3,146 research outputs found
Pressure limiting propellant actuating system
A pressure limiting propellant activating system for simultaneously limiting the output force while maintaining a constant output pressure from the combustion chamber is described. The propellant actuated system includes an outer barrel, outer housing and a combustion chamber. A main piston is movable in the barrel housing when gas pressure is developed in the combustion chamber. A relief piston is concentrically mounted and fixedly movable with the main piston when gas pressure is exerted from the combustion. A relief piston has a force-activated separation mechanism for limiting the output force while simultaneously maintaining constant output pressure on the main piston from the combustion chamber
Insect (Arthropoda: Insecta) Composition in the Diet of Ornate Box Turtles (Terrapene ornata ornata) in Two Western Illinois Sand Prairies, with a New State Record for Cyclocephala (Coleoptera: Scarabaeidae)
A study of fecal samples collected over a two-year period from juvenile ornate box turtles (Terrapene ornata ornata Agassiz) revealed diets consisting of six orders of insects representing 19 families. Turtles were reared in captivity from eggs harvested from local, wild populations, and released at two remnant prairies. Identifiable insect fragments were found in 94% of samples in 2013 (n=33) and 96% in 2014 (n=25). Frequency of occurrence of insects in turtle feces is similar to results reported in previous studies of midwestern Terrapene species. A comparison of insect composition presented no significant difference between release sites. There is no significant difference in consumed insect species between turtles released into or outside of a fenced enclosure at the same site. Specimens of Cyclocephala longula LeConte collected during this study represent a new state record for Illinois
Self-trapping at the liquid vapor critical point
Experiments suggest that localization via self-trapping plays a central role
in the behavior of equilibrated low mass particles in both liquids and in
supercritical fluids. In the latter case, the behavior is dominated by the
liquid-vapor critical point which is difficult to probe, both experimentally
and theoretically. Here, for the first time, we present the results of
path-integral computations of the characteristics of a self-trapped particle at
the critical point of a Lennard-Jones fluid for a positive particle-atom
scattering length. We investigate the influence of the range of the
particle-atom interaction on trapping properties, and the pick-off decay rate
for the case where the particle is ortho-positronium.Comment: 12 pages, 3 figures, revtex4 preprin
Words are Malleable: Computing Semantic Shifts in Political and Media Discourse
Recently, researchers started to pay attention to the detection of temporal
shifts in the meaning of words. However, most (if not all) of these approaches
restricted their efforts to uncovering change over time, thus neglecting other
valuable dimensions such as social or political variability. We propose an
approach for detecting semantic shifts between different viewpoints--broadly
defined as a set of texts that share a specific metadata feature, which can be
a time-period, but also a social entity such as a political party. For each
viewpoint, we learn a semantic space in which each word is represented as a low
dimensional neural embedded vector. The challenge is to compare the meaning of
a word in one space to its meaning in another space and measure the size of the
semantic shifts. We compare the effectiveness of a measure based on optimal
transformations between the two spaces with a measure based on the similarity
of the neighbors of the word in the respective spaces. Our experiments
demonstrate that the combination of these two performs best. We show that the
semantic shifts not only occur over time, but also along different viewpoints
in a short period of time. For evaluation, we demonstrate how this approach
captures meaningful semantic shifts and can help improve other tasks such as
the contrastive viewpoint summarization and ideology detection (measured as
classification accuracy) in political texts. We also show that the two laws of
semantic change which were empirically shown to hold for temporal shifts also
hold for shifts across viewpoints. These laws state that frequent words are
less likely to shift meaning while words with many senses are more likely to do
so.Comment: In Proceedings of the 26th ACM International on Conference on
Information and Knowledge Management (CIKM2017
Turbulent dissipation in the ISM: the coexistence of forced and decaying regimes and implications for galaxy formation and evolution
We discuss the dissipation of turbulent kinetic energy Ek in the global ISM
by means of 2-D, MHD, non-isothermal simulations in the presence of model
radiative heating and cooling. We argue that dissipation in 2D is
representative of that in three dimensions as long as it is dominated by shocks
rather than by a turbulent cascade. Energy is injected at a few isolated sites
in space, over relatively small scales, and over short time periods. This leads
to the coexistence of forced and decaying regimes in the same flow. We find
that the ISM-like flow dissipates its turbulent energy rapidly. In simulations
with forcing, the input parameters are the radius l_f of the forcing region,
the total kinetic energy e_k each source deposits into the flow, and the rate
of formation of those regions, sfr_OB. The global dissipation time t_d depends
mainly on l_f. In terms of measurable properties of the ISM, t_d >= Sigma_g
u_rms^2/(e_k sfr_OB), where Sigma_g is the average gas surface density and
