Explosive Growth Phase Research Articles

Visual Analysis on the Research of Color-based Image Retrieval

This study retrieved relevant literature on color-based image retrieval in the Web of Science core database, and used bibliometrics and CiteSpace 6.1.R2 software to visually analyze the authors, institutions, and keywords of literature published in this field from 2005 to 2023. This study summarized the current status and development trend of color-based image retrieval and combined information extraction to select and include 716 articles for analysis. The results showed that: (1) In the last 20 years, the number of publications in this field has gone through a slow budding phase, a fluctuating growth phase, and an explosive growth phase; research in this area has been highly active in recent three years. (2) The authors of this field have a relatively even distribution of publications and some authors have formed close collaborative groups. (3) The research institutions mainly include research institutes and comprehensive universities, which have close collaborations with each other. (4) Co-occurrence and clustering analysis of keywords showed that research in this field is mainly focused on the main paths, research methods, and technological tools of color-based image retrieval, as well as key objects and potential influencing factors in the technological process. (5) Emerging keywords analysis predicted that more precise color description and extraction technology will be the focus of future research. In conclusion, color-based image retrieval is still in a hot research and technology explosion phase, and cooperation between countries, institutions, and authors should be strengthened to conduct more in-depth research.

Corporate culture: The interview evidence

Corporate culture: The interview evidence

Numerical Studies of Fast Pressure Crash Associated with Double Tearing Modes

The fast pressure crash associated with the nonlinear evolution of DTMs is investigated using a three-dimensional toroidal and nonlinear MHD code CLT. Our simulation results indicate that the fast pressure crash is not directly related to the explosive growth of DTM because the explosive growth of the DTM takes place in the earlier nonlinear phase and the fast pressure crash happens in the much later nonlinear stage. It is also found that the explosive growth lasts much longer than the fast pressure crash. At almost the end of the explosive growth phase, the magnetic fields around the magnetic axis become stochastic, and a strong radial flow is generated. The radial flow can effectively transfer the hot plasma around the magnetic axis into the outer cold region and consequently leads to the fast crash of the pressure in the core. As a result, the dependence of the crash time on the resistivity is very weak. It is also found that the geometry of Tokamaks has very weak influence on the fast pressure crash.

The water transport profile of Phyllostachys edulis during the explosive growth phase of bamboo shoots

The new bamboo shoots do not generate leaves during the explosive growth period. Thus, they cannot perform photosynthesis during this period. The water use profile and control mechanism of water transport during the explosive growth period of Moso bamboo (Phyllostachys edulis) shoots are still unclear. This study applied thermal dissipate probe (TDP) technology for monitoring the sap flow rate (Fs) dynamics in Moso bamboo during explosive growth phases (2008¬2010). We investigated the underlying mechanism of rapid growth by analyzing the water transport profile in a system consisting of the stem, rhizome, and shoot. We found that the Fs increase during explosive growth periods was consistent with the grow rate of bamboo shoots, the explosive growth phase was controlled by the sap flow. Water flew mainly from the rhizome toward the stem before shoot development but switched to the shoot during shooting. The water flow direction shifted from the stem and rhizome to the new shoot, ensuring the water and nutrient transport needed for growth and metabolisms. Diurnal Fs variations during growth periods followed a typical “single-peak” pattern with a daytime peak, resulting in a higher growth rate of bamboo shoots during the daytime. On the annual scale, Fs has an on-off-year alternation with higher on¬year rates than off¬year rates, which was consistent with the regulation of the bamboo shoot emergence. Correlation analysis found that leaf area index variations could explain the observed Fs variations of 95–97%. Economic bamboo forest management should ensure sufficient water supply during the explosive growth period of bamboo shoots. Further research should strengthen our knowledge about the hydraulic characteristics of Moso bamboo during explosive growth periods to ensure efficient forest management.

