950 resultados para Unsaturated bonds
Resumo:
Suction is an important stress variable that is required for reliable predictions of the likely performance of unsaturated soils. The axis translation technique is the best established method of measuring or controlling suction; however, the success of this application is heavily dependent on the rating of the high air entry filter (HAF) and how it is incorporated into the testing system. This paper reports some basic experiments in which samples of unsaturated kaolin were brought to saturation in stages using 5 bar and 15 bar HAFs. The results have shown that the water equilibrium in unsaturated soils is greatly affected by the rating of filters. The findings also suggest that the flow through unsaturated soils is not necessarily governed by the one-dimensional consolidation theory that was developed for saturated soils, and this may be attributed to the bimodal pore size distribution of unsaturated soils.
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Chromium(II) chloride converts alpha,beta-unsaturated aldehydes to the corresponding cyclopropanols.
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The efficiency of solar-energy-conversion devices depends on the absorption region and intensity of the photon collectors. Organic chromophores, which have been widely stabilized on inorganic semiconductors for light trapping, are limited by the interface between the chromophore and semiconductor. Herein we report a novel orange zinc germanate (Zn-Ge-O) with a chromophore-like structure, by which the absorption region can be dramatically expanded. Structural characterizations and theoretical calculations together reveal that the origin of visible-light response can be attributed to the unusual metallic Ge-Ge bonds which act in a similar way to organic chromophores. Benefiting from the enhanced light harvest, the orange Zn-Ge-O demonstrates superior capacity for solar-driven hydrogen production.
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The paper addresses the quality of the interface and edge bonded joints in layers of cross-laminated timber (CLT) panels. The shear performance was studied to assess the suitability of two different adhesives, Polyurethane (PUR) and Phenol-Resorcinol-Formaldehyde (PRF), and to determine the optimum clamping pressure. Since there is no established testing procedure to determine the shear strength of the surface bonds between layers in a CLT panel, block shear tests of specimens in two different configurations were carried out, and further shear tests of edge bonded specimen in two configurations were performed. Delamination tests were performed on samples which were subjected to accelerated aging to assess the durability of bonds in severe environmental conditions. Both tested adhesives produced boards with shear strength values within the edge bonding requirements of prEN 16351 for all manufacturing pressures. While the PUR specimens had higher shear strength values, the PRF specimens demonstrated superior durability characteristics in the delamination tests. It seems that the test protocol introduced in this study for crosslam bonded specimens, cut from a CLT panel, and placed in the shearing tool horizontally, accurately reflects the shearing strength of glue lines in CLT.
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Reaction of the tris(3-phenylpyrazolyl)methane sulfonate species (Tpms(Ph))Li with the copper(I) complex [Cu(MeCN)(4)][PF6] affords [Cu(Tpms(Ph))(MeCN)] 1. The latter, upon reaction with equimolar amounts of cyclohexyl-(CyNC) or 2,6-dimethylphenyl (XylNC) isocyanides, or excess CO, furnishes the corresponding Cu(I)complexes [Cu(Tpms(Ph))(CNR)] (R = Cy 2, Xyl 3) or [Cu(Tpms(Ph))(CO)] 4. The ligated isocyanide in 2 or 3 (or the acetonitrile ligand in 1)is displaced by 3-iminoisoindolin-1-one to afford 5, the first copper(I) complex containing an 3-iminoisoindolin-1-one ligand. The ligated acetonitrile in 1 undergoes nucleophilic attack by methylamine to give the amidine complex [Cu(Tpms(Ph)){MeC(NH)NHMe}] 6, whereas only the starting materials were recovered from the attempted corresponding reactions of 2 and 3 with methylamine. Complexes 1 or 6 form the trinuclear hydroxo-copper(II)species [(mu-Cu){Cu(mu-OH) (2)(Tpms(Ph))}(2)] 7 upon air oxidation in moist methanol. In all the complexes the scorpionate ligand facially caps the metal in the N,N,O-coordination mode.
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This case study focuses on the BPI’s recapitalization plan, its causes and the reasons for the early reimbursement of CoCos in June 2014. The need for a capital intervention and the subsequent subscription agreement with the Portuguese Government of €1 500 million Core Tier 1 instruments were the result of a temporary capital buffer for sovereign debt exposures imposed by the European Banking Authority. The capital increase, the positive earnings in 2012 and 2013, the improvements in the sovereign debt crisis, the implementation of Basel III, in addition to the public exchange offer and the conversion of deferred tax assets into tax credits are the main factors for concluding the entire recapitalization operation three years before the deadline.
