4,094 research outputs found
Extensive winter subglacial water storage beneath the Greenland Ice Sheet
This is the final version of the article. Available from AGU via the DOI in this record.Surface meltwater that reaches the base of the Greenland Ice Sheet exerts a fundamental impact on ice flow, but observations of catchment-wide movement and distribution of subglacial water remain limited. Using radar-sounding data from two seasons, we identify the seasonal distribution of subglacial water in western Greenland. Our analysis provides evidence of widespread subglacial water storage beneath Greenland in the wintertime. The winter storage is located primarily on bedrock ridges with higher bed elevations in excess of 200 m. During the melt season water moves to the subglacial troughs. This inverse relationship with topography indicates that the material properties of the glacier bed strongly influence subglacial drainage development. Both the spatial variations in bed properties and the initial state of the subglacial hydrology system at the start of the melt season lead to differing glacier dynamical responses to surface melting across the Greenland Ice Sheet.W.C. is a recipient of the NASA Earth and
Space Science Fellowship. D.M.S. is
supported by a grant from the NASA
Cryospheric Sciences Program. H.S. is
supported by grants from the NASA
Cryospheric Sciences and Sea Level Rise
Programs. T.T.C and R.E.B are supported
by grants from National Science
Foundation (NSF) and NASA
Cryospheric Sciences. S.P. is supported
by the Natural Environment Research
Councilās Centre for Polar Observatio
Low Sensitivity of T-Cell Based Detection of Tuberculosis among HIV Co-Infected Tanzanian In-Patients
Objective: To evaluate the performance of QuantiFERON-TB GOLD (QFTG) in aĀ resource-poor setting among patients with and without HIV infection.Design: Cross-sectional study.Setting: Two hospitals in Northern Tanzania.Subjects: Eighty three adult male and female inpatients.Intervention: All patients were screened for HIV infection and underwent tuberculinĀ skin test (TST) and QFTG.Results: Eighty-three subjects were enrolled, and 29 (35%) of 83 were HIV-infected.Ā QFTG yielded indeterminate results in 12 (22%; 95%CI 12%-34%) of 54 HIV-uninfectedĀ and 13 (45%; 95%CI 26%-64%) of 29 HIV-infected subjects (p=0.0323). Among thoseĀ with smear-positive pulmonary tuberculosis, TST was positive in 40 (100%; 95%CIĀ 91%-100%) of 40 HIV-uninfected subjects compared with seven (54%; 95%CI 25%-Ā 81%) of 13 HIV-infected subjects (p<0.0001), and QFTG was positive in 28(70%; 95%CIĀ 53%-83%) of 40 HIV-uninfected subjects compared with three (23%; 95%CI 5%-54%)Ā of 13 HIV-infected subjects (p=0.0029). Among medical inpatients at risk for latentĀ tuberculosis infection, TST was positive in seven (50%) of 14 HIV-uninfected patientsĀ and three (19%) of 16 HIV-infected patients (p=0.0701) and QFTG was positive amongĀ two (14%) of 14 HIV-uninfected patients and three (19%) of 16 HIV-infected patientsĀ (p=0.7437).Conclusions: The presence of HIV co-infection was associated with a significant reductionĀ in sensitivity of both the TST (p<0.0001) and QFTG (p=0.0029) for the diagnosis ofĀ active M.tuberculosis infection. The high proportion of indeterminate QFTG and lackĀ of sensitivity, particularly among HIV-infected patients, may limit its applicability inĀ settings like Tanzania. Larger studies in resource-poor settings are required.
