A floating-point digital receiver for MRI

A magnetic resonance imaging (MRI) system requires the highest possible signal fidelity and stability for clinical applications. Quadrature analog receivers have problems with channel matching, dc offset and analog-to-digital linearity. Fixed-point digital receivers (DRs) reduce all of these problems. We have demonstrated that a floating-point DR using large (order 124 to 512) FIR low-pass filters also overcomes these problems, automatically provides long word length and has low latency between signals. A preloaded table of finite impuls response (FIR) filter coefficients provides fast switching between one of 129 different one-stage and two-stage multrate FIR low-pass filters with bandwidths between 4 KHz and 125 KHz. This design has been implemented on a dual channel circuit board for a commercial MRI system.     

Convective heat transfer of gaseous solid suspension flow in a curved tube

Experimental study was performed on the convective heat transfer of gaseous solid suspension flow within helically coiled circular tube. The results show that the increase in heat transfer is greater than that due to the simple contribution of the increased heat capacity as the flowing media. This suggests that the addition of the suspended phase into the flows with curved stream lines can bring about the substantial reduction in the convective heat transfer resistance in the vicinity of the channel walls of the outer curvature portion. However, slight decrease in mixture Stanton number is also observed at the slight loading ratio region and the sublayer disturbing effect is seen to be gradually saturated at the higher loading region. Accordingly, overall reduction in the turbulence level also exists in the turbulent core of the flow and it is expected that there is an optimum solid loading ratio at which the viscous sublayer disturbing effect on the overall heat transfer performance is most effective.     

A method for measuring transients caused by interrupting currentusing a transmission line terminated in its characteristics impedance

A measurement method of transients caused by interrupting a current is described. In consideration of the fast transients and high-frequency discharge phenomena due to interrupting the current, a transmission-line system was introduced. It consists of a coaxial switch, coaxial cables as transmission lines on the right and left sides of the switch, and termination resistors. When the current is interrupted by the switch, the waveform across the termination resistor is measured by an oscilloscope. The impedance-matching technique for the cables was employed to minimize the effects of reflected waves. That is, the resistors were designed to match the characteristic impedance of the cables. The characteristics of the system were measured by a network analyzer. The VSWR of the system was within 1.33 in the frequency range below 500 MHz. The time-domain measurement using a transmission-line system terminated in its characteristic impedance clears up the process of the complicated transients caused by interrupting current     

垂直堆垛InAs量子点材料的分子束外延生长

用MBF设备以Stranski-Krastanov生长方式外延生长了5个周期垂直堆垛的InAs量子点，在生长过程中使用对形状尺寸控制法来提高垂直堆垛InAs量子点质量和均匀性。样品外延的主要结构是500nm的GaAs外延层，15nm的Al0．5Ga0．5As势垒外延层，5个周期堆跺的InAs量子点，50nm的Al0．5Ga0．5Asnm势垒外延层等。在生长过程中用反射式高能电子衍射仪(RHEED)实时监控。生长后用原子力显微镜(AFM)进行表面形貌的表征，再利用光制发光(PL)对InAs量子点进行观测。     

Improvement of stability of zeros in discrete-time multivariable systems using fractional-order hold

This paper is concerned with the stability of zeros of the discrete-time multivariable systems composed of a fractional-order hold (FROH), a continuous -time plant and a sampler in cascade. The properties of the limiting zeros are studied and a condition for obtaining stable zeros for sufficiently small sampling periods is derived. An approximate fractional-order hold (AFROH) is proposed as an implementation of FROH. It is shown that the AFROH as well as the FROH can locate the zeros of discrete-time multivariable systems inside the stable region and improve stability properties when the zero-order hold (ZOH) cannot. Experimental results of adaptive control with AFROH demonstrate a significant improvement of control performance compared with the use of a ZOH.     

An LMI approach to observer-based guaranteed cost control

This article presents a design method for an observer-based guaranteed cost controller for a class of uncertain linear systems, in which full state variables cannot be measured. The perturbations are assumed to be described by structural uncertainties. The linear matrix inequality (LMI) approach is applied to design the observer-based controller. The controller and observer gains are obtained by solving the LMI optimization and feasibility problems, respectively. A numerical example shows the potential of the proposed method. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007     

Separation of red (Y2O3: Eu3+), blue (Sr, Ca, Ba)10(PO4)6Cl2: Eu2+ and green (LaPO4: Tb3+, Ce3+) rare earth phosphors by liquid/liquid extraction

A novel process for separation of red (Y₂O₃: Eu³⁺), blue (Sr, Ca, Ba)₁₀(PO₄)₆Cl₂: Eu²⁺ and green (LaPO₄: Tb³⁺, Ce³⁺) fine tricolor phosphor powders was established. First, the green phosphor was extracted and separated from three phosphor mixtures in heptane/DMF(N, N-Dimethylformamide) system using stearylamine or laurylamine (DDA) as the cationic surfactant. Then, after being treated with 99.5% ethanol, the blue and red phosphors could be separated in Heptane/DMF system in presence of 1-octanesulfonic acid sodium salt as the anionic surfactant. Satisfactory separation results have been achieved through two steps extractions with their artificial mixtures. The grades and recovery of separated products reached respectively as follows: red product was 95.3% and 90.9%, blue product was 90.0% and 95.2%, and green product was 92.2% and 91.8%. Funded by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (ROCS, SEM [2005] No. 383)     

Study on demagnetizing field in coil method using FEM

The central demagnetizing factor was calculated when the B–H curve of the specimen is given by a straight line using three-dimensional axial symmetrical finite element method (FEM). It is shown that the results obtained with FEM are almost similar to those reported by Bozorth. The central demagnetizing factor was calculated and the distribution of lines of magnetic flux was examined when (1) the coil length is modified for a constant specimen length and (2) when the specimen length is changed for a constant coil length. Moreover, we examined the influence of the relative permeability on the central demagnetizing field and calculated the central demagnetizing factor for the material whose B–H curve is non-linear.