Electrochemical potentials of layered oxide and olivine phosphate with aluminum substitution: A first principles study

First-principles prediction of enhancement in the electrochemical potential of LiCoO₂ with aluminum substitution has been realized through earlier experiments. For safer and less expensive Li-ion batteries, it is desirable to have a similar enhancement for alternative cathode materials, LiFePO₄ and LiCoPO₄. Here, we present first-principles density functional theory based analysis of the effects of aluminum substitution on electrochemical potential of LiCoO₂, LiFePO₄ and LiCoPO₄. While Al substitution for transition metal results in increase in electrochemical potential of LiCoO₂, it leads to reduction in LiFePO₄ and LiCoPO₄. Through comparative topological analysis of charge density of these materials, we identify a ratio of Bader charges that correlates with electrochemical potential and determine the chemical origin of these contrasting effects: while electronic charge from lithium is transferred largely to oxygen in LiCoO₂, it gets shared by the oxygen and Co/Fe in olivine phosphates due to strong covalency between O and Co/Fe. Our work shows that covalency of transition metal–oxygen bond plays a key role in determining battery potential.     

COMPARISON OF BRANCH AND BOUND AND ITERATIVE HEURISTIC ALGORITHMS FOR FLOOR ALLOCATION OF ACTIVITY CLUSTERS IN MULTISTOREY BUILDINGS

The paper presents a branch and bound algorithm and an iterative heuristic algorithm for the optimal location of clusters in a multistorey building. The use of cluster analysis is proposed for grouping highly related activities. The vertical layout problem is formulated mathematically. Results obtained by both the algorithms are compared. Some practical problems are solved and the cost comparison made     

Survival of Lactic Acid Bacteria during Spray Drying of Plain Yogurt

Survival of Streptococcus salivarius subsp. thermophilus and Lactobacillus debrueckii subsp. bulgaricus was determined under various processing conditions for spray drying. Numbers of both microorganisms decreased with increased outlet or inlet air temperature, and atomizing air pressure. Outlet air temperature was a major parameter affecting number of survivors. Suitable conditions were inlet air 160°C, outlet air 60°C, atomizing air pressure 98 kPa, hot air flow 0.28 m³/ min, and feed temperature 30°C. Spray-dried yogurt powder showed lower survival for S. thermophilus and similar survival for L. bulgaricus as compared to freeze-dried powder.     

Determination of Retortable Pouch Heat Transfer Coefficients by Optimization Method

A computer-based optimization technique was developed for determining the apparent heat transfer coefficient (h) for retortable pouches heated by circulated hot water under overriding air pressure. The technique incorporated actual process data, a finite difference model and an optimization criteria to converge on h values. A water flow channel was constructed to fit inside a vertical retort which allowed direct water exposure on the pouch surface at a quantifiable velocity. Because the optimization technique was not dependent on analytical equations, it could be applied to such areas as future heat transfer studies of new retortable pouch materials, designing new pouch-holding cassettes and improving water flow patterns in retorts.     

Thermal Sterilization of Conduction-Heated Foods in Plastic Cylindrical Cans Using Convective Boundary Condition

A mathematical model was developed to evaluate thermal processing of foods in cylindrical plastic cans. This model included convective heat transfer coefficients for heating and cooling media, thermal diffusivities of plastic can wall and the canned food, and contact conductance between the plastic wall and the canned food. Temperatures estimated by the model at the coldest point in a can agreed closely with those determined experimentally during thermal processing. Thermal diffusivity of can wall and heat transfer coefficients of heating and cooling media considerably influenced the sterilizing values of the processed food.     

Analysis of a Lorentz force based vibration exciter using permanent magnets mounted on a piezoelectric stack

This work presents performance analysis of a Lorentz force based non-contact vibration exciter by mounting a couple of permanent magnets on a piezoelectric stack. A conductor is attached to the structure to be excited and is placed midway between unlike poles of a couple of permanent magnets. The permanent magnets are placed on a piezoelectric stack. This stack, because of its nano-positioning capabilities, can impart an accurate and adjustable harmonic vibratory motion to the couple of permanent magnets. The piezoelectric stack, because of its high stiffness remains uncoupled with the dynamics of the structure. Due to the relative motion between the magnets and the conductor, Lorentz force is generated within the conductor. This Lorentz force is responsible for vibration of the structure in a plane parallel to the pole faces of the magnets. This keeps the magnetic field almost independent of the vibration of the structure and the chance of the structure hitting the magnet during large vibration is totally eliminated. If the amplitude of displacement of the stack is kept constant, the non-contact excitation force in this exciter remains proportional to the excitation frequency. Though use of this exciter eliminates mass (apart from that of the conductor attached to the structure) and stiffness coupling, a known damping term gets added to that of the excited structure.     

Effect on Retortable Pouch Heat Transfer Coefficients of Different Thermal Processing Stages and Pouch Material

Apparent heat transfer coefficients (h) were determined for the come-up, heating, and cooling cycles of thermal processing for retortable pouches heated by circulating hot water under overriding air pressure. Values for h were converged on by a computer-based optimization method that incorporated process data, a finite difference model, and optimization criteria. For retortable pouches thermally processed in circulating water under overriding air pressure, h values for the come-up, heating, and cooling cycles were found not significantly different (95% confidence). This indicates that in mathematical models a constant h value may be assumed for the three thermal processing stages. Also, there was no significant difference between h values for aluminum foil/plastic laminate pouches and all-plastic pouches during the combined come-up and heating stages. Thus, the same h value for a given process is applicable to either pouch type.     

In Situ Determination of Apparent Thermophysical Properties of a Composite Slab Undergoing Transient State Heat Transfer

A method was developed to determine the thermophysical properties of a two layered composite slab whose one exposed surface was subjected to a known temperature history and whose other surface to convective and radiative heat exchange. The physical properties to be determined were the thermal conductivity and diffusivity of one of the two layers and the contact conductance between the two layers, the coefficient of convective surface heat transfer, and the absorbtivity of thermal radiation energy applicable to one exposed surface of the slab. The developed method was used to determine property values of the insulated wall of a still retort.     

Influence of Selected Thermal Processing Conditions on Steam Consumption and on Mass Average Sterilizing Values

The influence of can size, type of food (conductive or convective), retort temperatures, initial temperature of food and target sterilizing value on steam consumption was studied. A 2⁵ factorial design of experiments was used. Steam consumption was measured by using steam flow meters. A mass average sterilizing value was computed for each process by using experimentally determined heat penetration parameters. Steam consumption was significantly high for processing larger cans compared to smaller cans both containing equal quantities of conduction heating food simulant. The can size had no significant influence on steam consumptions with the convection heating food simulant. Steam consumption and mass average sterilizing values were reduced significantly by employing a high retort temperature to obtain a high target F_p value. With a low target F_p value, the type of food simulant did not affect significantly mass average sterilizing value.