Energetic Boundaries Research Articles

Lagrangian Study of Several Long-Lived Agulhas Rings

AbstractBy using a Lagrangian-averaged vorticity deviation (LAVD)-based vortex detection scheme, rotationally coherent Lagrangian vortices in the South Atlantic Ocean are detected. These vortices act as agents for water transport and can stay coherent in a limited time scale. Our study starts from the life cycle of several long-lived Agulhas rings detected with the LAVD-based vortex detection method. The life cycle of those long-lived Agulhas rings can be separated into two distinct stages: the growing stage and the decaying stage. It is found that at the growing stage, the ambient water spins in and provides effective shielding for the coherent core. The rate of change of material belt width with respect to the detection time scale at the end of the growing stage can represent the decay rate of coherence. We further find a linear relationship between the mean strain rate and the mean square root of kinetic energy (KE1/2). Mean finite-time Lyapunov exponents (FTLE) increase monotonically with the mean strain rate or mean KE1/2. The long existence of the Agulhas rings can be partly attributed to the energetic boundaries around the rings. The ratio of the boundary kinetic energy to the spatial mean kinetic energy (KE/MKE) is also found to be a contributing factor that can influence the lifetime of Agulhas rings. In the retroflection area, the short-lived Agulhas rings might be attributed to the low KE/MKE in this area.

On the source region and orientations of nightside auroral arcs

Using large data base of stable auroral arcs observed at Gillam we identified those passes of POES spacecraft which were magnetically conjugate to these arcs. We studied statistically arc locations with respect to the energetic particle isotropy boundaries (IBs), which are the well-known markers of the magnetotail regions. In the dusk and night sectors we confirm previous finding that arcs tend to appear close to or poleward of the electron isotropy boundary (IBe), indicating the location of the arcs in the small BZ (large magnetic field curvature) region of the tail current sheet. Different from that, in the dawn sector significant fraction of arcs appears deeper in the magnetosphere, between electron and proton IBs, in the transition region between the current sheet and dipole-like magnetosphere. Addressing the orientations of stable arcs we use the empirical magnetospheric models to demonstrate that nearly sun-aligned plasma sheet structures in the tail are significantly rotated toward azimuthal alignment when mapped from the tail equator to the ionosphere. We discuss how the flow braking/rotation can provide (in direct or secondary/way) the E-W aligned arcs. Based on these results we argue that a significant fraction of the highlatitude stable auroral arcs could be formed by the fast flow convection channels (BBFs); particularly the observed dawn-dusk asymmetry in the relative location of arcs and isotropy boundary can be contributed by this mechanism.

Turbulence mediates marine aggregate formation and destruction in the upper ocean

Marine aggregates formed through particle coagulation, large ones (>0.05 cm) also called marine snow, make a significant contribution to the global carbon flux by sinking from the euphotic zone, impacting the Earth’s climate. Since aggregate sinking velocity and carbon content are size-dependent, understanding the physical mechanisms controlling aggregate size distribution is fundamental to determining the biological carbon pump efficiency. Theoretical, laboratory and in-situ studies of flocculation have suggested that turbulence in the benthic boundary layer is important for aggregate formation and destruction, but the small number of field observations has limited our understanding of the role of turbulence on aggregation processes in the ocean surface layer away from energetic boundaries. Using simultaneous field observations of turbulence and aggregates, we show how aggregate formation, destruction, morphology and size distribution in the ocean surface layer (10–100 m) are mediated by interactions between turbulence and aggregate concentration. Our findings suggest that turbulence enhances aggregate formation up to a critical turbulent kinetic energy dissipation rate of 10−6 (W kg−1), above which the smallest turbulent eddies limit aggregate size.

