共查询到20条相似文献,搜索用时 984 毫秒
1.
We consider the technique for obtaining electrodynamic disperse suspension of metal (Al, W, Cu) and dielectric (semiconductor) particles (SiO2, Al2O3, CuO, Cu2O) and its evaporation with the help of a diffusive electric discharge. The time dependences of current and integrated luminescence intensity in a pulsed electric discharge in a tube containing a film of a substance (Cu) of the electrodynamic disperse suspension are measured. 相似文献
2.
S. T. Surzhikov 《Technical Physics》2017,62(8):1177-1188
The drift–diffusion model of a Penning discharge in molecular hydrogen under pressures of about 1 Torr with regard to the external electric circuit has been proposed. A two-dimensional axially symmetric discharge geometry with a cylindrical anode and flat cathodes perpendicular to the symmetry axis has been investigated. An external magnetic field of about 0.1 T is applied in the axial direction. Using the developed drift–diffusion model, the electrodynamic structure of a Penning discharge in the pressure range of 0.5–5 Torr at a current source voltage of 200–500 V is numerically simulated. The evolution of the discharge electrodynamic structure upon pressure variations in zero magnetic field (the classical glow discharge mode) and in the axial magnetic field (Penning discharge) has been studied using numerical experiments. The theoretical predictions of the existence of an averaged electron and ion motion in a Penning discharge both in the axial and radial directions and in the azimuthal direction have been confirmed by the calculations. 相似文献
3.
The rotational (TR) and vibrational (Tv) temperatures of N2 molecules were measured in a high‐pressure cylindrical dielectric barrier discharge (C‐DBD) source in Ne with trace amounts (0.02 %) of N2 and dry air excited by radio‐frequency (rf) power. Both TR and Tv of the N2 molecules in the C 3Πu state were determined from an emission spectroscopic analysis the 2nd positive system (C 3Πu → B3Πg). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both TR and Tv also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N2 to the Ne in the discharge resulted in higher TR and Tv values and in a different pressure dependence of the rotational and vibrational temperatures. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
A self-consistent electrodynamic model based on analytic relations, which makes it possible to describe the electromagnetic
wave scattering from a thin (compared to the wavelength) plasma channel, is proposed. The results of experimental investigation
of the dynamics of the signal scattered by a single channel in air in the pressure range P
0 = 104−1.4 × 104 Pa are presented. The results are analyzed in terms of the electrodynamic model. 相似文献
5.
G. N. Zvereva 《Optics and Spectroscopy》2010,109(3):468-474
We calculate the concentration of plasma and gas-temperature components in a contracted filament of a glow capillary discharge
(R = 0.75 mm) in xenon for pressures of P = 100 and 400 Torr and currents of I = 6–15 mA for cases of with and without cryogenic cooling of the discharge. We find that the gas temperature in the channel
of the glow discharge has a value of 1000–2000 K, the concentration of xenon excimers attains a maximum at the boundary of
the filament with a value of 1010–1011 cm−3, and the efficiency of electric energy transformation into excimer radiation energy has a value of 0.1–5%. 相似文献
6.
The results of investigation of the energy and spectral characteristics of a He-Ne laser (λrad=1.52 μm) with transverse microwave discharge are presented. A single-frequency generation mode at a pressure above 6.0 mm
Hg was obtained with radiation power 7.0 mW and low level of amplitude noise (10−5 Hz−1/2). Active stabilization of the laser power was carried out, which allows reduction in radiation intensity fluctuations from
1–5 to 0.1 %.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 127–128, January–February, 2000. 相似文献
7.
E. Coetsee J. J. Terblans H. C. Swart 《Applied Physics A: Materials Science & Processing》2010,101(4):645-650
Y2SiO5:Ce phosphor thin films were grown onto Si(100) substrates with pulsed laser deposition (PLD) using a 248-nm KrF excimer laser.
