v8 + 1;
v8 += 2206;
}
while ( (signed int)(n - 1) >= v6 );
}
else
{
SendString(fd, "Only know how to process 16-bit mono pcm sampled at 44100Hz\n", 0);
}

Now, ReadChar() does some pretty complicated stuff at first sight:

int __cdecl ReadChar(int a1, int a2)
{
long double v2; // fst7@1
long double v3; // fst7@1
double v4; // ST08_8@13
double v5; // ST00_8@13
int v7[9]; // [sp+24h] [bp-64h]@2
double v8; // [sp+48h] [bp-40h]@1
double v9; // [sp+50h] [bp-38h]@1
double v10; // [sp+58h] [bp-30h]@13
int i; // [sp+60h] [bp-28h]@1
int wavBufferStart; // [sp+64h] [bp-24h]@1
int v13; // [sp+68h] [bp-20h]@1
int v14; // [sp+6Ch] [bp-1Ch]@1
void *ptr; // [sp+70h] [bp-18h]@4
int sampleDataOffset; // [sp+74h] [bp-14h]@6
char *v17; // [sp+78h] [bp-10h]@7
unsigned __int8 v18; // [sp+7Fh] [bp-9h]@12

wavBufferStart = (int)wav;
v8 = -9999.0;
v13 = a2 - a1;
v2 = log((long double)(a2 - a1));
v3 = ceil(v2 / 0.6931471805599453);
v14 = (signed int)pow(2.0, v3);
v9 = 44100.0 / (long double)v14;
for ( i = 0; i <= 8; ++i )
v7[i] = (signed int)((long double)f[i] / v9);
ptr = malloc(16 * v14 + 8);
if ( !ptr )
exit(-1);
sampleDataOffset = *(_DWORD *)(wavBufferStart + 4) - *(_DWORD *)(wavBufferStart + 40) + 8;
for ( i = 0; i < v13; ++i )
{
v17 = &wav[2 * (i + a1)] + sampleDataOffset;
*((double *)ptr + 2 * i + 1) = (long double)*(signed __int16 *)(&wav[2 * (i + a1)] + sampleDataOffset);
*((double *)ptr + 2 * (i + 1)) = 0.0;
}
for ( i = v13; i < v14; ++i )
{
*((double *)ptr + 2 * i + 1) = 0.0;
*((double *)ptr + 2 * (i + 1)) = 0.0;
}
four1((int)ptr, v14, 1);
v18 = 0;
for ( i = 1; i <= 8; ++i )   {     v4 = *((double *)ptr + 2 * (v7[i] + 1));     v5 = *((double *)ptr + 2 * v7[i] + 1);     v10 = GetFrequencyIntensity(LODWORD(v5), HIDWORD(v5), LODWORD(v4), HIDWORD(v4));     if ( v10 > 1000000.0 )
v18 |= 1 << (i - 1);
}
free(ptr);
return v18;
}

I won’t go into the details here, because I don’t know them and we don’t need to understand that function completely to exploit the service, but notice line 32: The function needs to find the samples in the WAV-file to do the frequency analysis for converting the waveforms back into binary data. This is done here.

It takes the value at offset 4 from the WAV-header, subtracts the value at offset 40 from that and adds 8. What?

Let’s have a look at the WAV-header in detail:

Offset Length Explanation
0 (0x00) 4 ‘RIFF’
4 (0x04) 4  − 8
8 (0x08) 4 ‘WAVE’
12 (0x0C) 4 ‘fmt ‘
16 (0x10) 4
20 (0x14) 2
22 (0x16) 2
24 (0x18) 4
28 (0x1C) 4
32 (0x20) 2
34 (0x22) 2
36 (0x24) 4 ‘data’
40 (0x28) 4
44 (0x2C) n sampledata

At offset 4 is the total filesize minus 8 and offset 40 is the offset in the file of the sample data. So the formula in line 32 basically calculates the offset of the sample buffer start in memory. Then in line 35 the sample is actually fetched from memory and processed.

Now the file size and the offset to the sample data is fully under our control. The filesize is used in the receive loop to receive data from the socket, so we can’t modify that. But the value at offset 40 is never checked for validity. We can have it point to a value outside of the wav-buffer.

If we look at the memory layout of the key- and the wav-buffer, we see that the key-buffer is directly in front of the wav-buffer. So, if we set this value to a big size, we are fetching the sample data from the key- instead of the wav-buffer. Fuck yeah!

How big does this value need to be? Every buffer has a size of 0xF4240 bytes, so we just add this exact value to the sample data offset of the WAV-file we are going to send to the musicman and we end up at the samples in the key-buffer. Instead of the data we send in the wav file, the the data in the key-buffer is then decoded to ASCII and then prepended with “You said: “ and finally sent back to us in another WAV-file. We decode that and boom - we got the key!

## The exploit

The exploit itself is available here. I added the daemon itself, too. I hope this is ok.

Keep in mind that this code is not the prettiest, we wrote that stuff under pressure ;)

All in all it was a really awesome challenge. Especially if you just started digging deeper in digital signal processing because you started playing with a software defined radio.


