Physics-informed machine learning for inorganic scintillator discovery.

Applications of inorganic scintillators-activated with lanthanide dopants, such as Ce and Eu-are found in diverse fields. As a strict requirement to exhibit scintillation, the 4f ground state (with the electronic configuration of [Xe]4fn 5d0) and 5d1 lowest excited state (with the electronic configuration of [Xe]4fn-1 5d1) levels induced by the activator must lie within the host bandgap. Here we introduce a new machine learning (ML) based search strategy for high-throughput chemical space explorations to discover and design novel inorganic scintillators. Building upon well-known physics-based chemical trends for the host dependent electron binding energies within the 4f and 5d1 energy levels of lanthanide ions and available experimental data, the developed ML model-coupled with knowledge of the vacuum referred valence and conduction band edges computed from first principles-can rapidly and reliably estimate the relative positions of the activator's energy levels relative to the valence and conduction band edges of any given host chemistry. Using perovskite oxides and elpasolite halides as examples, the presented approach has been demonstrated to be able to (i) capture systematic chemical trends across host chemistries and (ii) effectively screen promising compounds in a high-throughput manner. While a number of other application-specific performance requirements need to be considered for a viable scintillator, the scheme developed here can be a practically useful tool to systematically down-select the most promising candidate materials in a first line of screening for a subsequent in-depth investigation.

Piezomagnetism and magnetoelastic memory in uranium dioxide.

The thermal and magnetic properties of uranium dioxide, a prime nuclear fuel and thoroughly studied actinide material, remain a long standing puzzle, a result of strong coupling between magnetism and lattice vibrations. The magnetic state of this cubic material is characterized by a 3-k non-collinear antiferromagnetic structure and multidomain Jahn-Teller distortions, likely related to its anisotropic thermal properties. Here we show that single crystals of uranium dioxide subjected to strong magnetic fields along threefold axes in the magnetic state exhibit the abrupt appearance of positive linear magnetostriction, leading to a trigonal distortion. Upon reversal of the field the linear term also reverses sign, a hallmark of piezomagnetism. A switching phenomenon occurs at ±18 T, which persists during subsequent field reversals, demonstrating a robust magneto-elastic memory that makes uranium dioxide the hardest piezomagnet known. A model including a strong magnetic anisotropy, elastic, Zeeman, Heisenberg exchange, and magnetoelastic contributions to the total energy is proposed.The nuclear fuel uranium dioxide is of intrinsic interest due to its industrial applications but it also exhibits intriguing electronic and magnetic properties. Here, the authors demonstrate how its complex magnetic structure and interactions give rise to a strong piezomagnetic effect.

Pipe and grain boundary diffusion of He in UO2.

Molecular dynamics simulations have been conducted to study the effects of dislocations and grain boundaries on He diffusion in [Formula: see text]. Calculations were carried out for the {1 0 0}, {1 1 0} and {1 1 1} [Formula: see text] edge dislocations, the screw [Formula: see text] dislocation and Σ5, Σ13, Σ19 and Σ25 tilt grain boundaries. He diffusivity as a function of distance from the dislocation core and grain boundaries was investigated for the temperature range 2300-3000 K. An enhancement in diffusivity was predicted within 20 Å of the dislocations or grain boundaries. Further investigation showed that He diffusion in the edge dislocations follows anisotropic behaviour along the dislocation core, suggesting that pipe diffusion occurs. An Arrhenius plot of He diffusivity against the inverse of temperature was also presented and the activation energy calculated for each structure, as a function of distance from the dislocation or grain boundary.

Development of Xe and Kr empirical potentials for CeO2, ThO2, UO2 and PuO2, combining DFT with high temperature MD.

The development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO2, ThO2, UO2 and PuO2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO2, ThO2, UO2 and PuO2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO2 as well as advanced MOX fuels.

Anisotropic thermal conductivity in uranium dioxide.

The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.

The effect of airflow on thermographically determined temperature of the distal forelimb of the horse.

