Solute Trapping Research Articles

Solute trapping phenomenon in binary systems and hodograph-equation within effective mobility approach

The phase field model is developed by the effective mobility approach to slow and rapid solidification. The phase field model equations are reduced to the hodograph equation for solid-liquid interface movement which is applied to the problem of solute trapping in a binary alloy. A specific method based on the one-point Cauchy problem is developed for solution of the hodograph equation with the solute diffusion equation. The method is tested in comparison with the rapid solidification of Si–0.1 at.% As alloy previously analyzed experimentally and using phase field modelling.

Inverse kinematics solution and motion simulation of seven-degree-of-freedom ascending platform based on neural network

A pseudoinverse-based inverse kinetic solving scheme for 7-degree-of-freedom redundant aerial platform robotic arm, the scheme combines Minimum Velocity Norm scheme and damped least-square method, a close-loop damped minimum velocity norm scheme is set up which allows to avoid the joints’ limitation and to ensure the solution’s stability near the singularity position. Further, a genetic algorithm optimized BP neural network is built. Genetic algorithm can improve the training efficiency and avoid trapping in local optimal solution. The application of neural network can ensure the real-time of solution.

Transition Path Dynamics of a Dielectric Particle in a Bistable Optical Trap.

Many processes in chemistry, physics, and biology involve rare events in which the system escapes from a metastable state by surmounting an activation barrier. Examples range from chemical reactions, protein folding, and nucleation events to the catastrophic failure of bridges. A challenge in understanding the underlying mechanisms is that the most interesting information is contained within the rare transition paths, the exceedingly short periods when the barrier is crossed. To establish a model process that enables access to all relevant timescales, although highly disparate, we probe the dynamics of single dielectric particles in a bistable optical trap in solution. Precise localization by high-speed tracking enables us to resolve the transition paths and relate them to the detailed properties of the 3D potential within which the particle diffuses. By varying the barrier height and shape, the experiments provide a stringent benchmark of current theories of transition path dynamics.

Solving technician routing and scheduling problem using improved particle swarm optimization

In this paper, an improved particle swarm optimization (IPSO) algorithm is proposed to solve the technician routing and scheduling problem (TRSP). The TRSP consists of the assignment of technicians into teams, the assignment of teams to tasks, the construction of routes, and the selection of the day on which a service is provided by considering the proficiency level of workers and the proficiency requirement of the task. The paper considers the planning horizon as a multi-period covering 5 days, which further increases the complexity of the problem. Then a task can be fulfilled in any one of 5 days. The IPSO algorithm includes a particle swarm optimization (PSO) algorithm and one neighborhood operator. One neighborhood operator is used to avoid the local solution trap since the global best solution found by PSO is falling into a local solution trap. Further, the proposed algorithm’s performance is experimentally compared with the branch-and-cut algorithm for the solution of the TRSP, on the benchmark instances generated from the literature. The computational results show that IPSO provides better solutions considering the branch-and-cut algorithm within reasonable computing time.

Single-Molecule Plasmonic Optical Trapping

Summary The volume of the object that can be manipulated in solution is continuously decreasing toward an ultimate goal of a single molecule. However, Brownian motions suppress the molecular trapping. To date, free-molecule trapping in solution has not been accomplished. Here, we develop a strategy to directly trap, investigate, and release single molecules (∼2 nm) in solution by using an adjustable plasmonic optical nanogap, which has been further applied for selective single-molecule trapping. Comprehensive experiments and theoretical simulations demonstrated that the trapping force originated from plasmonic nanomaterials. This technique opens an avenue to manipulate single molecules and other objects in the size range of primary interest for physics, chemistry, and life and material sciences without the limitations of strong bonding group, ultra-high vacuum, and ultra-low temperature, and makes possible controllable single-molecule manipulation and investigation as well as bottom-up construction of nanodevices and molecular machines.

