Martian sub-surface ionising radiation: biosignatures and geology

The surface of Mars, unshielded by thick atmosphere or global magnetic field, is exposed to high levels of cosmic radiation. This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation is of prime astrobiological interest. Here, we present modelling results of the absorbed radiation dose as a function of depth through the Martian subsurface, suitable for calculation of biomarker persistence. A second major implementation of this dose accumulation rate data is in application of the optically stimulated luminescence technique for dating Martian sediments. <br><br> We present calculations of the dose-depth profile in the Martian subsurface for various scenarios: variations of surface composition (dry regolith, ice, layered permafrost), solar minimum and maximum conditions, locations of different elevation (Olympus Mons, Hellas basin, datum altitude), and increasing atmospheric thickness over geological history. We also model the changing composition of the subsurface radiation field with depth compared between Martian locations with different shielding material, determine the relative dose contributions from primaries of different energies, and discuss particle deflection by the crustal magnetic fields

Fluorescence characterization of clinically-important bacteria

Healthcare-associated infections (HCAI/HAI) represent a substantial threat to patient health during hospitalization and incur billions of dollars additional cost for subsequent treatment. One promising method for the detection of bacterial contamination in a clinical setting before an HAI outbreak occurs is to exploit native fluorescence of cellular molecules for a hand-held, rapid-sweep surveillance instrument. Previous studies have shown fluorescence-based detection to be sensitive and effective for food-borne and environmental microorganisms, and even to be able to distinguish between cell types, but this powerful technique has not yet been deployed on the macroscale for the primary surveillance of contamination in healthcare facilities to prevent HAI. Here we report experimental data for the specification and design of such a fluorescence-based detection instrument. We have characterized the complete fluorescence response of eleven clinically-relevant bacteria by generating excitation-emission matrices (EEMs) over broad wavelength ranges. Furthermore, a number of surfaces and items of equipment commonly present on a ward, and potentially responsible for pathogen transfer, have been analyzed for potential issues of background fluorescence masking the signal from contaminant bacteria. These include bedside handrails, nurse call button, blood pressure cuff and ward computer keyboard, as well as disinfectant cleaning products and microfiber cloth. All examined bacterial strains exhibited a distinctive double-peak fluorescence feature associated with tryptophan with no other cellular fluorophore detected. Thus, this fluorescence survey found that an emission peak of 340nm, from an excitation source at 280nm, was the cellular fluorescence signal to target for detection of bacterial contamination. The majority of materials analysed offer a spectral window through which bacterial contamination could indeed be detected. A few instances were found of potential problems of background fluorescence masking that of bacteria, but in the case of the microfiber cleaning cloth, imaging techniques could morphologically distinguish between stray strands and bacterial contamination

Sesgos y estrategias para la comparación de fracciones reveladas por análisis de grupos en segundo ciclo básico

Aprender fracciones es un desafío matemático considerable del segundo ciclo de enseñanza básica. Los estudiantes muchas veces usan, intuitivamente, sesgos y estrategias para la realización de tareas como la comparación de fracciones. En el presente trabajo, investigamos la variedad de sesgos y estrategias usadas por 490 estudiantes de segundo ciclo básico para responder a una tarea computarizada de comparación de fracciones. Los resultados promedio indican la presencia de un fuerte sesgo hacia razonar basados sólo en los numeradores y denominadores de las fracciones. Los resultados de un análisis de grupos complejizan esto, revelando que el razonamiento sesgado es sólo uno de al menos cinco diversos modos de razonar en la comparación de fracciones. Finalmente, argumentamos que el descubrimiento de estas diferencias entre grupos de estudiantes es una contribución tanto para la investigación como para la práctica pedagógica

Conjugacy of one-dimensional one-sided cellular automata is undecidable

Two cellular automata are strongly conjugate if there exists a shift-commuting conjugacy between them. We prove that the following two sets of pairs $(F,G)$ of one-dimensional one-sided cellular automata over a full shift are recursively inseparable: (i) pairs where $F$ has strictly larger topological entropy than $G$, and (ii) pairs that are strongly conjugate and have zero topological entropy. Because there is no factor map from a lower entropy system to a higher entropy one, and there is no embedding of a higher entropy system into a lower entropy system, we also get as corollaries that the following decision problems are undecidable: Given two one-dimensional one-sided cellular automata $F$ and $G$ over a full shift: Are $F$ and $G$ conjugate? Is $F$ a factor of $G$? Is $F$ a subsystem of $G$? All of these are undecidable in both strong and weak variants (whether the homomorphism is required to commute with the shift or not, respectively). It also immediately follows that these results hold for one-dimensional two-sided cellular automata.Comment: 12 pages, 2 figures, accepted for SOFSEM 201

