Viscosity of copolymers containing carbon black

The flow behavior of random copolymers of styrene and butyl methacrylate containing specific carbon blacks varying in surface area were studied at various temperatures and shear rates. Master curves of reduced viscosity as a function of shear rate were prepared for the pure copolymers at 150°C. The superposition required vertical and horizontal shifts, proportional to (a_T)^?1 and (a_T)^.53, respectively, where a_T is the shift factor. With the incorporation of carbon black, the viscous response is non-Newtonian exhibiting a yield stress at increasing filler concentration and surface area. Master curves of viscosity against shear rate were generated at fixed filler loadings and surface areas by using a single horizontal shift factor.     

Systematic design of wideband ΔΣ modulators for WiFi/WiMAX receivers

Modern multi-standard receivers in deep-submicron technologies pose significant design challenges on the analog baseband. Moving this analog filtering to the digital domain simplifies the design, yielding a process-scalable implementation. However, analog-to-digital converter (ADC) specifications now become more stringent and must be obtained by comprehending the standard and the system. Assuming a receiver NF of 5.96 dB and SNR degradation of 0.36 dB by the ADC, the proposed dual-mode WiFi/WiMAX receiver attains an input sensitivity of −74 dBm (20 MHz channel bandwidth). To accommodate the high dynamic range and the anti-alias rejection needed for the system, a Delta-Sigma (ΔΣ) ADC is proposed. Single-loop and Multi-Stage Noise-Shaping (MASH) architectures that achieve a SNR of 69 dB at a low oversampling ratio (OSR) of 8 for a conversion bandwidth of 40 MHz (108 Mbps, OFDM) are investigated at system level. Based on thermal noise, harmonic distortion, and power tradeoffs, a ΔΣ ADC design that meets the design specifications is presented.     

An Indian test facility to characterise diagnostic neutral beam for ITER

The diagnostic neutral beam (DNB) line shall be used to diagnose the He ash content in the D–T phase of the ITER machine using the charge exchange recombination spectroscopy (CXRS). Implementation of a successful DNB at ITER requires several challenges related to the production, neutralization and transport of the neutral beam over path lengths of 20.665 m, to be overcome. The delivery is aided if the above effects are tested prior to onsite commissioning. As DNB is a procurement package for INDIA, an ITER approved Indian test facility, INTF, is under construction at Institute for Plasma Research (IPR), India and is envisaged to be operational in 2015. The timeline for this facility is synchronized with the RADI, ELISE (IPP, Garching), SPIDER (RFX, Padova) in a manner that best utilization of configurational inputs available from them are incorporated in the design. This paper describes the facility in detail and discusses the experiments planned to optimise the beam transmission and testing of the beam line components using various diagnostics.     

Rheology of copolymers containing carbon black

The rheological response of random copolymers of styrene and butyl methacrylate containing carbon black simulates the behavior of toner in the electrophotographic process. Both the relative viscosity and the dependence of viscosity on shear rate were increased by raising the temperature and raising the concentration and surface area of carbon black. For high concentrations and surface areas of carbon black and at elevated temperatures, a well-defined yield stress varied from 2.5 × 10² to 1.6 × 10⁴ Pa, depending on the concentration and nature of the carbon black but independent of the type of polymer and temperature, implying the formation of a carbon black network. Plasticization by carbon black was favored at low surface area and concentration of carbon black and at elevated temperatures.     

Rheology of polymers containing carbon black

In order to elucidate the flow behavior of electrophotographic toner systems, shear stress was measured as a function of shear rate in a cone and plate rheometer for polymer melts containing carbon blacks of surface area 24 and 625 m²/g at several concentrations and temperatures. Polymers included high and low molecular weight polystyrene and poly(butyl methacrylate). The addition of carbon black to the polymers caused a large increase in viscosity, especially at low shear rates and shear stresses. As the concentration of carbon black was increased, the viscosity at low shear rates became unbounded below a value of the shear stress designated the yield stress. The absolute magnitude of the yield stress depended primarily on the concentration and surface area of the carbon black and was independent of the polymer and temperature. Apparently, carbon black forms an independent network within the polymer at low shear rates which precludes flow. In some cases, the viscosity of polymers filled with carbon black was lower than that of the pure polymer. This effect was favored for polystyrene compared to poly(butyl methacrylate) and was facilitated by increasing the molecular weight of polystyrene, reducing the surface area and concentration of carbon black, and by increasing the temperature and shear rate.     

