排序方式: 共有74条查询结果,搜索用时 109 毫秒
51.
Panagiota N. Eleni Magdalini K. KrokidaGregory L. Polyzois Constantinos A. CharitidisElias P. Koumoulos Vasiliki P. TsikourkitoudiIoannis Ziomas 《Polymer Degradation and Stability》2011,96(4):470-476
The degradation of maxillofacial prosthetic elastomers that occur during physical weathering is usually responsible for the replacement of the prosthesis. In this study the mechanical behaviour of a polydimethylsiloxane (PDMS) elastomer was investigated, after 1 year outdoor weathering in two different weathering locations in Greece (Thessaloniki, Athens). The hypothesis investigated was that irradiation time did not affect the measured properties. Specimens (Elastomer 42) were prepared according to manufacturer’s instructions and exposed to solar radiation for 1 year. Compression, tensile and nanoindentation tests were performed before and after the exposure. Compression and tensile data were also subjected to analysis of variance (ANOVA) and Tukey Post hoc tests at a level of α = .05. These properties were selected due to their clinical significance for fabrication and maintenance of a facial prosthesis. According to statistical analysis all the measured properties changed significantly after outdoor weathering. More specifically, most of the properties presented significant changes after six months of weathering. The observed changes also depended on the weathering locations. The hypothesis investigated was rejected. Material A became harder and the observed differences in the mechanical behaviour resulted from photo-degradation and hydrolysis that might occur due to weathering. The study also provides new information about maxillofacial prosthetics serviceability obtained from nanoindentation tests. 相似文献
52.
H. Eugene Stanley Xavier Gabaix Parameswaran Gopikrishnan Vasiliki Plerou 《Nonlinear dynamics》2006,44(1-4):329-340
We present an overview of recent research applying ideas of statistical physics to try to better understand puzzles regarding
economic fluctuations. One of these puzzles is how to describe outliers, phenomena that lie outside of patterns of statistical
regularity. We review evidence consistent with the possibility that such outliers may not exist. This possibility is supported
by recent analysis of a database containing the bid, ask, and sale price of each trade of every stock. Further, the data support
the picture of economic fluctuations, due to Plerou et al., in which a financial market alternates between being in an “equilibrium
phase” where market behavior is split roughly equally between buying and selling, and an “out-of-equilibrium phase” where
the market is mainly either buying or selling. 相似文献
53.
An SPE method followed by GC-electron capture detection (ECD) with confirmation by MS for the trace determination of four pesticides considered as endocrine-disrupting compounds (EDCs) in natural waters and sediments has been developed. Target analytes, fenarimol, fenvalerate, pendimethalin, and vinclozolin, belong to different chemical groups and are used mainly in agriculture. In the present study, analysis employs an offline SPE step for the extraction of the target analytes from natural waters. Sonication and subsequent SPE clean-up was used for extraction and purification of the sediment samples which were finally treated with activated copper powder. The type of SPE disk, eluents as well as solution parameters including pH value, and concentrations of salts and humic substances were examined for the efficiency of the method. The recoveries of all pesticides were in relatively high levels, ranging from 75 to 97% for waters and 71 to 84% for sediment samples. Both methods were applied to real water and sediment samples and the presence of the tested compounds was investigated. 相似文献
54.
Panagakou Vasiliki Psarrakos Panayiotis Yannakakis Nikos 《Aequationes Mathematicae》2021,95(5):889-914
Aequationes mathematicae - The cosine function is a classical tool for measuring angles in inner product spaces, and it has various extensions to normed linear spaces. In this paper, we investigate... 相似文献
55.
dos Santos JH Butler IS Daga V Hadjikakou S Hadjiliadis N 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(12):2725-2735
The pressure dependences of the Fourier transform micro-Raman spectra of four heterocyclic thioamides [[(bztzdtH)I2] x I2] (1) (bztzdtH = benzothiazole-2-thione), [(bztzdtH)I2] (2), [[(tzdtH)2I+] x I3- x 2I2] (3) (tzdtH = thiazoline-2-thione), and [[(bzimtH)I2]2 x I2 x 2H2O] (4) (bzimtH = benzimidazole-2-thione) have been studied between ambient pressure and 50 kbar. For 1, generation of I3- ions through disproportionation reactions is evident as the pressure is increased. There are empirical linear correlations between the frequency and (I-I) bond length and the applied pressure. The iodine adduct of thioamide 2 is more sensitive to pressure when compared to the 1 or 4 iodine adducts. This difference in behavior may be attributed to differences in crystal structures or to a lower I-I bond order. Monitoring of other vibrational transitions of the thiomide structure reveals several less important pressure dependences. 相似文献
56.
