பொருள் அறிவியல் & பொறியியல் இதழ்

In giant intermodal cells of green algae Chara collaria, cytoplasmic streaming is produced by ATP-dependent sliding between myosin heads extending from amorphous cytoplasmic organelles and actin filament arrays (actin cables) fixed on chloroplast rows. The velocity of cytoplasmic streaming is many times faster than the maximum myofilament sliding in skeletal muscle. In this article, we compared steady-state force-velocity (P-V) relations between cytoplasmic myosin and skeletal and cardiac muscle myosins using the centrifuge microscope, in which myosincoated latex beads were made to slide along the actin cables under various centrifugal forces. In contrast with the hyperbolic P-V relation of actin-myosin sliding in skeletal and cardiac myosins, the P-V relation of cytoplasmic myosin versus actin cable sliding was a straight line, indicating a very large duty ratio and a very small rate of chemomechanical energy conversion. Possible mechanisms of the ultra-fast actin-myosin sliding are discussed.
Highlights
• The velocity of cytoplasmic streaming, caused by ATP-dependent sliding between cytoplasmic myosin and actin cables in giant algal cells is many times faster than ATP-dependent actin-myosin sliding in skeletal and cardiac muscles.
• The mechanism of ultra-fast actin-myosin sliding was studied using the centrifuge microscope, in which beads coated with cytoplasmic myosin were made to slide along actin cables under various centrifugal forces serving as loads against cytoplasmic myosin versus actin cable sliding.
• Unlike the hyperbolic force-velocity (P-V) relation of skeletal and cardiac muscle actin-myosin sliding, the P-V relation of cytoplasmic actin myosin sliding was a straight line irrespective of the force generated by cytoplasmic myosin.
• These results indicate a very large duty ratio and a very small efficiency of chemo-mechanical energy conversion in cytoplasmic actin-myosin sliding.

Aspects of moulding technology have a great effect on the mechanical properties and curing behaviour of polymer concrete used to manufacture the base of precision tool machine. In this paper, the results and the analysis are both presented of an experimental investigation on the effects of moulding technology on polymer concrete (PC) used for manufacture the base of precision tool machine. Effect of voids population on compressive strength of polymer concrete was examined. Various frequencies were applied during the packing operation of the polymer concrete samples using the vibration table. The optimum frequency for vibration and for producing a PC sample with the highest compressive strength was found to be 18.9375 Hz, which resulted in 109 MPa compressive strength for basalt, sand and chalk composition. In addition influence of Dimethyl aniline (DMA) amount and moulding temperature on mixing process and the strength of matrix domain were experimented. The relation between time of viscosity build-up t (min), temperature T (°C) and DMA content C (%) were correlated. This relation was used to obtain the suitable time required for mixing to prevent the mixing while the polymeric binder reach the gelling time through the copolymerization process. Also mixing technology and its influence on mechanical properties of PC were investigated. The optimized mixing technology was reached. Enhancing certain aspects of moulding technology could lead to an elevation of the mechanical strength of PC that may assist in producing polymer concrete with a high level of compliance with the optimisation criteria for PC used in manufacturing bases for precision tool machinery.

Natural cellulose fiber extract from Pandanus tectorius (Screw pine) leaves is comprehensively investigated as viable alternative for synthetic based fibers made from petro-chemical which is non-degradable and toxic. Pandanus tectorius leaves fiber is extracted and investigated as reinforcement in polymer composite for engineering applications. The habitant are easily found and grown along mangroves and in local jungles located at shallow water. The plant can grow up to 14 meters tall. In order to use these continuous cellulose fibers as reinforcement in polymer composites, the microstructural analysis and yield content analysis were carried out using SEM micrographs to establish the certainty of using them as reinforcement fiber. The alkaline, bleaching and combined alkaline-bleach treatment is utilized in extraction of the cellulose fiber to evaluate the effect on the mechanical property. The cellulose percentage of the fiber was increased as the concentration and soaking time were increased. The extraction process resulted in 73% cellulose percentage for 10 wt.% NaOH and 120 minutes treatment. Hence, it caused 87% increment in cellulose percentage compared to the untreated leaf.

