bluuebunny/crossref_metadata_2025 huggingface dataset:
Tracing the Woes: An Empirical Analysis of the Airline Industry
Authors: Berry Steven , Jia Panle
Published: July 2010

The US airline industry went through tremendous turmoil in the early 2000s, with four major bankruptcies, two major mergers, and various changes in network structure. This paper presents a structural model of the industry, and estimates the impact of demand and supply changes on profitability. Compared with 1999, we find that, in 2006, air-travel demand was 8 percent more price sensitive, passengers displayed a stronger preference for nonstop flights, and changes in marginal cost significantly favored nonstop flights. Together with the expansion of low-cost carriers, they explain more than 80 percent of legacy carriers' variable profit reduction. (JEL L13, L25, L93)
Investigating the Strategic Influence of Customer and Employee Satisfaction on Firm Financial Performance
Authors: Dotson Jeffrey P. , Allenby Greg M.
Published: July 2010

The ability to demonstrate the impact of marketing action on firm financial performance is crucial for evaluating, justifying, and optimizing the expenditure of a firm's marketing resources. This presents itself as a formidable task when one considers both the variety and potential influence of marketing activity. We propose a hierarchical Bayesian model of simultaneous supply and demand that allows us to formally study the financial impact of a variety of marketing activities, including those that operate on different timescales. The supply-side model provides insight into how the firm allocates resources across its various subunits. We illustrate our approach in a services context by integrating data from three independent studies conducted by a large national bank. Our model allows customer and employee satisfaction to influence firm profitability by moderating the conditional relationship between the bank's operational inputs and its proclivity to produce revenue.
Internet Channel Entry: A Strategic Analysis of Mixed Channel Structures
Authors: Yoo Weon Sang , Lee Eunkyu
Published: July 2010

By analyzing various alternative mixed channel structures composed of a monopoly manufacturer and online and offline outlets, we investigate how the specific channel structure and varying market conditions moderate the impact of Internet channel entry on the channel members and consumers. As an extension of Balasubramanian's model [Balasubramanian, S. 1998. Mail versus mall: A strategic analysis of competition between direct marketers and conventional retailers. Marketing Sci. 17(3) 181–195], our game-theoretic model captures the fundamental difference between two different channel types and consumer heterogeneity in preference for the Internet channel use. The equilibrium solutions indicate that Internet channel entry does not always lead to lower retail prices and enhanced consumer welfare. We also find that an independent retailer might become worse off after adding its own Internet outlet under certain market conditions. We find that the impact of the Internet channel introduction substantially varies across channel structures and market environments. We explain these varied results by proposing a framework of five key strategic forces that shape the overall impact of the Internet channel introduction.
Identifying Unmet Demand
Authors: Chandukala Sandeep R. , Edwards Yancy D. , Allenby Greg M.
Published: July 2010

Brand preferences and marketplace demand are a reflection of the importance of underlying needs of consumers and the efficacy of product attributes for delivering value. Dog owners, for example, may look to dog foods to provide specific benefits for their pets (e.g., shiny coats) that may not be available from current offerings. An analysis of consumer wants for these consumers would reveal weak demand for product attributes resulting from low efficacy, despite the presence of strong latent interest. The challenge in identifying such unmet demand is in distinguishing it from other reasons for weak preference, such as general noninterest in the category and heterogeneous tastes. We propose a model for separating out these effects within the context of conjoint analysis, and we demonstrate its value with data from a national survey of toothpaste preferences. Implications for product development and reformulation are explored.
Feedback type as a moderator of the relationship between achievement goals and feedback reactions
Authors: Anseel Frederik , Van Yperen Nico W. , Janssen Onne , Duyck Wouter
Published: July 2010

The aim of the current study is to shed new light on the inconsistent relationship between performance‐approach (PAp) goals and feedback reactions by examining feedback type as a moderator. Results of a field experiment (N = 939) using a web‐based work simulation task showed that the effect of achievement‐approach goals was moderated by feedback type. Relative to individuals pursuing mastery‐approach goals, individuals pursuing PAp goals responded more negatively to comparative feedback but not to task‐referenced feedback. In line with the hypothesized mediated moderation model, the interaction between achievement goals and feedback type also indirectly affected task performance through feedback reactions. Providing employees with feedback is a key psychological principle used in a wide range of human resource and performance management instruments (e.g., developmental assessment centres, multi‐source/360° feedback, training, selection, performance appraisal, management education, computer‐adaptive testing, and coaching). The current study suggests that organizations need to strike a balance between encouraging learning and encouraging performance, as too much emphasis on comparative performance (both in goal inducement and in feedback style) may be detrimental to employees' reactions and rate of performance improvement.
Granular Formulations and Active Ingredient Distribution from a Rotary Spreader
Authors: Goss G. Robert , Bernal Y. , Johnsonbaugh A. , Henderson R.
Published: July 2010

