Heat transfer correlations for PCM-based heat sinks with plate fins

Characterization of melting process in a Phase Change Material (PCM)-based heat sink with plate fin type thermal conductivity enhancers (TCEs) is numerically studied in this paper. Detailed parametric investigations are performed to find the effect of aspect ratio of enclosure and the applied heat flux on the thermal performance of the heat sinks. Various non-dimensional numbers, such as Nusselt number (Nu), Rayleigh number (Ra), Stefan number (Ste) and Fourier number (Fo) based on a characteristic length scale, are identified as important parameters. The half fin thickness and the fin height are varied to obtain a wide range of aspect ratios of an enclosure. It is found that a single correlation of Nu with Ra is not applicable for all aspect ratios of enclosure with melt convection taken into account. To find appropriate length scales, enclosures with different aspect ratios are divided into three categories, viz. (a) shallow enclosure, (b) rectangular enclosure and (c) tall enclosure. Accordingly, an appropriate characteristic length scale is identified for each type of enclosure and correlation of Nu with Ra based on that characteristic length scale is developed. (C) 2010 Elsevier Ltd. All rights reserved.

Comparison of heat transfer correlations for cryogenic engine thrustchamber design

A comparative study of the correlations available in the literature is made to arrive at an appropriate pair for estimating the coolant-side and hot-gas-side heat transfer coefficients in the thrust chamber of a cryogenic engine. Based on this, the thermal analysis of a supercritical liquid hydrogen cooled engine is carried out. Results are presented for axial variation of heat transfer coefficients and temperature distributions for coolant and exposed wall. Tubular as well as milled channel configurations are considered for coolant flow.

Correlations between frequency of infra-red active vibrational modes and copper-oxygen distance in copper oxides. Application to superconductors

The infra-red spectra of a large number of ternary Cu(II) oxides with at least a quasi square-planar coordination of oxygen around the copper ions have been studied. The frequency of the bands with the highest frequency,v max, is found to correlate extremely well with the shortest Cu–O distance.v max increases at an impressive rate of sim20 cm–1 per 0.01 Å when the Cu–O distance becomes less than 1.97 Å, which is the Cu2+–O2– distance in square-planar CuO4 complexes as obtained from empirical ionic radii considerations. The marked sensitivity may be used as a ldquotitrationrdquo procedure not only to assign bands but also to obtain diagnostic information about local coordination in compounds derived, for example, from the YBa2Cu3O7–d structure such as LaCaBaCu3O7–d . The only example where this correlation fails is in the two-layer non-superconducting oxides derived from La2(Ca, Sr)Cu2O6. The significance of this result is discussed. The marked dependence of frequency on the bond-distance is qualitatively examined in terms of an increased electron-phonon coupling to account for the observed tendency of the superconducting transition temperature to go through a maximum as the average basal plane Cu–O distance is decreased.

Photochromism of alkylisophthalaldehydes in the solid state: structure–reactivity correlations

The crystal and molecular structures of the photochromic compounds 2,5-dimethylisophthalaldehyde (I) and 5-isopropyl-2-methylisophthalaldehyde (II) have been determined by single crystal X-ray analyses. The intramolecular gamma-hydrogen abstraction process involved in the photoenolisation of I and II in the solid state has been rationalised in the light of relevant geometrical parameters.

Evaluation of Erosion Resistance of Metallic Materials and the Role of Material Properties in Correlations

A study of the correlations between material properties and normalized erosion resistance (inverse of erosion rates) of various materials tested in the rotating disk and the flow venturi at various intensities indicates that different individual properties influence different stages of erosion. At high and low intensities of erosion, energy properties predominate the phenomenon, whereas at intermediate intensities strength and acoustic properties become more significant. However, both strength and energy properties are significant in the correlations for the entire spectrum of erosion when extensive cavitation and liquid impingement data from several laboratories involving different intensities and hydrodynamic conditions are considered. The use of true material properties improved the statistical parameters by 3 to 37%, depending on the intensity of erosion. It is possible to evaluate qualitatively the erosion resistances of materials based on the true stress-true strain curves.

Intraspecific variation in brain size and architecture : population divergence and phenotypic plasticity

Brain size and architecture exhibit great evolutionary and ontogenetic variation. Yet, studies on population variation (within a single species) in brain size and architecture, or in brain plasticity induced by ecologically relevant biotic factors have been largely overlooked. Here, I address the following questions: (i) do locally adapted populations differ in brain size and architecture, (ii) can the biotic environment induce brain plasticity, and (iii) do locally adapted populations differ in levels of brain plasticity? In the first two chapters I report large variation in both absolute and relative brain size, as well as in the relative sizes of brain parts, among divergent nine-spined stickleback (Pungitius pungitius) populations. Some traits show habitat-dependent divergence, implying natural selection being responsible for the observed patterns. Namely, marine sticklebacks have relatively larger bulbi olfactorii (chemosensory centre) and telencephala (involved in learning) than pond sticklebacks. Further, I demonstrate the importance of common garden studies in drawing firm evolutionary conclusions. In the following three chapters I show how the social environment and perceived predation risk shapes brain development. In common frog (Rana temporaria) tadpoles, I demonstrate that under the highest per capita predation risk, tadpoles develop smaller brains than in less risky situations, while high tadpole density results in enlarged tectum opticum (visual brain centre). Visual contact with conspecifics induces enlarged tecta optica in nine-spined sticklebacks, whereas when only olfactory cues from conspecifics are available, bulbus olfactorius become enlarged.Perceived predation risk results in smaller hypothalami (complex function) in sticklebacks. Further, group-living has a negative effect on relative brain size in the competition-adapted pond sticklebacks, but not in the predation-adapted marine sticklebacks. Perceived predation risk induces enlargement of bulbus olfactorius in pond sticklebacks, but not in marine sticklebacks who have larger bulbi olfactorii than pond fish regardless of predation. In sum, my studies demonstrate how applying a microevolutionary approach can help us to understand the enormous variation observed in the brains of wild animals a point-of-view which I high-light in the closing review chapter of my thesis.

