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61.
Hugo R. Fernandes Dilshat U. Tulyaganov Ashutosh Goel José M. F. Ferreira 《Journal of Thermal Analysis and Calorimetry》2011,103(3):827-834
This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the
system Li2O–SiO2–Al2O3–K2O. A glass with nominal composition 23Li2O–77SiO2 (mol%) (labelled as L23S77) and glasses containing Al2O3 and K2O with SiO2/Li2O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics
(GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation
of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR)
depict the role of Al2O3 as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture
of Q
3
and Q
4
(Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential
thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier
transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural
features of glasses, phase composition and thermo-physical properties of GCs has been discussed. 相似文献
62.
Nadezhda Rangelova Lachezar Radev Sanchi Nenkova Isabel M. Miranda Salvado Maria H. Vas Fernandes Michael Herzog 《Central European Journal of Chemistry》2011,9(1):112-118
Methylcellulose (MC) / SiO2 organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized
by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO2. AFM depicts surface roughness which depends on the silica precursor and MC content.
相似文献
63.
64.
Optimized HR-AR-DFB laser structures are proposed foreseeing their use in directly modulated optical communication systems. They present, simultaneously, high single-longitudinal-mode yield, stable single-longitudinal-mode operation, high power efficiency and stable emitted wavelength. Lasers harder to manufacture were previously proposed elsewhere and did not succeed in achieving such high performances. A detailed assessment of the proposed lasers is presented and discussed. 相似文献
65.
66.
67.
A set of experiments, using model compounds, was carried out in order to evaluate the influence of amide linkages on acidity measurements of humic substances (HS). Three benzene-carboxylic acids (2,4-dihydroxybenzoic acid; 3,5-dihydroxybenzoic acid, and phthalic acid) and two peptides (dl-alanyl-dl-alanine, and glycil-l-leucine) were employed to simulate the major acidic functional groups present in humic material. The acidity of the samples was measured, using the Schnitzer and Gupta methods, for each compound separately, as well as for selected mixtures with different compound combinations. General results showed that, in the absence of peptides, phenolic groups with high pKa values are not detected in the barium hydroxide reaction and the data so obtained do not represent the real concentrations of the acidic groups. For the mixtures containing peptides, the presence of amide linkages distorts the results relative to the total acidity (TA) mainly because under the extreme conditions of the reaction with Ba(OH)2 hydrolysis of the peptide occurs, consuming extra hydroxyl groups and increasing artificially the phenolic content. Such a condition is minimized by the reduction of the reaction time. 相似文献
68.
The efficiencies of direct lidars operating at 355, 532, 1064 and 1540-nm radiation wavelengths for early forest fire detection
were compared. For each wavelength, the range for reliable smoke-plume detection was estimated on the basis of a computer
simulation plume using a one-dimensional “top-hat” gas dynamic model for the calculation of the backscattering and extinction-coefficient
profiles within the plume. The agreement between the predicted signal-to-noise ratio (SNR) and experimental results for 532
and 1064-nm wavelength radiation is good. The decrease of the signal-to-noise ratio with distance is maximum for 355 nm and
minimum for 1064 nm. At 1540 nm, the decay of SNR with distance is slightly faster, but the SNR is higher than for other wavelengths,
leading to the highest detection efficiency for the same energy of the probing laser pulse. For a burning rate of 2 kg/s and
a laser beam divergence of 2.5 mr, the maximum distance for reliable detection varies between 6 and 12 km, depending on the
wavelength.
Received: 15 May 2002 / Revised version: 13 September 2002 / Published online: 22 January 2003
RID="*"
ID="*"Corresponding author. Fax: +351-21/841-8120, E-mail: rui.vilar@ist.utl.pt 相似文献
69.
D.M. Kane A.J. Fernandes R.P. Mildren 《Applied Physics A: Materials Science & Processing》2003,77(6):847-853
In earlier work we characterised single-pulse laser cleaning of medium-density (areal coverage 10–20%) alumina particles from glass surfaces with three different lasers. The method of measuring particle-removal efficiency involves optical microscopy imaging (digital) and subsequent image analysis of the area covered by, and/or the number of, particles before and after the single-pulse laser cleaning treatment. The sample-preparation technique used leads to both single particles and agglomerates on the surface. The issues of depth of focus in the imaging and grey-scale thresholding in the image analysis of such samples, with a range of particle and agglomerate sizes, has been systematically investigated. A protocol for optimum imaging and illumination of such samples is described herein. It has been developed based on the results of a systematic investigation of the effect of the image focal plane position relative to the surface also described herein. The image analysis to quantify the particles on the surface involves a judgement of the best threshold grey-scale level in the image to define the boundary between particles and background substrate. A quantitative appraisal of the impact on the laser cleaning efficiency results of a threshold grey-scale level that is set too high or too low, and how these results compare with those obtained for the best-judgement threshold grey-scale level, has been completed. PACS 81.65.Cf; 42.62.Cf; 42.70.Ce 相似文献
70.
U. Köster P. Carbonez A. Dorsival J. Dvorak R. Eichler S. Fernandes H. Frånberg J. Neuhausen Z. Novackova R. Wilfinger A. Yakushev 《The European physical journal. Special topics》2007,150(1):285-291
Refractory elements, i.e. elements with very high melting point and
low vapor pressure, cannot be released in atomic form from an ISOL target.
Therefore most of these elements are presently not available as ISOL beams.
However, when reactive gases are introduced
into the target, they may form volatile compounds with the refractory elements,
allowing for an easier transport to the ion source. Particularly useful are
high-temperature stable fluorides and oxides.
By these chemical evaporation methods so far ISOL beams of the refractory elements
C, Zr, Hf and Ta have been produced. We discuss how ISOL beams of B, Ti, Nb, Mo, Tc,
Ru, W, Re, Os and Ir could be produced in a similar way. 相似文献