bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Multiple Floating Structures With Nonlinear Constraints
Authors: Chakrabarti Subrata K. 
Published: July 2002

Abstract
A versatile and efficient numerical analysis is developed to compute the responses of a moored floating system composed of multiple floating structures. Structures such as tankers, semisubmersibles, FPSOs, SPARs, TLPs, and SPMs connected by mooring lines, connectors or fenders may be analyzed individually or collectively including multiple interaction. The analysis is carried out in the time domain assuming rigid body motion for the structures, and the solution is generated by a forward integration scheme. The analysis includes the nonlinearities in the excitation, damping, and restoring terms encountered in a typical mooring system configuration. It also allows for instabilities in the tower oscillation as well as slack mooring lines. Certain simplifications in the analysis have been made, which are discussed. The exciting forces in the analysis are wind, current, and waves (including a steady and an oscillating drift force), which are not necessarily collinear. The waves can be single frequency or composed of multiple frequency components. For regular waves either linear, stretched linear or fifth order theory may be used. The irregular wave may be included as a given spectral model (e.g., PM or JONSWAP). The vessels are free to respond to the exciting forces in six degrees of freedom—surge, sway, heave, roll, pitch, and yaw. The tower, when present, is free to respond in two degrees of freedom—oscillation and precession. The loads in the mooring lines are determined from prescribed tension-strain tables for the lines. Rigid mooring arms can be analyzed by allowing for compression in the load-strain table. Fenders may be input similarly through load compression tables. In order to establish the stability and accuracy of the solution, comparison of the results with linearized frequency domain analysis was made. The analysis is verified by several different model test results for different structure configurations in regular and random seas. Some of the interesting aspects of nonlinear system are shown with a few examples.
Approximate Two-Color Emission Pyrometry
Authors: Bhattacharjee S. , King M. , Cobb W. , Altenkirch R. A. , Wakai K. 
Published: July 2002

Abstract
Approximate methods for the determination of a temperature field using pure emission pyrometry applied to a two-dimensional nonoptically thin flame without variation along a line of sight are presented. In the absence of an absorption measurement, emission pyrometry depends on theoretical spectral information. Limitations of existing techniques stem from the fact that spectral information is a function of temperature only for the optically thin situation, by and large the situation to which current techniques apply, and temperatures above 1000 K. Through extensive narrow-band calculation using a simulated flame over polymethylmethacrylate, we show that the spectral information contained in the equivalent bandwidth ratio is approximately a constant for the 2.8 μm/1.8 μm band pair and appropriate bandwidths. The constant can be evaluated from emission measurements at a point where the temperature is known or can be estimated using, e.g., the maximum flame temperature of a simulated flame and the peak band intensities. The temperature field evaluated with this approximately constant value of the equivalent bandwidth ratio, Ar, is accurate to within five percent for temperatures down to 450 K. [S0022-1481(00)02601-3]
Simultaneous Measurement of the Orthogonal Components of Thermal
Diffusivity in PVC Sheet
Authors: Doss D. J. , Wright N. T. 
Published: July 2002

Abstract
An extension of the flash method is described that measures simultaneously the three orthogonal components of thermal diffusivity in specimens of moderate thermal diffusivity. Only part of the top face of the specimen is illuminated and the temperature histories are recorded at three points on the bottom face. A Marquardt parameter estimation algorithm coupled with a finite difference model of the diffusion equation analyzes these temperature histories to determine the components of thermal diffusivity. Illustrative measurements in stainless steel, glass, and PVC demonstrate that accurate three-dimensional thermal diffusivity measurements can be made in this way. The in-plane components of thermal diffusivity of as-supplied PVC sheet are shown to be about 20 percent greater than the out-of-plane component. This anisotropy appears to be due to the manufacturing process and exemplifies the need for such measurements. [S0022-1481(00)70101-0]
A Model of Dopant Transport During Bridgman Crystal Growth With
Magnetically Damped Buoyant Convection
Authors: Ma N. , Walker J. S. 
Published: July 2002

