1,660 research outputs found
Minimal energy control of a nanoelectromechanical memory element
The Pontryagin minimal energy control approach has been applied to minimise the switching energy in a nanoelectromechanical memory system and to characterise global stability of the oscillatory states of the bistable memory element. A comparison of two previously experimentally determined pulse-type control signals with Pontryagin control function has been performed, and the superiority of the Pontryagin approach with regard to power consumption has been demonstrated. An analysis of global stability shows how values of minimal energy can be utilized in order to specify equally stable states
Patterned superhydrophobic paper for microfluidic devices obtained by writing and printing
Published online: 26 July 2013This work outlines inexpensive patterning
methodologies to create open-air microfluidic paperbased
devices. A phase-separation methodology was
used to obtain biomimetic superhydrophobic paper,
hierarchically composed by micro and nano topographies.
Writing and printing are simple actions that can
be used to pattern flat superhydrophobic paper with
more wettable channels. In particular, inkjet printing
permits controlling the wettability of the surface by
changing the darkness of the printed regions. The
difference between capillary forces provides the
possibility to control and drive liquid flows through
the open path lines, just by titling the piece of paper.
Additionally, maintaining a continuous flow, it is
possible to direct the liquid at different volumetric
rates in a horizontal position along non-linear channel
paths printed/written over the surface
Layer-by-layer deposition of antimicrobial polymers on cellulosic fibers : a new strategy to develop bioactive textiles
In recent years, there has been an increase of infectious diseases caused by different microorganisms and the development of antibiotic resistance. In this way, the search for new and efficient antibacterial materials is imperative. The main polysaccharides currently used in the biomedical and pharmaceutical domains are chitin and its derivative chitosan (CH) and alginates (ALG). In this study, a simple technique of Layer by Layer (LbL) of applying polycation CH and polyanion ALG was used to prepare CH/ALG multilayers on cotton samples via the electrostatic assembly with success. The CH/ALG cotton samples (functionalized) were investigated for their antibacterial properties towards Staphylococcus aureus and Klebsiella pneumonia using the international standard method JIS L 1902:2002. The antibacterial activity of the functionalized samples was tested in terms of bacteriostatic and bactericidal activity, and results showed that the samples exhibited a bacteriostatic effect on the two bacteria tested, as expected. In addition, samples with five layers (CH/ALG/CH/ALG/CH) were more effective in inhibiting bacterial growth. This new coating for cellulosic fibers is a new strategy and may open new avenues for the development of antimicrobial polymers with potential application in health-care field.The authors would like to thank Fundacao para a Ciencia e Tecnologia (FCT) for the funding granted concerning the project - PTDC/EBB-BIO/113671/2009 (FCOMP-01-0124-FEDER-014752) Skin2Tex. Also, we would like to thank Fundo Europeu de Desenvolvimento Regional (FEDER) through COMPETE - Programa Operacional Factores de Competitividade (POFC) for the co-funding
Size dependent line broadening in the emission spectra of single GaAs quantum dots: Impact of surface charges on spectral diffusion
Making use of droplet epitaxy, we systematically controlled the height of
self-assembled GaAs quantum dots by more than one order of magnitude. The
photoluminescence spectra of single quantum dots revealed the strong dependence
of the spectral linewidth on the dot height. Tall dots with a height of ~30 nm
showed broad spectral peaks with an average width as large as ~5 meV, but
shallow dots with a height of ~2 nm showed resolution-limited spectral lines
(<120 micro eV). The measured height dependence of the linewidths is in good
agreement with Stark coefficients calculated for the experimental shape
variation. We attribute the microscopic source of fluctuating electric fields
to the random motion of surface charges at the vacuum-semiconductor interface.
Our results offer guidelines for creating frequency-locked photon sources,
which will serve as key devices for long-distance quantum key distribution.Comment: 6 pages, 6 figures; updated figs and their description
Fibers and 3D mesh scaffolds from biodegradable starch-based blends : production and characterization
The aim of this work is the production of fibers
from biodegradable polymers to obtain 3D scaffolds for
tissue engineering of hard tissues. The scaffolds required for
this highly demanding application need to have, as well as the
biological and mechanical characteristics, a high degree of
porosity with suitable dimensions for cell seeding and proliferation.
