2,408 research outputs found
Unobscured Type 2 Active Galactic Nuclei
Type 2 active galactic nuclei (AGNs) with intrinsically weak broad emission lines (BELs) would be exceptions to the unified model. After examining a number of proposed candidates critically, we find that the sample is contaminated significantly by objects with BELs of strengths indicating that they actually contain intermediate-type AGNs, plus a few Compton-thick sources as revealed by extremely low ratios of X-ray to nuclear IR luminosities. We develop quantitative metrics that show two (NGC 3147 and NGC 4594) of the remaining candidates to have BELs 2-3 orders of magnitude weaker than those of typical type 1 AGNs. Several more galaxies remain as candidates to have anomalously weak BELs, but this status cannot be confirmed with the existing information. Although the parent sample is poorly defined, the two confirmed objects are well under 1% of its total number of members, showing that the absence of a BEL is possible, but very uncommon in AGN. We evaluate these two objects in detail using multi-wavelength measurements including new IR data obtained with Spitzer and ground-based optical spectropolarimeteric observations. They have little X-ray extinction with N_H < ~10^(21) cm^(–2). Their IR spectra show strong silicate emission (NGC 4594) or weak aromatic features on a generally power-law continuum with a suggestion of silicates in emission (NGC 3147). No polarized BEL is detected in NGC 3147. These results indicate that the two unobscured type 2 objects have circumnuclear tori that are approximately face-on. Combined with their X-ray and optical/UV properties, this behavior implies that we have an unobscured view of the nuclei and thus that they have intrinsically weak BELs. We compare their properties with those of the other less-extreme candidates. We then compare the distributions of bolometric luminosities and accretion rates of these objects with theoretical models that predict weak BELs
Attachment-based family therapy for adolescents with suicidal ideation: a randomized controlled trial.
OBJECTIVE: To evaluate whether Attachment-Based Family Therapy (ABFT) is more effective than Enhanced Usual Care (EUC) for reducing suicidal ideation and depressive symptoms in adolescents. METHOD: This was a randomized controlled trial of suicidal adolescents between the ages of 12 and 17, identified in primary care and emergency departments. Of 341 adolescents screened, 66 (70% African American) entered the study for 3 months of treatment. Assessment occurred at baseline, 6 weeks, 12 weeks, and 24 weeks. ABFT consisted of individual and family meetings, and EUC consisted of a facilitated referral to other providers. All participants received weekly monitoring and access to a 24-hour crisis phone. Trajectory of change and clinical recovery were measured for suicidal ideation and depressive symptoms. RESULTS: Using intent to treat, patients in ABFT demonstrated significantly greater rates of change on self-reported suicidal ideation at post-treatment evaluation, and benefits were maintained at follow-up, with a strong overall effect size (ES = 0.97). Between-group differences were similar on clinician ratings. Significantly more patients in ABFT met criteria for clinical recovery on suicidal ideation post-treatment (87%; 95% confidence interval [CI] = 74.6-99.6) than patients in EUC (51.7%; 95% CI = 32.4-54.32). Benefits were maintained at follow-up (ABFT, 70%; 95% CI = 52.6-87.4; EUC 34.6%; 95% CI = 15.6-54.2; odds ratio = 4.41). Patterns of depressive symptoms over time were similar, as were results for a subsample of adolescents with diagnosed depression. Retention in ABFT was higher than in EUC (mean = 9.7 versus 2.9). CONCLUSIONS: ABFT is more efficacious than EUC in reducing suicidal ideation and depressive symptoms in adolescents. Additional research is warranted to confirm treatment efficacy and to test the proposed mechanism of change (the Family Safety Net Study).Clinical Trial Registry Information: Preventing Youth Suicide in Primary Care: A Family Model, URL: http://www.clinicaltrials.gov, unique identifier: NCT00604097
Unobscured Type 2 AGNs
Type 2 AGNs with intrinsically weak broad emission lines (BELs) would be
exceptions to the unified model. After examining a number of proposed
candidates critically, we find that the sample is contaminated significantly by
objects with BELs of strengths indicating that they actually contain
intermediate-type AGNs, plus a few Compton-thick sources as revealed by
extremely low ratios of X-ray to nuclear IR luminosities. We develop
quantitative metrics that show two (NGC 3147 and NGC 4594) of the remaining
candidates to have BELs 2-3 orders of magnitude weaker than those of typical
type-1 AGNs. Several more galaxies remain as candidates to have anomalously
weak BELs, but this status cannot be confirmed with the existing information.
Although the parent sample is poorly defined, the two confirmed objects are
well under 1% of its total number of members, showing that the absence of a BEL
is possible, but very uncommon in AGN. We evaluate these two objects in detail
using multi-wavelength measurements. They have little X-ray extinction with N_H
< 10^21 cm^{-2}. Their IR spectra show strong silicate emission (NGC 4594) or
weak aromatic features on a generally power law continuum with a suggestion of
silicates in emission (NGC 3147). No polarized BEL is detected in NGC 3147.
