92 research outputs found
The Loschmidt Echo as a robust decoherence quantifier for many-body systems
We employ the Loschmidt Echo, i.e. the signal recovered after the reversal of
an evolution, to identify and quantify the processes contributing to
decoherence. This procedure, which has been extensively used in single particle
physics, is here employed in a spin ladder. The isolated chains have 1/2 spins
with XY interaction and their excitations would sustain a one-body like
propagation. One of them constitutes the controlled system S whose reversible
dynamics is degraded by the weak coupling with the uncontrolled second chain,
i.e. the environment E. The perturbative SE coupling is swept through arbitrary
combinations of XY and Ising like interactions, that contain the standard
Heisenberg and dipolar ones. Different time regimes are identified for the
Loschmidt Echo dynamics in this perturbative configuration. In particular, the
exponential decay scales as a Fermi golden rule, where the contributions of the
different SE terms are individually evaluated and analyzed. Comparisons with
previous analytical and numerical evaluations of decoherence based on the
attenuation of specific interferences, show that the Loschmidt Echo is an
advantageous decoherence quantifier at any time, regardless of the S internal
dynamics.Comment: 12 pages, 6 figure
Anodal block permits directional vagus nerve stimulation
© 2020, The Author(s). Vagus nerve stimulation (VNS) is a bioelectronic therapy for disorders of the brain and peripheral organs, and a tool to study the physiology of autonomic circuits. Selective activation of afferent or efferent vagal fibers can maximize efficacy and minimize off-target effects of VNS. Anodal block (ABL) has been used to achieve directional fiber activation in nerve stimulation. However, evidence for directional VNS with ABL has been scarce and inconsistent, and it is unknown whether ABL permits directional fiber activation with respect to functional effects of VNS. Through a series of vagotomies, we established physiological markers for afferent and efferent fiber activation by VNS: stimulus-elicited change in breathing rate (ÎBR) and heart rate (ÎHR), respectively. Bipolar VNS trains of both polarities elicited mixed ÎHR and ÎBR responses. Cathode cephalad polarity caused an afferent pattern of responses (relatively stronger ÎBR) whereas cathode caudad caused an efferent pattern (stronger ÎHR). Additionally, left VNS elicited a greater afferent and right VNS a greater efferent response. By analyzing stimulus-evoked compound nerve potentials, we confirmed that such polarity differences in functional responses to VNS can be explained by ABL of A- and B-fiber activation. We conclude that ABL is a mechanism that can be leveraged for directional VNS
Reducing orbital eccentricity in binary black hole simulations
Binary black hole simulations starting from quasi-circular (i.e., zero radial
velocity) initial data have orbits with small but non-zero orbital
eccentricities. In this paper the quasi-equilibrium initial-data method is
extended to allow non-zero radial velocities to be specified in binary black
hole initial data. New low-eccentricity initial data are obtained by adjusting
the orbital frequency and radial velocities to minimize the orbital
eccentricity, and the resulting ( orbit) evolutions are compared with
those of quasi-circular initial data. Evolutions of the quasi-circular data
clearly show eccentric orbits, with eccentricity that decays over time. The
precise decay rate depends on the definition of eccentricity; if defined in
terms of variations in the orbital frequency, the decay rate agrees well with
the prediction of Peters (1964). The gravitational waveforms, which contain
cycles in the dominant l=m=2 mode, are largely unaffected by the
eccentricity of the quasi-circular initial data. The overlap between the
dominant mode in the quasi-circular evolution and the same mode in the
low-eccentricity evolution is about 0.99.Comment: 27 pages, 9 figures; various minor clarifications; accepted to the
"New Frontiers" special issue of CQ
Energy spectra, wavefunctions and quantum diffusion for quasiperiodic systems
We study energy spectra, eigenstates and quantum diffusion for one- and
two-dimensional quasiperiodic tight-binding models. As our one-dimensional
model system we choose the silver mean or `octonacci' chain. The
two-dimensional labyrinth tiling, which is related to the octagonal tiling, is
derived from a product of two octonacci chains. This makes it possible to treat
rather large systems numerically. For the octonacci chain, one finds singular
continuous energy spectra and critical eigenstates which is the typical
behaviour for one-dimensional Schr"odinger operators based on substitution
sequences. The energy spectra for the labyrinth tiling can, depending on the
strength of the quasiperiodic modulation, be either band-like or fractal-like.
