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1
Merz, Oliver. "Ansätze zur Stärkung der Rolle als Inhalte-Aggregator." MedienWirtschaft 13, no. 2 (2016): 46–48. http://dx.doi.org/10.15358/1613-0669-2016-2-46.
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Über längere Zeit war die Mediennutzung im Wohnzimmer durch den klassischen Fernseher mit linearen Angeboten geprägt. Schon seit einiger Zeit wandelt sich dies. Mittlerweile verfügt eine Reihe von Haushalten über Fernsehen, die neben der Nutzung linearer Programme auch den Zugriff auf Mediatheken sowie weitere Angebote relativ leicht und kostengünstig erlauben. Zudem erfolgt der Zugriff auf Inhalte auch über andere Endgeräte wie Tablets und Smartphones. Auch ist die Gemengelage komplexer geworden, müssen doch Inhalte, Endgeräte und Netze zusammenwirken. Es ist Zeit für eine kurze Zwischenbilanz nach der ersten Phase der Transformation des Inhaltekonsums im deutschen Wohnzimmer: Was hat sich bisher wirklich am Medienkonsum im Wohnzimmer verändert, was ist bald zu erwarten? Welche Angebote werden kommen, welche haben sich nicht bewährt? Welche Strategien verfolgen die unterschiedlichen Gruppen von Akteuren im deutschen Markt? Wir wollen dieses wichtige Thema mit zwei aufeinander folgenden „Standpunkten“ aufgreifen. In der heutigen Ausgabe finden sich die Einschätzungen eines Free-TV-Anbieters, eines Netzbetreibers „mit Inhalte-Ambitionen“ und eines Endgeräteherstellers. In der nächsten Ausgabe werden wir weitere wichtige Perspektiven ergänzen.
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Laukemann, Julia. "Wenn die Welt zum Wohnzimmer wird – Das Fernsehen von morgen und der ewige Kampf um Aufmerksamkeit." MedienWirtschaft 13, no. 3 (2016): 34–36. http://dx.doi.org/10.15358/1613-0669-2016-3-34.
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In der letzten Ausgabe der MW hatten wir „zum Kampf um das Wohnzimmer“ drei Unternehmen zu Wort kommen lassen: ProSiebenSat.1 TV Deutschland, Loewe Technologies und Vodafone. In der Einleitung hatten wir wie folgt auf die Thematik hingeführt: „Über längere Zeit war die Mediennutzung im Wohnzimmer durch den klassischen Fernseher mit linearen Angeboten geprägt. Schon seit einiger Zeit wandelt sich dies. Mittlerweile verfügt eine Reihe von Haushalten über Fernseher, die neben der Nutzung linearer Programme auch den Zugriff auf Mediatheken sowie weitere Angebote relativ leicht und kostengünstig erlauben. Zudem erfolgt der Zugriff auf Inhalte auch über andere Endgeräte wie Tablets und Smartphones. Auch ist die Gemengelage komplexer geworden, müssen doch Inhalte, Endgeräte und Netze zusammenwirken. Es ist Zeit für eine kurze Zwischenbilanz nach der ersten Phase der Transformation des Inhaltekonsums im deutschen Wohnzimmer: Was hat sich bisher wirklich am Medienkonsum im Wohnzimmer verändert, was ist bald zu erwarten? Welche Angebote werden kommen, welche haben sich nicht bewährt? Welche Strategien verfolgen die unterschiedlichen Gruppen von Akteuren im deutschen Markt?“ In der heutigen Ausgabe finden sich die Einschätzungen eines Pay-TVAnbieters, einer öffentlich-rechtlichen Rundfunkanstalt sowie die Beschreibung der Aktivitäten von Amazon. Mit diesen Perspektiven möchten wir das Bild mit der letzten Ausgabe begonnene Bild vervollständigen.
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Rowe, D. Bradley, Stuart L. Warren, Frank A. Blazich, and D. Mason Pharr. "Seedling Growth of Catawba Rhododendron. II. Photosynthesis and Carbohydrate Accumulation and Export." HortScience 29, no. 11 (November 1994): 1303–8. http://dx.doi.org/10.21273/hortsci.29.11.1303.
