bluuebunny/crossref_metadata_2025 huggingface dataset:
Modern Electronics for Geotechnical Engineers
Authors: Moore CA
Published: February 2009

The fundamental principles of microprocessors are described. Emphasis is placed on process control and data acquisition uses. The pinout and architecture of the CDP1802 are detailed.
Rectangular Hyperbola Fitting Method for One Dimensional Consolidation
Authors: Sridharan A , Rao AS
Published: February 2009

The time factor—degree of consolidation relation from the Terzaghi theory is assumed as a rectangular hyperbola over a wide range of the time factor. A new method is developed for determination of the coefficient of consolidation Cv from laboratory consolidation test data. The reliability and accuracy is shown to compare very well with the existing standard methods of Taylor and Casagrande. The time settlement curves on the semilogarithmic plots are reclassified and the new method is shown to be valid even for cases in which the curves are of shapes for which the earlier methods could not be applied. The laboratory test is rendered easier and simpler, with fewer readings required, and the initial compression does not affect the time versus the ratio of time to compression plot.
High Capacity Multiaxial Testing Device
Authors: Desai CS , Janardahanam R , Sture S
Published: February 2009

In the field conditions, geologic materials are subjected to three-dimensional states of stress. Hence, for appropriate simulation of the field conditions and for deriving constitutive models, it is desirable to test specimens of the materials under truly triaxial states of stress. This paper describes construction, details, and application of a truly triaxial device for testing materials of relatively high strength. A number of improvements over the previous designs are included, and the capability of the device to test a wide range of materials such as ballasts, concrete, rock, and wood is established.
A Proposed Standard Test Method for a Free Fall Penetration Test
Authors: Riggs CO
Published: February 2009

A standard test method for a free fall penetration test is proposed. Rigid constraints on both mass and geometry of the drive weight and the anvil should provide a reliably reproducible force at impact and a reliably reproducible energy within equivalent sampling rod-sampler configurations. It is stated within the proposed new standard method that the apparatus can be used to satisfy the requirements of ASTM Standard Method for Penetration Test and Split-Barrel Sampling of Soils (D 1586). It is recommended that the proposed standard method be submitted to approval by consensus process under the jurisdiction of ASTM Committee D-18.
Equivalent Opening Size of Geotextiles
Authors: Gerry BS , Raymond GP
Published: February 2009

A rapid increase in the use of geotextiles in civil engineering has highlighted the necessity to identify the geotextile's properties associated with different applications. One property of importance in filtration and separation is the nominal equivalent opening size (EOS). The EOS is generally defined as equivalent to the smallest spherical particles of which 5% by weight fails to pass through the geotextile after 20 min or other specified times of sieving. Unfortunately, data show that for thick nonwoven geotextiles in particular and to a lesser extent for other geotextiles experimental variations can be substantial unless careful procedural techniques are followed including correct positioning of specimen, suspension of specimen, rigorous production and maintenance of silica sand fractions, and minimizing of humidity effects. In certain applications, one of which is presented in some detail, the use of a 95% retention definition is shown to be a more useful practical definition and even this may be less than in situ performance EOS values (that is, the particle sizes retained in situ by the geotextile). In such cases a clear understanding of geotextile behavior and a reporting of test results over a complete testing range of 95% particle retention to 95% particle passing may be of considerable value in the proper selection of a geotextile. Field performance data are presented on the importance of EOS to railway track rehabilitation where lower than normal manufactured values of EOS are considered preferable.
Rapid Index Tests for Transitional Materials
Authors: Dusseault MB , Cimolini P , Soderberg H , Scafe DW
Published: February 2009

Two rapid semiquantitative repeatable index tests are presented. The static swell/slake test and the dynamic dispersion test have been designed to classify intact transitional materials (mudstones, silts, clay shales, and compaction shales) with respect to their swelling and slaking behavior. Tests may be performed over a wide range of conditions by varying saturating fluid salinities to evaluate sensitivity of the intact materials to water.
Laboratory Pull-Out Testing of Grid Reinforcements in Sand
Authors: Ingold TS
Published: February 2009

In many reinforced soil applications the critical mode of failure involves pull-out of the reinforcement from the soil. Although grid reinforcement is known to be very efficient in resisting pull-out failure, very little is published on the mechanisms of soil-grid interaction. To investigate soil-grid behavior, several series of pull-out tests were conducted using both metallic and plastic grids embedded in sand. The results of these tests are presented in this paper together with details of the apparatus and testing techniques used. Results are also given for ancillary testing carried out to assess the effects of grid member orientation with respect to the direction of the applied pull-out load. These tests clearly demonstrate that pull-out resistance is a function of the cumulative embedded area of the grid members normal to the direction of pull-out and not the embedded plan area of the reinforcement. Based on these observations an analytical model is developed for strong inextensible grids. Analytical and test results are compared and found to be in good agreement for both metallic and plastic grids.
Dynamic Shear Modulus and Damping Ratio from Random Loading Tests
Authors: Al-Sanad H , Aggour MS , Yang JCS
Published: February 2009

