8,218 research outputs found
A Ray-Tracing Model of the Vela Pulsar
In the relativistic plasma surrounding a pulsar, a subluminal ordinary-mode
electromagnetic wave will propagate along a magnetic field line. After some
distance, it can break free of the field line and escape the magnetosphere to
reach an observer. We describe a simple model of pulsar radio emission based on
this scenario and find that applying this model to the case of the Vela pulsar
reproduces qualitative characteristics of the observed Vela pulse profile.Comment: 23 pages, 9 figures, accepted for publication in Ap
Relativistic Viscous Hydrodynamics for Multi-Component Systems with Multiple Conserved Currents
We would like to formulate relativistic dissipative hydrodynamics for
multi-component systems with multiple conserved currents. This is important for
analyses of the hot matter created in relativistic heavy ion collisions because
particle creations and annihilations of various particle species are frequently
taking place there. We show that consistent formulation in such systems
involves many non-trivialities, and derive constitutive equations that satisfy
Onsager reciprocal relations and describe the systems without ambiguity.Comment: 4 pages, no figures - To appear in the conference proceedings for Hot
Quarks 2010, June 21-26, La Londe-les-Maures, Franc
Jet-fluid string formation and decay in high-energy heavy-ion collisions
We propose a new hadronization mechanism, jet-fluid string (JFS) formation
and decay, to understand observables in intermediate to high- regions
comprehensively. In the JFS model, hard partons produced in jet lose their
energy in traversing the QGP fluid, which is described by fully
three-dimensional hydrodynamic simulations. When a jet parton escapes from the
QGP fluid, it picks up a partner parton from a fluid and forms a color singlet
string, then it decays to hadrons. We find that high- values in JFS
are about two times larger than in the independent fragmentation model.Comment: 6 pages, 2 figures; Proceeding for poster sessions at Quark Matter
2006, Shanghai, China, 14-20 November 2006; to appear in Int. J. of Mod.
Phys.
A High Stellar Obliquity in the WASP-7 Exoplanetary System
We measure a tilt of 86+-6 deg between the sky projections of the rotation
axis of the WASP-7 star, and the orbital axis of its close-in giant planet.
This measurement is based on observations of the Rossiter-McLaughlin (RM)
effect with the Planet Finder Spectrograph on the Magellan II telescope. The
result conforms with the previously noted pattern among hot-Jupiter hosts,
namely, that the hosts lacking thick convective envelopes have high
obliquities. Because the planet's trajectory crosses a wide range of stellar
latitudes, observations of the RM effect can in principle reveal the stellar
differential rotation profile; however, with the present data the signal of
differential rotation could not be detected. The host star is found to exhibit
radial-velocity noise (``stellar jitter') with an amplitude of ~30m/s over a
timescale of days.Comment: ApJ accepted, 9 pages, 9 figure
The Effect of Social Distancing on the Reach of an Epidemic in Social Networks
How does social distancing affect the reach of an epidemic in social
networks? We present Monte Carlo simulation results of a capacity constrained
Susceptible-Infected-Removed (SIR) model. The key modelling feature is that
individuals are limited in the number of acquaintances that they can interact
with, thereby constraining disease transmission to an infectious subnetwork of
the original social network. While increased social distancing always reduces
the spread of an infectious disease, the magnitude varies greatly depending on
the topology of the network. Our results also reveal the importance of
coordinating social distancing policies at the global level. In particular, the
public health benefits from social distancing to a group (e.g., a country) may
be completely undone if that group maintains connections with outside groups
that are not following suit
The centrality dependence of v2/epsilon: the ideal hydro limit and eta/s
The large elliptic flow observed at RHIC is considered to be evidence for
almost perfect liquid behavior of the strongly coupled quark-gluon plasma
produced in the collisions. In these proceedings we present a two parameter fit
for the centrality dependence of the elliptic flow scaled by the spatial
eccentricity. We show by comparing to viscous hydrodynamical calculations that
these two parameters are in good approximation proportional to the shear
viscosity over entropy ratio and the ideal hydro limit of the ratio v2/epsilon.Comment: 4 pages, 8 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee - final version
without line number
Interplay between soft and hard hadronic components for identified hadrons in relativistic heavy ion collisions
We investigate the transverse dynamics in Au+Au collisions at \sqrt{s_NN}=200
GeV by emphasis upon the interplay between soft and hard components through p_T
dependences of particle spectra, ratios of yields, suppression factors, and
elliptic flow for identified hadrons. From hydrodynamics combined with
traversing minijets which go through jet quenching in the hot medium, we
calculate interactions of hard jets with the soft hydrodynamic components. It
is shown by the explicit dynamical calculations that the hydrodynamic radial
flow and the jet quenching of hard jets are the keys to understand the
differences among the hadron spectra for pions, kaons, and protons. This leads
to the natural interpretation for N_p/N_\pi ~ 1, R_{AA} >~ 1 for protons, and
v_2^p > v_2^\pi recently observed in the intermediate transverse momentum
region at Relativistic Heavy Ion Collider (RHIC).Comment: 11 pages, 9 figures; some references added; title changed, some data
points included in figure
Unified description of Bjorken and Landau 1+1 hydrodynamics
We propose a generalization of the Bjorken in-out Ansatz for fluid
trajectories which, when applied to the (1+1) hydrodynamic equations, generates
a one-parameter family of analytic solutions interpolating between the
boost-invariant Bjorken picture and the non boost-invariant one by Landau. This
parameter characterises the proper-time scale when the fluid velocities
approach the in-out Ansatz. We discuss the resulting rapidity distribution of
entropy for various freeze-out conditions and compare it with the original
Bjorken and Landau results.Comment: 20 pages, 5 figure
Chromosome dynamics: Fuzzy sequences, specific attachments?
AbstractThe assembly of condensed chromosomes in a cell-free system is inhibited by the addition of proteins that bind AT-rich DNA. Does this implicate the AT-rich scaffold attachment regions (SARs) in the formation of chromosomes
- …