Two-shell Structure Research Articles

Analysis of Composition Formulas for Face-centered Cubic Solid Solution Alloys via Nearest-neighbor Two-shell Structure with Cowley Parameters

Analysis of Composition Formulas for Face-centered Cubic Solid Solution Alloys via Nearest-neighbor Two-shell Structure with Cowley Parameters

BILOZERSKA SERIES OF THE UKRAINIAN SHIELD: PROBLEMS OF STRATIGRAPHY AND CORRELATION

The article discusses the problematic issues of the geological structure of the Bilozersky synclinorium of the Ukrainian Shield, its stratigraphic structure, formation composition and absolute age of the rock associations that compose it. The interrelationships of interregional correlation of the Bilozerska and Kryvyi Rih series of the Ukrainian Shield are considered. Significant adjustments to the current stratigraphic scheme of the Bilozerska series are proposed. The necessity of abolishing the upper metasedimentary stratum (Pereverzevska Suite) and returning to the traditional twoshell structure of the Bilozerska series, which consists of a sub-iron-bearing essentially terrigenous and iron-bearing terrigenous-chemogenic ferruginous-siliceous suite, is noted. The author’s interpretation of the folded structure of the central zone of the Bilozerska structure is proposed, which allows to explain all the complexities of its stratigraphy in a consistent manner, to reconcile the stratigraphic position of the Teplivska Association of the Bilozersky synclinorium with the position of the Talc Horizon of the Kryvyi Rih series, and to show a complete correspondence in the general sequence of stratons between the sediments of the Bilozerska and Kryvyi Rih series. The complete lithologic, stratigraphic, and formational correlation of the Bilozerska series with the section of the Kryvyi Rih series within the Skelyuvatsko- Saksagan sedimentary cycle is shown by a set of features. It is recommended to unite the Kryvyi Rih and Bilozerska series into a single supra-regional and superserial taxon – the Kryvyi Rih-Bilozersky complex.

Implosion dynamics and radiation characteristics of preconditioned hybrid X-pinch driven by double pulse current

Preconditioned hybrid X-pinch (HXP) experiments have been performed on the Qin-1 facility to investigate the effect of the prepulse current on the implosion dynamics and radiation characteristics. HXPs with molybdenum wires of ∼1.2 mm in length and 25 to 50 μm in diameter have been tested. Driven by the prepulse current, the molybdenum wire is heated to a core-corona structure with a Joule energy deposition of 0.5–4.8 eV/atom, which is smaller than its atomization enthalpy. The radial expansion velocity of the wire core is 0.5–3 km/s. The main current of 450 kA/400 ns is applied ∼610 ns after the prepulse current. The implosion dynamics of the preconditioned HXP is characterized by two-shell structure implosion. Immediately after the main current starts, the current mainly passes through the corona plasma located in a large radius, and the implosion of corona plasma lasts for ∼100 ns until the corona plasma collides with the wire core. Then, the current distribution switches from the corona plasma to the wire core, which results in the onset of implosion of the wire core. The implosion of the wire core generates hot spots and x-ray radiation. The calculated inductance and radius of the current sheath agree with the experimental results. The corona plasma performs as a current switch, which allows the main current passing through the wire core after 100 ns. It indirectly contributes to sharpening the main current used for implosion of the wire core. A single hot spot with x-rays over 2.5 keV is measured using the preconditioned HXP.

Electron count and electronic structure of bare icosahedral Au32 and Au33 ionic nanoclusters and ligated derivatives. Stable models with intermediate superatomic shell fillings.

DFT calculations were carried out on bare Au32 and Au33 nanoclusters with various charges, in order to analyze their stability with respect to different cluster electron numbers. Results indicate that in addition to the neutral Au32 hollow species, significant HOMO-LUMO gaps are computed for [Au32]8+ (hollow) and [Au32]4+ (two-shell structure). Species with smaller HOMO-LUMO gaps can reach stability upon "passivation" by a ligand shell, as experimentally exemplified. Icosahedral frameworks of Ih or lower symmetry are favored for the cationic nanoclusters whereas different structures are computed for the anionic ones.