When using a spinner spreader, particle size distribution may affect a gravimetric distribution pattern, larger particles being thrown farther than smaller particles. If active ingredient (AI) concentrations were uneven with respect to particle size, it is possible that a gravimetric distribution analysis (i.e., a spreader calibration) would not accurately reflect AI distribution. This paper discusses granule uniformity and its effect on granular formulation gravimetric distribution and AI distribution. A more uniform particle size provides a more even AI distribution.
Linking Ecosystems, Food Webs, and Fish Production: Subsidies in Salmonid Watersheds
Authors: Wipfli Mark S. , Baxter Colden V.
Published: July 2010

Physical characteristics of riverine habitats, such as large wood abundance, pool geometry and abundance, riparian vegetation cover, and surface flow conditions, have traditionally been thought to constrain fish production in these ecosystems. Conversely, the role of food resources (quantity and quality) in controlling fish production has received far less attention and consideration, though they can also be key productivity drivers. Traditional freshwater food web illustrations have typically conveyed the notion that most fish food is produced within the local aquatic habitat itself, but the concepts and model we synthesize in this article show that most fish food comes from external or very distant sources—including subsidies from marine systems borne from adult returns of anadromous fishes, from fishless headwater tributaries that transport prey to downstream fish, and from adjacent streamside vegetation and associated habitats. The model we propose further illustrates how key trophic pathways and food sources vary through time and space throughout watersheds. Insights into how food supplies affect fishes can help guide how we view riverine ecosystems, their structure and function, their interactions with marine and terrestrial systems, and how we manage natural resources, including fish, riparian habitats, and forests.

las características físicas de los hábitats fluviales, tales como abundancia de madera, geometría y abundancia de cuerpos de agua, cobertura de vegetación riparia y condiciones de flujo superficial han sido comúnmente consideradas como determinantes de la producción de peces en este tipo de ecosistemas. Alternativamente, el papel del suministro alimenticio (calidad y cantidad) en el control de la producción de peces ha recibido mucha menos atención y consideración pese a que también puede ser un elemento clave en cuanto al control de la productividad. Las clásicas ilustraciones de redes alimenticias de ambientes de agua dulce han dado la impresión de que la mayor parte del alimento de los peces se produce dentro del propio hábitat acuático local, pero los conceptos y el modelo que se presentan en este artículo muestran que gran parte del alimento de los peces proviene de fuentes externas o muy distantes –incluyendo subsidios por parte de los sistemas marinos como el retorno de adultos de peces anádromos, tributarios paralelos que transportan las presas hacia los peces que habitan río abajo, vegetación ribereña y hábitats asociados. El modelo que se propone, además, explica cómo las vías tróficas clave y los suministros alimenticios, varían a través del tiempo y del espacio entre cuencas. El conocimiento de cómo los suministros de alimento afectan a los peces, puede ayudar a mejorar la forma en la que se estudian los ecosistemas fluviales, a entender su estructura y función, sus interacciones con sistemas marinos y terrestres y a optimizar el manejo de los recursos naturales, incluyendo peces, hábitats riparios y forestales.
Ação política e pensamento social em Josué de Castro
Authors: Bizzo Maria Letícia Galluzzi
Published: July 2010

O estudo analisa elementos centrais do pensamento social e da ação política do médico Josué de Castro (1908-1973), entre os anos 1930 e 1950. Objetiva problematizar, na construção de sua ideia de 'fome', categorias cognitivo-sociais presentes, bem como convergências com outros ideários. Foram analisadas fontes primárias - quatro escritos de Castro - e fontes publicadas por autores coetâneos, complementado com levantamento historiográfico e exame de aspectos-chave de sua atuação como deputado e fundador de entidades contra a fome. A trajetória científico-político-intelectual de Castro centrou-se na concepção de 'fome' como fenômeno biológico-social identitário do brasileiro, origem dos males do país e entrave à nacionalidade, demandante de reformas econômico-sociais modernizantes. Na sua obra, há categorias também presentes no conjunto do pensamento social brasileiro, como as de monocultura latifundiária colonialista semifeudal, de Estado irracional e de defesa do público sobre o privado. Entre ideias convergentes com as da nutrição internacional, está a preocupação com a alimentação coletiva sob o aspecto biológico-social. A produção científico-intelectual de Castro tornou-se possível especialmente devido ao cenário de construção do Estado e é marcada por relações do cientista com instituições, poder público e organismos internacionais. Seu engajamento político e social manifesta-se por meio de suas convicções científicas, dando visibilidade à fome como objeto científico-político.
Recursos naturais, espaço social e estratégias de vida em assentamentos da reforma agrária na Amazônia brasileira (Sudeste Paraense)
Authors: Naase Karin Marita
Published: July 2010

