The spin dynamics of the underdoped superconductor YBa 2 Cu 3 O 6.7 (T c ϳ 67 K) was revealed to have an incommensurate wave vector dependence with "pillars" in the dispersion relation at the positions ( 1 2 6 d, 1 2 , 0) and ( 1 2 , 1 2 6 d, 0). This is the same symmetry as that found in La 22x Sr x CuO 4 . The value of the incommensurability, d 0.11 6 0.01 r.l.u ϳ 1 8 , is very close to the value expected from the hole concentration. These results have demonstrated that the spin dynamics do not depend on the details of Fermi surface but have an analogous form to that for the proposed stripe domain structure.
Carbon-substituted MgB 2 single crystals, Mg(B 1-x C x ) 2 of 0.3-1.0 mm size were grown for x=0.02-0.15 by a high-pressure technique. The doping dependence of lattice constants studied in a range of x=0.0-0.2 shows a monotonic decrease in a, while the c parameter remains almost invariant. Using X -ray diffraction and Auger electron spectroscopy, the solubility limit of C in MgB 2 was estimated to be about 15±1%, which is substantially larger than that reported for the polycrystalline samples synthesized by encapsulation techniques.Measurements of temperature dependence of magnetization and resistivity showed a dramatic decrease in T c with C -substitution, followed by complete suppression of superconductivity for x>0.125. Resistivity measurements in magnetic fields parallel and perpendicular to the basal plane of the crystals showed a nearly isotropic state in the heavily -doped crystals (x>0.1).
With significantly improved sample quality and instrumental resolution, we clearly identify in the (π,0) ARPES spectra from YBa2Cu3O6.993, in the superconducting state, the long-sought 'peakdip-hump' structure. This advance allows us to investigate the large a-b anisotropy of the in-plane electronic structure including, in particular, a 50% difference in the magnitude of the superconducting gap that scales with the energy position of the hump feature. This anisotropy, likely induced by the presence of the CuO chains, raises serious questions about attempts to quantitatively explain the YBa2Cu3O 7−δ data from various experiments using models based on a perfectly square lattice.PACS numbers: 74.25.Jb, 74.72.Bk, 79.60.Bm High-temperature superconductivity (HTSC) is intimately related to the CuO 2 plane, which is the only common structural feature in all cuprates. This fact has led most of the proposed microscopic theories to assume a CuO 2 square planar structure. However, for the practical reason of sample quality, some of the most important and defining experiments have been performed on YBa 2 Cu 3 O 7−δ (Y123), which does not have a square lattice, but rather an orthorhombic structure (b/a ≈ 1.015), caused by the presence of a CuO chain layer [1]. This orthorhombicity, according to LDA calculation [2], should result in significant anisotropy in the in-plane electronic structure (this term will be used throughout this paper to refer to the electronic states associated with the CuO 2 plane), making it problematic to compare theories based on a square lattice with experimental data from Y123. Therefore, it is crucial to quantify the effect of orthorhombicity, if any, on the in-plane electronic structure in Y123. The problem is that angle-resolved photoemission spectroscopy (ARPES), being a uniquely powerful tool for this important task, has, until now, not been particularly effective for the study of Y123 [3]. The important 'peak-dip-hump' structure, which is seen routinely in Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) [4] has never been observed in Y123. This absence, together with the presence of a surface state [5], raises questions about ARPES data from Y123, and the universality of the superconducting peak in the cuprates.This paper reports a breakthrough in this important issue, made possible by significantly improved sample quality and instrumental resolution. By isolating a surface state peak near the Fermi energy (E F ), we can clearly resolve a 'peak-dip-hump' structure in the ARPES spectra around (π, 0) in Y123 that resembles the superconducting peak observed in Bi2212 [4]. More significantly, we find a strong a-b asymmetry of the in-plane electronic structure, such as the superconducting gap magnitude, which differs by about 50%. We argue that such a strong inplane a-b anisotropy should be taken into account when interpreting experiments performed on Y123.ARPES experiments were carried out at beamline 5-4 at SSRL, which is equipped with a normal-incidencemonochromator and a SCIENTA SES-200 analyzer. Untwinned Y...
Orally ingested collagen undergoes degradation to small di-or tripeptides, which are detected in circulating blood 2 h after ingestion. The influence of collagen-derived peptides on dermal extracellular matrix components and cell proliferation was studied using cultured human dermal fibroblasts. Of the various collagenous peptides tested here, the dipeptide proline-hydroxyproline (Pro-Hyp) enhanced cell proliferation (1.5-fold) and hyaluronic acid synthesis (3.8-fold) at a dose of 200 nmol ⁄ mL. This was concomitant with a 2.3-fold elevation of hyaluronan synthase 2 (HAS2) mRNA levels. Small interfering RNA (siRNA)-mediated knockdown of the HAS2 gene in human dermal fibroblasts inhibited Pro-Hyp-induced HAS2 mRNA transcription and cell mitotic activity. Addition of genistein or H7, a protein kinase inhibitor, abolished the Pro-Hyp-induced HAS2 mRNA stimulation. Pro-Hyp elevated phosphorylation of signal transducer and activator of transcription 3 (STAT3) within a short time period (60 min). These results suggest that Pro-Hyp stimulates both cell mitotic activity and hyaluronic acid synthesis, which is mediated by activation of HAS2 transcription.
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