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Trending Papers in astrophysics

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5
Do extra dimensions explain entanglement?
From Paper: Does extra dimensions explain entanglement?
Published: Aug 2020
We invite collaborators to co-author this white paper in order to collect scientific evidence connecting extra dimensions and entanglement.
Submitted by Matheus Lobo
6
The Big Bang Firewall
Published: Aug 2020
A model for a cyclic big bang as the result of a giant cosmic firewall is conjectured in this white paper.
Submitted by Matheus Lobo
10
Connecting optical morphology, environment, and HI mass fraction for low-redshift galaxies using deep learning
A galaxy's morphological features encode details about its gas content, star formation history, and feedback processes which regulate its growth and evolution. We use deep convolutional neural networks (CNNs) to capture all of a galaxy's morphological information in order to estimate its neutral atomic hydrogen (HI) content directly from SDSS $gri$ image cutouts. We are able to predict a galaxy's HI mass fraction, $\mathcal M \equiv M_{\rm HI}/M_\star$, to within 0.25~dex accuracy using CNNs. The HI-morphology connection learned by the CNN appears to be constant in low- to intermediate-density galaxy environments, but it breaks down in the highest-density environments, i.e., for normalized overdensity parameter $\log(1+\delta_5) \gtrsim 0.5$ for the ALFALFA $\alpha.40$ sample, $\log(1+\delta_5) \gtrsim 0.1$ for the xGASS representative sample. This transition can be physically interpreted as the onset of ram pressure stripping, tidal effects, and other gas depletion processes in clustered environments. We also use a visualization algorithm, Gradient-weighted Class Activation Maps (Grad-CAM), to determine which morphological features are associated with low or high gas content. These results demonstrate that CNNs are powerful tools for understanding the connections between optical morphology and other properties, as well as for probing other latent variables, in a quantitative and interpretable manner.
Submitted by Patrick Lu
7
Ultraviolet-Based Science in the Solar System: Advances and Next Steps
We review the importance of recent UV observations of solar system targets and discuss the need for further measurements, instrumentation and laboratory work in the coming decade. In the past decade, numerous important advances have been made in solar system science using ultraviolet (UV) spectroscopic techniques. Formerly used nearly exclusively for studies of giant planet atmospheres, planetary exospheres and cometary emissions, UV imaging spectroscopy has recently been more widely applied. The geyser-like plume at Saturn's moon Enceladus was discovered in part as a result of UV stellar occultation observations, and this technique was used to characterize the plume and jets during the entire Cassini mission. Evidence for a similar style of activity has been found at Jupiter's moon Europa using Hubble Space Telescope (HST) UV emission and absorption imaging. At other moons and small bodies throughout the solar system, UV spectroscopy has been utilized to search for activity, probe surface composition, and delineate space weathering effects; UV photometric studies have been used to uncover regolith structure. Insights from UV imaging spectroscopy of solar system surfaces have been gained largely in the last 1-2 decades, including studies of surface composition, space weathering effects (e.g. radiolytic products) and volatiles on asteroids (e.g. [2][39][48][76][84]), the Moon (e.g. [30][46][49]), comet nuclei (e.g. [85]) and icy satellites (e.g. [38][41-44][45][47][65]). The UV is sensitive to some species, minor contaminants and grain sizes often not detected in other spectral regimes. In the coming decade, HST observations will likely come to an end. New infrastructure to bolster future UV studies is critically needed. These needs include both developmental work to help improve future UV observations and laboratory work to help interpret spacecraft data. UV instrumentation will be a critical tool on missions to a variety of targets in the coming decade, especially for the rapidly expanding application of UV reflectance investigations of atmosphereless bodies.
Submitted by Patrick Lu
31
Pseudospectral Calculation of the Wavefunction of Helium and the Negative Hydrogen Ion
Authors:
Paul E. Grabowski, David F. Chernoff
Published: Sep 2009
We study the numerical solution of the non-relativistic Schr\"{o}dingerequation for two-electron atoms in ground and excited S-states usingpseudospectral (PS) methods of calculation. The calculation achievesconvergence rates for the energy, Cauchy error in the wavefunction, andvariance in local energy that are exponentially fast for all practicalpurposes. The method requires three separate subdomains to handle thewavefunction's cusp-like behavior near the two-particle coalescences. The useof three subdomains is essential to maintaining exponential convergence. Acomparison of several different treatments of the cusps and the semi-infinitedomain suggest that the simplest prescription is sufficient. For many purposesit proves unnecessary to handle the logarithmic behavior near thethree-particle coalescence in a special way. The PS method has many virtues: noexplicit assumptions need be made about the asymptotic behavior of thewavefunction near cusps or at large distances, the local energy is exactlyequal to the calculated global energy at all collocation points, local errorsgo down everywhere with increasing resolution, the effective basis usingChebyshev polynomials is complete and simple, and the method is easilyextensible to other bound states. This study serves as a proof-of-principle ofthe method for more general two- and possibly three-electron applications.
