Effect of ball milling in a tumbling ball mill on the properties of multi-wall carbon nanotubes

The effects of ball milling on various properties of ground multi-wall carbon nanotubes were studied. These properties were granulometry, SEM,specific surface area, density, crystalline structure, surface chemical analysis and thermogravimetry. The mean size of agglomerates, initially at 35 m, decreases to reach a limit value of 2.5m, corresponding to a competition between agglomeration and fragmentation. A kinetic study,based on a decomposition of size distributions measured for different times, has permitted to propose a grinding mechanism. As grinding proceeds, the specific surface area first increases from 175 to 244m2 g−1 and then decreases, while the real density increases from 1800 to 2150 kgm−3 to level off at 2070 kgm−3. Moreover, macroporosity disappears totally, giving access first to mesoporosity and then to microporosity. The nanotubes are probably cut to give access to the internal porosity. An increase of the proportion of oxygen adsorbed on carbon (from 3% to 8.7% after 600 min grinding) implies that it may be possible to functionalise the nanotubes. Thanks to these different morphological changes numerous applications of ground nanotubes can be considered. Moreover, the use of a tumbling ball mill allows a massive production of cut nanotubes

On the interest of using degradable fillers in co-ground composite materials

The article presents the results of a study whose objective is to show the interest of using vegetable and biodegradable fillers in composite materials. The incorporation of fillers made up of starch in the synthetic polymeric matrix was carried out by co-grinding, a process supporting the dispersion of one component in another one and thus supporting the homogeneity of the composite properties. The follow-up of the particle size and morphology has permitted to identify how the composite is formed. We could note that co-grinding makes it possible to improve the mechanical properties of the composite material, not only through a better dispersion of the filler in the matrix, but also thanks to a modification of the interface properties. Finally a study on the material degradation in water has shown that the incorporation of a vegetable, degradable and cheap filler in the synthetic matrix and the application of co-grinding during an adapted time offer interesting water-resistant properties

How to combine a hydrophobic matrix and a hydrophilic filler without adding a compatibilizer – Co-grinding enhances use properties of renewable PLA-starch composites

In order to avoid the use of compatibilizers or plasticizers, co-grinding was performed to produce PLA – starch composite materials. Fragmentation and agglomeration phenomena were analysed to propose a production mechanism. Co-grinding enhances dispersion of the filler in the matrix and interactions between the materials. Consequently while blending the two materials has a negative effect on mechanical properties, co-grinding permits to improve them if optimized operating conditions are applied. Water uptake and diffusion are also controlled by co-grinding conditions. This treatment allows the production of composite materials offering good use properties without any use of a compatibilizer or a plasticizer

Matrix-filler interactions in a co-ground ecocomposite: surface properties and behaviour in water

Ecocomposites made up of polystyrene and starch were produced by co-grinding. The mechanism by which the composite is formed was identified by following the particle size and morphology. The size reduction of the matrix particles is favoured by the presence of starch which adheres on polystyrene surface, playing the role of agglomeration inhibitor between matrix particles. Thus, the filler is well dispersed in the matrix, permitting a good homogeneity of the composite properties. The hydrophilic behaviour of starch is reduced by co-grinding, resulting of a decrease of the acid and non dispersive components of the surface energies. Consequently the interactions between the initially hydrophobic matrix and hydrophilic filler are enhanced without using a compatibilizer. Thus, the water-resistance of the co-ground composite materials is better compared to blends since blends pellets introduced in water are rapidly disintegrated while an adapted co-grinding time permits to avoid this problem. It was seen that the diffusion coefficient of water in the composite pellets decreases with an increase of the co-grinding time for the lower filler rates, while it is the opposite for high filler rates. Moreover, the diffusion coefficient increases with the filler ratio

Chemistry course for radiochemistry engineers on the platform Moodle: a support to self-education for undergraduate students

The education challenges at present times include the incorporation of information and communication technologies (ICT) in the learning-teaching process. In Higher Education the agreement between the volume of information to be processed by the student, the available student’s time and the assimilation of the courses contents is very important. The new study plans in Cuban Universities include the reduction of the number of face to face hours and the increase of the available time for the student’s independent study. Then, it is necessary to develop abilities that upgrade learning capacity during a lifetime through the self-education. The first version of a course on chemistry for radiochemistry students using the platform Moodle and Open Educational Resources (OER) as a support to the undergraduate course is presented. The detailed topic plan of the course of chemistry for radiochemists, which was distributed week by week, and different activities combining communication, interactive and collaborative modules were implemented on the platform Moodle. The whole system was tested during the first semester of the 2010-2011 academic year. The course evaluation results were carried out through a survey among the students and discussion forums. The results showed a good acceptance by the students, a better efficiency in the teaching-learning process given by better planning of the individual study, a better preparation to perform the laboratory practices, the new possibilities of communication between students and teachers, the access to OER and greater self-conscious of the students on their own process of learning

