8,433 research outputs found
Effects of S-wave thresholds
The opening of a new S-wave threshold is frequently accompanied by an abrupt
dip in the magnitude of an amplitude for an already-open channel. One familiar
example is the behavior of the I=0 S-wave scattering amplitude at threshold. Numerous other examples of this phenomenon in recent data
are noted, and a unified description of the underlying dynamics is sought.Comment: 17 pages, 2 figures. Two additional references; typographic
correction. To be published in Phys. Rev.
Measurement of the 187Re({\alpha},n)190Ir reaction cross section at sub-Coulomb energies using the Cologne Clover Counting Setup
Uncertainties in adopted models of particle+nucleus optical-model potentials
directly influence the accuracy in the theoretical predictions of reaction
rates as they are needed for reaction-network calculations in, for instance,
{\gamma}-process nucleosynthesis. The improvement of the {\alpha}+nucleus
optical-model potential is hampered by the lack of experimental data at
astrophysically relevant energies especially for heavier nuclei. Measuring the
Re187({\alpha},n)Ir190 reaction cross section at sub-Coulomb energies extends
the scarce experimental data available in this mass region and helps
understanding the energy dependence of the imaginary part of the
{\alpha}+nucleus optical-model potential at low energies. Applying the
activation method, after the irradiation of natural rhenium targets with
{\alpha}-particle energies of 12.4 to 14.1 MeV, the reaction yield and thus the
reaction cross section were determined via {\gamma}-ray spectroscopy by using
the Cologne Clover Counting Setup and the method of {\gamma}{\gamma}
coincidences. Cross-section values at five energies close to the
astrophysically relevant energy region were measured. Statistical model
calculations revealed discrepancies between the experimental values and
predictions based on widely used {\alpha}+nucleus optical-model potentials.
However, an excellent reproduction of the measured cross-section values could
be achieved from calculations based on the so-called Sauerwein-Rauscher
{\alpha}+nucleus optical-model potential. The results obtained indicate that
the energy dependence of the imaginary part of the {\alpha}+nucleus
optical-model potential can be described by an exponential decrease. Successful
reproductions of measured cross sections at low energies for {\alpha}-induced
reactions in the mass range 141{\leq}A{\leq}187 confirm the global character of
the Sauerwein-Rauscher potential
Aging in One-Dimensional Coagulation-Diffusion Processes and the Fredrickson-Andersen Model
We analyse the aging dynamics of the one-dimensional Fredrickson-Andersen
(FA) model in the nonequilibrium regime following a low temperature quench.
Relaxation then effectively proceeds via diffusion limited pair coagulation
(DLPC) of mobility excitations. By employing a familiar stochastic similarity
transformation, we map exact results from the free fermion case of diffusion
limited pair annihilation to DLPC. Crucially, we are able to adapt the mapping
technique to averages involving multiple time quantities. This relies on
knowledge of the explicit form of the evolution operators involved. Exact
results are obtained for two-time correlation and response functions in the
free fermion DLPC process. The corresponding long-time scaling forms apply to a
wider class of DLPC processes, including the FA model. We are thus able to
exactly characterise the violations of the fluctuation-dissipation theorem
(FDT) in the aging regime of the FA model. We find nontrivial scaling forms for
the fluctuation-dissipation ratio (FDR) X = X(tw/t), but with a negative
asymptotic value X = -3*pi/(6*pi - 16) = -3.307. While this prevents a
thermodynamic interpretation in terms of an effective temperature, it is a
direct consequence of probing FDT with observables that couple to activated
dynamics. The existence of negative FDRs should therefore be a widespread
feature in non mean-field systems.Comment: 39 pages, 4 figure
Realistic Expanding Source Model for Invariant One-Particle Multiplicity Distributions and Two-Particle Correlations in Relativistic Heavy-Ion Collisions
We present a realistic expanding source model with nine parameters that are
necessary and sufficient to describe the main physics occuring during
hydrodynamical freezeout of the excited hadronic matter produced in
relativistic heavy-ion collisions. As a first test of the model, we compare it
to data from central Si + Au collisions at p_lab/A = 14.6 GeV/c measured in
experiment E-802 at the AGS. An overall chi-square per degree of freedom of
1.055 is achieved for a fit to 1416 data points involving invariant pi^+, pi^-,
K^+, and K^- one-particle multiplicity distributions and pi^+ and K^+
two-particle correlations. The 99-percent-confidence region of parameter space
is identified, leading to one-dimensional error estimates on the nine fitted
parameters and other calculated physical quantities. Three of the most
important results are the freezeout temperature, longitudinal proper time, and
baryon density along the symmetry axis. For these we find values of 92.9 +/-
4.4 MeV, 8.2 +/- 2.2 fm/c, and 0.0222 + 0.0096 / - 0.0069 fm^-3, respectively.Comment: 37 pages and 12 figures. RevTeX 3.0. Submitted to Physical Review C.
