Formation and electronic structure of an atypical Cu A site

PmoD, a recently discovered protein from methane-oxidizing bacteria, forms a homodimer with a dicopper CuA center at the dimer interface. Although the optical and electron paramagnetic resonance (EPR) spectroscopic signatures of the PmoD CuA bear similarities to those of canonical CuA sites, there are also some puzzling differences. Here we have characterized the rapid formation (seconds) and slow decay (hours) of this homodimeric CuA site to two mononuclear Cu2+ sites, as well as its electronic and geometric structure, using stopped-flow optical and advanced paramagnetic resonance spectroscopies. PmoD CuA formation occurs rapidly and involves a short-lived intermediate with a max of 360 nm. Unlike other CuA sites, the PmoD CuA is unstable, decaying to two type 2 Cu2+ centers. Surprisingly, NMR data indicate that the PmoD CuA has a pure σu∗ ground state rather than the typical equilibrium between σu∗ and πu of all other CuA proteins. EPR, ENDOR, ESEEM, and HYSCORE data indicate the presence of two histidine and two cysteine ligands coordinating the CuA core in a highly symmetrical fashion. This report significantly expands the diversity and understanding of known CuA sites.Fil: Ross, Matthew O.. Northwestern University; Estados UnidosFil: Fisher, Oriana S.. Northwestern University; Estados UnidosFil: Morgada, Marcos Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Krzyaniak, Matthew D.. Northwestern University; Estados UnidosFil: Wasielewski, Michael R.. Northwestern University; Estados UnidosFil: Vila, Alejandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Hoffman, Brian M.. Northwestern University; Estados UnidosFil: Rosenzweig, Amy C.. Northwestern University; Estados Unido

CVD-diamond-based thermocouple for high sensitive temperature measurements

The possibility to realize a high sensitive thermocouple by means of boron doped chemical vapour deposition (CVD) diamond was investigated. The thermoelectric power of p-type diamond, grown by plasma enhanced CVD was studied for films of electrical resistivity in the 0.2-40 Ω cm range in order to asses the dependence of thermocouple sensitivity on the doping level. The p-type diamond films were prepared by CH3OH + B2O3 vapour addition to a 1% CH4-H2 gas mixture during the growth. The conductive films were then tested tracing the I-V characteristic in order to study the conduction properties of the films. An appropriate experimental setup was built to evaluate the thermoelectric properties of the grown samples for different temperatures imposed between two ends of the samples. Firstly, the output voltage was measured maintaining a reference temperature of 273 K at one end and varying the second temperature between 275.5 and 360.5 K. A constant value of the temperature drop of 5 K was then used for an accurate evaluation of the thermoelectric properties of the diamond films for different value of the average temperature. The measurements provided values of thermoelectric power in the range 0.3-0.6 mV/K while conductivity increases. These values showed different decreasing behaviour with increasing temperature for different resistivity of the sample. In particular, more relevant changes in thermoelectric power were measured for high resistive sample

Extreme ultraviolet single-crystal diamond detectors by chemical vapor deposition

High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210-2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i. e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping-detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nm and He I 58.4 nm emission lines were clearly detected. The measured time response of 0.2 s is totally due to the instrumental readout time constants. In both experimental setups an extremely good stability and reproducibility of the device response were obtained, whereas no persistent photoconductivity nor undesirable pumping effects were observed

Analysis of traps in CVD diamond films through thermal depumping of nuclear detectors

Carrier free paths in chemical vapour deposition (CVD) diamond films depend on the presence of traps, which therefore strongly affect the performance of those CVD diamond based devices which rely on the electronic properties of the material, like radiation detectors. For the same reason, these devices can in turn be used as tools to study carrier dynamics. It is well known that some traps may be saturated by pre-irradiation with ionizing radiation (e.g. β-particles), a process called "pumping" or "priming". Not all traps behave in the same way. Due to the large bandgap of diamond, both shallow (not affected by pumping) and deep traps for electrons and holes may exist. We measured, using 5.5 MeV 241Am α-particles, the response of high quality CVD diamond based detectors after successive annealing steps performed at selected temperatures. The analysis of the decay of the detector efficiency with annealing time at several temperatures allows a quantitative evaluation of the activation energy of these defects. Two main trapping centres connected to the pumping process were found, both related to holes, having activation energies of about 1.6 eV and 1.3 eV respectivel

