Fragmentation Events Research Articles

The power to detect recent fragmentation events using genetic differentiation methods.

Habitat loss and fragmentation are imminent threats to biological diversity worldwide and thus are fundamental issues in conservation biology. Increased isolation alone has been implicated as a driver of negative impacts in populations associated with fragmented landscapes. Genetic monitoring and the use of measures of genetic divergence have been proposed as means to detect changes in landscape connectivity. Our goal was to evaluate the sensitivity of Wright’s F st, Hedrick’ G’st, Sherwin’s MI, and Jost’s D to recent fragmentation events across a range of population sizes and sampling regimes. We constructed an individual-based model, which used a factorial design to compare effects of varying population size, presence or absence of overlapping generations, and presence or absence of population sub-structuring. Increases in population size, overlapping generations, and population sub-structuring each reduced F st, G’st, MI, and D. The signal of fragmentation was detected within two generations for all metrics. However, the magnitude of the change in each was small in all cases, and when N e was >100 individuals it was extremely small. Multi-generational sampling and population estimates are required to differentiate the signal of background divergence from changes in Fst, G’st, MI, and D associated with fragmentation. Finally, the window during which rapid change in Fst, G’st, MI, and D between generations occurs can be small, and if missed would lead to inconclusive results. For these reasons, use of F st, G’st, MI, or D for detecting and monitoring changes in connectivity is likely to prove difficult in real-world scenarios. We advocate use of genetic monitoring only in conjunction with estimates of actual movement among patches such that one could compare current movement with the genetic signature of past movement to determine there has been a change.

Dynamical evolution of high area-to-mass ratio objects in Molniya orbits

For special demands, some notable orbit types have been developed by human, including the Molniya orbits, which have a relatively high eccentricity up to about 0.7, and a period of 12h. Considering that space debris with high area-to-mass ratio (A/M) has been discovered, such objects may also exist in Molniya orbits due to spacecraft and upper stages fragmentation events. However, there are not sufficient studies of the complex dynamical phenomena of such orbits. These studies can enrich the knowledge about the long-term evolution of these orbits, be helpful to propose uncatalogued objects observation and identification, and also set the protected region as well as active debris removal. In this paper, the characteristics of 2:1 resonance of Molniya satellite orbits are studied. A large set of numerical simulations, including all the relevant perturbations, is carried out to further investigate the main characteristics, and special attention is payed to the dynamical evolution of objects with high A/M, particularly affected by the direct solar radiation pressure. The long-term dynamical evolution of orbital elements, as well as the dependency of lifetime on the A/M value, is discussed.

Multiple and Sequential Data Acquisition Method: An Improved Method for Fragmentation and Detection of Cross-Linked Peptides on a Hybrid Linear Trap Quadrupole Orbitrap Velos Mass Spectrometer

The identification and validation of cross-linked peptides by mass spectrometry remains a daunting challenge for protein-protein cross-linking approaches when investigating protein interactions. This includes the fragmentation of cross-linked peptides in the mass spectrometer per se and following database searching, the matching of the molecular masses of the fragment ions to the correct cross-linked peptides. The hybrid linear trap quadrupole (LTQ) Orbitrap Velos combines the speed of the tandem mass spectrometry (MS/MS) duty circle with high mass accuracy, and these features were utilized in the current study to substantially improve the confidence in the identification of cross-linked peptides. An MS/MS method termed multiple and sequential data acquisition method (MSDAM) was developed. Preliminary optimization of the MS/MS settings was performed with a synthetic peptide (TP1) cross-linked with bis[sulfosuccinimidyl] suberate (BS(3)). On the basis of these results, MSDAM was created and assessed on the BS(3)-cross-linked bovine serum albumin (BSA) homodimer. MSDAM applies a series of multiple sequential fragmentation events with a range of different normalized collision energies (NCE) to the same precursor ion. The combination of a series of NCE enabled a considerable improvement in the quality of the fragmentation spectra for cross-linked peptides, and ultimately aided in the identification of the sequences of the cross-linked peptides. Concurrently, MSDAM provides confirmatory evidence from the formation of reporter ions fragments, which reduces the false positive rate of incorrectly assigned cross-linked peptides.

