bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Applied Potential on Environment-Assisted Cracking of Zirconium Alloys
Authors: Roy Ajit K. , Valliyil Unnikrishnan , Govindaraj Elumalai
Published: September 2009

Zircaloy-2 and Zircaloy-4 have been tested by the slow-strain-rate technique at ambient and elevated temperatures in an acidic environment relevant to the proposed geologic repository at the Yucca Mountain site. Tests were performed with and without cathodic and anodic applied potentials. The results of stress corrosion cracking testing without applied potentials indicate that the ductility of both alloys was enhanced in terms of percent elongation, percent reduction in area, failure strain, and the time-to-failure with increasing temperature indicating improved ductility. However, the magnitude of true failure stress was gradually reduced at higher testing temperatures. The application of anodic and cathodic controlled potentials during slow-strain-rate testing enhanced the cracking susceptibility of both alloys showing more pronounced effect at anodic applied potentials. The corrosion potential for both alloys, became more active at the elevated temperature. The morphology of failure at cathodic potentials was ductile, showing dimpled microstructure. However, transgranular brittle failure was observed with both alloys at anodic controlled potentials.
Asymptotic Stress Fields for Thermomechanically Loaded Cracks in FGMs
Authors: Jain Nitesh , Chona Ravinder , Shukla Arun
Published: September 2009

The problem of a stationary crack in functionally graded materials (FGM), subjected to a combination of thermal and mechanical loading is considered. An asymptotic analysis coupled with Westergaard's stress function approach is used to characterize the stress field around the crack tip. Thermal and mechanical properties (e.g., elastic modulus, coefficient of thermal expansion, and thermal conductivity) are assumed to vary exponentially. The crack is assumed to be inclined to the direction of the property gradation. The thermal loading is taken to be a uniform heat flow in a direction inclined to the crack. The principal of superposition from linear elasticity is used to solve the problem, whereby the problem is divided into a number of subproblems. The first four terms in the expansion of the stress field are derived to explicitly bring out the influence of nonhomogeneity on the structure of the stress field. It is observed that the presence of heat flow produced no additional singularity and hence the classical inverse square root singularity still prevails around the crack tip. Using these stress field contours of constant maximum shear stress are generated and the effect of thermal loading on the crack-tip stress field is discussed.
An Experimental and Numerical Study of the Fracture Strength of Welded Structural Hollow Section X-Joints
Authors: Björk Timo , Marquis Gary , Pellikka Veli , Ilvonen Reijo
Published: September 2009

The effect of the geometry and material properties on the fracture strength of welded X-joints fabricated from structural hollow section (SHS) profiles has been studied experimentally and by using nonlinear finite element analysis (FEA). The current paper focuses on four joints tested at -40°C. This was one part of an extensive series of laboratory experiments performed at temperatures +20°Cï -60°C. At sub-zero temperatures the primary fracture mode was mainly ductile followed by final brittle failure. The radius and material properties in the corner area of a SHS are dependent on the fabrication method of the SHS. In cold-formed sections the corner radius is typically large and the yield strength is greater than the nominal yield strength of the base material. This bigger corner radius can provide different stiffness and load carrying capacity as compared to joints fabricated from hot-formed sections. Numerical simulation and experimental tests focused on the importance of this corner effect and the separate role geometry, yield strength, and fracture toughness on the total fracture strength of the joint.
Constraint Corrected J-R- Curve and its Application to Fracture Assessment for X80 Pipelines
Authors: Zhu Xian-Kui , Leis Brian N.
Published: September 2009

Single specimen J-R curve testing for X80 pipeline steel was conducted using single edge notched bend (SENB) and single edge notched tension (SENT) specimens with various crack lengths. Test data indicate that the J-R curves for this steel are strongly constraint dependent. To facilitate transferability of experimental J-R curves to those for actual cracked components, this paper develops a constraint corrected J-R curve for X80 steel. A modified J-Q theory that can consider the global bending stress influence is proposed so as to correctly quantify constraint effect on the crack-tip fields and the J-R curves. Results show that the modified J-Q solution can well match numerical crack-tip fields for bending specimens, with Q being a load-independent constraint parameter under large scale yielding. Based on the experimental data and numerical analysis, a constraint corrected J-R curve is formulated as a function of the parameter Q and crack extension ▵a for X80 steel. A general procedure to predict J-R curves for actual cracked components is then outlined.Comparison indicates that the predicted J-R curves developed in this paper agree well with the experimental data for both SENB and SENT specimens. To demonstrate its application in failure assessment, the constraint corrected J-R curve for X80 steel is used to determine failure loads for a surface cracked pipeline. Reasonable agreement to available analytic solution is achieved.
Use of Miniaturized Compact Tension Specimens for Fracture Toughness Measurements in the Upper Shelf Regime
Authors: Lucon Enrico , Scibetta Marc , Chaouadi Rachid , Walle Eric van
Published: September 2009

