The state of iron in andalusite

Iron in andalusite (Al₂SiO₅) with concentrations of 1.5 … 4.3 wt-% has been reported in the literature to occupy mainly Al1 sites as Fe³⁺, and only small portions occupy Al2 sites as Fe³⁺ and Fe²⁺. In no case a magnetic hyperfine splitting has been found at temperatures above 77 K. We have studied natural samples of andalusite containing 0.3 and 0.5 wt-% only. Mössbauer spectra recorded at 80 and 300 K show magnetically split spectra and, for the 0.5% sample, an additional doublet can be seen. The spectra are interpreted as being due to a slow paramagnetic relaxation resulting in Fe³⁺ and Fe²⁺ hyperfine multiplets. An increase in the Fe concentration reduces the paramagnetic relaxation time. It seems that the andalusite structure can contain a limited number of Fe²⁺ only, and a similar limitation does not exist for Fe³⁺ ions.     

Conductivity anisotropy in the antiferromagnetic state of iron pnictides

Recent experiments on iron pnictides have uncovered a large in-plane resistivity anisotropy with a surprising result: The system conducts better in the antiferromagnetic x direction than in the ferromagnetic y direction. We address this problem by calculating the ratio of the Drude weight along the x and y directions, D(x)/D(y), for the mean-field Q=(π,0) magnetic phase diagram of a five-band model for the undoped pnictides. We find that D(x)/D(y) ranges between 0.2相似文献   

Ground state formation in a strong hubbard correlation regime in iron monosilicide

Low-temperature anomalies in the physical properties of iron monosilicide are analyzed based on the results of thorough measurements of the conductivity, Hall coefficients, thermo emf, and magnetic characteristics of high-quality single-crystal FeSi samples at liquid helium (LHe) and intermediate temperatures. It is demonstrated that the most adequate and consistent interpretation of the experimental magnetic, transport, and optical characteristics can be given within the framework of the Hubbard model. The model parameters are determined and the arguments are presented which provide evidence of the spin polaron formation and the density of state (DOS) renormalization taking place in FeSi in the vicinity of the Fermi energy at intermediate temperatures. It was found that a decrease in the sample temperature in the region of T < T _c ≈ 15 K is accompanied by a transition to a coherent regime of the spin density fluctuations. As a result, the ferro-magnetic character of the interaction leads to the formation of magnetic microdomains with a characteristic size ～10 Å. The exchange-induced magnetization enhancement in the vicinity of charge carriers in these microdomains probably accounts for the anomalous components in the Hall coefficient and the magnetization hysteresis observed in FeSi at LHe temperatures. The nature of the low-temperature transition at T _m ≈ 7 K in the system of interacting magnetic microparticles in iron monosilicide is discussed.     

On the possibility of revealing the transition of a baryon pair state to a six-quark confinement state

Proton-proton collisions are considered to find favourable conditions for searching for the transition of a baryon pair state to a hexa-quark confinement state (3q) + (3q) → (6q)_cnf. It is admitted that central pp collisions in a definite range of the initial energy can lead to creation of an intermediate compound system where the hexa-quark dibaryon can be formed. Criteria for selection of central collision events and for manifestation of the quark-structure dibaryon production are proposed.     

On the trail of a new state of matter

Following the results collected in the past 30 years within the heavy-ion scientific program, the progress achieved so far at the CERN LHC during the first data taking period is reviewed.     

ESR identification of the iron double electron trap state in GaP

By Electron Spin Resonance (ESR) it has been found that neutral substitutional iron impurities in gallium phosphide can trap two electrons. The 3d⁷-character of the two-electron trap state of iron in GaP was inferred from the characteristic angular dependence of the Zeeman-splitting of its Γ₈-ground state.     

On the bound state spectrum of a many-electron-proton system

An equation is obtained for the pairing amplitude in a many-electron-proton system at finite temperature. It is noted that under certain approximations it can be solved to give temperature-dependent discrete energy spectra.     

On the work done in changing the state of a black hole

We examine the process of slowly lowering a charged particle to the event horizon of a static charged black hole and then allowing it to be absorbed by the black hole. This process is examined both using the laws of black-hole thermodynamics and using general relativity. The work done in this process is calculated. In addition, we calculate the change in the mass, charge, and area of the black hole. We find that the area (i.e., entropy) is left unchanged.     

Oxidation state of iron in mantle-derived magmas of the Icelandic rift zone

Olivine tholeiites are mantle-derived magmas that are formed by partial melting of their deep sources and which have equilibrated with mineral assemblages at slightly different subcrustal pressure-temperature conditions prior to eruption. The minimum depth of the pre-eruptive reservoirs of these magmas is in the order of 10–15 km and their liquidus temperatures fall within the range of 1180–1240 C. Three types of primitive olivine tholeiites are exposed along the rift zones in Iceland. In the present study, the ferric/ferrous ratios of natural glasses (pillow crusts) of the three types of olivine tholeiites were obtained by Mössbauer spectrometry. This technique is particularly well suited for the analysis of high-Mg glasses since it resolves microcrystallites of olivine which contribute to ferrous iron in chemical analysis. All results fall within 10–15% Fe(III). At the liquidus temperature of these glasses, this ferric/ferrous ratio corresponds to fugacity close to the fayalite-magnetite-quartz-oxygen (FMQ) buffer with an uncertainty of less than one log unit in fO₂. This result confirms that there is no significant difference in the oxidation state of the three magma types.     

