Phenolics, depsides and triterpenes from the chilean lichen pseudocyphellaria nudata (zahlbr.) D.J. Galloway

Indexación: ScieloThe lichen Pseudocyphellaria nudata is a species endemic to southern South América. From the lichen tallus, methyl orsellinate, 2-methoxy-3,6-dimethyl-4-hydroxybenzaldehyde, methyl-evernate, tenuiorin, hopan-6ß,22-diol and hopan-6α,76,22-triol were isolated and identified as the main lichen constituents. This is the first report of the occurrence of 2-methoxy-3,6-dimethyl-4-hydroxybenzaldehyde in lichens.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=s0717-97072008000300017&nrm=is

Vegetation density as deduced from ERTS-1 MSS response

Reflectance from vegetation increases with increasing vegetation density in the 0.75- to 1.35 micron wavelength interval. Therefore, ERTS-1 bands 6 (0.7 to 0.8 micron) and 7 (0.8 to 1.1 micron) contain information that should relate to the probable yield of crops and the animal carrying capacity of rangeland. The results of an experiment designed specifically to test the relations among leaf area index (LAI), plant population, plant cover and plant height, and the ERTS-1 MSS responses for 3 corn, 10 sorghum, and 10 cotton fields are given. Plant population was as useful as LAI for characterizing the sorghum and corn fields, and plant height was as good as LAI for characterizing cotton fields. These findings generally support the utility of ERTS-1 data for explaining variability in green biomass, harvestable forage and other indicators of productivity

A new fluorescence reaction in DNA cytochemistry: Microscopic and spectroscopic studies on the aromatic diamidino compound M&B 938

We describe the fluorescence properties and cytochemical applications of the aromatic diamidine M&B 938. Treatment of cell smears (chicken blood, Ehrlich ascites tumor, rat bone marrow, mouse mast cells, and Trypanosoma cruzi epimastigotes) with aqueous solutions of M&B 938 (0.5–1 μg/ml at pH 6–7; UV excitation) induced bright bluish-white fluorescence in DNA-containing structures (interphase and mitotic chromatin, AT-rich kinetoplast DNA of T. cruzi), which was abolished by previous DNA extraction. DNA was the unique fluorescent polyanion after staining with M&B 938 at neutral or alkaline pH, other polyanions such as RNA and heparin showing no emission. M&B 938-stained mouse metaphase chromosomes revealed high fluorescence of the AT-rich centromeric heterochromatin, and strong emission of heterochromatin in human chromosomes 1, 9, 15, 16, and Y was found after distamycin A counterstaining. On agarose gel electrophoresis, M&B 938-stained DNA markers appeared as fluorescent bands. The 1.635-kBP fragment from DNA ladder revealed a higher emission value than that expected from linear regression analysis. Spectroscopic studies showed bathochromic and hyperchromic shifts in the absorption spectrum of M&B 938 complexed with DNA, as well as strong enhancement of fluorescence at 420 nm. In the presence of poly(dA)-poly(dT), the emission of M&B 938 was 4.25-fold higher than with DNA; no fluorescence was observed with poly(dG)-poly(dC). Experimental results and considerations of the chemical structure suggest that the minor groove of AT regions of DNA could be the specific binding site for M&B 938, which shows interesting properties and useful applications as a new DNA fluorochrome

Low power consumption mini rotary actuator with SMA wires

Shape memory alloys (SMAs) are smart materials widely used as actuators for their high power to weight ratio despite their well-known low energy efficiency and limited mechanical bandwidth. For robotic applications, SMAs exhibit limitations due to high power consumption and limited stroke, varying from 4% to 7% of the total length. Hysteresis, during the contraction and extension cycle, requires a complex control algorithm. On the positive side, the small size and low weight are eminently suited for the design of mini actuators for robotic platforms. This paper describes the design and construction of a light weight and low power consuming mini rotary actuator with on-board contact-less position and force sensors. The design is specifically intended to reduce (i) energy consumption, (ii) dimensions of the sensory system, and (iii) provide a simple control without any need for SMA characterisation. The torque produced is controlled by on-board force sensors. Experiments were performed to investigate the energy consumption and performance (step and sinusoidal angle profiles with a frequency varying from 0.5 to 10 Hz and maximal amplitude of 15?). We describe a transient capacitor effect related to the SMA wires during the sinusoidal profile when the active SMA wire is powered and the antagonist one switched-off, resulting in a transient current time varying from 300 to 400 ms

Pair-induced spectral changes and variability in compact X-ray sources

Inverse Compton scattering of ultraviolet photons by GeV electrons produces γ-rays which in turn create electron–positron pairs if the source is sufficiently compact. The pairs modify the emergent radiation spectrum through their own inverse Compton scattering and through thermal Comptonization after they have cooled to sub-relativistic temperatures. Recent calculations of spectral reprocessing under these conditions are extended to situations in which the Thomson optical depth of the pair plasma exceeds unity, and to demonstrate time-dependent behaviour explicitly. The relevance of our results to X-ray observations of active galactic nuclei, binary X-ray sources and γ-ray bursters is discussed briefly

Resolución de problemas científicos escolares y promoción de competencias de pensamiento científico. ¿Qué piensan los docentes de química en ejercicio?

