Cutting efficiency of air-turbine burs on cast titanium and dental casting alloys.

OBJECTIVE: The purpose of this study was to investigate the cutting efficiency of air-turbine burs on cast free-machining titanium alloy (DT2F) and to compare the results with those for cast commercially pure (CP) Ti, Ti-6Al-4V alloy, and dental casting alloys. METHODS: The cast metal (DT2F, CP Ti, Ti-6Al-4V, Type IV gold alloy and Co-Cr alloy) specimens were cut with air-turbine burs (carbide burs and diamond points) at air pressures of 138 or 207 kPa and a cutting force of 0.784 N. The cutting efficiency of each bur was evaluated as volume loss calculated from the weight loss cut for 5 s and the density of each metal. The bulk microhardness was measured to correlate the machinability and the hardness of each metal. RESULTS: The amounts of DT2F cut with the carbide burs were significantly (p < 0.05) greater than for the other titanium specimens at either 138 or 207 kPa. The diamond points exhibited similar machining efficiency among all metals except for Type IV gold alloy. The increase in the volume loss of Co-Cr alloy (Vitallium) cut with the diamond points showed a negative value (-29%) with an increase in air pressure from 138 to 207 kPa. There was a negative correlation between the amounts of metal removed (volume loss) and the hardness (r2 = 0.689) when the carbide burs were used. SIGNIFICANCE: The results of this study indicated that a free-machining titanium alloy (DT2F) exhibited better machinability compared to CP Ti and Ti-6Al-4V alloy when using carbide fissure burs. When machining cast CP Ti and its alloys, carbide fissure burs possessed a greater machining efficiency than the diamond points and are recommended for titanium dental prostheses.

The machinability of cast titanium and Ti-6Al-4V.

This study investigated the machinability (ease of metal removal) of commercially pure (CP) titanium and Ti-6Al-4V alloy. Both CP Ti and Ti-6Al-4V were cast into magnesia molds. Two types of specimens (with alpha-case and without alpha-case) were made for CP Ti and Ti-6Al-4V. Machinability (n = 5) was evaluated as volume loss (mm3) by cutting/grinding the 3.0 mm surface using fissure burs and silicon carbide (SiC) under two machining conditions: (1) two machining forces (100 or 300 gf) at two rotational speeds (15000 or 30000 rpm) for 1 min, and (2) constant machining force of 100 gf and rotational speed of 15000 rpm for 1, 2, 5, 10, and 30 min. As controls, conventionally cast Co-Cr and Type IV gold alloys were evaluated in the same manner as the titanium. When fissure burs were used, there was a significant difference in the machinability between CP titanium with alpha-case and without alpha-case. On the other hand, there was no appreciable difference in the amount of metal removed for each tested metal when using the SiC points.

Fate of Escherichia coli O157:H7 as affected by pH or sodium chloride and in fermented, dry sausage.

The influence of pH adjusted with lactic acid or HCl or sodium chloride concentration on survival or growth of Escherichia coli O157:H7 in Trypticase soy broth (TSB) was determined. Studies also determined the fate of E. coli O157:H7 during the production and storage of fermented, dry sausage. The organism grew in TSB containing less than or equal to 6.5% NaCl or at a pH of 4.5 to 9.0, adjusted with HCl. When TSB was acidified with lactic acid, the organism grew at pH 4.6 but not at pH 4.5. A commercial sausage batter inoculated with 4.8 x 10(4) E. coli O157:H7 per g was fermented to pH 4.8 and dried until the moisture/protein ratio was less than or equal to 1.9:1. The sausage chubs were then vacuum packaged and stored at 4 degrees C for 2 months. The organism survived but did not grow during fermentation, drying, or subsequent storage at 4 degrees C and decreased by about 2 log10 CFU/g by the end of storage. These studies reveal the importance of using beef containing low populations or no E. coli O157:H7 in sausage batter, because when initially present at 10(4) CFU/g, this organism can survive fermentation, drying, and storage of fermented sausage regardless of whether an added starter culture was used.

Faults in the mojave desert, california, as revealed on enhanced landsat images.

