Academic literature on the topic 'Pollen grain size'
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Journal articles on the topic "Pollen grain size"
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Hao, Kai, Zhi-Xi Tian, Zi-Chen Wang, and Shuang-Quan Huang. "Pollen grain size associated with pollinator feeding strategy." Proceedings of the Royal Society B: Biological Sciences 287, no. 1933 (2020): 20201191. http://dx.doi.org/10.1098/rspb.2020.1191.
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Angiosperm pollen grain diameter varies greatly from a few microns to over 100, but the selective forces driving the interspecific variation in pollen size remain unclear. Although both pre- and post-pollination hypotheses have been proposed, empirical evidence remains scarce. Here we propose that visits by pollen-foraging pollinators have selected against large pollen grains. An association between pollinator behaviour and pollen grain size was confirmed by field studies of 80 flowering species in natural communities, showing that pollinators positively collected pollen in those species with relatively smaller pollen grains but rarely did so in species with larger ones. Allowing for the confounding effects of pollinator type, flower size or style length and pollen grain number, we found a significant effect of pollen-foraging behaviour on variation in pollen grain size, particularly in bee-pollinated plants. While these results suggest that many plant species whose pollen is collected or consumed by pollinators produce small pollen grains, it remains unclear whether pollen grain size is directly affected by pollinator foraging habit or indirectly mediated by pollen number trade-offs.
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De Freitas, Jéssica Mena Barreto, Andrielle Wouters Kuhn, Viviane Dal-Souto Frescura, Liliana Essi, and Solange Bosio Tedesco. "Differences in stomatal and pollen grain dimensions and pollen viability between Paspalum rawitscheri populations." Ciência e Natura 42 (June 29, 2020): e46. http://dx.doi.org/10.5902/2179460x40749.
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The objective of this study was to evaluate stomatal and pollen grain size and to estimate pollen viability of individuals from different populations of Paspalum rawitscheri (Parodi) Chase ex G.H. Rua Valls. To analyze stomatal size, slides were made of the adaxial leaf epidermis using the epidermal impression method. The height and width of 100 stomata per population were analyzed. Pollen was obtained from inflorescences to evaluate pollen grain size and pollen viability. Pollen grains were stained with 2% acetic orcein, 2% acetic carmine, or Alexander’s reactive stain. Per population, 1600 grains of pollen were observed for viability, and 50 grains of pollen were measured. There were significant differences between populations in stomatal height and pollen grain height and width. The populations also differed in pollen viability, with the Santa Maria population showing the lowest viability. The differences in stomatal and pollen grain size suggest genetic variability in the evaluated populations. Moreover, low pollen viability in one population indicates that its decline may be related to low fertility. Keywords: Grass. Ploidy. Fertility. Threatened species.
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Pietarinen, Päivi, and Hanna-Leena Pasonen. "Pollen performance and male fitness in an anemophilous, monoecious tree, Betula pendula." Canadian Journal of Botany 82, no. 9 (2004): 1284–91. http://dx.doi.org/10.1139/b04-069.
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Betula pendula Roth clones were examined to study the relationship between pollen grain size and pollen tube growth rate and pollen and seed performance. Two hypotheses were tested: (i) pollen donors with larger pollen grains have faster growing pollen tubes and (ii) maternal plants produce more seeds when inflorescences have been pollinated by pollen from donors with fast pollen tube growth. Pollen from 15 plants was collected, and pollen grain sizes and pollen tube growth rates were studied in vitro. Eight maternal clones were pollinated by pollen from seven paternal clones, pollen tube growth rates of the pollen donors were measured on each maternal plant, and the number and mass of the resulting seeds were analysed. There was no correlation between pollen grain size and pollen tube growth rate in vitro. Also, there was no relationship between pollen tube growth rate and the number of produced or aborted seeds. Thus, the hypothesis that larger pollen grains would have longer pollen tubes was not supported by the present study. The results of the present study do not support the idea that pollen donors with fast pollen tube growth should sire more and better seeds.Key words: Betula pendula, female choice, nonrandom abortion, pollen competition, sexual selection.
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khalik, Kadry Abdel, Suad Al Ruzayza, Abdullah Assiri, and Ahmed Elkordy. "Pollen morphology of Malvaceae genera from Saudi Arabia and its taxonomic significance." MAY 2021, no. 15(05):2021 (May 10, 2021): 725–42. http://dx.doi.org/10.21475/ajcs.21.15.05.p3129.