Mitochondrial DNA Nucleoid Redistribution after Mitochondrial Network Fragmentation as Visualized by 3D Super-Resolution Biplane Fpalm Microscopy

Mitochondrial (mt) network undergoes locally frequent fragmentation and fusion events. When integrated over time, its basic morphology encompasses highly interconnected mt reticulum, a single mitochondrion within the cell (1). Upon certain insults and/or pathological states fragmented network persists. MtDNA is organized in nucleoids containing assessor proteins and recruited proteins of mt replication/ transcription machinery. It is debated on their uniform size and whether a single nucleoid contains a single mtDNA molecule or up to average 6 mtDNA molecules. To image nucleoid distribution within mt network, we employed 3D super-resolution fluorescent photactivable localization microscopy of Biplane schema (1). Mt network of hepatocellular carcinoma HepG2 cells was imaged first by its matrix space using mtEos2 or as outer mitochondrial membrane contour using Eos2-conjugates of truncated FIS1 protein (not inducing massive fission, Eos2-FIS1tr). Resulting 3D images confirm the existence of highly-connected mt network and unlike conventional confocal microscopy, 3D BiplaneFPALM distinguished a hollow character of mt reticulum tubules when visualized by Eos2-FIS1tr. Upon network fragmentation, hollow max ∼2 micrometer spheres occurred. Imaging of mt nucleoids confirmed the existence of ∼1000 nucleoids per cell with size distribution from 50 nm to 300 nm. Optimized dual transfection strategy had to be employed for simultaneous imaging of network (mtEos or Eos2-FIS1tr) and nucleoids (mtSSB-PSCFP2). Images revealed an equidistant nucleoid distribution of an average distance of ∼1 micrometer between nucleoids. Fragmentation by different agents led to observations of clusters of mt nucleoids within the spherical fragmented objects thus formed.Supported by grants P302/10/0346, P305/12/P388 and P305/12/1247 of GACR and ME09029 (Czech Ministry of Education); and 1R01GM091791-02 (NIH).(1) Mlodzianoski MJ, Schreiner JM, Callahan SP, Smolkova K, Dlaskova A, Santorova J, Ježek P, Bewersdorf J. Opt Express 2011;19:15009–19.

In Vitro Oxidation of Snap-25 Leads to Double Disulfide Bond Formation and Protein Destabilization

SNAP-25 contains two of the four helixes that form the SNARE complex, critical for neuronal exocytosis. The helixes are linked together with a cysteine-rich domain, which is the site of various post-translational modifications such as palmitoylation and possibly oxidation. SNAP-25's linker contains 4 cysteines and thus could be both palmitoylated and oxidized. Palmitoylation anchors SNAP-25 to the membrane, while the level of oxidation may regulate transmitter release. Using standard MS/MS collision-induced dissociation (CID) in an Ion Trap mass spectrometer we analyzed peptide fragmentation patterns to determine fragmentation events, and observed single and double backbone cleavage along with heterolytic cleavage of disulfide bonds. We modeled these same events in the doubly disulfide linked SNAP25B peptide and used a cumulative hypergeometric distribution with top-down scoring to first identify, and then to differentiate all three bonding patterns. This is the first study to assign all double disulfide bonding patterns in a protein, and uses methodology fully compatible with standard large scale shotgun proteomics. In addition, the structural stability of oxidized and reduced SNAP-25 was determined with Circular Dichroism (CD). We observe that oxidized protein is less stable (lower melting temperature) than reduced protein. Additional experiments focus on the stability of the SNARE complex with oxidized samples and on the extent of SNAP-25 oxidation in brain tissue, with the ultimate goal to elucidate the effects of palmitoylation and oxidative stress on SNARE complex formation and vesicle fusion.

Mining workflow processes from distributed workflow enactment event logs

Workflow management systems help to execute, monitor and manage work process flow and execution. These systems, as they are executing, keep a record of who does what and when (e.g. log of events). The activity of using computer software to examine these records, and deriving various structural data results is called workflow mining. The workflow mining activity, in general, needs to encompass behavioral (process/control-flow), social, informational (data-flow), and organizational perspectives; as well as other perspectives, because workflow systems are "people systems" that must be designed, deployed, and understood within their social and organizational contexts. This paper particularly focuses on mining the behavioral aspect of workflows from XML-based workflow enactment event logs, which are vertically (semantic-driven distribution) or horizontally (syntactic-driven distribution) distributed over the networked workflow enactment components. That is, this paper proposes distributed workflow mining approaches that are able to rediscover ICN-based structured workflow process models through incrementally amalgamating a series of vertically or horizontally fragmented temporal workcases. And each of the approaches consists of a temporal fragment discovery algorithm, which is able to discover a set of temporal fragment models from the fragmented workflow enactment event logs, and a workflow process mining algorithm which rediscovers a structured workflow process model from the discovered temporal fragment models. Where, the temporal fragment model represents the concrete model of the XML-based distributed workflow fragment events log.

