Spl Part Research Articles

Fabrication of YBCO step-edge Josephson junctions by inverted cylindrical magnetron sputtering technique

The Inverted Cylindrical Magnetron Sputtering (ICMS) technique been used to fabricate YBCO step-edge dc SQUIDs. Steps are obtained by standard ion milling procedure on LaAlO/sub 3/ (100) substrates using Nb-masks patterned by reactive ion etching. Thin films are then deposited under different conditions (both step and deposition angles) and patterned by standard lithography and wet chemical etching. An analysis of junction properties in terms of step height and film thickness has been carried out. Measurements on current vs magnetic field and SQUID voltage response measurements have been performed. Their temperature dependences have been also considered. Operating temperature as high as 77 K has been achieved. At 4.2 K the SQUIDs show a maximum voltage to flux transfer function (/spl part/V//spl part//spl phi/)/sub max/=870 /spl mu/V//spl Phi//sub 0/ and a good periodicity of the V-/spl phi/ modulation up to 20 /spl Phi//sub 0/ without any sign of hysteresis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Operating strategies under emission constraints

The emission-constrained dispatch problem is formulated as a nonlinear constrained minimization problem. Consequently, the solution to the problem gives a continuous relationship between cost and annual emission for SO/sub 2/. It is shown that the power system should be operated at the same value of the Lagrangian multiplier, /spl eta/, in every hour where /spl eta/ is defined as /spl part/(production cost)//spl part/(hourly emission). The addition of /spl eta/ as a proxy cost of emission in the economical dispatch procedure achieves this goal. It is shown that the emission-/spl eta/ relationship obtained by NLCM procedure can be used to make operating decisions, in particular, the trading of allowances. >

Self-consistent multidimensional electron kinetic analysis for inductively coupled plasma sources

Based upon the kinetic equations coupled with electromagnetic analysis for the recently developed inductively coupled plasma sources (ICPS), a self-consistent electron kinetic model is presented for 2-D (r, z) in a cylindrically symmetric configuration space and 2-D (/spl nu//sub /spl part//, /spl nu//sub z/) in the velocity space, The EM model is based on the mode analysis, while the kinetic analysis gives the perturbed Maxwellian distribution of electrons by solving the Boltzmann-Vlasov equation. The kinetic analysis shows that the RF energy in an ICPS is extracted by a collisionless dissipation mechanism, once the electron thermovelocity is close to the RF phase velocities determined by the reactor height and mode indexes. In this context, the effect of varying the reactor geometry is reported in terms of the electron energy distribution function. The analytical results are compared to the experimental data of Barnes et al. (see Appl. Phys. Lett., vol.62, no.21, p.2622-4 (1993)), which shows qualitative agreements in many aspects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

System vulnerability as a concept to assess power system dynamic security

The concept of system vulnerability is introduced as a new framework for power system dynamic security assessment. This new concept combines information on the level of security and its trend with changing system condition. In this paper the transient energy function (TEF) method is used as a tool of analysis. The energy margin /spl Delta/V is used as an indicator of the level of security, and its sensitivity (/spl part//spl Delta/V//spl part/p) to a changing system parameter p as an indicator of its trend. The thresholds for acceptable levels of the security indicator (/spl Delta/V) and its trend (/spl part//spl Delta/V//spl part/p) are related to the stability limits of a critical system parameter. A method is proposed to determine these thresholds using heuristic techniques derived from operating practices and policies for a change in plant generation. Results from the IEEE 50 generator test system are presented to illustrate the procedure. >

Kernel estimation of the instantaneous frequency

Considers kernel estimators of the instantaneous frequency of a slowly evolving sinusoid in white noise. The expected estimation error consists of two terms. The systematic bias error grows as the kernel halfwidth increases while the random error decreases. For a nonmodulated signal g(t), the kernel halfwidth that minimizes the expected error is proportional to h/spl sim/[(/spl sigma//sup 2/)/(N|/spl part//sub t//sup 2/g|2)]/sup 1/5/ where /spl sigma//sup 2/ is the noise variance and N is the number of measurements per unit time. The author shows that estimating the instantaneous frequency corresponds to estimating the first derivative of a modulated signal, A(t)exp(i/spl phi/(t)). For instantaneous frequency estimation, the halfwidth which minimizes the expected error is larger: h/sub 1,3//spl sim/[(/spl sigma//sup 2/)/(A/sup 2/N|/spl part//sub t//sup 3/(e/sup i/spl phi/~(t/))|/sup 2/)]/sup 1//$ u7. Since the optimal halfwidths depend on derivatives of the unknown function, the authors initially estimate these derivatives prior to estimating the actual signal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis and design of an integrated silicon ARROW Mach-Zehnder micromechanical interferometer

