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Search Results: 1 - 10 of 465561 matches for " A. Martinez "
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A Novel Approach to a Piezoelectric Sensing Element
M. Martinez,A. Artemev
Journal of Sensors , 2010, DOI: 10.1155/2010/816068
Abstract: Piezoelectric materials have commonly been used in pressure and stress sensors; however, many designs consist of thin plate structures that produce small voltage signals when they are compressed or extended under a pressure field. This study used finite element methods to design a novel piezoelectric pressure sensor with a C-shaped piezoelectric element and determine if the voltage signal obtained during hydrostatic pressure application was enhanced compared to a standard thin plate piezoelectric element. The results of this study demonstrated how small deformations of this C-shaped sensor produced a large electrical signal output. It was also shown that the location of the electrodes for this sensor needs to be carefully chosen and that the electric potential distribution varies depending on the poling of the piezoelectric element. This study indicated that the utilization of piezoelectric materials of different shapes and geometries embedded in a polymer matrix for sensing applications has several advantages over thin plate solid piezoelectric structures. 1. Introduction Pressure gauges of different design types (e.g., U-shaped tube gauges, piston gauges, aneroid gauges, Bourdon tube, or diaphragm gauge [1, 2], optical fiber sensors [3, 4], different electronic sensors) are currently used in different applications. Electronic sensors are convenient because they allow for easy, direct integration into electronic control schemes which can be easily miniaturized and have a short response time when used under dynamic conditions. Electronic pressure sensors can be designed by using different electromechanical or magnetomechanical effects. Electronic sensor types include piezoelectric [5], piezoresistive [6], capacitive, magnetic (inductive), potentiometric, resonant, and surface acoustic wave sensors. In the fields of robotics and orthotics the McKibben actuators have been utilized to mimic the behavior of biological muscles. Son and Goulbourne, 2009 [7] showed how the use of the two electrical parameters capacitance or resistance could be used to measure the large strains/pressure of the actuating device. MEMS based on piezoresistive pressure sensors have also been considered for pressure measurement applications; however they posses low sensitivity and suffer thermal drift [6, 8]. Piezoelectric pressure sensors are commonly used in sensor designs due to their high reliability and robustness, large range of measurable pressure, and low sensitivity to the electro-magnetic field. In traditional piezoelectric pressure sensor designs, the piezoelectric
Fatores prognósticos no Mieloma Múltiplo
Martinez, Gracia A.;
Revista Brasileira de Hematologia e Hemoterapia , 2007, DOI: 10.1590/S1516-84842007000100007
Abstract: over the last 10 years, great changes have occurred in the treatment of multiple myeloma (mm) due to the use of new drugs. considering the new options, it is essential to recognize clinical and biological parameters to arrive at the best therapeutic choice. more recently the new international staging system (iss) for multiple myeloma was validated which utilizes two straight forward laboratory parameters: the b2 microglobulin (b2m) and albumin levels. stage i: b2m < 3.5 mg/l and albumin level > 3.5 g/dl with a median survival of 62 months; stage ii: b2m < 3.5 and albumin < 3.5 g/dl or b2m > 3.5 to < 5.5 g/dl with a median survival of 49 months; stage iii: > 5.5 g/dl with a median survival of 29 months. the importance of cytogenetics and molecular features as prognostic factors is being recognized. deletion of chromosome 13 or 13q, the t(4:14) translocation, p53 deletion and amplification of chromosome band 1q21 are all associated with poor prognosis.
External Pacemaker of Diagnose and Research, Experience in Military Hospital Center Mexico
Martinez G.A
Lecture Notes in Engineering and Computer Science , 2007,
Factors determining production (FDP) in basketball
Jose A. Martinez
Economics and Business Letters , 2012,
Abstract: The aim of this research was to introduce a simple and easily computable metric to assess the performance of basketball players through non-scoring box-score statistics. This metric was called Factors Determining Production (FDP). FDP was created through separating points made from the remaining variables which may bequantitatively recorded. FDP was derived from the outcome of several games, it considers both teams’ statistics, and it reflects the final result of a game with noticeable merit. This metric provides a simple linear weight formula which, together with the points made by each player, yields a comprehensible picture of how well a worker(player) performed. FDP has been validated through different statistical procedures and it overcomes Win Score from a theoretical viewpoint, because it departs production (points) from factors facilitating production.
Entropy of eternal black holes
Erik A. Martinez
Physics , 1995,
Abstract: The entropy of a quantum-statistical system which is classically approximated by a general stationary eternal black hole is studied by means of a microcanonical functional integral. This approach opens the possibility of including explicitly the internal degrees of freedom of a physical black hole in path integral descriptions of its thermodynamical properties. If the functional integral is interpreted as the density of states of the system, the corresponding entropy equals ${cal S} = A_H/4 - A_H/4 =0$ in the semiclassical approximation, where $A_H$ is the area of the black hole horizon. The functional integral reflects the properties of a pure state.
