Liquid microvortex generated around a laser focal point in anintense high-frequency electric field

A microvortex was discovered in liquid films when subjected to the combined action of a focused laser beam and a high-frequency electric field. The laser beam was perpendicular to both the surface of the liquid film and the direction of the electric field. The size of this opto-electrostatic microvortex (OEMV) in various liquids (water, ethanol, acetone, nitrobenzene) varied with the experimental conditions, but stayed in the 10-μm range. The velocity of the liquid flow in the vortex could be controlled by the intensity and frequency of the electric field (5.0×10⁴ to 0.8×10⁶ V/m, 2×10⁴ to 1×10⁶ Hz), by the laser power (0.01 to 2 W) and by the laser power density in the focal point. No microvortex was observed in benzene and chloroform. As an application of this phenomenon, single DNA molecules could be transported along the OEMV     

Applications of electrostatic stretch-and-positioning of DNA

The authors have previously reported that the electrostatic orientation and the dielectrophoresis (DEP) of DNA occur under ≈1 MHz, >1×10⁶ V/m field, by which DNA strands are stretched straight along field lines and positioned onto electrode edges. This paper presents some application of this stretch-and-positioning method to genetic engineering. It is shown that the DNA size distribution, as well as the activities of nuclease, can be determined by the measurement of the apparent length of stretched DNA. Several methods are developed to immobilize stretched DNA onto a substrate, including: (1) immobilization onto a conducting substrate for observations with the scanning tunneling microscopy, (2) anchoring onto a substrate only at both ends of the DNA using special electrode configuration, and/or molecular binding between avidin and biotin. The DNA can be held without contact to the substrate in the latter method, so that it does not cause steric hindrances to the DNA-binding enzymes. A novel fluid integrated circuit (FIC) device is proposed in which stretched DNA is cut by laser beam for the successive sequencing. A method to obtain unidirectionally oriented DNA is developed. The spatial resolution, and the small number of molecules required, are the advantages of the assays and measurements using electrostatic DNA manipulations over conventional biochemical methods. It is hoped that the methods may open a way to a novel category of “molecular biochemistry with spatial resolution.”     

Winter lightning on Japan Sea coast-development of measuring systemon progressing feature of lightning discharge

With the aid of recent optoelectronic techniques, the authors have developed a measuring instrument named ALPS (Automatic Lightning Discharge Progressing Feature Observation System) to determine the progress of lightning flashes. The progress velocities of stepped leaders for lightning in winter seasons were observed using the ALPS in the coastal area of the Japan Sea. The progress velocity of an individual step of a stepped leader can be expressed by a lognormal distribution and its mean value is 1.6×10⁶ m/s for upward leaders and 4.0×10⁶ m/s for downward leaders. The mean progress velocity of a total leader process is given as 0.8~2.7×10⁵ m/s for upward leaders and 2.9×10⁵ m/s for downward leaders     

Electrical conduction in double-layer P-SiO2/polymerdielectric structures

The dc electrical conduction in MI₁M and MI₁I₂M composite specimens has been studied, where I₁ is polyimide (PI) or polyester (PET), and I₂ is a thin plasma deposited silicon compound film (oxide, P-SiO₂, or nitride, P-SiN). The current-electric field (j(E,T)) characteristics have been measured over a wide range of E values (O⩽E⩽2×10 ⁵ V cm^-1) and temperatures (20⩽T⩽170°C). The observed transport characteristics are in broad agreement with data reported in the literature, except for PI based MI₁I₂M specimens, for which polarity dependent transport behavior occurs for T>60°C and E>2×10³ V cm^-1. The observed behavior of all specimen types can be explained in terms of protonic hopping conduction; the charge carriers are created by thermal dissociation and ionization of carboxylic acid (-COOH) groups, present in PI as several percent of unimidized polyamic acid, and in PET at chain ends. When the polarity is +MI₁I₂M-, the relatively abundant free protons in PI flow to the I₁/I₂ interface, where they can accumulate and give rise to a space charge-induced potential barrier of ~0.2 eV. By modifying Lewis' molecular dipole model so as to include this potential barrier, we derive expressions for j(E,T) which describe the experimentally observed polarity dependence in PI rather well. The effect is not observed in PET based MI₁I₂M specimens on account of the much lower concentration of free protons in this polymer     

