78 research outputs found
Local Magnetic Susceptibility of the Positive Muon in the Quasi 1D S=1/2 Antiferromagnet KCuF
We report muon spin rotation measurements of the local magnetic
susceptibility around a positive muon in the paramagnetic state of the quasi
one-dimensional spin 1/2 antiferromagnet KCuF. Signals from two distinct
sites are resolved which have a temperature dependent frequency shift which is
different than the magnetic susceptibility. This difference is attributed to a
muon induced perturbation of the spin 1/2 chain.Comment: 13 pages, 4 figures, The 2002 International Conference on Muon Spin
Rotation, Relaxation and Resonance, Virginia. US
Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance
Low energy -detected nuclear magnetic resonance (-NMR) was used
to investigate the spatial dependence of the hyperfine magnetic fields induced
by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001)
magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag
layer shows dramatic broadening compared to intrinsic Ag. This broadening is
attributed to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows a power law
decay away from the Ag/Fe interface with power , and a field
extrapolated to T at the interface.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
Spin Echo Decay in a Stochastic Field Environment
We derive a general formalism with which it is possible to obtain the time
dependence of the echo size for a spin in a stochastic field environment. Our
model is based on ``strong collisions''. We examine in detail three cases
where: (I) the local field is Ising-like, (II) the field distribution is
continuous and has a finite second moment, and (III) the distribution is
Lorentzian. The first two cases show a T2 minimum effect and are exponential in
time cubed for short times. The last case can be approximated by a
phenomenological stretched exponential.Comment: 11 pages + 3 postscript figure
Muonium as a hydrogen analogue in silicon and germanium; quantum effects and hyperfine parameters
We report a first-principles theoretical study of hyperfine interactions,
zero-point effects and defect energetics of muonium and hydrogen impurities in
silicon and germanium. The spin-polarized density functional method is used,
with the crystalline orbitals expanded in all-electron Gaussian basis sets. The
behaviour of hydrogen and muonium impurities at both the tetrahedral and
bond-centred sites is investigated within a supercell approximation. To
describe the zero-point motion of the impurities, a double adiabatic
approximation is employed in which the electron, muon/proton and host lattice
degrees of freedom are decoupled. Within this approximation the relaxation of
the atoms of the host lattice may differ for the muon and proton, although in
practice the difference is found to be slight. With the inclusion of zero-point
motion the tetrahedral site is energetically preferred over the bond-centred
site in both silicon and germanium. The hyperfine and superhyperfine
parameters, calculated as averages over the motion of the muon, agree
reasonably well with the available data from muon spin resonance experiments.Comment: 20 pages, including 9 figures. To appear in Phys. Rev.
Efficacy results of pimavanserin from a multi-center, open-label extension study in Parkinson's disease psychosis patients
This is the final version. Available on open access from Elsevier via the DOI in this recordIntroduction: Pimavanserin, a selective 5-HT2A inverse agonist/antagonist, was
approved for hallucinations and delusions associated with Parkinson’s disease psychosis
(PDP). We present durability of response with pimavanserin in patients with PDP for an
additional 4 weeks of treatment.
Methods: This was an open-label extension (OLE) study in patients previously
completing one of three double-blind, placebo-controlled (Core) studies. All patients
received pimavanserin 34 mg once daily. Efficacy assessments included the Scale for the
Assessment of Positive Symptoms (SAPS) PD and H+D scales, Clinical Global
Impression (CGI) Improvement and Severity scales and Caregiver Burden Scale (CBS),
through 4 weeks in the OLE. Safety assessments were conducted at each visit.
