Abrasive cutting factor as a characteristic reflecting the performance parameters of superabrasive grinding

The paper addresses the physical meaning and tendencies of variation of the abrasive cutting factor f _a = P _z /P _y as applied to the processes of grinding with superabrasive wheels. The author shows in which cases one should try to increase the f _a value. A classification of work materials by this factor is put forward.     

Effect of a nanoparticle-filled lubricant in turning of AISI 316L stainless steel (SS)

Release of heat and generation of friction associated with machining operation ever posture a problem which not only reduce the tool life but also impair the quality of the product. Nano cutting fluids play a significant role in machining operations and impact tool life and quality of work. In the present work, tool flank wear is analyzed during turning AISI 316L Stainless steel (SS) under a nano cutting environment. Experiments are conducted by turning of AISI 316L SS under wet machining with and without multiwalled carbon nanotube (MWCNT) inclusions in the conventional lubricant. The second order quadratic models were developed to predict tool wear using response surface methodology (RSM) based D-optimal design. Machining parameters such as speed, feed rate, and depth of cut are chosen as numerical factors and the type of lubricant is considered as the categorical factor. The results show that the influence of the feed rate is more significant while machining the AISI 316L SS with a whisker reinforced ceramic insert. The addition of MWCNTs in SAE20W40 enhances the tool performance with their enhanced penetration. After turning experiment, a scanning electron microscope (SEM) with energy dispersive X-ray (EDS) was used to investigate the tool wear.     

Field-Controllable Spin Filter Based on Parallel Quantum Dot Systems

In this paper, we investigate the spin-polarized transport through parallel N?dot (N = 1, 2, 3) systems in the strongly correlated regime. We focus our attention on the responses of the N _{t o t} = i n t e g e r states to an increasing magnetic field B, where N _{t o t} is the total charge number on the dots. We show that when the charge level ?? is chosen at the particle-hole (p-h) symmetric case, spin filtering is difficult to occur. While if ?? is beyond the p-h symmetric point, perfect spin-polarized currents could be achieved, and the spin directions can be easily manipulated by tuning external electric and/or magnetic fields, making it easy to be realized in future experiments of the ideas. To approach these problems, the celebrated numerical renormalization group (NRG) technique is implemented, the dynamical properties and the quantum fluctuations are shown.     

Effect of a protruding rod-supported disk on the drag of a nose-controlled cylinder

The drag C _x of a cylinder of diameter D with a front protruding disk supported on a rod of length l has been studied as a function of the relative distance l/D under the conditions of high (supersonic) flight velocities. It is established that the optimum (minimum) drug C _x exists, the value of which agrees with the results of numerical simulations.     

Analytic Expressions for a 2D Permanent Magnetic Lattice with a 3D Bias Magnetic Field for Ultracold Atoms

In this paper, we discuss a permanent magnetic lattice for trapping and manipulating ultracold atoms and quantum degenerate gases. Considering three components of an external bias magnetic field, B_1x, B_1y and B_1z which are applied for controlling the magnetic lattice parameters, we obtain analytic expressions for the magnetic field minima locations as well as their absolute values, curvatures of the absolute value of the magnetic field, trap frequencies and barrier heights between minima in all directions. B_1z had previously been considered in numerical works, but not in analytic calculations, due to difficulty in obtaining the analytic expressions for the physical parameters and sufficiency of considering only B_1x and B_1y. Including the third component in this study provides further control over the magnetic lattice parameters. Also, in the presence of unavoidable bias magnetic fields with a z-component such as the Earth’s magnetic field, our analytic calculations could be useful. In numerical calculations, we have considered up to n _s  = 1001 square magnetic slabs in each direction of the 2D lattice.     

Magnetic-Memory Effects in High-Purity Beryllium

We study the magnesium-thermal beryllium condensate in the course of natural aging after several procedures of treatment by weak constant magnetic fields. The amplitude-time dependences of the effective shear modulus (G _ef ~ f ²), low-frequency internal friction, the parameter r, and the ratio of dislocation velocities V _afef /V ₀ are analyzed. It was revealed that the hysteresis in the f ²(γ) curves disappears after ~120 h of natural aging and the sign of r(γ) and V _afef /V ₀(γ) is inverted. The nature of the detected effects is connected with the appearance of microcracks in the stage of elastic deformation and their healing as a result of the viscous motion of unpinned dislocations in the field of point defects in the basal slip plane.     

