Papers by Jonathan Paredes
Two-phase refrigerant flow boiling was shown to be effective in handling hot-spots. The footprint... more Two-phase refrigerant flow boiling was shown to be effective in handling hot-spots. The footprint heat transfer coefficients followed the local heat flux and formed a self-compensating cooling mechanism by increasing the local heat transfer coefficient at the hot-spot. Data reduction using one-dimensional heat conduction overestimated the heat transfer coefficient at the hot-spots and underestimated it around its location. Heat spreading effects should be taken into account for more precise calculations (work in progress). Existing two-phase heat transfer prediction methods for micro-channels are accurate and can be applied to nonuniform heat flux conditions, independently of the data reduction method. The three-zone model of Thome et al. was found to be the most accurate, placing 53.3% of the predicted data within ±30% of the experimental values. If the hot-spot is placed toward the outlet, the resulting pressure drop will be smaller and the base temperature lower. The thermal resistance of two-phase flow cooling decreased with increasing heat flux and became smaller than that of the composite wall at high heat fluxes.
2004 had not been a good year for Compsis. Founded in 1989 in the Brazilian industrial city of Sã... more 2004 had not been a good year for Compsis. Founded in 1989 in the Brazilian industrial city of São José dos Campos, Compsis had grown steadily and successfully. In its largest service line, systems integration for electronic toll collection (ETC), the company had gained the dominant share of the Brazilian market and had even managed projects in Australia and India.
Astrophysical Journal, 2011
We report on the gamma-ray activity of the blazar Mrk 501 during the first 480 days of Fermi oper... more We report on the gamma-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average LAT gamma-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 +/- 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of 2), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 +/- 0.14, and the softest one is 2.51 +/- 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3GeV. In this paper, we also present the first results from the 4.5-month-long multifrequency campaign (2009 March 15 - August 1) on Mrk 501, which included the VLBA, Swift, RXTE, MAGIC and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton model. In the framework of this model, we find that the dominant emission region is characterized by a size <~ 0.1 pc (comparable within a factor of few to the size of the partially-resolved VLBA core at 15-43 GHz), and that the total jet power (~10^{44} erg s^{-1}) constitutes only a small fraction (~10^{-3}) of the Eddington luminosity. The energy distribution of the freshly-accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3GeV-10TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks.
A search for direct pair production of supersymmetric top squarks (t 1 ) is presented, assuming t... more A search for direct pair production of supersymmetric top squarks (t 1 ) is presented, assuming thet 1 decays into a top quark and the lightest supersymmetric particle,χ 0 1, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted Standard Model background of 13.5 + 3.7 − 3.6 (4.4 + 1.7 − 1.3 ) events in two signal regions based on L dt = 4.7 fb −1 of pp collision data taken at √ s = 7 TeV with the ATLAS detector at the LHC. An exclusion region in thet 1 versusχ 0 1 mass plane is evaluated: 370 < mt 1 < 465 GeV is excluded for mχ0 1 ∼ 0 GeV while mt 1 = 445 GeV is excluded for mχ0 1 ≤ 50 GeV. Technology, Ankara; (e)
Astrophysical Journal, 2005
The properties of the orbit and the donor star in the high mass X-ray binary microquasar LS 5039 ... more The properties of the orbit and the donor star in the high mass X-ray binary microquasar LS 5039 indicate that accretion processes should mainly occur via a radiatively driven wind. In such a scenario, significant X-ray variability would be expected due to the eccentricity of the orbit. The source has been observed at X-rays by several missions, although with a poor coverage that prevents to reach any conclusion about orbital variability. Therefore, we conducted RossiXTE observations of the microquasar system LS 5039 covering a full orbital period of 4 days. Individual observations are well fitted with an absorbed power-law plus a Gaussian at 6.7 keV, to account for iron line emission that is probably a diffuse background feature. In addition, we have taken into account that the continuum is also affected by significant diffuse background contamination. Our results show moderate power-law flux variations on timescales of days, as well as the presence of miniflares on shorter timescales. The new orbital ephemeris of the system recently obtained by Casares et al. have allowed us to show, for the first time, that an increase of emission is seen close to the periastron passage, as expected in an accretion scenario. Moreover, the detected orbital variability is a factor of ~4 smaller than the one expected by using a simple wind accretion model, and we suggest that an accretion disk around the compact object could be responsible for this discrepancy. On the other hand, significant changes in the photon index are also observed clearly anti-correlated with the flux variations. We interpret the overall X-ray spectral characteristics of LS 5039 in the context of X-ray radiation produced by inverse Compton and/or synchrotron processes in the jet of this microquasar.
