Concentration dependence of the crystal nucleation kinetics in undercooled Cu-Ge melts.

The crystallization temperature of deeply undercooled Cu-Ge alloy melts is repeatedly measured. A statistical analysis is applied on the undercooling distributions obtained from nine different compositions, ranging from the pure semimetal (Ge) to the pure metal (Cu). By considering each undercooling distribution as an inhomogeneous Poisson process, the nucleation rates for every composition are calculated. The Thompson-Spaepen model for homogeneous nucleation in binary alloys is applied, enabling the estimation of nucleation parameters, such as kinetic pre-factors and interfacial energies, as a function of composition. Furthermore, the Turnbull coefficient α, a dimensionless solid-liquid interfacial energy constant, is also calculated as a function of alloy constitution, suggesting a dependence on the liquid composition. The composition-dependent changes of α are of considerable importance, since the α is originally defined for pure systems as a quantity dependent on crystal structure, and is nevertheless used for describing nucleation kinetics of binary and glass forming multi-component alloy systems.

Strain perceptibility of elements on the diffusion in Zr-based amorphous alloys.

With the discovery of bulk metallic glasses (BMGs), there has been considerable interest in understanding their mechanical behavior. In spite of these previous observations on the relation between plastic deformation of metallic glasses and their diffusion behavior, a detailed understanding on the diffusion of BMGs is still unexplored. We evaluated the contribution of deformation-induced structural transformations (elastic, anelastic, viscoplastic or viscoelastic responsive and plastic strain) on the diffusion of Zr-based bulk metallic glasses in as-cast, elastostatically stressed and plastically deformed states. Experimental investigations of the diffusion process and the elemental distributions in the glassy alloy were performed following plastic deformation by multiple cold rolling and elastostatic cyclic compression, respectively. We compared the vacancy model and the transition state model to verify the diffusion mechanism in the deformed bulk metallic glass. The diffusion of tracer atoms, i.e., Fe, in the bulk metallic glass is affected by viscoelastic responsive strain governing the transition-state model. In contrast, the diffusion of constituent atoms, i.e., Ti, Zr, in the bulk metallic glass is dominantly affected by plastic strain governing the vacancy model. The results reveal that the diffusion behavior of bulk glassy alloys can be changed by variation of the constituent elements and applying different strain modes upon deformation.

Interstitial clustering in metallic systems as a source for the formation of the icosahedral matrix and defects in the glassy state.

The paper presents molecular dynamics and -statics simulations of a prototypical mono-atomic metallic system (aluminum) and its defects in the crystalline and glassy states. It is shown that there is a thermodynamic driving force for the association of dumbbell interstitials in the crystalline lattice into clusters consisting of different amounts of defects. Clusters containing seven interstitials constitute perfect icosahedra. Within the general framework of the interstitialcy theory, melting of simple metallic crystals is intrinsically related to a rapid increase of the concentration of dumbbell interstitials, which remain identifiable structural units in the liquid state. Then, the glass produced by rapid melt quenching contains interstitial-type defects. The idea of the present work is to argue that the major structural feature of many metallic glasses-icosahedral ordering-originates from the clustering of interstitial-type defects frozen-in upon melt quenching. Separate defects and their small clusters represent the defect part of the glassy structure.

Analysis of medium-range order based on simulated segmented ring detector STEM-images: amorphous Si.

Properties of amorphous materials are connected to the local structure at the nanoscale, which is typically described in terms of short- and medium-range order (SRO, MRO). Variable resolution fluctuation electron microscopy (VR-FEM) is a sensitive method to characterize the underlying characteristic length scale of MRO of amorphous samples (Voyles, Gibson and Treacy, J. Electron Microsc. 49 (2000) 259). VR-FEM data was acquired using scanning transmission electron microscopy (STEM), collecting a large number of nano-beam diffraction patterns (NBDPs) with various probe sizes. Here we present an advanced method to accelerate the calculation of simulated FEM normalized variance profiles using a newly developed simulation and analysis approach with segmented ring detectors using the program STEMcl (Radek et al., Ultramicroscopy 188 (2018) 24). VR-FEM simulations are based on structures obtained from molecular dynamics (MD) simulations. A comparison between simulated and experimental VR-FEM profiles with respect to peak position, ratio and shape (and intensity) show good agreement. Moreover, a crystalline cluster of 1 nm in size was embedded into the MD box to test the validity of the paracrystalline approximation with the pair-persistence analysis suggested by Gibson et al. (Gibson, Treacy and Voyles, Ultramicroscopy 83 (2000) 169). The corresponding VR-FEM simulation and calculation of MROs yield close results to the size of the initially embedded crystalline cluster, which supports both the paracrystalline approach and the validity of the segmented detector simulation. Additionally, we conclude that continuous random network (CRN) amorphous silicon models contain a higher degree of MRO than experimentally expected.

STEMcl-A multi-GPU multislice algorithm for simulation of large structure and imaging parameter series.

Electron microscopy images are interference patterns and can generally not be interpreted in a straight forward manner. Typically, time consuming numerical simulations have to be employed to separate specimen features from imaging artifacts. Directly comparing numerical predictions to experimental results, realistic simulation box sizes and varying imaging parameters are needed. In this work, we introduce an accelerated multislice algorithm, named STEMcl, that is capable of simulating series of large super cells typical for defective and amorphous systems, in addition to parameter series using the massive parallelization accessible in today's commercial PC-hardware, e.g. graphics processing units (GPUs). A new numerical approach is used to overcome the memory constraint limiting the maximum computable system size. This approach creates the possibility to study systematically the contrast formation arising by structural differences. STEM simulations of structure series of a crystalline Si and an amorphous CuZr system are presented and the contrast formation of vacancies/voids are studied. The detectability of vacancies/voids in STEM experiments is discussed in terms of density changes.

Radioactive isotopes reveal a non sluggish kinetics of grain boundary diffusion in high entropy alloys.

High entropy alloys (HEAs) have emerged as a new class of multicomponent materials, which have potential for high temperature applications. Phase stability and creep deformation, two key selection criteria for high temperature materials, are predominantly influenced by the diffusion of constituent elements along the grain boundaries (GBs). For the first time, GB diffusion of Ni in chemically homogeneous CoCrFeNi and CoCrFeMnNi HEAs is measured by radiotracer analysis using the 63Ni isotope. Atom probe tomography confirmed the absence of elemental segregation at GBs that allowed reliable estimation of the GB width to be about 0.5 nm. Our GB diffusion measurements prove that a mere increase in number of constituent elements does not lower the diffusion rates in HEAs, but the nature of added constituents plays a more decisive role. The GB energies in both HEAs are estimated at about 0.8-0.9 J/m2, they are found to increase significantly with temperature and the effect is more pronounced for the CoCrFeMnNi alloy.

Finite element modelling of radial lentotomy cuts to improve the accommodation performance of the human lens.

PURPOSE: The use of a femtosecond laser to form planes of cavitation bubbles within the ocular lens has been proposed as a potential treatment for presbyopia. The intended purpose of these planes of cavitation bubbles (referred to in this paper as 'cutting planes') is to increase the compliance of the lens, with a consequential increase in the amplitude of accommodation. The current paper describes a computational modelling study, based on three-dimensional finite element analysis, to investigate the relationship between the geometric arrangement of the cutting planes and the resulting improvement in lens accommodation performance. The study is limited to radial cutting planes. METHODS: The effectiveness of a variety of cutting plane geometries was investigated by means of modelling studies conducted on a 45-year human lens. RESULTS: The results obtained from the analyses depend on the particular modelling procedures that are employed. When the lens substance is modelled as an incompressible material, radial cutting planes are found to be ineffective. However, when a poroelastic model is employed for the lens substance, radial cuts are shown to cause an increase in the computed accommodation performance of the lens. In this case, radial cuts made in the peripheral regions of the lens have a relatively small influence on the accommodation performance of the lens; the lentotomy process is seen to be more effective when cuts are made near to the polar axis. CONCLUSIONS: When the lens substance is modelled as a poroelastic material, the computational results suggest that useful improvements in lens accommodation performance can be achieved, provided that the radial cuts are extended to the polar axis. Radial cuts are ineffective when the lens substance is modelled as an incompressible material. Significant challenges remain in developing a safe and effective surgical procedure based on this lentotomy technique.

Non-destructive functionalisation for atomic layer deposition of metal oxides on carbon nanotubes: effect of linking agents and defects.