Times of impacts that deliver samples of Vesta to Earth derived from ultrasensitive 81Kr–Kr cosmic ray exposure age analysis of Eucrites

Concentrations and isotopic compositions of krypton have been measured in Eucrite falls using a new resonance ionization mass-spectrometer (RIMSKI). The high sensitivity of the apparatus allowed sample sizes to be reduced to 1–4mg for 81Kr–Kr cosmic ray exposure age determination. 81Kr CRE ages have been determined for: Bereba, Bouvante, Ibitira, Juvinas, Millbillillie, Padvarninkai, Pasamonte and Stannern with precision comparable to those reported by other groups for analyses of >100 times larger samples. The 81Kr–Kr CRE ages of Lakangaon (25.3±1.1My) and Bunburra Rockhole (27.6±1.4My) have been determined for the first time.The 81Kr CRE ages of 16 out of 17 ordinary Eucrite falls can be grouped into clusters at 10.6±0.4Ma, 14.4±0.6My, 21.7±0.4My, 25.4±0.4My, 37.8±0.6My using an analysis based on the Akaike information criterion, which is well suited to addressing such issues. This shows that most of the meteorites originate from five collision events over the last ∼50My, which is hard to reconcile with models requiring multiple fragmentation events between Vesta and Earth.

TWO-STAGE FRAGMENTATION FOR CLUSTER FORMATION: ANALYTICAL MODEL AND OBSERVATIONAL CONSIDERATIONS

Linear analysis of the formation of protostellar cores in planar magnetic interstellar clouds shows that molecular clouds exhibit a preferred length scale for collapse that depends on the mass-to-flux ratio and neutral-ion collision time within the cloud. We extend this linear analysis to the context of clustered star formation. By combining the results of the linear analysis with a realistic ionization profile for the cloud, we find that a molecular cloud may evolve through two fragmentation events in the evolution toward the formation of stars. Our model suggests that the initial fragmentation into clumps occurs for a transcritical cloud on parsec scales while the second fragmentation can occur for transcritical and supercritical cores on subparsec scales. Comparison of our results with several star forming regions (Perseus, Taurus, Pipe Nebula) shows support for a two-stage fragmentation model.

A remarkable case of micro-endemism in Laonastes aenigmamus (Diatomyidae, Rodentia) revealed by nuclear and mitochondrial DNA sequence data.

L. aenigmamus is endemic to the limestone formations of the Khammuan Province (Lao PDR), and is strongly specialized ecologically. From the survey of 137 individuals collected from 38 localities, we studied the phylogeography of this species using one mitochondrial (Cyt b) and two nuclear genes (BFIBR and GHR). Cyt b analyses reveal a strong mtDNA phylogeographical structure: 8 major geographical clades differing by 5–14% sequence divergence were identified, most of them corresponding to distinct karst areas. Nuclear markers display congruent results but with a less genetic structuring. Together, the data strongly suggest an inland insular model for Laonastes population structure. With 8 to 16 evolutionary significant units in a small area (about 200×50 km) this represents an exceptional example of micro-endemism. Our results suggest that L. aenigmamus may represent a complex of species and/or sub-species. The common ancestor of all Laonastes may have been widely distributed within the limestone formations of the Khammuan Province at the end of Miocene/beginning of the Pliocene. Parallel events of karst fragmentation and population isolation would have occurred during the Pleistocene or/and the end of the Pliocene. The limited gene flow detected between populations from different karst blocks restrains the likelihood of survival of Laonastes. This work increases the necessity for a strict protection of this rare animal and its habitat and provides exclusive information, essential to the organization of its protection.

