407 research outputs found
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Over-winter persistence of supraglacial lakes on the Greenland Ice Sheet: Results and insights from a new model
AbstractWe present a newly developed 1-D numerical energy-balance and phase transition supraglacial lake model: GlacierLake. GlacierLake incorporates snowfall, in situ snow and ice melt, incoming water from the surrounding catchment, ice lid formation, basal freeze-up and thermal stratification. Snow cover and temperature are varied to test lake development through winter and the maximum lid thickness is recorded. Average wintertime temperatures of −2 toand total snowfall of 0 to 3.45 m lead to a range of the maximum lid thickness from 1.2 to 2.8 m afterdays, with snow cover exerting the dominant control. An initial ice temperature ofwith simulated advection of cold ice from upstream results in 0.6 m of basal freeze-up. This suggests that lakes with water depths above 1.3 to 3.4 m (dependent on winter snowfall and temperature) upon lid formation will persist through winter. These buried lakes can provide a sizeable water store at the start of the melt season, expedite future lake formation and warm underlying ice even in winter.NER
Dual-satellite (Sentinel-2 and Landsat 8) remote sensing of supraglacial lakes in Greenland
Remote sensing is commonly used to monitor supraglacial lakes on
the Greenland Ice Sheet (GrIS); however, most satellite records must trade off
higher spatial resolution for higher temporal resolution (e.g. MODIS) or vice
versa (e.g. Landsat). Here, we overcome this issue by developing and applying
a dual-sensor method that can monitor changes to lake areas and volumes at
high spatial resolution (10–30 m) with a frequent revisit time ( ∼ 3 days). We achieve this by mosaicking imagery from the Landsat 8 Operational Land Imager (OLI) with
imagery from the recently launched Sentinel-2 Multispectral Instrument (MSI) for a ∼ 12 000 km2 area of West Greenland in the 2016 melt season. First, we
validate a physically based method for calculating lake depths with
Sentinel-2 by comparing measurements against those derived from the available
contemporaneous Landsat 8 imagery; we find close correspondence between the
two sets of values (R2 = 0.841; RMSE  =  0.555 m). This provides us
with the methodological basis for automatically calculating lake areas,
depths, and volumes from all available Landsat 8 and Sentinel-2 images. These
automatic methods are incorporated into an algorithm for Fully Automated
Supraglacial lake Tracking at Enhanced Resolution (FASTER). The FASTER
algorithm produces time series showing lake evolution during the 2016 melt
season, including automated rapid ( ≤ 4 day) lake-drainage identification.
With the dual Sentinel-2–Landsat 8 record, we identify 184 rapidly draining
lakes, many more than identified with either imagery collection alone (93
with Sentinel-2; 66 with Landsat 8), due to their inferior temporal
resolution, or would be possible with MODIS, due to its omission of small
lakes < 0.125 km2. Finally, we estimate the water volumes drained
into the GrIS during rapid-lake-drainage events and, by analysing downscaled
regional climate-model (RACMO2.3p2) run-off data, the water quantity that
enters the GrIS via the moulins opened by such events. We find that during
the lake-drainage events alone, the water drained by small lakes ( < 0.125 km2) is only 5.1 % of the total water volume drained by all
lakes. However, considering the total water volume entering the GrIS after
lake drainage, the moulins opened by small lakes deliver 61.5 % of the
total water volume delivered via the moulins opened by large and small lakes;
this is because there are more small lakes, allowing more moulins to open,
and because small lakes are found at lower elevations than large lakes, where
run-off is higher. These findings suggest that small lakes should be included
in future remote-sensing and modelling work.</p
Globalisation masculinities, empire building and forced prostitution: a critical analysis of the gendered impact of the neoliberal economic agenda in post-invasion/occupation Iraq
Adopting a transnational feminist lens and using a political economy approach, this article addresses both the direct and indirect consequences of the 2003 war in Iraq, specifically the impact on civilian women. Pre-war security and gender relations in Iraq will be compared with the situation post-invasion/occupation. The article examines the globalised processes of capitalism, neoliberalism and neo-colonialism and their impact on the political, social and economic infrastructure in Iraq. Particular attention will be paid to illicit and informal economies: coping, combat and criminal. The 2003 Iraq war was fought using masculinities of empire, post-colonialism and neoliberalism. Using the example of forced prostitution, the article will argue that these globalisation masculinities – specifically the privatisation agenda of the West and its illegal economic occupation – have resulted in women either being forced into the illicit (coping) economy as a means of survival, or trafficked for sexual slavery by profit-seeking criminal networks who exploit the informal economy in a post-invasion/occupation Iraq