A Molecular Dynamics Study of Atomic Correlations in Glassy BzS3t

Glassy B&, the parent compound of the superionic conductor LiI-Li&B& has been studied by the molecular dynamics technique using a new potential model. The results suggest that the glass is made up of local units of four-membered B2S2 rings bridged by sulfur atoms, leading to a chainlike structure. Various pair correlation functions have been analyzed, and the B2Sz rings have been found to be planar. The calculated neutron structure factor shows a peak at 1.4 A-' which has been attributed to B-B correlations at 5.6 A. The glass transition temperature of the simulated system has been calculated to be around 800 K.

Correlations, quantum entanglement and interference in nanoscopic systems

Several of the most interesting quantum effects can or could be observed in nanoscopic systems. For example, the effect of strong correlations between electrons and of quantum interference can be measured in transport experiments through quantum dots, wires, individual molecules and rings formed by large molecules or arrays of quantum dots. In addition, quantum coherence and entanglement can be clearly observed in quantum corrals. In this paper we present calculations of transport properties through Aharonov-Bohm strongly correlated rings where the characteristic phenomenon of charge-spin separation is clearly observed. Additionally quantum interference effects show up in transport through pi-conjugated annulene molecules producing important effects on the conductance for different source-drain configurations, leading to the possibility of an interesting switching effect. Finally, elliptic quantum corrals offer an ideal system to study quantum entanglement due to their focalizing properties. Because of an enhanced interaction between impurities localized at the foci, these systems also show interesting quantum dynamical behaviour and offer a challenging scenario for quantum information experiments.

A Study of Long-range Correlations in Schizophrenia EEG using Detrended Fluctuation Analysis

In this paper, we have studied electroencephalogram (EEG) activity of schizophrenia patients, in resting eyes closed condition, with detrended fluctuation analysis (DFA). The DFA gives information about scaling and long-range correlations in time series. We computed DFA exponents from 30 scalp locations of 18 male neuroleptic-naIve, recent-onset schizophrenia (NRS) subjects and 15 healthy male control subjects. Our results have shown two scaling regions in all the scalp locations in all the subjects, with different slopes, corresponding to two scaling exponents. No significant differences between the groups were found with first scaling exponent (short-range). However, the second scaling exponent (long-range) were significantly lower in control subjects at all scalp locations (p<0.05, Kruskal-Wallis test). These findings suggest that the long-range scaling behavior of EEG is sensitive to schizophrenia, and this may provide an additional insight into the brain dysfunction in schizophrenia.

Photobehavior of crystalline 4-styrylcoumarin dimorphs: structure-reactivity correlations

4-Styrylcoumarin crystallizes from chloroform and hexane mixture in two morphologically different modifications. The monoclinic form (needles, P2(1)/c) undergoes stereospecific photodimerization producing anti head-to-tail dimer across pyrone double bond, whereas the triclinic modification (prisms, P ($) over bar 1) dimerizes yielding photodimer of the same configuration, but across styrenic double bond. Single crystal X-ray analyses of the dimorphs reveal the packing differences permitting rationalization of the regio- and stereochemistry of the photoproducts. The significantly low dimer yield from the prismatic crystals is rationalized.

Studies in crystal engineering: structure�reactivity correlations of substituted styrylcoumarins and related systems

The solid state photochemical behaviour of 7-hydroxy-4-styrylcoumarin 1 and several of its derivatives and analogues has been investigated. All the compounds with the exception of 7-methoxy-4-styrylcoumarin 2 are photolabile and yield anti-HT dimers. It has been observed that chloro substitution in the systems studied does not lead to the expected beta-packing mode. The photobehaviour of 1 and 2 has been correlated with their crystal structures. Reasons for alpha-packing have been examined. The systematics in the arrangement of the carbonyl group and phenyl group of the close neighbours in the crystals of 1, 2 and a few other cases are presented.

Novel correlations in two dimensions: Some exact solutions

We construct a new many-body Hamiltonian with two- and three-body interactions in two space dimensions and obtain its exact many-body ground state for an arbitrary number of particles. This ground state has a novel pairwise correlation. A class of exact solutions for the excited states is also found. These excited states display an energy spectrum similar to the Calogero-Sutherland model in one dimension. The model reduces to an analog of the well-known trigonometric Sutherland model when projected on to a circular ring.

Saturated liquid viscosity correlations for alternative refrigerants

This article presents dimensionless equations for the temperature dependence of the saturated liquid viscosity of R32, R123, R124, R125, R134a, R141b, and R152a valid over a temperature range of engineering interest. The correlation has the form Phi(D)(n)=A+BTD where Phi(D) is the dimensionless fluidity (1/eta(D)) and T-D is a dimensionless temperature. n, A, and B are evaluated for each of the above refrigerants based on a least-squares fit to experimental data. This equation is found to provide an improved fit over those existing in the literature up to T-D=0.8.