回热器与制冷工质对复叠制冷系统性能的影响

建立了复叠制冷系统的热力学模型,对比分析了低温级冷凝温度、高温级冷凝温度以及回热器位置对R449A/CO₂、NH₃/CO₂、R404A/CO₂3种复叠制冷系统性能的影响。结果表明,相同低温级蒸发温度下,NH₃/CO₂系统的最佳低温级冷凝温度低于R449A/CO₂和R404A/CO₂系统的,NH₃/CO₂系统的最佳性能系数COP与R449A/CO₂的相差约2%,大幅高于R404A/CO₂系统的;复叠系统的CO2低温级设置回热器会使系统性能降低,而高温级设置回热器,R449A/CO2和NH₃/CO₂系统的性能下降,R404A/CO₂系统的性能提高。R449A在复叠制冷系统中性能优良,可作为低GWP冷媒推广使用。     

废纸纤维回用过程恶臭气体产生因素研究

本研究利用泵吸式气体检测仪对恶臭气体浓度进行检测,探究了废纸纤维回用过程中网下白水添加量、淀粉浓度、Na₂SO₄浓度对恶臭气体释放量的影响。结果表明,当网下白水添加量为0时,总挥发性有机化合物（TVOC）、H₂S和NH₃的释放量几乎均为0;增加网下白水添加量可使浆料中的恶臭气体释放量显著增加,证明微生物的大量繁殖是影响恶臭气体释放的主要因素之一。随着淀粉浓度的提高,H₂S和NH₃的释放量增长明显,但TVOC释放量与未加入淀粉时基本一致。Na₂SO₄对浆料中TVOC、H₂S和NH₃的产生均存在促进作用,随着浆料中Na₂SO₄浓度的升高,恶臭气体释放量显著增加。     

不同季节工况下变转速NH3/CO2复叠制冷系统性能研究

目的：研究在不同季节工况、蒸发温度为25 ℃条件下,高温压缩机转速对NH₃/CO₂复叠制冷系统性能的影响。方法：建立NH₃/CO₂复叠制冷系统模型并验证其可靠性,计算分析高温压缩机转速与系统高温蒸发温度、高温排气温度、中间温度、高温压缩机功率、制冷量、性能系数的变化关系。结果：仿真模型对制冷量的预测与理论值的相对误差小于14.1%。高温压缩机转速从2 300 r/min增至3 300 r/min,春季、夏季、秋季、冬季工况下的制冷量分别提升了31.7%,41.7%,33.9%,25.2%,且在低转速范围内冬季制冷量最高;高温压缩机功率呈两段式上升趋势,提升了40%～45%。结论：存在使得性能系数最大的最佳高温压缩机转速。基于系统对不同季节工况的适应性问题,提出了变转速NH₃/CO₂复叠制冷系统方案,与定转速系统相比每年可减少19.9%耗电量。     

碱木质素碳点的制备及对Fe3+检测性能研究

以碱木质素（Alkali lignin,AL）为碳源、乙二胺（Ethanediamine,EDA）为钝化剂、双氧水（H₂O₂）为氧化剂,利用简单、绿色、高效的水热法制备碱木质素碳点（ALE-CDs）。以荧光性能为指标,通过单因素实验优选出ALE-CDs的最佳制备工艺。结果表明,ALE-CDs表面存在大量的羟基（—OH）、羧基（—COOH）和氨基（—NH₂）等官能团,在水中具有优良的分散性和稳定性,荧光量子产率及寿命分别为19.20%和6.03 ns。利用ALE-CDs为荧光探针检测不同金属离子,发现ALE-CDs对Fe³⁺表现出较好的选择性,荧光强度与Fe³⁺浓度（0~50 μmol/L）呈良好的线性关系,Fe³⁺检出限约为1.66 μmol/L。     

玉米全粉中黄曲霉毒素B1标准物质的研制

目的 研制均匀性和稳定性满足计量要求的玉米全粉中黄曲霉毒素B₁成分分析标准物质,用于粮食及其制品中黄曲霉毒素B₁的质量控制。方法 采用高效液相色谱法对玉米全粉中黄曲霉毒素B₁候选物进行均匀性检验、稳定性考察,选取8家具有较高检测水平的实验室开展多家实验室联合定值。结果 均匀性检验通过方差分析可知,F_统计值＜F_临界值 。稳定性监测结果通过分析可知,候选物中黄曲霉毒素B₁未观测到不稳定性。确定了玉米全粉中黄曲霉毒素B₁标准值和不确定度。结论 该标准物质具有良好的均匀性,可在常温 (<25℃)下保存,在低于60℃的条件下运输。玉米全粉中黄曲霉毒素B₁标准物质定值结果为27±3μg/kg,k=2(95%置信区间),已被批准发布为国家二级标准物质。     

