Fragmentation Dynamics Research Articles

Fragmentation dynamics in an Abies religiosa forest of central Mexico

Fir (Abies Mill.) forests of Mexico are relicts of the boreal forests that advanced southwards during glaciation periods. Mexico is a center of diversification of the Abies genus, as there are eight species in its territory, six of which are endemic. The forests of Abies religiosa (Kunth) Schltdl. & Cham. near Mexico City are subject to a process of deterioration. We analyzed the fragmentation dynamics of the A. religiosa forest in the northern region of the Sierra Nevada, Mexico. Land cover change detection was done by means of high-resolution images acquired by the SPOT satellite in 2005, 2010, 2015, and 2018. Habitat fragmentation was observed, with a decrease in the size of dense Abies masses. The area covered by Abies decreased by 22.9%. The area occupied by forest openings increased 3% from 2005 to 2010 and then decreased by 1.8% and 1.6% in the following periods. The land patch type Other Forest Cover increased in both frequency and size, with the area increasing by 23.3%, which warns of a change process towards this patch type. The formation of increasingly smaller and isolated remnants of A. religiosa forest in the Sierra Nevada can lead to the loss of this vegetation relict and its replacement by other types of cover in the short term.

From Rural Spaces to Peri-Urban Districts: Metropolitan Growth, Sparse Settlements and Demographic Dynamics in a Mediterranean Region

Considering settlement characteristics and population dynamics together over multiple spatio-temporal scales, the present study analyzes the spatial distribution of sparse settlements and population surrounding a large city in Southern Europe (Athens, Greece), in relation with long-term metropolitan growth and recent economic downturns. Results of the analysis identify regional-scale processes of urban compaction during economic expansion (2000s) with incorporation of scattered settlements in a high-density urban fabric, and moderate urban dispersion affecting low-density, peripheral areas in the subsequent period of recession (2010s). However, more heterogeneous dynamics were observed at the local scale. With economic expansion, a slight increase in the number of settlements was observed in local districts experiencing intense sprawl in earlier decades. With recession, a slight decrease in the number of settlements was, in turn, recorded in some rural districts surrounding compact urban centers, likely acting as local hotspots of urban re-densification. Given the multiplicity of socioeconomic factors involved, our findings highlight how urban development follows sequential phases of compaction and dispersion, based on locally differentiated spatial regimes characterizing settlement expansion and population growth. Sustainable urban management should face more actively with increasingly fragmented settlement dynamics at the fringe, prefiguring an appropriate spatial balance between urban centers and sparse settlements in light of recent demographic trends.

Fragmentation dynamics of Ar4He1000 upon electron impact ionization: Competition between ion ejection and trapping.

The fragmentation upon electron impact ionization of Ar4He1000 is investigated by means of mixed quantum-classical dynamics simulations. The Ar4 + dopant dynamics is described by a surface hopping method coupled with a diatomics-in-molecules model to properly take into account the multiple Ar4 + electronic surfaces and possible transitions between them. Helium atoms are treated individually using zero-point averaged dynamics, a method based on the building of an effective He-He potential. Fast electronic relaxation is observed from less than 2 ps to ∼30 ps, depending on initial conditions. The main fragments observed are Ar2 +Heq and Ar3 +Heq (q ≤ 1000), with a strong contribution of the bare Ar2 + ion, and neither Ar+ nor Ar+Heq fragments are found. The smaller fragments (q ≤ 50) are found to mostly come from ion ejection, whereas larger fragments (q > 500) originate from long-term ion trapping. Although the structure of the trapped Ar2 + ions is the same as in the gas phase, trapped Ar3 + and Ar4 + are rather slightly bound Ar2 +⋯Ar and Ar2 +⋯Ar⋯Ar structures (i.e., an Ar2 + core with one or two argon atoms roaming within the droplet). These loose structures can undergo geminate recombination and release Ar3 +Heq or Ar4 +Heq (q ≤ 50) in the gas phase and/or induce strong helium droplet evaporation. Finally, the translational energy of the fragment center of mass was found to be suitable to provide a clear signature of the broad variety of processes at play in our simulations.

Reply to “Remarks on Bank Competition and Convergence Dynamics”

In this reply, we provide detailed answers to the remarks made by Tsionas on the use of stochastic frontier-based measures of market power in a part of our empirical study, which examines the fragmentation and convergence dynamics of market power, concentration and credit risk in the euro area banking sector during 2005–2017. Our answers clarify all the issues raised by Tsionas and show that the only challenging, in our opinion, point of the criticism has been based on a hypothesis that does not hold in the case of our study.

