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This study provides accurate results for the electronic stopping cross sections of H, He, N, and Ne in silicon in low to intermediate energy ranges using various non-perturbative theoretical methods, including real-time time-dependent density functional theory, transport cross section, and induced-density approach. Recent experimental findings [Ntemou et al., Phys. Rev. B 107, 155145 (2023)] revealed discrepancies between the estimates of density functional theory and the observed values. We show that these discrepancies vanish by considering the nonuniform electron density of the deeper silicon bands for ion velocities approaching zero (v → 0). This indicates that mechanisms such as "elevator" and "promotion," which can dynamically excite deeper-band electrons, are active, enabling a localized free-electron gas to emulate ion energy loss, as pointed out by Lim et al. [Phys. Rev. Lett. 116, 043201 (2016)]. The observation and the description of a velocity-proportionality breakdown in electronic stopping cross sections at very low velocities are considered to be a signature of the contributions of deeper-band electrons. [ABSTRACT FROM AUTHOR]

In this research, the mass stopping powers, projected range, effective atomic numbers, effective electron density, radiation yield and stopping time of light and heavy charged particles such as electron, proton and alpha in the Rene alloys which consist of Rene N4, Rene N5, Rene 41, Rene 65, Rene 80, Rene 88, Rene 95 and Rene 104 were calculated for the first time. The calculations were performed by using the programs, which are called as ESTAR, SRIM and PAGEX codes. Moreover, all the results were compared with each other, and a comprehensive and comparative study of the theoretical results were presented. [ABSTRACT FROM AUTHOR]

While studying d(d,n)3He fusion in 1938, Ruhlig observed protons with energies larger than 15 MeV. Ruhlig suggested that these high-energy protons were generated by tritium-on-deuterium fusion neutrons scattering protons out of a thin cellophane foil placed inside a cloud chamber. This led Ruhlig to hypothesize that he was observing secondary (in-flight) tritium-on-deuterium fusions and conclude that the d(t,n) reaction "must be an exceedingly probable one." This was the first attempt to quantify the probability of d(t,n) fusion, using the ~1-MeV tritons generated by d(d,p)t fusion. This caused some Manhattan Project scientists to suggest that the d(t,n) cross sections are significantly higher than those for deuteron-on-deuterium fusion and led to the first measurement of d(3He,p) and d(t,n) cross sections in 1943. Here, we have used modern cross sections and stopping powers to estimate the expected numbers of high-energy protons associated with in-flight d(t,n) reactions in Ruhlig's experiment. Our estimate is four orders of magnitude lower than Ruhlig's observed rate. However, the number of high-energy protons in Ruhlig's experiment can be obtained via simulation if the protons are assumed to have been emitted by secondary in-flight d(3He,p) reactions, with various plausible assumptions about the experimental geometry and target-backing thickness. Our calculations demonstrate that quantitative information about the fusion of A = 3 ions with deuterium could have been obtained via experiments similar to Ruhlig's well in advance of the advent of 3He ion and triton beams in 1943. This opportunity seems to have been missed. [ABSTRACT FROM AUTHOR]

The International Atomic Energy Agency (IAEA) stopping power database is a highly valued public resource compiling most of the experimental measurements published over nearly a century. The database—accessible to the global scientific community—is continuously updated and has been extensively employed in theoretical and experimental research for more than 30 years. This work aims to employ machine learning algorithms on the 2021 IAEA database to predict accurate electronic stopping power cross sections for any ion and target combination in a wide range of incident energies. Unsupervised machine learning methods are applied to clean the database in an automated manner. These techniques purge the data by removing suspicious outliers and old isolated values. A large portion of the remaining data is used to train a deep neural network, while the rest is set aside, constituting the test set. The present work considers collisional systems only with atomic targets. The first version of the ESPNN (electronic stopping power neural-network code), openly available to users, is shown to yield predicted values in excellent agreement with the experimental results of the test set. [ABSTRACT FROM AUTHOR]

Peter Politzer (1937–2022) grew up with no doubt in his mind that he would pursue a career in chemistry. His research interests ranged from theoretical concepts such as electronegativity and chemical hardness to applications of electrostatic potentials and average local ionization energies to molecular interactive behavior and bonding, as well as to the study of chemical reactions and the reaction force in a variety of disciplines, including energetic materials. He will be remembered as a world-renowned leader in halogen bonding and other σ-hole bonding interactions and other areas of theoretical and computational chemistry, with over 520 research publications in scientific journals and books, leaving quite a legacy, with a marked tendency toward simplicity. [ABSTRACT FROM AUTHOR]

It is shown that the application of the universal Lindhard function for calculating the scattering cross section of atomic particles is, as a rule, limited to the region of scattering angles less than 20°. The results obtained for various popular interaction potentials are compared with the available experimental data. It is shown that the presence of inelastic channels in scattering leads to the appearance of additional maxima in the scattering cross section. Recommendations are given on the use of the universal Lindhard function to describe quasi-elastic scattering in the region η = εsin(θ/2) > 0.01, ε is the reduced impact energy, θ is the scattering angle. At high energies, the scattering is well described by screened Coulomb potentials, and the application of the Lindhard function provides an accuracy of 10% for calculating the scattering cross sections. [ABSTRACT FROM AUTHOR]

This work successfully fabricated graphitic carbon nitride and magnetically recoverable α-Fe2O3/g-C3N4/SiO2 photo-Fenton catalysts using thermal polycondensation and in situ-simple precursor drying-calcination process, respectively, was examined for model synthetic rhodamine B (RhB) dye in the presence of H2O2 and acidic pH under simulated visible light irradiation. An aqueous suspension of the reaction mixture of dye-containing wastewater was fully degraded and reached 97% of photo-Fenton degradation efficiency within 120 min followed by the production of hydroxyl radical (•OH). The dominant hydroxyl radical position generated surface charge, electrostatic potential distribution, and average local ionization potential, which contributed to the complete mineralization of RhB dye, according to the density functional theory (DFT) calculations. HPLC and GCMS experiments were performed to examine the degradation fragments of RhB and draw a plausible mechanistic pathway which showed that RhB degradation generated a series of N-deethylated products, followed by a one-time ring-opening, which indicated that photosensitization induced a photocatalysis reaction mechanism. [ABSTRACT FROM AUTHOR]

