Rethinking the regularity in mobility patterns of personal vehicle drivers: A multi-city comparison using a feature engineering approach     

Yuhan Ji  Song Gao  Tam Huynh  Chris Scheele  James Triveri  Jacob Kruse  Collin Bennett  Yicheng Wen 《Transactions in GIS》2023,27(3):663-685

Large-scale trajectory data offer a finer lens into the regularity in individual mobility choices. Previous studies have exerted efforts to measure the regularity in people's location visiting patterns. However, the complexity of travel behavior at different spatial and temporal scales has not been adequately considered. To capture regularity in a more comprehensive manner, we construct human mobility profiles with interpretable features at three levels, that is, location, motif, and route, on personal vehicle drivers. A feature engineering approach is designed to analyze the extent to which individuals exhibit multi-level regularity. The analysis pipeline includes feature selection, user segmentation and profiling, and feature importance evaluation. Our empirical study analyzed over 4 million trips of 3743 personal vehicle drivers collected over a month in six metropolitan areas in the United States. The weak correlations between features confirm the validity of quantifying regularity from different aspects. We discovered five clusters of drivers (i.e., gig drivers, homebodies, movers, typical drivers, and work-focused commuters) that differ in their regularity to commute to the workplace and the inclination to participate in non-work activities. A similar driver segmentation and profiling pattern is found in all of the studied metro areas. The minor differences are interpreted from the distribution of mobility features and urban features. The proposed method using multi-level feature engineering provides a generic framework to study regularity and can be readily adapted to other mobility data sources by customizing the features. The improved understanding of mobility patterns within the built environment is valuable for innovating urban transportation solutions.  相似文献   

Chemical pathway analysis of the Martian atmosphere: CO2-formation pathways     

Joachim W. Stock  Christopher S. Boxe  Ralph Lehmann  J. Lee Grenfell  A. Beate C. Patzer  Heike Rauer  Yuk L. Yung 《Icarus》2012,219(1):13-24

The chemical composition of a planetary atmosphere plays an important role for atmospheric structure, stability, and evolution. Potentially complex interactions between chemical species do not often allow for an easy understanding of the underlying chemical mechanisms governing the atmospheric composition. In particular, trace species can affect the abundance of major species by acting in catalytic cycles. On Mars, such cycles even control the abundance of its main atmospheric constituent CO₂. The identification of catalytic cycles (or more generally chemical pathways) by hand is quite demanding. Hence, the application of computer algorithms is beneficial in order to analyze complex chemical reaction networks. Here, we have performed the first automated quantified chemical pathways analysis of the Martian atmosphere with respect to CO₂-production in a given reaction system. For this, we applied the Pathway Analysis Program (PAP) to output data from the Caltech/JPL photochemical Mars model. All dominant chemical pathways directly related to the global CO₂-production have been quantified as a function of height up to 86 km. We quantitatively show that CO₂-production is dominated by chemical pathways involving HO_x and O_x. In addition, we find that NO_x in combination with HO_x and O_x exhibits a non-negligible contribution to CO₂-production, especially in Mars’ lower atmosphere. This study reveals that only a small number of chemical pathways contribute significantly to the atmospheric abundance of CO₂ on Mars; their contributions to CO₂-production vary considerably with altitude. This analysis also endorses the importance of transport processes in governing CO₂-stability in the Martian atmosphere. Lastly, we identify a previously unknown chemical pathway involving HO_x, O_x, and HO₂-photodissociation, contributing 8% towards global CO₂-production by chemical pathways using recommended up-to-date values for reaction rate coefficients.  相似文献   

Effects of salinity on anatomical features and physiology of a semi-mangrove plant Myoporum bontioides     

H.M. Xu  N.F.Y. Tam  Q.J. Zan  M. Bai  P.K.S. Shin  L.L.P. Vrijmoed  S.G. Cheung  W.B. Liao 《Marine pollution bulletin》2014

The effect of different concentrations of NaCl, 0, 100, 200, 300 and 400 mM, on the anatomical features and physiology of Myoporum bontioides was investigated. The photosynthetic rates (Pn) were significantly reduced by salt stress, with the lowest values at 400 mM NaCl. The content of malondialdehyde (MDA), proline and soluble sugar, as well as the activities of peroxidase (POD) and catalase (CAT) increased at the beginning, but became similar to the control as the experiment proceeded. The NaCl effect on superoxide dismutase (SOD) was different from the other parameters, with a significant reduction at 400 mM NaCl at Day 7. Salt glands were found in both upper and lower epidermis, and the ratios of the thickness of palisade to spongy mesophyll tissues increased with NaCl concentrations. The medullary ray was clearly damaged by NaCl at levels of 200 and 300 mM. These results demonstrated that M. bontioides could adapt to a relatively low salinity, and was not a halophilous species.  相似文献   

