Search results for "General Engineering"
showing 10 items of 2407 documents
Comparison of the activity, selectivity and decay properties of lay and hyultrastable zeolites during the cracking of alkanes
1984
Abstract The cracking of n-heptane on LaY ultrastable zeolite has been studied in a continuous glass flow reactor, at atmospheric pressure, up to 470°C. The initial selectivity to cracking, isomerization and disproportionation, kinetic rate constants, activation energies and decay parameters have been calculated and compared with those obtained using a HY ultrastable zeolite as a catalyst. It has been found that the HY ultrastable zeolite is about 7 times more active for cracking, and about 10 times more active for isomerization and disproportionation than the LaY ultrastable zeolite. The protolytic to β-cracking ratio is higher for the HY ultrastable zeolite. The deactivation takes place b…
Cracking of n-heptane on a hzsm-5 zeolite. The influence of acidity and pore structure
1985
Abstract The crackino of n-heptane on a HZSM-5 zeolite has been studied in a continuous qlass flow reactor, at atmospheric pressure, up to 470°C. The initial selectivities to the different reaction products, kinetic rate constants, activation energies and decay parameters have been calculated and compared with those obtained using a large pore zeolite (HYUS). A different product distribution is obtained with the two zeolites. In that way, and considering initial selectivities, different C 6 /C 1 , C 5 /C 2 , C 4 /C3, i-C 4 /n-C 4 , ethylene/ethane, propylene/propane ratios have been found on the two zeolite catalysts. The results have been quantitatively explained by considerinq a direct cr…
Analytical methods for the characterization and determination of nonionic surfactants in cosmetics and environmental matrices
2013
Nonionic synthetic surfactants, constituted of an assortment of classes, are common ingredients of industrial, household and body-care products. Alone or in combination with anionic surfactants, they perform a variety of functions including cleaning action, emulsification, skin conditioning, appearance and consistency modification, solubilization and dispersing agents. By far fatty alcohol ethoxylates (AEs) and alkylphenol ethoxylates (APEs) are more extensively used than any other nonionic surfactant class; however, works appearing in the literature making reference to the analysis of other nonionic surfactant classes have also been collected in this review. The production volume worldwide…
Visible Light Generation and its Influence on Supercontinuum in Chalcogenide As2S3 Microstructured Optical Fiber
2011
We demonstrate visible light generation in chalcogenide As2S3 microstructured optical fiber. The generated visible light causes irreversible damage to the fiber core because of the high absorption coefficient of chalcogenide glasses in the visible band. The SCs (supercontinua) are measured in both untapered and tapered As2S3 fibers, no wider SC is obtained in the tapered one. The SC growth is prevented by the visible light generation since the damage to the fiber core decreases the fiber transmission substantially. This effect can be avoided by designing the fiber to enable the pump source to work in single-mode operation.
Thermostimulated processes in statically and dynamically disordered luminescent solids
1993
Abstract Trap spectra depending on the concentration of defects in crystalline KBr-T1, LiF-Mg, Ti, A1 2 O 3 and glassy Na 2 O·SiO 2 are investigated. The nature of inhomogeneous broadening and continuous distribution of traps over activation energies at sufficiently high defect concentrations is considered. Impurity hopping controlled recombination of electronic excitations is observed. The presence of enlarged values of process activation energies and frequency factors is discussed in terms of the concept of dynamic disorder, taking into account the fluctuational changes in both the perfectpart and the structure of defects in the solid at high temperatures.
Inkjet printing Ag nanoparticles for SERS hot spots
2018
A novel inkjet printing based approach is developed for the fabrication of a customizable platform on glass substrates allowing for surface enhanced Raman spectroscopy (SERS) detection of analytes up to single hot spots generated by the spontaneous aggregation of Ag nanoparticles (Ag NPs) in pL scale droplets. After drying the printed droplets under ambient conditions, trace amounts of the analyte can be detected by SERS given the proximity to NP hot spots. By employing alizarin (10-5M) as a model system and scaling the ink droplet volume from 1 nL to 10 pL, the absolute quantity of hot spots has been derived in the printed droplets allowing detecting up to a few molecules in proximity to i…
Determination of biochemical parameters in human serum by near-infrared spectroscopy
2014
NIR offers multiple advantages for serum analysis, permitting a fast and direct determination of several parameters simultaneously, with low sample handling and without the need for reagents during the measurement step. The aim of this paper was to provide an evaluation of this technique in a real world scale, for the simultaneous determination of several parameters and based on a considerable number of samples. Direct near infrared (NIR) absorbance measurements were used to determine the concentration of clinical parameters in human serum that are required in routine biochemical tests. Total protein, albumin, total cholesterol, high-density lipoprotein (HDL cholesterol), low-density lipopr…
Physical model, theoretical aspects and applications of the flight of a ball in the atmosphere. Part III: Theory in the case of vertical angular freq…
1995
If a ball is viewed as a rigid body, its flight in the atmosphere can be described by six ordinary differential equations, which has been derived in the first part of this paper. In this following third part, some further theoretical aspects in the case of vertical angular frequency will be pointed out using an unknown transformation of the original independent variable, i.e. the time, as indicated in Part II. Last, but not least, the general case of angular frequency is to be treated. A rough qualitative discussion of the solutions is given as well as—if the equations are viewed as a three-dimensional dynamical system—the unique stable equilibrium, which depends on the spin. This equilibri…
Polymerization with heterogeneous metalorganic catalysts. VI. Differences in polymerization activity of α-olefins and some kinetic results on butene-…
1967
Relative changes in polymerization activity of ethylene, propylene, and butene-1 in Ziegler-Natta polymerization were compared by use of TiCl3 samples contaminated with O2 and H2O to various extents. Catalyst depletion varied for the three monomers which supported the existence of different active centers. In butene-1 polymerizations with the system Al(C2H5)2Cl–TiCl3, the formation of active centers involves an irreversible and a reversible (adsorption) reaction, the former pertaining to the formation of Al(C2H5)Cl2 and dependent upon the purity of the TiCl3. The kinetic treatment of the rate curves suggests a mixed order of catalyst deactivation and again points to the importance of Al(C2H…
Homogeneous Langmuir-Blodgett Film of Double-Chain Ammonium Amphiphile Complexed with Anionic Polymer
1988
Heterogeneous textures suggesting the coexistence of a fluid and a solid phase were found both in a surface monolayer and in a deposited Langmuir-Blodgett (LB) film of double-chain ammonium amphiphiles by fluorescence microscopy. Although an annealing of the surface monolayer at 40°C allowed crystal growth, the heterogeneous phase separation remained in the LB film. A drastic change of the fluorescence image shows that the recrystallization of the complexed monolayer with anionic polymers conducted the homogeneous monolayer.