31 research outputs found
Radiative Emission Mechanisms of Tidal Disruption Events
We describe how the various outcomes of stellar tidal disruption give rise to
observable radiation. We separately consider the cases where gas circularizes
rapidly into an accretion disc, as well as the case when shocked debris streams
provide the observable emission without having fully circularized. For the
rapid circularization case, we describe how outflows, absorption by
reprocessing layers, and Comptonization can cause the observed radiation to
depart from that of a bare disc, possibly giving rise to the observed
optical/UV emission along with soft X-rays from the disc. If, instead, most of
the debris follows highly eccentric orbits for a significant time, many
properties of the observed optical/UV emission can be explained by the scale of
those eccentric orbits and the shocks embedded in the debris flow near orbital
apocenter. In this picture, soft X-ray emission at early times results from the
smaller amount of debris mass deflected into a compact accretion disc by weak
shocks near the stellar pericenter. A general proposal for the near-constancy
of the ultraviolet/optical color temperatures is provided, by linking it to
incomplete thermalization of radiation in the atmosphere of the emitting
region. We also briefly discuss the radio signals from the interaction of
unbound debris and jets with the black hole environment.Comment: Accepted for publication in Springer Space Science Reviews. Chapter
in ISSI review "The Tidal Disruption of Stars by Massive Black Holes" vol. 7
Serum Antibody Levels to the Pneumocystis jirovecii Major Surface Glycoprotein in the Diagnosis of P. jirovecii Pneumonia in HIV+ Patients
infection has never been developed. major surface glycoprotein recombinant fragment C1 (MsgC1) in 110 HIV+ patients with active PcP (cases) and 63 HIV+ patients with pneumonia due to other causes (controls) by an enzyme-linked immunosorbent assay (ELISA). The cases had significantly higher IgG and IgM antibody levels to MsgC1 than the controls at hospital admission (week 0) and intervals up to at least 1 month thereafter. The sensitivity, specificity and positive predictive value (PPV) of IgG antibody levels increased from 57.2%, 61.7% and 71.5% at week 0 to 63.4%, 100%, and 100%, respectively, at weeks 3–4. The sensitivity, specificity and PPV of IgM antibody levels rose from 59.7%, 61.3%, and 79.3% at week 0 to 74.6%, 73.7%, and 89.8%, respectively, at weeks 3–4. Multivariate analysis revealed that a diagnosis of PcP was the only independent predictor of high IgG and IgM antibody levels to MsgC1. A high LDH level, a nonspecific marker of lung damage, was an independent predictor of low IgG antibody levels to MsgC1.The results suggest that the ELISA shows promise as an aid to the diagnosis of PCP in situations where diagnostic procedures cannot be performed. Further studies in other patient populations are needed to better define the usefulness of this serologic test
Healthcare Worker Occupation and Immune Response to Pneumocystis jirovecii
Humans may be a reservoir for this pathogen and transmit it from person to person
Dihydropteroate synthase mutations in Pneumocystis pneumonia: impact of applying different definitions of prophylaxis, mortality endpoints and mutant in a single cohort
Pneumocystis jirovecii dihydropteroate synthase (DHPS) gene mutations are well-reported. Although sulfa prophylaxis generally is associated with DHPS mutant infection, whether mutant infection is associated with poorer clinical outcomes is less clear. The differing definitions of sulfa prophylaxis and the different mortality endpoints used in these studies may be one explanation for the conflicting study results. Applying different definitions of prophylaxis, mortality endpoints and DHPS mutant to 301 HIV-infected patients with Pneumocystis pneumonia, we demonstrate that prophylaxis, irrespective of definition, increased the risk of infection with pure mutant (any prophylaxis: AOR 4.00, 95% CI: 1.83–8.76, p0.05). Future studies should standardize key variables associated with DHPS mutant infection as well as examine DHPS mutant subtypes (pure mutant vs. mixed infections) – perhaps even individual DHPS mutant genotypes – so that data can be pooled to better address this issue
The spectral evolution of AT 2018dyb and the presence of metal lines in tidal disruption events
We present light curves and spectra of the tidal disruption event (TDE)
ASASSN-18pg / AT 2018dyb spanning a period of one year. The event shows a
plethora of strong emission lines, including the Balmer series, He II, He I and
metal lines of O III 3760 and N III 4100, 4640
(blended with He II). The latter lines are consistent with originating from the
Bowen fluorescence mechanism. By analyzing literature spectra of past events,