u_rms is the rms velocity dispersion. For the solar neighborhood, t_d >=
1.5x10^7 yr. The global dissipation time is consistently smaller than the
crossing time of the largest energy-containing scales. In decaying simulations,
Ek decreases with time as t^-n, where n~0.8-0.9. This suggests a decay with
distance d as Ek\propto d^{-2n/(2-n)} in the mixed forced+decaying case. If
applicable to the vertical direction, our results support models of galaxy
evolution in which stellar energy injection provides significant support for
the gas disk thickness, but not models of galaxy formation in which this energy
injection is supposed to reheat an intra-halo medium at distances of up to
10-20 times the optical galaxy size, as the dissipation occurs on distances
comparable to the disk height.Comment: 23 pages, including figures. To appear in ApJ. Abstract abridge
Insect (Arthropoda: Insecta) Composition in the Diet of Ornate Box Turtles (Terrapene ornata ornata) in Two Western Illinois Sand Prairies, with a New State Record for Cyclocephala (Coleoptera: Scarabaeidae)
A study of fecal samples collected over a two-year period from juvenile ornate box turtles (Terrapene ornata ornata Agassiz) revealed diets consisting of six orders of insects representing 19 families. Turtles were reared in captivity from eggs harvested from local, wild populations, and released at two remnant prairies. Identifiable insect fragments were found in 94% of samples in 2013 (n=33) and 96% in 2014 (n=25). Frequency of occurrence of insects in turtle feces is similar to results reported in previous studies of midwestern Terrapene species. A comparison of insect composition presented no significant difference between release sites. There is no significant difference in consumed insect species between turtles released into or outside of a fenced enclosure at the same site. Specimens of Cyclocephala longula LeConte collected during this study represent a new state record for Illinois
Photometric Decomposition of Barred Galaxies
We present a non-parametric method for decomposition of the light of disk
galaxies into disk, bulge and bar components. We have developed and tested the
method on a sample of 68 disk galaxies for which we have acquired I-band
photometry. The separation of disk and bar light relies on the single
assumption that the bar is a straight feature with a different ellipticity and
position angle from that of the projected disk. We here present the basic
method, but recognise that it can be significantly refined. We identify bars in
only 47% of the more nearly face-on galaxies in our sample. The fraction of
light in the bar has a broad range from 1.3% to 40% of the total galaxy light.
If low-luminosity galaxies have more dominant halos, and if halos contribute to
bar stability, the luminosity functions of barred and unbarred galaxies should
differ markedly; while our sample is small, we find only a slight difference of
low significance.Comment: Accepted to appear in AJ, 36 pages, 9 figures, full on-line figures
available at http://www.physics.rutgers.edu/~sellwood/Reese.htm
Impact of Supernova feedback on the Tully-Fisher relation
Recent observational results found a bend in the Tully-Fisher Relation in
such a way that low mass systems lay below the linear relation described by
more massive galaxies. We intend to investigate the origin of the observed
features in the stellar and baryonic Tully-Fisher relations and analyse the
role played by galactic outflows on their determination. Cosmological
hydrodynamical simulations which include Supernova feedback were performed in
order to follow the dynamical evolution of galaxies. We found that Supernova
feedback is a fundamental process in order to reproduce the observed trends in
the stellar Tully-Fisher relation. Simulated slow rotating systems tend to have
lower stellar masses than those predicted by the linear fit to the massive end
of the relation, consistently with observations. This feature is not present if
Supernova feedback is turned off. In the case of the baryonic Tully-Fisher
relation, we also detect a weaker tendency for smaller systems to lie below the
linear relation described by larger ones. This behaviour arises as a result of
the more efficient action of Supernovae in the regulation of the star formation
process and in the triggering of powerful galactic outflows in shallower
potential wells which may heat up and/or expel part of the gas reservoir.Comment: 10 pages, 9 figures, accepted for publication in A&
Revisiting Clifford algebras and spinors III: conformal structures and twistors in the paravector model of spacetime
This paper is the third of a series of three, and it is the continuation of
math-ph/0412074 and math-ph/0412075. After reviewing the conformal spacetime
structure, conformal maps are described in Minkowski spacetime as the twisted
adjoint representation of the group Spin_+(2,4), acting on paravectors.
Twistors are then presented via the paravector model of Clifford algebras and
related to conformal maps in the Clifford algebra over the lorentzian R{4,1}$
spacetime. We construct twistors in Minkowski spacetime as algebraic spinors
associated with the Dirac-Clifford algebra Cl(1,3)(C) using one lower spacetime
dimension than standard Clifford algebra formulations, since for this purpose
the Clifford algebra over R{4,1} is also used to describe conformal maps,
instead of R{2,4}. Although some papers have already described twistors using
the algebra Cl(1,3)(C), isomorphic to Cl(4,1), the present formulation sheds
some new light on the use of the paravector model and generalizations.Comment: 17 page
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