Investigation of the Mechanism of Radiation Propagation at Side Illumination of a Light Guide

A design of a fiberoptic distributedtype detector of radiation sources arbitrarily located in the technological control zone is proposed. We have elaborated a method for recording scattered and directed radiation flows supplied to the side surface of the optical fiber based on measurement of the luminous flux diffusely scattered by the technological microdefects of the optical fiber. It has been established that the scattered flux is concentrated mainly in the optical fiber cladding. The detector sensitivity to the radiation from a gas flame, a laser diode, and background sources has been investigated.     

Temperature-, concentration- and pressure-dependence of the viscosity of liquid3He-4He mixtures at low temperatures

We have investigated the viscosity of liquid³He-⁴He mixtures at various³He - concentrations (0.98%x9.5%) in the temperature range1 mK T 100 mK and at pressures 0 bar P 20 bar. At T10 mK the Fermi-liquid behaviour T² = const. as well as x^4/3 could be confirmed. However, there are significant deviations from theoretical predictions for the magnitude of the viscosity as well as for its pressure dependence.     

A new acoustic spectroscopy: Resonance spectroscopy by the MIIR

Recent and remarkable advances in the experimental study of acoustic scattering from targets immersed in water are leading to a new spectroscopy: resonance acoustic spectroscopy. The discovery and improvement of an intriguing method, the Method of Isolation and Identification of Resonances (MIIR), has made possible experimental determination of the eigenfrequency spectra of aluminum-elastic cylinders and cylindrical shells. This method gives a quasilinear resonance spectra. In addition, it shows the importance of circumferential waves which generate standing waves. They allow us to explain the reradiation of targets after the end of insonification. The MIIR has numerous applications, especially in underwater acoustics and nondestructive testing.     

An electron microscopic study of nickel sulfide inclusions in toughened glass

It has been known since the early sixties that nickel sulfide inclusions cause spontaneous fracture of toughened (thermally tempered) glass, but despite the considerable amount of work done on this problem in the last four decades, failures still occur in the field with regularity. In this study we have classified (by viewing through a 60× optical microscope) inclusions into two groups, which are classic and atypical nickel sulfides. The classics look like the nickel sulfide inclusions found at the initiation-of-fracture of windows that have broken spontaneously. We have compared the structure and composition of the atypical inclusions with the structure and composition of the classics. All of the classic and atypical nickel sulfide inclusions studied in this work were found to have a composition in the range of Ni₅₂S₄₈to Ni₄₈S₅₂. Inclusions on the nickel rich side of stoichiometric NiS were found to be two-phase assemblies, and inclusions on the sulphur rich side of NiS were single phase. It had been proposed that the atypicals were passive, and of a different composition to the classics. However, we found that the difference between passive and dangerous nickel sulfide inclusions was not a difference in composition but rather a difference in the type of material in the internal pore space. The passive's had carbon char in their internal pore space, whereas the pore space of dangerous inclusions contained Na₂O. The presence of Na₂O and carbon char with the inclusions indicates that the formation of the inclusions results from a reaction of a nickel-rich phase with sodium sulphate and carbon.     

Cutting, by ‘pressing and slicing,’ of thin floppy slices of materials illustrated by experiments on cheddar cheese and salami

Why it is easier to cut with even the sharpest knife when pressing down and sliding than when merely pressing down alone is explained. A variety of cases of cutting where the blade and workpiece have different relative motions is analysed and it is shown that the greater the slice/push ratio given by (blade speed parallel to the cutting edge/blade speed perpendicular to the cutting edge), the lower the cutting forces. However, friction limits the reductions attainable at the highest . The analysis is applied to the geometry of a wheel cutting device (delicatessan slicer) and experiments with a cheddar cheese and a salami using such an instrumented device confirm the general predictions.     

Fatigue crack growth behaviour of tungsten carbide-cobalt hardmetals

Fatigue crack propagation studies have been carried out on a range of WC-Co hardmetals of varying cobalt content and grain size using a constant-stress intensity factor double torsion test specimen geometry. Results have confirmed the marked influence of mean stress (throughK _max), which is interpreted in terms of static modes of fracture occurring in conjunction with a true fatigue process, the existence of which can be rationalized through the absence of any frequency effect. Dramatic increases in fatigue crack growth rate are found asK _max approaches that value of stress intensity factor ( 0.9K_IC) for which static crack growth under monotonic load (or static fatigue) occurs in these materials. Lower crack growth rates, however, produce fractographic features indistinguishable from those resulting from fast fracture. These observations, and the important effect of increasing mean free path of the cobalt binder in reducing fatigue crack growth rate, can reasonably be explained through a consideration of the mechanism of fatigue crack advance through ligament rupture of the cobalt binder at the tip of a propagating crack.     

Structure and properties of injection-moulded nylon-6

The microstructure and morphology of injection-moulded nylon-6 has been studied using wide-angle and small-angle X-ray diffraction, optical microscopy and a density measurement technique. A non-spherulitic surface layer consisting of a metastable pseudohexagonal phase surrounds the moulding and the thickness of the layer is sensitive to mould temperature. This outer structure gives way to a monoclinic phase containing spherulites between 3 and 6 m diameter. The central core of the moulding consists almost entirely of the phase with spherulites 6 m diameter, approximately. Exposure of nylon-6 to boiling water had no significant effect on the morphology of the moulding but the phase in the surface layer was transformed to the monoclinic phase.     

Focusing of shock waves on reflection from concave curvilinear surfaces

Results from a comparative analysis of experimental and numerical simulation of the processes of reflection of plane shock waves from concave axisymmetric and two-dimensional surfaces are presented.Academic Scientific Complex The A. V. Luikov Heat and Mass Transfer Institute, Academy of Sciences of Belarus, Minsk. Scientific-Industrial Company Prostor, Moscow Region, Krasnoarmeisk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 548–552, November, 1993.     

Microstructure and tensile properties of BN/SiC coated Hi-Nicalon, and Sylramic SiC fiber preforms

Batch to batch and within batch variations, and the influence of fiber architecture on room temperature physical and tensile properties of BN/SiC coated Hi-Nicalon and Sylramic SiC fiber preform specimens were determined. The three fiber architectures studied were plain weave (PW), 5-harness satin (5HS), and 8-harness satin (8HS). Results indicate that the physical properties vary up to 10 percent within a batch, and up to 20 percent between batches of preforms. Load-reload (Hysteresis) and acoustic emission methods were used to analyze damage accumulation occurring during tensile loading. Early acoustic emission activity, before observable hysteretic behavior, indicates that the damage starts with the formation of nonbridged tunnel cracks. These cracks then propagate and intersect the load bearing 0° fibers giving rise to hysteretic behavior. For the Hi-Nicalon preform specimens, the onset of ° bundle cracking stress and strain appeared to be independent of the fiber architecture. Also, the 0° fiber bundle cracking strain remained nearly the same for the preform specimens of both fiber types. TEM analysis indicates that the CVI BN interface coating is mostly amorphous and contains carbon and oxygen impurities, and the CVI SiC coating is crystalline. No reaction exists between the CVI BN and SiC coating.     

Simulation of the Process of Water Freezing in a Round Pipe

The problem of freezing of pure water in a round pipe is treated with due regard for convection under asymmetric thermal boundary conditions in the absence of motion along the pipe. The problem is solved numerically using the control volume approach, SIMPLER algorithm, and the enthalpy method. Results are obtained for three Grashof (Gr) and six Biot (Bi) numbers: Gr = 1.55 × 10⁶, Bi = 0.305 (0 < ), Bi = 0.044 ( < 2); Gr = 1.24 × 10⁷, Bi = 0.610 (0 < ), Bi = 0.087 ( < 2); Gr = 9.89 × 10⁷, Bi = 1.220 (0 < ), Bi = 0.174 ( < 2). The correctness of calculation of the problem disregarding free-convection flows is analyzed.     