REASONS FOR PERFORMING STUDY: Current literature suggests that thermographic imaging of horses should be performed in a draught-free room. However, studies on the effect of airflow on determined temperature have not been published. OBJECTIVES: To investigate effects of airflow on thermographically determined temperature of horses' forelimbs; to assess the relationship of wind velocity, rectal temperature, ambient temperature and humidity. METHODS: Thermographic images were obtained for the forelimbs of 6 horses in a draught-free room. Three replicates (R) with defined wind velocities (R1, 0.5-1.0 m/s; R2, 1.3-2.6 m/s; and R3, 3.0-4.0 m/s) were conducted. Each replicate consisted of a baseline image, a 15 min phase with the wind on and a 15 min phase with the wind off. We exposed only the right leg to airflow and determined the temperature by thermography with the wind on and wind off. Temperature differences between baseline and wind on, between wind on and wind off and between different wind velocities were analysed by a general linear model, Student's paired t test and ANOVA. RESULTS: After the onset of wind, the temperature on the right forelimb decreased within 1-3 min (by approximately 0.6°C at R1, 1.5°C at R2 and 2.1°C at R3). With the wind off, the temperature increased within 3 min (by approximately 1.2°C at R1, 1.7°C at R2 and 2.1°C at R3). With increasing wind velocity, the temperature differences between baseline and wind on and between wind on and wind off increased significantly. CONCLUSIONS: Barely noticeable wind velocities caused a decrease in thermographically determined temperatures of the forelimbs of the horse. Further research is required to assess the influence of airflow on other parts of the body and at different ambient temperatures, as well as the effect on horses with inflammatory lesions, especially of the distal limbs. POTENTIAL RELEVANCE: It is essential for practitioners to perform thermography on horses in a draught-free environment in order to avoid false-positive or -negative diagnoses.

Chemical evolution via beta decay: a case study in strontium-90.

Using (90)Sr as a representative isotope, we present a framework for understanding beta decay within the solid state. We quantify three key physical and chemical principles, namely momentum-induced recoil during the decay event, defect creation due to physical displacement, and chemical evolution over time. A fourth effect, that of electronic excitation, is also discussed, but this is difficult to quantify and is strongly material dependent. The analysis is presented for the specific cases of SrTiO(3) and SrH(2). By comparing the recoil energy with available threshold displacement data we show that in many beta-decay situations defects such as Frenkel pairs will not be created during decay as the energy transfer is too low. This observation leads to the concept of chemical evolution over time, which we quantify using density functional theory. Using a combination of Bader analysis, phonon calculations and cohesive energy calculations, we show that beta decay leads to counter-intuitive behavior that has implications for nuclear waste storage and novel materials design.

Consistent detection of bovine papillomavirus in lesions, intact skin and peripheral blood mononuclear cells of horses affected by hoof canker.

REASONS FOR PERFORMING THE STUDY: Equine hoof canker is a chronic proliferative pododermatitis of as yet unknown aetiology. Like equine sarcoid disease, canker is a therapy-resistant disorder characterised by hyperkeratosis, acanthosis and a marked tendency to recur. HYPOTHESIS: There is an association of sarcoid-inducing bovine papillomaviruses of types 1 and 2 (BPV-1, BPV-2) with hoof canker disease. METHODS: Using PCR-based techniques, we assessed canker tissue, intact skin and/or peripheral blood mononuclear cells (PBMCs) of 25 canker-affected horses for the presence of sarcoid-associated BPV-1 and -2. RESULTS: Conventional PCR revealed BPV-1/-2 DNA in 24/24 canker, 12/13 skin and 10/11 PBMC DNA isolates. Using inverse PCR, full-length BPV episomes were detected in 1/5 canker specimens. Sequencing of viral early and late genes amplified from canker, intact skin and PBMC DNA of 2 cases revealed an overall identity of 98% to BPV-1. Viral DNA loads amounted to ≤16 copies per cell in canker tissue and intact skin, and to ≤0.35 copies per PBMC, as determined by quantitative PCR. Using RT-PCR, the viral major oncogene E5 was shown to be transcribed in 2/4 canker tissue specimens and 5/7 PBMC isolates. Immunocapture PCR from 7 canker and 6 skin extract supernatants revealed capsomere-associated viral DNA in one canker and one skin sample. Hoof tissue, skin and PBMCs collected from 13 individuals with no signs of canker or BPV-related malignancies scored negative throughout the experiments. CONCLUSION: These findings suggest that the observed presence of BPV-1/-2 in canker-affected horses is not coincidental but indicative of an active contribution to hoof canker disease. POTENTIAL RELEVANCE: The use of antivirals and/or immune modulators may help improving canker therapy.