An analysis and design procedure for an integrated silicon micromechanical (pressure sensitive) interferometer is presented. Optimized layer thicknesses of an SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2//Si ARROW yield an attenuation of only 2.7/spl times/10/sup /spl minus/3/ dB/cm. Lateral confinement is accomplished with a rib in the core layer. Sensitivity to mechanical measurands is achieved by having the sensing arm of the interferometer on a thin silicon diaphragm, realized by micromachining a cavity from the back of the wafer. An applied pressure P deflects the diaphragm, causing a change in optical path length, leading to a phase shift /spl phi/ with respect to the reference arm. Sensitivity is increased by thinning the diaphragm, although this increases the resonant attenuation envelope of the diaphragm. Sensitivity calculations based on a simple, first-order model of diaphragm deflection yield (/spl part//spl phi/)/(/spl phi//spl part/P)=1.29/spl times/10/sup /spl minus/14/ P for a specific diaphragm geometry. BPM simulations show that curvature losses due to the bending of the ARROW under deflection is negligible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Time-domain electromagnetic plane waves in static and dynamic conducting media. I

Solutions are derived for the time-domain Maxwell equations for static (J=/spl sigma/E) and dynamic (/spl tau//spl part///spl part/t+J= /spl sigma//sub 0/E) conducting media where the field is assumed to vary with respect to only one spatial direction, i.e., plane-wave propagation. The plane wave is introduced into the media via the imposition of an electric field boundary condition at the plane boundary of a half-space and it is assumed that the fields inside the half-space are initially zero. Solutions are derived directly from the first-order system of partial differential equations and it is shown that once the electric field at the plane boundary is imposed, the magnetic field is automatically determined for causal solutions. It is shown that the form of the Maxwell equations, without a magnetic conductivity term added, is sufficient to allow well and uniquely defined solutions of this problem. >

Temperature sensitivity of KDP for phase-matched frequency conversion of 1 μm laser light

The magnitudes of the derivatives of the phase-matching angles with respect to temperature |/spl part//spl theta//sub pm///spl part/T| (milli-radians/degree celsius), for critically phase-matched frequency conversion using KDP (KH/sub 2/PO/sub 4/) have been directly measured for the five most interesting processes to inertial confinement fusion (ICF) laser-system designers: 2/spl omega/ I, 2/spl omega/ II, 3/spl omega/ I, 3/spl omega/ II, and 4/spl omega/ I. These measurements span an approximate temperature range of 25 to 90/spl deg/C, and were performed at a fundamental (1/spl omega/) wavelength of /spl lambda/=1.064 pm. The results are used to calculate the phase-matching thermal-sensitivity parameter |/spl beta//sub T/| (centimeter/sup -1//milliradian), for each conversion process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Toroidal Resonators and Waveguides of Arbitrary Cross Section

After introducing a new method to solve Maxwell's equations using a complex electromagnetic field vector F, a rotational coordinate system xi, Theta, psi is introduced. In this coordinate system, the field vector components F/sub xi/, F/sub Theta/ may be expressed by F/sub psi/. This component can be obtained from a two-dimensional Hehlmholtz equation. Specifying xi, Theta by cylindrical coordinates r, z the complex Maxwell equation curl F= gamma F is solved for the axisymmetric case (/spl part///spl part/psi = 0) and for the nonsymmetric case. The differential equations for magnetic field lines are solved and surfaces on which the normal component of B and the tangential components of E vanish are recognized as metallic walls of toroidal resonators of various arbitrary cross sections. In the Appendix the results of the new method are compared with well known results for circular cylindrical waveguides.

On The General Relation Between /spl alpha/ and Q (Correspondence)

The relation between the quality factor Q and the attenuation constant /spl alpha/ of a transmission line has been known as follows: /spl alpha/ = /spl beta/ / /2Q where /spl beta/ is the phase constant. Recently from the following relation of propagation constant at resonance /spl Gamma/(/spl omega//sub 0/) + /spl part//spl Gamma/ / /spl part//spl omega/ /spl Delta//spl omega//spl cong/ i/spl beta/(/spl omega//sub 0/), where /spl Gamma/(/spl omega//sub 0/) = /spl alpha/(/spl omega//sub 0/) + i/spl beta/(/spl omega//sub 0/). Yeh derived a general relation between Q and /spl alpha/, namely, /spl alpha/ = /spl upsi//sub p/ / /spl upsi//sub g/ /spl beta/ / /2Q where /spl upsi//sub p/, and /spl upsi//sub g/ are the phase velocity and group velocity of the wave respectively. This general relation can be derived very simply from the generally accepted definition of /spl alpha/ and Q.