Flame spread over thin fuels in actual and simulated microgravity conditions

Most previous research on flame spread over solid surfaces has involved flames in open areas. In this study, the flame spreads in a narrow gap, as occurs in fires behind walls or inside electronic equipment. This geometry leads to interesting flame behaviors not typically seen in open flame spread, and also reproduces some of the conditions experienced by microgravity flames.Two sets of experiments are described, one involving flame spread in a Narrow Channel Apparatus (NCA) in normal gravity, and the others taking place in actual microgravity. Three primary variables are considered: flow velocity, oxygen concentration, and gap size (or effect of heat loss). When the oxidizer flow is reduced at either gravity level, the initially uniform flame front becomes corrugated and breaks into separate flamelets. This breakup behavior allows the flame to keep propagating below standard extinction limits by increasing the oxidizer transport to the flame, but has not been observed in other microgravity experiments due to the narrow samples employed. Breakup cannot be studied in typical (i.e., “open”) normal gravity test facilities due to buoyancy-induced opposed flow velocities that are larger than the forced velocities in the flamelet regime.Flammability maps are constructed that delineate the uniform regime, the flamelet regime, and extinction limits for thin cellulose samples. Good agreement is found between flame and flamelet spread rate and flamelet size between the two facilities. Supporting calculations using FLUENT suggest that for small gaps buoyancy is suppressed and exerts a negligible influence on the flow pattern for inlet velocities ?5 cm/s. The experiments show that in normal gravity the flamelets are a fire hazard since they can persist in small gaps where they are hard to detect. The results also indicate that the NCA quantitatively captures the essential features of the microgravity tests for thin fuels in opposed flow.     

BGA评估中使用的分析方法

球珊阵列（BGAs）在印刷电路板（PCB）组件上已经相当常见,进而带来了新的故障模式,要求新的分析工具或方法,以便正确评估这些元件。传统式SMT元件,如SOICs或OFPs,允许以可视方式检测焊点,查找异常情况;而BGAs则做不到这一点,因为大多数焊点隐藏在元件下面,人眼是看不到的。本文讨论了STI实验室遇到的部分故障模式,以及进行调查使用的工具和方法。     

Dystocia, stillbirth, gestation length, and birth weight in Holstein, Jersey, and reciprocal crosses from a planned experiment

Holstein and Jersey cows were mated to 4 Holstein (H) bulls and 4 Jersey (J) bulls to create HH, HJ, JH, and JJ genetic groups (sire breed listed first) in a diallele crossbreeding scheme. Calvings (n = 756) occurred in research herds in Virginia, Kentucky, and North Carolina with 243, 166, 194, and 153 calvings in the HH, HJ, JH, and JJ groups, respectively. Birth weights (BW), dystocia scores (0 for unassisted and 1 for assisted), and stillbirth (0 for alive or 1 for dead within 48 h) were recorded at calving. Gestation lengths (GL) were determined from breeding dates. An animal model was used to analyze BW and GL, and an animal model with logistic regression was used for dystocia and stillbirth. Fixed effects considered for model inclusion were genetic group, herd-year-season, sex, parity (primiparous or multiparous), twin status, and gestation length. Genetic group and effects significant in the model building process were kept in the final model for each trait. Heifer calves had lower BW, shorter GL, and had a lower odds ratio (0.53) for dystocia than bull calves. Twins had lower BW, shorter GL, were 3.86 times more likely to experience dystocia, and 7.80 times more likely to be stillborn than single births. Primiparous cows had calves with lower BW, shorter GL, were 2.50 times more likely to require assistance at birth, and were 2.35 times more likely to produce stillborns than calves from multiparous cows. Genetic group did not affect GL. Least squares means (kg) for BW were 37.7 ± 1.1, 29.1 ± 1.1, 30.3 ± 1.0, and 22.5 ± 1.3 for HH, HJ, JH, and JJ, respectively. Animals in HH weighed more than animals of other genetic groups; the JJ group had the smallest BW, with no differences for BW between HJ and JH. Probability of dystocia in JJ and JH were 5.73% and 18.98% of HH. Calves in HJ and HH were not different for dystocia. Calves in HJ were 3.38 times more likely to be stillborn than calves in JH, but no other genetic group differences were significant for probability of stillbirth. Groups HJ and JH differed for calving traits, with JH crosses experiencing less dystocia than HJ; JJ showed no indication of dystocia. No differences were observed between HH and JJ for stillbirths. Additional investigation of stillbirths in Jerseys is justified.     

