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# American Institute of Mathematical Sciences

October  2012, 32(10): 3665-3690. doi: 10.3934/dcds.2012.32.3665

## Averaging of an homogeneous two-phase flow model with oscillating external forces

 1 Department of Mathematics, Florida International University, DM413B, University Park, Miami, Florida 33199, United States

Received  April 2011 Revised  March 2012 Published  May 2012

In this article, we consider a non-autonomous diffuse interface model for an isothermal incompressible two-phase flow in a two-dimensional bounded domain. We assume that the external force is singularly oscillating and depends on a small parameter $\epsilon.$ We prove the existence of the uniform global attractor $A^{\epsilon}.$ Furthermore, using the method of [13] in the case of the two-dimensional Navier-Stokes systems, we study the convergence of $A^{\epsilon}$ as $\epsilon$ goes to zero. Let us mention that the nonlinearity involved in the model considered in this article is slightly stronger than the one in the two-dimensional Navier-Stokes system studied in [13].
Citation: T. Tachim Medjo. Averaging of an homogeneous two-phase flow model with oscillating external forces. Discrete & Continuous Dynamical Systems - A, 2012, 32 (10) : 3665-3690. doi: 10.3934/dcds.2012.32.3665
##### References:

show all references

##### References:
 [1] Theodore Tachim Medjo. A two-phase flow model with delays. Discrete & Continuous Dynamical Systems - B, 2017, 22 (9) : 3273-3294. doi: 10.3934/dcdsb.2017137 [2] Theodore Tachim Medjo. Pullback $\mathbb{V}-$attractor of a three dimensional globally modified two-phase flow model. Discrete & Continuous Dynamical Systems - A, 2018, 38 (4) : 2141-2169. doi: 10.3934/dcds.2018088 [3] Guochun Wu, Yinghui Zhang. Global analysis of strong solutions for the viscous liquid-gas two-phase flow model in a bounded domain. Discrete & Continuous Dynamical Systems - B, 2018, 23 (4) : 1411-1429. doi: 10.3934/dcdsb.2018157 [4] Ciprian G. Gal, Maurizio Grasselli. Longtime behavior for a model of homogeneous incompressible two-phase flows. Discrete & Continuous Dynamical Systems - A, 2010, 28 (1) : 1-39. doi: 10.3934/dcds.2010.28.1 [5] T. Tachim Medjo. Non-autonomous 3D primitive equations with oscillating external force and its global attractor. Discrete & Continuous Dynamical Systems - A, 2012, 32 (1) : 265-291. doi: 10.3934/dcds.2012.32.265 [6] Theodore Tachim-Medjo. Optimal control of a two-phase flow model with state constraints. Mathematical Control & Related Fields, 2016, 6 (2) : 335-362. doi: 10.3934/mcrf.2016006 [7] T. Tachim Medjo. A non-autonomous 3D Lagrangian averaged Navier-Stokes-$\alpha$ model with oscillating external force and its global attractor. Communications on Pure & Applied Analysis, 2011, 10 (2) : 415-433. doi: 10.3934/cpaa.2011.10.415 [8] Barbara Lee Keyfitz, Richard Sanders, Michael Sever. Lack of hyperbolicity in the two-fluid model for two-phase incompressible flow. Discrete & Continuous Dynamical Systems - B, 2003, 3 (4) : 541-563. doi: 10.3934/dcdsb.2003.3.541 [9] Yasuhito Miyamoto. Global bifurcation and stable two-phase separation for a phase field model in a disk. Discrete & Continuous Dynamical Systems - A, 2011, 30 (3) : 791-806. doi: 10.3934/dcds.2011.30.791 [10] K. Domelevo. Well-posedness of a kinetic model of dispersed two-phase flow with point-particles and stability of travelling waves. Discrete & Continuous Dynamical Systems - B, 2002, 2 (4) : 591-607. doi: 10.3934/dcdsb.2002.2.591 [11] Helmut Abels, Harald Garcke, Josef Weber. Existence of weak solutions for a diffuse interface model for two-phase flow with surfactants. Communications on Pure & Applied Analysis, 2019, 18 (1) : 195-225. doi: 10.3934/cpaa.2019011 [12] Brahim Amaziane, Leonid Pankratov, Andrey Piatnitski. An improved homogenization result for immiscible compressible two-phase flow in porous media. Networks & Heterogeneous Media, 2017, 12 (1) : 147-171. doi: 10.3934/nhm.2017006 [13] Stefan Berres, Ricardo Ruiz-Baier, Hartmut Schwandt, Elmer M. Tory. An adaptive finite-volume method for a model of two-phase pedestrian flow. Networks & Heterogeneous Media, 2011, 6 (3) : 401-423. doi: 10.3934/nhm.2011.6.401 [14] Marie Henry, Danielle Hilhorst, Robert Eymard. Singular limit of a two-phase flow problem in porous medium as the air viscosity tends to zero. Discrete & Continuous Dynamical Systems - S, 2012, 5 (1) : 93-113. doi: 10.3934/dcdss.2012.5.93 [15] Brahim Amaziane, Mladen Jurak, Leonid Pankratov, Anja Vrbaški. Some remarks on the homogenization of immiscible incompressible two-phase flow in double porosity media. Discrete & Continuous Dynamical Systems - B, 2018, 23 (2) : 629-665. doi: 10.3934/dcdsb.2018037 [16] Theodore Tachim Medjo. On the convergence of a stochastic 3D globally modified two-phase flow model. Discrete & Continuous Dynamical Systems - A, 2019, 39 (1) : 395-430. doi: 10.3934/dcds.2019016 [17] Feimin Huang, Dehua Wang, Difan Yuan. Nonlinear stability and existence of vortex sheets for inviscid liquid-gas two-phase flow. Discrete & Continuous Dynamical Systems - A, 2019, 39 (6) : 3535-3575. doi: 10.3934/dcds.2019146 [18] Yangyang Qiao, Huanyao Wen, Steinar Evje. Compressible and viscous two-phase flow in porous media based on mixture theory formulation. Networks & Heterogeneous Media, 2019, 14 (3) : 489-536. doi: 10.3934/nhm.2019020 [19] Steinar Evje, Huanyao Wen, Lei Yao. Global solutions to a one-dimensional non-conservative two-phase model. Discrete & Continuous Dynamical Systems - A, 2016, 36 (4) : 1927-1955. doi: 10.3934/dcds.2016.36.1927 [20] Jan Prüss, Jürgen Saal, Gieri Simonett. Singular limits for the two-phase Stefan problem. Discrete & Continuous Dynamical Systems - A, 2013, 33 (11&12) : 5379-5405. doi: 10.3934/dcds.2013.33.5379

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# print number of next page

I know I can use \thepage to print the current page number in my document. But is it possible to print the number of the next page, e.g. for phrases like "continue on page "?

Page numbering (displaying and referencing) should typically be handled using \labels and \refs. Here's an example showing why \thepage is not always accurate:

\documentclass{article}

\usepackage[nopar]{lipsum}

\begin{document}

\lipsum[1-4] \texttt{Page: \thepage}% On page 1, displays as "Page: 1"

\lipsum[5-7] \texttt{Page: \thepage}% On page 2, displays as "Page: 1"

\end{document}

The correct output is displayed when using the \label-\ref system:

\documentclass{article}

\usepackage[nopar]{lipsum}

\begin{document}

\lipsum[1-4] \label{pg:one}\texttt{Page: \pageref{pg:one}}% On page 1, displays as "Page: 1"

\lipsum[5-7] \label{pg:two}\texttt{Page: \pageref{pg:two}}% On page 2, displays as "Page: 2"

\end{document}

The above example works regardless of the representation of the page counter (given by \thepage). For example, one can only perform calculations on \thepage if it expands to a number (via \arabic{page}, typically). It would not be possible to use \thepage within the \frontmatter of a book or report, since then \thepage defaults to \roman{page}.

If you really want to perform calculations on the page number, use the \label-\ref system together with refcount:

\documentclass{article}

\usepackage[nopar]{lipsum}
\usepackage{refcount}

\begin{document}

\lipsum[1-4] \label{pg:one}\texttt{Page: \pageref{pg:one}}% On page 1, displays as "Page: 1"

\lipsum[5-7] \texttt{Page: \number\numexpr\getpagerefnumber{pg:one}+1\relax}% On page 2, displays as "Page: 2"

\end{document}

• I'm using a longtable which expands onto multiple pages. The last row of that longtable should state "continue on page xx" (the next page). I can't label any of the pages, since there's just one longtable environment, and even if I could, I wouldn't want to check where a new page begins, assign them a label each, and manually add a row to my table referring that label. There has to be some kind of automation, isn't it? – LukeLR Feb 1 '17 at 22:32
• @LukeLR: Why not just write "continued on next page"? – Werner Feb 1 '17 at 22:36
• In German, I wouldn't use any equivalent to "continued on next page". At least in my opinion, naming the page number is better german. It's just a detail, but I thought it should be possible. – LukeLR Feb 1 '17 at 22:39
• @LukeLR: The use of this application in longtable is not recommended (see the discussion between myself and the package author in chat). If you're interested in a longtable-specific solution, perhaps consider asking a follow-up question. – Werner Feb 1 '17 at 23:41
• Okay, I'll consider that. Thanks a lot for your efforts! – LukeLR Feb 2 '17 at 3:05

Yes, this is possible, even without the use of any extra packages. Just write a small makro in the preamble of your document like this:

\newcommand{\thenextpage}{
\number\numexpr\thepage+1\relax
}

Then use \thenextpage anywhere in your document to print the number of the next page.

