Vol. 49, No. 12 (2000)
2000-06-20
GENERAL
2000, 49 (12): 2315-2319.
doi: 10.7498/aps.49.2315
Abstract +
Utilizing double-wave theory, we describe the system of two-dimensional q-deform ed oscillators. The results show that the movement of particles is nonlinear.At the same time,when q→1 the theory reduces to the common two-dimensional harmoni c oscillator theory.
2000, 49 (12): 2320-2327.
doi: 10.7498/aps.49.2320
Abstract +
Phase synchronization in coupled chaotic systems is an interesting topic in recent years on nonlinear dynamics. Phase synchronization implies an ordered behavio r embedded in chaotic motions. Recent progress on phase synchronizations is revi ewed.The synchronization process is exhibited by applying the bifurcation tree.T he synchronization process is identified as transitions from high-to low-dimensional chaos.An alternative phase locking among various rational ratios is found. Chaos suppression and the restoration to chaos synchronization via period-doubli ng is studied.It is found that asymmetric coupling can greatly enhance the phase synchronization of coupled oscillators.
2000, 49 (12): 2328-2332.
doi: 10.7498/aps.49.2328
Abstract +
We present a method for the computation of Lyapunov exponents without reorthogon alization. In the low dimension of system(n<5) ,the equations needed in present algorithm is less than those in normal methods such as QR, SVD etc. This method is applicable to both discrete systems and continuous systems, and is still valid when the Lyapunov spectra is degenerate. Numerical analysis to Lorenz dynamical system indicates that the method converges quickly and steadly for arbitrary nonzero initial state.
2000, 49 (12): 2333-2339.
doi: 10.7498/aps.49.2333
Abstract +
Based on the deterministic and nonlinear characterization of the chaotic signals, a new reduced parameter nonlinear adaptive filter is proposed to make adaptive predictions of chaotic time series. The sigmoid function is introduced to nonlinear predictive filter for reducing unknown parameters of the second-order Volterra filters. A reduced parameter nonlinear adaptive filtering prediction schemeis suggested in order to track current chaotic trajectory by using precedent predictive error for adjusting filter parameters rather than approximating global o r local map of chaotic series. Experimental results show that this reduced param eter nonlinear adaptive filter, which is only trained with 50 samples and 20 ite rations, can be successfully used to make one-step and multi-step predictions of chaotic time series.
ATOMIC AND MOLECULAR PHYSICS
2000, 49 (12): 2340-2346.
doi: 10.7498/aps.49.2340
Abstract +
Based on ArS2 analysis potential function, which was calculated using ab initio MP2/6-31+G method and multi-body expansion theory, the dynamic proces s has been studied. The results indicated that the restraint of Ar and S2 due to physical adsorption, and the reaction of Ar and S2 is pri marily non-elasticity collision at a serial set of energies. Through analysis of inelastic collision products, it is shown that Ar atom can excite S2 (Ｘ3Σ－g) to S2(B3Σ－u) gradually.
2000, 49 (12): 2347-2351.
doi: 10.7498/aps.49.2347
Abstract +
The theoretical study on PuHn+(n=1,2,3) using density functional meth od(B3LYP) shows that PuH+ and PuH2+ can be stable and PuH3+(7Σ-) cannot be stable. Electronic ground sta tes are X7Σ-(PuH+) and X8Σ-(PuH2+),and their force constants and spectroscopic data have bee n worked out.
2000, 49 (12): 2352-2356.
doi: 10.7498/aps.49.2352
Abstract +
The studies on the potential energy curves of the electronic excited states 21Πg, 43Πg, b3Πu of Na2, the states a3Σ+u, 21 Πg, B1Πu, A1Σ+u of K2 and the state 11Πg of Cs 2 molecules by using the energy consistent method (ECM) are reported here . The results show that the present ECM potentials agree very well with the know n Rydberg-Klein-Rees data or the inverted perturbation approach data, and that they are much better than other analytical potentials such as the Morse and the Huxley-Murrell-Sorbie potentials for the electronic excited states of alkali dia tomic molecules.
