7,439 research outputs found
Dynamical Kohn Anomaly in Surface Acoustic Wave Response in Quantum Hall Systems Near
The dynamical analog of the Kohn Anomaly image of the Fermi Surface is
demonstrated for the response functions to the surface acoustic waves in
Quantum Hall Systems near . Kinks appear in the velocity shift
and attenuation coefficient . The effect is considerably
enhanced under periodic modulation and should be observable.Comment: 5 pages, 2 figures, the published versio
Summary of Jimsonde temperature profiles. Part 2: Programs, data comments
Natural environment criteria are established and interpreted for aeronautical vehicle design and engineering operations. Data summaries, computer formats, frequency distributions, and composite listings of the temperature profiles acquisition program are included
Composite fermions in the Fractional Quantum Hall Effect: Transport at finite wavevector
We consider the conductivity tensor for composite fermions in a close to
half-filled Landau band in the temperature regime where the scattering off the
potential and the trapped gauge field of random impurities dominates. The
Boltzmann equation approach is employed to calculate the quasiclassical
transport properties at finite effective magnetic field, wavevector and
frequency. We present an exact solution of the kinetic equation for all
parameter regimes. Our results allow a consistent description of recently
observed surface acoustic wave resonances and other findings.Comment: REVTEX, 4 pages, 1 figur
Modulation of the virus-receptor interaction by mutations in the V5 loop of feline immunodeficiency virus (FIV) following in vivo escape from neutralising antibody
<b>BACKGROUND:</b> In the acute phase of infection with feline immunodeficiency virus (FIV), the virus targets activated CD4+ T cells by utilising CD134 (OX40) as a primary attachment receptor and CXCR4 as a co-receptor. The nature of the virus-receptor interaction varies between isolates; strains such as GL8 and CPGammer recognise a "complex" determinant on CD134 formed by cysteine-rich domains (CRDs) 1 and 2 of the molecule while strains such as PPR and B2542 require a more "simple" determinant comprising CRD1 only for infection. These differences in receptor recognition manifest as variations in sensitivity to receptor antagonists. In this study, we ask whether the nature of the virus-receptor interaction evolves in vivo.<p></p>
<b>RESULTS:</b> Following infection with a homogeneous viral population derived from a pathogenic molecular clone, a quasispecies emerged comprising variants with distinct sensitivities to neutralising antibody and displaying evidence of conversion from a "complex" to a "simple" interaction with CD134. Escape from neutralising antibody was mediated primarily by length and sequence polymorphisms in the V5 region of Env, and these alterations in V5 modulated the virus-receptor interaction as indicated by altered sensitivities to antagonism by both anti-CD134 antibody and soluble CD134.<p></p>
<b>CONCLUSIONS:</b> The FIV-receptor interaction evolves under the selective pressure of the host humoral immune response, and the V5 loop contributes to the virus-receptor interaction. Our data are consistent with a model whereby viruses with distinct biological properties are present in early versus late infection and with a shift from a "complex" to a "simple" interaction with CD134 with time post-infection.<p></p>
Theory of Magneto--Acoustic Transport in Modulated Quantum Hall Systems Near
Motivated by the experimental results of Willett et al [Phys.Rev. Lett., {\bf
78}, 4478 (1997)] we develop a magneto-transport theory for the response of a
two dimensional electron gas (2DEG) in the Fractional Quantum Hall Regime near
Landau level filling factor to the surface acoustic wave (SAW) in
the presence of an added periodic density modulation. We assume there exists a
Composite Fermion Fermi Surface (CF-FS) at , and we show that the
deformation of the (CF-FS) due to the density modulation can be at the origin
of the observed transport anomalies for the experimental conditions. Our
analysis is carried out particularly for the non-local case which corresponds
to the SAW experiments. We introduce a new model of a deformed CF-FS. The model
permits us to explain anomalous features of the response of the modulated 2DEG
to the SAW near namely the nonlinear wave vector dependence of the
electron conductivity, the appearance of peaks in the SAW velocity shift and
attenuation and the anisotropy of the effect, all of which originate from
contributions to the conductivity tensor due to the regions of the CF-FS which
are flattened by the applied modulation.Comment: 13 pages, 4 figures, the published versio
Representation, searching and discovery of patterns of bases in complex RNA structures
We describe a graph theoretic method designed to perform efficient searches for substructural patterns in nucleic acid structural coordinate databases using a simplified vectorial representation. Two vectors represent each nucleic acid base and the relative positions of bases with respect to one another are described in terms of distances between the defined start and end points of the vectors on each base. These points comprise the nodes and the distances the edges of a graph, and a pattern search can then be performed using a subgraph isomorphism algorithm. The minimal representation was designed to facilitate searches for complex patterns but was first tested on simple, well-characterised arrangements of bases such as base pairs and GNRA-tetraloop receptor interactions. The method performed very well for these interaction types. A survey of side-by-side base interactions, of which the adenosine platform is the best known example, also locates examples of similar base rearrangements that we consider to be important in structural regulation. A number of examples were found, with GU platforms being particularly prevalent. A GC platform in the RNA of the Thermus thermophilus small ribosomal subunit is in an analogous position to an adenosine platform in other species. An unusual GG platform is also observed close to one of the substrate binding sites in Haloarcula marismortui large ribosomal subunit RNA
Virginia\u27s Law of Sovereign Immunity: An Overview
The immunity of a sovereign and its agents from liability for tortious conduct has long been a part of our common law. Its origin seems to be based on the theory, allied with the divine right of kings, that \u27the King can do no wrong\u27, together with the feeling that it was necessarily a contradiction of his sovereignty to allow him to be sued as of right in his own courts. More modern justifications include the desire to limit judicial interference with the workings of government. Naturally this desire has left may wrongs unredressed. Thus, the law has been forced to accommodate two competing interests: (1) functional government unencumbered by the courts; and (2) the need of injured parties for judicial relief
Atmospheric constraint statistics for the Space Shuttle mission planning
The procedures used to establish statistics of atmospheric constraints of interest to the Space Shuttle mission planning are presented. The statistics considered are for the frequency of occurrence, runs, and time conditional probabilities of several atmospheric constrants for each of the Space Shuttle mission phases. The mission phases considered are (1) prelaunch, (2) launch, (3) return to launch site, (4) abort once around landing, and (5) end of mission landing
Composite Fermions in Modulated Structures: Transport and Surface Acoustic Waves
Motivated by a recent experiment of Willett et al. [Phys. Rev. Lett. 78, 4478
(1997)], we employ semiclassical composite-fermion theory to study the effect
of a periodic density modulation on a quantum Hall system near Landau level
filling factor nu=1/2. We show that even a weak density modulation leads to
dramatic changes in surface-acoustic-wave (SAW) propagation, and propose an
explanation for several key features of the experimental observations. We
predict that properly arranged dc transport measurements would show a structure
similar to that seen in SAW measurements.Comment: Version published in Phys. Rev. Lett. Figures changed to show SAW
velocity shift. LaTeX, 5 pages, two included postscript figure
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