Zorbas V Smith AL Xie H Ortiz-Acevedo A Dalton AB Dieckmann GR Draper RK Baughman RH Musselman IH 《Journal of the American Chemical Society》2005,127(35):12323-12328
We have previously demonstrated that a designed amphiphilic peptide helix, denoted nano-1, coats and debundles single-walled carbon nanotubes (SWNTs) and promotes the assembly of these coated SWNTs into novel hierarchical structures via peptide-peptide interactions. The purpose of this study is to better understand how aromatic content impacts interactions between peptides and SWNTs. We have designed a series of peptides, based on the nano-1 sequence, in which the aromatic content is systematically varied. Atomic force microscopy measurements and optical absorption spectroscopy reveal that the ability to disperse individual SWNTs increases with increasing aromatic residues in the peptide. Altogether, the results indicate that pi-stacking interactions play an important role in peptide dispersion of SWNTs. 相似文献
57.
Ikonomidou VN Sergiadis GD 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,157(2):218-222
Magnetic resonance tagging usually relies on controlling the phase dispersion of the transverse magnetization component. Phase dispersion is, however, affected by the inherent phase of selective excitation pulses, thus limiting their combination with tagging sequences to the application of refocusable pulses, as in the localized spatial modulation of magnetization (L-SPAMM) technique. In this study, we examine the effect of selective excitation pulses on a L-SPAMM 1-1 sequence, showing that in the case of two identical pulses the phase component is canceled out, and thus preemphasis and refocus gradients are not needed, allowing us to take advantage of a constant gradient throughout the tagging sequence, and also that one might choose nonrefocusable maximum and minimum phase pulses. 相似文献
58.
Ortiz-Acevedo A Xie H Zorbas V Sampson WM Dalton AB Baughman RH Draper RK Musselman IH Dieckmann GR 《Journal of the American Chemical Society》2005,127(26):9512-9517
We have utilized reversible cyclic peptides (RCPs)-peptides containing alternating l- and d-amino acids with N- and C-termini derivatized with thiol-containing groups allowing reversible peptide cyclization-to solubilize and noncovalently functionalize carbon single-walled nanotubes (SWNTs) in aqueous solution. Solubilization occurs through wrapping of RCPs around the circumference of a SWNT, followed by the formation of head-to-tail covalent bonds, yielding closed rings on the nanotubes. By controlling the length of the RCPs, we have demonstrated limited diameter-selective solubilization of the SWNTs as revealed by UV/vis/NIR and Raman spectroscopies, as well as atomic force microscopy. 相似文献
59.
Catia de Bonis Cataldo Simari Vasiliki Kosma Barbara Mecheri Alessandra D’Epifanio Valentina Allodi Gino Mariotto Sergio Brutti Sophia Suarez Kartik Pilar Steve Greenbaum Silvia Licoccia Isabella Nicotera 《Journal of Solid State Electrochemistry》2016,20(6):1585-1598
An organically functionalized titania, TiO2-RSO3H, was evaluated as filler in sulfonated polyetheretherketone (sPEEK)-based composite membranes for application in high temperature direct methanol fuel cells. The presence of propylsulfonic acid groups covalently bound onto the TiO2 surface and the nanometric nature of the additive were analyzed by Raman spectroscopy and transmission electron microscopy, respectively. The properties of the sPEEK/TiO2-RSO3H composite membranes were compared with those of the pure sPEEK membranes and those of the sPEEK/TiO2 composite membranes containing pristine titania nanoparticles at same filler content. Water and methanol transport properties were investigated by NMR methods, including relaxation times and self-diffusion coefficients as function of temperature (up to 130 °C), and pressure (from 0 up to 2 kbar). The incorporation of the nanoadditivies in the sPEEK polymer demonstrates considerable effects on the morphology and stiffness of the membranes, as well as on the transport properties and barrier effect to the methanol crossover. In particular, the functionalization by propylsulfonic acid groups promotes a higher reticulation between the polymeric chains, increasing the tortuosity of the methanol diffusional paths, so reducing the molecular diffusion, while the proton mobility increases being favored by the Grotthus-type mechanism. Conductivity measurements point out that the filler surface functionalization avoids the reduction of the overall proton conduction of the electrolyte due to the embedding of the low-conducting TiO2. Finally, remarkable improvements were found when using the sPEEK/TiO2-RSO3H composite membrane as electrolyte in a DMFC, in terms of reduced methanol crossover and higher current and power density delivered. 相似文献
60.