电Fenton技术深度处理造纸废水

采用电Fenton技术深度处理二级生化后的造纸废水,以色度去除率和COD去除率为主要考察指标,研究不同因素对造纸废水深度处理效果的影响。反应的最佳条件为：反应时间120 min、初始pH值=3、电压12 V、Fe²⁺浓度0.8 mmol/L、H₂O₂浓度0.8 mmol/L、极板间距10 cm、电解质Na₂SO₄浓度6 g/L。最佳反应条件下,电Fenton法对造纸废水的色度去除率和COD_Cr去除率分别达到89.5%和68.4%。动力学分析表明,电Fenton技术对造纸废水COD的降解符合一级反应动力学规律,一级反应速率常数为k=0.2072 min^-1。     

MoS2/g-C3N4复合纳米催化剂光催化深度处理造纸废水研究

本研究采用N-甲基吡咯烷酮复合MoS₂与g-C₃N₄,制得MoS₂/g-C₃N₄复合纳米催化剂。采用X射线衍射仪（XRD）、X射线光电子能谱仪（XPS）、光致发光光谱仪（PL）和扫描电子显微镜（SEM）对复合纳米催化剂进行表征,并利用MoS₂/g-C₃N₄复合纳米催化剂光催化深度处理造纸废水。结果表明,少量MoS₂与g-C₃N₄复合可提高复合光催化剂的光催化活性,反应时间180 min、pH值5、1.5% MoS₂/g-C₃N₄复合纳米催化剂投加量为2 g/L时,对造纸废水的COD_Cr去除率和色度去除率最高,分别达到63.4%和83.2%。MoS₂/g-C₃N₄的光催化活性有所增强是由于MoS₂与g-C₃N₄的能带结构匹配,降低了光生电子-空穴的复合几率,从而提高了催化剂的光催化活性。     

基于NiO@Pt-离子液体/玻碳电极传感器检测肉制品中的亚硝酸盐

目的 制备了新型的NiO@Pt-AVIMBF₄/GCE传感器对肉制品中的亚硝酸盐进行快速分析。方法 在氧化镍纳米材料(Nickel oxide nanomaterials, NiO)基础上合成了NiO@铂纳米材料(Platinum nanomaterials, Pt),并复合1-乙烯基-3氨丙基咪唑四氟硼酸盐(APVIMBF₄)离子液体,制备了新型的NiO@Pt-AVIMBF₄,采用玻碳电极(Glassy carbon electrode, GCE)构建新型的NiO@Pt-AVIMBF₄/GCE传感器,通过对NiO@Pt-AVIMBF₄、静置时间等条件的优化,确定NiO@Pt-AVIMBF₄/GCE的最佳检测条件,对肉制品中的亚硝酸盐进行定量分析。结果 研究发现,NiO@Pt-AVIMBF₄具有良好的导电性、催化性和生物相容性能有效提高传感器的灵敏度,亚硝酸盐浓度与氧化峰电流在0.1~1100 μmol/L呈线性关系, R^₂=0.998,检出限0.019 μmol/L (S/N=3)且对实际样品的检测结果与国标规定方法检测结果一致。NiO@Pt-AVIMBF4/GCE重复性、重现性、稳定性良好,而且对常见干扰物质具有很好地抗干扰能力。结论 制备的NiO@Pt-AVIMBF₄/GCE简便、快捷,实用性强可应用于亚硝酸盐的快速定量分析。     

