Friction characteristics of polymers applicable to small-scale devices

A review of the critical features of a published micro-tribometer design, which was intended to improve on the dynamic response of typical commercial instruments, leads to its use with a modified technique. Data post-processing is introduced to partially compensate for some potential systematic errors. This approach is demonstrated by a preliminary study of the coefficient of friction (CoF) in sub-mm length reciprocating sliding motion for samples of polytetrafluoroethylene (PTFE) and an R11 acrylic formulation made by micro-stereo-lithography, with an SiO2-coated silicon wafer used as a control sample. Testing covered normal loads in the region of 10 mN–60 mN, at scan frequencies up to 9 Hz, corresponding to sliding speeds in the broad region of 1 mm s−1. While the control samples closely adhered to Amonton's laws over all the test parameter ranges, the CoFs of the two polymers showed contrasting patterns of dependence on sliding speed and repetition rate. Such results have implications for how polymers might be used effectively in future designs for small mechanical systems. They indicate a clear need for further development of the testing methods and large-scale studies of tribological behaviour and its underlying mechanisms under the specified micro-scale conditions

Tribological investigation for next-generation polymeric micro-systems.

The development of micro-fabrication processes for 3D microstructures has led to the production of low-cost, low-energy devices at millimeter scales known as MEMS for a wide range of electronic, mechanical, mechatronic and biomedical applications. As surface-to-volume ratio increases drastically with decreasing dimension, surface properties of the materials are the prominent factor at the interface between two solids and consequent tribological issues such as adhesion, friction and wear will arise in MEMS devices when surfaces are in, or have the potential for, sliding contact. Measurement techniques and principles used in micro-tribology are quite different from those in macro-tribology. Various specialized micro-tribometers have attracted recent attention in attempts to obtain consistent, accurate tribological measurements that could provide information for the design of MEMS components. However, even these have operational parameters quite different to those in the regime typical of MEMS devices. For example, the thermal properties of polymers might mean that they are especially sensitivity to the speeds and reciprocating scan frequencies of measurements. This is a serious concern because the selection of appropriate materials for such applications is very important in order to reduce not only friction and wear, but also the stiction of the parts. The immediate challenge is that there is very little reliable information about the properties of this new generation of engineering materials because of insufficient understanding and characterization of their behaviour at the microscale under a wide range of experimental conditions. With these points in mind, this thesis aims to prompt wide study of the micro-tribological properties of polymers for MEMS applications, providing preliminary new data on them while exploring in some detail possible uncertainty effects that could arise from the testing regimes of most micro-tribometers. It starts by re-commissioning and characterizing a unique, wide-bandwidth prototype micro-tribometer developed at Warwick, establishing good operating procedures by comparing measurements on materials widely discussed in the literature. New data has been collected on an acrylate resin typically used for micro-stereo-lithography, PTFE and oxide-coated silicon. It suggests that deviations from Amonton’s law in the ten millinewton range might be less severe than previously reported. Observing that the skill and time required for such testing makes it unattractive for a production control environment, the thesis then explores, via contact modelling, whether there is a useful correlation between Berkovich tip nano-hardness and the micro-friction of the polymeric samples: several plausible modelling assumptions are shown to lead to inconsistencies. Final discussions and recommendations consider how to move on from these experimental scoping studies to acquire detailed evaluations of the properties of the best candidates under typical usage conditions prior to designers of potential products taking these materials and processes at all seriously

A graph theory based energy routing algorithm in Energy Local Area Network (e-LAN)

The energy internet concept has been considered as a new development stage of the Smart Grid, which aims to increase the energy transmission efficiency and optimise the energy dispatching in time and space. Energy router is a core device in the energy internet and it connects all the devices together into a net structure and manages power flows among them. The research work presented in this paper described the energy router’s structure and function expectations from the network perspective, and improved the existing energy router design. Open-shortest-path first (OSPF) protocol and virtual circuit switching mode are referenced from the Internet in the energy local area network (e-LAN) design. This paper proposed a design of an energy routing algorithm based on graph theory in an e-LAN. A lowest-cost routing selection algorithm is designed according to the features of power transmission, and a source selection and routing design algorithm is proposed for very heavy load conditions. Both algorithms have been verified by case analyses

