188 research outputs found
Polaronic effects in monolayer black phosphorus on polar substrates
We investigate the effect of charge carrier interaction with surface optical
phonons on the band properties of monolayer black phosphorus induced by polar
substrates. We develop an analytical method based on the Lee-Low-Pines theory
to calculate the spectrum of Fr\"ohlich type continuum Hamiltonian in the
long-wavelength limit. We examine the modification of a band gap and
renormalization of effective masses due to the substrate-related polaronic
effect. Our results show that an energy gap in supported monolayer black
phosphorus is enlarged depending on a particular substrate and the interlayer
distance, . Among the substrate considered, the largest gap broadening at \AA{} is observed for the AlO substrate, which is found to
be meV. Carrier-phonon coupling also renormalizes the effective
masses which is more pronounced along the zigzag direction. Anisotropy of the
effective masses becomes stronger by the influence of the polaronic effect
corresponding to direction-dependent carrier-phonon coupling. We conclude that
substrate phonons have a non-negligible effect on the static band properties of
monolayer black phosphorus, which may be further exploited in its experimental
and theoretical studies
Variational Approach for the Effects of Periodic Modulations on the Spectrum of Massless Dirac Fermion
In the variational framework, we study the electronic energy spectrum of
massless Dirac fermions of graphene subjected to one-dimensional oscillating
magnetic and electrostatic fields centered around a constant uniform static
magnetic field. We analyze the influence of the lateral periodic modulations in
one direction, created by these oscillating electric and magnetic fields, on
Dirac like Landau levels depending on amplitudes and periods of the field
modulations. We compare our theoretical results with those found within the
framework of non-degenerate perturbation theory. We found that the technique
presented here yields energies lower than that obtained by the perturbation
calculation, and thus gives more stable solutions for the electronic spectrum
of massless Dirac fermion subjected to a magnetic field perpendicular to
graphene layer under the influence of additional periodic potentials.Comment: 8 pages, 7 figure
Boundaries of Subcritical Coulomb Impurity Region in Gapped Graphene
The electronic energy spectrum of graphene electron subjected to a
homogeneous magnetic field in the presence of a charged Coulomb impurity is
studied analytically within two-dimensional Dirac-Weyl picture by using
variational approach. The variational scheme we used is just based on utilizing
the exact eigenstates of two-dimensional Dirac fermion in the presence of a
uniform magnetic field as a basis for determining analytical energy eigenvalues
in the presence of an attractive/repulsive charged Coulomb impurity. This
approach allows us to determine under which conditions bound state solutions
can or can not exist in gapped graphene in the presence of magnetic field. In
addition, the effects of uniform magnetic field on the boundaries of
subcritical Coulomb impurity region in the massless limit are also analyzed.
Our analytical results show that the critical impurity strength decreases with
increasing gap/mass parameter, and also that it increases with increasing
magnetic field strength. In the massless limit, we investigate that the
critical Coulomb coupling strength is independent of magnetic field, and its
upper value for the ground-state energy is 0.752.Comment: 9 pages,10 figure
Effect of long-range structural corrugations on magnetotransport properties of phosphorene in tilted magnetic field
Rippling is an inherent quality of two-dimensional materials playing an
important role in determining their properties. Here, we study the effect of
structural corrugations on the electronic and transport properties of monolayer
black phosphorus (phosphorene) in the presence of tilted magnetic field. We
follow a perturbative approach to obtain analytical corrections to the spectrum
of Landau levels induced by a long-wavelength corrugation potential. We show
that surface corrugations have a non-negligible effect on the electronic
spectrum of phosphorene in tilted magnetic field. Particularly, the Landau
levels are shown to exhibit deviations from the linear field dependence. The
observed effect become especially pronounced at large tilt angles and
corrugation amplitudes. Magnetotransport properties are further examined in the
low temperature regime taking into account impurity scattering. We calculate
magnetic field dependence of the longitudinal and Hall resistivities and find
that the nonlinear effects reflecting the corrugation might be observed even in
moderate fields (\mbox{ T})
Lateral Spin Valve Based on the Two-Dimensional CrN/P/CrN Heterostructure
We propose a spin valve based on a blue-phosphorus monolayer sandwiched between two half-metallic two-dimensional CrN layers. We use density-functional theory combined with Boltzmann transport theory to investigate both the structural and the magnetic stability of the CrN/P/CrN heterostructure and to study its spin-dependent transport properties. Among the different possible layer stackings considered, only one is shown to be thermodynamically stable, corresponding to the AA stacking. In this geometry, the critical temperature of magnetic ordering is estimated to be around 150 K. The electronic structure of CrN/P/CrN is strongly dependent on the mutual orientation of the magnetic moments in individual CrN layers. If the alignment is parallel, only one spin channel predominantly contributes to the electronic bands in the vicinity of the Fermi energy. In the case of an antiparallel alignment, both spin channels contribute to the electronic states. The alteration of magnetic moments affects electronic transport, causing magnetoresistance of up to 12% at moderate dopings. © 2019 American Physical Society.The authors acknowledge Ankara University for use of the high-performance computing facility through the AYP under Grant No. 17A0443001. A.N.R. acknowledges support from the FLAG-ERA JTC2017 Project “Gransport”
