共查询到20条相似文献,搜索用时 125 毫秒
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文章通过对包钢BGⅢ型布料器结构进行分析,求出溜槽在整个旋转和倾动过程中对布料器各部件产生的最大值负荷。构建了合理的力学模型,核算了电机及油缸的负载能力,证明了原设计选型的合理性。同时为布料器其它部件的结构改进和受力计算提供基础数据支撑,为布料器的结构优化提供理论支持。 相似文献
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The results of experimental research are presented and discussed with focus on the internal well resistance of prefabricated vertical drains (PVD) under vacuum-induced water flow. Measured results included fluid flow rates for two different cross-sectional hydraulic profiles (Types I and II PVDs). Experimental results indicated linear relationships, independent of the PVD widths, between extracted fluid velocity and the applied hydraulic gradient. Data showed a laminar flow regime to predominate for test velocities corresponding to hydraulic gradients <0.5. The larger nominal hydraulic radius of the Type II PVD is credited with providing a flow rate equal to approximately 3.2 times that of the Type I PVD at approximately the same operating total head. There was no apparent dependency of the transmissivity θ on the width or lengths (3, 4, and 5 m) of the PVDs tested. In the case of the 100-mm-wide Type I PVD, θ = 618 mm2∕s was estimated from the measured data versus θ = 1,996 mm2∕s for Type II PVD with the same dimensions. 相似文献
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SL Berg DJ Murry CL McCully K Godwin FM Balis 《Canadian Metallurgical Quarterly》1998,4(11):2891-2894
O6-Benzylguanine (O6BG) irreversibly inactivates the single-turnover DNA repair protein alkylguanine-alkyltransferase. Thus, O6BG increases tumor-cell sensitivity to alkylating agents such as carmustine, lomustine, procarbazine, and temozolomide. We investigated the pharmacokinetic behavior of O6BG and O6-benzyl-8-oxoguanine (8-oxo-O6BG) in cerebrospinal fluid (CSF) and plasma after intraventricular administration of O6BG in a nonhuman primate model. In our study, three animals received a single 1-mg dose of O6BG into the lateral ventricle. CSF from the 4th ventricle and plasma samples were collected after administration, and O6BG and 8-oxo-O6BG concentrations were measured by high-performance liquid chromatography. Four additional animals received 1 mg of O6BG via the intralumbar route weekly for 6 weeks to assess the feasibility and toxicity of this route of administration. The peak O6BG CSF concentration was 412+/-86 microM, the t1/2 was 0.52+/-0.02 h, the clearance was 0.22+/-0.01 ml/min, and the area under the concentration-time curve was 319+/-15 microM x h in 4th ventricular CSF. The peak CSF concentration of 8-oxo-O6BG in CSF was 1.9+/-0.4 microM, the t1/2 was 0.76+/-0.03 h, and the area under the concentration-time curve was 5.0+/-1.1 microM x h. Both O6BG and 8-oxo-O6BG were detected in the plasma 0.5-3 h after intraventricular O6BG administration. The plasma peak concentration of O6BG was 0.4 microM at 30 min, and the concentration was <0.1 microM by 3 h. The plasma concentration of 8-oxo-O6BG was 0.2 microM at 30 min and 0.6 microM at 3 h. The animals tolerated the single intraventricular dose and 6 weekly intralumbar doses of O6BG without toxicity. We concluded that intrathecal administration of O6BG is well tolerated in the nonhuman primate and seems to have a substantial pharmacokinetic advantage over systemic administration for meningeal tumors. 相似文献
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OBJECTIVE: To compare the efficacy of the short-acting insulin analog lispro (LP) with that of regular insulin in IDDM patients treated with an external pump. RESEARCH DESIGN AND METHODS: Thirty-nine IDDM patients (age, 39.4 +/- 1.5 years; sex ratio, 22M/17W; BMI, 24.4 +/- 0.4 kg/m2; diabetes duration, 22.5 +/- 1.6 years) who were treated by external pump for 5.1 +/- 0.5 years were involved in an open-label, randomized, crossover multicenter study comparing two periods of 3 months of continuous subcutaneous insulin infusion with LP or with Actrapid HM, U-100 (ACT). Boluses were given 0-5 min (LP) or 20-30 min (ACT) before meals. Blood glucose (BG) was monitored before and after the three meals every day. RESULTS: The decrease in HbA1c was more pronounced with LP than with ACT (-0.62 +/- 0.13 vs. -0.09 +/- 0.15%, P = 0.01). BG levels