Competitive partitioning of rotational energy in gas ensemble equilibration

A wide-ranging computational study of equilibration in binary mixtures of diatomic gases reveals the existence of competition between the constituent species for the orbital angular momentum and energy available on collision with the bath gas. The ensembles consist of a bath gas AB(v;j), and a highly excited minor component CD(v';j'), present in the ratio AB:CD = 10:1. Each ensemble contains 8000 molecules. Rotational temperatures (T(r)) are found to differ widely at equilibration with T(r)(AB)/T(r)(CD) varying from 2.74 to 0.92, indicating unequal partitioning of rotational energy and angular momentum between the two species. Unusually, low values of T(r) are found generally to be associated with diatomics of low reduced mass. To test effects of the equi-partition theorem on low T(r) we undertook calculations on HF(6;4) in N(2)(0;10) over the range 100-2000 K. No significant change in T(r)(N2)/T(r)(HF) was found. Two potential sources of rotational inequality are examined in detail. The first is possible asymmetry of -Δj and +Δj probabilities for molecules in mid- to high j states resulting from the quadratic dependence of rotational energy on j. The second is the efficiency of conversion of orbital angular momentum, generated on collision with bath gas molecules, into molecular rotation. Comparison of these two possible effects with computed T(r)(AB)/T(r)(CD) shows the efficiency factor to be an excellent predictor of partitioning between the two species. Our finding that T(r) values for molecules such as HF and OH are considerably lower than other modal temperatures suggests that the determination of gas ensemble temperatures from Boltzmann fits to rotational distributions of diatomics of low reduced mass may require a degree of caution

Crystal structure of the yellow 1:2 molecular complex lumiflavin–bisnaphthalene-2,3-diol

In the first molecular complex of the physiologically active neutral form of isoalloxazine studied, lumiflavin–bisnaphthalene-2,3-diol, each flavin is sandwiched between two naphthalenediol molecules with extensive overlap but a moderately large (3·44 Å) spacing, indicating at most weak charge-transfer interaction and in agreement with the yellow colour of the complex, nearly the same as that of the parent lumiflavin

The discrimination of facial sex in developmental prosopagnosia

Developmental prosopagnosia (DP) is a neurodevelopmental condition characterised by difficulties recognising and discriminating faces. It is currently unclear whether the perceptual impairments seen in DP are restricted to identity information, or also affect the perception of other facial characteristics. To address this question, we compared the performance of 17 DPs and matched controls on two sensitive sex categorisation tasks. First, in a morph categorisation task, participants made binary decisions about faces drawn from a morph continuum that blended incrementally an average male face and an average female face. We found that judgement precision was significantly lower in the DPs than in the typical controls. Second, we used a sex discrimination task, where female or male facial identities were blended with an androgynous average face. We manipulated the relative weighting of each facial identity and the androgynous average to create four levels of signal strength. We found that DPs were significantly less sensitive than controls at each level of difficulty. Together, these results suggest that the visual processing difficulties in DP extend beyond the extraction of facial identity and affects the extraction of other facial characteristics. Deficits of facial sex categorisation accord with an apperceptive characterisation of DP

Seasonality in the Surface Energy Balance of Tundra in the Lower Mackenzie River Basin

This study details seasonal characteristics in the annual surface energy balance of upland and lowland tundra during the 1998–99 water year (Y2). It contrasts the results with the 1997–98 water year (Y1) and relates the findings to the climatic normals for the lower Mackenzie River basin region. Both years were much warmer than the long-term average, with Y1 being both warmer and wetter than Y2. Six seasons are defined as early winter, midwinter, late winter, spring, summer, and fall. The most rapid changes in the surface energy balance occur in spring, fall, and late winter. Of these, spring is the most dynamic, and there is distinct asymmetry between rates of change in spring and those in fall. Rates of change of potential insolation (extraterrestrial solar radiation) in late winter, spring, and fall are within 10% of one another, being highest in late winter and smallest in spring. Rates of change in air temperature and ground temperature are twice as large in spring as in fall and late winter, when they are about the same. Rates of change in components of the energy balance in spring are twice and 4 times as large as in fall and late winter, respectively. The timing of snowpack ripening and snowmelt is the major agent determining the magnitude of asymmetry between fall and spring. This timing is a result of interaction between the solar cycle, air temperature, and snowpack longevity. Based on evidence from this study, potential surface responses to a 18C increase in air temperature are small to moderate in most seasons, but are large in spring when increases range from 7% to 10% of average surface energy fluxes

