Absorption methods for the determination of mass transfer parameters of packing internals: A literature review

Methods for the determination of mass‐transfer coefficients and effective interfacial areas in packed absorption columns are reviewed. For each parameter, the methods are grouped into categories on the basis of their physical principle; the chemical systems used, experimental protocol, and the advantages and inconveniences are discussed. The treatment of end effects, the influence of packed bed height, and the recent efforts in standardization of measurement methods are also treated. The aim of the review is to give a broad overview of the methods used in literature in the last eight decades, some of which might be reconsidered in the light of modern measurement techniques and to evaluate them in relation to precision, practicality and hazardousness thereby to facilitate the search for reliable, precise, and convenient experimental practices. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3246–3275, 2017     

Epigenetic Regulation of Endothelial Dysfunction and Inflammation in Pulmonary Arterial Hypertension

Once perceived as a disorder treated by vasodilation, pulmonary artery hypertension (PAH) has emerged as a pulmonary vascular disease with severe endothelial cell dysfunction. In the absence of a cure, many studies seek to understand the detailed mechanisms of EC regulation to potentially create more therapeutic options for PAH. Endothelial dysfunction is characterized by complex phenotypic changes including unchecked proliferation, apoptosis-resistance, enhanced inflammatory signaling and metabolic reprogramming. Recent studies have highlighted the role of epigenetic modifications leading to pro-inflammatory response pathways, endothelial dysfunction, and the progression of PAH. This review summarizes the existing literature on epigenetic mechanisms such as DNA methylation, histone modifications, and non-coding RNAs, which can lead to aberrant endothelial function. Our goal is to develop a conceptual framework for immune dysregulation and epigenetic changes in endothelial cells in the context of PAH. These studies as well as others may lead to advances in therapeutics to treat this devastating disease.     

Modified fully utilized design (MFUD) method for stress and displacement constraints

The traditional fully stressed method performs satisfactorily for stress-limited structural design. When this method is extended to include displacement limitations in addition to stress constraints, it is known as the Fully Utilized Design (FUD). Typically, the FUD produces an overdesign, which is the primary limitation of this otherwise elegant method. We have modified FUD in an attempt to alleviate the limitation. This new method, called the Modified Fully Utilized Design (MFUD) method, has been tested successfully on a number of problems that were subjected to multiple loads and had both stress and displacement constraints. The solutions obtained with MFUD compare favourably with the optimum results that can be generated by using non-linear mathematical programming techniques. The MFUD method appears to have alleviated the overdesign condition and offers the simplicity of a direct, fully stressed type of design method that is distinctly different from optimization and optimality criteria formulations. The MFUD method is being developed for practicing engineers who favour traditional design methods rather than methods based on advanced calculus and non-linear mathematical programming techniques. The Integrated Force Method (IFM) was found to be the appropriate analysis tool in the development of the MFUD method. In this paper, the MFUD method and its optimality are examined along with a number of illustrative examples. © 1998 This paper was produced under the auspices of the U.S. Government and it is therefore not subject to copyright in the U.S.     

Grain velocity distribution in a mixed flow dryer

For corn drying one of the most popular possibilities in Europe is to use a mixed flow dryer. Large differences in the vertical grain particle velocity in this type of dryers are causing differences in the residence time. Hence, uneven drying occurs causing under-drying or over-drying of grain portions. To investigate the influences of the dryer walls and the air ducts on the particle velocity distribution experiments have been carried out in industrial and laboratory sized dryers and the measurements were compared with discrete element models. The particle flow velocity distribution between the air ducts is modelled analytically based on arching hypothesis. Using discrete element models the effects of different possible constructional modifications causing more even vertical grain particle velocity distribution were analyzed.     