Statistics of the field‐aligned currents at the high‐latitude energetic electron boundaries in the nightside: Cluster observation

AbstractMagnetic field disturbances with a clear bipolar signature are frequently observed when the Cluster spacecraft fleet passes through both southern and northern high‐latitude energetic electron boundaries at the nightside magnetosphere. The dominant variation of the bipolar signature is in the azimuthal direction of the local mean field‐aligned coordinate, indicating a field‐aligned current. From 2001 to 2008, we have examined 110 events with the magnetic field and energetic electron measurements. The main results can be summarized as follows: (1) The density and thickness of the field‐aligned current, calculated under the assumption of the one‐dimensional sheet, are in order of tens of nA/m2 and hundreds of kilometers, respectively. (2) Currents flowing into and away from the ionosphere tend to be observed in the postmidnight and premidnight sector, respectively, which have the same polarity as the region 1 current system. (3) These currents mainly distribute in the 60°–75° magnetic latitude region after mapping to the ionosphere. We also find that the current density and corresponding magnetic field variation are positively correlated with the Kp index and solar wind pressure, but almost independent of the AE index.

CONFECT: Conformations from an Expert Collection of Torsion Patterns

The generation of sets of low-energy conformations for a given molecule is a central task in drug design. Herein we present a new conformation generator called CONFECT that builds on our previously published library of torsion patterns. Conformations are generated as well as ranked by means of normalized frequency distributions derived from the Cambridge Structural Database (CSD). Following an incremental construction approach, conformations are selected from a systematic enumeration within energetic boundaries. The new tool is benchmarked in several different ways, indicating that it allows the efficient generation of high-quality conformation ensembles. These ensembles are smaller than those produced by state-of-the-art tools, yet they effectively cover conformational space.

Geometrically nonlinear higher-gradient elasticity with energetic boundaries

The objective of this contribution is to formulate a geometrically nonlinear theory of higher-gradient elasticity accounting for boundary (surface and curve) energies. Surfaces and curves can significantly influence the overall response of a solid body. Such influences are becoming increasingly important when modeling the response of structures at the nanoscale. The behavior of the boundaries is well described by continuum theories that endow the surface and curve with their own energetic structures. Such theories often allow the boundary energy density to depend only on the superficial boundary deformation gradient. From a physical point of view though, it seems necessary to define the boundary deformation gradient as the evaluation of the deformation gradient at the boundary rather than its projection. This controversial issue is carefully studied and several conclusions are extracted from the rigorous mathematical framework presented.In this manuscript the internal energy density of the bulk is a function of the deformation gradient and its first and second derivatives. The internal energy density of the surface is, consequently, a function of the deformation gradient at the surface and its first derivative. The internal energy density of a curve is, consequently, a function of the deformation gradient at the curve.It is shown that in order to have a surface energy depending on the total (surface) deformation gradient, the bulk energy needs to be a function of at least the first derivative of the deformation gradient. Furthermore, in order to have a curve energy depending on the total (curve) deformation gradient, the bulk energy needs to be a function of at least the second derivative of the deformation gradient. Clearly, the surface elasticity theory of Gurtin and Murdoch is intrinsically limited since it is associated with the classical (first-order) continuum theory of elasticity in the bulk. In this sense this contribution shall be also understood as a higher-gradient surface elasticity theory.

Globular Structure of M2 High Speed Steel by Thermomechanical Treatment in the Semisolid State

AbstractThe globular structure of M2 high speed steel in the rolled ‐ annealed and as cast conditions was investigated in the semisolid state. Metallographic observations resulted in globular austenite particles that were surrounded by a liquid phase. Dissolution of various carbides in the austenite phase at semisolid temperatures led to grain boundary liquation and formation of near‐spherical solid grains in a liquid matrix. Therefore, at the semisolid state, the solid particles were free from carbides. MC‐ type and M6C‐ type eutectic carbides re‐ precipitated at the grain boundaries during cooling of the samples from the semisolid temperature. The variation of shape factor versus holding time and holding temperature was examined. A transition value for shape factor changes in high speed steels was achieved. The growth rate constants of the Ostwald ripening and the coalescence mechanisms were calculated by using the experimentally determined rate constant. It was observed that less liquid droplets were enclosed inside the solid particles compared with non‐ferrous alloys. Besides, it has been shown that at high solid fraction, the Ostwald ripening mechanism plays a prominent role in the coarsening phenomenon in comparison with the coalescence mechanism. Grains can rotate and arrange low misorientation with each other at high liquid contents, therefore low energetic grain boundaries form between these grains. These grain boundaries play an important role in the coalescence mechanism.

