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Article Citation - WoS: 4Citation - Scopus: 9End-to-end security implementation for mobile devices using TLS protocol(Springer France, 2006) Kayayurt, Baris; Tuglular, Tugkan; Tuğlular, Tuğkan; Bilgisayar Mühendisliği BölümüEnd-to-end security has been an emerging need for mobile devices with the widespread use of personal digital assistants and mobile phones. Transport Layer Security Protocol (TLS) is an end-to-end security protocol that is commonly used on the Internet, together with its predecessor, SSL protocol. By implementing TLS protocol in the mobile world, the advantage of the proven security model of this protocol can be utilized. The main design goals of mobile end-to-end security protocol are maintainability and extensibility. Cryptographic operations are performed with a free library, Bouncy Castle Cryptography Package. The object oriented architecture of proposed end-to-end security protocol implementation makes the replacement of this library with another cryptography package easier. The implementation has been experimented with different cases, which represent use of different cryptographic algorithms.Article Citation - WoS: 17Silicon oxycarbide-based composites produced from pyrolysis of polysiloxanes with active Ti filler(Elsevier Sci Ltd, 2006) Akkas, H. Deniz; Ovecoglu, M. Lutfi; Tanoglu, Metin; Tanoğlu, MetinPhenyl (PPS) and methyl (PMS) containing polysiloxanes were pyrolyzed at elevated temperatures (900-1500 degrees C) under argon atmosphere to investigate the phase developments within the polymers. It was found that pyrolysis of the polymers under inert atmosphere up to 1300 degrees C leads to amorphous silicon oxycarbide (SiOxCy) ceramics. Conversions at higher temperatures results in the transformations into the crystalline beta-SiC phases. Ceramic matrix composites (CMCs) were developed based on the active filler controlled pyrolysis (AFCOP) of polysiloxanes with active Ti filler additions. CMC monoliths were prepared with 60-80 wt.% of active Ti particulates blended into polymer precursors. Green bodies of the composites were made by warm pressing under 15 MPa pressure and ceramics were obtained by pyrolysis at elevated temperatures between 900 and 1500 degrees C under argon atmosphere. The results showed that due to the incorporation of active Ti fillers, formation of crystalline phases such as TiC, TiSi, and TiO occured within the amorphous matrix due to the reactions between the Ti and the polymer decomposition products. The microstructural and mechanical characterization results of the composites are presented within the paper. (c) 2005 Elsevier Ltd. All rights reserved.Article Citation - WoS: 38Temperature dependence of electrical conductivity in double-wall and multi-wall carbon nanotube/polyester nanocomposites(Springer, 2007) Simsek, Yilmaz; Ozyuzer, Lutfi; Seyhan, A. Tugrul; Tanoglu, Metin; Schulte, Karl; Tanoğlu, MetinThe aim of this study is to investigate temperature dependence of electrical conductivity of carbon nanotube (CNT)/polyester nanocomposites from room temperature to 77 K using four-point probe test method. To produce nanocomposites, various types and amounts of CNTs (0.1, 0.3 and 0.5 wt.%) were dispersed via 3-roll mill technique within a specially formulized resin blend of thermoset polyesters. CNTs used in the study include multi walled carbon nanotubes (MWCNT) and double-walled carbon nanotubes (DWCNT) with and without amine functional groups (-NH2). It was observed that the incorporation of carbon nanotubes into resin blend yields electrically percolating networks and electrical conductivity of the resulting nanocomposites increases with increasing amount of nanotubes. However, nanocomposites containing amino functionalized carbon nanotubes exhibit relatively lower electrical conductivity compared to those with non-functionalized carbon nanotubes. To get better interpretation of the mechanism leading to conductive network via CNTs with and without amine functional groups, the experimental results were fitted to fluctuation-induced tunneling through the barriers between the metallic regions model. It was found that the results are in good agreement with prediction of proposed model.Article Citation - WoS: 37Mechanisms of cellular resistance to imatinib in human chronic myeloid leukemia cells(Taylor & Francis Ltd, 2007) Baran, Yusuf; Ural, Ali Ugur; Gunduz, Ufuk; Baran, YusufA