4,611 research outputs found
Break up of heavy fermions at an antiferromagnetic instability
We present results of high-resolution, low-temperature measurements of the
Hall coefficient, thermopower, and specific heat on stoichiometric YbRh2Si2.
They support earlier conclusions of an electronic (Kondo-breakdown) quantum
critical point concurring with a field induced antiferromagnetic one. We also
discuss the detachment of the two instabilities under chemical pressure. Volume
compression/expansion (via substituting Rh by Co/Ir) results in a
stabilization/weakening of magnetic order. Moderate Ir substitution leads to a
non-Fermi-liquid phase, in which the magnetic moments are neither ordered nor
screened by the Kondo effect. The so-derived zero-temperature global phase
diagram promises future studies to explore the nature of the Kondo breakdown
quantum critical point without any interfering magnetism.Comment: minor changes, accepted for publication in JPS
Long range order and two-fluid behavior in heavy electron materials
The heavy electron Kondo liquid is an emergent state of condensed matter that
displays universal behavior independent of material details. Properties of the
heavy electron liquid are best probed by NMR Knight shift measurements, which
provide a direct measure of the behavior of the heavy electron liquid that
emerges below the Kondo lattice coherence temperature as the lattice of local
moments hybridizes with the background conduction electrons. Because the
transfer of spectral weight between the localized and itinerant electronic
degrees of freedom is gradual, the Kondo liquid typically coexists with the
local moment component until the material orders at low temperatures. The
two-fluid formula captures this behavior in a broad range of materials in the
paramagnetic state. In order to investigate two-fluid behavior and the onset
and physical origin of different long range ordered ground states in heavy
electron materials, we have extended Knight shift measurements to
URuSi, CeIrIn and CeRhIn. In CeRhIn we find that the
antiferromagnetic order is preceded by a relocalization of the Kondo liquid,
providing independent evidence for a local moment origin of antiferromagnetism.
In URuSi the hidden order is shown to emerge directly from the Kondo
liquid and so is not associated with local moment physics. Our results imply
that the nature of the ground state is strongly coupled with the hybridization
in the Kondo lattice in agreement with phase diagram proposed by Yang and
Pines.Comment: 9 pages, 13 figure
Power spectrum for the Bose-Einstein condensate dark matter
We assume that dark matter is composed of scalar particles that form a
Bose-Einstein condensate (BEC) at some point during the cosmic evolution.
Afterwards, cold dark matter is in the form of a condensate and behaves
slightly different from the standard dark matter component. We study the large
scale perturbative dynamics of the BEC dark matter in a model where this
component coexists with baryonic matter and cosmological constant. The
perturbative dynamics is studied using neo- Newtonian cosmology (where the
pressure is dynamically relevant for the homogeneous and isotropic background)
which is assumed to be correct for small values of the sound speed. We show
that BEC dark matter effects can be seen in the matter power spectrum if the
mass of the condensate particle lies in the range 15meV < m < 700meV leading to
a small, but perceptible, excess of power at large scales.Comment: 7 pages, 4 figures, Accepted for publication in Physics Letters
The role of particle, energy and momentum losses in 1D simulations of divertor detachment
A new 1D divertor plasma code, SD1D, has been used to examine the role of recombination, radiation, and momentum exchange in detachment. Neither momentum or power losses by themselves are found to be sufficient to produce a reduction in target ion flux in detachment (flux rollover); radiative power losses are required to a) limit and reduce the ionization source and b) access low-target temperature, T_target, conditions for volumetric momentum losses. Recombination is found to play little role at flux rollover, but as T_target drops to temperatures around 1eV, it becomes a strong ion sink. In the case where radiative losses are dominated by hydrogen, the detachment threshold is identified as a minimum gradient of the energy cost per ionisation with respect to T_target. This is also linked to thresholds in T_target and in the ratio of upstream pressure to power flux. A system of determining the detached condition is developed such that the divertor solution at a given T_target (or lack of one) is determined by the simultaneous solution of two equations for target ion current - one dependent on power losses and the other on momentum. Depending on the detailed momentum and power loss dependence on temperature there are regions of T_target where there is no solution and the plasma 'jumps' from high to low T_target states. The novel analysis methods developed here provide an intuitive way to understand complex detachment phenomena, and can potentially be used to predict how changes in the seeding impurity used or recycling aspects of the divertor can be utilised to modify the development of detachment