Simulation of high speed impact, penetration and fragmentation problems on locally refined Cartesian grids

Techniques are presented to solve problems involving high speed material interactions that can lead to large deformations followed by fragmentation. To simulate such problems in an Eulerian framework on a fixed Cartesian mesh, interfaces (free surfaces as well as interacting material interfaces) are tracked as levelsets; to resolve shocks and interfaces, a quadtree adaptive mesh is employed. This paper addresses issues associated with the treatment of all interfaces as sharp entities by defining ghost fields on each side of the interface. Collisions between embedded objects are resolved using an efficient collision detection algorithm and appropriate interfacial conditions are supplied. Key issues of supplying interfacial conditions at the precise location of the sharp interface and populating the ghost cells with physically consistent values during and beyond fragmentation events are addressed. Numerous examples pertaining to impact, penetration, void collapse and fragmentation phenomena are presented along with careful benchmarking to establish the validity, accuracy and versatility of the approach.

Phylogenetic and mixed Yule‐coalescent analyses reveal cryptic lineages within two South American marine snails of the genus Crepipatella (Gastropoda: Calyptraeidae)

AbstractThe presence of sibling species within the marine gastropod genus Crepipatella has complicated the taxonomy of members of the group. Since the establishment of the genus, 15 species have been described, but recent studies have indicated that there are only five valid species, two of which inhabit the coasts of Chile, namely C. dilatata and C. fecunda. The two species are morphologically indistinguishable as adults, but can be differentiated on the basis of their encapsulated developmental stages. The primary aim of this study was to reconstruct phylogeny within the genus, and to establish species limits of C. dilatata and C. fecunda, using mitochondrial DNA data. To this end, we used maximum parsimony, maximum likelihood, and Bayesian inference to reconstruct phylogenies using 589 bp of the cytochrome oxidase I (COI) gene. The mtDNA phylogenies were then used as input in a general mixed Yule‐coalescent (GMYC) analysis to estimate species boundaries. In addition, quarter likelihood mapping was used to test a posteriori the confidence of inner branch patterns in the phylogenetic tree. Both DNA tree‐based and GMYC methods provide support for five isolated lineages within this species complex. Our data also suggest that Late Pleistocene and Holocene fragmentation and subsequent range expansion events may have shaped contemporary genetic patterns of Crepipatella in South America.

A semidetailed model of primary fragmentation of coal

A mathematical model has been developed to predict the primary fragmentation of coal particles under a wide range of heating conditions as a consequence of thermal stress and of overpressure generated by volatiles.The model calculates the temperature and devolatilization profiles within the particle during heat up, the stress profiles that arise within the particle as a consequence of temperature gradients and volatiles pressure, the probability, timing and mode of fragmentation of the particle based on Weibull theory [13]. Gradual transition from the chemico-physical properties of the original coal to those of the incipient char is allowed for. The model is used to interpret experimental results of primary fragmentation under different heat treatment conditions.Results show that different fragmentation patterns are possible according to initial particle size and heating severity. Under conditions typical of PF combustion, i.e. small particle size and very high temperature and heating rate, the main fragmentation pattern is exfoliation of the outer shell under the action of thermal shock which produces a multitude of fine particles. Under conditions typical of fixed/moving bed reactors, i.e. larger particles and lower temperature/heating rate, fragmentation occurs mainly at an inner radial position, close to the particle center, under the cooperative action of thermal stress and volatile overpressure, which produces a limited number of relatively coarse fragments. In some situations, such as for large particles and severe heating conditions, multiple successive events of exfoliation and fragmentation at the particle center are possible.

Potential effects of human pressure and habitat fragmentation on population viability of the Antillean manatee Trichechus manatus manatus: a predictive model

