Toward improvement of the properties of parts manufactured by FFF ( Fused Filament Fabrication) through understanding the influence of temperature and rheological behaviour on the coalescence phenomenon

In this paper, the printing temperature ranges of PLA and PEEK, two semi-crystalline thermoplastics, have been investigated for the Fused Filament Fabrication (FFF) process. The printing range, comprised between the melting temperature and the degradation of each polymer, is 160°C to 190°C for PLA and 350°C to 390°C for PEEK. The complex viscosity has been measured for both polymers within the printing range. The kinetics of coalescence has been registered by measuring the bonding length between two filaments of the same polymer according to the temperature. At 167°C, the filaments of PLA reached the maximum value of bonding length. For PEEK, the filaments reached the maximum value of bonding length at 380°C. For the both materials, the final height of the filament is 80% of the initial diameter. The comparison of the obtained results with experimental study and predictive model shows a good agreement when the polymer is totally in fusion state

Modeling the effect of soil meso- and macropores topology on the biodegradation of a soluble carbon substrate

Soil structure and interactions between biotic and abiotic processes are increasingly recognized as important for explaining the large uncertainties in the outputs of macroscopic SOM decomposition models. We present a numerical analysis to assess the role of meso- and macropore topology on the biodegradation of a soluble carbon substrate in variably water saturated and pure diffusion conditions . Our analysis was built as a complete factorial design and used a new 3D pore-scale model, LBioS, that couples a diffusion Lattice-Boltzmann model and a compartmental biodegradation model. The scenarios combined contrasted modalities of four factors: meso- and macropore space geometry, water saturation, bacterial distribution and physiology. A global sensitivity analysis of these factors highlighted the role of physical factors in the biodegradation kinetics of our scenarios. Bacteria location explained 28% of the total variance in substrate concentration in all scenarios, while the interactions among location, saturation and geometry explained up to 51% of it

Microscale heterogeneity of the spatial distribution of organic matter can promote bacterial biodiversity in soils: Insights from computer simulations

There is still no satisfactory understanding of the factors that enable soil microbial populations to be as highly biodiverse as they are. The present article explores in silico the hypothesis that the heterogeneous distribution of soil organic matter, in addition to the spatial connectivity of the soil moisture, might account for the observed microbial biodiversity in soils. A multi-species, individual-based, pore-scale model is developed and parameterized with data from 3 Arthrobacter sp. strains, known to be, respectively, competitive, versatile, and poorly competitive. In the simulations, bacteria of each strain are distributed in a 3D computed tomography (CT) image of a real soil and three water saturation levels (100, 50, and 25%) and spatial heterogeneity levels (high, intermediate, and low) in the distribution of the soil organic matter are considered. High and intermediate heterogeneity levels assume, respectively, an amount of particulate organic matter (POM) distributed in a single (high heterogeneity) or in four (intermediate heterogeneity) randomly placed fragments. POM is hydrolyzed at a constant rate following a first-order kinetic, and continuously delivers dissolved organic carbon (DOC) into the liquid phase, where it is then taken up by bacteria. The low heterogeneity level assumes that the food source is available from the start as DOC. Unlike the relative abundances of the 3 strains, the total bacterial biomass and respiration are similar under the high and intermediate resource heterogeneity schemes. The key result of the simulations is that spatial heterogeneity in the distribution of organic matter influences the maintenance of bacterial biodiversity. The least competing strain, which does not reach noticeable growth for the low and intermediate spatial heterogeneities of resource distribution, can grow appreciably and even become more abundant than the other strains in the absence of direct competition, if the placement of the resource is favorable. For geodesic distances exceeding 5 mm, microbial colonies cannot grow. These conclusions are conditioned by assumptions made in the model, yet they suggest that microscale factors need to be considered to better understand the root causes of the high biodiversity of soils

Infection Kinetics and Tropism of Borrelia burgdorferi sensu lato in Mouse After Natural (via Ticks) or Artificial (Needle) Infection Depends on the Bacterial Strain

