Leader propagation speed and the final jump distance of 8 m long laboratory sparks

Vertical profile of the leader in long laboratory sparks was analyzed using high speed video photographs. Sparks were generated in an 8 m gap of sphere – plane electrodes with positive impulse voltage of 250/2500 μs wave form. The spatial resolution of the high speed frame camera was 19.6 mm per pixel with a time resolution of 50 μs. It was found that the average final jump distance of five sparks was about 4 m and the average electric field in the final jump region is about 5 × 10⁵ V/m the leader speed varies from 1.3 × 10⁴ m/s to 3.1 × 10⁴ m/s as it propagates toward the ground. The average leader speed of the leader was in the order of 1.8 × 10⁴ m/s. The observations show that there is a significant increase in the leader speed just before the final jump.     

Channel tortuosity of long laboratory sparks

Channel tortuosity of 50 cm long laboratory sparks were measured by analyzing a set of images taken by three cameras. The cameras were placed at a radial distance of 200 cm from the spark gap. The angle between any two cameras was 120°. The sparks were generated between a steel rod and a plane electrode. The distribution of the direction change of the channel was found to be Gaussian with a standard deviation of 15.3°. The average tortuosity of the channel defined as the mean absolute value of the direction change was 11.8±1.4°, which is smaller than the average tortuosity of natural lightning and close to the tortuosity of triggered lightning. The average tortuosity is dependent on the segment length used in calculating the direction change. A gradual increase in the average tortuosity (0.08°/cm) was seen when the sparks propagated towards the plane electrode.     

30 cm口径离子推力器磁场设计

为了对30 cm口径离子推力器的磁场设计提出合理建议,研究了四极磁场结构下,不同尺寸的磁极宽度和磁极间距对磁极表面磁场强度和放电室电子约束长度的影响,并利用Maxwell-3D磁场分析软件得到柱段和锥段永磁体分别呈30,60和90夹角时的放电室磁场强度分布,根据不同磁场强度计算了电子温度、离子密度以及电离率等推力器放电参数。结果表明,当推力器放电电压为30 V时,磁极长度设计为0.008 m且磁极间距取为0.12 m,电子约束路径大约为50 m;柱段和锥段永磁体分别呈30,60和90夹角时,放电室磁场等势线基本在0.002~0.005 T之间;永磁体夹角为60时磁场分布和磁空区相比30和90夹角更为合理,此时的电子温度约在2~6 eV,等离子体密度约在41017~81017 m-3,电子碰撞频率比率约在0.2~1.8范围内。     

30cm口径离子推力器磁场设计

为了对30cm口径离子推力器的磁场设计提出合理建议,研究了四极磁场结构下,不同尺寸的磁极宽度和磁极间距对磁极表面磁场强度和放电室电子约束长度的影响,并利用Maxwell-3D磁场分析软件得到柱段和锥段永磁体分别呈30°,60°和90°夹角时的放电室磁场强度分布,根据不同磁场强度计算了电子温度、离子密度以及电离率等推力器放电参数。结果表明,当推力器放电电压为30V时,磁极长度设计为0.008m且磁极间距取为0.12m,电子约束路径大约为50m;柱段和锥段永磁体分别呈30°,60°和90°夹角时,放电室磁场等势线基本在0.002~0.005T之间;永磁体夹角为60°时磁场分布和磁空区相比30°和90°夹角更为合理,此时的电子温度约在2~6eV,等离子体密度约在4×1017~8×1017 m-3,电子碰撞频率比率约在0.2~1.8范围内。     

ICLAS of HDO between 13,020 and 14,115 cm

The high resolution absorption spectrum of monodeuterated water, HDO, has been recorded by Intracavity Laser Absorption Spectroscopy (ICLAS) in the 13,020–14,115 cm⁻¹ region dominated by the 4ν₃ band. The achieved noise equivalent absorption (α_min10⁻⁹ cm⁻¹) allowed detecting transitions with line strengths as small as 2×10⁻²⁷ cm/molecule which is about 10 times lower than the smallest line intensities previously detected in the region.The rovibrational assignment of the spectrum was based on the results of the variational calculations of Schwenke and Partridge (SP) as well as recent calculations using a new potential energy surface performed by Voronin, Tolchenov and Tennyson (VTT). 2157 transitions involving 21 upper vibrational states were assigned to HD¹⁶O while only four bands were previously reported in the region. A set of 157 new energy levels could be derived. It includes rotational levels of several highly excited bending states, in particular the (0 11 0) pure bending state. For some states like the (1 0 3) and (0 2 3) Fermi dyad, effective Hamiltonian modelling was needed to establish the vibrational assignments of some rotational levels. VTT calculations were found to significantly improve the SP results, the rms deviation of the calculated and observed energies being decreased from 0.23 to 0.06 cm⁻¹.Finally, 79 transitions of the 4ν₃ band of the HD¹⁸O isotopologue were assigned, leading to the derivation of 48 levels, which are the most excited energy levels reported so far for this isotopologue.     