Astronomy & Astrophysics, 2001
Observations of the extraordinarily bright optical afterglow (OA) of GRB 991208 started 2.1 d aft... more Observations of the extraordinarily bright optical afterglow (OA) of GRB 991208 started 2.1 d after the event. The flux decay constant of the OA in the R-band is -2.30 +/- 0.07 up to 5 d, which is very likely due to the jet effect, and after that it is followed by a much steeper decay with constant -3.2 +/- 0.2, the fastest one ever seen in a GRB OA. A negative detection in several all-sky films taken simultaneously to the event implies either a previous additional break prior to 2 d after the occurrence of the GRB (as expected from the jet effect). The existence of a second break might indicate a steepening in the electron spectrum or the superposition of two events. Once the afterglow emission vanished, contribution of a bright underlying SN is found, but the light curve is not sufficiently well sampled to rule out a dust echo explanation. Our determination of z = 0.706 indicates that GRB 991208 is at 3.7 Gpc, implying an isotropic energy release of 1.15 x 10E53 erg which may be relaxed by beaming by a factor > 100. Precise astrometry indicates that the GRB coincides within 0.2" with the host galaxy, thus given support to a massive star origin. The absolute magnitude is M_B = -18.2, well below the knee of the galaxy luminosity function and we derive a star-forming rate of 11.5 +/- 7.1 Mo/yr. The quasi-simultaneous broad-band photometric spectral energy distribution of the afterglow is determined 3.5 day after the burst (Dec 12.0) implying a cooling frequency below the optical band, i.e. supporting a jet model with p = -2.30 as the index of the power-law electron distribution.
European Journal of Biochemistry, 2002
In the fission yeast Schizosaccharomyces pombe the Wak1p/Win1p-Wis1p-Sty1p stress-activated prote... more In the fission yeast Schizosaccharomyces pombe the Wak1p/Win1p-Wis1p-Sty1p stress-activated protein kinase (SAPK) pathway relays environmental signals to the transcriptional machinery and modulates gene expression via a cascade of protein phosphorylation. Cells of S. pombe subjected to cold shock (transfer from 28 °C to 15 °C) transiently activated the Sty1p mitogen-activated protein kinase (MAPK) by phosphorylation. Induction of this response was completely abolished in cells disrupted in the upstream response regulator Mcs4p. The cold-triggered Sty1p activation was partially dependent on Wak1p MAPKKK and fully dependent on Wis1p MAPKK suggesting that the signal transmission follows a branched pathway, with the redundant MAPKKK Win1p as alternative transducer to Wis1p, which subsequently activates the effector Sty1p MAPK. Also, the bZIP transcription factor Atf1p became phosphorylated in a Sty1p-dependent way during the cold shock and this phosphorylation was found responsible for the increased expression of gpd1+, ctt1+, tps1+ and ntp1+ genes. Strains deleted in transcription factors Atf1p or Pcr1p were unable to grow upon incubation at low temperature whereas those disrupted in any member of the SAPK pathway were able to do so. These data reveal that S. pombe responds to cold by inducing the SAPK pathway. However, such activation is dispensable for yeast growth in cold conditions, supporting that the presence of Atf1/Pcr1 heterodimers, rather than an operative SAPK pathway, is critical to ensure yeast growth at low temperature by an as yet undefined mechanism.
A search for tt resonances in lepton+jets events with highly boosted top quarks collected in pp c... more A search for tt resonances in lepton+jets events with highly boosted top quarks collected in pp collisions at √ s = 7 TeV with the ATLAS detector
Simulaciones simples, utilizando una representación física a escala de una zona urbana y
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Papers by Jonathan Paredes