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1
Dowling, Natalie A., Stephen J. Hall e Richard McGarvey. "Assessing population sustainability and response to fishing in terms of aggregation structure for greenlip abalone (Haliotis laevigata) fishery management". Canadian Journal of Fisheries and Aquatic Sciences 61, n. 2 (1 febbraio 2004): 247–59. http://dx.doi.org/10.1139/f03-165.
Testo completoAbstract (sommario):
The greenlip abalone (Haliotis laevigata) population in Waterloo Bay, South Australia, has undergone collapse and fishery closure twice since 1978. A rich data set, including survey measures of degree of spatial aggregation, has been gathered over that time and provides a unique opportunity to identify factors accounting for persistence or collapse, an issue that is of significance to abalone fisheries worldwide. Statistical analyses of fishery and survey data were undertaken to infer functional relationships between catch, effort, recruitment, adult density, and extent of aggregation. Catch rates were hyperstable, an observation consistent with the targeting of large aggregations. Statistical analysis of recruitment showed a significant year effect, implying an environmental signal, and suggested that aggregation size impacts fertilization success. Aggregation size grew under closure, suggesting an impact of fishing on this demographic feature. Aggregative behaviour appears to be critical for subpopulation sustainability. Fishery collapse may be triggered by depletion of larger abalone aggregations by heavy fishing, resulting in declines in fertilized egg production. When heavy fishing coincides with unfavourable environmental conditions, recruitment may be insufficient to sustain the subpopulation. If aggregation is similarly critical for other subpopulations, management strategies could be adapted according to the extent of aggregation in each subpopulation.
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Martin, Ian D., e David R. Barton. "The formation of diapause aggregations by larvae of Neophylax fuscus Banks (Trichoptera: Limnephilidae) and their influence on mortality and development". Canadian Journal of Zoology 65, n. 11 (1 novembre 1987): 2612–18. http://dx.doi.org/10.1139/z87-396.
Testo completoAbstract (sommario):
Fifth-instar larvae of the caddisfly Neophylax fuscus Banks (Trichoptera: Limnephilidae) enter a 4-month diapause in April after aggregating on the undersides of stream rocks in gravel cases. Aggregations have up to several hundred members, and densities within aggregations range from 1000 to 17 263 cases/m2. Field experiments conducted between 1984 and 1986 showed that larvae preferred to settle where initial larvae had already attached, but that there was no evidence for a chemical cue for aggregation. Mortality during the diapause but before pupation averaged 37.9%. Both exposure to low water and high density within aggregations contributed to increased mortality. Parasitism and predation appeared to be rare. The developmental synchrony of pupae and emergence synchrony were related to aggregation density during diapause. Low density aggregations tended to have low synchrony of development and emergence, while high density aggregations had higher synchrony.
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Dowling, Natalie A., Stephen J. Hall e Richard McGarvey. "Simulations of random fishing behaviour as an independent validation for the effect of active targeting of greenlip abalone (Haliotis laevigata) aggregations". Canadian Journal of Fisheries and Aquatic Sciences 61, n. 2 (1 febbraio 2004): 260–72. http://dx.doi.org/10.1139/f03-164.
Testo completoAbstract (sommario):
Although active targeting of abalone aggregations is documented for various species, its impact on large aggregations is poorly understood. As large aggregations make the greatest contribution to reproductive success, yet are vulnerable to exploitation, it is important to understand how targeted fishing impacts aggregation structure. If observed postfishing patterns are equally likely to have occurred in response to more random, nontargeted fishing, then changes in aggregation patterns cannot be directly attributed to aggregation-based targeting behaviour. The effect of targeted fishing on greenlip abalone (Haliotis laevigata) aggregations was verified by simulating three different levels of "random" fishing behaviour to generate postfishing aggregation frequency distributions. Comparison of the output with postfishing survey distributions suggested that observed aggregation patterns could not have resulted from random search behaviour. The aggregation survey data can therefore be used as a valid basis on which to quantify both fishing behaviour in terms of aggregation-specific catch patterns and the response of aggregations to fishing.
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Rüger, Korbinian. "Aggregation with Constraints". Utilitas 32, n. 4 (7 luglio 2020): 454–71. http://dx.doi.org/10.1017/s095382082000014x.
Testo completoAbstract (sommario):
AbstractUtilitarianism is often criticized because of its reliance on the interpersonal aggregation of harms and benefits. However, since the rejection of all forms of interpersonal aggregation strikes most people as implausible, some critics of utilitarianism have proposed theories of Limited Aggregation. These occupy the middle ground between fully aggregative and non-aggregative views. Recently, Limited Aggregation has been criticized for having counterintuitive implications that seem even worse than the counterintuitive implications of fully aggregative and non-aggregative views it tried to escape. I here propose a new view of Limited Aggregation that does better than existing accounts in this regard. It is more modest than existing accounts of Limited Aggregation, but it retains the view's core idea. This, I claim, is the thought that sometimes very strong individual claims stand in the way of realizing the best outcome.
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Yu, Yushi, Jiangnan Sun, Yaqing Chang e Chong Zhao. "High fitness areas drive the aggregation of the sea urchin Mesocentrotus nudus". PeerJ 10 (19 gennaio 2022): e12820. http://dx.doi.org/10.7717/peerj.12820.
Testo completoAbstract (sommario):
Sea urchin aggregation is a common phenomenon in coastlines. However, it remains controversial whether sea urchins form resource aggregations or behavioral aggregations in a non-spawning season. To clarify, we studied the aggregative responses to food and predators in the sea urchin Mesocentrotus nudus when high fitness areas (HFAs) were scarce versus sufficient. By taking the occupied area of each sea urchin (test diameter + spines = 4.5 cm) as a square (4.5 cm × 4.5 cm), we set scarce HFAs for the sea urchins in Experiment 1 (the squares of HFAs: the area occupied by experimental sea urchins = 1:1) and sufficient HFAs for the sea urchins in Experiment 2 (the squares of HFAs: the area occupied by experimental sea urchins = 2:1). If M. nudus form resource aggregations, they would aggregate passively under the scarce HFAs conditions, but not in the sufficient HFAs conditions. Conversely, if M. nudus form behavioral aggregation, aggregation would occur in both scarce and sufficient HFAs. The present results showed that in the scarce HFAs, M. nudus in the food and predator groups were significantly closer to the food and further from predators, and had significantly more aggregated numbers in HFAs than those in the control group. Sea urchins did not aggregate in response to food or predators under the sufficient HFAs, although significantly more sea urchins of the experimental group was found in HFAs than that of the control group. Sea urchins (at least M. nudus) form resource aggregations that are driven by the scarce HFAs. This provides valuable information into the mechanisms of the aggregation of sea urchins.
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Burgos, Julian M., e John K. Horne. "Sensitivity analysis and parameter selection for detecting aggregations in acoustic data". ICES Journal of Marine Science 64, n. 1 (25 ottobre 2006): 160–68. http://dx.doi.org/10.1093/icesjms/fsl007.
Testo completoAbstract (sommario):
Abstract Burgos, J. M., and Horne, J. K. 2007. Sensitivity analysis and parameter selection for detecting aggregations in acoustic data. ICES Journal of Marine Science, 64: 160–168. A global sensitivity analysis was conducted on the algorithm implemented in the Echoview ® software to detect and describe aggregations in acoustic backscatter. Multiple aggregation detections were performed using walleye pollock (Theragra chalcogramma) data from the eastern Bering Sea. Walleye pollock form distinct aggregations and dense and diffuse layers. In each aggregation detection, input parameters defining minimum size, density, and distance to other aggregations were selected at random using a Latin hypercube sampling design. Sensitivity was quantified by testing for correlation among input parameters and a series of aggregation descriptors. In all, 336 correlation tests were performed, corresponding to a combination of seven detection input parameters, eight aggregation descriptors, and six transects. Among these, 181 tests were significant, indicating sensitivity between input parameters and aggregation descriptors. The aggregation-detection algorithm is sensitive to changes in threshold and minimum size, but less sensitive to changes in the connectivity criterion among aggregations.
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Shishkov, Olga, e Orit Peleg. "Social insects and beyond: The physics of soft, dense invertebrate aggregations". Collective Intelligence 1, n. 2 (ottobre 2022): 263391372211237. http://dx.doi.org/10.1177/26339137221123758.
Testo completoAbstract (sommario):
Aggregation is a common behavior by which groups of organisms arrange into cohesive groups. Whether suspended in the air (like honey bee clusters), built on the ground (such as army ant bridges), or immersed in water (such as sludge worm blobs), these collectives serve a multitude of biological functions, from protection against predation to the ability to maintain a relatively desirable local environment despite a variable ambient environment. In this review, we survey dense aggregations of a variety of insects, other arthropods, and worms from a soft matter standpoint. An aggregation can be orders of magnitude larger than its individual organisms, consisting of tens to hundreds of thousands of individuals, and yet functions as a coherent entity. Understanding how aggregating organisms coordinate with one another to form a superorganism requires an interdisciplinary approach. We discuss how considering the physics of an aggregation can yield additional insights to those gained from ecological and physiological considerations, given that the aggregating individuals exchange information, energy, and matter continually with the environment and one another. While the connection between animal aggregations and the physics of non-living materials has been proposed since the early 1900s, the recent advent of physics of behavior studies provides new insights into social interactions governed by physical principles. Current efforts focus on eusocial insects; however, we show that these may just be the tip of an iceberg of superorganisms that take advantage of physical interactions and simple behavioral rules to adapt to changing environments. By bringing attention to a wide range of invertebrate aggregations, we wish to inspire a new generation of scientists to explore collective dynamics and bring a deeper understanding of the physics of dense living aggregations.
