Hall magnetic shocks in plasma current layers

We present new analytical and numerical results of the dynamics of reversed field current layers in the Hall limit (i.e., characteristic length scales smaller than the ion inertial length). A rapid, localized thinning of the current layer leads to the generation of a nonlinear, shocklike structure that propagates in the B x inverted Delta(n) direction. This magnetic structure is self-supportive and can lead to a nonlocal thinning of the current layer and the release of magnetic energy.     

Stationary rarefaction wave in magnetized Hall plasmas

We demonstrate the existence of a stationary rarefaction wave in a current-carrying plasma. The result unexpectedly mismatches with the commonly accepted viewpoint about the impossibility of rarefaction shocks in gases or plasmas. The discovered wave may appear when the magnetic field has penetrated into the plasma and magnetized the electrons. At this stage, the wave front is formed at the cathode and propagates towards the anode through the magnetized quasineutral plasma. The case of low collisionality is investigated analytically. This phenomenon could explain the recent surprising experimental observations of a local plasma density drop in several laboratory plasmas.     

<Emphasis Type="Italic">parkin</Emphasis> counteracts symptoms in a <Emphasis Type="Italic">Drosophila</Emphasis> model of Parkinson's disease

Background

Parkinson's disease, a prevalent neurodegenerative disease, is characterized by the reduction of dopaminergic neurons resulting in the loss of motor control, resting tremor, the formation of neuronal inclusions and ultimately premature death. Two inherited forms of PD have been linked to mutations in the α-synuclein and parkin genes. The parkin protein functions as an ubiquitin ligase targeting specific proteins for degradation. Expression of human α-synuclein in Drosophila neurons recapitulates the loss of motor control, the development of neuronal inclusions, degeneration of dopaminergic neurons and the ommatidial array to provide an excellent genetic model of PD.

Results

To investigate the role of parkin, we have generated transgenic Drosophila that conditionally express parkin under the control of the yeast UAS enhancer. While expression of parkin has little consequence, co-expression of parkin with α-synuclein in the dopaminergic neurons suppresses the α-synuclein-induced premature loss of climbing ability. In addition directed expression of parkin in the eye counteracts the α-synuclein-induced degeneration of the ommatidial array. These results show that parkin suppresses the PD-like symptoms observed in the α-synuclein-dependent Drosophila model of PD.

Conclusion

The highly conserved parkin E3 ubiquitin ligase can suppress the damaging effects of human α-synuclein. These results are consistent with a role for parkin in targeting α-synuclein to the proteasome. If this relationship is conserved in humans, this suggests that up-regulation of parkin should suppress α-synucleinopathic PD. The development of therapies that regulate parkin activity may be crucial in the treatment of PD.

     

Hall magnetic reconnection rate

Two-dimensional Hall magnetohydrodynamic simulations are used to determine the magnetic reconnection rate in the Hall limit. The simulations are run until a steady state is achieved for four initial current sheet thicknesses: L=1,5,10, and 20c/omega(pi), where c/omega(pi) is the ion inertial length. It is found that the asymptotic (i.e., time independent) state of the system is nearly independent of the initial current sheet width. Specifically, the Hall reconnection rate is weakly dependent on the initial current layer width and is partial differential Phi/ partial differential t less, similar 0.1V(A0)B0, where Phi the reconnected flux, and V(A0) and B0 are the Alfvén velocity and magnetic field strength in the upstream region. Moreover, this rate appears to be independent of the scale length on which the electron "frozen-in" condition is broken (as long as it is 相似文献   

Liquid-crystalline phase behavior of a colloidal rod-plate mixture

The phase behavior of rod-plate mixtures was investigated using model systems containing unambiguously rod- and plate-shaped colloids. We find that the theoretically disputed biaxial nematic phase is unstable with respect to demixing into an isotropic and two uniaxial nematic phases. The phase behavior at very high densities is exceptionally rich and includes the coexistence of up to four different liquid crystalline phases, which stem from the coupling between the employed particle shapes and polydispersity.     

Buoyant magnetic flux tubes enhance radiation in Z pinches

In numerous experiments, magnetic energy coupled to strongly radiating Z-pinch plasmas exceeds the thermalized kinetic energy, sometimes by a factor of 2-3. We demonstrate that the enhanced energy coupling may be due to the buoyancy rise of toroidal magnetic flux tubes converging to the axis through the unstable pinch plasma. We derive an explicit formula for the enhanced dissipation rate and apply this formula to reconsider an old problem of power balance in a steady-state Z pinch, and then to analyze a new challenge of producing K-shell 3 to 10 keV radiation in long-pulse Z-pinch implosions.     

Dielectric spectroscopy of monatomic alcohols

The frequency dependences of permittivity ?(f) and dielectric loss tanδ(f) of monatomic alcohols are measured in range of frequencies f from 0.025 to 1000 kHz. Dielectric relaxation is observed in the investigated frequency range. Empirical correlation equations describing the relationships between the dielectric characteristics and physicochemical properties of monatomic alcohols are obtained.     

Low-temperature liquid extraction as a method of the pretreatment of phenol samples for reversed-phase HPLS

A new procedure was developed for the liquid—liquid extraction of phenols from aqueous solutions With acetonitrile. It is based on the ability of aqueous acetonitrile systems to form immiscible phases in the temperature range 271—269 K. The resulting duration of analysis is 40–45 min, the partition coefficient is 45–140, and the recovery is 97.8–99.2%. The procedure was proved applicable for sample pretreatment followed by determination by reversed-phase HPLC.     

Effect of desolvation of the reactants during change in the acidity of the medium on the electrophilic hydroxylation and nitration of alkanes

The effect of the acidity of the medium on the hydroxylation and nitration of alkanes (RH) in 90–98% H₂SO₄ at 25°C is described quantitatively by a model taking account of the thermodynamic activity of the RH, H₂O, and HSO₄^- particles. It was concluded that in the transition states the reagents H₃O₂⁺HSO₄^- and NO₂⁺ HSO₄^- are present as HO⁺ and NO₂⁺ ions without the bases H–O and HSO₄^-, the alkanes are present without hydrophobic shells, and the initial reaction products are ROH₂⁺ and RNO₂H⁺.