Laminar burning velocity of liquefied petroleum gas mixtures

This thesis reports experimental and theoretical studies of the laminar burning velocity of liquefied petroleum gas (LPG) measured using the constant volume bomb method. The test rig designed at Loughborough University was a rigid and spherical chamber with central ignition. The LPG gas used in this study is a mixture of propane and n-butane with volume percentage of n-butane ranging from 0 to 100. The laminar burning velocities of the LPG/air mixtures have been determined over a range of equivalence ratios (0.7 to 1.4), unburnt gas pressures and temperatures (0.5 to 37 bar and 293 to 530 K respectively). With the measured pressure/time history in the constant volume combustion chamber, a new combustion model, which was developed based on a commonly used two-zone combustion model, was used to determine the laminar burning velocity. To obtain a more accurate value of the laminar burning velocity, the assumptions in the two-zone combustion model were analysed, and two effects were considered in the new combustion model, i.e. the effect of flame thickness and the effect of temperature gradient in the burnt gas zone. [Continues.

Case Studies of Environmental Visualization

The performance gap between simulation and reality has been identified as a major challenge to achieving sustainability in the Built Environment. While Post-Occupancy Evaluation (POE) surveys are an integral part of better understanding building performance, and thus addressing this issue, the importance of POE remains relatively unacknowledged within the wider Built Environment community. A possible reason that has been highlighted is that POE survey data is not easily understood and utilizable by non-expert stakeholders, including designers. A potential method by which to address this is the visualization method, which has well established benefits for communication of big datasets. This paper presents two case studies where EnViz (short for “Environmental Visualization”), a prototype software application developed for research purposes, was utilized and its effectiveness tested via a range of analysis tasks. The results are discussed and compared with those of previous work that utilized variations of the methods presented here. The paper concludes by presenting the lessons drawn from the five-year period of EnViz, emphasizing the potential of environmental visualization for decision support in environmental design and engineering for the built environment, and suggests directions for future development

Scaling from single-point sap velocity measurements to stand transpiration in a multispecies deciduous forest: Uncertainty sources, stand structure effect, and future scenarios

9 páginas.-- 5 figuras.-- 2 tablas.-- 58 referencias[EN] A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability on transpiration upscaling and explore the potential impacts of future shifts in species composition on the forest water budget. We measured sap velocity in five tree species (Fagus grandifolia Ehrh., Acer rubrum L., Acer saccharum Marsh., Betula alleghaniensis Britton, and Betula papyrifera Marsh.) in a mature stand and a young stand in New Hampshire, USA. Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpiration will depend on the sap velocity, determined not only by radial variation and tree size, but also by the sapwood area distribution in the stand.[FR] Les études dont le but est d'estimer l'utilisation de l'eau a` l'échelle du peuplement dans les forêts mélangées font face a` un défi majeur : comment passer efficacement de l'échelle des arbres individuels a` l'échelle du peuplement. C'est le cas pour les écosystèmes forestiers dans le nord-est des États-Unis où les différences dans l'utilisation de l'eau entre les espèces et parmi les différentes catégories de taille n'ont pas fait l'objet d'études approfondies malgré leur pertinence pour une vaste gamme de services de l'écosystème. Nos objectifs consistaient a` évaluer l'importance des différentes sources de variation sur l'extrapolation de la transpiration et a` explorer les impacts potentiels des changements futurs dans la composition en espèces sur le bilan hydrique de la forêt. Nous avons mesuré la vitesse de la sève chez cinq espèces d'arbre (Fagus grandifolia Ehrh., Acer rubrum L., Acer saccharum Marsh., Betula alleghaniensis Britton et Betula papyrifera Marsh.) dans un peuplement mature et dans un jeune peuplement au New Hampshire (É.-U.). Nos résultats ont montré que la plus grande source potentielle d'erreur était la variation radiale et que la vitesse de la sève était davantage déterminée par la taille des arbres que par l'espèce. La surface totale de bois d'aubier avait un effet très déterminant sur la transpiration qui variait selon la taille et l'espèce d'arbre. Nous concluons que l'effet des changements potentiels dans la composition en espèces sur la transpiration dépendra de la vitesse de la sève qui est principalement déterminée par la variation radiale et la taille des arbres mais aussi de la distribution de la surface de bois d'aubier dans le peuplement.This work was funded by the University of New Hampshire and the New Hampshire Agricultural Experiment Station. The Bartlett Experimental Forest is operated by the USDA Forest Service Northern Research Station. S. Mcgraw, P. Pellissier, C. Breton, S. Alvarado-Barrientos, R. Snyder, and Z. Aldag assisted in the field and in the lab. The 2011 stand inventory was led by S. Goswami. Tree heights were measured and compiled by C. Blodgett, T. Fahey, and L. Liu. A. Richardson shared meteorology and solar radiation data from the Bartlett Amerflux tower. The stands used in this experiment are maintained and monitored by the MELNHE project under the direction of R. Yanai and M. Fisk, with funding from NSF grants DEB 0235650 and DEB 0949324Peer reviewe

