Diffusion of Small Molecules in Metal Organic Framework Materials

Ab initio simulations are combined with in situ infrared spectroscopy to unveil the molecular transport of H$_2$, CO$_2$, and H$_2$O in the metal organic framework MOF-74-Mg. Our study uncovers---at the atomistic level---the major factors governing the transport mechanism of these small molecules. In particular, we identify four key diffusion mechanisms and calculate the corresponding diffusion barriers, which are nicely confirmed by time-resolved infrared experiments. We also answer a long-standing question about the existence of secondary adsorption sites for the guest molecules, and we show how those sites affect the macroscopic diffusion properties. Our findings are important to gain a fundamental understanding of the diffusion processes in these nano-porous materials, with direct implications for the usability of MOFs in gas sequestration and storage applications.Comment: 5 pages, 2 figures and supplementary material, Phys. Rev. Let

Sewerage pumping station optimization under real conditions

Construction of a sewer system on a flat area is characterized by a large number of pumping stations (PS), which implies the probability of occurrence of technical problems and increases operational costs. The article focuses on drainage methods for municipalities situated on a flat area where it is necessary to build up a large number of pumping stations. Problems occur in case of multiple serial, parallel or combined connections of PSs. Energy costs can outweigh other costs, especially if the PS runs more than 2000 hours per year (Wilson et al., 2010). It has been shown that there is a large technical and economic potential for energy savings in sewage pumping. The pumping of waste waters in Slovakia is mostly based on the START-STOP method. This means that the pumps operate at all times at full power. In practice, we can also meet with oversizing of pumps. These and other facts lead to increased power consumption. Also rainwater infiltration and “black” stormwater connections belong to significant present problems in sewer system operation. Large amounts of storm water in a sewerage PS lead to increasing intensity of waste-water pumping, which is reflected in increasing operational costs. Optimization of such sewer system is based on mathematical modelling and was implemented in the “Ivanka pri Dunaji” municipality, close to Bratislava – the capital of Slovakia where the above mentioned problems in wastewater discharge cause considerable operating costs and inefficient performance of the system as a whole for a long time. Due to the enormous houses development, the system is inadequately loaded by rain waters as well. Also poor discipline of property owners contributes to the inauspicious situation to a great extent. Despite a ban of connections, paved areas are drained into the sewage system very often. The identification of such connections is very problematic with regard to ownership rights. Rain waters in sewages can degrade the quality of wastewaters, increase operating costs of pumping and reduce system life cycle. It was demonstrated by mathematical modelling that with the use of information technologies, it is possible to make the existing sewerage systems more effective or propose a new system of pumping and discharging waste waters.Pre výstavbu stokovej siete v rovinatom území je typické značné množstvo čerpacích staníc (ČS), čo implikuje pravdepodobnosť vzniku technických problémov a zvyšuje náklady na prevádzku. Príspevok je zameraný na spôsoby odkanalizovania obcí situovaných v rovinatom území, kde je potrebné budovať veľký počet čerpacích staníc (ČS). Problémy nastávajú pri niekoľkonásobnom sériovom, paralelnom alebo kombinovanom zapojení ČS. Spotreba energie tvorí často najväčšiu nákladovú položkou celkových nákladov generovaných počas životného cyklu čerpadla. Náklady na energiu môžu dominovať ostatným nákladom, hlavne ak je čerpadlo v chode viac ako 2000 hodín za rok (Wilson et al., 2010). Bolo dokázané, že existuje veľký technický a ekonomický potenciál úspor energie pri čerpaní splaškových vôd. V praxi sa môžeme veľmi často stretnúť s predimenzovaním čerpadiel. Tieto a ďalšie skutočnosti vedú k zvýšeniu spotreby elektrickej energie. Významným problémom pri prevádzke stokových sieti je aj infiltrácia dažďových vôd a nedovolené pripojenie dažďových zvodov do splaškovej kanalizácie. Množstvo dažďových vôd v ČS v značnej miere ovplyvňuje čerpanie OV, čo sa prejavuje zvýšením nákladov na prevádzku ČS. Optimalizácia takýchto sietí je v značnej miere založená na matematickom modelovaní a bola použitá na kanalizácií obce Ivanka pri Dunaji, kde vyššie uvedené problémy v odvádzaní odpadových vôd už dlhší čas spôsobujú nemalé prevádzkové problémy - zvýšenie prevádzkových nákladov a neefektívny výkon systému ako celku. Systém je v dôsledku enormnej výstavby rodinných domov neprimerane zaťažovaný aj vodami, ktoré zaťažujú systém v čase dažďa. Nemalou mierou k tomu prispieva zlá disciplína majiteľov nehnuteľností v zmysle napojenia spevnených plôch na kanalizáciu. Tieto plochy sú aj napriek zákazu pripojenia mnohokrát zvedené práve do systému splaškovej kanalizácie. Identifikácia takýchto napojení je problematická vzhľadom na vlastnícke práva majiteľov nehnuteľností a tieto napojenia nielenže zhoršujú kvalitu odpadovej vody, ale implikujú zvýšené prevádzkové náklady na čerpanie a znižujú životnosť systému. Matematickým modelovaním bolo preukázané, že pri využití informačných technológii môžeme zefektívniť prevádzku už jestvujúcich sieti alebo navrhnúť nový systém odvádzania a prečerpávania odpadových vôd

