FREE-RADICAL RETROGRADE-PRECIPITATION POLYMERIZATION: A MATHEMATICAL MODELING STUDY OF POLYMERIZATION OF STYRENE IN DIETHYL ETHER

Polymerizing a monomer above the lower critical solution temperature (LCST) of its polymer-monomer-(non)solvent mixture has demonstrated better control characteristics than conventional free-radical polymerization kinetics. Reaction kinetics of polymerization in a poor solvent are strongly influenced by heat and mass transfer properties, as understood from modeling the transport phenomena in our earlier work. The study has now been extended to model the reaction kinetics in a styrene-diethyl ether system. The model was based on the CCS model for free radical polymerization, with the modification proposed by Achilias-Kiparissides. Computer simulation results agree well with those obtained from experiments carried under similar conditions, with the onset of phase separation as the only adjustable parameter. Drawbacks of the model are lack of analysis for the effect of monomer concentration and the absence of an appropriate radical trapping mechanism.     

四种电力系统稳定器的性能比较

电力系统稳定器(PSS)为励磁系统产生辅助控制信号来改善系统阻尼进而抑制低频振荡。迄今为止,已提出了多种不同的PSS设计方法,并得到了不同程度的应用。在此背景下,通过小干扰特征值分析和大干扰故障时域仿真,对传统PSS(CPSS)、单神经元PSS(SNPSS)、自适应PSS(APSS)和多频带PSS(MBPSS)4种有代表性的PSS设计方法的原理和特性进行比较研究,为使比较研究具有共同的基础,这4种PSS的参数都采用最速下降法优化确定。最后,以8机24节点系统为例进行了大量仿真计算,对这4种PSS设计方法的性能进行了比较分析,得到了一些有意义的结论。     

VIRULENCE FACTORS ASSOCIATED WITH PATHOGENICITY OF AEROMONAS ISOLATES

Aeromonas species have been associated with diarrhea, and disseminating infections. Diarrhea is either "cholera-like" or "dysentery-like". Both types of diarrhea are normally mild. However, either type can be severe enough to cause hospitalization. The sources of Aeromonas in these infections are foods and water. Two virulence factors associated with Aeromonas diarrhea are a relatively heat-stable cholera-like enterotoxin and a heat-labile cytotoxic enterotoxin. Researchers who observed either of these enterotoxins rarely saw evidence of the other. These differences are probably due to the rare occurrence of the cholera-like toxin and to differences in purification methods. Human feeding studies showed that enterotoxin production is not sufficient for causation of diarrhea. The Aeromonas must also be able to colonize the intestine or invade the intestinal lining. Virulence factors associated with colonization or invasion have not been identified.     

PORE SIZE EFFECT IN THE FIREEZE DRYING PROCESS

SUMMARY— Experiment were conducted to determine the influence and/or effect of the structure of the dried material itself on transport rates. Drying rates were measured in the 0.2–3.0 mm Hg pressure range, the usual operating range of commercial freeze driers. Thermal conductivities of dried beef and heat and mass transfer were calculated from drying rate data and the structure of the freeze-dried material was studied by optical means. A simplified relationship between thermal conductivity and pore structure was derived. Results show drying rates were related to basic transport properties, thermal conductivity and pore structure.     

ESR study of hair and melanin–keratin mixtures – the effects of temperature and light

The ESR spectrum of hair presents a symmetrical absorption band with the same characteristics as pure melanin ( g = 2.0030; δ H = 5 G). Between 250°K and 490°K, the intensity of the signal increases as for pure melanin. This variation may be explained by a change in the moisture content of hair as function of the temperature. Below 250° K, in a frozen medium, melanin-water interactions remain constant and the number of radicals is no longer a function of temperature.
Under exposure to light of hair, melanin-derived radicals were formed. Stable and short-lived radicals were observed at λ > 345 nm; only unstable radicals were formed at λ > 450 nm. At shorter wavelengths (λ > 280 nm), a new asymmetric signal ( g = 2.0065 H = 20 G) appeared on UV exposure of black, grey or white hair; this signal was attributed to radicals formed in the direct excitation of keratin amino acids.
Le spectre RPE des cheveux     

X-band varactor tuned monolithic GaAs FET oscillators†

The design, fabrication and performance of X-band varactor-tuned monolithic GaAs FET oscillators is described. The design is based on small and large signal device characteristics. A manufacturable process is used in order to realize the oscillators. The experimental performance agrees with the theoretical expectations within 0·2% for the oscillation frequency and 4% for the tuning bandwidth. Best tuning bandwidth and output power values exceeded 2 GHz and 28 mW. Wafer dispersion depends on oscillator characteristics and varies between ±1% and ±7·7% for oscillators with a varactor in the FET source. The rf wafer yield is 65%. Finally, noise and temperature characteristics are given.     

DEVELOPMENT and EVALUATION of MICROWAVE HEATING of APPLE MASH AS A PRETREATMENT to PRESSING

Fuji, McIntosh, and Red Delicious apple mashes were heated in a 2450 MHz oven to achieve bulk temperatures of 40, 50, 60, and 70C. Three kilograms of mash at a depth of 0.016 m heated using 1500 W were the optimum parameters to heat apple mash in the microwave. Variety of the apple mash was shown not to have a significant effect on the heating performance. Comparing actual bulk temperature to the predicted bulk temperatures of 40, 50, 60, and 70C showed reproducibility of heating these mashes using microwave energy. Average variation between actual and predicted bulk temperatures were 1.48C for the Fuji mash, 0.98C for the McIntosh mash, and 1.13C for the Red Delicious mash. In addition, regional heating was investigated and four distinct regions of heating were observed: the corner, the edge, the middle, and the center. Color and moisture content of the mash were also measured and compared to unheated mash at 21C.