Growth mode control for direct-gap core/shell Ge/GeSn nanowire light emission

Germanium-tin is a promising semiconductor alloy system for novel light emitting devices and optical sensors in the mid-IR region. For sufficiently high Sn compositions, the material has a direct band-gap near 0.5 eV, and could have applications either as a detector or an emitter. Although high Sn compositions have been achieved in Ge1−xSnx through a variety of growth strategies, the understanding of how chemical vapor deposition conditions affect Sn composition and optical properties in core–shell Ge/Ge1−xSnx nanowires is still lacking. In this study, gas precursor partial pressures and shell growth temperatures are systematically varied to provide guiding principles to overcome obstacles for higher Sn incorporation. We achieve a direct band-gap material using an elastically compliant Ge core nanowire substrate. In the course of the growth study, we demonstrate several findings regarding the Ge1−xSnx shell growth mechanism. First, we observe an H2 passivation effect in which higher H2 to SnCl4 partial pressure ratio results in a concurrent increase in axial wire growth and decrease in radial growth. Second, we find that Ge1−xSnx shell growth in the studied CVD process is mass transport limited. Third, our results suggest that low shell growth temperature and high shell growth rate facilitate high Sn composition through metastable Sn solute trapping due to suppressed surface diffusion relative to the velocity of advancing shell surface steps. In this work, we demonstrate single nanowire photoluminescence at room temperature from core-shell Ge/Ge0.88Sn0.12 nanowires. Understanding the Ge1−xSnx shell growth mechanism via chemical vapor deposition (CVD) facilitates achieving minimal residual strain in the shell and the high crystalline quality and large Sn composition necessary for the observed optical properties. The results are universally applicable to Ge1−xSnx thin film epitaxy on compliant substrates including grown or etched nanowires, nanosheets, or free-standing 2D crystals.

Microfluidic water-assisted trap focusing method for ultra-large volume injection in reversed-phase nano-liquid chromatography coupled to electron ionization tandem-mass spectrometry

Herein we present an efficient, column-switching method that relies on a custom-made T-union passive diffusion micromixer to assist water dilution and promote trap solute focusing of a high sample volume dissolved in pure organic solvent using a 0.075mm i.d. nano-LC column. This method allows injecting 20 μL (or higher) of sample volume, speeding up the analysis time, with a 400-fold increase of the limits of quantitation for selected compounds. Five pesticides in different media were used as model compounds, and the analyses were carried out with a triple quadrupole mass spectrometer equipped with a Liquid Electron Ionization (LEI) LC-MS interface working in multiple reaction monitoring (MRM) mode. The system microfluidics were investigated using COMSOL modeling software. Robustness of the entire system was evaluated using a post-extraction addition soil extracts with limits of detection values spanning from 0.10 to 0.45µg/L. Reproducible results in terms of peak area, peak shape, and retention times were achieved in soil matrix. Repeatability test on peak area variations were lower than 10%.

Interface kinetics of rapid solidification of binary alloys by atomistic simulations: Application to Ti-Ni alloys

Using molecular dynamics and Monte Carlo simulations we investigate the non-equilibrium interfacial kinetics during rapid solidification of Ti-Ni alloys. According to the existing theories, the kinetic coefficient is related, via an analytical expression, to the equilibrium and non-equilibrium solute concentration profiles across the crystal-melt interface, the interface temperature and velocity, and the drag coefficient. The kinetic coefficient was obtained by deriving these properties from specifically designed atomistic simulations and then fitting using the analytical expression. The results show that the kinetic coefficient is only weakly anisotropic and increases with increasing temperature. The velocity-dependent partition coefficient, as described by two solute trapping models, the continuous growth and the local non-equilibrium models, were fitted to the molecular dynamics simulation results. In addition, molecular dynamics and semi-grand canonical Monte Carlo simulations suggest that complete solute trapping might occur only under certain conditions. This can be explained by the fact that the maximum achievable effective free energy driving force for solidification, which defines the complete solute trapping, is limited by the chemical potential and free energy profiles for the Ti-Ni alloy. The investigations, using molecular dynamics simulations, of the dependence of crystal-melt interface width on solidification velocity show, at high velocities, similar trend to that predicted by the hyperbolic phase field model which is suitable for studies of rapid solidification of alloys.

Tellurium determination by three modes of instrumental neutron activation analysis in aerosol filters and trap solutions for the simulation of a severe nuclear accident

Tellurium belongs to the elements not frequently determined by neutron activation analysis (NAA) or other analytical methods. We present results of a new methodological study using three independent modes of instrumental NAA (INAA) using the 123mTe, 131Te and 131I radionuclides. We compare the results obtained in terms of accuracy, precision and limits of detection (LOD). We utilized the INAA procedures tested for the tellurium determination in aerosol filters and trap solutions in a model experiment aimed at reducing the knowledge gap concerning the behaviour of 132Te, a radiologically significant fission product, which constitutes a considerable health risk towards the public in case of its release in a severe nuclear power plant accident. We found that the nuclear reaction 130Te(n,γ)131Te and gamma-ray spectrometric measurement of 131I, a descendant of 131Te, is the most sensitive way of Te determination by INAA providing as low LOD values as 0.15 µg of Te in the Teflon aerosol filters and 0.22 µg mL-1 in the 0.1 M NaOH trap solutions. The three independent INAA modes allowed employing the self-verification principle of INAA for increasing the trustworthiness of our results. Finally, we also point to the indispensable role of the non-destructive feature of INAA for assay of samples, such as Teflon aerosol filters, that are difficult to be analysed by other analytical methods requiring complete sample destruction without analyte losses.