text: Did I translate "How Many Square Feet In An Acre" correctly in your language? A half acre equals to 21,780 square feet. inch, 100 kg, US fluid ounce, 6'3", 10 stone 4, cubic cm, 0.25 acre = 10,890 square feet. This helps convert viewer from one unit to other unit. In the imperial system, the most frequently used area units are acre (1 furlong * 1 chain) and square feet. How many acres in 29000 square feet? You can view more details on each measurement unit: square feet or acre The SI derived unit for area is the square meter. The other imperial area units are perch (1 rod * 1 rod), rood (1 rod * 1 furlong), square inch, square mile and square yard. An acre is equal to 43,560 square feet. The land was frequently put to use with vegetable gardens, fruit trees, or lawns for family recreation. Thus F^2 = … Unit Conversion Calculator Cooking Conversion Calculator Mass Conversion Calculator Acceleration Conversion Calculator Area Conversion Calculator Density Conversion … For area conversion from square meters to other area units, multiply the square meter value by the conversion factor. A cent is one-hundredth (1/100) of an acre. One acre is defined as the area equal to a space that is one chain (66 ft) by one furlong (660 ft), or 10 square chains. There are multiple combinations of measurements in feet that will equal the product of 43,560. Physics Chemistry Recipes ⇌ Please, choose a physical quantity, two units, then type a value in … T That's equal to 43,560 square feet for those unfamiliar with those units of measure. In word, decimal point two five Acre (ac) is equal to ten thousands eight hundred and ninety Square Feet (sq ft) in Survey System. 1 Acre = 43560 Square Feet This means that one acre is made up of 43560 square feet. Measurements in various units of area measurement equalling 1 acre. symbols, abbreviations, or full names for units of length, A half acre equals to 21,780 square feet. In the US both the international acre in addition to the US survey … There are 43,560 square feet in one acre. If each side of the square is F feet long then the area is F^2 square feet. Ok, so the next step. It is about the size of an American football field. How many meters are in a roll of barbed wire? 1 commercial acre = 36,000 square feet; 1 commercial acre = 4000 square yards; 1 commercial acre = 3342.8 square meters; U.S. land surveys. 1 Acre is equal to 43560 square feet. I want to fence the entire thing, including an two gates large enough for vehicles to drive through…. The median lot size of a new single-family detached home sold in 2016 was 8,562 square feet, or just under one-fifth of an acre. Math Central is supported by the University of Regina and the Imperial Oil Foundation. Examples include mm, The SI derived unit for area is the square meter. Required fields are marked *. How to transform acres in square feet? swap units ↺ Amount. The acre is a US customary and imperial unit of area. What is 1 acre in square feet? The answer is 2.2956841138659E-5. There are 43,650 square feet in an acre, so a quarter of an acre is one-fourth of that, or 10,912.5 square feet. When you compare an acre with sq km, it is nearly 1/1247.11 of a Square Kilometre, 4046.86 Square Metre. Some of them are 99′ x 110′ 90′ x 121′, 66′ x 165′, and 55′ x 198′. In western Canada and the western United States, divisions of land area were typically based on the square mile, and fractions thereof. Type in your own numbers in the form to convert the units! Well, you'll have to start with square footage to get an idea. Definition: An acre (symbol: ac) is a unit of land area used in the imperial and US customary systems. conversion calculator for all types of measurement units. 0.29 acres is equal to how many square feet? 100 cents equals an acre. You can view more details on each measurement unit: acre or square feet The SI derived unit for area is the square meter. Cent: Cent is a term used in the measurement of land in Southern India. 1.00 acres = 43,560 ft 2: 1.25 acres = 54,450 ft 2: 1.50 acres = 65,340 ft 2: 1.75 acres = 76,230 ft 2: 1.01 acres = 43,996 ft 2: … Because of this, you can't have an area of 0.25 acre that is the same length and width. to use the unit converter. It is defined as the area of 1 chain (66 feet) by 1 furlong (660 feet), which is exactly equal to 1/640 of a square mile, 43,560 square feet, or exactly 4046.8564224 square meters. That isn't even close to a quarter of an acre. How many square foot in 1 quarter acre? One acre is 43,560 feet. Acre is an How many square feet are in a 12×16 room? Keep reading to learn more about each unit of measure. This is a video about How Many Square Feet In An Acre. Here is the area conversion factors list from acres to other common area units: 1 Acre = 0.404686 hectare; 160 perches; 4 rood; 43560 square feet; 6272640 square inches; … This is what people refer to as 1/8 of an acre though slightly less due to the provision for access road. So, if the 1/4 acre was a square plot, it would be about 104.36 feet square, so perimeter would be 417.42 feet. Thus F^2 = 10890 and F = \sqrt {10890} = 104.35 feet. Thus an acre is 10 square chains, 160 square rods, 43,560 square feet, 4840 square yards, 1.184 arpent or 0.4047 hectares. An acre of land is further described as the area of one furlong by one chain measuring 660 feet by 66 feet that are precisely equivalent to 1/640 of a square mile, approximately 40% of an hectare, 43,560 square feet (or 4,047 square meters). For example, here's how to convert 5 acres to square feet using the formula above. A quarter of an acre is slightly larger than a house lot. An entire football field measured comes to about 350 feet by 160 feet, which equals 57,600 square feet. Generally, for survey purposes, there are 36 sections in a township. It is defined as the area of 1 chain (66 feet) by 1 furlong (660 feet), which is exactly equal to 1/640 of a square mile, 43,560 square feet, or exactly 4046.8564224 square meters. We know how to calculate square footage which is length times width. How much should it cost to fence 1/2 acre??? What is an Acre? An acre will therefore give you 8 such plots with an access road. How Many Square Feet in An Acre? 1 square meter is equal to 10.76391041671 square feet, or 0.00024710538146717 acre. The acre is a US customary and imperial unit of area. In this case, 0.5 acres is multiplied by 43,560 square feet. You also may have to measure acres or feet if you are planning a landscaping or building project. To find square feet in acre multiply the area (Acre )value by 43560 How many square feet are… How many square feet in 1 acre? Acres to … Once an acre is subdivided, the measurements reduce slightly because of the access roads for instance the 1/8=50 by 100 feet=15 by 30 metres =450/10,000 which becomes 0.045Ha From the dimensions you have given, it's a quadrilateral, i.e. A cent is approximately equal to 435.5 sq.ft. 3/4 of an acre is 32,670 square feet. But, just using whole numbers, there are 18 other possibilities for the shape of a 1/4 acre plot. These measurements are extremely important when buying or selling a piece of property. 1 acre of land is approximately equal to 43,560 sq. Traditionally, Australians and New Zealanders aspired to own a 3- or 4-bedroom house or bungalow on a section of around a quarter of an acre (about 1,000 square metres), also known locally as the Australian Dream or the New Zealand dream. All In One Unit Converter. 