43,903 research outputs found
Temporal and Spectral Correlations of Cyg X-1
Temporal and spectral properties of X-ray rapid variability of Cyg X-1 are
studied by an approach of correlation analysis in the time domain on different
time scales. The correlation coefficients between the total intensity in 2-60
keV and the hardness ratio of 13-60 keV to 2-6 keV band on the time scale of
about 1 ms are always negative in all states. For soft states, the correlation
coefficients are positive on all the time scales from about 0.01 s to 100 s,
which is significantly different with that for transition and low states.
Temporal structures in high energy band are narrower than that in low energy
band in quite a few cases. The delay of high energy photons relative to low
energy ones in the X-ray variations has also been revealed by the correlation
analysis. The implication of observed temporal and spectral characteristics to
the production region and mechanism of Cyg X-1 X-ray variations is discussed.Comment: 17 pages, 6 figures included, to appear in Ap
Generalized Background-Field Method
The graphical method discussed previously can be used to create new gauges
not reachable by the path-integral formalism. By this means a new gauge is
designed for more efficient two-loop QCD calculations. It is related to but
simpler than the ordinary background-field gauge, in that even the triple-gluon
vertices for internal lines contain only four terms, not the usual six. This
reduction simplifies the calculation inspite of the necessity to include other
vertices for compensation. Like the ordinary background-field gauge, this
generalized background-field gauge also preserves gauge invariance of the
external particles. As a check of the result and an illustration for the
reduction in labour, an explicit calculation of the two-loop QCD
-function is carried out in this new gauge. It results in a saving of
45% of computation compared to the ordinary background-field gauge.Comment: 17 pages, Latex, 18 figures in Postscrip
Achieving precise mechanical control in intrinsically noisy systems
How can precise control be realized in intrinsically noisy systems? Here, we develop a general theoretical framework that provides a way of achieving precise control in signal-dependent noisy environments. When the control signal has Poisson or supra-Poisson noise, precise control is not possible. If, however, the control signal has sub-Poisson noise, then precise control is possible. For this case, the precise control solution is not a function, but a rapidly varying random process that must be averaged with respect to a governing probability density functional. Our theoretical approach is applied to the control of straight-trajectory arm movement. Sub-Poisson noise in the control signal is shown to be capable of leading to precise control. Intriguingly, the control signal for this system has a natural counterpart, namely the bursting pulses of neurons-trains of Dirac-delta functions-in biological systems to achieve precise control performance
Pressure-induced Spin-Peierls to Incommensurate Charge-Density-Wave Transition in the Ground State of TiOCl
The ground state of the spin-Peierls system TiOCl was probed using
synchrotron x-ray diffraction on a single-crystal sample at T = 6 K. We tracked
the evolution of the structural superlattice peaks associated with the
dimerized ground state as a function of pressure. The dimerization along the b
axis is rapidly suppressed in the vicinity of a first-order structural phase
transition at Pc = 13.1(1) GPa. The high-pressure phase is characterized by an
incommensurate charge density wave perpendicular to the original spin chain
direction. These results show that the electronic ground state undergoes a
fundamental change in symmetry, indicating a significant change in the
principal interactions.Comment: 5 pages, 4 figure
Multiple Reggeon Exchange from Summing QCD Feynman Diagrams
Multiple reggeon exchange supplies subleading logs that may be used to
restore unitarity to the Low-Nussinov Pomeron, provided it can be proven that
the sum of Feynman diagrams to all orders gives rise to such multiple regge
exchanges. This question cannot be easily tackled in the usual way except for
very low-order diagrams, on account of delicate cancellations present in the
sum which necessitate individual Feynman diagrams to be computed to subleading
orders. Moreover, it is not clear that sums of high-order Feynman diagrams with
complicated criss-crossing of lines can lead to factorization implied by the
multi-regge scenario. Both of these difficulties can be overcome by using the
recently developed nonabelian cut diagrams. We are then able to show that the
sum of -channel-ladder diagrams to all orders does lead to such multiple
reggeon exchanges.Comment: uu-encoded latex file with 11 postscript figures (20 pages