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 18:129-145 (2012) - DOI: https://doi.org/10.3354/esr00439 Potential effects of human pressure and habitat fragmentation on population viability of the Antillean manatee Trichechus manatus manatus: a predictive model Delma Nataly Castelblanco-Martínez1,*, Coralie Nourisson2, Ester Quintana-Rizzo3, Janneth Padilla-Saldivar1, Juan J. Schmitter-Soto1 1El Colegio de la Frontera Sur, Av. Centenario km 5.5, Chetumal, Quintana Roo, Mexico 2GEOMARE, Av. Miguel Alemán 616-4B, Col. Lázaro Cárdenas, Mazatlán, 82040 Sinaloa, Mexico 3University of South Florida, 140 7th Avenue South, St. Petersburg, Florida 33701, USA *Email: castelblanco.nataly@gmail.com ABSTRACT: We present a population viability analysis for the metapopulation of the Antillean manatee Trichechus manatus manatus with the aim of predicting its tendencies under various hypothetical scenarios of conservation. Multiple individual Monte Carlo simulations of deterministic and stochastic factors were run on VORTEX 9.73 software. Populations were defined using genetic structure, geographic barriers, and typical ranging behavior. Demographic characteristics and life history parameters were inferred from the most recent compilation of information on the subspecies or were extrapolated from the Florida manatee T. m. latirostris. The baseline model describes a metapopulation with a positive growth. This model was sensitive to changes in mortality, but did not show any significant response to variations in assumed carrying capacity, age at first reproduction, maximum reproductive age, or initial population size. We simulated different scenarios by modifying human pressure, habitat fragmentation, and catastrophic events (i.e. hurricanes). Additional combined models were developed to simulate the best- and worst-case scenarios for human pressure level and fragmentation. The model suggested that the metapopulation would not be able to withstand an annual anthropogenically induced mortality rate >5%. A decrease in the survival of transient individuals could also lead to a decline of the population. Variations of the hurricane parameters did not yield important changes in the population curves, but other effects of climatic change are discussed. The extensive geographical area used by manatees requires international collaboration to ensure the protection of the metapopulation through effective conservation strategies across countries. KEY WORDS: Population ecology · Trichechus manatus manatus · Human-related mortality · Connectivity · Tropical ecosystems · VORTEX Full text in pdf format PreviousNextCite this article as: Castelblanco-Martínez DN, Nourisson C, Quintana-Rizzo E, Padilla-Saldivar J, Schmitter-Soto JJ (2012) Potential effects of human pressure and habitat fragmentation on population viability of the Antillean manatee Trichechus manatus manatus: a predictive model. Endang Species Res 18:129-145. https://doi.org/10.3354/esr00439 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 18, No. 2. Online publication date: August 16, 2012 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2012 Inter-Research.

Visualization of beams from ionic liquid ion sources for focused ion beam applications

Ionic liquid ion sources (ILIS) share qualities with liquid metal ion sources necessary for focused ion beams (FIB) operation, such as pure ion emission and low energy spreads. These sources work at lower currents, room temperature, and are able to produce both positive and negative ions from a large number of ionic liquids. The influence of the applied voltage on the beam emitted from the ILIS based on the liquid EMI-BF4 (1-ethyl 3-methyl imidazolium tetrafluoroborate) is characterized by using a beam visualization system. As the applied voltage is increased, the source transitions from single to multiple beam emission. The visualization tool is also used to determine the spatial distribution of the neutral particle population contained within the beam emitted from ILIS. Cluster ions can break during flight, yielding a new ion and neutral particles. This neutral population can be highly energetic, and might be of interest for material treatment applications where charging of targets is undesirable. For FIB applications, these neutrals could lead to undesired effects in the sample, and so it is necessary to know the distribution of the neutrals within the beam in order to specify the filtering and optics required to implement an ILIS-based FIB. It is found that 20% of the ion beam results from fragmentation events, and that the neutral population is concentrated at the center of the beam.

Habitat fragmentation: Simple models for local persistence and the spread of invasive species

Understanding the persistence and growth of natural populations in environments subject to random localised change is relevant both to the conservation of threatened species and to the control of invasive species. By developing and analysing simple strategic growth models in environments subject to random fragmentation events, we show that simple approximations can be used to predict invasion speeds and extinction probabilities. The rate and size of fragmentation events interact in a nonlinear way, a finding with important consequences for the efficient control of invasive species. Infrequent, large-scale fragmentation events provide more effective means of control than more frequent, smaller scale efforts.

Conflicting evolutionary patterns due to mitochondrial introgression and multilocus phylogeography of the Patagonian freshwater crab Aegla neuquensis.

