Full Shells Research Articles

Structure and size of complete hydration shells of metal ions and inorganic anions in aqueous solution.

The structures of nine hydrated metal ions in aqueous solution have been redetermined by large angle X-ray scattering to obtain experimental data of better quality than those reported 40-50 years ago. Accurate M-OI and M-(OI-H)⋯OII distances and M-OI(H)⋯OII bond angles are reported for the hydrated magnesium(II), aluminium(III), manganese(II), iron(II), iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions; the subscripts I and II denote oxygen atoms in the first and second hydration sphere, respectively. Reported structures of hydrated metal ions in aqueous solution are summarized and evaluated with emphasis on a possible relationship between M-OI-OII bond angles and bonding character. Metal ions with high charge density have M-OI-OII bond angles close to 120°, indicative of a mainly electrostatic interaction with the oxygen atom in the water molecule in the first hydration shell. Metal ions forming bonds with a significant covalent contribution, as e.g. mercury(II) and tin(II), have M-OI-OII bond angles close to 109.5°. This implies that they bind to one of the free electron pairs in the water molecule. Comparison of M-O bond distances of hydrated metal ions in the solid state with one hydration shell, and in aqueous solution with in most cases at least two hydration shells, shows no significant differences. On the other hand, the X-O bond distance in hydrated oxoanions increases by ca. 0.02 Å in aqueous solution in comparison with the corresponding X-O distance in the solid state. A linear correlation is observed between volume, calculated from the van der Waals radius of the hydrated ion, and the ionic diffusion coefficient in aqueous solution. This correlation strongly indicates that monovalent metal ions, except lithium and silver(I), and singly-charged monovalent oxoanions have a single hydration shell. Divalent metal ions, bismuth(III) and the lanthanoid(III) and actinoid(III) ions have two hydration shells. Trivalent transition and tetravalent metal ions have two full hydration shells and portion of a third one. Doubly charged oxoanions have one well-defined hydration shell and an ill-defined second one.

Shell-Model Study of Nuclear Weak Rates relevant to Astrophysical Processes in Stars

New shell-model Hamiltonians which can successfully describe spin responses in nuclei are used to evaluate nuclear weak rates in stellar environments. The e-capture and β-decay rates for the nuclear pair with 31Mg-31Al, in the island of inversion, which have been pointed out to be important for the cooling of neutron star crusts, are studied by shell-model calculations with the effective interaction in sd-pf shell obtained by the extended Kuo-Krenciglowa (EKK) method. The weak rates induced by the Gamow-Teller transitions between the low-lying states in the nuclear pair lead to a nuclear Urca process. The spin-dipole strengths and e-capture rates for 78Ni are evaluated by shell-model with full pf-sdg shells including up to 5p-5h excitations outside filling configurations of 78Ni. The e-capture rates obtained are compared with RPA calculations and the effective rate formula. Weak rates for the second-forbidden transition in 20Ne are evaluated by the multipole expansion method of Walecka as well as the Behrens-Bühring method within sd-shell. Difference in the rates between the two methods is found to be rather small as far as the conserved-vector-current (CVC) relation is satisfied. Possible important contributions of the forbidden transition to the heating of the ONeMg core by double e-captures on 20Ne in a late stage of the evolution of the core and implications on the final fate of the core, whether core-collapse or thermonuclear explosion, are discussed.

Review of noble-gas spin amplification via the spin-exchange collisions

Due to isolation from the environment with the protection of the full electronic shells, nuclear spins of noble gas typically feature extraordinary long coherence times, high polarization and good chemical inertness, which makes themselves attractive in extensive scientific applications. Recently, the noble-gas spin amplification via the spin-exchange collisions between overlapping noble-gas spins and alkali-atom spins has been theoretically and experimentally demonstrated in various quantum techniques including maser, Floquet maser, spin-based amplifier, and Floquet spin amplifier. The noble-gas spin amplification can enhance the external oscillating magnetic field by a factor of more than 100 and realize ultrasensitive magnetometry, which is important for the detection of weak electromagnetic fields and hypothetical particles. Based on the spin amplification, experiments have been conducted to search for axion-like dark matter and exotic spin-dependent forces and new constraints have been established. This review summarizes the recent progress on noble-gas spin amplification, including the basic principles, methods, different types, the related applications ranging from magnetic-field sensing to searches for new physics, and prospects for further improvements.

