Release Of Stored Energy Research Articles

Shock Pressure Dependence of Hot Spots in a Model Plastic-Bonded Explosive.

Shock initiation of plastic-bonded explosives (PBX) begins with the formation of so-called "hot spots", which are energetic reactions localized in regions where the PBX microstructure concentrates the input shock wave energy. We developed a model PBX system to study hot spots which consists of a single crystal of the high explosive HMX (cyclotetramethylene-tetranitramine) embedded in a transparent polyurethane binder (J. Phys Chem. A, 2020, 124, 4646-4653). In the current work we use this model system to study the influence of input shock pressure (12-26 GPa) on hot spot generation using micrometer-resolved high-speed imaging and nanosecond-resolved optical pyrometry. By shocking ∼100 HMX single crystals (HMX-SC), two distinct shock pressure thresholds were observed. The threshold for producing single hot spots in some crystals was 15 GPa. At 23 GPa, hot spot density was sufficiently high to lead to rapid deflagration of the entire HMX-SC. It takes about 25 ns after the shock passes for the hot spots to appear to our visible-light detection apparatus which has a noise floor at about 2000 K. That indicates the shock produces nascent hot spots that undergo a thermal explosion that reaches temperatures >2000 K in 25 ns. The initial hot spot temperature is roughly 3800 K which settles down to 3400 K, the adiabatic flame temperature of HMX. The higher initial temperature is attributed to release of stored interfacial strain energy produced by the shock. An initial estimate for the velocity of the flame front originating at an HMX hot spot is 550 m/s.

Comparison of dynamical features between the fast H-L and the H-I-L transition for EAST RF-heated plasmas

In this paper, a comparison of dynamical features between the fast H-L and the H-I-L transition, which can be identified by the intermediate phase, or ‘I-phase’, has been made for radio-frequency (RF) heated deuterium plasmas in EAST. The fast H-L transition is characterized by a rapid release of stored energy during the transition transient, while the H-I-L transition exhibits a ‘soft’ H-mode termination. One important distinction between the transitions has been observed by dedicated probe measurements slightly inside the separatrix, with respect to the radial gradient of the floating potential, which corresponds to the E × B flow and/or the electron temperature gradient. The potential gradient inside the separatrix oscillates and persists during the stationary I-phase, and shows a larger amplitude than that before the fast H-L transition. The reduction of the gradient leads to the final transition to the L-mode for both the fast H-L and the H-I-L transition. These findings indicate that the mean E × B flow shear and/or edge electron temperature gradient play a critical role underlying the H-L transition physics. In addition, the back transition in EAST is found to be sensitive to magnetic configuration, where the vertical configuration, i.e., inner strike-point located at vertical target, favours access to the H-I-L transition, while the horizontal shape facilitates achievement of the fast H-L transition. The divertor recycling level normalized to electron density is higher before the fast H-L transition, as compared to that before the I-phase, which strongly suggest that the density of the recycled neutrals is an important ingredient in determining the back transition behaviour.

Twinning-related enhancement in strength and ductility of Cu-37Zn alloy by the cryogenic ultrasonic impact treatment supplemented with ECAP

The effects of ultrasonic impact treatment (UIT) and UIT with equal channel angular pressing (ECAP), on the microstructure of Cu37Zn alloy are studied at ambient and cryogenic temperatures. With decreasing process temperature, highly twinned areas of submicro/nano-scale thickness/spacing, together with dislocation tangles/cells, are introduced in the alloy. Direct microscopy observation and stored energy release analysis confirm enhanced twinnings in the cryo-UIT and cryo-UIT/ECAP treated alloy that simultaneously provide superior Vickers hardness and formability (twinning-induced plasticity effect).

