Experimental observation of the electron beam focusing effect induced by plasma currents with opposite directions.

We report on the experimental observation of the focusing effect of a 50MeV accelerator electron beam in a gas-discharge plasma target. The plasma is generated by igniting an electric discharge in two collinear quartz tubes, with the currents up to 1.5kA flowing in opposite directions in either of the two tubes. In such plasma current configuration, the electron beam is defocused in the first discharge tube and focused with a stronger force in the second one. With symmetric plasma currents, asymmetric effects are, however, induced on the beam transport process and the beam radius is reduced by a factor of 2.6 compared to the case of plasma discharge off. Experimental results are supported by two-dimensional particle-in-cell simulations.

Permeability enhancement of the KcsA channel under radiation of a terahertz wave.

Potassium ion channels are essential elements in cellular electrical excitability and help maintain a resting potential in nonexcitable cells. Their universality is based on a unique combination of strong selectivity for K^{+} ions and near-diffusion-limited permeation efficiency. Understanding how the channel regulates the ion conduction would be instructive to the treatment of ion channelopathies. In this work, by means of molecular dynamics simulations, we demonstrate the significantly enhanced permeation of KcsA channel in reaction to an external terahertz wave, due to the effective response of the K^{+} ions in the selectivity filter regions of the channel. Compared to the case without external terahertz wave, a fourfold increase in the ion current through the channel is found.

Resonant sheath heating in weakly magnetized capacitively coupled plasmas due to electron-cyclotron motion.

An electron heating mechanism based on a resonance between the cyclotron motion of electrons and the radio frequency sheath oscillations is reported in weakly magnetized capacitively coupled plasmas at low pressure. If half of the electron cyclotron period coincides with the radio frequency period, then electrons will coherently collide with the expanding sheath and gain substantial energy, which enhances the plasma density. A relation between the magnetic field and the driving frequency is found to characterize this resonance effect and the kinetics of electrons are revealed at resonance conditions for various driving frequencies.

Collective energy-spectrum broadening of a proton beam in a gas-discharge plasma.

An accurate understanding of ion-beam transport in plasmas is crucial for applications in inertial fusion energy and high-energy-density physics. We present an experimental measurement on the energy spectrum of a proton beam at 270 keV propagating through a gas-discharge hydrogen plasma. We observe the energies of the beam protons changing as a function of the plasma density and spectrum broadening due to a collective beam-plasma interaction. Supported by linear theory and three-dimensional particle-in-cell simulations, we attribute this energy modulation to a two-stream instability excitation and further saturation by beam ion trapping in the wave. The widths of the energy spectrum from both experiment and simulation agree with the theory.

Enhanced collective stopping and drift of electron beams in fusion plasmas with heavy-ion species.

The transport and energy deposition of relativistic electron beams in transversely nonuniform plasmas are investigated with two-dimensional electromagnetic particle-in-cell simulations. For the beam with radius much larger than plasma skin depth, the current filamentation instability excited by the electron beam can be observed, which breaks the beam into filaments and leads to the formation of strong magnetic fields consequently. The effects of plasma ion species are significant and asymmetric transverse magnetic fields are formed in plasmas with heavy-ion species due to the asymmetric neutralization of beam space charge by plasma ions. The asymmetric transverse magnetic fields contribute to the directional drift of beam electrons to lower plasma density regions, which may accelerate the filaments merger process and lead to highly localized beam-energy deposition in plasmas.

Observation of Nonlinear Standing Waves Excited by Plasma-Series-Resonance-Enhanced Harmonics in Capacitive Discharges.

We report the first experimental observation of nonlinear standing waves excited by plasma-series-resonance-enhanced harmonics in low pressure, very high frequency, parallel plate, capacitively coupled plasmas. Spatial structures of the harmonics of the magnetic field, measured by a magnetic probe, are in very good agreement with simulations based on a nonlinear electromagnetics model. At relatively low pressure, the nonlinear sheath motion generates high-order harmonics that can be strongly enhanced near the series resonance frequencies. Satisfying certain conditions, such nonlinear harmonics induce radial standing waves, with voltage and current maxima on axis, resulting in center-high plasma density. Excitation of higher harmonics is suppressed at higher pressures.

