Shell Structure Effects Research Articles

Systematic investigation of low-lying dipole modes using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory

Systematic investigations of the electric dipole $(E1)$ modes of excitation are performed using the canonical-basis time-dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) theory. The Cb-TDHFB is able to describe dynamical pairing correlations in excited states of nuclear systems. We apply the method to the real-time calculation of linear response in even-even nuclei with Skyrme functionals. Effects of shell structure, neutron skin, deformation, and neutron chemical potential (separation energy) are studied in a systematic way. This reveals a number of characteristic features of the low-energy $E1$ modes. We also find a universal behavior in the low-energy $E1$ modes for heavy neutron-rich isotopes, which suggests the emergence of decoupled $E1$ peaks beyond $N=82$.

Development of bi-stable and millimeter-scale displacement actuator using snap-through effect for reciprocating control fins

A new two-step amplifying mechanism combining a lever-arm with flexure hinges and a pre-curved thin shell structure is proposed to make a millimeter-scale linear actuator. A large amplification ratio can be obtained by the snap-through effect of a post-buckled shell structure without losing actuation force. The snap-through phenomenon of pre-curved thin-plate are numerically analyzed by using the finite-element software ABAQUS to specify the trigger force and displacement required to initiate the snap-through. The analytic results are in good agreement with the test results for the pre-curved shell structure. The trigger force and displacement for snap-through are supplied by the lever-arm with the piezo stack actuator. Amplification ratio of the lever-arm is drastically changed according to the external load. The lever-arm mechanism is designed to have enough actuation force and displacement to satisfy requirements such as trigger force and displacement of the bi-stable structure. The components of the designed actuators are manufactured and integrated. The designed two-step amplified actuator is experimentally validated to operate with an 8 mm stroke and 2 Hz bandwidth.

Switch from short-axis to intermediate-axis rotation in138Nd

It is pointed out that the triaxial bands in ${}^{138\ensuremath{-}140}$Nd and in the Lu/Er nuclei can be understood from the same shell structure effects. Two of the bands in ${}^{138}$Nd, interpreted as signature partners, exhibit a crossing at high spins with a signature splitting which is strongly reduced above the crossing. This behavior is unique among the yrast and close-to-yrast configurations, revealing the mechanism which induces a change of the rotation axis from short to intermediate in the triaxially deformed nucleus.

Partial ionization in dense plasmas: Comparisons among average-atom density functional models

Nuclei interacting with electrons in dense plasmas acquire electronic bound states, modify continuum states, generate resonances and hopping electron states, and generate short-range ionic order. The mean ionization state (MIS), i.e, the mean charge Z of an average ion in such plasmas, is a valuable concept: Pseudopotentials, pair-distribution functions, equations of state, transport properties, energy-relaxation rates, opacity, radiative processes, etc., can all be formulated using the MIS of the plasma more concisely than with an all-electron description. However, the MIS does not have a unique definition and is used and defined differently in different statistical models of plasmas. Here, using the MIS formulations of several average-atom models based on density functional theory, we compare numerical results for Be, Al, and Cu plasmas for conditions inclusive of incomplete atomic ionization and partial electron degeneracy. By contrasting modern orbital-based models with orbital-free Thomas-Fermi models, we quantify the effects of shell structure, continuum resonances, the role of exchange and correlation, and the effects of different choices of the fundamental cell and boundary conditions. Finally, the role of the MIS in plasma applications is illustrated in the context of x-ray Thomson scattering in warm dense matter.

Understanding Thomas-Fermi-Like approximations: Averaging over oscillating occupied orbitals

The Thomas-Fermi equation arises from the earliest density functional approximation for the ground-state energy of a many-electron system. Its solutions have been carefully studied by mathematicians, including J.A. Goldstein. Here we will review the approximation and its validity conditions from a physics perspective, explaining why the theory correctly describes the core electrons of an atom but fails to bind atoms to form molecules and solids. The valence electrons are poorly described in Thomas-Fermi theory, for two reasons: (1) This theory neglects the exchange-correlation energy, ``nature's glue'. (2) It also makes a local density approximation for the kinetic energy, which neglects important shell-structure effects in the exact kinetic energy that are responsible for the structure of the periodic table of the elements. Finally, we present a tentative explanation for the fact that the shell-structure effects are relatively unimportant for the exact exchange energy, which can thus be more usefully described by a local density or semilocal approximation (as in the popular Kohn-Sham theory): The exact exchange energy from the occupied Kohn-Sham orbitals has an extra sum over orbital labels and an extra integration over space, in comparison to the kinetic energy, and thus averages out more of the atomic individuality of the orbital oscillations.