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Catawba rhododendron (Rhododendron catawbiense Michx.) seedlings of two provenances, Johnston County, N.C. (35°45′N, 78°12′W, elevation = 67 m), and Yancey County, N.C. (35°45′N, 82°16′W, elevation = 1954 m), were grown in controlled-environment chambers for 18 weeks with days at 18, 22, 26, or 30C in factorial combination with nights at 14, 18, 22, or 26C. Seedlings of the higher-elevation provenance generally exhibited higher net leaf photosynthetic rates (PN)s than those from the lower elevation at all temperature combinations. Thus, it appears seedlings of the high-elevation provenance possess greater relative thermotolerance, expressed as net photosynthesis, than the low-elevation provenance. Eighty-seven days after initiation (DAI) of the experiment, PN showed a quadratic response to increasing day temperature, with the maximum occurring at 22C, whereas PN decreased linearly with increasing night temperature. At 122 DAI, PN increased linearly with increasing day temperature with nights at 22 and 26C. Highest PNs were at 30/22C and 26/22C. Carbohydrate export increased with increasing day temperature, whereas the response to night temperature was minimal. High levels of nonstructural carbohydrates occurred at thermoperiods (22/22C and 26/22C) that optimize seedling growth. However, definitive trends relating seedling growth to PNs, leaf carbohydrate levels, or to the amount of carbohydrate exported from the leaves were difficult to generalize due to numerous day × night interactions.
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Jiao, J., M. J. Tsujita, and B. Grodzinski. "Optimizing aerial environments for greenhouse rose production utilizing whole-plant net CO2 exchange data." Canadian Journal of Plant Science 71, no. 1 (January 1, 1991): 253–61. http://dx.doi.org/10.4141/cjps91-035.
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A daily growth model was developed for Samantha roses based on nondestructive measurements of whole-plant net CO2 exchange rate (NCER) under various aerial environmental conditions. Irradiance, CO2 concentration, and temperature accounted for 70, 20, and 5%, respectively, of the variance in whole-plant net photosynthesis explainable by a second-order polynomial model (R2 = 0.86). The predicted optimal temperatures for whole-plant net photosynthesis increased from 19 to 24 °C with increasing irradiance from 100 to 1200 μmol m−2 s−1 and CO2 concentration from 350 to 1500 μL L−1. Dark respiration rate increased exponentially with temperature and could be predicted by the Arrhenius equation. Even though respiratory carbon (C) loss at night increased linearly with daytime C gain, daily C gain (AC) was still proportional to daytime net photosynthesis. The relative contribution of irradiance (100–1200 μmol m−2s−1), day length (8–16 h), CO2 concentration (350–1500 μL L−1), day temperature (15–30 °C), and night temperature (15–25 °C) to plant daily growth was 64, 31, 4, 0.3, and 0.7%, respectively. Key words: Carbon balance, environment, modelling, photosynthesis, respiration, Rosa hybrida
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Purvis, Andy, Susanne A. Fritz, Jesús Rodríguez, Paul H. Harvey, and Richard Grenyer. "The shape of mammalian phylogeny: patterns, processes and scales." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1577 (September 12, 2011): 2462–77. http://dx.doi.org/10.1098/rstb.2011.0025.
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Mammalian phylogeny is far too asymmetric for all contemporaneous lineages to have had equal chances of diversifying. We consider this asymmetry or imbalance from four perspectives. First, we infer a minimal set of ‘regime changes’—points at which net diversification rate has changed—identifying 15 significant radiations and 12 clades that may be ‘downshifts’. We next show that mammalian phylogeny is similar in shape to a large set of published phylogenies of other vertebrate, arthropod and plant groups, suggesting that many clades may diversify under a largely shared set of ‘rules’. Third, we simulate six simple macroevolutionary models, showing that those where speciation slows down as geographical or niche space is filled, produce more realistic phylogenies than do models involving key innovations. Lastly, an analysis of the spatial scaling of imbalance shows that the phylogeny of species within an assemblage, ecoregion or larger area always tends to be more unbalanced than expected from the phylogeny of species at the next more inclusive spatial scale. We conclude with a verbal model of mammalian macroevolution, which emphasizes the importance to diversification of accessing new regions of geographical or niche space.
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Patterson, David T. "Effects of Day and Night Temperature on Goatsrue (Galega officinalis) and Alfalfa (Medicago sativa) Growth." Weed Science 41, no. 1 (March 1993): 38–45. http://dx.doi.org/10.1017/s0043174500057556.
