Flutter and Buffeting Analysis.?I: Finite-Element and RPE Solution

A finite-element formulation is developed for analyzing flutter instability and buffeting response of long-span bridges and their interaction. The flutter derivatives, instead of the indicial functions used by previous researchers, are applied in the random parametric excitation (RPE) analysis. This application makes finite-element formulation possible and results in much less computational effort in RPE analysis than those of previous analyses. With the finite-element program developed in the present study, as many modes as desired can be easily included in the flutter and buffeting analyses. Users have the choice of RPE or eigenvalue method for flutter analysis and RPE or spectral method for buffeting analysis.     

Processing,Microstructure, and Mechanical Properties of B4C ― TiB2 Particulate Sintered Composites. Part I. Pressureless Sintering and Microstructure Evolution

Pressureless sintering of boron carbide ceramics containing 0-25 vol. % TiB₂ phase, produced via an in-situ chemical reaction between B₄C, TiO₂, and elemental carbon, was studied in the isothermal and constant-heating-rate regimes. The presence of TiB₂ results in a decrease in activation energy for sintering from 717 kJ/mol at 0 vol. % TiB₂ to 266 kJ/mol at 25 vol. % TiB₂. Ceramic bodies of B₄C TiB₂ particulate composites with relative densities of up to 99% were sintered without pressure at temperatures of 2050-2100°C. Grain boundary diffusion is the primary mechanism of TiB₂ particle coarsening. TiB₂ particle size is bimodal depending on whether the particle is confined within a B₄C grain or located on the grain boundary. Densification behavior of the B₄C TiB₂ system is identical at different heating rates in the temperature range of 1800-2150°C.     

Substitutional solutes in AlRu—I. Effects of solute on moduli,lattice parameters and vacancy production

The effect of solute-related defects in AlRu are measured by changes that they produce in lattice parameter, specific gravity and elastic moduli. By comparison with the effects of off-stoichiometry on the same parameters in binary AlRu alloys, the solute-produced defects can be partially characterized. Cell occupancy numbers are calculated and used to infer that vacancies are formed on the Al-rich side of stoichiometry, but possibly on a less than one vacancy per excess Al atom basis. These data are also needed to test the effects on the solutes studied—Co, Fe and Ti—on mechanical hardening to be reported separately in Part II.     

Equilibrium pore surfaces,sintering stresses and constitutive equations for the intermediate and late stages of sintering—I. computation of equilibrium surfaces

The intermediate stage of sintering is characterized by equilibrium surfaces of the open pore space between the grains. These doubly curved surfaces are determined numerically for the three cubic arrangements of grains (simple cubic, b.c.c. and f.c.c). The numerical program constructs surfaces of constant mean curvature connected via the dihedral angle to grain boundaries having zero mean curvature. The pore morphologies resulting from the analysis are different from the conventional picture of interconnected pore channels along grain edges. According to the present results, open porosity rather consists of interconnected pillow-shaped gaps between next-nearest grain neighbors. The transition to closed porosity occurs when the connections between these gaps close, a process which leads to relatively large isolated pores on two-grain junctions between former next-nearest neighbors. The numerical results for the contact areas between grains and for the sintering stress are approximated by quadratic functions of the pore volume fraction and of the dihedral angle, and the best-fit coefficients are tabulated. The results are used in a companion paper in which constitutive equations for the mechanical behavior during sintering are derived.     

Shock synthesis of silicides—I. experimentation and microstructural evolution

Niobium and molybdenum silicides were synthesized by the passage of high-amplitude shock waves through elemental powder mixtures. These shock waves were generated by planar parallel impact of explosively-accelerated flyer plates on momentum-trapped capsules containing the powders. Recovery of the specimens reveaved unreacted, partially-reacted, and fully-reacted regions, in accord with shock energy levels experienced by the powder. Electron microscopy was employed to characterize the partially-and fully-reacted regions for the MoSi and NbSi systems, and revealed only equilibrium phases. Selected-area and compositions of the reacted products. Diffusion couples between Nb and Si were crystal structure and compositions of the reacted products. Diffusion couples between Nb and Si were fabricated for the purpose of measuring static diffusion rates and determining the phases produced under non-shock condition. Comparison of these non-shock diffusion results with the shock synthesis results indicates that a new mechanism is responsible for the production of the NbSi₂ and MoSi₂ phases under shock compression. At the local level the reaction can be rationalized, for example, in the NbSi systems under shock compression, through the production of a liquid-phase reaction product (NbSi₂) at the Nb-particle/Si-liquid interface, the formation of spherical nodules (∼2 μm diameter) of this product through interfacial tension, and their subsequent solidification.     

