469 research outputs found
High Energy Quark-Antiquark Elastic scattering with Mesonic Exchange
We studies the high energy elastic scattering of quark anti-quark with an
exchange of a mesonic state in the channel with .
Both the normalization factor and the Regge trajectory can be calculated in
PQCD in cases of fixed (non-running) and running coupling constant. The
dependence of the Regge trajectory on the coupling constant is highly
non-linear and the trajectory is of order of in the interesting physical
range.Comment: 29 page
Wide-field extended-resolution fluorescence microscopy with standing surface-plasmon-resonance waves
The resolution of conventional SPR imaging has been limited by the diffraction nature of light. A wide-field extended-resolution optical imaging technique, standing-wave surface plasmon resonance fluorescence (SW-SPRF) microscopy, has been developed. Based on evanescent SPR standing waves, SW-SPRF provides lateral resolution approaching 100 nm and offers the advantages of significant signal enhancement and background noise reduction. SW-SPRF has the potential for sensitive biomolecular detection, nanoscale imaging, and lithographic applications
The Soft Gluon Emission Process in the Color-Octet Model for Heavy Quarkonium Production
The Color-Octet Model has been used successfully to analyze many problems in
heavy quarkonium production. We examine some of the conceptual and practical
problems of the soft gluon emission process in the Color-Octet Model. We use a
potential model to describe the initial and final states in the soft gluon
emission process, as the emission occurs at a late stage after the production
of the heavy quark pair. It is found in this model that the soft gluon M1
transition, 1S0(8)->3S1(1), dominates over the E1 transition, 3PJ(8)->3S1(1),
for J/psi and psi' production. Such a dominance may help resolve the questions
of isotropic polarization and color-octet matrix element universality in the
Color-Octet Model.Comment: 26 pages, in LaTe
Recommended from our members
Effect of Age, Ethnicity, and Head Injury on the Association between APOE Genotypes and Alzheimer's Disease
The apolipoprotein E (APOE)-e4 allele is neither necessary nor sufficient to cause Alzheimer's disease (AD) because it develops in the absence of APOE e4, and some persons escape the disease despite having an APOE €4 allele. Although the presence of the €4 allele of the APOE gene has been consistently associated with an increased risk of it is apparent that the degree of risk may be modified by age, gender, ethnic group, certain risk factors, and possibly other genes. Roses et al. proposed that APOE genotypes have a direct influence on the age at onset of disease. In both familial and sporadic AD, an earlier age at onset among APOE €4 homozygous and APOE €4 heterozygous cases than among those cases with other APOE genotypes. Thus, it is possible that APOE genotypes strongly influence age at onset and that certain factors, both genetic and nongenetic, modify this effect by shifting the distribution curves. In this review we will discuss demographic and putative risk factors that may modify (enhance or diminish) the association between APOE genotypes and AD
Qualitative Real-Time Schlieren and Shadowgraph Imaging of Human Exhaled Airflows: An Aid to Aerosol Infection Control
Using a newly constructed airflow imaging system, airflow patterns were visualized that were associated with common, everyday respiratory activities (e.g. breathing, talking, laughing, whistling). The effectiveness of various interventions (e.g. putting hands and tissues across the mouth and nose) to reduce the potential transmission of airborne infection, whilst coughing and sneezing, were also investigated. From the digital video footage recorded, it was seen that both coughing and sneezing are relatively poorly contained by commonly used configurations of single-handed shielding maneuvers. Only some but not all of the forward momentum of the cough and sneeze puffs are curtailed with various hand techniques, and the remaining momentum is disseminated in a large puff in the immediate vicinity of the cougher, which may still act as a nearby source of infection. The use of a tissue (in this case, 4-ply, opened and ready in the hand) proved to be surprisingly effective, though the effectiveness of this depends on the tissue remaining intact and not ripping apart. Interestingly, the use of a novel ‘coughcatcher’ device appears to be relatively effective in containing coughs and sneezes. One aspect that became evident during the experimental procedures was that the effectiveness of all of these barrier interventions is very much dependent on the speed with which the user can put them into position to cover the mouth and nose effectively
Systematics of Heavy Quark Production at HERA
We discuss heavy quark and quarkonium production in various kinematic regions
at the HERA ep collider. In contrast to fixed target experiments, collider
kinematics allows the possibility of detailed measurements of particle
