Anisotropic enhancement of Yb3+ luminescence by disordered plasmonic networks self-assembled on RbTiOPO4 ferroelectric crystals.

Increasing Yb3+ absorption efficiency is currently desired in a number of applications including bio-imaging, photovoltaics, near infrared driven photocatalysis or ultra-short pulsed solid-state lasers. In this work, silver nanoparticles, which are connected forming disordered networks, have been self-assembled on Yb3+ doped RbTiOPO4 crystals to produce a remarkable enhancement of Yb3+ absorption, and hence in the photoluminescence of this ion. The results are interpreted taking into account the near-field response of the plasmonic networks, which display strong amplification of the electric field at the maximum of Yb3+ excitation at around 900 nm, together with the anisotropic character of the Yb3+ transitions in RbTiOPO4. We show that in the near field regime, the scattering of the plasmonic networks produces additional polarization field components to those of the incident field, which allows access to the largest transition dipolar moment of Yb3+ ions in RbTiOPO4. As a result, a much more efficient route for Yb3+ excitation takes place at the immediacy of the plasmonic networks. This work provides fundamental insights for improving the optical properties of rare earth ions by the suitable design of metallic nanoparticle arrangements, and constitutes a promising step towards the development of new multifunctional solid-state lasers.

[Tuberculous gumma or metastatic tuberculous abscess as initial diagnosis of tuberculosis in an immunocompetent patient: an unusual presentation]. / Goma o absceso tuberculoso metastásico como diagnóstico inicial de tuberculosis en un paciente inmunocompetente: una presentación inusual.

BACKGROUND AND OBJECTIVES: Tuberculous cold abscesses or gumma are an unusual form of tuberculosis. We report a case of gumma as initial diagnosis of disseminated tuberculosis. METHOD: This case was studied in 2012 in Barcelona ( Spain). Source data was compiled from the electronic clinical records, hospital reports and additional diagnostic testing. RESULTS: Immunocompetent inmate, born in Cape Verde, living in Spain since the age of four. Positive tuberculin skin test. Initial examination without interest, but a palpable mass in lower back. Fine needle aspiration of the abscess was positive (PCR and Lowenstein) for M. tuberculosis. Computed tomography showed lung cavitary nodes in apical part and lung upper right side. After respiratory isolation, antituberculous therapy and an excellent evolution, the patient was discharged from hospital with disseminated tuberculosis diagnosis. DISCUSSION: It is advisable to monitor the injuries since, although rare, it may be secondary to Mycobacterium tuberculosis infection, mainly in inmuno-compromised populations and in immigrants coming from hyper-endemic tuberculosis areas.

Goma o absceso tuberculoso metastásico como diagnóstico inicial de tuberculosis en un paciente inmunocompetente: una presentación inusual / Tuberculous gumma or metastatic tuberculous abscess as initial diagnosis of tuberculosis in an immunocompetent patient. an unusual presentation

Fundamento y Objetivo: Los abscesos fríos tuberculosos o gomas son inusuales y producto de la diseminación hematógena de micobacterias latentes, formando abscesos en extremidades o tronco, generalmente sin compromiso de tejidos profundos. Se presenta un caso de goma como diagnóstico inicial de tuberculosis diseminada. Métodos: Caso estudiado en 2012 por los servicios médicos del centro penitenciario de Hombres de Barcelona y el Servicio de Medicina Interna del Hospital Consorci Sanitari de Terrassa. Se recogen los datos de la historia clínica, de los informes hospitalarios y de las pruebas complementarias practicadas. Resultados: Preso, 35 años, de Cabo Verde, residente en España desde los 4 años. IDR Mantoux positiva. Inmunocompetente. Por síndrome constitucional se programó estudio hospitalario. Exploración anodina, excepto palpación de masa en región lumbar. La punción aspirativa fue positiva para M. tuberculosis mediante PCR y cultivo Lowenstein. La TC mostró nódulos pulmonares, apical D cavitado y en LSD. Tras aislamiento respiratorio, tratamiento antituberculoso y excelente evolución fue dado de alta con diagnóstico de tuberculosis diseminada. Discusión: Se recomienda vigilar lesiones que, aunque infrecuentes, pueden ser secundarias a infección por M tuberculosis, especialmente en población inmunocomprometida y en inmigrantes procedentes de zonas hiperendémicas de tuberculosis (AU)

