Cavity Control of Prefoldin Nano Actuator (PNA) by Temperature and pH

Nano-Micro Letters - A molecular dynamics study to investigate the cavity control of Prefoldin based bio nano actuator is presented in this paper. Prefoldin is a molecular chaperone with a...     

Improvement of Mechanical Properties of CrNiMoCuTi Stainless Steel With Addition of Vanadium

 The effect of vanadium (V) addition on the mechanical properties of a Cr Ni Mo Cu Ti stainless steel was studied and its influence on microstructural changes was also investigated. Results indicate that the structure of the solution treated specimens mainly comprises of austenite martensite, and adding V leads to the formation of a considerable amount of ferrite. Under this condition, austenite phase is not mechanically stable, and transforms to martensite by plastic deformation. The addition of 05% - 10% (in mass percent) of V increases the hardness and the strength of the 80% cold rolled and aged steel, without any effect on ductility. Improvement in mechanical properties is presumably attributed to the formation of a small amount of ferrite in the primary structure, and the formation of certain precipitates is accelerated by the addition of V during aging. By contrast, excessive V decreases the strength and ductility simultaneously. This is due to the strong effect of ferrite formation compared to the beneficial effect of precipitation. The loss of ductility caused by adding higher amount of V is due to the formation of ferrite phases which in turn are suitable nucleation sites for crack propagation.     

Thermal analysis and microstructural evaluation of conventional land developed high speed tool steels

Thermal analyses and microstructural evaluation were carried out for the conventional AISI M2 and M10 high speed steels as well as for alloys with varying Nb and/or Ti contents to assess their liquidus, solidus and other high temperature reactions. It has been found that the slope change of cooling curves marks the formation of MC type carbides, while the break is due to the crystallization of delta ferrite and much larger volume fraction of different type of carbides including M6C mostly by eutectic reactions. Results show that the formation of dendrites is the most basic characteristic of the solidification process for the AISI M2 and M10 alloys but for the steels containing niobium and/or titanium carbides, these primary carbides insert an inoculating effect and modify the coarse dendritic structure.     

Size dependency of self-diffusion and creep behavior of nanostructured metals

Grain boundary and bulk diffusion are two main governing processes of creep deformation in materials. Since the diffusion activation energy for nanostructured materials is lower than that for bulk, the diffusion is enhanced at the nano-scale, and nanosructured materials are expected to creep at lower temperatures and stresses. In this paper, a model has been developed to explain the effect of grain size on diffusion and creep behavior of nanostructures. Diffusion and creep phenomena have been shown to depend significantly upon size. Comparisons have been made with reported experimental results and related theoretical studies.     

Hydroxyapatite Modified with Carbon‐Nanotube‐Reinforced Poly(methyl methacrylate): A Nanocomposite Material for Biomedical Applications

The paper reports on a freeze‐granulation technique to prepare a novel nanocomposite of poly(methyl methacrylate) (PMMA)‐modified hydroxyapatite (HA) with multiwalled carbon nanotubes (MWCNTs) as reinforcement for a new generation biomedical bone cement and implant coatings. By using this technique it is possible to increase material homogeneity and also enhance the dispersion of MWCNTs in the composite matrix. The phase composition and the surface morphology of the nanocomposite material were studied using X‐ray diffraction, field‐emission scanning electron microscopy, and micro‐Raman spectroscopy. Additionally, nanomechanical properties of different concentrations of MWCNT‐reinforced nanocomposite were performed by a nanoindentation technique, which indicates that a concentration of 0.1 wt % MWCNTs in the PMMA/HA nanocomposite material gives the best mechanical properties.     

