677 research outputs found
Analysis of Possible Quantum Metastable States in Ballistic Graphene-based Josephson Junctions
Graphene is a relatively new material (2004) made of atomic layers of carbon
arranged in a honeycomb lattice. Josephson junction devices are made from
graphene by depositing two parallel superconducting leads on a graphene flake.
These devices have hysteretic current-voltage characteristics with a
supercurrent branch and Shapiro steps appear when irradiated with microwaves.
These properties motivate us to investigate the presence of quantum metastable
states similar to those found in conventional current-biased Josephson
junctions. We present work investigating the nature of these metastable states
for ballistic graphene Josephson junctions. We model the effective Washboard
potential for these devices and estimate parameters, such as energy level
spacing and critical currents, to deduce the design needed to observe
metastable states. We propose devices consisting of a parallel on-chip
capacitor and suspended graphene. The capacitor is needed to lower the energy
level spacing down to the experimentally accessible range of 1-20 GHz. The
suspended graphene helps reduce the noise that may otherwise come from
two-level states in the insulating oxide layer. Moreover, back-gate voltage
control of its critical current introduces another knob for quantum control. We
will also report on current experimental progress in the area of fabrication of
this proposed device.Comment: 4 pages, 5 figures, Accepted for publication in IEEE Transactions on
Applied Superconductivity from ASC 2010. Additional figures, additional
calculation
Chiasma
Newspaper reporting on events at the Boston University School of Medicine in the 1960s
Dynamic Versus Static Oxidation of Nb/Al-AlO/Nb Trilayer
High quality Nb-based superconductor-insulator-superconductor (SIS) junctions
with Al oxide (AlO) tunnel barriers grown from Al overlayers are widely
reported in the literature. However, the thin barriers required for high
critical current density (J) junctions exhibit defects that result in
significant subgap leakage current that is detrimental for many applications.
High quality, high-J junctions can be realized with AlN barriers, but
control of J is more difficult than with AlO. It is therefore of
interest to study the growth of thin AlO barriers with the ultimate goal of
achieving high quality, high-J AlO junctions. In this work, 100\%\
O and 2\%\ O in Ar gas mixtures are used both statically and
dynamically to grow AlO tunnel barriers over a large range of oxygen
exposures. In situ ellipsometry is used for the first time to extensively
measure AlO tunnel barrier growth in real time, revealing a number of
unexpected patterns. Finally, a set of test junction wafers was fabricated that
exhibited the well-known dependence of J on oxygen exposure (E) in order to
further validate the experimental setup
Probing the Space of Toric Quiver Theories
We demonstrate a practical and efficient method for generating toric Calabi-Yau quiver theories, applicable to both D3 and M2 brane world-volume physics. A new analytic method is presented at low order parametres and an algorithm for the general case is developed which has polynomial complexity in the number of edges in the quiver. Using this algorithm, carefully implemented, we classify the quiver diagram and assign possible superpotentials for various small values of the number of edges and nodes. We examine some preliminary statistics on this space of toric quiver theories
Phases of planar 5-dimensional supersymmetric Chern-Simons theory
In this paper we investigate the large- behavior of 5-dimensional
super Yang-Mills with a level Chern-Simons term and an
adjoint hypermultiplet. As in three-dimensional Chern-Simons theories, one must
choose an integration contour to completely define the theory. Using
localization, we reduce the path integral to a matrix model with a cubic action
and compute its free energy in various scenarios. In the limit of infinite
Yang-Mills coupling and for particular choices of the contours, we find that
the free-energy scales as for gauge groups with large values
of the Chern-Simons 't\,Hooft coupling, . If we also
set the hypermultiplet mass to zero, then this limit is a superconformal fixed
point and the behavior parallels other fixed points which have known
supergravity duals. We also demonstrate that gauge groups cannot have
this scaling for their free-energy. At finite Yang-Mills coupling we
establish the existence of a third order phase transition where the theory
crosses over from the Yang-Mills phase to the Chern-Simons phase. The phase
transition exists for any value of , although the details differ
between small and large values of . For pure Chern-Simons
theories we present evidence for a chain of phase transitions as
is increased.
