scholarly journals A new mathematical model to explore microbial processes and their constraints in phytoplankton colonies and sinking marine aggregates

2018 ◽  
Vol 4 (10) ◽  
pp. eaat1991 ◽  
Author(s):  
Nasrollah Moradi ◽  
Bo Liu ◽  
Morten Iversen ◽  
Marcel M. Kuypers ◽  
Helle Ploug ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Large Scale ◽  
Theoretical Models ◽  
Microbial Processes ◽  
Small Scale ◽  
Concentration Gradients ◽  
Constant Concentration ◽  
Physical Chemical ◽  
Theoretical Assumptions ◽  
Marine Aggregates

N2-fixing colonies of cyanobacteria and aggregates of phytoplankton and detritus sinking hundreds of meters per day are instrumental for the ocean’s sequestration of CO2from the atmosphere. Understanding of small-scale microbial processes associated with phytoplankton colonies and aggregates is therefore crucial for understanding large-scale biogeochemical processes in the ocean. Phytoplankton colonies and sinking aggregates are characterized by steep concentration gradients of gases and nutrients in their interior. Here, we present a mechanistic mathematical model designed to perform modeling of small-scale fluxes and evaluate the physical, chemical, and biological constraints of processes that co-occur in phytoplankton colonies and sinking porous aggregates. The model accurately reproduced empirical measurements of O2concentrations and fluxes measured in sinking aggregates. Common theoretical assumptions of either constant concentration or constant flux over the entire surface did not apply to sinking aggregates. Consequently, previous theoretical models overestimate O2flux in these aggregates by as high as 15-fold.

The influence of atmospheric waves on the general circulation of the middle atmosphere

1987 ◽  
Vol 323 (1575) ◽  
pp. 693-705 ◽  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Chemical Species ◽  
Theoretical Models ◽  
Irreversible Processes ◽  
Small Scale ◽  
Wind Fields ◽  
Meridional Transport ◽  
Radiative Balance

To a first approximation, the basic features of the globally averaged structure of the middle atmosphere (such as the warm stratopause and cold mesopause) can be understood on radiative grounds alone. However, dynamical processes must be invoked if the observed latitudinally varying structures of the zonal-mean temperature and wind fields are to be explained. Particularly large departures from a hypothetical radiatively determined state occur in the winter stratosphere (especially in the Northern Hemisphere) and in the upper mesosphere at the solstices. Simple theoretical models indicate that the primary dynamical mechanisms that drive the middle atmosphere away from radiative balance are wave motions, notably large-scale planetary waves and small-scale gravity waves. Much current research is being devoted to understanding the complex transient and irreversible processes by which such waves can influence the zonal-mean state and also lead to the meridional transport of chemical species.

scholarly journals <i>Letter to the Editor</i>: First direct observations of the reduced striations at pump frequencies close to the electron gyroharmonics

1999 ◽  
Vol 17 (9) ◽  
pp. 1235-1238 ◽  
Author(s):  
F. Honary ◽  
T. R. Robinson ◽  
D. M. Wright ◽  
A. J. Stocker ◽  
M. T. Rietveld ◽  
...  
Keyword(s):  
Large Scale ◽  
Electromagnetic Emission ◽  
Theoretical Models ◽  
Small Scale ◽  
Radio Waves ◽  
Radio Science ◽  
Ionospheric Physics ◽  
F Region ◽  
Direct Observations ◽  
Electron Gyrofrequency

Abstract. It is well known that the ionospheric plasma response to high-power HF radio waves changes drastically as the heater frequency approaches harmonics of the electron gyrofrequency. These include changes in the spectrum of the stimulated electromagnetic emission, reduction in the anomalous absorption of low-power diagnostic waves propagating through the heated volume, and reduction in the large scale F-region heating. Theoretical models as well as previous experimental evidence point towards the absence of small-scale field-aligned plasma density irregularities at pump frequencies close to electron gyroharmonics as the main cause of these changes. Results presented in this paper are the first direct observations of the reduced striations at the 3rd gyroharmonic made by the CUTLASS radar. In addition, simultaneous EISCAT observations have revealed that the "enhanced ion-line" usually present in the EISCAT ion-line spectrum during the first few seconds after heater switch on, persisted at varying strengths while the heater was transmitting at frequencies close to the 3rd electron gyroharmonics.Key words. Ionosphere (active experiments; ionospheric irregularities) · Radio science (ionospheric physics)

scholarly journals Nonstandard Mathematical Model for Fatigue Failure

2015 ◽  
Vol 13 ◽  
pp. 127-135
Author(s):  
Petru Cardei ◽  
Gheorghe Voicu ◽  
Mihai Matache ◽  
Iulian Voicea ◽  
Vergil Muraru ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Numerical Analysis ◽  
Structural Analysis ◽  
Computer Simulations ◽  
Theoretical Models ◽  
Small Scale ◽  
Material Structure ◽  
Quality Change ◽  
Physical Test ◽  
Complex Phenomena