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Ambarak, Muhammad Zhaqif, Medy Ompi, Darus Sa’dah J. Paransa, Joice R. T. S. L. Rimper, Antonius P. Rumengan e Nego E. Bataragoa. "Keanekaragaman Makrobentos yang Menempati Agregasi Kerang, Septifer bilocullaris di Tiwoho, Kabupaten Minahasa Utara, Sulawesi Utara". JURNAL PESISIR DAN LAUT TROPIS 9, n. 3 (4 ottobre 2021): 133. http://dx.doi.org/10.35800/jplt.9.3.2021.38043.
Testo completoAbstract (sommario):
The purpose of this study was to determine the type and diversity of macrobenthos that inhabit the aggregation of Septifer bilocularis shellfish in the coastal waters of Tiwoho, North Minahasa Regency, North Sulawesi. Sampling of macrobenthos was carried out using core (PVC), both at the position of small aggregation (AK), middle large aggregation (ABT), and large edge aggregation (ABP). Sampling was carried out 4 times on different aggregations of shellfish. The data has been analyzed using the Diversity Index (H), the dominance index (D), and the Uniformity Index (E). It was identified that there were 25 types of macrobenthos occupying all aggregations of septifer bilocularis shells, which came from 11 classes including Gastropods, Bivalves, Malacostraca, Florideiphyceae, Ulvophyceae Ophiuroidea, Clitelatta, Maxillopoda, Globothalamea, Tubothalamea and Phaeophyceae. Biota diversity index varies from 1.60 – 1.70 which indicates that the biota in each aggregation has moderate diversity. The uniformity index value also varied, namely 0.069 for macrobenthos occupying the small aggregation (AK), then 0.066 in the middle large aggregation (ABT) and 0.064 in the large margin aggregation (GBP), which indicates the low uniformity of the macrobenthos in each aggregation. The dominance index of all aggregations was obtained between 0.27 - 0.36, which indicates that there is no species dominance for macrobenthos occupying different shellfish aggregations.Keywords: Diversity, Macrobenthos, Septifer bilocularis, Tiwoho
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Nanami, Atsushi. "Spawning aggregations of checkered snapper (Lutjanus decussatus) and blackspot snapper (L. fulviflamma): seasonality, lunar-phase periodicity and spatial distribution within spawning ground". PeerJ 11 (11 settembre 2023): e15991. http://dx.doi.org/10.7717/peerj.15991.
Testo completoAbstract (sommario):
Snappers (family Lutjanidae) are important fisheries target species and some species are known to form spawning aggregations at particular spawning grounds. The present study investigated the ecological characteristics of fish aggregations of two snapper species (checkered snapper Lutjanus decussatus and blackspot snapper L. fulviflamma) that form at a particular site. Specifically, the aims were to clarify (1) seasonality and lunar-phase periodicity of fish aggregation formation, (2) fine-scale spatial distribution of fish density (spatial variations of fish density at intervals of several-tens meters) within the aggregation site, (3) size and age frequency distributions of fishes in the aggregation site, (4) gonad development, (5) to compare fish abundance between inside and outside the aggregation site, and (6) to verify that fish aggregations of the two snapper species were spawning aggregation. Underwater observations using a 600 m × 5 m transect revealed that greater fish abundance of Lutjanus decussatus was found monthly between May and October, and clear positive peaks in the fish abundance were found only around the last-quarter moon. This lunar-related periodicity in the increase of fish abundance was confirmed by a time-series analysis (correlogram). Within the aggregation site, L. decussatus showed a relatively uniform distribution. In contrast, greater fish abundance of L. fulviflamma was found monthly between April and October, and clear positive peaks in the fish abundance were found around the last-quarter moon (April, May, June and October) or new moon (July, August and September). This lunar-related periodicity was also confirmed by correlogram. Lutjanus fulviflamma showed a relatively clumped distribution within the aggregation site. Most females of the two species in the aggregation site had hydrated eggs, indicating that the two species form aggregations for reproduction. The two species, although occurring simultaneously, are considered to form aggregations of conspecifics only. For L. decussatus, average fork length and age of males and females were 229.2 mm and 243.9 mm and 9.4 years and 8.1 years, respectively. For L. fulviflamma, average fork length and age of males and females were 233.9 mm and 246.9 mm and 6.8 years and 8.1 years, respectively. Fish abundance inside the aggregation site was 266.8-fold and 141557.1-fold greater than those outside the aggregation site for L. decussatus and L. fulviflamma, respectively. These results showed that (1) fish aggregation formation of the two snapper species was predictably repeated in particular months and lunar-phase, (2) it was predictably found at the particular site, (3) the fish abundance in the aggregation site markedly exceeded the fish abundance outside the aggregation site, and (4) the two species form aggregations for reproduction. Therefore, it is suggested that the fish aggregations for the two species can be regarded as spawning aggregations.
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Vasconcelos, Raquel, Sara Rocha e Xavier Santos. "Sharing refuges on arid islands: ecological and social influence on aggregation behaviour of wall geckos". PeerJ 5 (10 gennaio 2017): e2802. http://dx.doi.org/10.7717/peerj.2802.
Testo completoAbstract (sommario):
BackgroundThe extent of social behaviour among reptiles is underappreciated. Two types of aggregations are recognized in lizards: ecological and social, i.e., related to the attraction to a site or to animals of the same species, respectively. As most lizards are territorial, aggregations increase the probability of aggressive interactions among individuals, a density-dependent behaviour.MethodsAfter some spurious observations of aggregation behaviour in the endemic Cabo Verde nocturnal geckoTarentola substituta,we conducted a field-based study in order to thoroughly characterize it. We sampled 48 transects and 40 10 × 10 m quadrats on São Vicente Island to describe the incidence, size and composition of aggregations and to study the effect of gecko and refuge density, plus refuge quality, on refuge sharing. We hypothesize that when density of animals and scarcity of high-quality refuges is higher, lizards have increased probability of aggregating. We also predict a consistent pattern of size and composition of groups (male–female pairs, only one adult male per group) throughout the year if there is a selected behaviour to avoid agonistic interactions, and low thermal advantage to aggregating individuals.ResultsWe present one of the first evidences of aggregation for Phyllodactylidae geckos. We found thatT. substitutaforms aggregations around 30–40% of the time, and that refuges are almost always shared by a female-male pair, sometimes with a juvenile, probably a mechanism to avoid aggressive interactions. We also observed that refuge sharing is dependent on refuge quality, as medium–large (thermally more stable and positively selected) rocks are shared much more frequently than small ones, but independent of adult sizes. Refuge sharing is also directly related to the density of geckos and inversely related to the density of high-quality refuges. We found no relation between body temperatures of geckos and refuge sharing when controlling the effect of rock/air temperature, suggesting that huddling does not improve thermoregulation.DiscussionOur results suggest that in this harsh environment (rocks reach 46 °C) aggregation incidence is mainly driven by an ecological factor (scarcity of high-quality refuges) and its intersexual composition by social factors (avoidance of agonistic interactions by males, and possible increased reproductive success of the pair). This study sheds some light on the little explored gecko aggregation behaviour and other studies should follow.
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Kovács, Zoltán, Tibor Csizmadia, István Mihálcz e Zsolt T. Kosztyán. "Multipurpose Aggregation in Risk Assessment". Mathematics 10, n. 17 (2 settembre 2022): 3166. http://dx.doi.org/10.3390/math10173166.
Testo completoAbstract (sommario):
Risk-mitigation decisions in risk-management systems are usually based on complex risk indicators. Therefore, aggregation is an important step during risk assessment. Aggregation is important when determining the risk of components or the overall risk of different areas or organizational levels. In this article, the authors identify different aggregation scenarios. They summarize the requirements of aggregation functions and characterize different aggregations according to these requirements. They critique the multiplication-based risk priority number (RPN) used in existing applications and propose the use of other functions in different aggregation scenarios. The behavior of certain aggregation functions in warning systems is also examined. The authors find that, depending on the aggregation location within the organization and the purpose of the aggregation, considerably more functions can be used to develop complex risk indicators. The authors use different aggregations and seriation and biclustering to develop a method for generating corrective and preventive actions. The paper provides contributions for individuals, organizations, and or policy makers to assess and mitigate the risks at all levels of the enterprise.
