Fragmentation Dynamics Research Articles

Partial and Contingent Recoil-Frame Covariance-Map Imaging.

When applied to multimass velocity-map imaging data, covariance analysis reveals correlations between different fragment ions formed from the same parent molecule and can provide detailed insights into the fragmentation dynamics. Covariances between the time-of-flight signals for two different ions show that they are formed in the same event, while covariances between their velocity-map images, often referred to as "recoil-frame covariances", reveal details of the correlated motion of the two fragments. In many cases, covariance analysis is complicated by the fact that fluctuations in experimental parameters such as laser or molecular beam intensities can lead to apparent correlations between unrelated ions. In the context of time-of-flight covariance signals, this problem has been overcome by the introduction of partial covariance and contingent covariance approaches. Here, we apply these approaches to recoil-frame covariance-map images. We also demonstrate that in many cases the total signal within each experimental cycle can be used as a useful proxy for independent explicit measurements of the varying experimental parameter(s).

Quantitative Analysis of Nitrotoluene Isomer Mixtures Using Femtosecond Time-Resolved Mass Spectrometry.

Discrimination of isomers in a mixture is a subject of ongoing interest in biology, pharmacology, and forensics. We demonstrate that femtosecond time-resolved mass spectrometry (FTRMS) effectively quantifies mixtures of ortho-, para-, and meta-nitrotoluenes, the first two of which are common explosive degradation products. The key advantage of the FTRMS approach to mixture quantification lies in the ability of the pump-probe laser control scheme to capture distinct fragmentation dynamics of each nitrotoluene cation isomer on femtosecond timescales, thereby allowing for discrimination of the isomers using only the signal of the parent molecular ion at m/z 137. Upon measurement of reference dynamics of each individual isomer, the molar fractions of binary and ternary mixtures can be predicted to within ∼5 and ∼7% accuracy, respectively.

On the Ejection of Filaments of Polymer Solutions Triggered by a Micrometer-Scale Mixing Mechanism.

Polymer filaments constitute precursor materials of so-called fiber mats, ubiquitous structures across cutting-edge technological fields. Thus, approaches that contribute to large-scale production of fibers are desired from an industrial perspective. Here, we use a robust liquid atomization device operated at relatively high flow rates, ~20 mL/min, as facilitating technology for production of multiple polymer filaments. The method relies on a turbulent, energetically efficient micro-mixing mechanism taking place in the interior of the device. The micro-mixing is triggered by radial implosion of a gas current into a liquid feeding tube, thus resulting in breakup of the liquid surface. We used poly(ethylene oxide) solutions of varying concentrations as test liquids to study their fragmentation and ejection dynamics employing ultra-high speed imaging equipment. Taking an energy cascade approach, a scaling law for filament diameter was proposed based on gas pressure, liquid flow rate and viscosity. We find that a filament dimensionless diameter, , scales as a non-dimensional liquid flow rate to the . The study aims to elucidate the underlying physics of liquid ejection for further applications in material production.

Beyond the Transition: Long-Term Population Trends in a Disadvantaged Region of Southern Europe, 1861–2017

The long-term impact of demographic transitions on the spatial distribution of human settlements was occasionally evaluated in Europe. Assuming the distinctive role of urban–rural divides, our study investigates local-scale population trends (1861–2017) in Southern Italy, a disadvantaged region of Mediterranean Europe, as a result of long-term socioeconomic transformations. A quantitative analysis of municipal-scale population data based on descriptive and exploratory multivariate statistics, mapping, inferential approaches, and regression models identified four time intervals with distinctive demographic dynamics: (i) a spatially homogeneous population growth between 1861 and 1911, (ii) a moderate population increase rebalancing a traditional divide in coastal and internal areas (1911–1951), (iii) accelerated population growth enlarging spatial divides in urban and rural districts (1951–1981), and (iv) population stability (or slight decline) leading to heterogeneous demographic patterns since the early 1980s. The first three stages reflect a prolonged transition from high fertility and mortality to high fertility and low mortality, with accelerated population growth typical of the latest stage of the first demographic transition. Outcomes of time interval (iv) reflect the early stages of the second demographic transition, with lowest-low fertility and rising life expectancy. While the first transition reflected spatially homogeneous population trends along a considerable time spam, the second transition has been associated with heterogeneous (leapfrog) demographic patterns as a result of socially mixed (and spatially) fragmented dynamics of growth and change.

