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Letteratura scientifica selezionata sul tema "Diel cycle"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 1 febbraio 2022

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Articoli di riviste sul tema "Diel cycle"

Thomas, H., S. E. Craig, B. J. W. Greenan, W. Burt, G. J. Herndl, S. Higginson, L. Salt, E. H. Shadwick e J. Urrego-Blanco. "Direct observations of diel biological CO<sub>2</sub> fixation on the Scotian Shelf, northwestern Atlantic Ocean". Biogeosciences 9, n. 6 (27 giugno 2012): 2301–9. http://dx.doi.org/10.5194/bg-9-2301-2012.

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Abstract. Much of the variability in the surface ocean's carbon cycle can be attributed to the availability of sunlight, triggering surface heat flux and photosynthesis, which in turn regulate the biogeochemical cycling of carbon over a wide range of time scales. The critical processes of this carbon cycle regulation, occurring at time scales of a day or less, however, have undergone few investigations, most of which have been limited to time spans of several days to months. Optical methods have helped to infer short-term biological variability, but complementing investigations of the oceanic CO2 system are lacking. We employ high-frequency CO2 and optical observations covering the full seasonal cycle on the Scotian Shelf, northwestern Atlantic Ocean, in order to unravel diel periodicity of the surface ocean carbon cycle and its effects on annual budgets. Significant diel periodicity in the surface CO2 system occurs only if the water column is sufficiently stable as observed during seasonal warming. During that time biological CO2 drawdown, or net community production (NCP), is delayed for several hours relative to the onset of photosynthetically available radiation (PAR), due to diel cycles in chlorophyll a concentration and to grazing. In summer, NCP decreases by more than 90%, coinciding with the seasonal minimum of the mixed layer depth and resulting in the disappearance of the diel CO2 periodicity in the surface waters.

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Ball, Becky A., e Ross A. Virginia. "Controls on diel soil CO2 flux across moisture gradients in a polar desert". Antarctic Science 27, n. 6 (15 giugno 2015): 527–34. http://dx.doi.org/10.1017/s0954102015000255.

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AbstractThe McMurdo Dry Valleys of Antarctica are a climate-sensitive ecosystem, where future projected climate warming will increase liquid water availability to release soil biology from physical limitations and alter ecosystem processes. For example, many studies have shown that CO2 flux, an important aspect of the carbon cycle, is controlled by temperature and moisture, which often overwhelm biotic contributions in desert ecosystems. However, these studies used either single-point measurements during peak times of biological activity or diel cycles at individual locations. Here, we present diel cycles of CO2 flux from a range of soil moisture conditions and a variety of locations and habitats to determine how diel cycles of CO2 flux vary across gradients of wet-to-dry soil and whether the water source influences the diel cycle of moist soil. Soil temperature, water content and microbial biomass significantly influenced CO2 flux. Soil temperature explained most of the variation. Soil CO2 flux moderately increased with microbial biomass, demonstrating a sometimes small but significant role of biological fluxes. Our results show that over gradients of soil moisture, both geochemical and biological fluxes contribute to soil CO2 flux, and physical factors must be considered when estimating biological CO2 flux in systems with low microbial biomass.

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Thomas, H., S. E. Craig, B. J. W. Greenan, W. Burt, G. J. Herndl, S. Higginson, L. Salt, E. H. Shadwick e J. Urrego-Blanco. "Direct observations of diel biological CO<sub>2</sub> fixation in the oceans". Biogeosciences Discussions 9, n. 2 (24 febbraio 2012): 2153–68. http://dx.doi.org/10.5194/bgd-9-2153-2012.

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Abstract. Much of the variability in the surface ocean's carbon cycle can be attributed to the availability of sunlight, through processes such as heat fluxes and photosynthesis, which regulate over a wide range of time scales. The critical processes occurring on timescales of a day or less, however, have undergone few investigations, and most of these have been limited to a time span of several days to months, or exceptionally, for longer periods. Optical methods have helped to infer short-term biological variability, however corresponding investigations of the oceanic CO2 system are lacking. We employ high-frequency CO2and optical observations covering the full seasonal cycle on the Scotian Shelf, Northwestern Atlantic Ocean, in order to unravel diel periodicity of the surface ocean carbon cycle and its effects on annual budgets. Significant diel periodicity occurs only if the water column is sufficiently stable as observed during seasonal warming. During that time biological CO2 drawdown, or net community production (NCP), is delayed for several hours relative to the onset of photosynthetically available radiation (PAR), due to diel cycles in chlorophyll-a concentration and to grazing, both of which, we suggest, inhibit NCP in the early morning hours. In summer, NCP decreases by more than 90 %, coinciding with the seasonal minimum of the mixed layer depth and resulting in the disappearance of the diel CO2 periodicity in the surface waters.

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Fleming, Sean W., Peter Hudson e Edward J. Quilty. "Interpreting nonstationary environmental cycles as amplitude-modulated (AM) signalsA paper submitted to the Journal of Environmental Engineering and Science." Canadian Journal of Civil Engineering 36, n. 4 (aprile 2009): 720–31. http://dx.doi.org/10.1139/s08-051.

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Inspired by an analogy to AM radio signals, amplitude modulation (AM) is proposed here as a useful view of nonstationary environmental periodicities, and applied to hydrologic and air quality datasets. Both example time series considered exhibit seasonally evolving diel cycles, with large (small) daily cycle amplitudes in summer (winter). The carrier wave is taken to be a sinusoidal daily cycle; this is multiplied by an information signal consisting of a sinusoidal annual cycle, forming an envelope to the diel variations. Our results suggest that amplitude modulation may offer a novel, compact, and accessible perspective, both qualitatively and quantitatively, on the net phenomenological behaviour arising from highly complex, nonlinear, and diverse environmental process dynamics. Physical interpretations, synergies with common environmental time series processing or analysis methods (Kolmogorov-Zurbenko filtering, classical spectral analysis, and singular systems analysis), and potential future research directions are also explored.

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Sweeney, Colm. "The diel carbon cycle of the Biosphere 2 ocean". Ecological Engineering 13, n. 1-4 (giugno 1999): 235–47. http://dx.doi.org/10.1016/s0925-8574(98)00101-3.

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Kopec, B. G., A. M. Lauder, E. S. Posmentier e X. Feng. "The diel cycle of water vapor in west Greenland". Journal of Geophysical Research: Atmospheres 119, n. 15 (11 agosto 2014): 9386–99. http://dx.doi.org/10.1002/2014jd021859.

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Carniatto, Natália, Rosemara Fugi, Geuza Cantanhêde, Éder André Gubiani e Norma Segatti Hahn. "Effects of flooding regime and diel cycle on diet of a small sized fish associated to macrophytes". Acta Limnologica Brasiliensia 24, n. 4 (12 aprile 2013): 363–72. http://dx.doi.org/10.1590/s2179-975x2013005000007.