Em torno de 38% de todas as famílias assentadas pela reforma agrária no Brasil encontram-se na Amazônia. Como problema, revela-se que muitos dos assentados não se encaixam dentro do público alvo da reforma agrária e que mais de 50% dos lotes concedidos pela reforma agrária já foram comercializados pelos assentados - antes de receberem a titulação do lote. Este artigo tem como pano de fundo uma pesquisa de campo realizada no Sudeste Paraense com o intuito de investigar as estratégias de vida dos assentados da reforma agrária e a relação entre os assentados e o Projeto de Assentamento (PA), entendendo-o como espaço social e como espaço de recursos naturais importantes. As perguntas desta contribuição são: quais as estratégias de vida dos assentados? Elas são sustentáveis? Quais as razões para o abandono e a comercialização dos lotes? Qual a relação dos assentados com os recursos naturais e o espaço social do PA? Qual o papel das políticas públicas? As questões em torno do bem coletivo e da gestão coletiva desses bens revelam-se de grande importância para responder as questões da pesquisa. Tanto a organização social dos assentados quanto as garantias institucionais dadas pelo Estado apresentam-se como os eixos centrais da nossa indagação.
Efficacy of Trastuzumab in Routine Clinical Practice and After Progression for Metastatic Breast Cancer Patients: The Observational Hermine Study
Authors: Extra Jean-Marc , Antoine Eric C. , Vincent-Salomon Anne , Delozier Thierry , Kerbrat Pierre , Bethune-Volters Anne , Guastalla Jean-Paul , Spielmann Marc , Mauriac Louis , Misset Jean-Louis , Serin Daniel , Campone Mario , Hebert Christophe , Remblier Céline , Bergougnoux Loïc , Campana Frank , Namer Moïse
Published: July 2010

Background.

The Hermine study observed the use of trastuzumab for metastatic breast cancer (MBC) in routine practice, including patients who received trastuzumab treatment beyond progression (TBP).

Patients and Methods.

The study observed 623 patients for ≥2 years. Treatment was given according to oncologists' normal clinical practices. Endpoints included duration of treatment, efficacy, and cardiac safety. The TBP subanalysis compared overall survival (OS) in 177 patients who received first-line trastuzumab and either continued trastuzumab for ≥30 days following progression or stopped at or before progression.

Results.

The median treatment duration was 13.3 months. In the first-, second-, and third-line or beyond treatment groups, the median time to progression (TTP) were 10.3 months, 9.0 months, and 6.3 months, and the median OS times were 30.3 months, 27.1 months, and 23.2 months, respectively. Heart failure was observed in 2.6% of patients, although no cardiac-associated deaths occurred. In the TBP subanalysis, the median OS duration from treatment initiation and time of disease progression were longer in patients who continued receiving trastuzumab TBP (>27.8 months and 21.3 months, respectively) than in those who stopped (16.8 months and 4.6 months, respectively). However, the groups were not completely comparable, because patients who continued trastuzumab TBP had better prognoses at treatment initiation. The median TTP was longer in patients who continued trastuzumab TBP (10.2 months) than in those who stopped (7.1 months).

Conclusion.

The Hermine findings confirm that the pivotal trials of first-line trastuzumab treatment in MBC patients are applicable in clinical practice. The subanalysis suggests that trastuzumab TBP offers a survival benefit to MBC patients treated with first-line trastuzumab.
Treatment Beyond Progression: Is It Moving from Belief to Evidence?
Authors: Yerushalmi Rinat , Gelmon Karen
Published: July 2010

This editorial comments on the manuscript of Extra and colleagues in this issue of The Oncologist reporting on the use of trastuzumab for metastatic breast cancer patients.
Methods for casting subterranean ant nests
Authors: Tschinkel Walter R.
Published: July 2010

The study of subterranean ant nests has been impeded by the difficulty of rendering their structures in visible form. Here, several different casting materials are shown to make perfect casts of the underground nests of ants. Each material (dental plaster, paraffin wax, aluminum, zinc) has advantages and limitations, which are discussed. Some of the materials allow the recovery of the ants entombed in the casts, allowing a census of the ants to be connected with features of their nest architecture. The necessary equipment and procedures are described in the hope that more researchers will study this very important aspect of ant natural history.
Straining and Attachment of Colloids in Physically Heterogeneous Porous Media
Authors: Bradford Scott A. , Bettahar Mehdi , Simunek Jirka , van Genuchten Martinus Th.
Published: July 2010

Colloid transport studies were conducted in water‐saturated physically heterogeneous systems to gain insight into the processes controlling transport in natural aquifer and vadose zone (variably saturated) systems. Stable monodispersed colloids (carboxyl latex microspheres) and porous media (Ottawa quartz sands) that are negatively charged were employed in these studies. The physically heterogeneous systems consisted of various combinations of a cylindrical sand lens embedded in the center of a larger cylinder of matrix sand. Colloid migration was found to strongly depend on colloid size and physical heterogeneity. A decrease in the peak effluent concentration and an increase in the colloid mass removal in the sand near the column inlet occurred when the median grain size of the matrix sand decreased or the size of the colloid increased. These observations and numerical modeling of the transport data indicated that straining was sometimes an important mechanism of colloid retention. Experimental and simulation results suggest that attachment was more important when the colloid size was small relative to the sand pore size. Transport differences between conservative tracers and colloids were attributed to flow bypassing of finer‐textured sands, colloid retention at interfaces of soil textural contrasts, and exclusion of colloids from smaller pore spaces. Colloid retention in the heterogeneous systems was also influenced by spatial variations in the pore water velocity. Parameters in straining and attachment models were successfully optimized to the colloid transport data. The straining model typically provided a better description of the effluent and retention data than the attachment model, especially for larger colloids and finer‐textured sands. Consistent with previously reported findings, straining occurred when the ratio of the colloid and median grain diameters was >0.5%.
Colloid Mobilization and Transport in Undisturbed Soil Columns. I. Pore Structure Characterization and Tritium Transport
Authors: Kjaergaard Charlotte , Poulsen Tjalfe G. , Moldrup Per , de Jonge Lis W.
Published: July 2010

