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ABSTRACT: The as-received direct-chill-cast (DC) and continuous-cast (CC) AA5052 and AA5182 hot bands were preheated at 454 °C for 4
hours, followed by cold rolling to an 80 pct reduction in thickness. The texture evolution of these cold-rolled samples during
isothermal annealing was investigated by X-ray diffraction. The variation in texture volume fractions with annealing time
was quantitatively analyzed by using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The differences in recrystallization
textures between the AA5052 and AA5182 alloys and between the DC and CC alloys were compared. It was found that the AA5052
alloy possessed a stronger cube recrystallization texture than the AA5182 alloy for the DC and CC materials. The recrystallization
textures of the AA5182 alloy were affected strongly by the annealing temperature. As the annealing temperature increased,
the cube recrystallization texture strengthened, whereas the R texture weakened. The annealing temperature had little influence
on the recrystallization textures of the AA5052 alloy. The DC AA5052 and 5182 alloys also exhibited stronger cube recrystallization
textures than the corresponding CC alloys. For the DC and CC AA5052 alloys, the n value in the JMAK-type equation increased with an increase in the annealing temperature, while the n values varied only slightly with the annealing temperature for the DC and CC AA5182 alloys.
Metallurgical and Materials Transactions A 05/2012; 35(11):3613-3629. · 1.54 Impact Factor
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ABSTRACT: The evolution of recrystallization and recrystallization texture during annealing after cold rolling of a continuous-cast
(CC) AA 3015 aluminum alloy with and without pretreatment was investigated in detail. It was found that the preheat treatment
prior to cold rolling significantly affected the recrystallization kinetics, the shape and size of recrystallized grains,
and the resulting texture of the CC AA 3015 aluminum alloy. In the case of the alloy without pretreatment, annealing at low
temperatures resulted in coarse elongated recrystallized grains and a very strong P texture. As the annealing temperature
increased, the size of the recrystallized grains dramatically decreased, the recrystallized grains became equiaxed, and the
strength of the P texture decreased. The transition behavior could be attributed to the effect of Zener-particle pinning caused
by concurrent precipitation. In contrast, the recrystallization texture of the CC AA 3015 aluminum alloy with pretreatment
was characterized by a major cube component and a minor R component, and the annealing temperature did not affect the recrystallization
texture. Moreover, concurrent precipitation retarded markedly the recrystallization of the CC AA 3015 aluminum alloy, decreased
the Johnson-Mehl-Avrami-Kolmogorov (JMAK) exponent from 2.0 to 0.5, and increased the activation energy for recrystallization
from 225 to 539 kJ/mol.
Metallurgical and Materials Transactions A 04/2012; 36(10):2829-2848. · 1.54 Impact Factor
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ABSTRACT: Forty Yersinia pestis isolates from endemic foci of plague in the Republic of Georgia, and six Y. pestis isolates from neighbouring former Soviet Union countries, were analysed for their biochemical and phenotypic properties, and their genetic relatedness was compared with Y. pestis strains KIM and CO92 by pulsed-field gel electrophoresis (PFGE). In addition, 11 Y. pestis isolates from the USA, together with published nucleotide sequences from Y. pestis strains KIM, CO92 and 91001, were compared with the 46 isolates in the present collection using multilocus sequence typing (MLST), based on sequence data for the 16S rRNA, hsp60, glnA, gyrB, recA, manB, thrA and tmk loci. Four virulence gene loci (caf1, lcrV, psaA and pla) were also sequenced and analysed. Two sequence types (ST1 and ST2), which differed by a single nucleotide, were identified by MLST. With the exception of a single isolate (771G), all of the Georgian Y. pestis isolates belonged to ST2. PFGE also grouped the Georgian Y. pestis isolates separately from the non-Georgian isolates. Overall, PFGE discriminated the Y. pestis isolates more effectively than MLST. The sequences of three of the four virulence genes (lcrV, psaA and pla) were identical in all Georgian and non-Georgian isolates, but the caf1 locus was represented by two allele types, with caf1 NT1 being associated with the non-Georgian isolates and caf1 NT2 being associated with the Georgian isolates. These results suggest that Georgian Y. pestis isolates are of clonal origin.
