Internal generation of waves on an arc in a rectangular grid system

This paper presents a technique to generate waves at oblique angles in finite difference numerical models in a rectangular grid system by using internal generation technique [Lee, C., Suh, K.D., 1998. Internal generation of waves for time-dependent mild-slope equations. Coast. Eng. 34, 35–57.] along an arc-shaped line source. Tests were made for four different types of wave generation layouts. Quantitative experiments were conducted under the following conditions: the propagation of waves on a flat bottom, the refraction and shoaling of waves on a planar slope, and the diffraction of waves to a semi-infinite breakwater. Numerical experiments were conducted using the extended mild-slope equations of Suh et al. [Suh, K.D., Lee, C., Park, W.S., 1997. Time-dependent equations for wave propagation on rapidly varying topography. Coast. Eng. 32, 91–117.]. The fourth layout type consisting of two parallel lines connected to a semicircle showed the best solutions, especially for a small grid size. This technique is useful for the numerical simulation of irregular waves with broad-banded directional spectrum using conventional spectral wave models for the reasonable estimation of bottom friction and wave-breaking.     

Developmental duration and morphology of the sea star asterias amurensis, in tongyeong, Korea

The process of embryogenesis and larval development of the asteroid sea star Asterias amurensis (Lütken) was observed, with special attention paid to morphological change and larval duration. In reproductive season, mature sea stars were collected under floating net cages, located in Tongyeong, southern Korea. The mature eggs are 138 μm in average diameter, semi-translucent and orange in color, sperms in good condition appear light cream to white-gray in color. Embryos develop through the holoblastic equal cleavage stage and a wrinkled blastula stage that lasts about 9 hours after fertilization. Gastrulae bearing an expanded archenteron hatch from the fertilization envelope 22 hours after fertilization. At the end of gastrulation, rudiments of the left and right coelom are formed. By day 2, larvae possess complete alimentary canal and begin to feed. At this stage, the larva is called early bipinnaria. In 6day-old larvae, the pre- and post- oral ciliated bands form complete circuits and the bipinnarial processes start to develop. By day 12, the lateral and anterior projection of the larval wall processes along the ciliated bands begins to thicken and curl, and the ciliated bands become more prominent. By day 32, early brachiolaria are presented with three pairs of brachiolar arms. Advanced brachiolaria with a well-developed brachiolar complex (three pairs of brachia and central adhesive disc) occur 6 weeks after fertilization. In the field, spawning of the sea star was observed in April to May, settlement form larvae and just settlements seem to occur from June to July, and early juveniles occur from August to September. Although we had not described the end of brachiolaria stage, it can be tentatively estimated that the duration of the pelagic stage of A. amurensis is 40 to 50 days.     

Hydrological effects of climate change,groundwater withdrawal,and land use in a small Korean watershed

The effects of variability in climate and watershed (groundwater withdrawal and land use) on dry‐weather streamflows were investigated using SWAT (Soil and Water Assessment Tool). The equation to predict the total runoff (TR) using climate data was derived from simulation results for 30 years by multiple regression analysis. These may be used to estimate effects of various climate variations (precipitation during the dry period, precipitation during the previous wet period, solar radiation, and maximum temperature). For example, if daily average maximum temperature increases by 3 °C, TR during the dry period will decrease by 27·9%. Similarly, groundwater withdrawals strongly affect streamflow during the dry period. However, land use changes (increasing urbanization) within the forested watershed do not appear to significantly affect TR during the dry period. Finally, a combined equation was derived that describes the relationships between the TR during the dry period and the climate, groundwater withdrawal and urban area proportion in a small monsoon watershed. This equation will be effective to predict the water availability during the dry periods in the future since it is closely related to changes of temperature, precipitation, solar radiation, urban area ratio, and groundwater withdrawal quantity. Copyright © 2007 John Wiley & Sons, Ltd.     

Evaluation of building period formulas for seismic design

Building period formulas in seismic design code are evaluated with over 800 apparent building periods from 191 building stations and 67 earthquake events. The evaluation is carried out with the formulas in ASCE 7‐05 for steel and RC moment‐resisting frames, shear wall buildings, braced frames, and other structural types. Qualitative comparison of measured periods and periods calculated from the code formulas shows that the formula for steel moment‐resisting frames generally predicts well the lower bound of the measured periods for all building heights. But the differences between the periods from code formula and measured periods of low‐ to‐medium rise buildings are relatively high. In addition, the periods of essential buildings designed with the importance factor are about 40% shorter than the periods of non‐essential buildings. The code formula for RC moment‐resisting frames describes well the lower bound of measured periods. The formula for braced frames accurately predicts the lower bound periods of low‐to‐medium rise buildings. The formula for shear wall buildings overestimates periods for all building heights. For buildings that are classified as other structural types, the measured building periods can be much shorter than the periods calculated with the code formula. Based on these observations, it is suggested to use C_r factor of 0.015 for shear walls and other structural types. Copyright © 2010 John Wiley & Sons, Ltd.     

