34,664 research outputs found
Drawer drive for space shuttle vacuum canister
A sliding drawer type canister was designed to contain long duration exposure facility experiments which require vacuum storage before and after space exposure. The elastomeric seals require high closing loads which are generated through camming levers and transmitted through a spring loaded pressure plate. Lubrication was provided by various dry surface coatings. Higher than expected friction required some redesign after which the assembly functioned well and provided good sealing
On the Role of Entanglement in Schroedinger's Cat Paradox
In this paper we re-investigate the core of Schroedinger's 'cat paradox'. We
argue that one has to distinguish clearly between superpositions of macroscopic
cat states and superpositions of entangled states which comprise both the state
of the cat. It is shown, that in the first instance recurrence to decoherence
or other mechanisms is not necessary in this special case in order to explain
the absence of macroscopic superpositions. Additionally, we present modified
versions of two quantum optical experiments as experimenta crucis. Applied
rigorously, quantum mechanical formalism reduces the problem to a mere
pseudo-paradox.Comment: 10 pages; LaTeX; contact information update
Scalar dark matter in the B-L model
The B-L extension of the Standard Model requires the existence of
right-handed neutrinos and naturally realizes the seesaw mechanism of neutrino
mass generation. We study the possibility of explaining the dark matter in this
model with an additional scalar field that is a singlet of the Standard Model
but charged under . An advantage of this scenario is that the
stability of the dark matter can be guaranteed by appropriately choosing its
B-L charge, without the need of an extra ad hoc discrete symmetry. We
investigate in detail the dark matter phenomenology of this model. We show that
the observed dark matter density can be obtained via gauge or scalar
interactions, and that semi-annihilations could play an important role in the
latter case. The regions consistent with the dark matter density are determined
in each instance and the prospects for detection in future experiments are
analyzed. If dark matter annihilations are controlled by the B-L gauge
interaction, the mass of the dark matter particle should lie below 5 TeV and
its direct detection cross section can be easily probed by XENON1T; if instead
they are controlled by scalar interactions, the dark matter mass can be much
larger and the detection prospects are less certain. Finally, we show that this
scenario can be readily extended to accommodate multiple dark matter particles.Comment: 24 page
Relationally Aggressive Media Exposure and Children’s Normative Beliefs: Does Parental Mediation Matter?
Research indicates that relationally aggressive media exposure is positively associated with relational aggression in children. Theories of media effects suggest that these associations may be mediated by aggressive cognitions. Although parental mediation can attenuate the effects of violent media, it is unknown whether there are similar benefits of parental mediation of relationally aggressive media. The current study examined concurrent and longitudinal associations between relationally aggressive television and movie exposure and normative beliefs about relational aggression, and whether parental mediation moderates these associations. Participants were 103 children (50% female) in grades 3-6 and their parents. The following year, 48 children (52% female) were again assessed. Relationally aggressive media exposure predicted concurrent relational aggression norms, even after controlling for physically aggressive media exposure and physical aggression norms. Relationally aggressive television and movie exposure predicted greater subsequent approval of relational aggression only among children whose parents engaged in low levels of active mediation
Hot Atmospheres, Cold Gas, AGN Feedback and the Evolution of Early Type Galaxies: a Topical Perspective
Most galaxies comparable to or larger than the mass of the Milky Way host
hot, X-ray emitting atmospheres, and many such galaxies are radio sources. Hot
atmospheres and radio jets and lobes are the ingredients of radio-mechanical
active galactic nucleus (AGN) feedback. While a consensus has emerged that such
feedback suppresses cooling of hot cluster atmospheres, less attention has been
paid to massive galaxies where similar mechanisms are at play. Observation
indicates that the atmospheres of elliptical and S0 galaxies were accreted
externally during the process of galaxy assembly and augmented significantly by
stellar mass loss. Their atmospheres have entropy and cooling time profiles
that are remarkably similar to those of central cluster galaxies. About half
display filamentary or disky nebulae of cool and cold gas, much of which has
likely cooled from the hot atmospheres. We review the observational and
theoretical perspectives on thermal instabilities in galactic atmospheres and
the evidence that AGN heating is able to roughly balance the atmospheric
cooling. Such heating and cooling may be regulating star formation in all
massive spheroids at late times.Comment: Final versio
Apparatus for making curved reflectors Patent
Forming mold for polishing and machining curved solar magnesium reflector with reinforcing rib
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