Interface velocity dependent solute trapping and phase selection during rapid solidification of laser melted hypo-eutectic Al-11at.%Cu alloy

Microstructure formation of a hypo-eutectic Al-11Cu (atom percent) alloy during solidification after laser melting has been studied by transmission electron microscopy (TEM). The evolution of the solid-liquid-interface velocity, VSL, during the solidification process has been determined from direct observation by in-situ TEM. This enabled correlating VSL with development of four distinct microstructure zones. Crystal growth mode transitions from planar to cellular, cellular to dendritic, dendritic to cellular, and cellular to planar, have been observed for the accelerating solid-liquid-interface. The transition from coupled two-phase growth to the single-phase growth occurred for VSL = Va = (0.80±0.05) m/s, where Va is the velocity of absolute stability, at the onset of banded morphology grain formation. The in-situ and post-mortem TEM uniquely permitted determination of the non-equilibrium solidus for the rapidly solidifying Al-11Cu alloy. Experimental evidence for solute clustering and chemical ordering tendencies at length scales on the order of ≤ 5nm has been detected in the single-phase regions of the banded grains. The structural features of the single-phase bands have been interpreted as signatures of ‘frozen in’ configurations present in the liquid boundary layer adjacent to the growing crystal, which has a width of about 3nm. The nano-scale spatiotemporal resolution experimental TEM studies performed here provided quantitative metrics, e.g. the solidification interface velocity dependent solute concentration of the α-Al phase and the near-atomic scale structure in the single-phase bands, that are uniquely suitable for comparison with theory and model predictions for solidification microstructure development in multicomponent alloys after laser melting.

Fabrication of high-strength Mg-Gd-Zn-Zr alloy via selective laser melting

A Mg-11.00Gd-1.77Zn-0.43Zr (wt.%) alloy named GZ112K was prepared by selective laser melting (SLM) with different processing parameters. The formability, element vaporization, microstructure and tensile properties of the SLMed samples at different scanning speed and hatch spacing were characterized. The process map at a constant laser power of 80 W for the alloy has been established. It shows that the optimum scanning speed and hatch spacing are 300–700 mm/s and 100 μm respectively. The SLMed samples have fine grains of about 2 μm and dispersed eutectic phase of β-(Mg,Zn)3Gd due to the very high cooling rate, high solid solubility of Gd and Zn elements in ɑ-Mg matrix owing to the effect of solute trapping. The SLMed GZ112K alloy with scanning speed of 300 mm/s and hatch spacing of 100 μm has yield strength (YS) of 325 MPa, ultimate tensile strength (UTS) of 332 MPa and elongation of 4.0% at room temperature. Compared with as-cast alloy, the SLMed GZ112K alloy has much higher YS (+162 MPa), UTS (+122 MPa) and comparable elongation (+0.4%).

Assessing the Effect of Laboratory Environment on Sample Contamination for I-129 Accelerator Mass Spectrometry.

Environmental contaminations of 129I were continuously monitored in various sample preparation rooms for accelerator mass spectrometry at the University of Tsukuba. Monitoring of 129I was performed in the rooms used for the treatment of samples in the past, in order to compare with the results obtained in the sample preparation rooms. Ambient levels of atmospheric 129I in each room were estimated from the measured concentrations in the alkali trap solutions. This article reports the results of one year of monitoring the temporal changes of stable iodine (127I) and 129I contamination rates in the alkali trap solutions. It was found that 129I contamination rates were lower than approximately 104 atoms cm-2 day-1 in the rooms where ether no samples or only samples with environmental background levels of 129I were handled. Values from 104 to 105 atoms cm-2 day-1 were recorded in another room where environmental samples, such as the samples derived from nuclear power plant accidents, were treated. Higher levels of 129I, ranging from 106 to 107 atoms cm-2 day-1, were recorded in rooms used for treating neutron-activated iodine. The experimental results show that the 129I level depended on the 129I sample-preparation histories for the respective rooms. It is possible to estimate the 129I contamination risk from the atmosphere to the samples by knowing the 129I level in the preparation room.

