1,559 research outputs found
Evaluating Landsat 8 evapotranspiration for water use mapping in the Colorado River Basin
AbstractEvapotranspiration (ET) mapping at the Landsat spatial resolution (100m) is essential to fully understand water use and water availability at the field scale. Water use estimates in the Colorado River Basin (CRB), which has diverse ecosystems and complex hydro-climatic regions, will be helpful to water planners and managers. Availability of Landsat 8 images, starting in 2013, provides the opportunity to map ET in the CRB to assess spatial distribution and patterns of water use. The Operational Simplified Surface Energy Balance (SSEBop) model was used with 528 Landsat 8 images to create seamless monthly and annual ET estimates at the inherent 100m thermal band resolution. Annual ET values were summarized by land use/land cover classes. Croplands were the largest consumer of âblueâ water while shrublands consumed the most âgreenâ water. Validation using eddy covariance (EC) flux towers and water balance approaches showed good accuracy levels with R2 ranging from 0.74 to 0.95 and the NashâSutcliffe model efficiency coefficient ranging from 0.66 to 0.91. The root mean square error (and percent bias) ranged from 0.48mm (13%) to 0.60mm (22%) for daily (days of satellite overpass) ET and from 7.75mm (2%) to 13.04mm (35%) for monthly ET. The spatial and temporal distribution of ET indicates the utility of Landsat 8 for providing important information about ET dynamics across the landscape. Annual crop water use was estimated for five selected irrigation districts in the Lower CRB where annual ET per district ranged between 681mm to 772mm. Annual ET by crop type over the Maricopa Stanfield irrigation district ranged from a low of 384mm for durum wheat to a high of 990mm for alfalfa fields. A rainfall analysis over the five districts suggested that, on average, 69% of the annual ET was met by irrigation. Although the enhanced cloud-masking capability of Landsat 8 based on the cirrus band and utilization of the Fmask algorithm improved the removal of contaminated pixels, the ability to reliably estimate ET over clouded areas remains an important challenge. Overall, the performance of Landsat 8 based ET compared to available EC datasets and water balance estimates for a complex basin such as the CRB demonstrates the potential of using Landsat 8 for annual water use estimation at a national scale. Future efforts will focus on (a) use of consistent methodology across years, (b) integration of multiple sensors to maximize images used, and (c) employing cloud-computing platforms for large scale processing capabilities
Temperature-driven shifts in the epibiotic bacterial community composition of the brown macroalgaFucus vesiculosus
The thallus surface of the brown macroalga Fucus vesiculosus is covered by a specific biofilm community. This biofilm supposedly plays an important role in the interaction between host and environment. So far, we know little about compositional or functional shifts of this epibiotic bacterial community under changing environmental conditions. In this study, the response of the microbiota to different temperatures with respect to cell density and community composition was analyzed by nonculture-based methods (denaturing gradient gel electrophoresis and 454 pyrosequencing of the 16S rRNA gene). Redundancy analysis showed that despite high variability among host individuals temperature accounted for 20% of the variation in the bacterial community composition, whereas cell density did not differ between groups. Across all samples, 4341 bacterial operational taxonomic units (OTUs) at a 97% similarity level were identified. Eight percent of OTUs were significantly correlated with low, medium, and high temperatures. Notably, the family Rhodobacteraceae increased in relative abundance from 20% to 50% with increasing temperature. OTU diversity (evenness and richness) was higher at 15°C than at the lower and higher temperatures. Considering their known and presumed ecological functions for the host, change in the epibacterial community may entail shifts in the performance of the host alga
The adjoint problem in the presence of a deformed surface: the example of the Rosensweig instability on magnetic fluids
The Rosensweig instability is the phenomenon that above a certain threshold
of a vertical magnetic field peaks appear on the free surface of a horizontal
layer of magnetic fluid. In contrast to almost all classical hydrodynamical
systems, the nonlinearities of the Rosensweig instability are entirely
triggered by the properties of a deformed and a priori unknown surface. The
resulting problems in defining an adjoint operator for such nonlinearities are
illustrated. The implications concerning amplitude equations for pattern
forming systems with a deformed surface are discussed.Comment: 11 pages, 1 figur
Hexagons become second if symmetry is broken
Pattern formation on the free surface of a magnetic fluid subjected to a
magnetic field is investigated experimentally. By tilting the magnetic field
the symmetry can be broken in a controllable manner. When increasing the
amplitude of the tilted field, the flat surface gives way to liquid ridges. A
further increase results in a hysteretic transition to a pattern of stretched
hexagons. The instabilities are detected by means of a linear array of magnetic
hall sensors and compared with theoretical predictions.Comment: accepted for publication by Physical Review E/Rapid Communicatio
BMP signaling balances proliferation and differentiation of muscle satellite cell descendants
