9,109 research outputs found
Comparison Between Damping Coefficients of Measured Perforated Micromechanical Test Structures and Compact Models
Measured damping coefficients of six different perforated micromechanical
test structures are compared with damping coefficients given by published
compact models. The motion of the perforated plates is almost translational,
the surface shape is rectangular, and the perforation is uniform validating the
assumptions made for compact models. In the structures, the perforation ratio
varies from 24% - 59%. The study of the structure shows that the
compressibility and inertia do not contribute to the damping at the frequencies
used (130kHz - 220kHz). The damping coefficients given by all four compact
models underestimate the measured damping coefficient by approximately 20%. The
reasons for this underestimation are discussed by studying the various flow
components in the models.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Finite-Size Effects on Return Interval Distributions for Weakest-Link-Scaling Systems
The Weibull distribution is a commonly used model for the strength of brittle
materials and earthquake return intervals. Deviations from Weibull scaling,
however, have been observed in earthquake return intervals and in the fracture
strength of quasi-brittle materials. We investigate weakest-link scaling in
finite-size systems and deviations of empirical return interval distributions
from the Weibull distribution function. We use the ansatz that the survival
probability function of a system with complex interactions among its units can
be expressed as the product of the survival probability functions for an
ensemble of representative volume elements (RVEs). We show that if the system
comprises a finite number of RVEs, it obeys the -Weibull distribution.
We conduct statistical analysis of experimental data and simulations that show
good agreement with the -Weibull distribution. We show the following:
(1) The weakest-link theory for finite-size systems involves the
-Weibull distribution. (2) The power-law decline of the
-Weibull upper tail can explain deviations from the Weibull scaling
observed in return interval data. (3) The hazard rate function of the
-Weibull distribution decreases linearly after a waiting time , where is the Weibull modulus and is the system size
in terms of representative volume elements. (4) The -Weibull provides
competitive fits to the return interval distributions of seismic data and of
avalanches in a fiber bundle model. In conclusion, using theoretical and
statistical analysis of real and simulated data, we show that the
-Weibull distribution is a useful model for extreme-event return
intervals in finite-size systems.Comment: 33 pages, 11 figure
Obeying a rule : Ludwig Wittgenstein and the foundations of Set Theory
In this paper we propose some reflections on Wittgensteinâs ideas about grammar and rules; then we shall consider some consequences of these for the foundations of set theory and, in particular, for the introduction of major concepts of set theory in education. For instance, a community of practice can decide to follow a particular rule that forbids the derivation of arbitrary sentences from a contradiction: since, according to Radfordâs perspective, knowledge is the result of thinking, and thinking is a cognitive social praxis, the mentioned choice can be considered as a form of real and effective knowledge
Numbers and Polynomials- 50 years since the publication of Wittgenstein\u27s Bemerkungen ĂŒber die Grundlagen der Mathematik (1956): Mathematical and Educational reflections
According to L. Wittgenstein, the meaning of a mathematical object is to be grounded upon its use. In this paper we consider Robinson theory Q, the subtheory of firstorder Peano Arithmetic PA; some theorems and conjectures can be interpreted over one model of Q given by a universe of polynomials; with respect to nonconstant polynomials some proofs by elementary methods are given and compared with corresponding results in the standard model of PA. We conclude that the creative power of the language can be pointed out in how the language itself is embedded into the rest of human activities, and this is an important track to follow for researchers in mathematics education
Two new intermediate polars with a soft X-ray component
Aims. We analyze the first X-ray observations with XMM-Newton of 1RXS J070407.9+262501 and 1RXS 180340.0+401214, in
order to characterize their broad-band temporal and spectral properties, also in the UV/optical domain, and to confirm them as intermediate polars.
Methods. For both objects, we performed a timing analysis of the X-ray and UV/optical light curves to detect the white dwarf spin pulsations and study their energy dependence. For 1RXS 180340.0+401214 we also analyzed optical spectroscopic data to determine the orbital period. X-ray spectra were analyzed in the 0.2â10.0 keV range to characterize the emission properties of both sources.
Results. We find that the X-ray light curves of both systems are energy dependent and are dominated, below 3â5 keV, by strong pulsations at the white dwarf rotational periods (480 s for 1RXS J070407.9+262501 and 1520.5 s for 1RXS 180340.0+401214). In 1RXS 180340.0+401214 we also detect an X-ray beat variability at 1697 s which, together with our new optical spectroscopy, favours an orbital period of 4.4 h that is longer than previously estimated. Both systems show complex spectra with a hard (temperature up to 40 keV) optically thin and a soft (kT ⌠85â100 eV) optically thick components heavily absorbed by material partially covering the X-ray sources.
Conclusions. Our observations confirm the two systems as intermediate polars and also add them as new members of the growing group of âsoftâ systems which show the presence of a soft X-ray blackbody component. Differences in the temperatures of the blackbodies are qualitatively explained in terms of reprocessing over different sizes of the white dwarf spot. We suggest that systems showing cooler soft X-ray blackbody components also possess white dwarfs irradiated by cyclotron radiation
Real and complex connections for canonical gravity
Both real and complex connections have been used for canonical gravity: the
complex connection has SL(2,C) as gauge group, while the real connection has
SU(2) as gauge group. We show that there is an arbitrary parameter
which enters in the definition of the real connection, in the Poisson brackets,
and therefore in the scale of the discrete spectra one finds for areas and
volumes in the corresponding quantum theory. A value for could be could
be singled out in the quantum theory by the Hamiltonian constraint, or by the
rotation to the complex Ashtekar connection.Comment: 8 pages, RevTeX, no figure
Nonlinear Kinetics on Lattices based on the Kinetic Interaction Principle
Master equations define the dynamics that govern the time evolution of
various physical processes on lattices. In the continuum limit, master
equations lead to Fokker-Planck partial differential equations that represent
the dynamics of physical systems in continuous spaces. Over the last few
decades, nonlinear Fokker-Planck equations have become very popular in
condensed matter physics and in statistical physics. Numerical solutions of
these equations require the use of discretization schemes. However, the
discrete evolution equation obtained by the discretization of a Fokker-Planck
partial differential equation depends on the specific discretization scheme. In
general, the discretized form is different from the master equation that has
generated the respective Fokker-Planck equation in the continuum limit.
Therefore, the knowledge of the master equation associated with a given
Fokker-Planck equation is extremely important for the correct numerical
integration of the latter, since it provides a unique, physically motivated
discretization scheme. This paper shows that the Kinetic Interaction Principle
(KIP) that governs the particle kinetics of many body systems, introduced in
[G. Kaniadakis, Physica A, 296, 405 (2001)], univocally defines a very simple
master equation that in the continuum limit yields the nonlinear Fokker-Planck
equation in its most general form.Comment: 26 page
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