The role of particle, energy and momentum losses in 1D simulations of divertor detachment
A new 1D divertor plasma code, SD1D, has been used to examine the role of recombination, radiation, and momentum exchange in detachment. Neither momentum or power losses by themselves are found to be sufficient to produce a reduction in target ion flux in detachment (flux rollover); radiative power losses are required to a) limit and reduce the ionization source and b) access low-target temperature, T_target, conditions for volumetric momentum losses. Recombination is found to play little role at flux rollover, but as T_target drops to temperatures around 1eV, it becomes a strong ion sink. In the case where radiative losses are dominated by hydrogen, the detachment threshold is identified as a minimum gradient of the energy cost per ionisation with respect to T_target. This is also linked to thresholds in T_target and in the ratio of upstream pressure to power flux. A system of determining the detached condition is developed such that the divertor solution at a given T_target (or lack of one) is determined by the simultaneous solution of two equations for target ion current - one dependent on power losses and the other on momentum. Depending on the detailed momentum and power loss dependence on temperature there are regions of T_target where there is no solution and the plasma 'jumps' from high to low T_target states. The novel analysis methods developed here provide an intuitive way to understand complex detachment phenomena, and can potentially be used to predict how changes in the seeding impurity used or recycling aspects of the divertor can be utilised to modify the development of detachment
Stripes and electronic quasiparticles in the pseudogap state of cuprate superconductors
This article is devoted to a discussion of stripe and electron-nematic order
and their connection to electronic properties in the pseudogap regime of
copper-oxide superconductors. We review basic properties of these
symmetry-breaking ordering phenomena as well as proposals which connect them to
quantum-oscillation measurements. Experimental data indicate that these orders
are unlikely to be the cause of the pseudogap phenomenon, implying that they
occur on top of the pseudogap state which itself is of different origin.
Specifically, we discuss the idea that the non-superconducting pseudogap ground
state hosts electron-like quasiparticles which coexist with a spin liquid,
realizing a variant of a fractionalized Fermi liquid. We speculate on how
stripe order in such a pseudogap state might offer a consistent description of
ARPES, NMR, quantum-oscillation, and transport data.Comment: 15 pages, 6 figs. Article prepared for a Physica C special issue on
"Stripes and Electronic Liquid Crystals
Phenotypic and functional analyses show stem cell-derived hepatocyte-like cells better mimic fetal rather than adult hepatocytes
Background & Aims: Hepatocyte-like cells (HLCs), differentiated from pluripotent stem cells by the use of soluble factors, can model human liver function and toxicity. However, at present HLC maturity and whether any deficit represents a true fetal state or aberrant differentiation is unclear and compounded by comparison to potentially deteriorated adult hepatocytes. Therefore, we generated HLCs from multiple lineages, using two different protocols,
for direct comparison with fresh fetal and adult hepatocytes.
Methods: Protocols were developed for robust differentiation. Multiple transcript, protein and functional analyses compared HLCs to fresh human fetal and adult hepatocytes.
Results: HLCs were comparable to those of other laboratories by multiple parameters. Transcriptional changes during differentiation mimicked human embryogenesis and showed more similarity to pericentral than periportal hepatocytes. Unbiased proteomics demonstrated greater proximity to liver than 30 other human organs or tissues. However, by comparison to fresh material,
HLC maturity was proven by transcript, protein and function to be fetal-like and short of the adult phenotype. The expression of 81% phase 1 enzymes in HLCs was significantly upregulated and half were statistically not different from fetal hepatocytes. HLCs secreted albumin and metabolized testosterone (CYP3A) and dextrorphan (CYP2D6) like fetal hepatocytes. In seven bespoke tests,
devised by principal components analysis to distinguish fetal from adult hepatocytes, HLCs from two different source laboratories consistently demonstrated fetal characteristics.
