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  • Publication
    Energy saving strategies and on-site power generation in a university building from a tropical climate
    (2021-01-02)
    Litardo, Jaqueline
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    Hidalgo-León, Rubén
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    Amoroso, Fernando
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    Soriano, Guillermo
    This paper compares the potential for building energy saving of various passive and active strategies and on-site power generation through a grid-connected solar photovoltaic system (SPVS). The case study is a student welfare unit from a university campus located in the tropical climate (Aw) of Guayaquil, Ecuador. The proposed approach aims to identify the most effective energy saving strategy for building retrofit in this climate. For this purpose, we modeled the base line of the building and proposed energy saving scenarios that were evaluated independently. All building simulations were done in OpenStudio-EnergyPlus, while the on-site power generation was carried out using the Homer PRO software. Results indicated that the incorporation of daylighting controls accounted for the highest energy savings of around 20% and 14% in total building energy consumption, and cooling loads, respectively. Also, this strategy provided a reduction of about 35% and 43% in total building energy consumption, and cooling loads, respectively, when combined with triple low-e coating glazing and active measures. On the other hand, the total annual electric energy delivered by the SPVS (output power converter) was 66,590 kWh, from where 48,497 kWh was supplied to the building while the remaining electricity was injected into the grid.
  • Publication
    Renormalon-based resummation of Bjorken polarised sum rule in holomorphic QCD
    (2024-10-01) ;
    Castro-Arriaza, Camilo
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    Approximate knowledge of the renormalon structure of the Bjorken polarised sum rule (BSR) Γ\oline 1p‑n(Q2) leads to the corresponding BSR characteristic function that allows us to evaluate the leading-twist part of BSR. In our previous work [1], this evaluation (resummation) was performed using perturbative QCD (pQCD) coupling a(Q2)≡αs(Q2)/π in specific renormalisation schemes. In the present paper, we continue this work, by using instead holomorphic couplings [a(Q2)↦A(Q2)] that have no Landau singularities and thus require, in contrast to the pQCD case, no regularisation of the resummation formula. The D=2 and D=4 terms are included in the Operator Product Expansion (OPE) of inelastic BSR, and fits are performed to the available experimental data in a specific interval (Qmin2,Qmax2) where Qmax2=4.74GeV2. We needed relatively high Qmin2≈1.7GeV2 in the pQCD case since the pQCD coupling a(Q2) has Landau singularities at Q2≲1GeV2. Now, when holomorphic (AQCD) couplings A(Q2) are used, no such problems occur: for the 3δAQCD and 2δAQCD variants the preferred values are Qmin2≈0.6GeV2. The preferred values of αs in general cannot be unambiguously extracted, due to large uncertainties of the experimental BSR data. At a fixed value of αsMS\oline (MZ2), the values of the D=2 and D=4 residue parameters are determined in all cases, with the corresponding uncertainties.
  • Publication
    A 9-h CV with one outburst in 4 yr of Kepler data
    (2019-10-11)
    Zhifei Yu
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    J R Thorstensen
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    S Rappaport
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    A Mann
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    T Jacobs
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    L Nelson
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    B T Gänsicke
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    D LaCourse
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    T Borkovits
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    J Aiken
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    D Steeghs
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    O Toloza
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    A Vanderburg
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    D N C Lin
    Abstract During a visual search through the Kepler main-field light curves, we have discovered a cataclysmic variable (CV) that experienced only a single 4-d long outburst over four years, rising to three times the quiescent flux. During the four years of non-outburst data the Kepler photometry of KIC 5608384 exhibits ellipsoidal light variations (‘ELVs’) with a ∼12 per cent amplitude and period of 8.7 h. Follow-up ground-based spectral observations have yielded a high-quality radial velocity curve and the associated mass function. Additionally, H α emission lines were present in the spectra even though these were taken while the source was presumably in quiescence. These emission lines are at least partially eclipsed by the companion K star. We utilize the available constraints of the mass function, the ELV amplitude, Roche lobe filling condition, and inferred radius of the K star to derive the system masses and orbital inclination angle: $M_{\rm wd} \simeq 0.46 \pm 0.02 \, \mathrm{M}_\odot$, $M_{\rm K} \simeq 0.41 \pm 0.03 \, \mathrm{M}_\odot$, and i ≳ 70°. The value of Mwd is the lowest reported for any accreting WD in a CV. We have also run binary evolution models using mesa to infer the most likely parameters of the pre-cataclysmic binary. Using the mass-transfer rates from the model evolution tracks we conclude that although the rates are close to the critical value for accretion disc stability, we expect KIC 5608384 to exhibit dwarf nova outbursts. We also conclude that the accreting white dwarf most likely descended from a hot subdwarf and, most notably, that this binary is one of the first bona fide examples of a progenitor of AM CVn binaries to have evolved through the CV channel.
  • Publication
    Active Galactic Nuclei population studies with the Cherenkov Telescope Array
    (2022-03-18)
    Araya, M.
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    Arqueros, F.
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    Arrabito, L.
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    Aschersleben, J.
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    Singh, C. B.
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    Barai, P.
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    Baxter, J.
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    Becciani, U.
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    Borquez. R.
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    Bednarek, W.
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    Belfiore, A.
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    Bellizzi, L.
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    P. Campaña
    The Cherenkov Telescope Array (CTA) observatory is the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Building on the strengths of current IACTs, CTA is designed to achieve an order of magnitude improvement in sensitivity, with unprecedented angular and energy resolution. CTA will also increase the energy reach of IACTs, observing photons in the energy range from 20 GeV to beyond 100 TeV. These advances in performance will see CTA heralding in a new era for high-energy astrophysics, with the emphasis shifting from source discovery, to population studies and precision measurements. In this talk we discuss CTA’s ability to conduct source population studies of W-ray bright active galactic nuclei and how this ability will enhance our understanding on the redshift evolution of this dominant W-ray source class.