Effect of a polybrominated diphenyl ether congener (BDE-47) on growth and antioxidative enzymes of two mangrove plant species, Kandelia obovata and Avicennia marina, in South China     

Ying Wang  Haowen Zhu  Nora Fung Yee Tam 《Marine pollution bulletin》2014

The effects of BDE-47 on the growth and antioxidative responses of the seedlings of Kandelia obovata (Ko) and Avicennia marina (Am) were compared in an 8-week hydroponic culture spiked with different levels of BDE-47, 0.1, 1, 5 and 10 mg l⁻¹. The two highest BDE-47 levels significantly suppressed the growth and increased the activities of three antioxidative enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), of Ko in week 1. However, SOD and POD activities at high levels of BDE-47 became lower than the control in week 8. On the contrary, growth of Am was not affected at all contamination levels, and the activities of three enzymes were enhanced by BDE-47 in weeks 1 and 4, but such stimulatory effect became insignificant in week 8. Avicennia was more tolerant to BDE-47 toxicity than Kandelia, as its antioxidative enzymes could better counter-balance the oxidative stress caused by BDE-47.  相似文献   

Structure and function of soil microbial community in artificially planted Sonneratia apetala and S. caseolaris forests at different stand ages in Shenzhen Bay,China     

Q. Yang  A.P. Lei  F.L. Li  L.N. Liu  Q.J. Zan  P.K.S. Shin  S.G. Cheung  N.F.Y. Tam 《Marine pollution bulletin》2014

The present study examined the relationships between soil characteristics, microbial community structure and function in the forests artificially planted with exotic Sonneratia apetala at stand ages of 1-, 2-, 7-, 10- and 14-years and Sonneratia caseolaris of 1-, 4-, 7-, 10- and 14-years in Futian National Nature Reserve, Shenzhen Bay, China. The 7-years old forests of both Sonneratia species reached peak growth and had the highest content of nitrogen and phosphorus, enzymatic activities, including dehydrogenase, cellulase, phosphatase, urease and ß-glucosidase, except arylsulphatase which increased continuously with stand ages. The microbial community structure reflected by phospholipid fatty acid (PLFA) profiles also reached the maximum value in the 7-years old forests and soil bacterial PLFAs in both forests were significantly higher than fungal PLFAs. The canonical correlation analysis revealed that differences in microbial structural variables were significantly correlated to the differences in their functional variables, and the highest correlation was found between the soil enzymatic activities and the content of carbon and nitrogen.  相似文献   

Long-term differences in annual litter production between alien (Sonneratia apetala) and native (Kandelia obovata) mangrove species in Futian,Shenzhen, China     

Lina Liu  Fenglan Li  Qiong Yang  Nora F.Y. Tam  Wenbo Liao  Qijie Zan 《Marine pollution bulletin》2014

Annual litter production in alien (Sonneratia apetala) and native (Kandelia obovata) mangrove forests in Shenzhen, China were compared from 1999 to 2010. S. apetala had significantly higher litter production than K. obovata, with mean annual total litter of 18.1 t ha⁻¹ yr⁻¹ and 15.2 t ha⁻¹ yr⁻¹, respectively. The higher litter production in S. apetala forest indicates higher productivity and consequently more nutrient supply to the estuarine ecosystems but may be more invasive due to positive plant-soil feedbacks and nutrient availability to this alien species. Two peaks were recorded in S. apetala (May and October), while only one peak was observed in K. obovata, in early spring (March and April). Leaf and reproductive materials were the main contributors to litter production (>80%) in both forests. These results suggest that the ecological function of S. apetala and its invasive potential can be better understood based on a long-term litter fall analysis.  相似文献   

Examining past temperature variability in Moosonee, Thunder Bay, and Toronto, Ontario, Canada through a day-to-day variability framework     

Benita Y. Tam  William A. Gough 《Theoretical and Applied Climatology》2012,110(1-2):103-113

