采用提高纸张定量减少层数制作伸性纸袋的探讨和建议

文中阐述了纸袋纸所要求的使用性能，通过对伸性纸袋的有关试验，验证了采用提高纸张定量，减少层数的纸袋具有较好的使用效果和经济效益，建议在实践中加以推广和应用之。     

最佳计算流体动力学（CFD）的流浆箱浆流

开发了最优化技术用于实现纸机流浆箱浆流的数字控制。对于特定的流浆箱和其中的部件或浆流情况，相关的最优化问题是通过对其进行数字描述并数字化控制来解决的。产生的内部软件通过两个实例进行阐述，即锥形总管的几何优化和堰板槽浆流的控制优化，包括流浆箱的传统堰板调节和可控浆浓流浆箱的数字化控制实例。[刊,英]（41）     

浆浓自控系统在纸机定量控制上的应用

2000年5月陆良银河纸业有限公司决定在原有2362型薄页纸机上开发卷烟滤嘴棒成型纸,决定对2362mm纸机进行改造,为确保生产出的纸张定量波动控制在±5%以内,拟采用高达测控公司浆浓自控系统对纸机上浆进行自动控制,确保纸机抄造正常,减少因定量波动而产生的残次品数量,并节约能源。该系统的应用具有一定的先进性和实用性。1流程介绍本公司纸机上浆系统采用冲浆池、冲浆泵上浆,自控部分及相关上浆流程如图1所示。2系统工作原理及硬件配置变送器包括1台高达公司的静刀浓度计,(DD2—Ⅲ)1台光华仪表K300电磁流量计(SE×10mm),2台电磁调节阀(unic…     

火炬松机械浆生产低定量涂布纸的可行性

火炬松木材价格比北方针叶木低,生长速率快,种植、采伐适应性强。但是,火炬松机械浆的质量差,主要用于生产低档纸例如新闻纸。加拿大造纸中心科技人员最新研究结果表明,火炬松机械浆通过低浓磨浆或化学品预处理可以明显地改进质量,从而可生产高档纸例如低定量涂布纸。     

流送系统的改进解决涂布纸纵向和横向定量波动问题

北美某纸厂的一台大型纸机生产低定量涂布纸,出现了严重的纵向和横向定量波动问题.Voith工艺分析团队对其流送系统进行了全面分析,包括脉冲研究、管道流动特性的工程评估、Tapio/TSO分析以及流浆箱的测绘.其中的造纸工艺师进行了震动研究,他用一台多通道光谱分析仪评估纸浆系统各点的压力脉冲变化(图31).     

Forced heat loss from body surface reduces heat flow to body surface

Heat stress is commonly relieved by forced evaporation from body surfaces. The mode of heat stress relief by heat extraction from the periphery is not clear, although it reduces rectal temperature. Radiant surface temperature (Ts) of the right half of the body surface was examined by thermovision in 4 lactating Holstein cows (30 kg of milk/d) during 7 repeated cycles of forced evaporation created by 30 s of wetting followed by 4.5 min of forced airflow. Wetting was performed by an array of sprinklers (0.76 m³/h), and forced airflow (>3 m/s velocity) over the right side of the body surface was produced by fans mounted at a height of 3 m above the ground. Sprinkling wetted the hind legs, rump, and chest, but not the lower abdomen side, front legs, or neck. The animals were maintained in shade at an air temperature of 28°C and relative humidity of 47%. Coat thickness was 1 to 2 mm, so Ts closely represented skin temperature. Mean Ts of 5 × 20 cm areas on the upper and lower hind and front legs, rump, chest, abdomen side, and neck were obtained by converting to temperature their respective gray intensity in single frames obtained at 10-s intervals. Little change occurred in Ts during the first wetting (0.1 ± 0.6°C), but it decreased rapidly thereafter (1.6 ± 0.6°C in the fifth wetting). The Ts also decreased, to a smaller extent, in areas that remained dry (0.7 ± 1.0°C). In all body sites, a plateau in Ts was reached by 2 min after wetting. The difference between dry and wet areas in the first cooling cycle was approximately 1.2°C. The Ts of different body areas decreased during consecutive cooling cycles and reached a plateau by 3 cooling cycles in dry sites (front leg, neck, abdomen side), by 5 cooling cycles in the hind leg, and 7 cooling cycles in the rump and chest. The reduction in mean Ts produced by 7 cycles was 4.0 to 6.0°C in wetted areas and 1.6 to 3.7°C in sites that were not wetted. Initial rectal temperature was 38.9 ± 0.1°C; it remained unchanged during first 5 cooling cycles, decreased by 0.1°C after 7 cooling cycles, and decreased to 38.4 ± 0.06°C after 8 to 10 cooling cycles, with no additional subsequent decrease. The concomitant reduction in Ts in dry and wet areas suggests an immediate vasoconstrictor response associated with heat extraction and later development of a cooler body shell. The reduction in rectal temperature represents a response involving transfer of heat from the body core to the body shell. This response mode requires consideration in settings of heat stress relief.     

