bluuebunny/crossref_metadata_2025 huggingface dataset:
Children's Well‐Being during Parents' Marital Disruption Process: A Pooled Time‐Series Analysis
Authors: Sun Yongmin , Li Yuanzhang
Published: March 2004

On the basis of a large, nationally representative multiwave panel, this research examines the extent to which parents' marital disruption process affects children's academic performance and psychological well‐being at 2time points prior to and 2 time points after parental divorce. The results of a pooled time‐series analysis show that compared with peers in intact families, children of divorce fare less well in most well‐being measures at all 4 time points, from approximately 3 years before divorce to 3 years after divorce. Interestingly, whereas the effects of the disruption process on students' test scores demonstrate a linear decline over time, the effects on their social‐psychological measures exhibit a U‐shaped time pattern. Families in the process of marital disruption are also characterized by a deficit in economic and social resources at various time points of this process. These differences in family resources either partially or completely mediate the detrimental effects of the disruption process over time. Furthermore, the process of marital disruption appears to affect girls to the same extent that it does boys. Finally, the causal role of divorce in affecting children is also discussed.
The Effects of Parent‐Adolescent Relationships and Parental Separation on Adolescent Well‐Being
Authors: Videon Tami M.
Published: March 2004

This article uses data from the National Longitudinal Study of Adolescent Health (Add Health) to investigate the short‐term effects of parental separation on adolescent delinquency and depression. Findings indicate that parent‐adolescent relationships prior to marital dissolution moderate the effects of parental separation on adolescent delinquency. The higher adolescents' satisfaction with their relationship with the same‐sex parent prior to residential separation the greater their increases in delinquent behavior when they are separated from this parent at Wave 2. These results highlight the importance of interpersonal relationships within the family prior to parental separation. Opposite‐sex parents constitute a significant influence on adolescents' depression regardless of family structure. These findings suggest that research on parental influences on children's well‐being needs to pay more attention to gender‐specific effects.
Older Women in Poverty: The Impact of Midlife Factors
Authors: Vartanian Thomas P. , McNamara Justine M.
Published: March 2004

This study investigates the factors contributing to older women's economic well‐being from a life course perspective, assessing the effects of both midlife characteristics and later life events on women between the ages of 66–70, and 71–85. Using the 1968–1997 Panel Study of Income Dynamics, the findings suggest that midlife characteristics such as workforce participation, income, and rural residence are strongly related to economic outcomes in old age. Late‐life events and characteristics, however, also contribute significantly to economic outcomes even when midlife factors are incorporated into analyses. In addition, both midlife and later life characteristics contribute to the persistence of poverty in old age, with many groups of ever poor women finding themselves in poverty for over 50% of their old age years.
Local/Global Effects of Mistuning on the Forced Response of Bladed Disks
Authors: Rivas-Guerra A. J. , Mignolet M. P.
Published: March 2004

The focus of the present investigation is on the assessment and modeling of the local (spanning only a few blades) and global (encompassing the entire disk) effects of mistuning on the forced response of bladed disks. To this end, the concept of localization is first revisited and a new measure of this effect is introduced in terms of the number of blades the mistuning of which actually affects the forced response of a central blade. Using this new metric, it is demonstrated that high responding blades typically exhibit a high level of localization and that the reverse is not necessarily true. Thus, localization is not only disk dependent but also varies from blade-to-blade on the same disk. This observation is then used to validate a partial mistuning approach to the determination of the maximum amplitude of response over the entire population of disks. The results of this study indicate that the largest amplification due to the mistuning occurs at very strong blade-to-blade coupling levels, at the contrary of a general perception, but is associated with large mistuning levels. Finally, the above phenomenological observations are used to devise a modeling technique of both local and global components of mistuning. An example of application is presented that demonstrates the high accuracy of this approach through the entire blade-to-blade coupling domain.
Two-Dimensional Spectroscopic Observation of Nonluminous Flames in a Regenerative Industrial Furnace Using Coal Gas
Authors: Hino Y. , Sugiyama S. , Suzukawa Y. , Mori I. , Konishi N. , Ishiguro T. , Kitawawa K. , Gupta A. K.
Published: March 2004

Thermal and chemical characteristics of the flames obtained from an industrial size regenerative combustion furnace have been obtained spectroscopically. The combustion characteristics of diffusion or premixed flames in the regenerative high-temperature air combustion facility have been examined using coal gas as the fuel. The fuel gas composition consisted of H2, hydrocarbon, CO, and N2. Monochromatic images of the flames have been observed in the emission mode using a CCD camera fitted with an optical band pass filter at the desired wavelength. The two-dimensional temperature distribution in the furnace has been determined using the two-line method by utilizing the Swan emission bands from within the flame. The emission intensity profiles of NO, as well as OH and CH radicals have also been observed spectroscopically. The results showed quite uniform two-dimensional temperature distribution and emission intensity of OH and CH radical species for the diffusion flame case as compared to the premixed case using high-temperature combustion air. The premixed flame case showed high local values and large fluctuations in the combustion zone for both emission intensity and temperature distribution. The temperature distribution of soot particles in the premixed flame was also determined using the two-color optical method. The results showed high local value of temperature, similar to that found for the gas temperature using signatures for C2 species at two different wavelengths. In contrast the distribution of temperature for soot particles was different. The location of the maximum soot temperature shifted to downstream positions of the flame as compared to the maximum gas temperature regions measured from the C2 species. The experimental results are discussed in conjunction with those obtained from the heat simulation analyses.
Experimental Investigation of SI Engine Performance Using Oxygenated Fuel
Authors: Al-Farayedhi A. A. , Al-Dawood A. M. , Gandhidasan P.
Published: March 2004

