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141.
We derive new expressions to estimate the burning velocity of a laminar gas flame in a simplified combustion model based on a one-step single reaction with transport coefficients (mass and heat) depending on temperature, and species with different specific heats. These new expressions generalize the bounds and approximations previously derived by Williams, von Karman, Zeldovich and Frank-Kamenetskii, Benguria and Depassier, and the matching asymptotic expansion method in a two zone model. The comparison of the flame speed predicted by these new analytical expressions with that numerically simulated by the full combustion model for a large variety of cases allows us to determine their range of validity. The upper bound based on the Benguria and Depassier method provides very good approximations for the actual propagation speed of combustion flames, being substantially better than the asymptotic method used in the recent papers. 相似文献
142.
Toni Andersson Miika Sumela Leonid Khriachtchev Markku Räsänen Vladimir Aseyev Heikki Tenhu 《Journal of Polymer Science.Polymer Physics》2008,46(6):547-557
Cationic poly(methacryl oxyethyl trimethylammonium chloride), PMOTAC, and its poly(oxyethylene), POE, grafted analog have been synthesised. The molar mass of the POE grafts was Mw = 200 g/mol, and the grafting degrees of the synthesised copolymers were 2, 5, and 15 mol %. The effect of the POE grafts on the solution properties and the conformation of the polycation has been investigated in aqueous NaNO3 by means of dynamic and static light scattering, viscometry, and Raman spectroscopy. It was found that the polyelectrolyte properties are more pronounced for the homopolymer than for the POE‐grafted copolymers. The increase of the POE‐grafting degree dramatically decreases the hydrodynamic radius of individual macromolecules and causes intermolecular association. It also suppresses the conformational response of the copolymers upon changing the ionic strength with respect to that of the homopolymer. DFT calculations have been used to estimate a possible mechanism of interaction between the POE grafts and the MOTAC repeating units. It has been revealed that the POE grafts are capable of forming intramolecular hydrogen bonds with the MOTAC groups. The latter was confirmed experimentally; addition of free POE chains to a solution of PMOTAC results in formation of intermolecular PMOTAC/POE complexes. Increasing the POE concentration decreases the solution viscosity. At the same time, the bimodal distributions of the hydrodynamic radius, which are typical for polyelectrolytes in salt‐free solutions, become monomodal representing the PMOTAC/POE complexes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 547–557, 2008 相似文献
143.
144.
145.
Dienes Y Eggenstein M Neumann T Englert U Baumgartner T 《Dalton transactions (Cambridge, England : 2003)》2006,(11):1424-1433
A series of dithieno[3,2-b:2',3'-d]phosphole-based transition metal complexes, including Au, Fe, Pt, Rh and W as central metals have been synthesised and characterised. Structural investigations by X-ray single crystal crystallography supported the high degree of pi-conjugation in the dithienophosphole ligands. This essential requirement for potential applications in molecular electronics and optoelectronics provides small band gaps for the materials. Investigations toward the optoelectronic properties of the respective complexes by fluorescence spectroscopy indicated that systematic alterations of the electronic structure are connected to different variables such as transition metal employed, functionalisation of the dithienophosphole ligands as well as complex geometries. The investigated Pt-based complexes exhibit only poor photoluminescence whereas Rh-, W- and Fe-based species with silyl functionalised dithienophosphole ligands show appreciable photophysical properties. The Au complexes investigated exhibit strong photoluminescence properties with very intriguing features in terms of excitation and emission wavelengths, intensity as well as selectivity. 相似文献
146.
Mario Salwiczek Sergey Samsonov Toni Vagt Elisabeth Nyakatura Emanuel Fleige Jorge Numata Helmut Cölfen Dr. M. Teresa Pisabarro Dr. Beate Koksch Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(31):7628-7636
Systematic model investigations of the molecular interactions of fluorinated amino acids within native protein environments substantially improve our understanding of the unique properties of these building blocks. A rationally designed heterodimeric coiled coil peptide (VPE/VPK) and nine variants containing amino acids with variable fluorine content in either position a16 or d19 within the hydrophobic core were synthesized and used to evaluate the impact of fluorinated amino acid substitutions within different hydrophobic protein microenvironments. The structural and thermodynamic stability of the dimers were examined by applying both experimental (CD spectroscopy, FRET, and analytical ultracentrifugation) and theoretical (MD simulations and MM‐PBSA free energy calculations) methods. The coiled coil environment imposes position‐dependent conformations onto the fluorinated side chains and thus affects their packing and relative orientation towards their native interaction partners. We find evidence that such packing effects exert a significant influence on the contribution of fluorine‐induced polarity to coiled coil folding. 相似文献
147.
Toni Grell Mauro Barbero Franco Pattarino Giovanni Battista Giovenzana Valentina Colombo 《Molecules (Basel, Switzerland)》2021,26(16)
The solvatomorphism of the anthelmintic drug moxidectin is investigated, and a new solvatomorph with nitromethane is reported. Moreover, the hitherto unknown crystal structures of the solvatomorphs with ethanol and 2-propanol are reported and discussed. The thermal characterization of these solvatomorphs through variable-temperature powder X-ray diffraction analysis (VT-PXRD) is also described, providing new insights into the crystallochemistry of this active pharmaceutical ingredient. 相似文献
148.
Vera Toni? 《Topology and its Applications》2010,157(3):674-691
We prove a generalization of the Edwards-Walsh Resolution Theorem:
Theorem.
Let G be an abelian group withPG=P, where. Letn∈Nand let K be a connected CW-complex withπn(K)≅G,πk(K)≅0for0?k<n. Then for every compact metrizable space X with XτK (i.e., with K an absolute extensor for X), there exists a compact metrizable space Z and a surjective mapπ:Z→Xsuch that
- (a)
- π is cell-like,
- (b)
- dimZ?n, and
- (c)
- ZτK.
149.
The presence of a crack in a rotor introduces a local flexibility which affects its dynamic response. Moreover, the crack may open and close during the vibration period. The crack status is a function of time and also depends on the rotational speed and the vibration amplitude of the rotor. This nonlinear case is still a challenging research topic especially in the field of closing crack in the rotating shaft. A cohesive zone model is developed in order to analyze the stiffness of a crack in a rotating shaft. The proposed expression will be compared to three different crack models, namely, a breathing crack model, a switching crack model and an open crack model. Moreover, a cohesive law to predict and to analyse the stress at the crack tip is presented. The numerical model is implemented using a finite element formulation. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
150.
Rakesh Puttreddy J. Mikko Rautiainen Toni Mkel Kari Rissanen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18783-18791
A study of the strong N?X????O?N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X???O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X???O XBs. The XB interaction energies vary from ?47.5 to ?120.3 kJ mol?1; the strongest N?I????O?N+ XBs approaching those of 3‐center‐4‐electron [N?I?N]+ halogen‐bonded systems (ca. 160 kJ mol?1). 1H NMR association constants (KXB) determined in CDCl3 and [D6]acetone vary from 2.0×100 to >108 m ?1 and correlate well with the calculated donor×acceptor complexation enthalpies found between ?38.4 and ?77.5 kJ mol?1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (RXB) between 0.65–0.67 for the N?I????O?N+ halogen bond. 相似文献