A new B-dot probe circuit for magnetic diagnostics of radio frequency discharges.

Accurate magnetic measurements in radio frequency capacitively coupled plasmas (CCP) are challenging due to the presence of inherently strong electric fields and relatively weak magnetic fields. In this work, a new B-dot probe circuit is presented, comprising two variable capacitors in a tunable series resonance circuit, with a center-tapped, step-up transformer. The output characteristics of the probe are predicted using two distinct equivalent circuit models, one for the differential mode and the other for the common mode. A Helmholtz coil and a Faraday cup are used for experimental validation of the predicted probe output. By tuning the two variable capacitors in the circuit, the magnetic probe can achieve improved signal-to-noise ratio by amplifying the inductive signal, while suppressing capacitive coupling interference. Using the newly designed probe, magnetic measurements in typical CCP are presented.

Automatic emissive probe apparatus for efficient plasma potential measurements.

The improved inflection point method of emissive probe is the most accurate method for plasma potential measurements, but its manual operation is quite cumbersome and time-consuming. This paper describes the design and test of an automatic emissive probe apparatus for efficient plasma potential measurements. The apparatus consists of a computer controlled data acquisition (DAQ) card, a working circuit composed of a biasing unit and a heating unit, as well as the emissive probe. The main feature of the apparatus is that both the biasing scan and the heating scan of the probe are controlled by the computer program through analog outputs of the DAQ card, which easily realizes the required timing between the biasing and heating scans of the probe. The apparatus can automatically execute the improved inflection point method of emissive probe and give the plasma potential result. The advantages of high-accuracy, high-efficiency, and durability of probe filament make the apparatus promising for extensive use in plasma potential measurements.

Differential responses of peach (Prunus persica) seedlings to elevated ozone are related with leaf mass per area, antioxidant enzymes activity rather than stomatal conductance.

To evaluate the ozone (O3) sensitivity among peach tree (Prunus persica) cultivars widely planted in Beijing region and explore the possible eco-physiological response mechanisms, thirteen cultivars of peach seedlings were exposed to either charcoal-filtered air or elevated O3 (E-O3, non-filtered ambient air plus 60 ppb) for one growing season in open-top chambers. Leaf structure, stomatal structure, gas exchange and chlorophyll a fluorescence, photosynthetic pigments, antioxidant defense system and lipid peroxidation were measured in three replicated chambers. Results showed that E-O3 significantly reduced abaxial epidemis thickness, but no effects on the thicknesses of adaxial epidemis, palisade parenchyma and spongy parenchyma. Stomatal area, density and conductance were not significantly affected by E-O3. E-O3 significantly accelerated leaf senescence, as indicated by increased lipid peroxidation and more declines in light-saturated photosynthetic rate and pigments contents. The reduced ascorbate content (ASC) was decreased but antioxidant enzyme activity (CAT, APX and SOD) and total antioxidant capacity (TAC) were significantly increased by E-O3 among cultivars. The cultivars with visible symptoms also had more reductions in net photosynthetic rate than those without visible symptoms. Ozone sensitivity among cultivars was strongly linked to leaf mass per area (LMA), antioxidant enzymes activity e.g. SOD, APX rather than stomatal parameters (stomatal area, density and conductance) and ASC. Results could provide a theoretical basis for selecting and breeding the ozone-resistant cultivars of peach trees grown in high O3-polluted regions.

Moderate drought did not affect the effectiveness of ethylenediurea (EDU) in protecting Populus cathayana from ambient ozone.