However, the eigenstates are multifractal. The temporal spreading of a
wavepacket is described in terms of the autocorrelation function C(t) and the
mean square displacement d(t). In all cases, we observe power laws for C(t) and
d(t) with exponents -delta and beta, respectively. For the octonacci chain,
0<delta<1, whereas for the labyrinth tiling a crossover is observed from
delta=1 to 0<delta<1 with increasing modulation strength. Corresponding to the
multifractal eigenstates, we obtain anomalous diffusion with 0<beta<1 for both
systems. Moreover, we find that the behaviour of C(t) and d(t) is independent
of the shape and the location of the initial wavepacket. We use our results to
check several relations between the diffusion exponent beta and the fractal
dimensions of energy spectra and eigenstates that were proposed in the
literature.Comment: 24 pages, REVTeX, 10 PostScript figures included, major revision, new
results adde
Assessment of industrial nitriding processes for fusion steel applications
The 9Cr steels EUROFER and F82H-mod are the candidate materials for future fusion reactors. The extension of the operation limits including temperature, strength and toughness are still the scope of ongoing research. In a pulsed reactor operation, fatigue lifetime is one of the major properties for the steels. While the oxide dispersion strengthened EUROFER-ODS variant showed significant improvements in this area, the production costs and availability of large quantities of materials drastically limits its applications.
In the present study, different surface nitriding treatments of EUROFER972 have been performed and the impact on microstructure, dynamic fracture toughness and high temperature fatigue has been analysed. Four different states of EUROFER including different heat treatments, nitriding of the surface and the ODS variant are tested and compared in this work.
Low cycle fatigue tests show the improvements after certain treatments. Charpy impact tests and microstructural investigation by scanning electron microscopy and analytical transmission electron microscopy are also performed to compare the materials against the reference (EUROFER97).
While conventional gas nitriding showed no beneficial effect on the material, the Hard-Inox-P treatment showed a significant improvement in the cycles to failure while retaining an acceptable toughness. Microstructural investigations showed the presence of very small chromium- and nitrogen-rich precipitates in the area close to the surface
Effectiveness and safety of opicapone in Parkinson's disease patients with motor fluctuations: The OPTIPARK open-label study
BACKGROUND: The efficacy and safety of opicapone, a once-daily catechol-O-methyltransferase inhibitor, have been established in two large randomized, placebo-controlled, multinational pivotal trials. Still, clinical evidence from routine practice is needed to complement the data from the pivotal trials. METHODS: OPTIPARK (NCT02847442) was a prospective, open-label, single-arm trial conducted in Germany and the UK under clinical practice conditions. Patients with Parkinsonâs disease and motor fluctuations were treated with opicapone 50âmg for 3 (Germany) or 6 (UK) months in addition to their current levodopa and other antiparkinsonian treatments. The primary endpoint was the Clinicianâs Global Impression of Change (CGI-C) after 3âmonths. Secondary assessments included Patient Global Impressions of Change (PGI-C), the Unified Parkinsonâs Disease Rating Scale (UPDRS), Parkinsonâs Disease Questionnaire (PDQ-8), and the Non-Motor Symptoms Scale (NMSS). Safety assessments included evaluation of treatment-emergent adverse events (TEAEs) and serious adverse events (SAEs). RESULTS: Of the 506 patients enrolled, 495 (97.8%) took at least one dose of opicapone. Of these, 393 (79.4%) patients completed 3âmonths of treatment. Overall, 71.3 and 76.9% of patients experienced any improvement on CGI-C and PGI-C after 3âmonths, respectively (full analysis set). At 6âmonths, for UK subgroup only (nâ=â95), 85.3% of patients were judged by investigators as improved since commencing treatment. UPDRS scores at 3âmonths showed statistically significant improvements in activities of daily living during OFF (meanâ±âSD change from baseline: ââ3.0â±â4.6, pâ<â0.0001) and motor scores during ON (ââ4.6â±â8.1, pâ<â0.0001). The meanâ±âSD improvements of ââ3.4â±â12.8 points for PDQ-8 and -6.8â±â19.7 points for NMSS were statistically significant versus baseline (both pâ<â0.0001). Most of TEAEs (94.8% of events) were of mild or moderate intensity. TEAEs considered to be at least possibly related to opicapone were reported for 45.1% of patients, with dyskinesia (11.5%) and dry mouth (6.5%) being the most frequently reported. Serious TEAEs considered at least possibly related to opicapone were reported for 1.4% of patients. CONCLUSIONS: Opicapone 50âmg was effective and generally well-tolerated in PD patients with motor fluctuations treated in clinical practice. TRIAL REGISTRATION: Registered in July 2016 at clinicaltrials.gov (NCT02847442)
Certified reference materials for radionuclides in Bikini Atoll sediment (IAEA-410) and Pacific Ocean sediment (IAEA-412)
The preparation and characterization of certified reference materials (CRMs) for radionuclide content in sediments collected offshore of Bikini Atoll (IAEA-410) and in the open northwest Pacific Ocean (IAEA-412) are described and the results of the certification process are presented. The certified radionuclides include: 40K, 210Pb (210Po), 226Ra, 228Ra, 228Th, 232Th, 234U, 238U, 239Pu, 239+240Pu and 241Am for IAEA-410 and 40K, 137Cs, 210Pb (210Po), 226Ra, 228Ra, 228Th, 232Th, 235U, 238U, 239Pu, 240Pu and 239+240Pu for IAEA-412. The CRMs can be used for quality assurance and quality control purposes in the analysis of radionuclides in sediments, for development and validation of analytical methods and for staff training
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