Relativistic kinetic theory for spin-1/2 particles: Conservation laws, thermodynamics, and linear waves.

We study a recently derived fully relativistic kinetic model for spin-1/2 particles. First, the full set of conservation laws for energy, momentum, and angular momentum are given together with an expression for the (nonsymmetric) stress-energy tensor. Next, the thermodynamic equilibrium distribution is given in different limiting cases. Furthermore, we address the analytical complexity that arises when the spin and momentum eigenfunctions are coupled in linear theory by calculating the linear dispersion relation for such a case. Finally, we discuss the model and give some context by comparing with potentially relevant phenomena that are not included, such as radiation reaction and vacuum polarization.

Exchange effects in plasmas: the case of low-frequency dynamics.

Recently, there has been a surge of interest in nonequilibrium collective quantum models, where particle dispersion and spin are examples of effects taken into account. Here, we derive a kinetic plasma model containing fermion exchange effects. Exchange interactions are of great importance in many systems and have no classical analogy. Our model therefore constitutes a possible probe of collective quantum phenomena in other regimes. As an example, we consider the influence of the exchange effect on low-frequency dynamics, in particular ion-acoustic waves. Comparisons to related computational techniques are given and the differences are highlighted. Furthermore, we discuss the applicability of our model, its limitations, and possible extensions.

Speedup of doping fronts in organic semiconductors through plasma instability.

The dynamics of doping transformation fronts in organic semiconductor plasma is studied for application in light-emitting electrochemical cells. We show that new fundamental effects of the plasma dynamics can significantly improve the device performance. We obtain an electrodynamic instability, which distorts the doping fronts and increases the transformation rate considerably. We explain the physical mechanism of the instability, develop theory, provide experimental evidence, perform numerical simulations, and demonstrate how the instability strength may be amplified technologically. The electrodynamic plasma instability obtained also shows interesting similarity to the hydrodynamic Darrieus-Landau instability in combustion, laser ablation, and astrophysics.

Spin contribution to the ponderomotive force in a plasma.

The concept of a ponderomotive force due to the intrinsic spin of electrons is developed. An expression containing both the classical as well as the spin-induced ponderomotive force is derived. The results are used to demonstrate that an electromagnetic pulse can induce a spin-polarized plasma. Furthermore, it is shown that, for certain parameters, the nonlinear backreaction on the electromagnetic pulse from the spin magnetization current can be larger than that from the classical free current. Suitable parameter values for a direct test of this effect are presented.

Localized whistlers in magnetized spin quantum plasmas.

The nonlinear propagation of electromagnetic (EM) electron-cyclotron waves (whistlers) along an external magnetic field, and their modulation by electrostatic small but finite amplitude ion-acoustic density perturbations are investigated in a uniform quantum plasma with intrinsic spin of electrons. The effects of the quantum force associated with the Bohm potential and the combined effects of the classical as well as the spin-induced ponderomotive forces (CPF and SPF, respectively) are taken into consideration. The latter modify the local plasma density in a self-consistent manner. The coupled modes of wave propagation is shown to be governed by a modified set of nonlinear Schrödinger-Boussinesq-like equations which admit exact solutions in form of stationary localized envelopes. Numerical simulation reveals the existence of large-scale density fluctuations that are self-consistently created by the localized whistlers in a strongly magnetized high density plasma. The conditions for the modulational instability (MI) and the value of its growth rate are obtained. Possible applications of our results, e.g., in strongly magnetized dense plasmas and in the next generation laser-solid density plasma interaction experiments are discussed.

Linearized kinetic theory of spin-1/2 particles in magnetized plasmas.

We have considered linear kinetic theory, including the electron-spin properties in a magnetized plasma. The starting point is a mean-field Vlasov-like equation, derived from a fully quantum-mechanical treatment, where effects from the electron-spin precession and the magnetic dipole force are taken into account. The general conductivity tensor is derived, including both the free current contribution and the magnetization current associated with the spin contribution. We conclude the paper with an extensive discussion of the quantum-mechanical boundary where we list parameter conditions that must be satisfied for various quantum effects to be influential.

Superluminal tunneling of microwaves in smoothly varying transmission lines.

Tunneling of microwaves through a smooth barrier in a transmission line is considered. In contrast to standard wave barriers, we study the case where the dielectric permittivity is positive, and the barrier is caused by the inhomogeneous dielectric profile. It is found that reflectionless, superluminal tunneling can take place for waves with a finite spectral width. The consequences of these findings are discussed, and an experimental setup testing our predictions is proposed.

Quantum plasma effects in the classical regime.

