How kinetics drives the two- to three-dimensional transition in semiconductor strained heterostructures: the case of InAs/GaAs(001)

The two- to three-dimensional growth transition in the InAs/GaAs(001) heterostructure has been investigated by atomic force microscopy. The kinetics of the density of three dimensional quantum dots evidences two transition thresholds at 1.45 and 1.59 ML of InAs coverage, corresponding to two separate families, small and large. Based on the scaling analysis, such families are characterized by different mechanisms of aggregation, involving the change of the critical nucleus size. Remarkably, the small ones give rise to a wealth of "monomers" through the erosion of the step edges, favoring the explosive nucleation of the large ones.Comment: 10 pages, 3 figures. Submitted to Phys. Rev. Let

Characterization of CMOS Spiral Inductors

In this work "full-wave" simulations of integrated inductors are presented and compared with measurements of fabricated CMOS chips. The good agreement between measurements and simulations demonstrates the accuracy of the tool, which is, hence, a cheaper alternative to experimental characterization. Furthermore, the proposed approach may give precious hints for performance improvements, by making internal device fields and currents available for the VLSI designer and providing compact, most effective, equivalent models

Methylglyoxal-dependent glycative stress and deregulation of SIRT1 functional network in the ovary of PCOS mice

Advanced glycation end-products (AGEs) are involved in the pathogenesis and consequences of polycystic ovary syndrome (PCOS), a complex metabolic disorder associated with female infertility. The most powerful AGE precursor is methylglyoxal (MG), a byproduct of glycolysis, that is detoxified by the glyoxalase system. By using a PCOS mouse model induced by administration of dehydroepiandrosterone (DHEA), we investigated whether MG-dependent glycative stress contributes to ovarian PCOS phenotype and explored changes in the Sirtuin 1 (SIRT1) functional network regulating mitochondrial functions and cell survival. In addition to anovulation and reduced oocyte quality, DHEA ovaries revealed altered collagen deposition, increased vascularization, lipid droplets accumulation and altered steroidogenesis. Here we observed increased intraovarian MG-AGE levels in association with enhanced expression of receptor for AGEs (RAGEs) and deregulation of the glyoxalase system, hallmarks of glycative stress. Moreover, DHEA mice exhibited enhanced ovarian expression of SIRT1 along with increased protein levels of SIRT3 and superoxide dismutase 2 (SOD2), and decreased peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC1 alpha), mitochondrial transcriptional factor A (mtTFA) and translocase of outer mitochondrial membrane 20 (TOMM20). Finally, the presence of autophagy protein markers and increased AMP-activated protein kinase (AMPK) suggested the involvement of SIRT1/AMPK axis in autophagy activation. Overall, present findings demonstrate that MG-dependent glycative stress is involved in ovarian dysfunctions associated to PCOS and support the hypothesis of a SIRT1-dependent adaptive response

Identification of a geometrically nonlinear micromorphic continuum via granular micromechanics

Describing the emerging macro-scale behavior by accounting for the micro-scale phenomena calls for microstructure-informed continuum models accounting properly for the deformation mechanisms identifiable at the micro-scale. Classical continuum theory, in contrast to the micromorphic continuum theory, is unable to take into account the effects of complex kinematics and distribution of elastic energy in internal deformation modes within the continuum material point. In this paper, we derive a geometrically nonlinear micromorphic continuum theory on the basis of granular mechanics, utilizing grain-scale deformation as the fundamental building block. The definition of objective kinematic descriptors for relative motion is followed by Piola’s ansatz for micro–macro-kinematic bridging and, finally, by a limit process leading to the identification of the continuum stiffness parameters in terms of few micro-scale constitutive quantities. A key aspect of the presented approach is the identification of relevant kinematic measures that describe the deformation of the continuum body and link it to the micro-scale deformation. The methodology, therefore, has the ability to reveal the connections between the micro-scale mechanisms that store elastic energy and lead to particular emergent behavior at the macro-scale

Geographic variability in the grey mullet Mugil cephalus: preliminary results of mtDNA and chromosome analyses

The grey mullet, Mugil cephalus, plays an important role in the fisheries and aquaculture of tropical and subtropical regions of the world. This species is considered cosmopolitan, but its distribution appears peculiar with regard to the coastal ecology of the species. A multidisciplinary study of the geographic variability of this species, through a cytogenetic, molecular and morphometric characterization, was undertaken to detect whether genetically distinct populations occur. The preliminary results from analyses of mitochondrial DNA and of chromosomes of seven different populations around the world are reported. The different populations analysed are well discriminated by mtDNA analyses: samples are clustered in four groups, Mediterranean, East Atlantic, Central Pacific and East Pacific, with a maximum sequence divergence of 3.3%. The karyotype of all the populations studied is uniformly composed of 48 acrocentric chromosomes, and neither heterochromatin distribution nor nucleolus organizer regions allow the identification of chromosomal markers useful in distinguishing these genetically differentiated groups of populations. © 1993

Increased cortical excitability after selective REM sleep deprivation in healthy humans: a transcranial magnetic stimulation study

REM sleep has antiepileptogenic properties whereas, its loss is known to have a proconvulsive role. However, the mechanisms underlying the proepileptogenic effects of REM sleep deprivation are yet not fully understood. The aim of our study was to evaluate the effects of selective REM sleep deprivation (SRD) on cortical excitability in healthy subjects by means of transcranial magnetic stimulation (TMS)

Double grain boundary configurations on graphite surfaces

We investigated the atomic structure of different kinds of grain boundaries on highly oriented pyrolytic graphite (HOPG) by scanning tunneling microscopy. We categorized several grain boundary configurations as a function of the misorientation angle between the adjacent grains, highlighting the occurrence of double grain boundaries (i.e., systems of two grain boundaries separated by a nanometric-scale inner region with specific atomic arrangement) for misorientation angles in the range 22°–32°. By using Molecular Dynamics simulations, we analyzed the structure and energy stability of single and double grain boundaries according to the misorientation angle. The experimental evidence is corroborated by Molecular Dynamics results and total energy calculations, which found a comparable stability between single and double grain boundaries for the same misorientation angle range. Our combination of experimental measurements and theoretical calculation extends the understanding of the structural configuration of large angle grain boundaries beyond the range of misorientation angles reported to date