9,960 research outputs found
Perturbative and non-perturbative QCD corrections to wide-angle Compton scattering
We investigate corrections to the handbag approach for wide-angle Compton
scattering off protons at moderately large momentum transfer: the photon-parton
subprocess is calculated to next-to-leading order QCD and contributions from
the generalized parton distribution E} are taken into account. Photon and
proton helicity flip amplitudes are non-zero due to these corrections which
leads to a wealth of polarization phenomena in Compton scattering. Thus, for
instance, the incoming photon asymmetry or the transverse polarization of the
proton are non-zero although small.Comment: 19 pages, 9 figures (using LATEX with epsfig
Kinetic modeling of Secondary Organic Aerosol formation: effects of particle- and gas-phase reactions of semivolatile products
The distinguishing mechanism of formation of secondary organic aerosol (SOA) is the partitioning of semivolatile hydrocarbon oxidation products between the gas and aerosol phases. While SOA formation is typically described in terms of partitioning only, the rate of formation and ultimate yield of SOA can also depend on the kinetics of both gas- and aerosol-phase processes. We present a general equilibrium/kinetic model of SOA formation that provides a framework for evaluating the extent to which the controlling mechanisms of SOA formation can be inferred from laboratory chamber data. With this model we examine the effect on SOA formation of gas-phase oxidation of first-generation products to either more or less volatile species, of particle-phase reaction (both first- and second-order kinetics), of the rate of parent hydrocarbon oxidation, and of the extent of reaction of the parent hydrocarbon. The effect of pre-existing organic aerosol mass on SOA yield, an issue of direct relevance to the translation of laboratory data to atmospheric applications, is examined. The importance of direct chemical measurements of gas- and particle-phase species is underscored in identifying SOA formation mechanisms
Proton mass effects in wide-angle Compton scattering
We investigate proton mass effects in the handbag approach to wide-angle
Compton scattering. We find that theoretical uncertainties due to the proton
mass are significant for photon energies presently studied at Jefferson Lab.
With the proposed energy upgrade such uncertainties will be clearly reduced.Comment: 4 pages, uses revtex, 3 figure
Transverse emittance dilution due to coupler kicks in linear accelerators
One of the main concerns in the design of low emittance linear accelerators
(linacs) is the preservation of beam emittance. Here we discuss one possible
source of emittance dilution, the coupler kick, due to transverse
electromagnetic fields in the accelerating cavities of the linac caused by the
power coupler geometry. In addition to emittance growth, the coupler kick also
produces orbit distortions. It is common wisdom that emittance growth from
coupler kicks can be strongly reduced by using two couplers per cavity mounted
opposite each other or by having the couplers of successive cavities
alternation from above to below the beam pipe so as to cancel each individual
kick. We therefore analyze consequences of alternate coupler placements.
We show here that for sufficiently large Q values, alternating the coupler
location from before to after the cavity leads to a cancellation of the orbit
distortion but not of the emittance growth, whereas alternating the coupler
location from before and above to behind and below the cavity cancels the
emittance growth but not the orbit distortion. These compensations hold even
when each cavity is individually detuned, e.g. by microphonics. Another
effective method for reducing coupler kicks that is studied is the optimization
of the phase of the coupler kick. This technique is independent of the coupler
geometry but relies on operating on crest. A final technique studied is
symmetrization of the cavity geometry in the coupler region with the addition
of a stub opposite the coupler, which reduces the amplitude of the off axis
fields and is thus effective for off crest acceleration as well.
We show applications of these techniques to the energy recovery linac (ERL)
planned at Cornell University
A Correlation Between Changes in Solar Luminosity and Differential Radius Measurements
Solar luminosity variations occurring during solar cycle 21 can be attributed in large part to the presence of sunspots and faculae. Nevertheless, there remains a residual portion of the luminosity variation distinctly unaccounted for by these phenomena of solar activity. At the Santa Catalina Laboratory for Experimental Relativity by Astrometry (SCLERA), observations of the solar limb are capable of detecting changes in the solar limb darkening function by monitoring a quantity known as the differential radius. These observations are utilized in such a way that the effects of solar activity are minimized in order to reveal the more fundamental structure of the photosphere. The results of observations made during solar cycle 21 at various solar latitudes indicate that a measurable change did occur in the global photospheric limb darkening function. It is proposed that the residual luminosity change is associated in part with this change in limb darkening
Development of a general purpose airborne simulator
Variable stability system development for General Purpose Airborne Simulator /GPAS
Octet-Baryon Form Factors in the Diquark Model
We present an alternative parameterization of the quark-diquark model of
baryons which particularly takes care of the most recent proton electric
form-factor data from the E136 experiment at SLAC. In addition to
electromagnetic form factors of the nucleon, for which good agreement with data
is achieved, we discuss the weak axial vector form factor of the nucleon as
well as electromagnetic form factors of and hyperons.
Technical advance in calculating the pertinent analytic expressions within
perturbative quantum chromodynamics is gained by formulating the wave function
of the quark-diquark system in a covariant way. Finally, we also comment on the
influence of Sudakov corrections within the scope of the diquark model.Comment: 16 pages, WU-B 93-07, latex, uuencoded postscript files of 7 figures
appended at the end of the latex fil
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