Abstract
This paper presents a model for the unsteady transport of a dopant during the vertical Bridgman crystal growth process with a planar crystal-melt interface and with an externally applied axial magnetic field. This dilute mass transport depends on the convective and diffusive mass transport of the dopant. The convective mass transport is driven by buoyant convection in the melt, which produces nonuniformities in the concentration in both the melt and the crystal. This convective transport is significant even for a strong magnetic field Bo=2 T. However, the electromagnetic damping of the melt motion produces a local region adjacent to the crystal-melt interface which is dominated by diffusion. Thus, this melt solidifies with a relatively radially uniform concentration, so that the radial distribution of dopants in the crystal is also relatively radially uniform. The transient model predicts the dopant distribution in the entire crystal. [S0022-1481(00)02301-X]
Calibration Issues in Development of ISO Standards for Fixed Steel
Offshore Structures
Authors: Moses Fred , Stahl Bernhard 
Published: July 2002

Abstract
A study supported by the American Petroleum Institute established that load and resistance factor design offers improvement in design and is supported by credible data, can yield improved designs of greater reliability and/or economy and is in reasonable accordance with current design practices. This paper discusses the criteria for calibrating the ISO-LRFD based on the API studies. Other topics include actual versus notional reliabilities, regional load factors, member versus system reliability, and selecting a design return period. The paper also describes safety indices for the combined loading interaction formulas. [S0892-7219(00)01301-7]
Offshore Safety Assessment and Safety-Based Decision-Making—The
Current Status and Future Aspects
Authors: Wang J. , Kieran O. 
Published: July 2002

Abstract
The offshore installations (safety case) regulations were developed in the UK in 1992 and came into force in 1993 in response to the accepted findings of the Piper Alpha enquiry. Recently, “the offshore installations and wells (design and construction, etc.) regulations” (DCR 1996) were introduced to offshore safety analysis. From the earliest stages of the installation's life cycle, operators must ensure that all safety-critical elements in both the software and system domains be assessed. Hazards can be identified and the risks associated with them can be assessed and evaluated using a number of techniques and decision-making strategies, all aimed at producing an installation with lifetime safety integrity. In this paper, following a brief review of the current status of offshore safety regulation in the UK, several offshore safety assessment frameworks are presented. These include top-down, bottom-up, probabilistic, and subjective approaches. The conditions under which each approach may be applied effectively and efficiently are discussed. Probabilistic safety-based decision-making and subjective safety-based decision-making are then studied. Two examples are used to demonstrate the decision-making approaches. Recommendations on further development in offshore safety analysis are suggested. [S0892-7219(00)00901-8]
In Vitro Efficacy of Nikkomycin Z against the Human Isolate of the Microsporidian Species
Encephalitozoon hellem
Authors: Bigliardi Elisa , Bernuzzi Anna Maria , Corona Silvia , Gatti Simonetta , Scaglia Massimo , Sacchi Luciano 
Published: July 2002

ABSTRACT

Since 1985 microsporidia have been recognized as a cause of emerging infections in humans, mainly in immunocompromised human immunodeficiency virus-positive subjects. As chitin is a basic component of the microsporidian infective stage, the spore, we evaluated in vitro the susceptibility of a human-derived strain of
Encephalitozoon hellem
to nikkomycin Z, a peptide-nucleoside antibiotic known as a competitive inhibitor of chitin synthase enzymes. Transmission electron microscopy showed that this drug, at 25 μg/ml, reduced the number of parasitic foci by about 35% ± standard deviation after 7 days of culture (
P
< 0.0001) and induced cell damage of both mature and immature spores and also other sporogonic and merogonic stages. In particular, an irregular outline of the cell shape and an abnormally condensed cytoplasm in meronts and sporonts were documented. Also, the polar tubule and the polaroplast membranes appeared disarrayed in the sporoblast stage. The spore wall showed an enlarged endospore and delaminated exospore. Mature spores had a complete cytoplasmic disorganization and a swollen and delaminated cell wall. No ultrastructural cell damage was observed in uninfected control cultures treated with the drug.
Enzymes Catalyzing the Early Steps of Clavulanic Acid Biosynthesis Are Encoded by Two Sets of Paralogous Genes in
Streptomyces clavuligerus
Authors: Jensen Susan E. , Elder Kenneth J. , Aidoo Kwamena A. , Paradkar Ashish S. 
Published: July 2002