Retrieved from arxiv
30
Spin effects in the phasing of gravitational waves from binaries on eccentric orbits
Authors:
Antoine Klein, Philippe Jetzer
Published: May 2010
We compute here the spin-orbit and spin-spin couplings needed for an accuratecomputation of the phasing of gravitational waves emitted by comparable-massbinaries on eccentric orbits at the second post-Newtonian (PN) order. We use aquasi-Keplerian parametrization of the orbit free of divergencies in the zeroeccentricity limit. We find that spin-spin couplings induce a residualeccentricity for coalescing binaries at 2PN, of the order of$10^{-4}$-$10^{-3}$ for supermassive black hole binaries in the LISA band.Spin-orbit precession also induces a non-trivial pattern in the evolution ofthe eccentricity, which could help to reduce the errors on the determination ofthe eccentricity and spins in a gravitational wave measurement.
Retrieved from arxiv
30
Compact binary waveform recovery from the cross-correlated data of two detectors by matched filtering with spinning templates
Authors:
Veréb, L., et al
Published: May 2010
We investigate whether the recovery chances of highly spinning waveforms bymatched filtering with randomly chosen spinning waveforms generated with theLAL package are improved by a cross-correlation of the simulated output of theL1 and H1 LIGO detectors. We find that a properly defined correlated overlapimproves the mass estimates and enhances the recovery of spin angles.
Retrieved from arxiv
29
Primordial features due to a step in the inflaton potential
Authors:
Dhiraj Kumar Hazra, Moumita Aich, Rajeev Kumar Jain, L. Sriramkumar, Tarun Souradeep
Published: May 2010
Certain oscillatory features in the primordial scalar power spectrum areknown to provide a better fit to the outliers in the cosmic microwavebackground data near the multipole moments of $\ell=22$ and 40. These featuresare usually generated by introducing a step in the popular, quadratic potentialdescribing the canonical scalar field. Such a model will be ruled out, if thetensors remain undetected at a level corresponding to a tensor-to-scalar ratioof, say, $r\simeq 0.1$. In this work, in addition to the popular quadraticpotential, we investigate the effects of the step in a small field model and atachyon model. With possible applications to future datasets (such as PLANCK)in mind, we evaluate the tensor power spectrum exactly, and include itscontribution in our analysis. We compare the models with the WMAP (five as wellas seven-year), the QUaD and the ACBAR data. As expected, a step at aparticular location and of a suitable magnitude and width is found to improvethe fit to the outliers (near $\ell=22$ and 40) in all these cases. We pointout that, if the tensors prove to be small (say, $r\lesssim 0.01$), thequadratic potential and the tachyon model will cease to be viable, and moreattention will need to be paid to examples such as the small field models.
Retrieved from arxiv
29
A two-mass expanding exact space-time solution
Authors:
Jean-Philippe Uzan, George F. R. Ellis, Julien Larena
Published: May 2010
In order to understand how locally static configurations aroundgravitationally bound bodies can be embedded in an expanding universe, weinvestigate the solutions of general relativity describing a space-time whosespatial sections have the topology of a 3-sphere with two identical masses atthe poles. We show that Israel junction conditions imply that two sphericallysymmetric static regions around the masses cannot be glued together. If one isinterested in an exterior solution, this prevents the geometry around themasses to be of the Schwarzschild type and leads to the introduction of acosmological constant. The study of the extension of the Kottler space-timeshows that there exists a non-static solution consisting of two static regionssurrounding the masses that match a Kantowski-Sachs expanding region on thecosmological horizon. The comparison with a Swiss-Cheese construction is alsodiscussed.
Retrieved from arxiv
28
Dense gas in nearby galaxies: XV. Hot ammonia in NGC253, Maffei2 and IC342
Authors:
R. Mauersberger, C. Henkel, A. Weiss, A. B. Peck, Y. Hagiwara
Published: Mar 2003
The detection of NH3 inversion lines up to the (J,K)=(6,6) level is reportedtoward the central regions of the nearby galaxies NGC253, Maffei2, and IC342.The observed lines are up to 406K (for (J,K)=(6,6)) and 848K (for the (9,9)transition) above the ground state and reveal a warm (T_kin= 100 - 140 K)molecular component toward all galaxies studied. The tentatively detected(J,K)=(9,9) line is evidence for an even warmer (>400K) component toward IC342.Toward NGC253, IC342 and Maffei2 the global beam averaged NH3 abundances are1-2 10^-8, while the abundance relative to warm H2 is around 10^-7. Thetemperatures and NH3 abundances are similar to values found for the Galacticcentral region. C-shocks produced in cloud-cloud collisions can explain kinetictemperatures and chemical abundances. In the central region of M82, however,the NH3 emitting gas component is comparatively cool (~ 30K). It must be dense(to provide sufficient NH3 excitation) and well shielded from dissociatingphotons and comprises only a small fraction of the molecular gas mass in M82.An important molecular component, which is warm and tenuous and characterizedby a low ammonia abundance, can be seen mainly in CO. Photon dominated regions(PDRs) can explain both the high fraction of warm H_2 in M82 and the observedchemical abundances.
Retrieved from arxiv
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