1,000 research outputs found
An Ultra-High-Vacuum Rotating Sample Manipulator with Cryogenic Cooling
We report a homebuilt ultra-high-vacuum (UHV) rotating sample manipulator
with cryogenic cooling. The sample holder is thermally anchored to a built-in
cryogenic cold head through flexible copper beryllium strips, permitting
continuous sample rotation. A similar contact mechanism is implemented for the
electrical wiring to the sample holder for thermometry. The apparatus thus
enables continuous sample rotation at regulated cryogenic temperatures in a UHV
environment. We discuss the potential applications of this apparatus for
cryogenic sputtering.Comment: Cryogenics, ultra-high vacuum, sample manipulato
Multi-band Superconductivity in the Chevrel Phases SnMo6S8 and PbMo6S8
Sub-Kelvin scanning tunnelling spectroscopy in the Chevrel Phases SnMo6S8 and
PbMo6S8 reveals two distinct superconducting gaps with Delta_1 = 3 meV, Delta_2
~ 1.0 meV and Delta_1 = 3.1 meV, Delta_2 ~ 1.4 meV respectively. The gap
distribution is strongly anisotropic, with Delta_2 predominantly seen when
scanning across unit-cell steps on the (001) sample surface. The spectra are
well-fitted by an anisotropic two-band BCS s-wave gap function. Our
spectroscopic data are confirmed by electronic heat capacity measurements which
also provide evidence for a twin-gap scenario.Comment: 5 pages, 4 figure
Long-range electronic reconstruction to a -dominated Fermi surface below the LaAlO/SrTiO interface
Low dimensionality, broken symmetry and easily-modulated carrier
concentrations provoke novel electronic phase emergence at oxide interfaces.
However, the spatial extent of such reconstructions - i.e. the interfacial
"depth" - remains unclear. Examining LaAlO/SrTiO heterostructures at
previously unexplored carrier densities cm,
we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic
of an anisotropic 3D Fermi surface with preferential orbital
occupancy extending over at least 100~nm perpendicular to the interface.
Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO emerge
simultaneously at higher . We distinguish three areas in doped
perovskite heterostructures: narrow ( nm) 2D interfaces housing
superconductivity and/or other emergent phases, electronically isotropic
regions far ( nm) from the interface and new intermediate zones where
interfacial proximity renormalises the electronic structure relative to the
bulk.Comment: Supplementary material available at Scientific Reports websit
Novel Association of HK1 with Glycated Hemoglobin in a Non-Diabetic Population: A Genome-Wide Evaluation of 14,618 Participants in the Women's Genome Health Study
Type 2 diabetes is a leading cause of morbidity and mortality. While genetic variants have been found to influence the risk of type 2 diabetes mellitus, relatively few studies have focused on genes associated with glycated hemoglobin, an index of the mean blood glucose concentration of the preceding 8–12 weeks. Epidemiologic studies and randomized clinical trials have documented the relationship between glycated hemoglobin levels and the development of long-term complications in diabetes; moreover, higher glycated hemoglobin levels in the subdiabetic range have been shown to predict type 2 diabetes risk and cardiovascular disease. To examine the common genetic determinants of glycated hemoglobin levels, we performed a genome-wide association study that evaluated 337,343 SNPs in 14,618 apparently healthy Caucasian women. The results show that glycated hemoglobin levels are associated with genetic variation at the GCK (rs730497; P = 2.8×10−12), SLC30A8 (rs13266634; P = 9.8×10−8), G6PC2 (rs1402837; P = 6.8×10−10), and HK1 (rs7072268; P = 6.4×10−9) loci. While associations at the GCK, SLC30A8, and G6PC2 loci are confirmatory, the findings at HK1 are novel. We were able to replicate this novel association in an independent validation sample of 455 additional non-diabetic men and women. HK1 encodes the enzyme hexokinase, the first step in glycolysis and a likely candidate for the control of glucose metabolism. This observed genetic association between glycated hemoglobin levels and HK1 polymorphisms paves the way for further studies of the role of HK1 in hemoglobin glycation, glucose metabolism, and diabetes
Leafy amaranthus consumption patterns in Ouagadougou, Burkina Faso
There is a new attention to vegetables as vital components of daily diet. A concerted effort to raise their standing has begun to change mentalities and to fuel a rapid growth of traditional leafy vegetables marketing and consumption in African cities. However, little is known about the production and consumption patterns of these plant foods. This study examined, through a field survey the socio-economic, food consumption and conservation aspects of leafy vegetables in the region of Ouagadougou. It was found that leafy vegetables are cultivated under both rain-fed and irrigated conditions in the villages and also in the city’s gardens. The study has demonstrated that there is considerable indigenous knowledge on the leafy vegetables of the region. Amaranth species are the most cultivated and marketed and have potential for commercialization. They are used for many dishes in the local kitchen. Leafy Amaranths are consumed during all seasons even though they are more available (and cheap) during rainy season (June to end October). Ninety-four per cent of the interviewed people use vegetable Amaranth in sauce. There is a growing trend to use cultivated (introduced) species of Amaranth, which were brought to Africa by colonial powers and gained