Diurnal variations and time to reach steady state of external markers used to estimate fecal excretion in sheep

The isotopic compositions of water fluxes provide valuable insights into the hydrological cycle and are widely used to quantify biosphere–atmosphere exchange processes. However, the combination of water isotope approaches with water flux components remains challenging. The Iso-SPAC (coupled heat, water with isotopic tracer in soil–plant–atmosphere-continuum) model is a useful framework for simulating the dynamics of water flux and its components, and for coupling with isotopic fractionation and mixing processes. Here, we traced the isotopic fractionation processes with separate soil evaporation (Ev) and transpiration (Tr), as well as their mixing in evapotranspiration (E) for simulating diurnal variations of isotope compositions in E flux (δE). Three sub modules, namely isotopic steady state (ISS), non-steady-state (NSS), and NSS Péclet, were tested to determine the true value for the isotope compositions of plant transpiration (δTr) and δE. In situ measurements of isotopic water vapor with the Keeling-plot approach for δE and robust eddy covariance data for E agreed with the model output (R2 = 0.52 and 0.98, RMSD = 2.72‰, and 39 W m−2), illustrating the robustness of the Iso-SPAC model. The results illustrate that NSS is a better approximation for estimating diurnal variations in δTr and δE, specifically during the alternating periods of day and night. Leaf stomata conductance regulated by solar radiation controlled the diurnal variations in transpiration fraction (Tr/E). The study emphasized that transpiration and evaporation, respectively, acted to increase and decrease the δ18O of water vapor that was affected by the diurnal trade-off between them.

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Simulation of the diurnal variations of the oxygen isotope anomaly (Δ<sup>17</sup>O) of reactive atmospheric species

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-30405-2010 ◽

2010 ◽

Vol 10 (12) ◽

pp. 30405-30451

Author(s):

S. Morin ◽

R. Sander ◽

J. Savarino

Keyword(s):

Steady State ◽

Chemical Reactions ◽

Atmospheric Chemistry ◽

Balance Equation ◽

Isotopic Signature ◽

Diurnal Variations ◽

Mass Balance Equation ◽

Computational Costs ◽

Atmospheric Species ◽

Atmospheric Nitrate

Abstract. The isotope anomaly (Δ17O) of secondary atmospheric species such as nitrate (NO3−) or hydrogen peroxyde (H2O2) has potential to provide useful constrains on their formation pathways. Indeed, the Δ17O of their precursors (NOx, HOx etc.) differs and depends on their interactions with ozone, which is the main source of non-zero Δ17O in the atmosphere. Interpreting variations of Δ17O in secondary species requires an in-depth understanding of the Δ17O of their precursors taking into account non-linear chemical regimes operating under various environmental settings. We present results from numerical simulations carried out using the atmospheric chemistry box model (CAABA/MECCA) to explicitly compute the diurnal variations of the isotope anomaly of short-lived species such as NOx and HOx. Δ17O was propagated from ozone to other species (NO, NO2, OH, HO2, RO2, NO3, N2O5, HONO, HNO3, HNO4, H2O2) according to the classical mass-balance equation, through the implementation of various sets of hypotheses pertaining to the transfer of Δ17O during chemical reactions. The model confirms that diurnal variations in Δ17O of NOx are well predicted by the photochemical steady-state relationship during the day, but that at night a different approach must be employed (i.e. "fossilization" of the Δ17O of NOx as soon as the photolytical lifetime of NOx drops below ca. 5 min). We quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H2O2 under the various environmental conditions analyzed, which is of particular relevance to larger-scale implementations of Δ17O where high computational costs cannot be afforded.

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Diurnal variations in the motility of algal populations

10.1101/854844 ◽

2019 ◽

Author(s):

D. Jin ◽

J Kotar ◽

E. Silvester ◽

K. C. Leptos ◽

O. A. Croze

Keyword(s):

