Phase Mixing of Nonlinear Plasma Oscillations in an Arbitrary Mass Ratio Cold Plasma

Nonlinear plasma oscillations in an arbitrary mass ratio cold plasma have been studied using 1-D particle-in-cell simulation. In contrast to earlier work for infinitely massive ion plasmas it has been found that the oscillations phase mix away at any amplitude and that the rate at which phase mixing occurs, depends on the mass ratio ($\Delta = m_{-}/m_{+}$) and the amplitude. A perturbation theoretic calculation carried upto third order predicts that the normalized phase mixing time $\omega_{p-} t_{mix}$ depends on the amplitude $A$ and the mass ratio $\Delta$ as $\sim [(A^{2}/24)(\Delta/\sqrt{1 + \Delta})]^{-1/3}$. We have confirmed this scaling in our simulations and conclude that stable non-linear oscillations which never phase mix, exist only for the ideal case with $\Delta = 0.0$ and $A < 0.5$. These cold plasma results may have direct relevance to recent experiments on superintense laser beam plasma interactions with applications to particle acceleration, fast ignitor concept etc.Comment: pp 10 and two figures in PS forma

A new regime of anomalous penetration of relativistically strong laser radiation into an overdense plasma

It is shown that penetration of relativistically intense laser light into an overdense plasma, accessible by self-induced transparency, occurs over a finite length only. The penetration length depends crucially on the overdense plasma parameter and increases with increasing incident intensity after exceeding the threshold for self-induced transparency. Exact analytical solutions describing the plasma-field distributions are presented.Comment: 6 pages, 2 figures in 2 separate eps files; submitted to JETP Letter

Electromagnetic energy penetration in the self-induced transparency regime of relativistic laser-plasma interactions

Two scenarios for the penetration of relativistically intense laser radiation into an overdense plasma, accessible by self-induced transparency, are presented. For supercritical densities less than 1.5 times the critical one, penetration of laser energy occurs by soliton-like structures moving into the plasma. At higher background densities laser light penetrates over a finite length only, that increases with the incident intensity. In this regime plasma-field structures represent alternating electron layers separated by about half a wavelength by depleted regions.Comment: 9 pages, 4 figures, submitted for publication to PR

Nonintegrable Interaction of Ion-Acoustic and Electromagnetic Waves in a Plasma

In this paper we re-examine the one-dimensional interaction of electromagnetic and ion acoustic waves in a plasma. Our model is similar to one solved by Rao et al. (Phys. Fluids, vol. 26, 2488 (1983)) under a number of analytical approximations. Here we perform a numerical investigation to examine the stability of the model. We find that for slightly over dense plasmas, the propagation of stable solitary modes can occur in an adiabatic regime where the ion acoustic electric field potential is enslaved to the electromagnetic field of a laser. But if the laser intensity or plasma density increases or the laser frequency decreases, the adiabatic regime loses stability via a transition to chaos. New asymptotic states are attained when the adiabatic regime no longer exists. In these new states, the plasma becomes rarefied, and the laser field tends to behave like a vacuum field.Comment: 19 pages, REVTeX, 6 ps figures, accepted for publication in Phys. Rev.

Temporary Acceleration of Electrons While Inside an Intense Electromagnetic Pulse

A free electron can temporarily gain a very significant amount of energy if it is overrun by an intense electromagnetic wave. In principle, this process would permit large enhancements in the center-of-mass energy of electron-electron, electron-positron and electron-photon interactions if these take place in the presence of an intense laser beam. Practical considerations severely limit the utility of this concept for contemporary lasers incident on relativistic electrons. A more accessible laboratory phenomenon is electron-positron production via an intense laser beam incident on a gas. Intense electromagnetic pulses of astrophysical origin can lead to very energetic photons via bremsstrahlung of temporarily accelerated electrons

A hysteretic multiscale formulation for nonlinear dynamic analysis of composite materials

