14,418 research outputs found
An Imaging and Spectral Study of Ten X-Ray Filaments around the Galactic Center
We report the detection of 10 new X-ray filaments using the data from the
{\sl Chandra} X-ray satellite for the inner ( parsec)
around the Galactic center (GC). All these X-ray filaments are characterized by
non-thermal energy spectra, and most of them have point-like features at their
heads that point inward. Fitted with the simple absorbed power-law model, the
measured X-ray flux from an individual filament in the 2-10 keV band is to ergs cm s and the
absorption-corrected X-ray luminosity is ergs s
at a presumed distance of 8 kpc to the GC. We speculate the origin(s) of these
filaments by morphologies and by comparing their X-ray images with the
corresponding radio and infrared images. On the basis of combined information
available, we suspect that these X-ray filaments might be pulsar wind nebulae
(PWNe) associated with pulsars of age yr. The fact
that most of the filament tails point outward may further suggest a high
velocity wind blowing away form the GC.Comment: 29 pages with 7 figures and 3 pages included. Accepted to Ap
Distribution of Spectral Lags in Gamma Ray Bursts
Using the data acquired in the Time To Spill (TTS) mode for long gamma-ray
bursts (GRBs) collected by the Burst and Transient Source Experiment on board
the Compton Gamma Ray Observatory (BATSE/CGRO), we have carefully measured
spectral lags in time between the low (25-55 keV) and high (110-320 keV) energy
bands of individual pulses contained in 64 multi-peak GRBs. We find that the
temporal lead by higher-energy gamma-ray photons (i.e., positive lags) is the
norm in this selected sample set of long GRBs. While relatively few in number,
some pulses of several long GRBs do show negative lags. This distribution of
spectral lags in long GRBs is in contrast to that in short GRBs. This apparent
difference poses challenges and constraints on the physical mechanism(s) of
producing long and short GRBs. The relation between the pulse peak count rates
and the spectral lags is also examined. Observationally, there seems to be no
clear evidence for systematic spectral lag-luminosity connection for pulses
within a given long GRB.Comment: 20 pages, 4 figure
Global axisymmetric stability analysis for a composite system of two gravitationally coupled scale-free discs
In a composite system of gravitationally coupled stellar and gaseous discs,
we perform linear stability analysis for axisymmetric coplanar perturbations
using the two-fluid formalism. The background stellar and gaseous discs are
taken to be scale-free with all physical variables varying as powers of
cylindrical radius with compatible exponents. The unstable modes set in as
neutral modes or stationary perturbation configurations with angular frequency
.Comment: 7 pages using AAS styl
Phase Separation of Bismuth Ferrite into Magnetite under Voltage Stressing
Micro-Raman studies show that under ~700 kV/cm of d.c. voltage stressing for
a few seconds, thin-film bismuth ferrite BiFeO3 phase separates into magnetite
Fe3O4. No evidence is found spectroscopically of hemite alpha-Fe2O3, maghemite
gamma-Fe2O3, or of Bi2O3. This relates to the controversy regarding the
magnitude of magnetization in BiFeO3.Comment: 9 pages and 2 figure
Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow
We perform molecular dynamics simulations of model granular systems
undergoing boundary-driven planar shear flow in two spatial dimensions with the
goal of developing a more complete understanding of how dense particulate
systems respond to applied shear. In particular, we are interested in
determining when these systems will possess linear velocity profiles and when
they will develop highly localized velocity profiles in response to shear. In
previous work on similar systems we showed that nonlinear velocity profiles
form when the speed of the shearing boundary exceeds the speed of shear waves
in the material. However, we find that nonlinear velocity profiles in these
systems are unstable at very long times. The degree of nonlinearity slowly
decreases in time; the velocity profiles become linear when the granular
temperature and density profiles are uniform across the system at long times.
We measure the time required for the velocity profiles to become linear
and find that increases as a power-law with the speed of the shearing
boundary and increases rapidly as the packing fraction approaches random close
packing. We also performed simulations in which differences in the granular
temperature across the system were maintained by vertically vibrating one of
the boundaries during shear flow. We find that nonlinear velocity profiles form
and are stable at long times if the difference in the granular temperature
across the system exceeds a threshold value that is comparable to the glass
transition temperature in an equilibrium system at the same average density.
Finally, the sheared and vibrated systems form stable shear bands, or highly
localized velocity profiles, when the applied shear stress is lowered below the
yield stress of the static part of the system.Comment: 11 pages, 14 figure
Approximate perturbed direct homotopy reduction method: infinite series reductions to two perturbed mKdV equations
An approximate perturbed direct homotopy reduction method is proposed and
applied to two perturbed modified Korteweg-de Vries (mKdV) equations with
fourth order dispersion and second order dissipation. The similarity reduction
equations are derived to arbitrary orders. The method is valid not only for
single soliton solution but also for the Painlev\'e II waves and periodic waves
expressed by Jacobi elliptic functions for both fourth order dispersion and
second order dissipation. The method is valid also for strong perturbations.Comment: 8 pages, 1 figur
Dynamic Evolution of a Quasi-Spherical General Polytropic Magnetofluid with Self-Gravity
In various astrophysical contexts, we analyze self-similar behaviours of
magnetohydrodynamic (MHD) evolution of a quasi-spherical polytropic magnetized
gas under self-gravity with the specific entropy conserved along streamlines.
In particular, this MHD model analysis frees the scaling parameter in the
conventional polytropic self-similar transformation from the constraint of
with being the polytropic index and therefore
substantially generalizes earlier analysis results on polytropic gas dynamics
that has a constant specific entropy everywhere in space at all time. On the
basis of the self-similar nonlinear MHD ordinary differential equations, we
examine behaviours of the magnetosonic critical curves, the MHD shock
conditions, and various asymptotic solutions. We then construct global
semi-complete self-similar MHD solutions using a combination of analytical and
numerical means and indicate plausible astrophysical applications of these
magnetized flow solutions with or without MHD shocks.Comment: 21 pages, 7 figures, accepted for publication in APS
MANAGERâS LEADERSHIP STYLES AND JOB PERFORMANCE OF COMPANY RANK AND FILE EMPLOYEES
In company management, several leadership styles are inherent and utilised by a manager or a leader. This study assessed the leadership styles of a manufacturing company manager and how the styles of leadership influence rank and file employeesâ performance. In particular, it evaluated the managerâs leadership styles as affirmed by the rank and file employees, and how these leadership styles influence the performance of said employees from the viewpoint of work quality, work quantity, job innovativeness, customer service and team spirit. The study was carried out through a descriptive survey research design utilising a standardised survey questionnaire. Findings revealed that the branch Manager highly utilised transactional and transformational leadership styles in managing the manufacturing company. The Laissez-faire leadership style was only moderately utilised while the autocratic leadership was the least utilised style also at the moderate level. These utilised leadership styles manifested strong influence on the performance and productivity of rank and file employees of the manufacturing company under study. Accordingly, the employees exhibited outstanding performance towards the delivery of their works. It is concluded that managing the human capital of any company elicits full utilisation of good leadership styles supportive to the attainment of the companyâs set goals and objectives and employeesâ desired outputs and productivity. The company under study should continuously utilise and sustain the use of transactional and transformational leadership styles to keep employeesâ productive performance, although there is always room for improvement. Other related studies may be pursued considering other variables or attributes of leadership styles not covered in this study.
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