bluuebunny/crossref_metadata_2025 huggingface dataset:
An Eddy Viscosity Calculation Method for a Turbulent Duct Flow
Authors: Antonia R. A. , Bisset D. K. , Kim J.
Published: May 2008

The mean velocity profile across a fully developed turbulent duct flow is obtained from an eddy viscosity relation combined with an empirical outer region wake function. Results are in good agreement with experiments and with direct numerical simulations in the same flow at two Reynolds numbers. In particular, the near-wall trend of the Reynolds shear stress and its variation with Reynolds number are similar to those of the simulations. The eddy viscosity method is more accurate than previous mixing length or implicit function methods.
Mean and Turbulence Characteristics of a Class of Three-Dimensional Wall Jets—Part 1: Mean Flow Characteristics
Authors: Padmanabham G. , Lakshmana Gowda B. H.
Published: May 2008

This paper reports experimental investigations on mean and turbulence characteristics of three-dimensional, incompressible, isothermal turbulent wall jets generated from orifices having the shapes of various segments of a circle. In Part 1, the mean flow characteristics are presented. The turbulence characteristics are presented in Part 2. The influence of the geometry on the characteristic decay region of the wall jet is brought out and the differences with other shapes are discussed. Mean velocity profiles both in the longitudinal and lateral planes are measured and compared with some of the theoretical profiles. Wall jet expansion rates and behavior of skin-friction are discussed. The influence of the geometry of the orifice on the various wall jet properties is presented and discussed. Particularly the differences between this class of geometry and rectangular geometries are critically discussed.
Mean and Turbulence Characteristics of a Class of Three-Dimensional Wall Jets—Part 2: Turbulence Characteristics
Authors: Padmanabham G. , Lakshmana Gowda B. H.
Published: May 2008

The mean flow characteristics of three-dimensional, incompressible, isothermal turbulent wall jets generated from orifices having the shapes of various segments of a circle are presented in Part 1 of this paper. In this part, the turbulence characteristics are presented. Turbulence quantities measured include normal stresses and Reynolds shear stresses in the characteristic-decay and in the radial-decay regions of the wall jets investigated. These results are compared with those available for two-dimensional and three-dimensional wall jets. The presence of counter-gradient regions and the feature of “energy reveral” are discussed.
Experimental Investigation of a Turbulent Flow in the Vicinity of an Appendage Mounted on a Flat Plate
Authors: Merati P. , McMahon H. M. , Yoo K. M.
Published: May 2008

Experimental measurements were carried out in an incompressible three-dimensional turbulent shear layer in the vicinity of an appendage mounted perpendicular to a flat plate. The thickness of the turbulent boundary layer as it approached the appendage leading edge was 76 mm or 1.07 times the maximum thickness of the appendage. As the oncoming boundary layer passed around the appendage, a strong secondary flow was formed which was dominated by a horseshoe root vortex. This secondary flow had a major effect in redistributing both the mean flow and turbulence quantities throughout the shear layer, and this effect persisted to a significant degree up to at least three chord lengths downstream of the appendage leading edge.
Maximum Pressure Head Due to Linear Valve Closure
Authors: Liou Chyr Pyng
Published: May 2008

The maximum pressure head resulting from one-speed closure of wide open valves is investigated. The dimensionless variables formulated in this study make the subtle effect of the initial valve head loss explicit and separate from that of the pipe frictional head loss. The maximum head is related to initial pipe frictional head loss, the initial valve head loss, the inherent flow characteristic of the valve, and the closure period by plots of dimensionless variables. The trends of the variation of the maximum pressure head are discussed. An example is used to illustrate the usage of the plots, and to show the advantage of having a global perspective of the phenomenon in the selection and sizing of valves from the water hammer point of view.
Torque Measurements of Corotating Disks in an Axisymmetric Enclosure
Authors: Hudson A. J. , Eibeck P. A.
Published: May 2008

Torque measurements, which can be related to viscous dissipation, were made in a simulated disk drive consisting of a single or multiple corotating disk stack enclosed in an axisymmetric shroud. The effects of rotational velocity, axial and radial spacing, and the position and thickness of simulated read/write arms between disks on torque were studied. Correlations are presented to describe the results of the unobstructed cases and the cases with the read/write arms at their innermost position, and a method is introduced to calculate the torque at intermediate arm positions.
LDV Measurements and Investigation of Flow Field Through Radial Turbine Guide Vanes
Authors: Eroglu Hasan , Tabakoff Widen
Published: May 2008

The results of LDV measurements and investigation of the detailed flow field in a radial inflow turbine nozzle are presented. The flow velocities were measured at upstream, inside and downstream of the nozzle blades for two different mass flow rates, using a three-component LDV system. Results are presented as contour plots of mean velocities, flow angles, and turbulence intensities. The flow field inside the nozzle blade passages was found to be influenced by the upstream scroll geometry. The flow turbulence increased in the downstream flow direction. The LDV mean flow results on the blade-to-blade midspan plane which is parallel to the end walls were also compared with an inviscid, “panel method” solution.
On the Mach Number Variation in Steady Flows of Dense Hydrocarbons
Authors: Cramer M. S.
Published: May 2008

