Geophysical measurements of perennial snow patches in Pirin Mountain, Bulgaria

Perennial snow patches are considered as indicators of permafrost occurence. There are no large glaciers on the territory of Bulgaria but small patches of snow and firn have been observed in the high mountains in the end of the summer. Perennial snow patches are considered as indicators of permafrost occurrence. In this paper we present results from geophysical investigations of Snezhnika microglacier situated in the Golyam Kazan cirque, Pirin Mountain, Bulgaria. Ground penetrating radar (GPR) and 2D Electro Resistivity Tomography (ERT) were used to estimate the thickness of the perennial snow patch as well as its subsurface structure. Measurements started in 2018 and continued over the next three years in order to evaluate changes in the snow patches' size and thickness. The mean thickness of Snezhnika is about 4–6 m, reaching up to 8 m in some areas. ERT measurements of the deeper parts of the microglacier beds show high electrical resistivities reaching over 60000 Ωm at a depth of 4–10 m. An anomaly at this depth is likewise distinguishable on the GPR profiles. These anomalies are interpreted as frozen zones and are consistently observed on the ERT and GPR profiles in the next two years of the study. These results imply for the first time the existence of permafrost in Pirin mountain and respectively in Bulgaria.

Remarkable Temperature Sensitivity of Partially Carbonized Carbon Fibers with Different Microstructures and Compositions

In order to explore effect of structure on the temperature sensitivity of partially carbonized carbon fibers, different heat treatment temperatures (700, 750 and 800 °C) and heat treatment times (3 and 9 min) were used to prepare fibers with different structures. The electrical resistivities were monitored whilst the room temperature was increased from 30 to 100 °C, which was used to characterize the temperature sensitivity. The fibers showed negative temperature coefficients in the temperature range. Infrared spectra, an element analysis, a scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction measurements were used to study the microstructure of the fibers. Through the analysis, the proportions of the graphite-like structure, graphitization degree and size of the graphite-like structure crystallite influenced the temperature sensitivity. The main electron transfer method used for the fibers was variable-range hopping. This indicated that the fibers had a potential application of preparing thermistors in polymer composites.

Studies of Thermodynamical and Electronic Transport Properties of Na–Sn Alloy

The concept of complex formation has been incorporated in the structure of the Faber–Ziman formula for the purpose of studying the composition dependence of the electrical resistivities of Zintl alloys, which possess the anomalous nature and exhibit a large deviation from the metallic behavior around a specific composition

Superconductivity in an extreme strange metal

Some of the highest-transition-temperature superconductors across various materials classes exhibit linear-in-temperature ‘strange metal’ or ‘Planckian’ electrical resistivities in their normal state. It is thus believed by many that this behavior holds the key to unlock the secrets of high-temperature superconductivity. However, these materials typically display complex phase diagrams governed by various competing energy scales, making an unambiguous identification of the physics at play difficult. Here we use electrical resistivity measurements into the micro-Kelvin regime to discover superconductivity condensing out of an extreme strange metal state—with linear resistivity over 3.5 orders of magnitude in temperature. We propose that the Cooper pairing is mediated by the modes associated with a recently evidenced dynamical charge localization–delocalization transition, a mechanism that may well be pertinent also in other strange metal superconductors.

FTIR, Optical, Electrical and Magnetic Properties of Sm3+ Doped Mg Nano Ferrites

Synthesized Sm, doped Mg nano ferrites with composition MgSmxFe2-xO4 (x = 0,0.025, 0.050, 0.075, 0.100) using the technique of citrate-gel auto-combustion method were analyzed through various experimental techniques. XRD analysis confirmed single-phase cubic spinel structure, while FTIR spectroscopic analysis displayed two absorption peaks that are characteristic of spinel nano ferrites. UV-visible spectral analysis was carried out to study the optical absorption behavior of the prepared ferrites. Two probe method was used to study the dc electrical resistivities of Sm doped Mg nanoferrites between 200 °C–500 °C. A plot between log (σT) vs. inverse temperature yields a curve that reveals prepared nano ferrites' semiconducting nature. A study of TEP (Thermo Electric Power) for prepared samples was carried out at a high temperature (573K). Seebeck coefficient and Curie Temperature of Sm doped Mg nanoferrites were observed. Measurements of magnetization were done by using VSM (Vibrating Sample Magnetometer).

Characteristic, Electrical and Optical Properties of Potassium Borate (KB5O8·4H2O) Hydrothermally Synthesised from Different Boron Sources

Potassium borate was hydrothermally synthesized from various of boron minerals (H3BO3, B2O3, Na2B4O7·5H2O and Na2B4O7·10H2O) at reaction conditions of 90 − 60°C and 120 − 15 min. The synthesised potassium borate was identified as “Santite (KB5O8·4H2O)” in X-Ray diffraction (XRD) analyses results. The specific band values between B and O atoms were characterized by Fourier transform infrared and Raman Spectroscopies. Multiangular particles were generally observed in the range of 234.94 nm − 3.41 µm. The use of different boron sources may affect the morphology. Higher reaction yields were determined in the use of boric acid (H3BO3). Optical absorption of potassium borate minerals was approximately 340 nm. AC and DC electrical properties of materials were determined by using current-voltage and capacitance voltage characteristics. Electrical resistivities of DC were found in the range of 4.17×108 – 4.07×1010 Ω.cm, whereas dielectric constants of AC were between 2×105 and 2×106.

