Effects of neuromuscular blocking agents on excitatory transmission and gamma-aminobutyric acidA-mediated inhibition in the rat hippocampal slice

BACKGROUND: Although neuromuscular blocking agents do not cross the blood-brain barrier, they may penetrate the central nervous system under particular circumstances and eventually cause neurotoxic consequences. METHODS: The effects of neuromuscular blocking agents on excitatory and inhibitory transmission in area CA1 of rat hippocampal slices were investigated using extracellular and intracellular recording techniques. RESULTS: Application of atracurium in the perfusion medium resulted in a dose-dependent enhancement of excitatory synaptic responses averaging 48.7 +/- 4.3% at a concentration of 10 nM. This effect was correlated with an increase in the size of the presynaptic fiber volley. Laudanosine, but not pancuronium bromide or vecuronium bromide, produced similar changes. In addition, atracurium and laudanosine blocked inhibitory transmission and reduced intracellularly recorded gamma-aminobutyric acidA receptor-mediated potentials. These effects were observed only at concentrations >1 microM and were not reproduced by pancuronium bromide and vecuronium bromide. CONCLUSIONS: Atracurium and its metabolite, laudanosine, contrary to pancuronium bromide and vecuronium bromide, produce two distinct effects on hippocampal slices. They enhance excitatory transmission and neuronal excitability and they block inhibitory gamma-aminobutyric acidA-mediated synaptic responses.     

The effect of defects on the fatigue crack initiation process in two p/m superalloys: part i. fatigue origins

Two high strength P/M nickel-base superalloys, AF-115 and AF2-1DA, with different defect populations, were tested to determine the effect of preexisting defects on the fatigue crack initiation process. Strain controlled continuous cycle fatigue tests were performed at room and at elevated temperature; these were followed by fractographic examination to characterize both the location and character of the fatigue origins. In most cases, particularly at elevated temperature, the initiation process was associated with a large pre-existing defect, either a pore or a nonmetallic inclusion. There was also a change in the location of the crack that caused failure as the strain range varied: at high strain ranges initiation occurred at or near the specimen’s surface, while at the lower strain ranges the failure originated in the specimen’s interior. The initiation mode for both alloys at room temperature was different than at elevated temperature. At room temperature, Stage I crystallographic cracking at or near the surface dominated the process in all strain range regimes. This difference was attributed, in part, to the differences in deformation mode for nickel-base superalloys at room and elevated temperature. Formerly with Metals and Ceramics Division, Air Force Materials Laboratory, Wright-Patterson AFB, OH.     

Computers and the 16th-century Chanson a pilot project at the University of Chicago

Conclusions One cardinal principle guided our evaluation of the data provided for us by the computer: never to be deluded into believing that the computer was in any way capable of analyzing a piece of music. Rather, we used the information made available by the computer as a means of substantiating or explaining the insights into a given composition that we gained by means of a direct confrontation with the music. In this way, the data supplied by the computer proved to be very useful in explaining why a particular portion of a chanson generates a sense of tension, while another section of the same piece creates a feeling of rest. Similarly, the electronically derived information was particularly helpful in setting up stylistic profiles of the various composers whose chansons were included in our sampling. In fact, the computer output was instrumental in helping to settle more than one problem of conflicting attributions, largely on the basis of these stylistic profiles. Like any other computerized process, our program elicited from the computer no analytical operation that could not have been done without the assistance of the computer. Very little precise measurement has been done in the analysis of the music of the Renaissance, however, and for good reason: the compilation of statistical data of the type we have described takes so much time that it can be considered feasible only with mechanical assistance. The ability we gained to apply to the chanson repertory a somewhat more precise system of analytical measurement was the most encouraging aspect of the pilot project. candidate for the Ph.D. in Physics     

Field and laboratory aging of polymeric distribution cableterminations. I. Field aging

This, two-part paper, describes the results of a research project aimed at understanding the magnitude of aging of polymeric cable terminations used in distribution. The termination types evaluated are currently used; hence, they have satisfied IEEE Standard 48. This standard does not address the issue of aging. Terminations made from 3 different polymer families and porcelain were evaluated. Presented in Part I, are the results of field aging from 5 outdoor sites in the USA over a 3 year period; and in Part II, results from accelerated aging fog chamber laboratory tests. The results from field aging show that only minor changes were produced. Some differences were observed in the electrical performance of formulations within the same polymer family, and among different polymer families. However, it was concluded that the performance of the terminations evaluated would not be compromised by aging produced changes in the weathershed housing     

Multiplication by integer constants

Methods are given for finding a sequence of ‘add’, ‘subtract’ and ‘shift’ instructions to multiply the contents of a register by an integer constant. Each method generalizes the previous one and requires only a few intermediate or scratch registers. A variation of the last method is used in the PL.8 compiler and uses an unnoticeable amount of the overall compile time. Some statistics roughly indicating the effectiveness of the methods are presented.     

Robust controller synthesis using the maximum entropy design equations

This note presents an application of the optimality conditions obtained in [1] for dynamic compensation in the presence of state-, control-, and measurement-dependent noise. By solving these equations, which represent a fundamental generalization of standard steady-state LQG theory, a series of increasingly robust control designs is obtained for the example considered in [2].     

Direct Adaptive Dynamic Compensation for Minimum Phase Systems With Unknown Relative Degree

We consider parameter-monotonic direct adaptive control for single-input-single-output minimum-phase linear time-invariant systems with knowledge of the sign of the high-frequency gain (first nonzero Markov parameter) and an upper bound on the magnitude of the high-frequency gain. The first part of the paper is devoted to fixed-gain analysis of single-parameter high-gain-stabilizing controllers. Two novel fixed-gain dynamic compensators are presented for stabilizing minimum-phase systems. One compensator stabilizes systems with arbitrary-but-known relative degree, while the other utilizes a Fibonacci series construction to stabilize systems with unknown-but-bounded relative degree. Next, we provide a general treatment of parameter-monotonic adaptive control, including a result that guarantees state convergence to zero. This result is then combined with the high-gain-stabilizing controllers to yield parameter-monotonic direct adaptive dynamic compensation for minimum-phase systems with either arbitrary-but-known or unknown-but-bounded relative degree     

Adaptive stabilization of a class of nonlinear systems withnonparametric uncertainty

We consider adaptive stabilization for a class of nonlinear second-order systems. Interpreting the system states as position and velocity, the system is assumed to have unknown, nonparametric position-dependent damping and stiffness coefficients. Lyapunov methods are used to prove global convergence of the adaptive controller. Furthermore, the controller is shown to be able to reject constant disturbances and to asymptotically track constant commands. For illustration, the controller is used to stabilize the van der Pol limit cycle, the Duffing oscillator with multiple equilibria, and several other examples