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This study attempts to identify basis-trading opportunities in the European banking sector by comparing two different measures for the market’s assessment of risk: market-observed CDS spreads and model-implied Z-spreads. Using a sample of 10 banks, over a period of 3 years following the European banking crisis, it can be concluded that there were arbitrage opportunities in the sector, as evidenced by the derived negative bases.
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The cocondensation of nickel with a number of unsaturated ligands was studied, as was the cocondensation with a number of mixed ligand systems. Enamines were found not to react with nickel while acrylonitrile was polymerized. In the mixed ligand syst.ems different products were obtained than when the ligands were cocondensed individually. Cocondensations of benzyl halide/allyl halide mixtures gave unstable products that were not observed when the halides were cocondensed individually. The effect of Kao-Wool insulation on nickel/benzyl halide cocondensations was found to be significant. Kao-Wool caused the bulk of the benzyl halide to be polymeri zed to a number of poly-benzylic species. An alkali metal reactor was designed for the evaporation of sodium and potassium atoms into cold solutions of metal halide and an or ganic substrate. This apparatus was used to synthesize Ni(P¢3 )3' but proved unsuccessful for synthesizing a nickel-enamine compound.
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The study examines the buddy film genre and the representation of masculinity in relation to the homosocial and the homoerotic. As a genre, the buddy films focus on male relationships, thematically seeking to mediate the boundaries surrounding the homosocial continuum and the intimacy and eroticism implicit in male bonding. Theories of genre, gender and identity are used to analyze the construction of masculine identity within the films. By providing a qualitative analysis of films from the 1960s to contemporary times, the research establishes a relationship between social changes, attitudes toward men and depictions of men. The buddy films adapt to address changes in the representation of masculinity, embodied in the difference between the male couple in the films. The early films of the 1960s served as templates that deconstructed traditional representations of male identity through articulating the tension within homosocial relationships. However, in the later films this tension became a refle~ive convention, acting to undermine the eroticism onto a displaced Other. The buddy film genre highlights the tension inherent to the male masquerade. This tension is situated in the need to represent the protagonist's homosocial relationship, while disavowing the eroticism that surrounds homosocial bonding. The structure of the buddy film genre, which focuses on the exploration of masculinity and representing the bonds of homosocial intimacy, makes these films a significant site for investigating the cultural construction of masculine identities.
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In 2007, Barry Bonds hit his 75 6th home run, breaking Hank Aaron's all-time record for most home runs in a Major League career. While it would be expected that such an accomplishment would induce unending praise and adulationfor the new record-holder, Bonds did not receive the treatment typically reserved for a beloved baseball hero. The purpose of this thesis is to assess media representations of the 2007 home run chase in order to shed light upon the factors which led to the mixed representations which accompanied BOlTds ' assault on Aaron's record. Drawingfrom Roland Barthes ' concept of myth, this thesis proposes that Bonds was portrayed in predominantly negative ways because he was seen as failing to embody the values of baseball's mythology. Using a qualitative content analysis of three major American newspapers, this thesis examines portrayals of Bonds and how he was shown both to represent and oppose elements from baseball's mythology, such as youth, and a distant, agrarian past. Recognizing the ways in which baseball is associated with American life, the media representations of Bonds are also evaluated to discern whether he was portrayed as personifYing a distinctly American set of values. The results indicate that, in media coverage of the 2007 home run chase, Bonds was depicted as a player of many contradictions. Most commonly, Bonds' athletic ability and career achievements were contrasted with unflattering descriptions of his character, including discussions of his alleged use of performance-enhancing substances. However, some coverage portrayed Bonds as embodying baseball myth. The findings contribute to an appreciation of the importance of historical context in examining media representations. This understanding is enhanced by an analysis of a selection of articles on Mark McGwire 's record-breaking season in 1998, and careful consideration of, and comparison to, the context under which Bonds performed in 2007. Findings are also shown to support the contemporary existence of a strong American baseball mythology. That Bonds is both condemned for failing to uphold the mythology and praised for personifYing it suggests that the values seen as inherent to baseball continue to act as an American cultural benchmark.
