Time-domain analytic solutions of two-wire transmission line excited by a plane-wave field

This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain. By the frequency-domain Baum Liu-Tesehe （BLT） equation, the time-domain analytic solutions are obtained and expressed in an infinite geometric series. Moreover, it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval. In other word, the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval. The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform, and the agreement is excellent.     

Analysis of Dα（Hα） spectrum emitted in front of the limiter in HT-7^＊

In order to understand the recycling and emission processes of hydrogen atoms in HT 7, spectral profiles of the Dα（Hα） line emitted in front of the limiter have been observed with a high-resolution spectrometer and simulated by using the neutral particle transport code DEGAS 2. The results show that four processes are necessary to interpret the Dα（Hα） line shape： 1） atom desorption, 2） molecular dissociation, 3） particle reflection, and 4） charge-exchange. The products of the first two processes are cold atoms which emit photons near the peak of Dα（Hα） line shape, and those from the last two are warm atoms contributing to the blue side of the spectrum. For a typical ohmic discharge （shot 68520 ne（0） ≈ 3× 10^19 m^-3. these components contribute 32%, 15%, 32% and 21%, respectively. Dα（Hα） line shapes under different plasma parameters are also discussed in this paper.     

Peak effect in surface resistance at microwave frequencies in Dy-123 thin films

A pronounced peak in the microwave (at frequency 9.55 GHz) surface resistance, R _s vs. T plot (where T is the temperature) has been observed in epitaxial DyBa₂Cu₃O_7−y superconducting thin films in magnetic fields (parallel to c-axis) in the range 2 to 8 kOe, and temperatures close to the superconducting transition temperature T _c(H). Our data suggest that the nature of peaks observed in the two films is different, thereby indicating different defect structures in the films.     

A Tunable Difference Frequency Spectrometer for Quantitative Analysis of Heavy Molecules

A continuous-wave (cw) mid-infrared spectrometer based on laser difference frequency generation (DFG) in gallium selenide (GaSe) crystal was developed for quantitative analysis of heavy molecules. The spectrometer and its spectroscopic applications to study of molecular line parameters (such as line strength, pressure broadening coefficients) are presented. The first measurement, to our knowledge, of the self and air broadening coefficients for the ₇ 8 _2,7 8 _1,7 ethylene (C₂H₄) transition line at 958.1531 cm^–1 is reported.     

二价钐离子谱线的非均匀加宽、荧光窄化和永久性光谱烧孔

基于光谱烧孔在高密度光存储中的可能应用,研究了谱线非均匀加宽、荧光谱线窄化、高温永久性光谱烧孔、烧孔机理、烧孔动力学过程和光谱孔的热稳定性。在国际上率先设计并研制出二价钐离子掺杂碱土金属氟卤化物混晶高温光谱烧孔体系,实现了室温永久性光谱烧孔,获得了室温寿命300h的光谱孔。利用时间分辨光谱分离出非均匀线形内的各局域组态,比较烧孔前后光谱再分布证实了三价钐离子的电子陷阱作用。利用Block理论分析了烧孔动力学过程。     

Ultra-broadband NMR probe: numerical and experimental study of transmission line NMR probe

We have reinvestigated a transmission line NMR probe first published by Lowe and co-workers in 1970s [Rev. Sci. Instrum. 45 (1974) 631; 48 (1977) 268] numerically and experimentally. The probe is expected to be ultra-broadband, thus might enable new types of solid-state NMR experiments. The NMR probe consists of a coil and capacitors which are connected to the coil at regular intervals. The circuit is the same as a cascaded LC low-pass filter, except there are nonzero mutual inductances between different coil sections. We evaluated the mutual inductances by Neumann's formula and calculated the electrical characteristics of the probe as a function of a carrier frequency. We found that they were almost the same as those of a cascaded LC low-pass filter, when the inductance L of a section was estimated from the inductance of the whole coil divided by the number of the sections, and if C was set to the capacitance in a section. For example, the characteristic impedance of a transmission line coil is given by Z=(L/C)(1/2). We also calculated the magnitude and the distribution of RF magnetic field inside the probe. The magnitude of RF field decreases when the carrier frequency is increased because the phase delay between neighboring sections is proportional to the carrier frequency. For cylindrical coils, the RF field is proportional to (pinu/2nu(d))(1/2)exp(-nu/nu(d)), where the decay frequency nu(d) is determined by the dimensions of the coil. The observed carrier frequency thus must be much smaller than the decay frequency. This condition restricts the size of transmission line coils. We made a cylindrical coil for a 1H NMR probe operating below 400 MHz. It had a diameter 2.3mm and a pitch 1.2mm. Five capacitors of 6pF were connected at every three turns. The RF field strength was 40 and 60 kHz at the input RF power 100 W by a calculation and by experiments, respectively. The calculations showed that the RF field inhomogeneity along the coil axis was caused by a standing wave of current, which arose from the reflections at the coil ends. The calculation showed that the homogeneity could be improved by decreasing the pitch near the both ends and making their impedance close to that at the center.     