In Situ Liquid-Cell TEM Observation of Multiphase Classical and Nonclassical Nucleation of Calcium Oxalate

Calcium oxalate (CaOx) is the major phase in kidney stones and the primary calcium storage medium in plants. CaOx can form crystals with different lattice types, water contents, and crystal structures. However, the conditions and mechanisms leading to nucleation of particular CaOx crystals are unclear. Here, liquid-cell transmission electron microscopy and atomistic molecular dynamics simulations are used to study in situ CaOx nucleation at different conditions. The observations reveal that rhombohedral CaOx monohydrate (COM) can nucleate via a classical pathway, while square COM can nucleate via a non-classical multiphase pathway. Citrate, a kidney stone inhibitor, increases the solubility of calcium by forming calcium-citrate complexes and blocks oxalate ions from approaching calcium. The presence of multiple hydrated ionic species draws additional water molecules into nucleating CaOx dihydrate crystals. These findings reveal that by controlling the nucleation pathways one can determine the macroscale crystal structure, hydration state, and morphology of CaOx.     

Classification of Hydrogels Based on Their Source: A Review and Application in Stem Cell Regulation

Stem cells are recognized by their self-renewal ability and can give rise to specialized progeny. Hydrogels are an established class of biomaterials with the ability to control stem cell fate via mechanotransduction. They can mimic various physiological conditions to influence the fate of stem cells and are an ideal platform to support stem cell regulation. This review article provides a summary of recent advances in the application of different classes of hydrogels based on their source (e.g., natural, synthetic, or hybrid). This classification is important because the chemistry of substrate affects stem cell differentiation and proliferation. Natural and synthetic hydrogels have been widely used in stem cell regulation. Nevertheless, they have limitations that necessitate a new class of material. Hybrid hydrogels obtained by manipulation of the natural and synthetic ones can potentially overcome these limitations and shape the future of research in application of hydrogels in stem cell regulation.     

Effect of oxide and carbide nanoparticles on tribological properties of phenolic-based nanocomposites

The phenolic-based composites and components are widely used because of their excellent thermal, tribological and mechanical behaviors. In the present study, phenolic resin composed of hexamine, novalac, furfural, and furfuryl alcohol has been used. The effects of two carbide nanoparticles (SiC and TiC) and two oxide nanoparticles (TiO₂ and ZrO₂) on the tribological properties of phenolic resin were experimentally investigated. This paper intends to identify the effects of different fillers, fraction of particles and normal load on wear rate and coefficient of friction in dry sliding wear of phenolic-based nanocomposites against hard metal. The proportions of fillers were 0.5, 1 and 2?vol% and experiments were carried out under 40, 50, 60 and 70?N loads and at 0.2?m/s speed. The fillers were mixed with phenolic resin and molded in the form of a cylinder (8.5?mm diameter?×?25?mm height). The samples were cured at 135?°C with a special heating cycle. The wear tests were performed on pin-on-disk testing apparatus at ambient temperature. The composite pins were tested in dry sliding against carbon steel disk. The worn surfaces of samples have been investigated by SEM and the effects of nanometer particles showed different wear mechanisms. Observations showed that carbide particles have better enhancing effect on tribological properties of phenolic resin as compared to the oxide particles. Nanocomposites with SiC particles showed the best tribological properties among the investigated samples. The optimal content of SiC nanoparticles were 1?vol%.     

Sol–gel fabrication and enhanced optical properties,photocatalysis, and surface wettability of nanostructured titanium dioxide films

TiO₂ photocatalytic film, annealed at temperatures of 500 °C and 700 °C, was prepared on SiO₂ pre-coated glass via sol–gel technique for photocatalytic purposes and effects of catalyst-type on its properties were investigated by an X-ray diffractometer (XRD), Scanning Electron Microscope, UV–vis spectrophotometer, and contact angle measurements. The XRD results showed that present phases depend upon catalyst used in the solution and phase transformation behaves in a temperature-dependent manner. For the layers derived from sols containing acidic catalysts, the anatase structure dominated and exhibited much better photocatalytic activity. The results indicated that the sample derived from sol comprises H₂SO₄ as catalyst, and exhibits anatase grains with the lowest size. This could be the reason for its better photocatalytic activity. Finally, samples derived from sol containing acidic catalysts showed superhydrophilicity and superior cleaning ability.