1,182 research outputs found
First principles investigation of the electronic structure of La2MnNiO6: A room-temperature insulating ferromagnet
Using first principles calculations within DFT based on the full potential
APW+lo method, we calculated the electronic and magnetic structures for the
ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site
projected density of states and electronic band structures. Our calculations
show that the ground state of La2MnNiO6 is ferromagnetic insulating with the
magnetization in agreement with Hund's first rule and experimental findings.Comment: 10 pages, 3 figure
Role of heat generation and thermal diffusion during frontal photopolymerization
Frontal photopolymerization (FPP) is a rapid and versatile solidification process that can be used to fabricate complex three-dimensional structures by selectively exposing a photosensitive monomer-rich bath to light. A characteristic feature of FPP is the appearance of a sharp polymerization front that propagates into the bath as a planar traveling wave. In this paper, we introduce a theoretical model to determine how heat generation during photopolymerization influences the kinetics of wave propagation as well as the monomer-to-polymer conversion profile, both of which are relevant for FPP applications and experimentally measurable. When thermal diffusion is sufficiently fast relative to the rate of polymerization, the system evolves as if it were isothermal. However, when thermal diffusion is slow, a thermal wavefront develops and propagates at the same rate as the polymerization front. This leads to an accumulation of heat behind the polymerization front which can result in a significant sharpening of the conversion profile and acceleration of the growth of the solid. Our results also suggest that a novel way to tailor the dynamics of FPP is by imposing a temperature gradient along the growth directio
Surface waves on a soft viscoelastic layer produced by an oscillating microbubble
Ultrasound-driven bubbles can cause significant deformation of soft viscoelastic layers, for instance in surface cleaning and biomedical applications. The effect of the viscoelastic properties of a boundary on the bubble-boundary interaction has been explored only qualitatively, and remains poorly understood. We investigate the dynamic deformation of a viscoelastic layer induced by the volumetric oscillations of an ultrasound-driven microbubble. High-speed video microscopy is used to observe the deformation produced by a bubble oscillating at 17-20 kHz in contact with the surface of a hydrogel. The localised oscillating pressure applied by the bubble generates surface elastic (Rayleigh) waves on the gel, characterised by elliptical particle trajectories. The tilt angle of the elliptical trajectories varies with increasing distance from the bubble. Unexpectedly, the direction of rotation of the surface elements on the elliptical trajectories shifts from prograde to retrograde at a distance from the bubble that depends on the viscoelastic properties of the gel. To explain these behaviours, we develop a simple three-dimensional model for the deformation of a viscoelastic solid by a localised oscillating force. By using as input for the model the values of the shear modulus obtained from the propagation velocity of the Rayleigh waves, we find good qualitative agreement with the experimental observations
Interplay of chemical pressure and hydrogen insertion effects in from first principles
Investigations within the local spin density functional theory (LSDF) of the
intermetallic hydride system were carried out for discrete
model compositions in the range . The aim of this
study is to assess the change of the cerium valence state in the neighborhood
of the experimental hydride composition, . In agreement
with experiment, the analyses of the electronic and magnetic structures and of
the chemical bonding properties point to trivalent cerium for . In contrast, for lower hydrogen amounts the hydride system stays in an
intermediate-valent state for cerium, like in . The influence
of the insertion of hydrogen is addressed from both the volume expansion and
chemical bonding effects. The latter are found to have the main influence on
the change of Ce valence character. Spin polarized calculations point to a
finite magnetic moment carried by the Ce states; its magnitude increases
with in the range
First principles study of the electronic and magnetic structures of the tetragonal and orthorhombic phases of Ca3Mn2O7
On the basis of density functional theory electronic band structure
calculations using the augmented spherical wave method, the electronic and
magnetic properties of the orthorhombic and tetragonal phases of Ca3Mn2O7 were
investigated and the spin exchange interactions of the orthorhombic phase were
analyzed. Our calculations show that the magnetic insulating states are more
stable than the non-magnetic metallic state for both polymorphs of Ca3Mn2O7,
the orthorhombic phase is more stable than the tetragonal phase, and the ground
state of the orthorhombic phase is antiferromagnetic. The total energies
calculated for the three spin states of the orthorhombic phase of Ca3Mn2O7 led
to estimates of the spin exchange interactions Jnn = -3.36 meV and Jnnn = -0.06
meV. The accuracy of these estimates were tested by calculating the Curie-Weiss
temperature within the mean-field approximation.Comment: 11 pages, 7 figure
An Unusual Case of Appendiceal Adenocarcinoma Presenting with Rectal Bleeding and Haematuria
Adenocarcinoma of the appendix is rare, usually being diagnosed intraoperatively when performing appendicectomy or at subsequent histological examination. Here we report a case with acute abdominal pain, rectal bleeding with haematuria being the presenting symptoms. Subsequent computerised tomography demonstrated a complex mass involving the ileum, right colon, sigmoid colon and bladder with inflammatory bowel disease being the most likely cause. At laparotomy a right hemicolectomy, sigmoid colectomy and partial cystectomy was performed with pathological specimens confirming an appendiceal adenocarcinoma as the primary source of the abdominal mass fistulating into adjacent structures. We conclude that although appendiceal tumours are rare – usually diagnosed at appendicectomy, they should be considered in the diagnosis of complex abdominal masses involving small bowel, large bowel and adjacent pelvic structures
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