Charge transfer via a two-strand superexchange bridge in DNA

Charge transfer in a DNA duplex chain is studied by constructing a system with virtual electrodes connected at the ends of each DNA strand. The systeym is described by the tight-binding model and its transport is analyzed by the transfer matrix method. The very weak distance dependence in long (G:C)(T:A)_M(G:C)_3 DNA chain observed in experiment [B. Giese, et al., Nature 412, 318 (2001)] is explained by a unistep two-strand superexchange bridge without the need for the multi-step thermally-induced hopping mechanism or the dephasing effect. The crossover number M_c of (T:A) base pairs, where crossover between strong and weak distance dependence occurs, reflects the ratio of intra- and inter-strand neighboring base-base couplings.Comment: accepted for publication in Phys. Rev. Let

Las noticias extranjeras en la televisión pública y privada de Chile comparada con la de catorce países.

Este trabajo analiza el impacto de las noticias extranjeras en dos noticiarios de televisión chilenos, en el marco del proyecto Foreign TV News Around the World. Todas las noticias emitidas son clasificadas en cuatro categorías, según lugar de ocurrencia e involucramiento nacional o extranjero. El espacio que se destina a cada una de ellas, así como los temas más habituales, son comparados según dos modelos televisivos: el de servicio público y el comercial. En definitiva se observa que, en Chile y en el resto de los países analizados, la tendencia es que las diferencias esperadas entre ambos tipos ideales son comparativamente menores

Chiral molecular films as electron polarizers and polarization modulators

Recent experiments on electron scattering through molecular films have shown that chiral molecules can be efficient sources of polarized electrons even in the absence of heavy nuclei as source of a strong spin-orbit interaction. We show that self-assembled monolayers (SAMs) of chiral molecules are strong electron polarizers due to the high density effect of the monolayers and explicitly compute the scattering amplitude off a helical molecular model of carbon atoms. Longitudinal polarization is shown to be the signature of chiral scattering. For elastic scattering, we find that at least double scattering events must take place for longitudinal polarization to arise. We predict energy windows for strong polarization, determined by the energy dependences of spin-orbit strength and multiple scattering probability. An incoherent mechanism for polarization amplification is proposed, that increases the polarization linearly with the number of helix turns, consistent with recent experiments on DNA SAMs.Comment: 5 Pages, 4 figure

Co-detección de Patógenos Periodontales en Pacientes Chilenos con Periodontitis Crónica

Indexación: ScieloLas enfermedades periodontales asociadas a la placa dental son un importante problema de salud pública. La etiología de estas patologías es de origen multifactorial e involucra factores del hospedero, medio ambiente y de carácter infeccioso asociados a bacterias embebidas en la placa dental. Las principales bacterias asociadas a la periodontitis crónica son Porphyromonas gingivalis, Treponema denticola y Tannerella forsythia, mientras que Aggregatibacter actinomycetemcomitans se ha asociado principalmente a la periodontitis agresiva. Otro microorganismo clave en el desarrollo de la enfermedad es Fusobacterium nucleatum, el cual tiene la capacidad de co-agregarse con los patógenos periodontales y así facilitar su colonización. Para demostrar la prevalencia de estas bacterias, la co-detección y la asociación entre pacientes chilenos fumadores y no fumadores, se analizaron 67 muestras mediante PCR convencional. Los resultados mostraron que un 90% de las muestras fueron positivas para F. nucleatum, siendo la bacteria más detectada. Al analizar la co-detección entre las distintas bacterias se observa que F nucleatum está presente en más de un 80% de los casos cuando se detecta cualquiera de las cuatro bacterias restantes, mientas que A. actinomycetemcomitans se detecta en no más de un 20% al amplificar cualquiera de las bacterias restantes. Por otra parte, los resultados por género indican que existen diferencias significativas en la detección de T. forsythia, F. nucleatum y A. actinomycetemcomitans. Al considerar el factor de tabaquismo se observó que ninguna de las muestras de pacientes fumadores resultó ser positiva para A. actinomycetemcomitans.Periodontal disease associated with dental plaque is a major public health problem. The etiology of these disorders is multifactorial involved seeing host factors, environmental factors and infectious nature associated with the presence of bacteria belonging to the plaque. The main bacteria associated with chronic periodontitis are Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia, while Aggregatibacter actinomycetemcomitans is mainly associated with aggressive periodontitis. Another key organism in the development of the disease is Fusobacterium nucleatum, which has the ability to co-aggregate with other periodontal pathogen. To demonstrate the prevalence of these bacteria and the association between Chilean smokers and nonsmokers patients, 67 samples were analyzed by conventional PCR. The results showed that 90% of the samples were positive for F nucleatum being the most commonly detected bacteria. By analyzing the co-detection between different bacteria shows that F nucleatum is present in more than 80% of cases when it detects any of the four remaining bacteria, which lie A. actinomycetemcomitans was detected in no more than 20% by amplifying any remaining bacteria. Moreover the results by gender indicate that significant differences exist in the detection of T forsythia, F. nucleatum and A. actinomycetemcomitans. In considering the factor of smoking was observed that none of the samples from smokers was found to be positive for A. actinomycetemcomitans.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0719-01072010000300003&nrm=is

Molecular architectures based on pi-conjugated block copolymers for global quantum computation

We propose a molecular setup for the physical implementation of a barrier global quantum computation scheme based on the electron-doped pi-conjugated copolymer architecture of nine blocks PPP-PDA-PPP-PA-(CCH-acene)-PA-PPP-PDA-PPP (where each block is an oligomer). The physical carriers of information are electrons coupled through the Coulomb interaction, and the building block of the computing architecture is composed by three adjacent qubit systems in a quasi-linear arrangement, each of them allowing qubit storage, but with the central qubit exhibiting a third accessible state of electronic energy far away from that of the qubits' transition energy. The third state is reached from one of the computational states by means of an on-resonance coherent laser field, and acts as a barrier mechanism for the direct control of qubit entanglement. Initial estimations of the spontaneous emission decay rates associated to the energy level structure allow us to compute a damping rate of order 10^{-7} s, which suggest a not so strong coupling to the environment. Our results offer an all-optical, scalable, proposal for global quantum computing based on semiconducting pi-conjugated polymers.Comment: To appear in J. Phys.: Conf. Series (2009