bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Frequency and Environment on Fatigue Crack Growth in A286 at 1100 F
Authors: Solomon HD , Coffin LF
Published: March 2009

Previous low-cycle fatigue tests on A286, which covered a frequency range of 5 to 0.1 cpm, have shown a pronounced frequency dependence when the tests were run in air. In contrast, tests run in a vacuum did not show such a frequency effect. This led to the conclusion that, in this frequency range, environmental effects were responsible for the frequency dependence.

Air crack propagation tests have also shown a strong frequency dependence. At frequencies below 0.02 cpm the air crack propagation tests showed a stronger frequency dependence than was observed at higher frequencies and resulted in pure time dependent, cycle independent failure. In order to explain this behavior and to see if it could be observed in low frequency vacuum tests, measurements of the crack propagation rate at 1100 F were made in a 10-8 torr vacuum.

These vacuum crack propagation results substantiated the assertion that at 1100 F, air produces a strong influence on the fatigue life or crack propagation rate. Additionally, these tests have shown that below 0.02 cpm the pure time dependent failure noted in air persisted in a vacuum. The vacuum results could be interpreted on the basis of a linear superposition model, where at low frequencies the behavior was that of a purely time dependent failure; at high frequencies, purely cycle dependent; and at intermediate frequencies, that of a linear superposition of these phenomena. In air this linear superposition model was not applicable because of the additional environmental interaction.
Temperature Dependence of Fatigue Crack Propagation in an Al-2.6Mg Alloy
Authors: Jeglic F , Niessen P , Burns DJ
Published: March 2009

Fatigue crack propagation has been studied in an Al-2.6Mg alloy between room temperature and 300 C. It is shown that the fatigue crack propagation rate is controlled by volume diffusion. The activation barrier for volume diffusion (Q0) is lowered by the applied stress intensity range ΔK so that Q(ΔK) = Q0 - C1 log ΔK. The driving force for the process is inversely proportional to the square of the stress intensity range: A(ΔK) = C2 ΔK-2. Fatigue crack propagation rate as a function of temperature and stress intensity range is given by daDN=C2ΔK-2exp⁡-[Q0-C1log⁡ΔKRT] A special case of this equation is the well-known Paris equation.
Creep-Fatigue Interaction during Crack Growth
Authors: Atanmo PN , McEvily AJ
Published: March 2009

The interaction between creep and fatigue processes has been investigated during crack growth in sheet specimens of the aluminum alloy 5052 at 400 F. Fractographic studies indicate that at high frequencies (1 /30 Hz) the fatigue process of crack advance is dominant, whereas at low frequencies (for example, 60 Hz) the creep process prevails. It was found that at low frequencies and at a low peak stress level (10 ksi) the cyclic process could lead to an increase in the total time to failure as compared to the creep process alone.
Thermal-Mechanical Fatigue Crack Propagation in Nickel- and Cobalt-Base Superalloys Under Various Strain-Temperature Cycles
Authors: Rau CA , Gemma AE , Leverant GR
Published: March 2009

Crack propagation rates under isothermal and thermal fatigue cycling have been determined for a conventionally-cast cobalt-base superalloy, and conventionally-cast and directionally-solidified nickel-base superalloys. Linear elastic fracture mechanics, where the crack growth rates under different strain ranges or for various crack lengths depend only on the strain intensity factor range, was found to be applicable over the range of crack growth rates of most practical importance. A comparison of crack growth rates is made for thermal fatigue under various strain-temperature cycles and isothermal low-cycle fatigue, and the influence of coatings and superimposed creep is discussed.
High-Temperature Fatigue Testing of Automotive Valve Steels
Authors: Vitcha ET
Published: March 2009

The elevated temperature bending fatigue strength of seven automotive exhaust valve alloys has been determined. Inconel 751 shows the highest fatigue strength of 45 ksi at 108 cycles 760 C (1400 F). Coatings in air atmosphere at elevated temperature generally reduced the fatigue strength. In corrosive atmospheres consisting of a simulated lead oxide environment or a carbon monoxide/carbon dioxide atmosphere, no protection was afforded by coatings of aluminum or aluminum chromium. Within the varying surface roughness tested only the as-forged surface representing a high surface roughness and decarburization showed a drop of 24 percent in fatigue strength. Compressively stressed Stellite 6 faced valves showed ten times improvement in thermal fatigue life.
Evaluation of Thermal Fatigue Resistance of Metals Using the Fluidized Bed Technique
Authors: Howes MAH
Published: March 2009

This paper presents details from the experience gained over the last twelve years with the fluidized bed method of thermal fatigue testing. The use of the fluidized bed is discussed, and comparisons are made with other methods of testing as to advantages and disadvantages. The design and construction of a fluidized bed test facility is described and performance characteristics noted. Configurations that have been used are disks, wedges, and “window” specimens. All of these specimens may be notched. Temperature gradients in the specimens may be controlled by bed temperatures, time of exposure, and fluidization conditions. The window specimen has been used to examine thermal fatigue resistance of welds between the same and dissimilar materials. The changes that occur during thermal cycling and the effects of thermal stresses on tempering and aging mechanisms are discussed. Finally, selection and treatment of materials to minimize thermal fatigue are considered.
Thermoacoustic Fatigue Testing Facility for Space Shuttle Thermal Protection System
Authors: Rucker CE , Grandle RE
Published: March 2009

