903 research outputs found
Screening effects in superconductors
The partition function of the Hubbard model with local attraction and long
range Coulomb repulsion between electrons is written as a functional integral
with an action involving a pairing field and a local potential
. After integration over and over fluctuations in , the
final form of involves a Josephson coupling between the local phases of
and a "kinetic energy" term, representing the screened Coulomb
interaction between charge fluctuations. The competition between Josephson
coupling and charging energy allows to understand the relation between
and composition in high- materials, in particular superlattices, alloys
and bulk systems of low doping.Comment: 4 pages, revtex, no figures, submitted to Physica B (Proceedings of
SCES '96 International Conference, held in Zurich from 19th to 21st of
August
Modified ultrafast thermometer UFT-M and temperature measurements during Physics of Stratocumulus Top (POST)
A modified UFT-M version of the ultrafast airborne thermometer UFT, aimed at in-cloud temperature measurements, was designed for the Physics of Stratocumulus Top (POST) field campaign. Improvements in its construction resulted in the sensor's increased reliability, which provided valuable measurements in 15 of the 17 flights. Oversampling the data allowed for the effective correction of the artefacts resulting from the interference with electromagnetic transmissions from on-board avionic systems and the thermal noise resulting from the sensor construction. The UFT-M records, when averaged to the 1.4 and 55 m resolutions, compared to the similar records of a thermometer in a Rosemount housing, indicate that the housing distorts even low-resolution airborne temperature measurements. Data collected with the UFT-M during the course of POST characterise the thermal structure of stratocumulus and capping inversion with the maximum resolution of ~1 cm. In this paper, examples of UFT-M records are presented and discussed
Analysis of time-profiles with in-beam PET monitoring in charged particle therapy
Background: Treatment verification with PET imaging in charged particle
therapy is conventionally done by comparing measurements of spatial
distributions with Monte Carlo (MC) predictions. However, decay curves can
provide additional independent information about the treatment and the
irradiated tissue. Most studies performed so far focus on long time intervals.
Here we investigate the reliability of MC predictions of space and time (decay
rate) profiles shortly after irradiation, and we show how the decay rates can
give an indication about the elements of which the phantom is made up.
Methods and Materials: Various phantoms were irradiated in clinical and
near-clinical conditions at the Cyclotron Centre of the Bronowice proton
therapy centre. PET data were acquired with a planar 16x16 cm PET system.
MC simulations of particle interactions and photon propagation in the phantoms
were performed using the FLUKA code. The analysis included a comparison between
experimental data and MC simulations of space and time profiles, as well as a
fitting procedure to obtain the various isotope contributions in the phantoms.
Results and conclusions: There was a good agreement between data and MC
predictions in 1-dimensional space and decay rate distributions. The fractions
of C, O and C that were obtained by fitting the decay
rates with multiple simple exponentials generally agreed well with the MC
expectations. We found a small excess of C in data compared to what was
predicted in MC, which was clear especially in the PE phantom.Comment: 9 pages, 5 figures, 1 table. Proceedings of the 20th International
Workshop on Radiation Imaging Detectors (iWorid2018), 24-28 June 2018,
Sundsvall, Swede
Corporate Culture and Its Connection with External and Internal Public Relations
The main aim of this article is to present the influence of corporate culture on company's stakeholders. This paper signalises the tendency in corporate communication with its internal and external publics. It is focused on two issues: corporate social responsibility and employer branding. Those two categories are consequences of corporate culture model.Głównym celem artykułu jest zaprezentowanie wpływu jaki wywiera charakter kultury korporacyjnej na związanych z przedsiębiorstwem interesariuszy (stakeholders). W artykule zasygnalizowane zostały główne tendencje wyznaczające charakter komunikacji między organizacją a jej wewnętrznym i zewnętrznym otoczeniem. Tekst koncentruje się na dwóch kwestiach: społecznej odpowiedzialności przedsiębiorstwa (corporate social responsibilty) i budowanie wizerunku pracodawcy (employer branding), które zaprezentowane zostały jako efekty określonego modelu kultury organizacyjnej
