Quantification of microsegregation during rapid solidification of Al-Cu powders

A new technique is introduced to quantify microsegregation during rapid solidification. The quantification involves calculation of the average solute solubility in the primary phase during solidification of an Al-Cu binary alloy. The calculation is based on using volume percent eutectic and weight percent of second phase (in the eutectic), which were obtained experimentally. Neutron diffraction experiments and stereology calculation on scanning electron microscope images were done on impulse atomized Al-Cu alloys of three compositions (nominal), 5 wt pct Cu, 10 wt pct Cu, and 17 wt pct Cu, atomized under N₂ and He gas. Neutron diffraction experiments yielded weight percent CuAl₂ data and stereology yielded volume percent eutectic data. These two data were first used to determine the weight percent eutectic. Using the weight percent eutectic and weight percent CuAl₂ in mass and volume balance equations, the average solute solubility in the primary phase could be calculated. The experimental results of the amount of eutectic, tomography results from previous work, and results from the calculations suggest that the atomized droplets are in metastable state during the nucleation undercooling of the primary phase, and the effect of metastability propagates through to the eutectic formation stage. The metastable effect is more pronounced in alloys with higher solute composition.     

Acrylic Homo- and Co-polymers Based on 2, 4-dichlorophenyl Methacrylate and 8-quinolinyl Methacrylate

The monomer 2, 4-dichlorophenyl methacrylate (2,4-DMA) was synthesized from 2, 4-dichlorophenol and characterized by conventional methods. The homopolymers of 2,4-dichlorophenyl methacrylate and its copolymers with 8-quinolinyl methacrylate (8-QMA) in different feed ratio were prepared by free radical polymerization using dimethyl formamide (DMF) as a solvent and 2,2-azobis iso butyronitrile (AIBN) as an initiator. The resulting polymers were characterized by using IR spectroscopy. Reactivity ratios of monomer were evaluated using UV-spectroscopy. Average molecular weights and polydispersity were determined by gel permeation chromatography (GPC). Solution viscosity was also obtained. The thermal analysis was carried out using TGA and DSC. The homo- and co-polymers were also tested for their antimicrobial properties against selected microorganism. The metal ion uptake capacity of synthesized copolymers was estimated by batch equilibration method using different metal ion solution under different experimental conditions. It is observed that due to the presence of pendant ester bound quinoline group, the copolymers are capable of adsorbing cations from their aqueous solution.     

An unslotted multichannel channel‐access protocol for distributed direct‐sequence networks

A multichannel reservation-based channel-access protocol is investigated in this paper. The available system bandwidth is divided into distinct frequency channels. Under the protocol, one channel (the control channel) is used to exchange reservation messages and the remaining channels (the traffic channels) are used for information-bearing traffic. The performance of this scheme is compared to that of a single-channel reservation-based protocol. A simple contention-based slotted-Aloha protocol is also considered. Performance results take into account the effects of multiple-access interference on acquisition and packet errors. Results show that the reservation-based approach is advantageous under conditions of high traffic. In addition, a pacing mechanism that mitigates multiple-access interference and promotes fairness is described, and results are presented that demonstrate its effectiveness. This revised version was published online in June 2006 with corrections to the Cover Date.     

Store Atomicity for Transactional Memory

We extend the notion of Store Atomicity [Arvind and Jan-Willem Maessen. Memory model = instruction reordering + store atomicity. In ISCA '06: Proceedings of the 33rd annual International Symposium on Computer Architecture, 2006] to a system with atomic transactional memory. This gives a fine-grained graph-based framework for defining and reasoning about transactional memory consistency. The memory model is defined in terms of thread-local Instruction Reordering axioms and Store Atomicity, which describes inter-thread communication via memory. A memory model with Store Atomicity is serializable: there is a unique global interleaving of all operations which respects the reordering rules and serializes all the operations in a transaction together. We extend Store Atomicity to capture this ordering requirement by requiring dependencies which cross a transaction boundary to point in to the initiating instruction or out from the committing instruction. We sketch a weaker definition of transactional serialization which accounts for the ability to interleave transactional operations which touch disjoint memory. We give a procedure for enumerating the behaviors of a transactional program—noting that a safe enumeration procedure permits only one transaction to read from memory at a time. We show that more realistic models of transactional execution require speculative execution. We define the conditions under which speculation must be rolled back, and give criteria to identify which instructions must be rolled back in these cases.     