Automatic Quantum Error Correction
Criteria are given by which dissipative evolution can transfer populations
and coherences between quantum subspaces, without a loss of coherence. This
results in a form of quantum error correction that is implemented by the joint
evolution of a system and a cold bath. It requires no external intervention
and, in principal, no ancilla. An example of a system that protects a qubit
against spin-flip errors is proposed. It consists of three spin 1/2 magnetic
particles and three modes of a resonator. The qubit is the triple quantum
coherence of the spins, and the photons act as ancilla.Comment: 16 pages 12 fig LaTex uses multicol, graphicx expanded version of
letter submitted to Phys Rev Let
Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes
We present theoretical and experimental studies of Schottky diodes that use
aligned arrays of single walled carbon nanotubes. A simple physical model,
taking into account the basic physics of current rectification, can adequately
describe the single-tube and array devices. We show that for as grown array
diodes, the rectification ratio, defined by the
maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts.
These tubes can be eliminated in a single voltage sweep resulting in a high
rectification array device. Further analysis also shows that the channel
resistance, and not the intrinsic nanotube diode properties, limits the
rectification in devices with channel length up to ten micrometer.Comment: Nano Research, 2010, accepte
Contemporary contestations over working time: time for health to weigh in
Non-communicable disease (NCD) incidence and prevalence is of central concern to most nations, along with international agencies such as the UN, OECD, IMF and World Bank. As a result, the search has begun for ‘causes of the cause’ behind health risks and behaviours responsible for the major NCDs. As part of this effort, researchers are turning their attention to charting the temporal nature of societal changes that might be associated with the rapid rise in NCDs. From this, the experience of time and its allocation are increasingly understood to be key individual and societal resources for health (7–9). The interdisciplinary study outlined in this paper will produce a systematic analysis of the behavioural health dimensions, or ‘health time economies’ (quantity and quality of time necessary for the practice of health behaviours), that have accompanied labour market transitions of the last 30 years - the period in which so many NCDs have risen sharply
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
Coital Experience Among Adolescents in Three Social-Educational Groups in Urban Chiang Mai, Thailand
This article compares coital experience of Chiang Mai 17–20-year-olds who were: (1) out-of-school; (2) studying at vocational schools; and (3) studying at general schools or university. Four-fifths, two-thirds and one-third, respectively, of males in these groups had had intercourse, compared to 53, 62 and 15 per cent of females. The gender difference for general school/university students, but not vocational school students, probably reflects HIV/AIDS refocusing male sexual initiation away from commercial sex workers. Vocational school females may have been disproportionately affected. Loss of virginity was associated, for both sexes, with social-educational background and lifestyle, and was less likely in certain minority ethnic groups. Among males, it was also associated with age and parental marital dissolution, and among females, with independent living and parental disharmony. Within social-educational groups, lifestyle variables dominated, but among general school/university students, parental marital dissolution (for males) and disharmony (for females) were also important, and Chinese ethnicity deterred male sexual experimentation
Epigenetics and the power of art
This review presents an epigenetic view on complex factors leading to development and perception of “genius.” There is increasing evidence which indicates that artistic creativity is influenced by epigenetic processes that act both as targets and mediators of neurotransmitters as well as steroid hormones. Thus, perception and production of art appear to be closely associated with epigenetic contributions to physical and mental health
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