249 research outputs found
A mixed life-cycle stage bloom of Syracosphaera bannockii (Borsetti and Cati, 1976) Cros et al. 2000 (Bay of Biscay, April 2010)
High concentrations (464 cells mL-1) of Syracosphaera bannockii have been identified for the first time, in the Bay of Biscay during April 2010. These high concentrations combined with coccolithophore community dominance (~87%) indicated that a bloom of S. bannockii had formed. While the bloom consisted mostly of heterococcolith coccospheres, both holococcolith coccospheres and holococcolith-heterococcolith combination coccospheres were observed. This is only the second time that combination coccospheres of S. bannockii have been observed
Photosynthetic adaptation of two semi-arid species of Gethyllis (Kukumakranka) to drought-and-shade stress
Gethyllis multifolia and Gethyllis villosa are winter-growing, summer-blooming, deciduous and
bulbous geophytes that grow naturally in the semi-arid âSucculent Karoo Biomeâ of South Africa.
G. multifolia is threatened in its natural habitat and resides in the âVulnerableâ category of the
âRed Data List of Southern African Plantsâ. Previous investigations suggested that G. multifolia is
more sensitive to drought stress than G. villosa and that both species adopted certain
morphological changes in their leaves during shade stress. Current models indicate that this
biome is being exposed to increasingly drier conditions and shading from encroaching indigenous
plant species. In this study, the photosynthetic gas exchange responses of both species to drought
and shade stresses were investigated and the âVulnerableâ conservation status of G. multifolia.
This investigation found that during drought stress G. villosa had a more enhanced
photosynthetic performance than
G. multifolia which appears not to be related to foliar adaptations such as speciïŹc leaf mass
(SLM), but to the G. villosa's leaves maintaining their stomatal conductance (Gs), photosynthetic
light compensation (LCP) and photon yields. Furthermore, during shade stress G. villosa also had
an improved photosynthetic performance by not altering its photosynthetic LCP during reduced light
conditions. It can be concluded that G. multifolia has a lower capacity than G. villosa to adapt
its photosynthetic apparatus to changing environments such as increasing drought and shaded
conditions. This may be a contributing factor to the threatened conservation status of G. multifolia.Web of Scienc
Phytoplankton dynamics in contrasting early stage North Atlantic spring blooms: composition, succession, and potential drivers
The spring bloom is a key annual event in the phenology of pelagic ecosystems, making a major contribution to the oceanic biological carbon pump through the production and export of organic carbon. However, there is little consensus as to the main drivers of spring bloom formation, exacerbated by a lack of in situ observations of the phytoplankton community composition and its evolution during this critical period.
We investigated the dynamics of the phytoplankton community structure at two contrasting sites in the Iceland and Norwegian basins during the early stage (25 Marchâ25 April) of the 2012 North Atlantic spring bloom. The plankton composition and characteristics of the initial stages of the bloom were markedly different between the two basins. The Iceland Basin (ICB) appeared well mixed down to >400 m, yet surface chlorophyll a (0.27â2.2 mg mâ3) and primary production (0.06â0.66 mmol C mâ3 dâ1) were elevated in the upper 100 m. Although the Norwegian Basin (NWB) had a persistently shallower mixed layer (<100 m), chlorophyll a (0.58â0.93 mg mâ3) and primary production (0.08â0.15 mmol C mâ3 dâ1) remained lower than in the ICB, with picoplankton (<2 ÎŒm) dominating chlorophyll a biomass. The ICB phytoplankton composition appeared primarily driven by the physicochemical environment, with periodic events of increased mixing restricting further increases in biomass. In contrast, the NWB phytoplankton community was potentially limited by physicochemical and/or biological factors such as grazing.