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Pollen morphology of 20 species belong to seven genera (Abutilon, Althaea, Hibiscus, Malva, Pavonia, Senra and Sida) of Malvaceae from Saudi Arabia were studied by using light microscope (LM) and scanning electron microscope (SEM). Quantitative and qualitative pollen morphological characters which vary among investigated taxa are found in the pollen polarity, symmetry, size, shape, polar axis, equatorial diameter, P/E ratio, average height and width of spine, aperature character and spine index. The pollen grains vary from spheroidal, prolate spheroidal, oblate spheroidal to suboblate. All taxa were characterized by relatively large to medium sized pollen grains, numerous pores scattered irregularly all over the grain, and echinate sculpturing. Sida ovata is the largest size pollen grain (138.95) µm. On the other hand, Malva parviflora showed the smallest pollen size (52.28 µm). The average height and width of spine varied greatly among studied taxa. The highest spines (20.65µm) found in Sida ovata, while the shortest (3.19 µm) was found in Abutilon pannosum. Results of the pollen shape, size, and exine sculpture characters offered useful data for evaluating the taxonomy of Malvaceae both on subgeneric and sectional levels. A key for the identification of the investigated taxa based on pollen grains characters is also provided
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Sosnoskie, L. M., T. M. Webster, D. Dales, G. C. Rains, T. L. Grey, and A. S. Culpepper. "Pollen Grain Size, Density, and Settling Velocity for Palmer Amaranth (Amaranthus palmeri)." Weed Science 57, no. 4 (2009): 404–9. http://dx.doi.org/10.1614/ws-08-157.1.
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Palmer amaranth is resistant to several herbicides, including glyphosate, and there is concern that the resistance traits can be transferred between spatially segregated populations via pollen movement. The objective of this study was to describe the physical properties of Palmer amaranth pollen, specifically size, density, and settling velocity (Vs), that influence pollen flight. The mean diameter for Palmer amaranth pollen, as determined by light microscopy, was 31 µm (range of 21 to 38 µm); mean pollen diameter as measured with the use of an electronic particle sizer was 27 µm (range of 21 to 35 µm). The mean density of the solid portion of the pollen grain was 1,435 kg m−3. Accounting for the density of the aqueous fraction, the mean density of a fully hydrated pollen grain was 1,218 kg m−3. By Stokes's law, the estimated mean theoreticalVsfor individual Palmer amaranth pollen grains was 3.4 cm s−1for the range of pollen diameters with a mean of 31 µm and 2.6 cm s−1for the range of pollen diameters with a mean of 27 µm. Results from laboratory studies indicated the majority of single pollen grains settled at a rate of 5.0 cm s−1. The difference between the theoretical and empirical estimates ofVswas likely due to changes in pollen density and shape postanthesis, which are not accounted for using Stokes's law, as well as the presence pollen clusters.
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Tejaswini. "Male gametophytic generation and a possible approach for selective pollination in carnation (Dianthus) breeding program." Plant, Soil and Environment 48, No. 8 (2011): 368–75. http://dx.doi.org/10.17221/4382-pse.
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Present study focuses on making best possible use of male gametophytic generation in carnation breeding program. Exploration of pollen population revealed the existence of variability in terms of pollen morphology and histochemical content among as well as within varieties and species of Dianthus caryophyllus and D. chinensis sufficient to make selection. Pollen grain size and histochemical content were found to be associated with germination capacity and pollen tube growth rate. In addition, pollen germination capacity and elongation of pollen tube in response to presence of culture filtrate from F. oxysporum. f.sp. dianthi causal organism of fusarium wilt in carnation was found to be governed by pollen grain size and histochemical content of pollen grains. Entire result suggests the possibility of selecting the desired pollen grains from a pollen population and possibility of attempting selective pollination in carnation breeding program.
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Shi, Yinping, Qiangsheng Wang, Jianming Yang, Congyi Sui, and Qingrong Sun. "493 Inducing Polyploidy Pollen in Apple Cultivars." HortScience 34, no. 3 (1999): 530B—530. http://dx.doi.org/10.21273/hortsci.34.3.530b.
