Allowance For Variation Research Articles

Discussion of “Drilled Shaft Side Friction in Gravelly Soils” by Kyle M. Rollins, Robert J. Clayton, Rodney C. Mikesell, and Bradford C. Blaise

The authors have addressed an important design problem: examining the uplift side resistance of drilled shafts in gravelly soils. Their approach was to use several series of tests they conducted in Utah and other data available in the literature. They took these field data, many of which had only limited field documentation such as only SPT N values and gradations, and compared their results with predictions that would be made from three different design models for side resistance. The first was the empirical Meyerhof model, which correlates N directly to side resistance, with different coefficients depending on whether the foundation is a driven pile or drilled shaft; the recommended drilled value is exactly one-half the driven value. The second was the empirical Reese and O’Neill method, which correlates the drilled shaft side resistance only to depth and no other ground property. The third is the Kulhawy method, which, as they say, “is based on basic soil mechanics principles with allowance for variations in soil properties based on construction procedures.” With their interpretation of the field data and their use of the design methods, all three methods fail miserably to predict the results. So they then present empirical modifications to each of the three design methods. The resulting prediction quality with the “new” empirical correlations may be closer to the means of the data, but the results vary greatly, by at least a factor of plus or minus 2 to 2.5. The authors never gave any statistics, so these quantifications are only visual. They also make the statement that the side resistance of drilled shafts in gravelly soils is much higher than that in sandy soil profiles, suggesting something special in the coarser soils. The discussers also have examined the problem of drilled shafts in gravelly soils in great detail Chen 2004 . We have little interest in the empirical methods selected by the authors, so we will leave them at this time. However, we will focus on the Kulhawy method that “is based on basic soil mechanics principles.” This method is very much dependent on the soil strength and the state of stress, in addition to the construction method. Obviously, these have to be evaluated properly for the method to “work.” The discussers do not believe the authors have done a proper job of evaluating the basic geotechnical properties of these soils.

Near-emitter region of thermoelectronic laser energy converter at high concentrations of a readily ionized additive

Fine structure of the near-emitter region of a thermoelectronic laser energy converter with a high concentration of atoms of a readily ionized additive at this electrode have been studied with allowance for variations in the electron temperature. It is established that the electron temperature near the emitter exhibits a change by a factor of several. The ion composition of the plasma in a near-emitter region qualitatively changes with a distance from the electrode.

Modeling drift currents in a shallow basin with allowance for variations in tangential stresses induced by wind waves

A coupling model for calculating wind-driven currents and waves in a shallow basin with allowance for current-wave interactions is introduced. The model is constructed on the basis of the three-dimensional σ-coordinate model of currents [3] and the SWAN (Simulating Waves Nearshore) spectral wave model [4]. The effect of waves on currents is taken into account in the coefficients of surface and bottom friction through roughness parameters. Results of combined modeling of stationary fields of currents and waves generated by spatially homogeneous wind are correlated with the corresponding results of separate modeling for a cylindrical basin of constant depth and the water area of Lake Donuzlav (the northwestern coast of the Crimea). The allowance for the effect of waves during calculation of tangential wind stresses in the model of currents is shown to be among major factors intensifying water circulation and forming spatial inhomogeneities of the vortex type. In addition, some cases of local decreases in tangential wind stresses are revealed; they appear when the lake is penetrated from the side of the open sea by relatively long waves, which significantly decrease the roughness of the water surface.

Early Impact of Endoparasitoid <I>Microctonus hyperodae</I> (Hymenoptera: Braconidae) After Its Establishment in <I>Listronotus bonariensis</I> (Coleoptera: Curculionidae) Populations of Northern New Zealand Pastures

