588 research outputs found
A novel crystal growth technique from the melt: Levitation-Assisted Self-Seeding Crystal Growth Method
No full textA Report on Literature Search and Archaeological Survey in the Vicinity of Point Comfort, Calhoun County, Texas
No full textDuring May 1979, archaeologists from the Center for Archaeological Research, The University of Texas at San Antonio, conducted literature research and an archaeological field survey of an area to be developed by the Formosa Plastic Company near Point Comfort, Calhoun County, Texas.
The field and literature survey was done under contract between the Center for Archaeological Research (UTSA) and the Pace Company of Houston, Texas. In this report, the results of the field survey are presented by Thomas C. Kelly, Research Associate of the Center; the literature review was prepared by Herbert Uecker, Technical Staff Assistant. All project work was done under the supervision of Dr. Thomas R. Hester, Director of the Center, and Mr. Jack D. Eaton, Assistant Director
A report on literature search and archaeological survey in the vicinity of Point Comfort, Calhoun County, Texas
No full textDuring May 1979, archaeologists from the Center for Archaeological Research, The University of Texas at San Antonio, conducted literature research and an archaeological field survey of an area to be developed by the Formosa Plastic Company near Point Comfort, Calhoun County, Texas. The field and literature survey was done under contract between the Center for Archaeological Research (UTSA) and the Pace Company of Houston, Texas. In this report, the results of the field survey are presented by Thomas C. Kelly, Research Associate of the Center; the literature review was prepared by Herbert Uecker, Technical Staff Assistant. All project work was done under the super-vision of Dr. Thomas R. Hester, Director of the Center, and Mr. Jack D. Eaton, Assistant Director.Formosa Plastic Compan
Effects of the Li-evaporation on the czochralski growth of gamma-LiAlO2
No full textTwo-inch-diameter gamma-LiAlO2 single crystals were grown from the melt by Czochralski method. The crystals were examined by optical methods, high-resolution X-ray diffraction and transmission electron microscopy (TEM). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the Li/Al ratio in the residual melts. The Li-evaporation from both melt and grown crystal is the main problem in the gamma-LiAlO2 growth and has to be controlled by acting on the vertical temperature gradient. Shallow gradients increase the Li-evaporation from the crystal surface resulting in boules with a milky rim. On the other hand, steep gradients may induce cracks in the boule and enhance the Li2O escape from melt with consequent variation of the composition. ICP-OES investigations reveal that melt compositions can vary in the range from 46.5 to 50mol% Li2O to obtain transparent LiAlO2 crystals. Beyond this value, the formation of inclusions inside the crystals is probable. We have established an optimized growth assembly, which allows remaining the melt composition stoichiometric. The as-grown crystals exhibit defects like subgrains, twins and a core of voids and fine-grained inclusions. The latter could be characterized by TEM as submicron LiAl5O8 crystallites. (c) 2007 Elsevier B.V. All rights reserved
Czochralski growth of Ti:Sapphire laser crystals
No full textThe laser efficiency of Ti3+:Al2O3 (Ti:Sapphire) is affected by residual absorption in the infrared region (800 nm) of the laser emission caused by Ti3+-Ti4+ pairs. Consequently, the ratio of the absorption coefficients at pump wavelength and at maximum of residual absorption forms the most important figure of merit (FoM) of Ti:Sapphire laser crystals. In general, to achieve sufficient FoM commercial Ti;Sapphire crystals are subject to a post-growth annealing under strongly reducing atmosphere to shift the balance between Ti3+ and Ti 4+ ions in favour of the former ion. However, due to the low diffusion velocities under these conditions, this process is very time-consuming, especially for larger crystals. To save this step the crystal growth process of Ti:Sapphire was performed in a special gas mixture to stabilize the Ti3+ ions during the growth. The stability range of Ti3+ at growth temperature was estimated on the basis of thermodynamic equilibrium calculations. Ti3+ ions exist at about 2050 °C only in very small "window" regarding the oxygen partial pressure. This "window" remains very small during cooling too. To meet these conditions, i.e. to create the optimum growth atmosphere the oxygen partial pressure of different gas mixtures was calculated. That way a gas mixture was found which allowed the growth of Ti:Sapphire crystals with diameter up to 55 mm and a FoM > 100 without subsequent annealing. Under these conditions the formation of aluminium suboxides and therewith of oxygen which can be trapped in the crystal as gaseous inclusions was suppressed efficiently
Physics-based Reconstruction Methods for Magnetic Resonance Imaging
No full textConventional Magnetic Resonance Imaging (MRI) is hampered by long scan times
and only qualitative image contrasts that prohibit a direct comparison between
different systems. To address these limitations, model-based reconstructions
explicitly model the physical laws that govern the MRI signal generation. By
formulating image reconstruction as an inverse problem, quantitative maps of
the underlying physical parameters can then be extracted directly from
efficiently acquired k-space signals without intermediate image reconstruction
-- addressing both shortcomings of conventional MRI at the same time. This
review will discuss basic concepts of model-based reconstructions and report
about our experience in developing several model-based methods over the last
decade using selected examples that are provided complete with data and code.Comment: 8 figures, review accepted to Philos. Trans. R. Soc.
Estudios epidemiológicos y de patogenicidad de Monosporascus cannonballus Pollack et Uecker
No full textEl ascomiceto Monosporascus cannonballus Pollack et Uecker es uno de los principales hongos asociados al síndrome del "colapso", que afecta al cultivo de cucurbitáceas en España y otros países. Las ascosporas son el inóculo principal del hongo, quedando en el suelo tras la descomposición de las raíces afectadas, pudiendo ser extraídas del suelo mediante un proceso físico, que permite su cuantificación a lo largo del tiempo. Basándose en esta técnica, se han realizado varios estudios epidemiológicos que han permitido obtener resultados innovadores.
Se ha estudiado la dinámica poblacional de las ascosporas de M. cannonballus en suelos con diferentes condiciones hídricas y de cultivo. En campos con cultivo de melón, se ha observado que el nivel de ascosporas alcanza un máximo siete meses después de la plantación (3-4 meses después del final del cultivo), para ir disminuyendo después progresivamente, hasta llegar a niveles similares a los iniciales a los doce meses de la plantación. En campos con encharcamiento invernal, se ha observado un descenso progresivo del nivel de ascosporas, constatando que éstas pueden sobrevivir en suelo al menos por un periodo de tres años, sin haber perdido su infectividad. M. cannonballus ha sido considerado como un hongo termófilo, típico de zonas desérticas y semiáridas; en este estudio se ha demostrado que es capaz de sobrevivir en zonas templadas y en condiciones de encharcamiento.
Se ha realizado un estudio de cuantificación de ascosporas en suelo de campos de melón de varias zonas productoras de la Comunidad Valenciana, detectándose ascosporas de M. cannonballus en todos ellos. En el momento de aparición de síntomas de "colapso", se han observado diferencias significativas entre los campos y entre las zonas síntomáticas y asintomáticas, a favor de unas u otras, según los campos. Al comparar los niveles iniciales de ascosporas en suelo con los obtenidos dos o tres meses tras el final del cultivo, se han visto situaciones contradictoriBeltrán Martínez, R. (2006). Estudios epidemiológicos y de patogenicidad de Monosporascus cannonballus Pollack et Uecker [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1865Palanci
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