6,048 research outputs found
Rapidity gap survival in the black-disk regime
We summarize how the approach to the black-disk regime (BDR) of strong
interactions at TeV energies influences rapidity gap survival in exclusive hard
diffraction pp -> p + H + p (H = dijet, Qbar-Q, Higgs). Employing a recently
developed partonic description of such processes, we discuss (a) the
suppression of diffraction at small impact parameters by soft spectator
interactions in the BDR; (b) further suppression by inelastic interactions of
hard spectator partons in the BDR; (c) correlations between hard and soft
interactions. Hard spectator interactions substantially reduce the rapidity gap
survival probability at LHC energies compared to previously reported estimates.Comment: 4 pages, 3 figures. Proceedings of XV International Workshop on
Deep-Inelastic Scattering and Related Subjects (DIS 2007), Munich, Germany,
Apr. 16-20, 200
Transverse imaging of the proton in exclusive diffractive pp scattering
In a recent paper (hep-ph/0608271) we describe a new approach to rapidity gap
survival (RGS) in the production of high-mass systems (H = dijet, Higgs, etc.)
in exclusive double-gap diffractive pp scattering, pp -> p + H + p. It is based
on the idea that hard and soft interactions are approximately independent (QCD
factorization), and allows us to calculate the RGS probability in a
model-independent way in terms of the gluon generalized parton distributions
(GPDs) in the colliding protons and the pp elastic scattering amplitude. Here
we focus on the transverse momentum dependence of the cross section. By
measuring the "diffraction pattern," one can perform detailed tests of the
interplay of hard and soft interactions, and even extract information about the
gluon GPD in the proton from the data.Comment: 4 pages, 2 figures, uses ws-procs9x6.cls. Proceedings of XIV
International Workshop on Deep Inelastic Scattering (DIS2006), Tsukuba City,
Japan, Apr 20 - 24, 200
Conformational transformations induced by the charge-curvature interaction at finite temperature
The role of thermal fluctuations on the conformational dynamics of a single
closed filament is studied. It is shown that, due to the interaction between
charges and bending degrees of freedom, initially circular aggregates may
undergo transformation to polygonal shape. The transition occurs both in the
case of hardening and softening charge-bending interaction. In the former case
the charge and curvature are smoothly distributed along the chain while in the
latter spontaneous kink formation is initiated. The transition to a
non-circular conformation is analogous to the phase transition of the second
kind.Comment: 23 pages (Latex), 10 figures (Postscript), 2 biblio file (bib-file
and bbl-file
Nonlinear Ionic Conductivity of Thin Solid Electrolyte Samples: Comparison between Theory and Experiment
Nonlinear conductivity effects are studied experimentally and theoretically
for thin samples of disordered ionic conductors. Following previous work in
this field the {\it experimental nonlinear conductivity} of sodium ion
conducting glasses is analyzed in terms of apparent hopping distances. Values
up to 43 \AA are obtained. Due to higher-order harmonic current density
detection, any undesired effects arising from Joule heating can be excluded.
Additionally, the influence of temperature and sample thickness on the
nonlinearity is explored. From the {\it theoretical side} the nonlinear
conductivity in a disordered hopping model is analyzed numerically. For the 1D
case the nonlinearity can be even handled analytically. Surprisingly, for this
model the apparent hopping distance scales with the system size. This result
shows that in general the nonlinear conductivity cannot be interpreted in terms
of apparent hopping distances. Possible extensions of the model are discussed.Comment: 7 pages, 6 figure
Recommended from our members
Detection of human influence on a new, validated 1500-Year temperature reconstruction
Climate records over the last millennium place the twentieth-century warming in a longer historical context. Reconstructions of millennial temperatures show a wide range of variability, raising questions about the reliability of currently available reconstruction techniques and the uniqueness of late-twentieth-century warming. A calibration method is suggested that avoids the loss of low-frequency variance. A new reconstruction using this method shows substantial variability over the last 1500 yr. This record is consistent with independent temperature change estimates from borehole geothermal records, compared over the same spatial and temporal domain. The record is also broadly consistent with other recent reconstructions that attempt to fully recover low-frequency climate variability in their central estimate. High variability in reconstructions does not hamper the detection of greenhouse gas-induced climate change, since a substantial fraction of the variance in these reconstructions from the beginning of the analysis in the late thirteenth century to the end of the records can be attributed to external forcing. Results from a detection and attribution analysis show that greenhouse warming is detectable in all analyzed high-variance reconstructions (with the possible exception of one ending in 1925), and that about a third of the warming in the first half of the twentieth century can be attributed to anthropogenic greenhouse gas emissions. The estimated magnitude of the anthropogenic signal is consistent with most of the warming in the second half of the twentieth century being anthropogenic
A mass spectrometric strategy for absolute quantification of Plasmodium falciparum proteins of low abundance
Selected reaction monitoring mass spectrometry has been combined with the use of an isotopically labelled synthetic protein, made up of proteotypic tryptic peptides selected from parasite proteins of interest. This allows, for the first time, absolute quantification of proteins from Plasmodium falciparum. This methodology is demonstrated to be of sufficient sensitivity to quantify, even within whole cell extracts, proteins of low abundance from the folate pathway as well as more abundant "housekeeping" proteins
Generalized parton distributions and rapidity gap survival in exclusive diffractive pp scattering
We propose a new approach to the problem of rapidity gap survival (RGS) in
the production of high-mass systems (H = dijet, heavy quarkonium, Higgs boson)
in double-gap exclusive diffractive pp scattering, pp -> p + (gap) + H + (gap)
+ p. It is based on the idea that hard and soft interactions proceed over
widely different time- and distance scales and are thus approximately
independent. The high-mass system is produced in a hard scattering process with
exchange of two gluons between the protons. Its amplitude is calculable in
terms of the gluon generalized parton distributions (GPDs) in the protons,
which can be measured in J/psi production in exclusive ep scattering. The hard
scattering process is modified by soft spectator interactions, which we
calculate in a model-independent way in terms of the pp elastic scattering
amplitude. Contributions from inelastic intermediate states are suppressed. A
simple geometric picture of the interplay of hard and soft interactions in
diffraction is obtained. The onset of the black-disk limit in pp scattering at
TeV energies strongly suppresses diffraction at small impact parameters and is
the main factor in determining the RGS probability. Correlations between hard
and soft interactions (e.g. due to scattering from the long-range pion field of
the proton, or due to possible short-range transverse correlations between
partons) further decrease the RGS probability. We also investigate the
dependence of the diffractive cross section on the transverse momenta of the
final-state protons ("diffraction pattern"). By measuring this dependence one
can perform detailed tests of the interplay of hard and soft interactions, and
even extract information about the gluon GPD in the proton. Such studies appear
to be feasible with the planned forward detectors at the LHC.Comment: 26 pages, 17 figures, uses revtex
Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production
We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian
width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The
observed structure may be due to the interference between a strange (or
anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L)
photoproduction leading to the same final state. The statistical significance
of the observed excess of events estimated as the log likelihood ratio of the
resonant signal+background hypothesis and the phi-production based background
only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1
table added, revise
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
abtrac
The necessary future of chiropractic education: a North American perspective
The chiropractic educational system in North America is currently in a state of flux. The attempted conversion of some chiropractic schools into "universities" and the want of university affiliation for chiropractic schools suggests that we are searching for a better alternative to the present system. In the early 20(th )century, the Flexner Report helped transform modern medical education into a discipline that relies on scientific and clinical knowledge. Some have wondered if it is time for a Flexner-type report regarding the education of doctors of chiropractic. This article outlines the current challenges within the chiropractic educational system and proposes positive changes for that system
- …