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Goatsrue, a perennial legume, is an exotic noxious weed currently found in the United States only in Cache County, Utah. It infests irrigated pastures, alfalfa fields, and noncropland areas. In order to compare their responses to temperature, goatsrue and alfalfa were grown in artificially illuminated controlled-environment chambers in 16 day/night temperature regimes ranging from 15/4 to 36/25 C. Growth analysis was used to evaluate effects of temperature on dry matter accumulation, leaf area production, and biomass allocation. Both species grew best at day/night temperatures of 22/25, 29/ 18, and 29/25 C. Leaf appearance rates were linearly related to mean daily temperature. Goatsrue produced fewer but larger leaves and a greater total leaf area than alfalfa. Biomass partitioning to leaves was greater in goatsrue, whereas partitioning to stems was greater in alfalfa. Response of vegetative dry matter production to temperature closely paralleled response of leaf area duration in both species. Alfalfa generally had a higher net assimilation rate, but the greater leaf area duration of goatsrue resulted in greater dry matter accumulation in this species after 50 d of growth. Overall responses to temperature were similar in the two species. Thus it seems likely that goatsrue could become a much more widely distributed weed in alfalfa.
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Petersen, K. F., T. Price, G. W. Cline, D. L. Rothman, and G. I. Shulman. "Contribution of net hepatic glycogenolysis to glucose production during the early postprandial period." American Journal of Physiology-Endocrinology and Metabolism 270, no. 1 (January 1, 1996): E186—E191. http://dx.doi.org/10.1152/ajpendo.1996.270.1.e186.
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Relative contributions of net hepatic glycogenolysis and gluconeogenesis to glucose production during the first 12 h of a fast were studied in 13 healthy volunteers by noninvasively measuring hepatic glycogen content using 13C nuclear magnetic resonance spectroscopy. Rates of net hepatic glycogenolysis were calculated by multiplying the change in liver glycogen content with liver volume determined by magnetic resonance imaging. Rates of gluconeogenesis were calculated as the difference between rates of glucose production determined with an infusion of [6,6-2H]-glucose and net hepatic glycogenolysis. At 6 P.M. a liquid mixed meal (1,000 kcal; 60% as glucose) was given, to which [2-2H]glucose was added to trace glucose absorption. Hepatic glycogen content was measured between 11 P.M. and 1 A.M. and between 3 and 6 A.M. At 11 P.M. the concentration was 470 mM and it decreased linearly during the night. The mean liver volume was 1.47 +/- 0.06 liters. Net hepatic glycogenolysis (5.8 +/- 0.8 mumol.kg body wt-1.min-1) accounted for, on average, 45 +/- 6% and gluconeogenesis for 55 +/- 6% of the rate of whole body glucose production (12.6 +/- 0.6 mumol.kg body wt-1.min-1). In conclusion, this study shows that, even early in the phase of the postabsorptive period when liver glycogen stores are maximal, gluconeogenesis contributes approximately 50% to hepatic glucose production.
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van As, Dirk, Michiel R. van den Broeke, and Michiel M. Helsen. "Strong-wind events and their impact on the near-surface climate at Kohnen Station on the Antarctic Plateau." Antarctic Science 19, no. 4 (August 16, 2007): 507–19. http://dx.doi.org/10.1017/s095410200700065x.
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AbstractStrong-wind events occur 10–20 times per year at Kohnen Station, East Antarctica (75°00′S, 0°04′E, 2892 m above sea level), and are often caused by warm-core cyclones in the north-eastern Weddell Sea. An uncommon event occurred in January 2002, when blocking both in the south Atlantic Ocean and in the south Tasman Sea caused a split-up of the circumpolar vortex, and large amounts of heat and moisture were transported onto the Antarctic Plateau. During strong-wind events over the plateau the near-surface temperature can increase by tens of degrees, which is partly caused by the advection of heat, but for an important part by the destruction of the stable temperature-deficit layer by enhanced vertical mixing. The temperature rise is larger during the winter/night than during the summer/day, due to a better-developed temperature deficit. Snowdrift during the January 2002 event linearly increased surface roughness for momentum with friction velocity, for values over about 0.18 m s-1. The cloud cover during the event reduced down-welling solar radiation by 32%, and increased the albedo from about 0.86 to 0.92. Changes in longwave radiation largely cancelled the daytime changes in shortwave radiation, thus net radiation was most affected at night.
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Lowder, Adam W., Helen T. Kraus, Frank A. Blazich, and Stuart L. Warren. "Day/Night Temperatures Influence Growth and Photosynthesis During Containerized Production of Selected Species of Helleborus (Hellebores)." Journal of Environmental Horticulture 28, no. 3 (September 1, 2010): 179–86. http://dx.doi.org/10.24266/0738-2898-28.3.179.
