A mathematical model explaining the molecular weights and distribution of very long chain dicarboxylic acids formed during the adaptive response of Sarcina ventriculi

A simple mathematical model is presented to explain a recent new discovery of an unusual membrane adaptive response in Sarcina ventriculi. In this response, this organism synthesizes very long chain alpha, omega-dicarboxylic acids ranging from 28 to 36 carbon atoms in length. The distribution of chain lengths of the new fatty acid species is not consistent with de novo synthesis but suggests elaboration from the existing regular-chain fatty acids by a coupling process. Here, we demonstrate, using a mathematical model, that if the molecular weights and relative abundances of regular chain fatty acids are known, the molecular weights and relative abundances of the new, very long chain dicarboxylic fatty acid species can be predicted using a model based on the random, pairwise combination of regular chain species. This combination takes place across the bilayer leaflet to form transmembrane fatty acids. It is proposed that this coupling phenomenon is regulated by the motional dynamics of the membrane.     

Dietary intake recorder based upon a single-board microcomputer

A food recording electronic device to simplify the collection of dietary data is described. The need for a subject to maintain a quantitative account of food intake, and for a dietitian to subsequently code this record prior to computer analysis, are both eliminated using this approach. In combination with an electronic kitchen balance, the recorder, which is based upon a single-board computer (SBC) and special keyboard, enables the weight, food type and time of consumption of each food to be recorded automatically in response to simple key entry. The resident program, transparent to the user, allows data from surveys lasting up to three weeks to be stored for subsequent serial downloading to a host computer.     

Tracking of complex binaural images

Subjects were presented with an initially stationary binaural image formed by the fusion of two identical pulses, without interaural time difference (ITD), at the two ears. The image was then made to traverse the subject's auditory perceptual space by introducing ITD, varying linearly with time, under computer control. The direction of movement, i.e. towards the right or left ear, could be reversed by the listener, by pressing a button. Subjects were requested to keep the image central, by pressing the button when they judged that deviation from subjective centre had occurred. Experiments of this type can be considered as analogous to Békésy audiometry, where the subject automatically traces his threshold of hearing, in that here the listener traces out his auditory perceptual centre as it varies with time. Hence, equivalent analyses to those employed for Békésy audiometry are possible. Subsequent to the initial part of the experiment, an additional pulse was added to one channel, preceding the original pulse, to form a pulse pair. The monaural masking of the original pulse by this additional pulse thus acts to shift the pre-existing binaural image. The effect of varying the amplitude and onset time of the masking pulse, relative to the original pulse, on the Békésy-type trace was examined.     

超滤-微滤膜过滤传质理论的研究进展

探讨了超滤-微滤膜过滤传质理论的研究状况,重点介绍了超滤-微滤膜过理论模型、非牛顿液体膜堵塞过滤以及动态过滤等常规过滤理论的研究进展,评述了超滤-微滤膜过滤传质机理的动态,指出了超滤-微滤膜过滤基本理论模型需进一步研究解决的问题.     

连接条件对00Cr25Ni7Mo3N双相不锈钢扩散连接的影响

利用热模拟试验机并结合扫描电镜(SEM)对00Cr25Ni7Mo3N超级双相不锈钢的超塑扩散连接进行实验研究,对不同连接条件下的孔洞形貌、界面组织进行相应的分析。研究结果表明,超塑性扩散连接试样的界面结合强度随扩散连接压力的增大、表面质量的提高及连接时间的延长而增大。扩散连接在连接温度1100℃时,连接压力为10MPa～20MPa;待连接表面经精磨处理后,连接时间10min～20min的条件下,可实现焊合率为96%～98%的扩散连接,且连接试样的初始连接界面消失,界面孔洞基本闭合,界面剪切结合强度达到407MPa～413MPa。     

Lateralization of human temporal lobe epilepsy by 31P NMR spectroscopic imaging at 4.1 T

OBJECTIVE: To compare the phosphorous metabolite ratios in the mesial temporal lobe of healthy volunteers (n = 20) with the corresponding ratios in patients with temporal lobe epilepsy (n = 30) using 31P NMR spectroscopic imaging and to lateralize the seizure focus in temporal lobe epilepsy patients using various phosphorous metabolite ratios-phosphocreatine to inorganic phosphate (PCr/Pi), PCr to adenosine triphosphate (PCr/gamma-ATP), and (gamma-ATP/Pi)--and to compare with clinical lateralization results. METHODS: All 31P NMR spectroscopic imaging studies were performed on a high-field, 4.1 T, whole-body NMR spectroscopic imaging system using a 31P/1H double-tuned volume coil. RESULTS: We found an average reduction of 15% in the PCr/Pi and gamma-ATP/Pi ratios compared with the corresponding ratios in healthy volunteers in the entire mesial temporal lobe, and more than a 30% reduction in these two ratios in the anterior region of the epileptogenic mesial temporal lobe. These ratios were also reduced significantly in the ipsilateral lobe when compared with their corresponding values in the contralateral lobe. In patients we lateralized the seizure focus, based on these 31P NMR data, and compared the results with the clinical lateralization. The lateralization based on either the PCr/Pi or the gamma-ATP/Pi ratio yielded a correspondence of 70 to 73% with the final clinical lateralization. In the subgroup of patients (n = 9) that needed intracranial EEG for the presurgical lateralization because of inconclusive results from the noninvasive methods, a 78% correspondence was found with the 31P NMR-based lateralization, whereas MRI provided a correspondence of only 33%, and scalp EEG provided a correspondence of only 56%. CONCLUSIONS: These results suggest the utility of adding the 31P NMR method to the group of noninvasive modalities used for presurgical decision making in temporal lobe epilepsy patients.