Search

AbstractSimulation of the 3-D, fully developed turbulent channel flows laden with various mass loading ratios of particles is made using an Eulerian-Lagrangian approach in which the carrier-fluid flow field is solved with a low-Reynolds-number k-εturbulence model while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion. Effects of inter-particle collisions and particle-wall collisions under different extents of wall roughness on particle dispersion are addressed in the study. A cost-effective searching algorithm of collision pair among particles is developed. It is found that the effects of inter-particle collisions on particle dispersion cannot be negligible when the ratio of the mean free time of particle to the mean particle relaxation time of particle is less or equal to O(10). In addition, the wall roughness extent plays an important role in the simulation of particle-wall collisions particularly for cases with small mass loading ratios.

Experimental observations on the effect of freezing cycles on the bond behavior between steel reinforcement and concrete are reported. Specimens that experienced 1, 10, and 30 freezing cycles are tested under monotonic and reversed cyclic loadings. Results are compared with experimental observations of identical specimens that did not experience freezing cycles. Under monotonic loading the maximum bond resistance decreases as the number of freezing cycles increases. For reversed cyclic loading the average value of bond factors ratio of maximum bond strengths to compressive strength in both directions decreases with an increasing number of freezing cycles. In addition, other mechanical properties of concrete experiencing freezing cycles are also determined. It is concluded that cyclic temperature changes do have definite effects on the bond strength of reinforced concrete structures and on the mechanical properties of concrete.

Experimental studies were conducted on the local bond stressslip relationships of deformed bars embedded in confined concrete under monotonic and cyclic loading in the temperature range between −10 °C and −70 °C 14 °F and −94 °F. The bond behavior between steel reinforcement and concrete under low temperature appears quite different from the bond behavior under normal temperature [+20°C(+68°F)].The main differences observed are in the values of maximum bond stress and in the relationship between maximum bond stress and concrete compressive strength. Under monotonic loading, the ratio of maximum bond strength at low temperature to that at normal temperature is almost identical to the ratio of the respective concrete compressive strength values.

Seismic response characteristics of a 25scale steel frame structure with added viscoelastic dampers are studied experimentally. The major emphasis is placed on the ambient temperature effect. It is shown that, while seismic response characteristics of a structure can be significantly improved with added dampers, their degree of effectiveness depends on the surrounding temperature within which they operate. Results also show that, even at very high temperatures, the viscoelastically damped structure can still achieve a significant reduction of structural response as compared with when no dampers are added. Designing viscoelastic dampers by considering the ambient temperature is addressed. Empirical equations are established based on regression analysis using data obtained from component tests of the dampers. These equations can satisfactorily estimate the dynamic properties of dampers under various ambient temperatures, excitation frequencies, and deformations. Numerical simulations are carried out on equivalent structural damping and structural response under various ambient temperatures. It has been demonstrated that the dynamic behavior of structures with added viscoelastic dampers can be satisfactorily predicted by conventional analytical tools.

This paper describes an experimental program of study on the sliding characteristics of Teflonstainless steel interfaces. The effects of normal pressure, sliding distance, normal pressure history, sliding velocity, sliding velocity history, normal pressure rate, and sliding work are identified and interpreted. Test results show that the friction force is independent of the normal pressure history and the sliding velocity history, and is also irrelevant to the normal pressure rate. In addition, the dependence of dynamic friction force on the normal contact pressure and the sliding velocity can be uncoupled. The dynamic friction force can be determined by multiplying the quasistatic friction force by an amplification factor. The reciprocal of the quasistatic friction coefficient is linearly dependent on the normal pressure only, and the amplification factor is solely a function of velocity. Moreover, the dynamic friction force decays during sliding, and the decaying is a function of excess dynamic sliding work.

This paper reports the dynamic responses of a onefifthscale gableframe structure composed of tapered members subjected to El Centro earthquake ground motions, using a shaking table. The test structure was designed according to the American Institute of Steel Construction AISC working stress design method. The widththickness ratio of the flange and the depththickness ratio of the web of the members satisfy the requirements of a compact section. The unbraced length also meets the criteria for a compact section based on the dimensions of the shallowend cross section. Failure of the test structure is due to lateral buckling of rafters. No local buckling prior to the lateral buckling is observed. The experimentally determined ultimate strength of the test structure is compared with those predicted by the codes AISC load and resistance factor design LRFD, AS 1250, and BS 5950. The experimental results are also compared with those of a similarly designed gable frame composed of prismatic members, tested under similar conditions.