Nonuniformity of starch/nanosilica composites and interfacial behaviour of water and organic compounds

Hydrated starch alone and in composition with nanosilica A-300 and quercetin (natural antioxidant) was studied in the form of powders (mechanical mixture) and gels using 1H NMR (at 200–280 K), FTIR (293 K), TG (293–573 K), TSDC (90–265 K) and quantum chemistry methods. Influence of weakly polar (chloroform-d, CDCl 3) and polar ((CD 3) 2SO, DMSO) deuterated solvents on bound water structure in these systems was also analysed at 200–280 K. The energetic and structural boundaries between weakly (unfrozen at 250–260 < T < 273 K) and strongly (unfrozen at 200 < T < 250–260 K) bound waters become nonabrupt after the addition of these solvents to quercetin/starch/nanosilica composites because of the differences in water interaction with these substances differently affecting its freezing point depression.

First Results from the THEMIS Mission

THEMIS was launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. During the first seven months of the mission the five satellites coasted near their injection orbit to avoid differential precession in anticipation of orbit placement, which started in September 2007 and led to a commencement of the baseline mission in December 2007. During the coast phase the probes were put into a string-of-pearls configuration at 100 s of km to 2 RE along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007. THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents. These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.

Using measures of cost distance in the estimation of polity boundaries in the Postclassic Yautepec valley, Mexico

The reconstruction of polity boundaries is essential for the study of political evolution, but few enhancements to archaeological boundary estimation methods have been proposed in recent years. New techniques of terrain modeling and geographical analysis provide the means to augment traditional methods of boundary estimation. In this paper, I review archaeological methods for estimating the spatial location of boundaries between independent polities and ways to modify these methods to explore the processes of political expansion in the evolution of complex societies. I demonstrate several of these methods using data from Postclassic polities in the Yautepec valley, Morelos, Mexico. Through time, seven independent polities were founded, expanded, and were ultimately incorporated within two levels of regional political administration. I apply new quantitative methods for the estimation of polity territories and explore the processes that resulted in the formation of a regional polity. The resulting boundaries are objective estimates of the location of borders based on energetic efficiency that can be systematically tested against theoretical models. These estimated boundaries provide a basis for exploring the social meaning of territorial divisions. Additionally, energetic boundaries provide a means for delineating local zones for landscape utilization and comparative analyses.

Mapping travelling convection vortex events with respect to energetic particle boundaries

Abstract. Thirteen events of high-latitude ionospheric travelling convection vortices during very quiet conditions were identified in the Greenland magnetometer data during 1990 and 1991. The latitudes of the vortex centres for these events are compared to the energetic electron trapping boundaries as identified by the particle measurements of the NOAA 10 satellite. In addition, for all events at least one close DMSP overpass was available. All but one of the 13 cases agree to an exceptional degree that: the TCV centres are located within the region of trapped, high energy electrons close to the trapping boundary for the population of electrons with energy greater than &gt;100 keV. Correspondingly, from the DMSP data they are located within the region of plasmasheet-type precipitation close to the CPS/BPS precipitation boundary. That is, the TCV centres map to deep inside the magnetosphere and not to the magnetopause.Key Words. Ionosphere (Electric fields and currents; Particle precipitation) · Magnetospheric physics (Magnetosphere-ionosphere interaction)

High‐latitude energetic particle boundaries and the polar cap: A statistical study