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Abstract Containerized seedlings of Helleborus foetidus L. (stinking hellebore), H. niger L. (Christmas rose), and H. ×hybridus L. (Lenten rose) were grown under long-day conditions in controlled-environment chambers for 95 days with 9-hr days of 14, 18, 22, 26, or 30C (57, 64, 72, 79, or 86F) in factorial combination with 15-hr nights of 10, 14, 18, 22, or 26C (50, 57, 64, 72, or 79F). Long-day conditions were provided by a 3-hr night interruption. Growth of each species responded differently to day and night temperatures. Calculated maximum root, top, and total dry weight, and leaf area of H. foetidus occurred with days/nights of 20/15, 18/13, 19/14, and 18/15C (68/59, 65/55, 66/57, and 65/59F), respectively. While night temperature (NT) had no effect on root:top ratio [RTR (root dry weight ÷ top dry weight)], RTR was greatest (0.65) with days of 22C (72F). Helleborus niger had calculated maximum root dry weight and total dry weight with days of 14C (57F) and nights of 16 and 13C (60 and 55F), respectively. Top growth of H. niger decreased linearly as NTs increased for days of 14 or 22C (57 or 72F). Day temperatures (DTs) had no effect on RTR, whereas RTR responded quadratically as NT increased with a calculated maximum RTR at nights of 19C (66F). Leaf area was maximized at days/nights of 14/10C (57/50F). At days of 22 or 26C (72 or 79F), top growth of H. ×hybridus responded quadratically as NT increased with maxima occurring at nights of 18 or 17C (64 or 63F). Root dry weight responded quadratically at days of 14, 22, or 26C (57, 72, or 79F) and calculated maxima occurred with nights of 18C (64F). At days of 22 or 26C (72 or 79F), there were quadratic responses in total dry weight with calculated maximum growth of H. ×hybridus at nights of 18 or 17C (64 or 63F), respectively. For days of 14, 22, or 30C (57, 72, or 86F), there were quadratic responses in RTR with greatest RTR calculated at nights of 15, 18, or 16C (59, 64, or 60F), respectively. There were quadratic responses at days of 22 or 26C (72 or 79F) for leaf area with calculated maxima at nights of 18 or 17C (64 or 63F), respectively. As DTs increased from 14 to 30C (57 to 86F) net CO2 assimilation (PN) of H. ×hybridus also increased linearly whereas increased NTs had no effect on PN. In contrast, stomatal conductance was not impacted by DT or NT.
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Patterson, David T. "Effects of Temperature and Photoperiod on Growth and Development of Sicklepod (Cassia obtusifolia)." Weed Science 41, no. 4 (December 1993): 574–82. http://dx.doi.org/10.1017/s0043174500076347.
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Sicklepod was grown in controlled-environment chambers in 16 day/night temperature regimes ranging from 19/11 to 34/26 C. Maximum dry weight, leaf area, plant height, node number, and leaf number after 46 d occurred at 29/26 and 34/26 C. Temperatures of 29/21 C or lower reduced dry weight by more than 50%. Leaf number, leaf weight, and leaf area were more sensitive to changes in day temperature, whereas plant height and root, stem, and total dry weight were more sensitive to night temperature. Dry matter production was more closely correlated with leaf area duration than with its other component, net assimilation rate. Leaf appearance rate and dry matter production were linearly related to average daily temperature. The low-temperature threshold for leaf production was 13 ± 1 C. Observations of plant development in photoperiods ranging from 10 to 16 h confirmed that sicklepod is a short-day plant with a critical day length of 13 to 14 h. No reproductive development occurred in photoperiods of 15 or 16 h. Seedlings that emerged in 10-h photoperiods required more than 1-wk exposure to short days to initiate and continue reproductive development. Plants from a North Carolina population flowered earlier than plants from a Florida population in photoperiods of 12, 13, or 14 h, but in an 11-h photoperiod the two populations flowered at the same time.
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Chechin, Dmitry G., Irina A. Makhotina, Christof Lüpkes, and Alexander P. Makshtas. "Effect of Wind Speed and Leads on Clear-Sky Cooling over Arctic Sea Ice during Polar Night." Journal of the Atmospheric Sciences 76, no. 8 (July 26, 2019): 2481–503. http://dx.doi.org/10.1175/jas-d-18-0277.1.