ABSTRACT

Genes encoding the proteins required for clavulanic acid biosynthesis and for cephamycin biosynthesis are grouped into a “supercluster” in
Streptomyces clavuligerus
. Nine open reading frames (ORFs) associated with clavulanic acid biosynthesis were located in a 15-kb segment of the supercluster, including six ORFs encoding known biosynthetic enzymes or regulatory proteins, two ORFs that have been reported previously but whose involvement in clavulanic acid biosynthesis is unclear, and one ORF not previously reported. Evidence for the involvement of these ORFs in clavulanic acid production was obtained by generating mutants and showing that all were defective for clavulanic acid production when grown on starch asparagine medium. However, when five of the nine mutants, including mutants defective in known clavulanic acid biosynthetic enzymes, were grown in a soy-based medium, clavulanic acid-producing ability was restored. This ability to produce clavulanic acid when seemingly essential biosynthetic enzymes have been mutated suggests that paralogous genes encoding functionally equivalent proteins exist for each of the five genes but that these paralogues are expressed only in the soy-based medium. The five genes that have paralogues encode proteins involved in the early steps of the pathway common to the biosynthesis of both clavulanic acid and the other clavam metabolites produced by this organism. No evidence was seen for paralogues of the four remaining genes involved in late, clavulanic acid-specific steps in the pathway.
Roles of
gyrA
Mutations in Resistance of Clinical Isolates and In Vitro Mutants of
Bacteroides fragilis
to the New Fluoroquinolone Trovafloxacin
Authors: Bachoual Rafik , Dubreuil Luc , Soussy Claude-James , Tankovic Jacques 
Published: July 2002

ABSTRACT

We determined whether
gyrA
mutations were present in fluoroquinolone-resistant laboratory mutants derived from the
Bacteroides fragilis
reference strain ATCC 25285 and in clinical isolates of
B. fragilis
. The two first-step mutants selected on ciprofloxacin (CIP) were devoid of
gyrA
mutations, whereas two of the three CIP-selected second-step mutants studied presented the same
gyrA
mutation leading to a Ser82Phe change. Unusual GyrA alterations, Asp81Asn or Ala118Val, were detected in two of the three first-step mutants selected on trovafloxacin (TRO), Mt3 and Mt1, respectively. The Ala118Val change had no effect on the susceptibility of Mt1 to CIP. No second-step mutant could be obtained with TRO as a selector. For the 12 clinical isolates studied, a Ser82Phe change in GyrA was found only in the 3 strains which showed the highest levels of TRO resistance (MIC, 4 μg/ml). Thus, the resistance phenotypes and genotypes observed in fluoroquinolone-resistant clinical isolates of
B. fragilis
were similar to those found in CIP-selected laboratory mutants, whereas peculiar mutational events could be selected in vitro with TRO.
Pharmacodynamics of Trovafloxacin and Levofloxacin against
Bacteroides fragilis
in an In Vitro Pharmacodynamic Model
Authors: Peterson M. L. , Hovde L. B. , Wright D. H. , Brown G. H. , Hoang A. D. , Rotschafer J. C. 
Published: July 2002

ABSTRACT

An in vitro pharmacodynamic investigation was conducted to explore whether the area under the concentration time curve from 0 to 24 h (AUC
0–24
)/MIC ratio could predict fluoroquinolone performance against
Bacteroides fragilis
. An in vitro model was used to generate kill curves for trovafloxacin (TVA) and levofloxacin (LVX) at AUC
0–24
/MIC ratios of 1 to 406 against three strains of
B. fragilis
(ATCC 25285, ATCC 23745, and clinical isolate M97-117). TVA and LVX were bolused prior to the start of experiments to achieve the corresponding AUC
0–24
/MIC ratio. Experiments were performed in duplicate over 24 h and in an anaerobic environment. Analyses of antimicrobial performance were conducted by comparing the rates of bacterial kill (K) using nonlinear regression analysis with 95% confidence intervals. Statistical significance was defined as a lack of overlap in the 95% confidence limits generated from the slope of each kill curve. For both TVA and LVX, K was maximized once an AUC
0–24
/MIC ratio of ≥40 was achieved and was not further increased despite a 10-fold increase in AUC
0–24
/MIC from approximately 40 to 400 against all three strains of
B. fragilis
. No significant differences were found in K between AUC
0–24
/MIC ratios of approximately 40 to 200. In experiments where AUC
0–24
/MIC ratios that were ≥ 5 and ≤ 44 were conducted, 64% demonstrated regrowth at 24 h. Resistant strains were selected in 50% of those experiments, demonstrating regrowth, which resulted in increased MICs of two- to 16-fold for both TVA and LVX. Regrowth did not occur, nor were resistant strains selected in any studies with an AUC/MIC that was > 44. Our findings suggest that fluoroquinolones provide antibacterial effects against
B. fragilis
in a concentration-independent manner associated with an AUC
0–24
/MIC ratio of ≥40. Also, the potential for the selection of resistant strains of
B. fragilis
may increase with an AUC
0–24
/MIC ratio of ≤44.
Plasmidic Extended-Spectrum β-Lactamases in
Vibrio cholerae
O1 El Tor Isolates in Argentina
Authors: Petroni Alejandro , Corso Alejandra , Melano Roberto , Cacace María Luisa , Bru Ana María , Rossi Alicia , Galas Marcelo 
Published: July 2002

