111 research outputs found
On the optimal demand-side management in microgrids through polygonal composition
This article presents a novel methodology for energy management in microgrids focused on the
demand side. It is inspired by the Tangram puzzle. The energy demand and production profiles are
represented by polygons and managed through computational geometry. Therefore, an optimization
problem is defined to place n energy demand profiles (pieces) to cover the total energy production
profile (target shape). The optimization problem is addressed with a genetic algorithm. It tries to
calculate the optimal positions of the polygons of the demands covering the maximum energy
production. Since the referred production comes from renewable energy sources in the microgrid,
this method allows reducing both the consumption of fossil fuels and energy bills
High frequency magnetic permeability of nanocomposite film
The high frequency magnetic permeability of nanocomposite film consisting of
the single-domain spherical ferromagnetic particles in the dielectric matrix is
studied. The permeability is assumed to be determined by rotation of the
ferromagnetic inclusion magnetic moments around equilibrium direction in AC
magnetic field. The composite is modeled by a cubic array of ferromagnetic
particles. The magnetic permeability tensor is calculated by solving the
Landau-Lifshits-Gilbert equation accounting for the dipole interaction of
magnetic particles. The permeability tensor components are found as functions
of the frequency, temperature, ferromagnetic inclusions density and magnetic
anisotropy. The obtained results show that nanocomposite films could have
rather high value of magnetic permeability in the microwave range
Response of parylene-coated NaI(Tl) scintillators at low temperature
Despite that it is widely used as a scintillator at room temperature, the hygroscopicity of NaI complicates its handling and limits its application for many purposes, for example as a cryogenic detector. To overcome this problem we study coating materials that can act as humidity barriers, in particular parylene, a polymer that can be deposited in very radiopure, thin and conformal layers. In this work, several NaI(Tl) samples coated with 2-5 µm parylene-C were tested at low temperature. Luminescence spectra under X-ray excitation are presented at several temperatures as well as the light output vs temperature at 1.5-300 K. Several thermoluminescence peaks were observed at around 60, 95 and 150 K during warm up to room temperature
The mechanical resistance of the coating under thermal cycles was also investigated, and we observed a degradation of the optical appearance and the light output after cooling down to about 100 mK, which compromises the reusability of the samples
Pumping current of a Luttinger liquid with finite length
We study transport properties in a Tomonaga-Luttinger liquid in the presence
of two time-dependent point like weak impurities, taking into account
finite-length effects. By employing analytical methods and performing a
perturbation theory, we compute the backscattering pumping current (I_bs) in
different regimes which can be established in relation to the oscillatory
frequency of the impurities and to the frequency related to the length and the
renormalized velocity (by the electron-electron interactions) of the charge
density modes. We investigate the role played by the spatial position of the
impurity potentials. We also show how the previous infinite length results for
I_bs are modified by the finite size of the system.Comment: 9 pages, 7 figure
Late-time cosmology in (phantom) scalar-tensor theory: dark energy and the cosmic speed-up
We consider late-time cosmology in a (phantom) scalar-tensor theory with an
exponential potential, as a dark energy model with equation of state parameter
close to -1 (a bit above or below this value). Scalar (and also other kinds of)
matter can be easily taken into account. An exact spatially-flat FRW cosmology
is constructed for such theory, which admits (eternal or transient)
acceleration phases for the current universe, in correspondence with
observational results. Some remarks on the possible origin of the phantom,
starting from a more fundamental theory, are also made. It is shown that
quantum gravity effects may prevent (or, at least, delay or soften) the cosmic
doomsday catastrophe associated with the phantom, i.e. the otherwise
unavoidable finite-time future singularity (Big Rip). A novel dark energy model
(higher-derivative scalar-tensor theory) is introduced and it is shown to admit
an effective phantom/quintessence description with a transient acceleration
phase. In this case, gravity favors that an initially insignificant portion of
dark energy becomes dominant over the standard matter/radiation components in
the evolution process.Comment: LaTeX file, 48 pages, discussion of Big Rip is enlarged, a reference
is adde
Mechanical behavior of concrete prisms reinforced with steel and GFRP bar systems
Being immune to corrosion, and having a tensile strength up to three times higher than structural steel, glass fiber reinforced polymer (GFRP) bars are suitable for reinforcing concrete structures exposed to aggressive environmental conditions. However, a relatively low elasticity modulus of GFRP bars (in respect to the steel) favors the occurrence of relatively large deformability of cracked reinforced concrete. Lack of ductility and degradation of properties under high temperature can be also identified as debilities of GFRP bars over steel ones. Combining GFRP and steel bars can be a suitable solution to overcoming these concerns. Nevertheless, the application of such hybrid reinforcement systems requires reliable material models. The influence of the relative area of GFRP and steel bars on the tensile capacity of cracked concrete (generally known as tension-stiffening effect), was never investigated from the experimental point of view, mainly crossing results from different tools on the assessment of the cracking process. This paper experimentally investigates deformations and cracking behavior of concrete prisms reinforced with steel bars and GFRP bars in different combinations. The test results of 11 elements are reported. A tensile stress-strain diagram is conceptually proposed for modelling the tension-stiffening effect in elements with such hybrid combination of the reinforcement. The cracking process in terms of crack width and crack spacing is analyzed considering the hybrid reinforcement particularities and a preliminary approach is proposed for the prediction of the crack width for this type of reinforced concrete elementsResearch Council of Lithuania (Research Project S-MIP-17-62). The second author also
590 wish to acknowledge the support provided by FCT through the PTDC/ECM591 EST/1882/2014 projec
Land Restoration for Achieving the Sustainable Development Goals - An International Resource Panel Think Piece
Structure of the parasite infracommunity of Sciades proops from the Japaratuba River Estuary, Sergipe, Brazil
First identification of natural infection of Rickettsia rickettsii in the Rhipicephalus sanguineus tick, in the State of Rio de Janeiro
Particulate soil organic carbon and stratification ratio increases in response to crop residue decomposition under no-till
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