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Publications

2015

Astrophysics and Astronomy

Articles 1 - 17 of 17

Full-Text Articles in Physical Sciences and Mathematics

Gravitons To Photons--Attenuation Of Gravitational Waves, Preston Jones, Douglas Singleton Nov 2015

Gravitons To Photons--Attenuation Of Gravitational Waves, Preston Jones, Douglas Singleton

Publications

In this essay, we examine the response of an Unruh–DeWitt (UD) detector (a quantum two-level system) to a gravitational wave background. The spectrum of the UD detector is of the same form as some scattering processes or three body decays such as muon-electron scattering or muon decay. Based on this similarity, we propose that the UD detector response implies a “decay” or attenuation of gravitons, G, into photons, γ, via G+G→γ+γ or G→γ+γ+G. Over large distances such a decay/attenuation may have consequences in regard to the detection of gravitational waves.

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The Impact Of Solar Wind Ulf Bz Fluctuations On Geomagnetic Activity For Viscous Timescales During Strongly Northward And Southward Imf, A. Osmane, A. P. Dimmock, R. Naderpour, T. I. Pulkkinen, K. Nykyri Nov 2015

The Impact Of Solar Wind Ulf Bz Fluctuations On Geomagnetic Activity For Viscous Timescales During Strongly Northward And Southward Imf, A. Osmane, A. P. Dimmock, R. Naderpour, T. I. Pulkkinen, K. Nykyri

Publications

We analyze more than 17 years of OMNI data to statistically quantify the impact of IMF Bz fluctuations on AL by using higher-order moments in the AL-distribution as a proxy. For strongly southward interplanetary magnetic field (IMF), the AL distribution function is characterized by a decrease of the skewness, a shift of its peak from −30 nT to −200 nT, and a broadening of the distribution core. During northward IMF, the distribution of AL is characterized by a significant reduction of the standard deviation and weight in the tail. Following this characterization of AL for southward and northward IMF, we …

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Testing Lorentz Symmetry With Planetary Orbital Dynamics, A. Hees, Q. G. Bailey, C. Le Poncin-Lafitte, A. Bourgoin, A. Rivoldini, B. Lamine, F. Meynadier, C. Guerlin, P. Wolf Sep 2015

Testing Lorentz Symmetry With Planetary Orbital Dynamics, A. Hees, Q. G. Bailey, C. Le Poncin-Lafitte, A. Bourgoin, A. Rivoldini, B. Lamine, F. Meynadier, C. Guerlin, P. Wolf

Publications

Planetary ephemerides are a very powerful tool to constrain deviations from the theory of general relativity (GR) using orbital dynamics. The effective field theory framework called the Standard-Model Extension (SME) has been developed in order to systematically parametrize hypothetical violations of Lorentz symmetry (in the Standard Model and in the gravitational sector). In this communication, we use the latest determinations of the supplementary advances of the perihelia and of the nodes obtained by planetary ephemerides analysis to constrain SME coefficients from the pure gravity sector and also from gravity-matter couplings. Our results do not show any deviation from GR and …

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Impact Of Declining Proposal Success Rates On Scientific Productivity, Ted Von Hippel, Priscilla Cushman, Todd Hoeksema, Chryssa Kouveliotou, James Lowenthal, Bradley Peterson, Keivan G. Stassun, Sep 2015

Impact Of Declining Proposal Success Rates On Scientific Productivity, Ted Von Hippel, Priscilla Cushman, Todd Hoeksema, Chryssa Kouveliotou, James Lowenthal, Bradley Peterson, Keivan G. Stassun,

Publications

Over the last decade proposal success rates in the fundamental sciences have dropped significantly. Astronomy and related fields funded by NASA and NSF are no exception. Data across agencies show that this is not principally the result of a decline in proposal merit (the proportion of proposals receiving high rankings is largely unchanged), nor of a shift in proposer demographics (seniority, gender, and institutional affiliation have all remained unchanged), nor of an increase (beyond inflation) in the average requested funding per proposal, nor of an increase in the number of proposals per investigator in any one year. Rather, the statistics …

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Solar Wind Energy Input To The Magnetosheath And At The Magnetopause, T. I. Pulkkinen, A. P. Dimmock, A. Osmane, K. Nykyri Jun 2015

Solar Wind Energy Input To The Magnetosheath And At The Magnetopause, T. I. Pulkkinen, A. P. Dimmock, A. Osmane, K. Nykyri

Publications

Using Time History of Events and Macroscale Interactions During Substorms observations, we show that the efficiency of the energy entry through the magnetopause as measured by the Poynting vector normal component depends on the combination of the solar wind speed and the southward component of the interplanetary magnetic field (IMF): Most efficient energy transfer occurs when the IMF BZ is only moderately negative, and the solar wind speed is high. This means that for the same level of solar wind driver parameters (electric field, epsilon, or other), different combinations of V and BZ will produce different driving at the magnetopause. …