We consider the steady flow of five commonly encountered hydrocarbons in their dense gas regime. Isentropic flows are first examined and it is shown that dense gas effects lead to a non-monotone variation of the Mach number with density. It is also demonstrated that these effects may give rise to an increase, rather than the classical decrease, in the Mach number across oblique compression shocks. Significant increases in the shock detachment angle are also reported.
Aerodynamic Sensitivity Analysis Methods for the Compressible Euler Equations
Authors: Baysal Oktay , Eleshaky Mohamed E.
Published: May 2008

A mathematical formulation is developed for aerodynamic sensitivity coefficients based on a discretized form of the compressible, two-dimensional Euler equations. A brief motivating introduction to the aerodynamic sensitivity analysis and the reasons behind an integrated flow/sensitivity analysis for design algorithms are presented. Two approaches to determine the aerodynamic sensitivity coefficients, namely, the finite difference approach, and the quasi-analytical approach are discussed with regards to their relative accuracies and involved computational efforts. In the quasi-analytical approach, the direct and the adjoint variable methods are formulated and assessed. Also, several methods to solve the system of linear algebraic equations, that arises in the quasi-analytical approach, are investigated with regards to their accuracies, computational time and memory requirements. A new flow prediction concept, which is an outcome of the direct method in the quasi-analytical approach, is developed and illustrated with an example. Surface pressure coefficient distributions of a nozzle-afterbody configuration obtained from the predicted flow-field solution are compared successfully with their corresponding values obtained from a flowfield analysis code and the experimental data.
Gravity-Driven Motion of a Layer of Viscoelastic Fluid Around a Horizontal Wire
Authors: Souza Mendes P. R. , Naccache M. F.
Published: May 2008

A theoretical study of the free-surface flow of a viscoelastic fluid around a horizontal cylinder is reported in this paper. The fluid layer has initially a uniform thickness, and, at some instant of time, it starts to flow due to the presence of a gravity field. The result sought is the film thickness as a function of time and angular position. The mass- and momentum-conservation principles are employed in conjunction with the Maxwell constitutive equation. Using an integral method, a system of two nonlinear equations is obtained. The results are compared with the ones for a Newtonian fluid, and the elastic effects are shown to change dramatically the flow.
Separation and Surface Nuclei Effects in a Cavitation Susceptibility Meter
Authors: d’Agostino L. , Acosta A. J.
Published: May 2008

This work is concerned with the effects of flow separation and surface nuclei on the operation of a fixed geometry Cavitation Susceptibility Meter (CSM) with laminar flow. Cavitation is induced under controlled conditions at the throat of a glass venturi tube for the measurement of the active nuclei concentration in water samples as a function of the applied tension. Both cavitation and flow velocity are monitored optically by a Laser Doppler Velocimeter. The throat pressure is determined indirectly from the upstream pressure and the local flow velocity. The results show that laminar flow separation and surface nuclei effects are the most stringent operational limitations. Separation in the diffuser increases the minimum attainable throat pressure above the susceptibility of most cavitation nuclei commonly found in technical waters. Surface nuclei can generate extensive sheet or spot cavitation at relatively high tensions even on optically finished glass surfaces. These phenomena are difficult to eliminate and bring therefore into question the practical utility of CSM’s with laminar flow and fixed geometry for the measurement of the dependence of the cavitating nuclei concentration over wide ranges of the applied tension, as required for cavitation studies.
A Statistical Analysis of Cavitation Erosion Pits
Authors: Belahadji B. , Franc J. P. , Michel J. M.
Published: May 2008

An optical interferometric technique has been used to determine the 3-D shape of cavitation erosion pits. The method which is particularly suitable to the determination of pit diameter and pit depth is used for a statistical analysis of cavitation erosion pits. We analyzed numerous samples which were eroded at various velocities with two different fluids (mercury and water) on two geometrically similar venturi test sections of different length scales. General properties of histograms of pit size are pointed out. The influence of flow velocity on pitting rates corresponding to limited ranges of pit size is discussed. The contribution of each pit diameter to the total eroded surface is analyzed. Some results are given on pit depths and pit volumes.
Local Anisotropy in Strained Turbulence at High Reynolds Numbers
Authors: Durbin P. A. , Speziale C. G.
Published: May 2008

It is shown that the hypothesis of local isotropy is implausible in the presence of significant mean rates of strain. In fact, it appears that in uniform shear flow near equilibrium, local isotropy can never constitute a systematic approximation, even in the limit of infinite Reynolds number. An estimate of the level of mean strain rate for which local isotropy is formally a good approximation is provided.
Partial Acoustic Filtering Applied to the Equations of Compressible Flow
Authors: Torczynski J. R.
Published: May 2008

