27,857 research outputs found
Building Cross Cultural Competencies.
The Building Cross Cultural Competencies project was developed with the aim of equipping undergraduate students at the University of York with skills to work in the globalised world, while at the same time assisting with the induction and orientation of international students, new to the institution and to study in the UK. The inspiration for the programme dates back to 2006, when one of the authors visited three Universities in New Zealand and Australia. These Universities were perceived to be further down the route to internationalisation (as defined by Knight 2003) than was the norm in the UK at the time. Innovations observed at Massey and Waikato Universities in New Zealand and the University of Sydney, Australia, were redesigned and redeveloped for use at the University of York, with the agreement of the staff involved at those institutions. In particular, a cross cultural communication module and two distinctive peer mentor schemes provided the nucleus of the idea for a new initiative at York that would span the employability and internationalisation agendas This paper identifies how the project redesigned and developed ideas taken from Australian and New Zealand Universities for use in a UK context. It makes links to the literature on student adjustment and institutional adaptation; peer teaching and cross cultural communication skills. It will also consider the problems and difficulties experienced as the project progressed
Improvements in estimating proportions of objects from multispectral data
Methods for estimating proportions of objects and materials imaged within the instantaneous field of view of a multispectral sensor were developed further. Improvements in the basic proportion estimation algorithm were devised as well as improved alien object detection procedures. Also, a simplified signature set analysis scheme was introduced for determining the adequacy of signature set geometry for satisfactory proportion estimation. Averaging procedures used in conjunction with the mixtures algorithm were examined theoretically and applied to artificially generated multispectral data. A computationally simpler estimator was considered and found unsatisfactory. Experiments conducted to find a suitable procedure for setting the alien object threshold yielded little definitive result. Mixtures procedures were used on a limited amount of ERTS data to estimate wheat proportion in selected areas. Results were unsatisfactory, partly because of the ill-conditioned nature of the pure signature set
Determining DfT Hardware by VHDL-AMS Fault Simulation for Biological Micro-Electronic Fluidic Arrays
The interest of microelectronic fluidic arrays for biomedical applications, like DNA determination, is rapidly increasing. In order to evaluate these systems in terms of required Design-for-Test structures, fault simulations in both fluidic and electronic domains are necessary. VHDL-AMS can be used successfully in this case. This paper shows a highly testable architecture of a DNA Bio-Sensing array, its basic sensing concept, fluidic modeling and sensitivity analysis. The overall VHDL-AMS fault simulation of the system is shown
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., Buneman, Weibel and
other two-stream instabilities) created in collisionless shocks are responsible
for particle (electron, positron, and ion) acceleration. Using a 3-D
relativistic electromagnetic particle (REMP) code, we have investigated
particle acceleration associated with a relativistic electron-positron jet
front propagating into an ambient electron-positron plasma with and without
initial magnetic fields. We find small differences in the results for no
ambient and modest ambient magnetic fields. New simulations show that the
Weibel instability created in the collisionless shock front accelerates jet and
ambient particles both perpendicular and parallel to the jet propagation
direction. Furthermore, the non-linear fluctuation amplitudes of densities,
currents, electric, and magnetic fields in the electron-positron shock are
larger than those found in the electron-ion shock studied in a previous paper
at the comparable simulation time. This comes from the fact that both electrons
and positrons contribute to generation of the Weibel instability. Additionally,
we have performed simulations with different electron skin depths. We find that
growth times scale inversely with the plasma frequency, and the sizes of
structures created by the Weibel instability scale proportional to the electron
skin depth. This is the expected result and indicates that the simulations have
sufficient grid resolution. The simulation results show that the Weibel
instability is responsible for generating and amplifying nonuniform,
small-scale magnetic fields which contribute to the electron's (positron's)
transverse deflection behind the jet head.Comment: 18 pages, 8 figures, revised and accepted for ApJ, A full resolution
of the paper can be found at
http://gammaray.nsstc.nasa.gov/~nishikawa/apjep1.pd
Particle Acceleration in Relativistic Jets due to Weibel Instability
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., the Buneman instability,
two-streaming instability, and the Weibel instability) created in the shocks
are responsible for particle (electron, positron, and ion) acceleration. Using
a 3-D relativistic electromagnetic particle (REMP) code, we have investigated
particle acceleration associated with a relativistic jet front propagating
through an ambient plasma with and without initial magnetic fields. We find
only small differences in the results between no ambient and weak ambient
magnetic fields. Simulations show that the Weibel instability created in the
collisionless shock front accelerates particles perpendicular and parallel to
the jet propagation direction. While some Fermi acceleration may occur at the
jet front, the majority of electron acceleration takes place behind the jet