Approaching black-box calculations of pump-probe fragmentation dynamics of polyatomic molecules

Abstract A general framework for the simulation of ultrafast pump-probe time resolved experiments based on Born-Oppenheimer molecular dynamics (BOMD) is presented. Interaction of the molecular species with a laser is treated by a simple maximum entropy distribution of the excited state occupancies. The latter decay of the electronic excitation into the vibrations is based on an on-the-fly estimation of the rate of the internal conversion, while the energy is distributed in a thermostat-like fashion. The approach was tested by reproducing the results of previous femtosecond studies on ethylene, naphthalene and new results for phenanthrene.

Experimental Study of the Dynamics of Laser Fragmentation of Nitrobenzene Vapors

The paper presents results of experimental study of the dynamics of laser-induced fragmentation of nitrobenzene molecules. It has been shown that when two laser pulses interacting with nitrocompound molecules and their decay products (NO fragments) are time delayed, it is possible to increase the sensitivity of the method of laser fragmentation/laser-induced fluorescence by approximately an order of magnitude for an optimal time delay between the pulses.

Fragmentation dynamics of positron-impact hydrogen ionization at near-threshold energies

Fragmentation dynamics of positron-impact hydrogen ionization at near-threshold energies

Three-body fragmentation dynamics of CH2CCH23+ investigated by 50-keV/u Ne8+ impact

The three-body fragmentation dynamics of triply charged allene (${\mathrm{CH}}_{2}{\mathrm{CCH}}_{2}^{3+}$) induced by 50-keV/u ${\mathrm{Ne}}^{8+}$ ion impact is studied by measuring the charged fragments in coincidence using the reaction microscope. We focus on the fragmentation dynamics of two completely measured fragmentation channels, ${\mathrm{H}}^{+}+{\mathrm{CH}}^{+}+{\mathrm{C}}_{2}\mathrm{H}{{}_{2}}^{+}$ and ${\mathrm{H}}^{+}+\mathrm{CH}{{}_{2}}^{+}+{\mathrm{C}}_{2}{\mathrm{H}}^{+}$, for which breakage of one CH bond and one CC bond occurred during fragmentation. Both concerted and sequential dissociation mechanisms are observed for these two channels. For sequential process, we found that CH bond cleavage in the first step followed by CC cleavage is the major contribution for both channels. However, the process in which breakage of the CC bond is prior to CH breakage is observed for only the ${\mathrm{H}}^{+}+\mathrm{CH}{{}_{2}}^{+}+{\mathrm{C}}_{2}{\mathrm{H}}^{+}$ channel. The relative contributions of different fragmentation pathways are determined.

MFsim\u2014an open Java all-in-one rich-client simulation environment for mesoscopic simulation

MFsim is an open Java all-in-one rich-client computing environment for mesoscopic simulation with Jdpd as its default simulation kernel for Molecular Fragment (Dissipative Particle) Dynamics. The new environment comprises the complete preparation-simulation–evaluation triad of a mesoscopic simulation task and especially enables biomolecular simulation tasks with peptides and proteins. Productive highlights are a SPICES molecular structure editor, a PDB-to-SPICES parser for particle-based peptide/protein representations, a support of polymer definitions, a compartment editor for complex simulation box start configurations, interactive and flexible simulation box views including analytics, simulation movie generation or animated diagrams. As an open project, MFsim allows for customized extensions for different fields of research.

Relation between pellet fragmentation kinetics and cellulolytic enzymes production by Aspergillus niger in conventional bioreactor with different impellers

The hydrodynamic environment in bioreactors affects the oxygen transfer rate and the shear conditions during microbial cultivations. Therefore, assessment of the effect of the hydrodynamic environment on cellular morphology can contribute to favoring the production of metabolites of interest. The aim of this work was to use image analysis in order to quantify the fragmentation of Aspergillus niger pellets in a conventional bioreactor operated using different impeller speeds, air flow rates, and impeller configurations including Rushton turbines and Elephant Ear impellers, with evaluation of the influence of the hydrodynamic environment on the production of cellulolytic enzymes. An empirical kinetic model was proposed to describe the dynamics of pellet fragmentation and quantify the shear conditions. The results showed that the agitation speed affected the dynamics of pellet fragmentation in two ways, by accelerating the damage process and by increasing the magnitude of the fragmentation. Both endoglucanase and β-glucosidase production exhibited a linear relationship with the pellet fragmentation percentage, which was directly related to the shear conditions. Interestingly, β-glucosidase production was favored under high shear conditions, while the highest endoglucanase production occurred under low shear conditions. These findings may be useful for defining suitable systems and operating conditions for the production of metabolites including enzymes in bioreactors, as well as defining conditions that favour a specific pre-determined enzyme cocktail.

