650 research outputs found
Non-Thermal Emission from AGN Coronae
Accretion disk coronae are believed to account for X-ray emission in Active
Galactic Nuclei (AGNs). In this paper the observed emission is assumed to be
due to a population of relativistic, non-thermal electrons (e.g. produced in a
flare) injected at the top of an accretion disk magnetic loop. While electrons
stream along magnetic field lines their energy distribution evolves in time
essentially because of inverse Compton and synchrotron losses. The
corresponding time dependent emission due, in the X-ray energy range, to the
inverse Compton mechanism, has been computed. Since the typical decay time of a
flare is shorter than the integration time for data acquisition in the X-ray
domain, the resulting spectrum is derived as the temporal mean of the real,
time-dependent, emission, as originated by a series of consecutive and
identical flares. The model outcome is compared to both the broad band BeppoSAX
X-ray data of the bright Seyfert 1 NGC 5548, and to a few general X-ray
spectral properties of Seyfert 1s as a class. The good agreement between model
and observations suggests that the presently proposed non-thermal,
non-stationary model could be a plausible explanation of AGN X-ray emission, as
an alternative to thermal coronae models.Comment: 15 pages, 4 postscript figure
Association between cognitive performance and cortical glucose metabolism in patients with mild Alzheimer's disease
Background: Neuronal and synaptic function in Alzheimer's disease (AD) is measured in vivo by glucose metabolism using positron emission tomography (PET). Objective: We hypothesized that neuronal activation as measured by PET is a more sensitive index of neuronal dysfunction than activity during rest. We investigated if the correlations between dementia severity as measured with the Mini Mental State Examination (MMSE) and glucose metabolism are an artifact of brain atrophy. Method: Glucose metabolism was measured using {[}F-18]fluorodeoxyglucose PET during rest and activation due to audiovisual stimulation in 13 mild to moderate AD patients (MMSE score >= 17). PET data were corrected for brain atrophy. Results: In the rest condition, glucose metabolism was correlated with the MMSE score primarily within the posterior cingulate and parietal lobes. For the activation condition, additional correlations were within the primary and association audiovisual areas. Most local maxima remained significant after correcting for brain atrophy. Conclusion: PET activity measured during audiovisual stimulation was more sensitive to functional alterations in glucose metabolism in AD patients compared to the resting PET. The association between glucose metabolism and MMSE score was not dependent on brain atrophy. Copyright (C) 2005 S. Karger AG, Basel
Radiographic parameters of the digit in a cohort population of amiata donkeys
Background: The most common musculoskeletal conditions reported in donkeys are related to the foot. Radiographic examinations are clinically important in the diagnosis of foot abnormalities and are commonly used. However, few studies have been conducted to establish the normal radiographic appearance of a donkey’s foot. Aim: To determine the radiographic features of the front digit in healthy Amiata donkeys. Methods: Radiographic examinations were performed on 56 forefeet of 28 Amiata donkeys. Three radiographic views of each front foot were taken: lateromedial, dorsopalmar and dorso-65°proximal/palmarodistal oblique. Seventeen angular and linear radiographic parameters and the crena solearis were evaluated in all forefeet, and 18 morphometric parameters were evaluated in 16 out of 56 forefeet. Statistical analysis was carried out on all the measures assessed. Results: The radiographic appearance of the forefoot was ascertained, and data were reported as median ± standard error, minimum and maximum values. No statistical differences were obtained between the right and left forefeet. Conclusion: The normal baseline parameters of the forefeet of Amiata donkeys were recorded and described and compared with other donkey breeds and horses. The findings highlighted that the donkey breed affects the radiographic parameters of the digit
Distribution of the integral membrane protein NADH-cytochrome b5 reductase in rat liver cells, studied with a quantitative radioimmunoblotting assay
Reconstructing individual responses to direct questions: a new method for reconstructing malingered responses
Introduction: The false consensus effect consists of an overestimation of how common a subject opinion is among other people. This research demonstrates that individual endorsement of questions may be predicted by estimating peers’ responses to the same question. Moreover, we aim to demonstrate how this prediction can be used to reconstruct the individual’s response to a single item as well as the overall response to all of the items, making the technique suitable and effective for malingering detection. Method: We have validated the procedure of reconstructing individual responses from peers’ estimation in two separate studies, one addressing anxiety-related questions and the other to the Dark Triad. The questionnaires, adapted to our scopes, were submitted to the groups of participants for a total of 187 subjects across both studies. Machine learning models were used to estimate the results. Results: According to the results, individual responses to a single question requiring a “yes” or “no” response are predicted with 70–80% accuracy. The overall participant-predicted score on all questions (total test score) is predicted with a correlation of 0.7–0.77 with actual results. Discussion: The application of the false consensus effect format is a promising procedure for reconstructing truthful responses in forensic settings when the respondent is highly likely to alter his true (genuine) response and true responses to the tests are missing
On the observed distributions of black hole masses and Eddington ratios from radiation pressure corrected virial indicators
The application of the virial theorem to the Broad Line Region of Active
Galactic Nuclei allows Black Hole mass estimates for large samples of objects
at all redshifts. In a recent paper we showed that ionizing radiation pressure
onto BLR clouds affects virial BH mass estimates and we provided empirically
calibrated corrections. More recently, a new test of the importance of
radiation forces has been proposed: the MBH-sigma relation has been used to
estimate MBH for a sample of type-2 AGN and virial relations (with and without
radiation pressure) for a sample of type-1 AGN extracted from the same parent
population. The observed L/LEdd distribution based on virial BH masses is in
good agreement with that based on MBH-sigma only if radiation pressure effects
are negligible, otherwise significant discrepancies are observed. In this paper
we investigate the effects of intrinsic dispersions associated to the virial
relations providing MBH, and we show that they explain the discrepancies
between the observed L/LEdd distributions of type-1 and type-2 AGN. These
discrepancies in the L/LEdd distributions are present regardless of the general
importance of radiation forces, which must be negligible only for a small
fraction of sources with large L/LEdd. Average radiation pressure corrections
should then be applied in virial MBH estimators until their dependence on
observed source physical properties has been fully calibrated. Finally, the
comparison between MBH and L/LEdd distributions derived from sigma-based and
virial estimators can constrain the variance of BLR physical properties in AGN.Comment: Astrophysical Journal Letters, in pres
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