3,259 research outputs found
Detect Spinons via Spin Transport
Existence of spinons is the defining property of quantum spin liquids. These
exotic excitations have (fractionalized) spin quantum number and no electric
charge, and have been proposed to form Fermi surfaces in the recently
discovered organic spin liquid candidates. However direct probes for them are
still lacking. In this paper we propose to experimentally identify the spinons
by measuring the spin current flowing through the spin liquid candidate
materials, which would be a direct test for the existence of spin-carrying
mobile excitations. By the nonequilibrium Green function technique we evaluate
the spin current through the interface between a Mott insulator and a metal
under a spin bias, and find that different kinds of Mott insulators, including
quantum spin liquids, can be distinguished by different relations between the
spin bias and spin current, In the end we will also discuss relations to
experiments and estimate experimentally relevant parameters.Comment: 7 pages with appendix, 3 figure
Disorder and metal-insulator transitions in Weyl semimetals
The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has
Weyl nodes in bulk excitations and Fermi arcs surface states. We study the
effects of disorder and localization in WSMs and find three exotic phase
transitions. (I) Two Weyl nodes near the Brillouin zone boundary can be
annihilated pairwise by disorder scattering, resulting in the opening of a
topologically nontrivial gap and a transition from a WSM to a three-dimensional
(3D) quantum anomalous Hall state. (II) When the two Weyl nodes are well
separated in momentum space, the emergent bulk extended states can give rise to
a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (III)
Two Weyl nodes can emerge near the zone center when an insulating gap closes
with increasing disorder, enabling a direct transition from a normal band
insulator to a WSM. We determine the phase diagram by numerically computing the
localization length and the Hall conductivity, and propose that the exotic
phase transitions can be realized on a photonic lattice.Comment: 7 pages with appendix, 6 figure
B\to X_s\gamma, X_s l^+ l^- decays and constraints on the mass insertion parameters in the MSSM
In this paper, we study the upper bounds on the mass insertion parameters
in the minimal supersymmetric standard model (MSSM).
We found that the information from the measured branching ratio of decay can help us to improve the upper bounds on the mass insertions
parameters \left (\delta^{u,d}_{AB})_{3j,i3}. Some regions allowed by the
data of are excluded by the requirement of a SM-like
imposed by the data of .Comment: 16 pages, 5 eps figure files, typos remove
Dissipative Chiral Channels, Ohmic Scaling and Half-integer Hall Conductivity from the Relativistic Quantum Hall Effect
The quantum Hall effect (QHE), which was observed in 2D electron gas under an
external magnetic field, stands out as one of the most remarkable transport
phenomena in condensed matter. However, a long standing puzzle remains
regarding the observation of the relativistic quantum Hall effect (RQHE). This
effect, predicted for a single 2D Dirac cone immersed in a magnetic field, is
distinguished by the intriguing feature of half-integer Hall conductivity
(HIHC). In this work, we demonstrate that the condensed-matter realization of
the RQHE and the direct measurement of the HIHC are feasible by investigating
the underlying quantum transport mechanism. We reveal that the manifestation of
HIHC is tied to the presence of dissipative half-integer quantized chiral
channels circulating along the interface of the RQHE system and a Dirac metal.
Importantly, we find that the Ohmic scaling of the longitudinal conductance of
the system plays a key role in directly measuring the HIHC in experiments.
Furthermore, we propose a feasible experimental scheme based on the 3D
topological insulators to directly measure the HIHC. Our findings not only
uncover the distinct transport mechanism of the HIHC for the RQHE, but also
paves the way to the measurement of the HIHC in future experiments.Comment: 14 pages, 9 figure
A Less Toxic Heparin Antagonist—Low Molecular Weight Protamine
A new thirteen amino acid peptide, named low molecular weight protamine (LMWP), was obtained through the enzymatic digestion of native protamine. Both in vitro and in vivo results showed that LMWP fully maintained the heparin neutralization function of protamine but had much lower immunogenicity and antigenicity. Unlike protamine, neither LMWP nor LMWP/heparin complexes caused significant blood platelet aggregation in rats. These results suggest that LMWP can be used as a substitute for protamine for developing a new generation of nontoxic heparin antagonists.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45793/1/10541_2004_Article_462566.pd
Gastric organoids: Progress and remaining challenges
The stomach is a complex and physiologically necessary organ, yet large differences in physiology between mouse and human stomachs have impeded translation of physiological discoveries and drug screens performed using murine gastric tissues. Gastric cancer (GC) is a global health threat, with a high mortality rate and limited treatment options. The heterogeneous nature of GC makes it poorly suited for current one size fits all standard treatments. In this review, we discuss the rapidly evolving field of gastric organoids, with a focus on studies expanding cultures from primary human tissues and describing the benefits of mouse organoid models. We introduce the differing methods for culturing healthy gastric tissue from adult tissues or pluripotent stem cells, discuss the promise these systems have for preclinical drug screens, and highlight applications of organoids for precision medicine. Finally, we discuss the limitations of these models and look to the future to present potential ways gastric organoids will advance treatment options for patients with GC
Spawning rings of exceptional points out of Dirac cones
The Dirac cone underlies many unique electronic properties of graphene and
topological insulators, and its band structure--two conical bands touching at a
single point--has also been realized for photons in waveguide arrays, atoms in
optical lattices, and through accidental degeneracy. Deformations of the Dirac
cone often reveal intriguing properties; an example is the quantum Hall effect,
where a constant magnetic field breaks the Dirac cone into isolated Landau
levels. A seemingly unrelated phenomenon is the exceptional point, also known
as the parity-time symmetry breaking point, where two resonances coincide in
both their positions and widths. Exceptional points lead to counter-intuitive
phenomena such as loss-induced transparency, unidirectional transmission or
reflection, and lasers with reversed pump dependence or single-mode operation.
These two fields of research are in fact connected: here we discover the
ability of a Dirac cone to evolve into a ring of exceptional points, which we
call an "exceptional ring." We experimentally demonstrate this concept in a
photonic crystal slab. Angle-resolved reflection measurements of the photonic
crystal slab reveal that the peaks of reflectivity follow the conical band
structure of a Dirac cone from accidental degeneracy, whereas the complex
eigenvalues of the system are deformed into a two-dimensional flat band
enclosed by an exceptional ring. This deformation arises from the dissimilar
radiation rates of dipole and quadrupole resonances, which play a role
analogous to the loss and gain in parity-time symmetric systems. Our results
indicate that the radiation that exists in any open system can fundamentally
alter its physical properties in ways previously expected only in the presence
of material loss and gain
The Reproducibility of Lists of Differentially Expressed Genes in Microarray Studies
Reproducibility is a fundamental requirement in scientific experiments and clinical contexts. Recent publications raise concerns about the reliability of microarray technology because of the apparent lack of agreement between lists of differentially expressed genes (DEGs). In this study we demonstrate that (1) such discordance may stem from ranking and selecting DEGs solely by statistical significance (P) derived from widely used simple t-tests; (2) when fold change (FC) is used as the ranking criterion, the lists become much more reproducible, especially when fewer genes are selected; and (3) the instability of short DEG lists based on P cutoffs is an expected mathematical consequence of the high variability of the t-values. We recommend the use of FC ranking plus a non-stringent P cutoff as a baseline practice in order to generate more reproducible DEG lists. The FC criterion enhances reproducibility while the P criterion balances sensitivity and specificity
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