bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling water erosion in the Sahel: application of a physically based soil erosion model in a gentle sloping environment
Authors: Visser S. M. , Sterk G. , Karssenberg D. 
Published: August 2005

AbstractWater is a major limiting factor in arid and semi‐arid agriculture. In the Sahelian zone of Africa, it is not always the limited amount of annual rainfall that constrains crop production, but rather the proportion of rainfall that enters the root zone and becomes plant‐available soil moisture. Maximizing the rain‐use efficiency and therefore limiting overland flow is an important issue for farmers. The objectives of this research were to model the processes of infiltration, runoff and subsequent erosion in a Sahelian environment and to study the spatial distribution of overland flow and soil erosion.The wide variety of existing water erosion models are not developed for the Sahel and so do not include the unique Sahelian processes. The topography of the Sahelian agricultural lands in northern Burkina Faso is such that field slopes are generally low (0–5°) and overland flow mostly occurs in the form of sheet flow, which may transport large amounts of fine, nutrient‐rich particles despite its low sediment transport capacity. Furthermore, pool formation in a field limits overland flow and causes resettlement of sediment resulting in the development of a surface crust.The EUROSEM model was rewritten in the dynamic modelling code of PCRaster and extended to account for the pool formation and crust development. The modelling results were calibrated with field data from the 2001 rainy season in the Katacheri catchment in northern Burkina Faso. It is concluded that the modified version of EUROSEM for the Sahel is a fully dynamic erosion model, able to simulate infiltration, runoff routing, pool formation, sediment transport, and erosion and deposition by inter‐rill processes over the land surface in individual storms at the scale of both runoff plots and fields. A good agreement is obtained between simulated and measured amounts of runoff and sediment discharge. Incorporating crust development during the event may enhance model performance, since the process has a large influence on infiltration capacity and sediment detachment in the Sahel. Copyright © 2005 John Wiley & Sons, Ltd.
Rates of erosion and topographic evolution of the Sierra Nevada, California, inferred from cosmogenic 26Al and 10Be concentrations
Authors: Stock Greg M. , Anderson Robert S. , Finkel Robert C. 
Published: August 2005

AbstractConcentrations of cosmogenic 26Al and 10Be in cave sediments and bedrock surfaces, combined with studies of landscape morphology, elucidate the topographic history of the southern Sierra Nevada over the past 5 Ma. Caves dated by 26Al/10Be in buried sediments reveal that river incision rates were moderate to slow between c. 5 and 3 Ma (≤0·07 mm a−1), accelerated between 3 and 1·5 Ma (c. 0·3 mm a−1), and then have subsequently become much slower (c. 0·02 mm a−1). Although the onset of accelerated incision coincides in time with both postulated Pliocene tectonism and pronounced global climate change, we argue that it primarily represents the response to a discrete tectonic event between 3 and 5 Ma. Dated cave positions reveal that, prior to 3 Ma, river canyons displayed up to 1·6 km of local relief, suggesting that Pliocene rock uplift elevated pre‐existing topography. Renewed incision beginning c. 3 Ma deepened canyons by up to 400 m, creating narrow inner gorges. Tributary streams exhibit strong convexities, indicating that the transient erosional response to Pliocene uplift has not yet propagated into upland surfaces. Concentrations of 26Al and 10Be in bare bedrock show that upland surfaces are eroding at slow rates of c. 0·01 mm a−1. Over the past c. 3 Ma, upland surfaces eroded slowly while adjacent rivers incised rapidly, increasing local relief. Although relief production probably drove at least modest crestal uplift, considerable pre‐Pliocene relief and low spatially averaged erosion rates suggest that climatically driven rock uplift is not sufficient to explain all uplift implied by tilted markers at the western edge of the range. Despite the recent pulse of erosion, spatially averaged erosion rates are low, and have probably acted to preserve the broad topographic form of the Sierra Nevada throughout much of the late Cenozoic. Copyright © 2005 John Wiley & Sons, Ltd.
Measuring middle Pleistocene erosion rates with cosmic‐ray‐produced nuclides in buried alluvial sediment, Fisher Valley, southeastern Utah
Authors: Balco Greg , Stone John O. H. 
Published: August 2005