Furthermore, the open cell porosity should have
adequate interconnectivity for a continuous flow of nutrients
and outflow of cell metabolic residues as well as to allow cell
growth into confluent layers. Blends of corn starch, a natural
biodegradable polymer, with other synthetic polymers (poly-
(ethylene vinyl alcohol), poly(e-caprolactone), poly(lactic
acid)) were selected for this work because of their good balance
of properties, namely biocompatibility, processability
andmechanical properties. Melt spinning was used to produce
fibers fromall the blends and 3Dmeshes fromone of the starchpoly(
lactic acid) blends. The experimental characterization
includedthe evaluationof the tensilemechanicalpropertiesand
thermal properties of the fibers and the compression stiffness,
porosity and degradation behavior of the 3Dmeshes
Charged black holes: Wave equations for gravitational and electromagnetic perturbations
A pair of wave equations for the electromagnetic and gravitational
perturbations of the charged Kerr black hole are derived. The perturbed
Einstein-Maxwell equations in a new gauge are employed in the derivation. The
wave equations refer to the perturbed Maxwell spinor and to the shear
of a principal null direction of the Weyl curvature. The whole
construction rests on the tripod of three distinct derivatives of the first
curvature of a principal null direction.Comment: 12 pages, to appear in Ap.
Shape control of QDs studied by cross-sectional scanning tunneling microscopy
In this cross-sectional scanning tunneling microscopy study we investigated
various techniques to control the shape of self-assembled quantum dots (QDs)
and wetting layers (WLs). The result shows that application of an indium flush
during the growth of strained InGaAs/GaAs QD layers results in flattened QDs
and a reduced WL. The height of the QDs and WLs could be controlled by varying
the thickness of the first capping layer. Concerning the technique of antimony
capping we show that the surfactant properties of Sb result in the preservation
of the shape of strained InAs/InP QDs during overgrowth. This could be achieved
by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer
prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was
investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show
that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick,
and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure
Bone, cartilage and osteochondral tissue engineering strategies using natural origin polymers and ceramics, growth factors and progenitor cells
[Excerpt] Tissue engineering (TE) has emerged in the last decade of the 20th century as an alternative approach to circumvent the existent limitations in the current therapies for organ failure or replacement.
The EU HIPPOCRATES project joined academic and industrial partners to develop novel products and concepts that can be used for bone, cartilage or osteochondral TE strategies. Several issues were addressed including i) the choice and study of adequate human cell cultures, (ii) the development of culture technology with which human tissues can be grown ex vivo in three dimensional
biodegradable matrices, (iii) the development of a material technology with which polymeric matrices can be produced, being suitable for cell culture (proliferation, differentiation), (iv) to assess the in-vivo functionality and clinical relevance of the tissue engineering strategies. [...]info:eu-repo/semantics/publishedVersio
Shape control of QDs studied by cross-sectional scanning tunneling microscopy
In this cross-sectional scanning tunneling microscopy study we investigated
various techniques to control the shape of self-assembled quantum dots (QDs)
and wetting layers (WLs). The result shows that application of an indium flush
during the growth of strained InGaAs/GaAs QD layers results in flattened QDs
and a reduced WL. The height of the QDs and WLs could be controlled by varying
the thickness of the first capping layer. Concerning the technique of antimony
capping we show that the surfactant properties of Sb result in the preservation
of the shape of strained InAs/InP QDs during overgrowth. This could be achieved
by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer
prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was
investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show
that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick,
and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure
Novel methodology based on biomimetic superhydrophobic substrates to immobilize cells and proteins in hydrogel spheres for applications in bone regeneration
Cell-based therapies for regenerative medicine have been characterized by the low retention and integration of injected cells into host structures. Cell immobilization in hydrogels for target cell delivery has been developed to circumvent this issue. In this work mesenchymal stem cells isolated from Wistar rats bone marrow (rMSCs) were immobilized in alginate beads fabricated using an innovative approach involving the gellification of the liquid precursor droplets onto biomimetic superhydrophobic surfaces without the need of any precipitation bath. The process occurred in mild conditions preventing the loss of cell viability. Furthermore, fibronectin (FN) was also immobilized inside alginate beads with high efficiency in order to mimic the composition of the extracellular matrix. This process occurred in a very fast way (around 5 min), at room temperature, without aggressive mechanical strengths or particle aggregation. The methodology employed allowed the production of alginate beads exhibiting a homogenous rMSCs and FN distribution. Encapsulated rMSCs remained viable and were released from the alginate for more than 20 days. In vivo assays were also performed, by implanting these particles in a calvarial bone defect to evaluate their potential for bone tissue regeneration. Microcomputed tomography and histological analysis results showed that this hybrid system accelerated bone regeneration process. The methodology employed had a dual role by preventing cell and FN loss and avoiding any contamination of the beads or exchange of molecules with the surrounding environment. In principle, the method used for cell encapsulation could be extended to other systems aimed to be used in tissue regeneration strategies.The authors acknowledge the financial support of the Portuguese Foundation for Science and Technology (PTDC/EME-TME/103375/2008 and PTDC/EBB-BIO/114320/2009) for the PhD fellowship to Ana Catarina Lima (SFRH/BD/71395/2010), A. Sofia Silva (SFRH/BD/51584/2011), and Patricia Batista (SFRH/BD/45511/2008)
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