4,328 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
Cables and fire hazards
Besides describing the experiments conducted to develop a nonflammable cable, this article discusses several considerations regarding other hazards which might result from cable fires, particularly the toxicity and opacity of the fumes emitted by the burning cable. In addition, this article examines the effects of using the Oxygen Index as a gauge of quality control during manufacture
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
Amino Acid Composition of Granules and Spots in Grana Padano Cheeses
Abstract Amino acids concentrated in Grana Padano cheese in two different physical forms, granules and spots. The major amino acid in the granules was tyrosine followed in concentration by phenylalanine and glutamic acid. Composition of spots was predominantly leucine and iso-leucine with tyrosine essentially absent. Composition of the free amino acids in the granules differed from that in the whole cheese. Bacterial populations were much higher in amino acid localization than in cheese as a whole, suggesting that bacterial action is a major contributing factor to the phenomenon of amino acid localization
Multi-Molecule Field-Coupled Nanocomputing for the Implementation of a Neuron
In recent years, several alternatives have been proposed to face CMOS scaling problems. Among these, molecular Field-Coupled Nanocomputing is a paradigm that encodes information in the spatial charges distribution and promises to consume a minimal amount of power. In this technology, circuits have always been designed using the same molecule type, and logic functions are obtained through specific layouts. This work demonstrates that multi-molecule circuits, which use different kinds of molecules in the same layout, enhance the circuit features and set up a new way to conceive molecular Field-Coupled Nanocomputing. In particular, by inserting different molecules with specific characteristics into appropriate layout positions, it is possible to obtain an artificial neuron behavior using the Majority Voter layout
Hip Joint Center Localization with an Unscented Kalman Filter
The accurate estimation of the hip joint centre (HJC) in gait analysis and in computer assisted orthopaedic procedures is
a basic requirement. Functional methods, based on rigid body localisation, assessing the kinematics of the femur during
circumduction movements (pivoting) have been used for estimating the HJC. Localising the femoral segment only, as it
is usually done in total knee replacement procedure, can give rise to estimation errors, since the pelvis, during the
passive pivoting manoeuvre, might undergo spatial displacements. This paper presents the design and test of an
unscented Kalman filter that allows the estimation of the HJC by observing the pose of the femur and the 3D
coordinates of a single marker attached to the pelvis. This new approach was validated using a hip joint mechanical
simulator, mimicking both hard and soft tissues. The algorithm performances were compared with the literature
standards and proved to have better performances in case of pelvis translation greater than 8 mm, thus satisfying the
clinical requirements of the application
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