6,044 research outputs found
Observations of MMOD Impact Damage to the ISS
This paper describes meteoroid and orbital debris (MMOD) damage observations on the International Space Station (ISS). Several hundred MMOD damage sites on ISS have been documented using imagery taken from ISS windows. MMOD damage sites visible from ISS windows are typically larger approximately 5mm diameter and greater due to the larger viewer-to-surface distance. Closer inspection of these surfaces by astronauts during spacewalks reveals many smaller features that are typically less distinct. Characterization of these features as MMOD or non- MMOD is difficult, but can be partially accomplished by matching physical characteristics of the damage against typical MMOD impact damage observed on ground-based impact tests. Numerous pieces of space-exposed ISS hardware were returned during space shuttle missions. Subsequent ground inspection of this hardware has also contributed to the database of ISS MMOD impact damage. A handful of orbital replacement units (ORUs) from the ISS active thermal control and electrical power subsystems were swapped out and returned during the Space Shuttle program. In addition, a reusable logistics module was deployed on ISS for a total 59.4 days on 11 shuttle missions between 2001 and 2011 and then brought back in the shuttle payload bay. All of this returned hardware was subjected to detailed post-flight inspections for MMOD damage, and a database with over 1,400 impact records has been collected. A description of the largest observed damage features is provided in the paper. In addition, a discussion of significant MMOD impact sites with operational or design aspects is presented. MMOD impact damage to the following ISS modules/subsystems is described: (1) Solar Arrays, (2) US and Russian windows, (3) Extravehicular Activity (EVA) handrails, (4) Radiators, and (5) Russian Functional Cargo Block (FGB) module
Rapidity gap survival in the black-disk regime
We summarize how the approach to the black-disk regime (BDR) of strong
interactions at TeV energies influences rapidity gap survival in exclusive hard
diffraction pp -> p + H + p (H = dijet, Qbar-Q, Higgs). Employing a recently
developed partonic description of such processes, we discuss (a) the
suppression of diffraction at small impact parameters by soft spectator
interactions in the BDR; (b) further suppression by inelastic interactions of
hard spectator partons in the BDR; (c) correlations between hard and soft
interactions. Hard spectator interactions substantially reduce the rapidity gap
survival probability at LHC energies compared to previously reported estimates.Comment: 4 pages, 3 figures. Proceedings of XV International Workshop on
Deep-Inelastic Scattering and Related Subjects (DIS 2007), Munich, Germany,
Apr. 16-20, 200
Transverse imaging of the proton in exclusive diffractive pp scattering
In a recent paper (hep-ph/0608271) we describe a new approach to rapidity gap
survival (RGS) in the production of high-mass systems (H = dijet, Higgs, etc.)
in exclusive double-gap diffractive pp scattering, pp -> p + H + p. It is based
on the idea that hard and soft interactions are approximately independent (QCD
factorization), and allows us to calculate the RGS probability in a
model-independent way in terms of the gluon generalized parton distributions
(GPDs) in the colliding protons and the pp elastic scattering amplitude. Here
we focus on the transverse momentum dependence of the cross section. By
measuring the "diffraction pattern," one can perform detailed tests of the
interplay of hard and soft interactions, and even extract information about the
gluon GPD in the proton from the data.Comment: 4 pages, 2 figures, uses ws-procs9x6.cls. Proceedings of XIV
International Workshop on Deep Inelastic Scattering (DIS2006), Tsukuba City,
Japan, Apr 20 - 24, 200
Comparison of Risk from Orbital Debris and Meteoroid Environment Models on the Extravehicular Mobility Unit (EMU)
A well-known hazard associated with exposure to the space environment is the risk of failure from an impact from a meteoroid and orbital debris (MMOD) particle. An extravehicular mobility unit (EMU) spacesuit impact during a US extravehicular activity (EVA) is of great concern as a large leak could prevent an astronaut from safely reaching the airlock in time resulting in a loss of life. A risk assessment is provided to the EVA office at the Johnson Space Center (JSC) by the Hypervelocity Impact Technology (HVIT) group prior to certification of readiness for each US EVA. Need to understand the effect of updated meteoroid and orbital debris environment models to EMU risk
Conformational transformations induced by the charge-curvature interaction at finite temperature
The role of thermal fluctuations on the conformational dynamics of a single
closed filament is studied. It is shown that, due to the interaction between
charges and bending degrees of freedom, initially circular aggregates may
undergo transformation to polygonal shape. The transition occurs both in the
case of hardening and softening charge-bending interaction. In the former case
the charge and curvature are smoothly distributed along the chain while in the
latter spontaneous kink formation is initiated. The transition to a
