High Energy Compaction Research Articles

Solid Electrolytes Based on NASICON-Structured Phosphates for Lithium Metal Batteries

All-solid-state lithium batteries are a promising alternative to commercially available lithium-ion batteries due to their ability to achieve high energy density, safety, and compactness. Electrolytes are key components of all-solid-state batteries, as they are crucial in determining the batteries’ efficiency. Herein, the structure of LiM2(PO4)3 (M = Ti, Ge, Zr) and lithium-ion migration mechanisms are introduced as well as different synthetic routes and doping (co-doping), and their influence on conductivity is discussed. The effective methods of reducing electrolyte/electrode interface resistance and improving ion-conducting properties are summarized. In addition, different polymer/NASICON composites are considered. The challenges and prospects of practical applications of NASICON-type lithium phosphates as electrolytes for all-solid-state batteries are discussed.

Electrochemical and mechanical characteristics of Al-(x)SiC composite fabricated by high energy compaction

Simultaneous compaction and sintering using the energy generated by the underwater explosion is a rapid method that does not have the negative consequences of normal sintering, such as unwanted reactions between components and grain growth. For this reason, this study used the energy from this process to produce Al/SiC composites with different amounts of SiC. As a result, 10, 20, and 30% of SiC powder were added to the Al powder, and then the samples were produced by compression under the influence of an underwater explosion. The results showed that as the amount of SiC increased, the samples' density and the amount of porosity for further agglomeration increased. Microstructural examination by Scanning Electron Microscopy (SEM) confirmed the increase in agglomeration with increasing SiC. Besides, Samples experienced an increase in hardness as the amount of SiC raised. Adding 10% of SiC increased the flexural strength while adding more (20 and 30%) increased the agglomeration resulting in a decrease in strength and elongation. Polarization and impedance spectroscopy (EIS) methods were used to study the samples' electrochemical behavior in a 3.5% NaCl solution. Results showed that the addition of SiC particles up to 10% (wt%) reduces the corrosion density from 9.7 (μA/cm2) to 2.06 (μA/cm2). The Al–10%SiC composite had the lowest corrosion current density compared to 20% and 30% SiC composites. In addition, the polarization resistance of the Nyquist plot for pure Al and Al composite containing 10% SiC was 3965 and 7862, respectively. Therefore, these results showed the beneficial effect of 10% SiC as reinforcing particles on the corrosion behavior of Al composites and thus improved corrosion resistance.

ARCHITECTURAL DESIGN AND OPTIMIZATION OF DISTRIBUTED ARITHMETIC BASED 2-D DISCRETE COSINE TRANSFORM

DCT is immensely used in Multimedia applications because it provides high energy compaction. The proposed architectural design of 1D-DCT employs an efficient computational technique, Distributed arithmetic and is synthesized using front end VLSI technique. The motive of utilising Distributed arithmetic is to have multiplier-less architecture that reduces the Area-delay product in comparison to the multiplier-based design by retaining the same structural regularities. The symmetric property of the DCT kernel matrix is applied to develop the proposed architecture which reduces the requirements of a number of multiplications by almost 50%. The 1D-DCT architecture is extended to 2D-DCT using only N 1D-DCT modules, while the conventional row-column decomposition method requires 2N 1D-DCT modules. The proposed 2D-DCT architecture is designed and implemented on a 65nm LX110T device of Vertex-5 FPGA and its performance evaluation is carried out. The debug and verification process has been carried out using the Virtual input-output technique. The results show improvement in delay and area consumption in contrast with existing models.

Speech Enhancement Algorithm Based on a Hybrid Estimator

Speech is the essential way to interact between humans or between human and machine. However, it is always contaminated with different types of environment noise. Therefore, speech enhancement algorithms (SEA) have appeared as a significant approach in speech processing filed to suppress background noise and return back the original speech signal. In this paper, a new efficient two-stage SEA with low distortion is proposed based on minimum mean square error sense. The estimation of clean signal is performed by taking the advantages of Laplacian speech and noise modeling based on orthogonal transform (Discrete Krawtchouk-Tchebichef transform) coefficients distribution. The Discrete Krawtchouk-Tchebichef transform (DKTT) has a high energy compaction and provides a high matching between Laplacian density and its coefficients distribution that affects positively on reducing residual noise without sacrificing speech components. Moreover, a cascade combination of hybrid speech estimator is proposed by using two stages filters (non-linear and linear) based on DKTT domain to lessen the residual noise effectively without distorting the speech signal. The linear estimator is considered as a post processing filter that reinforces the suppression of noise by regenerate speech components. To this end, the output results have been compared with existing work in terms of different quality and intelligibility measures. The comparative evaluation confirms the superior achievements of the proposed SEA in various noisy environments. The improvement ratio of the presented algorithm in terms of PESQ measure are 5.8% and 1.8% for white and babble noise environments, respectively. In addition, the improvement ratio of the presented algorithm in terms of OVL measure are 15.7% and 9.8% for white and babble noise environments, respectively.

