A derivation of the diffuse fraction's dependence on the clearness index

When averaged over many events having the same k_t, the average diffuse fraction carries an important quasi-universal functional dependence on the clearness index k_t. This paper presents a theoretical derivation of k(k_t). The atmosphere is modeled as having two homogeneous, nonselectively absorbing layers: an upper layer (roughly, the ozonosphere) with zero scattering and beam transmittance τ_u, and a lower layer with isotropic, nonselective scattering characterized by an albedo ω_l. After an analysis which traces generations of scattered photons, this model predicts a function which, upon adjusting ω_l and τ_u, fits the measured data closely.     

Influence of weld misalignment and weld metal overmatch on the prediction of fracture in pipeline girth welds

$\text{J-}\text{integral}$ estimates using elastic-plastic finite element calculations, are shown to compare well with experimental results from single edge-notch bend (SENB) specimens made of X483 grade line pipe steel.The influence of weld misalignment and weld metal overmatch on fracture of cracked girth welds is predicted, also using elastic-plastic finite element calculations. Weld metal overmatch reduces plastic strain levels in the weld and appears beneficial in reducing $\text{J-}\text{integral}$ magnitudes. Predicted values of $\text{J-}\text{integral}$ are shown to increase with weld misalignment. However, $\text{J-}\text{integral}$ magnitudes near the critical value for crack growth initiation were only attained after considerable plastic straining at or near limit load. This result suggests that limit load calculations may be more appropriate for prediction of failure of cracked girth welds than conventional fracture techniques.     

Two new decoding algorithms for Reed-Solomon codes

The subject of decoding Reed-Solomon codes is considered. By reformulating the Berlekamp and Welch key equation and introducing new versions of this key equation, two new decoding algorithms for Reed-Solomon codes will be presented. The two new decoding algorithms are significant for three reasons. Firstly the new equations and algorithms represent a novel approach to the extensively researched problem of decoding Reed-Solomon codes. Secondly the algorithms have algorithmic and implementation complexity comparable to existing decoding algorithms, and as such present a viable solution for decoding Reed-Solomon codes. Thirdly the new ideas presented suggest a direction for future research. The first algorithm uses the extended Euclidean algorithm and is very efficient for a systolic VLSI implementation. The second decoding algorithm presented is similar in nature to the original decoding algorithm of Peterson except that the syndromes do not need to be computed and the remainders are used directly. It has a regular structure and will be efficient for implementation only for correcting a small number of errors. A systolic design for computing the Lagrange interpolation of a polynomial, which is needed for the first decoding algorithm, is also presented.This research was supported by a grant from the Canadian Institute for Telecommunications Research under the NCE program of the Government of Canada     

An analysis of a class of algorithms for S-box construction

We analyze a very general class of algorithms for constructingm-bit invertible S-boxes called bit-by-bit methods. The method builds an S-box one entry at a time, and has been proposed by Adams and Tavares [2] and Forre [11] to construct S-boxes that satisfy certain cryptographic properties such as nonlinearity and the strict avalanche criterion. We prove, both theoretically and empirically, that the bit-by-bit method is infeasible form>6. The author is currently employed by the Distributed System Technology Center (DSTC), Brisbane, Australia. Correspondence should be sent to ISRC, QUT Gardens Point, 2 George Street, GPO Box 2434, Brisbane, Queensland 4001, Australia.     

Coupled electrothermal modeling of microheaters using SPICE

In this paper,,we report a novel simulation approach that computes both the transient and steady state electrothermal behavior in integrated circuit (IC) compatible thermally isolated microheaters. The resulting distribution of heat, current density and temperature, as well as the electrical terminal behavior have been obtained for realistic device structures. The results are based on a two-dimensional solution of the coupled system of partial differential equations that govern both electrical and heat transport in the device. Unlike standard numerical approaches for coupled systems, our technique is based on the behavioural models, available in most commercial circuit simulators (e.g., HSPICE), that allow synthesis of complex, nonlinear, and coupled circuit elements. The simulation results are in excellent agreement with measurement data of steady state and transient terminal characteristics, obtained under conditions of vacuum. We note that this modeling approach allows concurrent simulation (and subsequent optimization) of the performance of both the control electronics as well as the thermal element(s), within the same IC design environment     

Optical-induced spectral tuning in grating-assisted nonlinearcouplers

The spectral (wavelength) properties of the grating-assisted nonlinear coupler are investigated theoretically. The interaction of linear and nonlinear wavelength-dependent phase detuning leads to a rich display of new and useful characteristics. Among these are bandpass tuning and spectral shaping. The grating frequency is viewed as a `free design parameter' which may be judiciously chosen to bring about an optimum behavior for a given application. As a wavelength processing element, the coupler behaves as an extended and continuously tunable wavelength filter, with tuning proportional to the input power. As an an-optical switch, a broadened and virtually transparent passband is easily achieved, which has desirable consequences for ultra-fast (large bandwidth) switching. The coupler may be operated in two complimentary modes: The active mode, where the power level of an input pulse or signal interacts in a nonlinear fashion with the passband of the coupler; and the passive mode, where a separate idler input is used to bias the device for a desired response to a smaller injected signal     

An FDTD/ray-tracing analysis method for wave penetration through inhomogeneous walls

A novel method of studying wave penetration through inhomogeneous walls using the hybrid technique based on combining finite-difference time-domain (FDTD) and ray tracing methods is presented . The FDTD method is used to analyze the transmission characteristics of inhomogeneous walls. Using the knowledge of the tangential electric and magnetic field distributions along the borders of the FDTD computation domain, rays are sent out to cover the rest of the environment so that prediction of signal coverage can be made more efficiently without compromising the accuracy. Numerical results of the method have been compared and shown to agree very well with those of measurement and those of full wave analysis. Examples have shown the inadequacy of the traditional ray tracing method in the presence of walls made of concrete blocks. However, the proposed method can accurately predict signal coverage by taking into account the scattered fields by the inhomogeneity inside the walls. The method does not add much to computational complexity. Reduction in computation time is even more significant when the incident waves can be approximated to be plane waves and the wall structure is periodic.     

Hankel transform-domain analysis of scattered fields in multilayer planar waveguides and lasers with circular gratings

Radiation patterns of scattered fields with arbitrary azimuthal orders in multilayer planar waveguides and laser cavities with circularly symmetric gratings are formulated based on the volume current method. Full-wave Green's function analysis based on the integral transform method lies at the heart of this approach. Unlike the conventional approach, the dyadic Green's function relates some auxiliary fields to some auxiliary sources in the spectral domain. These auxiliary functions are defined to facilitate the spectral domain formulation in the cylindrical coordinate system and the use of transfer matrix method for obtaining a closed-form solution of the spectral Green's function in multilayer planar structures. More importantly, it is shown that the far-field pattern of the scattered field can be expressed directly in terms of the auxiliary fields in the Hankel transform domain.     

A simplified method for calculating the substation grounding gridresistance

A simple and accurate formula for calculating the grounding grid resistance is proposed in this paper. This method is based on a theoretical manipulation of the numerical moment method and of the current image. The formula is dependent on the substation grounding grid design, such as grid depth, grid size, number of meshes, grid-conductor diameter, etc. A comparison study is performed to check the accuracy of the proposed formula with respect to six different formulas and methods in the literature. An excellent agreement was found between the results of this formula and the results of a sophisticated computerized method