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Kumar, Mukesh, Monika Sethi, Shalli Rani, Dipak Kumar Sah, Salman A. AlQahtani e Mabrook S. Al-Rakhami. "Secure Data Aggregation Based on End-to-End Homomorphic Encryption in IoT-Based Wireless Sensor Networks". Sensors 23, n. 13 (6 luglio 2023): 6181. http://dx.doi.org/10.3390/s23136181.
Testo completoAbstract (sommario):
By definition, the aggregating methodology ensures that transmitted data remain visible in clear text in the aggregated units or nodes. Data transmission without encryption is vulnerable to security issues such as data confidentiality, integrity, authentication and attacks by adversaries. On the other hand, encryption at each hop requires extra computation for decrypting, aggregating, and then re-encrypting the data, which results in increased complexity, not only in terms of computation but also due to the required sharing of keys. Sharing the same key across various nodes makes the security more vulnerable. An alternative solution to secure the aggregation process is to provide an end-to-end security protocol, wherein intermediary nodes combine the data without decoding the acquired data. As a consequence, the intermediary aggregating nodes do not have to maintain confidential key values, enabling end-to-end security across sensor devices and base stations. This research presents End-to-End Homomorphic Encryption (EEHE)-based safe and secure data gathering in IoT-based Wireless Sensor Networks (WSNs), whereby it protects end-to-end security and enables the use of aggregator functions such as COUNT, SUM and AVERAGE upon encrypted messages. Such an approach could also employ message authentication codes (MAC) to validate data integrity throughout data aggregation and transmission activities, allowing fraudulent content to also be identified as soon as feasible. Additionally, if data are communicated across a WSN, then there is a higher likelihood of a wormhole attack within the data aggregation process. The proposed solution also ensures the early detection of wormhole attacks during data aggregation.
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Flynn, Adrian J., e John R. Paxton. "Spawning aggregation of the lanternfish Diaphus danae (family Myctophidae) in the north-western Coral Sea and associations with tuna aggregations". Marine and Freshwater Research 63, n. 12 (2012): 1255. http://dx.doi.org/10.1071/mf12185.
Testo completoAbstract (sommario):
A spawning aggregation of the lanternfish Diaphus danae in the Coral Sea, that is fed on by spawning aggregations of yellowfin and bigeye tuna, has been sampled by mid-water trawling for the first time. Males and females in the aggregation occurred at a ratio of 23 to 1 and occupied two non-overlapping size classes (males 71.2–95.1-mm standard length (SL), females 99.0–121.4-mm SL). Hydrated oocytes with single oil droplets, which indicated imminent spawning, were in higher proportion in the first trawl (2134 hours to 2234 hours) than in the final trawl (0324 hours to 0424 hours) through the aggregation. Maximum estimated female D. danae fecundity (25 803) and gonadosomatic index (34.01) were higher than for any other lanternfish species recorded. Bigeye tuna (Thunnus obesus) individuals collected from aggregations were estimated to have 81–319 D. danae specimens in their stomachs. The annual Coral Sea D. danae aggregation is the only confirmed lanternfish spawning aggregation in Australian waters. The D. danae spawning aggregation provides a rich, transient foraging resource for spawning bigeye and yellowfin tuna in the Coral Sea, these being the only known tuna spawning aggregations in the Eastern Tuna and Billfish Fishery.
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Archer, Stephanie K., Scott A. Heppell, Brice X. Semmens, Christy V. Pattengill-Semmens, Phillippe G. Bush, Croy M. Mccoy e Bradley C. Johnson. "Patterns of color phase indicate spawn timing at a Nassau grouper Epinephelus striatus spawning aggregation". Current Zoology 58, n. 1 (1 febbraio 2012): 73–83. http://dx.doi.org/10.1093/czoolo/58.1.73.
Testo completoAbstract (sommario):
Abstract Nassau grouper Epinephelus striatus are a large bodied, top level predator that is ecologically important throughout the Caribbean. Although typically solitary, Nassau grouper form large annual spawning aggregations at predictable times in specific locations. In 2003, The Cayman Islands Marine Conservation Board established protection for a newly rediscovered Nassau grouper spawning aggregation on Little Cayman, British West Indies. The large size of this aggregation provides a unique opportunity to study the behavior of Nassau grouper on a relatively intact spawning aggregation. During non-spawning periods Nassau grouper display a reddish-brown-and-white barred coloration. However, while aggregating they exhibit three additional color phases: “bicolor”, “dark”, and “white belly”. We video sampled the population on multiple days leading up to spawning across five spawning years. Divers focused a laser caliper equipped video camera on individual fish at the aggregation. We later analyzed the video to determine the length of the fish and record the color phase. Our observations show that the relative proportion of fish in the bicolor color phase increases significantly on the day leading up to the primary night of spawning. The increase in the proportion of the bicolor color phase from 0.05 early in the aggregation to 0.40 on the day of spawning suggests that this color phase conveys that a fish is behaviorally and physiologically prepared to spawn. Additionally, 82.7% of fish exhibiting dark or white belly coloration early in the aggregation period suggests that these color phases are not only shown by female fish as was previously posited.
15
Die, David J., e Nick Ellis. "Aggregation dynamics in penaeid fisheries: banana prawns (Penaeus merguiensis) in the Australian Northern Prawn Fishery". Marine and Freshwater Research 50, n. 7 (1999): 667. http://dx.doi.org/10.1071/mf98124.
Testo completoAbstract (sommario):
In the Gulf of Carpentaria, banana prawns (Penaeus merguiensis) form dense aggregations that are targeted by trawl vessels with the help of small aeroplanes and colour sounders. Such aggregating behaviour is rare in penaeids and may lead to a change in catchability when stock abundance changes. Commercial logbook data containing trawl-tow records have been used to identify the location, time of capture and biomass of over 600 banana prawn aggregations during 1991–92. The number of aggregations decreased by 83% in the first three weeks of the fishing season. The average biomass of an aggregation decreased even more rapidly than the number of aggregations and, after three weeks of fishing, it had been reduced by 93%. The apparent decrease in the biomass of aggregating prawns during the first three weeks of the season is, therefore, in the order of 99%. This is considerably greater than the 66% decrease that can be estimated from catch per unit of effort data. It also suggests that catchability is directly related to stock abundance. Assessment models that assume that catchability is independent of stock size may not be appropriate for the assessment of the status of common banana prawns in this fishery.
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Bejines, Carlos, Sergio Ardanza-Trevijano e Jorge Elorza. "On Self-Aggregations of Min-Subgroups". Axioms 10, n. 3 (24 agosto 2021): 201. http://dx.doi.org/10.3390/axioms10030201.
Testo completoAbstract (sommario):
Preservation of structures under aggregation functions is an active area of research with applications in many fields. Among such structures, min-subgroups play an important role, for instance, in mathematical morphology, where they can be used to model translation invariance. Aggregation of min-subgroups has only been studied for binary aggregation functions. However, results concerning preservation of the min-subgroup structure under binary aggregations do not generalize to aggregation functions with arbitrary input size since they are not associative. In this article, we prove that arbitrary self-aggregation functions preserve the min-subgroup structure. Moreover, we show that whenever the aggregation function is strictly increasing on its diagonal, a min-subgroup and its self-aggregation have the same level sets.
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Kelton, JG, JC Moore e WG Murphy. "Studies investigating platelet aggregation and release initiated by sera from patients with thrombotic thrombocytopenic purpura". Blood 69, n. 3 (1 marzo 1987): 924–28. http://dx.doi.org/10.1182/blood.v69.3.924.924.
Testo completoAbstract (sommario):
Abstract Many patients with thrombotic thrombocytopenic purpura (TTP) have a platelet aggregating factor in their serum that may be pathologically linked with the disease process. To help characterize the type of platelet aggregation and platelet release induced by the sera from seven TTP patients, we measured the ability of a variety of inhibitors of platelet function as well as the ability of monoclonal antibodies (MoAbs) against platelet glycoproteins to inhibit TTP sera-induced platelet aggregation and release. These results were compared with the ability of the same inhibitors to block platelet aggregation induced by ristocetin, collagen, ADP, thrombin, and IgG-immune complexes. Monoclonal antibody directed against platelet glycoprotein Ib totally inhibited ristocetin-induced aggregation and release but had no effect on aggregation and release induced by the TTP sera or by any of the other platelet agonists. However, the MoAb against glycoproteins IIb/IIIa inhibited aggregation and release caused by TTP sera as well as by collagen, thrombin, and ADP but had no effect on aggregation and release induced by ristocetin. The aggregating activity could be abolished by heparin but not by the serine protease inhibitor PMSF (1 mmol/L). And although monomeric human IgG and purified Fc fragments of IgG inhibited IgG-immune complex-induced aggregation and release, they had no effect on TTP sera-induced aggregation and release nor on aggregation and release induced by any of the other agonists. Consistent with these in vitro studies showing no effect of IgG were the in vivo observations that intravenous (IV) IgG was without effect when administered to three patients with TTP. This study indicates that although a von Willebrand factor (vWF)-rich preparation of cryoprecipitate enhances the in vitro platelet aggregation and release caused by sera from the seven TTP patients we studied, the pathway of aggregation and release is not via platelet glycoprotein Ib. Also the aggregating factor of TTP sera is not neutralized in vitro or in vivo by IgG.