SNAPSHOT USA 2019: a coordinated national camera trap survey of the United States.

With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14-week period (17 August-24 November of 2019). We sampled wildlife at 1,509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian's eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the United States. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban-wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot-usa, as will future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species-specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication.

Spatiotemporal patterns and ecological consequences of a fragmented landscape created by damming.

BackgroundDamming disrupts rivers and destroys neighboring terrestrial ecosystems through inundation, resulting in profound and long-lasting impacts on biodiversity and ecosystem processes far beyond the river system itself. Archipelagos formed by damming are often considered ideal systems for studying habitat fragmentation.MethodsHere we quantified the island attributes and landscape dynamics of the Thousand Island Lake (TIL) in China, which is one of the several long-term biodiversity/fragmentation research sites around the world. We also synthesized the major findings of relevant studies conducted in the region to further ecological understanding of damming and landscape fragmentation.ResultsOur results show that the vegetations on islands and the neighboring mainland were both recovering between 1985 and 2005 due to reforestation and natural succession, but the regeneration was partly interrupted after 2005 because of increasing human influences. While major changes in landscape composition occurred primarily in the lakefront areas and near-lakeshore islands, landscape patterns became structurally more complex and fragmented on both islands and mainland. About 80 studies from the TIL region show that the genetic, taxonomic, functional, and phylogenetic diversity on these islands were mainly influenced by island area at the patch scale, but fragmentation per se also affected species composition and related ecological processes at patch and landscape scales. In general, islands had lower species diversity but a steeper species-area relationship than the surrounding mainland. Fragmentation and edge effects substantially hindered ecological succession towards more densely vegetated forests on the islands. Environmental heterogeneity and filtering had a major impact on island biotic communities. We hypothesize that there are multiple mechanisms operating at different spatial scales that link landscape fragmentation and ecological dynamics in the TIL region, which beg for future studies. By focusing on an extensive spatiotemporal analysis of the island-mainland system and a synthesis of existing studies in the region, this study provides an important foundation and several promising directions for future studies.

Temporal edge effects structure the assemblages of Drosophilidae (Diptera) in a Restinga forest fragment in Southern Brazil

Anthropogenic habitat fragmentation directly affects ecological processes, leading to negative biodiversity impacts for insects and other biota. Increased edge effects are one consequence of fragmentation, and may alter the composition or abundance of species in the remaining habitat fragments. Understanding the ways in which edge effects impact upon the biota is essential for conservation decision-making in fragmented landscapes. Therefore, the aim of this study was to analyze the seasonal patterns of abundance, richness, and composition of Drosophilidae in a Restinga forest fragment in the extreme south of Brazil, as a function of the distance from the edge to the interior of the fragment. The data were analyzed using SIMPER analyses, which showed that the edge and the forest interior were most dissimilar during winter, followed by spring, autumn and summer. An NMDS and the SIMPER analyses showed that the lower dissimilarity between the edge and interior in spring, autumn and summer, compared to winter, is driven by immigration of individuals from outside of the forest fragment. Furthermore, some species were asymmetrically distributed in the fragment, with some species restricted to the edge of the fragment and others to the interior. This information aids in the understanding of the functioning and dynamics of fragmentation, which is fundamental for the maintenance and integrity of environments and their fauna.

