78 research outputs found
On numerical modeling of couple heat, air and moisture transfer through multilayered walls
This paper reports on numerical modeling of heat, air, and moisture transfer
through multilayered walls. Building materials are often subjected to temporal climatic
variations, which can induce a transfer of heat and moisture through the walls of the building
and the foundation soil. These materials are generally considered as porous media. The
coupled heat, air and moisture transfer in building materials is of paramount importance in the
construction area. In this way, a mathematical model has been elaborated and validated using
a benchmark example. Here, we aim to determine the energy losses. The capillary pressure is
considered as potential moisture which represents both the transport of vapor and liquid
phases of the water. Basing on basic functions of partial differential equations, one can
convert certain measurable properties of porous media as coefficients depending on the
temperature and the capillary pressure. The results obtained compare favorably with other
available in the literature
Reply to the comment by M. Rahman on “Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils” by M. Belkhatir et al. [C. R. Mecanique 338 (2010) 290–303]
Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils
Cellulose nanofibers produced from banana peel by chemical and mechanical treatments: characterization and cytotoxicity assessment
Cellulose nanoparticles from a vegetable source (cellulose fiber) have been evaluated for future use as reinforcement of polymeric matrixes (e.g., biodegradable films). Cellulose nanoparticles have numerous advantages: they are inexpensive and biodegradable, and they originate from renewable sources. Here, cellulose nanofibers (CNFs) were isolated from banana peel by chemical (alkaline treatment and bleaching followed by acid hydrolysis with 0.1, 1, or 10% (v/v) H2SO4) and mechanical (high pressure homogenizer) treatments. Atomic Force Microscopy (AFM) analysis showed all treatments effectively isolated banana fibers at the nanometer scale (average diameter of 3.72 nm). CNFs displayed -potential values ranging from -37.60 to -67.37 mV, which prevented their aggregation. CNFs had high crystallinity values, from 63.1 to 66.4%, which indicated they could be good reinforcing agents. FTIR results confirmed that the chemical and mechanical treatments removed the amorphous fractions. Regarding cytotoxicity, low CNF concentrations (50-500 g/mL) did not cause cell death, but CNFs at concentrations above 1000 g/mL significantly decreased cell viability. The use of different sulfuric acid concentrations provided more detailed knowledge of the treatment methods and CNF features, which could help to improve the CNF production process. The combination of chemical and mechanical treatments proved to be an efficient strategy to prepare CNFs from banana peels as a potential reinforcing agent of polymeric matrixes (e.g., food packaging).The authors would like to acknowledge the financial support
provided by Coordenaçao de Aperfeiçoamento de Pessoal de Nível ~
Superior (2952/2011), Conselho Nacional de Desenvolvimento Científico e Tecnologico (150523/2013-0 and 140274/2014-6), and
CAPES/FCT 349/13 for the PhD exchange program. Joana T. Martins
acknowledges the Foundation for Science and Technology for her
fellowship (SFRH/BPD/89992/2012). This study was supported by
FCT under the scope of the strategic funding of UID/BIO/04469/
2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684) and
BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by
the European Regional Development Fund under the scope of
Norte2020 - Programa Operacional Regional do Norte. This study
was also supported by FCT under the scope of the Project RECI/BBBEBI/0179/2012
(FCOMP-01-0124-FEDER-027462). The authors
would also like to acknowledge the Brazilian Nanotechnology National
Laboratory (LNNano) for allocation of the TEM and AFM
apparatus.info:eu-repo/semantics/publishedVersio
Dry, hydrophobic microfibrillated cellulose powder obtained in a simple procedure using alkyl ketene dimer
Preparation of cross-linked cellulose nanofibril aerogel with water absorbency and shape recovery
CRITICAL UNDRAINED SHEAR STRENGTH OF LOOSE-MEDIUM SAND-SILT MIXTURES UNDER MONOTONIC LOADINGS
Empirical relationships are developed for estimating the undrained critical shear strength
based on experimental triaxial tests under monotonic loadings. The effect of fines content
on the undrained shear strength is analyzed for different combinations of density states.
The parametric study indicates that in terms of the soil void ratio and fines content properties,
the undrained critical shear strength may increase, or decrease as the amount of fines
content increases, consequently showing vulnerability to liquefaction influenced by the fines
content percentage. A series of monotonic undrained triaxial tests have been undertaken on
a reconstituted saturated sand-silt mixtures specimen. Beyond 30% of fines content, it is
shown that a fraction of silt participates in the soil skeleton chain force. In this context,
the concept of the equivalent intergranular void ratio may be an appropriate parameter to
express the critical shear strength of the soil under investigation. This parameter is able
to control the undrained shear strength of non plastic silt and sand mixtures for different
density states
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