The cosmological dependence of galactic specific angular momenta     

Vincent Eke  †  George Efstathiou  Lisa Wright 《Monthly notices of the Royal Astronomical Society》2000,315(2):L18-L22

Hydrodynamical simulations of galaxy formation in spatially flat cold dark matter (CDM) cosmologies with and without a cosmological constant (Λ) are described. A simple star formation algorithm is employed and radiative cooling is allowed only after redshift z =1 so that enough hot gas is available to form large, rapidly rotating stellar discs if angular momentum is approximately conserved during collapse. The specific angular momenta of the final galaxies are found to be sensitive to the assumed background cosmology. This dependence arises from the different angular momenta contained in the haloes at the epoch when the gas begins to collapse and the inhomogeneity of the subsequent halo evolution. In the Λ-dominated cosmology, the ratio of stellar specific angular momentum to that of the dark matter halo (measured at the virial radius) has a median value of ∼0.24 at z =0. The corresponding quantity for the Λ=0 cosmology is over three times lower. It is concluded that the observed frequency and angular momenta of disc galaxies pose significant problems for spatially flat CDM models with Λ=0 but may be consistent with a Λ-dominated CDM universe.  相似文献   

Chemical Composition of Ancient Celadon Material （1127-1279 A.D.） from Zhejiang, China and Its Implication     

PENG Zicheng LEUNG Po Lau YU Peter CHENG Peikai LI Mai 《《地质学报》英文版》2006,80(5):759-762

The microprobe EDXRF equipment was used for analysis of the major and trace elements in glaze layer-transitive layer-body layer of the celadon from the Altar Yao （Kiln） and Laohudong Yao in the Southern Song Dynasty （1127-1279 A.D.）, Zhejiang, China. The K values of the discriminant factor for the celadon wares are larger than 8, which means the celadon of the Altar Yao and Laohudong Yao are different from that of the Longquan Yao. The former two belong to the Guan Yao system （the Chinese imperial kilns）, but the latter to the Min Yao system （the Chinese popular kilns）. The principle component analysis shows their relationship between the Altar and Laohudong wares with provenance postulation. The thickness of the transitive layer in the Altar and Laohudong wares is obviously different, which reveals the microstructure characteristics of the celadon even though both kinds of wares belong to the imperial kiln system.  相似文献   

Polyorogenic reworking of ore‐controlling shear zones at the South Range of the Sudbury impact structure: A telltale story from in situ U–Pb titanite geochronology          下载免费PDF全文

Konstantinos Papapavlou  James R. Darling  Peter C. Lightfoot  Stephanie Lasalle  Lisa Gibson  Craig D. Storey  Desmond Moser 《地学学报》2018,30(3):254-261

The post‐impact orogenic evolution of the world class Ni–Cu–PGE Sudbury mining camp in Ontario remains poorly understood. New temporal constraints from ore‐controlling, epidote–amphibolite facies shear zones in the heavily mineralised Creighton Mine (Sudbury, South Range) illuminate the complex orogenic history of the Sudbury structure. In situ U–Pb dating of shear‐hosted titanite grains by LA‐ICP‐MS reveals new evidence for shear zone reworking during the Yavapai (ca. 1.77–1.7 Ga), Mazatzalian–Labradorian (1.7–1.6 Ga) and Chieflakian–Pinwarian (1.5–1.4 Ga) accretionary events. The new age data show that the effects of the Penokean orogeny (1.9–1.8 Ga) on the structural architecture of the Sudbury structure have been overestimated. At a regional scale, the new titanite age populations corroborate that the Southern Province of the Canadian Shield documents the same tectonothermal episodes that are recorded along orogenic strike within the accretionary provinces of the Southwestern United States.  相似文献   

Office of Naval Research contributions to neural networks andsignal processing in oceanic engineering     

Miller  W. McKenna  T. Lau  C. 《Oceanic Engineering, IEEE Journal of》1992,17(4):299-307

The authors summarize many of the highlights and accomplishments of the Office of Naval Research's neural network basic research programs and share a bit of the historical perspective that serves as a source of pride in the world of Navy science and technology, namely, the long-term support and resulting payoff of Navy-sponsored research in neural networks. The significant problems that must be overcome before neural network applications will become widely available to the Navy community are surveyed  相似文献   

Induction of Metamorphosis in the Asian Shore Crab <Emphasis Type="Italic">Hemigrapsus sanguineus</Emphasis>: Effects of Biofilms and Substratum Texture     

Mia K. Steinberg  Lisa S. Krimsky  Charles E. Epifanio 《Estuaries and Coasts》2008,31(4):738-744

