Erosion and cavity characteristics in rotating components

An investigation of the initiation and growth of erosion and of the effect of velocity and pressure on erosion in a rotating disk is presented. Also, the role of an intervening noncavitating period on erosion is studied. The results indicate that at high intensities the peak rate of erosion decreases with increases in pressure. The erosion rate/time curves obtained for metallic materials are explained by the eroded particle distribution and the cavity size. The average size of the eroded particles decreased when pressure and tensile strength of the material were increased. The erosion rate peaked after an intervening noncavitating period. The use of the rate of erosion, defined as an average over the entire test duration, in the equation governing the theory of erosion resulted in reasonably good correlations. The correlations reveal that it is possible to predict the length, width, and area of a cavity when the cavitation parameter σ is known. The normalized width of a cavity may be estimated if its normalized length is known.

Squeezed states, photon-number distributions, and U(l) invariance

We study the photon-number distribution in squeezed states of a single-mode radiation field. A U(l)-invariant squeezing criterion is compared and contrasted with a more restrictive criterion, with the help of suggestive geometric representations. The U(l) invariance of the photon-number distribution in a squeezed coherent state, with arbitrary complex squeeze and displacement parameters, is explicitly demonstrated. The behavior of the photon-number distribution for a representative value of the displacement and various values of the squeeze parameter is numerically investigated. A new kind of giant oscillation riding as an envelope over more rapid oscillations in this distribution is demonstrated.

Interior Photon Absorption Based Adaptive Regularization Improves Diffuse Optical Tomography

An adaptive regularization algorithm that combines elementwise photon absorption and data misfit is proposed to stabilize the non-linear ill-posed inverse problem. The diffuse photon distribution is low near the target compared to the normal region. A Hessian is proposed based on light and tissue interaction, and is estimated using adjoint method by distributing the sources inside the discretized domain. As iteration progresses, the photon absorption near the inhomogeneity becomes high and carries more weightage to the regularization matrix. The domain's interior photon absorption and misfit based adaptive regularization method improves quality of the reconstructed Diffuse Optical Tomographic images.

Global solutions describing the collapse of a spherical or cylindrical cavity

The collapse of a spherical (cylindrical) cavity in air is studied analytically. The global solution for the entire domain between the sound front, separating the undisturbed and the disturbed gas, and the vacuum front is constructed in the form of infinite series in time with coefficients depending on an ldquoappropriaterdquo similarity variable. At timet=0+, the exact planar solution for a uniformly moving cavity is assumed to hold. The global analytic solution of this initial boundary value problem is found until the collapse time (=(gamma–1)/2) for gamma le 1+(2/(1+v)), wherev=1 for cylindrical geometry, andv=2 for spherical geometry. For higher values of gamma, the solution series diverge at timet — 2(beta–1)/ (v(1+beta)+(1–beta)2) where beta=2/(gamma–1). A close agreement is found in the prediction of qualitative features of analytic solution and numerical results of Thomaset al. [1].

Squeezed vacuum as an eigenstate of two-photon annihilation operator

We introduce the inverse annihilation and creation operators a-1 and a(dagger-1) by their actions on the number states. We show that the squeezed vacuum exp(1/2xia(dagger2)]\0] and squeezed first number state exp[1.2xia(dagger2)]\n = 1] are respectively the eigenstates of the operators (a(dagger-1)a) and (aa(dagger-1)) with the eigenvalue xi.

Boson Inverse Operators and a New Family of Two-photon Annihilation Operators

We introduce the inverse of the Hermitian operator (acircacirc†) and express the Boson inverse operators acirc-1 and acirc†-1 in terms of the operators acirc, acirc† and (acircacirc†)-1. We show that these Boson inverse operators may be realized by Susskind-Glogower phase operators. In this way, we find a new two-photon annihilation operator and denote it as acirc2(acircacirc†)-1. We show that the eigenstates of this operator have interesting non-classical properties. We find that the eigenstates of the operators (acircacirc†)-1 acirc2, acirc(acircacirc†)-1 acirc and acirc2(acircacirc†)-1 have many similar properties and thus they constitute a family of two-photon annihilation operators.

Solubilization of n-decane into n-decyl-polyoxyethylene surfactants: A cavity forming free energy based model

The present paper reports the results of a theoretical study of the forces and factors driving the solubilization of n-alkane solubilizates into the micellar core of some non-ionic surfactants, based on a micellar model which includes the cavity forming free energy as a component of micellization. The solubilizate is n-decane and the non-ionic surfactants considered are n-decyl-polyoxyethylene surfactants. The extent of solubilization, i.e. the mole fraction of the solubilizate within the core has been calculated. The results indicate that the incorporated solubilizate has more translational and rotational degrees of freedom as compared to those of the tail parts of the surfactants present in the core. This drives the total free energy of aggregation after solubilization into a more favourable direction. The results are in fair agreement with the experimental results.

Photoinduced transparency of effective three-photon absorption coefficient for femtosecond laser pulses in Ge16As29Se55 thin films

We report a dramatic change in effective three-photon absorption coefficient of amorphous Ge16As29Se55 thin films, when its optical band gap decreases by 10 meV with 532 nm light illumination. This large change provides valuable information on the higher excited states, which are otherwise inaccessible via normal optical absorption. The results also indicate that photodarkening in chalcogenide glasses can serve as an effective tool to tune the multiphoton absorption in a rather simple way. (C) 2011 American Institute of Physics.

