Structural and Mechanical Properties Changes of Ethylene‐α‐olefin Copolymer Blends Induced by Thermal Treatments and Composition

Summary: Blends of single‐site catalysed ethylene‐α‐butene (C₄VLDPE) and ethylene‐α‐octene (C₈VLDPE) copolymers were prepared by melt extrusion. The phase morphology, thermal and mechanical properties of the blends have been investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile test and dynamic mechanical analysis (DMA). Depending on the composition and thermal history, significant differences in structure and behaviour were found. It was also found that some degree of co‐crystallization occurred for quenched blends; whereas most of the oven slowly cooled blends showed two well‐defined melting peaks, indicating that the slow cooling favoured partial segregation of the fractions with different degrees of branching to form two morphologies. Moreover, SEM revealed morphology of the thinner crystals distributed in‐between the thicker sheaf‐like crystals for the slowly cooled blends with 20–50% C₈VLDPE. Therefore, the synergism in mechanical properties for the blends with 20–50% C₈VLDPE is due to a combination of larger crystal size, more complete phase separation and interfacial interaction produced by the segregation effect of the slow cooling treatment. DMA studies showed that the storage modulus increased as the addition of C₈VLDPE and modulus for the slowly cooled blends are about twice those measured for the quenched ones, indicating higher stiffness of the blends. The smooth shift of β relaxation temperature with addition of C₈VLDPE for both sets of blends confirmed the miscibility in the amorphous phase.

SEM image of the C₄VLDPE‐C₈VLDPE (50/50) blend after oven slow cooling treatment.     

Water productivity and water footprint: misguided concepts or useful tools in water management and policy?

Water productivity (WP) and water footprint (WFP) are popular concepts in research and discourses on water management. Yet there are concerns about their theoretical validity and practical value. This paper shows that the water production function, the concept with a sound theoretical foundation, is the basis for WP. Total WFP is the reciprocal of WP. The practical value of WP and WFP depends on the context of water use and stress. Maximizing WP, not a panacea to all water problems, mainly suits arid rainfed areas. In other regions, economic and marginal WP for increasing overall production should take precedence in water management and policy decisions.     

Maximizing multiprocessor performance with the SUIF compiler

This article describes automatic parallelization techniques in the SUIF (Stanford University Intermediate Format) compiler that result in good multiprocessor performance for array-based numerical programs. Parallelizing compilers for multiprocessors face many hurdles. However, SUIF's robust analysis and memory optimization techniques enabled speedups on three fourths of the NAS and SPECfp95 benchmark programs     

High-power distributed Bragg reflector lasers operating at 1065nm

A report is presented on distributed Bragg reflector lasers emitting in excess of 700 mW in a single-spatial and single-spectral mode at 1065 nm. The threshold current of these devices is ~30 mA, there is an L-I slope of 0.74 W/A, and a sidemode suppression ratio greater than 30 dB. The current and thermal tuning are 0.016 A/mA and 0.7 A/degC, respectively.     

Limnology and culture-based fisheries in non-perennial reservoirs in Sri Lanka

This study was carried out to investigate the possibility of using the limnological characteristics of non‐perennial reservoirs in Sri Lanka for the future management of culture‐based fisheries. Forty‐five reservoirs were randomly selected to study their limnology, out of which 32 were stocked with fish fingerlings of Chinese and Indian carps, tilapia and freshwater prawn at stocking densities ranging from 218–4372 fingerlings ha^?1. Of these, 23 reservoirs were harvested at the end of the culture period (6–10 months). Thirteen limnological parameters were measured during the water retention period of each of the 45 reservoirs between November 2001 and January 2004. The mean values of the limnological parameters were used to ordinate the reservoirs through principal component analysis. Ordination showed a productivity gradient among reservoirs where Secchi disc depth, total phosphorus, chlorophyll‐a, inorganic turbidity and organic turbidity were identified as key factors. The total fish yield of culture‐based fisheries was positively correlated to the scores of the first principal component axis. This study reveals that it is possible to classify non‐perennial reservoirs in Sri Lanka based on the above limnological parameters in order to develop culture‐based fisheries and that they could be applicable in comparable water bodies elsewhere in the tropics.     

