3,970 research outputs found
Quantum thermodynamic Carnot and Otto-like cycles for a two-level system
From the thermodynamic equilibrium properties of a two-level system with
variable energy-level gap , and a careful distinction between the Gibbs
relation and the energy balance equation , we infer some important aspects of the
second law of thermodynamics and, contrary to a recent suggestion based on the
analysis of an Otto-like thermodynamic cycle between two values of of
a spin-1/2 system, we show that a quantum thermodynamic Carnot cycle, with the
celebrated optimal efficiency , is possible in
principle with no need of an infinite number of infinitesimal processes,
provided we cycle smoothly over at least three (in general four) values of
, and we change not only along the isoentropics, but also
along the isotherms, e.g., by use of the recently suggested maser-laser tandem
technique. We derive general bounds to the net-work to high-temperature-heat
ratio for a Carnot cycle and for the 'inscribed' Otto-like cycle, and represent
these cycles on useful thermodynamic diagrams.Comment: RevTex4, 4 pages, 1 figur
Thermodynamic analysis of turbulent combustion in a spark ignition engine. Experimental evidence
A method independent of physical modeling assumptions is presented to analyze high speed flame photography and cylinder pressure measurements from a transparent piston spark ignition research engine. The method involves defining characteristic quantities of the phenomena of flame propagation and combustion, and estimating their values from the experimental information. Using only the pressure information, the mass fraction curves are examined. An empirical burning law is presented which simulates such curves. Statistical data for the characteristics delay and burning angles which show that cycle to cycle fractional variations are of the same order of magnitude for both angles are discussed. The enflamed and burnt mass fractions are compared as are the rates of entrainment and burning
Combustion and operating characteristics of spark-ignition engines
The spark-ignition engine turbulent flame propagation process was investigated. Then, using a spark-ignition engine cycle simulation and combustion model, the impact of turbocharging and heat transfer variations or engine power, efficiency, and NO sub x emissions was examined
A nonlinear model dynamics for closed-system, constrained, maximal-entropy-generation relaxation by energy redistribution
We discuss a nonlinear model for the relaxation by energy redistribution
within an isolated, closed system composed of non-interacting identical
particles with energy levels e_i with i=1,2,...,N. The time-dependent
occupation probabilities p_i(t) are assumed to obey the nonlinear rate
equations tau dp_i/dt=-p_i ln p_i+ alpha(t)p_i-beta(t)e_ip_i where alpha(t) and
beta(t) are functionals of the p_i(t)'s that maintain invariant the mean energy
E=sum_i e_ip_i(t) and the normalization condition 1=sum_i p_i(t). The entropy
S(t)=-k sum_i p_i(t) ln p_i(t) is a non-decreasing function of time until the
initially nonzero occupation probabilities reach a Boltzmann-like canonical
distribution over the occupied energy eigenstates. Initially zero occupation
probabilities, instead, remain zero at all times. The solutions p_i(t) of the
rate equations are unique and well-defined for arbitrary initial conditions
p_i(0) and for all times. Existence and uniqueness both forward and backward in
time allows the reconstruction of the primordial lowest entropy state. The time
evolution is at all times along the local direction of steepest entropy ascent
or, equivalently, of maximal entropy generation. These rate equations have the
same mathematical structure and basic features of the nonlinear dynamical
equation proposed in a series of papers ended with G.P.Beretta, Found.Phys.,
17, 365 (1987) and recently rediscovered in S. Gheorghiu-Svirschevski,
Phys.Rev.A, 63, 022105 and 054102 (2001). Numerical results illustrate the
features of the dynamics and the differences with the rate equations recently
considered for the same problem in M.Lemanska and Z.Jaeger, Physica D, 170, 72
(2002).Comment: 11 pages, 7 eps figures (psfrag use removed), uses subeqn, minor
revisions, accepted for Physical Review
The smallest refrigerators can reach maximal efficiency
We investigate whether size imposes a fundamental constraint on the
efficiency of small thermal machines. We analyse in detail a model of a small
self-contained refrigerator consisting of three qubits. We show analytically
that this system can reach the Carnot efficiency, thus demonstrating that there
exists no complementarity between size and efficiency.Comment: 9 pages, 1 figure. v2: published versio
Application of Digital Image Correlation (DIC) in resonance machines for measuring fatigue crack growth