On the Optimal Design of Steel Shells with Technological Constraints

This paper is concerned with determining the optimum conditions of steel cylindrical shells with technological limitations and one behavioral constraint, related to a specific constitutive law for limiting load-carrying capacity. The optimum structural design in the plastic range of circular cylindrical full shells composed of rings of variable thickness is given. A numerical procedure for determining the optimal dimensions of shell rings is given. A shell collapse mechanism is assumed in the kinematic part, which satisfies requirements. Within the optimum conditions, the power of the dissipation energy of rings assuming the hexagon Hodge condition of plasticity are derived. A series of numerical solutions and results of optimal structural designs for a shell that is simply supported at the ends are presented. In one example of optimally calculated shells, the length X1 of one ring was varied.

Anionic character of the conduction band of sodium chloride

The alkali halides are ionic compounds. Each alkali atom donates an electron to a halogen atom, leading to ions with full shells. The valence band is mainly located on halogen atoms, while, in a traditional picture, the conduction band is mainly located on alkali atoms. Scanning tunnelling microscopy of NaCl at 4 K actually shows that the conduction band is located on Cl− because the strong Madelung potential reverses the order of the Na+ 3s and Cl− 4s levels. We verify this reversal is true for both atomically thin and bulk NaCl, and discuss implications for II-VI and I-VII compounds.

Determining Partial Atomic Charges for Liquid Water: Assessing Electronic Structure and Charge Models.

Partial atomic charges provide an intuitive and efficient way to describe the charge distribution and the resulting intermolecular electrostatic interactions in liquid water. Many charge models exist and it is unclear which model provides the best assignment of partial atomic charges in response to the local molecular environment. In this work, we systematically scrutinize various electronic structure methods and charge models (Mulliken, natural population analysis, CHelpG, RESP, Hirshfeld, Iterative Hirshfeld, and Bader) by evaluating their performance in predicting the dipole moments of isolated water, water clusters, and liquid water as well as charge transfer in the water dimer and liquid water. Although none of the seven charge models is capable of fully capturing the dipole moment increase from isolated water (1.85 D) to liquid water (about 2.9 D), the Iterative Hirshfeld method performs best for liquid water, reproducing its experimental average molecular dipole moment, yielding a reasonable amount of intermolecular charge transfer, and showing modest sensitivity to the local water environment. The performance of the charge model is dependent on the choice of the density functional and the quantum treatment of the environment. The computed molecular dipole moment of water generally increases with the percentage of the exact Hartree-Fock exchange in the functional, whereas the amount of charge transfer between molecules decreases. For liquid water, including two full solvation shells of surrounding water molecules (within about 5.5 Å of the central water) in the quantum chemical calculation converges the charges of the central water molecule. Our final pragmatic quantum chemical charge-assigning protocol for liquid water is the Iterative Hirshfeld method with M06-HF/aug-cc-pVDZ and a quantum region cutoff radius of 5.5 Å.

Ni-Ti supermirror coated onto a curved substrate for nested neutron-focusing optics

Low neutron intensity is a critical problem for neutron scattering measurements at compact sources Among various other methods, reflection-based neutron-focusing devices have been developed to increase the neutron flux on samples. In this study, we utilized nested neutron-focusing optics to converge a neutron beam with large divergence. These optics consisted of nested full conical shells that were assembled from supermirror-coated thin glass sheets with an initially cylindrical form. Specifically, an optimized m = 2 Ni/Ti supermirror coating was applied to the concave sides of cylindrical thin glass substrates utilizing a dedicated DC magnetron sputtering system. A particle collimation system was also incorporated into the deposition process to achieve excellent thickness uniformity for the supermirror coating. As a result, the characterized thickness variation was within 2% on the inner sides of the curved substrates. The internal stress of the supermirror coating was effectively reduced to approximately -135 MPa under a 0.4 Pa working gas pressure. The supermirror coating provided a reflectivity of over 78% with a momentum transfer Q ranging from 0.1 to 0.45 nm−1. Consequently, the neutron flux collected by the focusing optics was enhanced by a factor of 26 compared to a conventional pinhole design according to our experimental results.

