5,056 research outputs found
On the Theory of Relativistic Strong Plasma Waves
The influence of motion of ions and electron temperature on nonlinear
one-dimensional plasma waves with velocity close to the speed of light in
vacuum is investigated. It is shown that although the wavebreaking field weakly
depends on mass of ions, the nonlinear relativistic wavelength essentially
changes. The nonlinearity leads to the increase of the strong plasma
wavelength, while the motion of ions leads to the decrease of the wavelength.
Both hydrodynamic approach and kinetic one, based on Vlasov-Poisson equations,
are used to investigate the relativistic strong plasma waves in a warm plasma.
The existence of relativistic solitons in a thermal plasma is predicted.Comment: 13 pages, 8 figure
Progress on the hybrid gun project at UCLA
UCLA/INFN-LNF/Univ. Rome has been developing the hybrid gun which has an RF gun and a short linac for velocity bunching in one structure. After the cavity was manufactured at INFN-LNF in 2012, tests of the gun was carried out at UCLA. The field in the standing wave part was 20 % smaller than the simulation but the phase advance was fine. The cavity was commissioned successfully up to 13 MW. The beam test was performed at 11.5 MW and demonstrated the bunch compression
Second Stage String Fragmentation Model
A string model, advocated by Bowler, provides a physical and intuitive
picture of heavy quark fragmentation. When supplemented by an ad hoc factor of
(1-z), to suppress fragmentation near z=1, it supplies an excellent fit to the
data. We extend Bowler's model by accounting for the further decay of the
massive mesonic states produced by the initial string breaking. We find that
each subsequent string break and cascade decay beyond the first, introduces a
factor of (1-z). Furthermore we find that including a finite mass for the
quarks, which pop out of the vacuum and split the string, forces the first
string breaking to produce massive states requiring further decay. This
sequence terminates at the second stage of fragmentation where only relatively
"light" heavy meson systems are formed. Thus we naturally account for the
phenomenologically required factor of (1-z). We also predict that the ratio of
(primary) fragments-vector/(vector plus scalar) should be .61. Our second stage
string fragmentation model provides an appealing picture of heavy quark
fragmentation.Comment: 15 page
Novel Studies on the \eta' Effective Lagrangian
The effective Lagrangian for \eta' incorporating the effect of the QCD
\theta-angle has been developed previously. We revisit this Lagrangian and
carry out its canonical quantization with particular attention to the test
function spaces of constraints and the topology of the \eta'-field. In this
way, we discover a new chirally symmetric coupling of this field to chiral
multiplets which involves in particular fermions. This coupling violates P and
T symmetries. In a subsequent paper, we will evaluate its contribution to the
electric dipole moment (EDM) of fermions. Our motivation is to test whether the
use of mixed states restores P and T invariance, so that EDM vanishes. This
calculation will be shown to have striking new physical consequences.Comment: 14 pages, 1 figure; V2: NEW TITLE; revised version to be published in
JHEP; references adde
Semiclassical Decay of Excited String States on Leading Regge Trajectories
We study the decay of hadrons based on a semiclassical string model. By
including quark mass effects we find that the width to mass ratio \G/m is an
increasing function of , which increases most rapidly for massive quarks.
This is consistent with the available data. The decay probability of hadrons on
the leading Regge trajectories is computed taking the effect of the string
rotation into account. The resulting decay probability is no longer uniform
along the length of the string but varies in a manner that is in qualitative
agreement with the available data. We argue in favour of possible experiments
that would test our predictions more accurately and help open a window to the
nonperturbative aspects of QCD.Comment: 15 PAGES, UR-1326, ER-40685-776, SU-4240-55
Long Term Implications of Climate Change on Crop Planning
The effects of climate change have been much speculated on in the past few years. Consequently, there has been intense interest in one of its key issues of food security into the future. This is particularly so given population increase, urban encroachment on arable land, and the degradation of the land itself. Recently, work has been done on predicting precipitation and temperature for the next few decades as well as developing optimisation models for crop planning. Combining these together, this paper examines the effects of climate change on a large food producing region in Australia, the Murrumbidgee Irrigation Area. For time periods between 1991 and 2071 for dry, average and wet years, an analysis is made about the way that crop mixes will need to change to adapt for the effects of climate change. It is found that sustainable crop choices will change into the future, and that large-scale irrigated agriculture may become unviable in the region in all but the wettest years
Excitation of nonlinear two-dimensional wake waves in radially-nonuniform plasma
It is shown that an undesirable curvature of the wave front of
two-dimensional nonlinear wake wave excited in uniform plasma by a relativistic
charged bunch or laser pulse may be compensated by radial change of the
equilibrium plasma density.Comment: 6 pages, 4 figure
Observation of Plasma Focusing of a 28.5 GeV Positron Beam
The observation of plasma focusing of a 28.5 GeV positron beam is reported.
The plasma was formed by ionizing a nitrogen jet only 3 mm thick. Simultaneous
focusing in both transverse dimensions was observed with effective focusing
strengths of order Tesla per micron. The minimum area of the beam spot was
reduced by a factor of 2.0 +/- 0.3 by the plasma. The longitudinal beam
envelope was measured and compared with numerical calculations
Determinants of Survival in Malignant Pleural Mesothelioma: A Surveillance, Epidemiology, and End Results (SEER) Study of 14,228 Patients
INTRODUCTION: Left untreated, malignant pleural mesothelioma (MPM) is associated with uniformly poor prognosis. Better survival has been reported with surgery-based multimodality therapy, but to date, no trial has demonstrated survival benefit of surgery over other therapies. We evaluated whether cancer-directed surgery influenced survival independently from other predictors in a large population-based dataset. METHODS: The SEER database was explored from 1973 to 2009 to identify all cases of pathologically-proven MPM. Age, sex, race, year of diagnosis, histology stage, cancer-directed surgery, radiation, and vital status were analyzed. The association between prognostic factors and survival was estimated using Cox regression and propensity matched analysis. RESULTS: There were 14,228 patients with pathologic diagnosis of MPM. On multivariable analysis, female gender, younger age, early stage, and treatment with surgery were independent predictors of longer survival. In comparison to no treatment, surgery alone was associated with significant improvement in survival [adjusted hazard ratio (adj HR) 0.64 (0.61-0.67)], but not radiation [adj HR 1.15 (1.08-1.23)]. Surgery and radiation combined had similar survival as surgery alone [adj HR 0.69 (0.64-0.76)]. Results were similar when cases diagnosed between 1973 and 1999 were compared to cases diagnosed between 2000 and 2009. CONCLUSIONS: Despite developments in surgical and radiation techniques, the prognosis for MPM patients has not improved over the past 4 decades. Cancer-directed surgery is independently associated with better survival, suggesting that multimodal surgery-based therapy can benefit these patients. Further research in adjuvant treatment is necessary to improve prognosis in this challenging disease
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