On a New Approach for Constructing Wormholes in Einstein-Born-Infeld Gravity

We study a new approach for the wormhole construction in Einstein-Born-Infeld gravity, which does not require exotic matters in the Einstein equation. The Born-Infeld field equation is not modified from "coordinate independent" conditions of continuous metric tensor and its derivatives, even though the Born-Infeld fields have discontinuities in their derivatives at the throat in general. We study the relation of the newly introduced conditions with the usual continuity equation for the energy-momentum tensor and the gravitational Bianchi identity. We find that there is no violation of energy conditions for the Born-Infeld fields contrary to the usual approaches. The exoticity of energy-momentum tensor is not essential for sustaining wormholes. Some open problems are discussed.Comment: Minor revision to improve the clarity, Corrected typos, Added reference and footnot

implications for paleobiogeography, paleoecology, and evolution, with a taxonomic review of Mongolian armored dinosaurs

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 지구환경과학부, 2022. 8. 이융남.갑옷공룡(Ankylosauria)은 사족보행인 초식 공룡의 한 무리로 골편(骨片, osteoderm)들이 융합된 두개골(頭蓋骨, skull)과 몸통의 배측면(背側面, dorsolateral)에 골편들이 부시상(副矢狀, parasagittal)으로 덮고 있는 것이 특징이다. 2007년과 2008년 사이에 한국-몽골 국제공룡탐사에 의해 갑옷공룡 표본들이 고비사막에서 추가로 발견됐다. 본 표본들은 상부 백악기 Cenomanian–Turonian 바얀시레층(Bayanshiree Formation), middle–upper Campanian 바룬고욧층(Baruungoyot Formation), 그리고 upper Campanian–lower Maastrichtian 네메겟층(Nemegt Formation)에서 발견됐다. 바얀시레(Bayan Shiree)의 바얀시레층에서 산출된 새로운 두개골 표본 세 개를 통해 Talarurus plicatospineus의 정의를 재정립할 수 있었다. 힐멘자프(Hermiin Tsav)의 네메겟층에서 산출된 두개골을 포함한 부분적인 두후골격(頭後骨格, postcranial)은 새로운 분류군으로 확인돼 Tarchia tumanovae로 명명됐다. 힐멘자프의 바룬고욧층에서 산출된 새로운 두후골격 표본은 불분명한 안킬로사우루스과(Ankylosauridae)로 분류됐다. 계통발생 분석(phylogenetic analysis) 결과는 Talarurus속이 Saichania chulsanensis, Tarchia kielanae, 그리고 Zaraapelta nomadis를 포함한 아시아의 파생된 안킬로사우루스아과(Ankylosaurinae)의 자매 분류군(sister taxon)임을 보여준다. 또한 안킬로사우루스아과의 아시아에서 북아메리카 대륙으로의 이주(移住, migration)가 Cenomanian 이전에 있었음을 보여준다. Talarurus속과 바얀시레층의 또 다른 안킬로사우루스과인 Tsagantegia속 사이의 주둥이 형태 차이는 이들의 생태지위 분할(niche partitioning)을 시사한다. Tar. tumanovae의 인골뿔(鱗骨–, squamosal horn)은 외피층(外皮層, external dermal layer)과 그 밑에 있는 진정인골뿔(眞情鱗骨–, squamosal horn proper)로 나뉜다. 외피층의 불규칙한 복면(腹面, ventral) 가장자리는 흡수된 표면을 나타낼 수 있으며, 이는 일부 안킬로사우루스아과의 인골뿔이 극단적인 개체발생적(ontogenetic) 변화를 겪었음을 시사한다. 또한 배천추(背薦椎, dorsosacral vertebra)의 늑골(肋骨, rib) 부위와 꼬리의 국소적 골절 흔적은 이들의 세력투쟁행위(agonistic behavior)의 증거를 제공한다. Tar. tumanovae의 비대칭인 꼬리곤봉(tail club)은 이런 행위로 인한 뼈의 비정상적인 성장 때문인 것으로 보인다. 더 나아가, 안킬로사우루스과(Ankylosauridae)의 섭식방법은 상부 백악기 middle Campanian–early Maastrichtian 중에 대량섭식(bulk-feeding)에서 선택적 섭식(selective feeding)으로 바뀐 것으로 보인다. 안킬로사우루스과의 이런 생태지위 변화는 서식지 변화와 다른 대량섭식 초식 공룡과의 경쟁 때문인 것으로 여겨진다. 아시아의 안킬로사우루스과는 후두골격이 뻣뻣해지고 뒷발의 지골(趾骨, pedal phalanges) 수가 줄어드는 방향으로 진화했다. 안킬로사우루스과에는 두 가지 형태의 측면(側面, flank) 갑옷, 하나는 가시형(spine-like)의 골편, 그리고 다른 하나는 용골(龍骨, keel)이 발달한 능형(菱形, rhomboid)의 골편이 있음이 확인됐다. 안킬로사우루스과에서는 땅파기와 관련된 독특한 해부학적 특징들도 확인됐다. 땅파기와 관련된 특징들로는 배복(背腹, dorsoventral) 방향으로 납작한 방추형(紡錘形, fusiform)의 몸통, 광범위하게 융합된 척추, 전후(前後, anteroposteriorly) 방향으로 넓은 늑골, 잘 발달된 삼각흉근능선(三角胸筋稜線, deltopectoral crest)을 가진 강건한 상완골(上腕骨, humerus), 잘 발달된 주두돌기(肘頭突起, olecranon process)를 가진 짧은 척골(尺骨, ulna), 모종삽형(trowel-like) 앞발, 그리고 지골 수가 줄어든 뒷발이 있다. 비록 굴착형(fossorial) 동물은 아니었지만, 안킬로사우루스과는 자기 방어와 생존을 위해 땅을 잘 파헤쳤을 것으로 보인다. 더 나아가, 본 학위논문에서는 몽골에서 알려진 10종의 갑옷공룡에 대한 분류학적 리뷰를 실시하였다.Ankylosaurs are a group of dinosaurs that are quadrupedal, herbivorous, and have a heavily ornamented skull and parasagittal rows of osteoderms covering the dorsolateral surfaces of the body. Additional ankylosaur specimens were discovered in the Gobi Desert of Mongolia by the Korea-Mongolia International Dinosaur Expedition between 2007 and 2008. They were excavated from the Upper Cretaceous Bayanshiree (Cenomanian–Turonian), Baruungoyot (middle–upper Campanian), and Nemegt (upper Campanian–lower Maastrichtian) formations. Based on the three new skulls from the Bayanshiree Formation of Bayan Shiree cliffs, the diagnosis of Talarurus plicatospineus is