Background and Objectives: Tuberculous cold abscesses or gumma are an unusual form of tuberculosis. We report a case of gumma as initial diagnosis of disseminated tuberculosis. Method: This case was studied in 2012 in Barcelona (Spain). Source data was compiled from the electronic clinical records, hospital reports and additional diagnostic testing. Results: Immunocompetent inmate, born in Cape Verde, living in Spain since the age of four. Positive tuberculin skin test. Initial examination without interest, but a palpable mass in lower back. Fine needle aspiration of the abscess was positive (PCRand Lowenstein) for M. tuberculosis. Computed tomography showed lung cavitary nodes in apical part and lung upper right side. After respiratory isolation, antituberculous therapy and an excellent evolution, the patient was discharged from hospital with disseminated tuberculosis diagnosis. Discussion: It is advisable to monitor the injuries since, although rare, it may be secondary to Mycobacterium tuberculosis infection, mainly in inmuno-compromised populations and in immigrants coming from hyper-endemic tuberculosis areas (AU)

Channel waveguides on RbTiOPO4 by Cs+ ion exchange.

In this Letter we report Cs(+) ion exchange channel waveguides on RbTiOPO(4) (RTP) for what we believe is the first time. A Ti channel mask was fabricated on an RTP substrate by conventional photolithography. The ion exchange process was carried out in a CsNO(3) melt, and the channels produced ranged from 6 to 11 µm in width. The near-field pattern of the modes was recorded, and type II second harmonic generation in waveguide regime was obtained, producing 512.5 nm green light. The optical characterization shows optical losses of 3.8 dB/cm.

Excited state properties of formamide in water solution: an ab initio study.

We present ab initio quantum calculation of the optical properties of formamide in vapor phase and in water solution. We employ time dependent density functional theory for the isolated molecule and many-body perturbation theory methods for the system in solution. An average over several molecular dynamics snapshots is performed to take into account the disorder of the liquid. We find that the excited state properties of the gas-phase formamide are strongly modified by the presence of the water solvent: the geometry of the molecule is distorted and the electronic and optical properties are severely modified. The important interaction among the formamide and the water molecules forces us to use fully quantum methods for the calculation of the excited state properties of this system. The excitonic wave function is localized both on the solute and on part of the solvent.

Role of cellulose oxidation in the yellowing of ancient paper.

The yellowing of paper on aging causes major aesthetic damages of cultural heritage. It is due to cellulose oxidation, a complex process with many possible products still to be clarified. By comparing ultraviolet-visible reflectance spectra of ancient and artificially aged modern papers with ab initio time-dependent density functional theory calculations, we identify and estimate the abundance of oxidized functional groups acting as chromophores and responsible of paper yellowing. This knowledge can be used to set up strategies and selective chemical treatments preventing paper yellowing.

Efficient Type II phase-matching second-harmonic generation in Ba:Yb:Nb:RbTiOPO4/RbTiOPO4 waveguides.

Efficient Type II phase-matching second-harmonic generation of a 1125 nm fundamental beam has been obtained using Ba:Yb:Nb:RbTiOPO(4)/RbTiOPO(4) waveguides grown by liquid phase epitaxy. The refractive indices of the epitaxial layer have been measured at different wavelengths, and the Sellmeier coefficients of the chromatic dispersion curves have been obtained. The phase-matching curve shows that the Ba(2+) doping in RbTiOPO(4) contributes to increase the phase-matching range until 900 nm. The measured effective refractive indices of the propagation modes agree well with the theoretical calculations.

Coexistence of negatively and positively buckled isomers on n+-doped Si(111) − 2 × 1.

A long-standing puzzle regarding the Si(111) − 2 × 1 surface has been solved. The surface energy gap previously determined by photoemission on heavily n-doped crystals was not compatible with a strongly bound exciton known from other considerations to exist. New low-temperature angle-resolved photoemission and scanning tunneling microscopy data, together with theory, unambiguously reveal that isomers with opposite bucklings and different energy gaps coexist on such surfaces. The subtle energetics between the isomers, dependent on doping, leads to a reconciliation of all previous results.

Ab initio calculation of optical spectra of liquids: many-body effects in the electronic excitations of water.

We present ab initio calculations of the excited state properties of liquid water in the framework of many-body Green's function formalism. Snapshots taken from molecular dynamics simulations are used as input geometries to calculate electronic and optical spectra, and the results are averaged over the different configurations. The optical absorption spectra with the inclusion of excitonic effects are calculated by solving the Bethe-Salpeter equation. The insensitivity of screening effects to a particular configuration make these calculations feasible. The resulting spectra, which are strongly modified by many-body effects, are in good agreement with experiments.

Model of droplet dynamics in the Argentine ant Linepithema Humile (Mayr).

