5,267 research outputs found
Noise and Periodic Modulations in Neural Excitable Media
We have analyzed the interplay between noise and periodic modulations in a
mean field model of a neural excitable medium. To this purpose, we have
considered two types of modulations; namely, variations of the resistance and
oscillations of the threshold. In both cases, stochastic resonance is present,
irrespective of if the system is monostable or bistable.Comment: 13 pages, RevTex, 5 PostScript figure
Zinc(II) coordination polymers with pseudopeptidic ligands
Two new phenyl-bridged pseudopeptidic ligands have been prepared and structurally characterised. The nature of the ligandsâ substituents play an important role in the nature of the solid state structure yielding either hydrogen bonded linked sheets of molecules or infinite hydrogen bonded networks. Both these ligands were reacted with a range of zinc(II) salts with the aim of synthesising coordination polymers and networks and exploring the role that anions could play in determining the final structure. The crystal structures of four of these systems (with ZnSO4 and ZnBr2) were determined; in one case, a 3D coordination network was obtained where zincâligand coordination bonds generated the 3D arrangements. Three other 3D networks were obtained by anion-mediated hydrogen bonding of coordination 1D chains or 2D sheets. These four very different structures highlight the important role played by the ligandsâ substituents and the counteranions present in the system
Ozone membrane contactor to intensify gas/liquid mass transfer and contaminants of emerging concern oxidation
A tubular porous borosilicate membrane contactor was investigated for ozone gas/water mass transfer and the removal of contaminants of emerging concern (CECs) in water. Ozone gas/water contact occurs on the membrane shell-side, which is coated with a photocatalyst (TiO2-P25), as the ozone gas stream is fed from the lumen side and permeates through the pores generating micro-sized ozone bubbles uniformly delivered to the annular reaction zone where the contaminated water to be treated flows. Under continuous flow, water pH at 3.0 and temperature at 20 oC, the volumetric mass transfer coefficient (KLa) ranged from 3.5 to 9.0 min-1 and improved with the increase of gas flow rate (QG, 1.5-fold from 0.15 to 1.0 Ndm3 min-1) and liquid flow rate (QL, 2.0-fold from 20 to 50 L h-1), due to enhanced turbulence on the membrane shell-side and annular zone. The mass transfer efficiency was more pronounced as the QG decreased and the QL increased, which is advantageous for large-scale applications. The main resistances to ozone transfer were in the water phase boundary layer (53-76%) and in the membrane (24-47%; kM = (1.14 ¹ 0.01) à 10-4 m s-1). For an ozone dose of 12 g m-3 and residence time of 3.9 s, removals ⼠80% were achieved for 13 of 19 CECs spiked in demineralized water (each 10 Οg L-1), demonstrating the applicability of this membrane contactor for ozonation treatment. Photocatalytic ozonation (O3/UVC/TiO2) did not significantly improve the treatment performance due to the low residence time inside the contactor
Treatment of wastewater containing mineral oil by sorption onto granulated cork
The aim of this work is the development of a new method to remove oils from wastewaters, namely hydrocarbons. These contaminants, when present in high concentrations, are efficiently removed by physical and chemical processes, such as gravity separators, flocculation and flotation processes; however for low concentrations, these methods are not applicable [1]. Moreover, advanced separation processes such as membrane separation [2] and activated carbon adsorption [3] are expensive options for the treatment of oil-containing wastewaters. This new technique is based on oil and hydrocarbonsâ sorption on cork granules.This work is supported by project HIDROCORK "Utilization of Cork Wastes and By-Products for Elimination of Oils and Fats from Waters", financed by QREN (National Strategic Reference Framework). This work is also partially supported by project PEst-C/EQBILA0020/2011, financed by FEDER through COMPETE_ Programa Operacional Factores de Competitividade and by FCT -Fundação para a CiĂŞncia e a Tecnologia
Studies on sorption and regeneration of granulated cork for oil and grease removal
The aim of this work is to develop a method to recover sorbed oil and grease from granulated cork, in order to promote biomass regeneration. Experimental procedure involved biomass saturation with oil, followed by chemical regeneration. Oil removal by elution was tested using HNO3 and NaOH solutions, cationic and anionic surfactants and organic solvents, namely carbon tetrachloride and n-hexane. Chemical desorption efficiency using organic solvents achieved values of 90 Âą 6 % and 72 Âą 6 % for CCl4 and n-hexane, respectively. Although the use of organic solvents proved to be an efficient process, it involves high costs and a negative environmental impact. Physical regeneration could be an alternative to the use of solvents for oil removal from granulated cork.This work is supported by project HIDROCORK âUtilization of Cork Wastes and By-Products for Elimination of Oils and Fats from Watersâ, financed by QREN (National Strategic Reference Framework). This work is also partially supported by project PEst-C/EQB/LA0020/2011, financed by FEDER through COMPETE - Programa Operacional Factores de Competitividade and by FCT - Fundação para a CiĂŞncia e a Tecnologia. A. Pintor also acknowledges her PhD fellowship by FCT (SFRH / BD / 70142 / 2010)