Numerical simulation of long laboratory sparks generated by positive switching impulses

A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252–1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic – L.T.E. – physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7–193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7–193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardières Group, Research on long gap discharges at Les Renardières, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.     

Absorption spectroscopy of ammonia between 6526 and 6538 cm−1

The spectral measurements of ammonia absorption lines from 6526 to 6538 cm^?1 have been performed at room temperature by using fiber-coupled distributed feedback (DFB) diode laser operating at 1.531 μm. As many as 152 lines of ammonia and its line intensities, self-broadening and air-broadening coefficients were obtained, which include many weak lines not previously reported. The 20 strongest lines were obtained using the traditional direct absorption spectroscopy technology with a 30 cm single-path cell and the other 132 lines were acquired using a compact system based on off-axis integrated-cavity output spectroscopy (OA-ICOS) with an effective optical path of 36.62 m.     

High-resolution synchrotron far-infrared spectroscopy of acrolein: The vibrational levels below 700 cm

The far-infrared spectrum of acrolein, CH₂CHCHO, is studied in the 100–360 cm⁻¹ region using continuum radiation from a synchrotron source. The combination of a very high resolution spectrometer, a long absorption path, and a low sample pressure, yields observed line widths of less than 0.0008 cm⁻¹. Observation of the ν₁₈ (157.9 cm⁻¹), and ν₁₃ (323.8 cm⁻¹) fundamental bands, together with six hot bands in the same regions, gives information on eight low-lying vibrational states of the molecule, including the Fermi and Coriolis interactions among them. Combining the present assignments with previous data on the ν₁₂ (564.34 cm⁻¹) and ν₁₇ (593.08 cm⁻¹) fundamental bands, all ten excited vibrational levels below 700 cm⁻¹ are analyzed in terms of one 1-state fit, two 2-state fits, and one 5-state fit.     

High-resolution infrared and theoretical study of four fundamental bands of gaseous 1,3,4-oxadiazole between 800 and 1600 cm

The Fourier transform infrared spectrum of gaseous 1,3,4-oxadiazole, C₂H₂N₂O, has been recorded in the 800–1600 cm⁻¹ wavenumber region with a resolution around 0.0030 cm⁻¹. The four fundamental bands ν₉(B₁; 852.5 cm⁻¹), ν₁₄(B₂; 1078.5 cm⁻¹), ν₄(A₁; 1092.6 cm⁻¹), and ν₂(A₁; 1534.9 cm⁻¹) are analyzed by the standard Watson model. Ground state rotational and quartic centrifugal distortion constants are obtained from a simultaneous fit of ground state combination differences from three of these bands and previous microwave transitions. Upper state spectroscopic constants are obtained for all four bands from single band fits using the Watson model. The ν₄ and ν₁₄ bands form a c-Coriolis interacting dyad, and the two bands are analyzed simultaneously by a model including first and second order Coriolis resonance using the ab initio predicted Coriolis coupling constant . An extended local resonance in ν₂ is explained as higher order b-Coriolis type resonance with ν₆ + ν₁₀, which is further perturbed globally by the ν₁₅ + ν₁₀ level. A fit of selected low-J transitions to a triad model including ν₂(A₁), ν₆ + ν₁₀(B₁), and ν₁₅ + ν₁₀(A₂) using an ab initio calculated Coriolis coupling constant is performed.The rotational constants, ground state quartic centrifugal distortion constants, anharmonic frequencies, and vibration–rotational constants (α-constants) predicted by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, are compared with the present experimental data, where there is generally good agreement. A complete set of anharmonic frequencies and α-constants for all fundamental levels of the molecule is given.     

