This work studies the feasibility of a pioneer technology for on-board hydrogen production: the Ammonia Cracking Hollow Fibre Converter. The catalytic activity of a series of ruthenium-based ...catalysts supported on carbon xerogel, during the ammonia cracking reaction, was studied in a catalytic packed bed reactor. To improve their physical-chemical properties, carbon xerogels were activated in either carbon dioxide or ammonia atmosphere. The most active catalyst (i.e. Ru-NCX) was then deposited inside the micro-structured hollow fibre support by a combination of sol-gel and incipient wetness impregnation methods. At 450 °C and 1 atm the hollow fibre reactor was 4.6 times more efficient than the packed bed reactor (i.e. rNH3 = 6.5 × 104 molNH3/m3·h·gcat and rNH3 = 3.0 × 105 molNH3/m3·h·gcat, respectively), due to its narrower residence time distribution and reduced mass transfer limitations. Furthermore, the use of the hollow fibre converter entailed significantly lower pressure drop (i.e. >99% less), volume (i.e. 80% less) and catalyst loading (i.e. 80% less) compared to the packed bed reactor. Therefore, the potential of this new technology is enormous, as it will push the incorporation of green ammonia in the present-day fuel scenario.
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•The HFC represents an innovative solution to face on-board H2 production challenges.•Sol-gel method ensures a uniform deposit of carbon xerogels inside the HF substrate.•At 500 °C, NH3 conversion in the HFR was 12 times larger than that of the PBR.•The HFC needs smaller volume (93% less) and fewer catalyst (80% less) than the PBR.
In this research activated carbons (AC) from barley husk (BMWA), corn cob (CMWA), and Agave salmiana leaves (AMWA) were obtained by chemical activation with phosphoric acid for the removal of ...methylene blue (MB). Taguchi experimental design (L9) was applied to conduct the experiments at different levels by altering four operating parameters. The effects of control factors on the AC yield were studied by analysis of variance (ANOVA). Power microwave of 200 W (level 1), radiation time of 4 min (level 2), H3PO4 at 60% (level 2), and nitrogen flow rate of 200 cm3/min (level 3) were de optimal conditions. AC with yields of 72% for AMWA, 96% for CMWA, and 93% for BMWA were obtained. AC showed mesoporous structures, anionic surfaces charges, and significant removal efficiencies of MB as a result of the effects of the activation agent and microwaves. It is the first report of the use of AMWA to obtain AC, as well as the use of microwave to optimize this process using nitrogen flow.
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•First report on the use of A. salmiana leaves to obtain activated carbons•First report on the use of microwave ovens to obtain activated carbons•Power microwave of 200 W, radiation time of 4 min, H3PO4 at 60%, and nitrogen flow rate of 200 cm3/min were de optimal conditions•Activated carbons were obtained with yields 72% -96%.
Graphene plasmons are emerging as an alternative solution to noble metal plasmons, adding the advantages of tunability via electrostatic doping and long lifetimes. These excitations have been so far ...described using classical electrodynamics, with the carbon layer represented by a local conductivity. However, the question remains, how accurately is such a classical description representing graphene? What is the minimum size for which nonlocal and quantum finite-size effects can be ignored in the plasmons of small graphene structures? Here, we provide a clear answer to these questions by performing first-principles calculations of the optical response of doped nanostructured graphene obtained from a tight-binding model for the electronic structure and the random-phase approximation for the dielectric response. The resulting plasmon energies are in good agreement with classical local electromagnetic theory down to ∼10 nm sizes, below which plasmons split into several resonances that emphasize the molecular character of the carbon structures and the quantum nature of their optical excitations. Additionally, finite-size effects produce substantial plasmon broadening compared to homogeneous graphene up to sizes well above 20 nm in nanodisks and 10 nm in nanoribbons. The atomic structure of edge terminations is shown to be critical, with zigzag edges contributing to plasmon broadening significantly more than armchair edges. This study demonstrates the ability of graphene nanostructures to host well-defined plasmons down to sizes below 10 nm, and it delineates a roadmap for understanding their main characteristics, including the role of finite size and nonlocality, thus providing a solid background for the emerging field of graphene nanoplasmonics.
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•Mesoporous carbon/TiO2 hybrids for VOCs depollution of air streams.•Optimising the TiO2 particles incorporation on mesoporous carbon is a key parameter.•Hydrophobic carbon/TiO2 ...hybrid increase ca. 15–20 % the photoactivity of bare TiO2.•The photocatalytic system developed allows the treatment of polluted air streams at demanding operating conditions.