• What happens when \renewcommand{\thepage}{\roman{page}}? – Werner Feb 1 '17 at 18:35
• @Werner \newcommand*{\thenextpage}{\begingroup\addtocounter{page}{1}\thepage\addtocounter{page}{-1}\endgroup} works with Roman page numbers. But, the main problem is usually that the page number is not known in advance because of the asynchronous output routine. Therefore, this will only work in a reliable way, if the location is somewhat known, e.g. at the start of a chapter or right after a \clearpage. – Heiko Oberdiek Feb 1 '17 at 19:14

format: plain


text:
DiffAqua: A Differentiable Computational Design Pipeline for Soft Underwater Swimmers with Shape Interpolation
1MIT CSAIL 2ETH Zürich
The overview of our differentiable pipeline for both forward and backward propagation.
Abstract
The computational design of soft underwater swimmers is challenging because of the high degrees of freedom in soft-body modeling. In this paper, we present a differentiable pipeline for co-designing a soft swimmer's geometry and controller. Our pipeline unlocks gradient-based algorithms for discovering novel swimmer designs more efficiently than traditional gradient-free solutions. We propose Wasserstein barycenters as a basis for the geometric design of soft underwater swimmers since it is differentiable and can naturally interpolate between bio-inspired base shapes via optimal transport. By combining this design space with differentiable simulation and control, we can efficiently optimize a soft underwater swimmer's performance with fewer simulations than baseline methods. We demonstrate the efficacy of our method on various design problems such as fast, stable, and energy-efficient swimming and demonstrate applicability to multi-objective design.
Paper
DiffAqua: A Differentiable Computational Design Pipeline for Soft Underwater Swimmers with Shape Interpolation
ACM Transactions on Graphics, Proceedings of ACM SIGGRAPH, 2021
[Paper] [Video] [Code] [Slides]
Citation
@article{ma2021diffaqua,
title={DiffAqua: A Differentiable Computational Design Pipeline for Soft Underwater Swimmers with Shape Interpolation},
author={Ma, Pingchuan and Du, Tao and Zhang, John Z and Wu, Kui and Spielberg, Andrew and Katzschmann, Robert K and Matusik, Wojciech},
journal={ACM Transactions on Graphics (TOG)},
volume={40},
number={4},
pages={1--14},
year={2021},
publisher={ACM New York, NY, USA}
}
Video
Results
The illustration of the Wasserstein barycentric interpolation on the shape and the actuators .
Co-optimization (bottom) outperforms control-only optimization (top 3) when designing the fastest swimmer.
Related Projects
ACM Transactions on Graphics, Proceedings of ACM SIGGRAPH Asia, 2020
[Project Page] [Paper] [Appendix] [Code] [Slides]


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# Number of Maximum Overlap in n-Dimensions

Given a list of compact axis-aligned intervals (in 1-D), rectangles (in 2-D), cuboids (3-D) etc, what is the maximum number that overlap at any point?

In 1-D there's a fairly simple solution that exploits the the ordering of R: assuming you have a set of pairs $\{[a_1,b_1],...,[a_n,b_n]\}$ sort all of the a's and b's (together) then scan from a_min to b_max adding one to the count of overlap whenever you encounter $a_i$ for any i and subtracting one whenever you see a $b_j$ for any j. Then just keep track of the maximum value of count that you see.

I'm not sure how to extend this to 2-D, let alone n-D. Any ideas?

• Let $f_{n}(B)$ be an algorithm that solves this problem for a set of $n$D hyperrectangles $B$. If you have $f_n$, you can compute $f_{n+1}$. Let the set of boxes you have be $B$, let $H$ be any set of parallel axis aligned hyperplane, such that the union covers all the vertices of the boxes in $B$. Note $f_{n+1}(B) = \max_{h\in H} \{ f_n (\{ h\cap b: b\in B\}) \}$. This is the exact algorithm you have if $n=1$. – Chao Xu Apr 14 '13 at 1:58
• @ChaoXu Hmm, if I'm understanding you in 2D, if we select H to be to be the simplest set of parallel axis aligned hyperplanes (i.e. lines), we just take lines aligned with the horizontal (say) side of the rectangles (so 2/rectangle). Then we run $f_1$ on each "slice" generated by taking the intersection of each line in H with every rectangle in B and just take the max of that. Clever. I suppose this relies on a generalization of the theorem that in 1-D the point of maximum overlap occurs on an endpoint? (If theres a good proof of that I'd like to see it) – nimish Apr 14 '13 at 2:10
• It doesn't always occur on an endpoint, for example consider two rectangles that creates a cross shape. You want to prove it occurs at a boundary($\partial$) of the hyperrectangle. A good proof: For any two closed sets $A$ and $B$, $\partial(A\cap B)\subset \partial(A) \cup \partial(B)$. – Chao Xu Apr 14 '13 at 3:46
• So does that mean I need H to contain all sides of every hyperrectangle? Or am I safe with just taking the minimum number needed to cover the vertices? My intuition for the 1-D case is that if you find the maximum overlap in the interior of the overlapping intervals, you can then move infinitesimally to the left or right until you hit an endpoint of some interval. Also, you should put this up as an answer so I can accept it. – nimish Apr 14 '13 at 15:38

Let $f_n(B)$ be an algorithm that solves this problem for a set of $nD$ hyperrectangles $B$. If you have $f_n$, you can compute $f_{n+1}$. Let the set of boxes you have be $B$, let $H$ be any set of parallel axis aligned hyperplane, such that the union covers all the vertices of the boxes in $B$. Note $f_{n+1}(B)=\max_{h\in H}\{f_n(\{h\cap b: b\in B\})\}$. This is the exact algorithm you have if $n=1$.
This works because point intersect most rectangle can be at the boundary of the intersection. You want to prove it occurs at a boundary($\partial$) of the hyperrectangle. A good proof: For any two closed sets $A$ and $B$, $\partial(A\cap B)\subset \partial(A)\cup \partial(B)$.
This is a well-known variant of Klee's measure problem. The best algorithm known, due to Timothy Chan, runs in roughly $O(n^{d/2})$ time, ignoring polylogarithmic factors. Faster algorithms are known for the special cases of fat boxes and boxes with one or more fixed coordinates; see recent work by Karl Bringmann and Hakan Yıldız, respectively.


text:
# Quark Matter 2017

5-11 February 2017
Hyatt Regency Chicago
America/Chicago timezone

## Measurements of the dielectron continuum in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC

7 Feb 2017, 09:10
20m
Regency C

### Regency C

Oral Electromagnetic Probes

### Speaker

Oton Vazquez Doce (Technische Universitaet Muenchen (DE))

### Description

Dielectrons produced in ultra-relativistic heavy-ion collisions at the LHC provide a unique probe of the whole system evolution as they are unperturbed by final-state interactions. The dielectron continuum is extremely rich in physics sources: on top of ordinary Dalitz and resonance decays of pseudoscalar and vector mesons, thermal black-body radiation is of particular interest as it carries information about the temperature of the hot and dense system created in such collisions. Dielectron invariant-mass distribution is furthermore sensitive to medium modifications of the spectral function of short-lived vector mesons that are linked to the potential restoration of chiral symmetry at high temperatures. Correlated electron pairs from semi-leptonic charm and beauty decays provide complementary information about the heavy-quark energy loss.

In this talk, we will present an extensive summary of the LHC Run-1 results in all three collisions systems: pp, p-Pb and Pb-Pb, the former two providing crucial vacuum and cold-nuclear matter references for the latter. Furthermore, we will discuss the status of the ongoing Run-2 pp and Pb-Pb analyses with a focus on pp collisions collected with a trigger on high charged-particle multiplicities and conclude with an outlook for future measurements in Run-3 following the ALICE detector upgrades during the second long shutdown phase.

Collaboration ALICE Electromagnetic Probes

### Primary author

Oton Vazquez Doce (Technische Universitaet Muenchen (DE))


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# A small water pump would take 2 hours to fill an empty tank

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A small water pump would take 2 hours to fill an empty tank [#permalink]

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Can someone assist me with solving this question?

A small water pump would take 2 hours to fill an empty tank. A larger pump would take 1/2 hour to fill the same tank. How many hours would it take both pumps, working at their respective constant rates, to fill the empty tank if they began pumping at the same time?

A) 1/4
B) 1/3
C) 2/5
D) 5/4
E) 3/2
[Reveal] Spoiler: OA
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07 Feb 2012, 07:09
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domu904 wrote:
Can someone assist me with solving this question?

A small water pump would take 2 hours to fill an empty tank. A larger pump would take 1/2 hour to fill the same tank. How many hours would it take both pumps, working at their respective constant rates, to fill the empty tank if they began pumping at the same time?

A) 1/4
B) 1/3
C) 2/5
D) 5/4
E) 3/2

Rate of the small pump is 1/2 tank/hour (rate is reciprocal of time);
Rate of the larger pump is 2 tank/hour;

Combined rate of the two pumps is 1/2+2=5/2 tank/hour, hence together they will fill the empty tank in 1/(5/2)=2/5 hours (time=job/rate).

Theory on work/rate problems:
two-consultants-can-type-up-a-report-126155.html?hilit=know%20rate%20work%20reciprocal#p1030079

Hope it helps.

P.S. Please post PS questions in the PS subforum: gmat-problem-solving-ps-140/ and DS questions in the DS subforum: gmat-data-sufficiency-ds-141/

No posting of PS/DS questions is allowed in the main Math forum.
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Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

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Hi All,

We're given the rates of two entities that will share a job together - this is the standard "set-up" for a Work Formula question.

Work Formula = (A)(B)/(A+B) where A and B are the respective amounts of time needed to individually complete a job.

Pump A = 2 hours to fill a tank
Pump B = 1/2 hour to fill a tank

Working together, it takes....

(2)(1/2)/(2 + 1/2) = 1/2.5 hours to fill the tank together...