Clinical Microbiology and Infection 06/2008; 14(5):429-36. · 4.54 Impact Factor
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ABSTRACT: Concurrent precipitation has a profound influence on the recrystallization behavior of aluminum alloys. This paper will highlight
its effects on recrystallization kinetics and texture and its subsequent effects on mechanical anisotropy (earing) and general
mechanical property behavior of aluminum alloys.
JOM: the journal of the Minerals, Metals & Materials Society 10/2005; 57(11):44-47. · 1.42 Impact Factor
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ABSTRACT: As-received commercial direct chill cast (DC) and continous cast (CC) AA5052 hot bands were isothermally annealed at different
temperatures. The variations of electrical resistivity, hardness, microstructure, and texture of these hot bands during annealing
were examined. Texture was investigated by X-ray diffraction. The variation in texture volume fractions with annealing time
was quantitatively analyzed by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The orientation maps of the partially and
fully recrystallized samples were characterized by electron backscattered diffraction (EBSD). It was found that electrical
resistivity of the CC AA5052 hot band was higher than that of the DC AA5052 hot band. The electrical resistivity of CC AA5052
decreased more significantly than that of DC AA5052 during isothermal annealing. The DC AA5052 hot band was more easily recrystallized
than CC AA5052 hot band during annealing. After complete recrystallization, DC AA5052 hot band possessed a stronger cube texture
than the CC AA5052 hot band. The texture evolutions of DC and CC AA5052 can be expressed quantitatively by the JMAK equation
after the volume fractions of the texture components are calculated by an improved integration method. Annealing temperature
had an influence on the n values in the JMAK-type equations. The n values are small at low annealing temperatures.
Metallurgical and Materials Transactions A 08/2005; 36(9):2505-2515. · 1.54 Impact Factor
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ABSTRACT: Through-thickness texture variation in cold-rolled AA 5182 aluminum alloy with an initial {001}〈110〉 texture was investigated Through-thickness texture variation in cold-rolled AA 5182 aluminum alloy with an initial {001}〈110〉 texture was investigated
by X-ray diffraction. A detailed quantitative analysis of texture volume fractions in several layers was performed. The effect by X-ray diffraction. A detailed quantitative analysis of texture volume fractions in several layers was performed. The effect
of initial through-thickness texture gradient and roll-gap geometry on the texture evolution during multipass rolling was of initial through-thickness texture gradient and roll-gap geometry on the texture evolution during multipass rolling was
determined. A pronounced texture variation through the thickness was found in the initial material. The shear deformation determined. A pronounced texture variation through the thickness was found in the initial material. The shear deformation
produced by the friction between the roll and the sheet contact surface may be neglected in the present experiment with oil produced by the friction between the roll and the sheet contact surface may be neglected in the present experiment with oil
as a lubricant. At low strains with the l/h ratio from 0.9 to 2.0, the shear deformation caused by the roll-gap geometry slightly decreased the lattice rotation from as a lubricant. At low strains with the l/h ratio from 0.9 to 2.0, the shear deformation caused by the roll-gap geometry slightly decreased the lattice rotation from
the {001}〈110〉 orientation to the C orientation at the intermediate layer, while the roll-gap geometry did not produce a shear the {001}〈110〉 orientation to the C orientation at the intermediate layer, while the roll-gap geometry did not produce a shear
strain at large strains with higher values of the l/h ratio. The strong initial r-cube texture at the center layer stimulated the transformation from the r-cube orientation to strain at large strains with higher values of the l/h ratio. The strong initial r-cube texture at the center layer stimulated the transformation from the r-cube orientation to
the C orientation and the formation of the β fiber during rolling. the C orientation and the formation of the β fiber during rolling.