Atomic, Molecular and Cluster Science with the Reaction Microscope Endstation at FLASH2

The reaction microscope (REMI) endstation for atomic and molecular science at the free-electron laser FLASH2 at DESY in Hamburg is presented together with a brief overview of results recently obtained. The REMI allows coincident detection of electrons and ions that emerge from atomic or molecular fragmentation reactions in the focus of the extreme-ultraviolet (XUV) free-electron laser (FEL) beam. A large variety of target species ranging from atoms and molecules to small clusters can be injected with a supersonic gas-jet into the FEL focus. Their ionization and fragmentation dynamics can be studied either under single pulse conditions, or for double pulses as a function of their time delay by means of FEL-pump–FEL-probe schemes and also in combination with a femtosecond infrared (IR) laser. In a recent upgrade, the endstation was further extended by a light source based on high harmonic generation (HHG), which is now available for upcoming FEL/HHG pump–probe experiments.

Fragmentation, Disintegration, and Resurgence: Assessing the Islamist Field in Yemen

The well-developed literature on Islamist politics has tended to focus on partisan and welfare institutions within the context of existing states. Civil war raises important questions about whether and how the relevance of such institutions changes when the state itself fragments. This article seeks to understand Islamism in Yemen as a kind of post-organizational political field. At a theoretical scale, Yemen’s civil war and the transformation of the country’s Islamist politics offers lessons about the fixity of categorical distinctions within and across forms of Islamist activity. This article works to map dynamics of fragmentation within pre-war Islamist organizations, the disintegration of authority among Islamist leaders in the context of war, and the effect of each of these processes on the resurgence and partial transformation of particular Islamist claims. The field, as an analytic approach less firmly tied to the state itself, allows for a consideration of Islamist politics as articulated locally but shaped as well by transnational engagement with ideas and institutions.

Essential fragmentation metrics for agricultural policies: Linking landscape pattern, ecosystem service and land use management in urbanizing China

Fragmentation, as one of the most distinct characteristics of agricultural landscapes worldwide, has resulted in a diversity of ecological consequences. It remains as a gap in the literature on how provisioning service changes in association with agricultural fragmentation and land use management. Addressing such a gap at a national level should provide essential insights for policymakers. This paper identifies the essential metrics from a set of landscape metrics for describing agricultural fragmentation and further develops an integrated fragmentation index (IFI). Using the IFI, spatiotemporal dynamics of agricultural fragmentation across Chinese cities from 2010 to 2017 are captured. In particular, an increasing trend of fragmentation is identified and southern China is characterized by more fragmented agricultural landscapes than the other parts. Spatial regression, with the Cobb-Douglas Production Function as the theoretical basis, is employed to quantify the relationships among provisioning service, agricultural fragmentation, and land use management. It is discovered that landscape fragmentation would impair the supply of the provisioning service and sustainable land use management regulates the provisioning service in a positive way. We argue that alleviating the landscape fragmentation issue would not be achieved with simple measurement. Cooperation of a series of administrative acts, such as land reclamation, land use transfer, household registration system reform and improvement of employment and welfare system, should be fundamental and practical approaches. The present study demonstrates a novel methodological framework to unravel the effect of agricultural fragmentation on provisioning services, which should be useful for understanding the complex human-ecosystem interactions.

Bank Competition and Credit Risk in Euro Area Banking: Fragmentation and Convergence Dynamics

Consolidation in euro area banking has been the major trend post-crisis. Has it been accompanied by more or less competition? Has it led to more or less credit risk? In all or some countries? In this study, we examine the evolution of competition (through market power and concentration) and credit risk (through non-performing loans) in 2005–2017 across all euro area countries (EA-19), as well as core (EA-Co) and periphery (EA-Pe) countries separately. Using Theil inequality and convergence analysis, our results support the continued existence of fragmentation as well as of divergence within and/or between core and periphery with respect to competition and credit risk, especially post-crisis, in spite of some partial reintegration trends. Policy measures supporting faster convergence of our variables would be helpful in establishing a real banking union.

Ultrafast Proton Transfer Dynamics on the Repulsive Potential of the Ethanol Dication: Roaming-Mediated Isomerization versus Coulomb Explosion.

If a molecular dication is produced on a repulsive potential energy surface (PES), it normally dissociates. Before that, however, ultrafast nuclear dynamics can change the PES and significantly influence the fragmentation pathway. Here, we investigate the electron-impact-induced double ionization and subsequent fragmentation processes of the ethanol molecule using multiparticle coincident momentum spectroscopy and ab initio dynamical simulations. For the electronic ground state of the ethanol dication, we observe several fragmentation channels that cannot be reached by direct Coulomb explosion (CE) but require preceding isomerization. Our simulations show that ultrafast hydrogen or proton transfer (PT) can stabilize the repulsive PES of the dication before the direct CE and form intermediate H2 or H2O. These neutrals stay in the vicinity of the precursor, and roaming mechanisms lead to isomerization and finally PT resulting in emission of H3+ or H3O+. The present findings can help to understand the complex fragmentation dynamics of molecular cations.

