Operator and integro-differential representations of conditional and unconditional stochastic subsurface flow     

S. Orr  S. P. Neuman 《Stochastic Environmental Research and Risk Assessment (SERRA)》1994,8(2):157-172

Operator representations of stochastic subsurface flow equations allow writing their solutions implicitly or explicitly in terms of integro-differential expressions. Most of these representations involve Neumann series that must be truncated or otherwise approximated to become operational. It is often claimed that truncated Neumann series allow solving groundwater flow problems in the presence of arbitrarily large heterogeneities. Such claims have so far not been backed by convincing computational examples, and we present an analysis which suggests that they may not be justified on theoretical grounds. We describe an alternative operator representation due to Neuman and Orr (1993) which avoids the use of Neumann series yet accomplishes a similar purpose. It leads to a compact integro-differential form which provides considerable new insight into the nature of the solution. When written in terms of conditional moments, our new representation contains local and nonlocal effective parameters that depend on scale and information. As such, these parameters are not unique material properties but may change as more is learned about the flow system.  相似文献   

Determination of Aquitard/Aquiclude Hydraulic Properties from Arbitrary Water-Level Fluctuations by Deconvolution   总被引：1，自引：0，他引：1  

Shlomo P. Neuman  David A. Gardner 《Ground water》1989,27(1):66-76

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Aeolian sediment flux decay: Non-linear behaviour on developing deflation lag surfaces     

Cheryl Mckenna Neuman  W. G. Nickling 《地球表面变化过程与地形》1995,20(5):423-435

Wind tunnel simulations of the effect of non-erodible roughness elements on sediment transport show that the flux ratio q/q_s, shear velocity U*, and roughness density λ are co-dependent variables. Initially, the sediment flux is enhanced by kinetic energy retention in relatively elastic collisions that occur at the roughness element surfaces, but at the same time, the rising surface coverage of the immobile elements reduces the probability of grain ejection. A zone of strong shearing stress develops within 0·03 to 0·04 m of the rough bed because of a relative straightening of velocity profiles which are normally convex with saltation drag. This positive influence on fluid entrainment is opposed by declining shear stress partitioned to the sand bed. Similarly, because the free stream velocity U_f is fixed while U_* increases, velocity at height z and particle momentum gain from the airstream decline, leading eventually to lower numbers of particles ejected on average at each impact. When the ratio of the element basal area to frontal area σ is approximately equal to 3·5, secondary flow effects appear to become significant, so that the dimensionless aerodynamic roughness parameter Z₀/h and shear stress on the exposed sand bed T_s decrease. It is at this point that grain supply to the airstream and saltation drag appear to be significantly reduced, thereby intensifying the reduction in U_*. The zone of strong fluid shear near the bed dissipates.  相似文献   

Book reviews     

Peter J. McCabe  Dennis R. Neuman  Friedrich-W. Wellmer 《Natural Resources Research》1995,4(2):208-209

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Happy to Be Home: Place-Based Attachments,Family Ties,and Mobility among Rural Stayers     

Cheryl E. Morse  Jill Mudgett 《The Professional geographer》2018,70(2):261-269

Migration research has traditionally centered on tracing movement; however, the experience of staying in place has begun to capture scholarly attention. Drawing on data from an online residential decision-making survey, this article focuses specifically on the reasons that contented Vermonters cite for remaining in their home state. A statistical analysis of responses reveals the dominance of place-based factors and family ties in stayers' residential decision making. Contented stayers highly value landscape and community, as well as living near family. Biographical sketches of individual respondents show the emotional dimensions of choosing to stay, as well as the diverse forms of mobility that contented stayers exercise to remain happy at home. In its focus on stayers, this research situates itself within new geographic inquiries into place attachment and studies of “immobile” populations.  相似文献   

The Multifunctionality of Country Stores: Insights on Resilience from Rural Vermont          下载免费PDF全文

Cheryl Morse 《Geographical review》2018,108(3):457-475

A multifunctionality analysis of built environments within rural landscapes can deepen understanding of how contemporary rural places function. There is an urgent need for this knowledge as small towns in the United States lose socio‐economic infrastructure resulting from restructuring, demographic change, and the centralization of services. This qualitative and exploratory study of country stores in rural Vermont finds that stores operate as key socio‐spatial nodes within broader geographic networks. Analysis of the goods, functions, and services stores furnish reveals the reflexive relationships stores have with the physical and cultural geographies of their regions. In moments of community crisis and under certain conditions, stores exhibit hyper‐functionality. Built environments and their socio‐spatial roles in multifunctional landscapes should be included in analyses of rural community resilience.  相似文献   

