405 research outputs found
Probing scattering phase shifts by attosecond streaking
Attosecond streaking is one of the most fundamental processes in attosecond
science allowing for a mapping of temporal (i.e. phase) information on the
energy domain. We show that on the single-particle level attosecond streaking
time shifts contain spectral phase information associated with the
Eisenbud-Wigner-Smith (EWS) time delay, provided the influence of the streaking
infrared field is properly accounted for. While the streaking phase shifts for
short-ranged potentials agree with the associated EWS delays, Coulomb
potentials require special care. We show that the interaction between the
outgoing electron and the combined Coulomb and IR laser fields lead to a
streaking phase shift that can be described classically
Probing Electron Correlation via Attosecond XUV Pulses in the Two-Photon Double Ionization of Helium
Recent experimental developments of high-intensity, short-pulse XUV light
sources are enhancing our ability to study electron-electron correlations. We
perform time-dependent calculations to investigate the so-called "sequential"
regime (photon energy above 54.4 eV) in the two-photon double ionization of
helium. We show that attosecond pulses allow to induce and probe angular and
energy correlations of the emitted electrons. The final momentum distribution
reveals regions dominated by the Wannier ridge break-up scenario and by
post-collision interaction.Comment: 4 pages, 5 figure
Universal features in sequential and nonsequential two-photon double ionization of helium
We analyze two-photon double ionization of helium in both the nonsequential
and sequential regime. We show that the energy spacing between the two emitted
electrons provides the key parameter that controls both the energy and the
angular distribution and reveals the universal features present in both the
nonsequential and sequential regime. This universality, i.e., independence of
photon energy, is a manifestation of the continuity across the threshold for
sequential double ionization. For all photon energies, the energy distribution
can be described by a universal shape function that contains only the spectral
and temporal information entering second-order time-dependent perturbation
theory. Angular correlations and distributions are found to be more sensitive
to the photon energy. In particular, shake-up interferences have a large effect
on the angular distribution. Energy spectra, angular distributions
parameterized by the anisotropy parameters, and total cross sections presented
in this paper are obtained by fully correlated time-dependent ab initio
calculations.Comment: 12 pages, 8 figure
Treatment-resistant major depression: Rationale for NMDA receptors as targets and nitrous oxide as therapy
Major depressive disorder (MDD) remains a huge personal and societal encumbrance. Particularly burdensome is a virulent subtype of MDD, treatment resistant major depression (TMRD), which afflicts 15–30% of MDD patients. There has been recent interest in N-methyl-d-aspartate receptors (NMDARs) as targets for treatment of MDD and perhaps TMRD. To date, most pre-clinical and clinical studies have focused on ketamine, although psychotomimetic and other side effects may limit ketamine’s utility. These considerations prompted a recent promising pilot clinical trial of nitrous oxide, an NMDAR antagonist that acts through a mechanism distinct from that of ketamine, in patients with severe TRMD. In this paper, we review the clinical picture of TRMD as a subtype of MDD, the evolution of ketamine as a fast-acting antidepressant, and clinical and basic science studies supporting the possible use of nitrous oxide as a rapid antidepressant
Certification of Confluence Proofs using CeTA
5 pages, International Workshop on Confluence 20145 pages, International Workshop on Confluence 2014CeTA was originally developed as a tool for certifying termination proofs which have to be provided as certificates in the CPF-format. Its soundness is proven as part of IsaFoR, the Isabelle Formalization of Rewriting. By now, CeTA can also be used for certifying confluence and non-confluence proofs. In this system description, we give a short overview on what kind of proofs are supported, and what information has to be given in the certificates. As we will see, only a small amount of information is required and so we hope that CSI will not stay the only confluence tool which can produce certificates
On the formalization of termination techniques based on multiset orderings
Multiset orderings are a key ingredient in certain termination techniques like the recursive path ordering and a variant of size-change termination. In order to integrate these techniques in a certifier for termination proofs, we have added them to the Isabelle Formalization of Rewriting. To this end, it was required to extend the existing formalization on multiset orderings towards a generalized multiset ordering. Afterwards, the soundness proofs of both techniques have been established, although only after fixing some definitions. Concerning efficiency, it is known that the search for suitable parameters for both techniques is NP-hard. We show that checking the correct application of the techniques-where all parameters are provided-is also NP-hard, since the problem of deciding the generalized multiset ordering is NP-hard. © René Thiemann, Guillaume Allais, and JulianNagele
