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621.
Considering the hyperbolic symmetric system of moments associated with the relativistic Boltzmann-Chernikov equation and closed
through procedures of Extended Thermodynamics, we determine numerically the maximum characteristic wave velocity for degenerate
and non-degenerate gases. As predicted by recent results, this velocity increases monotonically with respect to the number
of moments and tends asymptotically to the speed of light. We show that many moments are often required to approach with a
good approximation the speed of light. The dependence of the maximum characteristic wave velocity on the properties of the
materials is also investigated and it turns out that it depends significantly on the chemical potential only in the case of
Fermions gases.
Received April 24, 1999 相似文献
622.
Donata Di Tommaso Roberto Calabrese Domenico Rotilio 《Journal of separation science》1998,21(10):549-553
Hydroxytyrosol (HTy) is a potent natural antioxidant found in olive oil and in mill waste waters. Although wines are rich in polyphenols, hydroxytyrosol has not been identified in wines so far. We have analyzed ten wines from different grape varieties grown in several Italian regions, using a gas-chromatograph coupled to a mass selective detector (GC-MS). Solid-phase extraction of wine samples was performed on a C18 column, with ethyl acetate used as eluting agent. Eluates were derivatized with bis(trimethylsilyl)trifluoroacetamide (BSTFA) and analyzed by GC-MS using one target and two qualifying ions. The detection limit was 15 pg/μL, with 49% average recovery. Under these experimental conditions hydroxytyrosol was detected in all wines analyzed. Its average concentrations in red and white wines were 4.0 mg/L and 1.9 mg/L, respectively. 相似文献
623.
Dino Ferri Dietmar Wolff Jürgen Springer Oriano Francescangeli Michele Laus Annino Sante Angeloni Giancarlo Galli Emo Chiellini 《Journal of Polymer Science.Polymer Physics》1998,36(1):21-29
The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 21–29, 1998 相似文献
624.
Dr. Kumar Bhaskar Pal Dr. Ester Maria Di Tommaso Dr. A. Ken Inge Prof. Berit Olofsson 《Angewandte Chemie (International ed. in English)》2023,62(20):e202301368
We report an efficient radical-mediated C−C coupling through photoredox-catalyzed reactions of 4-alkyl-dihydropyridines (DHPs) and vinylbenziodoxol(on)es (VBX, VBO). This transition-metal-free and mild photocatalytic method has excellent functional group tolerance and affords vinylated products in good yields, with complete retention of the alkene configuration. The utility of the methodology is demonstrated by the diastereoselective synthesis of C-vinyl glycosides. Preliminary mechanistic studies suggest that the C−C bond formation is stereospecific and proceeds through a concerted radical coupling transition state. 相似文献
625.
Dr. Sara Cuadros Dr. Giulio Goti Giorgia Barison Alfredo Raulli Tommaso Bortolato Prof. Giorgio Pelosi Dr. Paolo Costa Prof. Luca Dell'Amico 《Angewandte Chemie (International ed. in English)》2023,62(31):e202303585
Here, we report a general approach to the synthesis of the difluoroalkyl bicycloalkanes (CF2-BCAs), as structural surrogates of aryl ketones and ethers. The chemistry is driven by a dihydrobenzoacridine photocatalyst, that engages in a catalytic electron-donor acceptor (EDA) complex, or directly reduces the fluorinated substrate. These two convergent manifolds lead to the generation of the R-CF2 radical, that reacts with the [1.1.1]- or [3.1.1.]-propellane. The method is extremely general, and extendable to complex bioactive molecules (30 examples, up to 87 % yield). The structural features of the CF2-BCP hybrid bioisostere were investigated by single crystal X-ray. Finally, we synthesised a CF2-BCP analogue of a Leukotriene A4 hydrolase inhibitor, replacing the original aryl ether motif. In silico docking studies indicated that this new analogue maintains the same arrangement within the enzyme pocket, profiling the use of the CF2-BCA hybrid bioisostere in medicinal chemistry settings. 相似文献
626.
627.
Tommaso Rigon 《商业与工业应用随机模型》2023,39(2):232-250
There is an increasingly rich literature about Bayesian nonparametric models for clustering functional observations. Most recent proposals rely on infinite-dimensional characterizations that might lead to overly complex cluster solutions. In addition, while prior knowledge about the functional shapes is typically available, its practical exploitation might be a difficult modeling task. Motivated by an application in e-commerce, we propose a novel enriched Dirichlet mixture model for functional data. Our proposal accommodates the incorporation of functional constraints while bounding the model complexity. We characterize the prior process through a urn scheme to clarify the underlying partition mechanism. These features lead to a very interpretable clustering method compared to available techniques. Moreover, we employ a variational Bayes approximation for tractable posterior inference to overcome computational bottlenecks. 相似文献
628.
The angular dependence of the light scattered from polydisperse solutions of rod‐like or worm‐like linear polymers formed by the polymerization of rod‐like macromolecular monomers was studied with the aid of computer simulations. Except at very low conversion degrees, these ensembles are characterized by curved Zimm‐like plots. An appraisal of the use of polynomial fittings for the derivation of the weight‐average molecular weight (Mw) and of the z‐average square radius of gyration (<Rg2>z) from such plots is presented and discussed. Depending on the average size and shape distribution, the use of polynomial fittings allows the applicability of the Zimm method well beyond the standard condition q2<Rg2>z<<1, q being the scattering wavevector. In addition, the derivation of the w/z‐average mass/length ratio ML of the polymers from only partially linear Casassa plots, from which large errors in the derived ML values can be made, is analyzed. By combining the Casassa method with the complementary Holtzer plots, it is usually possible to assess the reliability of the results and give an estimate of their accuracy. However, it was also found that apparently linear Casassa plots, allowing a good estimate of the ML value, may arise in particular situations even when the Holtzer plot would indicate otherwise. 相似文献