Chiral Bis(N‐arylamino)phosphine‐oxazolines: Synthesis and Application in Asymmetric Catalysis

N‐Arylation or N‐alkylation of chiral 1,2‐diamines followed by ring closure with phosphorus trichloride (PCl₃) and subsequent coupling with an oxazoline alcohol resulted in a new class of N,P ligands. The corresponding iridium tetrakis[3,5‐bis(trifluormethyl)phenyl]borate (BAr_F) complexes were found to be efficient catalysts for the enantioselective hydrogenation of unfunctionalized olefins and α,β‐unsaturated carboxylic esters.     

凹栅槽AlGaN/GaN HEMTs器件退火处理效应

研究了如何减小等离子体干法刻蚀导致的大肖特基漏电. 用X射线光电能谱（XPS）分析刻蚀前后的AlGaN表面,发现刻蚀后AlGaN表面出现了N空位,导致肖特基栅电流偏离热电子散射模型,N空位做为一种缺陷使得肖特基结的隧穿几率增大,反向漏电增大,肖特基势垒降低. 介绍了一种AlGaN/GaN HEMTs器件退火处理方法,优化退火条件为400℃, N2氛围退火10min. 退火后,栅金属中的Ni与Ga原子反应从而减少N空穴造成的缺陷,器件肖特基反向漏电减小三个量级,正向开启电压升高,理想因子从3.07降低到了2.08.     

Polymer‐Supported N‐Phenylsulfonyloxaziridine (Davis Reagent): A Versatile Oxidant

An efficient preparation of a new recyclable polymer‐supported oxidizing agent based on N‐phenylsulfonyloxaziridine has been developed. This new polymer‐supported oxidant was shown to effect a clean and selective conversion of a range of sulfides, selenides, amines, phosphines and enolates to the corresponding sulfoxides, selenoxides, N‐oxides, phosphine oxides and α‐hydroxy carbonyl compounds. It also enabled tetrahydrobenzimidazoles to be oxidatively rearranged to spiro‐fused 5‐imidazolones. Recycling of the polymer‐supported oxidant is possible with minimal loss of activity after several reoxidations.     

The profile of temperature and voltage dependent series resistance and the interface states in (Ni/Au)/Al0.3Ga0.7N/AlN/GaN heterostructures

The temperature dependence of capacitance-voltage (C-V) and the conductance-voltage (G/w-V) characteristics of (Ni/Au)/Al_0.3Ga_0.7N/AlN/GaN heterostructures were investigated by considering the effect of series resistance (R_s) and interface states N_ss in a wide temperature range (79-395 K). Our experimental results show that both R_s and N_ss were found to be strongly functional with temperature and bias voltage. Therefore, they affect the (C-V) and (G/w-V) characteristics. The values of capacitance give two peaks at high temperatures, and a crossing at a certain bias voltage point (∼3.5 V). The first capacitance peaks are located in the forward bias region (∼0.1 V) at a low temperature. However, from 295 K the second capacitance peaks appear and then shift towards the reverse bias region that is located at ∼−4.5 V with increasing temperature. Such behavior, as demonstrated by these anomalous peaks, can be attributed to the thermal restructuring and reordering of the interface states. The capacitance (C_m) and conductance (G/w-V) values that were measured under both reverse and forward bias were corrected for the effect of series resistance in order to obtain the real diode capacitance and conductance. The density of N_ss, depending on the temperature, was determined from the (C-V) and (G/w-V) data using the Hill-Coleman Method.     

Highly Efficient Alkyne Hydroarylation with Chelating Dicarbene Palladium(II) and Platinum(II) Complexes

1 We report on a novel reaction protocol for the coupling of arenes with alkynes (the Fujiwara reaction), yielding products of formal trans‐hydroarylation of the triple bond. The protocol makes use of a chelating N‐heterocyclic dicarbene palladium(II) complex as catalyst and allows us to perform the reaction in a few hours with only 0.1 mol % catalyst yielding the trans‐hydroarylation product in high yields and with excellent selectivity. We discuss the applicability of this reaction protocol, which appears at present quite general with respect to the alkyne, albeit limited to electron‐rich arenes. We also present the results of catalyst optimisation with respect to the nature of the nitrogen substituents in the carbene units, of the bridging group between the carbene units and of the coordinated anionic ligands. Finally, we also discuss the catalytic performance of a related chelating dicarbene complex of platinum(II).     

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