295 research outputs found
Grand canonical ensemble of a -dimensional Reissner-Nordstr\"om black hole in a cavity
The grand canonical ensemble of a -dimensional Reissner-Nordstr\"om black
hole space in a cavity is analyzed. The realization of this ensemble is made
through the Euclidean path integral approach by giving the Euclidean action for
the black hole with the correct topology, and boundary conditions corresponding
to a cavity, where the fixed quantities are the temperature and the electric
potential. One performs a zero loop approximation to find and analyze the
stationary points of the reduced action. This yields two solutions for the
electrically charged black hole, , which is the smaller and unstable,
and , which is the larger and stable. One also analyzes the most
probable configurations, which are either a stable charged black hole or hot
flat space, mimicked by a nongravitating charged shell. Making the
correspondence between the action and the grand potential, one can get the
black hole thermodynamic quantities, such as the entropy, the mean charge, the
mean energy, and the thermodynamic pressure, as well as the Smarr formula,
shown to be valid only for the unstable black hole. We find that thermodynamic
stability is related to the positivity of the heat capacity at constant
electric potential and area of the cavity. We also comment on the most
favorable thermodynamic phases and phase transitions. We then choose ,
which is singled out naturally from the other higher dimensions as it provides
an exact solution for the problem, and apply all the results previously found.
The case is mentioned. We compare thermodynamic radii with the photonic
orbit radius and the Buchdahl-Andr\'easson-Wright bound radius in
-dimensional Reissner-Nordstr\"om spacetimes and find they are unconnected,
showing that the connections displayed in the Schwarzschild case are not
generic, rather they are very restricted holding only in the pure gravitational
situation.Comment: 28 pages, 5 figure
Structural behaviour analysis of Faria Guimarães station
No presente estudo efectua-se a modelação e análise do comportamento estrutural da estação
Faria Guimarães, do Metro do Porto. A estação é constituída por um cruzamento oblíquo de
duas grandes galerias executadas através do método SEM/NATM. A obra é de elevada
complexidade devido aos condicionamentos geométricos da estação e obras adjacentes, à grande
heterogeneidade do maciço e à ocupação intensa da superfície. A análise do comportamento
estrutural da estação foi realizada recorrendo a modelos numéricos 2D e 3D, bem como a
resultados obtidos com a observação da estação.In present paper the modelling and structural behaviour analysis of the Faria Guimarães station,
of Metro do Porto, is presented. The station includes the inclined intersection of two large
galleries executed through SEM/NATM method. The work is highly complex due to geometric
limitations of the station and adjacent works, the heterogeneity of the rock mass and the dense
occupation at surface. The structural behaviour analysis of the station was performed using 2D
and 3D numerical models, as well as results obtained through the observation of the station.Fundação para a Ciência e Tecnologia (FCT) - Projecto POCI/ECM/57495/2004, intitulado Geotechnical Risk in Tunnels for High Speed Trains
Normal modes of Proca fields in AdS spacetime
A normal mode analysis for Proca fields in the anti-de Sitter (AdS) spacetime
is given. It is found that the equations for the Proca field can be decoupled
analytically. This is performed by changing the basis of the vector spherical
harmonics (VSH) decomposition. The normal modes and the normal mode frequencies
of the Proca equation in the AdS spacetime are then analytically determined. It
is also shown that the Maxwell field can be recovered by taking the massless
limit of the Proca field with care so that the nonphysical gauge modes are
eliminated.Comment: 6 page
Integration of Single Cell Traps, Chemical Gradient Generator and Photosensors in a Microfluidic Platform for the Study of Alpha-Synuclein Toxicity in Yeast
AbstractAlpha-synuclein (aSyn) is a key player in Parkinson's disease. Genetically engineered yeast cells producing aSyn fused with GFP (aSyn-GFP) have been used to study this protein. In this work, we present a microfluidic platform with integrated photosensors that captures single yeast cells in arrays of hydrodynamic traps and exposes them to a chemical gradient of precise composition. This platform enables the study of the effects of aSyn expression level and aggregation in genetically modified yeast cells by chemical stimulation. The photosensors allow the detection of cells in the traps by measuring the variations in light transmission or of the fluorescence produced by aSyn-GFP for real-time signal acquisition
A novel control strategy based on predictive control for a bidirectional interleaved three-phase converter
An experimental confirmation of predictive control
applied to a bidirectional interleaved three-phase (BIT) converter
is presented. The BIT converter is a powerful solution for
numerous applications, mainly, renewables interface, motor
drivers, active rectifiers, and active power filters. However, a
precise and robust digital control strategy is required,
maintaining a low computational effort. In this paper, a
predictive control based on continuous control set is proposed as
a new control scheme for the BIT converter, permitting the
control of the ac side current with fixed switching frequency and
with a faster response. The predictive control scheme applied to
the BIT converter is defined along the paper, evidencing in detail
the digital employment aspects according to the discrete-time
model of the BIT converter. An explicit experimental validation
under realistic operating conditions is presented using a
developed laboratorial prototype, highlighting the convenience of
the control applied to the BIT converter.This work has been supported by FCT – Fundação para a
Ciência e Tecnologia in the scope of the project: PEstUID/CEC/00319/2013.
