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Experimental analysis of the cyclic behaviour of Kaolin at high temperature
No full textThis paper presents the results of an experimental study related to the thermal effects on kaolin clay cyclic mobility. The thermal effects were identified by comparing the experimental results of cyclic triaxial tests performed at high temperature (90 C) with results of the same type of test carried out at ambient temperature (22 C). For the testing, a new temperature-controlled triaxial apparatus, developed by the authors, was employed. Experimental evidence shows that shear cycles on the heated samples induced smaller axial strain and pore-water pressure per cycle in comparison with the unheated samples. In addition, shear-induced pore-water pressure at large strains in the heated sample was slightly lower than in the unheated sample. In other words, the heated samples behaved as if they were denser, which is a result of thermal hardening. These results may be applied in geotechnical and earthquake engineering applications as a soil improvement technique.LM
K-band single-chip electron spin resonance detector
No full textWe report on the design, fabrication, and characterization of an integrated detector for electron spin resonance spectroscopy operating at 27 GHz. The microsystem, consisting of an LC-oscillator and a frequency division module, is integrated onto a single silicon chip using a conventional complementary metal-oxide-semiconductor technology. The achieved room temperature spin sensitivity is about 10(8) spins/G Hz(1/2), with a sensitive volume of about (100 mu m)(3). Operation at 77 K is also demonstrated. (C) 2012 Elsevier Inc. All rights reserved.LMIS1LMIS
Recent Progress in Metal Borohydrides for Hydrogen Storage
No full textThe prerequisite for widespread use of hydrogen as an energy carrier is the development of new materials that can safely store it at high gravimetric and volumetric densities. Metal borohydrides M(BH 4) n (n is the valence of metal M), in particular, have high hydrogen density, and are therefore regarded as one such potential hydrogen storage material. For fuel cell vehicles, the goal for on-board storage systems is to achieve reversible store at high density but moderate temperature and hydrogen pressure. To this end, a large amount of effort has been devoted to improvements in their thermodynamic and kinetic aspects. This review provides an overview of recent research activity on various M(BH 4) n, with a focus on the fundamental dehydrogenation and rehydrogenation properties and on providing guidance for material design in terms of tailoring thermodynamics and promoting kinetics for hydrogen storage.LME
Millimeter-wave to near-terahertz sensors based on reversible insulator-to-metal transition in VO2
No full textIn the quest for low power bio-inspired spiking sensors, functional oxides like vanadium dioxide are expected to enable future energy efficient sensing. Here, we report uncooled millimeter-wave spiking detectors based on the sensitivity of insulator-to-metal transition threshold voltage to the incident wave. The detection concept is demonstrated through actuation of biased VO2 switches encapsulated in a pair of coupled antennas by interrupting coplanar waveguides for broadband measurements, on silicon substrates. Ultimately, we propose an electromagnetic-wave-sensitive voltage-controlled spike generator based on VO2 switches in an astable spiking circuit. The fabricated sensors show responsivities of around 66.3 MHz.W-1 at 1 mu W, with a low noise equivalent power of 5 nW.Hz(-0.5) at room temperature, for a footprint of 2.5 x 10(-5) mm(2). The responsivity in static characterizations is 76 kV.W-1. Based on experimental statistical data measured on robust fabricated devices, we discuss stochastic behavior and noise limits of VO2 -based spiking sensors applicable for wave power sensing in mm-wave and sub-terahertz range.Vanadium dioxide is a strongly correlated material interesting for its ultra-fast resistive switching controlled by an electric-field-driven insulator-metal transition. Here, VO2 stochastic oscillator power sensors for mm-wave to sub-THz radiation are demonstrated, displaying high responsivities, low noise, and a small scalable footprint.NANOLA
On the different regimes of stochastic gradient descent
