Subunit composition of neurofilaments specifies axonal diameter

Neurofilaments (NFs), which are composed of NF-L, NF-M, and NF-H, are required for the development of normal axonal caliber, a property that in turn is a critical determinant of axonal conduction velocity. To investigate how each subunit contributes to the radial growth of axons, we used transgenic mice to alter the subunit composition of NFs. Increasing each NF subunit individually inhibits radial axonal growth, while increasing both NF-M and NF-H reduces growth even more severely. An increase in NF-L results in an increased filament number but reduced interfilament distance. Conversely, increasing NF-M, NF-H, or both reduces filament number, but does not alter nearest neighbor interfilament distance. Only a combined increase of NF-L with either NF-M or NF-H promotes radial axonal growth. These results demonstrate that both NF-M and NF-H play complementary roles with NF-L in determining normal axonal calibers.     

Distribution of movement time in a target-aiming task

Various characteristics of the distribution of movement time were analyzed for a task involving serial and rotary arm movements aimed at a target. For experimental data generated from five Ss, (a) the distribution tended to be unimodal and more peaked than a normal distribution, (b) the skewness of the distribution was predominantly positive and (c) the standard deviation, in addition to the mean, of movement time was significantly affected by the complexity of the task as measured by Fitts' index of difficulty, while the skewness and the kurtosis were not. For the average results for the Ss, a first-order linear model with the standard deviation of movement time as the dependent variable and Fitts' index as the independent one explained 67% of the variation in standard deviation as compared to 98% of the variation in mean movement time accounted for by the Fitts' index.     

Crib death in the eastern regions of Norway 1984-1992. A survey of risk factors

Cot death is the most important cause of death during the first year of life after the newborn period in Norway. A case control study was performed by sending questionnaires to 188 cot death parents and 475 control parents with infants matched for age, sex and time of birth. 76% of the cot death parents and 79% of the control parents completed the questionnaires. The male/female ratio of the babies in both groups was 64/36. The age distribution showed a peak between two and four months. 65% succumbed during the winter months. During the winter 32% died outdoors. This was true for only 16% of those who died during summer. A higher proportion of the cot death cases than the controls were premature (more than eight weeks). 78% of the cot death victims usually slept prone, whereas this was true for only 50% of the controls (p < 0.01). 91% of the cot death victims were found dead in a prone position. When comparing live babies during the first three months of life, significantly more cot death mothers than control mothers had stopped breastfeeding. A larger proportion of the cot death victims than the controls had had apparent life threatening events (p < 0.01). Foam mattresses were equally frequent in both groups.     

屈强比对高强钢断裂韧性的影响

通过控制组织形态，对化学尬发相同，屈强比不同的两种钢材进行三点弯曲ＣＴＯＤ试验，并利用三维有限元法分析裂纹法端的应力应变分布。结果表明，高屈强比的材料，由于裂纹尖端应力水平高，脆性启裂ＣＴＯＤ值δｃ明显低于低屈强比的材料；而对有延性裂纹扩展的ＣＴＯＤ临界值δｕ和δｍ，高屈强比的材料同于低屈强比双相钢，这是因为低屈强比材料内部存在微观组织非均质，有应变集中所致。     

Cognitive arithmetic and problem solving: a comparison of children with specific and general mathematics difficulties

This study examined problem-solving and number-fact skills in two subgroups of third-grade children with mathematics difficulties (MD): MD-specific (n = 12) and MD-general (n = 12). The MD-specific group had difficulties in mathematics but not in reading, and the MD-general group had difficulties in reading as well as in mathematics. A comparison group of nonimpaired children (n = 24) also was included. The findings showed that on both story and number-fact problems, the MD-specific group performed worse than the nonimpaired group in timed conditions but not in untimed conditions. The MD-general group, on the other hand, performed worse than the nonimpaired group, regardless of whether tasks were timed or not. An analysis of children's strategies in untimed conditions showed that both the MD-specific and the MD-general groups relied more on backup strategies than the nonimpaired group. However, children in the MD-specific group executed backup strategies more skillfully than children in the MD-general group, allowing them to achieve parity with children in the nonimpaired group when tasks were not timed. The findings suggest that children with specific MD have circumscribed deficits associated with fact retrieval, whereas children with general MD have more basic delays associated with problem conceptualization and execution of calculation procedures.     

Thromboembolism after foot and ankle surgery. A multicenter study

Thromboembolic disease presents a potentially fatal complication to patients undergoing orthopaedic surgery. Although the incidence after hip and knee surgery has been studied and documented, its incidence after surgery of the foot and ankle is unknown. For this reason, a prospective multicenter study was undertaken to identify patients with clinically evident thromboembolic disease to evaluate potential risk factors. Two thousand seven hundred thirty-three patients were evaluated for preoperative risk factors and postoperative thromboembolic events. There were six clinically significant thromboembolic events, including four nonfatal pulmonary emboli, after foot and ankle surgery. The incidence of deep vein thrombosis was six of 2733 (0.22%) and that of nonfatal pulmonary emboli was four of 2733 (0.15%). Factors found to correlate with an increased incidence of deep vein thrombosis were nonweightbearing status and immobilization after surgery. On the basis of these results, routine prophylaxis for thromboembolic disease after foot and ankle surgery probably is not warranted.