Size-evolution towards metallic behavior in nano-sized gold and platinum clusters as revealed by 197Au Mössbauer spectroscopy

Four types of molecular Au₅₅ clusters, with different types of ligands, have been studied using ¹⁹⁷Au Mössbauer spectroscopy. Emission Mössbauer measurements were also performed on the larger Pt309 cluster, in which ¹⁹⁷Au was produced by neutron activation. There is a large influence of the ligands on the charge densities at the surface atoms of the metal atom cluster cores. For the Au₅₅ clusters, the inner core atoms have a different charge density at the nucleus than the bulk metal, and it depends also slightly on the type of ligands on it. For the Pt₃₀₉ compound, the inner core atoms have the same charge density at the nucleus as in the corresponding bulk metal. We, therefore, conclude that the inner core of the Pt₃₀₉ cluster is metallic with respect to the electronic charge densities, while this is not yet the case for the Au₅₅ cluster.     

Isothermal solid–liquid transitions in the (Ni,B)/ZrB2 system as revealed by sessile drop experiments

In the framework of joining processes of ultrahigh temperature ceramics (UHTCs), sessile drop experiments were performed in the Ni–B/ZrB₂ system in the range 1110° ≤ T ≤ 1200 °C. They show that, at temperatures between 1110 and 1150 °C, isothermal solid–liquid transitions occur in a sequence; while in fact at T ≥ 1200 °C, the drop melts without any further phase transition, at lower temperatures, complete melting is followed by a solidification stage and final remelting. This complex behavior, which can be very relevant when utilizing Ni–B alloys for brazing processes (e.g., by the transient liquid phase bonding technique), is successfully interpreted on the basis of the complete B–Ni–Zr phase diagram newly computed by CALPHAD: Isothermal sections, calculated between 1110 and 1150 °C, show that the composition of the drop enters, crosses, and leaves the primary solidification region of the Zr₂Ni₂₁B₆ ternary compound. The use of thermodynamic modeling for the explanation of experimental data sets a link between wetting and joining experiments and phase diagrams assessment.     

Anisotropic mobility and carrier dynamics in the β-type BEDT-TTF salts as studied by inter-layer transverse magnetoresistance

Abstract

A new method to estimate an in-plane conduction anisotropy in a quasi-two-dimensional (q2D) layered conductor by measuring the inter-layer transverse magnetoresistance is proposed. We applied this method to layered organic conductors β-(BEDT-TTF)₂X (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, C₁₀H₈S₈; X = IBr₂, I₂Br) by applying magnetic field rotating within the basal plane at 4.2 K. We found the anisotropic behaviour of carrier mobility μ. From this, anomalous distribution of carrier lifetime τ on the Fermi surface is derived, by the use of Fermi surface data reported for the materials. Calculations of the non-uniform susceptibility χ₀(q) suggest that carrier scattering is enhanced at specific k-points related to partial nesting of the Fermi surface. The present method is thus demonstrated to be an efficient experimental tool to elucidate anisotropic carrier dynamics in q2D conductors.     

β-Crystal in the iPP melt encapsulated by transcrystallinity and spherulites: effect of molecular weight

The crystallization in isotactic polypropylene (iPP) melt inclusions, encapsulated by transcrystallinity and spherulites, was investigated by polarized light microscope. Generally, owing to the proceeding of crystallization in melt inclusions, a negative pressure will be built up. Up to a critical value, the negative pressure is released by the formation of cavitation in melt. Unexpectedly, β-crystals with different morphologies emerge at different locations in the melt inclusions. For low molecular weight iPP, only smaller β-crystals around bubbles are discernable. Turn to higher molecular weight iPP, apart from the smaller β-crystals, fan-shaped ones can be developed under suitable conditions (e.g., lower than 131 °C) at the growth front of spherulites and transcrystallinity. Considering the characteristics of molecular weight and morphology, it is proposed that β-crystals are induced by different mechanisms. That is, smaller β-crystals are resulted from the stress caused by the appearance of bubbles while the fan-shaped ones are derived due to the temperature gradient during the release of negative pressure.     

