70 research outputs found
Simulation of the Burridge-Knopoff Model of Earthquakes with Variable Range Stress Transfer
Simple models of earthquake faults are important for understanding the
mechanisms for their observed behavior, such as Gutenberg-Richter scaling and
the relation between large and small events, which is the basis for various
forecasting methods. Although cellular automaton models have been studied
extensively in the long-range stress transfer limit, this limit has not been
studied for the Burridge-Knopoff model, which includes more realistic friction
forces and inertia. We find that the latter model with long-range stress
transfer exhibits qualitatively different behavior than both the long-range
cellular automaton models and the usual Burridge-Knopoff model with nearest
neighbor springs, depending on the nature of the velocity-weakening friction
force. This result has important implications for our understanding of
earthquakes and other driven dissipative systems.Comment: 4 pages, 5 figures, published on Phys. Rev. Let
A comprehensive review on the ferroelectric orthochromates: Synthesis, property, and application
Multiferroics represent a class of advanced materials for promising
applications and stand at the forefront of modern science for the special
feature possessing both charge polar and magnetic order. Previous studies
indicate that the family of RECrO3 (RE = rare earth) compounds is likely
another rare candidate system holding both ferroelectricity and magnetism.
However, many issues remain unsolved, casting hot disputes about whether RECrO3
is multiferroic or not. For example, an incompatibility exists between reported
structural models and observed ferroelectric behaviors, and it is not easy to
determine the spin canting degree. To address these questions, one key step is
to grow single crystals because they can provide more reliable information than
other forms of matter do. In this review, the parent and doped ferroelectric
YCrO3 compounds are comprehensively reviewed based on scientific and patent
literatures from 1954 to 2022. The materials syntheses with different methods,
including poly-, nano-, and single-crystalline samples and thin films, are
summarized. The structural, magnetic, ferroelectric and dielectric, optical,
and chemical-pressure (on Y and Cr sites by doping) dependent chemical and
physical properties and the corresponding phase diagrams, are discussed.
Diverse (potential) applications, including anti-corrosion, magnetohydrodynamic
electrode, catalyst, negative-temperature-coefficient thermistor, magnetic
refrigeration, protective coating, and solid oxide fuel cell, are present. To
conclude, we summarize general results, reached consensuses, and existing
controversies of the past nearly 69 years of intensive studies and highlight
future research opportunities and emerging challenges to address existing
issues.Comment: 69 pages, 35 figures, accepted by Coordination Chemistry Review
Ligand Selectivity in the Recognition of Protoberberine Alkaloids by Hybrid-2 Human Telomeric G-Quadruplex: Binding Free Energy Calculation, Fluorescence Binding, and NMR Experiments
The human telomeric G-quadruplex (G4) is an attractive target for developing anticancer drugs. Natural products protoberberine alkaloids are known to bind human telomeric G4 and inhibit telomerase. Among several structurally similar protoberberine alkaloids, epiberberine (EPI) shows the greatest specificity in recognizing the human telomeric G4 over duplex DNA and other G4s. Recently, NMR study revealed that EPI recognizes specifically the hybrid-2 form human telomeric G4 by inducing large rearrangements in the 50-flanking segment and loop regions to form a highly extensive four-layered binding pocket. Using the NMR structure of the EPI-human telomeric G4 complex, here we perform molecular dynamics free energy calculations to elucidate the ligand selectivity in the recognition of protoberberines by the human telomeric G4. The MM-PB(GB)SA (molecular mechanics-Poisson Boltzmann/Generalized Born) Surface Area) binding free energies calculated using the Amber force fields bsc0 and OL15 correlate well with the NMR titration and binding affinity measurements, with both calculations correctly identifying the EPI as the strongest binder to the hybrid-2 telomeric G4 wtTel26. The results demonstrated that accounting for the conformational flexibility of the DNA-ligand complexes is crucially important for explaining the ligand selectivity of the human telomeric G4. While the MD-simulated (molecular dynamics) structures of the G-quadruplex-alkaloid complexes help rationalize why the EPI-G4 interactions are optimal compared with the other protoberberines, structural deviations from the NMR structure near the binding site are observed in the MD simulations. We have also performed binding free energy calculation using the more rigorous double decoupling method (DDM); however, the results correlate less well with the experimental trend, likely due to the difficulty of adequately sampling the very large conformational reorganization in the G4 induced by the protoberberine binding
