Segregated structures in carbon black-containing immiscible polymer blends: HIPS/LLDPE systems

The structure/electrical resistivity relationship in CB-loaded immiscible HIPS/LLDPE blends was studied. Effects of CB content and location, dispersed polymer phase size and shape, dispersed phase viscosity, and processing procedures were examined. The elongated dispersed phase in CB-containing blends is essential for promoting conductivity in formulations prepared by melt mixing and compression molding. However, the same formulations proved highly resistive when injection-molded, due to orientation and excessive shearing. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1097–1106, 1997     

Conductive polymer blends with low carbon black loading: Polypropylene/polyamide

The electrical resistivity and morphology of polypropylene/nylon (PP/Ny) immiscible blends incorporated with carbon black (CB) were studied. CB was found to be preferentially located in the Ny phase or upon the Ny/PP interface. Blends with a co-continuous phase morphology depicted especially low resistivity values, due to a “double percolation” effect. The blend preparation sequence tends to affect the phase morphology, thus influencing the system's resistivity. Polymer polarity and crystallinity are important factors determining the blend's morphology, which relates directly to the electrical resistivity obtained.     

Energy-efficient optical acquisition schemes in wireless sensor networks

Energy-efficiency is an essential feature of wireless sensor networks (WSNs) where the longevity of autonomous sensor nodes is limited by their battery life and/or energy-harvesting capability. Base-station-initiated optical wireless communication with nodes equipped with a passive optical transmitter in the form of a corner cube retroreflector (CCR) provides sensor acquisition with no energy expenditure on the part of the sensor node itself and is therefore an attractive option for WSN. However, the return signal from an illuminated sensor node is a stochastic variable dependant on fabrication parameters, ambient conditions and receiver noise so that the sensor acquisition process is inherently error-prone. In this paper we propose an energy-aware, base station-initiated interrogation scheme based on exponentially increasing beam scan areas, that takes into consideration the error-prone trait of CCR-outfitted sensor nodes. We analyse the scheme performance subject to different values of signal variance and various cost functions. We extend the analysis to address the circumstance of a spatially-limited sensor-failure event, such as may be caused by deliberate tampering or by environmental factors. We show that agile beam-steering on the basis of accrued knowledge of contaminated sensor distributions promotes energy-conserving acquisition. The validity of a Poisson spatial distribution model for the sensor dispersion is discussed and the impact of this initial assumption on acquisition error is demonstrated.     

Analyzing the performance of a nanosatellite cluster-detector array receiver for laser communication

This work analyzes laser communication between a cluster of nanosatellites, which is a concentrated formation of small lightweight satellites and a ground station. The scenario under consideration is a cluster of nanosatellites communicating by means of a laser beam with a detector array receiver that is located on the earth's surface and equipped with a common optical system for all incoming beams. The beams are concentrated to spots over the detector plane by the receiver's optics. The detector array enables the ground station to communicate with a tight concentration of the nanosatellites, which reduces system complexity and cost. A critical parameter that determines the successful receipt and subsequent decoding of a transmitted signal for a given configuration is the angular separation between the satellites within the cluster. This separation must be retained to prevent critical overlapping of the spots on the detector's surface. The maximum allowable overlapping is calculated in terms of given bit-error rate. The spatial spreading of the beams, caused by scattering from aerosols in different layers of the atmosphere, is calculated for the case of single scattering. A stratified model of the atmosphere is used. Turbulence influences the beam width, especially for the case of short exposure, and is primarily caused by temperature changes, which result in fluctuations in the refractive index. In this research, a new approach is adopted for analyzing communication network performance through the atmosphere by applying optical-transfer function (OTF) concepts used in imaging and remote sensing. We evaluate the effectiveness of this new approach in applications where spatial spread between the users is very important.     