Dynamic shear modulus and damping ratio determination from random loading tests on dry Monterey and Ottawa sands in a resonant column device, in addition to sinusoidal loading, are presented. In the random excitation test, white noise was used to excite the specimens, and the responses of the specimens were analyzed by the random decrement technique. Using a sine-wave generator, the dynamic soil properties were also determined by the conventional technique. The results obtained indicated a good agreement between the modulus and damping obtained from the application of sinusoidal or random loading. It was concluded that the relationship of shear modulus and damping ratio with shear strain amplitude is independent of random or sinusoidal forcing functions within the range of variables tested.
The Methylene Blue Test for Bentonite Liner Quality Control
Authors: Alther GR
Published: February 2009

An in-situ procedure for evaluating the quality of soil and soil/bentonite admix liners is described. The methylene blue (MB) test is based on the principle that cationic dyes base exchange in proportion to the clay content in soils or clay slurries. The number of exchangeable ions present is determined by replacing these ions with methylene blue.

The MB test is the accepted standard of measurement of clay levels in bentonite bonded molding sands used in the foundry and steel industries. Lab tests have shown that the methylene blue method is useful to test the quality of bentonite liners, bentonite slurries, and soil bentonite backfills for slurry trenches.
Improved Rectangular Hyperbola Method for the Determination of Coefficient of Consolidation
Authors: Sridharan A , Prakash K
Published: February 2009

From the Terzaghi's theory of consolidation, it can be shown that the T/U versus T relation is a rectangular hyperbola over a fairly wide range of degree of consolidation. In the plot of T/U versus T, a straight line is fitted for the range of 60 to 90% degree of consolidation with a high precision. A method of calculating the coefficient of consolidation Cv is presented. The results are compared with the results obtained by the conventional methods, viz, square root of time fitting method and logarithm of time fitting method.
Interpretation of Lateral Statnamic Load Test Results
Authors: El Naggar MH
Published: February 2009

The Statnamic device has been used to test piles in the lateral direction. This paper describes a dynamic analysis approach for the prediction of the static lateral behavior of piles using the results of the Statnamic lateral test. The objectives of this analysis are twofold: to simulate the pile head displacement-time history observed during the test using the measured load time history at the pile head and varying the soil parameters along the pile shaft until a satisfactory match is achieved and to predict the static lateral load-deflection curve of the pile using the soil parameters established through the matching process. The dynamic analysis was used to analyze some Statnamic lateral tests, and satisfactory agreement between the computed and measured displacement-time histories was achieved. The predictions of the proposed approach in the given case studies were in good agreement with the static lateral load test results. The results obtained thus far suggest that the Statnamic lateral test and the described model are successful in the prediction of the lateral load-deflection behavior of piles. Both the Statnamic lateral test and the one-dimensional analysis are simple, fast, and inexpensive, and the approach promises to be very useful in the prediction of the lateral load-deflection behavior of foundations.
Evaluation of Surface-Related Phenomena Using Sedimentation Tests
Authors: Fam M , Dusseault M
Published: February 2009

Sedimentation tests are suggested to assess the sensitivity of clay-water systems to environmental changes. A simple framework based on a parallel structure assumption was developed to analyze data from sedimentation tests. The slope of the relationship between the final sediment volume and the ionic concentration, plotted on a log-log scale, is related to the specific surface Sa, the double layer thickness ϑ, and to the specific gravity Gs. A new parameter, λ, the reactivity coefficient, where λ = Sa · ϑ · Gs · ρw, is introduced to help identification of reactive clay-water systems. High values of λ identify systems that are sensitive to changes in pore fluid characteristics. An experimental procedure is suggested to acquire relevant sedimentation parameters. Data collected during sedimentation tests of kaolinite, bentonite, and disaggregated Pierre shale, Mancos shale, and Queenston shale are used to verify the model. Agreement between experimental data and the model suggests that this simple technique can be used to identify reactive shales in the field. Other applications arise in tailing pond modeling, drilling mud management, and clay liner reliability assessment.
Consolidation and Permeability Behavior of High Porosity Baltic Seabed Sediments
Authors: Ag A , Silva AJ
Published: February 2009

The consolidation and permeability (hydraulic conductivity) characteristics of the high-porosity surficial seabed sediments from a test site in the Eckernförde Bay, Baltic Sea, were studied using a constant rate of strain (CRS) consolidation and hydraulic conductivity testing system employing flow pumps. These silty clay sediments are characterized by high void ratios, high organic content, and variable concentration of methane gas. Results from CRS consolidation tests show appreciable apparent overconsolidation of the sediments at the upper 200 cm with a gradual transition to normally consolidated states below 250 cm in depth. The highly compressible nature of the material is reflected in the large values of the compression index. The hydraulic conductivity of the box core samples ranges from 2.5 × 10−7 to 3.0 × 10−6 cm/s for void ratios ranging from 4.5 to 7.0 with a linear relationship between void ratio and log of hydraulic conductivity. The engineering behavior of these sediments is of practical significance in geoacoustic modeling of the seafloor for studies related to mine countermeasure programs.
Model Tests for Uplift Resistance of Piles in Sand
Authors: Al-Mhaidib AI , Edil TB
Published: February 2009

