High Internal Energy Research Articles

Photo-dissociation of naphthalene dimer cations stored in a compact electrostatic ion storage ring.

Naphthalene dimer cations [C10H8]2 + have been produced by using an electron cyclotron resonance plasma ion source and stored in a compact electrostatic ion storage ring. We show that the radiative cooling of these cations is much slower than the isolated monomer naphthalene cations. We also report on photo-dissociation studies in the gas phase of naphthalene dimer cations at high internal energy. The dissociation energy is estimated to 0.5 eV in close agreement with previous measurements but a factor of 2 smaller than recent (density functional theory (DFT) and ab initio) theoretical studies. As uncertainties on theory as well as on the experiment cannot be as large as this difference, we conclude that this discrepancy may be due to temperature effects with possible isomerization. As an interpretation of the photo-dissociation spectrum of naphthalene dimer cations, we propose a tentative simple analytical model based on effective Morse potentials. These effective potentials are expected to "average" temperature effects that would apparently result in a smaller energy difference between the fundamental and dissociation states due to the twisting vibration modes of the naphthalene dimer cations.

Dynamics Insight into Isomerization and Dissociation of Hot Criegee Intermediate CH3CHOO.

We study the isomerization and dissociation of syn-CH3CHOO with high internal energies by combining electronic structure calculations, ab initio molecular dynamics, and RRKM microcanonical variational transition-state theories. The results show a striking effect of the internal energy on the reaction fate of syn-CH3CHOO. With lower internal energies, syn-CH3CHOO prefers isomerizing to vinyl hydroperoxide, which then produces hydroxyl radical. As the available internal energy increases, the O-elimination channel becomes more competitive and eventually the dominant channel. A third channel leading to methyl dioxirane is found to be less competitive than the former two. However, this channel is highly exothermic and produces greenhouse gases CH4 and CO2; thus, further investigation is needed to quantify its potential impact on the atmosphere. The present study provides new insight on clarifying the unimolecular reaction fate of hot syn-CH3CHOO and theoretical solutions for revealing the impact of internal energy on the complex gas phase reactions.

Simulation of Delamination Growth at CFRP-Tungsten Aerospace Laminates Using VCCT and CZM Modelling Techniques

Delamination analysis in advanced composites is required for the laminate design phase and also during the operation of composite aerospace structures to estimate the criticality of flaws and damage. The virtual crack closure technique (VCCT) and cohesive zone modelling (CZM) have been applied to delamination simulation as numerical tools of crack modelling. VCCT and CZM have their unique advantages and disadvantages per application. This study focuses on the application of VCCT to a brittle delamination in a hybrid tungsten–carbon-fibre reinforced composite (CFRP-W) and pursues to identify the challenges due to very high internal residual stresses and strain energy as well as unstable crack propagation. The CFRP-W composites have application areas in high-performance, light-weight radiation protection enclosures of satellite electronics and ultra-high frequency (e.g. 5G) systems. In our work, we present the effects of free-edge stress concentrations and interfacial separation prior to nodal release on a combined VCCT-CZM model and compare the results to pure VCCT and CZM models of the interfacial crack. Parameter notes are given based on the results to apply the combined method for delamination analyses with interfaces heavily loaded by internal residual strains.

Fully anharmonic infrared cascade spectra of polycyclic aromatic hydrocarbons.

The infrared (IR) emission of polycyclic aromatic hydrocarbons (PAHs) permeates our universe; astronomers have detected the IR signatures of PAHs around many interstellar objects. The IR emission of interstellar PAHs differs from their emission as seen under conditions on Earth as they emit through a collisionless cascade down through their excited vibrational states from high internal energies. The difficulty in reproducing interstellar conditions in the laboratory results in a reliance on theoretical techniques. However, the size and complexity of PAHs require careful consideration when producing the theoretical spectra. In this work, we outline the theoretical methods necessary to lead to fully theoretical IR cascade spectra of PAHs including: an anharmonic second order vibrational perturbation theory treatment, the inclusion of Fermi resonances through polyads, and the calculation of anharmonic temperature band shifts and broadenings (including resonances) through a Wang-Landau approach. We also suggest a simplified scheme to calculate vibrational emission spectra that retain the essential characteristics of the full IR cascade treatment and can directly transform low temperature absorption spectra in IR cascade spectra. Additionally we show that past astronomical models were in error in assuming a 15 cm-1 correction was needed to account for anharmonic emission effects.