Metallurgical and Materials Transactions A 04/2005; 36(5):1329-1338. · 1.54 Impact Factor
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ABSTRACT: The texture evolution of continuous-cast AA 5xxx-series aluminum alloys during cold rolling was investigated by X-ray diffraction. Texture volume fractions were calculated
by an improved integration method. The results show that the relationship between the texture volume fractions and true strain
can be quantified by mathematical formulae. The effect of alloy composition as well as initial microstructure and texture
on rolling-texture evolution can be evaluated by the k
i and n
i values in the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The k
i value reflects the rate of formation or disappearance of the texture components. The high-Fe AA 5754 aluminum alloy exhibits
the lowest formation rate of the β fiber among the AA 5005, 5052, 5754, 5182, and high-Fe 5754 aluminum alloys.
Metallurgical and Materials Transactions A 12/2003; 35(1):265-277. · 1.54 Impact Factor
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ABSTRACT: Hot bands of direct chill cast (DC) and continuous cast (CC) aluminium alloy 5052 were cold rolled to different reductions after being annealed at 454 ° C for 4 h. The texture evolution during cold rolling was investigated for both DC and CC AA 5052 by determining the orientation distribution functions of the cold rolled specimens via X-ray diffraction. Texture evolution during cold rolling was predicted by empirical formulas of the variation of the texture components with true strain. The results show that the processing method (DC versus CC) has an effect on the texture of annealed hot bands and the texture evolution during subsequent cold rolling.
Materials Science and Technology 09/2003; 19(10):1379-1385. · 0.77 Impact Factor
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ABSTRACT: Virulence of Vibrio vulnificus correlates with changes in colony morphology that are indicative of a reversible phase variation for expression of capsular polysaccharide (CPS). Encapsulated variants are virulent with opaque colonies, whereas phase variants with reduced CPS expression are attenuated and are translucent. Using TnphoA mutagenesis, we identified a V. vulnificus CPS locus, which included an upstream ops element, a wza gene (wza(Vv)), and several open reading frames with homology to CPS biosynthetic genes. This genetic organization is characteristic of group 1 CPS operons. The wza gene product is required for transport of CPS to the cell surface in Escherichia coli. Polar transposon mutations in wza(Vv) eliminated expression of downstream biosynthetic genes, confirming operon structure. On the other hand, nonpolar inactivation of wza(Vv) was specific for CPS transport, did not alter CPS biosynthesis, and could be complemented in trans. Southern analysis of CPS phase variants revealed deletions or rearrangements at this locus. A survey of environmental isolates indicated a correlation between deletions in wza(Vv) and loss of virulent phenotype, suggesting a genetic mechanism for CPS phase variation. Full virulence in mice required surface expression of CPS and supported the essential role of capsule in the pathogenesis of V. vulnificus.
Infection and Immunity 12/2001; 69(11):6893-901. · 4.16 Impact Factor
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ABSTRACT: An outbreak of illness with flulike symptoms among state workers responding to a Pfiesteria bloom that resulted in fish death and distress on the Chicamacomico River on Maryland's Eastern Shore was investigated. Using case-control methodology, seven workers present at the Chicamacomico were compared to seven occupationally matched controls not present. Participants completed questionnaires assessing their exposures to water and their symptom histories and were assessed with a standard neuropsychological test battery. Three months later, the same questionnaires and neuropsychological tests were repeated. Three of the seven exposed workers cited minimal direct contact with water and four cited none. During the event, four developed burning eyes or nares and six developed a headache or sore throat. Six developed crampy abdominal pain, nausea, or diarrhea within 4 h of their exposure. In contrast, the only aforementioned symptom reported by controls was headache in two individuals. Acute and follow-up neuropsychological tests showed no consistent pattern of deficiency among the exposed. In conclusion, a flulike clinical illness was observed following exposure to a Pfiesteria-related fish kill, possibly as a result of inhalation of toxic aerosols.