Process parameters were varied during the growth process and the effect on the surface morphology and cathodoluminescence
(CL) was analysed. The process parameters that were changed included the following: gas pressure (vacuum (5×10−6 Torr), 1×1−2 Torr and 1 Torr O2), different gas species (O2, Ar and N2 at a pressure of 455 mTorr), laser fluence (1.6±0.1 J cm−2 and 3.0±0.3 J cm−2) and substrate temperature (400 and 600°C). The surface morphology was investigated with atomic force microscopy (AFM). The
morphology of the thin films ablated in vacuum and 10 mTorr ambient O2 showed more or less the same trend. An increase in the pressure to 1 Torr O2, however, showed a definite increase in deposited particle sizes. Ablation in N2 gas resulted in small particles of 20 nm in diameter and ablation in O2 gas produced bigger particles of 20, 30 and 40 nm as well as an agglomeration of these particles into bigger size clusters
of 80 to 100 nm. Ablation in Ar gas led to particle sizes of 30 nm and the particles were much more spherically defined and
evenly distributed on the surface. The higher fluence deposition led to bigger particle and grain sizes as well as thicker
layers with respect to the lower fluence. The particle sizes of the higher fluence vary mainly between 130 and 140 nm and
the lower fluence sizes vary between 50 and 60 nm. The higher fluence particles consist of smaller particles ranging from
5 to 30 nm as measured with AFM. The surface structure of the thin film ablated at 400°C substrate temperature is less compact
(lesser agglomeration of particles than at 600°C). The increase in substrate temperature definitely resulted in a rougher
surface layer. CL was measured to investigate the effect of the surface morphology on the luminescent intensities. The increased
O2 ambient (1 Torr) resulted in a higher CL intensity compared to the thin films ablated in vacuum. The thin film ablated in
Ar gas showed a much higher CL intensity than the other thin films. Ablation at a high fluence resulted in a higher CL intensity.
The higher substrate temperature resulted in better CL intensities. The more spherically shaped particles and rougher surface
led to increase CL intensities. 相似文献
8.
O. A. Emel’yanov 《Technical Physics》2008,53(7):866-874
The pulsed electrodynamic fracture of thin (10–50 nm) aluminum films deposited onto polymer substrates is experimentally studied.
The fracture of the films manifests itself in the form of discontinuity (crack) channel growth across an applied electric
field. The roles of a magnetic pressure, thermomechanical stresses, and Joule heating at the tip of a growing crack are analyzed
at high current densities (∼1010−1012 A/m2). In contrast to the results well known for the electrodynamic fracture of bulk metallic samples, the first two factors in
the films are insignificant. The effect of the electric explosion of the crack tip is found to play a key role in the beginning
of fracture. 相似文献
9.
We present a system for molecular spectroscopy using a broadband mid-infrared laser with near-infrared detection. Difference
frequency generation of a Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from 2100–3700 cm−1 (2.7–4.7 μm) with average power up to 40 mW. The MIR spectrum was upconverted to near-infrared wavelengths for broadband
detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of
240 cm−1 (7.2 THz) with 0.048 cm−1 (1.4 GHz) resolution, and absolute frequency scale uncertainty was better than 0.005 cm−1 (150 MHz). The minimum detectable absorption coefficient per spectral element was determined to be 4.4×10−7 cm−1 from measurements in low pressure CH4, leading to a projected detection limit of 2 parts-per-billion of methane in pure nitrogen. In a natural atmospheric sample,
the methane detection limit was found to be 30 parts-per-billion. The spectral range, resolution, and frequency accuracy of
this system show promise for determination of trace concentrations in gas mixtures containing both narrow and broad overlapping
spectral features, and we demonstrate this in measurements of air and solvent samples. 相似文献
10.
Using the technique of helicity amplitudes, the electromagnetic process e
+
e
− → μ+μ− is theoretically investigated in the one-photon approximation. The structure of the triplet states of the final (μ+μ−) system is analyzed. It is shown that in the case of unpolarized electron and positron the finalmuons are also unpolarized,
but their spins are strongly correlated. Explicit expressions for the components of the correlation tensor of the final (μ+μ−) system are derived. The formula for the angular correlation at the decays of final muons μ+ and μ−, produced in the process e
+
e
− → μ+μ−, is obtained. It is demonstrated that spin correlations of muons in the process of electron-positron pair annihilation have
the purely quantum character, since one of the incoherence inequalities for the correlation-tensor components is always violated.
The additional contribution of the weak interaction of lepton neutral currents through the virtual Z
0 boson is considered; it is established that, taking into account the weak interaction, the qualitative character of the muon
spin correlations does not change.
The text was submitted by the authors in English. 相似文献
11.