Complete preprint, including device-independent (dvi), PostScript, and LaTeX
versions of the text, plus PostScript files of all figures, are available at
http://t2.lanl.gov/publications/publications.html or at
ftp://t2.lanl.gov/publications/res
Resonance contributions to HBT correlation radii
We study the effect of resonance decays on intensity interferometry for heavy
ion collisions. Collective expansion of the source leads to a dependence of the
two-particle correlation function on the pair momentum K. This opens the
possibility to reconstruct the dynamics of the source from the K-dependence of
the measured HBT radii. Here we address the question to what extent resonance
decays can fake such a flow signal. Within a simple parametrization for the
emission function we present a comprehensive analysis of the interplay of flow
and resonance decays on the one- and two-particle spectra. We discuss in detail
the non-Gaussian features of the correlation function introduced by long-lived
resonances and the resulting problems in extracting meaningful HBT radii. We
propose to define them in terms of the second order q-moments of the correlator
C(q, K). We show that this yields a more reliable characterisation of the
correlator in terms of its width and the correlation strength `lambda' than
other commonly used fit procedures. The normalized fourth-order q-moments
(kurtosis) provide a quantitative measure for the non-Gaussian features of the
correlator. At least for the class of models studied here, the kurtosis helps
separating effects from expansion flow and resonance decays, and provides the
cleanest signal to distinguish between scenarios with and without transverse
flow.Comment: 23 pages, twocolumn RevTeX, 12 eps-figures included, minor changes
following referee comment
Iterated maps for clarinet-like systems
The dynamical equations of clarinet-like systems are known to be reducible to
a non-linear iterated map within reasonable approximations. This leads to time
oscillations that are represented by square signals, analogous to the Raman
regime for string instruments. In this article, we study in more detail the
properties of the corresponding non-linear iterations, with emphasis on the
geometrical constructions that can be used to classify the various solutions
(for instance with or without reed beating) as well as on the periodicity
windows that occur within the chaotic region. In particular, we find a regime
where period tripling occurs and examine the conditions for intermittency. We
also show that, while the direct observation of the iteration function does not
reveal much on the oscillation regime of the instrument, the graph of the high
order iterates directly gives visible information on the oscillation regime
(characterization of the number of period doubligs, chaotic behaviour, etc.)