Journal of Toxicology and Environmental Health Part A 09/2001; 63(8):553-64. · 1.83 Impact Factor
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Antimicrobial Agents and Chemotherapy 04/2001; 45(3):649-59. · 4.84 Impact Factor
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ABSTRACT: We sequenced a 705-bp fragment of the recA gene from 113 Vibrio cholerae strains and closely related species. One hundred eighty-seven nucleotides were phylogenetically informative, 55 were phylogenetically uninformative, and 463 were invariant. Not unexpectedly, Vibrio parahaemolyticus and Vibrio vulnificus strains formed out-groups; we also identified isolates which resembled V. cholerae biochemically but which did not cluster with V. cholerae. In many instances, V. cholerae serogroup designations did not correlate with phylogeny, as reflected by recA sequence divergence. This observation is consistent with the idea that there is horizontal transfer of O-antigen biosynthesis genes among V. cholerae strains.
Infection and Immunity 01/2001; 68(12):7180-5. · 4.16 Impact Factor
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ABSTRACT: Vibrio cholerae can switch from a smooth to a wrinkled or rugose colony phenotype characterized by the secretion of a polysaccharide that enables the bacteria to survive harsh environmental conditions. In order to understand the genetic basis of rugosity, we isolated TnphoA-induced stable, smooth mutants of two O1 El Tor rugose strains and mapped the insertion sites in several of the mutants using a modified Y-adapter PCR technique. One of the TnphoA insertions was mapped to the first gene of the vps region that was previously shown to encode the rugose polysaccharide biosynthesis cluster. Three insertions were mapped to a previously unknown hlyA-like gene, also in the vps region. Five other insertions were found in loci unlinked to the vps region: (i) in the epsD gene (encodes the "secretin" of the extracellular protein secretion apparatus), (ii) in a hydG-like gene (encodes a sigma(54)-dependent transcriptional activator similar to HydG involved in labile hydrogenase production in Escherichia coli, (iii) in a gene encoding malic acid transport protein upstream of a gene similar to yeiE of E. coli (encodes a protein with similarities to LysR-type transcriptional activators), (iv) in dxr (encodes 1-deoxy-D-xylulose 5-phosphate reductoisomerase), and (v) in the intergenic region of lpd and odp (encode enzymes involved in the pyruvate dehydrogenase complex formation). These data suggest the involvement of a complex regulatory network in rugose polysaccharide production and highlight the general utility of the Y-adapter PCR technique described here for rapid mapping of transposon insertion sites.
Infection and Immunity 01/2001; 68(12):6857-64. · 4.16 Impact Factor
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ABSTRACT: A rapid protocol for subtyping vancomycin-resistant enterococci by pulsed-field gel electrophoresis is reported. The procedure is simple and potentially cost-effective and allows reproducible subtyping of the strains in approximately 1 day.
Journal of Clinical Microbiology 12/2000; 38(11):4242-5. · 4.15 Impact Factor
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ABSTRACT: Vibrio cholerae is the causal organism of the diarrheal disease cholera. The rugose variant of V. cholerae is associated with the secretion of an exopolysaccharide. The rugose polysaccharide has been shown to confer increased resistance to a variety of agents, such as chlorine, bioacids, and oxidative and osmotic stresses. It also promotes biofilm formation, thereby increasing the survival of the bacteria in the aquatic environments. Here we show that the extracellular protein secretion system (gene designated eps) is involved directly or indirectly in the production of rugose polysaccharide. A TnphoA insertion in epsD gene of the eps operon abolished the production of rugose polysaccharide, reduced the secretion of cholera toxin and hemolysin, and resulted in a nonmotile phenotype. We have constructed defined mutations of the epsD and epsE genes that affected these phenotypes and complemented these defects by plasmid clones of the respective wild-type genes. These results suggest a major role for the eps system in pathogenesis and environmental survival of V. cholerae.
