ABSTRACT
X-ray quasi-periodic oscillations (QPOs) in active galactic nucleus (AGN) allow us to probe and understand the nature of accretion in highly curved space–time, yet the most robust form of ...detection (i.e. repeat detections over multiple observations) has been limited to a single source to-date, with only tentative claims of single observation detections in several others. The association of those established AGN QPOs with a specific spectral component has motivated us to search the XMM–Newton archive and analyse the energy-resolved light curves of 38 bright AGNs. We apply a conservative false alarm testing routine folding in the uncertainty and covariance of the underlying broad-band noise. We also explore the impact of red-noise leak and the assumption of various different forms (power-law, broken power-law, and Lorentzians) for the underlying broad-band noise. In this initial study, we report QPO candidates in six AGNs (seven including one tentative detection in MRK 766) from our sample of 38, which tend to be found at characteristic energies and, in four cases, at the same frequency across at least two observations, indicating they are highly unlikely to be spurious in nature.
Any literature investigation of Laser Powder Bed Fusion (L-PBF) manufacturing of metal parts would reveal that the development of internal stresses is a serious limitation in the application of this ...technology. Researchers have used a variety of different methods to quantify this stress and investigate scanning strategies aimed at reducing or distributing this stress more evenly in the part. The most common methods used to assess the levels of stress in parts are deflection based. These techniques provide a rapid method to give a quantitative comparison of scan strategies and parameters. Although studies have calculated the levels of stress relieved by the measured deflection, these studies often neglect the stresses that remain in the part after release. This study shows that these stresses can still be considerable. Non-destructive diffraction based methods can be used to calculate the profile of stress in a part but these are often prohibitively expensive or difficult to use on a large scale. This study presents a methodology which combines deflection based methods with either the hole drilling or contour methods. Results show that these experiments can be completed in a cost effective manner, with standard lab based equipment to generate a through thickness measurement of residual stress.
The global oceans are considered a major sink of atmospheric carbon dioxide (CO2). Rain is known to alter the physical and chemical conditions at the sea surface, and thus influence the transfer of ...CO2 between the ocean and atmosphere. It can influence gas exchange through enhanced gas transfer velocity, the direct export of carbon from the atmosphere to the ocean, by altering the sea skin temperature, and through surface layer dilution. However, to date, very few studies quantifying these effects on global net sea-air fluxes exist. Here, we include terms for the enhanced gas transfer velocity and the direct export of carbon in calculations of the global net sea-air fluxes, using a 7-year time series of monthly global climate quality satellite remote sensing observations, model and in-situ data. The use of a non-linear relationship between the effects of rain and wind significantly reduces the estimated impact of rain-induced surface turbulence on the rate of sea-air gas transfer, when compared to a linear relationship. Nevertheless, globally, the rain enhanced gas transfer and rain induced direct export increase the estimated annual oceanic integrated net sink of CO2 by up to 6%. Regionally, the variations can be larger, with rain increasing the estimated annual net sink in the Pacific Ocean by up to 15% and altering monthly net flux by > ± 50%. Based on these analyses, the impacts of rain should be included in the uncertainty analysis of studies that estimate net sea-air fluxes of CO2 as the rain can have a considerable impact, dependent upon the region and timescale.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A divergent and concise base‐promoted Dieckmann‐type keto‐ester condensation strategy is demonstrated to generate two unique spirocyclohexadiene‐isoxazoline moieties. The consecutive ...di‐bromination–elimination–bromination of the corresponding spiro moiety has been successfully utilized to furnish the desired core structure of many bromotyrosine derived spiroisoxazoline natural products. The spiroisoxazoline acid was further coupled with the desired diamine to accomplish the first total synthesis of 11‐deoxyfistularin‐3. This strategy could serve as an efficient alternative to previously developed oxidative dearomatizing spirocyclization of phenol as the essential step to synthesize this class of natural products.
A complementary route for spiroisoxazolines leads to the total synthesis of 11‐deoxyfistularin‐3.
Key Uncertainties in the Recent Air‐Sea Flux of CO2 Woolf, D.K.; Shutler, J.D.; Goddijn‐Murphy, L. ...