1/2.5 = 2/5 hours

[Reveal] Spoiler:
C

GMAT assassins aren't born, they're made,
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# Special Offer: Save $75 + GMAT Club Tests 60-point improvement guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Intern Joined: 29 Nov 2015 Posts: 13 Followers: 0 Kudos [?]: 5 [0], given: 44 Re: A small water pump would take 2 hours to fill an empty tank [#permalink] ### Show Tags 29 Dec 2015, 11:08 Bunuel wrote: domu904 wrote: Can someone assist me with solving this question? A small water pump would take 2 hours to fill an empty tank. A larger pump would take 1/2 hour to fill the same tank. How many hours would it take both pumps, working at their respective constant rates, to fill the empty tank if they began pumping at the same time? A) 1/4 B) 1/3 C) 2/5 D) 5/4 E) 3/2 Rate of the small pump is 1/2 tank/hour (rate is reciprocal of time); Rate of the larger pump is 2 tank/hour; Combined rate of the two pumps is 1/2+2=5/2 tank/hour, hence together they will fill the empty tank in 1/(5/2)=2/5 hours (time=job/rate). Answer: C. Hi, the logic I used was pretty much the same as yours, still Idk where I went wrong... small pump fills 1 tank in 2 hours -> 1/2 tank in 1 hour -> 1/4 tank in 1/2 hour big pump fills 1 tank in 1/2 hour 1/4 + 1 = 5/4 work which will take 4/5 hours EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 7214 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Followers: 315 Kudos [?]: 2134 [1] , given: 161 Re: A small water pump would take 2 hours to fill an empty tank [#permalink] ### Show Tags 29 Dec 2015, 23:46 1 This post received KUDOS Expert's post Hi sarathvr, With the work that you've done, you have calculated how much of the tank would be filled in 1/2 an hour by the two pumps (working together). In 1/2 hour: The small pump would fill 1/4 of the tank The large pump would fill 1/1 of the tank Combined, that is 1/4 + 4/4 = 5/4 of the tank in 1/2 an hour. This means that the two pumps would OVER-FILL the tank in 1/2 an hour. By extension, it would take LESS than 1/2 an hour to fill the tank, so the answer CAN'T be 4/5 of an hour. If you're going to use this approach, then you would have to MULTIPLY both sides by 4/5.... (5/4 of a tank)(4/5) = (1/2 hour)(4/5) 20/20 of a tank = 4/10 of an hour 1 tank = 2/5 of an hour GMAT assassins aren't born, they're made, Rich _________________ # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

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Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

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30 Dec 2015, 07:33
EMPOWERgmatRichC wrote:
Hi sarathvr,

With the work that you've done, you have calculated how much of the tank would be filled in 1/2 an hour by the two pumps (working together).

In 1/2 hour:
The small pump would fill 1/4 of the tank
The large pump would fill 1/1 of the tank

Combined, that is 1/4 + 4/4 = 5/4 of the tank in 1/2 an hour. This means that the two pumps would OVER-FILL the tank in 1/2 an hour. By extension, it would take LESS than 1/2 an hour to fill the tank, so the answer CAN'T be 4/5 of an hour.

If you're going to use this approach, then you would have to MULTIPLY both sides by 4/5....

(5/4 of a tank)(4/5) = (1/2 hour)(4/5)
20/20 of a tank = 4/10 of an hour
1 tank = 2/5 of an hour

GMAT assassins aren't born, they're made,
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OK yes! I didn't realise the over-full thing, so yeah that made sense.

But I still didn't understand the logic behind multiplying by 4/5 :/
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Re: A small water pump would take 2 hours to fill an empty tank [#permalink]

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30 Dec 2015, 11:16
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Hi sarathvr,

The math that you did calculated the time it takes to fill 5/4 of a tank, but the question asks you to fill 4/4 of a tank. Mathematically, since we're dealing with rates, to decrease 5/4 to 4/4 we have to multiply by 4/5. Since we're multiplying one side of the 'equation' by 4/5, we have to multiply the other side by 4/5 also...

(5/4 of a tank)(4/5) = (1/2 hour)(4/5)
20/20 of a tank = 4/10 of an hour
1 tank = 2/5 of an hour

GMAT assassins aren't born, they're made,
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Re: A small water pump would take 2 hours to fill an empty tank   [#permalink] 30 Dec 2015, 11:16
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What is machine learning?

What is the definition of machine learning? What are the advantages of machine learning?

In his book Machine Learning: A Probabilistic Perspective (2012), Kevin P. Murphy defines machine learning as

a set of methods that can automatically detect patterns in data, and then use the uncovered patterns to predict future data, or to perform other kinds of decision making under uncertainty (such as planning how to collect more data!)

He divides machine learning into three categories

• supervised learning (or predictive), where the goal is to learn a mapping from inputs $$\boldsymbol{x}$$ to outputs $$y$$, given a labeled set of input-output pairs
• unsupervised learning (or descriptive), where the goal is to find "interesting patterns" in the data
• reinforcement learning, which is useful for learning how to act or behave when given occasional reward or punishment signals

What are the advantages of machine learning?

It can potentially be used to (at least partially) automate tasks that involve data analysis that were previously performed only by humans (e.g. translation). However, machine learning cannot automate all tasks: for example, it cannot infer causal relations from the data (which often must be done by humans), unless you include causal inference as part of machine learning. See e.g. Is machine learning less useful for understanding causality, thus less interesting for social science?.


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Astrophysics (astro-ph)