An experimental program using large model piles in sand was conducted to study the shaft resistance behavior of piles subject to uplift loads. Model single pipe piles of different diameters (45 to 178 mm) were subjected to static uplift loading to failure. The piles, which had an embedded length of about 1.7 to 2 m, were installed in a large test pit (3 by 3 by 3 m) by three different methods (driving, jacking, and a reference undisturbed method with negligible lateral displacement) to assess the influence of method of installation on shaft resistance. The tests were performed in two initial densities of a sand (loose and dense). The experimental results were analyzed statistically. The results show that the initial sand density and the method of pile installation are the most significant factors that affect uplift capacity. Installation methods that cause less disturbance give higher uplift capacity. Unit shaft resistance could be reduced as much as by half depending on the method of pile installation relative to the undisturbed method. The displacement at the ultimate uplift load is in the range of 5 to 12.5 mm and independent of soil type and pile diameter, but depends on method of pile installation.
Mechanism Controlling the Shrinkage Limit of Soils
Authors: Sridharan A , Prakash K
Published: February 2009

Based on the results from an extensive experimental program involving a number of natural soils as well as pure clays with extreme clay mineral types, namely kaolinite and montmorillonite, as the principal clay minerals, a hypothesis explaining the mechanisms controlling the shrinkage limit has been proposed. The shrinkage limit of a natural soil has been shown to be primarily a result of the packing phenomenon, which in turn is governed by the grain-size distribution of the soil; the shrinkage limit of pure clays appears to be affected by the fabric also. Even though clay-sized particles play an important role in the shrinkage phenomenon, there is an optimum clay content at which the shrinkage limit of a soil can become minimum. It has been further illustrated that the shrinkage limit is not at all related to the plasticity characteristics of the soil. As the factors governing the shrinkage limit are entirely different from those controlling the swelling of soils, the shrinkage limit cannot indicate the swelling behavior of the soil.
The In-Plane Permeability of Geotextiles
Authors: Gerry BS , Raymond GP
Published: February 2009

Since about 1965, synthetic fabrics commonly known as geotextiles have contributed to the solution of many civil engineering drainage, separation, and reinforcement problems. In recent years an effort has been made to develop general guidelines for the selection of geotextiles for various specific uses. One of these uses of geotextiles is in railroad track rehabilitation. A primary function of a geotextile for use in track rehabilitation is to facilitate the lateral drainage of excess water from the track load-bearing area to the drainage ditches. As the ballast above the geotextile becomes fouled, the importance of the in-plane drainage capability of the geotextile becomes more and more important. Accordingly, the work presented herein addresses the measurement of the in-plane permeability of geotextiles. Laboratory tests conducted over normal loads likely to be incurred in the track suggest that only thick nonwoven geotextiles are likely to possess coefficients of inplane permeability sufficient to maintain a satisfactory long-term performance. Geotextile specimens removed from beneath ballast substantiate this finding. Furthermore, tests performed on the geotextiles removed from in-track strongly suggest that better performance is obtained from those thick nonwoven geotextiles with low equivalent opening sizes (EOS). From the data it is recommended that in order to meet the in-plane permeability requirement, geotextiles for track rehabilitation be thick nonwoven geotextiles with an EOS preferably less than 40-µm (No. 400) sieve.
Infiltration Testing for Hydraulic Conductivity of Soil Liners
Authors: Stewart JP , Nolan TW
Published: February 2009

This paper describes the use of single ring infiltrometers for evaluating the hydraulic conductivity of compacted soil liners. Procedures are presented for installation and monitoring of infiltrometers in the field. Results of hydraulic conductivity estimated from infiltrometer tests on six laboratory model liners are presented and compared with the results of conventional laboratory tests. In addition, the distribution of soil saturation after prolonged infiltration testing showed that the permeant tended to follow preferred paths and did not generally advance as a uniform front as commonly assumed.
Modified Free Swell Index for Clays
Authors: Sivapullaiah PV , Sitharam TG , Subba Rao KS
Published: February 2009

Free swell tests are commonly used for identifying expansive clays and to predict the swelling potential. The method as proposed by Holtz and Gibbs suffers from inaccuracies in volume measurement of dry powder in air. In this paper, a nondimensional modified free swell index is proposed, which removes the uncertainties present in the Holtz and Gibbs method. The modified free swell index is shown to bear unique correlations with liquid limit (volume basis) and percent swell of oedometer specimens compacted to proctor optimum conditions.
Heat and Moisture Transfer Characteristics of Compacted Mackenzie Silt
Authors: Evgin E , Svec OJ
Published: February 2009

