Who has long commutes to low-wage jobs? Gender,race, and access to work in the New York region     

Sara McLafferty  Valerie Preston 《Urban geography》2013,34(9):1270-1290

Geographies of home and work have changed as public investment has favored central and distant suburban locations and as income inequality has increased. These changes result in shifting geographies of advantage that (dis)benefit gender and racial/ethnic groups unevenly. We examine commuting differentials by gender and race/ethnicity based on combinations of wages and commute times using data for the New York region.We find that Black, Asian, and Hispanic women and men are concentrated in jobs that have long commutes and low-wages, and Black and Hispanic workers’ concentrations increased from 2000–2010.Although Asian men and women remain overrepresented in that category, their share decreased in the 2000's.The urban core has become a region of heightened advantage, as White men, and an increasing share of White women, commute short times to well-paid jobs. Disadvantage has expanded for Black and Latina women whose long commutes are not compensated by well-paid employment.  相似文献   

Rock fall dynamics and deposition: an integrated analysis of the 2009 Ahwiyah Point rock fall,Yosemite National Park,USA   总被引：1，自引：0，他引：1  

Valerie L. Zimmer  Brian D. Collins  Greg M. Stock  Nicholas Sitar 《地球表面变化过程与地形》2012,37(6):680-691

We analyzed a combination of airborne and terrestrial LiDAR, high‐resolution photography, seismic, and acoustic data in order to gain insights into the initiation, dynamics, and talus deposition of a complex rock fall. A large (46 700 m³) rock fall originated from near Ahwiyah Point in eastern Yosemite Valley and fell a total of 730 m to the valley floor on 28 March 2009. Analyses of remote sensing, seismic, and acoustic data were integrated to reconstruct the rock fall, which consisted of (1) the triggering of a 25 400 m³ rock block in an area of intersecting and sometimes highly weathered joint planes, (2) the sliding and subsequent ballistic trajectory of the block from a steeply dipping ledge, (3) dislodging of additional rock from the cliff surface from beneath the rock fall source area, (4) a mid‐cliff ledge impact that detached a volume of rock nearly equivalent in volume to the initial block, (5) sliding of the deteriorating rock mass down the remainder of the cliff, and (6) final impact at the base of the cliff that remobilized the existing talus downward and outward and produced an airblast that knocked down hundreds of trees. The depositional geomorphology indicates that the porosity of the fresh talus is significantly lower than that expected for typical blocky talus slopes, likely because the rock debris from this event was pulverized into smaller, more poorly sorted fragments and densified via dynamic compaction when compared to less energetic, fragmental‐type rock falls. These results suggest that accumulation of individual rock‐fall boulders tends to steepen talus slopes, whereas large, energetic rock falls tend to flatten them. Detachment and impact signals were recorded by seismic and acoustic instruments and highlight the potential use of this type of instrumentation for generalized rock fall monitoring, while LiDAR and photography data were able to quantify the cliff geometry, rock fall volume, source and impact locations, and geomorphological changes to the cliff and talus. Published in 2012. This article is a US Government work and is in the public domain in the USA.  相似文献   

Macroscopic and spectroscopic analysis of lanthanide adsorption to bacterial cells     

Bryne T. Ngwenya  J. Fred W. Mosselmans  Kirk D. Atkinson  Janette Tourney  Valerie Olive 《Geochimica et cosmochimica acta》2009,73(11):3134-6719

This study was designed to combine surface complexation modelling of macroscopic adsorption data with X-ray Absorption Spectroscopic (XAS) measurements to identify lanthanide sorption sites on the bacterial surface. The adsorption of selected representatives for light (La and Nd), middle (Sm and Gd) and heavy (Er and Yb) lanthanides was measured as a function of pH, and biomass samples exposed to 4 mg/L lanthanide at pH 3.5 and 6 were analysed using XAS. Surface complexation modelling was consistent with the light lanthanides adsorbing to phosphate sites, whereas the adsorption of middle and heavy lanthanides could be modelled equally well by carboxyl and phosphate sites. The existence of such mixed mode coordination was confirmed by Extended X-ray Absorption Fine Structure (EXAFS) analysis, which was also consistent with adsorption to phosphate sites at low pH, with secondary involvement of carboxyl sites at high adsorption density (high pH). Thus, the two approaches yield broadly consistent information with regard to surface site identity and lanthanide coordination environment. Furthermore, spectroscopic analysis suggests that coordination to phosphate sites is monodentate at the metal/biomass ratios used. Based on the best-fitting pK_a site, we infer that the phosphate sites are located on N-acetylglucosamine phosphate, the most likely polymer on gram-negative cells with potential phosphate sites that deprotonate around neutral pH.  相似文献   

Ecosystem carbon stocks across a tropical intertidal habitat mosaic of mangrove forest,seagrass meadow,mudflat and sandbar          下载免费PDF全文

