2,264 research outputs found
Low-disturbance wind tunnels
During the past years, there was an extensive program under way at the Langley Research Center to upgrade the flow quality in several of the large wind tunnels. This effort has resulted in significant improvements in flow quality in these tunnels and has also increased the understanding of how and where changes in existing and new wind tunnels are most likely to yield the desired improvements. As part of this ongoing program, flow disturbance levels and spectra were measured in several Langley tunnels before and after modifications were made to reduce acoustic and vorticity fluctuations. A brief description of these disturbance control features is given for the Low-Turbulence Pressure Tunnel, the 4 x 7 Meter Tunnel, and the 8 Foot Transonic Pressure Tunnel. To illustrate typical reductions in disturbance levels obtained in these tunnels, data from hot-wire or acoustic sensors are presented. A concept for a subsonic quiet tunnel designed to study boundary layer stability and transition is also presented. Techniques developed at Langley in recent years to eliminate the high intensity and high-frequency acoustic disturbances present in all previous supersonic wind tunnels are described. In conclusion, the low-disturbance levels present in atmospheric flight can now be simulated in wind tunnels over the speed range from low subsonic through high supersonic
Millimeter imaging of HD 163296: probing the disk structure and kinematics
We present new multi-wavelength millimeter interferometric observations of
the Herbig Ae star HD 163296 obtained with the IRAM/PBI, SMA and VLA arrays
both in continuum and in the 12CO, 13CO and C18O emission lines. Gas and dust
properties have been obtained comparing the observations with self-consistent
disk models for the dust and CO emission. The circumstellar disk is resolved
both in the continuum and in CO. We find strong evidence that the circumstellar
material is in Keplerian rotation around a central star of 2.6 Msun. The disk
inclination with respect to the line of sight is 46+-4 deg with a position
angle of 128+-4 deg. The slope of the dust opacity measured between 0.87 and 7
mm (beta=1) confirms the presence of mm/cm-size grains in the disk midplane.
The dust continuum emission is asymmetric and confined inside a radius of 200
AU while the CO emission extends up to 540 AU. The comparison between dust and
CO temperature indicates that CO is present only in the disk interior. Finally,
we obtain an increasing depletion of CO isotopomers from 12CO to 13CO and C18O.
We argue that these results support the idea that the disk of HD 163296 is
strongly evolved. In particular, we suggest that there is a strong depletion of
dust relative to gas outside 200 AU; this may be due to the inward migration of
large bodies that form in the outer disk or to clearing of a large gap in the
dust distribution by a low mass companion.Comment: Accepted for publication on A&A, 16 page
Food, microbes, sex and old age: on the plasticity of gastrointestinal innervation
The gastrointestinal tract is innervated by its own enteric nervous system and by extrinsic neurons that connect it with the central nervous system. Innervation allows the gastrointestinal tract to sense and respond to diverse stimuli, adjusting motility and secretion, but also affecting our physiology, behaviour and immunity. The mechanisms underlying the formation of gastrointestinal neurons are beginning to be elucidated; those that keep them plastic over an organism's lifetime remain to be explored. Here, we review the effects of microbiota, nutrients, sex and ageing on the morphology and function of gastrointestinal innervation in mammals, and discuss how this plasticity shapes gut-brain crosstalk and whole-body physiology. We also highlight insights gained by nascent studies of the enteric innervation of Drosophila melanogaster
Public relations of public schools recommended and in use for conducting good schools, including improving the curriculum and securing better housing.
Thesis (M.A.)--Boston Universit
General Relativistic Magnetohydrodynamic Simulations of the Hard State as a Magnetically-Dominated Accretion Flow
(Abridged) We present one of the first physically-motivated two-dimensional
general relativistic magnetohydrodynamic (GRMHD) numerical simulations of a
radiatively-cooled black-hole accretion disk. The fiducial simulation combines
a total-energy-conserving formulation with a radiative cooling function, which
includes bremsstrahlung, synchrotron, and Compton effects. By comparison with
other simulations we show that in optically thin advection-dominated accretion
flows, radiative cooling can significantly affect the structure, without
necessarily leading to an optically thick, geometrically thin accretion disk.
We further compare the results of our radiatively-cooled simulation to the
predictions of a previously developed analytic model for such flows. For the
very low stress parameter and accretion rate found in our simulated disk, we
closely match a state called the "transition" solution between an outer
advection-dominated accretion flow and what would be a magnetically-dominated
accretion flow (MDAF) in the interior. The qualitative and quantitative
agreement between the numerical and analytic models is quite good, with only a
few well-understood exceptions. According to the analytic model then, at
significantly higher stress or accretion, we would expect a full MDAF to form.