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AIM: In this paper we assessed the effects of flooding (low and high water period) on the feeding activity and diet composition of Serrapinus notomelas in patches of the macrophyte Eichhornia azurea in a shallow floodplain lake (upper Paraná River Floodplain, Brazil). We also assessed the variations of diet composition and feeding activity along the diel cycle. METHODS: Traps were used to catch the fish inside of macrophyte patches monthly from June/2007 to May/2008. A total of 1038 stomachs were examined. We assessed the feeding activity with the mean stomach fullness degree method. To summarize and support the results of diet composition in the different periods (low and high water periods) and times (dawn, light period, and dusk), was applied a nonmetric multidimensional scaling (NMS). RESULTS: The feeding activity of S. notomelas did not differ between low and high water periods, but it differed along the diel cycle. The feeding activity was higher during the light period and dusk, at both the low and high water period. The diet composition differed significantly between low and high water periods, and also along the diel cycle. In the low water the diet of S. notomelas was composed mainly by algae and in the high water by Cladocera. Algae were consumed mainly during the light period while Cladocera in dawn and dusk. CONCLUSIONS: Our results indicate that the oscillations in the water level affect the diet composition, but not the feeding activity of S. notomelas. These seasonal changes are probably related to the temporal abundance of food resources, thus, when Cladocera density was low (low water), S. notomelas consumed mainly algae but when Cladocera was more abundant (high water), it became a common food resource.

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Watras, Carl J., Kenneth A. Morrison, Noah R. Lottig e Timothy K. Kratz. "Comparing the diel cycles of dissolved organic matter fluorescence in a clear-water and two dark-water Wisconsin lakes: potential insights into lake metabolism". Canadian Journal of Fisheries and Aquatic Sciences 73, n. 1 (gennaio 2016): 65–75. http://dx.doi.org/10.1139/cjfas-2015-0172.

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The cycling of organic carbon is fundamental to aquatic ecosystems, reflecting processes that extend from terrestrial watersheds to fish. Here, we use embedded fluorescence sensors that sample at high frequency to investigate the daily dynamics of a proxy for the major pool of organic carbon (chromophoric dissolved organic matter, CDOM) in a clear-water Wisconsin lake (∼3 mg C·L−1). We compare the diel CDOM cycle in this lake with cycles observed previously in two dark-water lakes (10 to 20 mg C·L−1). Despite differences in DOM quality and quantity, diel fluorescence cycles were evident in the epilimnia and hypolimnia of all three lakes. The amplitude differed among lakes, but the timing of the diel cycles was similar, with increases in fluorescence during nighttime and decreases during daylight (except in the aphotic hypolimnion of the darkest lake). The amplitude of the diel cycle increased with increasing DOM concentration, and estimates of DOM turnover based on the magnitude of oscillation ranged from 0.28 mg C·L−1·day−1 in the darkest lake to 0.14 mg C·L−1·day−1 in the clear lake. Independent estimates of free water metabolism based on the daily dynamics of O2 or CO2 were in general agreement, ranging from 0.32 to 0.06 mg C·L−1·day−1. Although absolute rates of turnover varied directly with DOM concentration, relative rates were highest in clear waters (∼5%·day−1). We conclude that these daily oscillations may be a common property of lakes and that they may provide insights into internal DOM processing over short time scales.

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Briggs, Nathan, Kristinn Guðmundsson, Ivona Cetinić, Eric D'Asaro, Eric Rehm, Craig Lee e Mary Jane Perry. "A multi-method autonomous assessment of primary productivity and export efficiency in the springtime North Atlantic". Biogeosciences 15, n. 14 (25 luglio 2018): 4515–32. http://dx.doi.org/10.5194/bg-15-4515-2018.

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Abstract. Fixation of organic carbon by phytoplankton is the foundation of nearly all open-ocean ecosystems and a critical part of the global carbon cycle. But the quantification and validation of ocean primary productivity at large scale remains a major challenge due to limited coverage of ship-based measurements and the difficulty of validating diverse measurement techniques. Accurate primary productivity measurements from autonomous platforms would be highly desirable due to much greater potential coverage. In pursuit of this goal we estimate gross primary productivity over 2 months in the springtime North Atlantic from an autonomous Lagrangian float using diel cycles of particulate organic carbon derived from optical beam attenuation. We test method precision and accuracy by comparison against entirely independent estimates from a locally parameterized model based on chlorophyll a and light measurements from the same float. During nutrient-replete conditions (80 % of the study period), we obtain strong relative agreement between the independent methods across an order of magnitude of productivities (r2=0.97), with slight underestimation by the diel cycle method (−19 ± 5 %). At the end of the diatom bloom, this relative difference increases to −58 % for a 6-day period, likely a response to SiO4 limitation, which is not included in the model. In addition, we estimate gross oxygen productivity from O2 diel cycles and find strong correlation with diel-cycle-based gross primary productivity over the entire deployment, providing further qualitative support for both methods. Finally, simultaneous estimates of net community productivity, carbon export, and particle size suggest that bloom growth is halted by a combination of reduced productivity due to SiO4 limitation and increased export efficiency due to rapid aggregation. After the diatom bloom, high Chl a-normalized productivity indicates that low net growth during this period is due to increased heterotrophic respiration and not nutrient limitation. These findings represent a significant advance in the accuracy and completeness of upper-ocean carbon cycle measurements from an autonomous platform.

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Liu, Riyue, Yaxin Liu, Yue Chen, Yuanchao Zhan e Qinglu Zeng. "Cyanobacterial viruses exhibit diurnal rhythms during infection". Proceedings of the National Academy of Sciences 116, n. 28 (24 giugno 2019): 14077–82. http://dx.doi.org/10.1073/pnas.1819689116.

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As an adaptation to the daily light–dark (diel) cycle, cyanobacteria exhibit diurnal rhythms of gene expression and cell cycle. The light–dark cycle also affects the life cycle of viruses (cyanophages) that infect the unicellular picocyanobacteriaProchlorococcusandSynechococcus, which are the major primary producers in the oceans. For example, the adsorption of some cyanophages to the host cells depends on light, and the burst sizes of cyanophages are positively correlated to the length of light exposure during infection. Recent metatranscriptomic studies revealed transcriptional rhythms of field cyanophage populations. However, the underlying mechanism remains to be determined, as cyanophage laboratory cultures have not been shown to exhibit diurnal transcriptional rhythms. Here, we studied variation in infection patterns and gene expression ofProchlorococcusphages in laboratory culture conditions as a function of light. We found three distinct diel-dependent life history traits in dark conditions (diel traits): no adsorption (cyanophage P-HM2), adsorption but no replication (cyanophage P-SSM2), and replication (cyanophage P-SSP7). Under light–dark cycles, each cyanophage exhibited rhythmic transcript abundance, and cyanophages P-HM2 and P-SSM2 also exhibited rhythmic adsorption patterns. Finally, we show evidence to link the diurnal transcriptional rhythm of cyanophages to the photosynthetic activity of the host, thus providing a mechanistic explanation for the field observations of cyanophage transcriptional rhythms. Our study identifies that cultured viruses can exhibit diurnal rhythms during infection, which might impact cyanophage population-level dynamics in the oceans.

