Université catholique de Louvain

About: Université catholique de Louvain is a education organization based out in Louvain-la-Neuve, Belgium. It is known for research contribution in the topics: Population & Catalysis. The organization has 25319 authors who have published 57360 publications receiving 2172080 citations. The organization is also known as: University of Louvain & UCLouvain.

How linker’s modification controls swelling properties of highly flexible iron(III) dicarboxylates MIL-88

Abstract: A series of organically modified iron(III) terephthalate MIL-88B and iron(III) 4,4′-biphenyl dicarboxylate MIL-88D flexible solids have been synthesized and characterized through a combination of X-ray diffraction, IR spectroscopy, and thermal analysis (MIL stands for Material from Institut Lavoisier). The swelling amplitude of the highly flexible MOFs tuned by introducing functional groups onto the phenyl rings shows a clear dependence on the steric hindrance and on the number of groups per aromatic ring. For instance, while the introduction of four methyl groups per spacer in dried MIL-88B results in a large permanent porosity, introducing two or four methyl groups in MIL-88D allows an easier pore opening in the presence of liquids without drastically decreasing the swelling magnitude. The influence of the degree of saturation of the metal center and the nature of the solvent on the swelling is also discussed. Finally, a computationally assisted structure determination has led to a proposal of plausible...

Conditional nonparametric frontier models for convex and nonconvex technologies: A unifying approach

Abstract: The explanation of productivity differentials is very important to identify the economic conditions that create inefficiency and to improve managerial performance. In the literature two main approaches have been developed: one-stage approaches and two-stage approaches. Daraio and Simar (2005, J Prod Anal 24(1):93-121) propose a fully nonparametric methodology based on conditional FDH and conditional order-m frontiers without any convexity assumption on the technology. However, convexity has always been assumed in mainstream production theory and general equilibrium. In addition, in many empirical applications, the convexity assumption can be reasonable and sometimes natural. Lead by these considerations, in this paper we propose a unifying approach to introduce external-environmental variables in nonparametric frontier models for convex and nonconvex technologies. Extending earlier contributions by Daraio and Simar (2005, J Prod Anal 24(1):93-121) as well as Cazals et al. (2002, J Econometrics 106:1-25), we introduce a conditional DEA estimator, i.e., an estimator of production frontier of DEA type conditioned to some external-environmental variables which are neither inputs nor outputs under the control of the producer. A robust version of this conditional estimator is proposed too. These various measures of efficiency provide also indicators of convexity which we illustrate using simulated and real data.

The Thermoelectric Properties of Bismuth Telluride

Abstract: DOI: 10.1002/aelm.201800904 made for efficient thermoelectric cooling or temperature management uses Bi2Te3 alloys. Such solid-state devices dominate the market for temperature control in optoelectronics. As the need to eliminate greenhouse-gas refrigerants increases, Peltier cooling is becoming more attractive particularly in small systems where efficiencies are comparable to traditional refrigerant based cooling. Such small devices may enable distributive heating/ cooling (only where and when it is needed) with higher system level energy efficiency, for example in electric vehicles where energy for heating/cooling competes with vehicle range. Even for thermoelectric power generation, e.g., recovery of waste heat, Bi2Te3 alloys are most used because of superior efficiency up to 200 °C and the technology to make devices with Bi2Te3 is most advanced.[1–3] While the material and production technology for making Bi2Te3-based devices has remained essentially unchanged since the 1960s, our understanding of these materials has advanced considerably. Most recently, the interest in topological insulators (TI) has led to new insights into the complex electronic structure[4,5] revealing that with the accuracy in assessing the band structures available today, improvements in the electronic structure by band engineering should not only be possible but predictable.[6–9] Indeed, the p-type alloys chosen for use in commercial Peltier coolers appear to have unintentionally arrived at a composition close to a band convergence. The understanding of defects and doping is also advancing rapidly that will lead to new strategies for additional improvements in the electronic properties. The thermal conductivity of Bi2Te3-based alloys can also be engineered, where in particular there is much recent interest in microstructure engineering or nanostructuring.[10–22] Reduced thermal conductivity has led to numerous reports of exceptionally high efficiency (zT) that would be sufficient to revolutionize the industry. However, between measurement and material uncertainties, a revolutionary new Bi2Te3-based material has not made it to the market. Because even small but reliable improvements could make significant impact, it is worthwhile to better understand all the complex, interdependent effects of band engineering and microstructure engineering. To demonstrate and quantify improvements in thermoelectric properties, it is necessary to have well characterized properties or reliable benchmarks for comparison. Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi2Te3 (or more precisely its alloys with Sb2Te3 for p-type and Bi2Se3 for n-type material) has the highest thermoelectric figure of merit, zT, of any material around room temperature. Since thermoelectric technology will be greatly enhanced by improving Bi2Te3 or finding a superior material, this review aims to identify and quantify the key material properties that make Bi2Te3 such a good thermoelectric. The large zT can be traced to the high band degeneracy, low effective mass, high carrier mobility, and relatively low lattice thermal conductivity, which all contribute to its remarkably high thermoelectric quality factor. Using literature data augmented with newer results, these material parameters are quantified, giving clear insight into the tailoring of the electronic band structure of Bi2Te3 by alloying, or reducing thermal conductivity by nanostructuring. For example, this analysis clearly shows that the minority carrier excitation across the small bandgap significantly limits the thermoelectric performance of Bi2Te3, even at room temperature, showing that larger bandgap alloys are needed for higher temperature operation. Such effective material parameters can also be used for benchmarking future improvements in Bi2Te3 or new replacement materials.