Kinetic Energy Distributions Research Articles

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes via site-selective ionization.

C-I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy. At greater C-I separations, beyond the critical distance, CT is no longer possible and the measured kinetic energies of the charged iodine atoms report on the neutral dissociation process. The time and momentum resolved measurements allow determination of the timescales and the respective product momentum and kinetic energy distributions for both isomers, which are interpreted in terms of rival 'direct' and 'indirect' dissociation pathways. The measurements are compared with a classical over the barrier model, which reveals that the onset of the indirect dissociation process is delayed by ∼1 ps relative to the direct process. The kinetics of the two processes show no discernible difference between the two parent isomers, but the branching between the direct and indirect dissociation channels and the respective product momentum distributions show isomer dependencies. The greater relative yield of indirect dissociation products from 262 nm photolysis of 3-iodothiophene (cf. 2-iodothiophene) is attributed to the different partial cross-sections for (ring-centred) π∗ ← π and (C-I bond localized) σ∗ ← (n/π) excitation in the respective parent isomers.

Vortex dynamics characteristics in the tip region based on Wray–Agarwal model

In order to solve the blockage effect and energy dissipation phenomenon caused by cavitation in the low-pressure vortex core region, this paper analyzes the spatial evolution of vorticity intensity and turbulent kinetic energy intensity under different cavitation conditions based on the Wray–Agarwal (WA) model. First, the tip leakage flow characteristics are studied, the evolution of vorticity and vorticity intensity is analyzed, then the distribution of turbulent kinetic energy distribution in the blade tip region is studied, and finally, the vorticity transport characteristics of the tip region are analyzed. It is found that the tip leakage rate is less affected by the vortex cavitation of the tip leakage, and there is a strong interaction between the leakage flow at the tip leading edge and the trailing edge, and the separation vortices and low-speed regions formed in the end-wall region cause blockage of the flow passage. Low pressure causes cavitation to cover most regions of the suction surface, inhibiting the formation and development of the tip leakage vortices. The distribution range of high turbulent kinetic energy region is almost the same as that of high-vorticity region, and there is a positive correlation between the two intensities. Severe cavitation causes the high turbulent kinetic energy region at the outlet of the flow passage to develop in the radial and axial directions of the impeller, which increases the turbulent dissipation and energy loss. The change of vorticity transport intensity caused by cavitation is mainly reflected in the expansion contraction term, and the Coriolis force term plays a dominant role in the vorticity transport process. This paper provides a reference for further improving the performance of mixed-flow pumps.

Study of non-constant local cavitation suppression in micro-wedge structure

To alleviate the negative impacts of cavitation phenomenon on hydrodynamic machinery, such as mechanical vibration and noise, a hydrofoil model is established based on the micro-wedge structure, and numerical simulation of the hydrofoil is carried out by using the modified turbulence model k–omega shear stress transport (SST k–ω) to analyze the lift coefficient of drag, pressure pulsation, cavitation volume fraction, cavitation volume morphology, and turbulent kinetic energy distribution, and to reveal the inhibition of cavitation mechanism of the chord direction of the placement and the height of the micro-wedge structure coupling. The results show that the height of the micro-wedge structure determined by the thickness of the boundary layer is an important parameter affecting the cavitation performance, and the micro-wedge structure with a smaller height will produce better cavitation suppression, and the height of 0.05 mm has the best suppression effect, and the suppression of the main frequency of pulsation and the amplitude of pulsation shows a positive effect. The micro-wedge structure arranged on the hydrofoil can delay the change cycle of the cavitation volume to different degrees, in which the chordwise position of 3.5 mm has the best cavitation suppression effect, and the cavitation suppression rate is about 16.7%.

