关于渗流有限单元法因时空离散而产生的误差讨论

应用有限单元法进行地下水模拟及管理,由于把本来连续的时间和空间离散化,因而会造成一定误差,有时这种误差是不容忽视的.通过计算实例,分析了不同的空间、时间离散格式而产生的误差,应用迭加原理及特征值有限单元法,将因空间和时间离散而产生的误差区分开来,并探讨了减小误差的方法.     

Effects of vertical mixing parameterization on the mixed layer depth over the North Pacific in a global OGCM

We present MLD variability over the North Pacific Ocean in a global ocean general circulation model and impacts of three different vertical mixing schemes on it, based on statistical measures (annual mean difference, root-mean-square difference and correlation coefficient). The constant vertical mixing scheme tends to underestimate MLD over the whole basin. The Pacanowski-Philander scheme tends to overestimate MLD (> 20 m) in the mid- to high latitude during summer, implying that vertical mixing in the mid- to high latitude may not be represented properly by simple internal mixing mechanisms such as stratification or vertical shear of horizontal velocity. On the other hand, the new vertical mixing scheme (Noh et al. 2002) gives the most consistent MLD and its seasonal and spatial variability when compared with observation. These results suggest that parameterization of vertical mixing has significant effects on simulation of the seasonal and spatial variability of MLD over the North Pacific Ocean.     

由多震相走时和波形作三维地震成像

本项成果包括：提出天然地震走时反演层析成像技术,采用下列方法使得处理结果得以改善：１）利用３２个地震,４０４条射线的Ｐｇ,Ｓｇ,Ｐｍ,Ｓｍ,Ｐｎ,Ｓｎ等震相增加约束条件：２）用已有精度较高的人工地震测深化结果作速度约束;３）用波形反演来修改模型,把波源,介质吸收,散射等物理特征集中反映在记录中,把诸多物理量开发出来互为约束,以修改后的模型再作反演,使解的稳定性大大提高;４）采用最优化过程,选择遗传     

Changes in the frequency, scale, and failing areas of latest Quaternary (<29.4 cal. ka B.P.) slope failures along the SW Ulleung Basin, East Sea (Japan Sea), inferred from depositional characters of densely dated turbidite successions

The depositional characters of densely dated turbidite successions originating from the southwestern margin of the Ulleung Basin reveal changes in high-resolution frequency, failing areas, and relative volumes of slope failures over the past 29.4 cal. ka. Between 29.4 and 19.1 cal. ka B.P., various thin- to very thick-bedded turbidites accumulated at an average recurrence interval of ca. 605 years. After 19.1 cal. ka B.P., turbidites were deposited with an average recurrence interval of 3,183 years, and their thickness abruptly decreased upward. These features suggest that various-scale slope failures occurred frequently during the eustatic lowering of sea level, and the frequency and relative volumes of slope failures suddenly decreased after sea level began to rise. When sea level was lowest (20.0–19.1 cal. ka B.P.), successive stacks of very thick turbidites can most likely be ascribed to larger-volume mass failures. An upward change from muddy to sandy turbidites around 21.4 cal. ka B.P. suggests that the failing areas retrograded from the muddy upper-middle slope to the sandy uppermost slope when sea level was nearly at its lowest. Based on these findings together with published evidence, frequent mass failures between 29.4 and 19.1 cal. ka B.P. were plausibly triggered by earthquakes, in combination with reduced hydrostatic pressure that promoted gas-hydrate dissolution during the eustatic lowering of sea level. These data on the frequency, scale, failing areas, and triggering causes of slope failures along the southwestern margin over the past 29.4 cal. ka, not documented in earlier studies, provide invaluable information to better understand the basin-scale characters and occurrences of latest Quaternary slope failures in the Ulleung Basin.     

Global mean sea surface and marine gravity anomaly from multi-satellite altimetry: applications of deflection-geoid and inverse Vening Meinesz formulae

