Relationship between erosion and sediment yield in drainage basins of loess gully-hilly areas

From a long-term point of view, the balance between erosion and sediment yield in a drainage system can basically realize, i.e., the delivery ratio can be close to 1. However, substantial variations among individual rainfall events or between annual delivery ratio exist, causing frequent sediment retaining or re-erosion and re-delivery of the retained sediments in a short period of time. Thus the delivery ratio will be < 1 or > 1. The sediment delivery ratio is closely related to the spatial distribution of rainfall and magnitude of rise and fall of peak flood and that of runoff depth in the drainage system. Delivery ratio of single event in a drainage system and changes of delivery capacity of silt-laden runoff in various classes of gullies can be expressed by transformation mechanism of shear force of a single rainstorm event with flood resulting from increase and decrease of peak flood per unit area.     

Identification of soil–structure interaction effect in base-isolated bridges from earthquake records

Identification of system parameters with the help of records made on base-isolated bridge during earthquakes provides an excellent opportunity to study the performance of the various components of such bridge systems. Using a two-stage system identification methodology for non-classically damped systems, modal and structural parameters of four base-isolated bridges are reliably identified using acceleration data recorded during 18 earthquakes. Physical stiffness of reinforced concrete columns, dynamic properties of soil and foundation impedance are found by available theoretical models in conjunction with pertinent information from the recorded accelerographs. Soil–structure interaction (SSI) effect in these bridges is examined by comparing the identified and physical stiffness of the sub-structure components. It is found that SSI is relatively pronounced in bridges founded in weaker soils and is more strongly related to the ratio of pier flexural stiffness and horizontal foundation stiffness than soil shear modulus, G_s, alone. However, substantial reduction in G_s is observed for moderate seismic excitation and this effect should be taken into account while computing foundation impedance.     

Seasonal and event-scale variations in solute chemistry for four Sierra Nevada catchments

Hydrobiogeochemical processes controlling stream water chemistry were examined in four small (<5 km²) catchments having contrasting bedrock lithologies in the western Sierra Nevada foothills of California. The Mediterranean climate with its cool/wet and hot/dry cycle produces strong seasonal patterns in hydrological, biological and geochemical processes. Stream water solutes fall into three general groups according to seasonal fluctuation in concentration: strong, rainy season minimum–dry season maximum (Cl⁻, SO₄²⁻, base cations); weak, rainy season minimum–dry season maximum (Si); and rainy season maximum–dry season minimum (NO₃⁻ and K⁺). Solute dynamics in soil solutions and stream water suggest that mixing of drainage waters from bedrock and soil sources regulate stream water solute concentrations. Patterns are further altered by the leaching of solutes accumulated in the soil over the summer period of desiccation and the temporal discoupling of nutrient cycles that occurs due to differences in the timing between vegetation growth (late spring) and leaching (early winter). Solute concentrations are remarkably similar between watersheds with varying bedrock types, with the exception of nitrate, sulfate and bicarbonate. Three watersheds have nitrogen-bearing metasedimentary bedrock that contributes to elevated nitrate concentrations in stream waters. Watersheds whose bedrock includes mineralized veins of sulfide and carbonate minerals similarly have greater sulfate and bicarbonate concentrations in stream water. Hydrobiogeochemical processes are highly dynamic at the seasonal and storm-event temporal scales and spatially complex at the watershed scale making management of stream water chemical composition, such as nitrate concentrations, very challenging.     

Evolving Spatial Form of Urban‐Rural Interaction in the Pearl River Delta,China

Much of the development literature and the theory of urban transition have been based on an arbitrary division of production space into city and countryside. Despite growing recognition of the need for an integrated approach to urban‐rural relations, controversial issues related to the definition and measurement of the phenomenon remain unresolved. This case study of spatial transformation in China's Pearl River Delta analyzes with greater precision the geographic extent and functional attributes of a zone of urban‐rural interaction located outside and between major metropolitan centers. This zone has been the spatial focus of industrial and commercial development, although most of its population remains officially classified as “agricultural.” The peri‐urban zone was initially left behind by the central cities in terms of its contribution to the regional economy. After a decade of postreform development, this zone has moved ahead of the central cities and become the region's main destination for in‐migrants and foreign investment. The growth of the zone of urban‐rural interaction outside the central cities has absorbed a significant amount of the increased urban population, but it has not brought about a reduction of regional economic inequality because of the persistence of a backward economy in the periphery. Theoretical questions are raised concerning the validity of several fundamental assumptions underlying the conventional model of urban transition.     

离散气候系统中的周期与混沌

从零维气候模式导出了一个非线性映象公式，对由该公式表征的气候系统的平衡态和稳定域进行了研究。通过迭代计算揭露海洋热贮存C对气候系统的调控作用。计算结果表明，存在一个控制气候系统行为的很窄的C值敏感区；当C值大于敏感区上界时，气候系统趋向平衡态，即现代气候；当C值小于敏感区下界时，系统失稳。在敏感区内则呈现出周期与混沌行为，且随着C的增加，勾画出通过周期倍分岔通向混沌的道路。     