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Kelton, JG, JC Moore e WG Murphy. "Studies investigating platelet aggregation and release initiated by sera from patients with thrombotic thrombocytopenic purpura". Blood 69, n. 3 (1 marzo 1987): 924–28. http://dx.doi.org/10.1182/blood.v69.3.924.bloodjournal693924.
Testo completoAbstract (sommario):
Many patients with thrombotic thrombocytopenic purpura (TTP) have a platelet aggregating factor in their serum that may be pathologically linked with the disease process. To help characterize the type of platelet aggregation and platelet release induced by the sera from seven TTP patients, we measured the ability of a variety of inhibitors of platelet function as well as the ability of monoclonal antibodies (MoAbs) against platelet glycoproteins to inhibit TTP sera-induced platelet aggregation and release. These results were compared with the ability of the same inhibitors to block platelet aggregation induced by ristocetin, collagen, ADP, thrombin, and IgG-immune complexes. Monoclonal antibody directed against platelet glycoprotein Ib totally inhibited ristocetin-induced aggregation and release but had no effect on aggregation and release induced by the TTP sera or by any of the other platelet agonists. However, the MoAb against glycoproteins IIb/IIIa inhibited aggregation and release caused by TTP sera as well as by collagen, thrombin, and ADP but had no effect on aggregation and release induced by ristocetin. The aggregating activity could be abolished by heparin but not by the serine protease inhibitor PMSF (1 mmol/L). And although monomeric human IgG and purified Fc fragments of IgG inhibited IgG-immune complex-induced aggregation and release, they had no effect on TTP sera-induced aggregation and release nor on aggregation and release induced by any of the other agonists. Consistent with these in vitro studies showing no effect of IgG were the in vivo observations that intravenous (IV) IgG was without effect when administered to three patients with TTP. This study indicates that although a von Willebrand factor (vWF)-rich preparation of cryoprecipitate enhances the in vitro platelet aggregation and release caused by sera from the seven TTP patients we studied, the pathway of aggregation and release is not via platelet glycoprotein Ib. Also the aggregating factor of TTP sera is not neutralized in vitro or in vivo by IgG.
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Lee, Sunwoo, Tuo Zhang e A. Salman Avestimehr. "Layer-Wise Adaptive Model Aggregation for Scalable Federated Learning". Proceedings of the AAAI Conference on Artificial Intelligence 37, n. 7 (26 giugno 2023): 8491–99. http://dx.doi.org/10.1609/aaai.v37i7.26023.
Testo completoAbstract (sommario):
In Federated Learning (FL), a common approach for aggregating local solutions across clients is periodic full model averaging. It is, however, known that different layers of neural networks can have a different degree of model discrepancy across the clients. The conventional full aggregation scheme does not consider such a difference and synchronizes the whole model parameters at once, resulting in inefficient network bandwidth consumption. Aggregating the parameters that are similar across the clients does not make meaningful training progress while increasing the communication cost. We propose FedLAMA, a layer-wise adaptive model aggregation scheme for scalable FL. FedLAMA adjusts the aggregation interval in a layer-wise manner, jointly considering the model discrepancy and the communication cost. This fine-grained aggregation strategy enables to reduce the communication cost without significantly harming the model accuracy. Our extensive empirical study shows that, as the aggregation interval increases, FedLAMA shows a remarkably smaller accuracy drop than the periodic full aggregation, while achieving comparable communication efficiency.
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Teng, Che-Ming, Ya-Fei Kang, Ya-Ling Chang, Feng-Nien Ko, Shu-Chen Yang e Feng-Lin Hsu. "ADP-mimicking Platelet Aggregation Caused by Rugosin E, an Ellagitannin Isolated from Rosa rugosa Thunb". Thrombosis and Haemostasis 77, n. 03 (1997): 555–61. http://dx.doi.org/10.1055/s-0038-1656005.
Testo completoAbstract (sommario):
SummaryAmong the nine ellagitannins, rugosin E was the most potent platelet aggregating agent with an EC50 of 1.5 ± 0.1 µM in rabbit platelets and 3.2 ±0.1 µM in human platelets. The aggregations caused by rugosin E and ADP were inhibited by EGTA, PGE1, mepacrine, sodium nitroprusside and neomycin, but not by indomethacin, verapamil, TMB-8, BN52021 and GR32191B. Rugosin E-induced thromboxane formation was suppressed by indomethacin, EGTA, PGE,, verapamil, mepacrine, TMB-8 and neomycin. ADP-scavenging agents, such as CP/CPK and apyrase inhibited concentration-dependently ADP (20 εM)-, but not rugosin E (5 εM)-induced platelet aggregation. In thrombin (0.1 U/ml)-treated and degranulated platelets, rugosin E and ADP still caused 63.5 ± 3.0% and 61.2 ± 3.5% of platelet aggregation, respectively. Selective ADP receptor antagonists, ATP and FSBA inhibited rugosin E- and ADP-induced platelet aggregations in a concentration-dependent manner. Both rugosin E and ADP did not induce platelet aggregation in ADP (1 mM)-desensitized platelets. In contrast to ADP, rugosin E did not decrease cAMP formation in washed rabbit platelets. Both rugosin E and ADP did not cause phosphoinositide breakdown in [3H]myo-inositol-labeled rabbit platelets. In fura-2/AM- load platelets, both rugosin E and ADP induced increase in intracellular calcium concentration and these responses were inhibited by ATP and PGEj. All these data suggest that rugosin E may be an ADP receptor agonist in rabbit platelets.
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Azzimonti, Marina, Eva de Francisco e Per Krusell. "Aggregation and Aggregation". Journal of the European Economic Association 6, n. 2-3 (aprile 2008): 381–94. http://dx.doi.org/10.1162/jeea.2008.6.2-3.381.
Testo completo
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Copping, Joshua P., Bryce D. Stewart, Colin J. McClean, James Hancock e Richard Rees. "Does bathymetry drive coastal whale shark (Rhincodon typus)aggregations?" PeerJ 6 (8 giugno 2018): e4904. http://dx.doi.org/10.7717/peerj.4904.
Testo completoAbstract (sommario):
BackgroundThe whale shark (Rhincodon typus) is known to aggregate in a number of coastal locations globally, however what causes these aggregations to form where they do is largely unknown. This study examines whether bathymetry is an important driver of coastal aggregation locations forR. typusthrough bathymetry’s effect on primary productivity and prey availability. This is a global study taking into account all coastal areas withinR. typus’range.MethodsR. typusaggregation locations were identified through an extensive literature review. Global bathymetric data were compared atR. typusaggregation locations and a large random selection of non-aggregation areas. Generalised linear models were used to assess which bathymetric characteristic had the biggest influence on aggregation presence.ResultsAggregation sites were significantly shallower than non-aggregation sites and in closer proximity to deep water (the mesopelagic zone) by two orders of magnitude. Slope at aggregation sites was significantly steeper than non-aggregation sites. These three bathymetric variables were shown to have the biggest association with aggregation sites, with up to 88% of deviation explained by the GLMs.DiscussionThe three key bathymetric characteristics similar at the aggregation sites are known to induce upwelling events, increase primary productivity and consequently attract numerous other filter feeding species. The location of aggregation sites in these key areas can be attributed to this increased prey availability, thought to be the main reasonR. typusaggregations occur, extensively outlined in the literature. The proximity of aggregations to shallow areas such as reefs could also be an important factor why whale sharks thermoregulate after deep dives to feed. These findings increase our understanding of whale shark behaviour and may help guide the identification and conservation of further aggregation sites.
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Mangubhai, Sangeeta, Muhammad Saleh, Suprayitno, Andreas Muljadi, Purwanto, Kevin L. Rhodes e Katherina Tjandra. "Do Not Stop: The Importance of Seamless Monitoring and Enforcement in an Indonesian Marine Protected Area". Journal of Marine Biology 2011 (2011): 1–11. http://dx.doi.org/10.1155/2011/501465.
Testo completoAbstract (sommario):
The harvesting of groupers (Serranidae) in Indonesia for the live reef food fish trade (LRFFT) has been ongoing since the late 1980s. Eight sites in Komodo National Park that included two fish spawning aggregation (FSA) sites were monitored for groupers and humphead wrasse,Cheilinus undulatus, from 1998 to 2003 and from 2005 to 2008 to examine temporal changes in abundance and assess the effectiveness of conservation and management efforts. Monitoring identified FSA sites for squaretail coralgrouper,Plectropomus areolatus, and brown-marbled grouper,Epinephelus fuscoguttatus. Both species formed aggregations before and during full moon from September to December, prior to lapses in monitoring (2003–2005) and in enforcement (2004-2005). Following these lapses, data reveal substantial declines inP. areolatusabundance and the apparent extirpation of one aggregation at one site. Other non-aggregating species targeted by the LRFFT showed similar declines at three of eight monitored sites. This paper highlights the impact of FSA fishing and the need for a seamless monitoring and enforcement protocol in areas where aggregation fishing pressure is high. Within Komodo National Park, local fishers, particularly those operating on behalf of the LRFFT, pose a serious threat to population persistence of species targeted by this trade.
