4,251 research outputs found
Theory of nuclear excitation by electron capture for heavy ions
We investigate the resonant process of nuclear excitation by electron
capture, in which a continuum electron is captured into a bound state of an ion
with the simultaneous excitation of the nucleus. In order to derive the cross
section a Feshbach projection operator formalism is introduced. Nuclear states
and transitions are described by a nuclear collective model and making use of
experimental data. Transition rates and total cross sections for NEEC followed
by the radiative decay of the excited nucleus are calculated for various heavy
ion collision systems
Extension of nano-confined DNA: quantitative comparison between experiment and theory
The extension of DNA confined to nanochannels has been studied intensively
and in detail. Yet quantitative comparisons between experiments and model
calculations are difficult because most theoretical predictions involve
undetermined prefactors, and because the model parameters (contour length, Kuhn
length, effective width) are difficult to compute reliably, leading to
substantial uncertainties. Here we use a recent asymptotically exact theory for
the DNA extension in the "extended de Gennes regime" that allows us to compare
experimental results with theory. For this purpose we performed new
experiments, measuring the mean DNA extension and its standard deviation while
varying the channel geometry, dye intercalation ratio, and ionic buffer
strength. The experimental results agree very well with theory at high ionic
strengths, indicating that the model parameters are reliable. At low ionic
strengths the agreement is less good. We discuss possible reasons. Our approach
allows, in principle, to measure the Kuhn length and effective width of a
single DNA molecule and more generally of semiflexible polymers in solution.Comment: Revised version, 6 pages, 2 figures, 1 table, supplementary materia
Microwave photon-mediated interactions between semiconductor qubits
The realization of a coherent interface between distant charge or spin qubits
in semiconductor quantum dots is an open challenge for quantum information
processing. Here we demonstrate both resonant and non-resonant photon-mediated
coherent interactions between double quantum dot charge qubits separated by
several tens of micrometers. We present clear spectroscopic evidence of the
collective enhancement of the resonant coupling of two qubits. With both qubits
detuned from the resonator we observe exchange coupling between the qubits
mediated by virtual photons. In both instances pronounced bright and dark
states governed by the symmetry of the qubit-field interaction are found. Our
observations are in excellent quantitative agreement with master-equation
simulations. The extracted two-qubit coupling strengths significantly exceed
the linewidths of the combined resonator-qubit system. This indicates that this
approach is viable for creating photon-mediated two-qubit gates in quantum dot
based systems.Comment: 14 pages, 10 figures and 6 table
Spitzer Observations of Spacecraft Target 162173 (1999 JU3)
Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Hayabusa-2
sample return mission, and a potential target of the Marco Polo sample return
mission. Earth-based studies of this object are fundamental to these missions.
We present a mid-infrared spectrum (5-38 microns) of 1999 JU3 obtained with
NASA's Spitzer Space Telescope in May 2008. These observations place new
constraints on the surface properties of this asteroid. To fit our spectrum we
used the near-Earth asteroid thermal model (NEATM) and the more complex
thermophysical model (TPM). However, the position of the spin-pole, which is
uncertain, is a crucial input parameter for constraining the thermal inertia
with the TPM; hence, we consider two pole orientations. In the extreme case of
an equatorial retrograde geometry we derive a lower limit to the thermal
inertia of 150 J/m^2/K/s^0.5. If we adopt the pole orientation of Abe et al.
(2008a) our best-fit thermal model yields a value for the thermal inertia of
700+/-200 J/m^2/K/s^0.5 and even higher values are allowed by the uncertainty
in the spectral shape due to the absolute flux calibration. The lower limit to
the thermal inertia, which is unlikely but possible, would be consistent with a
fine regolith similar to wthat is found for asteroid 433 Eros. However, the
thermal inertia is expected to be higher, possibly similar to or greater than
that on asteroid 25143 Itokawa. Accurately determining the spin-pole of
asteroid 162173 will narrow the range of possible values for its thermal
inertia.Comment: 4 pages, 2 figures; to be published as a Letter in Astronomy and
Astrophysic
Intrinsic profiles and capillary waves at homopolymer interfaces: a Monte Carlo study
A popular concept which describes the structure of polymer interfaces by
``intrinsic profiles'' centered around a two dimensional surface, the ``local
interface position'', is tested by extensive Monte Carlo simulations of
interfaces between demixed homopolymer phases in symmetric binary (AB)
homopolymer blends, using the bond fluctuation model. The simulations are done
in an LxLxD geometry. The interface is forced to run parallel to the LxL planes
by imposing periodic boundary conditions in these directions and fixed boundary
conditions in the D direction, with one side favoring A and the other side
favoring B. Intrinsic profiles are calculated as a function of the ``coarse
graining length'' B by splitting the system into columns of size BxBxD and
averaging in each column over profiles relative to the local interface
position. The results are compared to predictions of the self-consistent field
theory. It is shown that the coarse graining length can be chosen such that the
interfacial width matches that of the self-consistent field profiles, and that
for this choice of B the ``intrinsic'' profiles compare well with the
theoretical predictions.Comment: to appear in Phys. Rev.