Temperature-dependent structure of an intermetallic ErPdSi single crystal: A combined synchrotron and in-house X-ray diffraction study
We have grown intermetallic ErPdSi single crystals employing
laser-diodes with the floating-zone method. The temperature-dependent
crystallography was determined using synchrotron and in-house X-ray powder
diffraction measurements from 20 to 500 K. The diffraction patterns fit well
with the tetragonal 4/ space group (No. 139) with two chemical formulas
within one unit cell. Our synchrotron X-ray powder diffraction study shows that
the refined lattice constants are = 4.10320(2) {\AA}, = 9.88393(5)
{\AA} at 298 K and = 4.11737(2) {\AA}, = 9.88143(5) {\AA} at 500 K,
resulting in the unit-cell volume = 166.408(1) {\AA} (298 K) and
167.517(2) {\AA} (500 K). In the whole studied temperature range, we did
not find any structural phase transition. Upon cooling, the lattice constants a
and c are shortened and elongated, respectively.Comment: 5 Figures, 4 Table
Near mean-field behavior in the generalized Burridge-Knopoff earthquake model with variable range stress transfer
Simple models of earthquake faults are important for understanding the
mechanisms for their observed behavior in nature, such as Gutenberg-Richter
scaling. Because of the importance of long-range interactions in an elastic
medium, we generalize the Burridge-Knopoff slider-block model to include
variable range stress transfer. We find that the Burridge-Knopoff model with
long-range stress transfer exhibits qualitatively different behavior than the
corresponding long-range cellular automata models and the usual
Burridge-Knopoff model with nearest-neighbor stress transfer, depending on how
quickly the friction force weakens with increasing velocity. Extensive
simulations of quasiperiodic characteristic events, mode-switching phenomena,
ergodicity, and waiting-time distributions are also discussed. Our results are
consistent with the existence of a mean-field critical point and have important
implications for our understanding of earthquakes and other driven dissipative
systems.Comment: 24 pages 12 figures, revised version for Phys. Rev.
MgF as an effective additive for improving ionic conductivity of ceramic solid electrolytes
As typical solid-state electrolytes (SSEs),
{Na}{Zr}{Si}{P}{O} NASICONs provide an ideal
platform for solid-state batteries (SSBs) that display higher safety and
accommodate higher energy densities. The critical points for achieving SSBs
with higher efficiencies are to improve essentially the ionic conductivity and
to reduce largely the interfacial resistance between SSEs and cathode
materials, which would necessitate extremely high level of craftsmanship and
high-pressure equipment. An alternative to higher-performance and lower-cost
SSBs is additive manufacturing. Here, we report on an effective additive,
MgF, which was used in synthesizing NASICONs, resulting in SSEs with fewer
defects and higher performance. With an addition of mere 1 wt MgF
additive, the total room-temperature ionic conductivity of the NASICON
electrolyte reaches up to 2.03 mS cm, improved up to 181.3,
with an activation energy of 0.277 eV. Meanwhile, the stability of the Na
plating/stripping behavior in symmetric cells increases from 236 to 654 h. We
tried to reveal the microscopic origins of the higher ionic conductivity of
MgF-doped NASICONs by comprehensive in-house characterizations. Our study
discovers a novel MgF additive and provides an efficient way to prepare
higher-performance SSEs, making it possible to fabricate lower-cost SSBs in
industries.Comment: 16 pages, 7 figure
Alterations in cellular metabolisms after TKI therapy for Philadelphia chromosome-positive leukemia in children: A review
Incidence rates of chronic myeloid leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) are lower but more aggressive in children than in adults due to different biological and host factors. After the clinical application of tyrosine kinase inhibitor (TKI) blocking BCR/ABL kinase activity, the prognosis of children with CML and Ph+ ALL has improved dramatically. Yet, off-target effects and drug tolerance will occur during the TKI treatments, contributing to treatment failure. In addition, compared to adults, children may need a longer course of TKIs therapy, causing detrimental effects on growth and development. In recent years, accumulating evidence indicates that drug resistance and side effects during TKI treatment may result from the cellular metabolism alterations. In this review, we provide a detailed summary of the current knowledge on alterations in metabolic pathways including glucose metabolism, lipid metabolism, amino acid metabolism, and other metabolic processes. In order to obtain better TKI treatment outcomes and avoid side effects, it is essential to understand how the TKIs affect cellular metabolism. Hence, we also discuss the relevance of cellular metabolism in TKIs therapy to provide ideas for better use of TKIs in clinical practice
- …