794 research outputs found
Bound States of Conical Singularities in Graphene-Based Topological Insulators
We investigate the electronic structure induced by wedge-disclinations
(conical singularities) in a honeycomb lattice model realizing Chern numbers
. We establish a correspondence between the bound state of (i) an
isolated -flux, (ii) an isolated pentagon or heptagon
defect with an external flux of magnitude through
the center and (iii) an isolated square or octagon defect without external
flux, where is the flux quantum. Due to the above correspondence,
the existence of isolated electronic states bound to the disclinations is
robust against various perturbations. These results are also generalized to
graphene-based time-reversal invariant topological insulators.Comment: 5+4 pages, 4+3 figures, revised introduction and Fig.
Dimensional reduction by pressure in the magnetic framework material CuF(DO)pyz: from spin-wave to spinon excitations
Metal organic magnets have enormous potential to host a variety of electronic
and magnetic phases that originate from a strong interplay between the spin,
orbital and lattice degrees of freedom. We control this interplay in the
quantum magnet CuF(DO)pyz by using high pressure to drive the
system through a structural and magnetic phase transition. Using neutron
scattering, we show that the low pressure state, which hosts a two-dimensional
square lattice with spin-wave excitations and a dominant exchange coupling of
0.89 meV, transforms at high pressure into a one-dimensional spin-chain
hallmarked by a spinon continuum and a reduced exchange interaction of 0.43
meV. This direct microscopic observation of a magnetic dimensional crossover as
a function of pressure opens up new possibilities for studying the evolution of
fractionalised excitations in low dimensional quantum magnets and eventually
pressure-controlled metal--insulator transitions
Ehrenfest relations and magnetoelastic effects in field-induced ordered phases
Magnetoelastic properties in field-induced magnetic ordered phases are
studied theoretically based on a Ginzburg-Landau theory. A critical field for
the field-induced ordered phase is obtained as a function of temperature and
pressure, which determine the phase diagram. It is found that magnetic field
dependence of elastic constant decreases discontinuously at the critical field,
Hc, and that it decreases linearly with field in the ordered phase (H>Hc). We
found an Ehrenfest relation between the field dependence of the elastic
constant and the pressure dependence of critical field. Our theory provides the
theoretical form for magnetoelastic properties in field- and pressure-induced
ordered phases.Comment: 7 pages, 3 figure
A calorimetric study of the thermal denaturation of whey proteins in simulated milk ultrafiltrate
Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: β-lactoglobulin, α-lactalbumin, serum albumin, γ-globulin, apo- and Fe-lactoferrin, lysozyme, ribonuclease, α-chymotrypsin and xanthine oxidase. Denaturation enthalpies (ΔHD), denaturation temperatures (TD) and the half width of the denaturation peaks in DSC thermograms (ΔT½D) were determined and the degree of renaturation was estimated by rescanning previously denatured samples. A fair correlation between the results obtained by DSC and other more classical methods was found in general. However, for some proteins (α-lactalbumin, lysozyme, ribonuclease and xanthine oxidase), which have so far been considered relatively thermostable, calorimetry reveals conformational changes starting at temperatures as low as about 45 °C. In these cases thermostability observed after heat treatment of milk should be interpreted in terms of renaturation and not of high temperatures of denaturatio
Slave-boson mean-field theory of the Mott transition in the two-band Hubbard model
Abstract.: We apply the slave-boson approach of Kotliar and Ruckenstein to the two-band Hubbard model with an Ising like Hund's rule coupling and bands of different widths. On the mean-field level of this approach we investigate the Mott transition and observe both separate and joint transitions of the two bands depending on the choice of the inter- and intra-orbital Coulomb interaction parameters. The mean-field calculations allow for a simple physical interpretation and can confirm several aspects of previous work. Beside the case of two individually half-filled bands we also examine what happens if the original metallic bands possess fractional filling either due to finite doping or due to a crystal field which relatively shifts the atomic energy levels of the two orbitals. For appropriate values of the interaction and of the crystal field we can observe a band insulating state and a ferromagnetic meta
Quantum and classical criticality in a dimerized quantum antiferromagnet
A quantum critical point (QCP) is a singularity in the phase diagram arising
due to quantum mechanical fluctuations. The exotic properties of some of the
most enigmatic physical systems, including unconventional metals and
superconductors, quantum magnets, and ultracold atomic condensates, have been
related to the importance of the critical quantum and thermal fluctuations near
such a point. However, direct and continuous control of these fluctuations has
been difficult to realize, and complete thermodynamic and spectroscopic
information is required to disentangle the effects of quantum and classical
physics around a QCP. Here we achieve this control in a high-pressure,
high-resolution neutron scattering experiment on the quantum dimer material
TlCuCl3. By measuring the magnetic excitation spectrum across the entire
quantum critical phase diagram, we illustrate the similarities between quantum
and thermal melting of magnetic order. We prove the critical nature of the
unconventional longitudinal ("Higgs") mode of the ordered phase by damping it
thermally. We demonstrate the development of two types of criticality, quantum
and classical, and use their static and dynamic scaling properties to conclude
that quantum and thermal fluctuations can behave largely independently near a
QCP.Comment: 6 pages, 4 figures. Original version, published version available
from Nature Physics websit
No clear trends in expatriation of non-human primate research from ÂSwitzerland between 2004 and 2017
Animal experimentation is commonly practiced in scientific research worldwide. However, there are no globally accepted standards for regulating the ethical boundaries and accepted practices for animal experimentation. Large differences exist between countries. A report suggested that some researchers, especially from countries with more stringent animal experimentation regulations, may be relocating experimental research to countries with less stringent regulations. We followed a systematic literature review approach to identity publications and determine whether there is an increasing trend in expatriation of non-human primate experimentation by researchers based in Switzerland. We used the Projects People Publications database, which contains projects funded by the Swiss National Science Foundation, to identify researchers conducting experiments using non-human primates. This list of names, together with terms referring to non-human primates were used to search the Web of Science. Publications without an author affiliated to a Swiss institution, no living or only with free non-human primates, and non-original research were excluded. For each publication, we recorded the place of experimentation, funding source, number of animals, species and the statement of ethical approval. We retained 120 publications, involving more than 2,429 non-human primates. Macaca mulatta and Macaca fascicularis were the most common species. We could not confirm an increasing trend in expatriation of non-human primate experimentation outside of Switzerland. Over time, publications appeared to report the ethical approval number more consistently. These results should be interpreted with caution because the sample included only studies that were: 1) published and 2) reported in the Web of Science. Consequently, studies with insignificant results may have been excluded because these studies are rarely published, and studies of poor quality may have been excluded because they are often published in lower quality journals, not indexed by the Web of Science
The calmodulin fraction responsible for contraction in an intestinal smooth muscle
AbstractFreeze-dried fibers of smooth muscle from Taenia coli were used to determine the concentration of calmodulin responsible for contraction. About 10% of the total intracellular calmodulin (12.6 μmol/kg wet wt) is directly involved in initiation of smooth muscle contraction
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