The development of a reusable space shuttle by NASA in the next decade depends in part on the design of a satisfactory thermal protection system (TPS). The booster and orbiter parts of the shuttle require TPS panels which will withstand thermoacoustic fatigue. The Langley Research Center has begun tests on early panel designs in a new acoustic fatigue facility which is capable of simulating the combined elevated temperature and acoustic environments which these panels are expected to experience. The capabilities of the facility and computer system are outlined, and problems encountered in establishing the test methods are discussed. The digital computer system which controls the acoustic and thermal test sequence and which records data from more than 20 transducers is described. Tests of a Haynes 25 TPS panel are described, and representative data from tests of the panel at 650 C are included.
Fatigue in the Design of High-Temperature Alloys
Authors: Merrick HF , Maxwell DH , Gibson RC
Published: March 2009

Nickel-base superalloys are used extensively in modern gas turbine engines and are subjected to a broad range of environmental conditions. At ambient and moderately elevated temperatures improved fatigue resistance can be obtained through refinement of grain size. Thermomechanical working, for example, microduplex processing, offers a means to achieve very fine grain sizes and exceptional fatigue strengths. At high temperatures grain boundaries are a source of weakness. Significant improvements in fatigue resistance can be achieved by the elimination of transverse grain boundaries. High-strain fatigue studies show that deformation occurs by coarse planar slip. Recent developments have enabled a combination of γ and oxide dispersion strengthening to be achieved. This opens possibilities for improved fatigue resistance by promoting slip dispersal. Fatigue resistance is influenced also by environmental factors. The present trend in alloy development is to provide materials having high inherent oxidation and sulfidation resistance.
Creep Testing of Alpha Iron During Thermal Cycling
Authors: Eylon D , Brandon DG , Rosen A
Published: March 2009

The creep properties of alpha iron under thermal cycling conditions were investigated. A special creep testing equipment and creep testing method for nonuniform temperature conditions are described. It was found that creep rates under thermal cycling conditions are lower than the creep rates calculated from results of isothermal creep experiments. The increased creep resistance of alpha iron under thermal cycling conditions was found to be independent of the cycle time but dependent on the dwell time at the high temperature part of the cycle.
Effects of Combined Creep and Fatigue Loading on an Austenitic Stainless Steel at High Temperature
Authors: White WE , Coote RI , Le May I
Published: March 2009

Preliminary data relating to the fatigue life and fracture morphology of an austenitic stainless steel at temperatures of 475 and 745 C are presented. From metallographic examination, fracture at 475 C was seen to be transcrystalline and ductile in nature, while at 745 C it appears that grain boundary cavities formed and subsequently linked up to give a mixed intercrystalline-transcrystalline fracture, the proportion of each depending on the level of the applied stress; fractographic examination supports these observations. Many grain boundary carbides were present on the intercrystalline fracture surfaces formed at 745 C, and the role of these in initiating crack formation is considered worthy of further study.
Effect of Several Metallurgical Variables on the Thermal Fatigue Behavior of Superalloys
Authors: Boone DH , Sullivan CP
Published: March 2009

The effect of several metallurgical variables on the thermal fatigue behavior of high-temperature materials systems was studied using a highly characterized high-velocity hot gas stream to produce a well-defined strain/temperature/time cycle. Metallurgical factors considered were: alloy compositions in both cast cobalt- and nickel-base superalloys, degree of microstructural refinement, grain orientation, effect of presence and morphology of carbides, surface/environmental interaction (surface stability), and protective coatings. The nickel-base alloys studied were superior or equivalent to the cobalt-base alloys when compared on uncoated and coated bases. Within a given alloy class the effect of alloy chemistry as it affects oxidation behavior was shown to be significant. On polycrystalline substrates, an inward type of diffusion aluminide coating improved fatigue performance, whereas an outward type was detrimental. “Overlay” coatings show a great deal of potential in providing an optimum in mechanical/protective response. Columnar-grained alloys when strained along the growth direction gave fatigue resistance superior to their polycrystalline counterparts. The importance of recognizing the unique compositional/microstructural/mechanical nature of a coating in achieving optimum thermal fatigue resistance for high-temperature materials systems is emphasized.
Low-Cycle Fatigue Behavior of Zircaloy at 573 K
Authors: Hosbons RR
Published: March 2009

The 573 K low-cycle fatigue behavior of Zircaloy-2 in various metallurgical states has been studied. Reduction in area as measured in tension tests was found to be a good parameter in determining fatigue life. Holdtimes in tension of 1 h or less did not affect the fatigue life but one of 5 h reduced it. An atmosphere containing iodine reduces the fatigue life under the conditions tested by 40 percent.
Effect of Interrupting Fatigue by Periods of Heat for Aluminum Alloy Structural Elements
Authors: Heath-Smith JR , Kiddle FE
Published: March 2009

Effects of heat on fatigue have been studied by interrupting fatigue tests at ambient temperature by single periods of heating with and without steady load applied. The tests employed constant amplitude and random loading on various structural elements in a number of aluminium-copper alloy materials. Heating was applied at temperatures in the range 100 to 150 C for times ranging from 1 h to 20 000 h.

