Upregulated expression of oncomodulin, the beta isoform of parvalbumin, in perikarya and axons in the diencephalon of parvalbumin knockout mice

The calcium-binding proteins parvalbumin, calbindin D-28k, calretinin and calcineurin are present in subsets of GABAergic gigantic calyciform presynaptic terminals of the reticular thalamic nucleus (RTN). Previously it was hypothesized that GABA and calcium-binding proteins including parvalbumin are not only colocalized in the same neuron subpopulation, but that GABA synthesis and parvalbumin expression could be also genetically regulated by a common mechanism. Moreover, parvalbumin expression levels could influence GABA synthesis. For this, we analyzed GABA immunoreactivity in RTN gigantic calyciform presynaptic terminals of parvalbumin–deficient (PV−/−) mice. With respect to GABA immunoreactivity we found no differences compared to wild–type animals. However, using a polyclonal parvalbumin antibody raised against full-length rat muscle parvalbumin on brain sections of PV−/− mice, we observed paradoxical parvalbumin immunoreactivity in partly varicose axons in the diencephalon, mainly in the lamina medullaris externa surrounding the thalamus. A detailed immunohistochemical, biochemical and molecular biological analysis revealed this immunoreactivity to be the result of an upregulation of oncomodulin (OM), the mammalian beta isoform of parvalbumin in PV−/− mice. In addition, OM was present in a sparse subpopulation of neurons in the thalamus and in the dentate gyrus. OM expression has not been observed before in neurons of the mammalian brain; its expression was restricted to outer hair cells in the organ of Corti. Our results indicate that the absence of parvalbumin has no major effect on the GABA-synthesizing system in RTN presynaptic terminals excluding a direct effect of parvalbumin on this regulation. However, a likely homeostatic mechanism is induced resulting in the upregulation of OM in selected axons and neuronal perikarya. Our results warrant further detailed investigations on the putative role of OM in the brain

Reactive Hall constant of Strongly Correlated Electrons

The zero-temperature Hall response within tight-binding models of correlated electrons is studied. Using the linear response theory and a linearization in the magnetic field B, a general relation for the reactive (zero frequency) Hall constant in the fast (transport) limit is derived, involving only matrix elements between the lowest excited states at B=0; for noninteracting fermions, the Boltzmann expression is reproduced. For a Fermi liquid with a well defined Fermi surface and linear gapless excitations an analogous expression is found more generally. In the specific case of quasi-one-dimensional correlated systems a relation of $R^0_H$ to the charge stiffness D is recovered. Similar analysis is performed and discussed for D and the compressibility.Comment: 8 pages, submitted to Phys.Rev.

Competition and coexistence of bond and charge orders in (TMTTF)2AsF6

(TMTTF)2AsF6 undergoes two phase transitions upon cooling from 300 K. At Tco=103 K a charge-ordering (CO) occurs, and at Tsp(B=9 T)=11 K the material undergoes a spin-Peierls (SP) transition. Within the intermediate, CO phase, the charge disproportionation ratio is found to be at least 3:1 from carbon-13 NMR 1/T1 measurements on spin-labeled samples. Above Tsp, up to about 3Tsp, 1/T1 is independent of temperature, indicative of low-dimensional magnetic correlations. With the application of about 0.15 GPa pressure, Tsp increases substantially, while Tco is rapidly suppressed, demonstrating that the two orders are competing. The experiments are compared to results obtained from calculations on the 1D extended Peierls-Hubbard model.Comment: 4 pages, 5 figure

In-Situ Infrared Transmission Study of Rb- and K-Doped Fullerenes

We have measured the four IR active $C_{60}$ molecular vibrations in $M_{x}C_{60}$ $(M = K, Rb)$ as a function of doping $x$. We observe discontinuous changes in the vibrational spectra showing four distinct phases (presumably $x = 0, 3, 4$, and 6). The $1427cm^{-1}$ and $576cm^{-1}$ modes show the largest changes shifting downward in frequency in four steps as the doping increases. Several new very weak modes are visible in the $x=6$ phase and are possibly Raman modes becoming weakly optically active. We present quantitative fits of the data and calculate the electron-phonon coupling of the $1427cm^{-1}$ IR mode.Comment: 3 pages, Figure 1 included, 3 more figures available by request. REVTEX v3.0 IRC60DO

Vanishing Hall Constant in the Stripe Phase of Cuprates

The Hall constant R_H is considered for the stripe structures. In order to explain the vanishing of R_H in LNSCO at x = 1/8, we use the relation of R_H to the Drude weight D as well as direct numerical calculation, to obtain results within the t-J model, where the stripes are imposed via a charge potential and a staggered magnetic field. The origin of R_H ~ 0 is related to a maximum in D and the minimal kinetic energy in stripes with a hole filling ~ 1/2. The same argument indicates on a possibility of R_H ~ 0 in the whole range of static stripes for x < 1/8.Comment: RevTeX, 4 pages, 5 figure

Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3

We have observed an unusual form of creep at low temperatures in the charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW motion becomes limited by thermally-activated phase advance past individual impurities, demonstrating the importance of local pinning and related short-length-scale dynamics. Unlike in vortex lattices, elastic collective dynamics on longer length scales results in temporally ordered motion and a finite threshold field. A first-order dynamic phase transition from creep to high-velocity sliding produces "switching" in the velocity-field characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys. Rev. Let

Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3

In the Peierls state very thin samples of TaS_3 (cross-section area \sim 10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the threshold field. With approaching the Peierls transition temperature, T_P, the smearing evolves into smooth growth of conductance from zero voltage interpreted by us as the contribution of fluctuations to the non--linear conductance. We identify independently the fluctuation contribution to the linear conductance near T_P. Both linear and non-linear contributions depend on temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently reveal the same process. We reject creep of the {\it continuous} charge-density waves (CDWs) as the origin of this effect and show that it is spontaneous phase slippage that results in creep of the CDW. A model is proposed accounting for both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR

Variable-range hopping in quasi-one-dimensional electron crystals

We study the effect of impurities on the ground state and the low-temperature dc transport in a 1D chain and quasi-1D systems of many parallel chains. We assume that strong interactions impose a short-range periodicicity of the electron positions. The long-range order of such an electron crystal (or equivalently, a $4 k_F$ charge-density wave) is destroyed by impurities. The 3D array of chains behaves differently at large and at small impurity concentrations $N$. At large $N$, impurities divide the chains into metallic rods. The low-temperature conductivity is due to the variable-range hopping of electrons between the rods. It obeys the Efros-Shklovskii (ES) law and increases exponentially as $N$ decreases. When $N$ is small, the metallic-rod picture of the ground state survives only in the form of rare clusters of atypically short rods. They are the source of low-energy charge excitations. In the bulk the charge excitations are gapped and the electron crystal is pinned collectively. A strongly anisotropic screening of the Coulomb potential produces an unconventional linear in energy Coulomb gap and a new law of the variable-range hopping $-\ln\sigma \sim (T_1 / T)^{2/5}$. $T_1$ remains constant over a finite range of impurity concentrations. At smaller $N$ the 2/5-law is replaced by the Mott law, where the conductivity gets suppressed as $N$ goes down. Thus, the overall dependence of $\sigma$ on $N$ is nonmonotonic. In 1D, the granular-rod picture and the ES apply at all $N$. The conductivity decreases exponentially with $N$. Our theory provides a qualitative explanation for the transport in organic charge-density wave compounds.Comment: 20 pages, 7 figures. (v1) The abstract is abridged to 24 lines. For the full abstract, see the manuscript (v2) several changes in presentation per referee's comments. No change in result

From Luttinger to Fermi liquids in organic conductors

This chapter reviews the effects of interactions in quasi-one dimensional systems, such as the Bechgaard and Fabre salts, and in particular the Luttinger liquid physics. It discusses in details how transport measurements both d.c. and a.c. allow to probe such a physics. It also examine the dimensional crossover and deconfinement transition occurring between the one dimensional case and the higher dimensional one resulting from the hopping of electrons between chains in the quasi-one dimensional structure.Comment: To be published In the book "The Physics of Organic Conductors and Superconductors", Springer, 2007, ed. A. Lebe

Bottom pressure signals at the TAG deep-sea hydrothermal field : evidence for short-period, flow-induced ground deformation

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L19301, doi:10.1029/2009GL040006.Bottom pressure measurements acquired from the TAG hydrothermal field on the Mid-Atlantic Ridge (26°N) contain clusters of narrowband spectral peaks centered at periods from 22 to 53.2 minutes. The strongest signal at 53.2 min corresponds to 13 mm of water depth variation. Smaller, but statistically significant, signals were also observed at periods of 22, 26.5, 33.4, and 37.7 min (1–4 mm amplitude). These kinds of signals have not previously been observed in the ocean, and they appear to represent vertical motion of the seafloor in response to hydrothermal flow - similar in many ways to periodic terrestrial geysers. We demonstrate that displacements of 13 mm can be produced by relatively small flow-induced pressures (several kPa) if the source region is less than ∼100 m below the seafloor. We suggest that the periodic nature of the signals results from a non-linear relationship between fluid pore pressure and crustal permeability