Controlling the Degree of Coverage of the Pt Shell in Pd@Pt Core–Shell Nanocubes for Methanol Oxidation Reaction

The synthesis of Pd@Pt core–shell nanocubes was achieved through a direct seed-mediated growth method. This process represents a simple and cost-effective way to produce core–shell nanocubes. The morphology of the Pd@Pt core–shell nanocubes varied from simple cubic to concave cubic, depending on the reducing agent and the Pt content. The selection of the reducing agent is important because the reduction rate is directly related to the shell growth. The catalytic activity and stability of the Pd@Pt core–shell nanocubes in the methanol oxidation reaction were different for the nanocubes with partial and full Pt shells.

Realization of valley polarization in monolayer WS2 via 3d transition metal atom adsorption

The great challenge in the development of valleytronics is the ability to induce and manipulate permanent valley polarization in an efficient way, which is crucial for theoretical and practical implications of valley-related physics and devices. Here, using first-principles calculation, valley polarization can be induced and controlled in a WS2 monolayer by adsorbing a 3d transition metal (TM, Sc–Zn) atom. Most 3d TM atoms have large adsorption energy, except for those with half-filled d5 and full d10 shells. With the introduction of the 3d TM atom, the system generates a local out-of-plane magnetic moment at the position of the 3d TM atom, forming an effective out-of-plane Zeeman effect. Meanwhile, the redistributed surface charges form an asymmetric electric field and imbalanced charge distribution in the K and K′ valleys. The lack of time inversion symmetry and the broken space inversion symmetry further enhance the spin–orbit coupling (SOC) interaction. A remarkable spin–orbit splitting and valley splitting occur in the K and K′ valleys in the conduction band minimum. The valley degeneracy is lifted by the effective out-of-plane Zeeman field originating from the TM adatom, which generates a permanent valley polarization. This is also expected for other honeycomb materials with strong SOC and absence of inversion symmetry.

Why are trace amounts of chloride so highly surface-active?

On many metals, small quantities of chloride are known to be adsorbed at potentials well below the potential of zero charge and to influence other electrochemical processes. In order to understand this behavior, we have investigated the adsorption of a single Cl− ion from aqueous solution by a combination of density functional theory and classical molecular dynamics, taking Au(111) as a model surface. While in the vacuum, Cl is adsorbed directly on the surface in the 3-fold hollow sites, whereas in aqueous solution, the optimal position lies a fraction of an Ångstrom towards the solution, where the ion is almost fully solvated and mobile in the direction parallel to the surface. As a result, the adsorption of a single ion is exothermic by about −0.6 eV, even at the potential of zero charge. This adsorption behavior is limited to low coverages because the adsorbates repel each other and because full solvation shells can only form at low coverage.

Size and shape-dependent melting mechanism of Pd nanoparticles

Molecular dynamics simulation was employed to understand the thermodynamic behavior of cuboctahedron (cub) and icosahedron (ico) nanoparticles with 2–20 number of full shells. The original embedded atom method (EAM) was compared to the more recent highly optimized version as inter-atomic potential. The thermal stability of clusters were probed using potential energy and specific heat capacity as well as structure analysis by radial distribution function (G(r)) and common neighbor analysis (CNA), simultaneously, to make a comprehensive picture of the solid-state and melting transitions. The result shows ico is the only stable shape of small clusters (Pd55–Pd309 using original EAM and Pd55 using optimized version) those are melting uniformly due to their small diameter. An exception is cub Pd309 modeled via optimized EAM that transforms to ico at elevated temperatures. A similar cub to ico transition was predicted by original EAM for Pd923–Pd2075 clusters, while for the larger clusters both cub and ico are stable up to the melting point. As detected by $G(r)$ and CNA, moderate and large cub clusters were showing surface melting by nucleation of the liquid phase at (100) planes and growth of liquid phase at the surface before inward growth. While diagonal (one corner to another) melting was dominating over ico clusters owing to their partitioned structure, which retarded the growth of the liquid phase. The large ico clusters, using optimized EAM, presented a combination of surface and diagonal melting due to the simultaneous diagonal melting started from different corners. Finally, the melting temperature as well as latent heat of fusion were calculated and compared with the available models and previous studies, which showed, unlike the present result, the models failed to predict size-dependent motif cross-over.