Gas contained in a rectangular laser cell of large length and small width is subjected to large, transient, spatially nonuniform, volumetric heating when pumped. The heating time scale is much longer than the time required for an acoustic wave to traverse the width but can be comparable to the time required for an acoustic wave to traverse the length. Approximate equations describing the motion are derived by applying partial acoustic filtering to the equations of motion: pressure waves traversing the width are removed while pressure waves traversing the length are retained. For a simplified one-dimensional example, a significant density variation is found across the width of the laser cell; moreover, this density variation is in good agreement with a numerical solution of the unapproximated gas dynamic equations although the latter requires two orders of magnitude more computational time
Elevation Changes in Antarctica Mainly Determined by Accumulation Variability
Authors: Helsen Michiel M. , van den Broeke Michiel R. , van de Wal Roderik S. W. , van de Berg Willem Jan , van Meijgaard Erik , Davis Curt H. , Li Yonghong , Goodwin Ian
Published: May 2008

Antarctic Ice Sheet elevation changes, which are used to estimate changes in the mass of the interior regions, are caused by variations in the depth of the firn layer. We quantified the effects of temperature and accumulation variability on firn layer thickness by simulating the 1980–2004 Antarctic firn depth variability. For most of Antarctica, the magnitudes of firn depth changes were comparable to those of observed ice sheet elevation changes. The current satellite observational period (∼15 years) is too short to neglect these fluctuations in firn depth when computing recent ice sheet mass changes. The amount of surface lowering in the Amundsen Sea Embayment revealed by satellite radar altimetry (1995–2003) was increased by including firn depth fluctuations, while a large area of the East Antarctic Ice Sheet slowly grew as a result of increased accumulation.
Heave of Spillway Structures on Clay Shales
Authors: Peterson R , Peters N
Published: May 2008

Construction of spillways on clay shale in Western Canada has resulted in some serious heave problems. This paper briefly describes the clay shales of the area and gives typical laboratory swelling test results. It has not yet been possible to predict total heave and rate of heave from laboratory tests. Observational programs to check the performance of existing structures as well as special tests were undertaken to provide information required for design. Typical heave observations at spillways showing the effect of seepage, frost action, and hold-down piles are included.
Some Recent Research on the Bearing Capacity of Foundations
Authors: Meyerhof George Geoffrey
Published: May 2008

The first part of the paper summarizes the results of recent research on the bearing capacity of spread foundations of various shapes under a central vertical load and outlines the effects of foundation depth, eccentricity and inclination of the load. Simple formulae have been derived for use in practice and their application to the design of rigid and flexible foundations is briefly indicated.The second part of the paper discusses the bearing capacity of single piles under vertical and inclined loads. The bearing capacity of piled foundations and free-standing pile groups is outlined, and the results of model tests on pile groups under central and eccentric loads are briefly analysed in relation to some problems in practice.
Volume Changes in Undisturbed Clay Profiles in Western Canada
Authors: Hamilton J J
Published: May 2008

As part of an over-all study of the performance of building foundations in highly plastic soil areas of western Canada, the Division of Building Research has been measuring ground movements and changes in soil moisture conditions in grass-covered, undisturbed soil profiles under climatic conditions ranging from sub-humid to semi-arid. Results of measurements begun in 1951 in Winnipeg, Manitoba, and more recently those in Regina, Eston, and Tisdale, Saskatchewan, are reported. Results of a theoretical soil moisture depletion calculation, based on Thornthwaite's potential evapo-transpiration concept, are presented. It is proposed as a more rational way of measuring the vegetation-climate factor in humid to sub-humid climates than simply comparing air temperature and precipitation with long-term averages. Empirical relationships are suggested between calculated soil moisture depletion, the depth of free water table, and the depth of frost penetration under similar thermal conditions but different soil moisture conditions. Shrinkage in situ of undisturbed, unsaturated soils at temperatures well below 32° F has been observed and is attributed to thermal air-void volume change.
The Modulus of Elasticity of Leda Clay from Field Measurements
Authors: Bozozuk M
Published: May 2008

The construction of the Ottawa Sewage Treatment Plant provided an opportunity to measure bottom heave in two large excavations in clay. With gauges installed prior to excavation, elastic heave, swelling, and heave due to pile driving were measured in an excavation 31.5 ft. deep. Using a Poisson's ratio of 0.4, the modulus of elasticity determined from field measurements compared favourably with the initial tangent modulus from the best unconfined compression strength tests. In the other excavation a drop in the ground water table produced an elastic settlement that exceeded the elastic heave resulting from unloading by excavation.
Application of the Resistance-Capacitance Heat-Flow Analog to Soil Systems
Authors: Pedersen Roger J , Schenck, Jr. Hilbert
Published: May 2008

An electrical analog of two-dimensional heat transfer systems, easily constructed of small resistors and capacitors, has many uses in the shady of heat transfer in soils. Scale factors are established and a 146-node model is applied to the design of a pit to be used for inserting thermistor probes laterally into a soil mass. The model is also used to obtain general solution maps to other soil systems with results displayed on generalized graphs of equivalent depths. This graphical approach, explained herein, is useful for illustrating the effect of local anomalies in two-dimensional soil systems having sinusoidal surface temperatures. Limitations of this simple analog model are discussed.
Mathematical Analysis of Swell Pressure With Time for Partly Saturated Clays
Authors: Baker R , Kassiff G
Published: May 2008