The current experimental study aims to examine the effects of using oxygenates as a replacement of lead additives in gasoline on performance of a typical SI engine. The tested oxygenates are MTBE, methanol, and ethanol. These oxygenates were blended with a base unleaded fuel in three ratios (10, 15, and 20 vol.%). The engine maximum output and thermal efficiency were evaluated at a variety of engine operating conditions using an engine dynamometer setup. The results of the oxygenated blends were compared to those of the base fuel and of a leaded fuel prepared by adding TEL to the base. When compared to the base and leaded fuels, the oxygenated blends improved the engine brake thermal efficiency. The leaded fuel performed better than the oxygenated blends in terms of the maximum output of the engine except in the case of 20 vol.% methanol and 15 vol.% ethanol blends. Overall, the methanol blends performed better than the other oxygenated blends in terms of engine output and thermal efficiency.
Theory and Test Correlation for Laminate Stacking Factor Effect on Homopolar Bearing Stiffness
Authors: Kenny A. , Palazzolo A. , Montague G. T. , Kascak A. F.
Published: March 2004

The effect of the laminate stacking factor on homopolar magnetic bearing performance is examined. Stacked laminates are used on the bearing rotor and in the stator. These laminate stacks have anisotropic permeability. Equations for the effect of the stacking factor on homopolar bearing position stiffness are derived. Numerical results are calculated and compared to measurements. These results provide an answer for the common discrepancy between test and theory for homopolar magnetic bearing position stiffnesses.
Fuel System Suitability Considerations for Industrial Gas Turbines
Authors: Elliott F. G. , Kurz R. , Etheridge C. , O’Connell J. P.
Published: March 2004

Industrial Gas Turbines allow operation with a wide variety of gaseous and liquid fuels. To determine the suitability for operation with a gas fuel system, various physical parameters of the proposed fuel need to be determined: heating value, dew point, Joule-Thompson coefficient, Wobbe Index, and others. This paper describes an approach to provide a consistent treatment for determining the above physical properties. Special focus is given to the problem of determining the dew point of the potential fuel gas at various pressure levels. A dew point calculation using appropriate equations of state is described, and results are presented. In particular the treatment of heavier hydrocarbons, and water is addressed and recommendations about the necessary data input are made. Since any fuel gas system causes pressure drops in the fuel gas, the temperature reduction due to the Joule-Thompson effect has to be considered and quantified. Suggestions about how to approach fuel suitability questions during the project development and construction phase, as well as in operation are made.
Calculation of Surface Roughness Effects on Air-Riding Seals
Authors: Guardino C. , Chew J. W. , Hills N. J.
Published: March 2004

The effects of surface roughness on air-riding seals are investigated here using the Rayleigh pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various two-dimensional or three-dimensional roughness patterns on the stationary wall. A “unit-based” approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of surface roughness on the net lift force. The effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.
Development of Operating Temperature Prediction Method Using Thermophysical Properties Change of Thermal Barrier Coatings
Authors: Fujii T. , Takahashi T.
Published: March 2004

Thermal barrier coatings (TBCs) have become an indispensable technology as the temperature of turbine inlet gas has increased. TBCs reduce the temperature of the base metal, but a reduction of internal pores by sintering occurs when using TBCs, and so the thermal barrier performance of TBCs is deteriorated. This in turn increases the temperature of the base metal and could shorten its lifespan. The authors have already clarified by laboratory acceleration tests that the deterioration of the thermal barrier performance of TBCs is caused by a decrease in the noncontact area that exists inside TBCs. This noncontact area is a slit space that exists between thin layers and is formed when TBCs are coated. This paper examines the relations between the decrease of the noncontact area and the exposure conditions, by measuring the thermal conductivity and the porosity of TBCs exposed to the temperatures that exist in an actual gas turbine, and derives the correlation with exposure conditions. As a result, very high correlations were found between the thermal conductivity and exposure conditions of TBCs, and between the porosity and exposure conditions. A very high correlation was also found between the thermal conductivity and porosity of TBCs. In addition, techniques for predicting TBC operating temperature were examined by using these three correlations. The correlation of diameter and exposure conditions of the gamma prime phase, which exists in nickel base super alloys, is used as a general method for predicting the temperature of parts in hot gas paths. This paper proposes two kinds of operating temperature prediction methods, which are similar to this general method. The first predicts the operating temperature from thermal conductivity measurements of TBCs before and after use, and the second predicts the operating temperature from thermal conductivity measurements of TBCs after use and porosity measurements before use. The TBC operating temperatures of a combustor that had been used for 12,000 hours with an actual E-class gas turbine were predicted by these two methods. The advantage of these methods is that the temperature of all parts with TBC can be predicted.
Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes
Authors: Pawloski J. L. , Ching C. Y. , Shoukri M.
Published: March 2004