Ion bombardment is an important tool of materials processing, but usually leads to erosion of the surface and significant thickness reductions when thin layers are used. The growing use of polymer thin films in a variety of applications, from coatings and membranes to biomedical and electronic devices, calls for a deeper understanding of the thinning process induced by energetic ions espe-cially for very thin films. Here, thinning and surface morphology changes induced by high-energy ion bombardment in PMMA and PVC thin films were investigated, focusing on the role of the initial thickness of the films and the stopping power of the ions. We used thin films with initial thicknesses varying from 13 to 800 nm, and light and heavy ions as projectiles in the energy range of 2–2000 MeV, where the electronic stopping dominates. Thickness reductions as a function of fluence were monitored and thinning cross sections were extracted from curves. A supralinear scaling between the thinning cross sections and the electronic stopping power of the beams was observed, with a much enhanced thinning efficiency for the swift heavy ions. The scaling with the stopping power dE/dx is almost independent of the initial thickness of the films. At intermediate and large fluences, changes in the physicochemical properties of the irradiated polymers may modulate and decelerate the thinning process of the remaining film. The importance of this secondary process depends on the stopping power and the balance between erosion and the chemical transformations induced by the beam. We also observe a trend for the thinning efficiency to become larger in very thin films. Depending on the type of beam and polymer, this effect is more or less pronounced. PMMA films irradiated with 2 MeV H+ show the most systematic correlation between initial thickness and thinning cross sections, while in PVC films the initial thickness plays a minor role for all investigated beams. [ABSTRACT FROM AUTHOR]

Electronic excitation of an atom by an ion in the energy regime below ∼ 20 keV/u can be strongly coupled with elastic scattering. This feature may cause noticeable deviations in the energy loss of light ions such as protons and deuterons from velocity-proportionality and is found to be an essential ingredient in the understanding of the stopping behavior near the threshold. We have incorporated this effect into the PASS stopping code and, in this way, expanded the range of validity of the code down to around 1 keV/u. Comparison of calculated with measured stopping cross sections for protons in Ag, Au, Cu, and Ni shows good agreement with recent data that deviate dramatically from the commonly assumed velocity proportionality. Most of these data were determined by the analysis of reflected-ion spectra. Computation of reflected-ion spectra with energy-loss functions from PASS leads to good agreement with measured spectra. A direct consequence of the coupling with elastic collisions is isotope dependence of the electronic-stopping cross section. Conventional stopping theory denies the existence of a significant isotope effect. Present calculations suggest an effect in the 1–10% range for hydrogen in Si at energies around and below 10 keV/u. This is found to be compatible with experimental data. [ABSTRACT FROM AUTHOR]

The Bloch correction is known as the link between Bethe's quantum theory of the stopping of charged particles in matter and Bohr's classical theory. Less well-known and underestimated in the literature, is its role as the link between the energy loss of heavy vs light ions. At the same time, the role of another key parameter, the ion charge, has been unclear until a few years ago, not the least due to the almost universal use of the competing effective-charge concept. We show that proper account of the Bloch correction and the ion charge forms the key to a qualitative and quantitative description of the electronic energy loss of heavy ions. In the standard textbook versions, neither Bohr nor Bethe stopping provide a valid description below the Bragg maximum, since logarithmic dependencies on the velocity cause the stopping cross section to become negative. Although this obstacle can easily be repaired by more accurate evaluation of the underlying integrals, we found the Bloch correction to be more tightly connected with these logarithms than expected. This requires caution in practical applications. [ABSTRACT FROM AUTHOR]

Polycarbonate-bismuth oxide composite has been used as a beta-ray sensor in the previous works. Calculation of two main quantities namely stopping power and range of electrons in this material can be useful to evaluate the optimal thickness of the sensor. Thus, in this study, the range of electrons and stopping power of polycarbonate/bismuth oxide composite for several pure beta-emitters were estimated using the ESTAR program. Simulation findings indicated that the amount of concentration of the heavy metal oxide particles into the composite is an important factor to determine the range and stopping power of the electrons. Also, in the experimental phase, the response of the 50 wt% nanocomposite with thickness of 1 mm against the beta-rays of the P-32 source at the average energy of 695 keV in different activities was measured using an electrometer at a constant voltage of 800 V. Results showed that the response of the sample ranging from 4 to 6 mCi was linear with R² = 0.9757. [ABSTRACT FROM AUTHOR]

In this research, the effect of deuterium beam energy distribution function resulting from TNSA and RPA mechanisms on the fast ignition of D/He3 fuel pellet has been investigated. The fuel is irradiated with a deuterium beam through a conical guide. The energy distribution function will be different in different mechanisms. Penetration depth and stopping power of ignitor beam with mono-energy, Maxwellian and Gaussian distribution of energy are calculated. Calculations show that the Maxwellian beam from TNSA mechanism, penetrates up to about 100 µm in the fuel and the height of deposition peak is still in plasma corona. The height of the peak has also increased about 25 times compared to the case where the Gaussian beam is considered. Also, the obtained results are shown that the energy deposit of the deuterium beam resulting the RPA mechanism will be completely localized and will be more concentrated in the dense fuel core. [ABSTRACT FROM AUTHOR]

