176 research outputs found
A study of transport suppression in an undoped AlGaAs/GaAs quantum dot single-electron transistor
We report a study of transport blockade features in a quantum dot
single-electron transistor, based on an undoped AlGaAs/GaAs heterostructure. We
observe suppression of transport through the ground state of the dot, as well
as negative differential conductance at finite source-drain bias. The
temperature and magnetic field dependence of these features indicate the
couplings between the leads and the quantum dot states are suppressed. We
attribute this to two possible mechanisms: spin effects which determine whether
a particular charge transition is allowed based on the change in total spin,
and the interference effects that arise from coherent tunneling of electrons in
the dot
III-V nanowires and nanowire optoelectronic devices
III–V nanowires (NWs) have been envisioned as nanoscale materials for next-generation technology with good functionality, superior performance, high integration ability and low cost, because of their special growth modes and unique 1D structure. In this review, we summarize the main challenges and important progress of the fabrication and applications of III–V NWs. We start with the III–V NW growth, that significantly influences the NW morphology and crystal quality. Attention is then given to the fabrication of some advanced III–V structures composed of axial and radial junctions. After that, we review the advantages, challenges, and major breakthroughs of using III–V NWs as solar energy harvesters and light emitters. Finally, we attempt to give a perspective look on the future development trends and the remaining challenges in the research field of III–V NWs
Radio-frequency reflectometry on an undoped AlGaAs/GaAs single electron transistor
Radio frequency reflectometry is demonstrated in a sub-micron undoped
AlGaAs/GaAs device. Undoped single electron transistors (SETs) are attractive
candidates to study single electron phenomena due to their charge stability and
robust electronic properties after thermal cycling. However these devices
require a large top-gate which is unsuitable for the fast and sensitive radio
frequency reflectometry technique. Here we demonstrate rf reflectometry is
possible in an undoped SET.Comment: Four pages, three figures, one supplementary fil
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Investigating Vibrio parahaemolyticus interactions with the Pacific oyster, Crassostrea gigas
Vibrio parahaemolyticus is a Gram-negative, halophilic, human pathogenic bacterium ubiquitous in the marine environment. Like many Vibrio species, V. parahaemolyticus commonly associates with shellfish, particularly oysters. Ingestion of a raw or under cooked oysters contaminated with V. parahaemolyticus can cause gastroenteritis, which is typically self-limiting and rarely causes death. Globally, oyster production is highly lucrative, especially on the West Coast of the United States where approximately 60% of oyster production occurs each year. Outbreaks of V. parahaemolyticus can result in a significant public health problem as well as an economic burden for the oyster farms implicated in the outbreak. With the increase in overall V. parahaemolyticus outbreaks, improved post-harvest processing strategies have been developed to reduce this natural contaminant. Depuration was developed to allow shellfish to purge contaminants from their tissues into the clean, flowing seawater where they are held. This post-harvest processing technique can typically reduce fecal contaminants from the oyster tissues but is relatively ineffective at eliminating V. parahaemolyticus and other Vibrio species.. Thus, improved methods for reducing this and other human pathogenic Vibrio are needed to effectively produce safer oysters for the consumer. To develop more effective and novel V. parahaemolyticus intervention strategies, first we must identify the factors that are involved in V. parahaemolyticus colonization of the oyster, allowing them toresist depuration. This study sought to investigate specific factors utilized by V. parahaemolyticus and, in the process, determined that various strains of V. parahaemolyticus have different alleles of the Type IV pili, mannose-sensitive hemagglutinin (MSHA)and chitin-regulated pilus (PilA). In addition, we expanded our investigations into the allelic diversity of MSHA and PilA from Vibrio cholerae and Vibrio vulnificus and found that V. cholerae strains that possess the Type IV toxin co-regulated pilus (TCP) maintained highly conserved MSHA and PilA sequences while strains of V. cholerae without TCP, and all of the V. vulnificus and V. parahaemolyticus strains examined, had highly divergent sequences with no discernable connection to isolation source or observed phenotype. Following that discovery, we determined that Type I, and Type IV pili, as well as polar and lateral flagellar systems contribute to V. parahaemolyticus persistence in the Pacific oyster during depuration, while Type III secretion systems and phase variation do not. Overall, we have identified factors involved in colonization of the Pacific oyster by V. parahaemolyticus. Future studies investigating conditions that affect pili and flagella production in V. parahaemolyticus may provide novel depuration conditions that could easily and effectively increase the efficiency of oyster depuration, ultimately reducing the risk of seafood-borne illness by V. parahaemolyticus associated with oysters
Shadow epitaxy for in-situ growth of generic semiconductor/superconductor devices
Uniform, defect-free crystal interfaces and surfaces are crucial ingredients
for realizing high-performance nanoscale devices. A pertinent example is that
advances in gate-tunable and topological superconductivity using
semiconductor/superconductor electronic devices are currently built on the hard
proximity-induced superconducting gap obtained from epitaxial indium
arsenide/aluminium heterostructures. Fabrication of devices requires selective
etch processes; these exist only for InAs/Al hybrids, precluding the use of
other, potentially superior material combinations. We present a crystal growth
platform -- based on three-dimensional structuring of growth substrates --
which enables synthesis of semiconductor nanowire hybrids with in-situ
patterned superconductor shells. This platform eliminates the need for etching,
thereby enabling full freedom in choice of hybrid constituents. We realise and
characterise all the most frequently used architectures in superconducting
hybrid devices, finding increased yield and electrostatic stability compared to
etched devices, along with evidence of ballistic superconductivity. In addition
to aluminium, we present hybrid devices based on tantalum, niobium and
vanadium.
