2,947 research outputs found
A nonlinear programming approach to kinematic shakedown analysis of frictional materials
AbstractThis paper develops a novel nonlinear numerical method to perform shakedown analysis of structures subjected to variable loads by means of nonlinear programming techniques and the displacement-based finite element method. The analysis is based on a general yield function which can take the form of most soil yield criteria (e.g. the Mohr–Coulomb or Drucker–Prager criterion). Using an associated flow rule, a general yield criterion can be directly introduced into the kinematic theorem of shakedown analysis without linearization. The plastic dissipation power can then be expressed in terms of the kinematically admissible velocity and a nonlinear formulation is obtained. By means of nonlinear mathematical programming techniques and the finite element method, a numerical model for kinematic shakedown analysis is developed as a nonlinear mathematical programming problem subject to only a small number of equality constraints. The objective function corresponds to the plastic dissipation power which is to be minimized and an upper bound to the shakedown load can be calculated. An effective, direct iterative algorithm is then proposed to solve the resulting nonlinear programming problem. The calculation is based on the kinematically admissible velocity with one-step calculation of the elastic stress field. Only a small number of equality constraints are introduced and the computational effort is very modest. The effectiveness and efficiency of the proposed numerical method have been validated by several numerical examples
Finite element analysis of anchor plates using non-coaxial models
AbstractThe non-coaxial model simulating the non-coincidence between the principal stresses and the principal plastic strain rates is employed within the framework of finite element method (FEM) to predict the behaviors of anchors embedded in granular material. The non-coaxial model is developed based on the non-coaxial yield vertex theory, and the elastic and conventional coaxial plastic deformations are simulated by using elasto-perfectly plastic Drucker-Prager yield function according to the original yield vertex theory. Both the horizontal and vertical anchors with various embedment depths are considered. Different anchor shapes and soil friction and dilation angles are also taken into account. The predictions indicate that the use of non-coaxial models leads to softer responses, compared with those using conventional coaxial models. Besides, the predicted ultimate pulling capacities are the same for both coaxial and non-coaxial models. The non-coaxial influences increase with the increasing embedment depths, and circular anchors lead to larger non-coaxial influences than strip anchors. In view of the fact that the design of anchors is mainly determined by their displacements, ignoring the non-coaxiality in finite element numerical analysis can lead to unsafe results
SrKZnMnAs: a ferromagnetic semiconductor with colossal magnetoresistance
A bulk diluted magnetic semiconductor (Sr,K)(Zn,Mn)As was
synthesized with decoupled charge and spin doping. It has a hexagonal
CaAlSi-type structure with the (Zn,Mn)As layer forming
a honeycomb-like network. Magnetization measurements show that the sample
undergoes a ferromagnetic transition with a Curie temperature of 12 K and
\revision{magnetic moment reaches about 1.5 /Mn under = 5 T
and = 2 K}. Surprisingly, a colossal negative magnetoresistance, defined as
, up to 38\% under a low field of = 0.1
T and to 99.8\% under = 5 T, was observed at = 2 K. The
colossal magnetoresistance can be explained based on the Anderson localization
theory.Comment: Accepted for publication in EP
Evolution of asexual and sexual reproduction in the aspergilli
Aspergillus nidulans has long-been used as a model organism to gain insights into the genetic basis of asexual and sexual developmental processes both in
other members of the genus Aspergillus, and filamentous fungi in general. Paradigms have been established concerning the regulatory mechanisms of conidial
development. However, recent studies have shown considerable genome divergence in the fungal kingdom, questioning the general applicability of findings from
Aspergillus, and certain longstanding evolutionary theories have been questioned. The phylogenetic distribution of key regulatory elements of asexual reproduction in
A. nidulans was investigated in a broad taxonomic range of fungi. This revealed that some proteins were well conserved in the Pezizomycotina (e.g. AbaA, FlbA, FluG,
NsdD, MedA, and some velvet proteins), suggesting similar developmental roles. However, other elements (e.g. BrlA) had a more restricted distribution solely in the
Eurotiomycetes, and it appears that the genetic control of sporulation seems to be more complex in the aspergilli than in some other taxonomic groups of the
Pezizomycotina. The evolution of the velvet protein family is discussed based on the history of expansion and contraction events in the early divergent fungi. Heterologous expression of the A. nidulans abaA gene in Monascus ruber failed to induce development of complete conidiophores as seen in the aspergilli, but did result in
increased conidial production. The absence of many components of the asexual developmental pathway from members of the Saccharomycotina supports the hypothesis
that differences in the complexity of their spore formation is due in part to the increased diversity of the sporulation machinery evident in the Pezizomycotina. Investigations were also made into the evolution of sex and sexuality in the aspergilli. MAT loci were identified from the heterothallic Aspergillus (Emericella) heterothallicus
and Aspergillus (Neosartorya) fennelliae and the homothallic Aspergillus pseudoglaucus (=Eurotium repens). A consistent architecture of the MAT locus was seen in
these and other heterothallic aspergilli whereas much variation was seen in the arrangement of MAT loci in homothallic aspergilli. This suggested that it is most likely that
the common ancestor of the aspergilli exhibited a heterothallic breeding system. Finally, the supposed prevalence of asexuality in the aspergilli was examined. Investigations were made using A. clavatus as a representative ‘asexual’ species. It was possible to induce a sexual cycle in A. clavatus given the correct MAT1-1 and
MAT1-2 partners and environmental conditions, with recombination confirmed utilising molecular markers. This indicated that sexual reproduction might be possible in
