Chiral-selective growth of single-walled carbon nanotubes on stainless steel wires

Single-walled carbon nanotubes (SWCNTs) were successfully grown on calcined stainless steel wires at 700 °C using CO as the carbon source. By contrast, the raw stainless steel wires produced only necklace-like multi-walled carbon nanotubes. Photoluminescence spectroscopy studies showed that SWCNTs grown from calcined stainless steel have a narrow diameter distribution and a high chiral selectivity of (6,5) nanotubes. The pre-growth heat treatment of the stainless steel leads to formation of iron and chromium oxides. The reduction of iron oxide results in formation of Fe nanoparticles which, anchored by chromium oxide, account for the chiral-selective growth of SWCNTs.     

Optimization of genetic algorithm for reconstruction of cross‐phase modulation frequency‐resolved optical gating data

We implemented a frequency‐resolved optical gating (FROG) measurement method using cross‐phase modulation in a highly birefringent microstructure optical fiber. The standard FROG data reconstruction algorithm of generalized projection failed for this setup and we successfully used the genetic algorithm (GA) instead which is less prone to get stuck to local minima. GA has several parameters that must be set up to suitable values. We describe the experimental setup and the algorithm and present our findings on what GA parameters are crucial and what are their optimal values. A single run of the algorithm takes 7 min on contemporary CPUs, making the algorithm suitable for routine laboratory work. Copyright © 2010 John Wiley & Sons, Ltd.     

Activities of Pt/Sibunit-1562 catalysts in the ORR in PEMFC: Effect of Pt content and Pt load at cathode

In this paper, a systematic investigation was carried out of activities at 80 °C of Pt supported on Sibunit-1562 graphitized carbon in the electroreduction of oxygen in the polymer electrolyte fuel cell. Pt content in the Pt/Sibunit-1562 catalysts was 20, 40, and 60 wt.% and Pt load at the cathode was varied in the 200–6.25 μg_Pt cm⁻² interval. The results were compared with the activity of commercial 20 wt.% Pt/Vulcan XC-72 catalyst. To optimize the transport properties of the cathode layer and maintain its thickness upon using Pt/Sibunit −1562 catalysts with varied Pt content and Pt loads a definite amount of Vulcan-XC-72 carbon support was added to the cathode catalytic inks. Higher activity of Pt/Sibunit-1562 catalysts was found as compared to that of commercial 20 wt.% Pt/Vulcan XC-72 with similar particle size of the active component.     

Engineering of the space-variant linear polarization of vortex-beams in biaxially induced crystals

We considered the propagation of Bessel beams through the biaxially induced birefringent crystal implemented by the mechanical torsion of the uniaxial crystal around its optical axis. Analyzing the solutions to the wave equation in the form of eigenmodes, we found that the system enables us to convert the beams with a uniform distribution of the linear polarization at the beam cross section into radially, azimuthally, and spirally polarized beams. Moreover, we revealed that the above system permits us to convert the beams with the space-variant linear polarization in accordance with the rule -s?s+1, where s is the topological index of the centered polarization singularity.     

White-light interferometry on rough surfaces--measurement uncertainty caused by noise

White-light interferometry on rough surfaces is an optical method for the measurement of the geometrical form of objects. The longitudinal coordinate of the measured surface is obtained from the measured interferogram by means of an evaluation method. However, the longitudinal coordinate cannot be determined completely accurately because the interferogram is affected by noise. We calculate the lower limit of the longitudinal measurement uncertainty caused by noise by use of the Cramer-Rao inequality. Additionally, we calculate the lower limit of the longitudinal measurement uncertainty caused by shot noise only.     

经济高效的矢量控制驱动(上) 使用单旁路电流传感

本文描述了基于飞思卡尔MC56F8013/23数字信号控制器的三相AC感应电机矢量驱动解决方案.     

