Coefficients Of Opposite Sign Research Articles

Stabilized convection in a ternary mixture with two Soret coefficients of opposite sign

We performed ground-based experiments on the sample polystyrene–toluene–cyclohexane in order to complement the experimental activities in microgravity conditions related to the ESA projects DCMIX4 and Giant Fluctuations. After applying a stabilizing thermal gradient by heating from above a layer of the fluid mixture, we studied over many hours the density variations in the bidimensional horizontal field by means of a Shadowgraph optical setup. The resulting images evidence the appearance of convective instability after a diffusive time associated with the binary molecular solvent consisting of toluene and cyclohexane, confirming the negative sign of the Soret coefficient of this mixture. After a larger diffusive time related to mass diffusion of the polystyrene in the binary solvent, convection was suppressed by the increasing stabilizing density gradient originated by the Soret-induced concentration gradient of the polymer. This is compatible with a positive sign of the Soret coefficient of the polymer in the binary solvent.Graphic

Does Gross or Net Debt Matter More for Emerging Market Spreads?

AbstractDoes gross or net debt matter for long‐term sovereign spreads in emerging markets? The topic is important for understanding the borrowing cost implications of public asset–liability management decisions (e.g., using assets to lower debt). We investigate this question using data on emerging market economies (EMEs) over the period 1998–2014. We find that both gross debt and assets have a significant impact on long‐term sovereign bond spreads in emerging markets, with effects roughly offsetting each other (coefficients of opposite sign and similar magnitude). Hence, net debt seems more appropriate than gross debt when evaluating the impact of indebtedness on spreads. The empirical results suggest that an increase in net debt by 10 percentage points of GDP implies an increase in the spread by 100–120 basis points, and the effect is larger during periods of domestic distress. The key results from this empirical study are quite robust to alternative specifications and subgroups of EMEs.

Hybrid metaheuristic for generalised assignment

This paper investigates the classical generalised assignment problem (GAP), a challenging combinatorial optimisation problem that arises in numerous applications and that has attracted a great deal of research. For solving it we propose a hybrid metaheuristic combining guided search (GS), iterated local search (ILS), and very large-scale neighbourhood search (VLSN). The hybrid method is iterative. It starts with a random assignment, and in every iteration it acts in the following way: 1) The best current assignment is perturbed. 2) An exponential size neighbourhood of the perturbed assignment is constructed. It is the feasible solution set of a special GAP where only two fixed machines can execute a job. The neighbourhood construction is guided by a technique penalising poor machine/job selections. 3) The exponential neighbourhood is searched for improvement. Exploring the neighbourhood amounts to solving a monotone binary program (BP) – a monotone BP is one with two non-zero coefficients of opposite sign per column. We prove that the proposed metaheuristic runs in polynomial-time when applied to a variation of GAP. Good computational results in terms of solution quality, as well as of computation speed, are obtained with two new best values on hard instances.

Does Gross or Net Debt Matter More for Emerging Market Spreads?

Does gross or net debt matter for long-term sovereign spreads in emerging markets? The topic is important for undestanding the borrowing cost implications of public assetliability management decisions (e.g. using assets to lower debt). We investigate this question using data on emerging market economies (EMEs) over the period 1998–2014. We find that both gross debt and assets have a significant impact on long-term sovereign bond spreads in emerging markets, with effects roughly offsetting each other (coefficients of opposite sign and similar magnitude). Hence, net debt seems more appropriate than gross debt when evaluating the impact of indebtedness on spreads. The empirical results suggest that an increase in net debt by 10 percentage points of GDP implies an increase in the spread by 100–120 basis points, and the effect is larger during periods of domestic distress. The key results from this empirical study are quite robust to alternative specifications and subgroups of EMEs.

Does Gross or Net Debt Matter More for Emerging Market Spreads?