聚乙烯醇—鱼明胶—龙葵花青素复合膜的制备、结构表征及性能分析

目的：筛选出结构与性能最优的聚乙烯醇—鱼明胶—龙葵花青素（PVA/FG-SNA）复合包装膜。方法：通过正交试验优化PVA-FG膜的制备工艺,采用厚度、水分含量、水蒸气透过率（WVP）、拉伸强度（TS）、断裂伸长率（EB）、傅立叶红外光谱分析（FTIR）、X衍射分析（XRD）、扫描电镜分析（SEM）、热重分析（TG）探究不同质量分数SNA对PVA-FG膜性能和微观结构的影响,并监测PVA/FG-SNA复合膜的pH颜色响应和NH₃灵敏度。结果：当PVA-FG复配质量比为60∶40、加热温度为95 ℃、加热时间为1.5 h时,PVA-FG膜的水溶性为（36.03±2.63）%,WVP为2.91×10^-4 g·mm/（m²·h·Pa）;随着SNA质量分数的增加,PVA-FG膜的厚度、水分含量、WVP和EB随之增加。当SNA质量分数为0.2%时,复合膜的厚度为（0.07±0.01） mm,水分含量为（11.09±0.25）%,WVP为5.45×10^-4 g·mm/（m²·h·Pa）,TS为（21.12±1.07） MPa,EB为（373.77±8.59）%,且复合膜的各组分之间相容性较好。此外,PVA/FG-0.2% SNA膜在NH₃气氛条件下的颜色响应良好,可作为pH指示膜。结论：PVA-FG复合基膜的疏水性能和机械性能与SNA质量分数呈负相关,SNA可显著增强膜的pH和NH₃敏感性。     

Ni/γ-AlO2O3油脂加氢催化剂的制备研究

以γ-AlO₂O₃为载体,硝酸镧为助剂,采用沉淀法制备了负载型Ni/γ-γ-AlO₂O₃油脂加氢催化剂。考察了中和反应温度、中和反应时间、搅拌速度和老化时间对催化剂活性的影响,得到催化剂最佳制备条件为：中和反应温度85℃,中和反应时间60 min,搅拌速度300 r/min,老化时间1.5 h。分别采用X射线衍射、物理吸附和激光粒度测定对自制催化剂和两种进口催化剂进行了表征,结果表明自制催化剂的比表面积和粒度分布与进口催化剂接近,孔容、孔径较进口催化剂大得多。采用棕榈油加氢反应对比了3种催化剂的加氢性能,结果显示自制催化剂活性优于进口催化剂。     

Screening test for rapid food safety evaluation by menadione-catalysed chemiluminescent assay

The chemiluminescent assay of menadione-catalysed H₂O₂ production by living mammalian cells was proposed to be useful for rapid food safety evaluation. The tested foods were extracted with water, ethanol and dimethylsulfoxide, and each extract was incubated with NIH3T3, Neuro-2a and HepG2 cells for 4 h. Menadione-catalysed H₂O₂ production by living mammalian cells exposed to each extract was determined by the chemiluminescent assay requiring only 10 min, and the viability of the cells was estimated as percentage based on H₂O₂ production by intact cells. In this study the cytotoxicity of food was rated in order of inhibitory effect on H₂O₂ production by intact cells. The well known natural toxins such as Fusarium mycotoxin, tomato toxin tomatine, potato toxin solanine and marine toxins terodotoxin and brevetoxin could be detected by the above chemiluminescent assay.     

Polyethyleneimine/chitosan hexamer-mediated gene transfection into intestinal epithelial cell cultured in serum-containing medium

In search of an efficient nonviral vector, polyethyleneimine (PEI)-based vectors were examined. In general, the transfection efficiency of nonviral vectors is suppressed by serum. Here we show that PEI based vectors, particularly, the chitosan hexamer-PEI vector, could perform efficient gene transfection into intestinal epithelial cells (IEC-6) in the presence of serum. The conjugation order of the two polymers with a plasmid (first, chitosan hexamer; second, PEI) was found to be an important factor in enhancing transfection efficiency.     