SIMULATION OF FLUCTUATIONS OF AGGRESSIVE ALIEN SPECIES IN CONTINUOUS MODELS WITH INDEPENDENT REGULATION

Traditional models in biology do not describe modern extraordinary situations when the whole species composition is mixed. The article deals with oscillatory equations and non-dissipative population dynamics for specific environmental situations that are associated with alien species in ecosystems. During the invasion of new species, the resistance of the biotic environment may be completely absent for a considerable time. Under such conditions, with a high specific fecundity, nonstationary regimes of change in numbers arise. A pest outbreak is realized with an explosive growth phase. All outbreaks of fish and insects are some brief extreme episodes that end with a new state of the environment and the aggressive new species. Completion options are varied even in the example of one malicious species of comb jelly Mnemiopsis leidyi in Azov and Caspian Sea. Transition to relaxation oscillations after a comb jelly outbreak is possible. A new species may become a small group or even disappear in case minN(t; r) = 0. The paper proposes a model based on the lagging regulation for actual scenarios of population behaviour in a new environment. In computational experiments we have shown the conditions for stabilization after an outbreak in an extremely small group of individuals or complete disappearance after collapse. A separate scenario describes the complete depletion of environmental resources during fluctuations with asignificant amplitude. The most relevant is the model scenario of stabilization at minimum values after a rapid change in the phases of the outbreak and a transition to the depression of the pest number in the modification of the differential equation of Bazykin and Hutchinson model.

Nonlinear evolution of double tearing mode with guiding magnetic field

Nonlinear dynamic evolution of the double tearing mode (DTM) with a guiding magnetic field (By0) is investigated by magnetohydrodynamical numerical simulation. The dynamic process of DTM depends weakly on the guiding field in the weak guiding field regime (By0≤1), but is suppressed by a strong guiding field (By0>2). During the explosive nonlinear phase, the maximum reconnection rate (γmax) increases weakly with the increase of the resistivity as γmax~η0.06 for By0≤1, but for By0>2, γmax is nearly independent of the resistivity. The maximum reconnection rate in the explosive growth phase increases with increase of the initial current sheet separation. A secondary tearing instability is observed at moderate current sheet separation. A strong guiding field suppresses the formation of a secondary island. Based on the simulation results, it is found that the secondary tearing instability occurs only when the length-to-thickness aspect ratio of the reconnection region exceeds about 20.

The inversion layer of electric fields and electron phase-space-hole structure during two-dimensional collisionless magnetic reconnection

Based on two-dimensional fully kinetic simulations that resolve the electron diffusion layer in undriven collisionless magnetic reconnection with zero guide field, this paper reports the existence and evolution of an inversion layer of bipolar electric fields, its corresponding phase-space structure (an electron-hole layer), and the implication to collisionless dissipation. The inversion electric field layer is embedded in the layer of bipolar Hall electric field and extends throughout the entire length of the electron diffusion layer. The electron phase-space hole structure spontaneously arises during the explosive growth phase when there exist significant inflows into the reconnection layer, and electrons perform meandering orbits across the layer while being cyclotron-turned toward the outflow directions. The cyclotron turning of meandering electrons by the magnetic field normal to the reconnection layer is shown to be a primary factor limiting the current density in the region where the reconnection e...