Four-Component Gas/Oil Displacements in One Dimension: Part I: Global Triangular Structure

This paper presents an analysis of the mathematical structure of three-component and four-component gas displacements. The structure of one-dimensional flows in which components partition between two phases is governed by the geometry of a set of equilibrium tie lines. We demonstrate that for systems of four components, the governing mass conservation laws for the displacement can be represented by an eigenvalue system whose coefficient matrix has a global triangular structure, which is defined in the paper, for only specific types of phase behavior. We show that four-component systems exhibit global triangular structure if and only if (1) tie lines meet at one edge of the quaternary phase diagram or (2) if tie lines lie in planes. For such systems, shock and rarefaction surfaces coincide and are planes. We prove that systems are of category (2) if equilibrium ratios (K-values) are independent of mixture composition. In particular, for such systems shock and rarefaction curves will coincide. We also show that for systems with variable K-values, the rarefaction surfaces are almost planar in a precise sense, which is described in the paper. Therefore, systems with variable K-values may be well approximated by assuming shock and rarefaction surfaces do coincide. For these special systems the construction of solutions for one-dimensional, two-phase flow with phase behavior simplifies considerably. In Part II, we describe an application of these ideas to systems in which K-values are constant.     

Analysis of an Inhomogeneous Semitransparent Plasma by the Lines in the Emission Spectrum

Using the methods of numerical simulation, we have investigated the dependence of the intensity and parameters of the spectral line profiles in the radiation of semitransparent plasma on its optical thickness, the degree of inhomogeneity, and the parameter distribution. As a model, we used the equilibrium plasma of argon with a given temperature profile on the observation line. The calculation has been performed for the spectral lines of the argon atom characterized by different broadening constants. On the basis of the results obtained it has been shown that it is possible to diagnose the plasma and determine the degree of its inhomogeneity and reabsorption by the parameters of the self-reversed profiles of the spectral lines. To diagnose the plasma in the absence of self-reversal, we propose to use the line intensities in the emission spectra of the plasma, including those obtained by probing it by its self-radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 404–411, May–June, 2005.     

Large transversals to small families of unit disks

Summary It is proved that if the nonempty intersection of bounded closed convex sets AnB is contained in (A + F)U(B+F) and one of the following holds true: (i) the space X is less-than-three dimensional, (ii) AUB is convex, (iii) F is a one-point set, then AnBCA+F or AnBCB+F (Theorems 2 and 3). Moreover, under some hypotheses the characterization of A and B such that AnB is a summand of AUB is given (Theorem 3).     

Parametric study of 2D potential structures induced by RF sheaths coupled with transverse currents in front of ICRH antenna

Hot-spot formation on the corners of the ICRH antenna can be explained by high DC potential structures, which accelerate ion fluxes and generate strong convective fluxes to the antenna surface. This comes from RF sheaths at the end of open magnetic lines, which rectify RF potential resulting from parallel electric fields. As these electric fields are not homogeneous in front of the antenna, transverse potential gradients generate transverse polarization currents which modify the potential structure. These potentials are studied with a simple flux-tube model and then a 2D-fluid model was elaborated to obtain analytical expressions for rectified potential with respect to these transverse currents. We compare them to numerical results coming from a 2D-fluid code executed in a poloidal plane in front of the antenna. Then we build a potential peak criterion to determine the peaking of DC-potential structures for typical parameters in Tore Supra. Finally, current interaction between different magnetic line lengths is approached.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.