9,264 research outputs found
Review of Habitable Softgoods Inflatable Design, Analysis, Testing, and Potential Space Applications
Inflatable space structures have the potential to significantly reduce the required launch volume of large crewed pressure vessels for space exploration missions. Mass savings can also be achieved via the use of high specific strength softgoods materials, and the reduced design penalty from launching the structure in a densely packaged state. Inflatable softgoods structures have been investigated since the late 1950's, and several major development programs at NASA and in industry have helped advance the state-of-the-art in this technology area. This paper discusses the design, analysis, structural testing, and potential applications for inflatable softgoods structures. In particular, this paper will discuss the design of the multi-layer softgoods shell (inner layer, bladder, structural restraint layer, micrometeoroid orbital debris protection layers, thermal insulation layers, and atomic oxygen layer (for low earth orbit) and the results of material and module-level testing that has been conducted over the past two decades at NASA. Finally, the current utilization of expandable spacecraft structures is discussed, as well as potential future applications including airlocks and habitats on the Lunar Orbital Platform-Gateway, and the surface of the Moon and Mars
Is the Cosmic Microwave Background Circularly Polarized?
The primordial anisotropies of the cosmic microwave background (CMB) are
linearly polarized via Compton-scattering. The Faraday conversion process
during the propagation of polarized CMB photons through regions of the
large-scale structure containing magnetized relativistic plasma, such as galaxy
clusters, will lead to a circularly polarized contribution. Though the
resulting Stokes-V parameter is of order 10^-9 at frequencies of 10 GHz, the
contribution can potentially reach the total Stokes-U at low frequencies due to
the cubic dependence on the wavelength. In future, the detection of circular
polarization of CMB can be used as a potential probe of the physical properties
associated with relativistic particle populations in large-scale structures.Comment: 4 pages, 1 figure; Phys. Rev. Lett. submitte
Left-Right Symmetry and Supersymmetric Unification
The existence of an SU(3) X SU(2)_L X SU(2)_R X U(1) gauge symmetry with g_L
= g_R at the TeV energy scale is shown to be consistent with supersymmetric
SO(10) grand unification at around 1O^{16} GeV if certain new particles are
assumed. The additional imposition of a discrete Z_2 symmetry leads to a
generalized definition of R parity as well as highly suppressed Majorana
neutrino masses. Another model based on SO(10) X SO(10) is also discussed.Comment: 11 pages, 2 figures not included, UCRHEP-T124, Apr 199
Limits on Low Energy Photon-Photon Scattering from an Experiment on Magnetic Vacuum Birefringence
Experimental bounds on induced vacuum magnetic birefringence can be used to
improve present photon-photon scattering limits in the electronvolt energy
range. Measurements with the PVLAS apparatus (E. Zavattini {\it et al.}, Phys.
Rev. D {\bf77} (2008) 032006) at both nm and 532 nm lead to
bounds on the parameter {\it A}, describing non linear effects in QED, of
T @ 1064 nm and T @ 532 nm, respectively, at 95% confidence level,
compared to the predicted value of T. The
total photon-photon scattering cross section may also be expressed in terms of
, setting bounds for unpolarized light of m and m. Compared to the expected QED scattering cross
section these results are a factor of higher and represent
an improvement of a factor about 500 on previous bounds based on ellipticity
measurements and of a factor of about on bounds based on direct
stimulated scattering measurements
Creep Burst Testing of a Woven Inflatable Module
A woven Vectran inflatable module 88 inches in diameter and 10 feet long was tested at the NASA Johnson Space Center until failure from creep. The module was pressurized pneumatically to an internal pressure of 145 psig, and was held at pressure until burst. The external environment remained at standard atmospheric temperature and pressure. The module burst occurred after 49 minutes at the target pressure. The test article pressure and temperature were monitored, and video footage of the burst was captured at 60 FPS. Photogrammetry was used to obtain strain measurements of some of the webbing. Accelerometers on the test article measured the dynamic response. This paper discusses the test article, test setup, predictions, observations, photogrammetry technique and strain results, structural dynamics methods and quick-look results, and a comparison of the module level creep behavior to the strap level creep behavior
The young stellar population at the center of NGC 205
Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center
a population of young blue stars. Their origin is still matter of debate, the
central fresh star formation activity possibly being related to dynamical
interactions between NGC 205 and M31. Aims. The star formation history in the
central 30\arcsec (120 pc) around the NGC 205 central nucleus is
investigated in order to obtain clues to the origin of the young stellar
population. Methods. Deep HST/ACS CCD photometry is compared with theoretical
isochrones and luminosity functions to characterize the stellar content of the
region under study and compute the recent SF rate. Results. Our photometry
reveals a previously undetected blue plume of young stars clearly
distinguishable down to I26. Our analysis suggests that 1.9
M were produced between approximately 62 Myr and 335 Myr ago in the NGC
205 inner regions, with a latest minor episode occurring 25 Myr ago. This
implies a star formation rate of M/yr over this
period. Conclusions. The excellent fit of the observed luminosity function of
young main sequence stars obtained with a model having a constant star
formation rate argues against a tidally triggered star formation activity over
the last 300 Myr. Rather, a constant SF may be consistent with NGC 205
being on its first interaction with M 31.Comment: 5 pages, 2 figures, accepted for publication in A&A letter
Unification of gauge couplings and the tau neutrino mass in Supergravity without R-parity
Minimal R-parity violating supergravity predicts a value for
smaller than in the case with conserved R-parity, and therefore closer to the
experimental world average. We show that the R-parity violating effect on the
prediction comes from the larger two-loop b-quark Yukawa contribution
to the renormalization group evolution of the gauge couplings which
characterizes R-parity violating supergravity. The effect is correlated to the
tau neutrino mass and is sensitive to the initial conditions on the soft
supersymmetry breaking parameters at the unification scale. We show how a few
percent effect on may naturally occur even with tau neutrino
masses as small as indicated by the simplest neutrino oscillation
interpretation of the atmospheric neutrino data from Super-Kamiokande.Comment: Latex, 21 pages including 2 figure
Infrared spectroscopy of Nova Cassiopeiae 1993 (V705 Cas). IV. A closer look at the dust
Nova Cassiopeiae 1993 (V705 Cas) was an archetypical dust-forming nova. It
displayed a deep minimum in the visual light curve, and spectroscopic evidence
for carbon, hydrocarbon and silicate dust. We report the results of fitting the
infrared spectral energy distribution with the DUSTY code, which we use to
determine the properties and geometry of the emitting dust. The emission is
well described as originating in a thin shell whose dust has a carbon:silicate
ratio of ~2:1 by number (1.26:1 by mass) and a relatively flat size
distribution. The 9.7micron and 18micron silicate features are consistent with
freshly-condensed dust and, while the lower limit to the grain size
distribution is not well constrained, the largest grains have dimensions
\~0.06micron; unless the grains in V705 Cas were anomalously small, the sizes
of grains produced in nova eruptions may previously have been overestimated in
novae with optically thick dust shells. Laboratory work by Grishko & Duley may
provide clues to the apparently unique nature of nova UIR features.Comment: 11 pages, 9 fugure
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