Latency of auditory brain-stem responses and otoacoustic emissions using tone-burst stimuli

A comparison of the latency of auditory brain-stem responses (ABR) and evoked otoacoustic emissions (EOAE) has led to an interpretation for the travel of transients in the peripheral auditory system that is consistent with both sets of data. The "cochlear echo" theory for the origin of the EOAE indicates that the latency of a particular frequency component back to the ear canal should be twice the forward latency of its characteristic place in the cochlea. The latency of wave V of the ABR to tone-burst stimuli can be described as the sum of two components: (1) a component that varies with intensity and frequency in an orderly and predictable manner and (2) a component that is independent of both intensity and frequency. Because the EOAE data can be predicted by taking twice the value of component (1) of the ABR latency, this component is interpreted to be due to mechanical travel through the cochlea. A consequence of this interpretation is that the remaining neural component of the ABR latency must be relatively independent of frequency and intensity.     

Lithiation and electrophilic substitution of 8-chlorodibenz[b,f][1,4]-oxazepine-10-tert-butylcarbamate: The preparation of novel fused heterocyclic derivatives of 8-chlorodibenzoxazepine

Lithiation of 8-chlorodibenz[b,f][1,4]oxazepine-10-tert-butylcarbamate ( 1 ) is described. Electrophilic substitution of the resulting N-Boc dibenzoxazepine α- lithioamine 2 with ketones, aldehydes, nitriles, iso-cyanates and imines, followed by an in-situ cyclization, gave fused carbamates 5–26 , fused 2H-imidazol-2-ones 27–29 , fused hydantoins 30–32 , and fused ureas 33–35 , respectively, in 11–66% yield.     

The Zygmund Morse-Sard Theorem

The classical Morse-Sard Theorem says that the set of critical values off:R ^n+k →R ⁿ has Lebesgue measure zero iff ∈C ^k+1. We show theC ^k+1 smoothness requirement can be weakened toC ^k+Zygmund. This is corollary to the following theorem: For integersn >m >r > 0, lets = (n ?r)/(m ?r); iff:R ⁿ →R ^m belongs to the Lipschitz class Λ _s andE is a set of rankr forf, thenf(E) has measure zero.     

Preparation of a DSCG-like bisbenzofuran

The preparation of 6,6′-[(2-hydroxy-1,3-propanediyl)]bis(oxy)]bis(3-hydroxy)]-2-benzofurancarboxylic acid) diethyl ester trisodium salt trihydrate ( 6 ), a compound structurally related to disodium cromoglycate (DSCG), is described.     

A semi-micro synthesis of selenophene

A semi-micro preparation of selenophene is described which offers a convenient technique for the production of milligram quantities of the heterocycle. Selenophene is synthesized from bis-(trimethylsilyl)-1,3-butadiyne and sodium hydrogen selenide generated in situ from selenium and sodium borohydride in DMF-water. J. Chem. Soc., 14, 1115 (1977)     

Capillary electrochromatography of Triton X-100

Nonionic surfactants such as Triton X-100 (TX-100) are comprised of a mixture of oligomers with a varying degree of length in the ethoxylate chain. The development of chromatographic methods for resolution of the various oligomers of TX-100 is of environmental importance, and can be useful for quality control and characterization in industrial manufacture. Capillary electrochromatography (CEC) is fast becoming a capable separation technique that combines the benefits of both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). This report presents a novel CEC method for separation of the various TX-100 oligomers. A comparison of monomeric vs. polymeric stationary phases for separation of TX-100 was conducted. Since the oligomers of TX-100 were better resolved on a monomeric phase as compared to polymeric phase, a systematic mobile phase tuning was performed utilizing a monomeric CEC-C18-3 microm-100 A stationary phase. Various mobile phase parameters such as acetonitrile (ACN) content, Tris concentration, pH, voltage, and temperature were manipulated in order to achieve the optimum separation of oligomers in less than 30 min.     

Synthesis of benzofuro[3,2-b] quinolin-6(11H) one and derivatives

A new and efficient synthesis of benzof'uro[3,2-b]quinolin-6(11H) one ( 3 ) is reported, by treatment of 2- {[(phenoxy)acetyl]amino} benzoic acid ( 6a ) with polyphosphoric acid. An intermediate in the conversion of 3 to 6a , namely, 2-(3-benzofuranylamino)benzoic acid ( 7 ), was defined. An improved method for the synthesis of 6a is also described, which was used to prepare analogs ( 6b-n ) of 6a . In addition, an 11-alkoxy derivative ( 8 ) and 11-dialkylamino derivatives ( 10 and 11 ) of benzofuro [3,2-b]quinoline were prepared from 3 .     

Magnetic properties of the semiconducting lanthanide cuprates Ln2CuO4 and their interpretation: Evidence for a new series of planar copper antiferromagnets

The magnetic susceptibility of the semiconducting lanthanide cuprates Nd₂CuO₄, Pr₂CuO₄, Eu₂CuO₄, and Sm₂CuO₄ has been measured in the range 4–300 K. Below 300 K, the Cu²⁺ ions are ordered antiferromagnetically in the CuO₂ planes of these compounds, and the exchange interactions involving the Ln³⁺ ions are relatively weak. The suceptibility of the Ln³⁺ ions obeys the Curie-Weiss law at elevated temperatures, but deviations from this law occur at lower temperatures. An attempt is made to account for these deviations by fitting theoretical expressions for the susceptibility of isolated Ln³⁺ ions under the influence of a cubic crystal field to the experimental data. Excellent agreement is obtained for Nd³⁺ and Eu³⁺ over the entire temperature range and for Pr³⁺ and Sm³⁺ at elevated temperatures. Deviations at lower temperatures for the latter two ions may be due to structural changes, exchange interactions involving the Ln³⁺ ions, or possibly oxygen nonstoichiometry. The susceptibility parameters derived by fitting the theoretical expressions to the experimental data are also discussed. It is concluded that these compounds form an interesting new series of planar Cu²⁺-ion antiferromagnets.     

Capillary electrochromatography of methylated benzo[a]pyrene isomers. II. Effect of stationary phase tuning

For Part II of our ongoing study, we present a strategy for stationary phase optimization for the capillary electrochromatographic (CEC) separation of the 12 methylated benzo[a]pyrene (MBAP) isomers. Utilizing the optimum mobile phase conditions from Part I of our study as a guide, seven commercially available stationary phases have been evaluated for their ability to separate highly hydrophobic MBAP isomers. Ranging in design from high-performance liquid chromatography (HPLC) to CEC application, each phase was slurry packed in house and tested for CEC suitability and performance. Several stationary phase parameters were investigated for their effects on MBAP separation including bonding type (monomeric or polymeric, % carbon loading, surface coverage), pore size, particle size, and type of alkyl substituent. In this manner, the present state of commercially available packings has been assessed in our laboratory. Utilizing the optimum polymeric C18-5 microm-100 A-PAH stationary phase, the effects of CEC packed bed length and capillary inside diameter (I.D.) were also evaluated. A 50 microm I.D. capillary, 25 cm packed bed length and 75% (v/v) acetonitrile, 12.5 mM Tris, pH 8.0, 20 degrees C at 30 kV, provided resolution of 11 out of 12 MBAP isomers thus showing the effectiveness of CEC for analysis of structurally similar methylated polyaromatic hydrocarbons.