CHANGING SPATIAL CHARACTERISTICS OF WILLAMETTE VALLEY FARMS

This article reflects on the racial configuration of urban space. Previous research tends to posit racial segregation and diversity as either endpoints on a continuum of racial dominance or mirror images of one another. We argue that segregation and diversity must be jointly understood; they are necessarily related, although not inevitably as binary opposites. Our view is that the neighborhood geographies of U.S. metropolitan areas are simultaneously and increasingly marked by both racial segregation and racial diversity. We offer an approach that classifies neighborhoods based jointly on their compositional diversity and their racial dominance, illustrated by an examination of the neighborhood racial structure of several large metropolitan areas for 1990 and 2000. Compositional diversity increased in all metropolitan areas in ways rendered visible by our approach, including a sharp reduction in the number of highly segregated white neighborhoods, transitioning mostly into moderately diverse yet still white-dominated neighborhoods, and a fourfold increase in the number of highly diverse neighborhoods. Even so, many highly segregated spaces remain, especially for whites and blacks. Latino-dominated spaces show a mix of persistence and emergence. Although compositional diversity is increasing, highly diverse neighborhoods are still rare and are the least persistent of all racial configurations. Our approach clearly demonstrates the “both/and”-ness of segregation and diversity.     

Scaling ethnic segregation: causal processes and contingent outcomes in Chinese residential patterns

This paper advances a contingent perspective of residential segregation that recognizes it as a universal phenomenon of residential differentiation, yet one that results from different causal processes and which results in different spatial outcomes. The analytical separation of groups, contexts and scale is key to understanding the nature of segregation, i.e., what it signifies to the group and to the host society. We argue that segregation is created and maintained by different choices and constraints occurring across dimensions of production, reproduction and consumption. Spatial outcomes vary considerably, and may be arrayed in regard to the permanence of segregation, whether it facilitates identity maintenance, and whether segregation itself empowers or marginalizes the ethnic population. To demonstrate our approach, we analyze the segregation experiences of Chinese ethnics. Our argument is organized around the global, national and local scales at which causal processes shape the Chinese experience of segregation.     

Comparison of linear and nonlinear dimension reduction techniques for automated process monitoring of a decentralized wastewater treatment facility

Multivariate statistical methods for online process monitoring have been widely applied to chemical, biological, and engineered systems. While methods based on principal component analysis (PCA) are popular, more recently kernel PCA (KPCA) and locally linear embedding (LLE) have been utilized to better model nonlinear process data. Additionally, various forms of dynamic and adaptive monitoring schemes have been proposed to address time-varying features in these processes. In this analysis, we extend a common simulation study in order to account for autocorrelation and nonstationarity in process data and comprehensively compare the monitoring performances of static, dynamic, adaptive, and adaptive–dynamic versions of PCA, KPCA, and LLE. Furthermore, we evaluate a nonparametric method to set thresholds for monitoring statistics and compare results with the standard parametric approaches. We then apply these methods to real-world data collected from a decentralized wastewater treatment system during normal and abnormal operations. From the simulation study, adaptive–dynamic versions of all three methods generally improve results when the process is autocorrelated and nonstationary. In the case study, adaptive–dynamic versions of PCA, KPCA, and LLE all flag a strong system fault, but nonparametric thresholds considerably reduce the number of false alarms for all three methods under normal operating conditions.     

A regional soil and sediment geochemical study in northern California

Regional-scale variations in soil geochemistry were investigated in a 20,000-km² study area in northern California that includes the western slope of the Sierra Nevada, the southern Sacramento Valley and the northern Coast Ranges. Over 1300 archival soil samples collected from the late 1970s to 1980 in El Dorado, Placer, Sutter, Sacramento, Yolo and Solano counties were analyzed for 42 elements by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry following a near-total dissolution. These data were supplemented by analysis of more than 500 stream-sediment samples from higher elevations in the Sierra Nevada from the same study site. The relatively high-density data (1 sample per 15 km² for much of the study area) allows the delineation of regional geochemical patterns and the identification of processes that produced these patterns. The geochemical results segregate broadly into distinct element groupings whose distribution reflects the interplay of geologic, hydrologic, geomorphic and anthropogenic factors. One such group includes elements associated with mafic and ultramafic rocks including Cr, Ni, V, Co, Cu and Mg. Using Cr as an example, elevated concentrations occur in soils overlying ultramafic rocks in the foothills of the Sierra Nevada (median Cr = 160 mg/kg) as well as in the northern Coast Ranges. Low concentrations of these elements occur in soils located further upslope in the Sierra Nevada overlying Tertiary volcanic, metasedimentary and plutonic rocks (granodiorite and diorite). Eastern Sacramento Valley soil samples, defined as those located east of the Sacramento River, are lower in Cr (median Cr = 84 mg/kg), and are systematically lower in this suite compared to soils from the west side of the Sacramento Valley (median Cr = 130 mg/kg). A second group of elements showing a coherent pattern, including Ca, K, Sr and REE, is derived from relatively silicic rocks types. This group occurs at elevated concentrations in soils overlying volcanic and plutonic rocks at higher elevations in the Sierras (e.g. median La = 28 mg/kg) and the east side of the Sacramento Valley (median 20 mg/kg) compared to soils overlying ultramafic rocks in the Sierra Nevada foothills (median 15 mg/kg) and the western Sacramento Valley (median 14 mg/kg). The segregation of soil geochemistry into distinctive groupings across the Sacramento River arises from the former presence of a natural levee (now replaced by an artificial one) along the banks of the river. This levee has been a barrier to sediment transport. Sediment transport to the Valley by glacial outwash from higher elevations in the Sierra Nevada and, more recently, debris from placer Au mining has dominated sediment transport to the eastern Valley. High content of mafic elements (and low content of silicic elements) in surface soil in the west side of the valley is due to a combination of lack of silicic source rocks, transport of ultramafic rock material from the Coast Ranges, and input of sediment from the late Mesozoic Great Valley Group, which is itself enriched in mafic elements. A third group of elements (Zn, Cd, As and Cu) reflect the impact of mining activity. Soil with elevated content of these elements occurs along the Sacramento River in both levee and adjacent flood basin settings. It is interpreted that transport of sediment down the Sacramento River from massive sulfide mines in the Klamath Mountains to the north has caused this pattern. The Pb, and to some extent Zn, distribution patterns are strongly impacted by anthropogenic inputs. Elevated Pb content is localized in major cites and along major highways due to inputs from leaded gasoline. Zinc has a similar distribution pattern but the source is tire wear.