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Laser–solid interactions are highly suited as a potential source of high energy X-rays for nondestructive imaging. A bright, energetic X-ray pulse can be driven from a small source, making it ideal for high resolution X-ray radiography. By limiting the lateral dimensions of the target we are able to confine the region over which X-rays are produced, enabling imaging with enhanced resolution and contrast. Using constrained targets we demonstrate experimentally a
X-ray source, improving the image quality compared to unconstrained foil targets. Modelling demonstrates that a larger sheath field envelope around the perimeter of the constrained targets increases the proportion of electron current that recirculates through the target, driving a brighter source of X-rays.
Hannah C Kinney, Department of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, USA,
Robin L Haynes, Department of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, USA,
Dawna D Armstrong, Retired Professor Pathology Baylor College of Medicine, Department of Pathology, Houston, USA,
Richard D Goldstein, Department of Psychosocial Oncology and Palliative Care, Dana-Farber Cancer Institute, Department of Medicine, Boston Children's Hospital and Harvard Medical School, Boston, USA
The terrifying aspect of the sudden infant death syndrome (SIDS) is that it occurs in infants who seem healthy and then die without warning when put down to sleep. SIDS is not typically witnessed and it is surmized that death occurs during sleep, or during one of the many transitions to waking that occur during normal infant sleep-wake cycles (1). Multiple sleep-related mechanisms have been proposed to cause SIDS (1, 2). These mechanisms include suffocation/asphyxiation in the face-down sleep position, central and/or obstructive sleep apnea, impaired-state-dependent responses to hypoxia and/ or hypercarbia, inadequate autoresuscitation, defective autonomic regulation of blood pressure or thermal responses, and abnormal arousal to life-threatening challenges during sleep.
In this chapter, we review the hypothesis and the neuropathologic evidence that SIDS is precipitated by a dentate gyrus-related seizure or a limbic-related instability that involves the central homeostatic network (CHN). We begin with an overview of this hypothesis, and then review our neuropathologic evidence for an epileptiform hippocampal lesion in the brain of a subset of SIDS infants and young children (41-50% respectively) who died suddenly and unexpectedly (3-5). We then consider the putative mechanism whereby dentate lesions cause seizures, the role of the hippocampus as part of the CHN in stress responses (such as the face-down sleep position), and the potential interactions of brainstem serotonergic (5-HT) deficits and the hippocampus in the pathogenesis of sudden death in infants. We conclude with further directions for research into the role of the hippocampus in sudden and unexpected death in early life.
The Limbic Seizure-Related Hypothesis in SIDS
In 1986, Harper suggested that some SIDS deaths may be due to a fatal seizure during sleep that arises in forebrain-limbic-related circuits (6). This hypothesis arose from the recognition of the following inter-related phenomena: limbic regions are particularly susceptible to epileptogenesis; sleep states lower the threshold for seizure; and SIDS is linked to sleep and arousal. Sleep itself is thought to be a precarious state, in part because of the loss of the major “back-up” forebrain systems of waking which influence the final common pathways in the brainstem that mediate central cardiorespiratory function during sleep. Forebrain limbic regions, such as the hippocampus and amygdala, which are part of the CHN, modulate brainstem cardiorespiratory control in a manner influenced by the sleep-waking cycles.
Relationships between snow structure, climatic factors, and the nature of avalanche events in the San Juan Mountains of Colorado, U.S.A., are analyzed. Physical and mechanical properties of the snow cover have been monitored on a continuous basis by conventional methods as well as through the application of a profiling snow-density gauge. Temperature-gradient metamorphism is the dominant mechanism which determines the character of the local snow structure. Properties unique to well-developed temperature-gradient snow (depth hoar) are discussed. Three specific metamorphic processes are described which contribute to a highly varied and mechanically weak snow structure. Analysis of fracture-line profile data allow general studies of the local snow climate to be compared with the stratigraphy of actual release zones. Fracture-line data support the conclusion that meteorological conditions prevailing at the time of new-snow deposition play a less significant role in the eventual release of slab avalanches than metamorphic processes which influence the snow cover between storm periods. Shear failure zones are consistently composed of weak layers metamorphosed weeks and even months prior to the precipitation event which triggers the release.
