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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Zinc oxide (ZnO) is a wide band gap semiconductor with potential applications in optoelectronics, transparent electronics, and spintronics. The high efficiency of UV emission in this material could be harnessed in solid-state white lighting devices. The problem of defects, in particular, acceptor dopants, remains a key challenge. In this review, defects in ZnO are discussed, with an emphasis on the physical properties of point defects in bulk crystals. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. However, experiments and theory have shown that O vacancies are deep donors, while Zn interstitials are too mobile to be stable at room temperature. Group-III (B, Al, Ga, and In) and H impurities account for most of the n-type conductivity in ZnO samples. Interstitial H donors have been observed with IR spectroscopy, while substitutional H donors have been predicted from first-principles calculations but not observed directly. Despite numerous reports, reliable p-t...

Defects in ZnO

Contemporary theories of defects and impurities in semiconductors rely to a large extent on supercell calculations within density-functional theory using the approximate local-density approximation (LDA) or generalized gradient approximation (GGA) functionals. Such calculations are, however, affected by considerable uncertainties associated with: (i) the ``band-gap problem,'' which occurs not only in the Kohn-Sham single-particle energies but also in the quasiparticle gap (LDA or GGA) calculated from total-energy differences, and (ii) supercell finite-size effects. In the case of the oxygen vacancy in ZnO, uncertainties (i) and (ii) have led to a large spread in the theoretical predictions, with some calculations suggesting negligible vacancy concentrations, even under Zn-rich conditions, and others predicting high concentrations. Here, we critically assess (i) the different methodologies to correct the band-gap problem. We discuss approaches based on the extrapolation of perturbations which open the band gap, and the self-consistent band-gap correction employing the $\text{LDA}+U$ method for $d$ and $s$ states simultaneously. From the comparison of the results of different gap-correction, including also recent results from other literature, we conclude that to date there is no universal scheme for band gap correction in general defect systems. Therefore, we turn instead to classification of different types of defect behavior to provide guidelines on how the physically correct situation in an LDA defect calculation can be recovered. (ii) Supercell finite-size effects: We performed test calculations in large supercells of up to 1728 atoms, resolving a long-standing debate pertaining to image charge corrections for charged defects. We show that once finite-size effects not related to electrostatic interactions are eliminated, the analytic form of the image charge correction as proposed by Makov and Payne leads to size-independent defect formation energies, thus allowing the calculation of well-converged energies in fairly small supercells. We find that the delocalized contribution to the defect charge (i.e., the defect-induced change of the charge distribution) is dominated by the dielectric screening response of the host, which leads to an unexpected effective $1/L$ scaling of the image charge energy, despite the nominal $1/{L}^{3}$ scaling of the third-order term. Based on this analysis, we suggest that a simple scaling of the first order term by a constant factor (approximately 2/3) yields a simple but accurate image-charge correction for common supercell geometries. Finally, we discuss the theoretical controversy pertaining to the formation energy of the O vacancy in ZnO in light of the assessment of different methodologies in the present work, and we review the present experimental situation on the topic.

Assessment of correction methods for the band-gap problem and for finite-size effects in supercell defect calculations: Case studies for ZnO and GaAs

/pdf/developing-new-routine-for-processing-two-dimensional-31m8us3p8o.pdf

Developing New Routine for Processing Two-Dimensional Coincidence Doppler Energy Spectra and Evaluation of Electron Subsystem Properties in Metals

Stress measurements were performed using accelerator-based γ-ray induced positron annihilation spectroscopy technique, which allows probing of defects at high depths in thick materials up to several centimeters. Induced stresses due to tensile, fatigue, cold work, and bending tests were investigated in steel alloys of about 1-cm thickness. The measurements showed the dependence of the line-shape parameter of the annihilation peak S on the induced deformation in the four tests. They also revealed an interesting behavior for the change of S parameter with tensile deformation, related to the engineering stress-strain curve of the material. Transmission electron microscopy measurements of dislocation density in cold work deformation suggested that the saturation of positron annihilation parameters often observed in cold work data is not due to compete positron trapping at defects. It was also shown that the S parameter has a weak sensitivity and quickly saturates in fatigue test when compared with the other m...

High depth nondestructive stress measurements on thick steel alloys

A new monoenergetic MeV positron beam source was designed and constructed at the Lawrence Livermore National Laboratory (LLNL) positron facility The positron source provides a low emittance beam with high energy resolution for channeling, scattering, and in-flight annihilation experiments New beam optics for extracting slow positrons from a moderator mounted in a Pelletron electrostatic accelerator is presented A beam line was designed and constructed to energy analyze the output of the accelerator and to provide adjustable size and angular divergence beams to a target station A post target large angle acceptance magnet separates positrons transmitted through the target from forward gamma ray emission

Improved source and transport of monoenergetic MeV positrons

Site-fractions of indium impurity probe atoms occupying up to three inequivalent Al-sites in Al3Ti, Al3V and Al3Zr phases were measured using perturbed angular correlation of gamma rays (PAC). Sites were identified via characteristic nuclear quadrupole interactions. Ratios of site-fractions were measured in thermal equilibrium in the range 600 to 1,210 K. Arrhenius plots of the ratios were fitted with thermally activated expressions, yielding differences in vibrational entropies and site-enthalpies. Enthalpy differences were greatest for Al3Zr, ~0.22 eV, and smaller for Al3Ti and Al3V, which is correlated with the excess volume of the transition-metal atom over the Al-atom. Vibrational entropy differences were small, in the range 0 to −0.25 kB.

Site preferences of indium impurity atoms in intermetallics having Al3Ti or Al3Zr crystal structures

α-Al2O3 powder is widely used in numerous applications, especially in optical ceramics and crystals growth. However, achieving perfect dispersibility is essential in these applications and requires a complete understanding of the dispersion mechanism as well as high technology processing. In this paper, a step-by-step horizontal ball-milling method was adopted to improve the dispersibility of α-Al2O3 powders through coprecipitation. Effects of ball milling processes and Al3+ concentration on the particle size and the dispersity of alumina precursor were systematically investigated. The presence of absorbed sulfate ion on the surface of the particles could inhibit aggregation processes. Precursors were evolved into α-Al2O3 phase after subsequent calcination of 1180 °C in air. The work shows that step-by-step horizontal ball-milling achieves a well-dispersible powder with quasi-spherical morphology and narrow size distribution in the range of 150 ~ 200 nm.

Farida Selim

Papers

Developing New Routine for Processing Two-Dimensional Coincidence Doppler Energy Spectra and Evaluation of Electron Subsystem Properties in Metals

High depth nondestructive stress measurements on thick steel alloys

Improved source and transport of monoenergetic MeV positrons

Site preferences of indium impurity atoms in intermetallics having Al3Ti or Al3Zr crystal structures

High dispersibility of α-Al2O3 powders from coprecipitation method by step-by-step horizontal ball-milling