Micromechanical model of bovine Haversian bone predicts strain amplification through soft interfaces

Context. Recent observations of brown dwarf spectroscopic variability in the infrared infer the presence of patchy cloud cover. Aims. This paper proposes a mechanism for producing inhomogeneous cloud coverage due to the depletion of cloud particles through the Coulomb explosion of dust in atmospheric plasma regions. Charged dust grains Coulomb-explode when the electrostatic stress of the grain exceeds its mechanical tensile stress, which results in grains below a critical radius a < aCoulcrit being broken up. Methods. This work outlines the criteria required for the Coulomb explosion of dust clouds in substellar atmospheres, the effect on the dust particle size distribution function, and the resulting radiative properties of the atmospheric regions. Results. Our results show that for an atmospheric plasma region with an electron temperature of Te = 10 eV (≈ 105 K), the critical grain radius varies from 10-7 to 10-4 cm, depending on the grains’ tensile strength. Higher critical radii up to 10-3 cm are attainable for higher electron temperatures. We find that the process produces a bimodal particle size distribution composed of stable nanoscale seed particles and dust particles with a ≥ aCoulcrit , with the intervening particle sizes defining a region devoid of dust. As a result, the dust population is depleted, and the clouds become optically thin in the wavelength range 0:1 - 10 μm, with a characteristic peak that shifts to higher wavelengths as more sub-micrometer particles are destroyed. Conclusions. In an atmosphere populated with a distribution of plasma volumes, this will yield regions of contrasting radiative properties, thereby giving a source of inhomogeneous cloud coverage. The results presented here may also be relevant for dust in supernova remnants and protoplanetary disks.PostprintPeer reviewe

Optical thickness measurement with multi-wavelength THz interferometry

AbstractWe report unambiguous thickness measurement with an all-optical THz source. The optical thickness variation of a test target was measured in a Mach–Zehnder interferometer to approximately 0.5% of the illumination wavelength using an optical parametric THz laser. The frequency of the laser was continuously tuneable, enabling a synthetic wavelength to be produced by sequential illumination at discrete frequencies, thus extending the unambiguous measurement range to half the synthetic wavelength. The all-optical source provides some advantages with respect to opto-electronic and electronic sources, particularly measurement speed and resolution

The braincase and inner ear of ‘Metriorhynchus’ cf. ‘M.’ brachyrhynchus – implications for aquatic sensory adaptations in crocodylomorphs

During their long evolutionary history crocodylomorphs achieved a great diversity of body sizes, ecomorphotypes and inferred feeding ecologies. One unique group of crocodylomorphs are the thalattosuchians, which lived during the Jurassic and Cretaceous (ca. 191–125 Ma). They transitioned from shallow marine species, like teleosauroids, into fully pelagic forms with paddle shaped limbs and a vertically orientated tail fluke, the metriorhynchids. The osteological adaptations that allowed metriorhynchids to live in the water are generally well understood, but less is known about their neurosensory and endocranial systems, such as the brain, inner ears, sinuses and cranial nerves and how they relate to their aquatic lifestyle. Based on micro-computed tomography (μCT) data and three-dimensional models, we here describe the braincase and endocranial anatomy of a fully marine metriorhynchid, ‘Metriorhynchus’ cf. ‘M.’ brachyrhynchus (NHMUK PV OR 32617). We found several neuroanatomical features that likely helped this species function in its marine environment. These include a unique flexure in the brain endocast not seen in other thalattosuchians. Other features that have previously been seen in thalattosuchians include enlarged cerebral hemispheres, a hypertrophied venous sinus system, enlarged internal carotid arteries and foramina, and closed/absent lateral pharyngotympanic foramina. The specimen also possesses a pelagic metriorhynchid bony labyrinth morphology, with a compact and dorsoventrally short shape, thick semicircular canals, an enlarged vestibule and potentially a short cochlear duct. A review of character distribution confirms that some of these features evolved at the base of Thalattosuchia in semiaquatic species, long before metriorhynchids became pelagic, suggesting that endocranial anatomy helped allow metriorhynchoids colonize the ocean realm.Fil: Schwab, Julia A.. University of Edinburgh; Reino UnidoFil: Young, Mark T.. University of Edinburgh; Reino UnidoFil: Herrera, Laura Yanina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Witmer, Lawrence. Ohio University; Estados UnidosFil: Walsh, Stig A.. University of Southampton; Reino UnidoFil: Katsamensis, Orestis. Faculty Of Engineering And Physical Sciences; Reino UnidoFil: Brusatte, Stephen L.. University of Edinburgh; Reino Unid