On 16–18 June 2008 the US National Snow and Ice Data Center held a GLIMS workshop in Boulder, CO, USA, focusing on formulating procedures and best practices for operational glacier mapping using satellite imagery. Despite the progress made in recent years, there still remain many cases where automatic delineation of glacier boundaries in satellite imagery is difficult, error prone or time-consuming. This workshop identified six themes for consideration by focus groups: (1) mapping clean ice and lakes; (2) mapping ice divides; (3) mapping debris-covered glaciers; (4) assessing changes in glacier area and elevation through comparisons with older data; (5) digital elevation model (DEM) generation from satellite stereo pairs; and (6) accuracy and error analysis. Talks presented examples and work in progress for each of these topics, and focus groups worked on compiling a summary of available algorithms and procedures to address and avoid identified hurdles. Special emphasis was given to establishing standard protocols for glacier delineation and analysis, creating illustrated tutorials and providing source code for available methods. This paper summarizes the major results of the 2008 GLIMS workshop, with an emphasis on definitions, methods and recommendations for satellite data processing. While the list of proposed methods and recommendations is not comprehensive and is still a work in progress, our goal here is to provide a starting point for the GLIMS regional centers as well as for the wider glaciological community in terms of documentation on possible pitfalls along with potential solutions.
Passive-microwave satellite remote sensing can greatly enhance large-scale snow measurements based on visible satellite data alone because of the ability to acquire data through most clouds or during darkness as well as to provide a measure of snow depth or water equivalent. This study provides preliminary results from the comparison and evaluation of several different passive-microwave algorithms. These algorithms represent examples which include both mid- and high-frequency channels, vertical and horizontal polarizations and polarization-difference approaches. In our comparisons we utilize larger, more comprehensive, validation datasets which can be expected to provide a full range of snow/climate conditions rather than limited data which may only represent a snapshot in time and space. Evaluation of snow extent derived from passive-microwave data is undertaken through comparison with the U.S. National Oceanic and Atmospheric Administration (NOAA) Northern Hemisphere snow charts which are based on visible-band satellite data. Results clearly indicate those time periods and geographic regions where the two techniques agree and where they tend to consistently disagree. Validation of snow water equivalent derived from passive-microwave data is undertaken using measurements from snow-course transects in the former Soviet Union. Preliminary results indicate a general tendency for nearly all of the algorithms to underestimate snow water equivalent.
In this study, we report on the spatial and temporal distribution of seasonal snow depth derived from passive microwave satellite remote-sensing data (e.g. SMMR from 1978 to 1987 and SMM/ I from 1987 to 2006) in China. We first modified the Chang algorithm and then validated it using meteorological observation data, considering the influences from vegetation, wet snow, precipitation, cold desert and frozen ground. Furthermore, the modified algorithm is dynamically adjusted based on the seasonal variation of grain size and snow density. Snow-depth distribution is indirectly validated by MODIS snow-cover products by comparing the snow-extent area from this work. The final snow-depth datasets from 1978 to 2006 show that the interannual snow-depth variation is very significant. The spatial and temporal distribution of snow depth is illustrated and discussed, including the steady snow-cover regions in China and snow-mass trend in these regions. Though the areal extent of seasonal snow cover in the Northern Hemisphere indicates a weak decrease over a long period, there is no clear trend in change of snow-cover area extent in China. However, snow mass over the Qinghai–Tibetan Plateau and northwestern China has increased, while it has weakly decreased in northeastern China. Overall, snow depth in China during the past three decades shows significant interannual variation, with a weak increasing trend.
Asia, a region grappling with the impacts of climate change, increasing natural disasters, and transboundary water issues, faces major challenges to water security. Water resources there are closely tied to the dramatic Hindu-Kush Himalayan (HKH) mountain range, where over 46,000 glaciers hold some of the largest repositories of fresh water on earth (Qiu 2010). Often described as the water tower of Asia, the HKH harbors the snow and ice that form the headwaters of the continent's major rivers (Bandyopadhyay 2013). Downstream, this network of river systems sustains more than 1.3 billion people who depend on these freshwater sources for their consumption and agricultural production, and increasingly as a source of hydropower (Immerzeel, Van Beek, and Bierkens 2010; National Research Council 2012; Rasul 2014).