The heat and moisture transfer characteristics of a silt from the Mackenzie River Valley have been determined in a laboratory investigation. A dual gamma-ray scanner was used to measure the changes in density and volumetric moisture content along the soil samples. The coefficients of soil-water diffusivity under isothermal conditions and under temperature gradients have been obtained. The development of a calibration curve for the analysis of gamma-ray readings has been described. The shortcomings of the procedures used for the measurement of transport coefficients have been discussed.
Assessing Frost Damage in Compacted Clay Liners
Authors: Benson CH , Chamberlain EJ , Erickson AE , Wang X
Published: February 2009

Methods used to assess frost damage (here defined as a large increase in hydraulic conductivity) in compacted clay liners are reviewed and evaluated using data collected from two test pads that were instrumented and then exposed to winter weather. The methods include comparisons of measurements of either water content and dry unit weight or hydraulic conductivity made before and after winter exposure. Field and laboratory methods of assessing hydraulic conductivity are considered.

The comparison shows that assessments based on water content and dry unit weight can be misleading. Assessments based on hydraulic conductivity are recommended. Field hydraulic conductivity tests can be useful provided the soil is not disturbed or smeared and the test method permits evaluation of liners partially penetrated by frost. In this study, however, the field tests yielded only qualitative results. Laboratory tests can also be used provided undisturbed specimens of sufficient size are collected. Specimens 70 mm in diameter were of adequate size in this study. Suitable specimens can be collected as blocks from thawed soil or with a core barrel while the soil is frozen. Collecting specimens in thin-wall sampling tubes (i.e., “Shelby” tubes) causes significant disturbance of thawed soil and thus is not recommended. Data are also presented to illustrate that laboratory tests should be conducted at effective stresses similar to those existing in the field.
Use of Stereophotogrammetry to Analyze the Development of Shear Bands in Sand
Authors: Harris WW , Viggiani G , Mooney MA , Finno RJ
Published: February 2009

Experimental results are presented from plane-strain compression of a fine-grained, water-saturated loose sand. Together with local measurements of boundary stresses and deformations, systematic analysis of photographs of the deforming specimen allowed for measuring deformations and computing strain fields inside and outside the shear band. The principles, details, and accuracy of the procedure are described. The capabilities of stereophotogrammetry are illustrated through typical results obtained from undrained and drained tests. A gradual transition from homogeneous deformation to temporary modes of localized strain to a highly localized strain field is systematically observed. Prior to strain localization in the region where the final shear band eventually forms, the soil contracts more than the rest of the specimen. As soon as the final band is fully formed, the soil inside the band either remains at constant volume or dilates. The nonuniformity of volumetric response throughout the specimen in globally undrained conditions implies there is water flow within the specimen.
Size Effects for Multi-Axial Tension Testing of HDPE and PVC Geomembranes
Authors: Merry SM , Bray JD
Published: February 2009

Geosynthetics may be subjected to multi-axial stress states from plane strain loading, such as dragdown along lined slopes and from out-of-plane loading conditions imposed by localized subsidence beneath waste containment cover and liner systems. The multiaxial tension test is useful in evaluating the performance of geosynthetics subjected to multi-axial stress states. However, widespread acceptance and use of this test has been slow due to the perceived requirement of a large-diameter test apparatus with its corresponding high cost. The development of a fully automated axisymmetric tension test apparatus and the results from laboratory testing of two geomembranes (HDPE and PVC) are presented in this paper. With this test apparatus, any one of four clamping rings of different diameters may be used to restrain the geomembrane during a particular test. Critical aspects of the test equipment and test procedures are described. The laboratory results indicate that use of a clamping ring with a significantly smaller diameter than currently required will provide comparable results provided that guidelines concerning the ratio of the clamping ring diameter to the material thickness are adopted and that stress-strain-time compatibility is maintained. This finding is supported by relevant membrane theory.
A New Boundary Stress Transducer for Small Soil Models in the Centrifuge
Authors: Pang PLR
Published: February 2009

The need to obtain reliable boundary stress measurements in centrifugal models of reinforced earth retaining walls has led to the development of a new form of boundary stress transducer. A rectangular sensitive face 100 mm long by 10 mm wide has been chosen to capture sufficient soil grains to give a representative soil pressure. Calibrations of the transducers under a layer of sand in the centrifuge were in good agreement with the deadweight calibrations. When used in a series of centrifuge model tests, the new transducers performed reliably in an environment that was anticipated to have a relatively large stress gradient.
A New Technique to Evaluate Erosivity of Cohesive Material
Authors: Rohan K , Lefebvre G , Douville S , Milette J-P
Published: February 2009

