3,039 research outputs found
Nonlinear evolution of r-modes: the role of differential rotation
Recent work has shown that differential rotation, producing large scale
drifts of fluid elements along stellar latitudes, is an unavoidable feature of
r-modes in the nonlinear theory. We investigate the role of this differential
rotation in the evolution of the l=2 r-mode instability of a newly born, hot,
rapidly rotating neutron star. It is shown that the amplitude of the r-mode
saturates a few hundred seconds after the mode instability sets in. The
saturation amplitude depends on the amount of differential rotation at the time
the instability becomes active and can take values much smaller than unity. It
is also shown that, independently of the saturation amplitude of the mode, the
star spins down to rotation rates that are comparable to the inferred initial
rotation rates of the fastest pulsars associated with supernova remnants.
Finally, it is shown that, when the drift of fluid elements at the time the
instability sets in is significant, most of the initial angular momentum of the
star is transferred to the r-mode and, consequently, almost none is carried
away by gravitational radiation.Comment: 10 pages, 5 figure
Detecting Man-in-the-Middle Attacks against Transport Layer Security Connections with Timing Analysis
The Transport Layer Security (TLS) protocol is a vital component to the protection of data as it traverses across networks. From e-commerce websites to Virtual Private Networks (VPNs), TLS protects massive amounts of private information, and protecting this data from Man-in-the-Middle (MitM) attacks is imperative to keeping the information secure. This thesis illustrates how an attacker can successfully perform a MitM attack against a TLS connection without alerting the user to his activities. By deceiving the client machine into using a false certificate, an attacker takes away the only active defense mechanism a user has against a MitM. The goal for this research is to determine if a time threshold exists that can indicate the presence of a MitM in this scenario. An analysis of the completion times between TLS handshakes without a MitM, with a passive MitM, and with an active MitM is used to determine if this threshold is calculable. Any conclusive findings supporting the existence of a timing baseline can be considered the first steps toward finding the value of the threshold and creating a second layer defense to actively protect against a MitM
A Spatially-Resolved Spectroscopic Study of the Galactic Supernova Remnant Kesteven 75 with the Chandra X-ray Observatory
https://scholarworks.moreheadstate.edu/student_scholarship_posters/1236/thumbnail.jp
Nucleosynthesis Constraints on Scalar-Tensor Theories of Gravity
We study the cosmological evolution of massless single-field scalar-tensor
theories of gravitation from the time before the onset of annihilation
and nucleosynthesis up to the present. The cosmological evolution together with
the observational bounds on the abundances of the lightest elements (those
mostly produced in the early universe) place constraints on the coefficients of
the Taylor series expansion of , which specifies the coupling of the
scalar field to matter and is the only free function in the theory. In the case
when has a minimum (i.e., when the theory evolves towards general
relativity) these constraints translate into a stronger limit on the
Post-Newtonian parameters and than any other observational
test. Moreover, our bounds imply that, even at the epoch of annihilation and
nucleosynthesis, the evolution of the universe must be very close to that
predicted by general relativity if we do not want to over- or underproduce
He. Thus the amount of scalar field contribution to gravity is very small
even at such an early epoch.Comment: 15 pages, 2 figures, ReVTeX 3.1, submitted to Phys. Rev. D1
Neutrinos and Big-Bang Nucleosynthesis
Observations of clusters and super clusters of galaxies have indicated that
the Universe is more dominated by baryons than ever estimated in the
homogeneous cosmological model for primordial nucleosynthesis. Recent
detections of possibly low deuterium abundance in Lyman- clouds along
the line of sight to high red-shift quasars have raised another potential
difficulty that \he4 is overproduced in any cosmological models which satisfy
the low deuterium abundance constraint. We show that the inhomogeneous
cosmological model with degenerate electron-neutrino can resolve these two
difficulties.Comment: 7 pages, latex, 3 figures. To appear in Nucl. Phys. A62
Anti-Proton Evolution in Little Bangs and Big Bang
The abundances of anti-protons and protons are considered within
momentum-integrated Boltzmann equations describing Little Bangs, i.e.,
fireballs created in relativistic heavy-ion collisions. Despite of a large
anti-proton annihilation cross section we find a small drop of the ratio of
anti-protons to protons from 170 MeV (chemical freeze-out temperature) till 100
MeV (kinetic freeze-out temperature) for CERN-SPS and BNL-RHIC energies thus
corroborating the solution of the previously exposed "ani-proton puzzle". In
contrast, the Big Bang evolves so slowly that the anti-baryons are kept for a
long time in equilibrium resulting in an exceedingly small fraction. The
adiabatic path of cosmic matter in the phase diagram of strongly interacting
matter is mapped out
Spontaneous alternating behavior, attention, and exploration: the effects of colchicine lesions in the rat hippocaompal formation
This study investigated perseverative behavior, attention, and exploratory behaviors via discrete lesions of the rat hippocampal formation. It was hypothesized that lesions which interrupted input to the hippocampus and output to cortical and subcortical regions would induce these behaviors. Forty-four male Long-Evan rats were randomly divided into four treatment groups: cerebral spinal fluid, and three colchicine lesioned groups, 10-COL, 15-COL, and 25-COL. The animals were compared based upon performance in a standard Tmaze to test perseveration. Behaviors were also observed in an activity chamber to measure locomotion, attention, and exploration. Animals in the 25-COL group demonstrated a significant increase in activity and perseveration as well as a decrease in exploration and attention compared to all other groups. Disrupting the convergence of information to the hippocampal formation interferes with output to subcortical and cortical regions, inducing behavioral changes associated with the structures of the hippocampal system
Deconvolving the information from an imperfect spherical gravitational wave antenna
We have studied the effects of imperfections in spherical gravitational wave
antenna on our ability to properly interpret the data it will produce. The
results of a numerical simulation are reported that quantitatively describe the
systematic errors resulting from imperfections in various components of the
antenna. In addition, the results of measurements on a room-temperature
prototype are presented that verify it is possible to accurately deconvolve the
data in practice.Comment: 5 pages, 2 figures, to be published in Europhysics Letter
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