2,583 research outputs found
Holographic Nuclei : Supersymmetric Examples
We provide a dual gravity description of a supersymmetric heavy nucleus,
following the idea of our previous paper arXiv:0809.3141. The supersymmetric
nucleus consists of a merginal bound state of baryons distributed over a
ball in 3 dimensions. In the gauge/string duality, the baryon in N=4 super
Yang-Mills (SYM) theory corresponds to a D5-brane wrapping S^5 of the AdS_5 x
S^5 spacetime, so the nucleus corresponds to a collection of D5-branes. We
take a large and a near horizon limits of a back-reacted geometry generated
by the wrapped D5-branes, where we find a gap in the supergravity
fluctuation spectrum. This spectrum is a gravity dual of giant resonances of
heavy nuclei, in the supersymmetric toy example of QCD.Comment: 9 pages, 6 figures; v2:a refernce adde
All-or-none switching of transcriptional activity on single DNA molecules caused by a discrete conformational transition
Recently, it has been confirmed that long duplex DNA molecules with sizes
larger than several tens of kilo-base pairs (kbp), exhibit a discrete
conformational transition from an elongated coil state to a compact globule
state upon the addition of various kinds of chemical species that usually
induce DNA condensation. In this study, we performed a single-molecule
observation on a large DNA, Lambda ZAP II DNA (ca. 41 kbp), in a solution
containing RNA polymerase and substrates along with spermine, a tetravalent
cation, at different concentrations, by use of fluorescence staining of both
DNA and RNA. We found that transcription, or RNA production, is completely
inhibited in the compact state, but is actively performed in the unfolded coil
state. Such an all-or-none effect on transcriptional activity induced by the
discrete conformational transition of single DNA molecules is discussed in
relation to the mechanism of the regulation of large-scale genetic activity.Comment: 14 pages, 2 figure
Chiral Phase Transitions in QCD at Finite Temperature: Hard-Thermal-Loop Resummed Dyson-Schwinger Equation in the Real Time Formalism
Chiral phase transition in thermal QCD is studied by using the
Dyson-Schwinger (DS) equation in the real time hard thermal loop approximation.
Our results on the critical temperature and the critical coupling are
significantly different from those in the preceding analyses in the ladder DS
equation, showing the importance of properly taking into account the essential
thermal effects, namely the Landau damping and the unstable nature of thermal
quasiparticles.Comment: 4 pages including 2 figures (ps file), to appear in the proceedings
of the 4th International Conference on Physics and Astrophysics of
Quark-Gluon Plasma (ICPAQGP-2001), 26-30 November 2001, Jaipur, Indi
Detecting mode entanglement: The role of coherent states, superselection rules and particle statistics
We discuss the possibility of observing quantum nonlocality using the
so-called mode entanglement, analyzing the differences between different types
of particles in this context. We first discuss the role of coherent states in
such experiments, and we comment on the existence of coherent states in nature.
The discussion of coherent states naturally raises questions about the role of
particle statistics in this problem. Although the Pauli exclusion principle
precludes coherent states with a large number of fermionic particles, we find
that a large number of fermionic coherent states, each containing at most one
particle, can be used to achieve the same effect as a bosonic coherent state
for the purposes of this problem. The discussion of superselection rules arises
naturally in this context, because their applicability to a given situation
prohibits the use of coherent states. This limitation particularly affects the
scenario that we propose for detecting the mode entanglement of fermionic
particles.Comment: 7 pages (two-column
The Orbit and Position of the X-ray Pulsar XTE J1855-026 - an Eclipsing Supergiant System
A pulse timing orbit has been obtained for the X-ray binary XTE J1855-026
using observations made with the Proportional Counter Array on board the Rossi
X-ray Timing Explorer. The mass function obtained of ~16Mo together with the
detection of an extended near-total eclipse confirm that the primary star is a
supergiant as predicted. The orbital eccentricity is found to be very low with
a best fit value of 0.04 +/- 0.02. The orbital period is also refined to be
6.0724 +/- 0.0009 days using an improved and extended light curve obtained with
RXTE's All Sky Monitor. Observations with the ASCA satellite provide an
improved source location of R.A. = 18h 55m 31.3s}, decl. = -02o 36' 24.0"
(2000) with an estimated systematic uncertainty of less than 12". A
serendipitous new source, AX J1855.4-0232, was also discovered during the ASCA
observations.Comment: Accepted for publication in the Astrophysical Journa
The Low-Mass X-ray Binary X1822-330 in the Globular Cluster NGC 6652: A Serendipitous ASCA Observation
The Low Mass X-ray Binary (LMXB) X1822-330 in NGC 6652 is one of 12 bright,
or transient, X-ray sources to have been discovered in Globular Clusters. We
report on a serendipitous ASCA observation of this Globular Cluster LMXB,
during which a Type I burst was detected and the persistent, non-burst emission
of the source was at its brightest level recorded to date. No orbital
modulation was detected, which argues against a high inclination for the
X1822-330 system. The spectrum of the persistent emission can be fit with a
power law plus a partial covering absorber, although other models are not ruled
out. Our time-resolved spectral analysis through the burst shows, for the first
time, clear evidence for spectral cooling from kT=2.4+/-0.6 keV to kT=1.0+/0.1
keV during the decay. The measured peak flux during the burst is ~10% of the
Eddington luminosity for a 1.4 Msun neutron star. These are characteristic of a
Type I burst, in the context of the relatively low quiescent luminosity of
X1822-330.Comment: 9 pages, 5 figures, accepted for Ap
Modeling of vegetated rivers for inbank and overbank flows
Model parameters such as friction factor and eddy viscosity in the Shiono & Knight method (SKM) are considered through experimental data obtained from a vegetated open channel. The experiment was conducted in a rectangular open channel with cylindrical rods as vegetation. Velocity, Reynolds stresses and boundary shear stress were measured with Acoustic Doppler Velocimetry (ADV) and a Preston tube re-spectively. Both friction factor and eddy viscosity were calculated using the measured data and found to be not constant in the shear layer generated by rods. The analytical solutions of SKM to predict velocity and boundary shear stress currently in use were based on the constant assumption of these parameters. In this pa-per a new analytical solution was derived by taking into a variation of these parameters account and was also verified with the experimental data. This solution was also applied to flow in compound channel with vegeta-tion. The new solution gives a good prediction of the lateral distribution of depth-averaged velocity and boundary shear stress in vegetated channels, and it predicts the boundary shear stress better than that of the original solution without considering the secondary flow term in particular
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