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YAGER, RONALD R. "CHOQUET AGGREGATION USING ORDER INDUCING VARIABLES". International Journal of Uncertainty, Fuzziness and Knowledge-Based Systems 12, n. 01 (febbraio 2004): 69–88. http://dx.doi.org/10.1142/s0218488504002667.
Testo completoAbstract (sommario):
We discuss the OWA and Choquet integral aggregation operators and point out the central role the ordering operation plays in these operators. We extend the capabilities of the Choquet integral aggregation by allowing the ordering to be induced by some values other then those being aggregated. This allows us to consider an induced Choquet Choquet integral aggregation operator. We look at the properties of this operator. We then look at its applications. Among the applications considered are aggregations guided by linguistic and other ordinal structures. We look at the use of induced aggregation in nearest neighbor methods. We also consider the Choquet aggregation of complex objects such as matrices and vectors.
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Yanhua, Hu, e Xincai Zhang. "Aggregation Tree Based Data Aggregation Algorithm in Wireless Sensor Networks". International Journal of Online Engineering (iJOE) 12, n. 06 (30 giugno 2016): 10. http://dx.doi.org/10.3991/ijoe.v12i06.5408.
Testo completoAbstract (sommario):
Abstract: In wireless sensor networks, efficient and effective data aggregation algorithms can prolong the network lifecycle by reducing communication of redundant data and improve the security of the networks. Tradition data aggregation algorithms in wireless sensor networks mainly aim to improve the energy utilization, and ignore the security and lifecycle. In order to get a good trade-off between these requirements, we proposed a data aggregation algorithm based on constructing a data aggregation tree. After give a formalism description of the problem, we proposed a data aggregation tree constructing algorithm. By minimize the maximal energy consumption of nodes, the algorithm can prolong the lifecycle. In data aggregation scheduling algorithm, we select the number of communications carefully to get the trade-off between low weighted delay and high network lifecycle. The simulation experiments show that, the proposed data aggregation algorithm consumes less energy while aggregating data from sensor nodes, and thus can prolong the network lifecycle.
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Saravanan, K., e R. Asokan. "An New Efficient Cluster Based Detection Mechanisms for Distributed Denial of Services (DDoS) Attacks". International Journal of Mathematics and Computers in Simulation 15 (27 novembre 2021): 147–52. http://dx.doi.org/10.46300/9102.2021.15.27.
Testo completoAbstract (sommario):
Cluster aggregation of statistical anomaly detection is a mechanism for defending against denial of service attack (dos) and distributed denial-of-service (DDoS) attacks. DDoS attacks are treated as a congestioncontrol problem; because most of the congestion is occurred in the malicious hosts not follow the normal endto- end congestion control. Upstream routers are also notified to drop such packets in order that the router’s resources are used to route legitimate traffic hence term cluster aggregation. If the victim suspects that the cluster aggregations are solved by most of the clients, it increases the complexity of the cluster aggregation. This aggregation solving technique allows the traversal of the attack traffic throughout the intermediate routers before reaching the destination. In this proposal, the aggregation solving mechanism is cluster aggregation to the core routers rather than having at the victim. The router based cluster aggregation mechanism checks the host system whether it is legitimate or not by providing a aggregation to be solved by the suspected host.
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Hornberger, Zachary, Bruce Cox e Raymond R. Hill. "Analysis of the effects of spatiotemporal demand data aggregation methods on distance and volume errors". Journal of Defense Analytics and Logistics 5, n. 1 (10 maggio 2021): 29–45. http://dx.doi.org/10.1108/jdal-03-2020-0003.
Testo completoAbstract (sommario):
Purpose Large/stochastic spatiotemporal demand data sets can prove intractable for location optimization problems, motivating the need for aggregation. However, demand aggregation induces errors. Significant theoretical research has been performed related to the modifiable areal unit problem and the zone definition problem. Minimal research has been accomplished related to the specific issues inherent to spatiotemporal demand data, such as search and rescue (SAR) data. This study provides a quantitative comparison of various aggregation methodologies and their relation to distance and volume based aggregation errors. Design/methodology/approach This paper introduces and applies a framework for comparing both deterministic and stochastic aggregation methods using distance- and volume-based aggregation error metrics. This paper additionally applies weighted versions of these metrics to account for the reality that demand events are nonhomogeneous. These metrics are applied to a large, highly variable, spatiotemporal demand data set of SAR events in the Pacific Ocean. Comparisons using these metrics are conducted between six quadrat aggregations of varying scales and two zonal distribution models using hierarchical clustering. Findings As quadrat fidelity increases the distance-based aggregation error decreases, while the two deliberate zonal approaches further reduce this error while using fewer zones. However, the higher fidelity aggregations detrimentally affect volume error. Additionally, by splitting the SAR data set into training and test sets this paper shows the stochastic zonal distribution aggregation method is effective at simulating actual future demands. Originality/value This study indicates no singular best aggregation method exists, by quantifying trade-offs in aggregation-induced errors practitioners can utilize the method that minimizes errors most relevant to their study. Study also quantifies the ability of a stochastic zonal distribution method to effectively simulate future demand data.
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Zahedi Khameneh, Azadeh, e Adem Kilicman. "Some Construction Methods of Aggregation Operators in Decision-Making Problems: An Overview". Symmetry 12, n. 5 (1 maggio 2020): 694. http://dx.doi.org/10.3390/sym12050694.
Testo completoAbstract (sommario):
Aggregating data is the main line of any discipline dealing with fusion of information from the knowledge-based systems to decision-making. The purpose of aggregation methods is to convert a list of objects, all belonging to a given set, into a single representative object of the same set usually by an n-ary function, so-called aggregation operator. As the useful aggregation functions for modeling real-life problems are limited, the basic problem is to construct a proper aggregation operator, usually a symmetric one, for each situation. During the last decades, a number of construction methods for aggregation functions have been developed to build new classes based on the existing well-known operators. There are three main construction methods in common use: transformation, composition, and convex combination. This paper compares these methods with respect to the type of aggregating problems that can be handled by each of them.
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Carter, A. J., e S. Heptinstall. "Platelet Aggregation in Whole Blood: The Role of Thromboxane A2 and Adenosine Diphosphate". Thrombosis and Haemostasis 54, n. 03 (1985): 612–16. http://dx.doi.org/10.1055/s-0038-1660081.
Testo completoAbstract (sommario):
SummaryThe platelet aggregation that occurred in whole blood in response to several aggregating agents (collagen, arachidonic acid, adenosine diphosphate, adrenaline and thrombin) was measured using an Ultra-Flo 100 Whole Blood Platelet Counter. The amounts of thromboxane B2 produced were measured by radioimmunoassay. The effects of various inhibitors of thromboxane synthesis and the effects of apyrase, an enzyme that destroys adenosine diphosphate, were determined.Platelet aggregation was always accompanied by the production of thromboxane B2, and the amounts produced depended on the nature and concentration of the aggregating agent used. The various inhibitors of thromboxane synthesis - aspirin and flurbiprofen (cyclo-oxygenase inhibitors), BW755C (a cyclo-oxygenase and lipoxygenase inhibitor) and dazoxiben (a selective thromboxane synthase inhibitor) - did not markedly inhibit aggregation. Results obtained using apyrase showed that adenosine diphosphate contributed to the aggregation process, and that its role must be acknowledged when devising means of inhibiting platelet aggregation in vivo.
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Burgess-Wilson, ME, SR Cockbill, GI Johnston e S. Heptinstall. "Platelet aggregation in whole blood from patients with Glanzmann's thrombasthenia". Blood 69, n. 1 (1 gennaio 1987): 38–42. http://dx.doi.org/10.1182/blood.v69.1.38.38.
Testo completoAbstract (sommario):
Abstract We examined platelet aggregation in platelet-rich plasma (PRP) and in whole blood from two patients with Glanzmann's thrombasthenia. In PRP, aggregation was measured by monitoring the changes in light absorbance that occurred in response to aggregating agents; to measure platelet aggregation in whole blood, we used a platelet counting technique. In PRP, the patients' platelets showed defective aggregation in response to ADP, adrenaline, arachidonic acid (AA), and collagen, but normal agglutination occurred in response to ristocetin. In whole blood, however, platelet aggregation in response to the aggregating agents appeared to be either very similar to that which occurred in blood from normal subjects or only slightly reduced. There was a reduced response to all concentrations of ADP and to low concentrations of collagen but a normal response to all concentrations of adrenaline, AA, and higher concentrations of collagen. Conversely, there seemed to be an increased agglutination response to ristocetin. The abnormality in our two patients with Glanzmann's thrombasthenia probably lies in the inability of their platelets to form large, macroscopic aggregates rather than in platelet aggregation per se.