Nonsequential two-photon double ionization of helium
We present accurate time-dependent ab initio calculations on fully
differential and total integrated (generalized) cross sections for the
nonsequential two-photon double ionization of helium at photon energies from 40
to 54 eV. Our computational method is based on the solution of the
time-dependent Schroedinger equation and subsequent projection of the wave
function onto Coulomb waves. We compare our results with other recent
calculations and discuss the emerging similarities and differences. We
investigate the role of electronic correlation in the representation of the
two-electron continuum states, which are used to extract the ionization yields
from the fully correlated final wave function. In addition, we study the
influence of the pulse length and shape on the cross sections in time-dependent
calculations and address convergence issues.Comment: 14 pages, 10 figures; final version (acknowledgements and reference
added, typos fixed
Diagnosis of Alzheimer's Disease Based on Disease-Specific Autoantibody Profiles in Human Sera
After decades of Alzheimer's disease (AD) research, the development of a definitive diagnostic test for this disease has remained elusive. The discovery of blood-borne biomarkers yielding an accurate and relatively non-invasive test has been a primary goal. Using human protein microarrays to characterize the differential expression of serum autoantibodies in AD and non-demented control (NDC) groups, we identified potential diagnostic biomarkers for AD. The differential significance of each biomarker was evaluated, resulting in the selection of only 10 autoantibody biomarkers that can effectively differentiate AD sera from NDC sera with a sensitivity of 96.0% and specificity of 92.5%. AD sera were also distinguishable from sera obtained from patients with Parkinson's disease and breast cancer with accuracies of 86% and 92%, respectively. Results demonstrate that serum autoantibodies can be used effectively as highly-specific and accurate biomarkers to diagnose AD throughout the course of the disease
Time-resolved photoemission by attosecond streaking: extraction of time information
Attosecond streaking of atomic photoemission holds the promise to provide
unprecedented information on the release time of the photoelectron. We show
that attosecond streaking phase shifts indeed contain timing (or spectral
phase) information associated with the Eisenbud-Wigner-Smith time delay matrix
of quantum scattering. However, this is only accessible if the influence of the
streaking infrared (IR) field on the emission process is properly accounted
for. The IR probe field can strongly modify the observed streaking phase shift.
We show that the part of the phase shift ("time shift") due to the interaction
between the outgoing electron and the combined Coulomb and IR laser fields can
be described classically. By contrast, the strong initial-state dependence of
the streaking phase shift is only revealed through the solution of the
time-dependent Schr\"odinger equation in its full dimensionality. We find a
time delay between the hydrogenic 2s and 2p initial states in He+ exceeding
20as for a wide range of IR intensities and XUV energies
Three-Dimensional Maps of All Chromosomes in Human Male Fibroblast Nuclei and Prometaphase Rosettes
Studies of higher-order chromatin arrangements are an essential part of ongoing attempts to explore changes in epigenome structure and their functional implications during development and cell differentiation. However, the extent and cell-type-specificity of three-dimensional (3D) chromosome arrangements has remained controversial. In order to overcome technical limitations of previous studies, we have developed tools that allow the quantitative 3D positional mapping of all chromosomes simultaneously. We present unequivocal evidence for a probabilistic 3D order of prometaphase chromosomes, as well as of chromosome territories (CTs) in nuclei of quiescent (G0) and cycling (early S-phase) human diploid fibroblasts (46, XY). Radial distance measurements showed a probabilistic, highly nonrandom correlation with chromosome size: small chromosomes—independently of their gene density—were distributed significantly closer to the center of the nucleus or prometaphase rosette, while large chromosomes were located closer to the nuclear or rosette rim. This arrangement was independently confirmed in both human fibroblast and amniotic fluid cell nuclei. Notably, these cell types exhibit flat-ellipsoidal cell nuclei, in contrast to the spherical nuclei of lymphocytes and several other human cell types, for which we and others previously demonstrated gene-density-correlated radial 3D CT arrangements. Modeling of 3D CT arrangements suggests that cell-type-specific differences in radial CT arrangements are not solely due to geometrical constraints that result from nuclear shape differences. We also found gene-density-correlated arrangements of higher-order chromatin shared by all human cell types studied so far. Chromatin domains, which are gene-poor, form a layer beneath the nuclear envelope, while gene-dense chromatin is enriched in the nuclear interior. We discuss the possible functional implications of this finding
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