Variance and Covariance Computations for 2-D ARMA Processes

An algorithm is presented to compute the variance of the output of a two-dimensional (2-D) stable auto-regressive moving-average (ARMA) process driven by a white noise bi-sequence with unity variance. Actually, the algorithm is dedicated to the evaluation of a complex integral of the form , where and G(z₁,z₂) = B(z₁, z₂) / A(z₁, z₂) is stable (z₁,z₂)-transferfunction. Like other existing methods, the proposed algorithmis based on the partial-fraction decomposition G(z₁,z₂)G(z ₁ ^-1 , z ₂ ^-1 ) = X(z₁, z₁) / A(z₁,z₂)+ X(z ₁ ^-1 , z ₂ ^-1 ) / A(z ₁ ^-1 , z ₂ ^-1 ). However,the general and systematic partial-fraction decomposition schemeof Gorecki and Popek [1] is extended to determine X(z₁,z₂).The key to the extension is that of bilinearly transforming thediscrete (z₁, z₂)-transfer function G(z₁,z₂)into a mixed continuous-discrete (s₁, z₂)-transferfunction . As a result, the partial-fraction decomposition involves only efficient DFT computations for the inversion of a matrix polynomial, and the value of I is finally determined by the residue method with finding the roots of a 1-D polynomial. The algorithm is very easy to implement and it can be extended to the covariance computation for two 2-D ARMA processes.     

Piffalls in atmospheric correction of ocean color imagery: how should aerosol optical properties be computed?

Current methods for the atmospheric correction of ocean-color imagery rely on the computation of optical properties of a mixture of chemically different aerosol particles through combination of the mixture with it into an effective, single-particle component that has an average refractive index. However, a multi-component approach in which each particle type independently grows and changes its refractive index with increasing humidity is more realistic. Computations based on Mie theory and radiative transfer are used to show that the two approaches result in top-of-the-atmosphere radiances that differ more than the water-leaving radiance. Thus, proper atmospheric correction requires a multicomponent approach for the computation of realistic aerosol optical properties.     

FIUT: A new method for mining frequent itemsets

This paper proposes an efficient method, the frequent items ultrametric trees (FIUT), for mining frequent itemsets in a database. FIUT uses a special frequent items ultrametric tree (FIU-tree) structure to enhance its efficiency in obtaining frequent itemsets. Compared to related work, FIUT has four major advantages. First, it minimizes I/O overhead by scanning the database only twice. Second, the FIU-tree is an improved way to partition a database, which results from clustering transactions, and significantly reduces the search space. Third, only frequent items in each transaction are inserted as nodes into the FIU-tree for compressed storage. Finally, all frequent itemsets are generated by checking the leaves of each FIU-tree, without traversing the tree recursively, which significantly reduces computing time. FIUT was compared with FP-growth, a well-known and widely used algorithm, and the simulation results showed that the FIUT outperforms the FP-growth. In addition, further extensions of this approach and their implications are discussed.     

Simplified small-scale backlight unit tester

A novel design is the concept of using charge coupled device camera embedded with calibrated image processing algorithm as a two-dimensional luminance meter to measure the luminance and uniformity of small-scale backlight of unit. A small-scale backlight unit tester was successfully realized and performed to verify this concept.     

An improved tabu search for economic dispatch with multiple minima

This paper develops an improved tabu search algorithm (ITS) for economic dispatch (ED) with noncontinuous and nonsmooth cost functions. ITS employs a flexible memory system to avoid the entrapment in a local minimum and developed the ideal of "distance" to the fitness to accelerate optimization. The new approach extends simple tabu search algorithm (STS) to real valued optimization problem and applies parallelism to weaken the dependence of the convergence rate of modified tabu search algorithm (NITS) on the initial condition. Effectiveness of the method was compared with many conventional methods. Results show that the proposed algorithm can provide accurate solutions with reasonable performance and has a great potential for other applications in the power system     