Substorm convection and current system deduced from the global simulation

The substorm mechanism is investigated by analyzing the numerical results obtained through the use of the recently refined magnetohydrodynamic model. After showing the growth phase features, the numerical solution reproduces the observed signatures of a substorm onset, including the formation of a near‐Earth neutral line (NENL), earthward directed flow in the plasma sheet, a dipolarization, a geosynchronous D deflection, the development of the nightside field aligned currents (FACs), and electrojets in the ionosphere. The onset is triggered by a sudden collapse of the plasma sheet and a successive formation of a high‐pressure region in the inner magnetosphere. The energy source of this high‐pressure region is the magnetic tension released from the NENL. The tail disturbance is primary transmitted to the ionosphere by the region 2 FAC accompanying the high‐pressure region formed in the inner magnetosphere. The associated nightside region 1 FAC is not connected to the traditional current wedge but to the cusp region. The region 1 FAC path to the ionosphere develops from dayside to nightside, so as to construct a grand loop with the region 2 FAC from the partial ring current. In the grand loop, the region 1 FAC provides a short circuit in the ionosphere for the region 2 FAC. In the expansion phase, convection enhances to relax the distorted pressure distribution formed at the onset, accompanied by a further development of dipolarization and a thickening of the plasma sheet in the magnetosphere and increases in the westward and eastward electrojets in the ionosphere. The present model can explain the explosive growth phase and the thinning of the midtail plasma sheet just after the onset.

Open Geospace General Circulation Model simulation of a substorm: Axial tail instability and ballooning mode preceding substorm onset

Recent global simulations of substorms show that before the onset of near‐Earth reconnection the pressure equilibrium in the tail breaks down. This instability has no cross‐tail variation and is thus not a ballooning mode, and it is also distinct from the tearing mode. Here, we analyze an Open Geospace General Circulation Model simulation run of the 23 March 2007 substorm and find the same instability. Because this mode has no significant cross‐tail variation associated with it we call it the KY0 mode. Besides the KY0 mode we also find the classical ballooning mode in the simulation. It has a wavelength of ∼0.5 RE and is marginally, but sufficiently, resolved as shown by a higher‐resolution control run. These results suggest a new scenario for the substorm expansion phase onset. During the growth phase magnetic flux is added to the lobes and the plasma sheet thins but remains in equilibrium. When force balance is no longer possible the KY0 instability grows and accelerates plasma tailward. The divergence of the resulting tailward flow reduces the normal magnetic field and thereby makes the current sheet tearing unstable. The tearing mode grows right out of the KY0 mode. The classical ballooning mode grows at the same time and is superimposed on the KY0 mode, but its role in initiating reconnection is still unclear. The growth time of the KY0 mode, ∼2 min, is both consistent with the notion of an explosive growth phase and with recent ground‐based observation of the initial growth of auroral arcs before auroral breakup.

Nonlinear evolution of double tearing mode in Hall magnetohydrodynamics

Nonlinear evolution of a double tearing mode for different plasma resistivities (η) and ion inertial lengths (di) is investigated using Hall magnetohydrodynamics simulations. In the Hall dominant regime, the magnetic field configuration in the reconnection region evolves from Y-type to X-type geometry, which leads to fast reconnection in the nonlinear growth phase. The maximum growth rate of total kinetic energy of plasma γmax in the explosive growth phase is found to have a di2/5η1/10 scaling and the maximum total kinetic energy (Ek)max scales as di4/5. In the regime with weak Hall effect, it is found that the elongated thin current sheet formed in the early phase is broken into two X-points, forming a magnetic island in the late stage, instead of shrinking to an X-type geometry.

Flattened current sheet and its evolution in substorms

In this research, the properties of a tail current sheet, which has a flattened geometry, and its evolution during substorm activity have been investigated. The geometrical configuration of the magnetic field and the spatial distribution of the current density in a flattened current sheet have been revealed with certainty for the first time. It is found that such a flattened current sheet has sufficiently strong By (GSM) within its neutral sheet that the magnetic field lines (MFLs) in the neutral sheet are lie almost in the GSM equatorial plane and that the normal directions are generally northward. Detailed analyses show that, the magnetic field lines are spiral‐like, not plane curves, which are left‐handed or right‐handed spirals for By > 0 or By < 0. This magnetic rotation occurs predominantly in the neutral sheet. The flattened current sheet may be very thin, and the thickness of the neutral sheet is much less than the minimum radius of the curvature of the MFLs in the current sheet. The analysis also suggests that the neutral sheet current is field‐aligned and lies mainly duskward. The curvature current makes little contribution to the total current in the flattened current sheet. The main current carriers in the neutral sheet of the flattened current sheet are electrons. A statistical survey shows that there is one positive correlation between By in the flattened current sheet and IMF By and penetration efficiency is 0.67. Flattened current sheets may occur in both quiet and disturbed periods and may appear at all phases of the substorms. During the growth phase of a substorm event, the neutral sheet of the flattened current sheet is shown to become progressively thinner, while the associated current density is increasing gradually. It is found that the northern turning of the IMF has triggered the explosive growth phase at the end of the growth phase, which lasts several minutes. At the explosive growth phase, the flattened current sheet becomes much thinner and the current density in the neutral sheet then increases considerably and reaches a value larger than 0.017 μAm−2. Just after the onset of the substorm, the current density in the neutral sheet drops abruptly and varies turbulently.

