726 research outputs found
Influence of Rotations on the Critical State of Soil Mechanics
The ability of grains to rotate can play a crucial role on the collective
behavior of granular media. It has been observed in computer simulations that
imposing a torque at the contacts modifies the force chains, making support
chains less important. In this work we investigate the effect of a gradual
hindering of the grains rotations on the so-called critical state of soil
mechanics. The critical state is an asymptotic state independent of the initial
solid fraction where deformations occur at a constant shear strength and
compactness. We quantify the difficulty to rotate by a friction coefficient at
the level of particles, acting like a threshold. We explore the effect of this
particle-level friction coefficient on the critical state by means of molecular
dynamics simulations of a simple shear test on a poly-disperse sphere packing.
We found that the larger the difficulty to rotate, the larger the final shear
strength of the sample. Other micro-mechanical variables, like the structural
anisotropy and the distribution of forces, are also influenced by the
threshold. These results reveal the key role of rotations on the critical
behavior of soils and suggest the inclusion of rotational variables into their
constitutive equations.Comment: 9 pages, 8 figures, Accepted for publication in Computer Physics
Communication
La práctica evaluativa de los aprendizajes en el área de Comunicación del nivel secundario desde las percepciones de sus principales actores
La práctica evaluativa es entendida como parte del quehacer cotidiano que realiza el docente en su aula, y que favorece en gran medida el aprendizaje de sus estudiantes. Asimismo, es una actividad sobre la que los docentes requieren tener claridad en ciertos aspectos teóricos que brinden el soporte necesario para su realización.
Esta investigación da respuesta al siguiente problema de investigación ¿Cómo se realiza la práctica evaluativa de los aprendizajes en el área de Comunicación del VII ciclo del nivel secundario desde las percepciones de docentes y estudiantes en una Institución educativa pública de Lima?
La investigación es cualitativa, nivel descriptivo y emplea el método el estudio de casos. Para el recojo de información se aplica dos técnicas. La entrevista a 3 docentes del área de Comunicación y el focus group a 30 estudiantes del VII ciclo del nivel secundario, a fin de conocer las percepciones de estos sobre la práctica evaluativa de los aprendizajes en el área de Comunicación.
Entre los principales hallazgos se destaca el hecho que los docentes y estudiantes manifiestan que la práctica evaluativa tiene un fuerte carácter formativo, porque se procura que los estudiantes estén conscientes de su aprendizaje brindándoles los elementos necesarios para ello. Además, se propicia la participación de los estudiantes en la evaluación, a través de la auto y coevaluación; se destaca el empleo de instrumentos de corte cualitativo como las rúbricas y listas de cotejo, que ayudan a la visualización con mayor claridad de los aspectos a mejorar.Tesi
Interacting entropy-corrected holographic dark energy with apparent horizon as an infrared cutoff
In this work we consider the entropy-corrected version of interacting
holographic dark energy (HDE), in the non-flat universe enclosed by apparent
horizon. Two corrections of entropy so-called logarithmic 'LEC' and power-law
'PLEC' in HDE model with apparent horizon as an IR-cutoff are studied. The
ratio of dark matter to dark energy densities , equation of state parameter
and deceleration parameter are obtained. We show that the cosmic
coincidence is satisfied for both interacting models. By studying the effect of
interaction in EoS parameter, we see that the phantom divide may be crossed and
also find that the interacting models can drive an acceleration expansion at
the present and future, while in non-interacting case, this expansion can
happen only at the early time. The graphs of deceleration parameter for
interacting models, show that the present acceleration expansion is preceded by
a sufficiently long period deceleration at past. Moreover, the thermodynamical
interpretation of interaction between LECHDE and dark matter is described. We
obtain a relation between the interaction term of dark components and thermal
fluctuation in a non-flat universe, bounded by the apparent horizon. In
limiting case, for ordinary HDE, the relation of interaction term versus
thermal fluctuation is also calculated.Comment: 20 pages, 8 figures, figures changed, some Ref. is added, changed
some sentences, accepted by General relativity and gravitation (GERG
Medical imaging: Foundations and scope
Indexación: Scopus; Radalyc.En la actualidad es innegable la utilidad de las diversas modalidades
de imagenología médica como apoyo clínico tanto en
la generación de diagnósticos de un buen número de enfermedades
como en la planeación de tratamientos tendientes a
proporcionar una alternativa de solución a las personas que,
por una u otra razón, manifiestan algún desequilibrio en su
salud. Entre las modalidades imagenológicas que, frecuentemente,
se utilizan en el ámbito médico se pueden mencionar:
Ultrasonido (US), Resonancia Magnética (MRI), Tomografía
Computarizada sencilla (CT) y multicapa (MSCT), Tomografía
Computarizada por Emisión de Positrones (PET) y Tomografía
Computarizada por Emisión de Fotones simples (SPECT).
En este sentido, este artículo tiene como finalidad presentar
una descripción ordenada, coherente y sistemática de cada
una de las mencionadas modalidades y establecer la vinculación
de la MSCT con situaciones clínicas íntimamente relacionadas
con la anatomía cardiaca y procesos de hipertensión.
