Foamed and solid polypropylene/carbon fiber (PP–CF) composites containing various CF contents (0–10vol.%) were injection-molded. Foamed composites were achieved using dissolved pressurized nitrogen ...gas. The effects of foaming on the fibers inter-connectivity and orientation, electrical percolation threshold, through-plane electrical conductivity, longitudinal and transversal in-plane conductivities, dielectric permittivity, and electromagnetic interference (EMI) shielding effectiveness (SE) were investigated. Cell growth increased the fibers inter-connectivity by biaxial stretching of the matrix and also changed the fiber orientation. The introduction of foaming reduced the density of the injection-molded samples by 25%, lowered the volume fraction of the percolation threshold from 8.5 to 7vol.% CF, enhanced the through-plane conductivity up to a maximum of six orders of magnitude, increased the dielectric permittivity and resulted in the increase of the specific EMI SE up to 65%. Moreover, the uniformity of in-plane and through-plane conductivities as well as EMI SE along the injection-molded samples was greatly improved by foaming. The relationships between the microstructure and electrical properties were also established. The results reveal that lightweight conductive products with lower fiber content and enhanced electrical and EMI shielding properties can be fabricated with the aid of injection foam molding for applications in electronics, aerospace and automotive industries.
Hydrologic connectivity among wetlands is poorly characterized and understood. Our inability to quantify this connectivity compromises our understanding of the potential impacts of wetland loss on ...watershed structure, function and water supplies. We develop a computationally efficient, physically based subsurface–surface hydrologic model to characterize both the subsurface and surface hydrologic connectivity of geographically isolated wetlands and explore the time and length variations in these connections to a river within the Prairie Pothole Region of North America. Despite a high density of geographically isolated wetlands (i.e., wetlands without surface inlets or outlets), modeled connections show that these wetlands are not hydrologically isolated. Subsurface connectivity differs significantly from surface connectivity in terms of timing and length of connections. Slow subsurface connections between wetlands and the downstream river originate from wetlands throughout the watershed, whereas fast surface connections were limited to large events and originate from wetlands located near the river. This modeling approach provides first ever insight on the nature of geographically isolated wetland subsurface and surface hydrologic connections to rivers, and provides valuable information to support watershed-scale decision making for water resource management.
Endovascular abdominal and thoracic aortic aneurysm repair and are widely used to treat increasingly complex aneurysms. Secondary endoleaks, defined as those detected more than 30 days after the ...procedure and after previous negative imaging, remain a challenge for aortic specialists, conferring a need for long-term surveillance and reintervention. Endoleaks are classified on the basis of their anatomic site and aetiology. Type 1 and type 2 endoleaks (EL1 and EL2) are the most common endoleaks necessitating intervention. The management of these requires an understanding of their mechanics, and the risk of sac enlargement and rupture due to increased sac pressure. Endovascular techniques are the main treatment approach to manage secondary endoleaks. However, surgery should be considered where endovascular treatments fail to arrest aneurysm growth. This chapter reviews the aetiology, significance, management strategy and techniques for different endoleak types.
Large‐scale cross‐site scientific synthesis on low‐flow storage–discharge relation can promote developing transferable hypotheses on the interactions among critical zone attributes and on how such ...interactions affect catchments’ water vulnerabilities. This study leverages cross‐site empirical and theoretical analyses and develops a similarity index, based on the interactions among critical zone attributes, to help determine the less‐explored influence of upland hillslope groundwater subsidy on storage–discharge relation. We show that an increase in the relative extent of upland hillslope groundwater subsidy to low‐flow discharge, occurring through deep slow low‐moving (e.g., bedrock) storage unit, leads to (a) an increase in the nonlinearity of low‐flow discharge sensitivity to storage (β1) and (b) an increase in the convexity of low‐flow storage–discharge relation. Our findings also raise new hypotheses on the applicability of Boussinesq‐based hydraulic groundwater theory at low‐flow condition. Empirical results show that in a portion of our study catchments, particularly in those with a relatively small extent of upland hillslope groundwater subsidy, the theory’s proposed range of nonlinearity sufficiently explains the nonlinearity of low‐flow storage–discharge relation. However, in catchments with a strong influence of upland hillslope groundwater subsidy through deep slow‐moving storage unit, the current state of hydraulic groundwater theory, using one single (non)linear representative storage unit, may not be sufficient to explain the large nonlinearity and convexity of low‐flow storage–discharge relation (or the long tail of hydrograph late recession). Considering β1 informs the low‐flow vulnerability of catchments, the findings of this study deepen and generalize our understanding of where low‐flow discharge is vulnerable to storage’s change.
