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排序方式: 共有492条查询结果,搜索用时 15 毫秒
1.
Isaac Isarn Leïla Bonnaud Lluís Massagus ngels Serra Francesc Ferrando 《Polymer International》2020,69(3):280-290
The enhancement of the thermal conductivity, keeping the electrical insulation, of epoxy thermosets through the addition of pristine and oxidized carbon nanotubes (CNTs) and microplatelets of boron nitride (BN) was studied. Two different epoxy resins were selected: a cycloaliphatic (ECC) epoxy resin and a glycidylic (DGEBA) epoxy resin. The characteristics of the composites prepared were evaluated and compared in terms of thermal, thermomechanical, rheological and electrical properties. Two different dispersion methods were used in the addition of pristine and oxidized CNTs depending on the type of epoxy resin used. Slight changes in the kinetics of the curing reaction were observed in the presence of the fillers. The addition of pristine CNTs led to a greater enhancement of the mechanical properties of the ECC composite whereas the oxidized CNTs presented a greater effect in the DGEBA matrix. The addition of CNTs alone led to a marked decrease of the electrical resistivity of the composites. Nevertheless, in the presence of BN, which is an electrically insulating material, it was possible to increase the proportion of pristine CNTs to 0.25 wt% in the formulation without deterioration of the electrical resistivity. A small but significant synergic effect was determined when both fillers were added together. Improvements of about 750% and 400% in thermal conductivity were obtained in comparison to the neat epoxy matrix for the ECC and DGEBA composites, respectively. © 2019 Society of Chemical Industry 相似文献
2.
Ingrid Martorell Francesc X Grau 《International Journal of Heat and Mass Transfer》2003,46(13):2389-2402
The present work deals with the natural convection flow and heat transfer from a horizontal plate cooled from above. Experiments are carried out for rectangular plates having aspect ratios between φ=0.036 and 0.43 and Rayleigh numbers in the range 290?Raw?3.3×105. These values of Raw and φ have been selected below those commonly considered in previous research in view of a future application to the design of printed circuit boards. The plates are made of two different metals, copper and steel. The choice of a metal is relevant to the present problem because the plates are heated by means of an electric current. Important variations of the surface temperature are observed along the transverse direction for the steel plates. The surface of the copper plates is almost isothermal because of the high thermal conductivity of the metal.Calculations for a semi-infinite plate are carried out to predict the transverse profiles of the surface temperature and heat flux and to visualize the structure of the flow. Three-dimensional calculations are also used at a qualitative level to observe the changes in the flow structure due to the finite length of the plate. Present results are compared with both previous experimental work and analyses that are based on boundary layer theory. It is shown that analyses for an infinite boundary layer are not completely applicable to the present problem because of its different physics. The most relevant feature of the natural convection flow, which is not predicted by boundary layer analyses, is a thermal plume rising near the center of the plate.Present heat transfer results differ from previous experimental work because of the lower Rayleigh numbers and aspect ratios investigated here. The Nusselt number is found to depend on Rawn, with the exponent n=0.17 being lower than most of the values reported in the literature. This comparatively low value is related to the transverse conduction of heat through the air, which becomes increasingly significant as Raw approaches zero. It is shown that such a low-Raw effect can be accounted for in a physically consistent manner by adding a constant term to the heat transfer correlation. On the other hand, it is found that the Nusselt number does not significantly depend on the aspect ratio in the range of φ investigated contrary to what has been previously reported for wider plates. 相似文献
3.
An in situ NMR study of tert-butanol dehydration in 95 and 85% sulfuric acid did not indicate the formation of tert-butyl cations as active reaction intermediates. Instead, only NMR lines from oxonium ions under the condition of fast exchange with water and the acid were observed. It is most likely that, in the concentrated acid, the active intermediates of this reaction are represented by tert-butyl sulfuric ester which probably is a precursor of invisible tert-butyl carbenium ions representing short-lived excited or transition states. 相似文献
4.
Fatin N. Mohd Jaya Sergio G. Garcia Francesc E. Borras Dolores Guerrero Godfrey C. F. Chan Marcella Franquesa 《International journal of molecular sciences》2021,22(9)
Regulatory B (Breg) cells are endowed with immune suppressive functions. Various human and murine Breg subtypes have been reported. While interleukin (IL)-10 intracellular staining remains the most reliable way to identify Breg cells, this technique hinders further essential functional studies. Recent findings suggest that CD9 is an effective surface marker of murine IL-10 competent Breg cells. However, the stability of CD9 and its relevance as a unique marker for human Breg cells, which have been widely characterized as CD24hiCD38hi, have not been investigated. Here, we demonstrate that CD9 expression is sensitive to in vitro B cell stimulations. CD9 expression could either be re-expressed or downregulated in purified CD9-negative B cells and CD9-positive B cells, respectively. We found no significant differences in the Breg differentiation capacity of the CD9-negative and CD9-positive B cells. Furthermore, CD9-positive B cells co-express CD40 and CD86, suggesting their nature as B cell activation or co-stimulatory molecules, rather than regulatory ones. Therefore, we report the relatively unstable CD9 as a distinct surface molecule, indicating the need for further research for a more reliable marker to purify human Breg cells. 相似文献
5.
Fernando Corvillo Laura Gonzlez-Snchez Alberto Lpez-Lera Emilia Arjona Giovanni Ceccarini Ferruccio Santini David Araújo-Vilar Rebecca J Brown Joan Villarroya Francesc Villarroya Santiago Rodríguez de Crdoba Teresa Caballero Pilar Nozal Margarita Lpez-Trascasa 《International journal of molecular sciences》2021,22(12)
6.