A field study was conducted to evaluate the effects of ambient ozone (O3) on an O3-sensitive poplar (Populus cathayana) by using ethylenediurea (EDU) as a chemical protectant under two soil water treatments (well-watered (WW) and moderate drought (MD, 50-60% of WW in volumetric soil water content). EDU was applied as foliar spray at 0, 300, 450, and 600ppm. Photosynthetic parameters, pigment contents, leaf nitrogen, antioxidant capacity, growth, and biomass were measured. The 8h (9:00-17:00) average ambient O3 concentration was 71.7ppb, and AOT40 was 29.2ppmh during the experimental period (9 June to 21 September), which was high enough to cause plant injury. MD had significantly negative effects on P. cathayana, as indicated by reduced photosynthesis, growth, and biomass, and higher MDA contents. On the other hand, EDU significantly increased photosynthesis rate, chlorophyll a fluorescence, Vcmax and Jmax, photosynthetic pigments, total antioxidant capacity, tree growth and biomass accumulation, and reduced lipid peroxidation, but there was no significant interaction between EDU and drought for most parameters, indicating that EDU can efficiently protect Populus cathayana against ambient O3 and the protection was not affected by soil water contents when soil water reached moderate drought level. Among all doses, EDU at 450ppm provided maximum protection. Comparison of EDU-treated and non-treated P. cathayana could be used as a biomarker system in risk assessment of the effects of ambient O3 on forest health.

Experimental Observation and Computational Analysis of Striations in Electronegative Capacitively Coupled Radio-Frequency Plasmas.

Self-organized spatial structures in the light emission from the ion-ion capacitive rf plasma of a strongly electronegative gas (CF_{4}) are observed experimentally for the first time. Their formation is analyzed and understood based on particle-based kinetic simulations. These "striations" are found to be generated by the resonance between the driving radio frequency and the eigenfrequency of the ion-ion plasma (derived from an analytical model) that establishes a modulation of the electric field, the ion densities, as well as the energy gain and loss processes of electrons in the plasma. The growth of the instability is followed by the numerical simulations.

Cloning and Characterization of the Acetylcholinesterase1 Gene of Tetranychus cinnabarinus (Acari: Tetranychidae).

The carmine spider mite, Tetranychus cinnabarinus (Boisduval), is a major agriculture pest. It can be found worldwide, has an extensive host plant range, and has shown resistance to pesticides. Organophosphate and carbamate insecticides account for more than one-third of all insecticide sales. Insecticide resistance and the toxicity of organophosphate and carbamate insecticides to mammals have become a growing concern. Acetylcholinesterase (AChE) is the major targeted enzyme of organophosphate and carbamate insecticides. In this study, we fully cloned, sequenced and characterized the ace1 gene of T. cinnabarinus, and identified the differences between T. cinnabarinus AChE1, Tetranychus urticae Koch AChE1, and human AChE1. Resistance-associated target-site mutations were displayed by comparing the AChE amino acid sequences and their AChE three-dimensional (3D) structures of the insecticide-susceptible strains of T. cinnabarinus and T. urticae to that of a T. urticae-resistant strain. We identified variation in the active-site gorge and the sites interacting with gorge residues by comparing AChE1 3D structures of T. cinnabarinus, T. urticae, and humans, though their 3D structures were similar. Furthermore, the expression profile of T. cinnabarinus AChE, at the different developmental stages, was determined by quantitative real-time polymerase chain reaction; the transcript levels of AChE were higher in the larvae stage than in other stages. The changes in AChE expression between different developmental stages may be related to their growth habits and metabolism characteristics. This study may offer new insights into the problems of insecticide resistance and insecticide toxicity of nontarget species.

Transcriptome Analysis of the Carmine Spider Mite, Tetranychus cinnabarinus (Boisduval, 1867) (Acari: Tetranychidae), and Its Response to ß-Sitosterol.

Tetranychus cinnabarinus (Acari: Tetranychidae) is a worldwide polyphagous agricultural pest that has the title of resistance champion among arthropods. We reported previously the identification of the acaricidal compound ß-sitosterol from Mentha piperita and Inula japonica. However, the acaricidal mechanism of ß-sitosterol is unclear. Due to the limited genetic research carried out, we de novo assembled the transcriptome of T. cinnabarinus using Illumina sequencing and conducted a differential expression analysis of control and ß-sitosterol-treated mites. In total, we obtained >5.4 G high-quality bases for each sample with unprecedented sequencing depth and assembled them into 22,941 unigenes. We identified 617 xenobiotic metabolism-related genes involved in detoxification, binding, and transporting of xenobiotics. A highly expanded xenobiotic metabolic system was found in mites. T. cinnabarinus detoxification genes-including carboxyl/cholinesterase and ABC transporter class C-were upregulated after ß-sitosterol treatment. Defense-related proteins, such as Toll-like receptor, legumain, and serine proteases, were also activated. Furthermore, other important genes-such as the chloride channel protein, cytochrome b, carboxypeptidase, peritrophic membrane chitin binding protein, and calphostin-may also play important roles in mites' response to ß-sitosterol. Our results demonstrate that high-throughput-omics tool facilitates identification of xenobiotic metabolism-related genes and illustration of the acaricidal mechanisms of ß-sitosterol.

Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation.

We report the formation of wave-like structures and nanostructured fuzzes in the polycrystalline tungsten (W) irradiated with high-flux and low-energy helium (He) ions. From conductive atomic force microscope measurements, we have simultaneously obtained the surface topography and current emission images of the irradiated W materials. Our measurements show that He-enriched and nanostructured strips are formed in W crystal grains when they are exposed to low-energy and high-flux He ions at a temperature of 1400 K. The experimental measurements are confirmed by theoretical calculations, where He atoms in W crystal grains are found to cluster in a close-packed arrangement between {101} planes and form He-enriched strips. The formations of wave-like structures and nanostructured fuzzes on the W surface can be attributed to the surface sputtering and swelling of He-enriched strips, respectively.

[Comparison of stilbene synthase from different plant sources for resveratrol biosynthesis].

Resveratrol is a natural phytoalexin with special pharmacological and health functions. Stilbene synthase (STS) is a key and rate-limiting enzyme in the biosynthesis of resveratrol that is present only in a limited number of plants. The content of resveratrol from Polygonum cuspidatum is more than 1000 times higher than grapes and peanuts. We speculate that the catalytic ability of different STS may be one of the reasons causing differences in the content of resveratrol. To verify the above speculation, Vitis vinifera stilbene synthase gene (VvSTS) was amplified according to overlap PCR protocol with genomic DNA as template. VvSTS and PcSTS (PcPKS5) were analyzed through heterologous expression in Escherichia coli. The expression products were purified with Ni-NTA sepharose affinity chromatography and desalted through PD-10 column. The molecular weight of the two fusion proteins was about 43 kDa. Enzyme reaction and product analysis showed that the two products were resveratrol. The enzyme kinetic analysis showed that the catalyze efficiency (Kcat/Km) of PcPKS5 was 2.4 times of the VvSTS. Our findings confirms that STS from certain plants has much higher catalytic capability.

[Salidroside biosynthesis pathway: the initial reaction and glycosylation of tyrosol].

Salidroside, the 8-O-beta-D-glucoside of tyrosol, is a novel adaptogenic drug extracted from the medicinal plant Rhodiola sachalinensis A. Bor. Due to the scarcity of R. sachalinensis and its low yield of salidroside, there is great interest in enhancing the production of salidroside by biotechnological process. Glucosylation of tyrosol is thought to be the final step in salidroside biosynthesis. In our related works, three UGT clones were isolated from the roots and the cultured cells. Our intention was to combine the catalytic specificity of these UGTs in vitro in order to change the level of salidroside in vivo by over-expression of the above UGTs. However, as the aglycone substrate of salidroside, the biosynthetic pathway of tyrosol and its regulation are less well understood. The results of related studies revealed that there are two different possibilities for the tyrosol biosynthetic pathway. One possibility is that tyrosol is produced from a p-coumaric acid precursor, which is derived mainly from phenylalanine. The second possibility is that the precursor of tyrosol might be tyramine, which is synthesized from tyrosine. Our previous work demonstrated that over-expression of the endogenous phenylalanine ammonia-lyase gene (PALrs1) and accumulation of p-coumaric acid did not facilitate tyrosol biosynthesis. In contrast, the data presented in our recent work provide in vitro and in vivo evidence that the tyrosine decarboxylase (RsTyrDC) is most likely to have an important function in the initial reaction of the salidroside biosynthesis pathway in R. Sachalinensis.