Pressure Dependence of T<Emphasis Type="Italic">c</Emphasis> in High Temperature Superconductors: Role of Interlayer Interactions

We have studied the role of interlayer interactions (W) in the pressure dependence of T _c of layered superconductors. The expressions for dT _c /dP are obtained by including the effects of layered structure within the framework of two different proposed models, namely the negative-U Hubbard model and the Hirsch model. We observe that the inclusion of interlayer interaction provides better explanation of pressure dependence of T _c . Our numerical results show that the systems having one CuO₂ layer per unit cell may be well described by small values of W while the larger values of W accounts for the systems having two or more superconducting layers in a unit cell. The calculated values of dT _c /dP vs. W are found to be in good agreement with those of experimental results obtained for various high T _c superconductors of cuprate family.     

Improved predictability of forming limit curves through microstructural inputs

Forming Limit Curves (FLCs) were determined experimentally through limiting dome height (LDH) tests in AA1050, AISI 316L and AISI 304L. FLCs were also simulated through FE (finite element) analysis. Simulations involved both constant and varying (with strain and strain path) material properties — namely, strain hardening exponent (n) and normal anisotropy ( $\bar r$ ).Varying n values were estimated from limited experimental data (from tensile tests) and the implicit assumption that n scales with in-grain misorientation developments and formation of strain induced martensite. $\bar r$ , on the other hand, could be estimated from crystallographic texture only for AA1050. Simulations with varying $\bar r$ in AA1050 had shown a clear, though numerically marginal, improvement. On the other hand, varying n could remarkably improve the FLC predictability in 316L and 304L, especially in the biaxial region.     

Investigation of ITS-90 Inconsistencies in Overlap Region of the Water-indium,Water-tin,and Water-zinc Sub-ranges

One of the significant uncertainties in Standard Platinum Resistance Thermometer (SPRT) calibration by fixed-points method is Type I non-uniqueness (sub-range inconsistencies). Sub-ranges water-tin (W ₉ ) and water-indium (W ₁₀ ) lies in the water-zinc (W ₈ ) sub-range of the International Temperature Scale of 1990. Therefore, three sub-range inconsistencies [W ₈ and W ₉ (SRI _8–9 ), W ₈ and W ₁₀ (SRI _8–10 ), and W ₉ and W ₁₀ (SRI _9–10 )] occur. This paper investigated these inconsistencies using the calibration data of 12 SPRTs from six manufacturers. The result shows that the magnitude of the inconsistency for SRI _8–9 , SRI _8–10 , and SRI _9–10 are about 2.5, 2.2 and 1.8 mK, respectively.     

Effect of bimodularity on frequency response of cylindrical panels using Galerkin time domain approach

The forced vibration analysis of bimodulus material laminated structures is a challenging problem due to non-smooth nonlinear nature of governing equations. The most commonly used direct time integration schemes show numerical instability and do not predict steady state response except for limited number of cases without considering in-plane inertia. This is due to the sudden change of restoring force from positive/negative half cycle to negative/positive half cycle exciting higher modes/harmonics at every instant of a cycle change leading to numerical instability in the time marching scheme. In the present work, Galerkin time domain approach is successfully used for the forced vibration analysis of bimodular cylindrical panels. The effect of bimodularity ratio on the frequency response of cylindrical panels for few typical geometrical and lamination parameters is studied for the first time. It is found that the positive half cycle amplitude is greater than the negative half cycle amplitude for E _2t /E _2c < 1 and is smaller for E _2t /E _2c > 1. Further, the percentage difference of positive and negative half cycle amplitudes decreases with the increase in E _2t /E _2c . The stresses under dynamic loading are different for positive and negative half of a vibration cycle.     

