Conversational maxims and scaffolded learning in children with learning disabilities: is the flying buttress a better metaphor?

BACKGROUND: To compare half-Fourier acquisition single-shot turbo spin-echo spin-echo (HASTE) magnetic resonance cholangiopancreatography (MRCP) with two-dimensional turbo spin-echo (2D TSE) MRCP for imaging pancreatobiliary diseases. METHODS: Twenty-seven patients with biliary or pancreatic disease underwent MRCP on a 1.0-T scanner with a body phased-array coil. A T2-weighted HASTE sequence (18 s) and a T2-weighted 2D TSE sequence (45 s) were used during a breath-hold by the patient. The source images and maximum intensity projection images of both sequences were reviewed independently by two radiologists. RESULTS: Motion artifacts were more severely pronounced with 2D TSE sequences than with HASTE sequences (p < 0.001). All obstructions and their sites were accurately identified with both sequences. Filling defects (calculi) in bile ducts were identified in all 22 segments (100%) with HASTE-MRCP, whereas calculi in 19 of 22 segments (86%) were identified with 2D TSE-MRCP (p = 0.25). Three missed sites on 2D TSE-MRCP were intrahepatic bile ducts. CONCLUSIONS: HASTE-MRCP is superior to 2D TSE-MRCP in terms of detecting motion artifacts and visualization of the pancreatic ducts. HASTE-MRCP is comparable to 2D TSE-MRCP for visualization of the biliary ducts and their obstruction and is superior to 2D TSE-MRCP for identification of calculi in intrahepatic bile ducts.     

氯碱装置中塑料设备的耐腐蚀性能

对塑料设备在氯碱装置中的耐腐蚀特性及实际应用中的防腐效果进行了分析，并介绍了塑料设备的腐蚀检查内容及检修频率，为氯碱装置的建设和生产中塑料设备的选材及腐蚀防护提供参考。     

Teenage driving fatalities

BACKGROUND/PURPOSE: A recent legislative effort in New Hampshire to institute a graduated licensing system for teenagers (TA) led to an analysis of state data on fatal crashes involving TA drivers. This provides an overview of these events and suggests possible prevention strategies. METHODS: Data on fatal crashes involving TA drivers was obtained for the years 1991 through 1996 from the Fatal Accident Unit, Division of State Police, New Hampshire Department of Safety. RESULTS: From 1991 through 1996, there were 100 events resulting in 109 total deaths, of which 76 were TA. Five involved motorcycles. Four drivers struck pedestrians, and two struck children on bicycles. In one case, an object fell from a truck, crushing a car. The remaining 88 were single- or multiple-car crashes, and these were analyzed further. Two thirds of the drivers were boys. The driver breakdown by age was 15 years, 3; 16 years, 21; 17 years, 26; 18 years, 20; 19 years, 18. The TA driver was killed in 47% of the events. Nineteen percent resulted in the death of the driver of another car. In 62 events, there were passengers in the TA's car, and in 55% of these, a passenger was killed. Twenty percent of the crashes involved drugs or alcohol, and almost two thirds of these occurred between 10:00 PM and 6:00 AM. Seat belts were not used by at least 72% of those injured fatally. In 59%, known traffic violations, usually speeding, contributed. More detailed data were available for 1995 through 1996, during which there were 30 crashes resulting in 33 deaths. Speed limit did not correlate with number of crashes. One-car crashes outnumbered multiple-car, 57% to 43%. Ninety percent occurred on single-lane roads. Most significantly, 63% of the drivers had been licensed less than 1 year and 47% less than 6 months. In this latter group, drugs and alcohol played no role, and none occurred between 11:00 PM and 6:00 AM. CONCLUSIONS: Two at-risk groups exist. The first is inexperienced sober TA drivers on single-lane roads during conventional hours. As experience increases, the second group appears: TA who have been drinking and are out late at night. Prevention strategies must take into account these two groups.     

Binding, encapsulation and ejection: substrate dynamics during a chaperonin-assisted folding reaction

Mitochondrial malate dehydrogenase (mMDH) folds more rapidly in the presence of GroEL, GroES and ATP than it does unassisted. The increase in folding rate as a function of the concentration of GroEL-ES reaches a maximum at a stoichiometry which is approximately equimolar (mMDH subunits:GroEL oligomer) and with an apparent dissociation constant K' for the GroE acceptor state of at least 1 x 10(-8) M. However, even at chaperonin concentrations which are 4000 x K', i.e. at negligible concentrations of free mMDH, the observed folding rate of the substrate remains at its optimum, showing not only that folding occurs in the chaperonin-mMDH complex but also that this rate is uninhibited by any interactions with sites on GroEL. Despite the ability of mMDH to fold on the chaperonin, trapping experiments show that its dwell time on the complex is only 20 seconds. This correlates with both the rate of ATP turnover and the dwell time of GroES on the complex and is only approximately 5% of the time taken for the substrate to commit to the folded state. The results imply that ATP drives the chaperonin complex through a cycle of three functional states: (1) an acceptor complex in which the unfolded substrate is bound tightly; (2) an encapsulation state in which it is sequestered but direct protein-protein contact is lost so that folding can proceed unhindered; and (3) an ejector state which forces dissociation of the substrate whether folded or not.     

Clinical and immunologic criteria of the activity of different variants of the course of rheumatoid arthritis

Clinical and immunological studies were carried out in 24 IgM-RF seropositive and 10 seronegative patients with rheumatoid arthritis (RA). Manifest disorders of microcirculation were noted in the examinees, which was confirmed by changes in platelet hemostasis, detection of antibodies to cardiolipins and of Von Willebrandt's factor antigen, and a high level of circulating immune complexes. Analysis of laboratory and immunological findings showed an association of extraarticular symptoms of RA and detection of anticardiolipin antibodies and Von Willebrandt's factor antigen. The activity of the pathological process correlated with the time course of these parameters.     

Deduction of pulmonary microvascular hematocrit from indicator dilution curves

We have developed a new model describing the relationship between plasma and red cell tracers flowing through the lung. The model is the result of an analysis of the transport of radiolabeled plasma albumin between two flowing phases and shows that differences between red cell and plasma tracer curves are related to microvascular hematocrit. The model was tested in an isolated, blood-perfused dog lung preparation in which we injected 51Cr-labeled red cells and 125I-labeled plasma albumin into the pulmonary artery. From the tracer concentration-time curves at the venous outflow, we calculated hr, the ratio of microvascular hematocrit to large-vessel hematocrit. In 18 baseline experiments, hr = 0.92 +/- 0.01 (mn +/- sem) at a blood flow rate of 10.7 +/- 0.3 ml s-1. We determined the effects of (a) glass bead embolization, (b) alloxan, and (c) lobe ligation on hr. Embolization attenuated the separation between plasma and red cells (increased hr), probably as a consequence of passive vasodilation. Alloxan enhanced separation of plasma and red cells (decreased hr), possibly as a result of arteriolar vasoconstriction. Ligation of a fraction of the perfused tissue at constant flow did not cause significant change in hr in the remaining perfused tissue. The model assumes that large-vessel transit times are uniform and that all dispersion occurs in the microvasculature. A theoretical analysis apportioning dispersion between large and small vessels disclosed that the error associated with these assumptions is likely to be less than 15% of the measured hr. We conclude from this study that the microvascular hematocrit model describes experimental plasma and red cell curves. The results imply that hr can be readily deduced from tagged red cells and plasma and can be accounted for in calculating permeability-surface area in diffusing tracer experiments.