Numerical simulation of a novel small water turbine generator for installation in a deep-flow hydroponics system

Hydroponics systems are crucial for providing sustainable and cost-effective choices when soils are unavailable for conventional farming. The application of water flow rates within hydroponics systems to generate electricity is another idea that can be used in the field of power generation. This paper presents the determination of the mechanical power efficiency of a novel small water turbine generator for use in a deep-flow hydroponics system (DFT). The system was designed, analysed, and calculated for the most suitable geometries of the water pipeline inlet, DFT system, main structure of the PVC Tee Pipe Fitting, and a water turbine wheel using computational fluid dynamics software. The diameter of the water turbine wheel in this research was 48 mm. A DFT hydroponic system was modelled for the purposes of this research. We conducted a numerical simulation with water flow rates of 6, 8, and 10 l/min to evaluate the turbulent kinetic energy distribution in the DFT hydroponic system. The numerical simulation employed the control volume methodology, and the k-epsilon turbulence model was applied to obtain the computational conclusions. The highest torque and power that a novel small water turbine for installation in a DFT system could generate at a maximum flow rate of 0.000167 m3/s were 0.082 N.m. and 1.9568 watts, respectively. The forces generated by the fluid's speed and pressure can then be transferred to the building process of a novel small water turbine wheel. The FEA numerical result shows that the maximum value of the total deformation at a wheel speed of 228 rpm is 7.0 x 10-5 mm. The numerical simulations used in this study could potentially be used to further develop prototypes for innovative miniature water turbines that generate commercial electricity.

Dissociative ionization and post-ionization alignment of aligned O2 in an intense femtosecond laser field.

We examined dissociative ionization of O2 in an intense femtosecond laser field (782 nm, 120 fs, 4 × 1014 W cm-2) by recording the kinetic energy distribution of O+ emitted along the laser polarization direction as a function of the delay time between the pump pulse (9 × 1013 W cm-2) for the molecular alignment and the probe pulse for the dissociative ionization. We found the two distinct rotational revival patterns which are out-of-phase by π with each other in the kinetic energy distribution of O+. One of the patterns shows the dissociative ionization is enhanced when the O2 axis is parallel to the laser polarization direction, suggesting that the ionization is induced by the electron emission from the 3σg orbital. On the other hand, the other pattern shows that the dissociative ionization is enhanced when the O2 axis is perpendicular to the laser polarization direction, suggesting that the ionization is induced by the electron emission from the 1πu orbital. Because of the collection efficiency of the time-of-flight mass spectrometer, the enhancement of the O+ yield at the anti-alignment time delay indicates that the electron emission from the 1πu orbital is followed by the molecular alignment of O2+ in the course of the dissociation. We performed classical trajectory Monte-Carlo simulation of O2+ with the dissociation and rotational coordinates in the light-dressed potential to evaluate the effect of the post-ionization alignment by the probe pulse.

Adsorbate dissociation due to heteromolecular electronic energy transfer from fluorobenzene thin films.

Study of the near-UV photodissociation dynamics for monolayer (ML) quantities of CH3I on thin films of a series of fluorobenzenes and benzene (1-25 ML) grown on a Cu(100) substrate finds that in addition to gas-phase-like neutral photodissociation, CH3I dissociation can be enhanced via electronic energy transfer to the CH3I following photoabsorption in several of the thin films studied. Distinct CH3 photofragment kinetic energy distributions are found for CH3I photodissociation on C6H5F, 1,4-C6H4F2 and C6H6 thin films, and distinguished from neutral photodissociation pathways using polarized incident light. The effective photodissociation cross section for CH3I on these thin films is increased as compared to that for the higher F-count fluorobenzene thin films due to the additional photodissociation pathway available. Quenching by the metal substrate of the photoexcitation via this new pathway suggests a significantly longer timescale for excitation than that of neutral CH3I photodissociation. The observations support a mechanism in which neutral photoexcitation in the thin film (i.e. an exciton) is transported to the interface with CH3I, and transfers the electronic excitation to the CH3I which then dissociates. The unimodal CH3 photofragment distribution and observed kinetic energies on the fluorobenzene thin films suggest that the dissociation occurs via the 3Q1 excited state of CH3I.

