2,797 research outputs found
Tunable Entanglement, Antibunching and Saturation effects in Dipole Blockade
We report a model that makes it possible to analyze quantitatively the dipole
blockade effect on the dynamical evolution of a two two-level atom system
driven by an external laser field. The multiple excitations of the atomic
sample are taken into account. We find very large concurrence in the dipole
blockade regime. We further find that entanglement can be tuned by changing the
intensity of the exciting laser. We also report a way to lift the dipole
blockade paving the way to manipulate in a controllable way the blockade
effects. We finally report how a continuous monitoring of the dipole blockade
would be possible using photon-photon correlations of the scattered light in a
regime where the spontaneous emission would dominate dissipation in the sample.Comment: 5 pages, 5 figure
Inventory and new records of Polychaete species from the Cap Bon peninsula , North East coast of Tunisia, Western Mediterranean Sea
An inventory of polychaete species is presented from the north-east coast of Tunisia with an historic review of the previous literature from Tunisian coasts. Altogether 40 families, 146 genera, and 238 species are currently known from the area, of which 86 taxa, 4 families (Chrysopetalidae, Pilargidae, Protodrilidae and Saccocirridae) and 40 genera (Saccocirrus, Protodrilus, Parathelepus, Thelepus, Petta, Isolda, Brada, Tharyx, Paraprionospio, Jasmineira, Hypsicomus, Euchone, Pseudobranchiomma, Laonome, Galathowenia, Lugia, Pseudomystides, Protomystides, Pirakia, Mysta, Eurysyllis, Parapionosyllis, Streptosyllis, Paraehlersia, Sigambra,
Ancistrosyllis, Kefersteinia, Chrysopetalum, Bhawania, Fimbriosthenelais, Subadyte, Panthalis, Dorvillea, Scalibregma, Paradoneis, Cirrophorus, Metasychis, Websterinereis, Euniphysa and Mastobranchus) are new additions to the polychaete fauna of Tunisia. The list, which provides a synthesis of the regional taxonomic work, including coastal areas from Sidi Daoud to the area of Menzel Hurr (Cap Bon Peninsula, Western Mediterranean Sea), can serve as a baseline for future studies
First principles calculation of vibrational Raman spectra in large systems: signature of small rings in crystalline SiO2
We present an approach for the efficient calculation of vibrational Raman
intensities in periodic systems within density functional theory. The Raman
intensities are computed from the second order derivative of the electronic
density matrix with respect to a uniform electric field. In contrast to
previous approaches, the computational effort required by our method for the
evaluation of the intensities is negligible compared to that required for the
calculation of vibrational frequencies. As a first application, we study the
signature of 3- and 4-membered rings in the the Raman spectra of several
polymorphs of SiO2, including a zeolite having 102 atoms per unit cell.Comment: 4 pages, 2 figures, revtex4 Minor corrections; accepted in Phys. Rev.
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Fast quasi-adiabatic dynamics
We work out the theory and applications of a fast quasi-adiabatic approach to
speed up slow adiabatic manipulations of quantum systems by driving a control
parameter as near to the adiabatic limit as possible over the entire protocol
duration. Specifically, we show that the population inversion in a two-level
system, the splitting and cotunneling of two-interacting bosons, and the
stirring of a Tonks-Girardeau gas on a ring to achieve mesoscopic
superpositions of many-body rotating and non-rotating states, can be
significantly speeded up.Comment: 5 pages, 6 figure
Glycoprotein L sets the neutralization profile of murid herpesvirus 4
Antibodies readily neutralize acute, epidemic viruses, but are less effective against more indolent pathogens such as herpesviruses. Murid herpesvirus 4 (MuHV-4) provides an accessible model for tracking the fate of antibody-exposed gammaherpesvirus virions. Glycoprotein L (gL) plays a central role in MuHV-4 entry: it allows gH to bind heparan sulfate and regulates fusion-associated conformation changes in gH and gB. However, gL is non-essential: heparan sulfate binding can also occur via gp70, and the gB–gH complex alone seems to be sufficient for membrane fusion. Here, we investigated how gL affects the susceptibility of MuHV-4 to neutralization. Immune sera neutralized gL− virions more readily than gL+ virions, chiefly because heparan sulfate binding now depended on gp70 and was therefore easier to block. However, there were also post-binding effects. First, the downstream, gL-independent conformation of gH became a neutralization target; gL normally prevents this by holding gH in an antigenically distinct heterodimer until after endocytosis. Second, gL− virions were more vulnerable to gB-directed neutralization. This covered multiple epitopes and thus seemed to reflect a general opening up of the gH–gB entry complex, which gL again normally restricts to late endosomes. gL therefore limits MuHV-4 neutralization by providing redundancy in cell binding and by keeping key elements of the virion fusion machinery hidden until after endocytosis
