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951.
A thermodynamic model of magnetic insulator-to-metal transitions is presented. As the parameters are varied it shows with increasing temperatures; (a) antiferromagnetic insulator → paramagnetic insulator; or (b) antiferromagnetic insulator → metal → paramagnetic insulator; or (c) antiferromagnetic insulator → metal; or (d) metal at all temperatures. Behaviors (b) and (c) are separated by a classical critical point. The model reproduces well the behavior encounted in (V1-xCrx)2O3 and can be applied to magnetic semiconductors in general. 相似文献
952.
Summary Bohm's theory on plasma probes has been modified, by taking into account the effect of the applied RF voltage on the ion saturation
current, for explaining the experimentally detected behaviour of the plasma sheath resonance frequency in a low-temperature
and low-density plasma
Riassunto La teoria di Bohm sulle sonde nei plasmi è stata modificata, tenendo conto dell'effetto dovuto alla tensione RF applicata sulla corrente ionica di saturazione. Si spiega cosi l'andamento della frequenza di risonanza plasma-guaina ionica, rilevato sperimentalmente, in un plasma a bassa temperatura e bassa densità.
Резюме Предлагается модификация теории Бома для плазменных зондов, которая учитывает влияние приложенного радиочастотного напряжения на ионный ток насыщения. Предложенная модификация позволяет объяснить экспериментально обнаруженное поведение резонансной частоты плазменной оболочки при низкой температуре и при низкой плотности плазмы.相似文献
953.
E. M. Gopalakrishna W. H. Watson M. Hoeneisen M. Silva 《Journal of chemical crystallography》1977,7(1):49-57
Ovatifolin, C17H22O5, is a sesquiterpene lactone isolated from the aerial parts ofPodanthus mitiqui Lindl. (Compositae) collected near Pichidangui, Chile. Extracts of the plant exhibit cytotoxic activity against KB cell cultures. The pale yellow crystals belong to the orthorhombic space groupP212121 with cell dimensionsa = 8.159(1),b = 6.640(1), andc = 29.314(4) Å. Data were collected on an automatic diffractometer and the structure was solved by direct methods. The model was refined anisotropically to anR value of 0.047 using all 1742 measured intensities. The 10-memberedtrans-trans-germacradiene ring adopts a chair-chair conformation with C(4) and C(10) methyl groups orientedsyn on the face of the molecule. The conformation leads to a crossed double-bond system in which transannular interactions shift the ultraviolet absorption to 210 nm. The five-membered lactone ring adopts a distorted chair conformation and istrans-fused to the 10-membered ring.FASTBIOS contribution number 36. 相似文献
954.
In the light of Einstein's equations a system only containing two scalar fields is considered: One is of long range and attractive, the other is of short range and repulsive. The sources of these fields are taken to be nonsingular and spherically symmetric. All components of the energy-momentum tensor are continuous. A static solution of the equations is obtained in the weak-field approximation. The source of the gravitational field shows a finite concentration on the center of symmetry and dilutes monotonically to zero outwards. A Schwarzschild-type gravitation is found at infinity. 相似文献
955.
G.N. De Oliveira Ana P. Santana J.A. Dias Da Silva 《Linear and Multilinear Algebra》1983,14(2):157-163
We study the problem of finding conditions for two star products of n vectors to be equal when the vectors in each star product are not linearly independent, and the problem of finding conditions for one star product to be zero. We reprove results of M. Marcus and J. Chollet in a very simple way. We present also some open problems. 相似文献
956.
The transfer matrix approach is applied to calculate the spectral density of electronic states for the W(001) surface. We use a tight-binding hamiltonian with a nine function basis: 6s, 6p and 5d. Results for points along the Σ and ? symmetry lines are presented for occupied states. Both surface and bulk features of the spectral density are in good agreement with angularly resolved photoemission spectra. 相似文献
957.
958.
The metal-insulator (M-I) transition in vanadium sesquioxide V2O3 has been investigated by time differential perturbed angular correlation measurements of the electric fieldgradient (EFG) and the magnetic hyperfine field at dilute111Cd impurities. The EFG undergoes a first-order change at the M-I transition at Tt=160 K, but does not reflect the high temperature resistivity anomaly. The increase of the EFG with temperature in the metallic phase can be attributed to thermal variations of the oxygen sublattice. The temperature dependence of the magnetic hyperfine field in the insulating phase follows a Brioullin function with a saturation value of Hhf(O)=15 KOe and an extrapolated Neel temperature, which, depending on the impurity concentration, varies between 188 and 230 K. 相似文献
959.
O.A.C. Nunes 《Solid State Communications》1982,44(1):59-62
The magnon damping in an electron-magnon system in the presence of a laser beam and a d.c. magnetic field is discussed. It is shown that near the laser-cyclotron resonance, and for the laser beam propagating perpendicularly to the magnetic field the magnon population in a relatively narrow range of k may grow with time. 相似文献
960.
O.A.C. Nunes 《Solid State Communications》1982,44(8):1275-1276
The rate of change in the magnon population due to scattering by free carriers in the presence of a laser field is calculated. It is found that spin waves propagating parallel to the direction of propagation of the radiation field may be amplified over a relatively narrow band of q values. 相似文献