Entropy-driven phases at high coverage adsorption of straight rigid rods on two-dimensional square lattices.

Polymers are frequently deposited on different surfaces, which has attracted the attention of scientists from different viewpoints. In the present approach polymers are represented by rigid rods of length k (k-mers), and the substrate takes the form of an L×L square lattice whose lattice constant matches exactly the interspacing between consecutive elements of the k-mer chain. We briefly review the classical description of the nematic transition presented by this system for k≥7 observing that the high-coverage (θ) transition deserves a more careful analysis from the entropy point of view. We present a possible viewpoint for this analysis that justifies the phase transitions. Moreover, we perform Monte Carlo (MC) simulations in the grand canonical ensemble, supplemented by thermodynamic integration, to first calculate the configurational entropy of the adsorbed phase as a function of the coverage, and then to explore the different phases (and orientational transitions) that appear on the surface with increasing the density of adsorbed k-mers. In the limit of θ→1 (full coverage) the configurational entropy is obtained for values of k ranging between 2 and 10. MC data are discussed in comparison with recent analytical results [D. Dhar and R. Rajesh, Phys. Rev. E 103, 042130 (2021)2470-004510.1103/PhysRevE.103.042130]. The comparative study allows us to establish the applicability range of the theoretical predictions. Finally, the structure of the high-coverage phase is characterized in terms of the statistics of k×l domains (domains of l parallel k-mers adsorbed on the surface). A distribution of finite values of l (l≪L) is found with a predominance of k×1 (single k-mers) and k×k domains. The distribution is the same in each lattice direction, confirming that at high density the adsorbed phase goes to a state with mixed orientations and no orientational preference. An order parameter measuring the number of k×k domains in the adsorbed layer is introduced.

Alternative characterization of the nematic transition in deposition of rods on two-dimensional lattices.

We revisit the problem of excluded volume deposition of rigid rods of length k unit cells over square lattices. Two new features are introduced: (a) two new short-distance complementary order parameters, called Π and Σ, are defined, calculated, and discussed to deal with the phases present as coverage increases; (b) the interpretation is now done beginning at the high-coverage ordered phase which allows us to interpret the low-coverage nematic phase as an ergodicity breakdown present only when k≥7. In addition the data analysis invokes both mutability (dynamical information theory method) and Shannon entropy (static distribution analysis) to further characterize the phases of the system. Moreover, mutability and Shannon entropy are compared, and we report the advantages and disadvantages they present for their use in this problem.

Phase transitions in a system of long rods on two-dimensional lattices by means of information theory.

The orientational phase transitions that occur in the deposition of longitudinal polymers of length k (in terms of lattice units) are characterized by information theory techniques. We calculate the absolute value of an order parameter δ, which weights the relative orientations of the deposited rods, which varies between 0.0 (random orientation) and 1.0 (fully oriented in either of the two equivalent directions in an L×L square lattice). A Monte Carlo (MC) algorithm is implemented to induce a dynamics allowing for accommodation of the rods for any given density or coverage θ (ratio of the occupied sites over all the sites in the lattice). The files storing δ(t) (with time t measured in MC steps) are then treated by data recognizer wlzip based on data compressor techniques yielding the information content measured by a parameter η(θ). This allows us to recognize two maxima separated by a well-defined minimum for η(θ) provided k≥7. The first maximum is associated with an isotropic-nematic (I-N) phase transition occurring at intermediate density, while the second maximum is associated with some kind of nematic-isotropic transition at high coverage. In the cases of k<7, the curves for η(θ) are almost constant, presenting a very broad maximum which can hardly be associated with a phase transition. The study varies L and k, allowing for a basic scaling of the found critical densities towards the thermodynamic limit. These calculations confirm the tendency obtained by different methods in the case of the intermediate-density I-N phase transition, while this tendency is established here in the case of the high-density phase transition.

Age and gender differences in Clostridium difficile-related hospitalization trends in Madrid (Spain) over a 12-year period.

