215 research outputs found
A model for liquid-striped liquid phase separation in liquids of anisotropic polarons
The phase separation between a striped polaron liquid at the particular
density and a high density polaron liquid is described by a modified Van der
Waals scheme. The striped polaron liquid represents the pseudo gap matter or
Wigner-like polaron phase at 1/8 doping in cuprate superconductors. The model
includes the tendency of pseudo- Jahn-Teller polarons to form anisotropic
directional bonds at a preferential volume with the formation of different
liquid phases. The model gives the coexistence of a first low density polaron
striped liquid and a second high density liquid that appears in cuprate
superconductors for doping larger than 1/8. We discuss how the strength of
anisotropic bonds controls the variation the phase separation scenarios for
complex systems in the presence of a quantum critical point where the phase
separation vanishes.Comment: 10 pages, 3 figure
Multiorbital analysis of the effects of uniaxial and hydrostatic pressure on in the single-layered cuprate superconductors
The origin of uniaxial and hydrostatic pressure effects on in the
single-layered cuprate superconductors is theoretically explored. A two-orbital
model, derived from first principles and analyzed with the fluctuation exchange
approximation gives axial-dependent pressure coefficients, , , with a hydrostatic response
for both La214 and Hg1201 cuprates, in qualitative
agreement with experiments. Physically, this is shown to come from a unified
picture in which higher is achieved with an "orbital distillation",
namely, the less the main band is hybridized with the
and orbitals higher the . Some implications for obtaining higher
materials are discussed.Comment: 6pages, 4 figure
Flux dynamics in NdO1-xFxFeAs bulk sample
We present data of multi harmonic magneto-dynamic experiments. In particular,
we performed ac magnetic susceptibility experiments on layered pnictide-oxide
quaternary compound NdOFeAs doped with fluorine. The experiments allow measure
the critical temperature and probe the flux dynamic behavior using the third
harmonic component of the ac susceptibility of a NdF0.16FeAsO0.84 bulk sample
as a function of temperature and frequency of the applied ac magnetic fields.
Measured signals are connected with the non-linear superconducting flux dynamic
behavior and are characterized by a flux critical states sustaining a
superconducting critical current. In this framework the irreversibility line
that describes the stable superconducting state has been extracted from the
onset of the third harmonic signal vs. frequency. Finally we present also the
analysis of the flux dynamic dimensionality in the investigated sample.Comment: 10 pages, 5 figure
Vesicular PtdIns(3,4,5) P 3 and Rab7 are key effectors of sea urchin zygote nuclear membrane fusion
Regulation of nuclear envelope (NE) dynamics is an important example of the universal phenomena of membrane fusion. The signalling molecules involved in nuclear membrane fusion may also be conserved in the formation of both pronuclear and zygote NEs in the fertilised egg. Here, we determine that Class I PI3-kinases are needed for in vitro nuclear envelope formation. We show that, in vivo, PtdIns(3,4,5)P3 is transiently located in vesicles around the male pronucleus at the time of nuclear envelope formation and around male and female pronuclei prior to membrane fusion. We illustrate that Class I PI3-kinase activity is also necessary for fusion of the female and male pronuclear membranes. We demonstrate, by coincidence amplified-FRET monitored by fluorescence lifetime imaging microscopy (FLIM), a protein-lipid interaction of Rab7 GTPase and PtdIns(3,4,5)P3 occurring during pronuclear membrane fusion to create the zygote nuclear envelope. We present a working model, which includes several molecular steps in the pathways controlling fusion of NE membranes.</jats:p
Inhomogeneity of charge density wave order and quenched disorder in a high Tc superconductor
It has recently been established that the high temperature (high-Tc)
superconducting state coexists with short-range charge-density-wave order and
quenched disorder arising from dopants and strain. This complex, multiscale
phase separation invites the development of theories of high temperature
superconductivity that include complexity. The nature of the spatial interplay
between charge and dopant order that provides a basis for nanoscale phase
separation remains a key open question, because experiments have yet to probe
the unknown spatial distribution at both the nanoscale and mescoscale (between
atomic and macroscopic scale). Here we report micro X-ray diffraction imaging
of the spatial distribution of both the charge-density-wave puddles (domains
with only a few wavelengths) and quenched disorder in HgBa2CuO4+y, the single
layer cuprate with the highest Tc, 95 kelvin. We found that the
charge-density-wave puddles, like the steam bubbles in boiling water, have a
fat-tailed size distribution that is typical of self-organization near a
critical point. However, the quenched disorder, which arises from oxygen
interstitials, has a distribution that is contrary to the usual assumed random,
uncorrelated distribution. The interstitials-oxygen-rich domains are spatially
anti-correlated with the charge-density-wave domains, leading to a complex
emergent geometry of the spatial landscape for superconductivity.Comment: 11 pages, 3 figure
Spatial Regulation of Membrane Fusion Controlled by Modification of Phosphoinositides
Membrane fusion plays a central role in many cell processes from vesicular
transport to nuclear envelope reconstitution at mitosis but the mechanisms that
underlie fusion of natural membranes are not well understood. Studies with
synthetic membranes and theoretical considerations indicate that accumulation of
lipids characterised by negative curvature such as diacylglycerol (DAG)
facilitate fusion. However, the specific role of lipids in membrane fusion of
natural membranes is not well established. Nuclear envelope (NE) assembly was
used as a model for membrane fusion. A natural membrane population highly
enriched in the enzyme and substrate needed to produce DAG has been isolated and
is required for fusions leading to nuclear envelope formation, although it
contributes only a small amount of the membrane eventually incorporated into the
NE. It was postulated to initiate and regulate membrane fusion. Here we use a
multidisciplinary approach including subcellular membrane purification,
fluorescence spectroscopy and Förster resonance energy transfer
(FRET)/two-photon fluorescence lifetime imaging microscopy (FLIM) to demonstrate
that initiation of vesicle fusion arises from two unique sites where these
vesicles bind to chromatin. Fusion is subsequently propagated to the endoplasmic
reticulum-derived membranes that make up the bulk of the NE to ultimately
enclose the chromatin. We show how initiation of multiple vesicle fusions can be
controlled by localised production of DAG and propagated bidirectionally.
Phospholipase C (PLCÎł), GTP hydrolysis and
(phosphatidylinsositol-(4,5)-bisphosphate (PtdIns(4,5)P2) are
required for the latter process. We discuss the general implications of membrane
fusion regulation and spatial control utilising such a mechanism
Two-bands superconductivity with intra- and interband pairing for synthetic superlattices
We consider a model for superconductivity in a two-band superconductor,
having an anisotropic electronic structure made of two partially overlapping
bands with a first hole-like and a second electron-like fermi surface. In this
pairing scenario, driven by the interplay between interband and
intraband pairing terms, we have solved the two gap equations at the
critical temperature and calculate and the chemical potential
as a function of the number of carriers for various values of pairing
interactions, , , and . The results show the
complexity of the physics of condensates with multiple order parameters with
the chemical potential near band edges.Comment: 6 pages, 2 figure
- âŠ