The South American curculionid Listronotus bonariensis (Kuschel) is an important pest of pastures in New Zealand. Population census data were gathered for L. bonariensis in northern New Zealand pastures during 1980-1983 in the absence of parasitism and again in 1991-1996 after the introduction and establishment of the braconid parasitoid Microctonus hyperodae Loan as a biological control agent. M. hyperodae achieved high rates of parasitism, with 75-90% of overwintering L. bonariensis parasitized within 3 yr of the parasitoid establishing at a site. Multistratum analysis of variance (ANOVA), with allowance for variation in host plant resource (numbers of Neotyphodium-free grass tillers), indicated reduction in the abundance of L. bonariensis life stages in the early part of life cycle. Although providing evidence for suppression of L. bonariensis, these analyses indicated the regulatory role of M. hyperodae was weak because L. bonariensis populations continued to exhibit marked intergenerational variability in abundance. Analyses of life tables indicated larval + pupal survival contributed most to intergenerational changes in abundance, irrespective of presence or absence of M. hyperodae. However, the density dependence of the stage survivals was modified in the presence of the parasitoid, with loss of density-dependent mortality in overwintering adults and increased density dependence in population natality. Regression analyses indicated dual contribution of parasitism and host plant resource to regulation of population natality and population trend in L. bonariensis. We conclude that M. hyperodae is a useful adjunct to host plant resistance in reducing the economic status of L. bonariensis populations in northern New Zealand pastures.

Best Practices: An Outcomes-Based Approach to Decisions About Drug Coverage Policies in British Columbia

Best Practices: An Outcomes-Based Approach to Decisions About Drug Coverage Policies in British Columbia

Geotechnical Problems in Urban Underground Construction

Basic problems that Moscow builders, scientists, and designers have encountered in exploiting the underground space of the capital are disclosed. The following are classed among these problems: computational and analytical developments that make it possible to design enclosing pit structures optimally with consideration of the effect of the procedural sequence of work production; to make reliable predictions of the settlements of buildings and structures falling within the zone of influence of underground construction with allowance for variations in the hydrogeological regime; development of protective measures for the existing urban setting; implementation of a complex monitoring system utilizing modern methods of deformation measurement for buildings and soil masses during construction of unique entities with an underground section; and, development of a series of regulatory documents for underground construction.

Effect of the Error in Determination of Pipeline Parameters on Characteristics of a Gamma-Absorption Densimeter of a Transported Binary Mixture

Mathematical relations which make it possible to estimate the effect of errors in determination of pipeline parameters on the error in measurements of the density of a binary mixture with reference to a cement mortar is considered. The results of calculations of the mass radiation attenuation coefficients as functions of the gamma-quantum energy are given for main components of the tested object with allowance for variation of the cement formula. On the basis of the data and formulas obtained, which establish requirements for the recorded signal of a densimeter, the presence of optimum ranges of the gamma-quantum energies of the source and a significant in uence on the signal and the necessity to take the multiplicative component of the instrumental error of the densimeter into account are demonstrated. Recommendations on the choice and calculation of particular parameters and optimization conditions of the densimeter are given with reference to the formulated problem of testing.

Discrete Fourier-series method in problems of bending of variable-thickness rectangular plates

The approach to the solution of the boundary-value problems of bending of elastic rectangular plates of variable thickness is presented. It is proposed to introduce into the resolving system of partial differential equations additional functions which enables the variables to be formally separated and the problem to be reduced to a unidimensional one by representing all the functions as a Fourier series in a single coordinate. In this case the problem can be solved by the stable numerical method of discrete orthogonalization. To calculate the additional functions, Fourier series of discretely assigned functions with allowance for variations in the plate thickness are used. The boundary-value problems for rectangular plates of variable thickness were solved assuming that their weight is unchanged.

Bénard-Marangoni Instability of a Two-Layer System with Allowance for Variations in the Interfacial Internal Energy

The effect of variations of the internal surface energy due to local increments in the interfacial area on the conditions of onset of thermocapillary Marangoni instability in a two-layer system of reduced-viscosity fluids is studied. It is shown that in the linear approximation the effect considered leads to stabilization of the development of the monotonic instability mode.

Optimum design and operation of a pump-piping-storage system

The study reported in this paper is undertaken to develop a computer simulation and an optimum design and operation strategy for a general storage system. The influence of various design parameters on the total operation cost of the system for a general delivery regime is also studied. The computer program which incorporates a general procedure for the design and control of the pump-piping-storage system is presented. The main considerations in the reported study are the worst-case storage capacity analysis and the allowance for variations in the friction factors. The computer model of the system is applicable to any of pump-piping-storage system with appropriate changes in some of the system parameters. Two important parameters of the system are the average standby and operation times. The solution of the cost optimisation problem is undertaken using non-linear programming.