Steady State ◽

Diurnal Cycle ◽

Swimming Speed ◽

Dark Period ◽

Beat Frequency ◽

Diurnal Variations ◽

Power Balance ◽

Diurnal Cycles ◽

Flagellar Beat ◽

The Mean

ABSTRACTThe motility of microalgae has been studied extensively, particularly in model microorganisms such as Chlamy-domonas reinhardtii. For this and other microalgal species, diurnal cycles are well-known to control the metabolism, growth and cell division. Diurnal variations, however, have been largely neglected in quantitative studies of motility. Here, we demonstrate using tracking microscopy how the motility statistics of C. reinhardtii are modulated by diurnal cycles. We discovered that the mean swimming speed is greater during the dark period of a diurnal cycle. From this measurement, using a hydrodynamic power balance, we conjecture that this is a result of the mean flagellar beat frequency being modulated by the flagellar ATP. Our measurements also quantify the diurnal variations of the orientational and gravitactic transport of C. reinhardtii. We discuss the implications of our frequency results in the context of cellular bioenergetics. Further, we explore the population-level consequences of diurnal variations of motility statistics by evaluating a prediction for how the gravitactic steady state changes with time during a diurnal cycle.SIGNIFICANCEWe report tracking microscopy measurements which demonstrate that the mean swimming speed of C. reinhardtii is significantly greater during the dark period of a diurnal cycle. Using hydrodynamic (low Reynolds number) power balance, we also inferred the mean flagellar beat frequency from the swimming speed, hypothesising that the observed variations in this frequency correlate with the diurnal regulation of flagellar ATP. Diurnal variations of the orientational and gravitactic transport of C. reinhardtii were also quantified and used in a continuum model to predict that, at the population scale, the steady state vertical distribution of C. reinhardtii is broader during the dark period. Our findings could have significant implications for microalgal biotechnologies, e.g. microalgal harvesting, and plankton migration in the ocean.

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Concentrative and reversible character of intestinal amino acid transport

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1963.205.2.255 ◽

1963 ◽

Vol 205 (2) ◽

pp. 255-260 ◽

Cited By ~ 31

Author(s):

Halvor N. Christensen ◽

Bruce H. Feldman ◽

A. Baird Hastings

Keyword(s):

Amino Acids ◽

Steady State ◽

Amino Acid ◽

Fecal Excretion ◽

Intestinal Loop ◽

Acid Transport ◽

Steady State Distribution ◽

State Distribution ◽

Outward Migration

Either α-aminoisobutyric acid-1-C14 or 1-aminocyclopentanecarboxylic acid-1-C14 was injected into a rat and, after at least 24 hr, a suitable dilution of the same solution of the amino acid was introduced into an intestinal loop in situ and the change in its distribution observed by radioisotope counting. The two amino acids could be concentrated from the small intestine to establish steady-state distribution ratios of from 12 to 100, for the plasma level with respect to the level in the lumen. These values are far higher than the distribution ratios produced across excised intestine. These steady-state values were approached from either above or below, by absorption or release of the amino acid. The release was accelerated by the presence of the same or another amino acid of high transport affinity in fluid perfusing the intestinal loop, an action that tends to identify the outward migration from lumen to plasma with a transport process. The test amino acids were released into the colon also, although at slower rates, the steady-state distribution ratio lying in the neighborhood of unity. This release appears also to be a specific process, and to account for the slow fecal excretion of these difficultly metabolized amino acids.

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Studies on Water in the Hydration Chamber of a Modified Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069715 ◽

1970 ◽

Vol 28 ◽

pp. 544-545

Author(s):

R. C. Moretz ◽

G. G. Hausner ◽

D. F. Parsons

Keyword(s):

Thin Film ◽

Thin Films ◽

Electron Microscope ◽

Steady State ◽

Room Temperature ◽

Small Mass ◽

Equilibrium Pressure ◽

Biological Objects ◽

Mechanical Pump ◽

Differential Pumping

Use of the electron microscope to examine wet objects is possible due to the small mass thickness of the equilibrium pressure of water vapor at room temperature. Previous attempts to examine hydrated biological objects and water itself used a chamber consisting of two small apertures sealed by two thin films. Extensive work in our laboratory showed that such films have an 80% failure rate when wet. Using the principle of differential pumping of the microscope column, we can use open apertures in place of thin film windows.Fig. 1 shows the modified Siemens la specimen chamber with the connections to the water supply and the auxiliary pumping station. A mechanical pump is connected to the vapor supply via a 100μ aperture to maintain steady-state conditions.

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Continuous hydrogenolysis of acetal-stabilized lignin in flow

Green Chemistry ◽

10.1039/d0gc02928a ◽

2021 ◽

Author(s):

Wu Lan ◽

Yuan Peng Du ◽

Songlan Sun ◽

Jean Behaghel de Bueren ◽

Florent Héroguel ◽

...

Keyword(s):

Steady State ◽

Challenges And Opportunities

We performed a steady state high-yielding depolymerization of soluble acetal-stabilized lignin in flow, which offered a window into challenges and opportunities that will be faced when continuously processing this feedstock.

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