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A Statistical Study Of The Dawn-Dusk Asymmetry Of Ion Temperature Anistrophy And Mirror Mode Occurrence In The Terrestrial Dayside Magnetosheath Using Themis Data, A. P. Dimmock, A. Osmane, T. I. Pulkkinen, K. Nykyri Jun 2015

A Statistical Study Of The Dawn-Dusk Asymmetry Of Ion Temperature Anistrophy And Mirror Mode Occurrence In The Terrestrial Dayside Magnetosheath Using Themis Data, A. P. Dimmock, A. Osmane, T. I. Pulkkinen, K. Nykyri

Publications

We present a statistical study of ion temperature anisotropy and mirror mode activity in the Earth's dayside magnetosheath using 6 years of Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations focusing on the quantification of dawn-dusk asymmetry as a function of upstream conditions and distance from the magnetopause. Our statistical data show a pronounced dusk favored asymmetry of T⊥/T∥ which drives a similar asymmetry of mirror mode activity. T⊥/T∥ decreases with increasing solar wind Alfvén Mach number, whereas mirror mode occurrence increases. In both cases, the relative asymmetry between the dawn and dusk flanks decrease with increasing …

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Magnetic Flux Circulation In The Rotationally Driven Giant Magnetospheres, P. A. Delamere, A. Otto, X. Ma, F. Bagenal, R. J. Wilson Jun 2015

Magnetic Flux Circulation In The Rotationally Driven Giant Magnetospheres, P. A. Delamere, A. Otto, X. Ma, F. Bagenal, R. J. Wilson

Publications

The giant‐planet magnetodiscs are shaped by the radial transport of plasma originating in the inner magnetosphere. Magnetic flux transport is a key aspect of the stretched magnetic field configuration of the magnetodisc. While net mass transport is outward (ultimately lost to the solar wind), magnetic flux conservation requires a balanced two‐way transport process. Magnetic reconnection is a critical aspect of the balanced flux transport. We present a comprehensive analysis of current sheet crossings in Saturn's magnetosphere using Cassini magnetometer data from 2004 to 2012 in an attempt to quantify the circulation of magnetic flux, emphasizing local time dependence. A key …

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Book Review: The Scientific Exploration Of Venus, T. D. Oswalt Jun 2015

Book Review: The Scientific Exploration Of Venus, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of The Scientific Exploration of Venus, by Fredric W. Taylor. Cambridge, 2014 295p bibl index, 9781107023482 $48.00

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Core-Collapse Supernovae Overview With Swift Collaboration, Kiranjyot Gill, Michele Zanolin, Marek Szczepańczyk Apr 2015

Core-Collapse Supernovae Overview With Swift Collaboration, Kiranjyot Gill, Michele Zanolin, Marek Szczepańczyk

Publications

The Core-Collapse supernovae (CCSNe) mark the dynamic and explosive end of the lives of massive stars. The mysterious mechanism, primarily focused with the shock revival phase, behind CCSNe explosions could be explained by detecting the corresponding gravitational wave (GW) emissions by the laser interferometer gravitational wave observatory, LIGO. GWs are extremely hard to detect because they are weak signals in a floor of instrument noise. Optical observations of CCSNe are already used in coincidence with LIGO data, as a hint of the times where to search for the emission of GWs. More of these hints would be very helpful. For …

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A Statistical Study Into The Spatial Distribution And Dawn-Dusk Asymmetry Of Dayside Magnetosheath Ion Temperatures As A Function Of Upstream Solar Wind Conditions, A. P. Dimmock, K. Nykyri, H. Karimabadi, A. Osmane, T. I. Pulkkinen Apr 2015

A Statistical Study Into The Spatial Distribution And Dawn-Dusk Asymmetry Of Dayside Magnetosheath Ion Temperatures As A Function Of Upstream Solar Wind Conditions, A. P. Dimmock, K. Nykyri, H. Karimabadi, A. Osmane, T. I. Pulkkinen

Publications

The magnetosheath contains the shocked solar wind and behaves as a natural filter to the solar wind plasma before it reaches the magnetosphere. The redistribution of kinetic energy at the bow shock results in significant thermalization of the solar wind plasma, resulting in a magnetosheath temperature profile which is highly nonhomogeneous and nonisotropic and differs between the dawn and dusk flanks. The present study attempts to study the spatial distribution of magnetosheath ion temperature as a function of upstream solar wind conditions. We pay particular attention to the dawn/dusk asymmetry in which we attempt to quantify using experimental data collected …

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Asymmetric Kelvin-Helmholtz Propagation At Saturn's Dayside Magnetopause, X. Ma, B. Stauffer, P. A. Delamere, A. Otto Mar 2015

Asymmetric Kelvin-Helmholtz Propagation At Saturn's Dayside Magnetopause, X. Ma, B. Stauffer, P. A. Delamere, A. Otto