This study aimed to analyze temporal trends by gender and age in Clostridium difficile infection (CDI)-related hospitalization rates in the Autonomous Community of Madrid (Spain) over a 12-year period. A population-based cross-sectional study of all hospital admissions with a CDI diagnosis from 2003 to 2014 was carried out. Annual age-specific hospitalization rates were calculated by gender. All the analyses were performed separately for total hospitalizations and hospitalizations with CDI as the primary diagnosis. Joinpoint regression models were used to analyze time trends. A total of 13,526 hospital discharges were identified (26.8 % with CDI as the primary diagnosis). In both sexes, a gradient in age-specific rates was observed, ranging in 2014 from 5.92 hospitalizations per 100,000 person-years in patients <15 years of age to 378.96 in patients ≥85 years of age. Since 2009, in the age group of 15-44 years, both men and women presented an increasing trend of around 18 %. A significantly increasing trend was detected in women of age 45-84 years, with an estimated annual percentage of change of 7.6 % in the age group of 45-64 years, and rounding with 4.5 % in the age group of 65-84 years. In men of age 45-64 years, the average annual percentage of increase was 4.7 %, and it was 21.1 % between 2010 and 2014 in the age group of 65-74 years. No trends were identified in the 85 years and over age group. Surveillance methods to assess trends by age group should be implemented. Preventive and therapeutic initiatives should remain a priority.

La infeccion tuberculosa del sistema nervioso central: en el centro Hospitalario San Juan de Dios de Bogota (1975-1986) estudio de 86 casos / Tuberculosis infection of the central nervous system: at the Centro Hospitalario San Juan de Dios de Bogota (1975-1986) study of 86 cases

Este es el segundo estudio de la infeccion tuberculossa del sistema nervioso central (SNC) del Centro Hospitalario San Juan de Dios de Bogota, realizado en el periodo 1975-1986 y comprende 86 casos. El primer estudio correspondio al periodo 1960-1974 con 165 casos. Las formas clinicas se clasificaron en 3 grupos: meningoencefaliticas, espinales y lesiones expansivas intracraneanas. El diagnostico se confirmo por uno o varios de los siguientes hechos: el aislamiento del bacilo tuberculoso en el liquido cefalorraquideo (LCR), los hallazgos histopatologicos a nivel del SNC en los casos autopsiados, la respuesta favorable al tratamiento tuberculostatico cuando se realizo, o la presencia de tuberculosis extraneural asociada a un LCR sugestivo de meningitis cronica. Se hace enfasis en que persiste la alta incidencia de la enfermedad en esta institucion; la mortalidad global fue del 58% pero disminuyo al 33% en el grupo de los pacientes que recibieron un tratamiento temprano. Se llama la atencion sobre los hallazgos tomograficos como factores de pronostico y de seguimiento. Ademas se recalca la necesidad de tener medios diagnostico rapidos, sensibles y especificos como la deteccion de antigenos del bacilo tuberculoso en el LCR.

Histoplasmosis: experiencia del Hospital San Juan de Dios de Bogota, 1954-1986 / Histoplasmosis: experience in Hospital San Juan de Dios, Bogota, 1954-1986

Se estudiaron 7 casos de histoplasmosis, 3 en hombres y 4 en mujeres, con edades promedio de 31.5 anos (rango entre 11 y 50 anos), cuatro de los cuales prevenian de areas rurales (55.5%). En dos pacientes asintomaticos el diagnostico se hizo casualmente por la realizacion de radiografias de torax de rutina y se comprobo posteriormente con el material resecado quirurgicamente. No requirieron tratamiento farmacologico especifico. Entre los pacientes sintomaticos las manifestaciones clinicas variaron entre cuadros leves, moderadas y severas. Un paciente presento ulcera en la lengua como unica manifestacion y el tratamiento requerido fue la extirpacion total de la lesion. Dos pacientes manifestaron formas moderadas de la enfermedad por meningitis cronicas diagnosticadas por pruebas serologicas y de fijacion del complemento. Sus manifestaciones fueron principalmente alteraciones de conducta, comportamiento inapropiado, deterioro intelectual, episodios psicoticos, anisocoria y alteraciones de la marcha. En una paciente se realizo tratamietno con anfotericina B sin exito y la otra fallecio despues de derivacion ventriculo-atrial efectuada en otra institucion, la cual probablemente disemino la enfermedad. Dos pacientes manifestaron formas severas de la enfermedad por histoplasmosis generalizada. Uno de ellos fallecio y otro presento ascitis. Se hace revision del tema incluyendo aspectos historicos, epidemiologicos, patologicos, clinicos y de diagnostico