Piecewise straightening and Lipschitz simplicial volume

We study the Lipschitz simplicial volume, which is a metric version of the simplicial volume. We introduce the piecewise straightening procedure for singular chains, which allows us to generalize the proportionality principle and the product inequality to the case of complete Riemannian manifolds of finite volume with sectional curvature bounded from above. We obtain also yet another proof of the proportionality principle in the compact case by a direct approximation of the smearing map.Comment: v2: small changes in the introduction, references and section 2.3 (one minor mistake corrected) v3: corrected sections 2.1, 2.2 v4: new section 2.1 about 'exponential' neighbourhoods, more details about the procedure itself in section 2.3, barycentric C^1 homology corrected to piecewise C^1 in section

Effect of lattice disorder on the thermal conductivity of ZnBeSe, ZnMgSe and ZnBeMgSe crystals

Zn1-x-yBexMgySe mixed crystals investigated in this work were grown from the melt by the high pressure high temperature modified Bridgman method in the range of composition 0 < x,y < 0.33. Photopyroelectric (PPE) calorimetry in the back (BPPE) and front (FPPE) configuration was applied for thermal investigation of solid samples. The thermal diffusivity and effusivity of investigated crystals were derived from the experimental data. Since dynamic thermal parameters are connected with each other, thermal conductivity of the specimens was calculated from theoretical dependencies between them. The influence of the beryllium (x) and magnesium (y) content on thermal properties of these crystals have been presented and discussed. Order-disorder effects observed for these materials previously have been also taken into account. Finally, thermal diagrams, i.e. thermal conductivity versus composition were presented and discussed applying model given by Sadao Adachi

Photoluminescence of ZnBeMnSe solid solutions

In this paper optical properties of Zn1-x-yBexMnySe mixed semiconductors were studied as a function of both, temperature and excitation power. The crystals under investigation were grown by the high-pressure, high-temperature vertical Bridgman technique within the range of the composition 0.05 ≤ x,y ≤ 0.2. Photoluminescence spectra for the lowest content of Mn and Be exhibit character typical for II-VI semiconductors together with intensive yellow-orange manganese emission. Evolution of the excitonic emission as the function of temperature allowed determining the energy gap of the investigated semiconductors. Absorbance and photoluminescence excitation spectra confirmed crystal field splitting of excited atomic terms of manganese ions into the states, denoted according to the crystal field theory in the case of tetrahedral symmetry. Temperature and laser power dependences of luminescence showed anomalous behavior of the manganese emission. It turned out that the position of the Mn2+ related luminescence band does not change monotonically with the variation of the temperature or the excitation power. Finally, switching of the manganese emission has been observed. By increasing laser power of exciting radiation, the Mn-related emission could be quenched by almost two orders in magnitude. This effect was especially strong at low temperature and it was fully reversible

Lock-in thermography versus PPE calorimetry for accurate measurements of thermophysical properties of solid samples: a comparative study

The aim of this paper is to compare the measurement accuracy of photopyroelectric calorimetry in back detection configuration (BPPE) and infrared lock-in thermography (LT) for thermal diffusivity measurement of solid samples. For this purpose, the following materials with well-known thermal properties have been selected: glassy carbon (type G), LiTaO3 crystal and binary II-VI semiconductors (based on CdSe and CdTe). The advantages and drawbacks of the two techniques have been analyzed both theoretically and experimentally

Thermal characterization of ZnBeMnSe mixed compounds by means of photopyroelectric and lock-in thermography methods

In this work a thermal characterization (measurement of dynamic thermal parameters) of quaternary Zn1-x-yBexMnySe mixed crystals was carried out. The crystals under investigation were grown from the melt by the modified high pressure Bridgman method with different Be and Mn content. The effect of Be and Mn content on thermal properties of Zn1-x-yBexMnySe compounds was analyzed, by using the photopyroelectric (PPE) method in the back configuration (BPPE) for thermal diffusivity measurements, and the PPE technique in the front configuration (FPPE) for thermal effusivity investigations. Infrared lock-in thermography (IRT) was used in order to validate the BPPE results. The measured thermal effusivity and diffusivity allowed the calculation of thermal conductivity of the investigated materials

