1,444 research outputs found
Pseudogap, charge order, and pairing density wave at the hot spots in cuprate superconductors
We address the timely issue of the presence of charge ordering at the
hot-spots in the pseudo-gap phase of cuprate superconductors in the context of
an emergent SU(2)-symmetry which relates the charge and pairing sectors.
Performing the Hubbard-Stratonovich decoupling such that the free energy stays
always real and physically meaningful we exhibit three solutions of the
spin-fermion model at the hot spots. A careful examination of their stability
and free energy shows that, at low temperature, the system tends towards a
co-existence of charge density wave (CDW) and the composite order parameter
made of diagonal quadrupolar density wave and pairing fluctuations of Ref.
[Nat. Phys. , 1745 (2013)].The CDW is sensitive to the shape of the
Fermi surface in contrast to the diagonal quadrupolar order, which is immune to
it. SU(2) symmetry within the pseudo-gap phase also applies to the CDW state,
which therefore admits a pairing density pave counterpart breaking time
reversal symmetry.Comment: 15 pages, 15 figures, final version + typo corrected in Eq. (12
Charge orders, magnetism and pairings in the cuprate superconductors
We review the recent developments in the field of cuprate superconductors
with the special focus on the recently observed charge order in the underdoped
compounds. We introduce new theoretical developments following the study of the
antiferromagnetic (AF) quantum critical point (QCP) in two dimensions, in which
preemptive orders in the charge and superconducting (SC) sectors emerged, that
are in turn related by an SU(2) symmetry. We consider the implications of this
proliferation of orders in the underdoped region, and provide a study of the
type of fluctuations which characterize the SU(2) symmetry. We identify an
intermediate energy scale where the SU(2) pairing fluctuations are dominant and
argue that they are unstable towards the formation of a Resonant Peierls
Excitonic (RPE) state at the pseudogap (PG) temperature . We discuss the
implications of this scenario for a few key experiments.Comment: 16 pages, 17 figure
collective mode as A Raman resonance in cuprate superconductors
We discuss the possible existence a spin singlet excitation with charge
(-mode) originating the Raman resonance in cuprate
superconductors. This -mode relates the -wave superconducting singlet
pairing channel to a -wave charge channel. We show that the boson
forms a particle-particle bound state below the threshold of the
particle-hole continuum where is the maximum -wave gap. Within a
generalized random phase approximation and Bethe-Salpether approximation study,
we find that this mode has energies similar to the resonance observed by
Inelastic Neutron Scattering (INS) below the superconducting (SC) coherent peak
at in various SC cuprates compounds. We show that it is a very good
candidate for the resonance observed in Raman scattering below the
peak in the symmetry. Since the -mode sits in the channel,
it may be observable via Raman, X -ray or Electron Energy Loss Spectroscopy
probes
Strong competition between -loop-current order and -wave charge order along the diagonal direction in a two-dimensional hot spot model
We study the fate of the so-called -loop-current order that
breaks both time-reversal and parity symmetries in a two-dimensional hot spot
model with antiferromagnetically mediated interactions, using Fermi surfaces
relevant to the phenomenology of the cuprate superconductors. We start from a
three-band Emery model describing the hopping of holes in the CuO plane
that includes two hopping parameters and , local on-site
Coulomb interactions and and nearest-neighbor
couplings between the fermions in the copper [Cu] and
oxygen [O and O] orbitals. By focusing on the lowest-energy
band, we proceed to decouple the local interaction of the Cu orbital in
the spin channel using a Hubbard-Stratonovich transformation to arrive at the
interacting part of the so-called spin-fermion model. We also decouple the
nearest-neighbor interaction to introduce the order parameter of the
-loop-current order. In this way, we are able to construct a
consistent mean-field theory that describes the strong competition between the
composite order parameter made of a quadrupole-density-wave and -wave
pairing fluctuations proposed in Efetov \emph{et al.} [Nat. Phys. \textbf{9},
442 (2013)] with the -loop-current order parameter that is argued
to be relevant for explaining important aspects of the physics of the pseudogap
phase displayed in the underdoped cuprates.Comment: 16 pages, 5 figures. v2: minor revisions, references added. The
magnetic moment per unit-cell associated with the
-loop-current-phase is calculated and compared with experimental
results. Accepted for publication in Physical Review
The photometry of hollow light guides