AbstractCosmic‐ray‐produced 10Be and 26Al in riverborne quartz sediment are commonly used to estimate average catchment‐scale erosion rates. Likewise, the concentrations of these nuclides in ancient sediments, stored in a depositional basin, carry a record of past erosion rates in the sediment source area. This is important because such a record could be compared to records of climate change or tectonic events to elucidate relationships between climate, tectonics and erosion. If the sediments are shielded from the cosmic‐ray flux after deposition, for example in deep water, their nuclide concentrations need only be corrected for radioactive decay since deposition in order to determine past erosion rates. Where sediment is deposited subaerially and buried relatively slowly, on the other hand, the additional nuclide concentration that builds up during sediment accumulation and storage must be reconstructed and subtracted in order to recover the initial nuclide concentrations in the sediment and thence the past erosion rates. We describe an example of this process for an early to middle Pleistocene section of alluvial sediment in Fisher Valley, Utah. We use stratigraphic observations as well as an independently known age model for the sediment section to: (a) subtract post‐depositional nuclide concentrations and reconstruct past erosion rates between 0·7 and 0·6 Ma; and (b) estimate the uncertainty in the results that arises from imperfect dating of the section and the natural variability in accumulation rates. The present basin‐averaged erosion rate in Fisher Valley is near 125 m Ma−1, and middle Pleistocene basin‐averaged erosion rates varied between 80 and 220 m Ma−1. Changes in the erosion rate over time do not appear to be connected to glacial–interglacial climate changes, but may be related to episodic subsidence of the basin. Uncertainties are small in the case of low erosion rates and high sediment accumulation rates, and large in the opposite situation. In this example, we could reduce the uncertainties by increasing the sampling density or by better relating our sample locations to the small‐scale stratigraphy of the sedimentary section. In general, future attempts to reconstruct past erosion rates from cosmogenic‐nuclide concentrations in ancient alluvium will be most successful in situations where post‐depositional nuclide accumulation is minimized, for example in lakes or marine basins. Copyright © 2005 John Wiley & Sons, Ltd.
Tie channel sedimentation rates, oxbow formation age and channel migration rate from optically stimulated luminescence (OSL) analysis of floodplain deposits
Authors: Rowland Joel C. , Lepper Kenneth , Dietrich William E. , Wilson Cathy J. , Sheldon R. 
Published: August 2005

AbstractUsing optically stimulated luminescence (OSL) analysis we obtained depositional ages ranging from 25 ± 10 to 928 ± 144 years before present for sediments deposited in oxbow lakes along three lowland river systems. The dated sediments were collected from the banks of tie channels along the Lower Mississippi River, the Fly River in Papua New Guinea, and Birch Creek along the Yukon River in Alaska. Tie channels connect the oxbow lakes to the main stem river and allow the exchange of water and suspended sediment between the two. The banks consist of fine sand and sandy silt beds interlayered with silt and clay. OSL samples were collected both horizontally from exposed banks and vertically by coring through levee crests; sample collection was targeted at beds containing appreciable quantities of fine sand. OSL ages were determined using single‐grain or in some cases single‐aliquot techniques and dose distribution analysis. Samples were first collected along the Lower Mississippi tie channel to compare OSL dates with historical data sources and test the applicability of OSL in these settings; the OSL dates agreed closely with historical data. In all three river systems, OSL dating allowed the determination of vertical accretion rates, tie channel advancement rates, and oxbow lake ages. In Papua New Guinea, OSL sampling also provides an estimate of lateral migration rates of the Fly River and allows a comparison of modern mineinfluenced deposition rates with natural background rates over the last 1000 years. Results from Papua New Guinea and the Mississippi River suggest that the advancement rate of tie channels responds directly to changes in the sediment load of the main stem river. Copyright © 2005 John Wiley & Sons, Ltd.
Assessing household health expenditure with Box–Cox censoring models
Authors: Chaze Jean‐Paul 
Published: August 2005

AbstractIn order to assess the combined presence of zero expenditures and a heavily skewed distribution of positive expenditures, the Box–Cox transformation with location parameter is used to define a set of models generalising the standard Tobit, Heckman selection and double‐hurdle models. Extended flexibility with respect to previous specifications is introduced, notably regarding negative transformation parameters, which may prove necessary for medical expenditures, and corner‐solution outcomes. An illustration is provided by the analysis of household health expenditure in Switzerland. Copyright © 2005 John Wiley & Sons, Ltd.
A dynamic analysis of disability and labour force participation in Ireland 1995–2000
Authors: Gannon Brenda 
Published: August 2005

AbstractThis paper aims to analyse the effect of disability on participation in the labour force, using the Irish component of the European Community Household Panel Survey 1995–2000. A range of panel models are considered, but to allow for any unobserved influences or state dependence in labour force participation, our preferred model is a dynamic panel model. We show how the estimates of current disability are changed once we control for the effect of past disability and previous participation. We compare base estimates of disability with those controlling for unobserved heterogeneity and past participation. The results suggest that the base effect of disability is overestimated by between 40–60% for men and by 5–10% for women. Copyright © 2005 John Wiley & Sons, Ltd.
Utilization of public health centres in Portugal: effect of time costs and other determinants. Finite mixture models applied to truncated samples
Authors: Lourenço Óscar D. , Ferreira Pedro L. 
Published: August 2005

