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21.
Aminals as substrates for sulfur ylides: a synthesis of functionalized aziridines and N-heterocycles
Sulfur ylides stabilized by Ar, vinyl, or amide groups react with five-membered-ring tert-butylsulfinyl aminals to give functionalized chiral, nonracemic aziridines in high yield and with good selectivities (up to 15:1 trans:cis, up to >95:5 trans dr, always >95:5 cis dr). The intermediate aziridines can be converted into pyrrolidines or piperidines depending on the reaction conditions. 相似文献
22.
Constantinos G. Panayiotou 《Journal of solution chemistry》1991,20(1):97-114
The LFAS (Lattice-Fluid Associated Solution) model, which has been applied to alkanol + alkane and to alkanol + alkanol mixtures is now extended to mixtures consisting of one self-associated and one active or weakly self-associated component. The types of association complexes considered are AnBm and AnB with a single A-B bond each. The model is subsequently applied to binary alkanol + amine mixtures with an emphasis on vapor-liquid equilibria. Self-association constants for n-alkyl amines and dialkyl amines are presented along with the pure component lattice-fluid scaling constants. These parameters are used for correlating pure component data on vapor pressures, heats of vaporization, and orthobaric densities as well as mixing properties of amine + alkane mixtures.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60th birthday, Clermont-Ferrand, France, 17–18 May 1990. 相似文献
23.
Theofanis P. Lambrou Christos G. Panayiotou Santiago Felici Baltasar Beferull 《Wireless Personal Communications》2010,54(1):187-201
Reliable monitoring of a large area with a Wireless Sensor Network (WSN) typically requires a very large number of stationary nodes, implying a prohibitive cost and excessive (radio) interference. Our objective is to develop an efficient system that will employ a smaller number of stationary nodes that will collaborate with a small set of mobile nodes in order to improve the area coverage. The main strength of this collaborative architecture stems from the ability of the mobile sensors to sample areas not covered (monitored) by stationary sensors. An important element of the proposed system is the ability of each mobile node to autonomously decide its path based on local information (i.e. a combination of self collected measurements and information gathered by stationary sensors in the mobile’s communication range), which is essential in the context of large, distributed WSNs. The contribution of the paper is the development of a simple distributed algorithm that allows mobile nodes to autonomously navigate through the field and improve the area coverage. We present simulation results based on a real sparse stationary WSN deployment for the coverage improvement scenario. 相似文献
24.
P. N. Manoudis I. Karapanagiotis A. Tsakalof I. Zuburtikudis B. Kolinkeová C. Panayiotou 《Applied Physics A: Materials Science & Processing》2009,97(2):351-360
A very simple method that can be used to impart superhydrophobicity to stone surfaces of monuments using common and low-cost
materials that are already employed or are easy to be found by conservators is presented. A siloxane-nanoparticle dispersion
is sprayed on a stone, and this process can result in the formation of a rough two-length-scale hierarchical structure that
exhibits water repellent properties, provided that the nanoparticle concentration in the dispersion is higher than a critical
value. Superhydrophobicity (static contact angle >150° and contact angle hysteresis <7°) is achieved, by this simple method
(i) on the surfaces of three types of stones, Opuka, Božanovsky and Hořicky, which have been used for the restoration of the
castle of Prague, (ii) using two poly (alkyl siloxane) products such as Rhodorsil 224 and Porosil VV plus, which are utilized
by conservators and (iii) using common nanoparticles such as silica (SiO2), alumina (Al2O3), tin oxide (SnO2) and titanium oxide (TiO2). It is shown that the stone substrate and the nanoparticle size (5–50 nm) or type have almost no effect on the wettability
of the superhydrophobic surfaces, as comparable contact angles were measured on the three stone substrates, treated with any
siloxane-particle composite. Treatments of the stones with pure (hydrophobic) siloxanes and siloxane-SiO2 (superhydrophobic) composites result in comparable reductions of the water vapor permeability and the water amounts absorbed
by capillarity. Consequently, the use of nanoparticles in the protective coatings does not have any obvious effect on the
results of the aforementioned tests. However, the aesthetic appearance of the three stones, included in this study, is highly
affected by the nanoparticles. 相似文献
25.
The needs of the wireless and mobile user regarding information access and services are quite different than those of the desktop user. This need is not about browsing the Web but about receiving personalized services that are highly sensitive to the immediate environment and requirements of the user. Personalization appears to be the most appropriate solution to this need. It comes into aid by creating personalized portals that are specific for the wireless user, which (a) are focus on the local content and (b) directly tones down factors that break up the functionally of the Internet/wireless services when viewed through wireless devices; factors like the click count, user response time (the choice factor) and the size of the wireless network traffic. In this paper we present a flexible personalization system for the wireless user that takes into consideration user mobility, the local environment and the user and device profile. The system utilizes the various characteristics of mobile agents to support flexibility, scalability, modularity and user mobility. We present metrics appropriate to the wireless environment, and an initial performance evaluation indicating improvement ranging from 33% up to, for certain metrics, 60%. 相似文献
26.