The Distinctive Regulation of Cyanobacterial Glutamine Synthetase

Glutamine synthetase (GS) features prominently in bacterial nitrogen assimilation as it catalyzes the entry of bioavailable nitrogen in form of ammonium into cellular metabolism. The classic example, the comprehensively characterized GS of enterobacteria, is subject to exquisite regulation at multiple levels, among them gene expression regulation to control GS abundance, as well as feedback inhibition and covalent modifications to control enzyme activity. Intriguingly, the GS of the ecologically important clade of cyanobacteria features fundamentally different regulatory systems to those of most prokaryotes. These include the interaction with small proteins, the so-called inactivating factors (IFs) that inhibit GS linearly with their abundance. In addition to this protein interaction-based regulation of GS activity, cyanobacteria use alternative elements to control the synthesis of GS and IFs at the transcriptional level. Moreover, cyanobacteria evolved unique RNA-based regulatory mechanisms such as glutamine riboswitches to tightly tune IF abundance. In this review, we aim to outline the current knowledge on the distinctive features of the cyanobacterial GS encompassing the overall control of its activity, sensing the nitrogen status, transcriptional and post-transcriptional regulation, as well as strain-specific differences.Deutsche Forschungsgemeinschaft KL 3114/2-1Ministerio de Economía y Competitividad BIO2016-75634-PFEDER BIO2016-75634-

Co-grinding significance for calcium carbonate–calcium phosphate mixed cement. Part I: effect of particle size and mixing on solid phase reactivity

In part I of this study we aim to evaluate and control the characteristics of the powders constituting the solid phase of a vaterite CaCO3–dicalcium phosphate dihydrate cement using a co-grinding process and to determine their impact on cement setting ability. An original methodology involving complementary analytical techniques was implemented to thoroughly investigate the grinding mechanism of separated or mixed reactive powders and the effects on solid phase reactivity. We showed that the association of both reactive powders during co-grinding improves the efficiency of this process in terms of the particle size decrease, thus making co-grinding adaptable to industrial development of the cement. For the first time the usefulness of horizontal attenuated total reflection Fourier transform infrared spectroscopy to follow the chemical setting reaction at 37°C in real time has been demonstrated. We point out the antagonist effects that co-grinding can have on cement setting: the setting time is halved; however, progress of the chemical reaction involving dissolution–reprecipitation is delayed by 30 min, probably due to the increased contact area between the reactive powders, limiting their hydration. More generally, we can take advantage of the co-grinding process to control powder mixing, size and reactivity and this original analytical methodology to better understand its effect on the phenomena involved during powder processing and cement setting, which is decisive for the development of multi-component cements

Xenosurveillance reflects traditional sampling techniques for the identification of human pathogens: A comparative study in West Africa

BACKGROUND: Novel surveillance strategies are needed to detect the rapid and continuous emergence of infectious disease agents. Ideally, new sampling strategies should be simple to implement, technologically uncomplicated, and applicable to areas where emergence events are known to occur. To this end, xenosurveillance is a technique that makes use of blood collected by hematophagous arthropods to monitor and identify vertebrate pathogens. Mosquitoes are largely ubiquitous animals that often exist in sizable populations. As well, many domestic or peridomestic species of mosquitoes will preferentially take blood-meals from humans, making them a unique and largely untapped reservoir to collect human blood. METHODOLOGY/PRINCIPAL FINDINGS: We sought to take advantage of this phenomenon by systematically collecting blood-fed mosquitoes during a field trail in Northern Liberia to determine whether pathogen sequences from blood engorged mosquitoes accurately mirror those obtained directly from humans. Specifically, blood was collected from humans via finger-stick and by aspirating bloodfed mosquitoes from the inside of houses. Shotgun metagenomic sequencing of RNA and DNA derived from these specimens was performed to detect pathogen sequences. Samples obtained from xenosurveillance and from finger-stick blood collection produced a similar number and quality of reads aligning to two human viruses, GB virus C and hepatitis B virus. CONCLUSIONS/SIGNIFICANCE: This study represents the first systematic comparison between xenosurveillance and more traditional sampling methodologies, while also demonstrating the viability of xenosurveillance as a tool to sample human blood for circulating pathogens