The initiation of fatigue cracks was affected by heating, particularly at temperatures above 110 C when the effects occurred comparatively rapidly. The two mechanisms of importance were changes in microstructure at the machined surface which encouraged initiation, and changes in residual stress by creep which encouraged or discouraged initiation according to the creep being compressive or tensile.

It is suggested that similar mechanisms operate also during the crack propagation phase of the fatigue life.
Effect of Surface Integrity on Fatigue of Structural Alloys at Elevated Temperatures
Authors: Prevey PS , Koster WP
Published: March 2009

Surface integrity is a subject covering the description and control of the many possible alterations produced in the surface of a component during manufacturing. Surface integrity is evaluated by measuring the influence of machined surface layers on component reliability. This is accomplished primarily through fatigue testing under both low-cycle and high-cycle conditions. Considerable data have been developed permitting definition of characteristic changes in fatigue strength of a variety of high-strength structural alloys as a function of several different metal removal methods and also variations within these methods.

High-cycle fatigue data have been developed in the cantilever bending mode at temperatures ranging from ambient to 1400 F. Low-cycle fatigue data have been obtained in four-point bending over the same temperature range following the development of a specialized testing technique.

Data are presented showing fatigue behavior of Inconel 718, René 80, and René 95 using specimens finished by variations of grinding, turning, electrochemical machining, and electrical discharge machining.
Comparison of Experimental and Theoretical Thermal Fatigue Lives for Five Nickel-Base Alloys
Authors: Spera DA
Published: March 2009

Alloys investigated were Nimonic 90, IN 100, coated IN 100, B 1900, coated B 1900, MAR M200, and MAR M200DS (directionally solidified). Maximum temperatures ranged from 770 to 1120 C (1420 to 2050 F). Specimen geometries included tapered disks, double-edged wedges, and cambered airfoils. The disks and wedges were heated and cooled in fluidized beds. The airfoil specimens were heated by a Mach 1 natural gas burner and rapid-air cooled, with and without spanwise loading. Life calculations included two distinct failure modes: conventional low-cycle fatigue and cyclic creep. Required material properties were limited to conventional thermal, tensile, and creep-rupture data. The complete life calculation system included the calculation of transient temperature distributions, thermal strains, stresses, creep damage, fatigue damage, and finally cycles to first crack. Calculated lives were within a factor of two for 76 of the 86 data points analyzed. Cyclic creep accounted for 80 per cent of all the calculated damage.
Temperature Effects on the Strainrange Partitioning Approach for Creep Fatigue Analysis
Authors: Halford GR , Hirschberg MH , Manson SS
Published: March 2009

Examination is made of the influence of temperature on the strain-range partitioning approach to creep fatigue. Results for 2¼Cr-1Mo steel and Type 316 stainless steel show the four partitioned strainrange-life relationships to be temperature insensitive to within a factor of two on cyclic life. Monotonic creep and tensile ductilities were also found to be temperature insensitive to within a factor of two.

The approach provides bounds of cyclic life that can be readily established for any type of inelastic strain cycle. Continuous strain cycling results obtained over a broad range of high temperatures and frequencies are in excellent agreement with bounds provided by the approach.
Method for Low-Cycle Fatigue Design Including Biaxial Stress and Notch Effects
Authors: Gonyea DC
Published: March 2009

A design procedure for predicting low-cycle fatigue cracking is developed that is applicable for most mechanical and thermal cycling problems. Included in the procedure are effects due to stress risers and biaxial stress fields. Use is made of the uniaxial low-cycle fatigue curve and the “cyclic ”stress-strain curve, both obtained from standard low-cycle fatigue testing. Major aspects of the analysis include an effective strain parameter which is employed as the cracking criterion and the use of Neuber's equation to estimate stress concentration effects. To illustrate the use and validity of the procedure, data from mechanically and thermally cycled grooved cylinders are presented and compare well with predictions.
The Challenge to Unify Treatment of High Temperature Fatigue—A Partisan Proposal Based on Strainrange Partitioning
Authors: Manson SS
Published: March 2009

This paper was presented as an overview lecture summarizing the 1972 International Symposium on Fatigue at Elevated Temperatures held at Storrs, Conn. Starting with the observation of the diversity of subjects covered and lack of unanimity of approaches used, it becomes clear that there exists an urgent need for a unifying framework around which the many facets can be coherently structured. It is proposed that the strainrange partitioning concept has the potential of serving as such a framework. The method divides the imposed strain into four basic ranges involving time-dependent and time-independent components. It is shown that some of the results presented at the symposium can be better correlated on the basis of this concept than by alternative methods. It is also suggested that methods of data generation and analysis can be helpfully guided by this approach. Potential applicability of the concept to the treatment of frequency and holdtime effects, environmental influence, crack initiation and growth, thermal fatigue, and code specifications are then considered briefly. A required experimental program is outlined.
Summary and Analysis of the Attributes of Methods of Surface Texture Measurement
Authors: Rose JG , Hutchinson JW , Galloway BM
Published: March 2009

It is well established among researchers in the pavement friction area that type of surface texture greatly influences the friction properties of pavement surfaces. Although it is recognized that other factors not necessarily related to surface texture also affect surface friction, various agencies in this country and abroad are engaged in developing methods for measuring pavement surface texture. Some 20-odd extant methods are currently used. The relative attributes of many of these methods are questioned, since results of tests using these methods have not, on the whole, produced consistent or reproducible quantitative results.