Bone–titanium oxide interface in humans revealed by transmission electron microscopy and electron tomography

Osseointegration, the direct contact between an implant surface and bone tissue, plays a critical role in interfacial stability and implant success. Analysis of interfacial zones at the micro- and nano-levels is essential to determine the extent of osseointegration. In this paper, a series of state-of-the-art microscopy techniques are used on laser-modified implants retrieved from humans. Partially laser-modified implants were retrieved after two and a half months'' healing and processed for light and electron microscopy. Light microscopy showed osseointegration, with bone tissue growing both towards and away from the implant surface. Transmission electron microscopy revealed an intimate contact between mineralized bone and the laser-modified surface, including bone growth into the nano-structured oxide. This novel observation was verified by three-dimensional Z-contrast electron tomography, enabling visualization of an apatite layer, with different crystal direction compared with the apatite in the bone tissue, encompassing the nano-structured oxide. In conclusion, the present study demonstrates the nano-scale osseointegration and bonding between apatite and surface-textured titanium oxide. These observations provide novel data in human specimens on the ultrastructure of the titanium–bone interface.     

Exploiting β-cyclodextrin as functional monomer in molecular imprinting for achieving recognition in aqueous media

A series of molecularly imprinted polymers (MIPs) for 4,4′-(1,4-phenylenediisopropylidene)bisphenol (BPP) were prepared by using β-cyclodextrin (β-CD) as functional monomer, toluene 2,4-diisocyanate (TDI) or 4,4′-Diphenylmethane diisocyanate (DDI) as the cross-linker. The results of binding experiments showed that the MIPs can bind the template selectively in aqueous media. The binding specificity mechanism of the polymers was investigated in detail. The template molecule is too large and cannot be included in the cavity of one β-CD molecule. The mutual orientation of β-CD molecules in the imprinted polymers is regulated by molecular imprinting, so that they can cooperatively bind the template molecule. It is suggested that the major contribution to the recognition ability of the imprinted polymer was the stereo-shape effect inherent in the MIPs. The study indicated that hydrophobic effects play an important role in the recognition process.     

Formation mechanism of lamellae during β→α transformation in polycrystalline dual-phase Ti alloys

Phase field simulations incorporating contributions from chemical free energy and anisotropic interfacial energy are presented for the β→α transformation in Ti-6Al-4 V alloy to investigate the growth mechanism ofα lamellae of various morphologies from undercooled β matrix.The α colony close to realistic microstructure was generated by coupling the Thermo-Calc thermodynamic parameters of α and β phases with the phase field governing equations.The simulations show that α lamellar side branches with feathery morphology can form under a certain combination of interfacial energy anisotropy and temperature.α lamellae tend to grow slowly at high heat treatment temperature and become wider and thicker as temperature increase from 800 to 900 ℃ provided that the interfacial energy anisotropy ratio kx: ky was set as 0.1: 0.6.Besides,higher interfacial energy anisotropy can accelerate the formation of α lamellae,and the equilibrium shape of α lamellae changes from rod to plate as the interface energy anisotropy ratio kx∶ ky vary from 0.1∶ 0A to 0.1∶ 0.8 under 820 ℃.Experiments were conducted to study the α lamellar side branches in Ti-6Al-4 V (Ti-6.01Al-3.98 V,wt.％) and Ti-4211 (Ti-4.02Al-2.52V-1.54Mo-1.03Fe,wt.％) alloys with lamellar microstructure.Electron backscatter diffraction (EBSD) results show that α lamellar side branches and their related lamellae share the same orientation.The predicted temperature range for α lamellar side branches formation under various interfacial energy anisotropy is consistent with experimental results.     

