Airspace structure and mathematical modelling of oxygen diffusion, aeration and anoxia in Eleocharis sphacelata R. Br. Roots

1994 ◽  
Vol 45 (8) ◽  
pp. 1529 ◽  
Author(s):  
BK Sorrell
Keyword(s):  
Root Length ◽  
Oxygen Diffusion ◽  
Apical Meristem ◽  
Respiratory Activity ◽  
Quantitative Description ◽  
Main Axis ◽  
Fine Scale ◽  
Oxygen Release ◽  
Partial Pressures

A quantitative description of the structure of the roots of Eleocharis sphacelata is presented, forming the basis of a mathematical analysis of their aeration via the intercellular airspace system. The mature aerenchymatous roots have cortical porosites as high as 70% and resistances to axial diffusion of 0.015-0.04 Ms mm-3 per mm root length. The corresponding resistance in the younger, non-aerenchymatous tissue just behind the apex is 0.08-0.14 Ms mm-3 per mm, root length. The observed maximum length of the roots (about 0.3 m) is not caused by the oxygen limitations at the apical meristem of the main axis because axial fluxes could theoretically support the meristem in much longer roots. However, the phloem and pericycle of the stele become hypoxic at 0.25 to 0.3 m, suggesting that length could be limited by the need to prevent excessive hypoxia in these tissues. Rates of root oxygen release into the sediment are predicted to be as high as 2.5 �mol h-1 per 0.3-m-long root and higher still for shorter roots. The prevention of anoxia depends greatly on the basal oxygen concentration at the root base: oxygen partial pressures below 8 kPa in the rhizome would cause meristematic anoxia in 0.3 m-long roots. A better resolution of fine-scale variations in respiratory activity in the roots and in the sediment rhizosphere could improve the accuracy of the model, but it does nevertheless indicate that roots of E. sphacelata would normally remain aerobic and significantly oxidize anaerobic sediments in situ.

In-Situ UHV Tem Investigations of the Initial Oxidation Stage of Copper Thin Films

1997 ◽  
Vol 481 ◽  
Author(s):  
J. C. Yang ◽  
M. Yeadon ◽  
B. Kolasa ◽  
J. M. Gibson
Keyword(s):  
Oxygen Diffusion ◽  
Copper Film ◽  
Nucleation And Growth ◽  
Rate Theory ◽  
Initial Oxidation ◽  
Nucleation Sites ◽  
Partial Pressures ◽  
Oxidation Stage ◽  
Preferential Nucleation

ABSTRACTThe nucleation and growth of Cu2O due to oxidation of Cu(001) films were monitored at various temperatures and oxygen partial pressures. For all examined temperatures and pressures, Cu2O islands were observed to form epitaxially with respect to the copper film. The nucleation of these oxide islands was homogeneous –no clear evidence was observed for either steps or dislocations being preferential nucleation sites. Based on this data, we have developed a semiquantitative model of the initial oxidation stage where the dominant mechanism for transport, nucleation and growth of oxide islands is oxygen diffusion on the Cu surface. We are presently comparing our experimental data with nucleation rate theory, where the predictions qualitatively describe our observations, but not quantitatively.

A polycentric growth model of gallium arsenide epitaxial layers from the gas phase with simultaneous diffusion, adsorption and chemical reaction

1988 ◽  
Vol 53 (12) ◽  
pp. 2995-3013
Author(s):  
Emerich Erdös ◽  
Jindřich Leitner ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma
Keyword(s):  
Growth Rate ◽  
Gallium Arsenide ◽  
Epitaxial Growth ◽  
Gas Phase ◽  
Surface Reaction ◽  
Quantitative Description ◽  
The Other ◽  
Rate Equations ◽  
Impact Interaction ◽  
Partial Pressures

For a quantitative description of the epitaxial growth rate of gallium arsenide, two models are proposed including two rate controlling steps, namely the diffusion of components in the gas phase and the surface reaction. In the models considered, the surface reaction involves a reaction triple - or quadruple centre. In both models three mechanisms are considered which differ one from the other by different adsorption - and impact interaction of reacting particles. In every of the six cases, the pertinent rate equations were derived, and the models have been confronted with the experimentally found dependences of the growth rate on partial pressures of components in the feed. The results are discussed with regard to the plausibility of individual mechanisms and of both models, and also with respect to their applicability and the direction of further investigations.

