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We use a mathematical model to investigate the effect of basal topography and ice surface slope on transport and deposition of sediment within a water-filled subglacial channel. In our model, three zones of different behaviour occur. In the zone furthest upstream, variations in basal topography lead to sediment deposition under a wide range of conditions. In this first zone, even very small and gradually varying basal undulations (~5 m amplitude) can lead to the deposition of sediment within a modelled channel. Deposition is concentrated on the downstream gradient of subglacial ridges, and on the upstream gradient of subglacial troughs. The thickness and steepness of the ice sheet has a substantial impact on deposition rates, with shallow ice profiles strongly promoting both the magnitude and extent of sediment deposition. In a second zone, all sediment is transported downstream. Finally, a third zone close to the ice margin is characterised by high rates of sediment deposition. The existence of these zones has implications for esker formation and the dynamics of the subglacial environment.
The coronavirus disease 2019 (COVID-19) pandemic has significantly increased depression rates, particularly in emerging adults. The aim of this study was to examine longitudinal changes in depression risk before and during COVID-19 in a cohort of emerging adults in the U.S. and to determine whether prior drinking or sleep habits could predict the severity of depressive symptoms during the pandemic.
Participants were 525 emerging adults from the National Consortium on Alcohol and NeuroDevelopment in Adolescence (NCANDA), a five-site community sample including moderate-to-heavy drinkers. Poisson mixed-effect models evaluated changes in the Center for Epidemiological Studies Depression Scale (CES-D-10) from before to during COVID-19, also testing for sex and age interactions. Additional analyses examined whether alcohol use frequency or sleep duration measured in the last pre-COVID assessment predicted pandemic-related increase in depressive symptoms.
The prevalence of risk for clinical depression tripled due to a substantial and sustained increase in depressive symptoms during COVID-19 relative to pre-COVID years. Effects were strongest for younger women. Frequent alcohol use and short sleep duration during the closest pre-COVID visit predicted a greater increase in COVID-19 depressive symptoms.
The sharp increase in depression risk among emerging adults heralds a public health crisis with alarming implications for their social and emotional functioning as this generation matures. In addition to the heightened risk for younger women, the role of alcohol use and sleep behavior should be tracked through preventive care aiming to mitigate this looming mental health crisis.
This study aimed to investigate general factors associated with prognosis regardless of the type of treatment received, for adults with depression in primary care.
We searched Medline, Embase, PsycINFO and Cochrane Central (inception to 12/01/2020) for RCTs that included the most commonly used comprehensive measure of depressive and anxiety disorder symptoms and diagnoses, in primary care depression RCTs (the Revised Clinical Interview Schedule: CIS-R). Two-stage random-effects meta-analyses were conducted.
Twelve (n = 6024) of thirteen eligible studies (n = 6175) provided individual patient data. There was a 31% (95%CI: 25 to 37) difference in depressive symptoms at 3–4 months per standard deviation increase in baseline depressive symptoms. Four additional factors: the duration of anxiety; duration of depression; comorbid panic disorder; and a history of antidepressant treatment were also independently associated with poorer prognosis. There was evidence that the difference in prognosis when these factors were combined could be of clinical importance. Adding these variables improved the amount of variance explained in 3–4 month depressive symptoms from 16% using depressive symptom severity alone to 27%. Risk of bias (assessed with QUIPS) was low in all studies and quality (assessed with GRADE) was high. Sensitivity analyses did not alter our conclusions.
When adults seek treatment for depression clinicians should routinely assess for the duration of anxiety, duration of depression, comorbid panic disorder, and a history of antidepressant treatment alongside depressive symptom severity. This could provide clinicians and patients with useful and desired information to elucidate prognosis and aid the clinical management of depression.
Sample preparation techniques for radiocarbon analysis of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in freshwater, as well as CO2 and CH4 in gas mixtures are presented. Focused efforts have been on developing a robust and low-background wet oxidation extraction method for DOC in freshwater, following routine methods developed for stable carbon isotope analysis and adapted for radiocarbon (14C) analysis. DIC (by acidification) and DOC (by wet oxidation) are converted to CO2 in pre-baked septum-fitted borosilicate bottles, where the resulting CO2 is extracted from the dissolved and headspace portions on a low-flow He-carrier flow-through system interfaced to a vacuum extraction line. A peripheral CH4 extraction line interfaces to the flow line to separate CH4 from environmental samples following the methods of Pack et al. 2015. High sample throughput and low blanks are achievable with this method. DIC and DOC blanks are consistently <0.7 pMC, while CO2 and CH4 blanks are typically <0.1 pMC.
