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Mass transfer and hydrogen burning in white dwarf binaries
Full text linkThe thesis is devoted to a study of mass transfer, non-explosive hydrogen burning and the effects of the magnetic field in cataclysmic variables (CVs) in the context of their evolution and possible paths to Supernovae type Ia. I focused on the observational properties of CVs hosting massive white dwarfs (WDs) and/or accreting at high rate. My aims were to detect signatures of quiescent hydrogen burning, follow novae as they settle into quiescence and to assess whether the WD magnetic field alters secular evolution and the outcome of the nova explosions. The thesis consists of three chapters. The first one focuses on observations of VY Scl-type nova-like systems, or "anti-dwarf novae'', exploring the idea that they can burn hydrogen during their optical low states. I analysed all the available archival X-ray and UV observations, in both, their high and their low states, and found that the proposed hydrogen burning at high atmospheric temperatures is ruled out.
VY Scl-type stars cannot be Supernova type Ia progenitors since they either burn hydrogen but have too low-mass WDs or undergo rare nova explosions, expelling more material than was accreted. In the second chapter I investigate two post-novae with massive WDs, confirming the magnetic nature of one of them, and revealing that the second one is an intermediate polar candidate. I also show that a nova explosion in a magnetic system can leave an imprint on the surface of a WD, detectable in soft X-rays for several years after the explosion. It may be due to residual localized hydrogen burning, but a more likely explanation is a temperature gradient in the WD atmosphere.
The last chapter represents monitoring of the old magnetic nova GK Per performed with Swift, Chandra and NuSTAR telescopes during its recent dwarf nova outburst. The main goal was to study the effects of increased mass transfer through the disk in a magnetic system. I measured the WD spin-up rate, localized the emission sites of different spectral components, revealed shrinking of the inner radius of accretion disk and redistribution of the accretion energy as the mass transfer grows
V4743 Sgr, a magnetic nova?
No full textTwo XMM-Newton observations of Nova V4743 Sgr (Nova Sgr 2002) were performed shortly after it returned to quiescence, 2 and 3.5 yr after the explosion. The X-ray light curves revealed a modulation with a frequency of ≃0.75 mHz, indicating that V4743 Sgr is most probably an intermediate polar (IP). The X-ray spectra have characteristics in common with known IPs, with a hard thermal plasma component that can be fitted only assuming a partially covering absorber. In 2004, the X-ray spectrum had also a supersoft blackbody-like component, whose temperature was close to that of the white dwarf (WD) in the supersoft X-ray phase following the outburst, but with flux by at least two orders of magnitude lower. In quiescent IPs, a soft X-ray flux component originates at times in the polar regions irradiated by an accretion column, but the supersoft component of V4743 Sgr disappeared in 2006, indicating a possible origin different from accretion. We suggest that it may have been due to an atmospheric temperature gradient on the WD surface, or to continuing localized thermonuclear burning at the bottom of the envelope, before complete turn-off. An optical spectrum obtained with Southern African Large Telescope (SALT) 11.5 yr after the outburst showed a prominent He II λ4686 line and the Bowen blend, which reveal a very hot region, but with peak temperature shifted to the ultraviolet range. V4743 Sgr is the third post-outburst nova and IP candidate showing a low-luminosity supersoft component in the X-ray flux a few years after the outburst
X-ray spectra and light curves of cooling novae and a nova like
No full textWe present X-ray observations of novae V2491 Cyg and KT Eri about 9 yr post-outburst of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM-Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at ˙m = 1.4 × 10-9-10-8 M⊙yr-1, while for KT Eri, ˙m < 2 × 10-10 M⊙ yr. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of 39 min, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at ˙m ∼ 1.8 × 10-11 M⊙ yr-1, one magnitude lower than KT Eri, consistently with its U Gem outburst behaviour and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system's low inclination, probably due to the X-ray flux of the secondary. A period of 81 min is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: The accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.Fil: Sun, Bangzheng. University of Wisconsin; Estados UnidosFil: Orio, Marina. University of Wisconsin; Estados Unidos. Inaf Istituto Di Astrofisica Spaziale E Fisica Cosmica; ItaliaFil: Dobrotka, Andrej. Slovak University of Technology in Bratislava; EslovaquiaFil: Luna, Gerardo Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Universidad Nacional de Hurlingham; ArgentinaFil: Shugarov, Sergey. Astronomical Institute of the Slovak Academy of Sciences; Eslovaquia. M.V. Lomonosov Moscow State University; RusiaFil: Zemko, Polina. University of Padova; Itali
Oxigen Reserve index as a non-invasive indicator of arterial partial pressure of oxygen in anaesthetised dogs
No full textreservedThe aim of this study was to evaluate the potential use of the oxygen reserve index (ORi) as a non-invasive estimator of the partial pressure of oxygen (PaO2) in a hyperoxemic condition (100 -- 200 mmHg) in anaesthetised dogs. In this range of PaO2 traditional pulse-oximeters cannot be applied as the arterial haemoglobin is fully saturated and the measurement return by the instrument is > 98%. The only way to assess the oxygenation status is arterial blood gas analysis, which is invasive, intermittent and challenging.
