Inverse shape design for heat conduction problems via the ball spine algorithm

ABSTRACT

In this article, a novel iterative physical-based method is introduced for solving inverse heat conduction problems. The method extends the ball spine algorithm concept, originally developed for inverse fluid flow problems, to inverse heat conduction problems by employing a subtle physical-sense rule. The inverse problem is described as a heat source embedded within a solid medium with known temperature distribution. The object is to find a body configuration satisfying a prescribed heat flux originated from a heat source along the outer surface. Performance of the proposed method is evaluated by solving many 2-D inverse heat conduction problems in which known heat flux distribution along the unknown surface is directly related to the Biot number and surface temperature distribution arbitrarily determined by the user. Results show that the proposed method has a truly low computational cost accompanied with a high convergence rate.     

Optimal Porosity in an Air Heater Conduit Filled with a Porous Matrix

In the present study, flow and forced convective heat transfer in an air heater conduit filled with a porous matrix with a uniform constant solar heat flux has been investigated analytically, based on minimal entropy generation principle. While trying to decrease entropy generation due to heat transfer, pressure loss entropy generation increases, which indicates that an optimal porosity value exists. The influence of Reynolds number, fluid properties, constant uniform heat flux, flow, and geometry of the system on the optimum matrix porosity has been investigated. It was revealed that optimum matrix porosity values increase as Reynolds number increases. In the range of the present study, a correlation predicting optimal matrix porosity was proposed using least squares analysis.     

A framework for identification of high-value customers by including social network based variables for churn prediction using neuro-fuzzy techniques

Customer churn has become a significant problem and is one of the prime challenges that many in the services industry are facing. While all kinds of churn lead to incur loss, the loss of low-value customers will be naturally less damaging than the loss of loyal and high-value ones. So companies need to build a churn prediction model for their high-value customers. In this paper, a two-phase framework for prediction of high-value customer churn has been proposed. Phase 1 is the identification phase which takes into account social-network based variables of customers in identifying the high-value ones. The data of an identified high-value customer is used as the input for Phase 2 to prepare the churn prediction model. Data of a major telecommunication company has been used to implement the framework. The customers were clustered by using K-means algorithm. After ranking clusters, the top-cluster was selected according to clusters ratings. The data belonging to the top cluster is used in churn prediction model building phase. In this phase, two neuro-fuzzy techniques, namely the adaptive neuro-fuzzy inference system (ANFIS) and the locally linear neuro-fuzzy (LLNF) have been applied together with locally linear model tree (LoLiMoT) learning algorithm on churn data. A new algorithm has been devised for comparing these methods with the most widely used neural networks such as multi layer perceptron (MLP) and radial basis function (RBF) networks. Results of comparison indicate that the neuro-fuzzy techniques perform better than neural network models and they are a good candidate for churn prediction purposes.     

An In Vitro Evaluation of Fenugreek Mucilage as a Potential Excipient for Oral Controlled-Release Matrix Tablet

A polysaccharide mucilage derived from the seeds of fenugreek, Trigonella foenum-graceum L (family Fabaceae) was investigated for use in matrix formulations containing propranolol hydrochloride. Methocel® hypomellose K4M was used as a standard controlled release polymer for comparison purposes. In this study the effect of lactose on the release behaviour of propranolol hydrochloride from matrices formulated to contain the fenugreek mucilage also was investigated. An increase in concentration of the mucilage in matrices resulted in a reduction in the release rate of propranolol hydrochloride comparable to that observed with hypomellose matrices. The rate of release of propranolol hydrochloride from fenugreek mucilage matrices was mainly controlled by the drug:mucilage ratio. However, the mechanism of release from matrices containing drug:mucilage ratios of 1:1, 1:1.25, 1:1.5, and 1:2 remained the same. The kinetics of release, utilising the release exponent n, showed that the values of n were between 0.46–0.57 indicating that the release from fenugreek mucilage matrices was predominantly by diffusion. The presence of lactose in matrices containing mucilage increased the release rate of propranolol hydrochloride. This is due to a reduction in tortuoisity and increased pore size of channels caused by lactose through which propranolol diffuses and therefore diffusion of water into the tablet is facilitated.     