First-order transitions and triple point on a random p-spin interaction model
The effects of competing quadrupolar- and spin-glass orderings are
investigated on a spin-1 Ising model with infinite-range random -spin
interactions. The model is studied through the replica approach and a phase
diagram is obtained in the limit . The phase diagram, obtained
within replica-symmetry breaking, exhibits a very unusual feature in magnetic
models: three first-order transition lines meeting at a commom triple point,
where all phases of the model coexist.Comment: 9 pages, 2 ps figures include
Temperature-doping phase diagram of layered superconductors
The superconducting properties of a layered system are analyzed for the cases
of zero- and non-zero angular momentum of the pairs. The effective
thermodynamic potential for the quasi-2D XY-model for the gradients of the
phase of the order parameter is derived from the microscopic superconducting
Hamiltonian. The dependence of the superconducting critical temperature T_c on
doping, or carrier density, is studied at different values of coupling and
inter-layer hopping. It is shown that the critical temperature T_c of the
layered system can be lower than the critical temperature of the
two-dimensional Berezinskii-Kosterlitz-Thouless transition T_BKT at some values
of the model parameters, contrary to the case when the parameters of the
XY-model do not depend on the microscopic Hamiltonian parameters.Comment: To be published in Phys. Rev.
Interaction-induced Bose Metal in 2D
We show here that the regularization of the conductivity resulting from the
bosonic interactions on the `insulating' (quantum disordered) side of an
insulator-superconductor transition in 2D gives rise to a metal with a finite
conductivity, , as temperature tends to zero. The Bose
metal is stable to weak disorder and hence represents a concrete example of an
interaction-induced metallic phase. Phenomenological inclusion of dissipation
reinstates the anticipated insulating behaviour in the quantum-disordered
regime. Hence, we conclude that the traditionally-studied
insulator-superconductor transition, which is driven solely by quantum
fluctuations, corresponds to a superconductor-metal transition. The possible
relationship to experiments on superconducting thin films in which a
low-temperature metallic phase has been observed is discussed.Comment: A figure has been added and the physics has been clarified. To appear
in PR
Time reparametrization group and the long time behaviour in quantum glassy systems
We study the long time dynamics of a quantum version of the
Sherrington-Kirkpatrick model. Time reparametrizations of the dynamical
equations have a parallel with renormalization group transformations, and
within this language the long time behaviour of this model is controlled by a
reparametrization group (RG) fixed point of the classical dynamics. The
irrelevance of the quantum terms in the dynamical equations in the aging regime
explains the classical nature of the violation of the fluctuation-dissipation
theorem.Comment: 4 page
Monitoring Proton Therapy Through In-Beam PET: An Experimental Phantom Study
In this paper, we investigate the use of a positron emission tomography (PET) system to monitor the proton therapy. The monitoring procedure is based on the comparison between the β+ activity generated in the irradiated volume during the treatment, with the β+ activity distribution obtained with Monte Carlo (MC) simulation. The dedicated PET system is a dual head detection system; each head is composed of nine scintillating LYSO crystal matrices read out independently with a custom modularized acquisition system. Our experimental data were acquired at the Cyclotron Centre Bronowice, Institute Nuclear Physics in Kraków, Poland, and were simulated with the FLUKA MC code. Homogeneous and heterogeneous plastic phantoms were irradiated with monoenergetic 130 MeV protons. The capabilities of our PET system to distinguish different irradiated materials were investigated, and the proton pencil-beams were used as probes. Our focus was to analyze the activity width and the total activity event number in several cases. Irradiations were performed using either single pencil-beams one at a time, or two pencil-beams during the same data taking. The comparison of 1-D activity profile for experimental data and MC simulation were always in good agreement showing that, the treatment quality assessment in proton therapy can be based on β+ activity measurements
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