Search results for "ACTIVATION"
showing 10 items of 2079 documents
The phase situation and ferroelectric properties in the mixed crystals [4-NH2PyH][SbCl4(1−x)Br4x]
2008
Abstract The group of mixed crystals of general formula: [4-APyH][SbCl4(1−x) Br4x] with x ranging from 0 to 1 was studied by means of differential scanning calorimetry, dilatometry and dielectric spectroscopy. The ferroelectric properties are preserved for mixed crystals with replacement fraction, x, less than 0.30. Moreover, such a substitution of the chlorine atoms by the bromine ones significantly lowers the temperature of the structural phase transition shifting it from 240 K for pure [4-APyH][SbCl4] to about 185 K for the mixed crystals richer in bromine. The dielectric relaxation process exhibited by the mixed crystal with x = 0.90 in the radio-frequency region was analyzed and the ac…
Photocatalytic and Catalytic Reactions in Gas–Solid and in Liquid–Solid Systems
2019
Abstract Heterogeneous photocatalytic and thermal-catalytic reactions are here presented focusing the differences and similarities between the two processes. When possible, the comparison was made for the same chemical reaction in the presence of an inorganic material playing the role of both catalyst or/and photocatalyst. Several examples are presented where a catalytic reaction can occur at milder experimental conditions and, particularly, at lower temperature when the system is also irradiated by UV and/or visible light. The differences in mechanistic aspects, conversions, and selectivities between catalytic and photocatalytic reactions will be also considered because these occurrences a…
Effect of Experimental and Sample Factors on Dehydration Kinetics of Mildronate Dihydrate: Mechanism of Dehydration and Determination of Kinetic Para…
2014
The dehydration kinetics of mildronate dihydrate [3-(1,1,1-trimethylhydrazin-1-ium-2-yl)propionate dihydrate] was analyzed in isothermal and nonisothermal modes. The particle size, sample preparation and storage, sample weight, nitrogen flow rate, relative humidity, and sample history were varied in order to evaluate the effect of these factors and to more accurately interpret the data obtained from such analysis. It was determined that comparable kinetic parameters can be obtained in both isothermal and nonisothermal mode. However, dehydration activation energy values obtained in nonisothermal mode showed variation with conversion degree because of different rate-limiting step energy at hi…
MOCVD growth of CdTe on glass: analysis of in situ post-growth annealing
2004
Abstract In this paper, we analyse the growth by MOCVD of CdTe on glass substrates using in situ post-growth annealing. First, in order to perform a systematic study, polycrystalline layers of CdTe were deposited by MOCVD on glass substrates. The structure and morphology of the layers was investigated as a function of different growth parameters, temperature, VI/II precursor molar ratio and substrate position on the susceptor. An activation energy of Ek=20.7 kcal/mol was obtained from the experimental data. In order to better understand the process and the effects of different growth parameters, a numerical model that simulated the gas flow in the reactor, was developed. Secondly we analyse…
Inorganic materials acting as heterogeneous photocatalysts and catalysts in the same reactions
2016
General considerations on the differences and similarities between heterogeneous photocatalysis and thermal catalysis are presented. Some research papers are reviewed where a reaction has been carried out in the presence of an inorganic material used both as catalyst and photocatalyst. The existing literature often compares catalytic reactions undertaken with the contemporaneous presence of radiation, showing only that photocatalytic reactions can occur under milder experimental conditions and at much lower temperatures. Nevertheless, differences in mechanistic aspects, conversions and selectivities between catalytic and photocatalytic reactions should also be highlighted. These are due to …
C–S bond cleavage by cobalt: synthesis, characterization and crystal structure determination of 1,2-di-(o-salicylaldiminophenylthio)ethane and its Co…
2002
1,2-Di-(o-salicylaldiminophenylthio)ethane reacts with Co(II) salts to form a complex with oxidative cleavage of the C–S bond, to result in the formation of a Co(III) complex of the cleaved ligands.
Crystal structure, dielectric properties and molecular motions in ( i -C 4 H 9 NH 3 ) 3 Bi 2 Br 9
2000
Abstract The crystal structure of ( i -C 4 H 9 NH 3 ) 3 Bi 2 Br 9 at room temperature has been determined and refined to R =0.036. The crystal is orthorhombic, space group Ama 2. The structure is built up of the i -butylammonium cations and isolated Bi 2 Br 9 3− anions. The complex dielectric permittivity along the a -axis has been measured between 500 Hz and 1000 MHz in the vicinity of two phase transitions at 252 and 263 K. The dielectric response close to 252 K is well described by the Debye equation. The activation energy of the reorientation of the i -butylammonium cations is found to be 0.68 eV. The temperature dependencies of the proton relaxation time T 1 and of the second moment of…
Modelling of the cation motions in complex system: case of Na-mordenites
2002
Abstract Semi-empirical inter-atomic potentials and Monte Carlo algorithms are proposed to predict the evolution of the interaction energy between sodium ions and a mordenite type aluminosilicate network as a function of Si/Al ratio. This result is favourably compared with the activation energy barriers for Na + `jumps' responsible for the polarization change, measured by thermally stimulated current (TSC) spectroscopy, for Na-mordenites characterized by Si/Al ratios ranged from 5.5 to 12. Finally, we propose a possible mechanism for the cation motions, which involves activation barriers within the same order of magnitude than those measured by TSC.
Elevated NKG2D ligand expression in experimental autoimmune encephalomyelitis
2014
T cells remain unclear. Expressing myelin-reactive T cell receptor (TCR) is not sufficient to make a T cell encephalitogenic. In fact, the frequencies of myelin-reactive T cells are comparable between MS patients and healthy individuals, but the ones in MS patients have activated/memory phenotypes. In the animal model of MS, experimental autoimmune encephalomyelitis (EAE), myelin-specific T cells activated with antigen presenting cells (APCs) plus myelin peptide are encephalitogenic, whereas T cells activated with anti-CD3/CD28 antibodies are not. This suggests that APCs provide critical cytokines beyond T cell receptor activation and co-stimulation, contributing to encephalitogenicity. To …
Binding and activation of human and mouse complement by Cryptosporidium parvum (Apicomplexa) and susceptibility of C1q- and MBL-deficient mice to inf…
2008
Cryptosporidium parvum is a protozoan parasite (Apicomplexa) that causes gastrointestinal disease in animals and humans. Whereas immunocompetent hosts can limit the infection within 1 or 2 weeks, immunocompromised individuals develop a chronic, life-threatening disease. The importance of the adaptive cellular immune response, with CD4+ T-lymphocytes being the major players, has been clearly demonstrated. Several non-adaptive immune mechanisms have been suggested to contribute to the host defence, such as interferon-gamma (IFN-gamma) from NK cells, certain chemokines, beta-defensins and pro-inflammatory cytokines, but the influence of the complement systems has been less well studied. We ana…