Relatively new optical techniques are utilized to study the oxidation of low-index crystal faces of a zirconium doped single crystal β-NiAl. With these non-destructive techniques residual stress, phase composition and thickness of the scales were determined at various temperatures. The results are compared with the results obtained from an undoped counterpart. Interesting differences in scale stress, thickness and phase composition have been observed. The residual stress evolves rather differently than that on the undoped counterpart. Initial lower stress levels in the doped crystal convert to higher stresses at higher oxidation temperatures. The orientation dependence and a stress anomaly observed with the undoped single crystal β-NiAl are still present on the doped sample. Fluorescence and Raman results indicate a higher concentration of θ-Al₂O₃ on all crystallographic phases with Zr doping. The oxide scales are also thinner on the Zr doped specimen.

This paper will propose a complete solution with a novel simulation set up to get the final vibration data of seated human body inside an automobile structure without carrying out measurement tests. Furthermore, it will improve the existing technology in assessing the dynamic interaction between the human body and a car seat subjected to different conditions and establish a clear idea about the vibration effects, vibration transmissibility, damping, variable stiffness, natural frequencies, modal analysis, random vibration, harmonic aspects, mode superposition, response spectrum, transient effects etc. The research will provide a novel solution of the entire system rather than focussing only on a very specific portion of the system, thus, trying to close the gap in present technological areas and omitting the time consuming and expensive testing methods in the modern industries. This research will contribute a cutting edge landmark by providing a simulation model to predict final vibration level inside the human body and car seat to avoid the time consuming and expensive testing methods. It will help better understanding the impact and estimation of the vibration level inside the car seat and occupant human body.

The non-linear dynamic aspects and efforts will be made to understand, characterize and optimize the level of vibration by establishing a computational simulations model of the car seat and the occupant to match the experimental results.

Some technologies have been achieved to judge the dynamic interaction between the human body and a car seat, though such technologies cover only either vibration effects or dynamics or measurement techniques or small portion of the car and human body without considering all the real life factors like pre-stressed bodies, variable stiffness, equivalent stiffness and damping factors based on the behaviour of the human muscles, bones and postures.

So, efforts will be made to establish numerical and simulation models for the non-linear bio-dynamics of the seated human body, polyurethane foam cushions, dynamic contacts between the human body and the seat, occupant under the real life car motion, vibration testing of the car seat and finally, to provide a comprehensive solution to judge the vibration levels, which eventually will lead the various industries to avoid the time consuming and expensive testing methods.

Benzo[1,2-b:5-B’]dithiophene (BDT)–based small molecules with acceptor-donor-acceptor (A-D-A) structure were designed based on the experimental system BDTT-S-TR (1) for use as potential donor materials for organic photovoltaic (OPV) devices. Their geometry structures, electronic properties and other key parameters related to OPVs such as absorption spectra, energetic driving forces ΔE L-L, power conversion efficiencies (PCEs) and intramolecular charge transfer properties have been investigated by means of density functional theory (DFT) and time dependent density functional theory (TDDFT) methods. These have been exploited as donor materials for a heterojunction with [6,6] phenyl-C71-butyric acid methyl ester (PC70BM) as acceptor material. Based on Marks model, an excellent agreement between the experimental and predicted PCE was obtained for the reported system 1/PC70BM and a significant improvement in PCEs of BHJ devices based on 2-4/PC70BM was manifested. The charge transfer rates of the interfacial charge transfer Kint er−CT and recombination Kint er −CR in 1-4/PC70BM heterojunctions have been calculated using Marcus-Levich-Jortner rate equation. The calculations show that the ratios Kint er-CT / kint er-CR for the 2-4/PC70BM heterojunctions are ~104 times higher than that of the 1/PC70BM. From these predictions, we reached our purpose to provide rational design of three novel molecules that will be more promising candidates for high-efficiency SMs OPVs materials.

In the present work, Co3O4, 1% chromium doped Co3O4 (1% Cr:Co3O4), and 5% chromium doped Co3O4 (5% Cr:Co3O4) was successfully prepared by simple chemical co-precipitation method followed by calcination at 400°C for 3 h. The synthesized nanoparticles materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), Brunauer Emmett Teller analysis (BET), and UV-visible spectroscopy. XRD confirmed the formation of cubic nature of nanoparticles while SEM images shown spherical structure. BET analysis confirmed the mesoporous behaviour of nanoparticles. UV-Visible spectra have been used to determine band gap and photo-oxidation behaviour of organic dye methyl orange. Experimental data suggested that 5% Cr:Co3O4 nanoparticles catalyst possessed the highest catalytic activity towards MB degradation in aqueous solution at the tested concentration level of 50 mg/L, higher than that of pure Co3O4.