Diatoms dominated the ICB, with the genus Chaetoceros (1â166 cells mLâ1) being succeeded by Pseudo-nitzschia (0.2â210 cells mLâ1). However, large diatoms (>10 ÎŒm) were virtually absent (<0.5 cells mLâ1) from the NWB, with only small nano-sized (<5 ÎŒm) diatoms (i.e. Minidiscus spp.) present (101â600 cells mLâ1). We suggest microzooplankton grazing, potentially coupled with the lack of a seed population of bloom-forming diatoms, was restricting diatom growth in the NWB, and that large diatoms may be absent in NWB spring blooms. Despite both phytoplankton communities being in the early stages of bloom formation, different physicochemical and biological factors controlled bloom formation at the two sites. If these differences in phytoplankton composition persist, the subsequent spring blooms are likely to be significantly different in terms of biogeochemistry and trophic interactions throughout the growth season, with important implications for carbon cycling and organic matter export
Beam-induced Fe nanopillars as tunable domain-wall pinning sites
Focused-electron-beam-induced deposition (FEBID) is employed to create freestanding magnetic nanostructures. By growing Fe nanopillars on top of a perpendicular magnetic domain wall (DW) conduit, pinning of the DWs is observed due to the stray fields emanating from the nanopillar. Furthermore, a different DW pinning behavior is observed between the up and down magnetic states of the pillar, allowing to deduce the switching fields of the pillar in a novel way. The implications of these results are two-fold: not only can 3-dimensional nano-objects be used to control DW motion in applications, it is also proposed that DW motion is a unique tool to probe the magnetic properties of nano-objects
Growth and mortality of coccolithophores during spring in a temperate Shelf Sea (Celtic Sea, April 2015)
Coccolithophores are key components of phytoplankton communities, exerting a critical impact on the global carbon cycle and the Earthâs climate through the production of coccoliths made of calcium carbonate (calcite) and bioactive gases. Microzooplankton grazing is an important mortality factor in coccolithophore blooms, however little is currently known regarding the mortality (or growth) rates within non-bloom populations. Measurements of coccolithophore calcite production (CP) and dilution experiments to determine microzooplankton (â€63âŻÂ”m) grazing rates were made during a spring cruise (April 2015) at the Central Celtic Sea (CCS), shelf edge (CS2), and within an adjacent April bloom of the coccolithophore Emiliania huxleyi at station J2.
CP at CCS ranged from 10.4 to 40.4âŻÂ”mol C mâ3 dâ1 and peaked at the height of the spring phytoplankton bloom (peak chlorophyll-a concentrations âŒ6âŻmgâŻmâ3). Cell normalised calcification rates declined from âŒ1.7 to âŒ0.2âŻpmol C cellâ1 dâ1, accompanied by a shift from a mixed coccolithophore species community to one dominated by the more lightly calcified species E. huxleyi and Calciopappus caudatus. At the CCS, coccolithophore abundance increased from 6 to 94 cells mLâ1, with net growth rates ranging from 0.06 to 0.21 dâ1 from the 4th to the 28th April. Estimates of intrinsic growth and grazing rates from dilution experiments, at the CCS ranged from 0.01 to 0.86 dâ1 and from 0.01 to 1.32 dâ1, respectively, which resulted in variable net growth rates during April. Microzooplankton grazers consumed 59 to >100% of daily calcite production at the CCS. Within the E. huxleyi bloom a maximum density of 1986 cells mLâ1 was recorded, along with CP rates of 6000âŻÂ”mol C mâ3 dâ1 and an intrinsic growth rate of 0.29 dâ1, with âŒ80% of daily calcite production being consumed.
Our results show that microzooplankton can exert strong top-down control on both bloom and non-bloom coccolithophore populations, grazing over 60% of daily growth (and calcite production). The fate of consumed calcite is unclear, but may be lost either through dissolution in acidic food vacuoles, and subsequent release as CO2, or export to the seabed after incorporation into small faecal pellets. With such high microzooplankton-mediated mortality losses, the fate of grazed calcite is clearly a high priority research direction
Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB
The neutron irradiation-induced structural changes in nuclear grade graphites PCEA and PCIB were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). The graphite samples were irradiated at the Advanced Test Reactor at the Idaho National Laboratory. Received doses ranged from 1.5 to 6.8 displacements per atom and irradiation temperatures varied between 350 °C and 670 °C. XRD and Raman measurements provided evidence for irradiation induced crystallite fragmentation, with crystallite sizes reduced by 39â55%. Analysis of TEM images was used to quantify fringe length, tortuosity, and relative misorientation of planes, and indicated that neutron irradiation induced basal plane fragmentation and curvature. EELS was used to quantify the proportion of sp2 bonding and specimen density; a slight reduction in planar-sp2 content (due to the buckling basal planes and the introduction of non-six-membered rings) agreed with the observations from TEM
Cystic Fibrosis Transmembrane Conductance Regulator Modulator Therapy: A Review for the Otolaryngologist
Background: Cystic fibrosis (CF) is a genetic disease that may result in multiple systemic disorders and potentially fatal severe respiratory compromise. However, the advent of CF transmembrane conductance regulator (CFTR) modulators has changed the management of CF for patients with select mutations. Although clinical trials have highlighted increased pulmonary function and decreased exacerbations as a result of these novel therapies, their effect on the sinuses has not been well-described. Objective: Our objective is to review the CFTR modulators to provide otolaryngologists, physicians who frequently care for patients with CF, a basic understanding of these drugs and their effects on chronic rhinosinusitis (CRS) in patients with CF. Methods: The clinically approved and available CFTR modulators and specific indications for their use are reviewed. Additionally, a systematic review of these therapies and effects on CRS in CF was performed. Results: Four Food and Drug Administration approved CFTR modulators are available for patients with CF. Current drugs are approved for gating, residual function, or F508del mutations. Multiple reports describe CFTR modulatorsâ increase in transepithelial ion transport in nasal epithelial cultures; however, clinical studies regarding effects of these modulators on sinonasal health are limited to 5 studies that present new data of the effects of CFTR modulators in CRS. Conclusions: CFTR modulators have changed management of CF. Initial studies of these medications demonstrate promising results in CF; however, there is a paucity of literature describing the effect of CFTR modulators on CF-associated CRS, although initial results are encouraging
