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991.
Partial discharges are a transient phenomena whose measurement is remarkably important for electrical equipment diagnosis and maintenance. These discharges appear in the measurement circuit as very narrow current pulses of some nanoseconds. Therefore, discharge pulse detection is a particularly difficult problem, especially because they are superposed on the high voltage waveforms that cause them. In this paper, we present an inductively coupled probe able to measure this physical phenomenon by means of a very simple and inexpensive device that can be installed in the equipment under test. After modeling the probe, its response will be compared to that of commercial devices using both calibrated discharges and partial discharges occurring at real power. 相似文献
992.
J. G. Chacón-Nava A. Martínez-Villafañe F. M. Almeraya-Calderón F. H. Stott J. G. González-Rodríguez 《Journal of Materials Engineering and Performance》2001,10(6):699-704
The erosion-corrosion (E-C) behavior of SA213-T22 steel has been studied in a laboratory fluidized-bed (FB) facility in the
temperature range from 100 to 600 °C. Tests were carried out on pin specimens in air using alumina particles of 560 μm average size at impact velocities from 1.5 to 4.5 m/s. The trends of wear with temperature showed small weight gains at
velocities up to 1.5 m/s. Erodent deposition was a dominant process at temperatures below about 300 °C and velocities below
about 2 m/s. At higher velocities, a peak wastage temperature was observed at about 350 °C. The wastage/temperature curves
observed in both cases suggested four temperature regions. In each region, a different E-C regime operates. Scanning electron
microscopy (SEM) revealed various wastage mechanisms, i.e., (a) oxide chipping, (b) development of a compact and adherent oxide scale, (c) oxide and metal removal, and (d) fracture
and spalling within the oxide layer and at the scale/metal interface. In the present study, the latter mechanism was responsible
for the high wastage rates observed at temperatures above about 450 °C and impact velocities above 3.5 m/s. 相似文献
993.
I. Tabernero A. Lamikiz E. Ukar S. Martínez A. Celaya 《The International Journal of Advanced Manufacturing Technology》2014,70(5-8):843-851
Coaxial laser material deposition (also known as laser-cladding process) is being used for selective material deposition on complex parts since the 1990s. Its main applications include coatings, rapid manufacturing, or high added value part repairing. The main advantages of the coaxial laser-cladding process are the high-quality bonding interface between added and substrate material, excellent mechanical behavior, and high precision of the resulting geometry in comparison with conventional welding processes. Moreover, the laser-cladding process involves low-heat input, which leads on minimum thermal distortions and reduced heat-affected zone. Thus, high responsibility components like aeronautic turbine parts, tooling for die and mold industry or medical implants, among others, can be processed with laser cladding. This paper presents a laser material deposition process model for the estimation of the geometric characteristics of added material layers, including the prediction of the 3D shape of single and multiple clads and considering overlapping effect, which is the common situation on industrial applications. The model only needs the typical process parameters as the laser power, substrate material, powder material and size, etc. The model has been applied to different laser material deposition strategies and validated for two different materials (AISI D2 and Inconel 718) by experimental testing, obtaining good agreement between estimated and measured values. Finally, a case study for a turbine engine fixture is presented as a possible application. Therefore, the proposed algorithm can be applied for estimating the resulting geometry of the laser-cladding process and predict the optimum laser-cladding strategy, number of layers, and distance between layers before programming the operation. 相似文献
994.
995.
Phospholipids are essential components of plant cell membranes whose acyl composition appears to be influenced by oil composition
in the sunflower. In the current study, we have determined the diacylglycerol profile of the main phospholipids using phospholipase
C degradation and separation of the diacylglycerols by HPLC and GLC. The main polar lipid molecular species were defined in
different classes of sunflower kernel: PC, PE, and PI. The proportions of each were determined at different stages of development
in order to define the point at which the mutations carried by each sunflower line affected the phospholipid composition of
the seeds. The results indicated that modifications to intraplastidial de novo FA synthesis affected the seed phospholipid profile during the whole period of the seed formation, including accumulation
and maturation, whereas the influence of mutations in the endoplasmic reticulum desaturases were more readily detected at
later stages of development. These results are discussed in terms of the pathways involved in glycerolipid synthesis and phospholipid
conversion in sunflower seeds. 相似文献
996.