NUMERICAL STUDY ON NONLINEAR INTERACTION BETWEEN TROPICAL CYCLONE AND SEA*

Given time-independent monthly mean sea temperature,numerical simulation was done of the path of the tropicalcy clone Forrest and its related physical quantity field in terms of the improved version of the σ-coordinate 10-level primitive equation model for tropical cyclones developed by the Guangzhou Institute of Marine Meteorology.Result ssuggest the similarity between the simulated and observed physical quantity fields except that the simulated path was to the right of the observed,with the deviation increasing with time.Sea and tropical cyclone,in effect,interact mutually.In an attempt to compare the results from coupling and uncoupling experiments,an oceanic mixed layer model was formulated based on experiments with sea response to cyclone and integrated in synchronous coupling with the aforementioned version of tropical cyclones,the computational domain covering the western North Pacific with the coastal configuration involved.The coupling experiment shows that the negative feedback of the interaction between sea and mature cyclone leads to weaker sea response as compared to the uncoupling case.Except for the location of the divergence core of oceanic current,the mixed layer depth and inhomogeneous distribution of sea surface temperature (SST) caused by the cyclone-core position and intensity,the values of the maximum oceanic current,departure of the mixed layer depth and SST drop were smaller in the coupling than in the uncoupling case,and so was the maximum wind near the cyclone core.The path from the coupling run is to the left of the course in the uncoupling experiment but closer to the observed one though remaining somewhat leftward.Even on a scale of less than 3 days,the effects of sea and sea-cyclone interaction on the cyclone were by no means negli-gible.     

天津局地气候的反演建模及其研究

利用天津月平均温度Ｔ、气压Ｐ和雨量Ｒ的时间序列反演出一组近似描写天津（Ｔ－Ｐ－Ｒ）局地气候的动力方程，并对其演化特性及内部相互作用机制进行了研究。     

EFFECT OF WINTER MONSOON ON SUMMER MONSOON THROUGH AIR-SEA INTERACTION

In this paper the relationships between the sea surface temperature (SST) of Xisha and that in the northern Indianand northern Pacific Oceans,the geopotential height at 500 hPa level of the Northern Hemisphere,and rainfall in Chinaare studied statistically using data in the period of 1961—1992.Results show that in winter,the interannual variation inSST of Xisha describes that for a large oceanic region off the East Asia coast,and is closely related to the activity of EastAsia winter monsoon.On the other hand,there exist very high values of auto-correlation of Xisha SST anomaly fromDecember through the following July,but the anomalous condition is hardly correlated to that in the preceding autumn.The winter monsoon related anomalous SST condition in Xisha has a strong tendency to persist through the succeedingsummer monsoon season with the same sign.In addition,correlation maps of monthly mean rainfall in China with re-spect to Xisha SST of the same month show positive correlations with confidence level above 95% to the east of 110°Eand to the south of Changjiang (Yangtze) River during the months of October through April;the region becomes smal-ler in May and changes correlation sign in June;the positive correlation region is located in the middle and lower reachesof Changjiang River from July to September.The air-sea interaction plays an important role in these processes.     

The Speciation of (CH3)2Sn2+ in Electrolyte Solution Containing the Major Components of Natural Waters

Hydrolysis constants of dimethyltin(IV) cation, in different salt solutions (CaCl₂: 0.15 I 0.90; MgCl₂: 0.30 I 0.60; NaCl-–NaClO₄, NaCl-–NaNO₃ mixtures: I = 3; NaCl-–Na₂SO₄ mixtures: I = 1 mol dm^-3) were determined by potentiometric ([H⁺]-glass electrode) measurements. These data, together with previous data (De Stefano et al., 1996b) were interpreted in terms of DHT (Debye–Hückel type) and Pitzer equations. The mixed electrolyte solution results also allowed us to obtain and parameters for the Pitzer equation. Calorimetric measurements were made at different ionic strengths in order to find the temperature dependence of hydrolysis constants and of the relative interaction parameters. The body of results allows us to determine the speciation of natural waters in a wide range of ionic strengths and temperatures.     

A computational workflow for rupture‐to‐structural‐response simulation and its application to Istanbul

Scenario‐based earthquake simulations at regional scales hold the promise in advancing the state‐of‐the‐art in seismic risk assessment studies. In this study, a computational workflow is presented that combines (i) a broadband Green's function‐based fault‐rupture and ground motion simulation—herein carried out using the “UCSB (University of California at Santa Barbara) method”, (ii) a three‐dimensional physics‐based regional‐scale wave propagation simulation that is resolved at  Hz, and (iii) a local soil‐foundation‐structure finite element analysis model. These models are interfaced with each other using the domain reduction method. The innermost local model—implemented in ABAQUS—is additionally enveloped with perfectly matched layer boundaries that absorb outbound waves scattered by the structures contained within it. The intermediate wave propagation simulation is carried out using Hercules , which is an explicit time‐stepping finite element code that is developed and licensed by the CMU‐QUAKE group. The devised workflow is applied to a  km region on the European side of Istanbul, which was modeled using detailed soil stratigraphy data and realistic fault rupture properties, which are available from prior microzonation surveys and earthquake scenario studies. The innermost local model comprises a chevron‐braced steel frame building supported by a shallow foundation slab, which, in turn, rests atop a three‐dimensional soil domain. To demonstrate the utility of the workflow, results obtained using various simplified soil‐structure interaction analysis techniques are compared with those from the detailed direct model. While the aforementioned demonstration has a limited scope, the devised workflow can be used in a multitude of ways, for example, to examine the effects of shallow‐layer soil nonlinearities and surface topography, to devise site‐ and structure‐specific seismic fragilities, and for calibrating regional loss models, to name a few.