Dependence of disperse dye diffusion on the structure and morphology of oriented heat–set polyester fibres

The structural parameters that predominantly influence dye diffusion behaviour in heat–set polyester fibres have been identified. Dye diffusion has been shown to depend on two factors: the volume of the accessible region (amorphous region) and the tortuosity of the dye diffusion path. The accessible region can be represented in terms of the amorphous volume per crystal, and the tortuosity can be expressed quantitatively by combining the orientation of the amorphous phase and the nature of coupling between the amorphous and the crystalline regions. An integrated model has been proposed by combining these parameters, and has been shown to correlate well with dye uptake in polyester fibres heat–set under slack and taut conditions.     

High-frequency performance of metamorphic InP/In0.53Ga0.47As/InP DHBT in common base configuration on GaAs substrates

In this work, we report the detailed high-frequency noise and power characterization of metamorphic InP double heterojunction bipolar transistors in common base configuration. The noise and power performances were investigated for 5×10 μm² device. A minimum noise figure of 2.3 dB with an associated gain of 14.5 dB at 2 GHz, and a maximum output power of 13.0 dBm with a power added efficiency of 47.8% at 2.4 GHz were obtained.     

Design and Modeling of a Nanomechanical Sensor Using Silicon Photonic Crystals

Conventionally a line defect in the photonic crystal (PhC) is used to create a waveguide for light propagation through the PhC. A PhC based filter is designed by introducing micro-cavities within the line defect so as to form the resonant bandgap structure for PhC. Such a PhC waveguide (PhCWG) filter shows sharp resonant peak in output wavelength spectrum. We proposed a suspended silicon bridge structure comprising this PhCWG filter structure. Since the output resonant wavelength is sensitive to the shape of air holes and defect length of the micro-cavity. Shift of the output resonant wavelength is observed for suspended PhCWG beam structure under particular force loading. In other words, the induced strain modifies the shape of air holes and the spacing among them. Such an effect leads to shift of resonant wavelength. Under optical detection limitation of 0.1 nm for resonant wavelength shift, the sensing capability of this nanomechanical sensor is derived as that vertical deformation is 20-25 nm at the center and the smallest strain is 0.005% for defect length. This innovative design conceptualizes a new application area for PhCs, i.e., the nanometer-scale physical sensors for strains and forces.     

Influence of initial mixing methods on melt‐extruded single‐walled carbon nanotube–polypropylene nanocomposites

We report the first direct comparison of melt‐extruded polypropylene–single‐walled carbon nanotube (PP/SWNT) nanocomposites prepared by three different initial mixing methods. The standard deviation of the G‐band intensity obtained using Raman mapping was found to be the best measure of dispersion uniformity in the extruded composites, and dispersion uniformity was found to generally correlate with rheological and thermal properties. For all three initial mixing methods, both unmodified and sidewall‐functionalized purified SWNTs were evaluated. Surprisingly, in all cases, dodecylated SWNTs prepared using the reductive alkylation method were less uniformly dispersed in the final composite than the unmodified SWNTs. The simplest process, dry blending, resulted in poor nanotube dispersion and only polymer crystallization was significantly affected by the presence of the nanotubes. A slightly more complex rotary evaporation process resulted in significantly more uniform dispersion and significant changes in rheological properties, polymer crystallization, and thermal stability. The most elaborate process tested, hot coagulation, enabled the most uniform dispersion and the greatest change in properties but also resulted in some polymer degradation. POLYM. ENG. SCI., 50:1831–1842, 2010. © 2010 Society of Plastics Engineers     

Estimating regularity in epileptic seizure time-series data

The authors apply Ziv-Lempel (LZ) complexity and approximate entropy (ApEn) as measures to quantify the regularity in the various epochs of epileptic seizure time series data. They demonstrate the potential of complexity measures such as LZ and ApEn in quantifying the regularity at different epochs of epileptic seizure time-series data. It is clearly shown that these measures have high values at the beginning and the end of the seizure, and that they decrease during mid-seizure. In fact, the authors observe in the histogram plot that the frequency of the complexity measure in mid-seizure is quite prominent. This gives one an idea about the epoch where one can find more regular patterns. These measures can also be used as relative indices (comparing across state), rather than absolute indices, by using a larger number of subjects to obtain statistical validity in comparing across conditions. The analysis of time series obtained from complex systems, such as the brain, by the above measures provides an alternative easy way to quantify the regularity with finite-length segments (of the order of 1000 samples). The same can be inferred by calculating the correlation dimension and Lyapunov exponent, but the algorithms used to estimate these invariants are susceptible to error due to the finite sample size and are also highly sensitive to noise. The computational complexity of these algorithms is also high. The authors have also applied these measures across the various states of epilepsy     

Three-dimensional filtering of engineering surfaces using envelope system

With the advent of cheap and powerful computers, three-dimensional evaluation of surfaces is possible. This article deals with the development of a computational method for three-dimensional filtering of surface using the envelope system (E-System, a dialation using a sphere) concept. The shape of the envelope surface is dependent only on the prominent peak points on the surface. The computational method developed uses this set of prominent points to facilitate fast evaluation of the envelope surface. Roughness values obtained by two, two-and-a-half, and three-dimensional evaluation of typical surfaces are also given. This procedure of waviness filtering gives a strong base for an integrated approach for surface and form measurements.     

Die attach failures related to wafer back metal processing—an AES study

Die attach failures on Cr/Ni/Au back-metallised silicon wafers have been studied under different process conditions. The Auger studies on the failed devices show that the formation of nickel oxide causes poor die attachment even for an Au film thickness of ∼ 500 Å. The failures simulated experimentally revealed that nickel oxide formation depends on the film sintering conditions.