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Viscosimetric measurements were obtained with the ternary systems polystyrene/dioxane/methanol, polystyrene/benzene/methanol and poly(methyl methacrylate)/dioxane/cyclohexane, changing the solvent mixture composition at constant temperature. The polystyrene and poly(methyl methacrylate) systems exhibit a transition phenomenon with solvent-mixture composition in which the polymer is just above the theta condition. In the case where two theta conditions occur ((θ-intra, θ-inter) the transition point is closely related to the intramolecular theta conditions. Moreover the intramolecular theta conditions vary with the molecular weight in the region of molecular weights where the preferential adsorption also varies. This variation induces a variation of the transition point with molecular weight which obeys a formula analogous to that giving the variation of the preferential adsorption with molecular weight. 相似文献
3.
In order to overcome the difficulty of the determination of the molecular weight of a polymer in the low molecular weight region by viscometry using the Mark–Houwink–Sakurada (MHS) equation, we have proposed the Dondos–Benoit relationship [η]?1 = A2 + AM?1/2, for a number of polymer–solvent systems, for which we give the numerical values of the parameters A1 and A2. Furthermore, we suggest a method for the determination of the above parameters using the MHS constants a and k. 相似文献
4.
Enhanced Structural Stability and Photo Responsiveness of CH3NH3SnI3 Perovskite via Pressure‐Induced Amorphization and Recrystallization 下载免费PDF全文
5.
Constantinos Marios Angelopoulos Author Vitae Sotiris Nikoletseas Author Vitae 《Journal of Systems and Software》2010,83(12):2471-2477
We study the problem of fast and energy-efficient data collection of sensory data using a mobile sink, in wireless sensor networks in which both the sensors and the sink move. Motivated by relevant applications, we focus on dynamic sensory mobility and heterogeneous sensor placement. Our approach basically suggests to exploit the sensor motion to adaptively propagate information based on local conditions (such as high placement concentrations), so that the sink gradually “learns” the network and accordingly optimizes its motion. Compared to relevant solutions in the state of the art (such as the blind random walk, biased walks, and even optimized deterministic sink mobility), our method significantly reduces latency (the improvement ranges from 40% for uniform placements, to 800% for heterogeneous ones), while also improving the success rate and keeping the energy dissipation at very satisfactory levels. 相似文献
6.
This paper presents findings on the use of Web sites as a political marketing tool in the context of the 2007 Greek national elections. The questions guiding this research are how popular were online campaigns in terms of candidate use of Web sites and which trust and credibility-building Web site design cues were leveraged by candidates. This study also explored differences in online campaign practices both between Greek political parties and between the 2007 national Greek elections and the 2002 federal US elections. 相似文献
7.
The Universal Mobile Telecommunication Standard (UMTS) is continuously evolving to meet the growing demand of modern mobile and Internet applications for high capacity and advanced features in security and quality of service. Although admittedly enhanced in terms of security when compared to 2G systems, UMTS still has weaknesses that can lead to security incidents. In this paper, we investigate the vulnerabilities of the UMTS security architecture that can be exploited by a malicious individual to mount Denial of Service (DoS) attacks. Our focus is on signaling-oriented attacks above the physical layer. We describe and analyze several novel attacks that can be triggered against both core UMTS architecture as well as hybrid UMTS/WLAN realms. An additional contribution of this paper is the presentation of an extensive survey of similar attacks in UMTS and related protocol infrastructures such as IP Multimedia Subsystem (IMS). Finally, we offer some suggestions that would provide greater tolerance to the system against DoS attacks. 相似文献
8.
Bayesian feature and model selection for Gaussian mixture models 总被引:1,自引:0,他引:1
Constantinopoulos C Titsias MK Likas A 《IEEE transactions on pattern analysis and machine intelligence》2006,28(6):1013-1018
We present a Bayesian method for mixture model training that simultaneously treats the feature selection and the model selection problem. The method is based on the integration of a mixture model formulation that takes into account the saliency of the features and a Bayesian approach to mixture learning that can be used to estimate the number of mixture components. The proposed learning algorithm follows the variational framework and can simultaneously optimize over the number of components, the saliency of the features, and the parameters of the mixture model. Experimental results using high-dimensional artificial and real data illustrate the effectiveness of the method. 相似文献
9.
This paper aims to contribute to the growing body of research on online political marketing by investigating the use of websites as a marketing tool in the 2007 and 2009 general elections in Greece. The two main research objectives are firstly to establish the key factors affecting voters’ trust when it comes to using politicians’ websites and secondly to examine whether and to what extent the influence of trust-building factors changes over-time, as the online environment matures. The key findings of this research are that users tend to visit the websites of favoured candidates, which reinforces their positive perceptions of them, while as far as the websites themselves and their content and the services provided are concerned there is still room for improvement. 相似文献
10.