Subsystem density functional theory with meta generalized gradient approximation exchange-correlation functionals

We analyze the methodology and the performance of subsystem density functional theory (DFT) with meta-generalized gradient approximation (meta-GGA) exchange-correlation functionals for non-bonded systems. Meta-GGA functionals depend on the Kohn-Sham kinetic energy density (KED), which is not known as an explicit functional of the density. Therefore, they cannot be directly applied in subsystem DFT calculations. We propose a Laplacian-level approximation to the KED which overcomes the problem and provides a simple and accurate way to apply meta-GGA exchange-correlation functionals in subsystem DFT calculations. The so obtained density and energy errors, with respect to the corresponding supermolecular calculations, are comparable with conventional approaches, depending almost exclusively on the approximations in the non-additive kinetic embedding term. An embedding energy error decomposition explains the accuracy of our method.Comment: 14 pages, 3 figure

What memory binding functions is the hippocampus responsible for?

The role of the hippocampus in binding information in working memory (WM) is little understood. When complex experiences comprise associations between different pieces of information such as objects and locations (relational binding), the function of the hippocampus is required to hold them in WM (Mitchell et al., 2000; 2006; Piekema, 2006). However, recent evidence suggests that if the to-be-associated information leads to the formation of integrated objects such as coloured shapes (conjunctive binding), the hippocampus is less involved in holding temporary representations of these complex events in WM (Baddeley et al., 2010; Piekema, 2006). We investigated the relational and conjunctive binding hypotheses of the hippocampal functions in a patient with right hippocampal damage. The patient and controls were asked to study visual arrays of stimuli which consisted of shape-colour relations (shape-colour pairs) or shape-colour conjunctions (coloured shapes). After the study array, they were presented with a new screen consisting of one set of shapes (line drawings) and one set of colours. They were asked to reconstruct the bindings by selecting the shapes and their corresponding colours. As compared to healthy controls, the patient was impaired in holding relations of shapes and colours in WM whereas he could retain the conjunctions similarly to controls. These results lend support to the role of the hippocampus in supporting memory for inter-item associations but not memory for conjunctions of features which define objects' identity

Coherent molecule formation in anharmonic potentials near confinement-induced resonances

We perform a theoretical and experimental study of a system of two ultracold atoms with tunable interaction in an elongated trapping potential. We show that the coupling of center-of-mass and relative motion due to an anharmonicity of the trapping potential leads to a coherent coupling of a state of an unbound atom pair and a molecule with a center of mass excitation. By performing the experiment with exactly two particles we exclude three-body losses and can therefore directly observe coherent molecule formation. We find quantitative agreement between our theory of inelastic confinement-induced resonances and the experimental results. This shows that the effects of center-of-mass to relative motion coupling can have a significant impact on the physics of quasi-1D quantum systems.Comment: 7 pages, 4 figure

Variational study of U(1) and SU(2) lattice gauge theories with Gaussian states in 1+1 dimensions

We introduce a method to investigate the static and dynamic properties of both Abelian and non-Abelian lattice gauge models in 1+1 dimensions. Specifically, we identify a set of transformations that disentangle different degrees of freedom, and apply a simple Gaussian variational ansatz to the resulting Hamiltonian. To demonstrate the suitability of the method, we analyze both static and dynamic aspects of string breaking for the U(1) and SU(2) gauge models. We benchmark our results against tensor network simulations and observe excellent agreement, although the number of variational parameters in the Gaussian ansatz is much smaller.Comment: 19 pages, 6 figures. Added references and corrected typo

Bowen ratio estimates of evapotranspiration for stands on the Virgin River in Southern Nevada