Infection and Immunity 05/2000; 68(4):1967-74. · 4.16 Impact Factor
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ABSTRACT: The DNA sequence of the O-antigen biosynthesis cluster (wbf) of a recently emergent pathogen, Vibrio cholerae serogroup O139, has been determined. Here we report the sequence of the genes downstream of the O139 wbfX gene and analysis of the genes flanking the wbf gene cluster in other serogroups. The gene downstream of wbfX, designated rjg (right junction gene), is predicted to be not required for O-antigen biosynthesis but appears to be a hot spot for DNA rearrangements. Several variants of the rjg gene (three different insertions and a deletion) have been found in other serogroups. DNA dot blot analysis of 106 V. cholerae strains showed the presence of the left and right junction genes, gmhD and rjg, respectively, in all strains. Further, these genes mapped to a single I-CeuI fragment in all 21 strains analyzed by pulsed-field gel electrophoresis, indicating a close linkage. The insertion sequence element IS1358, found in both O1 and O139 wb* regions, is present in 61% of the strains tested; interestingly, where present, it is predominantly linked to the wb* region. These results indicated a cassette-like organization of the wb* region, with the conserved genes (gmhD and rjg) flanking the divergent, serogroup-specific wb* genes and IS1358. A similar organization of the wb* region in other serogroups raises the possibility of the emergence of new pathogens by homologous recombination via the junction genes.
Infection and Immunity 11/1999; 67(10):5033-40. · 4.16 Impact Factor
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ABSTRACT: Sixty-six Corynebacterium diphtheriae strains (62 of the gravis biotype and 4 of the mitis biotype) isolated during the Georgian diphtheria epidemic of 1993 to 1998 and 13 non-Georgian C. diphtheriae strains (10 Russian and 3 reference isolates) were characterized by (i) biotyping, (ii) toxigenicity testing with the Elek assay and PCR, (iii) the randomly amplified polymorphic DNA (RAPD) technique, and (iv) pulsed-field gel electrophoresis (PFGE). Fifteen selected strains were ribotyped. Six RAPD types and 15 PFGE patterns were identified among all strains examined, and 12 ribotypes were found among the 15 strains that were ribotyped. The Georgian epidemic apparently was caused by one major clonal group of C. diphtheriae (PFGE type A, ribotype R1), which was identical to the predominant epidemic strain(s) isolated during the concurrent diphtheria epidemic in Russia. A dendrogram based on the PFGE patterns revealed profound differences between the minor (nonpredominant) epidemic strains found in Georgia and Russia. The methodologies for RAPD typing, ribotyping, and PFGE typing of C. diphtheriae strains were improved to enable rapid and convenient molecular typing of the strains. The RAPD technique was adequate for biotype differentiation; however, PFGE and ribotyping were better (and equal to each other) at discriminating between epidemiologically related and unrelated isolates.
Journal of Clinical Microbiology 11/1999; 37(10):3265-70. · 4.15 Impact Factor
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ABSTRACT: Gram-positive organisms, including vancomycin-resistant enterococci (VRE), have emerged as major pathogens on the organ transplant service at our institution. We hypothesized that our use of vancomycin as part of routine surgical prophylaxis increased the risk of VRE colonization and infection; conversely, there was concern that failure to use vancomycin prophylaxis would increase peri-operative morbidity due to gram-positive organisms.
Renal transplant recipients (n = 88) were randomized to receive either a) vancomycin/ceftriaxone or b) cefazolin; and pancreas transplants (n = 24) to receive either a) vancomycin/gentamicin or b) cefazolin/gentamicin. Stool samples or rectal swabs were obtained for culture for enterococci within 24 h of transplantation and weekly while hospitalized.
