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

Eu-ドープBaTiO 3 ナノスケール系の改良型および遅延型放射放出反応

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Publisher's Note: “Nonlinear alternating current conduction in polycrystalline manganites” [J. Appl. Phys. 115, 243707 (2014)]

The journey of theoretical study on semiconductors is reviewed in a non-conventional way. We have started with the basic introduction of Hartree-Fock method and introduce the fundamentals of Density Functional Theory (DFT). From the oldest Local Density Approximations (LDA) to the most recent developments of semi-local corrections [Generalised Gradient Approximation (GGA), Meta-GGAs], hybrid functionals and orbital dependent methodologies are discussed in detail. To showcase the performance of DFT, results obtained via different approximations are compared. We indicate the success of semi-local approximations in structural properties prediction. We also show how less computationally costly but withstand architecture of some semi-local DFT methods can solve the long riddle of bandgap underestimation. In semiconductor physics, the importance of not only the band structure prediction, but also, the proper calculation of Fermi energy, and, exact finding of band alignment is argued. The comparison of Fermi energy dependent properties can channelize the theoretical studies on modern age environment-friendly researches on semiconductors, like artificial photocatalysis, energy efficient opto-electronic devices, etc. This prescription on proper choice of DFT method is potentially competent to complement the experimental findings as well as can open up a pathway of advanced semiconducting materials discoveries.

Semiconductor Physics: A Density Functional Journey

Optical properties, like complex dielectric constant, absorption coefficient, refractive index and reflectivity have been analysed via density functional theory (DFT) of As and Ga doped free standing (FS) germanium (Ge) nanosheet. Position dependent (same or different sub-lattice positions) doping mechanism of foreign elements along with concentration variation up to 6.25%, in pristine germanene layer has been adopted for the whole work. Interesting modifications in optical anisotropy than pristine layer have been observed as a consequence of doping. Such modifications, like enhancement or reduction of peak intensity or shifting of peak positions may be useful to design smart germanene based opto-electronics devices in upcoming future.

Modifications of optical properties in doped germanene nanosheet

Graphyne, another similar structure of graphene, consists of double-and triple-bonded units of 
carbon atoms. The presence of triple bonds in graphyne can have intriguing features, having other 
geometry instead of hexagonal as possessed by graphene.

Debnarayan Jana

Papers

Eu-ドープBaTiO 3 ナノスケール系の改良型および遅延型放射放出反応

Publisher's Note: “Nonlinear alternating current conduction in polycrystalline manganites” [J. Appl. Phys. 115, 243707 (2014)]

Semiconductor Physics: A Density Functional Journey

Modifications of optical properties in doped germanene nanosheet

- Electronic and Optical Properties of Boron- and Nitrogen-Functionalized Graphene Nanosheet