8,159 research outputs found
Ion Trap Mass Spectrometers for Identity, Abundance and Behavior of Volatiles on the Moon
NASA GSFC and The Open University (UK) are collaborating to deploy an Ion Trap Mass Spectrometer on the Moon to investigate the lunar water cycle. The ITMS is flight-proven throughthe Rosetta Philae comet lander mission. It is also being developed under ESA funding to analyse samples drilled from beneath the lunar surface on the Roscosmos Luna-27 lander (2025).Now, GSFC and OU will now develop a compact ITMS instrument to study the near-surface lunar exosphere on board a CLPS Astrobotic lander at Lacus Mortis in 2021
Energy in one dimensional linear waves in a string
We consider the energy density and energy transfer in small amplitude,
one-dimensional waves on a string, and find that the common expressions used in
textbooks for the introductory physics with calculus course give wrong results
for some cases, including standing waves. We discuss the origin of the problem,
and how it can be corrected in a way appropriate for the introductory calculus
based physics course.Comment: 5 page
Weak Cosmic Censorship: As Strong as Ever
Spacetime singularities that arise in gravitational collapse are always
hidden inside of black holes. This is the essence of the weak cosmic censorship
conjecture. The hypothesis, put forward by Penrose 40 years ago, is still one
of the most important open questions in general relativity. In this Letter, we
reanalyze extreme situations which have been considered as counterexamples to
the weak cosmic censorship conjecture. In particular, we consider the
absorption of scalar particles with large angular momentum by a black hole.
Ignoring back reaction effects may lead one to conclude that the incident wave
may overspin the black hole, thereby exposing its inner singularity to distant
observers. However, we show that when back reaction effects are properly taken
into account, the stability of the black-hole event horizon is irrefutable. We
therefore conclude that cosmic censorship is actually respected in this type of
gedanken experiments.Comment: 4 page
Breakup of the aligned H molecule by xuv laser pulses: A time-dependent treatment in prolate spheroidal coordinates
We have carried out calculations of the triple-differential cross section for
one-photon double ionization of molecular hydrogen for a central photon energy
of ~eV, using a fully {\it ab initio}, nonperturbative approach to solve
the time-dependent \Schro equation in prolate spheroidal coordinates. The
spatial coordinates and are discretized in a finite-element
discrete-variable representation. The wave packet of the laser-driven
two-electron system is propagated in time through an effective short iterative
Lanczos method to simulate the double ionization of the hydrogen molecule. For
both symmetric and asymmetric energy sharing, the present results agree to a
satisfactory level with most earlier predictions for the absolute magnitude and
the shape of the angular distributions. A notable exception, however, concerns
the predictions of the recent time-independent calculations based on the
exterior complex scaling method in prolate spheroidal coordinates
[Phys.~Rev.~A~{\bf 82}, 023423 (2010)]. Extensive tests of the numerical
implementation were performed, including the effect of truncating the Neumann
expansion for the dielectronic interaction on the description of the initial
bound state and the predicted cross sections. We observe that the dominant
escape mode of the two photoelectrons dramatically depends upon the energy
sharing. In the parallel geometry, when the ejected electrons are collected
along the direction of the laser polarization axis, back-to-back escape is the
dominant channel for strongly asymmetric energy sharing, while it is completely
forbidden if the two electrons share the excess energy equally.Comment: 17 pages, 9 figure
Vortex-induced dissipation in narrow current-biased thin-film superconducting strips
A vortex crossing a thin-film superconducting strip from one edge to the
other, perpendicular to the bias current, is the dominant mechanism of
dissipation for films of thickness d on the order of the coherence length XI;
and of width w much narrower than the Pearl length LAMBDA >> w >> XI. At high
bias currents, I* < I < Ic, the heat released by the crossing of a single
vortex suffices to create a belt-like normal-state region across the strip,
resulting in a detectable voltage pulse. Here Ic is the critical current at
which the energy barrier vanishes for a single vortex crossing. The belt forms
along the vortex path and causes a transition of the entire strip into the
normal state. We estimate I* to be roughly Ic/3. Further, we argue that such
"hot" vortex crossings are the origin of dark counts in photon detectors, which
operate in the regime of metastable superconductivity at currents between I*
and Ic. We estimate the rate of vortex crossings and compare it with recent
experimental data for dark counts. For currents below I*, i.e., in the stable
superconducting but resistive regime, we estimate the amplitude and duration of
voltage pulses induced by a single vortex crossing.Comment: 9 pages, 3 figure
Ideas and Enhancements Related to Mobile Applications to Support Type 1 Diabetes
