Stabilized Spin-Polarized Jellium Model and Odd-Even Alternations in Jellium Metal Clusters

In this paper, we have considered the mechanical stability of a jellium system in the presence of spin degrees of freedom and have generalized the stabilized jellium model, introduced by J. P. Perdew, H. Q. Tran, and E. D. Smith [Phys. Rev. B42, 11627 (1990)], to a spin-polarized case. By applying this generalization to metal clusters (Al, Ga, Li, Na, K, Cs), we gain additional insights about the odd-even alternations, seen in their ionization potentials. In this generalization, in addition to the electronic degrees of freedom, we allow the positive jellium background to expand as the clusters' polarization increases. In fact, our self-consistent calculations of the energetics of alkali metal clusters with spherical geometries, in the context of density functional theory and local spin density approximation, show that the energy of a cluster is minimized for a configuration with maximum spin compensation (MSC). That is, for clusters with even number of electrons, the energy minimization gives rise to complete compensation ($N_\uparrow=N_\downarrow$), and for clusters with odd number of electrons, only one electron remains uncompensated ($N_\uparrow-N_\downarrow=1$). It is this MSC-rule which gives rise to alternations in the ionization potentials. Aside from very few exceptions, the MSC-rule is also at work for other metal culsters (Al, Ga) of various sizes.Comment: 18 pages, Rev_Tex, 14 figures in PostScript, Extended and improved version of our recent article with the same titl

Surface Polaron Formation in the Holstein model

The effect of a solid-vacuum interface on the properties of a strongly coupled electron-phonon system is analyzed using dynamical mean-field theory to solve the Holstein model in a semi-infinite cubic lattice. Polaron formation is found to occur more easily (i.e., for a weaker electron-phonon coupling) on the surface than in the bulk. On the other hand, the metal-insulator transition associated to the binding of polarons takes place at a unique critical strength in the bulk and at the surface.Comment: 5 pages, 3 figure

Growth performance of rainbow trout (Oncorhynchus mykiss) with respect to nutritional factors in north Iran (Haraz River)

Monthly samples of six fish farms from January 2010 to December 2010 in the northern Iran, Haraz River, were used to determine relationship between chemical parameters of main water, inlet and outlet and their effects on fish growth and production. Results revealed that concentration of nutrients in outlet was more than that of inlet of farms, and statistical analysis showed that there were significant differences between stations (p0.05) in different months. Correlation between daily growth, SGR, FCR, production and chemical parameters of water were analyzed by Pearson correlation. The results revealed negative correlation (α= 0.01) between nitrite and daily growth (P=0.004, Pearson correlation=-0.24), ammonium and SGR (P=0.0001, Pearson correlation=-0.272), although there were no correlation for FCR, and nutritional parameters (p>0.05)

Enhancing energy transfer in quantum systems via periodic driving: Floquet master equations

We provide a comprehensive study of the energy transfer phenomenon -- populating a given energy level -- in 3- and 4-level quantum systems coupled to two thermal baths. In particular, we examine the effects of an external periodic driving and the coherence induced by the baths on the efficiency of the energy transfer. We consider the Floquet-Lindblad and the Floquet-Redfield scenarios, which both are in the Born-Markov, weak-coupling regime but differ in the treatment of the secular approximation, and for the latter, we develop an appropriate Floquet-type master equation by employing a partial secular approximation. Throughout the whole analysis we keep Lamb-shift corrections in the master equations. We observe that, especially in the Floquet-Redfield scenario, the driving field can enhance the energy transfer efficiency compared to the nondriven scenario. In addition, unlike degenerate systems where Lamb-shift corrections do not contribute significantly on the energy transfer, in the Redfield and the Floquet-Redfield scenarios these corrections have nonnegligible effects

Effect of Argon CarriEffect of Argon Carrier Gas Flux on TiO2 Nanostructures

TiO2 nanowires (NWs) have been fabricated by thermal evaporation method, using the vapor–liquid–solid (VLS) growth method and Au thin layer as a catalyst which were coated on titanium/quartz substrate. Optical and microstructure properties of TiO2 NWs have been reviewed under different argon carrier gas flows. The gas flow was varied from 60 to 170 sccm. The X-ray diffraction patterns showed that TiO2 NWs formed in rutile phase and their preferred orientation was in (110). The field emission scanning electron microscope figures indicated that with increasing gas flow, nanowires became thinner and longer. The absorbance curve of TiO2 nanowires has been drawn by using spectrophotometer and their band gap was measured. Our results showed that the band gap has been enhanced in comparison with bulk one due to the quantum confinement. Also, the band gap enhanced from 3.35 to 3.45 eV by increasing the argon flow, since the wires became thinner and longer. The Williamson–Hall mechanism was applied as the vital tools for characterization of crystallite size and microstrain. Also, microstructure properties have been studied by X-ray diffraction analysis such as; dislocation density and texture coefficient. The crystallinity of TiO2 NWs has been made better by enhancing Ar flow due to increasing of VLS growth method

Essays in public and urban economics

The first chapter provides evidence on the incidence and distortionary effects of taxes on rental properties, using a unique administrative dataset on housing transactions in Tehran. I exploit a special feature of the tax code in the Tehran rental market where the tax-exemption threshold is based on the property’s size (square meters). Large bunching occurs below the tax cutoff, suggesting strong behavioral responses to the kink. I also find higher after-tax rents above the kink. Based on these variations, I develop a structural framework with property taxes and costs of filing to estimate the price elasticities of housing size supply and demand simultaneously. I also examine the question of who bears the property tax burden. I estimate a mid-run (10-year) price elasticity of housing size supply of 1.36, and a price elasticity of housing size demand of -0.17. I find high, but incomplete pass through of the rental tax - implying that most filing costs are borne by renters. The second chapter provides new evidence on causal impact of air pollution on the housing market. In a co-authored paper, we utilize the dramatic increase in the level of air pollution in Tehran, induced by unprecedented international sanction regimes imposed on Iran because of their nuclear program in 2010. Following some of the sanctions that targeted Iran’s import of gasoline, Iran began rapidly to increase its fuel production capacity by converting petrochemical plants to gasoline production refineries. The policy caused substantial increase in the level of air pollution as a result of the domestically produced low-quality gasoline. Using this natural experiment and unique administrative data on Tehran’s housing market, we find that a 30 parts-per-billion increase of outdoor concentration of Nitrogen Dioxide leads to approximately a 3 to 6 percent decrease in housing prices. We also find that higher price-rent ratio is associated with lower level of air pollution. Our welfare analysis suggests that air quality deteriorations induced by the 2010 gasoline sanctions are associated with $11 to$16 billion aggregate reduction in housing values in 2011

Classifying Quadratic Quantum P^2s by using Graded Skew Clifford Algebras

We prove that quadratic regular algebras of global dimension three on degree-one generators are related to graded skew Clifford algebras. In particular, we prove that almost all such algebras may be constructed as a twist of either a regular graded skew Clifford algebra or of an Ore extension of a regular graded skew Clifford algebra of global dimension two. In so doing, we classify all quadratic regular algebras of global dimension three that have point scheme either a nodal cubic curve or a cuspidal cubic curve in P^2