Hydrogeophysical coupled inversion in coastal aquifers: the Argentona case

<p>Most, if not all, models of real aquifers go through a calibration process to adjust their hydraulic and solute transport parameters in order to bring the simulations outputs closer to the field observations. In coastal aquifers, the datasets are commonly composed of head time series, solute concentrations from water samples, and water and formation electrical conductivity, these last being of particular importance in coastal settings due to their relevance for seawater detection. Argentona is a well-instrumented field site of a coastal alluvial aquifer located 40 km NE of Barcelona, where a 2-year Cross-Hole Electrical Resistivity Tomography (CHERT) experiment was performed. CHERT provided high resolution electrical resistivity data in depth and allowed the visualization of dynamic aquifer processes. In the present work, we test the calibration of the Argentona SWI model using both the hydrological and the geophysical datasets. To do so, a density-dependent groundwater model was combined with CHERT forward modeling within a parameter calibration framework. In the process we pay attention to the CHERT capacity to recover aquifer salinities, to the coupling of the hydrological and geophysical simulations through petrophysics, to the use of the field specific relations and to the inverse problem parametrization, among other things. Pre-calibration analysis showed the sensitivity of the formation electrical resistivities to the porosities and to the petrophysical parameters, so the inverse problem solves for hydraulic transmissivities, porosities and petrophysical parameters. From the comparison of the preliminary results from the hydrological and the hydrogeophysical calibration, we observe that they point towards a better calibration of model porosities when the electrical resistivity is included in the inverse problem. The results will be compared to other parameter estimation methods, such as laboratory tests, the tidal method and heat tests, also performed at the Argentona site. We will conclude on the added value of the geophysical dataset in the calibration process, the possible improvements and drawbacks of the method.</p>

Evidence of Hole Self-Doping due to Excess Oxygen Addition in Polycrystal LaMnO3

We have presented the evidence of hole self-doping due to excess oxygen addition in polycrystal LaMnO3 (LMO). The polycrystal LMO samples were prepared by use of a solid-state reaction method. Powder mixtures with a molar ratio of 1:1 between La2O3 and Mn2O3 were pre-annealed at 1100oC for 18 hours in the atmospheres of oxygen gas, helium gas and vacuum. By this heat treatment, non-crystalline LMO samples were produced. After that, the non-crystalline LMO samples were grinded and were pressed into pellets at the pressure of 3t/cm3. The pellets were annealed at 1100oC and 1300oC for 18 hours in the same atmospheres as the pre-annealing. Through these processes, polycrystal LMO samples were finally produced. To investigate crystallographic structure of the LMO samples, X-ray diffraction (XRD) measurements were performed by use of Cu-K radiation. From the experimental results of XRD measurements, we have found that all LMO samples have perovskite structure and are polycrystals. In addition, to investigate surface structure of the LMO samples, scanning electron microscope (SEM) measurements were carried out. Electrical resistivities (ERs) of the polycrystal LMO samples were measured as a function of temperature (4K-300K). The ERs of polycrystal LMO samples produced in an oxygen gas atmosphere show lower values as compared with other LMO ones in He gas and vacuum atmospheres. Especially, the temperature dependence of the ER for a polycrystal LMO sample produced at the annealing temperature of 1100oC in an oxygen atmosphere shows a metallic behavior. Thus, we have considered that this LMO sample has the largest hole self-doping concentration in all LMO ones.

FTIR, Optical, Electrical and Magnetic properties of Sm+3 doped Mg Nano Ferrites by Citrate-Gel Auto combustion method

Sm, doped Mg nano ferrites with composition Mg Sm x Fe2 − x O4 (where X = 0.000, 0.025, 0.050, 0.075,0.1) were synthesized by citrate-gel auto-combustion method. The Samples were analyzed through various experimental techniques. The structural confirmation was done with the basic characterization techniques such as XRD (X-ray Powder Diffraction) and Fourier Transform Infrared (FTIR) spectroscopic analysis. To study the optical absorption behavior of the prepared ferrites, UV-visible spectral analysis was carried out. XRD analysis established the formation of single-phase cubic spinel structure of the materials. FTIR spectra has shown two absorption peaks that are characteristic of spinel nano ferrites. The dc electrical resistivities of the Sm doped Mg nano ferrites were studied by using two probe method at the temperature range of 200–500 °C. A plot of log (σT) vs inverse of temperature yields a curve which reveals a semiconducting nature of prepared nano ferrites. The Thermo Electric Power (TEP) studies of prepared samples carried out at high temperature (573K). The values of the Seebeck coefficient and curie temperature of Sm doped Mg nano ferrites were observed. The magnetization measurements were carried out by using Vibrating Sample Magnetometer (VSM).