CLASSICAL AREA OF PHENOMENOLOGY
2000, 49 (12): 2357-2368.
doi: 10.7498/aps.49.2357
Abstract +
Conventional X-ray radiography is based on absorption contrast and assumes geome trical optics. An “in-line” method and theory of hard X-ray phase-contrast ima ging were introduced. The differences between the conventional X-ray absorption contrast image and the phase contrast image were distinguished by using radiogra phs of biological samples. The effect of X-ray source size on the image contrast was investigated. Moreover, the key parameters of absorption contrast image and phase contrast image were simulated theoretically and discussed.
2000, 49 (12): 2369-2373.
doi: 10.7498/aps.49.2369
Abstract +
A model for magnetically confined discharge carbon monoxide laser is presented. Electron energy distribution function, the influence of the magnetic field on electron impact excitation, the vibration-to-translation and vibration-to-vibratio n excitation rates of CO molecule are discussed. The vibrational-state populatio ns of CO molecule and small-signal gain with magnetic field are calculated and s tudied also. After a magnetic field has been added， there appears a hole in the distribution of the vibrational-state populations of CO molecule and the small- signal gain is higher in this region.
2000, 49 (12): 2374-2377.
doi: 10.7498/aps.49.2374
Abstract +
A novel semiconductor laser structure is put forward to resolve the major difficulties of high power laser diodes. In this structure, several active regions are cascaded by tunnel junctions to form a large optical cavity and to achieve super high efficiency. This structure can solve the problems of catastrophic optical damage of facet, thermal damage and poor light beam quality effectively. Low-pressure metalorganic chemical vapor deposition method is adopted to grow the novel semiconductor laser structures, which are composed of Si:GaAs/C:GaAs tunnel junctions, GaAs/InGaAs strain quantum well active regions. External differential q uantum efficiency as high as 2.2 and light power output of 2.5W per facet (under 2A drive current) are achieved from an uncoated novel laser device with three a ctive regions.
2000, 49 (12): 2378-2382.
doi: 10.7498/aps.49.2378
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The analysis and calculation of the compensation for the phase mismatch of the f requency-doubling using the frequency space chirp introduced from prisms are mad e. The result shows that suitable lens can compensate the phase mismatch in a ce rtain extent resulting from wide femtosecond spectrum when the spectrum is space chirped. By means of this method, the experiment of second harmonic generatio n is carried out using a home-made femtosecond KLM Ti:sapphire laser and BBO cry stal. The conversion efficiency of SHG is 63%. The average output power of blue light is 320mW. The central wavelength is 420nm. The spectrum bandwidth is 5.5nm . It can sustain the pulse width of 33.6fs. The tuning range of blue light is 40 4-420nm，when the femtosecond Ti:sapphire optical pulse is tuned using the prism s in the cavity.
2000, 49 (12): 2383-2388.
doi: 10.7498/aps.49.2383
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The characteristics of smoothing quasi-far-field speckles using a zero-correlati on phase plate are simulated numerically in general cases.A comparison between t he speckles with a zero-correlation phase plate and those with a random phase pl ate (in combination with a two-element polarization control plate) is given.The zero-correlation phase plates are designed for the perfect near-field irradiatio n and the far-field application.However,the results show that the quasi-far-fiel d speckle intensity modulations using a zero-correlation phase plate are much sm aller than those with a random phase plate under the case of defocus distance le ss than 0.002355λf2/d2 and the incident field with random variations of amplitude (≤10%) and phase (≤λ/20).Therefore,the zero-correlat ion phase plates can still smooth quasi-far-field speckles effectively.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2000, 49 (12): 2389-2393.
doi: 10.7498/aps.49.2389
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The X-ray emission spectra from highly stripped plasma of gold has been observed by focusing a Nd-glass frequency-tripled laser beam onto the surface of the gol d dot at the XINGGUANG Ⅱ laser facilities. The spectra of gold ions in the rang e of 0.0003nm—0.0004nm was recorded using the plate PET (2d=0.8742nm) crystal spectrometer. The code of average energy of relativistic subarrays was built on the basis of the code MCDF (Multi-Configuration-Dirac-Fock). Using the spin-orbi t-split-arrays (SOSA) formalism, mean wavelengths and full widths at half height of isolated peaks of subarrays of lower charged gold ions, isoelectronic with C u,Zn,Ga and Ge, was calculated. Twenty-six lines are interpreted, they pertain mainly to transitions of 3d-nf (n=5,6, 7) of gold ions from Ni-like to As-like. These results of experiment and calculation have important application in pla sma diagnostics and examination of high Z elemental atomic structure calculation .
