Epoxy composites with covalently anchored amino-functionalized SWNTs: Towards the tailoring of physical properties through targeted functionalization

Functionalization of single-walled carbon nanotubes (SWNTs) with covalently grafted amine moieties provides reactive fillers with potential for covalent anchoring to an epoxy matrix. Manufacturing and characterization of a high performance epoxy system reinforced with as-grown and aminated SWNTs are presented through four different approaches. Epoxy composite materials incorporating SWNTs aminated through sidewall addition reactions present enhanced mechanical, thermal and electrical properties, beyond the effect of unfunctionalized SWNTs. The functionalization pathways studied here lead to a composite with specific improvements in some of the physical properties of the epoxy matrix, which enables the tailored design of the composite's properties through functionalization. The amination via diazonium reaction with 4-aminobenzylamine is especially effective in enhancing the tensile and impact properties of the epoxy composites (44% improvement in impact strength at 0.1 wt% loading) and leads to the highest increase in elastic modulus reported so far for the integration of aminated nanotubes into epoxy resin. Composites incorporating aminated SWNTs throughout the 1,3-dipolar cycloaddition reaction stand out for their thermo-oxidative stability and thermomechanical properties. The incorporation of as-produced arc-discharge SWNTs into the TGAP/DDS epoxy matrix leads to composite materials with the highest electrical conductivity among all the studied samples. This journal is © The Royal Society of Chemistry.The present work was carried out with financial support from the NRC-CSIC collaboration project and fellowships from MICINN Spanish Ministry (FPU grant) and CAI-DGA and Europa XXI programmes. J.M.G.D. would like to thank Dr Benoit Simard and Dr Yadienka Martinez of SIMS-NRC for their close collaboration. Special thanks go to Prof. Maurizio Prato for kindly allowing a short research stay in his group, and his entire team. Epoxy reagents were received as a gift from Huntsman, which is gratefully acknowledged.Peer Reviewe

Coexistence of two spin frustration pathways in the quantum spin liquid Ca_10Cr_7O_28

Kagome antiferromagnetic lattices are of high interest because the geometric frustration is expected to give rise to highly degenerated ground states that may host exotic properties such as quantum spin liquid (QSL). Ca_10Cr_7O_28 has been reported to display all the features expected for a QSL. At present, most of the literature reports on samples synthesized with starting materials ratio CaO/Cr_2O_3 3:1, which leads to a material with small amounts of CaCrO_4 and CaO as secondary phases; this impurity excess affects not only the magnetic properties but also the structural ones. In this work, samples with starting material ratios CaO/Cr_2O_3 3:1, 2.9:1, 2.85:1, and 2.8:1 have been synthesized and studied by X-ray diffraction with Rietveld refinements, selected area electron diffraction measurements, high-resolution transmission electron microscopy (HRTEM), low-temperature magnetometry, and magnetic calorimetry. This result shows that a highly pure Ca_10Cr_7O_28 phase is obtained for a CaO/Cr_2O_3 ratio of 2.85:1 instead of the 3:1 usually reported; the incorrect stoichiometric ratio leads to a larger distortion of the corner-sharing triangular arrangement of magnetic ions Cr+5 with S = 1/2 in the Kagome lattice. In addition, our study reveals that there exists another frustration pathway which is an asymmetric zigzag spin ladder along the directions [211], [12-1], and [1- 1-1], in which the Cr-Cr distances are shorter than in the Kagome layers

System size resonance in coupled noisy systems and in the Ising model

We consider an ensemble of coupled nonlinear noisy oscillators demonstrating in the thermodynamic limit an Ising-type transition. In the ordered phase and for finite ensembles stochastic flips of the mean field are observed with the rate depending on the ensemble size. When a small periodic force acts on the ensemble, the linear response of the system has a maximum at a certain system size, similar to the stochastic resonance phenomenon. We demonstrate this effect of system size resonance for different types of noisy oscillators and for different ensembles -- lattices with nearest neighbors coupling and globally coupled populations. The Ising model is also shown to demonstrate the system size resonance.Comment: 4 page

Molecular dynamics simulations of lead clusters

Molecular dynamics simulations of nanometer-sized lead clusters have been performed using the Lim, Ong and Ercolessi glue potential (Surf. Sci. {\bf 269/270}, 1109 (1992)). The binding energies of clusters forming crystalline (fcc), decahedron and icosahedron structures are compared, showing that fcc cuboctahedra are the most energetically favoured of these polyhedral model structures. However, simulations of the freezing of liquid droplets produced a characteristic form of ``shaved'' icosahedron, in which atoms are absent at the edges and apexes of the polyhedron. This arrangement is energetically favoured for 600-4000 atom clusters. Larger clusters favour crystalline structures. Indeed, simulated freezing of a 6525-atom liquid droplet produced an imperfect fcc Wulff particle, containing a number of parallel stacking faults. The effects of temperature on the preferred structure of crystalline clusters below the melting point have been considered. The implications of these results for the interpretation of experimental data is discussed.Comment: 11 pages, 18 figues, new section added and one figure added, other minor changes for publicatio

Non-L\'evy mobility patterns of Mexican Me'Phaa peasants searching for fuelwood

We measured mobility patterns that describe walking trajectories of individual Me'Phaa peasants searching and collecting fuelwood in the forests of "La Monta\~na de Guerrero" in Mexico. These one-day excursions typically follow a mixed pattern of nearly-constant steps when individuals displace from their homes towards potential collecting sites and a mixed pattern of steps of different lengths when actually searching for fallen wood in the forest. Displacements in the searching phase seem not to be compatible with L\'evy flights described by power-laws with optimal scaling exponents. These findings however can be interpreted in the light of deterministic searching on heavily degraded landscapes where the interaction of the individuals with their scarce environment produces alternative searching strategies than the expected L\'evy flights. These results have important implications for future management and restoration of degraded forests and the improvement of the ecological services they may provide to their inhabitants.Comment: 15 pages, 4 figures. First version submitted to Human Ecology. The final publication will be available at http://www.springerlink.co

Low frequency of TERT promoter mutations in gastrointestinal stromal tumors (GISTs).