Succinct descriptions of all currently known methods of surface texture measurement are presented. Studies which have related surface texture to pavement skid resistance obtained by skid test devices are reported; many reported methods of texture measurement have apparently never been subjected to correlation study.

The need for a standard method of test which will provide a valid assessment of a pavement surface texture and thereby improve communication of surface characteristics is emphasized. Current efforts toward establishment of such standardization are reviewed.
Pros and Cons of Biodegradation
Authors: Patterson WA
Published: March 2009

Durability in plastics has been a cherished research objective. For those plastics, however, which may end up in litter or in landfills, durability is now considered by some as undesirable. One result has been plastics which will disintegrate when exposed to ultraviolet light with ultimate biodegradation postulated. This paper questions the principles on which this development is based and concludes that it will not solve any environmental problems, and it is not a conservation measure.
Pressures on Building Facades: Wind and Temperature
Authors: Robertson LE
Published: March 2009

While field measurements of pressures on real buildings have been accomplished, such measurements are both expensive and time consuming. Predictions of facade pressures for specific buildings can be made during the design process by testing a scale model of the building in a boundary layer wind tunnel and by combining the wind tunnel data with environmental data dealing with wind speed and air temperature. These wind and temperature data are then used in conjunction with known or assumed permeabilities of the exterior wall and of building interiors so as to determine internal pressures from stack-effect. From the difference between external pressures and internal pressures the net steady-state pressure is then determined and added to the fluctuating component of wind pressures to determine the total pressure to be resisted by the facade.
Design Considerations
Authors: Koppes WF
Published: March 2009

Many matters must be considered in the design of windows and curtain walls, but those of concern here are the design considerations affecting performance. Both windows and walls have the same basic function of contributing to the control of the interior environment, and serving, in effect, as a filtering system.

The two major design considerations applying to both windows and walls are structural integrity and weathertightness. In the design of curtain walls a third major consideration is ample provision for movement. Structurally, wind loading is the chief concern, and the need for stiffness, rather than strength, usually governs. Both weathertightness and provision for movement are largely dependent on proper joint design.

Other important design considerations affecting performance are moisture control, thermal insulation, control of sound transmission, and firestopping. As compared with the frequent evaluation of structural integrity and weathertightness by specially developed test methods, these characteristics, however, have only rarely been tested.
Test Methods for Hardware Used on Windows and Walls
Authors: Muessel DC
Published: March 2009

Proper window hardware does affect the overall performance of a wall or window system. Improper hardware selection allows or can cause air and water leakage or other catastrophic failures. Various performance tests for window hardware are summarized in this paper.
Use and Application of Tests
Authors: Sakhnovsky AA
Published: March 2009

The use of laboratory tests for quality control and certification of curtain walls and windows is discussed. Detailed shop drawings for the test specimen are as important as the test results. Problems with testing, the use of laboratory tests by government agencies, and field testing are also discussed.
Fatigue at Elevated Temperatures
Authors: Carden AE , McEvily AJ , Wells CH
Published: March 2009

Description

One the most complete books of its type ever published, this book contains 60 papers dealing with the mechanism of fatigue, test methods, materials, thermal ratcheting, and lifetime prediction and design.
Viscosity Testing of Asphalt and Experience with Viscosity Graded Specifications
Authors: Gunderman WG
Published: March 2009

Description

The Symposium on Viscosity Testing of Asphalt and Experience with Viscosity Graded Specifications was presented at the Seventy-fifth Annual Meeting of the American Society for Testing and Materials held in Los Angeles, Calif., 25—30 June 1972. Committee D04 on Road and Paving Materials sponsored the symposium. W. G. Gunderman, Highway Research Board, National Academy of Sciences, presided as symposium chairman.
Cryogens and Gases: Testing Methods and Standards Development
Authors: Vance RW
Published: March 2009

Description

The Symposium on Cryogens and Gases: Testing Methods and Standards Development was given at the Seventy-fifth Annual Meeting of the American Society for Testing and Materials held in Los Angeles, Calif., 25–30 June 1972. Committee F07 on Aerospace Industry Methods sponsored the symposium. R. W. Vance, Cryogenic Society of America, served as symposium chairman, and M. C. Miyaji, General Dynamics, was co-chairman. R. E. Biever, Cryogenic Distributors, presided at the two sessions.
Analytical Methods Developed for Application to Lunar Samples Analyses
Authors: Flory DA
Published: March 2009

Description

The symposium on Analytical Methods Developed for Application to Lunar Samples Analyses was given at the Seventy-fifth Annual Meeting of the American Society for Testing and Materials held in Los Angeles, Calif., 25—30 June 1972. Committee F07 on Aerospace Industry Methods sponsored the symposium. D. A. Flory, University of Houston, presided as symposium chairman.
Window and Wall Testing
Authors: Rosen HJ
Published: March 2009

Description

High rise structures with extensive use of glass present architectural problems discussed in seven extensive papers.
Estimating the Hazard of Chemical Substances to Aquatic Life
Authors: Cairns J , Dickson KL , Maki AW
Published: March 2009

Description

With the signing of the Toxic Substances Control Act in 1976, this timely publication will assist anyone involved in the assessment of hazards chemicals to pose to aquatic life-whether from industry government, or academia. Topics covered include toxicological effects, environmental concentration, environmental fate, hazard assessment and evaluation of proposed test procedures for estimating hazards to aquatic life.
Empirical Support for an Evolutionary Model of Self‐Destructive Motivation
Authors: Brown R. Michael , Brown Stephanie L. , Johnson Aron , Olsen Berit , Melver Kristen , Sullivan Mark
Published: March 2009

We tested predictions generated from an evolutionary account of self‐destructive motivation in two survey studies of 18–24‐year‐old university students. As hypothesized, hierarchical regressions showed that the positive relationship between perceived burden to family and suicide ideation was amplified for participants with low measured health and romantic relationship satisfaction, and for participants with relatively young mothers. The moderating effect of maternal age was also observed in logistic regressions of suicide attempts. These effects occurred independently of depression, hopelessness, and other relevant extraneous variables. Results have implications for understanding self‐destructive motivation, assessing suicide risk, and preventing suicidal thinking and behavior.
Epidemiologic Characteristics and Trends of Fatal Suicides among the Elderly in Taiwan
Authors: Liu Hui‐Li
Published: March 2009

Taiwan has one of the highest suicide rates in the world, especially among its elderly. The epidemiologic characteristics and trends of the surging elderly suicide rates from 1993 to 2003 are described, with a special emphasis on the risk groups, the methods used in suicide, and their geographical variations. Data on annual mortality for persons over 65 years of age with external cause‐of‐death codes E950–E959 were obtained from the Death Certification data file provided by the Department of Health and used in the analysis. The suicide rate for each 5‐year age group over 65 years old increased during the 11‐year period. Elderly males had the highest suicide rate and experienced an increased rate of 49% during the decade. The average suicide ratio between elderly males and females was about 2:1. Never‐married males had the highest age‐adjusted as well as sex‐ and marital status‐specific suicide rates, and showed an increased rate of 66% over the 11‐year period. Geographical variations in suicide rates were significant, with the lest urbanized eastern Taiwan having a higher rate than other regions. Hanging, strangulation, and suffocation were the most used methods for committing suicide by the elderly, but their use had decreased from 63% to 54% during the decade; but jumping off a building and drowning increased significantly. Variation in suicide rate among months was not significant. With the increase in the elderly suicide rate, more governmental and societal interventions are needed to alleviate this social and human problem.
Correlates of Serious Suicidal Ideation and Attempts in Female Adult Sexual Assault Survivors
Authors: Ullman Sarah E. , Najdowski Cynthia J.
Published: March 2009

Relations between (a) serious suicidal ideation and attempts and (b) demographics, trauma history, assault characteristics, post‐assault outcomes, and psy‐chosocial variables were examined among female adult sexual assault survivors. Younger, minority, and bisexual survivors reported greater ideation. More traumas, drug use, and assault disclosure related to greater attempts, whereas perceived control over recovery was related to fewer attempts. Child sexual abuse and some assault characteristics predicted suicidal behavior. Depression was related to suicidal behavior until psychosocial variables were accounted for. Specifically, using substances to cope and self‐blame predicted greater ideation, whereas receiving aid/information support was related to less ideation. Implications for research and treatment are discussed.
The Role of Body Image and Disordered Eating as Risk Factors for Depression and Suicidal Ideation in Adolescents
Authors: Brausch Amy M. , Gutierrez Peter M.
Published: March 2009

There is much empirical literature on factors for adolescent suicide risk, but body image and disordered eating are rarely included in these models. In the current study, disordered eating and body image were examined as risk factors for suicide ideation since these factors are prevalent in adolescence, particularly for females. It was hypothesized that disordered eating and body image, in addition to depressive symptoms, would contribute to suicide ideation. It was also hypothesized that these relationships would be stronger for females than for males. Structural equation modeling was used to test a model of risk for suicide ideation incorporating the above factors in a sample of 392 high school students. Results indicated that disordered eating contributed to both suicide ideation and depressive symptoms, while body image only contributed to depressive symptoms. Depressive symptoms contributed to suicide ideation. The model was found to be cross‐validated with males and females, and no gender differences emerged. Implications of these findings and their importance in constructing future models of adolescent suicide risk are discussed.
Linkage Analysis Reveals the Independent Origin of Poeciliid Sex Chromosomes and a Case of Atypical Sex Inheritance in the Guppy (Poecilia reticulata)
Authors: Tripathi Namita , Hoffmann Margarete , Weigel Detlef , Dreyer Christine
Published: March 2009