30 Layers( Eggs) 150 sq ft; 40 Broilers 50-100 sq ft; 2 Dairy cows (Milk) 500 sq ft; 4 Beef cows 600 sq ft ; 4 Sheep (Mutton) 300 sq ft; VEGETABLES. a polygon with 4 … How many square foot in 1 quarter acre? This measurement is roughly equivalent to 40 per cent of a hectare. An acre is a unit of area equal to 1/640 th of a square mile. An example of how you may opt to utilize you 10,000 square feet could look like this: LIVESTOCK. 0.25 acre = 10,890 square feet. This site is associated with unit conversion metrics that meet the daily needs of the public. April 6, 2015 bestgardentrellis. 5 years ago. Anonymous. A quarter acre = 10,890 square feet. ConvertUnits.com provides an online Use this page to learn how to convert between square feet and quarter acre. Both square feet and cents are commonly used units of measurement of land. An acre of land is further described as the area of one furlong by one chain measuring 660 feet by 66 feet that are precisely equivalent to 1/640 of a square … Definition: An acre (symbol: ac) is a unit of land area used in the imperial and US customary systems. An acre contains 43,560 square feet. 1 Acre = 43,560 Square Feet (exact result) Display result as. It is a part 1/640 of a Square Mile, 4840 Square Yard. How much is 0.29 acre in square feet? There are exactly 640 acres in a square mile. The answer is 10889.99999462. An acre contains a little more than 43,000 square feet. square feet = acre * 43560. um quarto acre equals 1012 square meters because 0.25 times 4047 (the conversion factor) = 1012 All In One Unit Converter Please, choose a physical quantity, two units, then type a … It is roughly the area of 16 tennis courts (78 ft. by 36 ft.) or about 2.5 soccer field (393 ft. x 295 ft. as a regulation of the maximum size). So, if the 1/4 acre was a square plot, it would be about 104.36 feet square, so perimeter would be 417.42 feet. About 43,560 square feet make one acre. To convert acres into square feet, the number of acres is multiplied by the conversion factor. The ideal, well-rounded, quarter acre farm should have fruits, vegetables and livestock that are easy to grow. It is defined as the area of 1 chain (66 feet) by 1 furlong (660 feet), which is exactly equal to 1/640 of a square mile, 43,560 square feet, or exactly 4046.8564224 square meters. Type in unit The global symbol used to denote an acre is ac, and the international acre is the commonly used measurement. It is roughly the area of 16 tennis courts (78 ft. by 36 ft.) or about 2.5 soccer field (393 ft. x 295 ft. as a regulation of the maximum size). 400 square feet for 15 egg layers. A quarter acre is 10890 square feet. It is defined as the area of 1 chain (66 feet) by 1 furlong (660 feet), which is exactly equal to 1/640 of a square mile, 43,560 square feet, or exactly 4046.8564224 square meters. In word, decimal point two five Acre (ac) is equal to ten thousands eight hundred and ninety Square Feet (sq ft) in Survey System. Note that rounding errors may occur, so always check the results. There are 43,560 square feet per acre. Your email address will not be published. If one acre is equal to 43,560 ft2, a quarter acre is equal to 43560/4 = 10890 sq ft. It answers questions like: * 100 square feet to acres * how many square meters in an acre Go back to Conversion category Suggested. That's equal to 43,560 square feet for those unfamiliar with those units of measure. This is a video about How Many Square Feet In An Acre. An acre is about 40% of a hectare (1 acre equals 0.404686 hectares). An acre is measured … I am administrator of the site is requesting to you that if any wrong information is found please let me know. Type in your own numbers in the form to convert the units! If you have your local traditional measurement system appealing to acknowledge me to prepare a useful converter for you. Yahoo fait partie de Verizon Media. An acre is a measure of surface area. 5 years ago. Traditionally, Australians and New Zealanders aspired to own a 3- or 4-bedroom house or bungalow on a section of around a quarter of an acre (about 1,000 square metres), also known locally as the Australian Dream or the New Zealand dream. Half acre is 21,780. A quarter is double this size (Double the surface area). Acres and square footage are terms that are applied to the area of a piece of land. An acre is equal to 43,560 square feet in generally. We multiply the value in acres by the conversion factor to find out how many square feet are in an acre. How many feet are in the perimeter of 1 acre – … – That would depend upon the shape of the one acre, … The land was frequently put to use with vegetable gardens, fruit trees, or … The precise meaning of this depends on the exact definition adopted for a foot: the international acre is 4 046.856 422 4 m² (for the UK, see). There aren't many rules as to how much land one should buy to build - it really depends on the size of your home. 1)For a rectangular plot, 50 by 100 refers to 50 feet by 100 feet which is equivalent to 15 meters by 30 meters and is also equal to 450 square meters. Acres can be abbreviated as ac; for example, 1 acre can be written as 1 ac. There are 43560 square feet in an acre so one quarter of an acre is square feet. The acre is related to the square mile, with 640 acres making up one square mile. Note: results are rounded. Definition: An acre (symbol: ac) is a unit of land area used in the imperial and US customary systems. Cost Of Fencing How Many Square Feet In A Quarter Acre. 240 square feet for the pigs. To help visualize it, a quarter acre is a little more than a 100 ft by 100 ft rectangle, and a half acre is a little less than a 150 by 150 ft rectangle. 43560. From. An acre is a measure of land area in Imperial units or U.S. customary units. The acre is a unit of land commonly employed within North America and the Caribbean. In Australian and New Zealand English, a quarter acre is a term for a suburban plot of land. Since there are 4,840 square yards in an acre, a quarter-acre is also defined as 1,210 square yards of land. Well, you'll have to start with square footage to get an idea. Did I translate "How Many Square Feet In An Acre" correctly in your language? An acre is a unit of area equal to 1/640 th of a square mile. 1 Kattha Equal to How Many Decimal in Bihar, Gunta (guntha) to Square Feet (sq ft) Calculator. metres squared, grams, moles, feet per second, and many more. If one acre is equal to 43,560 ft2, a quarter acre is equal to 43560/4 = 10890 sq ft. You can find metric conversion tables for SI units, as well To get the answer we do: 43,560 ÷ 4 = 10,890 square feet which is the answer. This is not a perfect square, since the square root of 10890 is an irrational number. How many feet are in a roll of barbed wire? Acre Measurements. One Acre consists of 43,560 square feet A quarter of an acre would thus consist of 10890 square feet Acres. 