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Burgess-Wilson, ME, SR Cockbill, GI Johnston e S. Heptinstall. "Platelet aggregation in whole blood from patients with Glanzmann's thrombasthenia". Blood 69, n. 1 (1 gennaio 1987): 38–42. http://dx.doi.org/10.1182/blood.v69.1.38.bloodjournal69138.
Testo completoAbstract (sommario):
We examined platelet aggregation in platelet-rich plasma (PRP) and in whole blood from two patients with Glanzmann's thrombasthenia. In PRP, aggregation was measured by monitoring the changes in light absorbance that occurred in response to aggregating agents; to measure platelet aggregation in whole blood, we used a platelet counting technique. In PRP, the patients' platelets showed defective aggregation in response to ADP, adrenaline, arachidonic acid (AA), and collagen, but normal agglutination occurred in response to ristocetin. In whole blood, however, platelet aggregation in response to the aggregating agents appeared to be either very similar to that which occurred in blood from normal subjects or only slightly reduced. There was a reduced response to all concentrations of ADP and to low concentrations of collagen but a normal response to all concentrations of adrenaline, AA, and higher concentrations of collagen. Conversely, there seemed to be an increased agglutination response to ristocetin. The abnormality in our two patients with Glanzmann's thrombasthenia probably lies in the inability of their platelets to form large, macroscopic aggregates rather than in platelet aggregation per se.
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Hosn, Wafa Aboul, e John A. Downing. "Influence of Cover on the Spatial Distribution of Littoral-zone Fishes". Canadian Journal of Fisheries and Aquatic Sciences 51, n. 8 (1 agosto 1994): 1832–38. http://dx.doi.org/10.1139/f94-185.
Testo completoAbstract (sommario):
Littoral-zone fish are thought to reduce predation pressure by seeking refuge within macrophyte beds or near the lake bottom, or by aggregating. We used underwater video to measure the spatial aggregation of prey fishes in the littoral habitat. At low density, fish were more aggregated off the bottom in open habitats than when found off the bottom within macrophyte beds. At high densities, fish were primarily observed near the lake bottom, and the presence or absence of macrophyte beds had little influence on spatial behavior. No difference could be detected in the degree of aggregation seen in fish on the lake bottom inside or outside macrophyte beds. Our results lend field support to theoretical and laboratory research that suggests aggregative behavior in littoral-zone fish is strongly influenced by fish density and by habitat structure.
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Li, Xiang, M. Fikret Ercan e Hong Cai Chen. "A Geometry Based Algorithm for Swarm Aggregations". Applied Mechanics and Materials 536-537 (aprile 2014): 1052–58. http://dx.doi.org/10.4028/www.scientific.net/amm.536-537.1052.
Testo completoAbstract (sommario):
This paper describes a Geometry Based algorithm (GBA) developed for aggregation behavior of a swarm of simple robots. Aggregation is one of the primary behaviors for swarm robots. Decentralization and stability for single-swarm aggregations are the two major properties of the GBA algorithm presented in this paper. Our analysis, together with extensive simulation studies considering various swarm size and configurations, indicate that the GBA algorithm is scalable and effective for swarm aggregations.
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Hayashi, S., I. Shimizu, H. Miyauchi e S. Watanabe. "Increased platelet aggregation in psoriasis". Acta Dermato-Venereologica 65, n. 3 (1 maggio 1985): 258–62. http://dx.doi.org/10.2340/0001555565258262.
Testo completoAbstract (sommario):
Platelet aggregation was measured in fasting platelet-rich plasma in 25 psoriatics, 6 of whom were diabetic, 50 normal controls, and 24 diabetics. The aggregating agents employed to induce platelet aggregation included ADP, epinephrine and collagen. Platelet aggregation was significantly increased in psoriatics compared with normal controls. An additive effect was observed when diabetes was associated with psoriasis, with platelet aggregation being further increased by ADP. Platelet aggregability was re-evaluated in 7 psoriatics after they presented with clearing of the rash. The increased platelet aggregation with ADP and epinephrine was significantly reduced when the skin lesions had cleared.
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Stafford, Richard, Mark S. Davies e Gray A. Williams. "Self-Organization of Intertidal Snails Facilitates Evolution of Aggregation Behavior". Artificial Life 14, n. 4 (ottobre 2008): 409–23. http://dx.doi.org/10.1162/artl.2008.14.4.14401.
Testo completoAbstract (sommario):
Many intertidal snails form aggregations during emersion to minimize desiccation stress. Here we investigate possible mechanisms for the evolution of such behavior. Two behavioral traits (following of mucus trails, and crevice occupation), which both provide selective advantages to individuals that possess the traits over individuals that do not, result in self-organization of aggregations in crevices in the rock surface. We suggest that the existence of self-organizing aggregations provides a mechanism by which aggregation behavior can evolve. The inclusion of an explicitly coded third behavior, aggregation, in a simulated population produces patterns statistically similar to those found on real rocky shores. Allowing these three behaviors to evolve using an evolutionary algorithm, however, results in aggregation behavior being selected against on shores with high crevice density. The inclusion of broadcast spawning dispersal mechanisms in the simulation, however, results in aggregation behavior evolving as predicted on shores with both high crevice density and low crevice density (evolving in crevices first, and then both in crevices and on flat rock), indicating the importance of environmental interactions in understanding evolutionary processes. We propose that self-organization can be an important factor in the evolution of group behaviors.
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Anschau, Valesca, e Rafael Sanjuán. "Fibrinogen Gamma Chain Promotes Aggregation of Vesicular Stomatitis Virus in Saliva". Viruses 12, n. 3 (4 marzo 2020): 282. http://dx.doi.org/10.3390/v12030282.
Testo completoAbstract (sommario):
The spread of viruses among cells and hosts often involves multi-virion structures. For instance, virions can form aggregates that allow for the co-delivery of multiple genome copies to the same cell from a single infectious unit. Previously, we showed that vesicular stomatitis virus (VSV), an enveloped, negative-strand RNA virus, undergoes strong aggregation in the presence of saliva from certain individuals. However, the molecular components responsible for such aggregation remain unknown. Here we show that saliva-driven aggregation is protein dependent, and we use comparative proteomics to analyze the protein content of strongly versus poorly aggregating saliva. Quantitative analysis of over 300 proteins led to the identification of 18 upregulated proteins in strongly aggregating saliva. One of these proteins, the fibrinogen gamma chain, was verified experimentally as a factor promoting VSV aggregation in a dose-dependent manner. This study hence identifies a protein responsible for saliva-driven VSV aggregation. Yet, the possible involvement of additional proteins or factors cannot be discarded.
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Cui, Baorang, Fei Pan, Bin Ding, Feng Zhang, Yong Ma e Yuli Chen. "Fiber Aggregation in Nanocomposites: Aggregation Degree and Its Linear Relation with the Percolation Threshold". Materials 16, n. 1 (20 dicembre 2022): 15. http://dx.doi.org/10.3390/ma16010015.
Testo completoAbstract (sommario):
Fiber aggregation in nanocomposites has an important effect on macroscopic electrical performance. To quantitatively evaluate its effect, an index to characterize the degree of aggregation is imperative and, ideally, it should have three features simultaneously, i.e., (1) single-parametric, dimensionless, and physically meaningful, (2) applicable to different aggregation topologies, and (3) one-to-one, corresponding to material electrical properties. However, these features remain largely unexplored. Here, we propose a new aggregation degree that is defined as the average increment of the fiber number connecting with each one when fibers aggregate from a uniform distribution state. This index is applicable to different aggregation topologies, from lump-like to network-like aggregating clusters. By geometric probability analysis and numerical validations, we demonstrate the index can be concisely expressed by the characteristic parameters of the aggregating cluster since it only depends on the local features. Interestingly, a one-to-one linear relation between the aggregation degree and the percolation threshold is found, which is independent of the distribution law of the fibers. This work may provide a guide to the property characterization, performance prediction, and material design of nanocomposites, and give physical insight into the understanding of systems with similar non-uniform distributions.
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Tao, Yunting, Fanyu Kong, Jia Yu e Qiuliang Xu. "EPPSA: Efficient Privacy-Preserving Statistical Aggregation Scheme for Edge Computing-Enhanced Wireless Sensor Networks". Security and Communication Networks 2022 (2 maggio 2022): 1–12. http://dx.doi.org/10.1155/2022/7359134.
Testo completoAbstract (sommario):
In edge computing-enhanced wireless sensor networks (WSNs), multidimensional data aggregation can optimize the utilization of computation resources for data collection. How to improve the efficiency of data aggregation has gained considerable attention in both academic and industrial fields. This article proposes a new efficient privacy-preserving statistical aggregation scheme (EPPSA) for WSNs, in which statistical data can be calculated without exposing the total number of sensor devices to control center. The EPPSA scheme supports multiple statistical aggregation functions, including arithmetic mean, quadratic mean, weighted mean, and variance. Furthermore, the EPPSA scheme adopts the modified Montgomery exponentiation algorithms to improve the aggregation efficiency in the edge aggregator. The performance evaluation shows that the EPPSA scheme gets higher aggregation efficiency and lower communication load than the existing statistical aggregation schemes.