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Abstract A simple analytical model of the atmospheric boundary layer (ABL) coupled to sea ice is presented. It describes clear-sky cooling over sea ice during polar night in the presence of leads. The model solutions show that the sea ice concentration and wind speed have a strong impact on the thermal regime over sea ice. Leads cause both a warming of the ABL and an increase of stability over sea ice. The model describes a sharp ABL transition from a weakly stable coupled state to a strongly stable decoupled state when wind speed is decreasing. The threshold value of the transition wind speed is a function of sea ice concentration. The decoupled state is characterized by a large air–surface temperature difference over sea ice, which is further increased by leads. In the coupled regime, air and surface temperatures increase almost linearly with wind speed due to warming by leads and also slower cooling of the ABL. The cooling time scale shows a nonmonotonic dependency on wind speed, being lowest for the threshold value of wind speed and increasing for weak and strong winds. Theoretical solutions agree well with results of a more realistic single-column model and with observations performed at the three Russian “North Pole” drifting stations (NP-35, -37, and -39) and at the Surface Heat Budget of the Arctic Ocean ice camp. Both modeling results and observations show a strong implicit dependency of the net longwave radiative flux at the surface on wind speed.
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Yates, K. K., and R. B. Halley. "CO<sub>3</sub><sup>2−</sup> concentration and pCO<sub>2</sub> thresholds for calcification and dissolution on the Molokai reef flat, Hawaii." Biogeosciences 3, no. 3 (July 24, 2006): 357–69. http://dx.doi.org/10.5194/bg-3-357-2006.
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Abstract. The severity of the impact of elevated atmospheric pCO2 to coral reef ecosystems depends, in part, on how seawater pCO2 affects the balance between calcification and dissolution of carbonate sediments. Presently, there are insufficient published data that relate concentrations of pCO2 and CO32− to in situ rates of reef calcification in natural settings to accurately predict the impact of elevated atmospheric pCO2 on calcification and dissolution processes. Rates of net calcification and dissolution, CO32− concentrations, and pCO2 were measured, in situ, on patch reefs, bare sand, and coral rubble on the Molokai reef flat in Hawaii. Rates of calcification ranged from 0.03 to 2.30 mmol CaCO3 m−2 h−1 and dissolution ranged from –0.05 to –3.3 mmol CaCO3 m−2 h−1. Calcification and dissolution varied diurnally with net calcification primarily occurring during the day and net dissolution occurring at night. These data were used to calculate threshold values for pCO2 and CO32− at which rates of calcification and dissolution are equivalent. Results indicate that calcification and dissolution are linearly correlated with both CO32− and pCO2. Threshold pCO2 and CO32− values for individual substrate types showed considerable variation. The average pCO2 threshold value for all substrate types was 654±195 μatm and ranged from 467 to 1003 μatm. The average CO32− threshold value was 152±24 μmol kg−1, ranging from 113 to 184 μmol kg−1. Ambient seawater measurements of pCO2 and CO32− indicate that CO32− and pCO2 threshold values for all substrate types were both exceeded, simultaneously, 13% of the time at present day atmospheric pCO2 concentrations. It is predicted that atmospheric pCO2 will exceed the average pCO2 threshold value for calcification and dissolution on the Molokai reef flat by the year 2100.
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K. K. Yates and R. B. Halley. "CO<sup>2−</sup><sub>3</sub> concentration and pCO<sub>2</sub> thresholds for calcification and dissolution on the Molokai reef flat, Hawaii." Biogeosciences Discussions 3, no. 1 (January 31, 2006): 123–54. http://dx.doi.org/10.5194/bgd-3-123-2006.
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Abstract. The severity of the impact of elevated atmospheric pCO2 to coral reef ecosystems depends, in part, on how seawater pCO2 affects the balance between calcification and dissolution of carbonate sediments. Presently, there are insufficient published data that relate concentrations of pCO2 and CO32− to in situ rates of reef calcification in natural settings to accurately predict the impact of elevated atmospheric pCO2 on calcification and dissolution processes. Rates of net calcification and dissolution, CO32− concentrations, and pCO2 were measured, in situ, on patch reefs, bare sand, and coral rubble on the Molokai reef flat in Hawaii. Rates of calcification ranged from 0.003 to 0.23 g CaCO3 m−2 h−1 and dissolution ranged from −0.005 to −0.33 g CaCO3 m−2 h−1. Calcification and dissolution varied diurnally with net calcification primarily occurring during the day and net dissolution occurring at night. These data were used to calculate threshold values for pCO2 and CO32− at which rates of calcification and dissolution are equivalent. Results indicate that calcification and dissolution are linearly correlated with both CO32− and pCO2. Threshold pCO2 and CO32− values for individual substrate types showed considerable variation. The average pCO2 threshold value for all substrate types was 654±195 µatm and ranged from 467 to 1003 µatm. The average CO3−- threshold value was 152±24 µmol kg-1, ranging from 113 to 184 µmol kg−1. Ambient seawater measurements of pCO2 and CO32− indicate that CO32− and pCO2 threshold values for all substrate types were both exceeded, simultaneously, 13% of the time at present day atmospheric pCO2 concentrations. It is predicted that atmospheric pCO2 will exceed the average pCO2 threshold value for calcification and dissolution on the Molokai reef flat by the year 2100.
