2,596 research outputs found
Tachyonic preheating using 2PI-1/N dynamics and the classical approximation
We study the process of tachyonic preheating using approximative quantum
equations of motion derived from the 2PI effective action. The O(N) scalar
(Higgs) field is assumed to experience a fast quench which is represented by an
instantaneous flip of the sign of the mass parameter. The equations of motion
are solved numerically on the lattice, and the Hartree and 1/N-NLO
approximations are compared to the classical approximation. Classical dynamics
is expected to be valid, since the occupation numbers can rise to large values
during tachyonic preheating. We find that the classical approximation performs
excellently at short and intermediate times, even for couplings in the larger
region currently allowed for the SM Higgs. This is reassuring, since all
previous numerical studies of tachyonic preheating and baryogenesis during
tachyonic preheating have used classical dynamics. We also compare different
initializations for the classical simulations.Comment: 32 pages, 21 figures. Published version: Some details added, section
added, references added, conclusions unchange
Employment Expectations and Gross Flows by Type of Work Contract
There is growing interest in understanding firms’ temporary and permanent employment practices and how institutional changes shape them. Using data on Spanish establishments, we examine: (a) how employers adjust temporary and permanent job and worker flows to prior employment expectations, and (b) how the 1994 and 1997 labour reforms promoting permanent employment affected establishments’ employment practices. Generally, establishments’ prior employment expectations are realized through changes in all job and worker flows. However, establishments uniquely rely on temporary hires as a buffer to confront diminishing long-run employment expectations. None of the reforms significantly affected establishments’ net temporary or permanent employment flows.http://deepblue.lib.umich.edu/bitstream/2027.42/40032/3/wp646.pd
Systemic Effects Induced by Hyperoxia in a Preclinical Model of Intra-abdominal Sepsis
Supplemental oxygen is a supportive treatment in patients with sepsis to balance tissue oxygen delivery and demand in the tissues. However, hyperoxia may induce some pathological effects. We sought to assess organ damage associated with hyperoxia and its correlation with the production of reactive oxygen species (ROS) in a preclinical model of intra-abdominal sepsis. For this purpose, sepsis was induced in male, Sprague-Dawley rats by cecal ligation and puncture (CLP). We randomly assigned experimental animals to three groups: control (healthy animals), septic (CLP), and sham-septic (surgical intervention without CLP). At 18 h after CLP, septic (n = 39), sham-septic (n = 16), and healthy (n = 24) animals were placed within a sealed Plexiglas cage and randomly distributed into four groups for continuous treatment with 21%, 40%, 60%, or 100% oxygen for 24 h. At the end of the experimental period, we evaluated serum levels of cytokines, organ damage biomarkers, histological examination of brain and lung tissue, and ROS production in each surviving animal. We found that high oxygen concentrations increased IL-6 and biomarkers of organ damage levels in septic animals, although no relevant histopathological lung or brain damage was observed. Healthy rats had an increase in IL-6 and aspartate aminotransferase at high oxygen concentration. IL-6 levels, but not ROS levels, are correlated with markers of organ damage. In our study, the use of high oxygen concentrations in a clinically relevant model of intra-abdominal sepsis was associated with enhanced inflammation and organ damage. These findings were unrelated to ROS release into circulation. Hyperoxia could exacerbate sepsis-induced inflammation, and it could be by itself detrimental. Our study highlights the need of developing safer thresholds for oxygen therapy
The generating function for a particular class of characters of SU(n)
We compute the generating function for the characters of the irreducible
representations of SU(n) whose associated Young diagrams have only two rows
with the same number of boxes. The result is a rational determinantal
expression in which both the numerator and the denominator have a simple
structure when expressed in terms of Schur polynomials.Comment: 7 pages, no figure
Causal symmetries
Based on the recent work \cite{PII} we put forward a new type of
transformation for Lorentzian manifolds characterized by mapping every causal
future-directed vector onto a causal future-directed vector. The set of all
such transformations, which we call causal symmetries, has the structure of a
submonoid which contains as its maximal subgroup the set of conformal
transformations. We find the necessary and sufficient conditions for a vector
field \xiv to be the infinitesimal generator of a one-parameter submonoid of
pure causal symmetries. We speculate about possible applications to gravitation
theory by means of some relevant examples.Comment: LaTeX2e file with CQG templates. 8 pages and no figures. Submitted to
