Design of multi-frequency microstrip antennas using multiple rings

An electromagnetically coupled feed arrangement is proposed for simultaneously exciting multiple concentric ring antennas for multi-frequency operation. This has a multi-layer dielectric configuration in which a transmission line is embedded below the layer containing radiating rings. Energy coupled to these rings from the line beneath is optimised by suitably adjusting the location and dimensions of stubs on the line. It has been shown that the resonant frequencies of these rings do not change as several of these singlefrequency antennas are combined to form a multi-resonant antenna. Furthermore, all radiators are forced to operate at their primary mode and some harmonics of the lower resonant frequency rings appearing within the frequency range are suppressed when combined. The experimental prototype antenna has three resonant frequencies at which it has good radiation characteristics.     

Satellite image segmentation using hybrid variable genetic algorithm

Image segmentation is an important task in image processing and analysis. Many segmentation methods have been used to segment satellite images. The success of each method depends on the characteristics of the acquired image such as resolution limitations and on the percentage of imperfections in the process of image acquisition due to noise. Many of these methods require a priori knowledge which is difficult to obtain. Some of them are parametric statistical methods that use many parameters which are dependent on image property. In this article, a new unsupervised nonparametric method is developed to segment satellite images into homogeneous regions without any a priori knowledge. The new method is called hybrid variable genetic algorithm (HVGA). The variability is found in the variable number of cluster centers and in the changeable mutation rate. In addition, this new method uses different heuristic processes to increase the efficiency of genetic algorithm in avoiding local optimal solutions. Experiments performed on two different satellite images (Landsat and Spot) proved the high accuracy and efficiency of HVGA compared with another two unsupervised and nonparametric segmentation methods genetic algorithm (GA) and self‐organizing map (SOM). The verification of the results included stability and accuracy measurements using an evaluation method implemented from the functional model (FM) and field surveys. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 199–207, 2009     

Flutter stabilization of cantilevered plates using a bonded patch

In recent years, many researchers have studied active vibration suppression of fluttering plates using piezoelectric actuators. Lots of these researchers have focused on optimal placement of piezoelectric patches to obtain maximum controllability of the plate. Although mass and stiffness characteristics of bonded patches can alter the aeroelastic behavior of fluttering plates, few of the investigators have considered the effect of the mentioned parameters in the optimization process. This paper investigates the effect of a bonded patch on the aeroelastic behavior of cantilevered plates in supersonic flow and examines the optimal location of the patch for the best controllability performance. For mathematical simulation of the structure, linear von Karman plate theory along with first-order piston theory is employed. The results obtained through this study reveal that a bonded patch with a small mass ratio can change the system critical dynamic pressure significantly. The maximum raise of the critical dynamic pressure is acquired when the bonded patch is placed on the leading edge of the plate. A variation of the system??s aerodynamic characteristics, subsequently, influences the control performance of the bonded patch and alters the optimal patch location.     

Rotator attitude measurement using GPS based on Kalman filter algorithm

研究了用单天线全球定位系统(GPS)接收机的载波信号正弦相位调制波实时测量旋转体姿态的基本原理和方法,设计了一种实现旋转体姿态测量的卡尔曼滤波算法.为了克服多天线姿态测量存在的天线相位延迟、噪声相互独立等不利因素,将单天线置于相位中心偏离旋转轴心位置.分析了旋转体姿态与GPS接收机载波信号之间的关系,给出载波信号的数学模型,在GPS接收机跟踪环路建立了包含姿态信息的载波信号卡尔曼滤波模型,对环路的跟踪性能与姿态算法进行MATLAB仿真.结果表明,此算法的跟踪环路带宽窄,能有效抑制噪声干扰,较好地实现了对旋转信号的跟踪,并且姿态测量精度比较高.     

Solidification/stabilization of electric arc furnace dust using coal fly ash. Analysis of the stabilization process

In this paper, the stabilization of electric arc furnace (EAF) dust containing hazardous metals such as Pb, Cd, Cr or Zn is described. The treatment involves a waste solidification/stabilization (S/S) process, using coal fly ash as the fundamental raw material and main binder. The article also contains a brief review of the most important recent publications related to the use of fly ash as S/S agents.The efficacy of the process has been evaluated mainly through leaching tests on the solidified products and compliance with some imposed leachate limits. The concentration of metals leaching from the S/S products was strongly leachate pH dependent; thus, the final pH of the leachate is the most important variable in reaching the limits and, therefore, in meeting the stabilization goals.In this study, the dependence relationship between the leachate pH and the concentrations of metals in the leachate are analyzed; in some cases, this allows us to estimate the speciation of contaminants in the S/S solids and to understand the mechanism responsible for reduced leachability of heavy metals from solidified wastes.     