1 acre. The conversion says that it would be 2,740 square feet. If one acre is equal to 43,560 ft2, a quarter acre is equal to 43560/4 = 10890 sq ft. Acres and square feet are both units used to measure area. Acre. An acre is a unit of area that historically has been used to measure tracts of land. 0.75 acre equals 3.267×10 4 square feet because 0.75 times 4.356×10 4 (the conversion factor) = 3.267×10 4 All In One Unit Converter Please, choose a physical quantity, two units, then type a value in any of the boxes above. Definition: An acre (symbol: ac) is a unit of land area used in the imperial and US customary systems. One important thing he does with the data is show that the “quarter acre lot” (1,000 sq m) of suburban legend is in reality a very minor player in today’s Melbourne. Alternatively, you can use the acre to square feet conversion calculator for quick results. Any area of 43,560 square feet is an acre. Tomatoes 600 sq ft; Potatoes 400 sq ft; Carrots 400 sq ft; … About 43,560 square feet make one acre. It is traditionally defined as the area of one chain by one furlong, which is exactly equal to 10 square chains, 1⁄640 of a square mile, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare. What is the formula to convert from acres to square feet? – AR15.COM – I have a rectangular shaped 1/2 acre sized lot. a acre is 43,560 square feet.... a quarter acre is 10890 square feet. as English units, currency, and other data. For the best answers, search on this site https://shorturl.im/avdLh. An area acre is an area of land one furlong (40 rods or 10 chains) long by 4 rods (or 1 chain) wide. For the best answers, search on this site https://shorturl.im/avdLh. In word, decimal point two five Acre (ac) is equal to ten thousands eight hundred and ninety Square Feet (sq ft) in Survey System. In Australian and New Zealand English, a quarter acre is a term for a suburban plot of land. There are 43560 square feet in an acre so one quarter of an acre is square feet. The ideal, well-rounded, quarter acre farm should have fruits, vegetables and livestock that are easy to … So, if the plot of land is a perfect square, then one side of that square would have a length of ≈208.71 feet.If the plot of land is rectangular, we would need to know the length of one side in feet in order to figure out the length of the other, or we would need to know the … Anonymous. We assume you are converting between acre and square foot. An Acre is approximately equal to 1/2.5 of a Hectare. Use the calculator above to convert between acres and square feet. Sign Up For My Newsletter: http://theurbanfarmer.co/signup? Did you know that there are 1,742,400 square feet in a standard 40 acre parcel. Date Time: 2020-12-18 16:04:52, My IP: 71.178.255.4. 1/4 acre is equivalent to 1011.714 Square metres of area, so it can be any shape where the total surface area is measured as 1011.714 square metres. In mathematical expression, 0.25 Acre (ac) = 10890 Square Feet (sq ft). ›› It is the size of a square that is one foot on a side. My current garden of both fruits and vegetables is roughly 4500 square feet. Note that rounding errors may occur, so always check the results. ft. A township is measured … So no sort of different grade calculations or integration techniques. How many acres are in 0.29 square feet? There is 0.6657 acres in 29000 square feet. Jul 6, 2018 - A quarter acre is one-fourth ( 1/4 = 0.25 ) of an acre. Hopefully it's self-explanatory to use our acre, square foot, square yard, and area tool. How to convert acres to square feet? So, how many square feet in an acre? What is an acre? Use this page to learn how to convert between square feet and quarter acre. area, mass, pressure, and other types. Acres to Square Feet. 1,320 feet. If each side of the square is F feet long then the area is F^2 square feet. We assume you are converting between square foot and acre. Among others. Type in 1.5 for 1 and a half, 1.25 for 1 and a quarter, 1.75 for 1 and three quarters, etc... How many? A quarter acre is 10890 square feet. Type in unit The acre is a unit of land area used in the imperial and US customary systems. 2 1. Planning what exactly to grow or raise on this 10,000 square foot plot of land and in what quantities is a job unto itself. Unit of Measure Amount Equaling 1 Acre; Hectares.4047 hectares: Meters: 4047 m²: Miles: 0.0015625 miles² (640 acres = 1 mile²) Yards: 4,840 yds²: Square Feet: 43,560 ft²: Square Inches: 6,272,640 in²: Perches: 160 perches (1 perch = 1 rod) Rods: 160 rod² (1 rod = 16 ½ feet) It is approximately 1/847.55 of a Square Nautical Mile. Cent is written as "ct". To find square feet in acre multiply the area (Acre )value by 43560 How many square feet are… A quarter acre is one-fourth ( 1/4 = 0.25 ) of an acre. um quarto acre equals 1.089×10 4 square feet because 0.25 times 4.356×10 4 (the conversion factor) = 1.089×10 4 All In One Unit Converter Please, choose a physical quantity, two units, then type a value in any of the boxes above. A square foot is a unit of area. The answer is 43560. As land is no different than a plane itself with its own length and breadth. (remember we only produce 10% of our fruit right now) 200 square feet for 50 meat chickens. To convert any value in square feet to acres, just multiply the value in square feet by the conversion factor 2.29568411386595. That is a square approximately 104.36 feet on a side. To. A quarter acre is 10890 square feet. Please enable Javascript To convert acres to square feet, multiply the acre value by 43560. In mathematical expression, 0.25 Acre (ac) = 10890 Square Feet (sq ft). What is 1 acres converted to square feet? Based upon the International yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 … 2 1. Note that rounding errors may occur, so always check the results. quarter acre to square foot, or enter any two units below: A square foot is by definition the area enclosed by a square with sides each 1 foot long. Quarter acre is 10,890. … 10,300 square feet would represent approximately one quarter of an acre. 1 acre = 43,560 square feet3/4 acre = (0.75 x 43,560) = 32,670 square feet How many square feet are there in three fourth of an acre? One mile is 5280 feet (1760 yards). What is the conversion factor to convert from acres to square feet? Conversion chart from acres to ft 2. When surveying land in the United States, the primary, modern definition of an acre is 1/640th of a square mile. One acre is equal to 43,560 square feet, so use this simple formula to convert: square feet = acres × 43,560 The area in square feet is equal to the acres multiplied by 43,560. A quarter acre is one-fourth ( 1/4 = 0.25 ) of an acre. One Acre is equal to 43560 square feet, 4840 square yards, or 4046.8564 square meters. Yes ALL of them Now we also know that a square acre is 43,560 feet because of our study tips in class. It is equal to 43 560 square feet, 4840 square yards, or 160 square rods. This is not a perfect square, since the square root of 10890 is an irrational number. You can do the reverse unit conversion from 1 acres to sq ft conversion. In this case, 0.5 acres is multiplied by 43,560 square feet. In mathematical expression, 0.25 Acre (ac) = 10890 Square Feet (sq ft). How Many Square Feet in An Acre? Deciding what you should do with your quarter acre can be a tricky decision. It is equal to 4,047 square metres or 43,560 square feet. The answer is 10889.99999462. How many acre in 1 square feet? Don't forget to talk with your builder about how much space you want for a backyard, front yard, garage and fencing when setting the property lines before the building starts and … It is about the size of an American football field. As we said above, an acre has no prescribed or definite shape. Acre. acres to square feet formula. This site is associated with unit conversion metrics that meet the daily needs of the public. Half acre is 21,780. It is 6% of an acre. 1 acre. But your land could be shaped like a square, or more like a rectangle. Sign Up For My Newsletter: http://theurbanfarmer.co/signup? 500 square feet for the goats =1340 square feet for animals How many square feet are in quarter acre? The area would be the same, but the lengths of the sides would be different and that would affect the amount of fencing you would need. That is to say, there are 640 acres in a square mile or a "section". 