non-circular conformation is analogous to the phase transition of the second
kind.Comment: 23 pages (Latex), 10 figures (Postscript), 2 biblio file (bib-file
and bbl-file
Experimental investigation of the mechanical stiffness of periodic framework-patterned elastomers
Recent advances in the cataloguing of three-dimensional nets mean a systematic search for framework structures with specific properties is now feasible. Theoretical arguments about the elastic deformation of frameworks suggest characteristics of mechanically isotropic networks. We explore these concepts on both isotropic and anisotropic networks by manufacturing porous elastomers with three different periodic net geometries. The blocks of patterned elastomers are subjected to a range of mechanical tests to determine the dependence of elastic moduli on geometric and topological parameters. We report results from axial compression experiments, three-dimensional X-ray computed tomography imaging and image-based finite-element simulations of elastic properties of framework-patterned elastomers
Nonlinear Ionic Conductivity of Thin Solid Electrolyte Samples: Comparison between Theory and Experiment
Nonlinear conductivity effects are studied experimentally and theoretically
for thin samples of disordered ionic conductors. Following previous work in
this field the {\it experimental nonlinear conductivity} of sodium ion
conducting glasses is analyzed in terms of apparent hopping distances. Values
up to 43 \AA are obtained. Due to higher-order harmonic current density
detection, any undesired effects arising from Joule heating can be excluded.
Additionally, the influence of temperature and sample thickness on the
nonlinearity is explored. From the {\it theoretical side} the nonlinear
conductivity in a disordered hopping model is analyzed numerically. For the 1D
case the nonlinearity can be even handled analytically. Surprisingly, for this
model the apparent hopping distance scales with the system size. This result
shows that in general the nonlinear conductivity cannot be interpreted in terms
of apparent hopping distances. Possible extensions of the model are discussed.Comment: 7 pages, 6 figure
Generalized parton distributions and rapidity gap survival in exclusive diffractive pp scattering
We propose a new approach to the problem of rapidity gap survival (RGS) in
the production of high-mass systems (H = dijet, heavy quarkonium, Higgs boson)
in double-gap exclusive diffractive pp scattering, pp -> p + (gap) + H + (gap)
+ p. It is based on the idea that hard and soft interactions proceed over
widely different time- and distance scales and are thus approximately
independent. The high-mass system is produced in a hard scattering process with
exchange of two gluons between the protons. Its amplitude is calculable in
terms of the gluon generalized parton distributions (GPDs) in the protons,
which can be measured in J/psi production in exclusive ep scattering. The hard
scattering process is modified by soft spectator interactions, which we
calculate in a model-independent way in terms of the pp elastic scattering
amplitude. Contributions from inelastic intermediate states are suppressed. A
simple geometric picture of the interplay of hard and soft interactions in
diffraction is obtained. The onset of the black-disk limit in pp scattering at
TeV energies strongly suppresses diffraction at small impact parameters and is
the main factor in determining the RGS probability. Correlations between hard
and soft interactions (e.g. due to scattering from the long-range pion field of
the proton, or due to possible short-range transverse correlations between
partons) further decrease the RGS probability. We also investigate the
dependence of the diffractive cross section on the transverse momenta of the
final-state protons ("diffraction pattern"). By measuring this dependence one
can perform detailed tests of the interplay of hard and soft interactions, and
even extract information about the gluon GPD in the proton. Such studies appear
to be feasible with the planned forward detectors at the LHC.Comment: 26 pages, 17 figures, uses revtex
Phase Transitions in a Dusty Plasma with Two Distinct Particle Sizes
In semiconductor manufacturing, contamination due to particulates
significantly decreases the yield and quality of device fabrication, therefore
increasing the cost of production. Dust particle clouds can be found in almost
all plasma processing environments including both plasma etching devices and in
plasma deposition processes. Dust particles suspended within such plasmas will
acquire an electric charge from collisions with free electrons in the plasma.
If the ratio of inter-particle potential energy to the average kinetic energy
is sufficient, the particles will form either a liquid structure with short
range ordering or a crystalline structure with long range ordering. Otherwise,
the dust particle system will remain in a gaseous state. Many experiments have
been conducted over the past decade on such colloidal plasmas to discover the
character of the systems formed, but more work is needed to fully understand
these structures. The preponderance of previous experiments used monodisperse
spheres to form complex plasma systems
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