Geotechnical Lessons Learned From Earthquakes

Geotechnical earthquake engineering is an experience-driven discipline. Field observations are particularly important because it is difficult to replicate in the laboratory, the characteristics and response of soil deposits built by nature over thousands of years. Further, much of the data generated by a major earthquake is perishable, so it is critical that it is collected soon after the event occurs. Detailed mapping and surveying of damaged and undamaged areas provides the data for the well-documented case histories that drive the development of many of the design procedures used by geotechnical engineers. Thus, documenting the key lessons learned from major earthquake events around the world contributes significantly to advancing research and practice in geotechnical earthquake engineering. This is one of the primary objectives of the Geotechnical Extreme Events Reconnaissance (GEER) Association. Some of GEER’s findings from recent earthquakes are described in this paper. In particular, the use of advanced reconnaissance techniques is highlighted, as well as specific technical findings from the 1999 Kocaeli, Turkey earthquake, the 2007 Pisco, Peru earthquake, the 2010 Haiti earthquake, and the 2010 Maule, Chile earthquake

Flow Resistance Dynamics in Step-pool Channels: 2. Partitioning Between Grain, Spill, and Woody Debris Resistance

In step-pool stream channels, flow resistance is created primarily by bed sediments, spill over step-pool bed forms, and large woody debris (LWD). In order to measure resistance partitioning between grains, steps, and LWD in step-pool channels we completed laboratory flume runs in which total resistance was measured with and without grains and steps, with various LWD configurations, and at multiple slopes and discharges. Tests of additive approaches to resistance partitioning found that partitioning estimates are highly sensitive to the order in which components are calculated and that such approaches inflate the values of difficult-to-measure components that are calculated by subtraction from measured components. This effect is especially significant where interactions between roughness features create synergistic increases in resistance such that total resistance measured for combinations of resistance components greatly exceeds the sum of those components measured separately. LWD contributes large proportions of total resistance by creating form drag on individual pieces and by increasing the spill resistance effect of steps. The combined effect of LWD and spill over steps was found to dominate total resistance, whereas grain roughness on step treads was a small component of total resistance. The relative contributions of grain, spill, and woody debris resistance were strongly influenced by discharge and to a lesser extent by LWD density. Grain resistance values based on published formulas and debris resistance values calculated using a cylinder drag approach typically underestimated analogous flume-derived values, further illustrating sources of error in partitioning methods and the importance of accounting for interaction effects between resistance components

APC-β-catenin-TCF signaling silences the intestinal guanylin-GUCY2C tumor suppressor axis.

Sporadic colorectal cancer initiates with mutations in APC or its degradation target β-catenin, producing TCF-dependent nuclear transcription driving tumorigenesis. The intestinal epithelial receptor, GUCY2C, with its canonical paracrine hormone guanylin, regulates homeostatic signaling along the crypt-surface axis opposing tumorigenesis. Here, we reveal that expression of the guanylin hormone, but not the GUCY2C receptor, is lost at the earliest stages of transformation in APC-dependent tumors in humans and mice. Hormone loss, which silences GUCY2C signaling, reflects transcriptional repression mediated by mutant APC-β-catenin-TCF programs in the nucleus. These studies support a pathophysiological model of intestinal tumorigenesis in which mutant APC-β-catenin-TCF transcriptional regulation eliminates guanylin expression at tumor initiation, silencing GUCY2C signaling which, in turn, dysregulates intestinal homeostatic mechanisms contributing to tumor progression. They expand the mechanistic paradigm for colorectal cancer from a disease of irreversible mutations in APC and β-catenin to one of guanylin hormone loss whose replacement, and reconstitution of GUCY2C signaling, could prevent tumorigenesis

GREENLAND REVISITED: LAKE EFFECTS ON COASTAL NUTRIENT FLUXES

Retreat of continental ice sheets exposed ~15% of Earth’s land surface from the Last Glacial Maximum (LGM) to about 6 ka and recent warming has increased glacial melting and meltwater solute fluxes to the oceans. Additional solutes originate from non-glacial streams in landscapes exposed since the LGM. As presented in last year’s pandemic-modified Birdsall-Dreiss lecture, Greenlandic glacial and non-glacial streams have distinct solute concentrations because of differing chemical weathering regimes of comminuted glacial sediment. In this year’s lecture, we evaluate an ~46 km2 non-glacial watershed near Sisimiut, Greenland to assess how lakes may impact non-glacial solute fluxes. Snow accumulates in the watershed from October to freshet in early May, after which discharge responds solely to precipitation events. Three main tributaries provide 92% of flow to the outlet stream and drain sub-watersheds with median slope angles of 16 to 18% and small upland lakes that cover 0.5 and 3.8% of the land area. In contrast, the outlet stream discharges from a landscape with a median slope of ~6% that includes one large and one small lake covering 23% of the area. Streams above and below the outlet lakes show similar variations in solute concentrations through the melt season. However, soon after freshet the outlet stream has major element concentrations ~20% greater than in the tributaries. The excess solute concentrations decrease linearly for ~90 days at which time the tributaries and outlet have similar concentrations. The excess solutes at the outlet may result from over-winter mineral dissolution in lake sediments, cryogenic solute enrichment during lake freeze-in, or dilute runoff in tributaries from snowmelt during and soon after freshet. In contrast, the outlet stream has a 0.6 to 3 times deficit of PO4, NO3, and Si compared with the tributaries, suggesting assimilation within the lake. NH4 concentrations switch from ~60% deficit to ~ 60% excess, reflecting a switch from a lake sink to source. The differences between tributary and outlet stream compositions suggest lake development may have altered coastal nutrient fluxes from non-glacial streams post-LGM. These variations will modify differences in glacial and non-glacial nutrient fluxes to coastal ecosystems, both since the LGM and as melting increases in a future warmer world

