Stability and vibrational spectra of toroidal isomers of C 240

To study the thermodynamic and mechanical stability of toroidal isomers of C ₂₄₀, we use a semi-empirical tight-binding theory and calculate their electronic structure, cohesive energy and vibrational spectra within the harmonic approximation. From these, we deduce their free energy at temperatures up to 1500K. The results are also compared to the isomer with icosahedral symmetry. Finally, we discuss within this approach, their stability and abundance.     

A new quantum-dot cellular automata full-adder

A novel expandable five-input majority gate for quantum-dot cellular automata and a new full-adder cell are presented. Quantum-dot cellular automata (QCA) is an emerging technology and a possible alternative for semiconductor transistor based technologies. A novel QCA majority-logic gate is proposed. This component is suitable for designing QCA circuits. The gate is simple in structure and powerful in terms of implementing digital functions. By applying these kinds of gates, the hardware requirement for a QCA design can be reduced and circuits can be simpler in level, gate counts and clock phases. In order to verify the functionality of the proposed device, some physical proofs are provided. The proper functionality of the FA is checked by means of computer simulations using QCADesigner tool. Both simulation results and physical relations confirm our claims and its usefulness in designing every digital circuit.     

High-pressure phases of hydrogen cyanide: formation of hydrogenated carbon nitride polymers and layers and their electronic properties

We have performed a set of first-principles simulations to consider the possible phase transitions in molecular crystals of HCN under high pressure. Our calculations reveal several transition paths from the orthorhombic phase to tetragonal and then to triclinic phases. The transitions from the orthorhombic to the tetragonal phases are of the second order, whereas those from the tetragonal to the triclinic phases turn out to be of the first-order type and characterized by an abrupt decrease in volume. Our calculations show that, by adjustment of the temperature and pressure of the HCN molecular crystal, novel layered and polymeric crystals with insulating, semiconducting or metallic properties can be found. Based on our simulation results, two different crystal formation mechanisms are deduced. The stabilities of the predicted structures at ambient pressure are further assessed by performing phonon or MD simulations. In addition, the electron transport properties of the predicted polymers are obtained using the non-equilibrium Green's function technique combined with density functional theory. The results show that the polymers have metallic-like I-V characteristics.     

Prediction of the penetrated rust into the microcracks of concrete caused by reinforcement corrosion

Consider a steel-rust-concrete composite consisting of a circular cylindrical concrete cover and a coaxial uniformly corroding steel reinforcement. Prediction of the amount of rust penetrated into the microcracks of concrete cover from a set of data measured at the surface of the concrete is of particular interest. The steel is assumed to be linear isotropic and rust follows a power law stress–strain relation. For the concrete, anisotropic behavior and post-cracking softening model is employed. The formulations lead to a nonlinear boundary value problem which is solved analytically. A key parameter β, defined as the ratio of the volume of corrosion products inside the cracks to the volume of the cracks, is calculated. With some efforts, this parameter is also extracted from the available theoretical and experimental studies for the purpose of comparison. The effects of the mechanical properties of rust and concrete on β is addressed.     

A novel low-power full-adder cell for low voltage

This paper presents a novel low-power majority function-based 1-bit full adder that uses MOS capacitors (MOSCAP) in its structure. It can work reliably at low supply voltage. In this design, the time-consuming XOR gates are eliminated. The circuits being studied are optimized for energy efficiency at 0.18-μm CMOS process technology. The adder cell is compared with seven widely used adders based on power consumption, speed, power-delay product (PDP) and area efficiency. Intensive simulation runs on a Cadence environment and HSPICE show that the new adder has more than 11% in power savings over a conventional 28-transistor CMOS adder. In addition, it consumes 30% less power than transmission function adder (TFA) and is 1.11 times faster.     

Two new low-power Full Adders based on majority-not gates

Two novel low-power 1-bit Full Adder cells are proposed in this paper. Both of them are based on majority-not gates, which are designed with new methods in each cell. The first cell is only composed of input capacitors and CMOS inverters, and the second one also takes advantage of a high-performance CMOS bridge circuit. These kinds of designs enjoy low power consumption, a high degree of regularity, and simplicity. Low power consumption is targeted in implementation of our designs. Eight state-of-the-art 1-bit Full Adders and two proposed Full Adders are simulated using 0.18 μm CMOS technology at many supply voltages. Simulation results demonstrate improvement in terms of power consumption and power-delay product (PDP).     

Utility-based adaptive radio resource allocation in OFDM wireless networks with traffic prioritization

In this letter, a joint transmit scheduling and dynamic sub-carrier and power allocation method is proposed to exploit multi-user diversity in downlink packet transmission in an OFDM wireless network with mixed real-time and non-real-time traffic patterns. To balance efficiency and fairness and to satisfy the QoS requirements of real-time users, we utilize a utility-based framework and propose a polynomial-time heuristic algorithm to solve the formulated optimization problem. The distinguishing feature of the proposed method is that it gives in one shot, the transmission scheduling, the sub-carriers assigned to each user, and the power allocated to each sub-carrier, based on a fair and efficient framework while satisfying the delay requirements of real-time users.     

Application of elastically supported single-walled carbon nanotubes for sensing arbitrarily attached nano-objects

The potential application of SWCNTs as mass nanosensors is examined for a wide range of boundary conditions. The SWCNT is modeled via nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The added nano-objects are considered as rigid solids, which are attached to the SWCNT. The mass weight and rotary inertial effects of such nanoparticles are appropriately incorporated into the nonlocal equations of motion of each model. The discrete governing equation pertinent to each model is obtained using an effective meshless technique. The key factor in design of a mass nanosensor is to determine the amount of frequency shift due to the added nanoparticles. Through an inclusive parametric study, the roles of slenderness ratio of the SWCNT, small-scale parameter, mass weight, number of the attached nanoparticles, and the boundary conditions of the SWCNT on the frequency shift ratio of the first flexural vibration mode of the SWCNT as a mass sensor are also discussed.