391 research outputs found
A Self Assembled Nanoelectronic Quantum Computer Based on the Rashba Effect in Quantum Dots
Quantum computers promise vastly enhanced computational power and an uncanny
ability to solve classically intractable problems. However, few proposals exist
for robust, solid state implementation of such computers where the quantum
gates are sufficiently miniaturized to have nanometer-scale dimensions. Here I
present a new approach whereby a complete computer with nanoscale gates might
be self-assembled using chemical synthesis. Specifically, I demonstrate how to
self-assemble the fundamental unit of this quantum computer - a 2-qubit
universal quantum controlled-NOT gate - based on two exchange coupled
multilayered quantum dots. Then I show how these gates can be wired using
thiolated conjugated molecules as electrical connectors. A qubit is encoded in
the ground state of a quantum dot spin-split by the Rashba interaction.
Arbitrary qubit rotations are effected by bringing the spin splitting energy in
a target quantum dot in resonance with a global ac magnetic field by applying a
potential pulse of appropriate amplitude and duration to the dot. The
controlled dynamics of the 2-qubit controlled-NOT operation (XOR) can be
realized by exploiting the exchange coupling with the nearest neighboring dot.
A complete prescription for initialization of the computer and data
input/output operations is presented.Comment: 22 pages, 4 figure
Peak effect and its evolution with defect structure in YBa2Cu3O7-d thin films at microwave frequencies
The vortex dynamics in YBa2Cu3O7-d thin films have been studied at microwave
frequencies. A pronounced peak in the surface resistance, Rs, is observed in
these films at frequencies of 4.88 and 9.55 GHz for magnetic fields varying
from 0.2 to 0.8 T. The peak is associated with an order-disorder transformation
of the flux line lattice as the temperature or field is increased. The
occurrence of the peak in Rs is crucially dependent on the depinning frequency,
wp and on the nature and concentration of growth defects present in these
films. Introduction of artificial defects by swift heavy ion irradiation with
200 MeV Ag ion at a fluence of 4x1010 ions/cm2 enhances wp and suppresses the
peak at 4.88 GHz but the peak at 9.55 GHz remains unaffected. A second peak at
lower temperature has also been observed at 9.55 GHz. This is related to twin
boundaries from angular dependence studies of Rs. Based on the temperature
variation of Rs, vortex phase diagrams have been constructed at 9.55 GHz.Comment: 8 pages, 4 figures Submitted to Physical Review
Critical Currents and Vortex States at Fractional Matching Fields in Superconductors with Periodic Pinning
We study vortex states and dynamics in 2D superconductors with periodic
pinning at fractional sub-matching fields using numerical simulations. For
square pinning arrays we show that ordered states form at 1/1, 1/2, and 1/4
filling fractions while only partially ordered states form at other filling
fractions, such as 1/3 and 1/5, in agreement with recent imaging experiments.
For triangular pinning arrays we observe matching effects at filling fractions
of 1/1, 6/7, 2/3, 1/3, 1/4, 1/6, and 1/7. For both square and triangular
pinning arrays we also find that, for certian sub-matching fillings, vortex
configurations depend on pinning strength. For weak pinning, ordering in which
a portion of the vortices are positioned between pinning sites can occur.
Depinning of the vortices at the matching fields, where the vortices are
ordered, is elastic while at the incommensurate fields the motion is plastic.
At the incommensurate fields, as the applied driving force is increased, there
can be a transition to elastic flow where the vortices move along the pinning
sites in 1D channels and a reordering transition to a triangular or distorted
triangular lattice. We also discuss the current-voltage curves and how they
relate to the vortex ordering at commensurate and incommensurate fields.Comment: 14 figure
Does Women's Preference for Highbrow Leisure Begin in the Family? Comparing Leisure Participation among Brothers and Sisters
Peak effect in a superconducting DyBa2Cu3O7-y film at microwave frequencies
We report the observation of a peak in the microwave (9.55 GHz) surface
resistance in an epitaxial DyBa2Cu3O7-y superconducting film in magnetic fields
(parallel to the c axis) ranging between 0.2 to 0.9 Tesla. Such a peak is
absent in the measurements done in zero-field. The temperature and field
dependence of the peak suggests that this peak could be associated with the
peak effect phenomenon reflecting the order-disorder transformation in the
flux-line lattice. A strong dependence of this peak effect at frequencies close
to the depinning frequency of the flux line lattice is observed.Comment: 1 text, 4 figures (all postscript) to be published in Phys. Rev.
