983 resultados para Polymer Science and Rubber Technology


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This occasional paper examines the experiences of three leading global centres of the ICT industry – India, Silicon Valley, and Estonia – to reflect on how the lessons of these models can be applied to the context of countries in the Caribbean region.Several sectors of the technology industry are considered in relation to the suitability for their establishment in the Caribbean. Animation is an area that is showing encouraging signs of development in several countries, and which offers some promise to provide a significant source of employment in the region. However, the global market for animation production is likely to become increasingly competitive, as improved technology has reduced barriers to entry into the industry not only in the Caribbean, but around the world. The region’s animation industry will need to move swiftly up the value chain if it is to avoid the downsides of being caught in an increasingly commoditized market. Mobile applications development has also been widely a heralded industry for the Caribbean. However, the market for consumer-oriented smartphone applications has matured very quickly, and is now a very difficult sector in which to compete. Caribbean mobile developers would be better served to focus on creating applications to suit the needs of regional industries and governments, rather than attempting to gain notice in over-saturated consumer marketplaces such as the iTunes App Store and Google Play. Another sector considered for the Caribbean is “big data” analysis. This area holds significant potential for growth in coming years, but the Caribbean, which is generally considered to be a datapoor region, currently lacks a sufficient base of local customers to form a competitive foundation for such an industry. While a Caribbean big data industry could plausibly be oriented toward outsourcing, that orientation would limit positive externalities from the sector, and benefits from its establishment would largely accrue only to a relatively small number of direct participants in the industry. Instead, development in the big data sector should be twinned with the development of products to build a regional customer base for the industry. The region has pressing needs in areas such as disaster risk reduction, water resource management, and support for agricultural production. Development of big data solutions – and other technology products – to address areas such as these could help to establish niche industries that both support the needs of local populations, and provide viable opportunities for the export of higher-value products and services to regions of the world with similar needs.

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This document was adapted from a paper originally presented to the 8th Annual Caribbean Conference of Comprehensive Disaster Management, held in Montego Bay, Jamaica in December, 2013. It summarizes several activities that ECLAC has undertaken to assess the current state of information and communications technology (ICT) in the field of disaster risk management (DRM) as practiced in the Caribbean. These activities included an in-depth study that encompassed a survey of disaster management organizations in the region, an Expert Group Meeting attended by the heads of several national disaster offices, and a training workshop for professionals working in DRM in the Caribbean. One of the notable conclusions of ECLAC’s investigation on this topic is that the lack of human capacity is the single largest constraint that is faced in the implementation of ICT projects for DRM in the Caribbean. In considering strategies to address the challenge of limited human capacity at a regional level, two separate issues are recognized – the need to increase the ICT capabilities of disaster management professionals, and the need to make ICT specialists available to disaster management organizations to advise and assist in the implementation of technology-focused projects. To that end, two models are proposed to engage with this issue at a regional level. The first entails the establishment of a network of ICT trainers in the Caribbean to help DRM staff develop a strategic understanding of how technology can be used to further their organizational goals. The second is the development of “Centres of Excellence” for ICT in the Caribbean, which would enable the deployment of specialized ICT expertise to national disaster management offices on a project-by-project basis.

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This study investigates the extent to which the digital boom has had repercussions on productive activity, in terms of both manufacturing (ict goods) and services (ict services), in addition to its potential ramifications in the rest of the Mexican economy. Input-output matrices are used and compared to those of Brazil and the United States. Mexico has fallen behind, particularly in the production of ict goods, and the productive chains of this activity have weakened. The ict services sector offers much greater potential than has been exploited thus far, with the advantage that it involves comparatively more value added and has major diversification possibilities. It is considered essential to find more effective industrial policies targeted on the ict goods and services sectors; but the experience of countries such as Brazil, which have applied more proactive approaches with mixed results, suggests that this will be challenging.

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New information technologies and new forms of documentary production have led archivists to rethink the role of archival science in the so-called information age. Since the late 1980s, the principles, methods and concepts stated by the well-known manuals of the 19th and the 20th centuries have been reconsidered along with their application to the organic sets of document in the 21st century. In this new scenario of reformulation and reinterpretation regarding the perspectives on archival knowledge organization, two trends with different approaches have emerged in North America and Europe: postmodern archival science and contemporary diplomatics, respectively. The first one was introduced by Terry Cook, who proposed a reformulation of the basic concepts and the functional analysis method focusing on the process and context of document creation. The second approach originated in Italy and incorporated all the theoretical and methodological models of classic diplomatics. The studies following this new trend were disseminated by Luciana Duranti and aimed to ensure the production, access and use of the documentation generated in the present times focusing on document typology, as opposed by the postmodern approach. The purpose of this study is to elucidate the connection points and distinct features between the two trends concerning the organization of archival knowledge.