Objectives: This study examined the effects of anodal transcranial direct current stimulation (a-tDCS) on sentence and word comprehension in healthy adults. Methods: Healthy adult participants, aged between 19 and 30 years, received either a-tDCS over the left inferior frontal gyrus (n=18) or sham stimulation (n=18). Participants completed sentence comprehension and word comprehension tasks before and during stimulation. Accuracy and reaction times (RTs) were recorded as participants completed both tasks. Results: a-tDCS was found to significantly decrease RT on the sentence comprehension task compared to baseline. There was no change in RT following sham stimulation. a-tDCS was not found to have a significant effect on accuracy. Also, a-tDCS did not affect accuracy or RTs on the word comprehension task. Conclusions: The study provides evidence that non-invasive anodal electrical stimulation can modulate sentence comprehension in healthy adults, at least compared to their baseline performance. (JINS, 2019, 25, 331–335)
Ice-wedge activity can be used to reconstruct past environmental conditions. We investigated the moisture source and timing of ice-wedge formation on the Blackstone Plateau. A section of permafrost exposed ice wedges that developed at two distinct depths: the first set formed syngenetically and penetrated alluvial silts from the top of permafrost; the second set, truncated by an erosional or thaw contact, was found solely in icy muddy gravels (>3.1 m depth). The δ18O and D-excess records of the ice wedges suggest that they formed from freezing of snow meltwater whose isotopic composition evolved during meltout. The 14CDOC results suggest that climate was favorable to ice-wedge growth between 32,000–30,000 and 14,000–12,500 cal yr BP, but there was likely a hiatus during the last glacial maximum due to climate being too dry. During the early to mid-Holocene, ice wedges were inactive as a result of warmer and wetter climate. Ice wedge re-initiated around 6360 cal yr BP, with a peak in activity between 3980 and 920 cal yr BP, a period characterized by cool and moist climate. Overall, timing of ice-wedge activity was broadly consistent with the climate and vegetation evolution in the western Arctic.
A paleoclimatic reconstruction for the past 35,000 years for northern Oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs. High-pH groundwaters (pH up to 11.9) discharge from the mantle sequence of the Oman Ophiolite as the product of modern, low-temperature serpentinization. Under arid climatic conditions, hyperalkaline discharge occurs at the surface. Uptake of atmospheric CO2 precipitates characteristic laminated travertines, accompanied by strong kinetic depletion of 13C and 18O. Pluvial climates supporting a shallow bicarbonate-groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite-replaced roots and stems. All such carbonates have modern initial 14C contents, allowing radiocarbon dating and paleoclimatic reconstruction for the late Pleistocene and Holocene. Our reconstruction shows a dominantly wet late Pleistocene up to 19,000 yr B.P., when a phase of climatic deterioration began, leading to a period of hyperaridity which dominated from ca. 16,300 to 13,000 yr B.P. The early Holocene pluvial occurred from 12,500 to ca. 6500 yr B.P. and was followed by renewed climatic deterioration and the current phase of hyperaridity. Comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the A'Rub al Khali of central Saudi Arabia and the summer insolation-driven monsoon record of east Africa and the Arabian Sea is remarkably good.
This study presents new ages for the northwest section of the Laurentide Ice Sheet (LIS) glacial chronology from material recovered from two retrogressive thaw slumps exposed in the Richardson Mountains, Northwest Territories, Canada. One study site, located at the maximum glacial limit of the LIS in the Richardson Mountains, had calcite concretions recovered from aufeis buried by glacial till that were dated by U/Th disequilibrium to 18,500 cal yr BP. The second site, located on the Peel Plateau to the east yielded a fossil horse (Equus) mandible that was radiocarbon dated to ca. 19,700 cal yr BP. These ages indicate that the Peel Plateau on the eastern flanks of the Richardson Mountains was glaciated only after 18,500 cal yr BP, which is later than previous models for the global last glacial maximum (LGM). As the LIS retreated the Peel Plateau around 15,000 cal yr BP, following the age of the Tutsieta phase, we conclude that the presence of the northwestern margin of the LIS at its maximum limit was a very short event in the western Canadian Arctic.
