Efficient Reflectance and Visibility Approximations for Environment Map Rendering

We present a technique for approximating isotropic BRDFs and precomputed self-occlusion that enables accurate and efficient prefiltered environment map rendering. Our approach uses a nonlinear approximation of the BRDF as a weighted sum of isotropic Gaussian functions. Our representation requires a minimal amount of storage, can accurately represent BRDFs of arbitrary sharpness, and is above all, efficient to render. We precompute visibility due to self-occlusion and store a low-frequency approximation suitable for glossy reflections. We demonstrate our method by fitting our representation to measured BRDF data, yielding high visual quality at real-time frame rates.     

Analysis and comparison of real-time sine-wave generation for PWMcircuits

Four methods for hardware and software generation in real time of sine waves suitable for PWM circuits are presented. The sine waves are derived from a truncated modified cosine Taylor series, wt(π-wt) function, a digitally filtered trapezoid, and a second-order differential equation. Triplen injection is incorporated by the addition of a defined magnitude triangular waveform of three times the fundamental frequency. Each sine wave generating technique is implemented, as applicable, in a programmable logic cell array and/or in microprocessor-based software. In each case, the output spectra and total harmonic distortion are compared with computer-simulated results     

Top management support of R&D projects: a strategic leadershipperspective

A study of top management support of 213 R&D projects in 21 major firms revealed significant relationships between independent informants' perceptions of top management support, project characteristics, and project performance. Testing a model based on a strategic leadership perspective, top management support was found to be directed at certain types of projects, i.e., those that were expected to make greater contributions to business goals, represented larger investments, were seeking new products and process versus incremental improvements, and had originated from business sources as opposed to R&D. In addition, even after controlling for these project characteristics, projects with top management support were less likely to be terminated. In contrast, after controlling for project characteristics, completed projects with top management support were not judged to make greater contributions to the firm's business goals suggesting top management may not be able to pick winners. Findings are discussed in terms of future research and implications for top management leadership within R&D     

Strains of Synechocystis sp. PCC 6803 with altered PsaC. II. EPR and optical spectroscopic properties of FA and FB in aspartate, serine, and alanine replacements of cysteines 14 and 51

A psaC deletion mutant of the unicellular cyanobacterium Synechocystis sp. PCC 6803 was utilized to incorporate site-specific amino acid substitutions in the cysteine residues that ligate the FA and FB iron-sulfur clusters in Photosystem I (PS I). Cysteines 14 and 51 of PsaC were changed to aspartic acid (C14DPsaC, C51DPsaC, C14D/C51DPsaC), serine (C14SPsaC, C51SPsaC), and alanine (C14APsaC, C51APsaC), and the properties of FA and FB were characterized by electron paramagnetic resonance spectroscopy and time-resolved optical spectroscopy. The C14DPsaC-PS I and C14SPsaC-PS I complexes showed high levels of photoreduction of FA with g values of 2.045, 1. 944, and 1.852 after illumination at 15 K, but there was no evidence of reduced FB in the g = 2 region. The C51DPsaC-PS I and C51SPsaC-PS I complexes showed low levels of photoreduction of FB with g values of 2.067, 1.931, and 1.881 after illumination at 15 K, but there was no evidence of reduced FA in the g = 2 region. The presence of FB was inferred in C14DPsaC-PS I and C14SPsaC-PS I, and the presence of FA was inferred in C51DPsaC-PS I and C51SPsaC-PS I by magnetic interaction in the photoaccumulated spectra and by the equal spin concentration of the irreversible P700(+) cation generated by illumination at 77 K. Flash-induced optical absorbance changes at 298 K in the presence of a fast electron donor indicate that two electron acceptors function after FX in the four mutant PS I complexes at room temperature. These data suggest that a mixed-ligand [4Fe-4S] cluster is present in the mutant sites of C14X-PS I and C51X-PS I (where X = D or S), but that the proposed spin state of S = 3/2 renders the resonances undetectable in the g = 2 region. The C14APsaC-PS I, C51APsaC-PS I and C14D/C51DPsaC-PS I complexes show only the photoreduction of FX, consistent with the absence of PsaC. These results show that only those PsaC proteins that contain two [4Fe-4S] clusters are capable of assembling onto PS I cores in vivo.     

