Radiation-hydrodynamic simulations of directly driven fusion experiments at the Omega Laser Facility predict absorption accurately when targets are driven at low overlapped laser intensity. ...Discrepancies appear at increased intensity, however, with higher-than-expected laser absorption on target. Strong correlations with signatures of the two-plasmon decay (TPD) instability-including half-harmonic and hard-x-ray emission-indicate that TPD is responsible for this anomalous absorption. Scattered light data suggest that up to ≈30% of the laser power reaching quarter-critical density can be absorbed locally when the TPD threshold is exceeded. A scaling of absorption versus TPD threshold parameter was empirically determined and validated using the laser-plasma simulation environment code.
Relative role of intrinsic density‐dependent factors (such as inter‐ and intraspecific competition, predation) and extrinsic density‐independent factors (environmental changes) in population dynamics ...is a key issue in ecology. Density‐dependent mechanisms are considered as important drivers of population dynamics in many vertebrate and insect species; however, their influence on the population dynamics of freshwater invertebrates is not clearly understood. In this study, I examined interannual variations in the abundance of the glacial relict amphipod Monoporeia affinis in a small subarctic lake based on long‐term (2002–2019) monitoring data. The results suggest that the population dynamics of amphipods in the lake is influenced by the combined effects of both intrinsic and extrinsic factors. The reproductive success of amphipod cohorts was inversely related to its initial abundance, indicating it is influenced by density‐dependent factors. M. affinis recruitment was negatively correlated with population density and near‐bottom temperature but positively correlated with food availability, which is defined as the concentration of chlorophyll a. Multiple regression with chlorophyll, temperature, and abundance of parent cohort as independent factors explained about 80% of the variation in the reproductive success of amphipods. The negative correlation between amphipod recruitment and water temperature indicates that the current climate conditions adversely affect the populations of glacial relict amphipods even in cold‐water lakes of the subarctic zone. Results of this study can be useful in environmental assessments to separate population oscillations connected with density‐dependent mechanisms from human‐mediated changes.
Long‐term (2002–2019) variations in the abundance of the glacial relict amphipod Monoporeia affinis in a small subarctic lake were examined. The results suggest that population dynamics of amphipods is influenced by the combined effects of both intrinsic (population density) and extrinsic (water temperature, food availability) factors.
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•Highly dispersed Co NPs on a beta zeolite surface were prepared by ESA.•PdCo bimetallic catalysts with high catalytic dehydrogenation activity were prepared by UGR.•Synergy of PdCo ...intermetallic electron transfer and SMSI improved the catalytic performance.•Pd1Co9/beta exhibited the superior catalytic 12H-NEC dehydrogenation activity.
Research and development of high-performance catalysts is a key technology to realize hydrogen energy storage and transportation based on liquid organic hydrogen carriers. Co/beta was prepared using beta zeolite as a carrier via an electrostatic adsorption (ESA)-chemical reduction method, and it was used as the template and reducing agent to prepare bimetallic catalysts via an ultrasonic assisted galvanic replacement process (UGR). The fabricated PdCo/beta were characterized by TEM, XPS, FT-IR, XRD, H2-TPR, and H2-TPD. It was shown that the ultrafine PdCo nanoparticles (NPs) are evenly distributed on the surface of the beta zeolite. There is electron transfer between metal NPs and strong-metal-support-interaction (SMSI), which results in highly efficient catalytic dodecahydro-N-ethylcarbazole (12H-NEC) dehydrogenation performance of PdCo bimetallic catalysts. The dehydrogenation efficiency reached 100 % in 4 h at 180 °C and 95.3 % in 6 h at 160 °C. The TOF of 146.22 min−1 is 7 times that of Pd/beta. The apparent activation energy of the reaction is 66.6 kJ/mol, which is much lower than that of Pd/beta. Under the action of ultrasonic waves, the galvanic replacement reaction is accelerated, and the intermetal and metal-carrier interactions are enhanced, which improves the catalytic reaction performance.
A combined approach to study cold rarefied matter is introduced that includes a semianalytical method based on the free-energy minimization and ab initio calculations based on the finite-temperature ...density-functional theory. The approach is used to calculate the ionization state of hydrocarbon (CH) under the shock-release conditions in inertial confinement fusion. Furthermore, the dielectric constant of CH is calculated using the Kubo-Greenwood formulation and contribution from atomic polarizabilities is found to be as important as the free-electron contribution. Using the ionization state and dielectric constant, the electron density profile in the rarefaction wave of the shock-release plasma is obtained.