Distortion generated by a moving weld pool of elliptical cross sectionin the welding of thin metal sheets

Much analytical work exists dealing with distortion in thinmetallic sheets produced by moving heat sources. We consider here the caseof the distortion generated in a weld pool whose cross section is in theform of an ellipse in a thin sheet of metal, but with some allowance forvariations through the thickness of the material. An essential feature isthe presence of this molten pool. The presence of the molten region ensuresthat stresses arising from viscous flow and pressure are many orders ofmagnitude smaller then those present in the solid region and can thereforebe neglected. In the present analysis all deformations that arise areassociated with the equations of linear thermoelastic theory. The problemis tackled analytically and expressions obtained for the stresses in thework piece.

Investigation of the velocity fluctuation spectrum of a vortex flow of vibrationally excited molecular gas in a glow discharge

The flow velocity fluctuations in a gas laser are measured under non-self-maintained glow discharge conditions. Spectra of the pulsating velocity signal on the frequency interval up to 2 kHz and the time dependence of the signal under glow and neutral flow conditions for pure nitrogen, a mixture of nitrogen and helium, and a trial CO2-N2-He mixture are obtained. Deformation (due to the action of the discharge) of the spectra of the transverse velocity component in the wake of a right circular cylinder is observed. In order to analyze the data obtained a model of the dynamic response of the pulsating velocity is constructed and a model of the Karman vortex street behind a body is generalized with allowance for variations of the oscillation phase in the street.

Utility of existing Vogt-Koyanagi-Harada syndrome diagnostic criteria at initial evaluation of the individual patient: a retrospective analysis

The diagnosis of Vogt-Koyanagi-Harada syndrome is hampered by its variable manifestations and the lack of unique ancillary and laboratory findings. In this study, the diagnostic criteria established in 1978 by the American Uveitis Society (AUS) are retrospectively analyzed via their application to a population of 71 consecutive patients, using only those features present at the initial evaluation. All patients were previously diagnosed with Vogt-Koyanagi-Harada syndrome based on the clinical features and course of the disease combined with fluorescein angiography with or without ultrasonography in selected cases. Mean age of all patients was 36.7 years ± 15.1 years. Fifty (70%) were female and 45 (65%) were Hispanic. Patients presenting acutely, subacutely, and in the chronic stages met the AUS criteria for Vogt-Koyanagi-Harada syndrome in 56%, 48%, and 58% of cases, respectively. Allowance for variation in features, incomplete cases, and modification of the disease by treatment might increase the sensitivity of the criteria. While diagnostic criteria in general are useful for establishing the likelihood that a patient has a disease, the current AUS criteria for the diagnosis of Vogt-Koyanagi-Harada syndrome do not seem adequate.

Effect of selective water intake on the oxygen regime of a stratified reservoir

1. A mathematical model of the oxygen regime of a stratified reservoir, which makes it possible to calculate this regime for a selective water intake with allowance for variation of the balance between the production, expiration, and destruction of phytoplankton with varying depth of this intake, and also with consideration given to photosynthetic aeration of the epilimnion and hypolimnion, is developed. 2. Results of this calculation indicate that the oxygen content near the bottom of the reservoir increases with increasing depth of selective water intake, and reaches a maximum when water is drawn off only from the hypolimnion. On the whole, these results suggest that selective water intake can be used as a rather effective nature-conserving measure to improve the oxygen regime of a reservoir in its near-bottom layers and to prevent the development of starvation phenomena here. 3. With the reservoir in service, this goal can be achieved by drawing off water from the hypolimnion using a bottom water outlet, which can be activated during the summer when the oxygen content near the bottom drops to a critical level (below 4 mg/liter), or by increasing the drawdown of water during this period through the turbines of the hydroelectric plant (with water drawn off from the zone of the thermocline). Under these conditions, however, the intake of water from the surface layer (epilimnion), for example, by drawing it down through a spillway dam, as computational results have shown, may lead only to degradation of the reservoir's oxygen regime.

