An LP-based heuristic procedure for the generalized assignment problem with special ordered sets

The generalized assignment problem with special ordered sets (GAPS2), is the problem of allocating n tasks to m time-periods, where each task must be assigned to a time-period, or shared between two consecutive time-periods. For reasonably large values of m and n the NP-hard combinatorial problem GAPS2 becomes intractable for standard mathematical programming software, hence there is a need for heuristic algorithms to solve such problems. It will be shown how an LP-based heuristic developed previously for the well-established generalized assignment problem can be modified and extended to solve GAPS2. Encouraging results, in terms of speed and accuracy, in particular when compared to an existing heuristic for GAPS2, are described.     

A wavelet-based procedure for process fault detection

To detect faults in a time-dependent process, we apply a discrete wavelet transform (DWT) to several independently replicated data sets generated by that process. The DWT can capture irregular data patterns such as sharp "jumps" better than the Fourier transform and standard statistical procedures without adding much computational complexity. Our wavelet coefficient selection method effectively balances model parsimony against data reconstruction error. The few selected wavelet coefficients serve as the "reduced-size" data set to facilitate an efficient decision-making method in situations with potentially large-volume data sets. We develop a general procedure to detect process faults based on differences between the reduced-size data sets obtained from the nominal (in-control) process and from a new instance of the target process that must be tested for an out-of-control condition. The distribution of the test statistic is constructed first using normal distribution theory and then with a new resampling procedure called "reversed jackknifing" that does not require any restrictive distributional assumptions. A Monte Carlo study demonstrates the effectiveness of these procedures. Our methods successfully detect process faults for quadrupole mass spectrometry samples collected from a rapid thermal chemical vapor deposition process     

Magnetism in SiC implanted with high doses of Fe and Mn

High concentrations (0.1–5 at.%) of Mn or Fe were introduced into the near-surface region (≤2000 Å) of 6H-SiC substrates by direct implantation at ～300°C. After annealing at temperatures up to 1000°C, the structural properties were examined by transmission electron microscopy (TEM) and selected-area diffraction pattern (SADP) analysis. The magnetic properties were examined by SQUID magnetometry. While the Mn-implanted samples were paramagnetic over the entire dose range investigated, the Fe-implanted material displayed a ferromagnetic contribution present at <175 K for the highest dose conditions. No secondary phases were detected, at least not to the sensitivity of TEM or SADP.     

Menstrual cycle and age: influence on parenchymal contrast medium enhancement in MR imaging of the breast

PURPOSE: To quantify how frequently mesenteric adenitis clinically mimics appendicitis and to determine its appearance at computed tomography (CT). MATERIALS AND METHODS: The medical records of 651 consecutive patients with an admission diagnosis of appendicitis were reviewed to determine how often mesenteric adenitis was the discharge diagnosis. The CT scans of a separate group of 18 patients with a discharge diagnosis of mesenteric adenitis were reviewed. These patients were part of a group of 100 consecutive patients prospectively evaluated with CT of the appendix for clinically suspected appendicitis. RESULTS: Fifty of 651 patients (7.7%) with an admission diagnosis of appendicitis had a discharge diagnosis of mesenteric adenitis. Mesenteric adenitis constituted 50 of the 252 (19.8%) discharge diagnoses other than appendicitis. All 18 CT scans of mesenteric adenitis showed three or more nodes that measured at least 5 mm in shortest axis clustered in the right lower quadrant, with a normal appendix identified. Eight patients had associated ileal or ileocecal wall thickening. CONCLUSION: Mesenteric adenitis is an important clinical mimic of appendicitis. It appears at CT as clustered, enlarged mesenteric lymph nodes with a normal appendix, and there may be associated ileitis or ileocolitis noted.     

Development and characterization of magnetorheological polymer gels

Magnetorheological materials have been used in many applications in recent years. To develop new materials, polyurethane and silicone polymer gels were investigated. Rheology is qualitatively controlled for each system by controlling the concentration of reactants and diluents. The resulting polymers have solid, gel, or liquid states, depending on the crosslinking and dilution. The gels were characterized through kinetic analysis. Differential scanning calorimetry (DSC) was used with analysis methods to find the kinetic properties for diluted and undiluted polyurethane systems. Heat of reaction, order of reaction, preexponential constant, and activation energy were obtained from the experimental DSC data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2733–2742, 2002