22,997 research outputs found
A Representation of the Virasoro Algebra via Wigner-Heisenberg Algebraic Technique to Bosonic Systems
Using the Wigner-Heisenberg algebra for bosonic systems in connection with
oscillators we find a new representation for the Virasoro algebra.Comment: Revised version. Revtex, 7 pages, no figures. This work was presented
in the XXII Brazilian National Meeting on Particles and Fields
(October/2001), to appear in Braz. J. of Phys., 33, 1 (2003
New strategies for the production of biosurfactants towards biomedical applications
Microbial adhesion to biomaterial surfaces and subsequent biofilm formation has been observed on nearly all medical devices with severe economic and medical consequences. The significant resistance of biofilms to conventional antibiotic therapies has encouraged the development of new biomaterials and coatings. Biosurfactants represent an interesting approach as they can be used to modify the surface properties conferring it an anti-adhesive and antimicrobial activity, leading to new and effective means of combating colonization by pathogenic microorganisms without the use of synthetic drugs and chemicals. These microbial compounds constitute a diverse group of surface-active molecules occurring in a variety of chemical structures. Biosurfactants from lactic acid bacteria have been used as a strategy to avoid microbial colonization of silicone rubber voice prostheses. Also, they were found to be active against several bacteria and filamentous fungi responsible for diseases and infections in the urinary, vaginal and gastrointestinal tracts, and in the skin. Nevertheless, it is important to stress that the insufficient data on their toxicity for humans, as well as their high costs of large-scale production, have been restraining their commercialization and use in most medical applications. Many biotechnological strategies have been pursued to reduce the biosurfactants production costs including the use of agro-industrial wastes as substrates, optimization of medium and culture conditions, and efficient recovery processes. However, the improvements obtained from these strategies are marginal and to successfully compete with synthetic surfactants, novel microorganisms must be designed. The use of hyper-producer strains allows increasing the production yields and consequently reducing costs. These strains can be screened from the natural environment, or engineered using synthetic biology approaches. Hence, data on the genes involved on the production of biosurfactants is critical for designing organisms with improved features. Once the genes have been indentified and isolated, they can be expressed in other microorganisms, or they can be modified or placed under regulation of strong promoters to increase their expression and so enhance production. This knowledge will also allow the production of novel biosurfactants with specific new properties for different industrial applications. Further advances in genetic engineering of the known biosurfactant molecules could yield potent biosurfactants with altered antimicrobial profiles and decreased toxicity against mammalian cells
Inhibition of bacterial adhesion on medical devices
Microbial infections resulting from bacterial adhesion to biomaterial surfaces
have been observed on almost all medical devices. Biofilm infections pose
a number of clinical challenges due to their resistance to immune defence mechanisms
and antimicrobials, and, regardless of the sophistication of the implant, all
medical devices are susceptible to microbial colonisation and infection. Research
efforts are currently directed towards eliminating or reducing infection of medical
devices. Strategies to prevent biofilm formation include physiochemical modification
of the biomaterial surface to create anti-adhesive surfaces, incorporation of
antimicrobial agents into medical device polymers, mechanical design alternatives,
and release of antibiotics. Nevertheless, the success of these alternatives has been
modest, mainly due to the various environments into which devices are placed and
the diversity of ways in which organisms can colonise surfaces. Biosurfactants have
been reported as a promising strategy as they effectively inhibit bacterial adhesion
and retard biofilm formation, and are thus potentially useful as a new generation of
anti-adhesive and antimicrobial coatings for medical device
On disturbances caused by pressure taps in highly elastic flows
The objective of this work is to characterise the onset of laterally
asymmetric flow of viscoelastic solutions around a confined microfluidic
cylinder, which was encountered in a recent study [Rodrigues et al.,
, 104406 (2020)]. To this
end, two non-Newtonian fluids were employed in the same micro-geometry. Two
microchannels were studied, both with a cylinder of diameter 75
m, aspect ratio (channel height over width) of 0.37 and blockage
ratio (cylinder diameter over channel width) of 0.28, differing only on the
width of the pressure taps, located 500 m up- and downstream from
the respective cylinder face, on opposing walls. The working fluids consist of
two poly(ethylene oxide) (PEO) solutions: a weakly shear-thinning elastic fluid
and an elastic shear-thinning fluid. Micro-Particle Image Velocimetry
(PIV) and streak imaging techniques were used to evaluate the
flow over a Weissenberg number range: , while maintaining a
low Reynolds number, . The elastic shear-thinning solution showed
laterally asymmetric flow past the cylinder with both pressure tap designs,
while with the weakly shear-thinning solution asymmetric flow was only observed
with the wider pressure tap intake. In both cases, the fluids preferentially
chose the cylinder/wall gap opposing the upstream pressure tap, which was found
to influence the flow greatly, seemingly associated with time-dependent flow
and possibly the lateral flow asymmetry itself. This work brings to light the
necessary compromise between optimal pressure tap design for quality pressure
measurements and minimal flow interference, due to the increased susceptibility
of elastic microfluidic flows to flow perturbations
Potential applications of the Escherichia coli heat shock response in synthetic biology
The Escherichia coli heat shock response (HSR) is a complex mechanism triggered by heat shock and by a variety of other growth-impairing stresses. We explore here the potential use of the E. coli HSR mechanism in synthetic biology approaches. Several components of the regulatory mechanism (such as heat shock promoters, proteins, and RNA thermosensors) can be extremely valuable in the creation of a toolbox of well-characterized biological parts to construct biosensors or microbial cell factories with applications in the environment, industry, or healthcare. In the future, these systems can be used for instance to detect a pollutant in water, to regulate and optimize the production of a compound with industrial relevance, or to administer a therapeutic agent in vivo.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the
strategic funding of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01-0145-FEDER-006684) and under the
scope of the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462). The authors also acknowledge
financial support from BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional
Development Fund under the scope of Norte2020–Programa Operacional Regional do Norte, and a Postdoctoral grant
(UMINHO/BPD/37/2015) to J.L.R. funded by the FCT.info:eu-repo/semantics/publishedVersio
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