4,132 research outputs found
Feasibility study of an optical radiometer for determining the composition of the Mars atmosphere from shock layer radiation during entry, volume II Final report
Optical radiometer feasibility study for determining composition of Mars atmosphere from shock layer radiation during entry - instrumentatio
Electroweak form factors of heavy-light mesons -- a relativistic point-form approach
We present a general relativistic framework for the calculation of the
electroweak structure of heavy-light mesons within constituent-quark models. To
this aim the physical processes in which the structure is measured, i.e.
electron-meson scattering and semileptonic weak decays, are treated in a
Poincar\'e invariant way by making use of the point-form of relativistic
quantum mechanics. The electromagnetic and weak meson currents are extracted
from the 1- and 1--exchange amplitudes that result from a
Bakamjian-Thomas type mass operator for the respective systems. The covariant
decomposition of these currents provides the electromagnetic and weak
(transition) form factors. Problems with cluster separability, which are
inherent in the Bakamjian-Thomas construction, are discussed and it is shown
how to keep them under control. It is proved that the heavy-quark limit of the
electroweak form factors leads to one universal function, the Isgur-Wise
function, confirming that the requirements of heavy-quark symmetry are
satisfied. A simple analytical expression is given for the Isgur-Wise function
and its agreement with a corresponding front-form calculation is verified
numerically. Electromagnetic form factors for and and weak
-decay form factors are calculated with a simple
harmonic-oscilllator wave function and heavy-quark symmetry breaking due to
finite masses of the heavy quarks is discussed.Comment: 20 pages, 14 figure
Tunable multi-photon Rabi oscillations in an electronic spin system
We report on multi-photon Rabi oscillations and controlled tuning of a
multi-level system at room temperature (S=5/2 for Mn2+:MgO) in and out of a
quasi-harmonic level configuration. The anisotropy is much smaller than the
Zeeman splittings, such as the six level scheme shows only a small deviation
from an equidistant diagram. This allows us to tune the spin dynamics by either
compensating the cubic anisotropy with a precise static field orientation, or
by microwave field intensity. Using the rotating frame approximation, the
experiments are very well explained by both an analytical model and a
generalized numerical model. The calculated multi-photon Rabi frequencies are
in excellent agreement with the experimental data
Form factors of heavy-light systems in point-form relativistic quantum mechanics: the Isgur-Wise function
We investigate electromagnetic and weak form factors of heavy-light mesons in
the context of point-form relativistic quantum mechanics. To this aim we treat
the physical processes from which such electroweak form factors are extracted
by means of a coupled channel approach which accounts for the dynamics of the
intermediate gauge bosons. It is shown that heavy-quark symmetry is respected
by this formulation. A simple analytical expression is obtained for the
Isgur-Wise function in the heavy-quark limit. Breaking of heavy-quark symmetry
due to realistic values of the heavy-quark mass are studied numerically.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
Coherent manipulation of electron spins up to ambient temperatures in Cr(S=1/2) doped KNbO
We report coherent spin manipulation on Cr (\emph{S} = 1/2, \emph{I} =
0) doped KNbO, which constitutes a dilute two-level model relevant for
use as a spin qubit. Rabi oscillations are observed for the first time in a
spin system based on transition metal oxides up to room temperature. At liquid
helium temperature the phase coherence relaxation time \emph{} reaches
s and, with a Rabi frequency of 20 MHz, yields a single qubit
figure of merit \emph{} of about 500. This shows that a diluted ensemble
of Cr (\emph{S} = 1/2) doped KNbO is a potential candidate for
solid-state quantum information processing.Comment: 4 page
Trapped ion mobility spectrometry and PASEF enable in-depth lipidomics from minimal sample amounts