The primary aim of the study was to investigate the relationship between the ORi, a parameter measured non-invasively with a multi-wavelength pulse co-oximeter, and PaO2, measured with the arterial blood gas analysis. A second goal was to trace how did the ORi change at changing the inspired fraction of oxygen (FiO2) in order to estimate the error of single ORi measurement from the scattering of ORi values. Ultimately, we focused on finding cut-off values of ORi that indicate upper-limits for PaO2 that have clinical application.
The study enrolled 16 dogs undergoing general anaesthesia for elective procedures requiring the insertion of an arterial catheter and mechanical ventilation. An adhesive sensor was wrapped around the tongue and connected to a pulse co-oximeter (Rad 97, Masimo Corp.) that calculated the ORi. For each dog at least 2 arterial blood samples were collected for analysis.
A total of 35 paired measurements were collected. A moderate positive correlation was observed between ORi and PaO2 with the correlation coefficient of 0.68. Tracing the ORi probes we calculated the error of single ORi measurement that was 0.02. The Youden index was used to identify 0.55 as value of ORi able to detect a PaO2 > 150 mmHg with the highest sensitivity and specificity.
We can conclude that ORi can be used as a non-invasive monitoring of blood oxygenation status in anaesthetized dogs since it’s variation reflects the variation of the PaO2, although it does not replace blood gas analysis for assessment of oxygenation.The aim of this study was to evaluate the potential use of the oxygen reserve index (ORi) as a non-invasive estimator of the partial pressure of oxygen (PaO2) in a hyperoxemic condition (100 -- 200 mmHg) in anaesthetised dogs. In this range of PaO2 traditional pulse-oximeters cannot be applied as the arterial haemoglobin is fully saturated and the measurement return by the instrument is > 98%. The only way to assess the oxygenation status is arterial blood gas analysis, which is invasive, intermittent and challenging.
The primary aim of the study was to investigate the relationship between the ORi, a parameter measured non-invasively with a multi-wavelength pulse co-oximeter, and PaO2, measured with the arterial blood gas analysis. A second goal was to trace how did the ORi change at changing the inspired fraction of oxygen (FiO2) in order to estimate the error of single ORi measurement from the scattering of ORi values. Ultimately, we focused on finding cut-off values of ORi that indicate upper-limits for PaO2 that have clinical application.
The study enrolled 16 dogs undergoing general anaesthesia for elective procedures requiring the insertion of an arterial catheter and mechanical ventilation. An adhesive sensor was wrapped around the tongue and connected to a pulse co-oximeter (Rad 97, Masimo Corp.) that calculated the ORi. For each dog at least 2 arterial blood samples were collected for analysis.
A total of 35 paired measurements were collected. A moderate positive correlation was observed between ORi and PaO2 with the correlation coefficient of 0.68. Tracing the ORi probes we calculated the error of single ORi measurement that was 0.02. The Youden index was used to identify 0.55 as value of ORi able to detect a PaO2 > 150 mmHg with the highest sensitivity and specificity.
