A local spin study for magnetic model complex HHeH

Chemists, physicists and material scientists havegiven great attention to the theoretical studies of mag-netic systems owing to their significance in the fun-damental research areas as well as their potential ap-plications in the field of high technologie…     

Computer comparisons of variables in capillary gas chromatography

A series of computer-constructed van Deemter curves that permits evaluation of a number of variables in capillary gas chromatography is presented. The graphs permit the comparison of inter-related parameters, including the choice of carrier gas (hydrogen vs helium vs nitrogen), column length (10-100 m), column diameter (0.20, 0.25, 0.32, 0.4 mm), solute partition ratios (0-10), and liquid phase film thickness (0.1, 0.25, 0.5, 1.0 μm). The curves are evaluated, both in terms of the relative magnitude of the optimum average linear carrier gas velocity, and in terms of the significance of the sharpness of the curve.     

Ab initio and DFT studies on van der Waals trimers: the OCS.(CO2)2 complexes

Ab initio calculations [MP2, MP4SDTQ, and QCISD(T)] using different basis sets [6-31G(d,p), cc-pVXZ (X = D, T, Q), and aug-cc-pVDZ] and density functional theory [B3LYP/6-31G(d,p)] calculations were carried out to study the OCS.(CO2)2 van der Waals trimer. The DFT has proved inappropriate to the study of this type of systems where the dispersion forces are expected to play a relevant role. Three minima isomers (two noncyclic and one cyclic) were located and characterized. The most stable isomer exhibits a noncyclic barrel-like structure whose bond lengths, angles, rotational constants, and dipole moment agree quite well with the corresponding experimental values of the only structure observed in recent microwave spectroscopic studies. The energetic proximity of the three isomers, with stabilization energies of 1442, 1371, and 1307 cm-1, respectively, at the CBS-MP2/cc-pVXZ (X = D, T, Q) level, strongly suggests that the two unobserved structures should also be detected as in the case of the (CO2)3 trimer where both noncyclic and cyclic isomers have been reported to exist. The many-body symmetry-adapted perturbation theory is employed to analyze the nature of the interactions leading to the formation of the different structures. The three-body contributions are small and stabilizing for the two most stable structures and almost negligible for the cyclic isomer.     

Thermodynamically stable dispersions induced by depletion interactions

When small particles are added to a colloidal dispersion of large particles, a depletion interaction between large particles occurs because the small ones are depleted from the gaps between the former particles. In the present paper, a cell model is employed to examine the behavior of a dispersion of large particles immersed in an electrolyte solution containing small particles. In this model, each cell consists of one large particle in its center and an associated atmosphere. Double-layer, van der Waals, and depletion interactions, as well as entropic effects, have been taken into account. When the change of the free energy with respect to that of the electrolyte solution is negative (and this happens in most cases), the dispersions of large particles are stable from a thermodynamic point of view. With increasing volume fraction of the small particles, the free energy change becomes more negative. The formation of gels observed experimentally in concentrated emulsions is explained through the formation of a thermodynamically stable dispersion.     

A geometric programming approach to the Van der Waerden conjecture on doubly stochastic matrices

LetD _p be the set of all doubly stochastic square matrices of orderp i.e. the set of allp × p matrices with non-negative entries with row and column sums equal to unity. The permanent of ap × p matrixA = (a _ij ) is defined byP(A) = _Sp II _i=1 ^p a _i(i) whereS _p is the symmetric group of orderp. Van der Waerden conjectured thatP(A) p !/p ^p for all A AD _p with equality occurring if and only ifA = J _p , whereJ _p is the matrix all of whose entries are equal to 1/p.The validity of this conjecture has been shown for a few values ofp and for generalp under certain assumptions. In this paper the problem of finding the minimum of the permanent of a doubly stochastic matrix has been formulated as a reversed geometric program with a single constraint and an equivalent dual program is given. A related problem of reversed homogeneous posynomial programming problem is also studied.     

Multi-layer graphene membrane based memory cell

The scheme and operational principles of the nanoelectromechanical memory cell based on the bending of a multi-layer graphene membrane by the electrostatic force are proposed. An analysis of the memory cell total energy as a function of the memory cell sizes is used to determine the sizes corresponding to a bistable memory cell with the conducting ON and non-conducting OFF states and to calculate the switching voltage between the OFF and ON states. It is shown that a potential barrier between the OFF and ON states is huge for practically all sizes of a bistable memory cell which excludes spontaneous switching and allows the proposed memory cell to be used for long-term archival storage.     

Modeling of four-electrode system to determine the resistance of antistatic coatings – Optimizing the size of the measurement area

In the paper, mathematical models for determination of resistivity of thin antistatic coatings are presented. The models use the four-points method and the method of images. The relations between the sample size and the distance between the electrode set and the edge of the sample were analyzed. It was found that the distance between the electrode set and the object edge should be at least 5 times greater than the electrode spacing to allow us using much simpler formulas for infinite flat object with measurement uncertainty below 5%. The correctness of theoretical considerations was verified experimentally.     

Strong Resistivity Anomaly in a New Low-Dimensional Conductor HfTe5

Temperature dependence of the resistivity, Hall coefficient and magnetic susceptibility of HfTe₅ with 1.5 wt. %, Zr is reported. Anisotropic large diamagnetism is reported and has the peak in the vicinity of 76 K. Temperature dependence of Hall coefficient under 117 kOe elearly shows the destruction of Fermi surface at about 90 K. HfTe₅ can be considered to be a semimetal and observed resistivity anomaly may be accompanied by the CDW formation along c-axis. We also discuss the mixed crystal effect with ZrTe₅ and present the data of quantum oscillation observed at low temperature.     

Nonlinear free vibrations of curved double walled carbon nanotubes using differential quadrature method

Nonlinear free vibration analysis of curved double-walled carbon nanotubes (DWNTs) embedded in an elastic medium is studied in this study. Nonlinearities considered are due to large deflection of carbon nanotubes (geometric nonlinearity) and nonlinear interlayer van der Waals forces between inner and outer tubes. The differential quadrature method (DQM) is utilized to discretize the partial differential equations of motion in spatial domain, which resulted in a nonlinear set of algebraic equations of motion. The effect of nonlinearities, different end conditions, initial curvature, and stiffness of the surrounding elastic medium, and vibrational modes on the nonlinear free vibration of DWCNTs is studied. Results show that it is possible to detect different vibration modes occurring at a single vibration frequency when CNTs vibrate in the out-of-phase vibration mode. Moreover, it is observed that boundary conditions have significant effect on the nonlinear natural frequencies of the DWCNT including multiple solutions.