Previously unknown strike-slip and normal faults in the central and eastern Mojave Desert have been revealed on Landsat Thematic Mapper images enhanced by four-component processing. This method provides color images on which lithologies are discriminated by their contrasting absorption and reflection, primarily at infrared wavelengths and particularly with regard to their ferric iron, ferrous iron, and hydroxyl contents, while retaining landform depiction. These discriminants represent a new type of geophysical display for geologic mapping in regions of well-exposed bedrock. Faults are revealed on the images by abrupt spectral and textural contrasts that coincide with aligned topographic features. The newly discovered faults form part of an extensive regional network of right shear that connects faults in the Death Valley region with the San Andreas fault system. They support a heterogeneous strain model for late Cenozoic tectonic evolution of the region. Regional structural relations indicate a westward migration of the locus of strain through time. Some of the newly identified faults bound blocks that have experienced contrasting rotational histories since early Miocene time.

Activities and incision patterns of ABC excinuclease on modified DNA containing single-base mismatches and extrahelical bases.

ABC excision nuclease of Escherichia coli is a DNA repair enzyme that recognizes major helical distortions caused by bulky base adducts and incises on both sides of the adduct, thus removing the modified nucleotides in the form of a 12-13-base long oligomer. We tested the enzyme with substrates that contained unusual helical structures caused by single-base mismatches or one, three, or four extrahelical bases (loops). We find that the enzyme does not cut DNAs containing helical perturbations caused by these structures. However, when the mismatched or extrahelical bases are modified with 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide, a reagent specific for unpaired G and T residues, the enzyme incises at the modified nucleotides in the regular manner. In addition, we find that when mismatches and loops are located near pyrimidine dimers and (6-4) photoproducts they do not inhibit incision at the photoproducts by the excinuclease but sometimes affect the incision pattern. Our results indicate that ABC excinuclease may be a useful enzymatic reagent to probe the structural changes caused by mismatches and deletions in DNA and provide additional information on the requirements for incision by this repair enzyme.

Genomic analysis I: inheritance units and genetic selection in the rapid discovery of locus linked DNA markers.

We propose, and test using a Monte-Carlo analysis (a computer-based numerical analysis using a random number generator), a novel and efficient method to obtain sets of DNA markers linked to any inherited genetic locus. The method consists of a targeted search that is based on the common inheritance among members of an outbred pedigree, of discrete chromosome lengths, which we call inheritance units, to obtain DNA markers linked to the locus. In cases where two individuals inherit the same trait through two different lines of descent from a common ancestor, the set of inheritance units in each of the two genomes includes an inheritance unit that is identical in both individuals for a substantial distance on both sides of the DNA sequence which confers the trait. The power of the technique derives from the genetic selection that reduces the size and number of the inheritance units as the generational distance between the two individuals being compared increases.

Genomic analysis II: isolation of high molecular weight heteroduplex DNA following differential methylase protection and Formamide-PERT hybridization.

Understanding the nature of DNA sequence differences among individuals is important to the understanding of fundamental questions in biology. To analyze such differences in complex genomes new approaches must be developed. We report two new techniques which aid in this effort. First, we have developed a modification of the Phenol Emulsion Reassociation Technique (PERT) that allows hybridization of long (20 kb and longer) single copy heteroduplex DNA fragments from human genomic DNAs. Secondly, by using a differential methylase protection technique we have shown that double methylase resistant heteroduplex DNA molecules can be size fractionated away from reannealed single methylase resistant homoduplex DNA molecules. These methods will be useful in obtaining DNA from chromosomal subregions linked to the inheritance of a specific trait or condition as described in the preceding paper and could also be used to create a map of the chromosomal subregion which includes the gene for the trait.

Detection of single base-pair mismatches in DNA by chemical modification followed by electrophoresis in 15% polyacrylamide gel.

We have developed a method for distinguishing fragments of DNA that contain single-base mismatches from their perfectly paired homologues. Single-stranded regions within a duplex fragment are accessible to 1-cyclohexyl-3-(2-[4-(4-methyl)morpholinyl]ethyl)carbodiimide, which reacts with unpaired guanidylate and thymidylate residues in DNA. Intact linear duplex DNA molecules do not react with carbodiimide, whereas DNA molecules containing single-base mismatches react quantitatively. After carbodiimide reaction, the DNA molecules are electrophoresed in high-percentage polyacrylamide gels so that modified and unmodified fragments can be resolved. Application of this technique should make it possible to locate and purify DNA fragments that exhibit sequence differences from those that do not; these might be used to signal phenotypic variation as well as to diagnose inherited disease.

