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Information Center for Mathematical Science

세미나

Information Center for Mathematical Science

세미나

한국고등과학원 세미나

Mean dimension and the embedding problem in dynamical systems.

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

고려대학교 지구환경과학과 세미나

서울대학교 지구환경과학부 세미나

서울대학교 지구환경과학부 세미나

Subsurface contamination by heavy metals, radionuclides, or organic contaminants is a big concern for human health and environmental protection. In situ bioremediation is one option for reducing levels of contaminants. Dissimilatory iron- and sulfate-reducing Bacteria (DIRB and DSRB) are common subsurface microorganisms as iron and sulfate are abundant in many natural environments. DIRB and DSRB couple the oxidation of organic carbon or H2 to the reduction of iron and sulfate, which plays important roles in cycling of carbon, metals, and sulfur in the subsurface environment. DIRB and DSRB have also profound implications for the fate and transport of heavy metals, radionuclides or organic contaminants in aquatic and terrestrial systems. For example, the growth of DIRB and DSRB often reduces contaminants either directly or by the production of reactive Fe(II) and sulfur species. In this presentation, we will discuss 1) the effects of several electron donors on the enrichment of specific communities capable of reducing iron and sulfate, and 2) the effects of sulfate reduction on FeIII (hydr)oxide reduction and microbial community development.

서울대학교 지구환경과학부 세미나

Rechargeable battery systems based on Mg-ion chemistries are generating signi cant interest as potential alternative to Li-ion batteries. Despite the wealth of local structural information that could potentially be gained from Nuclear Magnetic Resonance (NMR) experiments of Mg-ion battery materials, low natural abundance, low gyromagnetic ratio, and signi cant quadrupole moment of 25Mg all contribute to the challenging nature of this nucleus. Computational pre-diction of NMR parameters and several advanced pulse sequences are invaluable aids, both in performing such experiments and in interpreting the observed spectra. In the rst part of this talk, I will discuss the application of this approach to Mg-ion battery cathodes, which often incorporate paramagnetic transition metal ions; the hyper ne shift mechanism and implications for signal enhancement will be shown.[1] In the second part, I will illustrate how ab initio calcu-lations of the electronic structure and Mg-ion migration barriers could be used to interpret the ionic motion in Mg3Bi2 as shown through variable-temperature 25Mg NMR experiments.[2,3]

서울대학교 지구환경과학부 세미나

서울대학교 지구환경과학부 세미나

본 강연은 환경, 보건, 생의학 분야의 과학사, 과학기술과 사회(STS)의 연구분야들의 사례들을 통해 과학기술과 사회의 상호작용을 어떻게 이해할 것인지를 소개하는 것을 큰 목적으로 한다. 강의의 초반부에서는 20세기 과학의 상업화를 추동하며 그 모델을 제공했던 스탠포드 대학에서의 과학 상업화에 대한 강연자 본인의 과학사적 연구를 소개할 것이다. 이를 통해 과학의 상업화 과정에 관련된 법과 제도, 윤리적 논란들을 소개하며 과학사를 통해 과학기술과 사회와의 접점을 어떻게 바라볼 수 있는지를 간략히 논의해볼 것이다. 이와 함께 지식 생산의 법과 정치경제에 관심을 가지게 된 강연자가 어떻게 보건과 환경 영역의 법, 규제 연구들로 관심을 넓혀가고 있는지를 간략히 소개할 것이다.

서울대학교 지구환경과학부 세미나

We define subducting plate geometries in the Nazca subduction zone by (re)locating intra-slab earthquakes in southern Peru (14–18°S) and using previously published converted phase analysis results to clarify the slab geometry and inferred relationships to the seismicity. We also provide both P- and S-wave velocity models of the subducting Nazca Plate and mantle layer above the slab using double-difference tomography to understand upper-plate volcanism and subduction zone process. The double-difference constraints for determining the hypocenters and velocity model ensure high accuracy of the relative location of earthquakes with respect to velocity structure. The relocated seismicity shows a smooth contortion in the slab-dip transition zone for ∼400 km between the shallow (30°)-to-flat dipping interface to the northwest and the 30°-dipping interface to the southeast. We find a significant slab-dip difference (up to 10°) between our results and previous slab models along the profile region sampling the horizontal slab at a depth of ∼85–95 km. Robust features in both P- and S-wave tomography inversions are both arc-normal and along-arc velocity variations. In the arc-normal direction, all profile results show that the slab velocities beneath the forearc (down to a depth of ∼100 km) transition to higher velocities beneath the backarc (at ∼100–140 km depth). In the along-arc direction, velocities of the subducting flat slab are shown to be depressed compared to those of the normal-dip slab. In addition, high shear-wave velocities and low Vp/Vs are detected in the mantle layer above the flat slab, indicating its cold and dry environment. Such differences in the velocity structures for the slab and mantle wedge between the two regions may indicate different hydration states, which greatly affects the upper-plate structure of southern Peru.