Tests performed under simulated regime, use simulating tools with different structures and often have a corresponding physical test to complete certain conclusions in order to explain complex phenomena that are difficult, impossible, or very costly to run physically. Computer simulations are also called virtual tests beside which there are mechanical or small scale analog simulators. Among the virtual tests for mechanical structures there are structural analysis tests that use numerical analysis methods. Sometimes, in order to understand the phenomena that occurs in the material structure, new complex theoretical models were used for explaining the material quality change. One such application is proposed, which incorporates an old author’s model, for the fatigue and quality phenomenon study of the material change.

scholarly journals Energy Conversion in Protocells with Natural Nanoconductors

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Jian Xu ◽  
T. Kyle Vanderlick ◽  
David A. LaVan
Keyword(s):  
Energy Conversion ◽  
Large Scale ◽  
Numerical Models ◽  
Salt Water ◽  
Ion Concentration ◽  
Small Scale ◽  
Lipid Bilayer Membranes ◽  
Concentration Gradients ◽  
Supported Lipid Bilayer ◽  
Conversion Scheme

While much nanotechnology leverages solid-state devices, here we present the analysis of designs for hybrid organic-inorganic biomimetic devices, “protocells,” based on assemblies of natural ion channels and ion pumps, “nanoconductors,” incorporated into synthetic supported lipid bilayer membranes. These protocells mimic the energy conversion scheme of natural cells and are able to directly output electricity. The electrogenic mechanisms have been analyzed and designs were optimized using numerical models. The parameters that affect the energy conversion are quantified, and limits for device performance have been found using numerical optimization. The electrogenic performance is compared to conventional and emerging technologies and plotted on Ragone charts to allow direct comparisons. The protocell technologies summarized here may be of use for energy conversion where large-scale ion concentration gradients are available (such as the intersection of fresh and salt water sources) or small-scale devices where low power density would be acceptable.

scholarly journals Lyman-α Forest and Cosmic Weak Lensing in a Warm Dark Matter Universe

2014 ◽  
Vol 31 ◽  
Author(s):  
Katarina Markovič ◽  
Matteo Viel
Keyword(s):  
Dark Matter ◽  
Large Scale ◽  
Theoretical Models ◽  
Large Scale Structure ◽  
Mass Function ◽  
Scale Structure ◽  
Small Scale ◽  
Current State ◽  
Upper Limits ◽  
Order Of Magnitude

AbstractWe review the current state of the theory of large-scale structure in a warm dark matter (WDM) cosmological model. In particular, we focus on the non-linear modelling of the matter power spectrum and on the mass function of dark matter haloes. We describe the results of N-body simulations with WDM and mention the effects that could be induced by baryonic physics. We also examine the halo model of large-scale structure and its recently suggested modifications for a WDM cosmology, which account for the small-scale smoothness of the initial matter density field and better fit the results of N-body simulations. Having described the theoretical models, we discuss the current lower limits on the WDM particle mass, mwdm, which correspond to upper limits on the WDM temperature under the assumption that the particles are thermal relics. The best such constraints come from the Lyα forest and exclude all masses below 3.3 keV at the 2σ confidence level. We finally review the forecasts for future lensing surveys, which will be of the same order of magnitude as the already existing constraints from the Lyα forest data but explore a different redshift regime.

scholarly journals Connecting empirical phenomena and theoretical models of biological coordination across scales

2019 ◽  
Vol 16 (157) ◽  
pp. 20190360 ◽  
Author(s):  
Mengsen Zhang ◽  
Christopher Beetle ◽  
J. A. Scott Kelso ◽  
Emmanuelle Tognoli
Keyword(s):  
Large Scale ◽  
Theoretical Models ◽  
Kuramoto Model ◽  
Small Scale ◽  
Large Scale Systems ◽  
Social Coordination ◽  
Level Statistics ◽  
Coordination Behaviour ◽  
Multiple Levels ◽  
The Kuramoto Model

Coordination in living systems—from cells to people—must be understood at multiple levels of description. Analyses and modelling of empirically observed patterns of biological coordination often focus either on ensemble-level statistics in large-scale systems with many components, or on detailed dynamics in small-scale systems with few components. The two approaches have proceeded largely independent of each other. To bridge this gap between levels and scales, we have recently conducted a human experiment of mid-scale social coordination specifically designed to reveal coordination at multiple levels (ensemble, subgroups and dyads) simultaneously. Based on this experiment, the present work shows that, surprisingly, a single system of equations captures key observations at all relevant levels. It also connects empirically validated models of large- and small-scale biological coordination—the Kuramoto and extended Haken–Kelso–Bunz (HKB) models—and the hallmark phenomena that each is known to capture. For example, it exhibits both multistability and metastability observed in small-scale empirical research (via the second-order coupling and symmetry breaking in extended HKB) and the growth of biological complexity as a function of scale (via the scalability of the Kuramoto model). Only by incorporating both of these features simultaneously can we reproduce the essential coordination behaviour observed in our experiment.

scholarly journals Behavioral self-organization underlies the resilience of a coastal ecosystem

