A low‐disturbance nonequilibrium molecular dynamics algorithm applied to the determination of thermal conductivities

A new nonequilibrium molecular dynamics algorithm is proposed for the determination of thermal conductivity and other transport properties. The proposed algorithm aims at diminishing the energy drift problem observed in this type of method while conserving linear momentum and being compatible with constrained molecules. The features of the proposed algorithm are evaluated by determining thermal conductivities of water at 323 K, n‐octane at 300 K, and argon close to its triple point, and by comparing these results with those obtained using established methods. The analysis of systems presenting diverse molecular characteristics allowed us to assess the usefulness of the proposed algorithm. The energy drift and temperature variation were reduced in the range of 10–80%, depending on the parameters of the proposed algorithm and the characteristics of the system. The determined thermal conductivities showed good agreement when compared to experimental and simulation data. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2881–2890, 2015     

Patterned Electroconductive Networks in Ag-Polyamide 6 Composites by Laser Ablation

A simple, fast, and cost-effective method to fabricate conductive paths on insulating Ag-containing polyamide 6 (PA6) composites by laser beam treatment is presented in this study. First, Ag-hybrid microparticles (Ag-MP) with a total metal load of up to 19 wt% are synthesized based on a reactive encapsulation strategy utilizing activated anionic polymerization of ε-caprolactam in solution, in the presence of Ag nanoparticles. Then, the Ag-MP are compression molded into plates (Ag-PL) on which a scanning laser treatment is applied to create conductive paths in their selected parts. A comparison between structural, morphological, and thermal properties of the Ag-MP and the molded Ag-PL composites is performed. The electric conductive properties of the Ag-loaded hybrid materials are investigated before and after laser ablation, and it is concluded that the laser treatment results in selected paths with widths in the range of 500 µm with conductivity values in the range of 1.12 to 8.90 S m⁻¹ while the untreated Ag-PA6 surface remains isolating with conductivity values of 1.27 × 10⁻⁰⁸ S m⁻¹. These results prove that applying laser ablation with controlled parameters on initially insulating Ag-PL composites can efficiently produce conductive line patterns in composite plates.     

Hyperbaric storage at variable room temperature – a new preservation methodology for minced meat compared to refrigeration

Hyperbaric storage (HS) at variable room temperature (RT) has been proposed as an alternative to refrigeration at atmospheric pressure (RF/AP) for food preservation. Little information is available regarding the effect of HS in meat products. In this study the RT/HS effect was evaluated at 100 MPa and variable RT (≈20 °C) for minced meat preservation up to 24 h, initially for one batch. A further two different batches were studied independently. Microbiological and physicochemical parameters were analyzed to assess the feasibility of RT/HS, using storage at RF/AP and variable RT/AP (≈20 °C), for comparison. A post-hyperbaric storage (post-HS) was also tested over 4 days at RF/AP. For the first batch the results showed that RT/HS allowed a decrease of the total aerobic mesophile value (P < 0.05) when compared to the initial sample, whereas at RF/AP and RT/AP, values increased to > 6 Log CFU g⁻¹ after 24 h. Similarly, Enterobacteriaceae increased > 1 and > 2 Log CFU g⁻¹ at RF/AP and RT/AP, respectively, while yeasts and molds presented similar and lower overall loads compared to the initial samples for all storage conditions, whereas RT/HS always allowed lower counts to be obtained. Regarding pH, lipid oxidation, and color parameters, RT/HS did not cause significant changes when compared to RF/AP, except after 24 h, where pH increased. The three batches presented similar results, the differences observed being mainly due to the heterogeneity of the samples. RT/HS is a potential quasi-energetic costless alternative to RF for at least short-term preservation of minced meat. © 2018 Society of Chemical Industry     

Massive MIMD neural network simulations: The connections dilemma

We present two strategies for the simulation of massive neural networks on message-passing MIMD machines. In the first strategy all interconnections between neurons are stored explicitly in interconnection matrices. During simulation, every processor is responsible for certain submatrices of these interconnection matrices. The fact that message-passing MIMD processors do not provide virtual memory seriously limits the size of the networks that can be simulated, since interconnection matrices require huge amounts of memory. An alternative strategy is not to store the connections explicitly, but generate the interconnections as they are needed. This circumvents memory limitations, but because interconnections need to be generated multiple times, it is inherently slower than the first implementation. This yields the connections dilemma: the choice between fast simulation of small networks as against slower simulation of massive networks. We present, analyze and bench-mark parallel implementations for both strategies. An efficient connection-look-up algorithm, which can be used for any network with static interconnections, ensures that simulation times for the second strategy are only marginally longer than for the first strategy. We show that for our users the connections dilemma is no longer a dilemma: by means of our look-up algorithm the simulation of massive networks becomes possible; furthermore the time to design and construct a network, prior to simulation, is considerably shorter than it is for the matrix version, and in addition this time is independent of network size. Although we have implemented both strategies on a parallel computer, the algorithms presented here can be used on any machine with memory limitations, such as personal computers.