Pre- and post-estrogen administration in global cerebral ischemia reduces blood-brain barrier breakdown in ovariectomized rats
The aim of present study was to determine the effect of estrogen treatment on blood-brain barrier permeability in rats with induced global cerebral ischemia. The study included six-month-old female Sprague-Dawley rats which were divided into the following groups: Control-Ischemia-Reperfusion (C + I-R); Ovariectomy-Ischemia-Reperfusion (Ovx + I-R); Ovariectomy + Estrogen + Ischemia-Reperfusion (Ovx + E + I-R); Ovariectomy + Ischemia-Reperfusion + Estrogen (Ovx + I-R + E). Ischemia-reperfusion was induced by clamping two carotid arteries, then opening the clamp. Blood-brain barrier permeability was visualized by Evans Blue extravasation and quantified by spectrophotometry. Our results indicate that following ischemia-reperfusion the BBB permeability is increased in ovariectomized rats (Evans Blue extravasation) compared to the control group in the cortex, thalamus, hippocampus, cerebellum and brain stem, while in the midbrain no significant increase was detected. In contrast, BBB permeability in the groups treated with estrogen, administered either before or after ischemia-reperfusion, was significantly lower than in ovariectomized animals. In conclusion, the increase in BBB permeability resulting from experimentally induced cerebral ischemia was prevented by exogenous estrogen treatment. The study results indicate that estrogen may be used for therapeutic purposes in ischemia-reperfusion
Two-Dimensional Chromium Bismuthate: A Room-Temperature Ising Ferromagnet with Tunable Magneto-Optical Response
We present a density-functional-theory-based study of a two-dimensional phase of chromium bismuthate (CrBi), a previously unknown material with exceptional magnetic and magneto-optical characteristics. Monolayer CrBi is a ferromagnetic metal with strong spin-orbit coupling induced by the heavy bismuth atoms, resulting in a strongly anisotropic Ising-type magnetic ordering with the Curie temperature estimated to be higher than 300 K. The electronic structure of the system is topologically nontrivial, giving rise to a nonzero Berry curvature in the ground magnetic state, leading to the anomalous Hall effect with a conductivity plateau of about 1.5e2/h at the Fermi level. Remarkably, the Hall conductivity and the magneto-optical constant are found to be strongly dependent on the direction of magnetization. Besides, monolayer CrBi demonstrates the polar magneto-optical Kerr effect in the visible and near-ultraviolet spectral ranges with the maximum rotation angles of up to 10 mrad. Our findings suggest that monolayer CrBi is a promising system for practical applications in magneto-optical and spintronic devices. © 2021 American Physical Society.The authors acknowledge the Ankara University for high performance computing facility through the AYP under Grant No. 17A0443001. This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Project No. 119F361. The numerical calculations reported in this paper were partially performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources)
99mTc-IgG-Lung Scintigraphy in the Assessment of Pulmonary Involvement in Interstitial Lung Disease and Its Comparison With Pulmonary Function Tests and High-Resolution Computed Tomography: A Preliminary Study
Background: The discrimination of inactive inflammatory processes from the active form of the disease is of great importance in the management of interstitial lung disease (ILD).
Objectives: The aim of this study was to determine the efficacy of 99mTc-IgG scan for the detection of severity of disease compared to high-resolution computed tomography (HRCT) and pulmonary function test (PFT).
Patients and Methods: Eight known cases of ILD including four cases of Mustard gas (MG) intoxication and four patients with ILD of unknown cause were included in this study. A population of six patients without lung disease was considered as the control group. The patients underwent PFT and high-resolution computed tomography scan, followed by 99mTc-IgG scan. They were followed up for one year. 99mTc-IgG scan assessment of IgG uptake was accomplished both qualitatively (subjectively) and semiquantitatively.
Results: All eight ILD patients demonstrated a strong increase in 99mTc-IgG uptake in the lungs, compared to the control patients. The 99mTc-IgG scan scores were higher in the patient group (0.64[95% confidence interval (CI)=0.61-0.69])) than the control group (0.35 (0.35[95% CI=0.28-0.40]), (P 0.05). There were no significant correlations between 99mTc-IgG score and HRCT patterns including ground glass opacity, reticular fibrosis and honeycombing (P value > 0.05).
Conclusion: The present results confirmed that 99mTc-IgG scan could be applied to detect the severity of pulmonary involvement, which was well correlated with HRCT findings. This data also showed that the 99mTc-IgG scan might be used as a complement to HRCT in the functional evaluation of the clinical status in ILD; however, further studies are recommended
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