Among different teleost fish species, diverse sex-determining mechanisms exist, including environmental and genetic sex determination, yet chromosomal sex determination with male heterogamety (XY) prevails. Different pairs of autosomes have evolved as sex chromosomes among species in the same genus without evidence for a master sex-determining locus being identical. Models for evolution of Y chromosomes predict that male-advantageous genes become linked to a sex-determining locus and suppressed recombination ensures their co-inheritance. In the guppy, Poecilia reticulata, a set of genes responsible for adult male ornaments are linked to the sex-determining locus on the incipient Y chromosome. We have identified >60 sex-linked molecular markers to generate a detailed map for the sex linkage group of the guppy and compared it with the syntenic autosome 12 of medaka. We mapped the sex-determining locus to the distal end of the sex chromosome. We report a sex-biased distribution of recombination events in female and male meiosis on sex chromosomes. In one mapping cross, we observed sex ratio and male phenotype deviations and propose an atypical mode of genetic sex inheritance as its basis.
Nucleotide Polymorphism and Within-Gene Recombination in Daphnia magna and D. pulex, Two Cyclical Parthenogens
Authors: Haag Christoph R , McTaggart Seanna J , Didier Anaïs , Little Tom J , Charlesworth Deborah
Published: March 2009

Theory predicts that partially asexual organisms may make the “best of both worlds”: for the most part, they avoid the costs of sexual reproduction, while still benefiting from an enhanced efficiency of selection compared to obligately asexual organisms. There is, however, little empirical data on partially asexual organisms to test this prediction. Here we examine patterns of nucleotide diversity at eight nuclear loci in continentwide samples of two species of cyclically parthenogenetic Daphnia to assess the effect of partial asexual reproduction on effective population size and amount of recombination. Both species have high nucleotide diversities and show abundant evidence for recombination, yielding large estimates of effective population sizes (300,000–600,000). This suggests that selection will act efficiently even on mutations with small selection coefficients. Divergence between the two species is less than one-tenth of previous estimates, which were derived using a mitochondrial molecular clock. As the two species investigated are among the most distantly related species of the genus, this suggests that the genus Daphnia may be considerably younger than previously thought. Daphnia has recently received increased attention because it is being developed as a model organism for ecological and evolutionary genomics. Our results confirm the attractiveness of Daphnia as a model organism, because the high nucleotide diversity and low linkage disequilibrium suggest that fine-scale mapping of genes affecting phenotypes through association studies should be feasible.
Examining Interpopulation Variation in Bluegill Growth Rates and Size Structure: Effects of Harvest, Maturation, and Environmental Variables
Authors: Hoxmeier R. John H. , Aday D. Derek , Wahl David H.
Published: March 2009

Understanding how life history variation and the environment affect growth and population size structure is an important theme of fisheries ecology. However, the interactions among important biotic and abiotic factors and their relative importance in the context of population‐specific variation are seldom considered. We used an information theoretic approach to investigate how environmental variables interact with important life history parameters to influence population size structure of bluegills Lepomis macrochirus. We sampled bluegill populations in 23 Illinois reservoirs to examine the effects of temperature, water transparency, and prey availability and bluegill density, harvest, and size at maturation on bluegill growth and population size structure. Good growth and large body size were associated with warm, clear lakes containing abundant prey resources. An exception to this pattern was early growth (length at age 2): Larger body size at age 2 was associated with relatively low Secchi depth (i.e., turbid water). In addition, size at maturation was positively related to size of adult male bluegills. Interestingly, bluegill density and harvest mortality—factors that are often considered important within populations—did not contribute much explanatory power to our among‐system models. Whereas harvest and density‐dependent growth have been shown to influence individual bluegill populations, their effects across a range of populations appear to be mitigated by temperature, water transparency, and prey availability. Although growth of individuals can be influenced by a variety of factors, our investigation suggests that fairly straightforward mechanisms at broader spatial scales are responsible for explaining variation among populations.
THM-coupled finite element analysis of frozen soil: formulation and application
Authors: Nishimura S. , Gens A. , Olivella S. , Jardine R. J.
Published: March 2009

A fully coupled thermo-hydro-mechanical (THM) finite element (FE) formulation is presented that considers freezing and thawing in water-saturated soils. The formulation considers each thermal, hydraulic and mechanical process, and their various interactions, through fundamental physical laws and models. By employing a combination of ice pressure, liquid pressure and total stress as state variables, a new mechanical model has been developed that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. Important frozen soil features such as temperature and porosity dependence of shear strength are captured inherently by the model. Potential applications to geotechnics include analysis of frost heave, foundation stability or mass movements in cold regions. The model's performance is demonstrated with reference to the in situ pipeline frost heave tests conducted by Slusarchuk et al. Detailed consideration is given to FE mesh design, the influence of hydraulic parameters, and the treatment of air/ground interface boundary conditions. The THM simulation is shown to reproduce, with fair accuracy, the observed pipeline heave and the porosity growth driven by water migration.
Ground energy systems: from analysis to geotechnical design
Authors: Preene M. , Powrie W.
Published: March 2009

