Effect of sepiolite (magnesium silicate) on the dynamic properties of butadiene-styrene rubber vulcanizates

The influence of the new mineral filler Pansil, a natural magnesium silicate (sepiolite), on the properties of SBR vulcanizates is studied and compared with other synthetic silicas and a carbon black N-330 (HAF) at various filler concentrations.A series of dynamic tests was carried out in traction-compression and shear at various frequencies, temperatures and strain amplitudes.The so-called Payne effect was observed as the strain amplitude was increased. The variation of tan with the dynamic deformation was more pronounced in the Pansil filled compounds. The needle-shaped nature and the large internal surface (mesopores) of the new mineral filler may give rise to a high adsorption of rubber chain segments with the subsequent increase in heat generation. However, when the Pansil was treated with a silane coupling agent (Silane A-189) the heat generation decreased.By applying the time-temperature superposition principle, master curves for the storage modulus and loss factor tan were derived over a wide frequency range.     

Dynamic contact of a beam against rigid obstacles: Convergence of a velocity-based approximation and numerical results

Motivated by the study of vibrations due to looseness of joints, we consider the motion of a beam between rigid obstacles. Due to the non-penetrability condition, the dynamics is described by a hyperbolic fourth order variational inequality. We build a family of fully discretized approximations of this problem by combining some classical space discretizations with velocity based time-stepping algorithms for discrete mechanical systems subjected to unilateral constraints. We prove the stability and the convergence of these numerical methods. Finally we propose some examples of implementation using either Hermite or B-spline finite element approximations.     

Dynamic effects in inefficiency: Evidence from the Colombian banking sector

Firms face a continuous process of technological and environmental changes that requires them to make managerial decisions in a dynamic context. However, costs and constraints prevent firms from making instant adjustments towards optimal conditions and may cause inefficiency to persist in time. We propose a dynamic inefficiency specification that captures differences in the adjustment costs among firms and non-persistent effects of inefficiency heterogeneity. The model is fitted to a ten year sample of Colombian banks. The new specification improves model fit and have effects on efficiency estimations. Overall, Colombian banks present high inefficiency persistence but important differences between institutions are found. In particular, merged banks present low adjustment costs that allow them to recover rapidly efficiency losses derived from merging processes.     

Partially Observable Markov Decision Processes incorporating epistemic uncertainties

The use of Markov Decision Processes for Inspection Maintenance and Rehabilitation of civil engineering structures relies on the use of several transition matrices related to the stochastic degradation process, maintenance actions and imperfect inspections. Point estimators for these matrices are usually used and they are evaluated using statistical inference methods and/or expert evaluation methods. Thus, considerable epistemic uncertainty often veils the true values of these matrices. Our contribution through this paper is threefold. First, we present a methodology for incorporating epistemic uncertainties in dynamic programming algorithms used to solve finite horizon Markov Decision Processes (which may be partially observable). Second, we propose a methodology based on the use of Dirichlet distributions which answers, in our sense, much of the controversy found in the literature about estimating Markov transition matrices. Third, we show how the complexity resulting from the use of Monte-Carlo simulations for the transition matrices can be greatly overcome in the framework of dynamic programming. The proposed model is applied to concrete bridge under degradation, in order to provide the optimal strategy for inspection and maintenance. The influence of epistemic uncertainties on the optimal solution is underlined through sensitivity analysis regarding the input data.     

Performance bounds on optimal fixed prices

We consider the problem of selling a fixed stock of items over a finite horizon when the buyers arrive following a Poisson process. We obtain a general lower bound on the performance of using a fixed price rather than dynamically adjusting the price. The bound is 63.21% for one unit of inventory, and it improves as the inventory increases. For the one-unit case, we also obtain tight bounds: 89.85% for the constant-elasticity and 96.93% for the linear price-response functions.     

Dynamic programming in stochastic control of systems with delay

We consider optimal control problems for systems described by stochastic differential equations with delay (SDDE). We prove a version of Bellman's principle of optimality (the dynamic programming principle) for a general class of such problems. That the class in general means that both the dynamics and the cost depends on the past in a general way. As an application, we study systems where the value function depends on the past only through some weighted average. For such systems we obtain a Hamilton-Jacobi-Bellman partial differential equation that the value function must solve if it is smooth enough. The weak uniqueness of the SDDEs we consider is our main tool in proving the result. Notions of strong and weak uniqueness for SDDEs are introduced, and we prove that strong uniqueness implies weak uniqueness, just as for ordinary stochastic differential equations.     