For quantum effects to be significant in plasmas it is often assumed that the temperature over density ratio must be small. In this paper we challenge this assumption by considering the contribution to the dynamics from the electron spin properties. As a starting point we consider a multicomponent plasma model, where electrons with spin-up and spin-down are regarded as different fluids. By studying the propagation of Alfvén wave solitons we demonstrate that quantum effects can survive in a relatively high-temperature plasma. The consequences of our results are discussed.

Quantum-electrodynamical photon splitting in magnetized nonlinear pair plasmas.

We present for the first time the nonlinear dynamics of quantum electrodynamic (QED) photon splitting in a strongly magnetized electron-positron (pair) plasma. By using a QED corrected Maxwell equation, we derive a set of equations that exhibit nonlinear couplings between electromagnetic (EM) waves due to nonlinear plasma currents and QED polarization and magnetization effects. Numerical analyses of our coupled nonlinear EM wave equations reveal the possibility of a more efficient decay channel, as well as new features of energy exchange among the three EM modes that are nonlinearly interacting in magnetized pair plasmas. Possible applications of our investigation to astrophysical settings, such as magnetars, are pointed out.

Using high-power lasers for detection of elastic photon-photon scattering.

The properties of four-wave interaction via the nonlinear quantum vacuum is investigated. The effect of the quantum vacuum is to generate photons with new frequencies and wave vectors, due to elastic photon-photon scattering. An expression for the number of generated photons is derived, and using state-of-the-art laser data it is found that the number of photons can reach detectable levels. In particular, the prospect of using the high-repetition Astra Gemini system at the Rutherford Appleton Laboratory is discussed. The problem of noise sources is reviewed, and it is found that the noise level can be reduced well below the signal level. Thus, detection of elastic photon-photon scattering may for the first time be achieved.

Nonlinear standing waves in bounded plasmas.

An analytical model for nonlinear volume oscillations in a bounded cold plasma is developed. Although here the familiar propagating wave solutions do not exist, exact nonlinear standing waves subject to appropriate boundary conditions can nevertheless be found. The behaviors of the electrons and ions are described self-consistently in terms of Lagrangian variables. The analytical solutions are compared with that from particle-in-cell simulations. Good agreement is found in the regimes of interest.

Proposal for detection of QED vacuum nonlinearities in Maxwell's equations by the use of waveguides.

We present a novel method for detecting nonlinearities, due to quantum electrodynamics through photon-photon scattering, in Maxwell's equation. The photon-photon scattering gives rise to self-interaction terms which are similar to the nonlinearities due to the polarization in nonlinear optics. These self-interaction terms vanish in the limit of parallel propagating waves, but if, instead of parallel propagating waves, the modes generated in waveguides are used, there will be a nonzero total effect. Based on this idea, we calculate the nonlinear excitation of new modes and estimate the strength of this effect. Furthermore, we suggest a principal experimental setup.

Efficient TGF-beta induction of the Smad7 gene requires cooperation between AP-1, Sp1, and Smad proteins on the mouse Smad7 promoter.

Sma- and Mad-related protein 7 (Smad7) is an antagonist of transforming growth factor-beta (TGF-beta) signaling, which has been shown to be induced by TGF-beta itself and also by other stimuli. In an effort to understand the molecular mechanisms underlying the transcriptional regulation of the Smad7 gene by TGF-beta, we cloned and functionally characterized a mouse genomic DNA fragment encompassing the mouse Smad7 proximal promoter. This region was found to contain a CpG island and to be devoid of a classical TATA box. Cloned upstream of a promoter-lacking luciferase reporter gene, this region conferred robust TGF-beta-induced transcription. Point mutations in a palindromic Smad binding element, abolished TGF-beta inducibility completely. Through the use of electrophoretic mobility shift assays, we showed the presence of Smad2, Smad3, and Smad4 in complexes binding to the Smad binding element. Interestingly, we also found that point mutation and/or deletion of binding sites for the transcription factors activator protein-1 and Sp1 led to an attenuation of the basal promoter activity, as well as of the TGF-beta-mediated induction of Smad7. Taken together, our data imply that Smads, together with activator protein-1 and Sp1 transcription factors, are essential for efficient Smad7 promoter activity.

Parametric excitation of Alfven waves by gravitational radiation

We consider the parametric excitation of Alfven waves by gravitational radiation propagating on a Minkowski background, parallel to an external magnetic field. As a starting point, standard ideal magnetohydrodynamics equations incorporating the curvature of space-time has been derived. The growth rate of the Alfven waves has been calculated, using the normal-mode approach. Various astrophysical applications of our investigations are discussed, and finally we demonstrate that the coupling coefficients of the interacting modes fulfill the Manley-Rowe relations.

Increased smad expression and activation are associated with apoptosis in normal and malignant prostate after castration.