Material Geographies and Postcolonialism   总被引：1，自引：0，他引：1  

Cheryl McEwan 《Singapore journal of tropical geography》2003,24(3):340-355

While postcolonial studies have inspired new ideas, a new language and a new theoretical inflection for a wide range of teaching and research in human geography, there have been few sustained discussions about what might constitute a postcolonial geography. This paper attempts to deal with this absence by exploring the possibilities of material geographies of postcolonialism. It suggests that geographers are particularly well placed to respond to criticisms of postcolonialism as remaining overwhelmingly textual, cultural and/or historical in focus by contributing towards a productive engagement between postcolonialism and the material realities of global inequalities, and towards a revivified political and ethical project. It explores how particular tactics might inform postcolonial methodologies within geography and makes some tentative suggestions on what a postcolonial political praxis might look like.  相似文献   

Diets of short-tailed shearwaters in the southeastern Bering Sea     

George L. Hunt  Jr.  Cheryl Baduini  Jaime Jahncke 《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26)

In the late 1990s, the southeastern Bering Sea exhibited a number of anomalous conditions, including a major die-off of short-tailed shearwaters (Puffinus tenuirostris), a trans-equatorial migrant that constitutes a major portion of the marine bird biomass in the southeastern Bering Sea. As part of a larger study of the ecological role of the inner or structural front over the southeastern Bering Sea shelf, in 1997–1999, we collected short-tailed shearwaters to determine diet composition. In spring 1997, we found that short-tailed shearwaters were consuming predominately the euphausiid Thysanoessa raschii, a diet expected on the basis of past studies. However, in subsequent years, short-tailed shearwater diets in spring contained increasingly larger proportions of fish, in particular, sandlance (Ammodytes hexapterus), as well as other species of euphausiids (T. inermis in 1999). In summer and fall collections, short-tailed shearwater diets were more varied than in spring, and included both fish (age-0 gadids, 21–35% by weight) and a wider variety of euphausiid species (T. inermis and T. spinifera). In summer and fall, crab zoea (August 1998) and copepods (August 1999) were eaten by shearwaters collected while feeding within the inner front. Diets in 1997–1999 were broader than those found in previous studies of short-tailed shearwaters over the inner shelf and Bristol Bay, which had documented diets composed almost solely of T. raschii. Our data are consistent with the hypothesis that euphausiids were less available to short-tailed shearwaters foraging over the middle and coastal domains of the southeastern Bering Sea in 1997–1999 than has previously been true. Our results are also consistent with hypothesis that the inner front can affect the availability of prey to shearwaters.  相似文献   

Application of a coupled discontinuous–continuous Galerkin finite element shallow water model to coastal ocean dynamics     

Cheryl Ann Blain  T. Christopher Massey 《Ocean Modelling》2005,10(3-4):283-315

A coupled discontinuous–continuous Galerkin (DG–CG) shallow water model is compared to a continuous Galerkin generalized wave-continuity equation (GWCE) based model for the coastal ocean, whereby local mass imbalance typical of GWCE-based solutions is eliminated using the coupled DG–CG approach. Two mass imbalance indicators for the GWCE-based model are presented and analyzed. The indicators motivate discussion on the suitability of using a GWCE-based model versus the locally conservative coupled DG–CG model. Both realistic and idealized test problems for tide, wind, and wave-driven circulation form the basis of the study. For the problems studied, coupled DG–CG solutions retain the robustness of well-documented solutions from GWCE-based models and also capture the dynamics driven by small-scale, highly advective processes which are problematic for GWCE-based models. Issues associated with the coupled DG–CG model are explored, including increased cost due to increased degrees of freedom, the necessary application of slope limiters, as well as the actual coupling process.  相似文献   

Maximum likelihood Bayesian averaging of airflow models in unsaturated fractured tuff using Occam and variance windows     

Eric Morales-Casique  Shlomo P. Neuman  Velimir V. Vesselinov 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(6):863-880

We use log permeability and porosity data obtained from single-hole pneumatic packer tests in six boreholes drilled into unsaturated fractured tuff near Superior, Arizona, to postulate, calibrate and compare five alternative variogram models (exponential, exponential with linear drift, power, truncated power based on exponential modes, and truncated power based on Gaussian modes) of these parameters based on four model selection criteria (AIC, AICc, BIC and KIC). Relying primarily on KIC and cross-validation we select the first three of these variogram models and use them to parameterize log air permeability and porosity across the site via kriging in terms of their values at selected pilot points and at some single-hole measurement locations. For each of the three variogram models we estimate log air permeabilities and porosities at the pilot points by calibrating a finite volume pressure simulator against two cross-hole pressure data sets from sixteen boreholes at the site. The traditional Occam’s window approach in conjunction with AIC, AICc, BIC and KIC assigns a posterior probability of nearly 1 to the power model. A recently proposed variance window approach does the same when applied in conjunction with AIC, AICc, BIC but spreads the posterior probability more evenly among the three models when used in conjunction with KIC. We compare the abilities of individual models and MLBMA, based on both Occam and variance windows, to predict space–time pressure variations observed during two cross-hole tests other than those employed for calibration. Individual models with the largest posterior probabilities turned out to be the worst or second worst predictors of pressure in both validation cases. Some individual models predicted pressures more accurately than did MLBMA. MLBMA was far superior to any of the individual models in one validation test and second to last in the other validation test in terms of predictive coverage and log scores.  相似文献