Thirty-two component finite element models of a horse and donkey digit.

REASONS FOR PERFORMING STUDY: The finite element (FE) method is the most powerful modelling technique available to explicate the biomechanics of the digit. It has already proved to be of high value in human podiatry. However, accurate models of the complex anatomy of the horse and donkey digit are currently lacking. OBJECTIVES: To develop FE models of the horse and donkey digit from computed tomography data, including all functionally relevant anatomy, and to perform simulations to replicate prestrain in the flexor tendons and quasistatic weightbearing. METHODS: Computed tomography data of the front right digits were obtained under general anaesthesia. The anatomy was rationalised into 32 functional components. The FE models were generated using a forward engineering technique. Linear or nonlinear material properties were applied according to published data. Prestraining of the flexor tendons was achieved by z-direction displacement, and loading by the application of 1 x body mass. RESULTS: The resultant FE models comprised over 10(6) elements. Z-direction displacement of the digital flexor tendons to compensate for general anaesthesia relaxation gave von Mises stress levels up to 134 MPa for the deep and 0.56 MPa for the superficial in the horse and 0.78 MPa and 0.27 MPa in the donkey, respectively. Weightbearing resulted in capsular deformation patterns consistent with in vivo observations, and maximum stress levels of 1.46 MPa for the horse and 0.89 MPa for the donkey. CONCLUSION: These high resolution FE models could give new insight into the biomechanics of the equid digit and provide new data regarding stress and strain levels within the tissues of the digit that are unobtainable by other means. POTENTIAL RELEVANCE: Application of the FE modelling technique could enable investigation of the biomechanics of orthopaedic problems and may provide a mechanistic basis for enhanced preventative and remedial management and treatment.

Development of a twenty-one-component finite element distal hind limb model: stress and strain in bovine digit structures as a result of loading on different floorings.

Finite element modeling is a unique way of introducing technical and material research into medical science. A bovine distal hind limb was scanned using computed tomography for geometric image capture and the data were subsequently divided (segmented) into 4 tissue types: bone, bone marrow, soft tissue, and the horn capsule. Material data from previous studies were integrated into the model. Flexor tendons were assembled as longitudinal structures starting at their cross-sectional areas at the height of the metatarsophalangeal joint, proceeding in the plantaro-distal direction and meeting the distal phalanx at the tuberculum flexorium. Three different flooring situations (full support floor, bearing weight in the abaxial half of the lateral claw and in the dorsal halves of both claws, respectively) were created to evaluate the effects of loading. Full support resulted in von Mises stress levels between 3.5 and 1.5 MPa for the osseous structures and some regions of the segmented soft tissue; stress patterns in the bulb and sole of the claw capsule (1.5 MPa) and in the floor (0.5 MPa) were similar to pressure plate data in vivo and in vitro, with corresponding strain values of 2.4%. Reduced support resulted in higher stresses (up to approximately 8 MPa) in bones, claw capsules, and tendons; high strains ( approximately 11%) were found in the soft tissue, depending on how the floor was constructed. Although the models may still be anatomically improved, stress and strain calculations are possible with results comparable to related research, and the model shows interaction between the 2 digits. This possibly will help with further understanding of the biomechanical function of this 2-digit structure. With respect to clinical interpretation, reduced support to the bovine hind limb increases focal stress peaks in the different tissues, which may indicate a location of potential injury.

Thermodynamics of fission products in UO(2 ± x).