Using caffeic acid and p-hydroxybenzoic acid as templates, two molecularly imprinted polymers (MIPs) were prepared that were used for isolation of polyphenols from olive mill waste water samples (OMWWs) without previous pre-treatment. For the preparation of the caffeic acid MIPs 4-vinylpyridine, allylurea, allylaniline and methacrylic acid were tested as functional monomers, ethylene glycol dimethylacrylate (EDMA), pentaerythritol trimethylacrylate (PETRA) and divinylbenzene 80 (DVB80) as cross-linkers and tetrahydrofuran as porogen. For p-hydroxybenzoic acid 4-vinylpyridine, allylurea and allylaniline were tested as functional monomers, EDMA and PETRA as cross-linkers and acetonitrile as porogen. The performance of the synthesized polymers was evaluated against seven structurally related compounds by means of polymer-based HPLC. The two polymers that presented the most interesting properties were further evaluated by batch rebinding and from the derived isotherms their capacity and binding strength were determined. Using solid-phase extraction (SPE), their ability to recognize and bind the template molecule from an aqueous solution as well as the pH dependence of the binding strength were explored. After establishing the best SPE protocol, an aqueous model mixture of compounds and a raw OMWWs sample were loaded on the two best polymers. The result of the consecutive use of the two polymers on the same sample was explored. It was concluded that acidic conditions favour the recognition abilities of both polymers and that they can be used for a quick and efficient isolation of the polyphenol fraction directly from raw OMWW. 相似文献
27.
Combining prolinamides with 2-pyrrolidinone: Novel organocatalysts for the asymmetric aldol reaction
Ismini Vlasserou Maria Sfetsa Dimitrios-Triantafyllos Gerokonstantis Christoforos G. Kokotos Panagiota Moutevelis-Minakakis 《Tetrahedron》2018,74(19):2338-2349
Peptides and especially prolinamides have been identified as excellent organocatalysts for the aldol reaction. The combination of prolinamides with derivatives bearing the 2-pyrrolidinone scaffold, deriving from pyroglutamic acid, led to the identification of novel organocatalysts for the intermolecular asymmetric aldol reaction. The new hybrids were tested both in organic and aqueous media. Among the compounds tested, 22 afforded the best results in petroleum ether, while 25 afforded the products in brine in high yields and selectivities. Then, various ketones and aldehydes were utilized and the products of the aldol reaction were obtained in high yields (up to 100%) with excellent diastereo- (up to 97:3 dr) and enantioselectivities (up to 99% ee). 相似文献
28.
Eleftheria Athanasopoulou Christoforos N. Hadjicostis 《Journal of Signal Processing Systems》2008,53(3):411-418
This paper obtains lower and upper bounds for the switching activity on the state lines of a finite state machine (FSM) that
is driven by typical input sequences. More specifically, the paper provides bounds on the average Hamming distance which is
in turn proportional to the switching activity and the overall power dissipation in the system. By introducing the concepts
of a distance matrix and a weight matrix, and by exploiting the symmetry of the distance matrix, we are able to obtain bounds
that are provably tighter than existing bounds and, as demonstrated by our experimental results, they can offer significant
improvements in many cases of interest. Since our bounds are independent of the state assignment and the actual implementation,
they can be used at an early stage of the FSM design to indicate the largest/smallest possible power consumption.
