Semi-empirical Expression Research Articles

Model Tests on Horizontal Impedance Functions of Fixed-Head Inclined Pile Groups under Soil Nonlinearity

The effects of soil nonlinearity on the dynamic behavior of fixed-head floating inclined pile groups are investigated experimentally in the form of horizontal impedance functions (IFs) and internal forces in piles. A 2×2 model of inclined pile groups embedded in dry cohesionless soil and subjected to a broad range of lateral harmonic loadings at the pile-cap level are examined. Piles with a spacing-to-the-diameter ratio (s/d) of 5 with practical pile inclinations of 0, 5, and 10° along the direction of loading are reported. Results show a profound impact of local nonlinearity and resonance of soil on the horizontal impedance functions. The inclined pile groups show higher values of horizontal IFs than the vertical pile group, in accordance with the general understanding. Influence of pile inclinations on the horizontal IFs is further examined through the variation of soil reactions along the depth of the piles. Semiempirical expressions for estimating the soil reactions, as a function of pile inclinations, are proposed. As for the internal forces in piles, bending strains for the inclined piles are smaller than the vertical pile; the axial strains show an opposite behavior.

Understanding Tow Tank Measurements of Total Drag for Long Thin Circular Cylinders

Both the experimental measurements and numerical computations tell us that thin circular cylinders own turbulent boundary layer (TBL) characteristics which are dissimilar from planar geometries once the TBL thickness (δ) exceeds the cylinder radius. But the exceedingly long cylinders that serve as acoustic array systems have resorted to tow tank measurements due to the experimental complexities of axial sag or the required simplifications for efficient predictions. One key measurement in the tow tank experiments is the total drag, where the respective average tangential coefficients have been assessed relative to various scaled cylinder lengths, such as the length-based Reynolds number. We now know that the skin friction whose axial summation provides the total drag is governed by the radius-based Reynolds number as well. Herein, we revisit the many tow tank experiments to isolate the measurement discrepancies attributed to these two distinct Reynolds numbers. Once separated, these measurements provide a vital answer to the transformation of the TBL spatial growth to a temporal one (no additional net δ growth). This final stage is readily identifiable by a streamwise constant skin friction as given by near-wall flow homogeneity. This understanding lends subsequent evaluation of the TBL momentum thickness at the cylinder trailing edge. The present process involves applying several semiempirical expressions formed from the experimental and numerical evidence that supply the spatially evolving TBL characteristics along thin cylinders. Besides gaining an enhanced understanding of the TBL behavior, these semiempirical expressions are further clarified to form a final set that are helpful for design engineers of tow array devices in the military and oceanographic communities.

Elemental vacancy diffusion database from high-throughput first-principles calculations for fcc and hcp structures

This work demonstrates how databases of diffusion-related properties can be developed from high-throughput ab initio calculations. The formation and migration energies for vacancies of all adequately stable pure elements in both the face-centered cubic (fcc) and hexagonal close packing (hcp) crystal structures were determined using ab initio calculations. For hcp migration, both the basal plane and z-direction nearest-neighbor vacancy hops were considered. Energy barriers were successfully calculated for 49 elements in the fcc structure and 44 elements in the hcp structure. These data were plotted against various elemental properties in order to discover significant correlations. The calculated data show smooth and continuous trends when plotted against Mendeleev numbers. The vacancy formation energies were plotted against cohesive energies to produce linear trends with regressed slopes of 0.317 and 0.323 for the fcc and hcp structures respectively. This result shows the expected increase in vacancy formation energy with stronger bonding. The slope of approximately 0.3, being well below that predicted by a simple fixed bond strength model, is consistent with a reduction in the vacancy formation energy due to many-body effects and relaxation. Vacancy migration barriers are found to increase nearly linearly with increasing stiffness, consistent with the local expansion required to migrate an atom. A simple semi-empirical expression is created to predict the vacancy migration energy from the lattice constant and bulk modulus for fcc systems, yielding estimates with errors of approximately 30%.