The stabilities of selected fission products-Xe, Cs, and Sr-are investigated as a function of non-stoichiometry x in UO(2 ± x). In particular, density functional theory (DFT) is used to calculate the incorporation and solution energies of these fission products at the anion and cation vacancy sites, at the divacancy, and at the bound Schottky defect. In order to reproduce the correct insulating state of UO(2), the DFT calculations are performed using spin polarization and with the Hubbard U term. In general, higher charge defects are more soluble in the fuel matrix and the solubility of fission products increases as the hyperstoichiometry increases. The solubility of fission product oxides is also explored. Cs(2)O is observed as a second stable phase and SrO is found to be soluble in the UO(2) matrix for all stoichiometries. These observations mirror experimentally observed phenomena.

A subset of equine sarcoids harbours BPV-1 DNA in a complex with L1 major capsid protein.

Bovine papillomavirus type 1 or 2 (BPV-1, BPV-2) are accepted causal factors in equine sarcoid pathogenesis. Whereas viral genomes are consistently found and expressed within lesions, intact virions have never been detected, thus permissiveness of sarcoids for BPV-1 replication remains unclear. To reassess this issue, an immunocapture PCR (IC/PCR) was established using L1-specific antibodies to capture L1-DNA complexes followed by amplification of the viral genome. Following validation of the assay, 13 sarcoid-bearing horses were evaluated by IC/PCR. Samples were derived from 21 tumours, 4 perilesional/intact skin biopsies, and 1 serum. Tissue extracts from sarcoid-free equines served as controls. IC/PCR scored positive in 14/24 (58.3%) specimens obtained from sarcoid-patients, but negative for controls. Quantitative IC/PCR demonstrated <125 immunoprecipitable viral genomes/50 microl extract for the majority of specimens. Moreover, full-length BPV-1 genomes were detected in a complex with L1 proteins. These complexes may correspond to virion precursors or intact virions.

Comparison of stress zones in finite element models of deformed bovine claw capsules.

Pathological claw formations occur subsequent to irregular or prolonged claw trimming periods and as a result of improper flooring. Clinical experience and material testing finds horn of minor quality to be associated with the malformations. Finite element models (FEM) of a flat claw (FC), a contracted claw (CC), and a laminitic claw (LC) were designed from native claw specimens to combine material properties and altered claw geometry for stress analysis. The FEM were created by digitizing the typically deformed exungulated claw capsule by means of computed tomography or digital photography. The derived geometry data were meshed with finite elements and the material properties were attributed. Loading was performed via vertical load vectors according to the suspensory and support apparatus of the bovine digit. All FEM were loaded on soft floors. Loading of the FEM of the FC with 756 N exhibited maximum stress values of 3.32 MPa in the dorsal wall, that of the CC exhibited comparably lower stress of 1.33 MPa in the distal abaxial wall, and the model of the LC showed maximum stress of 4.51 MPa in the region of the dorsal border, all at the same loading. The solar surfaces and the corresponding imprints showed stress concentrations in the palmar aspect of the bulb in the FC, a highly stressed bearing margin of the abaxial wall in the CC, and a diffusely stressed sole and bulb in the LC in contrast to the sound claw models. The FEM of the selected pathological claw forms (FC, CC, LC) calculated high stress zones exactly at locations in the claw wall and sole where clinical experts expect the typical claw lesions for these pathologies. These results were obtained simply by exchanging the outer form of the claw capsules; the method of loading and type of flooring for these pathological models were equivalent to those of the sound FEM. It is highly possible that the stress zones derived from these calculations represent corium compression in reality, and these data support the pathophysiological theory that claw lesions may arise as a consequence thereof.

Emergence of MRSA infections in horses in a veterinary hospital: strain characterisation and comparison with MRSA from humans.

Methicillin-resistant Staphylococcus aureus has become an emerging public health problem worldwide, no longer only associated with healthcare-associated infections. With the exception of some recent reports concerning infections in cats, dogs and horses, infections with MRSA in companion animals have been infrequently reported. Here we submit findings for MRSA infections in horses in a central European university hospital.