On thermodynamics near a steady state

The statistical deduction of a stability criterion for steady states (a generalization of the Glansdorff-Prigogine criterion) given in a previous paper is extended in some respects. Dynamical coefficients for the motion of small deviations from a steady state are expressed by correlation functions. The stability criterion is applied to some models of chemical reactions and to a model for second break-down in semiconductors.     

On the stationary state of a mixture of reacting gases

An attempt to determine the characteristics of the equilibrium state of a reacting mixture of ideal gases with the help of numerical methods similar to those used in simulating reacting gas flows is undertaken. It was demonstrated that, instead of the classical equilibrium state, a dynamic stationary state can be obtained for which the rates of the individual reactions are nonzeros. The possibility of the existence of such states in nature was explored. Methods ensuring the realization of classical chemical equilibrium are proposed. The analysis presented in the current paper can be useful for specialists in numerical simulations of reacting gas flows and for students and teachers in fields related to physical chemistry.     

On the destruction of the superconducting state of a multiconductor composite

The kinetics of thermal instability in the form of an initially arising local region of normal conductivity is investigated using a model of a discrete superconducting medium in which the components are assumed to interact thermally across a thermally thin intermediate layer. It is found that certain characteristic features of the transient processes occurring at currents close to the minimum current for propagation of the normal zone must be taken into account in an experimental determination of the normal-zone propagation velocities in multiconductor composites. Zh. Tekh. Fiz. 69, 133–136 (February 1999)     

On a characterization of the state space of quantum mechanics

A characterization of state spaces of Jordan algebras by Alfsen and Shultz is improved to a form with more physical appeal (proposed by Wittstock) in the simplified case of a finite dimension.On leave from Research Institute for Mathematical Sciences, Kyoto University, Kyoto 606, Japan     

On the ground state of an impurity in a dilute fermi gas

The system under consideration is a large collection of identical fermions (B), forming a background, into which is inserted a relatively small number of distinct impurity (I) particles. The background is considered to be dilute in the sense that R ? a, where R is the average separation of the B particles, and a is the range of their interaction potential; and the I particles are so dilute with respect to the B particles that I-I interactions can be ignored. The I particles are then all essentially at rest in their ground state. The BB and BI interaction potentials are chosen to be hard cores of the same range a. A series expansion is developed for the ground-state energy of the I particles, and the first four terms are calculated explicitly using two distinct methods, employing Feynman and Goldstone diagrams respectively. It is shown that each method has distinct advantages over the other, and that a judicious combination of both can be used to considerable benefit.     

On magnetic transition of the plane spiral in a commensurate intermediate state

The temperature dependence of the wave vector of a plane spiral in rhombohedral crystals is studied. The conditions are shown under which there occurs temperature-induced transition of the spiral structure into intermediate commensurate phase. The instability of paramagnetic phase with respect to the formation of magnetic spiral near a Lifshitz point is investigated.     

On the phase state of the core matter in a high-power discharge through a wire

Experimental facts attesting to a two-phase (liquid-metal-vapor) state of the matter in the core produced in a high-power discharge through thin wires are presented. The modern technique of multiframe x-ray shadow photography has made it possible to observe vapor bubbles in the core and their interaction with the shock wave penetrating from the corona. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 5, 349–354 (10 March 1999)     

On the cross-section peaks for a heavy-quark bound state

We discuss the values of resonance peaks of the cross section of a heavy-quark bound state obtained by means of a Green function method applied to a Coulombic model and compare the result to the ϒ and J/ψ data.     

On the ground state energy of a two-dimensional electron fluid

A new theory of the ground state energy of a two-dimensional electron fluid is presented. It is shown that the ring diagram contribution changes its analytical behavior atr _s =2^1/2, wherer _s is the usual density parameter defined by r_S = 1/a ₀( n)^1/2,a ₀ being the Bohr radius andn is the electron density. For smallr _s , a high density series is obtained in agreement with the previous calculation. For larger _s , a hitherto unknown low density series is obtained. In the low density region, the first order exchange energy is completely cancelled out by a term from the ring contribution so that the ground state energy decreases in proportion tor _s ^–2/3 , followed byr _s ^/–4/3 and higher order terms. The energy is found to be minimum atr _s=1.4757, the minimum value being –0.481915 Rydbergs.     

On the ground state energy of a two-dimensional electron fluid

A new theory of the ground state energy of a two-dimensional electron fluid is presented. It is shown that the ring diagram contribution changes its analytical behavior atr _s =2^1/2, wherer _s is the usual density parameter defined by r_S = 1/a ₀(π n)^1/2,a ₀ being the Bohr radius andn is the electron density. For smallr _s , a high density series is obtained in agreement with the previous calculation. For larger _s , a hitherto unknown low density series is obtained. In the low density region, the first order exchange energy is completely cancelled out by a term from the ring contribution so that the ground state energy decreases in proportion tor _s ^?2/3 , followed byr _s ^/?4/3 and higher order terms. The energy is found to be minimum atr _s=1.4757, the minimum value being ?0.481915 Rydbergs.