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This study compares information-seeking behavior of Bachelor of Science and Master of Science students in the fields of agricultural extension and education. The authors surveyed Iranian students in departments of agricultural extension and education at four universities in Tehran, Shiraz, Mollasani, and Kermanshah. This study focused on three aspects: (1) comparison of amounts of information-seeking behavior between Bachelor of Science and Master of Science agricultural extension and education students; (2) comparison of information-seeking behavior varieties in Bachelor of Science and Master of Science agricultural extension and education students; (3) Comparison of amounts of available information resources at four universities and its effectiveness on students' information-seeking behavior; and (4) comparison of research and educational outputs in Bachelor of Science and Master of Science students. Scale free technique, division by mean method, principal components analysis technique, Delphi method, t-test, correlation and regression tools were used for data analysis. This study revealed that Bachelor of Science students' information-seeking behavior is for improving educational output, but Master of Science students' information-seeking behavior is for promoting research output. Among varieties of Internet searching skills, library searching skills, and awareness of library information-seeking methods with students' information-seeking behavior, there are not significant differences between two groups of students.

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As I write this on the first business day of 2010, I find myself thinking about the importance of respecting alternative views --- not only alternative political views, but also alternative scientific views. Good science requires that we understand the limits of knowledge and continuously seek the truth through respectful questioning, replication and review. In the climate change debate, which recently culminated in a disappointing and largely ineffective conference in Copenhagen, these salient principles of science were grossly violated. Well respected climate scientists proceeded well beyond the limits of their knowledge and became policy advocates. They demeaned anyone who dared to disagree with their findings or to suggest that limiting CO2 emissions may not be the best policy choice at the present time. Disagreeing with the “experts” became disrespected professional behavior, even within the academic community. This approach has not served the interests of anyone very well.

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The present paper presents a historical study on the acceptance of Newton's corpuscular theory of light in the early eighteenth century. Isaac Newton first published his famous book Opticks in 1704. After its publication, it became quite popular and was an almost mandatory presence in cultural life of Enlightenment societies. However, Newton's optics did not become popular only via his own words and hands, but also via public lectures and short books with scientific contents devoted to general public (including women) that emerged in the period as a sort of entertainment business. Lectures and writers stressed the inductivist approach to the study of nature and presented Newton's ideas about optics as they were consensual among natural philosophers in the period. The historical case study presented in this paper illustrates relevant aspects of nature of science, which can be explored by students of physics on undergraduate level or in physics teacher training programs.

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Liquid Crystal Polymer Brushes and their Application as Alignment Layers in Liquid Crystal Cells Polymer brushes with liquid crystalline (LC) side chains were synthesized on planar glass substrates and their nematic textures were investigated. The LC polymers consist of an acrylate or a methacrylate main chain and a phenyl benzoate group as the mesogenic unit which is connected to the main chain via a flexible alkyl spacer composed of six CH2 units. The preparation of the LC polymer brushes was carried out according to the “grafting from” technique: polymerization is carried out from azo-initiators that have been previously self-assembled on the substrate. LC polymer brushes with a thickness from a few nm to 230 nm were synthesized by varying the monomer concentration and the polymerization time. The LC polymer brushes were thick enough to allow for direct observation of the nematic textures with a polarizing microscope. The LC polymer brushes grown on untreated glass substrates exhibited irregular textures (“polydomains”). The domain size is in the range of some micrometers and depends only weakly on the brush thickness. The investigations on the texture-temperature relationship of the LC brushes revealed that the brushes exhibit a surface memory effect, that is, the identical texture reappears after the LC brush sample has experienced a thermal isotropization or a solvent treatment, at which the nematic LC state has been completely destroyed. The surface memory effect is attributed to a strong anchoring of the orientation of the mesogenic units to heterogeneities at the substrate surface. The exact nature of the surface heterogeneities is unknown. The effect was observed for the LC brushes swollen with low molecular weight nematic molecules, as well. Rubbing the glass substrate with a piece of velvet cloth prior to the surface modification with the initiator and the brush growth gives rise to the formation of homogenous alignment of the mesogenic units in the LC polymer side chains. Monodomain textures were obtained for these LC brushes. The mechanism for the homogeneous alignment is based on the transfer of Nylon fibers during the rubbing process. A surfactant was mixed with the azo-initiator in modifying rubbed substrates for subsequent brush generation. Such brushes exhibited biaxial optical properties. Hybrid LC cells made from a substrate modified with biaxial brushes and a rubbed glass substrate show an orientation with a tilt angle of a = –15.6 . This work shows that LC brushes grown on rubbed surfaces fulfill the important criteria for alignment layers: the formation of macroscopic monodomains. First results indicate that by diluting the brush with molecules which are also covalently bound to the surface but induce a different orientation, a system is obtained in which the two conflicting alignment mechanisms can be used to generate a tilted alignment. In order to allow for an application of the alignment layers into a potential product, subsequent work should focus on the questions how easy and in which range the tilt angle can be controlled.