The void fractions, flow regimes, and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. A capacitance sensor for instantaneous void fraction measurements was developed. The mean and probability density function of the instantaneous void fraction signal can be used to effectively identify the different flow regimes. The current flow regime data show significant differences in the transitional boundaries of the existing flow regime maps. Property correction factors for the flow regime maps are recommended. The pressure drop measurements were compared to the predictions from four existing two-phase flow pressure drop models. Though some of the models performed better for certain flow regimes, none of the models were found to give accurate results over the entire range of flow regimes.
A New Tool for Design and Certification of Aircraft Turbine Rotors
Authors: Leverant G. R. , Millwater H. R. , McClung R. C. , Enright M. P.
Published: March 2004

This paper summarizes recent enhancements to a probabilistic damage tolerance software code, DARWINTM, that can be used for design certification of aircraft jet engine titanium disks/rotors that may contain melt-related anomalies. Evaluations of DARWINTM by engine manufacturers are also discussed, including comparisons with existing codes for accuracy and time efficiency. In addition, relevant test results, including various fatigue tests on material containing melt-related anomalies, are summarized.
Modeling the Performance Characteristics of Diesel Engine Based Combined-Cycle Power Plants—Part I: Mathematical Model
Authors: Danov Stan N. , Gupta Ashwanti K.
Published: March 2004

In this two-part series publication, a mathematical model of the energy conversion process in a diesel engine based combined-cycle power plant has been developed. The examined configuration consists of a turbocharged diesel engine (the topping cycle), a heat recovery steam generator (HRSG) and a steam turbine plant (the bottoming cycle). The mathematical model describes the processes that occur simultaneously in the diesel engine cylinders, turbocharger, air filter, air inlet pipes, exhaust pipes, HRSG, steam turbine, and the associated auxiliary equipment. The model includes nonlinear differential equations for modeling the energy conversion in the diesel engine cylinders, fuel combustion, gas exchange process, energy balance in the turbocharger, inlet pipes and exhaust system, heat balance in the HRSG, and steam turbine cycle. The fifth-order Kuta-Merson method has been applied for numerical solution of these simultaneous equations via an iterative computing procedure. The model is then used to provide an analysis of performance characteristics of the combined-cycle power plant for steady-state operation. The effect of change in the major operating variables (mutual operation of diesel engine, HRSG, and steam turbine) has been analyzed over a range of operating conditions, including the engine load and speed. The model validation and the applications of the model are presented in Part II (Results and Applications) of this two-part series publication.
Modeling the Performance Characteristics of Diesel Engine Based Combined-Cycle Power Plants—Part II: Results and Applications
Authors: Danov Stan N. , Gupta Ashwani K.
Published: March 2004

In this two-part series publication a mathematical model of the energy conversion process in a diesel engine based combined-cycle power plant has been developed and verified. The examined configuration consists of a turbocharged diesel engine (the topping cycle), a heat recovery steam generator (HRSG) and a steam turbine plant (the bottoming cycle). The model is then used to provide an analysis of performance characteristics of the combined-cycle power plant for steady-state operation. Numerous practical performance parameters of interest have been generated, such as the mean indicated pressure, specific fuel consumption, hourly fuel consumption, brake horsepower of diesel engine, mass flow rate, pressure, and temperature of gases and air, respectively, through the gas turbine and compressor (in the frame of a turbocharger), temperature of flue gases at boiler inlet and outlet, mass flow rate of exhaust gases through the convection coils, and mass flow rate, temperature, pressure, and enthalpy of superheated steam. The performance maps have been derived. The effect of change in the major operating variables (mutual operation of diesel engine, HRSG, and steam turbine) has been analyzed over a range of operating conditions, including the engine load and speed. The model is used as a desktop design tool for accurate predictions of cycle performance, as well as insight into design trends.
Thermodynamic Analysis of Zero-Atmospheric Emissions Power Plant
Authors: Martinez-Frias Joel , Aceves Salvador M. , Smith J. Ray , Brandt Harry
Published: March 2004

