Ferrite nucleation and growth during continuous cooling

The austenite decomposition has been investigated in two hypoeutectoid plain carbon steels under continuous cooling conditions using a dilatometer on a Gleeble 1500 thermomechanical simulator. The experimental results were used to verify model calculations based on a fundamental approach for the dilute ternary system, Fe-C-Mn. The austenite-to-ferrite transformation start temperature can be predicted from a nucleation model for slow cooling rates and small austenite grain sizes, where ferrite nucleates at austenite grain corners. The nuclei are assumed to have an equilibrium composition and a pillbox shape in accordance with minimal interfacial energy. For higher cooling rates or larger austenite grain sizes, early growth has to be taken into account to describe the transformation start, and nucleation is also encouraged at the remaining sites of the austenite grain boundaries. In contrast to nucleation, growth of the ferrite is characterized by paraequilibrium;i.e., only carbon can redistribute, whereas the diffusion of Mn is too slow to allow full equilibrium in the ternary system. However, Mn segregation to the moving ferrite-austenite interface has to be considered. The latter, in turn, exerts a solute draglike effect on the boundary movement. Thus, growth kinetics are controlled by carbon diffusion in austenite modified by interfacial segregation of Mn. Employing a phenomenological segregation model, good agreement has been achieved with the measurements. This article is based on a presentation made during TMS/ASM Materials Week in the symposium entitled “Atomistic Mechanisms of Nucleation and Growth in Solids,” organized in honor of H.I. Aaronson’s 70th Anniversary and given October 3–5, 1994, in Rosemont, Illinois.     

An Efficient Optimized Handover in Cognitive Radio Networks Using Cooperative Spectrum Sensing

Cognitive radio systems necessitate the incorporation of cooperative spectrum sensing among cognitive users to increase the reliability of detection. We have found that cooperative spectrum sensing is not only advantageous, but is also essential to avoid interference with any primary users. Interference by licensed users becomes a chief concern and issue, which affects primary as well as secondary users leading to restrictions in spectrum sensing in cognitive radios. When the number of cognitive users increases, the overheads of the systems, which are meant to report the sensing results to the common receiver, which becomes massive. When the spectrum, which is in use becomes unavailable or when the licensed user takes the allocated band, these networks have the capability of changing their operating frequencies. In addition, cognitive radio networks are seen to have the unique capability of sensing the spectrum range and detecting any spectrum, which has been left underutilized. Further this capability of recognizing the spectrum range based on the dimensions detected, allows for determination of the band, which may be utilized. The main objective of this paper is to analyze the cognitive radio’s spectrum sensing ability and evolving a self-configured system with dynamic intelligence networks without causing any interference to the primary user. The paper also brings focus to the quantitative analysis of the two spectrum sensing techniques namely; Energy Detection and Band Limited White Noise Detection. The estimation technique for detecting spectrum noise is based on the detection of probability and probability of false alarms at different Signal-to-Noise Ratio (SNR) levels using Additive White Gaussian Noise signal (AWGN). The efficiency of the proposed Cooperative CUSUM spectrum sensing algorithm performs better than existing optimal rules based on a single observation spectrum sensing techniques under cooperative networks.     

On the modal behavior of a three-dimensional functionally graded cantilever beam: Poisson’s ratio and material sampling effects

Modal behavior of a three-dimensional (3D) homogeneous and functionally graded (FG) cantilever beam is studied using the Rayleigh–Ritz (RR) method and the finite element method (FEM). The effect of Poisson’s ratio and material sampling point on the natural frequencies is further addressed using the FEM. The natural frequencies (first three) obtained using the RR method converge as the number of admissible shape functions increase. The natural frequencies (first 15) obtained using the FEM vary considerably with the material gradation, more so for the lower modes than for the higher modes. Poisson’s ratio significantly changes the torsional natural frequencies of the homogeneous and graded beams. Considerable change in the natural frequencies is seen for the linear graded beams whose material properties are sampled at the element centroid rather than at Gaussian integration points. This difference is easily observed for beams modeled using a coarse mesh rather than a fine mesh. The natural frequencies of the y   direction hyperbolic tangent beam with material nonhomogeneity parameter β=100$\beta =100$ matches well with those of the y direction bi-material beam. The natural frequencies of the power-law graded 3D cantilever beam obtained using the FEM matches closely with the 2D reference (Qian and Ching, 2004 [1]) solution obtained using the meshless local Petrov–Galerkin method.     