Performance analysis and experimental verification of a multi-sleeve tubular still filled with different gas media

A novel nonconcentrical multi-sleeve tubular still for triple-effect solar desalination device is described in this study. An experimental and analytical analysis is given to investigate how the water production performance is affected by different gas media, which are air, oxygen, helium and carbon dioxide. The water production rate and the temperature value of every measured point inside the device with different gas media were obtained through the experiments. Experimental results show that, when the heating temperature is 85°C and the gas medium is oxygen, the water production rate can reach to 0.58kg·h−1. It is increased by 31.82% compared with the rate when the gas medium is air. In addition, the internal heat and mass transfer mechanism of the device with different gas media was analyzed. The semi-empirical expression of the water production rate is given. According to the experimental data, the Dv under different conditions is obtained. The results obtained are then compared against the experimental results, and it is found that the trend of theoretical water production rate is consistent with the experimental results. The reasons for deviation are analyzed.

The cone penetration test in unsaturated sands

Laboratory-controlled cone penetration test results for an unsaturated sand are presented, obtained using a suction-controlled calibration chamber. The cone penetration resistances are found to increase significantly, owing to the presence of suction, when compared with those for saturated or dry states, for a given relative density and net confining stress. Increases of as much as 50% for a relative density of 0·33 and net confining stress of 50 kPa are recorded. When suction is included in the effective stress, the same semi-empirical expressions used for saturated sands are found to link penetration resistance to the relative density and effective confining stress. The expressions may also be used to back-calculate the suction changes in a soil profile when cone penetration resistances for two unsaturated states are known. It is also shown that failure to account for suction influences may lead to significant and non-conservative overestimations of relative density or peak friction angle.

Semi empirical formula for electronic stopping power determination of 24Mg, 27Al and 28Si ions crossing Formvar foil in the ion energy domain of LSS theory

We have determined continuous stopping power of heavy ions in thin Formvar foil for 28Si, 27Al and 24Mg ions over an energy range of (0.1–0.5)MeV/nucleon. Heavy Ions Elastic Recoil Detection Analysis (HI-ERDA) technique coupled with time of flight (ToF) spectrometer has been used to measure energy loss of charged particles in this thin absorber. Lindhard, Scharff and Schiott (LSS) theory compared with the corresponding determined stopping values in Formvar, shows significantly large deviations. However, a novel semi empirical expression has been proposed here and tested for better stopping power calculations at low velocity in the ion energy domain of LSS theory for 28Si, 27Al and 24Mg ions crossing thin Formvar foil. The results were compared to the obtained experimental stopping power data, predictions of LSS theory and also to those generated by SRIM-2010 computer code. The obtained results exhibit good agreement with experimental data.

SHEAR RESPONSE INVESTIGATION OF HSRC DEEP BEAMS WITHOUT WEB REINFORCEMENT PART I: COMPARISON OF DESIGN EQUATIONS

Currently, there is no general agreement on a theory describing the response of reinforced concrete members without web reinforcement. Many structural systems are usually performed using empirical or semi-empirical expressions provided by codes of practice that do not consider the influence of many governing parameters. In this paper, a comparison between values of current experimental shear strength and those of various international design approaches like ACI, Canadian, FIB and the method proposed by Sudheer, Zararis ,Zsutty ,Shah ,Bazant and Russo. Eighteen simple span high strength reinforced concrete “HSRC” deep beams without web reinforcement were tested and analyzed under two static point loads at mid-span of the beam to examine the contribution of various parameters on the shear capacity of HSRC beams. The main studied parameters are f‟cu=50 MPa, three values of tension reinforcement-ρ%-(0.73%,1.21% &1.83%) and shear span to effective depth ratio-a/d-( 2,1.5 &1). As a conclusion of this paper, ACI and FIB code provisions for shear in HSC are safe for use with the exception that CSA should be used with care. Despite numerous studies, there is still a need to develop a clear understanding of the shear behavior of HSC beams without web reinforcement. Therefore, this experimental program was arranged to evaluate the shear behavior and to increase the shear database on HSRC deep beams.

