84 research outputs found
Magnon-polaron and Spin-polaron Signatures in the Specific Heat and Electrical Resistivity of in Zero Magnetic Field, and the Effect of Bond Environment
, an perovskite manganite oxide,
exhibits a non trivial behavior in the vicinity of the sharp peak found in the
resistivity as a function of temperature in zero magnetic field. The
various features seen on are discussed in terms of competing phase
transitions. They are related to the bond environment depending on
the content of the crystallographic site. A Ginzburg-Landau type theory is
presented for incorporating concurrent phase transitions. The specific heat
of such a compound is also examined from 50 till 200 K. A log-log analysis
indicates different regimes. In the low temperature conducting ferromagnetic
phase, a collective magnon signature () is found as for what
are called magnon-polaron excitations. A law is found at
high temperature and discussed in terms of the fractal dimension of the
conducting network of the weakly conducting (so-called insulating) phase and
Orbach estimate of the excitation spectral behaviors. The need of considering
both independent spin scattering and collective spin scattering is thus
emphasized. The report indicates a remarkable agreement for the Fisher-Langer
formula, i.e. at second order phase transitions. Within
the Attfield model, we find an inverse square root relationship between the
critical temperature(s) and the total local strain.Comment: 19 pages, 5 figures; to be published in Phys Rev
Anomalous temperature behavior of resistivity in lightly doped manganites around a metal-insulator phase transition
An unusual temperature and concentration behavior of resistivity in
has been observed at slight doping
(). Namely, introduction of copper results in a splitting of
the resistivity maximum around a metal-insulator transition temperature
into two differently evolving peaks. Unlike the original -free
maximum which steadily increases with doping, the second (satellite) peak
remains virtually unchanged for , increases for and finally
disappears at with . The observed phenomenon
is thought to arise from competition between substitution induced strengthening
of potential barriers (which hamper the charge hopping between neighboring
sites) and weakening of carrier's kinetic energy. The data are well fitted
assuming a nonthermal tunneling conductivity theory with randomly distributed
hopping sites.Comment: 10 REVTEX pages, 2 PostScript figures (epsf.sty); to be published in
JETP Letter
Strongly Enhanced Current Densities in Superconducting Coated Conductors of YBa2Cu3O7-x + BaZrO3
There are numerous potential applications for superconducting tapes, based on
YBa2Cu3O7-x (YBCO) films coated onto metallic substrates. A long established
goal of more than 15 years has been to understand the magnetic flux pinning
mechanisms which allow films to maintain high current densities out to high
magnetic fields. In fact, films carry 1-2 orders of magnitude higher current
densities than any other form of the material. For this reason, the idea of
further improving pinning has received little attention. Now that
commercialisation of conductors is much closer, for both better performance and
lower fabrication costs, an important goal is to achieve enhanced pinning in a
practical way. In this work, we demonstrate a simple and industrially scaleable
route which yields a 1.5 to 5-fold improvement in the in-field current
densities of already-high-quality conductors
Unusual thermoelectric behavior of packed crystalline granular metals
Loosely packed granular materials are intensively studied nowadays.
Electrical and thermal transport properties should reflect the granular
structure as well as intrinsic properties. We have compacted crystalline
based metallic grains and studied the electrical resistivity and the
thermoelectric power as a function of temperature () from 15 to 300K. Both
properties show three regimes as a function of temperature. It should be
pointed out : (i) The electrical resistivity continuously decreases between 15
and 235 K (ii) with various dependences, e.g. at low ,
while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near
60K, and (v) presents a rather unusual square root of temperature dependence at
low temperature. It is argued that these three regimes indicate a competition
between geometric and thermal processes, - for which a theory seems to be
missing in the case of TEP. The microchemical analysis results are also
reported indicating a complex microstructure inherent to the phase diagram
peritectic intricacies of this binary alloy.Comment: to be published in J. Appl. Phys.22 pages, 8 figure
Quasiparticle contribution to heat carriers relaxation time in DyBaCuO from heat diffusivity measurements
It is shown that the controversy on phonons or electrons being the most
influenced heat carriers below the critical temperature of high-T
superconductors can be resolved. Electrical and thermal properties of the same
DyBaCuO monodomain have been measured for two highly different
oxygenation levels. While the oxygenated sample DyBaCuO has very
good superconducting properties ( K), the DyBaCuO
sample exhibits an insulator behavior. A careful comparison between
measurements of the {\bf thermal diffusivity} of both samples allows us to
extract the electronic contribution. This contribution to the relaxation time
of heat carriers is shown to be large below and more sensitive to the
superconducting state than the phonon contribution.Comment: 13 pages, 6 figure
Exponential and power law distribution of mass clusters in a (magnetic-like) deposition model of elongated grains in 2D piles
A generalized so called magnetically controlled ballistic rain-like
deposition (MBD) model of granular piles has been numerically investigated in
2D. The grains are taken to be elongated disks whence characterized by a
two-state scalar degree of freedom, called ''nip'', their interaction being
described through a Hamiltonian. Results are discussed in order to search for
the effect of nip flip (or grain rotation from vertical to horizontal and
conversely) probability in building a granular pile. The characteristics of
creation of + (or ) nip's clusters and clusters of holes (missing nips) are
analyzed. Two different cluster-mass regimes have been identified, through the
cluster-mass distribution function which can be exponential or have a power law
form depending on whether the nip flip (or grain rotation) probability is large
or small. Analytical forms of the exponent are empirically found in terms of
the Hamiltonian parameters.Comment: submitted to Int.J. Mod. Phys. C; 16 figures; 79 reference
Glutathione S-transferase M1-null genotype as risk factor for SOS in oxaliplatin-treated patients with metastatic colorectal cancer
Background: Oxaliplatin is used as a neo-adjuvant therapy in hepatic colorectal carcinoma metastasis. This treatment has significant side effects, as oxaliplatin is toxic to the sinusoidal endothelial cells and can induce sinusoidal obstruction syndrome (SOS), which is related to decreased overall survival. Glutathione has an important role in the defence system, catalysed by glutathione S-transferase (GST), including two non-enzyme producing polymorphisms (GSTM1-null and GSTT1-null). We hypothesise that patients with a non-enzyme producing polymorphism have a higher risk of developing toxic injury owing to oxaliplatin. Methods: In the nontumour-bearing liver, the presence of SOS was studied histopathologically. The genotype was determined by a semi-nested PCR. Results: Thirty-two of the 55 (58%) patients showed SOS lesions, consisting of 27% mild, 22% moderate and 9% severe lesions. The GSTM1-null genotype was present in 25 of the 55 (46%). Multivariate analysis showed that the GSTM1-null genotype significantly correlated with the presence of (moderate-severe) SOS (P=0.026). Conclusion: The GSTM1-null genotype is an independent risk factor for SOS. This finding allows us, in association with other risk factors, to conceive a potential risk profile predicting whether the patient is at risk of developing SOS, before starting oxaliplatin, and subsequently might result in adjustment of treatment
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