பொருள் அறிவியல் & பொறியியல் இதழ்

Electrical signals emanating from biological cells can convey clinical information on the functionality thereof. However, measurement of such small signals caused primarily by ionic activity inside the cell, known as action potential, poses a great challenge to biomedical scientists. The electrical signals of the biological cells result from exchange of ions through the cell membrane. The characteristics of action potentials may reveal a great deal of information about the causes and symptoms of abnormal cell behaviour. Hence, it is imperative to capture high quality action potentials through the use of nano-sensors from within the cell. Recently, developments in silicon nanowires (SiNW) fabrication techniques have demonstrated a great potential for them to be used as nano-electrodes. Largescale assembly and integration of addressable complementary silicon nanowires arrays have been demonstrated for multiplexed biosensor arrays. The fabrication process resulted in a high-yield, high performance devices arrays for chemical and biological detection. In this paper, we seek to model the electrical interface that is responsible for recording the biological signals. We present electrical equivalent circuits that model the boundary between the biological cell and the nanowire electrode. Impedance measurement curves of nanowires for various sizes of length and diameter have also been presented and discussed. The impedance graphs show a hyperbolic dependence of resistance on length and diameter of nanowires. This non-linear behaviour may be mitigated in software algorithms when interpreting the measured cell signals.

A series of experimental Al-Zn-Mg-(Cu) alloys with a semi-constant Zn:Mg ratio were produced via hot rolling. The effects of Cu in these alloys on the activation energy for precipitation, the response to natural aging, the size of the precipitate free zone, and the corrosion resistance were investigated.

The aim of this research is to study the fatigue life enhancement produced in quenched and tempered AISI4340 steel with a tensile strength of 2000 MPa after being submitted to shot peening surface treatments. These treatments generate compressive residual stress fields in a superficial layer of the material at the same time as inducing some kind of damage on the surface. Different kind of projectiles were chosen to perform the treatment (ceramic and steel shots), studying the way these affected the fatigue life of the specimens.

The surface topography of the samples was analysed using a roughness tester and by means of scanning electron microscopy (SEM). The compressive residual stress profile induced by these treatments was measured using X-ray diffraction (XRD) plus electro-polishing. The fatigue behaviour of the treated samples was subsequently studied by means of 4-point rotating bending tests and their fracture surfaces were analysed using SEM.

The best fatigue performance was obtained after shot peening with ceramic beads under 8A Almen intensity. The main difference in relation to the treatment performed under the same intensity but using steel cut wire shots was the much lower surface damage induced by the impacts with the ceramic shots compared with the cut wire projectiles, which in turn is justified by the greater geometric perfection and hardness of the former. Furthermore, fatigue specimens shot peened with ceramic beads under 8A intensity always gave rise to internal fatigue crack initiation, which took place outside the zone subjected to residual compressive stresses. Moreover, fatigue initiation was always linked to the presence of hard and rigid alumina inclusions, which acted as microstructural stress concentrators.

The synthesis of novel microstructured LiFePO₄ with advantageous nanosheets for Li ion conductivity was attempted. Using layered NH₄FePO₄•H₂O as raw material, LiFePO₄ nanosheet was synthesized by the hydrothermal process in LiCl solution. Prepared NH₄FePO₄•H₂O was several tens micrometer sized sheet with about 200 nm in thickness. As Li ion resource, various LiCl solution like deionized water, ethanol, and ethylene glycol were prepared through subsequent hydrothermal process and the effect of a kind of solvents for LiCl solution on the microstructure of products treated by the hydrothermal process was investigated for LiFePO₄ nanosheets synthesis. The products of LiFePO₄ nanosheet were characterized by XRD, SEM, TEM, FT-IR and ICP. Regardless of a kind of solvents, LiFePO₄ nanosheet was composed of arranged nano-blocks, although the size and morphology of nano-blocks was different in each solvent.

This paper challenges the ISO standard 14577 that determines the elastic indentation modulus by violating the first energy law, violating the physically deduced dimensional law, and omitting easily detected phase change onsets as well as initial surface effects under load. The double iteration for incorrect fitting indentation modulus to Hook's law Young's modulus of a standard with up to 11 free parameters must be cancelled and discontinued. The iterative evaluation of the elastic modulus E_r-ISO can by far not be reproduced by iteration-free direct calculation of E_r, when using the underlying formulas for S, hc, A_hc, and ε. For cubic aluminium the divergence amounts to a factor of 3.5 or 3.1, respectively (both smaller for the non-iterated calculations). Every interpretation of indentation moduli as single unidirectional "Young's moduli" is false. They are mixtures from all directions and include shear moduli. The three different packing diagrams of body centered cubic α-iron exemplify the mixture of three independent Young's moduli (and thus also three shear moduli) even in this simple but already anisotropic case. More linear moduli ensue in lower symmetry crystals as exemplified with α-quartz. The first physical indentation modulus is deduced by removal of the physical errors of E_r-ISO, or after indenter compliance correction E_ISO. E_phys does no longer violate the energy law. Five face-dependent elastic indentation moduli of α-quartz at the obsolete E_r-ISO level and two tensional Hook-law Young's moduli are compared with all of its six resonance ultrasound spectroscopy (RUS) evaluated Young's moduli, and with the bulk modulus. The dilemma between ISO and physics is particularly detrimental, as E_ISO is used for the calculation of very frequently applied mechanical parameters. These propagate the errors into failure risks of falsely calculated materials with severe violation of the basic energy law and other physical laws for daily life. Difficulties with the urgent settlement by new ISO standards are discussed. First suggestions for the use of E_phys, or S_phys, or eventually measured bulk modulus K are made. This should be urgently evaluated and discussed.

