1,777 research outputs found
Four-path interference and uncertainty principle in photodetachment microscopy
We study the quantal motion of electrons emitted by a pointlike monochromatic
isotropic source into parallel uniform electric and magnetic fields. The
two-path interference pattern in the emerging electron wave due to the electric
force is modified by the magnetic lens effect which periodically focuses the
beam into narrow filaments along the symmetry axis. There, four classical paths
interfere. With increasing electron energy, the current distribution changes
from a quantum regime governed by the uncertainty principle, to an intricate
spatial pattern that yields to a semiclassical analysis.Comment: submitted to Europhysics Letter
Temperature dependence of chemical and biophysical rate processes: Phenomenological approach to deviations from Arrhenius law
Arrhenius plots, which are used to represent the effects of temperature on the rates of chemical and biophysical processes and on various transport phenomena in materials science, may exhibit deviations from linearity. Account of curvature is provided here by a formula which involves a deformation of the exponential function, of the kind recently encountered in treatments of non-extensivity in statistical mechanics. We present here examples on diverse topics – respiration rates of plants, speed of gliding of bacteria, quantum mechanical tunneling in a chemical reaction – illustrating the variety of possible applications and the additional insight that can be gained
Evidence for an Excited Hyperon State in pp -> p K^+ Y^{0*}
Indications for the production of a neutral excited hyperon in the reaction
pp -> p K^+ Y^{0*} are observed in an experiment performed with the ANKE
spectrometer at COSY-J\"ulich at a beam momentum of 3.65 GeV/c. Two final
states were investigated simultaneously, viz. Y^{0*} -> pi^+X^- and pi^-X^+,
and consistent results were obtained in spite of the quite different
experimental conditions. The parameters of the hyperon state are M(Y^{0*})=
(1480 +/- 15) MeV/c^2 and Gamma(Y^{0*})= (60 +/- 15) MeV/c^2. The production
cross section is of the order of few hundred nanobarns. Since the isospin of
the Y^{0*} has not been determined here, it could either be an observation of
the Sigma(1480), a one-star resonance of the PDG tables, or alternatively a
Lambda hyperon. Relativistic quark models for the baryon spectrum do not
predict any excited hyperon in this mass range and so the Y^{0*} may be of
exotic nature.Comment: 4 pages, 3 figures, accepted for publication in Phys.Rev.Let
Exact exchange-correlation potential for a time-dependent two electron system
We obtain an exact solution of the time-dependent Schroedinger equation for a
two-electron system confined to a plane by an isotropic parabolic potential
whose curvature is periodically modulated in time. From this solution we
compute the exact time-dependent exchange correlation potential v_xc which
enters the Kohn-Sham equation of time-dependent density functional theory. Our
exact result provides a benchmark against which various approximate forms for
v_xc can be compared. Finally v_xc is separated in an adiabatic and a pure
dynamical part and it is shown that, for the particular system studied, the
dynamical part is negligible.Comment: 23 pages, 6 figure
On minimal affinizations of representations of quantum groups
In this paper we study minimal affinizations of representations of quantum
groups (generalizations of Kirillov-Reshetikhin modules of quantum affine
algebras introduced by Chari). We prove that all minimal affinizations in types
A, B, G are special in the sense of monomials. Although this property is not
satisfied in general, we also prove an analog property for a large class of
minimal affinization in types C, D, F. As an application, the Frenkel-Mukhin
algorithm works for these modules. For minimal affinizations of type A, B we
prove the thin property (the l-weight spaces are of dimension 1) and a
conjecture of Nakai-Nakanishi (already known for type A). The proof of the
special property is extended uniformly for more general quantum affinizations
of quantum Kac-Moody algebras.Comment: 38 pages; references and additional results added. Accepted for
publication in Communications in Mathematical Physic
Electrosynthesis of Aryliminophosphoranes in Continuous Flow
A practical electrochemical method for synthesizing aryliminophosphoranes from widely available nitro(hetero)arenes in a continuous-flow system is presented. The utilization of flow technology offers several advantages to our approach, including the elimination of the need for a supporting electrolyte and enhanced scalability. Our method demonstrates good tolerance towards various functional groups, with electron-deficient nitroarenes being particularly suitable for this strategy. In addition, we have demonstrated the versatility of aryliminophosphoranes as intermediates in synthesizing anilines, amines, and amides. To further enhance the utility of our approach, we have developed a telescoped method that utilizes a tube-in-tube setup for the in-situ production of isocyanates
Electron propagation in crossed magnetic and electric fields
Laser-atom interaction can be an efficient mechanism for the production of
