Adaptive Zoning for Transport Mode Choice Modeling

Adaptive zoning is a recently introduced method for improving computer modeling of spatial interactions and movements in the transport network. Unlike traditional zoning, where geographic locations are defined by one single universal plan of discrete land parcels or ‘zones’ for the study area, adaptive zoning establishes a compendium of different zone plans, each of which is applicable to one journey origin or destination only. These adaptive zone plans are structured to represent strong spatial interactions in proportionately more detail than weaker ones. In recent articles, it has been shown that adaptive zoning improves, by a large margin, the scalability of models of spatial interaction and road traffic assignment. This article confronts the method of adaptive zoning with an application of the scale and complexity for which it was intended, namely an application of mode choice modeling that at the same time requires a large study area and a fine‐grained zone system. Our hypothesis is that adaptive zoning can significantly improve the accuracy of mode choice modeling because of its enhanced sensitivity to the geographic patterns and scales of spatial interaction. We test the hypothesis by investigating the performance of three alternative models: (1) a spatially highly detailed model that is permissible to the maximum extent by available data, but requires a high computational load that is generally out of reach for rapid turnaround of policy studies; (2) a mode choice model for the same area, but reducing the computational load by 90% by using a traditional zone system consisting of fewer zones; and (3) a mode choice model that also reduces the computational load by 90%, but based on adaptive zoning instead. The tests are carried out on the basis of a case study that uses the dataset from the London Area Transport Survey. Using the first model as a benchmark, it is found that for a given computational load, the model based on adaptive zoning contains about twice the amount of information of the traditional model, and model parameters on adaptive zoning principles are more accurate by a factor of six to eight. The findings suggest that adaptive zoning has a significant potential in enhancing the accuracy of mode choice modeling at the city or city‐region scale.     

HST BVI photometry of Triton and Proteus

BVI photometry of Triton and Proteus was derived from HST images taken in 1997. The VEGAMAG photometric technique was used. Triton was found to be brighter by a few percent than observations of the 1970's and 1980's, as expected due to the increasingly greater exposure of the bright south polar region. The leading side was also found to be brighter than the trailing side by 0.09 mag in all filters—50% larger than reported by Franz [Franz, O.G., 1981. Icarus 45, 602-606]. Contrary to our previous results [Pascu, D., et al., 1998. Bull. Am. Astron. Soc. 30, 1101], we found no episodic reddening. Our previous conclusions were based on an inaccurate early version of the Charge Transfer Efficiency (CTE) correction. The present result limits the start of the reddening event reported by Hicks and Buratti [Hicks, M.D., Buratti, B.J., 2004. Icarus 171, 210-218]. Our (B-V) result of 0.70±0.01 supports the global blueing described by Buratti et al. [Buratti, B.J., Goguen, J.D., Gibson, J., Mosher, J., 1994. Icarus 110, 303-314]. Our observations of July 1997 agree with the Voyager results and are among the bluest colors seen. We found Proteus somewhat brighter than earlier studies, but in good agreement with the recent value given by Karkoschka [Karkoschka, E., 2003. Icarus 162, 400-407]. A leading/trailing brightness asymmetry was detected for Proteus, with the leading side 0.1 mag brighter. The unique differences in action of the endogenic and exogenic processes on Triton and Proteus provides an opportunity to separate the endogenic and exogenic effects on Triton.     

Robotics in the service of astronomy

Alex Ellery reviews current and forthcoming applications of robotics in the development and performance of astronomical and space instruments.     

Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE‐type silicate‐bearing irons

