Boiling from metal surfaces immersed in liquid nitrogen and liquid hydrogen

A study of bubble nucleation in liquid nitrogen and liquid hydrogen has been made in a 120 mm bubble chamber using a high speed cine camera.The initiation and growth of bubbles from artificially prepared cavities was studied. These cavities, produced in both copper and brass surfaces, had mouth radii ranging from 50 μm to 190 μm with depths varying from 110 μm to 500 μm. The liquids were superheated by either heating the surface containing the cavities or by reducing the pressure of the liquid, or by combining both of these methods.The heat fluxes required for initiation of boiling were greater than those required to sustain nucleation from a given site. The growth rate of the bubbles at constant liquid pressure was dependent on a number of factors. It changes as a bubble grew out of the thermal or superheated layer above the metal surface. After an initial period of more rapid growth the vapour volume increased linearly with time. The growth rate was dependent on the liquid used; being slower in liquid hydrogen than in liquid nitrogen. Formulae were obtained which predicted the observed variations in growth rate and departure volume.No nucleation was observed from the test surfaces for a pressure drop alone; the surfaces had to be heated before nucleation would occur. It is thought that this was due to the existence of a zero contact angle for cryogenic liquids on solid surfaces.     

Glycerol as a carbon source for lipase production by the fungus rhizopus delemar

The ability of the fungus Rhizopus delemar to synthesize lipase (glycerol ester hydrolase, E.C. 3.1.1.3) when grown on glycerol as the prime carbon source was investigated. Glucose, glycerol and olive oil all supported fungal growth and lipase production. Maximum net and specific lipase activities obtained in glycerol were greater than those obtained in glucose and olive oil, and were reached earlier and maintained longer during growth. In glucose media, lipase activity did not appear until the glucose had been consumed. Differences in lipase activity between glycerol and glucose media were not due to pH‐mediated lipase inactivation. In both glucose and glycerol media the appearance of lipolytic activity coincided with the appearance of lipase polypeptide. The data are consistent with the postulate that lipase synthesis is subject to catabolite repression by glucose. These studies identify a simple, single‐phase medium for lipase production and establish the utility of glycerol for amplifying enzyme levels.     

Neuroadaptive output feedback control for nonlinear nonnegative dynamical systems with actuator amplitude and integral constraints

A neuroadaptive output feedback control architecture for nonlinear nonnegative dynamical systems with input amplitude and integral constraints is developed. Specifically, the neuroadaptive controller guarantees that the control amplitude as well as the integral of the control input over a given time interval are constrained, and the physical system states remain in the nonnegative orthant of the state space. The proposed approach is used to control the infusion of the anesthetic drug propofol for maintaining a desired constant level of depth of anesthesia for noncardiac surgery in the face of infusion rate constraints and an integral drug dosing constraint over a specified time period. Copyright © 2010 John Wiley & Sons, Ltd.     

Reliability properties of low-voltage ferroelectric capacitors and memory arrays

We report on the reliability properties of ferroelectric capacitors and memory arrays embedded in a 130-nm CMOS logic process with 5LM Cu/FSG. Low voltage (<1.5 V) operation is enabled by the 70-nm thick MOCVD PZT ferroelectric films. Data loss resulting from high temperature bakes is primarily caused by the imprint effect, which shows /spl sim/1.5 eV time-to-fail activation energy. Excellent bit endurance properties are observed on fully packaged memory arrays, with no degradation up to 10/sup 13/ write/read polarization switching cycles. Retention measured after 10/sup 12/ switching cycles demonstrates no degradation relative to arrays with minimal cycling.     