Global biogeochemical cycles,
December 2019, 20191201, 2019-12, Letnik:
33, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The contemporary air‐sea flux of CO2 is investigated by the use of an air‐sea flux equation, with particular attention to the uncertainties in global values and their origin with respect to that ...equation. In particular, uncertainties deriving from the transfer velocity and from sparse upper ocean sampling are investigated. Eight formulations of air‐sea gas transfer velocity are used to evaluate the combined standard uncertainty resulting from several sources of error. Depending on expert opinion, a standard uncertainty in transfer velocity of either ~5% or ~10% can be argued and that will contribute a proportional error in air‐sea flux. The limited sampling of upper ocean fCO2 is readily apparent in the Surface Ocean CO2 Atlas databases. The effect of sparse sampling on the calculated fluxes was investigated by a bootstrap method, that is, treating each ship cruise to an oceanic region as a random episode and creating 10 synthetic data sets by randomly selecting episodes with replacement. Convincing values of global net air‐sea flux can only be achieved using upper ocean data collected over several decades but referenced to a standard year. The global annual referenced values are robust to sparse sampling, but seasonal and regional values exhibit more sampling uncertainty. Additional uncertainties are related to thermal and haline effects and to aspects of air‐sea gas exchange not captured by standard models. An estimate of global net CO2 exchange referenced to 2010 of −3.0 ± 0.6 Pg C/year is proposed, where the uncertainty derives primarily from uncertainty in the transfer velocity.
Plain Language Summary
The oceanic carbon sink reduces the rate of accumulation of CO2 in the atmosphere but is also responsible for the acidification of the ocean. One method of estimating the size of the oceanic carbon sink depends on a calculation of upward and downward flows of CO2 at the sea surface. This study revisits this calculation using updated knowledge of the transfer processes at the sea surface and the results of a large international collaborative effort (Surface Ocean CO2 Atlas) to collect and compile measurements of CO2 in the upper ocean. Greater sampling of the oceans improves estimates, but direct calculation in each year is not practical. Instead, we calculate fluxes in a recent year (2010) using upper ocean measurements of CO2 over many years. The remaining uncertainty is dominated by limited knowledge of the efficiency of stirring of gas across the sea surface, the air‐sea transfer velocity. The study suggests a relatively large downward flow of CO2 into the ocean compared to previous applications of this method and other methods to estimate the oceanic carbon sink. Increased knowledge is rewarded by reduced uncertainty in the net global flux; that flux is estimated at −3.0 ± 0.6 Pg C/year. Further understanding of transfer velocities and better sampling may reduce the uncertainty in the future.
Key Points
Increased understanding of air‐sea gas transfer processes and better sampling of the upper ocean enables higher confidence in calculations of air‐sea CO2 fluxes
The calculations imply a relatively large global net air‐to‐sea flux of −3.0 Pg C/year (referenced to 2010)
This flux is known within 0.6 Pg C/year, where uncertainty in air‐sea transfer velocity is the largest contribution to the combined uncertainty
Monoclonal antibody-conjugated sphere-shaped gold nanoparticles were combined with single-walled carbon nanotubes (SWCNTs) to create a nanohybrid system to selectively detect and eradicate multiple ...drug resistant Salmonella (MDRS) typhimurium DT104 bacteria. The Raman signal intensity from Rhodamine 6G (Rh6G) modified monoclonal AC04 antibody SWCNTs-gold nanoparticle (SWCNT-GNPs) hybrid provided a SERS enhancement by several orders of magnitude to detect the MDRS bacteria over the GNP system. A targeted photothermolysis experiment using 670 nm light at 2 W cm(-2) for 15 min, resulted in selective and irreparable damage to more than 99% Salmonella DT104 at the concentration of 10(5) CFU mL(-1). In comparison to solely SWCNTs or GNPs, our SWCNT-GNPs nanohybrids have also shown a better photothermal efficiency.
Floating wave buoys are widely considered as a global standard for wave data. Marine renewable energy presents a relatively new industry for wave measurements, requiring a high level of accuracy for ...applications including resource assessment, performance assessment and engineering design. This study draws on the unique deployment of four identical wave buoys in close proximity and a period of data from a free-floating buoy to classify spurious low frequency measurements as erroneous. The nature of the occurrence of these errors, and their effect on the validity of measurements are also examined. The work shows that the errors are directly related to the drag forces on the buoy, but with a correctly designed filter, the effect of the errors on the wave measurements can be mitigated. A variable filter process is described which improves the accuracy of measurements captured by these buoys. This is recommended for all interpretation of these data, and is essential for any detailed statistical analysis.
