6,279 research outputs found
Olefin oligomerisation over nanocrystalline MFI-based micro/mesoporous zeotypes synthesised via bottom-up approaches
The oligomerisation of 1-butene was studied under high-pressure continuous-flow conditions (200–250 °C, 30–40 bar), in the presence of micro/mesoporous zeotypes based on the MFI topology, which were prepared via different non-destructive bottom-up strategies: crystallization of silanized protozeolitic units; co-templating with a dual function (polymeric) template; and using a sole structure directing agent (non-surfactant and non-polymeric) to generate mesoporosity. The synthesis method influenced the material properties and consequently the catalytic performance. In targeting hydrocarbons with boiling point ranges characteristics of diesel, the zeotypes benefited from regular morphology, reduced crystallite size, mesoporosity and enhanced molar ratio of Lewis (L) to Brønsted (B) acid sites (L/B). In general, the zeotypes outperformed commercial zeolite ZSM-5. The best-performing zeotype was prepared according to the Serrano strategy based on the crystallization of silanized zeolitic seeds, and led to 97% conversion and an average space-time yield of liquid products of 1077 mg gcat−1 h−1, at 250 °C, 40 bar. The zeotypes seemed more stable than the commercial zeolite, based on molecular level characterization studies of the used/regenerated catalysts, with some differences in catalytic activity.publishe
Contrasting the effectiveness and efficiency of virtual reality and real environments in the treatment of acrophobia
Previous studies reported good results in using virtual reality for the treatment of acrophobia. Similarly this paper reports the use of a virtual environment for the treatment of acrophobia. In the study, 10 subjects were exposed to three sessions of simulated heights in a virtual reality (VR) system, and 5 others were exposed to a real environment. Both groups revealed significant progress in a range of anxiety, avoidance and behaviour measurements when confronted with virtual as well as real height circumstances. Despite VR participants experiencing considerably shorter treatment times than the real-world subjects, significant improvements were recorded on the Behavioural Avoidance Test, the Attitudes Toward Heights Questionnaire and the Acrophobia Questionnaire. These results are suggestive of a possible higher effectiveness and efficiency of VR in treating acrophobia
Numerical optimal control of HIV transmission in Octave/MATLAB
We provide easy and readable GNU Octave/MATLAB code for the simulation of
mathematical models described by ordinary differential equations and for the solution of optimal
control problems through Pontryagin’s maximum principle. For that, we consider a normalized
HIV/AIDS transmission dynamics model based on the one proposed in our recent contribution (Silva,
C.J.; Torres, D.F.M. A SICA compartmental model in epidemiology with application to HIV/AIDS in
Cape Verde. Ecol. Complex. 2017, 30, 70–75), given by a system of four ordinary differential equations.
An HIV initial value problem is solved numerically using the ode45 GNU Octave function and three
standard methods implemented by us in Octave/MATLAB: Euler method and second-order and
fourth-order Runge–Kutta methods. Afterwards, a control function is introduced into the normalized
HIV model and an optimal control problem is formulated, where the goal is to find the optimal
HIV prevention strategy that maximizes the fraction of uninfected HIV individuals with the least
HIV new infections and cost associated with the control measures. The optimal control problem is
characterized analytically using the Pontryagin Maximum Principle, and the extremals are computed
numerically by implementing a forward-backward fourth-order Runge–Kutta method. Complete
algorithms, for both uncontrolled initial value and optimal control problems, developed under the
free GNU Octave software and compatible with MATLAB are provided along the article.publishe
Effect of poling on the mechanical properties of β-poly(vinylidene fluoride)
In this work, mechanical and thermal experimental techniques have been applied in order
to relate the mechanical response with the microscopic variations of the material. Stress-strain
results along the main directions of β-poly(vinylidene fluoride), β-PVDF, in poled and non-poled
samples enables to investigate the influence of the poling process on the mechanical response of the
material. Further, differential scanning calorimetry experiments allow the investigation of the effect
of poling in the degree of crystallinity of the material as well as on the stability of the crystalline
phase. Thermogravimetric analysis was used to investigate the kinetics of the thermal degradation
of poled and non-poled β-PVDF samples. The differences observed between the two materials
suggest that the poling affects the mechanical properties of the material especially in the direction
parallel to the polymeric chains and originates changes at a molecular level that remain beyond the
melting of the material.(undefined
A new electromagnetic actuation system on an industrial sewing machine with on-line efficiency monitoring
This paper briefly reviews the study to evaluate the standard presser foot performance and a new actuation set-up to avoid the bouncing and the lack of fabric control. The compression force and displacement waveforms are also presented and widely discussed, as well as the seam’s quality analysis. A spectral (Fast Fourier Transform and Harmonic Distortion) analysis on the obtained waveforms, as well as an Admissible Displacement Limits (ADL) analysis are also described as important techniques to be used to supervise the presser foot force and to monitor the feeding efficiency. ADL have proved to be a better method. Further research should be undertaken in this area, in order to achieve, in a near future, a closed loop control of the presser foot.Fundação para a Ciência e a Tecnologia (FCT
Early Carboniferous synorogenic basins evolution of the Ossa-Morena and
The stratigraphic record of the Early Carboniferous in Iberia reveals that synorogenic deposition was
important and occurred simultaneously in basins influenced by extension and contraction with gravitational instability.
In NW Iberia (Galicia – Trás-os-Montes Zone) contraction was dominant and the deposition took place in a forebulge
outwards from the nappe stacking front. Here, synorogenic deposits were strongly affected by folding and thrusting as
they were imbricated and incorporated in the allochthonous pile. In a different way, in SW Iberia (Ossa-Morena Zone)
synorogenic deposition was influenced by extension and happened simultaneously with the onset of significant
magmatism
Surface rehabilitation of Portland cement concrete (PCC) pavements using single or double surface dressings with soft bitumen, conventional or modified emulsions
Surface dressings are a sustainable maintenance alternative for pavements with surface distresses, due to
the low amount of resources involved. This paper aims to analyze the viability of using twelve different
surface dressing solutions, including three binders (conventional and modified emulsions, and a soft
160/220 bitumen) and a covering with diluted emulsion, for surface treatment of Portland cement concrete
(PCC) pavements. Several test methods were used to evaluate the macrotexture, skid resistance,
adhesion, and resistance to wearing on a large scale prototype. In general, single surface dressings
increased further the macrotexture of the concrete pavement surface. The skid resistance of single and
double surface dressings was similar. The best surface dressing in the pull-off test was that with the
160/220 bitumen. The conventional and modified emulsions presented similar mechanical adhesion in
the Vialit plate test. Concerning the prototype wearing test, the best result was obtained for the double
surface dressing with bitumen covered with diluted emulsion. Based on this work’s results, the surface
dressings are a potential surface rehabilitation alternative for concrete pavements.This work was partially financed by FCT / MCTES through
national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. This work is financed by national funds
through FCT - Foundation for Science and Technology, under grant
agreement SFRH/BD/137421/2018 attributed to the 1st author
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