ABSTRACT

Since 1992 there have been seven major outbreaks of cholera in Argentina. Susceptibility analysis of 1,947 isolates (40% of reported cases) of
Vibrio cholerae
O1 biotype El Tor suggested the presence of extended-spectrum β-lactamases (ESBLs) in 28 isolates. Because of their different susceptibility profiles,
V. cholerae
isolates M1502, M1516, M1573, and M3030 (all of which are of the Ogawa serotype) were selected for the present study. By susceptibility analysis, isoelectric focusing, and PCR-based restriction fragment length polymorphism analysis, CTX-M-type enzymes were identified in three isolates, whereas a PER-2-type enzyme, in addition to a TEM-1-like enzyme, was identified in the other isolate. The presence of these ESBLs in
V. cholerae
isolates resulted in MICs well below those commonly observed for members of the family
Enterobacteriaceae
. Genes that encode both ESBLs were transferred to
Escherichia coli
by conjugation, together with all determinants of resistance to non-β-lactam antibiotics (gentamicin, kanamycin, and sulfamethoxazole for all isolates; amikacin and streptomycin for three isolates; trimethoprim, tetracycline, and chloramphenicol for two isolates). Plasmid profile analysis and Southern blotting revealed the presence of single plasmids of about 150 kb in the four
V. cholerae
isolates and their respective transconjugants and revealed that the plasmids harbored genes encoding CTX-M-type or PER-2-type ESBLs. These results strongly suggest the broad spread of these ESBLs among genera belong to families other than the
Enterobacteriaceae
.
Rapid and Simple Method for the Most-Probable-Number Estimation of Arsenic-Reducing Bacteria
Authors: Kuai Linping , Nair Arjun A. , Polz Martin F. 
Published: July 2002

ABSTRACT

A rapid and simple most-probable-number (MPN) procedure for the enumeration of dissimilatory arsenic-reducing bacteria (DARB) is presented. The method is based on the specific detection of arsenite, the end product of anaerobic arsenate respiration, by a precipitation reaction with sulfide. After 4 weeks of incubation, the medium for the MPN method is acidified to pH 6 and sulfide is added to a final concentration of about 1 mM. The brightly yellow arsenic trisulfide precipitates immediately and can easily be scored at arsenite concentrations as low as 0.05 mM. Abiotic reduction of arsenate upon sulfide addition, which could yield false positives, apparently produces a soluble As-S intermediate, which does not precipitate until about 1 h after sulfide addition. Using the new MPN method, population estimates of pure cultures of DARB were similar to direct cell counts. MPNs of environmental water and sediment samples yielded DARB numbers between 10
1
and 10
5
cells per ml or gram (dry weight), respectively. Poisoned and sterilized controls showed that potential abiotic reductants in environmental samples did not interfere with the MPN estimates. A major advantage is that the assay can be easily scaled to a microtiter plate format, enabling analysis of large numbers of samples by use of multichannel pipettors. Overall, the MPN method provides a rapid and simple means for estimating population sizes of DARB, a diverse group of organisms for which no comprehensive molecular markers have been developed yet.
Secretion of RTX Leukotoxin by
Actinobacillus actinomycetemcomitans
Authors: Kachlany Scott C. , Fine Daniel H. , Figurski David H. 
Published: July 2002

