14,622 research outputs found
The Pairwise Peculiar Velocity Dispersion of Galaxies: Effects of the Infall
We study the reliability of the reconstruction method which uses a modelling
of the redshift distortions of the two-point correlation function to estimate
the pairwise peculiar velocity dispersion of galaxies. In particular, the
dependence of this quantity on different models for the infall velocity is
examined for the Las Campanas Redshift Survey. We make extensive use of
numerical simulations and of mock catalogs derived from them to discuss the
effect of a self-similar infall model, of zero infall, and of the real infall
taken from the simulation. The implications for two recent discrepant
determinations of the pairwise velocity dispersion for this survey are
discussed.Comment: minor changes in the discussion; accepted for publication in ApJ; 8
pages with 2 figures include
Scaling properties of the redshift power spectrum: theoretical models
We report the results of an analysis of the redshift power spectrum
in three typical Cold Dark Matter (CDM) cosmological models, where
is the cosine of the angle between the wave vector and the line-of-sight.
Two distinct biased tracers derived from the primordial density peaks of
Bardeen et al. and the cluster-underweight model of Jing, Mo, & B\"orner are
considered in addition to the pure dark matter models. Based on a large set of
high resolution simulations, we have measured the redshift power spectrum for
the three tracers from the linear to the nonlinear regime. We investigate the
validity of the relation - guessed from linear theory - in the nonlinear regime
where
is the real space power spectrum, and equals . The
damping function which should generally depend on , , and
, is found to be a function of only one variable
. This scaling behavior extends into the nonlinear regime,
while can be accurately expressed as a Lorentz function - well known from
linear theory - for values . The difference between
and the pairwise velocity dispersion defined by the 3-D peculiar velocity of
the simulations (taking ) is about 15%. Therefore is a
good indicator of the pairwise velocity dispersion. The exact functional form
of depends on the cosmological model and on the bias scheme. We have given
an accurate fitting formula for the functional form of for the models
studied.Comment: accepted for publication in ApJ;24 pages with 7 figures include
Spin-charge-lattice coupling near the metal-insulator transition in Ca3Ru2O7
We report x-ray scattering studies of the c-axis lattice parameter in
Ca3Ru2O7 as a function of temperature and magnetic field. These structural
studies complement published transport and magnetization data, and therefore
elucidate the spin-charge-lattice coupling near the metal-insulator transition.
Strong anisotropy of the structural change for field applied along orthogonal
in-plane directions is observed. Competition between a spin-polarized phase
that does not couple to the lattice, and an antiferromagnetic metallic phase,
which does, gives rise to rich behavior for B b.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Mesoscopic colonization of a spectral band
We consider the unitary matrix model in the limit where the size of the
matrices become infinite and in the critical situation when a new spectral band
is about to emerge. In previous works the number of expected eigenvalues in a
neighborhood of the band was fixed and finite, a situation that was termed
"birth of a cut" or "first colonization". We now consider the transitional
regime where this microscopic population in the new band grows without bounds
but at a slower rate than the size of the matrix. The local population in the
new band organizes in a "mesoscopic" regime, in between the macroscopic
behavior of the full system and the previously studied microscopic one. The
mesoscopic colony may form a finite number of new bands, with a maximum number
dictated by the degree of criticality of the original potential. We describe
the delicate scaling limit that realizes/controls the mesoscopic colony. The
method we use is the steepest descent analysis of the Riemann-Hilbert problem
that is satisfied by the associated orthogonal polynomials.Comment: 17 pages, 2 figures, minor corrections and addition
Novel pH control strategy for glutathione overproduction in batch cultivation of Candida utilis
The effects of pH values on cell growth and glutathione (GSH) production were studied in batch cultivation of Candida utilis. According to the fact that lower pH value favors cells growth but retards GSH production and higher pH value promotes GSH production while inhibits cells growth, a pH-shift strategy, optimized via simulating Gauss function, was developed. By applying two-stage pH-shift strategy of controlling pH at 5.0 for first 7.5 h and switching to 6.0 afterwards, final GSH yield and productivity reached 279 and 12.7 mg/l/h after 22 h cultivation, increased by 30 and 42%, respectively,compared to constant pH 5.5 operation. Moreover, by feeding glucose instead of sulphuric acid (H2SO4) solution to control pH, maximal GSH yield of 315 mg/l was achieved, suggesting application of pH-shift strategy for GSH overproduction as being feasible
Data taking strategy for the phase study in
The study of the relative phase between strong and electromagnetic amplitudes
is of great importance for understanding the dynamics of charmonium decays. The
information of the phase can be obtained model-independently by fitting the
scan data of some special decay channels, one of which is . To find out the optimal data taking strategy for a scan experiment
in the measurement of the phase in , the
minimization process is analyzed from a theoretical point of view. The result
indicates that for one parameter fit, only one data taking point in the
vicinity of a resonance peak is sufficient to acquire the optimal precision.