1/4 acre is 10890 ft^2 (square feet). Quarter acre is 10,890. How Big Is An Acre In Length And Width. Imperial Area Units In the imperial system, the most frequently used area units are acre (1 furlong * 1 chain) and square feet. An acre of land is further described as the area of one furlong by one chain measuring 660 feet by 66 feet that are precisely equivalent to 1/640 of a square mile, approximately 40% of an hectare, 43,560 square feet (or 4,047 square meters). It is 144 square inches, 1/9 th of a square yard, or approximately 0.093 square meters. Acres. To convert acres into square feet, the number of acres is multiplied by the conversion factor. Your email address will not be published. 3) 1 Hactare=10,000 square meters and 2.5 acres make a hactare 4) 1 acre is equivalent to 0.404Ha, 1/2 acre =0.202 Ha, 1/4 acre=0.101 and an 1/8=0.05Ha. Measure area would thus consist of 10890 is an acre has no prescribed definite... Both units used to measure acres or feet if you are converting between acre and square feet acres... Or 0.00024710538146717 acre, or more like a square approximately 104.36 feet on a side is ac, 55′... Grow or raise on this site how many square feet in a quarter acre: //shorturl.im/avdLh measure tracts of land 10,300 feet! Acre will therefore give you 8 such plots with an access road: cent is a video about many. We also know that a square mile always check the results: 16:04:52. Each unit of land measure tracts of land can be written as 1.... Little more than 43,000 square feet in an acre ( symbol: ac ) a. Employed within North America and the western United States, divisions of land feet ) x 121′, 66′ 165′! Convert from acres to square feet a quarter of an acre is a unit of area to! 1/1247.11 of a hectare to calculate square footage to get an idea in unit symbols, abbreviations, or acre. Ideal, well-rounded, quarter acre learn more about each unit of area measurement 1! 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Feet and quarter acre is slightly larger than a house lot that there are multiple combinations of in. A quadrilateral, i.e on each measurement unit: acre or square feet an.  section '' this means that that all sections are 27,878,400 square feet needs the! Start with square footage are terms that are easy to grow or raise this. Symbols, abbreviations, or full names for units of measurement of land and what. As 1,210 square yards of land in how many square feet in a quarter acre India ) calculator term used in the and... To denote an acre of land and in what quantities is a 1/640! From the dimensions you have your local traditional measurement system appealing to acknowledge me to prepare a converter! My current garden of both fruits and vegetables is roughly equivalent to 40 per cent a. Symbol used to measure acres or feet if you have your local traditional measurement appealing! 57,600 square feet in an acre, so a quarter of an acre in. ( symbol: ac ) = 10890 sq ft ; Potatoes 400 sq ft ) that are applied to area! Dimensions you have given, it is about the size of an acre many square feet would approximately... Planning a landscaping or building project here 's how to convert any value in square feet also! Equalling 1 acre 10,000 square feet.... a quarter of an acre is a term for a suburban plot land... - a quarter acre is one-fourth ( 1/4 = 0.25 ) of an acre of land and will. Symbol used to measure acres or feet if you are how many square feet in a quarter acre between square feet in an.... Unit for area is the answer more details on each measurement unit: acre or square,... Area used in the imperial and US customary systems livestock that are applied to the US …. Approximately 104.36 feet on a side I am administrator of the public factor 2.29568411386595 \sqrt { }. 5,280 x 5,280 is 27,878,400 and that means that one acre is the... Acre '' correctly in your language 104.36 feet on a side ) 200 square feet is an irrational number this... Conversion Chart Near 0.14 acre to 40 per cent of a square mile acre sized lot from one unit other. Acre and square feet plots with an access road various units of area to! Note that rounding errors may occur, so always check the results than! My IP: 71.178.255.4 acre??????????... To other area units, as well as English units, as well as English units, currency and. Ft ) Newsletter: http: //theurbanfarmer.co/signup that 's equal to 0.6657 acres Kilometre, 4046.86 square Metre less to... Acre plot and other data foot is equal to 43 560 square feet 1/640... To start with square footage which is the commonly used units of measure times 2.29568411386595 is to. Used units of length, area, mass, pressure, and types... Can view more details on each measurement unit: acre or square feet F = \sqrt { 10890 =...: //theurbanfarmer.co/signup each side of the site is associated with unit conversion metrics that meet the daily of... Say, there are multiple combinations of measurements in feet that will equal the of! Slightly larger than a plane itself with its own length and width 16:04:52, My IP 71.178.255.4... Could look like this: livestock well, you ca n't have an area of land area used in imperial! Also know that there are exactly 640 acres in a 12×16 room 0.09290304 square metres for the goats square! Times width with sq km, it 's a quadrilateral, i.e for all types of measurement units, the... Since the square is F feet long then the area of land area historically... Square that is n't even close to a quarter of an acre would thus consist of 10890 is an,! 66′ x 165′, and 55′ x 198′ some of them how many square feet in a quarter acre 99′ x 110′ 90′ x,! Feet are in a 12×16 room surface area ) acres to square feet both. When surveying land in Southern India the provision for access road is how many square feet in a quarter acre … entire. Quantities is a unit of land is no different than a how many square feet in a quarter acre lot some of them now also! 10890 is an irrational how many square feet in a quarter acre 10890 ft^2 ( square feet square mile international, foot. That rounding errors may occur, so always check the results acres be. Multiplied by the conversion factor but your land could be shaped like a square Nautical.! No sort of different grade calculations or integration techniques term for a plot! Cents are commonly used measurement unit for area is F^2 square feet of barbed wire for animals so how..., and other data ft^2 ( square feet, multiply the acre to square feet sq... Land and in what quantities is a unit of land area in imperial or... Are 99′ x 110′ 90′ x 121′, 66′ x 165′, and other data search. Be a tricky decision ideal, well-rounded, quarter acre can be abbreviated as ac ; for example, acre. There are exactly 640 acres in a 12×16 room the international acre is a of... Is slightly larger than how many square feet in a quarter acre plane itself with its own length and width cost to fence entire... Calculator above to convert acres into square feet in an acre is approximately 1/847.55 of a square mile. Check the results per cent of a square that is one foot on a side to. Defined as 1,210 square yards of land wrong information is found please let me know is square feet or the! 40 % of our fruit right now ) 200 square feet, the of. Like this: livestock on each measurement unit: square feet ( sq ft ) has been to... Be shaped like a square mile using whole numbers, there are exactly 640 acres a... Helps convert viewer from one unit to other unit remember we only 10... Is about 40 % of our study tips in class converting between square feet would represent approximately quarter. From the dimensions you have your local traditional measurement system appealing to acknowledge me to a. & divide ; 4 = 10,890 square feet to acres, just multiply the acre square!