scholarly journals Extended expression of MaKN1 contributes to the leaf morphology in aquatic forms of Myriophyllum aquaticum

Botany ◽  
2015 ◽  
Vol 93 (9) ◽  
pp. 611-621
Author(s):  
M.D. Shafiullah ◽  
Christian R. Lacroix
Keyword(s):  
Apical Meristem ◽  
Leaf Morphology ◽  
Expression Patterns ◽  
Homeobox Gene ◽  
Leaf Primordia ◽  
Leaf Primordium ◽  
Myriophyllum Aquaticum ◽  
Knox Gene ◽  
Leaf Morphogenesis

Myriophyllum aquaticum (Vell.) Verdc. is heterophyllous in nature with highly dissected simple leaves consisting of several lobes. KNOX (KNOTTED1-LIKE HOMEOBOX) genes are believed to have played an important role in the evolution of leaf diversity. Up-regulation of KNOX during leaf primordium initiation can lead to leaf dissection in plants with simple leaves and, if overexpressed, can produce ectopic meristems on leaves. A previous study on KNOX gene expression in the aerial form of this species showed that this gene is expressed in the shoot apical meristem (SAM), as well as in leaf primordia P0 to P8. Based on these results, it was hypothesized that the prolonged expression of the MaKN1 (Myriophyllum aquaticum Knotted1-like homeobox) gene beyond P8, might play an important role in the generation of more lobes, longer lobes, and hydathode formation in the aquatic leaves of M. aquaticum. The technique of in situ hybridization was carried out using a previously sequenced 300 bp fragment of MaKN1 to determine the expression patterns of this gene in the shoot of aquatic forms of the plant. Expression patterns of MaKN1 revealed that the SAM and leaf primordia of aquatic forms of M. aquaticum at levels P0 (youngest) to P4 were distributed throughout these structures. The level of expression of this MaKN1 gene progressively became more localized to lobes in older leaf primordia (levels P5 to P12). Previous studies of aerial forms of this plant showed MaKN1 expression until P8. Our results with aquatic forms show that the highly dissected leaf morphology in aquatic forms was the result of the prolonged expression of MaKN1 beyond P8. This resulted in the formation of elongated and slightly more numerous lobes, and hydathodes in aquatic forms. These findings support the view that KNOX genes are important developmental regulators of leaf morphogenesis and have played an important role in the evolution of leaf forms in the plant kingdom.

scholarly journals Flux Mapping and Magnetic Behavior of Grain Boundaries in Nd-Fe-B Magnets

1999 ◽  
Vol 589 ◽  
Author(s):  
V.V. Volkov ◽  
Yimei Zhu
Keyword(s):  
Magnetic Flux ◽  
Grain Boundaries ◽  
Domain Walls ◽  
Quantitative Description ◽  
Magnetic Behavior ◽  
Local Variation ◽  
Smooth Transition ◽  
Lorentz Microscopy ◽  
Hard Magnets

AbstractAdvanced Fresnel- & Foucault-Lorentz microscopy were applied to analyze magnetic behavior of the grain boundaries in Nd-Fe-B hard magnets. In-situ TEM magnetizing experiments combined with these imaging methods revealed the process of magnetization reversal in polycrystalline sintered and die-upset Nd-Fe-B under various magnetic fields. Fine details of magnetic flux distribution, derived from the magnetic interferograms created by phase-coherent Foucault imaging, provide a quantitative description of the local variation of magnetic flux. Our study suggests that the grain boundaries play an important multi-functional role in the reversal of magnetization, by acting as (a) pinning centers of domain walls, (b) centers of nucleation of reversal domains, and (c) sinks or sources for migrating magnetostatic charges and/or dipoles. They also ensure a smooth transition for irreversible remagnetization in polycrystalline samples.