coherent electrons. We analyze the dynamics of monoenergetic electrons in the
presence of uniform, perpendicular magnetic and electric fields. The Green
function technique is used to derive analytic results for the field--induced
quantum mechanical drift motion of i) single electrons and ii) a dilute Fermi
gas of electrons. The method yields the drift current and, at the same time it
allows us to quantitatively establish the broadening of the (magnetic) Landau
levels due to the electric field: Level number k is split into k+1 sublevels
that render the th oscillator eigenstate in energy space. Adjacent Landau
levels will overlap if the electric field exceeds a critical strength. Our
observations are relevant for quantum Hall configurations whenever electric
field effects should be taken into account.Comment: 11 pages, 2 figures, submitte
Effect of fulvic acids on lead-induced oxidative stress to metal sensitive Vicia faba L. plant
Lead (Pb) is a ubiquitous environmental pollutant capable to induce various morphological, physiological, and biochemical functions in plants. Only few publications focus on the influence of Pb speciation both on its phytoavailability and phytotoxicity. Therefore, Pb toxicity (in terms of lipid peroxidation, hydrogen peroxide induction, and photosynthetic pigments contents) was studied in Vicia faba plants in relation with Pb uptake and speciation. V. faba seedlings were exposed to Pb supplied as Pb(NO3)2 or complexed by two fulvic acids (FAs), i.e. Suwannee River fulvic acid (SRFA) and Elliott Soil fulvic acid (ESFA), for 1, 12, and 24 h under controlled hydroponic conditions. For both FAs, Pb uptake and translocation by Vicia faba increased at low level (5 mg l−1), whereas decreased at high level of application (25 mg l−1). Despite the increased Pb uptake with FAs at low concentrations, there was no influence on the Pb toxicity to the plants. However, at high concentrations, FAs reduced Pb toxicity by reducing its uptake. These results highlighted the role of the dilution factor for FAs reactivity in relation with structure; SRFA was more effective than ESFA in reducing Pb uptake and alleviating Pb toxicity to V. faba due to comparatively strong binding affinity for the heavy metal
Ballistic matter waves with angular momentum: Exact solutions and applications
An alternative description of quantum scattering processes rests on
inhomogeneous terms amended to the Schroedinger equation. We detail the
structure of sources that give rise to multipole scattering waves of definite
angular momentum, and introduce pointlike multipole sources as their limiting
case. Partial wave theory is recovered for freely propagating particles. We
obtain novel results for ballistic scattering in an external uniform force
field, where we provide analytical solutions for both the scattering waves and
the integrated particle flux. Our theory directly applies to p-wave
photodetachment in an electric field. Furthermore, illustrating the effects of
extended sources, we predict some properties of vortex-bearing atom laser beams
outcoupled from a rotating Bose-Einstein condensate under the influence of
gravity.Comment: 42 pages, 8 figures, extended version including photodetachment and
semiclassical theor
Which leukocyte subsets predict cardiovascular mortality? From the LUdwigshafen RIsk and Cardiovascular Health (LURIC) Study
AbstractObjectiveWhite blood cells are known to predict cardiovascular mortality, but form a highly heterogeneous population. It is therefore possible that specific subtypes disproportionally contribute to the prediction of cardiovascular outcomes. Therefore, we compared leukocyte subsets alone and in conjunction with an established inflammatory marker, C-reactive protein, for predicting death due to cardiovascular disease in a high-risk population.MethodsPatients, 3316, (mean [SD] age, 62 [10] years) scheduled for coronary angiography were prospectively followed up. Neutrophil, monocyte and lymphocyte counts were determined. Neutrophil and monocyte subsets were further analysed on the basis of surface expression of CD11b, CD18, CD31, CD40 and CD58. Lymphocytes were further subdivided into CD3, CD4, CD8, and CD19 subsets. The association between each marker and subsequent cardiovascular mortality was assessed using multivariable Cox regression models.ResultsDuring a median follow-up period of 7.8 years, 745 (22.5%) patients died, of which 484 were due to cardiovascular events. After entering conventional risk factors and removing patients with a current infection, neutrophil count (HR [95% CI]=1.90 [1.39, 2.60], P<0.001) and the neutrophil/lymphocyte ratio (HR [95% CI]=1.68 [1.24, 2.27], P=0.003) emerged as independent predictors of cardiovascular mortality. After mutual adjustment, neutrophil count (HR [95% CI]=1.87 [1.35, 2.50], P<0.001) out-performed C-reactive protein (HR [95% CI] 1.32 [0.99, 1.78], P=0.06) as a predictor of cardiovascular mortality.ConclusionsDue to its predictive potential and inexpensive determination, assessment of high neutrophil counts may represent an important marker, possibly improving cardiovascular mortality risk prediction
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