In the nuclear field, the importance of direct fracture toughness measurements on reactor pressure vessel (RPV) materials has been nowadays widely recognized, as opposed to Charpy-based estimations. However, sample dimensions have to be kept small in order to optimize the use of available material (often in the form of previously broken Charpy specimens) or, in the case of new irradiations, make effective use of the limited space available inside irradiation facilities. One of the most appealing geometries for fracture toughness measurements is the miniature Compact Tension specimen, MC(T), which has the following dimensions: B = 4.15 mm, W = 8.3 mm, cross section 10 x 10 mm2. Four MC(T) specimens can be machined out of a broken half Charpy, and in the case of irradiation ten MC(T) samples occupy approximately the same volume as a full-size Charpy specimen. A comprehensive investigation is presented in this paper, aimed at assessing the applicability of MC(T) specimens to measure fracture toughness in fully ductile (upper shelf) conditions. In this study, 18 1TC(T) and 20 MC(T) specimens have been tested at different temperatures from three RPV steels and one low-alloy C-Mn steel. The results obtained clearly show that MC(T) samples exhibit lower fracture toughness properties, both in terms of initiation of ductile tearing (according to various test standards) and resistance to ductile crack propagation (J-R curve). The reduction of tearing resistance might be attributed to work hardening prevailing over loss of constraint in the uncracked ligament for a side-grooved specimen, or to the inadequacy of J-integral to represent ductile crack extension in very small specimens. Both arguments need to be verified with further investigations.
Application of the Reference Temperature to the Evaluation of Cleavage Fracture in HSLA-100 Steel
Authors: Graham Stephen M. , Mercier Gerard P. , L'Heureux Brian P.
Published: September 2009

The purpose of this study was to evaluate the fracture behavior of HSLA-100 steel at a temperature of -40°C (-40°F). Tests were conducted on three different compositions and two orientations of HSLA-100. HY-100 was also tested to provide a baseline for comparison. Various fracture-related tests were conducted, including traditional test methods, such as the Charpy V-notch and the Dynamic Tear, and more recent methods, such as ductile crack growth initiation (Jic) and the reference temperature. Transition temperatures from the Charpy tests were all very similar, falling around -129°C (-200°F), although the upper shelf Charpy energy for the HY-100 was lower than the HSLA-100 steels. Dynamic tear energies at -40°C for the four steels ranged from 800 to 1800 J. The average reference temperature of all four steels, measured according to ASTM E 1921, was around -151°C (-240°F), with one composition of HSLA-100 coming in as low as -179°C (-290°F) and another as high as -123°C (-190°F). Fracture toughness tests were conducted according to E 1820 at temperatures of -40, -29, and -8°C. These temperatures were more than 83°C above the highest of the reference temperatures, so cleavage fracture was not expected to occur. The HY-100 specimens exhibited an average initiation toughness of 227 kJ/m2 (1296 Ib/in.) and crack growth remained ductile throughout the tests. Even though the HSLA-100 exhibited initiation toughnesses more than twice as high as the HY-100, many of the tests terminated in cleavage fracture after amounts of ductile crack growth varying from 0 to 1.85 mm (0.073 in.). This was an unexpected result based on good Charpy and dynamic tear energies at -40°C, and low reference temperatures. The higher initiation toughness and tearing resistance of HSLA-100 allowed very high stresses to develop in the fracture process zone. As ductile crack growth occurred, the fracture process zone swept through an increasing volume of metal, which increased the probability of cleavage fracture. It is shown that the load required to reach these levels of crack driving force may be above gross section yielding of a typical structure. In this case failure by gross section yielding would occur before fracture. This is demonstrated with the aid of a failure assessment diagram.
Prediction of the Shape of the KJ Ductile-to-Brittle Transition Temperature Curve for Ferritic Pressure Vessel Steels Using the Material's Resistance to Crack Extension KJ versus Δa Curve
Authors: Wardle G. , Geary W.
Published: September 2009

Fracture toughness (KJ (cleavage) ) measurements made within the ductile-to-brittle transition region for ferritic pressure vessel steels are not always described by the shape of the Master Curve currently given in ASTM Standard E 1921. The objective of this paper is to show how the shape of the transition toughness curve may be related to the shape of the material's resistance to crack extension curve (KJR) once the crack tip starts to blunt and ductile crack extension precedes cleavage failure. Using an empirical relationship between the mean ductile crack extension (Δa) prior to the onset of cleavage failure and temperature (Δa=λexp(ϕT)), then the relationship between KJ and T may simply be given by KJ=KA+α[λexp(ϕT)]β, where KA, α, and β are simply the coefficients to an offset power law to KJ versus Δa data given by KJR=KA+α(Δa)β. For specimens of different sizes, a reference temperature TK may be defined for a given reference level of Δa or equivalent KJ. Unique curves may be defined for materials with differing crack extension resistance curves through plots of KJ versus (T-TΔa(ref)) or (T-TK(ref)). The generalized form of the transition curve may be given by KJ=KA+α{Δa(ref)exp[ϕ(T-TΔa(ref))]}β, or KJ=KA+(K(ref)-KA){exp[ϕ(T-TK(ref))]}β. Experimentally, ϕ has been estimated as approximately 0.08 for nuclear pressure vessel materials such as A533B/A508. Using a specific situation wherein the value of KA=30 MPa √m, K(ref)=100 MPa √m, and β=0.25 then, for a B=25-mm specimen, within experimental scatter this provides an almost exact match to the Master Curve given by KJ=30+70exp[0.019(T-TK100)]. The predictions of transition curve shape using the material's resistance to crack extension curve are believed to be complementary to the Master Curve method, and may describe the shape of the transition curve when there is ductile crack extension prior to cleavage failure. Further work is recommended to investigate the relationship between the predicted ductile-to-brittle transition curve and the Master Curve for probabilities of cleavage failure post-initiation.
Analysis of Dynamic Fracture and Crack Arrest of an HSLA Steel in an SE(T) Specimen
Authors: Link Richard E.
Published: September 2009

