461 research outputs found
Bessel beams of two-level atoms driven by a linearly polarized laser field
We study Bessel beams of two-level atoms that are driven by a linearly
polarized laser field. Starting from the Schroedinger equation, we determine
the states of two-level atoms in a plane-wave field respecting propagation
directions both of the atom and the field. For such laser-driven two-level
atoms, we construct Bessel beams beyond the typical paraxial approximation. We
show that the probability density of these atomic beams obtains a non-trivial,
Bessel-squared-type behavior and can be tuned under the special choice of the
atom and laser parameters, such as the nuclear charge, atom velocity, laser
frequency, and propagation geometry of the atom and laser beams. Moreover, we
spatially and temporally characterize the beam of hydrogen and selected
(neutral) alkali-metal atoms that carry non-zero orbital angular momentum
(OAM). The proposed spatiotemporal Bessel states (i) are able to describe, in
principle, twisted states of any two-level system which is driven by the
radiation field and (ii) have potential applications in atomic, nuclear
processes and quantum communication.Comment: 13 pages, 5 figures, appeared as a EPJD highlight on Thursday, 01
August 2013
http://www.epj.org/index.php?option=com_content&view=article&id=684%3Aepjd-highlight-novel-beams-made-of-twisted-atoms&catid=112%3Aepj-d&Itemid=466&lang=e
Radiative Capture of Twisted Electrons by Bare Ions
Recent advances in the production of twisted electron beams with a
subnanometer spot size offer unique opportunities to explore the role of
orbital angular momentum (OAM) in basic atomic processes. In the present work,
we address one of these processes: radiative recombination of twisted electrons
with bare ions. Based on the density matrix formalism and the non-relativistic
Schr\"odinger theory, analytical expressions are derived for the angular
distribution and the linear polarization of photons emitted due to the capture
of twisted electrons into the ground state of (hydrogen-like) ions. We show
that these angular and polarization distributions are sensitive to both, the
transverse momentum and the topological charge of the electron beam. To observe
in particular the value of this charge, we propose an experiment that makes use
of the coherent superposition of two twisted beams.Comment: 5 pages, 3 figure
Atomic ionization by twisted photons: Angular distribution of emitted electrons
We investigate the angular distribution of electrons that are emitted in the
ionization of hydrogen-like ions by twisted photons. Analysis is performed
based on the first-order perturbation theory and the non-relativistic
Schr\"odinger equation. Special attention is paid to the dependence of the
electron emission pattern on the impact parameter b of the ion with respect to
the centre of the twisted wave front. In order to explore such a dependence,
detailed calculations were carried out for the photoionization of the 1s ground
and 2 py excited states of neutral hydrogen atoms. Based on these calculations,
we argue that for relatively small impact parameters the electron angular
distributions may be strongly affected by altering the position of the atom
within the wave front. In contrast, if the atom is placed far from the front
centre, the emission pattern of the electrons is independent on the impact
parameter b and resembles that observed in the photoionization by plane wave
photons.Comment: 23 pages, 6 figure
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Evaluation of geothermal foams
Efforts to evaluate drilling foams for geothermal applications and to recommend a program for developing geothermal drilling foams are described. The advantages of foams, zones that favor the use of foams, types of foaming agents, and the selection and testing of foams are discussed. (MHR
Sonoluminescence: Nature's Smallest BlackBody
The Spectrum of the light emitted by a sonoluminescing bubble is extremely
well fit by the spectrum of a blackbody. Furthermore the radius of emission can
be smaller than the wavelength of the light. Consequences, for theories of
sonoluminescence are discussed.Comment: 8 pages, 3 Figure
An Alternative Method to Deduce Bubble Dynamics in Single Bubble Sonoluminescence Experiments
In this paper we present an experimental approach that allows to deduce the
important dynamical parameters of single sonoluminescing bubbles (pressure
amplitude, ambient radius, radius-time curve) The technique is based on a few
previously confirmed theoretical assumptions and requires the knowledge of
quantities such as the amplitude of the electric excitation and the phase of
the flashes in the acoustic period. These quantities are easily measurable by a
digital oscilloscope, avoiding the cost of expensive lasers, or ultrafast
cameras of previous methods. We show the technique on a particular example and
compare the results with conventional Mie scattering. We find that within the
experimental uncertainties these two techniques provide similar results.Comment: 8 pages, 5 figures, submitted to Phys. Rev.