On the optimization of experimental parameters in photopyroelectric investigation of thermal diffusivity of solids

In this paper, the possibility of optimizing the experimental conditions for a correct photopyroelectric evaluation of the thermal diffusivity of solid samples is studied. For this purpose, a glassy carbon sample, with known thermal properties, was selected as test material and two types of techniques were applied in order to get the value of its thermal diffusivity: (i) the photopyroelectric calorimetry in back detection configuration and (ii) the infrared thermography. Assuming that the values of thermal diffusivity obtained by thermography are correct (a non-contact technique), we studied how to eliminate the underestimation (due to the presence of the coupling fluid) of the results in the back photopyroelectric calorimetry investigations. Experiments with different types of coupling fluids and numerical simulations were performed in order to evaluate the influence of the coupling fluid on the value of the thermal diffusivity. The conclusion is that a proper choice of the type of coupling fluid and some improvements performed in the experimental design of the photopyroelectric calorimetry detection cell (with the purpose of reducing the coupling fluid’s thickness), can eliminate the difference between the results obtained with the two photothermal (contact and non-contact) techniques

Thermal characterization of II–VI binary crystals by photopyroelectric calorimetry and infrared lock-in thermography

In this paper, a complete thermal characterization (measurement of all static and dynamic thermal parameters) of some selected II-VI binary crystals was carried out. The semiconductors under investigation were grown from the melt by high-pressure/high-temperature modified Bridgman method. The contact photopyroelectric (PPE) method in back configuration (BPPE) and non-contact infrared lock-in thermography technique were used in order to get the thermal diffusivity of the investigated crystals. The thermal effusivity of the samples was obtained by using the PPE technique in the front configuration (FPPE), together with the thermal wave resonator cavity (TWRC) method. Knowing the values of the thermal effusivity and thermal diffusivity, the remaining two thermal parameters, i.e., thermal conductivity and specific heat were calculated

Surface investigations of ZnBeMnSe mixed crystals by means of the piezoelectric spectroscopy and the AFM technique

Piezoelectric photoacoustic spectroscopy with a piezoelectric detection has been used for measurements of the amplitude and phase spectra of Zn1-x-yBexMnySe mixed semiconductors. The investigated crystals were grown from the melt by the modified high pressure Bridgman method under the argon overpressure. The preliminary study of the sample’s surface of the investigated crystals was carried out using the AFM technique. The influence of a different surface treatment on the amplitude and phase piezoelectric spectra as well as on AFM images is presented and analyzed. The correlations between these two techniques have been found and are discussed. Piezoelectric (PZE) spectra were analyzed using an extended and modified Jackson-Amer theory

Characterization of thermal properties of Cd1-x-yZnxMgySe mixed crystals by means of photopyroelectric and infrared imaging techniques

In this work a complete thermal characterization of Cd1-x-yZnxMgxSe mixed crystals was carried out. Bulk semiconductors under investigation were grown from the melt by a high pressure modified Bridgman method for different x and y content. The photopyroelectric method in the back configuration (BPPE) and the infrared (IR) lock-in thermography have been applied to measure values of the thermal diffusivity. Thermal effusivity of the samples was obtained with the PPE technique in the front configuration (FPPE), coupled with a thickness (TWRC-thermal wave resonator cavity) scanning procedure. Measured thermal effusivity together with the thermal diffusivity allowed calculating the thermal conductivity of the investigated materials. For the calculation of the specific heat the densities of the samples were estimated from their weight and geometry. The effect of Mg/Zn content ratio on thermal properties of this quaternary CdZnMgSe compounds was analyzed and discussed