Search results for "engineering.material"
showing 10 items of 2352 documents
Quantum-chemical simulations of free and bound hole polarons in corundum crystal
1997
Abstract The semi-empirical method of the so-called intermediate neglect of differential overlap (INDO) has been applied to the calculations of the hole small-radius polarons in corundum crystals. Results for optimized atomic and electronic structure using two different approaches (the molecular cluster and periodic, supercell model) are critically compared. It is shown that the main results are similar in both cases.
Production of π0 and η mesons in Cu+Au collisions at sNN=200GeV
2018
Production of π0 and η mesons has been measured at midrapidity in Cu+Au collisions at sNN=200GeV. Measurements were performed in π0(η)→γγ decay channel in the 1(2)-20GeV/c transverse momentum range. A strong suppression is observed for π0 and η meson production at high transverse momentum in central Cu+Au collisions relative to the p+p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au+Au with comparable nuclear overlap. The η/π0 ratio measured as a function of transverse momentum is consistent with mT-scaling parametrization down to pT=2GeV/c, its asymptotic value is constant and consistent with Au+Au and p+p and does not show…
A single photon source based on NV centers in diamond nanocrystals
2009
The development of reliable devices to generate single photons is crucial for applications in quantum cryptography, as well as for fundamental quantum optics experiments. Due to their extremely high photostability at room temperature, optically active defects in solids, the so called color centers, are among the most promising candidates. Single NV(nitrogen-vacancy) centers in diamond have been demonstrated to be able to generate single photons and have already shown advantages compared to attenuated laser pulses in a quantum cryptography experiment [1]. The nitrogen-vacancy center (NV center) in diamond consists of a substitutional nitrogen atom and an adjacent vacancy. This complex exhibi…
Thermodynamic, dynamic and transport properties of quantum spin liquid in herbertsmithite from experimental and theoretical point of view
2019
In our review we focus on the quantum spin liquid, defining the thermodynamic, transport and relaxation properties of geometrically frustrated magnets (insulators) represented by herbertsmithite $\rm ZnCu_{3}(OH)_6Cl_2$.
Universal Behavior of Quantum Spin Liquid and Optical Conductivity in the Insulator Herbertsmithite
2018
We analyze optical conductivity with the goal to demonstrate experimental manifestation of a new state of matter, the so-called fermion condensate. Fermion condensates are realized in quantum spin liquids, exhibiting typical behavior of heavy fermion metals. Measurements of the low-frequency optical conductivity collected on the geometrically frustrated insulator herbertsmithite provide important experimental evidence of the nature of its quantum spin liquid composed of spinons. To analyze recent measurements of the herbertsmithite optical conductivity at different temperatures, we employ a model of strongly correlated quantum spin liquid located near the fermion condensation phase transiti…
Toward a holistic environmental impact assessment of marble quarrying and processing: proposal of a novel easy-to-use IPAT-based method.
2016
Marble is a natural dimension stone that is widely used in building due to its resistance and esthetic qualities. Unfortunately, some concerns have arisen regarding its production process because quarrying and processing activities demand significant amounts of energy and greatly affect the environment. Further, performing an environmental analysis of a production process such as that of marble requires the consideration of many environmental aspects (e.g., noise, vibrations, dust and waste production, energy consumption). Unfortunately, the current impact accounting tools do not seem to be capable of considering all of the major aspects of the (marble) production process that may affect th…
Synthesis of refractory metal nuggets and constraints on the thermal histories of nugget-bearing Ca, Al-rich inclusions
2015
Tiny refractory metal nuggets are mainly observed inside Ca, Al-rich inclusions (CAIs) from chondritic meteorites and are commonly assumed to be condensates from a solar composition gas. However, recent detailed studies of metal nugget compositions and their comparison with predictions from condensation show that the observed abundance patterns are extremely difficult to achieve in this way. As a test for the proposed alternative, precipitation from a silicate liquid, we conducted melting experiments, in which nine different refractory metals (nugget components) were equilibrated with each other along with a CAI-like liquid at reducing conditions. When quenched, minerals similar to those in…
Luminescence of coesite
2015
Coesite is a polymorph modification of crystalline silicon dioxide with a tetrahedral structure. The luminescence of a single crystal of synthetic coesite was studied under excitation using x-rays, an electron beam, and excimer lasers KrF (248 nm), ArF (193 nm) and F2 (157 nm). Luminescence bands in the regions of 2.5 eV and 4.4 eV appear. The blue band is dependent on temperature and is composed of decay kinetics. Three main decay times are revealed, exhibiting luminescence of a different nature in the same range of the spectrum. One is in the ns range of time with a time constant of about 2 ns. The two other decay times are in the regions of 5 μs and 700 μs. The 5 μs component is also see…
Effect of sintering process and additives on the properties of cordierite based ceramics
2013
It is possible to obtain cordierite ceramics with high temperature synthesis using both synthetic and raw natural materials. This paper discusses the possibilities to obtain cordierite ceramics, replacing part of required oxides with raw materials from various Latvian deposits of dolomite and clay. The obtained raw cordierite powders were ground in two modes (3 and 12 hours) and fired at 1200 °C. Ceramic samples were characterized by hydrostatic weighting method; crystalline phase composition was studied by XRD. Obtained samples were evaluated by their mechanical (compressive) strength and linear coefficient of thermal expansion (CTE). Thermal shock resistance was tested using water quenchi…
Chalcogen adsorption and surface magnetism
2000
Abstract Investigations concerning the electronic and magnetic properties of oxygen and sulfur adsorbed on magnetized surfaces were carried out by means of angle and spin resolving photoelectron spectroscopy. Iron(110), a polycrystalline iron alloy, and an amorphous metallic glass (Fe 79 B 16 Si 5 ) served as ferromagnetic substrates. Exchange splittings of the O 2p and S 3p derived levels could be detected, demonstrating a magnetic coupling between the chemisorbate and iron. This observation presents a prerequisite for an induced magnetic moment within the adsorbate overlayer. For sulfur an adsorbate-induced structure only in the minority spin channel near the Fermi level was observed whic…