The formation of droplets of ants Linepithema humile (Mayr) is observed under certain experimental conditions: a fluctuating aggregate forms at the end of a rod and a droplet containing up to 40 ants eventually falls down. When the flux of incoming ants is sufficient, this process can continue for several hours, leading to the formation and fall of tens of droplets. Previous work indicates that the time series of drop-to-drop intervals may result from a nonlinear low-dimensional dynamics, and the interdrop increments exhibit long-range anticorrelations. A model of aggregation and droplet formation, based on experimental observations, is introduced and shown to reproduce these properties.

Field theory for a reaction-diffusion model of quasispecies dynamics.

RNA viruses are known to replicate with extremely high mutation rates. These rates are actually close to the so-called error threshold. This threshold is in fact a critical point beyond which genetic information is lost through a second-order phase transition, which has been dubbed as the "error catastrophe." Here we explore this phenomenon using a field theory approximation to the spatially extended Swetina-Schuster quasispecies model [J. Swetina and P. Schuster, Biophys. Chem. 16, 329 (1982)], a single-sharp-peak landscape. In analogy with standard absorbing-state phase transitions, we develop a reaction-diffusion model whose discrete rules mimic the Swetina-Schuster model. The field theory representation of the reaction-diffusion system is constructed. The proposed field theory belongs to the same universality class as a conserved reaction-diffusion model previously proposed [F. van Wijland et al., Physica A 251, 179 (1998)]. From the field theory, we obtain the full set of exponents that characterize the critical behavior at the error threshold. Our results present the error catastrophe from a different point of view and suggest that spatial degrees of freedom can modify several mean-field predictions previously considered, leading to the definition of characteristic exponents that could be experimentally measurable.

Topology of technology graphs: small world patterns in electronic circuits.

Recent theoretical studies and extensive data analyses have revealed a common feature displayed by biological, social, and technological networks: the presence of small world patterns. Here we analyze this problem by using several graphs obtained from one of the most common technological systems: electronic circuits. It is shown that both analogic and digital circuits exhibit small world behavior. We conjecture that the small world pattern arises from the compact design in which many elements share a small, close physical neighborhood plus the fact that the system must define a single connected component (which requires shortcuts connecting different integrated clusters). The degree distributions displayed are consistent with a conjecture concerning the sharp cutoffs associated to the presence of costly connections [Amaral et al., Proc. Natl. Acad. Sci. USA 97, 11 149 (2000)], thus providing a limit case for the classes of universality of small world patterns from real, artificial networks. The consequences for circuit design are outlined.

The small world of human language.

Words in human language interact in sentences in non-random ways, and allow humans to construct an astronomic variety of sentences from a limited number of discrete units. This construction process is extremely fast and robust. The co-occurrence of words in sentences reflects language organization in a subtle manner that can be described in terms of a graph of word interactions. Here, we show that such graphs display two important features recently found in a disparate number of complex systems. (i) The so called small-world effect. In particular, the average distance between two words, d (i.e. the average minimum number of links to be crossed from an arbitrary word to another), is shown to be d approximately equal to 2-3, even though the human brain can store many thousands. (ii) A scale-free distribution of degrees. The known pronounced effects of disconnecting the most connected vertices in such networks can be identified in some language disorders. These observations indicate some unexpected features of language organization that might reflect the evolutionary and social history of lexicons and the origins of their flexibility and combinatorial nature.

Complexity and fragility in ecological networks.

A detailed analysis of three species-rich ecosystem food webs has shown that they display skewed distributions of connections. Such graphs of interaction are, in fact, shared by a number of biological and technological networks, which have been shown to display a very high homeostasis against random removals of nodes. Here, we analyse the responses of these ecological graphs to both random and selective perturbations (directed against the most-connected species). Our results suggest that ecological networks are very robust against random removals but can be extremely fragile when selective attacks are used. These observations have important consequences for biodiversity dynamics and conservation issues, current estimations of extinction rates and the relevance and definition of keystone species.

Phenotypic and dynamical transitions in model genetic networks. II. Application to the evolution of segmentation mechanisms.

