On the thermal stability of xanthan gum

The thermal stability of xanthan gum in dilute aqueous solutions at 90°C is considered. The relative viscosity as a function of ageing time is discussed, and it has been found to depend on the polymer concentration and conformation as well as on the salt content. The effectiveness of a quencher demonstrates the existence of a free-radical process in the degradation. During ageing, the molecular weight first decreases by rapid random hydrolysis of the main chain and loss of the pyruvate and acetate substituents. Later, oligomers are formed corresponding to a breakdown of both the side chain and the main chain. The identification of cellodextrins in the oligomer pool demonstrates the second effect.     

离心制冷机组冷凝/蒸发系统的化学清洗

针对该厂离心制冷机组冷凝 /蒸发系统严重积垢危及设备安全运行这一现状 ,研究出了一种适宜的清洗方案并成功地应用于现场。为化学清洗技术如何有效地用于制冷行业特殊污垢的处理 ,提供了一个成功的范例     

Internet上化学化工资源

详细介绍了Internet上的化学化工资源及域名地址。     

The use of a mixing-sensitive chemical reaction for the study of pulp fibre suspension mixing

The competitive, consecutive chemical reactions between 1-naphthol and diazotized sulfanilic acid were utilized to study the mixing of a pulp fibre suspension in a 22 L stirred tank reactor. Mixing quality was determined from the distribution between the mono and bis substituted reaction products once a correlation was made for the adsorption of the product dyes onto the suspended fibres. The technique was found to be adequate for assessing micromixing and turbulence intensity within a fibre suspension provided the measured product distribution, Xs, was between 0.4 and 0.01. Thus the mixing conditions that could be assessed depended on both the energy dissipation within the mixer and the amount of the fibre present. For the experimental conditions chosen for this study energy dissipation rates would typically have to be less than 80 W/kg and the suspension mass concentration less than 2.5%. When compared with water, a reduction in turbulence levels at both the impeller zone and a remote zone in the stirred vessel was observed for fibre mass concentrations as low as 0.5%. The turbulence decreased as the suspension mass concentration was increased. This decrease is attributed to energy dissipation by friction at fibre-fibre contact points as the fibres move relative to one another in the flow. This sink removes energy from the turbulence cascade which never shows up as small-scale fluid deformations leading to better mixing.     

Acquired Predator Recognition by Fathead Minnows: Influence of Habitat Characteristics on Survival

In this study we conditioned fathead minnows (Pimephales promelas) to recognize the odor of a perch (Perca flavescens) by exposing them to perch odor coupled with minnow alarm cue. We then staged encounters between the predator and prey in order to assess whether the predator odor training had any effect on survival of the prey. We tested for a survival effect in the presence and absence of shelter. Our results indicate that fish trained with alarm signals to recognize predators gained a survival benefit during staged encounters with a predator and that habitat characteristics influenced the survival of conditioned fish.     

Flavonoid pigments in chalkhill blue (Lysandra coridon Poda) and other lycaenid butterflies

Nine flavonoids, namely, kaempferol, kaempferol 7-rharanoside, kaempferol 3-rhamnoside, kaempferol 3-glucoside, kaempferol 3-glucoside, 7-rhamnoside, quercetin 3-glucoside, quercetin 3,7-diglucoside, isorhamnetin 3-glucoside, and isorhamnetin 3,7-diglucoside, have been identified in the body and wings of the chalkhill blue butterflyLysandra coridon Poda. Flavonoids have also been found in 15 of a further 17 lycaenid species examined. Analysis of the two-dimensional paper chromatographic flavonoid patterns and aglycone results has shown that the flavonoid content ofL. coridon and the other lycaenids is dependent on the flavonoid content of the larval diet. Differences in the flavonoid patterns ofL. coridon and its leguminous larval food plantsHippocrepis comosa, Anthyllis vulneraria, andLotus corniculatus, indicate that the ingested flavonoids are metabolized byL. coridon or its gut flora before sequestration. Despite the presence of fiavones, glycoflavones, and isoflavones in the larval food plant species, only flavonols are sequestered by the lycaenid species examined. The relationship between lycaenid butterflies and their larval food plants, and the possible role(s) of flavonoids in lycaenids has been discussed. Interactions between ants, plants, flavonoids, and myrmecophilous lycaenids have also been considered.     

Chemical Composition Determination at the Bottom Region of a Recovery Boiler Furnace by Direct Minimization of Gibbs Free Energy

An optimization strategy has been applied to describe the chemical composition at the furnace bottom in the Kraft recovery boiler of a pulp production process. The concentrations of each involved chemical species were calculated through an optimization approach, minimizing the Gibbs free energy of the system. Various systems were proposed and tested, assuming different chemical species and phases number. Because serious initialization problems were found at this stage for some of the proposed systems, an optimization heuristic method (PSO) was used for the first approach to the problem. Once the appropriate phases number and chemical species in the system were determined, the initialization problems disappeared and the use of a deterministic optimization method (SQP) became viable. The proposed approach has shown to be satisfactory to reproduce industrial data and also data reported in the open scientific literature.     

Sex-identifying urine and molt signals in lobster (Homarus americanus)

During courtship, premolt female lobsters,Homarus americanus, choose a male and initiate a pair bond by repeated approaches to his shelter. The male allows such a female to share his shelter for about one week. This knowledge formed the basis to search for quantitative evidence for lobster sex pheromone(s) used in courtship: male cues to allow premolt females to identify a preferred male, and female cues to allow males to identify a premolt mature female. In each of four 1500-liter naturalistic aquaria, the behavioral responses of one female and two male lobsters to male and female lobster urine (0.5 ml) and body odor (20 ml) stimuli were observed. These stimuli were injected once or twice per day into a continuously flowing delivery tube attached to lobster shelters. Habituation to stimulus introduction—a serious problem in earlier experiments—was apparently avoided in the more natural social and physical environment we employed in these experiments. We demonstrated that male and female molt body odors contain different chemical substances: females responded to male molt body odor and males responded to female molt body odor but not vice versa. In general, male and female intermolt urine caused strong responses; however, females responded only weakly to male urine. This suggests that male and female urine are chemically different. Female urine and molt body odor caused a typically male high-on-legs response. These results show that molt body odors and intermolt urine contain sex-specific substances, which may be used in lobster courtship as well as other social interactions.     

电解铝厂整流变电所直流大母线施工技术

介绍电解铝工艺设备中直流汇流母线的加工和安装施工技术.