Wave propagation within random packings of spheres     

K. Walton 《Geophysical Journal International》1988,92(1):89-97

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On the Facular Area Surrounding Decaying Sunspots     

G.?A.?ChapmanEmail author  A.?S.?Hoffer  S.?R.?Walton 《Solar physics》2005,226(1):37-43

The change in facular area around decaying sunspots is investigated. The data are from full-disk photometric images from CFDT1 (5 arc sec pixels) obtained at the Ca ii K-line = 393.4 nm. The 31 active regions are from a list previously used to study the decay rate of sunspots. We find a weak, marginally significant relation between spot decay rate and growth of the surrounding facular region (r² = 0.1255). We conclude that, for this group of decaying sunspots, the growth or decay of the surrounding facular region was not clearly related to the decay rate of an active regions sunspots.  相似文献   

The Behavior of Sunspot Contrast during Cycle 23     

M. J. Wesolowski  S. R. Walton  G. A. Chapman 《Solar physics》2008,248(1):141-154

Results are presented from a study of various sunspot contrast parameters in broadband red (672.3 nm) Cartesian full-disk digital images taken at the San Fernando Observatory (SFO) over eight years, 1997 – 2004, of the twenty-third sunspot cycle. A subset of over 2700 red sunspots was analyzed and values of average and maximum sunspot contrast as well as maximum umbral contrast were compared to various sunspot parameters. Average and maximum sunspot contrasts were found to be significantly correlated with sunspot area (r _s=− 0.623 and r _s=− 0.714, respectively). Maximum umbral contrast was found to be significantly correlated with umbral area (r _s=− 0.535). These results are in agreement with the works of numerous other authors. No significant dependence was detected between average contrast, maximum contrast, or maximum umbral contrast during the rising phase of the solar cycle (r _s=0.024, r _s=0.033, and r _s=0.064, respectively). During the decay phase, no significant correlation was found between average contrast or maximum contrast and time (r _s=− 0.057 and r _s=0.009, respectively), with a weak dependence seen between maximum umbral contrast and cycle (r _s=0.102).  相似文献   

Recharge and Groundwater Flow Within an Intracratonic Basin,Midwestern United States          下载免费PDF全文

Samuel V. Panno  Zohreh Askari  Walton R. Kelly  Thomas M. Parris  Keith C. Hackley 《Ground water》2018,56(1):32-45

The conservative nature of chloride (Cl^?) in groundwater and the abundance of geochemical data from various sources (both published and unpublished) provided a means of developing, for the first time, a representation of the hydrogeology of the Illinois Basin on a basin‐wide scale. The creation of Cl^? isocons superimposed on plan view maps of selected formations and on cross sections across the Illinois Basin yielded a conceptual model on a basin‐wide scale of recharge into, groundwater flow within and through the Illinois Basin. The maps and cross sections reveal the infiltration and movement of freshwater into the basin and dilution of brines within various geologic strata occurring at basin margins and along geologic structures. Cross‐formational movement of brines is also seen in the northern part of the basin. The maps and cross sections also show barriers to groundwater movement created by aquitards resulting in areas of apparent isolation/stagnation of concentrated brines within the basin. The distribution of Cl^? within the Illinois Basin suggests that the current chemical composition of groundwater and distribution of brines within the basin is dependent on five parameters: (1) presence of bedrock exposures along basin margins; (2) permeability of geologic strata and their distribution relative to one another; (3) presence or absence of major geologic structures; (4) intersection of major waterways with geologic structures, basin margins, and permeable bedrock exposures; and (5) isolation of brines within the basin due to aquitards, inhomogeneous permeability, and, in the case of the deepest part of the basin, brine density effects.  相似文献   

Aquifer system response time and groundwater supply management   总被引：1，自引：0，他引：1  

Walton WC 《Ground water》2011,49(2):126-127

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Extreme <Superscript>15</Superscript>N Depletion in Seagrasses     

M. E. M. Walton  I. Al-Maslamani  N. Haddaway  H. Kennedy  A. Castillo  E. S. Al-Ansari  I. Al-Shaikh  M. Abdel-Moati  M. A. A. Al-Yafei  L. Le Vay 《Estuaries and Coasts》2016,39(6):1709-1723