Multifunctional ZnO-Based Thin-Film Bulk Acoustic Resonator for Biosensors

Zinc oxide (ZnO) and its ternary alloy magnesium zinc oxide (Mg _x Zn_1−x O) are piezoelectric materials that can be used for high-quality-factor bulk acoustic wave (BAW) resonators operating at GHz frequencies. Thin-film bulk acoustic resonators (TFBARs) are attractive for applications in advanced communication and in various sensors as they offer the capability of monolithic integration of BAW resonators with radio-frequency integrated circuits (RF ICs). In this paper we report Mg _x Zn_1−x O-based TFBAR biosensors. The devices are built on Si substrates with an acoustic mirror consisting of alternating quarter-wavelength silicon dioxide (SiO₂) and tungsten (W) layers to isolate the TFBAR from the Si substrate. High-quality ZnO and Mg _x Zn_1−x O thin films are achieved through a radio-frequency (RF) sputtering technique. Tuning of the device operating frequency is realized by varying the Mg composition in the piezoelectric Mg _x Zn_1−x O layer. Simulation results based on a transmission-line model of the TFBAR show close agreement with the experimental results. ZnO nanostructures are grown on the TFBAR’s top surface using metal- organic chemical vapor deposition (MOCVD) to form the nano-TFBAR sensor, which offers giant sensing area, faster response, and higher sensitivity over the planar sensor configuration. Mass sensitivity higher than 10³ Hz cm²/ng is achieved. In order to study the feasibility of the nano-TFBAR for biosensing, the nanostructured ZnO surfaces were functionalized to selectively immobilize␣DNA, as verified by hybridization with its fluorescence-tagged DNA complement.     

便携式电池供电医疗设备使用钽电容的考量因素

背景介绍便携式电池供电医疗设备的种类繁多,而能够可靠地为这些设备供电的充电器控制电路也有多种选择。精心选择如钽电容这样的无源元件,可以提升便携式设备内充电器控制和储能系统的整体性能。便携式电池供电医疗设备的供电既可以使用一次性电池,也可以使用用电池充电器充电的后备可充电电池。对医疗设备便携性和易用性的需求已经催生了充电控制电路的多项改良。     

Effect of cracks on hygric and thermal characteristics of concrete

The effect of cracks on the moisture and heat transport and storage properties, basic physical properties and compressive strength of six different types of high performance concrete is analyzed in the paper. The cracks in the material specimens are randomly distributed, imposed by thermal treatment. Experimental results show that the presence of cracks affects all hygric and thermal parameters except for the specific heat capacity in quite a significant way. Also, the effects of microsilica addition and of the size and presence of aggregates are important. The liquid water transport is influenced by cracks, microsilica and aggregates in the most remarkable way, together with the compressive strength. Water vapor transport parameters, water sorption parameters, thermal conductivity and open porosity are also subject of significant changes and can indicate the damage induced by cracks with a sufficient sensitivity.     

Synthesis and Optical Properties of KYF4/Yb,Er Nanocrystals,and their Surface Modification with Undoped KYF4

KYF₄/Yb³⁺, Er³⁺ nanocrystals with a mean diameter of approximately 13 nm were synthesized at 200 °C in the high boiling organic solvent N‐(2‐hydroxyethyl)ethylenediamine (HEEDA). The particles crystallize in the cubic phase known from α‐NaYF₄ and form transparent colloidal solutions in tetraethylene glycol (TEG) or propanol. Solutions containing 1 wt % of the nanocrystals in TEG display visible upconversion emission upon continuous wave (CW) excitation at 978 nm. Growing undoped KYF₄ on the surface of the KYF₄/Yb³⁺, Er³⁺ nanocrystals increases the upconversion efficiency by more than a factor of 20. The XRD data of these particles, display a slight increase in the mean particle size from 13 to 15.5 nm, indicating that only a part of the subsequently added KYF₄ shell material is deposited onto the particle surface. Nevertheless the performed surface modification obviously leads to core/shell structured particles.