直流非转移弧等离子喷枪中电弧的工作特性研究

利用计算机数值模拟技术，采用有限容积方法，针对自制的低能耗、高效率内送粉等离子喷涂设备，对喷枪内部电弧长度及其对流体特性的影响进行了分析研究。结果表明，通过增加进气流量和减少电流的大小，均使得等离子电弧长度增加，阳极弧根位置逐渐向下游移动，但是产生这两种现象的机理以及对气流温度和速度的影响是不同的。     

一个面积和功耗优化且适用于10/100 Base-T以太网的CMOS时钟恢复电路

提出了一个新的用于10 / 10 0 Base- T以太网中面积和功耗优化的时钟恢复电路.它采用双环路的结构,加快了锁相环路的捕获和跟踪速度;采用复用的方式,通过选择信号控制电路可分别在10 Mbps或10 0 Mbps模式下独立工作且能方便地实现模式间的互换,与采用两个独立的CDR电路相比节省了一半的面积;同时,电路中采用一般的延迟单元来取代DL L,并能保证环路性能不随工艺温度等条件引起的延迟单元、延迟时间的变化而变化,从而节省了功耗.Hspice模拟结果显示,在Vdd=2 .5 V时,10 0 Mbps模式下电路的功耗约为75 m W,稳态相差为0 .3 ns;10 Mbps模式时电路功耗为5 8m W     

Endgroup analysis of polyethylene glycol polymers by matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry

Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) by external injection of matrix-assisted laser desorbed and ionized (MALDI) polymers offers good possibilities for characterization of low molecular weight homopolymers (MW range up to 10 kDa). The molecular masses of the molecular weight distribution (MWD) components of underivatized and derivatized (dimethyl, dipropyl, dibutyl and diacetyl) polyethylene glycol (PEG) 1000 and 4000 were measured by MALDI-FTICR-MS. These measurements have been performed using a commercial FTICR spectrometer with a home-built external ion source. MALDI of the samples with a 2,5-dihydroxybenzoic acid matrix in a 1000:1 matrix-to-analyte molar ratio produces sodiated molecules in a sufficient yield to trap the ions in the ICR cell. The masses of the molecular weight distribution of PEG components were measured in broad-band mode with a mass accuracy of < 5 ppm in the mass range around 1000 u and within 40 ppm accuracy around 4000 u. From these measurements, the endgroup mass of the polymer was determined by correlation of the measured component mass with the degree of polymerization. The masses of the PEG endgroups have been determined within a deviation of 3-10 millimass units for the PEG1000 derivatives and 10-100 millimass units for the PEG4000 derivatives, thus confirming the identity of the distal parts of the model compounds.     

Glucuronidation of N-hydroxy heterocyclic amines by human and rat liver microsomes

The food-borne carcinogenic and mutagenic heterocyclic aromatic amines undergo bioactivation to the corresponding N-hydroxy (OH)-arylamines and the subsequent N-glucuronidation of these metabolites is regarded as an important detoxification reaction. In this study, the rates of glucuronidation for the N-OH derivatives of 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP), 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) by liver microsomal glucuronosyltransferase were compared to that of the proximate human urinary bladder carcinogen, N-OH-aminobiphenyl (N-OH-ABP) and the proximate rat colon carcinogen N-OH-3,2'-dimethyl-4-amino-biphenyl (N-OH-DMABP). Human liver microsomes catalyzed the uridine 5'-diphosphoglucuronic acid (UDPGA)-dependent glucuroidation of N-OH-IQ, N-OH-PhIP, N-OH-Glu-P-1 and N-OH-MeIQx at rates of 59%, 42%, 35% and 27%, respectively, of that measured for N-OH-ABP (11.5 nmol/min/mg). Rat liver microsomes also catalyzed the UDPGA-dependent glucuronidation of N-OH-PhIP, N-OH-Glu-P-1 and N-OH-IQ at rates of 30%, 20% and 10%, respectively of that measured for N-OH-DMABP (11.2 nmol/min/mg); activity towards N-OH-MeIQx was not detected. Two glucuronide(s) of N-OH-PhIP, designated I and II, were separated by HPLC. Conjugate II was found to be chromatographically and spectrally identical with a previously reported major biliary metabolite of PhIP in the rat, while conjugate I was identical with a major urinary metabolite of PhIP in the dog. Hepatic microsomes from rat, dog and human were found to catalyze the formation of both conjugates. The rat preferentially formed conjugate II (I to II ratio of 1:15), while the dog and human formed higher relative amounts of conjugate I (I to II ratio of 2.5:1.0 and 1.3:1.0 respectively). Fast atom bombardment mass spectrometry of conjugates I and II gave the corresponding molecular ions and showed nearly identical primary spectra. However, collision-induced spectra were distinct and were consistent with the identity of conjugates I and II as structural isomers. Moreover, the UV spectrum of conjugate I exhibited a lambda max at 317 nm and was essentially identical to that of N-OH-PhIP, while conjugate II was markedly different with a lambda max of 331 nm. Both conjugates were stable in 0.1 N HCl and were resistant to hydrolysis by rat, dog and human liver microsomal beta-glucuronidases.(ABSTRACT TRUNCATED AT 400 WORDS)     