• We study a generalized nonlocal theory of gravity which, in specific limits, can become either the curvature non-local or teleparallel non-local theory. Using the Noether Symmetry Approach, we find that the coupling functions coming from the non-local terms are constrained to be either exponential or linear in form. It is well known that in some non-local theories, a certain kind of exponential non-local couplings are needed in order to achieve a renormalizable theory. In this paper, we explicitly show that this kind of coupling does not need to by introduced by hand, instead, it appears naturally from the symmetries of the Lagrangian in flat Friedmann-Robertson-Walker cosmology. Finally, we find de-Sitter and power law cosmological solutions for different nonlocal theories. The symmetries for the generalized non-local theory is also found and some cosmological solutions are also achieved under the full theory.
• In both WMAP and Planck observations on the temperature anisotropy of cosmic microwave background (CMB) radiation a number of large-scale anomalies were discovered in the past years, including the CMB parity asymmetry in the low multipoles. By defining a directional statistics, we find that the CMB parity asymmetry is directional dependent, and the preferred axis is stable, which means that it is independent of the chosen CMB map, the definition of the statistic, or the CMB masks. Meanwhile, we find that this preferred axis strongly aligns with those of the CMB quadrupole, octopole, as well as those of other large-scale observations. In addition, all of them aligns with the CMB kinematic dipole, which hints to the non-cosmological origin of these directional anomalies in cosmological observations.
• As is well known, some aspects of General Relativity and Cosmology can be reproduced without even using Einstein's equation. As an illustration, the 0 - 0 component of the Schwarzschild space can be obtained by the requirement that the geodesic of slowly mov- ing particles match the Newtonian equation. Given this result, we shall show here that the remaining component (grr) can be obtained by requiring that the inside of a Newtonian ball of dust matched at a free falling radius with the external space of unspecified type. This matching determines the external space to be of Schwarzschild type. By this, it is also possi- ble to determine that the constant of integration that appears in the Newtonian Cosmology, coincides with the spatial curvature of the FLRW metric. All we assumed was some classical boundary conditions and basic assumptions.
• We have conducted experimental measurements and numerical simulations of a precession driven flow in a cylindrical cavity. The study is dedicated to the precession dynamo experiment currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and aims at the evaluation of the hydrodynamic flow with respect to its ability to drive a dynamo. We focus on the strongly non-linear regime in which the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves arising from non-linear self-interactions. We obtain an excellent agreement between experiment and simulation with regard to both, flow amplitudes and flow geometry. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double role structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around ${\rm{Rm}}^{\rm{c}}\approx 430$ which is well within the range of the planned liquid sodium experiment.
• The detection of redshifted 21cm-line signal from neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR) is complicated by intense foregrounds such as galactic synchrotron and extragalactic radio galaxies. The 21cm-Lyman-$\alpha$ emitter(LAE) cross-correlation is one of the tools to reduce the foreground effects because the foreground emission from such radio sources is statistically independent of LAE distribution. LAE surveys during the EoR is ongoing at redshift $z=6.6$ and $7.3$ by Subaru Hyper Suprime-Cam (HSC), and Prime Focus Spectrograph (PFS) will provide precise redshift information of the LAEs discovered by the HSC survey. In this paper, we investigate the detectability of the 21cm-signal with the 21cm-LAE cross-correlation by using our improved reionization simulations that are consistent with the neutral hydrogen fraction at $z\sim6$ indicated by QSO spectra and the observed Thompson scattering optical depth. We also focus on the error budget and evaluate it quantitatively in order to consider a strategy to improve the signal-to-noise ratio. In addition, we explore an expansion of the LAE survey to suggest optimal survey parameters and show a potential to measure a characteristic size of ionized bubbles via the turnover scale of the cross-power spectrum. As a result, we find that the Murchison Widefield Array (MWA) has ability to detect the cross-power spectrum signal on large scales by combining LAE Deep field survey of HSC. Especially, we show that the sensitivity is improved dramatically at small scales by adding redshift information from the PFS measurements. Finally, we find that a wider LAE survey is better than a deeper survey with a fixed observation time in order to detect the cross-spectrum and that Square Kilometre Array (SKA) has a potential to measure the turnover scale with an accuracy of $6\times10^{-3}~{\rm Mpc^{-1}}$.
• The collapsar model has proved highly successful in explaining the properties of long gamma-ray bursts (GRBs), with the most direct confirmation being the detection of a supernova (SN) coincident with the majority of nearby long GRBs. Within this model, a long GRB is produced by the core-collapse of a metal-poor, rapidly rotating, massive star. The detection of some long GRBs in metal-rich environments, and more fundamentally the three examples of long GRBs (GRB 060505, GRB 060614 and GRB 11005A) with no coincident SN detection down to very deep limits is in strong contention with theoretical expectations. In this paper we present MUSE observations of the host galaxy of GRB 111005A, which is the most recent and compelling example yet of a SN-less, long GRB. At z = 0.01326, GRB 111005A is the second closest GRB ever detected, enabling the nearby environment to be studied at an unprecedented resolution of 100 pc^2. From the analysis of the MUSE data cube, we find GRB 111005A to have occurred within a metal-rich environment with little signs of ongoing star formation. Spectral analysis at the position of the GRB indicates the presence of an old stellar population (age>=10 Myr), which limits the mass of the GRB progenitor to M_(ZAMS) < 15 Msun, in direct conflict with the collapsar model. Our deep limits on the presence of any SN emission combined with the environmental conditions at the position of GRB 111005A necessitate the exploration of a novel long GRB formation mechanism that is unrelated to massive stars.
• The astronomical community continues to be interested in suitable programmable slit masks for use in multi-object spectrometers (MOSs) on space missions. There have been ground-based MOS utilizing digital micromirror devices (DMDs) and they have proven to be highly accurate and reliable instruments. This paper summarizes the results of a continuing study to investigate the performance of DMDs under conditions associated with space deployment. This includes the response of DMDs to radiation, to the vibration and mechanical shock loads associated with launch, and the operability of DMD under cryogenic temperatures. The optical contrast ratio and a study of the long-term reflectance of a bare device have also been investigated. The results of the radiation testing demonstrate that DMDs in orbit would experience negligible heavy-ion induced single event upset (SEU) rate burden, we predict SEU rate of 5.6 micromirrors per 24 hours. Vibration and mechanical shock testing was performed according to the NASA General Environmental Verification Standard (GEVS), no mirrors failed in the devices tested. The results of low temperature testing suggest that DMDs are not affected by the thermal load and operate smoothly at temperatures at least as low as 78 K. The reflectivity of a bare DMD did not measurably change even after being exposed to ambient conditions over a period of 13 months. The measured contrast ratio (on state vs off state of the DMD micromirrors) was greater than 6000/:1 when illuminated with an f/4 optical beam. Overall, DMDs are extremely robust and promise to provide a reliable alternative to micro shutter arrays (MSA) to be used in space as remotely programmable slit masks for MOS design.
• We study one loop quantum gravitational corrections to the long range force induced by the exchange of a massless scalar between two massive scalars. The various diagrams contributing to the flat space S-matrix are evaluated in a general covariant gauge and we show that dependence on the gauge parameters cancels at a point considerably \it before forming the full S-matrix, which is unobservable in cosmology. It is possible to interpret our computation as a solution to the effective field equations --- which could be done even in cosmology --- but taking account of quantum gravitational corrections from the source and from the observer.
• Very Low-Mass Stars in particular M dwarfs are an important source of information for probing the low mass end of the main sequence, down to the hydrogen burning limit. The presence first of molecules and then of condensed particulates greatly complicates the understanding of their physical properties, and thus makes the determination of their fundamental stellar parameters challenging. Accurate knowledge of their atmospheric parameters and especially their composition is essential for understanding the chemical history of our Galaxy. The purpose of this work is to perform a detailed study of the high-resolution H-band spectra of M dwarfs. The determination of atmospheric parameters of late-type stars is difficult because the spectra of these cool stars contain many overlapping absorption lines, preventing the determination of atmospheric parameters. The high spectral resolution in H-band provides a unique opportunity to constrain the processes that occur in a cool atmosphere.he high-resolution APOGEE spectra, covering the entire H-band, provides the opportunity to measure physical stellar atmospheric parameters of M dwarfs. We performed a spectral synthesis analysis using a full grid of synthetic spectra computed from BT-Settl models and obtained stellar parameters such as effective temperature, surface gravity, and metallicity.We determine the fundamental parameters such as effective temperature, surface gravity, and metallicity for 45 M dwarfs using high-resolution H-band spectra.
• The Fermi Large Area Telescope (LAT) revealed that blazars, representing the most extreme radio-loud active galactic nuclei (AGN) population, dominate the census of the gamma-ray sky, and a significant correlation was found between radio and gamma-ray emission in the 0.1-100 GeV energy range. However, the possible connection between radio and very high energy (VHE, E>0.1 TeV) emission still remains elusive and unexplored, owing to the lack of a homogeneous coverage of the VHE sky. The main goal of this work is to quantify and assess the significance of a possible connection between the radio emission on parsec scale measured by the very long baseline interferometry (VLBI) and GeV-TeV gamma-ray emission in blazars, which is a central issue for understanding the blazar physics and the emission processes. We investigate the radio VLBI and high energy gamma-ray emission by using two large and unbiased AGN samples extracted from the first and second Fermi-LAT catalogs of hard gamma-ray sources detected above 10 GeV (1FHL) and 50 GeV (2FHL). For comparison, we perform the same correlation analysis by using the 0.1-300 GeV gamma-ray energy flux provided by the third Fermi-LAT source catalog. We find that the correlation strength and significance depend on the gamma-ray energy range with a different behavior among the blazar sub-classes. Overall, the radio and gamma-ray emission above 10 GeV turns out to be uncorrelated for the full samples and for all of the blazar sub-classes with the exception of high synchrotron peaked (HSP) objects, which show a strong and significant correlation. On the contrary, when 0.1-300 GeV gamma-ray energies are considered, a strong and significant correlation is found for the full blazar sample as well as for all of the blazar sub-classes. We interpret and explain this correlation behavior within the framework of the blazar spectral energy distribution properties.
• Fast variations of gamma-ray flux from Active Galactic Nuclei and Gamma-Ray Bursts can constrain Lorentz Invariance Violation (LIV) because of the delayed (or advanced) arrival of photons with higher energies: this approach has lead to the current world-best limits on the energy scale of Quantum Gravity. Here we report on constraints on LIV studying the gamma-ray emission up to TeV energies from the Galactic Crab pulsar, recently discovered by the MAGIC collaboration. A likelihood analysis of the pulsar events reconstructed for energies above 400 GeV finds no significant variation of energy-dependent arrival time, and 95% CL limits are then obtained on the effective LIV energy scale after taking into account systematic uncertainties. Only a factor of about two less constraining than the current world-best limit on a quadratic LIV scenario, pulsars are now well established as a third and independent class of astrophysical objects suitable to constrain the characteristic energy scale of LIV.
• We constructed for the first time a stellar density profile of 47 Tucanae (47 Tuc) out of $\sim$ 5.5 times its tidal radius ($r_t$) using high-quality deep $BV$ photometry. After carefully considering the influence of photometric errors, and Milky Way and Small Magellanic Cloud composite stellar population contamination, we found that the cluster stellar density profile reaches a nearly constant value from $\sim$ 1.7$r_t$ outwards, which does not depend on the direction from the cluster's center considered. These results visibly contrast with recent distinct theoretical predictions on the existence of tidal tails or on a density profile that falls as $r^{-4}$ at large distances, and with observational outcomes of a clumpy structure as well. Our results suggest that the envelope of 47 Tuc is a halo- like nearly constant low density structure.
• We have explored the outskirts of dark matter haloes out to 2.5 times the virial radius using a large sample of halos drawn from Illustris, along with a set of zoom simulations (MUGS). Using these, we make a systematic exploration of the shape profile beyond R$_{vir}$. In the mean sphericity profile of Illustris halos we identify a dip close to the virial radius, which is robust across a broad range of masses and infall rates. The inner edge of this feature may be related to the virial radius and the outer edge with the splashback radius. Due to the high halo-to-halo variation this result is visible only on average. However, in four individual halos in the MUGS sample, a decrease in the sphericity and a subsequent recovery is evident close to the splashback radius. We find that this feature persists for several Gyr, growing with the halo. This feature appears at the interface between the spherical halo density distribution and the filamentary structure in the environment. The shape feature is strongest when there is a high rate of infall, implying that the effect is due to the mixing of accreting and virializing material. The filamentary velocity field becomes rapidly mixed in the halo region inside the virial radius, with the area between this and the splashback radius serving as the transition region. We also identify a long-lasting and smoothly evolving splashback region in the radial density gradient in many of the MUGS halos.
