Revista de Ciências e Engenharia de Materiais

In 1971, Harrington et al. put forward a hypothesis, in which helix-coil transition in the hinge region of myosin subfragment-2 (S-2) contributes to muscle contraction. The helix-coil transition hypothesis has been, however, ignored by muscle investigators over many years. In 1992, we worked with him to examine the effect of polyclonal antibody to myosin subfragment-2 (anti-S-2 antibody), and found that the antibody eliminated Ca2+-activated isometric force generation of skinned vertebrate muscle fibers without affecting MgATPase activity. Further studies using the same antibody indicated functional communication between myosin head and myosin S-2, including regulation of binding strength between myosin head and actin filament during Ca2+-activated contraction in vertebrate muscle fibers. These findings indicate that the swinging lever arm hypothesis, in which muscle contraction results from active rotation of myosin head converter domain, is incomplete because it ignores of the role of myosin S-2. Much more experimental work is necessary to reach full understanding of muscle contraction mechanism at the molecular level.

Zinc telluride (ZnTe) thin films were fabricated by thermal evaporation method on corning glass substrates. ZnTe thin films were doped with silver (Ag) by dipping in low concentrated solution (0.2 g/200 ml) of AgNO3 × H2O at room temperature. X-ray diffraction technique was used to investigate the structural behavior of ZnTe samples. Optical investigations were done by using spectrophotometer. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to analyze the surface and composition of the thin film samples respectively. Electrical investigations were done by using Van Der Pauw and Hall measurement system. It was found that prepared samples showed polycrystalline structure with <111> as preferred orientation. Optical study showed that with increasing thickness, grain size increased but optical transmission and energy band gap were decreased. It was observed that value of resistivity of these samples decreased with increasing thickness and Ag composition. The results were compared before and after Ag doping in ZnTe thin films samples for the solar cell applications.

Aluminum oxide nanoparticles (Al2O3+SDS and Al2O3) were synthesized by a simple sol-gel method for demetallization of nickel from crude oil-water mixture in a batch adsorption process for the first time. The samples were dried, calcined at 550°C, cooled and characterized using scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The XRD confirmed that Al2O3 phase were synthesized with more minor impurities of bauxite and silica in Al2O3 without SDS. Particle size estimations were 197 and 183 nm for the Al2O3 with and without SDS, respectively. SEM showed larger rectangular porous crystallites and thinner netlike- vertical platy crystallites for the former and later samples respectively while the EDS confirmed the presence of Al and O in them. The batch adsorption showed that the %Removal (%R) of the adsorption process increase gradually with increase in adsorbent from 0.02 to 0.1 g to a maximum at 86.1% for Al2O3+SDS but decrease with increase in the adsorbent dosage for Al2O3 with %R maximum of 78% at the least (0.02 g) dosage. On the other hand, at constant adsorbent dosage, %R of 94 and 93% for a 1:3 crude oil-water mixture were obtained for Al2O3+SDS and Al2O3, respectively. This confirmed greater capacity of Al2O3+SDS for the removal of Ni2+ ions from crude oil over the control.

Spider silk (SS) is naturally tough; however, it turns soft when wet by water. Spiders produce high-quality silk threads by adjusting the molecular assemblage of SS-proteins and the arrangements structure of threads and recombinant spider dragline silk (RSDS). The general wet spinning techniques for producing recombinant spidroins results in uncorrected explanation to the natural spinning technique. In this study, we use tailored-SS with relative low molecular weight of 47 kD to produce a water-soluble RSDS protein. We built a microfluidic ship and used it to spun SS using aqueous solutions-micro-technique (wet spinning). This was done in order to mimic the spider-spinning processes using a steady post-spin drawing process. We succeeded to produce assemblies of spidroins with fibril structure. Then, compact constituting of micro-threads followed these wet spinning processes. Wet spinning was followed by improving the orientation, crystalline structure, and fibril melting of the hierarchical structure. The initial mechanical characterization (tensile strength) of the RSDSs attained about 510 MPa with respective extension 44%.

In this study mathematical analysis of spring back was done for optimization of sheet metal bending process. The influence of sheet metal thickness, sheet metal type, friction, tool radius and tool shape on spring back for Aluminium, copper, mild steel and High strength steels, sheet metal have been used as variable to conducted this study. Since, the effects of each variable on the formation of spring back on sheet metal forming are investigated the following way. This empirical result shows that increasing sheet metal thickness from 0.8 mm to 4.5 mm the spring back is reduced 16% and 20.35%. When increasing of sheet metal strength spring back increases because spring back of the sheet should depend on the yield strength of the material. As the materials yield strength increase the spring back after un-loading condition also increases. The effects of material type as shows that, using Aluminium sheet metal instead of high strength sheet metals spring back is reduced by 56.%. Also, for decreasing of the tool radius leads reducing spring back. Spring back of deferential die 12% lower than edge bending die. In addition to these, if increasing the friction coefficient from 0.01 to 0.50 the spring back also increases by 52% because of increasing of friction force and this force generates higher amount of spring back. Thus the effects of material type, tool geometry, working condition and the thickness of sheet metal types were studied and investigated. Since, ultimately utilizing and compensation of tool is considered for prevention of spring back and optimizing of sheet metal bending process as well.

