Dalton's and Amagat's laws fail in gas mixtures with shock propagation

A shock propagating through a gas mixture leads to pressure, temperature, and density increases across the shock front. Rankine-Hugoniot relations correlating pre- and post-shock quantities describe a calorically perfect gas but deliver a good approximation for real gases, provided the pre-shock conditions are well characterized with a thermodynamic mixing model. Two classic thermodynamic models of gas mixtures are Dalton's law of partial pressures and Amagat's law of partial volumes. We measure post-shock temperature and pressure in experiments with nonreacting binary mixtures of sulfur hexafluoride and helium (two dramatically disparate gases) and show that neither model can accurately predict the observed values, on time scales much longer than that of the shock front passage, due to the models' implicit assumptions about mixture behavior on the molecular level. However, kinetic molecular theory can help account for the discrepancy. Our results provide starting points for future theoretical work, experiments, and code validation.

Native American recruitment into breast cancer screening: the NAWWA project

BACKGROUND

American Indian women's historically low breast cancer incidence and mortality rates have gradually increased such that in many parts of the United States they equal "U.S. All Races" rates. Thus, American Indian women need screening to maintain their low rates.

METHODS

In an outreach program, local American Indian women were trained as lay health advisers, "Native Sisters," to locate and contact American Indian women in the Denver metropolitan area and provide education and encouragement to increase participation in mammography screening. Participation was monitored and interviews collected descriptive information and information about risk factors for breast cancer. An interrupted-time-series design was used to assess changes in mammography participation.

RESULTS

The NAWWA program increased recruitment of American Indian women (p < 0.05). Women recruited by the Native Sisters were more likely to be currently on hormone replacement therapy and to be menopausal.

CONCLUSIONS

The lay health adviser program was effective in recruiting American Indian women to have screening mammography. Barriers to participation were complex and often involved cultural values and beliefs.

Guidelines for the restoration of Class V lesions

Approximately 18 percent of all permanent teeth have Class V lesions. In addition, the prolonged retention of teeth in an increasingly older population is expected to increase the prevalence of Class V lesions. Much has been written about the merits of various techniques for restoring such lesions, but little information is available comparing and contrasting all the material and procedural options available to the general dentist. Etiologies, indications for treatment, and restorative materials are discussed to provide guidance in planning treatment. A diagnostic decision tree is proposed for this dynamic area of restorative dentistry.

Van der Waals Epitaxial Growth of agr-Alumina Nanocrystals on Mica

Lattice mismatch stresses, which severely restrict heteroepitaxial growth, are greatly minimized when thin alumina films are grown by means of van der Waals forces on inert mica substrates. A 10-nanometer-thick epitaxial film exhibits crystallographic sixfold symmetry, a lattice constant close to that of the basal plane [0001] of alpha-alumina (sapphire), and an aluminum: oxygen atomic ratio of 1:1.51 +/- 0.02 (measured by x-ray photoelectron spectroscopy), again the same as for bulk sapphire. The film is free of steps and grain boundaries over large areas and appears to be an ideal model system for studying adhesion, tribology, and other surface phenomena at atomic scales.

[Infectious endocarditis of the heart valves and valvular prostheses. report of 21 cases]

During 1978, and 1979, the Surgery Division of The Cardiology and Pneumology Hospital of The National Medical Center (Mexican Institute for Social Security), studied and treated surgically twenty one cases -- in twenty patients -- of infectious endocarditis. Nine patients had an active infection in the heart valves and twelve in the prosthesis. The survival rate of the first group was 88.88% and of the second group 58.33%. The causes of death were due to the hemodynamic damage that the valvular or prosthetic dysfunction leads to, when there is a delay in the arrival of the patient to a medical unit of third level. The conventional medical treatment applicable to a reduced number of cases whose characteristics are discussed do not operate when dealing with patients with infected prosthesis or valve infections caused by non-gram positive bacteria. We conclude that this problem demands a better approach, principally surgical, to improve the prognosis of these patients.