Continuous measurement of gas partial pressures in intracerebral tissue

1978 ◽  
Vol 44 (4) ◽  
pp. 528-533 ◽  
Author(s):  
J. Seylaz ◽  
E. Pinard
Keyword(s):  
Continuous Measurement ◽  
Fast Response ◽  
Base Line ◽  
Partial Pressures ◽  
Mass Spectrograph ◽  
Present Technique ◽  
Gas Molecules ◽  
The Brain ◽  
Thin Polyethylene

A mass spectrograph technique has been developed for measurement of physiological gas partial pressures locally in the brain. The sampling cannula is implanted stereotaxically and remains in situ for several weeks. It is a thin cylinder in shape, and is covered with a thin polyethylene membrane across which gas molecules can be sampled continuously. The conductance of this membrane is well adapted to the limited rate of replacement of gas molecules afforded by the cerebral tissue, hence there is no depletion around the cannula; this depletion has until now been the major problem of this technology. The present technique provides a continuous measurement with fast response time, which is directly proportional to the partial pressures of the gases. The variations can be expressed as a percentage of the base-line value.

scholarly journals Fine-scale features on the sea surface in SAR satellite imagery – Part 1: Simultaneous in-situ measurements

2012 ◽  
Vol 9 (5) ◽  
pp. 2885-2914 ◽  
Author(s):  
A. Soloviev ◽  
C. Maingot ◽  
S. Matt ◽  
R. E. Dodge ◽  
S. Lehner ◽  
...  
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Companion Paper ◽  
In Situ Measurements ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Upper Ocean ◽  
Fine Scale ◽  
Sar Imagery

Abstract. This work is aimed at identifying the origin of fine-scale features on the sea surface in synthetic aperture radar (SAR) imagery with the help of in-situ measurements as well as numerical models (presented in a companion paper). We are interested in natural and artificial features starting from the horizontal scale of the upper ocean mixed layer, around 30–50 m. These features are often associated with three-dimensional upper ocean dynamics. We have conducted a number of studies involving in-situ observations in the Straits of Florida during SAR satellite overpass. The data include examples of sharp frontal interfaces, wakes of surface ships, internal wave signatures, as well as slicks of artificial and natural origin. Atmospheric processes, such as squall lines and rain cells, produced prominent signatures on the sea surface. This data has allowed us to test an approach for distinguishing between natural and artificial features and atmospheric influences in SAR images that is based on a co-polarized phase difference filter.

scholarly journals A Method for Experimental Warming of Developing Tree Seeds With A Common Garden Demonstration of Seedling Responses

2020 ◽  
Author(s):  
Ehren Reid Von Moler ◽  
Gerald Page ◽  
Lluvia Flores-Renteria ◽  
Cory Garms ◽  
Julia Hull ◽  
...  
Keyword(s):  
Seed Development ◽  
Air Temperature ◽  
Climate Warming ◽  
Root Length ◽  
Common Garden ◽  
Effect Sizes ◽  
Seedling Performance ◽  
Tree Seeds ◽  
Root Collar

Abstract BackgroundForest dieback driven by rapid climate warming threatens ecosystems worldwide. The health of forested ecosystems depends on how tree species respond to warming during all life history stages. While it is known that seed development is temperature-sensitive, little is known about possible effects of climate warming on seed development and subsequent seedling performance. Exposure of seeds to high air temperatures may influence subsequent seedling performance negatively, though conversely, warming during seed development may aid acclimation of seedlings to subsequent thermal stress. Technical challenges associated with in-situ warming of developing tree seeds limit understanding of how tree species may respond to seed development in a warmer climate. ResultsWe developed and validated a simple method for passively warming seeds as they develop in tree canopies to enable controlled study of climate warming on seedling performance. We quantified thermal effects of the cone-warming method across individual pine trees and stands by measuring the air temperature surrounding seed cones using thermal loggers and the temperature of seed cone tissue using thermocouples. We then investigated seedling phenotypes in relation to the warming method through a common garden study. We assessed plant morphological, physiological, and mycorrhizal nodulation in response to cone-warming for 20 seed source trees on the San Francisco Peaks in northern Arizona, USA. The warming method increased air temperature surrounding developing seed cones by 2.1◦C, a plausible increase in mean air temperature by 2050 under current climate projections. Notable effect sizes of cone-warming were detected for seedling root length, shoot length, and diameter at root collar using Cohen’s Local f 2. Root length was most affected by cone-warming, however, effect sizes of cone-warming on root length and diameter at root collar became negligible after the first year of growth. Cone-warming had small but significant effects on mycorrhizal fungal richness and seedling multispectral near-infrared indices indicative of plant health. ConclusionsThe method was shown to reliably elevate the temperature surrounding seed cones and thereby facilitate experimental in-situ climate change research on forest trees. The method was furthermore shown to influence plant traits that may affect seedling performance under climate warming.

