533 research outputs found
Spectroscopic ellipsometry study of barrier width effect in self-organized InGaAs/GaAs QDs laser diodes
Molecular beam epitaxy (MBE) is used to grow InGaAs/GaAs quantum dots (QDs) laser diodes (LDs) with different barrier widths (5, 10 and 15 nm) at 580 ºC on GaAs substrates. Optical properties of the InGaAs/GaAs QDs LDs have been investigated by using the spectroscopic ellipsometry (SE) technique. A general oscillator optical model has been utilized to fit the experimental data in order to obtain the LD layer thicknesses, refractive index and absorption coefficient. The dielectric function, the energy band gap and the surface and volume energy loss functions are computed in the energy range 1-6 eV. The optical properties of the deposited InGaAs/GaAs QDs LDs are found to be affected by the barrier width, which give more insight into carriers dynamics and optical parameters in these devices. The refractive indices, the extinction coefficients and the dielectric constants of the LDs with barrier widths 15 and 10 nm are relatively larger than those of the LD with barrier width 5 nm. These indicate that optical properties of LDs with larger barrier widths (15 and 10 nm) will be improved. The interband transition energies in the three devices have calculated and identified. Two energy gaps at 1.04 and ~1.37 eV are obtained for all the heterostructures which indicates that fabricated LDs may be operating for a wavelength of 1.23 m at room temperature
Digestive alkaline proteases from the Tunisian barbel (Barbus callensis): Characterization and application as a detergent additive, in chicken feather-degradation and as a dehairing agent
Alkaline crude enzymes from the viscera of the Tunisian barbel (Barbus callensis) were extracted and characterized. Proteolytic crude extract from barbel viscera was active and stable in alkaline solution. The optimum pH and temperature were 11.0 and 55 °C, respectively, using casein as a substrate. The crude alkaline protease was extremely stable in the pH range of 5.0-12.0. Zymography activity staining using casein as a substrate showed the presence of at least five distinct proteases. The crude alkaline proteases showed stability towards various surfactants, bleach agents and compatibility with some commercial detergents. Alkaline proteases from the viscera of the barbel were tested in chicken feather-degradation and showed important feather degrading activity. Complete solubilisation of whole feathers was observed after 24h of incubation at 50°C. Additionally, crude alkaline protease demonstrated powerful capabilities of hair removal from skin and the collagen, the major leather-forming protein, was not significantly degraded. Considering its promising properties, alkaline crude enzyme from the viscera of the Tunisian barbel may be considered as a potential candidate for future use in several biotechnological processes
Structural connectivity modifications in the brain of selected patients with tumour after its removal by surgery (a case study)
Acknowledgments This study was possible by partial financial support from the following agencies: Funda¸c˜ao Arauc´aria, Brazilian National Council for Scientific and Technological Development (CNPq), and Coordination for the Improvement of Higher Education Personnel (CAPES). S˜ao Paulo Research Foundation (FAPESP 2018/03211-6, 2022/13761-9). We thank 105 Group Science (www.105groupscience.com).Peer reviewe
Multiscale model for the templated synthesis of mesoporous silica: the essential role of silica oligomers
A detailed theoretical understanding of the synthesis mechanism of periodic mesoporous silica has not yet been achieved. We present results of a multiscale simulation strategy that, for the first time, describes the molecular-level processes behind the formation of silica/surfactant mesophases in the synthesis of templated MCM-41 materials. The parameters of a new coarse-grained explicit-solvent model for the synthesis solution are calibrated with reference to a detailed atomistic model, which itself is based on quantum mechanical calculations. This approach allows us to reach the necessary time and length scales to explicitly simulate the spontaneous formation of mesophase structures while maintaining a level of realism that allows for direct comparison with experimental systems. Our model shows that silica oligomers are a necessary component in the formation of hexagonal liquid crystals from low-concentration surfactant solutions. Because they are multiply charged, silica oligomers are able to bridge adjacent micelles, thus allowing them to overcome their mutual repulsion and form aggregates. This leads the system to phase separate into a dilute solution and a silica/surfactant-rich mesophase, which leads to MCM-41 formation. Before extensive silica condensation takes place, the mesophase structure can be controlled by manipulation of the synthesis conditions. Our modeling results are in close agreement with experimental observations and strongly support a cooperative mechanism for synthesis of this class of materials. This work paves the way for tailored design of nanoporous materials using computational models