⁶⁸Ga-Bisphosphonates for the Imaging of Extraosseous Calcification by Positron Emission Tomography

Abstract Radiolabelled bisphosphonates (BPs) and [18F]NaF (18F-fluoride) are the two types of radiotracers available to image calcium mineral (e.g. bone), yet only [18F]NaF has been widely explored for the non-invasive molecular imaging of extraosseous calcification (EC) using positron emission tomography (PET) imaging. These two radiotracers bind calcium mineral deposits via different mechanisms, with BPs chelating to calcium ions and thus being non-selective, and [18F]NaF being selective for hydroxyapatite (HAp) which is the main component of bone mineral. Considering that the composition of EC has been reported to include a diverse range of non-HAp calcium minerals, we hypothesised that BPs may be more sensitive for imaging EC due to their ability to bind to both HAp and non-HAp deposits. We report a comparison between the 68Ga-labelled BP tracer [68Ga]Ga-THP-Pam and [18F]NaF for PET imaging in a rat model of EC that develops macro- and microcalcifications in several organs. Macrocalcifications were identified using preclinical computed tomography (CT) and microcalcifications were identified using µCT-based 3D X-ray histology (XRH) on isolated organs ex vivo. The morphological and mineral analysis of individual calcified deposits was performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). PET imaging and ex vivo analysis results demonstrated that while both radiotracers behave similarly for bone imaging, the BP-based radiotracer [68Ga]Ga-THP-Pam was able to detect EC more sensitively in several organs in which the mineral composition departs from that of HAp. Our results strongly suggest that BP-based PET radiotracers such as [68Ga]Ga-THP-Pam may have a particular advantage for the sensitive imaging and early detection of EC by being able to detect a wider array of relevant calcium minerals in vivo than [18F]NaF, and should be evaluated clinically for this purpose

Deformation mechanisms of idealised cermets under multi-axial loading

The response of idealised cermets comprising approximately 60% by volume steel spheres in a Sn/Pb solder matrix is investigated under a range of axisymmetric compressive stress states. Digital volume correlation (DVC) analysis of X-ray micro-computed tomography scans (μ-CT), and the measured macroscopic stress-strain curves of the specimens revealed two deformation mechanisms. At low triaxialities the deformation is granular in nature, with dilation occurring within shear bands. Under higher imposed hydrostatic pressures, the deformation mechanism transitions to a more homogeneous incompressible mode. However, DVC analyses revealed that under all triaxialities there are regions with local dilatory and compaction responses, with the magnitude of dilation and the number of zones wherein dilation occurs decreasing with increasing triaxiality. Two numerical models are presented in order to clarify these mechanisms: (i) a periodic unit cell model comprising nearly rigid spherical particles in a porous metal matrix and (ii) a discrete element model comprising a large random aggregate of spheres connected by non-linear normal and tangential “springs”. The periodic unit cell model captured the measured stress-strain response with reasonable accuracy but under-predicted the observed dilation at the lower triaxialities, because the kinematic constraints imposed by the skeleton of rigid particles were not accurately accounted for in this model. By contrast, the discrete element model captured the kinematics and predicted both the overall levels of dilation and the simultaneous presence of both local compaction and dilatory regions with the specimens. However, the levels of dilation in this model are dependent on the assumed contact law between the spheres. Moreover, since the matrix is not explicitly included in the analysis, this model cannot be used to predict the stress-strain responses. These analyses have revealed that the complete constitutive response of cermets depends both on the kinematic constraints imposed by the particle aggregate skeleton, and the constraints imposed by the metal matrix filling the interstitial spaces in that skeleton.The authors are grateful to the Office of Naval Research (ONR) for their financial support through grant number N00014121063

