Particle melting in high temperature supersonic low pressure plasma jets

A numerical model has been developed to predict the temperature history of particles injected into a low pressure dc plasma jet. The temperature and velocity fields of the plasma jet are predicted as a free jet by solving the parabolized compressible Navier-Stokes equations using a spatial marching scheme. Particle trajectories and heat transfer characteristics are calculated using the predicted plasma jet temperature and velocity fields. Correction factors have been introduced to take into account noncontinuum effects encountered in the low pressure environment. The exchange of energy and momentum between the injected particles and plasma flow was treated by considering the source terms in the governing equations. The plasma jet profiles as well as the particle/plasma interactions with different jet pressure ratios (from underexpanded to overexpanded) have been investigated. The effect of particle loading on the resulting jet profiles, particle trajectories, and temperature profiles is presented and discussed. This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

Noninvasive prediction of intracranial pressure curves using transcranial Doppler ultrasonography and blood pressure curves

BACKGROUND AND PURPOSE: Until now the assessment of intracranial pressure (ICP) required invasive methods. The objective of this study was to introduce an approach to a noninvasive assessment of continuous ICP curves. METHODS: The intracranial compartment was considered a "black box" system with an input signal, the arterial blood pressure (ABP), and an output signal, the ICP. A so-called weight function described the relationship between ABP and ICP curves. Certain parameters, called transcranial Doppler (TCD) characteristics, were calculated from the cerebral blood flow velocity (FV) and the ABP curves and were used to estimate this weight function. From simultaneously sampled FV, ABP, and (invasively measured) ICP curves of a defined group of patients with severe head injuries, the TCD characteristics and the weight function were computed. Multiple regression analysis revealed a mathematical formula for calculating the weight function from TCD characteristics. This formula was used to generate the ICP simulation. FV, ABP, and ICP recordings from 11 patients (mean age, 46 +/- 14 years) with severe head injury were studied. In each patient, ICP was computed by a simulation procedure, generated from the data of the remaining 10 patients. The simulation period was 100 seconds. RESULTS: Corresponding pressure trends with a mean absolute difference of 4.0 +/- 1.8 mm Hg between computed and measured ICP were observed. Shapes of pulse and respiratory ICP modulations were clearly predicted. CONCLUSIONS: These results demonstrate that this method constitutes a promising step toward a noninvasive ICP prediction that may be clinically applicable under well-defined conditions.     

Effect of high pressure on interdiffusion in Cu-Zn alloys at temperatures near the melting point

Interdiffusion of copper and zinc alloys of Cu-28.5 at. pct Zn and Cu-4.9 at. pct Zn has been investigated under pressures from 0.101 to 3240 MPa in the temperature range from 1256 to 1377 K. The diffusion coefficients decrease with increasing pressure. The activation energy for impurity diffusion of zinc in copper increases with pressure. The ratio of the activation volume to the molar volume of copper is between 0.75 and 0.90. It is concluded that the impurity diffusion of zinc in copper occurs predominantly by the monovacancy mechanism at temperatures near the melting point of the alloy.     

The efficacy of the high volume counterpulsation technique at very low levels of aortic pressure

Nitric oxide synthase activity was measured in Langerhans islets isolated from control and streptozotocin diabetic rats. The activity of the enzyme was linear up to 150 micrograms of protein from control rats and was optimal at 0.1 microM calcium, when it was measured after 45 min of incubation at 37 degrees C in the presence of 200 microM arginine. Specific activity of the enzyme was 25 x 10(-4) nmol [3H]citrulline 45 min-1 mg protein-1. Streptozotocin diabetic rats exhibited less enzyme activity both in total pancreas homogenate and in isolated Langerhans islets when compared to control animals. Nitric oxide synthase activity measured in control and diabetic rats 15 days after the last streptozotocin injection in the second group of animals corresponded only to a constitutive enzyme since it was not inhibited by aminoguanidine in any of the mentioned groups. Hyperglycemia in diabetic rats may be the consequence of impaired insulin release caused at least in part by reduced positive modulation mediated by constitutive nitric oxide synthase activity, which was dramatically reduced in islets severely damaged after streptozotocin treatment.     

On differential thermal analyzer curves for the melting and freezing of alloys

Using a heat-flow model of a differential thermal analyzer and thermal characteristics obtained by fitting experimental results for a pure metal, the response of the differential thermal analyzer is modeled for the melting and solidification of alloys. The enthalpy-temperature relation used for the alloy simulations is obtained by two different methods: (1) equilibrium and Scheil considerations derived solely from thermodynamic information and (2) solute-diffusion micromodels coupled to the differential thermal analysis (DTA) heat-flow equations. During the consideration of pure material melting, simple expressions are obtained for the effect of sample size and heating rate on the DTA melting onset temperature, peak temperature, and peak height, which assist in the proper calibration of a differential thermal analyzer. For alloys, the smearing effect of the DTA heat flow at different heating and cooling rates is demonstrated for various solidification-path features. In particular, the DTA peak temperature during melting, which is often selected as the liquidus temperature experimentally, is shown to be significantly higher than the liquidus temperature for small-freezing-range alloys and/or for alloys with slow solid diffusion. The DTA curves calculated for freezing with dendritic growth due to supercooling, quantify the errors associated with the determination of the liquidus temperature on cooling.     