Analytical models of local bond stressslip relationships are established based on an experimental program of 65 specimens in the temperature range between -70°Cand -10°Cand at normal temperature (+20°C).One can conclude that low temperature has little influence on the relationship between concrete compressive strength, fc′,and the maximum bond stress, tmaxas well as bond behavior, except that an increase in compressive strength is associated with an increase in bond strength. An analytical model for cyclic loading is established by estimating the deterioration of bond resistance and reloading stiffness. The deterioration appears to be closely related to the effective energy dissipated during the loading cycles. This analytical model has been applied to describe the bond stressslip relationship of the concretesteel interface under monotonic, repeatedcyclic, and reversedcyclic loading conditions. Very good correlations between the numerical predictions and the experimental results were obtained.

Highstrength concrete has been used extensively in highrise buildings and longspan bridges. However, very little is known regarding its mechanical properties at low temperature. This paper presents the results of an experimental study on the mechanical properties of highstrength concrete in the temperature range between +20°Cand -70°C+68°Fand -94°F without considering the effect of freezing cycles. Test results show that the values of compressive and splitting tensile strength, modulus of elasticity and Poisson's ratio increase as the temperature decreases. The ratio of bond strength at low temperature and the bond strength at normal temperature are generally larger under reversed cyclic loading than under monotonic or repeated cyclic loading. The rate of increase in compressive and splitting tensile strength, Young's modulus, local bond strength and Poisson's ratio for highstrength concrete at corresponding different low temperatures -10°C,-30°-C,-50°Cand -70°C,i.e., +14°F,-22°F,-58°Fand -94°F is generally lower than that for normal strength concrete.

Laboratory experiments on the local bond behavior of highstrength concrete were carried out under monotonic, repeated cyclic and reversed cyclic loading conditions in the temperature range of -10°Cand -70°C+14°Fand -94°F. The values of maximum bond stress and the relationship between maximum bond stress and concrete compressive strength at low temperature are quite different from those at normal temperature [+20°C(+68°F)],especially under reversed cyclic loading. The experimental results are also compared with those for normal strength concrete observed and reported in an earlier study. Under monotonic loading conditions the ratio of maximum bond stress at low temperature to the maximum bond stress at normal temperature is different between high strength and normal strength concrete. Under reversed cyclic loading the average value of the bond factors maximum bond stress divided by the concrete compressive strength of both loading directions is smaller than those under monotonic or repeated cyclic loading conditions.

Laboratory studies were conducted on concrete compressive and splitting tensile strength, modulus of elasticity, and Poisson's ratio and on the local bond strength between concrete and steel under both monotonic and cyclic loadings in the temperature range of 20 °C and -70°C.These properties have increased value as temperature decreases. The ratio of bond strength at low temperature and the bond strength at normal temperature are generally smaller under repeated cyclic loading than under monotonic loading, while the ratio of the corresponding strength under reversed cyclic loading is larger than that under monotonic loading. The effects of cyclic temperature changes freezing cycles on concrete properties were also investigated. Results show that there is a reduction in concrete compressive strength, bond strength, and the value of Young's Modulus.

In the United States, design of steel gable frames normally follows the guidelines prescribed by the American Institute of Steel Construction for assumed wind and gravity loadings. In this study, a pinnedbase steel gable frame structure composed of prismatic members is constructed, and the dynamic characteristics of that structure are investigated using the shaking table. The tests are carried well into the inelastic range so that ultimate lateral strength under seismic excitation can be quantified. It is observed that for such structures the response modification factor adopted by the Applied Technology Council ATC should be assumed with caution. In addition, the excessive elastic and inelastic story drifts, which are attributed to the pinnedbase condition, require careful evaluation to ensure structural safety against large sidesways. The excessive story drift is likely one of the major reasons for the severe nonstructural damage of steel gable frames during the 1985 Chile earthquake and the 1987 Edgecumbe earthquake.

