Effects of Frequency on AC Conductivity and Magnetoresistance in Doped La0.65Ca0.35MnO3 Manganites

The effects of frequency on the alternating-current (AC) conductivity of polycrystalline La_0.65Ca_0.35MnO₃ compounds prepared by solid-state reaction with various heat treatments have been studied. The AC conductivity and magnetoresistance (MR) are affected by the heat treatment temperature. The MR is enhanced at and below the transition temperature (T _C). The AC transport behavior of this system shows pronounced negative MR even at small applied magnetic fields for temperatures well below T _C. It is observed that such effects originate from spin-dependent scattering at grain boundaries as a consequence of spin disorder at the interfaces of the boundaries and spin scattering within the grains. The real part of the AC conductivity σ′ exhibits a pronounced frequency dependence, measured in the frequency range f < 100 kHz. The minimum occurs at a frequency that is temperature dependent. The MR below T _C and the frequency dependence of the AC electrical conductivity σ′(f) are interpreted as being consequences of cluster and grain boundary effects.     

Neural network modeling of arc spot welding

This study presents neural network (NN) for the prediction of ultimate capacity of arc spot welding. The proposed NN model is based on experimental results. The ultimate capacity of arc spot welding is modeled in terms of weld strength, average welding thickness and diameter. The results of the proposed NN model are later compared with results of existing codes and are found to more accurate. Moreover, the proposed NN model is presented in explicit form as a mathematical function. Parametric studies are also carried out to analyze the effect of each variable. The proposed NN model is a unified formulation valid for governing shear failures.     

On-line evolutionary optimization of an industrial fed-batch yeast fermentation process

This paper presents two genetic algorithms based on optimization methods to maximize biomass concentration, and to minimize ethanol formation. The objective function is maximized according to the values of feed flow rate, using genetic search approaches. Five case studies were carried out for different initial conditions, which strongly influence the optimal profiles of feed flow rate for the fermentation process. The ethanol and glucose disturbance effects were examined to stress the effectiveness of proposed approaches. The proposed genetic approaches were implemented for an industrial scale baker's yeast fermentor which produces Saccharomyces cerevisiae known as baker's yeast. The results show that optimal feed flow rate was obtained in a satisfactory and successful way for fed-batch fermentation process.     

Polymorphic transformation of Cu<Subscript>1.80</Subscript>Te crystals

The polymorphic transformation of Cu_1.80Te crystals has been studied by X-ray diffraction at temperatures from 290 to 1100 K. The low-temperature, hexagonal phase has been shown to transform to an fcc phase at 730 K. The transformation is reversible. From the temperature-dependent lattice parameters of the two phases, we have evaluated their thermal expansion coefficients.     

Electrochemical fabrication and modelling of mechanical behavior of a tri-layer polymer actuator

Stability and performance of electrochemically synthesized tri-layer polypyrrole based actuators were reported. Concentrations were optimized as 0.05 M pyrrole and 0.05 M tetrabutylammonium hexaflurophosphate in propylene carbonate (PC). The force output of the actuators ranged from 0.2 to 0.4 mN. Cyclic deflection tests on PC based actuators for a duration of 3 h indicated that the displacement decreased by 60%. However, actuation could be regenerated by immersing the actuator into the electrolyte solution. Surface resistivity measurements on the actuators prior to and after 3 h continuous deflection did not show any significant change in the resistivity of the PPy layer. A triple-layer model of the polymer actuator was developed based on the classic bending beam theory by considering strain continuity between PPy and PVDF. Results predicted by the model were in good agreement with the experimental data.     

Transmitter-Receiver Path Selection for Cell Range Extension Using Multi-Hop D2D

Conventional approach of dealing with more users per coverage area in cellular networks implies densifying the amount of (Access Point) AP which will eventually result in a larger carbon footprint. In this paper, we propose a base station off-loading and cell range extension (CRE) scheme based on multi-hop device-to-device (MHD2D) path selection between transmitter and receiver node. The paper also provides derivations of upper and lower bounds for energy efficiency, capacity, and transmit power. The proposed path selection scheme is inspired by the foraging behavior of honey bees. We present the algorithm as a modified variant of the artificial bee colony algorithm (MVABC). The proposed optimization problem is modeled as a minimization problem where we optimize the Energy Efficiency (EE). The proposed path selection MVABC is compared with the Genetic Algorithm (GA) and also with classical artificial bee colony (ABC) through simulations and statistical analysis. The student’s t-test, p-value, and standard error of means (SEM) clearly show that MVABC based path selection out-performs the GA and classical ABC schemes. MVABC based approach is 66% more efficient when compared with classic ABC and about 62% efficient when compared with GA based scheme.     

Fullerene Production in a Graphite Tubular Reactor

Effects of operational parameters on the production yield of fullerenes have been detailed by many researchers and up to 20% fullerene yields were attained at optimized pressure, current, and electrode gap. Many of the tests were carried out under static helium pressure and no reference was made to helium flow during the arcing process. It is, however, known that helium flow enhances the fullerene yield. In this study, a tubular graphite reactor was placed into a stainless steel chamber and the arc was generated inside the tubular reactor. Fresh helium was fed at one end of the tubular reactor and vacuum was applied to the other end. Changing the helium flow rate affected the residence time of the particles in the reactive zone. Fullerene yields were obtained to be as high as 32%, which is much above the literature stated values.     

Counterion-coupled gemini (Cocogem) surfactants based on dodecylisopropylol amine and dicarboxylic acids: synthesis,characterization and evaluation as biocide against SRB

New cocogem surfactants were synthesized by interaction of dodecylisopropylol amine with dicarboxylic (oxalic, succinic, adipic, sebacic, tartaric, maleic, fumaric, isophthalic) acids. By tensiometric method, the surface activity of aqueous solutions of the synthesized cocogem surfactants at the border with air was studied and, by conductometric method, the specific electrical conductivity of these solutions was determined. The degree of counterion binding (β), critical micelle concentration (CMC), effectiveness of surface tension reduction (π_CMC), surface excess concentration (Γ_max), area per molecule at the interface (A_min), changes of Gibbs free energies of adsorption (ΔG_ad) and micellization (ΔG_mic) have been calculated. The character of change of the colloidal-chemical indices depending on spacer-group nature and length has been clarified. So, with an elongation of the spacer group and when passing from cis-form to trans-form, the value of CMC decreases. The obtained cocogem surfactants exhibit a considerable bactericidal effectiveness against sulfate-reducing bacteria. The bactericide properties of the cocogem surfactants containing in the spacer chain a saturated hydrocarbon fragment and benzene ring are stronger than for the others.     

Activity-Based Costing and Management applied in a hybrid Decision Support System for order management

This article introduces a new Cost Management and Decision Support System (DSS) applicable to Order Management. This model is better fit and compatible with today's competitive, and constantly changing, business environment. The presented Profitable-To-Promise (PTP) approach is a novel modeling approach which integrates System Dynamics (SD) simulation with Mixed-Integer Programming (MIP). This Order Management model incorporates Activity-Based Costing and Management (ABC/M) as a link to merge the two models, MIP and SD. This combination is introduced as a hybrid Decision Support System. Such a system can evaluate the profitability of each Order Fulfillment policy and generate valuable cost information. Unlike existing optimization-based DSS models, the presented hybrid modeling approach can perform on-time cost analysis. This will lead to better business decisions based on the updated information.