H2CO and CH3OH maps of the Orion Bar photodissociation region
A previous analysis of methanol and formaldehyde towards the Orion Bar
concluded that the two molecular species may trace different physical
components, methanol the clumpy material, and formaldehyde the interclump
medium. To verify this hypothesis, we performed multi-line mapping observations
of the two molecules to study their spatial distributions. The observations
were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular
resolution of ~11''. Additional data for H2CO from the Plateau de Bure array
are also discussed. The data were analysed using an LVG approach.
Both molecules are detected in our single-dish data. Our data show that CH3OH
peaks towards the clumps of the Bar, but its intensity decreases below the
detection threshold in the interclump material. When averaging over a large
region of the interclump medium, the strongest CH3OH line is detected with a
peak intensity of ~0.06K. Formaldehyde also peaks on the clumps, but it is also
detected in the interclump gas. We verified that the weak intensity of CH3OH in
the interclump medium is not caused by the different excitation conditions of
the interclump material, but reflects a decrease in the column density of
methanol. The abundance of CH3OH relative to H2CO decreases by at least one
order of magnitude from the dense clumps to the interclump medium.Comment: 11 pages, accepted for publication in A&
Isolation and Characterization of Adhesive Secretion from Cuvierian Tubules of Sea Cucumber Holothuria forskåli (Echinodermata: Holothuroidea)
The sea cucumber Holothuria forskåli possesses a specialized system called Cuvierian tubules. During mechanical stimulation white filaments (tubules) are expelled and become sticky upon contact with any object. We isolated a protein with adhesive properties from protein extracts of Cuvierian tubules from H. forskåli. This protein was identified by antibodies against recombinant precollagen D which is located in the byssal threads of the mussel Mytilus galloprovincialis. To find out the optimal procedure for extraction and purification, the identified protein was isolated by several methods, including electroelution, binding to glass beads, immunoprecipitation, and gel filtration. Antibodies raised against the isolated protein were used for localization of the adhesive protein in Cuvierian tubules. Immunostaining and immunogold electron microscopical studies revealed the strongest immunoreactivity in the mesothelium; this tissue layer is involved in adhesion. Adhesion of Cuvierian tubule extracts was measured on the surface of various materials. The extracted protein showed the strongest adhesion to Teflon surface. Increased adhesion was observed in the presence of potassium and EDTA, while cadmium caused a decrease in adhesion. Addition of antibodies and trypsin abolished the adhesive properties of the extract
International Union of Pharmacology. XLV. Classification of the Kinin Receptor Family: from Molecular Mechanisms to Pathophysiological Consequences
Kinins are proinflammatory peptides that mediate numerous vascular and pain responses to tissue injury. Two pharmacologically distinct kinin receptor subtypes have been identified and characterized for these peptides, which are named B1 and B2 and belong to the rhodopsin family of G protein-coupled receptors. The B2 receptor mediates the action of bradykinin (BK) and lysyl-bradykinin (Lys-BK), the first set of bioactive kinins formed in response to injury from kininogen precursors through the actions of plasma and tissue kallikreins, whereas the B(1) receptor mediates the action of des-Arg9-BK and Lys-des-Arg9-BK, the second set of bioactive kinins formed through the actions of carboxypeptidases on BK and Lys-BK, respectively. The B2 receptor is ubiquitous and constitutively expressed, whereas the B1 receptor is expressed at a very low level in healthy tissues but induced following injury by various proinflammatory cytokines such as interleukin-1beta. Both receptors act through G alpha(q) to stimulate phospholipase C beta followed by phosphoinositide hydrolysis and intracellular free Ca2+ mobilization and through G alpha(i) to inhibit adenylate cyclase and stimulate the mitogen-activated protein kinase pathways. The use of mice lacking each receptor gene and various specific peptidic and nonpeptidic antagonists have implicated both B1 and B2 receptors as potential therapeutic targets in several pathophysiological events related to inflammation such as pain, sepsis, allergic asthma, rhinitis, and edema, as well as diabetes and cancer. This review is a comprehensive presentation of our current understanding of these receptors in terms of molecular and cell biology, physiology, pharmacology, and involvement in human disease and drug development
Polarized superfluid state in a three-dimensional fermionic optical lattice
We study ultracold fermionic atoms trapped in a three dimensional optical
lattice by combining the real-space dynamical mean-field approach with
continuous-time quantum Monte Carlo simulations. For a spin-unpolarized system
we show results the density and pair potential profile in the trap for a range
of temperatures. We discuss how a polarized superfluid state is spatially
realized in the spin-polarized system with harmonic confinement at low
temperatures and present the local particle density, local magnetization, and
pair potential.Comment: 6 pages, 2 figure
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