Continuous phase stabilization and active interferometer control using two modes

We present a computer-based active interferometer stabilization method that can be set to an arbitrary phase difference and does not rely on modulation of the interfering beams. The scheme utilizes two orthogonal modes propagating through the interferometer with a constant phase difference between them to extract a common relative phase and generate a linear feedback signal. Switching times of 50?ms over a range of 0–6π radians at 632.8?nm are experimentally demonstrated. The relative interferometer phase can be stabilized up to several days to within ± 3°.     

Question of the motion of a system of sequential coaxial vortex rings in a homogeneous fluid

Results are presented of an experimental investigation of the singularities of the motion of a system of interacting toroidal vortices in a homogeneous fluid.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 1, pp. 26–28, January, 1989.     

Possibility of using low-energy nuclear transitions as benchmarks for frequency stabilization

The fundamental possibility of using low-energy nuclear transitions for obtaining highly stable frequency standards is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 12, pp. 3–4, December, 2007.     

Symmetry tests using the half-integer flux quantum effect in cuprate superconducting rings

The presence or absence of the half-integer flux quantum effect in controlled orientation tricrystal grain boundary rings is a general test of the phase of the superconducting order parameter. One such test proves that this effect is symmetry dependent, and that the order parameter in YBa₂Cu₃O₇- has lobes and nodes consistent with d-wave symmetry. Our measurements show that the flux in the 1/2 integer ground state is quantized to ₀/2 within ± 3%. This puts limits on the imaginary component of the superconducting order parameter in YBa₂Cu₃O₇-.     

Real-time position and attitude sensing using CCD cameras inmagnetic suspension system applications

A position measurement system using CCD cameras is designed for large-gap magnetic suspension applications. White dots are placed on a magnetically suspended model, which is then scanned by CCD cameras against a black background. A real-time hardware system is applied to detect the coordinates of these white dots and generate corresponding attitude data for the suspended model by the lookup-table method. Circuit hardware is designed and implemented with efficient algorithms to accomplish the objective. The purpose of the real-time measurement system is to detect the position and attitude of the magnetically suspended model and to feed this information to the control circuit. System analysis and test results are presented     

The reactive stabilization of Al-Zn foams using a powder metallurgy approach

The Al-Zn binary system was chosen in order to study the possibility of generating a reactive foam system within the semi-solid region. The idea is to create foam at lower temperatures than the melting point of pure aluminum using a transient liquid phase that softens the matrix prior to bulk expansion. This minimizes crack formation, collapse, drainage and deformation generated during processing. The Al-Zn foams were fabricated via the powder metallurgy route by hot compaction and subsequently foamed using TiH₂ as a blowing agent. The investigated systems consist of low, medium and high concentrations of Zn (10 wt%, 33 wt% and 50 wt%) in an Al based matrix containing 0.8 wt% TiH₂. High temperature in situ confocal microscopy was used to study the formation of the transient liquid phase of the compacted elemental powders. As the percentage of Zn was increased, the liquidus temperature of the melt was lowered along with an increase in the volume of transient liquid phase. This reduces the mismatch between the hydrogen release temperature of the blowing agent and the liquidus temperature of the melt, thus increasing foaming stability. Reasonable foam structures near 300 vol% expansion and fair pore distributions were achieved at low concentrations of Zn (10 wt%) only above the alloy liquidus point. The mechanical compressive strength properties of the alloyed foam systems were also assessed.     

Behavior and modeling of confined concrete cylinders in axial compression using FRP rings

This study suggests a secondary dense lateral reinforcement for reinforced concrete (RC) columns that are located between the primary lateral reinforcement and concrete surface, which are used to delay the buckling of longitudinal reinforcement and increase the ductility of RC columns. ‘Dense’ means that the spacing of the lateral reinforcement is smaller than the maximum gravel size. This study conducted axial compressive tests on concrete cylinders confined by dense reinforcement in order to improve the effectiveness of the dense lateral reinforcement. FRP (Fiber Reinforced Polymer) rings were used for the reinforcement since they are corrosion resistant. The dense reinforcing method with FRP rings can successfully increase the peak strength of the concrete and the failure strain. The stress–strain curves of the confined concrete became almost bilinear with hardening behavior, which were similar to that of the concrete confined by the jackets of FRP sheets. This study also provides models of stress–strain in an axial direction and lateral strain. Based on the models, this study analyzes the confining effectiveness of the FRP rings on concrete.     