AbstractThe impact of time costs on the utilization of medical care has been a subject of theoretical and empirical research since the early 1970s.The main goal of this paper is to show the effect of time costs on the number of visits to general practitioners (GP) in Portuguese public health centres. We measured the elasticity of primary health care utilization relative to the total time spent in the health centre and relative to travel time. We also provided evidence regarding the impact of an appointment delay on the utilization of public GP services.Our data resulted from the application of an endogenous sampling scheme, resulting in a truncated‐at‐zero data set. To model our dependent variable, number of visits, and accounting for the truncated nature of the data we used a finite mixture model specification.The data were obtained from the most recent implementation in Portugal of the 2003/2004 Europep Survey.The two‐component negative binomial II finite mixture model led to the identification of two different latent classes of health centre users: a low‐users class that comprises 88% of patients with an estimated utilization mean of 4.3 GP visits per year and a frequent‐users class with an estimated utilization mean of 11.1 visits for the remaining 12% of the population.We failed to find any statistically significant elasticity of time cost utilization, when this variable is measured as the total time spent in the health centre. Regarding the effect of an appointment delay on health centre utilization we concluded that individuals respond to this variable by lowering the number of GP visits. This last finding may have policy implications, which will be discussed at the end of the paper. Copyright © 2005 John Wiley & Sons, Ltd.
Latent class models for use of primary care: evidence from a British panel
Authors: Bago d'Uva Teresa 
Published: August 2005

AbstractThis paper models access to and utilisation of primary care using data from the British Household Panel Survey for the period 1991–2001. A latent class panel data framework is adopted to model individual unobserved heterogeneity in a flexible way. Accounting for the panel structure of the data leads to a substantial improvement in fit, and permits the identification of latent classes of users of health care. Analysis by gender shows that men and women respond differently to some factors, in particular, to age and income. There is evidence of a positive impact of income on the probability of seeking primary care. This effect is especially significant in the case of women. For both genders, the marginal effect of income on the propensity to visit a GP is greater for individuals who are less likely to seek primary care. A latent class aggregated count data model for the number of GP visits classifies individuals in three latent classes and shows a positive income effect particularly amongst those with lower levels of utilisation. Copyright © 2005 John Wiley & Sons, Ltd.
Effect of morphology and discharge on hyporheic exchange flows in two small streams in the Cascade Mountains of Oregon, USA
Authors: Wondzell Steven M. 
Published: August 2005

AbstractStream‐tracer injections were used to examine the effect of channel morphology and changing stream discharge on hyporheic exchange flows. Direct observations were made from well networks to follow tracer movement through the hyporheic zone. The reach‐integrated influence of hyporheic exchange was evaluated using the transient storage model (TSM) OTIS‐P. Transient storage modelling results were compared with direct observations to evaluate the reliability of the TSM. Results from the tracer injection in the bedrock reach supported the assumption that most transient storage in headwater mountain streams results from hyporheic exchange. Direct observations from the well networks in colluvial reaches showed that subsurface flow paths tended to parallel the valley axis. Cross‐valley gradients were weak except near steps, where vertical and cross‐valley hydraulic gradients indicated a strong potential for stream water to downwell into the hyporheic zone. The TSM parameters showed that both size and residence time of transient storage were greater in reaches with a few large log‐jam‐formed steps than in reaches with more frequent, but smaller steps. Direct observations showed that residence times in the unconstrained stream were longer than in the constrained stream and that little change occurred in the location and extent of the hyporheic zone between low‐ and high‐baseflow discharges in any of the colluvial reaches. The transient storage modelling results did not agree with these observations, suggesting that the TSM was insensitive to long residence‐time exchange flows and was very sensitive to changes in discharge. Disagreements between direct observations and the transient storage modelling results highlight fundamental problems with the TSM that confound comparisons between the transient storage modelling results for tracer injections conducted under differing flow conditions. Overall, the results showed that hyporheic exchange was little affected by stream discharge (at least over the range of baseflow discharges examined in this study). The results did show that channel morphology controlled development of the hyporheic zone in these steep mountain stream channels. Copyright © 2005 John Wiley & Sons, Ltd.
The effects of spatial configuration on preschoolers' attention strategies, selective attention, and incidental learning
Authors: Blumberg Fran C. , Torenberg Meira 
Published: August 2005

AbstractThis study investigated the effects of spatial arrangement on preschool children's selective attention and incidental learning. Three‐ and four‐year old children were shown a multi‐coloured box designated as a ‘special place’ containing miniature chairs and models of animals. One category of objects were designated as relevant and one as irrelevant. Relevant items were placed in each of the apparatus' corners, in the middle of its walls, or in two corners and in the middle of two walls. Findings revealed that children shown relevant items in corners demonstrated the greatest number of correct relocations for relevant items while those shown relevant items in the middle of the walls showed the greatest number of correct relocations for irrelevant items. Findings also suggest that for both age groups, the ability to recall relevant items may have been independent of their ability to demonstrate a selective attention strategy. Copyright © 2005 John Wiley & Sons, Ltd.
Effects of surface modification of poly (3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx) on physicochemical properties and on interactions with MC3T3‐E1 cells
Authors: Li Jing , Yun Huan , Gong Yandao , Zhao Nanming , Zhang Xiufang 
Published: August 2005