A New Kind of Graded Lie Algebra and Parastatistical Supersymmetry
In this paper the usual graded Lie algebra is generalized to a new
form, which may be called graded Lie algebra. It is shown that there
exists close connections between the graded Lie algebra and
parastatistics, so the can be used to study and analyse various
symmetries and supersymmetries of the paraparticle systems
ABCG2 Is a Selectable Marker for Enhanced Multilineage Differentiation Potential in Periodontal Ligament Stem Cells.
Periodontal ligament stem cells (PDLSCs) provide an important source for tissue regeneration and may become especially useful in the formation of osteogenic seeds. PDLSCs can be cultured, expanded, and differentiated in vitro; thus, they may be applied in the long-term treatment of the defects in the dental regions. Here we studied numerous potential markers allowing the selection of human PDLSCs with a maximum differentiation potential. We followed the expression of the ATP-binding cassette subfamily G member 2 (ABCG2) membrane transporter protein and isolated ABCG2-expressing cells by using a monoclonal antibody, recognizing the transporter at the cell surface in intact cells. The expression of the ABCG2 protein, corresponding to the so-called side-population phenotype in various tissue-derived stem cells, was found to be a useful marker for the selection of PDLSCs with enhanced osteogenic, chondrogenic, and adipogenic differentiation. These findings may have important applications in achieving efficient dental tissue regeneration by using stem cells from extracted teeth
Phenotyping vs. genotyping for prediction of clopidogrel efficacy and safety: the PEGASUS-PCI study
Background: Prognostic values of genotyping and
phenotyping for assessment of clopidogrel responsiveness have
been shown in independent studies. Objectives: To compare
different assays for prediction of events during long-term
follow-up. Methods: In this prospective cohort study polymorphisms
of CYP2C19*2 and CYP2C19*17 alleles, vasodilator-
stimulated phosphoprotein phosphorylation (VASP)
assay, multiple electrode aggregometry (MEA), cone and
platelet analyser (CPA) and platelet function analyser (PFA-
100) were performed in 416 patients undergoing percutaneous
coronary intervention. The rates of events were recorded during
a 12-month follow-up. Results: Platelet aggregation by MEA
predicted stent thrombosis (2.4%) better (c-index = 0.90;
P < 0.001; sensitivity = 90%; specificity = 83%) than the
VASP assay, CPA or PFA-100 (c-index 0.05;
sensitivity < 70%; specificity < 70% for all) or even the
CYP2C19*2 polymorphism (c-index 0.05; sensitivity
= 30%; specificity = 71%). Survival analysis indicated
that patients classified as poor responders by MEA had a
substantially higher risk of developing stent thrombosis or
MACE than clopidogrel responders (12.5% vs. 0.3%,
P < 0.001, and 18.5% vs. 11.3%, P = 0.022, respectively),
whereas poor metabolizers (CYP2C19*1/*2 or *2/*2 carriers)
were not at increased risks (stent thrombosis, 2.7% vs. 2.5%,
P > 0.05; MACE, 13.5% vs. 12.1%, P = 0.556). The incidence
of major bleedings (2.6%) was numerically higher in
patients with an enhanced vs. poor response to clopidogrel
assessed by MEA (4% vs. 0%) or in ultra-metabolizers vs.
regular metabolizers (CYP2C19*17/*17 vs. CYP2C19*1/*1;
9.5% vs. 2%). The classification tree analysis demonstrated that
acute coronary syndrome at hospitalization and diabetes
mellitus were the best discriminators for clopidogrel responder
status. Conclusions: Phenotyping of platelet response to clopidogrel
was a better predictor of stent thrombosis than
genotyping
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