The hybridisation of metal oxides and nanocarbons has created a promising new class of functional materials for environmental and sustainable energy applications. The performance of such hybrids can be further improved by rationally designing interfaces and morphologies. Atomic layer deposition (ALD) is among the most powerful techniques for the controlled deposition of inorganic compounds, due to its ability to form conformal coatings on porous substrates at low temperatures with high surface sensitivity and atomic control of film thickness. The hydrophobic nature of the nanocarbon surface has so far limited the applicability of ALD on CNTs. Herein we investigate the role of structural defects in CNTs, both intrinsic and induced by acid treatment, on coverage, uniformity and crystallinity of ZnO coatings. Furthermore, we demonstrate the potential of small aromatic molecules, including benzyl alcohol (BA), naphthalene carboxylic acid (NA) and pyrene carboxylic acid (PCA), as active nucleation sites and linking agents. Importantly, only PCA exhibits sufficiently strong interactions with the pristine CNT surface to withstand desorption under reaction conditions. Thus, PCA enables a versatile and non-destructive alternative route for the deposition of highly uniform metal oxide coatings onto pristine CNTs via ALD over a wide temperature range and without the typical surface corrosion induced by covalent functionalisation. Importantly, preliminary tests demonstrated that the improved morphology obtained with PCA has indeed considerably increased the hybrid's photocatalytic activity towards hydrogen evolution via sacrificial water splitting. The concept demonstrated in this work is transferable to a wide range of other inorganic compounds including metal oxides, metal (oxy)nitrides and metal chalcogenides on a variety of nanocarbons.

Nanomagnonic devices based on the spin-transfer torque.

Magnonics is based on signal transmission and processing by spin waves (or their quanta, called magnons) propagating in a magnetic medium. In the same way as nanoplasmonics makes use of metallic nanostructures to confine and guide optical-frequency plasmon-polaritons, nanomagnonics uses nanoscale magnetic waveguides to control the propagation of spin waves. Recent advances in the physics of nanomagnetism, such as the discovery of spin-transfer torque, have created possibilities for nanomagnonics. In particular, it was recently demonstrated that nanocontact spin-torque devices can radiate spin waves, serving as local nanoscale sources of signals for magnonic applications. However, the integration of spin-torque sources with nanoscale magnetic waveguides, which is necessary for the implementation of integrated spin-torque magnonic circuits, has not been achieved to date. Here, we suggest and experimentally demonstrate a new approach to this integration, utilizing dipolar field-induced magnonic nanowaveguides. The waveguides exhibit good spectral matching with spin-torque nano-oscillators and enable efficient directional transmission of spin waves. Our results provide a practical route for the implementation of integrated magnonic circuits utilizing spin transfer.

Impact of plastic deformation and shear band formation on the boson heat capacity peak of a bulk metallic glass.

The effect of annealing on the low-temperature heat capacity of a bulk Pd38.5Ni40P21.5 metallic glass is investigated for as-quenched and deformed (rolled) states. Although the boson heat capacity peak increases with increasing strain, it relaxes faster and to a lower level compared to that of the as-quenched state after annealing treatments both below and above the glass transition temperature Tg. The glass is found to retain a certain "memory" on the room-temperature plastic deformation even after annealing above Tg. Indications for two counteracting processes that might be related to different types of shear bands are observed.

Shear modulus measurements on isolated human lens nuclei.

The use of a spinning lens test to determine ex vivo the shear modulus of 22 isolated human lens nuclei with ages ranging from 34 to 63 years is described. In this test procedure, the lens nucleus is spun about its polar axis. Images of the nucleus viewed from directions perpendicular to the polar axis are collected; these are used to quantify the deformations induced in the nucleus by the rotational motion. Data on these deformations are used to infer, by applying finite element inverse analysis, values for the shear modulus of the nucleus. The data on shear modulus obtained from this test program indicate that the nucleus stiffens very rapidly with age. These data are shown to compare well with the results of a related study (Wilde et al., 2012) in which the shear modulus of the nucleus is determined by similar spinning lens tests conducted on the entire lens substance.

Shear modulus data for the human lens determined from a spinning lens test.

