Charge-induced strains in single-walled carbon nanotubes

This paper investigates the electromechanical coupling in single-walled carbon nanotubes. In the model system, the extra electric charge of the nanotube is assumed to be uniformly distributed on carbon atoms. The electrostatic interactions between charged carbon atoms are calculated using the Coulomb law. The deformation of the charged nanotube is obtained by using the molecular structural mechanics method and considering the electrostatic interactions as an external loading acting on carbon atoms. The axial strain is found to be a symmetric function of applied charge, and our predictions are in very good agreement with those from ab initio calculations. The present results indicate that the nanotube aspect ratio has a strong effect on the axial strain when the ratio is less than 10 and the general trend is that the strain increases with the aspect ratio. The peak axial and radial strains occur at nanotube diameters of around 1.2-1.5?nm.     

Air cushion press for excellent uniformity, high yield, and fast nanoimprint across a 100 mm field

Imprint pressure uniformity is crucial to the pattern uniformity and yield of nanoimprint lithography (NIL) and, hence, its applications. We studied a novel imprint method, air cushion press (ACP), in which the mold and substrate are pressed against each other by gas pressure rather than solid plates, and compared it with a common method, solid parallel-plate press (SPP). We found that (a) under normal imprinting conditions the measured pressure distribution across a 100-mm-diameter single imprint field in ACP is nearly an order of magnitude more uniform; (b) ACP is immune to any dust and topology variations on the backside of the mold or substrate; (c) when a dust particle is between the mold and substrate, ACP reduces the damage area by orders of magnitude; (d) ACP causes much less mold damage because of significantly less lateral shift between the mold and substrate; and (e) ACP has much smaller thermal mass and therefore significantly faster speed for thermal imprinting.     

TaSi2 nanowires: A potential field emitter and interconnect

TaSi2 nanowires have been synthesized on a Si substrate by annealing NiSi2 films at 950 degrees C in an ambient containing Ta vapor. The nanowires could be grown up to 13 microm in length. Field-emission measurements show that the turn-on field is low at 4-4.5 V/microm and the threshold field is down to 6 V/microm with the field enhancement factor as high as 1800. The metallic TaSi2 nanowires exhibit excellent electrical properties with a remarkable high failure current density of 3 x 10(8) A cm(-2). In addition, effects of annealing temperatures and capability of metal silicide mediation layer on the growth of nanowires are addressed. This simple approach promises future applications in nanoelectronics and nano-optoelectronics.     

Chloroform in indoor swimming-pool air: Monitoring and modeling coupled with the effects of environmental conditions and occupant activities

Human exposure to chloroform in indoor swimming pools has been recognized as a potential health concern. Although environmental monitoring is a useful technique to investigate chloroform concentrations in indoor swimming-pool air, in practice, the interpretations of measured data would inevitably run into difficulties due to the complex interactions among the numerous variables, including environmental conditions and occupant activities. Considering of the relevant variables of environmental conditions and occupant activities, a mathematical model was first proposed to predict the chloroform concentration in indoor swimming-pool air. The developed model provides a straightforward, conceptually simple way to predict the indoor air chloroform concentration by calculating the mass flux, J, and the Péclet number, Pe, and by using a heuristic value of the indoor airflow recycle ratio, R. The good agreement between model simulation and measured data demonstrates the feasibility of using the presented model for indoor air quality management, operational guidelines and health-related risk assessment.     

A mechatronic positioning system actuated using a micro DC-motor-driven propeller–thruster

One of the greatest challenges facing designers in the mechatronics field is the development of autonomous systems capable of guiding an airborne object along a given trajectory or maintaining its position in a specified location. Nonetheless, developing such ability is essential to support emerging UAV (Unmanned Aerial Vehicle) requirements in the civil and military domains. Accordingly, this study commences by constructing a mechatronic system featuring a manipulator arm actuated by a DC-motor-driven constant-pitch propeller and then develops suitable control schemes to regulate the power supplied to the DC motor such that the manipulator arm is driven through a specified rotational displacement. Three different control schemes are implemented to regulate the displacement of the manipulator arm, namely a fixed gain PID controller, a function-based variable gain PID controller and a fuzzy gain-mixing PID controller. The feasibility of the three control systems is evaluated both numerically and experimentally. It is shown that the fixed gain PID controller results in a significant overshoot of the manipulator arm and leads to a loss of control. However, the function-based variable gain PID controller and the fuzzy gain-mixing PID controller both ensure an accurate tracking performance, even when the manipulator arm is manually perturbed during rotation.     