Simplifications and improvements in unified constitutive equations for creep and plasticity—I. Equations development

An improved version of the MATMOD unified constitutive equations for creep and plasticity is developed. The new physical-phenomenological model, MATMOD-BSSOL, is the first version of the equations that is capable of modeling both solute strengthening and complex strain softening phenomena, but it combines the capabilities of previous versions in a way that simplifies the equations and minimizes the number of material constants. The major improvement present in MATMOD-BSSOL is the way in which solute strengthening is treated; both athermal flow stress plateaus and Class I steady state creep are simulated via the effects of solute concentration on the evolution of short range back stresses, which are already present in the equations to treat directional strain hardening. The physical significance of this new approach to modeling solute effects and the way in which it unifies the low and high temperature behavior of alloys are discussed.     

Monte-carlo simulations of interstitial diffusion and trapping—I. One type of traps and dislocations

The long-range tracer diffusion coefficient of interstitials their jump rate and their distribution among different sites in one-, two- and three-dimensional lattices have been determined by Monte-Carlo calculations. In one part of this study traps or antitraps were introduced with equilibrium site energies being lower or higher, respectively, and energies of the surrounding saddle points being higher or lower when compared with the normal sites. Already a small decrease of the saddle point energies around the trap sites, reduces the diffusion coefficient remarkably. For an overall constant saddle point energy the results could be compared with various trapping models, but for lower or higher energy barriers around the trap sites new analytical solutions for the site occupancy and the diffusivity had to be derived which are in agreement with the computer calculations. According to the theoretical results the free energy of a site is also determined by its accessibility where lower saddle points decrease the free energy and vice versa. In a second part of this study a site energy distribution was constructed which corresponds to the elastic interaction energy between an interstitial solute and an edge dislocation. Again the segregation of solute atoms in trap sites of the dislocation is strongly dependant on the distribution of saddle point energies and remarkable deviations from the treatment of Cottrell and Bilby occur if the saddle point energy is lowered in the same way as the energy of the equilibrium points.     

Copper Demand from China’s Wire and Cable Industry-Part I

<正>1. Reality of China’s wire and cable industry China, with a total wire and cable industry output value in excess of the United States, has     

Preparation of cerium and yttrium doped ZnO nanoparticles and tracking their structural,optical,and photocatalytic performances

Yttrium(Y) and cerium(Ce) co-doped ZnO nanoparticles(NPs) were synthesized via the simple sol-gel auto-combustion route.The effect of Ce and Y doping on the structure,morphology,optical,Zeta potential,and photocatalytic activities of ZnO NPs was examined by Fourier transform infrared(FTIR)spectrometer,X-ray diffraction(XRD),transmission electron microscope(TEM),UV-vis spectrophotometer,and Zetasizer instrument.XRD data show that the fabricated samples crystallize into a hexagonal wurtzite struct...     

China''''s imports and exports of tungsten,molybdenum,tin and antimony by category

~~China's imports and exports of tungsten,molybdenum,tin and antimony by category~~     

Synthesis of γ-TiAl by Reactive Spark Plasma Sintering of Cryomilled Ti and Al Powder Blend,Part I: Influence of Processing and Microstructural Evolution

To provide insight into the influence of an electric field on the kinetics of diffusion, fully lamellar γ-TiAl was processed by a rapid, two-stage, solid-state reactive sintering via spark plasma sintering (SPS) of a cryomilled Ti, Al powder blend. Cryomilling was implemented in the current study to attain a nanostructured grain size in the Ti and Al powder blend, and thereby provide insight into the influence of grain size on the underlying diffusion kinetics. Following a two-step process involving SPS at 873 K (600 °C) for 15 minutes and 1523 K (1250 °C) for 30 minutes, a fully lamellar TiAl alloy, with submicron lamellar spacing, was successfully obtained. Microstructural refinement in the Ti and Al powders during cryomilling led to an increase in solid-state diffusion, and the underlying mechanisms are discussed in detail.     

“I have always thought about death, a death that I might give myself”.