La razón por la cual se hace énfasis en la MSCT es debido a
que, por una parte, se cuenta con un número importante de
bases de datos tanto de sujetos fisiológicos como de sujetos
patológicos y, por la otra, que se tiene previsto presentar un
conjunto de técnicas computacionales que serán exploradas
en el desarrollo de futuras investigaciones en el contexto de
aspectos anatómico-cardiológicos que influyen directa o indirectamente
en la aparición, desarrollo y prevalencia de procesos
hipertensivos.Nowdays, several forms of medical imaging are usefulness in
clinical support for both diagnostics diseases generation and
treatment planning designed to provide an alternative solution
to people who, for one or another reason, manifest an
imbalance in your health. Among the imaging modalities that
frequently are used in the medical field may include: Ultrasound
(US), magnetic resonance imaging (MRI), simple computed
tomography (CT) and multilayer computed tomography
(MSCT), CT positron emission tomography (PET) Computed
tomography and single photon emission (SPECT). In this sense,
this article presents an orderly, coherent and systematic
description of these modalities and it establishes relationship
with the MSCT modality and clinical situations closely related
to cardiac anatomy and hypertension processes. The reason
emphasis on MSCT is done is because, on the one hand, we
have a large number of databases both physiological subjects
and pathological subjects and, on the other, we plan to
present a set of computational techniques that will be explored
in future research, in the context of cardiologic anatomical
aspects, with directly or indirectly influence in the emergence,
development and prevalence of hypertensive processes.http://www.redalyc.org/articulo.oa?id=5594990700
Measurement of the W+W-gamma Cross Section and Direct Limits on Anomalous Quartic Gauge Boson Couplings at LEP
The process e+e- -> W+W-gamma is analysed using the data collected with the
L3 detector at LEP at a centre-of-mass energy of 188.6GeV, corresponding to an
integrated luminosity of 176.8pb^-1. Based on a sample of 42 selected W+W-
candidates containing an isolated hard photon, the W+W-gamma cross section,
defined within phase-space cuts, is measured to be: sigma_WWgamma = 290 +/- 80
+/- 16 fb, consistent with the Standard Model expectation. Including the
process e+e- -> nu nu gamma gamma, limits are derived on anomalous
contributions to the Standard Model quartic vertices W+W- gamma gamma and W+W-Z
gamma at 95% CL: -0.043 GeV^-2 < a_0/Lambda^2 < 0.043 GeV^-2 0.08 GeV^-2 <
a_c/Lambda^2 < 0.13 GeV^-2 0.41 GeV^-2 < a_n/Lambda^2 < 0.37 GeV^-2
Production of Single W Bosons at \sqrt{s}=189 GeV and Measurement of WWgamma Gauge Couplings
Single W boson production in electron-positron collisions is studied with the
L3 detector at LEP. The data sample collected at a centre-of-mass energy of
\sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1.
Events with a single energetic lepton or two acoplanar hadronic jets are
selected. Within phase-space cuts, the total cross-section is measured to be
0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation.
Including our single W boson results obtained at lower \sqrt{s}, the WWgamma
gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma =
0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13
Search for an invisibly decaying Higgs boson in e^+e^- collisions at \sqrt{s} = 183 - 189 GeV
A search for a Higgs boson decaying into invisible particles is performed
using the data collected at LEP by the L3 experiment at centre-of-mass energies
of 183 GeV and 189 GeV. The integrated luminosities are respectively 55.3 pb^-1
and 176.4 pb^-1. The observed candidates are consistent with the expectations
from Standard Model processes. In the hypothesis that the production cross
section of this Higgs boson equals the Standard Model one and the branching
ratio into invisible particles is 100%, a lower mass limit of 89.2 GeV is set
at 95% confidence level
Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV
A search for the lightest neutral scalar and neutral pseudoscalar Higgs
bosons in the Minimal Supersymmetric Standard Model is performed using 176.4
pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of
189 GeV. No signal is observed, and the data are consistent with the expected
Standard Model background. Lower limits on the masses of the lightest neutral
scalar and pseudoscalar Higgs bosons are given as a function of tan(beta).
Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h
> 77.1 GeV and m_A > 77.1 GeV
Measurement of Bose-Einstein Correlations in e+e- -> W+W- at root(s)=189GeV
We investigate Bose-Einstein correlations (BEC) in W-pair production at
root(s)=189GeV using the L3 detector at LEP. We observe BEC between particles
from a single W decay in good agreement with those from a light-quark Z decay
sample. We investigate their possible existence between particles coming from
different W's. No evidence for such inter-W BEC is found
Measurement of the Lifetime of the Tau Lepton
The tau lepton lifetime is measured with the L3 detector at LEP using the
complete data taken at centre-of-mass energies around the Z pole resulting in
tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result
with the muon lifetime supports lepton universality of the weak charged current
at the level of six per mille. Assuming lepton universality, the value of the
strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/-
0.015(exp.) +/- 0.014 (theory)
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