Experimental results of swell pressure under complete inundation show that the curve of pressure against log of time has a typical reversed S shape, similar to that of consolidation. No endeavour, however, has been made to explain this behaviour theoretically.The paper deals with the mathematical derivation of the swell pressure function and the definition of the parameters involved. Under certain simplified assumptions, it is shown that the dissipation of the suction during a swelling test is proportional to the development of the swell pressure and that the dissipation function is mathematically identical with that of the consolidation process. The solution of this function yielded a rather simple expression for the swell pressure, which agrees with values obtained when the clay is saturated and results in a fraction of the initial suction when the clay is partly saturated.
The Ultimate Uplift Capacity of Foundations
Authors: Meyerhof G G , Adams J I
Published: May 2008

The ultimate uplift capacity of foundations with special reference to transmission tower footings is evaluated. A number of model uplift tests made by the authors and by others were studied and compared with full-scale tests. These tests showed a complex failure mechanism which varied with the depth of the foundation. Using simplifying assumptions a general theory was produced. It was shown that with suitable modification for shape and depth a useful relationship was available for computing the full-scale uplift capacity of foundations. It was further shown by model tests that the theory could be modified to take into account group action. Further research is required to evaluate the effect of combined loads and long-term effects.
Lateral resistance and deflection of rigid walls and piles in layered soils
Authors: Meyerhof G. G. , Mathur S. K. , Valsangkar A. J.
Published: May 2008

The ultimate lateral resistance and the lateral deflection at working loads of rigid vertical walls and piles with a free head subjected to horizontal load and embedded in two-layered soils of sand and clay have been investigated. Part 1 deals with the behaviour of rigid walls, and the analyses are compared with the results of model wall tests in layered soils. Part 2 treats the behaviour of rigid piles, and the analyses are compared with the results of model tests on piles and pile groups in layered soils and some field case records.
The influence of geotechnical engineering on the evolution of offshore structures in the North Sea
Authors: Gibson R. E. , Dowse B. E. W.
Published: May 2008

The selection of the type of drilling or production platform appropriate to a particular off shore site depends, chiefly, upon the likely severity of the marine environment, the nature of the seabed, and the geotechnical properties of the underlying soils and whether there exists a requirement for on-site oil storage. Although these physical factors have all played important roles in shaping the evolution of offshore structures, particularly in the North Sea, economic considerations and the national preferences of client companies have on occasion been decisive.This paper traces the evolution of offshore oil production structures for the North Sea with particular emphasis on the role played by geotechnical engineering during the conception, design, and construction of some of the largest movable structures in the world.
The effect of stress on the primary permeability of rock cores—a facet of hydraulic fracturing
Authors: Heystee R. , Roegiers J.-C.
Published: May 2008

Recent laboratory hydraulic fracturing experiments have shown that fluid penetration into the rock mass adjacent to the borehole being pressurized has a significant influence on the magnitude of the breakdown pressure. One factor affecting the degree of penetration of the pressurizing fluid is the permeability of the rock mass, which in turn is a function of the state of stress present in the rock mass. To study this permeability–stress relationship, a radial permeameter was constructed and three rock types tested. Derived expressions show that during radially divergent and convergent flow in the permeameter, the state of stress in the rock specimen is tensile and compressive respectively. The radial permeameter test results show that the permeability of rock increases significantly under tensile stress conditions and reduces under compressive stress conditions. The results from this study were used to develop a conceptual model which explains the dependency of breakdown pressure levels on the pressurization rate.
Urban landslides in the vicinity of Vancouver, British Columbia, with special reference to the December 1979 rainstorm
Authors: Eisbacher G. H. , Clague J. J.
Published: May 2008

Historical landslides in the urbanized Vancouver region, southwestern British Columbia, have almost commonly occurred along escarpments within and at the margins of gently rolling upland surfaces underlain by Pleistocene unconsolidated sediments. The most common and most destructive landslides are debris avalanches and debris flows. They are triggered by intense autumn and winter rainstorms, when water infiltrates and saturates the surficial layer of weathered colluvium. After failure the veneer of debris gains momentum and picks up additional soil and uprooted vegetation. Debris avalanches may temporarily block gullies swollen with runoff water, thus changing into rapidly moving debris flows.A severe rainstorm in December 1979 was accompanied by destructive debris avalanches and debris flows in urban areas in the vicinity of Vancouver. A search of local newspapers and meteorological records back to 1900 indicates that this event was not unique, for at least 26 other comparable storms have triggered landslides in the Vancouver region during this century. Thus it is likely that landslides similar to those of December 1979 will occur repeatedly in the future. The danger of such landslides to life and property will grow if potentially hazardous sites are urbanized without appropriate protective measures.
Simple shear creep tests on frozen soils
Authors: Weaver J. S. , Morgenstern N. R.
Published: May 2008

