卫星地球站上行系统测试

根据<卫星广播电视地球站工程技术验收规定>和<验收测试方案>的技术要求,结合广东卫星地球站的具体情况,讨论数字压缩DVB-S标准的卫星上行系统信源编码后的指标测试,不包括MPEG-2编码器的码流分析、系统视音频指标等项目的测试.     

有线数字电视的抗干扰特性和故障原因分析

分析有线数字电视和有线模拟电视抗干扰能力的差异,指出有线数字电视信号经过载波调制处理以后,它的抗干扰能力大大降低了,因此有必要对有线数字电视抗干扰的性能进行重新评价,提出"当系统网络没有故障时,有线数字电视抗干扰;当系统网络发生故障时,有线数字电视怕干扰;当有线数字电视出现问题时,系统网络必然有故障"的初步结论,并介绍一些有线数字电视发生故障的现象和维修、预防的方法。     

Leptin up-regulates the lactogenic effect of prolactin in the bovine mammary gland in vitro

The ability of leptin to up-regulate prolactin action in the mammary gland is well established. We examined the effect of leptin and prolactin on traits associated with lactation. Leptin and prolactin enhanced proliferation (thymidine incorporation) of the mammary gland cells, elevated the cells’ proliferation in a dose-responsive manner, and synergized to elevate the expression of amino acid metabolism via a 90% increase in aminopeptidase N expression. Leptin and prolactin decreased apoptosis (decreased caspase-3 expression by 60%) in the same manner. Leptin enhanced the effect of prolactin on all of these processes in bovine mammary explants. Leptin and prolactin regulated mTOR (mammalian target of rapamycin) by increasing expression by 66%, which is one of the signal-transduction junctions involved in the regulation of proliferation, apoptosis, and protein synthesis. These findings support the hypothesis that leptin up-regulates prolactin action in the bovine mammary gland.     

Utilization and partition of dietary nitrogen in dairy cows fed grass silage-based diets

Data from 207 production trials (998 treatment means) were used to study the effects of animal and dietary characteristics on the efficiency of N utilization for milk protein production, and on fecal N, urinary N, and total manure N output. The average efficiency of transferring dietary N to milk N (MNE; milk N/N intake) was 277 (SD = 36.0) g/kg. Nitrogen efficiency was poorly related to milk yield. Dietary concentrations of crude protein (CP) and protein balance in the rumen (PBV) were the best single predictors of MNE. Dietary CP concentration explained variation in MNE better than did N intake. Bivariate models with PBV or metabolizable protein (MP) explained the variation better than CP alone. The effects of protein feeding parameters on MNE were consistent among data subsets from studies investigating the effects of the amount and protein concentration of concentrate supplement, silage digestibility, silage fermentation quality, or substitution of grass silage with legume silage. The model with total dry matter and N intakes as independent variables explained fecal, urinary, and total manure N output more precisely than N intake alone. The model of fecal N output suggested that the true digestibility of dietary N was 0.91, and that metabolic and endogenous N was the major component in fecal N. The proportion of urine N in manure N was strongly related to dietary CP concentration. Including the concentration of dietary carbohydrates only slightly improved the models, indicating that the most effective strategy to improve MNE and to decrease N losses in manure, especially in urine, is to avoid feeding diets with excessively high CP concentration and especially excess ruminally degradable CP.     

Effect of supplementation of garlic powder on rumen ecology and digestibility of nutrients in ruminants

BACKGROUND: The present study investigated the effect of garlic powder (GAP) supplementation on rumen fermentation pattern, nutrient digestibility and intake in ruminants fed on straw as a roughage source. RESULTS: Dry matter intake and apparent digestibility of nutrients were similar among treatments. The apparent digestibility of crude protein tended to be higher in cattle supplemented with GAP compared to those fed without GAP (P = 0.08). Ruminal populations of protozoa and bacteria were decreased, as influenced by GAP supplementation. Ruminal pH and NH₃‐N were similar among treatments, while blood urea nitrogen tended to be decreased (P < 0.05). Total volatile fatty acids (VFAs) were not affected by GAP supplementation but individual VFAs were significantly different (P < 0.05), especially C3; meanwhile, C2:C3 ratio was reduced by GAP supplementation (P < 0.05). In addition, N balances were significantly increased as level of GAP supplementation increased and was highest at 120 g d^?1 GAP. CONCLUSION: Results of this study suggest that feeding of GAP at 80 g d^?1 with urea‐treated rice straw could enhance ruminal propionate production and thus lower C2:C3 ratio, decreasing the protozoal population, as well as increasing N retention and absorption in ruminants. Copyright © 2008 Society of Chemical Industry     