Wurtzite GaN-based heterostructures by molecular beam epitaxy

Progress in plasma and reactive molecular beam epitaxy (PMBE and RMBE) grown n- and p-type GaN and GaN-AlGaN-based epitaxial films and optoelectronic devices is reviewed. The growth of GaN by RMBE (PMBE) is achieved by employing ammonia gas (plasma activated nitrogen) as the nitrogen source with resultant growth rates of about 2 μm/h (⩾1 μm/h). The structural, electrical, and optical properties of binary and ternary (Al,Ga)N and (In,Ga)N layers point to high quality. The GaN layers with Mg as the dopant atoms are p-type without any postgrowth treatment, but the hole concentrations are limited to mid 10¹⁷ cm^-3 although reports in the low 10¹⁸ cm^-3 dot the literature. The background carrier concentration, mobility, optical characteristics and ability to dope p-type depend significantly on the substrate temperature and V-III ratio employed, AlGaN-GaN, and GaN-InGaN electroluminescent devices have been realized but lack commercial quality. The AlGaN-GaN photodiodes by RMBE exhibited a maximum zero-bias responsivity of 0.12 A/W at 364 nm, which decreased by more than three orders of magnitude for wavelengths longer than 390 nm. A reverse bias of -10 V raised the responsivity to 0.15 A/W without any significant increase in noise. The noise equivalent noise power near zero bias is below the detection limit of the measurement setup. At a reverse bias of 28 V, the total noise equivalent power is 2.06×10^-11 W     

Stratified gas-liquid two-phase electrohydrodynamics in horizontalpipe flow

Stratified gas-liquid two-phase electrohydrodynamics in pipe flow has been studied experimentally and numerically. Experimental studies were conducted using 1.27 and 1.9×10^-2 m-inner diameter horizontal tubes with air-water two-phase flow for the range of gas surface velocity of 10±²-10 m/s, liquid surface velocity of 10^-2-2×10^-1 m/s, and applied voltage of 0-20 kV. Experimental results are analysed by an area-averaged two-fluid one-dimensional model. The results show that the effect of the applied electric field is significantly influenced by the flow regime transition boundaries between stratified smooth-to-wavy and stratified wavy-to-intermittent flow. However, the time-averaged void fraction was not observed to be significantly influenced by applied electric fields     

InGaN-based blue laser diodes

The continuous-wave (CW) operation of InGaN multiquantum-well (MQW) structure laser diodes (LDs) was demonstrated at room temperature (RT) with a lifetime of 100 h. The threshold current and the voltage of the LDs were 50 mA and 5 V, respectively. The threshold current density was 8.8 kA/cm². The carrier lifetime and the threshold carrier density were estimated to be 3.5 ns and 1.8×10²⁰/cm³, respectively. The Stokes shift of the energy difference between the absorption and the emission energy of the InGaN MQW LD's were 140 meV. Both spontaneous and stimulated emission of the LD's originated from this deep localized energy state which is equivalent to a quantum dot-like state. From the measurements of gain spectra and an external differential quantum efficiency dependence on the cavity length, the differential gain coefficient, the transparent carrier density, threshold gain and internal loss were estimated to be 5.8×10^-17 cm², 9.3×10 ¹⁹ cm^-3, 5200 cm^-1, and 43 cm^-1 respectively     

Nonequilibrium electron distributions and high-field electrontransport in an AlxGa1-xAs-based p-i-nnanostructure semiconductor-a picosecond Raman probe