This paper presents a theoretical thermodynamic analysis of a zero-atmospheric emissions power plant. In this power plant, methane is combusted with oxygen in a gas generator to produce the working fluid for the turbines. The combustion produces a gas mixture composed of steam and carbon dioxide. These gases drive multiple turbines to produce electricity. The turbine discharge gases pass to a condenser where water is captured. A stream of pure carbon dioxide then results that can be used for enhanced oil recovery or for sequestration. The analysis considers a complete power plant layout, including an air separation unit, compressors and intercoolers for oxygen and methane compression, a gas generator, three steam turbines, a reheater, two preheaters, a condenser, and a pumping system to pump the carbon dioxide to the pressure required for sequestration. This analysis is based on a 400 MW electric power generating plant that uses turbines that are currently under development by a U.S. turbine manufacturer. The high-pressure turbine operates at a temperature of 1089 K (1500°F) with uncooled blades, the intermediate-pressure turbine operates at 1478 K (2200°F) with cooled blades and the low-pressure turbine operates at 998 K (1336°F). The power plant has a net thermal efficiency of 46.5%. This efficiency is based on the lower heating value of methane, and includes the energy necessary for air separation and for carbon dioxide separation and sequestration.
Characterization of Ceramic Matrix Composite Fasteners Exposed in a Combustor Linear Rig Test
Authors: Verrilli M. J. , Brewer D.
Published: March 2004

Combustion tests on SiC/SiC CMC components were performed in an aircraft combustion environment using the rich-burn, quick-quench, lean-burn (RQL) sector rig. SiC/SiC fasteners were used to attach several of these components to the metallic rig structure. The effect of combustion exposure on the fastener material was characterized via microstructural examination. Fasteners were also destructively tested, after combustion exposure, and the failure loads of fasteners exposed in the sector rig were compared to those of as-manufactured fasteners. Combustion exposure reduced the average fastener failure load by 50% relative to the as-manufactured fasteners for exposure times ranging from 50 to 260 hours. The fasteners exposed in the combustion environment demonstrated failure loads that varied with failure mode. Fasteners that had the highest average failure load, failed in the same manner as the unexposed fasteners.
Adaptive Selection of Aircraft Engine Technologies in the Presence of Risk
Authors: Roth B. A. , Graham M. D. , Mavris D. N. , Macsotai N. I.
Published: March 2004

The objective of this paper is to describe a method for selecting optimal engine technology solution sets while simultaneously accounting for the presence of technology risk. This method uses a genetic algorithm in conjunction with technology identification, evaluation, and selection methods to find optimal combinations of technologies. The unique feature of this method is that the technology evaluation itself is probabilistic in nature. This allows the performance impact and associated risk of each technology to be quantified in terms of a distribution on key engine technology metrics. The resulting method can best be characterized as a concurrent genetic algorithm/Monte Carlo analysis that yields a performance and risk-optimal technology solution set. This solution set is inherently a robust solution because the method will naturally strive to find those technologies representing the best compromise between performance improvement and technology risk. Finally, a practical demonstration of the method and accompanying results is given for a typical commercial aircraft engine technology selection problem.
Numerical Solution of Wave Diffraction Problem in the Time Domain With the Panel-Free Method
Authors: Qiu W. , Chuang J. M. , Hsiung C. C.
Published: March 2004

A panel-free method (PFM) was developed earlier to solve the radiation problem of a floating body in the time domain. In the further development of this method, the diffraction problem has been solved. After removing the singularity in the Rankine source of the Green function and representing the body surface mathematically by Non-Uniform Rational B-Splines (NURBS) surfaces, integral equations were globally discretized over the body surface by Gaussian quadratures. Computed response functions and forces due to diffracted waves for a hemisphere at zero speed were compared with published results.
Transit Draft Heave and Pitch Motion Analysis of the Mobile Offshore Base (MOB) Using Reverse MI/SO Techniques
Authors: Falzarano Jeffrey , Cheng Jun , Rodrigues William
Published: March 2004

A major design feature of the Mobile Offshore Base (MOB) is its ability to transit anywhere in the world in the required time frame. This means that the Single Base Units (SBU’s) of the MOB must be able to transit in severe environmental conditions. In these extreme sea conditions, a primary cause for concern is the large accelerations that the vessel motions might experience due to the high static stability of the MOB at Transit Draft. Furthermore, since the vessel has minimum freeboard in this condition, it is exposed to green water over the pontoon tops. The submergence of the pontoon deck causes a considerable loss in the vessel’s restoring moment. These concerns have warranted a study by the Office of Naval Research into the Transit Draft Dynamics of the MOB. A part of the research in progress involves the development of a nonlinear system modeling and optimization tool utilizing Reverse MI/SO (Multiple-Input/Single Output) techniques. Reverse MI/SO is based on the statistical signal processing of the recorded time histories of the excitation and response of the nonlinear multi-degree-of-freedom system. This method of analysis is functional and reliable in identifying an ideal representation of the linear and nonlinear terms of the system under consideration. Reverse MI/SO is a frequency domain analysis technique that also provides coherence functions for each of the terms in the model enabling an evaluation of the correctness of the proposed integro-diffrential equation of motion representing the system. In this paper we analyze the large amplitude heave and pitch motion of the MOB. It is a well-known fact in linear ship motions theory that for a symmetric ship with zero forward speed the cross-coupling added mass and damping coefficients are zero [1]. However, for large amplitude (nonlinear) motions of the MOB, we find these linear coefficients to be non-zero.
Intercomparison of Sea-State and Zero-Crossing Parameters From the WACSIS Field Experiment and Interpretation Using Video Evidence
Authors: Barstow, Stephen F. , Krogstad Harald E. , Lønseth Lasse , Mathisen Jan Petter , Mørk Gunnar , Schjølberg Peter
Published: March 2004