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To perform apple polyploid breeding the ways of inducing polyploidy pollen with temperature and chemicals were studied. Materials include 13 diploid cultivars: Red Chief, Dai Hong, Rose Red, Golden Delicious, Mollie's Delicious, Gala, Bella, Jonathan, Fuji, Qiu Kou Hong, and Yan Qing, OBIR-2T-47. Chemicals: Chloroform, N-nitroso-ethylurea. At the beginning of PMC meiosis, fruiting branching groups were covered with plastic bags to raise temperature or were treated with chemical. After covering, temperature during the day increased 2 °C, generally not lower than 0 °C. Whether branches received high temperature or chemicals treatment, polyploidy pollen was induced to produce. The pollen grain of CK is tricolporat, its polar view is triangular, and its diameter almost 40 μm, showing no difference in size. Rate of empty pollen grain is low. Pollen grains that were treated were different in size, and rate of empty pollen is high, part of pollen grains germinating colporat change into tetracolporat with a few polycolporat, its polar view is square, round, and oval. The diameter of large pollen grains was 45-48 μm, increased by 11-12%. Giant pollen grain are 50-68 μm, increased by 25%-70%. Rate of induction is different in different cultivars. For most cultivars, giant pollen grain is 0.3%-0.5%. Gala and OBIR-2T-47 were higher, reaching 2.5%-7%. Chemicals caused damage on cultivars. Delicious strains were easily damaged.
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Zhuikova, Tatyana Valerievna, Anna Andreevna Kovalenko, and Anna Vladimirovna Mezina. "Variability of male gametophyte traits in morphological forms of Taraxacum officinale Wigg. s.l. under conditions of technogenic soil transformation." Samara Journal of Science 10, no. 2 (2021): 31–39. http://dx.doi.org/10.17816/snv2021102104.
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The paper studies endogenous, individual and group variability of the traits pollen grain fertility and size of fertile pollen grains among two morphological forms of Taraxacum officinale Wigg. s.l., growing in coenopopulations in the gradient of technogenic soil transformation. The study area is the Pritagil zone of the Middle Urals (Nizhny Tagil city, Sverdlovsk Region, N 58, E 60). It was found that the studied morphological forms of dandelion in most cases are characterized by average endogenous, individual and group variability of the trait pollen grain fertility and low endogenous and individual variability of the trait pollen grain size. The group variability for this trait is medium and low. The endogenous variability of pollen grain fertility and size among f. dahlstedtii on agrozems is slightly higher than on technozems. Among f. pectinatiforme the endogenous variability of pollen grain fertility is higher on agrozems only. An increase in the level of soil contamination on agrozems leads to a decrease in the endogenous variability of pollen grain fertility among both forms of dandelion. On technozems a similar reaction is expressed only among f. pectinatiforme . The analysis of the studied trait in the entire gradient of technogenic soil transformation indicates a significant influence of this factor only on the endogenous variability of pollen grain fertility among f. dahlstedtii . Despite the absence of statistically significant differences in the individual variability of the pollen grain fertility trait between dandelion forms, on average, the coefficients of its variation on agrozems are lower among f. dahlstedtii , and on technozems - among f. pectinatiforme . The same conclusion applies to the individual variability of the trait size of fertile pollen grains. In general, among f. dahlstedtii the coefficients of variation of the studied signs of the male gametophyte are lower in agrozems than in technozems, among f. pectinatiforme the picture is reversed. On average, the proportion of plants with low ( C ᵥ 11%) individual variability in pollen grain fertility among f. dahlstedtii out of all the studied coenopopulations is 43,3% versus 61,7% among f. pectinatiforme . The influence of technogenic transformation of the environment is manifested in an increase in the proportion of f. pectinatiforme plants with a low level of variability of the studied traits in the coenopopulations of the buffer and impact zones. Among f. dahlstedtii the reverse pattern is characteristic only for pollen fertility. The group variability of pollen grain fertility in both agrozems and technozems is higher among f. dahlstedtii . With an increase in pollution on agro-soils, this indicator increases among both forms of dandelion, and decreases in technozems. There is a tendency to increase the group variability of pollen grain fertility among plants of both forms of T . officinale on technozems. An increase in the level of soil contamination on agrozems leads to an increase in the group variability of the trait size of fertile pollen grains among f. dahlstedtii and a decrease among f. pectinateforme . On technozems the opposite effect is noted. In general, the group variability of the studied trait among plants of both morphological forms of dandelion on agrozems is higher than on technozems.
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Atlagic, Jovanka, Ana Marjanovic-Jeromela, Radovan Marinkovic, and Sreten Terzic. "Pollen grain traits of oil species from the Novi Sad collection." Genetika 41, no. 3 (2009): 263–70. http://dx.doi.org/10.2298/gensr0903263a.