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Nobel, Park S., and Hehui Zhang. "Photosynthetic Responses of Three Codominant Species from the North-western Sonoran Desert - a C3 Deciduous Sub-shrub, a C4 Deciduous Bunchgrass, and a CAM Evergreen Leaf Succulent." Functional Plant Biology 24, no. 6 (1997): 787. http://dx.doi.org/10.1071/pp96127.
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To investigate seasonal and annual influences of environmental conditions on leaf net CO2 uptake (A), three codominant species from the north-western Sonoran Desert differing in photosynthetic pathway and leaf phenology were examined: the C3 deciduous sub-shrub Encelia farinosa, the C4 deciduous bunchgrass Pleuraphis rigida, and the CAM evergreen leaf succulent Agave deserti. To allow interspecific comparisons and to predict field responses from 1974 through 1995, an environmental productivity index (EPI) model previously developed for CAM plants was used, which scaled the responses of A to water, temperature, and photosynthetic photon flux (PPF) over 24-h periods to individual dimensionless values. The net CO2 uptake predicted using the EPI approach agreed well with field measurements. Agave deserti was the most drought-tolerant and E. farinosa was the least; the optimum day/night air temperatures and the PPF requirement for A were highest for P. rigida and lowest for A. deserti. For 1974 through 1995, daily EPI averaged over a year was highest for E. farinosa, indicating that it operates closest to its photosynthetic optimum. However, the predicted A was highest for P. rigida. Variations in A were annually bimodal, with the greatest differences among the three species in wet years. Afor all three species increased linearly as annual rainfall increased. Leaf area per plant for E. farinosa was highest in the winter and early spring and did not respond appreciably to summer rainfall; leaf area for P. rigida was also highest in the winter. For the evergreen A. deserti, which based on ground cover is the dominant species at the field site, new leaves unfolded in response to both winter and summer rainfall but most photosynthetic area was contributed by older leaves, leading to the highest annual plant net CO2 uptake.
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Fleming, Z. L., P. S. Monks, A. R. Rickard, D. E. Heard, W. J. Bloss, P. W. Seakins, T. J. Still, et al. "Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002." Atmospheric Chemistry and Physics 6, no. 8 (June 20, 2006): 2193–214. http://dx.doi.org/10.5194/acp-6-2193-2006.
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Abstract. Peroxy radical (HO2+ΣRO2) measurements, using the PEroxy Radical Chemical Amplification (PERCA) technique at the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head in summer 2002, are presented and put into the context of marine, boundary-layer chemistry. A suite of other chemical parameters (NO, NO2, NO3, CO, CH4, O3, VOCs, peroxides), photolysis frequencies and meteorological measurements, are used to present a detailed analysis of the role of peroxy radicals in tropospheric oxidation cycles and ozone formation. Under the range of conditions encountered the peroxy radical daily maxima varied from 10 to 40 pptv. The diurnal cycles showed an asymmetric shape typically shifted to the afternoon. Using a box model based on the master chemical mechanism the average model measurement agreement was 2.5 across the campaign. The addition of halogen oxides to the model increases the level of model/measurement agreement, apparently by respeciation of HOx. A good correlation exists between j(HCHO).[HCHO] and the peroxy radicals indicative of the importance of HCHO in the remote atmosphere as a HOx source, particularly in the afternoon. The peroxy radicals showed a strong dependence on [NO2] with a break point at 0.1 ppbv, where the radicals increased concomitantly with the reactive VOC loading, this is a lower value than seen at representative urban campaigns. The HO2/(HO2+ΣRO2) ratios are dependent on [NOx] ranging between 0.2 and 0.6, with the ratio increasing linearly with NOx. Significant night-time levels of peroxy radicals were measured up to 25 pptv. The contribution of ozone-alkenes and NO3-alkene chemistry to night-time peroxy radical production was shown to be on average 59 and 41%. The campaign mean net ozone production rate was 0.11±0.3 ppbv h-1. The ozone production rate was strongly dependent on [NO] having linear sensitivity (dln(P(O3))/dln(NO)=1.0). The results imply that the N(O3) (the in-situ net photochemical rate of ozone production/destruction) will be strongly sensitive in the marine boundary layer to small changes in [NO] which has ramifications for changing NOx loadings in the European continental boundary layer.