In this work, a theoretical study on the photoconductivity of a bifacial silicon solar cell under monochromatic illumination and constant magnetic field is presented. Analytical expression of the photoconductivity is established according to base depth, illumination wavelength, junction recombination velocity and magnetic field value. The photoconductivity profile versus wavelength shows two energy absorption peaks corresponding to specific wavelengths. Based on a linear model of the photoconductivity versus junction recombination velocity, in a given interval, we determine an equivalent capacitance which depends on both wavelength and magnetic field.

Heterostructures prepared from graphene and fluorographene (FG) using the technology of 2D printing on solid and flexible substrates were fabricated and studied. Excellent stability of printed graphene layers and, to a lesser degree, composite graphene:PEDOT:PSS layers were shown. Extraordinary properties of FG as an insulating layer for graphene-based heterostructures at fluorination degree above 30% were demonstrated. It is shown that the leakage current in thin (20-40 nm) films is normally smaller than 10-8 A/cm2, the breakdown field being greater than 108 V/cm. In hybrid structures with printed FG layers in which graphene was transferred onto, or capsulated with, an FG layer, an increase in charge-carrier mobility and material conductivity amounting to 5-6 times was observed. The spectrum of future applications of FG layers can be further extended due to the possibility of obtaining, from weakly fluorinated graphene (<20%), functional layers exhibiting a negative differential resistance behavior and, at fluorination degrees of 20-23%, field-effect-transistor channels with current modulation reaching several orders. Composite or bilayer films based on fluorographene and V2O5 or polyvinyl alcohol exhibit a stable resistive switching behavior. On the whole, graphene/FG heterostructures enjoy huge potential for their use in a wide spectrum of application, including flexible electronics.

Synthesis of carbon dots carried out by the method of hydrothermal treatment of carbon precursors, such as glucose, citric acid and soot from birch bark in aqueous ammonia. The lateral dimensions distribution of the carbon dots was measured, from which the average dimensions were determined, which are in the range 10-12 nm in the case of glucose, citric acid and 20-22 nm in the case of soot. Water suspensions with carbon dots from both glucose and citric acid show strong absorption in the visible region from 300 to 500 nm, while carbon dots synthesized from soot have strong absorption in the ultraviolet region but are transparent in the visible region. The infrared absorption spectra were measured, which showed the presence of oxygen groups on the surface of synthesized carbon dots. Investigation of luminescence spectra have shown that carbon dots synthesized from glucose and soot luminesce equally in the violet region of the spectrum and the wavelength of the radiation is being dependent on the excitation wavelength. The luminescence intensity depends on the carbon dots dimensions and on the presence of oxygen groups on their surface. Luminescent carbon dots synthesized from glucose, citric acid and soot are ecological, biocompatible and have great prospects for their application in the field of biology and medicine.

This paper explores the concept of creep activation energy, comparing the currently used Arrhenius equation to an outcome of the using Gibbs free energy. The consequence of these differing approaches is illustrated using large datasets. By examining the fundamental approach to creep activation energy, this article highlights potential advances in the field of creep in terms of activation energy, modelling, region splitting and mechanism mapping.

In this study, we use the finite element method to analyse the behaviour of cracks emanating from microcavities in the bone cement, binding the cup to the bone, according to their size and position around the cavity, the position of the patient, the cavity’s location and the inter-defects distance (cavity-crack, crack-crack). We show that the most unstable stress intensity factor, in mode I, when the crack located in the cement’s centre and propagating along this thickness. This instability is all the more important that its size increases, tends towards the cavity, the cracks are located in a vicinity one to other and that the patient is in a squatting position. The predominant fracture mode, in mode I and II, depends on the crack’s position priming site around the microcavities. This work allows the better understanding of the interconnection phenomena of the microcavities experimentally observed.

The research investigated to determine enhancement in the tensile properties of self-cure acrylic resin reinforced with siwak fiber and bamboo fibers which were cut into 2, 6, and 12 mm lengths and used at three different concentrations of (3, 6, and 9 wt.%). The mixture of resin and fiber were cured at 2.5 bar and 55°C in a water bath for 30 min. The cured resin specimen tested for tensile properties (tensile strength, young modulus, elongation percentage at break) following the specification of ASTM No. 638. The results illustrated that the tensile strength and young modulus tended to be improved with fiber length and concentration, the largest values of tensile strength and young modulus for specimens reinforced with bamboo fibers are (72.4 MPa and 5.208 GPa) while for specimens reinforced with siwak fibers are (71 MPa and 4.9 GPa) at optimum condition of weight fraction (9%) and fiber length (12 mm) which was significantly higher than other formulations.