Classical and Quantum gravit
Increasing Competitiveness through the Implementation of Lean Management in Healthcare
The main aim of this paper was two-fold: first, to design a participative methodology that facilitates lean management implementation in healthcare by adopting the action research approach; second, to illustrate the usefulness of this methodology by applying it to the sleep unit of a public hospital in Spain. This methodology proposes the implementation of lean management in its broadest sense: adopting both lean principles and some of its practical tools or practices in order to achieve competitive advantage. The complete service value chain was considered when introducing changes through lean management implementation. This implementation involved training and involving staff in the project (personnel pillar), detecting and analysing "waste" in value chain processes (processes pillar) and establishing control and measurement mechanisms in line with objectives (key performance indicators pillar) and putting in place improvement actions to achieve these objectives. The application of this methodology brought about an improvement in the management of patient flow in terms of effectiveness, efficiency and quality but also an internal transformation towards lean culture
Spin dynamics for bosons in an optical lattice
We study the internal dynamics of bosonic atoms in an optical lattice. Within
the regime in which the atomic crystal is a Mott insulator with one atom per
well, the atoms behave as localized spins which interact according to some spin
Hamiltonian. The type of Hamiltonian (Heisenberg, Ising), and the sign of
interactions may be tuned by changing the properties of the optical lattice, or
applying external magnetic fields. When, on the other hand, the number of atoms
per lattice site is unknown, we can still use the bosons to perform general
quantum computation
STUDY OF THE O-18+Ni-64 TWO-NEUTRON TRANSFER REACTION AT 84 MeV BY MAGNEX
A study of the two-neutron transfer reaction of the O-18 + Ni-64 system at 84 MeV incident energy to the ground and first 2(+) excited state of the residual Ni-66 nucleus is presented. The experiment was performed at the INFN-LNS (Italy) by using the large acceptance MAGNEX spectrometer. Theoretical models are used in order to disentangle the competition between long-range and short-range correlations
Influence of Gas Pressure and Blowing Agent Content on the Formation of Aluminum Alloy Foam
Apart from density and alloy composition, the structure of solid metallic foams determines their mechanical performance. Herein, the effect of ambient pressure on the foaming behavior of AlSi6Cu4 precursors is studied. In situ X ray radioscopy is applied while foaming in a furnace chamber pressurized up to 40 amp; 8201;bar. The content of the blowing agent TiH2 is varied for each of the pressures chosen. The foam density and morphology are analyzed quantitatively using time resolved X ray radioscopy sequences and postsolidification X ray tomography data. The optimal content of blowing agent as well as the pore sizes and distributions is found to depend strongly on the ambient pressure. At high pressures very small, round, and uniformly distributed pores are formed and crack formation is avoided during the gas nucleation stage, which helps to prevent structural defects. Adjusting the ambient pressure allows for better control of the foam structure and density, which is relevant for commercial production and applicatio
Long-range versus short-range correlations in the two-neutron transfer reaction Ni 64 (O 18, O 16) Ni 66
Recently, various two-neutron transfer studies using the (18O,16O) reaction were performed with a large success. This was achieved because of a combined use of the microscopic quantum description of the reaction mechanism and of the nuclear structure. In the present work we use this methodology to study the two-neutron transfer reaction of the 18O+64Ni system at 84 MeV incident energy, to the ground and first 2+ excited state of the residual 66Ni nucleus. All the experimental data were measured by the large acceptance MAGNEX spectrometer at the Instituto Nazionale di Fisica Nucleare \u2013Laboratori Nazionali del Sud (Italy). We have performed exact finite range cross section calculations using the coupled channel Born approximation (CCBA) and coupled reaction channel (CRC) method for the sequential and direct two-neutron transfers, respectively. Moreover, this is the first time that the formalism of the microscopic interaction boson model (IBM-2) was applied to a two-neutron transfer reaction. From our results we conclude that for two-neutron transfer to the ground state of 66Ni, the direct transfer is the dominant reaction mechanism, whereas for the transfer to the first excited state of 66Ni, the sequential process dominates. A competition between long-range and short-range correlations is discussed, in particular, how the use of two different models (Shell model and IBM's) help to disentangle long- and short-range correlations
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