2000, 49 (12): 2394-2398.
doi: 10.7498/aps.49.2394
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General but simplified dispersion relation for the lower hybrid wave in low hybrid current drive (LHCD) regime is derived by expanding technique through the small parameter δ=(ω2pe/ω2)-1.The up ward and the downward shifts of the parallel refractive index,and the relevant m ode conversion due to toroidal effects (such as the R-1 dependence of the toroidal magnetic field and the Shafnanov shift of magnetic surfaces) are d iscussed.A sufficient condition for the wave that is possible to penetrate into the inner region of the plasma column is obtained,which has a relationship with the experimentally observed LHCD density limit.A scaling about the critical dens ity is found to be nec∝f4/3Ｂ2/3Ａ4/3,with f,B,A being the wave frequency,the magnetic field and the aspect ratio,r espectively.There exists a quite good agreement between theory and experiments.T he simplified equations for wave propagation can be used as a subroutine in a co mplete LHCD code.
2000, 49 (12): 2399-2403.
doi: 10.7498/aps.49.2399
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The one-dimensional electron density perturbation is derived by using the cold f luid equation, Poisson's equation and the continuity equation, which is generated by a driving laser pulse propagating through a tenuous plasma. The upshifting of the frequency of a trailing pulse induced by density perturbation is studied by using optical metric. The results show that it is possible that the photon wi ll gain energy from the wake field when assuming photon number to be conserved, i.e., the photon will be accelerated.
2000, 49 (12): 2404-2407.
doi: 10.7498/aps.49.2404
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A theoretical model for studying the heavy particle transport in a cathode sheath is developed.The velocity distribution functions near a planar cathode are deduced.The expressions for neutral and ionic fluxes of neutral and ionic particles near a planar cathode are also obtained.The result predicated by the theoretica l model is in accordance Monte Carlo simulation.
2000, 49 (12): 2408-2413.
doi: 10.7498/aps.49.2408
Abstract +
X-ray spectra, angular distributions of X-ray fluxes and evolutions of X-ray spe ctra from the front and the rear of gold foil target with different thickness ha ve been measured on “Xingguang” laser facility, in which the gold foil targets were irradiated by smoothing 1.053μm laser beam . The processes of laser and r adiation ablation to gold foil have been studied. Quantitative X-ray spectra fro m the front and the rear of gold foil under several conditions such as different foil thickness, different laser power densities and X-ray emission angles have been obtained. At the same time, radiative heat wave has also been observed fro m the evolutions of X-ray spectra emitted from the rear of gold foils of differe nt thickness.
2000, 49 (12): 2414-2419.
doi: 10.7498/aps.49.2414
Abstract +
Quasi-steady-state H-mode has been achieved by combination of two lower hybrid w aves in HT-6M tokamak.Plasma energy confinement time increases by two times,and the particle confinement time increases by a factor of three under a high plasma density condition.The wave diffusion and current radial diffusion code is used to simulate the experimental data on HT-6M.The calculated results show that the off-axis power deposition of lower hybrid wave is formed due to the low toroidal magnetic field and high plasma density.Reversed sheared(RS) configuration of th e plasma current density is formed during H-mode phase.The RS configuration and internal transport barrier are attributed to the enhanced confinement improvemen t.The experimental data also gives the evidence for the reversed shear formation .
