Grain growth of high Tc YBa2Cu3O7−x

Grain growth during sintering of the polycrystalline high onset temperature superconductor YBa₂Cu₃O_7−x has been examined by measuring grain sizes at various temperatures for different times above 900°C. The grain size distribution is found to be predominately lognormal after some sintering time. The mean grain size increases with both temperature and time. The standard deviation of the grain size distribution increases with temperature, but appears to be independent of time. The grain growth law may have an exponent of five. The grain growth rate may be affected by the grain size of the calcined powder.     

An experimental investigation of electrically thick rectangular microstrip antennas

The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured.     

Dual-band reactively loaded microstrip antenna

A previously derived theory is applied to a microstrip antenna with a reactive load to produce a dual-band radiator. A model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally. Comparisons of theoretical predictions and experimental data are made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance of the stub.     

Scaled model measurements of embedding impedances for SIS waveguide mixers

Several scaled models have been used to determine the contributions of various waveguide mount parameters to the embedding impedance of a mm-wave SIS mixer. Measured effects of waveguide height, substrate orientation and width, junction location, lead inductance and RF-filter impedance are presented and discussed.     

Sodium nitroprusside: pharmacology, toxicology and therapeutics

Sodium nitroprusside is a potent, effective, and readily reversible direct vasodilating agent. It is broken down by hemoglobin into cyanide, which is in part detoxified by liver and kidney to thiocyanate. Some cyanide, especially in nitroprusside- "resistant" individuals who need large amounts of the drug, appears to remain free to cause cyanide poisoning. Patients requiring inordinate amounts probably should not continue to receive the drug, although maximum dosage limits for long-term therapy are not established. Blood thiocyanate levels do not indicate the extent to which free cyanide is limiting oxygen utilization in essential tissue, nor do blood cyanide levels. Metabolic acidosis, elevated lactate levels, elevated lactate/pyruvate ratios, and elevated mixed venous blood oxygen content are at present the best indications of the presence of cyanide poisoning during nitroprusside administration. Nitroprusside appears useful for induction of hypotension during surgery, and for treatment of hypertensive emergencies from all causes, although continuance for more than a few days is probably unwise. The reductions of cardiac afterload and ventricular filling pressure by nitroprusside appear useful in treatment of severe myocardial failure or infarction, but studies of myocardial cyanide toxicity are needed before complete acceptance of this therapy is warranted. Initial dose rates between 0.5 and 1.5 mug/kg/min are recommended only as starting points for very careful titration. Total projected intra-operative dosage should be calculated as quickly as possible and should not exceed 3-3.5 mg/kg. It is hoped that future studies will reveal the maximum dose of nitroprusside that can safely be metabolized in a 24-hour period, and may indicate that cofactors of rhodanase such as thiosulfate, or cobalamins such as hydroxocobalamin, can be administered with nitroprusside to prevent cyanide poisoning.     

Conservative management of chronic renal failure

Failing kidneys can play havoc with other parts of the body. Specific treatment of these associated problems may help ward off uremia and preserve whatever renal function remains. Sodium levels may drop if too much water is mistakenly given to counteract kidney failure. Hyperkalemia can lead to cardiac arrest if potassium levels aren't reduced without delay. Acidosis also may reach life-threatening proportions, especially if diarrhea occurs. Almost all patients with chronic renal failure have a bleeding tendency and anemia, with the hematocrit dipping as low as 20 percent. Over half have decreased tolerance to carbohydrares, although severe hyperglycemia is rare. Disorders of calcium metabolism also are common, ranging from asymptomatic hypocalcemia to osteomalacia. The kidneys' impaired filtration ability should be kept in mind when drugs are prescribed. Dosages may need to be cut to avoid an adverse reaction.     

Effects of low-intensity ultrasound on the central nervous system of primates

The brains of anesthesized squirrel monkeys were exposed to 2.25 to 5 MHz ultrasound at low intensities (average power from 3 mW/cm2 to 0.9 W/cm2). The exposure produced evoked potentials recorded by EEG electrodes chronically implanted in the midline parietal region. Computer analysis of the waveforms showed that ultrasound produced a transient upward shift in both the peak frequency and in its amplitude. Complete adaptation occurred with 3 min of continuous exposure to either CW or pulsed irradiation.     

Influence of membrane heterogeneity on kinetics of nonelectrolyte tracer flows

The importance of various unsaturated fatty acid triglycerides to the repair of faulty skin barrier function was studied in essential fatty acid-deficient rats. Following cutaneous application of the pure triglycerides for up to 5 days, the hitherto high rate of transepidermal water loss, characteristic of essential fatty acid deficiency in rats, was reduced by the triglycerides of linoleic and gamma-linolenic acids. Incorporation of the applied fatty acids into the lecithin of the epidermis accompanied these changes in water loss, indicating that cutaneously applied triglycerides may be metabolized by the skin and incorporated into complex lipids. Other fatty acid triglycerides, including alpha-linolenic, dihomo-gamma-linolenic, arachidonic and omega-7-heneicosatrienoic acid, did not lower the rate of transepidermal water loss, although all were incorporated into epidermal structural lipids. The non-essential oleic acid also had no effect upon the rate of transepidermal water loss. These data suggest that of the two main essential fatty acids that occur in skin, linoleic acid and arachidonic acid, the former specifically plays an important role in regulating barrier function whereas the later may have a separate function, such as serving as a precursor of prostaglandins.