1,154 research outputs found
Surface Acoustic Wave Single-Electron Interferometry
We propose an experiment to observe interference of a single electron as it
is transported along two parallel quasi-one-dimensional channels trapped in a
single minimum of a travelling periodic electric field. The experimental device
is a modification of the surface acoustic wave (SAW) based quantum processor.
Interference is achieved by creating a superposition of spatial wavefunctions
between the two channels and inducing a relative phase shift via either a
transverse electric field or a magnetic field. The interference can be used to
estimate the decoherence time of an electron in this type of solid-state
device
Comparison of homoeolocus organisation in paired BAC clones from white clover (Trifolium repens L.) and microcolinearity with model legume species
<p>Abstract</p> <p>Background</p> <p>White clover (<it>Trifolium repens </it>L.) is an outbreeding allotetraploid species and an important forage legume in temperate grassland agriculture. Comparison of sub-genome architecture and study of nucleotide sequence diversity within allopolyploids provides insight into evolutionary divergence mechanisms, and is also necessary for the development of whole-genome sequencing strategies. This study aimed to evaluate the degree of divergence between the O and P' sub-genomes of white clover through sequencing of BAC clones containing paired homoeoloci. The microsyntenic relationships between the genomes of white clover and the model legumes <it>Lotus japonicus </it>and <it>Medicago truncatula </it>as well as <it>Arabidopsis thaliana </it>were also characterised.</p> <p>Results</p> <p>A total of four paired homoeologous BACs were selected and sequenced to generate 173 kb of overlapping sequence between the O and P' sub-genomes. Equivalent gene content was generally observed, apart from small-scale deletions, in contrast to conservation of intergenic sequences, which varied between the four selected regions. Measurement of the number of synonymous substitutions between homoeologous genes led to estimation of a 4.2 million year divergence time between the two sub-genomes. Microsynteny was observed between the genomes of white clover and <it>L. japonicus </it>for all four targeted regions, but corresponding <it>M. truncatula </it>genomic regions were only identified for two BAC pairs.</p> <p>Conclusions</p> <p>This study describes the first analysis of sub-genome structural conservation across selected genomic regions in white clover. Although the high levels of sequence conservation between the O and P' sub-genomes would complicate efforts for whole genome sequence assembly, the conserved microsynteny with model legume genomes, especially that of <it>L. japonicus</it>, will be highly valuable for the future of white clover genomics and molecular breeding.</p
Identifying a Two-State Hamiltonian in the Presence of Decoherence
Mapping the system evolution of a two-state system allows the determination
of the effective system Hamiltonian directly. We show how this can be achieved
even if the system is decohering appreciably over the observation time. A
method to include various decoherence models is given and the limits of this
technique are explored. This technique is applicable both to the problem of
calibrating a control Hamiltonian for quantum computing applications and for
precision experiments in two-state quantum systems. For simple models of
decoherence, this method can be applied even when the decoherence time is
comparable to the oscillation period of the system.Comment: 8 pages, 6 figures. Minor corrections, published versio
Molecular characterisation and genetic mapping of candidate genes for qualitative disease resistance in perennial ryegrass (Lolium perenne L.)
<p>Abstract</p> <p>Background</p> <p>Qualitative pathogen resistance in both dicotyledenous and monocotyledonous plants has been attributed to the action of resistance (R) genes, including those encoding nucleotide binding site – leucine rich repeat (NBS-LRR) proteins and receptor-like kinase enzymes. This study describes the large-scale isolation and characterisation of candidate R genes from perennial ryegrass. The analysis was based on the availability of an expressed sequence tag (EST) resource and a functionally-integrated bioinformatics database.</p> <p>Results</p> <p>Amplification of R gene sequences was performed using template EST data and information from orthologous candidate using a degenerate consensus PCR approach. A total of 102 unique partial R genes were cloned, sequenced and functionally annotated. Analysis of motif structure and R gene phylogeny demonstrated that <it>Lolium </it>R genes cluster with putative ortholoci, and evolved from common ancestral origins. Single nucleotide polymorphisms (SNPs) predicted through resequencing of amplicons from the parental genotypes of a genetic mapping family were validated, and 26 distinct R gene loci were assigned to multiple genetic maps. Clusters of largely non-related NBS-LRR genes were located at multiple distinct genomic locations and were commonly found in close proximity to previously mapped defence response (DR) genes. A comparative genomics analysis revealed the co-location of several candidate R genes with disease resistance quantitative trait loci (QTLs).</p> <p>Conclusion</p> <p>This study is the most comprehensive analysis to date of qualitative disease resistance candidate genes in perennial ryegrass. SNPs identified within candidate genes provide a valuable resource for mapping in various ryegrass pair cross-derived populations and further germplasm analysis using association genetics. In parallel with the use of specific pathogen virulence races, such resources provide the means to identify gene-for-gene mechanisms for multiple host pathogen-interactions and ultimately to obtain durable field-based resistance.</p
A critical assessment of the pairing symmetry in NaxCoO2.yH2O
We examine each of the symmetry-allowed pairing states of NaxCoO2.yH2O and
compare their properties to what is experimentally and theoretically
established about the compound. In this way, we can eliminate the vast majority
of states that are technically allowed and narrow the field to two, both of
f-wave type states. We discuss the expected features of these states and
suggest experiments that can distinguish between them. We also discuss
odd-frequency gap pairing and how it relates to available experimental
evidence
Square lattice Ising model susceptibility: Series expansion method and differential equation for
In a previous paper (J. Phys. A {\bf 37} (2004) 9651-9668) we have given the