• The Juno Orbiter has provided improved estimates of the even gravitational harmonics J2 to J8 of Jupiter. To compute higher-order moments, new methods such as the Concentric Maclaurin Spheroids (CMS) method have been developed which surpass the so far commonly used Theory of Figures (ToF) method in accuracy. This progress rises the question whether ToF can still provide a useful service for deriving the internal structure of giant planets in the Solar system. In this paper, I apply both the ToF and the CMS method to compare results for polytropic Jupiter and for the physical equation of state H/He-REOS.3 based models. An accuracy in the computed values of J2 and J4 of 0.1% is found to be sufficient in order to obtain the core mass safely within 0.5 Mearth numerical accuracy and the atmospheric metallicity within about 0.0004. ToF to 4th order provides that accuracy, while ToF to 3rd order does not for J4. Furthermore, I find that the assumption of rigid rotation yields J6 and J8 values in agreement with the current Juno estimates, and that higher order terms (J10 to J18) deviate by about 10% from predictions by polytropic models. This work suggests that ToF4 can still be applied to infer the deep internal structure, and that the zonal winds on Jupiter reach less deep than 0.9 RJup.
• Our study exploits the Constant Intensity Cut principles applied simultaneously to muonic and electromagnetic detectors of cosmic rays. We use the fact that the ordering of events according to their signal sizes induced in different types of surface detectors provides information about the mass composition of primary cosmic-ray beam, with low sensitivity to details of hadronic interactions. Composition analysis at knee energies is performed using Monte Carlo simulations for extensive air showers having maxima located far away from a hypothetical observatory. Another type of a hypothetical observatory is adopted to examine composition of ultra-high energy primaries which initiate vertical air showers with maxima observed near surface detectors.
• The initial mass function for the stars is often modeled by a lognormal distribution. This paper is devoted to demonstrating the advantage of introducing a left and right truncated lognormal probability density function, which is characterized by four parameters. Its normalization constant, mean, the variance, second moment about the origin and distribution function are calculated. The chi-square test and the Kolmogorov--Smirnov test are performed on four samples of stars.
• In this work, we explore the long-term variability properties of the blazar PKS 0219-164 in the radio and the $\gamma$-ray regime, utilizing the OVRO 15 GHz and the \fermi/LAT observations from the period 2008--2017. We found that $\gamma$-ray emission is more variable than the radio emission implying that $\gamma$ ray emission possibly originated in more compact regions while the radio emission represented continuum emission from the large scale jets. Also, in $\gamma$-ray the source exhibited spectral variability characterized by the \emph softer-when-brighter trend, a less frequently observed feature in the high energy emission by BL Lacs. In radio, using Lomb-Scargle periodogram and weighted wavelet z-transform, we detected a strong signal of quasi-periodic oscillation (QPO) with a periodicity of 270 $\pm$ 26 days with possible harmonics of 550 $\pm$ 42 and 1150 $\pm$ 157 days periods. At a time when the issue of the detection of QPOs in blazars is still under debate, the observed QPO with high statistical significance ( $\sim$ 97\% -- 99\% global significance over underlying red-noise processes) and persistent over nearly 10 oscillations could make one of the strongest cases for the detection of QPOs in blazar light curves. We discuss various blazar models that might lead to the $\gamma$-ray and radio variability, QPO, and the achromatic behavior seen in the high energy emission from the source.
• We present a search for optical bursts from the repeating fast radio burst FRB 121102 using simultaneous observations with the high-speed optical camera ULTRASPEC on the 2.4-m Thai National Telescope and radio observations with the 100-m Effelsberg Radio Telescope. A total of 13 radio bursts were detected, but we found no evidence for corresponding optical bursts in our 70.7-ms frames. The 5-sigma upper limit to the optical flux density during our observations is 0.33 mJy at 767nm. This gives an upper limit for the optical burst fluence of 0.046 Jy ms, which constrains the broadband spectral index of the burst emission to alpha < -0.2. Two of the radio pulses are separated by just 34 ms, which may represent an upper limit on a possible underlying periodicity (a rotation period typical of pulsars), or these pulses may have come from a single emission window that is a small fraction of a possible period.
• NGC6217 is a nearby spiral galaxy with a starburst region near its center. Evidence for a low luminosity Active Galactic Nucleus (AGN) in its core has also been found in optical spectra. Intriguingly, X-ray observations by ROSAT revealed three knots aligned with the galaxy center, resembling a jet structure. This paper presents a study of XMM-Newton observations made to assess the hypothesis of a jet emitted from the center of NGC6217. The XMM data confirm the knots found with ROSAT and our spectral analysis shows that they have similar spectral properties with a hard photon index Gamma~1.7. The core of NGC6217 is well fitted by a model with an AGN and a starburst component, where the AGN contributes at most 46% of the total flux. The candidate jet has an apparent length ~15 kpc and a luminosity of ~5 X 10^38 erg/s. It stands out by being hosted by a spiral galaxy, since jets are more widely associated with ellipticals. To explain the jet launching mechanism we consider the hypothesis of an advection dominated accretion flow with a low accretion rate. The candidate jet emitted from NGC6217 is intriguing since it represents a challenge to the current knowledge of the connection between AGN, jets and host galaxies.
• Magnetorotational instability (MRI) is one of the fundamental processes in astrophysics, driving angular momentum transport and mass accretion in a wide variety of cosmic objects. Despite much theoretical/numerical and experimental efforts over the last decades, its saturation mechanism and amplitude, which sets the angular momentum transport rate, remains not well understood, especially in the limit of high resistivity, or small magnetic Prandtl numbers typical to interiors of protoplanetary disks, liquid cores of planets and liquid metals in laboratory. We investigate the nonlinear development and saturation properties of the helical magnetorotational instability (HMRI) in a magnetized Taylor-Couette flow using direct numerical simulations. From the linear theory of HMRI, it is known that the Elsasser number, or interaction parameter plays a special role for its dynamics and determines its growth rate. We show that this parameter is also important in the nonlinear problem. By increasing its value, a sudden transition from weakly nonlinear, where the system is slightly above the linear stability threshold, to turbulent regime occurs. We calculate the azimuthal and axial energy spectra corresponding to these two regimes and show that they differ qualitatively. Remarkably, the nonlinear states remain in all cases nearly axisymmetric suggesting that HMRI turbulence is quasi two-dimensional in nature. Although the contribution of non-axisymmetric modes increases moderately with the Elsasser number, their total energy remains much smaller than that of the axisymmetric ones.
• The MAGIC telescopes, located at the Roque de los Muchachos Observatory (2200 a.s.l.) in the Canary Island of La Palma, are placed on the top of a mountain, from where a window of visibility of about 5 deg in zenith and 80 deg in azimuth is open in the direction of the surrounding ocean. This permits to search for a signature of particle showers induced by earth-skimming cosmic tau neutrinos in the PeV to EeV energy range arising from the ocean. We have studied the response of MAGIC to such events, employing Monte Carlo simulations of upward-going tau neutrino showers. The analysis of the shower images shows that air showers induced by tau neutrinos can be discriminated from the hadronic background coming from a similar direction. We have calculated the point source acceptance and the expected event rates, assuming an incoming tau neutrino flux consistent with IceCube measurements, and for a sample of generic neutrino fluxes from photo-hadronic interactions in AGNs. The analysis of about 30 hours of data taken toward the sea leads to a point source sensitivity for tau neutrinos at the level of the down-going point source analysis of the Pierre Auger Observatory.
• We describe an OctTree algorithm for the MPI-parallel, adaptive mesh-refinement code \sc FLASH, which can be used to calculate the gas self-gravity, and also the angle-averaged local optical depth, for treating ambient diffuse radiation. The algorithm communicates to the different processors only those parts of the tree that are needed to perform the tree walk locally. The advantage of this approach is a relatively low memory requirement, important in particular for the optical depth calculation, which needs to process information from many different directions. This feature also enables a general tree-based radiation transport algorithm that will be described in a subsequent paper, and delivers excellent scaling up to at least 1500 cores. Boundary conditions for gravity can be either isolated or periodic, and they can be specified in each direction independently, using a newly developed generalisation of the Ewald method. The gravity calculation can be accelerated with the \em adaptive block update technique by partially re-using the solution from the previous time-step. Comparison with the \sc Flash internal multi-grid gravity solver shows that tree based methods provide a competitive alternative, particularly for problems with isolated or mixed boundary conditions. We evaluate several multipole acceptance criteria (MACs) and identify a relatively simple APE MAC which provides high accuracy at low computational cost. The optical depth estimates are found to agree very well with those of the \sc RADMC-3D radiation transport code, with the tree solver being much faster. Our algorithm is available in the standard release of the \sc FLASH code in version 4.0 and later.
• Measuring the imprint of primordial gravitational waves in the cosmic microwave background (CMB) polarisation field is one of the main goals in modern cosmology. However, the so called $B$-mode polarisation can be generated by different sources besides the primary one predicted by inflationary theories, known as secondary $B$-mode signal. Among them, CMB lensing and astrophysical foregrounds play an important role. Moreover, a partial sky analysis leads to a leakage between $E$-modes and $B$-modes. In this article, we use the well known Minkowski functionals (MF) statistics to study the significance of this leakage in the CMB lensing $B$-mode signal. We find that the MF can detect the $E$-to-$B$ leakage contamination, thus it should not be neglected in future CMB data analysis.
• We compute the tensor spectral index $n_t$, tensor-to-scalar ratio $r$, consistency relation and other inflation parameters in the general monomial multifield slow-roll inflation models with potentials $V \sim\sum_i\lambda_i \left|\phi_i\right|^{p_i}$ analytically. The general models give a novel relation that the tensor and scalar spectral index $n_t$, $n_s$ and also the consistency relation $n_t/r$ are all nearly proportional to the logarithm of the number of fields $N_f$ when $N_f$ is getting extremely large with the order of magnitude around $\mathcal{O}(10^{40})$. Requiring the slow variation parameter $\epsilon\lesssim 0.1$ then gives the upper bound of $N_f$ with $N_f\lesssim N_*e^{ZN_*}$ where $N_*$ is the number of e-foldings before the end of inflation and $Z$ is a value depends on the specific probability distributions of $\lambda_i$ and $p_i$. We also find a relation between the inflationary observables which is independent of the specific probability distributions. Besides, $n_t/r$ is differ from the single-field result $-1/8$ with substantial probability except for a few very special cases. In the end, we derive theoretical bounds for tensor-to-scalar ratio $r>2/N_*$ ($r\gtrsim0.03$) and for $n_t$ which can be tested by observation in the near future.
• We investigate the properties of a sunspot light-bridge, focusing on the changes produced by the impact of a plasma blob ejected from a C-class flare. We observed a sunspot in active region NOAA 12544 using spectropolarimetric raster maps of the four Fe I lines around 15655 Å with the GREGOR Infrared Spectrograph (GRIS), narrow-band intensity images sampling the Fe I 6173 Å line with the GREGOR Fabry-Pérot Interferometer (GFPI), and intensity broad band images in G-band and Ca II H band with the High-resolution Fast Imager (HiFI). All these instruments are located at the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The data cover the time before, during, and after the flare event. The analysis is complemented with Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data from the Solar Dynamics Observatory (SDO). The physical parameters of the atmosphere at differents heights were inferred using spectral-line inversion techniques. We identify photospheric and chromospheric brightenings, heating events, and changes in the Stokes profiles associated to the flare eruption and the subsequent arrival of the plasma blob to the light bridge, after traveling along an active region loop. The measurements suggest that these phenomena are the result of reconnection events driven by the interaction of the plasma blob with the magnetic field topology of the light bridge.
• We report the first intensity correlation measured with star light since Hanbury Brown and Twiss' historical experiments. The photon bunching $g^{(2)}(\tau, r=0)$, obtained in the photon counting regime, was measured for 3 bright stars, $\alpha$ Boo, $\alpha$ CMi, and $\beta$ Gem. The light was collected at the focal plane of a 1~m optical telescope, was transported by a multi-mode optical fiber, split into two avalanche photodiodes and digitally correlated in real-time. For total exposure times of a few hours, we obtained contrast values around $2\times10^{-3}$, in agreement with the expectation for chaotic sources, given the optical and electronic bandwidths of our setup. Comparing our results with the measurement of Hanbury Brown et al. on $\alpha$ CMi, we argue for the timely opportunity to extend our experiments to measuring the spatial correlation function over existing and/or foreseen arrays of optical telescopes diluted over several kilometers. This would enable $\mu$as long-baseline interferometry in the optical, especially in the visible wavelengths with a limiting magnitude of 10.