Eleftheria Athanasopoulou received the Diploma degree in Electrical and Computer Engineering from the University of Patras in 2000, the M.S. degree in Electrical Engineering from the University of Illinois at Urbana-Champaign in 2002, and the Ph.D. degree in Electrical and Computer Engineering from the University of Illinois at Urbana-Champaign in 2007. She is currently a postdoctoral research associate in the Coordinated Science Laboratory at the University of Illinois at Urbana-Champaign. Her research interests include discrete event systems, monitoring and supervisory control, statistical model classification under noisy observations, hidden Markov models, graphical models, and stochastic processes with applications to failure diagnosis, security, wireless networks, and probabilistic computational biology. Christoforos N. Hadjicostis received S.B. degrees in Electrical Engineering, in Computer Science and Engineering, and in Mathematics, the M.Eng. degree in Electrical Engineering and Computer Science in 1995, and the Ph.D. degree in Electrical Engineering and Computer Science in 1999, all from the Massachusetts Institute of Technology, Cambridge, MA. In August 1999 he joined the Faculty at the University of Illinois at Urbana-Champaign where he is currently an Associate Professor with the Department of Electrical and Computer Engineering and a Research Associate Professor with the Coordinated Science Laboratory. His research interests include systems and control, fault-tolerant combinational and dynamic systems, and fault diagnosis and management in large-scale systems and networks. 相似文献
Christoforos N. Hadjicostis (Corresponding author)Email: |
Eleftheria Athanasopoulou received the Diploma degree in Electrical and Computer Engineering from the University of Patras in 2000, the M.S. degree in Electrical Engineering from the University of Illinois at Urbana-Champaign in 2002, and the Ph.D. degree in Electrical and Computer Engineering from the University of Illinois at Urbana-Champaign in 2007. She is currently a postdoctoral research associate in the Coordinated Science Laboratory at the University of Illinois at Urbana-Champaign. Her research interests include discrete event systems, monitoring and supervisory control, statistical model classification under noisy observations, hidden Markov models, graphical models, and stochastic processes with applications to failure diagnosis, security, wireless networks, and probabilistic computational biology. Christoforos N. Hadjicostis received S.B. degrees in Electrical Engineering, in Computer Science and Engineering, and in Mathematics, the M.Eng. degree in Electrical Engineering and Computer Science in 1995, and the Ph.D. degree in Electrical Engineering and Computer Science in 1999, all from the Massachusetts Institute of Technology, Cambridge, MA. In August 1999 he joined the Faculty at the University of Illinois at Urbana-Champaign where he is currently an Associate Professor with the Department of Electrical and Computer Engineering and a Research Associate Professor with the Coordinated Science Laboratory. His research interests include systems and control, fault-tolerant combinational and dynamic systems, and fault diagnosis and management in large-scale systems and networks. 相似文献
29.
Superhydrophobic composite films produced on various substrates 总被引:1,自引:0,他引:1
Manoudis PN Karapanagiotis I Tsakalof A Zuburtikudis I Panayiotou C 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):11225-11232
Hydrophilic silica (SiO2) nanoparticles were dispersed in solutions of poly(methyl methacrylate) (PMMA) and in solutions of a commercial poly(alkyl siloxane) (Rhodorsil 224), and the suspensions were sprayed on glass surfaces. The effect of the particle concentration on the hydrophobic character of PMMA-SiO2 and Rhodorsil-SiO2 films was investigated and showed the following: (i) Static contact angles (theta s), measured on surfaces that were prepared from dilute dispersions (particle concentration <1% w/v), increase rapidly with particle concentration and reach maximum values (154 and 164 degrees for PMMA-SiO2 and siloxane-SiO2, respectively). Further increases in particle concentration do not have any effect on theta s. (ii) The effect of particle concentration on the contact angle hysteresis (thetaAlpha - thetaR) is more complicated: as the particle concentration increases, we first notice an increase in hysteresis, which then decreases and finally becomes constant at elevated particle concentrations. The lowest thetaAlpha - thetaR values were 5 degrees for PMMA-SiO2 and 3 degrees for siloxane-SiO2, respectively. (iii) SEM and AFM images show that a two-length-scale hierarchical structure is formed on the surface of the superhydrophobic films. It is demonstrated that superhydrophobicity can be achieved using various hydrophilic nanoparticles (alumina and tin oxide nanoparticles were successfully tested) and that the substrate has almost no effect on the hydrophobic character of the applied coatings, which were produced on silicon, concrete, aluminum, silk, wood, marble, and of course glass. The results are discussed in light of Wenzel and Cassie-Baxter models. 相似文献
30.
One-Pass EAP-AKA Authentication in 3G-WLAN Integrated Networks 总被引:1,自引:1,他引:1
The incorporation of Wireless Local Area Networks (WLANs) within the third generation (3G) networks materializes the next
generation of mobile/wireless systems, named 3G-WLANs integrated networks. This paper proposes an improved authentication
procedure for the 3G-WLANs integrated networks that enables a WLAN user to get access to the 3G packet switched services or
to the public Internet through the 3G public land mobile network. The proposed procedure reduces significantly the authentication
overhead compared to the legacy one, without compromising the provided security services. A security analysis of the proposed
authentication procedure is elaborated that ensures the correctness of the authentication procedure, the provision of advanced
security services and the elimination of possible attacks that may threaten the proposed authentication procedure. In addition,
an energy cost analysis is carried out that compares the energy consumption induced by the legacy and the proposed authentication
procedures. Finally, a communication cost analysis is provided that estimates the cost improvement of the proposed over the
legacy authentication procedure.
相似文献
Christos XenakisEmail: |