Development of an induction melting process for materials with low electrical conductivity or high melting point

A hybrid process combining a cold crucible and a nontransferred plasma has been proposed. By using this process, not only metals with a high melting point but also dielectric materials can be melted without contamination. Also, good homogeneity of alloying elements can be expected by using this process because of the induction mixing taking place in the molten charge. By using the hybrid process, silicon was melted and held with almost no contact with the crucible. A heat-transfer analysis taking account of the dependence of electrical conductivity on temperature was performed on a silicon charge as a semiconductor. The effects of operating parameters, such as magnetic flux density, radius of the charge, and frequency of the coil current, were studied on the equilibrium temperature at which the heat generation rate in a charge balances with the heat removal rate. The critical temperature over which induction heating is possible was theoretically derived and was compared with the value obtained in an experiment. Formerly Undergraduate Student, Department of Materials Processing Engineering, Nagoya University     

Ectopic pregnancy diagnosis in very high risk patients

SETTING: Hepatosplenic abscesses in neutropenic patients, especially during the recovery phase, are almost always attributed to fungal infections. We report similar lesions due to Mycobacterium tuberculosis in neutropenic patients in a tertiary care centre in India. OBJECTIVE: To characterize the features of hepatosplenic tuberculosis in neutropenic patients. DESIGN: Retrospective comparison of disease pattern and response to treatment of hepatosplenic tuberculosis in febrile neutropenia patients (four of 30 with severe prolonged neutropenia) and in non neutropenic patients diagnosed during the same 12-month period (n = 4, control group). RESULTS: The disease in the neutropenic patients typically presented during the recovery phase of neutropenia, with ultrasonic abnormalities similar to those seen in hepatosplenic fungal infections. In contrast to the marked organomegaly and typical granulomatous response found in the control group, the disease in the neutropenic patients was characterised by an absence of organomegaly, non-involvement of other sites, poor inflammatory response and a high bacillary load. The initial response to therapy was satisfactory in both groups. CONCLUSION: Tuberculosis needs to be considered in the diagnostic work-up of hepatosplenic abscesses that occur during the recovery phase of neutropenia.     

Multizone photorefractive keratectomy for high and very high myopia: long-term results

PURPOSE: To compare 2 year results of multizone excimer laser photorefractive keratectomy (PRK) in eyes with myopia (spherical equivalent [SE]) from 6.00 to 10.00 diopters (D) with those in eyes with myopia from 10.25 to 25.75 D. SETTING: Wellington Hospital and Laser Vision Harley Street, London, England. METHODS: Of the 281 PRK cases with an SE of at least -6.00 D, 59 eyes had a minimum follow-up of 2 years. Twenty-six of these had an SE from -6.00 to -10.00 D and 33, from -10.25 to -25.75 D. The single-pass, multizone technique was used to create ablation zones at 5.0, 5.5, and 6.0 mm. Postoperatively, patients received a minimum of 4 weeks of fluorometholone 0.1%; those exhibiting regression after corticosteroids were discontinued were restarted on a tapering regimen. RESULTS: The refraction stabilized 3 months postoperatively in the -6.00 to -10.00 D group, and the final mean SE refraction was a small undercorrection. Two years postoperatively, 88.5% of eyes had a visual acuity of 20/40 or better, and 77.0% were within +/- 1.00 D of the intended correction. In eyes with myopia greater than 10.00 D, regression continued during the 2 years and refraction did not stabilize. Forty-two percent had an uncorrected acuity of 20/40 or better, and 48.0% were within +/- 1.00 D of the intended correction. The incidence and severity of haze were higher in the group with myopia greater than 10.00 D. The overall incidence of complications was low. CONCLUSION: Two years after multizone PRK, refractive and visual acuity results in eyes with myopia from 6.00 to 10.00 D were good. Results in eyes with myopia of more than 10.00 D were not satisfactory, and refraction had not stabilized.     

A method for a simulation of continuous intracranial pressure curves

The study introduces a method to simulate continuously an intracranial pressure (ICP) wave form. In a system analysis approach the intracranial compartment was viewed as a black box with arterial blood pressure (ABP) as an input signal and ICP as an output. A weight function was used to transform the ABP curve into the ICP curve. The output ICP waveform was generated using a weight function derived from the transcranial Doppler blood flow velocity (FV) and ABP curves. In order to establish the relationship between TCD characteristics and weight functions simultaneous recordings of FV, ABP, and ICP curves of a defined group of patients were used. A linear function between the TCD characteristics and the weight functions was obtained by calculating a series of multiple regression analyses. Given examples demonstrate the procedure's capabilities in predicting the mean ICP, the pulse and respiratory waveform modulations, and the trends of ICP changes.     

The critical pressure and impeding pressure of Al evaporation during induction skull melting processing of TiAl

In this article, two key pressures, the critical pressure P _crit and the impeding pressure P _impe of elemental evaporation, are defined and studied based on the calculation relationship between the evaporation loss rate N _m and the chamber pressure P during melting of titanium-aluminum alloys. When the chamber pressure is below P _crit or above P _impe, N _m tends to the maximum or the minimum value and remains almost unchanged. However, if P _crit<P<P _impe, with the increase of the chamber pressure, N _m declines sharply. A method has been put forward to calculate P _crit and P _impe of Al evaporation in a Ti-XAl (at pct) (X=25 to 50) melt. The calculation result shows that P _crit or P _impe is a second-order function of the molar percentage of Al and the melt temperature.