The performance of a series of Adsorbent-Photocatalyst Hybrids (APHs) based on graphitized mesoporous carbons and TiO2, for the photooxidation of formaldehyde and trichloroethylene in gas phase has been studied. TiO2 was incorporated to different carbonaceous materials including a commercial mesoporous carbon, Starbons with different hydrophobicity and micro-mesoporosity and activated carbon. However, the actual performance of the APHs is strongly affected by the nature of the carbonaceous material and the synthesis route selected to prepare the carbon/TiO2 hybrids. The results obtained show the importance of the preparation route for the optimum distribution of the TiO2 nanoparticles on the porous carbon and the influence on its photocatalytic properties. The photocatalysts prepared via mechanical mixing exhibit higher activity than those synthetized by incipient wet impregnation. The hybrid based on the hydrophobic Starbon ST-800 and TiO2 achieved total removal of formaldehyde at high gas flow, improving by a 15 % the degradation rate of bare TiO2, without formation of undesired by-products. Moreover, in the case of the organochloride compound, both the reaction rate and the selectivity to CO2 were promoted over ST-800/TiO2, being the most photoactive material of the series with a great stability over reaction time.
•Virtual reality technologies can provide an immersive experience without risks.•Robots are a core element to improve the competitiveness of the industry.•The future of manufacturing requires the ...interaction between humans and robots.
Nowadays, we are involved in the fourth industrial revolution, commonly referred to as “Industry 4.0,” where cyber-physical systems and intelligent automation, including robotics, are the keys. Traditionally, the use of robots has been limited by safety and, in addition, some manufacturing tasks are too complex to be fully automated. Thus, human-robot collaborative applications, where robots are not isolated, are necessary in order to increase the productivity ensuring the safety of the operators with new perception systems for the robot and new interaction interfaces for the human. Moreover, virtual reality has been extended to the industry in the last years, but most of its applications are not related to robots. In this context, this paper works on the synergies between virtual reality and robotics, presenting the use of commercial gaming technologies to create a totally immersive environment based on virtual reality. This environment includes an interface connected to the robot controller, where the necessary mathematical models have been implemented for the control of the virtual robot. The proposed system can be used for training, simulation, and what is more innovative, for robot controlling in an integrated, non-expensive and unique application. Results show that the immersive experience increments the efficiency of the training and simulation processes, offering a cost-effective solution.
This research presents a new theory that explains analytically the behaviour of any fully developed incompressible turbulent pipe flow, steady or unsteady. We propose the name of theory of underlying ...laminar flow (TULF), because its main consequence is the description of any turbulent pipe flow as the sum of two components: the underlying laminar flow (ULF) and the purely turbulent component (PTC). We use the framework of the TULF to explain analytically most of the important and interesting phenomena reported in He & Jackson (
J. Fluid Mech.
, vol. 408, 2000, pp. 1–38). To do so, we develop a simple model for the pressure gradient and Reynolds shear stress that could be applied to the linearly accelerated pipe flow described by He & Jackson (2000). The following features of the unsteady flow are explained: the deformation undergone by the mean velocity profiles during the transient, the velocity overshoot observed in the more rapid excursions, the dual deformation of mean velocity profiles when overshoots are present, the laminarisation effects described during acceleration, the rapid decrease of the Reynolds shear stress upon approaching the wall that brings forth the laminar sublayer, and some other minor effects. A new field is defined to characterise the degree of turbulence within the flow, directly calculable from the theory itself. Arguably, this new field would describe the degree of turbulence in a pipe flow more accurately than the familiar turbulence intensity parameter. Finally, a paradox is found in the deformation of the unsteady mean velocity profiles with respect to equal-Reynolds-number steady profiles, which is duly explained. The research also predicts the occurrence of mean velocity undershoots if the flow is decreased rapidly enough.
Classical research mainly conducted with European-American families has identified the combination of warmth and strictness (authoritative style) as the parenting always associated with the highest ...scores on developmental outcomes. Additionally, despite the benefits of empathy for prosocial behaviors and protection against antisocial behaviors, most research has considered the contribution of specific practices (e.g., reasoning or power assertion), but not so much the parenting styles. Similarly, family studies tend to study the relationship between parenting and global self-perceptions (self-esteem), but not so much those of each dimension (self-concept).