A single edge notch tension, SE(T), specimen was used to measure the dynamic fracture toughness and the crack arrest toughness of a tough HSLA steel in the ductile-brittle transition region. The SE(T) specimen was considerably smaller (W = 152 mm) than wide-plate specimens that have been typically used in other crack arrest tests. A thermal gradient was applied across the ligament of the specimen to facilitate a brittle crack initiation in the low temperature region of the specimen. The cleavage crack propagated into warmer and, consequently, tougher material which led to crack arrest. Transient, three-dimensional, finite element analyses of the tests were performed to determine the dynamic fracture and crack arrest toughness of the steel. The analyses employed both linear elastic and visco-plastic constitutive models. Dynamic strain measurements recorded during the run-arrest event were used to determine the crack tip position as a function of time during the event. This information was used as a boundary condition for the analysis. The measured strains were compared with strains predicted by the finite element analysis to validate the model. The dynamic response of the specimen, the effect of crack speed on the driving force, and the evolution of crack tip plasticity during the run-arrest event are discussed.
Simulation on the Decrease in Threshold Stress Intensity Factor (SIF) Range due to High Maximum SIF
Authors: Meshii Toshiyuki , Ishihara Kenichi , Asakura Toshiyuki
Published: September 2009

In this paper, a method is proposed to quantitatively estimate the decrease in threshold stress intensity factor (SIF) range due to high maximum SIF, that is observed for some materials in constant maximum SIF fatigue crack growth tests. The parameters for the simulation were inversely determined from the experimental data of carbon steel, Al and Ti alloys with the aid of genetic algorithm. The set of candidate parameters named as a “generation” were repeatedly generated and evaluated until the experimental data were reproduced by the simulation. A very interesting fact was that though the test conditions for these three materials were different, the obtained simulation parameters seemed to be independent of material. Finally, the proposed method was validated by comparing predictions with experimentally determined values of the decrease in threshold on an embrittled carbon steel.
Anomalous Fatigue Crack Growth Data Generated Using the ASTM Standards
Authors: Forth S. C. , Newman J. C. , Forman R. G.
Published: September 2009

The ASTM standard for fatigue crack growth, E 647, was co-developed by industry and government in the late 1970s to define a standard procedure for generating material crack growth behavior under a variety of loading conditions. The standard specifies tolerances on laboratory procedures, specimen configurations to generate material characterization information of a high integrity. Recent research developing fatigue crack growth rate data has uncovered significant issues with the standard test method and specimen configurations. The data generated has been largely dependent on specimen configuration, i.e., M(T) and C(T) specimens produce very different crack growth rate curves; C(T) specimens of different sizes do not generate the same material response; and finally, the development of steady-state, as defined using constant ▵K testing, does not agree with the data generated with the standard ASTM test method. Therefore, in this paper the authors present data that does not lend confidence in the integrity of the standard C(T) specimen tested using the ASTM standard method and investigate causes for the observed anomalous crack growth rate behavior.
Experimental Evaluation of the J or C* Parameter for a Range of Cracked Geometries
Authors: Davies C. M. , Kourmpetis M. , O'Dowd N. P. , Nikbin K. M.
Published: September 2009

In the current ASTM Standard Test Method for Measurement of Creep Crack Growth Rates in Metals (E 1457) the experimental C* parameter is related to the load and creep load line displacement rate through the geometry related η factor. In this work η factors for a range of geometries are presented. The geometries examined are the compact tension specimen, C(T), single edge notch specimen in tension, SEN(T), and bending, SEN(B), double edge notch specimen in tension, DEN(T), middle crack specimen in tension, M(T) and the C-shaped specimen in tension CS(T). Calculations have been performed for a linear elastic-power law hardening material but the resulting η factors are applicable to either power law plastic or power law creeping materials. Values for ηLLD and ηCMOD, based on the load line displacement and crack mouth opening displacement, respectively, have been determined. A wide range of crack depths, 0.1⩽a/W⩽0.7, where a is crack length and W is specimen width, and hardening exponents, 3 ⩽N⩽10, under plane stress and plane strain conditions have been examined using the finite element method. The influence of specimen length, crack length, material properties and out of plane stress state on the η factor has also been considered. It has been found that for shallow cracks the value of η depends quite strongly on the exponent, N in the material power law, regardless of whether η is defined based on the load line displacement or crack mouth opening displacement. The ηLLD factor has also been found to be strongly sensitive to plane stress/strain conditions imposed, a/W and specimen length, whereas η CMOD depends more weakly on a/W and is almost independent of specimen length for the cases examined. There is, however, no clear trend in these variations over the range of specimen geometries and a/W examined. These results are found to be consistent with those in the literature. Recommendations are made regarding the most appropriate values for η, depending on the specimen type and geometry while taking into account the variability due to the material properties, out of plane stress state and variations between the numerical analyses.
Control of Construction Dewatering by Use of Piezometers
Authors: Gould J. P.
Published: September 2009