Hydrogen embrittlement of a Ti-strengthened 250 grade maraging steel

Constant extension-rate tensile tests are performed to investigate the effects of strain rate and environmental hydrogen concentration on the tensile properties of various aged T-250 specimens. The 426 °C (800 °F) underaged specimens are very sensitive to strain rate; the 482 °C (900 °F) peak-aged specimens exhibit a reduced ductility under low strain rates; and the 593 °C (1100 °F) overaged specimens are insensitive to strain rate when tested in air. The excellent resistance to embrittlement of the overaged specimens in gaseous hydrogen could be associated with the extensive formation of reverted austenite and the incoherent Ni₃Ti precipitates. The tensile-fractured surfaces of such specimens reveal a ductile dimple fracture. However, the peak-aged specimens are susceptible to gaseous hydrogen embrittlement, and the embrittled region shows a primary fracture mode of quasi-cleavage. The least resistant to hydrogen embrittlement of the underaged specimens is characterized by a more brittle fracture appearance, that is, intergranular fracture, under a low strain rate or in the gaseous hydrogen environment.     

Non-newtonian flow modeling in the mixing section of a single-screw extruder with flow analysis network method

The flow of non-Newtonian fluids obeying the power-law relation through the mixing sections of a single-screw extruder is analyzed with a modified flow analysis network (FAN) method. Three types of mixing elements, the Maddock, the dulmage, and the blister ring elements, are studied. The Maddock and the blister ring elements are dispersive type elements. They generate high pressure drop, and yield a negative pressure gradient which indicates poor pumping capability. The flow fields are rather regular in these elements. On the other hand, the dulmage element is a distributive type element. It generates a low pressure drop, and yields a positive pressure gradient at low extrusion rate which indicates better pumping capability than the dispersive type elements. Extensive flow splitting and reorientation is observed in this element. The power-law exponent has significant effect on pumping characteristics. However, the overall flow patterns of Newtonian fluids and power-law fluids in these mixing elements are quite similar.     

Embrittlement of T-200 maraging steel in a hydrogen sulfide solution

Slow displacement rate tensile tests were carried out to investigate the effect of hydrogen embrittlement (HE) on notched tensile strength (NTS) and fracture characteristics of aged T-200 maraging steel. Hydrogen diffusivity, permeation flux and apparent hydrogen solubility were determined by an electrochemical permeation method, and correlated with the HE susceptibility and microstructures of the specimens. The results indicated that all aged specimens were susceptible to HE in the saturated H₂S solution, to different degrees. The susceptibility in the decreasing order of severity was observed to be under-aged, peak-aged, and over-aged conditions. The main trend was that the specimen with the highest diffusivity and permeation flux of hydrogen had the greatest NTS loss. Reverted austenite, if present in the microstructure, acted as irreversible traps for hydrogen and hence, improved the HE resistance. At similar strength and hydrogen solubility level, the more reverted austenite the less susceptibility to HE of specimens was resulted. The detailed microstructures of distinct specimens and their performances in hydrogen-containing environments are discussed.     

A mathematical model of hydrogen permeation in pure iron

A one-dimensional problem of hydrogen permeation through thin plates is analysed. The permeation process is considered as a two-stage transient process. The first stage is assumed to be transportation, and the second diffusion. The non-linear time-dependent diffusion equation is then solved by employing a finite difference scheme. The result shows that the lag time is a quadratic function of the plate thickness. Also, the square of the hydrogen concentration asymptotically tends to be linear across the plate thickness.     

Pitfalls in Atmospheric Correction of Ocean Color Imagery: How Should Aerosol Optical Properties be Computed?: Reply to Comment.

Gordon [Appl. Opt. 42, 542 (2003)] argues that use of external rather than internal mixing when aerosol optical properties are computed will not seriously affect atmospheric correction of ocean color imagery, in spite of the fact that top of the atmosphere reflectances computed with the two approaches differ significantly as shown by Yan et al. [Appl. Opt. 41, 412 (2002)]. We apply an algorithm for simultaneous retrieval of aerosol optical properties and chlorophyll concentrations to demonstrate that use of the internal-mixing approach leads to atmospheric corrections that differ significantly from those obtained with the more realistic external-mixing approach. For relative humidities of 90% or more, the differences in retrieved aerosol optical properties and chlorophyll concentrations, incurred by application of the internal-mixing approach, become unacceptably large.