revised. A new skull with a partial postcranial skeleton collected from the Nemegt Formation in Hermiin Tsav turned out to be a new taxon, Tarchia tumanovae sp. nov. A new articulated postcranial specimen from the Baruungoyot Formation in Hermiin Tsav is classified as an indeterminate ankylosaurid dinosaur. The phylogenetic analysis showed that Talarurus is sister to the clade that includes the derived Asian ankylosaurines (Saichania chulsanensis, Tarchia kielanae, and Zaraapelta nomadis). It also showed that there was the dispersal of ankylosaurines from Asia to western North America before the Cenomanian. The rostral differences between Talarurus and Tsagantegia, another ankylosaurine from the Bayanshiree Formation, suggest possible niche partitioning among these taxa. The squamosal horns of Tar. tumanovae are divided into the external dermal layer and the underlying squamosal horn proper. The irregular ventral margin of the base of the upper dermal layer may represent a resorption surface, suggesting that the squamosal horns of some ankylosaurines underwent extreme ontogenetic remodeling. Localized pathologies on the dorsosacral ribs and the tail provide evidence of agonistic behavior. The tail club knob asymmetry of Tar. tumanovae resulted from restricted bone growth due to tail club strikes. Furthermore, ankylosaurid diets shifted from low-level bulk feeding to selective feeding during the Baruungoyot and the Nemegt “age” (middle Campanian–lower Maastrichtian). This ankylosaurid niche shifting might have responded to habitat change and competition with other bulk-feeding herbivores. Asian ankylosaurids evolved rigid bodies with a decreased number of pedal phalanges. There were also at least two forms of flank armor within Ankylosauridae, one with spine-like osteoderms and the other with keeled rhomboidal osteoderms. Unique anatomical features related to digging are present in Ankylosauridae, such as dorsoventrally flattened and fusiform body shapes, extensively fused series of vertebrae, anteroposteriorly broadened dorsal ribs, a robust humerus with a well-developed deltopectoral crest, a short and robust ulna with a well-developed olecranon process, a trowel-like manus, and decreased numbers of pedal phalanges. Although not fossorial, ankylosaurids were likely to dig the substrate, taking advantage of it for self-defense and survival. Moreover, all ten ankylosaur species known in Mongolia are reviewed in this dissertation.I. INTRODUCTION 1 II. MATERIALS AND METHODS 6 III. GEOLOGICAL SETTING 8 III-1. Bayanshiree Formation 8 III-2. Baruungoyot Formation 13 III-3. Nemegt Formation 18 IV. RESULTS 25 IV-1. Systematic paleontology 25 Talarurus plicatospineus Maleev, 1952b 25 Tarchia Maryanska, 1977 44 Tarchia tumanovae sp. nov. 45 Ankylosauridae, gen. et sp. indet. 73 V. PHYLOGENETIC ANALYSES 99 V-1. Phylogenetic placement of Talarurus plicatospineus 99 V-2. Phylogenetic placement of Tarchia tumanovae sp. nov. 103 VI. DISCUSSION 105 VI-1. Paleoecology of Talarurus and Tsagantegia 105 VI-2. Squamosal horn remodeling in ankylosaurines 110 VI-3. Evidence of agonistic behavior in ankylosaurines 111 VI-4. Niche shifting in Mongolian ankylosaurids 114 VI-5. Postcranial evolution of ankylosaurids 117 VI-6. Digging ability of ankylosaurids 121 VII. TAXONOMIC REVIEW OF MONGOLIAN ANKYLOSAURS 125 VII-1. Introduction 125 VII-2. Systematic paleontology 126 Shamosaurus scutatus Tumanova, 1983 126 Minotaurasaurus ramachandrani Miles and Miles, 2009 132 Pinacosaurus grangeri Gilmore, 1933 137 Saichania chulsanensis Maryaska, 1977 148 Talarurus plicatospineus Maleev, 1952b 155 Tarchia kielanae Maryanska, 1977 160 Tarchia teresae Penkalski and Tumanova, 2017 165 Tarchia tumanovae sp. nov. 170 Tsagantegia longicranialis Tumanova, 1993 171 Zaraapelta nomadis Arbour et al., 2014b 175 VIII. CONCLUSIONS 179 REFERENCES 182 APPENDIX 1. Institutional abbreviations 228 APPENDIX 2. Abbreviations used in figures 229 APPENDIX 3. Data matrix related to chapter V-1 231 APPENDIX 4. Character statements related to chapter V-2 238 APPENDIX 5. Data matrix related to chapter V-2 239 국문초록 240 감사의 글 243박