major advancement in the treatment of chronic myeloid leukemia (CML) has been the development of imatinib, which has shown striking activity in the chronic phase and the accelerated phase, but less so in the blast phase of the disease. Despite high rates of hematologic and cytogenetic responses to therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of patients with CML. Various cellular mechanisms may be involved in the nature of cellular resistance. Increased amount of target, alteration in structure of target proteins, decreased drug uptake and increased detoxification are well-known mechanisms of resistance. On the other hand, in some cases, even if anticancer drugs reach their sites of action, bypassing drug efflux system of the cells, some cells still may survive via the dysregulation of apoptotic signalling. In this study, mechanisms of resistance to imatinib-induced apoptosis in human Meg-01 CML cells were examined. Continuous exposure of cells to step-wise increasing concentrations of imatinib resulted in the selection of 200- and 1000 nM imatinib-resistant sub-lines referred to as Meg-01/IMA-0,2 and Meg-01/1MA-1, respectively. MTT cell proliferation, cell cycle analyses and trypan blue dye exclusion analyses showed that Meg-0l/IMA-1 cells were resistant to imatinib-induced apoptosis as compared to parental sensitive cells. There was an increased expression of BCR/ABL, Bcl-2 and an increase in mitochondrial membrane potential (MMP) detected in resistant cells comparing to parental sensitive cells. There was no mutation detected in imatinib binding site of ABL kinase region. Various diverse mechanisms have been reported for their involvement in the multidrug resistance. In this study, it has been shown that the degree of BCR/ABL expression appears to be directly proportional to the levels of imatinib resistance. In addition, there have been BCR/ABL-independent mechanisms reported for deriving resistance against imatinib. Our results revealed that besides BCR/ABL overexpression, imatinib resistance also depends on the inhibition of apoptosis as a result of up-regulation of anti-apoptotic stimuli and down-regulation of pro-apoptotic stimuli through MMP but does not depend on any mutation on imatinib binding site of ABL kinase.Article Citation - WoS: 32Upregulation of multi drug resistance genes in doxorubicin resistant human acute myelogeneous leukemia cells and reversal of the resistance(Maney Publishing, 2007) Baran, Yusuf; Guer, Bala; Kaya, Pelin; Ural, Ali Ugur; Avcu, Ferit; Guenduez, Ufuk; Baran, YusufThe major problem in the treatment of acute myeloid leukemia (AML) patients results from multidrug resistance to administered anticancer agents. Drug resistance proteins, MDR1 and MRP1, which work as drug efflux pumps, can mediate the multidrug resistance of human leukemia cells. In this study, the mechanisms of resistance to doxorubicin-induced cell death in human HL60 AML cells were examined. Continuous exposure of cells to step-wise increasing concentrations of doxorubicin resulted in the selection of HL60/DOX cells, which expressed about 10.7-fold resistance as compared to parental sensitive cells. The expression analyses of MRP1 and MDR1 drug efflux proteins in doxorubicin-sensitive and -resistant HL60 cells revealed that there was an upregulation of MRP1 gene in HL60/DOX cells as compared to parental sensitive cells. On the other hand, while there was no expression of MDR1 gene in parental cells, the expression of MDR1 gene was upregulated in HL60/DOX cells. HL60/DOX cells also showed cross-resistance to cytosine arabinoside (Ara-c). This resistance was reversed by a combination therapy of Ara-c and cyclosporine A. However, the expression levels of CD15 and CD16 surface markers were significantly decreased in HL60/DOX cells.Article Citation - WoS: 140Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites(Elsevier Sci Ltd, 2007) Bozkurt, Emrah; Kaya, Elcin; Tanoglu, Metin; Tanoğlu, MetinMechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy natiocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T-g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix. (C) 2007 Elsevier Ltd. All rights reserved.Conference Object Citation - WoS: 1A study of multiple drug resistance mechanisms improved against Bortezomib on multiple myeloma cell lines in vitro(Amer Soc Hematology, 2007) Uyuklu, Tolga; Ural, A. Ugur; Sarper, Metal; Avcu, Ferit; Baran, Yusuf; Elci, Pinar; Akar, Nejat; Baran, Yusuf[No