The paper describes a program of mechanical testing on donated human eye bank lenses. The principal purpose of the tests was to obtain experimental data on the shear modulus of the lens for use in future computational models of the accommodation process. Testing was conducted using a procedure in which deformations are induced in the lens by spinning it about its polar axis. Shear modulus data were inferred from these observed deformations by means of a finite element inverse analysis procedure in which the spatial variation of the shear modulus within the lens is represented by an appropriate function (see Burd et al., 2011 for a detailed specification of the design of the spinning lens test rig, experimental protocols and associated data analysis procedures that were employed in the tests). Inferred data on lens shear modulus are presented for a set of twenty-nine lenses in the age range 12 years to 58 years. The lenses were tested between 47 h and 110 h from the time of death (average post-mortem time 74 h). Care was taken to exclude any lenses that had been affected by excessive post-mortem swelling, or any lenses that had suffered mechanical damage during storage, transit or the testing process. The experimental data on shear modulus indicate that, for young lenses, the cortex is stiffer than the nucleus. The shear modulus of the nucleus and cortex both increase with increasing age. The shear modulus of the nucleus increases more rapidly than the cortex with the consequence that from an age of about 45 years onwards the nucleus is stiffer than the cortex. The principal shear modulus data presented in the paper were obtained by testing at a rotational speed of 1,000 rpm. Supplementary tests were conducted at rotational speeds of 700 rpm and 1,400 rpm. The results from these supplementary tests are in good agreement with the data obtained from the principal 1,000 rpm tests. Studies on the possible effects of lens drying during the test suggested that this factor is unlikely to have led to significant errors in the experimental determination of the shear modulus. The shear modulus data presented in the paper are used to develop 'age-stiffness' models to represent the shear modulus of the lens as a function of age. These models are in a form that may be readily incorporated in a finite element model of the accommodation process. A comparison is attempted between the shear modulus data presented in the current paper and equivalent data published by previous authors. This comparison highlights various limitations and inconsistencies in the data sets.

Nucleation barriers for the liquid-to-crystal transition in Ni: experiment and simulation.

Nucleation in undercooled Ni is investigated by a combination of differential scanning calorimetry (DSC) experiments and Monte Carlo (MC) simulation. By systematically varying the sample size in the DSC experiments, nucleation rates J over a range of 8 orders of magnitude are obtained. Evidence is given that these rates correspond to homogeneous nucleation. Free energy barriers ΔG*, as extracted from the measured J, are in very good agreement with those from the MC simulation. The MC simulation indicates a nonspherical geometry of crystalline clusters, fluctuating between prolate and oblate shape at a given size. Nevertheless, the temperature dependence of ΔG* is well described by classical nucleation theory.

Size-dependent hysteresis and phase formation kinetics during temperature cycling of metal nanopowders.

We present a description of the evolution of a polymorphically transforming metal nanoparticle ensemble subjected to a temperature cycling with constant rates of temperature change. The calculations of the time dependence of the volume fraction of the new phase show the existence of size-dependent hysteresis and its main features. The statistical analysis makes it possible to introduce and determine the size-dependent superheating limit and supercooling limit.

An improved spinning lens test to determine the stiffness of the human lens.

It is widely accepted that age-related changes in lens stiffness are significant for the development of presbyopia. However, precise details on the relative importance of age-related changes in the stiffness of the lens, in comparison with other potential mechanisms for the development of presbyopia, have not yet been established. One contributing factor to this uncertainty is the paucity and variability of experimental data on lens stiffness. The available published data generally indicate that stiffness varies spatially within the lens and that stiffness parameters tend to increase with age. However, considerable differences exist between these published data sets, both qualitatively and quantitatively. The current paper describes new and improved methods, based on the spinning lens approach pioneered by Fisher, R.F. (1971) 'The elastic constants of the human lens', Journal of Physiology, 212, 147-180, to make measurements on the stiffness of the human lens. These new procedures have been developed in an attempt to eliminate, or at least substantially reduce, various systematic errors in Fisher's original experiment. An improved test rig has been constructed and a new modelling procedure for determining lens stiffness parameters from observations made during the test has been devised. The experiment involves mounting a human lens on a vertical rotor so that the lens spins on its optical axis (typically at 1000 rpm). An automatic imaging system is used to capture the outline of the lens, while it is rotating, at pre-determined angular orientations. These images are used to quantify the deformations developed in the lens as a consequence of the centripetal forces induced by the rotation. Lens stiffness is inferred using axisymmetric finite element inverse analysis in which a nearly-incompressible neo-Hookean constitutive model is used to represent the mechanics of the lens. A numerical optimisation procedure is used to determine the stiffness parameters that provide a best fit between the finite element model and the experimental data. Sample results are presented for a human lens of age 33 years.

Implications of stunting on morphology of freshwater fishes.

The purpose of this study was to assess morphological differences between stunted and non-stunted white perch Morone americana and green sunfish Lepomis cyanellus. Few female M. americana were captured; thus, morphological differences between adult males and juveniles were assessed for M. americana. Similarly, few immature (juvenile) L. cyanellus were captured for the stunted morphotype; thus, male and female morphological differences were assessed for L. cyanellus. Features of the head tended to be relatively larger in stunted fish of both species, whereas the mid-body tended to be relatively larger in non-stunted M. americana, but not in non-stunted L. cyanellus. Adult and juvenile morphology overlapped considerably in non-stunted M. americana, but there was a clear distinction between adult and juvenile morphology of stunted M. americana. There was little sexual dimorphism in shape in stunted L. cyanellus, whereas sexual dimorphism was evident in non-stunted L. cyanellus. It appears that selective forces imposed by predation and food limitation may contribute to morphological diversification between stunted and non-stunted fishes.