Synthesis and characterization of a single-crystal chemical-vapor-deposition diamond particle detector

The growth conditions and the detection properties of a homoepitaxial diamond film, deposited in Roma "Tor Vergata" University Laboratories by microwave chemical vapor deposition on a high-pressure high-temperature single-crystal substrate are reported. An energy resolution as low as 1.1% was achieved when irradiating the device with 5.5 MeV Am-241 α-particles. The dependence of the charge collection efficiency and the energy resolution on the applied voltage are reported as well. A clear saturation plateau was observed in both curves. Preliminary results with 14.8 MeV neutron irradiation are reported, showing a well separated C-12(n,α(0))Be-9 reaction peak

Thermal detrapping analysis of pumping-related defects in diamond

A method is presented to selectively characterize the traps involved in the pumping procedure of diamond films. The pumping process strongly reduces the concentration of active carrier trapping centers, leading to an enhancement of electronic properties of such material, and is obtained by irradiating the diamond films with ionizing radiation. Since the improved transport properties lead to an increased efficiency when diamond films are used as radiation detectors, valuable information on this process can be obtained by analyzing the response of diamond based particle detectors. For this purpose a high-quality diamond film was grown by microwave chemical vapor deposition and a particle detector was realized. Its response to a 5.5-MeV 241Am α-particles was measured after successive annealing steps performed at different temperatures in the 180-228°C range. Before each annealing curve at a given temperature, the detector was driven to the pumped state through β-particle irradiation. The efficiency versus annealing time curves evidence a thermally induced detrapping, confirming the pumping mechanism as a filling and consequent passivation of defects. The analysis of the decay time of the detector efficiency as a function of temperature allows the determination of the activation energy of these defects, which is Ea=1.62±0.15 e

Registro, clasificación y estudio de imágenes digitalizadas de resonancia magnética del cerebro humano (...) como complemento al estudio de modificaciones cerebrales relacionadas a la edad, el sexo y/o patología

