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101.
102.
Adriana Lídia Santana Cristiano Giacomelli Paula Nunes Oliveira Alfredo Tibúrcio Nunes Pires José Roberto Bertolino Almir Spinelli 《Journal of Polymer Science.Polymer Physics》2009,47(2):215-225
The effect of poly(2‐vinyl pyridine) (P2VP) and poly(4‐vinyl pyridine) (P4VP) isomers on the growth of surface films on copper substrates was studied by electrochemical, spectroscopic, thermogravimentric, and microscopic methods. In acid environment (3% v/v acetic acid) and in the presence of KSCN, electrochemically generated copper cations reacted rapidly with SCN? and P2VP or P4VP, yielding coordination compounds, which deposited onto copper surfaces as films. The characteristics of such polymer–metal complexes (films) were markedly isomer‐dependent. Cu(I)/P2VP/SCN? complexes with monovalent cations and sulfur‐coordinated thiocyanate were obtained in the presence of P2VP, whereas the formation of Cu(II)/P4VP/SCN? complexes with divalent cations and nitrogen‐coordinated thiocyanate was observed in the presence of P4VP. Interestingly, similar physical–chemical properties (electronic structure, stoichiometry, and thermal behavior) were observed for materials synthesized by electrochemical and chemical methods. These results suggest, therefore, that control over the surface properties of copper substrates can be achieved using electrosynthesized films based on different PVP isomers. Besides acting as effective protective barriers against aggressive media and thus reducing the metal dissolution (corrosion) kinetics, these materials are potentially attractive for other applications in which surface properties are paramount, such as in catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 215–225, 2009 相似文献
103.
There is now strong observational evidence that the expansion of the Universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead general relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. Here we show that this may not be so easy, demonstrating explicitly that a generalized dark energy model can match the growth rate of the Dvali-Gabadadze-Porrati model and reproduce the 3+1 dimensional metric perturbations. Cosmological observations are then unable to distinguish the two cases. 相似文献
104.
Kinematical assumptions leading to the approximate theory of small strain accompanied by moderate rotations are discussed with reference to a three-dimensional continuous body. In particular, the relationship with Korn's inequality is examined. It is found that for bounded bodies the coincidence of small strain and moderate rotation on subsets of non-zero volume measure is not possible. Two explicit examples are presented to illustrate this point. 相似文献
105.
A theoretical investigation of friction-induced self-excited oscillations for systems with one degree of freedom is proposed.
The friction force is assumed as an odd function of the relative sliding velocity with a jump discontinuity at a value of
zero for the relative sliding velocity. The friction characteristic is approximated with a piecewise linear function, i.e.
straight line segments with a suitable slope. For the generic system belonging to the class in question, the stick-slip instability
region is located on a suitable dimensionless map.
Sommario Viene proposta un'indagine teorica sulle oscillazioni autoeccitate indotte dall'attrito per sistemi ad un grado di libertà. La forza d'attrito viene assunta come funzione dispari della velocità relativa tra le superfici accoppiate, con una discontinuità di prima specie in corrispondenza del valore nullo della velocità. La caratteristica d'attrito viene approssimata mediante una funzione lineare a tratti con segmenti di opportuna pendenza. Per il generico sistema appartenente alla classe in esame, si perviene all'individuazione, su opportuna mappa adimensionale, della regione di instabilità da stick-slip.相似文献
106.
A framework for the numerical analysis of bridges under wind excitation is outlined. It is based on structural finite element
scheme and cross-sectional wind load models. Two aspects are investigated: (1) how considering the mean steady configuration
in the aerodynamic stability calculation; and (2) the effects of load nonlinearities on structural response. A quasi-steady
load model is adopted, which is able to deal with the considered problems by using experimental data easily available in the
practice. By means of numerical examples, it is pointed out (1) that both the modifications in structural tangential stiffness
and in the aerodynamic coefficients due to the mean steady deformation may affect the aeroelastic stability threshold and
(2) that load linearization may produce an underestimation of the structural response. 相似文献
107.
Gerhard?TutzEmail author Micha?Schneider Maria?Iannario Domenico?Piccolo 《Advances in Data Analysis and Classification》2017,11(2):281-305
In CUB models the uncertainty of choice is explicitly modelled as a Combination of discrete Uniform and shifted Binomial random variables. The basic concept to model the response as a mixture of a deliberate choice of a response category and an uncertainty component that is represented by a uniform distribution on the response categories is extended to a much wider class of models. The deliberate choice can in particular be determined by classical ordinal response models as the cumulative and adjacent categories model. Then one obtains the traditional and flexible models as special cases when the uncertainty component is irrelevant. It is shown that the effect of explanatory variables is underestimated if the uncertainty component is neglected in a cumulative type mixture model. Visualization tools for the effects of variables are proposed and the modelling strategies are evaluated by use of real data sets. It is demonstrated that the extended class of models frequently yields better fit than classical ordinal response models without an uncertainty component. 相似文献
108.
109.
Albrow VE Ponder EL Fasci D Békés M Deu E Salvesen GS Bogyo M 《Chemistry & biology》2011,18(6):722-732
Sentrin specific proteases (SENPs) are responsible for activating and deconjugating SUMO (Small Ubiquitin like MOdifier) from target proteins. It remains difficult to study this posttranslational modification due to the lack of reagents that can be used to block the removal of SUMO from substrates. Here, we describe the identification of small molecule SENP inhibitors and active site probes containing aza-epoxide and acyloxymethyl ketone (AOMK) reactive groups. Both classes of compounds are effective inhibitors of hSENPs 1, 2, 5, and 7 while only the AOMKs efficiently inhibit hSENP6. Unlike previous reported peptide vinyl sulfones, these compounds covalently labeled the active site cysteine of multiple recombinantly expressed SENP proteases and the AOMK probe showed selective labeling of these SENPs when added to complex protein mixtures. The AOMK compound therefore represents promising new reagents to study the process of SUMO deconjugation. 相似文献
110.
Determination of the geographical origin of Brazilian wines by isotope and mineral analysis 总被引:1,自引:0,他引:1
Dutra SV Adami L Marcon AR Carnieli GJ Roani CA Spinelli FR Leonardelli S Ducatti C Moreira MZ Vanderlinde R 《Analytical and bioanalytical chemistry》2011,401(5):1575-1580
In the present research, we studied wines from three different south Brazilian winemaking regions with the purpose of differentiating
them by geographical origin of the grapes. Brazil's wide territory and climate diversity allow grape cultivation and winemaking
in many regions of different and unique characteristics. The wine grape cultivation for winemaking concentrates in the South
Region, mainly in the Serra Gaúcha, the mountain area of the state of Rio Grande do Sul, which is responsible for 90% of the
domestic wine production. However, in recent years, two new production regions have developed: the Campanha, the plains to
the south and the Serra do Sudeste, the hills to the southeast of the state. Analysis of isotopic ratios of 18O/16O of wine water, 13C/12C of ethanol, and of minerals were used to characterize wines from different regions. The isotope analysis of δ18O of wine water and minerals Mg and Rb were the most efficient to differentiate the regions. By using isotope and mineral
analysis, and discrimination analysis, it was possible to classify the wines from south Brazil. 相似文献