3,051 research outputs found
Investigation into time dependant degradation and atmospheric conditions on the wettability of nylon 6,6 which has undergone CO2 laser surface modification
Modification of the wettability of polymers has been demonstrated previously; however, it is known that the wettability modifications of these materials can degrade or vary over time. This can be seen to be crucial from a commercial point of view as this would indicate that a shelf-life has to be established. But at the same time, atmospheric parameters may affect the contact angle and must therefore be accounted for as a control variable in any long-term study of wettability. In this study four CO2 laser patterned nylon 6,6 samples with differing topographical patterns and one as-received sample were analysed over a 30 week period whilst stored in ambient air. By obtaining the characteristic contact angle every two weeks it was found that the contact angle varied erratically before ultimately increasing for all samples after the 30 weeks. White light interferometry analysis determined that the laser patterning gave rise to peak heights of up to 3 μm with roughness parameters Ra and Sa of up to 0.305 and 0.408 μm, respectively. X-ray photoelectron spectroscopy found that surface oxygen content increased by up to 7 %At. It was identified that there was a significant correlation between changes in barometric air pressure and contact angle, highlighting the need for further study to determine if this is a dominant factor
Effects of Positions in Knowledge Networks on Trust
This paper empirically explores relations between network positions in knowledge networks and trust. In social network theory the closure argument and the gossip argument describe this relation. These two arguments do not distinguish between different dimensions of trust. In this paper we estimate effects of closure positions on two dimensions of trust (trust in abilities and trust in intentions). The closure argument emphasizes that dense network structures enforce individuals to be trustworthy. The gossip argument emphasizes that dense networks amplifies gossip. Since it was found that different network positions are optimal for different tasks, we propose that the content of a network is an intrinsic characteristic of a network that influences whether gossip is neutral or judgmental. To discern between different contents we consider two task-specific knowledge networks. Empirical data were collected on a network of 55 individuals in the setting of account management. These data strongly support the gossip argument for both dimensions of trust. However, the data only gave weak and ambiguous support for the closure argument
Magnetoresistance of Three-Constituent Composites: Percolation Near a Critical Line
Scaling theory, duality symmetry, and numerical simulations of a random
network model are used to study the magnetoresistance of a
metal/insulator/perfect conductor composite with a disordered columnar
microstructure. The phase diagram is found to have a critical line which
separates regions of saturating and non-saturating magnetoresistance. The
percolation problem which describes this line is a generalization of
anisotropic percolation. We locate the percolation threshold and determine the
t = s = 1.30 +- 0.02, nu = 4/3 +- 0.02, which are the same as in
two-constituent 2D isotropic percolation. We also determine the exponents which
characterize the critical dependence on magnetic field, and confirm numerically
that nu is independent of anisotropy. We propose and test a complete scaling
description of the magnetoresistance in the vicinity of the critical line.Comment: Substantially revised version; description of behavior in finite
magnetic fields added. 7 pages, 7 figures, submitted to PR
Siegel Gauge in Vacuum String Field Theory
We study the star algebra of ghost sector in vacuum string field theory
(VSFT). We show that the star product of two states in the Siegel gauge is BRST
exact if we take the BRST charge to be the one found in hep-th/0108150, and the
BRST exact states are nil factors in the star algebra. By introducing a new
star product defined on the states in the Siegel gauge, the equation of motion
of VSFT is characterized as the projection condition with respect to this new
product. We also comment on the comma form of string vertex in the ghost
sector.Comment: 13 pages, lanlmac; v3: comment adde
Dependence of the Electroluminescence on the Spacer Layer Growth Temperature of Multilayer Quantum-Dot Laser Structures
Electroluminescence (EL) measurements have been performed on a set of In(Ga)As-GaAs quantum-dot (QD) structures with varying spacer layer growth temperature. At room temperature and low injection current, a superlinear dependence of the integrated EL intensity (IEL) on the injection current is observed. This superlinearity decreases as the spacer layer growth temperature increases and is attributed to a reduction in the amount of nonradiative recombination. Temperature-dependent IEL measurements show a reduction of the IEL with increasing temperature. Two thermally activated quenching processes, with activation energies of ˜ 157 meV and ˜ 320 meV, are deduced and these are attributed to the loss of electrons and holes from the QD ground state to the GaAs barriers. Our results demonstrate that growing the GaAs barriers at higher temperatures improves their quality, thereby increasing the radiative efficiency of the QD emission
Sine-Gordon Field Theory for the Kosterlitz-Thouless Transitions on Fluctuating Membranes
In the preceding paper, we derived Coulomb-gas and sine-Gordon Hamiltonians
to describe the Kosterlitz-Thouless transition on a fluctuating surface. These
Hamiltonians contain couplings to Gaussian curvature not found in a rigid flat
surface. In this paper, we derive renormalization-group recursion relations for
the sine-Gordon model using field-theoretic techniques developed to study flat
space problems.Comment: REVTEX, 14 pages with 6 postscript figures compressed using uufiles.
Accepted for publication in Phys. Rev.
An international educational perspective on technology and change
For a number of reasons design and technology has over the past decade played a very central and key role in educational reforms. Notably being at a pivotal point between core and foundation subjects, academic and vocational education and science and arts.
This paper will research, reflect and synthesise other approaches to technology education in a number of other countries including England and Wales, Scotland, France, Germany, Denmark, Italy, Russia, Japan, USA, Canada, Australia plus one developing and one Eastern European country.
Each of the selected countries will be analysed on the following profile along with a schematic over view of the educational system from its early years through to degree level.
Historical perspective
Overview and educational structure
Technology including Information Technology and Vocational Education
Key Points and Future aim
An Equilibrium-Correction Model for Dynamic Network Data
We propose a two-stage MRQAP to analyze dynamic network data, within the framework of an equilibrium-correction (EC) model. Extensive simulation results indicate practical relevance of our method and its improvement over standard OLS. An empirical illustration additionally shows that the EC model yields interpretable parameters, in contrast to an unrestricted dynamic model
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