68Ga-bisphosphonates for the imaging of extraosseous calcification by positron emission tomography

Radiolabelled bisphosphonates (BPs) and [18F]NaF (18F-fluoride) are the two types of radiotracers available to image calcium mineral (e.g. bone), yet only [18F]NaF has been widely explored for the non-invasive molecular imaging of extraosseous calcification (EC) using positron emission tomography (PET) imaging. These two radiotracers bind calcium mineral deposits via different mechanisms, with BPs chelating to calcium ions and thus being non-selective, and [18F]NaF being selective for hydroxyapatite (HAp) which is the main component of bone mineral. Considering that the composition of EC has been reported to include a diverse range of non-HAp calcium minerals, we hypothesised that BPs may be more sensitive for imaging EC due to their ability to bind to both HAp and non-HAp deposits. We report a comparison between the 68Ga-labelled BP tracer [68Ga]Ga-THP-Pam and [18F]NaF for PET imaging in a rat model of EC that develops macro- and microcalcifications in several organs. Macrocalcifications were identified using preclinical computed tomography (CT) and microcalcifications were identified using µCT-based 3D X-ray histology (XRH) on isolated organs ex vivo. The morphological and mineral analysis of individual calcified deposits was performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). PET imaging and ex vivo analysis results demonstrated that while both radiotracers behave similarly for bone imaging, the BP-based radiotracer [68Ga]Ga-THP-Pam was able to detect EC more sensitively in several organs in which the mineral composition departs from that of HAp. Our results strongly suggest that BP-based PET radiotracers such as [68Ga]Ga-THP-Pam may have a particular advantage for the sensitive imaging and early detection of EC by being able to detect a wider array of relevant calcium minerals in vivo than [18F]NaF, and should be evaluated clinically for this purpose

Preparation and Characterization of Large Unilamellar Vesicles Mixed with Trimethylchitosan (TMC): The Effect of Polyelectrolyte Concentration

Background: The effect of different concentrations of the absorption enhancer trimethylchitosan (TMC) to the physicochemical properties of large unilamellar vesicles (LUV) comprised of L-a-Phospahtidylcholine (PC) were investigated in the current study. Methods: The degree of quartenization (DQ) of trimethylchitosan was assessed with nuclear magnetic resonance ($^1$H NMR). The vesicles were characterized by means of dynamic light scattering (DLS), ζ-potential, differential scanning calorimetry (DSC) and contact angle goniometry (CAG) measurements. Results: The data showed that the surface charge of the PC liposomes was significantly altered as a function of the TMC concentration, giving evidence of presence of the polyelectrolyte to the liposome’s membrane. Varying the concentration of TMC affected the phase transition temperature (T$_m$) of the lipid, verifying the miscibility of the polyelectrolyte with the lipid bilayer. The association of the polymer with the liposomes was related to the amount of the polyelectrolyte present, reflecting changes to the wettability of the dispersion as measured by CAG. Conclusions: The results demonstrated that presence of TMC significantly modified the physical properties of liposomes. Such systems might have a potential use for mucosal delivery (e.g. nasal route of administration)

Virtual testing of advanced composites, cellular materials and biomaterials: A review

This paper documents the emergence of virtual testing frameworks for prediction of the constitutive responses of engineering materials. A detailed study is presented, of the philosophy underpinning virtual testing schemes: highlighting the structure, challenges and opportunities posed by a virtual testing strategy compared with traditional laboratory experiments. The virtual testing process has been discussed from atomistic to macrostructural length scales of analyses. Several implementations of virtual testing frameworks for diverse categories of materials are also presented, with particular emphasis on composites, cellular materials and biomaterials (collectively described as heterogeneous systems, in this context). The robustness of virtual frameworks for prediction of the constitutive behaviour of these materials is discussed. The paper also considers the current thinking on developing virtual laboratories in relation to availability of computational resources as well as the development of multi-scale material model algorithms. In conclusion, the paper highlights the challenges facing developments of future virtual testing frameworks. This review represents a comprehensive documentation of the state of knowledge on virtual testing from microscale to macroscale length scales for heterogeneous materials across constitutive responses from elastic to damage regimes