Mechanically Robust Si Nanorod Arrays on Cu/Ti Bilayer Film Coated Si Substrate for High Performance Lithium-Ion Battery Anodes

The deformation behavior and mechanical properties of a tilted Si nanorod array structure on Cu/Ti bilayer film coated Si substrate were studied for the first time by coupled atomic force microscopy and nanoindentation techniques. The individual Si nanorods fabricated by an oblique angle deposition technique are composed of many fine Si nanofibers with the diameter ranging from 10 to 50 nm. They are not brittle, but ductile. The ductile metallic Cu/Ti bilayer film roots contribute remarkably to the mechanical robustness of the Si nanorods. The toughening mechanism of such Si-based nanoanodes has been elucidated by experimental mechanics studies

Effect of Compression on the Transmission Loss of Porous Material

Porous materials are commonly applied in sound absorption in different places. Transmission loss, one of the vital parameters determining the performance of the material, will change when the material is compressed. Usually the compression that might affect the properties to the greatest extent are normal compression and the deformation can be simplified as 1D compression model. In order to verify the prediction, some formulas taking several parameters (porosity, tortuosity, flow resistivity and characteristic lengths) into account are applied and also the Johnson et al’s model of limp structure. Dynamic density of limp model and bulk modulus are thus obtained and to get the mathematical expression of the transmission coefficient and transmission loss, acoustic equations including Euler equation are applied to the boundary conditions between the material and the fluid (air in the experiment). The numerical predictions are later compared with experimental data collected with 4-mic 2-load measurement on Kundt standard impedance tube. Both the mathematical prediction and the experimental results shows that the transmission loss would decrease under compression and increase if the material is extended

Environmental Effects on Mechanical and Thermal Behaviors of Zinc Oxide Nanobelts and Dispersion of Carbon Nanostructures

One-dimensional (1-D) nanostructures, such as nanowires, nanobelts, and nanotubes of different materials, have significant applications as nanoscale interconnects and active/functional components of electronic and optoelectronic devices, sensors, actuators, nanoelectromechanical systems (NEMS), and energy generation/conversion systems. The thermal and mechanical stabilities of those nanodevices and nanoenabled energy systems are of both theoretical and practical interests. Thermodynamic properties of nanomaterials are different from those of bulk materials. As the size of a solid particle reduces to the nanometer scale, the surface-to-volume ratio increases and the melting temperature may remarkably decrease. The functionality and/or reliability of those nanodevices and nanoenabled energy systems are also determined by the elastic properties of individual 1-D nanostructures. When the environment changes, such as, humidity level, temperature, ultraviolet radiation, the mechanical behaviors of nanomaterials could simultaneously change as well. However, the mechanisms for how the mechanical and thermal behaviors of 1-D nanostructures depend on their surface conditions, size and surface structures are barely understood. ZnO nanostructure, one of the spotlights of current nanoscience and nanotechnology, will be employed to study the environmental effects on the thermal and mechanical behaviors of nanomaterials, respectively. The exceptional mechanical, superior thermal and electrical properties of carbon nanotubes (CNTs) and graphene have made them promising for many engineering applications, such as composite reinforcements, scanning probe tips, field emission sources, hydrogen storage systems, super-capacitors, quantum devices, and biosensors. A significant challenge for both fundamental research and practical applications of CNTs and graphene is to disperse CNTs and graphene sheets into certain media, such as ethanol, water, or polymers. Since CNTs and graphene are insoluble and tend to form bundles due to their strong hydrophobicity and van der Waals attractions, a great deal of effort has been invested to develop efficient and low-cost approaches to realize full dispersion of CNTs and graphene sheets. In this dissertation, the environmental effect on dispersion of CNTs and graphene sheets will also be discussed

Stretching Micro Metal Particles into Uniformly Dispersed and Sized Nanoparticles in Polymer.