Fuchsian linear differential equation satisfied by , the
``three-particle'' contribution to the susceptibility of the isotropic square
lattice Ising model. This paper gives the details of the calculations (with
some useful tricks and tools) allowing one to obtain long series in polynomial
time. The method is based on series expansion in the variables that appear in
the -dimensional integrals representing the -particle contribution to
the isotropic square lattice Ising model susceptibility . The
integration rules are straightforward due to remarkable formulas we derived for
these variables. We obtain without any numerical approximation as
a fully integrated series in the variable , where , with the conventional Ising model coupling constant. We also
give some perspectives and comments on these results.Comment: 28 pages, no figur
Employment Expectations and Gross Flows by Type of Work Contract
There is growing interest in understanding firms’ temporary and permanent employment practices and how institutional changes shape them. Using data on Spanish establishments, we examine: (a) how employers adjust temporary and permanent job and worker flows to prior employment expectations, and (b) how the 1994 and 1997 labour reforms promoting permanent employment affected establishments’ employment practices. Generally, establishments’ prior employment expectations are realized through changes in all job and worker flows. However, establishments uniquely rely on temporary hires as a buffer to confront diminishing long-run employment expectations. None of the reforms significantly affected establishments’ net temporary or permanent employment flows.http://deepblue.lib.umich.edu/bitstream/2027.42/40032/3/wp646.pd
Progress in development of graded bandgap thin film solar cells with electroplated materials
Photovoltaic devices are developed mainly based on p-n or p-i-n type device structures, and these devices can utilise only a fraction of the solar spectrum. In order to further improve device parameters and move towards low-cost and high-efficiency next generation solar cells, device architectures capable of harvesting all photons available should be designed and developed. One such architecture is the fully graded bandgap device structure as proposed recently based on both n-type and p-type window layers. These designs have been experimentally tested using well researched GaAs/AlGaAs system producing impressive device parameters of open circuit voltage (Voc) ~1175 mV and fill factor (FF) ~0.85. The devices have also been experimentally tested for the evidence of impurity photovoltaic (PV) effect and impact ionisation taking place within the same device. Since these structures have been experimentally proved with a well-established semiconductor, the effort has been focussed on developing these devices using low-cost and scalable electroplated semiconductors, in order to minimise manufacturing cost. This paper reviews and summarises the work carried out during the past decade on this subject. Graded bandgap devices produced using only two or three electroplated semiconductor layers have been explored and their conversion efficiencies have gradually increased from 10.0%, through 12.8% to 15.3% for different structures. While the work is progressing along this line, the paper summarises the achievements to date
Privatization and State Capacity in Postcommunist Society
Economists have used cross-national regression analysis to argue that postcommunist economic failure is the result of inadequate adherence liberal economic policies. Sociologists have relied on case study data to show that postcommunist economic failure is the outcome of too close adherence to liberal policy recommendations, which has led to an erosion of state effectiveness, and thus produced poor economic performance. The present paper advances a version of this statist theory based on a quantitative analysis of mass privatization programs in the postcommunist world. We argue that rapid large-scale privatization creates severe supply and demand shocks for enterprises, thereby inducing firm failure. The resulting erosion of tax revenues leads to a fiscal crisis for the state, and severely weakens its capacity and bureaucratic character. This, in turn, reacts back on the enterprise sector, as the state can no longer support the institutions necessary for the effective functioning of a modern economy, thus resulting in deindustrialization. Using cross-national regression techniques we find that the implementation of mass privatization programs negatively impacts measures of economic growth, state capacity and the security of property rights.http://deepblue.lib.umich.edu/bitstream/2027.42/40192/3/wp806.pd
Long term time variability of cosmic rays and possible relevance to the development of life on Earth
An analysis is made of the manner in which the cosmic ray intensity at Earth
has varied over its existence and its possible relevance to both the origin and
the evolution of life. Much of the analysis relates to the 'high energy' cosmic
rays () and their variability due to the changing
proximity of the solar system to supernova remnants which are generally
believed to be responsible for most cosmic rays up to PeV energies. It is
pointed out that, on a statistical basis, there will have been considerable
variations in the likely 100 My between the Earth's biosphere reaching
reasonable stability and the onset of very elementary life. Interestingly,
there is the increasingly strong possibility that PeV cosmic rays are
responsible for the initiation of terrestrial lightning strokes and the
possibility arises of considerable increases in the frequency of lightnings and
thereby the formation of some of the complex molecules which are the 'building
blocks of life'. Attention is also given to the well known generation of the
oxides of nitrogen by lightning strokes which are poisonous to animal life but
helpful to plant growth; here, too, the violent swings of cosmic ray
intensities may have had relevance to evolutionary changes. A particular
variant of the cosmic ray acceleration model, put forward by us, predicts an
increase in lightning rate in the past and this has been sought in Korean
historical records. Finally, the time dependence of the overall cosmic ray
intensity, which manifests itself mainly at sub-10 GeV energies, has been
examined. The relevance of cosmic rays to the 'global electrical circuit'
points to the importance of this concept.Comment: 18 pages, 5 figures, accepted by 'Surveys in Geophysics
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