Electrochemical Stability of Bipyridylimino Isoindoline Metal Complexes As Multi-Electron Anolyte Materials for Non-Aqueous Redox Flow Batteries

The development of grid scale energy storage will facilitate the integration of intermittent renewable electricity sources, such as wind and solar, into the grid. However, available technologies are limited by high cost or location dependence. Non-aqueous redox flow batteries (NAqRFBs) offer a scalable, non-geographically limited technology with the potential to provide a low cost, high energy density solution to the energy storage problem. Despite these promising attributes, the limited solubility and stability of current NAqRFB active species hinders implementation. In this work we explored a series of metal complexes of tridentate bipyridylimino isoindoline (BPI) ligands as anolyte materials for NAqRFBs. The goal was to evaluate the electrochemical stability of this class of materials and identify trends between the metal center and stability. Each complex exhibits 2 quasi-reversible redox events at -1.73 V and -1.83 V vs. Ag/Ag+. Bulk electrolysis through these 2 couples was used to quantify the electrochemical stability of each material and the following trend was identified: Co(BPI)2 = Ni(BPI)2 = Fe(BPI)2 > Zn(BPI)2 = Mg(BPI)2 > Mn(BPI)2. Co(BPI)2, Ni(BPI)2 and Fe(BPI)2 were all identified to be highly stable with no capacity fade observed over 50 cycles. This high stability is attributed to the tridentate, anionic ligand structure, which affords a stronger bond between the ligand and the metal center. Extended cycling experiments revealed that Ni(BPI)2 is stable through 2 negative electron transfers for over 200 cycles. Zn(BPI)2 and Mg(BPI)2 were both moderately stable as they have full valence shells while the instability of Mn(BPI)2 is attributed to rapid ligand exchange kinetics, which is common for Mn MCCs. For each of the unstable materials, post-cycling analysis revealed that ligand shedding is a prominent degradation mechanism. The developed stability trends can be used to guide the exploration and design of future NAqRFB active species to aid in the identification of electrochemically stable materials. Since solubility is also a concern, ligand functionalizations were identified that successfully enhanced the solubility of Ni(BPI)2 by three orders of magnitude, up to a maximum solubility of 0.7 M in acetonitrile. In conclusion, BPI MCCs exhibit remarkable stability, along with relatively high solubility, and we present the first demonstration of a stable 2 electron transfer for NAqRFB applications. These complexes can be paired with a suitable catholyte material to achieve a stable, high energy density, multi-electron transfer NAqRFB.

Stabilization and Encapsulation of Gold Nanostars Mediated by Dithiols.

Surface chemistry plays a pivotal role in regulating the morphology of nanoparticles, maintaining colloidal stability, and mediating the interaction with target analytes toward practical applications such as surface-enhanced Raman scattering (SERS)-based sensing and imaging. The use of a binary ligand mixture composed of 1,4-benzenedithiol (BDT) and hexadecyltrimethylammonium chloride (CTAC) to provide gold nanostars with long-term stability is reported. This is despite BDT being a bifunctional ligand, which usually leads to bridging and loss of colloidal stability. It is found however that neither BDT nor CTAC alone are able to provide sufficient colloidal and chemical stability. BDT-coated Au nanostars are additionally used as seeds to direct the encapsulation with a gold outer shell, leading to the formation of unusual nanostructures including semishell-coated gold nanostars, which are characterized by high-resolution electron microscopy and electron tomography. Finally, BDT is exploited as a probe to reveal the enhanced local electric fields in the different nanostructures, showing that the semishell configuration provides significantly high SERS signals as compared to other core-shell configurations obtained during seeded growth, including full shells.

