23 research outputs found
Raman and infrared studies of La_1-ySr_yMn_1-xM_xO_3 (M=Cr, Co, Cu, Zn, Sc or Ga): Oxygen disorder and local vibrational modes
We present results of our study of polarized Raman scattering and infrared
reflectivity of rhombohedral ceramic La_1-ySr_yMn_1-xM_xO_3 manganites in the
temperature range between 77 and 320K. In our samples, a part of the Mn atoms
is substituted by M = Cr, Co, Cu, Zn, Sc, or Ga with x in the range 0 -- 0.1.
The hole concentration was kept at the optimal value of about 32% by tuning the
Sr content y. We have monitored the distortions of the oxygen sublattice by the
presence of broad bands in the Raman spectra, the increase of d.c. resistivity
extracted from the infrared reflectivity, and the change of the critical
temperature of the ferromagnetic transition. Our results support the idea, that
these properties are mainly determined by the radius of the substituent ion,
its electronic and magnetic structure playing only a minor role. Furthermore,
the Raman spectra exhibit an additional A_g-like high frequency mode attributed
to the local breathing vibration of oxygens surrounding the substituent ion.
Its frequency and intensity strongly depend on the type of the substituent. In
the Co-substituted sample, the mode anomalously softens when going from 300 to
77K. The frequency of the bulk A_{1g} mode depends linearly on the angle of the
rhombohedral distortion.Comment: 11 pages, 11 Figures, best-fit values table added, a discussion adde
CuSiO_3 : a quasi - one - dimensional S=1/2 antiferromagnetic chain system
CuSiO_3, isotypic to the spin - Peierls compound CuGeO_3, was discovered
recently as a metastable decomposition product of the silicate mineral
dioptase, Cu_6Si_6O_{18}\cdot6H_2O. We investigated the physical properties of
CuSiO_3 using susceptibility, magnetization and specific heat measurements on
powder samples. The magnetic susceptibility \chi(T) is reproduced very well
above T = 8 K by theoretical calculations for an S=1/2 antiferromagnetic
Heisenberg linear chain without frustration (\alpha = 0) and a nearest -
neighbor exchange coupling constant of J/k_{B} = 21 K, much weaker than in
CuGeO_3. Below 8 K the susceptibility exhibits a substantial drop. This feature
is identified as a second - order phase transition at T_{0} = 7.9 K by specific
heat measurements. The influence of magnetic fields on T_{0} is weak, and ac -
magnetization measurements give strong evidence for a spin - flop - phase at
\mu_0H_{SF} ~ 3 T. The origin of the magnetic phase transition at T_{0} = 7.9 K
is discussed in the context of long - range antiferromagnetic order (AF) versus
spin - Peierls(SP)order. Susceptibility and specific heat results support the
AF ordered ground state. Additional temperature dependent ^{63,65}Cu nuclear
quadrupole resonance experiments have been carried out to probe the Cu^{2+}
electronic state and the spin dynamics in CuSiO_3
Self-consistent field theory of polarized BEC: dispersion of collective excitation
We suggest the construction of a set of the quantum hydrodynamics equations
for the Bose-Einstein condensate (BEC), where atoms have the electric dipole
moment. The contribution of the dipole-dipole interactions (DDI) to the Euler
equation is obtained. Quantum equations for the evolution of medium
polarization are derived. Developing mathematical method allows to study effect
of interactions on the evolution of polarization. The developing method can be
applied to various physical systems in which dynamics is affected by the DDI.
Derivation of Gross-Pitaevskii equation for polarized particles from the
quantum hydrodynamics is described. We showed that the Gross-Pitaevskii
equation appears at condition when all dipoles have the same direction which
does not change in time. Comparison of the equation of the electric dipole
evolution with the equation of the magnetization evolution is described.
Dispersion of the collective excitations in the dipolar BEC, either affected or
not affected by the uniform external electric field, is considered using our
method. We show that the evolution of polarization in the BEC leads to the
formation of a novel type of the collective excitations. Detailed description
of the dispersion of collective excitations is presented. We also consider the
process of wave generation in the polarized BEC by means of a monoenergetic
beam of neutral polarized particles. We compute the possibilities of the
generation of Bogoliubov and polarization modes by the dipole beam.Comment: 16 pages, 15 figures. arXiv admin note: substantial text overlap with
arXiv:1106.082
HTLV-1 infection in solid organ transplant donors and recipients in Spain
Background: HTLV-1 infection is a neglected disease, despite infecting 10–15 million people worldwide and
severe illnesses develop in 10% of carriers lifelong. Acknowledging a greater risk for developing HTLV-1
associated illnesses due to immunosuppression, screening is being widely considered in the transplantation
setting. Herein, we report the experience with universal HTLV testing of donors and recipients of solid organ
transplants in a survey conducted in Spain.