In the present study, 600 Spanish adolescents from 12 to 17 years old (
= 15.25,
= 2.01) were classified within one of the four household typologies (i.e., authoritative, indulgent, authoritarian, or neglectful). Adolescent developmental outcomes were cognitive empathy (adopting perspectives and emotional understanding), emotional empathy (empathic stress and empathic happiness), and self-concept (academic, social, emotional, family and physical).
The results showed that the indulgent parenting (warmth but not strictness) was related to equal or even better empathy and self-concept than the authoritative style (warmth and strictness), whereas non-warm parenting (authoritarian and neglectful) was consistently associated with poor results.
Overall, the present findings seriously question that parental strictness combined with parental warmth (authoritative style) is always the parenting style related to the greatest outcomes. By contrast, it seems that reasoning, warmth and involvement, without strictness (indulgent parenting) help adolescents to achieve a good orientation toward others in terms of cognitive and affective empathy and a good self-evaluation in terms of self-concept.
The occurrence of magnetohydrodynamic quasiperiodic flows with four fundamental frequencies in differentially rotating spherical geometry is understood in terms of a sequence of bifurcations breaking ...the azimuthal symmetry of the flow as the applied magnetic field strength is varied. These flows originate from unstable periodic and quasiperiodic states with broken equatorial symmetry, but having fourfold azimuthal symmetry. A posterior bifurcation gives rise to twofold symmetric quasiperiodic states, with three fundamental frequencies, and a further bifurcation to a four-frequency quasiperiodic state which has lost all the spatial symmetries. This bifurcation scenario may be favored when differential rotation is increased and periodic flows with m-fold azimuthal symmetry, m being a product of several prime numbers, emerge at sufficiently large magnetic field.
The change in mean-square nuclear charge radii δ⟨r^{2}⟩ along the even-A tin isotopic chain ^{108-134}Sn has been investigated by means of collinear laser spectroscopy at ISOLDE/CERN using the atomic ...transitions 5p^{2} ^{1}S_{0}→5p6 s^{1}P_{1} and 5p^{2} ^{3}P_{0}→5p6s ^{3}P_{1}. With the determination of the charge radius of ^{134}Sn and corrected values for some of the neutron-rich isotopes, the evolution of the charge radii across the N=82 shell closure is established. A clear kink at the doubly magic ^{132}Sn is revealed, similar to what has been observed at N=82 in other isotopic chains with larger proton numbers, and at the N=126 shell closure in doubly magic ^{208}Pb. While most standard nuclear density functional calculations struggle with a consistent explanation of these discontinuities, we demonstrate that a recently developed Fayans energy density functional provides a coherent description of the kinks at both doubly magic nuclei, ^{132}Sn and ^{208}Pb, without sacrificing the overall performance. A multiple correlation analysis leads to the conclusion that both kinks are related to pairing and surface effects.
Plasmonically enhanced optical dichroism has attracted substantial interest for its application in optical sensing, where the interplay between chirality emanating from both molecules and ...plasmon-supporting structures has been regarded as a critical ingredient. Here, we experimentally demonstrate that suitably self-assembled achiral plasmonic nanostructures produce a high degree of enhancement in the optical dichroism observed from chiral molecules placed in their vicinity. Specifically, we identify a near-field enhancement associated with plasmonic hotpots as the mechanism enabling our observation of visible-NIR circular dichroism emanating from small amounts of chiral molecules. Our structures consist of linear arrays of gold nanorods obtained by introducing chiral anionic surfactants, such as modified bile salts, which lead to selective destabilization of a cetyltrimethylammonium bromide coating layer on Au nanorods, thereby promoting a tip-to-tip oriented assembly. The proposed mechanism of plasmonically-enhanced circular dichroism is supported by deriving a simple, yet general theoretical formalism that confirms the observed results, revealing the role of optical hotspots at the gaps of linear tip-to-tip nanorod assemblies as the origin of enhancement in the dichroism from chiral molecules. Importantly, it is the refractive rather than the absorption-mediated chiral response of the molecules that produces dichroism in the visible-NIR plasmonic regime, far from their UV absorption resonances. The observed self-assembly mechanism suggests that chiral analytes not directly interacting with the nanorod surfaces, but just able to induce tip-to-tip aggregation, can be revealed by a CD signature in the plasmonic region, thereby supporting potential applications in ultrasensitive analysis.
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