1,146 research outputs found
Elastic Meson-Nucleon and Nucleon-Nucleon Scattering: Models vs. All Available Data
We consider simple-pole descriptions of soft elastic scattering at small
and , and allow for the presence of a hard pomeron. We have built and
analyzed an exhaustive dataset and we show that simple poles provide an
excellent description of the data in the region GeV
GeV, 6 GeV63 GeV. We show that new form factors have to be
used, and get information on the trajectories of the soft and hard pomerons.Comment: Contribution to the proceedings of the XIth International Conference
on Elastic and Diffractive Scattering, Chateau de Blois, France, May 15 - 20,
2005. Needs Blois.sty (provided
Temperature - pressure phase diagram of CeCoSi: Pressure induced high-temperature phase
We have studied the temperature-pressure phase diagram of CeCoSi by
electrical-resistivity experiments under pressure. Our measurements revealed a
very unusual phase diagram. While at low pressures no dramatic changes and only
a slight shift of the Ne\'{e}l temperature ( K) are observed,
at about 1.45 GPa a sharp and large anomaly, indicative of the opening of a
spin-density-wave (SDW) gap, appears at a comparatively high temperature K. With further increasing pressure shifts rapidly to low
temperatures and disappears at about 2.15 GPa, likely continuously in a quantum
critical point, but without evidence for superconductivity. Even more
surprisingly, we observed a clear shift of to higher temperatures upon
applying a magnetic field. We discuss two possible origins for , either
magnetic ordering of Co or a meta-orbital type of transition of Ce.Comment: 6 pages, 5 figure
Hard pomeron contribution to forward elastic scattering
The introduction of a hard singularity in fits to total cross sections and to
the ratio of real to imaginary parts enables to reproduce perfectly the data
for sqrt(s)< 100 GeV using only simple-pole parametrisations, both for the soft
and for the hard pomerons.Comment: Contribution to the proceedings of the XIth International Conference
on Elastic and Diffractive Scattering, Chateau de Blois, France, May 15 - 20,
2005. Needs Blois.sty (provided
Turing Instability in a Boundary-fed System
The formation of localized structures in the chlorine dioxide-idodine-malonic
acid (CDIMA) reaction-diffusion system is investigated numerically using a
realistic model of this system. We analyze the one-dimensional patterns formed
along the gradients imposed by boundary feeds, and study their linear stability
to symmetry-breaking perturbations (Turing instability) in the plane transverse
to these gradients. We establish that an often-invoked simple local linear
analysis which neglects longitudinal diffusion is inappropriate for predicting
the linear stability of these patterns. Using a fully nonuniform analysis, we
investigate the structure of the patterns formed along the gradients and their
stability to transverse Turing pattern formation as a function of the values of
two control parameters: the malonic acid feed concentration and the size of the
reactor in the dimension along the gradients. The results from this
investigation are compared with existing experiments.Comment: 41 pages, 18 figures, to be published in Physical Review
Avoided ferromagnetic quantum critical point in CeRuPO
CeRuPO is a rare example of a ferromagnetic (FM) Kondo-lattice system.
External pressure suppresses the ordering temperature to zero at about
GPa. Our ac-susceptibility and electrical-resistivity
investigations evidence that the type of magnetic ordering changes from FM to
antiferromagnetic (AFM) at about GPa. Studies in applied
magnetic fields suggest that ferromagnetic and antiferromagnetic correlations
compete for the ground state at , but finally the AFM correlations win.
The change in the magnetic ground-state properties is closely related to the
pressure evolution of the crystalline-electric-field level (CEF) scheme and the
magnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. The
N\'{e}el temperature disappears abruptly in a first-order-like fashion at
, hinting at the absence of a quantum critical point. This is consistent
with the low-temperature transport properties exhibiting Landau-Fermi-liquid
(LFL) behavior in the whole investigated pressure range up to 7.5 GPa.Comment: 12 figure
Effect of Co doping and hydrostatic pressure on SrFe2As2
We report a pressure study on electron doped SrFeCoAs by
electrical-resistivity () and magnetic-susceptibility ()
experiments. Application of either external pressure or Co substitution rapidly
suppresses the spin-density wave ordering of the Fe moments and induces
superconductivity in SrFeAs. At the broad superconducting (SC)
dome in the phase diagram exhibits its maximum K at
a pressure of only GPa. In
SrFeCoAs no superconductivity is observed anymore up to 2.8
GPa. Upon increasing the Co concentration the maximum of the SC dome shifts
toward lower pressure accompanied by a decrease in the value of . Even though, superconductivity is induced by both tuning methods, Co
substitution leads to a much more robust SC state. Our study evidences that in
SrFeCoAs both, the effect of pressure and Co-substitution, have
to be considered in order to understand the SC phase-diagram and further
attests the close relationship of SrFeAs and its sister compound
BaFeAs.Comment: 6 pages, 6 figure
Direct extraction of hadronic form factors from elastic-scattering data
Non-forward elastic hadron-scattering data are collected and analysed within
the Regge approach. Through an analysis of the data in small bins in , we
have directly extracted the pomeron trajectory and the hadronic form factors
(or reggeon couplings). We found higher values than usually used for the
intercept and for the slope of the soft pomeron trajectory. The presence of
zeros in for the effective hadronic form factors is emphasised.Comment: 4 pages, 5 figures, talk given at Diffraction 2004, Cala Gonone,
Sardinia, Italy, 18-23 September 200
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