Studies on the Effect of Processing Parameters on Microstructure and Properties of Magnesium Compacts Prepared via Powder Metallurgy

The present study involves the investigation on the effect of processing parameters of powder metallurgy on the microstructure and hardness characteristics of the green as well as sintered specimens of magnesium. The processing parameters include the high-energy ball milling time, compaction pressure, and sintering temperature. From SEM images of 1, 3, and 5 h ball-milled powders, it is revealed that the sequence of change of morphology and size of particles is: flattening (formation of lamellas), fracturing (cracking of lamellas), and dynamic balance (adherence of a small particle with other particles and fracturing), respectively. The average particle size decreases with increasing ball milling time. 0, 1, 3, and 5 h ball-milled powders are compacted at different pressures. It is found that green density of the compacts of ball-milled powders depends on the morphology of powder particles, particle size, and compaction pressure. The selected samples were sintered at 500, 550, and 600 °C for 1 h. SEM characterization indicates that grain growth occurs with increasing sintering temperature. With constant mass, the sintering theory indicates that grain growth of larger particles takes place at the expense of smaller particles due to the difference of surface curvature. The density and hardness of sintered samples were calculated by using Archimedes principle and Vickers hardness tester, respectively.

Robust Control of Permanent Magnet Synchronous Motor: Synergetic Approach

Permanent magnet synchronous motors (PMSM) are widely used in practice due to its high-energy efficiency, compactness, reliability and high regulation performance. When controlling a PMSM rotor speed, the main control principle is the principle of cascade control with PI-regulators, which includes an external control loop for speed and two internal loops for stator currents along the (d, q)-axes. There are attempts to eliminate the disadvantages of this principle using for the control laws synthesis of modern methods of nonlinear control such methods as linearization feedback, backstepping, predictive control, sliding mode control, methods of robust and adaptive control, fuzzy and neural network control, a combination of these methods etc. However, in most cases, the use of these methods are intended to by means of an appropriate method to synthesize a static or dynamic set points for the standard PI-controllers of rotor speed and currents. In this paper we propose to consider two approaches of synergetic control theory (SCT) to construct a robust control law of PMSM: a sliding mode control laws design by the SCT method with subsequent invariant manifolds aggregation and the principle of integral adaptation (PIA). These approaches implement vector control and are not guided by the standard structure of the principle of cascade regulation of PMSM. The proposed approaches simplify the stability analysis of the closed-loop system: stability conditions consist of stability conditions of functional equations of SCT and the stability conditions for finish decomposed system, which the dimension is substantially less than the dimension of the original system. From the results of the comparisons of synthesized the PMSM robust control laws, we can say that more preferable laws synthesized in accordance with the PIA. The theoretical positions of this paper are illustrated by the results of modeling, which are showing the fulfillment of the control tasks: the achievement of targets, robustness to the change of the PMSM load moment.

A novel and efficient 8-point DCT approximation for image compression

The Discrete Cosine Transform is widely used in the field of still image compression. Many integer approximations are given in the literature whereas the most of these transforms requires bit shift operations. This paper presents an efficient and low complexity integer approximation of the DCT for image compression. Our new approach involves replacing the bit shift elements of a variant of the Signed DCT transform by zeros, in order to eliminate the bit shift operations. As a result, all elements of the proposed transform are zeros and ± 1. Indeed, the proposed transform retains all the characteristics of its original transform, such as orthogonality and high energy compaction capabilities, while generating computing cost savings. Experiments show that the proposed transform has a good compromise performance-computational complexity as well as state-of the-art DCT approximations. Moreover, an efficient algorithm primarily involving a small amount of arithmetical computation is well developed as no multiplications and bit-shift operations are required, with only 16 additions being involved.

Design and characterization of an oxides hybrid dispersion strengthened iron based composite with a graded and architectural microstructure

A graded Fe based composite reinforced with tetragonal yttria stabilized zirconia, monoclinic zirconia, wüstite and at a less extent, Zr0.978Fe0.022O1.978 (tetragonal) and Zr0.85Y0.15O1.93 (cubic) was developed by high energy ball milling, compaction and sintering. Solid state sintering entailed (i) the growth of Fe grains which remained submicrometric and (ii) the coarsening of oxides reinforcements forming an interconnected network in the bulk graded composite.The increase of oxide reinforcements volume fraction enabled to obtain a material with a graded electrical resistivity and a slightly graded hardness; the bending resistance of the as-developed material was however decreased because of the weakness of the reinforcements – matrix bonds.