Plain Language Summary
There is limited knowledge of the ways watersheds generate stream low flow during dry periods, in watersheds with no (or little) streamflow observations and even in watersheds with extensive streamflow observations. This knowledge gap can limit the development of accurate models and hinder assessments of the impacts of global environmental changes on drought vulnerability. This study aims to address this knowledge gap by examining the a less‐explored way in which watersheds may generate a large amount of streamflow during dry periods from upland hillslopes located tens to hundreds of kilometers away from the mainstream. Our study shows that in some environments, this poorly quantified component of water balance may disproportionately (a) affect the relationship between watershed storage and streamflow discharge, which is used to develop a hydrologic model, and (b) contribute to the long tail of streamflow hydrograph during dry periods and thus reducing the vulnerability of drought. Our findings suggest that while the classical theory of streamflow generation can sufficiently explain the ways watersheds generate stream low flow in a portion of watersheds, the large contribution from upland hillslopes to low flow may result in certain watersheds being less low‐flow vulnerable than others.
Key Points
Upland hillslope groundwater subsidy increases the nonlinearity of low‐flow dynamics and alters the shape of storage–discharge relation
Hydraulic groundwater theory explains the estimated low‐flow nonlinearity in a portion (but not all) of the study catchments
Catchments with a limited extent of upland hillslope groundwater subsidy may be more low‐flow vulnerable than catchments with a larger upland subsidy
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•The crystallization behavior of polylactide under N2 pressure is investigated.•Crystallinity is remarkably enhanced by introducing foaming and additives.•The effects of crystals on ...the injection-molded foam morphology are discussed.
Polylactide (PLA) composite foams with two different void fractions of 30% and 55% were developed using regular foam injection molding (FIM) and FIM with mold opening, respectively. The microcellular structure and crystallization behavior were characterized using scanning electron microscopy and differential scanning calorimetry. The crystallization kinetics of the unfoamed samples was also analyzed with and without the presence of dissolved nitrogen (N2). The results showed that the presence of nanoclay and talc, presence of pressurized N2, foaming action, and mold opening all enhanced the PLA’s crystallization kinetics during injection molding, leading to a threefold increase in the final crystallinity. Consequently, the presence of nanoclay/talc together with the expedited crystallization enhanced the PLA foams’ morphology with a finer and more uniform cell structure (cell size<50μm) at a void fraction of 55%. The mechanisms of the formation of such morphologies were also derived.
Polylactide (PLA) and PLA composites with void fractions as high as 65% were fabricated using low-pressure foam injection molding (FIM) and high-pressure FIM (HPFIM) equipped with mold opening and ...gas counter pressure. The cellular morphology and crystallinity were characterized using scanning electron microscopy and differential scanning calorimetry, respectively. The mechanical (flexural and impact resistance) and thermal insulation properties were also measured. Unlike, talc, the addition of nanoclay markedly enhanced the ductility of solid PLA samples as well as significantly improved the cell morphology of foamed samples, which resulted in the increased specific modulus, strength and impact resistance. In all the PLA samples made using HPFIM, with an increased void fraction up to 55%, the flexural rigidity increased up to four times, the specific impact resistance increased up to 15%, and the thermal insulation increased up to three times. The results of this investigation revealed that low-density PLA composite foams with improved rigidity, impact strength, and thermal insulation can be developed using HPFIM for various applications such as transportation and construction industries.
Hydrologic functions of catchments are intrinsically diverse and defined as the ways catchments partition, store, and drain rainfall and snowmelt. Large‐sample hydrology (LSH) uses existing datasets ...of catchments to derive generalizable conclusions on hydrologic behaviors. LSH has the potential to synthesize the diversity of catchment hydrologic functions, allowing a robust extrapolation of streamflow generation mechanisms to poorly gauged regions. However, the descriptors of hydrologic functions, required to synthesize and extrapolate, have not been developed in LSH methodologies. This has potentially resulted in unexpectedly small associations between catchments' physical features and streamflow characteristics as well as poor predictability of the shape of streamflow hydrographs, as shown in recent LSH studies. Here, we propose three dimensionless indices—which directly quantify hydrologic functions—based on how interactions between a catchment’s climatic and physical attributes construct catchment functions. Using climatic and physical data as well as long‐term streamflow observations at hundreds of gauged catchments across the United States and Canada, our results depict that the use of interactive functional indices as catchment descriptors improves the performance of LSH methodologies (hierarchical clustering, multivariate regression, and random forests) in identifying hydrologic similarities in shape‐based streamflow signatures among catchments, and in predicting shape‐based streamflow signatures in poorly gauged regions. This research highlights the importance of physical interpretability of LSH models and showcases the development of parsimonious and process‐based catchment‐scale frameworks, allowing the analysis of globally available catchment data to progress the generalizable understanding of catchment hydrologic functions and streamflow generation mechanisms.
