Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Materials and structures with negative Poisson's ratio exhibit a counter-intuitive behaviour. Under uniaxial compression (tension), these materials and structures contract (expand) transversely. The materials and structures that possess this feature are also termed as 'auxetics'. Many desirable properties resulting from this uncommon behaviour are reported. These superior properties offer auxetics broad potential applications in the fields of smart filters, sensors, medical devices and protective equipment. However, there are still challenging problems which impede a wider application of auxetic materials. This review paper mainly focuses on the relationships among structures, materials, properties and applications of auxetic metamaterials and structures. The previous works of auxetics are extensively reviewed, including different auxetic cellular models, naturally observed auxetic behaviour, different desirable properties of auxetics, and potential applications. In particular, metallic auxetic materials and a methodology for generating 3D metallic auxetic materials are reviewed in details. Although most of the literature mentions that auxetic materials possess superior properties, very few types of auxetic materials have been fabricated and implemented for practical applications. Here, the challenges and future work on the topic of auxetics are also presented to inspire prospective research work. This review article covers the most recent progress of auxetic metamaterials and auxetic structures. More importantly, several drawbacks of auxetics are also presented to caution researchers in the future study.

Auxetic metamaterials and structures: a review

Over the coming few decades bioplastic materials are expected to complement and gradually replace some of the fossil oil based materials. Multidisciplinary research efforts have generated a significant level of technical and commercial success towards these bio-based materials. However, extensive application of these bio-based plastics is still challenged by one or more of their possible inherent limitations, such as poor processability, brittleness, hydrophilicity, poor moisture and gas barrier, inferior compatibility, poor electrical, thermal and physical properties. The incorporation of additives such as plasticizers into the biopolymers is a common practice to improve these inherent limitations. Generally, plasticizers are added to both synthetic and bio-based polymeric materials to impart flexibility, improve toughness, and lower the glass transition temperature. This review introduces the most common bio-based plastics and provides an overview of recent advances in the selection and use of plasticizers, and their effect on the performance of these materials. In addition to plasticizers, we also present a perspective of other emerging techniques of improving the overall performance of bio-based plastics. Although a wide variety of bio-based plastics are under development, this review focuses on plasticizers utilized for the most extensively studied bioplastics including poly(lactic acid), polyhydroxyalkanoates, thermoplastic starch, proteinaceous plastics and cellulose acetates. The ongoing challenge and future potentials of plasticizers for bio-based plastics are also discussed.

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Progress in bio-based plastics and plasticizing modifications

Recovery of metals and nonmetals from electronic waste by physical and chemical recycling processes

https://arpi.unipi.it/bitstream/11568/798598/2/polacco%20798598.pdf

A review of the fundamentals of polymer-modified asphalts: Asphalt/polymer interactions and principles of compatibility

We report a one-step oxidative method for the recycling of carbon fiber-reinforced polymer (CFRP) composite waste and the recovery of carbon fiber and the epoxy resin by treatment with peracetic acid (PAA) formed in situ from a mixture of acetic acid and hydrogen peroxide. The surfaces of the recovered carbon fibers were clean, and the tensile strength was comparable to that of the virgin fibers. A higher resin decomposition ratio of 97% could be achieved for the epoxy matrix under mild reaction conditions in comparison to other chemical recycling processes. ATR-FTIR, MALDI/TOF-MS, GPC, GC-MS, 1H NMR, and Pyro-GC/MS analyses showed the formation of low molecular weight oxidation products of amine-cured epoxy resin along with high molecular weight compounds of high viscosity. A possible reaction mechanism for the degradation of the epoxy matrix is proposed. All the solvents used were recovered in pure and reusable form with more than 90% recovery efficiency. The recovered epoxy was reused along with an adh...

An Efficient Method of Recycling of CFRP Waste Using Peracetic Acid

A novel sonochemical method is proposed for the recovery of carbon fiber from carbon fiber reinforced polymer (CFRP) composites by treatment with a mixture of dilute nitric acid and hydrogen peroxide in the presence of ultrasound. A maximum resin decomposition ratio of 95% could be obtained for the epoxy matrix. SEM and TGA data showed that the recovered fibers had very little or no epoxy resin and their tensile strength was comparable to that of the virgin fiber. ATR-FTIR, MALDI-TOF/MS, and 1H NMR analysis of the recovered solid and liquid byproducts showed the formation of decomposition products of cross-linked epoxy resin through nitration and oxidation reactions. This process opens the possibilities of an environmentally more benign process for CFRP waste decomposition and recovery of carbon fiber in the presence of ultrasound and H2O2 by eliminating the need for strong chemicals and high reaction temperatures and pressures.

A Novel Sonochemical Approach for Enhanced Recovery of Carbon Fiber from CFRP Waste Using Mild Acid–Peroxide Mixture

The micellar characteristics of a non-ionic, natural surfactant, saponin obtained from the soapnut tree, Sapindus mukorossi, were studied in aqueous solution. Critical micelle concentration of Sapindus saponin determined using conductivity measurements and UV absorption studies was 0.045 wt%. Increase in temperature and salt concentration led to decrease in the critical micelle concentration of Sapindus saponin. The critical micelle concentration was found to increase with increase in hardness of water and increase in pH. The micellar aggregation number was determined using cyclic voltammetry and was found to be between 13 and 21. The size of the Sapindus saponin micelles was determined using intrinsic viscosity measurements and was found to be independent of saponin concentration for concentrations above the CMC. Solubilisation of two types of crude oils and a vegetable oil was studied using micellar solubilisation technique. At lower concentrations of the surfactant, the micellar solubilisation...

Micellar Characterisation of Saponin from Sapindus Mukorossi

Milling and separation of the multi-component printed circuit board materials and the analysis of elutriation based on a single particle model

The unusual reinforcement mechanism exhibited by silica in epoxidized natural rubber (ENR) may be attributed to the specific chemical interaction or the chemical cross-linking taking place between silica and the epoxy groups while heating the mix. Evidence for the higher interaction is established through rheometric studies conducted at 180°C and changes in the dynamic mechanical characteristics studied over a wide temperature range using a dynamic viscoelastometer for the heated and unheated silica-filled mixes.

Susy Varughese

Papers

An Efficient Method of Recycling of CFRP Waste Using Peracetic Acid

A Novel Sonochemical Approach for Enhanced Recovery of Carbon Fiber from CFRP Waste Using Mild Acid–Peroxide Mixture

Micellar Characterisation of Saponin from Sapindus Mukorossi

Milling and separation of the multi-component printed circuit board materials and the analysis of elutriation based on a single particle model

Chemical interaction between epoxidized natural rubber and silica: Studies on cure characteristics and low‐temperature dynamic mechanical properties