Using the technique of helicity amplitudes, the electromagnetic process e
+
e
− → μ+μ− is theoretically investigated in the one-photon approximation. The structure of the triplet states of the final (μ+μ−) system is analyzed. It is shown that in the case of unpolarized electron and positron the final muons are also unpolarized,
but their spins are strongly correlated. Explicit expressions for the components of the correlation tensor of the final (μ+μ−) system are derived. The formula for the angular correlation at the decays of final muons μ+ and μ−, produced in the process e
+
e
− → μ+μ−, is obtained. It is demonstrated that spin correlations of muons in the process of electron-positron pair annihilation have
the purely quantum character, since one of the incoherence inequalities for the correlation tensor components is always violated.
The additional contribution of the weak interaction of lepton neutral currents through the virtual Z
0 boson is considered; it is established that, taking into account the weak interaction, the qualitative character of the muon
spin correlations does not change. 相似文献
12.
R. A. Akhmedzhanov A. L. Vikharev A. M. Gorbachev O. A. Ivanov A. L. Kolysko 《Technical Physics》1997,42(3):260-268
Results are presented from an investigation of the dynamics of ozone formation in a freely localized discharge generated by
a periodic train of 3-cm nanostructured microwave pulses in oxygen and air at a pressure p=3–30 Torr. Conditions for the efficient generation of ozone in air with the minimum production of nitrogen oxides are demonstrated
experimentally. It is shown that when the microwave pulse repetition frequency is high, heating of the gas and the buildup
of nitrogen oxides in the discharge in air reduce the ozone formation efficiency while under prolonged exposure the ozone
formed initially is destroyed. The energy cost of forming ozone in oxygen and air is determined as a function of the microwave
pulse length and repetition frequency and the gas pressure. The lowest energy cost of forming a single ozone molecule in these
experiments is 16 eV per molecule for a discharge in air and 4 eV per molecule in oxygen. It was observed that circulating
the gas through the discharge zone enhances th ozone formation efficiency. It is shown that there are optimal conditions for
ozone formation as a function of the reduced electric field in the plasma.
Zh. Tekh. Fiz. 67, 9–18 (March 1997) 相似文献
13.
Fast particles from laser-induced processes in ultra-dense deuterium D(−1) are studied. The time of flight shows very fast
particles, with energy above MeV. Such particles can be delayed or prevented from reaching the detector by inserting thin
or thick metal foils in the beam to the detector. This distinguishes them from energetic photons which pass through the foils
without delays. Due to the ultra-high density in D(−1) of 1029cm−3, the range for 3 MeV protons in this material is only 700 pm. The fast particles ejected and detected are thus mainly deuterons
and protons from the surface of the material. MeV particles are expected to signify fusion processes D+D in the material.
The number of fast particles released is determined using the known gain of the photomultiplier. The total number of fast
particles formed, assuming isotropic emission, is less than 109 per laser pulse at < 200 mJ pulse energy and intensity 1012W cm−2. A fast shockwave with 30keV u−1 kinetic energy is observed. 相似文献
14.
Photoacoustic spectroscopy for trace gas detection with cryogenic and room-temperature continuous-wave quantum cascade lasers 总被引:1,自引:0,他引:1
Virginie Zeninari Agnès Grossel Lilian Joly Thomas Decarpenterie Bruno Grouiez Bernard Bonno Bertrand Parvitte 《Central European Journal of Physics》2010,8(2):194-201
The main characteristics that a sensor must possess for trace gas detection and pollution monitoring are high sensitivity,
high selectivity and the capability to perform in situ measurements. The photacoustic Helmholtz sensor developed in Reims,
used in conjunction with powerful Quantum Cascade Lasers (QCLs), fulfils all these requirements. The best cell response is
# 1200 V W−1 cm and the corresponding ultimate sensitivity is j 3.3 × 10−10 W cm−11 Hz−11/2. This efficient sensor is used with mid-infrared QCLs from Alpes Lasers to reach the strong fundamental absorption bands
of some atmospheric gases. A first cryogenic QCL emitting at 7.9 μm demonstrates the detection of methane in air with a detection
limit of 3 ppb. A detection limit of 20 ppb of NO in air is demonstrated using another cryogenic QCL emitting in the 5.4 μm
region. Real in-situ measurements can be achieved only with room-temperature QCLs. A room-temperature QCL emitting in the
7.9 μm region demonstrates the simultaneous detection of methane and nitrous oxide in air (17 and 7 ppb detection limit, respectively).