While it is recognized that preferential flow may increase the transport of colloids, less is known about the actual influence of preferential flow on colloid mobilization in situ. Changes in pore structure upon soil exposure to drying and rewetting may additionally affect colloid mobilization. Information about the pore structure and the active flow volume, as well as the changes in these properties, are therefore important when investigating colloid mobilization. We investigate the pore structure characteristics and the transport of tritium (3H2O) during steady unsaturated flow conditions. A total of 54 soil columns sampled along a natural clay gradient representing six clay contents (12, 18, 24, 28, 37, and 43% clay) were equilibrated to three different initial matric potentials (IMP), ψ = −2.5, −100, and −15500 hPa. Pore structure characteristics were deduced from water retention characteristics and measurements of air‐filled porosity and air permeability. Tracer experiments were conducted at 1 mm h−1 and with a suction of 5 hPa. A mobile–immobile region model (MIM) and a three‐region model (2MIM) with two mobile and one immobile region were used for describing the breakthrough curves (BTCs). The 2MIM model was able to fit the data well and predicted the existence of two mobile flow regions, most pronounced at higher clay content. The 12% clay soil exhibited matrix‐dominated flow behavior, which is probably attributable to a large fraction of drained pores disconnecting the rapidly conducting flow system. Soils with ≥18% clay exhibited asymmetrical BTCs with early breakthrough and tailing and an increasing amount of immobile water, indicating preferential flow. Drying and rewetting, because of associated changes in the pore structure, significantly reduced the degree of preferential flow.
Capillary Pressure–Saturation Relations for Saprolite: Scaling With and Without Correction for Column Height
Authors: Perfect E. , McKay L. D. , Cropper S. C. , Driese S. G. , Kammerer G. , Dane J. H.
Published: July 2010

Dense nonaqueous phase liquids (DNAPLs) are important subsurface contaminants. Information is lacking on DNAPL behavior in heterogeneous porous media such as weathered rock (saprolite). We measured air–water and Fluorinert (a nontoxic DNAPL surrogate; 3M, St. Paul, MN)–water capillary pressure–saturation relations, θw(hc), close to saturation on an 18‐cm‐long by 10‐cm‐diameter undisturbed column of interbedded sandstone and clayshale saprolite. The Campbell empirical model was fitted to both θw(hc) relations. The resulting best‐fit parameters were 19.54 and 30.10 cm of H2O for the displacement capillary pressure head (h0) and 0.029 and 0.045 for the pore‐size distribution index (1/b), for the air–water and Fluorinert–water data, respectively. Corresponding model parameters corrected for the hydrostatic fluid distribution within the column were 14.08 and 15.96 cm of H2O for h0, and 0.026 and 0.034 for 1/b The correction procedure had a large effect on the Fluorinert–water θw(hc) relation and relatively little impact on the air–water θw(hc) relation. Parameters from the air–water relations were used to predict Fluorinert–water θw(hc) relations using the expression: (h0)2 = (σ2/σ1)(h0)1, where (h0)1, (h0)2 and σ1, σ2 are the capillary displacement pressure heads and interfacial tensions with water for air and Fluorinert, respectively. These analyses showed that direct measurements of the Fluorinert–water θw(hc) relation need to be corrected for column height. The corrected Fluorinert–water θw(hc) relation was accurately predicted (R2 ≅ 0.99) by both the fitted and corrected (h0)1 values. Thus, the error in prediction introduced by not considering column height or contact angle effects was relatively small. Our results show that scaled air–water θw(hc) relations can be used to predict DNAPL intrusion into water‐saturated saprolite at a physical point.
A Solute Flux Approach to Transport through Bounded, Unsaturated Heterogeneous Porous Media
Authors: Sun Alexander Y. , Zhang Dongxiao
Published: July 2010

In this paper, we present a solute flux approach for analyzing solute transport statistics in statistically nonstationary, unsaturated flow. Flow nonstationarity in the vadose zone may arise from a number of factors. It is useful to develop a systematic approach that incorporates these factors into an uncertainty analysis. We first derive the general forms for solute flux moments. The solute flux moments are associated with one‐ and two‐particle joint probability distribution functions (JPDF). We illustrate our results for certain forms of one‐particle and two‐particle JPDFs, in which the particle travel time is assumed to be lognormally distributed and the particle transverse displacement normally distributed. In the numerical examples, the Eulerian velocity moments is obtained by solving the head moment equations numerically using a finite‐difference method. Our results show that flow nonstationarity has a significant impact on the statistics of solute fluxes and solute breakthrough curves.
Correspondence and Upscaling of Hydraulic Functions for Steady‐State Flow in Heterogeneous Soils
Authors: Zhu Jianting , Mohanty Binayak P. , Warrick Arthur W. , van Genuchten Martinus Th.
Published: July 2010