Molecular dynamics study of the thermodynamic and kinetic properties of the solid-liquid interface in FeMn

The solid-liquid phase equilibria as a function of temperature and composition has been computed for the Fe-Mn system using a semi-grand canonical Monte Carlo technique. Interaction between atoms were modeled using a second nearest neighbor modified embedded atom method potential. In addition, the excess solid-liquid interfacial free energy (γ) and its anisotropy has been computed from the capillary fluctuation method. The results indicate that there is very little variation in γ with temperature/composition. We also propose a new MD simulation method for computing solute trapping behavior that is able to access relatively low interface velocities. The segregation coefficient as a function of velocity for the Fe-Mn system was determined for three temperatures and the results are discussed within the framework of previously proposed theoretical models.

Convective activity in a Martian magma chamber recorded by P‐zoning in Tissint olivine

AbstractThe Tissint Martian meteorite is an unusual depleted olivine‐phyric shergottite, reportedly sourced from a mantle‐derived melt within a deep magma chamber. Here, we report major and trace element data for Tissint olivine and pyroxene, and use these data to provide new insights into the dynamics of the Tissint magma chamber. The presence of irregularly spaced oscillatory phosphorous (P)‐rich bands in olivine, along with geochemical evidence indicative of a closed magmatic system, implies that the olivine grains were subject to solute trapping caused by vigorous crystal convection within the Tissint magma chamber. Calculated equilibration temperatures for the earliest crystallizing (antecrystic) olivine cores suggest a Tissint magma source temperature of 1680 °C, and a local Martian mantle temperature of 1560 °C during the late Amazonian—the latter being consistent with the ambient mantle temperature of Archean Earth.

Segregation and activation of Sb implanted in Si by UV nanosecond-laser-anneal-induced non-equilibrium solidification

In advanced logic devices, access resistance to transistors is dominated by metal–semiconductor contact resistivity. Recent studies report values below 1 × 10−9 ohm cm2, realizing metastable incorporation of dopants into epitaxially grown semiconductor materials. In this study, we have investigated segregation and activation of antimony (Sb) implanted in silicon (Si) epilayers by using UV nanosecond pulsed laser annealing (LA). The Sb-implanted Si epilayers were partially or fully molten by LA, followed by the analysis of atomic and electrically active dopant concentrations as well as the observation of surface morphology evolution. To discuss the impact of the solute trapping phenomenon on substitutional incorporation of the Sb atoms, we also simulated the evolution of solidification front velocity in the LA-induced non-equilibrium solidification. It is noteworthy that the active level of the Sb atoms largely surpasses their reported equilibrium solubility limit (∼2.6 × 1020 at./cm3 compared to ∼6.8 × 1019 at./cm3) when the non-equilibrium solidification approaches a near-complete solute trapping regime.

Multistable circular currents of polariton condensates trapped in ring potentials.

We demonstrate the formation and trapping of different stationary solutions, oscillatory solutions, and rotating solutions of a polariton condensate in a planar semiconductor microcavity with a built-in ring-shaped potential well. Multistable ring-shaped solutions are trapped in shallow potential wells. These solutions have the same ring-shaped density distribution but different topological charges, corresponding to different orbital angular momentum (OAM) of the emitted light. For stronger confinement potentials, besides the fundamental modes, higher excited (dipole) modes can also be trapped. If two modes are excited simultaneously, their beating produces a complex oscillation or rotation dynamics. When the two modes have the same OAM, a double-ring solution forms for which the density oscillates between the inner and the outer ring. When the two modes have different OAM, a rotating solution with fractional OAM is created.

High-power sonication of soy proteins: Hydroxyl radicals and their effects on protein structure.

