Superfluid State of 4He on Graphane and Graphene–Fluoride: Anisotropic Roton States

We explore the phase behavior of Helium films on two variants of graphene: graphane (graphene coated with H, denoted GH) and graphene–fluoride (GF). A semiempirical interaction with these substrates is used in T=0 K Path Integral Ground State and finite temperature Path Integral Monte Carlo simulations. We predict that ⁴He forms anisotropic fluid states at low coverage. This behavior differs qualitatively from that on graphite because of the different surface composition, symmetry and spacing of the adsorption sites. The ⁴He ground state on both substrates is thus a self-bound anisotropic superfluid with a superfluid fraction ρ _s /ρ lower than 1 due to the corrugation of the adsorption potential. In the case of GF such corrugation is so large that ρ _s /ρ=0.6 at T=0 K and the superfluid is essentially restricted to move in a multiconnected space, along the bonds of a honeycomb lattice. We predict a superfluid transition temperature T? 0.25 (1.1) K for ⁴He on GF (GH). We have studied the elementary excitation spectrum of ⁴He on GF at equilibrium density finding a phonon–maxon–roton dispersion relation that is strongly anisotropic in the roton region. We conclude that these new platforms for adsorption studies offer the possibility of studying novel superfluid phases of quantum condensed matter.     

Cd1−xZnxS supported on SBA-16 as photocatalysts for water splitting under visible light: Influence of Zn concentration

Cd_1−xZn_xS solid solutions (x = 0.05–0.3) supported on mesoporous silica SBA-16 substrate with 3D cubic structure were investigated for hydrogen production from water splitting under visible light. The influence of Zn concentration (x) in the Cd_1−xZn_xS solid solution and support morphology were investigated. The bare SBA-16 substrate was synthetized by the hydrothermal method whereas the Cd_1−xZn_xS photocatalysts were prepared by coprecipitation of metal sulfides from aqueous solutions of Cd²⁺ and Zn²⁺ using Na₂S as precipitating agent. An attempt has been made to determine the photocatalyst structures using several techniques including elemental analysis, N₂ adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) and Raman spectroscopy. Surface characterization of the samples by XPS indicates that Cd_1−xZn_xS nanoparticles are unevenly distributed on both external surface and within the pore network. An increase of the band gap energy with increasing Zn loading up to x = 0.2 in the Cd_1−xZn_xS solid solution was observed. As a consequence, H₂ evolution increases gradually with an increase of the Zn loading in the photocatalysts from 0.05 to 0.2 wt% being the Cd_0.8Zn_0.2S/SBA-16 system the most active among the catalysts studied. The highest activity of this photocatalyst was explained in terms not only of its large band gap energy but also by the enhancement of the interaction between the particles of solid solution and the SBA-16 substrate.     

Surface characterization by X-ray photoelectron spectroscopy and cyclic voltammetry of products formed during the potentiostatic reduction of chalcopyrite

Surface characterization of the transient products that precede chalcocite formation during chalcopyrite reduction was carried out. The experimental strategy employed in the present work consisted of the application of different potential pulses (fixed energetic conditions) on the surface of chalcopyrite electrodes in 1.7 M H₂SO₄. The chemical products formed at different potential pulses were characterized by cyclic voltammetry (CV) and XPS. Each electrogenerated species presented a specific voltammetric behavior and an XPS spectrum, in which the values of principal photoelectronic peak bond energies for Cu 2p_3/2, Fe 2p_3/2 and S 2p_3/2 and the atomic concentrations were considered. Several potential intervals could be identified: in 0.115 ≥ E_cat ≥ −0.085 V vs. SHE, an intermediate copper sulfide is formed whose composition is between those of chalcopyrite and bornite, such as talnakhite. The reduction of this product occurs slowly, giving bornite at potentials less than −0.085 V. In the applied potential region −0.085 ≥ E_cat > −0.185 V, the bornite gradually decomposes causing the incomplete conversion to chalcocite. In the potential interval −0.185 > E_cat ≥ −0.285 V, energetic conditions are large enough to allow the immediate decomposition of bornite, forming chalcocite in a more quantitative manner.     

CRITICAL FLUX DETERMINATION IN ULTRAFILTRATION OF WASTEWATER FROM A FOOD INDUSTRY BY OPTIMIZATION METHOD

Two ultrafiltration membranes with different geometries (spiral polymeric and tubular ceramic) but similar cutoffs were used to treat wastewater from a food industry. Hydrodynamic conditions were optimized by statistical methods as a strategy to get more accurate values of the critical parameters and then to produce higher water flux and minimization of membrane fouling. The validation of the optimization method was obtained by experimental critical flux determination at critical parameters. Membrane fluxes revealed significant differences during filtration. The polymeric membrane showed an optimal flux of 45.60 Lh^?1 m^?2 at 3.21 bar while operating at a stable time of 11.61 h, whereas optimal flux of the ceramic membrane was 32.43 Lh^?1 m^?2 at 3.98 bar for 16.03 h. Experimental critical flux values were only slightly lower than optimal fluxes for both membranes, showing the validity of the statistics models applied. Negligible osmotic pressure was found on the two membranes at critical flux parameters, indicating irreversible fouling for both cases. The polymeric membrane revealed strong fouling behavior and the ceramic membrane showed a weak form; the flux decline occurred first in the polymeric membrane, whereas the ceramic membrane exhibited high stability during the filtration operations. A high degree of purification of wastewater was obtained by this membrane at critical flux conditions.     