All these reliable measurements allow the estimated detection limit for various atmospheric gases using quantum cascade lasers
to be obtained. Each gas absorbing in the infrared may be detected at a detection limit in the ppb or low-ppb range. 相似文献
15.
U. Yusupaliev 《Bulletin of the Lebedev Physics Institute》2009,36(8):245-251
Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10−6 is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton)
at atmospheric pressure at a distance of ∼1.2–2.5 cm from the discharge boundary. It was shown that the structure of such
discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized
and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of
gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal
energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity. 相似文献
16.
QEPAS spectrophones: design, optimization, and performance 总被引:2,自引:0,他引:2
L. Dong A. A. Kosterev D. Thomazy F. K. Tittel 《Applied physics. B, Lasers and optics》2010,100(3):627-635
The impact of design parameters of a spectrophone for quartz-enhanced photoacoustic spectroscopy on its performance was investigated.
The microresonator of spectrophone is optimized based on an experimental study. The results show that a 4.4 mm-long tube with
0.6 mm inner diameter yields the highest signal-to-noise ratio, which is ∼30 times higher than that of a bare QTF at gas pressures
between 400 and 800 Torr. The optimized configuration demonstrates a normalized noise-equivalent absorption coefficient (1σ) of 3.3×10−9 cm−1W/Hz1/2 for C2H2 detection at atmospheric pressure. The effect of the changing carrier gas composition is studied. A side-by-side sensitivity
comparison between QEPAS and conventional photoacoustic spectroscopy technique is reported. 相似文献
17.
Trippa G Trine S Ventikos Y Coussios CC 《The Journal of the Acoustical Society of America》2012,131(5):3627-3637
An implementation of a quarter-wavelength standing wave separator that exploits an air drum to achieve the pressure node is presented and characterized experimentally. The air drum configuration was implemented and tested in a set-up with a 40 kHz transducer immersed in a water tank with the quarter-wavelength gap being approximately 9 mm wide. Injection of suspensions of 5 μm and 45 μm diameter polystyrene particles at flow rates of 30 ml/h and 60 ml/h was studied and particle deflection towards the pressure node at the air drum surface was observed for a range of acoustic pressures. Computational results on single particle trajectories show good agreement with the experimental findings for the 45 μm particles, but not for the 5 μm particles. These were considered to behave as aggregates of higher effective dimension, due to their much higher number density relative to the 45 μm particles in the suspensions used. The set-up developed in this study includes a robust method for achieving a pressure node in a quarter-wavelength system and can represent the first step toward the development of an alternative separator configuration in respect to small channel MHz range operated systems for the manipulation of particles streams. 相似文献
18.
19.
We present observations of sub-micron- to micron-sized particles generated by high fluence (≈2 J/cm2) 248-nm laser ablation of pressed polytetrafluorethylene (PTFE) targets in air at atmospheric pressure. The original target
material was hydrostatically compressed ≈7 μm PTFE powder, sintered at 275 °C. Collected ejecta due to laser irradiation consists
of four basic particle morphologies ranging from small particles 50–200 nm in diameter to larger particles ≈10 μm in diameter.
Many particles formed in air carry electric charge. Using charged electrodes we are able to collect charged particles to determine
relative numbers of ± charge. We observe roughly equal numbers of positively and negatively charged particles except for the
largest particles which were predominantly negative. For a range of particle sizes we are able to measure the sign and magnitude
of this charge with a Millikan-oil-drop technique and determine surface charge densities. The implications of these observations
with respect to pulsed laser deposition of PTFE thin films and coatings are discussed.
Received: 15 January 1999 / Accepted: 18 January 1999 / Published online: 7 April 1999 相似文献
20.
Summary An infra-red detector produced by the Elettronica SPA Company for the European Space Agency to be used in the Earth surface
mapping from aircraft has been tested in our laboratory. We present the characteristics of the detector working in the spectral
range (1÷2.5) μm. The acquisition system and the electronics are discussed and a detailed study of all the noise sources is
presented; the measured NEP is 3.2·10−14W Hz−1/2 at a temperature of 108 K.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献