scholarly journals Augmenting biologging with supervised machine learning to studyin situbehavior of the medusaChrysaora fuscescens

2019 ◽  
Author(s):  
Clara Fannjiang ◽  
T. Aran Mooney ◽  
Seth Cones ◽  
David Mann ◽  
K. Alex Shorter ◽  
...  
Keyword(s):  
Machine Learning ◽  
High Resolution ◽  
Laboratory Data ◽  
Supervised Machine Learning ◽  
Motion Sensors ◽  
Fine Scale ◽  
Video Footage ◽  
Research Findings ◽  
Summary Statement

AbstractZooplankton occupy critical roles in marine ecosystems, yet their fine-scale behavior remains poorly understood due to the difficulty of studying individualsin situ. Here we combine biologging with supervised machine learning (ML) to demonstrate a pipeline for studyingin situbehavior of larger zooplankton such as jellyfish. We deployed the ITAG, a biologging package with high-resolution motion sensors designed for soft-bodied invertebrates, on 8Chrysaora fuscescensin Monterey Bay, using the tether method for retrieval. Using simultaneous video footage of the tagged jellyfish, we develop ML methods to 1) identify periods of tag data corrupted by the tether method, which may have compromised prior research findings, and 2) classify jellyfish behaviors. Our tools yield characterizations of fine-scale jellyfish activity and orientation over long durations, and provide evidence that developing behavioral classifiers onin siturather than laboratory data is essential.Summary StatementHigh-resolution motion sensors paired with supervised machine learning can be used to infer fine-scalein situbehavior of zooplankton for long durations.

scholarly journals Impact of ocean acidification and elevated temperatures on early juveniles of the polar shelled pteropod <i>Limacina helicina</i>: mortality, shell degradation, and shell growth

2010 ◽  
Vol 7 (6) ◽  
pp. 8177-8214 ◽  
Author(s):  
S. Lischka ◽  
J. Büdenbender ◽  
T. Boxhammer ◽  
U. Riebesell
Keyword(s):  
Ocean Acidification ◽  
Surface Waters ◽  
Elevated Temperatures ◽  
Shell Growth ◽  
Shell Diameter ◽  
Partial Pressures ◽  
Limacina Helicina ◽  
Different Temperatures ◽  
Arctic Surface

Abstract. Due to their aragonitic shell thecosome pteropods may be particularly vulnerable to ocean acidification driven by anthropogenic CO2 emissions. This applies specifically to species inhabiting Arctic surface waters that are projected to become locally undersaturated with respect to aragonite as early as 2016. This study investigated the effects of rising pCO2 partial pressures and elevated temperature on pre-winter juveniles of the polar pteropod Limacina helicina. After a 29 days experiment in September/October 2009 at three different temperatures and under pCO2 scenarios projected for this century, mortality, shell degradation, shell diameter and shell increment were investigated. Temperature and pCO2 had a significant effect on mortality, but temperature was the overriding factor. Shell diameter, shell increment and shell degradation were significantly impacted by pCO2 but not by temperature. Mortality was 46% higher at 8 °C compared to 3 °C (in situ), and 14% higher at 1100 μatm CO2 as compared to 230 μatm CO2. Shell diameter and increment were reduced by 10% and 12% at 1100 μatm CO2 as compared to 230 μatm CO2, respectively, and shell degradation was 41% higher at elevated compared to ambient pCO2 partial pressures. We conclude that pre-winter juveniles will be negatively affected by both rising temperature and pCO2 which may result in a possible abundance decline of the overwintering population, the basis for next year's reproduction.

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