A comprehensive characterization of the lipidome from limited starting material remains very challenging. Here we report a high-sensitivity lipidomics workflow based on nanoflow liquid chromatography and trapped ion mobility spectrometry (TIMS). Taking advantage of parallel accumulation-serial fragmentation (PASEF), we fragment on average 15 precursors in each of 100 ms TIMS scans, while maintaining the full mobility resolution of co-eluting isomers. The acquisition speed of over 100 Hz allows us to obtain MS/MS spectra of the vast majority of isotope patterns. Analyzing 1 mu L of human plasma, PASEF increases the number of identified lipids more than three times over standard TIMS-MS/MS, achieving attomole sensitivity. Building on high intra- and inter-laboratory precision and accuracy of TIMS collisional cross sections (CCS), we compile 1856 lipid CCS values from plasma, liver and cancer cells. Our study establishes PASEF in lipid analysis and paves the way for sensitive, ion mobility-enhanced lipidomics in four dimensions
- and -spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects
A study of donor electron spins and spin--dependent electronic transitions
involving phosphorous (P) atoms in proximity of the (111) oriented
crystalline silicon (c-Si) to silicon dioxide (SiO) interface is
presented for [P] = 10 and [P] =
10 at about liquid He temperatures (
). Using pulsed electrically detected magnetic
resonance (pEDMR), spin--dependent transitions between the \Phos donor state
and two distinguishable interface states are observed, namely (i) \Pb centers
which can be identified by their characteristic anisotropy and (ii) a more
isotropic center which is attributed to E defects of the \sio bulk
close to the interface. Correlation measurements of the dynamics of
spin--dependent recombination confirm that previously proposed transitions
between \Phos and the interface defects take place. The influence of these
electronic near--interface transitions on the \Phos donor spin coherence time
as well as the donor spin--lattice relaxation time is then
investigated by comparison of spin Hahn--echo decay measurements obtained from
conventional bulk sensitive pulsed electron paramagnetic resonance and surface
sensitive pEDMR, as well as surface sensitive electrically detected inversion
recovery experiments. The measurements reveal that both and of
\Phos donor electrons spins in proximity of energetically lower interface
states at K are reduced by several orders of magnitude
Pulmonary Toxoplasmosis, a Rare but Severe Manifestation of a Common Opportunistic Infection in Late HIV Presenters: Report of Two Cases
Abstract : Pulmonary toxoplasmosis is rare, particularly in the era of highly active antiretroviral therapy (HAART). Here, we describe two severe cases in patients not known to be HIV-infected. In both patients, early diagnosis and therapy led to a favourable outcome. Pulmonary toxoplasmosis should be considered in the differential diagnosis in potentially HIV-infected patients with respiratory symptom
Serological diagnosis of echinococcosis: the diagnostic potential of native antigens
Purpose: Human alveolar (AE) and cystic echinococcosis (CE) caused by the metacestode stages of Echinococcus multilocularis and E. granulosus, respectively, lack pathognomonic clinical signs. Diagnosis therefore relies on the results of imaging and serological studies. The primary goal of this study was to evaluate the efficacy of several easy-to-produce crude or partially purified E. granulosus and E. multilocularis metacestode-derived antigens as tools for the serological diagnosis and differential diagnosis of patients suspicious for AE or CE. Methods: The sera of 51 treatment-naïve AE and 32 CE patients, 98 Swiss blood donors and 38 patients who were initially suspicious for echinococcosis but suffering from various other liver diseases (e.g., liver neoplasia, etc.) were analysed. Results: According to the results of enzyme-linked immunosorbent assays (ELISA), metacestode-derived antigens of E. granulosus had sensitivities varying from 81 to 97% and >99.9% for the diagnosis of CE and AE, respectively. Antigens derived from E. multilocularis metacestodes had sensitivities ranging from 84 to 91% and >99.9% for the diagnosis of CE and AE, respectively. Specificities ranged from 92 to >99.9%. Post-test probabilities for the differential diagnosis of AE from liver neoplasias, CE from cystic liver lesions, and screening for AE in Switzerland were around 95, 86 and 2.2%, respectively. Cross-reactions with antibodies in sera of patients with other parasitic affections (fasciolosis, schistosomosis, amebosis, cysticercosis, and filarioses) did occur at variable frequencies, but could be eliminated through the use of confirmatory testing. Conclusions: Different metacestode-derived antigens of E. granulosus and E. multilocularis are valuable, widely accessible, and cost-efficient tools for the serological diagnosis of echinococcosis. However, confirmatory testing is necessary, due to the lack of species specificity and the occurrence of cross-reactions to other helminthic disease
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