Effect of filler content and size on properties of composites

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.

Oroclinal Bending of the Southern Sierra Nevada Batholith

Structural, magmatic, and isotopic features of the southern Sierra Nevada batholith are deflected clockwise with respect to its central and northern parts. Directions of magnetization at three localities in the southern Sierra Nevada are progressively deflected; this is consistent with the hypothesis that the region was tectonically rotated in an orocline. No paleomagnetic deflection was observed northwest of the White Wolf-Kern Canyon fault system. Oroclinal bending ofa block bounded by the San Andreas, Garlock, and White Wolf-Kern Canyon faults may have occurred before about 16 x l0(6) years ago. The deformation may have been a response to shear at the western boundary of the North American plate caused by oblique subduction.

Chicken heart ubiquinol: cytochrome c reductase--isolation by affinity chromatography and resolution of enzyme into subunits

Chicken heart mitochondrial ubiquinol: cytochrome c reductase has been isolated as a monodisperse form by solubilization with Triton X-100 in low ionic strength and subsequent affinity chromatography. The enzyme complex contains less than 0.15 mumol ubiquinone and 12 mumol phospholipid per mumol enzyme. The spectrum of cytochrome b in the reduced exhibited two maximum alpha-absorption bands at 558 nm and 562 nm; a shoulder at 553 nm for c1. The purified enzyme complex consists of at least 9 subunits with apparent molecular weight of 47 K, 44 K, 36 K, 31 K, 25 K, 17 K, 15 K, 12 K and 9 K. The enzyme complex has been dissociated into subdomains of subunits in the presence of increasing concentration of salt and Triton X-100. Three subunits carrying the redox centers (cytochrome b, cytochrome c1 and Fe-S protein) have been further isolated.

Elevated levels of dietary ascorbic acid increase immune responses in channel catfish

Channel catfish fingerlings were fed purified diets containing 0 to 3000 mg/kg of ascorbic acid until external signs of scurvy were seen in the fish fed the ascorbic acid-deficient diet. At this time, resistance to bacterial infection, antibody production, complement activity and phagocytic activity were assessed for fish from the various dietary treatments. Mortality rates of fish experimentally infected with Edwardsiella ictaluri, the bacterium causing enteric septicemia in channel catfish, decreased with increases in dietary ascorbic acid doses, ranging from 100% for fish fed the ascorbic acid-deficient diet to 15% for fish fed 300 mg ascorbic acid per kilogram diet and 0 for fish fed 3000 mg ascorbic acid per kilogram diet. Antibody response to E. ictaluri antigen, hemolysis of sensitized sheep erythrocytes by complement activity and phagocytic engulfment of E. ictaluri by peripheral phagocytes were each impaired in fish fed the diet without supplemental ascorbic acid; intracellular bactericidal activity of the phagocytes was not affected by ascorbic acid deficiency. There were no differences in antibody production, complement activity, or phagocytic activities among fish fed diets containing 30-300 mg ascorbic acid/kg of diet. However, the dose level of 3000 mg ascorbic acid/kg significantly enhanced antibody production and complement activity.

Viral integration near c-myc in 10-20% of mcf 247-induced AKR lymphomas

We induced AKR thymomas by injecting retrovirus MCF 247 that we had tagged with a fragment of phage lambda in its U3 region. About 10-20% of the 26 primary tumors studied showed both rearranged and germline c-myc bands in Southern blots. The rearranged c-myc genes were cloned from two of the tumors and studied by Southern analysis in two others. In all four cases, rearrangement was due to integration of MCF 247 proviruses about 2 kilobases (kb) 5' of the three c-myc exons and in the opposite transcriptional orientation. Thus, viral integrations were clustered within a 1-kb range in the tumors that revealed c-myc rearrangements. Three of the four proviruses appeared to be intact, whereas the fourth had an internal deletion of about 3 kb.

Three human transforming genes are related to the viral ras oncogenes

Three distinct transforming genes present in human tumor cell lines are all related to the viral oncogenes of Harvey and Kirsten murine sarcoma viruses, designated v-H-ras and v-K-ras, respectively. The transforming gene of a bladder carcinoma cell line has been shown to be a human homolog to v-H-ras [Parada, L. F., Tabin, C. J., Shih, C. & Weinberg, R. A. (1982) Nature (London) 297, 474-478; Santos, E., Tronick, S. R., Aaronson, S. A., Pulciani, S. & Barbacid, M. (1982) Nature (London) 298, 343-347]. The transforming gene common to one colon (SK-CO-1) and two lung carcinoma (SK-LU-1 and Calu-1) cell lines is the same human homolog of v-K-ras as is the transforming gene previously identified in a lung carcinoma cell line Lx-1 [Der, C. J., Krontiris, T. G. & Cooper, G. M. (1982) Proc. Natl. Acad. Sci. USA 79, 3637-3640]. The transforming gene of SK-N-SH neuroblastoma cells is weakly homologous to both v-H-ras and v-K-ras. NIH 3T3 cells transformed with the SK-N-SH transforming gene contain increased levels of a protein serologically and structurally related to the protein products of the v-H-ras and v-K-ras genes. Therefore, it represents a third member of the ras gene family, which we have called N-ras. Based on the homology with the v-ras genes, we have established the orientation of transcription and approximate coding regions of the cloned human K-ras and N-ras genes.

