Predictive reverse osmosis (RO) models have been well-developed for many systems. However, the applications to dilute organic−water systems require the modification of transport models and the understanding of solute−polymer interactions. Studies with various substituted, nonionized phenolic compounds showed that these could cause substantial membrane water flux drop, even in dilute solutions with negligible osmotic pressure. Further, the organics could significantly adsorb on the cross-linked aromatic polyamide active layer. In some cases, even concentrations as low as 0.2 mM, 2,4-dinitrophenol (solution in particle-free, double-distilled water) can cause as much as a 70% flux drop with an aromatic polyamide membrane. Two models are presented in this paper:  a modified steady-state solution diffusion model and an unsteady-state diffusion adsorption model which are able to predict flux and permeate concentrations from a single RO experiment. Further, the development of these models allows for the understanding of the mechanisms of organic−membrane interactions. For instance, it has been proposed that increased adsorption inherently leads to an increase in flux drop. However, we have found, on one hand, that due to specific interactions with membrane water transport groups, chloro- and nitro-substituted phenols cause significant flux drops. On the other hand, benzene had a high physical adsorption but caused negligible flux drop. The results were further extended to nanofiltration experiments with an aromatic pollutant containing two types of charge groups. The adsorption and separation results are explained according to an ionization model.

Though not very often, in literature there are cases where discrepancies exist in temperature dependence of elastic constants of materials. A particular example of this case is the behavior of C 12 coefficient of a simple metal, aluminum. Here, we attempt to provide insight into various contributions to temperature-dependence in elastic properties by investigating the thermo-elastic properties of fcc aluminum as a function of temperature through the use of two computational techniques and experiments. First, ab initio calculations based on density functional theory (DFT) are used in combination with quasi-harmonic theory to calculate the elastic constants at finite temperatures through a strain-free energy approach. Molecular dynamics (MD) calculations using tight-binding potentials are then used to extract the elastic constants through a fluctuation-based formalism. Through this dynamic approach, the different contributions (Born, kinetic and stress fluctuations) to the elastic constants are isolated and the underlying physical basis for the observed thermally-induced softening is elucidated. The two approaches are then used to shed light on the relatively large discrepancies in the reported temperature dependence of the elastic constants of fcc aluminum. Finally, the polycrystalline elastic constants (and their temperature dependence) of fcc aluminum are determined using Resonant Ultrasound Spectroscopy (RUS) and compared to previously published data as well as the atomistic calculations performed in this work.

Recent experiments indicate that films of V1−xCrxO2 may be obtained which retain the tetragonal rutile phase to low temperature. In order to better understand this system we have calculated its electronic structure using density functional theory in the generalized gradient approximation and density functional theory with empirical on-site Coulomb correlations (LDA+U). Within these approximations we find that the ground state of rutile phase V1−xCrxO2 is quite simple. Both V and Cr are in the +4 state, implying that the V and Cr ions have moments of 1μB and 2μB, respectively. Similar to CrO2, V1−xCrxO2 is predicted to be ferromagnetic and half-metallic. Our results appear to be consistent with the experimental observations that VO2 is paramagnetic and metallic for temperatures above 340 K where it is stable. It is not clear, however, that these results are completely consistent with recent experimental observations of ferromagnetism at low temperature in V1−xCrxO2 for x=0.1 and x=0.2.

We present first-principles based density functional theory calculations of the electronic and magnetic structure of CrO 2 with 3d (Ti through Cu) and 4d (Zr through Ag) substitutional impurities. We find that the half-metallicity of CrO 2 remains intact for all of the calculated substitutions. We also observe two periodic trends as a function of the number of valence electrons: if the substituted atom has six or fewer valence electrons (Ti-Cr or Zr-Mo), the number of down spin electrons associated with the impurity ion is zero, resulting in ferromagnetic (FM) alignment of the impurity magnetic moment with the magnetization of the CrO 2 host. For substituent atoms with eight to ten (Fe-Ni or Ru-Pd with the exception of Ni), the number of down spin electrons contributed by the impurity ion remains fixed at three as the number contributed to the majority increases from one to three resulting in antiferromagnetic (AFM) alignment between impurity moment and host magnetization. The origin of this variation is the grouping of the impurity states into 3 states with approximate "t 2g " symmetry and 2 states with approximate "e g " symmetry. Ni is an exception to the rule because a Jahn-Teller-like distortion causes a splitting of the Ni e g states. For Mn and Tc, which have 8 valence electrons, the zero down spin and 3 down spin configurations are very close in energy. For Cu and Ag atoms, which have 11 valence electrons, the energy is minimized when the substituent ion contributes 5 Abstract down-spin electrons. We find that the interatomic exchange interactions are reduced for all substitutions except for the case of Fe for which a modest enhancement is calculated for interactions along certain crystallographic directions.Spintronic devices that make use of electron spin (in addition to charge) in order to control the flow of electrons have become increasingly important in recent years. These devices depend for their operation on spin-polarized currents, meaning that when a voltage is applied, unequal currents flow in the two spin-channels. For simplicity, we ignore small spin-orbit coupling effects in this discussion. The ultimate spin-polarized conductor is a half-metal; a material that is metallic in one spin channel, but insulating (or semiconducting) in the other because there is a gap in the density of states for that spin channel at the Fermi energy [1].

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