Significant Phonon Drag Enables High Power Factor in the AlGaN/GaN Two-Dimensional Electron Gas

In typical thermoelectric energy harvesters and sensors, the Seebeck effect is caused by diffusion of electrons or holes in a temperature gradient. However, the Seebeck effect can also have a phonon drag component, due to momentum exchange between charge carriers and lattice phonons, which is more difficult to quantify. Here, we present the first study of phonon drag in the AlGaN/GaN two-dimensional electron gas (2DEG). We find that phonon drag does not contribute significantly to the thermoelectric behavior of devices with ~100 nm GaN thickness, which suppress the phonon mean free path. However, when the thickness is increased to ~1.2 $\mu$m, up to 32% (88%) of the Seebeck coefficient at 300 K (50 K) can be attributed to the drag component. In turn, the phonon drag enables state-of-the-art thermoelectric power factor in the thicker GaN film, up to ~40 mW m$^{-1}$ K$^{-2}$ at 50 K. By measuring the thermal conductivity of these AlGaN/GaN films, we show that the magnitude of the phonon drag can increase even when the thermal conductivity decreases. Decoupling of thermal conductivity and Seebeck coefficient could enable important advancements in thermoelectric power conversion with devices based on 2DEGs

Chronic Stress Triggers Expression of Immediate Early Genes and Differentially Affects the Expression of AMPA and NMDA Subunits in Dorsal and Ventral Hippocampus of Rats

Indexación: Web of Science; Scopus.Previous studies in rats have demonstrated that chronic restraint stress triggers anhedonia, depressive-like behaviors, anxiety and a reduction in dendritic spine density in hippocampal neurons. In this study, we compared the effect of repeated stress on the expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunits in dorsal and ventral hippocampus (VH). Adult male Sprague-Dawley rats were randomly divided into control and stressed groups, and were daily restrained in their motion (2.5 h/day) during 14 days. We found that chronic stress promotes an increase in c-Fos mRNA levels in both hippocampal areas, although it was observed a reduction in the immunoreactivity at pyramidal cell layer. Furthermore, Arc mRNAs levels were increased in both dorsal and VH, accompanied by an increase in Arc immunoreactivity in dendritic hippocampal layers. Furthermore, stress triggered a reduction in PSD-95 and NR1 protein levels in whole extract of dorsal and VH. Moreover, a reduction in NR2A/NR2B ratio was observed only in dorsal pole. In synaptosomal fractions, we detected a rise in NR1 in dorsal hippocampus (DH). By indirect immunofluorescence we found that NR1 subunits rise, especially in neuropil areas of dorsal, but not VH. In relation to AMPA receptor (AMPAR) subunits, chronic stress did not trigger any change, either in dorsal or ventral hippocampal areas. These data suggest that DH is more sensitive than VH to chronic stress exposure, mainly altering the expression of NMDA receptor (NMDAR) subunits, and probably favors changes in the configuration of this receptor that may influence the function of this area.https://www.frontiersin.org/articles/10.3389/fnmol.2017.00244/ful

Langerin-Heparin Interaction: Two Binding Sites for Small and Large Ligands as revealed by a combination of NMR Spectroscopy and Cross-Linking Mapping Experiments

Langerin is a C-type lectin present on Langerhans cells that mediates capture of pathogens in a carbohydrate-dependent manner, leading to subsequent internalization and elimination in the cellular organelles called Birbeck granules. This mechanism mediated by langerin was shown to constitute a natural barrier for HIV-1 particle transmission. Besides interacting specifically with high mannose and fucosylated neutral carbohydrate structures, langerin has the ability to bind sulfated carbohydrate ligands as 6-sulfated galactosides in the Ca2+ dependent binding site. Very recently langerin was demonstrated to interact with sulfated glycosaminoglycans (GAGs), in a Ca2+ independent way, resulting in the proposal of a new binding site for GAGs. Based on those results, we have conducted a structural study of the interactions of small heparin (HEP) like oligosaccharides with langerin in solution. Heparin-bead cross-linking experiments, an approach specifically designed to identify HEP/HS binding sites in proteins were first carried out and experimentally validated the previously proposed model for the interaction of Lg ECD with 6 kDa HEP. High-resolution NMR studies of a set of 8 synthetic HEP-like trisaccharides harboring different sulfation patterns demonstrated that all of them bound to langerin in a Ca2+ dependent way. The binding epitopes were determined by STD NMR and the bound conformations by transferred NOESY experiments. These experimental data were combined with docking and molecular dynamics and resulted in the proposal of a binding mode characterized by the coordination of calcium by the two equatorial hydroxyl groups OH3 and OH4 at the non-reducing end. The binding also includes the carboxylate group at the adjacent iduronate residue. Such epitope is shared by all the 8 ligands, explaining the absence of any impact on binding from their differences in substitution pattern. Finally, in contrast to the small trisaccharides, we demonstrated that a longer HEP-like hexasaccharide, bearing an additional O-sulfate group at the non-reducing end, which precludes binding to the Ca2+ site, interacts with langerin in the previously identified Ca2+ independent binding site

