Perfect Reflection of Chiral Fermions in Gated Graphene Nanoribbons

We describe the results of a theoretical study of transport through gated metallic graphene nanoribbons using a non-equilibrium Green function method. Although analogies with quantum field theory predict perfect transmission of chiral fermions through gated regions in one dimension, we find \emph{perfect reflection} of chiral fermions in armchair ribbons for specific configurations of the gate. This effect should be measurable in narrow graphene constrictions gated by a charged carbon nanotube.Comment: 9 pages, 3 figures. Submitted to Nano Letter

Targeted Excited State Algorithms

To overcome the limitations of the traditional state-averaging approaches in excited state calculations, where one solves for and represents all states between the ground state and excited state of interest, we have investigated a number of new excited state algorithms. Building on the work of van der Vorst and Sleijpen (SIAM J. Matrix Anal. Appl., 17, 401 (1996)), we have implemented Harmonic Davidson and State-Averaged Harmonic Davidson algorithms within the context of the Density Matrix Renormalization Group (DMRG). We have assessed their accuracy and stability of convergence in complete active space DMRG calculations on the low-lying excited states in the acenes ranging from naphthalene to pentacene. We find that both algorithms offer increased accuracy over the traditional State-Averaged Davidson approach, and in particular, the State-Averaged Harmonic Davidson algorithm offers an optimal combination of accuracy and stability in convergence

Analytic response theory for the density matrix renormalization group

We propose an analytic response theory for the density matrix renormalization group whereby response properties correspond to analytic derivatives of density matrix renormalization group observables with respect to the applied perturbations. Both static and frequency-dependent response theories are formulated and implemented. We evaluate our pilot implementation by calculating static and frequency dependent polarizabilities of short oligo-di-acetylenes. The analytic response theory is competitive with dynamical density matrix renormalization group methods and yields significantly improved accuracies when using a small number of density matrix renormalization group states. Strengths and weaknesses of the analytic approach are discussed.Comment: 19 pages, 3 figure

The radical character of the acenes: A density matrix renormalization group study

We present a detailed investigation of the acene series using high-level wavefunction theory. Our ab-initio Density Matrix Renormalization Group algorithm has enabled us to carry out Complete Active Space calculations on the acenes from napthalene to dodecacene correlating the full pi-valence space. While we find that the ground-state is a singlet for all chain-lengths, examination of several measures of radical character, including the natural orbitals, effective number of unpaired electrons, and various correlation functions, suggests that the longer acene ground-states are polyradical in nature.Comment: 10 pages, 8 figures, supplementary material, to be published in J. Chem. Phys. 127, 200

An Introduction to the Density Matrix Renormalization Group Ansatz in Quantum Chemistry

The Density Matrix Renormalisation Group (DMRG) is an electronic structure method that has recently been applied to ab-initio quantum chemistry. Even at this early stage, it has enabled the solution of many problems that would previously have been intractable with any other method, in particular, multireference problems with very large active spaces. Historically, the DMRG was not originally formulated from a wavefunction perspective, but rather in a Renormalisation Group (RG) language. However, it is now realised that a wavefunction view of the DMRG provides a more convenient, and in some cases more powerful, paradigm. Here we provide an expository introduction to the DMRG ansatz in the context of quantum chemistry.Comment: 17 pages, 3 figure

Nuclear-localized human respiratory syncytial virus NS1 protein modulates host gene transcription

Human respiratory syncytial virus (RSV) is a common cause of lower respiratory tract infections in the pediatric, elderly, and immunocompromised individuals. RSV non-structural protein NS1 is a known cytosolic immune antagonist, but how NS1 modulates host responses remains poorly defined. Here, we observe NS1 partitioning into the nucleus of RSV-infected cells, including the human airway epithelium. Nuclear NS1 coimmunoprecipitates with Mediator complex and is chromatin associated. Chromatin-immunoprecipitation demonstrates enrichment of NS1 that overlaps Mediator and transcription factor binding within the promoters and enhancers of differentially expressed genes during RSV infection. Mutation of the NS1 C-terminal helix reduces NS1 impact on host gene expression. These data suggest that nuclear NS1 alters host responses to RSV infection by binding at regulatory elements of immune response genes and modulating host gene transcription. Our study identifies another layer of regulation by virally encoded proteins that shapes host response and impacts immunity to RSV

