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Search Results: 1 - 10 of 34755 matches for " Juan Camilo Conde Silvestre "
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Juan Manuel Hernández Campoy,Juan Camilo Conde Silvestre
International Journal of English Studies (IJES) , 2005, DOI: 10.6018/ijes.5.1.47901
Abstract: The diffusion of linguistic innovations and changes has become a common object of sociolinguistic and geolinguistic research. As such, the process has been studied from four complementary perspectives: (a) the communicative or interpersonal, (b) the time dimension, the social perspective and (d) the geographical or spatial. Despite the successful application of these methodologies to tracing the diffusion of innovations in progress and recently attested changes, attention is hardly ever given to reconstructing these four dimensions in connection with the diffusion of changes in the past. In this paper we consider the possibility of applying these methods and findings to the different faeets of the diffusion of a weIl attested change in the history of English: the spread of incipient standard spellings from London in the late Middle English period. Particular attention is given to the unfolding of this process in the course of time, its diffusion across social ranks and networks, as well as to its possible geographical circulation.
TiN Films Deposited by Laser CVD: A Growth Kinetics Study
A. J. Silvestre,O. Conde
Physics , 2002,
Abstract: Results on the chemical composition, structure and growth kinetics of titanium nitride (TiN) films deposited on mild steel substrates by pyrolytic laser-induced chemical vapour deposition (LCVD) are presented. Golden coloured lines of TiN were deposited from a reactive gas mixture of TiCl4, N2 and H2 using a continuous wave TEM00 CO2 laser beam as heat source. The chemical composition and structure of the films were determined by electron probe microanalysis (EPMA) and glancing incidence X-ray diffraction (GIXRD). A non-contact laser profilometer was used to measure the thickness profiles of the films. Using the data obtained in the steady-state region of the TiN laser-written lines, growth rates in the range 3.7 to 6.9 micrometers per second were deduced. The Arrhenius relation between the deposition rate and the deposition temperature yields an apparent activation energy of 46.9(+-)3.8 kJ.mol-1. This result enabled us to conclude that under our deposition conditions the LCVD of TiN is controlled by mass transport in the vapour phase. Keywords: Coatings; Titanium nitride (TiN); Laser chemical vapour deposition (LCVD); Growth mechanisms.
Cr2O3 thin films grown at room temperature by low pressure laser chemical vapour deposition
P. M. Sousa,A. J. Silvestre,O. Conde
Physics , 2010, DOI: 10.1016/j.tsf.2011.01.382
Abstract: Chromia (Cr2O3) has been extensively explored for the purpose of developing widespread industrial applications, owing to the convergence of a variety of mechanical, physical and chemical properties in one single oxide material. Various methods have been used for large area synthesis of Cr2O3 films. However, for selective area growth and growth on thermally sensitive materials, laser-assisted chemical vapour deposition (LCVD) can be applied advantageously. Here we report on the growth of single layers of pure Cr2O3 onto sapphire substrates at room temperature by low pressure photolytic LCVD, using UV laser radiation and Cr(CO)6 as chromium precursor. The feasibility of the LCVD technique to access selective area deposition of chromia thin films is demonstrated. Best results were obtained for a laser fluence of 120 mJ cm-2 and a partial pressure ratio of O2 to Cr(CO)6 of 1.0. Samples grown with these experimental parameters are polycrystalline and their microstructure is characterised by a high density of particles whose size follows a lognormal distribution. Deposition rates of 0.1 nm s-1 and mean particle sizes of 1.85 {\mu}m were measured for these films.
Influence of Carbon Content on the Crystallographic Structure of Boron Carbide Films
O. Conde,A. J. Silvestre,J. C. Oliveira
Physics , 2002,
Abstract: Boron carbide thin films were synthesised by laser-assisted chemical vapour deposition (LCVD), using a CO2 laser beam and boron trichloride and methane as precursors. Boron and carbon contents were measured by electron probe microanalysis (EPMA). Microstructural analysis was carried out by Raman microspectroscopy and glancing incidence X-ray diffraction (GIXRD) was used to study the crystallographic structure and to determine the lattice parameters of the polycrystalline films. The rhombohedral-hexagonal boron carbide crystal lattice constants were plotted as a function of the carbon content, and the non-linear observed behaviour is interpreted on the basis of the complex structure of boron carbide. Keywords: Boron carbide; Laser CVD; crystallographic structure; micro-Raman spectroscopy.