Stability,Sequentiality and Demand Driven Evaluation in Dataflow

We show that a given dataflow language l has the property that for any program P and any demand for outputs D (which can be satisfied) there exists a least partial computation of P which satisfies D, iff all the operators of l are stable. This minimal computation is the demand-driven evaluation of P. We also argue that in order to actually implement this mode of evaluation, the operators of l should be further restricted to be effectively sequential ones.     

eTuner: tuning schema matching software using synthetic scenarios

Most recent schema matching systems assemble multiple components, each employing a particular matching technique. The domain user mustthen tune the system: select the right component to be executed and correctly adjust their numerous “knobs” (e.g., thresholds, formula coefficients). Tuning is skill and time intensive, but (as we show) without it the matching accuracy is significantly inferior. We describe eTuner, an approach to automatically tune schema matching systems. Given a schema S, we match S against synthetic schemas, for which the ground truth mapping is known, and find a tuning that demonstrably improves the performance of matching S against real schemas. To efficiently search the huge space of tuning configurations, eTuner works sequentially, starting with tuning the lowest level components. To increase the applicability of eTuner, we develop methods to tune a broad range of matching components. While the tuning process is completely automatic, eTuner can also exploit user assistance (whenever available) to further improve the tuning quality. We employed eTuner to tune four recently developed matching systems on several real-world domains. The results show that eTuner produced tuned matching systems that achieve higher accuracy than using the systems with currently possible tuning methods.     

Optical technique for the automatic detection and measurement of surface defects on thin metallic wires

In industrial applications of thin metallic wires it is important to characterize the surface defects of the wires. We present an optical technique for the automatic detection of surface defects on thin metallic wires (diameters, 50-2000 mum) that can be used in on-line systems for surface quality control. This technique is based on the intensity variations on the scattered cone generated when the wire is illuminated with a beam at oblique incidence. Our results are compared with those obtained by atomic-force microscopy and scanning-electron microscopy.     

Theophylline induces diapause-like state in social wasps

Feeding of theophylline to hornet workers from their moment of eclosion during the summer results in the following effects on the hornets: loss of appetite for proteins, inhibited ovarial development, no cell-building activity, negative phototaxis, gradual slow-down of spontaneous motor activity, difficulty in flight and orientation, and an overall behavior pattern reminiscent of hornet queens in nature when they are in a state of winter diapause. These findings suggest that theophylline exerts anti-juvenile-hormone-like effects on hornets and raise the possibility of utilizing theophylline baits to suppress pest hornet populations.     

Performance of expanded graphite and expanded milled‐graphite fillers in thermosetting resins

Epoxy/expanded graphite (EG) and polyester/EG composites were prepared with the aid of sonication, while epoxy/expanded‐milled graphite (epoxy/milled‐EG) and polyester/expanded‐milled graphite (polyester/milled‐EG) composites were prepared on a three‐roll paint mill. The epoxy/EG and polyester/EG composites exhibit a sharp insulator/semiconductor transition at markedly low percolation thresholds, due to the vermicular shape of EG having high aspect ratio and surface area. The morphologies of epoxy and polyester resins incorporated with EG and milled‐EG fillers were observed by scanning electron microscopy (SEM). The results of dynamic mechanical analysis of the composites reveal that both EG and milled‐EG fillers increase the T_g of the epoxy matrix. Milled‐EG increases the G′ of the epoxy matrix, while EG decreases the G′ of the epoxy matrix, due to the existence of abundant pores in EG. The milled‐EG filler has the same effect on the polyester matrix as on the epoxy matrix, but the EG filler has no significant effect on the mechanical properties of polyester matrix. POLYM. COMPOS., 26:526–533, 2005. © 2005 Society of Plastics Engineers     

Deformation behaviour of coextruded multilayer composites with polycarbonate and poly(styrene-acrylonitrile)

The tensile properties of coextruded multilayer composites comprised of predominantly 49 alternating layers of polycarbonate (PC) and polystyrene- acrylonitrile (SAN) were investigated in the bulk and microscopically. The bulk was characterized by three types of behaviour: brittle fracture at low strains, ductile yielding with fracture during neck formation, and formation of a stable neck followed by drawing to high extension. Optical microscopy was utilized to correlate deformation mechanisms within each phase to the observed modes of deformation in the bulk. Optical microscopy showed that in all cases the initial irreversible deformation event was the formation of cracks or crazes in the SAN layers. Good adhesion between the layers resulted in the subsequent initiation of shear bands in the polycarbonate layers at the craze tips. Interaction of crazes and shear bands produced an expanded damage zone ahead of the propagating crack which delocalized the stress and delayed fracture. The ultimate mode of fracture depended on the relative thickness of the SAN and PC layers, as determined by the composition, and the strain rate.