An evolutionary lion optimization algorithm‐based image compression technique for biomedical applications

Recently, medical image compression becomes essential to effectively handle large amounts of medical data for storage and communication purposes. Vector quantization (VQ) is a popular image compression technique, and the commonly used VQ model is Linde–Buzo–Gray (LBG) that constructs a local optimal codebook to compress images. The codebook construction was considered as an optimization problem, and a bioinspired algorithm was employed to solve it. This article proposed a VQ codebook construction approach called the L2‐LBG method utilizing the Lion optimization algorithm (LOA) and Lempel Ziv Markov chain Algorithm (LZMA). Once LOA constructed the codebook, LZMA was applied to compress the index table and further increase the compression performance of the LOA. A set of experimentation has been carried out using the benchmark medical images, and a comparative analysis was conducted with Cuckoo Search‐based LBG (CS‐LBG), Firefly‐based LBG (FF‐LBG) and JPEG2000. The compression efficiency of the presented model was validated in terms of compression ratio (CR), compression factor (CF), bit rate, and peak signal to noise ratio (PSNR). The proposed L2‐LBG method obtained a higher CR of 0.3425375 and PSNR value of 52.62459 compared to CS‐LBG, FA‐LBG, and JPEG2000 methods. The experimental values revealed that the L2‐LBG process yielded effective compression performance with a better‐quality reconstructed image.     

Dielectric and structural studies of ferroelectric phase evolution in dipole-pair substituted barium titanate ceramics

Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ ceramics with x equal to 0, 0.0025, 0.005, 0.01, 0.025, and 0.05 have been prepared by conventional solid-state reaction. Structural and dielectric characterization have been performed to investigate the effect of dipole-pair substitution concentration on the macroscopic dielectric properties. Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ evolves from a classic ferroelectric to a diffuse phase transition (DPT) as x increases. Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ for x ≥ 0.01 possesses diffuseness parameters comparable to Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) and recently reported (Ba_0.97Pr_0.03)(Ti_0.9425Ce_0.05)O₃ (BPTC), yet it lacks the frequency and temperature dependence of T_m necessary to be a strictly defined relaxor ferroelectric. Additionally, Ba{[Ga_0.05,Ta_0.05]Ti_0.9}O₃ possesses a relative permittivity, ɛ_r, of 700 ± 16% and dissipation factor less than 0.05 at 10 kHz within the temperature range [−75°C, 120°C]. In comparison to BaTiO₃, Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ possesses enhanced electrical resistivity at and above room temperature. In situ XRD, including Rietveld refinement, have been performed to determine the lattice parameter, coefficient of thermal expansion, and phase transition temperature (T_c) of each composition within the temperature range [RT, 1000°C], thus linking the dielectric properties with the material's structure. These studies have been corroborated by temperature-dependent Raman spectroscopy to compare the T_c determined by electrical and structural characterization. The properties of Ba{[Ga_x,Ta_x]Ti_(1−2x)}O₃ are discussed in context with available models that describe donor and acceptor dopants spatially separated in the parent matrix, inter-relating lattice parameter, Curie temperature, and other material properties.     

Ceramic processing and multiferroic properties of the perovskite YMnO3-BiFeO3 binary system

The perovskite (1−x)YMnO₃−xBiFeO₃ binary system is very promising because of its multiferroic end members. Nanocrystalline phases have been recently obtained by mechanosynthesis across the system, and the perovskite structural evolution has been described. Two continuous solid solutions with orthorhombic Pnma and rhombohedral R3c symmetries were found, which coexist within a broad compositional interval of 0.5 ≤ x ≤ 0.9. This might be a polar-nonpolar morphotropic phase boundary region, at which strong phase-change magnetoelectric responses can be expected. A major issue is phase decomposition at moderate temperatures that highly complicates ceramic processing. This is required for carrying out a sound electrical characterization and also for their use in devices. We present here the application of Spark Plasma Sintering to the ceramic processing of YMnO₃-BiFeO₃ phases. This advanced technique, when combined with nanocrystalline powders, allowed densifying phases at reduced processing temperatures and times, so that perovskite decomposition was avoided. Electrical measurements were accomplished, and the response was shown to be mostly dominated by conduction. Nonetheless, the intrinsic dielectric permittivity was obtained, and a distinctive enhancement in the phase coexistence region was revealed. Besides, Rayleigh-type behavior characteristic of ferroelectrics was also demonstrated for all rhombohedral phases. Magnetic characterization was performed in this region, and antiferromagnetism was shown.     

