Inviscid fluid in high frequency excitation field

Summary The influence of high frequency excitations (HFE) on a fluid is investigated. The response to these excitations is decomposed in two parts: slow motion, which practically remains unchanged during the vanishingly small period , and fast motion whose value during this period is negligible in terms of displacements, but is essential in terms of the kinetic energy. After such a decomposition the slow and fast motions become nonlinearly coupled by the corresponding governing equations. This coupling leads to an effective potential energy which imparts some elastic properties to the fluid and stabilizes laminar flows.     

Irreversibilites in science and technology networks: An empirical and analytical approach

The theory of autopoiesis, i.e., self-referentiality in the operation of the system, provides us with a production rule for change in the structure of the network. Using information theory, a model system is developed to study the relative likelihood of dynamic transitions: various senses of irreversibility (emergence, and path dependency) are disinguished. A test for path dependency is applied to two sets of empirical data which supposedly reflect historical discontinuities: the budget of theFraunhofer Gesellschaft, and the citation network among AIDS research related journals. The model for the interaction between self-referential developments and goal-referential boundary conditions is further specified, using the example of technological trajectories and selection environments.     

The effect of plastic bending on the electrical properties of indium antimonide

High temperature plastic bending was used to introduce, into indium antimonide single crystals, an excess of dislocations having either In-atoms at the edge of their extra half-planes (In-dislocations), or having Sb-atoms there (Sb-dislocations). The densities of these two kinds of dislocations were estimated by etch pit techniques. Hall coefficient and electrical conductivity measurements, made on bent samples, indicated that both In- and Sb-dislocations act as acceptor centres in n-type material, and that In-dislocations act as acceptor centres in p-type material. The results are discussed in relation to the theories of Read [22] and Broudy [4].     

Where Are We in HTCS?

Address given at the closing of the conference on Major Trends in Superconductivity in the New Millennium, MTSC 2000 and the opening of the Symposium on Itinerant and Localized States in HTCS SILS in HTCS.     

Disciplinary variables that affect the shape of Bradford's bibliograph

The influence of various factors upon the shape of Bradford's bibliograph was assessed through an examination of 16 bibliographies, of which ten were comprehensive. We obtained a curvature score for each bibliograph plotted in a standard landscape format so as to permit comparison; we found that the amount of concave up curvature (convexity): (a) is negatively correlated with a bibliography's overall publication density; (b) depends on the status (technical vs. nontechnical) of the disciplinary source of a bibliography, with technical disciplines showing less convexity; and (c) is complexly affected by the historical changes in the discipline. Findings are discussed in the context of questions about the graphical formulation of Bradford's Law.     

Temperature dependence of high strain-rate impact fracture behaviour in highly filled polymeric composite and plasticized thermoplastic propellants

The effect of temperature and strain-rate on the fracture behaviour during high strain-rate ( 10³ sec^–1) impact of two highly filled polymeric composite propellants (containing segmented polyurethanes based on hydroxy-term inated polybutadiene (HTPB) or glycidyl azide polymer (GAP) filled with ammonium perchlorate (AP) particles) and a plasticized thermoplastic (cast double base (CDB) nitrocellulose-nitroglycerine) propellant have been examined over a wide temperature range encompassing the ittle-ductile transition. In the elastic region of the loaddisplacement curve, the yield stress and fracture toughness is highest for GAP/AP and lowest for HTPB/AP. In the elastic and post-yield ductile regions CDB is more fracture-resistant than GAP/AP and HTPB/AP over the temperature range –20 to 50° C, but below –40° C, where both CDB and GAP/AP are brittle, GAP/AP is more fracture-resistant than CDB (as observed in the elastic region). Although all the propellants are known to develop small cracks in the elastic and post-yield ductile regions of the load-displacement curve, the overall fracture behaviour is largely governed by viscoelastic properties (because the cracks close up in compression). The good mechanical properties of CDB, above the brittle-ductile transition temperature, can be attributed to the presence of a large-transition loss peak. In the composites, the fracture behaviour is also influenced to a lesser extent by the degree of filler-binder interactions. Dynamic mechanical analysis indicates that GAP/AP has a slightly higher degree of filler-binder interactions than HTPB/AP. A temperature-strain rate reduction has been obtained for the yield stress and the composite curve can be expressed by the equation _y =K ₁ +K ₂ log (ea _T ) whereK ₁ andK ₂ are constants anda _T is a shift factor.K ₂ is a material constant which reflects the temperature and strain-rate sensitivity.     

