Influence of MWCNT/surfactant dispersions on the mechanical properties of Portland cement pastes

This work studies the reinforcing effect of Multi Walled Carbon Nanotubes (MWCNT) on cement pastes. A 0.35% solid concentration of MWCNT in powder was dispersed in deionized water with sodium dodecyl sulfate (cationic surfactant), cetylpyridinium chloride (anionic surfactant) and triton X-100 (amphoteric surfactant) using an ultrasonic tip processor. Three concentrations of each surfactant (1mM, 10mM and 100mM) were tested, and all samples were sonicated until an adequate dispersion degree was obtained. Cement pastes with additions of carbon nanotubes of 0.15% by mass of cement were produced in two steps; first the dispersions of MWCNT were combined with the mixing water using an ultrasonic tip processor to guarantee homogeneity, and then cement was added and mixed until a homogeneous paste was obtained. Direct tensile strength, apparent density and open porosity of the pastes were measured after 7 days of curing. It was found that the MWCNT/surfactants dispersions decrease the mechanical properties of the cement based matrix due to an increased porosity caused by the presence of surfactants. © Published under licence by IOP Publishing Ltd

A questão da assimetria da informação e da incerteza da qualidade na indústria de alimentos: soluções possíveis.

Ocorrências de contaminações alimentares associadas ao ambiente comercial competitivo resultaram, na última década, em maior atenção à qualidade e segurança do alimento, tanto em ambito mundial como no mercado nacional. A predominância de atributos de experiência e de crença nos produtos alimentares acentuam os problemas de assimetria da informação entre os agentes de uma transação e permitem, por exemplo, que produtos com qualidades distintas sejam comercializados a preços semelhantes e dificultam a percepção do mercado sobre diferenças efetivas na qualidade dos produtos. Por meio de revisão bibliográfica, e de dados secundários, este trabalho apresenta os principais mecanismos que têm sido utilizados para minimizar esses problemas, tais como: a intervenção do Estado; a utilização da marca como sinalizador de diferenciação; a prática de rastreabilidade do produto e do sistema de produção e a adoção da certificação da qualidade e da segurança do produto. De forma geral observa-se que tais práticas têm induzido à adoção de formas de organização mistas, por meio da coordenação vertical e horizontal, nas cadeias de produção de alimentos

BVRI Surface Photometry of Isolated Spiral Galaxies

A release of multicolor broad band (BVRI) photometry for a subsample of 44 isolated spirals drawn from the Catalogue of Isolated Galaxies (CIG) is presented. Total magnitudes and colors at various circular apertures, as well as some global structural/morphological parameters are estimated. Morphology is reevaluated through optical and sharp/filtered R band images, (B-I) color index maps, and archive near-IR JHK images from the Two-Micron Survey. The CAS structural parameters (Concentration, Asymmetry, and Clumpiness) were calculated from the images in each one of the bands. The fraction of galaxies with well identified optical/near-IR bars (SB) is 63%, while a 17% more shows evidence of weak or suspected bars (SAB). The sample average value of the maximum bar ellipticity is 0.4. Half of the galaxies in the sample shows rings. We identify two candidates for isolated galaxies with disturbed morphology. The structural CAS parameters change with the observed band, and the tendencies they follow with the morphological type and global color are more evident in the redder bands. In any band, the major difference between our isolated spirals and a sample of interacting spirals is revealed in the A-S plane. A deep and uniformly observed sample of isolated galaxies is intended for various purposes including (i) comparative studies of environmental effects, (ii) confronting model predictions of galaxy evolution and (iii) evaluating the change of galaxy properties with redshift.Comment: 44 pages, 9 figures and 7 tables included. To appear in The Astronomical Journal. For the 43 appendix figures 4.1-4.43 see http://www.astroscu.unam.mx/~avila/Figs4.1_4.43.tar.gz (7.2 Mb tar.gz file

Entrance-channel Mass-asymmetry Dependence of Compound-nucleus Formation Time in Light Heavy-ion Reactions

The entrance-channel mass-asymmetry dependence of the compound nucleus formation time in light heavy-ion reactions has been investigated within the framework of semiclassical dissipative collision models. the model calculations have been succesfully applied to the formation of the $^{38}$Ar compound nucleus as populated via the $^{9}$Be+$^{29}$Si, $^{11}$B+$^{27}$Al, $^{12}$C+$^{26}$Mg and $^{19}$F+$^{19}$F entrance channels. The shape evolution of several other light composite systems appears to be consistent with the so-called "Fusion Inhibition Factor" which has been experimentally observed. As found previously in more massive systems for the fusion-evaporation process, the entrance-channel mass-asymmetry degree of freedom appears to determine the competition between the different mechanisms as well as the time scales involved.Comment: 12 pages, 3 Figures available upon request, Submitted at Phys. Rev.

Fine Structure Discussion of Parity-Nonconserving Neutron Scattering at Epithermal Energies

The large magnitude and the sign correlation effect in the parity non-conserving resonant scattering of epithermal neutrons from $^{232}$Th is discussed in terms of a non-collective $2p-1h$ local doorway model. General conclusions are drawn as to the probability of finding large parity violation effects in other regions of the periodic table.Comment: 6 pages, Tex. CTP# 2296, to appear in Z. Phys.

Computer simulation for the evaluation of recombination strategies in intrapopulation recurrent selection in Eucalyptus.

Intrapopulation recurrent selection (IRS) has proven to be a promising breeding method in eucalyptus, mainly through being easier to carry out when compared to reciprocal recurrent selection (RRS). However, the recombination strategies in IRS that have not yet been compared. Thus, the purpose of this study was to verify the efficiency of different recombination methods in IRS. To do so, computer simulation was used considering different heritabilities (0.1, 0.5, 1.0), different initial allelic frequencies (0.2, 0.8) and allelic interactions without dominance and with complete dominance. The initial population consisted of 1000 individuals, which were selected at random for the beginning of cycle zero. These individuals were interbred two by two. Three selection strategies were carried out and, consequently, three recombination methods: recombine the best individuals selected within the best progenies; the best individuals phenotypically selected regardless of their genealogy; or selection in the mean value of the best progenies selected. It was observed that recombination of the best individuals regardless of their genealogy and of the best individuals within the best progenies provided for gains superior to recombination having only the mean of the progenies as reference. The average degree of dominance and the heritability of the trait should be considered at the time of choosing the method of selection followed by recombination

Multivisceral intestinal transplantation: Surgical pathology

We report the diagnostic surgical pathology of two children who underwent multivisceral abdominal transplantation and survived for 1 month and 6 months. There is little relevant literature, and diagnostic criteria for the various clinical possibilities are not established; this is made more complicated by the simultaneous occurrence of more than one process. We based our interpretations on conventional histology, augmented with immunohistology, including HLA staining that distinguished graft from host cells in situ. In some instances functional analysis of T cells propagated from the same biopsies was available and was used to corroborate morphological interpretations. A wide spectrum of changes was encountered. Graft-versus-host disease, a prime concern before surgery, was not seen. Rejection was severe in 1 patient, not present in the other, and both had evidence of lymphoproliferative disease, which was related to Epstein-Barr virus. Bacterial translocation through the gut wall was also a feature in both children. This paper documents and illustrates the various diagnostic possibilities.. © 1989 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted