On the hyperfine interaction in rare-earth Van Vleck paramagnets at high magnetic fields

An influence of high magnetic fields on hyperfine interaction in the rare-earth ions with non-magnetic ground state (Van Vleck ions) is theoretically investigated for the case of $Tm^{3+}$ ion in axial symmetrical crystal electric field (ethylsulphate crystal). It is shown that magnetic-field induced distortions of $4f$-electron shell lead to essential changes in hyperfine magnetic field at the nucleus. The proposed theoretical model is in agreement with recent experimental data.Comment: 4 pages, no figures, submitted to J. Phys. : Cond. Mat

Some peculiarities of spin-lattice relaxation of impurity rare-earth ions in crystals, caused by the structure defects

The spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets (YAG) and for Yb3+ ions in CaF2 in the low-temperature range have been measured. For the first system the temperature dependence of the relaxation rate is determined to a great extent by the method of sample preparation. For samples grown by the method of the horizontally oriented crystallization the dependence is described as T1 -1 = ATn, n ≅ 4.7, which is an evidence of an influence of local structure disordering on the relaxation. The temperature dependence of the relaxation rate in CaF2:Yb is also "anomalous": T1 -1 = AT3.3. The results are compared with the previous data on the relaxation in similar systems, and with other cases of observation of "anomalous" temperature dependences. Different manifestations of the local crystal defects in spin-lattice relaxation are discussed. © Springer-Verlag 1998 Printed in Austria

Low-dose antibiotics: current status and outlook for the future

Antimicrobial therapy is a key factor in our success against pathogens poised to ravage at risk or infected individuals. However, we are currently at a watershed point as we face a growing crisis of antibiotic resistance among diverse pathogens. One area of intense interest is the impact of the application of antibiotics for uses other than the treatment of patients and the association with such utilization with emerging drug resistance. This Research Topic “Low- dose antibiotics: current status and outlook for the future” in Frontiers in Microbiology: Antimicrobials, Resistance and Chemotherapy details various aspects of the wide ranging effects of antimicrobial therapy from areas such as the regulation of host responses to modulation of bacterial virulence factors to acquisition of antibiotic resistance genes

Temperature dependence of the EPR linewidth of Yb3+ - ions in Y0.99Yb0.01Ba2Cu3OX compounds: Evidence for an anomaly near TC

Electron paramagnetic resonance experiments on doped Yb3+ ions in YBaCuO compounds with different oxygen contents have been made. We have observed the strong temperature dependence of the EPR linewidth in the all investigated samples caused by the Raman processes of spin-lattice relaxation. The spin-lattice relaxation rate anomaly revealed near TC in the superconducting species can be assigned to the phonon density spectrum changesComment: 10 pages, 4 figures Renewed versio

Role of the mean curvature in the geometry of magnetic confinement configurations

Examples are presented of how the geometric notion of the mean curvature is used for general magnetic field configurations and magnetic surfaces. It is shown that the mean magnetic curvature is related to the variation of the absolute value of the magnetic field along its lines. Magnetic surfaces of constant mean curvature are optimum for plasma confinement in multimirror open confinement systems and rippled tori.Comment: PDFLaTeX, 10 pages, 5 figure

Andreev reflection in Au/La_{2-x}Sr_{x}CuO_{4} point-contact junctions: separation between pseudogap and phase-coherence gap

We made point-contact measurements with Au tips on La_{2-x}Sr_{x}CuO_{4} samples with 0.08 < x < 0.20 to investigate the relationship between superconducting gap and pseudogap. We obtained junctions whose conductance curves presented typical Andreev reflection features at all temperatures from 4.2 K up to T_c^A close to the bulk T_c. Their fit with the BTK-Tanaka-Kashiwaya model gives good results if a (s+d)-wave gap symmetry is used. The doping dependence of the low temperature dominant isotropic gap component Delta_{s} follows very well the T_{c} vs. x curve. These results support the separation between the superconducting (Andreev) gap and the pseudogap measured by angle-resolved photoemission spectroscopy (ARPES) and tunneling.Comment: 4 pages, 5 eps figures, 1 table. SNS 2001 Conferenc