Instruments aboard SAMPEX have been used to monitor high latitude energetic particle boundaries. These boundaries are related to the polar cap areas threaded by open magnetic flux tubes. Variations of the area poleward of the energetic particle boundary and the boundary location itself are examined statistically for possible association with the interplanetary magnetic field (IMF) Bz, VBz, and Kp. We find the average location of the energetic particle boundary under weak IMF coupling conditions (i.e, |Bz| &lt; 2.0 nT) to be ≈ 69°, (≈ 71° at noon and ≈ 67° at midnight) with the data showing considerable scatter. The boundary varies with IMF |Bz| for |Bz|&gt; 2 nT and shifts equatorward at a rate of ≈ 0.4°/nT(≈ 0.1°/nT) for negative (positive) values of Bz. Varying the time offset of the hourly Bz values from 1 to 3 hours prior to the crossing had no significant effect on the correlation. The area poleward of the boundary is well represented by an offset circle fitted to the data. A weak dependence is also seen with VBz for VBz &lt; −1.0 mV/m with the boundary location shifting equatorward at a rate of ≈ 0.9°/(mV/m). The equatorward motion of the boundary with increasing Kp is most pronounced about midnight and least pronounced at noon. In comparison with plasma boundaries the energetic particle boundaries show a lower degree of correlation with Bz, VBz, and Kp. This finding suggests a temporal and spatial decoupling between plasma and energetic particle populations.

Mapping travelling convection vortex events with respect to energetic particle boundaries

Thirteen events of high-latitude ionospheric travelling convection vortices during very quiet conditions were identified in the Greenland magnetometer data during 1990 and 1991. The latitudes of the vortex centres for these events are compared to the energetic electron trapping boundaries as identified by the particle measurements of the NOAA 10 satellite. In addition, for all events at least one close DMSP overpass was available. All but one of the 13 cases agree to an exceptional degree that: the TCV centres are located within the region of trapped, high energy electrons close to the trapping boundary for the population of electrons with energy greater than >100 keV. Correspondingly, from the DMSP data they are located within the region of plasmasheet-type precipitation close to the CPS/BPS precipitation boundary. That is, the TCV centres map to deep inside the magnetosphere and not to the magnetopause.Key Words. Ionosphere (Electric fields and currents; Particle precipitation) · Magnetospheric physics (Magnetosphere-ionosphere interaction)

The Eighth Day: Social Evolution as the Self-Organization of Energy.

Contents Preface Introduction 1. Preliminaries Principles and Explanations Anthropological Antecedents Monism and Materialism Studies of and Society 2. Process Forms Equilibrium Equilibrium and Dissipative Structures Stability and Steady States Appendix: Note on Odum's Energy Quality 3. Dynamics The Laws of Thermodynamics Lotka's Principle Minimum Dissipation Principle Trigger-Flow Mechanisms and Principles 4. Self-Organization Introduction Equilibrium Bases of Self-Organization Autopoiesis Perturbations Self-Triggering Appendix: Order and Functional Organization 5. Culture Mental Self-Organization Informational Dynamics Cultural Process Appendix: and Values 6. Domestication Domestication? Why Bother? Ecological and Human Controls Human Dominance, Culture, and Power Indigenous California Society The Emergence of Social Hierarchies Political and Ideological Implications Notes 7. Natural Selection The Broader Issue In Equilibrium Structures Self-Organization of Dissipative Structures Selection and Epistemology 8. Boundary Dynamics Social Boundaries Energetic Boundaries Environments and Closure 9. The Meaning of Civilization as a Trigger The Origins and Future of Notes 10. Humanities The Classics Free-Floating Triggers 11. Expansion In Social Hierarchy: A Model Social Survival Vehicles and Coaxal Structures Novel and Secondary Constructions The Emergence of Hierarchy: Work and Regulation 12. and Industrialization Modeling Industrialization Expansion The Sector Model Interactive Changes among Sectors Expansion of the Regulatory Sector Regulation in Subnational Units Notes Postscript: Development and Contemporary Social Evolution References Index

An association between discrete aurora and energetic particle boundaries

NOAA 6 satellite observations at 850 km over the auroral zones have been examined. We find that regions of auroral electron percipitation (0.3–20 keV) with energy fluxes sufficient to produce discrete aurora are generally spatially associated with significant changes in the intensity of 30‐ to 800‐keV protons filling the atmospheric loss cone. The proton intensity changes often occur simultaneously with spatial changes in the intensity of energetic (&gt;30 keV) electron precipitation at the high‐latitude boundary of the electron population. The velocity‐space distribution of the proton precipitation agrees with that observed for earthward streaming protons at the outer boundary of the plasma sheet and also with those calculated to result from current sheet energization. This agreement between the proton distributions implies that electron precipitation responsible for discrete aurora often occurs at the outer boundary of the plasma sheet in association with boundaries and other spatial structure in the streaming ion distributions. This furthermore implies that the upward directed, field‐aligned currents associated with discrete aurora are also often associated with the streaming ion structures. The comparisons with the distributions of ions ejected from the current sheet suggest that discrete aurora often occur on magnetic field lines which map along the outer boundary of the plasma sheet into the tail current sheet and that the cause of these discrete aurora is associated with current sheet processes.