Dissociative electron attachment studies of gas-phase acetic acid using a velocity map imaging technique

Advancing instrumentation to explore dissociative electron attachment (DEA) studies allows previously unattainable information to be acquired. Using a newly constructed velocity map imaging spectrometer, we revisited a study on DEA to gas-phase acetic acid. We discuss possible fragmentation channels and compared the corresponding ion yields with previous high electron-energy resolution results. We focus on the channels occurring at higher energies, particularly near 10 eV, and calculate their thermodynamic thresholds. Moreover, we expand previous studies and perform time-sliced imaging near the 10 eV resonance to obtain the kinetic energy distribution of the fragment ions.

Connection of four-dimensional Langevin model and Hauser-Feshbach theory to describe statistical decay of fission fragments

ABSTRACT We have developed a novel theoretical method to obtain independent fission product yields and prompt neutron observables by connecting mass and total kinetic energy (TKE) distributions calculated by a four-dimensional Langevin dynamical model to a Hauser-Feshbach statistical decay model. In the Langevin calculations, mass distributions corresponding to the standard I and II modes were obtained separately and superposed to reproduce the fission fragment yield of spontaneous fission of 238 , 240 , 242 Pu and thermal neutron-induced fission of 239 Pu . This was achieved by using different neck parameters for these two modes in the two-center shell model shape parametrization, and a systematics of the superposing ratio was obtained as a function of N − Z / A of the fissioning nuclei. The Hauser-Feshbach calculations were performed using a nuclear reaction code TALYS for 239 Pu n , f reaction in the incident energy range from thermal up to 5 MeV , and the calculated prompt fission observables were compared with experimental and evaluated data. Although further improvements are needed for the most important nuclides, it turned out that the present methodology has the capability to prepare fission-related nuclear data for nuclides for which measurements are difficult.

Numerical Study of Bottom Shape Effect on the Mixing for Stirred Tank

Abstract In this work, computational fluid dynamics (CFD) was used to investigate the effect of the bottom shape on the flow field and mixing characteristics in an agitated vessel stirred by six-pitched blade turbine (PBT6). The simulation was based on the resolution of the Navier-Stokes equations using standard k-ε turbulence model. Hydrodynamic behavior of the stirred vessel with four types of bottom shapes was investigated, a flat bottom and three different semi-elliptical bottoms. The results show reasonably satisfactory agreement with the experimental data. The CFD simulation also showed that the semi-elliptical bottom shapes had a significant influence on the velocity profiles and on the turbulent kinetic energy distributions of the local flow generated at the bottom region of the vessel.

Charge transfer reaction at gas-liquid interface of aqueous tetrabutylammonium iodide solution: influence of ions on dynamical response of solvent

Abstract Tetrabutylammonium iodide (TBAI) is known to create an electric double layer at the air-water interface. In the present study, we investigated the charge-transfer-to-solvent reaction from iodide ions to liquid water near the gas-liquid interface of an aqueous TBAI solution using extreme UV (EUV) time-resolved photoelectron spectroscopy. Use of EUV radiation ensured accurate measurements of electron kinetic energy distributions by minimizing spectral distortions caused by electron inelastic scattering in the liquid and the influence of the electron transmission efficiency through the gas-liquid interface. The spectra observed for photodetached electrons exhibited a rapid energy shift and a variation of the bandwidth in subpicoseconds, and the rates of these changes clearly depended on the TBAI concentration. The results indicate that the dynamical response of solvent water changes in the presence of a high density of ions.

Submesoscale processes in the surface layer of the central Baltic Sea: A high-resolution modelling study

A high-resolution model with a horizontal resolution of 250 m was used to analyze the surface eddy fields and the distribution of kinetic energy in the Baltic Sea. The results indicate a close relationship between the wind speed and the kinetic energy at the surface and the vertically averaged kinetic energy in the sea, and a lagged correlation between the kinetic energy at the surface and the eddy field. The spatial patterns of kinetic energy indicate more energetic currents in the western and southern parts of the Baltic Sea. The distribution of vorticity is inhomogeneous and differs significantly between sea areas. Submesoscale features are also inhomogeneously distributed and occur more frequently in the Gdańsk Basin, the Gulf of Finland, and the western part of the northern Baltic proper.

