Some Physical Properties of Pure and Doped Polyvinyl Alcohol under Applied Stress

Thick films of polyvinyl alcohol (PVA) containing very finemetallic powder, copper (Cu), iron (Fe) and aluminum (Al) 2.5% by weight,were prepared by the casting method. The temperature dependence of Young'smodulus at constant stress, the stress dependence of Young's modulus(Y), the stress dependence of dielectric constant (ε) and stressdependence of phonon velocity, were studied. It was found that Young'smodulus (Y) of the pure sample has the lowest value and that of PVA + Alhas the highest value. This can be explained on the basis that Ydepends on the ratio between the energy of molecular interactions andthe energy of thermal motion of the sample units. We also found that thedielectric constant increases with the addition of metallic powder, andwith an increasing applied stress. The phonon velocity increased withincreasing stress. The increase of stress decreases imperfectionsleading to the increased phonon velocity. The electronic absorptionspectra of PVA is not affected by doping Al and Fe, whereas the PVA dopedwith Cu shows a shift of the absorption maxima toward a longer wavelength.The instantaneous elastic behavior may be observed only at lowtemperatures and very short creep times.     

Composite Polymers Transducers for Ultrasonic and Biological Applications

Ferrite polymer transducer and copolyesters are being used for ultrasonic generation to be used in technology and in biological applications like orthodontic treatment. The objectives of this study were to introduce a new piezoelectric composite polymers and to evaluate and compare their electric and mechanical properties with the widely used other materials. The resonance and antiresonance frequencies were measured for the materials in the radial mode. It is noticed that the resonance frequency decreased with increasing CoZn ferrite concentrations in polymers. The electromechanical coupling factor was determined to be of value 0.8 which is the highest value of the piezoelectric materials. It is very difficult to produce ceramic transducers in large sizes because they are fragile, thus the composite transducer could be an alternative. The ultrasonic wave velocity of the composite polymer is higher than that of other polymers and piezoelectric ceramics making them more attractive for many applications than ceramics. The Young's modulus of the composite polymer increased with increasing ferrite concentrations.     

Geophysical Investigations at Cairo’s Oldest,the Church of Abu Serga (St. Sergius), Cairo,Egypt

The results of an integrated geophysical survey at the archaeological site of Abu Serga church, Cairo, Egypt are presented and discussed. The aim was to investigate the ground conditions of the Church of Abu Serga (St. Sergius), the Cairo’s oldest, dated from 4th Century church, which is located at Qasr el-Shama in old Cairo in Egypt. In particular the objective is to study the subsurface geological structures at the location of the church, and to detect and possibly map any ancient remains concealed under the monument. The survey was conducted using two geophysical methods: the ground penetrating radar (GPR), which is a fully non-destructive method, and the electrical resistivity tomographies (ERTs). The usefulness of combining conventional geophysical mapping techniques and high resolution imaging methods in delineating shallow targets of archaeological interest at such complex archaeological sites, is studied. Ground penetrating radar time slices and 3D electrical tomography depth slices were used for the verification of specific anthropogenic anomalies, which were detected on the geophysical maps Processing of geophysical maps included filtering with the gradient and first derivative operators in the space domain and the upward continuation and Butterworth filters in the wave number domain. The integration of the geophysical measurements revealed that the present Crypt is not the original holy Crypt. The anomalous reflector is detected at depth of about 5 m below the sanctuary floor, in the form of buried ceiling of the original Crypt. The present Crypt is just a small low subterranean church belong to the 2nd century. High resistivity anomalies and distinct GPR signals were also observed deeper in the inner parts of the church. They are attributed to possible remains of ancient walls and surrounding tunnels, or other man-made structures concealed under the floor of the monument. The geophysical survey at Abu Serga church also demonstrates that the general features of the foundation soil are heterogeneous with abundance of fractures; the water table is very high at 1.8m below the sanctuary floors. The benefits of combined geophysical surveys in case of archaeological investigations at complex sites are highlighted.     