State of the Landscape and Dynamics of Loss and Fragmentation of Forest Critically Endangered in the Tropical Andes Hotspot: Implications for Conservation Planning

Abstract Currently, there is no precise information on the degree of transformation of Tropical Andes hotspot landscape and native ecosystems due to the intensification of agricultural and urban land-use. Proper knowledge of these changes would provide crucial information for planning conservation strategies. We evaluated the impact of the intensification of agricultural and urban land-use on the Inter-Andean Dry Forest and Tropical Montane Forest, both of which are categorized as Critically Endangered, and the state of the landscape in the High Rio Guayllabamba watershed, Ecuador, during the periods 1991–2005 and 2005–2017. The evaluation was carried out using Landsat satellite images of 30 x 30 m pixels and landscape metrics. We found an advanced state of landscape transformation. Since the 1990s, the loss of both ecosystems was largely caused by the conversion of forest to agriculture, resulting in substantial changes in the spatial configuration of these ecosystems. From 1991 to 2017, 19.8 % and 16.1 % of Inter-Andean Dry Forest and Tropical Montane Forest respectively, were converted to agriculture. The loss of Inter-Andean Dry Forest was 28 % and the number of forest patches increased by more than 150%. The loss of Tropical Montane Forest was 16.5 % and the number of forest patches increased by more than 300 %. The largest loss and fragmentation of forest cover occurred from 1991 to 2005. We suggested planning landscape-scale conservation, using the patch-corridor-matrix model. This model is appropriate given the current configuration of the landscape studied, with Inter-Andean Dry Forest and Tropical Montane Forest restricted to small patches sparsely distributed across the landscape.

Dynamics of Specific cfDNA Fragments in the Plasma of Full Marathon Participants.

Plasma cell-free DNA (cfDNA) is frequently analyzed using liquid biopsy to investigate cancer markers. We hypothesized that this concept might be applicable in exercise physiology. Here, we aimed to identify specific cfDNA (spcfDNA) sequences in the plasma of healthy humans using next-generation sequencing (NGS) and clearly define the dynamics regarding spcfDNA-fragment levels upon extreme exercises, such as running a full marathon. NGS analysis was performed using cfDNA of pooled plasma collected from healthy participants. We confirmed that the TaqMan-qPCR assay had high sensitivity and found that the spcfDNA sequence abundance was 16,600-fold higher than that in a normal genomic region. We then used the TaqMan-qPCR assay to investigate the dynamics of spcfDNA-fragment levels upon running a full marathon. The spcfDNA fragment levels were significantly increased post-marathon. Furthermore, spcfDNA fragment levels were strongly correlated with white blood cell and plasma myoglobin concentrations. These results suggest the spcfDNA fragments identified in this study were highly sensitive as markers of extreme physical stress. The findings of this study may provide new insights into exercise physiology and genome biology in humans.

Theory of polarization-averaged core-level molecular-frame photoelectron angular distributions: II. Extracting the x-ray-induced fragmentation dynamics of carbon monoxide dication from forward and backward intensities

Recent developments in high-repetition-rate x-ray free electron lasers (XFELs) such as the European XFEL and the LSCS-II, combined with coincidence measurements using the COLTRIMS-reaction microscope, are now opening a door to realize the long-standing dream of creating molecular movies of photo-induced chemical reactions in gas-phase molecules. In this paper, we propose a new theoretical method to experimentally visualize the dissociation of diatomic molecules via time-resolved polarization-averaged molecular-frame photoelectron angular distribution (PA-MFPAD) measurements using the COLTRIMS-reaction microscope and the two-color XFEL pump–probe set-up. We used first- and second-order scattering theory within the muffin-tin approximation, which is valid for a sufficiently high kinetic energy of photoelectrons, typically above 100 eV, and for long bond lengths. This leads to a simple extended x-ray absorption fine structure (EXAFS)-type formula for the forward and backward scattering peaks in the PA-MFPAD structure. This formula relies only on three semi-empirical parameters obtainable from the time-resolved measurements. It can be used as a ‘bond length ruler’ on experimental results. The accuracy and applicability of the new ruler equation are numerically examined against the PA-MFPADs of CO2+ calculated with full-potential multiple scattering theory as a function of the C–O bond length reported in the preceding work (Ota et al J. Phys. B: At. Mol. Opt.). The bond lengths retrieved from the PA-MFPADs via our EXAFS-like formula coincide within an accuracy of 0.1 Å with the original C–O bond lengths used in the reference ab initio PA-MFPADs. We expect time-resolved PA-MFPADs to become a new attractive tool to make molecular movies visualizing intramolecular reactions.