Abstract Available]Article Citation - WoS: 77Critical aspects related to processing of carbon nano tube/unsaturated thermoset polyester nanocomposites(Pergamon-elsevier Science Ltd, 2007) Seyhan, A. Tugrul; Gojny, Florian H.; Tanoglu, Metin; Schulte, Karl; Tanoğlu, MetinCarbon nanotubes (CNTs) have outstanding mechanical, thermal and electrical properties. As a result, particular interest has been recently given in exploiting these properties by incorporating carbon nanotubes into some form of matrix. Although unsaturated polyesters with styrene have widespread use in the industrial applications, surprisingly there is no study in the literature about CNT/thermoset polyester nanocomposite systems. In the present paper, we underline some important issues and limitations during the processing of unsaturated polyester resins with different types of carbon nanotubes. In that manner, 3-roll mill and sonication techniques were comparatively evaluated to process nanocomposites made of CNTs with and without amine (NH2) functional groups and polyesters. It was found that styrene evaporation from the polyester resin system was a critical issue for nanocomposite processing. Rheological behaviour of the suspensions containing CNTs and tensile strengths of their resulting nanocomposites were characterized. CNT/polyester suspensions exhibited a shear thinning behaviour, while polyester resin blends act as a Newtonian fluid. It was also found that nanotubes with amine functional groups have better tensile strength, as compared to those with untreated CNTs. Transmission electron microscopy (TEM) was also employed to reveal the degree of dispersion of CNTs in the matrix. (c) 2006 Elsevier Ltd. All rights reserved.Article Citation - WoS: 16Porous nanocomposites prepared from layered clay and PMMA [poly(methyl methacrylate)](Elsevier Sci Ltd, 2007) Tanoglu, Metin; Ergun, Yelda; Tanoğlu, MetinThe aim of the present work is the preparation of PMMA based porous nanocomposites that contain clay (montmorillonite, MMT) platelets as reinforcements within the cell walls of the porous structure. To render the clay layers organophilic, MMT was surface treated by an ion exchange reaction between interlayer cations of the clay and ammonium ions of a surfactant. Clay/PMMA based porous nanocomposites were prepared by polymerization of water-in-oil emulsions with and without clay addition. The microstructure and compressive mechanical behavior of the nanocomposites were investigated. The results of mechanical tests showed that the porous systems with the addition of 1 wt.% of organoclay (OMNIT) exhibited a 90% and 50% increase of collapse stress and elastic modulus values, respectively, as compared to neat porous PMMA. (c) 2006 Elsevier Ltd. All rights reserved.Article Citation - WoS: 3Regulation of mRNA stability through a pentobarbital-responsive element(Elsevier Science inc, 2007) Akgul, Bunyamin; Tu, Chen-Pei D.; Akgül, BünyaminPentobarbital, a general anesthetic and non-genotoxic carcinogen, can induce gene expression by activating transcription. In the Drosophila glutathione S-transferase D21 (gstD21) gene, pentobarbital's regulatory influence extends to the level of mRNA turnover. Transcribed from an intronless gene, gstD21 mRNA is intrinsically very labile. But exposure to pentobarbital renders it stabilized beyond what can be attributed to transcriptional activation. We aim here to identify cis-acting element(s) of gstD21 mRNA as contributors to the molecule's pentobarbital-mediated stabilization. In the context of hsp70 5'UTR and the 3'UTR of act5C, gstD21 mRNA, minus its native UTRs, is stable. Maintaining the same context of heterologous UTRs, we can reconstitute using the full-length gstD21 sequence the inherent instability of gstD21 mRNA and its stabilization by pentobarbital. Transgenic flies that express these chimeric gstD21 mRNA exhibit decay intermediates lacking 3'UTR, which are not stabilized by PB treatment. The 3'UTR sequence, when inserted downstream from a reporter transcript, stabilizes it 1.6-fold under PB treatment. The analysis of the decay intermediates suggests a polysome-associated decay pattern. We propose a regulatory model that features a 59-nucleotide pentobarbital-responsive element (PBRE) in the 3'UTR of gstD21 mRNA. (c) 2006 Elsevier Inc. All rights reserved.Article Citation - WoS: 180Mode I and mode II fracture toughness of E-glass non-crimp fabric/carbon nanotube (CNT) modified polymer based composites(Pergamon-elsevier Science Ltd, 2008) Seyhan, A. Tugrul; Tanoglu, Metin; Schulte, Karl; Tanoğlu, MetinIn this study, mode I and mode II interlaminar fracture toughness, and interlaminar shear strength of E-glass non-crimp fabric/carbon nanotube modified polymer matrix composites were investigated. The matrix resin containing 0.1 wt.