The modulus of elasticity of concrete is a fundamental parameter in analysis and design of reinforcedconcrete structures. The present ACI approach for Young's modulus is based on normal strength concrete. It may not be appropriate for highstrength concrete. Experimental studies were conducted on the static Young's modulus of normalstrength concrete and highstrength concrete. An empirical equation for Young's modulus of normalweight concrete determined by computer regression analysis, using the least square method, is described in this paper.

AbstractIn this paper, analytical simulations of the steel-laminated elastomeric bearing (SLEB) using a three-dimensional (3D) finite element model incorporating material, geometric nonlinearities, and a frictional contact algorithm in LS-DYNA code is conducted. In order to simulate the nonlinear responses of the elastomeric bearing under the compression and shear, a hyperviscoelastic rubber model such as The MAT_77_H (MAT_HYPERVISCOELASTIC_RUBBER) in LS- DYNA code is adopted. Based on the proposed material model for the SLEB, the interaction effects of the SLEB under compression, bending, and torsion are analyzed. Analytical results are compared with the test results of the SLEBs. A set of material parameters is proposed for 3D FEM analysis of SLEBs. The proposed material model demonstrates its accuracy.

Transarticular screw fixation with autograft is an established procedure for the surgical treatment of atlantoaxial instability. Removal of the posterior arch of C1 may affect the rate of fusion. This study assessed the rate of atlantoaxial fusion using transarticular screws with or without removal of the posterior arch of C1. We reviewed 30 consecutive patients who underwent atlantoaxial fusion with a minimum follow-up of two years. In 25 patients (group A) the posterior arch of C1 was not excised (group A) and in five it was (group B). Fusion was assessed on static and dynamic radiographs. In selected patients CT imaging was also used to assess fusion and the position of the screws. There were 15 men and 15 women with a mean age of 51.2 years (23 to 77) and a mean follow-up of 7.7 years (2 to 11.6). Stable union with a solid fusion or a stable fibrous union was achieved in 29 patients (97%). In Group A, 20 patients (80%) achieved a solid fusion, four (16%) a stable fibrous union and one (4%) a nonunion. In Group B, stable union was achieved in all patients, three having a solid fusion and two a stable fibrous union. There was no statistically significant difference between the status of fusion in the two groups. Complications were noted in 12 patients (40%); these were mainly related to the screws, and included malpositioning and breakage. The presence of an intact or removed posterior arch of C1 did not affect the rate of fusion in patients with atlantoaxial instability undergoing C1/C2 fusion using transarticular screws and autograft.Cite this article: Bone Joint J 2013;95-B:972–6.

ABSTRACTThis paper is concerned with the effects of column size, carbon fiber-reinforced plastics (CFRP) volumetric ratio, column side to corner radius ratio and column side aspect ratio on the confinement efficiency of rectangular concrete columns confined with CFRP. The confined concrete nonlinear constitutive relationships are adopted which account for concrete under unequal lateral confining stresses under multiaxial stress conditions. A stiffness reduction procedure upon concrete cracking or crushing is also proposed. The finite element model is initially confirmed by comparing its numerical solutions with the experimental results for various parameters. The effects of above parameters on the peak strength and ultimate strain of the confined concrete are then parametrically studied. The test results and results of the parametric study indicate that the column axial compressive strength and ultimate strain increase with CFRP volumetric ratio, but decrease as the column side to corner radius ratio or the column side aspect ratio increases. For columns of a particular corner radius and CFRP volumetric ratio, the column axial compressive strength and ultimate strain decrease as column size and column side to corner radius ratio increases.

We report CO-induced lifting of the hexagonal surface reconstruction on Au(001). Using in situ surface X-ray scattering, we determined a pressure−temperature phase diagram for the reconstruction and measured the dynamical evolution of the surface structure in real time. Our observations provide evidence that, under certain conditions, even macroscopic Au surfaces, much larger than catalytic Au nanoparticles (Haruta, M.Catal. Today1997, 36, 153), can exhibit some of the reactive properties and surface transitions observed in systems known to be catalytically active such as Pt(001).