During the WACSIS field experiment, wave elevation time series data were collected over the period December 1997 to May 1998 on and near the Meetpost Nordwijk platform off the coast of the Netherlands from an EMI laser, a Saab radar, a Baylor Wave Staff, a Vlissingen step gauge, a Marex radar and a Directional Waverider. This paper reports and interprets, with the help of simultaneous dual video recordings of the ocean surface, an intercomparison of both single wave and sea state wave parameters.
A Spectral Response Surface Method for Calculating Crest Elevation Statistics
Authors: Tromans Peter S. , Vanderschuren Luc
Published: March 2004

The statistics of wave crest elevation in a random, directionally spread sea are calculated using a novel approach. The nonlinearity of steep waves is modelled to second order using Sharma and Dean kinematics and a spectral response surface method is used to deduce the crest elevation corresponding to a given probability of exceedance. The spectral response surface method works in the probability domain, making it several times faster than conventional time domain simulation of random waves. However, the results from the two methods show good agreement. As expected, nonlinearity makes extreme crests higher than the corresponding linear ones.
Statistics of Wave Crests From Models vs. Measurements
Authors: Prevosto Marc , Forristall George Z.
Published: March 2004

The analysis phase of the Wave Crest Sensor Intercomparison Study (WACSIS) focussed on the interpretation of the wave data collected by the project during the winter of 1997–98. Many aspects of wave statistics have been studied, but the main emphasis has been on crest height distributions, and recommendations for crest heights to be used in air gap calculations. In this paper, we first describe comparisons of the crest height distributions derived from the sensors (radars, wave staffs, laser) and from simulations based on 3-D second-order irregular wave models. These comparisons permit us to make conclusions on the quality of these models and to qualify the ability of some sensors to measure the crest heights accurately. In the second part, two new parametric models of the crest height distributions are discussed and their superiority to standard parametric models is demonstrated.
Wave Statistics for Intermediate Depth Water—NewWaves and Symmetry
Authors: Taylor P. H. , Williams B. A.
Published: March 2004

A study has been made into the average shape of large crests and troughs during several storms using wave elevation data from the WACSIS measurement program. The analysis techniques adopted were data-driven at all times, in order to test whether second-order wave theory could reproduce important features in the field data. The sea surface displayed obvious nonlinear behavior, reflected in the fact that the shapes of crests were always sharper and larger than their trough equivalents. Assuming that the dominant nonlinear correction is second order in the wave steepness (but without a knowledge of the detailed form of second-order theory), the average shapes of maxima in the underlying linear wave components were shown to match NewWave. This NewWave is the scaled auto-correlation function for a linear random process with the same power spectrum as the measured waves. Thus, NewWave was shown to be an acceptable model for the linear part of large waves on intermediate water depth (here ∼17 m). Assuming that NewWave is a good model for the linear part of large crests and troughs, a value for the second-order coefficient required to estimate crest elevation statistics was derived from the measured data for several storms. This coefficient was in good agreement with the results of the second-order random simulations of Forristall and Prevosto [1]. As well as studying vertical asymmetry, required for crest and trough statistics, horizontal asymmetry was examined using the Hilbert transform. Compared to a large amount of vertical asymmetry, the analysis showed that there was virtually no horizontal asymmetry for the bulk of the waves in the records. However, there is a very small degree of horizontal asymmetry exhibited in the largest waves in the records. Thus, given a surface elevation record, it is difficult to distinguish the direction of the time axis, again consistent with most of the nonlinearity being due to simple second-order bound waves.
Analysis of WACSIS Data Using a Directional Hybrid Wave Model
Authors: Zhang Jun , Zhang Shaosong , Wang Zhongming
Published: March 2004

The Wave Crest Sensor Inter-comparison Study (WACSIS) employed many different types of sensors to measure ocean surface waves. These sensors were attached to a steel jacket platform located in 18 m deep water about 9 km from the Dutch coast. To investigate the suitability and consistency of different wave sensors, wave characteristics at the locations of some sensors were deterministically predicted based on three other wave measurements using a Directional Hybrid Wave Model (DHWM). The comparisons between the predictions and related measurements were applied to the examination of the consistency among different sensors. As an example, a mistake of the orientation of a current meter has been found through the comparisons. This study also demonstrates that consistency among different types of wave sensors is satisfactory and the DHWM is valuable to the analysis of field wave measurements.
Analysis and Applications of Second-Order Models for Maximum Crest Height
Authors: Krogstad Harald E. , Barstow Stephen F.
Published: March 2004