We can conclude that ORi can be used as a non-invasive monitoring of blood oxygenation status in anaesthetized dogs since it’s variation reflects the variation of the PaO2, although it does not replace blood gas analysis for assessment of oxygenation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The ability of oxygen reserve index to detect mild hyperoxemia in mechanically ventilated dogs: a preliminary study
No full textIntroduction:Mild hyperoxemia in humans could be detected with the oxygen reserve index (ORi) for arterial partial pressure of oxygen (PaO2) between 100 and 200 mmHg. This study evaluated the correlation of ORi with PaO2 and its ability to detect mild hyperoxemia in dogs.
Methods:This prospective observational study enrolled 23 adult anesthetized dogs undergoing elective procedures. The animals were ventilated under pressure-control ventilation with a peak inspiratory pressure of 10–12cm H2O and a respiratory rate adjusted to maintain normocapnia. Simultaneous measurements of ORi and PaO2 were collected, with a multi-wavelength pulse co-oximeter with a probe applied to the dog’s tongue, and a blood gas analyzer, respectively. Pearson correlation coefficient (r) was calculated between simultaneous measurements of ORi and PaO2. Youden index was used toidentify the ORi cutoff values predicting PaO2 hyperoxia thresholds ≥110, ≥120, ≥130, ≥140, and ≥150 mm Hg with the highest sensitivity and specificity. Diagnostic performances of ORi to detect the same hyperoxia thresholds were estimated using the area under the receiver operating characteristic curve (AUROC).The effects of perfusion index (PI),body temperature, arterial blood pH, partial pressure of carbon dioxide (pCO2), lactatemia, and hemoglobin on AUROC were evaluated.
Results: A total of 56 paired measurements of ORi and PaO2 were collected. Mean PaO2 value was 148.8 ±32.48 mm Hg and mean hemoglobin was 12.58±1.84 g/dL. A moderate positive correlation (r=0.53,P<0.001) between ORi and PaO2 was found. The ORicutoff value with the highest sensitivity (91%) was 0.3, indicating PaO2 ≥120 mm Hg, with 70% specificity and AUROC=0.84 (95%CI=0.68–1.01). The ORi value cutoff with the highest specificity (86%) was 0.6, indicating PaO2≥140 mm Hg, with 60% sensitivity and AUROC=0.79 (95% CI=0.67–0.91). The AUROCs of ORito detect hyperoxia thresholds tended to increase with decreasing blood pH, PI, and lactatemia and with increasing pCO2 and temperature, while hemoglobin did not affect diagnostic performance of ORi.
Conclusions: ORi may detect mild hyperoxemia with PaO2 between120 and 140 mm Hg and limit excessive hyperoxia in mechanically ventilated dogs, although it does not replace blood gas analysis for assessment of oxygenation
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Oxygen reserve index to predict oxygen status in anaesthetized dogs
No full textOxygen reserve index (ORi) is a non-invasive continuous parameter ranging from 0 to 1 that positively correlates with arterial oxygen content (PaO2) between 100-200 mmHg in humans. This prospective study investigated the relationship of ORi with PaO2, and its use to predict oxygen content in dogs.
In 21 anaesthetised mechanically ventilated healthy dogs undergoing elective procedures, PaO2 was measured by a blood gas analyser and at the time of blood collection the ORi recorded by Masimo multi-wavelength pulse CO-oximeter. Pearson coefficient (r) was used to assess the correlation between ORi and PaO2. To identify if factors known to affect the pulse oximeter reading, such as the weight, local perfusion, pH, PaCO2, and temperature, influenced ORi measurements, paired data were fitted in a linear model and the correlation between the model residuals and the confounders was calculated. Youden index was used to identify the ORi value that predicted PaO2 ≥ 150 mmHg with the highest sensitivity and specificity.
A total of 51 paired measurements of ORi and PaO2 were collected, and a moderate positive correlation (r = 0.6) was found. Plethysmographic curve appeared to influence the accuracy of ORi rather than the perfusion index. Only body weight mildly affected ORi measurements (r = 0.48, p < 0.05). An ORi ≥ 0.48 indicated a PaO2 ≥ 150 mmHg with as sensitivity of 87%.
The oxygen reserve index may be used to titrate oxygen administration in anaesthetised dogs, although it does not replace blood gas analysis for arterial oxygen content measurement
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