Pentacene stands out as a model molecule among organic semiconductors due to its ability to form well-ordered films that show a high field effect mobility. We discuss the processes involved in pentacene film growth, emphasizing differences with respect to inorganic films. The influence of growth parameters such as the substrate nature and temperature, the deposition rate, and the kinetic energy of the molecular beam on the structure and morphology of pentacene films are discussed. Finally, we overview recent attempts to model pentacene film nucleation and growth, and draw attention to the role of dislocations.

Leukocyte adhesion under flow in the microvasculature is a multistep process in which rolling adhesion is followed by firm arrest. These interactions are mediated by binding between receptors on the leukocyte surface and complementary ligands on the surface of endothelial cells. Previous work using a computational method called “adhesive dynamics” showed that the general shape of a state diagram for cell adhesive behavior in flow could be predicted by the bond reaction rates and their dependence on force. Other parameters, however, such as shear rate, particle size, and receptor and ligand density, determined the exact region of parameter space that corresponds to an adhesive behavior. In this paper, we present state diagrams for adhesion for a range of particle sizes to explain the rolling behavior for a wide range of cell diameters. Particle size is an easily controlled experimental variable, and if the locations of regions of desired adhesive behavior in the state diagram are known, then the size of particle needed to achieve a desired adhesive behavior can be predicted.

‘ND1406HP’ soybean [Glycine max(L.) Merr.] (Reg. No. CV‐516, PI 673929) was first tested as ND06‐4642 and was released in May 2014 by the North Dakota Agricultural Experiment Station, North Dakota State University (NDSU), to provide producers with a Maturity Group 0 conventional cultivar (0.6), generally adapted as a full‐season cultivar from 45 to 48° N latitude. ND1406HP was evaluated by the NDSU soybean breeding program in advanced yield trials for a total of 32 location‐years that included 2008 to 2013. Testing for iron‐deficiency chlorosis (IDC) was conducted from 2011 to 2013 at a total of 11 sites located in eastern North Dakota, based on four replicates per site. ND1406HP was released because it has (i) high yield in North Dakota environments, (ii) high protein and can be used to produce high‐quality tofu or soymilk, (iii) lodging resistance, and (iv) tolerance to IDC.

To examine the responses to early IV administration of an anticoagulant or placebo started within 24 hours of stroke among persons with an ipsilateral occlusion or severe stenosis of the internal carotid artery (ICA) identified by carotid duplex imaging.

To compare the baseline National Institutes of Health Stroke Scale (NIHSS) score and the Trial of Org 10172 in Acute Stroke Treatment (TOAST) stroke subtype as predictors of outcomes at 7 days and 3 months after ischemic stroke.

The purpose of the present study was to investigate the relative roles of protein kinase C (PKC) and myosin light chain kinase (MLCK) in phorbol ester-induced contraction of vascular smooth muscle through the use of PKC and calmodulin antagonists. Prior exposure to PKC antagonists staurosporine (0.03 microM) and H-7 (10 microM) had relatively little effect on contractions to phorbol 12-myristate 13-acetate (PMA), while contractions to norepinephrine and KCl were greatly inhibited. Prior exposure to the calmodulin antagonists calmidazolium (3 and 10 microM) and W-7 (10 microM) inhibited contractions to PMA in the presence and absence of extracellular Ca2+, while contractions to norepinephrine and KCl remained relatively unaffected. Calmidazolium and W-7 were relatively weak relaxants when applied during the PMA contraction, and the magnitudes of relaxation were similar to those observed in norepinephrine- and KCl-contracted tissues. Calmidazolium partially inhibited the PMA-induced translocation of PKC. These results suggest that 1) the calmodulin antagonists inhibit the development of PMA-induced contraction, at least in part, through inhibition of PKC translocation; 2) the mechanisms of phorbol ester- and agonist-induced translocation of PKC are distinct; 3) the potencies and inhibitory mechanisms of these agents depend on whether the agents are added before or during the contraction; and 4) the selectivity of these agents, as evaluated in enzyme preparations, may not be consistent with their cellular actions.