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Più fonti

Tesi sul tema "Diel cycle"

Currie, Rebecca J. (Rebecca Jean). "Upper and Lower Temperature Tolerances of Three Freshwater Game-Fish Species Exposed to Cycling Temperatures". Thesis, University of North Texas, 1995. https://digital.library.unt.edu/ark:/67531/metadc279105/.

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A total of 670 critical thermal maxima (CTMax) and minima (CTMin) were determined for three freshwater fishes acclimated to three constant temperatures and a diel regimen cycling between the lowest and highest acclimation temperatures. In all species temperature tolerance was directly related to acclimation temperature and slopes relating these variables indicate that acclimation temperature has a greater influence on tolerance of low rather than high temperatures. CTMax and CTMin values generated following exposure to 32 days of oscillating temperatures indicate that in general, fishes had temperature tolerance acclimation states consistent with the average temperature and not either the highest or lowest temperature of the diel cycle.

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Papadopoulou, Sofia. "The influence of diel cycles on the bacterial community composition of two boreal lakes : A case study in Jämtland". Thesis, Uppsala universitet, Limnologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447209.

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In the Boreal region, the length of day and night varies extremely over the year and organisms are exposed to different diel (24 h) fluctuations of light and temperature. Among them are pelagic populations of bacteria that are ubiquitous in freshwater ecosystems. The structure of prokaryotic assemblages in lakes is regulated by both abiotic and biotic parameters known to have diel patterns; yet, knowledge on changes of the active bacterial community composition (aBCC) over diel cycles is limited, especially at short temporal scales. Here, measurements of physicochemical parameters, nutrient levels and chlorophyll a concentrations, characterization of the carbon pool and 16S rRNA sequencing were used to elucidate the aBCC in a peat bog and the oligotrophic lake Klocka in Jämtland county, Sweden. I show that the activity of bacterioplankton communities remained relatively stable at 6-h intervals and did not follow any diel patterns during an uneven light regime period in June. However, the activity of peat bog communities changed in a cyclic pattern over three diel cycles during an even light period in September, whereas diel changes did not substantially differentiate between sampling periods and among depths in Klocka. The results of the thesis provide valuable insights into the importance of diel cycles in bacterial diversity and community dynamics in lentic habitats.

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Barkdull, Natalie Shepherd. "Impacts of Glacial Meltwater on Geochemistry and Discharge of Alpine Proglacial Streams in the Wind River Range, Wyoming, USA". BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8590.

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Shrinking alpine glaciers alter the geochemistry of sensitive mountain streams by exposing reactive freshly-weathered bedrock and releasing decades of atmospherically-deposited trace elements from glacier ice. Changes in the timing and quantity of glacial melt also affect discharge and temperature of alpine streams. To investigate the effects of glacier ice melt on the geochemistry and hydrology of proglacial streams in the arid Intermountain West, we sampled supraglacial meltwaters and proglacial streams in the Dinwoody Creek watershed in the Wind River Range, Wyoming during late summer 2015, when the contributions of glacier meltwater were highest. Supraglacial meltwater was enriched in 8 trace elements (Cd, Co, Cu, MeHg, Mn, Pb, THg, Zn) relative to proglacial meltwaters. Concentrations of major ions (Mg2+, K+, Na+, Ca2+, SO42-) and the remaining 30+ analyzed trace elements were enriched in proglacial streams relative to supraglacial meltwater. To evaluate the diurnal effects of glacial meltwater on the chemistry and hydrology of proglacial streams, we collected hourly water samples of Dinwoody Creek and deployed loggers to monitor water depth, temperature, and specific conductance (SPC) at 15-min intervals over a 1-week period. The influx of glacial meltwater between 10:00 and 20:00 diluted solute concentrations and affected the relative enrichment/depletion of highly soluble elements (major ions, alkaline earth elements), less than REEs. Stable isotopes of H and O (δD, δ18O) in Dinwoody Creek were more depleted during peak runoff (10:00 – 20:00) than base flow, reflecting contributions from isotopically depleted glacial meltwaters. Looping hysteresis patterns were observed between water depth versus DO, pH, temperature and SPC in glaciated streams. Hysteresis patterns were affected by changes in weather and varied depending on the type of stream (glaciated versus non-glaciated) and the distance to glacier toe. Combination of multiple hydrologic tracers (solute concentrations, high frequency logger data, stable isotopes) shows strong potential to improve estimates of glacial meltwater contributions to Dinwoody Creek. Our results suggest that elevated concentrations of heavy metals in glacier ice melt across the Intermountain West may negatively impact sensitive alpine streams.

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Grácio, Ana Rita Pereira. "Diel variation in movement patterns and habitat use by the near-threatened cabrera vole in mediterranean farmland". Master's thesis, Universidade de Évora, 2016. http://hdl.handle.net/10174/18612.

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As variações circadianas no comportamento animal e o seu impacto nas populações constituem desafios importantes em ecologia e conservação. Nesta tese documentam-se as variações circadianas no uso do habitat e padrões de movimento pelo rato de Cabrera, em habitats Mediterrânicos fragmentados. O estudo baseou-se no radio-seguimento de indivíduos em habitats dominados por herbáceas e arbustos. Os resultados indicaram que a proporção de tempo despendido em deslocações, a distância percorrida, e a selecção do tipo de vegetação, estão fortemente interrelacionados, variando consideravelmente ao longo de diferentes períodos do dia. Os ratos movimentaram-se mais frequentemente e maiores distâncias nos períodos diurnos, durante os quais as áreas dominadas por herbáceas foram usadas mais intensivamente. Durante a estação seca houve alguma tendência para a diminuição dos movimentos durante as horas mais quentes. Estes resultados são discutidos no sentido de mostrar como indicadores comportamentais podem contribuir para melhorar a gestão e conservação da espécie; ABSTRACT: Understanding the circadian variations in species behaviour and its impacts on population is a challenging topic in ecology and conservation. This thesis documents the circadian variations in habitat use and movement patterns by Cabrera voles in fragmented Mediterranean farmland. The study was based on radiotracking data of individuals living in habitat patches dominated by wet grasses and shrubs. Results indicated that the proportion of time animals spent moving, the distance moved and the selection strength of vegetation were closely linked behavioural traits, which varied considerably across the 24 hour cycle. Voles moved more frequently and over larger distances during daytime, which was when wet grasses were used more intensively. During the dry season there was some tendency for a decrease in movement activity during the hottest hours of the day. These results are used to discuss how behavioural indicators may be useful to improve conservation management of the species.

