254 research outputs found
Georg Pfeffer (2016) Verwandtschaft als Verfassung: Unbürokratische Muster öffentlicher Ordnung. Baden Baden: Nomos
Buchrezension
Rezension: Georg Pfeffer: Verwandtschaft als Verfassung: Unbürokratische Muster öffentlicher Ordnung
Georg Pfeffer (2016) Verwandtschaft als Verfassung: Unbürokratische Muster öffentlicher Ordnung. Baden Baden: Nomos
Buchrezension
Ultrafast gap dynamics upon photodoping the Mott-insulating phase of a two-dimensional organic charge-transfer salt
We investigate experimentally the ultrafast changes in the spectral response
of the Mott insulator -(BEDT-TTF)Cu[N(CN)]Cl (-Cl) upon
photodoping with intense excitation at 1.6 eV and probing with continuum pulses
simultaneously covering both the terahertz and infrared (IR) ranges (from 0 to
0.6 eV). A quantitative analysis of the differential reflectivity using a
multi-band Lorentzian model provide absolute changes in spectral weights and
objective global time constants for the relaxation vs. temperature. The
transient conductivity spectra deduced from the analysis suggest that the
transient photoinduced spectral weight is dominated by a progressive closure of
the Mott gap with increasing excitation density, i.e. due to changes in the
inter-Hubbard-band absorption by the remaining singly occupied states. We
critically examine this scenario compared to that proposed previously, whereby
the low-energy spectral weight is attributed to a Drude-like response of
photoexcited doublons/holons. We also consider the observed slowing down of the
relaxation rate with increasing excitation density, and temperature dependence
of the initial doublon/holon density in terms of the phonon-mediated gap
recombination model
Obligatory amino acid exchange via systems b0,+ like and y+L-like. A tertiary active transport mechanism for renal re-absorption of cystine and diabsic amino acids
Mutations in the rBAT gene cause type I cystinuria, a common inherited aminoaciduria of cystine and dibasic amino acids due to their defective renal and intestinal reabsorption (Calonge, M. J., Gasparini, P., Chillarón, J., Chillón, M., Gallucci, M., Rousaud, F., Zelante, L., Testar, X., Dallapiccola, B., Di Silverio, F., Barceló, P., Estivill, X., Zorzano, A., Nunes, V., and Palacín, M. (1994) Nat. Genet. 6, 420-426; Calonge, M. J., Volipini, V., Bisceglia, L., Rousaud, F., De Sanctis, L., Beccia, E., Zelante, L., Testar, X., Zorzano, A., Estivill, X., Gasparini, P., Nunes, V., and Palacín, M.(1995) Proc. Natl. Acad. Sci. U. S. A. 92, 9667-9671). One important question that remains to be clarified is how the apparently non-concentrative system bo,+-like, associated with rBAT expression, participates in the active renal reabsorption of these amino acids. Several studies have demonstrated exchange of amino acids induced by rBAT in Xenopus oocytes. Here we offer evidence that system bo,+-like is an obligatory amino acid exchanger in oocytes and in the 'renal proximal tubular' cell line OK. System bo, +-like showed a 1:1 stoichiometry of exchange, and the hetero-exchange dibasic (inward) with neutral (outward) amino acids were favored in oocytes. Obligatory exchange of amino acids via system bo,+-like fully explained the amino acid-induced current in rBAT-injected oocytes. Exchange via system bo,+-like is coupled enough to ensure a specific accumulation of substrates until the complete replacement of the internal oocyte substrates. Due to structural and functional analogies of the cell surface antigen 4F2hc to rBAT, we tested for amino acid exchange via system y+L-like. 4F2hc-injected oocytes accumulated substrates to a level higher than CAT1-injected oocytes (i.e. oocytes expressing system y+) and showed exchange of amino acids with the substrate specificity of system y+L and L-leucine-induced outward currents in the absence of extracellular sodium. In contrast to L-arginine, system y+L-like did not mediate measurable L-leucine efflux from the oocyte. We propose a role of systems bo,+-like and y+L-like in the renal reabsorption of cystine and dibasic amino acids that is based on their active tertiary transport mechanism and on the apical and basolateral localization of rBAT and 4F2hc, respectively, in the epithelial cells of the proximal tubule of the nephron
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