A massive ground-ice body was found exposed in the headwall of a thaw flow developed within the Chapman Lake terminal moraine complex on the Blackstone Plateau (Ogilvie Mountains, central Yukon Territory), which is contemporaneous to the Reid glaciation. Based on visible cryostructures in the 4-m-high headwall, two units were identified: massive ground ice, overlain sharply by 2 m of icy diamicton. The nature and origin of the Chapman Lake massive ground ice was determined using cryostratigraphy, petrography, stable O–H isotopes and the molar concentration of occluded gases (CO2, O2, N2 and Ar) entrapped in the ice, a new technique in the field of periglacial geomorphology that allows to distinguish between glacial and non-glacial intrasedimental ice. Collectively, the results indicate that the Chapman Lake massive ground ice formed by firn densification with limited melting–refreezing and underwent deformation near its margin. Given that the massive ground-ice body consists of relict glacier ice, it suggests that permafrost persisted, at least locally, on plateau areas in the central Yukon Territory since the middle Pleistocene. In addition, the d value of Chapman Lake relict glacier ice suggests that the ice covering the area during the Reid glaciation originated from a local alpine glaciation in the Ogilvie Mountains.
The A.E. Lalonde accelerator mass spectrometer (3MV, HVEE) was commissioned in early 2014 at the University of Ottawa (Canada). The radiocarbon sample preparation laboratory spent the better part of 2014 undertaking a quality control program, establishing pretreatment protocols, and streamlining sample processing. In the fall of 2014, the first unknown samples were accepted and in the first year of operation well over 1000 targets (~60% unknowns) were analyzed. Here, we present an overview of sample processing protocols and results from routinely measured standards, reference, and blank materials.
In this chapter we outline and discuss statistical approaches to the analysis of contest data, with an emphasis on testing key predictions and assumptions of the theoretical models described in Chapters 2 and 3. We use examples from an array of animal taxa, including cnidarians, arthropods and chordates, to illustrate these approaches and also the commonality of many key aspects of contest interactions despite the differing life histories and morphologies (including weaponry) of these organisms. We first deal with the analysis of contest outcomes, a useful approach for determining which traits contribute to an individual's resource holding potential (RHP). Here we outline alternative statistical approaches that treat the outcome as either an explanatory (independent) variable or as the response (dependent) variable. In both cases, we treat a single contest as one ‘experimental unit’ and consider ways in which multiple measures taken from the same experimental unit should be accounted for in the analysis. Thus, we introduce paired and repeated measures approaches for contest data and also the calculation of composite measures. We then discuss more complex mixed models, which are particularly useful for dealing with multi-party contests when multiple individuals from the same group occur in more than one observation. Having established what factors influence RHP, one might then ask questions about the roles of information-gathering and decision-making during contests. These questions are prompted by the theoretical models of dyadic contests discussed in Chapters 1 and 2, and we consider the advantages and limitations of using analysis of contest duration to distinguish between ‘mutual-’ and ‘self-assessment’ type contests. An additional tool that we can use to address this question is the analysis of escalation and de-escalation patterns, and we thus shift the focus to within-contest behavioural changes.
The Tarantula Survey is an ESO Large Programme which has obtained multi-epoch spectroscopy of over 1,000 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The assembled consortium will exploit these data to address a range of fundamental questions in both stellar and cluster evolution.
The purpose of this article is to describe and understand the nascent state of hospitality on the Victorian goldfields in the 1850s. The primary sources for such an account are the journals of miners, public officials, and other travellers spanning this decade. The gold rushes transformed hospitality in numerous ways; the number of travellers requiring hospitality increased exponentially, and significant commercialisation occurred to meet this increased demand. Despite mining representing a new wave of occupation of their lands (pastoralism being the first) Aboriginal people were often renowned for their hospitality on Victorian goldfields.
The molar ratios of atmospheric gases change during dissolution in water due to differences in their relative solubilities. We exploited this characteristic to develop a tool to clarify the origin of ice formations in permafrost regions. Extracted from ice, molar gas ratios can distinguish buried glacier ice from intrasedimental ground ice formed by freezing groundwaters. An extraction line was built to isolate gases from ice by melting and trapping with liquid He, followed by analysis of N2, O2,, Ar, 18OO2 and 15NN2, by continuous flow mass spectrometry. The method was tested using glacier ice, aufeis ice (river icing) and intrasedimental ground ice from sites in the Canadian Arctic. O2/Ar and N2/Ar ratios clearly distinguish between atmospheric gas in glacial ice and gases from intrasedimental ground ice, which are exsolved from freezing water. δ15NN2 and δ18OO2 in glacier ice, aufeis ice and intrasedimental ground ice do not show clear distinguishing trends as they are affected by various physical processes during formation such as gravitational settling, excess air addition, mixing with snow pack, and respiration.