This article has been made available through the Brunel Open Access Publishing Fund.A new multiscale finite element formulation is presented for nonlinear dynamic analysis of heterogeneous structures. The proposed multiscale approach utilizes the hysteretic finite element method to model the microstructure. Using the proposed computational scheme, the micro-basis functions, that are used to map the microdisplacement components to the coarse mesh, are only evaluated once and remain constant throughout the analysis procedure. This is accomplished by treating inelasticity at the micro-elemental level through properly defined hysteretic evolution equations. Two types of imposed boundary conditions are considered for the derivation of the multiscale basis functions, namely the linear and periodic boundary conditions. The validity of the proposed formulation as well as its computational efficiency are verified through illustrative numerical experiments

Genome-Wide Association Study Meta-Analysis for Parkinson Disease Motor Subtypes

Objective: To discover genetic determinants of Parkinson disease (PD) motor subtypes, including tremor dominant (TD) and postural instability/gait difficulty (PIGD) forms. Methods: In 3,212 PD cases of European ancestry, we performed a genome-wide association study (GWAS) examining 2 complementary outcome traits derived from the Unified Parkinson's Disease Rating Scale, including dichotomous motor subtype (TD vs PIGD) or a continuous tremor/PIGD score ratio. Logistic or linear regression models were adjusted for sex, age at onset, disease duration, and 5 ancestry principal components, followed by meta-analysis. Results: Among 71 established PD risk variants, we detected multiple suggestive associations with PD motor subtype, including GPNMB (rs199351, psubtype = 0.01, pratio = 0.03), SH3GL2 (rs10756907, psubtype = 0.02, pratio = 0.01), HIP1R (rs10847864, psubtype = 0.02), RIT2 (rs12456492, psubtype = 0.02), and FBRSL1 (rs11610045, psubtype = 0.02). A PD genetic risk score integrating all 71 PD risk variants was also associated with subtype ratio (p = 0.026, ß = -0.04, 95% confidence interval = -0.07-0). Based on top results of our GWAS, we identify a novel suggestive association at the STK32B locus (rs2301857, pratio = 6.6 × 10-7), which harbors an independent risk allele for essential tremor. Conclusions: Multiple PD risk alleles may also modify clinical manifestations to influence PD motor subtype. The discovery of a novel variant at STK32B suggests a possible overlap between genetic risk for essential tremor and tremor-dominant PD

Idiopathic pancreatitis is a consequence of an altering spectrum of bile nucleation time

<p>Abstract</p> <p>Background</p> <p>The pathogenesis of idiopathic pancreatitis (IP) remains poorly understood. Our hypothesis is that IP is a sequel of micro-crystallization of hepatic bile.</p> <p>Methods</p> <p>A prospective case control study compared 55 patients; symptomatic cholelithiasis - 30 (14 male, median age 36 years; mean BMI - 25.1 kg/m²), gallstone pancreatitis - 9 (3 male, median age 35 years; mean BMI - 24.86 kg/m²) and IP - 16 (9 male, median age 34 years; mean BMI -23.34 kg/m²) with 30 controls (15 male, median age 38 years; mean BMI = 24.5 kg/m²) undergoing laparotomy for conditions not related to the gall bladder and bile duct. Ultrafiltered bile from the common hepatic duct in patients and controls was incubated in anaerobic conditions and examined by polarized light microscopy to assess bile nucleation time (NT). In the analysis, the mean NT of patients with gallstones and gallstone pancreatitis was taken as a cumulative mean NT for those with established gallstone disease (EGD).</p> <p>Results</p> <p>Patients were similar to controls. Mean NT in all groups of patients was significantly shorter than controls (EGD cumulative mean NT, 1.73 +/- 0.2 days vs. controls, 12.74 +/- 0.4 days, P = 0.001 and IP patients mean NT, 3.1 +/- 0.24 days vs. controls, 12.74 +/- 0.4 days, P = 0.001). However, NT in those with IP was longer compared with those with EGD (mean NT in IP, 3.1 +/- 0.24 days vs. cumulative mean in EGD: 1.73 +/- 0.2 days, P = 0.002).</p> <p>Conclusion</p> <p>Nucleation time of bile in patients with IP is abnormal and is intermediate to nucleation time of lithogenic bile at one end of the spectrum of lithogenicity and non-lithogenic bile, at the other end.</p