Grain size effects on indentation-induced defect evolution and plastic deformation mechanism of ploycrystalline materials

Using molecular dynamics (MD) simulations, the defect evolution and plastic deformation mechanism of single-crystalline and polycrystalline copper under spherical nanoindentation are investigated and compared with previous nanoindentation simulations and experiments. To reveal the grain size effects on the indentation-induced internal stress and deformation behavior, the polycrystalline copper with different grain size are adopted in nanoindentation simulations, whose grain size are follow the inverse Hall-Petch relation. To study the grain boundary network effect, the grain boundary interface is further divided into three microstructural components with different dimensions. The results show that the indentation force of single-crystalline copper is larger than that of polycrystalline copper, and that of polycrystalline copper continuously decreases with the decrease of grain size due to softening phenomenon. The defect nucleation and propagation region in both single-crystalline and polycrystalline copper appear below the tool tip, due to the high internal stress and atomic potential energy induced by nanoindentation. The horizontal propagation of defects is faster and larger than the vertical propagation of that, and such defects are limited in the grains around the tool tip due to grain boundary network. An obvious stresses and potential energy gradient exist under tool tip in single-crystalline copper, and such gradients are possibly distributed along multiply direction in the polycrystalline copper. The internal stresses and atomic potential energy in the region of VP are highest, followed by that in TJ, GB and VP, resulting in the defect nucleation and propagation are more possible occur in VP than other microstructural components.

Investigations on the mechanism and behavior of dynamic energy absorption of metal foam

Abstract Metal foams have been widely used in the engineering fields due to its excellent energy absorption capacity under impact. Under different impact velocities, metal foam exhibits different energy absorption properties. It is important to investigate the mechanism and behavior of energy absorption of metal foam under impact. In this study, a 3D microscopic finite element model (FEM) of metal foam is first established to study energy absorption properties of metal foam. It is shown that the impact energy transfers into kinetic and internal energy of metal foam which varies under impact. The variation can be explained by plastic shock wave, which is produced and then propagates under impact. The theoretical model is proposed to discuss and predict kinetic energy and the difference between dynamic and quasi-static energy absorption behavior of metal foam. Effects of inertia and base material strain rate on plastic shock wave are investigated, and the mechanism of the two effects on dynamic energy absorption properties are studied. The results indicate that base material strain rate effect resists the formation of plastic shock wave, and leads to smaller kinetic energy, but higher internal energy.

Influence of Polymers on the Physical and Chemical Stability of Spray-dried Amorphous Solid Dispersion: Dipyridamole Degradation Induced by Enteric Polymers.

Amorphous solid dispersions (ASDs) are inherently unstable because of high internal energy. Evaluating physical and chemical stability during the process and storage is essential. Numerous researches have demonstrated how polymers influence the drug precipitation and physical stability of ASDs, while the influence of polymers on the chemical stability of ASDs is often overlooked. Therefore, this study aimed to investigate the effect of polymers on the physical and chemical stability of spray-dried ASDs using dipyridamole (DP) as a model drug. Proper polymers were selected by assessing their abilities to inhibit drug recrystallization in supersaturated solutions. HPMC E5, Soluplus®, HPMCP-55, and HPMCAS-LP were shown to be effective stabilizers. The optimized formulations were further stored at a high temperature (60°C) and high humidity (40°C, 75%RH) for 2months, and their physical and chemical stability was evaluated using polarizing optical microscopy, FTIR, HPLC, and mass spectrometry (MS). In general, crystallization was observed in all samples, which indicated the physical instability under stressed storage conditions. Also, it was noted that the polymers in ASDs rather than physical mixtures, induced a dramatic drug degradation after being exposed to a high temperature (HPMCP-55 > 80% and HPMCAS-LP > 50%) and high humidity (HPMCP-55 > 40% and HPMCAS-LP > 10%). The MS analysis further confirmed the degradation products, which might be generated from the reaction between dipyridamole and phthalic anhydride decomposed from HPMCP-55 and HPMCAS-LP. Overall, the exposure of ASDs to stressed conditions resulted in recrystallization and even the chemical degradation induced by polymers.