Accurate ab initio spin densities

We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys. 2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insights into chemically interesting features of the molecule under study such as the distribution of $\alpha$- and $\beta$-electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput. 2011, 7, 2740].Comment: 37 pages, 13 figure

Nuclear-localized human respiratory syncytial virus NS1 protein modulates host gene transcription

Human respiratory syncytial virus (RSV) is a common cause of lower respiratory tract infections in the pediatric, elderly, and immunocompromised individuals. RSV non-structural protein NS1 is a known cytosolic immune antagonist, but how NS1 modulates host responses remains poorly defined. Here, we observe NS1 partitioning into the nucleus of RSV-infected cells, including the human airway epithelium. Nuclear NS1 coimmunoprecipitates with Mediator complex and is chromatin associated. Chromatin-immunoprecipitation demonstrates enrichment of NS1 that overlaps Mediator and transcription factor binding within the promoters and enhancers of differentially expressed genes during RSV infection. Mutation of the NS1 C-terminal helix reduces NS1 impact on host gene expression. These data suggest that nuclear NS1 alters host responses to RSV infection by binding at regulatory elements of immune response genes and modulating host gene transcription. Our study identifies another layer of regulation by virally encoded proteins that shapes host response and impacts immunity to RSV

Deliberación.: Un concepto clave en la teoría de la democracia deliberativa de Jürgen Habermas

El artículo expone, en primer lugar, la relevancia de la deliberación como procedimiento en la teoría de la democracia deliberativa habermasiana. Luego se destaca la centralidad del procedimiento en el espacio público y en la configuración de una democracia de calidad. Finalmente se explicitan de forma sintética los aportes que puede realizar la teoría de la democracia deliberativa ante los desafíos teóricos y prácticos que representan la globalización, la interculturalidad y la exclusión.The following paper presents, firstly, the relevance of deliberation as a procedure in Habermas’s theory of deliberative democracy. Then, it highlights the centrality of the mentioned procedure in the public space and in the configuration of a quality democracy. Finally, it summarizes the contributions that the theory of deliberative democracy can make to the theoretical and practical challenges posed by globalization, multiculturalism and exclusion

Bien común y ética pública: Alcances y límites del concepto tradicional de bien común

Con el concepto de bien común se ha hecho referencia, a través de la historia, a aquellos bienes materiales e inmateriales que no se circunscriben a una persona sino que remiten a todos y cada uno de los miembros de la sociedad. Entre esos bienes suelen contarse elementos básicos para la supervivencia humana biológica, como el aire y el agua, pero también el derecho a participar en el usufructo de los bienes de la cultura. En algunos casos, el bien común es equiparado al bienestar general; en otros, a la suma de intereses particulares o al beneficio de la mayoría, como cuando se busca el mayor bien para el mayor número posible de individuos. Más allá de las diversas interpretaciones, la promoción del bien común sigue siendo en la actualidad un objetivo clave del Estado en el ideario democrático y un tema recurrente de la ética pública. En lo que sigue, se reconstruye críticamente el concepto tradicional de bien común, haciendo especial referencia a las obras de Platón, Aristóteles y Santo Tomas, con el fin de sentar bases para una nueva comprensión de la idea de bien común en sociedades pluralistas y democráticas.With the concept of commom good reference has been made, along history, to those material and immaterial goods which are not circumscribed to a person, but remit to each and every member of society. Among those goods, basic elements for biological human survival, such as air and water, are usually included, but also the right to participate of the profits of cultural goods. In some cases, commom good has been made equivalent to common wellfare; in others, to the summation of particular interests or to the benefit of the majority. Beyond the diverse interpretations, the promotion of common good continues at present to be a key aim of State in the democratic ideary and a recurrent issue in public ethics. In what follows, the concept of traditional common good has been reconstructed, making special reference to the works of Plato, Aristotle and St. Thomas, with the purpose of setting the basis for a new comprehension of the idea of common good in pluralist and democratic societies