| 81. |
- Mihai, Oana, 1975, et al.
(författare)
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The effect of Cu-loading on different reactions involved in NH3-SCR over Cu-BEA catalysts
- 2014
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 311, s. 170-181
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the effect of varying copper loading in Cu-BEA on different reactions involved in the SCR mechanism. The catalysts were characterized by BET, ICP-AES, and UV-Vis. Enlarged ammonia storage was observed when increasing the copper loading mainly owing to loosely bonded NH3, but for over-exchanged samples, a new high-temperature shoulder was also observed. The N2O production significantly grew with increasing copper loading. In addition, the reaction rates of NO oxidation and NH3 oxidation per Cu site were higher on the high-loaded copper samples compared to those with lower loading. However, the opposite results were found for NH3 SCR, but differences were small for this reaction. Ammonium nitrate formation and decomposition were examined during a variety of temperature-programmed desorption (TPD) experiments, and three regions related to the presence of acid sites and low- versus high-loaded copper sites were observed. When dosing NO2 before NH3, ammonium nitrate species were formed but in lower amounts than if NH3 and NO2 were dosed simultaneously.
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| 82. |
- Mihai, Oana, 1975, et al.
(författare)
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The Effect of NO2/NOx Feed Ratio on the NH3-SCR System Over Cu–Zeolites with Varying Copper Loading
- 2014
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 144:1, s. 70-80
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Tidskriftsartikel (refereegranskat)abstract
- In this study we examine the NO/NO2–NH3-SCR system over Cu–BEA with varying Cu loading. Significantly higher selective catalytic reduction (SCR) activity is observed at low temperature on highly loaded copper samples, whereas the reverse trend is noticed at high temperature. The N2O formation is substantially increased over “over-exchanged” Cu sites, where Cu co-ordinate to one Al and charge-balanced with one OH-group. This is also the case for NO2 reaction with NH3 to produce NO. Using transient experiments the formation/decomposition of ammonium nitrate species are examined. The decomposition depends on the temperature, the sequence of the feed as well as the type of copper species present.
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| 83. |
- Oltean, Mihai, 1976, et al.
(författare)
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Optimal Solution Volume for Luminal Preservation: A Preclinical Study in Porcine Intestinal Preservation
- 2016
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Ingår i: Transplantation Proceedings. - : Elsevier BV. - 0041-1345. ; 48:2, s. 532-535
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Tidskriftsartikel (refereegranskat)abstract
- Background. Rodent studies suggest that luminal solutions alleviate the mucosal injury and prolong intestinal preservation but concerns exist that excessive volumes of luminal fluid may promote tissue edema. Differences in size, structure, and metabolism between rats and humans require studies in large animals before clinical use. Methods. Intestinal procurement was performed in 7 pigs. After perfusion with histidine-tryptophan-ketoglutarate (HTK), 40-cm-long segments were cut and filled with 13.5% polyethylene glycol (PEG) 3350 solution as follows: VO (controls, none), V1 (0.5 mL/cm), V2 (1 mL/cm), V3 (1.5 mL/cm), and V4 (2 mL/cm). Tissue and luminal solutions were sampled after 8, 14, and 24 hours of cold storage (CS). Preservation injury (Chiu score), the apical membrane (Z0-1, brush-border maltase activity), and the electrolyte content in the luminal solution were studied. Results. In control intestines, 8-hour CS in HTK solution resulted in minimal mucosal changes (grade 1) that progressed to significant subepithelial edema (grade 3) by 24 hours. During this time, a gradual loss in ZO-1 was recorded, whereas maltase activity remained unaltered. Moreover, variable degrees of submucosal edema were observed. Luminal introduction of high volumes (2 mUmL) of PEG solution accelerated the development of the subepithelial edema and submucosal edema, leading to worse histology. However, ZO-1 was preserved better over time than in control intestines (no luminal solution). Maltase activity was reduced in intestines receiving luminal preservation. Luminal sodium content decreased in time and did not differ between groups. Conclusions. This PEG solution protects the apical membrane and the tight-junction proteins but may favor water absorption and tissue (submucosal) edema, and luminal volumes >2 mL/cm may result in worse intestinal morphology.
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| 84. |
- Oltean, Mihai, 1976, et al.