Spurred by a need to determine major (C, H, N and O) contents in biological tissue sections, a formalism for quantitative off-axis Scanning Transmission Ion Microscopy (OA-STIM) has been established. This can be used with, or without, simultaneous Elastic Backscattering Spectroscopy (EBS) to provide quantitative major element composition and thickness information. As part of the work, an empirical predictor with one free parameter for the proton–proton differential scattering cross section was implemented. The predictor values were in extremely close agreement with high accuracy literature data. For 2 MeV p– 12 C elastic scattering at forward angles ≤ 45°an interpolation procedure was used to determine the relative deviations from the Rutherford cross sections were determined to be ≤ 6. 4 %. The interpolation was based on a Coulomb field, angular momentum quantum number and nuclear structure dependent nuclear penetration factor. Finally, the quantitative combination of simultaneous OA-STIM and EBS data is discussed. [Display omitted] • A formalism to facilitate quantitative analysis of off-axis Scanning Transmission Ion Microscopy has been established. • An empirical predictor with one free parameter for the differential proton–proton scattering cross section d σ p − p / d Ω has been implemented. • The 12 C(p,p) 12 C cross section at ≤ 45 ° and 2 MeV deviates from the Rutherford value by a small amount. • The forward scattering cross sections at 2 MeV and ≤ 45 ° for 14 N(p,p) 14 and 16 O(p,p) 16 O likely deviate only slightly from the classical value. [ABSTRACT FROM AUTHOR]

The article presents a study exploring how thin-film design of amorphous hafnium oxide nanocomposites enabling strong interfacial resistive switching uniformity. It also explores a design concept of phase-separated amorphous nanocomposite thin films, presented that realizes interfacial resistive switching (RS) in hafnium oxide–based devices.

It has been shown that the formation of autoionization states makes the dominant contribution to inelastic energy loss and to ionization in keV atomic collisions, i.e., at velocities lower than the velocities of atomic electrons. Scaling laws have been proposed to calculate the cross sections for the formation of vacancies in inner K and L electron shells of colliding atoms. A model has been proposed to relate ionization processes and the observed inelastic energy losses. Auger transitions in a short-lived quasimolecule formed by two atoms approaching each other have been studied. The nature of the continuous component in electron spectra emitted in collisions has been determined. It has been shown that the excitation of autoionization states determines the stopping cross sections for keV atoms in matter. [ABSTRACT FROM AUTHOR]

Background: Manganese is a paramagnetic element suitable for magnetic resonance imaging (MRI) of neuronal function. However, high concentrations of Mn2+ can be neurotoxic. 52gMn may be a valid alternative as positron emission tomography (PET) imaging agent, to obtain information similar to that delivered by MRI but using trace levels of Mn2+, thus reducing its toxicity. Recently, the reaction natV(α,x)52gMn has been proposed as a possible alternative to the standard natCr(p,x)52gMn one, but improvements in the modeling were needed to better compare the two production routes. Purpose: This work focuses on the development of precise simulations and models to compare the 52gMn production from both reactions in terms of amount of activity and radionuclidic purity (RNP), as well as in terms of dose increase (DI) due to the co-produced radioactive contaminants, versus pure 52gMnCl2. Methods: The nuclear code Talys has been employed to optimize the natV(α,x)52gMn cross section by tuning the parameters of the microscopic level densities. Thick-target yields have been calculated from the expression of the rates as energy convolution of cross sections and stopping powers, and finally integrating the time evolution of the relevant decay chains. Dosimetric assessments of [xxMn]Cl2 have been accomplished with OLINDA software 2.2.0 using female and male adult phantoms and biodistribution data for 52gMnCl2 in normal mice. At the end, the yield of xxMn radioisotopes estimated for the two production routes have been combined with the dosimetric results, to assess the DI at different times after the end of the irradiation. Results: Good agreement was obtained between cross-section calculations and measurements.The comparison of the two reaction channels suggests that natV(α,x)52gMn leads to higher yield and higher purity,resulting inmore favorable radiation dosimetry for patients. Conclusions: Both natV(α,x) and natCr(p,x) production routes provide clinically acceptable 52gMnCl2 for PET imaging. However, the natV(α,x)52gMn reaction provides a DI systematically lower than the one obtainable with natCr(p,x)52gMn and a longer time window in which it can be used clinically (RNP ≥ 99%). [ABSTRACT FROM AUTHOR]

Our study has shown that in collisions p-He and p-Ar with energies above 50 keV fast electrons carry away as kinetic energy up to 70 % of energy released during particle stopping. Ignoring the fast electron contribution makes impossible bringing independently measured cross sections of elementary processes of ionization, excitation, stripping and charge exchange into compliance with measured cross sections of electronic stopping. Fast electron emission in collisions of energetic ions with solids may induce extra radiation effects (create additional vacancies and defects in solid). Mean kinetic energies of ejected electrons W e obtained from the analysis of cross section ratio agree well with directly measured energy spectra of the emitted electrons. The dynamic ionization theory implies the W e proportionality to initial velocity v. In the considered cases, such a dependence takes place at the velocities below 2 a.u. At higher velocities, the observed dependence is successfully described in the framework of the Born approximation. [ABSTRACT FROM AUTHOR]

Ion-scattering spectrometry is a technique used to obtain compositional depth profiles by bombarding a sample with accelerated ions and analyzing the scattered particle energy. To obtain the depth profile from the ion-scattering spectra, simulations are usually performed using kinematic factors, scattering cross sections, stopping cross sections, and straggling, and accurate values are required for accurate analysis. This study proposes a method for obtaining stopping cross sections for pre- and post-collision energies by measuring the ion scattering spectra at the same scattering angle and at two different incident angles. Using this method, the stopping cross sections for He+ in SiO 2 below 100 keV were measured. [ABSTRACT FROM AUTHOR]

