Thermodynamic criterion of separated eutectic phenomena

About 26 kinds of simple and complex binary eutectics were frozen directionally under the condition of electromagnetic stirring. It was found that anomalous eutectics including most metals/non-metals and some metal/intermetallic eutectics, can be separated on macroscopic scale by flow caused by electromagnetic stirring. Moreover, the eutectics in which one of their component phases possess an entropy of solution over 23 J mol-1K-1 showed notable separation. In addition, process factors also affect the formation of a separated eutectic. © 1998 Chapman & Hall     

Prevention of macrosegregation in squeeze casting of an Al-4.5 wt pct Cu alloy

The squeeze casting of an Al-4.5 wt pct Cu alloy was carried out to investigate the conditions for the formation and the prevention of macrosegregation. The effects of the process parameters, applied pressure, die temperature, pouring temperature, delay time, and humidity on the formation of macrosegregation were investigated in correlation with the evolution of macrostructure and shrinkage defects. Two critical applied pressures were defined: one is the critical applied pressure, P _SC , under which shrinkage defects form, and the other is the critical applied pressure, P _MS , above which macrosegregates form in the squeeze castings. A quantitative diagram describing the optimum process conditions was proposed for obtaining sound squeeze castings. It was found that the pouring temperature, the die temperature, the delay time, and the humidity are closely related to the two critical applied pressures P _SC and P _MS , in different manners. It was concluded that sound castings without macrosegregation and shrinkage defects can only be obtained when the applied pressure is in the range of P _SC <P<P _MS .     

Internal pressures and thermal pressure coefficients for solid polymers

The temperature and pressure dependence of the thermal pressure coefficient and internal pressure for eight polymer solids are calculated. The principal results are as follows: (1) The pressure dependence of the thermal pressure coefficient at constant temperature is relatively small. (2) For some solid polymers, as a function of temperature, a maximum in the thermal pressure coefficient is predicted in the solid region, and the temperatures corresponding to the maximum values are estimated. (3) For most solid polymers, the zeropressure internal pressure increases with increasing temperature over the entire temperature range to the glass transition temperature or the melting point. © 1995 John Wiley & Sons, Inc.     

Feldkamp and circle-and-line cone-beam reconstruction for 3D micro-CT of vascular networks

Detailed morphometric knowledge of the microvascular network is needed for studies relating structure to haemodynamic function in organs like the lung. Clinical volumetric CT is limited to millimetre-order spatial resolution. Since evidence suggests that small arterioles (50 to 300 micrometres) dominate pulmonary haemodynamics, we built a micro-CT scanner, capable of imaging excised lungs in 3D with 100 microm resolution, for basic physiology research. The scanner incorporates a micro-focal (3 microm) x-ray source, an xyz theta stage and a CCD-coupled image intensifier detector. We imaged phantoms and contrast-enhanced rat lungs, reconstructing the data with either the Feldkamp or the circle-and-line cone-beam reconstruction algorithm. We present reconstructions using 180 views over 360 degrees for the circular trajectory, augmented with views from a linear scan for the circle-and-line algorithm. Especially for platelike features perpendicular to the rotation axis and remote from the midplane, the circle-and-line algorithm produces superior reconstructions compared with Feldkamp's algorithm. We conclude that the use of nonplanar source trajectories to perform micro-CT on contrast-enhanced, excised lungs can provide data useful for morphometric analysis of vascular trees, currently down to the 130 microm level.     

Predicting length of stay in an acute psychiatric hospital

OBJECTIVE: Multivariate statistical methods were used to identify patient-related variables that predicted length of stay in a single psychiatric facility. The study investigated whether these variables remained stable over time and could be used to provide individual physicians with data on length of stay adjusted for differences in clinical caseloads and to detect trends in the physicians' practice patterns. METHODS: Data on all patients discharged over two six-month periods were collected at an acute psychiatric inpatient facility. Stepwise multiple regression analyses were conducted on the two datasets. RESULTS: The results from both analyses revealed that five variables significantly predicted length of stay and were stable over time. They were a primary diagnosis of schizophrenia, the number of previous admissions, a primary diagnosis of a mood disorder, age, and a secondary diagnosis of an alcohol- or other drug-related disorder. For some physicians, the mean length of stay of their patients differed significantly from the length predicted by the regression model--generally, it was shorter. CONCLUSIONS: The results demonstrate that patient-related predictors of length of stay in a single psychiatric hospital can be identified using relatively simple statistical procedures and can be consistent across a large dataset and over time.     

Correcting the bias of clerkship timing on academic performance

OBJECTIVES: To document the time-of-year bias in National Board of Medical Examiners subject examination (NBME) scores in a third-year pediatrics clerkship and to develop a grading method that neutralizes the bias. DESIGN: Interventional modeling of final grades. SETTING: University-based medical school. SUBJECTS AND METHODS: During each of the past 3 academic years, we conducted six 2-month pediatric clerkships for third-year students. To counter the time-of-year bias, NBME scores, clinical evaluations, and departmental examination scores for the current rotation were pooled with those from the rotations from the same time of year during the previous 2 years. Final grades for the current rotation were determined by cutoff points derived from that entire 3-year pool. We analyzed this approach by testing the time-of-year effects on NBME scores, clinical evaluations, and final grades while maintaining step 1 of the US Medical Licensing Examination as a preclinical baseline control. RESULTS: The scores for step 1 of the US Medical Licensing Examination did not differ significantly by time of year. Clinical evaluations and NBME scores showed significant upward trends as the academic year progressed. By contrast, according to design, final grades showed no significant time-of-year trend. CONCLUSIONS: Our results support previous reports of significant improvements in NBME scores across the academic year. Our method of computing final grades corrects for this time-of-year bias by judging students only in relation to those who took the rotation at the same time of year. It is our belief that the prevalence and significance of the time-of-year trend warrants such an adjustment in grading to help minimize the academic disadvantage faced by students early in their clinical training.     

Sesquiterpenoids of the drimane class from a sponge of the genus Dysidea

Ten sesquiterpenoids, including seven new ones, have been isolated from an undescribed sponge of the genus Dysidea. Compounds 1-8 are sesquiterpenoids of the drimane class, while 9 and 10 are 12-norsesquiterpenoids of the same structural class. The structures of novel compounds have been determined by combined spectroscopic methods. These compounds exhibited moderate antimicrobial and enzyme inhibitory (Na+/K(+)-ATPase and PLA2) activities.     

Modeling, analysis, and design of the quasi-charge control

A current-mode control technique, quasi-charge control (QCC), is studied. A small-signal model is developed for QCC. The model is derived for converters operating in the continuous conduction mode. The model is accurate up to half of the switching frequency. The proposed small-signal model is used to assess the dynamics of pulse-width-modulated (PWM) power converters with QCC, and to compare their performance to the current-injected control (CIC) and charge control (CC) schemes. As in CC, the QCC converges to CIC at light loads close to the boundary between continuous and discontinuous conduction modes. The dynamics of power converters with QCC or CC are more sensitive to load change and less sensitive to line change than those of power converters with CIC, especially the current loop dynamics. However, unlike in the case of CC, the dependency on the load/line can be controlled when the QCC is designed. Control design guidelines for DC-DC power converters and power factor correction rectifiers are presented, and experimental measurements are performed to verify the proposed model