Application of In Situ Neutron and X-Ray Measurements at High Temperatures in the Development of Co-Re-Based Alloys for Gas Turbines

Co-Re alloy development is prompted by the search for new materials for future gas turbines which can be used at temperatures considerably higher than the current day single crystal Ni-based superalloys. The Co-Re-based alloys have been designed to have very high melting range, and they are meant for application at +373 K (+100 °C) above Ni-superalloys. They are significantly different from the conventional Co-based alloys that are used in static components of today??s gas turbines, and the Co-Re alloys have never been used for structural applications before. The Co-Re-Cr system has complex microstructure with many different phases present. Phase transformations and stabilities of fine strengthening precipitates at high temperatures remain mostly unexplored in the Co-Re alloys, and to develop basic understanding, model ternary and quaternary compositions were studied within the alloy development program. In situ neutron and synchrotron measurements at high temperatures were extensively used for this purpose, and some recent results from the in situ measurements are presented. In particular, the effect of boron doping in Co-Re alloys and the stabilities of the fine TaC precipitates at high temperatures were investigated. A fine dispersion of TaC precipitates strengthens some Co-Re alloys, and their stabilities at the application temperatures are critical. In the beginning, the alloy development strategy is very briefly discussed.     

Densification and structural change of mechanically alloyed W-Cu composites

Fine-grained, high-density (97+ pct of theoretical density (TD)), 80W-20Cu wt pct (58W-42Cu at. pct) composites have been prepared using nonconventional alloying techniques. The W and Cu precursor powders were combined by a high-energy ball-milling procedure in air or hexane. The mechanically alloyed W+Cu powder mixtures were then cold pressed into green compacts and sintered at 1523 K. The milling medium and milling time were varied to increase product densities with a concomitant order-of-magnitude decrease in grain size. For densification, air was found to be a more effective medium than hexane. From microhardness measurements, it was concluded that the W-Cu alloys were dispersion and solution hardened, but were sensitive to entrapped residual impurities. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron micros-copy (SEM) analyses were used to demonstrate that the as-milled and sintered W-Cu alloy structures were metastable, decomposing into the starting W and Cu components upon heating at or above 723 K.     

Oxidative dehydrogenation and cracking of ethane and propane over LiDyMg mixed oxides

The oxidative dehydrogenation and cracking of ethane and propane over LiDyMg mixed oxides is reported. High yields of olefins and only moderate formation of carbon oxides was observed. Both are primary products that hardly interconvert under the reaction conditions used. Addition of chloride increases the rate of reaction, while slightly decreasing the selectivity to olefins. The addition of carbon dioxide strongly decreases the rate of reaction, the negative order of 0.5 indicating that two active Li⁺sites are blocked by the adsorption of one CO₂molecule. The reaction proceeds at low oxygen pressure primarily via elimination of dihydrogen, while at higher oxygen partial pressure the hydrogen elimination occurs via water formation. It is speculated that dehydrogenation and cracking involve Li⁺and a rather nucleophilic oxygen site.     

Pulsed laser reshaping and fragmentation of upconversion nanoparticles — from hexagonal prisms to 1D nanorods through “Medusa”-like structures

One dimensional (1D) nanostructures attract considerable attention, enabling a broad application owing to their unique properties. However, the precise mechanism of 1D morphology attainment remains a matter of debate. In this study, ultrafast picosecond (ps) laser-induced treatment on upconversion nanoparticles (UCNPs) is offered as a tool for 1D-nanostructures formation. Fragmentation, reshaping through recrystallization process and bioadaptation of initially hydrophobic (β-Na_1.5Y_1.5F₆: Yb³⁺, Tm³⁺/β-Na_1.5Y_1.5F₆) core/shell nanoparticles by means of one-step laser treatment in water are demonstrated. “True” 1D nanostructures through “Medusa”-like structures can be obtained, maintaining anti-Stokes luminescence functionalities. A matter of the one-dimensional UCNPs based on direction of energy migration processes is debated. The proposed laser treatment approach is suitable for fast UCNP surface modification and nano-to-nano transformation, that open unique opportunities to expand UCNP applications in industry and biomedicine.