New polyisobutylene-based model elastomeric ionomers: RheoLogical behavior

The rheological behavior of sulfonated polyisobutylene based elastomeric ionomers has been studied. The effects of molecular architecture, type of cation, and addition of excess neutralization agent were investigated. The effect of temperature was studied to a limited extent. In a specific case, the influence of an ionic plasticizer, zinc stearate was also examined. It was found that in these telechelic ionomers where the ionic groups are located exclusively at the chain ends, significant Ionic interactions may persist even at 180°C. The zinc-neutralized ionomers had the lowest viscosity as compared to the corresponding potassium- or calcium-neutralized ionomers. The covalent character of zinc is believed responsible for this behavior. Other factors being constant, the triarm based ionomers are more viscous than the monofunctional ionomers. A mixture of monofunctional ionomers with the triarm, species is a model for dangling chain ends, and results in a slight lowering of the viscosity under the conditions studied. Zinc stearate acts as an ionic plasticizer. Upon the addition of 15 percent by weight of zinc-stearate to the ionomer, the low shear rate viscosity drops by several orders of magnitude and renders the ionomer thermally processable at moderate temperatures.     

Mobile wireless network system simulation

This paper describes an advanced simulation environment which is used to examine, validate, and predict the performance of mobile wireless network systems. This simulation environment overcomes many of the limitations found with analytical models, experimentation, and other commercial network simulators available on the market today. We identify a set of components which make up mobile wireless systems and describe a set of flexible modules which can be used to model the various components and their integration. These models are developed using the Maisie simulation language. By modeling the various components and their integration, this simulation environment is able to accurately predict the performance bottlenecks of a multimedia wireless network system being developed at UCLA, determine the trade-off point between the various bottlenecks, and provide performance measurements and validation of algorithms which are not possible through experimentation and too complex for analysis.This work was supported in part by the Advanced Research Projects Agency, ARPA/CSTO, under Contract J-FBI-93-112 Computer Aided Design of High Performance Wireless Networked Systems, and by ARPA/CSTO under Contract DABT-63-94-C-0080 TransparentVirtual Mobile Environment.This paper was in part presented at the ACM Mobile Computing and Networking Conference (Mobicom '95), Berkeley, California, 14–15 November 1995.     

POEMS: end-to-end performance design of large parallel adaptive computational systems

The POEMS project is creating an environment for end-to-end performance modeling of complex parallel and distributed systems, spanning the domains of application software, runtime and operating system software, and hardware architecture. Toward this end, the POEMS framework supports composition of component models from these different domains into an end-to-end system model. This composition can be specified using a generalized graph model of a parallel system, together with interface specifications that carry information about component behaviors and evaluation methods. The POEMS Specification Language compiler will generate an end-to-end system model automatically from such a specification. The components of the target system may be modeled using different modeling paradigms and at various levels of detail. Therefore, evaluation of a POEMS end-to-end system model may require a variety of evaluation tools including specialized equation solvers, queuing network solvers, and discrete event simulators. A single application representation based on static and dynamic task graphs serves as a common workload representation for all these modeling approaches. Sophisticated parallelizing compiler techniques allow this representation to be generated automatically for a given parallel program. POEMS includes a library of predefined analytical and simulation component models of the different domains and a knowledge base that describes performance properties of widely used algorithms. The paper provides an overview of the POEMS methodology and illustrates several of its key components. The modeling capabilities are demonstrated by predicting the performance of alternative configurations of Sweep3D, a benchmark for evaluating wavefront application technologies and high-performance, parallel architectures.     

Optimization of conditions for hydrogen production from complex dairy wastewater by anaerobic sludge using desirability function approach

Present study deals with the multiple-response optimization for biohydrogen production using anaerobic sludge and outstanding approach to overcome the drawbacks of conventional response surface methodology (RSM). Dairy wastewater was used as source in batch fermentation was followed for this study. Response surface methodology (RSM), based on a three level, four variable Box–Behnken design, was employed to obtain the best possible combination of substrate concentration, pH, COD/N ratio and COD/P ratio for maximum H₂ yield (HY) and specific hydrogen production rate (SHPR). Experimental data were evaluated by applying RSM integrating a desirability function approach. The optimum H₂ yield and SHPR conditions were: substrate concentration 15.3 g COD/L, pH 5.5, COD/N ratio 100.5 and COD/P ratio 120 with maximum overall desirability D of 0.94. The confirmation experiment under these optimal condition showed a HY and SHPR of 13.54 mmol H₂/g COD and 29.91 mmol H₂/g-VSS.d, respectively. This was only 0.22% and 0.20%, respectively, different from the predicted values, suggesting that the desirability function approach with RSM was a useful technique to get the maximum H₂ yield and SHPR simultaneously.     