Soil hydraulic parameters at relatively large scales (e.g., remote sensing footprints) are important for land–atmosphere interaction and general circulation models as well as other applications. Within this context, we investigated two major issues involving soil hydraulic properties: (i) hydraulic parameter correspondence among some of the more commonly used soil hydraulic conductivity functions (i.e., the Gardner [G], Brooks–Corey [BC], and van Genuchten [VG] equations) and (ii) their application to upscaling of hydraulic properties for steady‐state flow in heterogeneous soils. We first establish parameter equivalence among the conductivity functions based on preserving macroscopic capillary lengths and predicting the same vertical water flux. Next we investigate the significance of parameter equivalence on averaging schemes for the hydraulic parameters to allow predictions of the ensemble characteristics for steady‐state flow. Results show that the hydraulic parameters correspond very well and that the same rules can be used for averaging the parameters of different hydraulic conductivity functions when predicting ensemble evaporation rates from heterogeneous soils having a relatively large suction at the soil surface (e.g., a dry surface condition and/or a shallow groundwater table). On the other hand, when the surface suction is finite (especially when the suction is relatively small and/or the groundwater table is deep), it is more difficult to obtain correspondence between the parameters of the different conductivity models. The hydraulic functions correspond especially poorly when infiltration is considered. Parameter equivalence between the hydraulic functions is always satisfied for the case of evaporation from a shallow water table, as long as the macroscopic capillary length is preserved.
Rainfall‐Induced Soil Surface Sealing: A Critical Review of Observations, Conceptual Models, and Solutions
Authors: Assouline S.
Published: July 2010

Rainfall‐induced soil surface sealing can have severe agricultural, hydrological, and environmental effects. Seal formation is a complex phenomenon dominated by a wide variety of factors involving soil properties, rainfall characteristics, and flow conditions. It has been studied through extensive experimental investigations as well as simulation models. This study reviews some of the main issues, in terms of morphology, phenomenology, and both conceptual and empirical modeling approaches to improve our perception of the phenomenon and our ability to simulate its effects on flow processes. The effects of different factors on infiltration during seal formation and in sealed soil profiles are highlighted, including seal representation, soil and rainfall properties, and field heterogeneity. New research opportunities toward a generalized formulation of the processes involved in soil sealing and a reliable quantitative prediction of its effects on flow processes are identified. These are related mainly to the ability to quantify and predict the relationships between soil hydraulic properties and physical, chemical, and biological factors that affect the soil resistance to destruction.
Faulting and Fracturing of Nonwelded Bishop Tuff, Eastern California: Deformation Mechanisms in Very Porous Materials in the Vadose Zone
Authors: Evans James P. , Bradbury Kelly Keighley
Published: July 2010

Field and microstructural studies were conducted on the basal, nonwelded and partially welded portions of the rhyolite Bishop Tuff in eastern California to examine the nature and processes of brittle deformation in these units. The nonwelded tuff consists of a variable sequence of finely laminated to massive pumice‐rich deposits, fine‐grained ash, and pyroclastic glass erupted from the Long Valley Caldera. The deposits are experiencing east–west extension in the hanging wall of the White Mountain fault, and small‐displacement faults and fractures cut the tuff. Deformation in the Bishop Tuff occurred by fracturing associated with faults, and by slip along narrow faults with smooth, often mineralized surfaces. Localization of fracturing appears to be a function of welding. Units with a greater degree of welding have a greater abundance of fractures associated with faults, whereas nonwelded portions typically have a narrow deformation band–type faults with little or no associated damage. Microstructural observations show that transgranular fractures lie along grain boundaries of pumice and feldspar phenocrysts, and these fractures are often filled with calcite. These deposits appear to have behaved as an open‐cell foam with a low strength, but with a cohesion that allowed the support of a differential stress to failure that resulted in subvertical open fractures and faults. These results demonstrate how brittle deformation may be manifested in nonwelded deposits in the vadose zone, and impart an anisotropy in which flow would be enhanced vertically and impeded horizontally. The Bishop Tuff is analogous to other nonwelded tuffs in the western USA. Thus, these results have implications for understanding deformation and flow in a variety of arid regions.
Effect of Soil Moisture and Irrigation on Propargyl Bromide Volatilization and Movement in Soil
Authors: Allaire S. E. , Yates S. R. , Ernst F. F.
Published: July 2010