Modulation of lifetimes and diastereomeric discrimination in triplet-excited substituted butane-1,4-diones through intramolecular charge-transfer quenching

Triplet lifetimes have been determined for the diastereomers of a broad set of butane-l,4-dione derivatives (1-3). A remarkable dependence of lifetimes on conformational preferences is revealed in that the lifetimes are shorter for the meso diastereomers of 1-3 than those for the racemic ones. The intramolecular beta-phenyl quenching is promoted in the case of meso diastereomers by virtue of the gauche relationship between the excited carbonyl group and the beta-aryl ring, while a distal arrangement in the lowest energy conformation (H-anti) in racemic diastereomers prevents such a deactivation. The involvement of charge transfer in the intramolecular beta-phenyl quenching is suggested by the correlation of the triplet lifetimes of the meso diastereomers of compounds 2 with the nature of the substituent on the beta-phenyl rings. In the case of racemic diastereomers, beta-methoxy substitution on the beta-phenyl ring (2-OCH3, 3-OCH3) also led to a decrease of the triplet lifetimes when compared to those of the nonsubstituted compounds (2-H, 3-H). This shortening is accounted for by the deactivation of a small proportion of the excited molecules through beta-phenyl quenching. In addition to the above factors, the lifetimes in the case of meso diastereomers can further be controlled by increasing the energy spacing between the T-1 and T-2 states, since beta-phenyl quenching occurs from the latter for compounds 2 and 3. Through a rational conformational control, a surprisingly long triplet lifetime (300 ns) has been measured for the first time for a purely n,pi* triplet-excited beta-phenylpropiophenone dimer (1-rac).

Photon-photon total cross-section

We study the total inelastic gamma gamma cross-section and discuss predictions from different models, with a special attention to their dependence on the input parameters. In particular we examine the results from a simple extension of the Regge Pomeron exchange model and those from the eikonalized mini-jet model. We then compare both of them with recent LEP data.

Solid state structural and solution studies on the formation of a flexible cavity for anions by copper(I) and 1,2-bis(diphenylphosphino)ethane

Copper(l) complexes of 1,2-bis(diphenylphosphino)ethane (dppe) with a stoichiometry Cu-2(dppe)(3)(X)(2) [X- = CN- (1), SCN- (2), NO3- (3)] are obtained from direct reactions of CuX and dppe. The complexes are structurally and spectroscopically (NMR and IR) characterized. The structure of the [Cu-2(dPPe)(3)](2+) dication is similar to the structural motif observed in many other complexes with a chelating dppe and a bridging dppe connecting two copper centers. In complexes 1 -3, the anions are confined to the cavity formed by the phosphines which force a monodentate coordination mode despite the predominant bidentate/bridging character of the anions. The coordination angles rather than the thermochemical radii dictate the steric requirement of anions. While the solution behavior of 3, with nitrate, is similar to complexes studied earlier, complexes with pseudohalides exhibit new solution behavior. (C) 2002 Elsevier Science Ltd. All rights reserved.

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part II-Numerical Studies

In this article, a single-phase, one-domain macroscopic model is developed for studying binary alloy solidification with moving equiaxed solid phase, along with the associated transport phenomena. In this model, issues such as thermosolutal convection, motion of solid phase relative to liquid and viscosity variations of the solid-liquid mixture with solid fraction in the mobile zone are taken into account. Using the model, the associated transport phenomena during solidification of Al-Cu alloys in a rectangular cavity are predicted. The results for temperature variation, segregation patterns, and eutectic fraction distribution are compared with data from in-house experiments. The model predictions compare well with the experimental results. To highlight the influence of solid phase movement on convection and final macrosegregation, the results of the current model are also compared with those obtained from the conventional solidification model with stationary solid phase. By including the independent movement of the solid phase into the fluid transport model, better predictions of macrosegregation, microstructure, and even shrinkage locations were obtained. Mechanical property prediction models based on microstructure will benefit from the improved accuracy of this model.

Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part I-Experimental Studies

Experimental studies were performed to investigate the role and influence of grain movement on macrosegregation and microstructure evolution during equiaxed solidification. Casting experiments were performed with a grain-refined Al-Cu alloy in a rectangular sand mold. For the aluminum alloy studied, the equiaxed grains are lighter than the bulk melt and thus float up. Experiments were designed to investigate floatation phenomena of equiaxed grains in the presence of thermosolutal convection. Cooling curves were recorded at key locations in both the casting and the chill. Quantitative image analysis and spatial chemical analysis were performed on the solidified casting to observe the chemical and microstructural inhomogeneity created by the melt convection and solid floatation. Several notable features that can be attributed to grain movement were observed in temperature histories, macrosegregation patterns, and microstructures. In our experiments, the floatation of grains influences the thermal conditions and the overall flow direction in the casting cavity. In some cases, the induced flow resulting from the grain movement caused a flow reversal. This in turn influences the solidification direction, microstructure evolution, and the overall macrosegregation behavior.

On cavity flow at high Reynolds numbers

The flow in a square cavity is studied by solving the full Navier–Stokes and energy equations numerically, employing finite-difference techniques. Solutions are obtained over a wide range of Reynolds numbers from 0 to 50000. The solutions show that only at very high Reynolds numbers (Re [gt-or-equal, slanted] 30000) does the flow in the cavity completely correspond to that assumed by Batchelor's model for separated flows. The flow and thermal fields at such high Reynolds numbers clearly exhibit a boundary-layer character. For the first time, it is demonstrated that the downstream secondary eddy grows and decays in a manner similar to the upstream one. The upstream and downstream secondary eddies remain completely viscous throughout the range of Reynolds numbers of their existence. It is suggested that the behaviour of the secondary eddies may be characteristic of internal separated flows.