This article, as well as the publication of a previously unpublished personal letter written by Jacques Derrida in his youth, relate to my thinking and research regarding the existential questions raised by philosophy and the act of suicide. Both the personal letter and the correspondence between Derrida and his close friend Michel Monory invite us to reflect on death and the enigma that suicidal ideation can take when presenting itself to a subject, while at the same time they provide us with valuable information about the origins of Derrida's oeuvre to come. Giving us a glimpse into the universe of a young tormented soul, who has already dreamed of “a book of extraordinary philosophy,” Jacques Derrida confides some of his philosophical, psychological, and—interesting in light of what we know will be his future—autobiographical reflections to his friend. I situate the context of this correspondence more precisely and give shape to the distant, buried form of what will have been friendship allowing us to gain a greater understanding of the act of autobiography, as well as the autobiographical pact—as Philippe Lejeune has theorized it—and how it relates to the work of mourning. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

How much do I tell thee? Strategies for managing information to parents among American adolescents from Chinese, Mexican, and European backgrounds.

Strategies for managing information about activities to parents, including partial disclosure, avoidance, lying, and full disclosure, were examined in 479 American adolescents (M = 16.38 years, SD = 0.77) varying in generational status and from Mexican, Chinese, and European backgrounds. Information management strategies for personal, prudential, and overlapping (multifaceted) activities as defined within social domain theory were examined. With age, parental education, and generational status controlled, Chinese American adolescents partially disclosed more to mothers about personal and multifaceted activities than did Mexican American adolescents and more to fathers about personal activities than did European American teens. In contrast, European and Mexican American adolescents fully disclosed more to mothers about personal activities than did Chinese-origin adolescents. Strategies varied by generation among Chinese American youth; second-generation adolescents avoided discussing activities with parents more than did immigrants. Adolescents who fully disclosed about all activities and lied less about multifaceted and personal activities reported stronger endorsement of obligations to assist their families, more trust in parents, and less problem behavior. More depressed mood was associated with more lying about personal activities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Should I stay or should I go? Attentional disengagement from visually unique and unexpected items at fixation.

Distinctive aspects of a scene can capture attention even when they are irrelevant to one’s goals. The authors address whether visually unique, unexpected, but task-irrelevant features also tend to hold attention. Observers searched through displays in which the color of each item was irrelevant. At the start of search, all objects changed color. Critically, the foveated item changed to an unexpected color (it was novel), became a color singleton (it was unique), or both. Saccade latency revealed the time required to disengage overt attention from this object. Singletons resulted in longer latencies, but only if they were unexpected. Conversely, unexpected items only delayed disengagement if they were singletons. Thus, the time spent overtly attending to an object is determined, at least in part, by task-irrelevant stimulus properties, but this depends on the confluence of expectation and visual salience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Power and conflict resolution in sibling, parent–child, and spousal negotiations.

This study used a within-family observational design to examine conflict strategies (planning, opposition) and resolutions (standoff, win-loss, compromise) across family subsystems, with an emphasis on power differences between parents and children during relatively symmetrical within-generation (spousal, sibling) and relatively asymmetrical between-generation (parent–child) dyadic interactions. Up to six dyads in 67 families (children's ages ranging from 3 to 12 years) discussed an unresolved conflict. Results revealed that within-generation discussions ended more in standoff, whereas between-generation discussions ended with more win-loss resolutions. Multilevel analyses indicated that parents engaged in more planning and opposition than children; however, they opposed more and planned less with their spouses than their children. In general, more planning and less opposition were associated with achieving resolutions rather than failing to resolve differences. Some effects were qualified by within-family differences between mothers versus fathers and older versus younger siblings, as well as between-family differences in younger siblings' age. Implications for theories of power and family relationship dynamics are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thin film forced velocity cells and cellular dendrites—I. Experiments

A new, compreheensive set of experimental systematics for the alloys succinonitrile-salol (S-Sa), succinonitrile-acetone (S-A), and pivalic acid-ethanol(P-E) is summarized. The contribution deals synthetically with transients involving the Mullins and Serkerka instability together with Ostwald ripening, pattern selection mechanisms, cell root instabilities, steady state wavelength and amplitude systematics spanning near threshold cellular and dendritic forms, anisotropic effects, facetting and hysteresis and systematics of the cell to dendrite transition. The observations reveal that there are two main stable or nearly stable branches of non-planar cellular solutions, both significantly involving solid state diffusion and excluding single-valued local equilibrium spatial structures. The normal single-valued,non-local equilibrium branch which we designated asdynamical has a scale decreasing with increasing velocity. The other triple-valued, near-marginal branch which we designate asquasi-equilibrium has a scale increasing with increasing velocity.     

Physical therapy: exercises and the modalities: when, what, and Why?

This article reviews the evidence for using modalities and/or exercise treatment in patients with nonspecific low back pain. Poor evidence of efficacy exists for the use of modalities in this patient group. Exercises are beneficial for patients with subacute and chronic nonspecific low back pain. Further studies are needed for type, frequency, duration, and intensity of exercises.