Testing and qualification of Control & Safety Rod and its drive mechanism of Fast Breeder Reactor

Prototype Fast Breeder Reactor (PFBR) has two independent fast acting diverse shutdown systems. The absorber rod of the first system is called Control & Safety Rod (CSR). CSR and its Drive Mechanism (CSRDM) are used for reactor control and for safe shutdown of the reactor by scram action. In view of the safety role, the qualification of CSRDM is one of the important requirements.CSR & CSRDM were qualified in two stages by extensive testing. In the first stage, the critical subassemblies of the mechanism, such as scram release electromagnet, hydraulic dashpot & dynamic seals and CSR subassembly, were tested and qualified individually simulating the operating conditions of the reactor. Experiments were also carried out on sodium vapour deposition in the annular gaps between the stationary and mobile parts of the mechanism.In the second stage, full-scale CSRDM and CSR were subjected to all the integrated functional tests in air, hot argon and subsequently in sodium simulating the operating conditions of the reactor and finally subjected to endurance tests. Since the damage occurring in CSRDM & CSR is mainly due to fatigue cycles during scram actions, the number of test cycles was decided based on the guidelines given in ASME, Section III, Div. 1. The results show that the performance of CSRDM & CSR is satisfactory. Subsequent to the testing in sodium, the assemblies having contact with liquid sodium/sodium vapour were cleaned using CO₂ process and the total cleaning process has been established, so that the mechanism can be reused in sodium. The various stages of qualification programmes have raised the confidence level on the performance of the system as a whole for the intended and reliable operation in the reactor.     

Relationship between perceived problem‐solving skills and academic performance of novice learners in introductory programming courses

Past research has shown that student problem‐solving skills may be used to determine student final exam performance. This study reports on the relationship between student perceived problem‐solving skills 1 1 Henceforth, for brevity, we drop the word “perceived” in “student perceived problem‐solving skills” and use either “student perceived problem solving” or simply “student PSS.”
and academic performance in introductory programming, in formative and summative programming assessment tasks. We found that the more effective problem solvers achieved better final exam scores. There was no significant difference in formative assessment performances between effective and poor problem solvers. It is also possible to categorize students on the basis of problem‐solving skills, in order to exploit opportunities to improve learning around constructivist learning theory. Finally, our study identified transferability skills and the study may be extended to identify the impact of problem solving transfer skills on student problem solving for programming.     

Hexavalent (Me - W/Mo)-modified (Ba,Ca)TiO3-Bi(Mg,Me)O3 perovskites for high-temperature dielectrics

We report on the synthesis of complex lead-free perovskite-type (1−x)(Ba_0.8Ca_0.2)TiO₃–xBi(Mg_0.75W_0.25)O₃ (BCT-xBMW) and (1−x)(Ba_0.8Ca_0.2)TiO₃-xBi(Mg_0.75Mo_0.25)O₃ (BCT-xBMM) solid solutions via conventional solid-state reaction route. The sintering temperature was adjusted as a function of composition x to obtain dense samples (relative densities over 95%) at the same time minimizing bismuth evaporation. X-ray diffraction analysis shows the formation of single-phase perovskites for 0 ≤ x ≤ 0.10 in the BCT-xBMW series and increasing concentrations of impurity phases for x ≥ 0.15 and for x ≥ 0.05 in BCT-xBMM. A transition from a tetragonal to pseudo-cubic perovskite structure is observed in BCT-xBMW and BCT-xBMM at x = 0.05. The dielectric response has been characterized between −60°C and 300°C for BCT-xBMW, and between 30°C and 300°C for BCT-xBMM using impedance spectroscopy, showing a transition from ferroelectric to relaxor-like behavior at x ≥ 0.05. Additional polarization and Raman spectroscopy measurements reveal the occurrence of highly disordered systems. Analysis of the Raman spectra indicates structural phase changes and lattice modifications caused by chemical substitution. For the composition 0.8Ba_0.8Ca_0.2TiO₃-0.2Bi(Mg_0.75W_0.25)O₃, a temperature-stable permittivity of about 600 (±15% between −60°C and 300°C) and small losses of tanδ < 0.02 for T ≤ 230°C at 1 kHz are observed_, making it a suitable dielectric material for high-temperature capacitors.     

Properties of n-type tetrahedral amorphous carbon (ta-C)/p-typecrystalline silicon heterojunction diodes

Heterojunction diodes fabricated by filtered cathodic vacuum arc (FCVA) deposition of n-type (nitrogen-doped) tetrahedral amorphous carbon (ta-C) on p-type crystalline silicon are analyzed in terms of their electronic and photoresponse properties. The thin ta-C films are deposited at room temperature allowing the ready formation of ideal step junctions. The abrupt nature of the heterojunctions is confirmed from SIMS measurements. Capacitance-voltage (C-V) characteristics also show that with an abrupt heterojunction between ta-C and Si, an interface state density of the order of 10¹¹ cm^-2 is obtained. Dark forward current density-voltage-temperature (J-V-T) characteristics are consistent with a current transport mechanism predominantly controlled by a tunnelling-recombination process through states at the ta-C/Si interface. The photospectral response and photovoltaic behavior of the junction are also presented as a function of doping in the ta-C. The response time of these unoptimized diodes is found to be in the range of 0.1-1.5 μs