Atomic and microstructural origins of stored energy release in neutron-irradiated silicon carbide

Here, we employ a combination of advanced synchrotron-based scattering characterization techniques to understand and unravel the atomic origins of the colossal stored energy release in neutron-irradiated silicon carbide. The quantification of the neutron irradiation-induced defects and their impact on the structure-property relationship are important for the design and safe operation of advanced fission and fusion reactors. Our experimental results show that the atomic structure in the as-irradiated samples is significantly perturbed due to a large fraction of vacancy- and interstitial-type defects that lead to complex microstructures and additional components in the x-ray diffraction and pair distribution function (PDF) results. We directly correlate the stored energy release to the recovery of the sublattices with PDF analysis, highlighting that the carbon interstitial- and vacancy-type defects contribute to stored energy more than those of silicon. We find these results to be striking and believe our discoveries to be timely and noteworthy given the technological importance of silicon carbide to the nuclear fission and fusion communities.

A physical model of mantis shrimp for exploring the dynamics of ultrafast systems

Efficient and effective generation of high-acceleration movement in biology requires a process to control energy flow and amplify mechanical power from power density-limited muscle. Until recently, this ability was exclusive to ultrafast, small organisms, and this process was largely ascribed to the high mechanical power density of small elastic recoil mechanisms. In several ultrafast organisms, linkages suddenly initiate rotation when they overcenter and reverse torque; this process mediates the release of stored elastic energy and enhances the mechanical power output of extremely fast, spring-actuated systems. Here we report the discovery of linkage dynamics and geometric latching that reveals how organisms and synthetic systems generate extremely high-acceleration, short-duration movements. Through synergistic analyses of mantis shrimp strikes, a synthetic mantis shrimp robot, and a dynamic mathematical model, we discover that linkages can exhibit distinct dynamic phases that control energy transfer from stored elastic energy to ultrafast movement. These design principles are embodied in a 1.5-g mantis shrimp scale mechanism capable of striking velocities over 26 m [Formula: see text] in air and 5 m [Formula: see text] in water. The physical, mathematical, and biological datasets establish latching mechanics with four temporal phases and identify a nondimensional performance metric to analyze potential energy transfer. These temporal phases enable control of an extreme cascade of mechanical power amplification. Linkage dynamics and temporal phase characteristics are easily adjusted through linkage design in robotic and mathematical systems and provide a framework to understand the function of linkages and latches in biological systems.

Research on size effect of fracture toughness of sandstone using the center-cracked circular disc samples

In order to investigate the size effect and reason of rock fracture toughness, the split loading test was carried out in the GCTS rock mechanics testing machine using the center-cracked circular disc (CCCD) samples with diameters of 50 mm, 100 mm, 150 mm and 205 mm, respectively. The lengths of fracture process zone (lFPZ) were determined by the maximum normal stress criterion. The size effect of the lFPZ , fracture toughness test value (KIc), and fracture energy (Gf) were analyzed. The influence of the lFPZ on the size effect of the KIc was revealed. The crack growth paths and failure characteristics of the samples were discussed. The results show that the lFPZ and the KIc increase linearly with the sample size, and there is obvious size effect within the range of the test. The KIc and the lFPZ do not always increase linearly with the size in a larger size range, but gradually stabilize by extrapolation analysis. The lFPZ increases with the size, which means the release of stored energy increases with the size corresponding to the size effect of the Gf, and in turn leads to the size effect of the KIc. It is helpful to deeply understand the cause of the size effect reason of rock fracture toughness.

A high power density photoactive thermal energy storage material for rapid heat release at low temperatures

Developing of photoactive chemical heat storage materials with high power density and rapid heat release ability at low temperatures is a key challenge for efficient utilize of solar thermal energy. Herein, a photoactive chemical heat storage material is presented which fluorinated azobenzene (AzoF) is covalently attached onto reduced graphene oxide (rGO). The AzoF-rGO complex exhibits excellent heat storage density up to 364.4 kJ kg−1, maximum power density of 2419.7 W kg−1 and good storage half-life of 55.6 h because of the intermolecular hydrogen bond and the intermolecular interactions between azobenzene as a result of high attachment density. This AzoF-rGO complex also shows remarkable cycle performance through green light for 50 cycles without degradation and rapid heat release ability at low temperatures, which realizes high rate heat release for short-term rapid and concentrated heating. This work develops a promising AzoF-rGO photoactive chemical heat storage material, which not only has high heat storage density and power density but also realize the rapid heat release of stored solar energy at low temperatures, shows that it has great practical application potential in making full use of solar thermal energy in the future.

