678 research outputs found
APEX-CHAMP+ high-J CO observations of low-mass young stellar objects: II. Distribution and origin of warm molecular gas
The origin and heating mechanisms of warm (50<T<200 K) molecular gas in
low-mass young stellar objects (YSOs) are strongly debated. Both passive
heating of the inner collapsing envelope by the protostellar luminosity as well
as active heating by shocks and by UV associated with the outflows or accretion
have been proposed. We aim to characterize the warm gas within protosteller
objects, and disentangle contributions from the (inner) envelope, bipolar
outflows and the quiescent cloud. High-J CO maps (12CO J=6--5 and 7--6) of the
immediate surroundings (up to 10,000 AU) of eight low-mass YSOs are obtained
with the CHAMP+ 650/850 GHz array receiver mounted on the APEX telescope. In
addition, isotopologue observations of the 13CO J=6--5 transition and [C I]
3P_2-3P_1 line were taken. Strong quiescent narrow-line 12CO 6--5 and 7--6
emission is seen toward all protostars. In the case of HH~46 and Ced 110 IRS 4,
the on-source emission originates in material heated by UV photons scattered in
the outflow cavity and not just by passive heating in the inner envelope. Warm
quiescent gas is also present along the outflows, heated by UV photons from
shocks. Shock-heated warm gas is only detected for Class 0 flows and the more
massive Class I sources such as HH~46. Outflow temperatures, estimated from the
CO 6--5 and 3--2 line wings, are ~100 K, close to model predictions, with the
exception of the L~1551 IRS 5 and IRAS 12496-7650, for which temperatures <50 K
are found. APEX-CHAMP+ is uniquely suited to directly probe a protostar's
feedback on its accreting envelope gas in terms of heating, photodissociation,
and outflow dispersal by mapping 1'x1' regions in high-J CO and [C I] lines.Comment: 18 pages, accepted by A&A, A version with the figures in higher
quality can be found on my website: http://www.cfa.harvard.edu/~tvankemp
Are language production problems apparent in adults who no longer meet diagnostic criteria for attention-deficit/hyperactivity disorder?
In this study, we examined sentence production in a sample of adults (Nâ=â21) who had had attention-deficit/hyperactivity disorder (ADHD) as children, but as adults no longer met DSM-IV diagnostic criteria (APA, 2000). This âremittedâ group was assessed on a sentence production task. On each trial, participants saw two objects and a verb. Their task was to construct a sentence using the objects as arguments of the verb. Results showed more ungrammatical and disfluent utterances with one particular type of verb (i.e., participle). In a second set of analyses, we compared the remitted group to both control participants and a âpersistentâ group, who had ADHD as children and as adults. Results showed that remitters were more likely to produce ungrammatical utterances and to make repair disfluencies compared to controls, and they patterned more similarly to ADHD participants. Conclusions focus on language output in remitted ADHD, and the role of executive functions in language production
Spin-dependent transport in metal/semiconductor tunnel junctions
This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. A transport model is presented that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin-splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunnelling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface.
Measurements are presented of the circular-polarization-dependent photocurrent (the so-called helicity asymmetry) in thin-film tunnel junctions of Co/Al2O3/GaAs. In the absence of a tunnel barrier, the helicity asymmetry is caused by magneto-optical effects (magnetic circular dichroism). In the case where a tunnel barrier is present, the data cannot be explained by magneto-optical effects alone; the deviations provide evidence that spin-polarized tunnelling due to optical spin orientation occurs. In Co/Ï-MnAl/AlAs/GaAs junctions no deviations from the magneto-optical effects are observed, most probably due to the weak spin polarization of Ï-MnAl along the tunnelling direction; the latter is corroborated by bandstructure calculations. Finally, the application of photoexcited GaAs for spin-polarized tunnelling in a scanning tunnelling microscope is discussed.
Herschel observations of the hydroxyl radical (OH) in young stellar objects
Water in Star-forming regions with Herschel (WISH) is a Herschel Key Program
investigating the water chemistry in young stellar objects (YSOs) during
protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical
network most closely linked to the formation and destruction of H2O.
High-temperature chemistry connects OH and H2O through the OH + H2 H2O + H
reactions. Formation of H2O from OH is efficient in the high-temperature regime
found in shocks and the innermost part of protostellar envelopes. Moreover, in
the presence of UV photons, OH can be produced from the photo-dissociation of
H2O. High-resolution spectroscopy of the OH 163.12 micron triplet towards HH 46
and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far
Infrared (HIFI) on board Herschel. The low- and intermediate-mass YSOs HH 46,
TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were
observed with the Photodetector Array Camera and Spectrometer (PACS) in four
transitions of OH and two [OI] lines. The OH transitions at 79, 84, 119, and
163 micron and [OI] emission at 63 and 145 micron were detected with PACS
towards the class I low-mass YSOs as well as the intermediate-mass and class I
Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333
IRAS 2A, though the 119 micron was detected in absorption. With HIFI, the
163.12 micron was not detected from HH 46 and only tentatively detected from
NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46
constrains the line width (FWHM > 11 km/s) and indicates that the OH emission
likely originates from shocked gas. This scenario is supported by trends of the
OH flux increasing with the [OI] flux and the bolometric luminosity. Similar OH
line ratios for most sources suggest that OH has comparable excitation
temperatures despite the different physical properties of the sources.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue
Chronic medical conditions and mental health in older people: disability and psychosocial resources mediate specific mental health effects
HERSCHEL-HIFI spectroscopy of the intermediate mass protostar NGC7129 FIRS 2
HERSCHEL-HIFI observations of water from the intermediate mass protostar
NGC7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this
star formation environment. Six spectral settings, covering four H216O and two
H218O lines, were observed and all but one H218O line were detected. The four
H2 16 O lines discussed here share a similar morphology: a narrower, \approx 6
km/s, component centered slightly redward of the systemic velocity of NGC7129
FIRS 2 and a much broader, \approx 25 km/s component centered blueward and
likely associated with powerful outflows. The narrower components are
consistent with emission from water arising in the envelope around the
intermediate mass protostar, and the abundance of H2O is constrained to \approx
10-7 for the outer envelope. Additionally, the presence of a narrow
self-absorption component for the lowest energy lines is likely due to
self-absorption from colder water in the outer envelope. The broader component,
where the H2O/CO relative abundance is found to be \approx 0.2, appears to be
tracing the same energetic region that produces strong CO emission at high J.Comment: 6 pages, 4 figures, accepted by A&
The decline and rise of neighbourhoods: the importance of neighbourhood governance
There is a substantial literature on the explanation of neighbourhood change. Most of this literature concentrates on identifying factors and developments behind processes of decline. This paper reviews the literature, focusing on the identification of patterns of neighbourhood change, and argues that the concept of neighbourhood governance is a missing link in attempts to explain these patterns. Including neighbourhood governance in the explanations of neighbourhood change and decline will produce better explanatory models and, finally, a better view about what is actually steering neighbourhood change
Erratum to: Circulating tumor DNA as a biomarker for monitoring early treatment responses of patients with advanced lung adenocarcinoma receiving immune checkpoint inhibitors.
The following error appeared in Section 3.5 in Ref. [1]. Instead of âProgressive disease-L1 expression data were available for 87 patientsâ, the text should read âPD-L1 expression data were available for 87 patientsâ. We apologize for this error.</p
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