ABSTRACT

Actinobacillus actinomycetemcomitans
, the etiologic agent for localized juvenile periodontitis and certain other human infections, such as endocarditis, expresses a leukotoxin that acts on polymorphonuclear leukocytes and macrophages. Leukotoxin is a member of the highly conserved repeat toxin (RTX) family of bacterial toxins expressed by a variety of pathogenic bacteria. While the RTX toxins of other bacterial species are secreted, the leukotoxin of
A. actinomycetemcomitans
is thought to remain associated with the bacterial cell. We have examined leukotoxin production and localization in rough (adherent) and smooth (nonadherent) strains of
A. actinomycetemcomitans
. We found that leukotoxin expressed by the rough, adherent, clinical isolate CU1000N is indeed cell associated, as expected. However, we were surprised to find that smooth, nonadherent strains of
A. actinomycetemcomitans
, including Y4, JP2 (a strain expressing a high level of toxin), and CU1060N (an isogenic smooth variant of CU1000N), secrete an abundance of leukotoxin into the culture supernatants during early stages of growth. After longer times of incubation, leukotoxin disappears from the supernatants, and its loss is accompanied by the appearance of a number of low-molecular-weight polypeptides. The secreted leukotoxin is active, as evidenced by its ability to kill HL-60 cells in vitro. We found that the growth phase and initial pH of the growth medium significantly affect the abundance of secreted leukotoxin, and we have developed a rapid (<2 h) method to partially purify large amounts of leukotoxin. Remarkably, mutations in the
tad
genes, which are required for tight nonspecific adherence of
A. actinomycetemcomitans
to surfaces, cause leukotoxin to be released from the bacterial cell. These studies show that
A. actinomycetemcomitans
has the potential to secrete abundant leukotoxin. It is therefore appropriate to consider a possible role for leukotoxin secretion in the pathogenesis of
A. actinomycetemcomitans
.
The Locus of Enterocyte Effacement (LEE)-Encoded Regulator Controls Expression of Both LEE- and Non-LEE-Encoded Virulence Factors in Enteropathogenic and Enterohemorrhagic
Escherichia coli
Authors: Elliott Simon J. , Sperandio Vanessa , Girón Jorge A. , Shin Sooan , Mellies Jay L. , Wainwright Leslie , Hutcheson Steven W. , McDaniel Timothy K. , Kaper James B. 
Published: July 2002

ABSTRACT

Regulation of virulence gene expression in enteropathogenic
Escherichia coli
(EPEC) and enterohemorrhagic
E. coli
(EHEC) is incompletely understood. In EPEC, the plasmid-encoded regulator Per is required for maximal expression of proteins encoded on the locus of enterocyte effacement (LEE), and a LEE-encoded regulator (Ler) is part of the Per-mediated regulatory cascade upregulating the
LEE2
,
LEE3
, and
LEE4
promoters. We now report that Ler is essential for the expression of multiple LEE-located genes in both EPEC and EHEC, including those encoding the type III secretion pathway, the secreted Esp proteins, Tir, and intimin. Ler is therefore central to the process of attaching and effacing (AE) lesion formation. Ler also regulates the expression of LEE-located genes not required for AE-lesion formation, including
rorf2
,
orf10
,
rorf10
,
orf19
, and
espF
, indicating that Ler regulates additional virulence properties. In addition, Ler regulates the expression of proteins encoded outside the LEE that are not essential for AE lesion formation, including TagA in EHEC and EspC in EPEC. Δ
ler
mutants of both EPEC and EHEC show altered adherence to epithelial cells and express novel fimbriae. Ler is therefore a global regulator of virulence gene expression in EPEC and EHEC.
Genetic Dissection of Primary and Secondary Responses to a Widespread Natural Pathogen of the Gut,Eimeria vermiformis
Authors: Smith Adrian L. , Hayday Adrian C. 
Published: July 2002

ABSTRACTBecause most pathogens initially challenge the body at epithelial surfaces, it is important to dissect the mechanisms that underlie T-cell responses to infected epithelial cells in vivo. The coccidian parasites of the genusEimeriaare protozoan gut pathogens that elicit a potent, protective immune response in a wide range of host species. CD4+ αβ T cells and gamma interferon (IFN-γ) are centrally implicated in the primary immunoprotective response. To define any additional requirements for the primary response and to develop a comparison between the primary and the secondary response, we have studiedEimeriainfections of a broad range of genetically altered mice. We find that a full-strength primary response depends on β2-microglobulin (class I major histocompatibility complex [MHC] and class II MHC and on IFN-γ and interleukin-6 (IL-6) but not on TAP1, perforin, IL-4, Fas ligand, or inducible nitric oxide synthetase. Indeed, MHC class II-deficient and IFN-γ-deficient mice are as susceptible to primary infection as mice deficient in all αβ T cells. Strikingly, the requirements for a highly effective αβ-T-cell-driven memory response are less stringent, requiring neither IFN-γ nor IL-6 nor class I MHC. The class II MHC dependence was also reduced, with adoptively transferable immunity developing in MHC class II−/−mice. Besides the improved depiction of an immune response to a natural gut pathogen, the finding that effective memory can be elicited in the absence of primary effector responses appears to create latitude in the design of vaccine strategies.