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A combined experimental-numerical study to tensile behaviour of limestone
In this paper, a combined experimental-computational study of double-edge notched stone specimen subject to cyclic tensile loading is presented. In the experimental part, the load-deformation response and the local displacement field are recorded. Both experimental results are used to validate a numerical model for the description of fracture within finite elements. The model uses displacement discontinuities to model cracks. These discontinuities are implemented using the partition of unity property of finite element shape functions. In the discontinuity, a combined damage-plasticity cohesive law is used. Numerical simulations are compared with experimental observations
Double symmetry breaking of solitons in one-dimensional virtual photonic crystals
We demonstrate that spatial solitons undergo two consecutive spontaneous
symmetry breakings (SSBs), with the increase of the total power, in nonlinear
photonic crystals (PhCs) built as arrays of alternating linear and nonlinear
stripes, in the case when maxima of the effective refractive index coincide
with minima of the self-focusing coefficient, and vice versa, i.e.,the
corresponding linear and nonlinear periodic potentials are in competition. This
setting may be induced, as a virtual PhC, by means of the EIT
(electromagnetically-induced-transparency) technique, in a uniform optical
medium. It may also be realized as a Bose-Einstein condensate (BEC) subject to
the action of combined periodic optical potential and periodically modulated
Feshbach resonance. The first SSB happens at the center of a linear stripe,
pushing a broad low-power soliton into an adjacent nonlinear stripe and
gradually suppressing side peaks in the soliton's shape. Then, the soliton
restores its symmetry, being pinned to the midpoint of the nonlinear stripe.
The second SSB occurs at higher powers, pushing the narrow soliton off the
center of the nonlinear channel,while the soliton keeps its internal symmetry.
The results are obtained by means of numerical and analytical methods. They may
be employed to control switching of light beams by means of the varying power.Comment: 8 pages, 5 figures, Phys. Rev. A, in pres
Environmental adaptation, phenotypic plasticity, and associative learning in insects: the desert locust as a case study
The ability to learn and store information should be adapted to the environment in which animals operate to confer a selective advantage. Yet the relationship between learning, memory, and the environment is poorly understood, and further complicated by phenotypic plasticity caused by the very environment in which learning and memory need to operate. Many insect species show polyphenism, an extreme form of phenotypic plasticity, allowing them to occupy distinct environments by producing two or more alternative phenotypes. Yet how the learning and memories capabilities of these alternative phenotypes are adapted to their specific environments remains unknown for most polyphenic insect species. The desert locust can exist as one of two extreme phenotypes or phases, solitarious and gregarious. Recent studies of associative food–odor learning in this locust have shown that aversive but not appetitive learning differs between phases. Furthermore, switching from the solitarious to the gregarious phase (gregarization) prevents locusts acquiring new learned aversions, enabling them to convert an aversive memory formed in the solitarious phase to an appetitive one in the gregarious phase. This conversion provides a neuroecological mechanism that matches key changes in the behavioral environments of the two phases. These findings emphasize the importance of understanding the neural mechanisms that generate ecologically relevant behaviors and the interactions between different forms of behavioral plasticity
Student-produced podcasts as an assessment tool: an example from Geomorphology
The emergence of user-friendly technologies has made podcasting an accessible learning tool in undergraduate teaching. In a geomorphology course, student-produced podcasts were used as part of the assessment in 2008-2010. Student groups constructed radio shows aimed at a general audience to interpret and communicate geomorphological data within the context of relevant social and environmental issues. Questionnaire results suggest that the novel format engaged students, and promoted group working, IT, language and oral communication skills, and a deeper understanding of the context of geomorphic data. For teachers, podcasting technology offers efficient teaching of oral communication, with opportunities for distance and self-directed learning
JIEM's third year - Present status and future avenues
This editorial builds upon the guidelines developed by the Journal of Industrial Engineering and Management (JIEM) since its inception (Sallan et al., 2010; Simo et al., 2009; Fernandez et al., 2008) and reflects some relevant information about the evolution of JIEM during 2010, together with novel features that have been implemented so far or which are planned to be realized.Peer Reviewe
Radiative cooling in collisionally and photo ionized plasmas
We discuss recent improvements in the calculation of the radiative cooling in
both collisionally and photo ionized plasmas. We are extending the spectral
simulation code Cloudy so that as much as possible of the underlying atomic
data is taken from external databases, some created by others, some developed
by the Cloudy team. This paper focuses on recent changes in the treatment of
many stages of ionization of iron, and discusses its extensions to other
elements. The H-like and He-like ions are treated in the iso-electronic
approach described previously. Fe II is a special case treated with a large
model atom. Here we focus on Fe III through Fe XXIV, ions which are important
contributors to the radiative cooling of hot, 1e5 to 1e7 K, plasmas and for
X-ray spectroscopy. We use the Chianti atomic database to greatly expand the
number of transitions in the cooling function. Chianti only includes lines that
have atomic data computed by sophisticated methods. This limits the line list
to lower excitation, longer wavelength, transitions. We had previously included
lines from the Opacity Project database, which tends to include higher energy,
shorter wavelength, transitions. These were combined with various forms of the
g-bar approximation, a highly approximate method of estimating collision rates.