Publications

At Saturn's magnetopause, the shear flows are maximized (minimized) in the prenoon (postnoon) sector due to the rapid planetary rotation and the corotating magnetodisc. As such, the prenoon sector is expected to be more Kelvin‐Helmholtz (KH) unstable than the postnoon sector; however, in situ Cassini data analyses showed that the evidence of KH activity favors the postnoon sector. In this study, we use a two‐dimensional MHD simulation to demonstrate that fast‐growing KH modes strongly deform and diffuse the boundary layer on a time scale of a few minutes in the prenoon sector. Therefore, the KH observational signature is difficult to …

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To Apply Or Not To Apply: A Survey Analysis Of Grant Writing Costs And Benefits, Ted Von Hippel, Courtney Von Hippel Mar 2015

To Apply Or Not To Apply: A Survey Analysis Of Grant Writing Costs And Benefits, Ted Von Hippel, Courtney Von Hippel

Publications

We surveyed 113 astronomers and 82 psychologists active in applying for federally funded research on their grant-­‐writing history between January, 2009 and November, 2012. We collected demographic data, effort levels, success rates, and perceived non-­‐financial benefits from writing grant proposals. We find that the average proposal takes 116 PI hours and 55 CI hours to write; although time spent writing was not related to whether the grant was funded. Effort did translate into success, however, as academics who wrote more grants received more funding. Participants indicated modest non-­‐monetary benefits from grant writing, with psychologists reporting a somewhat greater benefit overall …

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What Do We Know About Lorentz Symmetry?, Q. G. Bailey Mar 2015

What Do We Know About Lorentz Symmetry?, Q. G. Bailey

Publications

Precision tests of Lorentz symmetry have become increasingly of interest to the broader gravitational and high-energy physics communities. In this talk, recent work on violations of local Lorentz invariance in gravity is discussed, including recent analysis constraining Lorentz violation in a variety of gravitational tests. The arena of short-range tests of gravity is highlighted, demonstrating that such tests are sensitive to a broad class of unexplored signals that depend on sidereal time and the geometry of the experiment.

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Bayesian Investigation Of Isochrone Consistency Using The Old Open Cluster Ngc 188, Shane Hills, Ted Von Hippel, Stéphane Courteau, Aaron M. Geller Mar 2015

Bayesian Investigation Of Isochrone Consistency Using The Old Open Cluster Ngc 188, Shane Hills, Ted Von Hippel, Stéphane Courteau, Aaron M. Geller

Publications

This paper provides a detailed comparison of the differences in parameters derived for a star cluster from its color– magnitude diagrams (CMDs) depending on the filters and models used. We examine the consistency and reliability of fitting three widely used stellar evolution models to 15 combinations of optical and near-IR photometry for the old open cluster NGC 188. The optical filter response curves match those of theoretical systems and are thus not the source of fit inconsistencies. NGC 188 is ideally suited to this study thanks to a wide variety of high-quality photometry and available proper motions and radial velocities …

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Short-Range Gravity And Lorentz Violation, Quentin G. Bailey, V. Alan Kostelecký, Rui Xu Jan 2015

Short-Range Gravity And Lorentz Violation, Quentin G. Bailey, V. Alan Kostelecký, Rui Xu

Publications

Comparatively few searches have been performed for violations of local Lorentz invariance in the pure-gravity sector. We show that tests of short-range gravity are sensitive to a broad class of unconstrained and novel signals that depend on the experimental geometry and on sidereal time.

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Exploring How Social Media Can Be Used To Promote Space Awareness: A Case Study Of The Yuri's Night Web 2.0, Alan Steinberg, Jeffrey Alles, Ryan L. Kobrick Jan 2015

Exploring How Social Media Can Be Used To Promote Space Awareness: A Case Study Of The Yuri's Night Web 2.0, Alan Steinberg, Jeffrey Alles, Ryan L. Kobrick

Publications

Despite the importance of social media as an inexpensive and efficient means of communication, it is not clear to what degree space advocacy groups are making a strong organized effort to use the resources available to them. Moreover, there is no previous literature that specifically examines the use of social media tools by space organizations. This study seeks to start a larger dialog regarding how the space advocacy community can make use of these tools to promote their mission. Using a case study approach, this article focuses specifically on the organization of Yuri’s Night to explore how this group is …

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Quantum Tests Of The Einstein Equivalence Principle With The Ste-Quest Space Mission, Brett Altschul, Quentin G. Bailey, Luc Blanchet, Kai Bongs, Philippe Bouyer, Luigi Cacciapuoti, Et Al. Jan 2015

Quantum Tests Of The Einstein Equivalence Principle With The Ste-Quest Space Mission, Brett Altschul, Quentin G. Bailey, Luc Blanchet, Kai Bongs, Philippe Bouyer, Luigi Cacciapuoti, Et Al.

Publications

We present in detail the scientific objectives in fundamental physics of the Space–Time Explorer and QUantum Equivalence Space Test (STE–QUEST) space mission. STE–QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing …

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