An Analytical Model for Material Removal in Abrasive Jet Machining for Brittle Materials

Optical microscopy has indicated that the abrasive particles used in abrasive jet machining have sharp edges with the shapes similar to cone or pyramid. Moreover, microscopic examination of cross section of work samples eroded by AJM shows that, for brittle materials, material removal is due to intersection and propagation of cracks produced by adjacent impacting particles on target surface. An analytical model has been developed based on the above observations for predicting the material removal in abrasive jet machining process. The model also suggests the critical value of mass flow rate which has been substantiated experimentally. In addition, the influence of velocity and mass flow rate of abrasive particles on material removal rate is briefly described.     

ENHANCEMENT OF THE SEDIMENTATION RATES OF FIBROUS SUSPENSIONS

The settling of suspensions of slender rod-like particles with large aspect ratios was studied. The novel technique of enhancement of sedimentation rates by the addition of buoyant particle promoters was applied to such suspensions. The settling rates could be increased by many times by this simple technique. Sedimentation velocity increases of between 5 to 7 times have been observed for fibrous suspensions of concentrations of about 0.5%. A statistical analysis of the experimental data was performed to establish a correlation for the enhancement in settling velocities. The sediment volume was unaffected by the presence of buoyant particles. The buoyant parjticles were found to adsorb some surfactants onto their surfaces.     

Moisture Diffusion Inside Paper Materials in the Hygroscopic Range and Characteristics of Diffusivity Parameters

Some current models for moisture diffusion in paper in the hygroscopic range are analyzed. In general, two types of diffusion models can be recognized. Models of the first type treat paper as a homogeneous medium with moisture flux that is proportional to the gradient in moisture content. Although useful in some instances this approach fails frequently because it homogenizes the internal dynamics and relaxation processes occurring within the paper material. Recent studies have shown that a subtler approach which treats paper as a composite of fibers and void spaces is more successful at describing moisture transport dynamics. A review of these studies along with a generalization of this approach to three dimensions is considered here. The parameters appearing in such models can be identified with the physical processes of diffusion through the void space and through the fiber matrix. Diffusivities in these individual phases are supplemented by a local kinetic coefficient representing moisture flux interchange between the void and fiber phases. When the local moisture exchange coefficient takes on large values, the fibers and the void spaces are at local equilibrium with no net exchange of moisture. Under such conditions, the model reduces to the simpler Fickian diffusion model with nonlinear moisture diffusivity equivalent to earlier models.     

A Differential CMOS Current-Mode Variable Gain Amplifier with Digital dB-Linear Gain Control

A novel CMOS variable gain amplifier operating on current signals with a dB-linear gain control is presented. The gain control is achieved by multiplying a digitally synthesized exponentially varying control current signal by a differential input signal in the current domain. A current amplifier at the output sets the gain to the desired level. Current-mode operation allows for a reduced supply voltage by minimizing the voltage swing at the low impedance nodes of the circuit. Multiple circuit realizations for various blocks are presented allowing for designs meeting different constraints. Experimental realization of the variable gain amplifier shows the validity of the presented approach.     

Generalized Jastrow variational method for dense Fermi systems

In this paper, we outline a simple method whereby the antisymmetry of the wave function can be incorporated exactly in the Jastrow many-body theory. Applications of this method to the “homework problem” for neutron matter using the hypernetted-chain approximation give results in very good agreement with the Fermi-hypernetted chain approximation calculations of Fantoni and Rosati. The calculations for liquid³He at a Fermi wave numberk _F=0.75 Å^?1 give results close to the Monte Carlo calculations of Ceperley, Chester, and Kalos.     

Structural,microstructural and electrochemical studies on LiMn2-x(GdAl)xO4 with spinel structure as cathode material for Li-ion batteries

Gd and Al co-doped LiMn_2-x(GdAl)_xO₄ (x?=?0, 0.01, 0.02, 0.03, 0.04 and 0.05) materials with spinel structure were synthesized by sol–gel method. Powder X-ray diffraction results confirm the formation of cubic spinel structure and average particle sizes are found to be between 80 and 110?nm from FE-SEM and TEM analysis. Decrease in peak potential difference as a function of doping in Cyclic Voltammetry results establishes enhancement in Li⁺ intercalation and de-intercalation. Electrochemical Impedance Spectroscopy (EIS) results showed that accumulation of charges on electrode has improved with doping over pristine samples. At a doping of x?=?0.02 charge transfer resistance values were found to be least. First cycle charge–discharge profiles for LiMn_1.96(GdAl)_0.02O₄ shows 139.2?mAh/g discharge capacity over other doped derivatives and pure LiMn₂O₄ (119.6?mAh/g) in aqueous Li₂SO₄ electrolyte. Doping of x?=?0.02 exhibit good cycling performance with only a total 4% capacity loss after 30 cycles.     

Optical properties of coloured transparent alumina gel monolith glasses

Optical properties of transparent alumina prepared through gel process at room temperature and coloured with dopants have been studied. The absorption bands, molar absorptivity, effect of concentration and the dependence of oxidation state of copper on the copper content and water content are similar to the random network glasses. The ultraviolet absorption edge at lower energies confirm the disordered nature of the transition phase aluminasγ andδ. The absorption bands in the visible suggest the octahedral symmetry of oxygen around aluminum.     

Teratocarcinosarcoma of the paranasal sinuses: a clinicopathologic and immunohistochemical study

We observed endothelin (ET)-induced contractile responses on prostatic and epididymal segments, as well as the facilitation of an electrically stimulated tone on prostatic segments of isolated rat vas deferens. In both segments, the selective ET(B)-receptor agonists, IRL 1620 and sarafotoxin S6c, produced only a small contraction or no contraction at a concentration of 1 microM. The rank order of contraction potencies (pD2 value) was ET-1 = ET-2 > ET-3 > sarafotoxin S6c = IRL 1620. The maximum responses of ET-induced contractions in the prostatic segments were larger than those in the epididymal segments. The contractile response to ET-3 was antagonized by pretreatment for 30 min with BQ-123 (10 nM), a selective ET(A) receptor antagonist, and BQ-788 (1 microM), a selective ET(B) receptor antagonist. The contractile responses to ET-1 were antagonized by pretreatment with BQ-123 (10 microM), but not with BQ-788 (1 microM). The ET-3-induced facilitation on the twitch response to electrical stimulation in the prostatic segment of the vas deferens was antagonized by BQ-123 (0.1 microM) and BQ-788 (1 microM). The ET-1-induced facilitation was antagonized by pretreatment with BQ-123 (3 microM), but not with BQ-788 (10 microM). These results suggest that in rat vas deferens the ET(A) receptors are divided into BQ-123-sensitive ET(A1) and BQ-123-insensitive ET(A2) subtypes, and the production of a contractile response of smooth muscle as well as the facilitation of neurotransmission are accomplished through mediation by ET(A1)- and ET(A2)-subtypes.     

Characteristics of the surfaces obtained in electro-discharge machining

According to the established thermal theories on electro-discharge machining (edm), the size of the craters produced in edm is proportional to the discharge energy, which is equal to the product of mean pulse current and pulse duration for a constant gap voltage. As a practical edm surface is a random superposition of such craters, the behaviour of the surfaces largely depends on the two important parameters, pulse current and pulse duration. With the help of multiple linear regression analysis, the effect of pulse duration and pulse current on the surface topography parameters R_q and β* has been studied. sem photomicrographs have been taken in support of the qualitative evidence