Heating of slip lines and bands as a quasi-athermic mechanism of plastic deformation of crystals at low temperatures

We discuss theoretically a mechanism of violation of the Arrhenius law for the rate of plastic deformation, on the one hand, and of the appearance of plateau-like segments in the temperature dependence of the thermal-activation parameters, on the other, during deformation of crystals at low (<10 K) temperatures, which is associated with heating of the crystal by slip lines and bands. Via a self-consistent solution of the heat-conduction equation with allowance for variation of its coefficients and the rate of plastic deformation with temperature it is found that both a stable and an unstable regime (in the thermal sense) of propagation of slip lines and expansion of slip bands are possible depending on the ratio between the heating level and the level of strain hardening of the strain localization sites. The first regime is associated with the appearance of quasi-athermic plateaus in the temperature dependences of the thermally-activation parameters, and the second one leads to an instability (stepped) in the plastic deformation that is characteristic at low temperatures.

The determinants of variations in exit rates

A conceptual model of the determinants of exit across spatial areas is presented and empirically tested. The relative merits of two different methods of calculating exit rates are discussed, and results compared. In the empirical estimation, entry is found to be the dominant determinant of exit. However, other factors also have a systematic effect: among these are local income, the rate of change of unemployment, relevant managerial skills, and population density. Making allowance for variations in industrial structure across areas has some effect on the results, but does not eliminate the effect of variables other than entry.

Biologically Bounded Risk Assessment for Receptor-Mediated Nongenotoxic Carcinogens

We have developed a biologically bounded marginal effect model for use in risk assessment of human exposure to receptor-mediated nongenotoxic carcinogens. Schematically this model can be reduced to four components: CI, the absence of an observable biological response; CII, observable biochemical responses but no observable pathology; CIII, observable pathology; and CIV, both observable pathology and lethality. The inflection point in the marginal response curve between CI and CII is defined as the biologically evaluated scientifically tested no observable effect level (BESTNOEL). We demonstrate the utility of this approach by applying it to the well-studied nongenotoxic carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Using a well-developed mechanistic understanding of the initial interactions of TCDD with the cell, we justify the selection of the minimal effective dose for CYP1A1 mRNA induction as the BESTNOEL. With allowance for variation in human sensitivity to TCDD, the BESTNOEL is assigned a human liver tissue burden of approximately 0.25–25 ppt and an allowable daily intake level in the range of 15–1500 fg/kg/day. In the future, the BESTNOEL can help establish a lower boundary for acceptable extrapolation when using either statistical or biologically based attributable risk models.

Bid-ask spreads in the interbank foreign exchange markets

This study provides evidence on quotations and bid-ask spreads in the wholesale foreign exchange market, and introduces a method to document variation in the placement of quotes relative to asset value. I find that spreads widen with proxies for inventory-carrying costs, including forecasts of price risk and a measure of liquidity costs. Increases in spreads before nontrading periods can also be attributed to inventory costs. The location of currency quotes in relation to value is not constant, and the outcome of hypothesis tests regarding changes in currency value can be sensitive to allowances for variation in quote location.

A Framework for Offshore Risk Criteria

AbstractSome suggestions are put forward concerning a framework for offshore risk criteria. A proposal is made for general criteria based on group (societal) risk, formulated in a way that is consistent with criteria based on individual risk. The group risk criteria address Lord Cullen's suggestion that due regard should be had to risk aversion to major accidents. The criteria include tolerable levels of individual risk that reflect accident mortality data, and as such may accommodate the ‘real improvement in safety’ advocated by Lord Cullen. The framework is designed to make allowance for variations between offshore installations, and embraces a general application of the ALARP principle.

Kinetics of phase separation in colloids II. Non-linear evolution of a metastable colloid

We study the evolution of a system of dropwise aggregates suspended in a macroscopically homogeneous metastable colloid with account of both the reduction in metastability (the decrease in the parent colloid supersaturation) and the continuing initiation of new nuclei in the metastable surroundings. The growing aggregates are distributed over size and the distribution density is governed by an equation of the Fokker-Planck type with allowance for variations in the growth rate of a single aggregate. A complementary equation relates the supersaturation to the total rate of absorption of colloidal particles by the aggregates. A method of solving those equations is worked out. It permits the supersaturation and diverse characteristics of the distribution density to be found as functions of time. The former quantity is monotonously declining to zero and the dispersion of the latter one is either decreasing or increasing with time depending on the level of random fluctuations of the growth rate. If the fluctuations are absent, the evolving system of the aggregates is tending to a monodisperse one, what calls in question the validity of underlying assumptions inherent to the classical theory of Ostwald ripening.