A novel selective-excitation RF pulse for magnetic resonance imaging

OBJECT: A selective-excitation radiofrequency (RF) pulse that uses hard pulses composed of a sequence of composite pulses with positive and negative phases (P/N pulse) is proposed herein. Because the amplitude of the RF signal is unchanged during the excitation, RF amplification can be accomplished using a nonlinear RF power amplifier (i.e., class C or D type). MATERIALS AND METHODS: In this article, Fourier series have been first used to analyze the equivalence between the proposed P/N pulse and the conventional soft pulse on selective excitation. Subsequently, computer simulations based on density-matrix theory are used to compare the excitation profiles of both the soft and the P/N pulses. RESULTS: The excitation profiles of the P/N pulses have been measured experimentally through a home-built 0.3-T magnetic resonance imaging (MRI) system. In addition, several slices of images have been obtained as proofs by using the multislice two-dimensional spin echo sequence through replacement of the conventional soft pulse by the proposed P/N pulse. CONCLUSION: Because the perfect selectivity of the proposed P/N pulse, it can be used for imaging studies to improve the efficiency of amplification at the lowest cost.     

Effect of Dietary Red Meat on Colorectal Cancer Risk—A Review

Heme iron overload has been implicated as the main cause of the increased risk of cancer due to the consumption of red meat. However, fish and shellfish, teas, and spices contain up to five times more iron than red meat. There is insufficient evidence that iron intake in dietary red meat is the primary causal factor for colorectal cancer. In addition, harmful substances produced during the preparation of red meat, including heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PAHs), N‐nitroso compounds, and acrylamide, are extrinsic factors that increase carcinogenicity. HCAs are produced during the cooking of red meat, poultry meat, and fish. PAHs may also be produced during the cooking of diverse food groups, such as dairy products, fruits, vegetables, and cereals. The average daily intake of red meat among Korean individuals is 62 g; the amount of PAHs entering the body via red meat is less than the average amount of PAHs the body is exposed to in the air. Therefore, it is difficult to conclude that dietary red meat is the main cause of colorectal cancer. Rather, there may be an intricate influence of multiple factors, including fruit and vegetable intake, alcohol consumption, smoking, overweight, obesity, and stress.     

SnWO4/g-C3N4复合光催化剂降解亚甲基蓝溶液

采用溶剂热法制备SnWO_4/g-C_3N_4复合光催化剂,在可见光降解亚甲基蓝实验中研究复合催化剂的光催化性能。考察催化剂投加量、亚甲基蓝溶液初始浓度、溶液pH值、盐效应对光催化性能的影响及SnWO_4/g-C_3N_4复合光催化剂的重复利用性。实验结果表明,在催化剂投加量1.0 g·L~(-1)、亚甲基蓝溶液初始浓度15 mg·L~(-1)和溶液pH值7.08时,在可见光条件下反应3 h,亚甲基蓝溶液脱色率达到94.2%;NaCl对光催化降解亚甲基蓝具有抑制作用,加入10 mmol·L~(-1)的NaCl溶液后亚甲基蓝的脱色率降为76.0%;复合光催化剂循环使用5次后,暗吸附后光照3 h,亚甲基蓝溶液的总脱色率仍可达到78.7%,重复利用性良好。     

分子筛催化剂上N2O催化分解的研究进展

氧化亚氮(N2O)会造成温室效应和臭氧层破坏,N2O的控制日益引起关注。催化分解技术是控制N2O的有效手段,分别对Fe基、Cu基和Co基分子筛催化剂催化分解N2O的研究现状进行总结和评述,并展望未来发展方向。     

Au基MOFs双功能催化剂的制备及其催化CO2与苯胺/H2反应性能

以UiO-66(Zr)、MIL-100(Fe)、MIL-100(Cr)、MIL-101(Cr)、NH 2-MIL-101(Al)为载体,Au为活性组分,制备Au/UiO-66(Zr)、Au/MIL-100(Fe)、Au/MIL-100(Cr)、Au/MIL-101(Cr)、Au/NH 2-MIL-101(Al)双功能催化剂。采用XRD、BET、NH 3-TPD、HRTEM等表征催化剂的结构,在釜式反应器中评价催化剂对CO 2与苯胺/H 2反应生成N-甲基苯胺与N,N-二甲基苯胺的N-甲基化反应性能,考察反应条件对催化剂催化性能的影响。结果表明,催化剂的XRD特征衍射峰与相应MOFs的模拟特征峰基本一致;负载Au后催化剂仍具有高的比表面积和大的孔容、孔径;不同MOFs负载Au的催化剂具有不同的酸强度和酸量;Au纳米粒子的分散性很好,粒径为(3~7)nm。制备的催化剂均具有催化CO2与苯胺/H2的N-甲基化反应性能,其中质量分数2%Au/MIL-101(Cr)催化剂催化性能最好,苯胺转化率为45.26%,N-甲基苯胺和N,N-二甲基苯胺选择性分别为73.50%和26.50%,重复使用性能优异。