Nitrate content in lettuce (Lactuca sativa L) heads in relation to plant spacing,nitrogen form and irrigation level

A field study was conducted at two locations (Jordan valley and Al‐Jubeiha) with different rainfall levels, altitudes and temperature ranges. The study was established to evaluate the optimum planting density, nitrogen (N) form and irrigation level to attain the best quality of lettuce crop in terms of minimum nitrate (NO₃) content and to minimise the impact on the environment. Seeds of ‘Amar’ lettuce were sown 1 month before transplanting. Three forms of N fertiliser (Ca(NO₃)₂, (NH₄)₂SO₄ and CO(NH₂)₂) were applied at three times at a total rate of 100 kg N ha^?1. Three in‐row spacings (15, 20 and 25 cm) were assigned. Two irrigation levels were applied: level 1 had twice the amount of irrigation water as level 2, which was achieved by doubling the number of irrigation lines. The results indicated that N form significantly increased both N and NO₃ contents. Ca(NO₃)₂ was the most effective in increasing the N and NO₃ contents in lettuce leaf tissues, followed by CO(NH₂)₂ and then (NH₄)₂SO₄. The outer leaves (green colour) had about five times the NO₃ content of the inner leaves (pale yellow colour). However, the effect of N form on production, total N absorption and N recovery was significant in the following order: (NH₄)₂SO₄ > Ca(NO₃)₂ > CO(NH₂)₂. Increasing the plant spacing resulted in a significant increase in N and NO₃ contents in the lettuce leaves. Copyright © 2004 Society of Chemical Industry     

Application of the micrometeorological mass balance method to the determination of ammonia loss from a grazed sward

The micrometeorological mass balance method has been assessed with a view to its use in the determination of ammonia (NH₃) loss from grazed swards. The method involves the measurement of wind speed and the concentration of NH₃ in air at different heights above the sward at its windward boundary and a position leeward of the grazed area. The flux of NH₃ is calculated from these measurements and a continuous record of wind direction. Quantitative recovery of NH₃ from air flows up to 10 litre min^?1 was achieved using a simple trap containing dilute orthophosphoric acid and a gas dispersion tube. Wind speed measured at a height of 0.25 m at six different positions above a previously grazed sward varied by <2%. The NH₃ concentration at the same positions was affected by the distance between the windward edge of the sward and the sampling position (i.e. the fetch) and by heterogeneity in the distribution of sources of NH₃ (urine- or dung-affected areas). However, the normalised horizontal flux through 0.25 m (wind speedXNH₃ concentration/fetch) varied by less than ±8.1% probably due to mixing through fluctuations in wind direction (approximately ±30° on the mean) as air passed over the sources of NH₃ during each measurement period. Plots of wind speed or NH₃ concentration versus logarithm of height indicated that each approximated a linear relationship. This facilitated the calculation of the NH₃ flux per unit land area and reduced the total error to about 10%. The total loss of NH₃ derived by summing losses during individual sampling intervals of 2 to 18 h within a 24 h period was essentially the same as that derived by averaging wind speeds and NH₃ concentrations measured continuously over the same 24 h period. The flux of NH₃ from a ryegrass sward grazed by yearling steers ranged from 0.01 to 0.14 kg N ha^?1 h^?1 during a 2 day grazing period within a 28 day rotation and during the 5 days following removal of animals. A pronounced diurnal variation was observed in the flux of NH₃, the maximum occurring between 13.00 and 20.00 hours on each day. Rainfall and low rates of evapotranspiration reduced the flux to <0.02 kg N h^?1 h^?1. The total loss of NH₃ during 28 days was 20.7 kg N ha^?1.     

Carotenoid pigments in kale are influenced by nitrogen concentration and form

The objective of these experiments was to investigate the effects of N rate and form on the accumulation of lutein, β‐carotene and chlorophyll pigments in the leaf tissues of kale. Winterbor, Toscano and Redbor kale cultivars were greenhouse grown using nutrient solution culture. In the first study, N treatments were 6, 13, 26, 52 and 105 mg L^?1 at a constant 1 NH₄‐N:3 NO₃‐N ratio. On a fresh weight basis, plant pigment concentrations (lutein, β‐carotene and chlorophylls) were not affected by N rate. When calculated on a dry weight basis, however, carotenoid pigments increased linearly in response to increasing N rate. In a second study, N rate was held constant at 105 mg L^?1 and N form was changed as follows: 100% NH₄‐N:0% NO₃‐N, 75% NH₄‐N:25% NO₃‐N, 50% NH₄‐N:50% NO₃‐N, 25% NH₄‐N:75% NO₃‐N and 0% NH₄‐N:100% NO₃‐N. Increasing NO₃‐N in nutrient solutions from 0 to 100% resulted in increases in both lutein and β‐carotene concentrations. Increases in carotenoid concentrations would be expected to increase the nutritional value of kale. Therefore N management should be considered in crop production programmes designed to increase the concentrations of nutritionally valuable carotenoids. Copyright © 2007 Society of Chemical Industry     