Structures with deep foundations and projects near waterways frequently require major dewatering operations to carry out construction in the dry. Maintaining the undisturbed condition of foundation soils and stability of cut slopes and cofferdams may necessitate specific limitations on pore water pressures during construction. One practical method for controlling dewatering procedures is to install piezometers to observe the reduction in pore pressures. This paper describes piezometers for such a purpose and illustrates their use in determining the adequacy of pressure relief or of drawdown in several practical problems.
Foundation Problems Related to Ground Surface Subsidence in Mexico City
Authors: Zeevaert Leonardo
Published: September 2009

Ground surface subsidence is an important consideration in connection with foundations in Mexico City. The ground settlement assumes different values throughout the city depending upon the rate of reduction of the piezometric water pressures in the subsoil and different thickness and compressibility of the clay deposit. The problems encountered are many and varied. In places where the water table has been lowered in highly compressible volcanic clay, shrinkage takes place to a high degree and large fissures and cracks develop in the ground surface and in the clay deposits. To solve this foundation problem in these areas, the clay cracks must be treated to restore continuity in the subsoil conditions before constructing foundations. In areas where pile foundations support buildings, the clay around the piles may shrink away, causing the piles to buckle. The occurrence of large differential vertical movements of the ground surface damages public utilities such as sewage, streets, and highways. Maintenance of these services becomes a matter of primary importance. The maximum ground surface subsidence took place in Mexico City around the year 1949, when the rate of settlement of the ground surface amounted to about 35 cm (14 in.) per yr (1), with respect to the second sand stratum.
Investigation of Landslides by Seismic and Electrical Resistivity Methods
Authors: Trantina John A.
Published: September 2009

This paper describes briefly the seismic refraction and electrical resistivity methods and their application to the study of landslides. The results of a study of two landslides in which the two geophysical methods were used to define the slide surface are discussed and compared with results obtained by drilling and sampling.
Investigation and Correction of Landslides
Authors: Buckingham Earl M.
Published: September 2009

The Coast Range of California is young geologically and is composed of materials of low strength. Accelerated urban development in the San Francisco Bay area has created a serious landslide problem. A study of local topography and geology, plus an understanding of the forces involved, is essential to the visualization of the shape and action of a slide. This visualization should be verified by subsurface exploration before the design of corrective work. Modern equipment has simplified the construction of adequate and safe drainage works. While most slides will respond to drainage or other treatment, it is important to recognize that there are cases where it is not sound engineering to attempt correction. Mathematical analysis of landslides is approximate at best, but it does serve as an aid to judgment. Current laboratory procedures should be revised to more nearly simulate field conditions.
Use of Slope Indicator to Measure Movements in Earth Slopes and Bulkheads
Authors: Henderson R. P. , Matich M. A. J.
Published: September 2009

The paper describes some experiences in using the Wilson slope indicator apparatus to measure movements in earth slopes and in steel sheet pile bulkheads. In two cases involving an earth slope and a highway fill, horizontal ground movements were measured. In one case a high earth slope containing an important water main was instrumented to detect possible movement caused by construction. Results of observations are presented in graphical form. It is believed that the examples given illustrate the practicality of measuring ground movements with the slope indicator. The instrument is also used to measure the deflected shapes and bending moments in steel sheet pile bulkheads. Five examples, representing a variety of bulkheads and soil conditions, are described briefly. All the structures are located in Hamilton Harbour, Ontario. The process of converting instrument readings to bending moment in the sheet piling is also discussed, and actual results of measured, deflected shapes, and observed bending moments are given.
The Use of Slope Measuring Devices to Determine Movements in Earth Masses
Authors: Wilson S. D.
Published: September 2009

The precise measurement of movements in the interior of earth masses is difficult but necessary. During the past 10 years the author has been closely associated with the development of instrumentation for this purpose. Experience gained with over a hundred projects indicates that (1) such measurements can be made successfully and (2) such information is informative, and in many instances essential, to the solution of the specific problem. This is particularly true in the case of landslides where it is necessary to know the depth and thickness of the movement zone if corrective treatment is to be accomplished. The classic symmetry of a circular arc type of slide, for example, is often radically altered by geologic and other discontinuities.
Investigation and Solution of a Landslide Problem Involving a High Transmission Tower
Authors: Holtz W. G.
Published: September 2009

