PEEK filament characteristics before and after extrusion within fused filament fabrication process

Journal of Materials Science - The heating and extrusion process in fused filament fabrication (FFF) is significantly shorter than the conventional extrusion process where longer heating times and...     

Context-Based Constraints in Security: Motivations and First Approach

Recent research in security shows a real need for contextual information in building highly adaptive security systems. The need for such security for web services is fast becoming imperative. In this paper, we review the main contributions in this domain. Based, on this study we present a glimpse at the CoDiS project; a generic layer for the rapid prototyping of context-based security systems, aiming at getting around the limitations of existing systems.     

Studies on the thermal and mechanical behavior of PLA‐PET blends

The increasing use of bio‐sourced and biodegradable polymers such as poly(lactic acid) (PLA) in bottle packaging presents an increasing challenge to the polyethylene terephthalate (PET) recycling process. Despite advanced separation technologies to remove PLA from PET recyclate, PLA may still be found in rPET process streams. This study explores the effects of PLA on the mechanical properties and crystallization behavior of blends of PET containing 0.5–20% PLA produced by injection molding. SEM indicates an immiscible blend of the two polymers and TGA confirms the independent behavior of the two polymers under thermal degradation conditions. Temperature‐modulated DSC studies indicate that adding PLA to PET increases the rigid amorphous fraction of the PET moiety. Critical amounts of PLA induce stress oscillation behavior during mechanical testing. The mechanical behavior of the samples is explained by antagonistic interaction between increased rigid amorphous fraction and decreased fracture strength arising from an increased population of PLA microparticles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44147.     

Gaussian beams in hollow metal waveguides: experiment

Gaussian beams have been widely used for propagating electromagnetic waves in free space and in certain other optical systems. It has been suggested that recurring forms of such beams might also be useful for propagation in planar or rectangular metal waveguides. Experimental verification of the recurrence of the Gaussian field distribution in metal waveguides is reported here.     

Characterization of aquatic particles by direct FTIR analysis of filters and quantification of elemental and molecular compositions

This paper presents the first characterization of aquatic particles and particulate organic matter (POM) by attenuated total reflectance infrared spectroscopy (ATR-FTIR) using particles deposited on filters. Particles from 30 water samples from the St. Lawrence System (Canada) were analyzed. ATR-FTIR spectra revealed changes in numerous organic and inorganic functional group contents. Particles from marine waters contained POM enriched in amide, N-H, and aliphatic groups, while terrigenous POM had more COO(-)/COOH and aromatic groups. The spectra showed the selective degradation of amide, N-H, aliphatic, and carbohydrate-like structures during the sinking of the particles. Partial least-squares (PLS) regression of the ATR-FTIR spectra was used to quantify 12 important elemental and molecular parameters, such as amino acids, bacterial biomarkers, and degradation indices. Most parameters were quantified with good accuracy compared to conventional methods (<15% error). The spectral regions leading to the best quantifications and the PLS loadings revealed that aromatic cycles, other unsaturated structures, and COO(-)/COOH groups were degraded at a much slower rate than N-molecules, such as amino acids, and carbohydrates. Marine POM was enriched in CH(3) groups. CH(3) groups appeared highly labile and abundant in bacterial POM. ATR-FTIR represents a new and powerful method for a rapid, inexpensive, and nondestructive characterization of particles collected by filtration revealing important biogeochemical processes involving POM.     

MaDViWorld: a software framework for massively distributed virtual worlds

The MaDViWorld project represents an original attempt to define an appropriate software architecture for supporting massively distributed virtual world systems. A non‐massively distributed virtual world system is typically engineered as a client–server application for which a single server or more rarely a small cluster of servers contain all the world pertinent data and assume the world accessibility, consistency and persistence. On the client side, many of them enable interaction with the other users and the various objects of the world. The main originality of our approach resides in the fact that the server part of the proposed system is no more limited to a few centralized servers, but can be distributed on arbitrarily many of them. Indeed, MaDViWorld, the prototypal software framework already implemented using Java and RMI by our group, allows for creating the rooms of a given world on several machines, each running the server application. It is then possible to connect the rooms by way of simple doors and to populate them with active objects. Finally, avatars managed by the client application visit the rooms and interact with the active objects either directly on the remote host or locally by cloning or transporting them first to the client machine. This paper draws from the experience gained with the development of our first prototype in order to discuss, both at the user's and the vi‐world developer's level, the main software engineering issues related to the implementation of such massively distributed virtual world systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Electrical characterization of thiols self-assembled layers on GaP (1 1 1) structures

