69 research outputs found
Magnetocaloric effect and magnetic cooling near a field-induced quantum-critical point
The presence of a quantum critical point (QCP) can significantly affect the
thermodynamic properties of a material at finite temperatures T. This is
reflected, e.g., in the entropy landscape S(T, r) in the vicinity of a QCP,
yielding particularly strong variations for varying the tuning parameter r such
as pressure or magnetic field B. Here we report on the determination of the
critical enhancement of near a B-induced QCP via
absolute measurements of the magnetocaloric effect (MCE), , and demonstrate that the accumulation of entropy around the QCP can be
used for efficient low-temperature magnetic cooling. Our proof of principle is
based on measurements and theoretical calculations of the MCE and the cooling
performance for a Cu-containing coordination polymer, which is a very
good realization of a spin-1/2 antiferromagnetic Heisenberg chain - one of the
simplest quantum-critical systems.Comment: 21 pages, 4 figure
Centrality and dE_{T}/d\etadN_{ch}/d\eta$ in Heavy Ion Collisions at Mid-Rapidity
The PHENIX experiment at RHIC has measured transverse energy and charged
particle multiplicity at mid-rapidity in Au + Au collisions at
= 19.6, 130, 62.4 and 200 GeV as a function of centrality. The presented
results are compared to measurements from other RHIC experiments, and
experiments at lower energies. The dependence of
and per pair of participants is consistent with logarithmic
scaling for the most central events. The centrality dependence of
and is similar at all measured incident
energies. At RHIC energies the ratio of transverse energy per charged particle
was found independent of centrality and growing slowly with . A
survey of comparisons between the data and available theoretical models is also
presented.Comment: Proccedings of the Workshop: Focus on Multiplcity at Bari, Italy,
June 17-19,2004. To be submitted to the Jornal of Physics, "Conference
series". Includes: 20 Pages, 15 figures, 3 Tables, 80 Referencie
A new kaonic helium measurement in gas by SIDDHARTINO at the DAFNE collider*
The SIDDHARTINO experiment at the DA{\Phi}NE Collider of INFN-LNF, the pilot
run for the SIDDHARTA-2 experiment which aims to perform the measurement of
kaonic deuterium transitions to the fundamental level, has successfully been
concluded. The paper reports the main results of this run, including the
optimization of various components of the apparatus, among which the degrader
needed to maximize the fraction of kaons stopped inside the target, through
measurements of kaonic helium transitions to the 2p level. The obtained shift
and width values are {\epsilon}_2p = E_exp-E_e.m = 0.2 {\pm} 2.5(stat) {\pm}
2(syst) eV and {\Gamma}_2p = 8 {\pm} 10 eV (stat), respectively. This new
measurement of the shift, in particular, represents the most precise one for a
gaseous target and is expected to contribute to a better understanding of the
kaon-nuclei interaction at low energy
Overlapping political budget cycles in the legislative and the executive
We advance the literature on political budget cycles by testing separately for cycles in expenditures for elections in the legislative and the executive. Using municipal data, we can separately identify these cycles and account for general year effects. For the executive branch, we show that it is important whether the incumbent re-runs. To account for the potential endogeneity associated with this decision, we apply a unique instrumental variables approach based on age and pension eligibility rules. We find sizable and significant effects in expenditures before council elections and before joint elections when the incumbent re-runs
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