208 research outputs found
Classification and Asymptotic Scaling of Hadron Light-Cone Wave-Function Amplitudes
We classify the hadron light-cone wave-function amplitudes in terms of parton
helicity, orbital angular momentum, and quark flavor and color symmetries. We
show in detail how this is done for the pion, meson, nucleon, and delta
resonance up to and including three partons. For the pion and nucleon, we also
consider four-parton amplitudes. Using the scaling law derived recently, we
show how these amplitudes scale in the limit that all parton transverse momenta
become large.Comment: 28 pages, no figur
Does fix the Electromagnetic Form Factor at ?
We show that the decay is a reliable
source of information for the electromagnetic form factor of the pion at
by using general arguments to estimate, or
rather, put upper bounds on, the background processes that could spoil this
extraction. We briefly comment on the significance of the resulting
.Comment: 10 pages revtex manuscript, one figure--not included, U. of MD PP
#94-00
Proton-Proton Near-Forward Hard Elastic Scattering
We calculate the leading twist contribution to near-forward proton-proton
(and proton-antiproton) elastic scattering with large momentum transfer, in the
multiple scattering (Landshoff) mechanism. The amplitude in the near-forward
region is dominated by singlet exchange for all three valence quark-quark
scatterings. We assume the existence of a hard singlet quark-quark amplitude,
which we estimate to be . For a three-quark state whose
transverse size is less than , Sudakov resummation
accounts for both approximate \d \sigma^{pp}/ \d t \sim t^{-8} at moderate
, and \d \sigma^{pp}/ \d t \sim t^{-10} at larger . The transition from
approximate to behavior is strongly correlated with the
transverse size of the valence three-quark state in the proton.Comment: 34 pages, LaTe
Spin Structure of the Pion in a Light-Cone Representation
The spin structure of the pion is discussed by transforming the wave function
for the pion in the naive quark model into a light-cone representation. It is
shown that there are higher helicity () states in
the full light-cone wave function for the pion besides the ordinary helicity
() component wave functions as a consequence from
the Melosh rotation relating spin states in light-front dynamics and those in
instant-form dynamics. Some low energy properties of the pion, such as the
electromagnetic form factor, the charged mean square radius, and the weak decay
constant, could be interrelated in this representation with reasonable
parameters.Comment: 15 Latex pages, 2 figures upon reques
Semileptonic six fermion processes at future colliders: signal and irreducible background for top and WWZ physics
We compute several total and differential cross sections relevant to top and
WWZ physics at future colliders taking into account the full set of
Feynman diagrams for six fermion final states. We also include in our
calculations initial state radiation and beamstrahlung effects, and the most
important QCD corrections in an approximate (naive) form. We compare such a
complete approach with "production x decay" approximation and we suggest that
in many physical studies the former is needed.Comment: 28 pages including 8 figures (7 ps). Latex. Uses Axodraw. Minor
changes and some typos correcte
PLAST: parallel local alignment search tool for database comparison
Background: Sequence similarity searching is an important and challenging task in molecular biology and next-generation sequencing should further strengthen the need for faster algorithms to process such vast amounts of data. At the same time, the internal architecture of current microprocessors is tending towards more parallelism, leading to the use of chips with two, four and more cores integrated on the same die. The main purpose of this work was to design an effective algorithm to fit with the parallel capabilities of modern microprocessors. Results: A parallel algorithm for comparing large genomic banks and targeting middle-range computers has been developed and implemented in PLAST software. The algorithm exploits two key parallel features of existing and future microprocessors: the SIMD programming model (SSE instruction set) and the multithreading concept (multicore). Compared to multithreaded BLAST software, tests performed on an 8-processor server have shown speedup ranging from 3 to 6 with a similar level of accuracy. Conclusions: A parallel algorithmic approach driven by the knowledge of the internal microprocessor architecture allows significant speedup to be obtained while preserving standard sensitivity for similarity search problems.
Data Assimilation Enhancements to Air Force Weathers Land Information System
The United States Air Force (USAF) has a proud and storied tradition of enabling significant advancements in the area of characterizing and modeling land state information. 557th Weather Wing (557 WW; DoDs Executive Agent for Land Information) provides routine geospatial intelligence information to warfighters, planners, and decision makers at all echelons and services of the U.S. military, government and intelligence community. 557 WW and its predecessors have been home to the DoDs only operational regional and global land data analysis systems since January 1958. As a trusted partner since 2005, Air Force Weather (AFW) has relied on the Hydrological Sciences Laboratory at NASA/GSFC to lead the interagency scientific collaboration known as the Land Information System (LIS). LIS is an advanced software framework for high performance land surface modeling and data assimilation of geospatial intelligence (GEOINT) information
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Individual common variants exert weak effects on the risk for autism spectrum disorders.
While it is apparent that rare variation can play an important role in the genetic architecture of autism spectrum disorders (ASDs), the contribution of common variation to the risk of developing ASD is less clear. To produce a more comprehensive picture, we report Stage 2 of the Autism Genome Project genome-wide association study, adding 1301 ASD families and bringing the total to 2705 families analysed (Stages 1 and 2). In addition to evaluating the association of individual single nucleotide polymorphisms (SNPs), we also sought evidence that common variants, en masse, might affect the risk. Despite genotyping over a million SNPs covering the genome, no single SNP shows significant association with ASD or selected phenotypes at a genome-wide level. The SNP that achieves the smallest P-value from secondary analyses is rs1718101. It falls in CNTNAP2, a gene previously implicated in susceptibility for ASD. This SNP also shows modest association with age of word/phrase acquisition in ASD subjects, of interest because features of language development are also associated with other variation in CNTNAP2. In contrast, allele scores derived from the transmission of common alleles to Stage 1 cases significantly predict case status in the independent Stage 2 sample. Despite being significant, the variance explained by these allele scores was small (Vm< 1%). Based on results from individual SNPs and their en masse effect on risk, as inferred from the allele score results, it is reasonable to conclude that common variants affect the risk for ASD but their individual effects are modest
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