Methods: All hospitals belonging to the Spanish HTLV network were invited to participate in the study. Briefly, HTLV
antibody screening was performed retrospectively in all specimens collected from solid organ donors and recipients
attended since the year 2008.
Results: A total of 5751 individuals were tested for HTLV antibodies at 8 sites. Donors represented 2312
(42.2%), of whom 17 (0.3%) were living kidney donors. The remaining 3439 (59.8%) were recipients. Spaniards
represented nearly 80%.
Overall, 9 individuals (0.16%) were initially reactive for HTLV antibodies. Six were donors and 3 were recipients.
Using confirmatory tests, HTLV-1 could be confirmed in only two donors, one Spaniard and another from
Colombia. Both kidneys of the Spaniard were inadvertently transplanted. Subacute myelopathy developed
within 1 year in one recipient. The second recipient seroconverted for HTLV-1 but the kidney had to be
removed soon due to rejection. Immunosuppression was stopped and 3 years later the patient remains in
dialysis but otherwise asymptomatic.
Conclusion: The rate of HTLV-1 is low but not negligible in donors/recipients of solid organ transplants in
Spain. Universal HTLV screening should be recommended in all donor and recipients of solid organ
transplantation in Spain. Evidence is overwhelming for very high virus transmission and increased risk along
with the rapid development of subacute myelopath
Rapid subacute myelopathy following kidney transplantation from HTLV-1 donors: role of immunosuppresors and failure of antiretrovirals
Two kidney transplant recipients from a single donor became infected with HTLV-1 (human T-lymphotropic virus type 1) in Spain. One developed myelopathy 8 months following surgery despite early prescription of antiretroviral therapy. The allograft was removed from the second recipient at month 8 due to rejection and immunosuppressors discontinued. To date, 3 years later, this patient remains infected but asymptomatic. HTLV-1 infection was recognized retrospectively in the donor, a native Spaniard who had sex partners from endemic regions. Our findings call for a reappraisal of screening policies on donor-recipient organ transplantation. Based on the high risk of disease development and the large flux of persons from HTLV-1 endemic regions, pre-transplant HTLV-1 testing should be mandatory in Spain
Ein Patient - mehrere Möglichkeiten
In diesem ausführlichen Bericht wird ein Patient mit einer Frontzahnkrone auf Zahn 11 versorgt. Hierzu werden eine konventionelle Metallkeramikkrone und zwei Vollkeramikkronen angefertigt – eine davon basiert auf Presskeramik (Glaskeramik), die andere auf Zirkoniumdioxid. Das Ziel dieses Vorgehens ist, die für diesen Patienten beste Lösung herauszufinden. Der Schwerpunkt der Entscheidungskriterien wird dabei auf die Ästhetik gelegt, denn die Material- und Methodenvielfalt macht die Entscheidung nicht einfach. Somit schließen sich Fragen an, wie: Welche Parameter müssen berücksichtigt werden? Benötigen wir überhaupt eine derartig große Palette an Werkstoffen? Die klinischen und materialkundlichen Aspekte, Herstellungsschritte sowie Wahlkriterien werden in dem vorliegenden Beitrag ausführlich vorgestellt und diskutiert
Influence of Mn site doping on electrical resistivity of polycrystalline La1-yAyMn1-xBxO3 (A=Ba, Sr; B=Cu, Cr, Co) Manganites
We have the measured electrical resistivity of La1-yBayMn1-xCuxO3 (0.17≤y≤0.30; 0.04≤x≤0.10), La1-ySryMn1-xCrxO3 and La1-ySryMn1-xCoxO3 (0.270≤y≤0.294; 0.02≤x≤0.10) polycrystalline samples in the 25-325 K temperature range. The increase of Mn site doping concentration leads to an increase of the electrical resistivity of the samples and the appearance of a “double-peak” structure in the electrical resistivity versus temperature graphs. The first peak represents the insulator-metal transition in vicinity of the paramagnetic-ferromagnetic transition (TC). We have found that the intensity of the second peak increases with an increase of concentration of Mn substituents, due to the hole scattering by the random potential of the Mn site impurities