No full textModern deep networks are trained with stochastic gradient descent (SGD) whose key hyperparameters are the number of data considered at each step or batch size B, and the step size or learning rate n. For small B and large n, SGD corresponds to a stochastic evolution of the parameters, whose noise amplitude is governed by the “temperature” T ≡ n/B. Yet this description is observed to break down for sufficiently large batches B ≥ B∗, or simplifies to gradient descent (GD) when the temperature is sufficiently small. Understanding where these cross-overs take place remains a central challenge. Here, we resolve these questions for a teacher-student perceptron classification model and show empirically that our key predictions still apply to deep networks. Specifically, we obtain a phase diagram in the B-n plane that separates three dynamical phases: i) a noise-dominated SGD governed by temperature, ii) a large-first-step-dominated SGD and iii) GD. These different phases also correspond to different regimes of generalization error. Remarkably, our analysis reveals that the batch size B∗ separating regimes (i) and (ii) scale with the size P of the training set, with an exponent that characterizes the hardness of the classification problem.PCS
Towards personalized mapping through lumbosacral spinal cord task fMRI
No full textThe lumbosacral spinal cord contains neural circuits crucial for locomotion, organized into rostrocaudal levels with distinct somatosensory and motor neuron pools that project to and from the muscles of the lower limbs. However, the specific spinal levels that innervate each muscle and the locations of neuron pools vary significantly between individuals, presenting challenges for targeted therapies and neurosurgical interventions aimed at restoring locomotion. Non-invasive approaches to functionally map the segmental distribution of muscle innervation—or projectome—are therefore essential. Here, we developed a pipeline dedicated to record blood oxygenation level dependent (BOLD) signals in the lumbosacral spinal cord using functional magnetic resonance imaging (fMRI). We assessed spinal activity across different conditions targeting the extensor/flexor muscles of the right leg (ankle, knee, and hip) in 12 healthy participants. To enhance clinical relevance, we included not only active movements but also two conditions that did not rely on participants’ performance: passive stretches and muscle-specific tendon vibration, which activates proprioceptive afferents of the vibrated muscle. BOLD activity patterns were primarily located on the side ipsilateral to the movement, stretch, or vibration, both at the group and participant levels, indicating the BOLD activity being associated with the projectome. The fMRI-derived rostrocaudal BOLD activity patterns exhibited mixed alignment with expected innervation maps from invasive studies, varying by muscle and condition. While some muscles and conditions matched well across studies, others did not. Significant variability among individual participants underscores the need for personalized mapping of projections for targeted therapies and neurosurgical interventions. To support the interpretation of BOLD activity patterns, we developed a decision tree-based framework that combines reconstruction of neural structures from high-resolution anatomical MRI datasets and muscle-specific fMRI activity to produce personalized projectomes. Our findings provide a valuable proof-of-concept for the potential of fMRI to map the lumbosacral spinal cord’s functional organization, while shedding light on challenges associated with this endeavor.MIPLA
Dynamic system modeling of thermally-integrated concentrated PV-electrolysis
No full textUnderstanding the dynamic response of a solar fuel processing system utilizing concentrated solar radiation and made of a thermally-integrated photovoltaic (PV) and water electrolyzer (EC) is important for the design, development and implementation of this technology. A detailed dynamic non-linear process model is introduced for the fundamental system components (i.e. PV, EC, pump etc.) in order to investigate the coupled system behaviour and performance synergy notably arising from the thermal integration. The nominal hydrogen production power is 2 kW at a hydrogen system effciency of 16-21 % considering a high performance triple junction III-V PV module and a proton exchange membrane EC. The device operating point relative to the maximum power point of the PV was shown to have a differing influence on the system performance when subject to temperature changes. The non-linear coupled behaviour was characterised in response to step changes in water flowrate and solar irradiance and hysteresis of the current-voltage operating point was demonstrated. Whilst the system responds thermally to changes in operating conditions in the range of 0.5-2 minutes which leads to advantageously short start-up times, a number of control challenges are identified such as the impact of pump failure, electrical PV-EC disconnection, and the potentially damaging accentuated temperature rise at lower water flowrates. Finally, the simulation of co-generation of heat and hydrogen for various operating conditions demonstrates the significant potential for system effciency enhancements and the required development of control strategies for demand matching is discussed.LRESEThis is an Open Access article under the terms of the Creative Commons Attribution Licens