Jumping Platonic Solids on a Vibrating Plate

AbstractThe mechanical excitation of solid bodies by a vibrating plate is not only an interesting fundamental problem, but also has relevance in many mechanical systems, for example, in the preparation of granular gases in microgravity. Herein, the energy input by an oscillating plate is numerically investigated as a function of the excitation parameters for selected Platonic solids and their behavior compared to that of a jumping sphere. The most important additional features, not relevant for spheres, are the excitation of body rotations and a permanent energy exchange between the rotational and translational degrees of freedom during the collisions with the plate. The distribution of kinetic energies is analyzed by a numerical simulation of the dynamics, using structures which emulate the mechanical behavior of regular polyhedra.

Exploring the conformational dynamics and thermodynamics of EGFR S768I and G719X + S768I mutations in non-small cell lung cancer: An in silico approaches.

Non-small cell lung cancer (NSCLC) is often driven by mutations in the epidermal growth factor receptor (EGFR) gene. However, rare mutations such as G719X and S768I lack standard anti-EGFR targeted therapies. Understanding the structural differences between wild-type EGFR and these rare mutants is crucial for developing EGFR-targeted drugs. We performed a systematic analysis using molecular dynamics simulations, essential dynamics (ED), molecular mechanics Poisson-Boltzmann surface area, and free energy calculation methods to compare the kinetic properties, molecular motion, and free energy distribution between wild-type EGFR and the rare mutants' structures G719X-EGFR, S768I-EGFR, and G719X + S768I-EGFR. Our results showed that S768I-EGFR and G719X + S768I-EGFR have higher global and local conformational flexibility and lower thermal and global structural stability than WT-EGFR. ED analysis revealed different molecular motion patterns between S768I-EGFR, G719X + S768I-EGFR, and WT-EGFR. The A-loop and αC-helix, crucial structural elements related to the active state, showed a tendency toward active state development, providing a molecular mechanism explanation for NSCLC caused by EGFR S768I and EGFR G719C + S768I mutations. The present study may be helpful in the development of new EGFR-targeted drugs based on the structure of rare mutations. Our findings may aid in developing new targeted treatments for patients with EGFR S768I and EGFR G719X + S768I mutations.

A new channel structure for strengthening heat transfer of SCO2 printed circuit heat exchanger (PCHE): variable sectional semicircular channel

In this paper, a mathematical and physical model is established to study the convective heat transfer performance of supercritical carbon dioxide (SCO2) in three kinds of horizontal semicircular channels (uniform cross-sectional channel, diverging and converging channels). The accuracy of the numerical model is verified by comparing with the experimental data. The computational results demonstrate that the converging channel can strengthen heat transfer effectively compared with the uniform cross-sectional channel under the same heat transfer area. In the range of calculated working conditions, the use of a converging channel resulted in a maximum improvement of 42.26% in the heat transfer performance of SCO2. However, the diverging channel deteriorates the heat transfer. It is discovered that the improvement of the field coordination of SCO2 in the converging channel is one of the main reasons for its enhanced heat transfer. In addition, the different distribution of turbulent kinetic energy and thermal conductivity are also an important factor affecting the heat transfer performance of SCO2 in different channels. Finally, we propose a new heat transfer correlation of the SCO2 cooling process in the horizontal semicircular converging channel. Compared with the five selected correlations, the new correlation has the best prediction accuracy, and its mean absolute relative error (MARE) and root mean square error (RMSE) are 9.49% and 10.6%, respectively. Our work will provide new insights and theoretical guidance for the design and optimization of coolers in SCO2 Brayton cycle system.