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The collection of oil species in Novi Sad contains 12 species represented with 1-4 cultivars or landraces. In the continuous work on this collection in the sense of breeding of some of those species and their usage as a source of 'desirable genes' we analyzed pollen grain morphology (shape and size), as well as pollen viability. To determine mentioned pollen traits we used Axiovert 40C microscope together with a software package (AxioVision LE; Rel.4.3.) for measurement of pollen length and width. Pollen viability was determined using a staining method (ALEXANDER, 1969). The results showed that species differ by pollen grain shape (round, egg-shaped, triangular and rod) as well as by shape of exine (thick and spiky, thick to thin). In some species there was a specific number of apertures present (1-11). The size of viable pollen grains ranged from 29,10/12,58? (coriander) to 176,63/169,94? (oil gourd), while non-viable pollen grains were always smaller (27,27/10,97? to 119,62/100,86?) at the same plant species. Pollen viability of most species was around 80%. Lowest pollen viability was found in white flax (56,98%), and the highest in oil pumpkin (91,43%).
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AROGUNDADE, Oluwabunmi Okerinmola, and Hameedat O. LAWAL. "Palynological Studies of Three Taxa and One F1 Hybrid in the Genus Talinum Adans." Notulae Scientia Biologicae 10, no. 2 (2018): 175–81. http://dx.doi.org/10.15835/nsb10210214.
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Acetolysed pollen grains of Talinum paniculatum (Jacq.) Gaertn., Talinum triangulare (Jacq.) Willd. pink petals, Talinum triangulare (Jacq.) Willd. white petals and Talinum triangulare (Jacq.) Willd. pink and white petals F1 hybrid were studied in order to document their morphological structures and ascertain features of taxonomic significance among them. All the taxa have generic features which support their classification as a genus as well as distinct features which ascertain their individuality. Generic features include monad pollen unit, acolpate and monocolpate pollen grains as well as circular and ovate pollen shapes. The delimiting features include additional dyads pollen units in T. triangulare white petal and the F1 hybrid of T. triangulare pink and white petals, quadrangular pollen shape in T. paniculatum, bicolpate pollen grain in the F1 hybrid, tricolpate pollens in T. triangulare white petal and T. paniculatum, tetracolpate pollens in T. triangulare pink petal and T. paniculatum and pentacolpate pollen grains in T. paniculatum only. The shape of the pores in T. paniculatum also separated it from the varieties and hybrid of T. triangulare. Based on the pollen size, the pollens of T. paniculatum are Media (25 - 50 µm) while those of the two varieties of T. triangulare and their F1 hybrid are Magna (50 - 100 µm). The taxa of Talinum in this study can be separated based on their palynological features.
Dissertations / Theses on the topic "Pollen grain size"
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Lamborn, Ellen. "The evolution of pollen grain size variation in Mimulus (Scrophulariaceae)." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269837.
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Sarkissian, Taline S. "The evolutionary genetics and adaptive significance of intraspecific variation in pollen grain size in Brassica rapa L." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ48038.pdf.
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Farooq, Jan Verfasser], Hermann [Akademischer Betreuer] Behling, Lisa [Akademischer Betreuer] Schüler, et al. "Palynological studies and Holocene ecosystem dynamics in north western Khyber Pakhtunkhwa Province of Pakistan in the Hindu Kush Himalayan region : Trends of pollen grain size variation in C3 and C4 Poaceae species using pollen morphology for future assessment of grassland ecosystem dynamics / Jan Farooq. Betreuer: Hermann Behling. Gutachter: Lisa Schüler ; Erwin Bergmeier ; Markus Hauck ; Elvira Hörandl ; Dirk Hölscher ; Dirk Gansert ; Erwin Bergmeier ; Hermann Behling." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://d-nb.info/1098531043/34.
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Katsiotis, Andreas. "The determination and use of pollen grain size in four ploidy levels and the cytogenetics of tetraploid - octoploid hybrids in search of 2n gametes in Avena." 1993. http://catalog.hathitrust.org/api/volumes/oclc/30336117.html.
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Farooq, Jan. "Palynological studies and Holocene ecosystem dynamics in north western Khyber Pakhtunkhwa Province of Pakistan in the Hindu Kush Himalayan region." Thesis, 2015. http://hdl.handle.net/11858/00-1735-0000-0028-8741-2.