TEM study of metastable β-phase decomposition in rapidly solidified Ti-6Al-4V alloy

A new rationale is presented for various decomposition products obtained from the metastable -phase found in Ti-6A1-4V alloy produced by hot isostatic pressing comminuted melt-spun fibres and cooled to room temperature by furnace cooling. This alloy has an -matrix with about 8 vol% retained -phase, which is supersaturated with -stabilizers to such an extent that the martensitic transformation has been suppressed. The metastable -phase decomposes by different modes during continuous cooling, depending on the actual composition of individual -grains. Less enrichment of vanadium and iron favours the direct formation of the equilibrium -phase from the -matrix, while greater enrichment of vanadium and iron leads to a spinodal decomposition of the metastable -phase, resulting in a + two-phase structure. During further continuous cooling, the -phase which is lean in -stabilizers will transform into isothermal -phase. In addition, an unknown phase has also been observed in the -phase, which is typified by the appearance of 1/2{112} reflections in the SAD patterns.     

Universality and the scaling laws in the superfluid phase transition of3He-4He mixtures

From the second-sound velocityU ₂ near the superfluid transition point, the superfluid densities in³He-⁴He mixtures, _s (X) and _s (), were deduced along the paths of constant³He concentrationX and of constant chemical potential difference of³He and⁴He. The following critical exponents of _s are determined: (a) =XX for _s (X) in the(X, T) plane,(b) X for _s (X) in the(, T) plane, and(c) for _s () in the(, T) plane. It is found that and _X change by about 4–6% relative to with increasing³He concentration up toX=0.4 and by 8–10% up toX=0.53. It seems that, belowX=0.53, universality hold for . Values of have been found to be in good agreement with the critical exponent of _s in pure⁴He under constant pressure. The values of and _X forX0.53 are also found to be consistent with the scaling relations in the (,T) plane of³He-⁴He mixture.Work performed in part while at the Electrotechnical Laboratory.     

Dynamics of a nonlinear periodic structure with cyclic symmetry

Summary The free and forced motions of a nonlinear periodic structure with cyclic symmetry are studied. The structure consists of a number of identical linear flexural members coupled by means of nonlinear stiffnesses of the third degree. It is found that this system can only possessn similar nonlinear modes of free oscillation, and that no other modes are possible. Moreover, there exist pairs of nonlinear modes with mutually orthogonal nodal diameters having, in general, distinct backbone curves. A multiple-scales averaging analysis is used to study the nonlinear interaction between a pair of modes with orthogonal nodal diameters. As a result of this analysis, it is found that all pairs of nonliner modes along with all their linear combinations are orbitally unstable, and the only possible orbitally stable periodic motions are free travelling waves, that propagate through the structure in the clockwise and anti-clockwise directions. Under harmonic forcing, a bifuraction of a stable branch of forced travelling waves from a branch of forced normal mode motions is detected, and jump phenomena between branches of periodic solutions are observed. The analytical results are in agreement with experimental observations of an earlier work, and, in addition, are verified by numerical simulations.     

Microstructural analysis of the calcium aluminosilicate (CAS) glass-ceramic matrix in SiCf/CAS composites deformed at a high temperature

The calcium aluminosilicate (CAS: anorthite) glass-ceramic matrix materials in the SiCf/CAS composites deformed in compression at a high temperature were analyzed for microstructures. The matrix region right above the top of the SiC fiber ( 0°) showed high density of dislocations as well as twins. On the other hand, the matrix region remote from the top of the SiC fiber ( 90°) showed only a twinned structure. This experimental result was compared with the Meyer et al.'s mechanical modeling indicating that the interfacial traction of the matrix region right on the top of the fiber is significantly high compared to the remote stress and thus it rate limits the creep deformation of the composite.     

Numerical Calculation of the Flow Regimes of a Fluid Partially Filling a Horizontal Rotating Heat‐Exchange Cylinder

Consideration is given to a numerical determination of a twodimensional unsteady viscous flow with the free surface in a stationarily rotating horizontal cylinder in which heatexchange processes are carried out. The markerandcell method in a polar coordinate system is used. The features of modeling of the walllayer regime and the circulating flow regime that occur in rapid and slow rotation of the cylinder, respectively, are discussed. Based on the given results of numerical calculations, the influence of the Reynolds number on the character of flow is analyzed.     