[Plant-specific type III polyketide synthases superfamily: crystal structures and functions].

Plant type III polyketide synthase (PKS) generates backbones of a variety of plant secondary metabolites with diverse functions, and has long been models to elucidate the relationship between the three-dimensional structure and function. More than 80 type IIII PKS crystal structures with different functions have been reported in Protein Data Bank, including the crystal structures of the well-studied Chalcone Synthase of plant type III PKS, as well as the 6 other kinds of PKSs in the family, which are critical for understanding the structural basis for diverse starter molecule selectivity, polyketide chain length and the cyclization reaction. Structure-based analysis and site-directed mutagenesis are foundation for the investigation of enzyme engineering, genetic and metabolic engineering. This review summarized 7 plant-specific type III PKS in the aspects of their crystal structures and functions.

Time evolution and energy deposition for ion clusters injected into magnetized two-component plasmas.

A two-dimensional particle-in-cell simulation model is proposed to study the time evolution and energy deposition for ion clusters injected into magnetized two-component plasmas. The injection of an isolated ion cluster is studied in the case of weak and strong magnetic fields. For strong magnetic fields, the ions tend to deposit their energy smoothly along the trajectory of the cluster, due to the confinement by the strong magnetic fields. However, in the case of weak magnetic fields, a large amount of energy is deposited by the ions near the initial cluster injection position, where the cluster density is expected to be largest. We attribute these to the influences of interference effects between the cluster ions, which have close relations to the distances between the ions. Furthermore, the influences of various magnetic fields, injection angles, and injection velocities on the time evolution and energy deposition of a beam pulse, which contains several similar ion clusters, are investigated in detail. The influences of different magnetic fields on the beam pulse show similar to that of a single ion cluster. For increasing injection angles, the beam velocity perpendicular to the magnetic field increases, leading to increasing oscillations in the beam trajectory and energy deposition profile. Besides, the amount of energy that transferred from the beam pulse to the plasma increases as the beam injection velocity approaches the electron thermal velocity.

Collisionless bounce resonance heating in dual-frequency capacitively coupled plasmas.

We present the experimental evidence of the collisionless electron bounce resonance heating (BRH) in low-pressure dual-frequency capacitively coupled plasmas. In capacitively coupled plasmas at low pressures when the discharge frequency and gap satisfy a certain resonant condition, the high energy beamlike electrons can be generated by fast sheath expansion, and heated by the two sheaths coherently, thus the BRH occurs. By using a combined measurement of a floating double probe and optical emission spectroscopy, we demonstrate the effect of BRH on plasma properties, such as plasma density and light emission, especially in dual-frequency discharges.

A tyrosine decarboxylase catalyzes the initial reaction of the salidroside biosynthesis pathway in Rhodiola sachalinensis.

Salidroside, the 8-O-ß-D-glucoside of tyrosol, is the main bioactive component of Rhodiola species and is found mainly in the plant roots. It is well known that glucosylation of tyrosol is the final step in the biosynthesis of salidroside; however, the biosynthetic pathway of tyrosol and its regulation are less well understood. A summary of the results of related studies revealed that the precursor of tyrosol might be tyramine, which is synthesized from tyrosine. In this study, a cDNA clone encoding tyrosine decarboxylase (TyrDC) was isolated from Rhodiola sachalinensis A. Bor using rapid amplification of cDNA ends. The resulting cDNA was designated RsTyrDC. RNA gel-blot analysis revealed that the predominant sites of expression in plants are the roots and high levels of transcripts are also found in callus tissue culture. Functional analysis revealed that tyrosine was best substrate of recombinant RsTyrDC. The over-expression of the sense-RsTyrDC resulted in a marked increase of tyrosol and salidroside content, but the levels of tyrosol and salidroside were 274 and 412%, respectively, lower in the antisense-RsTyrDC transformed lines than those in the controls. The data presented here provide in vitro and in vivo evidence that the RsTyrDC can regulate the tyrosol and salidroside biosynthesis, and the RsTyrDC is most likely to have an important function in the initial reaction of the salidroside biosynthesis pathway in R. sachalinensis.