MicroRNA Profiling and Bioinformatics Target Analysis in Dorsal Hippocampus of Chronically Stressed Rats: Relevance to Depression Pathophysiology

Indexación: Scopus.1Laboratory of Neuroplasticity and Neurogenetics, Faculty of Chemical and Pharmaceutical Sciences, Department of Biochemistry and Molecular Biology, Universidad de Chile, Santiago, Chile, 2National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Durham, NC, United States, 3Centro de Genómica y Bioinformática, Facultad de Ciencias, Universidad Mayor, Santiago, Chile, 4Millennium Institute for Integrative Biology (iBio), FONDAP Center for Genome Regulation, Departamento de Genética Molecular y Microbiología, Pontificia Universidad Católica de Chile, Santiago, Chile, 5Department of Kinesiology, Faculty of Health Sciences, Universidad Católica del Maule, Talca, Chile, 6Escuela de Química y Farmacia, Facultad de Medicina, Universidad Andres Bello, Santiago, Chile.This study was supported by the following grants: FONDECYT 1120528 (JLF), Fondo Central de Investigación, Universidad de Chile ENL025/16 (JLF), ES090079 (JAC). Research in RG and EV laboratories is funded by Instituto Milenio iBio – Iniciativa Científica Milenio MINECON.Studies conducted in rodents subjected to chronic stress and some observations in humans after psychosocial stress, have allowed to establish a link between stress and the susceptibility to many complex diseases, including mood disorders. The studies in rodents have revealed that chronic exposure to stress negatively affects synaptic plasticity by triggering changes in the production of trophic factors, subunit levels of glutamate ionotropic receptors, neuron morphology, and neurogenesis in the adult hippocampus. These modifications may account for the impairment in learning and memory processes observed in chronically stressed animals. It is plausible then, that stress modifies the interplay between signal transduction cascades and gene expression regulation in the hippocampus, therefore leading to altered neuroplasticity and functioning of neural circuits. Considering that miRNAs play an important role in post-transcriptional-regulation of gene expression and participate in several hippocampus-dependent functions; we evaluated the consequences of chronic stress on the expression of miRNAs in dorsal (anterior) portion of the hippocampus, which participates in memory formation in rodents. Here, we show that male rats exposed to daily restraint stress (2.5 h/day) during 7 and 14 days display a differential profile of miRNA levels in dorsal hippocampus and remarkably, we found that some of these miRNAs belong to the miR-379-410 cluster. We confirmed a rise in miR-92a and miR-485 levels after 14 days of stress by qPCR, an effect that was not mimicked by chronic administration of corticosterone (14 days). Our in silico study identified the top-10 biological functions influenced by miR-92a, nine of which were shared with miR-485: Nervous system development and function, Tissue development, Behavior, Embryonic development, Organ development, Organismal development, Organismal survival, Tissue morphology, and Organ morphology. Furthermore, our in silico study provided a landscape of potential miRNA-92a and miR-485 targets, along with relevant canonical pathways related to axonal guidance signaling and cAMP signaling, which may influence the functioning of several neuroplastic substrates in dorsal hippocampus. Additionally, the combined effect of miR-92a and miR-485 on transcription factors, along with histone-modifying enzymes, may have a functional relevance by producing changes in gene regulatory networks that modify the neuroplastic capacity of the adult dorsal hippocampus under stress. © 2018 Muñoz-Llanos, García-Pérez, Xu, Tejos-Bravo, Vidal, Moyano, Gutiérrez, Aguayo, Pacheco, García-Rojo, Aliaga, Rojas, Cidlowski and Fiedler.https://www.frontiersin.org/articles/10.3389/fnmol.2018.00251/ful

Fijación de CO2 por Pinus sylvestris L. y Quercus pyrenaica Willd. en los montes «Pinar de Valsaín» y «Matas de Valsaín»

Biomass and carbon dioxide accumulated amounts have been estimated in two Pinus sylvestris and Quercus pyrenaica forests («Matas de Valsaín» and «Pinar de Valsaín», Segovia). Data obtained in samplings made by CIFOR-INIA for both species have been utilized in this study. For each species, three trees per diameter class were selected, being then felled and separated into their biomass fractions (stems, branches with diameter over 7 cm, branches with diameter between 2 and 7 cm and branches thinner than 2 cm). Every tree fraction was weighed at field. The stump of one tree per diameter class was also extracted and weighed. Dry weights were determined at the laboratory through a sample of each fraction, and linear regression models to relate dry biomass with diameter for each biomass fraction were fitted. Using these models, a biomass table was constructed to be applied to inventory data (number of trees per diameter class) for determining total biomass within the stands. The CO2 fixed per biomass unit was calculated through the ratio biomass/carbon. Balances of net CO2 fixation have been determined knowing the annual increment and annual extractions.Se ha realizado una estimación de la biomasa y del dióxido de carbono que hay acumulado en las masas de Pinus sylvestris y Quercus pyrenaica de los montes «Matas de Valsaín» y «Pinar de Valsaín» (Segovia). Para ello se han utilizado los datos de muestreos realizados por el CIFOR-INIA para ambas especies. Se eligen al menos tres pies por clase diamétrica, se apearon y se separaron en fracciones de biomasa (fuste, ramas de diámetro mayor de 7 cm, ramas de diámetro entre 2 y 7 cm, ramas menores de 2 cm) que se pesaron en campo. Se extrajo el tocón de un pie por clase diamétrica y se pesó en verde. En laboratorio se determinó el peso seco de las muestras y se hallaron modelos para las distintas fracciones que relacionasen la biomasa seca y con el diámetro. Con estos modelos se calcularon unos valores modulares que se aplicaron a los datos del número de pies, obtenidos de los inventarios, para estimar la biomasa total de los montes. El CO2 se estima mediante la relación entre el porcentaje de carbono en la biomasa seca y la cantidad de carbono en una molécula de CO2. Se han realizado balances de fijación neta de CO2 conociendo los crecimientos y las extracciones anuales