Explanation of Non-linear In-Plane Resistivity and Hall Coefficient in the Normal State of Cuprates: Polaronic Approach

We present a theoretical study of the in-plane resistivity ρ _{a b} (T) and Hall coefficient R _H (T) within the polaronic model and precursor pairing scenario by considering a two-component charge carrier picture in the normal state of high-temperature superconducting cuprates (HTSC). Here, we use a Boltzmann-equation approach and extended BCS-like model to compute ρ _{a b} (T) and R _H (T) in the τ-approximation. The opening of the pseudogap (PG) in the normal state of the cuprates should affect their transport properties. We have found that the transition to the PG regime and the effective conductivity of charge carriers in the normal state are responsible for the pronounced non-linear temperature dependence of ρ _{a b} and R _H . With the two-component model analysis, we conclude that the opening of the BCS-like PG, while the non-linear temperature dependence of ρ _{a b} and R _H could be understood as a consequence of pairing fluctuations in the PG state of cuprate superconductors. The calculated results for ρ _{a b} (T) and R _H (T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also show that the energy scales of the binding energies of charge carriers are identified by PG crossover temperature on the cuprate phase diagram.     

On VLSI interconnect optimization and linear ordering problem

Some well-known VLSI interconnect optimizations problems for timing, power and cross-coupling noise immunity share a property that enables mapping them into a specialized Linear Ordering Problem (LOP). Unlike the general LOP problem which is NP-complete, this paper proves that the specialized one has a closed-form solution. Let f(x,y):?²→? be symmetric, non-negative, defined for x≥0 and y≥0, and let f(x,y) be twice differentiable, satisfying ? ² f(x,y)/?x?y<0. Let π be a permutation of {1,…,n}. The specialized LOP comprises n objects, each associated with a real value parameter r _i , 1≤i≤n, and a cost f(r _i ,r _j ) associated to any two objects if |π(i)?π(j)|=1,1≤i,j≤n, and f(r _i ,r _j )=0 otherwise. We show that the permutation π which minimizes \(\sum_{i= 1}^{n - 1} f( r_{\pi^{ - 1}( i )},r_{\pi^{ - 1}( i + 1 )} )\), called “symmetric hill”, is determined upfront by the relations between the parameter values r _i .     

Magnetic structure of a spherical cluster of monodomain particles

A numerical model is proposed for simulating the magnetic properties of a system (N-cluster) comprising a finite number N of monodomain particles uniformly distributed over a spherical surface. The calculation algorithm is based on the Monte Carlo method. In the absence of an external magnetic field, the magnetic moment of any spherical N-cluster vanishes due to the formation of vortex structures, with a measure of vorticity offered by the toroid moment Q. The results of model calculations show that the value of Q in N-clusters with 4 < N < 20 amounts to about 80% of the maximum and is virtually independent of N, while exhibiting weak even-odd oscillations.     

The dependence of the temperature of crystal-liquid phase transition on the size and shape of simple nanocrystal

The dependence of melting temperature T _m on the size and shape of an n -dimensional nanocrystal of elementary single-component substance is studied. The nanocrystal has the form of an n-dimensional parallelepiped with a square base. The ratio of the length of side rib to the length of base rib (which is equal to f) defines the form of the system. It is demonstrated that, if the surface pressure is ignored, the value of T _m decreases with isomorphic (f = const) decrease in the size of nanocrystal. In so doing, the more the value of form parameter f deviates from unity, the more appreciable the size dependence of T _m will be. However, if the surface pressure (“Laplace pressure”) is taken into account in the case of decrease in size, the value of T _m may vary significantly. In so doing, if the surface pressure compresses the nanocrystal, this leads to an increase in T _m when its size decreases. In the case of stretching of nanocrystal by surface pressure, the drop of T _m with isomorphic decrease in size increases. It is demonstrated that the surface pressure may both attenuate (at low values of T _m ) and intensify (at high values of T _m ) the dimensional oscillation of melting temperature. This variation of oscillation of dimensional dependence will be most pronounced for substances with high values of Grueneisen parameter. The variation of melting temperature with decreasing crystal dimension n is studied. It is demonstrated that, in the case of isomorphic decrease in the size of nanocrystal, the coefficient of thermal expansion at melting temperature increases and reaches a maximum, and the specific energies of activation processes and the surface energy decrease and reach a minimum.     