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Fleming, Z. L., P. S. Monks, A. R. Rickard, D. E. Heard, W. J. Bloss, P. W. Seakins, T. J. Still, et al. "Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002." Atmospheric Chemistry and Physics Discussions 5, no. 6 (November 28, 2005): 12313–71. http://dx.doi.org/10.5194/acpd-5-12313-2005.
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Abstract. Peroxy radical (HO2+ΣRO2) measurements, using the PEroxy Radical Chemical Amplification (PERCA) technique at the North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) at Mace Head in summer 2002, are presented and put into the context of marine, boundary-layer chemistry. A suite of other chemical parameters (NO, NO2, NO3, CO, CH4, O3, VOCs, peroxides), photolysis frequencies and meteorological measurements, are used to present a detailed analysis of the role of peroxy radicals in tropospheric oxidation cycles and ozone formation. Under the range of conditions encountered the peroxy radical daily maxima varied from 10 to 40 pptv. The diurnal cycles showed an asymmetric shape typically shifted to the afternoon. Using a box model based on the master chemical mechanism the average model measurement agreement was 2.5 across the campaign. The addition of halogen oxides to the model increases the level of model/measurement agreement, apparently by respeciation of HOx. A good correlation exists between j(HCHO).[HCHO] and the peroxy radicals indicative of the importance of HCHO in the remote atmosphere as a HOx source, particularly in the afternoon. The peroxy radicals showed a strong dependence on [NOx] with a break point at 0.1 ppbv, where the radicals increased concomitantly with the reactive VOC loading, this is a lower value than seen at representative urban campaigns. The HO2/(HO2+ΣRO2) ratios are dependent on [NOx] ranging between 0.2 and 0.6, with the ratio increasing linearly with NOx. Significant night-time levels of peroxy radicals were measured up to 25 pptv. The contribution of ozone-alkenes and NO3-alkene chemistry to night-time peroxy radical production was shown to be on average 59 and 41%. The campaign mean net ozone production rate was 0.11±0.3 ppbv h−1. The ozone production rate was strongly dependent on [NO] having linear sensitivity (dln(P(O3))/dln(NO)=1.0). The results imply that the N(O3) (the in-situ net photochemical rate of ozone production/destruction) will be strongly sensitive in the marine boundary layer to small changes in [NO] which has ramifications for changing NOx loadings in the European continental boundary layer.
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Xu, X., C. Yi, and E. Kutter. "Stably stratified canopy flow in complex terrain." Atmospheric Chemistry and Physics 15, no. 13 (July 10, 2015): 7457–70. http://dx.doi.org/10.5194/acp-15-7457-2015.
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Abstract. Stably stratified canopy flow in complex terrain has been considered a difficult condition for measuring net ecosystem–atmosphere exchanges of carbon, water vapor, and energy. A long-standing advection error in eddy-flux measurements is caused by stably stratified canopy flow. Such a condition with strong thermal gradient and less turbulent air is also difficult for modeling. To understand the challenging atmospheric condition for eddy-flux measurements, we use the renormalized group (RNG) k–&varepsilon; turbulence model to investigate the main characteristics of stably stratified canopy flows in complex terrain. In this two-dimensional simulation, we imposed persistent constant heat flux at ground surface and linearly increasing cooling rate in the upper-canopy layer, vertically varying dissipative force from canopy drag elements, buoyancy forcing induced from thermal stratification and the hill terrain. These strong boundary effects keep nonlinearity in the two-dimensional Navier–Stokes equations high enough to generate turbulent behavior. The fundamental characteristics of nighttime canopy flow over complex terrain measured by the small number of available multi-tower advection experiments can be reproduced by this numerical simulation, such as (1) unstable layer in the canopy and super-stable layers associated with flow decoupling in deep canopy and near the top of canopy; (2) sub-canopy drainage flow and drainage flow near the top of canopy in calm night; (3) upward momentum transfer in canopy, downward heat transfer in upper canopy and upward heat transfer in deep canopy; and (4) large buoyancy suppression and weak shear production in strong stability.
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Ahlm, L., E. D. Nilsson, R. Krejci, E. M. Mårtensson, M. Vogt, and P. Artaxo. "A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest." Atmospheric Chemistry and Physics 10, no. 6 (March 31, 2010): 3063–79. http://dx.doi.org/10.5194/acp-10-3063-2010.
Full textAbstract:
Abstract. Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53 m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.
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Ahlm, L., E. D. Nilsson, R. Krejci, E. M. Mårtensson, M. Vogt, and P. Artaxo. "A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest." Atmospheric Chemistry and Physics Discussions 9, no. 6 (December 15, 2009): 26881–924. http://dx.doi.org/10.5194/acpd-9-26881-2009.