Cytoprotective and antioxidant activity studies of jaggery sugar

Jaggery and other sugars namely white, refined and brown sugars were evaluated for cytoprotectivity on NIH 3T3 fibroblasts and erythrocytes, DPPH radical scavenging activity, reducing power and DNA protection. In addition, total phenol content and phenolic acid composition were also determined. Results indicated a total phenolic content of 26.5, 31.5, 372 and 3837 μg GAE/g for refined, white, brown and jaggery, respectively. The HPLC analysis revealed the presence of different phenolic acids in brown sugar and jaggery. On NIH 3T3 cells oxidation, at 4 mg/ml concentration, jaggery showed 97% protection compared to brown sugar, and both sugars effectively reduced erythrocyte oxidation. A dose dependent reducing power and DPPH radical scavenging activity was also observed for jaggery and brown sugar. An EC₅₀ of 7.81 and 59.38 μg/ml were observed for jaggery and brown sugar in the DPPH scavenging assay. In DNA oxidation studies, higher protection was observed in jaggery followed by brown, white and refined sugar treated samples.     

Influence of banded fertiliser on the chemical environment surrounding the band: I.—Effect on pH and solution nitrogen

The influence of several banded fertilizers on soil pH, soil solution pH, and concentration of NH₄-N, NO₂-N and NO₃-N at two distances from the band was studied. Treatments consisted of various combinations of monocalcium phosphate (MCP), KCl, NH₄-NO₃, (NH₄)₂HPO₄ and urea applied on a nutrient element basis of 22.4 or 67.2 kg/ha. Urea treatments produced the highest initial pH, and MCP treatments resulted in the lowest pH values. The greatest pH changes during a 32-day incubation period resulted from treatments that contained urea, (NH₄)₂ HPO₄ or NH₄NO₃. Changes in pH with time, for treatments containing the N sources, reflected the rate of nitrification of NH₄-N to NO₃-N which, in turn, controlled the solution concentrations of NH₄-N and NO₃-N. The NO₂-N content near 67.2 kg/ha urea applications increased with time to potentially toxic concentrations (over 500 ppm). Combination of MCP with urea markedly lowered pH and NO₂-N content compared to treatments in which MCP was not supplied. Application of (NH₄)₂HPO₄ or urea at 22.4 kg/ha resulted in a rapid increase in NO₃-N and decrease in pH with time. The pH decrease and accumulation of NO₃-N were much slower when (NH₄)₂HPO₄ or urea was applied at 67.2 kg/ha.     

Effects of exogenous amylolytic or fibrolytic enzymes inclusion on in vitro fermentation of lactating dairy cow diets in a dual-flow continuous-culture system

The objective of this study was to determine the effects of including exogenous amylolytic or fibrolytic enzymes in a diet for high-producing dairy cows on in vitro ruminal fermentation. Eight dual-flow continuous-culture fermentors were used in a replicated 4 × 4 Latin square. The treatments were control (CON), a xylanase and glucanase mixture (T1), an α-amylase mixture (T2), or a xylanase, glucanase, and α-amylase mixture (T3). Treatments were included at a rate of 0.008% of diet dry matter (DM) for T1 and T2 and at 0.02% for T3. All treatments replaced the equivalent amount of soybean meal in the diet compared with CON. All diets were balanced to have the same nutrient composition [30.2% neutral detergent fiber (NDF), 16.1% crude protein (CP), and 30% starch; DM basis], and fermentors were fed 106 g/d divided into 2 feedings. At each feeding, T2 was pipetted into the respective fermentor and an equivalent amount of deionized water was added to each fermentor to eliminate potential variation. Experimental periods were 10 d (7 d for adaptation and 3 d for sample collection). Composite samples of daily effluent were collected and analyzed for volatile fatty acids (VFA), NH₃-N, and lactate concentrations, degradability of DM, organic matter, NDF, CP, and starch, and flow and metabolism of N. Samples of fermentor contents were collected from each fermentor at 0, 1, 2, 4, 6, and 8 h after feeding to determine kinetics of pH, NH₃-N, lactate, and VFA concentrations over time. All data were analyzed using PROC GLIMMIX of SAS (SAS Institute Inc.), and the repeated variable of time was included for kinetics measurements. Treatment did not affect mean pH, degradability, N flow and metabolism, or the concentrations of VFA, NH₃-N, or lactate in the effluent samples. Treatment did not affect pH, acetate:propionate ratio, or the concentrations of lactate, NH₃-N, total VFA, acetate, propionate, butyrate, isobutyrate, valerate, or caproate. However, the concentration of total VFA tended to change at each time point depending upon the treatment, and T2 tended to have a greater proportion of 2-methylbutyrate and isovalerate than CON, T1, or T3. As 2-methylbutyrate and isovalerate are branched-chain VFA that are synthesized from branched-chain amino acids, T2 may have an increased fermentation of branched-chain amino acids or decreased uptake by fibrolytic microorganisms. Although we did not observe changes in N metabolism due to the enzymes, there could be changes in microbial populations that utilize branched-chain VFA. Overall, the tested enzymes did not improve in vitro ruminal fermentation in the diet of high-producing dairy cows.     