Transforming growth factor (TGF)-beta1 is induced in the prostate after castration and has been implicated in apoptosis of epithelial cells during involution. TGF-beta1-mediated receptor activation induces phosphorylation of Smad2 and Smad3, which form complexes with Smad4, that translocate to the nucleus to regulate transcription of target genes. Smad6 and Smad7 antagonize the action of signal-transducing Smads. We have examined the immunohistochemical expression of different Smad molecules in the epithelium of rat ventral prostate before and after castration, in androgen-sensitive Dunning R3327 PAP prostatic tumor cells from untreated and castrated rats, and after treatment with estrogen. In the ventral prostate, a significant increase of phosphorylated Smad2 (P-Smad2) was observed after castration. In prostatic tumor cells we observed an increased expression of Smad2 and P-Smad2 after treatment. The levels of Smad3 and, in particular, Smad4 were enhanced in the normal ventral prostate, as well as in the tumors after castration. Interestingly, Smad6 and Smad7 expression was also up-regulated in cells with increased Smad2 activation. The staining for Smad2, P-Smad2, Smad3, Smad4, and Smad7 was nuclear in some cells and was present in areas with a large number of apoptotic cells identified by various morphological criteria, formation of apoptotic bodies and, in adjacent sections, by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. Our results suggest that the signal transduction pathway for TGF-beta, leading to apoptosis, is activated in the normal prostate after castration and in the tumor model after castration, without or with estrogen treatment.

Enhanced synthesis of platelet-derived growth factor following injury induced by 6-hydroxydopamine in rat brain.

The kinetics of platelet-derived growth factor messenger RNA synthesis in the substantia nigra and in the striatum, before and after unilateral intranigral 6-hydroxydopamine injection, was studied and compared with that after sham operation by a quantitative reverse transcription-polymerase chain reaction. The kinetics of brain-derived neurotrophic factor messenger RNA was studied as a comparison. Furthermore, the expression of platelet-derived growth factor A- and B-chain proteins was analysed by enzyme-linked immunosorbent assay and immunohistochemistry. In the ipsilateral striatum of 6-hydroxydopamine-lesioned rats, the signal density of messenger RNA for both A- and B-chains had already increased at one day and remained at an elevated level during the observation period of four weeks. In the substantia nigra ipsilateral to the lesion, a strongly increased level of B-chain and, to a lesser extent, of A-chain messenger RNA was already detected at 4h, reaching a maximal level at one day. No significant increase was seen either in sham-operated rats or in the contralateral striatum and substantia nigra. Amounts of platelet-derived growth factor proteins were examined separately by enzyme-linked immunosorbent assay in both sides of the substantia nigra, striatum and cortex. Three days after 6-hydroxydopamine lesions the levels of both platelet-derived growth factor A- and B-chains increased in the ipsilateral striatum, substantia nigra, and cortex. An increase in the A-chain was also observed in the contralateral side of the brain. The signal for brain-derived neurotrophic factor messenger RNA increased in the striatum in the lesioned side and, to a lesser extent, in the contralateral side, as well as in the substantia nigra, where a significant difference was observed when compared with the contralateral side. Semiquantitative immunohistochemical analysis on the substantia nigra confirmed the enhanced platelet-derived growth factor expression, revealing that the majority of the platelet-derived growth factor-producing cells were neurons. In summary, we have shown that platelet-derived growth factor messenger RNA as well as its protein are induced after injury to dopaminergic cells. These data indicate an important role of platelet-derived growth factor in the dopaminergic system.

Apoptosis and expression of Bcl-2 after compression trauma to rat spinal cord.

We have evaluated by in situ nick-end labeling the presence of apoptotic cells in the spinal cord of rats with compression injury at the level of Th8-9 of mild, moderate, and severe degrees resulting in no neurologic deficit, reversible paraparesis, and paraplegia, respectively. Rats with compression injury surviving 4 or 9 days showed apoptotic glial cells in the longitudinal tracts of the Th8-9, the cranial Th7, and the caudal Th10 segments. The apoptotic cells were most frequently observed in Th7. They did not express glial fibrillar acidic protein (GFAP) and their morphology was compatible with that of oligodendrocytes. Neurons of the gray matter did not present signs of apoptosis. In addition, we studied the immunohistochemical expression of Bcl-2, an endogenous inhibitor of apoptosis. Compression induced Bcl-2 immunoreactivity in axons of the long tracts, particularly after moderate and severe compression and 1-day survival. Neurons of dorsal root ganglia were immunoreactive but the neurons of the spinal cord were unstained. The accumulation, presumably caused by arrested axonal transport in sensory pathways, was absent in rats surviving 9 days. In conclusion, compression trauma to rat spinal cord induces signs of apoptosis in glial cells, presumably oligodendrocytes of the long tracts. This may induce delayed myelin degeneration after trauma to the spinal cord. Bcl-2 does not seem to be upregulated in oligodendrocytes.