Slatted floors and solid floors: stress and strain on the bovine hoof capsule analyzed in finite element analysis.

An established finite element model of a bovine claw was used to compare mechanical stress levels in a loaded model claw on different types of flooring. The following situations were compared: a claw standing on a solid floor, a claw standing on the edge of a short tie stand, and claws standing on slatted floors with slats of 28 and 40 mm (wide) running parallel and perpendicular to the claw axis. Finite element analysis allowed visualization of stress peaks seen predominantly in the weight-bearing border of the dorsal abaxial wall and of the bulbar region and in the proximal axial wall. Maximum stress values of 13 MPa were found in the model claw loaded on the solid floor and values of 18 to 22 MPa were seen in the model claw loaded on the edge of the solid floor. On slatted floors, stresses increased in the situation in which the claw was not supported under the abaxial wall. Comparison between the other slatted floors showed little difference in amounts of mechanical stress. A clear distinction was detected between the solid floor with full claw contact and the slatted floors. From the point of view of the mechanical stress seen in finite element analysis, a large contact area between claw and floor, as seen in the solid surface floor, is preferable. When use of slatted floors is unavoidable, direction of the slats should run perpendicular to the direction of the walkway to prevent even more mechanical impact in certain footing situations.

A finite element model of the bovine claw under static load for evaluation of different flooring conditions.

AIM: To create a computer-based finite element (FE) model of the bovine claw and to use finite element analysis (FEA) to estimate stress and deformation of a physiologically-shaped model claw under static load, to visualise potential material weakness and to evaluate the effect of different flooring conditions. METHODS: Model geometry was derived using digitalised images from a recently trimmed, sound, hind claw from a 4-year-old Austrian Fleckvieh cow. Material properties of bovine claw horn were defined from preliminary investigations and recently established material data, using a modulus of elasticity from 200 to 600 N/mm2. Meshing of the model was performed with 42,127 elements based on 116,141 nodes. Loading of the model was defined at 756 N per claw on a hard and soft surface. RESULTS: The FE model of the bovine claw under a load of 756 N showed only minimal deformation, most of which took place at the axial wall. Highest stresses were evident in the proximal axial wall, the outer edge of the weight-bearing surface and under the heels. The claw-floor contact image showed a pressure distribution resembling the distal rim of the claw wall. On the hard surface, the maximum stresses were three times higher than those on the soft surface. CONCLUSIONS AND CLINICAL RELEVANCE: FEA allowed visualisation of the effects that loading on different floor surfaces have on the biomechanics of the claw. Uneven preparation of the claw sole resulted in high stresses at and close to irregularities of the sole. Consequences were more severe on harder flooring. The model supports the hypothesis that mechanical factors play a substantial role in the pathogenesis of claw lesions.

Elastic properties of hoof horn on different positions in the bovine claw.

Hind claws of 15 adult, sound Fleckvieh cows were used for material analysis. The elastic modulus was tested in tension tests according to EN ISO 527 and ASTM D 638-03 at a universal material testing machine. Samples were taken from different segments of the bovine claw to find the differences in material properties. Samples orientation was parallel to the horn tubules and transversal, respectively. Dry matter of the test samples was determined at the time of testing. Elastic modulus values were highest with mean = 659.7 N/mm2 at the dorsal wall. Values dropped axial to 416.3 N/mm2, abaxial to 343.9 N/mm2 for longitudinal (parallel) samples and to 433.1 N/mm2 for transversal samples. The elastic modulus of the sole segment was found to be 172.1 N/mm2. No difference was calculated neither between right and left feet, lateral and medial claws, nor between longitudinal and transversal samples.

Ultrasonographic investigation of the atlanto-occipital articulation in the horse.