Ground energy systems use the ground and groundwater beneath a site as a heat source or sink to reduce energy costs and improve the environmental performance of buildings. The design and performance of the ground element of these systems (boreholes and ground loops) are dominant factors in the capital and operating costs of the system, yet, at present, such systems are often specified with little geotechnical input. This paper reviews some of the existing design approaches from a geotechnical perspective, and identifies potential failure modes (short term, long term and regulatory related) for ground energy systems. Short-term failures may result from deficiencies in the capacity of the infrastructure forming the ground element and/or from poor connection between the infrastructure and the ground. Long-term failures may derive from misestimation of loads and/or ground parameters. Possible future directions in the design of ground energy systems are discussed, and the need for informed geotechnical input to ground energy system design is highlighted.
Can web crawlers revolutionize ecological monitoring?
Authors: Galaz Victor , Crona Beatrice , Daw Tim , Bodin Örjan , Nyström Magnus , Olsson Per
Published: March 2009

Despite recent advances, ecosystem service monitoring is limited by insufficient data, the complexity of social–ecological systems, and poor integration of information that tracks changes in ecosystems and economic activities. However, new information and communication technologies are revolutionizing the generation of, and access to, such data. Can researchers who are interested in ecological monitoring tap into these increased flows of information by “mining” the internet to detect “early‐warning” signs that may signal abrupt ecological changes? Here, we explore the possibility of using web crawlers and internet‐based information to complement conventional ecological monitoring, with a special emphasis on the prospects for avoiding “late warnings”– that is, when ecosystems have already shifted to less desirable states. Using examples from coral reef ecosystems, we explore the untapped potential, as well as the limitations, of relying on web‐based information to monitor ecosystem services and forewarn us of negative ecological shifts.
Death Anxiety: An Analysis of an Evolving Concept
Authors: Lehto Rebecca Helen , Stein Karen Farchaus
Published: March 2009

This article identifies defining attributes, antecedents, and consequences of the concept of death anxiety using Rodgers (2000) evolutionary method of concept analysis. The literature on death anxiety was systematically reviewed for the years 1980–2007. Articles were summarized and coded. Inductive data analyses resulted in defining attributes (emotion, cognitive, experiential, developmental, sociocultural shaping, and source of motivation), antecedents (stressful environments and the experience of unpredictable circumstances, diagnosis of a life-threatening illness or the experience of a life-threatening event, and experiences with death and dying), and consequences (adaptive and maladaptive presentations). Results are important because little systematic inquiry of death anxiety exists in nursing literature.
Burial Sites, Informal Rights and Lost Kingdoms: Contesting Land Claims in Mpumalanga, South Africa
Authors: James Deborah
Published: March 2009

In the new South Africa, the promise of land restitution raised millennial-style expectations amongst dispossessed and dispersed former landholders. Partly prompted by emerging policy discourses, iconic tropes of localized cultural experience such as grave sites, initiation lodges and cattle byres acquired new significance. Because they proved what the Land Claims Commission calls ‘informal rights’ to land, they became verifiable evidence of effective possession, and thus grounds on which to claim the restoration of such land. The meaning of land, the nature of ownership and the legitimacy of its restoration were all matters contested between claimants, policy makers and human rights lawyers. They were also contested by those at different levels in the hierarchical social order of the new South Africa. Members of the African nationalist political elite, in dialogue with lawyers, cherished one set of understandings, while ordinary migrant/country-dwellers tended to hold to another. Both, however, were mediated through the new discourse on informal rights. It is neither purely through the activities of cosmopolitan elites with their ‘political demand for land’ nor through the unmediated localist experience of less sophisticated country-dwellers with more practical orientations that the significance of land becomes evident, but in the interaction between the two. Based on local understandings, transformed in the course of thirty years of ‘land back’ struggles, and finally negotiated over the course of the last ten years, a new diasporic consensus on what ‘the land’ signifies has been established.
Recombinant Ov-ASP-1, a Th1-Biased Protein Adjuvant Derived from the Helminth Onchocerca volvulus, Can Directly Bind and Activate Antigen-Presenting Cells
Authors: He Yuxian , Barker Sophie J. , MacDonald Angus J. , Yu Yu , Cao Long , Li Jingjing , Parhar Ranjit , Heck Susanne , Hartmann Susanne , Golenbock Douglas T. , Jiang Shibo , Libri Nathan A. , Semper Amanda E. , Rosenberg William M. , Lustigman Sara
Published: March 2009

We previously reported that rOv-ASP-1, a recombinant Onchocerca volvulus activation associated protein-1, was a potent adjuvant for recombinant protein or synthetic peptide-based Ags. In this study, we further evaluated the adjuvanticity of rOv-ASP-1 and explored its mechanism of action. Consistently, recombinant full-length spike protein of SARS-CoV or its receptor-binding domain in the presence of rOv-ASP-1 could effectively induce a mixed but Th1-skewed immune response in immunized mice. It appears that rOv-ASP-1 primarily bound to the APCs among human PBMCs and triggered Th1-biased proinflammatory cytokine production probably via the activation of monocyte-derived dendritic cells and the TLR, TLR2, and TLR4, thus suggesting that rOv-ASP-1 is a novel potent innate adjuvant.
Ncf1 Provides a Reactive Oxygen Species-Independent Negative Feedback Regulation of TLR9-Induced IL-12p70 in Murine Dendritic Cells
Authors: Richter Cornelia , Juan Martina Herrero San , Will Jutta , Brandes Ralf P. , Kalinke Ulrich , Akira Shizuo , Pfeilschifter Josef M. , Hultqvist Malin , Holmdahl Rikard , Radeke Heinfried H.
Published: March 2009