BackgroundMultiple loci and population genetic methods were employed to study the phylogeographic history of the Patagonian freshwater crab Aegla neuquensis (Aeglidae: Decopoda). This taxon occurs in two large river systems in the Patagonian Steppe, from the foothills of the Andes Mountains east to the Atlantic Ocean.Methodology/Principal FindingsA nuclear phylogeny and multilocus nested clade phylogeographic analysis detected a fragmentation event between the Negro and Chico-Chubut river systems. This event occurred approximately 137 thousand years ago. An isolation-with-migration analysis and maximum-likelihood estimates of gene flow showed asymmetrical exchange of genetic material between these two river systems exclusively in their headwaters. We used information theory to determine the best-fit demographic history between these two river systems under an isolation-with-migration model. The best-fit model suggests that the Negro and the ancestral populations have the same effective population sizes; whereas the Chico-Chubut population is smaller and shows that gene flow from the Chico-Chubut into the Negro is four times higher than in the reverse direction. Much of the Chico-Chubut system appears to have only been recently colonized while the Negro populations appear to have been in place for most of the evolutionary history of this taxon.Conclusions/SignificanceDue to mitochondrial introgression, three nuclear loci provided different phylogeographic resolution than the three mitochondrial genes for an ancient fragmentation event observed in the nuclear phylogeny. However, the mitochondrial locus provided greater resolution on more recent evolutionary events. Our study, therefore, demonstrates the need to include both nuclear and mitochondrial loci for a more complete understanding of evolutionary histories and associated phylogeographic events. Our results suggest that gene flow between these systems, before and after fragmentation was through periodic paleolakes that formed in the headwaters region. Fragmentation between the Negro and Chico-Chubut systems was driven by the disappearance of these paleolakes during the Patagonian Glaciation.

Simulation of the mineral breakage using a fractal approach

Hukki's law is an empirical law, which does not take into account several events of energy loss during the mineral fragmentation processes. Since experimental results are very difficult to obtain for a large range of fragment sizes, the verification of the law is very difficult. The relation between the fracture and fragmentation processes with fractal geometry has been proposed some decades ago. Empirical laws along this context show basic features of fractal geometry, mainly self-affinity and the power law behavior. Thus, in this paper, a model to simulate the fragmentation process and to check the relationship between energy consumption and fragment sizes was developed. The model is represented on a regular lattice where links represent pathways for fracture processes. The energy of fragmentation events was modeled by a probability distribution function. In the proposed model there is no mass loss and the fracture propagation occurs as self-avoiding random walks on the regular lattice.

Statistical analysis of fragmentation channels of small multicharged molecular ions

Laser-induced multiple ionization and Coulomb explosion of small molecules may lead on average to more than one fragmentation event per laser pulse even when experiments are performed at very low gas pressures in the 10−8–10−9 mbar range. In order to bypass the failure of coincidence techniques in this case, Frasinski et al (1989 Science 246 1029) proposed an alternative technique denoted covariance mapping based on correlated fluctuations of digitized ion signals coming from identical fragmentation channels. A probabilistic approach of the detected signals shows that covariance eliminates false coincidences due to fragments from different fragmentation channels, and false coincidences due to fragments from the same fragmentation channel, but which do not originate from the same unimolecular fragmentation events. The analysis is extended to devices which do not accept more than one count per time-of-flight bin such as multichannel scalers or time-to-digital converters. It is still possible to remove false coincidences using covariance but with a formulation which is noticeably different from the initial proposal for digitized signals.

Simulating dynamic fragmentation processes with particles and elements

The dynamic fragmentation of brittle materials has been extensively studied via experiment, analytic theory, and numerical modeling. While analytic theories capture specific aspects of the fragmentation process observed experimentally, numerical models can produce a wide range of results dependent upon their makeup. This study examines dynamic fragmentation using particle and clustered particle (continuum) simulation approaches. The fragmentation of 1D string, 3D bar, and 3D plate geometries are examined along with the effects of irreversible damage and initial temperature (defects). The results highlight three distinct physical processes that can play an important role in a dynamic fragmentation event: crack nucleation, free surface sublimation (phase changes), and crack branching. Each process leaves a signature with regard to the resulting fragment size distribution and can be affected by the numerical discretization of the system. The findings of this work are intended to provide general guidance with regard to modeling dynamic fragmentation.

Plume Fragmentation by Bulk Interactions in Turbulent Rayleigh-Bénard Convection

Using compressed gases with Prandtl numbers near 0.7, we obtained flow visualizations of turbulent Rayleigh-Bénard convection in a cylindrical sample with an aspect ratio Γ≡D/L≅10 (D is the diameter and L the height) by the shadowgraph method. Focusing on the plumes under the top plate, we found that their length had a log-normal distribution, suggesting a fragmentation process. Fragmentation events could be visually identified in the images and involved plume interactions with bulk fluctuations or upwelling domain walls. We found the mean spacing between plumes to vary with the Rayleigh number in proportion to the volume-averaged Kolmogorov length of the turbulent bulk fluctuations, providing further evidence for plume-bulk interactions.