Domínguez M Alvarez R Pérez M Palczewski K de Lera AR 《Chembiochem : a European journal of chemical biology》2006,7(11):1815-1825
Artificial visual pigment formation from ring-demethylated retinals was studied in an effort to understand the effect that methyl groups on the chromophore cyclohexenyl ring have on the visual cycle. The stereoselective synthesis of the 11-cis-ring-demethylated analogues involves thallium-accelerated Suzuki cross-coupling reactions and highly stereocontrolled Wittig reactions to form key bonds. Only 11-cis-1,1,5-trisdemethylretinal (2) failed to form an artificial pigment, whilst variable pigment-formation yields were determined for the remaining analogues, increasing with the number (and location) of the chromophore hydrophobic ring methyl groups. Our results with the monodemethylated analogues 11-cis-5-demethylretinal (4) and 11-cis-1-demethylretinal (5) show that the C1-2-CH(3) groups are more important for pigment formation than the C5-CH(3) substituent. This is reflected in the absorption maxima of the artificial pigments, with values closer to that of native rhodopsin for 4. Docking studies based on a rhodopsin crystal structure, however, predict a lower pigment stability for 4 than for 5. Gas-phase DFT (B3LYP/6-31G*) computations of the free-ligand geometries, conformational searches about the C6--C7 bond, and docking studies revealed that, although the conformation of bound 5 is close to that of the native chromophore, the ligand needs to overcome the energy cost of shifting the unbound favored 6-s-trans conformation to the bound 6-s-cis form. In addition, the presence of an extra methyl group at C18 (11-cis-18-methylretinal, 7) is tolerated well and adds further stability to the complex, most probably due to increased hydrophobic interactions. 相似文献
997.
Gries R Khaskin G Daroogheh H Mart C Karadag S Er MK Britton R Gries G 《Journal of chemical ecology》2006,32(12):2667-2677
The sex pheromone of the pistachio twig borer, Kermania pistaciella (Lepidoptera: Oinophilidae), one of the most important insect pests of pistachio, Pistacia vera, in Turkey and Iran, was identified. In gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometric
analyses of pheromone gland extracts of female K. pistaciella from Turkey, (2S,12Z)-2-acetoxy-12-heptadecene was identified as the major candidate pheromone component. In field experiments in Turkey, lures
containing synthetic (2S,12Z)-2-acetoxy-12-heptadecene attracted large numbers of male moths. Its attractiveness was significantly reduced by the presence
of the R-enantiomer or of either enantiomer of the corresponding alcohol. (2S,12Z)-2-Acetoxy-12-heptadecene is the first pheromone component identified in the Oinophilidae and the first secondary acetate
pheromone component identified in the Lepidoptera.
An erratum to this article can be found at 相似文献
998.
Maritza F. Díaz Gómez Goitybell Martínez Téllez Maikel Arteaga Cruz Rafael Garcés Mancheno 《Journal of the American Oil Chemists' Society》2006,83(11):943-946
Ozonized theobroma fat is used as raw material in the manufacture of pessaries and cosmetic creams. Ozonization of theobroma
fat with water was carried out at different applied ozone dosages, and the resultant PV, acid value, iodine value, total hydroperoxide
content, and FA content were determined. PV and total hydroperoxide content showed a notable increase with applied ozone dosage
up to 35.7 mg/g. Acid value varied slightly from 4.1 to 9.9 mg KOH/g, and the iodine value fell to zero. PV and total hydroperoxide
content increased slightly with a higher applied ozone dosage. The comparison of total hydroperoxide measurement using ferrous
oxidation in xylenol orange assay and traditional iodometric assay for PV determination showed a significant linear correlation.
Small amounts of oleic acid were found in ozonized theobroma fat samples with iodine value equaling zero, which demonstrated
that iodine value determination is an inexact assay. During ozonization of theobroma fat, an increase in acid value of 18.9-fold
with respect to the initial value was observed owing to decomposition of peroxide. 相似文献
999.
Varietal and crop year effects on lipid composition of walnut (Juglans regia) genotypes 总被引:1,自引:0,他引:1
Marcela L. Martínez Miguel A. Mattea Damián M. Maestri 《Journal of the American Oil Chemists' Society》2006,83(9):791-796
The FA, unsaponifiable, and volatile constituents of oil from three walnut varieties from two consecutive crop years were
studied. The walnut oils (WO) were rich in PUFA and low in saturated FA. The tocopherol fraction consisted mainly of γ-tocopherol.
High contents of β-sitosterol were found, together with campesterol and Δ5-avenasterol in similar amounts. Methylsterols present in WO were identified as cycloartenol, cyclolaudenol, cycloeucalenol,
and 24-methylenecycloartanol. The hydrocarbon fraction was characterized by the predominance of C14–C20
n-alkanes. The major volatiles were aldehydes produced through the linoleic acid oxidative pathway. FA, methylsterols, and
some hydrocarbons presented statistically significant differences among varieties. Most of this variation was due to the genotype.
The Franquette variety was noteworthy by its higher oil and oleic acid contents. In contrast, tocopherols and volatile compounds
showed minor differences among varieties; they were strongly influenced by the crop year. Chemical data were subjected to
principal component analysis. The parameters that gave the greatest discrimination between the walnut varieties were oleic
and linolenic acids, tetradecane, eicosane, tetracosane, cycloartenol, and 24-methylenecycloartanol. These components presented
the major varietal influences and could be useful to determine the identity of walnut genotypes. 相似文献