IL-13 induces expression of CD36 in human monocytes through PPARgamma activation
No full textThe class B scavenger receptor CD36 is a component of the pattern recognition receptors on monocytes that recognizes a variety of molecules. CD36 expression in monocytes depends on exposure to soluble mediators. We demonstrate here that CD36 expression is induced in human monocytes following exposure to IL-13, a Th2 cytokine, via the peroxisome proliferator-activated receptor (PPAR)gamma pathway. Induction of CD36 protein was paralleled by an increase in CD36 mRNA. The PPARgamma pathway was demonstrated using transfection of a PPARgamma expression plasmid into the murine macrophage cell line RAW264.7, expressing very low levels of PPARgamma, and in peritoneal macrophages from PPARgamma-conditional null mice. We also show that CD36 induction by IL-13 via PPARgamma is dependent on phospholipase A2 activation and that IL-13 induces the production of endogenous 15-deoxy-Delta12,14-prostaglandin J2, an endogenous PPARgamma ligand, and its nuclear localization in human monocytes. Finally, we demonstrate that CD36 and PPARgamma are involved in IL-13-mediated phagocytosis of Plasmodium falciparum-parasitized erythrocytes. These results reveal a novel role for PPARgamma in the alternative activation of monocytes by IL-13, suggesting that endogenous PPARgamma ligands, produced by phospholipase A2 activation, could contribute to the biochemical and cellular functions of CD36.LIS
Regulation of gene expression by activation of the peroxisome proliferator-activated receptor gamma with rosiglitazone (BRL 49653) in human adipocytes
No full textTo better define the mechanism of action of the thiazolidinediones, we incubated freshly isolated human adipocytes with rosiglitazone and investigated the changes in mRNA expression of genes encoding key proteins of adipose tissue functions. Rosiglitazone (10(-6) M, 4 h) increased p85alphaphosphatidylinositol 3-kinase (p85alphaPI-3K) and uncoupling protein-2 mRNA levels and decreased leptin expression. The mRNA levels of insulin receptor, IRS-1, Glut 4, lipoprotein lipase, hormone-sensitive lipase, acylation-stimulating protein, fatty acid transport protein-1, angiotensinogen, plasminogen activator inhibitor-1, and PPARgamma1 and gamma2 were not modified by rosiglitazone treatment. Activation of RXR, the partner of PPARgamma, in the presence of rosiglitazone, increased further p85alphaPI-3K and UCP2 mRNA levels and produced a significant augmentation of Glut 4 expression. Because p85alphaPI-3K is a major component of insulin action, the induction of its expression might explain, at least in part, the insulin-sensitizing effect of the thiazolidinediones.LIS
Correlation of fluorescence microscopy, electron microscopy, and NanoSIMS stable isotope imaging on a single tissue section
No full textCorrelative light and electron microscopy allows localization of specific molecules at the ultrastructural level in biological tissue but does not provide information about metabolic turnover or the distribution of labile molecules, such as micronutrients. We present a method to directly correlate (immuno)fluorescent microscopy, (immuno)TEM imaging and NanoSIMS isotopic mapping of the same tissue section, with nanometer-scale spatial precision. The process involves chemical fixation of the tissue, cryo sectioning, thawing, and air-drying under a thin film of polyvinyl alcohol. It permits to effectively retain labile compounds and strongly increases NanoSIMS sensitivity for C-13-enrichment. The method is illustrated here with correlated distribution maps of a carbonic anhydrase enzyme isotype, beta -tubulin proteins, and C-13- and N-15-labeled labile micronutrients (and their anabolic derivates) within the tissue of a reef-building symbiotic coral. This broadly applicable workflow expands the wealth of information that can be obtained from multi-modal, sub-cellular observation of biological tissue. Loussert-Fonta et al. have developed a method to directly correlate fluorescent microscopy, (immuno)TEM imaging and NanoSIMS isotopic mapping of the same tissue section, with nanometer-scale spatial precision. They illustrate the technique by imaging tissue from a symbiotic coral, Stylophora pistillata.LGBPV-LA