• Accurate shape measurements are essential to infer cosmological parameters from large area weak gravitational lensing studies. The compact diffraction-limited point-spread function (PSF) in space-based observations is greatly beneficial, but its chromaticity for a broad band observation can lead to new subtle effects that could hitherto be ignored: the PSF of a galaxy is no longer uniquely defined and spatial variations in the colours of galaxies result in biases in the inferred lensing signal. Taking Euclid as a reference, we show that this colourgradient bias (CG bias) can be quantified with high accuracy using available multi-colour Hubble Space Telescope (HST) data. In particular we study how noise in the HST observations might impact such measurements and find this to be negligible. We determine the CG bias using HST observations in the F606W and F814W filters and observe a correlation with the colour, in line with expectations, whereas the dependence with redshift is weak. The biases for individual galaxies are generally well below 1%, which may be reduced further using morphological information from the Euclid data. Our results demonstrate that CG bias should not be ignored, but it is possible to determine its amplitude with sufficient precision, so that it will not significantly bias the weak lensing measurements using Euclid data.
• We present the first good evidence for exocomet transits of a host star in continuum light in data from the Kepler mission. The Kepler star in question, KIC 3542116, is of spectral type F2V and is quite bright at $K_p = 10$. The transits have a distinct asymmetric shape with a steeper ingress and slower egress that can be ascribed to objects with a trailing dust tail passing over the stellar disk. There are three deeper transits with depths of $\simeq 0.1\%$ that last for about a day, and three that are several times more shallow and of shorter duration. The transits were found via an exhaustive visual search of the entire Kepler photometric data set, which we describe in some detail. We review the methods we use to validate the Kepler data showing the comet transits, and rule out instrumental artifacts as sources of the signals. We fit the transits with a simple dust-tail model, and find that a transverse comet speed of $\sim$35-50 km s$^{-1}$ and a minimum amount of dust present in the tail of $\sim 10^{16}$ g are required to explain the larger transits. For a dust replenishment time of $\sim$10 days, and a comet lifetime of only $\sim$300 days, this implies a total cometary mass of $\gtrsim 3 \times 10^{17}$ g, or about the mass of Halley's comet. We also discuss the number of comets and orbital geometry that would be necessary to explain the six transits detected over the four years of Kepler prime-field observations. Finally, we also report the discovery of a single comet-shaped transit in KIC 11084727 with very similar transit and host-
• The string theory predicts many light fields called moduli and axions, which cause a cosmological problem due to the overproduction of their coherent oscillation after inflation. One of the prominent solutions is an adiabatic suppression mechanism, which, however, is non-trivial to achieve in the case of axions because it necessitates a large effective mass term which decreases as a function of time. The purpose of this paper is twofold. First, we provide an analytic method to calculate the cosmological abundance of coherent oscillation in a general situation under the adiabatic suppression mechanism. Secondly, we apply our method to some concrete examples, including the one where a string axion acquires a large effective mass due to the Witten effect in the presence of hidden monopoles.
• Among the competing evolution theories for sdB stars is the binary evolution scenario. EC 20117-4014 is a spectroscopic binary system consisting of a pulsating sdB star and an F5V star, however the period and semimajor axis have not been precisely determined. To narrow down sdB binary evolution scenarios, the orbital characteristics of the binary system were determined. This paper presents the photometric results and orbital characteristics of the EC 20117-4014 binary system using 20 years of data. The results show seasonal and day-to-day pulsation amplitude variations. The day-to-day pulsation amplitude variation of the first largest amplitude pulsation (7.29 mHz) may be caused by a rotational splitting. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P = 794.6 days), orbital separation (r = 2.13 AU), and other orbital information. This analysis indicated that the system is likely to have experienced binary evolution and lost its hydrogen envelope through stable Roche lobe overflow, thus supporting a current leading hypotheses for the origin of subdwarf B (sdB) stars. The residuals of O-C data points after fitting with the sine curves shows small variations, which may imply an elliptical orbit or existence of other companions. In addition to those results, the pulsation period change was obtained from the photometry data, $\dot{P}$ = 5.4 ($\pm$0.7) $\times$ $10^{-14}$, which shows that this star is just before the ending of the core burning phase.
• Exploring weakly perturbed Keplerian motion within the restricted three-body problem, Lidov (1962) and, independently, Kozai (1962) discovered coupled oscillations of eccentricity and inclination (the KL-cycles). Their classical studies were based on an integrable model of the secular evolution, obtained by double averaging of the disturbing function approximated with its first non-trivial term. This was the quadrupole term in the series expansion with respect to the ratio of the semimajor axis of the disturbed body to that of the disturbing body. If the next (octupole) term is kept in the expression for the disturbing function, long-term modulation of the KL-cycles can established (Ford et al., 2000, Naoz et al., 2011, Katz et al., 2011). Specifically, flips between the prograde and retrograde orbits become possible. Since such flips are observed only when the perturber has a non-zero eccentricity, the term "Eccentric Kozai-Lidov Effect" (or EKL-effect) was proposed by Lithwick and Naoz (2011) to specify such behaviour. We demonstrate that the EKL-effect can be interpreted as a resonance phenomenon. To this end, we write down the equations of motion in terms of "action-angle" variables emerging in the integrable Kozai-Lidov model. It turns out that for some initial values the resonance is degenerate and the usual "pendulum" approximation is insufficient to describe the evolution of the resonance phase. Analysis of the related bifurcations allows us to estimate the typical time between the successive flips for different parts of the phase space.
• In what is being dubbed as the great American solar eclipse, on 21 August 2017, a total solar eclipse will sweep across the continental Unites States. Given the path of the eclipse and the length of totality available for eclipse observations, this eclipse will offer unprecedented opportunities for observations of the Sun's coronal structure and diagnostics of the coronal magnetic field. The Sun's coronal magnetic field is notoriously difficult to constrain and theoretical computational models must be relied upon for gaining insight on the coronal structure. Well-constrained solar coronal field models are crucial for understanding the origin of, and predicting solar storms that generate severe space weather. Here we present a technique for predicting and inferring the structure of the coronal field based on a data driven solar surface flux transport model which is forward run to 21 August 2017 to predict the Sun's surface field distribution. The predicted solar surface field is subsequently used as input in a potential field source surface model to generate the coronal structure during the imminent solar eclipse. Our results -- which can be verified during the 21 August 2017 eclipse observations -- indicate the presence of two helmet streamers, one each in the eastern and western limb on the southern solar hemisphere and significant radial open-flux at the poles indicating the accumulation of unipolar, polar fields in the build-up to the minimum of sunspot cycle 24. The South (open) polar flux appears to be stronger indicating an asymmetric sunspot cycle 25 with stronger activity in the southern hemisphere. The CESSI prediction of the coronal field expected during the 21 August, 2017 great American solar eclipse, accompanying images and data is available at the CESSI prediction website: http://www.cessi.in/solareclipse2017.
• We study a sample of 19 galaxy clusters in the redshift range $0.15<z<0.30$ with highly complete spectroscopic membership catalogues (to $K < K^{\ast}(\rm z)+1.5$) from the Arizona Cluster Redshift Survey (ACReS); individual weak-lensing masses and near-infrared data from the Local Cluster Substructure Survey (LoCuSS); and optical photometry from the Sloan Digital Sky Survey (SDSS). We fit the scaling relations between total cluster luminosity in each of six bandpasses (${\it grizJK}$) and cluster mass, finding cluster luminosity to be a promising mass proxy with low intrinsic scatter $\sigma_{\ln L|M}$ of only $\sim 10-20$ per cent for all relations. At fixed overdensity radius, the intercept increases with wavelength, consistent with an old stellar population. The scatter and slope are consistent across all wavelengths, suggesting that cluster colour is not a function of mass. Comparing colour with indicators of the level of disturbance in the cluster, we find a narrower variety in the cluster colours of 'disturbed' clusters than of 'undisturbed' clusters. This trend is more pronounced with indicators sensitive to the initial stages of a cluster merger, e.g. the Dressler Schectman statistic. We interpret this as possible evidence that the total cluster star formation rate is 'standardised' in mergers, perhaps through a process such as a system-wide shock in the intracluster medium.
• Recent studies suggest that globular clusters (GCs) may retain a substantial population of stellar-mass black holes (BHs), in contrast to the long-held belief of a few to zero BHs. We model the population of BH low-mass X-ray binaries (BH-LMXBs), an ideal observable proxy for elusive single BHs, produced from a representative group of Milky Way GCs with variable BH populations. We simulate the formation of BH-binaries in GCs through exchange interactions between binary and single stars in the company of tens to hundreds of BHs. Additionally, we consider the impact of the BH population on the rate of compact binaries undergoing gravitational wave driven mergers. The characteristics of the BH-LMXB population and binary properties are sensitive to the GCs structural parameters as well as its unobservable BH population. We find that GCs retaining $\sim 1000$ BHs produce a galactic population of $\sim 150$ ejected BH-LMXBs whereas GCs retaining only $\sim20$ BHs produce zero ejected BH-LMXBs. Moreover, we explore the possibility that some of the presently known BH-LMXBs might have originated in GCs and identify five candidate systems.
• We report finding high-velocity components in the H\alpha emission wings of St 2-22 spectra, obtained in 2005. This discovery have encouraged us to start the present study, aiming to show that this little studied object is a jet producing symbiotic system. We used high-resolution optical and low-resolution near infrared spectra, as well as available optical and infrared photometry, to evaluate some of the physical parameters of the St 2-22 components and the characteristics of the jets. The evaluated parameters of the components confirmed that St 2-22 is a S-type symbiotic star. Our results demonstrate that an unnoticed outburst of St 2-22, similar to those in classical symbiotics, occurred in the first half of 2005. During the outburst, collimated, bipolar jets were ejected by the hot component of St 2-22 with an average velocity of about 1700 km/s.
• We study the X-ray phases of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer, 6-year radio observations from the Nanshan Telescope, and the ephemeris from Jodrell Bank Observatory. It is found that the X-ray phases in different energy bands and the radio phases from Nanshan Telescope show similar behaviors, including long-time evolution and short-time variations. Such strong correlations between the X-ray and radio phases imply that the radio and X-ray timing noises are both generated from the pulsar spin that cannot be well described by the the monthly ephemeris from the Jodrell Bank observatory. When using the Nanshan phases as references to study the X-ray timing noise, it has a significantly smaller variation amplitude and shows no long-time evolution, with a change rate of $(-1.1\pm1.1)\times10^{-7}$ periods per day. These results show that the distance of the X-ray and radio emission regions on the Crab pulsar has no detectable secular change, and it is unlikely that timing-noises resulted from any unique physical processes in the radio or X-ray emitting regions. The similar behaviors of the X-ray and radio timing noises also imply that the variation of the interstellar medium is not the origin of the Crab pulsar's timing noises, which is consistent with the results obtained from the multi-frequency radio observations of PSR B1540-06.
• We review the status of the Starobinsky-like models for inflation beyond minimal gravity and discuss the unitarity problem due to the presence of a large non-minimal gravity coupling. We show that the induced gravity models allow for a self-consistent description of inflation and discuss the implications of the inflaton couplings to the Higgs field in the Standard Model.
• Recent reports claiming association of the massive star binary system $\gamma^2$Velorum (WR 11) with a high-energy $\gamma$-ray source observed by \textitFermi-LAT contrast the so-far exclusive role of $\eta$ Carinae as the hitherto only detected $\gamma$-ray emitter in the source class of particle-accelerating colliding-wind binary (CWB) systems. We offer support to this claim of association by providing dedicated model predictions for the nonthermal photon emission spectrum of $\gamma^2$ Velorum. We use three-dimensional magneto-hydrodynamic modeling (MHD) to investigate the structure and conditions of the wind-collision region (WCR) of $\gamma^2$ Velorum including the important effect of radiative braking in the stellar winds. A transport equation is then solved throughout the computational domain to study the propagation of relativistic electrons and protons. The resulting distributions of particles are subsequently used to compute nonthermal photon emission components. In agreement with observation in X-ray spectroscopy, our simulations yield a large shock-cone opening angle. We find the nonthermal $\gamma$-ray emission of $\gamma^2$ Velorum to be of hadronic origin owing to the strong radiation fields in the binary system which inhibit the acceleration of electrons to energies sufficiently high for efficient inverse Compton radiation. We also discuss the strong dependence of a hadronic $\gamma$-ray component on the energy-dependent diffusion used in the simulations. Of two mass-loss rates for the WR star found in literature, only the higher one is able to accommodate the observed $\gamma$-ray spectrum with reasonable values for important simulation parameters such as the injection ratio of high-energy particles within the WCR.
