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61.
62.
Natacha Malecki Pascal Carato Raymond Houssin Philippe Cotelle Jean-Pierre Hénichart 《Monatshefte für Chemie / Chemical Monthly》2005,41(3):1601-1606
It is demonstrated that electron-rich disubstituted acetophenones react according to various electrophilic nitration conditions that generally lead to ipso substitution accompanying the conventional reaction. The hydroxy substituent does not seem prone to favor such behaviour. 相似文献
63.
Hankel Determinant and Orthogonal Polynomials for a Gaussian Weight with a Discontinuity at the Edge
We compute asymptotics for Hankel determinants and orthogonal polynomials with respect to a discontinuous Gaussian weight, in a critical regime where the discontinuity is close to the edge of the associated equilibrium measure support. Their behavior is described in terms of the Ablowitz–Segur family of solutions to the Painlevé II equation. Our results complement the ones in [33]. As consequences of our results, we conjecture asymptotics for an Airy kernel Fredholm determinant and total integral identities for Painlevé II transcendents, and we also prove a new result on the poles of the Ablowitz–Segur solutions to the Painlevé II equation. We also highlight applications of our results in random matrix theory. 相似文献
64.
65.
An uranyl isophthalate has been hydrothermally synthesized at 200 °C for 24 h, from a mixture of uranyl nitrate, isophthalic acid, and hydrazine in water. It was characterized by single-crystal analysis [triclinic, P ?1, a = 7.3934(3) ?, b = 13.3296(5) ?, c = 15.4432(5) ?, α = 111.865(2)°, β = 90.637(2)°, γ = 104.867(2)°, V = 1355.49(9) ?(3)] and different spectroscopic techniques (Raman, IR-ATR, UV-visible). The 3D structure of the phase (UO(2))(8)O(2)(OH)(4)(H(2)O)(4)(1,3-bdc)(4)·4H(2)O (1,3-bdc = 1,3-benzenedicarboxylate) reveals octanuclear units based on the association of 7-fold coordinated uranyl cations (pentagonal bipyramid) involving a rare case of cation-cation interaction together with edge-sharing polyhedral connection mode. UV-visible absorption spectroscopy confirmed that uranium was only involved in the structure as uranyl forms (excluding the presence of tetravalent or pentavalent uranium). Additionally, μ-Raman and IR-ATR experiments allowed assigning four uranyl contributions to the four types of uranyl entities in the structure, in agreement with the XRD analysis. 相似文献
66.
In the present article, we develop a new functional framework for the study of scalar wave scattering by objects, called multi-screens, that are arbitrary arrangements of thin panels of impenetrable materials. From a geometric point of view, multi-screens are a priori non-orientable non-Lipschitz surfaces. We use our new framework to study boundary integral formulations of the scattering by such objects. 相似文献
67.
We obtain an asymptotic expansion for the solution of the Cauchy problem for the Korteweg-de Vries (KdV) equation
for small, near the point of gradient catastrophe (x
c
, t
c
) for the solution of the dispersionless equation u
t
+ 6uu
x
= 0. The sub-leading term in this expansion is described by the smooth solution of a fourth order ODE, which is a higher
order analogue to the Painlevé I equation. This is in accordance with a conjecture of Dubrovin, suggesting that this is a
universal phenomenon for any Hamiltonian perturbation of a hyperbolic equation. Using the Deift/Zhou steepest descent method
applied on the Riemann-Hilbert problem for the KdV equation, we are able to prove the asymptotic expansion rigorously in a
double scaling limit. 相似文献
68.
Natacha Altamirano Romain Pascalie Robert B. Mann 《General Relativity and Gravitation》2018,50(10):120
Motivated by the recent increased interest in energy non-conserving models in cosmology, we extend the analysis of the cosmological consequences of the Classical Channel Model of Gravity (CCG). This model is based on the classical–quantum interaction between a test particle and a metric (classical) and results in a theory with a modified Wheeler–deWitt equation that in turn leads to non conservation of energy. We show that CCG applied to a cosmological scenario with primordial matter leads to an emergent dark fluid that at late times behaves as a curvature term in the Friedmann equations, showing that the late time behaviour is always dominated by the vacuum solution. We discuss possible observational constraints for this model and that—in its current formulation—CCG eludes any meaningful constraints from current observations. 相似文献
69.