production in the proton fragmentation region. One thus can study parton
correlations in the proton Fock states materialized by the virtual photon
probe. We discuss various configurations of inelastic electron-proton
scattering, including peripheral, diffractive, and deep inelastic processes. In
particular, we show that intrinsic heavy quark Fock states can be identified by
the observation of quarkonium production at large and a low mean
transverse momentum which is insensitive to the virtuality of the photon.Comment: 17 pages, postscript. To obtain a copy of this paper send e-mail to
[email protected]
Color-Octet Fraction in J/Psi Production and Absorption
The cross section between a pair and a nucleon is small and
sensitive to the separation if the pair is in a color-singlet
state, but very large and insensitive to the separation if it is in a
color-octet state. We use this property in an absorption model involving both
color components to deduce the color structure of pairs produced in
reactions. Our analysis shows that the NA3, NA38 and E772
data are not inconsistent with the theoretical picture that color-octet and
color-singlet precursors are produced in roughly equal proportions if the
produced color-singlet precursors are pointlike and transparent. However, if
the color-singlet precursors are not transparent but have a cross section of a
few mb, these data do show a definite preference for a larger fraction of
color-singlet precursors. In either case, the color-octet fraction increases
with , approaching unity as becomes large.Comment: 9 pages, updated to include new result
Molecular Basis for Cooperative Binding of Anionic Phospholipids to the PH Domain of the Arf GAP ASAP1
SummaryWe have defined the molecular basis for association of the PH domain of the Arf GAP ASAP1 with phospholipid bilayers. Structures of the unliganded and dibutyryl PtdIns(4,5)P2-bound PH domain were solved. PtdIns(4,5)P2 made contact with both a canonical site (C site) and an atypical site (A site). We hypothesized cooperative binding of PtdIns(4,5)P2 to the C site and a nonspecific anionic phospholipid to the A site. PtdIns(4,5)P2 dependence of binding to large unilamellar vesicles and GAP activity was sigmoidal, consistent with cooperative sites. In contrast, PtdIns(4,5)P2 binding to the PH domain of PLC δ1 was hyperbolic. Mutation of amino acids in either the C or A site resulted in decreased PtdIns(4,5)P2-dependent binding to vesicles and decreased GAP activity. The results support the idea of cooperative phospholipid binding to the C and A sites of the PH domain of ASAP1. We propose that the mechanism underlies rapid switching between active and inactive ASAP1
Color-Octet Production at Low
We study contributions from color-octet quarkonium formation mechanisms to
hadroproduction at low . We include transitions of
color-octet states into ``direct'' and into
which decay radiatively into a . Together with earlier work, this
calculation constitutes a complete analysis of -integrated
production at leading twist. We find that the leading-twist contribution is not
sufficient to reproduce the observed production rates and polarization of the
and . Hence there must exist other important quarkonium
production mechanisms at low .Comment: REVTEX, 18 pages, 4 figures include
Maternal age effect and severe germ-line bottleneck in the inheritance of human mitochondrial DNA
The manifestation of mitochondrial DNA (mtDNA) diseases depends on the frequency of heteroplasmy (the presence of several alleles in an individual), yet its transmission across generations cannot be readily predicted owing to a lack of data on the size of the mtDNA bottleneck during oogenesis. For deleterious heteroplasmies, a severe bottleneck may abruptly transform a benign (low) frequency in a mother into a disease-causing (high) frequency in her child. Here we present a high-resolution study of heteroplasmy transmission conducted on blood and buccal mtDNA of 39 healthy mother–child pairs of European ancestry (a total of 156 samples, each sequenced at ∼20,000× per site). On average, each individual carried one heteroplasmy, and one in eight individuals carried a disease-associated heteroplasmy, with minor allele frequency ≥1%. We observed frequent drastic heteroplasmy frequency shifts between generations and estimated the effective size of the germ-line mtDNA bottleneck at only ∼30–35 (interquartile range from 9 to 141). Accounting for heteroplasmies, we estimated the mtDNA germ-line mutation rate at 1.3 × 10−8 (interquartile range from 4.2 × 10−9 to 4.1 × 10−8) mutations per site per year, an order of magnitude higher than for nuclear DNA. Notably, we found a positive association between the number of heteroplasmies in a child and maternal age at fertilization, likely attributable to oocyte aging. This study also took advantage of droplet digital PCR (ddPCR) to validate heteroplasmies and confirm a de novo mutation. Our results can be used to predict the transmission of disease-causing mtDNA variants and illuminate evolutionary dynamics of the mitochondrial genome
- …