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Neves, Leonardo Mitrano. "Estrutura e diversidade das assembleias de peixes recifais na Ba?a da Ilha Grande: import?ncia de vari?veis f?sicas, da estrutura do habitat e varia??es temporais de curto prazo". Universidade Federal Rural do Rio de Janeiro, 2013. https://tede.ufrrj.br/jspui/handle/jspui/2485.

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Rocky reef fish assemblages change along extreme environmental conditions gradients; both spatial (across gradients of distance from the river mouths) and short term temporal (diel cycle of light intensity). Moreover, changes in connection to habitat heterogeneity can occur, even for tropical rocky reefs with a more homogenous habitat structure. Knowledge of the way that fish assemblages respond to these changes is fundamental to identify the variables that determine spatial patterns and to predict how impacts in great or low intensity can affect diversity. The main aims of this study were: (1) to determine influence of physical (distance from river mouth and wave exposure), biological (benthic cover) and structural (substratum height and number of shelters) variables in structuring fish assemblages, species richness, abundance, biomass and trophic groups diversity; (2) to assess diel changes in composition and structure of fish assemblages; (3) to relate changes in species composition (beta diversity) with habitat heterogeneity for a small scale (among transects in a given area), and the relationship between beta and alfa diversity (species richness, richness estimation and Shannon diversity). Subaquatic visual census were carried out in Ilha Grande coastal reefs, encompassing (1) islands distributed along a spatial gradient of distance from river mouth; (2) six different time periods, i.e., sunrise (06:00h), morning (08:30h), afternoon (14:00h), sunset (17:30h), early night (19:30h) and night (21:00h) in two shallow coastal reef; and (3) in transect in four areas to assess beta biodiversity. Habitat structure (benthic cover and topographic complexity) assessment was performed (objectives 1 and 3). The distance from river mouth explained from 12.4% to 38.2% of the estimated components of variation (ECV) of PERMANOVA for all analyzed response variables, playing a major role in determining spatial patterns of fish assemblages. Differences between reefs close and far from river mouth reached a maximum of 4.5x for richness, 11x for biomass and 10x for abundance. The substrate height was positively related to fish abundance, species richness and trophic groups diversity (ECV between 7.3 % and 17.4%), whereas the number of shelters was positively associated to small-sized species abundance such as Stegastes fuscus, Emblemariopsis signifer and Scartella cristata. Benthic cover had significant influence to determine spatial pattern in fish assemblage structure and diversity of trophic groups (ECV = 8% and 10%, respectively), but not in species richness, biomass and fish abundance. Wave exposure had significant influence on fish assemblage structure only (ECV = 10%). The fish assemblage changes drastically along diel cycle. Species richness and fish abundance were at the highest during the period of the day with intermediary values at twilight periods, and at the lowest during the night. The highest difference in assemblage structure was found between the periods of the day and the night. The families Sciaenidae, mainly represented by Pareques acuminatus, and Pempheridae represented by Pempheris schomburgkii were more abundant during the night, whereas Haemulidae Haemulon steindachneri, Pomacentridae Abudefduf saxatilis, Chaetodondidae Chaetodon striatus, and Labrisomidae Malacoctenus delalandii were more abundant during the day. The twilight periods were similar in assemblage structure, and had as characteristics species of the day (H. steindachneri, M. acutirostris) and the night (P. acuminatus), reflecting a transitional period. Significant positive relationship was detected between habitat heterogeneity and beta diversity. The area with more ix homogeneous habitat and low variation in fish assemblage was dominated by little threedimensionally complex organisms (zoanthids), while areas that had fleshy algae, turf and zoanthids with a more even percentage cover had higher heterogeneity and beta diversity. For all measures of examined alfa diversity, the area with more heterogeneous habitat and with the highest beta diversity had the highest alfa diversity compared with areas with more homogenous habitat e lowest beta diversity. However, positive relationship between alfa and beta diversity was significant for species richness, but not for estimate of richness and Shannon index. This study demonstrated that changes in assemblages in spatial and short term (from transects to 10 km, and diel cycle) scales may be attributed to changes in local habitat structure, both composition of dominant benthic organisms and habitat heterogeneity and can be associated to behavioral characteristics mainly related to strategies of food acquirement and protection against predation
As assembleias de peixes recifais variam atrav?s de gradientes de mudan?as extremas nas condi??es ambientais, tanto espaciais (ao longo de gradientes de dist?ncia da foz de rios) quanto em escalas temporais curtas (ao longo do ciclo di?rio de intensidade luminosa). Al?m disto, varia??es em resposta ao n?vel de heterogeneidade do habitat tamb?m podem ocorrer, mesmo entre recifes rochosos situados fora de intensos gradientes ambientais. Entender como as assembleias de peixes respondem a tais mudan?as ? fundamental para identificar vari?veis determinantes dos padr?es espaciais e predizer como impactos de grande e pequena intensidade podem afetar os padr?es de diversidade. Os principais objetivos deste estudo foram: (1) determinar a influ?ncia de vari?veis f?sicas (dist?ncia da foz do rio e exposi??o a ondas), biol?gicas (cobertura b?ntica) e estruturais (altura do substrato e n?mero de ref?gios) na estrutura??o das assembleias de peixes, riqueza de esp?cies, abund?ncia, biomassa e diversidade dos grupos tr?ficos; (2) avaliar as mudan?as ao longo do ciclo di?rio na composi??o e estrutura da assembleia de peixes recifais; (3) relacionar a varia??o na composi??o de esp?cies (beta diversidade) com a heterogeneidade do habitat, para uma pequena escala (entre transectos de uma mesma ?rea), e as rela??es entre a beta diversidade e medidas de diversidade alfa (riqueza de esp?cies, estimativa da riqueza e diversidade de Shannon). Para tal, censos visuais subaqu?ticos foram realizados (1) em cost?es rochosos da ba?a da Ilha Grande, em ilhas localizadas atrav?s de um gradiente de dist?ncia da foz de rios; (2) em seis diferentes hor?rios, compreendendo o amanhecer (06:00h), manh? (08:30h), tarde (14:00h), anoitecer (17:30h) e in?cio da noite (19:30h) e noite (21:00h) em dois recifes rochosos rasos; e (3) em transectos de quatro ?reas para avaliar diversidade beta. Avalia??es da estrutura do habitat (cobertura b?ntica e complexidade topogr?fica) foram realizadas (para objetivos 1 e 3). A dist?ncia da foz do rio explicou entre 12,4% a 38,2% da estimativa dos componentes de varia??o (ECV) da PERMANOVA de todas as vari?veis respostas analisadas, desempenhando um papel principal nos padr?es espaciais da assembleia de peixes. Diferen?as entre recifes pr?ximos e distantes da foz atingiram um m?ximo de at? 4,5x para a riqueza, 11x para a biomassa e 10x para a abund?ncia. A altura do substrato foi positivamente relacionada com a abund?ncia de peixes, riqueza de esp?cies e diversidade dos grupos tr?ficos (ECV entre 7,3% a 17,4%), enquanto o n?mero de ref?gios foi associado positivamente com a abund?ncia de esp?cies de pequeno porte, como Stegastes fuscus, Emblemariopsis signifer e Scartella cristata. O efeito da cobertura b?ntica foi significativo em determinar os padr?es espaciais da estrutura da assembleia de peixes e da diversidade dos grupos tr?ficos (ECV = 8% e 10%, respectivamente), por?m n?o foram observadas influ?ncias significativas da cobertura b?ntica na riqueza de esp?cies, biomassa e abund?ncia. A exposi??o ?s ondas teve um efeito significativo apenas para a estrutura da assembleia de peixes (ECV = 10%). As assembleias de peixes variaram drasticamente ao longo do ciclo di?rio. A riqueza de esp?cies e a abund?ncia de peixes foram maiores durante os hor?rios do dia, com valores intermedi?rios nos hor?rios crepusculares e atingiram os menores valores durante a noite. Maiores diferen?as na estrutura da assembleia foram observadas entre o per?odo diurno e noturno. Durante a noite, as fam?lias Sciaenidae, representado por Pareques acuminatus, e Pempheridae vii representado por Pempheris schomburgkii foram mais abundantes, enquanto Haemulidae Haemulon steindachneri, Pomacentridae Abudefduf saxatilis, Chaetodondidae Chaetodon striatus, e Labrisomidae Malacoctenus delalandii foram abundantes durante o dia. Os hor?rios crepusculares foram semelhantes entre si, sendo caracterizados por esp?cies tanto dos hor?rios do dia (H. steindachneri, M. acutirostris) quanto da noite (P. acuminatus), refletindo esse per?odo de transi??o. Rela??es positivas significativas foram detectadas entre a heterogeneidade do habitat e a beta diversidade. A ?rea com habitat mais homog?neo e de menor varia??o na composi??o da assembleia foi dominada por organismos tridimensionalmente pouco complexos (zoant?deos), enquanto a ?reas que apresentaram algas frondosas, matriz de algas epil?ticas (MAE) e zoant?deos com uma percentagem de cobertura mais equitativa, tiveram a maior heterogeneidade do habitat e beta diversidade. Para todas as medidas de diversidade alfa utilizadas, a ?rea com habitat mais heterog?neo e com maior beta diversidade, apresentou uma diversidade alfa maior do que a ?rea com habitat mais homog?neo e de menor beta diversidade. Entretanto, as rela??es positivas entre a beta diversidade e a diversidade alfa foram significativas apenas para a riqueza de esp?cies, e n?o para a estimativa da riqueza e a diversidade de Shannon. Este estudo demonstrou que varia??es nas assembleias em escalas espaciais e temporais curtas (desde entre transectos at? 10 km, e ao longo do ciclo di?rio) podem ser atribu?das a mudan?as na estrutura dos habitats locais, tanto na composi??o dos organismos bent?nicos dominantes quanto na heterogeneidade do habitat e podem ser associadas a caracter?sticas comportamentais principalmente associadas a estrat?gias de obten??o de alimento e prote??o contra preda??o