Finite element analysis for estimating steel structure responses under a variety of marine-collision actions

This study conducted a series of ship collision analyses to observe the effect of external parameters on the responses of steel structures. Variations in mass are represented by using different ship types as the striking ship, while an oblique collision was conducted initially and was compared to a perpendicular collision scenario. The other involved ship was denoted as the struck ship, and the side structures of a RoRo passenger ship were designated as the target. Crashworthiness criteria produced by the finite element analysis can be summarised to illustrate the trends in structural responses for the selected parameters. Based on this summary of the FE solutions, satisfactory results were obtained, as the rigid striking ship successfully produced a higher internal energy. In terms of the damage extent, the larger dimensions of the cargo carrier as the striking ship (compared to the struck ship) significantly crushed the target structure.

Nonequilibrium internal energy distributions during dissociation

In this work, we propose a model for nonequilibrium vibrational and rotational energy distributions in nitrogen using surprisal analysis. The model is constructed by using data from direct molecular simulations (DMSs) of rapidly heated nitrogen gas using an ab initio potential energy surface (PES). The surprisal-based model is able to capture the overpopulation of high internal energy levels during the excitation phase and also the depletion of high internal energy levels during the quasi-steady-state (QSS) dissociation phase. Due to strong coupling between internal energy and dissociation chemistry, such non-Boltzmann effects can influence the overall dissociation rate in the gas. Conditions representative of the flow behind strong shockwaves, relevant to hypersonic flight, are analyzed. The surprisal-based model captures important molecular-level nonequilibrium physics, yet the simple functional form leads to a continuum-level expression that now accounts for the underlying energy distributions and their coupling to dissociation.

Atomistic study of inelastic deformation in aluminium grain boundary fractures

The plastic work of fracture in a deformable solid has been believed to be related to only the ideal brittle fracture energy. However, additional factors affecting the plastic work must also exist because the plastic work is a path function. In the present work, first-principles calculations and molecular dynamics simulations of tensile tests were performed on Σ3(1 1)[1 1 0] and Σ11(1 3)[1 1 0] symmetric tilt aluminium grain boundaries, where the grain boundary energy of the Σ11(1 3) grain boundary is higher than that of the Σ3(1 1)[1 1 0] gain boundary. The calculations showed that, although the ideal brittle fracture energy for the Σ11(1 3) grain boundary was almost the same as that for the Σ3(1 1) grain boundary, the plastic work for the former was larger than that for the latter, resulting in a larger fracture energy for the Σ11(1 3) grain boundary. Local inelastic deformation occurred around the atoms with high internal energy at the grain boundary for the Σ11(1 3) grain boundary. It is therefore suggested that the plastic work is a function of both the grain boundary energy and the ideal brittle fracture energy.

Wear Behavior and Microstructure of Mg-Sn Alloy Processed by Equal Channel Angular Extrusion.

Mg-5wt.% Sn alloy is often used in portable electronic devices and automobiles. In this study, mechanical properties of Mg-5wt.% Sn alloy processed by Equal Channel Angular Extrusion (ECAE) were characterized. More precisely, its hardness and wear behavior were measured using Vickers hardness test and a pin-on-disc wear test. The microstructures of ECAE-processed Mg-Sn alloys were investigated by scanning electron microscope and X-ray diffraction. ECAE process refined the grain sizes of the Mg-Sn alloy from 117.6 μm (as-cast) to 88.0 μm (one pass), 49.5 μm (two passes) and 24.4 μm (four passes), respectively. Meanwhile, the hardness of the alloy improved significantly. The maximum wear resistance achieved in the present work was around 73.77 m/mm3, which was obtained from the Mg-Sn alloy treated with a one-pass ECAE process with a grain size of 88.0 μm. The wear resistance improvement was caused by the grain size refinement and the precipitate of the second phase, Mg2Sn against the oxidation of the processed alloy. The as-cast Mg-Sn alloy with the larger grain size, i.e., 117.6 μm, underwent wear mechanisms, mainly adhesive wear and abrasive wear. In ECAE-processed Mg-Sn alloy, high internal energy occurred due to the high dislocation density and the stress field produced by the plastic deformation, which led to an increased oxidation rate of the processed alloy during sliding. Therefore, the oxidative wear and a three-body abrasive wear in which the oxide debris acted as the three-body abrasive components became the dominant factors in the wear behavior, and as a result, reduced the wear resistance in the multi-pass ECAE-processed alloy.