2000, 49 (12): 2420-2426.
doi: 10.7498/aps.49.2420
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To explore more simple and efficient ion extraction methods used in atomic vapor laser isotope separation (AVLIS),two-dimensional(2D) PIC-MCC simulation code is used to simulate and compare several methods: parallel electrode method,Π type electrode method,improved M type electrode method,and radio frequency (RF) reso nance method.The simulations show that,the RF resonance method without magnetic field is the best among others,then the improved M type electrode method.The res ult of simulation of Π type electrode method is quite different from that calcu lated by 2D electron equilibrium model.The RF resonance method with or without m agnetic field has guite different results.Strong resonance occurs in the simulation without magnetic field,whereas no significant resonance occurs under weak magnetic field.And that is quite different from the strong resonance phenomena occurving in the 1D PIC simulation with weak magnetic field.As for practical applications,the RF resonance method without magnetic field has pros and cons, compare d with the M type electrode method.
2000, 49 (12): 2427-2432.
doi: 10.7498/aps.49.2427
Abstract +
The distribution mode of arc current density determines the distribution modes o f both arc heat flux and arc pressure, which are the basis to understand the phy sical nature of welding arc and to establish the mathematical model of welding p rocesses. Based on the general principle of arc physics, a distribution model of current density on the deformed weldpool surface is established in this paper. Quantitative analysis is carried out to determine the influence of weldpool surf ace shape on the distribution of current density. The predicted results show tha t the distribution of current density is bimodal distribution near the arc cente rline, and that with increasing distance from the arc centerline the bimodal dis tribution is gradually diminished. The distribution mode of current density is m arkedly modified by the shape of weldpool surface. According to this distributio n model, the predicted weld geometry is in agreement with the measured one.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2000, 49 (12): 2433-2436.
doi: 10.7498/aps.49.2433
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As a kind of important ferroelectric materials, lithium niobate is studied using shell model. The inter-ionic potential parameters and the shell model parameter s are determined by empirical parameterization. Three-body bond bending terms is used to model the directional character of covalent bonds. Employment of relaxe d fitting method makes our result better than the old one.
2000, 49 (12): 2437-2442.
doi: 10.7498/aps.49.2437
Abstract +
Single-phase filled skutterudite compounds,CeyFexCo4- xSb12(x=0—3.0，y=0—0.74)，were synthesized by a melting metho d.Effect of Fe content on Ce filling fraction,the crystal structure and the ther moelectric transport properties of CeyFexCo4-xS b12 saturated by Ce were investigated.Ce filling fraction increased l inearly with increasing Fe content.The lattice constants a of CeyFexCo4-xSb12 increased with increasing Fe content a nd Ce filling fraction.All samples showed p-type conduction.Hall coefficient RH decreased with increasing Fe content.Hole concentration p and electri cal conductivity σ increased with increasing Fe content.Seebeck coefficient α decreased with increasing Fe content.While Fe/Co ratio was about 1.5/2.5,the lat tice thermal conductivity (κl) reached the minimum values.
2000, 49 (12): 2443-2447.
doi: 10.7498/aps.49.2443
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This article deduced a theoretical method to obtain the second order partial der ivatice of shear modulus with respect to pressure G″P from the theor y of electron structure for crystal materials.We obtained G″P0=-0.033GPa-1 for 93 tungsten alloy,and applied this result in the fini te strain theory of Birch-Murnaghan,when comparing the calculated results of G″ P0=-0.033GPa-1 with the results of G″P=0, we find the results of G″P=0 are greater than that of the results o f G″P≠0.The difference between them becomes greater when the pressu re increases. Therefore,we can conclude that G″P cannot be neglected at high pressures.
2000, 49 (12): 2448-2454.
doi: 10.7498/aps.49.2448
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The relative surface parameters were determined by photovoltaic method in p and n type silicon in a wafer under the atmospheric, oxygenic, and nitric environmen ts, respectively. The inherent mechanism is approached according to the paramete r variations, and the relative physical phenomena are explained.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2000, 49 (12): 2455-2459.
doi: 10.7498/aps.49.2455
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Starting from the general transmission line equation with an electron beam, a se lf-consistent nonlinear analysis on complex cavity gyrotron with gradual transit ion is presented, in which the multiple modes interacting with an electron beam and the mode coupling are taken into account. The interaction between the electr on beam and H51-H52 RF field for third-harmonic gyrotron i s simulated numerically. The influences of multiple modes on the interaction are analyzed.