The Physical Health of Caregivers of Children With Life-Limiting Conditions:A Systematic Review

CONTEXT: Parental caregiving for a child with a life-limiting condition (LLC) is complex physical and mental work. The impact of this caregiving on parents' physical health is unknown. OBJECTIVES: (1) To review existing evidence on the physical health of parents caring for a child with a LLC and (2) to determine how physical health of parents is measured. DATA SOURCES: Medline, Embase, PsycINFO, and Cumulative Index of Nursing and Allied Health Literature were searched. STUDY SELECTION: Peer-reviewed articles were included if they reported primary data on the physical health of a caregiver of a child with a LLC. Studies were excluded if they described only the caregiver's mental health or if the caregivers were bereaved at the time of data collection. DATA EXTRACTION: Of 69 335 unique citations, 81 studies were included in the review. RESULTS: Caregiver health was negatively impacted in 84% of studies. Pain and sleep disturbance were the most common problems. Ways of measuring the physical health of caregiver varied widely. We found an absence of in-depth explorations of the social and economic contexts, which could potentially mitigate the impact of caregiving. Furthermore, we find health interventions tailored to this group remain largely unexplored. LIMITATIONS: Studies were heterogenous in methodology, making comparisons of results across studies difficult. CONCLUSIONS: These findings support the need for improving access to interventions aimed at improving physical health in this population. The rate of health-seeking behaviors, preventive health care access and screening for health conditions is understudied and represent important directions for further research

OCEANIC FLUXES FROM PROGLACIAL AND DEGLACIAL WATERSHEDS IN WESTERN GREENLAND

Weathering in western Greenland occurs in two distinct environments: proglacial watersheds that extend from the margin of the Greenland Ice Sheet (GIS) and derive water from ice melt, and deglacial watersheds that develop on terrains unconnected to the GIS and derive water from annual precipitation. Proglacial and deglacial watersheds currently provide equal amounts of runoff in western Greenland. These watersheds may contribute different solute fluxes to the oceans depending on exposure age, climate, and weathering environment. We test this hypothesis by comparing chemical compositions of streams in four deglacial watersheds (Sisimiut, Nerumaq, Qorlortoq, Kangerlussuaq) and one proglacial watershed (Watson River Akuliarusiarsuup Kuua River; AKR) along a ~160 km transect from the coast to the GIS. Recent work found that weathering reactions in the deglacial watersheds shift from being dominated by carbonate dissolution inland to sulfide oxidation near the coast. Silicate weathering, based on increased Si, Na and K concentrations, is a minor source of solutes to deglacial streams and is less extensive near the GIS than the coast, where older moraines experience greater precipitation. In general, specific conductivity (SpC: 48-301 μS/cm) and pH (7.0-8.2) increase inland as precipitation decreases and fresh mineral surfaces become more common. The AKR, in contrast, has lower average SpC (11.9 uS/cm) and pH (6.86) than the deglacial streams. Low SpC reflects dilution by ice melt and short residence time of water in the subglacial system. Proglacial flow is enriched in Si compared to deglacial flow particularly near headwaters, indicating higher silicate weathering rates in the pro- and sub-glacial systems. Low pH values indicate: 1) equilibration with atmospheric CO2 in the supraglacial system near headwaters, and 2) acid production generated by sulfide oxidation in the hyporheic zone identified by elevated SO4 concentrations. However, Ca, Mg and HCO3 are the dominant ions over the length of the AKR indicating that dissolution of carbonate is the predominant form of weathering. Our results indicate the two types of watersheds provide distinct fluxes of solutes to the oceans that are likely to change as ice sheets retreat and advance with changing climate

Hydrologic exchange and chemical weathering in a proglacial watershed near Kangerlussuaq, west Greenland