Kinetics of heterogeneous nucleation on intrinsic nucleants in pure fcc transition metals.

Nucleation during solidification is heterogeneous in nature in an overwhelmingly large fraction of all solidification events. Yet, most often the identity of the heterogeneous nucleants that initiate nucleation remains a matter of speculation. In fact, a series of dedicated experiments needs to be designed in order to verify if nucleation of the material under study is based on one type of heterogeneous nucleant and if the potency of that nucleant is constant, e.g. for a population of individual droplets, or stays constant over time, e.g. throughout repeated melting/solidification cycles. In this work it is demonstrated that one way to circumvent ambiguities and analyze nucleation kinetics under well-defined conditions experimentally is given by performing statistically significant numbers of repeated single-droplet experiments. The application of proper statistics analyses based upon a non-homogeneous Poisson process is shown to yield nucleation rates that are independent of a specific nucleation model. Based upon this approach nucleation undercooling measurements on pure Au, Cu and Ni as model materials have confirmed that the experimental strategy and analysis method are valid. The results are comparable to those obtained by classical nucleation theory applied to experimental data that has been verified to comply with the assertions that are necessary for applying this model framework. However, the results reveal also other complex nucleant-sample interactions such as an initial transient undercooling behavior and impurity removal during repeated cycling treatments. The transient undercooling behavior has been analyzed by a nucleant refining model to provide new insight on the operation of melt fluxing treatments.

Methodology for assessing rice varieties for resistance to the lesser grain borer, Rhyzopertha dominica.

Several physical and chemical attributes of rice were evaluated to determine which character would be best to use to assess multiple rice varieties for resistance to the lesser grain borer, Rhyzopertha dominica (F.). Laboratory tests were conducted on single varieties of long-, short-, and medium grain-rice to develop procedures and methodologies that could be used for large-scale screening studies. Progeny production of R. dominica was positively correlated with the percentage of broken hulls. Although kernel hardness, amylose content, neonate preference for brown rice, and adult emergence from neonates varied among the three rice varieties tested they did not appear to be valid indicators of eventual progeny production, and may not be useful predictors of resistance or susceptibility. Soundness and integrity seem to be the best characters to use for varietal screening studies with R. dominica.

Susceptibility of eggs and adult fecundity of the lesser grain borer, Rhyzopertha dominca, exposed to methoprene.

A series of tests were conducted to determine the susceptibility of eggs and neonates of the lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae = Bostrychidae), exposed to the insect growth regulator, methoprene, on filter paper and on rough rice. In the first test, the hatch rate of eggs exposed on filter paper treated with methoprene at the label rate of 0.003 mg [AI]/cm(2) when used as a surface treatment in structures was 52.0 +/- 7.3% compared to 93.0 +/- 3.3% on untreated controls. In the second test, eggs were exposed to a dose-response series of 0.00003 to 0.03 mg[AI]/cm(2). Egg hatch was directly proportional to concentration and ranged from 85.0 +/- 2.0% on untreated controls to 26.7 +/- 8.3% at the highest concentration tested. In the third test, 1 ppm of methoprene was sprayed on long grain rough rice (paddy) (Cocodrie variety), and then individual kernels were cracked and an egg of R. dominica was placed directly on the kernel. On untreated rice kernels, 67.5 +/- 11.6% of the eggs hatched and were able to bore inside, and all of these larvae emerged as adults. In contrast, 40.0 +/- 5.3% of the eggs placed on treated cracked kernels were able to develop to where the larvae were visible through X-ray detection, but none emerged as adults. In the final test, newly-emerged adults were exposed on rough rice treated with 1 ppm methoprene. The number of eggs from adults on untreated rice was 52.1 +/- 4.3 eggs per female, and on treated rice the average egg production was 12.5 +/- 1.1 eggs per female. Methoprene applied on a surface or on rough rice affected development of egg hatch also reduced fecundity of parent adults exposed on the treated rough rice.

Compartment syndrome following ankle sprain.

Injury to the perforating branch of the peroneal artery has not been reported previously as a cause of acute compartment syndrome following soft-tissue injury to the ankle. We describe the case of a 23-year-old male who sustained such an injury resulting in an acute compartment syndrome. In a review of the literature, we could find only five previous cases, all of which gave rise to a false aneurysm which was detected after the acute event.