Turismo acessível para todos, um paradigma emergente e um desafio para a oferta turística. O caso dos espaços museológicos e empreendimentos turísticos de Cascais.

Reflexão sobre o turismo acessível para todos, como modelo que se revela cada vez mais essencial para todo o sistema turístico, que se afirma não só pela sua relevância social, cívica e demográfica mas também pelas potencialidades económicas associadas. Todavia, o turismo acessível constitui um desafio de adaptação para a oferta turística instalada há vários anos, em destinos turísticos mais antigos, como é o caso de Cascais.Reflection on accessible tourism for all, as an increasingly essential model for the touristic system, that claims not only for its social, civic and demographic significance, but also for the economic potential associated. However, the accessible tourism is an adaptation challenge for the elderly tourism supply, at long-established tourism destinations, such as Cascais

Identification of the Active and Selective Sites over a Single Pt Atom-Alloyed Cu Catalyst for the Hydrogenation of 1,3-Butadiene: A Combined DFT and Microkinetic Modeling Study

Selective hydrogenation of butadiene to butenes is an important industrial process, and a single Pt atom alloyed with a Cu(111) surface shows superior activity and selectivity for this reaction. By utilizing density functional theory calculations combined with microkinetic modeling, herein, we systematically studied the hydrogenation of butadiene over the Pt/Cu(111) single-atom alloy (SAA) catalyst and identified the active sites and probed the product selectivity at different sites under reaction conditions. Although the structure of the SAA is found stable in vacuum, it is likely that aggregation of surface Pt atoms could be induced upon butadiene adsorption, and the aggregated structure shows lower activity than the single Pt site. In addition, we found that the Cu site shows almost identical hydrogenation activity with the Pt site, while considering the concentration of the surface Pt sites, which gives a good explanation on the experimental observations reported previously that the activity of the Pt/Cu(111) SAA catalyst was unaffected by the occupation of CO at Pt sites. Furthermore, all butene isomers produced would preferably desorb rather than being further hydrogenated to butane at the surface sites considered. Although the selectivity between butene isomers over the single Pt sites is different from that over the Cu sites, the overall SAA catalyst gives the same selectivity trend with the single Pt sites. Our work shows, at the molecular level, how different sites over the Pt/Cu(111) SAA catalyst contribute to the hydrogenation activity and product selectivity

Visible-Light-Promoted Oxidative [4 + 2] Cycloadditions of Aryl Silyl Enol Ethers

Visible-light-promoted oxidative [4 + 2] cycloadditions of ε,3-unsaturated silyl enol ethers have been developed to efficiently and diastereoselectively construct polycyclic skeletons under mild conditions. The diastereoselectivities were dependent on the stereoconfiguration of silyl enol ether, substitutions on the link, as well as electric properties of substitutions on aryl rings. The intermediates could be trapped by TEMPO, oxygen or methanol. Mechanistic studies indicated the reaction was initiated by one-electron oxidation of the silyl enol ether

Significance of Surface Formate Coverage on the Reaction Kinetics of Methanol Synthesis from CO₂ Hydrogenation over Cu