There is a longstanding challenge to disperse metal nanoparticles uniformly in bulk polymers for widespread applications. Conventional scale-down techniques often are only able to shrink larger elements (such as microparticles and microfibers) into micro/nano-elements (i.e. nanoparticles and nanofibers) without much altering their relative spatial and size distributions. Here we show an unusual phenomenon that tin (Sn) microparticles with both poor size distribution and spatial dispersion were stretched into uniformly dispersed and sized Sn nanoparticles in polyethersulfone (PES) through a stack and draw technique in thermal drawing. It is believed that the capillary instability plays a crucial role during thermal drawing. This novel, inexpensive, and scalable method overcomes the longstanding challenge to produce bulk polymer-metal nanocomposites (PMNCs) with a uniform dispersion of metallic nano-elements

Enhanced Nucleate Boiling on Horizontal Hydrophobic-Hydrophilic Carbon Nanotube Coatings

Ideal hydrophobic-hydrophilic composite cavities are highly desired to enhance nucleate boiling. However, it is challenging and costly to fabricate these types of cavities by conventional micro/nano fabrication techniques. In this study, a type of hydrophobic-hydrophilic composite interfaces were synthesized from functionalized multiwall carbon nanotubes by introducing hydrophilic functional groups on the pristine multiwall carbon nanotubes. This type of carbon nanotube enabled hydrophobic-hydrophilic composite interfaces were systematically characterized. Ideal cavities created by the interfaces were experimentally demonstrated to be the primary reason to substantially enhance nucleate boilin

A Generic Bamboo-Based Carbothermal Method for Preparing Carbide (SiC, B\u3csub\u3e4\u3c/sub\u3eC, TiC, TaC, NbC, Ti\u3csub\u3ex\u3c/sub\u3eNb\u3csub\u3e1-x\u3c/sub\u3eC, and Ta\u3csub\u3ex\u3c/sub\u3e Nb\u3csub\u3e1-x\u3c/sub\u3eC) Nanowires

Finding a general procedure to produce a whole class of materials in a similar way is a desired goal of materials chemistry. In this work, we report a new bamboo-based carbothermal method to prepare nanowires of covalent carbides (SiC and B4C) and interstitial carbides (TiC, TaC, NbC, TixNb1−xC, and TaxNb1−xC). The use of natural nanoporous bamboo as both the renewable carbon source and the template for the formation of catalyst particles greatly simplifies the synthesis process. Based on the structural, morphological and elemental analysis, volatileoxides or halides assisted vapour–liquid–solid growth mechanism was proposed. This bamboo based carbothermal method can be generalized to other carbide systems, providing a general, one-pot, convenient, low-cost, nontoxic, mass production, and innovative strategy for the synthesis of carbide nanostructures

From human-human collaboration to human-robot collaboration: automated generation of assembly task knowledge model

Task knowledge is essential for robots to proactively perform collaborative assembly tasks with a human partner. Representation of task knowledge, such as task graphs, robot skill libraries, are usually manually defined by human experts. In this paper, different from learning from demonstrations of a single agent, we propose a system that automatically constructs task knowledge models from dual-human demonstrations in the real environment. Firstly, we track and segment video demonstrations into sequences of action primitives. Secondly, a graph-based algorithm is proposed to extract structure information of a task from action sequences, with task graphs as output. Finally, action primitives, along with interactive information between agents, temporal constraints, are modelled into a structured semantic model. The proposed system is validated in an IKEA table assembly task experiment

Petrogenesis of the quartz diorite from the Lietinggang-Leqingla Pb-Zn-Fe-Cu- (Mo) deposit in southern Tibet: implications for the genesis of a skarn-type polymetallic deposit in the Tibetan-Himalayan collisional orogen

publishedVersio

Experiments on bright field and dark field high energy electron imaging with thick target material

Using a high energy electron beam for the imaging of high density matter with both high spatial-temporal and areal density resolution under extreme states of temperature and pressure is one of the critical challenges in high energy density physics . When a charged particle beam passes through an opaque target, the beam will be scattered with a distribution that depends on the thickness of the material. By collecting the scattered beam either near or off axis, so-called bright field or dark field images can be obtained. Here we report on an electron radiography experiment using 45 MeV electrons from an S-band photo-injector, where scattered electrons, after interacting with a sample, are collected and imaged by a quadrupole imaging system. We achieved a few micrometers (about 4 micrometers) spatial resolution and about 10 micrometers thickness resolution for a silicon target of 300-600 micron thickness. With addition of dark field images that are captured by selecting electrons with large scattering angle, we show that more useful information in determining external details such as outlines, boundaries and defects can be obtained.Comment: 7pages, 7 figure