Key Technology of Real-Time Road Navigation Method Based on Intelligent Data Research

The effect of traffic flow prediction plays an important role in routing selection. Traditional traffic flow forecasting methods mainly include linear, nonlinear, neural network, and Time Series Analysis method. However, all of them have some shortcomings. This paper analyzes the existing algorithms on traffic flow prediction and characteristics of city traffic flow and proposes a road traffic flow prediction method based on transfer probability. This method first analyzes the transfer probability of upstream of the target road and then makes the prediction of the traffic flow at the next time by using the traffic flow equation. Newton Interior-Point Method is used to obtain the optimal value of parameters. Finally, it uses the proposed model to predict the traffic flow at the next time. By comparing the existing prediction methods, the proposed model has proven to have good performance. It can fast get the optimal value of parameters faster and has higher prediction accuracy, which can be used to make real-time traffic flow prediction

Phytophthora Root Rot Resistance in Soybean E00003

Phytophthora root rot (PRR) is a devastating disease in soybean [Glycine max (L.) Merr.] production. Michigan elite soybean E00003 is resistant to Phytophthora sojae and has been used as a resistance source in breeding. Genetic control of PRR resistance in this source is unknown. To facilitate marker-assisted selection (MAS), the PRR resistance loci in E00003 and their map locations need to be determined. In this study, a genetic mapping approach was used to identify major PRR -resistant loci in E00003. The mapping population consists of 240 F4–derived lines developed by crossing E00003 with the P. sojae susceptible line PI 567543C. In 2009 and 2010, the mapping population was evaluated in the greenhouse for PRR resistance against P. sojae races 1, 4, and 7, using modified rice (Oryza sativa L.) grain inoculation method. The population was genotyped with seven simple sequence repeat (SSR) and three single nucleotide polymorphism (SNP) markers derived from bulk segregant analysis. The heritability of resistance in the population ranged from 83 to 94%. A major locus, contributing 50 to 76% of the phenotypic variation, was mapped within a 3 cM interval in the Rps1 region. The interval was further saturated with more BARCSOY SSRs and SNPs with TaqMan assays. Two SSRs and three SNPs within the Rps1k gene were highly associated with PRR resistance in the mapping population. The major resistance gene in E00003 is either allelic or tightly linked to Rps1k.The molecular markers located in the Rps1k gene can be used to improve MAS for PRR resistance

Word Searching in Scene Image and Video Frame in Multi-Script Scenario using Dynamic Shape Coding

Retrieval of text information from natural scene images and video frames is a challenging task due to its inherent problems like complex character shapes, low resolution, background noise, etc. Available OCR systems often fail to retrieve such information in scene/video frames. Keyword spotting, an alternative way to retrieve information, performs efficient text searching in such scenarios. However, current word spotting techniques in scene/video images are script-specific and they are mainly developed for Latin script. This paper presents a novel word spotting framework using dynamic shape coding for text retrieval in natural scene image and video frames. The framework is designed to search query keyword from multiple scripts with the help of on-the-fly script-wise keyword generation for the corresponding script. We have used a two-stage word spotting approach using Hidden Markov Model (HMM) to detect the translated keyword in a given text line by identifying the script of the line. A novel unsupervised dynamic shape coding based scheme has been used to group similar shape characters to avoid confusion and to improve text alignment. Next, the hypotheses locations are verified to improve retrieval performance. To evaluate the proposed system for searching keyword from natural scene image and video frames, we have considered two popular Indic scripts such as Bangla (Bengali) and Devanagari along with English. Inspired by the zone-wise recognition approach in Indic scripts[1], zone-wise text information has been used to improve the traditional word spotting performance in Indic scripts. For our experiment, a dataset consisting of images of different scenes and video frames of English, Bangla and Devanagari scripts were considered. The results obtained showed the effectiveness of our proposed word spotting approach.Comment: Multimedia Tools and Applications, Springe