The paper presents a laboratory technique to evaluate the erosivity of cohesive soils, which permits, in addition to determining the critical shear stress, the observation of the rate and the mode of erosion throughout the test. The technique is similar to the pinhole test except that the hydraulic conditions are monitored at the entrance and exit of the specimen and that the eroded soil is recovered for the different stages of the test. The Moody diagram can be used to assess the evolution of the friction factor of the eroded surface during the test. Typical results are presented for tests on intact and sensitive structured clays of Eastern Canada. Erosion of intact clays has not been observed at the clay particle level but rather at the level of coarser grains or clay chunks associated with heterogeneities or fissures.
Centrifuge Testing of Vertically Loaded Battered Pile Groups in Sand
Authors: Zhang L , McVay MC , Lai P
Published: February 2009

Vertical load tests were carried out on 3 by 3 and 4 by 4 fixed head battered pile groups on a centrifuge. These tests simulated 0.43-m-wide by 13.7-m-long square piles founded in loose (Dr = 36%) and medium dense (Dr = 55%) sands at three-diameter spacing. The axial load and shear in each pile were measured during the tests. Numerical analysis was also carried out to predict the battered pile behavior using a coupled bridge foundation-superstructure finite element code (FLPIER). It was found that the vertical capacity of a battered pile group was slightly larger than that of a corresponding plumb pile group. The shear forces and bending moments in battered piles induced by design vertical loads were approximately one third of the ultimate lateral capacity.
The Application of Computer-Assisted Tomography in the Analysis of Fracture Geometry
Authors: Walters DA , Wong RCK , Kantzas A
Published: February 2009

An experimental study was conducted to investigate the surface characteristics of an oil sand fracture. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tension test. A computer-assisted tomography scanning analysis was performed to determine the fracture geometry. The fracture was shown to be a variable aperture system that would have significant effects of the permeability of the fracture. The aperture distributions of the fractures were found to follow a log-normal distribution, similar to that of previously studied rock fractures.
Shear Strength Characteristics of Madinah Clay with Sand Compaction Piles
Authors: Gutub MZA , Khan AM
Published: February 2009

Shear strength characteristics of soft Madinah clay have been investigated from a series of consolidated undrained (CU) direct shear tests on specimens without and with circular sand drains of variable diameters. The investigation is conducted to study the shear strength behavior of soft Madinah clay in the presence of sand drains provided for the purpose of accelerating drainage and enhancing its response towards stabilization by preloading. The experimental shear strength test results have been compared with the theoretical values based on shear strength of clay-sand composite material derived from the shear properties of the individual materials. The shear strength parameters obtained from this study are expected to be of benefit and practical use for carrying out stability analysis of structures like embankments and foundations supported by clay and stabilized with vertical sand drains. Useful data were obtained showing a positive influence of the sand drain system on the enhancement of shear strength characteristics of soft Madinah clay.
Experience with the Use of Methylcellulose as a Viscous Pore Fluid in Centrifuge Models
Authors: Stewart DP , Chen Y-R , Kutter BL
Published: February 2009

In geotechnical modeling, the use of a pore fluid having viscosity greater than that of water is a well-established method of satisfying the scaling laws relating to movement of pore fluid through the soil during dynamic loading events. This has often been achieved with either silicone oil or mixtures of water and glycerol. However, there are a number of inherent drawbacks and difficulties in using silicone oil in particular, and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has been used recently with success. This paper presents test data documenting the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration. The relative performance of the fluid is illustrated with data from two centrifuge model tests, one with pure water as the pore fluid and one with an HPMC solution having viscosity ten times that of water.
Air Volume Change Measurement in Unsaturated Soil Testing Using a Digital Pressure-Volume Controller
Authors: Adams BA , Wulfsohn D , Fredlund DG
Published: February 2009

One of the challenges associated with the testing of unsaturated soils is the measurement of air volume change induced by stress changes. This paper reports the results of an evaluation of a digital pressure-volume controller as an air volume change indicator. Effects of temperature, confined volume, and precompression of the measurement medium on the p-V characteristics and the device response were determined. The device was also used to measure air volume changes of unsaturated soil specimens undergoing isotropic consolidation and axial loading in constant water content tests in a triaxial cell. The results show that the controller performs satisfactorily as an air volume change measurement device. It also permits measurement of air volume change simultaneously with the implementation of the axis-translation technique, making it a versatile device in the testing of unsaturated soils.
Ultrasonic Method for Evaluation of Annular Seals for Wells and Instrument Holes
Authors: Yesiller N , Edil TB , Benson CH
Published: February 2009