<p>Abstract</p> <p>Background</p> <p>The capacity of muscle to grow or to regenerate after damage is provided by adult stem cells, so called satellite cells, which are located under the basement lamina of each myofiber. Upon activation satellite cells enter the cell cycle, proliferate and differentiate into myoblasts, which fuse to injured myofibers or form new fibers. These processes are tightly controlled by many growth factors.</p> <p>Results</p> <p>Here we investigate the role of bone morphogenetic proteins (BMPs) during satellite cell differentiation. Unlike the myogenic C2C12 cell line, primary satellite cells do not differentiate into osteoblasts upon BMP signaling. Instead BMP signaling inhibits myogenic differentiation of primary satellite cells <it>ex vivo</it>. In contrast, inhibition of BMP signaling results in cell cycle exit, followed by enhanced myoblast differentiation and myotube formation. Using an <it>in vivo </it>trauma model we demonstrate that satellite cells respond to BMP signals during the regeneration process. Interestingly, we found the BMP inhibitor <it>Chordin </it>upregulated in primary satellite cell cultures and in regenerating muscles. In both systems <it>Chordin </it>expression follows that of Myogenin, a marker for cells committed to differentiation.</p> <p>Conclusion</p> <p>Our data indicate that BMP signaling plays a critical role in balancing proliferation and differentiation of activated satellite cells and their descendants. Initially, BMP signals maintain satellite cells descendants in a proliferating state thereby expanding cell numbers. After cells are committed to differentiate they upregulate the expression of the BMP inhibitor <it>Chordin </it>thereby supporting terminal differentiation and myotube formation in a negative feedback mechanism.</p
Tidal propagation in strongly convergent channels
Simple firstâ and secondâorder analytic solutions, which diverge markedly from classical views of cooscillating tides, are derived for tidal propagation in strongly convergent channels. Theoretical predictions compare well with observations from typical examples of shallow, âfunnelâshapedâ tidal estuaries. A scaling of the governing equations appropriate to these channels indicates that at first order, gradients in crossâsectional area dominate velocity gradients in the continuity equation and the friction term dominates acceleration in the momentum equation. Finite amplitude effects, velocity gradients due to wave propagation, and local acceleration enter the equations at second order. Applying this scaling, the firstâorder governing equation becomes a firstâorder wave equation, which is inconsistent with the presence of a reflected wave. The solution is of constant amplitude and has a phase speed near the frictionless wave speed, like a classical progressive wave, yet velocity leads elevation by 90°, like a classical standing wave. The secondâorder solution at the dominant frequency is also a unidirectional wave; however, its amplitude is exponentially modulated. If inertia is finite and convergence is strong, amplitude increases along channel, whereas if inertia is weak and convergence is limited, amplitude decays. Compact solutions for secondâorder tidal harmonics quantify the partially canceling effects of (1) time variations in channel depth, which slow the propagation of low water, and (2) time variations in channel width, which slow the propagation of high water. Finally, it is suggested that phase speed, alongâchannel amplitude growth, and tidal harmonics in strongly convergent channels are all linked by morphodynamic feedback
Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin
Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf
Soft and flexible poly(ethylene glycol) nanotubes for local drug delivery
Nanotubes are emerging as promising materials for healthcare applications but the selection of clinically relevant starting materials for their synthesis remains largely unexplored. Here we present, for the first time, the synthesis of poly(ethylene glycol) (PEG) based nanotubes via the photopolymerization of poly(ethylene glycol) diacrylate and other diacrylate derivatives within the pores of anodized aluminum oxide templates. Template-assisted synthesis allowed the manufacture of a diverse set of polymeric nanotubes with tunable physical characteristics including diameter (âŒ200â400 nm) and stiffness (405â902 kPa). PEG nanotubes were subjected to cytotoxicty assessment in cell lines and primary stem cells and showed excellent cytocompatability (IC50 > 120 ÎŒg mlâ1). Nanotubes were readily drug loaded but released the majority of the drug over 5 days. Direct administration of drug loaded nanotubes to human orthotopic breast tumors substantially reduced tumor growth and metastasis and outperformed i.v. administration at the equivalent dose. Overall, this nanotube templating platform is emerging as a facile route for the manufacture of poly(ethylene glycol) nanotubes
Null Killing Vector Dimensional Reduction and Galilean Geometrodynamics
The solutions of Einstein's equations admitting one non-null Killing vector
field are best studied with the projection formalism of Geroch. When the
Killing vector is lightlike, the projection onto the orbit space still exists
and one expects a covariant theory with degenerate contravariant metric to
appear, its geometry is presented here. Despite the complications of
indecomposable representations of the local Euclidean subgroup, one obtains an
absolute time and a canonical, Galilean and so-called Newtonian, torsionless
connection. The quasi-Maxwell field (Kaluza Klein one-form) that appears in the
dimensional reduction is a non-separable part of this affine connection, in
contrast to the reduction with a non-null Killing vector. One may define the
Kaluza Klein scalar (dilaton) together with the absolute time coordinate after
having imposed one of the equations of motion in order to prevent the emergence
of torsion. We present a detailed analysis of the dimensional reduction using
moving frames, we derive the complete equations of motion and propose an action
whose variation gives rise to all but one of them. Hidden symmetries are shown
to act on the space of solutions.Comment: LATEX, 41 pages, no figure
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