Search results for "techniques"
showing 10 items of 4426 documents
A demagnetization circuit for forward converters
2009
This paper presents a demagnetization circuit able to operate the forward converter with an higher efficiency and with a wider input range. In particular, by the means of few added components, the magnetizing energy and the leakage one are continuously recovered, and the transformer reset and the primary mosfet OFF voltage clamp to the input, both under steady state and transient operations, are provided. The reduced voltage stress allows the converter to operate with a duty extended to unity over the typical 70% limit of the Active Clamp topology, with smaller output inductance, better converter dynamics and wider input range. Furthermore, thanks to this technique, by employing a duty appr…
Frame-based and frameless endoscopic procedures in the third ventricle.
1997
Stereotactic guidance is useful for planning an accurate trajectory to the third ventricle. A guiding block with a ball joint was developed for frame-based endoscopy and adaptors for arm-based and armless navigation systems. Between 1992 and 1996, 52 patients were operated on endoscopically in the third ventricle under stereotactic guidance. Thirty-eight ventriculostomies, 13 biopsies and 10 cystic lesions were performed. The coordinates of two points were calculated; one in the foramen of Monro and the second in the third ventricle. The ventriculostomy was performed under endoscopic control bluntly with a Fogarty catheter in front of the basilar artery. Twenty-seven (71%) of the patients h…
Analysis of the spatial distribution of free radicals in ammonium tartrate by pulse EPR techniques
2009
Using pulse electron paramagnetic resonance (EPR) on a series of l(+)-ammonium tartrate (AT) dosimeters exposed to radiations with different linear energy transfer (LET), we assessed the ability of pulse EPR spectroscopy to discriminate the quality of various radiation beams such as (60)Co gamma-ray photons, protons and thermal neutrons at various doses by analyzing the local radical distributions produced by the different beams. We performed two types of pulse EPR investigations: two-pulse electron spin echo decay obtained by varying the microwave power, and a double electron-electron resonance (DEER) study. Both methods provide information about the dipolar interactions among the free rad…
Of Thiols and Disulfides: Methods for Chemoselective Formation of Asymmetric Disulfides in Synthetic Peptides and Polymers.
2018
In protein or peptide chemistry, thiols are frequently chosen as a chemical entity for chemoselective modification reactions. Although it is a well-established methodology to address cysteines and homocysteines in aqueous media to form S-C bonds, possibilities for the chemoselective formation of asymmetric disulfides have been less approached. Focusing on bioreversibility in conjugation chemistry, the formation of disulfide bonds is highly desirable for the attachment of thiol-containing bioactive agents to proteins or in cross-linking reactions, because disulfide bonds can combine stability in blood with degradability inside cells. In this Concept article, recent approaches in the field of…
Studies on pathways of ring opening of benzene in a Fenton system
1995
Ring-opened products of benzene metabolism have been postulated to play a role in hematotoxicity and leukemogenesis. The reaction of benzene in the Fenton system was reexamined to determine the presence of compounds which might serve as intermediates in the formation of trans, trans-muconaldehyde (MUC), a microsomal hematotoxic metabolite of benzene. Benzene dihydrodiol (DHD) was found in this system based on coelution with authentic standard, ultraviolet (UV) absorption characteristics, and molecular weight. Incubation of DHD in the Fenton system resulted in the formation of phenol (PH), catechol (CAT), and products which reacted with thiobarbituric acid to form chromogens absorbing at 495…
Drift velocity of free electrons in liquid argon
1999
Abstract A measurement of the drift velocity of free electrons in liquid argon has been performed. Free electrons have been produced by photoelectric effect using laser light in a so-called “laser chamber”. The results on the drift velocity vd are given as a function of the electric field strength in the range 0.5 kV / cm ⩽| E |⩽12.6 kV / cm and the temperature in the range 87 K ⩽T⩽94 K . A global parametrization of v d (| E |,T) has been fitted to the data. A temperature dependence of the electron drift velocity is observed, with a mean value of Δ v d /( Δ T v d )=(−1.72±0.08)%/ K in the range of 87–94 K.
Automatic early detection of decay in citrus fruit using optical technologies and machine learning techniques
2015
Los cítricos representan el cultivo frutal de mayor valor en términos de comercio internacional, siendo España el primer exportador mundial de cítricos para consumo en fresco. Sin embargo, la presencia de podredumbres causadas por hongos del género Penicillium se encuentra entre los principales problemas que afectan la postcosecha y comercialización de cítricos. Un número reducido de frutas infectadas puede contaminar una partida completa de cítricos durante el almacenamiento de la fruta por largos períodos de tiempo o en el transporte al extranjero, lo que conlleva grandes pérdidas económicas y el desprestigio de los productores de cítricos. Por lo tanto, la detección temprana de infeccion…
Non-conventional methods and media for the activation and manipulation of carbon nanoforms
2013
Very often, chemical transformations require tedious and long procedures, which, sometimes, can be avoided using alternative methods and media. New protocols, enabling us to save time and solvents, allow us also to explore new reaction profiles. This Tutorial Review focuses on the physical and chemical behavior of carbon nanoforms, CNFs (fullerenes, nanotubes, nanohorns, graphene, etc.) when non-conventional methods and techniques, such as microwave irradiation, mechano-chemistry or highly ionizing radiations are employed. In addition, the reactivity of CNFs in non-conventional media such as water, fluorinated solvents, supercritical fluids, or ionic liquids is also discussed.
Spatial Distribution of Fungal Communities in an Arable Soil.
2015
Fungi are prominent drivers of ecological processes in soils, so that fungal communities across different soil ecosystems have been well investigated. However, for arable soils taxonomically resolved fine-scale studies including vertical itemization of fungal communities are still missing. Here, we combined a cloning/Sanger sequencing approach of the ITS/LSU region as marker for general fungi and of the partial SSU region for arbuscular mycorrhizal fungi (AMF) to characterize the microbiome in different maize soil habitats. Four compartments were analyzed over two annual cycles 2009 and 2010: a) ploughed soil in 0-10 cm, b) rooted soil in 40-50 cm, c) root-free soil in 60-70 cm soil depth a…
Utility of the polymerase chain reaction-restriction fragment length polymorphisms of the intergenic spacer region of the rDNA for characterizing Gib…
2004
Summary In the present report, a total of thirty-one isolates of Gibberella fujikuroi (Sawada) Wollenw. species complex of Fusarium (section Liseola) morphologically classified as F. moniliforme according to the taxonomy of Nelson, Toussoun and Marasas (1983) were analyzed for their ability to produce fumonisin B1 and fumonisin B2 by an optimized liquid chromatographic method. They were isolated from three hosts (Zea mays, Musa sapientum and Pinus pinea). The results indicate that M. sapientum is a preferential host for G. fujikuroi isolates with low or null capacity for producing fumonisins, while isolates from Z. mays and P. pinea are generally high fumonisin producers. The molecular char…