Long RE123 coated conductors with high critical current over 500 A/cm by IBAD/PLD technique

We have developed long RE₁Ba₂Cu₃O_7?X (RE123) coated conductors with large current capacity by the ion beam assisted deposition (IBAD) and the pulsed laser deposition using hot wall heating (HW-PLD) technique. As a result, we could fabricate an 8 m-long Gd₁Ba₂Cu₃O_7?X (Gd123) coated wire with the minimum and maximum critical current (I_c) of 951 A/cm-w and 1003 A/cm-w at 77 K, 0 T, respectively, measured in 0.7 m-long sections by the standard 4-probe technique. Furthermore, we succeeded in preparation of over 600 m-long Gd123 coated wire with the uniform I_c distribution over 600 A/cm-w. It had average, maximum and minimum I_c of 665, 698, 609 A/cm-w, respectively. The n-values of the sample showed the maximum I_c and minimum I_c were 40 and 36, respectively. As a result, we set the new world record of I_c × L value as 374535 A m (= 609 A × 615 m). The in-field performance of this long wire was quite high as well; the minimum I_c exceeded 50 A/cm-w at 77 K, 3 T.     

g-factor of magnesium particles of diameter between 10 and 30 Å

ESR measurements of Mg particles smaller than about 40 Å show evidence for a quantum size effect on the g-value. The large g-shift of our bulk Mg has allowed us to follow the evolution of the g-factor as a function of particle size. The theoretical model of Myles and Buttet, which predicts a gradual change from the bulk g-value to the free electron g-value when the size decreases is in qualitative agreement with the experimental data.     

30 Years of sonochemistry links with China

Most scientists consider that sonochemistry became recognised as a discrete subject in the 1980’s – some 40 years ago which coincidentally is when my own interests in the subject began. This review briefly outlines how I first became involved in sonochemistry and then in its development. However its main theme is the way in which my links with China through sonochemistry have developed from their beginnings in 1990. This was the subject of my presentation at AOSS4 and involves a range of topics which started with the extraction of natural products and surface treatment but later expanded to include therapeutic ultrasound and environmental protection.     

High-resolution infrared spectroscopy of NNO and NNO in the 1200–3500 cm region

We present a continuation of our investigation of the second most abundant isotopic species of nitrous oxide, ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, in the infrared (IR). Our two previous contributions looked at the 3500–9000 cm⁻¹ region for ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O, respectively, in the 3500–9000 cm⁻¹ region. The use of highly enriched isotopologue samples in this study allowed us to go further into the IR, down to 1200 cm⁻¹. A total of 2 2742 transitions have been assigned based on the effective Hamiltonian model, with 108 of them being reported here for the first time. Rovibrational analyses of 98, 101, 8, 3, 6, 1 and 1 bands for the ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁵N¹⁵N¹⁶O, ¹⁴N¹⁵N¹⁸O, ¹⁵N¹⁴N¹⁸O, ¹⁴N¹⁵N¹⁷O and ¹⁵N¹⁴N¹⁷O isotopologues, respectively, were also performed.     

The high-resolution infrared spectrum of isoxazole vapor between 800 and 1700 cm

The Fourier transform gas-phase IR spectrum of isoxazole, C₃H₃NO, between 550 and 1700 cm⁻¹ was measured with a resolution of ca. 0.003 cm⁻¹. Ten fundamental bands in the region 800-1700 cm⁻¹ have been analyzed by the Watson Hamiltonian model to yield upper state spectroscopic constants. A number of local resonances have been identified in the bands and explained qualitatively, and the unobserved ν₁₄(A″) fundamental band has been located at 897.5(5) cm⁻¹ from its perturbation effects on the neighboring fundamentals.     

The high-resolution infrared spectrum of pyrrole between 900 and 1500 cm revisited

The Fourier transform gas-phase infrared spectrum of pyrrole, C₄H₅N, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 900-1500 cm⁻¹ spectral region. Four fundamental bands, ν₈(A₁; 1016.9 cm⁻¹), ν₂₃(B₂; 1049.1 cm⁻¹), ν₇(A₁; 1074.6 cm⁻¹), ν₂₀(B₂; 1424.4 cm⁻¹) and the overtone band 2ν₁₆(A₁; 962.7 cm⁻¹) have been analysed using the Watson model. The ν₈ and 2ν₁₆ bands are unperturbed; the ν₇ and ν₂₃ bands are locally perturbed, while the ν₂₀ band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and I^r-representation as well as A-reduction and III^r-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data.     