Electrical Transport Properties in Ta-Doped SnO<sub>2</sub> Thin Films

The structure, carrier concentration and low temperature magnetoresistance of Tantalum-doped Tin oxide thin films prepared by RF magnetron sputtering method have been investigated. Hall coefficient is negative at all measuring temperatures, which confirms the n-type characteristic of the films with metallic characteristic. The low temperature magnetoresistance measurement show negative magnetoresistance at all measured temperatures from 2 to 30 K. However, weak-localization theories can not explain the behavior of the negative magnetoresistance of our samples. We fitted the magnetoresistance data of the samples with semiempirical expression that takes into account the third order sd exchange Hamiltonians. The theory and experiment are in excellent agreement. This strongly suggests that the magnetoresistance in SnO2: Ta film originates from the scattering of conduction electrons due to localized magnetic moments.

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

Optical properties and relaxation mechanisms of PbS quantum dots in glass matrix (PbS:Glass) have been systematically investigated by transmission and (steady-state and transient) photoluminescence spectroscopy. Key parameters are determined by combining the data with semiempirical expressions, based on which the recombination mechanisms including spontaneous and stimulated emissions have been discussed as a function of temperature by referring to a multilevel model including intrinsic (or band-to-band transition), bright, dark, and ground states. The results disclose that (i) the existence of a dark exciton state is the main reason for thermal quenching of the emission even at low temperatures due to the strong multiacoustic phonon coupling, (ii) the ``intrinsic'' spontaneous emission related to the intrinsic state is observed with an approximately nanosecond lifetime, in contrast to the ``regular'' spontaneous emission from the bright exciton state with an approximately microsecond lifetime, and (iii) stimulated emission, which has a lifetime of 20--40 ps and shows power-dependence of excitation density (or temperature), only appears from the intrinsic state but not the (bright) exciton state when enough accumulation of photogenerated carriers is reached. Furthermore, we find that the thermal conductivity will become crucial for future PbS:Glass related optoelectronic device applications.

The number of bound vibrational levels in a diatomic molecule

A simple semiempirical expression has been developed for estimating the effective non-integer vibrational index at dissociation, υD, in diatomic systems. The expression is given by,υD=1.78349×Deωe-58,where the dissociation energy and the fundamental vibrational frequency must be expressed in the same units. This expression gives reliable results for a wide variety of ground electronic states of neutral systems, but underestimates the vibrational index for diatomic cations, most excited states and zero bond-order molecules. The expression is successful for electronic states that have a Birge–Sponer plot displaying a downward curvature as the dissociation limit is approached.

Modelling powder mixing in mass flow discharge: A kinematic approach

The dynamics of a powder flowing in a mass flow regime through a storage bin with a conical hopper, is a well studied problem. However, many challenges remain, including quantification of the mixing that occurs during discharge through the hopper. We have formulated a model based on the conservation of volume of the powder and a semi-empirical expression for velocity profile, (see [1,2]), and used this to estimate mixing parameters. We have specifically considered the case of an inflow which is disposed in homogeneous horizontal layers as it enters the storage bin. When the powder, in successive layers, enters the hopper, it accelerates and its velocity along the longitudinal axis of the hopper is greater than at the walls. Portions of layers high in the hopper may overtake layers closer to the exit resulting in mixing of the layers. Using this model we are able to quantify the percentage of each layer in a given output volume and present results for typical hopper geometries.