Estudio del manejo de serpientes venenosas y actuación en caso de mordedura

La tenencia de serpientes venenosas, ya sea como mascotas o como miembros de exposiciones o de parques zoológicos, requiere de las instalaciones y de la infraestructura necesarias para garantizar la seguridad de los propietarios, y del conocimiento de su manejo. Los dispositivos utilizados tienen diversos fines: protección personal (gafas, guantes, polainas, botas), sujeción (ganchos, tubos de contención, bolsas de transporte) o alimentación (pinzas, abrebocas, sondas). En caso de mordedura, se debe recurrir a asistencia hospitalaria para que se proceda a la administración del suero antiofídico específico lo antes posible. Como primeros auxilios se debe mantener a la víctima tranquila e inmóvil, limpiar la mordedura y aplicar una bomba de succión de veneno.When venomous snakes are keep in captivity, as a pet or spice as a part of collections from zoo, some infrastructure and facilities for ensuring the people safety must be available and the staff must know how to use them. Many devices for the snakes handling have been marketed: personal protection equipment (glasses, gloves, shoes, gaiter), snake fastening devices (hooks, restlessness tubes, transport bags) or feeding gadgets (tweezers, mouth openers, feeding tubes). When somebody is bitten, hospital emergency service must be requested as soon as possible and so the specific antivenom serum will be administered. The first aid would consist on keeping the bitten individual at ease and at rest, cleaning the bite injury and using a venom suction pump

DC and RF Performance of AlGaN/GaN HEMTs on SiC at High Temperatures

GaN-based transistors have demonstrated to be the most promising candidates for applications with high power and high frequency requirements, and working in harsh environments. They take advantage of some interesting properties of nitrides such as their thermal stability or high electron velocity, together with a high sheet carrier density (~1013 cm-2) provided by AlGaN/GaN heterostructures thanks to the favorable band offsets and internal piezoelectric fields. In above applications, transistors may work in small signal amplifiers under high ambient temperatures, or in power amplifiers where channel temperatures may increase significantly. Thus, high temperature (HT) operation and related reliability issues have become important research topics in GaN electronics. Although some works have been recently published about DC characterization of HEMTs at HT [1-5], there are few papers studying their behaviour at RF [4,5]. This work aims to understand the small signal performance of AlGaN/GaN HEMTs on SiC at HT, using DC and RF measurements combined with proper modeling and small signal parameters extraction

Basement membrane-rich Organoids with functional human blood vessels are permissive niches for human breast cancer metastasis

Metastasic breast cancer is the leading cause of death by malignancy in women worldwide. Tumor metastasis is a multistep process encompassing local invasion of cancer cells at primary tumor site, intravasation into the blood vessel, survival in systemic circulation, and extravasation across the endothelium to metastasize at a secondary site. However, only a small percentage of circulating cancer cells initiate metastatic colonies. This fact, together with the inaccessibility and structural complexity of target tissues has hampered the study of the later steps in cancer metastasis. In addition, most data are derived from in vivo models where critical steps such as intravasation/extravasation of human cancer cells are mediated by murine endothelial cells. Here, we developed a new mouse model to study the molecular and cellular mechanisms underlying late steps of the metastatic cascade. We have shown that a network of functional human blood vessels can be formed by co-implantation of human endothelial cells and mesenchymal cells, embedded within a reconstituted basement membrane-like matrix and inoculated subcutaneously into immunodeficient mice. The ability of circulating cancer cells to colonize these human vascularized organoids was next assessed in an orthotopic model of human breast cancer by bioluminescent imaging, molecular techniques and immunohistological analysis. We demonstrate that disseminated human breast cancer cells efficiently colonize organoids containing a functional microvessel network composed of human endothelial cells, connected to the mouse circulatory system. Human breast cancer cells could be clearly detected at different stages of the metastatic process: initial arrest in the human microvasculature, extravasation, and growth into avascular micrometastases. This new mouse model may help us to map the extravasation process with unprecedented detail, opening the way for the identification of relevant targets for therapeutic intervention