Graphene as Gas Sensors

The triatomic and tetratomic gas molecule adsorption effects on the electrical conductivity of graphene are investigated by the tight-binding model, Green's function method, and coherent potential approximation. We find that the electrical conductivity of graphene sheet is sensitive to the adsorption of these gases.     

Output feedback controller for hysteretic time-delayed MIMO nonlinear systems

In this paper, an H ^?? output feedback controller is developed for a class of time-delayed MIMO nonlinear systems, containing backlash as an input nonlinearity. Particularly, a state observer is proposed to estimate unmeasurable states. The control law can be divided into two elements: An adaptive interval type-2 fuzzy part which approximates the uncertain model. The second part is an H ^??-based controller, which attenuates the effects of external disturbances and approximation errors to a prescribed level. Furthermore, the Lyapunov theorem is used to prove stability of proposed controller and its robustness to external disturbance, hysteresis input nonlinearity, and time varying time-delay. As an example, the designed controller is applied to address the tracking problem of 2-DOF robotic manipulator. Simulation results not only verify the robust properties but also in comparison with an existing method reveal the ability of the proposed controller to exclude the effects of unknown time varying time-delays and hysteresis input nonlinearity.     

The effect of severe plastic deformation and annealing conditions on mechanical properties and restoration phenomena in an ultrafine-grains Fe-28.5%Ni steel

The effect of annealing condition on the microstructure evolution, together with mechanical properties of Fe-28.5Ni steel processed by one and six cycles of accumulative roll bonding (ARB), was explored. The evolution of microstructure was studied by means of Electron Backscattered Diffraction method. The ARB-processed specimens were annealed for 30 minutes between 500°C and 600°C, and the effect of these annealing processes was elaborated. Results showed a significantly reduced martensite phase during ARB process cycles. Moreover, a refined and stabilised ultrafine structure was obtained in 6-cycle ARB-processed specimen. Results also show that by annealing the 1-cycle specimen at 550°C, no significant microstructural change and mechanical properties variation are identified. As such, no significant microstructural change and mechanical properties variation were notified for annealing of 6-cycle ARB-processed specimen at 500°C. However, annealing at 600°C in both conditions led to a complete recrystallisation of the deformed structure. Annealing at 550°C in 6-cycle ARB-processed specimen showed partial recrystallisation as well as an abnormal grain growth characteristic. The abnormal grain growth was seen by annealing of 1-cycle ARB-processed specimen at 600°C. The changing features of dislocations were discussed in these specimens in terms of changing the dynamics of low- and high-angle grain boundaries. Tensile test results also showed a significant increase in the yield/ultimate tensile strengths with the application of ARB cycles. Although ARB process led to a rapid reduction of total elongation, full restoration during high-temperature annealing returned this value back to the initial, non-deformed, condition.     

Remove Degeneracy in Relativistic Symmetries for Manning-Rosen Plus Quasi-Hellman Potentials by Tensor Interaction

The relativistic Dirac equation under spin and pseudo-spin symmetries is investigated for Manning-Rosen plus quasi-Hellman potentials with tensor interaction. For the first time we consider the Hulthen plus Yukawa for tensor interaction. The Formula method is used to obtain the energy eigen-values and wave functions. We also discuss about the energy eigen-values and the Dirac spinors for the Manning-Rosen plus quasi-Hellman potentials for the spin and pseudo-spin symmetry with Formula method. To show the accuracy of the present model, some numerical results are shown in both pseudo-spin and spin symmetry limits.     

Synthesis of colloidal nanoscaled copper-indium-gallium-selenide (CIGS) particles for photovoltaic applications

In this work, Cu(In,Ga)Se(2) (CIGS) nanoparticles were synthesized using a wet chemical method. The method is based on a non-vacuum thermal process that does not use selenization. The effects of temperature, source materials, and growth conditions on the phase and particle size were investigated. X-ray diffraction results confirm the formation of a tetragonal CIGS structure as the main phase with the purity more than 99% obtained by energy-dispersive X-ray spectroscopy (EDX). The morphology and size of the samples were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using these methods, 20-80nm particles were obtained. Through measurements of the absorption spectra of CIGS nanoparticles, the band gap of the synthesized material was determined to be about 1.44eV, which corresponds to an acceptable wavelength region for absorber layers in solar cells.     

An improved heuristic for the far from most strings problem

The Far From Most Strings Problem (FFMSP) asks for a string that is far from as many as possible of a given set of strings. All the input and the output strings are of the same length, and two strings are far if their Hamming distance is greater than or equal to a given threshold. FFMSP belongs to the class of sequence consensus problems which have applications in molecular biology, amongst others. FFMSP is NP-hard. It does not admit a constant-ratio approximation either, unless P=NP. In the last few years, heuristic and metaheuristic algorithms have been proposed for the problem, which use local search and require a heuristic, also called an evaluation function, to evaluate candidate solutions during local search. The heuristic function used, for this purpose, in these algorithms is the problem’s objective function. However, since many candidate solutions can be of the same objective value, the resulting search landscape includes many points which correspond to local maxima. In this paper, we devise a new heuristic function to evaluate candidate solutions. We then incorporate the proposed heuristic function within a Greedy Randomized Adaptive Search Procedure (GRASP), a metaheuristic originally proposed for the problem by Festa. The resulting algorithm outperforms state-of-the-art with respect to solution quality, in some cases by orders of magnitude, on both random and real data in our experiments. The results indicate that the number of local optima is considerably reduced using the proposed heuristic.     

Comments on “Natural frequencies of a uniform cantilever with a tip mass slender in the axial direction”

Using a power series expansion for the roots of the characteristic equation, the natural frequencies of a cantilevered Euler–Bernoulli beam with an end rigid mass are computed. Results are obtained for a range of center of mass offsets from the end of the beam. The results of current study corrects significant errors in the previous work by Rama Bhat and Wagner (1976).     

Crystal Structure of <Emphasis Type=Italic>N</Emphasis>-(2-Pyridylmethylene)benzene-1,4-diamine

Abstract  

The crystal structure of amino containing Schiff base, N-(2-pyridylmethylene)benzene-1,4-diamine, was determined via X-ray diffraction analysis. The title compound crystallizes in orthorhombic system, space group Pc2 ₁ n, with unit cell dimensions a = 5.8945(6), b = 11.9233 (10), c = 14.5356 (16) ?, V = 1021.59 (18) ?³, Z = 4. The molecules are linked by intermolecular N–H···N hydrogen bonds to form supramolecular sheets along with the bc crystallographic plane. The crystal structure is further stabilized by C–H···π stacking interactions.     

Phenylphosphinic acid‐catalyzed synthesis of 6‐unsubstituted dihydropyrimidinones under solvent‐free conditions

Phenylphosphinic acid is found to catalyze the three‐component condensation of an aldehyde, enaminone, and urea or thiourea to afford the corresponding 6‐unsubstituted dihydropyrimidinones in high to excellent yields. This methodology is simple and fast synthetic route for the preparation of interesting class of heterocycles.     

The structure of finite groups with trait of non-normal subgroups

In this paper, we investigate the finite groups all of whose non-normal nilpotent subgroups are cyclic. We show that such groups are solvable with cyclic centers. If G is a non-supersolvable group, then G has only one non-cyclic Sylow subgroup which is either isomorphic to Q₈ or is of type (q, q).