Decrease in Bz prior to the dipolarization in the near‐Earth plasma sheet

We examine in detail the rapid decrease in Bz just before dipolarizations observed by the Geotail satellite in the near‐Earth plasma sheet at (XGSM, YGSM) = (−8.3 RE, −5.1 RE). The observations were made using high‐time‐resolution data from a fluxgate magnetometer (16‐Hz sample), a search‐coil magnetometer (128 Hz), and an electric field antenna (64 Hz). Two dipolarizations were observed during a short time interval of 2 min. The magnetic Bz component suddenly decreased 2–4 s prior to the dipolarization. Characteristic waves with frequencies of 5–20 Hz and amplitudes of 1–3 mV m−1 and 5–15 nT s−1 were observed in the electric and magnetic field data at the time of the sudden decreases in Bz. We discuss two possible causes of the sudden decreases in Bz prior to the dipolarizations: (1) passage of a field‐aligned line current associated with the substorm current wedge and (2) explosive growth phase and subsequent disruption of the tail current caused by the observed characteristic field oscillations.

Magnetic field fluctuations during substorm‐associated dipolarizations in the nightside plasma sheet around X = −10 RE

Using high‐time‐resolution data for the magnetic field (1/16 s), plasma moment (12 s), and electric field (3 s) obtained by Geotail, we have investigated various characteristics of magnetic field fluctuations for 21 events of substorm‐associated near‐Earth dipolarization at XGSM = −8 ∼ −11 RE and ∣YGSM∣ < 5 RE. The dipolarizations were always accompanied by fluctuations of the magnetic field. The amplitude of the fluctuations tends to be larger for smaller ambient magnetic field. For several events we found that magnetic field elevation angles show rapid decrease prior to the rapid increase (features like explosive growth phase). Compressional fluctuations of magnetic field intensity B show characteristic spikes of a sudden decrease and increase with a timescale of seconds. For quite a few cases the fluctuations are accompanied by enhancements of earthward plasma velocity. The spectral shape of the B fluctuations had a steeper slope (f−2.7) at higher frequency range at 1.0–0.2 Hz than at 0.01–0.2 Hz (f−2.0) for the events closer to the cross‐tail current sheet (smaller ambient‐B region). We found that the steeper slope extends to lower frequency range below 0.2 Hz for the events away from the current sheet (larger ambient‐B region). This fact may suggest transition from three‐dimensional to two‐dimensional turbulence from smaller B to larger B region. We also investigated correlation of fluctuations in plasma velocity and magnetic field for waves with periods around 60 s. The correlations were rather weak, suggesting that non‐MHD plasma processes are going on. For these waves, the magnetic and plasma pressure variations were clearly antiphase.