Colour change and weight loss of apple slices during drying

Drying of apple slices was studied in a conventional tray drier (initial slice thickness=0.3–1.0 cm, drier temperature=60–100 °C) and in a computer-controlled tunnel drier (initial slice thickness=0.8 cm, air tempera ture=50–100 °C, air flow rate=2.4 m/s). In most of the experiments the drying behaviour was characterized by a constant rate period, followed by a falling rate period. The constant rate drying period did not occur, and the colour of the dried slices was improved substantially with tunnel drying under computer control, when a linearly decreasing temperature profile from 100 °C to 70 °C was used. The quality improvement may be attributed partly ot the elimination of the continuous water film covering the surface in the constant rate drying period, which may serve as a medium for the reaction and transport of the chemical species.

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Farbveränderungen und Gewichtsverluste von Apfelstücken während des Trocknens

Zusammenfassung Apfelscheiben (0,3–1,0 cm) wurden in einem konventionellen Hordentrockner (60 bis 100 °C) und einem rechnerkontrollierten Tunneltrockner (Scheiben 0,8 cm, Lufttemperatur 50 bis 100 °C, Luftfluß 2,4 m · s^–1) getrocknet. Bei den meisten Experimenten wurde eine zweiphasige Trocknung beobachtet. Eine regelmäßige Trocknung fand dagegen bei einem gesteuerten, linearen Temperaturgradienten von 100 zu 70 °C statt. Dies verbesserte die Qualität der Produkte, offensichtlich wegen des Vermeidens einer Wasserfilm-Bildung auf den Oberflächen der Apfelstücke während des Trocknens. Ein derartiger Film kann ein Medium für Reaktionen und den Transport von Reaktanden Scin.

     

浅谈白条肉在冷却和冻结过程中的干耗

目前在猪肉的冷加工过程中,一般冷却肉的加工温度为0～15℃,冷冻肉的加工温度为-40～-15℃.肉类在冷加工过程中,由于表面层的水分蒸发,使肉类不断减重,这种减重的现象,称为"脱水",俗称"干耗".     

普洱茶发酵过程中茶多糖分子量变化研究

从不同微生物发酵的普洱茶中提取茶多糖,并对其分离纯化?分子量分析,明确茶多糖在发酵过程中的变化规律。采用热水浸提乙醇沉淀法提取茶多糖,双氧水脱色,再用凝胶色谱(GPC)法测定其分子量。结果表明,由木霉和酵母发酵的普洱茶多糖提取物中糖分与蛋白质含量均随着发酵时间的延长而增加。由木霉发酵的普洱茶中多糖的分子量随着发酵时间的延长先增大然后减小;由酵母发酵的普洱茶中多糖的分子量未呈现出规律性变化。结果表明,茶原料、发酵的微生物种类以及发酵时间等对发酵普洱茶中多糖分子量都有影响。     

Controlling the weight loss of fresh produce during postharvest storage under a nano-size mist environment

Weight loss and chilling injury often occur during the refrigerated storage of fresh produce, leading to significant economic costs to horticultural industries. The postharvest quality of three types of horticultural produce, eggplant fruit (Solanum melongena), mizuna (Brassica rapa) and fig fruit (Ficus carica), was investigated under storage environments of two kinds of fine mists producing relative humidity as high as 95% at 5.5 and 7 °C for 10, 6 and 8 days, respectively. Mists generated by nanomist humidifiers (nanomists) had average particle diameters less than 100 nm, while ultrasonic humidifiers (ultrasonic mists) generated average particle diameters of 216 nm. The results show that the weight loss rates of the samples stored under nanomist humidifiers were 3.7%, 5.3% and 8.8% for mizuna, eggplant and fig, respectively, while those stored under ultrasonic mist were 7.3%, 8.5% and 14.7%, respectively. The eggplant fruits stored in the nanomist chamber had a lower index of chilling injury than those stored in the ultrasonic mist. The stomatal pores of the samples exposed to the nanomists closed by 34.7 and 51.5 μm² for mizuna and fig, respectively, compared with their initial openings, while in the ultrasonic mists, they closed by 15.8 and 25.5 μm², respectively. The color of mizuna stored in the nanomist was greener than those placed in the ultrasonic mist during the postharvest storage period.     