This work has been supported by
COMPETE: POCI-01-0145-FEDER-007043 and FCT –
Fundação para a Ciência e Tecnologia within the Project
Scope: UID/CEC/00319/2013. This work is financed by the
ERDF – European Regional Development Fund through the
Operational Programme for Competitiveness and
Internationalisation < COMPETE 2020 Programme, and by
National Funds through the Portuguese funding agency, FCT <
Fundação para a Ciência e a Tecnologia, within project
SAICTPAC/0004/2015< POCI< 01<0145<FEDER<016434. Mr.
Tiago Sousa is supported by the doctoral scholarship
SFRH/BD/134353/2017 granted by the Portuguese FCT
agency.info:eu-repo/semantics/publishedVersio
Surface response methodology towards optimal carotenoids production by Gordonia Alkanivorans Strain 1B [Poster]
ABSTRACT: The process of obtaining carotenoids, mainly towards sectors that may influence the human health, such as pharmaceutical and cosmetic, is strictly regulated because of the potential toxicity of the synthetically derived pigments. Thus, microbial pigments are in increasing demand since they are a promising natural and safe alternative source for various industrial applications. Gordonia alkanivorans strain 1B is a fructophilic desulfurizing bacterium, which was also shown to be a good producer of carotenoids. However, its production abilities presented a great variation, depending on the conditions it was submitted to. In previous works, both the carbon source and sulfur source, demonstrated a great influence in the total carotenoid concentration, especially when combined with the presence of a light source. So, in this study, a surface response methodology based on the Doehlert distribution for two factors (% of glucose in a mix glucose + fructose (10 g/L total sugars), and sulfate concentration) was used aiming to get the optimal carotenoids production by G. alkanivorans strain 1B.N/
A novel microfluidic cell co-culture platform for the study of the molecular mechanisms of Parkinson's Disease and other synucleinopathies
Copyright © 2016 Fernandes, Chutna, Chu, Conde and Outeiro. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.Although, the precise molecular mechanisms underlying Parkinson's disease (PD) are still elusive, it is now known that spreading of alpha-synuclein (aSyn) pathology and neuroinflammation are important players in disease progression. Here, we developed a novel microfluidic cell-culture platform for studying the communication between two different cell populations, a process of critical importance not only in PD but also in many biological processes. The integration of micro-valves in the device enabled us to control fluid routing, cellular microenvironments, and to simulate paracrine signaling. As proof of concept, two sets of experiments were designed to show how this platform can be used to investigate specific molecular mechanisms associated with PD. In one experiment, naïve H4 neuroglioma cells were co-cultured with cells expressing aSyn tagged with GFP (aSyn-GFP), to study the release and spreading of the protein. In our experimental set up, we induced the release of the contents of aSyn-GFP producing cells to the medium and monitored the protein's diffusion. In another experiment, H4 cells were co-cultured with N9 microglial cells to assess the interplay between two cell lines in response to environmental stimuli. Here, we observed an increase in the levels of reactive oxygen species in H4 cells cultured in the presence of activated N9 cells, confirming the cross talk between different cell populations. In summary, the platform developed in this study affords novel opportunities for the study of the molecular mechanisms involved in PD and other neurodegenerative diseases.JF was supported by FCT (SFRH/BD/73908/2010). TO is supported by the DFG Center for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB). The work was also supported by FCT through the Associated Laboratory IN—Institute of Nanoscience and Nanotechnology and the research project EXCL/CTM-NAN/0441/2012.info:eu-repo/semantics/publishedVersio
Influence of culture conditions towards optimal carotenoid production by Gordonia alkanivorans strain 1B
ABSTRACT: With the increasing awareness on the toxicity of several synthetic dyes, demand for pigments from natural sources, such as microbial carotenoids, has gained interest as a promising safe alternative colour additive. In this study, a surface response methodology based on the Doehlert distribution for two factors [% of glucose in a mixture of glucose + fructose (10 g/L total sugars), and sulfate concentration] was used towards the optimal carotenoids production by Gordonia alkanivorans strain 1B in the presence of light (400 lx). Time influence on pigment production by this bacterium was also evaluated, as well as the cell viability profile during longer incubation periods at optimal conditions. Indeed, the highest carotenoid production (2596-3100 mu g/g(DCW)) was obtained when strain 1B was cultivated in the optimal conditions: glucose 10 g/L and sulfate >= 22 mg/L, in the presence of light for 19 days at 30 degrees C, 150 rpm. Flow cytometry showed that the highest production was somehow related with the cellular stress. These results highlight the great potential of strain 1B as a new hyperpigment producer to be exploited towards several applications.info:eu-repo/semantics/publishedVersio
Performance evaluation of a proportional integral with proportional derivative feedforward voltage control for UPSs
This paper presents a performance evaluation of a proportional-integral (PI) with proportional-derivative (PD) feedforward control for the output voltage of a single-phase off-line uninterruptible power supply (UPS) without using additional sensors. The control system is explained and simulation results are presented to analyze the steady state and transient response of the implemented voltage control. A laboratorial prototype was developed, and acquired experimental results considering linear and nonlinear loads are presented and discussed, corroborating the obtained simulation results.SFRH/BD/134353/2017info:eu-repo/semantics/publishedVersio
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