Hall-Thruster Scaling Laws

The area of application of the Hall effect thrusters is constantly expanding, both in the direction of reduced power and toward an increase of power and specific impulse. The two main problems are studied in this paper. The first is to examine the possibility of providing the similarity of plasma parameters in Hall effect thrusters, and the second is to estimate the best achievable output characteristics when scaling Hall effect thrusters. It is shown that a strict similarity of plasma parameters is possible only for the same type of propellant at the same discharge voltage at invariance of at least two dimensionless scaling parameters. Based on the analysis of the similarity criteria and available experimental data, a speculative assertion is made, that in the optimal mode, all the geometrical dimensions of the Hall thruster should be changed in the same proportion. For this type of scaling, the semi-empirical expression for the mass utilization efficiency is obtained under the invariance of the heat flux on the discharge-channel walls. This expression is used to investigate the regularities of performance changes in the optimal mode by varying the discharge power and discharge voltage, and using different types of propellants.

LHC and dark matter signals ofZ′bosons

We customize the simulation code Fully Exclusive $W$, $Z$ Production to study ${Z}^{\ensuremath{'}}$ production at the LHC for both $\sqrt{s}=8\text{ }\text{ }\mathrm{TeV}$ and 14 TeV. Using the results of our simulation for several standard benchmark ${Z}^{\ensuremath{'}}$ models, we derive a semiempirical expression for the differential cross section that permits the determination of ${Z}^{\ensuremath{'}}$ couplings in a model-independent manner. We evaluate cross sections and other observables for large classes of models, including the common ${\mathrm{E}}_{6}$, left-right and $B\ensuremath{-}L$ models, as a function of model parameters. We also consider a hidden sector ${Z}^{\ensuremath{'}}$ that couples to standard model fermions via kinetic and mass mixing and serves as a mediator of isospin-violating interactions with dark matter. We combine the results of LHC ${Z}^{\ensuremath{'}}$ searches and dark matter direct detection experiments with global electroweak data to obtain mass-dependent constraints on the model parameters.

Stiffness of Clays and Silts: Normalizing Shear Modulus and Shear Strain

AbstractAn analysis is presented of a database of 67 tests on 21 clays and silts of undrained shear stress-strain data of fine-grained soils. Normalizations of secant G in terms of initial mean effective stress p′ (i.e., G/p′ versus log γ) or undrained shear strength cu (i.e., G/cu versus log γ) are shown to be much less successful in reducing the scatter between different clays than the approach that uses the maximum shear modulus, Gmax, a technique still not universally adopted by geotechnical researchers and constitutive modelers. Analysis of semiempirical expressions for Gmax is presented and a simple expression that uses only a void-ratio function and a confining-stress function is proposed. This is shown to be superior to a Hardin-style equation, and the void ratio function is demonstrated as an alternative to an overconsolidation ratio (OCR) function. To derive correlations that offer reliable estimates of secant stiffness at any required magnitude of working strain, secant shear modulus G is norma...

Study on the Aerodynamics Mechanism of Passenger Car under Unsteady Crosswind

Regular formulae for lateral aerodynamic force cannot give precise prediction under unsteady crosswind. By generalizing potential flow theory and taking the aerodynamic derivative into consideration, the semi-empirical expression for lateral aerodynamic force is derived. In order to determine the coefficients in the semi-empirical formula, the model of a typical double-deck coach is investigated in a sequence of numerical simulations under pure crosswind condition (i.e. linear crosswind, pseudo-step crosswind, sinusoidal crosswind). Moreover, advantages of the semi-empirical formula over the regular one are revealed. Further inspections into the flow field derived from the theory of vortex motion indicate that the deviation between the prediction given by semi-empirical formulae and that by numerical simulation is caused by the non-viscous assumption in potential flow theory. The lateral aerodynamic force depends linearly on the crosswind aerodynamic derivative. Situations in which the coach is moving in the direction perpendicular to the wind velocity are also studied to find the cause of the error in semi-empirical formula. Furthermore, the semi-empirical formula is revised by introducing the “damping model method”. A relatively complete system of prediction for lateral aerodynamic force on a coach, which is of practical engineering significance, has been constructed.

