Performance analysis of an improved MMSE multiuser receiver formismatched delay channels

Motivated by the fact that time delays in a practical direct-sequence code-division multiple-access (DS-CDMA) system can never be perfectly estimated, an improved minimum-mean squared-error (MMSE)-based receiver is proposed and analyzed. Via the simple assumption of a probability distribution for the delay estimation errors, the proposed receiver can achieve a performance superior to that of the conventional MMSE (CMMSE) receiver. The performances of this improved receiver and the CMMSE receiver are compared in terms of the mean squared error (MSE), probability of error, and asymptotic multiuser efficiency (AME). As the original definition of AME does not consider mismatched channels, the behavior of three single-user receivers bearing imperfect delay estimation is also investigated. These single-user receivers are employed to define a more appropriate AME. Finally, an efficient update mechanism to accommodate dynamic channel statistics, and thus practical implementation, is proposed     

High speed p-type SiGe modulation-doped field-effect transistors

We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (f_T) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (g_m) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K     

一种制备磁性粉末的新技术--均匀颗粒成型法

采用均匀颗粒成型法（Uniform Dropler Spray-UDS）制备Fe基合金粉末，该方法制备的颗粒粒度分布均匀，性能一致，大大优于传统的粉末制备方法（如破碎法、气雾化），具有广阔的应用前景。本文分析了粉末制备过程中颗粒尺寸的影响因素，结果表明：颗粒的大小主要取决于坩埚底部小孔、坩埚内外气体压强差以及振荡频率三个独立变量。     

Profile dependence and measurement of absolute Raman scattering cross-section in optical fibres

A simple measurement method for the absolute Raman scattering cross-section of an optical fibre is presented. This method does not require a high power pump laser and it measures the fibre directly. It is also shown that the calculation of the cross-section depends on the fibre structure, such as its refractive index profile and the differential attenuation between the pump wavelength and Raman wavelength.<>     

Kinetic Study on Absorption of SO2 and NOX with Acidic NaClO2 Solutions Using the Spraying Column

The operating conditions of this study are close to the typical operating conditions of flue gas desulfurization system in coal-fired power plants. The aim of this study is to investigate the absorption kinetics of SO2 and NO from simulated flue gas into an aqueous solution of acidic sodium chlorite using a bench-scale spraying column. The range of absorption rates measured in this study is between 1.91×10?11 and 9.59×10?10?mol?s?1?cm?2. The range of rate constants measured in this study is between 1.32×107 and 1.21×108?(L?mol?1)1.9?s?1, and the average rate constant is 6.16×107?(L?mol?1)1.9?s?1. The activation energy and frequency factor are 129 Kcal/mol (53.97 KJ/mol) and 6.93×1016?[(L/mol)1.9/s], respectively.     

Shallow Turbulent Flows by Video Imaging Method

Shallow turbulent flows were produced in a tank of small thickness to study the friction effects on large-scale turbulent motion of small depth. The tank was constructed of two parallel walls. The space between the parallel walls (4.4, 1.57, and 0.59 cm) was small compared with the height (107 cm) and the width (212 cm) of the tank, and was varied during the experiments for different friction effects. Turbulent flows were produced by the injection of water in the form of starting jets into the tank filled with water. The large-scale turbulent flow in the small space between the walls of the tank is confined to essentially two-dimensional motion, and the motion is retarded by the force of friction. Dye was injected with the source fluid as the tracer for the highly unsteady and quasitwo-dimensional turbulent motion. From the initiation of the turbulent motion at the source to the final interaction of the jets with the tank bottom, the entire sequence of events was recorded by a pair of video cameras. The depth-averaged concentration of the dye was analyzed using the recorded video images.     

Photoreactivation of Escherichia coli following medium-pressure ultraviolet disinfection and its control using chloramination.

Ultraviolet (UV) disinfection is becoming increasingly popular as an alternative disinfection technology to chlorination in recent years. In this study, we investigated the photoreactivation of Escherichia coli following medium-pressure (MP) UV disinfection of synthetic water by a bench-scale collimated beam apparatus. The UV doses ranged from 1.6 -19.7 mWs/cm2 and photoreactivation was investigated for 6 hours under fluorescent light. In addition, chloramination was applied after UV disinfection to investigate its ability to control photoreactivation. It was found that photoreactivation occurred for all UV doses tested and the increase in bacteria numbers ranged from 0.04 to 1.35 log10. However, the degree of photoreactivation decreased with increased UV doses. Chloramination experiments revealed that the addition of 0.5 mg/l of monochloramine resulted in suppression of photoreactivation for 1 hour only. An increased monochloramine dose of 1 mg/l was found to prevent photoreactivation for the entire duration of the experiment. The results of this study have shown that photoreactivation occurs even after MP UV disinfection, although it is of a lesser extent at higher UV doses. This study has also established that secondary chloramination can effectively suppress and eliminate photoreactivation with a chloramine dose of 1 mg/l.     

Self-Consistent Effects on the Starting Current of Gyrotron Oscillators

Self-consistent effects on the starting current of gyrotron oscillators are examined. Field profiles in the open cavity are shown to be sensitive to the interaction dynamics. This can either significantly raise or lower the oscillation threshold, particularly for the low-Q modes. The transition from resonant-mode oscillations at the low magnetic field to backward-wave oscillations at the high magnetic field is demonstrated.     

Positively Thermo‐Sensitive Monodisperse Core–Shell Microspheres

In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.