The exchange of proglacial river water with active layer pore water could alter water chemical compositions in glacial outwash plains and oceanic solute fluxes. To evaluate effects of this exchange, we sampled Watson River and adjacent pore water during the 2013 melt season at two sandurs in western Greenland; one in Sandflugtdalen and the other near the confluence with Søndre Strømfjord. We measured temperature, specific conductivity, and head gradients between the river and bank over a week-long period at Sandflugtdalen, as well as sediment hydraulic conductivity and chemical compositions of waters from both sites. Specific conductivity of pore water is four to ten times greater than river water as solutes are concentrated from weathering reactions, cryoconcentration, and evaporation. Pore water compositions are predominantly altered by carbonate dissolution and sulfide mineral oxidation. High concentrations of HCO3 and SO4 result from solute recycling and dissolution of secondary Ca-Mg carbonate/sulfate salts initially formed by near-surface evaporation in the summer and at depth by freeze-in of the active layer and cryoconcentration in the winter. High hydraulic conductivity (10−5 to 10−4 m/s) and diurnal fluctuations of river stage during our study caused exchange of river and pore water immediately adjacent to the river channel, with a net loss of river water to the bank. Pore water \u3e6 m from the river continuously flowed away from the river. Approximately 1–8% of the river discharge through the Sandflugtdalen was lost to the river bank during our 6.75 day study based on calculations using Darcy’s Law. Although not sampled, some of this water should discharge to the river during low river stage early and late in the melt season. Elevated pore water solute concentrations in sandurs and water exchange at diurnal and seasonal frequency should impact fluxes of solutes to the ocean, although understanding the magnitude of this effect will require long-term evaluation throughout the melt season

Are social organizational factors independently associated with a current bacterial sexually transmitted infection among urban adolescents and young adults?

This study explored the relationship between the social organization of neighborhoods including informal social control and social cohesion and a current bacterial sexually transmitted infection (STI) among adolescents and young adults in one U.S. urban setting. Data for the current study were collected from April 2004 to April 2007 in a cross-sectional household study. The target population included English-speaking, sexually-active persons between the ages of 15 and 24 years who resided in 486 neighborhoods. The study sample included 599 participants from 63 neighborhoods. A current bacterial STI was defined as diagnosis of a chlamydia and/or gonorrhea infection at the time of study participation. Participants reported on informal social control (i.e. scale comprised of 9 items) and social cohesion (i.e. scale comprised of 5 items) in their neighborhood. In a series of weighted multilevel logistic regression models stratified by gender, greater informal social control was significantly associated with a decreased odds of a current bacterial STI among females (AOR 0.53, 95% CI 0.34, 0.84) after controlling for individual social support and other factors. The association, while in a similar direction, was not significant for males (AOR 0.73, 95% CI 0.48, 1.12). Social cohesion was not significantly associated with a current bacterial STI among females (OR 0.85, 95% CI 0.61, 1.19) and separately, males (OR 0.98, 95% CI 0.67, 1.44). Greater individual social support was associated with an almost seven-fold increase in the odds of a bacterial STI among males (AOR 6.85, 95% CI 1.99, 23.53), a finding which is in contrast to our hypotheses. The findings suggest that neighborhood social organizational factors such as informal social control have an independent relationship with sexual health among U.S. urban youth. The causality of the relationship remains to be determined

Implementation of an Integrated Approach to the National HIV/AIDS Strategy for Improving Human Immunodeficiency Virus Care for Youths

Importance Youths aged 13 to 24 years old living with human immunodeficiency virus (HIV) are less likely than adults to receive the health and prevention benefits of HIV treatments, with only a small proportion having achieved sustained viral suppression. These age-related disparities in HIV continuum of care are owing in part to the unique developmental issues of adolescents and young adults as well as the complexity and fragmentation of HIV care and related services. This article summarizes a national, multiagency, and multilevel approach to HIV care for newly diagnosed youths designed to bridge some of these fragmentations by addressing National HIV/AIDS Strategy goals for people living with HIV. Design, Setting, and Participants Three federal agencies developed memoranda of understanding to sequentially implement 3 protocols addressing key National HIV/AIDS Strategy goals. The goals were addressed in the Adolescent Trials Network, with protocols implemented in 12 to 15 sites across the United States. Outcome data were collected from recently diagnosed youth referred to the program. Main Outcomes and Measures Cross-agency collaboration, youth-friendly linkage to care services, community mobilization to address structural barriers to care, cooperation among services, proportion of all men who have sex with men who tested, and rates of linkage to prevention services. Results The program addressed National HIV/AIDS Strategy goals 2 through 4 including steps within each goal. A total of 3986 HIV-positive youths were referred for care, with more than 75% linked to care within 6 weeks of referral, with almost 90% of those youths engaged in subsequent HIV care. Community mobilization efforts implemented and completed structural change objectives to address local barriers to care. Age and racial/ethnic group disparities were addressed through targeted training for culturally competent, youth-friendly care, and intensive motivational interviewing training. Conclusions and Relevance A national program to address the National HIV/AIDS Strategy specifically for youths can improve coordination of federal resources as well as implement best-practice models that are adapted to decrease service fragmentation and systemic barriers at local jurisdictions