Abstract
The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the ...Dirac semimetal ZrTe
5
. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, spectroscopic, thermoelectric and charge transport measurements on such ZrTe
5
samples. The measured properties: magnetization, ultrasound propagation, scanning tunneling spectroscopy, and Raman spectroscopy, show no signatures of a Fermi surface instability, consistent with in-field single crystal X-ray diffraction. Instead, a direct comparison of the experimental data with linear response calculations based on an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the observed Hall response emerges from the interplay of the intrinsic properties of the ZrTe
5
electronic structure and its Dirac-type semi-metallic character.
•A reactor with optical ports and TGA suited for single particle gasification was developed.•Inhomogeneous particles affect gasification kinetics.•The surface temperature of single particles was ...measured during gasification.•A relationship between particle surface temperature and reactivity was discovered.•Quantitative gas analysis with in-situ Raman spectroscopy was performed.
The newly developed HITECOM reactor provides the possibility of in-situ analysis of single particle reactions. It combines the capabilities of a magnetic suspension thermobalance with state of the art optical analysis. The surface temperature and carbon conversion of single particles are measured under well-defined flow conditions. The generated data enables the detailed validation of CFD single particle models. For this reactor, a special temperature resistant particle holder had to be constructed, which is able to fix various particles in direct flow during gasification. An in-situ Raman spectroscopy setup was established for quantitative gas analysis at pressures between 1 and 20bar and temperatures up to 965°C. Here, a pulsed Nd:YAG laser at 355nm was used as excitation source. The Rayleigh/Raman scattering was measured perpendicular to the flow direction with a spectrograph and ICCD camera. From the recorded spectra the gas concentrations were calculated. Generally, the calculated concentrations of CO, CO2 and N2 match the reference values from the gas chromatograph.
In the present study, single coal particles of one Central German lignite and one hard coal were analyzed and monitored during gasification. The particle diameter ranged from 1 to 3mm. Gasification experiments with CO2 were carried out under isothermal conditions at 1bar total pressure and temperatures of 800–1200°C.
The experimental data were adjusted with models by data fitting. It was found that the Random Pore Model (RPM) matches the carbon conversion of the hard coal sample and the Shrinking Core Model (SCM) matches the carbon conversion of the lignite sample.
Further analysis revealed that inhomogeneous particles affect gasification kinetics. The differences in reactivity between several particles from the hard coal are significantly larger than for the lignite particles, which is in accordance to the results of the respective ultimate and proximate analyses.
Additionally, it was discovered that the difference between gas and particle temperature is negligible for low reactive feedstocks within the investigated temperature range (ΔT⩽5K at 1070°C, hard coal), whereas there was a significant difference for reactive particles (ΔT⩽40K at 1070°C, lignite).
The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the Dirac ...semimetal ZrTe
. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, spectroscopic, thermoelectric and charge transport measurements on such ZrTe
samples. The measured properties: magnetization, ultrasound propagation, scanning tunneling spectroscopy, and Raman spectroscopy, show no signatures of a Fermi surface instability, consistent with in-field single crystal X-ray diffraction. Instead, a direct comparison of the experimental data with linear response calculations based on an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the observed Hall response emerges from the interplay of the intrinsic properties of the ZrTe
electronic structure and its Dirac-type semi-metallic character.
Conditioning and monitoring of grinding wheels Wegener, K.; Hoffmeister, H.-W.; Karpuschewski, B. ...
CIRP annals,
2011, 2011-00-00, 20110101, Letnik:
60, Številka:
2
Journal Article, Conference Proceeding
Recenzirano
The preparation of grinding tools is the most important enabling factor in the grinding process. It influences the material removal rate, the grinding forces, the surface quality as well as the ...material properties of the subsurface zone, and is the key issue for subsequent wear of grinding tools. The evolving and conventional conditioning technologies are reviewed based on technical and commercial aspects. Terms in the field of conditioning are defined. Strong emphasis today is put on the description and monitoring of the abrasive layer. For optimization of the dressing process, prediction of the grinding wheel topography and the ground surface are emerging scientific topics.
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