Display omitted
•Spurious wave height measurements from buoy examined.•Significant low freq errors identified in wave buoy record.•High drift forces identified as the cause of the errors.•Errors do not affect frequencies above 0.065Hz.•More advanced filtering required to remove errors.
We report a strategy to fabricate a rapid and stable surface-enhanced Raman scattering (SERS)-based hybrid nanomaterial using gold nanopopcorns attached single-walled carbon nanotubes (AuNP@f
...-SWCNTs) for label-free detection and photothermal killing of bacteria. Herein, previously ester-functionalized single-walled carbon nanotubes (f
-SWCNTs) undergo 1,3-dipolar cycloaddition reaction with
generated nitrile imine under Microwave (MW) irradiation to form a doubly ester terminated SWCNTs cycloadduct (f
-SWCNTs). The ester terminals are further modified with 4-aminothiophenol (4-ATP) under MW-irradiation to form thiol-terminated SWCNTs templates (f
-SWCNTs) that allow gold nanopopcorns (AuNPs) to covalently and uniformly attach at a minimum inter-particle distance thus yielding a hybrid nanomaterial (AuNP@f
-SWCNT) with good aqueous stability and abundant 'hotspots'. Consequently, monoclonal
antibody-conjugated bioassays fabricated with our AuNP@f
-SWCNT substrates (mAb-AuNP@f
-SWCNT) rapidly detect
in water with good selectivity and impressive SERS sensitivity. The detection limit of
, selected as a model to establish proof of principle, was found to be 1.0×10
CFU/mL. Furthermore, the AuNP@f
-SWCNT hybrid nanomaterial offers impressive photothermal pathogen killing effects. The synergy-type enhancement effect arising from the inherent noble properties of the respective components of the hybrid nanomaterial indicate that our AuNP@f
-SWCNT has the potential for further application in multiplex detection in samples.
Plant resource partitioning of chemical forms of nitrogen (N) may be an important factor promoting species coexistence in N-limited ecosystems. Since the microbial community regulates N-form ...transformations, plant partitioning of N may be related to plant-soil feedbacks. We conducted a ¹⁵N tracer addition experiment to study the ability of two alpine plant species, Acomastylis rossii and Deschampsia caespitosa, to partition organic and inorganic forms of N. The species are codominant and associated with strong plant-soil feedbacks that affect N cycling. We manipulated interspecific interactions by removing Acomastylis or Deschampsia from areas where the species were codominant to test if N uptake patterns varied in the presence of the other species. We found that Deschampsia acquired organic and inorganic N more rapidly than Acomastylis, regardless of neighbor treatment. Plant N uptake--specifically ammonium uptake--increased with plant density and the presence of an interspecific neighbor. Interestingly, this change in N uptake was not in the expected direction to reduce niche overlap and instead suggested facilitation of ammonium use. To test if N acquisition patterns were consistent with plant-soil feedbacks, we also compared microbial rhizosphere extracellular enzyme activity in patches dominated by one or the other species and in areas where they grew together. The presence of both species was generally associated with increased rhizosphere extracellular enzyme activity (five of ten enzymes) and a trend towards increased foliar N concentrations. Taken together, these results suggest that feedbacks through the microbial community, either in response to increased plant density or specific plant neighbors, could facilitate coexistence. However, coexistence is promoted via enhanced resource uptake rather than reduced niche overlap. The importance of resource partitioning to reduce the intensity of competitive interactions might vary across systems, particularly as a function of plant-soil feedbacks.
ABSTRACT
The emissivity of the accretion flow is a key parameter affecting the shape of both the energy and variability power spectra of active galactic nuclei (AGNs). We explore the energy ...dependence of the power spectrum for five AGNs, across the XMM–Newton bandpass, and across the 0.01–1 mHz frequency range, finding a ubiquitous flattening of the power spectrum towards higher energies. We develop a framework to explore this behaviour and thereby extract the energy dependence of the emissivity assuming a simple disc-like geometry for the inflow. We find that the emissivity ranges from ${\underset{\sim}{\propto}} R^{-2}$ at energies around the soft excess and increases to ${\underset{\sim}{\propto}} R^{-4}$ or steeper above 4–6 keV. We describe the changing emissivity index with a linear function in energy, finding the best-fitting slopes to vary between AGNs. We attempt to correlate the slope of the linear function against key AGN parameters but, as yet, the sample size is too small to confirm hints of a correlation with Eddington ratio.
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