三轴飞行仿真转台结构有限元分析

通过建立三轴转台的有限元模型,对其进行了结构刚度、模态分析和结构优化设计。通过改善台体机械结构,来满足结构刚度的要求;利用有限元模态分析,合理安排谐振点,同时利用优化方法,采用混合罚函数法,转化为无约束优化问题,再采用Powell法求解出外框的目标尺寸。通过上述分析计算,使台体结构更加合理,同时也说明了在三轴转台机械系统设计中有限元的重要性。     

Sympathetic response to stimulation of the pontine A5 region in conscious rabbits

OBJECT: This study is a retrospective analysis of clinical data obtained in 28 patients affected by obstructive hydrocephalus who presented with signs of midbrain dysfunction during episodes of shunt malfunction. METHODS: All patients presented with an upward gaze palsy, sometimes associated with other signs of oculomotor dysfunction. In seven cases the ocular signs remained isolated and resolved rapidly after shunt revision. In 21 cases the ocular signs were variably associated with other clinical manifestations such as pyramidal and extrapyramidal deficits, memory disturbances, mutism, or alterations in consciousness. Resolution of these symptoms after shunt revision was usually slow. In four cases a transient paradoxical aggravation was observed at the time of shunt revision. In 11 cases ventriculocistemostomy allowed resolution of the symptoms and withdrawal of the shunt. Simultaneous supratentorial and infratentorial intracranial pressure recordings performed in seven of the patients showed a pressure gradient between the supratentorial and infratentorial compartments, with a higher supratentorial pressure before shunt revision. Inversion of this pressure gradient was observed after shunt revision and resolution of the gradient was observed in one case after third ventriculostomy. In six recent cases, a focal midbrain hyperintensity was evidenced on T2-weighted magnetic resonance imaging sequences at the time of shunt malfunction. This rapidly resolved after the patient underwent third ventriculostomy. CONCLUSIONS: It is probable that in obstructive hydrocephalus, at the time of shunt malfunction, the development of a transtentorial pressure gradient could initially induce a functional impairment of the upper midbrain, inducing upward gaze palsy. The persistence of the gradient could lead to a global dysfunction of the upper midbrain. Third ventriculostomy contributes to equalization of cerebrospinal fluid pressure across the tentorium by restoring free communication between the infratentorial and supratentorial compartments, resulting in resolution of the patient's clinical symptoms.     

Laboratory investigation of the mass stability of sampling cassettes from inhalable aerosol samplers

A study was conducted to evaluate the mass stability of the materials used in the construction of samplers with internal cassettes for the gravimetric measurement of inhalable aerosol exposures. The internal cassettes from IOM samplers were studied. Results indicate that the mass stability of filters is uniform, but the mass stability of the cassette material may dramatically affect the results of the measurement. Cassettes constructed from plastic exhibited drastic shifts in mass depending on the environmental conditions of their storage. Under room humidity, the plastic cassettes absorbed 1 to 2 mg of water over several days. When these cassettes were placed in a desiccator, they lost mass consistently but did not approach a stable mass. Studies repeated with cassettes made of stainless steel showed negligible mass variability. Based on this study, the use of stainless steel cassettes is recommended for gravimetric determinations of aerosol exposure, although field blanks may in some cases be used for correction of data from plastic cassettes. This study shows the need to evaluate the mass stability of the cassette material of any sampling device where an internal cassette is weighed together with the filter.     

Discordance of databases designed for claims payment versus clinical information systems. Implications for outcomes research

OBJECTIVE: To determine the suitability of insurance claims information for use in clinical outcomes research in ischemic heart disease. DESIGN: Concordance study of two databases. SETTING: Tertiary care referral center. PATIENTS: A total of 12,937 consecutive patients hospitalized for cardiac catheterization for suspected ischemic heart disease between July 1985 and May 1990. INTERVENTIONS: Two-by-two tables were used to compute overall and kappa measures of agreement comparing clinical versus claims data for 12 important predictors of prognosis in patients with ischemic heart disease. MEASUREMENTS: Kappa statistics (agreement adjusted for chance agreement) were used to quantify agreement rates. RESULTS: Agreement rates between the clinical and claims databases ranged from 0.83 for the diagnosis of diabetes to 0.09 for the diagnosis of unstable angina (kappa values). Claims data failed to identify more than one half of the patients with prognostically important conditions, including mitral insufficiency, congestive heart failure, peripheral vascular disease, old myocardial infarction, hyperlipidemia, cerebrovascular disease, tobacco use, angina, and unstable angina, when compared with the clinical information system. CONCLUSIONS: Our results suggest that insurance claims data lack important diagnostic and prognostic information when compared with concurrently collected clinical data in the study of ischemic heart disease. Thus, insurance claims data are not as useful as clinical data for identifying clinically relevant patient groups and for adjusting for risk in outcome studies, such as analyses of hospital mortality.     