Propargyl bromide (3‐bromo‐propyne, 3BP) is a potential replacement for the soil fumigant methyl bromide. Since little is known about its movement in soil, a study was conducted to compare the volatilization and movement of 3BP in the soil profile for different irrigation treatments. A rectangular soil column was used to simulate a bed–furrow system. The surface of the bed was covered with high‐density polyethylene (HDPE) plastic (i.e., a tarp). The furrow was left uncovered. Multiple volatilization chambers were used to measure emissions from the furrows, the slopes of the bed, and the bed. The soil was fumigated by injecting 1.0 mL of 3BP to the center of the column. Three treatments were studied, no irrigation, a single 5‐h surface irrigation 24 h after fumigation, and a 2‐h daily surface irrigation. Volatilization was about three times greater from nonirrigated soil. Irrigation and higher initial soil moisture content were more effective in controlling 3BP volatilization than the use of a HDPE tarp. Volatilization and degradation were similar for both irrigation treatments, but the 2‐h irrigation had the advantage of requiring one‐third less water. Volatilization rates from the slopes of the bed were lower than from the bed surface. To obtain accurate total mass, volatilization chambers should cover the whole bed–furrow system. Short advective gas and liquid fluxes created by the irrigation had pronounced and prolonged effect on 3BP distribution and degradation. Henry's Law could not be used to predict the 3BP distribution pattern in the liquid phase even long after the irrigation ceased.
Hydraulic Properties of Soil–Straw Mixtures
Authors: Garnier P. , Ezzine N. , De Gryze S. , Richard G.
Published: July 2010

Crop residue management at the soil surface controls C sequestration and soil erosion. The size and distribution of crop residues incorporated into the topsoil affect soil physical properties. The objective of this work was to analyze the immediate effect of straw incorporation on the hydraulic properties of soil. Laboratory experiments were performed to determine the retention and the hydraulic conductivity curves of soil and wheat (Triticum aestivum L.) straw mixtures. The samples consisted of 1‐cm straw pieces mixed with loamy soil aggregates of 2 to 3 mm in diameter. Volumetric straw contents were 0, 0.1, 0.2, and 0.3 cm3 cm−3 Suction table and pressure extractor methods were used to measure the water retention curve. Hydraulic conductivity curves were obtained using Wind's evaporation method. At a constant water pressure head, gravimetric water content increased with increasing straw content. The relationship between water pressure and volumetric water content did not differ significantly between the treatments. An additive model based on the sum of the water retention of straw and soil measured separately gave a good estimation of the water retention measured in the mixture. Hydraulic conductivity decreased with increasing straw content for the same water pressure head. Tomographic images showed that mixing straw into the soil created new pores in the samples. Results from simulations of straw decomposition indicated that (i) the uptake of water by straw has to be taken into account when calculating how much water should be added gravimetrically in an incubation experiment and (ii) changes in hydraulic conductivity due to the presence of straw can have an impact on water and C dynamics.
Modeling Coupled Evaporation and Seepage in Ventilated Cavities
Authors: Ghezzehei T. A. , Trautz R. C. , Finsterle S. , Cook P. J. , Ahlers C. F.
Published: July 2010

Cavities excavated in unsaturated geological formations are important to activities such as nuclear waste disposal and mining. Such cavities provide a unique setting for simultaneous occurrence of seepage and evaporation. Previously, inverse numerical modeling of field liquid‐release tests and associated seepage into cavities were used to provide seepage‐related large‐scale formation properties, ignoring the impact of evaporation. The applicability of such models was limited to the narrow range of ventilation conditions under which the models were calibrated. The objective of this study was to alleviate this limitation by incorporating evaporation into the seepage models. We modeled evaporation as an isothermal vapor diffusion process. The semiphysical model accounts for the relative humidity (RH), temperature, and ventilation conditions of the cavities. The evaporation boundary layer thickness (BLT) over which diffusion occurs was estimated by calibration against free‐water evaporation data collected inside the experimental cavities. The estimated values of BLT were 5 to 7 mm for the open underground drifts and 20 mm for niches closed off by bulkheads. Compared with previous models that neglected the effect of evaporation, this new approach showed significant improvement in capturing seepage fluctuations into open cavities of low RH. At high relative‐humidity values (>85%), the effect of evaporation on seepage was very small.
Physical and Numerical Model of Colloidal Silica Injection for Passive Site Stabilization
Authors: Gallagher Patricia M. , Finsterle Stefan
Published: July 2010

Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. This technology is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location by using the natural or augmented groundwater flow. In this research, a box model was used to investigate the ability to uniformly deliver colloidal silica stabilizer to loose sands using low‐head injection and extraction wells. Five injection wells and two extraction wells were used to deliver stabilizer in a generally uniform pattern to the loose sand formation. Numerical modeling was used to identify the key parameters affecting stabilizer migration and to determine their effective values for the box experiment. In our modeling approach, the stabilizer is treated as a miscible fluid, the viscosity of which is a function of time and the concentration of stabilizer in the pore water. Inverse modeling techniques are employed to reproduce data from the laboratory experiment for the determination of soil and stabilizer properties. While the details of the stabilizer distribution were difficult to reproduce with the simplified conceptual model we used, the overall system behavior was well captured, providing confidence that numerical simulation is a useful tool for designing centrifuge model tests, pilot tests, and eventually field stabilizer‐injection projects.
Hydraulic Properties of a Desert Soil Chronosequence in the Mojave Desert, USA
Authors: Young M. H. , McDonald E. V. , Caldwell T. G. , Benner S. G. , Meadows D. G.
Published: July 2010