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Electromagnetic interference (EMI) is an escalating concern in the modern electronic climate. As such it has become a critical area to consider when designing and packaging electronics. In this context, Electroless Silver Coated nanocenosphere (SCNC) in Poly Methyl Methacrylate (PMMA) and Acrylonitrile Butadiene Styrene (ABS) composites has been tried for its EMI shielding effectiveness. The strategy is to render the polymer conductive by dispersing SCNC in various proportions in these polymers separately and to promote wave absorption by making sheet of the polymer-based composite. In our study EDX (Energy Dispersive X-Ray) analysis confirmed the presence of Ag on the coated nano cenosphere. This was further, confirmed through Phase analysis by XRD (X-Ray Diffractometer) analysis. SEM (Scanning Electron Microscope) analysis was conducted to see the size, shape and adherence of the Ag coating on nanoenosphere particles and to observe the distribution of these particles in polymer matrix in the composite sheet. BET Surface area of electroless coated powders was quite high indicating good surface properties.

The processing methods, electrical properties (surface resistivity) and electromagnetic behavior (EMI shielding effectiveness) were investigated. Shielding effectiveness (SE) values of approximately 25 dB at a frequency of 1 GHz was obtained for coatings of Electroless Silver coated nanocenospheres in ABS polymer which was further increased by adding other conductive nano fillers (Graphene and multi walled Carbon Nano tube) along with coated nanocenospheres.

The reproduction of a 3D bone structure with suitable porosity, which allows the flow of nutrients, blood, oxygen and mineral, remains a problem using conventional methods. A material that mimics their properties was developed by optimizing the ratio of a biodegradable blend of immiscible polylactic acid (PLA) and poly-ε-caprolactone (PCL). In this study, PLA and PCL particularly optimize the strength of the artificial cancellous bone by supplying the initial support strength lasting 6 months to 2 years and allowing for the gradual degradation desired in the human body. This study focused on the mechanical properties of successfully printed 3D structures. The ultimate tensile strength was modified by blending different ratios of PLA and PCL resulting in an optimum value of approximately 30 MPa when the ratio of PLA to PCL reached 3:1. The addition of 1 wt.% of titanium dioxide (TiO₂) to the immiscible PLA/PCL composite and the modification of the interface area between them resulted in the formation of a binding force that allowed for an increase in the tensile strength up to 37 MPa. Besides the mechanical properties, the in vitro biocompatibility of PLA/ PCL/TiO₂ composites was examined. A vigorous cell growth was observed in the cells cultivated with the PLA/PCL/TiO₂ composites and the unimpeded ability to differentiate into osteoblast also was found. The resulting properties of the 3D printed structures indicate promising applications in the fields of bone tissue engineering and cancellous bone grafting.

The objective of this work is to compare the mechanical properties including tensile, bending and impact properties between different glass fiber architecture reinforced polyester composites which are fabricated by a hand lay-up technique. The effects of stacking sequences of glass fibers consists of five layers which mainly are plain woven, short fiber, and sandwich layer glass composites on the mechanical properties of composites have been studied. The results showed that the tensile and bending properties of all different composite laminates are significantly higher compared to the neat resin. The plain woven glass reinforced polyester composites showed the highest values compared with other composite laminates. As the glass fiber mats a core are tightly packed and absorbs the impact stresses and distributes them evenly in the composites sandwich layer, the glass composites showed the highest value of impact strength compared with other composite laminates. Moreover, from SEM investigations, in these composites, there is an inverse relationship between the amount of delamination and the amount of hackles, and as the hackles increase the mechanical properties including tensile and bending of these composites are enhanced.

The curcumin loaded PMMA-AA/ZnO nanocomposite potentially inhibited the growth of AGS cancer tumour in male Swiss albino mouse, which showed a promising targeted cancer therapy. Interestingly the given bio-nanocomposite was rapidly cleared from the organs with negligible exhibition of toxicity. From the obtained results it is understood that the apoptosis has been occurred through mitochondrial disruption-mediated pathway. Also these nanomaterials could efficiently hinder the Go/G1 transition along with cycle progression at S-phase transition due to the radiation-induced DNA damage. These findings declared that the auspicious candidate, curcumin could be successfully delivered into the target by the polymer encapsulated ZnO NPs and exhibited a potent activity against gastric cancer cells at molecular and cellular levels as well as cell proliferation in a panel of tumour cells