Direct simple shear tests have been conducted on a variety of reconstituted frozen soils and on ice in order to investigate the load transfer process associated with the adfreeze bond to piles, and to obtain creep properties of frozen soils. The test develops uniform shear strain between plates of different roughnesses provided the applied shear stress is less than the ad freeze strength of the pile. Tests have been performed at about −1°C for durations up to 45 days to explore ultimate creep rates. The long-term flow of ice in this test is consistent with previously published power law relations. The experimental data on the frozen soils indicate how creep rate tends to decrease with increasing density except for dirty ice, which displays creep rates slightly higher than those observed for pure ice.
Equipment and techniques for offshore survey and site investigations
Authors: Sly P. G.
Published: May 2008

This contribution presents a recent review of equipment and field techniques applicable to offshore seabed survey work and site investigation, with particular reference to Canadian interests.During the past decade many advances have taken place in equipment design and in under standing the behaviour of mechanical sampling devices and the inadequacies of data derived from samples physically removed from the site. There has been a significant improvement in the ability of both remote and contact sensory systems to characterize and resolve differences in the physical and mechanical properties of bottom sediment materials, and the use of even simplistic remotely sensed data, if rapidly obtained and processed, offers significant economic advantages. The trend towards greater use of in situ tests will continue.The application of facies concepts, in planning field surveys, may provide opportunities for improved sample recovery, reduced sampling, and greater confidence in data interpretation.Data, comments, and examples refer to a number of Canadian situations, for example, deep ocean studies, shelf studies (such as on the Labrador Shelf, the Scotian Shelf, and the Beaufort Sea), inter-island studies in the Canadian Arctic, and inland studies in the Great Lakes and smaller lake and river systems.
The theory of one-dimensional consolidation of saturated clays. II. Finite nonlinear consolidation of thick homogeneous layers
Authors: Gibson Robert E. , Schiffman Robert L. , Cargill Kenneth W.
Published: May 2008

The one-dimensional consolidation of a thick clay layer, initially consolidated fully under its own weight, is considered. Account is taken of the variation of the coefficients of permeability and compressibility as consolidation proceeds. To render the theory consistent finite strains are permitted. Comparisons with conventional theory, in a practical example, show that nonlinear finite strain theory predicts the progress of consolidation settlement to be substantially swifter than indicated by conventional theory, although the dissipation of excess pore pressure may be slower. The consequences of this indicate that conventional consolidation theory has the potential to seriously underestimate the excess pore water pressure in a soft layer. As a result, the estimated shear strength would, if an effective stress analysis were used, be overestimated; a potentially unsafe design could emerge.
Mather and landslides: 1838
Authors: White George W. , Legget Robert F.
Published: May 2008

In the first report of the Geological Survey of the state of Ohio there is an account of erosion along the shore of Lake Erie in the vicinity of Cleveland. This is illustrated by a plate which includes a good section of a landslip on retrogressive circular failure planes. Since the report was published in 1838, this observation of the curved failure surfaces in clay slides antedates those of Logan (1842) and Collin (1846). The use of groynes for shore protection is suggested and the phenomenon of piping appears to be suggested.
The bearing capacity of rigid piles and pile groups under inclined loads in clay
Authors: Meyerhof G. G.
Published: May 2008

The ultimate bearing capacity of rigid vertical and batter piles and pile groups in clay has been determined under various inclinations of the load, varying from the vertical to horizontal directions. The results of load tests on single model piles of different lengths and inclinations and on free-standing groups and piled foundations are compared with theoretical estimates. The influence of load inclination on the bearing capacity can be represented by simple interaction relationships between the axial and normal components of the ultimate load. The effect of eccentricity of the load on the ultimate bearing capacity of pile groups is discussed on the basis of previous theory and model test results.
Dynamic response curves for vertically loaded floating pile foundations
Authors: Kuhlemeyer Roger L.
Published: May 2008

Response curves that can be easily used by designers are presented for vertically loaded floating piles. The good accuracy of the theory used was previously confirmed. A design example is presented that illustrates application of the curves.
Evaluation of pile load tests in the Edmonton area
Authors: Thomson S.
Published: May 2008

The design of cast-in-place concrete piles is essentially empirical; hence, an examination of commercial pile load tests is of value. The test data of four pile load tests consisted of the vertical movement of the top of the pile and the load on top of the pile. It was therefore necessary to calculate the shaft and base loads assuming that the till was homogeneous with regard to strength over the length of the pile.The results of the back analyses suggest that the design procedures are valid within practical limits for the prediction of load carrying capacity and for immediate settlement.
Lateral load tests in clay using inflatable air jacks
Authors: Olsson Lars
Published: May 2008