Fundamental thermodynamical equation of a self-gravitating system
Erik A. Martinez
Physics , 1996, DOI: 10.1103/PhysRevD.53.7062
Abstract: The features of the fundamental thermodynamical relation (expressing entropy as function of state variables) that arise from the self-gravitating character of a system are analyzed. The models studied include not only a spherically symmetric hot matter shell with constant particle number but also a black hole characterized by a general thermal equation of state. These examples illustrate the formal structure of thermodynamics developed by Callen as applied to a gravitational configuration as well as the phenomenological manner in which Einstein equations largely determine the thermodynamical equations of state. We consider in detail the thermodynamics and quasi-static collapse of a self-gravitating shell. This includes a discussion of intrinsic stability for a one-parameter family of thermal equations of state and the interpretation of the Bekenstein bound. The entropy growth associated with a collapsing sequence of equilibrium states of a shell is computed under different boundary conditions in the quasi-static approximation and compared with black hole entropy. Although explicit expressions involve empirical coefficients, these are constrained by physical conditions of thermodynamical origin. The absence of a Gibbs-Duhem relation and the associated scaling laws for self-gravitating matter systems are presented.
Quasilocal Energy for a Kerr black hole
Erik A. Martinez
Physics , 1994, DOI: 10.1103/PhysRevD.50.4920
Abstract: The quasilocal energy associated with a constant stationary time slice of the Kerr spacetime is presented. The calculations are based on a recent proposal \cite{by} in which quasilocal energy is derived from the Hamiltonian of spatially bounded gravitational systems. Three different classes of boundary surfaces for the Kerr slice are considered (constant radius surfaces, round spheres, and the ergosurface). Their embeddings in both the Kerr slice and flat three-dimensional space (required as a normalization of the energy) are analyzed. The energy contained within each surface is explicitly calculated in the slow rotation regime and its properties discussed in detail. The energy is a positive, monotonically decreasing function of the boundary surface radius. It approaches the Arnowitt-Deser-Misner (ADM) mass at spatial infinity and reduces to (twice) the irreducible mass at the horizon of the Kerr black hole. The expressions possess the correct static limit and include negative contributions due to gravitational binding. The energy at the ergosurface is compared with the energies at other surfaces. Finally, the difficulties involved in an estimation of the energy in the fast rotation regime are discussed.
Microcanonical functional integral and entropy for eternal black holes
Erik A. Martinez
Physics , 1994, DOI: 10.1103/PhysRevD.51.5732
Abstract: The microcanonical functional integral for an eternal black hole system is considered. This requires computing the microcanonical action for a spatially bounded spacetime region when its two disconnected timelike boundary surfaces are located in different wedges of the Kruskal diagram. The path integral is a sum over Lorentzian geometries and is evaluated semiclassically when its boundary data are chosen such that the system is approximated by any Lorentzian, stationary eternal black hole. This approach opens the possibility of including explicitly the internal degrees of freedom of a physical black hole in path integral descriptions of its thermodynamical properties. If the functional integral is interpreted as the density of states of the system, the corresponding entropy equals ${\cal S} = A_H/4 - A_H/4 = 0$ in the semiclassical approximation, where $A_H$ is the area of the black hole horizon. The functional integral reflects the properties of a pure state. The description of the black hole density of states in terms of the eternal black hole functional integral is also discussed.
The postulates of gravitational thermodynamics
Erik A. Martinez
Physics , 1996, DOI: 10.1103/PhysRevD.54.6302
Abstract: The general principles and logical structure of a thermodynamic formalism that incorporates strongly self-gravitating systems are presented. This framework generalizes and simplifies the formulation of thermodynamics developed by Callen. The definition of extensive variables, the homogeneity properties of intensive parameters, and the fundamental problem of gravitational thermodynamics are discussed in detail. In particular, extensive parameters include quasilocal quantities and are naturally incorporated into a set of basic general postulates for thermodynamics. These include additivity of entropies (Massieu functions) and the generalized second law. Fundamental equations are no longer homogeneous first-order functions of their extensive variables. It is shown that the postulates lead to a formal resolution of the fundamental problem despite non-additivity of extensive parameters and thermodynamic potentials. Therefore, all the results of (gravitational) thermodynamics are an outgrowth of these postulates. The origin and nature of the differences with ordinary thermodynamics are analyzed. Consequences of the formalism include the (spatially) inhomogeneous character of thermodynamic equilibrium states, a reformulation of the Euler equation, and the absence of a Gibbs-Duhem relation.
Ergodic Properties of Infinite Harmonic Crystals: an Analytic Approach
S. Graffi,A. Martinez
Physics , 1996, DOI: 10.1063/1.531741
Abstract: We give through pseudodifferential operator calculus a proof that the quantum dynamics of a class of infinite harmonic crystals becomes ergodic and mixing with respect to the quantum Gibbs measure if the classical infinite dynamics is respectively ergodic and mixing with respect to the classical infinite Gibbs measure. The classical ergodicity and mixing properties are recovered as $\hbar\to 0$, and the infinitely many particles limits of the quantum Gibbs averages are proved to be the averages over a classical infinite Gibbs measure of the symbols generating the quantum observables under Weyl quantization.
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