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1.
Phys Rev Lett ; 122(18): 185002, 2019 May 10.
Artículo en Inglés | MEDLINE | ID: mdl-31144895

RESUMEN

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.

2.
Phys Rev Lett ; 116(25): 255002, 2016 Jun 24.
Artículo en Inglés | MEDLINE | ID: mdl-27391730

RESUMEN

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.

3.
J Econ Entomol ; 108(2): 769-79, 2015 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-26470189

RESUMEN

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.


Asunto(s)
Acetilcolinesterasa/genética , Tetranychidae/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Clonación Molecular , Humanos , Datos de Secuencia Molecular , Conformación Proteica , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Tetranychidae/crecimiento & desarrollo
4.
World J Microbiol Biotechnol ; 29(12): 2343-52, 2013 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-23775786

RESUMEN

The filamentous fungus Botrytis cinerea is an important agricultural pathogen affecting a wide range of cultivated plants. Since World War II, chemical fungicides have been the go-to method for agricultural pathogen control. However, the potential adverse environmental and health effects of these chemicals have led to an increasing demand for alternative methods of pathogen control, including biological control agents. In this study, we identified a bacterial isolate with strong antagonistic activity against B. cinerea. An analysis of the 16S rRNA gene sequence for this isolate identified it as a novel strain of Bacillus subtilis. Culture media from this isolate were harvested and fractionated using ion exchange and gel filtration chromatography. The fraction exhibiting the highest level of antifungal activity was identified, and its sequence determined by electrospray tandem mass spectrometry had significant similarity to flagellin. This flagellin-like protein was exogenously expressed in Escherichia coli, and screened for antifungal activity against B. cinerea. This flagellin-like protein demonstrated clear antifungal activity of inhibiting B. cinerea growth.


Asunto(s)
Antifúngicos/farmacología , Bacillus subtilis/aislamiento & purificación , Bacillus subtilis/metabolismo , Botrytis/efectos de los fármacos , Flagelina/aislamiento & purificación , Flagelina/farmacología , Secuencia de Aminoácidos , Antibiosis , Antifúngicos/química , Antifúngicos/metabolismo , Bacillus subtilis/genética , Botrytis/crecimiento & desarrollo , Cromatografía en Gel , Cromatografía por Intercambio Iónico , Medios de Cultivo , Bases de Datos Genéticas , Flagelina/química , Flagelina/genética , Flagelina/metabolismo , Datos de Secuencia Molecular , Filogenia , ARN Ribosómico 16S/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Proteínas Recombinantes/farmacología , Alineación de Secuencia , Espectrometría de Masas en Tándem
5.
Phys Rev E ; 108(6-2): 065203, 2023 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-38243529

RESUMEN

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.

6.
Phys Rev E ; 105(2-1): 024104, 2022 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-35291137

RESUMEN

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.

7.
Phys Rev Lett ; 107(5): 055002, 2011 Jul 29.
Artículo en Inglés | MEDLINE | ID: mdl-21867075

RESUMEN

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.

8.
Physiol Plant ; 142(4): 390-406, 2011 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-21496031

RESUMEN

The development of the stone and formation of peach (Prunus persica) fruit were explored in this work using a proteomic approach. Sixty-eight proteins with different expression patterns were identified in both the endocarp and mesocarp during early fruit development (from 28 to 59 days after flowering) and the majority were involved in primary or secondary metabolism. In contrast to most proteins associated with primary metabolism in the endocarp, whose expression is down-regulated, expression of pyruvate dehydrogenase (PDH) unexpectedly increased exponentially. Moreover, its expression pattern was linearly positively correlated with the exponentially growing lignin content (R = 0.940), which suggests that PDH may play a role in endocarp lignification. Our data also revealed different spatiotemporal expressions of enzymes involved in the lignin and flavonoid pathways that provided proteome-level evidence to support the hypothesis that these two pathways are competitive during endocarp development. In addition, we observed endocarp-specific oxidative stress and propose that it may act as a stimulating factor in activating lignification and subsequent programmed cell death in the endocarp.