A micro-arc oxidation coating on Ti6Al4V alloy was modified by addition of micro-Al₂O₃ particles to a sodium phosphate solution. The coating structure and phase were characterized by scanning electron microscopy and X-ray diffraction, and the oxidation resistance and thermal shock properties of the coating were investigated. Results showed that a coating denser than the original coating was produced. This new coating was composed of Al₂TiO₅ and TiO₂. The oxidation resistance and thermal shock property of the coating improved with addition of Al₂O₃ particles to the electrolyte relative to the sample prepared without the particles in the electrolyte. Moving Al₂O₃ particles were adsorbed on the coating surface and penetrated through it. As a result, the phase structure and properties of the original coating were modified.

Cu-13Al-0.545Be shape memory alloy are heat treatment at different temperature and time. The microstructure of alloy after heat treatment at 850°C, 650°C and aging at 150°C ,450°C and 550°C for 2, 4 and 6 h study by optical microscope and X-ray diffraction. Bending test is use to show effect of heat treatment on super-elastic and shape memory effect.

Micro hardness test used to show effect of heat treatment on micro hardness .shape memory effect increase at heat treatment 650°C and aging at 150°C, while at 450°C and 550°C will decrease because precipitate formation rate rises with increase in temperature and time. The hardness and precipitates in the alloy increases with increasing ageing duration. Higher ageing temperature avoids the imperfection by moving and filling the empty space thereby hardens the alloy.

Nanofiber is a broad phrase generally referring to a fibre with a diameter less than 1 micron. While glass fibres have existed in the sub-micron range for some time and polymeric meltblown fibres are just beginning to break the micron barrier, sub-half-micron diameters have been used for air filtration in commercial, industrial and defence applications for more than twenty years. They have been shown to deliver improved filter life, increased contaminate holding capacity and enhanced filtration efficiency. Small fibres in the sub-micron range, in comparison with larger ones, are well known to provide higher filter efficiency at the same pressure drop in the interception and inertial impaction stages of the filtration process. In particular, nanofibers provide marked increases in filtration efficiency at relatively small (and in some cases immeasurable) decreases in permeability. Nanofiber filter media have enabled new levels of filtration performance in several diverse applications with a broad range of environments and contaminants. While nano fibre size lead to a higher pressure drop, interception and inertial impaction efficiencies will increase faster, and therefore more than compensating for the rise in pressure drop. Thus, in the particle size of interest, i.e. from sub-micron upwards, better filter efficiency can be achieved at the same pressure drop, or conversely, the same filter efficiency at a lower pressure drop can be achieved with nanofibres. This paper will discuss a process for making nanofibers, as well as the benefits, limitations, construction, and applications of filters using nanofiber media.

In addition to polar molecules, there is no polar atom in the natural world, which is a deep-rooted traditional concept that has lasted for more than a century. However, our research showed that alkali-metal atoms form an exception. In theory, we proved that alkali atom may be polar atom doesn't conflict with quantum mechanics, which is a great breakthrough in measurement theory of quantum mechanics. Variation of the capacitance with temperature and density offers a means of separating polar and nonpolar atom, but no one has done these experiments so far. If alkali atom is nonpolar atom, its capacitance should be independent of temperature and density, because atomic nucleus located at the center of the electron cloud. Our experiments showed that Na, K, Rb and Cs atoms are polar atoms, because their capacitance is not only related to temperature, but also to density. Unlike alkali atoms, the capacitance of Hg gas is independent of temperature and density, so mercury is nonpolar atom. Therefore atoms can be divided into two categories: polar and nonpolar atom, this discovery will lead to an exciting revolution in Bose- Einstein condensation (BEC) research and condensed matter physics. BEC experiments have been carried out for decades, but the number of condensed atoms is still very small (<107) because scientists has never applied an electric field. Our innovation lies in the application of an electric field, we don't need magnetic field and lasers. When V=390 volts, condensates contained up to 2.51 × 1017 sodium atoms; when V=350 volts, condensates contained up to 1.93 × 1017 cesium atoms, large-scale BEC at T=343 K or 353 K has been observed. Now scientists generally assume that polar molecules may be used as candidate materials for quantum computers. In the future, polar atoms will replace polar molecules as candidate materials for quantum computers, because of its very small moment of inertia.