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Giron, Aline Karen Santana. "Variaçãos sazonal e migração vertical da comunidade zooplanctônica (exceto Rotifera) do reservatório de Itupararanga, Votorantim, SP". Universidade Federal de São Carlos, 2013. https://repositorio.ufscar.br/handle/ufscar/1528.

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The present study aimed to analyse the Itupararanga reservoir zooplankton community in relation to diel and seasonal variation and vertical migration of the organisms in the water column and verify if there are patterns of variation. For this two samples were performed in the reservoir in 2011: in February, rainy period and in july, dry period. The collections were performed in diel cycle (every four hours), in three different layers of the water column (surface, middle and bottom) and in two environments of the reservoir (dam and central body). Stratification in the water column was observed for both environments and both periods. 25 species of the mesozooplankton were identified. Chaoborus larvae were more abundant in February in relation to july and the opposite was observed for cladocerans and copepods. Among the copepods, dominance of juvenile stages (nauplii and copepodites) was observed in both environments and periods. Among the adults of copepods the specie more abundant was Notodiaptomus deitersi (1.298 org.m3) and among the cladocerans was Bosmina freyi (32.282 org.m3). The peak of the total density of the zooplankton community occurred during the dry period in the dam environment with 81.211 org.m3. Chaoborus exercised predation pressure on microcrustaceans during the rainy period. During the dry period, in the absence of Chaoborus in the water column, cladocerans and copepods were more ecologically successful. For all of the groups was observed the usual pattern of vertical migration; reverse migration was not observed. Despite predation pressure, the microcrustaceans not altered their vertical distribution for decrease special overlap with Chaoborus. For all of the groups the migration pattern adopted seems a result of escape from predators and search for good food resources.
O presente estudo teve como objetivo analisar a comunidade zooplanctônica do reservatório de Itupararanga com relação à variação nictemeral, sazonal e migração vertical dos organismos na coluna de água e verificar a existência de padrões de variação. Para isto foram realizadas duas coletas no reservatório no ano de 2011: em fevereiro, período chuvoso e em julho, período seco. As coletas foram realizadas no ciclo nictemeral (de 4 em 4 horas), em três diferentes estratos da coluna de água (superfície, meio e fundo) e em dois pontos do reservatório (barragem e corpo central). Foi observada estratificação na coluna de água para ambos os pontos e em ambos os meses. Foram identificadas 25 espécies do mesozooplâncton. Larvas de Chaoborus spp. foram mais abundantes em fevereiro com relação a julho sendo o contrário observado para Cladocera e Copepoda. Entre os Copepoda observou-se dominância dos estágios juvenis (náuplios e copepoditos) para ambos os pontos e em ambos os períodos. Entre os adultos a espécie de Copepoda mais abundante foi Notodiaptomus deitersi (1.298 org.m3) e entre os Cladocera a espécie mais abundante foi Bosmina freyi (32.282 org.m3). O pico de densidade total da comunidade zooplanctônica ocorreu durante o período seco no ponto da barragem com 81.211 org.m3. Chaoborus exerceu pressão de predação sobre os microcrustáceos durante o período chuvoso. Durante o seco, na ausência de Chaoborus na coluna de água, foi observado maior sucesso ecológico para Cladocera e Copepoda. Para todos os grupos foi observado o padrão comum de migração vertical; migração reversa não foi observada. Apesar da pressão de predação, os microcrustáceos não ajustaram sua distribuição vertical de forma a diminuir a sobreposição espacial com Chaoborus. Para todos os grupos considerados o padrão de migração adotado parece ter sido resultado da fuga de predadores e busca por boas condições alimentares.