Full textAbstract:
Abstract. Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53 m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. The primary goal is to quantify the dry deposition sink and to investigate whether particle deposition velocities change when going from the clean wet season into the more polluted dry season. Furthermore, it is tested whether the rain forest is always a net sink of particles in terms of number concentrations, or if particle emission from the surface under certain circumstances may dominate over the dry deposition sink. The particle deposition velocity vd increased linearly with increasing friction velocity in both seasons and the relations are described by vdd=(2.7 u* −0.2)×10−3 (dry season) and vdw=2.5 u*×10−3 (wet season), where u* is the friction velocity. The fact that the two relations are very similar to each other indicates that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle deposition velocities in this study are low compared to studies over boreal forests. The reason is probably domination of accumulation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. Net particle deposition fluxes prevailed in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of natural biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.
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Cellot, Sonia, Jana Krosl, Keith Humphries, and Guy Sauvageau. "Revealing the Interplay of Extrinsic Versus Intrinsic Regulators of Self-Renewal in Hoxb4-Transduced HSCs." Blood 104, no. 11 (November 16, 2004): 367. http://dx.doi.org/10.1182/blood.v104.11.367.367.
Full textAbstract:
Abstract By modulating levels of Pbx-1, a homeodomain protein and DNA binding cofactor of Hoxb4, it is possible to generate pluripotent, ultracompetitive in vivo repopulating Hoxb4hi and Pbx1lo hematopoietic stem cells (HSCs) (Immunity, 2003, Krosl et al). Despite the tremendous regenerative potential demonstrated by these cells, the total in vivo HSC pool in recipients remained within physiological limits (~20 000 HSC/mouse), implying that environmental factors (niche availability?) restricted their expansion. These studies thus implied that bypassing the in vivo constraints of niche availability by culturing the transduced HSCs in vitro might reveal the intrinsic expansion potential of these cells. To study this hypothesis, Hoxb4hiPbx1lo transduced HSCs were generated by co-infecting primary mouse bone marrow (BM) cells with retroviruses encoding antisense Pbx1 cDNA plus YFP, and Hoxb4 plus GFP. At the end of the co-culture with retroviral producers, double gene transfer (Hoxb4hiPbx1lo ) was ~20% as determined by flow cytometric analysis of GFP and YFP co-expression. These cells were then cultured in the presence of serum and cytokines for additional 12–16 days, and the numbers of total cells, clonogenic progenitors and HSCs were determined at regular intervals. To quantify the magnitude of the in vitro HSC expansion, CRU assays for determination of cells with long-term lympho-myeloid repopulation potential were performed after removal of BM cells from co-culture with retroviral producers, and then at various time points. The increase in HSC numbers over time in culture was calculated as the ratio between absolute numbers of Hoxb4hiPbx1lo HSCs at a given time point, and their numbers at initiation of culture. In our initial experiment, numbers of Hoxb4hiPbx1lo CRU increased from 1000 at day 0 to 1.2 x 107 at day 12, for a net 10 000-fold expansion. After transplantation into irradiated mice, these cells underwent an additional 360-fold in vivo expansion to regenerate HSC pools of recipients up to, but not above, normal levels. Southern blot analyses of proviral integrations in DNA isolated from sorted Mac-1+, B-220+ and CD4+CD8+ cells derived from primary and secondary recipients demonstrated that cultured Hoxb4hiPbx1lo HSCs retained their ability to differentiate into all hematopoietic lineages examined. To estimate the numbers of distinct Hoxb4hiPbx1lo HSCs in cultures, BM cells from primary recipients of 1 x 106 cells from a 16-day expansion culture were plated in methylcellulose, and the clonal origin of individual myeloid colonies was determined by Southern blot analysis. These experiments showed that several distinct HSC clones reconstituted each recipient, and that some clones reconstituted at least 2 mice, illustrating the polyclonal nature and self-renewal activity of the cultured HSCs. Together, our experiments show that after unprecedented levels of in vitro expansion, Hoxb4hiPbx1lo HSCs remained capable of reconstituting myeloid and lymphoid systems of primary and secondary recipients, and yet responsive to the in vivo regulatory mechanisms that limit total stem cell pool size, reflecting the interplay between autonomous and non-cell autonomous control of HSC self-renewal. Decreasing Pbx1 levels in Hoxb4 overexpressing HSCs could thus be used as a tool for studying mechanisms of self-renewal and replicative senescence, and may lead to clinically relevant protocols for HSC expansion.