Expressions for the maximum crest height are reviewed and tested on data from five different sensors in the WACSIS data set. The overall agreement is good and the analysis supports that second-order models give accurate expressions for the distribution of the maximum crest height for varying water depth and wave steepness. In the second part of the paper, the expressions are combined with the existing extreme crest and wave height framework and applied to sets of time series and long term wave data. It is concluded that the second-order models represent a definite improvement over earlier empirical parametrizations.
Heave Response of Classic Spar With Variable Geometry
Authors: Tao Longbin , Lim Kay Yeong , Thiagarajan Krish
Published: March 2004

Spar platforms with cylindrical shape and constant cross-section area may experience resonant heave motions in sea states with long peak periods, which are probably excessive for riser integrity due to its low damping and relatively low natural heave period. Changes to hull shape and cross-section that produce more benign heave behavior were discussed by some researchers in the past. In this study, the viscous damping of spar structures is explicitly calculated, and incorporated to the potential solution. It is concluded that the heave resonant response can be considerably reduced by alternative hull shapes via increased damping mechanism and the natural heave period being kept outside the range of the wave energy.
Criteria for Cost Effectiveness of Safety Measures
Authors: Skjong Rolf , Ronold Knut O.
Published: March 2004

The paper demonstrates that a simple method exists, by which easily accessible information aggregated in national statistics can be used to derive acceptance criteria for use in cost effectiveness evaluations. Cost effectiveness assessment is normally used for risks that should be made as low as reasonably practicable. These are risks, which are neither intolerably high nor negligible. Examples of users of such criteria are the national and international regulators that implement safety related regulations and industrial companies that operate in an industrial self-regulation regime and therefore define and implement their own risk control strategies. The criteria are derived by combining societal indicators published by the United Nations development program and national statistics. It is observed that in an unregulated market, individuals invest in their own safety or in the safety of their own family. In the same way as the societal indicators indicate how much the regulator should use on safety, the data on how much individuals spend on safety when the decision is up to them indicate when the regulator should not regulate. The idea is then that when individuals make better use of the available resources there is no reason to regulate. As a last point, when it comes to cost effectiveness, the paper demonstrates that situations may well occur for which a wealthy country should invest in safety and a poor country should not.
Role of a Cysteine Synthase in
Staphylococcus aureus
Authors: Lithgow James K. , Hayhurst Emma J. , Cohen Gerald , Aharonowitz Yair , Foster Simon J.
Published: March 2004

The gram-positive human pathogen
Staphylococcus aureus
is often isolated with media containing potassium tellurite, to which it has a higher level of resistance than
Escherichia coli
. The
S. aureus cysM
gene was isolated in a screen for genes that would increase the level of tellurite resistance of
E. coli
DH5α. The protein encoded by
S. aureus cysM
is sequentially and functionally homologous to the
O
-acetylserine (thiol)-lyase B family of cysteine synthase proteins. An
S. aureus cysM
knockout mutant grows poorly in cysteine-limiting conditions, and analysis of the thiol content in cell extracts showed that the
cysM
mutant produced significantly less cysteine than wild-type
S. aureus
SH1000.
S. aureus
SH1000 cannot use sulfate, sulfite, or sulfonates as the source of sulfur in cysteine biosynthesis, which is explained by the absence of genes required for the uptake and reduction of these compounds in the
S. aureus
genome.
S. aureus
SH1000, however, can utilize thiosulfate, sulfide, or glutathione as the sole source of sulfur. Mutation of
cysM
caused increased sensitivity of
S. aureus
to tellurite, hydrogen peroxide, acid, and diamide and also significantly reduced the ability of
S. aureus
to recover from starvation in amino acid- or phosphate-limiting conditions, indicating a role for cysteine in the
S. aureus
stress response and survival mechanisms.
H Protein of Bacteriophage
16-3
and RkpM Protein of
Sinorhizobium meliloti
41 Are Involved in Phage Adsorption
Authors: Putnoky Péter , Deák Veronika , Békási Krisztina , Pálvölgyi Adrienn , Maász Anita , Palágyi Zsuzsanna , Hoffmann Gyula , Kerepesi Ildikó
Published: March 2004

The strain-specific capsular polysaccharide KR5 antigen of
Sinorhizobium meliloti
41 is required both for invasion of the symbiotic nodule and for the adsorption of bacteriophage
16-3
. In order to know more about the genes involved in these events, bacterial mutants carrying an altered phage receptor were identified by using host range phage mutants. A representative mutation was localized in the
rkpM
gene by complementation and DNA sequence analysis. A host range phage mutant isolated on these phage-resistant bacteria was used to identify the
h
gene, which is likely to encode the tail fiber protein of phage
16-3
. The nucleotide sequences of the
h
gene as well as a host range mutant allele were also established. In both the bacterial and phage mutant alleles, a missense mutation was found, indicating a direct contact between the RkpM and H proteins in the course of phage adsorption. Some mutations could not be localized in these genes, suggesting that additional components are also important for bacteriophage receptor recognition.
A Subassembly of R27-Encoded Transfer Proteins Is Dependent on TrhC Nucleoside Triphosphate-Binding Motifs for Function but Not Formation
Authors: Gilmour Matthew W. , Taylor Diane E.
Published: March 2004