For several iron ions the two databases are almost entirely complementary. We
adopt a hybrid approach in which we use Chianti where possible, supplemented by
lines from the Opacity Project for shorter wavelength transitions. The total
cooling including the lightest thirty elements differs significantly from some
previous calculations
Interpolating vector fields for near identity maps and averaging
For a smooth near identity map, we introduce the notion of an interpolating
vector field written in terms of iterates of the map. Our construction is based
on Lagrangian interpolation and provides an explicit expressions for autonomous
vector fields which approximately interpolate the map. We study properties of
the interpolating vector fields and explore their applications to the study of
dynamics. In particular, we construct adiabatic invariants for symplectic near
identity maps. We also introduce the notion of a Poincar\'e section for a near
identity map and use it to visualise dynamics of four dimensional maps. We
illustrate our theory with several examples, including the Chirikov standard
map and a symplectic map in dimension four, an example motivated by the theory
of Arnold diffusion.Comment: 28 pages, 9 Figure
The Balmer decrement of SDSS galaxies
High resolution spectra are necessary to distinguish and correctly measure
the Balmer emission lines due to the presence of strong metal and Balmer
absorption features in the stellar continuum. This accurate measurement is
necessary for use in emission line diagnostics, such as the Balmer decrement
(i.e. Halpha/Hbeta), used to determine the attenuation of galaxies. Yet at high
redshifts obtaining such spectra becomes costly. Balmer emission line
equivalent widths are much easier to measure, requiring only low resolution
spectra or even simple narrow band filters and therefore shorter observation
times. However a correction for the stellar continuum is still needed for this
equivalent width Balmer decrement. We present here a statistical analysis of
the Sloan Digital Sky Survey Data Release 7 emission line galaxy sample, using
the spectrally determined Balmer emission line fluxes and equivalent widths.
Using the large numbers of galaxies available in the SDSS catalogue, we
determined an equivalent width Balmer decrement including a statistically-based
correction for the stellar continuum. Based on this formula, the attenuation of
galaxies can now be obtained from low spectral resolution observations. In
addition, this investigation also revealed an error in the Hbeta line fluxes,
within the SDSS DR7 MPA/JHU catalogue, with the equivalent widths
underestimated by average ~0.35A in the emission line galaxy sample. This error
means that Balmer decrement determined attenuations are overestimated by a
systematic 0.1 magnitudes in A_V, and future analyses of this sample need to
include this correction.Comment: 10 pages, accepted MNRA
Modeling the ionizing spectra of H ii regions: individual stars versus stellar ensembles
Aims. We study how IMF sampling affects the ionizing flux and emission line
spectra of low mass stellar clusters. Methods. We performed 2 x 10^6 Monte
Carlo simulations of zero-age solar-metallicity stellar clusters covering the
20 - 10^6 Mo mass range. We study the distribution of cluster stellar masses,
Mclus, ionizing fluxes, Q(H0), and effective temperatures, Tclus. We compute
photoionization models that broadly describe the results of the simulations and
compare them with photoionization grids. Results. Our main results are: (a) A
large number of low mass clusters (80% for Mclus = 100 Mo) are unable to form
an H ii region. (b) There are a few overluminous stellar clusters that form H
ii regions. These overluminous clusters preserve statistically the mean value
of obtained by synthesis models, but the mean value cannot be used as a
description of particular clusters. (c) The ionizing continuum of clusters with
Mclus < 10^4 Mo is more accurately described by an individual star with
self-consistent effective temperature(T*) and Q(H0) than by the ensemble of
stars (or a cluster Tclus) produced by synthesis models. (d)Photoionization
grids of stellar clusters can not be used to derive the global properties of
low mass clusters. Conclusions. Although variations in the upper mass limit,
mup, of the IMF would reproduce the effects of IMF sampling, we find that an ad
hoc law that relates mup to Mclus in the modelling of stellar clusters is
useless, since: (a) it does not cover the whole range of possible cases, and
(b) the modelling of stellar clusters with an IMF is motivated by the need to
derive the global properties of the cluster: however, in clusters affected by
sampling effects we have no access to global information of the cluster but
only particular information about a few individual stars.Comment: A&A in pres
Employer\u27s Liability for Employee He Was Compelled to Hire
Should an employer be liable for the torts of his employee if he was compelled to employ him?The master is charged with the obligation of selecting competent workmen. Therefore, if the element of employee selection is removed as a prerogative of the employer, does not this remove the master-servant relationship? If the employer through no fault of his own cannot completely direct and control the employee, is not the necessary privity between master and servant absent? Is it reasonable that the employer be liable for the misconduct of a person whose selection and/or control has been taken out of his hands? A review of existing case law is required to answer these questions
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