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Khyber Pakhtunkhwa (31 ° 49'N, 70 ° 55'E bis 35 ° 50'N, 71 ° 47'E) liegt im Nordwesten Pakistans im Süden Asiens. Das Hindukusch-Gebirge in Afghanistan liegt im Westen, dem indischen Himalaya im Nordosten und die Karakorum Berge südlich vom tibetischen Hochland auf der Nordseite. Diese Arbeit besteht überwiegend aus drei separaten Studien entlang eines 200 km langen Transekts mit einem Höhengradienten ausgehend von den Sedimentbecken im Peshawar Tal (275 m ü.M.) bis hinauf zu den Malam Jabba Hills im Swat-Tal (2600 m ü.M.).
Die erste Studie, die auf einer Datengrundlage von 160 Poaceae Arten beruht, zeigt Trends, dass polyploide C3- und C4-Poaceae-Arten größere Pollenkkörner als die jeweiligen diploiden Arten haben. In diesem Datensatz haben alle C4-Arten größere Pollenkörner als die C3-Arten. Ob Grassländer von C3 oder C4 Arten dominiert werden kann in verschiedenen Regionen und Lebensräumen durch die Untersuchung der Muster des Trends von zu- oder abnehmenden Pollenkorngrößen ermittelt werden. In unserem Datensatz ist Polyploidie bei C4-Gräsern häufiger als bei den C3 Arten. Die verwendete Methode kann auf Poaceae-Pollenkörner in Umweltarchiven angewendet werden, um das Klima der Vergangenheit zu rekonstruieren und die Dynamik der früheren Graslandökosysteme zu bewerten. Dieser Ansatz wird nicht nur bei laufenden paläoökologischen Studien helfen aufzuklären, wie die Änderungen der Vegetations-zusammensetzung und die Veränderungen in Biomen vergangener Graslandökosysteme zu entschlüsseln sind, sondern auch nützliche Erkenntnisse für die Vorhersage zukünftiger Entwicklungen ermöglichen.
Die zweite Studie befasst sich mit modernen Pollenspektren aus Oberflächenproben und ihre Beziehung zu der umgebenden Vegetation, die nützliche Daten für die Interpretation von holozänen Pollenprofilen bietet. Dabei konnten entlang eines 200 km langen Höhengradienten vier verschiedene Höhenstufen unterschieden werden, wo die dominierenden Pflanzenfamilien, Poaceae, Asteraceae, Cyperaceae, Verbenaceae, Acanthaceae und Euphorbiaceae eine signifikante Korrelation mit dem gefunden Pollenniederschlag hatten, während sich bei anderen Familien, den Boraginaceae, Saxifragaceae, Apiaceae, Balsaminaceae und Rubiaceae große Unterschiede zu der zugehörigen Vegetationszusammensetzung ergaben. Für die Kalibrierung und Interpretation fossiler Pollendaten sollte also immer auch die aktuellen Beziehungen von Pollenniederschlag und Vegetationsdaten zumindest auf der Familienebene berücksichtigt werden.
Die dritte Studie befasst sich mit einem Pollenprofil aus der Kabal Swat-Region, welches eine detaillierte Geschichte der Vegetation und des Klimas des Hindukuschs der letzten 3300 Jahre, also dem späten Holozäns enthält. Von 3300 bis 2400 cal BP, war eine subtropische semiaride krautige Vegetation hauptsächlich durch Cyperaceae- und Poaceae-Arten vertreten. Sie wurde ersetzt von gemischten Nadelwäldern mit Taxus, Pinus, sowie Juglans, Poaceae und Cyperaceae während der Zeit von 2400 bis 900 cal BP, was auf eine vergleichsweise moderate Klimaschwankung während des späten Holozäns weist. Der Rückgang der Poaceae von 2400 bis1500 cal BP und eine erneute Zunahme von 1500 bis 1200 cal BP Jahre zeigen, dass das Kabal Swat nass-kühlere und trocken-wärmere Phasen durchmachte. Nadelbäume in den gemischten Nadelwäldern treten heute bei größeren Höhe im alpinen Bereich auf. Weitere hochauflösende holozäne Pollenprofile des Hindukusch sind notwendig, um einen ausführlicheren Vergleich zu anderen süd- und zentralasiatischen Paläo-Archiven zu ermöglichen, die auch ein detaillierteres und anwendbares Wissen für Management und Naturschutzfragen ergeben.