Numerical study assessing various ammonia/methane reaction models for use under gas turbine conditions

Ammonia as an alternative fuel and hydrogen carrier has received increased attention in recent years. To explore the potential of co-firing ammonia with methane for power generation, studies involving robust mathematical analyses is required to progress towards industrial implementation. To explore the chemical kinetic mechanisms best suited to ammonia/methane combustion in gas turbines, five different detailed mechanisms are compared to assess their efficacy in representing the reaction kinetics under practical gas turbine combustor operating conditions. Ignition delay time is compared with recently published predictions showing that the mechanisms of Tian and Teresa exhibit the best accuracy over a large range of conditions. A one-dimensional simulation was also conducted using a Chemical Reactor Network (CRN) model, thus providing a relatively quick estimation of the combustion mechanisms under swirling combustion conditions. The simulation of NOx emissions indicate that the Tian mechanism performs better than the others considered. Hence, the Tian mechanism was selected as the most appropriate for further studies of ammonia/methane combustion through a set of experiments carried out at various equivalence ratios and pressure conditions. Finally, sensitivity and pathway analyses were also performed to identify important reactions and species under high-pressure conditions, areas that need more attention for model development and emission control in future studies

Interatomic distances and atomic valences in NaZn_(13)

The crystal structure of NaZn_(13) and of several homologous compounds AB_(13) was reported by Ketelaar and by Zintl & Hauke to be based on space group O_h^6-Fm3c, with 8 :Na in 8(a): ¼, ¼:, ¼; ... ; 8 Zn_I in 8(b): 0, 0, 0; .... ; and 96 Zn_(II) in 96(i): 0, y, z; ... . Approximate values were reported for the parameters a_0, y, and z; for NaZn_(13) Zintl & Hauke reported 12.27 Å, 0.178, and 0.122 for these three parameters. Each Zn_I is surrounded by twelve Zn_(II) at the vertices of a nearly regular icosahedron, and each Na by twenty-four Zn_(II) at the vertices of a snub cube. Our interest in the structure was largely concerned with the valences of the two different kinds of Zn atoms, it being presumptive that Zn_I has a larger valence than Zn_(II) because its icosahedral coordination requires it to be smaller than Zn_(II). Lines on new powder photographs of NaZn_(13) were measured and the intensities were estimated visually with as much precision as possible. Least-squares treatments were employed in order to obtain the best possible values for the three parameters; the values obtained are a_0 = 12.2836 ± 0.0003Å, y = 0.1806 ± 0.0003, and z = 0.1192 ± 0.0003. The uncertainties given are calculated standard deviations. Analysis of the interatomic distances yields a selfconsistent interpretation in which Zn_I is assumed to be quinquevalent and Zn_(II) quadrivalent, while Na may have a valence of unity or one as high as 1¼, the excess over unity being suggested by the interatomic distances and being, if real, presumably a consequence of electron transfer. A valence electron number of approximately 432 per unit cell is obtained, which is in good agreement with the value 428.48 predicted on the basis of a filled Brillouin polyhedron defined by the forms {444}, {640}, and {800}

Mutli-objective optimisation of GENIE Earth system models

Overview:•GENIE Project•Multi-objective Optimisation•Surrogate Modelling•Grid Computing Infrastructure•Parameter Estimation for a new Ocean Mixing Scheme•Conclusion