Impact of tunnel barrier strength on magnetoresistance in carbon nanotubes

We investigate magnetoresistance in spin valves involving CoPd-contacted carbon nanotubes. Both temperature and bias voltage dependence clearly indicate tunneling magnetoresistance as the origin. We show that this effect is significantly affected by the tunnel barrier strength, which appears to be one reason for the variation between devices previously detected in similar structures. Modeling the data by means of the scattering matrix approach, we find a non-trivial dependence of the magnetoresistance on the barrier strength. Furthermore, analysis of the spin precession observed in a nonlocal Hanle measurement yields a spin lifetime of $\tau_s = 1.1\,$ns, a value comparable with those found in silicon- or graphene-based spin valve devices.Comment: 10 pages, 5 figures, 1 tabl

NASA Advanced Explorations Systems: 2018 Advancements in Life Support Systems

The NASA Advanced Exploration Systems (AES) Life Support Systems (LSS) project strives to develop reliable, energy-efficient, and low-mass spacecraft systems to provide envi-ronmental control and life support systems (ECLSS) critical to enabling long duration human missions beyond low Earth orbit (LEO). Highly reliable, closed-loop life support systems are among the capabilities required for the longer duration human space exploration missions planned in the mid-2020s and beyond. The LSS Project is focused on three life support areas: air revitalization, wastewater processing/water management and environmental monitoring. Building upon the International Space Station (ISS) LSS systems (where applicable), the three-fold mission of the LSS Project is to address discrete LSS technology gaps, to improve the reliability of LSS systems, and to advance LSS systems toward integrated testing aboard the ISS. This paper is a follow on to the AES LSS development status reported in 2017 and provides additional details on the progress made since that publication with specific attention to the status of the Aerosol Sampler ISS Flight Experiment, the Spacecraft Atmosphere Monitor (SAM) Flight Experiment, the Brine Processor Assembly (BPA) Flight Experiment as well as the progress of the terrestrial development in air, water and environmental monitoring technologies

Resaca supports range expansion of invasive apple snails (Pomacea maculata Perry, 1810; Caenogastropoda: Ampullariidae) to the Rio Grande Valley, Texas

Resacas, or oxbow lakes, form from old river channels. In the Rio Grande, resacas provide habitat for diverse wildlife, including native and non-native species. Biologists unexpectedly found pink egg masses on emergent vegetation (November 2015) and later adult apple snails (May 2016) within a resaca at a former fish hatchery in Brownsville, Texas. This report extends the non-native range of Pomacea maculata Perry, 1810 by 429 km southeast in Texas. Our findings imply that abandoned waterbodies, such as fish hatcheries, can act as unrecognized conduits for non-native invasive species

Going to Bat(s) for Studies of Disease Tolerance

A majority of viruses that have caused recent epidemics with high lethality rates in people, are zoonoses originating from wildlife. Among them are filoviruses (e.g., Marburg, Ebola), coronaviruses (e.g., SARS, MERS), henipaviruses (e.g., Hendra, Nipah) which share the common features that they are all RNA viruses, and that a dysregulated immune response is an important contributor to the tissue damage and hence pathogenicity that results from infection in humans. Intriguingly, these viruses also all originate from bat reservoirs. Bats have been shown to have a greater mean viral richness than predicted by their phylogenetic distance from humans, their geographic range, or their presence in urban areas, suggesting other traits must explain why bats harbor a greater number of zoonotic viruses than other mammals. Bats are highly unusual among mammals in other ways as well. Not only are they the only mammals capable of powered flight, they have extraordinarily long life spans, with little detectable increases in mortality or senescence until high ages. Their physiology likely impacted their history of pathogen exposure and necessitated adaptations that may have also affected immune signaling pathways. Do our life history traits make us susceptible to generating damaging immune responses to RNA viruses or does the physiology of bats make them particularly tolerant or resistant? Understanding what immune mechanisms enable bats to coexist with RNA viruses may provide critical fundamental insights into how to achieve greater resilience in humans

Characterizing the Diverse Cells that Associate with the Developing Commissures of the Zebrafish Forebrain

During embryonic development of bilateral organisms, neurons send axons across the midline at specific points to connect the two halves of the nervous system with a commissure. Little is known about the cells at the midline that facilitate this tightly regulated process. We exploit the con served process of vertebrate embryonic development in the zebrafish model system to elucidate the identity of cells at the midline that may facilitate postoptic (POC) and anterior commissure (AC) development. We have discovered that three differentgfap+ astroglial cell morphologies persist in contact with pathfinding axons throughout commissure formation. Similarly, olig2+ progenitor cells occupy delineated portions of the postoptic and anterior commissures. These early olig2+ progenitors demonstrate glial-like morphologies despite the lack of a myelination marker. Moreover, we conclude that both the gfap+ and olig2+ progenitor cells give rise to neuronal populations in both the telencephalon and diencephalon. Interestingly, these varied cell populations showed significant developmental heterochrony between the telencephalon and diencephalon. Lastly, we also showed that fli1a+ mesenchymal cells migrate along the presumptive commissure regions before and during midline axon crossing. Furthermore, following commissure maturation, specific blood vessels formed at the midline of the POC and immediately ventral and parallel to the AC. This comprehensive account of the cellular populations that correlate with the timing and position of commissural axon pathfinding has supported the conceptual modeling and identification of the early forebrain architecture that may be necessary for proper commissure development