Los valores de ángulos medidos en imágenes, entre ellas las de resonancia magnética del cerebro, son independientes del tamaño de la imagen. Esta propiedad permitiría determinar, en ambos sexos, variaciones con la edad y, eventualmente, la patología de zonas del cerebro involucradas. Cuando un ángulo varía significativamente en alguna de las condiciones anteriormente citadas sugiere que la modificación compromete la forma. Debido a que cada ángulo se traza entre reparos anatómicos confiables, perfectamente identificables en cada imagen, una variación significativa en la medida del ángulo es indicativa de variación de la posición de los reparos anatómicos en la superficie imagen del cerebro y, por lo tanto, de la zona cerebral que los incluye. Consecuentemente, una significativa variación de los ángulos con relación a límites de normalidad según sexo y edad podría aportar un dato de relevancia para el diagnóstico de patologías. Uno de los objetivos de este proyecto fue determinar el valor de dos ángulos correspondientes a la imagen del lóbulo parietal de los dos hemisferios en el mismo rango de edad en ambos sexos. Utilizando el programa Scion Image for Windows en imágenes parasagitales de resonancia magnética de 65 sujetos sin patología psiquiátrica ni neurológica, de ambos sexos y entre 41 y 60 años, se trazaron en cada hemisferio dos ángulos adyacentes sobre la superficie del lóbulo parietal, entre reparos anatómicos confiables. El vértice de los ángulos coincidía con el punto de intersección del borde dorsal del cuerpo calloso con la recta que pasa por los puntos más distantes del borde ventral del cuerpo calloso. Los lados de los ángulos cortaban a la imagen del borde del cerebro a nivel del límite del lóbulo frontal con el parietal y de este con el occipital. Para el procesamiento de datos se utilizó análisis de varianza (ANOVA). Los resultados mostraron que los ángulos homólogos no difieren significativamente entre sexos. Sin embargo, mediciones de longitud y de superficie de la zona indican que son mayores en el sexomasculino.Es necesario incrementar el número de casos para obtener valores controles confiables y compararlos con casos patológicos. Se concluye que la forma de la región estudiada en el rango de edades considerado es semejante en ambos sexos. Las variaciones de valores de los ángulos, independientemente del sexo, podrían ser de utilidad clínica en la búsqueda de señales de patología psiquiátrica y/ o neurológica.Angle values measured in images, including magnetic resonance imaging of the brain, are independent of image size. This property would determine, in both sexes, changes with age and eventually the pathology of brain areas involved. When an angle varies significantly in any of the above conditions suggests that compromises the form modification .Because each angle is plotted between reliable anatomic landmarks, identifiable in eachimage, a significant variation in the angle measure is indicative of variation of the position of the anatomic landmarks in the brain imaging surface and, therefore, the brain area that includes them. Consequently, a significant variation of angles relative to normal limits by sex and age could provide relevant information for diagnosis of diseases. One objective of this project was to determine the value of two angles corresponding to the image of the parietal lobe of both hemispheres at the same age in both sexes. Using the program Scion Image for Windows in parasagittal MRIs of 65 subjects without psychiatric or neurological disease, of both sexes and between 41 and 60 years, they were drawn in each hemisphere two adjacent angles on the surface of the parietal lobe between reliable anatomic landmarks. The apex angles coincide with the intersection point of the dorsal edge of the corpus callosum with the line passing through the most distant points of the ventral edge of the corpus callosum, the sides of the angles cut to the image edge brain level limit the frontal lobe with parietal and occipital it. For data processing analysis of variance (ANOVA) was used.The results showed that the homologous angles did not differ significantly between the sexes. However measurements of length and surface area indicate that are higher in males. It needs to increase the number of cases to obtain reliable values compared with controls and pathological cases. It is concluded that the shape of the region studied in the age range considered, it is similar in both sexes. Variations angle values, regardless of sex, could be clinically useful in the search for signs of psychiatric and / or neurological disorders

Low-cost technologies for arsenic removal in the Chaco-Pampean Plain, Argentina

Groundwater of the Chaco-Pampean plain of Argentina contains levels of arsenic (As) exceeding drinking water standards. The situation is more serious in rural areas, causing a high incidence of CERHA (Chronic Endemic Regional Hydroarsenicism). Results of treatment experiments involving either heterogeneous photocatalysis (HP) or zerovalent iron (ZVI) in plastic bottles to remove As from groundwater are presented as low-cost technologies to remove As. For HP tests, synthetic or natural samples containing As placed in bottles impregnated with a TiO2 layer and exposed to solar or artificial UV light followed by an addition of iron resulted in As concentration well below drinking water standards. For ZVI tests, iron wool was shown to be a better iron source than packing wire for As removal. Solar irradiation, in synthetic as well as in natural samples, improves As removal, avoiding the use of high amounts of iron

Distribution of electrically active defects in chemical vapor deposition diamond: Model and measurement

Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CVD) diamond films are located within the grains or in grain boundaries. Their geometrical distribution in the sample is different and is usually unknown. We present here a method to quantitatively evaluate the concentration and distribution of in-grain and grain-boundary located active carrier traps. Since the impact of these two kinds of defects on the performance of CVD diamond based devices is different, it is possible to obtain the defect distribution by measuring the response of diamond alpha particle detectors as a function of film thickness. The Hecht theory, describing the efficiency of a semiconductor particle detector, has been modified to take into account the polycrystalline nature of CVD diamond. This extended Hecht model was then used to fit experimental data and extract quantitative information about the defect distribution