Microscopic Theory, Analysis, and Interpretation of Conductance Histograms in Molecular Junctions

Molecular electronics break-junction experiments are widely used to investigate fundamental physics and chemistry at the nanoscale. Reproducibility in these experiments relies on measuring conductance on thousands of freshly formed molecular junctions, yielding a broad histogram of conductance events. Experiments typically focus on the most probable conductance, while the information content of the conductance histogram has remained unclear. Here, we develop a theory for the conductance histogram by merging the theory of force-spectroscopy with molecular conductance. To do so, we propose a microscopic model of the junction evolution under the modulation of external mechanical forces and combine it with the statistics of junction rupture and formation. Our formulation focuses on contributions to the conductance dispersion that emerge due to changes in the conductance during mechanical manipulation. The final shape of the histogram is determined by the statistics of junction rupture and formation. The procedure yields analytical equations for the conductance histogram in terms of parameters that describe the free-energy profile of the junction, its mechanical manipulation, and the ability of the molecule to transport charge. All physical parameters that define our microscopic model can be extracted from separate conductance and rupture force measurements on molecular junctions. Our theory accurately fits experimental conductance histograms and augments the information content that can be extracted from experiments. Further, the predicted behavior with respect to physical parameters can be used to design experiments with narrower conductance distribution and to test the range of validity of the model

Modeling the hot flow behavior of a Fe-22Mn-0.41C-1.6Al-1.4Si TWIP steel microalloyed with Ti, V and Nb

The present research work analyses the influence of Ti, V and Nb microalloying elements on the hot flow behavior of a high-Mn Twinning Induced Plasticity (TWIP) steel. For this purpose, flow curves were obtained by uniaxial hot compression tests performed at four strain rates (10(-1), 10(-2), 10(-3) and 10(-4) s(-1)) and three temperatures (900, 1000 and 1100 degrees C). The models of Estrin, Mecking and Berg-strom; Avrami and Tegart, and Sellars were applied to determine the hot working constants used to derive the constitutive equations describing the flow curves. The analysis of modeling parameters of the hot flow curves shows that Ti, V and Nb additions to TWIP steel generated slight increase in the peak stress (sigma(p)), retardation of the dynamic recrystallization (DRX) onset, particularly at low temperature, and decrease in the activation energy required to recrystallization (Q(t)). Likewise, the softening effect promoted by DRV and DRX was more evident at high temperatures and low strain rates. On the other hand, the resulting deformed microstructures, analyzed by the SEM-EBSD technique, showed that the most important refining effect on recrystallized austenitic grain was in the presence of V and Ti. The good agreement between the experimental and predicted hot flow curves demonstrated that the developed constitutive equations predict with reasonable accuracy the hot flow behavior of the studied TWIP steels. (C) 2015 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author's final draft

Accuracy of the tuberculosis point-of-care Alere determine lipoarabinomannan antigen diagnostic test using α-mannosidase treated and untreated urine in a cohort of people living with HIV in Guatemala

BACKGROUND: Improved point-of-care diagnostic tests for tuberculosis (TB) in severe immune suppressed people living with HIV (PLWH) are needed to decrease morbidity and mortality outcomes. The aim of the study is to evaluate the performance of the lipoarabinomannan antigen test (LAM-test) with and without α-mannosidase pre-treated urine in a cohort of PLWH in primary care clinics in Guatemala. We further determined TB incidence, and mortality rates and its risk factors in PLWH with TB symptoms. METHODS: Prospective longitudinal study of PLWH with TB symptoms. Urine samples were collected at 2 HIV sites to test the sensitivity of the LAM-test in urine with and without α-mannosidase pre-treatment. A composite reference standard of either a positive Mycobacterium tuberculosis complex culture and/or GeneXpert RESULTS: The overall sensitivity of the LAM-test was of 56.1% with 95% CI of (43.3-68.3). There were no differences in the LAM-test sensitivity neither by hospital nor by CD4 T cell values. LAM-test sensitivity in PLWH with \u3c 200 CD4 T cells/µl was of 62.2% (95% CI 46.5-76.2). There were no significant differences in sensitivity when comparing LAM-test results obtained from untreated vs. α-mannosidase treated urine [55.2% (95% CI 42.6-67.4) vs. 56.9% (95% CI 44-69.2), respectively]. TB incidence in our cohort was of 21.4/100 person years (PYs) (95% CI 16.6-27.6), and mortality rate was of 11.1/100 PYs (95% CI 8.2-15.0). Importantly, PLWH with a positive LAM-test result had an adjusted hazard ratio (aHR) of death of 1.98 (1.0-3.8) with a significant p value of 0.044 when compared to PLWH with a negative LAM-test result. CONCLUSIONS: In this study, α-mannosidase treatment of urine did not significantly increase the LAM-test performance, however; this needs to be further evaluated in a large-scale study due to our study limitations. Importantly, high rates of TB incidence and mortality were found, and a positive LAM-test result predicted mortality in PLWH with TB clinical symptoms

