Magnetic correlations in La(2-x)Sr(x)CuO4 from NQR relaxation and specific heat

La-139 and Cu-63 Nuclear Quadrupole Resonance (NQR) relaxation measurements in La(2-x)Sr(x)CuO4 for O = to or less than 0.3 and in the temperature range 1.6 + 450 K are analyzed in terms of Cu(++) magnetic correlations and dynamics. It is described how the magnetic correlations that would result from Cu-Cu exchange are reduced by mobile charge defects related to x-doping. A comprehensive picture is given which explains satisfactorily the x and T dependence of the correlation time, of the correlation length and of the Neel temperature T(sub n)(x) as well as being consistent with known electrical resistivity and magnetic susceptibility measurements. It is discussed how, in the superconducting samples, the mobile defects also cause the decrease, for T yields T(sub c)(+) of the hyperfine Cu electron-nucleus effective interaction, leading to the coexistence of quasi-localized, reduced magnetic moments from 3d Cu electrons and mobile oxygen p-hole carriers. The temperature dependence of the effective hyperfine field around the superconducting transition yields an activation energy which could be related to the pairing energy. New specific heat measurements are also presented and discussed in terms of the above picture

ADIPOSE TISSUE GROWTH AND MAINTENANCE

Because obesity is fast becoming a global health pandemic, understanding the molecular and cellular processes that regulate fat mass has acquired new importance. Characterized by an increase in adipose tissue to the point where it is associated with adverse health effects, the prevalence of obesity has nearly tripled over the past fifty years. Though for many years adipose tissue was considered to be merely a storage depot for fatty acids, it is now regarded as an important endocrine organ involved in the regulation of energy balance, glucose and lipid homeostasis, blood pressure control, reproduction, inflammation and immune response. Obesity has an enormous economic burden and it is the second leading cause of preventable death. The source of increased fat mass in obesity is currently attributed to two mechanisms: adipocyte hypertrophy, the process by which preexisting fat cells increase in size due to an accumulation of lipids, and adipocyte differentiation from fat precursor cells. Stem cells are defined by the ability to self-renew and differentiate into a variety of cell types. While some adult organs, including the intestine (Cheng and Leblond, 1974), skin (Oshima et al., 2001), blood (Spangrude et al., 1988), and parts of the brain (Doetsch et al., 1999; Reynolds and Weiss, 1992), are maintained by stem cells, others, such as the pancreas (Dor et al., 2004), are not. Though it was recently demonstrated that there is a substantial degree of cellular turnover within the human adipocyte population (Spalding et al., 2008), the source of new adipocytes during one\u2019s lifetime has been entirely attributed to the differentiation of new adipocytes from preadipocytes and/or stem cells (Avram et al., 2007; Greenwood and Hirsch, 1974; Hausman et al., 2001; Lemonnier, 1972; Salans et al., 1971; Spalding et al., 2008; Tang et al., 2008). Adipocytes are thought to represent a terminal stage of differentiation and are widely believed to lack proliferative ability (Prins and O'Rahilly, 1997). Through four independent experimental approaches \u2014dilution of an inducible histone 2B-green fluorescent protein (H2BGFP) through cell division, incorporation of BrdU, labeling with the cell cycle marker Ki67, and genetic lineage analysis, we aimed to investigate the adult adipose tissue maintenance and its behavior in the cell cycle

Anelastic relaxation and 139^{139}La NQR in La2−x_{2-x}Srx_xCuO4_4 around the critical Sr content x=0.02

Anelastic relaxation and $^{139}$La NQR relaxation measurements in La$_{2-x}$Sr$_x$CuO$_4$ for Sr content x around 2 and 3 percent, are presented and discussed in terms of spin and lattice excitations and ordering processes. It is discussed how the phase diagram of La$_{2-x}$Sr$_x$CuO$_4$ at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02) could be more complicate than previous thought, with a transition to a quasi-long range ordered state at T = 150 K, as indicated by recent neutron scattering data. On the other hand, the $^{139}$La NQR spectra are compatible with a transition to a conventional AF phase around T = 50 K, in agreement with the phase diagram commonly accepted in the literature. In this case the relaxation data, with a peak of magnetic origin in the relaxation rate around 150 K at 12 MHz and the anelastic counterparts around 80 K in the kHz range, yield the first evidence in La$_{1.98}$Sr$_{0.02}$CuO$_4$ of freezing involving simultaneously lattice and spin excitations. This excitation could correspond to the motion of charged stripes.Comment: 10 pages, 8 figure

Two-bands effect on the superconducting fluctuating diamagnetism in MgB&#8322

The field dependence of the magnetization above the transition temperature Tc in MgB₂ is shown to evidence a diamagnetic contribution consistent with superconducting fluctuations reflecting both the σ and π bands. In particular, the upturn field Hup in the magnetization curve, related to the incipient effect of the magnetic field in quenching the fluctuating pairs, displays a double structure, in correspondence to two correlation lengths. The experimental findings are satisfactorily described by the extension to the diamagnetism of a recent theory for paraconductivity, in the framework of a zero-dimensional model for the fluctuating superconducting droplets above Tc

Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study

$^{19}$F NMR measurements in SmFeAsO$_{1-x}$F$_x$, for $0.15\leq x\leq 0.2$, are presented. The nuclear spin-lattice relaxation rate $1/T_1$ increases upon cooling with a trend analogous to the one already observed in CeCu$_{5.2}$Au$_{0.8}$, a quasi two-dimensional heavy-fermion intermetallic compound with an antiferromagnetic ground-state. In particular, the behaviour of the relaxation rate either in SmFeAsO$_{1-x}$F$_x$ or in CeCu$_{5.2}$Au$_{0.8}$ can be described in the framework of the self-consistent renormalization theory for weakly itinerant electron systems. Remarkably, no effect of the superconducting transition on $^{19}$F $1/T_1$ is detected, a phenomenon which can hardly be explained within a single band model.Comment: 4 figure