Densification mechanism and its effect on the magnetic properties of Nd-Fe-B bonded magnets through the new high-energy compaction method

Abstract Gas-atomized Nd-Fe-B magnetic powders were subjected to magnetic pulse compaction, which is very high-energy compaction method, can be densified in a short time with various binder contents at different compaction pressures. The powders were rapidly forced together with in an abbreviated period, and formed a well-packed dense sample with full density during the magnetic pulse compaction process. The influence of density on the magnetic properties of the Nd-Fe- B magnet was investigated. The relative density increased with pressure and highest density of 6.9 g/cm3 was achieved at a consolidation pressure of 3 GPa. The optimized binder content and pressure were found to be 1 wt% and 3 GPa, respectively, for achieving the highest density. The remanence and maximum energy product of the Nd-Fe-B magnets gradually increased with increasing density. The significant improvement in density can effectively offers high remanence of 6.635 kG and maximum energy product of 8.5 MGOe.

Simulation of PCM‐saturated porous solid matrix for thermal energy storage using the phase‐field method

AbstractLatent heat storage systems using phase change materials (PCMs) are considered an attractive technique for storing the available thermal energy due to their high energy storage capacity, compactness and ability to store heat at an almost constant temperature. However, the PCMs suffer from their low thermal conductivity that affects the heat transfer rates and leads to slow charging and discharging processes. Therefore, many approaches have been adopted for improving the low thermal conductivity of PCMs. In the underlying research work, a latent heat storage medium using a PCM‐saturated highly conductive porous metal foam is being studied. High porosity cellular metal foams are proved to be promising materials for enhancing the heat transfer performance of the PCMs due to their high surface area to volume ratio, ultra light weight and relatively high thermal conductivity. A macroscopic description of the PCM‐saturated porous material with intrinsically coupled and incompressible solid and fluid constituents is presented, based on the Theory of Porous Media (TPM). The heat transfer process between the metal foam and the PCM is described using the local thermal non‐equilibrium model, where the phase‐field method (PFM) is employed to account for the phase change process. The PFM relies on specification of the free energy density function and employs a phase‐field variable that defines the state of the material (solid or liquid). Finally, numerical examples using the finite element method are presented to show the ability of the phase‐field‐porous media approach in simulating the phase change problems on the macro scale.

Exploring approximations in 4- and 8- point DTT hardware architectures for low-power image compression

Due to the intensive use of discrete transforms in picture coding, the search for fast and power-efficient approaches for their hardware implementation gains importance. The Discrete Tchebichef Transform (DTT) represents a discrete class of the Chebyshev orthogonal polynomials, and it is an alternative for the Discrete Cosine Transform, commonly used in picture coding. High energy compaction and decorrelation are the main properties of the DTT. The state-of-the-art approximate DTT matrix is composed of 0, 1, − 1, 2, and − 2 coefficient values. In this work, we propose a new approximation for both the 4-point and 8-point integer DTT with better quality and power-efficiency. We explore the effects of coefficient truncation, whose values are 1/16, − 1/16, 1/8, − 1/8, 1/4, and − 1/4. Considering operations with integers, the smaller values of coefficients causes truncation in the internal transform calculations and leads to smaller values for the non-diagonal residues, which reduces the non-orthogonality. We have also selectively pruned the rows of the state-of-the-art approximate DTT matrix. The results show that the proposed pruned approximate DTT hardwired solutions increases the maximum frequency up to 5%, minimizes circuit area by over 30%, with savings of up to 32.4% in power dissipation with a higher compression ratio and fewer quality losses in the compressed image, when compared with state-of-the-art approximate DTT hardware designs.

Improved Binary Tree Coding for Image Compression using Modified Singular Value Decomposition

Reducing the transmission cost while maintaining the quality of image data is the most challenging part in data transmission. In this paper, we report the possibility of improving the quality of image reconstruction by using modified singular value decomposition (SVD) and binary tree coding with adaptive scanning order (BTCA) for grayscale image compression. This method uses modified rank one updated SVD as a pre-processing step for binary tree coding to increase the quality of the reconstructed image. The high energy compaction in SVD process offers high image quality with less compression and is requires more number of bits for reconstruction. BTCA compression, also gives high image quality by coding more significant coefficients using adaptive scanning order from bottom to top with high compression rate. The proposed method uses both SVD and BTC for image compression and is tested with several test images and results are compared with those of SPIHT, JPEG, JPEG2000 and BTCA. The results show significant improvement in PSNR at high bitrates as compared to other methods.