Isolating the Isomeric Hydrogen Bonding Signatures of the Cyanide-Water Complex by Cryogenic Ion Trap Vibrational Spectroscopy.

The vibrational spectroscopy of the cyanide-water complex and its fully deuterated isotopologue is studied in the spectral range from 800 to 3800 cm-1. Infrared/infrared double-resonance population labeling spectroscopy of the cryogenically cooled, messenger-tagged complexes isolates the spectral signature of the two quasi-isoenergetic, singly hydrogen-bonded isomers HOH···NC- and HOH···CN-. The infrared photodissociation spectra are assigned based on a comparison to simulated anharmonic spectra. Infrared multiple photon dissociation spectra in the temperature range from 6 to 300 K confirm the stability of the two isomers at lower temperatures and provide evidence for a considerably more dynamic structure, also involving doubly hydrogen-bonded configurations, at higher internal energies. The observed red shifts ΔνOH of the hydrogen-bonded O-H stretches, 671 cm-1 (HOH···NC-) and 812 cm-1 (HOH···CN-), confirm the universal correlation of ΔνOH with the corresponding proton affinities.

Nature of the Enhanced Self-Heating Ability of Imperfect Energetic Crystals Relative to Perfect Ones

It is extensively deemed that the increased self-heating ability of defects relative to perfect crystals increases the sensitivity, or reduces the safety, of energetic materials. Nevertheless, the nature of such increased self-heating ability remains unclear. The present work provides insight into the origin of such ability by ReaxFF reactive molecular dynamics simulations on the thermal decay of perfect and twinned β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under three typical heating conditions—constant-temperature, programmed, and adiabatic—that represent various rates of heat exchange between the HMX crystal and environment. As a result, it is found that the enhanced self-heating ability stemmed from the high internal energy of the molecules around the defects, and such ability is remarkably exhibited with low heat-exchange rates between the energetic materials EMs and environment. Adiabatic heating is an extreme to exhibit the most remarkable such ability, as the superiority of the high...

Dissociative Photoionization of 1-Halogenated Silacyclohexanes: Silicon Traps the Halogen.

The threshold photoelectron spectra and threshold photoionization mass spectra of 1-halogenated-1-silacyclohexanes, for the halogens X = F, Cl, Br, and I, have been obtained using synchrotron vacuum ultraviolet radiation and photoelectron photoion coincidence spectroscopy. As confirmed by a similar ionization onset and density functional theory molecular orbitals, the ionization to the ground state is dominated by electron removal from the silacyclohexane ring for X = F, Cl, and Br, and from the halogen lone pair for X = I. The breakdown diagrams show that the dissociative photoionization mechanism is also different for X = I. Whereas the parent ions decay by ethylene loss for X = F to Br in the low-energy regime, the iodine atom is lost for X = I. The first step is followed by a sequential ethylene loss at higher internal energies in each of the compounds. It is argued that the tendency of silicon to lower bond angles stabilizes the complex cation in which C2H4 is η2-coordinated to it, and which precedes ethylene loss. Together with the relatively strong silicon-halogen bonds and the increased inductive effect of the silacyclohexane ring in stabilizing the cation, this explains the main differences observed in the fragmentation of the halogenated silacyclohexane and halogenated cyclohexane ions. The breakdown diagrams have been modeled taking into account slow dissociations at threshold and the resulting kinetic shift. The 0 K appearance energies have been obtained to within 0.08 eV for the ethylene loss for X = F to Br (10.56, 10.51, and 10.51 eV, respectively), the iodine atom loss for X = I (10.11 eV), the sequential ethylene loss for X = F to I (12.29, 12.01, 11.94, and 11.86 eV, respectively), and the minor channels of H loss for X = F (10.56 eV) and propylene loss in X = Cl (also at 10.56 eV). The appearance energies for the major channels likely correspond to the dissociative photoionization reaction energy.