Books on the topic "Pollen grain size"
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Little, Martin Lewis. Pollen and grain size records in abyssal sediments of the northwest Pacific Ocean as proxies of Plio-Pleistocene climate change. Brock University, Dept. of Earth Sciences, 2005.
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Lézine, Anne-Marie. Vegetation at the Time of the African Humid Period. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.530.
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An orbitally induced increase in summer insolation during the last glacial-interglacial transition enhanced the thermal contrast between land and sea, with land masses heating up compared to the adjacent ocean surface. In North Africa, warmer land surfaces created a low-pressure zone, driving the northward penetration of monsoonal rains originating from the Atlantic Ocean. As a consequence, regions today among the driest of the world were covered by permanent and deep freshwater lakes, some of them being exceptionally large, such as the “Mega” Lake Chad, which covered some 400 000 square kilometers. A dense network of rivers developed.What were the consequences of this climate change on plant distribution and biodiversity? Pollen grains that accumulated over time in lake sediments are useful tools to reconstruct past vegetation assemblages since they are extremely resistant to decay and are produced in great quantities. In addition, their morphological character allows the determination of most plant families and genera.In response to the postglacial humidity increase, tropical taxa that survived as strongly reduced populations during the last glacial period spread widely, shifting latitudes or elevations, expanding population size, or both. In the Saharan desert, pollen of tropical trees (e.g., Celtis) were found in sites located at up to 25°N in southern Libya. In the Equatorial mountains, trees (e.g., Olea and Podocarpus) migrated to higher elevations to form the present-day Afro-montane forests. Patterns of migration were individualistic, with the entire range of some taxa displaced to higher latitudes or shifted from one elevation belt to another. New combinations of climate/environmental conditions allowed the cooccurrences of taxa growing today in separate regions. Such migrational processes and species-overlapping ranges led to a tremendous increase in biodiversity, particularly in the Saharan desert, where more humid-adapted taxa expanded along water courses, lakes, and wetlands, whereas xerophytic populations persisted in drier areas.At the end of the Holocene era, some 2,500 to 4,500 years ago, the majority of sites in tropical Africa recorded a shift to drier conditions, with many lakes and wetlands drying out. The vegetation response to this shift was the overall disruption of the forests and the wide expansion of open landscapes (wooded grasslands, grasslands, and steppes). This environmental crisis created favorable conditions for further plant exploitation and cereal cultivation in the Congo Basin.
Book chapters on the topic "Pollen grain size"
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Stanton, Maureen L., and Robert E. Preston. "Pollen Allocation in Wild Radish: Variation in Pollen Grain Size and Number." In Biotechnology and Ecology of Pollen. Springer New York, 1986. http://dx.doi.org/10.1007/978-1-4613-8622-3_74.
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Nguri, Evans Matu. "Interviewing for Television." In Advances in Media, Entertainment, and the Arts. IGI Global, 2016. http://dx.doi.org/10.4018/978-1-4666-9613-6.ch009.
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An examination of television interviewing in Kenya provides an emerging sketch of its practice and theory. This Chapter considers television interviewing at three levels that it considers as prioritized by the times - interviewing at the change frontier site, interviewing on behalf of bio-change beings that Kenyans have become, and interviewing with pollen grains of theory in journalism and consequent echoes of its outcome. The Chapter considers three case studies of interviewing in Kenya - the presidential debate, live field reporting and TV opinion polls.The Chapter concludes with a sketch that also suggests certain claims - that television as a medium has not risen to its natural place because it's cameras are not focused on the space of great needs of the people particularly at the change frontier; that moving to a high value question interviewing and a treatment of interviewing as a full-fledged production is a fresh and a rich depth offer for viewers; and that the television interview is a critical forgery of rhetoric in a change thirsty society.
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Cavosie, Aaron J., and Luigi Folco. "Shock-twinned zircon in ejecta from the 45-m-diameter Kamil crater in southern Egypt." In Large Meteorite Impacts and Planetary Evolution VI. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.2550(17).