Effect of Intense Self-Irradiation on the Phase Composition of Metallic Plutonium

The crystal structure of film samples of "high-level" (based on ²³⁸Pu) and low-level (based on ²³⁹Pu) metallic plutonium during their prolonged (up to 343 days) storage (self-irradiation) at room temperature was studied by X-ray diffraction. In the samples of high-level plutonium, the -Pu and -Pu lattices coexist. In the period of 40-60 days, the other known crystal modifications of plutonium (-Pu, -Pu, -Pu, and -Pu) are also present. Low-level plutonium had only the -Pu lattice. A possible origin of this phenomenon is discussed.     

Modes of “normal” and “deteriorated” heat exchange in the single-phase near-critical region in the turbulent flow of helium in tubes

The results of a study of heat transfer to helium in the single-phase near-critical region are presented. The boundaries of existence of the modes of normal and deteriorated heat exchange are established. A calculating dependence for the local heat exchange is proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 4, pp. 606–612, April, 1976.     

The analysis of scientometric matrices for policy implications

A method is explained for analysing matrices of statistics where each element should be approximately proportional to some column coefficient and also to some row coefficient. Using U. S. patent data as an example it is shown that entries are usually proportional to country size and patent category size. Deviations from proportionality expectations when tabulated often suggest policy implications.     

Catalytic decomposition of hydrazine in weakly alkaline solutions on platinum nanoparticles

The kinetics and stoichiometry of catalytic decomposition of hydrazine in 0.01 M NaOH solutions in the presence of unstabilized (gray colloid) and stabilized with sodium polyacrylate (brown colloid) platinum nanoparticles were studied. The main decomposition products are ammonia and N₂ with H₂ impurity (up to 1.5%), i.e., hydrazine decomposition predominantly follows the stoichiometric equation 3N₂H₄ = 4NH₃ + N₂. The catalytic activity was studied as influenced by nanoparticle size distribution. Despite higher nanoparticle dispersion, the catalytic activity of the stabilized brown colloid is lower than that of the gray colloid. The reaction mechanism is discussed.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 531–535.Original Russian Text Copyright © 2004 by Ananev, Boltoeva, Sukhov, Bykov, Ershov.     

Thermal shock resistance of miniaturized multilayer ceramic capacitors

The thermal shock resistance of miniaturized multilayer ceramic capacitors (MLCs), of sizes 0402, 0603, 0805 and 1206, was investigated by comparing the leakage currents before and after thermal shock. It was generally found that smaller capacitors have a higher thermal shock resistance than larger ones. The 0402 MLC possesses a thermal shock resistance in excess of 420 C. The linear interdependence of thermal shock resistance and reciprocal of half thickness, as predicted by conventional thermal shock analysis, was not observed. Instead, the thermal shock resistance of an MLC was found to be inversely proportional to the total area of its ceramic surface. This confirms that pre-existing flaws on the ceramic surface dominate the crack initiation process and are therefore primarily responsible for determining the thermal shock resistance of an MLC.     

Microstructural study of two LAS-type glass-ceramics and their parent glass

The two glass-ceramics studied here derive from the complex system (MgO,ZnO,Li₂O)-Al₂O₃-SiO₂ and are obtained by controlled devitrification of the same parent glass. Although they have the same chemical composition, one is a -quartz (or -eucryptite) type while the other one is a -spodumene glass-ceramic. A detailed microstructural analysis of these materials has been performed at different scales by several complementary characterization methods (SEM, TEM, DTA, XRD and FTIR). This extensive study has shown the great microstructure difference (grain distribution, grain size, nature of vitreous and crystalline phases) between these two glass-ceramics obtained from the same parent glass.     

The stacked lamellar texture on the fracture surfaces of fibre composites

A fracture surface texture, which has been variously termed as lacerations, hackles or serrations, is often observed on the matrix surface of fibre composites, most often in resin-rich regions. This texture, referred to here as a stacked lamellar texture to emphasize its plate-like nature, was studied in an E-glass/epoxy composite. Scanning electron fractographs of these materials suggest that the stacked lamellar texture arises from crack fingers due to a meniscus instability mechanism interacting with a reorienting stress field.     

The effect of Si,Zr, Al and Mo on the structure and strength of Ti martensite

The structure and strength of martensite in near titanium alloys have been studied in the composition range (wt %) up to 10% Zr, 6%, Al, 1/2% Mo, 2.4% Si. [0001], 1/3 11¯20 dislocations, 1/3 10¯10 stacking faults and approximately {10¯11} twin related martensite plates are found to be common features of the martensite. Martensite midribs consist either of finely transformed material between martensite plates, or regions of low dislocation density within martensite plates.The martensite morphology is related to the alloy composition, changing from massive to plate-like with increasing solute content. The strength of the martensite is controlled largely by solid solution strengthening.     