Real-time observation of ultrafast molecular rotation in weakly bound dimers

The fragmentation dynamics of dicationic dimers of acetylene molecules initiated upon strong-field laser ionization is studied. Time-resolved pump-probe experiments with femtosecond laser pulses, accompanied by ab initio dynamical calculations, allow us to evaluate the detailed behavior of molecular ions during the dissociation process. The dynamical properties of the intermediate C2H2+⋯C2H2+ state created by the pump pulse are probed by a second pulse which causes further ionization. The time-dependent yield of a coincident C2H2+ + C2H22+ ion pair exhibits an oscillation feature with a periodicity of 240 ± 30 fs. Our studies demonstrate that this is caused by an ultrafast rotation of C2H2+ cations driven by intermolecular Coulomb force together with the orientation-dependent ionization rate. We suggest that the present observation of ultrafast molecular rotation can be a general phenomenon occurring in a wide variety of systems.Received 14 September 2020Accepted 31 March 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.023050Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLaser-cluster interactionUltrafast phenomenaVan der Waals interactionAtomic, Molecular & Optical

Characterizing changes in land cover and forest fragmentation from multitemporal Landsat observations (1993-2018) in the Dhorpatan Hunting Reserve, Nepal

Natural forces and anthropogenic activities greatly alter land cover, deteriorate or alleviate forest fragmentation and affect biodiversity. Thus land cover and forest fragmentation dynamics have become a focus of concern for natural resource management agencies and biodiversity conservation communities. However, there are few land cover datasets and forest fragmentation information available for the Dhorpatan Hunting Reserve (DHR) of Nepal to develop targeted biodiversity conservation plans. In this study, these gaps were filled by characterizing land cover and forest fragmentation trends in the DHR. Using five Landsat images between 1993 and 2018, a support vector machine algorithm was applied to classify six land cover classes: forest, grasslands, barren lands, agricultural and built-up areas, water bodies, and snow and glaciers. Subsequently, two landscape process models and four landscape metrics were used to depict the forest fragmentation situations. Results showed that forest cover increased from 39.4% in 1993 to 39.8% in 2018. Conversely, grasslands decreased from 38.2% in 1993 to 36.9% in 2018. The forest shrinkage was responsible for forest loss during the period, suggesting that the loss of forest cover reduced the connectivity between forest and non-forested areas. Expansion was the dominant component of the forest restoration process, implying that it avoided the occurrence of isolated forests. The maximum value of edge density and perimeter area fractal dimension metrics and the minimum value of aggregation index were observed in 2011, revealing that forests in this year were most fragmented. These specific observations from the current analysis can help local authorities and local communities, who are highly dependent on forest resources, to better develop local forest management and biodiversity conservation plans.

Bubble fragmentation dynamics in a subsonic Venturi tube for the design of a compact microbubble generator

Microbubble generators are in wide demand in industry following the discovery of a number of new functions of microbubble mixtures. This paper deals with a Venturi tube microbubble generator in which air bubbles at the inlet are fragmented in the diverging part of the tube. In contrast with past studies, we here regulated the flow subsonic so that fragmentation occurred without the help of pressure shock waves. Counting the microbubbles in image processing, we found that a single bubble fragmented into 20–400 microbubbles depending on the Weber number. The power efficiency is found to range from 30 to 50 percent and insensitive to the liquid viscosity. The mechanism of subsonic fragmentation is elucidated adopting particle tracking velocimetry, in association with a theoretical description of the translational motion and the shape oscillation of the bubble. The key event was found to be the bubble's rapid slip-back in the diverging part of the Venturi tube due to a positive pressure gradient. This provides a function that prevents large bubbles from being released from the subsonic Venturi tube.