National surveillance of dialysis associated diseases in the United States, 1995

Many fundamental and hot band absorption lines of 28Si35Cl+, 28Si37Cl+, 29Si35Cl+, and 30Si35Cl+ have been detectedbetween 630 and 700 cm-1 in a SiCl4/He discharge using diode laser velocity modulation spectroscopy. The datahave been fitted to give seven mass independent coefficients Ukl. The derived spectroscopic constants for 28Si35Cl+ include omegae = 678.24316(18) cm-1 and Be = 0.2870288(14) cm-1. The equilibrium internuclear distance is re =1.9439105(46) ?. The equilibrium dissociation energy calculated from Dunham's expanded Morse potential is De =49 431(57) cm-1. Copyright 1998 Academic Press.     

Pediatric hepatic trauma: does clinical course support intensive care unit stay?

PURPOSE: The objective of this study is to determine if grade of liver injury predicts outcome after blunt hepatic trauma in children and to initiate analysis of current management practices to optimize resource utilization without compromising patient care. METHODS: A retrospective review of 36 children who had blunt hepatic trauma treated at a pediatric trauma center from 1989 to present was performed. Hepatic injuries graded (AAST Organ Injury Scaling) ranged from grade I to IV. Injury Severity Score (ISS), Glasgow Coma Score (GCS), transfusion requirements, liver transaminase levels, associated injuries, intensive care unit (ICU) length of stay, and survival were analyzed. RESULTS: Mean (+/-SEM) age was 6.6+/-0.8 years, mean grade of hepatic injury was 2.4+/-0.2, mean ISS was 17+/-2.6, mean GCS was 13+/-1, and mean transfusion was 15.4 mL/kg of packed red blood cells (PRBC). There were three deaths with a mean ISS of 59+/-9 and a mean GCS of 3+/-0. Death was not associated with a high-grade liver injury, survivors versus nonsurvivors, 2.3+/-0.2 versus 2.7+/-0.3, but was associated with ISS, 13+/-1.4 versus 59+/-9 (P = .005) and GCS, 14+/-1 versus 3+/-0 (P = .005). Only one patient (grade III, ISS = 43) underwent surgery. There were no differences in mean ISS or GCS between grades I to IV patients. The hepatic injury grades of patients requiring transfusion versus no transfusion were significantly different, 3.4+/-0.2 versus 2.2+/-0.2 (P = 0.04). Abused patients had high-grade hepatic injuries and significant laboratory and clinical findings. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly higher in grade III and IV injuries than in grades I and II, 1,157+/-320 versus 333+/-61 (P= .02) and 1,176+/-299 versus 516+/-86 (P= .04), respectively. No children with grade I or II injury had a transfusion requirement or surgical intervention. There were no liver-related complications. CONCLUSIONS: Mortality and morbidity rates in pediatric liver injuries, grades I to IV, correlate with associated injuries not the degree of hepatic damage. ALT, AST, and transfusion requirements are significantly related to degree of liver injury. Low-grade and isolated high-grade liver injuries seldom require transfusion. Blunt liver trauma rarely requires surgical intervention. In retrospect, the need for expensive ICU observation for low-grade and isolated high-grade hepatic injuries is questionably warranted.     

Steady-state cerebral glucose concentrations and transport in the human brain

Understanding the mechanism of brain glucose transport across the blood-brain barrier is of importance to understanding brain energy metabolism. The specific kinetics of glucose transport have been generally described using standard Michaelis-Menten kinetics. These models predict that the steady-state glucose concentration approaches an upper limit in the human brain when the plasma glucose level is well above the Michaelis-Menten constant for half-maximal transport, Kt. In experiments where steady-state plasma glucose content was varied from 4 to 30 mM, the brain glucose level was a linear function of plasma glucose concentration. At plasma concentrations nearing 30 mM, the brain glucose level approached 9 mM, which was significantly higher than predicted from the previously reported Kt of approximately 4 mM (p < 0.05). The high brain glucose concentration measured in the human brain suggests that ablumenal brain glucose may compete with lumenal glucose for transport. We developed a model based on a reversible Michaelis-Menten kinetic formulation of unidirectional transport rates. Fitting this model to brain glucose level as a function of plasma glucose level gave a substantially lower Kt of 0.6 +/- 2.0 mM, which was consistent with the previously reported millimolar Km of GLUT-1 in erythrocyte model systems. Previously reported and reanalyzed quantification provided consistent kinetic parameters. We conclude that cerebral glucose transport is most consistently described when using reversible Michaelis-Menten kinetics.     

Synthesis and biological evaluation of certain new thiazolopyrimidines

A series of 5-methyl-3-phenyl thiazolo[5,4-e][1,2,4]triazolo[1,5-c] pyrimidin-2-thiones and 5-methyl-3-phenyl thiazolo[5,4-e]pyrimidino[3,4-b][1,2,4]triazin-2-thiones were prepared as potential antimicrobial and antitumor agents. Some of the tested compounds showed promising activity. The detailed synthesis, spectroscopic and biological data are reported.