Development of a two-dimensional binning model for N2–N relaxation in hypersonic shock conditions

A high fidelity internal energy relaxation model for N2–N suitable for use in direct simulation Monte Carlo (DSMC) modeling of chemically reacting flows is proposed. A novel two-dimensional binning approach with variable bin energy resolutions in the rotational and vibrational modes is developed for treating the internal mode of N2. Both bin-to-bin and state-specific relaxation cross sections are obtained using the molecular dynamics/quasi-classical trajectory (MD/QCT) method with two potential energy surfaces as well as the state-specific database of Jaffe et al. The MD/QCT simulations of inelastic energy exchange between N2 and N show that there is a strong forward-preferential scattering behavior at high collision velocities. The 99 bin model is used in homogeneous DSMC relaxation simulations and is found to be able to recover the state-specific master equation results of Panesi et al. when the Jaffe state-specific cross sections are used. Rotational relaxation energy profiles and relaxation times obtained using the ReaxFF and Jaffe potential energy surfaces (PESs) are in general agreement but there are larger differences between the vibrational relaxation times. These differences become smaller as the translational temperature increases because the difference in the PES energy barrier becomes less important.

The Onset of H + Ketene Products from Vinoxy Radicals Prepared by Photodissociation of Chloroacetaldehyde at 157 nm.

We investigate the unimolecular dissociation of the vinoxy radical (CH2CHO) prepared with high internal energy imparted from the photodissociation of chloroacetaldehyde (CH2ClCHO) at 157 nm. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling chlorine atoms, Cl((2)P3/2) and Cl((2)P1/2), and derived from this the resulting distribution of kinetic energy, P(ET), imparted to the Cl + vinoxy fragments upon dissociation. Using conservation of energy, the distribution of kinetic energy was used to determine the total internal energy distribution in the radical. The P(ET) derived for the C-Cl bond fission presented in this work suggests the vinoxy radicals are mostly formed in the à state. We also took ion images at m/z = 42 and m/z = 15 to characterize the branching between the unimolecular dissociation channels of the vinoxy radical to H + ketene and methyl + CO products. Our results show a marked change in the branching ratio between the two channels from the previous study on the photodissociation of chloroacetaldehyde at 193 nm by Miller et al. (J. Chem. Phys., 2004, 121, 1830) in that the production of ketene is now favored over the production of methyl. To help analyze the data, we developed a model for the branching between the two channels that takes into account how the change in rotational energy en route to the products affects the vibrational energy available to surmount the barriers to the channels. The model predicts the portion of the C-Cl bond fission P(ET) that produces dissociative vinoxy radicals, then predicts the branching ratio between the H + ketene and CH3 + CO product channels at each ET. The model uses Rice-Ramsperger-Kassel-Marcus rate constants at the correct sums and densities of vibrational states while accounting for angular momentum conservation. We find that the predicted portion of the P(ET) that produces H + ketene products best fits the experimental portion (that we derive by taking advantage of conservation of momentum) if we use a barrier height for the H + ketene channel that is 4.0 ± 0.5 kcal/mol higher than the isomerization barrier en route to CH3 + CO products. Using the G4 computed isomerization barrier of 40.6 kcal/mol, this gives an experimentally determined barrier to the H + ketene channel of 44.6 kcal/mol. From these calculations, we also predict the branching ratio between the H + ketene and methyl + CO channels to be ∼2.1:1.

Ambient ionization based on mesoporous graphene coated paper for therapeutic drug monitoring.