We also find the expectation values for supersymmetric circular Wilson loops
in these various scenarios and show that the Chern-Simons term leads to
different physical properties for fundamental and anti-fundamental Wilson
loops. Different choices of the integration contours also lead to different
properties for the loops.Comment: 40 pages, 17 figures, Minor corrections, Published versio
A missense variant in CST3 exerts a recessive effect on susceptibility to age-related macular degeneration resembling its association with Alzheimer’s disease
Age-related macular degeneration (AMD) and Alzheimer’s disease (AD) are degenerative, multifactorial diseases involving age-related accumulation of extracellular deposits linked to dysregulation of protein homeostasis. Here, we strengthen the evidence that an nsSNP (p.Ala25Thr) in the cysteine proteinase inhibitor cystatin C gene CST3, previously confirmed by meta-analysis to be associated with AD, is associated with exudative AMD. To our knowledge, this is the first report highlighting a genetic variant that increases the risk of developing both AD and AMD. Furthermore, we demonstrate that the risk associated with the mutant allele follows a recessive model for both diseases. We perform an AMD-CST3 case–control study genotyping 350 exudative AMD Caucasian individuals. Bringing together our data with the previously reported AMD-CST3 association study, the evidence of a recessive effect on AMD risk is strengthened (OR = 1.89, P = 0.005). This effect closely resembles the AD-CST3 recessive effect (OR = 1.73, P = 0.005) previously established by meta-analysis. This resemblance is substantiated by the high correlation between CST3 genotype and effect size across the two diseases (R2 = 0.978). A recessive effect is in line with the known function of cystatin C, a potent enzyme inhibitor. Its potency means that, in heterozygous individuals, a single functional allele is sufficient to maintain its inhibitory function; only homozygous individuals will lack this form of proteolytic regulation. Our findings support the hypothesis that recessively acting variants account for some of the missing heritability of multifactorial diseases. Replacement therapy represents a translational opportunity for individuals homozygous for the mutant allele
Clogging the machinery: the BBC's experiment in science coordination, 1949–1953
In 1949, physicist Mark Oliphant criticised the BBC’s handling of science in a letter to the Director General William Haley. It initiated a chain of events which led to the experimental appointment of a science adviser, Henry Dale, to improve the ‘coordination’ of science broadcasts. The experiment failed, but the episode revealed conflicting views of the BBC’s responsibility towards science held by scientists and BBC staff. For the scientists, science had a special status, both as knowledge and as an activity, which in their view obligated the BBC to make special arrangements for it. BBC staff, however, had their own professional procedures which they were unwilling to abandon. The events unfolded within a few years of the end of the Second World War, when social attitudes to science had been coloured by the recent conflict, and when the BBC itself was under scrutiny from the William Beveridge’s Committee. The BBC was also embarking on new initiatives, notably the revival of adult education. These contextual factors bear on the story, which is about the relationship between a public service broadcaster and the external constituencies it relies on, but must appear to remain independent from. The article therefore extends earlier studies showing how external bodies have attempted to manipulate the inner workings of the BBC to their own advantage (e.g. those by Doctor and Karpf) by looking at the little-researched area of science broadcasting. The article is largely based on unpublished archive documents
Molecular Epidemiology of Eastern Equine Encephalitis Virus, New York
Southern strains are undergoing amplification, perpetuation, and overwintering in New York
A PfRH5-Based Vaccine Is Efficacious against Heterologous Strain Blood-Stage Plasmodium falciparum Infection in Aotus Monkeys
SummaryAntigenic diversity has posed a critical barrier to vaccine development against the pathogenic blood-stage infection of the human malaria parasite Plasmodium falciparum. To date, only strain-specific protection has been reported by trials of such vaccines in nonhuman primates. We recently showed that P. falciparum reticulocyte binding protein homolog 5 (PfRH5), a merozoite adhesin required for erythrocyte invasion, is highly susceptible to vaccine-inducible strain-transcending parasite-neutralizing antibody. In vivo efficacy of PfRH5-based vaccines has not previously been evaluated. Here, we demonstrate that PfRH5-based vaccines can protect Aotus monkeys against a virulent vaccine-heterologous P. falciparum challenge and show that such protection can be achieved by a human-compatible vaccine formulation. Protection was associated with anti-PfRH5 antibody concentration and in vitro parasite-neutralizing activity, supporting the use of this in vitro assay to predict the in vivo efficacy of future vaccine candidates. These data suggest that PfRH5-based vaccines have potential to achieve strain-transcending efficacy in humans
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