Innovative ESD thermoplastic composites structured through meltflow processing

The amount of carbon black required to impart electrical conductivity to an insulating polymer can be dramatically reduced by its selective localization in a multi-component system which includes the insulating polymer The present report describes property-structure relationships of polypropylene/nylon/glass fiber (PP/PA/GF) composites with consistent resistivity levels within the 10⁶-10⁹ ohms/sq range achieved at very low carbon black loadings (less than 2%). The quaternary composites studied structure spontaneously during the hot compounding/processing steps and have unique triple-percolation structures. The results were compared with typical carbon black filled materials, which usually contain 15 to 20 wt% carbon black and are too conductive to meet the 10⁶-10⁹ ohms/sq range     

Hybrid particulate and fibrous injection molded composites: Carbon black/carbon fiber/polypropylene systems

The electrical properties of injection molded composite systems based on a polypropylene matrix and two types of carbonaceous fillers—carbon black (CB) and carbon fibers (CF)—were investigated. In addition to conductivity as a function of system compositions, conductivity profiles were studied. Inhomogeneous spatial distribution of CB particles in moldings containing either CB as a single filler or in combination with CF was found. Furthermore, unexpected fiber orientation transverse to the melt flow direction and disappearance of skin‐core orientation pattern, typical for injection molded fiber filled composites, were observed in the two filler samples. An amplification of the shear‐thinning behavior, characteristic for the polypropylene (PP) matrix, imposed by the inhomogeneity of the CB distribution resulting in flattening of the advancing melt front and velocity profile is suggested as underlying the observed phenomena. POLYM. COMPOS., 26:454–464, 2005. © 2005 Society of Plastics Engineers     

Thermo‐electric behavior (PTC) of carbon black–containing PVDF/UHMWPE and PVDF/XL‐UHMWPE blends

This paper describes the structure and electrical performance of PTC/NTC (positive temperature coefficient/negative temperature coefficient) effects and their reproducibility upon healing/cooling cycles. The following three‐component blends were studied: PVDF/UHMWPE/CB, PVDF/XL‐UHMWPE/CB and γ‐irradiated compression molded plaques of these blends. Carbon black (CB) particles are attracted to the UHMWPE (ultra high molecular weight polyethylene) and XL (cross‐linked)UHMWPE particles, which constitute the dispersed phase in the PVDF (polyvinylidene fluoride) matrix, but practically cannot or only very slightly penetrate them because of their extremely high viscosity. A double‐PTC effect was exhibited by all unirradiated samples. Irradiation of compression molded PVDF/UHMWPE/CB plaques does not add to their already outstanding reproducibility, and it results In a wide single‐PTC effect. Irradiation of compression molded PVDF/XL‐UHMV/PE/CB plaque, slabilizes their structure upon heating/cooling cycles and thus makes them reproducible PTC/NTC materials, still exhibiting a double‐PTC effect. The carbon black concentrations studied in this report are extremely low (< 2 phr CB) in comparison to other literature reports.     

Characterisation of Progressive Skeletal Muscle Fibrosis in the Mdx Mouse Model of Duchenne Muscular Dystrophy: An In Vivo and In Vitro Study

Duchenne muscular dystrophy (DMD) is a rare genetic disease leading to progressive muscle wasting, respiratory failure, and cardiomyopathy. Although muscle fibrosis represents a DMD hallmark, the organisation of the extracellular matrix and the molecular changes in its turnover are still not fully understood. To define the architectural changes over time in muscle fibrosis, we used an mdx mouse model of DMD and analysed collagen and glycosaminoglycans/proteoglycans content in skeletal muscle sections at different time points during disease progression and in comparison with age-matched controls. Collagen significantly increased particularly in the diaphragm, quadriceps, and gastrocnemius in adult mdx, with fibrosis significantly correlating with muscle degeneration. We also analysed collagen turnover pathways underlying fibrosis development in cultured primary quadriceps-derived fibroblasts. Collagen secretion and matrix metalloproteinases (MMPs) remained unaffected in both young and adult mdx compared to wt fibroblasts, whereas collagen cross-linking and tissue inhibitors of MMP (TIMP) expression significantly increased. We conclude that, in the DMD model we used, fibrosis mostly affects diaphragm and quadriceps with a higher collagen cross-linking and inhibition of MMPs that contribute differently to progressive collagen accumulation during fibrotic remodelling. This study offers a comprehensive histological and molecular characterisation of DMD-associated muscle fibrosis; it may thus provide new targets for tailored therapeutic interventions.     

The Cysteine Protease Giardipain-1 from Giardia duodenalis Contributes to a Disruption of Intestinal Homeostasis

In giardiasis, diarrhoea, dehydration, malabsorption, weight loss and/or chronic inflammation are indicative of epithelial barrier dysfunction. However, the pathogenesis of giardiasis is still enigmatic in many aspects. Here, we show evidence that a cysteine protease of Giardia duodenalis called giardipain-1, contributes to the pathogenesis of giardiasis induced by trophozoites of the WB strain. In an experimental system, we demonstrate that purified giardipain-1 induces apoptosis and extrusion of epithelial cells at the tips of the villi in infected jirds (Meriones unguiculatus). Moreover, jird infection with trophozoites expressing giardipain-1 resulted in intestinal epithelial damage, cellular infiltration, crypt hyperplasia, goblet cell hypertrophy and oedema. Pathological alterations were more pronounced when jirds were infected intragastrically with Giardia trophozoites that stably overexpress giardipain-1. Furthermore, Giardia colonization in jirds results in a chronic inflammation that could relate to the dysbiosis triggered by the protist. Taken together, these results reveal that giardipain-1 plays a key role in the pathogenesis of giardiasis.