Leveraging Wire Properties at the Microarchitecture Level

In future microprocessors, communication will emerge as a major bottleneck. The authors advocate composing future interconnects of some wires that minimize latency, some that maximize bandwidth, and some that minimize power. A microarchitecture aware of these wire characteristics can steer on-chip data transfers to the most appropriate wires, thus improving performance and saving energy     

In‐depth characterization of granular starch‐graft‐polyester compositions as obtained by in situ polymerization of lactones from the starch surface

The synthesis of poly(ε‐caprolactone) (PCL)‐grafted granular starch was carried out either in bulk (without solvent) or in toluene suspension by a two‐step procedure. First step relied upon the activation of the hydroxyl groups available at the starch surface by alkylaluminum derivatives like AlEt₃ and removal of non‐surface‐grafted organo‐aluminum active species. The latter species were made free in solution by reaction with the remaining water molecules still contaminating the polymerization medium despite intensive drying of the starch granules. In the second step, ε‐caprolactone was polymerized via a coordination‐insertion ring‐opening polymerization as initiated by the surface‐grafted aluminum alkoxide species. The present contribution aims at investigating various parameters such as nature of the alkyl aluminum activator and monomer (δ‐valerolactone was studied as well), temperature, concentration, and addition of a solvent (polymerization in toluene suspension), reaction time, and also the experimental procedure used to recover the polyester chains and measure the grafting efficiency. It turns out that, under the studied conditions, dialkylaluminum alkoxides surface‐grafted onto the starch granules were more likely generated and promote a fast polymerization reaction with the formation of grafted PCL chains with a molecular weight that can be as high as 225 000 (M_n value) for polymerization carried out in toluene suspension. Copyright © 2004 Society of Chemical Industry     

The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys

More than 5 years ago, wrought processing was first used to produce fully lamellar (FL) microstructures in TiAl alloys having grain sizes less than ≈400 μm. These alloys exhibit an improvement in overall balance of properties, especially at high temperatures. More recently, such microstructural forms led to exceptional yield strengths (500 to 1000 MPa at low temperatures) while maintaining attractive high-temperature properties. The improvements appeared to be related to an unusually high apparent sensitivity of strength to grain size. Studies reported an apparent value for the slope of the Hall-Petch (HP) plot approaching 5 MPa√m for FL gamma alloys, while that for single-phase or duplex microstructures is near unity. The present investigations examine the slope of the HP plot for FL microstructures, paying particular attention to the lamellar microstructural variables. Results show that the α ₂ lamellar thickness and spacing and the γ lamellar thickness can vary over more than two orders of magnitude with typical process methods. These spacings influence the value of k _y in the HP (grain size) relationship. Since they often change concomitantly with grain size in processing, they can give rise to a large scatter in the HP plot. The investigations also examine the flow behavior, glide barriers, and slip multiplicity for polysynthetically twinned (PST) crystals (the single-grain analogue of FL material), and then map this behavior into an explanation of the yield behavior of high-strength FL gamma alloys. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Recent advances in modeling response-time distributions in real-time systems

Real-time systems are an important class of process control systems that need to respond to events under time constraints, or deadlines. Such systems may also be required to deliver service in spite of hardware or software faults in their components. This fault-tolerant characteristic is especially critical in systems whose failure can cause economic disaster and/or loss of lives. This paper reports recent research in the area of analytical modeling of the three major characteristics of real-time systems: timeliness, dependability, and external environmental dependencies. The paper starts with a brief introduction to analytical modeling frameworks such as Markov models and stochastic petri nets. This is followed by an examination of advances in modeling response-time distributions, reliability, distributed messaging services, and software fault-tolerance in real-time systems.     

Adhesion and friction studies of silicon surfaces processed using a microparticle-based method

A surface processing method that combines electrostatic deposition of microparticles and dry etching is utilized to modify the surface topography of silicon surfaces to reduce adhesion and friction force. Microscale adhesion and friction tests were conducted on flat (smooth) and processed silicon surfaces with a low elastic modulus thermoplastic rubber (Santoprene) probe that allowed a large enough contact area to observe the feature size effect. Both adhesion and friction force of the processed surfaces were reduced comparing to that of the flat surfaces.     

Effect of cerium addition on microstructures of carbon-alloyed iron aluminides

The effect of Ce addition on the microstructure of carbon-alloyed Fe₃Al-based intermetallic has been studied. Three different alloys of composition, Fe-18.5Al-3.6C, Fe-20.0Al-20C and Fe-19.2Al-3.3C-0.07Ce (in at%), were prepared by electroslag remelting process. Their microstructures were characterized using optical and scanning electron microscopies. Stereological methods were utilized to understand the observed microstructures. All the alloys exhibited a typical two-phase microstructure consisting of Fe₃AlC carbides in an iron aluminide matrix. In the alloy without Ce addition, large bulky carbides were equally distributed throughout the matrix with many smaller precipitates interspersed in between. In the alloy with Ce addition, the carbide grain sizes were finer and uniformly distributed throughout the matrix. The effect of Ce addition on the carbide morphology has been explained based on the known effect of Ce in modifying carbide morphology in cast irons.     

Synthesis and study of RO performance of aromatic polyamide hydrazide membranes

Aromatic polyamide hydrazide polymeric membranes were synthesized by dissolving freshly prepared polymer in dimethyl acetamide using lithium salt as additive. The effect of various casting parameters like polymer to solvent ratio, additive to polymer ratio, time and temperature of solvent evaporation, etc., on the RO membrane performance was studied. The membrane performance under various operational parameters like applied pressure, feed molarity and temperature are presented. The membranes prepared from the polymer samples were characterised in terms of pure water permeability constant (A) and solute transport parameter (D_AM/Kδ).     

The nature of dislocation motion in quasicrystals

Calculations in a hydrodynamic model of quasicrystal dynamics show that dislocation motion in these systems is impeded by a drag far greater than that in crystals.     

Probabilistic Short-Circuit Uprating of Station Strain Bus System - Reliability and Operating Considerations

A probabilistic approach to the short-circuit current uprating of station strain bus system has been described in two companion papers [1,2]. This paper discusses the impact of using this approach on (1) the reliability of supply to low voltage buses at tapped stations, (2) the probability of operating the bulk electricity system in high risk states, and (3) the operating security after occurrences of contingencies involving strain bus failures. It was found that probabilistic uprating would not significantly affect the above system performance parameters.     

Novel AB crosslinked polymer networks based on 1‐vinylimidazole‐ terminated polyurethane and poly(methyl methacrylate)

1‐Vinylimidazole‐terminated telechelic polyurethanes were prepared from 1‐vinylimidazole and bromine‐terminated polyurethane. This vinyl‐terminated telechelic polyurethane (VTPU) and methyl methacrylate were polymerized in the presence of benzoyl peroxide to prepare novel AB crosslinked polymer networks (ABCPs). These were characterized by spectral, thermal and mechanical studies. The absence of the characteristic peak of vinyl group in infrared spectra of ABCP films confirms the occurrence of crosslinking. Static mechanical testing showed that the tensile strength of ABCP increases with increasing poly(methyl methacrylate) content. Dynamic mechanical studies revealed that ABCPs, at equal compositions of VTPU and methyl methacrylate, show good damping properties. Copyright © 2006 Society of Chemical Industry