1,721,037 research outputs found
The marine biogeochemistry of dissolved organic carbon and dissolved organic nutrients in the Atlantic Ocean
No full textThe marine biogeochemistry of dissolved organic carbon (DOC) has come underincreased scrutiny because of its involvement in the global carbon cycle andconsequently climate change. Dissolved organic nitrogen (DON) and phosphorus(DOP), which have historically been ignored because of their suggested “biologicalunavailability”, have now received greater attention due to their importance in nutrientcycling, particularly in oligotrophic ecosystems. DOM, a byproduct of photosyntheticproduction, has important ecological significance as a substrate that supportsheterotrophic bacterial growth, thereby causing oxygen consumption and regeneratinginorganic nutrients. In the open ocean the net production of DOC is ultimately due tothe decoupling of biological production and consumption processes. Concentrations ofDOM in the surface oceans, therefore, are controlled by both physical and biologicalprocesses. This research investigates the biological factors that control the distributionsof DOC, DON and DOP in surface waters, the importance of DOC degradation tooxygen consumption, the importance of DON and DOP degradation to remineraliseddissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), and theC:N:P stoichiometry of DOM pool in the Atlantic Ocean. Samples were collected on Atlantic Meridional Transects (AMT) cruise 16 and 17, which crossed the southerntemperate region, the southern subtropical gyre, the equatorial region, the northernsubtropical gyre, and the northern temperate region. This work described here wasperformed as a component of the AMT programme.Concentrations of DOC and TDN were determined using a high-temperature catalyticcombustion technique, and TDP concentrations were determined using a UV oxidationmethod. Concentrations of DON and DOP were estimated as the difference betweenthe independent measurements of TDN and TDP. The results showed that the highestDOM concentrations were found in surface (0-30 m) waters, ranging from 70-80 µMDOC, 4.8-6.5 µM DON and 0.2-0.3 µM DOP, and decreased with increasing waterdepth to 45-55 µM DOC, 2.6-4.0 µM DON and 0.04-0.05 µM DOP at 300 m. Thelowest DOM concentrations were observed in the deep (>1000 m) ocean, averaging 44µM DOC, 2.3 µM DON and 0.02 µM DOP. In the upper 300 m, the concentrations ofsemilabile (and labile) DOC decreased by 45-95% from the surface values. DON andDOP were the dominant components of the total dissolved nutrient pools in the upper50 m, accounting for up to 99% and 80% of the TDN and TDP pools, respectively. Inthe upper 300 m, semilabile (and labile) DON and DOP decreased by 50-65% and90-95% from the surface values, respectively.The decoupled correlations between DOC/DON/DOP and chlorophyll-a and rates ofcarbon fixation suggested that phytoplankton biomass and rates of primary productionwere not the important controls of the cumulative DOC, DON and DOP. Zooplanktongrazing was hypothesised to be an important factor in regulating the distributions ofDOC, DON and DOP in surface waters. Poor correlations between DOC/DON/DOPand DIN/DIP suggested that inorganic nutrients were not the significant controls inDOC, DON and DOP distributions. N and P were probably retained mainly in theorganic pool in the surface waters due to a hypothesised insufficient functioning of the microbial degradation. If the vertical migration of zooplankton was significant inbringing new nutrients into the surface waters, strong correlations between dissolvedorganic and inorganic nutrients should not be anticipated. Prochlorococcus spp.abundance was statistically linked with the concentrations of DOC, DON and DOP.The significant correlations may reflect the ability of Prochlorococcus to assimilate thelabile forms of dissolved organic nutrients (including DOC), which may bequantitatively significant in surface waters of the Atlantic Ocean.The C:N, N:P and C:P stoichiometry of the bulk DOM pool deviated from the Redfieldratio of 6:1, 16:1 and 106:1, ranging from 12-18, 20-100 and 300-1400, respectively, inthe upper 300 m, suggesting that the cumulative DOM was rich in C relative to N and P,and N relative to P compared to the Redfield trajectories. The offsets of the C:N:Pstoichiometry relatively to the Redfield ratio were due to nutrient limitations thatimposed on prokaryotic and eukaryotic microbial populations. The C:N:Pstoichiometry of the bulk DOM pool showed an increased trend, with C:N = 12-16,N:P = 20-25, and C:P = 300-350 in the upper 30 