170 research outputs found
Partially-disordered photonic-crystal thin films for enhanced and robust photovoltaics
We present a general framework for the design of thin-film photovoltaics
based on a partially-disordered photonic crystal that has both enhanced
absorption for light trapping and reduced sensitivity to the angle and
polarization of incident radiation. The absorption characteristics of different
lattice structures are investigated as an initial periodic structure is
gradually perturbed. We find that an optimal amount of disorder controllably
introduced into a multi-lattice photonic crystal causes the characteristic
narrow-band, resonant peaks to be broadened resulting in a device with enhanced
and robust performance ideal for typical operating conditions of photovoltaic
applications.Comment: 5 pages, 4 figure
Magnetotransport study of the charged stripes in high-T_c cuprates
We present a study of the in-plane and out-of-plane magnetoresistance (MR) in
heavily-underdoped, antiferromagnetic YBa_{2}Cu_{3}O_{6+x}, which reveals a
variety of striking features. The in-plane MR demonstrates a "d-wave"-like
anisotropy upon rotating the magnetic field H within the ab plane. With
decreasing temperature below 20-25 K, the system acquires memory: exposing a
crystal to the magnetic field results in a persistent in-plane resistivity
anisotropy. The overall features can be explained by assuming that the CuO_2
planes contain a developed array of stripes accommodating the doped holes, and
that the MR is associated with the field-induced topological ordering of the
stripes.Comment: 4 pages, 5 figures, invited paper at M2S-HTSC-VI, to be published in
Physics C (Proceedings of the International Conference on Materials and
Mechanisms of Superconductivity, High Temperature Superconductors VI
(M2S-HTSC-VI), Houston, Feb 20-25, 2000
ROCK-I regulates closure of the eyelids and ventral body wall by inducing assembly of actomyosin bundles
Rho-associated kinase (ROCK) I mediates signaling from Rho to the actin cytoskeleton. To investigate the in vivo functions of ROCK-I, we generated ROCK-I–deficient mice. Loss of ROCK-I resulted in failure of eyelid closure and closure of the ventral body wall, which gave rise to the eyes open at birth and omphalocele phenotypes in neonates. Most ROCK-I−/− mice died soon after birth as a result of cannibalization of the omphalocele by the mother. Actin cables that encircle the eye in the epithelial cells of the eyelid were disorganized and accumulation of filamentous actin at the umbilical ring was impaired, with loss of phosphorylation of the myosin regulatory light chain (MLC) at both sites, in ROCK-I−/− embryos. Stress fiber formation and MLC phosphorylation induced by EGF were also attenuated in primary keratinocytes from ROCK-I−/− mice. These results suggest that ROCK-I regulates closure of the eyelids and ventral body wall through organization of actomyosin bundles
Electrical Resistivity Anisotropy from Self-Organized One-Dimensionality in High-Temperature Superconductors
We investigate the manifestation of the stripes in the in-plane resistivity
anisotropy in untwinned single crystals of La_{2-x}Sr_{x}CuO_{4} (x = 0.02 -
0.04) and YBa_{2}Cu_{3}O_{y} (y = 6.35 - 7.0). It is found that both systems
show strongly temperature-dependent in-plane anisotropy in the lightly
hole-doped region and that the anisotropy in YBa_{2}Cu_{3}O_{y} grows with
decreasing y below about 6.60 despite the decreasing orthorhombicity, which
gives most direct evidence that electrons self-organize into a macroscopically
anisotropic state. The transport is found to be easier along the direction of
the spin stripes already reported, demonstrating that the stripes are
intrinsically conducting in cuprates.Comment: 5 pages, 4 figures (including one color figure), final version
accepted for publication in Phys. Rev. Let
A series of ENU-induced single-base substitutions in a long-range cis-element altering Sonic hedgehog expression in the developing mouse limb bud
AbstractMammal–fish-conserved-sequence 1 (MFCS1) is a highly conserved sequence that acts as a limb-specific cis-acting regulator of Sonic hedgehog (Shh) expression, residing 1 Mb away from the Shh coding sequence in mouse. Using gene-driven screening of an ENU-mutagenized mouse archive, we obtained mice with three new point mutations in MFCS1: M101116, M101117, and M101192. Phenotype analysis revealed that M101116 mice exhibit preaxial polydactyly and ectopic Shh expression at the anterior margin of the limb buds like a previously identified mutant, M100081. In contrast, M101117 and M101192 show no marked abnormalities in limb morphology. Furthermore, transgenic analysis revealed that the M101116 and M100081 sequences drive ectopic reporter gene expression at the anterior margin of the limb bud, in addition to the normal posterior expression. Such ectopic expression was not observed in the embryos carrying a reporter transgene driven by M101117. These results suggest that M101116 and M100081 affect the negative regulatory activity of MFCS1, which suppresses anterior Shh expression in developing limb buds. Thus, this study shows that gene-driven screening for ENU-induced mutations is an effective approach for exploring the function of conserved, noncoding sequences and potential cis-regulatory elements
Normal-state conductivity in underdoped La_{2-x}Sr_xCuO_4 thin films: Search for nonlinear effects related to collective stripe motion
We report a detailed study of the electric-field dependence of the
normal-state conductivity in La_{2-x}Sr_xCuO_4 thin films for two
concentrations of doped holes, x=0.01 and 0.06, where formation of diagonal and
vertical charged stripes was recently suggested. In order to elucidate whether
high electric fields are capable of depinning the charged stripes and inducing
their collective motion, we have measured current-voltage characteristics for
various orientations of the electric field with respect to the crystallographic
axes. However, even for the highest possible fields (~1000 V/cm for x=0.01 and
\~300 V/cm for x=0.06) we observed no non-linear-conductivity features except
for those related to the conventional Joule heating of the films. Our analysis
indicates that Joule heating, rather than collective electron motion, may also
be responsible for the non-linear conductivity observed in some other 2D
transition-metal oxides as well. We discuss that a possible reason why moderate
electric fields fail to induce a collective stripe motion in layered oxides is
that fairly flexible and compressible charged stripes can adjust themselves to
the crystal lattice and individual impurities, which makes their pinning much
stronger than in the case of conventional rigid charge-density waves.Comment: 10 pages, 10 figures, accepted for publication in Phys. Rev.
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