Nitrogen Induced Ferromagnetism In Cobalt Doped BaTiO3

The electronic structure and magnetism of Cobalt doped BaTiO3 (BaTi1-xCoxO3) is investigated. Substitutional Nitrogen on an Oxygen site is found to play an important role in inducing net magnetic moments in the system. The presence of a Nitrogen atom as nearest neighbour to a Cobalt atom is crucial in producing spin splitting of both the Nitrogen and Cobalt states thereby introducing a net local magnetic moment. The introduction of Nitrogen is further found to enhance ferromagnetic interactions between Cobalt atoms. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4747820]Physic

Unraveling the Catalytic Mechanism of Nitrile Hydratases

To elucidate a detailed catalytic mechanism for nitrile hydratases (NHases), the pH and temperature dependence of the kinetic constants kcat and Km for the cobalt-type NHase from Pseudonocardia thermophila JCM 3095 (PtNHase) were examined. PtNHase was found to exhibit a bell-shaped curve for plots of relative activity versus pH at pH 3.2–11 and was found to display maximal activity between pH 7.2 and 7.8. Fits of these data provided pKES1 and pKES2 values of 5.9 ± 0.1 and 9.2 ± 0.1 (kcat′ = 130 ± 1 s-1), respectively, and pKE1 and pKE2 values of 5.8 ± 0.1 and 9.1 ± 0.1 (kcat′/Km′ = (6.5 ± 0.1) × 103 s-1 mm-1), respectively. Proton inventory studies indicated that two protons are transferred in the rate-limiting step of the reaction at pH 7.6. Because PtNHase is stable at 60 °C, an Arrhenius plot was constructed by plotting ln(kcat) versus 1/T, providing Ea = 23.0 ± 1.2 kJ/mol. The thermal stability of PtNHase also allowed ΔH0 ionization values to be determined, thus helping to identify the ionizing groups exhibiting the pKES1 and pKES2 values. Based on ΔH0ion data, pKES1 is assigned to βTyr68, whereas pKES2 is assigned to βArg52, βArg157, or αSer112 (NHases are α2β2-heterotetramers). A combination of these data with those previously reported for NHases and synthetic model complexes, along with sequence comparisons of both iron- and cobalt-type NHases, allowed a novel catalytic mechanism for NHases to be proposed

Revisiting lagrange relaxation (LR) for processing large-scale mixed integer programming (MIP) problems

Lagrangean Relaxation has been successfully applied to process many well known instances of NP-hard Mixed Integer Programming problems. In this paper we present a Lagrangean Relaxation based generic solver for processing Mixed Integer Programming problems. We choose the constraints, which are relaxed using a constraint classification scheme. The tactical issue of updating the Lagrange multiplier is addressed through sub-gradient optimisation; alternative rules for updating their values are investigated. The Lagrangean relaxation provides a lower bound to the original problem and the upper bound is calculated using a heuristic technique. The bounds obtained by the Lagrangean Relaxation based generic solver were used to warm-start the Branch and Bound algorithm; the performance of the generic solver and the effect of the alternative control settings are reported for a wide class of benchmark models. Finally, we present an alternative technique to calculate the upper bound, using a genetic algorithm that benefits from the mathematical structure of the constraints. The performance of the genetic algorithm is also presented

Mutation of H63 and its Catalytic Affect on the Methionine Aminopeptidase from \u3cem\u3eEscherichia coli\u3c/em\u3e

In order to gain insight into the mechanistic role of a flexible exterior loop near the active site, made up of Y62, H63, G64, and Y65, that has been proposed to play an important role in substrate binding and recognition in the methionyl aminopeptidase from Escherichia coli (EcMetAP-I), the H63A enzyme was prepared. Mutation of H63 to alanine does not affect the ability of the enzyme to bind divalent metal ions. The specific activity of H63A EcMetAP-I was determined using four different substrates of varying lengths, namely, l-Met-p-NA, MAS, MGMM and MSSHRWDW. For the smallest/shortest substrate (l-Met-p-NA) the specific activity decreased nearly seven fold but as the peptide length increased, the specific activity also increased and became comparable to WT EcMetAP-I. This decrease in specific activity is primarily due to a decrease in the observed kcat values, which decreases nearly sixty-fold for l-Met-p-NA while only a four-fold decrease is observed for the tri- and tetra-peptide substrates. Interestingly, no change in kcat was observed when the octa-peptide MSSHRWDW was used as a substrate. These data suggest that H63 affects the hydrolysis of small peptide substrates whereas large peptides can overcome the observed loss in binding energy, as predicted from Km values, by additional hydrophilic and hydrophobic interactions

Superfluid and Fermi liquid phases of Bose-Fermi mixtures in optical lattices

We describe interacting mixtures of ultracold bosonic and fermionic atoms in harmonically confined optical lattices. For a suitable choice of parameters we study the emergence of superfluid and Fermi liquid (non-insulating) regions out of Bose-Mott and Fermi-band insulators, due to finite Boson and Fermion hopping. We obtain the shell structure for the system and show that angular momentum can be transferred to the non-insulating regions from Laguerre-Gaussian beams, which combined with Bragg spectroscopy can reveal all superfluid and Fermi liquid shells.Comment: 4 pages, 2 figure

Nonequilibrium dynamics in a two-channel Kondo system due to a quantum quench

Recent experiments by Potok et al. have demonstrated a remarkable tunability between a single-channel Fermi liquid fixed point and a two-channel non-Fermi liquid fixed point. Motivated by this we study the nonequilibrium dynamics due to a sudden quench of the parameters of a Hamiltonian from a single-channel to a two-channel anisotropic Kondo system. We find a distinct difference between the long time behavior of local quantities related to the impurity spin as compared to that of bulk quantities related to the total (conduction electrons + impurity) spin of the system. In particular, the local impurity spin and the local spin susceptibility are found to equilibrate, but in a very slow power-law fashion which is peculiar to the non-Fermi liquid properties of the Hamiltonian. In contrast, we find a lack of equilibration in the two particle expectation values related to the total spin of the system.Comment: 5 pages, 1 fig. Accepted in PR

Multibaseline gravitational wave radiometry

We present a statistic for the detection of stochastic gravitational wave backgrounds (SGWBs) using radiometry with a network of multiple baselines. We also quantitatively compare the sensitivities of existing baselines and their network to SGWBs. We assess how the measurement accuracy of signal parameters, e.g., the sky position of a localized source, can improve when using a network of baselines, as compared to any of the single participating baselines. The search statistic itself is derived from the likelihood ratio of the cross correlation of the data across all possible baselines in a detector network and is optimal in Gaussian noise. Specifically, it is the likelihood ratio maximized over the strength of the SGWB, and is called the maximized-likelihood ratio (MLR). One of the main advantages of using the MLR over past search strategies for inferring the presence or absence of a signal is that the former does not require the deconvolution of the cross correlation statistic. Therefore, it does not suffer from errors inherent to the deconvolution procedure and is especially useful for detecting weak sources. In the limit of a single baseline, it reduces to the detection statistic studied by Ballmer [Class. Quant. Grav. 23, S179 (2006)] and Mitra et al. [Phys. Rev. D 77, 042002 (2008)]. Unlike past studies, here the MLR statistic enables us to compare quantitatively the performances of a variety of baselines searching for a SGWB signal in (simulated) data. Although we use simulated noise and SGWB signals for making these comparisons, our method can be straightforwardly applied on real data.Comment: 17 pages and 19 figure