Polymeric ionic liquid as a dynamic coating additive for separation of basic proteins by capillary electrophoresis

A simple and economical capillary electrophoresis method has been developed for the analysis of four model basic proteins by employing a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium) bromide, as the dynamic coating additive. When a small amount of PIL was present in the background electrolyte, a cationic coating on the inner surface of fused-silica capillary was established. These PIL modified capillaries not only generated a stable reversed electroosmotic flow, but also effectively eliminated the wall adsorption of proteins. Several important parameters such as the PIL concentration in the background electrolyte, pH values and concentrations of the background electrolyte were optimized to improve the separation of basic proteins. Consequently, under the optimum conditions, a satisfied separation of basic proteins with peak efficiencies ranging from 247,000 to 540,000 (plates m⁻¹) had been accomplished within 11 min. The run-to-run RSDs (n = 3) of the migration times for the four basic proteins were all less than 0.37%.     

Epimerization and hydrolysis of 3,6-dimethyl-2,3,5,6-tetrahydro[1,2,4]thiadiazino[6,5,4-hi]indole 1,1-dioxide

In this study, configurational and chemical stability of (R,R),(S,S),(R,S),(S,R)-3,6-dimethyl-2,3,5,6-tetrahydro[1,2,4]thiadiazino[6,5,4-hi]indole 1,1-dioxide (1) were investigated by dynamic and stopped-flow HPLC methods. Single epimeric mixtures (R,R),(R,S)-1 and (S,S),(S,R)-1 were obtained combining synthetic and chromatographic strategies. Separation of (R,R)-1 and (R,S)-1 was achieved by chiral chromatography and absolute configuration of eluted epimers has been assigned basing on molecular modelling calculations. Epimerization and hydrolysis of (R,R),(R,S)-1 have been studied by classical off-column, dynamic HPLC and stopped-flow HPLC methods. The influence of different parameters, such as temperature, pH and dielectric constant was evaluated. The data obtained indicate that (R,R),(R,S)-1 undergoes to a rapid epimerization in aqueous solvent and hydrolysis in acidic conditions. Moreover, epimerization and hydrolysis were investigated in presence of an artificial membrane and in physiological buffers (pH 2.2 and 7.0 at 37.5°C) to simulate in vivo conditions.     

On-line coupling of dynamic microwave-assisted extraction to solid-phase extraction for the determination of sulfonamide antibiotics in soil

A rapid technique based on dynamic microwave-assisted extraction (DMAE) coupled on-line with solid-phase extraction (SPE) was developed for the determination of sulfonamides (SAs) including sulfadiazine, sulfameter, sulfamonomethoxine and sulfaquinoxaline in soil. The SAs were first extracted with acetonitrile under the action of microwave energy, and then directly introduced into the SPE column which was packed with neutral alumina for preconcentration of analytes and clean-up of sample matrix. Subsequently, the SAs trapped on the alumina were eluted with 0.3% acetic acid aqueous solution and determined by liquid chromatography-tandem mass spectrometry. The DMAE parameters were optimized by the Box-Behnken design. Maximum extraction efficiency was achieved using 320 W of microwave power; 12 mL of extraction solvent and 0.8 mL min⁻¹ of extraction solvent flow rate. The limits of detection and quantification obtained are in the range of 1.4-4.8 ng g⁻¹ and 4.6-16.0 ng g⁻¹ for the SAs, respectively. The mean values of relative standard deviation of intra- and inter-day ranging from 2.7% to 5.3% and from 5.6% to 6.7% are obtained, respectively. The recoveries of SAs obtained by analyzing four spiked soil samples at three fortified levels (20 ng g⁻¹, 100 ng g⁻¹ and 500 ng g⁻¹) were from 82.6 ± 6.0% to 93.7 ± 5.5%. The effect of standing time of spiked soil sample on the SAs recoveries was examined. The recoveries of SAs decreased from (86.3-101.9)% to (37.6-47.5)% when the standing time changed from one day to four weeks.     

Critical evaluation of novel dynamic flow-through methods for automatic sequential BCR extraction of trace metals in fly ash

Two novel dynamic extraction approaches, the so-called sequential injection microcolumn extraction and sequential injection stirred-flow chamber extraction, based on the implementation of a sample-containing container as an external extraction reactor in a sequential injection network, are for the first time, optimized and critically appraised for fractionation assays. The three steps of the original Community Bureau of Reference (BCR) sequential extraction scheme have been performed in both automated dynamic fractionation systems to evaluate the extractability of Cr, Cu, Ni, Pb, and Zn in a standard reference material of coal fly ash (NIST 1633b). In order to find the experimental conditions with the greatest influence on metal leachability in dynamic BCR fractionation, a full-factorial design was applied, in which the solid sample weight (100–500 mg) and the extraction flow rate (3.0–6.0 mL min⁻¹) were selected as experimental factors. Identical cumulative extractabilities were found in both sequential injection (SI)-based methods for most of assayed trace elements regardless of the extraction conditions selected, revealing that both dynamic fractionation systems, as opposed to conventional steady-state BCR extraction, are not operationally defined within the selected range of experimental conditions. Besides, the proposed automated SI assemblies offer a significant saving of operational time with respect to classical BCR test, that is, 3.3 h versus 48 h, for complete fractionation with minimum analyst involvement. Schematic illustration of automatic flow-based setups for dynamic fractionation of trace metals in fly ash