Results: Of 459 patients, 424 (92.4%) had a Week 4 efficacy assessment. At Week 4 (10
weeks total treatment), SAPS-PD mean (standard deviation) change from OLE baseline
was -1.8 (5.5) and for SAPS-H+D was -2.1 (6.2) with pimavanserin 34 mg. Patients
receiving placebo during the Core studies had greater improvements (SAPS-PD -2.9
[5.6]; SAPS-H+D -3.5 [6.3]) during the OLE. For participants treated with pimavanserin
8.5 or 17 mg during the Core studies, further improvement was observed during the OLE
with pimavanserin 34 mg. The mean change from Core Study baseline for SAPS-PD
score was similar among prior pimavanserin 34 mg and prior placebo-treated participants
(-7.1 vs. -7.0). The CGI-I response rate (score of 1 or 2) at Week 4 was 51.4%. Adverse
events were reported by 215 (46.8%) patients during the first 4 weeks of OLE. The most
common AEs were fall (5.9%), hallucination (3.7%), urinary tract infection (2.8%),
insomnia (2.4%), and peripheral edema (2.2%)
4
Conclusions: Patients previously on pimavanserin 34 mg during three blinded core
studies had durability of efficacy during the subsequent 4 week OLE SAPS-PD
assessment. Patients previously on blinded placebo improved after 4 weeks of OL
pimavanserin treatment. These results in over 400 patients from 14 countries support the
efficacy of pimavanserin for treating PDP.ACADIA Pharmaceuticals Inc. (San Diego, CA
Giant Vortices Below the Surface of NbSe Detected Using Low Energy -NMR
A low energy radioactive beam of polarized Li has been used to observe
the vortex lattice near the surface of superconducting NbSe. The
inhomogeneous magnetic field distribution associated with the vortex lattice
was measured using depth-resolved -detected NMR. Below one
observes the characteristic lineshape for a triangular vortex lattice which
depends on the magnetic penetration depth and vortex core radius. The size of
the vortex core varies strongly with magnetic field. In particular in a low
field of 10.8 mT the core radius is much larger than the coherence length. The
possible origin of these giant vortices is discussed.Comment: 5 pages, 3 figures. Submitted to Phys. Rev. Let
Muon spin relaxation study of spin dynamics in poly(triarylamine)
Organic semiconductors (OSCs) have been of great interest over the last couple of decades owing to their mechanic
flexibility, ease of processing, high tuneability and availability. One area of OSCs that is of growing interest is
polymers as they possess many of the desirable properties, in particular print processing and tunability of electronic
properties, necessary for application in devices such as organic solar cells and the spin valves being engineered for
hard disks and logic devices. Much focus has been given in recent years to the areas of research including the electron
and hole dynamics, transport mechanisms and spin relaxation in OSCs in order to utilise them in novel organic
devices. In this paper the µSR technique is applied to carry out an in depth study of the electron dynamics and spin
relaxation in the commonly used Poly(triarylamine) polymer (PTAA). It is shown that the electron wavefunction can
be considered localised to the aromatic rings providing a strong hyperfine coupling interaction with the muon. In
addition the presence of an electron spin relaxation (eSR) is demonstratated that resembles that previously reported in
the small organic molecule series
КЛАВИАТУРНЫЕ ШПИОНЫ
В данной работе приводится обзор клавиатурного шпионажа как одного из главных
видов электронного мошенничества. Описана его «легальная» сторона и рассмотрены
способы распространения. Так же приведены некоторые рекомендации защиты как от
программных, так и от аппаратных клавиатурных шпионов
Temporal mapping of photochemical reactions and molecular excited states with carbon specificity
Photochemical reactions are essential to a large number of important industrial and biological processes. A method for monitoring photochemical reaction kinetics and the dynamics of molecular excitations with spatial resolution within the active molecule would allow a rigorous exploration of the pathway and mechanism of photophysical and photochemical processes. Here we demonstrate that laser-excited muon pump-probe spin spectroscopy (photo-μSR) can temporally and spatially map these processes with a spatial resolution at the single-carbon level in a molecule with a pentacene backbone. The observed time-dependent light-induced changes of an avoided level crossing resonance demonstrate that the photochemical reactivity of a specific carbon atom is modified as a result of the presence of the excited state wavefunction. This demonstrates the sensitivity and potential of this technique in probing molecular excitations and photochemistry
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