Surratt JD Gómez-González Y Chan AW Vermeylen R Shahgholi M Kleindienst TE Edney EO Offenberg JH Lewandowski M Jaoui M Maenhaut W Claeys M Flagan RC Seinfeld JH 《The journal of physical chemistry. A》2008,112(36):8345-8378
Organosulfates of isoprene, alpha-pinene, and beta-pinene have recently been identified in both laboratory-generated and ambient secondary organic aerosol (SOA). In this study, the mechanism and ubiquity of organosulfate formation in biogenic SOA is investigated by a comprehensive series of laboratory photooxidation (i.e., OH-initiated oxidation) and nighttime oxidation (i.e., NO3-initiated oxidation under dark conditions) experiments using nine monoterpenes (alpha-pinene, beta-pinene, d-limonene, l-limonene, alpha-terpinene, gamma-terpinene, terpinolene, Delta(3)-carene, and beta-phellandrene) and three monoterpenes (alpha-pinene, d-limonene, and l-limonene), respectively. Organosulfates were characterized using liquid chromatographic techniques coupled to electrospray ionization combined with both linear ion trap and high-resolution time-of-flight mass spectrometry. Organosulfates are formed only when monoterpenes are oxidized in the presence of acidified sulfate seed aerosol, a result consistent with prior work. Archived laboratory-generated isoprene SOA and ambient filter samples collected from the southeastern U.S. were reexamined for organosulfates. By comparing the tandem mass spectrometric and accurate mass measurements collected for both the laboratory-generated and ambient aerosol, previously uncharacterized ambient organic aerosol components are found to be organosulfates of isoprene, alpha-pinene, beta-pinene, and limonene-like monoterpenes (e.g., myrcene), demonstrating the ubiquity of organosulfate formation in ambient SOA. Several of the organosulfates of isoprene and of the monoterpenes characterized in this study are ambient tracer compounds for the occurrence of biogenic SOA formation under acidic conditions. Furthermore, the nighttime oxidation experiments conducted under highly acidic conditions reveal a viable mechanism for the formation of previously identified nitrooxy organosulfates found in ambient nighttime aerosol samples. We estimate that the organosulfate contribution to the total organic mass fraction of ambient aerosol collected from K-puszta, Hungary, a field site with a similar organosulfate composition as that found in the present study for the southeastern U.S., can be as high as 30%. 相似文献
70.
Wang W Cuyckens F Van den Heuvel H Apers S Pieters L Steenkamp V Stewart MJ Luyckx VA Claeys M 《Rapid communications in mass spectrometry : RCM》2003,17(1):49-55
Two novel compounds, 8-C-D-glucopyranosyl-7-hydroxy-5-methylchromone-2-carboxylic acid and a 2-O'-p-coumaroyl derivative thereof, were identified in a herbal tea that caused severe vomiting in a South African patient who had taken the traditional remedy to clean his stomach. For structural characterization, electrospray (ES) ionization in combination with collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS) were used, as well as UV and nuclear magnetic resonance (NMR) spectroscopy. Specific ions or neutral losses generated under conditions of ES-MS/CID/MS permitted the establishment of structural features such as the free carboxyl group, the C-hexosidic part and the p-coumaroyl group. NMR spectroscopy was necessary to support the structure of the chromone-type aglycone and the glucosidic parts. Since the compounds are structurally related to aloesin and aloeresin A, which are chemotaxonomic markers of Aloe species, and have not been previously reported, we propose that they were formed by oxidative degradation during preparation of the herbal tea from an Aloe species or during its storage. 相似文献