Modeling analyte transport and capture in porous bead sensors

Porous agarose microbeads, with high surface to volume ratios and high binding densities, are attracting attention as highly sensitive, affordable sensor elements for a variety of high performance bioassays. While such polymer microspheres have been extensively studied and reported on previously and are now moving into real-world clinical practice, very little work has been completed to date to model the convection, diffusion, and binding kinetics of soluble reagents captured within such fibrous networks. Here, we report the development of a three-dimensional computational model and provide the initial evidence for its agreement with experimental outcomes derived from the capture and detection of representative protein and genetic biomolecules in 290 μm porous beads. We compare this model to antibody-mediated capture of C-reactive protein and bovine serum albumin, along with hybridization of oligonucleotide sequences to DNA probes. These results suggest that, due to the porous interior of the agarose bead, internal analyte transport is both diffusion and convection based, and regardless of the nature of analyte, the bead interiors reveal an interesting trickle of convection-driven internal flow. On the basis of this model, the internal to external flow rate ratio is found to be in the range of 1:170 to 1:3100 for beads with agarose concentration ranging from 0.5% to 8% for the sensor ensembles here studied. Further, both model and experimental evidence suggest that binding kinetics strongly affect analyte distribution of captured reagents within the beads. These findings reveal that high association constants create a steep moving boundary in which unbound analytes are held back at the periphery of the bead sensor. Low association constants create a more shallow moving boundary in which unbound analytes diffuse further into the bead before binding. These models agree with experimental evidence and thus serve as a new tool set for the study of bioagent transport processes within a new class of medical microdevices.     

Manipulation of extinction spectra of P3HT/PMMA medium arrays on silicon substrate containing self-assembled gold nanoparticles

In this study, we report a simple novel approach to modulate the extinction spectra of P3HT/PMMA by manipulating the medium arrays on a substrate that is coated with self-assembled gold nanoparticles. The 20 nm gold nanoparticles were synthesized and then self-assembled on the APTMS/silicon substrate surface by immersing the substrate into the gold colloid suspension. A high-resolution P3HT/PMMA photoluminescent electron beam resist was used to fabricate various square hole arrays on the substrate containing gold nanoparticles. The P3HT/PMMA medium composition causes the blue shifts in the extinction peaks of up to 40.6 nm by decreasing the period from 500 nm to 200 nm for P3HT/PMMA square hole arrays with a diameter of 100 nm. The magnitude of blue shift is directly proportional to the product of the changes of medium refractive index and the array structure factor. These peak shifts and intensity of extinction spectra for various P3HT/PMMA medium arrays are well described by the finite-difference time-domain (FDTD) simulation results. Since this simple cost-effective technique can tune the extinction spectrum of medium and adding the gold nanoparticles can give more functionalities for sensing applications, such as surface-enhanced Raman scattering (SERS), that provides good opportunities for the design and fabrication of new optoelectronic devices and sensors.     

Sensing of damage and healing in three-dimensional braided composites with vascular channels

With the rise of composite materials as replacements for traditional monolithic materials comes an increase in demand for multifunctionality. Prior studies have demonstrated the ability of an embedded, electrically percolating carbon nanotube network to respond electrically to the onset and progression of damage in composite structures. We build upon this work by incorporating healing functionality into braided composites through the use of a hollow channel resin delivery system. This study demonstrates the ability of a carbon nanotube network to sense crack filling during resin injection, thus providing the scientific basis required for sensing healing in advanced composites. With practical application in mind, a two-part healant system is employed in this study. Two methods for qualitatively assessing healing are employed and compared; these include elastic modulus/strain energy recovery and FTIR spectroscopy.     

黄铁矿作为锂电池正极材料的电化学性能

对天然黄铁矿进行深加工后获得平均粒径为13μm,w(Fe)、w(S)分别为45.30%、50.95%的超微细黄铁矿粉,并以高级脂肪酸盐对其进行改性,采用TG/DSC、XPS及XRD对粉体进行了表征。XRD和TG/DSC分析表明粉体主要物相为黄铁矿FeS2,表面包覆着有机改性剂;XPS分析结果表明,改性前后黄铁矿表面S分别以SO42-和[S2]2-形式存在,而Fe均以Fe3+形式存在。对粉体试样进行电化学阻抗谱、恒电流放电测试和循环伏安测试,结果表明,改性黄铁矿具有较小的电荷转移电阻和较好的导电性;常温下以0.354A电流放电,截止电压为0.5V,改性黄铁矿的放电电位平台为1.44V,放电比容量达850mAh/g,接近理论容量890mAh/g。     

Hydrogen production from hydrolysis of ammonia borane with limited water supply

Effect of limited water supply to hydrolysis of ammonia borane for hydrogen evolution is studied over the cases in which the initial molar ratio of water to ammonia borane (H₂O/AB) is set at 1.28, 2.57 and 4.50. The conversion efficiency of ammonia borane to hydrogen is estimated from the accumulated volume of produced hydrogen gas and the quantitative analysis of hydrolysate by solid-state ¹¹B NMR. Characteristics of hydrogen evolution are significantly influenced by both water dosage and injection rate of water. In the case that water is a limiting agent, namely, H₂O/AB = 1.28, less hydrogen is produced than that predicted stoichiometrically. In contrast, conversion efficiency of ammonia borane reaches nearly 100% for the case with H₂O/AB = 4.50. Injection rate of water to ammonia borane also affect profoundly the produced volume and production rate of hydrogen, if water is used as a limiting agent in the hydrolysis of ammonia borane. Nonetheless, boric acid and metaboric acid are found to be the dominant products in the hydrolysate from XRD, FT-IR and solid-state ¹¹B NMR analysis. The hydrogen storage capacity using limited water supply in this work could reach as high as about 5.33 wt%, based on combined mass of reactants and catalyst.