A trajectory surface hopping study of the vibration-induced autodetachment dynamics of the 1-nitropropane anion

In this study, we investigate the autodetachment dynamics of the 1-nitropropane anion after vibrational excitation of the energetically lowest C–H stretching mode using our recently developed extended quantum classical surface hopping approach including the detachment continuum. Therein the detachment from an electronic bound anion state is treated as a nonadiabatic transition into discretized detachment continuum states for an ensemble of classical nuclear trajectories propagated on quantum mechanical potential energy surfaces. The initial ensemble is obtained by sampling a phase space distribution accounting for the vibrational excitation of the C–H stretching mode of the molecule to match the experimental conditions. The simulated kinetic energy distribution of the ejected electrons reproduces characteristic features of the available experimental data. Analysis of the nuclear dynamics points out that the approach to neutral-like geometries with decreased pyramidalization angle of the NO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} group and reduced the N–O bond lengths are the crucial factors enhancing the ultrafast autodetachment process in vibrationally excited 1-nitropropane. This is facilitated when the dipole-bound first excited state of the anion is populated, which is structurally similar to the neutral system. Although only a small transient population of this state is observed, it acts as an efficient doorway to the detachment continuum and is responsible for a significant amount of the ejected electrons.

Influence of trailing edge flap length and deflection angle on the performance of the multiphase pump

At medium to high gas content rates, the gas-liquid separation phenomenon and the stagnation behaviors of the gas masses occurring in the impeller channels are essential factors affecting the hydraulic performance of multiphase pumps. This paper designs a split trailing edge flap suitable for the multiphase pump to improve the hydraulic performance in the impeller by varying the flap deflection angle and length. The model’s reliability was assessed by comparing the experimental outcome with the external characteristics of the experimental data. Based on the Eulerian-Eulerian multiphase model and the SST k‐ω turbulence model, the effects of different flap lengths on external characteristics, the turbulent kinetic energy and pressure distribution are analyzed. The study results show that when the length of the separated trailing edge flap is 0.25 l0 and the deflection angle is 5°, the transporting efficiency of the multiphase pump is the highest at IGVF=50% with an efficiency increase of 3.40% compared to the original model. Its optimal flap length scheme effectively reduces the radial pressure gradient and the inverse pressure gradient in the impeller channel, which suppresses the gas blockage phenomenon to a certain extent.

Using 2DVD technology to explore droplet characteristic variations of sprinkler irrigation as affected by a maize canopy

Canopy cover influences the water distribution and droplet characteristics of sprinkler irrigation, creating uncertainty in the design optimization of sprinkler irrigation systems. To evaluate the effects of canopy cover on water distribution and droplet characteristics of sprinkler irrigation, the radial distribution of droplet diameters, velocities, impact angles, shear stresses, and kinetic energies were investigated by an indoor experiment using a two-dimensional video disdrometer (2DVD) with Nelson R33LP low-pressure sprinklers at three operating pressures (100, 200, and 300 kPa), three nozzle diameters (4.4, 4.8, and 5.2 mm), and two growing stages of the maize canopy. Additionally, the water application rates were measured by catch-can devices for each treatment. The results show that small droplets passing through the canopy converge into larger-diameter droplets and large droplets passing through the canopy break up into smaller-diameter droplets. The canopy cover significantly affected droplet kinetic energy and velocity and reduced shear stress by 2.48–96.09 %, which could minimize the risk of soil erosion. Meanwhile, an increase in the leaf area index (LAI) reduced the kinetic energy by 0.26–99.00 %. Canopy cover also had an obvious effect on the irrigation uniformity coefficients (CU). The CU without the canopy exhibited a significant linear correlation with the CU with the canopy. When the irrigation CU without the canopy was 62.00 %, the maize canopy at the jointing stage improved it by 16.62 %, and when the CU without the canopy was 88.47 %, the maize canopy cover at the jointing stage reduced it by 4.68 %. An increase in operating pressure improved the uniformity of the sprinkler by 0.57–151.58 % and reduced shear stress by 2.80–95.11 %. An increasing nozzle size increased the application rate and specific power. This study provides technical support for the design of sprinkler irrigation systems.