Conclusions: HLCs from different sources are broadly comparable with unbiased proteomic evidence for faithful differentiation down the liver lineage. This current phenotype mimics human fetal rather than adult hepatocytes
On the multi-orbital band structure and itinerant magnetism of iron-based superconductors
This paper explains the multi-orbital band structures and itinerant magnetism
of the iron-pnictide and chalcogenides. We first describe the generic band
structure of an isolated FeAs layer. Use of its Abelian glide-mirror group
allows us to reduce the primitive cell to one FeAs unit. From
density-functional theory, we generate the set of eight Fe and As
localized Wannier functions for LaOFeAs and their tight-binding (TB)
Hamiltonian, . We discuss the topology of the bands, i.e. allowed and
avoided crossings, the origin of the d6 pseudogap, as well as the role of the
As orbitals and the elongation of the FeAs tetrahedron. We then
couple the layers, mainly via interlayer hopping between As orbitals,
and give the formalism for simple and body-centered tetragonal stackings. This
allows us to explain the material-specific 3D band structures. Due to the high
symmetry, several level inversions take place as functions of or
pressure, resulting in linear band dispersions (Dirac cones). The underlying
symmetry elements are, however, easily broken, so that the Dirac points are not
protected, nor pinned to the Fermi level. From the paramagnetic TB Hamiltonian,
we form the band structures for spin spirals with wavevector by coupling
and . The band structure for stripe order is studied as a
function of the exchange potential, , using Stoner theory. Gapping of
the Fermi surface (FS) for small requires matching of FS dimensions
(nesting) and -orbital characters. The origin of the propeller-shaped FS is
explained. Finally, we express the magnetic energy as the sum over
band-structure energies, which enables us to understand to what extent the
magnetic energies might be described by a Heisenberg Hamiltonian, and the
interplay between the magnetic moment and the elongation of the FeAs4
tetrahedron
Sympathetic Block for Treating Primary Erythromelalgia
Primary erythromelalgia is a rare condition that's characterized by erythema, an increased skin temperature and burning pain in the extremities. The pain is often very severe, and treating erythromelalgia is frustrating and difficult. We report here on the case of a 12-year old girl with primary erythromelalgia in both lower extremities. The pain was refractory to medical treatment, but a bilateral sympathetic block with lidocaine and triamcinolone resulted in relief from the pain. Our experience with this disease demonstrates that sympathetic blocks are effective in improving the symptoms and they may be attempted on erythromelalgia patients who do not respond to other treatments, including medication and epidural blocks
Evolution of Fruit Traits in Ficus Subgenus Sycomorus (Moraceae): To What Extent Do Frugivores Determine Seed Dispersal Mode?
Fig trees are a ubiquitous component of tropical rain forests and exhibit an enormous diversity of ecologies. Focusing on Ficus subgenus Sycomorus, a phenotypically diverse and ecologically important Old World lineage, we examined the evolution of fruit traits using a molecular phylogeny constructed using 5 kilobases of DNA sequence data from 63 species (50% of global diversity). In particular, we ask whether patterns of trait correlations are consistent with dispersal agents as the primary selective force shaping morphological diversity or if other ecological factors may provide a better explanation? Fig colour, size and placement (axial, cauliflorous, or geocarpic) were all highly evolutionarily liable, and the same fruit traits have evolved in different biogeographic regions with substantially different dispersal agents. After controlling for phylogenetic autocorrelation, we found that fig colour and size were significantly associated with fig placement and plant-life history traits (maximum plant height and leaf area, respectively). However, contrary to prevailing assumptions, fig placement correlated poorly with known dispersal agents and appears more likely determined by other factors, such as flowering phenology, nutrient economy, and habitat preference. Thus, plant life-history, both directly and through its influence on fig placement, appears to have played a prominent role in determining fruit traits in these figs
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