Microstructural evolution and microhardness variations in a Cu–36Zn–2Pb alloy processed by high-pressure torsion

A coarse-grained Cu–36Zn–2Pb alloy with an initial grain size of ~54 μm was processed by high-pressure torsion (HPT) at room temperature under an applied pressure of 6.0 GPa through 1–10 turns, and the evolution of microstructure and microhardness was investigated. Analysis by X-ray diffraction (XRD) showed that in HPT processing the β′-phase transforms to an α-phase and a {111} texture is formed. Microscopic examination showed that dislocations were first formed at equivalent strains of not more than ~25 and when the equivalent strain increased to ~40 there was evidence for twins and secondary twinning. Fine grains were formed with an increase in equivalent strain to ~100 and with further straining these refined grains acted as precursors for additional grain refinement. The refined equiaxed grain size was ~250 nm after HPT through an equivalent strain of ~100 and the results show the microhardness reached a saturation value of ~220 Hv.     

Planar optical waveguides formed in β-BBO by MeV O+ implantation

The planar waveguides have been fabricated in z-cut β-BaB₂O₄ crystal by 2.8 MeV O⁺ ion implantation with the doses of 8×10¹⁴ and 2×10¹⁵ ions/cm² at room temperature. The waveguides were characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 300°C for 20 and 40 min in air. The refractive index profile is reconstructed using the reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and a slight change increases with the doses, which are different from most of the observed ion-implanted waveguides.     

Giant phase transition properties at terahertz range in VO₂ films deposited by sol-gel method

VO(2) films were fabricated on high-purity single-crystalline silicon substrate by the sol-gel method, followed by rapid annealing. The composition and microstructure of the films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The results indicated a polycrystalline nature with high crystallinity and compact nanostructure for the films, and the concentration of +4 valence vanadium is 79.85%. Correlated with these, a giant transmission modulation ratio about 81% of the film was observed by terahertz time domain spectroscopy. The experimentally observed transmission characteristics were reproduced approximately, by a simulation at different conductivities across the phase transition. According to the effective-medium theory, we assumed that it is important to increase the concentration of +4 valence vanadium oxide phases and improve the compactness of the VO(2) films for giant phase transition properties. The sol-gel-derived VO(2) films with giant phase transition properties at terahertz range, and the study on their composition and microstructure, provide considerable insight into the fabrication of VO(2) films for the application in THz modulation devices.     

Preparation of 188Re-Labetalol as a β1-Adrenoceptor for Use in Nuclear Medicine

Radiochemistry - Labetalol was labeled with 188Re. The reaction conditions (amounts of stannous chloride and substrate, pH, time) were optimized, and the radiochemical yield as high as 95 ±...     

The Use of β-Cyclodextrin as a Pelletization Agent in the Extrusion/ Spheronization Process

Abstract

The use of β-cyclodextrin for the preparation of pellets by the extrusion/spheronization process is described for different formulations and processing conditions. Sieve analysis and friability tests were performed to assess the physical and technological characteristics of pellets. Satisfactory products were obtained with β-cyclodextrin contents up to 90% by weight.     

Bandgap modifications by lattice deformations in β-FeSi2 epitaxial films

The modifications of direct transition energies by lattice deformations were investigated in β-FeSi₂ epitaxial films, polycrystal films and single crystal, systematically. The lattice deformations depending on thermal annealing temperature (T_a) were observed in β-FeSi₂ epitaxial films. In photoreflectance (PR) measurements, the direct transition energies of the epitaxial films shifted to lower energies as the T_a increased. The polycrystal films did not show the lattice deformation and the shift of direct transition energies. These results show that the direct bandgap is modified by the lattice deformation originating from the lattice mismatch at the hetero-interface of β-FeSi₂/Si.     

