NANO SCIENCE AND ENGINEERING IN SOLID MECHANICS

According to National Science Foundation （NSF） Director A. Bement, ‘Transformative research is... research driven by ideas that stand a reasonable chance of radically changing our understanding of an important existing scientific concept or leading to the creation of a new paradigm or field of science is also characterized by its challenge to current understanding or its pathway to new frontiers.＇ Nanotechnology is one of such frontiers. It is the creation of new materials, devices and systems at the molecular level--phenomena associated with atomic and molecular interactions strongly influence macroscopic material properties with significantly improved mechanical, optical, chemical, electrical... properties. Former NSF Director Rita Colwell in 2002 declared, ‘nanoscale technology will have an impact equal to the Industrial Revolution＇. The transcendent technologies include nanotechnology, microelectronics, information technology and biotechnology as well as the enabling and supporting mechanical and civil infrastructure systems and materials. These technologies are the primary drivers of the twenty first century and the new economy. Mechanics is an essential eleraent in all of the transcendent technologies. Research opportunities, education and challenges in mechanics, including experimental, numerical and analytical methods in nanomechanics, carbon nano-tubes, bio-inspired materials, fuel cells, as well as improved engineering and design of materials are presented and discussed in this paper.

Nanomechanics and Ultrastructure of Bone:A Review

In this review,a brief presentation is first given to the hierarchical structure and mechanical behavior of bone.Then,the recent advancements in nanoscale characterization of bone ultrastructure and ingredients are discussed based on an extensive quantity of references in the literature.Moreover,computational and analytical bone mechanics at ultrastructure levels are critically reviewed with the growing body of knowledge in the field.The computational and analytical models are summarized in several categories for ease of understanding bone nanomechanics and their applicability/limitations.This review is expected to provide a well-informed foundation for the researchers interested in interrogating the complex biomechanical response of bone at its nanoscale hierarchy.

Effect of the potential function and strain rate on mechanical behavior of the single crystal Ni-based alloys:A molecular dynamics study

Molecular dynamics has been widely used to study the fundamental mechanism of Ni-based superalloys.However,the effect of the potential function and strain rate on mechanical behavior has rarely been mentioned in the previous molecular dynamics studies.In the present work,we show that the potential function of molecular dynamics can dramatically influence the simulation results of single crystal Ni-based superalloys.The microstructure and mechanical behavior of single crystal Ni-based superalloys under four commonly used potential functions are systematically compared.A most suitable potential function for the mechanical deformation is critically selected,and based on it,the role of strain rate on the mechanical deformation is investigated.

Application of Extreme Value Theory to Generation and Analysis of Pseudorandom Samples

The article deals with the methodology of pseudorandom data analysis. As a mathematical tool for carrying out the research the extreme value theory was used that creates one of the directions in mathematical statistics, and is related to investigating the extreme deviations from the median values in probability distributions. Also, the methods for estimating unknown parameters and algorithm of random-number generation are discussed. The models of treatment the extreme values are constructed which are based on machine generated sample and approach is proposed for their future application for constructing forecasting models.

A new modulated structure in α-Fe_2O_3 nanowires

A new modulated structure consisting of periodic （1120） stacking faults （SFs） in the α-Fe2O3 nanowires （NWs） formed by the thermal oxidation of Fe foils is reported, using a combination of high-resolution transmission electron microscopy （HRTEM） observations and HRTEM image simulations. The periodicity of the modulated structure is 1.53 nm, which is ten times （3500） interplanar spacing and can be described by a shift of every ten （3500） planes with 1/2 the interplanar spacing of the （1120） plane. An atomic model for the Fe203 structure is proposed to simulate the modulated structure. HRTEM simulation results confirm that the modulated structure in α-Fe2O3 NWs is caused by SFs.