Disorder and the extent of polymerization in calcium silicate and aluminosilicate glasses: O-17 NMR results and quantum chemical molecular orbital calculations

Estimation of the framework connectivity and the atomic structure of depolymerized silicate melts and glasses (NBO/T > 0) remains a difficult question in high-temperature geochemistry relevant to magmatic processes and glass science. Here, we explore the extent of disorder and the nature of polymerization in binary Ca-silicate and ternary Ca-aluminosilicate glasses with varying NBO/T (from 0 to 2.67) using O-17 NMR at two different magnetic fields of 9.4 and 14.1 T in conjunction with quantum chemical calculations. Non-random distributions among framework cations (Si and Al) are demonstrated in the variation of relative populations of oxygen sites with NBO/T. The proportion of non-bridging oxygen (NBO, Ca-O-Si) in the binary and ternary aluminosilicate glasses increases with NBO/T. While the trend is consistent with predictions from composition, the detailed fractions apparently deviate from the predicted values, suggesting further complications in the nature of polymerization. The proportion of each bridging oxygen in the glasses also varies with NBO/T. The fractions of Al-O-Si and Al-O-Al increase with increasing polymerization as CaO is replaced with Al₂O₃, while that of Si-O-Si seems to decrease, implying that activity of silica may decrease from calcium silicate to polymerized aluminosilicates (X_SiO2=constant). Quantum chemical molecular orbital calculations based on density functional theory show that a silicate chain with Al-NBO (Ca-O-Al) has an energy penalty (calculated cluster energy difference) of about 108 kJ/mol compared with the cluster with Ca-O-Si, consistent with preferential depolymerization of Si-networks, reported in an earlier O-17 NMR study [Allwardt, J., Lee, S.K., Stebbins, J.F., 2003. Bonding preferences of non-bridging oxygens in calcium aluminosilicate glass: Evidence from O-17 MAS and 3QMAS NMR on calcium aluminate glass. Am. Mineral.88, 949-954]. These prominent types of non-randomness in the distributions suggest significant chemical order in silicate glasses that leads to a decrease in silica activity coefficient and will be useful in modeling transport properties of melts.     

High-resolution numerical simulation of the Pacific Ocean

The present study developed Pacific Ocean models from the Research Institute for Applied Mechanics Ocean Model (RIAMOM) with very high horizontal (1/6° and 1/12°) and vertical (70 levels) resolutions. The hydrographic features of the simulations show good agreement with observed climatological features. Solution differences between the 1/6° and 1/12° models are small for general features of various physical components, but large for eddy fields and the strengths of western boundary currents and their extensions. However, the two high-resolution models show realistic climatological features of Pacific Ocean circulation patterns. Volume transports through major straits in the northwestern Pacific Ocean were also simulated and compared with previous observational results.     

Kinetics of high-pressure phase transformations: Implications to the evolution of the olivine → spinel transition in the downgoing lithosphere and its consequences on the dynamics of the mantle

The rate of a high-pressure phase transition increases exponentially with temperature (T) and overpressure or pressure beyond equilibrium (ΔP). It is also greatly promoted by introducing shear stress, diminishing grain size, and adding water or other catalysts to the reactants. For an isothermal and isobaric transition with no compositional change, if steady state of nucleation on grain surfaces is attained, the rate equation can be expressed: (1) before site saturation by: X = 1 − exp(−Kt⁴), where

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and (2) after site saturation by: X = 1 − exp(−K′T), where