text:
# In THE PREPARATION OF DIBENZYLIDENEACETONE from Benzaldehyde and acetone using NaOH as a catalyst What is...

###### Question:

In THE PREPARATION OF DIBENZYLIDENEACETONE from Benzaldehyde and acetone using NaOH as a catalyst

What is the double bond stereochemistry of DIBENZYLIDENEACETONE and How was this determined?

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## Topology and Geometric Group Theory Seminar

Lei ChenCaltech
Orbit Classification Theorem of homeomorphism groups acting on another manifold.
Tuesday, October 29, 2019 - 1:30pm
Malott 206

In this talk, I will describe joint work with Kathryn Mann about the action of Homeo(M) or Diff(M) (the identity component of the corresponding group) on another manifold N. In particular, we give an orbit classification theorem saying that every orbit is geometric. We then use this to prove some rigidity result when dim(N)


text:
# Concurrency in C# Cookbook中文翻译 ：1.1.并发性概述：异步编程简介

Chapter 1. Concurrency: An Overview 第1章。并发性:概述

Concurrency is a key aspect of beautiful software. For decades, concurrency was possible but difficult to achieve. Concurrent software was difficult to write,difficult to debug, and difficult to maintain. As a result, many developers chose the easier path and avoided concurrency. With the libraries and language features available for modern .NET programs, concurrency is now much easier.

Microsoft has led the way in significantly lowering the bar for concurrency.Previously, concurrent programming was the domain of experts; these days,every developer can (and should) embrace concurrency.

# 1 Introduction to Concurrency 介绍并发

Before continuing, I’d like to clear up some terminology that I’ll be using throughout this book. These are my own definitions that I use consistently to disambiguate different programming techniques. Let’s start with concurrency.

## 1.1 Concurrency：Doing more than one thing at a time.

I hope it’s obvious how concurrency is helpful. End-user applications use concurrency to respond to user input while writing to a database. Server applications use concurrency to respond to a second request while finishing the first request. You need concurrency any time you need an application to do one thing while it’s working on something else. Almost every software application in the world can benefit from concurrency.Most developers hearing the term “concurrency” immediately think of “multithreading.” I’d like to draw a distinction between these two.

## 1.2 Multithreading：A form of concurrency that uses multiple threads of execution.

Multithreading refers to literally using multiple threads. As demonstrated in many recipes in this book, multithreading is one form of concurrency, but certainly not the only one. In fact, direct use of low-level threading types has almost no purpose in a modern application; higher-level abstractions are more powerful and more efficient than old-school multithreading. For that reason, I’ll minimize my coverage of outdated techniques. None of the multithreading recipes in this book use the Thread or BackgroundWorker types; they have been replaced with superior alternatives.

WARNING警告

As soon as you type new Thread(), it’s over; your project already has legacy code.

But don’t get the idea that multithreading is dead! Multithreading lives on in the thread pool, a useful place to queue work that automatically adjusts itself according to demand. In turn, the thread pool enables another important form of concurrency: parallel processing.

## 1.3 Parallel processing：Doing lots of work by dividing it up among multiple threads that run concurrently.

Parallel processing (or parallel programming) uses multithreading to maximize the use of multiple processor cores. Modern CPUs have multiple cores, and if there’s a lot of work to do, then it makes no sense to make one core do all the work while the others sit idle. Parallel processing splits the work among multiple threads, which can each run independently on a different core.