An ultrasonic testing method employing the pulse-echo inspection technique was developed to assess the integrity of annular seals surrounding casings (i.e., instrument tubes or well casings). This nondestructive testing method permits testing a seal from inside a casing without disturbing the casing, seal, or formation. Seals constructed with cement-based and bentonite-based sealants surrounding various types and sizes of casings can be evaluated using the method. An evaluation is conducted by sending and receiving ultrasonic waves using a single piezoelectric transducer and commercially available hardware (a pulser receiver and a waveform analyzer). A probe was designed and constructed for downhole testing. Differences in the ultrasonic responses of the materials in contact with a casing are analyzed to determine the presence of different materials (seal or defects filled with air or water in a seal) outside a casing.
Measurement of Volume Changes in Triaxial Tests Using Digital Imaging Techniques
Authors: Macari EJ , Parker JK , Costes NC
Published: February 2009

Conventional procedures for the determination of volume changes in triaxial tests are based on the amount of pore fluid changes into or out of the fully saturated cylindrical specimen. As a triaxial soil specimen shears, the total volume may increase or decrease depending on the soil density, current state of stress, and the stress history. The measurement of these changes in volume are of great importance in the characterization of the soil's mechanical properties. This paper presents an innovative or alternative technique that has been used for measuring the volumetric deformation that cylindrical specimens experience during the shearing stages of a triaxial test. This method incorporates digital imaging techniques and computer-aided analysis to assess the changes in volume throughout a test. A detailed description of the hardware and other equipment is provided along with the data analysis methodology used to simplify the operation. Comparisons are made between the observed results and those obtained from conventional measurement techniques.
NMDA Receptor Activation Increases Free Radical Production through Nitric Oxide and NOX2
Authors: Girouard Helene , Wang Gang , Gallo Eduardo F. , Anrather Josef , Zhou Ping , Pickel Virginia M. , Iadecola Costantino
Published: February 2009

Reactive oxygen species (ROS) and nitric oxide (NO) participate in NMDA receptor signaling. However, the source(s) of the ROS and their role in the increase in cerebral blood flow (CBF) induced by NMDA receptor activation have not been firmly established. NADPH oxidase generates ROS in neurons, but there is no direct evidence that this enzyme is present in neurons containing NMDA receptors, or that is involved in NMDA receptor-dependent ROS production and CBF increase. We addressed these questions using a combination ofin vivoandin vitroapproaches. We found that the CBF and ROS increases elicited by topical application of NMDA to the mouse neocortex were both dependent on neuronal NO synthase (nNOS), cGMP, and the cGMP effector kinase protein kinase G (PKG). In mice lacking the NADPH oxidase subunit NOX2, the ROS increase was not observed, but the CBF increase was still present. Electron microscopy of the neocortex revealed NOX2 immunolabeling in postsynaptic somata and dendrites that also expressed the NMDA receptor NR1 subunit and nNOS. In neuronal cultures, the NMDA-induced increase in ROS was mediated by NADPH oxidase through NO, cGMP and PKG. We conclude that NADPH oxidase in postsynaptic neurons generates ROS during NMDA receptor activation. However, NMDA receptor-derived ROS do not contribute to the CBF increase. The findings establish a NOX2-containing NADPH oxidase as a major source of ROS produced by NMDA receptor activation, and identify NO as the critical link between NMDA receptor activity and NOX2-dependent ROS production.
The Sparseness of Neuronal Responses in Ferret Primary Visual Cortex
Authors: Tolhurst David J. , Smyth Darragh , Thompson Ian D.
Published: February 2009

Various arguments suggest that neuronal coding of natural sensory stimuli should be sparse (i.e., individual neurons should respond rarely but should respond reliably). We examined sparseness of visual cortical neurons in anesthetized ferret to flashed natural scenes. Response behavior differed widely between neurons. The median firing rate of 4.1 impulses per second was slightly higher than predicted from consideration of metabolic load. Thirteen percent of neurons (12 of 89) responded to <5% of the images, but one-half responded to >25% of images. Multivariate analysis of the range of sparseness values showed that 67% of the variance was accounted for by differing response patterns to moving gratings. Repeat presentation of images showed that response variance for natural images exaggerated sparseness measures; variance was scaled with mean response, but with a lower Fano factor than for the responses to moving gratings. This response variability and the “soft” sparse responses (Rehn and Sommer, 2007) raise the question of what constitutes a reliable neuronal response and imply parallel signaling by multiple neurons. We investigated whether the temporal structure of responses might be reliable enough to give additional information about natural scenes. Poststimulus time histogram shape was similar for “strong” and “weak” stimuli, with no systematic change in first-spike latency with stimulus strength. The variance of first-spike latency for repeat presentations of the same image was greater than the latency variance between images. In general, responses to flashed natural scenes do not seem compatible with a sparse encoding in which neurons fire rarely but reliably.
Distinct Subtypes of Basolateral Amygdala Taste Neurons Reflect Palatability and Reward
Authors: Fontanini Alfredo , Grossman Stephen E. , Figueroa Joshua A. , Katz Donald B.
Published: February 2009