AbstractAs a new member of the polyhydroxyalkanoate (PHA) family, poly (3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx) has better mechanical and processible properties than poly (3‐hydroxybutyrate) (PHB). Still, it is difficult to introduce functional groups to the polyester carbon chain of PHBHHx, which restricts the modification of PHBHHx for a wide range. In this study, a procedure for the modification of the surface of PHBHHx films under strongly alkaline conditions was described. Through this kind of modification, carboxyl and hydroxyl groups were introduced to the surface and the total surface free energy was increased, which was mainly due to the increased polar components. Meanwhile, this process makes the surface rougher, resulting in larger total surface areas. After mineralization in simulated body fluids (SBFs), the apatite nucleation and growth on the surface‐hydrolyzed PHBHHx films were significantly faster than on the unmodified PHBHHx films. This phenomenon should have a close relationship with the increased carboxyl and hydroxyl groups. The physicochemical properties also influenced the cell response to PHBHHx films. Compared to unmodified PHBHHx, fibronectin adsorption, and MC3T3‐E1 cell attachment and proliferation were significantly greater on surface‐hydrolyzed PHBHHx, which may be due to the increased surface free energy and rougher surface. Therefore, surface hydrolysis makes PHBHHx more suitable for osteoblast cell response and for application in bone‐tissue engineering. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Adhesion molecule expression by osteogenic cells cultured on various biodegradable scaffolds
Authors: Shur I. , Zilberman M. , Benayahu D. , Einav S. 
Published: August 2005

AbstractDesign of tissue‐engineered cell‐loaded device involves cells seeding onto scaffolds in vitro, allowing them to settle and grow before in vivo transplantation. Interaction between scaffold and cells is important in the development of desired tissues. The present study aimed to investigate the effect of cell–polymer interactions on cell morphology and expression of surface markers of osteogenic MBA‐15 cells cultured on various bioresorbable polymers. In this study, we used various polymers: poly(L‐lactic acid) (PLLA), poly(DL‐lactic acid) (PDLLA), poly(L‐lactic‐glycolic acid) (PLGA), and poly(DL‐lactide‐glycolide acid) PDLGA1 and PDLGA2. Expression of integrinα‐M (CD11b), selectin‐E (CD62E), and PECAM‐1 (CD31), important in cell–cell and cell–matrix interactions, were quantified by flow‐cytometry analysis. Cells grown on PDLGA1 films demonstrated fivefold increase in CD62E expression and two‐folds increase in CD11b expression. None of the polymers affected the levels of CD31. Identified differential effect of polymers on the expression of cell‐adhesion molecules by osteoprogenitors in vitro might help to choose optimal parameters for successful engraftment of cell‐loaded constructs. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005
Development of the uterine shell glands during the preovulatory and early gestation periods in oviparous and viviparous Lacerta vivipara
Authors: Heulin Benoit , Stewart James R. , Surget‐Groba Yann , Bellaud Patricia , Jouan Florence , Lancien Gérard , Deunff Jean 
Published: August 2005

AbstractThe evolutionary process leading to the emergence of viviparity in Squamata consists of lengthening the period of egg retention in utero coupled with marked reduction in the thickness of the eggshell. We used light microscopy and scanning electron microscopy to study uterine structure during the reproductive cycle of oviparous and viviparous females of the reproductively bimodal Lacerta vivipara. We compared the structure of the uterine shell glands, which secrete components of the eggshell, during preovulatory and early gestation phases of the reproductive cycle and also compared histochemistry of the eggshells. The uterine glands of both reproductive forms undergo considerable growth within a period of a few weeks during folliculogenesis and vitellogenesis preceding ovulation. The majority of the proteinaceous fibers of the shell membrane are secreted early in embryonic development and the uterine glands regress shortly thereafter. This supports previous observations indicating that, in Squamata, secretion of the shell membrane occurs very rapidly after ovulation. The most striking differences between reproductive modes were larger uterine glands at late vitellogenesis in oviparous females, 101 μm compared to 60 μm in viviparous females, and greater thickness of the shell membrane during early gestation in oviparous females (52–73 μm) compared to viviparous females (4–8 μm). Our intraspecific comparison supports the conclusions of previous studies that, prior to ovulation, the uterine glandular layer is less developed in viviparous than in oviparous species, and that this is the main factor accounting for differences in the thickness of the shell membrane of the two reproductive forms of squamates. J. Morphol. © 2005 Wiley‐Liss, Inc.