were lower with LP (7.93 +/- 0.15 vs. 8.61 +/- 0.18 mmol/l, P < 0.0001), particularly postprandial BG levels (8.26 +/- 0.19 vs. 9.90 +/- 0.20 mmol/l, P < 0.0001). Standard deviations of all the BG values (3.44 +/- 0.10 vs. 3.80 +/- 0.10 mmol/l, P = 0.0001) and of postprandial BG values (3.58 +/- 0.10 vs. 3.84 +/- 0.10 mmol/l. P < 0.02) were lower with LP. The rate of hypoglycemic events defined by BG < 3.0 mmol/l did not significantly differ between LP and ACT (7.03 +/- 0.94 vs. 7.94 +/- 0.88 per month, respectively), but the rate of occurrences of very low BG, defined as BG < 2.0 mmol/l, were significantly reduced with LP (0.05 +/- 0.05 vs. 0.47 +/- 0.19 per month, P < 0.05). At the end of the study, all but two (95%) of the patients chose LP for the extension phase. CONCLUSIONS: When used in external pumps, LP provides better glycemic control and stability than regular insulin and does not increase the frequency of hypoglycemic episodes. 相似文献
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SC Schold DM Kokkinakis JL Rudy RC Moschel AE Pegg 《Canadian Metallurgical Quarterly》1996,56(9):2076-2081
O6-Methylguanine-DNA methyltransferase (MGMT), a constitutively expressed DNA repair protein, removes alkyl groups from the O6-position of guanine in DNA. Tumor cells with high MGMT activity are resistant to nitrosoureas and other agents that form toxic O6-alkyl adducts. O6-Benzylguanine (BG) inactivates the MGMT protein and thereby enhances the sensitivity of tumor cells to alkylating drugs. However, the therapeutic potential of BG is limited by its poor solubility and its nonspecific inactivation of MGMT in normal tissues as well as in tumor tissues. Consequently, BG analogues are being developed to identify agents that have more favorable pharmacological characteristics. We evaluated O6-benzyl-2'-deoxyguanosine (dBG), the 2'-deoxyribonucleoside analogue of BG, for its ability to inhibit MGMT and to potentiate 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in a MGMT-positive human brain tumor xenograft, Daoy. When given i.p. 1 h before BCNU (25 mg/m2) to animals bearing s.c. tumors, dBG (134 mg/m2) produced a growth delay of 24.7 days, compared to 21.6 days after treatment with an equimolar dose of BG (90 mg/m2) plus BCNU and -0.6 days after treatment with BCNU alone. The combination of dBG + BCNU also increased the survival of animals bearing intracranial tumors by 65%. By increasing the dose of dBG to 300 mg/m2 (the maximum dose that could be delivered i.p. in a standard treatment volume), the growth delay of s.c. tumors increased from -0.1 days with BCNU alone to 39.3 days. dBG suppressed both tumor and liver MGMT activity to less than 1.5% of baseline, and dBG + BCNU induced extensive perivascular apoptosis. Because dBG is a 10-fold less potent MGMT inhibitor than BG in HT-29 cell extracts, these results illustrate the capacity of BG analogues to potentiate BCNU toxicity, despite less in vitro activity than the parent compound, and emphasize the importance of in vivo evaluation of BG analogues. 相似文献
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OBJECTIVE: Insulin sensitivity is impaired in patients with type II diabetes and is exacerbated by high mean blood glucose (BG). Potentially, large postprandial swings in BG could result in further decrements of insulin sensitivity. Because alpha-glucosidase inhibitors cause a marked reduction in the amplitude of BG changes, the aim of this study was to determine if such a BG-smoothing effect improves insulin sensitivity in well-controlled type II diabetic subjects treated with diet alone. RESEARCH DESIGN AND METHODS: Patients received either miglitol (BAY m 1099) (50 mg three times daily) or placebo for 8 weeks in a randomized double-blind parallel study. The miglitol (9 men, 2 women) and placebo (7 men, 3 women) groups were well matched (mean +/- SD) for age, weight, and blood glucose control (fasting BG, 6.4 +/- 1.0 vs. 6.9 +/- 1.6 mmol/l; HbA1, 7.7 +/- 1.0 vs. 7.9 +/- 0.4%; fructosamine, 0.99 +/- 0.08 vs. 1.07 +/- 0.17 mmol/l). The glucose metabolic clearance rate was calculated during the last 30 min of a 150 min glucose/insulin sensitivity test (glucose, 6 mg . kg-1 . min-1; insulin, 0.5 U . kg-1 . min-1). RESULTS: There was no significant improvement in metabolic clearance rate (0.21 +/- 0.27 vs. 0.16 +/- 0.35 l . kg-1 . min-1) for the miglitol- and placebo-treated groups, respectively. There were no statistically significant differences between miglitol and placebo for changes from baseline in BG (0.1 +/- 0.1 vs. -0.1 +/- 0.2 mmol/l), HbA1 (0.1 +/- 0.1 vs. 0.3 +/- 0.1%), and fructosamine (-0.06 +/- 0.02 vs. -0.03 +/- 0.02 mmol/l). CONCLUSIONS: Alpha-glucosidase-induced improvement in postprandial hyperglycemia does not result in increased insulin sensitivity. 相似文献