Enterococci were isolated on stool culture from 38 (34%) of 102 patients at the time of transplantation; 4 (11%) of the isolates were VRE. The percentage of patients who subsequently acquired VRE was low (1-7% per wk) but remained constant during hospitalization. There was no association between new VRE detection and vancomycin use for either prophylactic or therapeutic purposes. Forty-four patients (39%) had a post-operative infection with 46% of these infections due to gram-positive organisms; rates were unaffected by prophylactic vancomycin use. Pancreas transplant patients who did not receive vancomycin prophylaxis had a significantly longer initial hospitalization (p = 0.03); however, differences were not statistically significant when total length of stay (LOS) within the first 90 d of transplantation was compared.
Vancomycin surgical prophylaxis does not appear to have an effect on VRE colonization or infection, or on rates of infection with gram-positive bacteria. Elimination of vancomycin prophylaxis in renal transplant patients may be a reasonable part of an overall program to limit vancomycin usage, although as a single measure, its impact may be minimal. Vancomycin surgical prophylaxis may be of greater importance in pancreas transplants.
Clinical Transplantation 07/1999; 13(3):245-52. · 1.67 Impact Factor
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ABSTRACT: Despite its widespread prevalence, uncertainties remain about the relative contribution of various routes of transmission to the overall rate of infection with Toxoplasma gondii, particularly in developed countries. To explore the hypothesis that meat consumption is an important risk factor for infection, a cross-sectional seroprevalence study was performed on healthy adults in one region in the state of Maryland. The population included Seventh Day Adventists who as a group follow a diet containing no meat, and control community volunteers who were not Seventh Day Adventists. Thirty-one percent of the population had serologic evidence of T. gondii infection. People with T. gondii infection were older (49 versus 42 years old; P < 0.01, by t-test) and less likely to be Seventh Day Adventists (24% versus 50%; P < 0.01, by chi-square test) than people without T. gondii infection. When adjustments were made for age and gender through multiple logistic regression, Seventh Day Adventists had a significantly decreased risk of T. gondii infection (odds ratio = 0.21, 95% confidence interval = 0.09-0.46, P = 0.0001) compared with the controls. While the basis for this effect remains to be determined, one possible protective factor is the general adherence of Seventh Day Adventists to a diet that does not contain meat.
The American journal of tropical medicine and hygiene 06/1999; 60(5):790-2. · 2.59 Impact Factor
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ABSTRACT: Vibrio vulnificus is a human pathogen whose virulence has been associated with the expression of capsular polysaccharide (CPS). Multiple CPS types have been described; however, virulence does not appear to correlate with a particular CPS composition. Reversible-phase variation for opaque and translucent colony morphologies is characterized by changes in CPS expression, as suggested by electron microscopy of cells stained nonspecifically with ruthenium red. Isolates with opaque colony morphologies are virulent and appear to be more thickly encapsulated than naturally occurring translucent-phase variants, which have reduced, patchy, or absent CPS. Previously, we have shown that the virulence of translucent-phase variants was intermediate between opaque-phase variants and acapsular transposon mutants, suggesting a correlation between virulence and the amount of CPS expressed. In the present study, CPS expression of phase variants and genetically defined mutants of V. vulnificus M06-24/O was examined by using a CPS-specific monoclonal antibody with an enzyme-linked immunosorbent assay, flow cytometry, and immunoelectron microscopy. Semiquantitative analyses of CPS expression correlated well among these assays, confirming that the translucent-phase variant was intermediate in CPS expression and retained type I CPS-specific epitopes. Cell surface expression of CPS varied with the growth phase, increasing during logarithmic growth and declining in stationary culture. Significantly greater CPS expression (P = 0.026) was observed for cells grown at 30 degrees C than for those at 37 degrees C. These studies confirm that phase variation and virulence in V. vulnificus correlate with the amount of CPS expressed and demonstrate the fluidity of bacterial polysaccharide expression in response to environmental conditions.
Infection and Immunity 06/1999; 67(5):2250-7. · 4.16 Impact Factor
