C-Nucleoside studies-15: Synthesis of 3-β-D-arabinofuranosylpyrazoles and the D-arabinofuranosyl analogue of formycin

A synthesis of 7-amino-3-(β -D-arabinofuranosyl)pyrazolo[4 3-d]pyrimidine (13), the D-arabino analogue of formycin (1), from D-mannose is described. 1-(2,4-Dinitrophenyl)-3-(penta-O-acetyl-D-manno-pentahydroxypentyl)pyrazole was converted into the 4-nitro-derivative 18 in 90% yield using trifluoroacetyl nitrate. In four steps 18 was transformed into the 3-β-D-arabinofuranosylpyrazole 12 which gave the N-nitro derivative 24 in two further stages. Cine-substitution of the N-nitro group in 24 by cyanide ion was followed by elaboration of the pyrimidine ring to give 13. All the reactions proceeded with complete regio and stereoselectivity.     

Children's detection of pure-tone signals with random multitone maskers.

Preschoolers and adults were asked to detect a 1000-Hz signal, which was masked by a multitone complex. The frequencies and amplitudes of the components in the complex varied randomly and independently on each presentation. A staircase, cued two-interval, forced-choice procedure disguised as a "listening game" was used to obtain signal thresholds in quiet and in the presence of the multitone maskers. The number of components in the masker was fixed within an experimental condition and varied from 2 to 906 across experimental conditions. Thresholds were also measured with a broadband noise masker. Eight preschool children and eight adults were tested. Although individual differences were large, among both adults and children, there was little difference between the groups in the mean amount of masking produced by the maskers with large numbers of components (400 and 906). There was also a small but significant difference between adults and children in the mean amount of masking produced by the broadband noise. The difference between the groups was much larger with smaller numbers of components. Data obtained from the adults were basically similar to that previously reported [cf. Neff and Green, Percept. Psychophys. 41, 409-415 (1987); Oh and Lutfi, J. Acoust. Soc. Am. 104, 3489-3499 (1998)]: maskers comprised of 10-40 components produced as much as 30 to 60 dB of masking in some, but not all listeners. Those same maskers produced larger amounts of masking (70-83 dB) in many of the preschool children, although, as in the adult group, individual differences were large. The component-relative-entropy (CoRE) model [Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)] was used to describe the differences in performance between the children and adults. According to this model the average child appears to integrate information over a larger number of auditory filters than the average adult.     

Sectionally Semicomplemented Distributive Nearlattices

A nearlattice S is a meet semilattice together with the property that any two elements possessing a common upper bound have a supremum. Here the authors have introduced the notion of sectionally semicomplemented distributive nearlattices and given several characterizations of them. The skeleton SCon(S) of Con(S), the congruence lattice, consists of all those nearlattice congruences which are the pseudocomplements of members of Con(S). The relationship between skeletal congruences and kernel of skeletal congruences leads to numerous characterizations of sectionally semicomplemented distributive nearlattices and semiboolean algebras. For example we prove, for a distributive nearlattice S with 0, the following conditions are equivalent:

The dominant role of low-frequency interaural time differences in sound localization.

Two experiments are described in which listeners judge the apparent directions of virtual sound sources-headphone-presented sounds that are processed in order to simulate free-field sounds. Previous results suggest that when the cues to sound direction are preserved by the simulation, the apparent directions of virtual sources are nearly the same as the apparent directions of real free-field sources. In the experiments reported here, the interaural phase relations in the processing algorithms are manipulated in order to produce stimuli in which the interaural time difference cues signal one direction and interaural intensity and pinna cues signal another direction. The apparent directions of these conflicting cue stimuli almost always follow the interaural time cue, as long as the wideband stimuli include low frequencies. With low frequencies removed from the stimuli, the dominance of interaural time difference disappears, and apparent direction is determined primarily by interaural intensity difference and pinna cues.     

Hydrogenolysis of enol triflates; A new method for the reduction of ketones to methylene compounds

Hydrogenolysis of enol trifluoromethanesulphonates (enol triflates) gives the hydrocarbon in high yield; ketones can thus be converted to the corresponding methylene compounds in a two-step process under mild conditions.     

The enantiospecific synthesis of (4S,5R)-and (4S,5S)-4,5-dihydroxydecanoic acid γ-lactones,proposed autoregulators from Streptomyces griseus

Both the (4S,5R)- and (4S,5S)-isomers of 4,5-dihydroxydecanoic acid γ-lactone, natural products and proposed autoregulators of Streptomyces Griseus, have been synthesised directly and in high yield from D-ribose via a common intermediate.     

A model of head-related transfer functions based on principal components analysis and minimum-phase reconstruction.

Free-field to eardrum transfer functions (HRTFs) were measured from both ears of 10 subjects with sound sources at 265 different positions. A principal components analysis of the resulting 5300 HRTF magnitude functions revealed that the HRTFs can be modeled as a linear combination of five basic spectral shapes (basis functions), and that this representation accounts for approximately 90% of the variance in the original HRTF magnitude functions. HRTF phase was modeled by assuming that HRTFs are minimum-phase functions and that interaural phase differences can be approximated by a simple time delay. Subjects' judgments of the apparent directions of headphone-presented sounds that had been synthesized from the modeled HRTFs were nearly identical to their judgments of sounds synthesized from measured HRTFs. With fewer than five basis functions used in the model, a less faithful reconstruction of the HRTF was produced, and the frequency of large localization errors increased dramatically.     

Linear and angular annelation effects on the 13C NMR spectra of tricyclic aromatic ketones. 1—annelated indanones

Carbon-13 NMR chemical shifts are reported for nine tricyclic aromatic ketones formally derived from indanone. The influences of remote ring size, as well as linear, angular exo and angular endo ketone orientation are examined. Results are compared with available ¹H NMR data. For indanone itself, based on selective ¹H decoupling experiments, a recently reported CIDNP derived ¹³C signal assignment is shown to be in error.