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For the past 20 years, researchers have applied the Kalman filter to the modeling and forecasting the term structure of interest rates. Despite its impressive performance in in-sample fitting yield curves, little research has focused on the out-of-sample forecast of yield curves using the Kalman filter. The goal of this thesis is to develop a unified dynamic model based on Diebold and Li (2006) and Nelson and Siegel’s (1987) three-factor model, and estimate this dynamic model using the Kalman filter. We compare both in-sample and out-of-sample performance of our dynamic methods with various other models in the literature. We find that our dynamic model dominates existing models in medium- and long-horizon yield curve predictions. However, the dynamic model should be used with caution when forecasting short maturity yields
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The syntheses, catalytic reactivity and mechanistic investigations of novel Mo(IV) and Mo(VI) imido systems is presented. Attempts at preparing mixed bis(imido) Mo(IV) complexes of the type (RN)(R′N)Mo(PMe3)n (n = 2 or 3) derived from the mono(imido) complexes (RN)Mo(PMe3)3(X)2 (R = tBu (1) or Ar (2); X = Cl2 or HCl, Ar=2,6-iPr2C6H3) are also described. The addition of lithiated silylamides to 1 or 2 results in the unexpected formation of the C-H activated cyclometallated complexes (RN)Mo(PMe3)2(η2-CH2PMe2)(X) (R = Ar, X = H (3); R = tBu, X = Cl (4)). Complexes 3 and 4 were used in the activation of R′E-H bonds (E = Si, B, C, O, P; R′ = alkyl or aryl), which typically give products of addition across the M-C bond of the type (RN)Mo(PMe3)3(ER′)(X) (4). In the case of 2,6-dimethylphenol, subsequent heating of 4 (R = Ar, R′ = 2,6-Me2C6H3, E = O) to 50 °C results in C-H activation to give the cyclometallated complex (ArN)Mo(PMe3)3(κ2-O,C-OPh(Me)CH2) (5). An alternative approach was developed in synthesizing the mixed imido complex (ArN)(tBuN)Mo(PMe3)(η2-C2H4) (6) through EtMgBr reduction of (ArN)(tBuN)MoCl2(DME) in the presence of PMe3. Complex 6 reacts with various hydro- and chlorosilanes to give β-agostic silylamido complexes and in one case, when Me2SiHCl is the silane, leads to the silanimine complex (tBuN)Mo(η2-SiMe2-NAr)(Et)(η2-C2H4) (7). Mechanistic studies on the formation of the Mo(VI) tris(silyl) complex (tBuN)Mo(SiHPh)(H){(μ-NtBu)(SiHPh)}(PMe3)2 (8) were done from the addition of three equivalents of PhSiH3 to (tBuN)Mo(PMe3)(η2-C2H4), resulting in identification of β- and γ-agostic SiH…Mo intermediates. The reactivity of complex 8 towards ethylene and nitriles was studied. In both cases coupling of unsaturated substrates with the Mo-Si bond of the metalacycle was observed. In the case of nitriles, insertion into the 4-membered disilaazamolybdacycle results in complexes of the type (tBuN)Mo{(κ2-Si,C-SiHPh-NtBu-SiHPh-N=C(R)}(PMe3)2. Catalytic hydrosilylation of carbonyls mediated by the β-agostic silylamido complex (ArN)2Mo(η3-NtBu-SiMe2-H)(H) (9) was investigated. Stoichiometric reactions with organic substrates showed that catalysis with 9 does not proceed via the conventional insertion of substrate into the Mo-H bond.
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The unnatural threo-6-acetoxy-5-hexadecanolide and the natural mosquito oviposition pheromone erythro-6-acetoxy-5-hexadecanolide were synthesized in a diastereodivergent fashion in 44% and 33% overall yield respectively from 5-bromovaleric acid and undecanal. The key step utilized a chemoenzymatic epoxidation-lactonization of a naturally available fatty acid to form the 6-hydroxy-5-hexadecanolide core.17 The epoxidation strategy was later adapted to allow for an asymmetric synthesis. Shi epoxidation afforded highly enantioenriched (5R, 6R)-6-hydroxyhexadecanolide (er = 10) in 70 % overall yield. Other derivatives of the chiral ketone catalyst were also screened. Finally, attempts were made to obtain the correct stereochemistry at C(6) of the target with a dynamic kinetic transformation using lipase and a transfer hydrogenation catalyst. Epimerization of the lactol with the transfer hydrogenation catalyst was successful, but lipase mediated reactions halted at <10 % conversion.