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

Bacterial toxicity of graphene nanosheets in the form of graphene nanowalls deposited on stainless steel substrates was investigated for both Gram-positive and Gram-negative models of bacteria. The graphene oxide nanowalls were obtained by electrophoretic deposition of Mg2+-graphene oxide nanosheets synthesized by a chemical exfoliation method. On the basis of measuring the efflux of cytoplasmic materials of the bacteria, it was found that the cell membrane damage of the bacteria caused by direct contact of the bacteria with the extremely sharp edges of the nanowalls was the effective mechanism in the bacterial inactivation. In this regard, the Gram-negative Escherichia coli bacteria with an outer membrane were more resistant to the cell membrane damage caused by the nanowalls than the Gram-positive Staphylococcus aureus lacking the outer membrane. Moreover, the graphene oxide nanowalls reduced by hydrazine were more toxic to the bacteria than the unreduced graphene oxide nanowalls. The better antibacteri...

Toxicity of Graphene and Graphene Oxide Nanowalls Against Bacteria

High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.

Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview

Carbonaceous nanomaterials for the enhancement of TiO2 photocatalysis

Graphene: a new emerging lubricant ☆

Synthesis of titania/carbon nanotube heterojunction arrays for photoinactivation of E. coli in visible light irradiation

Vertically aligned multi-wall carbon nanotube (CNT) arrays were fabricated in tip-growth mode on Ni/Si substrates using plasma enhanced chemical vapor deposition. In a purification process including hydrogenation and acid washing of the Ni/CNTs, the oxygen-containing functional groups were substantially reduced and a wide hollow core at the tip of the CNTs was formed by removing the Ni seeds. Sol–gel silver nanoparticles were deposited on the surface of the unpurified Ni/CNTs, while they could also be embedded within the hollow core of the Ni-removed CNTs. The persistency of the silver ions in the Ni-removed Ag–CNTs in comparison to the release of the silver ions from the Ag–Ni/CNTs in a dilute HNO3 solution confirmed the effective embedding of the Ag nanoparticles within the hollow core of the Ni-removed CNTs. The Ni-removed Ag–CNTs showed a strong antibacterial activity against Escherichia coli bacteria in the dark (inactivation of 99.8 ± 0.1% of the bacteria as compared to the Ni-removed CNTs and the Ag–Ni/CNTs with 62 ± 11 and 47 ± 18% inactivation in 120 min), while the bacteria even exhibited some proliferation on the surface of the unpurified Ni/CNT arrays. In the context of cell membrane rupture of the bacteria through a direct contact mechanism, it was proposed that the Ni seeds acted as obstacles for an effective contact between the bacteria and the tips of the CNT arrays.

Silver nanoparticles within vertically aligned multi-wall carbon nanotubes with open tips for antibacterial purposes

In the present study, the sensitivity of SnO2 and CeO2/SnO2 sensors to ethanol in the presence of CO, LPG and CH4 gases were examined. SnO2 and CeO2/SnO2 were prepared by a sol–gel method and sintered at 600 and 800 °C. As SnO2 is doped with 2.0 wt.% ceria, at 300 °C, the sensitivity to ethanol with respect to methane, LPG and CO is enhanced by factors of about 5.3, 48.2 and 5.2, respectively. As the temperature is increased to 350 °C, the ceria-doped SnO2 becomes more sensitive to CO and LPG. The results revealed that, for all gases, the sensitivity of the sensors sintered at 600 °C was higher than the ones sintered at 800 °C, however, the effect was much more pronounced with regards to ethanol. In addition, doping the SnO2 sensor with CeO2 reduces the long recovery time observed for pure SnO2 sensor in presence of ethanol.

CeO2 doped SnO2 sensor selective to ethanol in presence of CO, LPG and CH4

SnO2-based semiconductor gas sensors have been successfully fabricated and tested for detecting carbon monoxide and methane. The sensitivity and selectivity of the sensors are tailored by incorporation of different additives such as platinum and cerium oxide. While platinum enhances the sensor response to CH4, ceria suppresses its sensitivity in favor of carbon monoxide. The effect of operating temperature on the performance of sensors is reported. Addition of 10% cerium oxide in the SnO2 sample leads to an insignificant response to methane even at an elevated temperature of 450°C, while its response to CO remains intact.

Cerium oxide/SnO2-based semiconductor gas sensors with improved sensitivity to CO

A novel vertically aligned carbon nanotube based electrical cell impedance sensing biosensor (CNT-ECIS) was demonstrated for the first time as a more rapid, sensitive and specific device for the detection of cancer cells. This biosensor is based on the fast entrapment of cancer cells on vertically aligned carbon nanotube arrays and leads to mechanical and electrical interactions between CNT tips and entrapped cell membranes, changing the impedance of the biosensor. CNT-ECIS was fabricated through a photolithography process on Ni/SiO2/Si layers. Carbon nanotube arrays have been grown on 9 nm thick patterned Ni microelectrodes by DC-PECVD. SW48 colon cancer cells were passed over the surface of CNT covered electrodes to be specifically entrapped on elastic nanotube beams. CNT arrays act as both adhesive and conductive agents and impedance changes occurred as fast as 30 s (for whole entrapment and signaling processes). CNT-ECIS detected the cancer cells with the concentration as low as 4000 cells cm−2 on its surface and a sensitivity of 1.7 × 10−3 Ω cm2. Time and cell efficiency factor (TEF and CEF) parameters were defined which describe the sensor's rapidness and resolution, respectively. TEF and CEF of CNT-ECIS were much higher than other cell based electrical biosensors which are compared in this paper.

https://www.rsc.org/suppdata/lc/c2/c2lc21028b/c2lc21028b.pdf

Shams Mohajerzadeh

Papers

Synthesis of titania/carbon nanotube heterojunction arrays for photoinactivation of E. coli in visible light irradiation

Silver nanoparticles within vertically aligned multi-wall carbon nanotubes with open tips for antibacterial purposes

CeO2 doped SnO2 sensor selective to ethanol in presence of CO, LPG and CH4

Cerium oxide/SnO2-based semiconductor gas sensors with improved sensitivity to CO

A vertically aligned carbon nanotube-based impedance sensing biosensor for rapid and high sensitive detection of cancer cells