The 400-ft high tower 2-C for the Sacramento River crossing of the Shasta-Tracy transmission line is located on a hill adjacent to the river. When the site was investigated in 1951, prior to construction, an old major slide caused by river dredging was evident; however it was decided that the tower could be safely located at the site if certain precautionary measures were taken. In 1955, a strong earthquake precipitated another major slide at this location, placing the scarp only 125 ft from one tower leg; therefore remedial measures were undertaken to increase the stability of the hill. This paper describes the investigations conducted to study the mechanics of the problem, the analysis of the slide condition, the remedial-construction measures performed, and subsequent field observations.
Areal Fill Settlements and Building Foundation Behavior at the San Francisco Airport
Authors: Roberts Don V. , Darragh Robert D.
Published: September 2009

Previously published data on allowable building settlements have not included cases where the settlements were due to the fill loads. In this paper, comparisons have been made between calculated and observed areal fill settlements of 1 to 4 ft at the San Francisco Airport. The effects of these settlements on buildings supported on pile foundations and spread footings are reported for three aircraft hangars and one terminal building. These data indicate that the Terzaghi theory of consolidation permits reasonably accurate settlement calculations for the consolidation of a postglacial marine clay (bay mud) under fill loads. Differences in fill thickness resulting from shear failures of the soft bay mud during site grading can cause serious problems in building and site behavior. Surcharge fills are effective in reducing postconstruction settlements and hangar foundation costs in areas of shallow bay mud. Light steel frame buildings supported on spread footings can withstand total settlements of 1 ft and differential settlements of several inches. Pile foundations must be designed for the negative friction forces imposed by subsiding soils if settlements are to be controlled.
Predicting Surface Subsidence from Basic Soil Tests
Authors: Gibbs Harold J. , Bara John P.
Published: September 2009

Standard soil index tests can be useful to predict near-surface subsidence of fine-grained soil resulting from initial wetting. The natural soil voids must be sufficient to allow a collapse of the soil structure and sufficient to allow saturation to develop a minimum consistency. By systematic sampling and laboratory testing investigations, the probability of subsidence was indicated for critical areas along the route of the proposed San Luis Canal in the San Joaquin Valley, Calif. Field ponding and laboratory consolidation tests provided observations of the amounts of subsidence for correlation with the results indicated by the sampling investigation.
Deep Bench Marks in Clay and Permafrost Areas
Authors: Bozozuk M. , Johnston G. H. , Hamilton J. J.
Published: September 2009

This paper describes the design and use of deep bench marks by the Division of Building Research of the National Research Council of Canada. The bench marks consist of an inner pipe protected by an outer casing from the effects of seasonal ground movements and frost action. In sensitive clays the bench mark is installed by jacking or driving the outer casing with relatively simple equipment. In stiffer clays it is inserted in an augered hole and then turned and pushed to refusal with a drill rig. In permafrost areas, the bench mark is placed in a drilled or steamed hole to a depth at which the lower portion of the inner rod is securely anchored in the perennially frozen ground. Details of bench mark assemblies and installation techniques for soft clays, stiff clays, and frozen ground are described.
Engineering Properties of Ocean Floor Soils
Authors: Smith R. J.
Published: September 2009

Increasing interest in use of the oceanic regions for various purposes necessitates development of ready means for determining variations in the supporting ability of sea floor soils. Some backlog of marine strength and consolidation information is available from foundation investigations for offshore shelf projects, and a few measurements have been made on deep-sea cores. Procedures to procure and test samples in near shore shallow waters have been developed; these are essentially modifications of the methods used on land. The techniques for investigating in normal oceanic depth waters are currently under examination. A sea floor soil program is comprised of preliminary site selection, bathymetric and sub-bottom survey, and core sampling, testing, and logging phases, each adapted to deep water circumstances. Measurement of shear strength of oceanographic cores by means of the laboratory vane appears to give acceptable results. Distinguishing the various abyssal muds and oozes can rapidly and accurately be done by X-ray diffractometry. Application of the seismologic approach and various types of in-place tests to deep-water soil investigations also show some promise.
The Role of Granulocyte-Colony Stimulating Factor (G-CSF) in the Healthy Brain: A Characterization of G-CSF-Deficient Mice
Authors: Diederich Kai , Sevimli Sevgi , Dörr Henrike , Kösters Evelin , Hoppen Maike , Lewejohann Lars , Klocke Rainer , Minnerup Jens , Knecht Stefan , Nikol Sigrid , Sachser Norbert , Schneider Armin , Gorji Ali , Sommer Clemens , Schäbitz Wolf-Rüdiger
Published: September 2009