Electron transport in an Al_xGa_1-xAs (x=0.3) based p-i-n nanostructure semiconductor under the application of an electric field has been studied at T=80 K by picosecond transient Raman spectroscopy. Single-particle excitations associated with spin-density fluctuations were used to directly measure electron distribution functions and drift velocities under various electric field intensities. Extremely nonequilibrium electron distributions were observed. Specifically, for an injected carrier density of n≅1×10¹⁸ cm^-3, a drift velocity V_d as high as 2.5×10⁷ cm/s was measured for an electric field intensity E=18 kV/cm. These experimental results are in good agreement with Ensemble Monte Carlo calculations     

1.047-μm Yb:Sr5(PO4)3F energystorage optical amplifier

The pumping and gain properties of Yb³⁺-doped Sr₅ (PO₄)₃F (Yb:S-FAP) are reported. Using a tunable, free running 900-nm Cr:LiSAF oscillator as a pump source for a Yb:S-FAP rod, the saturation fluence for pumping was measured to be 2.2 J/cm² based on either the spatial, temporal, or energy transmission properties of the Yb:S-FAP rod. The emission peak of Yb:S-FAP (1047.5 nm in air) is shown to overlap with that of Nd:YLiF₄ (Nd:YLF) to within 0.1 nm, rendering Yb:S-FAP suitable as an effective power amplifier for Nd:YLF oscillators. The small signal gain, under varying pumping conditions, was measured with a cw Nd:YLF probe laser. These measurements implied emission cross sections of 6.0×10^-20 and 1.5×10^-20 cm ² for π and σ polarized light. Respectively, which fall within the error limits of the previously reported values of 7.3×10^-20 and 1.4×10^-20 cm² for π and σ polarized light, obtained from purely spectroscopic techniques. The effects of radiation trapping on the emission lifetime have been quantified and have been shown to lead to emission lifetimes as long as 1.7 ms, for large optically dense crystals. This is substantially larger than the measured intrinsic lifetime of 1.10 ms. Yb:S-FAP crystal boules up to 25×25×175 mm in size, which were grown for the above experiments and were found to have acceptable loss characteristics (<~1%/cm) and adequately large laser damage thresholds at 1064 nm (~20 J/cm² at 3 ns). Overall, diode-pumped Yb:S-FAP amplifiers are anticipated to offer a viable means of amplifying 1.047-μm light, and may be particularly well suited to applications sensitive to overall laser efficiencies, such as inertial confinement fusion energy applications     

Design of a Compact Transmission Line Transformer for High Voltage Nanosecond Pulses

The area of pulsed-power technology covers a broad range of powers (up to 10¹⁴ W), voltages (up to 10⁶-10⁷ V), currents (as high as 10⁶ A or higher) and pulse durations (below 10^-8 s). State of the art systems have voltages up to a few hundred kilovolts at pulse lengths down to the nanosecond range. Special applications require extreme field strengths in the range of 1 GV/m. The design of a compact source, meeting the above requirement aims for 1 MV, 1 ns pulses. In this paper, we present a novel compact TLT (transmission line transformer). The TLT consists of 10 coaxial transmission lines which are connected in parallel at the input and in series at the output. To verify the theoretical analysis a model of the transmission line transformer has been simulated by a time domain electromagnetic field solver. An optimized transmission line transformer has been built and first measurements have been performed. The equivalent circuit model and the simulations agree with the experimental results. The effect of secondary mode suppression by means of ferrite has been investigated. Both simulations and experiments showed that ferromagnetic cores around each individual transmissions line in our design can be omitted.     