Activation cross sections of 103Rh(α,xn)106m,105g,104gAg and 103Rh(α,αxn)101m,102gRh radionuclides were measured at energies ranging from their respective threshold energies up to 40 MeV. Standard stacked foil activation technique was employed for irradiation. Residual activity was assayed using high-resolution gamma-ray spectrometry. Excitation functions were also theoretically calculated using TALYS nuclear reaction model to reproduce the experimental cross section data. The present data are compared with the available literature data, TENDL-2023 data using default values as well as the theoretical data calculated by TALYS-1.96. The shape and amplitude of the experimentally obtained excitation functions were well reproduced theoretically for all the studied radionuclides except for 105gAg, for which magnitude of the cross sections was not reproduced. The integral yields were also deduced using the measured cross sections and the stopping power of natural Rh from 40 MeV down to their threshold energies for these radionuclides, and compared with the experimental yield data available in the literature. [ABSTRACT FROM AUTHOR]

Fast charged particles interact with matter mainly by interaction with the electron shell of the atoms causing ionization and excitation, i.e. inelastic scattering. However, for lower velocity projectiles an important part of the energy loss is due to elastic scattering on the nuclei, which is called nuclear stopping. In the present paper we calculate the nuclear stopping cross section of protons and antiprotons in different materials. The obtained results are compared with calculations by other groups and with the electronic stopping cross sections. The difference between the results for protons and antiprotons is explained. [ABSTRACT FROM AUTHOR]

Atomistic simulations are performed to study the response of Xe gas bubbles in UO2 to ionizing fission products through the thermal spike approximation. A portion of the total electronic stopping power (Se) is taken as the thermal spike energy through a ratio variable ζ. The thermal spike energy causes extreme melting within the fission track cylindrical region. Molecular dynamics is employed to quantify the probability of a Xe gas atom to be re-solved (re-dissolved) back into the UO2 matrix. Subsequently, a re-solution model is developed and parametrized as a function of bubble radius (R), off-centered distance (r), and thermal spike energy (ζ S e ). The off-centered distance measures the shift of the thermal spike axis from the bubble center. To evaluate the re-solution model, independent fission product yield of U-235 fission due to thermal neutrons (0.0253 eV), taken from the JEFF-3.3 database, is used. The kinetic energy of the fission products is taken from the EXFOR database. Subsequently, the decay of Se over distance for each fission product is simulated. Finally, the evaluated re-solution rate (re-solution probability per second) is presented as a function of bubble radius for a range of ζ. [ABSTRACT FROM AUTHOR]

Three medicinally important radioisotopes of Ga, 66,67,68Ga, having half-lives ranging from minutes to days, could be produced from natZn(α,x) reactions. They have different applications in diagnosis and therapy in nuclear medicine depending on their decay properties and half-lives. 68Ge (T1/2 = 270.95 days) produced from natZn(α,x) reactions decays to 68Ga (T1/2 = 67.71 min) via electron capture (100%). So 68Ga can be produced for its practical application in medicine using 68Ge/68Ga generator where in-house medical cyclotron facilities are unavailable. Production and radiochemical separation of a particular radioisotope from natural zinc target with minimum contamination from other isotopes require accurate activation cross section data of all the produced radionuclides. Activation cross sections of long-lived radioisotopes of 68,69Ge, 66,67Ga and 65Zn produced from alpha irradiation of natural Zn targets were measured from their respective threshold up to 46.3 MeV. Using the experimentally measured cross section data and stopping power of natural Zn, thick target yields were calculated for these medicinally important radionuclides. The experimentally measured cross section data were compared with the earlier published literature data and theoretical data from TENDL-2021 nuclear data library based on the TALYS-1.96 code. Cross section data of the present work are found to be in good agreement with the literature data within experimental uncertainties for 68Ge, 66Ga and 65Zn while there are significant differences for 67Ga and 69Ge. [ABSTRACT FROM AUTHOR]

The behaviors of the positive definite Kohn-Sham kinetic energy density near the origin and at the asymptotic region play a major role in designing meta-generalized gradient approximations (meta-GGAs) for exchange in low-dimensional quantum systems. It is shown that near the origin of the parabolic quantum dot, the Kohn-Sham kinetic energy differs from its von Weizsäcker counterpart due to the p orbital contributions, whereas in the asymptotic region, the difference between the above two kinetic energy densities goes as ~p(r)/r2. All these behaviors have been explored using the twodimensional isotropic quantum harmonic oscillator as a test case. Several meta-GGA ingredients are then studied by making use of the above findings. Also, the asymptotic conditions for the exchange energy density and the potential at the meta-GGA level are proposed using the corresponding behaviors of the two kinetic energy densities. [ABSTRACT FROM AUTHOR]

We have examined and confirmed the previously unexplored concept of using Monte Carlo calculations in combination with measured projected ranges of ions implanted in solids to derive a quantitative description of nuclear interaction and electronic stopping. The study involved 98 ranges of 11B in Si between 1keV and 8MeV, contained in 12 sets of 10 different groups. Systematic errors by up to±8% were removed to establish a refined data base with 93 ranges featuring only statistical uncertainties (±1.8%). The Monte Carlo calculations could be set up to reproduce the refined ranges with a mean ratio 1.002±1.7%. The input parameters required for this very high level of agreement are as follows. Nuclear interaction is best described by the Kr-C potential, but in obligatory combination with the Lindhard-Scharff (LS) screening length. Up to 300keV, the electronic stopping cross section is proportional to the projectile velocity, Se=kSe,LS, with k=1.46±0.01. At higher energies, Se falls progressively short of kSe,LS. Around the Bragg peak, i.e., between 0.8 and 10MeV, Se is modeled by an adjustable function serving to tailor the peak shape properly. Calculated and measured isotope effects for ranges of 10B and 11B in Si agree within the experimental uncertainty (±0.25%). The range-based Se,R(E) reported here predicts the scarce experimental data derived from the energy loss in projectile transmission through thin Si foils to within 2% or better. By contrast, Se(E) data of available stopping power tables exhibit deviations from Se,R(E) between -40% and+14%. [ABSTRACT FROM AUTHOR]