(författare)
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Organ-Specific Solutions and Strategies for the Intestinal Preservation
- 2014
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Ingår i: International Reviews of Immunology. - : Informa UK Limited. - 0883-0185 .- 1563-5244. ; 33:3, s. 234-244
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Forskningsöversikt (refereegranskat)abstract
- Among the intraabdominal organs, the intestine is the most susceptible to storage injury and as a consequence its safe cold ischemic time in the clinic is restricted to below 10hours. The current practice for the intestinal preservation (IP) consists of an in-situ vascular flush with iced University of Wisconsin or Histidine-Tryptophan-Ketoglutarate solution followed by cold storage at 4°C. Mucosal injury is initiated within 1hour and rapidly progresses to mucosal breakdown; tissue injury worsens upon reperfusion and further impairs the mucosal barrier, favoring bacterial translocation and sepsis. In addition of releasing danger signals, an advanced ischemia-reperfusion injury (IRI) may increase graft immunogenicity and promote rejection. Several alternative approaches have been tested as alternatives to the static storage. The aim of this review is to summarize and discuss the various intraluminal interventions as additional strategies aiming to reduce the IP/reperfusion injury and highlight the underlying pathophysiological mechanisms.
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| 85. |
- Oltean, Mihai, 1976, et al.
(författare)
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The microsurgical training programme in Gothenburg, Sweden: early experiences
- 2017
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Ingår i: Journal of Plastic Surgery and Hand Surgery. - : Medical Journals Sweden AB. - 2000-656X .- 2000-6764. ; 51:3, s. 193-198
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Microsurgical techniques are increasingly used in routine surgical practice as well as in biomedical research. The training opportunities at standardised training courses are limited, and no microsurgical training facility or programme existed in Scandinavia before 2013. Methods: A microsurgery laboratory was set up and two different courses were started, aiming separately at biomedical researchers and surgeons. The course for biomedical researchers teaches basic microsurgical skills such as vessel isolation, cannulation, and arterial microvascular suture under magnification. The more advanced course for surgeons focuses on various techniques of microvascular and nerve anastomosis. Both courses use a combination of theory and practice, with emphasis on the practical part, the course for surgeons also includes clinically relevant information. Results: Twelve 5-day courses using both non-living models and exercises on laboratory animals have been conducted and attended by 49 researchers and 44 surgeons. The organisation and the programme of the training courses as well as 'The 4E concept' behind the course (educational curriculum, equipment, ergonomy, and evaluation) are further detailed. Conclusions: We have successfully established the first training laboratory and series of microsurgical training courses in Scandinavia at two different levels. The experience from the first 12 courses shows the need for this type of structured training, and confirms that the microsurgical education curriculums needs to be adapted to participants' prerequisites and expectations, and various difficulty levels should be considered.
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| 86. |
- Oprea, Corneliu I., et al.
(författare)
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Comparative computational IR, Raman and phosphorescence study of Ru- and Rh-based complexes
- 2013
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Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 111:9-11, s. 1526-1538
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Tidskriftsartikel (refereegranskat)abstract
- We report density functional theory (DFT) calculations providing the infrared and Raman spectra of [Ru(II)(bpy)(3-n)(dcbpy)(n)](2+) and [Rh(III)(bpy)(3-n)(dcbpy)(n)](3+) complexes, where bpy = 2,2-bipyridyl, dcbpy = 4,4-dicarboxy-2,2-bipyridyl, and n = 0, 1, 2, 3, studied in the context of dye-sensitised solar cells. We compare and contrast the role of the metallic ion and of the COOH groups on the vibration and phosphorescence properties of these complexes. The vibrational spectra are not very sensitive to the replacement of the metal ion, but the presence of carboxyl groups leads to a richer spectrum due to the additional bands caused by the COOH groups. Comparison with the limited experimental data available allowed the assignment of the Raman bands. The calculated phosphorescence lifetimes suffer only modest changes when the COOH groups are introduced but vary significantly when changing the metal ion, being two orders of magnitude larger for Rh(III) than for the Ru(II) complexes.
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| 87. |
- Oprea, Corneliu I., et al.
(författare)
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DFT calculations of a Metal-TCNE complex
- 2007
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Ingår i: Six International Conference of the Balkan Physical Union. - : AIP. - 9780735404045 ; , s. 716-716
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Konferensbidrag (refereegranskat)abstract
- For V[TCNE](x) y(solvent) (TCNE = tetracyanoethylene), the first room-temperature molecular magnet, the mechanism for the strong exchange coupling in the family M[TCNE](x) y(solvent) has remained an open question. hi an attempt to understand the magnetic ordering in these systems we performed density functional theory calculations on a six coordinated vanadium complex with four TCNE molecules. For this model system we find that the ferrimagnetic spin configuration is energetically more favorable and that the highest single-occupied orbital has pi* character.
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| 88. |
- Oprea, Corneliu I., et al.