A comparative study of statistical models for nuclear equation of state of stellar matter

We compare three different statistical models for the equation of state (EOS) of stellar matter at subnuclear densities and temperatures (0.5–10 MeV) expected to occur during the collapse of massive stars and supernova explosions. The models introduce the distributions of various nuclear species in nuclear statistical equilibrium, but use somewhat different nuclear physics inputs. It is demonstrated that the basic thermodynamical quantities of stellar matter under these conditions are similar, except in the region of high densities and low temperatures. We demonstrate that mass and isotopic distributions have considerable differences related to the different assumptions of the models on properties of nuclei at these stellar conditions. Overall, the three models give similar trends, but the details reflect the uncertainties related to the modeling of medium effects, such as the temperature and density dependence of surface and bulk energies of heavy nuclei, and the nuclear shell structure effects. We discuss importance of new physics inputs for astrophysical calculations from experimental data obtained in intermediate energy heavy-ion collisions, in particular, the similarities of the conditions reached during supernova explosions and multifragmentation reactions.

Well Wrapped Eggs: Effects of Egg Shell Structure on Heat Resistance and Hatchling Mass in the Invasive Land Snail Cornu aspersum

Journal of Experimental Zoology Part A: Ecological Genetics and PhysiologyVolume 319, Issue 2 p. Fm i-Fm i Features Well Wrapped Eggs: Effects of Egg Shell Structure on Heat Resistance and Hatchling Mass in the Invasive Land Snail Cornu aspersum First published: 12 February 2013 https://doi.org/10.1002/jez.1754Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume319, Issue2February 2013Pages Fm i-Fm i RelatedInformation

Double-Shelled Yolk–Shell Microspheres with Fe3O4 Cores and SnO2 Double Shells as High-Performance Microwave Absorbers

Double-shelled yolk–shell microspheres with Fe3O4 cores and SnO2 double shells have been successfully synthesized by combining the versatile sol–gel process and hydrothermal shell-by-shell deposition method. The as-synthesized double-shelled Fe3O4@SnO2 yolk–shell microspheres have uniform size, unique morphology, well-defined shells, favorable magnetization, large specific surface area, and high porosity and exhibit significantly enhanced microwave absorption properties in terms of both the maximum reflection loss value and the absorption bandwidth. The excellent microwave absorption properties of these microspheres may be attributed to the unique double-shelled yolk–shell structure and synergistic effect between the magnetic Fe3O4 cores and dielectric SnO2 shells.

Well Wrapped Eggs: Effects of Egg Shell Structure on Heat Resistance and Hatchling Mass in the Invasive Land Snail Cornu aspersum

In ectotherms, the temperature changes that accompany climate shifts, microhabitat changes, and species range extensions can have profound effects on the performance of organisms. The aim of this laboratory study on the terrestrial invasive gastropod Cornu aspersum was to investigate the effect of dietary calcium source on egg shell structure and heat resistance of eggs in two populations from different climatic regions of France (Western Atlantic and Mediterranean). To date no literature is known about heat stress in calcified ectothermic eggs while exposed to heat peaks using fluctuating thermal regimes and optimal humidity. In snails from the Mediterranean population fed exclusively with CaCO(3) from limestone we found the thinnest egg shells and the smallest hatchlings. Limestone represents the most accessible calcium source for snails, but is, however, responsible for thinner and more mineralized egg shells (higher ash content). Hence thicker egg shells result from a low mineralized mucopolysaccharide-glycoprotein matrix that could play a nutritional role for hatchlings. Exposed to heat peaks, eggs in both populations had lower incubation time variability at the detriment of hatching rate. This study highlights the need for functional studies in this invasive species to understand the effects on population dynamics of interacting biotic and abiotic environmental factors under climate and anthropic habitat changes.