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Verspecht, Florence. "Temporal dynamics of the coastal water column". University of Western Australia. School of Environmental Systems Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0097.

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Field measurements and numerical modelling of the shallow coastal waters offshore in south-western Australia were used to describe changes in the water column's vertical structure and the biological response on temporal scales of the order of hours and days. A cycle of chlorophyll a concentration, primary production, and photosystem II function on a diel timescale, which was related to changes in the solar irradiance and thermal structure, was identified. The diel cycle included (1) vertically well-mixed (or weakly linear) conditions in density and chlorophyll a early in the morning, resulting from vertical mixing through penetrative overnight convection; (2) depleted chlorophyll a concentration in the surface layer during the middle of the day due to photoinhibition; (3) an increased chlorophyll a concentration in the bottom layer by late afternoon due to optimum light conditions; and (4) the formation of a chlorophyll a break point (CBP) at the thermocline, which migrated downwards with the deepening surface mixed layer. On a longer timescale (days), moored acoustic instruments were used to derive echo level (EL), which approximated suspended particulate matter (SPM). Wind events ultimately controlled SPM, a conclusion based on (1) elevated EL during high windgenerated turbulence and bed shear stress, (2) positive time-lagged correlations between wind speed and EL at three field sites with different exposures to wave action, and (3) significant negative correlations between wind speed and depth-differentiated echo level (d(EL)/dz) at all sites. Sea breezes produced a similar response in EL through the water column to a small storm event, and wind-driven SPM resuspension resulted in a reduction in the sub-surface light climate (kd). Near-bed dissolved oxygen concentrations varied in accord with elevated wind speeds, EL and kd, highlighting a possible suppression of photosynthesis. One-dimensional modelling revealed that wind stirring was most often the dominant process in these waters. It was found that for a brief period during thermal stratification there was shear production of turbulent instabilities that migrated from the thermocline to the surface and the seabed. Convective cooling was not able to mix the water column entirely overnight without the addition of wind, and minimum wind speeds were determined for this complete vertical mixing. Bottom-generated turbulence was limited to a small region above the bed, and was deemed insignificant compared with mixing generated at the surface. Minimum wind speeds required for de-stratification and prevention of stratification were determined for summer, autumn and winter. A hypothetical desalination outfall was simulated for all seasons and it was concluded that positioning of the discharge at middepth was preferable compared to at the seabed. The results of this thesis advance the current knowledge of coastal biophysical oceanography and provide new insights into the temporal dynamics of the coastal water column of south-western Australia.

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Goebel, Patrick C. "Distribution, Abundance and Movement of Fish among Seagrass and Mangrove Habitats in Biscayne Bay". NSUWorks, 2016. http://nsuworks.nova.edu/occ_stuetd/403.

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Inshore tropical and subtropical estuaries harbor a relatively high abundance and diversity of organisms. Specifically within estuaries, mangrove and seagrass habitats provide shelter and food for a plethora of organisms, through some or all their life histories. Given the biological connection between offshore coral reefs and coastal estuaries, there is a critical need to understand the underlying processes that determine distribution and abundance patterns within mangrove-seagrass habitats. The predatory fish assemblage within the mangrove and seagrass beds of Biscayne Bay, Florida (USA), was examined over 24-hr. time periods along a distance and habitat gradient from the mangrove edge and nearshore environment (0–300 m) to farshore (301–700 m) seagrass beds. This thesis also investigated the occurrence, distribution and timing of reef fish movement between offshore coral reef habitat and inshore seagrass beds over 24-hr periods. Results indicate that fish predators differed over both the sampling period and with distance from mangrove edge. The results also demonstrated reef fishes move into Biscayne Bay at dusk and exit at dawn by utilizing Broad Creek Channel as a passageway. This work supports the idea of diel migration of selected reef fishes to inshore seagrass beds and highlights the importance of connective channels between habitats. The results suggest that the degradation or loss of seagrass habitat could differentially impact the life-history stages of reef fish species.

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Vaughan, Chester Dewey. "Cycle-to-cycle control of reconfigurable die sheet metal forming". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17953.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (leaves 85-86).
This research addresses cycle to cycle control as applied to a sheet metal stretch forming process. More specifically, it attempts to validate the use of cycle to cycle (CtC) control for a multiple input-multiple output process. The work presented in this thesis attempts to answer some basic manufacturing questions. The first is, "Can a multivariable discrete system control theory be used to model a sheet metal shape control process?" The second question is, "Does such a "cycle to cycle control system provide a significant improvement over the present industry standard control methods". To address these questions, CtC control methods are applied to a reconfigurable die stretch forming process. The theoretical foundation of the stretch forming process is presented. Several open and closed loop control methods are discussed. A methodology for evaluating the part quality is defined in terms of the process mean shift and variance. The system dynamics are presented in terms of unwanted process disturbances. In-depth experiments are then performed to quantify the process performance under CtC control. The CtC process yield is compared the process yield of an identical process under open loop control using the Expected Quality Loss Function. It is shown that implementation of the reconfigurable die under CtC control eliminates the process mean shift but increases the part variation. It is also shown that CtC control produces the highest yield of acceptable parts.
by Chester Dewey Vaughan, IV.
S.M.

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Meier, Fabian. "Solar thermochemical cycle for ammonia production based on aluminium-based redox reactions". Zürich : Eidgenössische Technische Hochschule, 2007. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=310.

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Libri sul tema "Diel cycle"

Gripari, Pierre. Histoire du méchant Dieu: Cycle secondaire. Lausanne: L'Age d'homme, 1988.

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Breaking the vicious cycle: Intestinal health through diet. Kirkton, Ontario: Kirkton Press, 1994.

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Brown, Ruth. Diez semillas. Valencia: Brosquil Edicions, 2003.

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Shannon, Marilyn M. Fertility, cycles & nutrition: How your diet affects your menstrual cycles & fertility. 3^a ed. Cincinnati, Ohio: Couple to Couple League International, 2001.

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Puckett, Ruby P. Food, nutrition, and medical nutrition therapy through the life cycle. 4^a ed. Dubuque, Iowa: Kendall/Hunt, 2009.

