17,842 research outputs found
Fractional analytic index
For a finite rank projective bundle over a compact manifold, so associated to
a torsion, Dixmier-Douady, 3-class, w, on the manifold, we define the ring of
differential operators `acting on sections of the projective bundle' in a
formal sense. In particular, any oriented even-dimensional manifold carries a
projective spin Dirac operator in this sense. More generally the corresponding
space of pseudodifferential operators is defined, with supports sufficiently
close to the diagonal, i.e. the identity relation. For such elliptic operators
we define the numerical index in an essentially analytic way, as the trace of
the commutator of the operator and a parametrix and show that this is homotopy
invariant. Using the heat kernel method for the twisted, projective spin Dirac
operator, we show that this index is given by the usual formula, now in terms
of the twisted Chern character of the symbol, which in this case defines an
element of K-theory twisted by w; hence the index is a rational number but in
general it is not an integer.Comment: 23 pages, Latex2e, final version, to appear in JD
Studies of nucleotide sequences in TMV-RNA. II - The action of spleen diesterase
Spleen diesterase action on polynucleotide and ribonucleic acid infectivit
The interaction energy of well-separated Skyrme solitons
We prove that the asymptotic field of a Skyrme soliton of any degree has a
non-trivial multipole expansion. It follows that every Skyrme soliton has a
well-defined leading multipole moment. We derive an expression for the linear
interaction energy of well-separated Skyrme solitons in terms of their leading
multipole moments. This expression can always be made negative by suitable
rotations of one of the Skyrme solitons in space and iso-space.We show that the
linear interaction energy dominates for large separation if the orders of the
Skyrme solitons' multipole moments differ by at most two. In that case there
are therefore always attractive forces between the Skyrme solitons.Comment: 27 pages amslate
Diffusion, dimensionality and noise in transcriptional regulation
The precision of biochemical signaling is limited by randomness in the
diffusive arrival of molecules at their targets. For proteins binding to the
specific sites on the DNA and regulating transcription, the ability of the
proteins to diffuse in one dimension by sliding along the length of the DNA, in
addition to their diffusion in bulk solution, would seem to generate a larger
target for DNA binding, consequently reducing the noise in the occupancy of the
regulatory site. Here we show that this effect is largely cancelled by the
enhanced temporal correlations in one dimensional diffusion. With realistic
parameters, sliding along DNA has surprisingly little effect on the physical
limits to the precision of transcriptional regulation.Comment: 8 pages, 2 figure
Determination of lunar ilmentite abundances from remotely sensed data
The mapping of ilmenite on the surface of the moon is a necessary precursor to the investigation of prospective lunar base sites. Telescopic observations of the moon using a variety of narrow bandpass optical interference filters are being performed as a preliminary means of achieving this goal. Specifically, ratios of images obtained using filters centered at 0.40 and 0.56 microns provide quantitative estimates of TiO2 abundances. Analysis of preliminary distribution maps of TiO2 concentrations allows identification of specific high-Ti areas. Investigations of these areas using slit spectra in the range 0.03 to 0.85 microns are underway to search for discrete spectral signatures attributable to ilmenite
Determination of lunar ilmenite abundances from remotely sensed data
The mineral ilmenite (FeTiO3) was found in abundance in lunar mare soils returned during the Apollo project. Lunar ilmenite often contains greater than 50 weight-percent titanium dioxide (TiO2), and is a primary potential resource for oxygen and other raw materials to supply future lunar bases. Chemical and spectroscopic analysis of the returned lunar soils produced an empirical function that relates the spectral reflectance ratio at 400 and 560 nm to the weight percent abundance of TiO2. This allowed mapping of the lunar TiO2 distribution using telescopic vidicon multispectral imaging from the ground; however, the time variant photometric response of the vidicon detectors produced abundance uncertainties of at least 2 to 5 percent. Since that time, solid-state charge-coupled device (CCD) detector technology capable of much improved photometric response has become available. An investigation of the lunar TiO2 distribution was carried out utilizing groundbased telescopic CCD multispectral imagery and spectroscopy. The work was approached in phases to develop optimum technique based upon initial results. The goal is to achieve the best possible TiO2 abundance maps from the ground as a precursor to lunar orbiter and robotic sample return missions, and to produce a better idea of the peak abundances of TiO2 for benefaction studies. These phases and the results are summarized
Predicting the effectiveness of hepatitis C virus neutralizing antibodies by bioinformatic analysis of conserved epitope residues using public sequence data
Hepatitis C virus (HCV) is a global health issue. Although direct-acting antivirals are available to target HCV, there is currently no vaccine. The diversity of the virus is a major obstacle to HCV vaccine development. One approach toward a vaccine is to utilize a strategy to elicit broadly neutralizing antibodies (bNAbs) that target highly-conserved epitopes. The conserved epitopes of bNAbs have been mapped almost exclusively to the E2 glycoprotein. In this study, we have used HCV-GLUE, a bioinformatics resource for HCV sequence data, to investigate the major epitopes targeted by well-characterized bNAbs. Here, we analyze the level of conservation of each epitope by genotype and subtype and consider the most promising bNAbs identified to date for further study as potential vaccine leads. For the most conserved epitopes, we also identify the most prevalent sequence variants in the circulating HCV population. We examine the distribution of E2 sequence data from across the globe and highlight regions with no coverage. Genotype 1 is the most prevalent genotype worldwide, but in many regions, it is not the dominant genotype. We find that the sequence conservation data is very encouraging; several bNAbs have a high level of conservation across all genotypes suggesting that it may be unnecessary to tailor vaccines according to the geographical distribution of genotypes
The Algebras of Large N Matrix Mechanics
Extending early work, we formulate the large N matrix mechanics of general
bosonic, fermionic and supersymmetric matrix models, including Matrix theory:
The Hamiltonian framework of large N matrix mechanics provides a natural
setting in which to study the algebras of the large N limit, including
(reduced) Lie algebras, (reduced) supersymmetry algebras and free algebras. We
find in particular a broad array of new free algebras which we call symmetric
Cuntz algebras, interacting symmetric Cuntz algebras, symmetric
Bose/Fermi/Cuntz algebras and symmetric Cuntz superalgebras, and we discuss the
role of these algebras in solving the large N theory. Most important, the
interacting Cuntz algebras are associated to a set of new (hidden) local
quantities which are generically conserved only at large N. A number of other
new large N phenomena are also observed, including the intrinsic nonlocality of
the (reduced) trace class operators of the theory and a closely related large N
field identification phenomenon which is associated to another set (this time
nonlocal) of new conserved quantities at large N.Comment: 70 pages, expanded historical remark
Recommended from our members
Case Study Shows Disconnect on Civic Journalism's Role
This in-depth case study examines attempts to transform a traditional newsroom to one oriented around civic journalism principles, offering a unique look at the resistance toward those principles even in a digital environment that facilitates new audience relationships. Civic journalism emphasizes understanding and addressing community concerns from a citizen perspective. This study finds that journalists still struggle to integrate citizens’ contributions into newsroom practice in meaningful ways
- …