Numerical Simulation Study on Flow Characteristics of Multistage Centrifugal Pumps under Different Inlet Gas Void Fractions

The flow characteristics of multistage centrifugal pumps in transporting gas–liquid mixed media are highly complex; particularly, the unstable flow of the passage at high gas contents exacerbates energy losses, leading to a decrease in pump efficiency and stability. The excess energy loss in the pump is not conducive to the concept of sustainable development. In this study, a numerical simulation of multistage centrifugal pumps was conducted based on the Euler–Euler heterogeneous two-fluid model. This research revealed that gas primarily accumulates on the suction side of each impeller stage, and the gas distribution decreases progressively with each stage. As the interstage gas volume fraction (IGVF) increases, the gas accumulation within the pump becomes more pronounced. The gas volume fraction of each component is negatively correlated with the flow rate, and the change is more obvious in the impeller. The turbulent kinetic energy distribution inside the impeller is positively correlated with the gas distribution. There is a large fluctuation at 0.6Q and 0.8Q, and the distribution of the impeller vortex is asymmetric. However, the impeller has a lower turbulent kinetic energy near 1.2Q, which indicates that the emergence of gas in the medium increases the high-efficiency area of the multistage pump to a certain extent. This paper reveals how the gas phase is distributed, how energy is lost in the multistage pump, and the gas–liquid two-phase flow characteristics in the pump, which have certain guiding significance for the design and working-condition adjustments of the gas–liquid mixed pump.

Effect of external electric field on agglomeration characteristics of Cu nanoparticles: A molecular dynamics study

In order to study the effect of electric field on the stability of Cu nanoparticles in water, molecular dynamics method was used to simulate the agglomeration characteristics of Cu nanoparticles. The microscopic agglomeration characteristics of nanoparticles by electric field were analyzed using the distribution and collision of nanoparticles in water at different times, as well as the potential energy, kinetic energy, diffusion coefficient and radial distribution function of the system. The results show that the collision of Cu nanoparticles was inhibited in the presence of both uniform and alternation electric fields. The total potential energy of the system decreases with each collision of particles. When all of the particles are agglomerated, the total potential energy of the system remains constant. According to the radial distribution function, when the electric field intensity increases, the degree of aggregation of water molecules on the particle surface strengthens and then weakens as the electric field strength. Meanwhile, the degree of aggregation decreases with the increasing frequency of the alternating electric field. The effect of electric field frequency on the diffusion coefficient of nanofluid is insignificant. However, as the strength of the electric field increases the diffusion coefficient of the nanofluid decreases, while the resistance coefficient of water molecules increases, and the presence of the electric field inhibits the movement of water molecules. The influence of electric field on the heat transfer and deposition characteristics of nanofluids can be obtained by experiments, but the influence mechanism is difficult to be analyzed by experimental means. The molecular dynamics method also provides a new idea to reveal the influence mechanism of electric field.

Predicting the effects of spatiotemporal modifications of muscle activation on the tentacle extension in squid.

Squid use eight arms and two slender tentacles to capture prey. The muscular stalks of the tentacles are elongated approximately 80% in 20-40ms towards the prey, which is adhered to the terminal clubs by arrays of suckers. Using a previously developed forward dynamics model of the extension of the tentacles of the squid Doryteuthis pealeii (formerly Loligo pealeii), we predict how spatial muscle-activation patterns result in a distribution of muscular power, muscle work, and kinetic and elastic energy along the tentacle. The simulated peak extension speed of the tentacles is remarkably insensitive to delays of activation along the stalk, as well as to random variations in the activation onset. A delay along the tentacle of 50% of the extension time has only a small effect on the peak extension velocity of the tentacle compared with a zero-delay pattern. A slight delay of the distal portion relative to the proximal has a small positive effect on peak extension velocity, whereas negative delays (delay reversed along stalk) always reduce extension performance. In addition, tentacular extension is relatively insensitive to superimposed random variations in the prescribed delays along the stalk. This holds in particular for small positive delays that are similar to delays predicted from measured axonal diameters of motor neurons. This robustness against variation in the activation distribution reduces the accuracy requirements of the neuronal control and is likely due to the non-linear mechanical properties of the muscular tissue in the tentacle.