Granulocyte-colony stimulating factor (G-CSF) is a hematopoietic growth factor that controls proliferation and differentiation of neural stem cells. Although recent studies have begun to explore G-CSF-related mechanisms of action in various disease models, little is known about its function in the healthy brain. In the present study, the effect of G-CSF deficiency on memory formation and motor skills was investigated. The impact of G-CSF deficiency on the structural integrity of the hippocampus was evaluated by analyzing the generation of doublecortin-expressing cells, the amount of bromodeoxyurine-labeled cells, the dendritic complexity in hippocampal neurons, the binding densities of NMDA and GABAAreceptors and the induction of long-term potentiation (LTP). G-CSF deficiency caused a disruption in memory formation and in the development of motor skills. These impairments were associated with reduced ligand binding densities of NMDA receptors in hippocampal subfields CA3 and the dentate gyrus. The reduced excitation was potentiated by increased ligand binding densities of GABAAreceptors resulting in a relative shift in favor of inhibition and impaired behavioral performance. These alterations were accompanied by impaired induction of LTP in the CA1 region. Moreover, G-CSF deficiency led to decreased dendritic complexity in hippocampal neurons in the dentate gyrus and the CA1 region. G-CSF deficiency also caused a reduction of neuronal precursor cells in the dentate gyrus. These findings confirm G-CSF as an essential neurotrophic factor, and point to a role in the proliferation, differentiation and functional integration of neural cells necessary for the structural and functional integrity of the hippocampal formation.
Mechanisms of Tactile Information Transmission through Whisker Vibrations
Authors: Lottem Eran , Azouz Rony
Published: September 2009

In their natural environment, rodents use their whiskers to locate and distinguish between objects of different textures and shapes. They do so by moving their whiskers actively as well as passively, through body and head movements. To determine the mechanisms by which surface coarseness is translated into neuronal discharges through passive whisker movements, we monitored head movements of awake behaving rats while approaching objects. We then replayed these movements in anesthetized rats, monitored the whiskers' movements across various surfaces, and concurrently recorded the activity of first-order sensory neurons. We found that whiskers, being the first stage of sensory information translation, shape transduction by amplifying small-amplitude high-frequency signals. Thus, surface coarseness is transmitted through high-velocity micromotions. Consistent with this, we find that during surface contact, discrete high-velocity movements, or stick-slip events, evoke first-order neuronal discharge. Transient ringing in whiskers, which primarily represents resonance vibrations, follows these events, but seldom causes neurons to discharge. These sensory transformations are influenced by the whiskers' biomechanical properties. To determine the resemblance of these tactile transformations during passive whisker movements and active whisking, we induced artificial whisking across various surface textures. We found that the processes by which tactile information becomes available to the animal are similar for these different modes of behavior. Together, these findings indicate that the temporal bandpass properties for spike generation in first-order neurons are matched by the biomechanical characteristics of whiskers, which translate surface coarseness into high-frequency whisker micromotions. These properties enable rodents to acquire tactile information through passive and active movements of their whiskers.
Decisions in Changing Conditions: The Urgency-Gating Model
Authors: Cisek Paul , Puskas Geneviève Aude , El-Murr Stephany
Published: September 2009

Several widely accepted models of decision making suggest that, during simple decision tasks, neural activity builds up until a threshold is reached and a decision is made. These models explain error rates and reaction time distributions in a variety of tasks and are supported by neurophysiological studies showing that neural activity in several cortical and subcortical regions gradually builds up at a rate related to task difficulty and reaches a relatively constant level of discharge at a time that predicts movement initiation. The mechanism responsible for this buildup is believed to be related to the temporal integration of sequential samples of sensory information. However, an alternative mechanism that may explain the neural and behavioral data is one in which the buildup of activity is instead attributable to a growing signal related to the urgency to respond, which multiplicatively modulates updated estimates of sensory evidence. These models are difficult to distinguish when, as in previous studies, subjects are presented with constant sensory evidence throughout each trial. To distinguish the models, we presented human subjects with a task in which evidence changed over the course of each trial. Our results are more consistent with “urgency gating” than with temporal integration of sensory samples and suggest a simple mechanism for implementing trade-offs between the speed and accuracy of decisions.
Stepwise Maturation of Apicobasal Polarity of the Neuroepithelium Is Essential for Vertebrate Neurulation
Authors: Yang Xiaojun , Zou Jian , Hyde David R. , Davidson Lance A. , Wei Xiangyun
Published: September 2009

During vertebrate neurulation, extensive cell movements transform the flat neural plate into the neural tube. This dynamic morphogenesis requires the tissue to bear a certain amount of plasticity to accommodate shape and position changes of individual cells as well as intercellular cohesiveness to maintain tissue integrity and architecture. For most of the neural plate–neural tube transition, cells are polarized along the apicobasal axis. The establishment and maintenance of this polarity requires many polarity proteins that mediate cell–cell adhesion either directly or indirectly. Intercellular adhesion reduces tissue plasticity and enhances tissue integrity. However, it remains unclear how apicobasal polarity is regulated to meet the opposing needs for tissue plasticity and tissue integrity during neurulation. Here, we show that N-Cad/ZO-1 complex-initiated apicobasal polarity is stabilized by the late-onsetting Lin7c/Nok complex after the extensive morphogenetic cell movements in neurulation. Loss of either N-Cad or Lin7c disrupts neural tube formation. Furthermore, precocious overexpression of Lin7c induces multiaxial mirror symmetry in zebrafish neurulation. Our data suggest that stepwise maturation of apicobasal polarity plays an essential role in vertebrate neurulation.
The Representation of Tool Use in Humans and Monkeys: Common and Uniquely Human Features
Authors: Peeters R. , Simone L. , Nelissen K. , Fabbri-Destro M. , Vanduffel W. , Rizzolatti G. , Orban G. A.
Published: September 2009

