70,826 research outputs found
Structure and dynamics of topological defects in a glassy liquid on a negatively curved manifold
We study the low-temperature regime of an atomic liquid on the hyperbolic
plane by means of molecular dynamics simulation and we compare the results to a
continuum theory of defects in a negatively curved hexagonal background. In
agreement with the theory and previous results on positively curved (spherical)
surfaces, we find that the atomic configurations consist of isolated defect
structures, dubbed "grain boundary scars", that form around an irreducible
density of curvature-induced disclinations in an otherwise hexagonal
background. We investigate the structure and the dynamics of these grain
boundary scars
Dark Matter annihilation energy output and its effects on the high-z IGM
We study the case of DM self annihilation, in order to assess its importance
as an energy injection mechanism, to the IGM in general, and to the medium
within particular DM haloes. We consider thermal relic WIMP particles with
masses of 10GeV and 1TeV and we analyse in detail the clustering properties of
DM in a CDM cosmology, on all hierarchy levels, from haloes and their
mass function, to subhaloes and the DM density profiles within them,
considering adiabatic contraction by the presence of a SMBH. We then compute
the corresponding energy output, concluding that DM annihilation does not
constitute an important feedback mechanism. We also calculate the effects that
DM annihilation has on the IGM temperature and ionization fraction, and we find
that assuming maximal energy absorption, at z ~ 10, for the case of a 1TeV
WIMP, the ionization fraction could be raised to and the
temperature to 10K, and in the case of a 10GeV WIMP, the IGM temperature could
be raised to 200K and the ionization fraction to . We
conclude that DM annihilations cannot be regarded as an alternative
reionization scenario. Regarding the detectability of the WIMP through the
modifications to the 21 cm differential brightness temperature signal
(Tb), we conclude that a thermal relic WIMP with mass of 1TeV is not
likely to be detected from the global signal alone, except perhaps at the 1-3mK
level in the frequency range 30MHz < < 35MHz corresponding to 40 < z <
46. However, a 10GeV mass WIMP may be detectable at the 1-3mK level in the
frequency range 55MHz < < 119MHz corresponding to 11 < z < 25, and at the
1-10mK level in the frequency range 30MHz < < 40MHz corresponding to 35 <
z < 46.Comment: 23 pages, 12 figures, accepted for publication in MNRA
Studies of lunar and Martian soil mechanics Third quarterly progress report, Jun. - Sep. 15, 1965
Lunar and Martian soil mechanics - soil shear strength and penetration resistance under high vacuum, and composition of desorbed gases from heated soil sample
Studies of lunar soil mechanics, final report, jun. 15, 1963 - dec. 15, 1964
Properties of simulated lunar soils in lunar environmen
Study to investigate the effects of ionizing radiation on transistor surfaces Third quarterly report, period ending, 31 Mar. 1966
Ionizing radiation effects on transistor surface
Design and implementation of a medium speed communications interface and protocol for a low cost, refreshed display computer
The design and implementation of hardware and software systems involved in using a 40,000 bit/second communication line as the connecting link between an IMLAC PDS 1-D display computer and a Univac 1108 computer system were described. The IMLAC consists of two independent processors sharing a common memory. The display processor generates the deflection and beam control currents as it interprets a program contained in the memory; the minicomputer has a general instruction set and is responsible for starting and stopping the display processor and for communicating with the outside world through the keyboard, teletype, light pen, and communication line. The processing time associated with each data byte was minimized by designing the input and output processes as finite state machines which automatically sequence from each state to the next. Several tests of the communication link and the IMLAC software were made using a special low capacity computer grade cable between the IMLAC and the Univac
Ionization Mechanisms in Jet-Dominated Seyferts: A Detailed Case Study
For the past 10 years there has been an active debate over whether fast
shocks play an important role in ionizing emission line regions in Seyfert
galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn
78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the
archetypal jet-driven bipolar velocity field, if shocks are important anywhere
they should be important in this object. Having mapped the emission line fluxes
and velocity field, we first compare the ionization conditions to standard
photoionization and shock models. We find coherent variations of ionization
consistent with photoionization model sequences which combine optically thick
and thin gas, but are inconsistent with either autoionizing shock models or
photoionization models of just optically thick gas. Furthermore, we find
absolutely no link between the ionization of the gas and its kinematic state,
while we do find a simple decline of ionization degree with radius. We feel
this object provides the strongest case to date against the importance of shock
related ionization in Seyferts.Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 222
"The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", T.
Storchi Bergmann, L.C. Ho & H.R. Schmitt, ed
Optical fiber coupling method and apparatus
Systems are described for coupling a pair of optical fibers to pass light between them, which enables a coupler to be easily made, and with simple equipment, while closely controlling the characteristics of the coupler. One method includes mounting a pair of optical fibers on a block having a large hole therein, so the fibers extend across the hole while lying adjacent and parallel to one another. The fibers are immersed in an etchant to reduce the thickness of cladding around the fiber core. The fibers are joined together by applying a liquid polymer so the polymer-air interface moves along the length of the fibers to bring the fibers together in a zipper-like manner, and to progressively lay a thin coating of the polymer on the fibers
Anomalous coupling between topological defects and curvature
We investigate a counterintuitive geometric interaction between defects and
curvature in thin layers of superfluids, superconductors and liquid crystals
deposited on curved surfaces. Each defect feels a geometric potential whose
functional form is determined only by the shape of the surface, but whose sign
and strength depend on the transformation properties of the order parameter.
For superfluids and superconductors, the strength of this interaction is
proportional to the square of the charge and causes all defects to be repelled
(attracted) by regions of positive (negative) Gaussian curvature. For liquid
crystals in the one elastic constant approximation, charges between 0 and
are attracted by regions of positive curvature while all other charges
are repelled.Comment: 5 pages, 4 figures, minor changes, accepted for publication in Phys.
Rev. Let
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