空间重构背景下城市多中心研究进展与规划实践

科学认知城市多中心演化规律和规划实践对理解中国在经济转型期的发展逻辑有重要意义。论文从城市多中心概念与测度、驱动机理、绩效研究,以及中国城市多中心的规划实践等方面梳理了相关进展。研究表明,多中心性的概念涵盖形态、功能和治理3个维度,通常基于中心与次中心的识别从不同维度进行测度;城市多中心是社会经济发展与体制交织、市场力量权衡选择和政府规划干预互馈的空间结果,触发和推动的主导因素既具有趋同性,也存在异质性;多中心发展策略在优化空间组织的同时可能带来一定负外部性,其合理性和有效性应纳入研究范畴;多中心发展是中央和地方各级政府进行空间治理、实现协同发展的关键举措,但规划实施成效有待检验。未来,城市多中心研究应重视理论体系和框架的创新,利用多源数据探究不同维度不同尺度的多中心性,重视城市多中心的动态演化模式与动力机制研究,加强对城市多中心多重绩效的系统分析,以及关注多中心规划实践涉及的多层次治理以及治理变革中的整合与冲突。     

3s23p–3s3p2 transitions in S iv

We use both the civ3 and mchf codes to calculate oscillator strengths of allowed and intercombination lines in the  3s²3p–3s3p²  multiplets. Valence, core–valence and some core–core correlation effects are included. The two approaches give results in excellent agreement. Core effects are particularly important for the intercombination lines, though relatively minor for allowed transitions.
We obtain a branching ratio of 1.42 with an estimated accuracy of 0.02 for the     transitions, compared with an experimental value of  1.12±0.1  . The A -values of the     intercombination lines are substantially different from those of previous calculations.     

Shoreline tufa and tufaglomerate from Pleistocene Lake Bonneville,Utah, USA: stable isotopic and mineralogical records of lake conditions,processes, and climate

Shoreline carbonate deposits of Pleistocene Lake Bonneville record the conditions and processes within the lake, including the evaporative balance as well as vertical and lateral chemical and isotopic gradients. Tufas (swash‐zone) and tufaglomerates (cemented, subaqueous colluvium or beachrock) on multiple, well‐developed shorelines near the Silver Island Range, Utah, also present an opportunity to examine physicochemical lake processes through time. Three shorelines are represented by carbonate deposits, including the 23–20 ka Stansbury stage, 15–14.5 ka Bonneville stage, and 14.5–14 ka Provo stage. Mean δ¹⁸O_VSMOW values of all three shorelines are statistically indistinguishable ( ～ 27 ± 1‰), when a few Bonneville samples of unusual composition are neglected. However, differences in primary carbonate mineralogy indicate that the correspondence is an artefact of the different fractionation factors between calcite or aragonite and water. Second, in order to sustain a much smaller, shallower lake during the colder Stansbury stage, the climate must have also been relatively dry. Third, δ¹⁸O values in tufa are higher than tufaglomerate by ～ 0.5‰, consistent with greater evaporative enrichment of lake water in the swash zone. Fourth, mean δ¹³C values for the Provo, Stansbury and Bonneville shorelines (4.4, 5.0 and 5.2‰, respectively) show that carbon species were dominated by atmospheric exchange, with the variations produced by differences in the oxidation of organic matter. Comparisons of shoreline carbonates with deep‐lake marls of the same approximate age indicate that shoreline carbonate was much higher in δ¹³C and δ¹⁸O values (both ～ 2.5‰) during Bonneville time, whereas isotopic differences were minor (both ～ 1‰) in Stansbury time. In particular, the Bonneville stage may have sustained large vertical or lateral isotopic gradients due to evaporative enrichment effects on δ¹⁸O values. In contrast, the lake during the much shallower Stansbury stage may have been well mixed. Differences in the primary mineralogy (Stansbury and Bonneville, aragonite > calcite; Provo, calcite > aragonite) reflect profound differences in lake chemistry in terms of open versus closed‐basin lakes. The establishment of a continuous outlet during Provo time probably reduced the Mg²⁺/Ca²⁺ ratio of lake water. Curiously, regardless of primary mineralogy, tufaglomerate cements are enriched in Na⁺ and Cl^? and depleted in Mg²⁺ relative to capping tufa of the same age. This probably reflects vital or kinetic effects in the swash zone (tufa). We suspect that ‘abiotic’ effects may have been important in the dark pore space of developing tufaglomerate, where the absence of light suppressed photosynthesis. Copyright © 2005 John Wiley & Sons, Ltd.     

Unusual isotopic phenomena in Welsh quarry water and carbonate crusts

Modern terrestrial speleothem-like calcareous deposits in streams draining a disused lime quarry on Black Mountain, South Wales have anomalously negative δ¹⁸O and δ¹³C compositions compared with other similar European deposits. Black Mountain water chemistry is unusual only in its locally very high pH (> 11.5) and carbonate ion concentrations. The high pH is caused by dissolution of lime spoil, resulting in high OH^– concentrations. This high alkalinity causes uptake of atmospheric CO₂ and strong fractionation of both carbon and oxygen stable isotopes, resulting in calcite precipitates with unusually negative isotopic compositions. Since shifts in δ¹⁸O of < 1° are highly significant for Holocene palaeoclimate reconstructions, depletions caused by hyperalkaline waters must be avoided. While extreme lime spoil contamination should be obvious, less heavily affected sites will record smaller fractionation effects and might escape detection. Even small depletions from low-level contamination will have large effects on palaeotemperatures based on carbonate crust δ¹⁸O values.     