Valerie X. H. Phang  L. M. Chou  Daniel A. Friess 《地球表面变化过程与地形》2015,40(10):1387-1400

Intertidal habitats provide numerous ecosystem services, including the sequestration and storage of carbon, a topic of great recent interest owing to land‐cover transitions and climate change. Mangrove forests and seagrass meadows form a continuum of intertidal habitats, alongside unvegetated mudflats and sandbars, however, studies that consider carbon stocks across these spatially‐linked, threatened ecosystems are limited world‐wide. This paper presents the results of a field‐based carbon stock assessment of aboveground, belowground and sediment organic carbon stock to a depth of 1 m at Chek Jawa, Singapore. It is the first study of ecosystem carbon stocks of both vegetated and unvegetated intertidal habitats in the tropics. Ecosystem carbon stocks were 497 Mg C ha^‐1 in the mangrove forest and 138 Mg C ha^‐1 in the seagrass meadow. Sediment organic carbon stock dominated the total storage in both habitats, constituting 62% and >99% in the mangrove forest and seagrass meadow, respectively. In the adjacent mudflat and sandbars, which had no vegetative components, sediment organic carbon stock ranged from 124–143 Mg C ha^‐1, suggesting that unvegetated habitats have a carbon storage role on the same order of importance as seagrass meadows. This study reinforces the importance of sediment in carbon storage within the intertidal ecosystem, and demonstrates the need to consider unvegetated habitats in intertidal ‘blue carbon’ stock assessments. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A new kind of nonlinear mild-slope equation for combined refraction-diffraction of multifrequency waves     

Yue Tang  Yvon Ouellet 《Coastal Engineering》1997,31(1-4)

This paper presents the numerical solution of a new nonlinear mild-slope equation governing waves with different frequency components propagating in a region of varying water depth. There are two new nonlinear equations. The linear part of the equations is the mild-slope equation, and one of the models has the same non-linearity as the Boussinesq equations. The new equations are directly applicable to the problems of nonlinear wave-wave interactions over variable depth. The equations are first simplified with the parabolic approximation, and then solved numerically with a finite difference method. The Crank-Nicolson method is used to discretize the models. The numerical models are applied to a set of published experimental cases, which are nonlinear combined refraction-diffraction with generation of higher harmonic waves. Comparison of the results shows that the present models generally predict the measurements better than other nonlinear numerical models which have been applied to the data set.  相似文献   

Spatialization of the SNOWPACK snow model for the Canadian Arctic to assess Peary caribou winter grazing conditions     

F. Ouellet  A. Langlois  E. A. Blukacz-Richards  C. A. Johnson  A. Royer  E. Neave 《自然地理学》2017,38(2):143-158

Abstract

Peary caribou is the northernmost designatable unit for caribou species, and its population has declined by about 70% over the last three generations. The Committee on the Status of Endangered Wildlife in Canada identified difficult grazing conditions through the snow cover as being the most significant factor contributing to this decline. This study focuses on a spatially explicit assessment tool using snow model simulations (Swiss SNOWPACK model driven in an off-line mode by spatialized meteorological forcing data generated by the Canadian Regional Climate Model) to characterize snow conditions for Peary caribou grazing in the Canadian Arctic. The life cycle of Peary caribou has been subdivided into three critical periods: summer foraging and fall breeding (July–October), winter foraging (November–March), and spring calving (April–June). Winter snow conditions are analyzed and snow simulations compared to Peary caribou island counts to identify a snow parameter that could potentially act as a proxy for grazing conditions and explain fluctuations in Peary caribou numbers. This analysis concludes that caribou counts are affected by simulated snow density values >300 kg m^?3. A software tool mapping possibly favorable and unfavorable grazing conditions based on snow is proposed at a regional scale across the Canadian Arctic Archipelago. Specific output examples are given to show the utility of the tool, mapping pixels with cumulative snow thickness above densities of 300 kg m^?3, where cumulative seasonal thicknesses >7000 cm are considered unfavorable.  相似文献   

The production relations of contract farming in Honduras     

Imbruce  Valerie 《GeoJournal》2008,73(1):67-82

Contract farmers in central Honduras have been producers of Asian vegetables for American markets since 1989. Contract farming holds the potential to provide benefits to small farmers who would otherwise be unable to access export markets but production relations between firms and farmers are often asymmetric and can be exploitative. Poor communication and legacies of mistrust between commodity agriculture and small farmers lead to ambiguities in the contracting system that are misinterpreted by both firms and farmers, creating social tensions between contracting parties. This article will consider how farmers’ navigation of the contracting system and competition between export firms has led to changes in the system. Through competition for a limited pool of outgrowers, firms adjust their policies in favor of farmers without explicit attempts of labor organization on the part of the farmers.

Valerie ImbruceEmail:

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