Unpredictability in seasonal infectious diseases spread
In this work, we study the unpredictability of seasonal infectious diseases
considering a SEIRS model with seasonal forcing. To investigate the dynamical
behaviour, we compute bifurcation diagrams type hysteresis and their respective
Lyapunov exponents. Our results from bifurcations and the largest Lyapunov
exponent show bistable dynamics for all the parameters of the model. Choosing
the inverse of latent period as control parameter, over 70% of the interval
comprises the coexistence of periodic and chaotic attractors, bistable
dynamics. Despite the competition between these attractors, the chaotic ones
are preferred. The bistability occurs in two wide regions. One of these regions
is limited by periodic attractors, while periodic and chaotic attractors bound
the other. As the boundary of the second bistable region is composed of
periodic and chaotic attractors, it is possible to interpret these critical
points as tipping points. In other words, depending on the latent period, a
periodic attractor (predictability) can evolve to a chaotic attractor
(unpredictability). Therefore, we show that unpredictability is associated with
bistable dynamics preferably chaotic, and, furthermore, there is a tipping
point associated with unpredictable dynamics
Fractional dynamics and recurrence analysis in cancer model
In this work, we analyze the effects of fractional derivatives in the chaotic
dynamics of a cancer model. We begin by studying the dynamics of a standard
model, {\it i.e.}, with integer derivatives. We study the dynamical behavior by
means of the bifurcation diagram, Lyapunov exponents, and recurrence
quantification analysis (RQA), such as the recurrence rate (RR), the
determinism (DET), and the recurrence time entropy (RTE). We find a high
correlation coefficient between the Lyapunov exponents and RTE. Our simulations
suggest that the tumor growth parameter () is associated with a chaotic
regime. Our results suggest a high correlation between the largest Lyapunov
exponents and RTE. After understanding the dynamics of the model in the
standard formulation, we extend our results by considering fractional
operators. We fix the parameters in the chaotic regime and investigate the
effects of the fractional order. We demonstrate how fractional dynamics can be
properly characterized using RQA measures, which offer the advantage of not
requiring knowledge of the fractional Jacobian matrix. We find that the chaotic
motion is suppressed as decreases, and the system becomes periodic for
. We observe limit cycles for and fixed points for . The fixed point is
determined analytically for the considered parameters. Finally, we discover
that these dynamics are separated by an exponential relationship between
and . Also, the transition depends on a supper transient which
obeys the same relationship
Comparison of amine-impregnated mesoporous carbon with microporous activated carbon and 13X zeolite for biogas purification
Synthesis and characterization of Al- and Ti-MCM-41 materials: application to oxidation of anthracene
Mesoporous matrices for the delivery of the broad spectrum bacteriocin, Nisin A
peer-reviewedMesoporous matrices of different pore size and chemical composition were explored as potential delivery matrices for the broad spectrum bacteriocin, nisin A. The adsorption of nisin A onto two mesoporous silicates (MPS - SBA-15, MCM-41) and two periodic mesoporous organosilanes (PMO - MSE, PMO-PA) was examined. It was found that hydrophobic interactions dominated in the adsorption of this peptide to the matrices, lending the highest adsorption to MCM-41 with a small pore size of 2.8 nm. The hydrophobic ethylene-bridged MSE (6 nm pore) improved the loading and protection of nisin A from degradation by a non-specific protease pepsin, over un-functionalised SBA-15 which had a slightly larger pore size and less hydrophobic moieties. Nisin A did not adsorb onto an amine-functionalised PMO. Upon suspension in modified fasted state simulated gastric fluid (pH 1.6), the highest release of nisin A was observed from MCM-41, with a lower release from SBA-15 and MSE, with release following Higuchi release kinetics. No release was detected into modified fasted state simulated intestinal fluid (pH 6.5) but despite this, the suspended matrices loaded with nisin A remained active against Staphylococcus aureus
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