we conclude that these lines are common in TDEs. The spectral diversity of
optical TDEs is thus larger than previously thought and includes N-rich events
besides H- and He-rich events. We study how the spectral lines evolve with
time, by means of their width, relative strength, and velocity offsets. The
velocity width of the lines starts at 13000 km s and decreases
with time. The ratio of He II to N III increases with time. The same is true
for ASASSN-14li, which has a very similar spectrum to AT 2018dyb but its lines
are narrower by a factor of 2. We estimate a black hole mass of
= by using the -
relation. This is consistent with the black hole mass derived using the MOSFiT
transient fitting code. The detection of strong Bowen lines in the optical
spectrum is an indirect proof for extreme ultraviolet and (reprocessed) X-ray
radiation and favors an accretion origin for the TDE optical luminosity. A
model where photons escape after multiple scatterings through a super-Eddington
thick disk and its optically thick wind, viewed at an angle close to the disk
plane, is consistent with the observations.Comment: Accepted version. Updated with new photometry and spectra, including
an X-shooter spectrum used to determine the BH mass. Two more figures added
and line measurements tabulated. No significant scientific updates and the
conclusions remain unaffecte
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Healthcare worker occupation and immune response to Pneumocystis jirovecii.
The reservoir and mode of transmission of Pneumocystis jirovecii remain uncertain. We conducted a cross-sectional study of 126 San Francisco General Hospital staff in clinical (n = 103) and nonclinical (n = 23) occupations to assess whether occupational exposure was associated with immune responses to P. jirovecii. We examined antibody levels by ELISA for 3 overlapping fragments that span the P. jirovecii major surface glycoprotein (Msg): MsgA, MsgB, and MsgC1. Clinical occupation participants had higher geometric mean antibody levels to MsgC1 than did nonclinical occupation participants (21.1 vs. 8.2, p = 0.004); clinical occupation was an independent predictor of higher MsgC1 antibody levels (parameter estimate = 0.89, 95% confidence interval 0.29-1.48, p = 0.003). In contrast, occupation was not significantly associated with antibody responses to either MsgA or MsgB. Healthcare workers may have occupational exposure to P. jirovecii. Humans may be a reservoir for P. jirovecii and may transmit it from person to person
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Antibody responses against Pneumocystis jirovecii in health care workers over time.
In a previous cross-sectional study, we showed that clinical staff working in a hospital had significantly higher antibody levels than nonclinical staff to Pneumocystis jirovecii. We conducted a longitudinal study, described here, to determine whether occupation and self-reported exposure to a patient with P. jirovecii pneumonia were associated with antibody levels to P. jirovecii over time. Baseline and quarterly serum specimens were collected and analyzed by using an ELISA that targeted different variants of the Pneumocystis major surface glycoprotein (MsgA, MsgB, MsgC1, MsgC3, MsgC8, and MsgC9). Clinical staff had significantly higher estimated geometric mean antibody levels against MsgC1 and MsgC8 than did nonclinical staff over time. Significant differences were observed when we compared the change in antibody levels to the different MsgC variants for staff who were and were not exposed to P. jirovecii pneumonia-infected patients. MsgC variants may serve as indicators of exposure to P. jirovecii in immunocompetent persons
Antibody Responses against Pneumocystis jirovecii in Health Care Workers Over Time
In a previous cross-sectional study, we showed that clinical staff working in a hospital had significantly higher antibody levels than nonclinical staff to Pneumocystis jirovecii. We conducted a longitudinal study, described here, to determine whether occupation and self-reported exposure to a patient with P. jirovecii pneumonia were associated with antibody levels to P. jirovecii over time. Baseline and quarterly serum specimens were collected and analyzed by using an ELISA that targeted different variants of the Pneumocystis major surface glycoprotein (MsgA, MsgB, MsgC1, MsgC3, MsgC8, and MsgC9). Clinical staff had significantly higher estimated geometric mean antibody levels against MsgC1 and MsgC8 than did nonclinical staff over time. Significant differences were observed when we compared the change in antibody levels to the different MsgC variants for staff who were and were not exposed to P. jirovecii pneumonia–infected patients. MsgC variants may serve as indicators of exposure to P. jirovecii in immunocompetent persons