1,087 research outputs found
Initiation of hepatitis C virus infection is dependent on cholesterol and cooperativity between CD81 and scavenger receptor B type I.
In the past several years, a number of cellular proteins have been identified as candidate entry receptors for hepatitis C virus (HCV) by using surrogate models of HCV infection. Among these, the tetraspanin CD81 and scavenger receptor B type I (SR-BI), both of which localize to specialized plasma membrane domains enriched in cholesterol, have been suggested to be key players in HCV entry. In the current study, we used a recently developed in vitro HCV infection system to demonstrate that both CD81 and SR-BI are required for authentic HCV infection in vitro, that they function cooperatively to initiate HCV infection, and that CD81-mediated HCV entry is, in part, dependent on membrane cholesterol
Coherent Optimal Control of Multiphoton Molecular Excitation
We give a framework for molecular multiphoton excitation process induced by
an optimally designed electric field. The molecule is initially prepared in a
coherent superposition state of two of its eigenfunctions. The relative phase
of the two superposed eigenfunctions has been shown to control the optimally
designed electric field which triggers the multiphoton excitation in the
molecule. This brings forth flexibility in desiging the optimal field in the
laboratory by suitably tuning the molecular phase and hence by choosing the
most favorable interfering routes that the system follows to reach the target.
We follow the quantum fluid dynamical formulation for desiging the electric
field with application to HBr molecule.Comment: 5 figure
Threshold Dose for Shrimp: A Risk Characterization Based on Objective Reactions in Clinical Studies
A DBPCFC [double-blind, placebo-controlled food challenge] of shrimp-allergic adults was conducted to obtain individual threshold doses. Results of this study and published research were combined and a population threshold for shrimp was determined from dose-distribution modeling. The shrimp-allergic population seems to have a higher threshold compared to other populations for other food allergens. Additional shrimp challenges should be done to confirm these initial results
Coherent control using adaptive learning algorithms
We have constructed an automated learning apparatus to control quantum
systems. By directing intense shaped ultrafast laser pulses into a variety of
samples and using a measurement of the system as a feedback signal, we are able
to reshape the laser pulses to direct the system into a desired state. The
feedback signal is the input to an adaptive learning algorithm. This algorithm
programs a computer-controlled, acousto-optic modulator pulse shaper. The
learning algorithm generates new shaped laser pulses based on the success of
previous pulses in achieving a predetermined goal.Comment: 19 pages (including 14 figures), REVTeX 3.1, updated conten
Design, construction and commissioning of the Braunschweig Icing Wind Tunnel
Beyond its physical importance in both fundamental and climate research, atmospheric icing is considered as a severe operational condition in many engineering applications like aviation, electrical power transmission and wind-energy production. To reproduce such icing conditions in a laboratory environment, icing wind tunnels are frequently used. In this paper, a comprehensive overview on the design, construction and commissioning of the Braunschweig Icing Wind Tunnel is given. The tunnel features a test section of 0.5 m × 0.5 m with peak velocities of up to 40 m s−1. The static air temperature ranges from −25 to +30 °C. Supercooled droplet icing with liquid water contents up to 3 g m−3 can be reproduced. The unique aspect of this facility is the combination of an icing tunnel with a cloud chamber system for making ice particles. These ice particles are more realistic in shape and density than those usually used for mixed phase and ice crystal icing experiments. Ice water contents up to 20 g m−3 can be generated. We further show how current state-of-the-art measurement techniques for particle sizing are performed on ice particles. The data are compared to those of in-flight measurements in mesoscale convective cloud systems in tropical regions. Finally, some applications of the icing wind tunnel are presented
Solitary coherent structures in viscoelastic shear flow: computation and mechanism
Starting from stationary bifurcations in Couette-Dean flow, we compute
nontrivial stationary solutions in inertialess viscoelastic circular Couette
flow. These solutions are strongly localized vortex pairs, exist at arbitrarily
large wavelengths, and show hysteresis in the Weissenberg number, similar to
experimentally observed ``diwhirl'' patterns. Based on the computed velocity
and stress fields, we elucidate a heuristic, fully nonlinear mechanism for
these flows. We propose that these localized, fully nonlinear structures
comprise fundamental building blocks for complex spatiotemporal dynamics in the
flow of elastic liquids.Comment: 5 pages text and 4 figures. Submitted to Physical Review Letter
Molecular Aspects of Secretory Granule Exocytosis by Neurons and Endocrine Cells
Neuronal communication and endocrine signaling are fundamental for integrating
the function of tissues and cells in the body. Hormones released by endocrine
cells are transported to the target cells through the circulation. By contrast, transmitter
release from neurons occurs at specialized intercellular junctions, the synapses.