front and cannot be characterized as Fermi acceleration. The simulation results
show that this instability is responsible for generating and amplifying highly
nonuniform, small-scale magnetic fields, which contribute to the electron's
transverse deflection behind the jet head. The ``jitter'' radiation (Medvedev
2000) from deflected electrons has different properties than synchrotron
radiation which is calculated in a uniform magnetic field. This jitter
radiation may be important to understanding the complex time evolution and/or
spectral structure in gamma-ray bursts, relativistic jets, and supernova
remnants.Comment: ApJ, in press, Sept. 20, 2003 (figures with better resolution:
http://gammaray.nsstc.nasa.gov/~nishikawa/apjweib.pdf
Particle Acceleration and Radiation associated with Magnetic Field Generation from Relativistic Collisionless Shocks
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., the Buneman instability,
two-streaming instability, and the Weibel instability) created in the shocks
are responsible for particle (electron, positron, and ion) acceleration. Using
a 3-D relativistic electromagnetic particle (REMP) code, we have investigated
particle acceleration associated with a relativistic jet front propagating
through an ambient plasma with and without initial magnetic fields. We find
only small differences in the results between no ambient and weak ambient
magnetic fields. Simulations show that the Weibel instability created in the
collisionless shock front accelerates particles perpendicular and parallel to
the jet propagation direction. The simulation results show that this
instability is responsible for generating and amplifying highly nonuniform,
small-scale magnetic fields, which contribute to the electron's transverse
deflection behind the jet head. The ``jitter'' radiation from deflected
electrons has different properties than synchrotron radiation which is
calculated in a uniform magnetic field. This jitter radiation may be important
to understanding the complex time evolution and/or spectral structure in
gamma-ray bursts, relativistic jets, and supernova remnants.Comment: 4 pages, 1 figure, submitted to Proceedings of 2003 Gamma Ray Burst
Conferenc
The Extraordinarily Rapid Expansion of the X-ray Remnant of Kepler's Supernova (SN1604)
Four individual high resolution X-ray images from ROSAT and the Einstein
Observatory have been used to measure the expansion rate of the remnant of
Kepler's supernova (SN 1604). Highly significant measurements of the expansion
have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All
measurements are consistent with a current expansion rate averaged over the
entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when
combined with the known age of the remnant, determines the expansion parameter
m, defined as , to be 0.93 (+/-0.06) (+0.07,-0.04). The error
bars on these results include both statistical (first set of errors) and
systematic (second set) uncertainty. According to this result the X-ray remnant
is expanding at a rate that is remarkably close to free expansion and nearly
twice as fast as the mean expansion rate of the radio remnant. The expansion
rates as a function of radius and azimuthal angle are also presented based on
two ROSAT images that were registered to an accuracy better than 0.5
arcseconds. Significant radial and azimuthal variations that appear to arise
from the motion of individual X-ray knots are seen. The high expansion rate of
the X-ray remnant appears to be inconsistent with currently accepted dynamical
models for the evolution of Kepler's SNR.Comment: 14 pages, including 7 postscript figs, LaTeX, emulateapj. Accepted by
Ap
Herwig++ 2.0 Release Note
A new release of the Monte Carlo program Herwig++ (version 2.0) is now
available. This is the first version of the program which can be used for
hadron-hadron physics and includes the full simulation of both initial- and
final-state QCD radiation.Comment: Source code and additional information available at
http://hepforge.cedar.ac.uk/herwig
X-ray emission from PSR B1800-21, its wind nebula, and similar systems
We detected X-ray emission from PSR B1800-21 and its synchrotron nebula with
the Chandra X-ray Observatory. The pulsar's observed flux is (1.4+/-0.2)
10^{-14} ergs cm^{-2} s^{-1} in the 1-6 keV band. The spectrum can be described
by a two-component PL+BB model, suggesting a mixture of thermal and
magnetospheric emission. For a plausible hydrogen column density n_{H}=1.4
10^{22} cm^{-2}, the PL component has a slope Gamma=1.4+/-0.6 and a luminosity
L_{psr}^{nonth}=4 10^{31}(d/4 kpc)^2 ergs s^{-1}. The properties of the thermal
component (kT=0.1-0.3 keV, L^{bol}=10^{31}-10^{33} ergs s^{-1}) are very poorly
constrained because of the strong interstellar absorption. The compact,
7''\times4'', inner pulsar-wind nebula (PWN), elongated perpendicular to the
pulsar's proper motion, is immersed in a fainter asymmetric emission. The
observed flux of the PWN is (5.5+/-0.6) 10^{-14} ergs cm^{-2} s^{-1} in the 1-8
keV band. The PWN spectrum fits by a PL model with Gamma=1.6+/-0.3, L=1.6
10^{32} (d/4 kpc})^2 ergs s^{-1}. The shape of the inner PWN suggests that the
pulsar moves subsonically and X-ray emission emerges from a torus associated
with the termination shock in the equatorial pulsar wind. The inferred
PWN-pulsar properties (e.g., the PWN X-ray efficiency, L_{pwn}/\dot{E}~10^{-4};
the luminosity ratio, L_{pwn}/L_{psr}^{nonth}=4; the pulsar wind pressure at
the termination shock, p_s=10^{-9} ergs cm^{-3}) are very similar to those of
other subsonically moving Vela-like objects detected with Chandra
(L_{pwn}/\dot{E}=10^{-4.5}-10^{-3.5}, L_{pwn}/L_{psr}^{nonth}~5,
p_s=10^{-10}-10^{-8} ergs cm^{-1}).Comment: 11 pages, 10 figures, 2 tables; submitted to ApJ. Version with the
high-resolution figures is available at
http://www.astro.psu.edu/users/green/B1800/B1800_ApJ.pd
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