Hybrid Image Compression using Modified Singular Value Decomposition and Adaptive Set Partitioning in Hierarchical Tree

Objectives: Image communication in web applications becomes handy because of highly developed compression tools. Human eye fixate on an image’s preview, carefully adjusting the quality and optimization settings until we’ve found that sweet spot, where the file size and quality are both the best they can possibly be. Method: This paper presents a new algorithm, which uses modified singular value decomposition (SVD) and adaptive Set Partition Hierarchical Tree (ASPIHT) for grayscale image compression. This hybrid method uses modified rank one updated SVD as a pre-processing step for ASPIHT to increase the quality of the reconstructed image. Findings: The high energy compaction in SVD process offers high image quality with less compression and requires a number of bits for reconstruction. On the other hand, ASPIHT compression also offers high image quality by coding more significant coefficients adaptively with high compression at specified bitrates. The proposed method is a combination of both SVD and ASPIHT for image compression and is tested with several test images and results are compared with those of SPIHT, ASPIHT without arithmetic coding and JPEG2000. Novelty: This method improves the quality of reconstruction without altering the compression rates of SPIHT algorithm. The tabulated results show significant improvement in PSNR at higher compression ratios as compared to other methods.

Lagrangian twin support vector regression and genetic algorithm based robust grayscale image watermarking

A novel imperceptible, secure and robust grayscale image watermarking scheme using Lagrangian twin support vector regression (LTSVR) and genetic algorithm (GA) in discrete Cosine transform (DCT) domain is presented in this manuscript. Fuzzy entropy is used to select the relevant blocks for embedding the watermark. Selected number of blocks based on fuzzy entropy not only reduces the dimensionality of the watermarking problem but also discards redundant and irrelevant blocks. Significant DCT coefficients having high energy compaction property of each selected block are used to form the image dataset to train LTSVR to find the non-linear regression function between the input and target vector. The adaptive watermark strength, different for each selected block, is decided by the GA process based on well defined fitness function. Due to good learning capability of image characteristics and high generalization property of LTSVR, watermark is successfully extracted from the watermarked images against a series of image processing operations. From the experimental and comparison results performed on standard and real world images, it is inferred that the proposed method is suitable for copyright protection applications where high degree of robustness is desirable.

ROLE OF ULTRASOUND IN MECHANISMS OF ANODE-CATHODE INTERACTIONS DURING ELECTROSPARK ALLOYING

The paper reveals results of investigations on mass transfer kinetics and dynamics of coating formation while using integral electrospark alloying method with additional ultrasonic exposure at different stages of formation. Nowadays, a classical method for electrospark alloying with hard-alloy anodes and impulse AC voltage frequency on the vibration exciter coil from 20 to 1600 Hz has been mainly used for application of protective and strengthening coatings within permissible thickness and characteristics. The key aspect of ultrasonic exposure application (frequency 22–44 kHz) during electrospark alloying is the possibility to increase further thickness of coatings to be formed even after reaching a brittle fracture threshold of the coating material. Methodology of the executed research activity has been based on integrated studies (gravimetric, metallographic, X-ray diffraction and electron microscopic) of coatings which are to be formed through compositions produced while using method of high-energy hot compaction and a “refractory carbide (WC) and a binding material“ system in the form of alloy based on nickel from the series of “colmonoy” Ni – Ni3B system which is alloyed with additions of copper and silicon. The initial surface treatment within ultrasonic frequency range (22–44 kHz) contributes to a noticeable increase in the mass transfer rate, which is primarily determined by chemical composition and thermodynamic stability of anodes. It is due to surface activation in the process of its preliminary deformation at ultrasonic frequency which creates additional conditions for striking of a spark.The final ultrasonic treatment improves coating quality due to its additional forging that leads to an increase of its structure homogeneity and density.

FPGA Implementation of Approximate 2D Discrete Cosine Transforms

Discrete cosine transform (DCT) is frequently used in image and video signal processing due to its high energy compaction property. Humans are able to perceive and identify the information from slightly erroneous images. It is enough to produce approximate outputs rather than absolute outputs which in turn reduce the circuit complexity. Numbers of applications like image and video processing need higher dimensional DCT algorithms. So the existing architectures of one dimensional (1D) approximate DCTs are reviewed and extended to two dimensional (2D) approximate DCTs. Approximate 2D multiplier-free DCT architectures are coded in Verilog, simulated in Modelsim to evaluate the correctness, synthesized to evaluate the performance and implemented in virtexE Field Programmable Gate Array (FPGA) kit. A comparative analysis of approximate 2D DCT architectures is carried out in terms of speed and area.