Desert pavements are prominent features in arid environments and consist of a surface layer of closely packed gravel that overlies a thin, gravel‐poor, vesicular A (Av) soil horizon. Well‐developed Av horizons form distinct and highly structured columnar peds. These structures, along with their silt‐ and clay‐rich texture, are hypothesized as controlling infiltration and hence the overall hydrologic conditions in the soil profile. The objectives of this study were to (i) evaluate how pedological development in near‐surface soil horizons in an arid alluvial fan complex affects the soil hydraulic characteristics, and (ii) to compare the use of Wooding's equation and inverse modeling for evaluating hydraulic conductivity in highly layered, near‐surface soils. These objectives were approached through field tension infiltrometer studies, soil sampling, and laboratory analyses of soil texture, water content, and soluble salt concentrations. Soils at five sites were studied at the Mojave National Preserve, California, representing a soil chronosequence (50–100000 yr) with varying degrees of desert pavement development. Results indicated 100‐fold and threefold declines, respectively, in saturated hydraulic conductivity (Ks) with both analytical methods, and αw using Wooding's method, as the soils aged. No clear trends in Ks or αw were detected in the underlying horizon, indicating that the controlling feature at these sites, in terms of water entry, was the Ks of the surface (Av) horizon. Soluble salt concentrations within the profile indicated reduced infiltration with increased pavement development. Results showed that surface age can be used as an excellent predictor of saturated hydraulic conductivity (r2 = 0.9254). Further, results suggest that Av horizon development represents a key process controlling water cycling, potentially influencing ecosystem function in arid lands.
Regolith Water in Zero‐Order Chaparral and Perennial Grass Watersheds Four Decades after Vegetation Conversion
Authors: Williamson Tanja N. , Newman Brent D. , Graham Robert C. , Shouse Peter J.
Published: July 2010

In 1960, areas of chaparral were converted to perennial grass after a fire burned most of the San Dimas Experimental Forest in southern California. This conversion provided an opportunity to compare regolith moisture patterns of zero‐order watersheds under native chaparral with those under nonnative veldt grass (Ehrharta calycina Sm.). We collected data as a function of vegetation type and watershed element to test the hypothesis that conversion from chaparral to grass altered water distribution in the vadose zone as a result of changes in the physical environment, including rooting depth and soil horizonation. Patterns in vadose zone water distribution during the dry season, including soil water potential and residual flux, were significantly different in converted areas, reflecting the different rooting habits of the two vegetation types. In chaparral areas, there was no significant change in soil water potential between the surface and the 150‐cm depth; soil water potential was consistently below −1.5 MPa, reflecting the extensive root system. In grass areas, soil water potential was most negative close to the surface, where grass roots were most abundant. Plant available water was present below the 100‐cm depth, suggesting that recharge to groundwater may occur under grass in average or wetter years. Under both vegetation types, the largest differences in residual water fluxes were near the soil–weathered rock contact. However, there was a significant relation between minor differences in fluxes and soil horizon boundaries, confirming the effects of vegetation conversion on soil properties and vadose zone soil water.
Experimental Determination of Effective Diffusion Parameters in the Matrix of Fractured Till
Authors: Helmke Martin F. , Simpkins William W. , Horton Robert
Published: July 2010

Diffusion is often the dominant mode of solute transport in soils when advection is minimal. This paper describes the application of a radial diffusion cell method to estimate the effective diffusion coefficient (De) and effective diffusive porosity (θDe) for use in solute transport models for fractured‐porous media. Twenty‐four experiments were conducted for 28 d using three conservative solutes (Br, PFBA, and PIPES) on eight late Wisconsinan and Pre‐Illinoian till samples from Iowa. The mean value of the total porosity (θT) of the till samples was 30.0%. Concentrations of the three tracers in the reservoir decreased with time and eventually approached equilibrium concentrations. A model simulated the observed concentration data and the modified goodness‐of‐fit (d1) values ranged from 0.878 to 0.950. Mean values of θDe from the model were 28.3 (Br−), 26.5 (PFBA), and 21.6% (PIPES) and there were significant differences in θDe among the three tracers (p = 0.05). Mean values of De were 5.6 × 10−10 m2 s−1 (Br−), 2.9 × 10−10 m2 s−1 (PFBA), and 1.3 × 10−10 m2 s−1 (PIPES). Values of De differed significantly by compound and were significantly different (p = 0.05) from the aqueous diffusion coefficient (D0). Calculated mean values of the first‐order mass exchange coefficient (α) were 8.4 × 10−7 (Br−), 4.1 × 10−7 (PFBA), and 1.6 × 10−7 s−1 (PIPES); they differed by compound (p = 0.05) and generally decreased with increasing molecular weight of the tracer. This study confirmed that the radial diffusion cell method is an efficient method to estimate effective diffusion parameters necessary to accurately model solute transport in fractured till and soil.
Electromagnetic Inversion of GPR Signals and Subsequent Hydrodynamic Inversion to Estimate Effective Vadose Zone Hydraulic Properties
Authors: Lambot S. , Antoine M. , van den Bosch I. , Slob E. C. , Vanclooster M.
Published: July 2010