Borrelia burgdorferi sl is a complex of pathogen bacteria transmitted to the host by Ixodes ticks. European Ixodes ricinus ticks transmit different B. burgdorferi species, pathogenic to human. Bacteria are principally present in unfed tick midgut, then migrate to salivary glands during blood meal and infect a new host via saliva. In this study, efficiency of transmission in a mouse model of three pathogen species belonging to the B. burgdorferi sl complex, B. burgdorferi sensu stricto (B31, N40, and BRE-13), B. afzelii (IBS-5), and B. bavariensis (PBi) is examined in order to evaluate infection risk after tick bite. We compared the dissemination of the Borrelia species in mice after tick bite and needle injection. Location in the ticks and transmission to mice were also determined for the three species by following infection kinetics. After inoculation, we found a significant prevalence in the brain for PBi and BRE-13, in the heart, for PBi, in the skin where B31 was more prevalent than PBi and in the ankle where both B31 and N40 were more present than PBi. After tick bite, statistical analyses showed that BRE-13 was more prevalent than N40 in the brain, in the bladder and in the inguinal lymph node. When Borrelia dissemination was compared after inoculation and tick bite, we observed heart infection only after tick inoculation of BRE-13, and PBi was only detected after tick bite in the skin. For N40, a higher number of positive organs was found after inoculation compared to tick bite. All European B. burgdorferi sl strains studied were detected in female salivary glands before blood meal and infected mice within 24 h of tick bite. Moreover, Borrelia-infected nymphs were able to infect mice as early as 12 h of tick attachment. Our study shows the need to remove ticks as early as possible after attachment. Moreover, Borrelia tropism varied according to the strain as well as between ticks bite and needle inoculation, confirming the association between some strains and clinical manifestation of Lyme borreliosis, as well as the role played by tick saliva in the efficiency of Borrelia infection and dissemination in vertebrates

Laser transmission welding as an assembling process for high temperature electronic packaging.

Higher efficiency, power density, reliability and longer lifetime of power electronic devices would stem from progresses in material science. In this work, we propose to use a high performance thermoplastic polymer PAEK as packaging box to extend the operating temperature above 200°C. More, the laser transmission welding process has been applied to PAEK to join the two-part module. In order to validate this assembling process, the temperature distribution inside the specimens was measured during laser transmission welding. The assembly consists of a quasi-amorphous sample as the upper part and a semi-crystalline sample as the lower part. The temperature fields were measured by infrared thermography with the camera sensor perpendicular to the welded interface. With an energy beam of 28 J.mm-2 and irradiation time of 15 s, we have noticed that the maximum temperature inside the sample is kept far from the PAEK degradation one. Moreover, the temperature at the interface reaches the melting temperature thus assuring enough mobility for polymeric chains to get adhesion at the interface. The location and size of the heat-affected zone has been determined. Finally, some frames were machined and successfully welded

Soil aggregates as biogeochemical reactors: Not a way forward in the research on soil‐atmosphere exchange of greenhouse gases

Over the last two decades, the fact that soils are significant sources of greenhouse gases (GHG), e.g., carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor, has received considerable attention from the scientific community. Many laboratory and field experiments have been carried out to investigate the release of GHG by soils, and a wide range of computer modeling approaches have been explored to encapsulate what is known about the process, as well as to improve its prediction at various spatial and temporal scales

In-situ infrared thermography measurements to master transmission laser welding process parameters of PEKK

The temperature field along the thickness of the specimens has been measured during transmission laser welding. Polyetherketoneketone (PEKK) is a very high performance thermoplastic with tunable properties. We have shown that this grade of PEKK can be turned to quasi-amorphous or semi-crystalline material, due to its slow kinetics of crystallization. Its glass transition temperature is 150 °C. The effect of its crystalline rate directly impacts its optical properties: the transmittance of quasi-amorphous PEKK is about 60% in the NIR region (wavelength range from 0.4 to 1.2 μm) whereas it is less than 3% for the semi-crystalline material. The welding tests have been carried out with an 808 nm laser diode apparatus. The heat field is recorded during the welding experiment by infrared thermography with the camera sensor perpendicular to the lasersheet and to the sample’s length to focus on the welded interface. The study is divided in two steps: firstly, a single specimen is irradiated with an energy density of 22 J.mm − 2 : the whole sample thickness is heated up, the maximum temperature reaches 222 ± 7 °C. This temperature corresponds to about T g + 70 °C, but the polymer does not reach its melting temperature. After that, welding tests were performed: a transparent (quasi-amorphous) sample as the upper part and an opaque (semi-crystalline) one as the lower part were assembled in static conditions. The maximum temperature reached at the welded interface is about 295 °C when the upper specimen is irradiated for 16 s with an energy density of 28 J.mm − 2 . The temperature at the welded interface stays above T g during 55 s and reached the melting temperature during 5 s before rapid cooling. These parameters are suitable to assemble both polymeric parts in a strong weld. This work shows that infrared thermography is an appropriate technique to improve the reliability of laser welding process of high performance thermoplastics