The collection of simulations in this work also provide important data for
interpreting other numerical results in the literature, as they span the most
common treatments of thermodynamics, including simulations evolving: 1) the
internal energy only; 2) the internal energy plus an explicit cooling function;
3) the total energy without cooling; and 4) total energy including cooling. We
find that the total energy formulation is a necessary prerequisite for proper
treatment of radiative cooling in MRI accretion flows.Comment: 13 pages, 7 figures, submitted to Ap
Combining the α1-Adrenergic Receptor Antagonist, Prazosin, with the β-Adrenergic Receptor Antagonist, Propranolol, Reduces Alcohol Drinking More Effectively Than Either Drug Alone
Background
Evidence suggests that activation of the noradrenergic system may contribute to alcohol drinking in animals and humans. Our previous studies demonstrated that blocking α1-adrenergic receptors with the antagonist, prazosin, decreased alcohol drinking in rats under various conditions. Since noradrenergic activation is also regulated by β-adrenergic receptors, we now examine the effects of the β-adrenergic receptor antagonist, propranolol, alone or in combination with prazosin, on alcohol drinking in rats selectively bred for high voluntary alcohol intake and alcohol preference (P line).
Methods
Two studies were conducted with male P rats. In study one, rats were allowed to become alcohol-dependent during 14 weeks of ad libitum access to food, water and 20% alcohol and the effect of propranolol (5–15 mg/kg, IP) and prazosin (1–2 mg/kg, IP) on alcohol intake during withdrawal were assessed. In study two, the effect of propranolol (5 mg/kg, IP) and prazosin (2 mg/kg, IP) on alcohol intake following prolonged imposed abstinence was assessed.
Results
Alcohol drinking following propranolol treatment was variable, but the combination of propranolol + prazosin consistently suppressed alcohol drinking during both alcohol withdrawal and following prolonged imposed abstinence, and the combination of these two drugs was more effective than was treatment with either drug alone.
Conclusions
Treatment with prazosin + propranolol, or a combination of other centrally active α1- and β-adrenergic receptor antagonists, may assist in preventing alcohol relapse in some individuals
Large dust particles in disks around T Tauri stars
We present 7-mm continuum observations of 14 low-mass pre-main-sequence stars
in the Taurus-Auriga star-forming region obtained with the Very Large Array
with ~1.5" resolution and ~0.3 mJy rms sensitivity. For 10 objects, the
circumstellar emission has been spatially resolved. The large outer disk radii
derived suggest that the emission at this wavelength is mostly optically thin.
The millimetre spectral energy distributions are characterised by spectral
indices alpha = 2.3 to 3.2. After accounting for contribution from free-free
emission and corrections for optical depth, we determine dust opacity indices
beta in the range 0.5 to 1.6, which suggest that millimetre-sized dust
aggregates are present in the circumstellar disks. Four of the sources with
beta > 1 may be consistent with submicron-sized dust as found in the
interstellar medium. Our findings indicate that dust grain growth to
millimetre-sized particles is completed within less than 1 Myr for the majority
of circumstellar disks.Comment: 11 pages, 4 figure
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A short-term longitudinal study of correlates and sequelae of attachment security in autism
In this short-term longitudinal study, thirty preschool-aged children with autism were first observed in Ainsworth’s Strange Situation procedure and, separately, interacting with the primary caregiver in the home. One year later, each child completed both a developmental assessment and an observational assessment of empathic responding. Behaviors typical for children with autism were distinguished from behaviors suggestive of relationally based attachment disorganization. Forty five percent of the children were classified as securely attached. The secure group demonstrated language skills superior to those of the insecurely attached group, concurrently and during the follow-up. Compared to parents of children who were insecurely attached, parents of securely attached children were rated as more sensitive. Compared to both organized insecure and disorganized children, secure children were rated as more responsive to an examiner’s apparent distress during the follow-up relative to their ratings at intake, whereas empathy ratings of children with insecure classifications did not increase. Importantly, attachment security was associated with empathy above and beyond the contribution of children’s language level. These results indicate that the sequelae of attachment security in autism may be similar to those documented for typically developing children.This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Institute on Deafness and Other Communication Disorders, as part of the Collaborative Programs of Excellence in Autism: [Program Project Grant Number HD-DCD35470] and Wellcome Trust: [Grant Number WT103343MA]
Exploring Brown Dwarf Disks
We discuss the spectral energy distribution of three very low mass objects in
Chamaeleon I for which ground-based spectroscopy and photometry as well as ISO
measurements in the mid-infrared are available (Comeron et al. 2000; Persi et
al. 2000). One of these stars (Cha Halpha1) is a bona-fide brown dwarf, with
mass 0.04-0.05 Msun. We show that the observed emission is very well described
by models of circumstellar disks identical to those associated to T Tauri
stars, scaled down to keep the ratio of the disk-to-star mass constant and to
the appropriate stellar parameters. This result provides a first indication
that the formation mechanism of T Tauri stars (via core contraction and
formation of an accretion disk) extends to objects in the brown dwarf mass
range.Comment: 4 pages, 4 figures, A&A Letters in pres
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