The electronic stopping cross section of Ti for light ions is measured in an energy range of 1.3–5.0 keV for H+, and 1.5–10.0 keV for He+. All measurements were performed using in-situ Time-of-Flight Low-Energy Ion Scattering (ToF-LEIS) on ultrathin Ti layers, enabling absolute energy loss measurements. Monte-Carlo simulations are used to fit the experimental spectra and to extract the stopping cross section quantitatively. The free electron gas model is applied to collect additional information on the electronic stopping of light ions in Ti. We further compare the presented experimental data with previously published experimental data, semi-empirical models, and theoretical predictions. [ABSTRACT FROM AUTHOR]

• TYtool: a software application useful for optimization and maximizing radionuclide production without exceeding the power limits of the target material or holder. • Provides fast computer aided calculations of optimal target thicknesses, particle energies and beam currents based on user input of particle energy, current range, and power limit of target and or holder. • Facilitates graphical representation of many basic plots such as cross section, mass stopping power, activity output, projected range and it is useful for many different particles, reactions and radionuclides. A software application useful for optimization and maximizing radionuclide production without exceeding the power limits of the target material or holder has been developed. The software (TYtool) can be used for target optimization including yield calculations vs time, thickness, and incident energy, W/mm through the target, and automated target thickness optimization with the Makkonen-Craig & Helariutta − or the novel Yield/Wapproach. TYtool also facilitates graphical representation of many basic plots such as cross section, mass stopping power, activity output, projected range and it is useful for many different particles, reactions, radionuclides via the default cross section data base or the import function for cross section and mass stopping power. The software is available for free at: https://gitlab.com/NM_Karolinska_Solna/TYtool. [ABSTRACT FROM AUTHOR]

This paper investigates wire X-pinch (WXP) evolutions by the Eulerian resistive magneto-hydrodynamic code, STHENO, on 2D/3D geometry. A single-fluid two-temperature model is applied to pinch plasmas in local thermal equilibrium. The equation of state based on the Thomas–Fermi model is used to determine the ionization degree of the plasma. Electron internal energy is determined by the local density, temperature, and ionization potential with the average ion charge state. Lee–More–Desjarlais transport models are employed to obtain the thermal conductivities and resistivity for a non-ideal plasma. The radiation loss rate is calculated by the Bremsstrahlung and recombination emissivity within the ionization balance. The crossing point, which is the central part of the X-pinch, is assumed to be an axisymmetric configuration on a small computational domain in the RZ plane. The 2D simulation demonstrates that the micrometer size plasma column is elongated axially with the onset of the neck cascading structure. The radiation power is calculated and compared with the measured x-ray power from a modular X-pinch device (120-kA in 650-ns) at Seoul National University. The time evolution of the radiation power reproduces the trend of the measured x ray. 3D analyses are performed for the aluminum WXP configurations by varying wire numbers and cross-angles. The relation between the radiation performance and the numbers of wires reveals that the current density, rather than the line density, determines the central pinching condition. In addition, the multiple plasma instabilities (m = 0) near the central regions are found to degrade the radiation performance on the small cross-angle WXP. [ABSTRACT FROM AUTHOR]

A modified mesoporous Y zeolite is developed to catalyze high ortho regioselective nitration of azobenzene with NO2 as the nitro source. The mesoporous Y zeolite is modified by the ion exchange method and characterized by various analyses involving FT-IR spectroscopy, and XPS and BET analyses. The ortho/para ratio of mononitration products is improved from 0.70 to 2.39 in the presence of the catalyst. Based on density functional theory (DFT), the active sites of nitration reaction are calculated by combining the electrostatic potential with the average local ionization energy, which are further support the electrophilic substitution mechanism of azobenzene in the catalytic nitration reaction. [ABSTRACT FROM AUTHOR]

We have studied the performance characteristics of a dye-doped cholesteric liquid crystal (CLC) laser as a function of the sample thickness. The study has been carried out both from the experimental and theoretical points of view. The theoretical model is based on the kinetic equations for the population of the excited states of the dye and for the power of light generated within the laser cavity. From the equations, the threshold pump radiation energy Eth and the slope efficiency η are numerically calculated. Eth is rather insensitive to thickness changes, except for small thicknesses. In comparison, g shows a much more pronounced variation, exhibiting a maximum that determines the sample thickness for optimum laser performance. The predictions are in good accordance with the experimental results. Approximate analytical expressions for Eth and η as a function of the physical characteristics of the CLC laser are also proposed. These expressions present an excellent agreement with the numerical calculations. Finally, we comment on the general features of CLC layer and dye that lead to the best laser performance. [ABSTRACT FROM AUTHOR]

We report electronic stopping cross section measurements for 4He in Ru. For this, 120 nm Ru is deposited on a silicon substrate, and the stopping cross section is obtained from the analysis of Rutherford backscattering (RBS) spectra. The results are compared with SRIM-2010 predictions, and a new parametrization for the energy dependence of the stopping cross section is proposed. [ABSTRACT FROM AUTHOR]

