Fabrication of CdS/polyacrylonitrile nanocomposites by γ-irradiation in an ethanol solution

The present work reported the successful preparation of CdS/polyacrylonitrile (CdS/PAN) nanocomposites in an ethanol solution via using γ-irradiation technique at room temperature and atmospheric pressure. Acrylonitrile (AN), CS₂ and CdCl₂·2.5H₂O were used as raw materials. Ethanol is chosen as the solvent. XRD analyses showed that the crystallinity of CdS was affected by some factors such as the amount of the organic component in the composites and the dose of irradiation. The optical properties of nanocomposites were also investigated.     

Relationship between soil bulk density and PVR of in situ γ spectra

This paper presents the specific relationship between soil bulk density and peak-to-valley ratio (PVR) of natural radionuclides in in situ γ spectra, by theoretical deduction, Monte Carlo simulation and experimental research. Results show that for an infinite half-space volume source, PVR is a constant independent of the diverse soil bulk density. But for a limited-scale volume source, PVR would decrease slowly with an increase in soil bulk density, and the smaller the source scale, the larger the PVR variation with soil bulk density. However, the PVR variation with bulk density is very small in general. For field measurements, the volume source thickness is uncontrollable in practice, and the volume source radius should not be as small as needed for the limitation of low detection efficiency. Hence the soil bulk density could not be determined through the information from PVR of field in situ γ spectra.     

β to ω phase transformation due to aging in a Ti–Mo alloy deformed in impact compression

We investigated the roles of vacancies and their clusters introduced in a Ti–20mass% Mo alloy by high-speed compression in the formation of aged ω-phase crystals. Specimens were deformed by a static compression mode and a high-speed compression mode, and were then aged. The relationships between morphology of aged ω-phase crystals and deformation modes are discussed along with the roles of vacancies and their clusters in the nucleation and growth of aged ω-phase crystals. Aged ω-phase crystals were found to be smaller but of higher density in a high-speed deformation specimen. These results suggest that vacancies and their clusters easily become nucleation sites of aged ω-phase crystals. Several aged ω-phase crystals in a high-speed deformation specimen were of string-like shape. High-resolution electron microscopy confirmed that the string-like crystals have the ω-phase crystal structure. One of the roles of vacancies of and their clusters introduced by high-speed deformation is considered to be relief of compressive stress, which is predicted to arise in the course of transformation.     

Melting of thin γFe–C films having (100), (110) and (111) surfaces in terms of molecular dynamics simulation

Structural changes associated with melting of thin γFe–C films having (100), (110) and (111) surfaces have been investigated by molecular dynamics simulation. Structures of thin film and bulk models of γFe containing about 0–4 at.% C were calculated at constant temperatures between 1000 and 1800 K. The liquidus temperature for each thin film model decreased with increasing the C concentration. Comparison between the atomic number density distributions of Fe and C showed: (i) The atomic number density of C near the surface increases before the formation of liquid near the surface. (ii) This increase becomes more prominent as temperature rises. (iii) Melting of γFe–C alloy would be rate-controlled by diffusion of C from the solid phase to the solid–liquid interface. These findings suggest that the increase in the C concentration enhances atomic vibrations of Fe near the surface and promotes melting of Fe at lower temperatures. Furthermore, it has been concluded from Lindemann's law of melting that surface melting occurs in γFe–C alloy having (110) surface more easily.     

Anisotropic Excitation Polarization Response from a Single White Light‐Emitting β‐NaYF4:Yb3+,Pr3+ Microcrystal

Precise knowledge about optical and structural performance of individual rare earth (RE)‐doped particles is extremely important for the optimization of luminescent particles and for fully exploiting their capability as multifunctional probes for interdisciplinary applications. In this work, optical and structural anisotropy of individual particles through RE‐doped single fluoride microcrystals with controllable morphology is reported. Unique luminescent phenomena, for example, white light‐emission from Pr³⁺ at single particle level and different photoluminescent spectra variation dependence on excitation polarization orientation at different excitation direction are observed upon excitation with a 980 nm linearly polarized laser. Based on the analysis of local site symmetry and electron cloud distribution of REs in hexagonal structure by density functional theory calculations, an exciting mechanism of excitation polarization response anisotropy is given for the first time, providing a guidance for emission polarization simultaneously. The structural anisotropy is presented in Raman spectra with obvious differing Raman curves, revealing the reason why there are differences between powder groups. Taking advantage of anisotropic crystals, potential applications in microscopic multi‐information transportation are suggested for the optical and structural performance anisotropy from RE‐doped fluoride single nano/microcrystals to ordered nano/microcrystal arrays, such as local rate probing in a flowing liquid.     