Enhanced Microdialysis Extraction Efficiency of Ibuprofen in Vitro by Facilitated Transport with β-Cyclodextrin

A novel approach to increase microdialysis recovery (extraction efficiency, E(d)) by facilitated transport through the microdialysis membrane is described. This new approach facilitates mass transport into the microdialysis probe by inclusion of a complexation agent in the microdialysis perfusion fluid. In these studies, β-cyclodextrin (β-CD) (0.25-2.0 w/v%) was included in the microdialysis perfusion fluid consisting of a Ringer's solution (155 mM NaCl, 4.0 mM KCl, 2.4 mM CaCl(2)). β-CD forms known inclusion complexes with 2-(4-isobutylphenyl)propionic acid (ibuprofen). Ibuprofen E(d) was significantly enhanced (1.5-2.0 times) through different microdialysis membrane materials. The effect of microdialysis membrane material (polycarbonate/polyether, AN-69, cuprophan), pH, β-CD concentration, and ibuprofen concentration on the E(d) was examined. Only the polycarbonate/polyether membrane was able to give an E(d) greater than 100%. In general, a maximum increase in E(d) was found when 0.5 w/v% β-CD was included in the perfusion fluid. Variations in the ibuprofen concentration external to the microdialysis probe did not significantly change E(d) when 0.5 w/v% β-CD was included in the perfusion fluid. In contrast to the ibuprofen data, β-CD inclusion in the microdialysis perfusion fluid did not affect antipyrine E(d). Antipyrine does not form known inclusion complexes with β-CD. The ability of β-CD to increase microdialysis E(d) is explained by facilitated transport.     

Effect of heat treatment on microstructure and microhardness evolution in a Ti–6Al–4V alloy processed by high-pressure torsion

A Ti–6Al–4V alloy was heat-treated to give two types of microstructures with different volume fraction of equiaxed α phase and lamellar (α + β) microstructure. Disks were cut from the heat-treated rods and processed by quasi-constrained high-pressure torsion (HPT) at room temperature with an applied pressure of 6.0 GPa and torsional straining from 1/4 to 20 turns. The results show that there is a gradual evolution of homogeneity in microhardness and grain size with increasing numbers of revolutions in HPT such that the microhardness values attain a maximum constant value across the disk after processing by HPT for 10 turns and the measured equilibrium grain sizes after 20 turns are ~130 nm in Ti64-1 and ~70 in Ti64-2. The results show also that a larger fraction of lamellar (α + β) in the microstructure of Ti–6Al–4V leads to a higher hardenability after processing by HPT.     

Fabrication of β- and β′′-Al2O3 tubes by pressureless powder packing forming and salt infiltration

A new forming method, pressureless powder packing (PLPP), was studied to fabricate the - and -Al2O3 tubes. Alkali sources were infiltrated into the pores of -Al2O3 tube preforms that had been prepared by the PLPP forming method. The composition for the synthesis of -Al2O3 phase was Na2O · 0. 138Li2 · 4.4Al2O3. The -Al2O3 fraction of calcined and sintered bodies was increased with the increase of calcination temperature, and phase formation was largely affected by the type of starting -Al2O3. Large particle size and narrow size distribution of fused -Al2O3 resulted in uniform green microstructure that enhanced the homogeneity of alkali salts after infiltration, which was very important for the -Al2O3 formation. Sintered microstructure was uniform in all specimens but further development was required for density improvement.     

Enhanced plasticity of Zr-based bulk metallic glass composite by in situ formed β-Zr dendritics

A Zr_56.2Ti_13.8Nb_5.0Cu_6.9Ni_5.6Be_12.5 bulk metallic glass composite with enhanced plasticity by in situ formed bcc β-Zr solid solution was prepared by water quenching. The ductile β phase with a volume fraction of about 30% possesses a developed dendritic morphology. The composite exhibits a pure plastic strain of 10.2% combined with a large elastic strain limit of 2% and a high ultimate strength of 1778 MPa upon room-temperature compression. Microscopic observation shows numbers of wave-like shear bands distributed on the surface of the compressive samples.     

An updated critical state model by incorporating inertial effects for granular material in solid–fluid transition regime

Granular Matter - This paper presents a computational framework that generates ensemble predictive mechanics models with uncertainty quantification (UQ). We first develop a causal discovery...