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1.
The racemic alcohols, 2-methylbutanol-l, 3-methylbutanol-2, pentanol-2 and hexanol-2 have been esterified with optically active mandelic or lactic acid, and the resultant mixtures of diastereoisomeric esters separated chromatographically with an optically inactive sulphonated polystyrene resin as the stationary phase and water or dilute aqueous sodium sulphate as the mobile phase. Lactate esters were more easily separated than mandelate esters. The Chromatographic separation of 26 mmole of (+/-)-3-methyl-2-butyl(+)-lactate and subsequent hydrolysis of the fractions containing only the ester of the (+)-alcohol yielded 1-2 mmole of pure 3-methyl-2-butanol. 相似文献
2.
Rueda M Rosario Posner Michael I Rothbart Mary K Davis-Stober Clintin P 《BMC neuroscience》2004,5(1):1-13
Background
The neurological complications of HIV infection remain poorly understood. Clinically, in vivo 1H magnetic resonance spectroscopy (MRS) demonstrates brain injury caused by HIV infection even when the MRI is normal. Our goal was to undertsand the dynamics of cerebral injury by performing a longitudinal in vivo 1H MRS study of the SIV/macaque model of neuroAIDS.Results
Eight rhesus macaques were infected with SIVmac251 and serially imaged with MRI and 1H MRS to terminal AIDS or the endpoint of 2 years. During acute infection, there were stereotypical brain MRS changes, dominated by a significant elevation of the Cho/Cr ratio in the frontal cortex. Subsequently, brain metabolic patterns diverged between animals. There was an elevation of basal ganglia Cho/Cr four weeks post-inoculation in 2 animals that developed SIV encephalitis (p = 0.022). Metabolite ratios averaged across all 8 animals were not significantly different from baseline at any time point after 2 weeks post inoculation. However, linear regression analysis on all 8 animals revealed a positive correlation between a change in frontal lobe Cho/Cr and plasma viral load (P < 0.001, R = 0.80), and a negative correlation between NAA/Cr in the basal ganglia and the plasma viral load (P < 0.02, R = -0.73). No MRI abnormalities were detected at any time.Conclusions
After infection with SIV, macaque brain metabolism changes in a complex manner that is dependent on brain region, host factors and viral load. An elevation of basal ganglia Cho/Cr 4 weeks after SIV infection may be marker of a propensity to develop SIV encephalitis. Elevations of Cho/Cr, often observed in CNS inflammation, were associated with increased plasma viral load during acute and chronic infection. Evidence of neuronal injury in the basal ganglia was associated with increased plasma viral load in the chronic stage of infection. These observations support the use of drugs capable of controlling the viral replication and trafficking of virus into the CNS, and may help explain the reduction in incidence of HIV-associated dementia in the era of HAART despite the inability of most of those drugs to effectively enter the CNS. 相似文献3.
Shi Xunqing Wang Zhiping John HL Pang Zhang Xueren Nie Jingxu 《Acta Mechanica Sinica》2002,18(3):274-287
In this study, a new unified creep constitutive relation and a modified energy-based fatigue model have been established respectively
to describe the creep flow and predict the fatigue life of Sn−Pb solders. It is found that the relation successfully elucidates
the creep mechanism related to current constitutive relations. The model can be used to describe the temperature and frequency
dependent low cycle fatigue behavior of the solder. The relation and the model are further employed in part II to develop
the numerical simulation approach for the long-term reliability assessment of the plastic ball grid array (BGA) assembly.
The project supported by the National Natural Science Foundation of China (59705008) 相似文献
4.
MRosario Rueda Michael I Posner Mary K Rothbart Clintin P Davis-Stober 《BMC neuroscience》2004,5(1):39
Background
Tasks involving conflict are widely used to study executive attention. In the flanker task, a target stimulus is surrounded by distracting information that can be congruent or incongruent with the correct response. Developmental differences in the time course of brain activations involved in conflict processing were examined for 22 four year old children and 18 adults. Subjects performed a child-friendly flanker task while their brain activity was registered using a high-density electroencephalography system. 相似文献5.
Two optically active liquid anion-exchangers have been synthesized. The separation factors of the enantiomers of sodium (+/-)-mandelate and sodium-N-acetyl-(+/-)-alanate have been determined by batchwise equilibration of aqueous solutions of the salts with chloroform solutions of each of the exchangers. Sodium mandelate has been resolved by Craig countercurrent extraction with one of these exchangers. Optically pure products can be obtained even though the liquid ion-exchanger is not optically pure. 相似文献
6.
Shi Xunqing John HL Pang Yang Qianjin Wang Zhiping Nie Jingxu 《Acta Mechanica Sinica》2002,18(4):356-367
In the present study, a facility, i.e., a mechanical deflection system (MDS), was established and applied to assess the long-term
reliability of the solder joints in plastic ball grid array (BGA) assembly. It was found that the MDS not only quickly assesses
the long-term reliability of solder joints within days, but can also mimic similar failure mechanisms in accelerated thermal
cycling (ATC) tests. Based on the MDS and ATC reliability experiments, the acceleration factors (AF) were obtained for different
reliability testing conditions. Furthermore, by using the creep constitutive relation and fatigue life model developed in
part I, a numerical approach was established for the purpose of virtual life prediction of solder joints. The simulation results
were found to be in good agreement with the test results from the MDS. As a result, a new reliability assessment methodology
was established as an alternative to ATC for the evaluation of long-term reliability of plastic BGA assembly.
The project supported by the National Natural Science Foundation of China (59705008) 相似文献
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Daniel Rothbart 《Foundations of Chemistry》1999,1(3):255-268
Based on the design of many modern chemical instruments, information about a specimen is retrieved after the specimen undergoes agitation, manipulation and disturbance of its internal state. But can we retain the traditional ideal that instruments should reveal properties that are definable independently of all modes of detection? In this paper I argue that the capacity of chemical instruments to convert experimental phenomena to information places constraints on the way in which the specimen is characterized. During research, the specimen is defined by those properties which permit its detection. Based on modern instrumentation, this constraint necessitates a conception of the specimen as a reactive system of dynamical properties. The dream of a purely transparent detection process violates the design of chemical instruments. This mutual dependence of instrument and specimen is illustrated by empirical studies of the geometrical configuration of DNA. 相似文献
10.
王恩耀 《核聚变与等离子体物理》1999,19(2):116-119
报道了HL-1M装置1998年度物理实验的进展情况。主要包括等离子体密度极限,中性束注入加热,离子回旋共振加热,低温杂波离子加热,多发弹丸注入,超声分子束注入等实验的情况。 相似文献