Paper spray (PS), as a new ambient ionization method, has been applied for direct qualitative and quantitative analysis. The high sensitivity and minimum internal energy (low spray voltage) with optimized paper spray conditions is a significant request for real application in POCT. In this study, a simple and efficient ambient ionization method is developed by spraying from a mesoporous graphene foams (MGFs)-modified paper surface. The good electrical conductivity of MGFs results in obvious spray voltage decrease. Meanwhile, the MGFs-paper substrate has a well improvement in separation and elution efficiency ascribing to ultrahigh specific surface area and π-π electrostatic stacking property of graphene. In combination a commercial triple quadrupole mass spectrometer, the paper spray is successfully used for analysis of amphetamine in saliva. The linear dynamic ranges expand 10 fold in comparison with unmodified chromatography papers and the low limit of quantitation (LOQ) is as low as 1 pg/mL. A small sample volume (0.5 μL) could be analyzed immediately after spotting, without any pretreatment. The performance of this method was demonstrated for application in fast point-of-care mass spectrometry.

Interface-induced formation of onion-like alloy nanocrystals by defects engineering

The ability to controlled introduction of defects, particularly twin defects in Pt-based nanocrystals (NCs) provides a possibility to regulate the performance of Pt-based nanocatalyst. However, because of the high internal strain energy existed in twinned structures, the fabrication of defects in Pt-based NCs is sufficiently challenging. Here we demonstrate a “low-temperature interface-induced assembly” approach that provides precise control over Pt–Cu nanoparticles assembled at the hexadecylamine/water interface, yielding onion-like Pt–Cu NCs exposed a high density of twin defects. Moreover, a bending mechanism is proposed to elucidate the appearance of twin defects and lattice expanding (contraction) based on aberration corrected scanning transmission electron microscopy analysis. This work opens new routes to engineer defects in metalbased alloy NCs, enabling more opportunities in catalysis.

Design and Analysis of a Flywheel Supported by Hybrid Magnetic Bearing

In this study, a design structure of a new flywheel supported by Hybrid Magnetic Bearing (HMB) with permanent magnet in rotor is modeled using 3D Software solid works. The hybrid magnetic bearing consists of two sets of Active Magnetic Bearing (AMB) and a set of Permanent Magnetic Bearing (PMB) as well as a frequency response analysis for a rotor dynamic system at a rotor speed of 20,000 rpm. In this system an axial PMB is located at the top of the rotor to provide a levitation force in order to suspend more flywheel weight, two radial and axial AMB are added to provide support in the radial and axial directions to improve stiffness by two orders of magnitude from 104 N/M to 106N/M and the damping of the flywheel energy storage system (FESS). The prototype HMB model flywheel structure presented in Fig. 6 with a storage capacity of 4 KW rotating at a speed of 20000 rpm has an advantage of simplicity in structure, high energy density, low frictional and internal energy losses, ultimately resulting in higher power output. A unique feature of this design is that the upper and the lower ends of the rotor and the stator core have been tapered compared to previous design ensuring that larger thrust and lower radial force are obtained.

Synthesis of Cubic Phase-Co Microspheres by Mechanical Solid-State Reaction-Thermal Decomposition and Research on Its Growth Kinetics

Cubic phase cobalt (Co), which can be used as a key component for composite materials given its excellent ductility and internal structure, is not easy to obtain at room temperature. In this study, oxalic acid and cobalt nitrate are used as raw materials to synthesize the cobalt oxalate precursor, which has a stable structure with a five-membered chelate ring. Cobalt oxalate microspheres, having a high internal energy content, were prepared by using mechanical solid-state reaction in the presence of a surfactant, which can produce spherical micelles. The thermal decomposition of the precursor was carried out by maintaining it in a nitrogen atmosphere at 450°C for 3 h. At the end of the procedure, 100 nm cubic phase-Co microspheres, stable at room temperature, were obtained. Isothermal and nonisothermal kinetic mechanisms of cobalt grain growth were investigated. The cubic-Co grain growth activation energy, Q, was calculated in this study to be 71.47 kJ/mol. The required reaction temperature was low, making the production process simple and suitable for industrial applications.