• HD66051 is an eclipsing system with an orbital period of about 4.75 d that exhibits out-of-eclipse variability with the same period. New multicolour photometric observations confirm the longevity of the secondary variations, which we interpret as a signature of surface inhomogeneities on one of the components. Using archival and newly acquired high-resolution spectra, we have performed a detailed abundance analysis. The primary component is a slowly rotating late B-type star ($T_{\rm eff} = 12500\pm200$ K; $\log g = 4.0$, $v\sin i = 27\pm2$ km s$^{-1}$) with a highly peculiar composition reminiscent of the singular HgMn-related star HD 65949, which seems to be its closest analogue. Some light elements as He, C, Mg, Al are depleted, while Si and P are enhanced. Except for Ni, all the iron-group elements, as well as most of the heavy elements, and in particular the REE elements, are overabundant. The secondary component was estimated to be a slowly rotating A-type star ($T_{\rm eff} \sim 8000$ K; $\log g = 4.0$, $v\sin i \sim 18$ km s$^{-1}$). The unique configuration of HD\u200966051 opens up intriguing possibilities for future research, which might eventually and significantly contribute to the understanding of such diverse phenomena as atmospheric structure, mass transfer, magnetic fields, photometric variability and the origin of chemical anomalies observed in HgMn stars and related objects.
• Aug 22 2017 astro-ph.EP arXiv:1708.05829v1
The ancestor philosophers' dream of thousands of new worlds is finally realised: about 3500 extrasolar planets have been discovered in the neighborhood of our Sun. Most of them are very different from those we used to know in our Solar System. Others orbit their parent star inside the belt known as Habitable Zone where a rocky planet with the appropriate climate could have the availability of liquid water on its surface. Those planets, in HZ or not, will be the object of observation that will be performed by new space-/ground-based instrumentation. Space missions, such as JWST and the very recently proposed ARIEL (ESA M-Class Mission), or ground based instruments (SPHERE@VLT, GPI@GEMINI and EPICS@ELT) have been proposed and built to measure the atmospheric transmission, reflection and emission spectra over a wide wavelength range. Most of exoplanets have local counterparts in the Solar System planets that are available for comparative studies, but there are also interesting outsider cases like super Earths. In our own system, proto-planet evolution was flanked by an active prebiotic chemistry that brought about the emergency of life on the Earth. The search for life signatures requires the knowledge of planet atmospheres, main objective of future exoplanetary space explorations. As, for now, we have only one example of life in the universe, we are bound to study terrestrial organisms to assess possibilities of life on other planets and guide our search for possible extinct or extant life on other planetary bodies. The planet atmosphere characteristics and possible biosignatures will be inferred by studying such composite spectrum in order to identify the emission/absorption lines/bands from atmospheric molecules as water, carbon monoxide, methane, ammonia etc.
• We report here the results of searching for inelastic scattering of dark matter (initial and final state dark matter particles differ by a small mass splitting) with nucleon with the first 79.6-day of PandaX-II data (Run 9). We set the upper limits for the spin independent WIMP-nucleon scattering cross section up to a mass splitting of 300 keV/c$^2$ at two benchmark dark matter masses of 1 and 10 TeV/c$^2$. The result does not support the hypothesis that the high energy recoil events in CRESST were resulted from the inelastic scattering between WIMPs and tungsten nuclei.
• We report constraints on the global $21$ cm signal due to neutral hydrogen at redshifts $14.8 \geq z \geq 6.5$. We derive our constraints from low foreground observations of the average sky brightness spectrum conducted with the EDGES High-Band instrument between September $7$ and October $26$, $2015$. Observations were calibrated by accounting for the effects of antenna beam chromaticity, antenna and ground losses, signal reflections, and receiver parameters. We evaluate the consistency between the spectrum and phenomenological models for the global $21$ cm signal. For tanh-based representations of the ionization history during the epoch of reionization, we rule out, at $\geq2\sigma$ significance, models with duration of up to $\Delta z = 1$ at $z\approx8.5$ and higher than $\Delta z = 0.4$ across most of the observed redshift range under the usual assumption that the $21$ cm spin temperature is much larger than the temperature of the cosmic microwave background (CMB) during reionization. We also investigate a `cold' IGM scenario that assumes perfect Ly$\alpha$ coupling of the $21$ cm spin temperature to the temperature of the intergalactic medium (IGM), but that the IGM is not heated by early stars or stellar remants. Under this assumption, we reject tanh-based reionization models of duration $\Delta z \lesssim 2$ over most of the observed redshift range. Finally, we explore and reject a broad range of Gaussian models for the $21$ cm absorption feature expected in the First Light era. As an example, we reject $100$ mK Gaussians with duration (full width at half maximum) $\Delta z \leq 4$ over the range $14.2\geq z\geq 6.5$ at $\geq2\sigma$ significance.
• We present techniques developed to calibrate and correct Murchison Widefield Array (MWA) low frequency (72-300 MHz) radio observations for polarimetry. The extremely wide field-of-view, excellent instantaneous (u, v)-coverage and sensitivity to degree-scale structure that the MWA provides enable instrumental calibration, removal of instrumental artefacts, and correction for ionospheric Faraday rotation through imaging techniques. With the demonstrated polarimetric capabilities of the MWA, we discuss future directions for polarimetric science at low frequencies to answer outstanding questions relating to polarised source counts, source depolarisation, pulsar science, low-mass stars, exoplanets, the nature of the interstellar and intergalactic media, and the solar environment.
• The detection of molecular species in the atmospheres of earth-like exoplanets orbiting nearby stars requires an optical system that suppresses starlight and maximizes the sensitivity to the weak planet signals at small angular separations. Achieving sufficient contrast performance on a segmented aperture space telescope is particularly challenging due to unwanted diffraction within the telescope from amplitude and phase discontinuities in the pupil. Apodized vortex coronagraphs are a promising solution that theoretically meet the performance needs for high contrast imaging with future segmented space telescopes. We investigate the sensitivity of apodized vortex coronagraphs to the expected aberrations, including segment co-phasing errors in piston and tip/tilt as well as other low-order and mid-spatial frequency aberrations. Coronagraph designs and their associated telescope requirements are identified for conceptual HabEx and LUVOIR telescope designs.
• We carried out targeted ALMA observations of 129 fields in the COSMOS region at 1.25 mm, detecting 152 galaxies at S/N$\geq$5 with an average continuum RMS of 150 $\mu$Jy. These fields represent a S/N-limited sample of AzTEC / ASTE sources with 1.1 mm S/N$\geq$4 over an area of 0.72 square degrees. Given ALMA's fine resolution and the exceptional spectroscopic and multiwavelength photometric data available in COSMOS, this survey allows us unprecedented power in identifying submillimeter galaxy counterparts and determining their redshifts through spectroscopic or photometric means. In addition to 30 sources with prior spectroscopic redshifts, we identified redshifts for 113 galaxies through photometric methods and an additional nine sources with lower limits, which allowed a statistically robust determination of the redshift distribution. We have resolved 33 AzTEC sources into multi-component systems and our redshifts suggest that nine are likely to be physically associated. Our overall redshift distribution peaks at $z\sim$2.0 with a high redshift tail skewing the median redshift to $\tilde{z}$=2.48$\pm$0.05. We find that brighter millimeter sources are preferentially found at higher redshifts. Our faintest sources, with S$_{1.25 \rm mm}$<1.25 mJy, have a median redshift of $\tilde{z}$=2.18$\pm$0.09, while the brightest sources, S$_{1.25 \rm mm}$>1.8 mJy, have a median redshift of $\tilde{z}$=3.08$\pm$0.17. After accounting for spectral energy distribution shape and selection effects these results are consistent with several previous submillimeter galaxy surveys, and moreover, support the conclusion that the submillimeter galaxy redshift distribution is sensitive to survey depth.
• We spectroscopically characterize the atmosphere of HD 106906b, a young low-mass companion near the deuterium burning limit. The wide separation to its host star of 7.1" makes it an ideal candidate for high-SNR and high-resolution spectroscopy. We aim to derive new constraints on HD 106906b's spectral type, effective temperature, and luminosity, and also provide a high-SNR template spectrum for future characterization of extrasolar planets. We obtained 1.1--2.5 $\mu$m integral field spectroscopy with the VLT/SINFONI instrument with a spectral resolution of R$\approx$2000--4000. New estimates of HD 106906b's parameters are derived by analyzing spectral features, comparing to spectral catalogs of other low-mass objects, and fitting with theoretical isochrones. We identify several spectral absorption lines that are consistent with a low mass for HD 106906b. We derive a new spectral type of L1.5$\pm$1.0, one subclass earlier than previous estimates. Through comparison with other young low-mass objects, this translates to a luminosity of log($L/L_\odot$)=$-3.65\pm0.08$ and an effective temperature of Teff = $1820\pm240$ K. Our new mass estimates range between $M=11.9^{+1.7}_{-0.8}$ $M_{\rm Jup}$ (hot start) and $M=14.0^{+0.2}_{-0.5}$ $M_{\rm Jup}$ (cold start). These limits take into account a possibly finite formation time, i.e., HD 106906b is allowed to be 0--3 Myr younger than its host star. We exclude accretion onto HD 106906b at rates $\dot{M}>4.8\times10^{-10}$ $M_{\rm Jup}$yr$^{-1}$ based on the fact that we observe no hydrogen (Paschen-$\beta$, Brackett-$\gamma$) emission. This is indicative of little or no circumplanetary gas. With our new observations, HD 106906b is the planetary-mass object with one of the highest SNR spectra yet. We make the spectrum available for download for future comparison with data from existing and next-generation (e.g, ELT, JWST) spectrographs.
• The HAWC observatory recently published their second source catalog with 39 very high energy gamma-ray sources based on 507 days of exposure time. Among these, there were 16 sources that are more than one degree away from any known TeV source. We studied 13 of these 16 sources with VERITAS and \textitFermi-LAT data. VERITAS, an array of four imaging atmospheric Cherenkov telescopes observing gamma rays with energies higher than 85 GeV, can provide a more detailed image of the source with much shorter exposure time and with better angular resolution. With \textitFermi-LAT data, we searched for the counterparts at lower energies (E>10 GeV). The exposure of VERITAS varies among the 13 sources, and we used eight years of \textitFermi-LAT data. VERITAS found weak gamma-ray emission in the region of PWN~DA~495 coinciding with 2HWC J1953+294 in this follow-up study. We will discuss the results especially focusing on the PWN~DA~495 region and the SNR~G~54.1+0.3 region where \textitFermi-LAT detected a GeV counterpart of SNR~G~54.1+0.3, a known TeV source detected by both VERITAS and HAWC.
• We provide new insight on the origin of the cold high-V$_{\rm los}$ peaks ($\sim$200 kms$^{-1}$) in the Milky Way bulge discovered in the APOGEE commissioning data \citepNidever2012. Here we show that such kinematic behaviour present in the field regions towards the Galactic bulge is not likely associated with orbits that build the boxy/peanut (B/P) bulge. To this purpose, a new set of test particle simulations of a kinematically cold stellar disk evolved in a 3D steady-state barred Milky Way galactic potential, has been analysed in detail. Especially bar particles trapped into the bar are identified through the orbital Jacobi energy $E_{J}$, which allows us to identify the building blocks of the B/P feature and investigate their kinematic properties. Finally, we present preliminary results showing that the high-V$_{\rm los}$ features observed towards the Milky Way bulge are a natural consequence of a large-scale \textitmidplane particle structure, which is unlikely associated with the Galactic bar.
• Context: Transmission spectroscopy has become a prominent tool for characterizing the atmospheric properties on close-in transiting planets. Recent observations have revealed a remarkable diversity in exoplanet spectra, which show absorption signatures of Na, K and $\mathrm{H_2O}$, in some cases partially or fully attenuated by atmospheric aerosols. Aerosols (clouds and hazes) themselves have been detected in the transmission spectra of several planets thanks to wavelength-dependent slopes caused by the particles' scattering properties. Aims: We present an optical 550 - 960 nm transmission spectrum of the extremely irradiated hot Jupiter WASP-103b, one of the hottest (2500 K) and most massive (1.5 $M_J$) planets yet to be studied with this technique. WASP-103b orbits its star at a separation of less than 1.2 times the Roche limit and is predicted to be strongly tidally distorted. Methods: We have used Gemini/GMOS to obtain multi-object spectroscopy hroughout three transits of WASP-103b. We used relative spectrophotometry and bin sizes between 20 and 2 nm to infer the planet's transmission spectrum. Results: We find that WASP-103b shows increased absorption in the cores of the alkali (Na, K) line features. We do not confirm the presence of any strong scattering slope as previously suggested, pointing towards a clear atmosphere for the highly irradiated, massive exoplanet WASP-103b. We constrain the upper boundary of any potential cloud deck to reside at pressure levels above 0.01 bar. This finding is in line with previous studies on cloud occurrence on exoplanets which find that clouds dominate the transmission spectra of cool, low surface gravity planets while hot, high surface gravity planets are either cloud-free, or possess clouds located below the altitudes probed by transmission spectra.
• The cosmic merger rate density of black hole binaries (BHBs) can give us an essential clue to constraining the formation channels of BHBs, in light of current and forthcoming gravitational wave detections. Following a Monte Carlo approach, we couple new population-synthesis models of BHBs with the Illustris cosmological simulation, to study the cosmic history of BHB mergers. We explore six population-synthesis models, varying the prescriptions for supernovae, common envelope, and natal kicks. In most considered models, the cosmic BHB merger rate follows the same trend as the cosmic star formation rate. The normalization of the cosmic BHB merger rate strongly depends on the treatment of common envelope and on the distribution of natal kicks. We find that most BHBs merging within LIGO's instrumental horizon come from relatively metal-poor progenitors (<0.2 Zsun). The total masses of merging BHBs span a large range of values, from ~6 to ~82 Msun. In our fiducial model, merging BHBs consistent with GW150914, GW151226 and GW170104 represent ~6, 3, and 12 per cent of all BHBs merging within the LIGO horizon, respectively. The heavy systems, like GW150914, come from metal-poor progenitors (<0.15 Zsun). Most GW150914-like systems merging in the local Universe appear to have formed at high redshift, with a long delay time. In contrast, GW151226-like systems form and merge all the way through the cosmic history, from progenitors with a broad range of metallicities. Future detections will be crucial to put constraints on common envelope, on natal kicks, and on the BHB mass function.