Sobre el impacto macroeconómico de los beneficios tributarios al capital

En este trabajo se cuantifica el impacto macroeconómico del beneficio tributario al capital establecido en Colombia en el 2003, en el contexto de un modelo de equilibrio general dinámico de previsión perfecta con oferta de trabajo endógena. Los ejercicios de calibración indican que hay ganancias importantes en términos de bienestar, acumulación de capital y empleo de fijar el beneficio tributario al capital de forma permanente, independientemente de cómo el gobierno reajuste su presupuesto. En el corto plazo, sin embargo, el impacto sobre el empleo y el producto depende de la forma en la que el gobierno financia el déficit generado por el beneficio tributario. Si las rigideces presupuestales obligan al gobierno a recurrir a impuestos distorsionantes sobre el consumo y/o el trabajo, el empleo y el producto caen en el corto plazo. Por el contrario, si el gobierno puede acudir a impuestos de suma fija para el cierre presupuestal, el empleo y el producto aumentan en el corto plazo. Se concluye que si bien el beneficio tributario al capital puede generar un efecto negativo sobre el empleo en el corto plazo, este efecto proviene del impacto negativo sobre la oferta de trabajo como consecuencia de la necesidad de financiar el beneficio con impuestos distorsionantes y no de un efecto sustitución en la demanda por trabajo, que es el efecto de corto plazo sobre el que se ha hecho énfasis en el debate de política.Beneficio tributario al capital, exenciones a la inversión, impuestos distorsionantes. Classification JEL: E2, E6, H2, H3.

Proporcionalidad en la designación de senadores por un parlamento autonómico

El Tribunal Constitucional desestima el recurso de amparo interpuesto por el Grupo Parlamentario Vox en el Parlamento de Cataluña contra el acuerdo de la Mesa de este, sobre la distribución del número de senadores que le corresponde designar proporcionalmente tras las elecciones al Parlamento de Cataluña de 2021. La Mesa aplica la fórmula Imperiali en el reparto de los ocho senadores a designar, entre los grupos parlamentarios, quedando excluido el recurrente, pero el Tribunal Constitucional no aprecia en tal decisión una vulneración de la adecuada representación proporcional que exige la Constitución, pues el eventual acuerdo de la Mesa no está limitado por la aplicación de una u otra regla concreta de proporcionalidad

El problema carcelario en el Departamento de Antioquia: apartes de una investigación

Con un criterio real y objetivo sobre la actualidad carcelaria en esta sección del País, intentamos la investigación, el análisis y la formulación de un plan de desarrollo con miras a resolver uno de los más serios interrogantes que afectan la estructura de la justicia en este Departamento. La observación directa, el acopio de datos y cifras obtenidas que se reflejan en forma alarmante, impresionan y con turban el ánimo de quien discurre por el intrincado laberinto de la cuestión carcelaria

Influence of Nb microaddition on microstructure and texture evolution in a Fe-21Mn-1.3Al-1.5Si-0.5C TWIP steel under uniaxial hot-tensile conditions

Advanced high-strength steels as Twinning Induced Plasticity (TWIP) steels have been developed using microalloying elements and subsequent thermo-mechanical processing techniques. Moreover, under hot-working conditions, these steels undergo significant microstructural changes as a result of preferred crystallographic orientation (texture) of grains. In order to evaluate this behavior, one non-microalloyed and other single Nb-microalloyed TWIP steels were melted in an induction furnace and cast into metal and sand molds. Samples with austenitic grain sizes between 400 and 2000 µm were deformed at 800 °C and strained at a constant strain rate of 10-3 s-1, and deformation state was examined by means of electron backscatter diffraction (EBSD) technique near to the fracture tip. It was found that non-microalloyed TWIP steel solidified in both metal and sand mold exhibits dynamically recrystallized grains. On the other hand, Nb microaddition has a strong influence in TWIP steel retarding the onset of recrystallization kinetics, showing low angle sub-structured grains. Furthermore, it was possible identifying the crystallographic orientation of grains using the inverse pole figures (IPF) and the orientation distribution function (ODF). Weak cube {001} recrystallization and E{111} ¿-fiber deformation textures components were detected.Peer ReviewedPostprint (author's final draft

Para recordar los inicios de la Ingeniería Biomédica en Antioquia

Por solicitud de mi querido discípulo en Ingeniería Biomédica de la Escuela de Ingeniería de Antioquia y del CES, el ingeniero Juan Carlos Ramírez Giraldo, para escribir un artículo sobre la Ingeniería Biomédica en nuestro medio, me propongo ahora transcribir una corta entrevista que fue realizada en 1972

Ruralidad en Colombia

Desde la llegada de Colón a América se inicia el conflicto de la tenencia de la tierra con el enfrentamiento entre los españoles y los indígenas y la falta de alimentos. Felipe II en 1573 establece las primeras leyes sobre la tenencia de la tierra en América. Desde la Independencia, la Colombia rural ha sido víctima de inseguridad, inequidad y desconocimiento de los gobiernos de turno. La tenencia de la tierra ha sido el argumento, desde el siglo pasado, como generadora de la inequidad social, el descontento y la violencia, sin analizar la causa de esta mala distribución. Sin embargo, no todo es negativo: se resalta la pacificación de lo rural con la presión militar contra las fuerzas irregulares, guerrilla y paramilitares en los últimos años; el gobierno actual, que le apunta al desarrollo agropecuario como una de las locomotoras para el progreso; y la Universidad de La Salle, que concentra todos sus esfuerzos en lo rural y para lo rural, gran ejemplo es el proyecto Utopía ubicado en los Llanos Orientales de Colombia