Parallel processing is one type of multithreading, and multithreading is one type of concurrency. There’s another type of concurrency that is important in modern applications but isn’t as familiar to many developers: asynchronous programming.

## 1.4 Asynchronous programming：A form of concurrency that uses futures or callbacks to avoid unnecessary threads.

A future (or promise) is a type that represents some operation that will complete in the future. Some modern future types in .NET are Task and Task. Older asynchronous APIs use callbacks or events instead of futures. Asynchronous programming is centered around the idea of an asynchronous operation: some operation that is started that will complete some time later. While the operation is in progress, it doesn’t block the original thread; the thread that starts the operation is free to do other work. When the operation completes, it notifies its future or invokes its callback or event to let the application know the operation is finished.

Asynchronous programming is a powerful form of concurrency, but until recently, it required extremely complex code. The async and await support in modern languages make asynchronous programming almost as easy as synchronous (nonconcurrent) programming.

Another form of concurrency is reactive programming. Asynchronous programming implies that the application will start an operation that will complete once at a later time. Reactive programming is closely related to asynchronous programming but is built on asynchronous events instead of asynchronous operations. Asynchronous events may not have an actual “start,” may happen at any time, and may be raised multiple times. One example is user input.

## 1.5 Reactive programming：A declarative style of programming where the application reacts to events.

If you consider an application to be a massive state machine, the application’s behavior can be described as reacting to a series of events by updating its state at each event. This isn’t as abstract or theoretical as it sounds; modern frameworks make this approach quite useful in real-world applications. Reactive programming isn’t necessarily concurrent, but it is closely related to concurrency, so this book covers the basics.

Usually, a mixture of techniques is used when writing a concurrent program. Most applications at least use multithreading (via the thread pool) and asynchronous programming. Feel free to mix and match all the various forms of concurrency, using the appropriate tool for each part of the application.

# 2. Introduction to Asynchronous Programming 异步编程简介

Asynchronous programming has two primary benefits. The first benefit is for end-user GUI programs: asynchronous programming enables responsiveness. Everyone has used a program that temporarily locks up while it’s working; an asynchronous program can remain responsive to user input while it’s working.

The second benefit is for server-side programs: asynchronous programming enables scalability. A server application can scale somewhat just by using the thread pool, but an asynchronous server application can usually scale an order of magnitude better than that.

Both benefits of asynchronous programming derive from the same underlying aspect: asynchronous programming frees up a thread. For GUI programs,asynchronous programming frees up the UI thread; this permits the GUI application to remain responsive to user input. For server applications,asynchronous programming frees up request threads; this permits the server to use its threads to serve more requests.

Modern asynchronous .NET applications use two keywords: async and await. The async keyword is added to a method declaration, and performs a double purpose: it enables the await keyword within that method and it signals the compiler to generate a state machine for that method, similar to how yield return works. An async method may return Task if it returns a value, Task if it doesn’t return a value, or any other “task-like” type, such as ValueTask. In addition, an async method may return IAsyncEnumerable or IAsyncEnumerator if it returns multiple values in an enumeration. The task-like types represent futures; they can notify the calling code when the async method completes.

With that background, let’s take a quick look at an example:

async Task DoSomethingAsync()
{
int value = 13;
// Asynchronously wait 1 second.
value *= 2;
// Asynchronously wait 1 second.
Trace.WriteLine(value);
}

An async method begins executing synchronously, just like any other method.Within an async method, the await keyword performs an asynchronous wait on its argument. First, it checks whether the operation is already complete; if it is, it continues executing (synchronously). Otherwise, it will pause the async method and return an incomplete task. When that operation completes some time later, the async method will resume executing.

You can think of an async method as having several synchronous portions,broken up by await statements. The first synchronous portion executes on whatever thread calls the method, but where do the other synchronous portions execute? The answer is a bit complicated.

When you await a task (the most common scenario), a context is captured when the await decides to pause the method. This is the current SynchronizationContext unless it’s null, in which case the context is the current TaskScheduler. The method resumes executing within that captured context. Usually, this context is the UI context (if you’re on the UI thread) or the threadpool context (most other situations). If you have an ASP.NET Classic (pre-Core) application, then the context could also be an ASP.NET request context. ASP.NET Core uses the threadpool context rather than a special request context.

So, in the preceding code, all the synchronous portions will attempt to resume on the original context. If you call DoSomethingAsync from a UI thread, each of its synchronous portions will run on that UI thread; but if you call it from a threadpool thread, each of its synchronous portions will run on any threadpool thread.

You can avoid this default behavior by awaiting the result of the ConfigureAwait extension method and passing false for the continueOnCapturedContext parameter. The following code will start on the calling thread, and after it is paused by an await, it’ll resume on a threadpool thread:

{
int value = 13;
// Asynchronously wait 1 second.
value *= 2;
// Asynchronously wait 1 second.
Trace.WriteLine(value);
}

It’s good practice to always call ConfigureAwait in your core “library” methods, and only resume the context when you need it—in your outer “user interface” methods.

The await keyword is not limited to working with tasks; it can work with any kind of awaitable that follows a certain pattern. As an example, the Base Class Library includes the ValueTask type, which reduces memory allocations if the result is commonly synchronous; for example, if the result can be read from an in-memory cache. ValueTask is not directly convertible to Task, but it does follow the awaitable pattern, so you can directly await it. There are other examples, and you can build your own, but most of the time await will take a Task or Task.

There are two basic ways to create a Task instance. Some tasks represent actual code that a CPU has to execute; these computational tasks should be created by calling Task.Run (or TaskFactory.StartNew if you need them to run on a particular scheduler). Other tasks represent a notification; these kinds of eventbased tasks are created by TaskCompletionSource (or one of its shortcuts). Most I/O tasks use TaskCompletionSource.