The experimental studies on III–V semiconductor compounds surface passivation phenomena are mainly dedicated to solve some technological problems as those regarding the ways to keep the chemical stability of native oxides on surfaces. Self-assembled monolayers (SAMs) provide a simple way to produce relatively ordered structures at a molecular scale, which seems to be capable to protect the clean surface against the evolution of oxidation process. In this respect, thin films of SAMs of aliphatic thiol (dodencanthiol—CH₃(CH₂)₁₁SH) and aromatic thiol (4, 4′ tiobisbenzenthiol-S (C₆H₄SH)₂ have been deposited on the surface of GaP (1 1 1) samples. The electrical properties measurements of some structures based on GaP compound was performed. There were recorded current–voltage (I–V) characteristics for complex structures AuGeNi/R-SH/GaP and AuGeNi/Ar-SH/GaP in darkness and also exposed to a Xe lamp. In dark and in “reverse bias” way, the I–V characteristics present the feature of a Zenner diode for GaP/Ar-SH and a gradual increase of current for GaP/R-SH. In dark and “in forward bias” way, the current increases as for a normal diode for both GaP/Ar-SH and GaP/R-SH structures. The complex structures (e.g.: In/AuGeNi/R-SH/GaP/R-SH/AuGeNi/In) are less sensitive to light. The SEM analysis performed on a GaP/R-SH surface shows a continuous packed up layer while GaP/Ar-SH looks like an inhomogeneous deposition of layers with different thickness regions. The diodes’ ideality factors determined from I–V characteristics are unusually high (n2) as a possible result of inhomogeneous Schottky contacts or due to ageing effects, in the field of degradation.     

A fully automatic CAD-CTC system based on curvature analysis for standard and low-dose CT data

Computed tomography colonography (CTC) is a rapidly evolving noninvasive medical investigation that is viewed by radiologists as a potential screening technique for the detection of colorectal polyps. Due to the technical advances in CT system design, the volume of data required to be processed by radiologists has increased significantly, and as a consequence the manual analysis of this information has become an increasingly time consuming process whose results can be affected by inter- and intrauser variability. The aim of this paper is to detail the implementation of a fully integrated CAD-CTC system that is able to robustly identify the clinically significant polyps in the CT data. The CAD-CTC system described in this paper is a multistage implementation whose main system components are: 1) automatic colon segmentation; 2) candidate surface extraction; 3) feature extraction; and 4) classification. Our CAD-CTC system performs at 100% sensitivity for polyps larger than 10 mm, 92% sensitivity for polyps in the range 5 to 10 mm, and 57.14% sensitivity for polyps smaller than 5 mm with an average of 3.38 false positives per dataset. The developed system has been evaluated on synthetic and real patient CT data acquired with standard and low-dose radiation levels.     

Lipolysis-Stimulated Lipoprotein Receptor Acts as Sensor to Regulate ApoE Release in Astrocytes

Astroglia play an important role, providing de novo synthesized cholesterol to neurons in the form of ApoE-lipidated particles; disruption of this process can increase the risk of Alzheimer’s disease. We recently reported that glia-specific suppression of the lipolysis-stimulated lipoprotein receptor (LSR) gene leads to Alzheimer’s disease-like memory deficits. Since LSR is an Apo-E lipoprotein receptor, our objective of this study was to determine the effect of LSR expression modulation on cholesterol and ApoE output in mouse astrocytes expressing human ApoE3. qPCR analysis showed that siRNA-mediated lsr knockdown significantly increased expression of the genes involved in cholesterol synthesis, secretion, and metabolism. Analysis of media and lipoprotein fractions showed increased cholesterol and lipidated ApoE output in HDL-like particles. Further, lsr expression could be upregulated when astrocytes were incubated 5 days in media containing high levels (two-fold) of lipoprotein, or after 8 h treatment with 1 µM LXR agonist T0901317 in lipoprotein-deficient media. In both conditions of increased lsr expression, the ApoE output was repressed or unchanged despite increased abca1 mRNA levels and cholesterol production. We conclude that LSR acts as a sensor of lipoprotein content in the medium and repressor of ApoE release, while ABCA1 drives cholesterol efflux, thereby potentially affecting cholesterol load, ApoE lipidation, and limiting cholesterol trafficking towards the neuron.     

Inverse gas chromatography used to follow kinetics of epoxy-amine reactions in the molten state

Polycondensation kinetics of epoxy-amine model systems were investigated with inverse gas chromatography. The results obtained were applied to the study of cross-linking kinetics of two epoxy prepolymers, tetraglycidyl diamino diphenyl methane and diglycidyl ether of bisphenol A, with diamino diphenyl sulphone. Data furnished by inverse gas chromatography showed zones of gelation and of vitrification. Based on kinetics established by isothermal microcalorimetry, it was possible to determine reaction advancement in these transition zones. The results show that advancement of both reaction systems to the transition points T₁ and T₂ is very sensitive to curing temperature and to the stoichiometry of the mixture. Finally, the vitreous transition temperatures of the cross-linked systems were determined and compared to those determined with differential scanning calorimetry.