다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Abstract BeC, a two-dimensional hypercoordinated nanostructure carbon compound, has been the focus of the nanoworld because of its high value of dynamical stability, in-plane stiffness, carrier mobility and the existence of band gap. In this work, we have explored the electronic and the optical properties of this material under the influence of static external perpendicular electric field within the framework of density functional theory. Under the influence of a uniform electric field, the band gap changes within the meV range. The electron energy loss function study reveals that this material has optical band gaps which remain constant irrespective of the applied electric field strength. The optical property also exhibits interesting features when the applied field strength is within 0.4–0.5 V/Å. We have also tried to explain the optical data from the respective band structures and thus paving the way to understand qualitatively the signature of the optical anisotropy from the birefringence study.

Optical properties of monolayer BeC under an external electric field: A DFT approach

Combined theoretical and experimental study of the electronic and optical property of Sb2WO6

This work reports a detailed and systematic theoretical study of the anisotropic thermoelectric properties of bulk Germanium Sulfide (GeS) in its orthorhombic Pnma phase. Density functional theory (DFT), employing the generalized gradient approximation (GGA), has been used to examine the structural and electronic band structure properties of bulk GeS. Electronic transport properties have been studied by solving semiclassical Boltzmann transport equations. A machine-learning approach has been used to estimate the temperature-dependent lattice part of thermal conductivity. The study reveals that GeS has a direct band gap of 1.20 eV. Lattice thermal conductivity is lowest along crystallographic a-direction, with a minimum of ∼0.98 Wm −1 K −1 at 700 K. We have obtained the maximum figure of merit (ZT) ∼ 0.73 at 700 K and the efficiency ∼7.86% in a working temperature range of 300 K–700 K for pristine GeS along crystallographic a-direction.

A study of anisotropic thermoelectric properties of bulk Germanium Sulfide in its Pnma phase: a combined first-principles and machine-learning approach

Phagraphene is a theoretically predicted sp2$sp^2$ hybridized, se‐mimetallic allotrope of graphene. The semimetallic nature of phagraphene is robust against external strain and B‐N co‐doping. Being experimentally realized in a nanoribbon form, this is quite fascinating in the present scenario. In this theoretical study, optical and thermoelectric properties of phagraphene and its site‐dependent B‐N co‐doped analogous configurations are critically investigated employing density functional theory. As a consequence of inherent rectangular symmetry and direction‐dependent behavior of the structures, anisotropic optical responses are obtained. The strain‐induced optical responses further confirm these observations. Different positions of the optical peaks for distinct configurations lead to an elegant way of structural identifications. The absorption spectra of the structures reveal that low‐energy optical transitions take place due to pz$p_z$ orbitals. Besides, static dielectric constant and refractive index are enhanced for the co‐doped structures. Furthermore, the thermoelectric responses of the structures are explored by adapting the semi‐classical Boltzmann transport equation. Importantly, a significantly higher figure of merit has been perceived, which is quite uncommon among graphene allotropes.

Optical and Thermoelectric Behavior of Phagraphene with Site‐Specific B‐N Co‐Doping

Positron annihilation technique is a well known technique to characterize the defects in a material. These defects can be identified by positron annihilation lifetime and coincidence Doppler broadening of positron annihilation radiation measurement. In this chapter we report the room temperature positron annihilation lifetime for single crystalline ZnO. From our study it is confirmed that the present crystal contains VZn–hydrogen complexes with low open volumes. Another important nuclear solid technique is the Mossbauer Spectroscopic technique which has been used to probe the local magnetic properties of a solid. Here we have summarized Mossbauer spectroscopic studies on ferrites.

Debnarayan Jana

Papers

Optical properties of monolayer BeC under an external electric field: A DFT approach

Combined theoretical and experimental study of the electronic and optical property of Sb2WO6

A study of anisotropic thermoelectric properties of bulk Germanium Sulfide in its Pnma phase: a combined first-principles and machine-learning approach

Optical and Thermoelectric Behavior of Phagraphene with Site‐Specific B‐N Co‐Doping

Probing Materials by Positron Annihilation Technique and Mossbauer Spectroscopy - Review