고속 영상 압축을 위한 근사 이산 코사인 변환

ABSTRACT For image data the discrete cosine transform (DCT) has comparable energy compaction capability to Karhunen-Loeve transform (KLT) which is optimal. Hence DCT has been widely accepted in various image and video compression standard such as JPEG, MPEG-2, and MPEG-4. Recently some approximate DCT’s have been reported, which can be computed much faster than the original DCT because their coefficients are either zero or the power of 2. Although the level of energy compaction is slightly degraded, the approximate DCT’s can be utilized in real time implementation of image or visual compression applications. In this paper, an approximate 8-point DCT which contains 17 non-zero power-of-2 coefficients and high energy compaction capability comparable to DCT is proposed. Transform coding experiments with several images show that the proposed transform outperforms the published works. 키워드 : 근사 DCT, 에너지 압축, 고속 구현, 변환의 직교성 Key word : Approximate DCT, Energy compaction, High speed implementation, Orthogonality of transformsJournal of the Korea Institute of Information andCommunication Engineering

Methods of compacting nanostructured tungsten–cobalt alloys from Nanopowders obtained by plasma chemical synthesis

The paper summarizes the experience of using traditional and modern methods of sintering WC–Co nanopowders obtained by plasma chemical synthesis. A comparative analysis of structure formation processes occurring at sintering WC–Co nanopowders in a quasi-steady and high-speed heating is carried out. It is shown that the basic regularities of structure evolution during sintering are rather general in nature and are similar both to conventional vacuum sintering and to high-energy compaction methods. It was established that, under high-speed heating conditions, a significant contribution to the acceleration of the sintering of nanopowder materials at low temperatures is made not only by a small grain size but also the process of grainboundary diffusion. It is shown that the samples of hard alloys sintered from tungsten carbide nanopowders produced by plasma chemical synthesis have significantly higher hardness and fracture toughness than those produced using conventional synthesis techniques and compacting. Using the technology of plasma chemical synthesis and spark plasma sintering, nanostructured WC and WC–Co samples with significantly better mechanical properties (hardness, fracture toughness) than those of conventional fine materials were obtained.

Effect of high energy milling and compaction pressure on density of a sintered Nb–20%Cu composite powder

This work reports the influence of the use of composite particles of composition Nb–20wt.%Cu and the compaction pressure on density and structure of sintered pieces. High energy milling is used to produce the composite powders. Milling times of 2, 20, 50 and 100h were used. The powders were pressed under 200, 300, 400 and 500MPa and sintered at 1100°C for 60min. After sintering, density was measured and cross sections of the structures were observed under SEM. The electric conductivity was also measured. Density and electric conductivity behave similarly with respect to compaction pressure and milling time. Cracks are created during pressing and ejection of the green pieces from the die. The cracks are mainly present in samples prepared with powders milled longer and are not closed by sintering. On the other hand, sintering can close most of the pores formed by the composite particles.

AN EFFICIENT RIPPLET-BASED SHRINKAGE TECHNIQUE FOR MR IMAGE RESTORATION

In this paper a new ripplet-based shrinkage technique is used to suppress noise from Magnetic Resonance Imaging (MRI). The propitious properties of ripplet transform such as anisotropy, high directionality, good localization, and high-energy compaction make the proposed method efficient and feature preserving when compared to other transforms. Ripplet transform provides efficient representation of edges in images with a higher potential for image processing applications such as image restoration, compression, and de-noising. The proposed method implies a new nonlinear ripplet-based shrinkage technique to extract the spatial and frequency information from MRI corrupted by noise. The choice of this new shrinkage technique is due to its simplicity, versatility, and its efficiency in removing noise from homogenous regions and those regions with singularities, when compared to the existing filtering techniques. Experiments were conducted on several diffusion weighed images and anatomical images. The results show that the proposed de-noising technique shows competitive performance compared to the current state-of-art methods. Qualitative validation was performed based on several quality metrics and profound improvement over existing methods was obtained. Higher values of Peak Signal to Noise Ratio (PSNR), Correlation Coefficient (CC), mean structural similarity index (MSSIM), and lower values of Root Mean Square Error (RMSE) and computational time were obtained for the proposed ripplet-based shrinkage technique when compared to the existing ones.