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101.
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Two glasses, the first one with the composition of Li2O·2SiO2 and the second one with the addition of CaO, P2O5 and CaF2 in the stoichiometric ratio corresponding to fluoroapatite were prepared and their tendency to crystallize has been studied
by non-isothermal DTA analysis. The values of kinetic parameters calculated using the isoconversional integral method have
been used to determine the temperature dependencies of both the length of isothermal induction period and the length of overall
isothermal crystallization for both glasses. The estimated dependencies indicate that the glass containing CaO, P2O5 and CaF2 has a lower thermal stability. 相似文献
104.
Eva Hoffmann GyÖrgy Marko-Varga Istvan Csiky Jan Årke JÖnsoon 《International journal of environmental analytical chemistry》2013,93(1-3):161-171
Abstract A three-column ion chromatographic system for the removal of humic substances from natural waters, and subsequent on-line concentration and determination of nitrate and sulfate using non-suppressed ion chromatography is presented. Humic substances are removed using disposable adsorption columns packed with chemically bonded amine silica material. The sample is directly transfered to an ion exchange column where the anions are concentrated ca 10 times. After reversing the flow, the ions are transferred to a third column where they are separated and quantified. The detection limit is less than 1 mg L?1 of nitrate or sulfate in water containing 45mgL?1 of humic acid. 相似文献
105.
Huebl H Stegner AR Stutzmann M Brandt MS Vogg G Bensch F Rauls E Gerstmann U 《Physical review letters》2006,97(16):166402
The hyperfine interaction of phosphorus donors in fully strained Si thin films grown on virtual Si(1-x)Ge(x) substrates with x< or =0.3 is determined via electrically detected magnetic resonance. For highly strained epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly below the limit predicted by valley repopulation. Within a Green's function approach, density functional theory shows that the additional reduction is caused by the volume increase of the unit cell and a relaxation of the Si ligands of the donor. 相似文献
106.
Classification is concerned with the development of rules for the allocation of observations to groups, and is a fundamental
problem in machine learning. Much of previous work on classification models investigates two-group discrimination. Multi-category
classification is less-often considered due to the tendency of generalizations of two-group models to produce misclassification
rates that are higher than desirable. Indeed, producing “good” two-group classification rules is a challenging task for some
applications, and producing good multi-category rules is generally more difficult. Additionally, even when the “optimal” classification
rule is known, inter-group misclassification rates may be higher than tolerable for a given classification model. We investigate
properties of a mixed-integer programming based multi-category classification model that allows for the pre-specification
of limits on inter-group misclassification rates. The mechanism by which the limits are satisfied is the use of a reserved
judgment region, an artificial category into which observations are placed whose attributes do not sufficiently indicate membership
to any particular group. The method is shown to be a consistent estimator of a classification rule with misclassification
limits, and performance on simulated and real-world data is demonstrated. 相似文献
107.
Spin echo MRI in the evaluation of hearts with a double outlet right ventricle: usefulness and limitations 总被引:1,自引:0,他引:1
Beekmana RP Roest AA Helbing WA Hazekamp MG Schoof PH Bartelings MM Sobotka MA de Roos A Ottenkamp J 《Magnetic resonance imaging》2000,18(3):245-253
The surgical approach to a double outlet right ventricle (DORV) is dependent on the spatial relationship of the semilunar valves, outflow tracts and ventricular septal defect (VSD). The purpose of the study was to assess the value of MRI for the evaluation of cardiovascular anatomy in patients before and after surgery for DORV. Spin echo MRI was performed in 12 patients with DORV (eight preoperative and four postoperative patients). Thin-section MRI was performed in three orthogonal planes and selected angulated views were obtained. Conventional imaging by color Doppler echocardiography and cine-angiocardiography and surgical findings, when present, served as the reference standards. The results found that the spatial relationship between semilunar valves and VSD was accurately assessed by MRI in eight out of eight preoperative patients. In the four postoperative cases MRI depicted the morphology of both outflow tracts and provided adequate information on their patency. Of the eight preoperative patients, five have undergone corrective surgery and the MRI findings were confirmed. MRI provided additional information to conventional imaging preoperatively in three cases in which the VSD opened into the outlet portion of the DORV, without there being a direct relation to a semilunar valve. In two preoperative cases in which the VSD was directly committed to the aorta, conventional imaging was conclusive. MRI was unable to depict aberrant chordae tendineae in four out of four cases. We conclude that MRI provides accurate additional anatomic information in patients with DORV, which is helpful in presurgical planning as well as during follow-up. Spin echo MRI does not visualize aberrant chordae tendineae. 相似文献
108.
The electronic conductivities of solid solutions La1?xBaxF3?x (0 ? x ? 0.0952) were investigated up to 533 K using the Hebb-Wagner dc polarization technique. The electrochemical cell (-)La|La1?xBaxF3?x|Pt(+) has been utilized with Pt as the ion-blocking electrode. Under steady-state conditions the La1?xBaxF3?x solid solutions exhibit electronic conductivity. The electronic conductivity vanishes in pure LaF3. Together with ac conductivity measurements it appears that the ionic transference number for La1?xBaxF3?x (0 ? x ? 0.0952) is essentially unity over the temperature range studied. 相似文献
109.
110.
van Pul C Roos FG Derksen OS Buijs J Vlaardingerbroek MT Kopinga K Wijn PF 《Magnetic resonance imaging》2004,22(9):1169-1180
In the neonatal brain, it is important to use a fast imaging technique to acquire all diffusion weighted images (DWI) for apparent diffusion coefficient (ADC) calculation. Taking into account the occurrence of typical echo planar imaging (EPI) artifacts, we have investigated whether single-shot (SSh) or multishot (MSh) DWI-EPI should be preferred. In 14 neonates, 17 adult patients and 5 adult volunteers, DWIs are obtained both with SSh and MSh EPI. The occurrence of artifacts and their influence on the ADC are explored and further quantified using simulations and phantom studies. Two radiologists scored overall image quality and diagnosability of all images. Single-shot and MSh DWI-EPI scored equally well in neonates with respect to overall image quality and diagnosability. In newborns, more motion artifacts in MSh can be noticed while N/2-ghost artifacts in SSh occur less frequently than in adults. Both N/2-ghost and motion artifacts result in significant ADC abnormalities. There is a serious risk that these artifacts will be mistaken for genuine diffusion abnormalities. N/2-ghost artifacts are hardly noticed in the neonatal brain, which might be due to smaller cerebrospinal fluid (CSF) velocity than in adults. Apparent diffusion coefficient values in MSh are unreliable if motion occurs. We conclude that for ADC calculations in neonates SSh DWI-EPI is more reliable than MSh. 相似文献