A self-consistent model of electron emission from metals

We present a model of electron emission from metals, which takes into account deviation of the electron distribution function from the Fermi equilibrium form inside the cathode under the emission effect. Using the Grad method electron distribution function, the emission boundary is expressed consecutively in terms of its hydrodynamic moments: temperature, average velocity, heat flux density. These hydrodynamic moments are caused by the emission itself and thus need a self-consistent determination. New easy-to-use equations for the emission current density, emission heat flux, and total energy distribution function of the emitted electrons are proposed. Consideration was made for a wide range of temperatures (⩽3500 K), field strengths (⩽1.5×10⁸ V/cm) and work function (3.0 to 4.5 eV) of the emitter. A considerable deviation from the Fowler-Nordheim (FN) theory was found at high current density (>10 ⁹ A/cm²)     

Image quality analysis for dual energy subtraction imaging with afemtosecond laser-based hard X-ray source

We present a study of image quality for dual energy subtraction imaging using an iodinated contrast agent and a femtosecond laser-based hard X-ray source. The INRS CPA laser (400 fs pulse focused on solid targets in a 3 μm spot at 4 × 10¹⁸ W cm^-2) was used to create a bright hard X-ray source (conversion efficiency of 10^-5 in the characteristic K_∝ line emission, 12 μm X-ray source diameter). A model of image quality has been developed and been benchmarked with specific experiments using specially made angiography phantoms     

Spectral analysis of the light emitted by streamers in hydrocarbonliquids

This paper presents the results of a spectroscopic study from 200 to 850 nm of the light emitted by streamers initiated in cyclohexane and n-pentane under step voltage in point-plane geometry. Experimental spectra of the light emitted by bush-like and filamentary streamers are composed of the H_α-Balmer line, the C₂ Swan band system and a background continuum. The diagnostic method we used for evaluating rotational and vibrational temperatures of excited C₂ in streamers was first tested on high-pressure corona discharges in nitrogen. For streamers in cyclohexane and n-pentane, it was impossible to determine the rotational temperature of C₂ and consequently the effective temperature of molecules in the streamer. Moreover, we found that vibrational populations of excited C₂ do not follow Boltzmann statistics. This indicates that excitation processes are due to chemical reactions. Electron densities deduced of the Stark broadening of H_α are in the range 4×10 ¹⁶ to 7×10¹⁶ cm^-3 for filamentary streamers and 2 to 6×10¹⁷ cm^-3 during the breakdown phase. For slow bush-like streamers, the electron density is not measurable     

The effect of electrode contamination, cleaning and conditioning onhigh-energy pulsed-power device performance

High-energy pulsed-power devices routinely use field strengths above those at which broad-area, cathode-initiated, HV vacuum-breakdown occur (>10⁷ to 3×10⁷ V/m). Examples include magnetically-insulated transmission lines and current convolutes, high-current-density electron and ion diodes, high-power microwave devices and cavities and other structures for electrostatic and RF accelerators. Energy deposited in anode surfaces may exceed anode plasma thermal-desorption creation thresholds on the time scale of the pulse. Stimulated desorption by electron or photon bombardment also can lead to plasma formation on electrode or insulator surfaces. Device performance is limited above these thresholds, particularly in pulse length and energy, by the formation and expansion of neutral and plasma layers formed primarily from electrode contaminants. In-situ conditioning techniques to modify and eliminate the contaminants through multiple HV pulses, low base pressures, RF discharge cleaning, heating, surface coatings and ion- and electron-beam surface treatment allow access to new regimes of performance through control of plasma formation and modification of the plasma properties. Experimental and theoretical progress from a variety of devices and small scale experiments with a variety of treatment methods are reviewed and recommendations given for future work     

基于中试平台的低低温电除尘器深度试验研究

基于50 000 m³/h实际烟气中试试验系统,采用常规采样枪+玻纤滤筒和一体化采样头+石英滤膜测定总尘,采用ELPI测定PM_2.5,采用自制的控制冷凝+异丙醇吸收系统测定SO₃,采用BDL型飞灰工况比电阻测试仪测定飞灰工况比电阻。试验结果表明,130℃、90℃、80℃时电除尘器出口烟尘浓度分别为11.7mg/m³、9.7 mg/m³、5.4 mg/m³,PM_2.5浓度分别为0.8 mg/m³、0.4 mg/m³、0.2 mg/m³,总尘及PM_2.5减排效果显著;电除尘器出口SO₃浓度分别为1.25 mg/m³、0.10 mg/m³、0.14 mg/m³,对应低低温电除尘系统的SO₃脱除效率分别为22.84%、96.15%、96.61%,低低温电除尘系统可脱除烟气中绝大部分SO₃;电除尘器入口飞灰工况比电阻分别为3.02×10¹³ Ω·cm、6.15×10¹² Ω·cm、5.24×10¹¹ Ω·cm。     