Abstract— The petrography and mineral and bulk chemistries of silicate inclusions in Sombrerete, an ungrouped iron that is one of the most phosphate‐rich meteorites known, was studied using optical, scanning electron microscopy (SEM), electron microprobe analysis (EMPA), and secondary ion mass spectrometry (SIMS) techniques. Inclusions contain variable proportions of alkalic siliceous glass (?69 vol% of inclusions on average), aluminous orthopyroxene (?9%, Wo_1–4Fs_25–35, up to ?3 wt% Al), plagioclase (?8%, mainly An_70–92), Cl‐apatite (?7%), chromite (?4%), yagiite (?1%), phosphate‐rich segregations (?1%), ilmenite, and merrillite. Ytterbium and Sm anomalies are sometimes present in various phases (positive anomalies for phosphates, negative for glass and orthopyroxene), which possibly reflect phosphate‐melt‐gas partitioning under transient, reducing conditions at high temperatures. Phosphate‐rich segregations and different alkalic glasses (K‐rich and Na‐rich) formed by two types of liquid immiscibility. Yagiite, a K‐Mg silicate previously found in the Colomera (IIE) iron, appears to have formed as a late‐stage crystallization product, possibly aided by Na‐K liquid unmixing. Trace‐element phase compositions reflect fractional crystallization of a single liquid composition that originated by low‐degree (?4–8%) equilibrium partial melting of a chondritic precursor. Compositional differences between inclusions appear to have originated as a result of a “filter‐press differentiation” process, in which liquidus crystals of Cl‐apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions. This process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host, yielding a dacite composition for some inclusions. Solidification was relatively rapid, but not so fast as to prevent flow and immiscibility phenomena. Sombrerete originated near a cooling surface in the parent body during rapid, probably impact‐induced, mixing of metallic and silicate liquids. We suggest that Sombrerete formed when a planetesimal undergoing endogenic differentiation was collisionally disrupted, possibly in a breakup and reassembly event. Simultaneous endogenic heating and impact processes may have widely affected silicate‐bearing irons and other solar system matter.     

Sediment Denitrification in Two Contrasting Tropical Shallow Lagoons

Sediment denitrification was monthly evaluated in two tropical coastal lagoons with different trophic states using the ¹⁵N isotope pairing technique. Denitrification rates were very low in both environments, always <5.0 μmol N₂ m^?2 h^?1 and were not significantly different between them. Oxygen consumption varied from 426 to 4248 μmol O₂ m^?2 h^?1 and was generally three times higher in the meso-eutrophic than the oligotrophic lagoon. The low denitrification activity was ascribed to both low water NO₃ ^? concentrations (<2.0 μM) and little nitrate supply from nitrification. There was no correlation of denitrification with nitrate or ammonium fluxes. Sediments in temperate environments with similar oxygen consumption rates usually presented a higher proportion of nitrification–denitrification rates. Sediment oxygen consumption was a good predictor of sediment denitrification in both studied lagoons.     

Challenges to the development of carbon markets in China

China has introduced several pilot emission trading schemes to build the basis for a national scheme. The potential scale of this initiative raises prospects for a regional carbon trading network as a way to further engage other major Asian economies. However, the Chinese carbon markets rest upon a unique political-economic context and institutional environment that are likely to limit their development and viability. This article offers an overview of such structural economic and political constraints. Four main challenges are identified, namely, inadequate domestic demand, limited financial involvement, incomplete regulatory infrastructure, and excessive government intervention. The first two challenges concern economic dimensions and may be partially addressed by the incentives created by the newly introduced emission trading schemes. The other two are more deeply entrenched in the dominant political system and governing practice. They require fundamental changes to the ways in which the state and the market interact. The success of China's carbon market reform depends crucially on the ability of the ongoing efforts to transform the distorted state–market relationship.

Policy relevance

The burgeoning carbon markets offer opportunities for emissions mitigation at lower costs and enable circulation of a new form of capital, i.e. carbon credits, across borders. China accounts for a gigantic share of global GHG emissions and has the potential to significantly scale up these opportunities. There are clear implications for market developers and participants worldwide, including climate policy makers who attempt to link their emission trading schemes to other schemes, firms who seek to take advantage of the inexpensive carbon offsets generated in developing countries, international financial institutions who endeavour to establish their business in an emerging major carbon market, etc. This article can inform their decisions by identifying key issues that may undermine their ability to achieve these goals. Policy makers and stakeholders will benefit from this analysis, which shows how the Chinese carbon markets operate in ways that may be different from their experience elsewhere.     

Confidence and Trust in Public Institution Natural Hazards Management: Case Studies in Urban and Rural China

This research aims to investigate the extent to which urban and rural residents trust grassroots-level institutions and how this might affect community resilience to environmental change in China. It focuses on the commitments of institutional actors and their capacities to manage natural hazards and coordinate the community's response. Semistructured interviews were conducted with megacity (Tianjin) and remote village (Wolong) residents in China. We found that public confidence in grassroots-level institutions is limited due to inherent constraints on resources and power. Residents of Wolong tend to recognize the commitment and role of those institutions in connecting individuals with one another, whereas their urban counterparts in Tianjin remain skeptical. Issues of solidarity might account for this difference. These findings will have implications for state–society cooperation and disaster risk comanagement in both urban and rural China.