• Various azole rings were linked to the core scaffold of Biginelli dihydropyrimidines (DHPMs). • DHPM-azole hybrids were tested for their α-glucosidase inhibitory and antimicrobial activities. • DHMPs carrying pyrazole and triazole rings were found to be efficient α-glucosidase inhibitors with concurrent antimicrobial activity. • DFTB and DFT calculations identified the lowest energy conformations and local reactivity properties. • MD simulations were utilized to determine the reactivity with water and to identify suitable excipients. In the current study, we designed three novel compounds by merging two valuable nitrogen-containing pharmacophores, namely dihydropyrimidine (DHPM) and azole, within a single molecule. To obtain the target molecules, azole-linked benzaldehydes were initially synthesized via nucleophilic aromatic substitution reaction between 4-fluorobenzaldehyde and pyrazole, imidazole, or 1,2,4-triazole. Afterward, Biginelli reaction was applied to yield azole-carrying DHPMs. Following structural confirmation, the obtained compounds were tested for their alpha (α)-glucosidase inhibitory and antimicrobial activities. According to the biological data, DHPM-P and DHPM-T showed strong inhibition values whereas DHPM-I failed to effectively inhibit the α-glucosidase enzyme. This situation was explained by molecular docking studies of all compounds into the binding site of alpha-glucosidase. The title compounds also presented moderate antibacterial and antifungal activities. Computational methods based on density functional tight binding (DFTB) and density functional theory (DFT) calculations, along with molecular dynamics (MD) simulations were used to analyze the reactive properties of the compounds. A combination of DFTB and DFT calculations was applied to obtain the lowest energy conformations of the molecules. Further computational analysis included calculations of local reactivity descriptors, such as molecular electrostatic potential and average local ionization energy, by applying DFT calculations. DFT calculations were also used to study intramolecular non-covalent interactions. MD simulations were employed to understand how the title molecules behave in water and to obtain their solubility parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

We study energy loss spectra of bromine ions scattered from silver thin films in the energy range of 4 to 36 MeV in forward reflection geometry. The different contributions to the energy loss are analyzed by complementary Monte Carlo simulations. We assess the dependence of the scattering yield and nuclear and electronic losses on the penetration depth of detected ions. For scattering from larger depth, we observe decreased elastic losses and increased trajectory length in comparison with predictions from single scattering, with increasing effects for lower energies. To investigate the entanglement of energy loss and depth information, electronic stopping cross sections are deduced from the experimental spectra by two different approaches: (a) assuming a single scattering model and (b) making use of Monte Carlo simulations. The data obtained from the two approaches are compared, and we assess the relative contributions from nuclear stopping and from the effect of multiple scattering on trajectory length. Results of both methods are discussed in the context of composition depth profiling and compared with data from literature and with Stopping and Range of Ions in Matter (SRIM) predictions resulting in good agreement. [ABSTRACT FROM AUTHOR]

Electronic stopping cross section of tungsten for light ions was experimentally measured in a wide energy interval (20 to 6000 keV for protons and 50 to 9000 keV for helium) in backscattering and transmission geometries. The measurements were carried out in three laboratories (Austria, Germany and Sweden) using five different set-ups, the stopping data deduced from different data sets showed excellent agreement amongst each other, with total uncertainty varying within 1.5–3.8% for protons and 2.2–5.5% for helium, averaged over the respective energy range of each data set. The final data is compared to available data and to widely adopted semi-empirical and theoretical approaches, and found to be in good agreement with most adopted models at energies around and above the stopping maximum. Most importantly, our results extend the energy regime towards lower energies, and are thus of high technological relevance, e.g., in fusion research. At these low energies, our findings also revealed that tungsten – featured with fully and partially occupied f- and d-subshells, respectively – can be modeled as an electron gas for the energy loss process. [ABSTRACT FROM AUTHOR]

Atoms subjected to extreme environmental conditions are of fundamental importance due to the modification of their electronic properties. In this work, we study the helium atom when immersed in a plasma environment. In order to describe the plasma medium, we use two models when solving the Schrödinger equation in a restricted Hartree–Fock approach: the Debye–Hückel screened (DHS) potential and a more general exponential-cosine screened Coulomb (ECSC) potential. The plasma length parameter, λ , in both model potentials characterizes the plasma screening effects which cause an increase or decrease in the electronic properties of the helium atom. We report results for the total electronic ground state energy, orbital energy, dipole oscillator strengths, generalized oscillator strengths (GOS), mean excitation energy, electrostatic dipole polarizability, and electronic stopping cross section. We find that the ECSC plasma model produces a less bound system than the DHS plasma model at the same value of the screening length, λ . However, the ECSC model potential has a stronger dipole transition from the 1s to the 2p and 3p states than the DHS model potential. Also, the ECSC potential predicts a higher static dipole polarizability than the DHS model potential, with a consequent lower mean excitation energy. We also find a larger GOS for the ECSC than for the DHS for the same momentum transfer at the same value of the screening length, λ . Consequently, the ECSC mode potential produces a larger electronic stopping cross section than the DHS for the same λ and projectile velocity. In the limit of λ → ∞ , we have excellent agreement with the free helium properties. These quantitative values for the electronic properties would be useful for the investigations of the atomic structure and collisions of helium atoms immersed in plasmas. [ABSTRACT FROM AUTHOR]

In this work, we present a study of hydrogen atoms interacting with hydrogen, nitrogen, and oxygen molecules in the gas phase in order to determine the projectile energy loss, the stopping cross section, and energy deposition with implication in hydrogen and proton dosimetry and radiotherapy. Our calculations are performed with a density-functional tight-binding (DFTB) as well as by an ab initio electron-nuclear dynamic (END). The H atoms have a low collision energy in the range of 1–100 eV for the DFTB and 1–1000 eV for the END. We decompose the projectile energy deposition into its electronic, nuclear, rotational, and vibrational energy target contributions. We find that for low collisions energy, DFTB and END are in fair agreement when comparing the nuclear and rotational contributions. However, we find discrepancies for the vibrational and electronic energy loss between both approaches. The largest discrepancy is found in the electronic energy loss as DFTB carries the electronic dynamics in the ground state. We confirm that the electronic stopping cross section is proportional to the projectile velocity as obtained by END showing a threshold effect and that it is underestimated by codes like SRIM. Our study shows that at low collision energies a quantum-classical molecular dynamics approach as DFTB can be used to determine the energy-loss process of a projectile penetrating a material target. Finally, we compare our results to available experimental data finding good agreement when extrapolated to high collision energies. [ABSTRACT FROM AUTHOR]