F. Figueras J. L. Flores G. Delahay A. Bourane J.-M. Clacens A. Desmartin-Chomel B. Coq A. Giroir-Fendler 《Topics in Catalysis》2006,39(1-2):59-64
Titanias of different surface areas have been sulfated and used as supports of Rh oxide for the selective catalytic reduction
of nitrogen oxides. Only the sulfation of TiO2 of large surface areas gives strong Br?nsted acid sites, retaining pyridine up to 773 K. Low surface area anatase is unable
to retain sulfates. The catalytic activities measured at 523 K, increase with the number of acid sites, and then reach a plateau,
showing the intervention of acidity in the SCR. This is true only for Rh but not for Pt. The investigation of the elemental
steps on Rh/sulfated TiO2 by in situ diffuse reflectance spectroscopy permits to clarify a few points: the oxidation of propene, presumably to acetaldehyde, occurs
by the reaction with nitrates adsorbed on the support. The further oxidation of this intermediate by NO2 yields an isocyanate, which can be hydrolysed to ammonia. 相似文献
7.
Nowadays, the use of Radio Frequency Identification (RFID) systems in industry and stores has increased. Nevertheless, some
of these systems present privacy problems that may discourage potential users. Hence, high confidence and effient privacy
protocols are urgently needed. Previous studies in the literature proposed schemes that are proven to be secure, but they
have scalability problems. A feasible and scalable protocol to guarantee privacy is presented in this paper. The proposed
protocol uses elliptic curve cryptography combined with a zero knowledge-based authentication scheme. An analysis to prove
the system secure, and even forward secure is also provided.
This work is supported by the Generalitat de Catalunya under Grant No. FIC 2007FIC 00880, and the projects of the Spanish
MCyT MTM2007-66842-C02-02 and TIN2006-15662-C02-02. 相似文献
8.
Rodríguez CE Arranz JA Colomé N Bech-Serra JJ Canals F Del Toro M Riudor E 《Proteomics. Clinical applications》2009,3(12):1430-1439
A variant phenotype of nonketotic hyperglycinemia has been described by our group associated with pulmonary hypertension. The aim of this study is to investigate the cerebrospinal fluid proteomes to get an insight into this neurodegenerative process producing leukoencephalopathy with white matter spongiform degeneration. DIGE and MALDI-TOF-TOF analyses were performed to carry out the proteomic study of four patients against three normal controls and one additional control of a classical nonketotic hyperglycinemia. The differential proteomic analysis showed a displacement of some series of spots toward the acidic side. The shifted proteins showed a high degree of carbonylation and increased methionine sulfoxidation was found in cystatin C and in vitamin-D-binding protein. These findings in addition to the increase of serum malondialdehyde concentration provide evidence of an oxidative stress in the patients under study, which is probably systemic rather than mainly confined to the CNS. The similarities of our findings with those found in other neurodegenerative diseases suggest that oxidative damage is commonly involved in these pathologies. DIGE technology improves the 2-D PAGE differential analysis and it is suitable in proteomic studies with a small number of cases. 相似文献
9.
In last years, Face recognition based on 3D techniques is an emergent technology which has demonstrated better results than
conventional 2D approaches. Using texture (180° multi-view image) and depth maps is supposed to increase the robustness towards
the two main challenges in Face Recognition: Pose and illumination. Nevertheless, 3D data should be acquired under highly
controlled conditions and in most cases depends on the collaboration of the subject to be recognized. Thus, in applications
such as surveillance or control access points, this kind of 3D data may not be available during the recognition process. This
leads to a new paradigm using some mixed 2D-3D face recognition systems where 3D data is used in the training but either 2D
or 3D information can be used in the recognition depending on the scenario. Following this concept, where only part of the
information (partial concept) is used in the recognition, a novel method is presented in this work. This has been called Partial
Principal Component Analysis (P2CA) since they fuse the Partial concept with the fundamentals of the well known PCA algorithm. This strategy has been proven
to be very robust in pose variation scenarios showing that the 3D training process retains all the spatial information of
the face while the 2D picture effectively recovers the face information from the available data. Furthermore, in this work,
a novel approach for the automatic creation of 180° aligned cylindrical projected face images using nine different views is
presented. These face images are created by using a cylindrical approximation for the real object surface. The alignment is
done by applying first a global 2D affine transformation of the image, and afterward a local transformation of the desired
face features using a triangle mesh. This local alignment allows a closer look to the feature properties and not the differences.
Finally, these aligned face images are used for training a pose invariant face recognition approach (P2CA). 相似文献
10.
José Ramón González de Mendívil José Enrique Armendáriz-Iñigo José Ramón Garitagoitia Francesc D. Muñoz-Escoí 《The Journal of supercomputing》2009,50(2):121-161
This paper provides a formal specification and proof of correctness of a basic Generalized Snapshot Isolation certification-based data replication protocol for database middleware architectures. It has been modeled using a state transition
system, as well as the main system components, allowing a perfect match with the usual deployment in a middleware system.
The proof encompasses both safety and liveness properties, as it is commonly done for a distributed algorithm. Furthermore,
a crash failure model has been assumed for the correctness proof, although recovery analysis is not the aim of this paper.
This allows an easy extension toward a crash-recovery model support in future works. The liveness proof focuses in the uniform
commit: if a site has committed a transaction, the rest of sites will either commit it or it would have crashed. 相似文献