Cell Fragment Formation, Migration, and Force Exertion on Extracellular Mimicking Fiber Nanonets.

Cell fragments devoid of the nucleus play an essential role in intercellular communication. Mostly studied on flat 2D substrates, their origins and behavior in native fibrous environments remain unknown. Here, cytoplasmic fragments' spontaneous formation and behavior in suspended extracellular matrices mimicking fiber architectures (parallel, crosshatch, and hexagonal) are described. After cleaving from the parent cell body, the fragments of diverse shapes on fibers migrate faster compared to 2D. Furthermore, while fragments in 2D are mostly circular, a higher number of rectangular and blob-like shapes are formed on fibers, and, interestingly, each shape is capable of forming protrusive structures. Absent in 2D, fibers' fragments display oscillatory migratory behavior with dramatic shape changes, sometimes remarkably sustained over long durations (>20 h). Immunostaining reveals paxillin distribution along fragment body-fiber length, while Forster Resonance Energy Transfer imaging of vinculin reveals mechanical loading of fragment adhesions comparable to whole cell adhesions. Using nanonet force microscopy, the forces exerted by fragments are estimated, and peculiarly small area fragments can exert forces similar to larger fragments in a Rho-associated kinase dependent manner. Overall, fragment dynamics on 2D substrates are insufficient to describe the mechanosensitivity of fragments to fibers, and the architecture of fiber networks can generate entirely new behaviors.

Low-Energy Fragmentation Dynamics at Copahue Volcano (Argentina) as Revealed by an Infrasonic Array and Ash Characteristics

Ash-rich eruptions represent a serious risk to the population living nearby as well as at thousands of kilometers from a volcano. Volcanic ash is the result of extensive magma fragmentation during an eruption, and it depends upon a combination of magma properties such as rheology, vesicularity and permeability, gas overpressure and the possible involvement of external fluids during magma ascent. The explosive process generates infrasonic waves which are directly linked to the outflow of the gas-particle mixture in the atmosphere. The higher the overpressure in the magma, the higher should be the exit velocity of the ejected material and the acoustic pressure related to this process. During violent eruptions, fragmentation becomes more efficient and is responsible for the extensive production of ash which is dispersed in the atmosphere. We show that the phase of intense ash emission that occurred during March 2016 at Copahue volcano (Argentina) generated a very low (0.1 Pa) infrasonic amplitude at 13 km, raising a number of questions concerning the links among acoustic pressure, gas overpressure and efficiency of magma fragmentation. Infrasound and direct observations of the eruptive plume indicate that the large quantity of ash erupted at Copahue was ejected with a low exit velocity. Thus, it was associated with eruptive dynamics driven by a low magma overpressure. This is more evident when infrasonic activity at Copahue is compared to the moderate explosive activity of Villarrica (Chile), recorded by the same array, at a distance of 193 km. Our data suggest a process of rigid fragmentation under a low magma overpressure which was nearly completely dissipated during the passage of the erupting mixture through the granular, ash-bearing crater infilling. We conclude that ash released into the atmosphere during low-energy fragmentation dynamics can be difficult to monitor, with direct consequences for the assessment of the related hazard and management of eruptive crises.