 Global mean sea surface heights (SSHs) and gravity anomalies on a 2^′×2^′ grid were determined from Seasat, Geosat (Exact Repeat Mission and Geodetic Mission), ERS-1 (1.5-year mean of 35-day, and GM), TOPEX/POSEIDON (T/P) (5.6-year mean) and ERS-2 (2-year mean) altimeter data over the region 0^∘–360^∘ longitude and –80^∘–80^∘ latitude. To reduce ocean variabilities and data noises, SSHs from non-repeat missions were filtered by Gaussian filters of various wavelengths. A Levitus oceanic dynamic topography was subtracted from the altimeter-derived SSHs, and the resulting heights were used to compute along-track deflection of the vertical (DOV). Geoidal heights and gravity anomalies were then computed from DOV using the deflection-geoid and inverse Vening Meinesz formulae. The Levitus oceanic dynamic topography was added back to the geoidal heights to obtain a preliminary sea surface grid. The difference between the T/P mean sea surface and the preliminary sea surface was computed on a grid by a minimum curvature method and then was added to the preliminary grid. The comparison of the NCTU01 mean sea surface height (MSSH) with the T/P and the ERS-1 MSSH result in overall root-mean-square (RMS) differences of 5.0 and 3.1 cm in SSH, respectively, and 7.1 and 3.2 μrad in SSH gradient, respectively. The RMS differences between the predicted and shipborne gravity anomalies range from 3.0 to 13.4 mGal in 12 areas of the world's oceans. Received: 26 September 2001 / Accepted: 3 April 2002 Correspondence to: C. Hwang Acknowledgements. This research is partly supported by the National Science Council of ROC, under grants NSC89-2611-M-009-003-OP2 and NSC89-2211-E-009-095. This is a contribution to the IAG Special Study Group 3.186. The Geosat and ERS1/2 data are from NOAA and CERSAT/France, respectively. The T/P data were provided by AVISO. The CLS and GSFC00 MSS models were kindly provided by NASA/GSFC and CLS, respectively. Drs. Levitus, Monterey, and Boyer are thanked for providing the SST model. Dr. T. Gruber and two anonymous reviewers provided very detailed reviews that improved the quality of this paper.     

Partitioning of Semivolatile Organic Compounds in the Presence of a Secondary Organic Aerosol in a Controlled Atmosphere

The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid -pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.     

A study on measurement and analysis of radon-222 (uranium series) emitted to the atmosphere from construction materials (cement block, kaolin brick, and gypsum board) in living environment

The purpose of this study was to measure, compare, and analyze the air concentration of radon that was emitted to the atmosphere from construction materials such as cement brick, tile, red clay tile, and gypsum tile. The study method was to use continuous radon monitoring equipment (RTM 1688-2) to measure concentrations of radon and thoron contained in brick, tile, red clay tile, and gypsum tile. According to the measurement results, the cement brick among the four samples showed the highest measurement value for radon, while the red clay tile showed the highest measurement value for thoron. When the radon emission concentration was estimated based on materials required for construction per unit area (3.3 m²) in an actual construction, the cement brick had the highest measurement values for radon and thoron. This study confirmed the degree of radon emission from construction materials. The purpose of this study was also to suggest a method to examine the effects of radon and reduce the dose of personal radiation exposure. It is believed that the government should be active in publicizing and managing use of construction materials that have lower levels of radon emission.     

Advances in computational morphodynamics using the International River Interface Cooperative (iRIC) software

Results from computational morphodynamics modeling of coupled flow–bed–sediment systems are described for 10 applications as a review of recent advances in the field. Each of these applications is drawn from solvers included in the public-domain International River Interface Cooperative (iRIC) software package. For mesoscale river features such as bars, predictions of alternate and higher mode river bars are shown for flows with equilibrium sediment supply and for a single case of oversupplied sediment. For microscale bed features such as bedforms, computational results are shown for the development and evolution of two-dimensional bedforms using a simple closure-based two-dimensional model, for two- and three-dimensional ripples and dunes using a three-dimensional large-eddy simulation flow model coupled to a physics-based particle transport model, and for the development of bed streaks using a three-dimensional unsteady Reynolds-averaged Navier–Stokes solver with a simple sediment-transport treatment. Finally, macroscale or channel evolution treatments are used to examine the temporal development of meandering channels, a failure model for cantilevered banks, the effect of bank vegetation on channel width, the development of channel networks in tidal systems, and the evolution of bedrock channels. In all examples, computational morphodynamics results from iRIC solvers compare well to observations of natural bed morphology. For each of the three scales investigated here, brief suggestions for future work and potential research directions are offered. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd     

Intranight optical variability in Seyfert 2 galaxies

Preliminary results from a pilot program to monitor the intranightoptical variability in Seyfert 2 galaxies are reported. This program is designed to test some of the prominent theoretical mechanismsproposed for the origin of optical microvariability in active galacticnuclei (AGN). Two out of 3 Seyfert 2 galaxies observed show evidence formicrovariations. This detection can provide important constraints forthe models utilizing discrete events on accretion disks.