The hot bands of silane between 2120 and 2270 cm

The infrared spectrum of the SiH₄ molecule has been recorded between 2040 and 2320 cm⁻¹ using the high-resolution Fourier interferometer of the Laboratoire de Photophysique Moléculaire (Orsay, France). The resolution was 5.4 × 10⁻³ cm⁻¹. In this region, many lines were previously analyzed and assigned to the ν₁/ν₃ stretching dyad of ²⁸SiH₄, ²⁹SiH₄, and ³⁰SiH₄ molecules [J. Mol. Spectrosc. 143 (1990) 35]. However, several lines in the spectrum were not assigned. The results obtained in our previous study [J. Mol. Spectrosc. 197 (1999) 307] of the infrared spectrum of ²⁸SiH₄, in the bending-stretching tetrad region at 3100 cm⁻¹, enabled us to assign 204 of the observed transitions to hot bands (the ν₁ + ν₂/ν₁ + ν₄/ν₂ + ν₃/ν₃ + ν₄ bending-stretching tetrad minus the ν₂/ν₄ bending dyad). These transitions were used to refine the set of the Hamiltonian parameters of the bending-stretching tetrad. The analysis is performed using the tensorial formalism developed in Dijon for tetrahedral molecules and implemented in the STDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html).     

长周期光纤光栅谐振波长与曝光量的变化关系

利用波动干涉理论推导了长周期光纤光栅的光栅方程. 利用色心模型和Kramers-Kronig原理，得到了长周期光纤光栅的中心谐振波长与曝光量的变化关系的理论公式，并进行了实验研 究. 理论和实验结果都表明，长周期光纤光栅的中心谐振波长与曝光量的关系按多项e负指 数之和规律变化，其变化率受到模板占空比的控制；另外，长周期光纤光栅的中心谐振波长 与模板占空比成反比关系. 关键词： 长周期光纤光栅 谐振波长 模板占空比     

N(2)O weak lines observed between 3900 and 4050 cm from long path absorption spectra

Previously unobserved nitrous oxide transitions around 2.5 μm are measured by intracavity laser absorption spectroscopy (ICLAS) analyzed by time-resolved Fourier transform (TRFT) spectrometer. With an accuracy of the order of 10⁻³ cm⁻¹, measured positions of 1637 assigned weak transitions are provided. They belong to 42 vibrational transitions, among which 33 are observed for the first time. These data are believed to be useful in particular to monitoring atmosphere purposes.     

Fourier transform measurements of SO2 absorption cross sections: II.: Temperature dependence in the 29 000–44 000 cm (227–345 nm) region

This paper is the second of a series that reports results on the measurements of the absorption cross section of SO₂ in the UV/visible region at high resolution and that investigates high temperatures in support to planetary applications. Absorption cross sections of SO₂ have been obtained in the 29 000–44 000 cm⁻¹ spectral range (227–345 nm) with a Fourier transform spectrometer at a resolution of 2 cm⁻¹ (0.4500 cm MOPD and boxcar apodisation). Pure SO₂ samples were used and measurements were performed at room temperature (298 K) as well as at 318, 338 and 358 K. Temperature effects in this spectral region are investigated and are favorably compared to existing studies in the literature. Comparison of the absorption cross section at room temperature shows good agreement in intensity with most of the literature data, but shows that most of the latter suffer from inaccurate wavelength scale definition. Moreover, literature data are often given only on restricted spectral intervals. Combined with the data described in the first part of this series of papers on SO₂, this new data set offers the considerable advantage of covering the large spectral interval extending from 24 000 to 44 000 cm⁻¹ (227–420 nm), at the four temperatures investigated.     

Evaluation of probe size in STEM imaging at 30 and 60 kV

In order to estimate the probe size on the specimen surface in a newly developed low-acceleration-voltage (30–60 kV) atomic-resolution scanning transmission electron microscopy (STEM), we compared the intensity profiles of experimentally obtained annular dark field (ADF)-STEM images of Si–Si dumbbells and those of images simulated using a multislice method which takes chromatic aberration into account. However, the simulated ADF images at 30 and 60 kV were found not to match the corresponding experimental images. Subsequently, the simulated images were convolved with probe functions (normal distributions) of different widths until a good match was obtained between the images. This allowed the probe shapes corresponding to the experimental conditions to be determined. ADF-STEM images with chromatic aberration could then be calculated by an incoherent superposition of these probe functions over a range of energies. The full widths at half maximum for the probe functions were estimated to be 99.2 pm for 30 kV and 92.8 pm for 60 kV. The D59 diameters were calculated to be 154.0 pm for 30 kV and 127.8 pm for 60 kV. This means that the 30-kV probe has a larger tail than the 60-kV probe.