4,520 research outputs found
The Taurus Boundary of Stellar/Substellar (TBOSS) Survey I: far-IR disk emission measured with Herschel
With Herschel/PACS 134 low mass members of the Taurus star-forming region
spanning the M4-L0 spectral type range and covering the transition from low
mass stars to brown dwarfs were observed. Combining the new Herschel results
with other programs, a total of 150 of the 154 M4-L0 Taurus members members
have observations with Herschel. Among the 150 targets, 70um flux densities
were measured for 7 of the 7 ClassI objects, 48 of the 67 ClassII members, and
3 of the 76 ClassIII targets. For the detected ClassII objects, the median 70um
flux density level declines with spectral type, however, the distribution of
excess relative to central object flux density does not change across the
stellar/substellar boundary in the M4-L0 range. Connecting the 70um TBOSS
values with the results from K0-M3 ClassII members results in the first
comprehensive census of far-IR emission across the full mass spectrum of the
stellar and substellar population of a star-forming region, and the median flux
density declines with spectral type in a trend analogous to the flux density
decline expected for the central objects. SEDs were constructed for all TBOSS
targets covering the optical to far-IR range and extending to the submm/mm for
a subset of sources. Based on an initial exploration of the impact of different
physical parameters; inclination, scale height and flaring have the largest
influence on the PACS flux densities. From the 24um to 70um spectral index of
the SEDs, 5 new candidate transition disks were identified. The steep 24um to
70um slope for a subset of 8 TBOSS targets may be an indication of truncated
disks in these systems.Two examples of mixed pair systems that include
secondaries with disks were measured. Finally, comparing the TBOSS results with
a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks
around the Taurus substellar population.Comment: 64 pages, 33 figures, 12 tables, accepted for publication in A&
Decay of the Z Boson into Scalar Particles
In extensions of the standard model, light scalar particles are often
possible because of symmetry considerations. We study the decay of the Z boson
into such particles. In particular, we consider for illustration the scalar
sector of a recently proposed model of the 17-keV neutrino which satisfies all
laboratory, astrophysical, and cosmological constraints.Comment: 11 pages (2 figures, not included) (Revised, Oct 1992). Some
equations have been corrected and 1 figure has been eliminate
The Brown-dwarf Atmosphere Monitoring (BAM) Project II: Multi-epoch monitoring of extremely cool brown dwarfs
With the discovery of Y dwarfs by the WISE mission, the population of field
brown dwarfs now extends to objects with temperatures comparable to those of
Solar System planets. To investigate the atmospheres of these newly identified
brown dwarfs, we have conducted a pilot study monitoring an initial sample of
three late T-dwarfs (T6.5, T8 and T8.5) and one Y-dwarf (Y0) for infrared
photometric variability at multiple epochs. With J-band imaging, each target
was observed for a period of 1.0h to 4.5h per epoch, which covers a significant
fraction of the expected rotational period. These measurements represent the
first photometric monitoring for these targets. For three of the four targets
(2M1047, Ross 458C and WISE0458), multi-epoch monitoring was performed, with
the time span between epochs ranging from a few hours to ~2 years. During the
first epoch, the T8.5 target WISE0458 exhibited variations with a remarkable
min-to-max amplitude of 13%, while the second epoch light curve taken ~2 years
later did not note any variability to a 3% upper limit. With an effective
temperature of ~600 K, WISE0458 is the coldest variable brown dwarf published
to-date, and combined with its high and variable amplitude makes it a
fascinating target for detailed follow-up. The three remaining targets showed
no significant variations, with a photometric precision between 0.8% and 20.0%,
depending on the target brightness. Combining the new results with previous
multi-epoch observations of brown dwarfs with spectral types of T5 or later,
the currently identified variables have locations on the colour-colour diagram
better matched by theoretical models incorporating cloud opacities rather than
cloud-free atmospheres. This preliminary result requires further study to
determine if there is a definitive link between variability among late-T dwarfs
and their location on the colour-colour diagram.Comment: 9 pages, 6 figures, 3 tables, accepted for publication in MNRA
Dust masses of disks around 8 Brown Dwarfs and Very Low-Mass Stars in Upper Sco OB1 and Ophiuchus
We present the results of ALMA band 7 observations of dust and CO gas in the
disks around 7 objects with spectral types ranging between M5.5 and M7.5 in
Upper Scorpius OB1, and one M3 star in Ophiuchus. We detect unresolved
continuum emission in all but one source, and the CO J=3-2 line in two
sources. We constrain the dust and gas content of these systems using a grid of
models calculated with the radiative transfer code MCFOST, and find disk dust
masses between 0.1 and 1 M, suggesting that the stellar mass / disk
mass correlation can be extrapolated for brown dwarfs with masses as low as
0.05 M. The one disk in Upper Sco in which we detect CO emission, 2MASS
J15555600, is also the disk with warmest inner disk as traced by its H - [4.5]
photometric color. Using our radiative transfer grid, we extend the correlation
between stellar luminosity and mass-averaged disk dust temperature originally
derived for stellar mass objects to the brown dwarf regime to , applicable to spectral types
of M5 and later. This is slightly shallower than the relation for earlier
spectral type objects and yields warmer low-mass disks. The two prescriptions
cross at 0.27 L, corresponding to masses between 0.1 and 0.2 M
depending on age.Comment: 9 pages,6 figures, accepted to ApJ on 26/01/201
Psychiatric Comorbidity and Complex Regional Pain Syndrome Through the Lens of the Biopsychosocial Model: A Comparative Study.
To compare the prevalence of psychiatric comorbidity between patients with complex regional pain syndrome (CRPS) of the hand and non-CRPS patients and to assess the association between biopsychosocial (BPS) complexity profiles and psychiatric comorbidity in a comparative study.