The amygdala processes multiple, dissociable properties of sensory stimuli. Given its central location within a dense network of reciprocally connected regions, it is reasonable to expect that basolateral amygdala (BLA) neurons should produce a rich repertoire of dynamical responses to taste stimuli. Here, we examined single BLA neuron taste responses in awake rats and report the existence of two distinct subgroups of BLA taste neurons operating simultaneously during perceptual processing. One neuron type produced long, protracted responses with dynamics that were strikingly similar to those previously observed in gustatory cortex. These responses reflect cooperation between amygdala and cortex for the purposes of processing palatability. A second type of BLA taste neuron may be part of the system often described as being responsible for reward learning: these neurons produced very brief, short-latency responses to rewarding stimuli; when the rat participated in procuring the taste by pressing a lever in response to a tone, however, those phasic taste responses vanished, phasic responses to the tone appearing instead. Our data provide strong evidence that the neural handling of taste is actually a distributed set of processes and that BLA is a nexus of these multiple processes. These results offer new insights into how amygdala imbues naturalistic sensory stimuli with value.
Functional Complementation ofGlra1spd-ot, a Glycine Receptor Subunit Mutant, by Independently Expressed C-Terminal Domains
Authors: Villmann Carmen , Oertel Jana , Ma-Högemeier Zhan-Lu , Hollmann Michael , Sprengel Rolf , Becker Kristina , Breitinger Hans-Georg , Becker Cord-Michael
Published: February 2009

The oscillator mouse (Glra1spd-ot) carries a 9 bp microdeletion plus a 2 bp microinsertion in the glycine receptor α1 subunit gene, resulting in the absence of functional α1 polypeptides from the CNS and lethality 3 weeks after birth. Depending on differential use of two splice acceptor sites in exon 9 of theGlra1gene, the mutant allele encodes either a truncated α1 subunit (spdot-trc) or a polypeptide with a C-terminal missense sequence (spdot-elg). During recombinant expression, both splice variants fail to form ion channels. In complementation studies, a tail construct, encoding the deleted C-terminal sequence, was coexpressed with both mutants. Coexpression with spdot-trc produced glycine-gated ion channels. Rescue efficiency was increased by inclusion of the wild-type motif RRKRRH. In cultured spinal cord neurons from oscillator homozygotes, viral infection with recombinant C-terminal tail constructs resulted in appearance of endogenous α1 antigen. The functional rescue of α1 mutants by the C-terminal tail polypeptides argues for a modular subunit architecture of members of the Cys-loop receptor family.
The Role of Sonic Hedgehog of Neural Origin in Thalamic Differentiation in the Mouse
Authors: Szabó Nora-Emöke , Zhao Tianyu , Zhou Xunlei , Alvarez-Bolado Gonzalo
Published: February 2009

The specification of the intricate neuronal assemblies that characterize the forebrain is not well understood. The ventral spinal cord is specified through a concentration gradient of Sonic hedgehog (Shh) protein secreted by the notochord.Shhis expressed also in the forebrain neuroepithelium (neural Shh) and the underlying notochord and prechordal plate. Neural Shh is essential for the development of the prethalamus (ventral thalamus), but its effects on the thalamus (dorsal thalamus) are still unclear. We hypothesized that neural Shh would act on a previously regionalized dorsal diencephalic region to promote the emergence of specific thalamic nuclear and histological traits. To find out, we generated a conditional mouse mutant line specifically lacking Shh expression in the diencephalic neuroepithelium. We show that the transcription factor Gbx2, required for thalamic development downstreamShh, is expressed in our mutant in a restricted thalamic region and is necessary and sufficient for the differentiation of the medial and intralaminar thalamic nuclei. In the rest of the thalamus, neuralShhis required to promote neuronal aggregation into nuclei as well as axonal extension. In this way, the individual thalamic nuclei show differential dependence onShh,Gbx2, or both for their differentiation. Additionally, Gbx2 is required for the survival of thalamic neurons.
A Loss of Parvalbumin-Containing Interneurons Is Associated with Diminished Oscillatory Activity in an Animal Model of Schizophrenia
Authors: Lodge Daniel J. , Behrens Margarita M. , Grace Anthony A.
Published: February 2009

Decreased GABAergic signaling is among the more robust pathologies observed postmortem in schizophrenia; however, the functional consequences of this deficit are still largely unknown. Here, we demonstrate, in a verified animal model of schizophrenia, that a reduced expression of parvalbumin (PV)-containing interneurons is correlated with a reduction in coordinated neuronal activity during task performance in freely moving rats. More specifically, methylazoxymethanol acetate (MAM)-treated rats display a decreased density of parvalbumin-positive interneurons throughout the medial prefrontal cortex (mPFC) and ventral (but not dorsal) subiculum of the hippocampus. Furthermore, the reduction in interneuron functionality is correlated with a significantly reduced gamma-band response to a conditioned tone during a latent inhibition paradigm. Finally, deficits in mPFC and ventral hippocampal oscillatory activity are associated with an impaired behavioral expression of latent inhibition in MAM-treated rats. Thus, we propose that a decrease in intrinsic GABAergic signaling may be responsible, at least in part, for the prefrontal and hippocampal hypofunctionality observed during task performance, which is consistently observed in animal models as well as in schizophrenia in humans. In addition, a deficit in intrinsic GABAergic signaling may be the origin of the hippocampal hyperactivity purported to underlie the dopamine dysfunction in psychosis. Such information is central to gaining a better understanding of the disease pathophysiology and alternate pharmacotherapeutic approaches.
Interpreting Stream Physical Characteristics in Index of Biotic Integrity Classifications: General Similarities and Specific Differences
Authors: Goldstein Robert M.
Published: February 2009