2000, 49 (12): 2460-2465.
doi: 10.7498/aps.49.2460
Abstract +
Effect of Ce filling fraction on the thermoelectric transport properties of p-ty pe Co-rich filled skutteudite compounds:CeyFe1.5Co2.5 Sb12 (y=0—0.46) were investigated. CeyFe1.5Co2.5Sb12 showed p-type conduction. Hall coefficient RH increased with increasing Ce filling fraction. Hole concentration p and electrical conductivity σ decreased with increasing Ce filling fraction. Se ebeck coefficient α increased with increasing Ce filling fraction. when Ce fill ing fraction was about 0.3, the lattice thermal conductivity κl reac hed the minimum value.It indicated that the effect of Ce rattling on phonon scat tering was the strongest as Sb-dodecahedron partial voids were filled by Ce. A m aximum ZT value of 1.1 was obtained for Co-rich Ce0.28Fe1.52Co2.48Sb12 at 750K.
2000, 49 (12): 2466-2471.
doi: 10.7498/aps.49.2466
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Phosphor-doped nano-crystalline silicon ((n))nc-Si:H) films are successfully gro wn on the p-type (100) oriented crystal silicon ((p) c-Si) substrate by conventi onal plasma-enhanced chemical vapor deposition method. The films are obtained us ing high H2 diluted SiH4 as a reaction gas source and usin g PH3 as the doping gas source of phosphor atoms. Futhermore, the het erojunction diodes are also fabricated by using (n)nc-Si:H films and (p)c-Si sub strate. I-V properties are investigated in the temperature range of 230—420K. T he experimental results domenstrate that (n)nc-Si:H/(p)c-Si heterojunction is a typical abrupt heterojunction having good rectifing and temperature properties. Carrier transport mechanisms are tunneling-recombination model at forward bias v oltages. In the range of low bias voltages (VFF>1.0V). The present heterojunction has high reverse breakdown voltage (>-75V) and low re verse current (≈nA).
2000, 49 (12): 2472-2476.
doi: 10.7498/aps.49.2472
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Full-Potential-Linear-Muffin-Tin-Orbital(FP-LMTO) method was employed to study t he structure and magnetism of iron.The three possible structures of iron were in vestigated over a range of atomic volumes in three magnetic states respectively. The total energies and magnetic moments in various volumes were obtained.The rel ations of pressure vs volume and bulk modulus vs volume were deduced also.The st ructural and magnetic stability of all the possible phases was discussed in diff erent ranges of atomic volume.The α→ε phase transition pressure was evaluated .By comparing our results with the experimental ones,they are in good agreement.
2000, 49 (12): 2477-2481.
doi: 10.7498/aps.49.2477
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The magnetic behavior of Ising multilayer system including nearest neighbor and next nearest neighbor interactions is investigated by use of variational cumulan t expansion (VCE) method. The formulae for spontaneous magnetization, coercivity , Curie point, Neel point, susceptbility and molecular field parameters respondi ng to the number of layers are deduced and discussed numerically. It is exactly demonstrated that, in 2-dimensional and 3-dimensional systems, the spontaneous m agnetization calculated by first order of the VCE is the same as the results of mean field theory. This means that the first order of VCE is valid in low temper ature. The validity of VCE in high temperature (above the critical point) is exp lained by the physical meaning of VCE method.
2000, 49 (12): 2482-2487.
doi: 10.7498/aps.49.2482
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This paper researches the direct up-conversion sensitization luminescence of ErY b codoped oxyfluoride glassceramics(ErYb:FOV) excited by CW 966nm-diode laser.It is found that the upconversion mechanism of direct upconversion sensitization l uminescence of YbEr:FOV sample is mainly the energy transfer between Er3+ and Yb3+ ion but not the step-by-step absorption of single Er3+ion.This oxyfluoride vitroceramics is forming PbxCd1-x F2 fluoride micro-crystallines.And the rare earth ions tend to concentrate in the micro-crystalline,in which there is an intense cluster effect .So upconversion luminescence is very strong. On the other hand,the log-log vari ation of up-conversion luminescence intensity with laser power emerges a kind of “typical saturation phenomenon”,in which F-P curve is bended gradually result ing from population exhausting in ground state.We also find a new kind of up-con version cooperative radiation fluorescence originating from a kind of Couple Sta te of cluster consisting of two Yb3+ions in this ErYb:FOV.