% of amino functionalized multi walled carbon nanotubes were prepared, utilizing the 3-roll milling technique. Composite laminates were manufactured via vacuum assisted resin transfer molding process. Carbon nanotube modified laminates were found to exhibit 8% and 11% higher mode 11 interlaminar fracture toughness and interlaminar shear strength values, respectively, as compared to the base laminates. However, no significant improvement was observed for mode I interlaminar fracture toughness values. Furthermore, Optical microscopy and scanning electron microscopy were utilized to monitor the distribution of carbon nanotubes within the composite microstructure and to examine the fracture surfaces of the failed specimens, respectively. (c) 2008 Elsevier Ltd. All rights reserved.Article Citation - WoS: 30Glycidyl-methacrylate-based electrospun mats and catalytic silver nanoparticles(Wiley-v C H verlag Gmbh, 2008) Demir, Mustafa M.; Ugur, Goekce; Gulgun, Mehmet Ali; Menceloglu, Yusuf Z.; Demir, MustafaP(AN-GMA) and PGMA fibers coated with monodisperse silver nanoparticles have been prepared by a combination of electrospinning and electroless plating. The morphology of the electrospun fibers remains unchanged after surface hydrazination. Oxidation of hydrazine in an ammoniacal solution of AgNO3 reduces and deposits silver atoms along the fiber surface, which then coalesce to Ag particles. The size of the silver nanoparticles is varied between 20-60 nm. Since the density of the active sites for silver reduction is lower in P(AN-GAAA), a smaller particle size could be obtained. The catalytic activity of the silver nanoparticles has been confirmed.Article Citation - WoS: 37Layered clay/epoxy nanocomposites: Thermomechanical, flame retardancy, and optical properties(Wiley, 2008) Kaya, Elcin; Tanoglu, Metin; Okur, Salih; Tanoğlu, MetinIn this study, layered clay/polymer nanocomposites were developed based on epoxy resins and montmorillonite as the nanoplatelet reinforcement. Clay particles were treated with hexadecyltrimethylammonium chloride (HTCA) through an ion exchange reaction. In this way, Na+ interlayer cations of the clay is exchanged with onium cation of the surfactant that turns the hydrophilic clays (MMT) to organophilic (OMMT) characteristics. Thermal analysis results revealed that the glass transition temperature (T-g) and the dynamic mechanical properties including the storage and loss modulus of the neat epoxy resin increases by the incorporation of clay particles. It was also found that flame resistance of the polymer is improved by the addition of the clay particles. (C) 2008 Wiley Periodicals, Inc.Article Citation - WoS: 6Citation - Scopus: 9Implementing fault-tolerance in real-time programs by automatic program transformations(Assoc Computing Machinery, 2008) Ayav, Tolga; Fradet, Pascal; Girault, Alain; Ayav, Tolga; Bilgisayar Mühendisliği BölümüWe present a formal approach to implement fault-tolerance in real-time embedded systems. The initial fault-intolerant system consists of a set of independent periodic tasks scheduled onto a set of fail-silent processors connected by a reliable communication network. We transform the tasks such that, assuming the availability of an additional spare processor, the system tolerates one failure at a time (transient or permanent). Failure detection is implemented using heartbeating, and failure masking using checkpointing and rollback. These techniques are described and implemented by automatic program transformations on the tasks' programs. The proposed formal approach to fault-tolerance by program transformations highlights the benefits of separation of concerns. It allows us to establish correctness properties and to compute optimal values of parameters to minimize fault-tolerance overhead. We also present an implementation of our method, to demonstrate its feasibility and its efficiency.Article Citation - WoS: 21Citation - Scopus: 22Use of polyethylene glycol coatings for optical fibre humidity sensing(Optical Soc Japan, 