3,274 research outputs found
New structures in the proton-antiproton system
In the most recent measurements of the reaction
by the BABAR collaboration, new structures have been found with unknown origin.
We examine a possible relation of the most distinct peak to the recently
observed . Alternatively, we analyse possible explanations due to
the nucleon and thresholds. The latter
could explain a periodicity found in the data
Chiral perturbation theory for electroweak reactions on deuterium
I summarize two recent applications of chiral perturbation theory to
electromagnetic reactions on deuterium: elastic electron-deuteron scattering,
and Compton scattering on deuterium. Both calculations have now been carried
out to three orders in the chiral expansion. The expansion shows good
convergence and is able to reproduce data for q < 600 MeV in e-d and for
omega=55-95 MeV in gamma-d. These results demonstrate that ChiPT can be used to
reliably compute operators and wave functions for low-momentum-transfer
reactions in light nuclear systems.Comment: 10 pages, 6 figures. Write-up of invited talk at INT Workshop on
"Nuclear Forces and the Quantum Many-Body Problem", October 4-8, 200
First mid-infrared spectrum of a faint high-z galaxy: Observations of CFRS 14.1157 with the Infrared Spectrograph on the Spitzer Space Telescope
The unprecedented sensitivity of the Infrared Spectrograph on the Spitzer
Space Telescope allows for the first time the measurement of mid-infrared
spectra from 14 to 38 microns of faint high-z galaxies. This unique capability
is demonstrated with observations of sources having 16 micron fluxes of 3.6 mJy
(CFRS 14.1157) and 0.35 mJy (CFRS 14.9025). A spectral-fitting technique is
illustrated which determines the redshift by fitting emission and absorption
features characteristic of nearby galaxies to the spectrum of an unknown
source. For CFRS 14.1157, the measured redshift is z = 1.00+/-0.20 in agreement
with the published result of z = 1.15. The spectrum is dominated by emission
from an AGN, similar to the nucleus of NGC 1068, rather than a typical
starburst with strong PAH emission like M82. Such spectra will be crucial in
characterizing the nature of newly discovered distant galaxies, which are too
faint for optical follow-up.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 5 figure
The size of the proton - closing in on the radius puzzle
We analyze the recent electron-proton scattering data from Mainz using a
dispersive framework that respects the constraints from analyticity and
unitarity on the nucleon structure. We also perform a continued fraction
analysis of these data. We find a small electric proton charge radius, r_E^p =
0.84_{-0.01}^{+0.01} fm, consistent with the recent determination from muonic
hydrogen measurements and earlier dispersive analyses. We also extract the
proton magnetic radius, r_M^p = 0.86_{-0.03}^{+0.02} fm, consistent with
earlier determinations based on dispersion relations.Comment: 4 pages, 2 figures, fit improved, small modifications, section on
continued fractions modified, conclusions on the proton charge radius
unchanged, version accepted for publication in European Physical Journal
Causality bounds for neutron-proton scattering
We consider the constraints of causality and unitarity for the low-energy
interactions of protons and neutrons. We derive a general theorem that
non-vanishing partial-wave mixing cannot be reproduced with zero-range
interactions without violating causality or unitarity. We define and calculate
interaction length scales which we call the causal range and the Cauchy-Schwarz
range for all spin channels up to J = 3. For some channels we find that these
length scales are as large as 5 fm. We investigate the origin of these large
lengths and discuss their significance for the choice of momentum cutoff scales
in effective field theory and universality in many-body Fermi systems.Comment: 36 pages, 10 figures, 7 tables, version to appear in Eur. Phys. J.
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Size-dependent particle activation properties in fog during the ParisFog 2012/13 field campaign
Fog-induced visibility reduction is responsible for a variety of hazards in the transport sector. Therefore there is a large demand for an improved understanding of fog formation and thus improved forecasts. Improved fog forecasts require a better understanding of the numerous complex mechanisms during the fog life cycle. During winter 2012/13 a field campaign called ParisFog aiming at fog research took place at SIRTA (Instrumented Site for Atmospheric Remote Sensing Research). SIRTA is located about 20 km southwest of the Paris city center, France, in a semi-urban environment. In situ activation properties of the prevailing fog were investigated by measuring (1) total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems; (2) interstitial hydrated aerosol and fog droplet size distributions at ambient conditions; and (3) cloud condensation nuclei (CCN) number concentration at different supersaturations (SS) with a CCN counter. The aerosol particles were characterized regarding their hygroscopic properties, fog droplet activation behavior and contribution to light scattering for 17 developed fog events. Low particle hygroscopicity with an overall median of the hygroscopicity parameter, κ, of 0.14 was found, likely caused by substantial influence from local traffic and wood burning emissions. Measurements of the aerosol size distribution at ambient RH revealed that the critical wet diameter, above which the hydrated aerosols activate to fog droplets, is rather large (with a median value of 2.6μm) and is highly variable (ranging from 1 to 5μm) between the different fog events. Thus, the number of activated fog droplets was very small and the non-activated hydrated particles were found to contribute significantly to the observed light scattering and thus to the reduction in visibility. Combining all experimental data, the effective peak supersaturation, SSpeak, a measure of the peak supersaturation during the fog formation, was determined. The median SSpeak value was estimated to be in the range from 0.031 to 0.046% (upper and lower limit estimations), which is in good agreement with previous experimental and modeling studies of fog
Rupture of multiple parallel molecular bonds under dynamic loading
Biological adhesion often involves several pairs of specific receptor-ligand
molecules. Using rate equations, we study theoretically the rupture of such
multiple parallel bonds under dynamic loading assisted by thermal activation.
For a simple generic type of cooperativity, both the rupture time and force
exhibit several different scaling regimes. The dependence of the rupture force
on the number of bonds is predicted to be either linear, like a square root or
logarithmic.Comment: 8 pages, 2 figure
Quantum-mechanical calculation of H on Ni(001) using a model potential based on first-principles calculations
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