A new method is described by which in situ lateral load tests in soft clay can be carried out. The method uses large, soft, flat jacks which are pushed down into the soil and inflated by air to the desired pressure. The system has been used to field-test total earth pressure cells.
Influence of climate on radial growth and cone production in subalpine fir (Abieslasiocarpa) and mountain hemlock (Tsugamertensiana)
Authors: Woodward Andrea , Silsbee David G. , Schreiner Edward G. , Means Joseph E.
Published: May 2008

Thirty years of cone production records for subalpine fir (Abieslasiocarpa (Hook.) Nutt.) and mountain hemlock (Tsugamertensiana (Bong.) Carr.) (two sites each) in the Cascade Mountains of Washington and Oregon were compared with basal area increment and weather records to determine relationships among weather, radial growth, and cone crop. Results show that the size of subalpine fir cone crops was negatively related to large crops and positively related to radial growth in the previous 2 years. Mountain hemlock cone crops were negatively related o a large cone crop and positively related to July or August temperature in the previous year. Radial growth in heavy cone years was inhibited more for subalpine fir than for mountain hemlock. Results are explained by differences in the location of cone production between species. It is concluded that global climate warming could result in fewer and more irregular cone crops for these species.
Land-use history (1720–1992), composition, and dynamics of oak–pine forests within the Piedmont and Coastal Plain of northern Virginia
Authors: Orwig David A. , Abrams Marc D.
Published: May 2008

Woody vegetation was surveyed in 58 forest stands in northern Virginia to examine the effects of previous land-use history on past and present-day forest composition and dynamics. Stands were separated using detrended correspondence analysis (DCA) and overstory importance values into three forest groups: (i) white oak (Quercusalba L.)–tulip-poplar (Liriodendrontulipifera L.) (ii) white oak–scarlet oak (Quercuscoccinea Muenchh.) and (iii) Virginia pine (Pinusvirginiana Mill.) The first DCA axis represents a successional continuum from more recently disturbed areas containing young pine forests to less disturbed mature oak stands, and is negatively correlated with stand age and species diversity. White oak and red oak (Quercusrubra L.) dominated presettlement forests in the area. Following European settlement, forests experienced intense logging associated with the charcoal iron industry, large-scale clearing for agriculture, and subsequent land abandonment. By coupling radial growth analysis with age–diameter figures, we evaluated the responses of stands to disturbances associated with various land-use practices. This analysis indicated that many Virginia pine stands resulted from agricultural abandonment during the early 1900s, while a majority of oak stands experienced peak recruitment and radial growth following periodic logging disturbances in the 1800s. Canopy closure, forest protection, and reduced fire and logging disturbance this century led to increases in dogwood (Cornusflorida L.) and blackgum (Nyssasylvatica Marsh.) in area forests. The oldest stands exhibited a lack of tall oak regeneration; however, they also contained a scarcity of potential oak replacement species. Therefore, oak will seemingly share future dominance with several mixed-mesophytic species, although the exact successional status of these stands is unresolved.
Comparative analysis of algorithms to generate adjacency constraints
Authors: Yoshimoto Atsushi , Brodie J. Douglas
Published: May 2008

A mathematical programming formulation of the area-based forest planning problem can result in a large number of adjacency constraints with much potential for redundancy. Two heuristic algorithms have been proposed for reducing redundant adjacency constraints generated by the conventional algorithm. In this paper another analytical algorithm is proposed, and its efficiency and that of the conventional algorithm and the two heuristics are evaluated and compared. Comparison is based on the number of constraints, and on the computational effort needed both to derive the adjacency constraints and to solve the associated planning problem. Evaluation for several adjacency maps shows that the conventional algorithm has the largest number of constraints, with a low degree of effort in derivation of adjacency constraints and a small computational task to find a final solution. The first heuristic algorithm has the smallest number of constraints but involves a high degree of effort and a large computational task. The second heuristic has a small number of constraints with a moderate degree of effort and a large computational task, and the proposed algorithm has a small number of constraints with a low degree of effort and a moderate to large computational task.
b-MINIMALITY
Authors: CLUCKERS RAF , LOESER FRANÇOIS
Published: May 2008

We introduce a new notion of tame geometry for structures admitting an abstract notion of balls. The notion is named b-minimality and is based on definable families of points and balls. We develop a dimension theory and prove a cell decomposition theorem for b-minimal structures. We show that b-minimality applies to the theory of Henselian valued fields of characteristic zero, generalizing work by Denef–Pas [25, 26]. Structures which are o-minimal, v-minimal, or p-minimal and which satisfy some slight extra conditions are also b-minimal, but b-minimality leaves more room for nontrivial expansions. The b-minimal setting is intended to be a natural framework for the construction of Euler characteristics and motivic or p-adic integrals. The b-minimal cell decomposition is a generalization of concepts of Cohen [11], Denef [15], and the link between cell decomposition and integration was first made by Denef [13].
A synthetic prostone activates apical chloride channels in A6 epithelial cells
Authors: Bao Hui Fang , Liu Lian , Self Julie , Duke Billie Jeanne , Ueno Ryuji , Eaton Douglas C.
Published: May 2008