Detection of sickle-cell mutation by electrophoresis of partial RNA:DNA hybrids following solution hybridization.

We have developed a method in which partially single-stranded (ss) DNA molecules containing a defined region of duplex RNA:DNA are electrophoretically separated in agarose gels. The partial hybrids are formed by solution hybridization with a uniform length RNA probe complementary to part of the DNA sequence of interest. Following hybridization, the RNA/DNA mixture is fractionated by agarose gel electrophoresis at high temperature to minimize intrastrand base pairing which causes mobility heterogeneity. Not requiring the steps of DNA transfer from the gel to a solid support and subsequent probing, pre-electrophoretic hybridization allows the direct identification of single-copy fragments. Conditions for the detection of single-copy genes in human DNA digested with specific restriction endonucleases were developed and applied to the diagnosis of sickle-cell disease. This method should be applicable for the analysis of DNAs of high complexity where the presence of DNA polymorphisms and interspersed repeated DNA sequences often make impossible the creation of complete RNA:DNA hybrids.

Shuttle imaging radar experiment.

The shuttle imaging radar (SIR-A) acquired images of a variety of the earth's geologic areas covering about 10 million square kilometers. Structural and geomorphic features such as faults, folds, outcrops, and dunes are clearly visible in both tropical and arid regions. The combination of SIR-A and Seasat images provides additional information about the surface physical properties: topography and roughness. Ocean features were also observed, including large internal waves in the Andaman Sea.

Transcription pattern of in vivo-labeled late simian virus 40 RNA: evidence that 16S and 19S mRNA's are derived from distinct precursor RNA populations.

The biosynthesis of the two major simian virus 40 mRNA molecules (19S mRNA and 16S mRNA) made at late times in the infective cycle was reinvestigated. By using a modified S1 nuclease technique, we were able to differentiate between pulse-labeled RNA precursor and the spliced mRNA. During a 5-min pulse-labeling with [3H]uridine in vivo, only precursor RNA molecules were detected. Experimental results with polyadenylic acid-selected 5-min pulse-labeled RNA are consistent with the notion that simian virus 40 late RNA can be polyadenylated before final splicing. Finally, 19S mRNA was spliced much more rapidly and appeared more quickly in the cytoplasm than 16S mRNA. Nevertheless, approximately one-half the precursor molecules were destined to become 16S mRNA. Thus, for at least these two viral mRNA's derived from a common transcription unit, the rate of splicing and the rate of nuclear exist are not major determinants of relative mRNA abundance.

Enzymatic analysis of 5-methylcytosine content in eukaryotic DNA. Study of intracellular Simian Virus 40 DNA.

An enzymatic method is described for the analysis of the content of 5-methylcytosine in the DNA of eukaryotic cells. The conventional acid hydrolysis procedure was found to result in variable deamination of 5-methylcytosine into thymine, making the exact quantitation difficult. We applied the enzymatic method for the analysis of a simple eukaryotic viral genome. Viral and cell DNA in Simian Virus 40-infected monkey kidney cells was labeled with [methyl-3H]methionine in vivo and their 5-methylcytosine content was analyzed. The content of 5-methylcytosine per thymine in the total intracellular viral DNA was found to be less than 10(-4) of the host DNA. The implication of this result with regard to eukaryotic gene expression is discussed.

Transcription pattern of in vivo-labeled late simian virus 40 RNA: equimolar transcription beyond the mRNA 3' terminus.

We have examined the pattern of RNA transcription on the L (late) DNA strand late in the simian virus 40 virus infectious cycle by separating pulse-labeled RNA chains according to size and hybridizing to an ordered series of DNA fragments obtained by restriction enzyme digestion. From this analysis, the 5' end of the nascent transcript occurs a short distance counterclockwise from 0.735. Transcription proceeds in a clockwise direction. There is equimolar transcription for at least 1,000 nucleotides beyond the 3' end of the mRNA (0.175). The 3' terminus for the largest molecules is in 0.43--0.655. Molecules which represent more than one circuit of the genome are not more than 1% of the total population of nascent molecules. Implications of these findings for models of the biogenesis of mRNA are discussed.