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Hollins-Martin, Caroline, Olga van den Akker, Colin Martin e Victor R. Preedy, a cura di. Handbook of diet and nutrition in the menstrual cycle, periconception and fertility. The Netherlands: Wageningen Academic Publishers, 2014. http://dx.doi.org/10.3920/978-90-8686-767-7.

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1947-, Sachs Judith, a cura di. Fat madness: How to stop the diet cycle and achieve permanent well-being. New York, New York: Berkley Books, 1994.

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Dell'Anna, Giuseppe. Dies critici: La teoria della ciclicità delle patologie nel XIV secolo. Galatina (Lecce): M. Congedo, 1999.

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Francis, Raymond. Never be fat again: The 6-week cellular solution to permanently break the fat cycle. Deerfield Beach, Fla: Health Communications, 2007.

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Powell, Chris. Choose to lose: The 7-day carb cycle solution. New York: Hyperion, 2011.

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Capitoli di libri sul tema "Diel cycle"

Prézelin, Barbara B. "Diel periodicity in phytoplankton productivity". In The Daily Growth Cycle of Phytoplankton, 1–35. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2805-6_1.

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Markager, Stiig, Anne-Mette Jespersen, Tom Vindbæk Madsen, Elisa Berdalet e Richard Weisburd. "Diel changes in dark respiration in a plankton community". In The Daily Growth Cycle of Phytoplankton, 119–30. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2805-6_10.

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Martin-Jézéquel, Véronique. "Effect of Si-status on diel variation of intracellular free amino acids in Thalassiosira weissflogii under low-light intensity". In The Daily Growth Cycle of Phytoplankton, 159–67. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2805-6_14.

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Warmer, Rüdiger. "Die Modernisierung der Informationstechnologie – eine nicht (nur) technische Herausforderung". In Der Enterprise Transformation Cycle, 337–45. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-22694-7_17.

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Weimar, Anne-Marie. "Die Hartz-Kommission im “Policy Cycle”". In Die Arbeit und die Entscheidungsprozesse der Hartz-Kommission, 41–78. Wiesbaden: VS Verlag für Sozialwissenschaften, 2004. http://dx.doi.org/10.1007/978-3-322-80558-4_2.

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Stibbe, Rosemarie. "Globales Life-Cycle-Controlling (LCC): Footprint-Indikatoren erobern die Praxis". In Globales Life-Cycle-Controlling, 5–38. Wiesbaden: Springer Fachmedien Wiesbaden, 2017. http://dx.doi.org/10.1007/978-3-658-15660-2_2.

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Steinhoff, Peter F. J. "Der Enterprise Transformation Cycle – Ein praxiserprobtes Modell für die erfolgreiche Unternehmenstransformation". In Der Enterprise Transformation Cycle, 3–20. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-22694-7_1.

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Sang, Nianli, e Antonio Giordano. "Cell Cycle Genes: pRb and p53". In When Cells Die II, 339–79. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2005. http://dx.doi.org/10.1002/0471476501.ch14.

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Rode-Schubert, Christina, e Patrick Müller. "Der Enterprise Transformation Cycle als ganzheitliche Methodik für die Entwicklung von Business Capabilities". In Der Enterprise Transformation Cycle, 111–28. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-22694-7_6.

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Kiel, Ernst, e Ines Muskau. "Der Enterprise Transformation Cycle als nachhaltiges Werkzeug für die digitale Transformation in der Energiewirtschaft". In Der Enterprise Transformation Cycle, 399–424. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-22694-7_20.

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Atti di convegni sul tema "Diel cycle"

Davami, K., M. Shaygan, M. K. Besharaty, A. Mellat e B. Serajzadeh. "Investigation on Heat Transfer and Its Effect on Titanium Hot Forging Process". In ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/ht2008-56499.

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Titanium forged components have been widely used in aircraft engine industry because of their superior specific strength to weight ratio at high temperature. Turbine disk is one of the most demanding forging parts. The flow stress of titanium alloy Ti-6Al-4V is strongly dependent on temperature and strain rate during hot forging. The cooling rate can be designed to manage the temperature profile of dies by distinct spray setup. The workpiece loses heat to die by contact when getting heat up for deformation. The study aims to assess the influence of the discrete cooling rate and interfacial contact heat transfer on the optimum plastic deformation and the optimum die life for a Ti-6Al-4V hot-die forging. A two-dimensional FEM model of titanium turbine disk is employed to study the mechanical and thermal interaction between the hot dies and the workpiece. After hundreds of runs of the forging cycles thermal-steady state is built up and the thermal-steady simulation is considered to reflect the actual production situation. The development of different microstructure and phase compositions in various regions of workpiece is the result of the high sensitivity of two-phase TI-6Al-4V to strain and temperature of plastic deformation. Proper selection of these parameters allows one to control its mechanical properties and avoid deformation failure. Providing the productivity and economic demands, thermal design is a more manageable way than strain rate control for hot die forging. Microstructure control and uniformity of deformation can be achieved through the selection of optimum processing conditions with the aid of processing maps. This research focuses on the effects of forging interfacial heat transfer coefficient and discrete cooling rate along tool cavity when other processes parameters such as strain rate and cycle time given fixed. The temperature control will help achieve a good balance among strength, ductility and fracture toughness. The flow stability, load and energy, die wear, and die tempering and chilling are investigated for a turbine disk hot-die forging using a two-dimensional FEM model.

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Owens, N. L. "Design for manufacturability in hermetic product die attach". In Fifth IEEE/CHMT International Electronic Manufacturing Technology Symposium, 1988, 'Design-to-Manufacturing Transfer Cycle. IEEE, 1988. http://dx.doi.org/10.1109/emts.1988.16150.

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Graham, W. F., B. C. Sakiadis e F. Schmitt. "'QL'-a new thermoplastic ribbon die attach adhesive". In Fifth IEEE/CHMT International Electronic Manufacturing Technology Symposium, 1988, 'Design-to-Manufacturing Transfer Cycle. IEEE, 1988. http://dx.doi.org/10.1109/emts.1988.16163.

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Alirezaee, Tayebeh, Colin Burvill, Bruce Field e Michael Carton. "Optimizing the Mould Die Design and Production Cycle". In ASME 2004 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASME, 2004. http://dx.doi.org/10.1115/detc2004-57629.

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Wahyuning Asih, Susi, e Maulida ZuhrotulJannah. "THE CORRELATIONSHIP BETWEEN SELF EFFICACY AND COMPLIANCE OF LOW SALT DIET IN THE ELDERLY WITH HYPERTENSION IN WORKING AREA OF JELBUK HEALTH CENTRE". In THE 4th INTERNATIONAL NURSING CONFERENCE “LIFE CYCLE APPROACH FOR SUCCESSFUL AGING”. Universitas Muhammadiyah Jember, 2019. http://dx.doi.org/10.32528/inc.v0i0.2692.