Juice-extracted grass pellets and sodium bicarbonate for cows fed timothy silage of two chop lengths

Eighteen multiparous Holstein cows in midlactation were used in a switchback design trial to evaluate the effect of chop length (3 or 30 mm) of timothy grass silage, containing less than 30% ADF and treated with formic acid, on DMI and cow performance. Within chop length, addition of NaHCO3 (2% of DMI) or the replacement of 30% of silage DM with juice-extracted grass pellets was also evaluated. Cows were fed a TMR composed of 90% silage and 10% concentrate. Silage preservation characteristics were not different between chop lengths. The DMI and apparent digestibility were similar among treatments. Yields of 4% FCM (24.9 vs. 22.7 kg/d), fat (1.03 vs. .93 kg/d), and protein (.83 vs .77 kg/d) were higher with the short chopped silage. Milk protein, milk NPN content, and serum urea were higher for cows fed long chopped silage. Yields of milk and milk constituents were not affected by the addition of juice-extracted grass pellets or NaHCO3. Fat percentage and fatty acid composition of milk remained unchanged by treatments. Reduction of particle size, from 30 to 3 mm, of timothy grass, treated with formic acid at harvest and using compaction at ensiling in bag silos, did not affect silage conservation characteristics but did improve milk, fat, and protein yields when cows were fed high silage diets.     

Effects of vesnarinone, a novel orally active inotropic agent with an immunosuppressive action, on experimental cardiac transplantation in rats

BACKGROUND: Vesnarinone (VES) has been used for treatment of patients with congestive heart failure. In addition to inotropic effects, it seems to have immunosuppressive action. We tested the hypothesis that VES suppresses graft rejection, inotropic dysfunction caused by early rejection, and chronic coronary obstruction in a heterotopic rat cardiac transplantation model. METHODS: (1) To study acute rejection, hearts from Lewis-Brown Norway (LBN) rats were transplanted into Lewis rats, which were treated with or without VES (50 or 100 mg/kg/day orally). (2) In a functional study, LBN hearts with or without VES (100 mg/kg/ day) were isolated and perfused on day 3 after transplantation to assess inotropic response to isoproterenol (3 x 10(-8) M). (3) To study chronic rejection, Lewis hearts were transplanted into Fisher 344 rats, which were treated with or without VES (50 mg/kg/day) for 90 days. Coronary obstructive disease was assessed by morphometric analysis. There were five to six animals in each group. RESULTS: (1) VES (100 mg/kg/day) prolonged LBN heart survival (11.7 +/- 0.7 vs. 9.6 +/- 0.7 days in control; P < 0.05). (2) Left ventricular developed pressure was depressed in transplanted hearts regardless of VES treatment (84 +/- 12, 90 +/- 8 vs. 144 +/- 16 mmHg in untransplanted hearts; P < 0.01). The developed pressure after administration of isoproterenol in VES-treated hearts (184 +/- 20 mmHg) was higher than transplanted hearts without VES (118 +/- 16 mmHg; P < 0.05), and similar to untransplanted hearts (203 +/- 27 mmHg; P = NS). (3) Transplanted hearts treated with or without VES showed similar grades of rejection (2.0 +/- 0.3 vs. 2.6 +/- 0.2; P = NS), intimal area (6,996 +/- 3,186 vs. 13,441 +/- 5,165 microns2; NS), and coronary luminal obstruction (45 +/- 16% vs. 67 +/- 14%; NS). CONCLUSIONS: VES produces mild prolongation in survival of rat heart grafts, but has no significant effect on chronic graft atherosclerosis. VES preserves the positive inotropic effects of isoproterenol that are otherwise deteriorated by early acute rejection.