Investigating the effects of water pretreatments on chromite liberation

ABSTRACT

Many studies investigated the effects of grinding aids on mechanical and breakage properties of particles, as well as the flowability of ore-water slurries in wet grinding mills. Only recently, it was showed that grinding aids can promote grain-boundary fracturing. This paper aims to observe the effects of water pretreatment on chromite liberation, to underlie some reactions between water and chromite samples which promote the liberation of coarse chromite grains, i.e. the grain-boundary fracturing. For the purpose of this study, two different chromite ore samples were initially pretreated under water at different sets of pH, temperature and pretreatment time. Then, the untreated and pretreated samples were broken in a drop-weight tester (J/g). Finally, the grade-recovery plots in the selected progeny size fractions of the untreated and pretreated samples were compared. The results show that the hydrolysis of ore samples in 15?min of pretreatment improves the grain-boundary fracturing. The results also suggest that mineral carbonation may be beneficial for chromite liberation.     

Experimental model of the behaviour of bolted angles connections with stiffeners

This paper presents the experimental results of twenty full scale specimens of steel bolted connections beam-to-column with top-and-seat angles in six groups, labelled L91-tp8, L82-tp8, L73-tp8, L91-tp10, L82-tp10 and L73-tp10 groups (L=length of top-and-seat angle, tp=stiffener thickness of top-and-seat angle), under static loading. This study was undertaken to analyse the influence of angles and beams with stiffeners on the behaviour of the beam-to-column joints. The main parameters observed are the evolution of the resistance, the stiffness, the rotation capacity, the ductility of a joint, and the energy dissipation capacity. The aim was to provide necessary data to improve the Eurocode 3.     

高效液相色谱法对天山花楸不同提取部位槲皮素含量的测定

利用高效液相色谱法对天山花楸枝、叶、果实等不同提取部位进行槲皮素含量的测定,色谱柱为Kromasil-C18(4.6mm×250mm,5μm),流动相为甲醇-0.4%磷酸(60:40),检测波长为368nm,流速为0.7ml/min,结果表明该方法可提供简便准确的含量测定方法。     

Exposure to Air Accelerates the Gelation of Gelatin: Steady and Dynamic Shear Rheological Characterization to See the Effect of Air on the Strength of Gelatin Gel

In the current study, the effect of air exposure to the gelatin solution on improvement of gel structure was investigated in terms of the steady and dynamic shear rheological properties. Prepared gelation solution (5% w/v) was covered to prevent air incorporation and it was subjected to 5 h gelatin and rheological analyses were carried out for the comparison of non-covered ones. It was observed that the preventing of air into the gelatin solution affected the rheological parameters. Apparent viscosity and complex viscosity values of samples increased during gelation and these values were measured to be tremendously high (1.894 and 8.346 Pa s, respectively) in non-covered gelatin solution while they were 0.474 and 1.611 Pa s in covered samples after 5 h gelation, respectively. Similarly, storage modulus (G′) of samples increased with the increase in gelation time and it was recorded to be 52.203 Pa in gelatin solution exposed to air while it was 9.848 Pa in gelatin solution covered to prevent air incorporation. These results showed importance of air in gelatin solution to the food industry using gelatin in food formulation for the structure of processed foods.     

Optimization of gum combination for instant pudding based on creep and recovery parameters by mixture design approach

In the present study, gum combinations used in the pudding formulation were optimized by mixture design approach based on creep and recovery measurements. For this aim, four different gums (carrageenan, alginate, guar and xanthan gum) and their different combinations were used in the formulation. The creep-recovery properties of the pudding samples prepared with different gums or gum combinations were investigated. Burger model was satisfactorily applied for the determination of the creep-recovery characteristics of the samples. The use of the carrageenan in the pudding formulation caused a decrease in deformation of the samples. Gel strength value of the pudding samples was also calculated using the data. In order to optimize the gum combination based on the creep-recovery measurements, mixture design was carried out, and it was seen that established models satisfactorily predicted the viscoelastic parameters of the samples. During the optimization of the gum combination used in the pudding formulation, desirability function was used to optimize the ingredients simultaneously based on the requirements. The gum combination including 59.5 % carrageenan and 40.5 % guar gum or 52.7 % carrageenan, 33.8 % guar gum and 13.5 % xanthan gum was determined to be the optimum in terms of quality of the product.     