We combine electromagnetic inversion of ground penetrating radar (GPR) signals with hydrodynamic inverse modeling to identify the effective soil hydraulic properties of a sand in laboratory conditions. Ground penetrating radar provides soil moisture time series that are subsequently used as input in the hydrodynamic inverse procedure. The technique relies on an ultrawide band (UWB) stepped frequency continuous wave (SFCW) radar combined with an off‐ground monostatic transverse electromagnetic (TEM) horn antenna. Ground penetrating radar signal forward modeling is based on the exact solution of the three‐dimensional Maxwell equations for describing free wave propagation and on linear systems in series and parallel for describing wave propagation in the antenna. Water flow in the sand is described by the one‐dimensional Richards equation using the Mualem–van Genuchten parameterization. Both model inversions are formulated by the classical least‐squares problem and are performed iteratively using advanced global optimization techniques. Compared with time domain reflectometry (TDR), results demonstrated the appropriateness of the GPR integrated approach to measure soil moisture remotely. In particular, the approach was found to be less sensitive to the inherent small‐scale heterogeneities. Hydrodynamic inversion of soil moisture data led to hydraulic parameters agreeing reasonably well with direct measurements. The observed discrepancies were attributed to the different characterization scales and samples. The overall integrated approach offers great promise to map the effective hydraulic properties of the shallow subsurface at a high spatial resolution.
Vertical Radar Profiles for the Characterization of Deep Vadose Zones
Authors: Cassiani Giorgio , Strobbia Claudio , Gallotti Laura
Published: July 2010

The deep vadose zone, down to a few tens of meters below the soil surface, is difficult to investigate and characterize, especially from a hydraulic point of view. We present a method well suited for this purpose, that makes use of a radar transmitting antenna at the surface and a radar receiving antenna deployed in a plastic‐cased borehole. The technique is often referred to as vertical radar profiling (VRP). Vertical radar profiling yields information on (i) the distribution of radar velocity as a function of depth, from which moisture content distributions can be inferred, and (ii) the presence of reflecting horizons within the formation, often associated with lithological contacts. High‐resolution, time‐lapse VRPs were acquired from October 2002 to December 2003 at a contaminated site in Trecate, Northern Italy, from several existing boreholes originally installed for monitoring and remediation, with the aim of characterizing the dynamic hydrologic behavior of the deep vadose zone. We discuss data acquisition, processing, and inversion of these VRP data to derive moisture content profiles as a function of time. The VRP‐derived moisture content profiles were used to calibrate a dynamic Richards' equation model via a Monte Carlo inversion approach. In this way, it was possible to identify the value of subsurface hydraulic parameters, in particular hydraulic conductivity, of the main lithological units, and the parameters' uncertainty. The location of lithology contacts was derived via analysis of up‐going radar reflection events contained in the same VRP data.
A Single‐Rod Probe for Time Domain Reflectometry Measurements of the Water Content
Authors: Oswald B. , Benedickter H. R. , Bächtold W. , Flühler H.
Published: July 2010

Time domain reflectometry (TDR) is an increasingly popular method for measuring the water content θ. As opposed to most or all previous studies, in this study we investigated a TDR probe that employs only one single metallic rod for measuring θ. The probe is based on the concept of a Sommerfeld wire. The electromagnetic behavior of the probe is analyzed and experimental results are presented that provide evidence of the probe's applicability and its working principles. Dielectric properties, and hence water contents, obtained with the single rod probe were compared with those of a standard two‐wire TDR probe, and with gravimetrically determined water contents. Additionally, we calculated the probe's region of influence (RoI), which was considerably larger than that of standard two‐wire probes. We also tested the RoI experimentally. The new probe is easier to install, robust, and has a larger sphere of influence over which the dielectric permittivity distribution is averaged.
Modeling Natural Attenuation of Multicomponent Fuel Mixtures in the Vadose Zone: Use of Field Data and Evaluation of Biodegradation Effects
Authors: Gaganis Petros , Kjeldsen Peter , Burganos Vasilis N.
Published: July 2010

Data from a controlled fuel source emplacement field experiment were used to explore the potential for predictive modeling using an approximate model and parameters from laboratory‐scale studies, and to quantify the effects of biodegradation on the natural attenuation of volatile organic compound (VOC) mixtures in the vadose zone. The application of a species grouping technique is investigated in an attempt to reduce the computational cost for predicting the fate of multicomponent mixtures with a minimum loss in accuracy. We show how several difficulties in vadose zone transport modeling may be reasonably well overcome by simplifications that are supported by field data and sensitivity calculations. The estimated case‐specific field‐scale biodegradation values for the majority of mixture compounds were found to fall within the range of biodegradation rate constants determined from experiments performed in columns that were filled with the field soil. A sensitivity analysis showed that using the upper or lower bounds of literature values for the biodegradation constants had a negligible effect on gas concentrations at the early stages of the contamination process, when contaminant concentrations were still high. This is a very encouraging result regarding the usefulness of model calculations in risk assessment procedures.