서울대학교 지구환경과학부 세미나

Oxygen (16O, 17O and 18O) and sulfur (32S, 33S, 34S and 36S) isotope ratios of and major ion (Na+, Ca2+, Cl-, NO3- and SO42-) concentrations in lakes, ponds and creeks from Deception Island, Antarctic Peninsula were analyzed to study the sources of sulfate, its oxidation, and the surficial processes of the dissolved sulfate. The positive relationship between the δ34Ssulfate (8.1 ‰ to 17.3 ‰) and the Cl-/SO42- molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals. The average sea salt fraction (28 %) and δ34Snss values (from 5.6 ‰ to 15.9 ‰) indicate that a combination of sea salt and marine biogenic sulfide provide the high δ34S end-member of the dissolved sulfates. The relatively low δ18Osulfate (from -4.6 ‰ to 0.7 ‰) of Deception Island water suggests a role of local water in the formation of sulfate. Slightly negative but mass-dependent Δ17Osulfate values imply that atmospheric oxidation by O3 and H2O2 are negligible, while these values might suggest a significant role of oxidation by molecular oxygen and •OH. The distinctly low δ34Ssulfate value of two samples suggests the input of sulfate from sulfide oxidation. Slight elevation of δ34Ssulfate values up to 17.3 ‰ compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of Deception Island water and sediments. Both Δ33Ssulfate and Δ36Ssulfate values are homogeneous and near zero, implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to Deception Island water.

서울대학교 지구환경과학부 세미나

서울대학교 지구환경과학부 세미나

perational Numerical Weather Prediction (NWP) model outputs are used to develop an algorithm of aviation turbulence forecasts. This computes a set of diagnostics that identify regions of strong spatial gradients of meteorological variables related to various generation mechanisms for Clear-Air and Mountain-Wave Turbulence. Then, using the empirical mapping technique, these indicators are converted into an equivalent Energy Dissipation Rate (EDR) to the 1/3 power. This atmospheric turbulence metric is the International Civil Aviation Organization standard for aircraft reporting and thus provides a convenient basis for verification. Implicit in the process is the assumption of a downscale cascade of energy from the large scales resolved by operational NWP models to the smaller scales aircraft feel as turbulence (~hundreds of meter) in the Upper Troposphere and Lower Stratosphere. Finally, probabilistic forecasts are provided from the diagnostic ensemble as well as from the NWP initial ensemble, so that it takes into account uncertainties in both the NWP model and turbulence diagnostics. Statistical verifications of the algorithm are examined using the Relative Operator Characteristic curves derived through comparisons to a global archive of in situ EDR data during the research period. It is found that probabilistic EDR forecast is superior to the current operational forecast product, which is based on a single turbulence index for turbulence potential.

한국천문연구원 콜로퀴움

The Galactic halo is thought to form, at least in part, from the accretion of dark-matter dominated mini-halos. These mini-halos are also responsible for donating the so-called CEMP-no stars to the halo, which are thought to be bona-fide second-generation stars. A recent study has suggested the existence of multiple pathways to form CEMP-no stars, based on the distinct morphological stellar distribution present in the A(C)-[Fe/H] space. In this talk, I will briefly review our current understanding of the chemodynamical nature of the CEMP-no stars and its implication on the nature of the first stars. I also present important evidence regarding Galactic assembly history revealed by the similarity of CEMP-no group morphology present among the metal-poor stars in satellite dwarf galaxies.

한국천문연구원 콜로퀴움

I will present key results from the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM), a high resolution survey of molecular gas in galaxy nuclei. First, I will show that CO can be used to easily and accurately measure the mass of the supermassive black holes lurking at galaxy centres. I will discuss substantial ongoing efforts to do this, and present many spectacular new ALMA measurements, the latest of which rival the best black hole measurements to date. This opens the way to literally hundreds of measurements across the Hubble sequence (in both active and non-active galaxies) with a unique method. Second, I will briefly show how the same data allow to study the spatially-resolved properties of the giant molecular clouds in all the galaxies studied. This will yield cloud censuses in non-local galaxies (including early-type galaxies) for the first time, providing a new tool to understand and contrast the star formation efficiency across galaxies. Already, it appears that basic cloud properties are not universal and vary systematically along the Hubble sequence, contrary to long-held assumptions.