Hydroxyapatite (HAp) having chemical formula Ca₁₀ (PO₄)₆(OH)₂ is the main chemical component of human bone tissue (70%), to cope up with the bone response as a bio active material. In this study Ni doped HAp powder with triclinic phase was synthesized by sol-gel method, by doping Ni of different concentrations (0.02, 0.04, 0.06, and 0.08). The various properties due to different concentration of Ni in HAp were characterized by X-ray diffraction analysis (XRD), Energy dispersive x-ray spectroscopy (EDX) and Fourier transform spectroscopy (FT-IR). The thermal gravimetric analysis (TGA-DTA) was also carried out to evaluate the stability of the synthesized HAP powder. Antibacterial activity of compounds against microbial pathogens was done using well diffusion method. High antibacterial activity was observed for Ca_0.98 Ni_0.02 (PO₄)(OH)₂. The transmission electron microscopic analysis confirms the presence of the spherical shape morphology of the prepared hydroxyapatite nanoparticle with the particle size of around 20 to 100 nm.

In the present work the modifications induced by the geomimetic processing on the environment of silicon and aluminum atoms are finely characterized by solid state MAS NMR. The raw clay (Lat), a lateritic clay from Yaoundé (Cameroon), contains kaolinite, quartz, hematite and goethite as major mineral phases. This material is treated under acidic conditions during 24 h (LatAF) and then under alkaline conditions during 18 days, leading to the final consolidated “geomimetic” product (LatAFCH). The samples have been characterized by ²⁹Si and ²⁷Al solid state NMR at each step of the process.
The NMR spectra obtained for the starting clay indicate the presence of Al_IV and Al_VI populations together with silicon Q² (0 or 1Al) and Q³ (0 or 1Al) environments located at δ_iso=-83 ppm and δ_iso=-91 ppm respectively.
The acidic reaction during 24 h, does not significantly affect the silicon-rich layers. It induces a conversion of part of Al_IV population into Al_VI environment mainly related to the occurrence of six-fold organo-aluminum complexes when using fulvic acid. With inorganic acid, Al dissolution prevails.
The neutralization (using lime) of the medium, followed by ageing for 18 days, promotes clay interactions with available calcium ions. The newly formed phases are cementitious CSH, CASH and CAH phases.

Durable superhydrophobic surface on metal substrates was fabricated using very applicable method. The fabrication method aimed to decrease surface free energy and increase surface roughness at same time the process have been accomplished via the addition of silica nano particles with Dodecyltrimethoxysilane (DCTES) bonded to the surface of the silica particles. Adhesive polystyrene was added to improve bond between substrate and functionalized silica. The method is cheap, promising to be applied in factories heat exchangers to reduce fouling and corrosion on the large industrial scale. Scanning electron microscopy (SEM) was used for surface morphology analysis, showing the roughness produced by surface treatment. The wettability of the micro-nano silica film varied from hydrophilicity (water contact angle 88°) to superhydrophobicity (water contact angle 165.2°), while sliding contact angles dramatically decreased (<4°) by adding Functionalized silica and/or adhesive polymer. Roughness increased with silica increment which improves the wettability. The coatings were electrochemically characterized by electrochemical impedance spectroscopy (EIS) and Tafel polarization curves; it was found that both systems had good performance against corrosion in 3.5% sodium chloride solution.

The investigation was carried out to study the effect of surface grinding on chloride induced stress corrosion cracking (CISCC) of austenitic stainless steels 304 at ambient temperature condition. The U-bend tests with thickness 13 mm as per ASTM G 30 were used to investigate the effect of surface grinding on chloride induced stress corrosion cracking (CISCC) of austenitic stainless steel 304 in a corrosive atmosphere containing sodium chloride at ambient temperature. At a high level of tensile residual stress had developed the pits on U-bend specimen surface at ambient temperature with the presence of low to high chloride concentration level. The experimental results recommend that develop a proper metallurgical fabrication criteria, specification, and procedures for pressure vessels to avoid a recurrence in future.

Boron steels are very interesting as wear resistant materials. In this research we propose a boron steel without alloys, 30MnB5, with a new thermal treatment that exceeds the mechanical characteristics of conventional treatment. The 30MnB5 steel, with the new sub-critical annealing and water quenching heat treatment, also exceeds the RAEX450. The new treatment has important advantages, such as: energy savings and reduction of costs and manufacturing times. It also has a more favourable ACV than 30MnB5 with conventional heat treatment and RAEX450. Its wear resistance is significantly improved compared to the classic heat-treated 30MnB5 and the RAEX450.