3,014 research outputs found
Effects of bleaching agents on dental restorative materials: A review of the literature and recommendation to dental practitioners and researchers
AbstractIn recent years, there has been an increased demand for improvement in the appearance of natural teeth. The conservative technique of tooth bleaching has gained attention and acceptance from both patients and clinicians. Despite increased popularity, there is controversy surrounding the adverse effects of bleaching on dental restorative materials. This article reviews the effects of bleaching agents on major categories of dental restorative materials and provides evidence-based recommendations to the clinicians and researchers. Current literature reveal that bleaching might have a detrimental effect on restorative materials. However, because of the variability in experimental design, there is a lack of consensus concerning the bleaching effects on restorative materials. A standardized and reproducible guideline for assessment of bleaching effects on restorative materials needs to be established and verified by future studies
Onset of chaotic gravitational lensing in non-Kerr rotating black holes with quadrupole mass moment
In the electromagnetic channel, chaotic gravitational lensing is a peculiar
phenomenon in strong gravitational lensing. In this work, we analyze the
properties and emergence of chaotic gravitational lensing in the Manko-Novikov
black hole spacetime. Aiming to understand better the underlying physics, we
elaborate on the boundaries of the accessible region in terms of the analyses
of the contours of the effective potentials. The latter is associated with the
two roots of a quadratic equation. In particular, we explore its interplay with
ergoregion, which leads to specific features of the effective potentials, such
as the emergence of cuspy edge and the formation of {\it pocket}, that serves
as a static constraint on the geodesics. Besides, we investigate the properties
of the radial and angular accelerations at the turning points in photons'
trajectories. Moreover, the accelerations are analyzed, which is argued to
provide a kinematic constraint on the geodesics. It is concluded that the onset
of the chaotic lensing is crucially related to both constraints, and as a
result, an arbitrarily slight deviation in the incident photon is significantly
amplified during the course of evolution through an extensive period,
demonstrating the complexity in the highly nonlinear deterministic
gravitational system.Comment: 18 pages, 13 figure
Multi-time scale stochastic production simulation under VHVDC long-term contract trading electricity quantity constraint
A two-layer multi-time scale stochastic production simulation framework is constructed to account for the long-term contract electricity quantity of ultra-high voltage direct current (UHVDC) transmission. On the upper layer, based on the characteristics of load demand and renewable energy output extracted from the historical operating data, monthly and daily production simulation models are carried out considering the seasonal characteristics of hydropower during a high-water period and low-water period to optimize the distribution of contract electric quantity sending through UHVDC transmission in the target year or month. According to the DC transmission electric quantity optimized by the daily production simulation in the upper layer, together with the forecast scenario, the lower layer of the framework provides the optimization of day-ahead scheduling and intra-day rolling dispatch in the implementation process. The day-ahead dispatch optimization makes full use of the adjustment capability of transmission and optimizes the DC transmission electric quantity correction. Its compensation is based on the result of the daily production simulation, then the correction will be returned to the upper layer to restart the optimization of the remaining UHVDC contract electric quantity of the subsequent period and its distribution plan. Combined with the day-ahead DC transmission plan, the intra-day rolling optimization is carried out to adjust the output of the unit using more accurate forecasting scenarios. The distributionally robust optimization model is used in the lower layer to convert an uncertain problem into a deterministic quadratically constrained quadratic programming (QCQP) problem according to the form of an uncertain distribution set. Then the QCQP problem is further converted into a linear programming (LP) problem by using the reformulation linearization technique (RLT). A test system with the energy composition and distribution referring to a real provincial power grid in northwest China is established for verification. The results show that the proposed method can effectively improve the economics of system operation and the accommodation of renewable energy based on ensuring security