Compressive strain-rates in discrete layers of a sub-alpine snow cover are analyzed. Individual layers are identified according to density and the dominant type of metamorphism which contributed to their formation. Data were collected during four winter seasons at the Institute of Arctic and Alpine Research (INSTAAR) snow-study site (3 400 m), Red Mountain Pass, south-western Colorado, U.S.A. At average densities of less than 250 kg m₋3 the influence of metamorphism on strain-rate is not apparent. However, at densities greater than 250 kg m₋3, two separate relationships emerge for strain as a function of crystal type and density. While two adjacent layers may exhibit comparable densities, a layer of sintered, fine grained (ET) snow indicates a strain-rate approximately one order of magnitude greater than an adjacent layer of cohesionless, coarse-grained (TG) snow.
A contradiction has existed in the literature as to the conditions favoring formation of “ablation hollows” (“suncups”) on a melting snow surface. Some experiments find that these features grow under direct sunlight and decay in overcast, windy weather; whereas others find just the opposite result, that they grow best under cloudy, windy conditions and decay if exposed to direct sunlight. We find that the hidden variable in past experiments, which acts as a switch to determine which mode of formation can operate, is the absence or abundance of dark insoluble impurities in the snow. Direct sunlight causes ablation hollows to grow in clean snow and to decay in dirty snow (for dirt content below a critical value), because the dirt migrates to the ridges between the hollows, lowering the albedo at the ridges. By contrast, when ablation is dominated by turbulent heat exchange, the presence of dirt favours development of ablation hollows because the dirt migrates to the ridges and insulates them; albedo reduction has a negligible effect on ablation.
This hypothesis is supported by an experiment which showed that the presence of a thin layer of volcanic ash on the snow inhibited formation of ablation hollows under direct sunlight.
The application of passive microwave radiometry to the remote sensing of snow properties is based on the ratio of emitted to scattered portions of the upwelling radiation. Increased scattering is indicative of increased snow amount, i.e. the number of snow grains present. However, scattering is also directly proportional to snow grain-size for a given snow amount. Current snow cover retrieval algorithms produce inaccurate results when snow grain-sizes are unusually large. Therefore, it is necessary to characterize snow grain-size on a regional scale (and perhaps local scale in extreme situations) in order to adjust passive microwave algorithms. Preliminary analysis indicates that: (1) algorithms are not as sensitive to the presence of large grain-sizes as the initial theory had indicated; (2) standard deviation of grain-size diameters throughout the total snow cover may often be less than 0.5 mm, thus average grain-size data may often serve to characterize the detailed stratigraphy of the total snow cover; (3) conditions in subfreezing snow which produce grain-sizes that greatly exceed a mean diameter value of 1–2 mm result from snow cover/climate relationships which can be modelled/monitored on a regional scale. A preliminary method is investigated for selecting snow retrieval algorithms according to prevailing regional-scale grain-size.
Mass-balance data for Blue Glacier are presented for the 31-year period 1956–86. The glacier location is strongly maritime with annual precipitation of 3500 to 5000 mm, most of which falls as winter snow. The low elevation of the glacier results in large amounts of summer ablation and thus significant annual mass exchange. Blue Glacier has been in approximate equilibrium with recent climate during the past 30 years with a slightly positive mean annual net balance of 0.3 m and a terminus advance of 150 m. Comparison with other glaciers in western North America indicates that this pattern of mass increase in response to recent climate is not typical but may be specific to a maritime location.
Due to heavy amounts of winter snowfall, an accumulation area ratio of only 0.5 is sufficient to maintain a zero balance on Blue Glacier. A strong gradient of increasing snowfall with elevation contributes to a linear relationship between net balance and elevation throughout the total altitude range of the glacier. This relationship is consistent over the period of record and is not dependent on an overall net positive balance, as the pattern persists even during periods of strongly negative mass balance. A relationship between measured mass balance and equilibrium-line altitude provides a reasonable method to compute mass balance.
The relationship of glacier response due to mass-balance changes is of fundamental importance when climate variations are to be understood. In this paper, two aspects of the problem are analyzed from field data: (1) advance/retreat of the glacier terminus due to changes in mass balance, and (2) cross-correlation of mass-balance data from two glaciers in the same climate zone. The results show: (1) the terminus can respond quickly in accordance with expected minimum time-scale, and (2) two glaciers in the same general climate zone may have very different yearly mass balance and advance/retreat behaviour. This latter result indicates the importance of local climate variations.