Does gross or net debt matter for long-term sovereign spreads in emerging markets? The topic is important for undestanding the borrowing cost implications of public assetliability management decisions (e.g. using assets to lower debt). We investigate this question using data on emerging market economies (EMEs) over the period 1998–2014. We find that both gross debt and assets have a significant impact on long-term sovereign bond spreads in emerging markets, with effects roughly offsetting each other (coefficients of opposite sign and similar magnitude). Hence, net debt seems more appropriate than gross debt when evaluating the impact of indebtedness on spreads. The empirical results suggest that an increase in net debt by 10 percentage points of GDP implies an increase in the spread by 100–120 basis points, and the effect is larger during periods of domestic distress. The key results from this empirical study are quite robust to alternative specifications and subgroups of EMEs.

Stationary states in a system of two linearly coupled 2D NLS equations with nonlinearities of opposite signs

We study, analytically and numerically, the stationary states in the system of two linearly coupled nonlinear Schrodinger equations in two spatial dimensions, with the nonlinear interaction coefficients of opposite signs. This system is the two-dimensional analogue of the coupled-mode equations for a condensate in the double-well trap (2004 Phys. Rev. A 69 033609). In contrast to the one-dimensional case, where there are stable bright solitons, in two spatial dimensions the Townes-type solitons of the system are unstable. With the use of a parabolic potential, the ground state of the system can be stabilized. It corresponds to strongly coupled condensates and is stable with respect to collapse. This is in sharp contrast to the one-dimensional case, where the ground state corresponds to weakly coupled condensates and is unstable. Moreover, the total number of atoms of the stable ground state can be much higher than the collapse threshold for a single two-dimensional condensate with a negative s-wave scattering length.

Whispering-gallery mode technique applied to the measurement of the dielectric properties of Langasite between 4 K and 300 K

We report new measurements of dielectric properties of Lanthanum gallium silicate (Langasite or LGS) conducted with the whispering-gallery mode technique at microwave frequencies and between 4.2 K and 300 K. The real part of the permittivity tensor of LGS presents two components having temperature coefficients of opposite sign. This unique property enables the design of a temperature compensated resonator that may be useful in building stable microwave oscillators or filters. We report also the first measurements of the two independent components of the imaginary part of the permittivity tensor. It appears LGS is a relatively high-loss dielectric material compared with sapphire or quartz.

The molecular dynamics study of shear thinning of the Lennard-Jones fluid

An extensive series of non-equilibrium molecular dynamics, NEMD, simulations have been performed of sheat thinning of the Lennard-Jones fluid. Calculations on over 100 state points have been used to characterise and parameterise the thermodynamic and dynamical behaviour of the fluid at high densities in the region in which non-newtonian phenomena become pronounced. This is typically at a shear rate of order unity in Lennard-Jones reduced units. The formalism derived by Hanley and Evans was used to characterise the shear rate dependence of the internal energy, pressure and viscosity. It was also shown to apply equally well to the shear rigidity modulus and self-diffusion coefficient. For the thermodynamic properties, they increase in proportion to the shear rate to the power of 1.5, whereas for the viscosity and self-diffusion coefficient the power is 0.5 but with coefficients of opposite sign. This is consistent with a demonstrated applicability of the Stokes-Einstein relationship in the shear thinning regime. The nature of the shear thinning is presented in terms of structure, through projected molecular coordinates on the MD cell sides, and dynamics via the force autocorrelation functions. A number of alternative empirical correlations involving the shear stress and other state variables are also given.

Control of Temperature Variation in the Frequency of Tuning Forks (with demonstrations)

The increasing use of tuning forks not only as frequency standards but as controlling devices for equipment requiring perfect synchronization calls either for very accurate temperature control with the ordinary steel fork, or for the development of forks in which the variation of frequency with temperature is negligibly small. Two methods have been employed to achieve this end—either the development of metal alloys having very small frequency-temperature coefficients, or the fabrication of compensated forks from two materials having coefficients of opposite sign. While alloy steels, such as Invar and Elinvar, can be produced having coefficients of the order of one-twentieth that of ordinary steel, yet very considerable variations in coefficients are found in individual samples of these alloys even when cut from the same piece of stock. The combination of two alloys having positive and negative temperature coefficients has proven a more practical means of producing forks of uniform qualities and with frequencies independent of temperature. Demonstrations of the thermal properties of forks of this type will be made.