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Aim of this thesis was to further extend the applicability of the Fourier-transform (FT) rheology technique especially for non-linear mechanical characterisation of polymeric materials on the one hand and to investigated the influence of the degree of branching on the linear and non-linear relaxation behaviour of polymeric materials on the other hand. The latter was achieved by employing in particular FT-rheology and other rheological techniques to variously branched polymer melts and solutions. For these purposes, narrowly distributed linear and star-shaped polystyrene and polybutadiene homo-polymers with varying molecular weights were anionically synthesised using both high-vacuum and inert atmosphere techniques. Furthermore, differently entangled solutions of linear and star-shaped polystyrenes in di-sec-octyl phthalate (DOP) were prepared. The several linear polystyrene solutions were measured under large amplitude oscillatory shear (LAOS) conditions and the non-linear torque response was analysed in the Fourier space. Experimental results were compared with numerical predictions performed by Dr. B. Debbaut using a multi-mode differential viscoelastic fluid model obeying the Giesekus constitutive equation. Apart from the analysis of the relative intensities of the harmonics, a detailed examination of the phase information content was developed. Further on, FT-rheology allowed to distinguish polystyrene melts and solutions due to their different topologies where other rheological measurements failed. Significant differences occurred under LAOS conditions as particularly reflected in the phase difference of the third harmonic, Ħ3, which could be related to shear thinning and shear thickening behaviour.

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In this work the surface layer formation in polymer melts and in polymer solutions have been investigated with the atomic force microscope (AFM). In polymer melts, the formation of an immobile surface layer results in a steric repulsion, which can be measured by the AFM. From former work it is know, that polydimethyl siloxane (PDMS) forms a stable surface layer for molecular weights above 12 kDa. In the present thesis, polyisoprene (PI) was investigated apart from PDMS, by a)measuring the steric surface interactions and b)measuring the surface slip in hydrodynamic experiments. If a polymer flows over a surface, the flow velocity at the surface is larger then zero. If case of a surface layer formation the flow plane changes to the top of the adsorbed layer and the surface slip is reduced to zero. By measuring the surface slip in hydrodynamic experiments, it is therefore possible to determine the presence of a stable surface layer. The results show no stable repulsion for PI and only a small decrease of the surface slip. This indicates that PI does not form a stable surface layer, but is only adsorbed weakly to the surface. Furthermore for 8 kDa PDMS the timescale of the formation of a surface layer was investigated by changing themaximal force the tip applied to the surface. With a repulsive force present, applying a higher force than 15 nN resulted in a destruction of the surface layer, indicated by attractive forces. Reducing the applied force below 15 nN then resulted in an increase of the repulsion to the former state during one minute, thus indicating that a surface layer can be formed within one minute even under the influence of continuous measurements. As a next step, mixtures of two PDMS homopolymers with different chain lengths have been investigated. The aim was to verify theoretical predictions that shorter chains should predominate at the surface due to their smaller loss in conformational entropy. The measurements where done in dependence of the volume fractions of short and long chain PMDS. The results confirmed the short chain dominance for all mixtures with less then 90 vol.% long chain PDMS. Surface layer formation in solution was investigated for superplasticizers which are industrially used as an additive to cement. They change the surface interaction between the cement grains from attractive to repulsive and the freshlymixed cement paste therefore becomes liquid. The aimin this part of the thesis was, to investigate cement particle interactions in a close to real environment. Therefore calcium silicate hydrate phases have been precipitated onto an AFM tip and onto a calcite crystal and the interaction between these surfaces have beenmeasured with and without addition of superplasticizers. The measurements confirmed the change from attraction to repulsion upon addition of superplasticizers. The repulsive steric interaction increased with the length of the sidechain of the superplasticizer, and the dependence of the range of the steric interactions on the sidechain length indicated that the sidechains are in a coiled conformation.