Structural studies of P22 phage, precursor particles, and proteins by laser Raman spectroscopy

For the study of the protein--protein and protein--nucleic acid interactions in the assembly of virus particles, laser Raman spectra have been obtained in H2O and D2O solutions and as a function of temperature for the following Salmonella phage P22 components: mature phage particles, isolated mature phage DNA, mature protein shells empty of DNA, precursor protein shells (procapsids), and purified coat, scaffolding and tail-spike proteins. The spectra confirm that the condensed DNA within the phage capsid assumes the B-form secondary structure similar to aqueous DNA and reveal no evidence of specific molecular interactions between subgroups of DNA and protein subunits of the phage capsid. No differences were detected in the highly irregular secondary structure of the major capsid protein in mature capsids, empty capsids (lacking DNA), procapsids, and empty procapsids (lacking scaffolding protein). Features of both primary and secondary structures of the viral scaffolding and tail-spike proteins are also revealed by the spectra. Differences in thermal stability of tyrosyl side-chain interactions were observed between scaffolding protein extracted from the procapsid and within the procapsid. These differences correspond to different hydrogen bonding configurations of p-hydroxyphenyl groups and provide indirect evidence for the participation of the scaffolding proteins in specific macromolecular interactions within the procapsid.

Genetic properties of chromosomally integrated 2 mu plasmid DNA in yeast

We obtained strains of yeast with large segments of 2 mu plasmid DNA integrated at several chromosomal locations by selecting genetically for recombination between a chromosomal sequence carried on a 2 mu-circle-containing hybrid plasmid and a homologous sequence on the chromosome. In all diploids examined, the presence of 2 mu circle sequences causes a marked instability of the chromosome into which the 2 mu DNA is inserted. Although in some cases the loss of genetic markers is due to physical loss of the entire chromosome, in most cases the loss of markers appears to be due to a mitotic homozygotization of markers: the allelic information from the homologous chromosome replaces the information distal to the integrated 2 mu DNA. The instability caused by integrated 2 mu DNA sequences requires the activity of the specialized site-specific recombination system encoded by the 2 mu plasmid. We propose that the presence of integrated 2 mu DNA allows efficient integration of additional copies of the intact 2 mu plasmid by the action of the plasmid-coded special recombination system. Unequal sister-strand exchanges within the inverted repetition would result in the formation of dicentric chromosomes whose breakage during mitosis might begin a cycle analogous to the breakage-fusion-bridge cycle described many years ago in maize.

Radiation from anisotropic Gaussian Schell-model sources

Expressions are derived for the radiant intensity generated by a planar, anisotropic, Gaussian, Schell-model source of any state of coherence. It is found that with an appropriate choice of the source parameters the radiant intensity may be rotationally symmetric about the source plane and may even become identical with the radiant intensity produced by a completely coherent and rotationally symmetric laser source.

Isolation of two endo-beta-N-acetylglucosaminidases from fig latex

Two endo-beta-N-acetylglucosaminidases (mannosyl-glycoprotein 1,4-N-acetamidodeoxy-beta-D-glycohydrolase, EC 3.2.1.96) (type F-I and type F-II) have been isolated from fig latex. At pH 7.0, type F-1 was retained by the DEAE-Sephadex A-50 column, whereas type F-II was not adsorbed by the column. The optimum pH of type F-I was found to be pH 5.9 and type F-II, pH 5.4. Type F-I enzyme hydrolyzes the tri-mannosyl derivatives di-N-acetylglucosaminylasparagine faster than the penta- or hexa-mannosyl compounds. Type F-II hydrolyzes the penta- and hexa-mannosyl derivatives, but not the tri-mannosyl compound.

Membrane-bound and water-soluble cytochrome c1 from Neurospora mitochondria

Cytochrome c1 is a subunit of ubiquinol--cytochrome c reductase (EC 1.10.2.2). In Neurospora crassa wild type 74A grown in the presence of chloramphenicol, the subunit is inserted only into the bilayer of the mitochondrial inner membranes without associating with other proteins. From these modified membranes a monodisperse (cytochrome c1)-Triton complex was isolated by subjecting the Triton-solubilized membranes to affinity chromatography on immobilized cytochrome c. A water-soluble pentamer of cytochrome c1 was prepared from the (cytochrome c1)-Triton complex by removing the detergent. By limited proteolytic digestion of the cytochrome c1-Triton complex with chymotrypsin, a water-soluble monomeric cytochrome c1 was prepared which has a molecular weight of only 24 000 as compared to 31 000 of the membrane-bound cytochrome c1. The 24 000-Mr cytochrome c1 and the 31 000-Mr cytochrome c1 have same light absorption spectra and cytochrome-c-binding properties. These results are used to propose the following model. Cytochrome c1 consists of a large hydrophilic part and a small hydrophobic part. The hydrophilic part extends from the mitochondrial inner membrane into the intermembrane space. This part carries the heme and interacts with cytochrome c. The hydrophobic part anchors the cytochrome c1 to the bilayer.

Comparison of radioimmunoassay and enzyme-linked immunosorbent assay for determining aflatoxin M1 in milk

Using a highly specific antibody against aflatoxin M1, a radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA) were developed for the quantitation of M1 in milk. RIA was sensitive in the range of 5-50 ng per assay but was subject to interference by whole milk. Extraction and cleanup were therefore necessary for the detection of M1 in milk at 0.5 ng/mL. An ELISA procedure was developed by using an aflatoxin M1-carboxymethyl-horseradish peroxidase conjugate as the ligand. Competitive assays revealed that this system was relatively more sensitive for M1 than for B1, and had a much lower degree of cross-reactivity for aflatoxins B2, G1, G2, B2a, and aflatoxicol. As low as 0.25 ng M1/mL in artificially contaminated milk (raw, whole, skim) could be detected by ELISA in 3 h without extraction or cleanup. Because of its simplicity, sensitivity, and specificity, ELISA is the preferred method for monitoring aflatoxin M1 in milk.