Investigation of the Shell Effect on Neutron Induced Cross Section of Actinides

Investigations has been made concerning the development of the effect of shell structure on neutron induced cross section, evaluations for Actinides elements in the energy range of 0-30 MeV. The EXIFON code, which is based on the analytical model for statistical multistep direct and multistep compound reactions, was used for the calculation of the cross section for (n-2n), (n-p) and (n-α) reaction channels. Results are compared with data from the experimental database, EXFOR from the IAEA nuclear data bank to deduce the shell effect. An empirical relation for the reaction cross section has been established for magic numbers nucleus in the (n-2n) reaction channel in the energy range. Results shows that the odd-even effect has also been observed as the cross section for odd-even nuclei are higher than their neighbouring even-even nuclei and with comparison in term of Shell correction, the cross section is higher when the Shell correction is not considered.

Describing Compton scattering and two-quanta positron annihilation based on Compton profiles: two models suited for the Monte Carlo method

An accurate description of the basic physics processes of Compton scattering and positron annihilation in matter requires the consideration of atomic shell structure effects and, in specific, the momentum distributions of the atomic electrons.Two algorithms which model Compton scattering and two-quanta positron annihilation at rest accounting for shell structure effects are proposed. Two-quanta positron annihilation is a physics process which is of particular importance for applications such as positron emission tomography (PET). Both models use a detailed description of the processes which incorporate consistently Doppler broadening and binding effects. This together with the relatively low level of complexity of the models makes them particularly suited to be employed by fast sampling methods for Monte Carlo particle transport. Momentum distributions of shell electrons are obtained from parametrized one-electron Compton profiles. For conduction electrons, momentum distributions are derived in the framework of a Fermi gas.The Compton scattering model uses an approach which does not employ any free parameter. In contrast, a few semi-empirical approximations are included for the description of the complex physics of electron-positron annihilation resulting in acollinear photons.Comparisons of the Compton scattering model with simpler approaches illustrate the detailed accounting for shell structure effects. A satisfactory agreement is found for comparisons of both newly-developed models with experimental data.

Synthesis and characterization of multilayer core–shell structure hollow spheres with low density, favorable magnetic and conductive properties

Multilayer core–shell structure hollow spheres were synthesized on the basis of hollow glass sphere (HGS) along with magnetic layer and conducting layer. The deposition of ferrite compound was conducted via chemical co-precipitation method onto HGS surface using ammonium acetate stabilizing precursor solution which performed as chemical plating process. The ratio of ammonium acetate: metal ion appeared to be critical when forming ferroferric oxide compounds. Sequentially, in situ chemical oxidative polymerization in H2O/C2H5OH/5-sulfosalicylic acid/pyrrole/FeCl3 system consequently obtained multilayer HGS@Ferrite@Polypyrrole composites. 5-Sulfosalicylic acid-FeCl3 constitutes a doping-initiating chelate which was found to provide good compactness and uniformity resulting in good conductivity. Qualitative characterization proved the core–shell structure and encapsulation effect. Doping amount and organic/inorganic ratio was quantitatively calculated. The HGS@Ferrite@PPy composite has remarkable excellent properties. The magnetization reaches 20.61emu/g as soft magnetic materials, with a hysteresis loop presenting superparamagnetic whose coercivity and remnant magnetization hitting zero. The conductivity was as high as 16.5S/cm much higher than other composites with similar structure. The cavity effect, magnetic loss and conducting loss combined provide this kind of material good electromagnetic wave absorption effect under low addition amount.

New mixed ligand coated platinum nanoparticles for heterogeneous catalytic applications

