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

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 $\Phi_0$ and to the shear $\sigma$ of a principal null direction of the Weyl curvature. The whole construction rests on the tripod of three distinct derivatives of the first curvature $\kappa$ of a principal null direction.Comment: 12 pages, to appear in Ap.

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

Hydrogel 3D in vitro tumor models for screening cell aggregation mediated drug response

Hydrogel-based 3D in vitro models comprising tumor ECM-mimetic biomaterials exhibit superlative potential as preclinical testing platforms for drug discovery and bioperformance screening. However, during hydrogel design and testing stages, the ideal selection between cancer cell laden 3D models or spheroid embedded hydrogel platforms remains to be elucidated. Selecting a disease-mimicking cellular arrangement within ECM hydrogels is paramount for anti-cancer therapeutics performance evaluation and may lead to differential outcomes. To investigate the effects assigned to varying cellular-arrangement, we developed dense 3D spheroid microtumors and cell-laden MG-63 osteosarcoma platforms embedded in GelMA and Matrigel ECM-mimetic scaffolds. These platforms enabled cancer cells/3D microtissues maturation and lorlatinib drug performance screening. Initial 3D spheroids assembly via the liquid overlay technique, resulted in the fabrication of dense cellular aggregates with reproducible size, morphology and necrotic core formation, thus mimicking the native tumor. Upon in vitro maturation, MG-63 spheroids encapsulated in hydrogel scaffolds exhibited significantly higher invasion and drug resistance than their cell laden hydrogel counterparts. Such data reveals inherent physiological and drug response variances among randomly distributed osteosarcoma cells and 3D spheroid-laden hydrogels. Overall, this highlights the importance of evaluating different cellular aggregation states when designing ECM-mimetic hydrogels for in vitro tumor modeling and high-throughput screening of anti-cancer therapeutics.publishe

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

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

Effect of solvent-dependent viscoelastic properties of chitosan membranes on the permeation of low molecular weight drugs

Chitosan (CTS), a widely used biopolymer in different biomedical applications, is a derivative of chitin, the most abundant polysaccharide found in the marine world. This work aimed at providing relevant information about the use of CTS membranes in separation applications or in sustained release systems of therapeutic molecules. Moreover, the mechanical characterization may be also very important in such kind of applications, especially if the materials are tested in adequate physiological conditions. Chitosan membranes, both non-crosslinked and crosslinked with genipin, were characterized by dynamic mechanical analysis, swelling and permeability experiments using a model molecule. The membranes were tested immersed in different mixtures of water/ethanol. The swelling equilibrium varied linearly with the volumetric composition of the solvent mixture. The mechanical properties of CTS increased with the enhancement of the crosslinking density. A peak of the loss factor appeared at 24.5% of water attributed to the α-relaxation of chitosan and simultaneously a reduction of the storage modulus was observed. This was the first time that the glass transition (Tg) dynamics was monitored in a polymer in immersion conditions, where the plasticizer composition in the bath changed in a controlled way. Permeability decreased sharply until it reached very small values around the Tg. We hypothesise that conformational mobility of the polymeric chains may play an important role in the diffusion properties of molecules through polymer matrices. Results may elucidate some aspects regarding to relationships between glass transition and transport properties that may be important in the use of CTS in TE 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