A Bowen ratio energy balance was conducted over a Tamarix ramosissima (saltcedar) stand growing in a riparian corridor along the Virgin River in southern Nevada. Measurements in two separate years were compared and contrasted on the basis of changes in growing conditions. In 1994, a drought year, record high temperatures, dry winds, and a falling water table caused partial wilt of outer smaller twigs in the canopy of many trees in the stand around the Bowen tower. Subsequently, evapotranspiration (ET) estimates declined dramatically over a 60‐day period (11 mm d−1 tod−1). In 1995, the Virgin River at the Bowen tower area changed its course, hydrologically isolating the Tamarix stand in the vicinity of the tower. In 1996, a 25% canopy loss was visually estimated for the Tamarix growing in the area of the tower. Higher soil temperatures relative to air temperatures were recorded in 1996 in response to this loss in canopy. With a more open canopy, thermally induced turbulence was observed in 1996. On day 160 of 1996, a 28°C rise over a 9‐hour period was correlated with increased wind speeds of greater than 4 m s−1. Subsequently, higher ET estimates were made in 1996 compared to 1994 (145 cm versus 75 cm). However, the energy balance was dominated by advection in 1996, with latent energy flux exceeding net radiation 65% of the measurement days compared to only 11% in 1994. We believe this advection was on a scale of the floodplain (hundreds of meters) as opposed to regional advection, since the majority of wind (90%) was in a N–S direction along the course of the river, and that a more open canopy allowed the horizontal transfer of energy into the Tamarix stand at the Bowen tower. Our results suggest that Tamarix has the potential to be both a low water user and a high water user, depending on moisture availability, canopy development, and atmospheric demand, and that advection can dominate energy balances and ET in aridland riparian zones such as the Virgin River

Frizzled receptor 6 marks rare, highly tumourigenic stem-like cells in mouse and human neuroblastomas

Copyright © 2011 Cantilena et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The article was made available through the Brunel Open Access Publishing Fund.Wnt signalling is an important component of vertebrate development, required for specification of the neural crest. Ten Wnt receptors [Frizzled receptor 1-10 (Fzd1-10)] have been identified so far, some of which are expressed in the developing nervous system and the neural crest. Here we show that expression of one such receptors, Fzd6, predicts poor survival in neuroblastoma patients and marks rare, HIF1/2 α-positive cells in tumour hypoxic areas. Fzd6 positive neuroblastoma cells form neurospheres with high efficiency, are resistant to doxorubicin killing and express high levels of mesenchymal markers such as Twist1 and Notch1. Expression of Fzd6 is required for the expression of genes of the noncanonical Wnt pathway and the spheres forming activity. When transplanted into immunodeficient mice, neuroblastoma cells expressing the Fzd6 marker grow more aggressively than their Fzd6 negative counterparts. We conclude that Fzd6 is a new surface marker of aggressive neuroblastoma cells with stem cell-like features.This work was sponsored by the Wellcome Trust, the RICC cancer fund, SPARKS, the Italian Association for Cancer Research, Regione Liguria and the Italian Ministry of Health

Physical interaction between MYCN oncogene and polycomb repressive complex 2 (PRC2) in neuroblastoma: Functional and therapeutic implications

This article is made available through the Brunel Open Access Publishing Fund. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.CLU (clusterin) is a tumor suppressor gene that we have previously shown to be negatively modulated by the MYCN proto-oncogene, but the mechanism of repression was unclear. Here, we show that MYCN inhibits the expression of CLU by direct interaction with the non-canonical E box sequence CACGCG in the 5′-flanking region. Binding of MYCN to the CLU gene induces bivalent epigenetic marks and recruitment of repressive proteins such as histone deacetylases and Polycomb members. MYCN physically binds in vitro and in vivo to EZH2, a component of the Polycomb repressive complex 2, required to repress CLU. Notably, EZH2 interacts with the Myc box domain 3, a segment of MYC known to be essential for its transforming effects. The expression of CLU can be restored in MYCN-amplified cells by epigenetic drugs with therapeutic results. Importantly, the anticancer effects of the drugs are ablated if CLU expression is blunted by RNA interference. Our study implies that MYC tumorigenesis can be effectively antagonized by epigenetic drugs that interfere with the recruitment of chromatin modifiers at repressive E boxes of tumor suppressor genes such as CLU.SPARKS, The Neuroblastoma Society, a Wellcome Trust grant (to A. S.), and the Italian Association for Cancer Research