Observation of hydrogen distribution in high-strength steel

The diffusible hydrogen in Cr-Mo steels are observed with autoradiography technique. Specimens with the diffusible hydrogen are prepared by an electrochemical cathodic charging method and those without the diffusible hydrogen by annealing at 373 K after charging hydrogen. TEM autoradiographs suggests, by the developed silver grains, that the hydrogen trapping sites are the grain boundary and internal interface of ferrite-cementite and ferrite-lath structure. After keeping the sample at 373 K, the silver grains disappeared. Most of hydrogen trapping sites release almost all the hydrogen at 373 K. It is clear that these sites of high-strength steels supplies the diffusible hydrogen. Hydrogen absorption characteristics of quench hardening tempering Cr-Mo steels have been evaluated by thermal desorption spectrometry (TDS). From tritium electron microscopic autoradiography and TDS analysis, the lower temperature (360 K–370 K) peaks show the diffusing hydrogen which is released a few days. The diffusible hydrogen from trapping sites such as the internal interface of ferrite-cementite or ferrite-lath structure are distinguished to the diffusing hydrogen.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

Mechanisms of uniform corrosion under corrosion deposits

The liquid-phase transport phenomena which occur at the surface of iron-base alloys during corrosion have been analysed. These mechanisms determine either the maintenance of bare metal or the precipitation of solid corrosion products, the build-up of a corrosion deposit and the control of its thickness, and finally, the kinetics of the electrochemical reactions under the deposit. Although it is shown that pure precipitation-redissolution or direct formation reactions are impossible, the only conceivable mechanisms are nevertheless closely related, because the transport of iron between the metal and the external corrosive medium occurs chiefly either via the solid phase of the deposit (for soluble deposits), or via the liquid phase permeating its porosities (for insoluble deposits). It is also shown that, depending on the precipitation conditions, any given solid compound Fe _n X₂ can lead to three types of deposit with quite different properties. (i) Soluble deposits: moderately protective, steady-state corrosion insensitive to potential, but highly sensitive to turbulence; (ii) Insoluble cationic deposits (controlled by the removal of Fe²⁺ cations by liquid-phase diffusion): highly protective, corrosion rate slightly sensitive to potential, and insensitive to turbulence. (iii) Insoluble anionic deposits (controlled by the diffusional supply of the precipitatable anion X ^n– : slightly or unprotective, corrosion slight or insensitive to the presence of the deposit; possibly profuse deposit if steady state corrosion is not attained. This theoretical analysis can retrospectively explain numerous experimental observations reported in the literature, such as the incubation time before the drop in corrosion rates, the multiple forms of CO₂ and H₂S corrosion, the role of Ca²⁺ ions, erosion-corrosion and bacterial corrosion. This analysis also paves the way for the reliable laboratory prediction of real corrosion rates under deposits.     

Phase transformations in the thermotropic liquid crystal polymer: 60/40 PABA/PET

Microstructures observed in 60/40 PABA/PET co-polyester in transmitted polarized light are reported. The microstructure changes as a function of temperature. Between 190 and 340 C the optical textures are similar to those seen in small molecule liquid crystals in the smectic C modification; above 340 C the textures are typical of nematic structures. At 420 C the specimen is totally isotropic and begins to degrade. Rapid cooling to below 190 C can quench in the high temperature phases, including the isotropic one. DSC traces show endotherms identifiable with the onset of mobility at 190 C, the transition from smectic C to nematic-like textures at 340 C and the development of the isotropic phase in the range 350 to 420 C. The smectic C to nematic transition in texture is associated with the appearance of a transient microstructure, known as a myelin texture, and reported here for the first time in a liquid crystal polymer.     

The microstructure of sintered Si-Al-O-N ceramics

Fine-grained ceramics, based on the substituted -Si₃N₄ crystal structure, have been prepared with near theoretical densities by pressureless sintering of compacts containing a large Y₂O₃ additive concentration. The microstructure contains two phases, and an Y/Al rich silicate glassy matrix, in the as-sintered condition. The matrix may be crystallized on heat treatment to a Si-substituted yttrium-aluminium garnet phase. The phase compositions and transformation mechanisms have been analysed by X-ray microanalysis, electron diffraction and imaging of thin sections.A preliminary survey of mechanical properties of these sintered ceramics shows that they are comparable with commercial hot-pressed silicon nitrides, particularly at high temperatures. The possibility of development of a range of ceramic alloys, dependent on their chemical environment and temperature of application, is discussed.     

Quantitative estimation of “big” and “little” science interrelation

Qantitative analysis of the interrelation of big and little science on the example of Research and Development of higher education in the USA has been made. The difference in the growth rates of big and little science is explained with the help of scientometric index of capital expenditures per researcher. An attempt has been made to compare the dynamics of efficiency of big and little science on the base of mean duration of a research project. Possibilities of an alternative index of a relative amount of preliminary researches (preprojects) are pointed out.