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A newly developed magnetic regenerator material Er(Ni0.075Co0.925)2, having high specific heat at temperatures from 10 to 20 K, has been tested inside the second regenerator of a two-stage GM cryocooler. Different working conditions have been examined: four Er(Ni0.075Co0.925)2/Pb material ratios, three displacer reciprocating speeds, and two cryocooler stroke lengths. In the best working conditions, the experimental results show a cooling power improvement up to 15% over the whole temperature range from 10 to 20 K compared to that of the same GM cryocooler employing only lead.  相似文献   
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Various lignocellulosic substrates, including microcrystalline cellulose, pinewood and hemp fibres, were treated with triethylaluminium and triethylboron in suspensions, in non‐swelling media. Chemical and spectroscopic analyses show that coupling surface reactions took place between one or two metal‐to‐carbon (Mt–C) bonds and the OH groups of the natural polymers. The remaining unreacted Mt–C bonds were exploited to graft numerous molecular structures derived from alcohols and amines. The occurrence of the second reaction was proved by Fourier‐transform infrared spectroscopy, elemental analyses, X‐ray photoelectron spectroscopy and contact angle measurements. Copyright © 2004 Society of Chemical Industry  相似文献   
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Organic-inorganic hybrid materials were prepared starting from tetraethoxysilane and α- or α,ω-triethoxysilane terminated poly(ε-caprolactone) (PCL-Si) using the sol-gel process. In all cases the formation of nanocomposites with a high level of interpenetration between organic and inorganic phases was noted. Poly(methyl methacrylate) slabs were dip-coated with PCL-Si/silica hybrids and a very strong increase of the flame resistance (also after UV irradiation) was noted for all coating compositions without marked differences with respect to hybrid compositions. This behavior was attributed to a preferential segregation of silica onto the outer surface, as evidenced by XPS analysis.  相似文献   
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α,ω-triethoxysilane terminated poly(ethylene oxide) (PEO-Si) was prepared and used to produce organic/inorganic hybrids by the sol-gel approach. These hybrids were used as coatings for flexible PVC tubes in order to reduce the plasticizer leaching from PVC medical devices. Extraction tests carried out with hexane indicated that all coating composition investigated are able to strongly reduce (about one order of magnitude) the leaching of di-ethylhexyl phthalate in hexane. The best results were obtained by an accurate balance of organic and inorganic phases content. XPS analysis showed a preferential segregation of silica onto the outer surface suggesting that a high inorganic content at the coating-extraction medium interface was present.  相似文献   
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We describe a method to characterize spatial or temporal changes in the optical properties of turbid media using diffuse reflectance images acquired under broad-beam illumination conditions. We performed experiments on liquid phantoms whose absorption (mu(a)) and reduced scattering (mu(s)') coefficients were representative of those of biological tissues in the near infrared. We found that the relative diffuse reflectance R depends on mu(a) and mu(s)' only through the ratio mu(a)/mu(s)' and that dependence can be well described with an analytical expression previously reported in the literature [S. L. Jacques, Kluwer Academic Dordrecht (1996)]. We have found that this expression for R deviates from experimental values by no more than 8% for various illumination and detection angles within the range 0 degrees-30 degrees. Therefore, this analytical expression for R holds with good approximation even if the investigated medium presents curved or irregular surfaces. Using this expression, it is possible to translate spatial or temporal changes in the relative diffuse reflectance from a turbid medium into quantitative estimates of the corresponding changes of (mu(a)/mu(s)')(1/2). In the case of media with optical properties similar to those of tissue in the near infrared, we found that the changes mu(a)/mu(s)' should occur over a volume approximately 2 mm deep and 4 mm x 4 mm wide to apply this expression.  相似文献   
29.
Renewable Energy Sources (RES) exploitation for electric energy and hydrogen production has been identified as one of the leading ways towards a future sustainable energy system. Hydrogen can be stored and transported in gaseous (GH2) or liquid form (LH2). When large hydrogen storage is required, liquefaction can be convenient with respect to compression, because of its higher storage density. LH2 can also be used as a coolant for superconducting lines, acting at the same time as energy vector and cryogen. In particular, in this paper we focus on the MgB2 material mainly due to economic considerations and working temperature match with LH2. A system for large scale RES exploitation allowing flexible and controlled delivery of electric energy and LH2 is presented. For the thermo-hydraulic design, a method is proposed which resorts to compressible fluid equations put in a convenient simplified form. A case application with 20 km distance between cooling stations is considered, and the need of taking into account LH2 compressibility for pipeline design is shown.  相似文献   
30.
The main goal of our study is to prepare and to understand the properties of cubic SiC nanowires (NWs) and to characterize its native silicon dioxide. The wires, with diameters ranging from 10 nm to 2 μm, have been prepared by a CVD process on Si (0 0 1) substrates, using CO as the carbon source and Ni as the catalyst. A structural and optical analysis, by means of TEM, micro-Raman and cathodoluminescence (CL) spectroscopy, has been performed. Two sets of samples have been studied, labelled A and B, which differ for growth process conditions. Set A showed two broad CL peaks. Set B showed a much weaker CL emission. This difference has been explained by means of TEM investigation and micro-Raman spectra: set A shows a thick amorphous silicon dioxide layer on the wire surface, whereas set B shows a thin or absent oxide layer. Consequently, the nature of the CL emission has to be ascribed mainly to oxide-related recombination.  相似文献   
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