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

Recent development in 2D materials beyond graphene

Flexible and wearable electronics are attracting wide attention due to their potential applications in wearable human health monitoring and care systems. Carbon materials have combined superiorities such as good electrical conductivity, intrinsic and structural flexibility, light weight, high chemical and thermal stability, ease of chemical functionalization, as well as potential mass production, enabling them to be promising candidate materials for flexible and wearable electronics. Consequently, great efforts are devoted to the controlled fabrication of carbon materials with rationally designed structures for applications in next-generation electronics. Herein, the latest advances in the rational design and controlled fabrication of carbon materials toward applications in flexible and wearable electronics are reviewed. Various carbon materials (carbon nanotubes, graphene, natural-biomaterial-derived carbon, etc.) with controlled micro/nanostructures and designed macroscopic morphologies for high-performance flexible electronics are introduced. The fabrication strategies, working mechanism, performance, and applications of carbon-based flexible devices are reviewed and discussed, including strain/pressure sensors, temperature/humidity sensors, electrochemical sensors, flexible conductive electrodes/wires, and flexible power devices. Furthermore, the integration of multiple devices toward multifunctional wearable systems is briefly reviewed. Finally, the existing challenges and future opportunities in this field are summarized.

Advanced Carbon for Flexible and Wearable Electronics.

All-polymer solar cells have shown great potential as flexible and portable power generators. These devices should offer good mechanical endurance with high power-conversion efficiency for viability in commercial applications. In this work, we develop highly efficient and mechanically robust all-polymer solar cells that are based on the PBDTTTPD polymer donor and the P(NDI2HD-T) polymer acceptor. These systems exhibit high power-conversion efficiency of 6.64%. Also, the proposed all-polymer solar cells have even better performance than the control polymer-fullerene devices with phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor (6.12%). More importantly, our all-polymer solar cells exhibit dramatically enhanced strength and flexibility compared with polymer/PCBM devices, with 60- and 470-fold improvements in elongation at break and toughness, respectively. The superior mechanical properties of all-polymer solar cells afford greater tolerance to severe deformations than conventional polymer-fullerene solar cells, making them much better candidates for applications in flexible and portable devices.

http://sciencemission.com/data/attachment.php?id=427&for_session=5f12dcbf83e038a697906b7b1b350568

Flexible, highly efficient all-polymer solar cells

Printable electronics present a new era of wearable electronic technologies. Detailed technologies consisting of novel ink semiconductor materials, flexible substrates, and unique processing methods can be integrated to create flexible sensors. To detect various stimuli of the human body, as well as specific environments, unique electronic devices formed by "ink-based semiconductors" onto flexible and/or stretchable substrates have become a major research trend in recent years. Materials such as inorganic, organic, and hybrid semiconductors with various structures (i.e., 1D, 2D and 3D) with printing capabilities have been considered for bio and medical applications. In this review, we report recent progress in materials and devices for future wearable sensor technologies.

Recent Progress in Materials and Devices toward Printable and Flexible Sensors

The development of input device technology in a conformal and stretchable format is important for the advancement of various wearable electronics. Herein, we report a capacitive touch sensor with good sensing capabilities in both contact and noncontact modes, enabled by the use of graphene and a thin device geometry. This device can be integrated with highly deformable areas of the human body, such as the forearms and palms. This touch sensor detects multiple touch signals in acute recordings and recognizes the distance and shape of the approaching objects before direct contact is made. This technology offers a convenient and immersive human–machine interface and additional potential utility as a multifunctional sensor for emerging wearable electronics and robotics.

Graphene-Based Three-Dimensional Capacitive Touch Sensor for Wearable Electronics

Large-area, ultrathin flexible tactile sensors with conformal adherence are becoming crucial for advances in wearable electronics, electronic skins and biorobotics. However, normal passive tactile sensors suffer from high crosstalk, resulting in inaccurate sensing, which consequently limits their use in such advanced applications. Active-matrix-driven tactile sensors could potentially overcome such hurdles, but it demands the high performance and reliable operations of the thin-film-transistor array that could efficiently control integrated pressure gauges. Herein, we utilized the benefit of the semiconducting and mechanical excellence of MoS2 and placed it between high-k Al2O3 dielectric sandwich layers to achieve the high and reliable performance of MoS2-based back-plane circuitry and strain sensor. This strategical combination reduces the fabrication complexity and enables the demonstration of an all MoS2-based large area (8 × 8 array) active-matrix tactile sensor offering a wide sensing range (1–120 k...

All MoS2-Based Large Area, Skin-Attachable Active-Matrix Tactile Sensor.

The surface of water provides an excellent environment for gliding movement, in both nature and modern technology, from surface living animals such as the water strider, to Langmuir–Blodgett films. The high surface tension of water keeps the contacting objects afloat, and its low viscosity enables almost frictionless sliding on the surface. Here we utilize the water surface as a nearly ideal underlying support for free-standing ultra-thin films and develop a novel tensile testing method for the precise measurement of mechanical properties of the films. In this method, namely, the pseudo free-standing tensile test, all specimen preparation and testing procedures are performed on the water surface, resulting in easy handling and almost frictionless sliding without specimen damage or substrate effects. We further utilize van der Waals adhesion for the damage-free gripping of an ultra-thin film specimen. Our approach can potentially be used to explore the mechanical properties of emerging two-dimensional materials. The mechanical testing of thin films is non-trivial, due to their very fine dimensions. Kim et al. use the inherent surface tension of water as a platform for the frictionless tensile testing of gold films, with a thickness as fine as 55 nm.

http://aptf.kaist.ac.kr/Publications/Kim%20et%20al.%20(Nature%20Communications%202013).pdf

Tensile testing of ultra-thin films on water surface

An active matrix-type stretchable display is realized by overlay-aligned transfer of inorganic light-emitting diode (LED) and single-crystal Si thin film transistor (TFT) with roll processes. The roll-based transfer enables integration of heterogeneous thin film devices on a rubber substrate while preserving excellent electrical and optical properties of these devices, comparable to their bulk properties. The electron mobility of the integrated Si-TFT is over 700 cm2 V−1 s−1, and this is attributed to the good interface between the Si channel and the thermally grown SiO2 insulator. The light emission properties of the LED are of wafer quality. The resulting display stably operates under tensile strains up to 40%, over 200 cycles, demonstrating the potential of stretchable displays based on inorganic materials.

Bongkyun Jang

Papers

Graphene-Based Three-Dimensional Capacitive Touch Sensor for Wearable Electronics

All MoS2-Based Large Area, Skin-Attachable Active-Matrix Tactile Sensor.

Tensile testing of ultra-thin films on water surface

Stretchable Active Matrix Inorganic Light-Emitting Diode Display Enabled by Overlay-Aligned Roll-Transfer Printing

Graphene-based stretchable/wearable self-powered touch sensor