Tracing a ray through uniformly subdividedn-dimensional space

Finding the cells intersected by a ray in a uniformly subdivided space is a technique used in accelerated ray tracing and also other computer graphics applications. A related problem is that of finding the sequence of grid points in a 3D voxel space, which best approximates a given line. This paper examines earch of these problems, introduces a unifying approach and provides a generalisation of previous algorithms.Written while on sabbatical leave from Department of Computer Science, QMW University of London, Mile End Road, London E1 4NS, UK     

Suicide trends in eight predominantly English-speaking countries 1960-1989

Suicide rates between 1960 and 1989 were explored for eight predominantly English speaking countries with similar national characteristics. New World countries showed significant similarities but differed from Old World countries. The two North American (NA) New World countries showed more similarity to each other than the two Australasian New World countries. The NA countries showed an unique plateau in the 1980s for males aged 15-29 years. Old World males of all ages showed common rises, suggesting a partial sex-specific influence in the young. However, trends among the 15- to 19-year-olds were significantly different to trends among the 20- to 29-year-olds in both sexes suggesting a substantial youth-related contribution to the rises. Rates among 15- to 19-year-old females rose in the early 1960s, ahead of males but in parallel with rises among older females, suggesting part of the rise was sex- as opposed to age-related. Although rates among the 15- to 19-year-old females showed little change since 1970, this may be partly a function of sex-related improvements-observable in older females disguising unfavourable youth-related influences. Possible aetiological factors are suggested but remain speculative. Studies of other nations with common cultural characteristics may clarify trends and aetiological issues. Care should be taken to differentiate sex- from age-related influences.     

Caprolactam production: A comparison of different layouts of the liquid-liquid extraction section

Two different layouts for the liquid-liquid extraction section of an industrial caprolactam process are evaluated. Laboratory mass transfer measurements on streams obtained from an industrial and a demonstration plant with different extraction sections are interpreted by a model describing the effect of surface contaminants on mass transfer coefficients. Indications of the impact of these layouts on the complexity of the extraction section, quality of products and efficiency of the extraction processes are given.     

Thermolithographic patterning of sol-gel metal oxides on micro hot plate sensing arrays using organosilanes

Sol-gel-derived SnO2 and Fe2O3 were selectively deposited on elements of micro hot plate (microHP) arrays. The silicon micromachined microHP arrays contain heating elements (100 microm x 100 microm) that are electronically addressable and thermally isolated from each other. Thin films of (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (TFS) or hexyltrichlorosilane (HFS) assembled on surfaces of the arrays served as thermally sensitive resists whereby heating of specific microHPs resulted in removal of organosilane films only in heated areas. TFS-masked surfaces were characterized with condensation figures and secondary ion mass spectrometry (SIMS) imaging. TFS was removed from regions heated above 400 degrees C to expose hydrophilic surfaces, while TFS films in unheated areas were unaffected and remained hydrophobic. Sol-gel tin oxide spin-coated on the thermally patterned arrays adhered only to the hydrophilic regions and was repelled from the hydrophobic areas masked by the TFS films. By using HFS films, it was possible to selectively deposit two sol-gel materials, SnO2 and Fe2O3, on different microHPs in the same array as confirmed by SIMS imaging. Both materials showed varying degrees of electrical response to hydrogen and methanol in gas-sensing measurements.     

Stable carbon isotope evidence for intrinsic bioremediation of tetrachloroethene and trichloroethene at area 6, Dover Air Force Base

Area 6 at Dover Air Force Base (Dover, DE) has been the location of an in-depth study by the RTDF (Remediation Technologies Development Forum Bioremediation of Chlorinated Solvents Action Team) to evaluate the effectiveness of natural attenuation of chlorinated ethene contamination in groundwater. Compound-specific stable carbon isotope measurements for dissolved PCE and TCE in wells distributed throughout the anaerobic portion of the plume confirm that stable carbon isotope values are isotopically enriched in 13C consistent with the effects of intrinsic biodegradation. During anaerobic microbial reductive dechlorination of chlorinated hydrocarbons, the light (12C) versus heavy isotope (13C) bonds are preferentially degraded, resulting in isotopic enrichment of the residual contaminant in 13C. To our knowledge, this study is the first to provide definitive evidence for reductive dechlorination of chlorinated hydrocarbons at a field site based on the delta13C values of the primary contaminants spilled at the site, PCE and TCE. For TCE, downgradient wells show delta13C values as enriched as -18.0/1000 as compared to delta13C values for TCE in the source zone of -25.0 to -26.0/1000. The most enriched delta13C value on the site was observed at well 236, which also contains the highest concentrations of cis-DCE, VC, and ethene, the daughter products of reductive dechlorination. Stable carbon isotope signatures are used to quantify the relative extent of biodegradation between zones of the contaminant plume. On the basis of this approach, it is estimated that TCE in downgradient well 236 is more than 40% biodegraded relative to TCE in the proposed source area.     