We included a total of 103 patients with CRPS of the hand and 290 patients with chronic hand impairments but without CRPS. Psychiatric comorbidities were diagnosed by a psychiatrist, and BPS complexity was measured by means of the INTERMED. The odds ratios (OR) of having psychiatric comorbidities according to BPS complexity were calculated with multiple logistic regression (adjusted for age, sex, and pain).
Prevalence of psychiatric comorbidity was 29% in CRPS patients, which was not significantly higher than in non-CRPS patients (21%, relative risk=1.38, 95% CI: 0.95 to 2.01 p=0.10). The median total scores of the INTERMED were the same in both groups (23 points). INTERMED total scores (0-60 points) were related to an increased risk of having psychiatric comorbidity in CRPS patients (OR=1.46; 95% CI: 1.23-1.73) and in non-CRPS patients (OR=1.21; 95% CI: 1.13-1.30). The four INTERMED subscales (biological, psychological, social, and health care) were correlated with a higher risk of having psychiatric comorbidity in both groups. The differences in the OR of having psychiatric comorbidity in relation to INTERMED total and subscale scores were not statistically different between the two groups.
The total scores, as well as all four dimensions of BPS complexity measured by the INTERMED, were associated with psychiatric comorbidity, with comparable magnitudes of association between the CRPS and non-CRPS groups. The INTERMED was useful in screening for psychological vulnerability in the two groups
Lower Bound on the Pseudoscalar Mass in the Minimal Supersymmetric Standard Model
In the Higgs sector of the Minimal Supersymmetric Standard Model, the mass of
the pseudoscalar is an independent parameter together with . If is small, then the process is
kinematically allowed and is suppressed only if is small. On the
other hand, the mass of the charged Higgs boson is now near , and the
decay is enhanced if is small. Since the former
has not been observed, and the branching fraction of cannot be
too small (by comparing the experimentally derived cross section
from the leptonic channels with the theoretical prediction), we can infer a
phenomenological lower bound on of at least 60 GeV for all values of
.Comment: 11 pages including 2 figs, reference adde
Performance analysis of grid-connected wind turbines
The development of wind turbines (WT) and the capacities of wind power plants have increased significantly in the last years. Wind power plants (WPP) must provide the power quality required by new regulations and the reliability of the power system that is interconnected to. It is very important to analyze and understand the sources of disturbances that affect the power quality. In this paper is analyzed the performance of three different popular wind generators that are connected to the power system. Based on this analysis was made a comparison for the three wind turbines studied that are: The squirrel-cage induction generator (SCIG), the doubly-fed induction generator (DFIG), and the permanent-magnet synchronous generator (PMSG). The fixed speed system is more simple and reliable, but severely limits the energy production of a wind turbine and power quality. In case of variable speed systems, comparisons shows that generator of similar rating can significantly enhance energy capture as well as power quality. Moreover, performance of their output power leveling is validated by a new method numerically as maximum energy function and leveling function. The performances of these wind turbines and their characteristics are analysed in steady-state. Wind turbines systems are modeled in Matlab/Simulink environment. Simulation results matched well with the theoretical turbines operation
The Taurus Boundary of Stellar/Substellar (TBOSS) Survey II. Disk Masses from ALMA Continuum Observations
We report 885m ALMA continuum flux densities for 24 Taurus members
spanning the stellar/substellar boundary, with spectral types from M4 to M7.75.
Of the 24 systems, 22 are detected at levels ranging from 1.0-55.6 mJy. The two
non-detections are transition disks, though other transition disks in the
sample are detected. Converting ALMA continuum measurements to masses using
standard scaling laws and radiative transfer modeling yields dust mass
estimates ranging from 0.3-20M. The dust mass shows a
declining trend with central object mass when combined with results from
submillimeter surveys of more massive Taurus members. The substellar disks
appear as part of a continuous sequence and not a distinct population. Compared
to older Upper Sco members with similar masses across the substellar limit, the
Taurus disks are brighter and more massive. Both Taurus and Upper Sco
populations are consistent with an approximately linear relationship in
to , although derived power-law slopes depend strongly
upon choices of stellar evolutionary model and dust temperature relation. The
median disk around early M-stars in Taurus contains a comparable amount of mass
in small solids as the average amount of heavy elements in Kepler planetary
systems on short-period orbits around M-dwarf stars, with an order of magnitude
spread in disk dust mass about the median value. Assuming a gas:dust ratio of
100:1, only a small number of low-mass stars and brown dwarfs have a total disk
mass amenable to giant planet formation, consistent with the low frequency of
giant planets orbiting M-dwarfs.Comment: 41 pages and 32 figures, with all tables and appendices presented
here in their entirety. Accepted for publication in AJ (November 26, 2017
Visible light-driven H2 production over highly dispersed Ruthenia on Rutile TiO2 nanorods
The immobilization of miniscule quantities of RuO2 (~0.1%) onto one-dimensional (1D) TiO2 nanorods (NRs) allows H2 evolution from water under visible light irradiation. Rod-like rutile TiO2 structures, exposing preferentially (110) surfaces, are shown to be critical for the deposition of RuO2 to enable photocatalytic activity in the visible region. The superior performance is rationalized on the basis of fundamental experimental studies and theoretical calculations, demonstrating that RuO2(110) grown as 1D nanowires on rutile TiO2(110), which occurs only at extremely low loads of RuO2, leads to the formation of a heterointerface that efficiently adsorbs visible light. The surface defects, band gap narrowing, visible photoresponse, and favorable upward band bending at the heterointerface drastically facilitate the transfer and separation of photogenerated charge carriers.Peer ReviewedPostprint (published version
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