High-power sonication (HPS) is shown to alter protein structure, thus, its functionality, via intermolecular interactions. This study evaluated the effects of HPS on molecular structure of soy proteins in aqueous medium. Free radicals generated during HPS were quantitated using the 5,5-dimethyl-l-pyrrolin N-oxide (DMPO) spin trap method. Electron paramagnetic resonance (EPR) was used to identify them as mostly hydroxyl radicals. The minimum saturation concentration of spin trap solution was determined to be 500mM of DMPO in water, when exposed to 5W/cm3 ultrasound power density (PD) for 10min; subsequently, this concentration was used for quantitating radicals generated in protein samples. Five aqueous soy protein systems, namely, 5% soy protein isolate (SPI), 5% SPI without isoflavonoids (NO-ISO SPI), subunit solutions 1% glycinin (11S) and 1% β conglycinin (7S), and 10% soy flakes (w/v), were sonicated at 2.5 and 5W/cm3 PDs. Only adducts of hydroxyl radicals (DMPO-OH) were detected in all of these aqueous systems. The highest concentration (3.68µM) of DMPO-OH adduct was measured in 11S subunit solution at 5W/cm3, whereas, the lowest (0.67µM) was in soy flakes solution at 2.5W/cm3. PD 5W/cm3 generated higher concentration of radicals in 7S subunit solution, NO-ISO SPI, and soy flakes protein, compared to sonication at PD 2.5W/cm3. No change in the protein electrophoretic patterns were observed due to HPS. However, some changes due to HPS were observed in the estimated secondary and tertiary structures, and the contents of free sulfhydryl groups and disulfide bonds in proteins.

Multiple origins of anomalous eutectic microstructure in rapidly solidified Mg-Al alloy

Mg-33.3 wt.%Al eutectic alloys were fabricated by melt spinning at wheel speeds from 5 to 50 ms−1. SEM and S/TEM analyses showed the formation of anomalous eutectic structures at all wheel speeds. Four distinctive eutectic microstructures were observed, depending on the wheel speed, each with a unique formation mechanism. At low wheel speeds, solute trapping and high interfacial energy resulted in the remelting of primarily grown regular eutectic microstructures and was responsible for the formation of the anomalous eutectic Type A. A coupled-to-decoupled-growth transition occurred at intermediate wheel speeds giving rise to the anomalous eutectic Type B. The decoupled nucleation and growth of the eutectic phases followed by a coupled dendritic growth lead to the formation of flower-like microstructures at anomalous eutectic Type C. At sufficiently high wheel speed, no sign of regular eutectic was found and a unique cellular microstructure of ϒ phase along with inter- or intragranular α phase grains was formed, anomalous eutectic Type D, as a result of the decoupled nucleation and growth of the eutectic phases. The observed microstructures were examined thoroughly, and the correlated formation mechanisms were discussed on the basis of the SEM images and S/TEM and EDS analysis.

Boundary interface conditions and solute trapping near the transition to diffusionless solidification

The process of rapid solidification of a binary mixture is considered in the framework of local nonequilibrium model (LNM) based on the assumption that there is no local equilibrium in solute diffusion in the bulk liquid and at the solid-liquid interface. According to LNM the transition to complete solute trapping and diffusionless solidification occurs at a finite interface velocity $V=V_D$, where $V_D$ is the diffusion speed in bulk liquid. In the present work, the boundary conditions at the phase interface moving with the velocity $V$ close to $V_D$ ($V \lesssim V_D$) have been derived to find the non-equilibrium solute partition coefficient. In the high-speed region, its comparison with the partition coefficient from the work [Phys. Rev. E 76 (2007) 031606] is given.

Propylene glycol: a promising preservative for insects, comparable to ethanol, from trapping to DNA analysis

AbstractRecent advances in DNA analysis allow us to identify an unprecedented number of insect samples collected by mass sampling techniques such as insect traps. In these circumstances, a preservative that can be applied from trap to storage is necessary to prevent degradation of DNA before analysis and save on the cost of labor for collecting insects from traps. Propylene glycol has a prominent feature as a trap solution. We aimed to examine the DNA preservability of 98% propylene glycol at 2 weeks and more than 6 months after initial collection in comparison with 99.5% ethanol, which is commonly used for storage of specimens for genetic analysis. We compared amplification performance of PCR targeting a specific region of the mitochondrial cytochrome c oxidase subunit I (COI) gene in the orders Hymenoptera, Diptera, and Coleoptera using two extraction methods varying in extraction efficiency. Even after 6 months, more than 75% of samples were recognized to have succeeded in PCR amplification irrespective of preservatives by the extraction method with higher extraction efficiency. It suggested that mitochondrial DNA was preserved in both solutions. However, dim bands in the electrophoreses of PCR products increased with time in extracts by another method with lower extraction efficiency. In Diptera and Coleoptera, the rate of dim bands increased more rapidly for ethanol‐preserved than for propylene glycol‐preserved specimens, indicating higher DNA preservability of propylene glycol over time for these taxa. On the other hand, in Hymenoptera, the preservatives did not affect PCR amplification performance. Considering its safer characteristics and high DNA preservability in a wide range of taxa, propylene glycol can be a promising solution from trapping of insects to storage for genetic analysis.