Density functional theory for the crystallization of two-dimensional dipolar colloidal alloys.

Two-dimensional mixtures of dipolar colloidal particles with different dipole moments exhibit extremely rich self-assembly behaviour and are relevant to a wide range of experimental systems, including charged and super-paramagnetic colloids at liquid interfaces. However, there is a gap in our understanding of the crystallization of these systems because existing theories such as integral equation theory and lattice sum methods can only be used to study the high temperature fluid phase and the zero-temperature crystal phase, respectively. In this paper we bridge this gap by developing a density functional theory (DFT), valid at intermediate temperatures, in order to study the crystallization of one and two-component dipolar colloidal monolayers. The theory employs a series expansion of the excess Helmholtz free energy functional, truncated at second order in the density, and taking as input highly accurate bulk fluid direct correlation functions from simulation. Although truncating the free energy at second order means that we cannot determine the freezing point accurately, our approach allows us to calculate ab initio both the density profiles of the different species and the symmetry of the final crystal structures. Our DFT predicts hexagonal crystal structures for one-component systems, and a variety of superlattice structures for two-component systems, including those with hexagonal and square symmetry, in excellent agreement with known results for these systems. The theory also provides new insights into the structure of two-component systems in the intermediate temperature regime where the small particles remain molten but the large particles are frozen on a regular lattice.

Design and fabrication technique for metal palates in maxillary complete dentures.

Polymethyl methacrylate exhibits excellent physical properties. Unfortunately, complete dentures fabricated from this material may still fracture. Maxillary complete dentures opposing natural dentition may have a tendency to develop recurrent midline fractures due to multiple reasons. A potential method of preventing this fracture is metal reinforcement of the palatal portion of the prosthesis. A technique will be presented describing a sequence that incorporates predictable design, fabrication and finishing of a metal palate for a maxillary complete denture.

Comparative effect of temperature on the oxidative metabolism of whole and disrupted cells of a psychrophilic and a mesophilic species of Bacillus.

We investigated the influence of temperature, in the range of 45 to 5 C, on the rate of oxidation of glucose and citrate by intact cells and cell-free extracts of psychrophilic Bacillus psychrophilus and mesophilic B. thuringiensis. Both glucose and endogenous oxidation by whole and disrupted cells of the psychrophile decreased more slowly with decrease in temperature than did glucose and endogenous oxidation by whole and disrupted cells of the mesophile. Similar results were obtained for the oxidation of citrate by cell-free extracts. Since substrate permeability is not involved in the oxidative metabolism of the cell-free extracts, we concluded that the internal enzymes of the psychrophile differ from those of the mesophile.

Taxonomy of psychrophilic strains of Bacillus.

The morphological and physiological characteristics of 20 isolates of psychrophilic Bacillus were compared with 29 strains representing nine species of mesophilic Bacillus and 2 strains of Sporosarcina ureae to determine the taxonomic position of the psychrophiles. The psychrophiles formed four distinct groups which were sufficiently different from the mesophiles to warrant their designation as new species of Bacillus. The names B. psychrosaccharolyticus, B. insolitus, B. globisporus, and B. psychrophilus are proposed for the new species.

Heat-labile enzymes in a psychrophilic bacterium.

The oxidative and fermentative activities of a psychrophilic bacterium (strain 82), whose maximal growth temperature is 35 C, were completely destroyed by exposure of the cells to 46 C for about 1 hr, whereas those of mesophilic Escherichia coli were unaffected. Similar results were obtained with cell-free extracts. In attempts to determine some of the specific enzymes inactivated in strain 82 by exposure to 46 C, it was found that reduced nicotinamide adenine dinucleotide oxidase was completely inactivated at 46 C in 2 hr. Also, cytochrome c reductase was completely destroyed at 46 C in 1 hr and was 70% destroyed at 40 C in 2 hr. The heat lability of the latter may determine the maximal growth temperature of the organism. In addition, the results indicated that the enzymes of strain 82 involved in the clastic split of pyruvate to formate and acetate are inactivated by exposure to 46 C and that the lactic and glycerol dehydrogenases are more heat-labile than those in E. coli. Succinic, nicotinamide adenine dinucleotide phosphate-alcohol, and glucose-6-phosphate dehydrogenases, however, in both strain 82 and E. coli, were essentially unaffected by exposure to 46 C for 2 hr.

Isolation of psychrophilic species of Bacillus.

Larkin, J. M. (Washington State University, Pullman), and J. L. Stokes. Isolation of psychrophilic species of Bacillus. J. Bacteriol. 91:1667-1671. 1966.-Ninety psychrophilic isolates of Bacillus were obtained from soil, mud, and water by selective enrichment at 0 C. They grew well at 0 C, optimally at 20 to 25 C, and failed to grow at 30 or 35 C. Their minimal and maximal growth temperatures were lower than those for mesophilic species of Bacillus by 10 C or more. Growth of psychrophilic isolates also occurred at -2 and -4.5 C, and both spore formation and spore germination occurred at 0 C.

Managanese oxidation by Sphaerotilus discophorus.

Johnson, A. H. (Washington State University, Pullman), and J. L. Stokes. Manganese oxidation by Sphaerotilus discophorus. J. Bacteriol. 91:1543-1547. 1966.-Cell suspensions of Sphaerotilus discophorus in 0.02 m potassium phosphate buffer (pH 7.2) readily oxidized MnSO(4) to dark-brown manganic oxide. The latter appeared to be MnO(2), since its color was the same as MnO(2) and, like the latter, it was readily soluble in HCl with the evolution of chlorine. The amount of O(2) consumed in the oxidation of Mn(++) was 63% or more of theoretical. The ability of the cells to oxidize Mn(++) was destroyed by heating the cells at 93 C for 5 min. Only cell suspensions prepared from cultures of S. discophorus grown with MnSO(4) were able to oxidize Mn(++). It was concluded that the oxidation of manganous ions by S. discophorus is catalyzed by an inducible enzyme(s).

Quantitative ecology of psychrophilic microorganisms.

To obtain information on the importance of psychrophiles in nature, 95 samples of soil, water, mud, and various foods were quantitatively assayed for their content of psychrophilic bacteria and fungi and also for mesophilic and thermophilic bacteria and fungi. Thousands to millions of psychrophilic bacteria were present per gram of soil and represented 0.5 to 86% of the bacterial population. Also, about 25% of the fungi in uncultivated soil were psychrophilic. In stream and river water, psychrophilic bacteria constituted 16 to 47% of the bacterial population; in lake water, 41 to 76%; and in lake mud, 11 to 33%. Large numbers of psychrophilic bacteria were present in dairy products, meats, and other foods, and accounted for 35 to 93% of the bacterial population of meats. In contrast, thermophilic bacteria usually comprised 1% or less of the bacterial population in all of the materials examined. The data indicate that psychrophiles are both ubiquitous and numerous in nature, and probably play important roles in the cycles of matter.