Solid-state additive manufacturing for metallized optical fiber integration
The formation of smart, Metal Matrix Composite (MMC) structures through the use of solid-state Ultrasonic Additive Manufacturing (UAM) is currently hindered by the fragility of uncoated optical fibers under the required processing conditions. In this work, optical fibers equipped with metallic coatings were fully integrated into solid Aluminum matrices using processing parameter levels not previously possible. The mechanical performance of the resulting manufactured composite structure, as well as the functionality of the integrated fibers, was tested. Optical microscopy, Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) analysis were used to characterize the interlaminar and fiber/matrix interfaces whilst mechanical peel testing was used to quantify bond strength. Via the integration of metallized optical fibers it was possible to increase the bond density by 20â22%, increase the composite mechanical strength by 12â29% and create a solid state bond between the metal matrix and fiber coating; whilst maintaining full fiber functionality
Separation of K+ and Bi3+ displacements in a Pb-free, monoclinic piezoelectric at the morphotropic phase boundary
The best piezoelectric properties of any perovskite oxide known are found in the solid solution of the relaxor Pb(Mg1/3Nb2/3)O3 and ferroelectric PbTiO3. Despite its impressive properties, this system has limited analogy. We present the compositional exploration of the Pb-free analogue (1-x)(K1/2Bi1/2)(Mg1/3Nb2/3)O3-x(K1/2Bi1/2)TiO3 (KBMN-KBT). We locate the morphotropic phase boundary between x = 0.86 and 0.88 changing from Cm to Pm symmetry and the optimally performing composition at x = 0.88. We report a piezoelectric figure of merit (d33*) of 192 pm Vâ1 from strain measurements. Diffraction methods reveal disordered displacements of K+ and Bi3+ which persist from the KBMN endmember through multiple changes in symmetry. Rearrangement of the Bi3+ displacements along the uncommon [011]c direction drives the physical response. Ferroelectric, dielectric, and piezoresponse force microscopy are used to study the progression of physical properties through the MPB and attribute the mechanism to a polarization rotation. Taking account for local, short-range, and average structural features yield a balanced perspective on the structure and properties of this system, isolating the driving force within this system to the Bi3+ bonding configuration. This work yields a strong analogy to the Pb-based analogue, and provides strategies for further optimization
Using the inertia of spacecraft during landing to penetrate regoliths of the Solar System
The high inertia, i.e. high mass and low speed, of a landing spacecraft has the potential to drive a penetrometer into the subsurface without the need for a dedicated deployment mechanism, e.g., during Huygens landing on Titan. Such a method could complement focused subsurface exploration missions, particularly in the low gravity environments of comets and asteroids, as it is conducive to conducting surveys and to the deployment of sensor networks. We make full-scale laboratory simulations of a landing spacecraft with a penetrometer attached to its base plate. The tip design is based on that used in terrestrial Cone Penetration Testing (CPT) with a large enough shaft diameter to house instruments for analysing pristine subsurface material. Penetrometer measurements are made in a variety of regolith analogue materials and target compaction states. For comparison a copy of the ACC-E penetrometer from the Huygens mission to Titan is used. A test rig at the Open University is used and is operated over a range of speeds from 0.9 to 3 m sâ1 and under two gravitational accelerations.
The penetrometer was found to be sensitive to the targetâs compaction state with a high degree of repeatability. The penetrometer measurements also produced unique pressure profile shapes for each material. Measurements in limestone powder produced an exponential increase in pressure with depth possibly due to increasing compaction with depth. Measurements in sand produced an almost linear increase in pressure with depth. Iron powder produced significantly higher pressures than sand presumably due to the rough surface of the grains increasing the grain-grain friction. Impacts into foamglas produced with both ACC-E and the large penetrometer produced an initial increase in pressure followed by a leveling off as expected in a consolidated material. Measurements in sand suggest that the pressure on the tip is not significantly dependent on speed over the range tested, which suggests bearing strength equations could be applied to impact penetrometry in sand-like regoliths.
In terms of performance we find the inertia of a landing spacecraft, with a mass of 100 kg, is adequate to penetrate regoliths expected on the surface of Solar System bodies. Limestone powder, an analogue for a dusty surface, offered very little resistance allowing full penetration of the target container. Both iron powder, representing a stronger coarse grained regolith, and foamglas, representing a consolidated comet crust, could be penetrated to similar depths of around two to three tip diameters. Speed tests suggest a linear dependence of penetration depth on impact speed
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