This paper presents a simple experimental procedure that greatly facilitates the use of digital imagecorrelation (DIC) techniques in fatigue test conducted in resonant testing machines, without the need of testinterruptions. This is possible due to the implementation of USB interface optical microscopes of very smalldimensions, so that they can be mounted on the specimen as a contact extensometer. Thus, the microscopesampleassembly oscillates at the resonance frequency of the test. This is how, although the resonant testingmachine is in motion, and although the specimen is subjected to fatigue, changing its dimensions according tothe applied load, the acquired image is completely static. This allows the evaluation of the plastic deformationsgenerated by the crack growth, avoiding the elastic ones. Preliminary results on monitoring cracks with thistechnique on flat specimens with cylindrical notches of 1050 aluminium alloy are also presented
Gemcitabine plus vinorelbine in elderly or unfit patients with non-small cell lung cancer
Cisplatin-based combinations are efficacious in increasing the overall survival of patients with non-small cell lung cancer (NSCLC), but their toxicity makes them unsuitable for elderly and unfit patients. The primary objective of this non-randomized phase II study was to evaluate the feasibility and activity of the gemcitabine plus vinorelbine combination in previously untreated elderly and/or unfit patients with measurable stage III or IV NSCLC. Forty-three patients aged â„ 65 years or with contraindications against cisplatin treatment (36 males and seven females: median age 66 years; range 48â75: PS 0 = 11, PS 1 = 19, PS 2 = 13) received intravenous (i.v.) gemcitabine 1000 mg mâ2, followed by vinorelbine 25 mg mâ2i.v. on day 1 and 8 every 21 days. Fifteen patients (34.9%) achieved partial remission (confidence interval: 27.6â42.2%) for a median duration of 6 months; the median survival of these patients has not yet been reached. A further 15 had stable disease for a median of 4 months and a median survival of 7 months. The 10 patients (23.2%) who experienced disease progression had a median survival of 4 months. Three patients are not evaluable. The 1-year actuarial survival rate is 31.1%. The treatment was well tolerated: only 35% of the patients had grade 3 or 4 granulocytopenia on day 14, none experienced episodes of neutropenic fever, and there was no evidence of severe haematological toxicity upon recycling. Only 9% of the patients suffered from gastrointestinal toxicity (grade 3); increased but reversible transaminase levels were observed in 11.6%. In conclusion, the results of this phase II study show that the combination of gemcitabine and vinorelbine is active and well tolerated in NSCLC, and thus encourage its use in elderly or unfit patients. © 2000 Cancer Research Campaig
Experiences of newly hired nurses during the Covid-19 emergency: descriptive qualitative research
Background and aim of the work: The Covid-19 pandemic led to an increased demand for healthcare professionals, particularly nurses. The Piacenza Local Health Service, Northern Italy, issued several calls for tenders in order to recruit nurses and the University anticipated graduation sessions, so several new graduates nurses found themselves facing their first work experience in the middle of the pandemic emergency. It is well known that being a first-time employee causes stress, but there are few studies yet investigating the perception of newly employed nurses during the pandemic. The aim of this research is therefore to describe the experience of these nurses. Methods: A descriptive qualitative study was conducted through interviews. The research was approved by the âArea Vasta Emilia Nord Ethics Committee. Results: 14 nurses were interviewed and nine themes were found. Emotions, awareness, job opportunities, professional liability, organisational aspects and relationship with the other. Conclusions: Our study shows how stress, anxiety and feelings of inadequacy characterise new nursesâ entry into the workplace. Emotional support strategies, such as counselling and emergency preparedness training, could help early career professionals to cope with complex and emotion-ally charged clinical care situations with greater resilience. Study registration: ClinicalTrials.gov Identifier: NCT05110859. (www.actabiomedica.it)
Wehrl information entropy and phase distributions of Schrodinger cat and cat-like states
The Wehrl information entropy and its phase density, the so-called Wehrl
phase distribution, are applied to describe Schr\"odinger cat and cat-like
(kitten) states. The advantages of the Wehrl phase distribution over the Wehrl
entropy in a description of the superposition principle are presented. The
entropic measures are compared with a conventional phase distribution from the
Husimi Q-function. Compact-form formulae for the entropic measures are found
for superpositions of well-separated states. Examples of Schr\"odinger cats
(including even, odd and Yurke-Stoler coherent states), as well as the cat-like
states generated in Kerr medium are analyzed in detail. It is shown that, in
contrast to the Wehrl entropy, the Wehrl phase distribution properly
distinguishes between different superpositions of unequally-weighted states in
respect to their number and phase-space configuration.Comment: 10 pages, 4 figure
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