781 research outputs found
Unconventional antiferromagnetic correlations of the doped Haldane gap system YBaNiZnO
We make a new proposal to describe the very low temperature susceptibility of
the doped Haldane gap compound YBaNiZnO. We propose a new
mean field model relevant for this compound. The ground state of this mean
field model is unconventional because antiferromagnetism coexists with random
dimers. We present new susceptibility experiments at very low temperature. We
obtain a Curie-Weiss susceptibility as expected
for antiferromagnetic correlations but we do not obtain a direct signature of
antiferromagnetic long range order. We explain how to obtain the ``impurity''
susceptibility by subtracting the Haldane gap contribution to
the total susceptibility. In the temperature range [1 K, 300 K] the
experimental data are well fitted by . In the temperature range [100 mK, 1 K] the experimental data are
well fitted by , where increases with
. This fit suggests the existence of a finite N\'eel temperature which is
however too small to be probed directly in our experiments. We also obtain a
maximum in the temperature dependence of the ac-susceptibility which
suggests the existence of antiferromagnetic correlations at very low
temperature.Comment: 19 pages, 17 figures, revised version (minor modifications
Evidence of quantum criticality in the doped Haldane system Y2BaNiO5
Experimental bulk susceptibility X(T) and magnetization M(H,T) of the
S=1-Haldane chain system doped with nonmagnetic impurities, Y2BaNi1-xZnxO5
(x=0.04,0.06,0.08), are analyzed. A numerical calculation for the low-energy
spectrum of non-interacting open segments describes very well experimental data
above 4 K. Below 4 K, we observe power-law behaviors, X(T)=T^-alpha and
M(H,T)/T^(1-alpha)=f(alpha,(H/T)), with alpha (<1) depending on the doping
concentration x.This observation suggests the appearance of a gapless quantum
phase due to a broad distribution of effective couplings between the
dilution-induced moments.Comment: 4 pages, 3 figure
Evidence for local lattice distortions in giant magnetocapacitive CdCr2S4
Raman scattering experiments on CdCr2S4 single crystals show pronounced
anomalies in intensity and frequency of optical phonon modes with an onset
temperature T*=130 K that coincides with the regime of giant magnetocapacitive
effects. A loss of inversion symmetry and Cr off-centering are deduced from the
observation of longitudinal optical and formerly infrared active modes for
T<T_c=84 K. The intensity anomalies are attributed to the enhanced electronic
polarizability of displacements that modulate the Cr-S distance and respective
hybridization. Photo doping leads to an annihilation of the symmetry reduction.
Our scenario of multiferroic effects is based on the near degeneracy of polar
and nonpolar modes and the additional low energy scale due to hybridization.Comment: 4 pages, 6 figure
Careful adjustment of Epo non-viral gene therapy for β-thalassemic anaemia treatment
BACKGROUND: In situ production of a secreted therapeutic protein is one of the major gene therapy applications. Nevertheless, the plasmatic secretion peak of transgenic protein may be deleterious in many gene therapy applications including Epo gene therapy. Epo gene transfer appears to be a promising alternative to recombinant Epo therapy for severe anaemia treatment despite polycythemia was reached in many previous studies. Therefore, an accurate level of transgene expression is required for Epo application safety. The aim of this study was to adapt posology and administration schedule of a chosen therapeutic gene to avoid this potentially toxic plasmatic peak and maintain treatment efficiency. The therapeutic potential of repeated muscular electrotransfer of light Epo-plasmid doses was evaluated for anaemia treatment in β-thalassemic mice. METHODS: Muscular electrotransfer of 1 μg, 1.5 μg, 2 μg 4 μg or 6 μg of Epo-plasmid was performed in β-thalassemic mice. Electrotransfer was repeated first after 3.5 or 5 weeks first as a initiating dose and then according to hematocrit evolution. RESULTS: Muscular electrotransfer of the 1.5 μg Epo-plasmid dose repeated first after 5 weeks and then every 3 months was sufficient to restore a subnormal hematrocrit in β-thalassemic mice for more than 9 months. CONCLUSION: This strategy led to efficient, long-lasting and non-toxic treatment of β-thalassemic mouse anaemia avoiding the deleterious initial hematocrit peak and maintaining a normal hematocrit with small fluctuation amplitude. This repeat delivery protocol of light doses of therapeutic gene could be applied to a wide variety of candidate genes as it leads to therapeutic effect reiterations and increases safety by allowing careful therapeutic adjustments
Monocarboxylate transporters in cancer