Electronic Granularity and the Work Function of Transparent Conducting ZnO:Al Thin Films

Controlling the efficiency of electron transport across oxide interfaces is essential for numerous emerging technologies including advanced photovoltaics and light emitting devices. This work illuminates the connections between granular structure, defect chemistry, and the work function of a technologically important transparent conductor, ZnO:Al. Visual evidence is provided for a model of grain boundary oxidation in the form of nanometer‐scale heterogeneity in the contact potential between grains and grain boundaries, a phenomenon referred to as electronic granularity. By correlating scanning probe data with photoemission spectroscopy we relate electronic granularity to defect chemistry and, importantly, account for the overall trends in work function. The resulting physical picture connects heterogeneity at the nanoscale to macroscopic properties, informs the design of transparent electrodes, and may be broadly relevant to granular oxide conductors.     

Synthesis and characterization of one-dimensional flat ZnO nanotower arrays as high-efficiency adsorbents for the photocatalytic remediation of water pollutants

We report on facile fabrication of 1-D flat ZnO nanotower arrays on various substrates, including a metal, a semiconductor and an insulator. The nanotowers have a unique flat basal section near the substrate and taper in stages to wire-like at the tip. Electron microscopy and X-ray photoelectron spectroscopy are used to characterize these new nanostructures, revealing that their morphologies are significantly influenced by reaction temperature. A qualitative formation mechanism is proposed based on the experimental observations. A proof-of-concept demonstration shows that the ZnO nanotower arrays are highly effective at adsorbing and subsequently photo-remediating a model pollutant (Eosin B) from water. These observations could promote new applications of photocatalytic adsorbents for wastewater treatment utilizing oxide semiconductor nanostructures.     

Kinetic analysis of biohydrogen production from complex dairy wastewater under optimized condition

Present work describes a kinetic analysis of various aspects of biohydrogen production in batch test using optimized conditions obtained previously. Monod model and Logistic equation have been used to find growth kinetic parameters in batch test under uncontrolled pH. The values of μ_m, K_s, and X_m were 0.64 h⁻¹, 15.89 g-COD L⁻¹, and 7.26 g-VSS L⁻¹, respectively. Modified Leudeking-Piret and Michaelis–Menten equation corroborates a flux of energy to hydrogen production pathway and energy sufficiency in the system. Modified Gompertz equation illustrates that the overall rate and hydrogen yield at 15 g-COD L⁻¹ was higher compared to a dark fermentation of other wastewaters. Besides, Andrew's equation also suggests that since the higher value of K_I (19.95 g-COD L⁻¹), k (255 mL h⁻¹ L⁻¹) was not inhibited at high S. The experimental results implied that the entire products during the fermentation process were growth and substrate degradation associated. The result also confirms that the acetate and butyrate were substantially used for hydrogen production in acidogenic metabolism under uncontrolled pH.     

MIDAS: integrated design and simulation of distributed systems

An approach called MIDAS is described that supports the design of distributed systems via iterative refinement of hybrid models. A hybrid model is a partially implemented design where some components exist as simulation models and others as operational subsystems. It is an executable model and may be used to determine the stochastic performance characteristics of a partially elaborated design. MIDAS enhances the applicability of hybrid models in system design with its support for interrupts and its inclusion of distributed components in the partially implemented design. The authors describe how an existing simulation language may be extended to program hybrid models, and show how simulation algorithms may be adapted to execute hybrid models. A prototype MIDAS implementation is operational and was used to develop a set of applications. The experimental results of the exercise are also described     

Fission yeast pak1+ encodes a protein kinase that interacts with Cdc42p and is involved in the control of cell polarity and mating

A STE20/p65pak homolog was isolated from fission yeast by PCR. The pak1+ gene encodes a 72 kDa protein containing a putative p21-binding domain near its amino-terminus and a serine/threonine kinase domain near its carboxyl-terminus. The Pak1 protein autophosphorylates on serine residues and preferentially binds to activated Cdc42p both in vitro and in vivo. This binding is mediated through the p21 binding domain on Pak1p and the effector domain on Cdc42p. Overexpression of an inactive mutant form of pak1 gives rise to cells with markedly abnormal shape with mislocalized actin staining. Pak1 overexpression does not, however, suppress lethality associated with cdc42-null cells or the morphologic defeat caused by overexpression of mutant cdc42 alleles. Gene disruption of pak1+ establishes that, like cdc42+, pak1+ function is required for cell viability. In budding yeast, pak1+ expression restores mating function to STE20-null cells and, in fission yeast, overexpression of an inactive form of Pak inhibits mating. These results indicate that the Pak1 protein is likely to be an effector for Cdc42p or a related GTPase, and suggest that Pak1p is involved in the maintenance of cell polarity and in mating.     

New polyisobutylene-based model ionomers

Mechanical properties of tri-arm polyisobutylene based ionomers have been investigated. Number average molecular weights (¯M_n's) of the polymers were varied from 8,300 to 34,000. The ionomer of lowest ¯M_n (8,300) exhibits very low extension at break (～ 150%) while the others with ¯M_n's of 11,000, 14,000 and 34,000 show very high extensions, often exceeding 1,000%, and display relatively low permanent set and low hysteresis behavior. Since the ionic bonding is located exclusively at the chain ends, end-linked pseudo networks are formed due to coulombic attractions.At higher temperatures the coulombic interactions are weakened and the networks can be compression molded (～150°C).