116 research outputs found
Statistical-mechanical theory of ultrasonic absorption in molecular liquids
We present results of theoretical description of ultrasonic phenomena in
molecular liquids. In particular, we are interested in the development of
microscopical, i.e., statistical-mechanical framework capable to explain the
long living puzzle of the excess ultrasonic absorption in liquids. Typically,
ultrasonic wave in a liquid can be generated by applying the periodically
alternating external pressure with the angular frequency that corresponds to
the ultrasound. If the perturbation introduced by such process is weak - its
statistical-mechanical treatment can be done with the use of the linear
response theory. We treat the liquid as a system of interacting sites, so that
all the response/aftereffect functions as well as the energy dissipation and
generalized (wave-vector and frequency dependent) ultrasonic absorption
coefficient are obtained in terms of familiar site-site static and time
correlation functions such as static structure factors or intermediate
scattering functions. To express the site-site intermediate scattering
functions we refer to the site-site memory equations in the mode-coupling
approximation for the first-order memory kernels, while equilibrium properties
such as site-site static structure factors, direct and total correlation
functions are deduced from the integral equation theory of molecular liquids
known as RISM or one of its generalizations. All the formalism is phrased in a
general manner, hence the obtained results are expected to work for arbitrary
type of molecular liquid including simple, ionic, polar, and non-polar liquids.Comment: 14 pages, 1 eps-figure, RevTeX4-forma
Low temperature acoustic properties of amorphous silica and the Tunneling Model
Internal friction and speed of sound of a-SiO(2) was measured above 6 mK
using a torsional oscillator at 90 kHz, controlling for thermal decoupling,
non-linear effects, and clamping losses. Strain amplitudes e(A) = 10^{-8} mark
the transition between the linear and non-linear regime. In the linear regime,
excellent agreement with the Tunneling Model was observed for both the internal
friction and speed of sound, with a cut-off energy of E(min) = 6.6 mK. In the
non-linear regime, two different behaviors were observed. Above 10 mK the
behavior was typical for non-linear harmonic oscillators, while below 10 mK a
different behavior was found. Its origin is not understood.Comment: 1 tex file, 6 figure
Casimir Surface Force on a Dilute Dielectric Ball
The Casimir surface force density F on a dielectric dilute spherical ball of
radius a, surrounded by a vacuum, is calculated at zero temperature. We treat
(n-1) (n being the refractive index) as a small parameter. The dispersive
properties of the material are taken into account by adopting a simple
dispersion relation, involving a sharp high frequency cutoff at omega =
omega_0. For a nondispersive medium there appears (after regularization) a
finite, physical, force F^{nondisp} which is repulsive. By means of a uniform
asymptotic expansion of the Riccati-Bessel functions we calculate F^{nondisp}
up to the fourth order in 1/nu. For a dispersive medium the main part of the
force F^{disp} is also repulsive. The dominant term in F^{disp} is proportional
to (n-1)^2{omega_0}^3/a, and will under usual physical conditions outweigh
F^{nondisp} by several orders of magnitude.Comment: 24 pages, latex, no figures, some additions to the Acknowledments
sectio
Data fusion of ultrasound and GPR signals for analysis of historic walls
[EN] This paper presents an application of ultrasounds and ground-penetrating radar (GPR) for analysis of historic walls. The objectives are to characterize the deformation of a historic wall under different levels of load weights and to obtain an enhanced image of the wall. A new method that fuses data from ultrasound and GPR traces is proposed which is based on order statistics digital filters. Application results are presented for non destructive testing (NDT) of two replicates of historic ashlars' masonry walls: the first one homogeneous and the second one containing controlled defects such as cracks and nooks. The walls are measured separately using ultrasounds and GPR at different load steps. Time and frequency parameters extracted from the signals and different B-Scans for each of the NDT techniques are obtained. After this, a new fused representation is obtained, which results demonstrate the improvement of characterization and defect detection in historic walls using data fusion.This work has been supported by Generalitat Valenciana under grant PROMETEO/2010/040, and Spanish Administration and European Union FEDER Prog. under grant TEC2011-23403 01/01/2012.Salazar Afanador, A.; Gosálbez Castillo, J.; Safont Armero, G.; Vergara Domínguez, L. (2012). Data fusion of ultrasound and GPR signals for analysis of historic walls. IOP Conference Series: Materials Science and Engineering. 42:1-4. https://doi.org/10.1088/1757-899X/42/1/012008S144
Prospective of the Application of Ultrasounds in Archaeology
[EN] This paper presents a prospective analysis of non destructive testing (NDT) based on
ultrasounds in the field of archaeology applications. Classical applications of ultrasounds techniques are reviewed, including ocean exploration to detect wrecks, imaging of archaeological sites, and cleaning archaeological objects. The potential of prospective applications is discussed from the perspective of signal processing, with emphasis on the area of linear time variant models. Thus, the use of ultrasound NDT is proposed for new ceramic cataloguing and restoration methods.This work has been supported by the Generalitat Valenciana under grant PROMETEO/2010/040, and the Spanish Administration and the FEDER Programme of the European Union under grant TEC2011-23403 01/01/2012.Salazar Afanador, A.; Rodriguez Martinez, A.; Safont Armero, G.; Vergara Domínguez, L. (2012). Prospective of the Application of Ultrasounds in Archaeology. IOP Conference Series: Materials Science and Engineering. 42:1-5. https://doi.org/10.1088/1757-899X/42/1/012010S154
Demography and Life Histories of Sympatric Patas Monkeys, Erythrocebus patas, and Vervets, Cercopithecus aethiops, in Laikipia, Kenya
Mortality patterns are thought to be strong selective forces on life history traits, with high adult mortality and low immature mortality favoring early and rapid reproduction. Patas monkeys (Erythrocebus patas) have the highest potential rates of population increase for their body size of any haplorhine primate because they reproduce both earlier and more often. We report here 10 yr of comparative demographic data on a population of patas monkeys and a sympatric population of vervet monkeys (Cercopithecus aethiops), a closely related species differing in aspects of social system, ecology, and life history. The data reveal that 1) adult female patas monkeys have significantly higher mortality than adult female vervets; 2) infant mortality in patas monkeys is relatively low compared to the norm for mammals because it is not significantly different from that of adult female patas monkeys; and 3) infant mortality is significantly higher than adult female mortality in vervets. For both species, much of the mortality could be attributed to predation. An epidemic illness was also a major contributor to the mortality of adult female patas monkeys whereas chronic exposure to pathogens in a cold and damp microenvironment may have contributed to the mortality of infant vervets. Both populations experienced large fluctuations during the study period. Our results support the prediction from demographic models of life history evolution that high adult mortality relative to immature mortality selects for early maturation
Modelling Sonoluminescence
In single-bubble sonoluminescence, a bubble trapped by a sound wave in a
flask of liquid is forced to expand and contract; exactly once per cycle, the
bubble emits a very sharp () pulse of visible light. This is a robust
phenomenon observable to the naked eye, yet the mechanism whereby the light is
produced is not well understood. One model that has been proposed is that the
light is "vacuum radiation" generated by the coupling of the electromagnetic
fields to the surface of the bubble. In this paper, we simulate vacuum
radiation by solving Maxwell's equations with an additional term that couples
the field to the bubble's motion. We show that, in the static case originally
considered by Casimir, we reproduce Casimir's result. In a simple purely
time-dependent example, we find that an instability occurs and the pulse of
radiation grows exponentially. In the more realistic case of
spherically-symmetric bubble motion, we again find exponential growth in the
context of a small-radius approximation.Comment: Expanded introduction, appendix on duality, 18 pages, plain Te
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