Fish assemblage-based indices of biotic integrity (IBIs) are commonly used by many states. These IBIs contain a core of common metrics and a few metrics that are specific to the local environmental setting and fish assemblage. This implies a consistency of responses as degradation increases, but the responses are modified by the local environmental setting. These implications lead to two hypotheses: (1) stream physical characteristics, such as substrate composition, geomorphologic composition, and hydraulic characteristics, will differ among integrity classes regardless of geographic location or environmental setting and (2) the differences in stream physical characteristics among integrity classes change due to the environmental setting. To test these hypotheses, fish assemblages and stream physical characteristics were examined across a priori defined degradation gradients in four diverse environmental settings by comparing species traits (preferences for substrate, preferences for geomorphic channel units, and locomotion morphology) and stream physical characteristics (substrate composition, geomorphic channel unit abundance, and stream hydraulic characteristics) among three IBI classes (high, moderate, and low). Across all environmental settings combined, Euclidean distances of species traits normalized to local reference conditions indicated differences in substrate preferences among each of the three integrity classes: substrate particle size preferences differed among all three integrity classes, geomorphic channel unit preference differed between the high-integrity sites and the other sites, and locomotion morphology differed between low-integrity sites and the other sites. These results indicate that degradation occurs in each of the three physical stream characteristics regardless of environmental setting. Within the individual environmental settings, there were some specific differences in the changes in substrate preferences, geomorphic unit preference, and locomotion morphology among integrity classes. Within individual environmental settings, differences in stream physical characteristics among integrity classes generally reflected the same differences as indicated by differences in fish assemblage composition.
Variation in Growth and Survival of Bluegills and Redbreast Sunfish in Georgia Rivers
Authors: Sammons Steven M. , Maceina Michael J.
Published: February 2009

Growth and survival of bluegills Lepomis macrochirus and redbreast sunfish L. auritus (N = 5,664) were examined in 13 river sections located in the southern half of Georgia. Bluegills tended to grow faster than redbreast sunfish within rivers where the two species were collected together. Annual survival of redbreast sunfish (range = 18–52%; mean = 38%) was greater than that of bluegills (range = 21–34%; mean = 29%). For both species, growth of males was generally greater than females, though annual survival did not differ significantly between sexes for either species. Growth of redbreast sunfish and bluegills appeared to increase along a northwest to southeast gradient across the state of Georgia. Growth variation of these sunfishes was likely mediated by prey availability, habitat, and physicochemical variables within each river section.
Instream Evaluation of Passive Integrated Transponder Retention in Brook Trout and Brown Trout: Effects of Season, Anatomical Placement, and Fish Length
Authors: Dieterman Douglas J. , Hoxmeier R. John H.
Published: February 2009

We examined effects of tagging season, anatomical placement of tags, and fish total length (TL) at tagging on 2-month retention of passive integrated transponder (PIT) tags in 181 brook trout Salvelinus fontinalis (99–302 mm TL) and 709 brown trout Salmo trutta (122–511 mm TL) in small streams of southeastern Minnesota. A lower percentage of brown trout retained their tags in spring (56%) than in fall (68%), but season did not affect tag retention in brook trout. Retention rates varied with anatomical placement for both species. For brook trout, retention was 70% when the PIT tag was placed into the body cavity using an insertion point that was posterior to the pelvic fins and 100% when the tag was placed into the dorsal musculature. Among brown trout, PIT tag retention was 56% for body cavity placement (posterior insertion) and 95% for dorsal musculature placement. Tag retention was not associated with fish TL for brown trout and was only weakly associated with TL of brook trout. Although reported retention rates of PIT tags implanted into the body cavity of salmonids have often exceeded 90%, our retention estimates were considerably lower. This discrepancy can be partially attributed to differences in laboratory versus field studies. However, most previous studies of salmonids have used body cavity insertion points that were anterior to the pelvic fins, whereas we used a posterior insertion point; this was probably the primary factor responsible for the difference in results. We caution against the assumption that retention of PIT tags is universally high, and we recommend the estimation of PIT tag retention before or during marking studies. We also provide a list of factors that should be considered and evaluated when designing PIT tag studies, especially tag retention studies.