609 research outputs found
Hard x ray spectroscopy and imaging by a reflection zone plate in the presence of astigmatism
The feasibility of an off axis x ray reflection zone plate to perform wavelength dispersive spectroscopy, on axis point focusing, and two dimensional imaging is demonstrated by means of one and the same diffractive optical element DOE at a synchrotron radiation facility. The resolving power varies between 30 and 400 in the range of 7.6 keV to 9.0 keV, with its maximum at the design energy of 8.3 keV. This result is verified using an adjustable entrance slit, by which horizontal H and vertical V focusing to 0.85 amp; 956;m H and 1.29 amp; 956;m V is obtained near the sagittal focal plane of the astigmatic configuration. An angular and axial scan proves an accessible field of view of at least 0.6 arcmin 0.8 arcmin and a focal depth of plus minus 0.86 mm. Supported by the grating efficiency of around 17.5 and a very short pulse elongation, future precision x ray fluorescence and absorption studies of transition metals at their K edge on an ultrashort timescale could benefit from our finding
A transitional fossil mite (Astigmata: Levantoglyphidae fam. n.) from the early Cretaceous suggests gradual evolution of phoresy-related metamorphosis
Abstract Metamorphosis is a key innovation allowing the same species to inhabit different environments and accomplish different functions, leading to evolutionary success in many animal groups. Astigmata is a megadiverse lineage of mites that expanded into a great number of habitats via associations with invertebrate and vertebrate hosts (human associates include stored food mites, house dust mites, and scabies). The evolutionary success of Astigmata is linked to phoresy-related metamorphosis, namely the origin of the heteromorphic deutonymph, which is highly specialized for phoresy (dispersal on hosts). The origin of this instar is enigmatic since it is morphologically divergent and no intermediate forms are known. Here we describe the heteromorphic deutonymph of Levantoglyphus sidorchukae n. gen. and sp. (Levantoglyphidae fam. n.) from early Cretaceous amber of Lebanon (129 Ma), which displays a transitional morphology. It is similar to extant phoretic deutonymphs in its modifications for phoresy but has the masticatory system and other parts of the gnathosoma well-developed. These aspects point to a gradual evolution of the astigmatid heteromorphic morphology and metamorphosis. The presence of well-developed presumably host-seeking sensory elements on the gnathosoma suggests that the deutonymph was not feeding either during phoretic or pre- or postphoretic periods
Tunneling broadening of vibrational sidebands in molecular transistors
Transport through molecular quantum dots coupled to a single vibration mode
is studied in the case with strong coupling to the leads. We use an expansion
in the correlation between electrons on the molecule and electrons in the leads
and show that the tunneling broadening is strongly suppressed by the
combination of the Pauli principle and the quantization of the oscillator. As a
consequence the first Frank-Condon step is sharper than the higher order ones,
and its width, when compared to the bare tunneling strength, is reduced by the
overlap between the groundstates of the displaced and the non-displaced
oscillator.Comment: 8 pages, 3 figures. PRB, in pres
Targeted next-generation sequencing of circulating free DNA enables non-invasive tumor detection in myxoid liposarcomas
Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges
Vibrationally inelastic electron transport through a molecular bridge that is
connected to two leads is investigated. The study is based on a generic model
of vibrational excitation in resonant transmission of electrons through a
molecular junction. Employing methods from electron-molecule scattering theory,
the transmittance through the molecular bridge can be evaluated numerically
exactly. The current through the junction is obtained approximately using a
Landauer-type formula. Considering different parameter regimes, which include
both the case of a molecular bridge that is weakly coupled to the leads,
resulting in narrow resonance structures, and the opposite case of a broad
resonance caused by strong interaction with the leads, we investigate the
characteristic effects of coherent and dissipative vibrational motion on the
electron transport. Furthermore, the validity of widely used approximations
such as the wide-band approximation and the restriction to elastic transport
mechanisms is investigated in some detail.Comment: Submited to PRB, revised version according to comments of referees
(minor text changes and new citations
Conductance Peak Height Correlations for a Coulomb-Blockaded Quantum Dot in a Weak Magnetic Field
We consider statistical correlations between the heights of conductance peaks
corresponding to two different levels in a Coulomb-blockaded quantum dot.
Correlations exist for two peaks at the same magnetic field if the field does
not fully break time-reversal symmetry as well as for peaks at different values
of a magnetic field that fully breaks time-reversal symmetry. Our results are
also relevant to Coulomb-blockade conductance peak height statistics in the
presence of weak spin-orbit coupling in a chaotic quantum dot.Comment: 5 pages, 3 figures, REVTeX 4, accepted for publication in Phys. Rev.
Cross-validated maximum likelihood enhances crystallographic simulated annealing refinement
Spin states of the first four holes in a silicon nanowire quantum dot
We report measurements on a silicon nanowire quantum dot with a clarity that
allows for a complete understanding of the spin states of the first four holes.
First, we show control of the hole number down to one. Detailed measurements at
perpendicular magnetic fields reveal the Zeeman splitting of a single hole in
silicon. We are able to determine the ground-state spin configuration for one
to four holes occupying the quantum dot and find a spin filling with
alternating spin-down and spin-up holes, which is confirmed by
magnetospectroscopy up to 9T. Additionally, a so far inexplicable feature in
single-charge quantum dots in many materials systems is analyzed in detail. We
observe excitations of the zero-hole ground-state energy of the quantum dot,
which cannot correspond to electronic or Zeeman states. We show that the most
likely explanation is acoustic phonon emission to a cavity between the two
contacts to the nanowire.Comment: 24 pages, 8 figures, both including supporting informatio
X-ray dark-field radiography for in situ gout diagnosis by means of an ex vivo animal study
Gout is the most common form of inflammatory arthritis, caused by the deposition of monosodium urate (MSU) crystals in peripheral joints and tissue. Detection of MSU crystals is essential for definitive diagnosis, however the gold standard is an invasive process which is rarely utilized. In fact, most patients are diagnosed or even misdiagnosed based on manifested clinical signs, as indicated by the unchanged premature mortality among gout patients over the past decade, although effective treatment is now available. An alternative, non-invasive approach for the detection of MSU crystals is X-ray dark-field radiography. In our work, we demonstrate that dark-field X-ray radiography can detect naturally developed gout in animals with high diagnostic sensitivity and specificity based on the in situ measurement of MSU crystals. With the results of this study as a potential basis for further research, we believe that X-ray dark-field radiography has the potential to substantially improve gout diagnostics
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