Since its initial invasion in the late 1980s, the Asian shore crab Hemigrapsus sanguineus has spread over 650 km along the Atlantic Coast of the United States. Larvae of this species can live in the water column for over 3 weeks, which provides ample time for transport to new locations. Previous research on the settlement and metamorphosis of H. sanguineus showed that postlarvae (megalopae) accelerate metamorphosis in response to very specific water-soluble cues. However, the response to substratum cues appears to be much broader. The experiments presented here were designed to test the metamorphic response to biofilms and substratum texture. We found that nylon mesh with pore size of 100 and 1,000 μm had a greater effect on mean time to metamorphosis than 10 and 2,000 μm mesh. Results also showed a positive response to natural rock substrata, and this response was most pronounced when megalopae were exposed to substrata with rough texture. In addition, we found that a combination of a textured surface and a natural biofilm accelerated metamorphosis more than either an abiotic substratum or a smooth surface covered with natural biofilm. A final experiment compared the effect of textural cues to that of a water-soluble cue found in exudate from adult H. sanguineus. Results indicated that both types of cue-induced metamorphosis to the same extent.  相似文献   

‘Jack of all trades’? The negotiation of interdisciplinarity within geography     

Lisa Lau  Margaret Pasquini 《Geoforum》2008,39(2):552-560

This paper explores the relationship between interdisciplinary studies and research and researchers’ positionalities, both within and beyond geography. The profound degree to which researchers’ assumptions, expectations and attitudes (which in turn are affected by their personal backgrounds, training, location, etc.) influences the very notion of interdisciplinarity, and what it involves and consists of, is often neither noted nor appreciated. This paper will illustrate, particularly through personal examples, how positionality is part of the circuit of knowledge production, informing academic research, employment and publishing to no small extent. The boundaries of interdisciplinary research are shown to be under constant negotiation, still far from mutual understanding or consensus, a fact which explains the often uneasy identification and negotiation of oneself as an interdisciplinary scholar. The paper concludes by making recommendations at individual and institutional level on how to overcome some of the constraints imposed by researchers’ positionalities to the promotion of interdisciplinary research.  相似文献   

A hybrid genetic algorithm with local optimiser improves calibration of a vegetation change cellular automata model     

Rachel Whitsed  Lisa T. Smallbone 《International journal of geographical information science》2017,31(4):717-737

Cellular automata (CA) models are commonly used to model vegetation dynamics, with the genetic algorithm (GA) being one method of calibration. This article investigates different GA settings, as well as the combination of a GA with a local optimiser to improve the calibration effort. The case study is a pattern-calibrated CA to model vegetation regrowth in central Victoria, Australia. We tested 16 GA models, varying population size, mutation rate, and level of allowable mutation. We also investigated the effect of applying a local optimiser, the Nelder?Mead Downhill Simplex (NMDS) at GA convergence. We found that using a decreasing mutation rate can reduce computational cost while avoiding premature GA convergence, while increasing population size does not make the GA more efficient. The hybrid GA-NMDS can also reduce computational cost compared to a GA alone, while also improving the calibration metric. We conclude that careful consideration of GA settings, including population size and mutation rate, and in particular the addition of a local optimiser, can positively impact the efficiency and success of the GA algorithm, which can in turn lead to improved simulations using a well-calibrated CA model.  相似文献   

Tropical air-sea interaction in general circulation models   总被引：10，自引：0，他引：10  

J D Neelin  M Latif  M A F Allaart  M A Cane  U Cubasch  W L Gates  P R Gent  M Ghil  C Gordon  N C Lau  C R Mechoso  G A Meehl  J M Oberhuber  S G H Philander  P S Schopf  K R Sperber  K R Sterl  T Tokioka  J Tribbia  S E Zebiak 《Climate Dynamics》1992,7(2):73-104

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Experimental modelling of the near-field thermal regime in a nuclear-fuel waste disposal vault     

H.S. Radhakrishna  K.C. Lau  A.M. Crawford 《Engineering Geology》1990,28(3-4):337-351

Experiments have been performed to study the thermal performance of a backfilled disposal vault in which the waste containers are emplaced in boreholes and surrounded by a bentonitesand buffer.

The near-field thermal regime in a buffer-backfill disposal vault in which the nuclear fuel waste is emplaced in canisters, is studied by one-eight scale experimental models. The thermal performance of the buffer and backfill are examined in a thermal drying environment prior to the ground water recharge of the disposal vault.

The formation of shrinkage cracks in the buffer due to drying and the response of these shrinkage cracks to the rewetting condition and their influence on the near-field thermal regime are assessed.  相似文献   

Gamma emitters in Hong Kong water     

Shun-Yin Lau  Chung-Keung Man  Wai-Kwok Ng  Shui-Chun Au 《Environmental Geology》1990,16(2):129-131

Water samples, representing seawater, river water, reservoir water, drinking water, and underground water were studied through gamma-ray spectral analysis. Only gamma emitters in the²³⁸U and²³²Th series and⁴⁰K were detected. No fission product was detected with specific activity above 0.1 Bq/kg. The present data could be the baseline for future monitoring of the radioactivity released from a nuclear plant being built at a 50-km distance from Hong Kong. The variation of detected specific activities may be due to geological differences and the effect of plants.  相似文献