Temperature variability in Moosonee, Thunder Bay, and Toronto, Ontario, Canada is examined through a day-to-day variability framework. Statistical measures used in this study include standard deviation (SD), day-to-day temperature variability (DTD), DTD/SD ratio (G), change in day-to-day variability (ΔDTD), and threshold measures of 5°C and 10°C. ΔDTD is the difference between day-to-day change in temperature maximum (DTDtmax) and day-to-day change in temperature minimum (DTDtmin). A distinct seasonal trend is reflected in DTD in Moosonee, Thunder Bay, and Toronto, where ΔDTD is greatest during spring. Monthly ΔDTD averages in Toronto, Thunder Bay, and Moosonee are affected by seasonal variation, the lake effect, and the freeze-up of nearby waterbodies. Yearly averages of ΔDTD have significantly increased over the past recent years in Moosonee and Thunder Bay; a continual increase in climate variability may be detrimental to the subsistence lifestyle of those living in these areas.  相似文献   

Ophiolitic detritus in Cretaceous clastic formations of the Dinarides (NW Croatia): evidence from Cr-spinel chemistry     

Borna Lužar-Oberiter  Tamás Mikes  Hilmar von Eynatten  Ljubomir Babić 《International Journal of Earth Sciences》2009,98(5):1097-1108

Cr-spinel is a common heavy mineral in the sandstones of Cretaceous synorogenic sedimentary formations of the NW Dinarides, Croatia. The rocks occur in isolated exposures in the uplifted basement units of Medvednica, Ivanščica, Žumberak and Samobor Mountains near Zagreb. In this area, evidence of the early Alpine evolution of the Dinarides is obscured due to strong dismemberment of pre-Tertiary tectonostratigraphic units resulting from an intense tectonic history, as well as due to the widespread sedimentary cover of the Pannonian Basin. Electron microprobe analyses of detrital Cr-spinels from the Oštrc Formation reveal that in the Early Cretaceous the ophiolitic source area was predominantly composed of harzburgite peridotites and associated cumulate rocks, which developed in a supra-subduction zone setting. The supply of Cr-spinels with the same chemical signature remained dominant until the end of the Cretaceous, suggesting that exposed remnants of the same ophiolite belt persisted through the Cretaceous and/or that recycling was significant. Similarities with data reported from the Northern Calcareous Alps and the Transdanubian Central Range imply that a rather extensive harzburgitic ophiolite belt probably extended along the Adriatic margin during the Early Cretaceous. A slight trend of increasing variation in the Cr# is observed from the Early to the latest Cretaceous, suggesting that the source areas became more heterogeneous with the ongoing Cretaceous tectonic evolution. Differences in Cr-spinel compositions in two contemporaneous latest Cretaceous formations are well in line with existing data on heavy mineral proportions, which together identify contrasting hinterland geology for these formations and strongly suggest the coeval existence of two separate basins. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Oxygen isotopes in the martian atmosphere: Implications for the evolution of volatiles     

Michael B. Mcelroy  Yuk Ling Yung 《Planetary and Space Science》1976,24(12):1107-1113

Non-thermal escape of oxygen by recombination of exospheric O₂⁺ combined with diffusive separation of gases at lower altitude provides a mechanism through which the Martian atmosphere may be enriched in ¹⁸O relative to ¹⁶O. Measurement of the abundance of ¹⁸O relative to ¹⁶O together with a determination of the turbopause may be used to develop important constraints on the history of Martian volatiles. Models for the interpretation of these data are developed and discussed in light of present information.  相似文献   

Preliminary study on biodegradation of phenanthrene by bacteria isolated from mangrove sediments in Hong Kong   总被引：18，自引：0，他引：18  

Tam NF  Guo CL  Yau WY  Wong YS 《Marine pollution bulletin》2002,45(1-12):316-324

Elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) have been found in mangrove sediments due to anthropogenic pollution, and microbial degradation has been suggested as the best way to remove PAHs from contaminated sediments. The degradation of phenanthrene, a model PAH compound by bacteria, either the enriched mixed culture or individual isolate isolated from surface mangrove sediments was examined. The effects of salinity, initial phenanthrene concentrations and the addition of glucose on biodegradation potential were also investigated. Results show that surface sediments collected from four mangrove swamps in Hong Kong had different degree of PAH contamination and had different indigenous phenanthrene-degrading bacterial consortia. The enriched bacteria could use phenanthrene as the sole carbon source for growth and degrade this PAH compound accordingly. A significant positive relationship was found between bacterial growth and percentages of phenanthrene degradation. The phenanthrene biodegradation ability of the enriched mixed bacterial culture was not related to the degree of PAH contamination in surface sediments. The growth and biodegradation percentages of the enriched mixed culture were not higher than that of the individual isolate especially at low salinity (0 and 10 ppt). High salinity (35 ppt) inhibited growth and biodegradation of phenanthrene of a bacterial isolate but less inhibitory effect was found on the mixed culture. The inhibitory effects of salinity could be reduced with the addition of glucose.  相似文献