Positive and negative exchange bias in IrMn/NiFe bilayers

We present the observation of double shifted hysteresis loops in IrMn/NiFe bilayer structures. The bilayer structures were fabricated using high vacuum DC magnetron sputtering system. The hysteresis loops of the as deposited samples show the double shifted loops at NiFe layer thicknesses 5 nm and 6 nm, whereas the IrMn layer thickness was kept constant at 15 nm. The results were interpreted as the contribution of both positive and negative exchange bias fields. We suppose that this phenomenon is occurring due to the ferromagnetic (FM) layer exchange coupled with the antiferromagnetic (AFM) layer in two different magnetization directions. The ferromagnetic coupling of the interface spins in some regions of the film generates the hysteresis loop shift toward negative fields and antiferromagnetic coupling toward positive fields in the other regions. The double shifted hysteresis loops disappeared after magnetic field annealing of the samples above Neel temperature of the AFM layer. The X-ray diffraction patterns of the sample show the IrMn (111) crystalline growth necessary for the development of exchange bias field in this system. The correlation between the Magnetic Force Microscopy (MFM) domain structures of the as deposited sample and the magnetization reversal process of the double shifted hysteresis loops were discussed. The results suggest that the larger multidomain formation in the AFM layer with different magnetization directions was responsible for the positive and negative exchange bias fields in IrMn/NiFe bilayer samples.     

基于自相关和倒谱法的基音检测改进算法

语音信号基音周期检测一直以来都是语音信号处理的关键技术和热点领域。对传统的基音检测方法进行研究分析,提出基于自相关和倒谱法的基音检测改进算法。先将语音信号进行最小均方误差(LMS)自适应滤波和非线性处理进行语音增强,后进行自相关法和倒谱法加权平方运算来检测基音周期。经Matlab实验仿真,该算法在低信噪比环境中能精确检测基音周期,较传统基音检测方法鲁棒性更好、更精确。     

Effect of propylene carbonate on the ionic conductivity of polyacrylonitrile‐based solid polymer electrolytes

Solid polymer electrolyte membranes consisting of polyacrylonitrile (PAN) as a host polymer, ammonium nitrate (NH₄NO₃) as a complexing salt, and propylene carbonate (PC) as a plasticizer were prepared by a solution casting technique. An increase in the amorphous nature of the polymer electrolytes was confirmed by X‐ray diffraction analysis. A shift in the glass‐transition temperature of the PAN/NH₄NO₃/PC electrolytes was observed in the differential scanning calorimetry thermograms; this indicated interactions between the polymer and the salt. The impedance spectroscopy technique was used to study the mode of ion conduction in the plasticized polymer electrolyte. The highest ionic conductivity was found to be 7.48 × 10^?3 S/cm at 303 K for 80 mol % PAN, 20 mol % NH₄NO₃, and 0.02 mol % PC. The activation energy of the plasticized polymer electrolyte (80 mol % PAN/20 mol % NH₄NO₃/0.02 mol % PC) was found to be 0.08 eV; this was considerably lower than that of the film without the plasticizers. The dielectric behavior of the electrolyte is discussed in this article. A literature survey indicated that the synthesis and characterization of ammonium‐salt‐doped, proton‐conducting polymer electrolytes based on PAN has been rare. The use of the best composition membrane (80 mol % PAN/20 mol % NH₄NO₃/0.02 mol % PC) proton battery was constructed and evaluated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41743.     

Continuous cooling deformation testing of steels

In the processing of steel, the design of any kind of heat treatment and/or thermomechanical processing schedule, to obtain a given microstructure, is greatly facilitated by the knowledge of the austenite-to-ferrite transformation characteristics. In the past, isothermal and continuous cooling tests were used in the laboratory to create time-temperature-transformation and continuous cooling transformation diagrams, respectively, which then served as the source of transformation data. The problem with such information is that it is only truly applicable to one particular microstructure, usually one resulting from a simple reheating cycle in the austenite region. Most industrial steel processing operations additionally involve several stages of high-temperature deformation leading to changes in the microstructure emerging from the final pass. To account for this situation, a novel laboratory method for the determination of the transformation characteristics, based on continuous cooling deformation testing, was developed. A major attraction of this test technique is that the specific microstructure, for which the transformation characteristics are required, can be generated by hot deformation and then immediately evaluated by continuous cooling deformation. In this article, the basic continuous cooling deformation test technique and general methods of data analysis are illustrated, using results from several different grades of steel. Formerly with the Department of Mining and Metallurgical Engineering, McGill University,     

Dissolution, solubility, XRD, and DSC studies on flurbiprofen-nicotinamide solid dispersions

Flurbiprofen-nicotinamide solid dispersions were prepared by the fusion method. The solid dispersions were evaluated for dissolution rate. The drug-carrier interaction in the liquid and solid states were studied by using phase solubility analysis, phase diagram, X-ray diffraction (XRD), and differential scanning calorimentry (DSC). Solid dispersions gave fast and rapid dissolution of flurbiprofen compared with the pure drug and the physical mixture. Phase diagram and DSC indicated that flurbiprofen and nicotinamide form a eutectic mixture. The aqueous solubility of flurbiprofen was enhanced in the presence of nicotinamide.