74,903 research outputs found
Tunneling Spectroscopy of Two-level Systems Inside Josephson Junction
We consider a two-level (TL) system with energy level separation Omega_0
inside a Josephson junction. The junction is shunted by a resistor R and is
current I (or voltage V = RI) biased. If the TL system modulates the Josephson
energy and/or is optically active, it is Rabi driven by the Josephson
oscillations in the running phase regime near the resonance 2eV = Omega_0. The
Rabi oscillations, in turn, translate into oscillations of current and voltage
which can be detected in noise measurements. This effect provides an option to
fully characterize the TL systems and to find the TL's contribution to the
decoherence when the junction is used as a qubit.Comment: 4 page
Incommensurate Magnetism around Vortices and Impurities in High- Superconductors
By solving self-consistently an effective Hamiltonian including interactions
for both antiferromagnetic spin-density wave (SDW) and d-wave superconducting
(DSC) orderings, a comparison study is made for the local magnetic structure
around superconducting vortices and unitary impurities. To represent the
optimally doped regime of cuprates, the parameter values are chosen such that
the DSC is dominant while the SDW is vanishingly small. We show that when
vortices are introduced into the superconductor, an oscillating SDW is induced
around them. The oscillation period of the SDW is microscopically found,
consistent with experiments, to be eight lattice constants (). The
associated charge-density wave (CDW) oscillates with a period of one half
() of the SDW. In the case of unitary impurities, we find a SDW
modulation with identical periodicity, however without an associated CDW. We
propose neutron scattering experiments to test this prediction.Comment: 5 pages, 4 eps figures (color) included in the tex
Measurement of energy eigenstates by a slow detector
We propose a method for a weak continuous measurement of the energy
eigenstates of a fast quantum system by means of a "slow" detector. Such a
detector is only sensitive to slowly-changing variables, e. g. energy, while
its back-action can be limited solely to decoherence of the eigenstate
superpositions. We apply this scheme to the problem of detection of quantum
jumps between energy eigenstates in a harmonic oscillator.Comment: 4 page
Characterization of InGaN and InAlN epilayers by microdiffraction X-Ray reciprocal space mapping
We report a study of InGaN and InAlN epilayers grown on GaN/Sapphire substrates by microfocused three-dimensional X-ray Reciprocal Space Mapping (RSM). The analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused X-ray beam, allows us to gain uniquely valuable information about the microstructure of III-N alloy epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain free. This indicates that the growth of InGaN epilayers follows the Volmer-Weber mechanism with nucleation of “seeds” on strain fields generated by the a-type dislocations which are responsible for the twist of underlying GaN mosaic blocks. In the case of InAlN epilayer formation of composition gradient was observed at the beginning of the epitaxial growth
Evaluating Maintainability Prejudices with a Large-Scale Study of Open-Source Projects
Exaggeration or context changes can render maintainability experience into
prejudice. For example, JavaScript is often seen as least elegant language and
hence of lowest maintainability. Such prejudice should not guide decisions
without prior empirical validation. We formulated 10 hypotheses about
maintainability based on prejudices and test them in a large set of open-source
projects (6,897 GitHub repositories, 402 million lines, 5 programming
languages). We operationalize maintainability with five static analysis
metrics. We found that JavaScript code is not worse than other code, Java code
shows higher maintainability than C# code and C code has longer methods than
other code. The quality of interface documentation is better in Java code than
in other code. Code developed by teams is not of higher and large code bases
not of lower maintainability. Projects with high maintainability are not more
popular or more often forked. Overall, most hypotheses are not supported by
open-source data.Comment: 20 page
4p states and X-Ray Spectroscopy
The 4p states in transition metals and their compounds usually play minor
roles on their physical quantities. Recent development of resonant x-ray
scattering (RXS) at the K-edge of transition metals, however, casts light on
the 4p states, because the signals on orbital and magnetic superlattice spots
are brought about by the modulation in the 4p states. The 4p states are
extending in solids and thereby sensitive to electronic states at neighboring
sites. This characteristic determines the mechanism of RXS that the intensity
on the orbital superlattice spots are mainly generated by the lattice
distortion and those on magnetic superlattice spots by the coupling of the 4p
states with the orbital polarization in the 3d states at neighboring sites.
Taking up typical examples for orbital and magnetic RXS, we demonstrate these
mechanisms on the basis of the band structure calculation. Finally, we study
the MCD spectra at the K-edge, demonstrating that the same mechanism as the
magnetic RXS is working.Comment: 9 pages, 9 figures, submitted to Physica Scripta (comment
Stretching single polysaccharide molecules using AFM: A potential method for the investigation of the intermolecular uronate distribution of alginate?
Illustrative examples of the way in which the molecular force-extension behaviour of polysaccharides is governed by the nature of the linkage between their constituent pyranose rings are presented for a series of standard homopolymers. These results agree with previously proposed general hypotheses regarding the possibility of generating force-induced conformational transitions, and with the predictions of a model in which the inter-conversion of pyranose conformers is assumed to be an equilibrium process on the timescale of the molecular stretching. Subsequently, we investigate the potential of the technique in the characterisation of co-polymeric polysaccharides in which the nature of the glycan linkages is different between the two distinct residue types. Specifically, we explore the possibility that the ratio of mannuronic acid (M) to guluronic acid (G) in alginate chains will be reflected in their single molecule stretching behaviour, owing to their contrasting equatorial and axial linkages. Furthermore, as the technique described interrogates the sample one polymer at a time we outline the promise of, and the obstacles to, obtaining a new level of characterisation using this methodology where differences observed in the single molecule stretching curves obtained from single alginate samples reflectsomething of the real intermolecular distribution of the M / G ratio
Identification and correction of systematic error in high-throughput sequence data
A feature common to all DNA sequencing technologies is the presence of base-call errors in the sequenced reads. The implications of such errors are application specific, ranging from minor informatics nuisances to major problems affecting biological inferences. Recently developed “next-gen” sequencing technologies have greatly reduced the cost of sequencing, but have been shown to be more error prone than previous technologies. Both position specific (depending on the location in the read) and sequence specific (depending on the sequence in the read) errors have been identified in Illumina and Life Technology sequencing platforms. We describe a new type of _systematic_ error that manifests as statistically unlikely accumulations of errors at specific genome (or transcriptome) locations. We characterize and describe systematic errors using overlapping paired reads form high-coverage data. We show that such errors occur in approximately 1 in 1000 base pairs, and that quality scores at systematic error sites do not account for the extent of errors. We identify motifs that are frequent at systematic error sites, and describe a classifier that distinguishes heterozygous sites from systematic error. Our classifier is designed to accommodate data from experiments in which the allele frequencies at heterozygous sites are not necessarily 0.5 (such as in the case of RNA-Seq). Systematic errors can easily be mistaken for heterozygous sites in individuals, or for SNPs in population analyses. Systematic errors are particularly problematic in low coverage experiments, or in estimates of allele-specific expression from RNA-Seq data. Our characterization of systematic error has allowed us to develop a program, called SysCall, for identifying and correcting such errors. We conclude that correction of systematic errors is important to consider in the design and interpretation of high-throughput sequencing experiments
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