m, C:N = 12-18, N:P = 50-100, andC:P = 700-1400 at 300 m, and C:N = 17-24, N:P = 79-132; C:P = 1791-2442 at 1000 m.The differences in the C:N:P stoichiometry of the bulk DOM pool between the upperand deep waters suggested preferential remineralisation of P relative to C and N, and Nrelative to C. A greater remineralisation length scale for DOC relative to DON andDOP produced a long-term, steady flux of C from the surface to the deep ocean.Therefore, CO2 fixed in the upper ocean during planktonic photosynthesis wascontinuously “pumped” into the ocean interior, and stored in the deep ocean up tothousands of years. The C:N, N:P and C:P stoichiometry of the semilabile (and labile)DOM pool generally agreed with the Redfield ratio (C:N = 6; N:P = 16; C:P = 106) inthe upper 30 m. At 100 m C:N ratio was 5-12, C:P ratio was 20-30, and C:P ratio was100-150. At 300 m, C:N ratio was 5-12, N:P ratio was 25-100, and C:P ratio was150-500. The findings suggested that in the upper 300 m, there was no preferential remineralisation between the semilabile (and labile) DOC and DON, however, thesemilabile (and labile) DOP seemed to be preferentially remineralised relative to thesemilabile (and labile) DOC and DON.In the upper thermocline (i.e. above 300 m), DOC degradation was important withrespect to oxygen consumption, contributing to as much as 25% of the apparentoxygen utilization (AOU). The remaining of 75% was attributable to POCdecomposition. However, the AOU contributable to DOC showed a function of latitude,with 15-55% found in the central subtropical Atlantic gyres and 15-25% in theequatorial region. The most likely explanation for the variation of DOC relative toPOC degradation with respect to AOU was the regional variability in the export ofPOC, which was suggested to be highest in the high nutrient regions of the equator andat the poleward margins of the subtropical gyres. As a result, DOC formed animportant contribution to AOU in oligotrophic regions, while POC was the dominantcontrol of AOU in upwelling regions. Some freshly-produced fractions of DON and DOP with turnover times of months toyears were capable of escaping rapid microbial degradation in surface waters andbecame entrained into deep waters via diffusive mixing. Subsequent microbialdegradation of these DON and DOP took place in the thermocline, regeneratinginorganic nutrients. Statistically significant correlations were observed between theDON-to-DIN and DOP-to-DIP relationships. Calculations of the fluxes of dissolvedorganic nutrients relative to inorganic nutrients suggested that in the upper thermocline(i.e. above 300 m), the downward fluxes of DON and DOP contributed to a total of 4%and 5% of the upward fluxes of DIN and DIP, respectively, into the euphotic zone. Theremaining of 95% of the upward dissolved inorganic nutrients fell out of the euphoticzone as particles in order to prevent nutrient accumulation and to maintain nutrientintegrity of the pelagic ecosystem
Nonlinearity-based single-channel monopulse tracking method for OFDM-aided UAV A2G communications
No full textUnmanned aerial vehicles (UAVs) have attracted great interest in rapid deployment for both civilian and military applications. The conventional UAV monopulse tracking technique requires dedicated pulses which suffer from multipath effect in air-to-ground (A2G) link with low elevation angles, whereas the orthogonal frequency division multiplexing (OFDM) for A2G high rate communication under frequency selective fading channel was not yet investigated for UAV target tracking at ground station. In this paper, we propose a single-channel monopulse tracking (SCMT) angle estimation method in OFDM tracking receiver exploiting square- and absolute-value nonlinear detection of amplitude-modulated difference signals. Extensive simulations are conducted to validate the proposed estimation method in terms of estimation range and estimation root mean squared error (RMSE). Results show that, the proposed angle estimation method exhibits S-shaped curve characteristic under different angle errors, which is insensitive to channels and modulations. The proposed method obtains angle estimation RMSEs smaller than 0.18◦ for antenna element distance d = 0.5 m with 10 MHz OFDM signals. For both square- and absolute-value methods, a maximum degradation of 0.02◦ for angle estimation RMSEs is observed under Rician channels compared with the estimation under additive white Gaussian noise (AWGN) channels, whereas the absolutevalue estimation outperforms the square-value estimation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