Quantifying the effects of accelerated weathering and linear drop impact exposures of an American football helmet outer shell material

American football helmets are subjected seasonally to a myriad of environmental conditions from expected use and storage and yet are reused without a relational understanding between service life degradation and changes in impact performance. Comprehensive investigations could link rates and degrees of material degradation to scientifically and clinically meaningful changes in helmet performance. Therefore, the purpose of this research was to preliminarily quantify the effects of accelerated weathering on (1) colorimetric, chemical, fluorescent, and thermal properties; (2) surface and bulk mechanical properties; and (3) impact performance of an American football helmet outer shell material. Helmet-grade plaques were exposed to 480 h of accelerated weathering. Surface-specific shifts ( p < 0.05) in colorimetric, chemical, fluorescent, thermal, and mechanical properties were observed at the plaque surface. Plaque-derived tensile specimens underwent monotonic tensile testing, and the photodegraded ∼1% of the Weathered plaque surface thickness led to 10%, 12%, and 9% increases ( p < 0.05) in Young’s modulus, yield stress, and ultimate tensile stress, respectively. Impact performance was analyzed with a protocol attempting to employ expected on-field impact conditions. Weathered and Non-weathered helmet surrogate systems managed impact energy progressively less effectively across five repetitive trials ( p < 0.05); yet the absence of significant Weathered differences demonstrated that the plaque–foam systems performed similarly. Results identified a battery of diagnostic tools to characterize the degradation of outer shell material exposed to accelerated weathering. Thus, the comprehensive approach herein may be used toward the evaluation of additional service life exposures, as well as examine on-field deterioration of full helmet outer shells.

Solution of the Skyrme–Hartree–Fock–Bogolyubov equations in the Cartesian deformed harmonic-oscillator basis.: (VII) hfodd (v2.49t): A new version of the program

We describe the new version (v2.49t) of the code HFODD which solves the nuclear Skyrme Hartree-Fock (HF) or Skyrme Hartree-Fock-Bogolyubov (HFB) problem by using the Cartesian deformed harmonic-oscillator basis. In the new version, we have implemented the following physics features: (i) the isospin mixing and projection, (ii) the finite temperature formalism for the HFB and HF+BCS methods, (iii) the Lipkin translational energy correction method, (iv) the calculation of the shell correction. A number of specific numerical methods have also been implemented in order to deal with large-scale multi-constraint calculations and hardware limitations: (i) the two-basis method for the HFB method, (ii) the Augmented Lagrangian Method (ALM) for multi-constraint calculations, (iii) the linear constraint method based on the approximation of the RPA matrix for multi-constraint calculations, (iv) an interface with the axial and parity-conserving Skyrme-HFB code HFBTHO, (v) the mixing of the HF or HFB matrix elements instead of the HF fields. Special care has been paid to using the code on massively parallel leadership class computers. For this purpose, the following features are now available with this version: (i) the Message Passing Interface (MPI) framework, (ii) scalable input data routines, (iii) multi-threading via OpenMP pragmas, (iv) parallel diagonalization of the HFB matrix in the simplex breaking case using the ScaLAPACK library. Finally, several little significant errors of the previous published version were corrected.

Characterization of polymer ultrasound contrast agents.

Ultrasound contrast agents are encapsulated microbubbles with unique acoustic scattering signatures. Polymer shelled agents have been shown to be advantageous for tissue perfusion studies and also more recently high‐frequency ultrasound applications. The thickness and material of the polymer shell can be more finely adjusted for the specific application in the production process. Only recently have independent measurements of the shell material parameters been attempted. We present a series of elastic shell parameter measurements made using two complementary techniques: high‐frequency acoustic microscopy and nano‐indentation (Hysitron device). The elastic properties of the thin films of the polymer material (Philips agents) were measured using both methods. Also variations of these techniques were applied to the full spherical shells to examine curvature effects. Acoustic microscopy measurements indicate values for acoustic impedance of 1.73 MRayl. Simulations are highlighted. [Work supported by NIH EB006372 and 2G12RR003016121.]