Though other species of primates also use tools, humans appear unique in their capacity to understand the causal relationship between tools and the result of their use. In a comparative fMRI study, we scanned a large cohort of human volunteers and untrained monkeys, as well as two monkeys trained to use tools, while they observed hand actions and actions performed using simple tools. In both species, the observation of an action, regardless of how performed, activated occipitotemporal, intraparietal, and ventral premotor cortex, bilaterally. In humans, the observation of actions done with simple tools yielded an additional, specific activation of a rostral sector of the left inferior parietal lobule (IPL). This latter site was considered human-specific, as it was not observed in monkey IPL for any of the tool videos presented, even after monkeys had become proficient in using a rake or pliers through extensive training. In conclusion, while the observation of a grasping hand activated similar regions in humans and monkeys, an additional specific sector of IPL devoted to tool use has evolved inHomo sapiens, although tool-specific neurons might reside in the monkey grasping regions. These results shed new light on the changes of the hominid brain during evolution.
The Structural Integrity of an Amygdala–Prefrontal Pathway Predicts Trait Anxiety
Authors: Kim M. Justin , Whalen Paul J.
Published: September 2009

Here, we used diffusion tensor imaging (DTI) and showed that the strength of an axonal pathway identified between the amygdala and prefrontal cortex predicted individual differences in trait anxiety. A functional magnetic resonance imaging (fMRI) functional localizer that has been shown to produce reliable amygdala activation was collected in 20 psychiatrically healthy subjects. Voxelwise regression analyses using this fMRI amygdala reactivity as a regressor were performed on fractional anisotropy images derived from DTI. This analysis identified a white matter pathway between the amygdala and ventromedial prefrontal cortex. Individual differences in the structural integrity of this putative amygdala–prefrontal pathway were inversely correlated with trait anxiety levels (i.e., higher pathway strength predicted lower anxiety). More generally, this study illustrates a strategy for combining fMRI and DTI to identify individual differences in structural pathways that predict behavioral outcomes.
Total and high molecular weight adiponectin are elevated in patients with Laron syndrome despite marked obesity
Authors: Kanety Hannah , Hemi Rina , Ginsberg Shira , Pariente Clara , Yissachar Eleanor , Barhod Ehud , Funahashi Tohru , Laron Zvi
Published: September 2009

Objective

Patients with Laron syndrome (LS; primary GH insensitivity) caused by molecular defects of the GH receptor gene, are characterized by dwarfism, profound obesity, and hyperlipidemia. The aim of the current study was to evaluate adiponectin levels in LS, as obesity is known to be associated with low adiponectin.

Design and methods

We studied nine untreated LS adult patients (5 males, 4 females) and six girls with LS receiving once-daily treatment by IGF1. Total and high molecular weight (HMW) adiponectin levels, adiponectin multimers distribution, and metabolic indices were analyzed in serum samples obtained during several years of follow-up.

Results

Adiponectin levels in the severely obese adult LS patients (percent body fat; females 61.0±2.5%, males 40.6±8.1%) were two- to three-fold higher than those reported for subjects of corresponding age, gender and degree of adiposity. Total adiponectin was significantly higher in females compared with males (21.4±3.5 vs 10.2±4.6 μg/ml, P<0.001). The elevated adiponectin in LS subjects was associated with an increased abundance of the HMW isoform, and positively correlated with body fat percentage (r=0.65, P=0.017) and leptin (r=0.65, P=0.012). There was no correlation between adiponectin levels (total and HMW) and the degree of insulin resistance in LS subjects or their blood lipids levels. Adiponectin was also high in young girls with LS (22.9±7.4 μg/ml) and did not change during long-term IGF1 replacement therapy.

Conclusion

Adiponectin hypersecretion in LS, despite profound obesity, suggests that GH activity may negatively impact adiponectin secretion from adipocytes.
Association of the +45T>G and +276G>T polymorphisms in the adiponectin gene with insulin resistance in nondiabetic Greek women
Authors: Melistas Labros , Mantzoros Christos S , Kontogianni Meropi , Antonopoulou Smaragdi , Ordovas Jose M , Yiannakouris Nikos
Published: September 2009

Objective

We explored potential associations of two single nucleotide polymorphisms (SNPs) in the adiponectin gene (ADIPOQ; +45T>G, rs2241766 and +276G>T, rs1501299) with circulating total and high-molecular weight (HMW) adiponectin, insulin resistance (IR), and markers of obesity in a healthy Greek female population.

Design and methods

The two SNPs were genotyped in 349 women without diabetes (mean age: 47.0±12.1 years, mean body mass index: 28.9±5.6 kg/m2). Total and HMW adiponectin concentrations, body composition variables, IR parameters, and plasma lipid levels were determined.