Multiprocessors from a software perspective

Like many architectural techniques that originated with mainframes. the use of multiple processors in a single computer is becoming popular in workstations and even personal computers. Multiprocessors constitute a significant percentage of recent workstation sales, and highly affordable multiprocessor personal computers are available in local computer stores. Once again, we find ourselves in a familiar situation: hardware is ahead of software. Because of the complexity of parallel programming, multiprocessors today are rarely used to speed up individual applications. Instead, they usually function as cycle-servers that achieve increased system throughput by running multiple tasks simultaneously. Automatic parallelization by a compiler is a particularly attractive approach to software development for multiprocessors, as it enables ordinary sequential programs to take advantage of the multiprocessor hardware without user involvement. This article looks to the future by examining some of the latest research results in automatic parallelization technology     

Single-frequency 1310-nm AlGaInAs-InP grating-outcoupled surface-emitting lasers

Single-frequency 1310-nm grating-outcoupled surface-emitting (GSE) semiconductor lasers with output slope efficiencies exceeding 0.1 mW/mA into multimode fibers, threshold currents below 22 mA, and >30-dB sidemode suppression ratios are reported. These GSE lasers consist of 500-/spl mu/m-long active ridges that excite one end of surface-emitting second-order outcoupling gratings with 200-/spl mu/m-long first-order distributed Bragg reflector gratings terminating the laser cavities at both ends. The grating outcouplers range from 10 to 50 /spl mu/m in length. These lasers have an open eye pattern for nonreturn-to-zero signals at 2.5 Gb/s into single-mode fibers. The full-width half-maximum far-field beam divergences range from 1.5/spl deg/ /spl times/ 8/spl deg/ to 5/spl deg/ /spl times/ 8/spl deg/.     

Scalar operand networks

The bypass paths and multiported register files in microprocessors serve as an implicit interconnect to communicate operand values among pipeline stages and multiple ALUs. Previous superscalar designs implemented this interconnect using centralized structures that do not scale with increasing ILP demands. In search of scalability, recent microprocessor designs in industry and academia exhibit a trend toward distributed resources such as partitioned register files, banked caches, multiple independent compute pipelines, and even multiple program counters. Some of these partitioned microprocessor designs have begun to implement bypassing and operand transport using point-to-point interconnects. We call interconnects optimized for scalar data transport, whether centralized or distributed, scalar operand networks. Although these networks share many of the challenges of multiprocessor networks such as scalability and deadlock avoidance, they have many unique requirements, including ultra-low latency (a few cycles versus tens of cycles) and ultra-fast operation-operand matching. This work discusses the unique properties of scalar operand networks (SONs), examines alternative ways of implementing them, and introduces the AsTrO taxonomy to distinguish between them. It discusses the design of two alternative networks in the context of the Raw microprocessor, and presents timing, area, and energy statistics for a real implementation. The paper also presents a 5-tuple performance model for SONs and analyzes their performance sensitivity to network properties for ILP workloads.     

Low-density polyethylene/sugarcane fiber composites from recycled polymer and treated fiber by steam explosion

Low-density polyethylene (LDPE) has caused serious environmental damages, and it has been a challenge for waste management in large cities. The LDPE recycling as composites with natural fibers such as sugarcane fibers (SCF) has been an interesting alternative to conciliate economic aspects with environmental benefits. In this study, SCF has been treated by steam explosion and incorporated to low-density polyethylene waste (LDPEW) to generate LDPEW/SCF composites with higher fiber/polymer interaction and improved mechanical properties. LDPEW/SCF composites with fibers content until 20 wt% showed mechanical properties with performance adequate for nobler applications when compared to the isolated recycled LDPEW.     

A rationale for introducing a subsidiary fishery in tropical reservoirs and lakes to augment inland fish production: case study from Sri Lanka

An extra 30–40 million tonnes of food fish will be required by 2050 to meet the increasing need for a growing population. In the wake of plateauing of the traditional food fish supplies from marine capture fisheries, the gap in the supplies will have to be met from aquaculture and other plausible strategies, including increased inland fish production. The existing fisheries in tropical reservoirs and lakes traditionally tend to target only table-sized fish, often exotics and/or translocated species, using a single type of gear, mostly gill nets. In such fisheries, many small indigenous species (SIS) are unexploited due to the prohibition of the use of suitable fishing gear. The status of fisheries for small, indigenous species of four Sri Lankan reservoirs was investigated with a view to identifying regulatory constraints to the establishment of SIS fisheries without adversely impacting existing commercial fisheries. It is estimated that a potential of 7.5 t per fisher per annum of SIS through the introduction of a new fishery is obtainable. This study is significant as SIS are recognized as important sources of essential macro- and micronutrients which can play a crucial role in combating malnutrition and micronutrient deficiencies in rural populations of many South and Southeast Asian countries.