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H T Davis

Publications and source records attributed to H T Davis.

11 recordsLinked to original sources
PubMed1988

Controlled environment vitrification system: an improved sample preparation technique.

The controlled environment vitrification system (CEVS) permits cryofixation of hydrated biological and colloidal dispersions and aggregates from a temperature- and saturation-controlled environment. Otherwise, specimens prepared in an uncontrolled laboratory atmosphere are subject to evaporation and heat transfer, which may introduce artifacts caused by concentration, pH, ionic strength, and temperature changes. Moreover, it is difficult to fix and examine the microstructure of systems at temperatures other than ambient (e.g., biological systems at in vivo conditions and colloidal systems above room temperature). A system has been developed that ensures that a liquid or partially liquid specimen is maintained in its original state while it is being prepared before vitrification and, once prepared, is vitrified with little alteration of its microstructure. A controlled environment is provided within a chamber where temperature and chemical activity of volatile components can be controlled while the specimen is being prepared. The specimen grid is mounted on a plunger, and a synchronous shutter is opened almost simultaneously with the release of the plunger, so that the specimen is propelled abruptly through the shutter opening into a cryogenic bath. We describe the system and its use and illustrate the value of the technique with TEM micrographs of surfactant microstructures in which specimen preparation artifacts were avoided. We also discuss applications to other instruments like SEM, to other techniques like freeze-fracture, and to novel "on the grid" experiments that make it possible to freeze successive instants of dynamic processes such as membrane fusion, chemical reactions, and phase transitions.

Microscopy, Electron↗
PubMed1987

Use of risk assessment methods in the certification of decontaminated buildings.

Accidental events such as fires, explosions, and leaks often result in large-scale contaminations of buildings with toxic chemicals. After decontamination, the certification for original use requires testing for residual contamination. The two basic kinds of sampling plans in use up to recently both fall short of the required performance. Their deficiencies are analyzed in terms of the scientific questions implicit in both the sampling plan and the subsequent statistical evaluation. A sampling strategy of a new kind is proposed and discussed in the same context. It is motivated by concern for the long-term safety of the building's occupants and is, therefore, based on factors important in risk assessment. Three different sampling plans are derived in the framework of this methodology, two of which have already been used in actual certification proceedings.

Algorithms↗
PubMed1986

Graphical analysis of multivariate pain data in analgesic trials.

In order to compare analgesic treatments effectively one must measure pain over time. In a single-dose clinical analgesic trial one typically obtains repeated pain measurements from each patient during a relatively short period (4-6 hours). Such measurements constitute multivariate data, which are usually reduced by simple addition to a single derived pain measure for analysis of between-treatment differences. In this article we consider graphical procedures for the display of multivariate, clinical analgesic data. The first of these are the traditional time-effect curves, with added "standard error bars." We also examine a multivariate display, the biplot, which is based on principal component analysis. This technique provides a representation of the raw pain scores at each time of measurement by a vector originating from the origin of a two-dimensional graph. The multivariate pain scores of individual patients are summarized by points on the graph. Differences in pain scores over time (or between treatment groups) may be examined by relating points (or ellipses representing treatment groups) to different vectors. Using actual data from a postsurgical analgesic trial, we compare the two approaches and show that the multivariate approach is a useful addition to the standard technique for display of such data.

Analgesics↗
PubMed1979

Ventricular ectopic beats and their relation to sudden and nonsudden cardiac death after myocardial infarction.

The role of ventricular ectopic beats (VEBs) in identifying patients who die of cardiac cause in the posthospital phase of myocardial infarction was evaluated in 940 patients who survived an acute coronary event. Six-hour Holter ECG recordings were obtained before hospital discharge, and VEBs were classified as complex (bigeminal, multiform, repetitive or R on T), simple (one or more VEBs that did not have complex patterns), or not present. Patients were followed 1-60 months (average 36 months) and cardiac mortality was categorized as sudden (less than or equal to 1 hour) or nonsudden (greater than 1 hour) among 98 witnessed cardiac deaths. Complex VEBs were associated with a significantly increased cardiac death rate, but did not discriminate between sudden and nonsudden death. Simple VEBs were associated with a 3-year cardiac mortality rate intermediate between those with complex and those with no VEBs. The relationship between complex VEBs and cardiac mortality was independent of 10 relevant clinical variables.

Aged↗
PubMed1977

Analgesic efficacy of an orally administered combination of pentazocine and aspirin. With observations on the use and statistical efficiency of GLOBAL subjective efficacy ratings.

The analgesic efficacy of a combination of pentazocine and aspirin (PA) in the ration 1:13 was compared with that of 650 mg of aspirin alone (A650) and with placebo (PBO), in 98 patients with postoperative pain. Two dose levels of the combination were compared: the lower dose (PA-L) consisted of pentazocine 25 mg and aspirin 325 mg, while the higher dose (PA-H) consisted of pentazocine 50 mg and aspirin 650 mg. All active treatments performed significantly better than PBO. PA-L performed as well as A650, while PA-H performed significantly better than A650. In addition to the usual subjective measures of analgesia, we obtained in 74 patients an evaluation of the overall (GLOBAL) performance of the treatment. This was rated on an ordinal scale of 1 ("poor") to 5 ("excellent"). On the GLOBAL scale, PBO had a mean score of 2.4 (fair-good); A650 and PA-L had scores of 3.6 and 3.9 respectively (good-very good): and PA-H had a score of 4.5 (very good-excellent). In five of six comparisons between treatment means, GLOBAL had the best discriminating power of all six measures. In the two comparisons of greatest interest (A650 against PBO and PA-H against A650), GLOBAL was more than twice as efficient as the TOTAL (summed pain score) measure. In comparing the statistical efficiency of different measures of the same analgesic effect, there is a problem in determining what are "clinically equivalent differences" on the various analgesic scales employed. We propose the use of the observed sample differences and the safeguard of repeating the comparisons over several studies to minimize the effect of random-origin bias.

Adult↗