Dielectric recovery of a residual SF6 plasma between twoparallel plane electrodes

The present work is a theoretical investigation into the dielectric strength of a thin column of hot SF₆ gas left between two contacts after the thermal quenching of an arc at current zero in a modern HV gas-blast circuit breaker. Because of time rapid decay of arc temperature during current zero, this hot gas is still in a plasma state (referred to as the residual plasma) with sufficiently high charge density (both electrons and ions) although electrical conductivity is low. The dielectric recovery of such a residual plasma differs from that of an infinitely large, uniform plasma in two aspects. Firstly, the presence of space charge can distort severely the local electric field and can influence strongly the generation and loss of charged particles by ionization and chemical reactions. Secondly, due to the finite size of the plasma column, electrons diffuse in an ambipolar manner, thus enhancing the loss of charged particles in the plasma. In the present investigation, the gap length between the contacts (electrodes) is 1.0×10^-2 m and the diameter of the plasma column varies between 50×10^-6 and 500×10 ^-6 m. Distribution of the number density of charged species on the axis is obtained by solving their continuity equations using the method of MacCormack with Shuman filter. It is found that formation of space charge creates strong ionization layers close to the electrodes and that the whole column could deviate from electrical neutrality due to the drift of charged particles. The breakdown field of such a bounded plasma at atmospheric pressure or above is approximately equal to the critical field for an infinite plasma within a numerical uncertainty of 5%     

Field effects on ionic and excitonic quenching for heavy ions inliquid Ar

An increase in scintillation of up to 17% has been observed application of low electric fields (<6 kV/cm) for ¹H, ⁴He, ¹⁸O and ³⁶Ar ions of energy 1-35 MeV/u. This increase occurs at a field much lower than that required for the proportional region (10⁶ V/cm). The observed phenomenon is attributed to the recovery of quenching in the high excitation density region of the particle track by the external field     

VUV laser in the Lyman band of molecular hydrogen pumped by fstitanium-sapphire laser pulses

We report lasing at 160 nm in the Lyman band of molecular hydrogen. The laser is pumped by 200 mJ/150 fs pulses from the ATLAS titanium-sapphire laser at our institute. The pump pulses are focused at an angle of incidence of 60° onto a 9-cm-long gold target to a line focus, generating traveling-wave excitation. With 80 mbar of hydrogen in the target chamber we measure an average gain of 1.1 cm^-1 and achieve a total gain-length product of 10. The evaluation of the far-field pattern shows that the beam originates from a region with an electron density of 5×10¹⁵ cm^-3. A simple model of the H₂ laser is presented which explains the main part of our observations and supports a pump mechanism of photoelectron pumping     

Diagnostic dielectric spectroscopy methods applied to water-treedcable

Considerable effort has gone into developing polymer formulations and cable designs to minimize failures through water tree growth. However, diagnostic techniques still are required to enable the estimation of the level of damage present within a service cable. This paper reports on progress regarding the application of dielectric spectroscopy to cable diagnostics. A 40 kV, crosslinked polyethylene (XLPE) insulated coaxial cable was used as a model power cable. Sample lengths were immersed in a potassium chloride solution and some of these were subjected to AC electrical stress. After an 8 week duration, a high density of tress was found in the electrically stressed cable. Dielectric spectra have been measured for both sample types in the frequency range of 10^-5 to 10⁵ Hz. Insertion loss measurements were also carried out in the frequency range of 3×10 ⁵ to 3×10⁹ Hz. From both types of measurement, it was possible to distinguish between the cables containing water trees and those that were free from water tree structures. These approaches could therefore be developed in order to provide diagnostics for the detection of water tree damage in electrical power cables