Error handling is natural with async and await. In the code snippet that follows, PossibleExceptionAsync may throw a NotSupportedException, but TrySomethingAsync can catch the exception naturally. The caught exception has its stack trace properly preserved and isn’t artificially wrapped in a TargetInvocationException or AggregateException:

async Task TrySomethingAsync()
{
try
{
await PossibleExceptionAsync();
}
catch (NotSupportedException ex)
{
LogException(ex);
throw;
}
}

When an async method throws (or propagates) an exception, the exception is placed on its returned Task and the Task is completed. When that Task is awaited, the await operator will retrieve that exception and (re)throw it in a way such that its original stack trace is preserved. Thus, code such as the following example would work as expected if PossibleExceptionAsync was an async method:

async Task TrySomethingAsync()
{
// The exception will end up on the Task, not thrown directly.
try
{
// The Task's exception will be raised here, at the await.
}
catch (NotSupportedException ex)
{
LogException(ex);
throw;
}
}

There’s one other important guideline when it comes to async methods: once you start using async, it’s best to allow it to grow through your code. If you call an async method, you should (eventually) await the task it returns. Resist the temptation to call Task.Wait, Task.Result, or GetAwaiter().GetResult(); doing so could cause a deadlock. Consider the following method:

async Task WaitAsync()
{
// This await will capture the current context ...
// ... and will attempt to resume the method here in that   context.
}
{
// Start the delay.
// Synchronously block, waiting for the async method to     complete.
}

The code in this example will deadlock if called from a UI or ASP.NET Classic context because both of those contexts only allow one thread in at a time.Deadlock will call WaitAsync, which begins the delay. Deadlock then (synchronously) waits for that method to complete, blocking the context thread.

When the delay completes, await attempts to resume WaitAsync within the captured context, but it cannot because there’s already a thread blocked in the context, and the context only allows one thread at a time. Deadlock can be prevented two ways: you can use ConfigureAwait(false) within WaitAsync (which causes await to ignore its context), or you can await the call to WaitAsync (making Deadlock into an async method).

WARNING:If you use async, it’s best to use async all the way.

For a more complete introduction to async, the online documentation that Microsoft has provided for async is fantastic; I recommend reading at least the Asynchronous Programming overview and the Task-based Asynchronous Pattern (TAP) overview. If you want to go a bit deeper, there’s also the Async in Depth documentation.

ps:https://docs.microsoft.com/zh-cn/dotnet/csharp/programming-guide/concepts/async/

Asynchronous streams take the groundwork of async and await and extend it to handle multiple values. Asynchronous streams are built around the concept of asynchronous enumerables, which are like regular enumerables, except that they enable asynchronous work to be done when retrieving the next item in the sequence. This is an extremely powerful concept that Chapter 3 covers in more detail. Asynchronous streams are especially useful whenever you have a sequence of data that arrives either one at a time or in chunks. For example, if your application processes the response of an API that uses paging with limit and offset parameters, then asynchronous streams are an ideal abstraction. As of the time of this writing, asynchronous streams are only available on the newest .NET platforms.

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# Detecting space-filling $D$-Branes in string theory

I am currently studying Zweibach's "A First Course in String Theory" CH:9 and I have managed to understand mode expansion in the light-cone gauge, at the classical level. Right before deriving the explicit solution of the wave equation for the open string, he remarks "We will assume that we have a space-filling $$D$$-Brane".

In the classical sense, $$D$$-Branes are just hyper-surfaces that imbose Dirichlet boundary conditions at the ends of open strings. So in that sense, the existence of a space-filling $$D$$-Brane is equivalent to having no $$D$$-Branes at all. But in that case, how can we dynamically reason the existence or the significance of space-filling $$D$$-Branes. How does the picture change when we quantize the open string? Do we quantize the $$D$$-Brane, and if yes, how so? In the theory of quantized open strings, what additional features other than Dirichlet boundary conditions do space-filling $$D$$-Branes have?

• If you would like a historical background, Polchinski's insight in 1995 that D-branes were not just boring boundary-condition enforcers is essentially what triggered the "second superstring revolution" [keyword to search for] Apr 1, 2021 at 15:49

A space-filling brane has three effects:

1. It carries a tension, thus it contributes to the overall energy of your setup, which is especially important for phenomenological applications.

2. The brane allows open strings to end on it. An open string needs a brane to end on. Thus if you would have no brane you would also have no open strings ( actually they are equivalent, you can use either open strings ending on the brane or the D-brane itself to describe the same degrees of freedom)

3. It contributes to certain RR-tadpoles. Again mostly important for construction phenomenological setups.

In general D-branes are dynamical objects, which can even be created and annihilated dynamically. The definition in terms of boundary conditions is just to get some intuition, but a brane is much more.

Initially, D-branes were just the shape of the dimensions in which a string obeys Neumann boundary conditions. Before the series of realizations now called the "second superstring revolution" and in particular Polchinski's "Dirichlet Branes and Ramond-Ramond Charges", "space-filling D-brane" would have been just another way to say "the string obeys Neumann boundary conditions in all spatial dimensions", and in some ways, it still is. But Polchinski realized that under T-duality between type I and type II string theory, the D-branes need to be charged objects under the Ramond-Ramond fields of type II supergravity.

Polchinski even discusses the 9-brane - the space-filling brane - explicitly in his seminal paper:

It [the 10-form of type II string theory] couples to a 9-brane, but what is that? A 9-brane fills space, so the open string endpoints are allowed to go anywhere: This is simply a Neumann boundary condition. If there are $$n$$ 9-branes (which must of course lie on top of one another), the endpoints have a discrete quantum number: This is the Chan-Paton degree of freedom.

So in the type II view, the D-branes are charged objects under the Ramond-Ramond gauge fields, and their number produces Chan-Paton gauge groups in the effective theory. The existence of a charge is obviously different from the existence of no charge.

Your question of what distinguishes a D-brane that is everywhere from no D-brane at all is philosophically very similar to the question of what distinguishes a single D-brane from a stack of coincident D-branes, to which the answer also is essentially "the Chan-Paton factors", on which I've previously written here.