Asunto(s)
Frutas/crecimiento & desarrollo , Proteínas de Plantas/metabolismo , Proteoma/análisis , Prunus/metabolismo , Análisis por Conglomerados , Electroforesis en Gel Bidimensional , Flavonoides/metabolismo , Frutas/genética , Frutas/metabolismo , Regulación de la Expresión Génica de las Plantas , Lignina/metabolismo , Estrés Oxidativo , Proteómica , Prunus/genética , Prunus/crecimiento & desarrollo , Complejo Piruvato Deshidrogenasa/metabolismo , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción
9.
Plant Cell Rep ; 30(8): 1443-53, 2011 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-21538102

RESUMEN

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.


Asunto(s)
Glucósidos/biosíntesis , Rhodiola/enzimología , Tirosina Descarboxilasa/metabolismo , Secuencia de Aminoácidos , Vías Biosintéticas , Clonación Molecular , ADN sin Sentido/genética , ADN Complementario/genética , ADN de Plantas/genética , Datos de Secuencia Molecular , Fenoles , Alcohol Feniletílico/análogos & derivados , Alcohol Feniletílico/metabolismo , Plantas Modificadas Genéticamente/enzimología , Plantas Modificadas Genéticamente/genética , Rhodiola/genética , Análisis de Secuencia de ADN
10.
Phys Rev E ; 104(4-2): 045209, 2021 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-34781465

RESUMEN

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.

11.
Phys Rev E ; 103(6-1): 063216, 2021 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-34271707

RESUMEN

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.

12.
Phys Rev E ; 101(4-1): 043203, 2020 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-32422758

RESUMEN

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.

13.
Planta ; 229(5): 1077-86, 2009 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-19225805

RESUMEN

Benzalacetone synthase (BAS) is a member of the plant-specific type III PKS superfamily that catalyzes a one-step decarboxylative condensation of 4-coumaroyl-CoA with malonyl-CoA to produce p-hydroxybenzalacetone. In our recent work (Ma et al. in Planta 229(3):457-469, 2008), a three-intron type III PKS gene (PcPKS2) was isolated from Polygonum cuspidatum Sieb. et Zucc. Phylogenetic and functional analyses revealed this recombinant PcPKS2 to be a BAS. In this study, another three-intron type III PKS gene (PcPKS1) and its corresponding cDNA were isolated from P. cuspidatum. Sequence and phylogenetic analyses demonstrated that PcPKS1 is a chalcone sythase (CHS). However, functional and enzymatic analyses showed that recombinant PcPKS1 is a bifunctional enzyme with both, CHS and BAS activity. DNA gel blot analysis indicated that there are two to four CHS copies in the P. cuspidatum genome. RNA gel blot analysis revealed that PcPKS1 is highly expressed in the rhizomes and in young leaves, but not in the roots of the plant. PcPKS1 transcripts in leaves were inducible by pathogen infection and wounding. BAS is thought to play a crucial role in the construction of the C(6)-C(4) moiety found in a variety of phenylbutanoids, yet so far phenylbutanoids have not been isolated from P. cuspidatum. However, since PcPKS1 and PcPKS2 (Ma et al. in Planta 229(3):457-469, 2008) have been identified in P. cuspidatum, it is possible that such compounds are also produced in that plant, albeit in low concentrations.


Asunto(s)
Acetona/metabolismo , Aciltransferasas/genética , Fallopia japonica/enzimología , Fallopia japonica/genética , Flavanonas/biosíntesis , Genes de Plantas , Intrones/genética , Acetona/química , Aciltransferasas/química , Aciltransferasas/metabolismo , Secuencia de Aminoácidos , Secuencia de Bases , Cromatografía Líquida de Alta Presión , ADN Complementario/genética , ADN Complementario/aislamiento & purificación , Electroforesis en Gel de Poliacrilamida , Flavanonas/química , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Concentración de Iones de Hidrógeno , Datos de Secuencia Molecular , Filogenia , Proteínas Recombinantes/metabolismo , Análisis de Secuencia , Especificidad por Sustrato
14.
Phys Rev E Stat Nonlin Soft Matter Phys ; 79(1 Pt 2): 016405, 2009 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-19257146

RESUMEN

Energy losses of test particles in magnetized two-component plasmas are investigated within the framework of the linearized Vlasov-Poisson theory, taking into account the dynamic polarization effects of both the plasma ions and electrons. General expressions of the potential and stopping power are obtained and calculations are performed for protons in a magnetized hydrogen plasma. The influences of the magnetic field, the angle between the proton velocity and magnetic field, and certain plasma parameters on the stopping power are studied. Numerical results show that for low particle velocities and strong magnetic field the dynamic polarization effects of the plasma ions become obvious and contribute mainly to the stopping power.