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The antitumor activity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) is limited by the O6-alkylguanine-DNA alkyltransferase (ATase) in tumor cells and by delayed myelosuppression. Inactivation of neoplastic ATase by O6-benzylguanine (BG) improves the therapeutic index for BCNU. We have demonstrated previously that BG + BCNU-induced myelosuppression in mice is reduced by expression of the BG-resistant ATase ada in murine bone marrow. We have now generated an amphotropic retrovirus containing the ada gene and tested the effectiveness of ada expression in preventing BG + BCNU cytotoxicity in human hematopoietic progenitor cells. A retroviral producer clone with a biological titer of 6.5 x 10(4) colony-forming units/ml and 4.4 pmol ATase/mg protein was used for transduction of bone marrow. Cocultivation of these ada producer cells with progenitor cells from six normal individuals resulted in 1.9-3. 9-fold protection against BG + BCNU-induced cytotoxicity in committed progenitor cell assays. Furthermore, this cytoprotective effect was associated with a high transduction efficiency (40%) and a 2-fold increase of ATase activity in the surviving committed progenitor cell colonies. These data provide a basis for testing the clinical effectiveness of retroviral ada gene transfer into hematopoietic cells to increase the therapeutic index of BG + BCNU. 相似文献
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Emmanuel Mignot Nicolas Rivière André Paquier Richard J. Perkins 《Canadian Metallurgical Quarterly》2011,137(3):289-299
Intense rainfall on urban areas can generate severe flooding in the city, and if the conditions are right, the flow in the streets can be supercritical. The redistribution of the flow in street intersections determines the flow rates and water levels in the street network. We have investigated the flow that occurs when two supercritical flows collide in a 90° junction formed by streets of identical cross section. Several flow configurations within the intersection are possible, depending on the position of the hydraulic jumps that form in and upstream of the intersection. Previous work has identified three flow types, with Type II flows being further classified into three subregimes. Hydraulic models have been developed, based on the principles of the conservation of flow and momentum flux in the intersection, which predict the angles at which the jumps will form. These models can be used to determine the flow type that will occur. Moreover, additional models have been developed for computing the outflow discharge distribution. For Type I flows, it has not been possible to develop such a hydraulic model for the discharge distribution, but some data are provided for one configuration to indicate the influence of different parameters. For Type II and Type III flows, such models are developed, and their predictions agree with data obtained from the channel intersection facility at the Laboratory of Fluid Mechanics and Acoustics in Lyon. 相似文献
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JL Beaudeux PJ Guillausseau J Peynet F Flourie M Assayag D Tielmans A Warnet F Rousselet 《Canadian Metallurgical Quarterly》1995,239(2):131-141