Impact of water and thermal induced crystallizations in a PC/MXD6 multilayer film on barrier properties

A multilayer film composed of alternating layers of polycarbonate (PC) and poly(m-xylene adipamide) (MXD6) was elaborated by using an innovative multilayer coextrusion process. Quasi-continuous thin MXD6 layers (nanolayers) alternating with PC layers were successfully obtained. The PC/MXD6 multilayer film showed a confining effect of MXD6 exerted by PC layers leading to an improvement of barrier properties despite a low degree of crystallinity (X c < 10 wt%). In order to further improve the barrier performances, crystallization treatments induced by water and by heating were then applied on the multilayer film and allowed reaching around 30 wt% of crystallinity in MXD6 layers. To decouple crystallization and geometrical constraint effects on the barrier properties in the multilayer films, the two treatments were also applied on MXD6 films. Surprisingly, despite an increase of the degree of crystallinity from 6 to 26%, water crystallization did not permit to improve gas barrier performances of the MXD6 film nor into the PC/MXD6 multilayer film. On the other hand, thermal crystallization of MXD6 in the multilayer film seems to be a more efficient route to strongly decrease the gas and moisture permeability, up to 75% for nitrogen, 58% for oxygen, 84% for carbon dioxide and 43% for water

Emergent properties of microbial activity in heterogeneous soil microenvironments:Different research approaches are slowly converging, yet major challenges remain

Over the last 60 years, soil microbiologists have accumulated a wealth of experimental data showing that the usual bulk, macroscopic parameters used to characterize soils (e.g., granulometry, pH, soil organic matter and biomass contents) provide insufficient information to describe quantitatively the activity of soil microorganisms and some of its outcomes, like the emission of greenhouse gases. Clearly, new, more appropriate macroscopic parameters are needed, which reflect better the spatial heterogeneity of soils at the microscale (i.e., the pore scale). For a long time, spectroscopic and microscopic tools were lacking to quantify processes at that scale, but major technological advances over the last 15 years have made suitable equipment available to researchers. In this context, the objective of the present article is to review progress achieved to date in the significant research program that has ensued. This program can be rationalized as a sequence of steps, namely the quantification and modeling of the physical-, (bio)chemical-, and microbiological properties of soils, the integration of these different perspectives into a unified theory, its upscaling to the macroscopic scale, and, eventually, the development of new approaches to measure macroscopic soil characteristics. At this stage, significant progress has been achieved on the physical front, and to a lesser extent on the (bio)chemical one as well, both in terms of experiments and modeling. In terms of microbial aspects, whereas a lot of work has been devoted to the modeling of bacterial and fungal activity in soils at the pore scale, the appropriateness of model assumptions cannot be readily assessed because relevant experimental data are extremely scarce. For the overall research to move forward, it will be crucial to make sure that research on the microbial components of soil systems does not keep lagging behind the work on the physical and (bio)chemical characteristics. Concerning the subsequent steps in the program, very little integration of the various disciplinary perspectives has occurred so far, and, as a result, researchers have not yet been able to tackle the scaling up to the macroscopic level. Many challenges, some of them daunting, remain on the path ahead

Lessons from a landmark 1991 article on soil structure: distinct precedence of non-destructive assessment and benefits of fresh perspectives in soil research

In 1991, at the launch of a national symposium devoted to soil structure, the Australian Society of Soil Science invited Professor John Letey to deliver a keynote address, which was later published in the society’s journal. In his lecture, he shared the outcome of his reflexion about what the assessment of soil structure should amount to, in order to produce useful insight into the functioning of soils. His viewpoint was that the focus should be put on the openings present in the structure, rather than on the chunks of material resulting from its mechanical dismantlement. In the present article, we provide some historical background for Letey’s analysis, and try to explain why it took a number of years for the paradigm shift that he advocated to begin to occur. Over the last decade, his perspective that soil structure needs to be characterised via non-destructive methods appears to have gained significant momentum, which is likely to increase further in the near future, as we take advantage of recent technological advances. Other valuable lessons that one can derive from Letey’s pioneering article relate to the extreme value for everyone, even neophytes, to constantly ask questions about where research on given topics is heading, what its goals are, and whether the methods that are used at a certain time are optimal