Effect of Mo3+ ions on Nd3+ spin-lattice relaxation in Y3Al5O12

The content of Mo3+ ions in YAG:Nd garnet samples prepared by different technologies has been studied, and the spin-lattice relaxation rate of these ions at temperatures of 4-5 K measured. It is concluded is drawn that Mo3+ ions can play the part of rapidly relaxing centers mediating the Nd3+ spin-lattice relaxation at liquid-helium temperatures. This may account for a number of features in the spin-lattice relaxation of rare-earth ions in garnets, observed earlier at low temperatures. © 1998 American Institute of Physics

Field dependence of spin-lattice relaxation of Nd3+ ions in y3Al5O12 crystals

Our studies involve measuring spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets over the temperature range 4-50 K at 9.25 and 36.4 GHz for different orientations of the external magnetic field in relation to the crystallographic axes. The temperature dependence of the relaxation rate is described by T1 -1=ATn + b exp(-ΔAT), where n varies from sample to sample, with n=1 for "perfect" samples (i.e., with the longest relaxation times). Here A is approximately 130 cm-1, which is the energy of the excited Kramers doublet of the neodymium ion closest to the ground state, and this makes it possible to interpret the second term in T1 -1 as the contribution of two-stage relaxation proceeding through the intermediate level Δ. A strong field dependence of these processes has been discovered: when the frequency was increased fourfold, the relaxation rate increased by a factor of 10. The effect is a specific manifestation of the degeneracy of the excited level, breaking of the symmetry of the crystalline field due to lattice defects, and the prevalence of deformations of a certain type in the spin-lattice interaction. ©1997 American Institute of Physics

Role of diffusion-weighted magnetic resonance imaging in diagnostics of symptomatic epilepsy with anomalies of brain

The paper presents the results ot the evaluation with MRI diffusion in the diagnosis of structural brain damage in children with symptomatic epilepsy in the background of developmental abnormalities of the brain and comparison of changes detected with routine MRI parameters. The features of morphological and functional changes in the brain substance, which allow to evaluate the development and course of epilepsy in children with congenital malformations of the brain. Syptoms of brain anomalies depend on the location and extent of violations.В статье приведены результаты оценки МРТ диффузии в диагностике структурных повреждений головного мозга у детей с симптоматической эпилепсией на фоне аномалий развития головного мозга и сопоставление выявленных изменений с параметрами рутинной МРТ. Описаны особенности морфофункциональных изменений вещества мозга, которые дают возможность оценивать развитие и течение эпилепсии у детей с аномалиями развития головного мозга. Симптомы аномалий головного мозга зависят от расположения и распространенности наррений

Specific indicators of MR diffusion in child cerebral palsy with symptomatic epilepsy

The article presents an analysis of 54 MR tomograms and 18 results diffusion weighted imaging children with symptomatic epilepsy with cerebral palsy. Routine MRI reveals structural disorders of the brain and the epileptogenic focus. Based on DW MRI proved imbalance neurogenesis in these children, which is characterized by a significant increase in the average performance of diffusing capacity of the brain due to lower fractional anisotropy in the fronto-temporal lobe, indicating that the permeability of the myelin sheath.В статье представлен анализ 54 MPT-томограмм и 26 результатов МР-диффузии у детей с симптоматической эпилепсии при детском церебральном параличе. Руганная МРТ исследование позволяет выявить структурные нарушения головного мозга, тоща как МР-диффузия устанавливает дисбаланс нейрогенеза у данных детей, который характеризуется достоверным повышением показателей средней диффузионной способности мозга на фоне снижения фракционной анизотропии в лобно­височной доле, что свидетельствует о проницаемости миелиновой оболочки