Stokes−Einstein−Debye failure in molecular orientational diffusion: exception or rule?

The Stokes–Einstein–Debye (SED) expression is used routinely to relate orientational molecular diffusivity quantitatively to viscosity. However, it is well-known that Einstein’s equations are derived from hydrodynamic theory for the diffusion of a Brownian particle in a homogeneous fluid and examples of SED breakdown and failure for molecular diffusion are not unusual. Here, using optical Kerr-effect spectroscopy to measure orientational diffusion for solutions of guanidine hydrochloride in water and mixtures of carbon disulfide with hexadecane, we show that these two contrasting systems each show pronounced exception to the SED relation and ask if it is reasonable to expect molecular diffusion to be a simple function of viscosity

Crystal templating through liquid–liquid phase separation

Controlled induction of crystal nucleation is a highly desirable but elusive goal. Attempts to speed up crystallization, such as high super saturation or working near a liquid–liquid critical point, always led to irregular and uncontrollable crystal growth. Here, we show that under highly nonequilibrium conditions of spinodal decomposition, water crystals grow as thin wires in a template-less formation of “Haareis”. This suggests that such nonequilibrium conditions may be employed more widely as mechanisms for crystal growth control

An investigation of ethnic and gender intercept bias in the SAT's prediction of college freshman academic performance

textIntercept bias in the SAT’s prediction of college freshman academic performance has long been found in studies evaluating the academic prediction of men and women, and various ethnic groups. Typically the college GPAs of women are underpredicted relative to men by approximately 2/10th of a standard deviation in GPA. In multicultural samples, relative to Whites, Asian American freshman performance is often underpredicted by a similar amount, and the performance of Blacks and Hispanics is overpredicted. The hypothesis of the study presented herein was that this differential prediction can be explained by a set of behavioral and attitudinal variables; i.e., that the inclusion of such variables into the prediction equation alongside SAT would result in the diminishment or elimination of observed differential prediction. It was also hypothesized that use of a GPA adjusted for differences in grading standards that exist across college disciplines and courses would contribute to the reduction of differential prediction. SAT scores, high school performance data, college grades and survey responses were obtained from a diverse sample of over nine hundred students at a large public university in the American Southwest. The data indicated that Asian American performance was not underpredicted by the SAT in this sample, although as anticipated, female performance was underpredicted and MexicanAmerican performance was overpredicted. Inadequate sample size precluded the analysis of African American students. In relation to the hypothesis, results were mixed. Although inclusion of the additional variables and the use of the adjusted GPA criterion did not significantly reduce Mexican-American overprediction, it reduced the underprediction of women’s performance to insignificance.Psycholog

Structural relaxation in the hydrogen-bonding liquids N-methylacetamide and water studied by optical Kerr-effect spectroscopy

Structural relaxation in the peptide model N-methylacetamide (NMA) is studied experimentally by ultrafast optical Kerr-effect spectroscopy over the normal-liquid temperature range and compared to the relaxation measured in water at room temperature. It is seen that in both hydrogen-bonding liquids, beta relaxation is present and in each case it is found that this can be described by the Cole-Cole function. For NMA in this temperature range, the alpha and beta relaxations are each found to have an Arrhenius temperature dependence with indistinguishable activation energies. It is known that the variations on the Debye function, including the Cole-Cole function, are unphysical, and we introduce two general modifications: one allows for the initial rise of the function, determined by the librational frequencies, and the second allows the function to be terminated in the alpha relaxation

Foraging in the Barbary dove: evolution, optimisation, and rules of thumb

Barbary Doves (Streptope/ia risoriet) were tested in two simple foraging experiments based on concurrent interval schedules of reinforcement, in both experiments food reinforcement was made available, independently on each option, for the first response to a schedule after some time had elapsed since reinforcement had last been delivered by that option. The two schedules were independent, and the mean interval between reinforcements on each was not always the same. For one experiment the response required was depressing one or other side of a floor panel, and the intervals between reinforcements were drawn from an exponential distribution, so that they were as variable as possible. In the other experiment the response requirement was a key peck; and intervals between reinforcements were either drawn from an exponential distribution; from a semi- variable arithmetic distribution; or from a completely regular set of fixed intervals.Results from these experiments are compared to the predictions of optimal foraging theory, assuming that the subjects are trying to maximize net energy intake. No agreement with prediction was here found for the floor panel experiment. For the key peck experiment it was found that visits to the better key were longer than to the key with the lower rate of payout, but that visits to the latter key were not instantaneous as had been predicted; nor was the interval between pecks uniform.Results from both experiments were also analysed in terms of the matching relation, though the utility of this procedure is here disputed.Data from the key peck experiment was tested to see if the Doves were using either of two 'rules of thumb' (behaviour generating rules) that have been proposed to account for behaviour on these schedules. No support at all was found for the notion that the proportion of reinforcements from the two options in the past was controlling the proportion of responses given to each option in the future (known as 'melioration'). Evidence for the theory of 'momentary maximising', predicting that each response would be placed on the option offering the highest momentary probability of reward, was hard to assess, because of the presence of a changeover delay in the key peck experiment. It seemed that, in general, responses were not placed so as to maximize momentary probability of reinforcement, but that a certain subset of responses, the first response to a new schedule, was well placed in this respect.These results are discussed in the context of a theory of the role of learning and behaviour in evolution known as 'Evolutionary Epistemology' which was not, however, directly tested

Dielectric relaxation of the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate: microwave and far-IR properties

Dielectric relaxation of the ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (EMI+ETS–), is studied using molecular dynamics (MD) simulations. The collective dynamics of polarization arising from cations and anions are examined. Characteristics of the rovibrational and translational components of polarization dynamics are analyzed to understand their respective roles in the microwave and terahertz regions of dielectric relaxation. The MD results are compared with the experimental low-frequency spectrum of EMI+ETS–, obtained via ultrafast optical Kerr effect (OKE) measurements

An SMP Soft Classification Algorithm for Remote Sensing

This work introduces a symmetric multiprocessing (SMP) version of the continuous iterative guided spectral class rejection (CIGSCR) algorithm, a semiautomated classification algorithm for remote sensing (multispectral) images. The algorithm uses soft data clusters to produce a soft classification containing inherently more information than a comparable hard classification at an increased computational cost. Previous work suggests that similar algorithms achieve good parallel scalability, motivating the parallel algorithm development work here. Experimental results of applying parallel CIGSCR to an image with approximately 10^8 pixels and six bands demonstrate superlinear speedup. A soft two class classification is generated in just over four minutes using 32 processors

Phonon-like hydrogen-bond modes in protic ionic liquids

Gigahertz- to terahertz-frequency infrared and Raman spectra contain a wealth of information concerning the structure, intermolecular forces, and dynamics of ionic liquids. However, these spectra generally have a large number of contributions ranging from slow diffusional modes to underdamped librations and intramolecular vibrational modes. This makes it difficult to isolate effects such as the role of Coulombic and hydrogen-bonding interactions. We have applied far-infrared and ultrafast optical Kerr effect spectroscopies on carefully selected ions with a greater or lesser degree of symmetry in order to isolate spectral signals of interest. This has allowed us to demonstrate the presence of longitudinal and transverse optical phonon modes and a great similarity of alkylammonium-based protic ionic liquids to liquid water. The data show that such phonon modes will be present in all ionic liquids, requiring a reinterpretation of their spectra