Silica colloidal crystals are face-centered cubic structures comprised of silica spheres with the diameters ranging between tens and hundreds of nanometers. The voids between the spheres form pores, ...which can be probed by nitrogen adsorption porosimetry. Here, we prepared two mesoporous samples and a macroporous reference sample and then measured nitrogen adsorption and desorption isotherms for further characterization. We proposed a straightforward procedure for calculation of the pore-size distribution of silica colloidal crystals from nitrogen adsorption isotherms. The procedure is based on the adsorption integral equation solution with a kernel of theoretical isotherms, consistent with the procedure used for many other porous materials. The solution is carried out using the non-negative least squares (NNLS) regression with Tikhonov regularization. The kernel of mesoporous isotherms is built on the basis of the macroscopic Derjaguin–Broekhoff–de Boer (DBdB) theory of capillary condensation considering the voids as a network of spheres. Application of our procedure for the analysis of the adsorption branches of experimental isotherms resulted in bimodal distributions, where the modes matched well with the sizes of the voids in the colloidal crystals face centered cubic structure: the main mode corresponds to the octahedral voids and the second mode to the tetrahedral voids. Furthermore, we modified the surface of the samples with organics and repeated the characterization procedure for the modified samples. The resulting pore-size distribution for the samples with the modified surface matched the original one quite closely. It demonstrates the procedure as a simple and efficient technique to estimate the pore-size distribution and justifies the spherical shape approximation for the voids in the silica colloidal crystals.
This paper describes the specific features of the formation of an unsupported nickel-tungsten sulfide nanosize catalyst in situ in a hydrocarbon feedstock from oil-soluble precursors—nickel and ...tungsten compounds in the presence of elemental sulfur additive. The catalysts formed at different times of the catalytic experiment (2, 5, 7 and 10 h) were analyzed by transmission electron microscopy and X-ray photoelectron spectroscopy. According to STEM-EDX elemental spectra, the formation of tungsten and nickel sulfides was established, with a further increase in the amount of active Ni-W-S phase on the surface of the crystalline nickel sulfide. It was found that the time of catalyst formation affects its morphology and phase composition. Evaluation of the hydrogenating catalytic activity confirms that an increase in the time of catalyst formation leads to an increase in its activity, which is associated with the peculiarities of the morphology of sulfide particle aggregates as well as an increase in the degree of promotion of tungsten disulfide crystallites by nickel atoms.
Graphical Abstract
The prospects for using dimethyl ether (DME) for enhancing the oil recovery are analyzed. The analysis is based on the results of physical (laboratory) and mathematical modeling of this technology. ...The mechanism of intensifying the oil extraction and enhancing the oil recovery by injecting dimethyl ether into a reservoir is considered. The major factors influencing the distribution ratio of DME between the oil and aqueous phases are evaluated. The advantages of injecting DME into a reservoir prior to injecting hydrocarbon gases and carbon dioxide are revealed. Combined technologies for enhancing the oil recovery, involving injection of DME, carbon dioxide, polymer solutions, and steam into a reservoir are analyzed. The possibility of using DME for separation of oily sludges is briefly discussed.
The specific features are presented of the two-stage synthesis of structured microsystems based on zinc-oxide nanorods by ultrasonic spray pyrolysis and the low-temperature hydrothermal method, with ...nucleation suppressed in the bulk of the solution. It is shown that the use of two-stage synthesis provides control over the size and aspect ratio of separate nanorods and over the structure of the microsystem of nanorods as a whole. It is proposed to monitor the concentration of intrinsic surface defects by measuring the photocurrent under irradiation through narrow-band interference light filters.
The linear stability of multiple coherent laser beams with respect to two-plasmon-decay instability in an inhomogeneous plasma in three dimensions has been determined. Cooperation between beams leads ...to absolute instability of long-wavelength decays, while shorter-wavelength shared waves are shown to saturate convectively. The multibeam, in its absolutely unstable form, has the lowest threshold for most cases considered. Nonlinear calculations using a three-dimensional extended Zakharov model show that Langmuir turbulence created by the absolute instability modifies the convective saturation of the shorter-wavelength modes, which are seen to dominate at late times.
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