many supposedly asexual aspergilli and beyond, providing general insights into the nature of asexuality in fungi.National Natural Science Foundation of China 31601446National Research Foundation of Korea 2016010945Intelligent Synthetic Biology Center of Global Frontier Projects 2015M3A6A8065838Biotechnology and Biological Sciences Research CouncilGovernment of IraqMinisterio de Economía y Competitividad BIO2015-67148-
Cultural Perspective on Parenting, Trait Emotional Intelligence and Mental Health in Taiwanese Children
The current study aims to clarify the associations as well as the pathways through which parenting and children's emotional intelligence (EI) may influence children's mental health with a cross-sectional sample of 675 school pupils (fourth grade, mean age = 10.4 years, 310 boy, 356 girls and 9 unidentified) in Taiwan. Hierarchical regression and path analyses were used to examine the relationships between parenting styles, children's trait EI, and their psychological symptoms, with children's psychological symptoms as the dependent variable. The results showed that authoritative parenting was positively associated with children‟s trait EI, which in turn had a negative effect on children‟s psychological symptoms, whereas authoritarian and Chinese-specific parenting styles had direct negative effect on children‟s psychological symptoms. These findings shed light on the pathways of the interrelations between different parenting styles, children's trait EI, and psychological symptoms, providing theoretical as well as practical implications for children's emotional development and mental health
Ion-beam-driven intense electrostatic solitary waves in reconnection jet
Electrostatic solitary waves (ESWs) have been reported inside reconnection jets, but their source and role remain unclear hitherto. Here we present the first observational evidence of ESWs generation by cold ion beams inside the jet, by using high-cadence measurements from the Magnetospheric Multiscale spacecraft in the Earth's magnetotail. Inside the jet, intense ESWs with amplitude up to 30 mV m(-1) and potential up to similar to 7% of the electron temperature are observed in association with accelerated cold ion beams. Instability analysis shows that the ion beams are unstable, providing free energy for the ESWs. The waves are observed to thermalize the beams, thus providing a new channel for ion heating inside the jet. Our study suggests that electrostatic turbulence can play an important role in the jet dynamics.Peer reviewe
Discussion: "Radial strain behaviors and stress state interpretation of soil under direct simple shear" by X. Kang, Y. Cheng, and L. Ge.
Two methods were used in determining the stress state of simple shear tests in the discussed paper. The authors stated that the second method was proposed by Oda and Konishi, based on the distribution law of contact force (Oda, M. and Konishi, J., “Rotation of Principal Stresses in Granular Material During Simple,” Soils and Foundations., Vol. 14, No. 4, 1974, pp. 39–53.). However, the relation used in the method was found by Roscoe et al. from experimental results (Roscoe, K. H., Bassett, R. H., and Cole, E. R. L., “Principal Axes Observed During Simple Shear of a Sand,” Proceedings of the Geotechnical Conference on Shear Strength Properties of Natural Soils and Rocks, Vol. 1, Norwegian Geotechnical Institute, Oslo, 1967, pp. 231–237.). In addition, the determination of the constant k, which used k = 1 − K0, was problematic in the discussed paper. First, the equation could only be deduced after some assumptions were made. Second, the value of k was not a constant if the K0 changed
On the emergent Semantic Web and overlooked issues
The emergent Semantic Web, despite being in its infancy, has already received a lotof attention from academia and industry. This resulted in an abundance of prototype systems and discussion most of which are centred around the underlying infrastructure. However, when we critically review the work done to date we realise that there is little discussion with respect to the vision of the Semantic Web. In particular, there is an observed dearth of discussion on how to deliver knowledge sharing in an environment such as the Semantic Web in effective and efficient manners. There are a lot of overlooked issues, associated with agents and trust to hidden assumptions made with respect to knowledge representation and robust reasoning in a distributed environment. These issues could potentially hinder further development if not considered at the early stages of designing Semantic Web systems. In this perspectives paper, we aim to help engineers and practitioners of the Semantic Web by raising awareness of these issues
Grain boundary effects on magnetotransport in bi-epitaxial films of LaSrMnO
The low field magnetotransport of LaSrMnO (LSMO) films
grown on SrTiO substrates has been investigated. A high qualtity LSMO film
exhibits anisotropic magnetoresistance (AMR) and a peak in the
magnetoresistance close to the Curie temperature of LSMO. Bi-epitaxial films
prepared using a seed layer of MgO and a buffer layer of CeO display a
resistance dominated by grain boundaries. One film was prepared with seed and
buffer layers intact, while a second sample was prepared as a 2D square array
of grain boundaries. These films exhibit i) a low temperature tail in the low
field magnetoresistance; ii) a magnetoconductance with a constant high field
slope; and iii) a comparably large AMR effect. A model based on a two-step
tunneling process, including spin-flip tunneling, is discussed and shown to be
consistent with the experimental findings of the bi-epitaxial films.Comment: REVTeX style; 14 pages, 9 figures. Figure 1 included in jpeg format
(zdf1.jpg); the eps was huge. Accepted to Phys. Rev.
Time and Amplitude of Afterpulse Measured with a Large Size Photomultiplier Tube
We have studied the afterpulse of a hemispherical photomultiplier tube for an
upcoming reactor neutrino experiment. The timing, the amplitude, and the rate
of the afterpulse for a 10 inch photomultiplier tube were measured with a 400
MHz FADC up to 16 \ms time window after the initial signal generated by an LED
light pulse. The time and amplitude correlation of the afterpulse shows several
distinctive groups. We describe the dependencies of the afterpulse on the
applied high voltage and the amplitude of the main light pulse. The present
data could shed light upon the general mechanism of the afterpulse.Comment: 11 figure
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