Binaural processing of noisy stimuli: internal/external noise ratios for diotic and dichotic stimuli

A set of ten digitized statistically similar Gaussian maskers was used in one-internal tone-in-noise detection experiments under diotic (NoSo) and dichotic (NoS pi) interaural conditions. Stimulus/response matrices were generated for each masker in the presence or absence of a target 500-Hz tone. For both NoSo and NoS pi, nonparametric analyses show that response probabilities and sensitivities vary significantly across noise waveforms, indicating a considerable external noise component in subject response variability. A parametric model is developed that maps individual stimulus waveforms onto a decision axis, facilitating evaluation of internal/external noise variance ratios. For both NoSo and NoS pi, internal and external noise variance are of similar magnitude.     

UV-laser ablation of ductile and brittle metal films

Single-shot laser damage of Ni and Cr films on fused silica substrates has been studied as a function of film thickness, utilizing 248 nm/14 ns pulses and detection by probe beam deflection. Threshold fluences for visible damage and vaporization are compared to predictions of the heat diffusion model. The model fits thresholds for visible damage well and identifies their origin, which is melting for Ni films and brittle-to-ductile phase transition for Cr films. When predicting thresholds for vaporization, the diffusion model is of limited success in case of Ni films but fails completely for Cr films, indicating that transient thermal properties of the material should be taken into account. Microscopic inspection shows that Cr films rupture at low fluences before entering the common sequence of melting and vaporizing with increasing fluence. 17 December 1996/Accepted: 17 December 1996     

Synthesis and properties of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]tetraphenylene

The X-ray crystal structure and photophysical properties of 1,6,7,12,13,18,19,24-octamethylacenaphthyleno[b,l]tetraphenylene, which has been synthesized via a Diels-Alder reaction of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene and 6,7-dihydro-6-hydroxy-7,9-dimethyl-8H-cyclopenta[a]acenaphthylene-8-one, are reported.     

Cascade reactions leading to the mechanism of action of vinaxanthone and xanthofulvin,natural products that drive nerve repair

The natural products vinaxanthone and xanthofulvin promote regeneration in animal models of spinal cord injury and corneal transplant. However, inhibition of the initially described biological target of these compounds, semaphorin 3A, does not fully account for the recovery demonstrated in vivo following administration of the natural products. Through chemical synthesis substantial quantities of both natural products have been accessed with early reaction development paving the way for synthesizing both compounds. The success of a model system, first disclosed herein, translated to the syntheses of both natural products. Following from this we also report for the first time the discovery of a new target of the natural products, the succinate receptor 1 (SUCNR1). Both natural products function as positive allosteric modulators of SUCNR1. As the first known allosteric modulators of SUCNR1, the compounds represent powerful new tools to understand the pharmacology of SUCNR1 and its control of growth and cellular defense.     

Untersuchungen on Thoriumoxid-Katalysatoren. II [8] Über den Einfluß Oberflächenchemischer Eigenschaften von ThO2− Katalysatoren auf die selektive Dehydratisierung von 2-Butanol

Studies on Thoria Catalysts. II. On the Influences of Surfacechemical Properties Tho₂-Catalysts on the Selective Dehydration of 2-Butanol Acid and basic properties as well as the interaction of 2-butanol with the surfaces of some ThO₂catalysts were studied. Sites of low acidity and basic sites of medium strength were found on the catalysts. After CO₂ adsorption we have shown by i.r. spectroscopy the formation of monodentate and bidentate carbonate as well as hydrocarbonate. There were indications of Lewis-type acid sites. Bands of alcoxide and carboxylate structure were observed in the i.r. spectra by interaction with 2-butanol and thoria. A mechanism is proposed for dehydration of 2-butanol.     

Stereoselective syntheses of dihydroxerulin and xerulinic acid, anti-hypocholesterolemic dyes from the fungus Xerula melanotricha

The title compounds 2 and 3, which are inhibitors of the biosynthesis of cholesterol, were synthesized in a convergent and perfectly stereoselective manner. In the key step, bromobutenolide 6 (obtained from levulinic acid in two steps) was coupled with either of the novel bis(stannanes) trans,cis,trans-35 or trans,trans,trans-35 [each accessible from 3-(tributylstannyl)allyl alcohol (17) in four steps], giving gamma-alkylidenebutenolide trans,trans,trans-32. This compound was coupled with iododiyne 42 or the bromoenediynoate 44 leading to dihydroxerulin (2) and to the (trimethylsilylethyl)ester 45 of xerulinic acid, respectively. Deprotection of the latter provided totally synthetic xerulinic acid (3) for the first time.