Background: Mobile devices have become increasingly important to young people who now use them to access a wide variety of health-related information. Research and policy related to the integration of health information and support with this technology do not effectively consider the viewpoint of a younger patient. Views of young people with type 1 diabetes are vital in developing quality services and improving their own health-related quality of life (HRQOL), yet research on their lifestyle and use of Web and mobile technology to support their condition and in non–health-related areas is sparse. Objective: To develop insight into young people with type 1 diabetes and their current use of Web and mobile technology and its potential impact on HRQOL. This can be achieved by constructing an in-depth picture of their day-to-day experiences from qualitative interviewing and exploring how they make use of technology in their lives and in relation to their condition and treatment. The goal was then to build something to help them, using the researcher’s technical expertise and seeking users’ opinions during the design and build, utilizing sociotechnical design principles. Methods: Data were collected by semistructured, in-depth qualitative interviews (N=9) of young people with type 1 diabetes aged 18-21. Interviews were transcribed and loaded onto NVivo for theme identification. Data analysis was undertaken during initial interviews (n=4) to locate potential ideas and enhancements for technical development. Latter interviews (n=5) assisted in the iterative sociotechnical design process of the development and provided additional developmental ideas. Results: Six themes were identified providing an understanding of how participants lived with and experienced their condition and how they used technology. Four technological suggestions for improvement were taken forward for prototyping. One prototype was developed as a clinically approved app. A number of ideas for new mobile apps and enhancements to currently existing apps that did not satisfactorily cater to this age group’s requirements for use in terms of design and functionality were suggested by interviewees but were not prototyped. Conclusions: This paper outlines the nonprototyped suggestions from interviewees and argues that young people with type 1 diabetes have a key role to play in the design and implementation of new technology to support them and improve HRQOL. It is vital to include and reflect on their suggestions as they have a radically different view of technology than either their parents or practitioners. We need to consider the relationship to technology that young people with type 1 diabetes have, and then reflect on how this might make a difference to them and when it might not be a suitable mechanism to use
Relativistic Dissipative Hydrodynamics: A Minimal Causal Theory
We present a new formalism for the theory of relativistic dissipative
hydrodynamics. Here, we look for the minimal structure of such a theory which
satisfies the covariance and causality by introducing the memory effect in
irreversible currents. Our theory has a much simpler structure and thus has
several advantages for practical purposes compared to the Israel-Stewart theory
(IS). It can readily be applied to the full three-dimensional hydrodynamical
calculations. We apply our formalism to the Bjorken model and the results are
shown to be analogous to the IS.Comment: 25 pages, 2 figures, Phys. Rev. C in pres
Finite-Range Gravity and Its Role in Gravitational Waves, Black Holes and Cosmology
Theoretical considerations of fundamental physics, as well as certain
cosmological observations, persistently point out to permissibility, and maybe
necessity, of macroscopic modifications of the Einstein general relativity. The
field-theoretical formulation of general relativity helped us to identify the
phenomenological seeds of such modifications. They take place in the form of
very specific mass-terms, which appear in addition to the field-theoretical
analog of the usual Hilbert-Einstein Lagrangian. We interpret the added terms
as masses of the spin-2 and spin-0 gravitons. The arising finite-range gravity
is a fully consistent theory, which smoothly approaches general relativity in
the massless limit, that is, when both masses tend to zero and the range of
gravity tends to infinity. We show that all local weak-field predictions of the
theory are in perfect agreement with the available experimental data. However,
some other conclusions of the non-linear massive theory are in a striking
contrast with those of general relativity. We show in detail how the
arbitrarily small mass-terms eliminate the black hole event horizon and replace
a permanent power-law expansion of a homogeneous isotropic universe with an
oscillatory behaviour. One variant of the theory allows the cosmological scale
factor to exhibit an `accelerated expansion'instead of slowing down to a
regular maximum of expansion. We show in detail why the traditional,
Fierz-Pauli, massive gravity is in conflict not only with the static-field
experiments but also with the available indirect gravitational-wave
observations. At the same time, we demonstrate the incorrectness of the widely
held belief that the non-Fierz-Pauli theories possess `negative energies' and
`instabilities'.Comment: 56 pages including 11 figures; significant modifications; in
particular, we demonstrate the incorrectness of the widely held belief that
the non-Fierz-Pauli theories should suffer from negative energies and
instabilities; to appear in Int. J. Mod. Phys.
Organics in comet 67P – a first comparative analysis of mass spectra from ROSINA–DFMS, COSAC and Ptolemy
The ESA Rosetta spacecraft followed comet 67P at a close distance for more than 2 yr. In addition, it deployed the lander Philae on to the surface of the comet. The (surface) composition of the comet is of great interest to understand the origin and evolution of comets. By combining measurements made on the comet itself and in the coma, we probe the nature of this surface material and compare it to remote sensing observations. We compare data from the double focusing mass spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission and previously published data from the two mass spectrometers COSAC (COmetary Sampling And Composition) and Ptolemy on the lander. The mass spectra of all three instruments show very similar patterns of mainly CHO-bearing molecules that sublimate at temperatures of 275 K. The DFMS data also show a great variety of CH-, CHN-, CHS-, CHO2- and CHNO-bearing saturated and unsaturated species. Methyl isocyanate, propanal and glycol aldehyde suggested by the earlier analysis of the measured COSAC spectrum could not be confirmed. The presence of polyoxymethylene in the Ptolemy spectrum was found to be unlikely. However, the signature of the aromatic compound toluene was identified in DFMS and Ptolemy data. Comparison with remote sensing instruments confirms the complex nature of the organics on the surface of 67P, which is much more diverse than anticipated
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