Numerical analysis for the prediction of bump prone conditions: A southern Appalachian pillar coal bump case study

Two miners were fatally injured when a pillar bump occurred during retreat mining in a southern West Virginia coal mine. The mine was operating in the Eagle seam with overmining in the No. 2 Gas and Powellton seams. A coal bump is defined as a sudden and violent failure of coal caused by the release of stored strain energy in the pillar. While significant strides have been made by academia, industry, and regulatory agencies to better understand bump conditions and mitigation techniques, coal bumps represent a long standing, highly site-specific engineering problem in which the exact failure mechanism is not clearly understood. In this case history, a cut-by-cut analysis of retreat mining operations was conducted on the 4 East Main leading up to the pillar bump event. Numerical input parameters were derived from site-specific geologic information and mine geometry for the analysis of pillar stress conditions and energy release using LaModel. An overview of stress conditions in the panel was presented including a precursor event that occurred two crosscuts inby the bump site. The methodology presented in the paper for the evaluation of the fatal bump event can be used for the identification of bump prone conditions prior to development and retreat of a mining area.

Signatures of Overaging in an Aqueous Dispersion of Carbopol.

In this work, we study the effect of the deformation field on the physical aging behavior of an aqueous Carbopol dispersion. It is composed of soft swollen particles of gel that get deformed and acquire a polygonal shape, with flat interfaces rendering the dispersion a soft solid-like consistency as filled volume fraction approaches unity. It has been proposed that owing to release of stored elastic energy in the deformed particles, Carbopol dispersion undergoes microstructural evolution that is reminiscent of physical aging in soft glassy materials. We observe that application of moderate magnitude of oscillatory strain to Carbopol dispersion slows down its relaxation dynamics, thereby showing characteristics of overaging. On the other hand, the sufficiently high magnitude of strain makes the relaxation dynamics faster, causing rejuvenation. We also solve the soft glassy rheology model, which, when subjected to the same flow field, corroborates with experimental observations on the Carbopol dispersion. This behavior, therefore, suggests that in a system of jammed soft particles of Carbopol, the particles occupying shallow energy wells upon application of moderate strain field adjust themselves in such a manner that they predominantly occupy the deeper energy wells leading to observe the overaging dynamics.

Low-temperature proton irradiation damage of isotropic nuclear grade IG-430 graphite

IG-430, a fine-grained, isotropic graphite grade is a promising candidate for the future Very High Temperature Reactors (VHTR). IG-430 which provides higher density, strength, and thermal conductivity, has already been developed as a graphite for next-generation HTGR, and is expected to be employed. This graphite grade, however, is lacking enough database that is needed for design. The present study aims to enhance the database with experimental data focusing on the low temperature regime (90–210 °C) by using 120–200 MeV protons to irradiate the IG-430 graphite to peak fluence of ~1.2 1025 m−2. It is anticipated that radiation-induced changes in the graphite properties and damage to be more pronounced in this low temperature regime than in elevated temperatures where damage annealing is taking place simultaneously. IG-430 graphite was characterized following irradiation for mechanical property changes (modulus and strength), dimensional stability and irradiation-induced growth as well as microstructural changes using high energy X-rays and different X-ray diffraction techniques. In assessing proton irradiation effects on the IG-430 graphite grade, comparison of radiation effects was made with the IG-43 grade, the un-purified version of IG-430, as well as other isotropic graphite grades. IG-430 was shown in this study to be better graphitized than other isotropic graphite grades. The study also revealed that during proton irradiation at low temperatures (~100 °C) the IG-430 exhibits stored energy release.

Dietary antioxidants attenuate the endocrine stress response during long-duration flight of a migratory bird.

