19,393 research outputs found
Fragmentation of spherical radioactive heavy nuclei as a novel probe of transient effects in fission
Peripheral collisions with radioactive heavy-ion beams at relativistic
energies are discussed as an innovative approach for probing the transient
regime experienced by fissile systems evolving towards quasi-equilibrium. A
dedicated experiment using the advanced technical installations of GSI,
Darmstadt, permitted to realize ideal conditions for the investigation of
relaxation effects in the meta-stable well. Combined with a highly sensitive
experimental signature, it provides a measure of the transient effects with
respect to the flux over the fission barrier. Within a two-step reaction
process, 45 proton-rich unstable spherical isotopes produced by
projectile-fragmentation of a stable 238U beam have been used as secondary
projectiles. The fragmentation of the radioactive projectiles on lead results
in nearly spherical compound nuclei which span a wide range in excitation
energy and fissility. The decay of these excited systems by fission is studied
with a dedicated set-up which permits the detection of both fission products in
coincidence and the determination of their atomic numbers with high resolution.
The width of the fission-fragment nuclear charge distribution is shown to be
specifically sensitive to pre-saddle transient effects and is used to establish
a clock for the passage of the saddle point. The comparison of the experimental
results with model calculations points to a fission delay of (3.3+/-0.7).10-21s
for initially spherical compound nuclei, independent of excitation energy and
fissility. This value suggests a nuclear dissipation strength at small
deformation of (4.5+/-0.5).1021s-1. The very specific combination of the
physics and technical equipment exploited in this work sheds light on previous
controversial conclusions.Comment: 38 pages, 15 figure
Psychophysiological correlates of peritraumatic dissociative responses in survivors of life-threatening cardiac events
The psychophysiological startle response pattern associated with peritraumatic dissociation (DISS) was studied in 103 survivors of a life-threatening cardiac event (mean age 61.0 years, SD 13.95). Mean time period since the cardiac event was 37 (79 IQD) months. All patients underwent a psychodiagnostic evaluation (including the Peritraumatic Dissociative Experiences Questionnaire) and a psychophysiological startle experience which comprised the delivery of 15 acoustic startle trials. Magnitude and habituation to trials were measured by means of electromyogram (EMG) and skin conductance responses (SCR). Thirty-two (31%) subjects were indexed as patients with a clinically significant level of DISS symptoms. High-level DISS was associated with a higher magnitude of SCR (ANOVA for repeated measures p = 0.017) and EMG (p = 0.055) and an impaired habituation (SCR slope p = 0.064; EMG slope p = 0.005) in comparison to subjects with no or low DISS. In a subgroup analysis, high-level DISS patients with severe post-traumatic stress disorder (PTSD; n = 11) in comparison to high-level DISS patients without subsequent PTSD (n = 19) exhibited higher EMG amplitudes during all trials (repeated measures analysis of variance IF = 5.511, p = 0.026). The results demonstrate exaggerated startle responses in SCR and EMG measures - an abnormal defensive response to high-intensity stimuli which indicates a steady state of increased arousal. DISS patients without PTSD exhibited balanced autonomic responses to the startle trials. DISS may, therefore, unfold malignant properties only in combination with persistent physiological hyperarousability. Copyright (C) 2002 S. Karger AG, Basel
Pauli Paramagnetic Effects on Vortices in Superconducting TmNi2B2C
The magnetic field distribution around the vortices in TmNi2B2C in the
paramagnetic phase was studied experimentally as well as theoretically. The
vortex form factor, measured by small-angle neutron scattering, is found to be
field independent up to 0.6 Hc2 followed by a sharp decrease at higher fields.