Synchrotron X-ray imaging and ultrafast tomography in situ study of the fragmentation and growth dynamics of dendritic microstructures in solidification under ultrasound

High speed synchrotron X-ray imaging and ultrafast tomography were used to study in situ and in real time the fragmentation and growth dynamics of dendritic microstructures of an Al-15%Cu alloy in solidification under ultrasound. An ultrasound of 30 kHz with vibration amplitude of 29 µm was applied into the alloy melt and produced a strong swirling acoustic flow of ~0.3 m/s. Efficient dendrite fragmentation occurred due to the acoustic flow and the dominant mechanism is the thermal perturbation remelting plus mechanical fracture and separation effect. Acoustic flow fatigue impact and phase collision effects were found to play a minor role in causing dendrite fragmentation. Just 10 s of ultrasound application at the early stage of solidification produced ~100% more dendrite fragments compared to the case without ultrasound, resulting in 20~25% reduction in the average grain size in the solidified samples. Furthermore, the dendrite morphology and tip growth velocity were mainly affected by the initial dendrite fragment number density and their distribution. The systematic and real-time datasets obtained in near operando conditions provided valuable 4D information for validation of numerical models and assistance in developing optimisation strategy for ultrasound melt processing in industry.

Self-organized initiatives: a planners’ subversive tool for fragmented urban spaces

ABSTRACT This article investigates whether self-organized initiatives are able to undermine the underlying dynamics of spatial fragmentation in Brazilian metropolises by promoting social connections between groups that are extremely diverse. Since self-organized initiatives not only promote spatial connections but also social connections between different groups, the central question here is: To what extent can self-organized initiatives promote social connection in the public spaces of highly fragmented and unequal urban contexts? The analysis was based on data collected from 22 in-depth interviews with members of self-organized initiatives, experts as well as field observations during some actions of the initiatives. The interviews were conducted in Brasília, Rio de Janeiro and São Paulo during two months of fieldwork. The results show that the self-organized initiatives studied were capable to mitigate conflicts and to create social connections. Nevertheless, it is still unclear how strong and long-lasting these social connections are.

Polymer scission in turbulent flows

Abstract

Land use land cover dynamics and fragmentation-induced changes in woody plant community structure in a mining landscape, Ghana

The study assessed the dynamics of mining land use land cover changes and consequent fragmentation impacts on woody plant community structure in the Ahafo Region, Ghana. Landsat images were utilised to determine land use and cover changes using a supervised classification method. Plant community structure was determined within 60 (20 × 20 m) plots that were randomly laid in equal numbers in fragmented and intact forests. Our findings showed that the mining landscape experienced a substantial land use/cover change between 2003 and 2018, with considerable forest cover loss at the expense of increasing cover of plantation, settlement/bare surface, mine site, and waterbody. Woody plant species diversity was significantly lower in the fragmented forest around the mine. Likewise, fragmentation caused a shift in plant species composition in the fragmented forest, whose composition was less homogenised compared to the intact forest. Plant abundance did not differ significantly between the two forests, but it was invasive and cultivated tree species that increased the total abundance of woody plants in the fragmented forests. The mining landscape was dominated by an invasive alien species, Broussonetia papyrifera which poses an ecological threat to native species. In conclusion, our findings suggest that mining contributed to intense land use/cover dynamics and fragmentation that impaired woody plant community structure around the mine. There is the need to accord priority to management intervention that would seek to manage and conserve the remaining forest fragments and its biodiversity in the mining landscape.

Gravitational waves from the fragmentation of axion-like particle dark matter

The misalignment mechanism allows for the efficient, and usually very cold, production of light scalar bosons, such as axion-like particles (ALPs), making them an appealing dark matter candidate. However, in certain cases, such as in the presence of a monodromy, the self-interactions of ALPs can be sufficiently strong such that the homogeneous field fragments soon after the onset of oscillations. The resulting large inhomogeneities can lead to the production of gravitational waves (GWs). We investigate the nonlinear dynamics of fragmentation, as well as of the subsequent turbulent regime, and calculate the stochastic GW background that is produced from this process. The GW background can be enhanced if the time evolution features an extended intermediate phase of ultrarelativistic dynamics due to a small mass at the bottom of the potential. Yet, this enhancement is limited by the requirement that the dark matter remains sufficiently cold. In some cases the resulting GWs may be within reach of future GW detectors, allowing a complementary probe of this type of dark matter.