Glucocorticoids (GCs) are metabolic hormones that promote catabolic processes, which release stored energy and support high metabolic demands such as during prolonged flights of migrating birds. Dietary antioxidants (e.g. anthocyanins) support metabolism by quenching excess reactive oxygen species produced during aerobic metabolism and also by activating specific metabolic pathways. For example, similar to GCs' function, anthocyanins promote the release of stored energy, although the extent of complementarity between GCs and dietary antioxidants is not well known. If anthocyanins complement GCs functions, birds consuming anthocyanin-rich food can be expected to limit the secretion of GCs when coping with a metabolically challenging activity, avoiding the exposure to potential hormonal detrimental effects. We tested this hypothesis in European starlings (Sturnus vulgaris) flying in a wind tunnel. We compared levels of corticosterone, the main avian GC, immediately after a sustained flight and at rest for birds that were fed diets with or without an anthocyanin supplement. As predicted, we found (i) higher corticosterone after flight than at rest in both diet groups and (ii) anthocyanin-supplemented birds had less elevated corticosterone after flight than unsupplemented control birds. This provides novel evidence that dietary antioxidants attenuate the activation of the HPA axis (i.e. increased secretion of corticosterone) during long-duration flight.

Influence of stress relief annealing temperature on the cutting edge microstructure and on the recovery of magnetic properties of grain oriented electrical steel

The effect of stress relief annealing temperature on the recovery of the magnetic properties deteriorated by strain and stresses introduced by shear cutting was analyzed in this study. Shear cut Epstein samples of grain oriented electrical steel were submitted to heat treatment at different annealing temperatures (600–900 °C). The magnetic properties were measured before and after annealing. The microstructures of the sheared edges before and after annealing were characterized using scanning electron microscope (SEM) equipped with electron backscattered diffraction (EBSD) in which it was possible to characterize the recovery and recrystallization processes responsible for the stored energy release in the shear cut region. The magnetic properties were improved with the increase of the annealing temperature due to recovery, recrystallization and the relief of residual stresses.

Particle acceleration with anomalous pitch angle scattering in 3D separator reconnection

Context.Understanding how the release of stored magnetic energy contributes to the generation of non-thermal high energy particles during solar flares is an important open problem in solar physics. There is a general consensus that magnetic reconnection plays a fundamental role in the energy release and conversion processes taking place during flares. A common approach for investigating how reconnection contributes to particle acceleration is to use test particle calculations in electromagnetic fields derived from numerical magnetohydrodynamic (MHD) simulations of reconnecting magnetic fields. These MHD simulations use anomalous resistivities that are orders of magnitude larger than the Spitzer resistivity that is based on Coulomb collisions. The processes leading to such an enhanced resistivity should also affect the test particles, for example, through pitch angle scattering. This study explores the effect of such a link between the level of resistivity and its impact on particle orbits and builds on a previous study using a 2D MHD simulation of magnetic reconnection.Aims.This paper aims to extend the previous investigation to a 3D magnetic reconnection configuration and to study the effect on test particle orbits.Methods.We carried out orbit calculations using a 3D MHD simulation of reconnection in a magnetic field with a magnetic separator. The orbit calculations use the relativistic guiding centre approximation but, crucially, they also include pitch angle scattering using stochastic differential equations. The effects of varying the resistivity and the models for pitch angle scattering on particle orbit trajectories, final positions, energy spectra, final pitch angle distribution, and orbit duration are all studied in detail.Results.Pitch angle scattering widens highly collimated beams of unscattered orbit trajectories, allowing orbits to access previously unaccessible field lines; this causes final positions to spread along other topological structures which could not be accessed without scattering. Scattered orbit energy spectra are found to be predominantly affected by the level of anomalous resistivity, with the pitch angle scattering model only playing a role in specific, isolated cases. This is in contrast to the study involving a 2D MHD simulation of magnetic reconnection, where pitch angle scattering had a more noticeable effect on the energy spectra. Pitch scattering effects are found to play a crucial role in determining the pitch angle and orbit duration distributions.