2000, 49 (12): 2488-2493.
doi: 10.7498/aps.49.2488
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This paper studies the steady state luminescent behavior of Yb3+Er3+ codoped and Er3+ mono-doped oxyfluoride vitroceramic mater ials.The cross-energy-transfer effect between Yb3+ and Er3+ ions in oxyfluoride vitroceramics(FOV)，oxyfluoride glass(FOG) and fluoride gl ass(ZBLAN) materials have been studied carefully also.Some new luminescence phen omenon is found,as described in the following.When the4G11/2 level of Er-doped FOV is excited by 377nm ultraviolet light，there appear a very strong green 4S3/2→4I15/2 fluo rescence and a middle strong red 4Ｆ9/2→4I15/2 fluorescence.However, when the 4G11/2 level of ErYb-codoped FOV is excited by 377nm ultraviolet light，the red4Ｆ9/2→4I15/2 fluorescence is increased about ten t imes, and meanwhile the green 4S3/2→4I15/ 2 fluorescence is decreased about 100 times.The variation of the red-green light ratio is about 1000 times.This interesting phenomenon exists only in FOV but not in FOG and ZBLAN.This paper also discuss how to apply this effect to th e Fluorescence Guard-Against-Forge in practice.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2000, 49 (12): 2494-2497.
doi: 10.7498/aps.49.2494
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The gravity behaviors in the combustion synthesis of Ti and carbon on the parabolic flight aircraft were investigated. The results showed that the combustion te mperatures vary with different gravity levels. Moreover, the study of gravity ef fect on combustion reaction in different sample orientations was also investigated.
2000, 49 (12): 2498-2501.
doi: 10.7498/aps.49.2498
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A series of porous TiC materials have been synthesized on a parabolic flight plane by using chemical ovens and the effects of gravity on the microstructures of combustion products were studied. As a result of the present work, the morpholog ies of combustion products obtained in the present microgravity environment are quite different from those under normal gravity conditions. In microgravity, TiC materials with more uniform distribution and finer porosity could be attained.
2000, 49 (12): 2502-2506.
doi: 10.7498/aps.49.2502
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The first and preliminary investigation of AlN composites thermal-treated under normal gravity and microgravity conditions by using chemical ovens was conducted during aircraft parabolic flights. The results indicated that, different micros tructures in the samples are associated with gravity level during parabolic flig ht, and microgravity condition allows the synthesis of AlN-borosilicate glass co mposite with improved microstructure, as compared with that under the terrestria l condition. It is favorable to produce AlN-borosilicate glass composites with a relatively uniform distribution of composition and structure. Finally, the use of chemical oven and the potential of material synthesis under microgravity cond ition are appreciated.
2000, 49 (12): 2507-2513.
doi: 10.7498/aps.49.2507
Abstract +
According to the Noxon method,the absorption characteristic of NO2 in the wavelength region 430-450nm is used to measure the NO2 Vertical Column Density (VCD) in the urban area .A new optical method using the differen tial optical absorption spectroscopy is developed to measure the NO2 VCD in the urban areas by using the solar light as the source, C-MOS linear imag e sensor as the detector and the sun spectrum taken at the summit of Yellow Moun tain as the reference spectrum.
LETTERS
2000, 49 (12): 2514-2518.
doi: 10.7498/aps.49.2514
Abstract +
There actually does not exist the plane electromagnetic wave described by sutra theory that electric field and magnetic field are in phase everywhere. The solut ion of Maxwell equations depends on the original value of electromagnetic field or boundary conditions. According to different fixed-solution conditions, the p lane electromagnetic modes obtained are different. The results indicate that the plane electromagnetic wave is a transverse wave; at different positions, the a mplitudes of periodically changing magnetic field blazed by periodically changin g electric field are different, so are the amplitudes of periodically changing electric field blazed by periodically changing magnetic field. The phase differe nce between electric field and magnetic field is different too.