Tunable magnetism and electron correlation in Titanium-based Kagome metals RETi3Bi4 (RE = Yb, Pr, and Nd) by rare-earth engineering

Rare-earth engineering is an effective way to introduce and tune the magnetism in topological Kagome magnets, which has been acting as a fertile platform to investigate the quantum interactions between geometry, topology, spin, and correlation. Here we report the structure and properties of three newly discovered Titanium-based Kagome metals RETi3Bi4 (RE = Yb, Pr, and Nd) with various magnetic states. They crystalize in the orthogonal space group Fmmm (No.69), where slightly distorted Ti Kagome lattice, RE triangular lattice, Bi honeycomb and triangular lattices stack along the a axis. By changing the rare earth atoms on RE zag-zig chains, the magnetism can be tuned from nonmagnetic YbTi3Bi4 to short-range ordered PrTi3Bi4 (Tanomaly ~ 8.2 K), and finally to ferromagnetic NdTi3Bi4 (Tc ~ 8.5 K). The measurements of resistivity and specific heat capacity demonstrate an evolution of electron correlation and density of states near the Fermi level with different rare earth atoms. In-situ resistance measurements of NdTi3Bi4 under high pressure further reveal a potential relationship between the electron correlation and ferromagnetic ordering temperature. These results highlight RETi3Bi4 as another family of topological Kagome magnets to explore nontrivial band topology and exotic phases in Kagome materials.Comment: Manuscript:17 pages, 5 figures; Supporting information:11 pages, 11 tables and 10 figure

Livestock grazing impacts on plateau pika (Ochotona curzoniae) vary by species identity

Livestock and small burrowing mammals are potential ecosystem engineers and major drivers of ecosystem processes. Small mammals, often considered competitors with livestock, have been reported to increase in recent years and have been identified for their negative impacts on ecosystem services such as plant production and soil carbon sequestration. However, these increases and impacts by small mammals have rarely been studied with respect to how they may be influenced by livestock grazing. Here we experimentally manipulated large enclosures on the alpine grassland of Qinghai-Tibetan plateau, each with different livestock assemblages: yak (Bos grunniens), Tibetan sheep (Ovis aries), mixed populations of yak and sheep, and a control plot containing no livestock to study the potential impacts of livestock on the dominant small mammalian herbivore in the region, the plateau pikas (Ochotona curzoniae). We found that during the period of peak vegetative growth all pika populations in livestock experimental plots increased compared with those in the control plots. Additionally, pika populations and active pika burrow density increased more in experimental plots containing yaks compared with the sheep-only experimental plots. These results provide evidence that livestock grazing can increase the risk of pika outbreaks, which has led to this species being classified as a pest and subject to widespread control measures. We suggest explicitly incorporating livestock species identity in addition to grazing intensity and duration into management considerations to ensure maintenance of native biodiversity and long-term sustainability on the alpine grasslands of the Qinghai-Tibetan plateau.</p

Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films

Doped HfO2 thin films exhibit robust ferroelectric properties even for nanometric thicknesses, are compatible with current Si technology and thus have great potential for the revival of integrated ferroelectrics. Phase control and reliability are core issues for their applications. Here we show that, in (111)-oriented 5%La:HfO2 (HLO) epitaxial thin films deposited on (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates, the flexoelectric effect, arising from the strain gradient along the films normal, induces a rhombohedral distortion in the otherwise Pca21 orthorhombic structure. Density functional calculations reveal that the distorted structure is indeed more stable than the pure Pca21 structure, when applying an electric field mimicking the flexoelectric field. This rhombohedral distortion greatly improves the fatigue endurance of HLO thin films by further stabilizing the metastable ferroelectric phase against the transition to the thermodynamically stable non-polar monoclinic phase during repetitive cycling. Our results demonstrate that the flexoelectric effect, though negligibly weak in bulk, is crucial to optimize the structure and properties of doped HfO2 thin films with nanometric thicknesses for integrated ferroelectric applications