Poly (l-lactic acid) synthesis using continuous microwave irradiation–simultaneous cooling method

Abstract

In this study, Poly(l-lactic acid) (PLLA) synthesis was studied using direct melt condensation polymerization (DMP) method in an experimental microwave (MW) system where external cooling was applied to keep both temperature (T) and MW power (P) continuous and constant during the polymerization. T, P, reaction time (t), catalyst type, and catalyst amount were considered to determine appropriate process conditions. In addition, some experiments were carried out under the similar process conditions using MW-assisted ring opening polymerization (MW-ROP) and conventional heating (CH) methods. These methods were compared in terms of process performance and various properties of the oligomeric PLLA. According to results, polymerization rate, polymer yield, average-molecular weight, the dispersity, and thermal properties of PLLA products were similar in both MW methods but higher than CH counterparts. Furthermore, low crystallinity of PLLA products synthesized by MW methods showed the effect of MW on the optical purity (L or D) of products. Finally, energy saving was accomplished by 73% and an increase of polymer production rate by 37.7% in MW-DMP method.     

Temperature Dependency of Steady, Dynamic, and Creep-Recovery Rheological Properties of Ice Cream Mix

In this study, effect of processing temperature (5, 15, 25, and 35 °C) on the steady, dynamic, and creep recovery rheological properties of the ice cream mix (ICM) was investigated. It was found that processing temperature significantly affected all rheological parameters of the ICM sample. The flow behavior of the ICM sample was fitted to the Ostwald de Waele model. The magnitude of storage modulus (G′) was higher than that of loss modulus (G″) indicating that ICM sample had weak gel-like structure. Modified Cox–Merz rules were satisfactorily applied to the ICM sample to observe relationship between steady and dynamic shear properties. Additionally, Burger model was used to characterize the viscoelastic properties of the ICM sample. The gel strength (S) value was also calculated, and a decrease was observed with the increase of temperature. Arrhenius equation satisfactorily described the temperature dependency of the rheological parameters such as apparent viscosity at 50 s^?1 (η ₅₀), consistency coefficient (K), the instantaneous shear modulus of the Maxwell unit (G ₀), permanent deformation (J _∞ ), and S values that may be predicted by using established equations depending on the temperature. The increase in processing temperature caused a decrease in resistance of the mixture subjected to the deformation, which is very important for production of high quality ice cream.     

Balancing desirable but conflicting objectives in the newsvendor problem

In this paper we study the problem of balancing two desirable but conflicting objectives in the newsvendor model. The standard objective in the newsvendor model is the expected profit maximization. Another objective (known as the "satisficing"--or, "aspiration-level"--objective) that has been studied in the literature is the probability of exceeding a prespecified and fixed target profit level. Since it may not always be obvious what the fixed target profit level should be, we introduce a more flexible satisficing objective where the target does not have to be prespecified. Our satisficing/aspiration-level objective is defined as the probability of exceeding the expected profit and it is a "moving" target that is a function of the order quantity. We provide a discussion of the properties of the newly introduced probability maximization objective. As a departure from previous work where the individual objectives were considered in isolation, in this paper we develop a model that unifies and integrates the two objectives. We use a scalarization method to combine the standard objective of expected profit maximization with the new objective of maximizing the probability of exceeding the moving target. A decision framework is developed within compromise programming that involves minimizing a generalized distance function measuring the "distance" from an ideal point to the efficient frontier. Several examples illustrate the results.     

Switched mode feedback control laws for nonholonomic systems in extended power form

A class of nonholonomic control systems in extended power form is studied. It is demonstrated that under appropriate assumptions Lagrange's equations, including classical nonholonomic constraints, can be transformed into the extended power form. A switched mode feedback controller is used to obtain global convergence of the states of the extended power form to the origin. This feedback controller can be interpreted as a hybrid system consisting of a high level discrete event supervisor and a family of low level feedback controllers. The closed loop system exhibits finite-time responses.