Effects of porous media thickness and its hydraulic gradient history on the formation of sand boils: Experimental investigation.

Sand boils occur where groundwater discharges to the land surface under sufficient hydraulic gradient to cause internal erosion and the upward transport of particles. A proper understanding of sand boil processes is essential in evaluating a wide range of geomechanical and sediment transport situations under which groundwater seepage occurs, such as the effects of groundwater discharge on beach stability. Although various empirical methods have been developed to estimate the critical hydraulic gradient (icr) leading to sand liquefaction, a prerequisite for sand boil occurrence, the effect of sand layer thickness and the implications of driving head fluctuations on the formation and reformation of sand boils have not been explored previously. This paper uses laboratory experiments to study sand boil formation and reformation for various sand thicknesses and hydraulic gradients to fill this knowledge gap. Sand layer thicknesses of 90 mm, 180 mm and 360 mm were adopted in evaluating sand boil reactivation, which was created by imposing hydraulic head fluctuations. While the first experiment (i.e., 90 mm sand layer) yielded a value for icr smaller (by 5%) than Terzaghi's (1922) value, the same theory underestimated icr by 12% and 4% for 180 mm and 360 mm sand layers, respectively. Moreover, icr needed for the reformation of sand boils decreased by 22%, 22% and 26% (relative to icr applicable to the initial sand boil) for the 90 mm, 180 mm and 360 mm sand layer thicknesses, respectively. We conclude that the formation of sand boils requires consideration of sand depth and the history of sand boil formation, particularly in relation to sand boils that form (and potentially reform) under oscillating pressures (e.g., tidal beaches).

Assessment of telemedicine versus in-person care in managing abdominal pain in children during the COVID-19 pandemic.

OBJECTIVES: The COVID-19 pandemic has led to a dramatic increase in telemedicine care delivery. This raises the question of whether the visit type affects the care provided to patients in the pediatric gastroenterology clinic. The aim of this study is to assess whether diagnostic, treatment, and outcome measures differ between telemedicine and in-person visits in patients seen in pediatric gastroenterology clinics for the chief complaint of abdominal pain. METHODS: We conducted a retrospective analysis of patients aged 0-22 who underwent their initial pediatric gastroenterology clinic visit, for abdominal pain, between March and September 2020 (n = 1769). The patients were divided into two groups: in-person or telemedicine. Clinical outcome measures were compared from the initial gastroenterology visit and followed for a total of 3 months. RESULTS: There was an increase number of images (M = 0.52 vs. 0.36, p < 0.001), labs (M = 4.87 vs. 4.05; p = 0.001), medications (M = 2.24 vs. 1.67; p < 0.001), and referrals (M = 0.70 vs. 0.54; p < 0.001) performed per visit in the in-person group. Electronic communications (3.97 vs. 5.12 p <0.003) was less frequent after in-person visits. There was no difference in number of procedures (M = 0.128 vs. 0.122, p = 0.718), emergency room visits (M = 0.037 vs. 0.017 p = 0.61), follow-up visits (M = 1.21 vs. 1.21 p = 0.922), or telephone encounters (M = 1.21 vs. 1.12 p = 0.35) between the two groups. CONCLUSION: Telemedicine utilizes less resources while having comparable outcome measurements in children with a chief complaint of abdominal pain.

Postpyloric Feeding Access in Infants and Children: A State of the Art Review.

Achieving postpyloric feeding access is a clinical challenge faced by the pediatric gastroenterologist in everyday practice. Currently, there is limited literature published on the topic. This article provides a practical summary of the literature on the different methods utilized to achieve postpyloric feeding access including bedside, fluoroscopic, endoscopic and surgical options. Indications and complications of these methods are discussed as well as a general approach to infants and children that require intestinal feeding.

Sediment mobilisation and release through groundwater discharge to the land surface: Review and theoretical development.

The discharge of groundwater to the land surface and to lakes and streams may express subsurface particles. This may lead to preferential pathways and increased fluxes of groundwater, sediment and contaminants, and modified subsurface structures. The current review attempts to describe and categorise the various forms through which sediment may be liberated in areas of groundwater discharge. Forces acting on subsurface particles in areas of groundwater discharge include seepage (drag), buoyancy and particle weight, amongst other, more complex forces. Equations for these can be combined to create formulae for approximating the conditions under which groundwater discharge will transport particles to the surface. Two forms of subsurface sediment transport are considered: (1) flow through an immobile granular matrix (suffusion and suffosion), and (2) flow through preferential pathways (i.e., often treated as pipes). Suffusion involves sediment movement that does not impact the soil's stability, whereas suffosion creates changes to soil stability and, consequently, soil volume. Preferential flow may arise from cracks in cohesive materials or through localised fluidization of non-cohesive soils, leading in some situations to sand boils. Guidance is presented on the minimum theoretical hydraulic gradient required for grains of various sizes to start to rise. New simple formulae are developed that build on existing theory, and these are compared to previous laboratory data, showing that suffusion is more or less predictable using the new simple method. However, experimental sand boils require larger hydraulic gradients compared to theory. The current analysis summarises the state of knowledge and persistent knowledge gaps associated with sediment ejection through groundwater discharge, which we expect has wide-ranging applications in terms of sediment transport in coastal regions and to surface water bodies, and where strong groundwater discharge is known to occur.

Study of the numerical artifacts in differential analysis of highly conducting gratings.

Li's Fourier factorization rule [J. Opt. Soc. Am. A13, 1870 (1996)] was recently shown to be problematic to apply to highly conducting metallic gratings. We provide further information about the applicability of different differential methods and are concerned with the relation of observed numerical artifacts, the total number of retained space harmonics, the presence of both positive and negative permittivity inside the groove region, and the validity of Li's inverse rule. Two different cases corresponding to lossless and low-loss binary metallic gratings are considered, and it is shown that an increase in the number of retained space harmonics can relieve the presence of numerical artifacts.