Probing the Inflow/Out-flow and Accretion Disk of Cyg X-1 in the High State with HETG/Chandra
Cyg X-1 was observed in the high state at the conjunction orbital phase (0)
with HETG/Chandra. Strong and asymmetric absorption lines of highly ionized
species were detected, such as Fe XXV, Fe XXIV, Fe XXIII, Si XIV, S XVI, Ne X,
and etc. In the high state the profile of the absorption lines are composed of
an extended red wing and a less extended blue wing. The red wings of higher
ionized species are more extended than that of lower ionized species. The
detection of these lines provides a way to probe the properties of the flow
around the companion and the black hole in Cyg X-1 during the high state. A
broad emission feature around 6.5 keV was significantly detected from the both
spectra of HETG/Chandra and PCA/RXTE. This feature appears to be symmetric and
can be fitted with a Gaussian function rather than the Laor disk line model of
fluorescent Fe K line from an accretion disk. The implications of
these results on the structure of the accretion flow of Cyg X-1 in the high
state are discussed.Comment: 16 pages, 4 fiugres. accepted for publication in the v597 n2 ApJ
November 10, 2003 issu
Dissipative dynamics of quantum discord under quantum chaotic environment
We investigate the dissipative dynamics of quantum discord in a decoherence
model with two initially entangled qubits in addition to a quantum kicked top.
The two qubits are uncoupled during the period of our study and one of them
interacts with the quantum kicked top. We find that the long time behavior of
quantum discord could be well described by the fidelity decay of the quantum
kicked top; for short time behavior, however, the phase of the amplitude of the
fidelity decay is necessary to provide more specific information about the
system. We have made comparison between the quantum kicked top and multi-mode
oscillator system in describing environment, and also compared the dynamics of
the entanglement with that of quantum discord.Comment: 5 pages, 3 figures, and Accepted by Europhysics Letter
A New Biometric Template Protection using Random Orthonormal Projection and Fuzzy Commitment
Biometric template protection is one of most essential parts in putting a
biometric-based authentication system into practice. There have been many
researches proposing different solutions to secure biometric templates of
users. They can be categorized into two approaches: feature transformation and
biometric cryptosystem. However, no one single template protection approach can
satisfy all the requirements of a secure biometric-based authentication system.
In this work, we will propose a novel hybrid biometric template protection
which takes benefits of both approaches while preventing their limitations. The
experiments demonstrate that the performance of the system can be maintained
with the support of a new random orthonormal project technique, which reduces
the computational complexity while preserving the accuracy. Meanwhile, the
security of biometric templates is guaranteed by employing fuzzy commitment
protocol.Comment: 11 pages, 6 figures, accepted for IMCOM 201
The Addition Spectrum of a Lateral Dot from Coulomb and Spin Blockade Spectroscopy
Transport measurements are presented on a class of electrostatically defined
lateral dots within a high mobility two dimensional electron gas (2DEG). The
new design allows Coulomb Blockade(CB) measurements to be performed on a single
lateral dot containing 0, 1 to over 50 electrons. The CB measurements are
enhanced by the spin polarized injection from and into 2DEG magnetic edge
states. This combines the measurement of charge with the measurement of spin
through spin blockade spectroscopy. The results of Coulomb and spin blockade
spectroscopy for first 45 electrons enable us to construct the addition
spectrum of a lateral device. We also demonstrate that a lateral dot containing
a single electron is an effective local probe of a 2DEG edge.Comment: 4 pages, 4 figures submitted to Physical Review
Multi loop soliton solutions and their interactions in the Degasperis-Procesi equation
In this article, we construct loop soliton solutions and mixed soliton - loop
soliton solution for the Degasperis-Procesi equation. To explore these
solutions we adopt the procedure given by Matsuno. By appropriately modifying
the -function given in the above paper we derive these solutions. We
present the explicit form of one and two loop soliton solutions and mixed
soliton - loop soliton solutions and investigate the interaction between (i)
two loop soliton solutions in different parametric regimes and (ii) a loop
soliton with a conventional soliton in detail.Comment: Published in Physica Scripta (2012
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