These results indicate that the two unobscured type-2 objects have
circumnuclear tori that are approximately face-on. Combined with their X-ray
and optical/UV properties, this behavior implies that we have an unobscured
view of the nuclei and thus that they have intrinsically weak BELs. We compare
their properties with those of the other less-extreme candidates. We then
compare the distributions of bolometric luminosities and accretion rates of
these objects with theoretical models that predict weak BELs.Comment: Accepted for publication in ApJ, 17 pages, 13 figure
Highly Polarized Optically-Selected BL Lacertae Objects
Observations of candidate BL Lacertae objects spectroscopically selected from
the Sloan Digital Sky Survey (SDSS) reveal a large fraction with high
polarization (P > 3%). This result confirms that synchrotron radiation makes an
important contribution to the observed optical continuum for most objects in
the sample. The SDSS sample can be divided into separate categories, with
objects of undetermined redshift generally having the highest optical
polarization. Polarization as high as 23% and the lack of spectral features
suggests that the synchrotron continuum completely dominates the spectra of
these sources. The mean polarization levels observed for objects having
measured redshifts is much lower, with the maximum observed polarization for
this group being ~10%. The lower polarizations of these objects are reminiscent
of the less spectacular polarization levels shown by BL Lac objects discovered
in X-ray surveys. We find no SDSS BL Lac candidates at z > 1 with P > 3%,
calling their classification as BL Lac objects into question. In addition, the
existence of radio-quiet BL Lac objects is not verified since none of 10
potentially radio-weak BL Lac candidates observed are highly polarized.
Regardless of whether the high-redshift and radio-weak objects are included in
this optical sample, the overall levels of polarization observed are
intermediate between those seen for X-ray and radio-selected BL Lac objects.Comment: 9 pages, 3 figures, 2 table
Gas-Phase Ambient Air Contaminants Exhibit Significant Dioxin-like and Estrogen-like Activity in Vitro
Several adverse health effects, such as respiratory and cardiovascular morbidity, have been linked to exposure to particulate matter in ambient air; however, the biologic activity of gas-phase ambient organic air contaminants has not been examined as thoroughly. Using aryl hydrocarbon receptor (AHR)–based and estrogen receptor (ER)–based cell bioassay systems, we assessed the dioxin-like and estrogenic activities of gas-phase organic ambient air contaminants compared with those of particulate-phase contaminants using samples collected between seasons over 2 years from an urban and a rural location in the Greater Toronto Area, Canada. The concentration of the sum (∑) of polycyclic aromatic hydrocarbons, which was highest in the gas phase, was 10–100 times more abundant than that of ∑polychlorinated biphenyls, ∑nitro-polycyclic aromatic hydrocarbons, and ∑organochlorine pesticides, and 10(3) to 10(4) times more abundant than ∑polychlorinated dibenzo-p-dioxins/dibenzofurans. Gas-phase samples induced significant AHR- and ER-dependent gene expression. The activity of the gas-phase samples was greater than that of the particulate-phase samples in the estrogen assay and, in one case, in the AHR assay. We found no strong associations between either summer or winter seasons or urban or rural locations in the relative efficacy of the extracts in either the ER or AHR assay despite differences in chemical composition, concentrations, and abundance. Our results suggest that mechanistic studies of the health effects of ambient air must consider gas and particulate phases because chemicals present in both phases can affect AHR and ER signaling pathways
Why do banks promise to pay par on demand?
We survey the theories of why banks promise to pay par on demand and examine evidence about
the conditions under which banks have promised to pay the par value of deposits and banknotes on
demand when holding only fractional reserves. The theoretical literature can be broadly divided into four
strands: liquidity provision, asymmetric information, legal restrictions, and a medium of exchange. We
assume that it is not zero cost to make a promise to redeem a liability at par value on demand. If so, then
the conditions in the theories that result in par redemption are possible explanations of why banks
promise to pay par on demand. If the explanation based on customers’ demand for liquidity is correct,
payment of deposits at par will be promised when banks hold assets that are illiquid in the short run. If
the asymmetric-information explanation based on the difficulty of valuing assets is correct, the
marketability of banks’ assets determines whether banks promise to pay par. If the legal restrictions
explanation of par redemption is correct, banks will not promise to pay par if they are not required to do
so. If the transaction explanation is correct, banks will promise to pay par value only if the deposits are
used in transactions. After the survey of the theoretical literature, we examine the history of banking in
several countries in different eras: fourth-century Athens, medieval Italy, Japan, and free banking and
money market mutual funds in the United States. We find that all of the theories can explain some of the
observed banking arrangements, and none explain all of them
High-Redshift SDSS Quasars with Weak Emission Lines
We identify a sample of 74 high-redshift quasars (z>3) with weak emission
lines from the Fifth Data Release of the Sloan Digital Sky Survey and present
infrared, optical, and radio observations of a subsample of four objects at
z>4. These weak emission-line quasars (WLQs) constitute a prominent tail of the
Lya+NV equivalent width distribution, and we compare them to quasars with more
typical emission-line properties and to low-redshift active galactic nuclei
with weak/absent emission lines, namely BL Lac objects. We find that WLQs
exhibit hot (T~1000 K) thermal dust emission and have rest-frame 0.1-5 micron
spectral energy distributions that are quite similar to those of normal
quasars. The variability, polarization, and radio properties of WLQs are also
different from those of BL Lacs, making continuum boosting by a relativistic
jet an unlikely physical interpretation. The most probable scenario for WLQs
involves broad-line region properties that are physically distinct from those
of normal quasars.Comment: Updated to match version published in ApJ. 20 pages, 12 figure
7th Annual Seminar on Securities Law
Materials from the UK/CLE 7th Annual Seminar on Securities Law held February 12-13, 1988
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