Nevertheless, the mechanisms by which signal molecules are synthesized,
stored, and eventually secreted by neurons and endocrine cells are very similar.
Neurons and endocrine cells have in common two different types of secretory
organelles, indicating the presence of two distinct secretory pathways. The synaptic
vesicles of neurons contain excitatory or inhibitory neurotransmitters, whereas the
secretory granules (also referred to as dense core vesicles, because of their electron
dense content) are filled with neuropeptides and amines. In endocrine cells, peptide
hormones and amines predominate in secretory granules. The function and content
of vesicles, which share antigens with synaptic vesicles, are unknown for most
endocrine cells. However, in B cells of the pancreatic islet, these vesicles contain
GABA, which may be involved in intrainsular signaling.'
Exocytosis of both synaptic vesicles and secretory granules is controlled by
cytoplasmic calcium. However, the precise mechanisms of the subsequent steps,
such as docking of vesicles and fusion of their membranes with the plasma membrane,
are still incompletely understood. This contribution summarizes recent observations
that elucidate components in neurons and endocrine cells involved in
exocytosis. Emphasis is put on the intracellular aspects of the release of secretory
granules that recently have been analyzed in detail
On the ground states of the Bernasconi model
The ground states of the Bernasconi model are binary +1/-1 sequences of
length N with low autocorrelations. We introduce the notion of perfect
sequences, binary sequences with one-valued off-peak correlations of minimum
amount. If they exist, they are ground states. Using results from the
mathematical theory of cyclic difference sets, we specify all values of N for
which perfect sequences do exist and how to construct them. For other values of
N, we investigate almost perfect sequences, i.e. sequences with two-valued
off-peak correlations of minimum amount. Numerical and analytical results
support the conjecture that almost perfect sequences do exist for all values of
N, but that they are not always ground states. We present a construction for
low-energy configurations that works if N is the product of two odd primes.Comment: 12 pages, LaTeX2e; extended content, added references; submitted to
J.Phys.
The optical response of Ba_{1-x}K_xBiO_3: Evidence for an unusual coupling mechanism of superconductivity?
We have analysed optical reflectivity data for Ba_{1-x}K_xBiO_3 in the
far-infrared region using Migdal-Eliashberg theory and found it inconsistent
with standard electron-phonon coupling: Whereas the superconducting state data
could be explained using moderate coupling, \lambda=0.7, the normal state
properties indicate \lambda \le 0.2. We have found that such behaviour could be
understood using a simple model consisting of weak standard electron-phonon
coupling plus weak coupling to an unspecified high energy excitation near 0.4
eV. This model is found to be in general agreement with the reflectivity data,
except for the predicted superconducting gap size. The additional high energy
excitation suggests that the dominant coupling mechanism in Ba_{1-x}K_xBiO_3 is
not standard electron-phonon.Comment: 5 pages REVTex, 5 figures, 32 refs, accepted for publication in Phys.
Rev.
Reconstructing Climate Policy: How Best to Engage China and Other Developing Countries?
Duke University organized the International Conference on Reconstructing Climate Policy: Moving Beyond the Kyoto Impasse, May 2003. The organizer invited me to specifically address the following two issues at the conference: 1) Whether is the proposal for joint accession by the U.S. and China in the interest of China?, and 2) Even if participating a global cap-and-trade regime is so beneficial to China as many economic studies suggest, why has China consistently refused in international negotiations even to discuss its participation in it?. In this paper, we look at the first issue from the following perspectives: a) how does China value importance of maintaining unity of the Group of 77?; b) what lessons has China learned from bilateral negotiations with the U.S. to work out the terms for China to get accession to the WTO?; c) what is the legitimacy of the U.S. insistence that it re-joins the Kyoto Protocol only if major developing countries join?; d) what are implications of the U.S. strikingly reversed position on the commitments of developing countries in New Delhi for initiating discussions on joint accession by the U.S. and China?; and e) how would joint accession by the U.S. and China be perceived?. We then address the second issue from the following perspectives: a) from the point of view of fairness, how do developing countries including China and India perceive emissions caps in the first place?; b) why have China and India been sceptical to international emissions trading?; c) how is an inflow of CDM investment in China perceived politically in comparison with the exports of emissions permits to the U.S.?; d) what are the implications of “lock in” to emissions cap, in particular no rules and principles for setting emissions targets for the commitment periods subsequent to Kyoto?; e) how to address the complex undertaking of setting emissions caps for developing countries, which must be linked to future, unobserved levels in comparison with the historically observed levels for industrialized countries?. Finally, the paper touches on the likely path forward
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