Development of the drag coefficient of a sphere translating through a viscoelastic fluid

Presentation at 15th OpenFOAM Workshop, June 22-25, 2020, Arlington, VA, USA

Advanced polymer simulation and processing

[Excerpt] Polymer processing techniques are of paramount importance in the manufacture of polymer parts. The key focus is on producing parts with the desired quality, which usually refers to mechanical performance, dimensional conformity, and appearance. To maximize the overall efficiency of polymer processing techniques, advanced modeling codes are needed along with experimental setups to simulate and optimize the processes. [...]This research was funded by FEDER through the COMPETE 2020 Programme and National Funds through FCT-Portuguese Foundation for Science and Technology under the projects UIDB/05256/2020 and UIDP/05256/2020. It was also funded by FCT through CMAT (Centre of Mathematics of the University of Minho) through projects UIDB/00013/2020 and UIDP/00013/2020

Gene silencing based on RNA-guided catalytically inactive Cas9 (dCas9): a new tool for genetic engineering in Leptospira

International audienceLeptospirosis is a worldwide zoonosis caused by pathogenic bacteria of the genus Leptospira, which also includes free-living saprophyte strains. Many aspects of leptospiral basic biology and virulence mechanisms remain unexplored mainly due to the lack of effective genetic tools available for these bacteria. Recently, the type II CRISPR/Cas system from Streptococcus pyogenes has been widely used as an efficient genome engineering tool in bacteria by inducing double-strand breaks (DSBs) in the desired genomic targets caused by an RNA-guided DNA endonuclease called Cas9, and the DSB repair associated machinery. In the present work, plasmids expressing heterologous S. pyogenes Cas9 in L. biflexa cells were generated, and the enzyme could be expressed with no apparent toxicity to leptospiral cells. However, L. biflexa cells were unable to repair RNA-guided Cas9-induced DSBs. Thus, we used a catalytically dead Cas9 (dCas9) to obtain gene silencing rather than disruption, in a strategy called CRISPR interference (CRISPRi). We demonstrated complete gene silencing in L. biflexa cells when both dCas9 and single-guide RNA (sgRNA) targeting the coding strand of the β-galactosidase gene were expressed simultaneously. Furthermore, when the system was applied for silencing the dnaK gene, no colonies were recovered, indicating that DnaK protein is essential in Leptospira. In addition, flagellar motor switch FliG gene silencing resulted in reduced bacterial motility. To the best of our knowledge, this is the first work applying the CRISPRi system in Leptospira and spirochetes in general, expanding the tools available for understanding leptospiral biology

Food preservation under pressure (hyperbaric storage) as a possible improvement/alternative to refrigeration

Food preservation is highly dependent on refrigeration, which is limited by its high energy costs. Among alternatives being developed, this review focused on hyperbaric storage (food preservation under pressure). This new preservation methodology has as main objective microbial growth inhibition similarly to freezing and refrigeration, showing a great potential to lower energy costs since refrigerated/room temperatures (RT) can be used. This, even at variable (uncontrolled) RT (up to 37 C), has been shown to preserve foods and thus achieving significant energy savings. Covering the earliest up to the more recent studies, this review aimed to gather information about the state of art of hyperbaric storage at refrigerated and RTs, with the primary objective of showing it potential and possible future applications of this new preservation method based on microbial growth inhibition under pressure, using pressure as the main variable to slow down microbial growth

The role of deformation history on stress relaxation and stress memory of filled rubber

Although the magnitudes of inelastic and viscoelastic effects in filled rubbers are small relative to that of the elastic response, these effects are nevertheless critical in applications such as gaskets, seals and dampers. This study investigates the role of deformation history on relaxation of rubber through time-dependent experiments following a range of deformation histories. Two grades of carbon-black filled EPDM were subjected to uniaxial tensile deformation followed by stress-relaxation or stress memory at fixed deformation. Stress relaxation was found to be highly dependent on strain levels following a single loading. When an additional load-unload cycle was added to the history, the rubbers relaxed an approximately constant fraction of stress after a given time, provided that the strain at stress relaxation was smaller than the historical maximum. This fraction was independent of both the applied strain and of the maximum strain, and suggests that the relaxation process is independent of scragging procedures used to control the modulus. Stress memory observed following load-unload cycles was also approximately independent of strain history