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Al-Shammary, Dhiah. "Jaccard Coefficients based Clustering of XML Web Messages for Network Traffic Aggregation". Journal of Al-Qadisiyah for computer science and mathematics 11, n. 2 (6 settembre 2019): 82–91. http://dx.doi.org/10.29304/jqcm.2019.11.2.592.
Testo completoAbstract (sommario):
This paper provides static efficient clustering model based simple Jaccard coefficients that supports XML messages aggregator in order to potentially reduce network traffic. The proposed model works by grouping only highly similar messages with the aim to provide messages with high redundancy for web aggregators. Web messages aggregation has become a significant solution to overcome network bottlenecks and congestions by efficiently reducing network volume by aggregating messages together removing their redundant information. The proposed model performance is compared to both K-Means and Principle Component Analysis (PCA) combined with K-Means. Jaccard based clustering model has shown potential performance as it only consumes around %32 and %25 processing time in comparison with K-Means and PCA combined with K-Means respectively. Quality measure (Aggregator Compression Ratio) has overcome both benchmark models
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Hordyk, Adrian R., Neil R. Loneragan, Geoff Diver e Jeremy D. Prince. "A cost-effective alternative for assessing the size of deep-water fish aggregations". Marine and Freshwater Research 62, n. 5 (2011): 480. http://dx.doi.org/10.1071/mf10260.
Testo completoAbstract (sommario):
Acoustic methodologies are important tools for monitoring deep-water fish and have the potential to provide high-precision estimates of aggregation size. However, they can be costly to design and implement for monitoring fish. Data from 2 years of scientific surveys of the spawning aggregations of orange roughy (Hoplostethus atlanticus, Collett, 1889) on the Cascade Plateau, Tasmania, collected using commercial fishing vessels and echosounders, were used to develop a cost-effective approach for estimating the size of deep-water aggregations. Criteria were developed to standardise the identification of orange roughy echo-traces from acoustic data from 23 surveys in 2001 and 19 in 2005. The spawning condition of the fish was monitored simultaneously with the acoustics in each year (n = 29 trawls each year). The volumes of the aggregations were estimated throughout the survey period. Although the precision of the estimated aggregation size is low, large amounts of data can be collected over extended periods by using this approach and the equipment on standard commercial fishing echosounders. Aggregation volumes varied markedly during each spawning season and changes in volume appear to be linked to the spawning biology. Monitoring the spawning biology, therefore, provides crucial complementary information for interpreting estimates of aggregation size from acoustic surveys.
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CALZADA, Catherine, Evelyne VERICEL e Michel LAGARDE. "Low concentrations of lipid hydroperoxides prime human platelet aggregation specifically via cyclo-oxygenase activation". Biochemical Journal 325, n. 2 (15 luglio 1997): 495–500. http://dx.doi.org/10.1042/bj3250495.
Testo completoAbstract (sommario):
There is mounting evidence that lipid peroxides contribute to pathophysiological processes and can modulate cellular functions. The aim of the present study was to investigate the effects of lipid hydroperoxides on platelet aggregation and arachidonic acid (AA) metabolism. Human platelets, isolated from plasma, were incubated with subthreshold (i.e. non-aggregating) concentrations of AA in the absence or presence of hydroperoxyeicosatetraenoic acids (HPETEs). Although HPETEs alone had no effect on platelet function, HPETEs induced the aggregation of platelets co-incubated with non-aggregating concentrations of AA, HPETEs being more potent than non-eicosanoid peroxides. The priming effect of HPETEs on platelet aggregation was associated with an increased formation of cyclo-oxygenase metabolites, in particular thromboxane A2, and was abolished by aspirin, suggesting an activation of cyclo-oxygenase by HPETEs. It was not receptor-mediated because the 12-HPETE-induced enhancement of AA metabolism was sustained in the presence of SQ29,548 or RGDS, which blocked the aggregation. These results indicate that physiologically relevant concentrations of HPETEs potentiate platelet aggregation, which appears to be mediated via a stimulation of cyclo-oxygenase activity.
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Reumers, Joke, Frederic Rousseau e Joost Schymkowitz. "Multiple Evolutionary Mechanisms Reduce Protein Aggregation". Open Biology Journal 2, n. 1 (31 dicembre 2009): 176–84. http://dx.doi.org/10.2174/1874196700902010176.
Testo completoAbstract (sommario):
The folding of polypeptides into stable globular protein structures requires protein sequences with a relatively high hydrophobicity and secondary structure propensity. These biophysical properties, however, also favor protein aggregation via the formation of intermolecular beta-sheets and, as a result, globular structure and aggregation are inextricable properties of protein polypeptides. Aggregates that are enriched in beta-sheet structures have been found in diseased tissues in association with at least twenty different human disorders and the effect of aggregation on protein function include simple loss-of-function but also often a gain of toxicity. Given both the ubiquity and the potentially lethal consequences of protein aggregation, negative selective pressure strongly minimizes aggregation. Various evolutionary strategies keep aggregation in check, including (1) the optimisation of the thermodynamic stability of the protein, which precludes aggregation by burial of the aggregation prone regions in solvent inaccessible regions of the structure, (2) segregation between folding nuclei and aggregation nuclei within a protein sequence, (3) the placement of so-called gatekeeper residues at the flanks of aggregating segments, that reduce the aggregation rate of (partially) unfolded proteins, and (4) molecular chaperones that target aggregation nucleating sequences directly, thereby further suppressing aggregation in a cellular environment. In this review we describe the intrinsic features built into protein sequence and structure that protect against aggregation.
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Putman, S. H., e S.-H. Chung. "Effects of Spatial System Design on Spatial Interaction Models. 1: The Spatial System Definition Problem". Environment and Planning A: Economy and Space 21, n. 1 (gennaio 1989): 27–46. http://dx.doi.org/10.1068/a210027.
Testo completoAbstract (sommario):
Rather little has been published about systematic empirical research on the problem of spatial aggregation and its effects on spatial interaction models. Of the work which has been published, all of it has dealt almost exclusively with single-parameter spatial interaction models. In this article five different aggregation procedures are examined. The experiments were based on the use of a multivariate multiparametric spatial interaction model. A first set of hypotheses tests was performed with respect to the sensitivity of model parameters to spatial aggregation methods. A second set was performed with respect to the sensitivity of model goodness-of-fit to the five spatial aggregation methods. Although questions remain, the results clearly show that the multiparametric model responds well to different aggregation algorithms. Some parameters showed substantial response, as they should, to different zonal aggregations, whereas others are shown to be much less responsive. Further, the results clearly indicate that systematic aggregation procedures generally produce better results than do random procedures. A future paper will continue with a discussion of zone definition criteria, and recommendations will be made with regard to aggregation algorithms.
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Johannes, Mark R. S. "Prey Aggregation Is Correlated with Increased Predation Pressure in Lake Fish Communities". Canadian Journal of Fisheries and Aquatic Sciences 50, n. 1 (1 gennaio 1993): 66–73. http://dx.doi.org/10.1139/f93-008.
Testo completoAbstract (sommario):
Aggregations of prey fish, golden shiner (Notemigonus crysoleucas), were examined during 7 yr of predator manipulations in two lakes to determine whether they responded to changes in predation pressure and varied with time-of-day, age, and habitat. Regression analysis was used to examine aggregation in 12 replicate prey densities from two time periods, two ages, two habitats, three sample series, and seven predator densities. Aggregation was assessed as the variance of mean densities for each treatment combination. Multiple regression and ANCOVA analyses indicated that (1) golden shiner aggregated more during day than night, (2) their aggregation was positively related to predator density, (3) young shiner aggregated more than older ones at low predator densities, and (4) aggregation in older shiner was more responsive to increased predator densities than aggregation in younger shiner. These results provide empirical evidence that golden shiner aggregation patterns respond to predation pressure and the response varies with time and age. These results also suggest that variance in net catches can provide an index of fish aggregation and that aggregation observed at the population level is not solely dependent on species and density, but is a behavioural response mediated by several factors including predators.
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Sils, D., S. E. Rodgers, J. V. Lloyd, K. M. Wilson, D. M. Siebert e F. Bochner. "Inhibition of platelet aggregation and thromboxane production by low concentrations of aspirin in vitro". Clinical Science 74, n. 5 (1 maggio 1988): 491–97. http://dx.doi.org/10.1042/cs0740491.