Spectral properties and geologic processes on Eros from combined NEAR NIS and MSI data sets

Abstract— From April 24 to May 14, 2000, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission's near infrared spectrometer (NIS) obtained its highest resolution data of 433 Eros. High signal‐to‐noise ratio NIS reflectance spectra cover a wavelength range of 800–2400 nm, with footprint sizes from 213 times 427 m to 394 times 788 m. This paper describes improvement in instrument calibration by remediation of internally scattered light; derivation of a “pseudo channel” for NIS at 754 nm using Multispectral Imager (MSI) Eros approach maps at 951 and 754 nm; synthesis of a 3127‐spectrum high‐resolution data set with the improved calibration and expanded wavelength coverage; and investigation of global and localized spectral variation with respect to mineralogy, composition, and space weathering of Eros, comparing the findings with previous analyses. Scattered light removal reduces the “red” slope of Eros spectra, though not to the level seen by telescopic observations. The pseudo channel completes sampling of Eros' 1 micron (Band I) absorption feature, enabling direct comparison of NIS data with other asteroid and meteorite spectra without additional scaling or correction. Following scattered light removal and wavelength range extension, the spectral parameters of average Eros plot well inside the S(IV) field of Gaffey et al. (1993) and are consistent with the L6 chondrite meteorite fields of Gaffey and Gilbert (1998). Although Eros shows no evidence of mineralogical heterogeneity, modest spectral variations correlate with morphologically and geographically distinct areas of the asteroid. Eros bright‐to‐dark spectral ratios are largely consistent with laboratory “space weathering” experiment results and modeling of space weathering effects. Eros brightness variation unaccompanied by significant spectral variation departs from “lunar‐type”—where band depths, slopes, and albedoes all correlate—and “Ida‐type”—where significant spectral variation is unaccompanied by corresponding brightness variation. The brightest areas on Eros—steep crater walls—have lesser spectral slope and deeper Band I, consistent with exposure of “fresher,” less space weathered materials. Bright crater slope materials have opx/(opx + olv) of 0.24–0.29 and may be more representative of the subsurface mineralogy than “average” Eros, which is probably affected by space weathering. The floors of the large craters Psyche and Himeros have lower albedo and contain the most degraded or altered looking materials. NIS spectra retain a “red” spectral slope at greater than 2 microns. The recalibrated and expanded NIS spectra show better agreements with mixing models based on space weathering of chondritic mixtures.     

The difficult combination of renting and building a house in urban Ghana: analysing the perception of low and middle income earners in Accra

This study examines the experiences of low and middle income earners in urban Ghana in combining renting and self-building a house with their meagre income. Using a case study of 3 building sites in Accra, this study employs semi-structured interview guide to gather qualitative data from fifty respondents. The conclusion of this study is that improving housing career amidst other competing responsibilities in the life course pathways imposes stress and huge financial burden on households in a manner that they are compelled to forgo or cut down on non-housing consumption such as clothing, up-keep of in-laws, marriage, higher educational qualification and cars among others. This study recommends a revisit of the discussion on the enforcement of the provisions of the Rent Act, 1963 and consideration of the practice of rent deposit and monthly rent. Affordable housing finance options should be a priority of African governments and their development partners.     

Spatial and Temporal Variation in Brackish Wetland Seedbanks: Implications for Wetland Restoration Following <Emphasis Type="Italic">Phragmites</Emphasis> Control

Chesapeake Bay tidal wetlands are experiencing a broad-scale, aggressive invasion by the non-native, clonal grass Phragmites australis. The grass is often managed with herbicides in efforts to restore native plant communities and wildlife habitat. Management efforts, however, can act as a disturbance, resulting in increased light availability, potentially fostering reinvasion from soil seedbanks. If native vegetation establishes quickly from seedbanks, the site should have greater resiliency against invasion, while disturbed sites where native plants do not rapidly establish may be rapidly colonized by P. australis. We surveyed the soil seedbank of three vegetation cover types in five Chesapeake Bay subestuaries: areas where P. australis had been removed, where P. australis was left intact, and with native, reference vegetation. We determined the total germination, the proportion of the seedbank that was attributable to invasive species, the richness, the functional diversity, and the overall composition of the seedbanks in each of the cover types (i.e., plots). After 2 years of herbicide treatment in the P. australis removal plots, vegetation cover type impacted the total germination or the proportion of invasive species in the seedbank. In contrast, we also found that seedbank functional composition in tidal brackish wetlands was not influenced by vegetation cover type in most cases. Instead, plots within a subestuary had similar seedbank functional composition across the years and were composed of diverse functional groups. Based on these findings, we conclude that plant community recovery following P. australis removal is not seed-limited, and any lack of native vegetation recruitment is likely the result of yet-to-be-determined abiotic factors. These diverse seedbanks could lead to resilient wetland communities that could resist invasions. However, due to the prevalence of undesirable species in the seedbank, passive revegetation following invasive plant removal may speed up their re-establishment. The need for active revegetation will need to be assessed on a case-by-case basis to ensure restoration goals are achieved.