A detector for filtering γ-ray spectra from weak fusion–evaporation reactions out of strong background and for Doppler correction: The recoil filter detector, RFD

A detector has been designed and built to assist in-beam γ-ray spectroscopy with fusion–evaporation reactions. It measures with high efficiency the evaporation residues that recoil out of a thin target into the angular interval from 1.8° to 9.0° at an adjustable distance of 1000–1350 mm from a target, in coincidence with γ-rays detected in a Ge-detector array. This permits filtering of such γ-rays out of a much stronger background of other reaction products and scattered beam. Evaporation residues are identified by their time-of-flight and the pulse height using a pulsed beam. The velocity vector of the γ-emitting recoil is also measured in the event-by-event mode, facilitating to correct the registered γ-ray energy for the Doppler shift, with the resulting significant improvement of the energy resolution. The heavy-ion detection scheme uses emission of secondary electrons caused by the recoiling ions when hitting a thin foil. These electrons are then electrostatically accelerated and focused onto a small scintillator that measures the summed electron energy, which is proportional to the number of electrons. The detector is able to operate at high frequency of the order of 1 MHz and detect very heavy nuclei with as low kinetic energy as 5 MeV. The paper describes the properties of the detector and gives examples of measurements with the OSIRIS, GAREL+ and EUROBALL IV γ-ray spectrometers. The usefulness of the technique for spectroscopic investigations of nuclei with a continuous beam is also discussed.     

New ‘ηpl'' and ‘γ'' functions to evaluate J–R curve from cracked pipes and elbows. Part I: theoretical derivation

Experimental evaluation of J–R curve in a crack growth situation requires ‘η_pl' and ‘γ' functions that are specific to a cracked geometry and loading condition. All derivations of existing ‘η_pl' and ‘γ' functions are for specific cracked geometry and loading. In this paper, direct limit load based general equations of ‘η_pl' and ‘γ' functions have been derived. Subsequently, new ‘η_pl' and ‘γ' functions, which are not available in the literature, for pipe and elbow geometry with various crack configurations under different loading conditions have been derived. The derivations of ‘η_pl' and ‘γ' functions for throughwall circumferentially cracked elbow under in-plane bending moment uses the very recently proposed new limit load formulas.     

Effect of small γ-precipitates on the two-way shape memory effect in Cu–Zn–Al alloys

The γ-precipitates in Cu–Zn–Al alloys, trained by the stabilization of the stress induced martensite (SSIM) method, have been studied. After the SSIM treatment, it was found that small γ-precipitates in the β-austenite are ellipsoidal, with a large strain field oriented in the same direction; while in the martensite the γ-precipitates changed their shape from ellipsoid to spheroid, and relaxed their strain fields. In order to check whether the strain field of the γ-precipitates is capable of producing a thermoelastic martensitic transformation, an in-situ observation, by heating a sample holder in TEM, was performed. It was found that during heating over a temperature A_s, the γ-precipitates with a spherical shape in the martensite recovered their strain field and elliptical shape. During cooling, the strain field of the γ-precipitates disappeared again. It was proposed that the strain field of the γ-precipitates, trained by the SSIM method, plays an important part in the thermoelastic martensitic transformation, and presents two-way shape memory effects.     

New ‘ηpl'' and ‘γ'' functions to evaluate J–R curve from cracked pipes and elbows. Part II: experimental and numerical validation

Experimental evaluation of J–R curve in a crack growth situation requires ‘η_pl' and ‘γ' functions that are specific to a cracked geometry and loading condition. In Part I [Engng. Fract. Mech., in press] of this paper, new η_pl and γ functions, which are not available in the literature, for pipe and elbow geometry with various crack configurations under different loading conditions have been derived. In this paper, some of these newly proposed η_pl and γ functions have been validated experimentally through comparison of crack initiation load and J–R curve. In few cases, numerical validation has also been provided by comparing the J-integral values calculated through η factor approach and finite element method.     

Prediction of flow stress in Ti–6Al–4V alloy with an equiaxed α + β microstructure by artificial neural networks

Flow stress during hot deformation depends mainly on the strain, strain rate and temperature, and shows a complex and nonlinear relationship with them. A number of semi-empirical models were reported by others to predict the flow stress during hot deformation. This work attempts to develop a back-propagation neural network model to predict the flow stress of Ti–6Al–4V alloy for any given processing conditions. The network was successfully trained across different phase regimes (α + β to β phase) and various deformation domains. This model can predict the mean flow stress within an average error of 5.6% from the experimental values, using strain, strain rate and temperature as inputs. This model seems to have an edge over existing constitutive model, like hyperbolic sine equation, and has a great potential to be employed in industries.     