The bicyclic fatty acid lubiprostone (formerly known as SPI-0211) activates two types of anion channels in A6 cells. Both channel types are rarely, if ever, observed in untreated cells. The first channel type was activated at low concentrations of lubiprostone (<100 nM) in >80% of cell-attached patches and had a unit conductance of ∼3–4 pS. The second channel type required higher concentrations (>100 nM) of lubiprostone to activate, was observed in ∼30% of patches, and had a unit conductance of 8–9 pS. The properties of the first type of channel were consistent with ClC-2 and the second with CFTR. ClC-2's unit current strongly inwardly rectified that could be best fit by models of the channel with multiple energy barrier and multiple anion binding sites in the conductance pore. The open probability and mean open time of ClC-2 was voltage dependent, decreasing dramatically as the patches were depolarized. The order of anion selectivity for ClC-2 was Cl > Br > NO3> I > SCN, where SCN is thiocyanate. ClC-2 was a “double-barreled” channel favoring even numbers of levels over odd numbers as if the channel protein had two conductance pathways that opened independently of one another. The channel could be, at least, partially blocked by glibenclamide. The properties of the channel in A6 cells were indistinguishable from ClC-2 channels stably transfected in HEK293 cells. CFTR in the patches had a selectivity of Cl > Br ≫ NO3≅ SCN ≅ I. It outwardly rectified as expected for a single-site anion channel. Because of its properties, ClC-2 is uniquely suitable to promote anion secretion with little anion reabsorption. CFTR, on the other hand, could promote either reabsorption or secretion depending on the anion driving forces.
Windkesselness of coronary arteries hampers assessment of human coronary wave speed by single-point technique
Authors: Kolyva Christina , Spaan Jos A. E. , Piek Jan J. , Siebes Maria
Published: May 2008

A novel single-point technique to calculate local arterial wave speed ( SPc) has recently been presented and applied in healthy human coronary arteries at baseline flow. We investigated its applicability for conditions commonly encountered in the catheterization laboratory. Intracoronary pressure (Pd) and Doppler velocity ( U) were recorded in 29 patients at rest and during adenosine-induced hyperemia in a distal segment of a normal reference vessel and downstream of a single stenosis before and after revascularization. Conduit vessel tone was minimized with nitroglycerin. Microvascular resistance (MR) and SPc were calculated from Pd and U. In the reference vessel, SPc decreased from 21.5 m/s (SD 8.0) to 10.5 m/s (SD 4.1) after microvascular dilation ( P < 0.0001). SPc was substantially higher in the presence of a proximal stenosis and decreased from 34.4 m/s (SD 18.2) at rest to 27.5 m/s (SD 13.4) during hyperemia ( P < 0.0001), with a concomitant reduction in Pd by 20 mmHg and MR by 55.4%. The stent placement further reduced hyperemic MR by 26% and increased Pd by 26 mmHg but paradoxically decreased SPc to 13.1 m/s (SD 7.7) ( P < 0.0001). Changes in SPc correlated strongly with changes in MR ( P < 0.001) but were inversely related to changes in Pd ( P < 0.01). In conclusion, the single-point method yielded erroneous predictions of changes in coronary wave speed induced by a proximal stenosis and distal vasodilation and is therefore not appropriate for estimating local wave speed in coronary vessels. Our findings are well described by a lumped reservoir model reflecting the “windkesselness” of the coronary arteries.
Regulation of Kv4 channel expression in failing rat heart by the thioredoxin system
Authors: Li Xun , Tang Kang , Xie Bin , Li Shumin , Rozanski George J.
Published: May 2008

Redox imbalance elicited by oxidative stress contributes to pathogenic remodeling of ion channels that underlies arrhythmogenesis and contractile dysfunction in the failing heart. This study examined whether the expression of K+ channels in the remodeled ventricle is controlled by the thioredoxin system, a principal oxidoreductase network regulating redox-sensitive proteins. Ventricular dysfunction was induced in rats by coronary artery ligation, and experiments were conducted 6–8 wk postinfarction. Biochemical assays of tissue extracts from infarcted hearts showed that thioredoxin reductase activity was decreased by 32% from sham-operated controls ( P < 0.05), whereas thioredoxin activity was 51% higher postinfarction ( P < 0.05). These differences in activities paralleled changes in protein abundance as determined by Western blot analysis. However, whereas real-time PCR showed thioredoxin reductase mRNA levels to be significantly decreased postinfarction, thioredoxin mRNA was not altered. In voltage-clamp studies of myocytes from infarcted hearts, the characteristic downregulation of transient-outward K+ current density was reversed by exogenous pyruvate (5 mmol/l), and this effect was blocked by the specific inhibitors of the thioredoxin system: auranofin or 13-cis-retinoic acid. Real-time PCR and Western blot analyses of myocyte suspensions from infarcted hearts showed that pyruvate increased mRNA and protein abundance of Kv4.2 and Kv4.3 channel α-subunits as well as the accessory protein KChIP2 when compared with time-matched, untreated cells ( P < 0.05). The pyruvate-induced increase in Kv4.x expression was blocked by auranofin, but the upregulation of KChIP2 expression was not affected. These data suggest that the expression of Kv4.x channels is redox-regulated by the thioredoxin system, which may be a novel therapeutic target to reverse or limit electrical remodeling of the failing heart.
Classifying individuals as physiological responders using hierarchical modeling
Authors: Barker Richard J. , Schofield Matthew R.
Published: May 2008