C. Jess Riedel Jul 04 2017 21:26 UTC

Even if we kickstart evolution with bacteria, the amount of time until we are capable of von Neumann probes is almost certainly too small for this to be relevant. See for instance [Armstrong & Sandberg](http://www.sciencedirect.com.proxy.lib.uwaterloo.ca/science/article/pii/S0094576513001148). It

...(continued)
xecehim Jun 27 2017 15:03 UTC

It has been [published][1]

wiadealo Nov 07 2016 09:27 UTC

Is it [fantasy][1] or real?

[1]: http://buchderfarben.de

climaiw Sep 12 2016 16:19 UTC

I would suggest planets where life can really make a difference.

resodiat Aug 23 2016 13:00 UTC

That is really a long-term perspective.

Māris Ozols Feb 18 2016 14:29 UTC

"...structures seen in the universe today, from clusters of galaxies to Donald Trump."

Jaiden Mispy May 23 2014 08:01 UTC

There's a nice summary of the context for this paper here: http://fioraaeterna.tumblr.com/post/56556056152/quasistars-a-real-life-black-hole-sun

Frédéric Grosshans Mar 05 2014 10:03 UTC

I read this paper as an appendix of an unwritten Fantasy novel, where a 21st century cosmologist is trapped in an alternate Aristotelian 13th century universe ! Thanks for the nice read !


text:
## Olivetti Club

Emily DautenhahnCornell University
A few perspectives on the heat kernel and its estimates
Tuesday, March 23, 2021 - 4:30pm
Online

What is a heat kernel? Why should you care? When can we estimate heat kernels and what do they look like? In this talk, we will attempt to answer these and related questions. We will begin by looking at the heat equation in $\mathbb{R}^n$ from both analytic and probabilistic perspectives and then consider how to estimate heat kernels in more general settings, such as on Riemannian manifolds. Very little background is assumed, and there will be pictures!


text:
# Initial Stages 2021

Jan 10 – 15, 2021
Weizmann Institute of Science
Asia/Jerusalem timezone
See you at IS2023 in Copenhagen in June 2023

## Dynamical modeling of the initial energy-momentum and baryon charge distributions for heavy-ion collisions at RHIC Beam Energy Scan energies

Jan 13, 2021, 7:25 PM
20m
Andrea’s room 1 (vDLCC)

### Andrea’s room 1

#### vDLCC

oral Collective dynamics from small to large systems

### Speaker

Dr Chun Shen (Wayne State University)

### Description

Building upon Ref. [1], we present an improved three-dimensional dynamical initialization model for heavy-ion collisions, implementing local energy-momentum conservation and baryon charge fluctuations at string junctions [2]. These improvements lead to an excellent description of the charged hadron and net proton rapidity distributions in Au+Au collisions from 7.7 to 200 GeV. Based on these results, we quantify the amount of baryon stopping at the initial impact, and baryon transport during the hydrodynamic evolution and hadronic scattering phases. The effects of the finite overlap time at low collision energies on hadronic flow observables are quantified. Keeping all model parameters fixed, we extrapolate our model to asymmetric (p, d, $^3$He, Cu)+Au collisions at RHIC BES energies. We achieve a good description of the measured particle rapidity distributions for those collision systems, demonstrating our model’s predictive power. We present first results on studies of anisotropic flow and net-proton cumulants, relevant for the critical point search.

[1] C. Shen and B. Schenke, “Dynamical initial state model for relativistic heavy-ion collisions,” Phys. Rev. C97 (2018), 024907
[2] D. Kharzeev, “Can gluons trace baryon number?,” Phys. Lett. B 378, 238 (1996)

### Primary authors

Dr Chun Shen (Wayne State University) Bjoern Schenke (Brookhaven National Lab)

### Presentation materials

 InitialStateModel_BES.pdf Recording