Theoretical Studies on Magnetic Structures,Hysteresis Loops and Size Effects of a Pair of Frustrated Double-Walled Nanotubes

We propose a theoretical quantum model and derive a set of analytic formulas to study the physical properties of a pair of double-walled magnetic nanotubes. The Heisenberg exchange parameters between the two walls of the nanotubes are assumed to differ only in sign. Thus, in the absence of external magnetic field, our calculated macroscopic properties of this pair of nanotubes are almost precisely identical, exhibiting fascinating duality of the nanosystems and demonstrating the correctness of our theoretical model. The two spin systems are all frustrated, so that sudden changes in the macroscopic properties are observed around T _M2 that is well below the transition temperature T _M1. However, only the inner shell consisting of smaller A-type spins has been obviously affected. In the temperature range T _M2 < T < T _M1, this shell becomes semi-antiferromagnetic and its magnetization is considerably suppressed, whereas as temperature falls below T _M2 the shell gradually restores its ferromagnetic nature. The longitudinal hysteresis behavior of such a double-waled nanotube is ferromagnetic-like below T _M2, but antiferromagnetic-like in the temperature interval T _M2 < T < T _M1. Moreover, we find that the diameter of the nanotube has seemly no effects on its physical properties, whereas its length does affects the two temperatures slightly, and also its spin configuration at very low temperatures if the tube is sufficiently long. More importantly, the theoretical results presented in this paper can be precisely reproduced with the quantum computational method we develop in recent years, justifying the validity of the numerical approach once again.     

Influence of graded interfaces on the exciton energy of type-I and type-II Si/Si<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript> Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> quantum wires

The exciton properties of Si/Si _1-x Ge _x cylindrical quantum wires (QWRs) are calculated using the variational method and taking into account the existence of an interface layer between the materials. We consider two possibilities for the conduction band lineup, type-I and type-II. Our numerical results show that an interfacial fluctuation of 15Å in a Si _0.85 Ge _0.15 (Si_0.70Ge_0.30) type-I (type-II) wire of 50Å wire radius leads to an exciton energy blue shift of the order of 10 (10) meV.     

Characteristics of Superconducting State in Vanadium: the Eliashberg Equations and Semi-analytical Formulas

The superconducting state in vanadium characterizes with the critical temperature (T _c ) equal to 5.3 K. The Coulomb pseudopotential, calculated with the help of the Eliashberg equations, possesses anomalously high value μ ^?(3Ω_max) = 0.259 or μ ^?(10Ω_max) = 0.368 (Ω_max denotes the maximum phonon frequency). Despite the relatively large electron-phonon coupling constant (λ = 0.91), the quantities such as the order parameter (Δ), the specific heat (C), and the thermodynamic critical field (H _c ) determine the values of the dimensionless ratios not deviating much from the predictions of the BCS theory: R _Δ = 2Δ(0)/k _B T _c = 3.68, R _C = ΔC(T _c ) /C ^N (T _c ) = 1.69, and \(R_{H}=T_{c}C^{N}\left (T_{c}\right )\slash {H^{2}_{c}}\left (0\right )=0.171\). This result is associated with the reduction of the strong-coupling and the retardation effects by the high value of the Coulomb pseudopotential. It has been shown that the results of the Eliashberg formalism can be relatively precisely reproduced with the help of the semi-analytical formulas, if the value of μ ^? is determined on the basis of the T _c -Allen-Dynes expression (μ A D? = 0.198). The attention should be paid to the fact that in the numerical and in the semi-analytical approach the comparable values of the thermodynamic parameters for the same μ ^? have been obtained only in the vicinity of the point μ ^? = 0.1.     

Error tolerance for the recognition of faulty strings in a regulated grammar using fuzzy sets

To overcome the limitations of context-free and context-sensitive grammars, regulated grammars have been proposed. In this paper, an algorithm is proposed for the recognition of faulty strings in regulated grammar. Furthermore, depending on the errors and certainty, it is decided whether the string belongs to the language or not based on string membership value. The time complexity of the proposed algorithm is O(|G _R ² |·|w|), where |G_R| represents the number of production rules and |w| is the length of the input string, w. The reader is provided with numerical examples by applying the algorithm to regularly controlled and matrix grammar. Finally, the proposed algorithm is applied in the Hindi language for the recognition of faulty strings in regulated grammar as a real-life application.