Electrical measurement of the junction temperature of an RF powertransistor

An enhanced electrical method is presented for measuring the average junction temperature of an RF bipolar transistor. A two-step procedure, previously developed for DC operation, is extended to include the junction temperature measurement for an RF power transistor in a tuned amplifier circuit. The measurement technique is convenient, since it can be used with normal, packaged devices, and does not require a complex heat flow model or ambient temperature measurements     

On the theory of 3-phase squirrel-cage induction motors includingspace harmonics and mutual slotting

General equations for squirrel-cage induction motors are derived based on the real geometry of the motor. The squirrel cage is described by its meshes; no equivalent windings are used. By means of complex time-dependent transformations free angles are introduced which simplify the set of equations when the specific geometrical properties of both types in which the asynchronous machines fundamentally can be divided are taken into account. The equations are general in the sense that all space harmonics are taken into account, due to the MMF and double slotting. This provides a better calculation of the synchronous, pulsating, and asynchronous torques. The final equations enable the formulation of some specific properties of both types in connection to their electromechanical behavior. Further, they are valid for star and delta connections and for any arbitrary source voltage     

A theoretical and photoelastic contact stress analysis relevant to orthopaedic knee prostheses

This study is based on a theoretical and photoelastic static contact stress analysis, relevant to the design of the plastic tibial plateau in an orthopaedic knee prosthesis. It involves the review of existing theoretical analyses concerned with the contact mechanics of layered elastic systems and, where possible, the validation of any relevant findings using two dimensional photoelasticity. Significant findings include the identification of a general minimum recommendable design thickness for the plastic tibial plateau, the endorsement of using the Hertzian contact theory to predict contact stress levels in the tibial plateau of certain knee implants and the slight improvement in contact conditions in the plastic when the plateau is perfectly bonded to its supporting metal tray.     

Kinetic behaviour of muscle LDH immobilized in nylon tubing

Immobilization was carried out of the lactate dehydrogenase (LDH) from rabbit muscle (EC 1.1.1.27), cross-linked through the bifunctional reactive glutar-aldehyde on to nylon tubing (1 m long, 53cm² internal surface area). Immobilized LDH inactivation kinetics are of first order (t_1/2 = 3·6 years, k = 5·4,e^?4 day^?1 to 5°C). The smaller effect of pH on activity than in the case of LDH in solution can be explained on the basis of limitation to proton diffusion towards the support. A limiting effect to free external diffusion of the substrate towards and products from the support was also observed, an effect which seems to determine the effective kinetic behaviour of immobilized LDH. The apparent optimum temperature is centred around 40°C, observing a clear inactivation (thermal denaturation) above this temperature. In the temperature range studied (10–40°C), the co-existence was seen of a kinetic control accompanied by another control, involving diffusional transport of substrates and products, on the global activity of the immobilized enzyme. This makes the Arrhenius profiles curvilinear. Both graphic and statistical non-linear regression analysis of the kinetic data—rate, v, versus substrate concentration [S]—carried out under conditions in which the diffusional limitations can be considered negligible (high recirculation flow rate), permitted investigation of the intrinsic kinetic behaviour of immobilized LDH. In this sense, it can be deduced that the rate equation to which these data seem to be fitted is of the polynomial quotient type in [S] of minimum degree 2:2. Although the diffusional limitations have a marked effect on the type of global kinetics shown by immobilized LDH, temperature was not found to affect its v[S] behaviour. The experimental evidence obtained thus indicates that the rate equation in the 10-40°C temperature range continues to be a rational equation of at least degree 2:2 in [S].     

Depletion of cortical norepinephrine in rats by 6-hydroxydopamine does not impair performance of a delayed-nonmatching-to-sample task.

Rats were trained on a spatial delayed-nonmatching-to-sample (DNMTS) task, matched for performance, and randomly assigned to treatment with dorsal noradrenergic bundle injections of either 6-hydroxydopamine, to deplete cortical norepinephrine (NE), or vehicle, to control for the effects of surgery. After recovery, there were no significant differences between the groups when retrained on the DNMTS task at retention intervals (RIs) from 0.1 to 15.0 sec. Furthermore, no differences were observed when rats were trained at a 6.0-sec RI filled with distracting stimuli or when dummy information runs were added to increase proactive interference. These results demonstrate that depletion of cortical NE cannot account for the DNMTS performance deficits observed in rats recovered from pyrithiamine-induced thiamine deficiency (R. L. Knoth and R. G. Mair, 1991; J. K. Robinson and Mair, 1992). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple access for UWB impulse radio with pseudochaotic time hopping

Pseudochaotic time hopping (PCTH) is a previously proposed encoding/modulation scheme for ultra-wideband (UWB) impulse radio. PCTH exploits concepts from symbolic dynamics to generate aperiodic spreading sequences, resulting in a noise-like spectrum. We present a multiple-access technique suitable for the PCTH scheme. In particular, we provide an analytical expression of the bit-error rate performance as a function of the number of users and validate it by simulation.     

Phase effects in a semiconductor laser with diffraction extraction of radiation

Phase effects arising in a semiconductor laser with diffraction extraction of radiation and a distributed Bragg reflector on the substrate side are taken into account exactly quantitatively and the possibilities of using these effects in lasers is analyzed. It is shown that the phase effects studied can be used to increase the laser efficiency substantially. Pis’ma Zh. Tekh. Fiz. 23, 7–11 (September 26, 1997)     

Richard Lester Solomon (1918–1995): Obituary.

Memorializes Richard Solomon, one of the major learning theorists of the 2nd half of the 20th century. Solomon was named the 1st James M. Skinner University Professor of Science in 1975, was elected to the National Academy of Sciences, and was awarded, among other honors, the Warren Medal for research by the Society of Experimental Psychologists, the American Psychological Association Distinguished Scientific Contribution Award, and the American Psychological Foundation's Award for Distinguished Teaching in Experimental Psychology. He conducted research on a broad array of topics such as word frequency and perceptual defense, children's estimation of the size of tokens, hoarding behaviors in rats, and personality ratings and sociometric patterns. His work made a major contribution to the exploration of Pavlovian conditioning. Other topics of research focused on in Solomon's laboratories included avoidance learning, learned helplessness, punishment, and the opponent-process theory of acquired motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Management of nasopharyngeal and oropharyngeal stenosis in children

Nasopharyngeal stenosis and oropharyngeal stenosis are rare and challenging problems in the pediatric population. The most common etiology is currently the surgical trauma associated with adenotonsillectomy. Stenosis can vary from a thin band to a complete obstructing cicatrix. Presenting symptoms range from mild hyponasal speech to severe airway obstruction. We present a series of eight children with varying degrees of stenosis and associated symptoms. Choice of treatment varied with the severity of disease. In our series, successful interventions included triamcinolone acetonide injection, lysis of adhesions, rotational and advancement mucosal flaps, and jejunal free flap. Preoperative evaluation and individualized surgical repair are essential for successful treatment.