Iron‐Oxide‐Based Nanovector for Tumor Targeted siRNA Delivery in an Orthotopic Hepatocellular Carcinoma Xenograft Mouse Model

Hepatocellular carcinoma (HCC) is one of the deadliest cancers worldwide. Small interfering RNA (siRNA) holds promise as a new class of therapeutics for HCC, as it can achieve sequence‐specific gene knockdown with low cytotoxicity. However, the main challenge in the clinical application of siRNA lies in the lack of effective delivery approaches that need to be highly specific and thus incur low or no systemic toxicity. Here, a nonviral nanoparticle‐based gene carrier is presented that can specifically deliver siRNA to HCC. The nanovector (NP‐siRNA‐GPC3 Ab) is made of an iron oxide core coated with chitosan‐polyethylene glycol (PEG) grafted polyethyleneimine copolymer, which is further functionalized with siRNA and conjugated with a monoclonal antibody (Ab) against human glypican‐3 (GPC3) receptor highly expressed in HCC. A rat RH7777 HCC cell line that coexpresses human GPC3 and firefly luciferase (Luc) is established to evaluate the nanovector. The nanoparticle‐mediated delivery of siRNA against Luc effectively suppresses Luc expression in vitro without notable cytotoxicity. Significantly, NP‐siLuc‐GPC3 Ab administered intravenously in an orthotopic model of HCC is able to specifically bound to tumor and induce remarkable inhibition of Luc expression. The findings demonstrate the potential of using this nanovector for targeted delivery of therapeutic siRNA to HCC.     

Transforming generate-and-test programs to execute under committed-choice AND-parallelism

This paper concerns the exploitation of user transparent inherent parallelism of pure Prolog programs using program transformation. We describe a novel paradigmenumerate-and-filter for transforming generate-and-test programs for execution under the committed-choice model extended to incorporate multiple solutions based on set enumeration. The paradigm simulates OR-parallelism by stream AND-parallelism integrating OR-parallelism, AND-parallelism, and stream parallelism. Generate-and-test programs are classified into three categories:simple generate-and-test, recursively embedded generate-and-test, and deeply intertwined generate-and-test. The intermediate programs are further transformed to reduce structure copying and metacalls. Algorithms are presented and demonstrated by transforming the representative examples of different classes of generate-and-test programs to Flat Concurrent Prolog equivalents. Statistics show that the techniques are efficient.Funded in part by Cleveland Advanced Manufacturing Program through the State of Ohio as a part of its core research program grant to Center of Automation and Intelligent Systems Research, Case Western Reserve University and NSF equipment grant CDA-8820390 to Kent State University.     

Effect of vacancy de-excitation parameters on L X-rays of Pb using H+ beam

The collision progression including ionization of an inner-shell by an energetic proton and decay of vacancy is a motivating theme in ion-beam analysis. To explore measured vacancy de-excitation parameters for Pb, intensity ratios are experimentally determined from L X-rays with proton impact in the energy range 225–400 keV. Predictions of UAECPSSR theory are employed for ionization cross-sections. For atomic parameters such as transition rates, fluorescence, Auger and Coster–Kronig (CK) yields, various databases are used. In this paper, significance of these features and current progress are discussed.     

Provably good multiprocessor scheduling with resource sharing

We present a 12(1+3R/(4m)) competitive algorithm for scheduling implicit-deadline sporadic tasks on a platform comprising m processors, where a task may request one of R shared resources.