Precision pointing of imaging spacecraft using gyro-based attitude reference with horizon sensor updates

Remote sensing satellites are required to meet stringent pointing and drift rate requirements for imaging operations. For achieving these pointing and stability requirements, continuous and accurate three-axis attitude information is required. Inertial sensors like gyros provide continuous attitude information with better short-term stability and less random errors. However, gyro measurements are affected by drifts. Hence over time, attitudes based on the gyro reference slowly diverge from the true attitudes. On the other hand, line-of-sight (LOS) sensors like horizon sensors provide attitude information with long-term stability. Their measurements however are affected by the presence of random instrumental errors and other systematic errors. The limitations of inertial and line-of-sight sensors are mutually exclusive. Hence, by optimal fusion of attitude information from both these sensors, it is possible to retain the advantages and overcome the limitations of both, thereby providing the precise attitude information required for control. This paper describes an improved earth-pointing scheme by fusion of the three-axis attitude information from gyros and horizon sensor roll and pitch measurements along with yaw updates from the digital sun sensor. A Kalman Filter is used to estimate the three-axis attitude by online estimation and corrections of various errors from the sensor measurements. Variations in orbit rate components are also accounted for using spacecraft position and velocity measurements from the satellite positioning system. Thus precise earth-pointing is achieved     

Fuel ignition and flame front stabilization in supersonic flow using electric discharge

Recent achievements in the field of stabilization of the front of high speed combustion using electric discharge are presented. Near-surface discharge at the plane wall between electrodes installed in the plane of the wall is applied in this study. Hydrogen and ethylene directly injected from the wall to the flow with a Mach number M = 2 and an air total temperature T ₀ = 300–760 K are used as fuel. The excess fuel coefficient calculated by the total air flow rate in the channel does not exceed ER = 0.1. The value of electric power input into the discharge is W _pl/H _tot < 2% of the total flow enthalpy, while the thermal power due to combustion exceeds W _com/H _tot > 100% at a low initial gas temperature. Electric discharge is first applied to stabilize combustion under conditions of a fixed separated zone and on the plane wall of the combustion chamber. A two-stage combustion regime is demonstrated. It is shown that the application of electric discharge makes it possible to achieve complete fuel combustion η > 0.9 in a wide range of experimental parameters.     

Wet nanomilling of naproxen using a novel stabilization mechanism via zirconium complexation

Using a novel electrostatic stabilization mechanism that utilizes complexation of Zr(IV) species by carboxylic acid groups at the particle surface, the true grinding limit of monocrystalline naproxen nanoparticles was identified at 30 nm under an optimized naproxen/Zr(IV)-salt formulation. In a stirred media mill, we studied the influence of stress energy and number of stress events by varying the milling bead diameter. Small milling beads provide a compromise between sufficiently high stress energy and stress number and are beneficial for nanomilling of naproxen in terms of grinding kinetics. It is shown that the product particle size can be controlled by adjusting the colloidal stability via the Zr(IV) concentration. Regardless of formulation properties, particle fracture propagates along the grain boundaries as revealed by crystallite size analysis. Investigations of the solvent phase and the particle geometry reveal that mechanical stress leads to enhanced solubility of the drug, which in return promotes recrystallization and thus particle growth. The solubility can be reduced by lowering the process temperature and stabilizer concentration. In contrast to inorganic nanoparticles, which are almost free of lattice imperfections at the true grinding limit, we find a clear indication of lattice strain in the stressed naproxen nanoparticles. Since the nanoparticle yield is still limited to 40% due to particle ripening, fast removal of the nanoparticles from the mill must be a further next step to be solved in nanoparticle processing.     

Porocritical fluid extraction from liquids using near-critical fluids

In this article, Californian-based scientist Marc Sims describes a process of liquid/liquid extraction using supercritical or near critical CO₂ as the extractant solvent in a membrane separation process. Using hollow fibre or spiral wound membranes, Sims found that the transport of solutes through a membrane in a near critical fluid resulted in highly efficient separations.