Prevalence and molecular characterization of plasmidmediated beta-lactamase genes among nosocomial Staphylococcus aureus isolated in Taiwan
Purpose: To analyze the drug susceptibility phenotypes and the patterns of plasmid-mediated β- lactamase genes among nosocomial Staphylococcus aureus drug resistance isolates in Taiwan.Methods: The antibiotic susceptibilities of 617 clinical Staphylococcus aureus isolates collected from 2005 - 2009 from Chiayi Christian Hospital (Chiayi, Taiwan) were examined in vitro against 8 antimicrobial agents using agar diffusion method. Among the clinical isolates, 114 strains of methicillinsensitive Staphylococcus aureus and 45 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolates were selected for plasmid profile analysis. The patterns of β-lactamase genes presented in plasmids were investigated by polymerase chain reaction analysis.Results: Most test strains were resistant to multiple antibiotics, particularly for the traditional agents such as ampicillin, penicillin, cephalexin and kanamycin. Plasmid profile analysis revealed that up to 36 % of the clinical strains harbored plasmids and were able to develop multi-drug resistant. Among them, most of the isolates harbored at least one plasmid (range 1 – 7) with a size range of 2.3 to 23 Kb. Among the several types of β-lactamases, blaTEM was the most prevalent.Conclusion: The results obtained from this study can serve as a valuable reference for the future control for clinical antibiotic resistant strains and more thorough discussions on resistance mechanisms.Keywords: Staphylococcus aureus, Antibiotic susceptibility, Nosocomial pathogens, Plasmid profile, β- lactamase
Dimethyl 2,5-bis(5-hexylthiophen-2-yl)benzene-1,4-dioate
In the title compound, C30H38O4S2, the centroid of the benzene ring lies on a center of inversion. The thiophene ring is aligned at 49.8 (1)° with respect to the benzene ring. The alkyl chain adopts an extended zigzag conformation
Role of dimensional crossover on spin-orbit torque efficiency in magnetic insulator thin films
Magnetic insulators (MIs) attract tremendous interest for spintronic
applications due to low Gilbert damping and absence of Ohmic loss. Magnetic
order of MIs can be manipulated and even switched by spin-orbit torques (SOTs)
generated through spin Hall effect and Rashba-Edelstein effect in heavy
metal/MI bilayers. SOTs on MIs are more intriguing than magnetic metals since
SOTs cannot be transferred to MIs through direct injection of electron spins.
Understanding of SOTs on MIs remains elusive, especially how SOTs scale with
the film thickness. Here, we observe the critical role of dimensionality on the
SOT efficiency by systematically studying the MI layer thickness dependent SOT
efficiency in tungsten/thulium iron garnet (W/TmIG) bilayers. We first show
that the TmIG thin film evolves from two-dimensional to three-dimensional
magnetic phase transitions as the thickness increases, due to the suppression
of long-wavelength thermal fluctuation. Then, we report the significant
enhancement of the measured SOT efficiency as the thickness increases. We
attribute this effect to the increase of the magnetic moment density in concert
with the suppression of thermal fluctuations. At last, we demonstrate the
current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up
to 15 nm. The switching current density is comparable with those of heavy
metal/ferromagnetic metal cases. Our findings shed light on the understanding
of SOTs in MIs, which is important for the future development of ultrathin
MI-based low-power spintronics
Is Fermi 1544-0649 a misaligned blazar? discovering the jet structure with VLBI
Fermi J1544-0649 is a transient GeV source first detected during its GeV
flares in 2017. Multi-wavelength observations during the flaring time
demonstrate variability and spectral energy distribution(SED) that are typical
of a blazar. Other than the flare time, Fermi J1544-0649 is quiet in the GeV
band and looks rather like a quiet galaxy (2MASX J15441967-0649156) for a
decade. Together with the broad absorption lines feature we further explore the
"misaligned blazar scenario". We analyzed the Very Long Baseline Array (VLBA)
and East Asian VLBI Network (EAVN) data from 2018 to 2020 and discovered the
four jet components from Fermi J1544-0649. We found a viewing angle around
3.7{\deg} to 7.4{\deg}. The lower limit of the viewing angle indicates a blazar
with an extremely low duty cycle of the gamma-ray emission, the upper limit of
it supports the "misaligned blazar scenario". Follow-up multi-wavelength
observations after 2018 show Fermi J1544-0649 remains quiet in GeV, X-ray, and
optical bands. Multi-messenger search of neutrinos is also performed, and an
excess of 3.1 {\sigma} significance is found for this source.Comment: Accepted for publication in ApJ. 13 pages, 7 figure
Downregulation of ASPP2 in pancreatic cancer cells contributes to increased resistance to gemcitabine through autophagy activation
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