A transmission-electron-microscopy study of a face-centred-cubic phase in an Al-Li-Cu-Mg-Zr alloy

Icosahedral T₂ phases can form either by solid-state precipitation or during solidification in Al-Li-Cu-Mg alloys. The T₂ phase forming during solidification can transform to an R phase at high annealing temperatures. The T₂ phase forming by solid-state precipitation coexists with the Y phase, which has a face-centred cubic (f.c.c.) structure with lattice parameter a2.0 nm and can form microtwins with the twin plane of (111). The orientation relationships between the C phase and the T₂ phase are: i¯5Y0 1 1, Y1 1 3; i¯3Y1 1 1, Y1 2 3, Y1 1 5; Y2 3 5; i2Y0 1 1, Y1 1 1, Y1 1 2, Y1 1 3, Y1 1 5.     

Phase decomposition in extruded Zn-Al based alloy

Ageing characteristics of an extruded eutectoid Zn-Al based alloy were investigated using X-ray diffraction and scanning electron microscopy techniques. The extruded alloy consisted of Al rich phase and Zn rich _E and phases. The original cast eutectoid Zn-Al alloy was extruded at 250 °C. Both supersaturated _s and _s phase decomposed during extrusion and appeared as fine and coarse lamellar structures. The _E and phases particles formed in the original interdendritic region. It was found that two Zn rich phases _E and decomposed sequentially during ageing at 170, 140 °C. The decomposition of the _E phase occurred as a discontinuous precipitation in the early stage of ageing and the decomposition of the phase took place in a four phase transformation: + T + in the prolonged ageing. Two typical morphologies of the decomposition of the Zn rich phases _E and were distinctive in back-scattered scanning electron microscopy.     

A comparison of exact first order and spring boundary conditions for scattering by thin layers

In scattering problems for time-harmonic elastic waves, thin elastic layers are often of interest, e.g., in laminates. Various ways of substituting such layers by some effective boundary conditions have been proposed, and these are briefly reviewed. A rational way of obtaining boundary conditions that are exact to first order in the layer thickness is then described. For a thin spherical layer numerical comparisons are performed between these exact first order boundary conditions, the commonly used spring boundary conditions and the exact solution, and it is shown that the exact boundary conditions are far superior to the spring boundary conditions in most situations. A drawback with the exact boundary conditions is that they are quite complicated.     

Influence of pore volume on laser performance of Nd : YAG ceramics

For present study, 1.1 at% Nd-doped YAG ceramics with a controlled pore volume (150–930 vol ppm) were fabricated by a solid-state reaction method using high-purity powders. The scattering coefficients of Nd:YAG ceramics, obtained from Fresnel' equation, increased simply with increases in the pore volume. The cw laser output power of Nd:YAG ceramics was clearly related to the scattering coefficients of the specimens examined in the present works, which in turn were affected on the pore volume. The effective scattering coefficients of Nd:YAG ceramics with a pore volume of 150 vol ppm were nearly equivalent to those of a 0.9 at%Nd:YAG single crystal by Czochralski method. As the exciting power was increased under excitation by an 808-nm diode laser, however, the laser output power of the Nd:YAG ceramics exceeded that of the Nd:YAG single crystal because of the fairly large amount of Nd additives. The lasing performance of the Nd:YAG ceramics changed drastically with change in pore volume. On the other hand, lasing performance was not affected by the existence of grain boundaries in the polycrystalline Nd:YAG ceramics.     

Investigation of the gapless state in bismuth-antimony alloys

The results are presented from an experimental study of the gapless state produced in semiconducting alloysBi _1–x Sb _x by pressure-induced band inversion. The magnetoresistance properties of the alloys have been investigated both in weak magnetic fields (H « 1) and in strong fields (H75 kOe) at liquidhelium temperatures in the Sb concentration interval 0.06x0.15 and pressure interval 1 bar p<20 kbar. At pressuresp close to the pressurep _k at which the gapless state is realized a semiconductor-semimetal-semiconductor transition is detected inBi _1–x Sb _x alloys withx=0.070 and 0.071. The rates of change of the gap _gL before and after inversion are determined: –(2.5±0.5)×10^–6 eV/bar and (1.5±0.5)×10^–6 eV/bar, respectively. A reduction in the carrier effective mass as _gL 0 is observed down to values of 10^–4 m ₀. It is shown that as _gL 0 the carrier mobilities in the alloys increase abruptly, the effect being a maximum in the purest alloys, where forT=4.2 K the mobility along the binary axis attains the record-high value of 3×10⁸ cm²/V · sec.