FGF receptor genes and breast cancer susceptibility: results from the Breast Cancer Association Consortium
Background:Breast cancer is one of the most common malignancies in women. Genome-wide association studies have identified FGFR2 as a breast cancer susceptibility gene. Common variation in other fibroblast growth factor (FGF) receptors might also modify risk. We tested this hypothesis by studying genotyped single-nucleotide polymorphisms (SNPs) and imputed SNPs in FGFR1, FGFR3, FGFR4 and FGFRL1 in the Breast Cancer Association Consortium.
Methods:Data were combined from 49 studies, including 53 835 cases and 50 156 controls, of which 89 050 (46 450 cases and 42 600 controls) were of European ancestry, 12 893 (6269 cases and 6624 controls) of Asian and 2048 (1116 cases and 932 controls) of African ancestry. Associations with risk of breast cancer, overall and by disease sub-type, were assessed using unconditional logistic regression.
Results:Little evidence of association with breast cancer risk was observed for SNPs in the FGF receptor genes. The strongest evidence in European women was for rs743682 in FGFR3; the estimated per-allele odds ratio was 1.05 (95 confidence interval=1.02-1.09, P=0.0020), which is substantially lower than that observed for SNPs in FGFR2.
Conclusion:Our results suggest that common variants in the other FGF receptors are not associated with risk of breast cancer to the degree observed for FGFR2. © 2014 Cancer Research UK
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Fish assemblage associated with aquatic macrophytes bank in mananged lakes of Central Amazon, Amazonas, Brazil
The co-management of fishery resources developed by Amazonian riverine people is concerned with the maintenance of suitable environments for fish stock conservation. This type of co-management strategy is based on rules of access and use for fishery resources. In this research we investigated the influence of using lakes (preserved and managed for subsistence) and its distance from the river (near and far) in the structure of the fish assemblages associated with floating meadows bank in floodplain lakes, Central Amazonian. Fish were caught during flood period using seine nets in six lakes in a distance ranging from 0.87 to 10.9 km from the river. In floating meadows bank were captured a total of 623 specimens of fish, over 56 species. The analysis of covariance (ANCOVA) indicates that the co-management of lakes and distance did not influence significantly the ecological attributes of fish assemblages (abundance, richness, total weight, Shannon-Weaver and Berger-Parker diversity, evenness and dominance). According to analysis of similarity (ANOSIM) there was no difference in species composition among the lakes. These results suggest other factors, such as: short time of effective management, the agriculture as the most important economic activity of subsistence, the lack of fisheries in large-scale which cause significant environmental changes and the existence of an ecological factor of great intensity, "the flood pulse", overlapping others of less intensity.O co-manejo dos recursos pesqueiros que vem sendo desenvolvido pelos ribeirinhos da Amazônia têm a preocupação de assegurar ambientes adequados para a conservação dos estoques. Esta estratégia de co-manejo é baseada em regras de acesso e uso dos recursos pesqueiros. Nesse estudo, foi investigada a influência do tipo de uso de lagos (preservados e manejados para subsistência) e a sua distância do rio (próximos e distantes) na estrutura das assembleias de peixes associadas aos bancos de macrófitas aquáticas em lagos de várzea, Amazônia Central. Os peixes foram capturados na cheia com rede de cerco em seis lagos com distância do rio variando de 0,87 a 10,9 km. Nas macrófitas aquáticas e capins flutuantes dos lagos foram capturados um total de 623 exemplares de peixes, distribuídos em 56 espécies. A análise de covariância (ANCOVA) indica que o co-manejo dos lagos e distância não influenciaram significativamente nos atributos ecológicos das assembleias (abundância, riqueza, peso total, diversidade de Shannon-Weaver, diversidade Berger-Parker, equitabilidade e dominância). A análise de similaridade (ANOSIM) também mostrou que não existe diferença na composição de espécies entre os tipos de lago. Estes resultados sugerem outros fatores, como o pouco tempo de manejo efetivo, a agricultura como sendo a principal atividade econômica de subsistência, inexistência de pescarias em larga escala que produzam alterações ambientais significativas e a existência de um fator ecológico de grande intensidade, o pulso de inundação, sobrepondo a outros de menor intensidade
Abiotic variability among different aquatic systems of the central Amazon floodplain during drought and flood events
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