A review of the mechanical integrity and electrochemical performance of flexible lithium-ion batteries

In the past two decades,various research works have been conducted in the field of flexible electronic devices(FEDs).Researchers have focused their efforts on solving the existing challenges in the electronic,electrochemical,and mechanical behaviors of FEDs.The importance of flexible lithium-ion batteries(FLIBs)in the area of FEDs is evident;however,less attention has been paid to the mechanical behavior of FLIBs in comparison with the material and electrochemical characteristics.The present paper reviewed the research works in the FLIBs,focusing on their mechanical integrity and electrochemical performances.First,an introduction to FLIBs was presented,and the previous review papers published in this field were briefly introduced.Then,a detailed review of the available electrochemical and mechanical research works on FLIBs was presented.Moreover,the mechanical testing methods(tensile,compressive,indentation,fatigue,and adhesion)for the characterization of FLIBs’components,the research works on the simulation and modeling of the mechanical behavior of FLIBs,and a summary of the present situation and the future trend of research in this field were reviewed and presented.

FINITE ELEMENT SIMULATION FOR YIELD STRESS OF HARD POLY(VINYL CHLORIDE)/ACRYLONITRILE-BUTADIENE-STYRENE BLENDS AT DIFFERENT CROSSHEAD SPEEDS

Hard poly（vinyl chloride） （PVC）/acrylonitrile-butadiene-styrene （ABS） blends were prepared using injection- molding and influence of crosshead speed on mechanical properties was examined. Based on morphology parameters obtained from transmission electron microscopy photography and the material parameters from true stress-strain curves of neat PVC and ABS, yield stresses of the blends at different crosshead speeds were simulated employing a two-dimensional nine-particle model based on the finite element analysis （FEA）. The FEA results were compared with the experimental yielding stress and the good agreement validated the simulation approach. The FEA approach allowed establishing a yielding criterion related to local yielding of the interstitial matrix between ABS particles.

QoS-aware dynamic bandwidth allocation algorithm for Gigabit-capable PONS

The Gigabit-capable passive optical network(GPON)technology is being considered as a promising solution for the next-generation broadband access network.Since the network topology of the GPON is point-to-multipoint,a media access control called dynamic bandwidth allocation(DBA)algorithm is an important factor for determining the performance of the GPON.In this paper,we propose a new DBA algorithm to effectively and fairly allocate bandwidths among end users.This DBA algorithm supports differentiated services-a crucial requirement for a converged broadband access network with heterogeneous traffic.In this article we first reviewed the signaling and configuration of the DBA,and then proposed a new DBA scheme that implemented QoS-based priority for this need to maximally satisfy the requirements of all optical network units(ONUs)and provide differentiated services.Analyses and simulation results show that the new algorithm can improve the bandwidth utilization and realize the fairness for both different ONUs and services.

Magnetocaloric effect in La_(0.7)Sr_(0.3)MnO_(3)/Ta_(2)O_(5) composites

The magnetocaloric effect (MCE) achieved for La_(0.7)Sr_(0.3)MnO_(3)/Ta_(2)O_(5) composites has been investigated. The maximum value of magnetic entropy change of La_(0.7)Sr_(0.3)MnO_(3) composites is found to decrease slightly with the further increasing of Ta_(2)O_(5) concentration. It is shown that La_(0.7)Sr_(0.3)MnO_(3)/Ta_(2)O_(5) composites exhibit much more uniform magnetic entropy change than that of gadolinium. Moreover, the results indicate that the temperature range between 100 K and 400 K can be covered using the La_(0.7)Sr_(0.3)MnO_(3)/Ta_(2)O_(5) composites. Therefore, MCE makes the composites promising for room-temperature magnetic cooling applications.

Flexible scheduling ensuring inter-ONU-group fairness in 1G/10G EPON coexistence system

In recent years, 10 Gbit/s Ethemet passive optical networks （10G EPON） have been gaining considerable interests because of its high bandwidth capability. To ensure smooth transition from 1 Gbit/s to 10 Gbit/s equipment and to avoid a significant one-time investment into such a cost-sensitive market, coexistence of gigabit Ethernet passive optical networks （GEPON） and 10G EPON system are necessary. In this article, coexistence system architecture and a novel bandwidth allocation algorithm called weight-optimized dynamic bandwidth allocation for coexistence EPON （WOCE-DBA） for the system is proposed. The simulation results show that this algorithm can guarantee fair bandwidth sharing among different optical network unit （ONU） groups, without ignoring the inter-ONU and intra-ONU fairness. Most importantly, it can flexibly adapt to the system composition variations and save efforts needed to modify the bandwidth scheduling mechanism during the migration process from GEPON to 10G EPON.