Role of molecular weight and hydrophobicity of amphiphilic tri-block copolymers in temperature-dependent co-micellization process and drug solubility

The binary P123 + F108, + F98, + F88, + F68, + F87 and + P84 systems were used to systematically explore the effect of molecular weight and hydrophobicity of Pluronic on the tendency of cooperative binding between parent copolymers and solubility of drug (ibuprofen) in these mixed Pluronic systems. Temperature-dependent co-micellization process in these systems was carefully investigated by using high sensitivity differential scanning calorimeter (HSDSC), dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). All the HSDSC thermograms for these systems consistently exhibit two endothermic (micellization) peaks apart by at least 13.3 °C. It was evidenced that micelles are mainly formed by P123, the copolymer with a lower critical micelle temperature (CMT), at low temperatures. Raising temperature would dehydrate the other Pluronic with a higher CMT to be integrated into the neat P123 micelles developed at low temperatures. When the temperature is further increased beyond the second endothermic peak, the mixed micelles with a two-shell structure and characteristic corona lengths of their parent copolymers are observed to prove the existence of cooperative binding between parent copolymers. All the binary mixed Pluronic systems used in this study exhibit cooperative binding to form unimodal distribution of mixed micelles, except the P123 + F68 system. The SAXS results show that P123 + F68 system at 65 °C exhibits bimodal distribution of aggregates with coexisting of neat F68 micelles (65% in number) and P123 + F68 mixed micelles (35% in number). It is interesting to find out that P123 and F68 with distinct polypropylene oxide (PPO) moieties (i.e., a difference of 37 PO units) would exhibit very weak cooperative binding to partially form mixed micelles. Addition of ibuprofen in the P123 + F68 system would substantially enhance the cooperative binding between P123 and F68 to form bimodal distribution of aggregates with coexisting of neat F68 micelles (drops down to 30% in number) and P123 + F68 mixed micelles (increases up to 70% in number). For the systems with ibuprofen incorporated, SAXS results demonstrate that the drug is mainly encapsulated in the core of neat micelles developed at low temperatures. The solubility of ibuprofen in the 0.5 wt% P123 + 0.368 wt% P84 system is as high as 2.62 mg/ml, which is 114 times more than that in pure water at 37 °C.

Superfluidity ofHe4nanoclusters in confinement

Structure and superfluid response of nanoscale size helium-four clusters enclosed in spherical cavities are studied by computer simulations. The curved surface causes the formation of well-defined concentric shells, thus imparting to the system a very different structure from that of free standing clusters. On a strongly attractive substrate, superfluidity is only observed at low density, in the single layer coating the inner surface of the cavity. If the substrate is very weak (e.g., Li), on the other hand, a superfluid two-shell structure can form, whose physical properties interpolate between two and three dimensions. It is shown how experimental signatures of this physical behavior can be detected through measurements of the momentum distribution.

Vortex states in de facto mesoscopic Mo80Ge20 pentagon plates

We present direct observations of vortex configurations in Mo80Ge20 pentagonal plates using a scanning SQUID microscope. The vortex distribution tends to adapt to one of five symmetric axes in a pentagon, as expected from the sample geometry. We found that, for a vorticity of six, the vortices form a two-shell structure in a small pentagon, and a single-shell structure in a larger pentagon. We revealed how the vortex configuration is strongly modified by the presence of a pinning site at the center of the pentagon. In particular, a two-shell structure is formed in the pinning-site sample with a vorticity of L = 4, while the second shell appeared in the pinning site-free sample with a vorticity up to L = 6. Furthermore, upon geometric confinement, the vortices attempt to form a symmetrical configuration reflecting the sample geometry even in the presence of a pinning site (or sites). The experimental results for pentagons are in good agreement with our theoretical predictions based on the nonlinear Ginzburg–Landau equation both for a pin-free pentagon and a pentagon with a pin at the center.

Vortex imaging in amorphous Mo80Ge20 pentagons

We present the direct observation of vortex configuration in Mo80Ge20 pentagons using the scanning SQUID microscope. Systematic measurements allow us to reveal how vortices are confined in a restricted sample as well as how vortex arrangement evolves with increasing the applied magnetic field. Vortex distribution in pentagon tends to take one of five symmetric axes of pentagon expected from sample geometry. We found that the rule of shell filling is different among various different sizes of the pentagons. For vorticity of six, vortices form a two-shell structure in small pentagon, while single shell structure in larger pentagon. We also demonstrate that the vortex dragging effect can be caused by the superconducting pick-up coil in a weak pinning specimen.