Numerical results are obtained by fitting simulated scan data. Besides the
results related to the relative phase between strong and electromagnetic
amplitudes, the method is extended to analyze the fits of other resonant
parameters, such as the mass and the total decay width of .Comment: 13 pages, 7 figure
20 K superconductivity in heavily electron doped surface layer of FeSe bulk crystal
A superconducting transition temperature Tc as high as 100 K was recently
discovered in 1 monolayer (1ML) FeSe grown on SrTiO3 (STO). The discovery
immediately ignited efforts to identify the mechanism for the dramatically
enhanced Tc from its bulk value of 7 K. Currently, there are two main views on
the origin of the enhanced Tc; in the first view, the enhancement comes from an
interfacial effect while in the other it is from excess electrons with strong
correlation strength. The issue is controversial and there are evidences that
support each view. Finding the origin of the Tc enhancement could be the key to
achieving even higher Tc and to identifying the microscopic mechanism for the
superconductivity in iron-based materials. Here, we report the observation of
20 K superconductivity in the electron doped surface layer of FeSe. The
electronic state of the surface layer possesses all the key spectroscopic
aspects of the 1ML FeSe on STO. Without any interface effect, the surface layer
state is found to have a moderate Tc of 20 K with a smaller gap opening of 4
meV. Our results clearly show that excess electrons with strong correlation
strength alone cannot induce the maximum Tc, which in turn strongly suggests
need for an interfacial effect to reach the enhanced Tc found in 1ML FeSe/STO.Comment: 5 pages, 4 figure
The finite size effect of galaxies on the cosmic virial theorem and the pairwise peculiar velocity dispersions
We discuss the effect of the finite size of galaxies on estimating
small-scale relative pairwise peculiar velocity dispersions from the cosmic
virial theorem (CVT). Specifically we evaluate the effect by incorporating the
finite core radius in the two-point correlation function of mass, i.e.
and the effective gravitational force
softening on small scales. We analytically obtain the lowest-order
correction term for which is in quantitative agreement with the
full numerical evaluation. With a nonzero and/or the cosmic virial
theorem is no longer limited to the case of . We present accurate
fitting formulae for the CVT predicted pairwise velocity dispersion for the
case of . Compared with the idealistic point-mass approximation
(), the finite size effect can significantly reduce the small-scale
velocity dispersions of galaxies at scales much larger than and .
Even without considering the finite size of galaxies, nonzero values for
are generally expected, for instance, for cold dark matter (CDM) models with a
scale-invariant primordial spectrum. For these CDM models, a reasonable force
softening r_s\le 100 \hikpc would have rather tiny effect. We present the CVT
predictions for the small-scale pairwise velocity dispersion in the CDM models
normalized by the COBE observation. The implication of our results for
confrontation of observations of galaxy pair-wise velocity dispersions and
theoretical predictions of the CVT is also discussed.Comment: 18 pages. LaTeX text and 8 postcript figures. submitted to Ap
Stealthy Deception Attacks Against SCADA Systems
SCADA protocols for Industrial Control Systems (ICS) are vulnerable to
network attacks such as session hijacking. Hence, research focuses on network
anomaly detection based on meta--data (message sizes, timing, command
sequence), or on the state values of the physical process. In this work we
present a class of semantic network-based attacks against SCADA systems that
are undetectable by the above mentioned anomaly detection. After hijacking the
communication channels between the Human Machine Interface (HMI) and
Programmable Logic Controllers (PLCs), our attacks cause the HMI to present a
fake view of the industrial process, deceiving the human operator into taking
manual actions. Our most advanced attack also manipulates the messages
generated by the operator's actions, reversing their semantic meaning while
causing the HMI to present a view that is consistent with the attempted human
actions. The attacks are totaly stealthy because the message sizes and timing,
the command sequences, and the data values of the ICS's state all remain
legitimate.
We implemented and tested several attack scenarios in the test lab of our
local electric company, against a real HMI and real PLCs, separated by a
commercial-grade firewall. We developed a real-time security assessment tool,
that can simultaneously manipulate the communication to multiple PLCs and cause
the HMI to display a coherent system--wide fake view. Our tool is configured
with message-manipulating rules written in an ICS Attack Markup Language (IAML)
we designed, which may be of independent interest. Our semantic attacks all
successfully fooled the operator and brought the system to states of blackout
and possible equipment damage
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