15.
Rev Sci Instrum ; 89(10): 105104, 2018 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-30399790

RESUMEN

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.

16.
Rev Sci Instrum ; 88(11): 115106, 2017 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-29195398

RESUMEN

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.

17.
Phys Rev E Stat Nonlin Soft Matter Phys ; 73(1 Pt 2): 016404, 2006 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-16486285

RESUMEN

We present a theoretical model for studying the interactions of charged particles with two-dimensional strongly coupled dusty plasmas, based on the quasilocalized charge approximation in which the static pair distribution function of a dust layer is determined from a molecular dynamics simulation. General expressions are derived for the perturbed dust-layer density, the induced potential in plasma, and the energy loss of a charged particle moving parallel to the dust layer. Numerical results show that the structure of Mach cones, excited in the dust layer by the charged particle, strongly depends on the plasma parameters such as the coupling parameter, the screening parameter, and the discharge pressure, as well as on the particle speed. In addition, it is found that the energy dissipation suffered by slow charged particles can be significantly enhanced in strongly coupled dusty plasmas when compared to the dissipation in weakly coupled plasmas.

18.
Phys Rev E Stat Nonlin Soft Matter Phys ; 69(3 Pt 2): 036403, 2004 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-15089411

RESUMEN

A hybrid theoretical model, capable of describing the characteristics of a collisional sheath driven by a sinusoidal current source and determining the energy and angular distributions of ions incident onto the substrate, is proposed. The model consists of one-dimensional time-dependent fluid equations coupled with the Poisson equation determining spatiotemporal evolution of the sheath and the Monte Carlo simulation predicting the energy and angular distributions of ions striking the electrode, in which charge-exchange collisions between ions and neutrals are included. Additionally, an equivalent circuit model in conjunction with the fluid equations is adopted to self-consistently determine the relationship between the instantaneous potential at a rf-biased electrode and the sheath thickness. It is found that the collisional effects would influence the height of the energy peaks in the ion energy distributions and the ion angular distributions.

19.
Phys Rev E Stat Nonlin Soft Matter Phys ; 66(2 Pt 2): 026413, 2002 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-12241303

RESUMEN

With a one-dimensional multiple ion dynamics model, we study characteristics of the collisionless radio-frequency (rf) sheaths in fluorocarbon plasmas and calculate the ion energy distributions impinging on rf-biased electrodes. All the time-dependent terms in the ion fluid equations are included and the relationship between the instantaneous sheath voltage and sheath thickness is determined self-consistently by an equivalent circuit equation. The numerical results show that, due to the existence of multi-ion species, the sheath structure in the present work is different from those of single-ion species plasmas, and multiple peaks appear in the ion energy distributions. It is also shown that some parameters such as the bias frequency, bias power, bulk plasma density, and electron temperature are crucial for determining the shape of the ion energy distribution in multicomponent plasmas.

20.
Phys Rev E Stat Nonlin Soft Matter Phys ; 70(5 Pt 2): 056406, 2004 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-15600764

RESUMEN

A two-dimensional hydrodynamic model for a monolayer of dust particles is used to study the Mach cones excited by a moving laser beam through dusty plasmas. Numerical results for the density perturbation and the velocity distribution of dust particles exhibit both compressional and shear-wave Mach cones. It is found that the compressional Mach cones exist in cases of both supersonic and subsonic excitations, and that they consist of multiple lateral or transverse wakes. On the other hand, realization of single shear-wave Mach cones depends closely on the excitation technique, the laser scanning speed, and the discharge pressures. It is found that, when the scanning direction of the laser beam is perpendicular to the laser force, a transition from multiple compressional Mach cones to a single shear Mach cone can be achieved either by lowering the scanning speed or by increasing the discharge pressures.

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