popularity because they were associated with high status. The introduced species are spreading quickly in a spontaneous manner. This can be a threat to biodiversity. There is need for a conservation initiative for the native species. In the commercialization of leafy vegetable and in particular for Amaranth, women play an important role. That could be optimized for marketing purpose to improve leafy vegetable adding-value. Because transportation is a cost increase factor, and given that cities should be targets for increased consumption, it is necessary to promote peri-urban agriculture of leafy vegetables, by policy guidelines. There is a need of documentation and dissemination of indigenous knowledge on indigenous leafy vegetables.Key words: vegetables, African greens, Amaranthus, micronutrients, biodiversity, horticulture, Ouagadougou, Burkina Fas
Detection of subthreshold pulses in neurons with channel noise
Neurons are subject to various kinds of noise. In addition to synaptic noise,
the stochastic opening and closing of ion channels represents an intrinsic
source of noise that affects the signal processing properties of the neuron. In
this paper, we studied the response of a stochastic Hodgkin-Huxley neuron to
transient input subthreshold pulses. It was found that the average response
time decreases but variance increases as the amplitude of channel noise
increases. In the case of single pulse detection, we show that channel noise
enables one neuron to detect the subthreshold signals and an optimal membrane
area (or channel noise intensity) exists for a single neuron to achieve optimal
performance. However, the detection ability of a single neuron is limited by
large errors. Here, we test a simple neuronal network that can enhance the
pulse detecting abilities of neurons and find dozens of neurons can perfectly
detect subthreshold pulses. The phenomenon of intrinsic stochastic resonance is
also found both at the level of single neurons and at the level of networks. At
the network level, the detection ability of networks can be optimized for the
number of neurons comprising the network.Comment: 14 pages, 9 figure
The distribution and movement patterns of four woodland caribou herds in Quebec and Labrador
Recent studies of woodland caribou (Rangifer tarandus caribou) in northern Quebec and central Labrador have demonstrated similar patterns of seasonal movements and distribution among four herds. Aerial surveys and radio-telemetry indicated that animals occupied forest-wetland habitat at densities of 0.03 caribou km2, or lower, for most of the year. Although females were widely dispersed at calving individuals demonstrated fidelity toward specific calving locations, in successive years. Caribou did not form large post-calving aggregations. Movement was greatest in the spring, prior to calving, and in the fall, during or immediately after rutting. Caribou were generally sedentary during summer and winter, although some moved relatively long distances to late-winter range. Although the herds occupy continuous range across Quebec and Labrador, our data indicate that the herds are largely discreete and should be managed individually
Development of integrated ecological standards of sustainable forest management at an operational scale
Within Canada, and internationally, an increasing demand that forests be managed to maintain all resources has led to the development of criteria and indicators of sustainable forest management. There is, however, a lack of understanding, at an operational scale, how to evaluate and compare forest management activities to ensure the sustainability of all resources. For example, nationally, many of the existing indicators are too broad to be used directly at a local scale of forest management; provincially, regulations are often too prescriptive and rigid to allow for adaptive management; and forest certification programs, often based largely on public or stake-holder opinion instead of scientific understanding, may be too local in nature to permit a comparison of operations across a biome. At an operational scale indicators must be relevant to forest activities and ecologically integrated. In order to aid decision-makers in the adaptive management necessary for sustainable forest management, two types of indicators are identified: those that are prescriptive to aid in planning forest management and those that are evaluative to be used in monitoring and suggesting improvements. An integrated approach to developing standards based on an ecosystem management paradigm is outlined for the boreal forest where the variability inherent in natural systems is used to define the limits within which forest management is ecologically sustainable. Sustainability thresholds are thus defined by ecosystem response after natural disturbances. For this exercise, standards are proposed for biodiversity, forest productivity via regeneration, soil conservation and aquatic resources. For each of these standards, planning indicators are developed for managing forest conditions while forest values are evaluated by environmental indicators, thus leading to a continuous cycle of improvement. Approaches to developing critical thresholds and corresponding prescriptions are also outlined. In all cases, the scale of evaluation is clearly related to the landscape (or FMU) level while the stand level is used for measurement purposes. In this view the forest should be managed as a whole even though forest interventions are usually undertaken at the stand level
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