Preservation of sliced cooked ham at 25, 30 and 37°C under moderated pressure (hyperbaric storage) and comparison with refrigerated storage

The feasibility of hyperbaric storage (HS) to substitute refrigeration as a lower energetic cost alternative to refrigeration, for sliced cooked ham preservation was assessed by using temperatures and pressures ranging 25–37◦C and 25–150 MPa for 4 and 8 h. At microbiological level, storage at 25 ◦C, 30 ◦C, and 37 ◦C, showed no effect on microbial growth at 25 MPa reaching levels similar to atmospheric pressure storage, around 5 log CFU/g for both total aerobic mesophiles (TAM) and lactic acid bacteria (LAB). Nevertheless, the storage at 50 MPa and 30 ◦C resulted in microbial growth inhibition, resulting in TAM and LAB counts similar to refrigeration, of about 3.8 log CFU/g for both the microorganisms. Additionally, the increase of the storage pressure to 100–150 MPa resulted in microbial inacti-vation, leading to microbial loads of almost 1 log CFU/g lower than refrigeration. In general, hyperbaric stored sliced cooked ham showed physicochemical parameters similar to the refrigerated samples. In conclusion, these results show that HS at uncontrolled (naturally variable room tem-perature conditions at 25–37 ◦C) is a promising alternative to refrigeration for cooked ham preservation. To this new preservation technology, no energetic costs are associated throughout storage, compared to refrigeration, needing only energy to generate the pressure and decompress, since no energy is required to maintain the pressure

Preservation under pressure (hyperbaric storage) at 25ºC, 30ºC and 37ºC of a highly perishable dairy food and comparison with refrigeration

Hyperbaric storage (HS) under mild pressure of requeijão, a traditional Portuguese whey cheese, as a case study of a highly perishable dairy food, was evaluated as a possible energy costless alternative to refrigeration. Whey cheese was stored for 4 and 8 hours, at different pressure levels (0.1, 100 and 150 MPa) and temperatures (25°C, 30°C and 37°C), and the results were compared with refrigeration (4°C). Microbial analyses showed that storage for 4 hours at 100 MPa was able to maintain microbial counts similar to refrigeration and initial load, ≈3 Log10 CFU/g, at all tested temperatures. By increasing the pressure to 150 MPa and the storage time to 8 hours, microbial loads were reduced to undetectable counts, with the exception for total aerobic mesophiles that were reduced to about ≈1 Log unit. HS in general maintained pH, water activity and lipid oxidation values, at levels similar to that in refrigeration

Time-dependent reliability analyses of prestressed concrete girders strengthened with CFRP laminates

This paper presents a time-dependent reliability analysis of prestressed concrete girders subjected to degradation caused by pitting corrosion. The procedure presented includes the effects of both spatial and temporal pitting corrosions on prestressing steel, as well as the degradation of the strengthening CFRP laminate used for the rehabilitation of the member. Results indicate that the correlation of corrosion in different segments of the prestressing tendons impacts on the computed safety index for the deteriorated structure. Ditlevsen bounds are proposed for a better approximation of the correlation between failure modes in the spatial discretisation. Results show that such approach produces adequate estimates of the reliability index over the full range of analysis in comparison with other tested models. It is also observed that the degradation of the CFRP laminates does not affect the reliability as significantly as corrosion, and that traffic loads, models uncertainties, corrosion error and corrosion rate are the most relevant variables in the analysis, followed by prestressing strength and concrete cover. The significance of the variables changes with time: the corrosion rate, corrosion model error and concrete cover increase in importance with the development of corrosion, whereas traffic loads become gradually less important