Effect of dietary crude protein modification on ammonia and nitrous oxide concentration on a tie-stall dairy barn floor

Dietary crude protein (CP) reduction is considered a useful strategy to minimize cow N excretion and NH₃ and N₂O emissions. The aim of the current work was to relate dietary CP modification to whole-animal N balance and subsequent NH₃ and N₂O concentrations on a tie-stall barn floor. The effect of temperature on NH₃ and N₂O concentration was also studied. Three Holstein mid to late lactating cows were confined in separate tie-stalls and randomly assigned to 3 diets with varying CP content [low CP (LCP): 14.1%; moderate CP (MCP): 15.9%; high CP (HCP): 16.9%]. Increasing N intake (from 438.6 to 522.8 g of N/d) improved milk yield (from 22.1 to 24.2 kg/d). However, N use efficiency tended to decrease with increasing dietary CP, as shown by milk N use efficiency (from 23.9 to 22.6%), milk urea N (from 15.4 to 18.7 mg/dL), and excreted N per milk yield unit (from 14.7 to 16.4 g of N/kg of milk). Because of higher N excretion, NH₃ concentration on the dairy barn floor increased (LCP: 7.1 mg of NH₃/m³; MCP: 10.4 mg of NH₃/m³; HCP: 10.8 mg of NH₃/m³). In contrast, N₂O concentration did not respond to dietary manipulation (mean 1.1 mg of N₂O/m³). Temperature, which ranged between 12.6 and 18.0°C, did not affect NH₃ and N₂O concentrations at the stall level. However, when fecal and urinary samples were incubated at 4, 19, and 29°C in the laboratory, ammonia concentration increased for all diets, especially for the MCP and HCP diets, as the temperature increased. In contrast, N2O concentration was negatively related to increasing temperature. In conclusion, data from the current trial demonstrate that lowering dietary CP minimizes NH₃ concentration on dairy stall floors although temperature controls the rate of NH₃ volatilization. On the other hand, N₂O concentration is not affected by dietary treatments on tie-stall floors.     

Technical note: measurement of ferritin in bovine milk and its clinical significance

A quantitative ELISA was developed for bovine milk ferritin with an assay limit of 0.16 ng/mL of bovine spleen ferritin. Ferritin-binding activity was detected in bovine milk samples, and this binding activity was inhibited by increasing ionic strength with the addition of 0.5 M (NH₄)₂SO₄. Heat treatment (60°C, 20 min) of bovine milk in the presence of 0.5 M (NH₄)₂SO₄ resulted in a 15 to 58% increase in ferritin concentrations compared with untreated samples. Although the recovery of bovine spleen ferritin added to milk was still low (55 to 90%), even in the presence of increased ionic strength with 0.5 M (NH₄)₂SO₄, recovery was improved by heat treatment at 60°C for 20 min (92 to 95%). Milk ferritin concentrations in 30 milk samples from quarters of 25 cows with mastitis (mean ± SE: 134.2 ± 28.7 ng/mL) were significantly higher than those in 17 quarter milk samples from 17 noninfected lactating cows (7.2 ± 1.2 ng/mL), suggesting that bovine milk contains putative ferritin-binding proteins that inhibit immunoassay for milk ferritin and that bovine milk ferritin is an indicator of IMI.