Damage Identification in Plate-type Structures Using 2-D Spatial Wavelet Transform and Flexibility-Based Methods

As dislocation emission is regarded as the critical point of brittle-to-ductile transition of fracture mechanism and the defects interact with domain walls motions due to their self-stress fields, the investigations on dislocation forces, especially the interaction force and the reaction between domain switching and dislocations, are the most important fundamentals of dislocation slip in the brittle-to-ductile transition and the pinning effect on domain wall motion mechanisms. In this paper, an innovative method base on the strain nucleus simulated by an assembly of four dislocations and the Green’s function integration is used to solve generalized stress field arising from domain switching. Then, the accurate expressions of the interaction forces, pinning forces and the image forces on dislocation are obtained and analyzed. At last, the lattice resistance is also discussed. The numerical results show that the dislocation emission is possible when temperature and load are proper, and the domain switching interaction force is the main driving force of dislocation slip in ferroelectric material under negative electric field load. The curve and equation of the lattice resistance correlated with temperature can also be fitted by the results of the proposed analytical method and corresponding experiments.     

Analytical equations for oscillation amplitude of MOS Colpitts oscillator

New analytical equations are presented for amplitude analysis of metal–oxide–semiconductor (MOS) Colpitts oscillator. These equations are obtained from a large signal analysis that includes MOS operation in the saturation, triode and cutoff regions. The analysis is based on a reasonable estimation for the output voltage waveform. The estimated waveform must satisfy the nonlinear differential equations governing the circuit. The validity of the proposed method and the resulting equations has been verified through simulations using TSMC 0.18?µm complementary MOS process. The results are also compared with the other methods. Simulation results show high validity of the proposed equations.     

A Fast Adaptive Salt and Pepper Noise Reduction Method in Images

In this paper, an effective filtering method is proposed to remove impulse noise from images. In this two-stage method, detected noise-free pixels remain unchanged. Afterwards, a Gaussian filter with adaptive variances according to the image noise level is applied on the noisy pixels. Experimental results show that the proposed method outperforms recent impulse denoising methods in terms of PSNR, MAE, IEF, and SSIM. Moreover, the speed of the method is comparable with them, and it can be used effectively in real-time applications.     

Calculation of Confined Phonon Spectrum in Narrow Silicon Nanowires Using the Valence Force Field Method

We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 1 nm to 10 nm. We use the modified valence force field (MVFF) method to compute the phononic dispersion and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance, and boundary-scattering-limited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e., the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical features of the channel. The 〈110#x232A; nanowire has the highest group velocity and thermal conductance, whereas the 〈111#x232A; has the lowest. The 〈111#x232A; channel is thus the most suitable orientation for thermoelectric devices based on Si nanowires since it also has a large power factor. Our findings could be useful in the thermal transport design of silicon-based devices for thermoelectric and thermal management applications.     

A new fast locking charge pump PLL: analysis and design

In this paper a new structure for a fast locking charge pump phase locked loop (CPPLL) is introduced which overcomes the trade-off between the settling time and overshoot of the system. This fast locking PLL uses an auxiliary bang–bang frequency comparator (BBFC) as a lock-aid. An additional charge pump current controlled by the output of the BBFC is injected into the main loop filter capacitor to accelerate the locking process. An analytical approach to extract the differential equation governing on the system’s dynamics is used to evaluate the performance of this fast locking PLL. A heuristic method that results in an approximate solution for the extracted differential equation is also proposed. The correctness of the presented differential equation and its closed-form solutions are verified by comparing the obtained closed-form solutions and simulation results. Using the obtained closed-form solutions, we predict the behavior of the system and design a fast BBFC-CPPLL which meets the system’s requirements. Correctness of the differential equation and its closed-form solutions are verified by comparing the obtained closed-form solutions and simulation results.     

A Low-Collision CSMA-Based Active RFID for Tracking Applications

Hardware complexity, active Tag power consumption, and Multiple Tags collection method are three critical parameters in all active radio frequency identification systems. In this work, both the MCU and RF operations are performed in single chip, which makes the Tag hardware smaller. A lot amount of energy is restored by setting Tags in the sleep mode in the most of times. Four commands are used for this system. At first, a unique ID is dedicated to each Tag by the ID allocation command. The polling command is implemented for searching desired Tags. By using of the ID clearing command, the object loses the passing permission for a given time or permanently. Utilizing the collection command, the information of all surrounding Tags are collected and monitored, simultaneously. The Carrier Sense Multiple Access method is used and its performance is evaluated. The maximum transmission range of 80 m at the output power of 4.5 dBm is obtained. An active Tag with unique ID is mounted on each vehicle. Receiver sensitivity of 97 dBm and current consumption of 1 $\mu \text{ A}$ in the sleep mode and 29.6 mA in the active mode are reported.