In vivo surface analysis of titanium and stainless steel miniplates and screws

OBJECTIVE: To determine the results peranal excision for rectal carcinoma. DESIGN: Retrospective case series. SETTING: A university-affiliated hospital. PATIENTS: Of 178 patients who presented for curative resection of rectal carcinoma between 1975 and 1993, 19 (10.7%) were deemed suitable for local excision. There were 10 men and 9 women with a mean age of 71.2 years. The follow-up ranged from 13 to 184 months. INTERVENTION: Peranal excision. MAIN OUTCOME MEASURES: Histologic differentiation, gross morphology, depth of invasion and size of the carcinoma, adequacy of margins of excision, complications of operation, rates of recurrence, results of salvage therapy and 5-year survival. RESULTS: There were no intraoperative complications. Postoperative complications included urinary retention (one patient) and bleeding (one patient). There were five local recurrences (26%). Salvage operations were performed in three (60%) patients and were successful in two of them. The 5-year cancer-specific survival rate was 82%. The recurrence rate was higher in patients with inadequate margins of excision and ulcerative lesions. Neither size nor grade of the carcinoma correlated with recurrence. CONCLUSIONS: Local excision of rectal carcinoma can be performed successfully in selected patients. Diligent follow-up is required, because up to 60% of local recurrences can be treated successfully.     

A strain hardening failure assessment diagram derived from carbon-manganese steel compact tension specimens

A failure assessment diagram is derived from carbon-manganese steel compact tension specimens. The diagram has been determined from an elastic-plastic finite element analysis of a compact tension specimen geometry. The diagram has been validated by using experimental fracture toughness data obtained on the same steel and specimen geometry modelled in the finite element analysis. The plastic collapse load has been determined empirically for this geometry.It is shown that a non-work-hardening failure assessment diagram is not a good representation of the experimental data and that the computed failure assessment diagram is more appropriate for describing the behaviour of the carbon-manganese steel specimens.     

Characteristic magnetic resonance imaging entheseal changes of knee synovitis in spondylarthropathy

Although studies generally support a positive association between alcohol consumption and lung-cancer risk, the relationship between specific alcoholic beverages and lung-cancer risk has been inconsistent. We examined recent and past alcoholic beverage intake among 261 incident cases and 615 population controls enrolled in a lung-cancer case-control study of African Americans and Caucasians in Los Angeles County between 1991 and 1994. An in-person interview elicited information about past alcohol intake from ages 30 to 40 y, smoking, other lung-cancer risk factors, as well as recent intake of alcohol, and recent dietary intake. An association was observed between recent hard-liquor consumption and lung-cancer risk. The odds ratio (OR) for 1 or more drinks (1.5 oz or 0.051 mL) per day of hard liquor compared with infrequent liquor drinking (0-3 drinks per month), adjusted for smoking, the matching factors, saturated fat and other alcoholic beverages was 1.87 [95% confidence interval (CI) = 1.02-3.42]. No appreciable association was observed for total alcohol, whereas small inverse associations were observed for beer and wine, although confidence intervals were wide. An elevated lung-cancer risk was also observed for past liquor consumption (between ages 30 and 40 y). The adjusted OR for 1 or more drinks per day of liquor compared with infrequent drinkers was 1.83 (95% CI = 1. 06-3.15). Confounding of the association between alcohol and lung cancer by smoking was apparent. Although we devoted considerable efforts to adjusting for smoking in our analyses, residual confounding is still possible because smoking and alcohol are closely associated. In addition, case-control studies including this study should be viewed with caution because of possible selection bias. An increased risk of lung cancer might occur with moderate drinking of hard liquor but confirmation is required in larger studies.