Molar mass profiling of synthetic polymers by free-solution capillary electrophoresis of DNA-polymer conjugates

The molar mass distribution of a polymer sample is a critical determinant of its material properties and is generally analyzed by gel permeation chromatography or more recently, by MALDI-TOF mass spectrometry. We describe here a novel method for the determination of the degree of polymerization of polydisperse, uncharged, water-soluble polymers (e.g., poly(ethylene glycol) (PEG)), based upon single-monomer resolution of DNA-polymer conjugates by free-solution capillary electrophoresis. This is accomplished by end-on covalent conjugation of a polydisperse, uncharged polymer sample (PEG) to a monodisperse, fluorescently labeled DNA oligomer, followed by electrophoretic analysis. The monodisperse, charged DNA "engine" confers to each conjugate an equal amount of electromotive force, while the varying contour lengths of the uncharged, polydisperse polymers engender different amounts of hydrodynamic drag. The balance of electromotive and hydrodynamic forces enables rapid, high-resolution separation of the DNA-polymer conjugates as a function of the size of the uncharged PEG tail. This provides a profile of the molar mass distribution of the original polymer sample that can be detected by laser-induced fluorescence through excitation of the dye-labeled DNA. We call this method free solution conjugate electrophoresis (FSCE). Theory-based analysis of the resulting electrophoresis data allows precise calculation of the degree of polymerization of the PEG portion of each conjugate molecule. Knowledge of the molecular mass of the uncharged polymer's repeat unit allows for direct calculation of the molar mass averages as well as sample polydispersity index. The results of these analyses are strikingly reminiscent of MALDI-TOF spectra taken of the same PEG samples. PEG samples of 3.4-, 5-, and 20-kDa nominal average molar mass were analyzed by FSCE and MALDI-TOF; the values of the molar mass averages, Mw and Mn, typically agree to within 5%. Measurements and molar mass calculations are performed without any internal standards or calibration. Moreover, when DNA-polymer conjugate analysis is performed in a chip-based electrophoresis system, separation is complete in less than 13 min. FSCE offers an alternative to MALDI-TOF for the characterization of uncharged, water-soluble polymers that can be uniquely conjugated to DNA.     

Nutrient requirements for dairy cattle of the National Research Council versus some commonly used ration software

The first edition of the Nutrient Requirements of Dairy Cattle was published by the National Research Council (NRC) in 1945. The current document is the sixth revised edition, published in 1989, and it appears that we are a few years from another edition being in print. Software designed to evaluate and formulate rations for dairy cattle commonly determine nutrient requirements using the NRC as a standard. However, the generation of new knowledge in dairy nutrition occurs more rapidly than the release of the NRC publication, and the developers of the software often modify the requirements based on more recently published research, geographical peculiarities, or factors not explicitly considered by NRC. The first step in evaluating or formulating rations is the prediction of dry matter intake (DMI). The primary variables used by NRC to predict DMI are body weight (BW) and fat-corrected milk (FCM) yield; however, developers of software programs often use different equations based on personal preference, availability of research data with given equations, and incorporation of other factors in addition to BW and FCM yield. The additional factors are included to provide a more dynamic estimation of DMI and, therefore, reduce the difference between predicted and actual DMI. Nutrients required for maintenance, lactation, and growth must be consumed in adequate quantities (e.g., kilograms or calories), but the dietary concentration of nutrients for a given animal group may differ because of DMI. Even when nutrients are fed above the requirements, dietary concentrations of nutrients may be important in some situations to minimize the risk of underfeeding caused by variability in the nutrient composition of feedstuffs and to account for interactions of certain nutrients (e.g., minerals). New research discoveries need to be incorporated into ration formulation strategies promptly, and the strategies used for ration formulation need to be dynamic.