The effect of rare-earth element additions on microstructural properties and irradiation behavior of an Fe-Ni-Cr alloy for LMFBR and fusion reactor applications

This study consists of a survey of the effect of yttrium, lanthanum, and cerium rare-earth additions on the microstructure and radiation swelling behavior of an Fe-25.6Ni-8.7Cr-3.3Ti-1.6Al alloy. The undoped alloy was investigated in the as-received, annealed, and arc-melted conditions, and twelve arc melted and rare-earth doped alloys were prepared (doping levels of 0.05, 0.1, 0.5, and 1.0 wt % for each of the three rare earths). The ion bombardments were carried out at 570 and 600(DEGREES)C with 4 MeV Ni or Fe ions to nominal 100 dpa and to 100 and 550 appm He. Lattice parameter, hardness, swelling, and optical and transmission electron microscopy observations were conducted;Ion bombardment at 600(DEGREES)C produced negligible swelling. For ion bombardment at 570(DEGREES)C and helium implantation to 100 appm He, the as-received, annealed, and arc-melted undoped alloy swelled 4.0, 5.1, and 3.8%, respectively. The increase in swelling upon annealing the as-received alloy is believed to be due to the removal of cold work. The subsequent decrease in swelling upon arc melting is interpreted in terms of the reduction in size of the large Ti-rich precipitate and the consequent increase in Ti in solid solution. For ion bombardment at 570(DEGREES)C and helium implantation to 550 appm He, the arc-melted undoped alloy gave 5.2% swelling (as compared to 3.8% for 100 appm He) due to the higher helium loading;The introduction of yttrium or cerium at levels between 0.1 and 1.0% gives rise to a reduction in swelling. This may be due to a decrease in the amount of G-phase precipitate and the size of the large Ti-rich particles. For concentrations above 0.5%, a rare-earth-rich precipitate appeared. At 1% concentrations, the precipitates were observed to swell themselves and to give rise to bulk matrix swelling. The optimum concentrations of Y or Ce for swelling reduction are therefore, considered to be about 0.2-0.4%. Lanthanum additions were not observed to suppress swelling;Unique surface deformations were observed as a result of ion bombardment, especially at and near grain boundaries. At low swelling, the grain boundary region was raised or ridged, probably because of the lateral extrusion-like action of the swelled grains. At higher swelling, the grain bodies were elevated above the grain boundary regions