The data are fitted well by solutions to the Eilenberger equations when
paramagnetic effects due to the exchange interaction with the localized 4f Tm
moments are included. The induced paramagnetic moments around the vortex cores
act to maintain the field contrast probed by the form factor.Comment: 4 pages, 4 figure
Spatially-Resolved Spectra of the "Teacup" AGN: Tracing the History of a Dying Quasar
The Sloan Digital Sky Survey (SDSS) Galaxy Zoo project has revealed a number
of spectacular galaxies possessing Extended Emission-Line Regions (EELRs), the
most famous being Hanny's Voorwerp galaxy. We present another EELR object
discovered in the SDSS endeavor: the Teacup Active Galactic Nucleus (AGN),
nicknamed for its EELR, which has a handle like structure protruding 15 kpc
into the northeast quadrant of the galaxy. We analyze physical conditions of
this galaxy with long-slit ground based spectroscopy from Lowell, Lick, and
KPNO observatories. With the Lowell 1.8m Perkin's telescope we took multiple
observations at different offset positions, allowing us to recover spatially
resolved spectra across the galaxy. Line diagnostics indicate the ionized gas
is photoionized primarily by the AGN. Additionally we are able to derive the
hydrogen density from the [S II] 6716/6731 ratio. We generated two-component
photoionization models for each spatially resolved Lowell spectrum. These
models allow us to calculate the AGN bolometric luminosity seen by the gas at
different radii from the nuclear center of the Teacup. Our results show a drop
in bolometric luminosity by more than two orders of magnitude from the EELR to
the nucleus, suggesting that the AGN has decreased in luminosity by this amount
in a continuous fashion over 46,000 years, supporting the case for a dying AGN
in this galaxy independent of any IR based evidence. We demonstrate that
spatially resolved photoionization modeling could be applied to EELRs to
investigate long time scale variability.Comment: 38 pages, 11 figures, accepted for publication in the Astrophysical
Journa
Large N limit of SO(N) gauge theory of fermions and bosons
In this paper we study the large N_c limit of SO(N_c) gauge theory coupled to
a Majorana field and a real scalar field in 1+1 dimensions extending ideas of
Rajeev. We show that the phase space of the resulting classical theory of
bilinears, which are the mesonic operators of this theory, is OSp_1(H|H
)/U(H_+|H_+), where H|H refers to the underlying complex graded space of
combined one-particle states of fermions and bosons and H_+|H_+ corresponds to
the positive frequency subspace. In the begining to simplify our presentation
we discuss in detail the case with Majorana fermions only (the purely bosonic
case is treated in our earlier work). In the Majorana fermion case the phase
space is given by O_1(H)/U(H_+), where H refers to the complex one-particle
states and H_+ to its positive frequency subspace. The meson spectrum in the
linear approximation again obeys a variant of the 't Hooft equation. The linear
approximation to the boson/fermion coupled case brings an additonal bound state
equation for mesons, which consists of one fermion and one boson, again of the
same form as the well-known 't Hooft equation.Comment: 27 pages, no figure
Dynamics of Social Balance on Networks
We study the evolution of social networks that contain both friendly and
unfriendly pairwise links between individual nodes. The network is endowed with
dynamics in which the sense of a link in an imbalanced triad--a triangular loop
with 1 or 3 unfriendly links--is reversed to make the triad balanced. With this
dynamics, an infinite network undergoes a dynamic phase transition from a
steady state to "paradise"--all links are friendly--as the propensity p for
friendly links in an update event passes through 1/2. A finite network always
falls into a socially-balanced absorbing state where no imbalanced triads
remain. If the additional constraint that the number of imbalanced triads in
the network does not increase in an update is imposed, then the network quickly
reaches a balanced final state.Comment: 10 pages, 7 figures, 2-column revtex4 forma
Time series of high resolution spectra of SN 2014J observed with the TIGRE telescope
We present a time series of high resolution spectra of the Type Ia supernova
2014J, which exploded in the nearby galaxy M82. The spectra were obtained with
the HEROS echelle spectrograph installed at the 1.2 m TIGRE telescope. We
present a series of 33 spectra with a resolution of R = 20, 000, which covers
the important bright phases in the evolution of SN 2014J during the period from
January 24 to April 1 of 2014. The spectral evolution of SN 2014J is derived
empirically. The expansion velocities of the Si II P-Cygni features were
measured and show the expected decreasing behaviour, beginning with a high
velocity of 14,000 km/s on January 24. The Ca II infrared triplet feature shows
a high velocity component with expansion velocities of > 20, 000 km/s during
the early evolution apart from the normal component showing similar velocities
as Si II. Further broad P-Cygni profiles are exhibited by the principal lines
of Ca II, Mg II and Fe II. The TIGRE SN 2014J spectra also resolve several very
sharp Na I D doublet absorption components. Our analysis suggests interesting
substructures in the interstellar medium of the host galaxy M82, as well as in
our Milky Way, confirming other work on this SN. We were able to identify the
interstellar absorption of M82 in the lines of Ca II H & K at 3933 and 3968 A
as well as K I at 7664 and 7698 A. Furthermore, we confirm several Diffuse
Interstellar Bands, at wavelengths of 6196, 6283, 6376, 6379 and 6613 A and
give their measured equivalent widths.Comment: 11 pages, 10 figures, accepted for publication in MNRA
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