Search results for "spheres"
showing 10 items of 329 documents
Development of core-shell colloids to study self-diffusion in highly concentrated dispersions
2007
To study single particle motion in highly concentrated colloidal dispersions, a host-tracer colloid system was developed, consisting of crosslinked polymer micronetwork spheres placed in a good solvent. The host colloid is made invisible to the experimental probe by matching its refractive index to that of the solvent. For the tracer particles a core-shell structure was chosen to ensure the interaction potential to be identical to that of the host particles. Therefore the shell was made of the same polymer as the host. The core differs in refractive index from the solvent and is therefore visible due to scattered light.
Accuracy of magnetic resonance enterography in the preoperative assessment of patients with Crohn's disease of the small bowel
2016
Aim to assess the accuracy of magnetic resonance-enterography in predicting the extension, location and characteristics of the small bowel segments affected by Crohn's disease. Method This is a prospective study including a consecutive series of 38 patients with small bowel Crohn's disease who underwent surgery at a specialized colorectal unit of a tertiary hospital. Preoperative magnetic resonance enterography was performed in all patients, following a homogeneous protocol, within the three months prior to surgery. A thorough exploration of the small bowel was performed during the surgical procedure, using calibration spheres, according to the discretion of the surgeon. The accuracy of mag…
Electrophysiological and hemodynamic mismatch responses in rats listening to human speech syllables
2016
International audience; Speech is a complex auditory stimulus which is processed according to several time-scales. Whereas consonant discrimination is required to resolve rapid acoustic events, voice perception relies on slower cues. Humans, right from preterm ages, are particularly efficient to encode temporal cues. To compare the capacities of preterms to those observed in other mammals, we tested anesthetized adult rats by using exactly the same paradigm as that used in preterm neonates. We simultaneously recorded neural (using ECoG) and hemodynamic responses (using fNIRS) to series of human speech syllables and investigated the brain response to a change of consonant (ba vs. ga) and to …
Stable Images and Discriminants
2020
We show that the discriminant/image of a stable perturbation of a germ of finite \(\mathcal {A}\)-codimension is a hypersurface with the homotopy type of a wedge of spheres in middle dimension, provided the target dimension does not exceed the source dimension by more than one. The number of spheres in the wedge is called the discriminant Milnor number/image Milnor number. We prove a lemma showing how to calculate this number, and show that when the target dimension does not exceed the source dimension, the discriminant Milnor number and the \(\mathcal {A}\)-codimension obey the “Milnor–Tjurina relation” familiar in the case of isolated hypersurface singularities. This relation remains conj…
Dosimetry comparison between TG-43 and Monte Carlo calculations using the Freiburg flap for skin high-dose-rate brachytherapy
2012
Abstract Purpose The purpose of this work was to evaluate whether the delivered dose to the skin surface and at the prescription depth when using a Freiburg flap applicator is in agreement with the one predicted by the treatment planning system (TPS) using the TG-43 dose-calculation formalism. Methods and Materials Monte Carlo (MC) simulations and radiochromic film measurements have been performed to obtain dose distributions with the source located at the center of one of the spheres and between two spheres. Primary and scatter dose contributions were evaluated to understand the role played by the scatter component. A standard treatment plan was generated using MC- and TG-43-based TPS appl…
High-pressure phases, vibrational properties, and electronic structure ofNe(He)2andAr(He)2: A first-principles study
2009
We have carried out a comprehensive first-principles study of the energetic, structural, and electronic properties of solid rare-gas RG-helium binary compounds, in particular, NeHe2 and ArHe2, under pressure and at temperatures within the range of 0T2000 K. Our approach is based on density-functional theory and the generalized gradient approximation for the exchange-correlation energy; we rely on total Helmholtz freeenergy calculations performed within the quasiharmonic approximation for most of our analysis. In NeHe2, we find that at pressures of around 20 GPa the system stabilizes in the MgZn2 Laves structure, in accordance to what was suggested in previous experimental investigations. In…
Equilibrium fluid-crystal interfacial free energy of bcc-crystallizing aqueous suspensions of polydisperse charged spheres
2015
The interfacial free energy is a central quantity in crystallization from the meta-stable melt. In suspensions of charged colloidal spheres, nucleation and growth kinetics can be accurately measured from optical experiments. In previous work, from this data effective non-equilibrium values for the interfacial free energy between the emerging bcc-nuclei and the adjacent melt in dependence on the chemical potential difference between melt phase and crystal phase were derived using classical nucleation theory. A strictly linear increase of the interfacial free energy was observed as a function of increased meta-stability. Here, we further analyze this data for five aqueous suspensions of charg…
Crossing the boundary between face-centred cubic and hexagonal close packed: the structure of nanosized cobalt is unraveled by a model accounting for…
2014
The properties of nanostructured cobalt in the fields of magnetic, catalytic and biomaterials depend critically on Co close packing. This paper reports a structural analysis of nanosized cobalt based on the whole X-ray diffraction (XRD) pattern simulation allowed by the Debye equation. The underlying structural model involves statistical sequences of cobalt layers and produces simulated XRD powder patterns bearing the concurrent signatures of hexagonal and cubic close packing (h.c.p. and f.c.c.). Shape, size distribution and distance distribution between pairs of atoms are also modelled. The simulation algorithm allows straightforward fitting to experimental data and hence the quantitative …
Computing the Arrangement of Circles on a Sphere, with Applications in Structural Biology
2009
International audience; Balls and spheres are the simplest modeling primitives after affine ones, which accounts for their ubiquitousness in Computer Science and Applied Mathematics. Amongst the many applications, we may cite their prevalence when it comes to modeling our ambient 3D space, or to handle molecular shapes using Van der Waals models. If most of the applications developed so far are based upon simple geometric tests between balls, in particular the intersection test, a number of applications would obviously benefit from finer pieces of information. Consider a sphere $S_0$ and a list of circles on it, each such circle stemming from the intersection between $S_0$ and another spher…
Glass transition of hard spheres in high dimensions
2009
We have investigated analytically and numerically the liquid-glass transition of hard spheres for dimensions $d\to \infty $ in the framework of mode-coupling theory. The numerical results for the critical collective and self nonergodicity parameters $f_{c}(k;d) $ and $f_{c}^{(s)}(k;d) $ exhibit non-Gaussian $k$ -dependence even up to $d=800$. $f_{c}^{(s)}(k;d) $ and $f_{c}(k;d) $ differ for $k\sim d^{1/2}$, but become identical on a scale $k\sim d$, which is proven analytically. The critical packing fraction $\phi_{c}(d) \sim d^{2}2^{-d}$ is above the corresponding Kauzmann packing fraction $\phi_{K}(d)$ derived by a small cage expansion. Its quadratic pre-exponential factor is different fr…