45,899 research outputs found
Integrability of the critical point of the Kagom\'e three-state Potts mode
The vicinity of the critical point of the three-state Potts model on a
Kagom\'e lattice is studied by mean of Random Matrix Theory. Strong evidence
that the critical point is integrable is given.Comment: 1 LaTex file + 3 eps files 7 page
Lateral vibration effects in atomic-scale friction
The influence of lateral vibrations on the stick-slip motion of a nanotip
elastically pulled on a flat crystal surface is studied by atomic force
microscopy (AFM) measurements on a NaCl(001) surface in ultra-high vacuum. The
slippage of the nanotip across the crystal lattice is anticipated at increasing
driving amplitude, similarly to what is observed in presence of normal
vibrations. This lowers the average friction force, as explained by the
Prandtl-Tomlinson model with lateral vibrations superimposed at finite
temperature. Nevertheless, the peak values of the lateral force, and the total
energy losses, are expected to increase with the excitation amplitude, which
may limit the practical relevance of this effect.Comment: To appear in Applied Physics Letter
Classes of generalized functions with finite type regularities
We introduce and analyze spaces and algebras of generalized functions which correspond to Hölder, Zygmund, and Sobolev spaces of functions. The main scope of the paper is the characterization of the regularity of distributions that are embedded into the corresponding space or algebra of generalized functions with finite type regularities
Numerical study of critical properties and hidden orders in dimerized spin ladders
Dimerized antiferromagnetic spin-1/2 ladders are known to exhibit a quantum
critical phase transition in the ground state, the existence or absence of
which is dependent on the dimerization pattern of the ladder. The gapped phases
cannot be distinguished by the conventional Landau long-range order parameter.
However, they possess a non-local (hidden) string order parameter, which is
non-zero in one phase and vanishes in the other. We use an exact
diagonalization technique to calculate ground state energies, energy gaps and
string order parameters of dimerized two- and three-leg Heisenberg ladders, as
well as a critical scaling analysis to yield estimates of the critical
exponents nu and beta.Comment: 7 pages, 14 figures. V.2: Extended version to appear in PR
Covariant Affine Integral Quantization(s)
Covariant affine integral quantization of the half-plane is studied and
applied to the motion of a particle on the half-line. We examine the
consequences of different quantizer operators built from weight functions on
the half-plane. To illustrate the procedure, we examine two particular choices
of the weight function, yielding thermal density operators and affine inversion
respectively. The former gives rise to a temperature-dependent probability
distribution on the half-plane whereas the later yields the usual canonical
quantization and a quasi-probability distribution (affine Wigner function)
which is real, marginal in both momentum p and position q.Comment: 36 pages, 10 figure
Outbursts from IGR J17473-2721
We have investigated the outbursts of IGR J17473-2721. We analyzed all
available observations carried out by RXTE on IGR J17473-2721 during its later
outburst and as well all the available SWIFT/BAT data. The flux of the latter
outburst rose in ~ one month and then kept roughly constant for the following ~
two months. During this time period, the source was in a low/hard state. The
source moved to a high/soft state within the following three days, accompanied
by the occurrence of an additional outburst at soft X-rays and the end of the
preceding outburst in hard X-rays. During the decay of this soft outburst, the
source went back to a low/hard state within 6 days, with a luminosity 4 times
lower than the first transition. This shows a full cycle of the hysteresis in
transition between the hard and the soft states. The fact that the flux
remained roughly constant for ~ two months at times prior to the spectral
transition to a high/soft state might be regarded as the result of balancing
the evaporation of the inner disk and the inward accretion flow, in a model in
which the state transition is determined by the mass flow rate. Such a balance
might be broken via an additional mass flow accreting onto the inner disk,
which lightens the extra soft outburst and causes the state transition.
However, the possibility of an origin of the emission from the jet during this
time period cannot be excluded. The spectral analysis suggests an inclined XRB
system for IGR J17473-2721. Such a long-lived preceding low/hard state makes
IGR J17473-2721 resemble the behavior of outbursts seen in black hole X-ray
binaries like GX 339-4.Comment: A&A in pres
Radially Polarized, Half-Cycle, Attosecond Pulses from Laser Wakefields through Coherent Synchrotron Radiation
Attosecond bursts of coherent synchrotron-like radiation are found when
driving ultrathin relativistic electron disks in a quasi-one-dimensional regime
of wakefield acceleration, in which the laser waist is larger than the wake
wavelength. The disks of overcritical density shrink radially due to the
focusing wake fields, thus providing the transverse currents for the emission
of an intense, radially polarized, half-cycle pulse of about 100 attoseconds in
duration. The electromagnetic pulse first focuses to a peak intensity 10 times
larger () than the driving pulse and then emerges as
a conical beam. Saturation of the emission amplitudes is derived analytically
and in agreement with particle-in-cell simulation. By making use of gas targets
instead of solids to form the ultrathin disks, the new scheme allows for high
repetition rate required for applications.Comment: 5 pages, 4 figure
Giant half-cycle attosecond pulses
Half-cycle picosecond pulses have been produced from thin photo-conductors,
when applying an electric field across the surface and switching on conduction
by a short laser pulse. Then the transverse current in the wafer plane emits
half-cycle pulses in normal direction, and pulses of 500 fs duration and 1e6
V/m peak electric field have been observed. Here we show that single half-cycle
pulses of 50 as duration and up to 1e13 V/m can be produced when irradiating a
double foil target by intense few-cycle laser pulses. Focused onto an
ultra-thin foil, all electrons are blown out, forming a uniform sheet of
relativistic electrons. A second layer, placed at some distance behind,
reflects the drive beam, but lets electrons pass straight. Under oblique
incidence, beam reflection provides the transverse current, which emits intense
half-cycle pulses. Such a pulse may completely ionize even heavier atoms. New
types of attosecond pump-probe experiments will become possible.Comment: 5 pages, 4 figures, to be presented at LEI2011-Light at Extreme
Intensities and China-Germany Symposium on Laser Acceleratio
Polarization phenomena in the reaction NN to NNpi near threshold
First calculations for spin-dependent observables of the reactions , and near threshold are presented,
employing the J\"ulich model for pion production. The influence of resonant
(via the excitation of the ) and non-resonant p-wave pion
production mechanisms on these observables is examined. For the reactions and nice agreement of our predictions with the
presently available data on spin correlation coefficents is observed whereas
for the description of the data is less satisfying.Comment: 10 pages, 4 figure
An accretion model for the growth of the central black hole associated with ionization instability in quasars
A possible accretion model associated with the ionization instability of
quasar disks is proposed to address the growth of the central black hole
harbored in the host galaxy.The mass ratio between black hole and its host
galactic bulge is a nature consequence of our model.Comment: submitted to ApJ, 15 page
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