Anisotropy of Young's modulus and tensile properties in cold rolled α′ martensite Ti–V–Sn alloys

Young's modulus and tensile properties of cold rolled Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloy plates consisting of α′ martensite were investigated as a function of tensile axis orientation in this work. A single phase of α′ (hcp) martensite is obtained in Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloys by quenching after solution treatment. By 86% cold rolling, acicular α′ martensite microstructures change into extremely refined dislocation cell-like structure with an average size of 60 nm, accompanied with the development of cold rolling texture in which the basal plane normal is tilted from the plate normal direction (ND) toward transverse direction (TD) at angles of ±49° for Ti–8% V alloy and ±46° for (Ti–8 mass% V)–4 mass% Sn alloy. No apparent anisotropy of Young's modulus (E) is observed for as-quenched Ti–8% V (E = 76–83 GPa) and (Ti–8% V)-4%Sn (E = 69–79 GPa). In contrast, Young's modulus increases with increasing angle from the rolling direction (RD) to TD for cold rolled Ti–8% V (E = 72–94 GPa) and (Ti–8% V)–4%Sn (E = 63–85 GPa). The observed anisotropy of Young's modulus can be reasonably explained in terms of the cold rolling α′ texture.0.2% proof stress and tensile strength are independent of tensile orientation for cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys. In contrast, larger elongation to fracture is obtained in specimens deviated by 30°, 45° and 60° from RD than by 0°, 75° and 90°. Scanning electron microscopy (SEM) fractographs reveal that quasi-cleavage-like fracture plane appears in 0° specimen of cold rolled Ti–8% V which shows brittle fracture and other specimens of cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys are fractured accompanied with necking and dimple formation. It is suggested from these results that brittle fracture is related to the activation of limited number of slip system and Sn addition leads to the activation of multiple slip systems.     

Friends in fission: US–Brazil relations and the global stresses of atomic energy, 1945–1955

This article considers a relatively unknown episode in the early Cold War that involved the US and Brazil, as well as a number of other countries. From 1950, the leading figure in Brazil's nuclear effort, Admiral Álvaro Alberto, established amicable connections with the representatives of other nations in order to make it possible for Brazil to develop an atomic energy complex. The U.S. reaction to the Brazilian initiative was sharp and restrictive, involving a combination of coercion and persuasion, and it reverberated in a larger matrix of hemispheric and global economic and security concerns. In this case, science diplomacy did not actually have the benign character often ascribed to it. We argue that it was instead an integral part of a set of diplomatic practices aimed at strengthening U.S. global hegemony rather than a means of addressing global concerns.     

A study of tensile properties in Al–Si–Cu and Al–Si–Mg alloys: Effect of β-iron intermetallics and porosity

The effect of β-iron intermetallics and porosity on the tensile properties in cast Al–Si–Cu and Al–Si–Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of β-iron intermetallics, most noticeable up to β-iron intermetallic lengths of 100 μm in 319.2 alloys, or 70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate–high Fe and high cooling rate–low Fe. The results are explained in terms of the β-Al₅FeSi platelet size and porosity values obtained.     

Electric and Mechanical Switching of Ferroelectric and Resistive States in Semiconducting BaTiO3–δ Films on Silicon

Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water‐based chemical‐solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n‐doping and nanostructuring a BaTiO₃ thin film on Si(001) is explored. It is found that the ferroelectric polarization can be reversed, and resistive switching can be measured, upon a mechanical load in epitaxial BaTiO_3?δ /La_0.7Sr_0.3MnO₃/SrTiO₃/Si columnar nanostructures. A flexoelectric effect is found, stemming from substantial strain gradients that can be created with moderate loads. Simultaneously, mechanical effects on the local conductivity can be used to modulate a nonvolatile resistive state of the BaTiO_3?δ heterostructure. As a result, three different configurations of the system become accessible on top of the usual voltage reversal of polarization and resistive states.     

Influence of subgrain orientation on martensitic transformation in β1–Cu–Zn–Al-single crystals

In β₁–Cu–Zn–Al single crystals the course of cyclic martensititic transformation ‘β₁ parent phase↔γ′₁ martensite’ induced by tensile stress were studied with use of X-ray topography, light microscopy and etch pits. Two groups of single crystals were studied. The first one (OR) contained single crystals of subgrain boundaries parallel to the direction of elongation [001], the second one (RA) consisted of single crystals of random subgrain boundaries orientations. Single crystals from the RA group cracked after about 300 cycles of martensitic transformation; single crystals from the OR group did not crack even after 1200 cycles. In OR single crystals changes of dislocation density inside the subgrains caused by cycling occurred much more slowly than in the RA single crystals. This has been related to the dislocation movement from inside the subgrains to their boundaries.