Valorisation of cork by-products for the treatment of vegetal and animal oil containing wastewaters
In this study, cork granules, which are by-products of the cork processing industry, were used as biosorbents for the removal of vegetable and animal oils from water. Simple oil-in-water emulsions were created by ultrasonic emulsification and batch adsorption tests were performed by contacting cork with these emulsions for a defined period of time. A mass transfer model was able to predict adequately the kinetic data, using a Linear Driving Force approximation for intraparticle diffusion and equilibrium described by the Langmuir-Freundlich equation. Maximum sorption capacities for vegetable and animal oil, as calculated by the Langmuir-Freundlich model, were 5 Âą 4 and 2.3 Âą 0.9 g g-1, respectively. Therefore, expanded cork granules proved to be an efficient, low-cost sorbent for both vegetable and animal oilsThis work is supported by project HIDROCORK âUtilization of Cork Wastes and By-Products for Elimination of Oils and Fats from Watersâ, supported by QREN (National Strategic Reference Framework). This work is also partially supported by project PEst-C/EQB/LA0020/2011, financed by FEDER through COMPETE -Programa Operacional Factores de Competitividade and by FCT -Fundação para a CiĂŞncia e a Tecnologia
Turning Carbon Dioxide and Ethane into Ethanol by Solar-Driven Heterogeneous Photocatalysis over RuO2- and NiO-co-Doped SrTiO3
[EN] The current work focused on the sunlight-driven thermo-photocatalytic reduction of carbon dioxide (CO2), the primary greenhouse gas, by ethane (C2H6), the second most abundant element in shale gas, aiming at the generation of ethanol (EtOH), a renewable fuel. To promote this process, a hybrid catalyst was prepared and properly characterized, comprising of strontium titanate (SrTiO3) co-doped with ruthenium oxide (RuO2) and nickel oxide (NiO). The photocatalytic activity towards EtOH production was assessed in batch-mode and at gas-phase, under the influence of different conditions: (i) dopant loading; (ii) temperature; (iii) optical radiation wavelength; (vi) consecutive uses; and (v) electron scavenger addition. From the results here obtained, it was found that: (i) the functionalization of the SrTiO3 with RuO2 and NiO allows the visible light harvest and narrows the band gap energy (ca. 14-20%); (ii) the selectivity towards EtOH depends on the presence of Ni and irradiation; (iii) the catalyst photoresponse is mainly due to the visible photons; (iv) the photocatalyst loses > 50% efficiency right after the 2nd use; (v) the reaction mechanism is based on the photogenerated electron-hole pair charge separation; and (vi) a maximum yield of 64 mu mol EtOH g(cat)(-1) was obtained after 45-min (85 mu mol EtOH g(cat)(-1) h(-1)) of simulated solar irradiation (1000 W m(-2)) at 200 degrees C, using 0.4 g L-1 of SrTiO3:RuO2:NiO (0.8 wt.% Ru) with [CO2]:[C2H6] and [Ru]:[Ni] molar ratios of 1:3 and 1:1, respectively. Notwithstanding, despite its exploratory nature, this study offers an alternative route to solar fuels' synthesis from the underutilized C2H6 and CO2.This work was financially supported by the Base Funding-UIDB/50020/2020 of the Associate Laboratory LSRE-LCM-funded by national funds through FCT/MCTES (PIDDAC). Larissa O. Paulista also wants to acknowledge for her doctoral fellowship (reference SFRH/BD/137639/2018), supported by FCT. Tania F. C. V. Silva and Vitor J. P. Vilar acknowledge the FCT Individual Call to Scientific Employment Stimulus 2017 (CEECIND/01386/2017 and CEECIND/01317/2017, respectively). Josep Albero and Hermenegildo Garcia are also grateful to the Spanish Ministry of Science and Innovation (RTI2018-098237-CO2-R1 and Severo Ochoa), Generalitat Valencia (Prometeo 2017/083) and European Union's Horizon 2020 research and innovation programme under grant agreement No 862453, project FlowPhotochem, by financial contribution.Paulista, LO.; Albero-Sancho, J.; Martins, RJE.; Boaventura, RAR.; Vilar, VJP.; Silva, TFCV.; GarcĂa GĂłmez, H. (2021). Turning Carbon Dioxide and Ethane into Ethanol by
Solar-Driven Heterogeneous Photocatalysis over RuO2- and
NiO-co-Doped SrTiO3. Catalysts. 11(4):1-18. https://doi.org/10.3390/catal1104046111811
A New Approach to Non-Commutative U(N) Gauge Fields
Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.Comment: 11 pages; v2 minor correction
Perturbing Topological Field Theories
The abelian Chern-Simons theory is perturbed by introducing local
gauge-invariant interaction terms depending on the curvature. The computation
of the correlation function of two Wilson lines for two smooth closed
nonintersecting curves is reported up to four loops and is shown to be
unaffected by radiative corrections. This result ensures the stability of the
linking number of the two curves with respect to the local perturbations which
may be added to the Chern-Simons action.Comment: 13 pages, 5 figures, corrected some typo
The Nondeterministic Waiting Time Algorithm: A Review
We present briefly the Nondeterministic Waiting Time algorithm. Our technique
for the simulation of biochemical reaction networks has the ability to mimic
the Gillespie Algorithm for some networks and solutions to ordinary
differential equations for other networks, depending on the rules of the
system, the kinetic rates and numbers of molecules. We provide a full
description of the algorithm as well as specifics on its implementation. Some
results for two well-known models are reported. We have used the algorithm to
explore Fas-mediated apoptosis models in cancerous and HIV-1 infected T cells
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