A series of platinum nanoparticles was prepared for the first time in presence of one hydrophobic ligand and one hydrophilic ligand containing terminal sulfonic acid headgroup. This mixed ligand combination causes stripe-like domains circumscribing the nanoparticles, thereby enhancing the catalytic efficiency compared to single ligand coated Pt nanocatalysts. This could be achieved by strategically replacing the hydrophilic ligand (3-mercaptopropane-1-sulfonic acid or MPSA) with hydrophobic ligands (linear alkanethiols like 1-octanethiol or OT) on the surface of the nanoparticles. Apart from the ligand composition, the metallic core of the nanocomposite also influences the catalytic efficiency of the ligand shell through a synergistic effect. Herein we report the effects of ligand shell composition and structure on the efficiency of the nanocomposites on catalytic acylation reactions. Quite high conversion of benzyl alcohol to benzyl acetate (with >99% selectivity) was observed when acetic acid was used as the acetylating reagent and MPSA–OT–Pt as nanocatalyst at 80°C. The turnover frequency of reaction using MPSA–OT–Pt nanocatalyst was found to be an order of magnitude higher than that using well known solid acid catalyst zeolite USY under identical reaction conditions. Further, the selectivity toward benzyl acetate using USY was ≤80%, the remaining 20% being dibenzylether. It was also found that the MPSA–OT–Pt nanocatalyst system shows higher activity than gold nanoparticles coated with same set of ligands (such as MPSA–OT–Au nanocatalyst). Additionally, the effects of changing the substrate (such as 1-butanol) and the acylating agent (such as propionic acid) were also studied.

Rubber modification of unsaturated polyester resin with core–shell rubber particles: Effect of shell composition

AbstractPoly(butyl acrylate)/poly(vinyl acetate‐co‐methyl methacrylate) PBA/P(VAc‐co‐MMA) core–shell rubber particles with various shell compositions, i.e., VAc/MMA weight ratios, were used to toughen unsaturated polyester. The morphology and surface‐free energy of the rubber particles were determined by transmission electron microscopy (TEM) and contact angle measurements, respectively. The effect of shell structure on the dispersion state of rubber particles inside the unsaturated polyester resin was studied by scanning electron microscopy and TEM. Increasing MMA units in the shell changed the particle dispersion state from small agglomerates or globally well‐dispersed particles to large aggregates in the cured‐resin matrix. For the blends that contain 5 wt% rubber, the highest un‐notched impact toughness, stress‐intensity factor (KIC), and fracture energy (GIC) were observed for the blend containing PVAc shell particles. The results showed that by increasing the particle level from 5 to 10 wt%, the highest KIC and GIC values were obtained for the blend containing rubber particles with VAc/MMA (80/20 wt/wt) copolymer shell. The crack‐tip damage zone in the neat and rubber‐modified unsaturated polyester resins was observed by means of transmission optical microscopy. In addition, using PVAc shell particles exhibited a minimum reduction in the volume shrinkage and tensile properties of the rubber‐modified resin. POLYM. ENG. SCI., 52:1928–1937, 2012. © 2012 Society of Plastics Engineers

Electric Microfield Distributions in Alkali Plasmas with Account of the Ion Structure in a Moderately Coupled Approximation

AbstractThe electric microfield distributions (EMD) have been calculated at the location of an ion for Alkali plasmas (Li+, Na+, K+, Cs+) using a coupling parameter integration technique originally developed by Ortner et al. for point‐like (structureless) ions [1]. EMD are studied in a frame of the Hellmann‐Gurskii‐Krasko (HGK) pseudopotential model, taking into account the quantum‐mechanical effects and the ion shell structure [2]. For determination of the radial distribution function the screened HGK pseudopotential in a moderately coupled approximation, based on a chain of Bogoljubow equations for the equilibrium distribution functions [3], taking into account not only the quantum‐mechanical effects, the ion shell structure but screening field effects has been used [4]. The new expressions for the screened HGK potential have been derived. At the derivation the electron‐electron corrected Kelbg micropotential instead of earlier applied Deutsch potential has been used. The results obtained for the EMDs in the Hellmann‐Gurskii‐Krasko moderately coupled approximation for a moderately coupled plasma in a framework of the Ortner model show a considerable improvement of the results obtained in the Debye screening approximation (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improving detection of foraminifera by cathodoluminescence

