Chemical Processing of Nanostructured Cemented Carbide

Chemical processing is becoming a vital component in the economic development of advanced engineering materials. Our research group on chemical processing has been focussed on the development of process to produce nanophase cemented carbide. It is a much more direct route for making WC/Co than traditional processing methods, and offers the potential for lower cost production of novel materials with homogeneous nanophase microstructures and improved properties. This paper addresses the scientific and technical issues relating to the chemical processing of nanophase WC/Co composite powder and their sintering.     

Linear microstrip surface coil for MR imaging of the rat spinal cord at 4.7 T

A new design of RF coil based on a quasi-transverse electromagnetic field is described. The coil was developed for the acquisition of MR images of the rat spinal cord at 4.7 T. Different materials for the construction of the coil were tested, and the best results were obtained with Teflon. The design of the microstrip coil enables the investigator to change the length of the coil in a longitudinal direction and yields a relatively high signal-to-noise ratio due to the restricted field of view. Low RF field penetration depth also helps in suppressing motion artifacts generated by, e.g., breathing or heartbeats.     

Improving Nonlocal Means Method via a No-reference Image Content Metric for MRI Denoising

The patch matching of the traditional Nonlocal means （NLM） filter mainly depends on structure similarity and cannot adapt to the patch rotation or mirroring transformation. Therefore, designing a measure with rorationally invariant similarity is of significant importance for improving the effectiveness of patch comparison of NLM. This paper proposes to apply a no-reference image content metric with the rotation-invariance to NLM for denoising Magnetic resonance （MR） images. The metric measures quantitatively the content of a patch in an image, including sharpness, contrast, and geometric features such as textures and edges. The metric values for every patch are computed and added into the Gaussian matching kernel of NLM so as to effectively perform patch matching. The main advantage of the proposed method is that it does not need to rotate patches in different orientations during patch matching. Experimental results show that the proposed method is superior to the traditional NLM, the state-of-the-art method Block-matching and 3- D （BM3D） filtering and the Unbiased NLM （UNLM） for MRI denoislng.     

用于束流输运计算的TRANSPORT-EM程序

一、TRANSPORT程序的功能及其局限性TRANSPORT程序是一个采用一、二阶传输矩阵和束矩阵计算粒子运动轨迹和束包络的计算程序。所计算的系统包括漂移空间、两极磁铁、四极磁铁、六极磁铁、螺线管、行波加速段等。该程序能够处理束心位移、元件不准直和绕光轴旋转公差等问题。并且,能够自动进行系统优化设计,自动调整元件的参数以满足对系统在聚焦成象和象差修正方面的要求。     

白云鄂博主东矿中贫氧化矿铌资源的特点及综合回收

包头白云鄂博主东矿中贫氧化矿中铌有很大的回收价值,本文探讨了主要铌矿物的特点及选矿性质,认为弱磁—强磁是初步富集铌的有效途径。本文还较为详细地介绍了从强磁中矿的稀土浮选尾矿回收铌得到富铌铁精矿的若干浮选工艺条件及浮选药剂。     

Spin injection in n-type resonant tunneling diodes

We have studied the polarized resolved photoluminescence of n-type GaAs/AlAs/GaAlAs resonant tunneling diodes under magnetic field parallel to the tunnel current. Under resonant tunneling conditions, we have observed two emission lines attributed to neutral (X) and negatively charged excitons (X⁻). We have observed a voltage-controlled circular polarization degree from the quantum well emission for both lines, with values up to −88% at 15 T at low voltages which are ascribed to an efficient spin injection from the 2D gases formed at the accumulation layers.     

EFFECT OF A MAGNETIC FIELD ON TWO-PHASE LIQUID METAL FLOW AND CAVITATION OCCURRENCE

To clarify the effect of a magetic field on two-phase bubble flow characteristics and cavitation occurrence, an analytical study of two-phase MHD flow with low quality is developed, taking into account slip and bubble expansion. Numerical calculation shows that the application of a magnetic field causes a decrease in pressure in the diverging passage and an increase in the incipient cavitation number.     

UNSTEADY HYDROMAGNETIC FREE CONVECTION FLOW OF A DISSIPATIVE AND RADIATING FLUID PAST A VERTICAL PLATE WITH CONSTANT HEAT FLUX

The effect of thermal radiation absorption on an unsteady free convective flow past a vertical plate is studied in the presence of a magnetic field and constant wall heat flux. Boundary layer equations are derived, and the resulting approximate nonlinear ordinary differential equations are solved analytically using asymptotic technique. A parametric study of all parameters involved is conducted, and a representative set of numerical results for the velocity and temperature profiles as well as the skin-friction parameter are illustrated graphically to show typical trends of the solutions.     

Monolithic carbon structures including suspended single nanowires and nanomeshes as a sensor platform

With the development of nanomaterial-based nanodevices, it became inevitable to develop cost-effective and simple nanofabrication technologies enabling the formation of nanomaterial assembly in a controllable manner. Herein, we present suspended monolithic carbon single nanowires and nanomeshes bridging two bulk carbon posts, fabricated in a designed manner using two successive UV exposure steps and a single pyrolysis step. The pyrolysis step is accompanied with a significant volume reduction, resulting in the shrinkage of micro-sized photoresist structures into nanoscale carbon structures. Even with the significant elongation of the suspended carbon nanowire induced by the volume reduction of the bulk carbon posts, the resultant tensional stress along the nanowire is not significant but grows along the wire thickness; this tensional stress gradient and the bent supports of the bridge-like carbon nanowire enhance structural robustness and alleviate the stiction problem that suspended nanostructures frequently experience. The feasibility of the suspended carbon nanostructures as a sensor platform was demonstrated by testing its electrochemical behavior, conductivity-temperature relationship, and hydrogen gas sensing capability.     

One-pot synthesis of magnetite nanopowder and their magnetic properties

Magnetite (Fe₃O₄) nanopowder can be prepared by one-pot solvothermal reaction of Fe-urea complex ([Fe(CON₂H₄)₆](NO₃)₃) in ethanol. The result of X-ray powder diffraction (XRD) suggests the formation of Fe₃O₄ whose lattice constant is 8.385 Å. The formation of Fe₃O₄ is further confirmed from X-ray photoelectron spectroscopy (XPS) measurements. Transmission electron micrograph (TEM) observations show that Fe₃O₄ particles are nearly spherical in shape. The crystallite size of Fe₃O₄ can be controlled from 9.7 to 20.5 nm by varying the solvothermal reaction time. Room temperature magnetization hysteresis curves exhibit almost immeasurable values of coercivity and remanence, suggesting that the Fe₃O₄ nanopowder possesses superparamagnetic characteristics. The saturation magnetization (Ms) increases from 32.6 to 42.9 emu/g when the reaction time increases from 10 to 50 h.