The effect of speckle disorder on a spin-polarized Fermi gas under harmonic confinement in one dimension

We present a numerical study on one-dimensional attractive Fermi gases with spin polarization in the presence of the harmonic confinement and the speckle disorder by making use of the local-density approximation based on the exact Bethe-ansatz solution. The effects of the disorder are investigated on the ground-state properties. For a clean system without trapping, the ground state is a partially polarized Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state, a full paired Bardeen–Cooper–Schrieffer (BCS) state or a fully polarized normal state. For a clean system in the presence of trapping, a two-shell structure exists with a polarized superfluid core surrounded by wings composed of either an unpolarized superfluid (FFLO-BCS) or a fully polarized normal (FFLO-N) gas. Between these two different phases, there exists a critical polarization where a pure FFLO state happens. In the presence of speckle disorder with fixed polarization, the system can be changed from FFLO-BCS to FFLO-N upon increasing the disorder amplitude, irrelevant to the attractive or repulsive nature of the speckle disorder. Given the dimensionless interaction strength γ0 and the disorder amplitude A, there is a critical polarization Pc below which the system is in a FFLO-BCS phase and above which it is in a FFLO-N phase.

Sintering process of amorphous SiO 2 nanoparticles investigated by AFM, IR and Raman techniques

We report an experimental investigation on the effects of thermal treatments at different temperatures (room—1270 K) and for different duration (0–75 h) on amorphous silica nanoparticles ( fumed silica) in powder tablet form. Three types of fumed silica are considered, comprising nearly spherical particles of 40 nm, 14 nm and 7 nm mean diameter. The experimental techniques used here are Raman and infrared absorption (IR) spectroscopy together with atomic force microscopy (AFM). Raman and IR spectra indicate that the structure of nanometer silica particles is significantly different with respect to that of a bulk silica glass. In particular, the main differences regard the positions of the IR band peaked at about 2260 cm −1, the Raman R-band peaked at about 440 cm −1 and the intensity of the D1 and the D2 Raman lines, related to the populations of 4- and 3-membered rings, respectively. Our data also indicate that, under thermal treatments, the structure of fumed silica samples is significantly changed, gradually relaxing towards that pertaining to ordinary bulk silica. These changes are interpreted here on the basis of the morphological information provided by the AFM measurements and assuming a two-shell structure for the fumed silica primary particles.

Two-component repulsive Fermi gases with population imbalance in elongated harmonic traps

We study the two-component repulsive Fermi gas with imbalanced populations in one dimension. Starting from the Bethe ansatz solution we calculate analytically the phase diagram for the homogeneous system. We show that three phases appear: the balanced phase, the fully polarized phase, and the partially polarized phase. By means of the local density approximation and the equation of state for the homogeneous system we calculate the density profile for the harmonically confined case. We show that a two-shell structure appears: at the center of the cloud we find the partially polarized phase and at the edges the fully polarized one. The radii of the inner and outer shells are calculated for different values of the polarization and the coupling strength. We calculate the dependence of the magnetization on the polarization for different values of the coupling strength and we show that the susceptibility is always finite.

Spin-density-functional theory for imbalanced interacting Fermi gases in highly elongated harmonic traps

We numerically study imbalanced two component Fermi gases with attractive interactions in highly elongated harmonic traps. An accurate parametrization formula for the ground state energy is presented for a spin-polarized attractive Gaudin-Yang model. Our studies are based on an accurate microscopic spin-density-functional theory through the Kohn-Sham scheme which employs the one-dimensional homogeneous Gaudin-Yang model with a Luther-Emery-liquid ground-state correlation as a reference system. A Thomas-Fermi approximation is examined incorporating the exchange-correlation interaction. By studying the charge and spin density profiles of the system based on these methods, we gain a quantitative understanding of the role of attractive interactions and polarization on the formation of the two-shell structure, with the coexisted Fulde-Ferrell-Larkin-Ovchinnikov-type phase in the center of the trap and either the BCS superfluid phase or the normal phase at the edges of the trap. Our results are in good agreement with the recent theoretical consequences.