This is the submitted version of the manuscript. The accepted, peer reviewed
version is available from Advanced Materials:
http://doi.org/10.1002/adma.201908411
Previous title: Shadow lithography for in-situ growth of generic
semiconductor/superconductor device
Ten-fold enhancement of InAs nanowire photoluminescence emission with an InP passivation layer
In this letter, we demonstrate that a significant improvement of optical performance of InAs nanowires can be achieved by capping the core InAs nanowires with a thin InP shell, which successfully passivates the surface states reducing the rate of non-radiative recombination. The improvements have been confirmed by detailed photoluminescence measurements, which showed up to ten-fold increase in the intensity of room-temperature photoluminescence from the capped InAs/InP nanowires compared to the sample with core-only InAs nanowires. Moreover, the nanowires exhibit high stability of total photoluminescence emission strength across temperature range from 10 to 300 K as a result of strong quantum confinement. These findings could be the key to successful implementation of InAs nanowires into optoelectronic devices
Risk of being granted disability pension among incident cancer patients before and after a structural pension reform:A Danish population-based, matched cohort study
OBJECTIVE: This study aimed to examine the risk of being granted a disability pension (DP) among incident cancer patients up to five years after diagnosis compared to a match control group, before and after the structural reform of the Danish Disability Pension Act in 2013. METHODS: All 20–60-year-old incident cancer-diagnosed individuals from 2000 to 2015 were identified in the Danish Cancer Registry. A control group, not previously diagnosed with cancer, was identified in Statistics Denmark matched by gender, age, education, and household income. Risk differences (RD) in cumulative incidence proportions of being granted a DP between cancer patients and controls were analyzed before and after the reform. RESULTS: In total, 111 773 incident cancer patients and 506 904 controls were included in the study. Before reform 10 561 cancer patients and 11 231 controls were granted DP; and 2570 cancer patients and 2646 controls were granted DP after the reform. The adjusted RD of being granted DP was significantly higher for cancer patients versus controls at all time points before the reform. The RD increased the most during the first (RD 3.6, 95% CI 3.5–3.7) and second (RD 7.2, 95% CI 7.0–7.4) follow-up year and levelled off the remaining three years. After the reform, the adjusted RD were lower for all 1–5 follow-up years compared to before the reform (RD range 2.8–7.7, 95% CI 2.6–8.1). CONCLUSION: The 2013 reform of the Disability Pension Act reduced the risk of cancer patients being granted DP. The impact on a personal level should be further explored
Rarity patterns and conservation priorities in Cactaceae species from the Southern Central Andes : a case study from the CalchaquÃes Valleys, Salta, Argentina
En este trabajo se estudiaron 34 especies de Cactaceae de los Valles CalchaquÃes, Argentina, para determinar 1) el nivel de rareza de las especies, 2) la proporción de especies raras entre grupos taxonómicos y ecológicos, y 3) la consistencia espacial de la rareza a lo largo del rango de distribución. Se definió a la rareza a través de un modelo que combina medidas del rango geográfico de distribución y el tamaño poblacional local de cada especie. La rareza no se concentró en ningún grupo taxonómico o ecológico particular de Cactaceae; sin embargo, 28 especies presentaron algún nivel de rareza. En la mayorÃa de las especies, la rareza varió a lo largo del área de distribución geográfica; sólo cinco especies fueron consistentemente raras en todas las poblaciones evaluadas. Seis especies fueron calificadas como extremadamente raras; todas de la subfamilia Cactoideae, cuatro endémicas del sur de los Andes Centrales y difiriendo en su forma de crecimiento. Sólo dos de las 34 especies estudiadas presentaron una rareza extrema y constante a lo largo de toda su distribución. La determinación del nivel de rareza fue útil para identificar especies que pueden estar en peligro o que pueden necesitar más estudios. Este trabajo permitió indicar qué especies de Cactaceae son más vulnerables a las perturbaciones antropogénicas o naturales, en comparación con las especies comunes. Muchas de las especies Cactaceae identificadas aquà como raras fueron mencionados por la IUCN en las categorÃas intermedias de extinción, por lo que la rareza parece estar relacionada con la vulnerabilidad a la extinción en la parte más sur de los Andes Centrales.In this study, 34 Cactaceae species from the CalchaquÃes Valleys, Argentina, were studied to determine 1) species rarity level, 2) proportion of rare species among taxonomic and ecological groups and, 3) whether rareness is consistently distributed throughout the species geographical ranges. We used a model where rarity is defined by the geographic range and the local population size to define species rarity. Rareness was not concentrated in any particular taxonomic or ecological group of Cactaceae; however 28 species were rare at some level. In most species, rarity varied across the geographical range, only five species remained consistently rare in all the surveyed populations. Six species qualified as extremely rare, all from the Cactoideae subfamily, four endemic to the southernmost Central Andes and differing in their growth forms. Only two of the 34 studied species, appeared as both extremely and consistently rare across its distribution. Determining rarity levels is useful for identifying species that may be in danger and/or in need for further studies. Rarity, used as an indicator of species vulnerability, allowed us, to identify Cactaceae species that are more vulnerable to anthropogenic or natural disturbance, compared with common species. Many of the Cactaceae species identified here as rare were mentioned by IUCN at intermediate categories of extinction. Our approach seems then to yield useful results and rareness in the present context appears to be related with vulnerability to extinction within the southernmost Central Andes
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