2,606 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
Cell surface engineering to control cellular interactions
Cell surface composition determines all interactions of the cell with its environment, thus cell functions such as adhesion, migration and cellâcell interactions can potentially be controlled by engineering and manipulating the cell membrane. Cell membranes present a rich repertoire of molecules, therefore a versatile ground for modification. However the complex and dynamic nature of the cell surface is also a major challenge for cell surface engineering that should also involve strategies compatible with cell viability. Cell surface engineering by selective chemical reactions or by the introduction of exogenous targeting ligands can be a powerful tool for engineering novel interactions and controlling cell function. In addition to chemical conjugation and modification of functional groups, ligands of interest to modify the surface of cells include recombinant proteins, liposomes or nanoparticles. Here, we review recent efforts to perform changes to cell surface composition. We focus on the engineering of the cell surface with biological, chemical or physical methods to modulate cell functions and control cellâcell and cellâmicroenvironment interactions. Potential applications of cell surface engineering are also discussed
Surface properties of extracts from cork black condensate
The insulation corkboard production generates black condensate
(BC), a paste-like solid waste. It is hydrophobic and
has the potential to be used as protective coating. To evaluate
this potential, coatings were prepared from BC extracts and
their surface behavior was evaluated by contact angle (CA)
measurements. The CA dynamics were recorded as a function
of time; advancing CAs were also registered; the
approaches were applied according to Fowkes, Owens-
Wendt-Rabel-Kaelble (OWRK), and Van Oss to determine
the surface energy (SE) for each coating. Depending on the
liquid probe, three phenomena were observed: water evaporation,
diiodomethane diffusion into the coating, and rearrangement
of the chemical groups on the coating surface,
when glycerol was dropped onto the surface. Based on the
results from the CA dynamics, the applicability of the coatings
against hydrophobic environments was limited owing to
its affinity to apolar compounds. The results show that the
coating prepared by the toluene BC extract was the best coating.
The key data were: water CA of 99.38, total SE (between
37.4 mN m-1 and 40.1 mN m-1), SE polar component
(0.1 mN m-1), and the acidic and basic characters were negligible.
It can be concluded that the BC extracts have potential
for coatings.R.P. acknowledges a post-doc research grant BPD/39333/2007 from the Portuguese Foundation for Science and Technology (FCT). We gratefully acknowledge Amorim Isolamentos S.A. for the supply of black condensate
Thermal Transport Imaging in the Quantum Hall Edge Channel
Research focused on heat transport in the quantum Hall (QH) edge channel has
successfully addressed fundamental theoretical questions surrounding the QH
physics. However, the picture of the edge channel is complicated by the
phenomenon of energy dissipation out of the edge, and theories treating this
dissipation are lacking. More experimental data is also needed to determine the
coupling mechanism by which energy leaves the edge channel. We developed a
method to map the heat transport in the QH edge to study the dissipation of
heat. We locally heated the QH edge and locally detected the temperature
increase while continuously varying the distance between heater and
thermometer. We thereby obtained the thermal decay length of the edge state,
which we found to depend on magnetic field strength
Multiwavelength and polarization lidar measurements of Asian dust layers over Tsukuba, Japan: a case study
International audienceElastic and polarization lidar was used to measure the vertical profiles of aerosol backscattering coefficients at wavelengths of 355, 532, 735, and 1064 nm, and the depolarization ratio at 532 nm in order to study the aerosol properties in the free troposphere over Tsukuba, Japan, in 2006. An elevated dust layer was observed at altitudes between 3 and 8.5 km on 1 April during the Asian dust period. The wavelength exponents of the aerosol backscattering coefficient (k) were ?0.1 to 0.5, and the depolarization ratio (?p) was 25% for the dust layer, suggesting the predominance of supermicrometer-sized (coarse mode) nonspherical particles. An aerosol layer observed at altitudes between 1.5 and 5 km on 19 October during the less-dust period exhibited the values of k=1.0 to 1.6 and ?p=1 to 13%, suggesting the predominance of submicrometer-sized (fine mode) particles. In those layers, the values of k and ?p varied with height; they were also negatively correlated, suggesting that the proportion of the coarse nonspherical particles to total particles varied. The particle size distributions estimated from the observed values and the theoretical computation revealed number mode radii of 0.3 &mum; for the coarse mode and 0.1 &mum; for the fine mode, assuming bimodal distribution. These results were consistent with those obtained from the sky-radiometer measurements, although they revealed another mode in the larger radius. The column volume concentration derived from the lidar was 48% lower than that derived from the sky-radiometer on 1 April and 16% lower on 19 October. The optical thickness derived from the lidar was 12% lower than that obtained from the sky-radiometer on 1 April and 29% higher on 19 October. Further case study is necessary to validate the method for estimating aerosol properties based on the lidar measurement
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.
Supercritical fluids: an emerging technology for the preparation of scaffolds for tissue engineering
[Excerpt] The field of tissue engineering has evolved greatly since the idea
of combining active compounds and scaffolds to create artificial
tissues. Small molecular weight drugs that control proliferation
differentiation of cells can be incorporated into biodegradable
scaffolds to induce cellular differentiation and tissue remodeling.
The scaffold plays, therefore an important role not only as a physical
support but also in the cell proliferation and differentiation.
One of the most important stages of tissue engineering is the
design and processing of a porous 3D structure, with high porosity,
high interconnectivity between the porous and uniform distribution.
A variety of processing techniques have been developed and
include solvent casting and particles leaching, compression
moulding and particle leaching, thermally induced phase separation,
gas-foaming processes, among others. The main disadvantages
of these methods are the use of organic solvents and the high
temperatures required. The presence of residual organic solvents is
being rigorously controlled by international safety regulations, it is
necessary to warrant the complete removal and absence of these
substances, without exposing bioactive compounds to high temperatures,
which may degrade them. Supercritical fluid technology
appears, therefore as an interesting alternative to the traditional
processing methods.[...]info:eu-repo/semantics/publishedVersio
Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots
We report strong heavy hole-light mixing in GaAs quantum dots grown by
droplet epitaxy. Using the neutral and charged exciton emission as a monitor we
observe the direct consequence of quantum dot symmetry reduction in this strain
free system. By fitting the polar diagram of the emission with simple
analytical expressions obtained from kp theory we are able to extract
the mixing that arises from the heavy-light hole coupling due to the
geometrical asymmetry of the quantum dot.Comment: 4 pages, 2 figure
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