Results

In single SNP analysis adjusting for several potential confounders, SNP +276G>T was associated with higher fasting insulin levels (P=0.01) and higher homeostasis model assessment index for IR (HOMA-IR; P=0.009), and SNP +45T>G was associated with lower insulin levels and HOMA-IR (P=0.05 and P=0.07 respectively). No association with total or HMW adiponectin, plasma lipid levels, and body composition variables was observed; however, haplotype analysis revealed that subjects homozygous for the most common +45T/+276G haplotype had lower total adiponectin levels than did noncarriers of this haplotype (P=0.02). The observed differences in HOMA-IR were very significant among women with a higher body fat (BF) percentage (≥ the population median of 41%; all P≤0.005), but not among leaner individuals (P for interactions 0.01–0.07), thus suggesting that ADIPOQ effects on insulin sensitivity may depend upon BF status.

Conclusion

Our data suggest a significant role of ADIPOQ variants at positions +45 and +276 in the development of IR in healthy Greek women possibly through an interaction with BF.
Mental Health and Academic Success in College
Authors: Eisenberg Daniel , Golberstein Ezra , Hunt Justin B
Published: September 2009

Mental health problems represent a potentially important but relatively unexplored factor in explaining human capital accumulation during college. We conduct the first study, to our knowledge, of how mental health predicts academic success during college in a random longitudinal sample of students. We find that depression is a significant predictor of lower GPA and higher probability of dropping out, particularly among students who also have a positive screen for an anxiety disorder. In within-person estimates using our longitudinal sample, we find again that co-occurring depression and anxiety are associated with lower GPA, and we find that symptoms of eating disorders are also associated with lower GPA. This descriptive study suggests potentially large economic returns from programs to prevent and treat mental health problems among college students, and highlights the policy relevance of evaluating the impact of such programs on academic outcomes using randomized trials.
Epilepsy and insular Grade II gliomas: an interdisciplinary point of view from a retrospective monocentric series of 46 cases
Authors: Taillandier Luc , Duffau Hugues
Published: September 2009

OBJECT

There are few data in the literature concerning a multimodal approach to insular WHO Grade II gliomas (GIIGs) and the control of epilepsy after treatment. In this paper, the authors describe a monocentric series of 46 cases in which patients underwent various sequential treatments for insular GIIGs. On the basis of global results with regard to epilepsy, the respective interests in the various treatments are discussed.

METHODS

Available data on 46 patients harboring insular GIIGs were extracted from a local database of 288 GIIGs. The various therapeutic sequences were analyzed in parallel with the course of seizure frequency.

RESULTS

Despite the usual difficulties with seizure quantification in retrospective studies, the authors showed that 1) the negative course of seizure frequency was mostly connected to tumor progression, 2) surgery almost always had a favorable effect on epilepsy, and 3) chemotherapy had a mostly favorable effect with acceptable tolerance. The authors were unable to draw conclusions about the role of radiotherapy given the too few cases.

CONCLUSIONS

This extensive experience with insular GIIGs tends to confirm interest in their surgical removal and supports interest in chemotherapy from an epileptological point of view.
The pH Response and Sensing Mechanism of n-Type ZnO/Electrolyte Interfaces
Authors: Al-Hilli Safaa , Willander Magnus
Published: September 2009

Ever since the discovery of the pH-sensing properties of ZnO crystals, researchers have been exploring their potential in electrochemical applications. The recent expansion and availability of chemical modification methods has made it possible to generate a new class of electrochemically active ZnO nanorods. This reduction in size of ZnO (to a nanocrystalline form) using new growth techniques is essentially an example of the nanotechnology fabrication principle. The availability of these ZnO nanorods opens up an entire new and exciting research direction in the field of electrochemical sensing. This review covers the latest advances and mechanism of pH-sensing using ZnO nanorods, with an emphasis on the nano-interface mechanism. We discuss methods for calculating the effect of surface states on pH-sensing at a ZnO/electrolyte interface. All of these current research topics aim to explain the mechanism of pH-sensing using a ZnO bulk- or nano-scale single crystal. An important goal of these investigations is the translation of these nanotechnology-modified nanorods into potential novel applications.
L'Institut de Technologie "MARA" de Kuala Lumpur
Authors: De Beer Brigitte
Published: September 2009

3) Brigitte de Beer has united in this article the reflexions which her experience as a teacher in the MARA Institute at Kuala Lumpur inspired. It was in 1966 that MARA was created to assure the advancement of the middle and lower class Malays, to enable them to reach the economic and technical level of the non-bumiputra. The ITM forms technicians of all varieties. The spirit of studies there seems very open to diversity, both through the teaching of numerous foreign languages, as well as through a desire to make a clean break with the traditional rural milieu of the students. It seems that, by a sage dose of innovation and prudence, the ITM may succeed in inserting its students in the modern technical world and the Malaysian community.
Universités et revues de sciences humaines aux Philippines
Authors: Veslot Jean-Louis
Published: September 2009

1) In the chapter Notes-Documents, Jean Louis Veslot gives first a bird's eye view of Philippino universities, and then makes an inventory of the existing social science reviews often due to initiative of these same universities. The enumeration, if it does not pretend to be exhaustive, gives, with indication of the most interesting articles which might have appeared there, a list of the more important reviews which attest to the vitality of research in the Philippines.