A Model for Static Recrystallization through Strain-Induced Boundary Migration

Control over the inelastic deformation of polycrystals aimed at achieving desired performance characteristics of finished products is impossible without analyzing the structural evolution of the material at different scale levels. A major task in this respect is to develop physically sound mathematical models for describing the internal structure evolution as it determines the material properties. An effective tool for addressing this task is a multilevel approach to describing the thermomechanical processing of crystalline materials, in which carriers and physical mechanisms of processes are considered explicitly. Thermomechanical processing allows a good control over the defect and grain/subgrain structure of the material to achieve desired macrocharacteristics. This paper explores the subgrain/grain structure evolution during static recrystallization that occurs through strain-induced boundary migration. Modeling is carried out in two stages. The first stage models the plastic deformation of a crystalline material at room temperature. The second stage considers holding at an elevated temperature resulting in recrystallization. Both stages are modeled within a unified multilevel approach. The problem of modeling static recrystallization is formulated, and an algorithm for its numerical implementation is described. The modeling results are obtained for a bicrystal in which each grain is represented by a group of lower-scale elements (subgrains). Recrystallization causes profound changes in the subgrain structure geometry, the average size of subgrains, and their shape change. Recrystallized subgrains are more elongated compared to the original ones. During recrystallization more defective grains are replaced with less defective grains, and as a result the energy stored in the material decreases. The developed model qualitatively describes the release of stored energy. Numerical experiments revealed a critical plastic strain value below which recrystallization does not occur.

Oxygen Is the High-Energy Molecule Powering Complex Multicellular Life: Fundamental Corrections to Traditional Bioenergetics.

A fundamental re-assessment of the overall energetics of biochemical electron transfer chains and cycles is presented, highlighting the crucial role of the highest-energy molecule involved, O2. The chemical energy utilized by most complex multicellular organisms is not predominantly stored in glucose or fat, but rather in O2 with its relatively weak (i.e., high-energy) double bond. Accordingly, reactions of O2 with organic molecules are highly exergonic, while other reactions of glucose, fat, NAD(P)H, or ubiquinol (QH2) are not, as demonstrated in anaerobic respiration with its meager energy output. The notion that “reduced molecules” such as alkanes or fatty acids are energy-rich is shown to be incorrect; they only unlock the energy of more O2, compared to O-containing molecules of similar mass. Glucose contains a moderate amount of chemical energy per bond (<20% compared to O2), as confirmed by the relatively small energy output in glycolysis and the Krebs cycle converting glucose to CO2 and NADH. Only in the “terminal” aerobic respiration reaction with O2 does a large free energy change occur due to the release of oxygen’s stored chemical energy. The actual reaction of O2 in complex IV of the inner mitochondrial membrane does not even involve any organic fuel molecule and yet releases >1 MJ when 6 mol of O2 reacts. The traditional presentation that relegated O2 to the role of a low-energy terminal acceptor for depleted electrons has not explained these salient observations and must be abandoned. Its central notion that electrons release energy because they move from a high-energy donor to a low-energy acceptor is demonstrably false. The energies of (at least) two donor and two acceptor species come into play, and the low “terminal” negative reduction potential in aerobic respiration can be attributed to the unusually high energy of O2, the crucial reactant. This is confirmed by comparison with the corresponding half-reaction without O2, which is endergonic. In addition, the electrons are mostly not accepted by oxygen but by hydrogen. Redox energy transfer and release diagrams are introduced to provide a superior representation of the energetics of the various species in coupled half-reactions. Electron transport by movement of reduced molecules in the electron transfer chain is shown to run counter to the energy flow, which is carried by oxidized species. O2, rather than glucose, NAD(P)H, or ATP, is the molecule that provides the most energy to animals and plants and is crucial for sustaining large complex life forms. The analysis also highlights a significant discrepancy in the proposed energetics of reactions of aerobic respiration, which should be re-evaluated.

The control of nocifensive movements in the caterpillar Manduca sexta.

In response to a noxious stimulus on the abdomen, caterpillars lunge their head towards the site of stimulation. This nocifensive 'strike' behavior is fast (∼0.5 s duration), targeted and usually unilateral. It is not clear how the fast strike movement is generated and controlled, because caterpillar muscle develops peak force relatively slowly (∼1 s) and the baseline hemolymph pressure is low (<2 kPa). Here, we show that strike movements are largely driven by ipsilateral muscle activation that propagates from anterior to posterior segments. There is no sustained pre-strike muscle activation that would be expected for movements powered by the rapid release of stored elastic energy. Although muscle activation on the ipsilateral side is correlated with segment shortening, activity on the contralateral side consists of two phases of muscle stimulation and a marked decline between them. This decrease in motor activity precedes rapid expansion of the segment on the contralateral side, presumably allowing the body wall to stretch more easily. The subsequent increase in contralateral motor activation may slow or stabilize movements as the head reaches its target. Strike behavior is therefore a controlled fast movement involving the coordination of muscle activity on each side and along the length of the body.

