A catalyst system consisting of the palladium(0) complex Pd2(dba)3 and tri(p‐tolyl)phosphine was found to efficiently promote the decarboxylation of allyl benzoates with formation of allylarenes. This catalytic C O activation followed by extrusion of carbon dioxide and C C bond formation represents a sustainable alternative to traditional waste‐intensive cross‐couplings. The scope of the transformation includes allyl and cinnamyl esters of various ortho‐substituted benzoic acids. For particularly activated substrates, the palladium catalyst can optionally be replaced by an inexpensive nickel complex.
The hypothesis that dissolved organic carbon (DOC) enhances the mass transfer of hydrophobic organic compounds from nonaqueous phase liquids (NAPLs) into the aqueous phase above that attributable to dissolved molecular diffusion alone was tested. In controlled experiments, mass transfer rates of five NAPL-phase PAHs (log K(OW) 4.15-5.39) into the aqueous phase containing different concentrations of DOC were measured. Mass transfer rates were increased by up to a factor of 4 in the presence of DOC, with the greatest enhancement being observed for more hydrophobic compounds and highest DOC concentrations. These increases could not be explained by dissolved molecular diffusion alone, and point to a parallel DOC-mediated diffusive pathway. The nature of the DOC-mediated diffusion pathway as a function of the DOC concentration and PAH sorption behavior to the DOC was investigated using diffusion-based models. The DOC-enhanced mass transfer of NAPL-phase hydrophobic compounds into the aqueous phase has important implications for their bioremediation as well as bioconcentration and toxicity. 相似文献
A novel buffering method is presented to improve the stability of zinc oxide processed in aqueous solutions. By buffering the aqueous solution with a suitable quantity of sacrificial zinc species, the dissolution of functional zinc oxide structures and the formation of unwanted impurities can be prevented. The method is demonstrated for ZnO films and nanowires processed in aqueous solutions used for the selective etching of mesoporous anodic alumina templates and the electrochemical deposition of Cu2O. In both cases, improved ZnO stability is observed with the buffering method. ZnO‐Cu2O heterojunction solar cells (bilayer and nanowire cells) synthesized using both traditional and buffered deposition methods are characterized by impedance spectroscopy and solar simulation measurements. Buffering the Cu2O deposition solution is found to reduce unwanted recombination at the heterojunction and improve the photovoltaic performance. 相似文献
A data set was established to calculate the phase equilibria in the systems Si-Al-Zr-O-N and Si-Al-B-O-N. Complete phase diagrams of the quasibinary and quasiternary boundary systems, calculated by this data set, agree well with literature phase diagrams. To calculate equilibria of the multicomponent systems, Eriksson's program was modified to accept ionic species. The equilibria of some concentrations are plotted versus the temperature in phase amount diagrams. 相似文献
Traumatic vertebral artery injuries are relatively rare. Until recently, insufficient neurodiagnostic technology and a lack of normative data for the population of USAF aviators prevented recommending flying waivers following such vascular injuries. We report the case of an aviator who experienced a traumatic right vertebral artery occlusion with distal embolization. Timely access to a state-of-the-art neurodiagnostic evaluation, which included time-of-flight magnetic resonance angiography (MRA), and standard contrast angiography, provided anatomic imaging at the time of injury and during the recuperative period. Sophisticated neurologic testing protocols at the Armstrong Laboratory's Aeromedical Clinical Sciences Division, Brooks Air Force Base, TX, assessed in-depth this individual's functional status. Consult Service evaluators then compared his performance data with current data in the Head Injury Study in Aviators (HISA) data base. MRA, in comparison with standard contrast angiography, demonstrated anatomic stability of his vascular and neurologic lesions. He demonstrated a functional capacity consistent with normal neurologic functioning in aviators which permitted recommending an occupational (flying) waiver. This case exemplified application of sophisticated ACS neurologic testing protocols to aeromedical evaluations and the use of MRA technology as a vascular screening tool during medical followup. 相似文献
BACKGROUND: Carvedilol has improved the symptomatic status of patients with moderate to severe heart failure in single-center studies, but its clinical effects have not been evaluated in large, multicenter trials. METHODS AND RESULTS: We enrolled 278 patients with moderate to severe heart failure (6-minute walk distance, 150 to 450 m) and a left ventricular ejection fraction < or = 0.35 at 31 centers. After an open-label, run-in period, each patient was randomly assigned (double-blind) to either placebo (n = 145) or carvedilol (n = 133; target dose, 25 to 50 mg BID) for 6 months, while background therapy with digoxin, diuretics, and an ACE inhibitor remained constant. Compared with placebo, patients in the carvedilol group had a greater frequency of symptomatic improvement and lower risk of clinical deterioration, as evaluated by changes in the NYHA functional class (P = .014) or by a global assessment of progress judged either by the patient (P = .002) or by the physician (P < .001). In addition, treatment with carvedilol was associated with a significant increase in ejection fraction (P < .001) and a significant decrease in the combined risk of morbidity and mortality (P = .029). In contrast, carvedilol therapy had little effect on indirect measures of patient benefit, including changes in exercise tolerance or quality-of-life scores. The effects of the drug were similar in patients with ischemic heart disease or idiopathic dilated cardiomyopathy as the cause of heart failure. CONCLUSIONS: These findings indicate that, in addition to its favorable effects on survival, carvedilol produces important clinical benefits in patients with moderate to severe heart failure treated with digoxin, diuretics, and an ACE inhibitor. 相似文献