Drip loss,peroxidase and sensory changes in kiwi fruit slices during frozen storage

The biochemical, sensory and drip loss changes that occur during processing and prolonged frozen storage of kiwi fruit slices (cvs Abbott and Hayward) were studied. Fruit slices were frozen at ?40°C, packed in polyethylene bags and stored at ?18°C for 11 months. Maturity characteristics (pH, acidity, dry matter, soluble solids) were determined on raw fruit. Objective (proteins, peroxidase (EC 1.11.1.7) activity, drip loss) and subjective (sensory tests) analyses were carried out during processing and storage, and indicated a good quality of the frozen kiwi fruit slices after 11 months of storage. There were significant differences (P < 0.05) between the studied varieties with respect to drip loss during frozen storage and colour after 11 months. Best results were obtained with cv Hayward. This variety showed less drip loss after thawing and after 11 months storage presented the same green colour as after freezing, while cv Abbott became yellowish-green.     

Pepsin-induced changes in the size and molecular weight distribution of bovine casein during enzymatic hydrolysis

Bovine casein was digested with pepsin at pH 2.0 in a batch-stirred tank reactor. To investigate the effect of peptic digestion on the aggregate size and molecular weight distribution of bovine casein, the resulting hydrolysates were examined by size-exclusion chromatography coupled with multiangle laser light scattering and dynamic light scattering. Casein was resolved by size-exclusion chromatography into 2 major peaks corresponding to aggregates and monomers, both of which showed a continuous decrease as hydrolysis proceeded. However, the ratio of aggregates to monomers was maintained at almost 1 (2:2.5) during the initial 30-min hydrolysis, indicating that the caseins in solution were in a type of equilibrium between aggregates and monomers. Upon peptic hydrolysis, casein aggregates increased in size and molecular weight, and exhibited a decrease in intermolecular repulsion. This finding was confirmed by dynamic light scattering measurements, which traced the changes in the hydrodynamic radii and light scattering intensities of casein hydrolysates. In addition, the release kinetics of peptide fractions with different molecular weights was also examined. It was concluded that the increase in hydrophobic attraction and the reduction in intermicellar repulsion might promote the growth in aggregate size of bovine casein during the limited hydrolysis.     

Effects of atmospheric composition on respiratory behavior, weight loss, and appearance of Camembert-type cheeses during chamber ripening

Respiratory activity, weight loss, and appearance of Camembert-type cheeses were studied during chamber ripening in relation to atmospheric composition. Cheese ripening was carried out in chambers under continuously renewed, periodically renewed, or nonrenewed gaseous atmospheres or under a CO₂ concentration kept constant at either 2 or 6% throughout the chamber-ripening process. It was found that overall atmospheric composition, and especially CO₂ concentration, of the ripening chamber affected respiratory activity. When CO₂ was maintained at either 2 or 6%, O₂ consumption and CO₂ production (and their kinetics) were higher compared with ripening trials carried out without regulating CO₂ concentration over time. Global weight loss was maximal under continuously renewed atmospheric conditions. In this case, the airflow increased exchanges between cheeses and the atmosphere. The ratio between water evaporation and CO₂ release also depended on atmospheric composition, especially CO₂ concentration. The thickening of the creamy underrind increased more quickly when CO₂ was present in the chamber from the beginning of the ripening process. However, CO₂ concentrations higher than 2% negatively influenced the appearance of the cheeses.     

Effect of prenatal multiple micronutrient supplements on maternal weight and skinfold changes: a randomized double-blind clinical trial in Mexico

BACKGROUND: Recent trials of prenatal multivitamin-mineral supplements have yielded mixed findings for outcomes such as birth size, but the benefits of prenatal multivitamin-mineral supplements for maternal outcomes are unknown. OBJECTIVE: The main objective of this study was to examine the effect of prenatal multiple micronutrient supplements (MM) compared to iron only (FE) supplements on changes in maternal weight and body composition during pregnancy and the early postpartum period. METHODS: A randomized double-blind clinical trial was conducted in semi-rural Mexico. Women received either MM or FE supplements, 6 days per week from early pregnancy to delivery. Anthropometric measurements were obtained at recruitment, 26 and 37 weeks pregnancy, and 1 month postpartum. Women in both groups were similar at recruitment except that body-mass index (BMI) was greater in the FE group. RESULTS: Mean weight gain during pregnancy was significantly greater (-0.6 kg) in the MM group (n = 283) compared to the FE group (n = 287), but not after adjusting for maternal BMI at recruitment. Overweight women in the MM group gained 0.53 kg between recruitment and 1 month postpartum, whereas those in the FE group lost 0.63 kg; there were no differences between experimental groups among non-overweight women (p =.06 for interaction). CONCLUSIONS: Compared to iron supplements, MM supplements did not increase weight gain during pregnancy after adjusting for baseline differences in BMI but may lead to greater postpartum weight retention among overweight women.