Status and Plans for the Array Control and Data Acquisition System of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the next-generation atmospheric
Cherenkov gamma-ray observatory. CTA will consist of two installations, one in
the northern, and the other in the southern hemisphere, containing tens of
telescopes of different sizes. The CTA performance requirements and the
inherent complexity associated with the operation, control and monitoring of
such a large distributed multi-telescope array leads to new challenges in the
field of the gamma-ray astronomy. The ACTL (array control and data acquisition)
system will consist of the hardware and software that is necessary to control
and monitor the CTA arrays, as well as to time-stamp, read-out, filter and
store -at aggregated rates of few GB/s- the scientific data. The ACTL system
must be flexible enough to permit the simultaneous automatic operation of
multiple sub-arrays of telescopes with a minimum personnel effort on site. One
of the challenges of the system is to provide a reliable integration of the
control of a large and heterogeneous set of devices. Moreover, the system is
required to be ready to adapt the observation schedule, on timescales of a few
tens of seconds, to account for changing environmental conditions or to
prioritize incoming scientific alerts from time-critical transient phenomena
such as gamma ray bursts. This contribution provides a summary of the main
design choices and plans for building the ACTL system.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Sterile inflammation as a factor in human male infertility: Involvement of Toll like receptor 2, biglycan and peritubular cells
Changes in the wall of seminiferous tubules in men with impaired spermatogenesis imply sterile inflammation of the testis. We tested the hypothesis that the cells forming the wall of seminiferous tubules, human testicular peritubular cells (HTPCs), orchestrate inflammatory events and that Toll like receptors (TLRs) and danger signals from the extracellular matrix (ECM) of this wall are involved. In cultured HTPCs we detected TLRs, including TLR2. A TLR-2 ligand (PAM) augmented interleukin 6 (IL-6), monocyte chemo-attractant protein-1 (MCP-1) and pentraxin 3 (PTX3) in HTPCs. The ECM-derived proteoglycan biglycan (BGN) is secreted by HTPCs and may be a TLR2-ligand at HTPCs. In support, recombinant human BGN increased PTX3, MCP-1 and IL-6 in HTPCs. Variable endogenous BGN levels in HTPCs derived from different men and differences in BGN levels in the tubular wall in infertile men were observed. In testes of a systemic mouse model for male infertility, testicular sterile inflammation and elevated estradiol (E2) levels, BGN was also elevated. Hence we studied the role of E2 in HTPCs and observed that E2 elevated the levels of BGN. The anti-estrogen ICI 182,780 blocked this action. We conclude that TLR2 and BGN contribute to sterile inflammation and infertility in man
Sterile inflammation as a factor in human male infertility: Involvement of Toll like receptor 2, biglycan and peritubular cells
Changes in the wall of seminiferous tubules in men with impaired spermatogenesis imply sterile inflammation of the testis. We tested the hypothesis that the cells forming the wall of seminiferous tubules, human testicular peritubular cells (HTPCs), orchestrate inflammatory events and that Toll like receptors (TLRs) and danger signals from the extracellular matrix (ECM) of this wall are involved. In cultured HTPCs we detected TLRs, including TLR2. A TLR-2 ligand (PAM) augmented interleukin 6 (IL-6), monocyte chemo-attractant protein-1 (MCP-1) and pentraxin 3 (PTX3) in HTPCs. The ECM-derived proteoglycan biglycan (BGN) is secreted by HTPCs and may be a TLR2-ligand at HTPCs. In support, recombinant human BGN increased PTX3, MCP-1 and IL-6 in HTPCs. Variable endogenous BGN levels in HTPCs derived from different men and differences in BGN levels in the tubular wall in infertile men were observed. In testes of a systemic mouse model for male infertility, testicular sterile inflammation and elevated estradiol (E2) levels, BGN was also elevated. Hence we studied the role of E2 in HTPCs and observed that E2 elevated the levels of BGN. The anti-estrogen ICI 182,780 blocked this action. We conclude that TLR2 and BGN contribute to sterile inflammation and infertility in man
On the definition of a unique effective temperature for non-equilibrium critical systems
We consider the problem of the definition of an effective temperature via the
long-time limit of the fluctuation-dissipation ratio (FDR) after a quench from
the disordered state to the critical point of an O(N) model with dissipative
dynamics. The scaling forms of the response and correlation functions of a
generic observable are derived from the solutions of the corresponding
Renormalization Group equations. We show that within the Gaussian approximation
all the local observables have the same FDR, allowing for a definition of a
unique effective temperature. This is no longer the case when fluctuations are
taken into account beyond that approximation, as shown by a computation up to
the first order in the epsilon-expansion for two quadratic observables. This
implies that, contrarily to what often conjectured, a unique effective
temperature can not be defined for this class of models.Comment: 32 pages, 5 figures. Minor changes, published versio
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