Resaca supports range expansion of invasive apple snails (Pomacea maculata Perry, 1810; Caenogastropoda: Ampullariidae) to the Rio Grande Valley, Texas

Resacas, or oxbow lakes, form from old river channels. In the Rio Grande, resacas provide habitat for diverse wildlife, including native and non-native species. Biologists unexpectedly found pink egg masses on emergent vegetation (November 2015) and later adult apple snails (May 2016) within a resaca at a former fish hatchery in Brownsville, Texas. This report extends the non-native range of Pomacea maculata Perry, 1810 by 429 km southeast in Texas. Our findings imply that abandoned waterbodies, such as fish hatcheries, can act as unrecognized conduits for non-native invasive species

Aggregation and mobility of membrane proteins interplay with local lipid order in the plasma membrane of T cells

To disentangle the elusive lipid-protein interactions in T-cell activation, we investigate how externally imposed variations in mobility of key membrane proteins (T-cell receptor [TCR], kinase Lck, and phosphatase CD45) affect the local lipid order and protein colocalisation. Using spectral imaging with polarity-sensitive membrane probes in model membranes and live Jurkat T cells, we find that partial immobilisation of proteins (including TCR) by aggregation or ligand binding changes their preference towards a more ordered lipid environment, which can recruit Lck. Our data suggest that the cellular membrane is poised to modulate the frequency of protein encounters upon alterations of their mobility, for example in ligand binding, which offers new mechanistic insight into the involvement of lipid-mediated interactions in membrane-hosted signalling events

Stress-Dependent Opioid And Adrenergic Modulation Of Newly Retrieved Fear Memory

Recent studies on the effect of stress on modulation of fear memory in our laboratory have uncovered endogenous opioid and adrenergic based modulation systems, working in concert, that limit the strengthening or weakening of newly acquired fear memory during consolidation under conditions of mild or intense stress, respectively. The present study sought to determine if similar stress-dependent modulation, mediated by endogenous opioid and adrenergic systems, occurs during reconsolidation of newly retrieved fear memory. Rats underwent contextual fear conditioning followed 24 h later by reactivation of fear memory; a retention test was administered the next day. Stress was manipulated by varying duration of recall of fear memory during reactivation. In the first experiment, vehicle or the opioid-receptor blocker naloxone was administered immediately after varied durations (30 or 120 s) of reactivation. The results indicate that (1) reactivation, in the absence of drug, has a marked effect on freezing behavior-as duration of reactivation increases from 30 to 120 s, freezing behavior and presumably fear-induced stress increases and (2) naloxone, administered immediately after 30 s (mild stress) or 120 s (intense stress) of reactivation, enhances or impairs retention, respectively, the next day. In the second experiment, naloxone and the g-adrenergic blocker propranolol were administered either separately or in combination immediately after 120 s (intense stress) reactivation. The results indicate that separate administration of propranolol and naloxone impairs retention, while the combined administration fails to do so. Taken together the results of the two experiments are consistent with a protective mechanism, mediated by endogenous opioid and adrenergic systems working in concert, that limits enhancement and impairment of newly retrieved fear memory during reactivation in a stress-dependent manner. (C) 2013 Elsevier Inc. All rights reserved

Manipulation of Fgf and Bmp signaling in teleost fishes suggests potential pathways for the evolutionary origin of multicuspid teeth

Teeth with two or more cusps have arisen independently from an ancestral unicuspid condition in a variety of vertebrate lineages, including sharks, teleost fishes, amphibians, lizards, and mammals. One potential explanation for the repeated origins of multicuspid teeth is the existence of multiple adaptive pathways leading to them, as suggested by their different uses in these lineages. Another is that the addition of cusps required only minor changes in genetic pathways regulating tooth development. Here we provide support for the latter hypothesis by demonstrating that manipulation of the levels of Fibroblast growth factor (Fgf) or Bone morphogenetic protein (Bmp) signaling produces bicuspid teeth in the zebrafish (Danio rerio), a species lacking multicuspid teeth in its ancestry. The generality of these results for teleosts is suggested by the conversion of unicuspid pharyngeal teeth into bicuspid teeth by similar manipulations of the Mexican Tetra (Astyanax mexicanus). That these manipulations also produced supernumerary teeth in both species supports previous suggestions of similarities in the molecular control of tooth and cusp number. We conclude that despite their apparent complexity, the evolutionary origin of multicuspid teeth is positively constrained, likely requiring only slight modifications of a pre-existing mechanism for patterning the number and spacing of individual teeth. © 2013 Wiley Periodicals, Inc