Laser-Assisted Deposition of r-B4C Coatings Using Ethylene as Carbon Precursor
M. J. Santos,A. J. Silvestre,O. Conde
Physics , 2002,
Abstract: Rhombohedral B4C coatings were synthesised on fused silica substrates by CO2 laser-assisted chemical vapour deposition (LCVD), using a dynamic reactive atmosphere of BCl3, C2H4 and H2. Films with carbon content from 15 to 22 at.% were grown at deposition rates as high as 0.12 micrometers per second. The kinetics of the reactive system used to deposit the B4C films and the influence of growth conditions on the structure and morphology of the deposits were investigated. Keywords: Rhombohedral boron carbide (r-B4C), Laser-CVD, growth kinetics.
The Role of Carbon Precursor on Boron Carbide Synthesis by Laser-CVD
A. J. Silvestre,M. J. Santos,O. Conde
Physics , 2002,
Abstract: This paper focuses on the synthesis of rhombohedral B4C (r-B4C) coatings by CO2 laser-assisted chemical vapour deposition (LCVD), using a dynamic reactive atmosphere of BCl3, H2 and CH4 or C2H4. The influence of the carbon precursor on the deposition kinetics is discussed. The use of ethylene as carbon precursor presents several advantages over the use of methane, which is the conventional carbon precursor in CVD processes. These advantages are mainly related to its high absorption coefficient at the laser wavelength and a higher sticking coefficient, which enables to attain higher deposition rates and film thickness control at lower carbon precursor concentration. Films with carbon content from 15 to 22 at.% were grown at a deposition rate as high as 0.12 micrometers per second. Keywords: Rhombohedral boron carbide (r-B4C), Laser CVD.
Una analogía sobre el tiempo: entre historiografía e historiofotía, Octubre y Koyaanisqatsi
Aljuri Pimiento,Juan Camilo;
Historia Crítica , 2006,
Abstract: this article starts from the idea that temporality in film and historiography is different. while in the latter, for example, it is common to talk about events, junctures, long duration and cycles, in film more common terms are ralenti (slow-motion), condensation, acceleration and inversion. despite this difference, the article sustains that cinematic representation reproduces, in its own language, conceptions of temporality that history uses. to demonstrate how such a ?translation? would operate, this article, following the concept of historiophoty coined by hayden white, analyzes the films of october by eisenstein and koyaanisqatsi by reggio. with this exercise, it explores one, out of many possible ways, of using film as a source for historiographic studies.
Local Commons and Cross-Effects of Population and Inequality on the Local Provision of Environmental Services
Cárdenas,Juan Camilo;
Lecturas de Economía , 2005,
Abstract: tthe potential effect of population density over scarce natural resources has been present since the beginning of the environmental and resource debates. the role that inequality plays in this relationship has been less studied. this paper proposes that better distributions of land can lessen the effect of population pressure over land degradation, mainly by changing the use of labor and by providing incentives for more sustainable farm and land-use practices. using gis technologies and data from more than 100 "veredas" in the boyacá region (colombia), the econometric results support the proposition that under better distribution of land, the effect of population density on land degradation is smaller.
Estimación de la Curva de Phillips neokeynesiana para Colombia: 1990-2006
Galvis,Juan Camilo;
Lecturas de Economía , 2010,
Abstract: this paper seeks to verify empirically the existence of a new keynesian phillips curve for the colombian economy. this allows determining if inflation dynamics are likely explained by microeconomic foundations. additionally, this approach enables the analysis of price rigidities in the economy. the results suggest that: (1) unit labor costs explain inflation dynamics; (2) eighty percent of firms set their prices every five quarters; and, (3) productivity changes explain marginal costs.
Nino Vargas,Juan Camilo;
Antipoda. Revista de Antropología y Arqueología , 2010,
Abstract: in the early 20th century, the swedish anthropologist gustaf bolinder contacted the indigenous population of the ariguaní river in north colombia, known at the time as "chimila". as had other explorers and ethnologists, bolinder portrayed them as seriously disintegrated group which was almost extinct. the present article analyzes the process that gave rise to this idea, moving further from those interpretations that understand the ethnographic reports as either neutral descriptions or ethnocentric constructions. it is argued that the conception of chimila decadence was the result of a complex process of cultural interaction, in which indigenous practices and representations oriented toward isolationism, catastrophism and rejection of outsiders had an important infuence. the article also introduces two unpublished texts of bolinder on the subject.
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