The peculiar properties of layered Double Hydroxides (LDH) have progressively drawn the attention of the scientific community. The main characteristic of LDH is the ability to capture anionic species (organic and inorganic) to build different composites. This is made possible by the sandwich structure of the LDH, similar to the brucite architecture, made up of positive charged lamellas interspersed by anions. Several distant fields, ranging from medicine to physics and engineering, exhibit interest in LDH applications. To satisfy all those requirements, energy was spent to sculpt LDHs physical and chemical properties and for designing layered double hydroxides “ad hoc” for different needs and employments. Notably, among the many applications, those related to metallurgical processes and products are of particular interest. This paper presents the characteristics, the main preparation routes and reviews the applications of LDH to metallurgy with some examples taken from the experimental research of the author.

This study investigates the effect of unsaturated polyester resin chemical composition on the coefficient of thermal expansion, damping properties, flexural strength, tensile strength and hardness. The resin is used as binder in polymer concrete for manufacturing the bases of precision tool machines in previous work published by the authors. Resins of various ratios of styrene-ARAPOL and methyl methacrylate (MMA)-ARAPOL were made and their curing kinetics was studied using viscosity measurements and exothermic reaction temperature profiles. The resins were studied using dynamic mechanical analysis and in-house thermal expansion measuring devices. It was found that ARAPOL–MMA (60:40) has the highest damping factor of 5.46%, and the thermal expansion coefficient of 7.98 × 10- 5/°C. This composition also has the optimum flexural and tensile strengths at 128 MPa and 58.6 MPa

Polypropylene (PP) represents about a quarter of commercial plastics produced around the world. Despite its huge commercial success, PP polymer is not suitable for the applications that require long-term exposure to high temperatures (>80°C), due to its chemical and physical stability. The PP chain is prone to the oxidative chaindegradation and exhibits a relatively low material softening temperature. This paper discusses a new research approach by developing the PP-bonded hindered phenol (PP-HP) antioxidants to address this scientifically challenging issue. We have investigated two PP-HP structures, one with two methylene units adjacent to the hindered phenol group (HP-L) and one without this spacer (HP-S). In general, PP-HP polymers are advantaged with the ability to incorporate a suitable concentration of HP antioxidant groups with homogeneous distribution along the polymer chain, which provide effective protection to the PP chains from oxidative degradation. In addition, the specific PP-HP-L structure can also engage in a facile crosslinking reaction to form a 3-D network during the oxidation reaction. In one accelerated oxidation test in air at 190-210°C, the regular commercial PP polymer (containing common antioxidants and stabilizers) degrades within a few minutes; a PP-HP-L copolymer with about 1 mol% HP-L group shows almost no detectable weight loss after 24 hrs. In an ASTM endurance test at 140°C in air, the commercial PP shows 1% weight loss within about 10 days. On the other hand, the PP-HP-L polymer lasts for more than 30 years. Overall, the experiment results present the potential of expanding PP applications into a much higher temperature range (>140°C) under oxygen oxidative environments

This study deals with the functional properties of honeycomb panels for structural applications, thermal management and sound/heat insulation to design more eco-friendly products. Using honeycomb panels filled with polyurethane (PU) and Phase Change Materials (PCM) led to fulfill desired properties such as minimum density, high stiffness, rigidity and strength and improved thermal properties and heat insulation. Mechanical responses of such panels were investigated along with thermal measurements. Functional roles in structural and thermal management applications may provide advantages such as low cost and high performance in housing, aerospace, automotive, packaging and transportation sectors.

This paper is presented a theoretical study of electronic, magnetic and chemical bonding properties of spinel CdCr2O4 with a general formula of AB2X4 (A, B=transition- metal, X=oxides, chalcogenides) using density functional calculation method combined with spin- polarized theory within generalized gradient approximation. Density functional calculation is performed to observe the effects of magnetic ordering on the electronic and chemical bonding properties of spinel CdCr2O4 with both cubic and tetragonal structure from a pyrochlore lattice, using Quantum ESPRESSO package. Consequently, in order to investigate the magnetic properties in paramagnetic, ferromagnetic and antiferromagnetic orderings of spinel CdCr2O4, a first-principles study of the electronic structure as well as chemical bonding properties of spinel CdCr2O4 compound in two different structural form is performed: the cubic structure in order to investigate the desired properties in paramagnetic and ferromagnetic orderings, and tetragonal structure to calculate the same properties in antiferromagnetic ordering