Mutual Macromolecular Crowding in Polymer Solutions

Ogston and Laurent conceived and established a theory for steric exclusion of spherical particles such as globular proteins by a suspension of randomly oriented fibers. In their model, a protein can just touch the surface of a fiber, so the space occupied by the fiber itself, in addition to a cylindrical shell with a thickness equal to the radius of the protein, are spaces excluded to the protein. In a suspension of many fibers, the effective concentration of the protein is increased, because the available volume is reduced. This model was successfully applied to explain a number of properties (association and conformational equilibria, partition between compartments, osmotic pressure, etc.) for solutions of proteins in the presence of flexible polymers such as hyaluronan (HA), and the relevance of steric exclusion to the properties of biological tissues was established. Because small globular proteins are excluded only from a cylindrical shell immediately surrounding a linear HA chain, the crowding effect is sensitive to the mass concentration of the polymer segments, but not the molecular mass of the polymer chain. Matsuoka and Cowman subsequently developed a semi-empirical expression to quantitatively account for the concentration, shape, and molecular mass dependence of physicochemical properties (steady shear viscosity, osmotic pressure, light scattering, etc.) of HA or other polymer solutions. A connection between the Ogston-Laurent and Matsuoka-Cowman approaches will be presented, providing a firm foundation for understanding polymer solution properties on the basis of mutual macromolecular crowding, where steric exclusion depends on the effective hydrodynamic volume of the polymer. This theory can be employed to explain the dependence of amyloid protein fibril formation on the molecular mass of crowding polymers.

Prediction of Temperature and Moisture Distributions in Hardening Concrete By Using a Hydration Model

This paper presents an integrated procedure to predict the temperature and moisture distributions in hardening concrete considering the effects of temperature and aging. The degree of hydration is employed as a fundamental parameter to evaluate hydro-thermal-mechanical properties of hardening concrete. The temperature history and temperature distribution in hardening concrete is evaluated by combining cement hydration model with three-dimensional finite element thermal analysis. On the other hand, the influences of both self-desiccation and moisture diffusion on variation of relative humidity are considered. The self-desiccation is evaluated by using a semi-empirical expression with desorption isotherm and degree of hydration. The moisture diffusivity is expressed as a function of degree of hydration and current relative humidity. The proposed procedure is verified with experimental results and can be used to evaluate the early-age crack of hardening concrete.

Knudsen Diffusivity and Permeability of PEMFC Microporous Coated Gas Diffusion Layers for Different Polytetrafluoroethylene Loadings

The Knudsen diffusivity and viscous permeability of proton exchange membrane fuel cell microporous coated gas diffusion layers are obtained experimentally for different polytetrafluoroethylene loadings. Pressure drop across the microporous coated gas diffusion layers is measured at varying flow rates and using different gases. A semi-empirical expression proposed by Knudsen is used to analyze the experimental results and is shown to accurately predict gas transport in microporous coated gas diffusion layers. The Knudsen diffusivity of the microporous coated gas diffusion layers is shown to decrease with increased PTFE loading. The compressible form of Darcy's law is shown to overestimate the viscous permeability of microporous coated gas diffusion layers because it cannot account for gas slip at the pore walls.

Convective heat transfer in foams under laminar flow in pipes and tube bundles

The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.

A statistical interpretation of molecular delta layer depth profiles

The delta layer depth response predicted by a simple statistical sputtering model is compared with molecular sputter depth profile data obtained on Langmuir–Blodgett delta layer systems. All input parameters of the statistical sputtering model are determined from low‐fluence molecular dynamics simulations performed for 20‐keV C60 cluster bombardment of silicon, making the model de facto parameter free. It is found that both calculated and measured depth response functions can be parametrised by the semiempirical Dowsett expression. The resulting parameters (leading and trailing edge slope, full‐width at half‐maximum) agree surprisingly well with those determined from the measured depth profiles. Copyright © 2012 John Wiley & Sons, Ltd.