2,938 research outputs found
Attenuation of TeV -rays by the starlight photon field of the host galaxy
The absorption of TeV -ray photons produced in relativistic jets by
surrounding soft photon fields is a long-standing problem of jet physics. In
some cases the most likely emission site close to the central black hole is
ruled out because of the high opacity caused by strong optical and infrared
photon sources, such as the broad line region. Mostly neglected for jet
modeling is the absorption of -rays in the starlight photon field of
the host galaxy. Analyzing the absorption for arbitrary locations and
observation angles of the -ray emission site within the host galaxy we
find that the distance to the galaxy center, the observation angle, and the
distribution of starlight in the galaxy are crucial for the amount of
absorption. We derive the absorption value for a sample of TeV detected
blazars with a redshift . The absorption value of the -ray
emission located in the galaxy center may be as high as with an average
value of . This is important in order to determine the intrinsic blazar
parameters. We see no significant trends in our sample between the degree of
absorption and host properties, such as starlight emissivity, galactic size,
half-light radius, and redshift. While the uncertainty of the spectral
properties of the extragalactic background light exceeds the effect of
absorption by stellar light from the host galaxy in distant objects, the latter
is a dominant effect in nearby sources. It may also be revealed in a
differential comparison of sources with similar redshifts.Comment: 9 pages, 4 figures; accepted for publication in MNRA
Fast Variations of Gamma-Ray Emission in Blazars
The largest group of sources identified by EGRET are Blazars. This sub-class
of AGN is well known to vary in flux in all energy bands on time-scales ranging
from a few minutes (in the optical and X-ray bands) up to decades (radio and
optical regimes). In addition to variations of the gamma-ray flux between
different viewing periods, the brightest of these sources showed a few
remarkable gamma-ray flares on time-scales of about one day, confirming the
extension of the ``Intraday-Variability (IDV)'' phenomenon into the GeV range.
We present first results of a systematic approach to study fast variability
with EGRET data. This statistical approach confirms the existence of IDV even
during epochs when no strong flares are detected. This provides additional
constraints on the site of the gamma-ray emission and allows cross-correlation
analyses with light curves obtained at other frequencies even during periods of
low flux. We also find that some stronger sources have fluxes systematically
above threshold even during quiescent states. Despite the low count rates this
allows explicit comparisons of flare amplitudes with other energy bands.Comment: 5 pages including figures, LaTex, uses aipproc.sty, to appear in the
proceedings of the 4th Compton Symposium at Williamsburg, V
Supporting Treatment Adherence Readiness through Training (START) for patients with HIV on antiretroviral therapy: study protocol for a randomized controlled trial.
BackgroundFew HIV antiretroviral adherence interventions target patients before they start treatment, assess adherence readiness to determine the timing of treatment initiation, or tailor the amount of adherence support. The Supporting Treatment Adherence Readiness through Training (START) intervention, based on the information-motivation-behavioral skills model of behavior change, is designed to address these gaps with the inclusion of (1) brief pill-taking practice trials for enhancing pretreatment adherence counseling and providing a behavioral criterion for determining adherence readiness and the timing of treatment initiation and (2) a performance-driven dose regulation mechanism to tailor the amount of counseling to the individual needs of the patient and conserve resources. The primary aim of this randomized controlled trial is to examine the effects of START on antiretroviral adherence and HIV virologic suppression.Methods/designA sample of 240 patients will be randomized to receive START or usual care at one of two HIV clinics. Primary outcomes will be optimal dose-taking adherence (>85 % prescribed doses taken), as measured with electronic monitoring caps, and undetectable HIV viral load. Secondary outcomes will include dose-timing adherence (>85 % prescribed doses taken on time) and CD4 count. Primary endpoints will be month 6 (short-term effect) and month 24 (to test durability of effect), though electronic monitoring will be continuous and a fully battery of assessments will be administered every 6 months for 24 months.DiscussionIf efficacious and cost-effective, START will provide clinicians with a model for assessing patient adherence readiness and helping patients to achieve and sustain readiness and optimal treatment benefits.Trial registrationClinicalTrials.gov identifier NCT02329782 . Registered on 22 December 2014
Variability Time Scales of TeV Blazars Observed in the ASCA Continuous Long-Look X-ray Monitoring
Three uninterrupted, long (lasting respectively 7, 10, and 10 days) ASCA
observations of the well-studied TeV-bright blazars Mrk 421, Mrk 501 and PKS
2155-304 all show continuous strong X-ray flaring. Despite the relatively faint
intensity states in 2 of the 3 sources, there was no identifiable quiescent
period in any of the observations. Structure function analysis shows that all
blazars have a characteristic time scale of ~ a day, comparable to the
recurrence time and to the time scale of the stronger flares. On the other
hand, examination of these flares in more detail reveals that each of the
strong flares is not a smooth increase and decrease, but exhibits substructures
of shorter flares having time scales of ~10 ks. We verify via simulations that
in order to explain the observed structure function, these shorter flares
("shots") are unlikely to be fully random, but in some way are correlated with
each other. The energy dependent cross-correlation analysis shows that
inter-band lags are not universal in TeV blazars. This is important since in
the past, only positive detections of lags were reported. In this work, we
determine that the sign of a lag may differ from flare to flare; significant
lags of both signs were detected from several flares, while no significant lag
was detected from others. However, we also argue that the nature of the
underlying component can affect these values. The facts that all flares are
nearly symmetric and that fast variability shorter than the characteristic time
scale is strongly suppressed, support the scenario where the light crossing
time dominates the variability time scales of the day-scale flares.Comment: 29 pages, 12 figures, accepted for publication in Ap
Facial expressions of pain: the role of the serotonergic system
Rationale
Although interest in the neurobiology of facial communication of pain has increased over the last decades, little is known about which neurotransmitter systems might be involved in regulating facial expressions of pain.
Objectives
We aim to investigate whether the serotonergic system (5-HT), which has been implicated in various aspects of pain processing as well as in behavioral response inhibition, might play a role in facial expressions of pain. Using acute tryptophan depletion (ATD) to manipulate 5-HT function, we examined its effects on facial and subjective pain responses.
Methods
In a double-blind, placebo-controlled within-subject design, 27 participants received either an ATD or a control drink in two separate sessions. Approximately 5-h post-oral consumption, we assessed pain thresholds (heat, pressure) as well as facial and subjective responses to phasic heat pain. Moreover, situational pain catastrophizing and mood were assessed as affective state indicators.
Results
ATD neither influenced pain thresholds nor self-report ratings, nor catastrophizing or mood. Only facial responses were significantly affected by ATD. ATD led to a decrease in pain-indicative as well as in pain-non-indicative facial responses to painful heat, compared to the control condition.
Conclusions
Decrease in brain 5-HT synthesis via ATD significantly reduced facial responses to phasic heat pain; possibly due to (i) diminished disposition to display social behavior or due to (ii) decreased facilitation of excitatory inputs to the facial motor neuron
Outlaw Community Innovations
Recent studies of outlaw communities provide qualitative evidence of their existence and the organisation of the underlying innovation processes. We provide descriptive results from a large scale survey of two online outlaw communities focussing on Microsoft's XBox. In line with previous findings, we identify two types of participants in outlaw communities - user innovators and adopters. Based on 2,256 responses, we find that users modify their XBox mainly to be able to increase the set of available functions of their XBox. Users are also motivated to modify their XBox for the sake of having fun and to conduct pirate behaviour. Finally, the results from our survey suggest that user innovators are largely intrinsically motivated by fun and the intellectual stimulation of writing code for homebrew software
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