In the article the results of an investigation conducted within the framework of the project FONDECYT 1070795 are exposed. The aims of the research were to identify and characterize the representations and knowledge that teachers in service have, from an average level of education, with respect to the competences of scientific thought and problem solution, and the way in which both should be approached. With the use of an intentional sample of 133, teachers selected from a total of 117 who were incorporated to other phases of the research trough the administration of a questionnaire especially designed, was show the predominance of a very fragmented image, sometimes contradictory, about the solution of problems and about relation between competences of scientific thought; this representation incorporates aspects of great value for the formation of the competent students, and at the same time it includes other aspects that in no way favor this formation, according to the present assessments. It is remarkable that both competences for scientific thought and solution of problems are not constituted as a totality and coherent system in the thinking of the teachers who participated in the research. It should be pointed out that we found data that show an oscillating valuation of the subjective character of the problematic situations and the problem itself; these data show, as well, that teachers give a very important role to language. It is stated that teachers give an oscillating value to the fact that students must deal with theories. It should be noted too that their approaches to the algorithmic processes are very vague, and sometimes contradictory.En el artículo se exponen los resultados de una investigación realizada en el marco del proyecto FONDECYT 1070795, cuyo objetivo consistió en identificar y caracterizar las nociones que tienen los profesores de nivel medio respecto a las competencias de pensamiento científico y solución de problemas, y la manera en que ambos deben trabajarse en la enseñanza de la química. Con el empleo de una muestra intencional de 33 profesores, seleccionados de un total de 117 que se incorporaron a otras fases de la investigación y mediante la administración de un cuestionario especialmente diseñado, se logró poner de manifiesto que en ellos predomina una imagen fragmentada y a veces contradictoria de la solución de problemas y de las competencias de pensamiento científico; dicha representación incorpora aspectos de inestimable valor para la formación del estudiante competente, a la vez que incluye otros que en manera alguna favorecen dicha formación en correspondencia con las exigencias actuales. Es notable que competencias de pensamiento científico y solución de problemas no se constituyan como sistema totalmente coherente en la conceptualización de los profesores investigados. Como dato relevante, se constató la oscilante valoración del carácter subjetivo de las situaciones problémicas y los problemas; junto al papel importante que, en opinión de gran parte de los profesores, desempeña el lenguaje, se le otorga un valor oscilante al trabajo con la teoría por parte de los estudiantes; igualmente resulta difusa, y a veces contradictoria, su aproximación a los procesos de algoritmización

Resolución de problemas científicos escolares y promoción de competencias de pensamiento científico. ¿Qué piensan los docentes de química en ejercicio?

En el artículo se exponen los resultados de una investigación realizada en el marco del proyecto FONDECYT 1070795, cuyo objetivo consistió en identificar y caracterizar las nociones que tienen los profesores de nivel medio respecto a las competencias de pensamiento científico y solución de problemas, y la manera en que ambos deben trabajarse en la enseñanza de la química. Con el empleo de una muestra intencional de 33 profesores, seleccionados de un total de 117 que se incorporaron a otras fases de la investigación y mediante la administración de un cuestionario especialmente diseñado, se logró poner de manifiesto que en ellos predomina una imagen fragmentada y a veces contradictoria de la solución de problemas y de las competencias de pensamiento científico; dicha representación incorpora aspectos de inestimable valor para la formación del estudiante competente, a la vez que incluye otros que en manera alguna favorecen dicha formación en correspondencia con las exigencias actuales. Es notable que competencias de pensamiento científico y solución de problemas no se constituyan como sistema totalmente coherente en la conceptualización de los profesores investigados. Como dato relevante, se constató la oscilante valoración del carácter subjetivo de las situaciones problémicas y los problemas; junto al papel importante que, en opinión de gran parte de los profesores, desempeña el lenguaje, se le otorga un valor oscilante al trabajo con la teoría por parte de los estudiantes; igualmente resulta difusa, y a veces contradictoria, su aproximación a los procesos de algoritmización.In the article the results of an investigation conducted within the framework of the project FONDECYT 1070795 are exposed. The aims of the research were to identify and characterize the representations and knowledge that teachers in service have, from an average level of education, with respect to the competences of scientific thought and problem solution, and the way in which both should be approached. With the use of an intentional sample of 133, teachers selected from a total of 117 who were incorporated to other phases of the research trough the administration of a questionnaire especially designed, was show the predominance of a very fragmented image, sometimes contradictory, about the solution of problems and about relation between competences of scientific thought; this representation incorporates aspects of great value for the formation of the competent students, and at the same time it includes other aspects that in no way favor this formation, according to the present assessments. It is remarkable that both competences for scientific thought and solution of problems are not constituted as a totality and coherent system in the thinking of the teachers who participated in the research. It should be pointed out that we found data that show an oscillating valuation of the subjective character of the problematic situations and the problem itself; these data show, as well, that teachers give a very important role to language. It is stated that teachers give an oscillating value to the fact that students must deal with theories. It should be noted too that their approaches to the algorithmic processes are very vague, and sometimes contradictory