Secondary radiation in transmission-type X-ray tubes: Simulation, practical issues and solution in the context of X-ray microtomography

In laboratory-based X-ray radiography and computed tomography, the X-rays are assumed to originate from one single focal spot with a finite spot size, which is generated by focussing accelerated electrons on the target material. However, apart from this focal spot, X-rays can also be produced elsewhere in the tube system. A major contribution of this parasitic radiation originates from electrons that are backscattered from the target material, into the X-ray tube system, where they can produce so-called off-focus or secondary X-rays. This phenomenon has been widely studied for rotating anode X-ray tubes in medical imaging systems, but not for transmission-type microfocus X-ray tubes. This paper presents a study on the origin of secondary radiation in this kind of X-ray tubes, which is performed by Monte Carlo simulations and by experimental measurements. The impact of this phenomenon on the imaging process is studied, and two correction methods are proposed, both on the hardware and on the software levels.     

Biomimetic neural network for modifying biological dynamics during hybrid experiments

Electrical stimulation of nerve tissue and recording of neural electrical activity are the basis of emerging prostheses and treatments for many neurological disorders. Here we present closed-loop bio-hybrid experiment using in vitro biological neuronal network (BNN) with an artificial neural network (ANN) implemented in a neuromorphic board. We adopted a neuromorphic board which is able to perform real-time event detection and trigger an electrical stimulation of the BNN. This system embeds an ANN, based on Izhikevich neurons which can be put in uni- and bi-directional communication with the BNN. The ANN used in the following experiments was made up of 20 excitatory neurons with inhibition synapse and with synaptic plasticity to design central pattern generator. Open-loop and closed-loop hybrid experiments show that the biological dynamics can be modified. This work can be seen as the first step towards the realization of an innovative neuroprosthesis.     

Le millefeuille: Algorithme de routage pour réseau en mode paquet et réseau en mode connecté

We present in this paper an innovating routing method on constrained capacity based on the actual link load ratio. This method is used during the data network or switching network design step. Its goal is to use all the free capacity of the network, by splitting the flow along several paths, and lowering the maximal link load on the network. We present a routing method and a non additive metric on the network components for the computation of the paths. We compare this multi-routings method to disjoint multi-routing methods and show the interest of this method. It provides the network higher resistance to flow increase, and higher resistance to single link failure.     

Selective toxicity of the general anesthetic propofol for GABAergic neurons in rat brain cell cultures

The intravenous, short-acting general anesthetic propofol was applied to three-dimensional (aggregating) cell cultures of fetal rat telencephalon. Both the clinically used formulation (Disoprivan, ICI Pharmaceuticals, Cheshire, England) and the pure form (2,6-diisopropylphenol) were tested at two different periods of brain development: immature brain cell cultures prior to synaptogenesis and at the time of intense synapses and myelin formation. At both time periods and for clinically relevant concentrations and time of exposure (i.e., concentrations > or = 2.0 micrograms/ml for 8 hr), propofol caused a significant decrease of glutamic acid decarboxylase activity. This effect persisted after removal of the drug, suggesting irreversible structural changes in GABAergic neurons. The gamma-aminobutyric acid type A (GABAA) blocking agents bicuculline and picrotoxin partially attenuated the neurotoxic effect of propofol in cultures treated at the more mature phase of development. This protective effect was not observed in the immature brain cells. The present data suggest that propofol may cause irreversible lesions to GABAergic neurons when given at a critical phase of brain development. In contrast, glial cells and myelin appeared resistant even to high doses of propofol.     

Spatial proximity to others determines how humans inhabit virtual worlds

Highly immersive three-dimensional virtual worlds have emerged as a popular medium for human social interactions. These environments enable multimodal sensory engagement and provide an immersive graphical representation of physical space where users can interact via avatars. However, when compared to two-dimensional virtual settings such as chats, virtual worlds impose constraints on social interactions due to the physical distance between individuals. Using the popular platform of Second Life as a model, we examined how humans manage this interindividual distance in virtual worlds. Taking advantage of methods developed in population ecology, we investigated how avatars are distributed in relation to each other to populate a virtual world. Our results revealed a striking dichotomy in the spatial relationships between avatars. Considerable aggregation, largely independent of population density, was observed alongside surprisingly marked physical isolation. These findings demonstrate that the spatial proximity to others determines how humans inhabit virtual worlds.     

Electron diffraction analysis of individual single-walled carbon nanotubes

We present a detailed electron diffraction study of individual single-walled carbon nanotubes. A novel sample preparation procedure provides well-separated, long and straight individual single-shell nanotubes. Diffraction experiments are carried out at 60 kV, below the threshold for knock-on damage in carbon nanotubes. We describe experimental parameters that allow single-tube electron diffraction experiments with widely available thermal emission transmission electron microscopes. Further, we review the simulation of diffraction patterns for these objects.     

Fully Transparent Friction‐Modulation Haptic Device Based on Piezoelectric Thin Film

Standing Lamb waves in vibrating plates enable haptic interfaces. If the out‐of‐plane displacement of these waves exceeds 1 µm at frequencies above 25 kHz, a silent friction modulation can be created between a human finger and a vibrating plate. A fully transparent friction‐modulation haptic device based on a piezoelectric thin film is demonstrated. The antisymmetric Lamb mode induced at 73 kHz allows for a functional performance that fulfills all conditions for practical use. Out‐of‐plane displacement reaches 2.9 µm when 150 V unipolar voltage is applied. The average transmittance of the whole transducer reaches 75%. The key points of this technology are: 1) a thin HfO₂ layer between lead zirconate titanate film and substrate that prevents chemical reaction between them; 2) the efficient integration of transparent indium tin oxide electrodes and solution‐derived piezoelectric lead zirconate titanate thin film onto optical‐grade fused silica; and 3) the use of a transparent insulating layer made of SU‐8 photoresist.     

A uniform random test data generator for path testing

Path-oriented Random Testing (PRT) aims at generating a uniformly spread out sequence of random test data that execute a single control flow path within a program. The main challenge of PRT lies in its ability to build efficiently such a test suite in order to minimize the number of rejects (test data that execute another control flow path). We address this problem with an original divide-and-conquer approach based on constraint reasoning over finite domains, a well-recognized Constraint Programming technique. Our approach first derives path conditions by using backward symbolic execution and computes a tight over-approximation of their associated subdomain by using constraint propagation and constraint refutation. Second, a uniform random test data generator is extracted from this approximated subdomain. We implemented this approach and got experimental results that show the practical benefits of PRT based on constraint reasoning. On average, we got a two-order magnitude CPU time improvement over standard Random Testing on a set of paths extracted from classical benchmark programs.     

Nonlocal PDEs on Graphs: From Tug-of-War Games to Unified Interpolation on Images and Point Clouds

In this paper, we introduce a new general class of partial difference operators on graphs, which interpolate between the nonlocal \(\infty \)-Laplacian, the Laplacian, and a family of discrete gradient operators. In this context, we investigate an associated Dirichlet problem for this general class of operators and prove the existence and uniqueness of respective solutions. We show that a certain partial difference equation based on this class of operators recovers many variants of a stochastic game known as ‘Tug-of-War’ and extends them to a nonlocal setting. Furthermore, we discuss a connection with certain nonlocal partial differential equations. Finally, we propose to use this class of operators as general framework to solve many interpolation problems in a unified manner as arising, e.g., in image and point cloud processing.