The hydrogenation of CO₂ to methanol over copper-based catalysts has attracted considerable attention recently. Among all the proposed reaction mechanisms, a large number of experimental and theoretical studies have focused on the one that includes a HCOO intermediate due to the fact that high coverages of formate over catalyst surfaces were observed experimentally. To systematically understand the influence of formate species coverage on the reaction kinetics of methanol synthesis, the energetics of the CO₂ hydrogenation pathway over clean and one- or two-formate preadsorbed Cu(211) are obtained using density functional theory calculations, and these energetics are further employed for microkinetic modeling. We find that the adsorption energies of the intermediates and transition states involved in the reaction pathway are changed in the presence of spectating formate species, and consequently, the potential energy diagrams are varied. Microkinetic analysis shows that the turnover frequencies (TOFs) over different formate preadsorbed surfaces vary under the same reaction condition. In particular, the reaction rates obtained over clean Cu(211) are generally the lowest, while those over one- or two-formate preadsorbed surfaces depend on the reaction temperatures and pressures. Meanwhile, we find that only when the formate coverage effect is considered, some of the TOFs obtained from microkinetic modeling are in fair agreement with previous experimental results under similar conditions. After the degree of rate control analysis, it is found that the combination of HCOO and HCOOH hydrogenation steps can be treated as the “effective rate-determining step”, which can be written as HCOO* + 2H* → H₂COOH* + 2*. Therefore, the formation of methanol is mainly controlled by the surface coverage of formate and hydrogen at the steady state, as well as the free energy barriers of the effective rate-determining step, i.e., effective free energy barriers

Nickel-Catalyzed Cross-Coupling of Allyl Alcohols with Aryl- or Alkenylzinc Reagents

Nickel-catalyzed cross-coupling of allyl alcohols with aryl- and alkenylzinc chlorides through C–O bond cleavage was performed. Reaction of (<i>E</i>)-3-phenylprop-2-en-1-ol and 1-aryl-prop-2-en-1-ols with aryl- or alkenylzinc chlorides gave linear cross-coupling products. Reaction of 1-phenyl- or 1-methyl-substituted (<i>E</i>)-3-phenylprop-2-en-1-ol with aryl- or alkenylzinc chlorides resulted in 3-aryl/alkenyl-substituted (<i>E</i>)-(prop-1-ene-1,3-diyl)­dibenzenes or 3-aryl/alkenyl-substituted (<i>E</i>)-(but-1-enyl)­benzene. Reaction of allyl alcohol with <i>p</i>-Me₂NC₆H₄ZnCl resulted in a mixture of normal coupling product 4-allyl-<i>N,N</i>-dimethylaniline and its isomerized product <i>N,N</i>-dimethyl-4-(prop-1-en-1-yl)­aniline

Base-Pairing Energies of Proton-Bound Heterodimers of Cytosine and Modified Cytosines: Implications for the Stability of DNA <i>i</i>‑Motif Conformations

The DNA <i>i</i>-motif conformation was discovered in (CCG)•(CGG)<i>_n</i> trinucleotide repeats, which are associated with fragile X syndrome, the most widespread inherited cause of mental retardation in humans. The DNA <i>i</i>-motif is a four-stranded structure whose strands are held together by proton-bound dimers of cytosine (C⁺•C). The stronger base-pairing interactions in C⁺•C proton-bound dimers as compared to Watson–Crick G•C base pairs are the major forces responsible for stabilization of <i>i</i>-motif conformations. Methylation of cytosine results in silencing of the FMR1 gene and causes fragile X syndrome. However, the influence of methylation or other modifications such as halogenation of cytosine on the base-pairing energies (BPEs) in the <i>i</i>-motif remains elusive. To address this, proton-bound heterodimers of cytosine and 5-methylcytosine, 5-fluorocytosine, 5-bromocytosine, and 5-iodocytosine are probed in detail. Experimentally, the BPEs of proton-bound heterodimers of cytosine and modified cytosines are determined using threshold collision-induced dissociation (TCID) techniques. All modifications at the 5-position of cytosine are found to lower the BPE and therefore would tend to destabilize DNA <i>i</i>-motif conformations. However, the BPEs in these proton-bound heterodimers still significantly exceed those of the Watson–Crick G•C and neutral C•C base pairs, suggesting that C⁺•C mismatches are still energetically favored such that <i>i</i>-motif conformations are preserved. Excellent agreement between TCID measured BPEs and B3LYP calculated values is found with the def2-TZVPPD and 6-311+G­(2d,2p) basis sets, suggesting that calculations at these levels of theory can be employed to provide reliable energetic predictions for related systems

Transition-Metal-Free Cross-Coupling of Aryl and Heteroaryl Thiols with Arylzinc Reagents

Cross-coupling of (hetero)­arylthiols with arylzinc reagents via C–S cleavage was performed under transition-metal-free conditions. The reaction displays a wide scope of substrates and high functional-group tolerance. Electron-rich and -deficient (hetero)­arylthiols and arylzinc reagents can be employed in this transformation. Mg²⁺ and Li⁺ ions were demonstrated to facilitate the reaction