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, where X is volume fraction of completion of transformation, t is time, and the C's are characteristic constants. C₁ and C₉ are functions of grain size, C₃ and C₆ are functions of shear stress. All the C's are almost independent of temperature and pressure. Thus, if X as a function of T, ΔP, and t over a narrow P-T range can be experimentally determined, the C's can be calculated and the effect of grain size and shear stress on the rate of transformation can be evaluated. The isothermal and isobaric rate equations for a given composition, shear stress, and grain size are then experimentally determinable. The non-isothermal and non-isobaric rate equation can be calculated from the isothermal and isobaric ones if the rate of penetration into the metastability field is known. The important feature of the kinetics of high-pressure phase transitions predicted by these rate equations is that for a given rate of penetration into the metastability field, there can be defined a characteristic temperature, T_ch, below which the rate of the transition is virtually zero no matter how metastable the material is. For the olivine → spinel transition in the mantle, this characteristic temperature may be as high as 700° C. Thus, in a fast moving downgoing slab, the temperature at its cold center may remain below T_ch even down to depths in excess of 600 km, thereby greatly depressing the olivine—spinel phase boundary.At an early stage in the development of a downgoing slab, the plunging speed is slow. This allows the interior of the slab to heat up and the olivine → spinel transition to proceed rapidly and near equilibrium. As a result, the olivine—spinel phase boundary in the slab will be distorted upwards. The rising of the denser spinel phase then provides an additional driving force which accelerates the plate. Since the upper portion of the slab is pulled from below and the lower portion pushed from above, earthquakes of down-dip extension will occur in the upper mantle while those of down-dip compression will originate in the transition zone. Because the transformation occurs close to equilibrium, there will be an aseismic region separating the two seismic zones. When the plate velocity exceeds a certain limit, the temperature in the cold interior becomes low enough to depress the olivine → spinel transition. The phase boundary is then distorted downwards. The buoyant force thereby created will reduce the driving force, and the plunging speed of the plate will approach a steady state. In addition, the buoyant force will compress the slab from below and result in earthquakes of down-dip compression throughout the length of the slab. Now the olivine → spinel transition is so far from equilibrium that the reaction becomes implosive. A rise in frequency of deep earthquakes towards the implosion region in the lower transition zone is thus predicted. Therefore, as well as stabilizing the plate velocity, the olivine → spinel transition may also control earthquake distributions throughout the downgoing slab.     

The effect of crystal field stabilization on the olivine→spinel transition in the system Mg2SiO4 - Fe2SiO4

Crystal field stabilization (CFS) plays a significant role in determining equilibrium phase boundaries in olivine→spinel transformations involving transition-metal cations, including Fe²⁺ which is a major constituent of the upper mantle. Previous calculations for Fe₂SiO₄ ignored pressure and temperature dependencies of crystal field stabilization enthalpies (CFSE) and the electronic configurational entropy (S _CFS). We have calculated free energy changes (ΔG _CFS) due to differences of crystal field splittings between Fe₂SiO₄ spinel and fayalite from: ΔG _CFS=?ΔCFSE?TΔS _CFS, as functions of P and T, for different energy splittings of t _2g orbital levels of Fe²⁺ in spinel. The results indicate that ΔG _CFS is always negative, suggesting that CFS always promotes the olivine→spinel transition in Fe₂SiO₄, and expands the stability field of spinel at the expense of olivine. Because of crystal field effects, transition pressures for olivine→spinel transformations in compositions (Mg_1?x Fe _x )₂SiO₄ are lowered by approximately 50x kbar, which is equivalent to having raised the olivine→spinel boundary in the upper mantle by about 15 km.     

Evaluation of the seismic performance of a three‐story ordinary moment‐resisting concrete frame

This study focuses on the seismic performance of Ordinary Moment‐Resisting Concrete Frames (OMRCF) designed only for gravity loads. For this purpose, a 3‐story OMRCF was designed in compliance with the minimum design requirements in the American Concrete Institute Building Code ACI 318 (1999). This model frame was a regular structure with flexure‐dominated response. A 1/3‐scale 3‐story model was constructed and tested under quasi‐static reversed cyclic lateral loading. The overall behavior of the OMRCF was quite stable without abrupt strength degradation. The measured base shear strength was larger than the design base shear force for seismic zones 1, 2A and 2B calculated using UBC 1997. Moreover, this study used the capacity spectrum method to evaluate the seismic performance of the frame. The capacity curve was obtained from the experimental results for the specimen and the demand curve was established using the earthquake ground motions recorded at various stations with different soil conditions. Evaluation of the test results shows that the 3‐story OMRCF can resist design seismic loads of zones 1, 2A, 2B, 3 and 4 with soil types S_A and S_B . For soil type S_C , the specimen was satisfactory in seismic zones 1, 2A, 2B and 3. For soil type S_D , the OMRCF was only satisfactory for seismic zones 1 and 2A. Copyright © 2004 John Wiley & Sons, Ltd.