2,704 research outputs found
Impact of high-frequency pumping on anomalous finite-size effects in three-dimensional topological insulators
Lowering of the thickness of a thin-film three-dimensional topological
insulator down to a few nanometers results in the gap opening in the spectrum
of topologically protected two-dimensional surface states. This phenomenon,
which is referred to as the anomalous finite-size effect, originates from
hybridization between the states propagating along the opposite boundaries. In
this work, we consider a bismuth-based topological insulator and show how the
coupling to an intense high-frequency linearly polarized pumping can further be
used to manipulate the value of a gap. We address this effect within recently
proposed Brillouin-Wigner perturbation theory that allows us to map a
time-dependent problem into a stationary one. Our analysis reveals that both
the gap and the components of the group velocity of the surface states can be
tuned in a controllable fashion by adjusting the intensity of the driving field
within an experimentally accessible range and demonstrate the effect of
light-induced band inversion in the spectrum of the surface states for high
enough values of the pump.Comment: 6 pages, 3 figure
Isospin dependence of nucleon effective mass in Dirac Brueckner-Hartree-Fock approach
The isospin dependence of the nucleon effective mass is investigated in the
framework of the Dirac Brueckner-Hartree-Fock (DBHF) approach. The definition
of nucleon scalar and vector effective masses in the relativistic approach is
clarified. Only the vector effective mass is the quantity related to the
empirical value extracted from the analysis in the nonrelatiistic shell and
optical potentials. In the relativistic mean field theory, where the nucleon
scalar and vector potentials are both energy independent, the neutron vector
potential is stronger than that of proton in the neutron rich nuclear matter,
which produces a smaller neutron vector effective mass than that of proton. It
is pointed out that the energy dependence of nucleon potentials has to be
considered in the analysis of the isospin dependence of the nucleon effective
mass. In the DBHF the neutron vector effective mass is larger than that of
proton once the energy dependence of nucleon potentials is considered. The
results are consistent with the analysis of phenomenological isospin dependent
optical potentials.Comment: 4 pages, 3 Postscript figure
Observation of Full-Parameter Jones Matrix in Bilayer Metasurface
Metasurfaces, artificial 2D structures, have been widely used for the design
of various functionalities in optics. Jones matrix, a 2*2 matrix with eight
parameters, provides the most complete characterization of the metasurface
structures in linear optics, and the number of free parameters (i.e., degrees
of freedom, DOFs) in the Jones matrix determines the limit to what
functionalities we can realize. Great efforts have been made to continuously
expand the number of DOFs, and a maximal number of six has been achieved
recently. However, the realization of 'holy grail' goal with eight DOFs (full
free parameters) has been proven as a great challenge so far. Here, we show
that by cascading two layer metasurfaces and utilizing the gradient descent
optimization algorithm, a spatially varying Jones matrix with eight DOFs is
constructed and verified numerically and experimentally in optical frequencies.
Such ultimate control unlocks new opportunities to design optical
functionalities that are unattainable with previously known methodologies and
may find wide potential applications in optical fields.Comment: 53 paegs, 4 figure
Inhibition of SREBP by a Small Molecule, Betulin, Improves Hyperlipidemia and Insulin Resistance and Reduces Atherosclerotic Plaques
SummarySterol regulatory element-binding proteins (SREBPs) are major transcription factors activating the expression of genes involved in biosynthesis of cholesterol, fatty acid and triglyceride. In this study, we identified a small molecule, betulin, that specifically inhibited the maturation of SREBP by inducing interaction of SREBP cleavage activating protein (SCAP) and Insig. Inhibition of SREBP by betulin decreased the biosynthesis of cholesterol and fatty acid. In vivo, betulin ameliorated diet-induced obesity, decreased the lipid contents in serum and tissues, and increased insulin sensitivity. Furthermore, betulin reduced the size and improved the stability of atherosclerotic plaques. Our study demonstrates that inhibition SREBP pathway can be employed as a therapeutic strategy to treat metabolic diseases including type II diabetes and atherosclerosis. Betulin, which is abundant in birch bark, could be a leading compound for development of drugs for hyperlipidemia
Elevation of Inducible Nitric Oxide Synthase and Cyclooxygenase-2 Expression in the Mouse Brain after Chronic Nonylphenol Exposure
The present study was performed to investigate the effects of chronic administration of nonylphenol (NP) on the expression of inflammation-related genes in the brains of mice. NP was given orally by gavages at 0, 50, 100, and 200 mg/kg/d. The expression of inflammatory enzymes, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), was evaluated by immunohistochemistry and immunoblotting assays. The nitric oxide (NO) level and nitric oxide synthase (NOS) activity were also measured by biochemical analyses. The results showed that NP at a high dose (200 mg/kg/d) significantly increased the expression of iNOS and COX-2 in both the hippocampus and cortex. In parallel with the increase in iNOS expression, the NO level was significantly greater at the dose of 200 mg/kg/d, compared to the control. The activity of NOS was also increased in the brain of mice at the dose of 100 and 200 mg/kg/d. These findings demonstrate that NP may have the potential to induce the chronic inflammation or cause neurotoxicity in the mouse brain
Slow cooling and efficient extraction of C-exciton hot carriers in MoS2 monolayer
In emerging optoelectronic applications, such as water photolysis, exciton fission and novel photovoltaics involving low-dimensional nanomaterials, hot-carrier relaxation and extraction mechanisms play an indispensable and intriguing role in their photo-electron conversion processes. Two-dimensional transition metal dichalcogenides have attracted much attention in above fields recently; however, insight into the relaxation mechanism of hot electron-hole pairs in the band nesting region denoted as C-excitons, remains elusive. Using MoS2 monolayers as a model two-dimensional transition metal dichalcogenide system, here we report a slower hot-carrier cooling for C-excitons, in comparison with band-edge excitons. We deduce that this effect arises from the favourable band alignment and transient excited-state Coulomb environment, rather than solely on quantum confinement in two-dimension systems. We identify the screening-sensitive bandgap renormalization for MoS2 monolayer/graphene heterostructures, and confirm the initial hot-carrier extraction for the C-exciton state with an unprecedented efficiency of 80%, accompanied by a twofold reduction in the exciton binding energy
DocAsRef: An Empirical Study on Repurposing Reference-Based Summary Quality Metrics Reference-Freely
Automated summary quality assessment falls into two categories:
reference-based and reference-free. Reference-based metrics, historically
deemed more accurate due to the additional information provided by
human-written references, are limited by their reliance on human input. In this
paper, we hypothesize that the comparison methodologies used by some
reference-based metrics to evaluate a system summary against its corresponding
reference can be effectively adapted to assess it against its source document,
thereby transforming these metrics into reference-free ones. Experimental
results support this hypothesis. After being repurposed reference-freely, the
zero-shot BERTScore using the pretrained DeBERTa-large-MNLI model of <0.5B
parameters consistently outperforms its original reference-based version across
various aspects on the SummEval and Newsroom datasets. It also excels in
comparison to most existing reference-free metrics and closely competes with
zero-shot summary evaluators based on GPT-3.5.Comment: Accepted into Findings of EMNLP 202
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