Tumors are highly plastic metabolic entities composed of cancer and host cells that can adopt different metabolic phenotypes. For energy production, cancer cells may use 4 main fuels that are shuttled in 5 different metabolic pathways. Glucose fuels glycolysis that can be coupled to the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) in oxidative cancer cells or to lactic fermentation in proliferating and in hypoxic cancer cells. Lipids fuel lipolysis, glutamine fuels glutaminolysis, and lactate fuels the oxidative pathway of lactate, all of which are coupled to the TCA cycle and OXPHOS for energy production. This review focuses on the latter metabolic pathway. Lactate, which is prominently produced by glycolytic cells in tumors, was only recently recognized as a major fuel for oxidative cancer cells and as a signaling agent. Its exchanges across membranes are gated by monocarboxylate transporters MCT1-4. This review summarizes the current knowledge about MCT structure, regulation and functions in cancer, with a specific focus on lactate metabolism, lactate-induced angiogenesis and MCT-dependent cancer metastasis. It also describes lactate signaling via cell surface lactate receptor GPR81. Lactate and MCTs, especially MCT1 and MCT4, are important contributors to tumor aggressiveness. Analyses of MCT-deficient (MCT and MCT) animals and (MCT-mutated) humans indicate that they are druggable, with MCT1 inhibitors being in advanced development phase and MCT4 inhibitors still in the discovery phase. Imaging lactate fluxes non-invasively using a lactate tracer for positron emission tomography would further help to identify responders to the treatments
Random interactions and spin-glass thermodynamic transition in the hole-doped Haldane system YCaBaNiO
Magnetization, DC and AC bulk susceptibility of the =1 Haldane chain
system doped with electronic holes, YCaBaNiO
(0x0.20), have been measured and analyzed. The most striking
results are (i) a sub-Curie power law behavior of the linear susceptibility,
, for temperature lower than the Haldane gap
of the undoped compound (x=0) (ii) the existence of a spin-glass thermodynamic
transition at = 2-3 K. These findings are consistent with (i) random
couplings within the chains between the spin degrees of freedom induced by hole
doping, (ii) the existence of ferromagnetic bonds that induce magnetic
frustration when interchain interactions come into play at low temperature.Comment: 4 pages, 4 figures, to appear in Phys. Rev.
Gauge Invariant Factorisation and Canonical Quantisation of Topologically Massive Gauge Theories in Any Dimension
Abelian topologically massive gauge theories (TMGT) provide a topological
mechanism to generate mass for a bosonic p-tensor field in any spacetime
dimension. These theories include the 2+1 dimensional Maxwell-Chern-Simons and
3+1 dimensional Cremmer-Scherk actions as particular cases. Within the
Hamiltonian formulation, the embedded topological field theory (TFT) sector
related to the topological mass term is not manifest in the original phase
space. However through an appropriate canonical transformation, a gauge
invariant factorisation of phase space into two orthogonal sectors is feasible.
The first of these sectors includes canonically conjugate gauge invariant
variables with free massive excitations. The second sector, which decouples
from the total Hamiltonian, is equivalent to the phase space description of the
associated non dynamical pure TFT. Within canonical quantisation, a likewise
factorisation of quantum states thus arises for the full spectrum of TMGT in
any dimension. This new factorisation scheme also enables a definition of the
usual projection from TMGT onto topological quantum field theories in a most
natural and transparent way. None of these results rely on any gauge fixing
procedure whatsoever.Comment: 1+25 pages, no figure
Anomalous spectral weight in photoemission spectra of the hole doped Haldane chain Y2-xSrxBaNiO5
In this paper, we present photoemission experiments on the hole doped Haldane
chain compound . By using the photon energy dependence of
the photoemission cross section, we identified the symmetry of the first
ionisation states (d type). Hole doping in this system leads to a significant
increase in the spectral weight at the top of the valence band without any
change in the vicinity of the Fermi energy. This behavior, not observed in
other charge transfer oxides at low doping level, could result from the
inhomogeneous character of the doped system and from a Ni 3d-O 2p hybridization
enhancement due to the shortening of the relevant Ni-O distance in the
localized hole-doped regions.Comment: 5 pages, 4 figure
Singlet Ground State of the Quantum Antiferromagnet Ba3CuSb2O9
We present local probe results on the honeycomb lattice antiferromagnet
Ba3CuSb2O9. Muon spin relaxation measurements in zero field down to 20 mK show
unequivocally that there is a total absence of spin freezing in the ground
state. Sb NMR measurements allow us to track the intrinsic susceptibility of
the lattice, which shows a maximum at around 55 K and drops to zero in the
low-temperature limit. The spin-lattice relaxation rate shows two
characteristic energy scales, including a field-dependent crossover to
exponential low-temperature behavior, implying gapped magnetic excitations.Comment: Accepted for publication in Physical Review Letter
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