Key Points
Inclusion of interactive functional indices, developed independent of streamflow data, improves performance of hierarchical clustering
Functional indices improve regression and random forests accuracy in extrapolating the predictions of shape‐based streamflow signatures
Climatic information could sufficiently explain (dis)similarity in magnitude‐based, but not in shape‐based, streamflow signatures
•The new approach was able to reproduce hillslope flow and transport dynamics.•Macro scale subsurface heterogeneity significantly impacts the shape of TTD.•Infiltration rate impacts MTT but not the ...shape of dimensionless TTD.•Impact of hydrological boundaries on TTD depend on subsurface heterogeneity level.•The pore scale micro heterogeneity only slightly influences the TTD.
Defining the catchment transit time distribution remains a challenge. Here, we used a new semi-analytical physically-based integrated subsurface flow and advective–dispersive particle movement model to assess the subsurface controls on subsurface water flow paths and transit time distributions. First, we tested the efficacy of the new model for simulation of the observed groundwater dynamics at the well-studied S-transect hillslope (Västrabäcken sub-catchment, Sweden). This system, like many others, is characterized by exponential decline in saturated hydraulic conductivity and porosity with soil depth. The model performed well relative to a tracer-based estimate of transit time distribution as well as observed groundwater depth–discharge relationship within 30m of the stream. Second, we used the model to assess the effect of changes in the subsurface permeability architecture on flow pathlines and transit time distribution in a set of virtual experiments. Vertical patterns of saturated hydraulic conductivity and porosity with soil depth significantly influenced hillslope transit time distribution. Increasing infiltration rates significantly decreased mean groundwater age, but not the distribution of transit times relative to mean groundwater age. The location of hillslope hydrologic boundaries, including the groundwater divide and no-flow boundary underlying the hillslope, changed the transit time distribution less markedly. These results can guide future decisions on the degree of complexity that is warranted in a physically-based rainfall–runoff model to efficiently and explicitly estimate time invariant subsurface pathlines and transit time distribution.
Headwater groundwater subsidy, defined here as out‐of‐catchment groundwater flow contribution from a headwater catchment to its larger parent watershed (i.e., higher‐order stream), can influence the ...water quality and quantity of regional water resources. But the integrated flow and transport modeling approaches currently being implemented to quantify this subsidy are limited by an absence of critical field observations, such as water table dynamics and groundwater age that are required to test such models. Here we couple tracer (and hydrometric) observations from the well‐studied 4.5‐ha M8 headwater catchment in the Maimai experimental watershed with a new semianalytical free‐surface integrated flow and transport model. Our main research goals are to quantify the magnitude, age, and flow paths of the headwaters groundwater subsidies at the Maimai experimental watershed. Additionally, we explore through virtual experiments the effects of watershed slope, watershed active thickness, and recharge rate on the age, flow path, and magnitude of out‐of‐catchment headwater groundwater subsidies versus within‐catchment (or local) groundwater flow contributions. Our results show that more than 50% of groundwater recharged in the Maimai headwaters subsidizes their parent watershed. The relative proportion of headwaters groundwater subsidies is inversely proportional to recharge rate and/or directly proportional to slope angle. Our results also show that the age of the headwater groundwater subsidies is more than 500 years, almost 9 times older than the age of within‐catchment groundwater flow contributions. These findings highlight the need to consider headwaters groundwater subsidies in groundwater management area considerations.
Key Points
More than 50% of recharge within the Maimai headwaters discharges into their parent watershed
This groundwater subsidy from headwaters to parent watershed can be hundreds of years old
Recharge rate and watershed slope appear to control the age and magnitude of groundwater subsidy
As Norway considers revising triage approaches following their first adolescent cohort with human papillomavirus (HPV) vaccination entering the cervical cancer screening program, we analyzed the ...health impact and cost-effectiveness of alternative primary HPV triage approaches for women initiating cervical cancer screening in 2023. We used a multimodeling approach that captured HPV transmission and cervical carcinogenesis to evaluate the health benefits, harms and cost-effectiveness of alternative extended genotyping and age-based triage strategies under five-yearly primary HPV testing (including the status-quo screening strategy in Norway) for women born in 1998 (ie, age 25 in 2023). We examined 35 strategies that varied alternative groupings of high-risk HPV genotypes ("high-risk" genotypes; "medium-risk" genotypes or "intermediate-risk" genotypes), number and types of HPV included in each group, management of HPV-positive women to direct colposcopy or active surveillance, wait time for re-testing and age at which the HPV triage algorithm switched from less to more intensive strategies. Given the range of benchmarks for severity-specific cost-effectiveness thresholds in Norway, we found that the preferred strategy for vaccinated women aged 25 years in 2023 involved an age-based switch from a less to more intensive follow-up algorithm at age 30 or 35 years with HPV-16/18 genotypes in the "high-risk" group. The two potentially cost-effective strategies could reduce the number of colposcopies compared to current guidelines and simultaneously improve health benefits. Using age to guide primary HPV triage, paired with selective HPV genotype and follow-up time for re-testing, could improve both the cervical cancer program effectiveness and efficiency.
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