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101.
Cristian Lenart Frank Sottile 《Proceedings of the American Mathematical Society》2003,131(11):3319-3328
We define skew Schubert polynomials to be normal form (polynomial) representatives of certain classes in the cohomology of a flag manifold. We show that this definition extends a recent construction of Schubert polynomials due to Bergeron and Sottile in terms of certain increasing labeled chains in Bruhat order of the symmetric group. These skew Schubert polynomials expand in the basis of Schubert polynomials with nonnegative integer coefficients that are precisely the structure constants of the cohomology of the complex flag variety with respect to its basis of Schubert classes. We rederive the construction of Bergeron and Sottile in a purely combinatorial way, relating it to the construction of Schubert polynomials in terms of rc-graphs.
102.
Cristian Carrera‐Figueiras Manuel Aguilar‐Vega 《Journal of Polymer Science.Polymer Physics》2005,43(19):2625-2638
The synthesis, thermal, and gas transport properties of poly(hexafluoroisopropylidene isophthalamide), HFA/ISO homopolymer, and HFA/TERT‐co‐HFA/ISO copolyamides with different poly(hexafluoroisopropilydene‐5‐t‐butylisophthalamide), HFA/TERT, ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of HFA/TERT in the polyamide increases. The gas permeability coefficients in the polyamides and copolyamides are independent of pressure or decrease slightly particularly with CO2, N2, and CH4. It was seen that HFA/TERT is 2–6 times more permeable than HFA/ISO, depending on the gas being considered. This was assigned to the presence of the bulky lateral substituent, t‐butyl group in HFA/TERT and HFA/TERT‐co‐HFA/ISO copolyamides. This substituent increases fractional free‐volume, as expected. Therefore, the gas permeability and diffusion coefficients generally increase with increasing fractional free‐volume. The experimental results for the gas permeability and permselectivity for the copolyamides was well represented by a logarithmic mixing rule of the homopolyamides permeability coefficients and their volume fraction. The selectivity of gas pairs, such as O2/N2, CO2/CH4, and N2/CH4 decreased slightly with the addition of HFA/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2625–2638, 2005 相似文献
103.
104.
105.
Summary The behaviour of seasonal and yearly average of the monthly means of maximum and minimum daily surface temperature, covering
the period 1951–90, in some stations of the Italian Hydrographic Service spread over the region of Friuli-Venezia Giulia has
been analysed by the Spearm test with the aim of determining a possible trend. A a variety of situations resulted, which are
displayed in the figures. As an example, for the stations ofUdine andTrieste the monthly temperature patterns have also been considered in more detail. Moreover, after spatial averaging over the region
of either minimum or maximum temperature data, including all the examined stations, any significant trend did not appear.
In particular, a comparison with the trend analysis of the historical series of Wien (Austria) and of three important Italian
Observatories, namely Milan (Brera), Florence (Ximeniano) and Rome (Collegio Romano) has been also carried out.
Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome. 相似文献
106.
Aurora Molinari Alfonso Oliva Marlene Arismendi Elizabeth Imbarack Cristian Glvez Javier Maldonado Arturo San Feliciano 《Journal of heterocyclic chemistry》2015,52(2):620-622
New fused pyrazolo‐1,4‐naphthoquinones were prepared from the reaction of hydrazines with 6‐(4‐methyl‐3‐pentenyl)‐1,4‐naphthoquinone. The reaction was extended to hydroxylamine to afford the corresponding isoxazolo‐1,4‐napthoquinone compound. 相似文献
107.
108.
Graziano Baccolini Carla BogaCamilla Delpivo Gabriele Micheletti 《Tetrahedron letters》2011,52(14):1713-1717
A series of hydantoins and thiohydantoins have been synthesized in water at room temperature from urea (or N-methylurea, or thiourea) and simple aldehydes (as glyoxal, and its simple derivatives) in the presence of phosphoric anhydride. The reaction time is 10 min using an equimolar amount of P4O10 with respect to the other reagents, but the reaction occurs also, even if with longer reaction times, with very small amounts of P4O10.In addition, this method provides a clean and ‘green’ approach to hydantoins, compounds of great interest in biological and pharmacological fields. 相似文献
109.
Gallego NC He L Saha D Contescu CI Melnichenko YB 《Journal of the American Chemical Society》2011,133(35):13794-13797
In-situ small-angle neutron scattering studies of H(2) confined in small pores of polyfurfuryl alcohol-derived activated carbon at room temperature have provided for the first time its phase behavior in equilibrium with external H(2) at pressures up to 200 bar. The data were used to evaluate the density of the adsorbed fluid, which appears to be a function of both pore size and pressure and is comparable to the density of liquid H(2) in narrow nanopores at ~200 bar. The surface-molecule interactions responsible for densification of H(2) within the pores create internal pressures that exceed the external gas pressure by a factor of up to ~50, confirming the benefits of adsorptive storage over compressive storage. These results can be used to guide the development of new carbon adsorbents tailored for maximum H(2) storage capacities at near-ambient temperatures. 相似文献
110.
Beleaga A Bojan VR Pöllnitz A Raţ CI Silvestru C 《Dalton transactions (Cambridge, England : 2003)》2011,40(35):8830-8838
The reaction of RH (1) with Hg(OAc)(2), in EtOH, gave the acetate RHgOAc (2) [R = 2,6-[O(CH(2)CH(2))(2)NCH(2)](2)C(6)H(3)]. The corresponding RHgCl (3) was obtained from 2 and LiCl. The reaction of 3 with TeCl(4) (1:1 molar ratio), in anhydrous 1,4-dioxane, resulted in the transfer of the organic ligand from mercury to tellurium and the isolation of the unexpected ionic compounds [RTe](2)[Hg(2)Cl(6)] (4) and [RH(3)][HgCl(4)] (5). The molecular structures of 1-4 and 5·H(2)O were established by single-crystal X-ray diffraction. The acetate 2 and the chloride 3 are monomeric in solid state. In both mercury and tellurium organometallic compounds the organic group acts as an (N,C,N) "pincer" ligand. This coordination pattern provided stability for the rare [RTe](+) cation. Weak cation-anion interactions [Te···Cl 3.869(3) ?] are present between [RTe](+) and the dinuclear anion [Hg(2)Cl(6)](2-) in the crystal of 4. Theoretical calculations with DFT methods were performed for models of 3 and 4. The results show that in the cation of 4 the coordination of the nitrogen atoms play an important role for the stabilization of the structure found in the crystal whereas in 3 the coordination of the nitrogen atoms to the metal centre stabilizes to a less extent the structure found in solid state. 相似文献