Equatorial spread F irregularity characteristics over São Luís, Brazil, using VHF radar and GPS scintillation techniques

Multitechnique observations may considerably improve our understanding of factors responsible for the generation, growth, and dynamics of the destabilized nighttime equatorial F region plasma irregularities. In order to investigate the dynamics of plasma density irregularities of different scale sizes, a campaign of observations was conducted during 11–20 November 2001 at the Brazilian magnetic equatorial station São Luís (2.57°S, 44.21°W, dip latitude 1.73°S). We carried out observations using VHF coherent backscatter radar, two spaced GPS‐based scintillation monitors, and one digisonde. Range type spread F on ionograms and radar plume signatures on range‐time‐intensity maps of the VHF radar started at similar times. In order to compare GPS L1 (1.575 GHz) scintillations and radar plumes we used the scintillation S4 index computed for the signal transmitted by the highest elevation satellite. GPS scintillations were not observed during the initial bottom‐type layer shown by the radar; however, stronger scintillations (higher S4 values) were observed concurrently to stronger radar echoes. Although the time duration of GPS scintillation is longer than the duration of the plumes observed by the radar, ionosonde spread F is still much longer than scintillation occurrence, confirming that smaller scale‐size irregularities decay faster. Zonal and vertical velocities of 5‐m irregularities measured by the radar were analyzed jointly with the apparent zonal velocity of ∼400‐m irregularities measured by the spaced‐receiver scintillation method. Larger values of the zonal velocity measured by the scintillation technique were found during the explosive growth phase of radar plumes associated with large values of vertical drifts measured by the radar.

Current point formation and magnetic reconnection process in nonlinearly destabilized double tearing modes

Magnetic reconnection process triggered by the nonlinearly destabilized double tearing mode (DTM) is studied in detail. A localized plasma current, which is referred as a current point, is formed at the X-type reconnection region of the outer magnetic island in the nonlinear growth phase of DTM [Phys. Rev. Lett. 89, 205002 (2002)]. Magnetic reconnection process with a current point shows new features different from those with the well-known Sweet–Parker type current sheet. In contrast to the latter one, the inverse aspect ratio of the plasma current at the reconnection region of the outer magnetic island, δ/Δ, increases in the Rutherford type phase and decreases after the nonlinear destabilization of DTM is triggered. The weak dependence of the temporal growth rate on the plasma resistivity in the explosive growth phase is due to this unique temporal evolution of the spatial structure of a current point. The simulations in toroidal geometry show that a current point with coherent character is also formed even in the stochastic magnetic field resultant from overlapping magnetic islands with different helicity.

Substorm Trigger Processes in the Magnetotail: Recent Observations and Outstanding Issues

The present article reviews recent studies about near-Earth substorm processes. A focus is placed on the relationship between two fundamental processes, that is, tail current disruption (TCD) and the formation of a near-Earth neutral line (NENL). The former is inferred to cause dipolarization, and the latter is often associated with the fast plasma flow in the plasma sheet. Whereas it is inferred from the directions of fast plasma flows that the NENL is formed at 20–30 RE from the Earth, dipolarization is most manifest in the near-Earth (6.6–12 RE) region. The observation of the fast plasma flow prior to substorm (Pi2) onsets favors the idea that the NENL is formed first and dipolarization is the effect of the pile-up of magnetic flux convected earthward from the NENL, which is called the pile-up model. The present paper addresses several outstanding issues regarding this model, including (1) the interpretation of plasma flow deceleration in terms of the flux pile up, (2) highly irregular magnetic fluctuations observed in the near- Earth region, (3) the spatial coherency of the fast plasma flow, (4) the spatial structure and expansion of dipolarization region, and (5) the explosive growth phase. The paper also proposes the possibility that TCD is an independent process, but the formation of the NENL sets a favorable condition for it.

