Unconstrained model predictive control and suboptimality estimates for nonlinear continuous-time systems

This paper presents a continuous-time version of recent results on unconstrained nonlinear model predictive control (MPC) schemes. Based on a controllability assumption and a corresponding infinite-dimensional optimization problem, performance estimates and stability conditions are derived in terms of the prediction horizon and the sampling time of the MPC controller. Moreover, improved estimates for small sampling times are discussed and a comparison to the application of the discrete-time results in a sampled-data context is provided.     

Accelerated Fretting Wear Tests for Contacts Exposed to Atmosphere

Engineering components can be subjected to normal and/or rotational fretting wear with contacts that are intermittently exposed to the atmosphere. Exposure to the environment may lead to the alteration at the contact due to the changing role of third body particles such as hard oxides which can result in abrasion. The abrasion due to hard oxide particles differs for the closed contact and intermittently opened contact. In the former scenario, the oxides are compacted into tribo-film, while in the latter case they remain loose, leading to bigger role of abrasion. Standard fretting test setup employed to estimate the fretting wear characteristic operates with a constant load such that the contact remains closed between the counter surfaces and does not simulate the opening and closing of the contacts as observed in certain applications. The forceful interruptions to the experiments to simulate open and close condition of the contact require considerable amount of time and effort. In this paper, an accelerated test procedure is proposed and investigated to capture the effect of intermittent opening of the contact without stopping the experiments. A test rig is designed to simulate the opening and closing conditions, and tests were performed with abrasive diamond-like particles. Friction and wear results are compared with those of intermittently contact opening conditions along with operating wear mechanisms. Scanning electron microscope analysis showed that the wear mechanism observed in the case of fretting with intermittent opening of contact is similar to that of fretting with diamond-like abrasives at the contact.     

Capacity management under uncertainty with inter-process, intra-process and demand interdependencies in high-flexibility environments

In this paper, we develop models for capacity planning within the framework of stochastic processing times and stochastic demand for different process outcomes in high-flexibility environments. We particularly address stochastic interdependencies between processing times for different processes (inter-process correlation), interdependencies between the capacity consumption (task times) of different executions of the same task in a given production stage (intra-process correlation) as well as interdependencies between the demand for different process outcomes. After presenting the base model, we conduct extensive sensitivity analyses and analyze the main relationships between different model variables. We use process and demand data from the financial industry to demonstrate the applicability and relevance of our findings.     

Identification and Optimization of the First Highly Selective GLUT1 Inhibitor BAY‐876

Despite the long‐known fact that the facilitative glucose transporter GLUT1 is one of the key players safeguarding the increase in glucose consumption of many tumor entities even under conditions of normal oxygen supply (known as the Warburg effect), only few endeavors have been undertaken to find a GLUT1‐selective small‐molecule inhibitor. Because other transporters of the GLUT1 family are involved in crucial processes, these transporters should not be addressed by such an inhibitor. A high‐throughput screen against a library of ～3 million compounds was performed to find a small molecule with this challenging potency and selectivity profile. The N‐(1H‐pyrazol‐4‐yl)quinoline‐4‐carboxamides were identified as an excellent starting point for further compound optimization. After extensive structure–activity relationship explorations, single‐digit nanomolar inhibitors with a selectivity factor of >100 against GLUT2, GLUT3, and GLUT4 were obtained. The most promising compound, BAY‐876 [N⁴‐[1‐(4‐cyanobenzyl)‐5‐methyl‐3‐(trifluoromethyl)‐1H‐pyrazol‐4‐yl]‐7‐fluoroquinoline‐2,4‐dicarboxamide], showed good metabolic stability in vitro and high oral bioavailability in vivo.     

Liquid Phase CO2-Analytics for Standardized Mass Transfer Characterization in Packed Columns

Mass transfer parameters are necessary for the design of absorption and desorption processes in packed columns. To determine the effective interfacial area and liquid side mass transfer parameters, CO₂ absorption and desorption are frequently used. Reliable analytics for concentration determination are essential to obtain correct results. In this work two methods of CO₂ liquid phase analysis are compared: first, the back titration of unreacted NaOH after prior precipitation of the bound CO₂; secondly, the inorganic carbon analysis with a commercial inorganic carbon analyzer.     

Influence of drying conditions on colour,betacyanin content and antioxidant capacities in dried red-fleshed dragon fruit (Hylocereus polyrhizus)

In this study, drying of red-fleshed dragon fruit at different temperatures (40, 50, 60, 70 and 80 °C) and air velocities (1.0 and 1.5 m s⁻¹) was conducted under the specific humidity of 25 g H₂O kg⁻¹ dry air. The results showed that drying at higher temperatures resulted in shorter drying times. However, temperature and air velocity did not significantly affect the total betacyanin contents and antioxidant capacities in dried products. Seven betacyanins identified by LC-MS were betanin, isobetanin, phyllocactin, isophyllocactin, betanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside, isobetanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside and decarboxylated phyllocactin. In addition, the temperature increased the isomerisation of betacyanins. The most preferable condition for preserving the colour and betacyanin contents of red-fleshed dragon fruit was the drying at a temperature of 80 °C and air velocity of 1.5 m s⁻¹ since it could shorten the drying time and give a bright red colour to the dried product as well as it had no significant impact on the betacyanins.     

Electrospray ionization mass spectrometry fingerprinting of Brazilian cacha?as produced in copper alembic and in stainless-steel column stills

Brazilian cacha?a can be produced in two different ways: distilled in stainless steel column or in copper alembic stills. We evaluated 36 samples of commercial non-aged cacha?as: 18 samples of sweetened cacha?as distilled in stainless steel column, and 18 samples distilled in copper alembic stills. Fingerprints were obtained through electrospray ionization mass spectrometry by recording the intensity of the 15 most abundant ions. Principal component analysis was applied to the data and separated the samples in two groups. However, after sample standardization with sugar (20?g?L^?1), it was not possible to group them by type of distillation. The results showed that the technique applied did not allow differentiation of cacha?as based on the distillation system, but for the presence or absence of sugar in them.     

Ilmenite with addition of NiO as oxygen carrier for chemical-looping combustion

The naturally occurring mineral ilmenite, FeTiO₃, has been examined as oxygen carrier for chemical-looping combustion. NiO-based particles have been used as an additive, in order to examine if it is possible to utilize the catalytic properties of metallic Ni to facilitate decomposition of hydrocarbons into more reactive combustion intermediates such as CO and H₂. Firstly, ilmenite was examined by oxidation and reduction experiments in a batch fluidized-bed reactor. These experiments indicated moderate reactivity between ilmenite and CH₄, which was used as reducing gas. However, adding 5 wt.% of NiO-based particles to the ilmenite improved the conversion of CH₄ greatly, resulting in an increase in combustion efficiency with a factor of 3. Secondly, 83 h of chemical-looping combustion experiments were conducted in a small circulating fluidized-bed reactor, using ilmenite as oxygen carrier and natural gas as fuel. A wide range of process parameters and different levels of NiO addition were examined. Occasionally, there were problems with the circulation of solids between the air reactor and fuel reactor, but most of the time the experiments worked well. The products were mostly CO₂, H₂O and unconverted CH₄. Adding small amounts of NiO-based particles to the reactor increased the conversion of the fuel considerably. For the base case conducted at 900°, the combustion efficiency was 76% for pure ilmenite and 90% for the corresponding experiments with 1 wt.% NiO-based particles added to the reactor. The properties of ilmenite were found to change considerably during operation. Used particles had lower density, were more reactive and more porous than fresh particles. These changes appear to have been physical, and no unexpected chemical phases could be identified.