Similarities of error regularization, sigmoid gain scaling, targetsmoothing, and training with jitter

The generalization performance of feedforward layered perceptrons can, in many cases, be improved either by smoothing the target via convolution, regularizing the training error with a smoothing constraint, decreasing the gain (i.e., slope) of the sigmoid nonlinearities, or adding noise (i.e., jitter) to the input training data, In certain important cases, the results of these procedures yield highly similar results although at different costs. Training with jitter, for example, requires significantly more computation than sigmoid scaling.     

Global systems in the post-cold war information age : Chips, orbits, and new stimuli for cooperation

The US space program is held back by the high cost and inflexibility of access to space using current launch systems. But as a result of impressive advances in hypersonic aeronautics and advanced materials in recent years, there are excellent prospects for developing a fully reusable air-breathing single-stage-to-orbit launch vehicle during the next decade. The National Aerospace Plane (NASP) is a US technology development program that could lead to immense reductions in low-earth orbit launch costs and provide the operational flexibility of aircraft-like operations. Such a capability would cause a broad rethinking of the “market” for space launch, leading to introduction of new services and uses of space, particularly those taking advantage of the capabilities of small satellites.     

A deconvolution technique for improved estimation of rapid changesin ion concentration recorded with ion-selective microelectrodes

In biological preparations, measurements of rapid, stimulus-evoked changes in ion concentration by ion-selective microelectrodes can be distorted by the limited bandwidth of these sensors. Techniques were developed to reconstruct the actual change in ion concentration using deconvolution of the electrode's output signal and the electrode's transfer function. In the vertebrate retina, a knowledge of the actual time course of a light-evoked increase in extracellular K+ concentration was used to provide a rigorous test of a hypothesis regarding the electrical origin of a clinically important component of the electroretinogram.     

Synthesis and antitumor activity of 1-β-D-arabinofuranosylcytosine conjugates of optical isomers of ether and thioether lipids

Four 1-β-D-arabinofuranosylcytosine conjugates (ara-C) (1a, b and 2a, b) ofsn−1 andsn−3 isomers of 1-O-octadecyl-2-O-palmitoylglycerol and its 1-S-alkyl analogue have been synthesized, and their antitumor activity against L1210 lymphoid leukemia in mice were compared with those of the previous conjugates (3a, b) of racemates in order to determine the significance of chirality of the glycerol moieties for activity. Administration (i.p.) of a single dose (300 mg/kg) of conjugates ofsn−1 (1a),sn−3 (2a) andrac (3a) isomers of the ether lipid increased lifespan of i.p. implanted L1210 lymphoid leukemic DBA/2J mice by 169, 175 and 236%, respectively. Thesn−1 (1b),sn−3 (2b), andrac (3b) isomers of the thioether lipid with a single dose of 300 mg/kg produced an increase in lifespan values of 238, 263 and 250%, respectively. The results indicate that chirality of the glycerol moieties appears not to be critical for the activity, and racemates 3a and 3b are promising prodrugs of ara-C for further clinical investigations. This material was presented in part at the 81 st Annual Meeting of the American Association for Cancer Research in Washington, D.C., May, 1990 (Abstract No. 2493).     

Lysolecithin acyltransferase in hamster intestinal mucosa

1-Acyl-lysolecithin acyltransferase has been demonstrated in the microsomal fraction of hamster intestinal mucosa. The characteristics of the enzyme, with respect to substrate concentration, time of incubation and protein concentration, were studied. Ca⁺⁺ was found to severely inhibit enzymatic activity. More modest inhibitors were found to be Mg⁺⁺ and F⁻; EDTA and albumin had no effect. Enzyme activity was reduced when palmityl CoA was substituted for oleoyl CoA as substrate. The specific activity of intestinal microsomes was modestly greater than liver microsomes.