Electromagnetics of substorm onsets in the near‐geosynchronous plasma sheet

A search of the CRRES database identified 20 events in which the satellite was located within the local‐time sector spanned by the substorm current wedge (SCW) as it formed. Poynting vectors for low‐frequency waves are derived from the electric and magnetic field measurements. In 19 of the events, data are inconsistent with the notion that the SCW initiates from the braking of earthward bulk flows emanating from a near‐Earth X line. Rather, the data support drift‐Alfvén ballooning in the near‐geosynchronous plasma sheet as being responsible for initiation of the SCW and substorm onset. Dipolarization at CRRES is preceded by eastward excursions of the electric field (trigger waves), at which time the first significant electromagnetic energy is observed flowing toward the ionosphere. Dipolarization and the SCW appear before ground onset, following one or more of these trigger waves. The so‐called “explosive growth phase” occurs in association with explosive growth of the trigger waves soon after onset. Seven characteristic features of substorm onsets and expansions observed at CRRES are described. Among these are two stages of expansion. The first expansion stage is initiated by the trigger waves (ballooning) in the near‐geosynchronous plasma sheet. Approximately 10 minutes later a second stage begins consistent with the arrival of earthward bulk flows emanating from a near‐Earth X line. Near‐geosynchronous substorm onsets can explain the observed increase in the occurrence rate of fast bulk flows earthward of its minimum value near X = −12 RE. Drift‐Alfvén ballooning also provides a possible causal link between observed reductions of the solar wind driver and substorm onsets.

Steady state assumptions in DALYs: effect on estimates of HIV impact.

OBJECTIVE: The disability adjusted life year (DALY) and the healthy life year (HeaLY) are both composite indicators of disease burden in a population, which combine healthy life lost from mortality...

Entropy antidiffusion instability and formation of a thin current sheet during geomagnetic substorms

In our recent study of the equilibrium configuration of the near‐Earth magnetotail, it is found that a steeper profile of entropy function S leads to the formation of a thinner current sheet. Here S = pVγ, where p is the plasma pressure and V is the volume of a unit magnetic flux tube. In the presence of density gradient at the edges of the current sheet, the lower‐hybrid‐drift instability may lead to pressure diffusion. Since the pressure generally decreases and the entropy function S increases tailward, the diffusion of plasma pressure results in a steepening, or antidiffusion, of the entropy profile. This, in turn, leads to a thinner current sheet, which enhances the pressure diffusion. This positive feedback process is called the entropy antidiffusion instability. On the basis of MHD simulations with a pressure diffusion, we find that the entropy antidiffusion instability leads to a further thinning of the near‐Earth current sheet and the onset of dipolarization of near‐Earth geomagnetic field lines. The growth rate of the instability is linearly proportional to the diffusion coefficient. The growth time at the final stage for the formation of a very thin current sheet is ∼1 min. This instability may explain the observed explosive growth phase of substorms and the onset of dipolarization of geomagnetic field lines.

Kinetic ballooning instability for substorm onset and current disruption observed by AMPTE/CCE

A new interpretation of AMPTE/CCE observation of substorm onset and current disruption and the corresponding physical processes are presented. Toward the end of late growth phase the plasma β increases to ≥50 and a low frequency instability with a wave period of 50–75 sec is excited and grows to a large amplitude at the current disruption onset. At the onset, higher frequency instabilities are excited so that the plasma and electromagnetic field form a turbulent state. Plasma transport takes place to modify the ambient pressure profile so that the ambient magnetic field recovers from a tail‐like geometry to a more dipole‐like geometry. A new theory of kinetic ballooning instability (KBI) is proposed to explain the low frequency instability and the high β threshold (βc≥50) observed by AMPTE/CCE. The stabilizing effect is mainly due to kinetic effects of trapped electrons and finite ion Larmor radii which give rise to a large parallel electric field and hence a parallel current that greatly enhances the stabilizing effect of field line tension. As a result βc is greatly increased over the ideal MHD ballooning instability threshold by ≥ O(10² ‐ 10³). The wave‐ion magnetic drift resonance effect produces a perturbed resonant ion velocity distribution centered at a duskward velocity roughly equal to the average ion magnetic drift velocity. This perturbed ion distribution explains the enhanced duskward ion flux during the explosive growth phase and can excite higher frequency instabilities (such as the cross‐field current instability).