Attractive Fermi Gases with Unequal Spin Populations in Highly Elongated Traps

We investigate two-component attractive Fermi gases with imbalanced spin populations in trapped one-dimensional configurations. The ground state properties are determined with the local density approximation, starting from the exact Bethe-ansatz equations for the homogeneous case. We predict that the atoms are distributed according to a two-shell structure: a partially polarized phase in the center of the trap and either a fully paired or a fully polarized phase in the wings. The partially polarized core is expected to be a superfluid of the Fulde-Ferrell-Larkin-Ovchinnikov type. The size of the cloud as well as the critical spin polarization needed to suppress the fully paired shell are calculated as a function of the coupling strength.

Adaptive Optics Imaging of IRAS 18276−1431: A Bipolar Preplanetary Nebula with Circumstellar “Searchlight Beams” and “Arcs”

We present high angular resolution images of the post-AGB nebula IRAS 18276-1431 (also known as OH 17.7-2.0) obtained with the Keck II adaptive optics (AO) system in its natural guide star (NGS) mode in the K_P, L_P, and M_S near-infrared bands. We also present supporting optical F606W and F814W HST images as well as interferometric observations of the 12^CO J = 1-0, 13^CO J = 1-0, and 2.6 mm continuum emission with OVRO. The envelope of IRAS 18276-1431 displays a clear bipolar morphology in our optical and NIR images with two lobes separated by a dark waist and surrounded by a faint 4.5'' × 3.4'' halo. Our K_P-band image reveals two pairs of radial searchlight beams emerging from the nebula center and several intersecting, arclike features. From our CO data we derive a mass of M > 0.38 (D/3 kpc)^2 M_☉ and an expansion velocity V_exp = 17 km s^-1 for the molecular envelope. The density in the halo follows a radial power law ∝r^-3, which is consistent with a mass-loss rate increasing with time. Analysis of the NIR colors indicates the presence of a compact central source of ~300-500 K dust illuminating the nebula in addition to the central star. Modeling of the thermal IR suggests a two-shell structure in the dust envelope: (1) an outer shell with inner and outer radius R_in ~ 1.6 × 10^16 and R_out ≥1.25 × 10^17 cm, dust temperature T_dust ~ 105-50 K, and a mean mass-loss rate of M ≈ 10^3 M_☉ yr^-1; and (2) an inner shell with R_in ~ 6.3 × 10 cm, T_dust ~ 500-105 K, and M ~ 3 × 10^-5 M_☉ yr^-1. An additional population of big dust grains (radius a ≥0.4 mm) with T_dust = 150-20 K and mass M_dust = (0.16-1.6) × 10^-3 (D/3 kpc)^2 M_☉ can account for the observed submillimeter and millimeter flux excess. The mass of the envelope enclosed within R_out = 1.25 × 10^17 cm derived from SED modeling is ~1 (D/3 kpc)^2 M_☉.

Binding Energies of Hexahydrated Alkaline Earth Metal Ions, M2+(H2O)6, M = Mg, Ca, Sr, Ba: Evidence of Isomeric Structures for Magnesium

Binding Energies of Hexahydrated Alkaline Earth Metal Ions, M²⁺(H₂O)₆, M = Mg, Ca, Sr, Ba: Evidence of Isomeric Structures for Magnesium

Monte Carlo simulations of helium bubble states

Excited He* (2 3S) atoms in normal liquid 4He(1 1S) environment exist inside ‘‘bubbles’’ that have sizes and shapes characteristic of the electronic state of He* as well as the thermodynamic state of the liquid. The bubbles are stabilized by the repulsive interaction of the Rydberg-like excited electron with bath He atoms. We employ classical computer simulation methods to characterize these ‘‘bubble states’’ in a high pressure (gigapascals) regime. We analyze for the presence of clusters (He*n) within the bubbles, and find the results sensitive to the electronic state involved as well as the pressure. The He*n along with the He atoms on the bubble’s inner surface behave like a single-shell solventberg at lower pressures, whereas a two-shell structure emerges in the high pressure regime. The simulated bubble radius varies between 6–8 a0 in the pressure range 14–0.5 GPa.