31,272 research outputs found
Multiferroicity in the frustrated spinel cuprate GeCuO
Different from other magnetically frustrated spinel systems,
GeCuO is a strongly tetragonal distorted spinel cuprate in which
edge-sharing CuO ribbons are running along alternating directions
perpendicular to the -axis. Here, GeCuO samples of high quality
were prepared via high pressure synthesis (at 4 GPa) and the corresponding
magnetic and dielectric properties were investigated. For the first time, we
observed a ferroelectric polarization emerging at T 33~K. Although
the ferroelectric polarization is weak in GeCuO (
0.2C/m), the existence of spin-induced multiferroicity provides a
strong constraint on the possible ground state magnetic structures and/or the
corresponding theoretical models of multiferroicity for GeCuO.Comment: https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.04140
Evolution of magnetic component in Yang-Mills condensate dark energy models
The evolution of the electric and magnetic components in an effective
Yang-Mills condensate dark energy model is investigated. If the electric field
is dominant, the magnetic component disappears with the expansion of the
Universe. The total YM condensate tracks the radiation in the earlier Universe,
and later it becomes thus is similar to the cosmological constant.
So the cosmic coincidence problem can be avoided in this model. However, if the
magnetic field is dominant, holds for all time, suggesting that it
cannot be a candidate for the dark energy in this case.Comment: 12 pages, 4 figures, minor typos correcte
Spectroscopic evidence for temperature-dependent convergence of light and heavy hole valence bands of PbQ (Q=Te, Se, S)
We have conducted temperature dependent Angle Resolved Photoemission
Spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS.
Our ARPES data provide direct evidence for the \emph{light} hole upper valence
bands (UVBs) and hitherto undetected \emph{heavy} hole lower valence bands
(LVBs) in these materials. An unusual temperature dependent relative movement
between these bands leads to a monotonic decrease in the energy separation
between their maxima with increasing temperature, which is referred as band
convergence and has long been believed to be the driving factor behind
extraordinary thermoelectric performances of these compounds at elevated
temperatures.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1404.180
Non-Markovian Fermionic Stochastic Schr\"{o}dinger Equation for Open System Dynamics
In this paper we present an exact Grassmann stochastic Schr\"{o}dinger
equation for the dynamics of an open fermionic quantum system coupled to a
reservoir consisting of a finite or infinite number of fermions. We use this
stochastic approach to derive the exact master equation for a fermionic system
strongly coupled to electronic reservoirs. The generality and applicability of
this Grassmann stochastic approach is justified and exemplified by several
quantum open system problems concerning quantum decoherence and quantum
transport for both vacuum and finite-temperature fermionic reservoirs. We show
that the quantum coherence property of the quantum dot system can be profoundly
modified by the environment memory.Comment: 10.5 pages, 3 figure
Orbital selectivity causing anisotropy and particle-hole asymmetry in the charge density wave gap of -TaS
We report an in-depth Angle Resolved Photoemission Spectroscopy (ARPES) study
on -TaS, a canonical incommensurate Charge Density Wave (CDW) system.
This study demonstrates that just as in related incommensurate CDW systems,
-TaSe and -NbSe, the energy gap () of
-TaS is localized along the K-centered Fermi surface barrels and is
particle-hole asymmetric. The persistence of even at
temperatures higher than the CDW transition temperature
in -TaS, reflects the similar pseudogap (PG) behavior observed
previously in -TaSe and -NbSe. However, in sharp contrast to
-NbSe, where is non-zero only in the vicinity
of a few "hot spots" on the inner K-centered Fermi surface barrels,
in -TaS is non-zero along the entirety of both
K-centered Fermi surface barrels. Based on a tight-binding model, we attribute
this dichotomy in the momentum dependence and the Fermi surface specificity of
between otherwise similar CDW compounds to the
different orbital orientations of their electronic states that are involved in
CDW pairing. Our results suggest that the orbital selectivity plays a critical
role in the description of incommensurate CDW materials.Comment: 6 pages, 4 figure
VOFilter, Bridging Virtual Observatory and Industrial Office Applications
VOFilter is an XML based filter developed by the Chinese Virtual Observatory
project to transform tabular data files from VOTable format into OpenDocument
format. VOTable is an XML format defined for the exchange of tabular data in
the context of the Virtual Observatory (VO). It is the first Proposed
Recommendation defined by International Virtual Observatory Alliance, and has
obtained wide support from both the VO community and many Astronomy projects.
OpenOffice.org is a mature, open source, front office applications suite with
the advantage of native support of industrial standard OpenDocument XML file
format. Using the VOFilter, VOTable files can be loaded in OpenOffice.org Calc,
a spreadsheet application, and then displayed and analyzed as other spreadsheet
files. Here, the VOFilter acts as a connector, bridging the coming VO with
current industrial office applications. Virtual Observatory and technical
background of the VOFilter are introduced. Its workflow, installation and usage
are presented. Existing problems and limitations are also discussed together
with the future development plans.Comment: Accepted for publication in ChJAA (9 pages, 2 figures, 185KB
Tidal impacts on primary production in the North Sea
This study highlights the importance of tides in controlling the spatial and
temporal distributions of phytoplankton and other factors related to growth,
such as nutrients and light availability. To quantify the responses of net
primary production (NPP) to tidal forcing, we conducted scenario model
simulations considering M2 and S2 tidal constituents using the
physical–biogeochemical coupled model ECOSMO (ECOSystem MOdel). The results were
analyzed with respect to a reference simulation without tidal forcing, with
particular focus on the spatial scale of the tidally induced changes. Tidal
forcing regulates the mixing–stratification processes in shelf seas such as
the North Sea and hence also influences ecosystem dynamics. In principle, the
results suggest three different response types with respect to primary
production: (i)Â in southern shallow areas with strong tidal energy
dissipation, tidal mixing dilutes phytoplankton concentrations in the upper
water layers and thereby decreases NPP. Additionally, tides increase
turbidity in near-coastal shallow areas, which has the potential to further
hamper NPP. (ii)Â In the frontal region of the southern North Sea, which is a
transition zone between stratified and mixed areas, tidal mixing infuses
nutrients into the surface mixed layer and resolves summer nutrient
depletion, thus sustaining the NPP during the summer season after spring
bloom nutrient depletion. (iii)Â In the northern North Sea, the NPP response
to tidal forcing is limited. Additionally, our simulations indicate that
spring bloom phenology is impacted by tidal forcing, leading to a later onset
of the spring bloom in large parts of the North Sea and to generally higher
spring bloom peak phytoplankton biomasses. By testing the related changes in
stratification, light conditions and grazing pressure, we found that all
three factors potentially contribute to the change in spring bloom phenology
with clear local differences. Finally, we also analyzed the impact of the
spring–neap tidal cycle on NPP. The annual mean impact of spring–neap tidal
forcing on NPP is limited. However, locally, we found substantial differences
in NPP either in phase or anti-phase with the spring–neap tidal cycle. These
differences could be attributed to locally different dominant factors such as
light or nutrient availability during spring tides. In general, we conclude
that in shallow shelf seas such as the North Sea, intensified vertical mixing
induced by tidal forcing could either promote NPP by counteracting nutrient
depletion or hinder NPP by deteriorating the light environment because of the
resuspension and mixing of suspended matter into the euphotic zone.</p
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