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Wu, J. D., Y. S. Lai, Y. L. Kuo, S. C. Hung e M. H. R. Jen. "Thermo-Mechanical Deformation and Stress Analysis of a Flip-Chip BGA". In ASME 2003 International Electronic Packaging Technical Conference and Exhibition. ASMEDC, 2003. http://dx.doi.org/10.1115/ipack2003-35082.

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This paper investigates thermo-mechanical deformation and stresses of a flip-chip package (FCBGA) with and without underfill materials. Chip carrier is a 2-2-2 build-up substrate with 40 × 40 mm2 dimension; while bump material employs Sn/37Pb eutectic solder. Temperature-dependent warpage (out-of-plane displacement) of a FCBGA is characterized via shadow moire´ technique. Results of warpage measurement reveal that packages do not follow the same path during thermal loading/unloading cycle (20-220-20 °C) for both FCBGA with and without underfills. This implies that both solder and underfill exhibit inelastic material response. Therefore, it is a necessity to consider nonlinear constitutive response of packaging materials when designing flip-chip packages. It is observed that FCBGA with underfill exhibit more warpage than packages without underfill due to higher CTE mismatch between underfills and silicon dies. Aspect of package geometry such as die-to-substrate thickness ratio is found to play important role in reducing package stresses. Especially, thinner die provides more direct impact to die stresses reduction than thinner substrate does.

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Tumnark, Piyaporn, Miguel Abreu, Miguel Macedo, Paulo Cardoso, Jorge Cabral e Filipe Conceição. "Modelling Weightlifting “Training-Diet-Competition” Cycle Ontology with Domain and Task Ontologies". In 10th International Conference on Knowledge Engineering and Ontology Development. SCITEPRESS - Science and Technology Publications, 2018. http://dx.doi.org/10.5220/0006929402070214.

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Fahim, Abdullah, Kamrul Hasan, Jeffrey C. Suhling e Pradeep Lall. "Creep Behavior of Various Materials Within PBGA Packages Subjected to Thermal Cycling Loading". In ASME 2020 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ipack2020-2655.

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Abstract Electronic packages are frequently exposed to a thermal cycling environment in real life applications. Particularly, the plastic ball grid array (PBGA) is one of the most widely used electronic package, and consists of various component materials, e.g. solder joint, silicon die, die attachment adhesive, mold compound, solder mask, etc. All of these materials play a significant role on the reliability of the overall package. Failure under creep deformation is one of the significant failure mode for electronic packages. Hence, it is important to study their creep behavior and evolution under the thermal cycling environment. These changes must be evaluated in order to understand and predict their failure behavior due to creep damage in operation. In our previous study, evolution of mechanical properties of SAC305 solder joints in a PBGA package up to 250 thermal cycles was evaluated using the nanoindentation technique. In this work, nanoindentation technique was utilized to understand the evolution of creep behavior of the SAC305 solder joint, die attachment adhesive, silicon die, and solder mask material for various durations of thermal cycling. Test specimens were first prepared by cross sectioning a PBGA package to reveal the different materials, followed by surface polishing to facilitate SEM imaging and nanoindentation testing. After preparation, the package samples were thermally cycled from T = −40 to 125 °C in an environmental chamber. At various points in the cycling (e.g. after 0, 50, 100, 250 and 500 cycles), the package was taken out from the chamber, and nanoindentation was performed on above mentioned materials to obtain creep behavior at room temperature (25 °C). From the nanoindentation test data, it was found that creep deformation of SAC305 increased upto 500 cycles. Die attachment and solder mask materials showed initial decrease in creep deformation up to 250 cycles and then increased value at 500 cycles. As expected, the silicon die material does not show any significant change in creep deformation behavior upto 500 cycles.

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Deshpande, Aditya, Sean B. Leen e Thomas H. Hyde. "Experimental and Numerical Characterisation of the Cyclic Thermo-Mechanical Behaviour of a High Temperature Forming Tool Alloy". In ASME 2009 Pressure Vessels and Piping Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/pvp2009-77192.

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This paper describes high temperature cyclic and creep relaxation testing and modelling of a high nickel-chromium material (XN40F) for application to the life prediction of superplastic forming (SPF) tools. An experimental test programme to characterise the high temperature cyclic elastic-plastic-creep behaviour of the material over a range of temperatures between 20°C and 900°C is described. The objective of the material testing is the development of a high temperature material model for cyclic analyses and life prediction of superplastic forming (SPF) dies for SPF of titanium aerospace components. A two-layer visco-plasticity model which combines both creep and combined isotropic-kinematic plasticity is chosen to represent the material behaviour. The process of material constant identification for this model is presented and the predicted results are compared with the rate-dependent (isothermal) experimental results. The temperature-dependent material model is furthermore applied to simulative thermo-mechanical fatigue (TMF) tests, designed to represent the temperature and stress-strain cycling associated with the most damaging phase of the die cycle. The model is shown to give good correlation with the test data, thus vindicating future application of the material model in thermo-mechanical analyses of SPF dies, for distortion and life prediction.

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Yueh, Yuh-Shan, e R. Allen Miller. "A Systematic Approach to Support Design for Manufacturability in Injection Molding and Die Casting". In ASME 1995 15th International Computers in Engineering Conference and the ASME 1995 9th Annual Engineering Database Symposium collocated with the ASME 1995 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/cie1995-0804.

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Abstract In designing a part to be produced by injection molding or die casting, designers need to consider manufacturing characteristics of the part such as filling and ejectability from the dies as well as functional issues. The typical design cycle is iterative, laborious and time-consuming. In this paper, we present a procedure for defining parting information (locations where the mold/die come together), and recognizing the links between part design and die/mold construction. Many decisions and design details, such as draft on surfaces parallel to the draw (die opening) direction, gate and runner locations, vent locations, etc., depend on the parting locations and characteristics. Parting information is normally not part of the geometric model of the part design. Parting design, including draw direction and parting location, is addressed through a custom user interface which contains several options related to different levels of geometric modeling data. The resulting specification is stored in a segment structure which provides a flexible parting description and fits within the B-rep hierarchy. The reasoning about the linking of related surfaces is accomplished by splitting and traversing the extracted geometric entities based on parting definition. The entities covered by the same die/mold component are aggregated as a face group which is a set of complete or partial surfaces with the parting definition as the boundary information and with the draw direction as the moving information. In this approach, manufacturing information can be strongly coupled with geometric data to form a complete part model which supports manufacturability assessment and facilitates any necessary shape transformations to achieve a manufacturable part in a straightforward manner so that design iterations can be controlled and development cost can be reduced.

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