Ultrasonic Anomaly Near the Charge Ordering Transition in Sr-Doped Nd0.3La0.2Ca0.5−x Sr x MnO3 Manganites

Sr doping in the charge-ordered compound Nd_0.3La_0.2Ca_0.5?x Sr _x MnO₃ has been systematically studied to examine its effect on ultrasonic velocity and elastic moduli as well as magnetic and electrical transport properties. DC electrical resistivity, ρ and AC susceptibility, χ′ measurements showed all samples exhibit metal-insulator (MI) behavior accompanied by ferromagnetic-paramagnetic (FM-PM) transition where the MI transition temperature, T _MI and FM-PM transition temperature, T _C increased with Sr content indicating the enhancement of double-exchange mechanism. Analysis of the resistivity change with respect to temperature, dlnρ/dT ^?1 versus T indicates onset of charge-ordering (CO) state where its CO transition temperature, T _CO decreased with Sr content indicating weakening of the CO state. On the other hand, both absolute longitudinal and shear velocities as well as elastic moduli measured at 80 K increased significantly with Sr doping indicating improvement in elastic properties, which is suggested to be due to the increase in formation of ferromagnetic domains. A longitudinal velocity anomaly characterized by a slope change around the vicinity of T _CO was observed for all samples. The longitudinal elastic anomaly is attributed to the Jahn–Teller (JT) effect of Mn³⁺ ions where analysis of the anomaly using the mean-field theory suggests involvement of the JT effect in the samples, which transforms from dynamic to static type with decreasing temperature. The elastic anomaly shifted down from 222 K (x=0) to 205 K (x=0.05) indicating that the static JT effect was weakened with Sr content.     

Delay Mitigation in the Malaysian Construction Industry

This paper describes the importance of applying proper management in dealing with delays in construction for a growing economy. The main objective of this paper is to identify the management tools that are practiced in the local construction industry in mitigating delay. It also aims to identify the main factors that lead to project delays and to suggest recommendations on how to overcome or mitigate effects of the problem. Data is gathered from responses from questionnaire survey and interviews with those involved in construction project. The surveys and research findings indicate that delay incidents occur mainly during the construction phase of a project and one or more parties usually contribute to delay. This paper highlights the importance of having more experienced and capable construction managers as well as skilled laborers to enable the industry to develop at a faster rate either nationally or internationally.     

Reflection and transmission coefficient of yttrium iron garnet filled polyvinylidene fluoride composite using rectangular waveguide at microwave frequencies

The sol-gel method was carried out to synthesize nanosized Yttrium Iron Garnet (YIG). The nanomaterials with ferrite structure were heat-treated at different temperatures from 500 to 1000 °C. The phase identification, morphology and functional groups of the prepared samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), respectively. The YIG ferrite nanopowder was composited with polyvinylidene fluoride (PVDF) by a solution casting method. The magnitudes of reflection and transmission coefficients of PVDF/YIG containing 6, 10 and 13% YIG, respectively, were measured using rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) in X-band frequencies. The results indicate that the presence of YIG in polymer composites causes an increase in reflection coefficient and decrease in transmission coefficient of the polymer.     

Enhancement of extrinsic magnetoresistance behavior in BiFeO3 doped La0.8Ag0.2MnO3 ceramic

BiFeO₃ (BFO) doped La_0.8Ag_0.2MnO₃ ceramics were prepared by the conventional solid-state synthesis method to investigate the effect of BFO on transport and magnetic properties as well as its influence on magnetoresistance (MR). X-ray diffraction analysis showed a decrease in unit cell volume indicating partial substitution of some BFO into the La_0.8Ag_0.2MnO₃ (LaAgMO) lattice while results of scanning electron microscope (SEM) showed improvement in grains connectivity and formation of more regular shaped grains with BFO doping. Energy Dispersive X-ray emission (EDX) analysis showed BFO mainly segregates at the grains boundaries of LaAgMO. Resistivity and susceptibility measurements showed both metal–insulator transition temperatures, T_MI and paramagnetic-to-ferromagnetic transition temperature, T_c decreased with increased BFO content indicating weakening of the double exchange, DE mechanism. The temperature dependence of MR showed a small peak around T_MI for all samples which is ascribed to the intrinsic MR effect. Below the MR peak, the MR increased almost linearly with decreasing temperature for all samples and this is ascribed to the phenomena of extrinsic MR. The highest MR% (at 40 K) was observed for the x=1.5% sample which showed a MR of more than twice that of the undoped (x=0%) sample. This extrinsic effect is suggested to be related to improved spin polarized tunneling of conduction electrons between grains under external field as a result of improved spin alignment. It is suggested that BFO induced some kind of magnetoelectric coupling between BFO and LaAgMO leading to the enhancement process.     

A simple vortex-assisted graphene oxide nanosheets dispersive micro-solid phase extraction combined with high-performance liquid chromatography for UV-Vis detection of tramadol in biological samples

This study developed a simple, rapid and sensitive method that utilizes vortex-assisted graphene oxide nanosheets dispersive micro-solid phase extraction of tramadol hydrochloride from biological samples. The data obtained from scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed the characteristics of graphene oxide nanosheets (GONSs). In order to increase the extraction efficiency, a vortex was applied in the extraction process. In this study, parameters affecting the extraction efficiency were identified and discussed. The optimal experimental parameters were as follows: pH, amount of GONSs, type and volume of desorption solvent, vortexing time, and addition of NaCl. Under optimized conditions, this method allowed the determination of tramadol in the range of 5–300 µg l^?1 and the limit of detection was 0.16 µg l^?1. The intra-day and inter-day precisions obtained were 2.4% and 3.8%, respectively. This method can be used as an analytical technique for the determination of tramadol in biological samples.     

Weighted Version of Extended Nearest Neighbors

This paper investigates the problem of stability analysis for switched complex dynamical networks with mixed time-varying delays and parameter uncertainties. The switched complex dynamical networks are composed of m modes that are switched from one to another based on time, state, etc. Although, the active subsystem is known in any instance, but the switching law such as transition probabilities are not known. The model for each mode is considered affine with matched and unmatched perturbations. The main purpose of the addressed problem is to design a filter error for the switched complex dynamical networks such that the dynamics of the error converges to the asymptotically irrespective of the admissible parameter variations with the gains. Then, by utilizing the Lyapunov functional method, the stochastic analysis combined with the matrix inequality techniques, a sufficient condition in terms of linear matrix inequalities is presented to ensure the $$H_\infty $$ performance of the complex dynamical system models. Finally, a numerical example is presented to illustrate the effectiveness of the proposed design method.