On a numerical subgrid upscaling algorithm for Stokes–Brinkman equations

This paper discusses a numerical subgrid resolution approach for solving the Stokes–Brinkman system of equations, which is describing coupled flow in plain and in highly porous media. Various scientific and industrial problems are described by this system, and often the geometry and/or the permeability vary on several scales. A particular target is the process of oil filtration. In many complicated filters, the filter medium or the filter element geometry are too fine to be resolved by a feasible computational grid. The subgrid approach presented in this paper is aimed at describing how these fine details are accounted for by solving auxiliary problems in appropriately chosen grid cells on a relatively coarse computational grid. This is done via a systematic and careful procedure of modifying and updating the coefficients of the Stokes–Brinkman system in chosen cells. This numerical subgrid approach is motivated from one side from homogenization theory, from which we borrow the formulations for the so-called cell problem, and from the other side from the numerical upscaling approaches, such as Multiscale Finite Volume, Multiscale Finite Element, etc. Results on the algorithm’s efficiency, both in terms of computational time and memory usage, are presented. Comparison of the full fine grid solution (when possible) of the Stokes–Brinkman system with the subgrid solution of the upscaled Stokes–Brinkman system (including effective permeabilities for the quasi-porous cells), are presented in order to evaluate the accuracy and the efficiency. Advantages and limitations of the considered subgrid approach are discussed.     

The lock-on effect in electron-beam-controlled gallium arsenideswitches

The authors analyze the lock-on effect, which is the inability of photoconductive or electron-beam-controlled semiconductor switches to recover to their initial hold-off voltages following the application of the laser or electron-beam pulse, if the applied voltage exceeds a certain value. For GaAs this threshold voltage corresponds to average electric fields in the range from 4 to 12 kV/cm. Experimental results on semi-insulating GaAs switches indicate that the corresponding lock-on current after e-beam irradiation is identical with the steady-state dark current. The highly resistive state of the switch before e-beam irradiation is shown to be a transient phase towards the much lower steady-state dark resistance, with a duration which depends on the impurity content of the switch material and the applied voltage. The irradiation of the GaAs samples with electrons or photons causes an acceleration of this temporal evolution; at sufficiently high laser or e-beam intensities, lock-on of the dark current after termination of the driving ionization source is observed. Based on the experimental results, a model is developed which describes the lock-on effect in terms of double injection and carrier trapping in deep intraband levels. The model explains the major characteristics of the lock-up effects and is supported by the qualitative agreement of the calculated current-voltage curves with the experimental data     

Micromachined high-Q inductors in a 0.18-μm copper interconnectlow-k dielectric CMOS process

On-chip spiral micromachined inductors fabricated in a 0.18-μm digital CMOS process with 6-level copper interconnect and low-K dielectric are described. A post-CMOS maskless micromachining process compatible with the CMOS materials and design rules has been developed to create inductors suspended above the substrate with the inter-turn dielectric removed. Such inductors have higher quality factors as substrate losses are eliminated by silicon removal and increased self-resonant frequency due to reduction of inter-turn and substrate parasitic capacitances. Quality factors up to 12 were obtained for a 3.2-nH micromachined inductor at 7.5 GHz. Improvements of up to 180% in maximum quality factor, along with 40%-70% increase in self-resonant frequency were seen over conventional inductors. The effects of micromachining on inductor performance was modeled using a physics-based model with predictive capability. The model was verified by measurements at various stages of the post-CMOS processing. Micromachined inductor quality factor is limited by series resistance up to a predicted metal thickness of between 6-10 μm     

Assessing the performance of air cleaning devices – A full-scale test method

Activated carbon filters have been used for purification of air and water in industrial applications. However, these technologies have not been applied to the non-industrial built environment in general and there is no standard to quantify or to classify the performance of these systems for in-duct mechanical system application. The development of a standard test procedure is a very timely effort, since it would create a benchmark for evaluating the contaminant reduction of these systems. A full-scale test facility was designed and constructed to investigate the removal effectiveness of commercial gas-phase air cleaning devices. The test rig was verified by conducting the system pre-qualification tests. These series of tests were designed to quantitatively verify the reliability of the test rig for gas filter application. These tests include air tightness, velocity uniformity, uniform dispersion of challenge contaminants, temperature and humidity control. This paper first describes the experimental set-up for testing of in-duct air cleaner systems and its verification, and then presents the experimental results of four different kinds of commercial gaseous filters.