2008) Acikgoz, Sabriye; Bilen, Bukem; Demir, Mustafa Muamer; Menceloglu, Yusuf Ziya; Skarlatos, Yani; Aktas, Gulen; Inci, Mehmet NaciHumidity induced change in the refractive index and thickness of the polyethylene glycol (PEG) coatings are in situ investigated for a range from 10 to 95%, using an optical waveguide spectroscopic technique. It is experimentally demonstrated that, upon humidity change, the optical and swelling characteristics of the PEG coatings can be employed to build a plastic fibre optic humidity sensor. The sensing mechanism is based on the humidity induced change in the refractive index of the PEG film, which is directly coated onto a polished segment of a plastic optical fibre with dip-coating method. It is observed that PEG, which is a highly hydrophilic material, shows no monotonic linear response to humidity but gives different characteristics for various ranges of humidity levels both in index of refraction and in thickness. It undergoes a physical phase change from a semi-crystal line structure to a gel one at around 80% relative humidity. At this phase change point, a drastic decrease occurs in the index of refraction as well as a drastic increase in the swelling of the PEG film. In addition, PEG coatings are hydrogenated in a vacuum chamber. It is observed that the hydrogen has a preventing effect on the humidity induced phase change in PEG coatings. Finally, the possibility of using PEG coatings in construction of a real plastic fibre optic humidity sensor is discussed. (C) 2008 The Optical Society of Japan.Conference Object Citation - WoS: 1Automatic enforcement of location aware user based network access control policies(World Scientific and Engineering Acad and Soc, 2008) Tuglular, Tugkan; Tuğlular, Tuğkan; Bilgisayar Mühendisliği BölümüMultiple interconnected network segments distributed across various locations, such as corporate networks, where users or employees constantly travel among segments and require to access servers, need to have network access control mechanisms that are able to adapt to these location changes. The idea of a firewall changing or adapting its rules depending on the location of users is presented by an architecture in this paper. This architecture proposes deployment of a policy server at the management level and policy agents at the firewall level, so that policy-driven network security management is enabled by specifying location aware user based network access control policies at the network security management and enforcing them at the managed firewalls. The architecture presented in this paper utilizes user VPN connection event triggers for dynamic policy configuration and automated policy deployment to firewalls. Location aware user based network access control policies, which are management level policies, are implemented using XACML. A network level policy is usually a configuration, or policy, file local to the firewall. The policy agent incorporated into the firewall performs the mapping from management level policy to firewall policy.Review Citation - WoS: 11Bisphosphonate treatment and radiotherapy in metastatic breast cancer(Humana Press inc, 2008) Ural, A. Ugur; Avcu, Ferit; Baran, Yusuf; Baran, YusufPatients with advanced breast cancer frequently develop metastasis to bone. Bone metastasis results in intractable pain and high risk of pathologic fractures due to osteolysis. The treatment of breast cancer patients with bone metastases requires a multidisciplinary approach. Radiotherapy is an established treatment for metastatic bone pain. It may be delivered either as a localized low dose treatment for localized bone pain or systemically for more widespread symptoms. Bisphosphonates have been shown to reduce morbidity and bone pain from bone metastases when given to patients with metastatic bone disease. In vivo studies indicate that early bisphosphonates administration in combination with radiotherapy improves remineralization and restabilization of osteolytic bone metastases in animal tumor models. This review focused on a brief discussion about biology of bone metastases, the effects of radiotherapy and bisphosphonate therapy, and possible mechanisms of combination therapy in metastatic breast cancer patients.Article Citation - WoS: 28Formation of Pseudoisocyanine J-Aggregates in Poly(vinyl alcohol) Fibers by Electrospinning(Amer Chemical Soc, 2009) Demir, Mustafa M.; Ozen, Bengisu; Ozcelik, Serdar; Demir, MustafaSubmicrometer