The transfer of plasmid DNA molecules between bacterial cells is achieved by a large array of conjugative transfer proteins which assemble into both cytoplasmic and membrane-associated complexes. TrhC is a membrane-associated protein that is required for the transfer of the IncHI1 resistance plasmid R27. Homologous proteins are encoded in all known conjugative systems, and each contains characteristic nucleoside triphosphate (NTP)-binding domains. An assembly of R27-encoded proteins was previously visualized by use of a TrhC-green fluorescent protein fusion, which appeared as discrete membrane-associated fluorescent foci. We have utilized this experimental system to determine the requirements for assembly of this TrhC-associated protein complex, and we found that 12 of the other 18 R27 transfer proteins are required for focus formation. An individual focus possibly represents a subassembly comprised of some or all of these transfer proteins. These data support the notion that the transfer apparatus is a multicomponent structure. In contrast, substitutions and deletions within TrhC NTP-binding motifs had minor effects on focus formation, but these mutations did affect plasmid transfer and bacteriophage susceptibility. These results indicate that TrhC requires intact NTP-binding motifs to function during conjugative transfer but that these motifs are not essential for the assembly of TrhC into a complex with other transfer proteins.
Molybdenum-Containing Arsenite Oxidase of the Chemolithoautotrophic Arsenite Oxidizer NT-26
Authors: Santini Joanne M. , vanden Hoven Rachel N.
Published: March 2004

The chemolithoautotroph NT-26 oxidizes arsenite to arsenate by using a periplasmic arsenite oxidase. Purification and preliminary characterization of the enzyme revealed that it (i) contains two heterologous subunits, AroA (98 kDa) and AroB (14 kDa); (ii) has a native molecular mass of 219 kDa, suggesting an α
2
β
2
configuration; and (iii) contains two molybdenum and 9 or 10 iron atoms per α
2
β
2
unit. The genes that encode the enzyme have been cloned and sequenced. Sequence analyses revealed similarities to the arsenite oxidase of
Alcaligenes faecalis
, the putative arsenite oxidase of the beta-proteobacterium ULPAs1, and putative proteins of
Aeropyrum pernix
,
Sulfolobus tokodaii
, and
Chloroflexus aurantiacus
. Interestingly, the AroA subunit was found to be similar to the molybdenum-containing subunits of enzymes in the dimethyl sulfoxide reductase family, whereas the AroB subunit was found to be similar to the Rieske iron-sulfur proteins of cytochrome
bc
1
and
b
6
f
complexes. The NT-26 arsenite oxidase is probably exported to the periplasm via the Tat secretory pathway, with the AroB leader sequence used for export. Confirmation that NT-26 obtains energy from the oxidation of arsenite was obtained, as an
aroA
mutant was unable to grow chemolithoautotrophically with arsenite. This mutant could grow heterotrophically in the presence of arsenite; however, the arsenite was not oxidized to arsenate.
The Tricarballylate Utilization (
tcuRABC
) Genes of
Salmonella enterica
Serovar Typhimurium LT2
Authors: Lewis Jeffrey A. , Horswill Alexander R. , Schwem Brian E. , Escalante-Semerena Jorge C.
Published: March 2004

The genes of
Salmonella enterica
serovar Typhimurium LT2 encoding functions needed for the utilization of tricarballylate as a carbon and energy source were identified and their locations in the chromosome were established. Three of the tricarballylate utilization (
tcu
) genes,
tcuABC
, are organized as an operon; a fourth gene,
tcuR
, is located immediately 5′ to the
tcuABC
operon. The
tcuABC
operon and
tcuR
gene share the same direction of transcription but are independently transcribed. The
tcuRABC
genes are missing in the
Escherichia coli
K-12 chromosome. The
tcuR
gene is proposed to encode a regulatory protein needed for the expression of
tcuABC
. The
tcuC
gene is proposed to encode an integral membrane protein whose role is to transport tricarballylate across the cell membrane.
tcuC
function was sufficient to allow
E. coli
K-12 to grow on citrate (a tricarballylate analog) but not to allow growth of this bacterium on tricarballylate.
E. coli
K-12 carrying a plasmid with wild-type alleles of
tcuABC
grew on tricarballylate, suggesting that the functions of the TcuABC proteins were the only ones unique to
S. enterica
needed to catabolize tricarballylate. Analyses of the predicted amino acid sequences of the TcuAB proteins suggest that TcuA is a flavoprotein, and TcuB is likely anchored to the cell membrane and probably contains one or more Fe-S centers. The TcuB protein is proposed to work in concert with TcuA to oxidize tricarballylate to
cis-
aconitate, which is further catabolized via the Krebs cycle. The glyoxylate shunt is not required for growth of
S. enterica
on tricarballylate. A model for tricarballylate catabolism in
S. enterica is
proposed.
Temperature Regulation of the Hemin Storage (Hms
+
) Phenotype of
Yersinia pestis
Is Posttranscriptional
Authors: Perry Robert D. , Bobrov Alexander G. , Kirillina Olga , Jones Heather A. , Pedersen Lisa , Abney Jennifer , Fetherston Jacqueline D.
Published: March 2004