Oxidation-reduction mechanisms in iron-bearing phyllosilicates

Reviewed in this article are the effects of structural Fe oxidation states on the physicochemical properties of smectite clay minerals. Reducing agents selected were dithionite (S₂O₄²⁻), sulfide (S²⁻), thiosulfate (S₂O₃²⁻), hydrazine (N₂H₄), ascorbic acid (C₆H₈O₆), hydroquinone (C₆H₆O₂), and sodium oxalate (Na₂C₂H₂O₄). Clay samples were prepared as aqueous suspensions of < 2 μm particle-size fractions of Na-saturated, freeze-dried ferruginous smectite. The reductive strength of each reducing agent, as determined by measuring the resultant level of Fe(II) in the clay mineral crystal using either a photo-colorimetric method or Mössbauer spectroscopy, decreased in the order S₂O₄²⁻ > S²⁻ > C₆H₈O₆ > S₂O₃²⁻ > C₆H₆O₂ ≈ C₂H₂O₄. The heat of reaction of three of these reducing agents with the clay was measured, and decreased in the order S₂O₄²⁻ > S₂O₃²⁻ > S²⁻. Compared to the order of reductive strength, the heats of reaction with S₂O₃²⁻ and S²⁻ are reversed, suggesting that entropy changes are greater in the S²⁻ treatment. Electron spin resonance (ESR) revealed that free radicals may be responsible for the greatest levels of reductive potential, which provides an important attribute by which potential reducing agents can be screened. Measurements of rheological properties of oxidized and reduced clay suspensions indicated that structural Fe(II) increases the viscosity of clay suspensions as a result of greater attractive forces between clay particles. The type of bonding between particles has yet to be ascertained. Microbial reduction of the clay produces moderate to high levels of reduction and causes changes in physico-chemical properties similar to chemical reduction of the clay.     

Prospects for insulin delivery by ex-vivo somatic cell gene therapy

The principle of insulin delivery by ex-vivo somatic cell gene therapy involves the removal of non-B-cell somatic cells (e.g. fibroblasts) from a diabetic patient, and genetically altering them in vitro to produce and secrete insulin. The cells can be grown in culture and returned to the donor as a source of insulin replacement. Cells modified in this way could be evaluated before implantation, and reserve stocks could be cryopreserved. By using the patient's own cells, the procedure should obviate the need for immunosuppression and overcome the problem of tissue supply, while avoiding a recurrence of cell destruction. Ex-vivo somatic cell gene therapy requires an accessible and robust cell type that is amenable to multiple transfections and subject to controlled proliferation. Special problems associated with the use of non-B-cell somatic cells include the processing of proinsulin to insulin, and the conferment of sensitivity to glucose-stimulated proinsulin biosynthesis and regulated insulin release. Preliminary studies using fibroblasts, pituitary cells, kidney (COS) cells and ovarian (CHO) cells suggest that these challenges could be met, and that ex-vivo somatic cell gene therapy offers a feasible approach to insulin replacement therapy.     

Taxometric analyses of sexual orientation and gender identity.

Taxa are nonarbitrary classes whose existence is an empirical question and not a matter of mere semantic convenience. Taxometric procedures detect whether numerical relations between purported indicators of conjectured taxa bear the hallmarks of true taxa. On the basis of theoretical considerations, the current study tested whether taxa underlie sexual orientation and related measures of gender identity. Two taxometric procedures, maximum covariance, making hits maximum (MAXCOV) and mean above minus below a cut (MAMBAC), were applied to Kinsey Scales and measures of childhood gender nonconformity and adult gender identity in a sample of nearly 5,000 members of the Australian Twin Registry. Results suggest that latent taxa underlie these measures. About 12–15% of men and 5–10% of women belong to latent taxa associated with homosexual preference. These percentages are greater than those of individuals who report homosexual preference, however, and hence it appears that an appreciable proportion of individuals in these taxa have heterosexual preference. An understanding of the origins of these latent taxa may be important to understanding the development of sexual orientation and gender identity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of antipredator responses in snakes: II. Effects of recent feeding on defensive behaviors of juvenile garter snakes (Thamnophis sirtalis).

The effect of having eaten a large meal (50% of body weight) on the defensive behavior of juvenile garter snakes (Thamnophis sirtalis) was investigated. Twenty-five 10-wk-old snakes were tested for antipredator responses (strikes) directed toward a threatening stimulus (moving and nonmoving human hand) before and after having eaten a large worm segment. Snakes directed significantly (p?