Dissociation dynamics of the diamondoid adamantane upon photoionization by XUV femtosecond pulses

This work presents a photodissociation study of the diamondoid adamantane using extreme ultraviolet femtosecond pulses. The fragmentation dynamics of the dication is unraveled by the use of advanced ion and electron spectroscopy giving access to the dissociation channels as well as their energetics. To get insight into the fragmentation dynamics, we use a theoretical approach combining potential energy surface determination, statistical fragmentation methods and molecular dynamics simulations. We demonstrate that the dissociation dynamics of adamantane dications takes place in a two-step process: barrierless cage opening followed by Coulomb repulsion-driven fragmentation.

Infrared-Assisted Synthesis of Prebiotic Glycine.

A novel approach has been developed to synthesize complex organic molecules (COMs) relevant to prebiotic chemistry, using infrared (IR) radiation to trigger the reaction. An original laboratory reactor working at low gas density and using IR irradiation was developed. In this way, glycine, the simplest brick of life, has been synthesized by assisting ion-molecule reaction with IR laser light. The ion-molecule complex constituted by acetic acid and hydroxylamine was formed in a mass spectrometer reactor and then irradiated with IR photons. As photoproducts, we obtained both glycine structures and some of its isomers. Anharmonic vibrational frequency calculations and fragmentation dynamics simulations allow for a better interpretation of the experimental data. This novel approach can be now extended to study other new synthetic pathways responsible for the formation of further COMs also with potential prebiotic relevance.

The nature of trade, global production fragmentation and inflationary dynamics: Cross‐country evidence

AbstractThis study investigates under which circumstances trade has impact on inflation dynamics by examining the independent effects of trade intensity, intra‐industry trade and trade on value added. Trade in goods is decomposed into consumption (final) goods and intermediate inputs to deepen the assessment of the role of the globalisation of production activities on inflation dynamics. Open‐economy new Keynesian Phillips curve (NKPC) analyses suggest that inflation is sensitive to domestic factors and that the relevance of external factors changes with respect to the nature of trade, country groups and time. Vertical intra‐industry trade in intermediate inputs and value‐added trade play important role, whereas final goods trade has no statistically significant effect on inflation dynamics.

Understanding Current and Future Fragmentation Dynamics of Urban Forest Cover in the Nanjing Laoshan Region of Jiangsu, China

Accurate acquisition of the spatiotemporal distribution of urban forests and fragmentation (e.g., interior and intact regions) is of great significance to contributing to the mitigation of climate change and the conservation of habitat biodiversity. However, the spatiotemporal pattern of urban forest cover changes related with the dynamics of interior and intact forests from the present to the future have rarely been characterized. We investigated fragmentation of urban forest cover using satellite observations and simulation models in the Nanjing Laoshan Region of Jiangbei New Area, Jiangsu, China, during 2002–2023. Object-oriented classification-based land cover maps were created to simulate land cover changes using the cellular automation-Markov chain (CA-Markov) model and the state transition simulation modeling. We then quantified the forest cover change by the morphological change detection algorithm and estimated the forest area density-based fragmentation patterns. Their relationships were built through the spatial analysis and statistical methods. Results showed that the overall accuracies of actual land cover maps were approximately 83.75–92.25% (2012–2017). The usefulness of a CA-Markov model for simulating land cover maps was demonstrated. The greatest proportion of forest with a low level of fragmentation was captured along with the decreasing percentage of fragmented area from 81.1% to 64.1% based on high spatial resolution data with the window size of 27 pixels × 27 pixels. The greatest increase in fragmentation (3% from 2016 to 2023) among the changes between intact and fragmented forest was reported. However, intact forest was modeled to have recovered in 2023 and restored to 2002 fragmentation levels. Moreover, we found 58.07 km2 and 0.35 km2 of interior and intact forests have been removed from forest area losses and added from forest area gains. The loss rate of forest interior and intact area exceeded the rate of total forest area loss. However, their approximate ratio (1) implying the loss of forest interior and intact area would have slight fragmentation effects on the remaining forests. This analysis illustrates the achievement of protecting and restoring forest interior; more importantly, excessive human activities in the surrounding area had been avoided. This study provides strategies for future forest conservation and management in large urban regions.

Unravelling the molecular phenomena of hydrogen peroxide (H2O2) through many-body fragmentation dynamics

SynopsisIon-induced fragmentation dynamics of H2O2 3+ has been studied to distangle molecular phenomena like concerted and sequential fragmentation routes.