16,509 research outputs found
Clustering transition in a system of particles self-consistently driven by a shear flow
We introduce a simple model of active transport for an ensemble of particles
driven by an external shear flow. Active refers to the fact that the flow of
the particles is modified by the distribution of particles itself. The model
consists in that the effective velocity of every particle is given by the
average of the external flow velocities felt by the particles located at a
distance less than a typical radius, . Numerical analysis reveals the
existence of a transition to clustering depending on the parameters of the
external flow and on . A continuum description in terms of the number
density of particles is derived, and a linear stability analysis of the density
equation is performed in order to characterize the transitions observed in the
model of interacting particles.Comment: 11 pages, 2 figures. To appear in PR
Von Neumann Regular Cellular Automata
For any group and any set , a cellular automaton (CA) is a
transformation of the configuration space defined via a finite memory set
and a local function. Let be the monoid of all CA over .
In this paper, we investigate a generalisation of the inverse of a CA from the
semigroup-theoretic perspective. An element is von
Neumann regular (or simply regular) if there exists
such that and , where is the composition of functions. Such an
element is called a generalised inverse of . The monoid
itself is regular if all its elements are regular. We
establish that is regular if and only if
or , and we characterise all regular elements in
when and are both finite. Furthermore, we study
regular linear CA when is a vector space over a field ; in
particular, we show that every regular linear CA is invertible when is
torsion-free elementary amenable (e.g. when ) and , and that every linear CA is regular when
is finite-dimensional and is locally finite with for all .Comment: 10 pages. Theorem 5 corrected from previous versions, in A.
Dennunzio, E. Formenti, L. Manzoni, A.E. Porreca (Eds.): Cellular Automata
and Discrete Complex Systems, AUTOMATA 2017, LNCS 10248, pp. 44-55, Springer,
201
Directed flow as effect of transient matter rotation in hadron and nucleus collisions
We discuss directed flow introduced for description of nucleus collisions and
consider its possible behavior in hadronic and nuclei reactions due to rotation
of the transient matter.Comment: 18 pages, 6 figure
Random solids and random solidification: What can be learned by exploring systems obeying permanent random constraints?
In many interesting physical settings, such as the vulcanization of rubber,
the introduction of permanent random constraints between the constituents of a
homogeneous fluid can cause a phase transition to a random solid state. In this
random solid state, particles are permanently but randomly localized in space,
and a rigidity to shear deformations emerges. Owing to the permanence of the
random constraints, this phase transition is an equilibrium transition, which
confers on it a simplicity (at least relative to the conventional glass
transition) in the sense that it is amenable to established techniques of
equilibrium statistical mechanics. In this Paper I shall review recent
developments in the theory of random solidification for systems obeying
permanent random constraints, with the aim of bringing to the fore the
similarities and differences between such systems and those exhibiting the
conventional glass transition. I shall also report new results, obtained in
collaboration with Weiqun Peng, on equilibrium correlations and
susceptibilities that signal the approach of the random solidification
transition, discussing the physical interpretation and values of these
quantities both at the Gaussian level of approximation and, via a
renormalization-group approach, beyond.Comment: Paper presented at the "Unifying Concepts in Glass Physics" workshop,
International Centre for Theoretical Physics, Trieste, Italy (September
15-18, 1999
Sperm mobility: mechanisms of fertilizing efficiency, genetic variation and phenotypic relationship with male status in the domestic fowl, Gallus gallus domesticus
When females are sexually promiscuous, sexual selection continues after insemination through sperm
competition and cryptic female choice, and male traits conveying an advantage in competitive fertilization
are selected for. Although individual male and ejaculate traits are known to influence paternity in a competitive
scenario, multiple mechanisms co-occur and interact to determine paternity. The way in which
different traits interact with each other and the mechanisms through which their heritability is maintained
despite selection remain unresolved. In the promiscuous fowl, paternity is determined by the number of
sperm inseminated into a female, which is mediated by male social dominance, and by the quality of the
sperm inseminated, measured as sperm mobility. Here we show that: (i) the number of sperm inseminated