Remote sensing of energetic particle boundaries

A discussion of the possible ways in which various surfaces such as the magnetopause, topology interfaces, and source boundaries (plasma sheet or flux transfer events) can be remotely sensed by energetic particles is presented, together with results of computer simulations of particles in a model magnetopause. The conclusions are that these boundaries can indeed be detected from a distance, but that care must be taken to identify the nature of the particle gradient, particularly if more than one gyro‐radius is being employed. The distances to the boundary calculated from the simple absorbing wall model will over‐estimate the true separation, but the direction determined from the simple model should be correct.

Energetic particle losses and trapping boundaries as deduced from calculations with a realistic magnetic field model

An interpretation of the stable trapping boundaries of energetic electrons and protons during quiet periods is given basing on a realistic magnetospheric magnetic field model. Particle losses are explained in terms of an ionospheric and drift loss cone filling due to a non-adiabatic pitch-angle scattering in the nightside magnetotail current sheet. The proposed mechanism is shown to provide a good agreement of the observed and calculated positions of the energetic particle trapping boundaries, as well as their energy dependence. The obtained results can be applied as a tool for investigating the magnetospheric magnetic field structure using the particle data of low-altitude satellites.

Satellite studies of magnetospheric substorms on August 15, 1968: 7. Ogo 5 energetic proton observations-spatial boundaries

Directional proton fluxes (0.1–0.8 Mev) observed at pitch angles near 90° to B during the growth phase of the 0714 UT August 15, 1968, substorm showed a strong east-west asymmetry. Since the Ogo 5 spacecraft was in the north edge of the midnight plasma sheet in a taillike magnetic field, the Lawrence Livermore Laboratory (LLL) spectrometer observed westward-directed fluxes having their gyrocenters located south of the satellite deeper in the sheet and eastward-directed fluxes having their gyrocenters north of the satellite toward the sheet boundary. We have used the directional flux variation to determine the flux profile north to south of Ogo 5 over ∼±0.4 RE approximately every 2 min during the substorm growth phase, 0640–0714 UT. At 0610 UT, before the substorm, the e fold length of the flux gradient was ∼1.3 RE, which slowly changed to ∼1.0 RE at 0640 UT, the start of the substorm growth phase. A thinning wave developed north of Ogo 5, showing an e fold length of ∼0.1 RE at 0700 UT, which dropped to ∼0.03 RE as the thinning wave passed south of the orbit of Ogo 5 just before the onset of expansion. The data suggest that the plasma sheet at ∼8 RE had shrunk from a half-thickness of >1.5 RE before the substorm to a few tenths of an earth radius. The velocity of the thinning wave perpendicular to B was found to vary from ∼4 km/sec at 0655 UT early in the growth phase to a peak of ∼10 km/sec just before expansion. The velocity of outward expansion of the plasma sheet in a direction inclined ∼45° to the GSM equator was estimated as 90 ± 30 km/sec.

The high-latitude ionosphere

This paper reviews information on the high-latitude ionosphere derived from the Alouette-ISIS program. It is primarily descriptive and deals mainly with F-region features. Particle effects in the D region and night E ionization are briefly considered. F-region features include the main trough, maxima and minima in electron density in the polar region, and electron-density irregularities revealed by the presence of spread echoes on topside ionograms. The relationship of these features to the plasmapause and the energetic particle boundaries is discussed. Although ionization effects in the D region are not directly detectable by the Alouette satellites, large increases in D-region ionization are produced at high latitudes by the influx of energetic particles which may be detected by some of the energetic particle counters on board. For both polar-cap and auroral events, empirical relations have been derived between particle fluxes and D-region radio-wave absorption measured by riometers.