Macrovascular disease represents a major cause of morbidity and mortality in patients with diabetes mellitus. Low-density lipoprotein (LDL) is involved in the pathogenesis of atherosclerotic lesions, through modifying processes such as oxidation. We examined the in vitro susceptibility to oxidation and the oxidizability of LDL isolated from the plasma of Type 1 and Type 2 diabetic patients. Two groups of diabetic patients (20 Type 1, 20 Type 2) were compared with sex- and age-matched non-diabetic control groups. In vitro oxidation of the purified LDL preparations was assessed by determination of the kinetics for the formation of conjugated dienes (lag phase duration, maximal rate and maximal dienes concentration) and by measurement of thiobarbituric acid-reacting substances (TBARS) in the presence of copper ions. LDL from both Type 1 and Type 2 diabetic patients exhibited a shorter lag phase duration for conjugated dienes formation (94 +/- 14 vs. 108 +/- 20 and 97 +/- 26 vs. 112 +/- 18 min for Type 1 and Type 2 diabetic groups vs. respective control groups, P < 0.05). We also observed an increase in maximal rate of conjugated dienes formation (2.21 +/- 0.55 vs. 1.52 +/- 0.31 and 2.02 +/- 0.55 vs. 1.52 +/- 0.31 nmol/mg LDL/min, P < 0.01) and of maximal production of TBARS (77.9 +/- 11.8 vs. 65.5 +/- 10.4 and 76.7 +/- 9.9 vs. 65.3 +/- 9.4 nmol/mg LDL protein, P < 0.05) in diabetic groups. Our results demonstrate both a higher susceptibility to oxidation and a higher oxidizability of LDL from diabetic patients, as much for Type 1 as Type 2 diabetic subjects with or without pre-existent vascular complications. This enhanced propensity of LDL oxidation in patients with diabetes mellitus could at least partly be attributable to quantitative and qualitative alterations in the chemical composition of LDL and to the glycoxidation process occurring on these lipoproteins. 相似文献
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The activity of O6-alkylguanine-DNA alkyltransferase (AGT) protects cells from killing by methylating or chloroethylating agents. AGT is strongly inhibited by O6-benzylguanine (ED50, 0.2 microM), and this drug is presently undergoing clinical trials to enhance chemotherapy by alkylating agents. Point mutations such as P140A (ED50, 5 microM) render AGT resistant to O6-benzylguanine (BG). Selection for such mutants may prove to be a problem in the use of BG, and a better knowledge of the factors underlying resistance to BG will enable the rational design of improved inhibitors able to inactivate these mutants. BG-resistant AGT mutants may also be valuable for expression in bone marrow stem cells to reduce myelosuppression brought about by alkylating agents, to increase the therapeutic index of therapies including BG, and for use as a selectable marker to allow other genes to be expressed in such stem cells. We have therefore set up a general screen to obtain such mutants by using the ability of AGT to protect Escherichia coli GWR109 lacking endogenous AGT from killing by N-methyl-N'-nitro-N-nitrosoguanidine. When the cells were rendered permeable to BG by mutating the lipopolysaccharide membrane component forming strain TRG8, the protection by AGT expression was abolished by treating the cells with BG. The known P140A mutant was used to test the system and was highly selected for by treatment with 50 microM BG and 40 microg/ml N-methyl-N'-nitro-N-nitrosoguanidine. The sequence coding for PVP at positions 138-140 in AGT was replaced with a random nucleotide sequence, and this library was used to transform TRG8. All of the 59 colonies analyzed having AGT activity that survived the selection from the pool of 36,000 transformants were resistant to BG. Many (69%) of these mutants contained lysine at position 140, and all of these showed the highest level of resistance with <10% loss of activity when crude cell extracts were incubated with 1.2 mM BG. This result was confirmed with three mutants (P138K/V139L/P140K, P138M/V139L/P140K, and P140K), which were purified to homogeneity. The next most common residues found at position 140 were arginine (7%) and asparagine (7%). Studies carried out with purified preparations of mutants P140R and P140N revealed that these mutations also provided resistance to BG but to a lesser extent than P140K (ED50s of 190 and 7 microM, respectively). These results indicate that: (a) this screening method can be used to evaluate BG resistance of single or multiple changes throughout the AGT sequence; and (b) replacement of proline-140 with lysine is the most effective point mutation at this site causing BG resistance and is more than 200 times more effective than replacement with alanine. 相似文献