The purpose of this study was to evaluate ultrasonographic imaging as a means of easy and noninvasive diagnosis of articular and periarticular structures of the atlanto-occipital articulation in the horse; and to find a safe approach to the atlanto-occipital joint. Ultrasonographic investigations were performed on 6 healthy horses and 16 specimens from horses humanely destroyed age 2-17 years (mean 9.56 years). Preliminary examinations included anatomical studies and preparation of cross-sections. On 4 horse specimens, puncture of the atlanto-occipital joint under ultrasonographic guidance was performed and a new lateral approach undertaken. For ultrasonographic investigations, the neck was divided into 4 zones according to anatomical and clinical modalities: 1) insertion of the funiculus nuchae; 2) tuberculum dorsale of the atlas; 3) atlanto-occipital joint and 4) region above the foramen alare. Each zone was examined in transverse and longitudinal planes proceeding from cranial to caudal. Ultrasonography was found to be useful for soft tissue imaging of this region and was performed down to the atlanto-occipital joint of which the joint surfaces, joint capsule and collateral ligament could be delineated in both planes. We conclude that ultrasonography of the neck is a useful technique, representing an easy to use and safe method. However, further studies are indicated which should be performed on live subjects.

Finite element analysis (FEA) as a model to predict effects of farriery on the equine hoof.

A finite element (FE) hoof capsule was built as a small, symmetrical forelimb hoof on IDEAS* as a model for calculation and visualisation of stress and displacement of the equine hoof capsule. The model's loading was performed according to the suspension of the coffin bone within the hoof wall (pulling force) and over the sole and frog (compressing force) with a total of 3000 N. Restraints of the model's ground nodes and surface wall nodes were defined for simulation of 4 shoeing situations: a regular horseshoe, a horseshoe with a toe clip, a horseshoe with regular side clips and a horseshoe with a toe clip and more caudally-placed side clips, all fixed to the hoof capsule with 3 nails on each side and each calculated in a tense and a loose nailed condition. Von Mises stresses were taken ranging from 1.22 N/mm2 in the weightbearing border of the side clip shoe fixed loosely to the capsule up to 16.67 N/mm2 in the hoof horn material surrounding the third nail. Further high stress zones were calculated in the proximal dorsal wall, the distal heel and the lateral hoof wall. Displacement values were taken showing movements of hoof wall, sole and frog according to the shoeing conditions. Maximal displacement was calculated in the hoof capsule shod with a regular horseshoe without a clip. Minimal displacement was found in the capsule with a toe clip and 2 side clips placed behind the 3rd nail. All models showed higher displacements when calculated with a loose nail fixation. Validation of the detailed features of the models is not yet possible. Finite element analysis (FEA) can be used practically to predict influences of various farrier techniques on the equine hoof in order to avoid possible harm to horses' feet in field studies.

Keratinopathogenic mould fungi and dermatophytes in healthy and diseased hooves of horses.

Specimens of hoof horn from 187 horses were examined for a possible relationship between clinically affected hooves and the occurrence of pathogenic fungi. Specimens were taken from the coronary band and from the stratum externum and medium of the coronary horn and transferred on to Sabouraud dextrose agar, with and without cycloheximide, and incubated at 28 degrees C. Dermatophytes and mould fungi were identified by their macroscopic and microscopic characteristics. The 732 isolates could be assigned to 26 species of moulds, two different species of the dermatophyte Microsporum and three different species of the dermatophyte Trichophyton. Depending on their pathogenic potential they were assigned to three groups: (i) fungi known to be keratinopathogenic (Acremonium blochii, Alternaria alternata, Alternaria chlamydospora, Geotrichum candidum, Microsporum ferrugineum, Microsporum gypseum, Scopulariopsis brevicaulis, Trichophyton species, Trichophyton mentagrophytes, Trichophyton schönleinii, 57 isolates), (ii) a group of uncertain pathogenicity (223 isolates), and (iii) a group of non-pathogenic species (452 isolates). Eighty per cent of the samples from horses with hoof horn lesions and 66.7 per cent of the samples from horses with slightly affected hoof horn contained fungi of the keratinopathogenic group, whereas only 8.9 per cent of the samples from horses with healthy hoof horn contained fungi of this group. There were no significant correlations between the clinical data and the age, sex or breed of the horses or their bedding and hygiene. Twelve species of fungi were isolated from the air in the horses' stables, but none of them belonged to the keratinopathogenic group.