Seagrass beds form an important part of the coastal ecosystem in many parts of the world but are very sensitive to anthropogenic nutrient increases. In the last decades, stable isotopes have been used as tracers of anthropogenic nutrient sources and to distinguish these impacts from natural environmental change, as well as in the identification of food sources in isotopic food web reconstruction. Thus, it is important to establish the extent of natural variations on the stable isotope composition of seagrass, validating their ability to act as both tracers of nutrients and food sources. Around the world, depending on the seagrass species and ecosystem, values of seagrass N normally vary from 0 to 8?‰ δ¹⁵N. In this study, highly unusual seagrass N isotope values were observed on the east coast of Qatar, with significant spatial variation over a scale of a few metres, and with δ¹⁵N values ranging from +2.95 to ?12.39?‰ within a single bay during March 2012. This pattern of variation was consistent over a period of a year although there was a seasonal effect on the seagrass δ¹⁵N values. Seagrass, water column and sediment nutrient profiles were not correlated with seagrass δ¹⁵N values and neither were longer-term indicators of nutrient limitation such as seagrass biomass and height. Sediment δ¹⁵N values were correlated with Halodule uninervis δ¹⁵N values and this, together with the small spatial scale of variation, suggest that localised sediment processes may be responsible for the extreme isotopic values. Consistent differences in sediment to plant ¹⁵N discrimination between seagrass species also suggest that species-specific nutrient uptake mechanisms contribute to the observed δ¹⁵N values. This study reports some of the most extreme, negative δ¹⁵N values ever noted for seagrass (as low as ?12.4?‰) and some of the most highly spatially variable (values varied over 15.4?‰ in a relatively small area of only 655 ha). These results are widely relevant, as they demonstrate the need for adequate spatial and temporal sampling when working with N stable isotopes to identify food sources in food web studies or as tracers of anthropogenic nutrients.  相似文献   

Light and dark soils at the apollo 16 landing site     

D. Heymann  J. R. Walton  J. L. Jordan  S. Lakatos  A. Yaniv 《Earth, Moon, and Planets》1975,13(1-3):81-110

On the basis of inert gas systematics alone, the soilsnow near the surface at the Apollo 16 landing site can be divided into three major groups: Group I (North Ray Crater Soils), Group II (Light Soils), and Group III (Dark Soils). Only five soils do not fit this scheme. The inert gas-based classification is correlated with the chemistry of the soils. Group I soils are relatively poor in K, Fe, Ti and Zn, compared to Group II and III soils. The classification is also correlated with reflectivity. Group I and II soils are generally the light soils in the landing area, while the Group III soils are the dark soils. The groups are not randomly distributed in the landing area. Group I soils occur only at stations 11 and 13 on the ejecta blanket of North Ray Crater. Group II soils occur abundantly at stations 1 and 2, and in spots on Stone Mountain. Group III soils are abundant on Stone Mountain and at station 10. We suggest here that Group I soils are principally derived from the light friable unit, one of the three units inside North Ray Crater, as described by Ulrich. We suggest that Group II soils are mainly derived from the light matrix breccia unit. Group III soils are mixtures of materials from all three units. We conclude that soils with the properties of Group III soils have been at the surface continuously for long times. However, going backwards in time, these soils probably had increasingly larger (Ar⁴⁰/Ar³⁶)t ratios. The ejecta blanket of North Ray Crater is a temporary ‘anomaly’ in the landing site. However, soils with the properties of Group I soils, but with larger (Ar⁴⁰/Ar³⁶)t ratios may turn up in Apollo 16 core tubes. The Group II soils show a record of solar wind exposure in the distant past (i.e., they have relatively large Art ⁴⁰/ARt ³⁶ ratios). From this we conclude that the regolith at Apollo 16 contains sizeable ‘pockets’ or horizons at depth which are the sources of the Group II soils. The materials in these pockets may be akin to soil 61 220.  相似文献   

A tale of two wave trains     

Todd L. Walton  Jr 《Ocean Engineering》1995,22(5)

The present study is an investigation into the transfer of the wave energy as it propagates through the surf zone and the consequent evolution of the wave trains and the corresponding envelope of the wave trains. The generation of long wave energy is investigated and one approach to developing the nonlinear transfer function for the transformation process is attempted. A nondimensionalized format for expressing the data is suggested for clarifying future studies of this type.  相似文献   

Utilizing in vivo nuclear magnetic resonance spectroscopy to study sublethal stress in aquatic organisms     

Viant MR  Pincetich CA  Walton JH  Tjeerdema RS  Hinton DE 《Marine environmental research》2002,54(3-5):553-557

In vivo nuclear magnetic resonance spectroscopy (NMR) is a powerful technique for characterizing the sublethal actions of physical and chemical stressors in live, intact organisms. In particular, 31P NMR is ideal for observing perturbations to cellular energetics since critical metabolite concentrations, including phosphagens, ATP and inorganic phosphate (Pi), can be measured non-invasively and in real time. This technique's versatility is demonstrated not only in the diversity of organisms that can be studied, but also in its broad-ranging applicability to environmental research. Illustrative studies include the actions of copper in adult red abalone (Haliotis rufescens) and changes in energetically important metabolites in developing medaka embryos (Oryzias latipes). Advantages and disadvantages of in vivo NMR will be discussed.  相似文献   

Projected sea level rise in Florida   总被引：1，自引：0，他引：1  

Todd L. Walton Jr.   《Ocean Engineering》2007,34(13):1832-1840

Future sea level rise will lead to salt water intrusion, beach/dune recession, and many other coastal problems. This paper addresses a data based forecasting approach to provide relative sea level rise estimates at locations in Florida where historical water level data exist. Many past estimates of sea level rise have treated the rise as a linear straight line trend over the historical data set. The present paper has allowed for acceleration (or deceleration) in sea level rise to account for the possibility of anthropogenic global warming and consequent higher (than linear straight line) future sea levels similar to values noted by global climatic modelers. Results of the present analysis show sea level rise for Florida being higher than past straight line trend results.  相似文献