Effect of Crystallization on Thermal Conductivity and Specific Heat of Two Corning Glass-Ceramics

A magnesium aluminosilicate glass-ceramic (Corning Code 9606) has been heat-treated at 900°, 1010°, 1200°, and 1260°C for up to 90 min., and the effect on the thermal conductivity between 30 and 300 K has been studied. It has been shown that the large increase of the thermal conductivity which results from the ceramming occurs predominantly when crystalline cordierite forms. At 1260°C, heat treatment for only 20 min leads to a thermal conductivity identical to that measured for commercial 9606, which has been cerammed for 8 h at the same temperature. This observation provides further evidence for the usefulness of commercial 9606 as a thermal conductivity standard. Measurements of the specific heats of Code 9606 before and after ceramming have been reviewed and have been found to be close to that of crystalline SiO₂ above ∼ 30 K, regardless of the state of ceramming. A review has also been made of thermal conductivity and specific heat of several ZrTiO₄ nucleated lithium aluminosilicate glass-ceramics at various states of ceramming. The thermal conductivity of these glass-ceramics seems to be sufficiently independent of chemical composition as well as of the degree of crystallization to warrant a recommended curve for this class of glass-ceramics.     

Biodesulfurization of dibenzothiophene sulfone by Arthrobacter sp. and studies with oxidized Illinois No. 6 coal

A bacterium identified as Arthrobacter sp. was grown on dibenzothiophene (DBT) sulfone as a sole source of sulfur, producing sulfite and sulfate. Sulfur in DBT sulfone (1.0 mM) was nearly quantitatively converted to sulfate by the organism. The organism could also use DBT sulfone as a sole source of carbon and energy. There was evidence for transient accumulation of benzoic acid in the culture medium after growth of the cells slowed. The DBT sulfoxide analogue 9-fluorenone was converted by resting cells to a product identified as 1,10-dihydroxy-1,10-dihydrofluoren-9-one, suggesting that DBT sulfone may be metabolized via an angular hydroxylation resulting in carbon- sulfur bond cleavage. This strain of Arthrobacter showed no ability to desulfurize oxidized Illinois No. 6 coal.     

Kinetics of hydantoin formation

The reaction of lignite in a slagging gasifier produces reactants which in turn form 5,5-dimethylhydantoin (DMH) as a major constituent in the condensate water. Variations in plant operating conditions made it impossible to accurately study the kinetics of formation of DMH in the actual gasifier water, and thus a model system was chosen. The reaction of acetone cyanohydrin in the presence of excess ammonium carbonate at concentrations approaching those obtained in the condensate water were studied at 50,70, and 90 °C. Secondorder kinetics were obeyed, and the pseudo second-order rate constants at the respective temperatures were 1.86, 3.6, and 4.62 dm³ mol^{? 1} h^{? 1}. Independent variation of the concentration of either acetone, cyanide, ammonia or carbonate gave results consistent with the interpretation that the formation of DMH is first order in all reactants: rate of formation of DMH = k[acetone][HCN][NH₃][CO₂]. The pseudo second-order rate constant is a complex rate constant including several rapid equilibria. A mechanism consistent with the kinetic data is presented.     

Short communication: Salt tolerance of Lactococcus lactis R-604 as influenced by mild stresses from ethanol,heat, hydrogen peroxide,and UV light

Lactococcus lactis is a culture widely used in salt-containing dairy products. Salt hinders bacterial growth, but exposure to environmental stress may protect cells against subsequent stress, including salt. The objective of this study was to evaluate the salt tolerance of L. lactis R-604 after exposure to various stresses. The culture was subjected to 10% (vol/vol) ethanol for 30 min, mild heat at 52°C for 30 min, 15 mM hydrogen peroxide for 30 min, or UV light (254 nm) for 5 min and compared with a control. Starting with 5 log cfu/mL for all treatments, growth was determined in M17 broth with 5 NaCl concentrations (0, 1, 3, 5, and 7% wt/vol). Plating was conducted daily for 5 d. Salt tolerance was enhanced with mild heat exposure before growth in M17 broth with 5% (wt/vol) NaCl on d 3, 4, and 5, and with exposure to hydrogen peroxide and ethanol stresses before growth in M17 broth with 5% (wt/vol) NaCl on d 4 and 5. Exposure of this culture to mild heat, hydrogen peroxide, or ethanol before growth in M17 broth containing 5% (wt/vol) salt can enhance its survival, which could be beneficial when using it in salt-containing dairy products.     

Factors influencing tenderness in steaks from Brahman cattle

The objective of this study was to identify a set of explanatory variables for Warner-Bratzler shear force and myofibril fragmentation indices after 7, 14, and 21d of aging; and sensory tenderness after 14d of aging of steaks from Brahman cattle. Insoluble collagen was negatively associated (P<0.001) with all tenderness traits across aging periods, and regression coefficients ranged from 5.69±0.49 to 9.12±0.29N for Warner-Bratzler shear force. The effect of lean color score (P<0.05) in analyses of unadjusted traits was diminished when data were adjusted for contemporary group (calves of the same sex, fed in one pen, and slaughtered the same day). Insoluble collagen may be of special importance and offer a unique opportunity to improve palatability of steaks from purebred Brahman cattle.