Describing the current state of gamification, Chamorro-Premuzic, Winsborough, Sherman, and Hogan (2016) provide a troubling contradiction: They offer examples of a broad spectrum of gamification interventions, but they then summarize the entirety of gamification as “the digital equivalent of situational judgment tests.” This mischaracterization grossly oversimplifies a rapidly growing area of research and practice both within and outside of industrial–organizational (I-O) psychology. We agree that situational judgment tests (SJTs) can be considered a type of gamified assessment, and gamification provides a toolkit to make SJTs even more gameful. However, the term gamification refers to a much broader and potentially more impactful set of tools than just SJTs, which are incremental, versatile, and especially valuable to practitioners in an era moving toward business-to-consumer (B2C) assessment models. In this commentary, we contend that gamification is commonly misunderstood and misapplied by I-O psychologists, and our goals are to remedy such misconceptions and to provide a research agenda designed to improve both the science and the practice surrounding gamification of human resource processes.
We present the first radiocarbon dates from previously unrecorded, secondary burials in the Cardamom Mountains, Cambodia. The mortuary ritual incorporates nautical tradeware ceramic jars and log coffins fashioned from locally harvested trees as burial containers, which were set out on exposed rock ledges at 10 sites in the eastern Cardamom Massif. The suite of 28 14C ages from 4 of these sites (Khnorng Sroal, Phnom Pel, Damnak Samdech, and Khnang Tathan) provides the first estimation of the overall time depth of the practice. The most reliable calendar date ranges from the 4 sites reveals a highland burial ritual unrelated to lowland Khmer culture that was practiced from cal AD 1395 to 1650. The time period is concurrent with the 15th century decline of Angkor as the capital of the Khmer kingdom and its demise about AD 1432, and the subsequent shift of power to new Mekong trade ports such as Phnom Penh, Udong, and Lovek. We discuss the Cardamom ritual relative to known funerary rituals of the pre- to post-Angkorian periods, and to similar exposed jar and coffin burial rituals in Mainland and Island Southeast Asia.
Objective: This study examined whether differences in habitual negative self-thinking and coping strategies might contribute to the age differences in worry and depression. Method: 60 undergraduate students (age range: 18–24 years, M = 19.10, SD = 1.3) and 45 community-dwelling older adults (age range: 60–89 years, M = 73.5, SD = 7.5) participated. Participants completed self-report measures of worry, depression, negative self-thinking, and coping styles. Results: We replicated previous findings that older adults were less worried and less depressed than younger adults. Older adults also reported engaging in less habitual negative thinking and using more problem solving as a coping strategy than younger adults. Furthermore, negative self-thinking and problem-solving skills were found to partially mediate age differences in worry and fully mediate depression scores. Conclusions: These results suggest that habitual negative thinking and problem-solving skills play a role in explaining the lower rates of worry and depression in older populations.
To explore current practices and decision making regarding antimicrobial prescribing among emergency department (ED) clinical providers.
We conducted a survey of ED providers recruited from 8 sites in 3 cities. Using purposeful sampling, we then recruited 21 providers for in-depth interviews. Additionally, we observed 10 patient-provider interactions at one of the ED sites. SAS 9.3 was used for descriptive and predictive statistics. Interviews were audio recorded, transcribed, and analyzed using a thematic, constructivist approach with consensus coding using NVivo 10.0. Field and interview notes collected during the observational study were aligned with themes identified through individual interviews.
Of 150 survey respondents, 76% agreed or strongly agreed that antibiotics are overused in the ED, while half believed they personally did not overprescribe. Eighty-nine percent used a smartphone or tablet in the ED for antibiotic prescribing decisions. Several significant differences were found between attending and resident physicians. Interview analysis identified 42 codes aggregated into the following themes: (1) resource and environmental factors that affect care; (2) access to and quality of care received outside of the ED consult; (3) patient-provider relationships; (4) clinical inertia; and (5) local knowledge generation. The observational study revealed limited patient understanding of antibiotic use. Providers relied heavily upon diagnostics and provided limited education to patients. Most patients denied a priori expectations of being prescribed antibiotics.
Patient, provider, and healthcare system factors should be considered when designing interventions to improve antimicrobial stewardship in the ED setting.
Infect Control Hosp Epidemiol 2014;35(9):1114-1125