2017 ◽  
Vol 114 (30) ◽  
pp. 8035-8040 ◽  
Author(s):  
Hélène de Paoli ◽  
Tjisse van der Heide ◽  
Aniek van den Berg ◽  
Brian R. Silliman ◽  
Peter M. J. Herman ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
Large Scale ◽  
Spatial Scales ◽  
Experimental Tests ◽  
Theoretical Models ◽  
Self Organization ◽  
Small Scale ◽  
Mussel Bed ◽  
Mussel Beds ◽  
Self Organized

Self-organized spatial patterns occur in many terrestrial, aquatic, and marine ecosystems. Theoretical models and observational studies suggest self-organization, the formation of patterns due to ecological interactions, is critical for enhanced ecosystem resilience. However, experimental tests of this cross-ecosystem theory are lacking. In this study, we experimentally test the hypothesis that self-organized pattern formation improves the persistence of mussel beds (Mytilus edulis) on intertidal flats. In natural beds, mussels generate self-organized patterns at two different spatial scales: regularly spaced clusters of mussels at centimeter scale driven by behavioral aggregation and large-scale, regularly spaced bands at meter scale driven by ecological feedback mechanisms. To test for the relative importance of these two spatial scales of self-organization on mussel bed persistence, we conducted field manipulations in which we factorially constructed small-scale and/or large-scale patterns. Our results revealed that both forms of self-organization enhanced the persistence of the constructed mussel beds in comparison to nonorganized beds. Small-scale, behaviorally driven cluster patterns were found to be crucial for persistence, and thus resistance to wave disturbance, whereas large-scale, self-organized patterns facilitated reformation of small-scale patterns if mussels were dislodged. This study provides experimental evidence that self-organization can be paramount to enhancing ecosystem persistence. We conclude that ecosystems with self-organized spatial patterns are likely to benefit greatly from conservation and restoration actions that use the emergent effects of self-organization to increase ecosystem resistance to disturbance.

Plastic Mechanism Analysis of Structural Performance of Web Girders During Ship Collision and Grounding

2014 ◽  
Author(s):  
Zhenguo Gao ◽  
Zhiqiang Hu
Keyword(s):  
Numerical Simulation ◽  
Deformation Process ◽  
Large Scale ◽  
Theoretical Models ◽  
Small Scale ◽  
Deformation Model ◽  
Mechanism Analysis ◽  
Plastic Mechanism ◽  
Ship Collision ◽  
The Web

The behavior of web girders is of crucial importance during ship collision and grounding accidents. A new theoretical deformation model for ship web girders subjected to in-plane localized force is proposed in this paper. It is based on a summary of the existing theoretical models and progressive deformation process of the web girder in the numerical simulation, which is a reproduction of a previous experiment. From the analysis of the deformation process of the web girder in the numerical simulation it is found that there are some important features which have not been considered by any of the existing models. Based on these new features, plastic analytical method is employed, and special emphasis is placed on the folding mechanism establishing and major energy dissipation pattern identifying. Thus, a new theoretical deformation model is proposed. The proposed model is verified by two previous experiments, one is small-scale and the other is large-scale. From the force-indentation curves in comparisons, it can be found that the results of the proposed method compare well with those of the experiments. Therefore, the proposed method can be a useful part in the quick and reliable assessment of the performance of the ship structures in the accidental collision and grounding events.

scholarly journals Direct validation of dune instability theory

2021 ◽  
Vol 118 (17) ◽  
pp. e2024105118
Author(s):  
Ping Lü ◽  
Clément Narteau ◽  
Zhibao Dong ◽  
Philippe Claudin ◽  
Sébastien Rodriguez ◽  
...  
Keyword(s):  
Growth Rate ◽  
Large Scale ◽  
Maximum Growth ◽  
Theoretical Models ◽  
Periodic Pattern ◽  
Small Scale ◽  
Gobi Desert ◽  
Linear Regime ◽  
Sources Of Information ◽  
Instability Theory

Modern dune fields are valuable sources of information for the large-scale analysis of terrestrial and planetary environments and atmospheres, but their study relies on understanding the small-scale dynamics that constantly generate new dunes and reshape older ones. Here, we designed a landscape-scale experiment at the edge of the Gobi desert, China, to quantify the development of incipient dunes under the natural action of winds. High-resolution topographic data documenting 42 mo of bedform dynamics are examined to provide a spectral analysis of dune pattern formation. We identified two successive phases in the process of dune growth, from the initial flat sand bed to a meter-high periodic pattern. We focus on the initial phase, when the linear regime of dune instability applies, and measure the growth rate of dunes of different wavelengths. We identify the existence of a maximum growth rate, which readily explains the mechanism by which dunes select their size, leading to the prevalence of a 15-m wavelength pattern. We quantitatively compare our experimental results with the prediction of the dune instability theory using transport and flow parameters independently measured in the field. The remarkable agreement between theory and observations demonstrates that the linear regime of dune growth is permanently expressed on low-amplitude bed topography, before larger regular patterns and slip faces eventually emerge. Our experiment underpins existing theoretical models for the early development of eolian dunes, which can now be used to provide reliable insights into atmospheric and surface processes on Earth and other planetary bodies.

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