Quicksort with unreliable comparisons: a probabilistic analysis
We provide a probabilistic analysis of the output of Quicksort when
comparisons can err.Comment: 29 pages, 3 figure
In vivo importance of heparan sulfate-binding glycoproteins for murid herpesvirus-4 infection
Many herpesviruses bind to heparan sulfate (HS). Murid herpesvirus-4 (MuHV-4) does so via its envelope glycoproteins gp70 and gH/gL. MuHV-4 gp150 further regulates an HS-independent interaction to make that HS-dependent too. Cell binding by MuHV-4 virions is consequently strongly HS-dependent. Gp70 and gH/gL show some in vitro redundancy: an antibody-mediated blockade of HS binding by one is well tolerated, whereas a blockade of both severely impairs infection. In order to understand the importance of HS binding for MuHV-4 in vivo, we generated mutants lacking both gL and gp70. As expected, gL−gp70− MuHV-4 showed very poor cell binding. It infected mice at high dose but not at low dose, indicating defective host entry. But once entry occurred, host colonization, which for MuHV-4 is relatively independent of the infection dose, was remarkably normal. The gL−gp70− entry deficit was much greater than that of gL− or gp70− single knockouts. And gp150 disruption, which allows HS-independent cell binding, largely rescued the gL−gp70− cell binding and host entry deficits. Thus, it appeared that MuHV-4 HS binding is important in vivo, principally for efficient host entry
Vaccination with murid herpesvirus-4 glycoprotein B reduces viral lytic replication but does not induce detectable virion neutralization
Herpesviruses characteristically disseminate from immune hosts. Therefore in the context of natural infection, antibody neutralizes them poorly. Murid herpesvirus-4 (MuHV-4) provides a tractable model with which to understand gammaherpesvirus neutralization. MuHV-4 virions blocked for cell binding by immune sera remain infectious for IgG-Fc receptor+ myeloid cells, so broadly neutralizing antibodies must target the virion fusion complex – glycoprotein B (gB) or gH/gL. While gB-specific neutralizing antibodies are rare, its domains I+II (gB-N) contain at least one potent neutralization epitope. Here, we tested whether immunization with recombinant gB presenting this epitope could induce neutralizing antibodies in naive mice and protect them against MuHV-4 challenge. Immunizing with the full-length gB extracellular domain induced a strong gB-specific antibody response and reduced MuHV-4 lytic replication but did not induce detectable neutralization. gB-N alone, which more selectively displayed pre-fusion epitopes including neutralization epitopes, also failed to induce neutralizing responses, and while viral lytic replication was again reduced this depended completely on IgG Fc receptors. gB and gB-N also boosted neutralizing responses in only a minority of carrier mice. Therefore, it appears that neutralizing epitopes on gB are intrinsically difficult for the immune response to target
Vast planes of satellites in a high resolution simulation of the Local Group: comparison to Andromeda
We search for vast planes of satellites (VPoS) in a high resolution
simulation of the Local Group performed by the CLUES project, which improves
significantly the resolution of former similar studies. We use a simple method
for detecting planar configurations of satellites, and validate it on the known
plane of M31. We implement a range of prescriptions for modelling the satellite
populations, roughly reproducing the variety of recipes used in the literature,
and investigate the occurence and properties of planar structures in these
populations. The structure of the simulated satellite systems is strongly
non-random and contains planes of satellites, predominantly co-rotating, with,
in some cases, sizes comparable to the plane observed in M31 by Ibata et al..
However the latter is slightly richer in satellites, slightly thinner and has
stronger co-rotation, which makes it stand out as overall more exceptional than
the simulated planes, when compared to a random population. Although the
simulated planes we find are generally dominated by one real structure, forming
its backbone, they are also partly fortuitous and are thus not kinematically
coherent structures as a whole. Provided that the simulated and observed planes
of satellites are indeed of the same nature, our results suggest that the VPoS
of M31 is not a coherent disc and that one third to one half of its satellites
must have large proper motions perpendicular to the plane
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