Effect of testing conditions on the laser flash thermal diffusivity measurements of ceramics

Several experimental techniques either under steady state or transient heat transfer conditions, have been developed to evaluate thermal conductivity and thermal diffusivity of materials. However, testing difficulties resulting from specimen size, extended testing time and heat losses, have somewhat impaired the applicability of many of them. In this respect, the use of the laser flash technique for thermal diffusivity measurements, is a very convenient alternative, considering its basic modeling equation is independent of the temperature gradient as well as the heat flow, and in addition the heat losses can be analytically treated. Another important advantage of the technique is its rapid experimental execution. In this work, it is presented as an investigation concerning how the testing conditions such as specimen coating, laser power and pulse duration, base line adoption, heat losses correction methods, and specimen thickness, may affect the thermal diffusivity measurements of some ceramic materials using the laser flash technique.     

Static solitary wave solution in 1D quantum quenched systems

We use Morita's formulation to describe quenched systems. Through the Holstein-Primakoff (HP) representation we quantize the system in 1D and it gives coupled non-linear Schrödinger equations. We show that a static solitary wave is a solution of these equations.     

The diffusivity of hydrogen in copper at low temperatures

An electrochemical method has been used to measure the diffusivity of hydrogen in copper in the temperature range 299–322.5 K. Both uncoated and Pd-coated copper foils were used. The measurements show, in combination with other data, that there are no deviations from classical Arrhenius diffusion behavior in the entire temperature range from 1200 down to 300 K.     

Thermodynamics of the quantum spin-S XXZ chain

The thermodynamics of the spin-S anisotropic quantum XXZ chain with arbitrary value of S and unitary norm, in the high-temperature regime, is reported. The single-ion anisotropy term and the interaction with an external magnetic field in the z-direction are taken into account. We obtain, for arbitrary value of S, the β-expansion of the Helmholtz free energy of the model up to order β⁶ and show that it actually depends on . Its classical limit is obtained by simply taking S→∞. At h=0 and D=0, our high temperature expansion of the classical model coincides with Joyce’s exact solution [11]. We study, in the high temperature region, some thermodynamic quantities such as the specific heat and the magnetic susceptibility as functions of spin and verify for which values of S those thermodynamic functions behave classically. Their finite temperature behavior is inferred from interpolation of their high- and low-temperature behavior, and shown to be in good agreement with numerical results. The finite temperature behavior is shown for higher values of spin.     

Leading non-cancelling infrared divergences in perturbative QCD

In perturbative QCD, for the inclusive cross section for the scattering of two coloured particles, we identify graphs which contribute to the general leading order α_s(α_s lnλ)ⁿ of uncancelled IR divergences, and we sum these contributions (λ is the IR cut-off). The work is done in the Coulomb gauge; an appendix discusses the Feynman gauge.     

Dispersion relations and sum rules for natural optical activity

Dispersion relations and sum rules are derived for the complex rotatory power of an arbitrary linear (nonmagnetic) isotropic medium showing natural optical activity. Both previously known dispersion relations and sum rules, as well as new ones, are obtained. It is shown that the Rosenfeld-Condon dispersion formula is inconsistent with the expected asymptotic behavior at high frequencies. A new dispersion formula based on quantum electrodynamics removes this inconsistency; however, it still requires modification in the lowfrequency limit.