Knowledge of the genetic control of segmentation in Drosophila has made insect segmentation a paradigmatic case in the study of the evolution of developmental mechanisms. In Drosophila, the patterns of expression of segmentation genes are established simultaneously in all segments by a complex set of interactions between transcriptional factors that diffuse in a syncytium occupying the whole embryo. Such mechanisms cannot act in short germ-band insects where segments appear sequentially from a cellularized posterior proliferative zone. Here, we compare mechanisms of segmentation in different organisms and discuss how the transition between the different types of segmentation can be explained by small and progressive changes in the underlying gene networks. The recent discovery of a temporal oscillation in expression during somitogenesis of vertebrate homologs of the pair-rule gene hairy enhances the plausibility of an earlier proposal that the evolutionary origin of both the short- and long germ-band modes of segmentation was an oscillatory genetic network (Newman 1993). An implication of this scenario is that the self-organizing, pattern-forming system embodied in an oscillatory network operating in the context of a syncytium (i.e., a reaction-diffusion system)-which is hypothesized to have originated the simultaneous mode of segmentation-must have been replaced by the genetic hierarchy seen in modern-day Drosophila over the course of evolution. As demonstrated by the simulations in the accompanying article, the tendency for "emergent" genetic networks, associated with self-organizing processes, to be replaced through natural selection with hierarchical networks is discussed in relation to the evolution of segmentation.

Phenotypic and dynamical transitions in model genetic networks. I. Emergence of patterns and genotype-phenotype relationships.

Genotype-phenotype interactions during the evolution of form in multicellular organisms is a complex problem but one that can be aided by computational approaches. We present here a framework within which developmental patterns and their underlying genetic networks can be simulated. Gene networks were chosen to reflect realistic regulatory circuits, including positive and negative feedback control, and the exchange of a subset of gene products between cells, or within a syncytium. Some of these networks generate stable spatial patterns of a subset of their molecular constituents, and can be assigned to categories (e.g., "emergent" or "hierarchic") based on the topology of molecular circuitry. These categories roughly correspond to what has been discussed in the literature as "self-organizing" and "programmed" processes of development. The capability of such networks to form patterns of repeating stripes was studied in network ensembles in which parameters of gene-gene interaction were caused to vary in a manner analogous to genetic mutation. The evolution under mutational change of individual representative networks of each category was also simulated. We have found that patterns with few stripes (< or =3) are most likely to originate in the form of a hierarchic network, whereas those with greater numbers of stripes (> or =4) originate most readily as emergent networks. However, regardless of how many stripes it contains, once a pattern is established, there appears to be an evolutionary tendency for emergent mechanisms to be replaced by hierarchic mechanisms. These results have potential significance for the understanding of genotype-phenotype relationships in the evolution of metazoan form.

Extinctions and taxonomy in a trophic model of coevolution.

We investigate the statistics of extinction sizes and the taxonomy in a trophic model of evolution recently proposed [Phys. Rev. Lett. 82, 652 (1999)]. By further exploring the parameters of this model, we find that the distribution of extinction sizes N(s) shows typically a characteristic maximum before developing the power-law behavior N(s) approximately s(-alpha) with alpha approximately 2, in agreement with empirical observations. Furthermore, the derivation of the alpha=-2 exponent given by Drossel [Phys. Rev. Lett. 81, 5011 (1998)] for this model is completed. The extinction sizes in each trophic level are also analyzed; one finds that at the fourth level and up (l> or =4) the extinction size statistics is a power law with exponent alpha(l) approximately 1.4, and exponential-like at the second level, also in agreement with some empirical data not previously explained by current models. On the other hand, in contrast to the observed power-law distribution of the number of species in genera, numerical simulations yield an exponential law. A modification of the model is presented that provides an approximate potential behavior for taxonomy, and some consequences for future modeling are outlined.

Gene networks capable of pattern formation: from induction to reaction-diffusion.

One of the main aims of developmental biology is to understand how a single and apparently homogeneous egg cell achieves the intricate complexity of the adult. Here we present two models to explain the generation of developmental patterns through interactions at the gene level. One model considers direct-contact induction between cells while the other takes into account diffusion of hormones. We show that sets of cells involving identical gene networks and communicating through hormones spontaneously exhibit ordered patterns. We have characterized these patterns and the specific networks responsible for them. The models allow to (i) compare diffusion and direct-contact induction processes as mechanisms of pattern generation; (ii) identify the possible range of behaviour of real gene networks and (iii) suggest causal mechanisms to generate known patterns. The evolutionary implications are discussed.

Self-synchronization and task fulfilment in ant colonies.

Some authors have hypothesized that the observed self-synchronized activity in ant colonies provides some adaptive advantages, and, in particular, it has been suggested that task realization may benefit from this ordered temporal pattern of behaviour (Robinson, 1992, Ann. Rev. Entomol, 37, 637-702; Hatcher et al., 1992, Naturwissenschaften, 79, 32-34). In this paper, we use a model of self-synchronized activity (the fluid neural network) to suggest that with self-synchronized patterns of activity a task may be fulfiled more effectively than with non-synchronized activity, at the same average level of activity per individual.