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ABSTRACT With an age of less than ~5000 yr and a diameter of 45 m, Kamil crater in Egypt is one of the youngest and smallest terrestrial impact craters known to date. Abundant evidence of shock-deformed sandstone has been reported from Kamil crater, including shatter cones, vesicular impact glass, high-pressure polymorphs of silica and car bon, planar deformation features (PDFs) and planar fractures (PFs) in quartz, dissociated zircon, melt veins, and intergranular melt, giving rise to a range of estimated shock pressures from ~20 to ~60 GPa. Here, we investigated shocked zircon from Kamil crater through characterization of microstructures in a centimeter-sized clast of shocked nonporous sandstone ejecta, previously described as containing quartz grains with PDFs and PFs, coesite, stishovite, diamond, and lechatelierite. Orientation analysis by electron backscatter diffraction (EBSD) showed that the quartz arenite consists of damaged detrital quartz grains surrounded by a matrix of either comminuted quartz or intergranular melt. Individual quartz grains are pervasively fractured (abundant PFs and PDFs); apparent isotropic crushing resulted in uniformly and highly dispersed orientation clusters on pole figures. Zircon grains are not abundant; however, four of 19 grains analyzed by EBSD contained {112} deformation twin lamellae, with individual lamellae ranging in length from 1 to 2 µm. Lengths of twin lamellae in Kamil zircon grains are anomalously short compared to those report-ed in shocked zircon from other impact structures, where individual lamellae are tens of micrometers long. Previous empirical studies have suggested that {112} twin lamellae in zircon form at ~20 GPa in non-porous target rocks, a finding supported by their coexistence, in some impactites, with high-pressure phases such as reidite. The only available experimental constraint, by diamond anvil cell, found {112} twins in zircon powder quenched at 20 GPa. The presence of coesite, stishovite, lechatelierite, and shocked quartz with PDFs in the studied sample is consistent with empirically derived pressure estimates of ~20 GPa for {112} twin formation in zircon in the ejecta sample from Kamil crater. Kamil thus represents the smallest and youngest impact structure where shock-twinned zircon has been reported. Given the apparent efficiency of {112} twin formation (21% of grains), shock-twinned zircon is here shown to provide a robust and readily identifiable record of shock deformation in a relatively common mineral at one of the smallest known terrestrial impact craters.
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Hallam, Tony. "Climate change." In Catastrophes and Lesser Calamities. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198524977.003.0010.
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Unlike the other factors that have been invoked to account for mass extinctions, climate change is manifest to us all, whether we travel from the tropics to the poles or experience the seasonal cycle. Over a longer timescale, the issue of global warming in the recent past and likely future, and its probable consequences for other aspects of the environment, has occupied a considerable amount of media attention. Those people who are unaware of the likely consequences of the burning of fossil fuels cannot count themselves as well educated. Over a longer timescale, geologists have been aware for many decades of significant climatic changes on a global scale leading to the appearance and disappearance of polar ice caps on a number of occasions. Steve Stanley, the distinguished palaeobiologist at Johns Hopkins University in Baltimore, has actively promoted the view that episodes of climatic cooling are the most likely cause of mass extinctions. However, we must consider also the significance of global warming, and for the continents, at any rate, the possible effects of changes in the humidity–aridity spectrum. Before examining the relationships between climatic change and mass extinctions we need to examine the criteria from the stratigraphic record that geologists use to determine ancient climates, or palaeo-climates. The most obvious way of detecting cold conditions in the past is to find evidence of the presence of ice. At the present day the sedimentary deposits associated with glaciers and ice sheets, which occur where melting ice dumps its rock load, range in grain size from boulders and pebbles to finely ground rock flour. Such deposits are known as boulder clay or till, and ancient examples consolidated into resistant rock as tillites. The surfaces of hard rock that have underlain substantial ice sheets bear characteristic linear striations indicating the former direction of ice movement, such as glaciers moving up or down a U-shaped valley. The striations are produced by pebbles embedded in the ice, and are a unique marker for glacial action. In the 1830s Louis Agassiz, the great Swiss naturalist, extrapolated from his knowledge of the margins of Alpine glaciers to propose that the whole of northern Europe had been covered by one or more ice sheets in the recent geological past.
Conference papers on the topic "Pollen grain size"
1
Grega, Lisa. "Very Low Reynolds Number Flow Over Non-Spherical Particles: Applications to Pollen Aerodynamics." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-67268.
