A recessed-gap capacitive-gate GaAs CCD

A MESFET-compatible structure for GaAs capacitive-gate CCDs that eliminates the necessity for submicrometer interelectrode gaps and simplifies device fabrication is presented. This recessed-gap structure solves problems of low gate-channel-gate breakdown and large parasitic gate-to-gate capacitance associated with ultrasmall gaps. Dark current is also reduced. Modeling and experimental results are reported     

Thermoeconomic optimization of a refrigeration plant

In this paper, thermoeconomic theory is applied to the economic optimization of a conventional refrigeration plant, aimed at minimizing its overall operation and amortization cost.Thermal systems cannot always be optimized by means of mathematical or numerical techniques, because a complete model of the plant is not always available, and, in any case, mathematical difficulties are often great, even for not particularly complex systems, and the help of computerized algorithms is needed.In this paper, a simplified cost minimization methodology is applied, based on the so-called Theory of Exergetic Cost, here utilized to evaluate the economic costs of all the internal flows and products of the installation. As shown in the paper, once these costs have been calculated, a design configuration not far from the real global optimum can be obtained by means of a sequential, local optimization of the system, carried out unit by unit, that is, breaking down the global problem into a sequence of simpler problems.In the paper, the case of a very simple plant is considered to develop a numerical example, and, in spite of the approximations introduced to simplify the optimization procedure, the results obtained show acceptable accuracy when compared with those provided by a conventional and more complex optimization methodology.     

Decreased erythrocyte Na+,K(+)-ATPase activity associated with cellular potassium loss in extremely low birth weight infants with nonoliguric hyperkalemia

To determine whether a shift of potassium ions from the intracellular space to the extracellular space accounts, in part, for the hyperkalemia seen in extremely low birth weight infants, we examined potassium concentration in serum and erythrocytes from extremely low birth weight infants with hyperkalemia (n = 12) or with normokalemia (n = 27). In addition, to determine whether the shift of potassium was associated with low sodium-potassium-adenosinetriphosphatase (Na+,K(+)-ATPase) activity, we studied the activity of ATPase in the last 16 infants enrolled in the study. Fluid intake and output were measured during the first 3 days of life. Infants were considered to have hyperkalemia if the serum potassium concentration was 6.8 mmol/L or greater. Blood was obtained daily for intracellular sodium and potassium levels by means of lysis of erythrocytes. The remaining erythrocyte membranes were frozen and analyzed for Na+,K(+)-ATPase activity. There were significantly lower intracellular potassium/serum potassium ratios in the infants with hyperkalemia for each day of the 3-day study (p < 0.001). In the hyperkalemic group, there was lower Na+,K(+)-ATPase activity than in the infants with normokalemia (p = 0.006). Low Na+,K(+)-ATPase activity was associated with lower intracellular potassium/serum potassium ratios (p = 0.006), higher serum potassium values (p = 0.02), and lower intracellular potassium concentration (p = 0.009). The urinary data demonstrated that there was no difference in glomerulotubular balance between the two groups. We conclude that nonoliguric hyperkalemia in extremely low birth weight infants may be due, in part, to a shift of potassium from the intracellular space to the extracellular space associated with a decrease in Na+,K(+)-ATPase activity.     

Reasoning with direction and rate of change in vegetation state transition modelling

Better integration in land planning and management can be supported through the use of suitable model-based tools. Vegetation state transition models have been noted as being useful in this context, providing a simple, useful means of capturing available ecological knowledge. We describe a simple ‘proof of concept’ rule-based system developed to contribute methodologically to management-oriented modelling of vegetated landscapes. The system is based upon a clear separation of direction from rate of change and the use of a general temporal reasoning system, a feature that facilitates modelling of situations where environmental change occurs causing an increase or decrease in rate without affecting direction of vegetation change. To ease model development and use the system represents vegetation dynamics in a way that has a close correspondence to the structure of understanding communicated by vegetation ecologists. A test model is described and run under different conditions to demonstrate the system. The results show that although the rule-based system and in particular the temporal reasoning system used operate successfully, there are a number of deficiencies in the modelling system as currently implemented. Future development possibilities are detailed along with a broader discussion regarding the needs of management-oriented modelling and the utility of state transition approaches.     

Efficient UV polymerisation of 3BCMU: Optical and waveguiding properties of the material

A modified method to synthesize 3BCMU and to polymerize it by ultraviolet (UV) radiation is presented; the polymerization technique gave a maximum yield of 18%. Langmuir-Blodgett and spin coated films of UV/poly-3BCMU have been fabricated. Visible and resonance Raman spectroscopy and waveguide tests were performed: the results are compared with those obtained with y/poly-3BCMU films.     

Ribozyme-mediated RNA degradation in nuclei suspension

Ribozymes containing 2'-fluoro- and 2'-amino-modified pyrimidine nucleosides in combination with terminal phosphorothioate linkages were targeted against HTLV-I tax RNA. In order to examine the activity of such chemically modified ribozymes in the nuclear environment, they were incubated with nuclei of a Tax-transformed mouse fibroblast cell line. Ribozyme cleavage of tax RNA was analyzed by the RNase protection assay. Comparison of the cleavage of tax RNA isolated nuclei with that of tax RNA present in nuclei suspension revealed a 30 times more efficient cleavage of the latter one. Pre-treatment with proteinase K and SDS abolished the enhancement of the ribozyme-mediated RNA cleavage. Catalytically inactive ribozymes did not yield any cleavage products. These results demonstrate an augmenting effect of nuclear proteins on the ribozyme-mediated RNA cleavage.     

HIV type 1 V3 sequences and the development of dementia during AIDS

OBJECTIVE: To study percentile distance growth pattern of Body Mass Index (BMI) of Punjabi male and female infants. DESIGN: Longitudinal. SETTING: Growth Clinic. SUBJECTS: 154 Punjabi infants (Male 86; Female 68), aged birth-12 months. FOLLOW-UP: Nude body weight and crownheel length of all babies at birth and whereafter, were measured at monthly age intervals with time tolerance to +/-3 days by the same investigator upto 12 months of life. RESULTS: Mean (+/- SD) values for BMI measured 12.2 +/- 1.40 kg/m2 and 16.5 +/- 1.40 kg/m2 at birth and 12 months, respectively in male infants. The corresponding figures for female infants were 12.5 +/- 1.60 kg/ m2 and 16.5 +/- 1.50 kg/m2. A rapid increase in BMI values amongst infants of both sexes between birth to about six months followed by flattening of curves upto 12 months of age indicates an age dependent nature of BMI during first half of infancy in comparison to latter half during which these demonstrated stable trend. These findings are in contrast to those of the western infants who showed a regular increase in BMI throughout the first year of life. Sex differences were not significant at majority of the age levels. CONCLUSIONS: Percentile grids presented for BMI represent a normal, healthy and well-nourished infant population which can be used to assess the adiposity status of infants of the two sexes during the first year of life.