4,155 research outputs found
Thermodynamically Stable One-Component Metallic Quasicrystals
Classical density-functional theory is employed to study finite-temperature
trends in the relative stabilities of one-component quasicrystals interacting
via effective metallic pair potentials derived from pseudopotential theory.
Comparing the free energies of several periodic crystals and rational
approximant models of quasicrystals over a range of pseudopotential parameters,
thermodynamically stable quasicrystals are predicted for parameters approaching
the limits of mechanical stability of the crystalline structures. The results
support and significantly extend conclusions of previous ground-state
lattice-sum studies.Comment: REVTeX, 13 pages + 2 figures, to appear, Europhys. Let
Econometric analysis of volatile art markets
A new heteroskedastic hedonic regression model is suggested which takes into account time-varying volatility and is applied to a blue chips art market. A nonparametric local likelihood estimator is proposed, and this is more precise than the often used dummy variables method. The empirical analysis reveals that errors are considerably non-Gaussian, and that a student distribution with time-varying scale and degrees of freedom does well in explaining deviations of prices from their expectation. The art price index is a smooth function of time and has a variability that is comparable to the volatility of stock indices.Volatility, art markets, hedonic regression, semiparametric estimation
A Curriculum of Activities and Materials Used in Teaching Decomposition and Flowcharting Skills in Grades 5-7
This curriculum project provides instructional activities and materials to be used in teaching decomposition and flowcharting skills to students in grades 5-7. It is indicated and supported by research that the use of a variety of activities geared toward problem solving are of great value to students who will make use of decomposition and flowcharting. This project is specifically designed for teachers in grades 5-7 who wish to prepare their students for programming activities on the microcomputer. The criteria for selection of activities and materials are included. This project includes activities categorized under one of the following headings: sequencing activities, selecting information activities, flowcharting activities, and working with computer activities. Finally, the materials and activities used in this project are listed by source so that teachers might find other references that could be helpful in teaching decomposition and flowcharting to students in grades 5-7
Generalized van der Waals theory of liquid-liquid phase transitions
In the framework of the thermodynamic perturbation theory for fluids we study
how the phase diagram of an isotropic repulsive soft-core attractive potential,
where a liquid-liquid phase transition exists in addition to the standard
gas-liquid phase transition, changes by varying the parameters of the
potential. We show that existence of the liquid-liquid transition is determined
by the interplay of the parameters of the potential and the structure of a
reference liquid.Comment: 5 pages, 6 figure
Electric Field Gradients at 57Fe in ZnFe2O4 and CdFe2O4
The nuclear quadrupole coupling constants and isomer shifts of 57Fe in the spinels ZnFe2O4 and CdFe2O4 were measured using the Mössbauer effect. The signs of the quadrupole coupling constants were determined from spectra which were taken in an applied magnetic field. The sign is negative in both spinels. The isomer shifts and FeâO distances indicate that Fe3+ in ZnFe2O4 is somewhat more covalently bonded than in CdFe2O4. The external field gradients at the Fe3+ positions can be interpreted in terms of the ionic pointâmultipole model modified by some charge transfer between oxygen and the cations. The point charge contribution to the field gradient is positive in case of ZnFe2O4 and nearly zero in case of CdFe2O4; the predominant contribution is due to the electric dipole moments of the oxygen ions and is negative. The dipole polarizability of the oxygen ion which gave the best fit is αD = 0.8âĂ
3αD=0.8Ă
3. The effect of charge transfer on the ionic field gradient is small.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70992/2/JCPSA6-55-11-5282-1.pd
Experimental evaluation of CO2 ejector cooling system for supermarkets at tropical zones
Cooling system for supermarkets, now-a-days in developing countries like India, mainly use man-made synthetic refrigerants/mixtures such as R134a, R404A and R410A (HFCs). These fluorinated refrigerants possess outrageous impact on the environment/ambient due of their high GWP and ODP. The EU F-gas regulation is formulated recently and came into force in 2014 in order to restrict the use of synthetic refrigerants for various HVAC applications. Under this regulation, it is also illegal to vent any such synthetic refrigerants to the atmosphere during the system servicing or end-of-life decommissioning. Sudden phase down of HFCs forced the present scenario to identify a potential replacement of these synthetic refrigerants. The influence of the same is comparatively high for developing countries. In the present study, the performance of a multi-ejector based supermarket cooling system is experimentally evaluated using natural refrigerant carbon dioxide (CO2). 33 kW cooling capacity of the system which is capable of maintaining three simultaneous different temperatures such as -29 °C for freezing, -6 °C for refrigeration and 7-11 °C for air-conditioning is examined at high ambient temperature context (up to 46 ÂșC gas cooler outlet temperature). The maximum COP of the supermarket cooling system appeared as 4.2. It is also observed that the maximum exergy efficiency of system is 0.316 obtained corresponding to 3.2 PIR of the system
The excess choice effect:The role of outcome valence and counterfactual thinking
Contrary to economic theory, psychological research has demonstrated increased choice can undermine satisfaction. When and why this 'excess choice effect' (ECE) occurs remains unclear. Building on theories of counterfactual thinking we argue the ECE is more likely to occur when people experience counterfactual thought or emotion and that a key trigger is a negative versus positive task outcome. Participants either selected a drink (Experiment 1) or chocolate (Experiment 2) from a limited (6) versus extensive (24) selection (Experiment 1) or were given no choice versus extensive (24) choice (Experiment 2). In both experiments, however, the choice was illusory: Half the participants tasted a 'good' flavour, half a 'bad' flavour. As predicted, extensive choice was only detrimental to satisfaction when participants tasted the 'bad' drink or chocolate, and this was mediated by the experience of counterfactual thought (Experiment 1) or emotion (Experiment 2). When outcomes were positive, participants were similarly satisfied with limited versus extensive and no choice versus extensive choice. Implications for our theoretical understanding of the ECE and for the construction of choice architectures aimed at promoting individual satisfaction and well-being are discussed.16 page(s
Phase Separation in Charge-Stabilized Colloidal Suspensions: Influence of Nonlinear Screening
The phase behavior of charge-stabilized colloidal suspensions is modeled by a
combination of response theory for electrostatic interparticle interactions and
variational theory for free energies. Integrating out degrees of freedom of the
microions (counterions, salt ions), the macroion-microion mixture is mapped
onto a one-component system governed by effective macroion interactions. Linear
response of microions to the electrostatic potential of the macroions results
in a screened-Coulomb (Yukawa) effective pair potential and a one-body volume
energy, while nonlinear response modifies the effective interactions [A. R.
Denton, \PR E {\bf 70}, 031404 (2004)]. The volume energy and effective pair
potential are taken as input to a variational free energy, based on
thermodynamic perturbation theory. For both linear and first-order nonlinear
effective interactions, a coexistence analysis applied to aqueous suspensions
of highly charged macroions and monovalent microions yields bulk separation of
macroion-rich and macroion-poor phases below a critical salt concentration, in
qualitative agreement with predictions of related linearized theories [R. van
Roij, M. Dijkstra, and J.-P. Hansen, \PR E {\bf 59}, 2010 (1999); P. B. Warren,
\JCP {\bf 112}, 4683 (2000)]. It is concluded that nonlinear screening can
modify phase behavior but does not necessarily suppress bulk phase separation
of deionized suspensions.Comment: 14 pages of text + 9 figure
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