Molecular vibrations of complexes with trigonal ligands: Part IX. Zr(BH4)4

The molecular vibrations of Zr(BH₄)₄ are analysed on the basis of a T_d model. Symmetry coordinates are described and classified into those of ligand vibrations and central-part vibrations. A simple force field is deduced, which gives satisfactory agreement with experimental vibrational frequencies and mean amplitudes of vibration. A continuation of the work by considering the probably more realistic T model is suggested.     

Links between microscopic and macroscopic fluid mechanics

The microscopic and macroscopic versions of fluid mechanics differ qualitatively. Microscopic particles obey time-reversible ordinary differential equations. The resulting particle trajectories {q(t)} may be time-averaged or ensemble-averaged so as to generate field quantities corresponding to macroscopic variables. On the other hand, the macroscopic continuum fields described by fluid mechanics follow irreversible partial differential equations. Smooth particle methods bridge the gap separating these two views of fluids by solving the macroscopic field equations with particle dynamics that resemble molecular dynamics. Recently, nonlinear dynamics have provided some useful tools for understanding the relationship between the microscopic and macroscopic points of view. Chaos and fractals play key roles in this new understanding. Non-equilibrium phase-space averages look very different from their equilibrium counterparts. Away from equilibrium the smooth phase-space distributions are replaced by fractional-dimensional singular distributions that exhibit time irreversibility.     

Gaussian Property of the Rings R(X) and R〈X〉

The content of a polynomial f over a commutative ring R is the ideal c(f) of R generated by the coefficients of f. A commutative ring R is said to be Gaussian if c(fg) = c(f)c(g) for every polynomials f and g in R[X]. A number of authors have formulated necessary and sufficient conditions for R(X) (respectively, R?X?) to be semihereditary, have weak global dimension at most one, be arithmetical, or be Prüfer. An open question raised by Glaz is to formulate necessary and sufficient conditions that R(X) (respectively, R?X?) have the Gaussian property. We give a necessary and sufficient condition for the rings R(X) and R?X? in terms of the ring R in case the square of the nilradical of R is zero.     

Listening experience with iterated rippled noise alters the perception of 'pitch' strength of complex sounds in the chinchilla

Behavioral responses obtained from chinchillas trained to discriminate a cosine-phase harmonic tone complex from wideband noise indicate that the perception of 'pitch' strength in chinchillas is largely influenced by periodicity information in the stimulus envelope. The perception of 'pitch' strength was examined in chinchillas in a stimulus generalization paradigm after animals had been retrained to discriminate infinitely iterated rippled noise from wideband noise. Retrained chinchillas gave larger behavioral responses to test stimuli having strong fine structure periodicity, but weak envelope periodicity. That is, chinchillas learn to use the information in the fine structure and consequently, their perception of 'pitch' strength is altered. Behavioral responses to rippled noises having similar periodicity strengths, but large spectral differences were also tested. Responses to these rippled noises were similar, suggesting a temporal analysis can be used to account for the behavior. Animals were then retested using the cosine-phase harmonic tone complex as the expected signal stimulus. Generalization gradients returned to those obtained originally in the na?ve condition, suggesting that chinchillas do not remain "fine structure listeners," but rather revert back to being "envelope listeners" when the periodicity strength in the envelope of the expected stimulus is high.     

Apparent auditory source width insensitivity in older hearing-impaired individuals

Previous studies have shown a loss in the precision of horizontal localization responses of older hearing-impaired (HI) individuals, along with potentially poorer neural representations of sound-source location. These deficits could be the result or corollary of greater difficulties in discriminating spatial images, and the insensitivity to punctate sound sources. This hypothesis was tested in three headphone-presentation experiments varying interaural coherence (IC), the cue most associated with apparent auditory source width. First, thresholds for differences in IC were measured for a broad sampling of participants. Older HI participants were significantly worse at discriminating IC across reference values than younger normal-hearing participants. These results are consistent with senescent increases in temporal jitter. Performance decreased with age, a finding corroborated in a second discrimination experiment using a separate group of participants matched for hearing loss. This group also completed a third, visual experiment, with both a cross-mapping task where they drew the size of the sound they heard and the identification task where they chose the image that best corresponded to what they heard. The results from the visual tasks indicate that older HI individuals do not hear punctate images and are relatively insensitive to changes in width based on IC.     

Adsorption at the liquid-vapor surface of a binary liquid mixture

In a binary liquid mixture, the component possessing the lowest surface tension preferentially adsorbs at the liquid-vapor surface. In the past this adsorption behavior has been extensively investigated for critical binary liquid mixtures near the mixture's critical temperature T(c). In this fluctuation-dominated regime the adsorption is described by a universal function of the dimensionless depth zxi where xi is the bulk correlation length. Fewer studies have quantitatively examined adsorption for off-critical mixtures because, in this case, one must carefully account for both the bulk and surface crossover from the fluctuation-dominated regime (close to T(c)) to the mean-field dominated regime (far from T(c)). In this paper we compare extensive liquid-vapor ellipsometric adsorption measurements for the mixture aniline+cyclohexane at a variety of critical and noncritical compositions with the crossover theory of Kiselev and co-workers [J. Chem. Phys. 112, 3370 (2000)].     

Solubilization chromatography: Ethers,carboxylic acids,and hydrocarbons

Synthetic mixtures of aliphatic and aromatic ethers, satmated fatty acids, and substituted benzenes and naphthalenes were separated by elution through columns of ion-exchange resins with aqueous solutions of acetic acid as eluent An attempt was made to use a resin of low capacity for the separation of such mixtures, and the results of this attempt are used to help elucidate the theory of solubilization chromatography