4,055 research outputs found
Dynamics of a Bose-Einstein Condensate of Excited Magnons
The emergence of a non-equilibrium Bose-Einstein-like condensation of magnons
in rf-pumped magnetic thin films has recently been experimentally observed. We
present here a complete theoretical description of the non-equilibrium
processes involved. It it demonstrated that the phenomenon is another example
of the presence of a Bose-Einstein-like condensation in non-equilibrium
many-boson systems embedded in a thermal bath, better referred-to as
Fr\"{o}hlich-Bose-Einstein condensation. The complex behavior emerges after a
threshold of the exciting intensity is attained. It is inhibited at higher
intensities when the magnon-magnon interaction drives the magnons to internal
thermalization. The observed behavior of the relaxation to equilibrium after
the end of the pumping pulse is also accounted for and the different processes
fully described.Comment: 42 pages, 11 figure
A novel topology for a HEMT negative current mirror
A new solution for the implementation of a HEMT negative current source is presented. The topology can be also profitably employed as a current mirror and as an active load in high-gain MMICs voltage amplifiers. A small-signal model of the proposed circuit is developed which allows to find accurate expressions for the required transfer functions (i.e., the output impedance of the current source, and the current gain of the circuit when operated as a current mirror). Design examples using Philips PML ED02AH GaAs PHEMT process are provided. Spice simulations show that a 10- kW output impedance for the current source and a 35dB voltage gain for a differential pair loaded with the proposed current mirror are easily achieved
Non-extensive entropy from incomplete knowledge of Shannon entropy?
In this paper we give an interpretation of Tsallis' nonextensive statistical
mechanics based upon the information-theoretic point of view of Luzzi et al.
[cond-mat/0306217; cond-mat/0306247; cond-mat/0307325], suggesting Tsallis'
entropy to be not a fundamental concept but rather a derived one, stemming from
an incomplete knowledge of the system, not taking properly into account its
interaction with the environment. This interpretation seems to avoid some
problems occurring with the original interpretation of Tsallis statistics.Comment: v.4. 11 pages. Title changed. Content substantially changed: added
discussion of several points raised by various referees and readers; Also
reference made to work by Luzzi, Vasconcellos, Galvao Ramos. Physica Scripta,
to appea
Questioning the validity of non-extensive thermodynamics for classical Hamiltonian systems
We examine the non-extensive approach to the statistical mechanics of
Hamiltonian systems with where is the classical kinetic energy. Our
analysis starts from the basics of the formalism by applying the standard
variational method for maximizing the entropy subject to the average energy and
normalization constraints. The analytical results show (i) that the
non-extensive thermodynamics formalism should be called into question to
explain experimental results described by extended exponential distributions
exhibiting long tails, i.e. -exponentials with , and (ii) that in the
thermodynamic limit the theory is only consistent in the range
where the distribution has finite support, thus implying that configurations
with e.g. energy above some limit have zero probability, which is at variance
with the physics of systems in contact with a heat reservoir. We also discuss
the (-dependent) thermodynamic temperature and the generalized specific
heat.Comment: To appear in EuroPhysics Letter
Method of comparison equations for cosmological perturbations
We apply the method of comparison equations to study cosmological
perturbations during inflation, obtaining the full power spectra of scalar and
tensor perturbations to first and to second order in the slow-roll parameters.
We compare our results with those derived by means of other methods, in
particular the Green's function method and the improved WKB approximation, and
find agreement for the slow-roll structure. The method of comparison equations,
just as the improved WKB approximation, can however be applied to more general
situations where the slow-roll approximation fails.Comment: 20 pages, 10 figure
Fine-Structure Map of the Histidine Transport Genes in \u3cem\u3eSalmonella typhimurium\u3c/em\u3e
Afine-structure genetic map of the histidine transport region of the Salmonella typhimurium chromosome was constructed. Twenty-five deletion mutants were isolated and used for dividing the hisJ and hisP genes into 8 and 13 regions respectively. A total of 308 mutations, spontaneous and mutagen induced, have been placed in these regions by deletion mapping. The histidine transport operon is presumed to be constituted of genes dhuA, hisJ, and hisP, and the regulation of the hosP and hisJ genes by dhuA is discussed. The orientation of this operon relative to purF has been established by three-point crosses as being: purF duhA hisJ hisP
Investigation of Lunar Surface Chemical Contamination by LEM Descent Engine and Associated Equipment
Lunar surface and atmospheric contamination study caused by LEM rocket exhaust and inorganic, organic, and microbiological contaminant
Improved WKB analysis of Slow-Roll Inflation
We extend the WKB method for the computation of cosmological perturbations
during inflation beyond leading order and provide the power spectra of scalar
and tensor perturbations to second order in the slow-roll parameters. Our
method does not require that the slow-roll parameters be constant. Although
leading and next-to-leading results in the slow-roll parameters depend on the
approximation technique used in the computation, we find that the inflationary
theoretical predictions obtained may reach the accuracy required by planned
observations. In two technical appendices, we compare our techniques and
results with previous findings.Comment: REVTeX 4, 13 pages, no figures, final version to appear in Phys. Rev.
Co-evaluation of climate services. A case study for hydropower generation
Climate services are attracting growing attention and interest as instruments to promote climate change adaptation.
The transparent assessment of the potential value brought by the services can play a major role. It can
foster the commitment of the user towards a co-generation process increasingly central to climate services
creation, can provide developers important information to better tailor the service to the user needs, and can
finally increase recognition of the value of the service boosting confidence and trust in the tool.
This study presents and then demonstrates the applicability of an evaluation methodology based on the
Bayesian framework derived from the information value theory. The specific case study is the Smart Climate
Hydropower Tool (SCHT), a climate service designed to support management decisions in hydropower generation.
The service uses freely available seasonal forecasts and machine learning algorithms to predict incoming
discharge to hydropower reservoirs. The user is ENEL Green Power Italy, and the testing environments are two
water basins in Colombia.
The study defines the expected value of perfect information, the expected value of the information currently
used by the hydropower producer and the expected value of the service information. It then discusses pros and
cons of the applicability of the method
Impact of a nursing information system in clinical practice: a longitudinal study project
Background: The implementation of adequate clinical information systems helps to deal with the immense
flow of health data to ensure the continuity of care and access to a safe and high-quality healthcare system.
Currently there is an increasing awareness of the importance of evaluating and measuring the impact of such
systems in clinical practice. Implementations often fail, due to inadequate interaction between technology
and human elements.
Methods: This article describes a research project aimed at evaluating the impact of a clinical nursing information
system (CNIS), called Professional Assessment Instrument (PAI), in clinical practice. The study will
evaluate PAI Quality, Nurses Satisfaction, PAI Use, Nurses and Environment Characteristics, Net Benefits
and Nurses’ Experiences related to the PAI use. A theoretical model developed for this research will guide
the study. A quali-quantitative longitudinal design will be performed involving two hospitals over a 9-month
period. To measure different dimensions that affect the success/failure of CNIS we will use different tools/
methods of data collection (questionnaires, psychometric tools, surveys and focus groups).
Expected Results: This study will evaluate the impact of a CNIS in hospitals providing an overview of the
factors which can help and hinder the implementation of an information system.
Conclusions: The results of the study will support interventions to improve and implement clinical information
systems designed to computerize nursing data, with positive effects on public health and research
in general, providing further evidence for health policy
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