In
Yersinia pestis
, the Congo red (and hemin) binding that is characteristic of the Hms
+
phenotype occurs at temperatures up to 34°C but not at higher temperatures. Manifestation of the Hms
+
phenotype requires at least five proteins (HmsH, -F, -R, -S, and -T) that are organized into two separate operons:
hmsHFRS
and
hmsT.
HmsH and HmsF are outer membrane proteins, while HmsR, HmsS, and HmsT are predicted to be inner membrane proteins. We have used transcriptional reporter constructs, RNA dot blots, and Western blots to examine the expression of
hms
operons and proteins. Our studies indicate that transcription from the
hmsHFRS
and
hmsT
promoters is not regulated by the iron status of the cells, growth temperature, or any of the Hms proteins. In addition, the level of mRNA for both operons is not significantly affected by growth temperature. However, protein levels of HmsH, HmsR, and HmsT in cells grown at 37°C are very low compared to those in cells grown at 26°C, while the amounts of HmsF and HmsS show only a moderate reduction at the higher growth temperature. Neither the Pla protease nor a putative endopeptidase (Y2360) encoded upstream of
hmsH
is essential for temperature regulation of the Hms
+
phenotype. However, HmsT at 37°C is sensitive to degradation by Lon and/or ClpPX. Thus, the stability of HmsH, HmsR, and HmsT proteins likely plays a role in temperature regulation of the Hms
+
phenotype of
Y. pestis
.
Proteome Analyses of Heme-Dependent Respiration inLactococcus lactis: Involvement of the Proteolytic System
Authors: Vido Karin , le Bars Dominique , Mistou Michel-Yves , Anglade Patricia , Gruss Alexandra , Gaudu Philippe
Published: March 2004

Sugar fermentation was long considered the sole means of energy metabolism available to lactic acid bacteria. We recently showed that metabolism ofLactococcus lactisshifts progressively from fermentation to respiration during growth when oxygen and heme are available. To provide insights into this phenomenon, we compared the proteomic profiles ofL. lactisunder fermentative and respiratory growth conditions in rich medium. We identified 21 proteins whose levels differed significantly between these conditions. Two major groups of proteins were distinguished, one involved in carbon metabolism and the second in nitrogen metabolism. Unexpectedly, enzymes of the proteolytic system (PepO1 and PepC) which are repressed in rich medium in fermentation growth were induced under respiratory conditions despite the availability of free amino acids. A triple mutant (dtpT dtpP oppA) deficient in oligopeptide transport displayed normal respiration, showing that increased proteolytic activity is not an absolute requirement for respiratory metabolism. Transcriptional analysis confirmed thatpepO1is induced under respiration-permissive conditions. This induction was independent of CodY, the major regulator of proteolytic functions inL. lactis. We also observed thatpepO1induction is redox sensitive. In acodYmutant,pepO1expression was increased twofold in aeration and eightfold in respiration-permissive conditions compared to static conditions. These observations suggest that new regulators activate proteolysis inL. lactis, which help to maintain the energetic needs ofL. lactisduring respiration.
The
Legionella pneumophila
PilT Homologue DotB Exhibits ATPase Activity That Is Critical for Intracellular Growth
Authors: Sexton Jessica A. , Pinkner Jerome S. , Roth Robyn , Heuser John E. , Hultgren Scott J. , Vogel Joseph P.
Published: March 2004

The ability of
Legionella pneumophila
to grow and cause disease in the host is completely dependent on a type IV secretion system known as the Dot/Icm complex. This membrane-spanning apparatus translocates effector molecules into host cells in a process that is poorly understood but that is known to require the putative ATPase DotB. One possible role for DotB is suggested by its similarity to the PilT family of proteins, which mediate pilus retraction. To better understand the molecular behavior of DotB, we have purified the protein and shown that it forms stable homohexameric rings and hydrolyzes ATP with a specific activity of 6.4 nmol of ATP/min/mg of protein. ATPase activity is critical to the function of DotB, as alteration of the conserved Walker box lysine residue resulted in a mutant protein, DotB K162Q, which failed to bind or hydrolyze ATP and which could not complement a Δ
dotB
strain for intracellular growth in macrophages. Consistent with the ability of DotB to interact with itself, the
dotBK162Q
allele exhibited transdominance over wild-type
dotB
, providing the first example of such a mutation in
L. pneumophila
. Finally, the DotB K162Q mutant protein had a significantly enhanced membrane localization in
L. pneumophila
compared to wild-type DotB, suggesting a relationship between nucleotide binding and membrane association. These results are consistent with a model in which DotB cycles between the cytoplasm and the Dot/Icm complex at the membrane, where it hydrolyzes nucleotides to provide energy to the complex.