Full textAbstract:
Flows at the very low Reynolds number regime (<10) typically have application to the understanding of the dispersion of micro-scale particulates in the atmosphere, as well as microorganisms. Most particulates are non-spherical, requiring specialized studies in order to determine their settling velocities, drag forces, or interactions. The present study considers flow over saccate pollen with the goal of better understanding their flight dynamics. The pollen grains of several gymnosperm groups consist of a main body and one to three air-filled bladders, or sacci, forming ellipsoidal lobes. Previous studies have demonstrated that sacci increased the resistance coefficient of the grain compared to one without sacci, thereby improving its aerodynamic efficiency by increasing dispersal distance. In order to better quantify the effect of sacci position, size, and orientation on pollen dispersion, scaled-up physical models were created based on electron microscopy images. Furthermore, surface ornamentation or texture could be added to the models, adding a higher degree of realism. The models were suspended inside of a glycerin-filled tank capable of translating at very low speeds, producing Reynolds numbers as low as 0.05. Particle Image Velocimetry (PIV) was used to measure velocity fields in the wake of the pollen models. This experimental arrangement facilitated the ability to produce both steady and unsteady (i.e. accelerating or decelerating) flows. Differences among the wake flowfields were related to previously made measurements of pollen shape factors. These studies suggested that both sacci size, orientation or relative position on the main body, as well as surface texture affected this shape factor. The PIV measurements are capable of resolving wake details which demonstrate a wide stagnant flow region behind the main body and between the sacci. This is in contrast to a typical spherical or ellipsoidal geometry, which would be characterized by a single stagnation streamline at the aft, with the flow remaining attached and no wake present when Re<1. At these low Reynolds numbers, there does not appear to be evidence of flow reversal between the sacci; however rapid flow deceleration was capable of producing such reversals.
2
Bhavnani, Anmol. "Utilization of Micro-Electronic-Machine Systems (MEMS) to Possible Future Use in the Enhanced Analysis of Safety in Nuclear Power Plants." In ASME 2002 Pressure Vessels and Piping Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/pvp2002-1527.
Full textAbstract:
The focal point of this paper is to go in-depth in to the potential utilization of MEMS to further enhance safety measures within nuclear power plants. Robots, which are being researched and developed in Sandia National Laboratories, sometimes built as small as the size of a pollen grain, can be utilized to constantly monitor the stress analysis within all aspects of running a Nuclear Power Plant. From cooling towers to detecting miniscule cracks within pipes, MEMS can be utilized to constantly detect and even possibly repair minor faults within the overall structure of a nuclear power plant. MEMS technologies provide the ability to reliably produce micro actuators and sensors to meet these mission requirements. MEMS technologies are also attracting an increasing interest from the commercial sector for various applications. Currently, Sandia National Laboratories has been developing MEMS technologies to support its core missions of weapon surety, stockpile maintenance, and national security interests. Already, the project has been responsible for numerous electromechanical systems in nuclear weapons, which ensure nuclear safety and provide reliable arming, fusing and firing. With these factors in consideration, the main idea of this paper is to present ideas for producing sensors and robots on a micro scale, which could be programmed to communicate and work within each other to have enhanced safety and efficiency within a nuclear power plant.
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Dai, Xun, Hong Liu, Hongman Jiang, and Ying Wang. "The Effect of Fabrication Process on Microstructure Evolution of N18 Alloy Sheets." In 18th International Conference on Nuclear Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/icone18-29339.
Full textAbstract:
The microstructure and texture evolution of N18 sheets are studied after a series of fabrication processes which contain hot rolling at 780°C, cold rolling with the total deformation of 10% and recrystallized annealing at 580°C for 1.5h. The results show that grain size and the density of low angle grain boundaries of the fabricated sheets increase with the increase of hot rolling pass, and there is a little difference of grains for cold rolling and recrystallized sheets that deformed grain could be observed on both of them, which indicates that dynamic recrystallization occurs during hot rolling, but the cold deformation was so limited that the sheets could not be fully recrystallized because of lack of recrystallization driving force. Second phase precipitated particles (SPPs) in as-received N18 sheets are smaller than that in the fabricated sheets. It may because that part of SPPs are dissolved during hot rolling which lead to the volume decrease and supersaturation elements separate out to form SPPs again or primary SPPs grow up during recrystallization which lead to volume extending. The N18 sheets mainly have (0001) texture before and after fabrication and the density of basal pole which was along normal orientation on rolling plane increases as rolling pass increasing but decreases after cold rolling and increase again after recrystallization. After fabrication, the value of fND increases for N18 sheets, but there were a little difference among different rolling pass. EBSD analysis shows that the grains of rolling sheets mainly display orientations with <10 1¯ 0>//RD and {0001} <10 1¯ 0> texture was stronger, and the grains of recrystallized sheets mainly display orientations with <11 2¯ 0>//RD made {0001} <11 2¯ 0> texture increasing.