Cathodoluminescence (CL) studies of Lower–Middle Oxfordian marls and limestones, as well as clasts from the uppermost Turonian–?Early Coniacian conglomerates of the Cracow Upland (southern Poland), reveal that the CL view of foraminifers from some lithologies differs from that in transmitted light. In particular, the CL technique revealed abundant tests of planktonic species Globuligerina oxfordiana in the Middle Oxfordian glauconitic marls, which under transmitted light are either poorly visible or remain completely undetected. Bright red–orange luminescence characterizes originally hyaline aragonitic tests of G. oxfordiana, but also several calcitic benthic species, in spite of their different taxonomic position and original test structure and mineralogy. In sponge microbial boundstones, foraminifers generally do not show the CL emission, or show a weak luminescence. Similarly, Late Cretaceous foraminifera represented mostly by planktonic taxa were detected or their view was clearly improved under CL only in some clasts from the uppermost Turonian–?Early Coniacian conglomerates filling karstic cavities. In other clasts, foraminifera are clearly visible only under normal transmitted light, therefore the luminescence signature is highly spatially variable. These results indicate a strong influence of lithology and diagenesis and rather minor effects of shell structure on luminescence of microfossils. The CL technique can be a useful tool in the detection and documentation of abundance patterns of foraminifers that are poorly preserved under transmitted light.

Enhancement of anodic oxidation of formic acid on palladium decorated Pt/C catalyst

A palladium decorated Pt/C catalyst, Pt@Pd/C, is prepared by a colloidal approach with a small amount of platinum as core. It is found that the catalyst shows excellent activity towards anodic oxidation of formic acid at room temperature and its activity is 60% higher than that of Pd/C. Decoration of palladium shell on the platinum core is supported by XPS results. Due to the use of platinum as core, active components are dispersed very well and the particle sizes are smaller than those of Pd/C. The cyclic voltammetry measurement clearly shows synthetic electro-oxidation effects of formic acid on Pt@Pd/C. It is speculated that the high performance of Pt@Pd/C may result from the unique core–shell structure and synergistic effect of Pt and Pd at the interface. The preparation method for Pt@Pd/C reported in this work will provide additional options for the design of catalysts for direct formic acid fuel cell (DFAFC).

Effect of shell structure in the fusion reactions

The fusion reactions are studied in the central collisions 82Se$ + $134Ba and 82Se$ + $138Ba by the improved isospin-dependent quantum molecular-dynamics model, where the nucleus 138Ba has a closed neutron shell N = 82 . Comparing the shell correction energies and fusion probabilities of these two reactions with the ones of other asymmetric or more symmetric reaction systems that form the same compound nuclei, we find the dependence of the fusion reaction on the nuclear shell structure of the colliding nuclei. The experimental data of the fusion probabilities are described well by the present model. The result suggests that the neutron shell closure N = 82 promotes fusion.

Electric Microfield Distributions in Alkali Plasmas with Account of the Ion Structure

AbstractThe electric microfield distributions at the location of an ion have been calculated using a coupling parameter integration technique for Alkali plasma (Li+, Na+, K+, Rb+, Cs+) proposed by Ortner et al. [1] and Monte‐Carlo simulations. Electric microfield distributions are studied in a frame of the Hellmann‐Gurskii‐Krasko pseudopotential model, taking into account the quantum‐mechanical effects and the ion shell structure [2]. For determination of the radial distribution function the screened Hellmann‐Gurskii‐Krasko pseudopotential in the Debye approximation taking into account not only the quantum‐mechanical effects, the ion shell structure but screening field effects has been used [3]. For the Hellmann‐Gurskii‐Krasko pseudopotential model the results obtained for the microfield in the framework of the Ortner model are found in a good agreement with the Monte‐Carlo simulations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electric Microfield Distributions in Li + Plasma With Account of the Ion Structure

AbstractThe electric microfield distributions at the location of an ion have been calculated using a coupling parameter integration technique for Li + plasma proposed by Ortner et al. [4] and Molecular Dynamics simulations. Electric microfield distributions are studied in a frame of the Hellmann‐Gurskii‐Krasko pseudopotential model, taking into account the quantum‐mechanical effects and the ion shell structure [34]. The screened Hellmann‐Gurskii‐Krasko pseudopotential taking into account not only the quantum‐mecanical effects, the ion shell structure but screening field effects has been derived by means of Bogoljubow method [40] and [42]. The screened pseudopotential is represented by a Fourier transform. For the Hellmann‐Gurskii‐Krasko pseudopotential model the results obtained for the microfield in the framework of the Ortner model are found in a good agreement with the Molecular Dynamics simulations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)