We report on the calculations of kinetic energy distribution (KED) functions of multiply charged, high-energy ions in Coulomb explosion (CE) of an assembly of elemental Xen clusters (average size = 200-2171) driven by ultra-intense, near-infrared, Gaussian laser fields (peak intensities 1015 - 4 × 1016 W cm-2, pulse lengths 65-230 fs). In this cluster size and pulse parameter domain, outer ionization is incomplete/vertical, incomplete/nonvertical, or complete/nonvertical, with CE occurring in the presence of nanoplasma electrons. The KEDs were obtained from double averaging of single-trajectory molecular dynamics simulation ion kinetic energies. The KEDs were doubly averaged over a log-normal cluster size distribution and over the laser intensity distribution of a spatial Gaussian beam, which constitutes either a two-dimensional (2D) or a three-dimensional (3D) profile, with the 3D profile (when the cluster beam radius is larger than the Rayleigh length) usually being experimentally realized. The general features of the doubly averaged KEDs manifest the smearing out of the structure corresponding to the distribution of ion charges, a marked increase of the KEDs at very low energies due to the contribution from the persistent nanoplasma, a distortion of the KEDs and of the average energies toward lower energy values, and the appearance of long low-intensity high-energy tails caused by the admixture of contributions from large clusters by size averaging. The doubly averaged simulation results account reasonably well (within 30%) for the experimental data for the cluster-size dependence of the CE energetics and for its dependence on the laser pulse parameters, as well as for the anisotropy in the angular distribution of the energies of the Xeq+ ions. Possible applications of this computational study include a control of the ion kinetic energies by the choice of the laser intensity profile (2D/3D) in the laser-cluster interaction volume. [ABSTRACT FROM AUTHOR]

Dissociation of CH4+ ions at 1000 eV induced by collision with Ar atoms was investigated by measuring the kinetic energies of the ionized fragments. At small scattering angles, including zero, H+, H2+, H3+, CH3+, CH2+, CH+, and C+ fragments were observed. The attractive part of the potential in the CH4+-Ar collision system played an important role in the formation of the ionized fragments. Rainbow scattering, leading to a large scattering cross section, was shown to be responsible for the increased formation of H3+. It is proposed that on collision-induced dissociation of CH4+, its three hydrogen atoms, which form a triangle, simultaneously react and move together to form H3+. [ABSTRACT FROM AUTHOR]

We have theoretically studied important dynamic processes involved in zero electron kinetic energy (ZEKE) spectroscopy using the density matrix method with the inverse Born-Oppenheimer approximation basis sets. In ZEKE spectroscopy, the ZEKE Rydberg states are populated by laser excitation (either a one- or two-photon process), which is followed by autoionizations and l-mixing due to a stray field. The discrimination field is then applied to ionize loosely bound electrons in the ZEKE states. This is followed by using the extraction field to extract electrons from the ZEKE levels which have a strength comparable to that of the extraction field. These extracted electrons are measured for the relative intensities of the ion states under investigation. The spectral positions are determined by the applied laser wavelength and modified by the extraction electric field. In this paper, all of these processes are conducted within the context of the density matrix method. The density matrix method can provide not only the dynamics of system's population and coherence (or phase) but also the rate constants of the processes involved in the ZEKE spectroscopy. Numerical examples are given to demonstrate the theoretical treatments. [ABSTRACT FROM AUTHOR]

Ultrafast photodynamics of furan has been studied by time-resolved photoelectron imaging (TRPEI) spectroscopy with an unprecedented time resolution of 22 fs. The simulation of the time-dependent photoelectron kinetic energy distribution (PKED) has been performed with ab initio nonadiabatic dynamics 'on the fly' in the frame of time-dependent density functional theory. Based on the agreement between experimental and theoretical time-dependent photoelectron signal intensity as well as on PKED, precise time scales of ultrafast internal conversion from S2 over S1 to the ground state S0 of furan have been revealed for the first time. Upon initial excitation of the S2 state which has π-π* character, a nonadiabatic transition to the S1 state occurs within 10 fs. Subsequent dynamics invokes the excitation of the C-O stretching and C-O-C out of plane vibrations which lead to the internal conversion to the ground state after 60 fs. Thus, we demonstrate that the TRPEI combined with high level nonadiabatic dynamics calculations provide fundamental insight into ultrafast photodynamics of chemically and biologically relevant chromophores. [ABSTRACT FROM AUTHOR]

Resolved sets of photoproducts arising from the photodissociation of axial and equatorial conformers of 3-pyrroline have been observed using H(Rydberg) atom photofragment translational spectroscopy following excitation in the wavelength range of 250-213 nm. 3-pyrroline (alternatively 2,5-dihydropyrrole) is a five membered partially saturated heterocycle in which the bonding around the N atom is pyramidal (sp3 hybridized) and the N-H bond can lie either axial or equatorial to the ring. Careful analysis of total kinetic energy release data derived from H atom time-of-flight measurements reveals excitation of the 3-pyrrolinyl cofragment consistent with N-H bond fission in both the axial and equatorial conformers. This allows determination of the energy difference between the ground state conformers to be 340±50 cm-1 and the N-H bond strength for axial and equatorial conformers as 31 610±50 and 31 270±50 cm-1, respectively. [ABSTRACT FROM AUTHOR]

Two different components of tunneling current in the TiN/HfSiOxN/SiO2/p-Si(100) metal-oxide-semiconductor capacitor have been presented. The tunneling currents were calculated by taking into account a longitudinal-transverse kinetic energy coupling. The calculated tunneling currents were compared with that measured ones by employing the electron and hole effective masses and phase velocities as fitting parameters. It has been shown that hole tunneling currents dominate at low voltages whereas at high voltages the tunneling currents are mainly contributed by electrons. It has also been found that the effective mass of hole in the HfSiOxN layer is higher than that of electron. The gate electron and substrate hole velocities are 1×105 m/s independent of the HfSiOxN thickness. In addition, it is speculated that the electron and hole effective masses in the HfSiOxN layer perhaps increase as its thickness decreases. [ABSTRACT FROM AUTHOR]