Testo completoAbstract (sommario):
1. The aspirin concentrations previously reported to inhibit platelet aggregation in vitro (40–500 μmol/l) are much greater than those required in vivo in man (5 μmol/l). 2. Human platelet-rich plasma was incubated with buffer or various aspirin concentrations at 37°C for up to 4.5 h. Platelet aggregation and thromboxane generation were measured in response to collagen (0.4–6.3 μg/ml) and adenosine 5′-pyrophosphate (0.5–4 μmol/l). 3. The concentration of aspirin needed to inhibit platelet aggregation in response to a critical concentration of aggregating agent (lowest concentration to cause greater than 50% aggregation) was lower than that required for higher concentrations of aggregating agent. 4. With more prolonged incubation times with aspirin, lower concentrations of aspirin inhibited platelet aggregation. 5. Inhibition of platelet aggregation and thromboxane formation by 10 μmol/l aspirin was maximal by 90 min. There was progressive inhibition by 3 μmol/l aspirin during incubation for 270 min. By the end of this time there was also significant inhibition by 1 μmol/l aspirin. 6. The apparent discrepancy between inhibitory aspirin concentrations in vivo and those observed in vitro in previous studies appears to have been resolved by extending the incubation time of platelets with low aspirin concentrations, thus mimicking the conditions in vivo.
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GREAR, DANIEL A., e PETER HUDSON. "The dynamics of macroparasite host-self-infection: a study of the patterns and processes of pinworm (Oxyuridae) aggregation". Parasitology 138, n. 5 (24 febbraio 2011): 619–27. http://dx.doi.org/10.1017/s0031182011000096.
Testo completoAbstract (sommario):
SUMMARYObjectives.Among parasites, Taylor's power law identifies a tight relationship in aggregation of macroparasite infection intensity with few exceptions; notably, the nematode family Oxyuridae tends to have higher than expected aggregation. Oxyuridae infect a wide range of mammalian hosts and have a unique reproductive strategy that involves conventional horizontal transmission, as well as re-infection of an already infected host. We asked the question, do the unique aspects of pinworm life-history explain an exception to the widely observed patterns of aggregation of parasite populations?Methods.We empirically examined the differences among Oxyuridae (genus:Syphacia) compared with other helminth (genus:Heligmosomoides) parasite aggregations in 2 rodent hosts with similar ecology: the yellow-necked mouse (Apodemus flavicollis) from Trento, Italy and the white-footed mouse (Peromyscus leucopus) from Pennsylvania, USA. To investigate the effects of pinworm life-history characteristics on generating aggregation, we present a stochastic model that explores aggregation under a range of host-self-infection, parasite death, and transmission scenarios.Results.Oxyuridae parasites had consistently greater aggregation compared to other nematodes regardless of host or parasite species identity, and pinworm aggregation exceeded the range of macroparasite aggregation described previously.Conclusions.Our simulations demonstrate that host-self-infection, on its own, is sufficient to generate aggregation values greater than the predicted values.
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Jin, LeSheng, Ronald R. Yager, Jana Špirková, Radko Mesiar, Daniel Paternain e Humberto Bustince. "OWA aggregation with dual preferences for basic uncertain information". Journal of Intelligent & Fuzzy Systems 40, n. 3 (2 marzo 2021): 4535–44. http://dx.doi.org/10.3233/jifs-201374.
Testo completoAbstract (sommario):
Basic Uncertain Information (BUI) as a newly introduced concept generalized a wide range of uncertain information. The well-known Ordered Weighted Averaging (OWA) operators can flexibly and effectively model bipolar preferences of decision makers over given real valued input vector. However, there are no extant methods for OWA operators to be carried out over given BUI vectors. Against this background, this study firstly discusses the interval transformation for BUI and elaborately explains the reasonability within it. Then, we propose the corresponding preference aggregations for BUI in two different decisional scenarios, the aggregation for BUI vector without original information influencing and the aggregation for BUI vector with original information influencing after interval transformation. For each decisional scenario, we also discuss two different orderings of preference aggregation, namely, interval-vector and vector-interval orderings, respectively. Hence, we will propose four different aggregation procedures of preference aggregation for BUI vector. Some illustrative examples are provided immediately after the corresponding aggregation procedures.
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Sugiyama, T., M. Okuma, F. Ushikubi, S. Sensaki, K. Kanaji e H. Uchino. "A novel platelet aggregating factor found in a patient with defective collagen-induced platelet aggregation and autoimmune thrombocytopenia". Blood 69, n. 6 (1 giugno 1987): 1712–20. http://dx.doi.org/10.1182/blood.v69.6.1712.1712.
Testo completoAbstract (sommario):
Abstract We found a novel platelet aggregating factor in a patient with steroid- responsive immune thrombocytopenic purpura that is associated with defective collagen-induced platelet functions. The aggregating factor and platelet functions were analyzed. The patient, a 58-year-old female, had purpura and prolonged bleeding time despite adequate platelet counts (greater than 140,000/microL) after steroid therapy. The patient's platelets responded normally to all agonists except collagen. Platelet adhesion to collagen fibrils was decreased. The patient's plasma induced irreversible aggregation and ATP release in normal platelet-rich plasma (PRP). This platelet aggregating factor was found in F(ab')2 fragments of the patient's IgG, which caused thromboxane B2 synthesis, elevation of cytoplasmic Ca2+ levels, and phosphorylation of 40 kDa protein in normal platelets. Platelet aggregation by the patient's IgG was inhibited by prostacyclin, dibutyryl cAMP, diltiazem, disodium ethylenediaminetetraacetate, and antimycin A plus iodoacetate, but ADP scavengers, cyclo-oxygenase inhibitors, and heparin had little or no effect. The aggregating activity of the patient's IgG absorbed to and eluted from normal platelets. The patient's Fab fragments did not induce platelet aggregation in eight of ten normal PRP but specifically inhibited aggregation induced by collagen and by the patient's IgG. The major component of an immunoprecipitate made with the patient's IgG from radiolabeled membrane proteins of normal platelet extract had a 62 kDa mol wt, while no such precipitate appeared in extracts of the patient's platelets. These results indicated that platelet aggregation by the patient's IgG was induced by the reaction of an antibody with a specific antigen on the normal platelet membrane through stimulus- response coupling. This antigen may be a collagen receptor on the platelet, most likely a polypeptide of 62 kDa under reducing condition. The defect of collagen-induced aggregation of the patient's platelets seemed to be due to alteration of the membrane protein related to this putative collagen receptor.
49
Sugiyama, T., M. Okuma, F. Ushikubi, S. Sensaki, K. Kanaji e H. Uchino. "A novel platelet aggregating factor found in a patient with defective collagen-induced platelet aggregation and autoimmune thrombocytopenia". Blood 69, n. 6 (1 giugno 1987): 1712–20. http://dx.doi.org/10.1182/blood.v69.6.1712.bloodjournal6961712.
Testo completoAbstract (sommario):
We found a novel platelet aggregating factor in a patient with steroid- responsive immune thrombocytopenic purpura that is associated with defective collagen-induced platelet functions. The aggregating factor and platelet functions were analyzed. The patient, a 58-year-old female, had purpura and prolonged bleeding time despite adequate platelet counts (greater than 140,000/microL) after steroid therapy. The patient's platelets responded normally to all agonists except collagen. Platelet adhesion to collagen fibrils was decreased. The patient's plasma induced irreversible aggregation and ATP release in normal platelet-rich plasma (PRP). This platelet aggregating factor was found in F(ab')2 fragments of the patient's IgG, which caused thromboxane B2 synthesis, elevation of cytoplasmic Ca2+ levels, and phosphorylation of 40 kDa protein in normal platelets. Platelet aggregation by the patient's IgG was inhibited by prostacyclin, dibutyryl cAMP, diltiazem, disodium ethylenediaminetetraacetate, and antimycin A plus iodoacetate, but ADP scavengers, cyclo-oxygenase inhibitors, and heparin had little or no effect. The aggregating activity of the patient's IgG absorbed to and eluted from normal platelets. The patient's Fab fragments did not induce platelet aggregation in eight of ten normal PRP but specifically inhibited aggregation induced by collagen and by the patient's IgG. The major component of an immunoprecipitate made with the patient's IgG from radiolabeled membrane proteins of normal platelet extract had a 62 kDa mol wt, while no such precipitate appeared in extracts of the patient's platelets. These results indicated that platelet aggregation by the patient's IgG was induced by the reaction of an antibody with a specific antigen on the normal platelet membrane through stimulus- response coupling. This antigen may be a collagen receptor on the platelet, most likely a polypeptide of 62 kDa under reducing condition. The defect of collagen-induced aggregation of the patient's platelets seemed to be due to alteration of the membrane protein related to this putative collagen receptor.
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TROIANO, LUIGI, e RONALD R. YAGER. "RECURSIVE AND ITERATIVE OWA OPERATORS". International Journal of Uncertainty, Fuzziness and Knowledge-Based Systems 13, n. 06 (dicembre 2005): 579–99. http://dx.doi.org/10.1142/s0218488505003680.
Testo completoAbstract (sommario):
An important issue when using the OWA aggregation operators is the determination of weights. One approach is to link the weights to a desired attitudinal character for the aggregation. The ME-OWA operators provide a pioneering example of this approach. Here we first present an alternative approach to generating OWA weights with a desired attitudinal character. We accomplish this by using a family of recursive OWA operators (R-OWA). We then generalize this with a class that allows of OWA aggregation by iteration (It-OWA). Both families are built with the constraint of keeping constant the attitudinal character at any recursion or any iteration step. This is particularly useful in aggregations that sequentially add arguments to the aggregation.