Las creencias sobre el conocimiento y sus efectos sobre desempeños específicos: el caso de las fracciones en matemática

Se exponen los resultados preliminares de un estudio de desempeño en tareas de comparación de fracciones y la posible influencia que las creencias epistemológicas de dominio general pueden tener sobre él. Se aplicó un cuestionario basado en el Inventario de Creencias Epistemológicas (EBI) a 57 sujetos de entre 18 y 25 años, y luego se les presentó un test de 180 ítems de comparación de fracciones. El objetivo fue revisar de qué manera las creencias acerca de la naturaleza y adquisición del conocimiento se relacionaban con el desempeño en dominios específicos de la matemática. Los resultados sugieren un efecto de las creencias acerca de la estructura del conocimiento, dado que los sujetos más cercanos al polo ingenuo en dicha dimensión son quienes obtienen, además, los resultados más bajos en todos los tipos de ítems de la tarea de comparación de fracciones

“Cuántos trozos le faltan”– Uso de estrategias de resta para la comparación de fracciones

La tarea matemática de comparación de fracciones engloba una multitud de procesos cognitivos y estrategias posibles de resolución. Estas estrategias no se limitan a aquéllas enseñadas en la escuela, sino que incluyen también varias desarrolladas espontáneamente por los estudiantes. Una de ellas es la de “razonamiento por gap”, donde se evalúa indirectamente el tamaño de una fracción a partir del número de trozos que a ésta le falta para “completar el entero”. Esta estrategia es matemáticamente incorrecta, pero permite obtener respuestas correctas en una gran cantidad de problemas de comparación de fracciones. En esta comunicación, presentamos datos preliminares de una muestra de adultos jóvenes (N=61) quienes contestaron un cuestionario de comparación mental de fracciones diseñado para evidenciar el uso de esta estrategia. Los resultados muestran que el desempeño es significativamente modulado por la utilidad del razonamiento por gap, sugiriendo que los participantes consideran esta dimensión al menos implícitamente. Discutimos implicancias de estos resultados para la enseñanza de las fracciones

Constraints on a potential aerial biosphere on Venus: II. Ultraviolet radiation

Despite the harsh conditions in the atmosphere of Venus, the possibility for an aerial habitable zone exists. A thermal habitable zone is predicted to exist at an altitude range of 62 to 48 km, above which temperatures drop below the lower thermal limit of cell growth and below which temperatures exceed the evaporation temperature. Many biocidal factors must be considered for the complete definition of an aerial habitable zone; in this study we consider the constraint specifically from the perspective of biocidal solar ultraviolet (UV) intensity in the atmosphere. We simulated the penetration of solar ultraviolet and visible light through the atmosphere using a radiative transfer model, to determine the spectral environment (and thus the UV biocidal effect) as a function of altitude in the atmosphere of Venus. At the top of the thermal aerial habitable zone (62 km) the incoming solar irradiance creates a severely challenging UV environment, with extremophiles such as Deinococcus radiodurans expected to be able to endure these UV conditions for approximately 80 s. At an altitude of around 59 km the biologically-weighted UV irradiance drops below that calculated for the Archean Earth, and continues to fall with decreasing altitude until at 54 km it is less than that found currently at the surface of Earth. Crucially, longer wavelength photosynthetically active light continues to penetrate to these altitudes and below, resulting in a solar radiation environment in the venusian atmosphere below around 54 km that screens biologically-damaging UV radiation yet permits the process of photosynthesis. Whilst not claiming to suggest the existence of an aerial habitable zone in general, by considering thermal conditions, ionising radiation and the UV flux environment of the venusian cloud deck alone, we define a potential habitable zone that extends from 59 km to 48 km. This region should form the focus of future remote and in situ astrobiological investigations of Venus

Limit laws of entrance times for low complexity Cantor minimal systems

This paper is devoted to the study of limit laws of entrance times to cylinder sets for Cantor minimal systems of zero entropy using their representation by means of ordered Bratteli diagrams. We study in detail substitution subshifts and we prove these limit laws are piecewise linear functions. The same kind of results is obtained for classical low complexity systems given by non stationary ordered Bratteli diagrams

Doing Gender Online : Digital Spaces for Identity Politics

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