Permanent exposure to pathogens requires decisions toward tolerance or immunity as a prime task of dendritic cells. The molecular mechanisms preventing uncontrolled immune responses are not completely clear. We investigated the regulatory function of Ncf1, an organizing protein of NADPH oxidase, in the signaling cascade of Toll-like receptors. TLR9-stimulated spleen cells from both Ncf1-deficient and B10.Q mice with a point mutation in exon 8 of Ncf1 exhibited increased IL-12p70 secretion compared with controls. This finding was restricted to stimulatory CpG2216 and not induced by CpG2088. Because only CpG/TLR9-induced IL-12p70 was regulated by Ncf1, we used TRIF−/− and MyD88−/− cells to show that TLR9/MyD88 was primarily affected. Interestingly, additional experiments revealed that spleen cells from NOX2/gp91phox-deficient mice and the blocking of electron transfer by diphenylene iodonium had no influence on CpG-induced IL-12p70, confirming an NADPH oxidase-independent function of Ncf1. Finally, proving the in vivo relevance CpG adjuvant-guided OVA immunization resulted in a strong augmentation of IL-12p70-dependent Th1 IFN-γ response only in Ncf1-deficient mice. These data suggest for the first time an important role for Ncf1 in the fine tuning of the TLR9/MyD88 pathway in vitro and in vivo that is independent of its role as an activator of NOX2.
The Receptor for Advanced Glycation End Products Impairs Host Defense in Pneumococcal Pneumonia
Authors: van Zoelen Marieke A. D. , Schouten Marcel , de Vos Alex F. , Florquin Sandrine , Meijers Joost C. M. , Nawroth Peter P. , Bierhaus Angelika , van der Poll Tom
Published: March 2009

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia. The receptor for advanced glycation end products (RAGE) is a multiligand receptor that is expressed ubiquitously in the lungs. Engagement of RAGE leads to activation of multiple intracellular signaling pathways, including NF-κB and subsequent transcription of several proinflammatory mediators. To determine the role of RAGE in the innate immune response to S. pneumoniae pneumonia, RAGE-deficient (RAGE−/−) and wild-type mice were intranasally inoculated with S. pneumoniae. S. pneumoniae pneumonia resulted in an up-regulation of constitutively present RAGE expression in lung tissue, especially in the interalveolar septae. RAGE−/− mice showed an improved survival, which was accompanied by a lower bacterial load in the lungs at 16 h and a decreased dissemination of the bacteria to blood and spleen at 16 and 48 h after inoculation. RAGE−/− macrophages showed an improved killing capacity of S. pneumoniae in vitro. Lung inflammation was attenuated in RAGE−/− mice at 48 h after inoculation, as indicated by histopathology and cytokine/chemokine levels. Neutrophil migration to the lungs was mitigated in the RAGE−/− mice. In addition, in RAGE−/− mice, activation of coagulation was diminished. Additional studies examining the effect of RAGE deficiency on the early (6-h) inflammatory response to S. pneumoniae did not reveal an early accelerated or enhanced immune response. These data suggest that RAGE plays a detrimental role in the host response to S. pneumoniae pneumonia by facilitating the bacterial growth and dissemination and concurrently enhancing the pulmonary inflammatory and procoagulant response.
Reduced c-myc Expression Levels Limit Follicular Mature B Cell Cycling in Response to TLR Signals
Authors: Meyer-Bahlburg Almut , Bandaranayake Ashok D. , Andrews Sarah F. , Rawlings David J.
Published: March 2009

The splenic B cell compartment is comprised of two major, functionally distinct, mature B cell subsets, i.e., follicular mature (FM) and marginal zone (MZ) B cells. Whereas MZ B cells exhibit a robust proliferative response following stimulation with the TLR4 ligand LPS, FM B cells display markedly delayed and reduced levels of proliferation to the identical stimulus. The current study was designed to identify a potential mechanism(s) accounting for this differential responsiveness. In contrast to the delay in cell cycle entry, FM and MZ B cells exhibited nearly identical LPS-driven alterations in the expression level of cell surface activation markers. Furthermore, both the NF-κB and mTOR signaling cascades were similarly activated by LPS stimulation in FM vs MZ B cells, while inducible activation of ERK and AKT were nearly absent in both subsets. MZ B cells, however, exhibited higher basal levels of phospho-AKT and pS6, consistent with a preactivated status. Importantly, both basal and LPS activation-induced c-myc expression was markedly reduced in FM vs MZ B cells and enforced c-myc expression fully restored the defective proliferative response in FM B cells. These data support a model wherein TLR responses in FM B cells are tightly regulated by limiting c-myc levels, thereby providing an important checkpoint to control nonspecific FM B cell activation in the absence of cognate Ag.