Creep forming of high strength polyethylene fiber prepregs for the production of ballistic protection helmets

Production of highly three dimensionally curved composite products with continuous fibers so far is dependent on drapability of the fibrous precursor. Drapability depends on the in-plane shear compliance of the precursor and on its bending flexibility. Elongation of the fibers usually gives a negligible contribution to drapability because high performance fibers typically show small elongations to failure. However, high strength polyethylene fibers are an exception. They may accumulate considerable creep elongation, provided that the loading time is sufficiently long. Choosing a proper processing temperature, somewhat below the melting temperature, allows that this sufficiently long processing time is still within the limits that are acceptable for industrial production. This paper explores the technique for creep forming of high strength polyethylene fiber prepregs for the production of full scale ballistic protection helmet shells. Such helmets show a highly three dimensionally curvature. It was found that such helmets can be made by creep-forming indeed. The helmets were free of wrinkles and showed excellent protection against supersonic projectiles. It was found to be very important that a homogeneous temperature distribution is provided during creep forming. Very high fiber tensile stresses occur during creep forming. Control of these high creep stresses is necessary.

Convective dynamos in spherical wedge geometry

AbstractSelf‐consistent convective dynamo simulations in wedge‐shaped spherical shells are presented. Differential rotation is generated by the interaction of convection with rotation. Equatorward acceleration and dynamo action are obtained only for sufficiently rapid rotation. The angular velocity tends to be constant along cylinders. Oscillatory large‐scale fields are found to migrate in the poleward direction. Comparison with earlier simulations in full spherical shells and Cartesian domains is made (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Computational Study of Copper(II) Complexation and Hydrolysis in Aqueous Solutions Using Mixed Cluster/Continuum Models

We use density functional theory (B3LYP) and the COSMO continuum solvent model to characterize the structure and stability of the hydrated Cu(II) complexes [Cu(MeNH(2))(H(2)O)(n-1)](2+) and [Cu(OH)(x)(H(2)O)(n-x)](2-x) (x = 1-3) as a function of metal coordination number (4-6) and cluster size (n = 4-8, 18). The small clusters with n = 4-8 are found to be the most stable in the nearly square-planar four-coordinate configuration, except for [Cu(OH)(3)(H(2)O)](-), which is three-coordinate. In the presence of the two full hydration shells (n = 18), however, the five-coordinate square-pyramidal geometry is the most favorable for Cu(MeNH(2))(2+) (5, 6) and Cu(OH)(+) (5, 4, 6), and the four-coordinate geometry is the most stable for Cu(OH)(2) (4, 5) and Cu(OH)(3)(-) (4). (Other possible coordination numbers for these complexes in the aqueous phase are shown in parentheses.) A small energetic difference between these structures (0.23-2.65 kcal/mol) suggests that complexes with different coordination numbers may coexist in solution. Using two full hydration shells around the Cu(2+) ion (18 ligands) gives Gibbs free energies of aqueous reactions that are in excellent agreement with experiment. The mean unsigned error is 0.7 kcal/mol for the three consecutive hydrolysis steps of Cu(2+) and the complexation of Cu(2+) with methylamine. Conversely, calculations for the complexes with only one coordination shell (four equatorial ligands) lead to a mean unsigned error that is >6.0 kcal/mol. Thus, the explicit treatment of the first and the second shells is critical for the accurate prediction of structural and thermodynamic properties of Cu(II) species in aqueous solution.

College Students’ Conceptions of Chemical Stability: The widespread adoption of a heuristic rule out of context and beyond its range of application

This paper reports evidence that learners commonly develop a notion of chemical stability that, whilst drawing upon ideas taught in the curriculum, is nevertheless inconsistent with basic scientific principles. A series of related small‐scale studies show that many college‐level students consider a chemical species with an octet structure, or a full outer shell, will necessarily be more stable than a related species without such an electronic configuration. Whilst this finding is in itself consistent with previous research, the present paper shows how students commonly apply this criterion without consideration of chemical context, or other significant factors such as net charge. Species that would seem highly unstable and non‐viable from chemical considerations, such as Na7−, C4+ and even Cl11−, are commonly judged as being stable. This research shows that many college‐level students are privileging a simple heuristic (species with full outer shells will be stable) when asked about the stability of chemical species at the submicroscopic level, to the exclusion of more pertinent considerations. Some students will even judge an atom in an excited state as more stable than when in the ground state, when an electron is promoted from an inner shell to ‘fill’ the outer shell. It is suggested that the apparently widespread adoption of a perspective that is so at odds with the science in the curriculum is highly significant for the teaching of chemistry, and indicates the need for more detailed studies of how such thinking develops and can be challenged.