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Light-pipes described in this paper guide light along an axis allowing it to escape from its surface for illumination purposes. Light is coupled into them by a beamer luminaire. The performance of a hollow light guide very much depends on the quality of the materials used to guide the light. The luminous characteristics of these materials influence a light-pipe’s overall performance. The first section of this paper describes measurement techniques for light incidence resolved measurements on materials. Common co-ordinate systems for describing the geometry and a data format to store the data are shown. The second section of this paper deals with light-pipe goniophotometry. A goniophotometer for light-pipes has been constructed at the Technical University of Berlin. To evaluate the results measurements are compared to these from a real installation
Die filling process simulation using discrete element method (DEM)
Powder compaction and sintering are important techniques for the mass production of geometrically complex parts. Powder is poured from a reservoir into the feeding shoe, which then passes the cavity one or more times thereby delivering powder into it. The powder is then compressed to create a relatively brittle green body. Finally, the green body is ejected from the cavity and sintered in a furnace where thermal activation below the melting point produces a fully dense structure. Necks form and grow between adjacent grains thereby eliminating the porosity of the part. In general, a consistent and uniform die filling process is always desirable. Heterogeneity during die filling can propagate through the subsequent processes and finally lead to serious product defects, such as cracking, low strength, distortion and shrinkage [1]. Capillary cohesion is known to influence strongly the strength and flow properties of granular materials. At low levels of water content, the water forms a discontinuous phase composed of interparticle bridges that are unevenly distributed in the bulk (the pendular state) [2]. For powder filling process these capillary forces may have strong influence in the particle dynamics and subsequent packing. An approach using discrete element method (DEM) simulation is proposed to reproduce die filling process and investigate process characteristics that affect final sand cake shape and may lead to in-homogeneities in powder during the filling process. Also an experimental apparatus able to reproduce the die filling process was built to validate numerical model. A coarse grain model is also necessary to reduce the model size (reduce the number of particles)
SOME RATS AND MICE OF THE MALAY ARCHIPELAGO
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Mediat. Inflamm.
There is increasing evidence that proteasomes have a biological role in the extracellular alveolar space, but inflammation could change their composition. We tested whether immunoproteasome protein-containing subpopulations are present in the alveolar space of patients with lung inflammation evoking the acute respiratory distress syndrome (ARDS). Bronchoalveolar lavage (BAL) supernatants and cell pellet lysate from ARDS patients (n = 28) and healthy subjects (n = 10) were analyzed for the presence of immunoproteasome proteins (LMP2 and LMP7) and proteasome subtypes by western blot, chromatographic purification, and 2D-dimensional gelelectrophoresis. In all ARDS patients but not in healthy subjects LMP7 and LMP2 were observed in BAL supernatants. Proteasomes purified from pooled ARDS BAL supernatant showed an altered enzyme activity ratio. Chromatography revealed a distinct pattern with 7 proteasome subtype peaks in BAL supernatant of ARDS patients that differed from healthy subjects. Total proteasome concentration in BAL supernatant was increased in ARDS (971 ng/mL perpendicular to 1116 versus 59 perpendicular to 25; P < 0.001), and all fluorogenic substrates were hydrolyzed, albeit to a lesser extent, with inhibition by epoxomicin (P = 0.0001). Thus, we identified for the first time immunoproteasome proteins and a distinct proteasomal subtype pattern in the alveolar space of ARDS patients, presumably in response to inflammation
Constraining the Hadronic Contributions to the Muon Anomalous Magnetic Moment
The mini-proceedings of the Workshop on "Constraining the hadronic
contributions to the muon anomalous magnetic moment" which included the "13th
meeting of the Radio MonteCarLow WG" and the "Satellite meeting R-Measurements
at BES-III" held in Trento from April 10th to 12th, 2013, are presented. This
collaboration meeting aims to bring together the experimental e+e- collider
communities from BaBar, Belle, BESIII, CMD2, KLOE, and SND, with theorists
working in the fields of meson transitions form factors, hadronic contributions
to (g-2)_\mu and effective fine structure constant, and development of Monte
Carlo generator and Radiative Corrections for precision e+e- and tau physics.Comment: 45 pages, 17 contributions. Editors: P. Masjuan and G. Venanzon
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