determines how many sperm reach the female sperm-storage sites, and that sperm mobility mediates the
fertilizing efficiency of inseminated sperm, mainly by determining the rate at which sperm are released
from the female storage sites, (ii) like social status, sperm mobility is heritable, and (iii) subdominant
males are significantly more likely to have higher sperm mobility than dominant males. This study indicates
that although the functions of social status and sperm mobility are highly interdependent, the lack of
phenotypic integration of these traits may maintain the variability of male fitness and heritability of fertilizing
efficiency
Electroweak String Configurations with Baryon Number
In the context of electroweak strings, the baryon number anomaly equation may
be reinterpreted as a conservation law for baryon number minus helicity. Since
the helicity is a sum of the link and twist numbers, linked or twisted loops of
electroweak string carry baryon number. We evaluate the change in the baryon
number obtained by delinking loops of electroweak string and show that
twisted electroweak string segments may be regarded as extended sphalerons. We
also suggest an alternative scenario for electroweak baryogenesis.Comment: 11 pages, figure available on request. Added discussion of
string-sphaleron connection for non-vanishing Weinberg angle and shortened
discussion on formation of linked configuration
An approach to the natural and engineered nanoparticles analysis in the environment by inductively coupled plasma mass spectrometry
Different approaches to the most relevant and recent studies and applications of inductively coupled plasma mass spectrometry (ICP-MS) applied to the analysis of natural and engineered nanoparticles in the environment are described. Usually several separation methods like polyacrylamide gel electrophoresis (PAGE), field-flow fractionation (FFF) and size exclusion chromatography (SEC) are used prior to the mass spectrometric measurements. In many cases the use of these hyphenated techniques provides important methodologies to know the bioavailability, mobility and toxicity of elements in life and environmental sciences. Alternatively, the capabilities of the single particle detection by ICP-MS (SD-ICP-MS) for the selective identification, characterization and determination of engineered nanoparticles will be also discussed
Monitoring of the arterial pressure in effort. dominant, not dominant arm or both?
Objetivo: evaluar la diferencia de los valores de Presión arterial (PA) entre ambos brazos, medida simultáneamente, durante una prueba de esfuerzo.
Diseño del estudio: estudio transversal. Series de casos. Nivel de evidencia: 3
Material y Métodos: La población se compone de 225 deportistas sanos que realizaron una prueba de esfuerzo en nuestro centro. 128 hombres y 97 mujeres. Edad: 17± 5,5 años.
Resultados: La PA tanto sistólica como diastólica no difiere significativamente entre ambos miembros superiores. No obstante, hemos encontrado casos de variabilidad individual donde la PA predomina en un brazo durante el reposo y en el otro brazo durante el máximo esfuerzo. Los valores de TA son independientes del brazo dominante.
Conclusiones: La posibilidad que el brazo donde predomina la PA de Reposo no coincida durante el máximo esfuerzo, hace necesario, en nuestra opinión, que se mida la PA en ambos miembros superiores durante la prueba de esfuerzoObjective: To evaluate different blood pressure readings between both arms.
Study design: cross-sectional study. Case series. Level of evidence: 3.
Methods: a population of 225 healthy athletes underwent stress tests in our center: 128 males and 97 females. Age range: 17 +/- 5.5 years.
Results: no significant differences in systolic or diastolic blood pressure readings were found between the right or left arm. We did, however, find cases where blood pressure is higher in one arm while resting and in the other arm during maximal exercise. Blood pressure readings were not associated with the dominant arm.
Conclusions: The possibility that the arm in which there is a predominant rest blood pressure does not coincide during maximum stress, makes it necessary, according to our judgment, to measure blood pressure in both upper limbs during stress test
Replica symmetry breaking in the `small world' spin glass
We apply the cavity method to a spin glass model on a `small world' lattice,
a random bond graph super-imposed upon a 1-dimensional ferromagnetic ring. We
show the correspondence with a replicated transfer matrix approach, up to the
level of one step replica symmetry breaking (1RSB). Using the scheme developed
by M\'ezard & Parisi for the Bethe lattice, we evaluate observables for a model
with fixed connectivity and long range bonds. Our results agree with
numerical simulations significantly better than the replica symmetric (RS)
theory.Comment: 21 pages, 3 figure
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