diameter, light emitting fibers of poly(vinyl alcohol) (PVA) doped with pseudoisocyanine (1, 1'-diethyl-2,2'-cyanine bromide, PIC) dye were prepared by electrospinning. A horizontal setup was employed with a stationary collector consisting of two parallel-positioned metal strips separated by a void gal). Formation of uniaxially aligned and randomly deposited fibers in electrospun films was confirmed by microscopy. Photoluminescence (PL) spectroscopy is used to evaluate spectral properties of both types of fibers doped with PIC. While PIC molecules were individually dispersed in PVA Solution, they assemble into J-aggregates upon electrospinning when the weight fraction of PIC molecules is above 2.5 wt%. The formation of J-aggregates was observed in both randomly deposited and Uniaxially aligned electrospun fibers. Moreover, the fibers aligned uniaxially showed a high degree of polarized emission (PL(parallel to)/PL(perpendicular to) = 10), arising from the orientation of J-aggregates along the fiber axis. On the other hand, isotropic emission of J-aggregates was observed from the fibers deposited randomly. As a conclusion, electrospinning was found to be an efficient and a practical method to form highly oriented J-aggregates dispersed into polymer fibers. To the best Of Our knowledge, it is the first time formation of J-aggregates (a bottom-up approach) and electrospinning (a top-down approach) is successfully combined.Article Citation - WoS: 40Investigation of Oxygen Permeation through Composites of PMMA and Surface-Modified ZnO Nanoparticles(Wiley-v C H verlag Gmbh, 2009) Hess, Sandra; Demir, Mustafa M.; Yakutkin, Vladimir; Baluschev, Stanislav; Wegner, Gerhard; Demir, Mustafaoxygen permeabilities of nanocomposite films consisting of poly(methyl methacrylate) (PMMA) and different amounts of spherical zinc oxide (ZnO) nanoparticles were determined to investigate the barrier effect of this material with respect to particle content. A method was applied which is based on quenching of an excited phosphorescent dye by oxygen. Possible effects of the nanoparticles on the response of the dye molecules were investigated and were ruled out.Article Citation - WoS: 71Tensile mechanical behavior and fracture toughness of MWCNT and DWCNT modified vinyl-ester/polyester hybrid nanocomposites produced by 3-roll milling(Elsevier Science Sa, 2009) Seyhan, A. Tugrul; Tanoglu, Metin; Schulte, Karl; Tanoğlu, MetinThis study aims to investigate the tensile mechanical behavior and fracture toughness of vinyl-ester/polyester hybrid nanocomposites containing various types of nanofillers, including multi- and double-walled carbon nanotubes with and without amine functional groups (MWCNTs, DWCNTs, MWCNT-NH2 and DWCNT-NH2). To prepare the resin suspensions, very low contents (0.05, 0.1 and 0.3 wt.%) of carbon nanotubes (CNTs) were dispersed within a specially synthesized styrene-free polyester resin, conducting 3-roll milling technique. The collected resin stuff was subsequently blended with vinyl-ester via mechanical stirring to achieve final suspensions prior to polymerization. Nanocomposites containing MWCNTs and MWCNT-NH2 were found to exhibit higher tensile strength and modulus as well as larger fracture toughness and fracture energy compared to neat hybrid polymer. However, incorporation of similar contents of DWCNTs and DWCNT-NH2 into the hybrid resin did not reflect the same improvement in the corresponding mechanical properties. Furthermore, experimentally measured elastic moduli of the nanocomposites containing DWCNTs, DWCNT-NH2, MWCNTs and MWCNT-NH2 were fitted to Halphin-Tsai model. Regardless of amine functional groups or content of carbon nanotubes, MWCNT modified nanocomposites exhibited better agreement between the predicted and the measured elastic moduli values compared to nanocomposites with DWCNTs. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to reveal dispersion state of the carbon nanotubes within the hybrid polymer and to examine the CNT induced failure modes that occurred under mechanical loading, respectively. Based on the experimental findings obtained, it was emphasized that the types of CNTs and presence of amine functional groups on the surface of CNTs affects substantially the chemical interactions at the interface, thus tuning the ultimate mechanical performance of the resulting nanocomposites. (C) 2009 Elsevier B.V. All rights reserved.