7,440 research outputs found
Static and Dynamic Spectroscopy of (Al,Ga)As/GaAs Microdisk Lasers with Interface Fluctuation Quantum Dots
We have studied the steady state and dynamic optical properties of
semiconductor microdisk lasers whose active region contains interface
fluctuation quantum dots in GaAs/(Ga,Al)As quantum wells. Steady-state
measurements of the stimulated emission via whispering gallery modes yield a
quality factor and a coupling constant . The
broad gain spectrum produces mode hopping between spectrally adjacent
whispering gallery modes as a function of temperature and excitation power.
Time- and energy-resolved photoluminescence measurements show that the emission
rise and decay rates increase significantly with excitation power. Marked
differences are observed between the radiative decay rates in processed and
unprocessed samples.Comment: To appear in Phys. Rev.
Laser-treated electrospun fibers loaded with nano-hydroxyapatite for bone tissue engineering
Core-shell polycaprolactone/polycaprolactone (PCL/PCL) and polycaprolactone/polyvinyl acetate (PCL/PVAc) electrospun fibers loaded with synthesized nanohydroxyapatite (HAn) were lased treated to create microporosity. The prepared materials were characterized by XRD, FTIR, TEM and SEM. Uniform and randomly oriented beadless fibrous structures were obtained in all cases. Fibers diameters were in the 150–300 nm range. Needle-like HAn nanoparticles with mean diameters of 20 nm and length of approximately 150 nm were mostly encase inside the fibers. Laser treated materials present micropores with diameters in the range 70–120 µm for PCL-HAn/PCL fibers and in the 50–90 µm range for PCL-HAn/PVAC material. Only samples containing HAn presented bioactivity after incubation during 30 days in simulated body fluid. All scaffolds presented high viability, very low mortality, and human osteoblast proliferation. Biocompatibility was increased by laser treatment due to the surface and porosity modification
Effective Dielectric Response of Metamaterials
We use a homogenization procedure for Maxwell's equations in order to obtain
in the local limit the frequency () dependent macroscopic dielectric
response of metamaterials made of natural constituents
with any geometrical shape repeated periodically with any structure. We
illustrate the formalism calculating for several
structures. For dielectric rectangular inclusions within a conducting material
we obtained a very anisotropic response which changes along one direction from
conductor-like at low to a resonant dielectric-like at large ,
attaining a very small reflectance at intermediate frequencies unrelated to
surface plasmon excitation and which can be tuned through geometrycal
tayloring. A similar behavior is obtained for other shapes close to the
percolation threshold.Comment: 16 pages 7 figures. Accepted in Phys. Rev. B (2009-06-08
Comparison of reaction networks of Wnt signaling
Wnt signaling is a vital biological mechanism that regulates crucial
development processes and maintenance of tissue homeostasis. Here, we extended
the parameter-free analysis of four mathematical models of the
beta-catenin-dependent Wnt signaling pathway performed by MacLean et al. (PNAS
USA 2015) using chemical reaction network theory. We showed that the reaction
networks of the four models considered (Lee, Schmitz, MacLean, and Feinberg)
coincide in basic structural and kinetic properties except in their
mono-stationarity/multi-stationarity, and their capacity for admitting a
degenerate equilibrium. Moreover, we showed that the embedded networks of the
Lee and Feinberg models are very similar, and the discordance of the Lee
network limits its mono-stationarity to mass action kinetics, which challenge
the absoluteness of model discrimination into mono-stationarity versus
multi-stationarity alone. Focusing, henceforth, on the three multi-stationary
networks, we showed that their finest independent decompositions are very
different and can be used to study further similarities and differences among
them. We also determined equilibria parametrizations of the networks and
inferred the presence of species with absolute concentration robustness.
Finally, direct comparison of the Schmitz and Feinberg networks with the
MacLean network yielded new results in three aspects: structural/kinetic
relationships between embedded networks relative to their set of common
species, connections between the positive equilibria of the subnetwork of
common reactions and the positive equilibria of the whole networks, and
construction of maximal concordant subnetwork containing the common reactions
of the networks under comparison. Thus, this work can provide general insights
in comparing mathematical models of the same or closely-related systems
Language in tuberculosis services: can we change to patient-centred terminology and stop the paradigm of blaming the patients?
The words 'defaulter', 'suspect' and 'control' have been part of the language of tuberculosis (TB) services for many decades, and they continue to be used in international guidelines and in published literature. From a patient perspective, it is our opinion that these terms are at best inappropriate, coercive and disempowering, and at worst they could be perceived as judgmental and criminalising, tending to place the blame of the disease or responsibility for adverse treatment outcomes on one side-that of the patients. In this article, which brings together a wide range of authors and institutions from Africa, Asia, Latin America, Europe and the Pacific, we discuss the use of the words 'defaulter', 'suspect' and 'control' and argue why it is detrimental to continue using them in the context of TB. We propose that 'defaulter' be replaced with 'person lost to follow-up'; that 'TB suspect' be replaced by 'person with presumptive TB' or 'person to be evaluated for TB'; and that the term 'control' be replaced with 'prevention and care' or simply deleted. These terms are non-judgmental and patient-centred. We appeal to the global Stop TB Partnership to lead discussions on this issue and to make concrete steps towards changing the current paradigm
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