We outline the use of hierarchical modeling for inference about the categorization of subjects into “responder” and “nonresponder” classes when the true status of the subject is latent (hidden). If uncertainty of classification is ignored during analysis, then statistical inference may be unreliable. An important advantage of hierarchical modeling is that it facilitates the correct modeling of the hidden variable in terms of predictor variables and hypothesized biological relationships. This allows researchers to formalize inference that can address questions about why some subjects respond and others do not. We illustrate our approach using a recent study of hepcidin excretion in female marathon runners (Roecker L, Meier-Buttermilch R, Brechte L, Nemeth E, Ganz T. Eur J Appl Physiol 95: 569–571, 2005).
Effect of Sucrose Concentration on Dental Biofilm Formed in situ and on Enamel Demineralization
Authors: Aires C.P. , Tabchoury C.P.M. , Del Bel Cury A.A. , Koo H. , Cury J.A.
Published: May 2008

The relationship between sucrose concentration and cariogenic potential was studied in situ. Adult volunteers wore intraoral palatal appliances containing human dental enamel blocks, which were extraorally submitted 8 times a day for 14 days, to the treatments: deionized distilled water and sucrose solutions from 1 to 40%. The biofilm formed was analyzed with respect to acidogenicity and biochemical composition; enamel demineralization was evaluated by microhardness. The results showed that 1% sucrose is less cariogenic than 5% or higher concentrations, although sucrose solution at 40% was still able to increase the concentration of insoluble polysaccharide in the biofilm formed. The findings suggest that the threshold of sucrose solution concentration for the formation of a cariogenic biofilm is 5%, which provided the same cariogenic potential as that observed for 10 and 20% sucrose solution.
The Effect of Adjacent Dentine Blocks on the Demineralisation and Remineralisation of Enamel in vitro
Authors: Lynch R.J.M. , ten Cate J.M.
Published: May 2008

The aim was to investigate interactions between enamel and dentine at low pH under conditions simulating those at the enamel-dentine junction. Sound enamel blocks were demineralised in acid-gel systems, at pH 4.6, either in isolation, next to one, or in the middle of two, abutting dentine blocks. The gels were initially infinitely undersaturated with respect to enamel. In a second study, enamel blocks containing pre-formed lesions were placed in acid-gel systems, at pH 5.0, either in isolation or next to dentine blocks. The systems were initially either partially or infinitely undersaturated. In the partially saturated systems, calcium and phosphate concentrations were representative of plaque fluid. In the first study, demineralisation of enamel next to one dentine block was reduced in inverse proportion to the distance from the dentine. Demineralisation of enamel between two dentine blocks was retarded markedly across the whole block. In the second study, in the partially saturated systems, enamel lesions next to dentine blocks remineralised, whereas those in isolation demineralised further. We suggest that diffusion of dissolved dentine mineral over the enamel in the infinitely undersaturated system was sufficient to reduce undersaturation, thus retarding demineralisation, and that in the partially saturated systems, dentine dissolution together with the added calcium phosphate caused remineralisation of enamel lesions. Fluoride released from dissolving dentine may have augmented these effects. Different rates of demineralisation in enamel and dentine, or enamel remineralisation with concurrent dentine demineralisation, enabled by differences in their solubilities, could help explain the progression of so-called ‘hidden caries’.
The Effect of Adding Calcium Lactate to Xylitol Chewing Gum on Remineralization of Enamel Lesions
Authors: Suda R. , Suzuki T. , Takiguchi R. , Egawa K. , Sano T. , Hasegawa K.
Published: May 2008

The purpose of the study was to determine whether adding calcium lactate to chewing gum containing xylitol enhances remineralization of enamel surfaces using an early caries lesion model. Enamel slabs were cut from human extracted sound teeth and artificial subsurface lesions created within each. Half the enamel slabs were used as controls and stored in a humidifier while half were mounted into oral appliances worn by 10 volunteers (22–27 years old, 2 males and 8 females) in a three-leg trial, during which they wore the appliance without chewing gum, chewed gum containing xylitol + calcium lactate or chewed gum containing only xylitol 4 times a day for 2 weeks. Calcium concentrations in the enamel surfaces of control and test slabs were measured by X-ray spectrometry and degrees of remineralization were calculated. The mean degree of remineralization was greater after chewing xylitol-Ca gum (0.46 ± 0.10) than after no gum (0.16 ± 0.14) or after chewing xylitol gum (0.33 ± 0.10) (p < 0.01). In conclusion, chewing gum containing xylitol + calcium lactate could enhance remineralization of enamel surface compared to chewing gum containing only xylitol or no gum chewing.