21,362 research outputs found
ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus
ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed it was highly
variable on the timescale of s in the hard X-ray (2-10 keV)
band, while the soft X-ray (0.5-2 keV) flux remained constant during the
observations.
The spectral analysis suggests that this object is seen through an obscuring
torus with the thickness of N. The
hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus; the
soft X-ray is dominated by the scattered central continuum from an extended
spatial region. Thus we have an obscured/absorbed and a scattered view of this
source as expected from the unification model for Seyfert galaxies.
More interestingly, the inferred X-ray column was observed to increase by
from 1994 to 1996, suggesting a ``patchy''
torus structure, namely the torus might be composed of many individual clouds.
The observed iron line feature near 6.4 keV with the equivalent width of 170 eV
is also consistent with the picture of the transmission of nuclear X-ray
continuum through a non-uniform torus.Comment: 10 pages, 6 figures. To be appear in PASJ 50 No.5 (1998 Oct.25 issue
Scaling analysis of Schottky barriers at metal-embedded semiconducting carbon nanotube interfaces
We present an atomistic self-consistent tight-binding study of the electronic
and transport properties of metal-semiconducting carbon nanotube interfaces as
a function of the nanotube channel length when the end of the nanotube wire is
buried inside the electrodes. We show that the lineup of the nanotube band
structure relative to the metal Fermi-level depends strongly on the metal work
function but weakly on the details of the interface. We analyze the
length-dependent transport characteristics, which predicts a transition from
tunneling to thermally-activated transport with increasing nanotube channel
length.Comment: To appear in Phys.Rev.B Rapid Communications. Color figures available
in PRB online versio
A further study of the possible scaling region of lattice chiral fermions
In the possible scaling region for an SU(2) lattice chiral fermion advocated
in {\it Nucl. Phys.} B486 (1997) 282, no hard spontaneous symmetry breaking
occurs and doublers are gauge-invariantly decoupled via mixing with composite
three-fermion-states that are formed by local multifermion interactions.
However the strong coupling expansion breaks down due to no ``static limit''
for the low-energy limit (). In both neutral and charged channels, we
further analyze relevant truncated Green functions of three-fermion-operators
by the strong coupling expansion and analytical continuation of these Green
functions in the momentum space. It is shown that in the low-energy limit,
these relevant truncated Green functions of three-fermion-states with the
``wrong'' chiralities positively vanish due to the generalized form factors
(the wave-function renormalizations) of these composite three-fermion-states
vanishing as O((pa)^4) for . This strongly implies that the composite
three-fermion-states with ``wrong'' chirality are ``decoupled'' in this limit
and the low-energy spectrum is chiral, as a consequence, chiral gauge
symmetries can be exactly preserved.Comment: A few typing-errors, in particular in Eq.50, have been correcte
Complete Real Time Solution of the General Nonlinear Filtering Problem without Memory
It is well known that the nonlinear filtering problem has important
applications in both military and civil industries. The central problem of
nonlinear filtering is to solve the Duncan-Mortensen-Zakai (DMZ) equation in
real time and in a memoryless manner. In this paper, we shall extend the
algorithm developed previously by S.-T. Yau and the second author to the most
general setting of nonlinear filterings, where the explicit time-dependence is
in the drift term, observation term, and the variance of the noises could be a
matrix of functions of both time and the states. To preserve the off-line
virture of the algorithm, necessary modifications are illustrated clearly.
Moreover, it is shown rigorously that the approximated solution obtained by the
algorithm converges to the real solution in the sense. And the precise
error has been estimated. Finally, the numerical simulation support the
feasibility and efficiency of our algorithm.Comment: 15 pages, 2-column format, 2 figure
Ultrasonic Wave Propagation in a Tooth Phantom
Although ultrasonic energy has been used widely for general medical diagnostic purposes and as a tool for the nondestructive inspection of engineering components, a lack of understanding of the fundamental wave propagation phenomena in teeth has largely precluded its application to dentistry. This paper studies the physics of ultrasound/teeth interactions. Based on the authors’ experience with the detection of defec engineering materials using ultrasound and the development of finite element computer code to study the wave propagation, initial studies have already been made on a tooth phantom. Results indicate that this numerical model can indeed be used to study the complex ultrasound interactions with dental anomalies, such as pulpitis and abscesses, and that such results could be used to optimize the design of appropriate transducers and equipment for dentistry applications. The primary reason why this technique is important and should take place is that ultrasonography has a great advantage over the presently available X-ray technology in that it does put any strain on the patient nor does it cause any pain. Most importantly, ultrasonic waves are nonionizing which, when used at low sound intensity levels, do not cause any health risks to the patient nor to the operator
Recommended from our members
Divine Innovation: Religion and Service Provision by Religious Organizations in India
This paper examines innovations to religious and non-religious service provision by religious organizations in India. We present a stylized Hotelling-style model in which two religious organizations position themselves at opposite locations to differentiate themselves on the religious spectrum in order to compete to attract adherents. Moreover, the model predicts that economic inequality can make both organizations increase their provision of non-religious services to retain adherents. In order to test our propositions, we present unique primary survey data on the economics of religion that we have collected from 2006-2008 on 568 Hindu, Muslim, Christian, Sikh and Jain religious organizations spread across seven Indian states. We use these data to provide qualitative and descriptive statistics from the survey that is consistent and provides initial support for our propositions. We show that these organizations have substantially increased their provision of religious and non-religious services, but that there are significant variations by religion. We also provide quantitative evidence based on econometric testing to highlight that Indian religious organizations are maximizing the differences in their ideology with respect to other organizations, and are also providing higher education and health services as economic inequality increases in India
On the existence and uniqueness of solutions to stochastic differential equations driven by G-Brownian motion with integral-Lipschitz coefficients
In this paper, we study the existence and uniqueness of solutions to
stochastic differential equations driven by G-Brownian motion (GSDEs) with
integral-Lipschitz conditions on their coefficients
- …