(författare)
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DFT study of electronic structure and optical properties of some Ru- and Rh-based complexes for dye-sensitized solar cells
- 2011
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Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 109:21, s. 2511-2523
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Tidskriftsartikel (refereegranskat)abstract
- The paper reports Time Dependent Density Functional Theory (TD DFT) calculations providing the structure, electronic properties and spectra of [Ru(II)(bpy)(3-n)(dcbpy)(n)](2+) and [Rh(III)(bpy)(3-n)(dcbpy)(n)](3+) complexes, where bpy = 2,2'-bipyridyl, dcbpy = 4,4'-dicarboxy-2,2'-bipyridyl, and n = 0, 1, 2, 3, studied as possible pigments for dye-sensitized solar cells. The role of the metallic ion and of the COOH groups on the optical properties of these complexes are compared and contrasted and their relevance as dyes for hybrid organic-inorganic photovoltaic cells is discussed. It was found that the optical spectra are strongly influenced by the metallic ion, with visible absorption bands for the Ru(II) complexes and only ultraviolet bands for the Rh(III) complexes. Upon excitation, the extra positive charge of the Rh(3+) centre tends to draw electrons towards the metal ion, facilitating some charge transfer from the ligand to the metal, whereas in the case of the Ru(2+) ion the electron transfer is clearly from the metal to the ligand. The carboxyl groups play an important role in strengthening the absorption bands in solution in the visible region. Of the complexes studied, the most suited as pigments for dye-sensitized solar cells are the [Ru(II)(bpy)(3-n)(dcbpy)(n)](2+) complexes with n = 1 and 2. This is based on the following arguments: (i) their intense absorption band in the visible region, (ii) the presence of the anchoring groups allowing the bonding to the TiO(2) substrate and the charge transfer, and (iii) the good energy level alignment with the conduction band edge of the semiconducting substrate and the redox level of the electrolyte.
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| 89. |
- Oprea, Corneliu I., et al.
(författare)
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DFT study of structure-properties correlations in [MnTPP][TCNE] quasi-one-dimensional molecular magnets
- 2011
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Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 129:6, s. 847-857
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Tidskriftsartikel (refereegranskat)abstract
- We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular magnets. By varying systematically the main angles, we are able to determine the geometry dependence of the exchange interaction. Structure-properties correlations in these charge-transfer salts reveal the determinant role of the Mn-(N C) TCNE bond angle on the strength of the ferrimagnetic coupling between the S(1) = 2 spin located on the Mn(III)-porphyrin donor and the S(2) = 1/2 spin positioned on the cyanocarbon acceptor. When the Mn-(N C) TCNE angle is decreased, the intrachain magnetic coupling strengthens, correlated with the increase in the d(z)(2) - pi* orbital overlap. The exchange coupling constants resulting from DFT calculations of extended systems, with periodic boundary conditions, were found to be consistent with those obtained for the dimers, but systematically smaller. The exchange constants vary strongly with the functional used, hybrid functionals such as B3LYP leading to results that better correlate with the experimental mean-field critical temperatures. The coupling constant varies significantly with the type of broken-symmetry approach, depending on the overlap between magnetic orbitals, but weakly on the basis set once polarization effects are included. The electronic structure calculations for the extended systems provide a density of states consistent with the energy spectrum of the corresponding dimer, allowing for an intuitive explanation of the intrachain ferrimagnetic ordering.
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| 90. |
- Oprea, Corneliu I., et al.
(författare)
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Theoretical study of neutral and reduced hexacyanobutadiene
- 2007
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0166-1280. ; 804:1-3, s. 111-116
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Tidskriftsartikel (refereegranskat)abstract
- The molecular structure and the electronic densities of neutral and anionic hexacyanobutadiene (HCBD), trans-C-4(CN)(6), as well as the electron affinity (EA) of HCBD have been studied using density functional theory (DFT) and perturbation theory (MP2) procedures. The optimized geometries showed that the HCBD molecule is not planar, with a 140 degrees torsion angle about the central C-C bond. While the optimized geometries are not very sensitive to the choice of either the method or the basis set, the adiabatic electron affinity varies significantly with both. All the DFT computed electron affinities overestimate the experimental value, the best results being obtained with the BLYP functional, whereas the MP2 calculations heavily underestimate it. At the NIP2 level, the EA value obtained after projecting out the major spin contaminating component (PMP2) is a good estimate of the EA, within 0.11 eV of the experiment. Although other studies suggested that single-point PMP2 calculations over DFT-optimized geometries could be a valuable alternative for the study of larger systems at low computational effort, our results indicate that this approach can increase the spin contamination and should be used with caution.
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