Somatic mutations in the promoter region of telomerase reverse transcriptase (TERT) gene, mainly at positions c. − 124 and c. − 146 bp, are frequent in several human cancers; yet its presence in gastrointestinal stromal tumor (GIST) has not been reported to date. Herein, we searched for the presence and clinicopathological association of TERT promoter mutations in genomic DNA from 130 bona fide GISTs. We found TERT promoter mutations in 3.8% (5/130) of GISTs. The c. − 124C4T mutation was the most common event, present in 2.3% (3/130), and the c. − 146C4T mutation in 1.5% (2/130) of GISTs. No significant association was observed between TERT promoter mutation and patient’s clinicopathological features. The present study establishes the low frequency (4%) of TERT promoter mutations in GISTs. Further studies are required to confirm our findings and to elucidate the hypothetical biological and clinical impact of TERT promoter mutation in GIST pathogenesis.This project was partially supported by Barretos Cancer Hospital internal research funds (PAIP) and CNPq Universal Grant (476192/2013-7) to RMR. NCC is a recipient of an FAPESP Doctoral Fellowship (2013/25787-3). Further funding from the project ‘Microenvironment, metabolism and cancer’ that was partially supported by Programa Operacional Regional do Norte (ON.2—O Novo Norte) under the Quadro de Referência Estratégico Nacional (QREN) and the Fundo Europeu de Desenvolvimento Regional (FEDER). IPATIMUP is an Associate Laboratory of the Portuguese Ministry of Science, Technology and Higher Education that is partially supported by the FCT

HIV/STI co-infection among men who have sex with men in Spain

In Spain, neither the HIV nor the STI national surveillance systems collect information on HIV/STI co-infection. However, there are two networks based on HIV/STI clinics which gather this data. We describe HIV prevalence in men who have sex with men (MSM) diagnosed with infectious syphilis and/or gonorrhoea in 15 STI clinics; and concurrent diagnoses of STI in MSM newly diagnosed with HIV in 19 HIV/STI clinics. In total, 572 MSM were diagnosed with infectious syphilis and 580 with gonorrhoea during 2005-2007. HIV prevalence among syphilis and gonorrhoea cases was 29.8% and 15.2% respectively. In the multivariate analysis, HIV/syphilis co-infection was associated with being Latin American; having a history of STI; reporting exclusively anal intercourse; and having sex with casual or several types of partners. HIV and gonorrhoea co-infection was associated with age older than 45 years; having no education or only primary education completed; and having a history of STI. In total, 1,462 HIV infections were newly diagnosed among MSM during 2003-2007. Of these, 31.0% were diagnosed with other STI at the same time. Factors associated with STI co-infection among new HIV cases in MSM were being Latin American; and having sex with casual partners or with both steady and casual partners. In Spain, a considerable proportion of MSM are co-infected with HIV and STI.This work was funded by two grants (36646/07; 36794/08) from the Foundation for Research and Prevention of AIDS in Spain (Fundación para la Investigación y la Prevención del SIDA en España–FIPSE).S

‘How can I be post-Soviet if I was never Soviet?’ Rethinking categories of time and social change – a perspective from Kulob, southern Tajikistan

Based on anthropological fieldwork conducted in the Kulob region of southern Tajikistan, this paper examines the extent to which the existing periodization ‘Soviet/post-Soviet’ is still valid to frame scholarly works concerning Central Asia. It does so through an analysis of ‘alternative temporalities’ conveyed by Kulob residents to the author. These alternative temporalities are fashioned in especially clear ways in a relationship to the physical transformations occurring to two types of housing, namely flats in building blocks and detached houses. Without arguing that the categories ‘Soviet’ and ‘post-Soviet’ have become futile, the author advocates that the uncritically use of Soviet/post-Soviet has the unwanted effect of shaping the Central Asian region as a temporalized and specialized ‘other’

Workforce scheduling and routing problems: literature survey and computational study

In the context of workforce scheduling, there are many scenarios in which personnel must carry out tasks at different locations hence requiring some form of transportation. Examples of these type of scenarios include nurses visiting patients at home, technicians carrying out repairs at customers’ locations and security guards performing rounds at different premises, etc. We refer to these scenarios as workforce scheduling and routing problems (WSRP) as they usually involve the scheduling of personnel combined with some form of routing in order to ensure that employees arrive on time at the locations where tasks need to be performed. The first part of this paper presents a survey which attempts to identify the common features of WSRP scenarios and the solution methods applied when tackling these problems. The second part of the paper presents a study on the computational difficulty of solving these type of problems. For this, five data sets are gathered from the literature and some adaptations are made in order to incorporate the key features that our survey identifies as commonly arising in WSRP scenarios. The computational study provides an insight into the structure of the adapted test instances, an insight into the effect that problem features have when solving the instances using mathematical programming, and some benchmark computation times using the Gurobi solver running on a standard personal computer