Non-abelian Action for Multiple Five-Branes with Self-Dual Tensors
We construct an action for non-abelian 2-form in 6-dimensions. Our action
consists of a non-abelian generalization of the abelian action of Perry and
Schwarz for a single five-brane. It admits a self-duality equation on the field
strength as the equation of motion. It has a modified 6d Lorentz symmetry. On
dimensional reduction on a circle, our action gives the standard 5d Yang-Mills
action plus higher order corrections. Based on these properties, we propose
that our theory describes the gauge sector of multiple M5-branes in flat space.Comment: LaTeX, 26 pages. v2: improved discussion of Lorentz symmetry. ref
added. v3: add comments in the discussion section on the inclusion of scalar
fields and supersymmetry; title changed to a more suitable one; version
published in JHE
Spiky Strings on I-brane
We study rigidly rotating strings in the near horizon geometry of the 1+1
dimensional intersection of two orthogonal stacks of NS5-branes, the so called
I-brane background. We solve the equations of motion of the fundamental string
action in the presence of two form NS-NS fluxes that the I-brane background
supports and write down general form of conserved quantities. We further find
out two limiting cases corresponding to giant magnon and single spike like
strings in various parameter space of solutions.Comment: 17 pages, major restructuring of text, added a referenc
Spatio-temporal variability in drifting Fish Aggregating Device (dFAD) beaching events in the Seychelles Archipelago
Purse-seine fisheries use drifting Fish Aggregating Devices (dFADs), human-made floating objects, to facilitate the capture of tropical tunas. Currently, the majority of dFADs are constructed primarily of highly durable non-biodegradable materials and there is no legal obligation to recover dFADs after deployment, leading to beaching events and potentially negative environmental impacts. We assessed beachings as a function of intra- and inter-annual trends, water depth, distance from land, seasonality, and benthic habitat within the local context of the Seychelles Archipelago using trajectories of dFADs deployed by French purse seiners over 2008-2020. Overall, 3842 beaching events associated with 2371 distinct dFAD tracking buoys were identified. Beachings occurred most frequently during the winter monsoon (December-March). Due to the shallow Mahe Plateau, beachings occurred in both nearshore (ā¤ 5 km from land) and offshore (> 5 km) regions, predominantly in estimated depths less than 60 m. Despite representing < 20% of overall mapped habitat, the benthic habitat "Coral/Algae"had the highest beaching rate (35.3% of beachings), and therefore, beachings pose a significant concern for conservation. Our results provide a detailed view of the spatio-temporal pattern of beachings in the Seychelles, supporting the development of mitigation and prevention methods to reduce marine debris and perturbations to the marine environment
Remote Manipulation of Droplets on a Flexible Magnetically Responsive Film
The manipulation of droplets is used in a wide range of applications, from lab-on-a-chip devices to bioinspired functional surfaces. Although a variety of droplet manipulation techniques have been proposed, active, fast and reversible manipulation of pure discrete droplets remains elusive due to the technical limitations of previous techniques. Here, we describe a novel technique that enables active, fast, precise and reversible control over the position and motion of a pure discrete droplet with only a permanent magnet by utilizing a magnetically responsive flexible film possessing actuating hierarchical pillars on the surface. This magnetically responsive surface shows reliable actuating capabilities with immediate field responses and maximum tilting angles of ???90??. Furthermore, the magnetic responsive film exhibits superhydrophobicity regardless of tilting angles of the actuating pillars. Using this magnetically responsive film, we demonstrate active and reversible manipulation of droplets with a remote magnetic force.open0
Three-point correlators for giant magnons
Three-point correlation functions in the strong-coupling regime of the
AdS/CFT correspondence can be analyzed within a semiclassical approximation
when two of the vertex operators correspond to heavy string states having large
quantum numbers while the third vertex corresponds to a light state with fixed
charges. We consider the case where the heavy string states are chosen to be
giant magnon solitons with either a single or two different angular momenta,
for various different choices of light string states.Comment: 15 pages. Latex. v2: Misprints corrected. Published versio
Three Spin Spiky Strings in beta-deformed Background
We study rigidly rotating strings in -deformed
background with one spin along AdS and two angular momenta along . We
find the spiky string solutions and present the dispersion relation among
various charges in this background. We further generalize the result to the
case of four angular momenta along .Comment: 12 pages, minor corrections, added references, to appear in JHE
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Glaciological Monitoring Using the Sun as a Radio Source for Echo Detection
Funder: NASA Cryospheric SciencesAbstract: Iceāpenetrating radar observations are critical for projecting iceāsheet contribution to seaālevel rise; however, these prognostic models have significant uncertainties due to an incomplete understanding of glacial subsurface processes. Existing radars that can characterize subsurface conditions are too resourceāintensive to simultaneously monitor ice sheets at both the necessary temporalādaily to multiannualāand spatialātributary to continentalāscales. Here, we investigate using an ambient radio source, instead of transmitting a signal, for glaciological monitoring. We demonstrate, for the first time, passive radio sounding using the Sun to accurately measure ice thickness on Store Glacier, Greenland. Passive radar sounding could provide lowāresource timeāseries measurements of the cryosphere, enabling us to observe and understand evolving englacial and subglacial conditions across Greenland and Antarctica with unprecedented coverage and resolution
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