Nanodiamond graphitization at heating and irradiation

In this work the graphitization and thermal stability of detonation nanodiamonds were studied. Received data showed that the temperature of graphitization of nanodiamond particles lies in wide range and the temperature of graphitization beginning depend on the particle size. It is established the influence of heating rate on the size of nanodiamond conglomerates. The analysis of literature shows that the graphitization processes take place at irradiation. Depending on the type and irradiation dose the point defects, amorphous and graphite phases can form in the diamond structure. Annealing of irradiation samples showed the defect structure restore to ideal lattice and the release of stored energy.

Evaluation of the propensity of strain burst in brittle granite based on post-peak energy analysis

The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under high-stress rock mass conditions. As a result of this, strain burst, which is the sudden release of stored strain energy in the surrounding rock mass, has become more prevalent and created a considerable threat to workers and construction equipment. It is, therefore, imperative to understand how strain burst mechanism and stored excess strain energy are affected due to the high confinement in deep underground conditions. For this purpose, post-peak energy distributions for brittle rocks were investigated using a newly developed energy calculation method associated with acoustic emission (AE). A series of quasi-static uniaxial and triaxial compression tests controlled by the circumferential expansion were conducted. Snap-back behaviour known as Class-II behaviour associated with energy evolution and the material response under self-sustaining failure were analysed on granites under a wide range of confining pressures (0–60 MPa). The experimental results underline that the energy evolution characteristics are strongly linked to confinement. Stored elastic strain energy (dUE), energy consumed by dominating cohesion weakening (dΦCW) and energy dissipated during mobilisation of frictional failure (dΦFM) showed a rising trend as the confining pressure was increased. An intrinsic ejection velocity was proposed to express the propensity of strain burst that was purely determined by the excess strain energy released from Class II rock.

Slow Coarsening in Jammed Athermal Soft Particle Suspensions.

We simulate a densely jammed, athermal assembly of repulsive soft particles immersed in a solvent. Starting from an initial condition corresponding to a quench from a high temperature, we find nontrivial slow dynamics driven by a gradual release of stored elastic energy, with the root mean squared particle speed decaying as a power law in time with a fractional exponent. This decay is accompanied by the presence within the assembly of spatially localized and temporally intermittent "hot spots" of nonaffine deformation, connected by long-ranged swirls in the velocity field, reminiscent of the local plastic events and long-ranged elastic propagation that have been intensively studied in sheared amorphous materials. The pattern of hot spots progressively coarsens, with the hot-spot size and separation slowly growing over time, and the associated correlation length in particle speed increasing as a sublinear power law. Each individual spot, however, exists only transiently within an overall picture of strongly intermittent dynamics.

Absorption and stimulated emission by a thin slab obeying the Lorentz oscillator model

In his celebrated 1916–17 papers in which he proposed the A and B coefficients for the spontaneous and stimulated emission of energy quanta from excited atoms, Einstein conjectured that stimulated emission involves the release of individual quanta (later dubbed “photons”) along the direction of an incident photon with the same energy, momentum, phase, and polarization state as that of the incident photon. According to classical electrodynamics, of course, an oscillating dipole must radiate an azimuthally symmetric electromagnetic field around its axis of oscillation. Nevertheless, Einstein suggested that the release of stored energy from excited atoms in the form of discrete quanta (photons) must be directional, and that, in the case of stimulated emission, the direction of the emitted photon must coincide with that of the incident photon. The goal of the present paper is to show that some of the prominent features of absorption and stimulated emission emerge from Maxwellian electrodynamics in conjunction with the simple mass-and-spring model of an atom known as the Lorentz oscillator model.