Ferroelectric-to-non-ergodic relaxor phase transition of (Bi0.5Na0.3K0.2) TiO3– (Ba0.8Ca0.2) TiO3 lead-free ceramics by SrTiO3 effect

In this work, a series compositions of [(0.95?x)(Bi_0.5Na_0.3K_0.2)TiO₃–xSrTiO₃–0.05(Ba_0.8Ca_0.2) TiO₃] Pb-free ceramics (0.0?≤?x?≤?0.2) abbreviation (BKNT–ST–BCT) were synthesized by conventional sintering method. Effect of ST addition on the crystal structure, domain structure, dielectric and ferroelectric properties were investigated. The crystal structure was monitored by XRD and the patterns shown phase crossover from tetragonal to pseudo-cubic caused by lower crystal symmetry of lattice effect at high content of ST. Morphology of sintered ceramics were characterized by SEM, while the domain structure of ST?=?0.0 at different temperatures was examined by In situ TEM. Diffused phase transition corresponding to ferroelectric to ergodic relaxor at lower T has been observed at depolarization temperature (T_d) at (ST < 0.15), while the permittivity peak which detected at ST?=?0.2 in whole range of temperature denote non-ergodic relaxor to paraelectric phase transition. All compositions show normal ferroelectric (P–E) loop at room temperature even ST?=?0.2 with low coercive field (E_c?~?15 kV/cm), while slim relaxor (P–E) loop was observed at (T?=?200 °C). Present normal ferroelectric properties of ST?=?0.2 are attributed to the domain growth and domain wall displacement above the domain switching electric field. All samples belonging to (x?≤?0.1) shown current peak corresponding to ferroelectric phase transition at domain switching field. Samples belonging to (x?≥?0.15) shown two nominal peaks where the second peak is corresponding to ferroelectric-to-another ferroelectric phase transition with different crystal symmetry.

     

Spectrum behavior for the nonlinear fractional point reactor kinetics model

The nonlinear fractional point reactor kinetics equation in the presence of Newtonian temperature reactivity feedback with a multi-group of delayed neutrons,which describes the spectrum behavior of neutron density into the homogenous nuclear reactors, is developed. This system is one of the most important stiff coupled nonlinear fractional differentials for nuclear reactor dynamics. The generalization of Taylor's formula that involves Caputo fractional derivatives is developed in an attempt to overcome the difficulty of the stiffness of the nonlinear fractional differential model. Moreover, the general fractional derivatives are calculated analytically throughout this work. Furthermore, the local and global estimated errors were analyzed, which suggest that the error quantification should take into account the possible grow in time of the error. This observation provides a motivation for going beyond more classical local-in-time concepts of error(local truncation error). The neutron density response with time is analyzed for the anomalous diffusion, sub-diffusion, and super-diffusion processes.     

Initial Magnetic Permeability of M-Type BaFe<Subscript>12</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>19</Subscript>-Polystyrene Composite

We reveal the potential effect of inclusion of M-type BaFe₁₂ O ₁₉ (BaM) particles in polystyrene (PS) polymer. BaM particles are attached rather well to a PS matrix with variable sizes and shapes. It demonstrated that the incorporation of BaM particles into a PS polymer would largely increase the initial magnetic permeability of BaM. Furthermore, it is significantly larger than corresponding values of commercially sintered MnZn ferrite. Therefore, BaM-PS composite imposes itself as a potential material in several applications such as flux amplifier and inductors.     

Some effects of copper-oxide additions to Co0.6Zn0.4Fe2O4

A series of samples of the system Co_0.6Zn_0.4Cu _x Fe_{2 –x} O₄ (x=0, 0.2, 0.4, 0.6 and 0.8) were prepared by the usual ceramic technique, X-ray analysis showed that the samples were cubic spinels (single phase). The lattice parameter, the theoretical density,D _x, the bulk density,D, and the porosity, p, were measured for the samples. The lattice parameter increased with the increase in Cu. Increases in the population of Fe²⁺ ions in octahedral sites with the introduction of Cu²⁺ resulted in increases in the lattice parameter. Differential thermal analysis (DTA) traces showed that there were exothermic peaks for the samples in the temperature range 120–190 C.