First-principles approach to rotational-vibrational frequencies and infrared intensity for H2_2 adsorbed in nanoporous materials

The absorption sites and the low-lying rotational and vibrational (RV) energy states for H$_2$ adsorbed within a metal-organic framework are calculated via van der Waals density functional theory. The induced dipole due to bond stretching is found to be accurately given by a first-principles driven approximation using maximally-localized-Wannier-function analysis. The strengths and positions of lines in the complex spectra of RV transitions are in reasonable agreement with experiment, and in particular explain the experimentally mysteriously missing primary line for para hydrogen

Real-time, in situ monitoring of surface reactions during plasma passivation of GaAs

Real-time, in situ observations of surface chemistry during the remote plasma passivation of GaAs is reported herein. Using attenuated total reflection Fourier transform infrared spectroscopy, the relative concentrations of -As-O, -As-H, -H2O, and -CH2 bonds are measured as a function of exposure to the effluent from a microwave discharge through NH3, ND3, H2, and D2. The photoluminescence intensity (PL) from the GaAs substrate is monitored simultaneously and used qualitatively to estimate the extent of surface state reduction. It was found that, while the -CHx(x = 2,3) and -As-O concentrations are reduced rapidly, the rates at which the -As-H concentration and the PL intensity increase are relatively slow. The concentration of -H2O on the GaAs surface increases throughout the process as surface arsenic oxides and the silica reactor walls are reduced by atomic hydrogen. These observations suggest that removal of elemental As by reaction with H at the GaAs–oxide interface limits the passivation rate

Competitive co-adsorption of CO2 with H2O, NH3, SO2, NO, NO2, N2, O2, and CH4 in M-MOF-74 (M= Mg, Co, Ni): the role of hydrogen bonding

The importance of co-adsorption for applications of porous materials in gas separation has motivated fundamental studies, which have initially focused on the comparison of the binding energies of different gas molecules in the pores (i.e. energetics) and their overall transport. By examining the competitive co-adsorption of several small molecules in M-MOF-74 (M= Mg, Co, Ni) with in-situ infrared spectroscopy and ab initio simulations, we find that the binding energy at the most favorable (metal) site is not a sufficient indicator for prediction of molecular adsorption and stability in MOFs. Instead, the occupation of the open metal sites is governed by kinetics, whereby the interaction of the guest molecules with the MOF organic linkers controls the reaction barrier for molecular exchange. Specifically, the displacement of CO2 adsorbed at the metal center by other molecules such as H2O, NH3, SO2, NO, NO2, N2, O2, and CH4 is mainly observed for H2O and NH3, even though SO2, NO, and NO2, have higher binding energies (~70-90 kJ/mol) to metal sites than that of CO2 (38 to 48 kJ/mol) and slightly higher than water (~60-80 kJ/mol). DFT simulations evaluate the barriers for H2O->CO2 and SO2->CO2 exchange to be - 13 and 20 kJ/mol, respectively, explaining the slow exchange of CO2 by SO2, compared to water. Furthermore, the calculations reveal that the kinetic barrier for this exchange is determined by the specifics of the interaction of the second guest molecule (e.g., H2O or SO2) with the MOF ligands

Puentes, 1802: la rupture du plus grand barrage du monde, ou le double echec d’Antonio de Robles. Le rapport Betancourt

Peer Reviewe

Promotion infirmière: la mobilité des personnes âgées : travail de Bachelor

Thème. Plusieurs études cherchent à démontrer que l’hospitalisation est un facteur de risque pour la perte de mobilité chez la personne âgée, principalement dans les unités de soins aigus. Une perte de mobilité entraine des répercussions multi-systémiques et augmente le risque d’isolement social et de dépression. En prévision du vieillissement de la population, il est important de se demander, comment et par quels moyens l’infirmier peut intervenir pour favoriser le développement de comportements de santé positifs liés à la mobilité chez la personne âgée hospitalisée et sa famille. Contenus. Ce travail est une revue de littérature analysant un total de six articles. Les recherches ont été menées sur différentes bases de données, parmi lesquelles Cinahl, PubMed et BDSP. Les articles concernant les interventions infirmières, les personnes âgées hospitalisées, la mobilité et l’approche systémique familiale ont été retenus. Discussion. Les différents articles analysés exposent des résultats similaires. Ceux-ci proposent des interventions telles que, la promotion de la mobilité, la mise en place de programmes de mobilité adaptés aux personnes âgées, l’amélioration des connaissances gériatriques au sein de l’équipe infirmière, une prise en soins interdisciplinaire de la personne âgée, l’utilisation d’échelles permettant d’évaluer et surveiller la mobilité et finalement l’inclusion dans le processus de soins de la famille. C’est dans cette optique que le choix du modèle de McGill est apparu comme approprié à cette démarche