We describe an embedded density functional theory (DFT) protocol in which the nonadditive kinetic energy component of the embedding potential is treated exactly. At each iteration of the Kohn–Sham equations for constrained electron density, the Zhao–Morrison–Parr constrained search method for constructing Kohn–Sham orbitals is combined with the King-Handy expression for the exact kinetic potential. We use this formally exact embedding protocol to calculate ionization energies for a series of three- and four-electron atomic systems, and the results are compared to embedded DFT calculations that utilize the Thomas–Fermi (TF) and the Thomas–Fermi–von Weisacker approximations to the kinetic energy functional. These calculations illustrate the expected breakdown due to the TF approximation for the nonadditive kinetic potential, with errors of 30%–80% in the calculated ionization energies; by contrast, the exact protocol is found to be accurate and stable. To significantly improve the convergence of the new protocol, we introduce a density-based switching function to map between the exact nonadditive kinetic potential and the TF approximation in the region of the nuclear cusp, and we demonstrate that this approximation has little effect on the accuracy of the calculated ionization energies. Finally, we describe possible extensions of the exact protocol to perform accurate embedded DFT calculations in large systems with strongly overlapping subsystem densities. [ABSTRACT FROM AUTHOR]

We calculated the kinetic energies of the H-atom in ice Ih between 5 and 269 K and in water in the range 293–673 K. To do so we used the literature optical vibration frequencies of ice and water of the different phases assuming the harmonic approximation and decoupling between the degrees of freedom of translation, rotation (libration), and internal vibrations. Apart for ice at 269 K, good agreement was obtained with published experimental values for both cases. Similar agreement with experiment was found for the case of water confined in 14 Å diameter carbon nanotubes at 268 K. However, serious deviations from measured values were found in nanotube water in the range 5–230 K. Possible reasons for those deviations are discussed. [ABSTRACT FROM AUTHOR]

Rotationally resolved spectra for Be2+ have been recorded using the pulsed-field ionization zero kinetic energy photoelectron technique. Vibrational levels in the range v+=0–6 were observed. The rotational selection rules confirmed that the ground state is 2Σu+, resulting from the removal of an electron from the σu antibonding orbital of Be2. The bond energy and equilibrium distance for Be2+ were found to be De+=16 438(5) cm-1 and Re+=2.211(8) Å. The ionization energy for Be2 [59 824(2) cm-1] was also refined by these measurements. Comparisons with high-level theoretical results indicate that the bonding in Be2+ is adequately described by multi reference singles and doubles configuration interaction (MRDCI) calculations that employ moderate to large scale basis sets. [ABSTRACT FROM AUTHOR]

Rotationally resolved spectra for Be2+ have been recorded using the pulsed-field ionization zero kinetic energy photoelectron technique. Vibrational levels in the range v+=0–6 were observed. The rotational selection rules confirmed that the ground state is 2Σu+, resulting from the removal of an electron from the σu antibonding orbital of Be2. The bond energy and equilibrium distance for Be2+ were found to be De+=16 438(5) cm-1 and Re+=2.211(8) Å. The ionization energy for Be2 [59 824(2) cm-1] was also refined by these measurements. Comparisons with high-level theoretical results indicate that the bonding in Be2+ is adequately described by multi reference singles and doubles configuration interaction (MRDCI) calculations that employ moderate to large scale basis sets. [ABSTRACT FROM AUTHOR]

An alternative balance equation for the kinetic energy density used in the kinetic variational theory (KVT) is proposed. The new equation is consistent with the well-known standard form interpreted in terms of a flux and a source for both a one-component fluid and a mixture. Within the proposed version, the KVT mean-field collision term produces contributions to the heat flux and the source of kinetic energy being absent in the original formulation. It is shown that the introduced modification can affect the KVT thermal conductivity of the mixture while for the one-component fluid it becomes important only in the second and higher orders in gradients. [ABSTRACT FROM AUTHOR]

We have investigated multiple ionization of N2 and O2 molecules by 52 nm extreme-ultraviolet light pulses at the free-electron laser facility SCSS in Japan. Coulomb break-up of parent ions with charge states up to 5+ is found by the ion-ion coincidence technique. The charge-state dependence of kinetic energy release distributions suggests that the electrons are emitted sequentially in competition with the elongation of the bond length. [ABSTRACT FROM AUTHOR]

The formation of soot begins with the nucleation of nanoparticles, a process difficult to model due to the complexity of the constituent particles. Fullerenes have characteristics resembling the particles found in soot, but their simpler structure makes simulations more tractable. We propose that the nucleation of fullerenes may serve as a window to the formation of soot nuclei. Using molecular dynamics simulations, we analyze the nucleation rates of homomolecular systems of C60, C80, C180, and C240 fullerenes as function of temperature and molecular mass. For temperatures lower than 1000 K, the four systems show similar characteristics, with significant nucleation rates, due to the low energy that favors binding. At higher temperatures, the high kinetic energy limits the binding probability between fullerenes, and molecular clusters are only detected in systems composed of C180 and C240. The analysis shows that particles with molecular masses between those of C80 and C180 could be critical for the transition from monomers to clusters. The computational findings are then related to experimental data of combustion-generated particles present in the literature to assess the feasibility of a physical nucleation pathway in high temperature regimes. The results obtained using molecular dynamics simulations highlight the importance of a physical nucleation pathway to describe the formation of molecular clusters when the particle concentration exceeds a critical value. These results represent the first step toward a more complete description of nanoparticle formation and soot nucleation in high temperature regimes. [ABSTRACT FROM AUTHOR]