6,768 research outputs found
Combined chips for atom-optics
We present experiments with Bose-Einstein condensates on a combined atom
chip. The combined structure consists of a large-scale "carrier chip" and
smaller "atom-optics chips", containing micron-sized elements. This allows us
to work with condensates very close to chip surfaces without suffering from
fragmentation or losses due to thermally driven spin flips. Precise
three-dimensional positioning and transport with constant trap frequencies are
described. Bose-Einstein condensates were manipulated with submicron accuracy
above atom-optics chips. As an application of atom chips, a direction sensitive
magnetic field microscope is demonstrated.Comment: 9 pages, 9 figure
Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)
Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km<sup>2</sup> spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Tropical broadleaf trees contribute almost half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which have a widespread distribution. The annual global isoprene emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene (440 to 660 Tg carbon) depending on the driving variables which include temperature, solar radiation, Leaf Area Index, and plant functional type. The global annual isoprene emission estimated using the standard driving variables is ~600 Tg isoprene. Differences in driving variables result in emission estimates that differ by more than a factor of three for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models, due to the substantial uncertainties in other model components, but at least some global models produce reasonable results when using isoprene emission distributions similar to MEGAN estimates. In addition, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and land-use) demonstrates the potential for large future changes in emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions
The Chandra X-ray view of the power sources in Cepheus A
The central part of the massive star-forming region Cepheus A contains
several radio sources which indicate multiple outflow phenomena, yet the
driving sources of the individual outflows have not been identified. We present
a high-resolution Chandra observation of this region that shows the presence of
bright X-ray sources, consistent with active pre-main sequence stars, while the
strong absorption hampers the detection of less luminous objects. A new source
has been discovered located on the line connecting H_2 emission regions at the
eastern and western parts of Cepheus A. This source could be the driving source
of HH 168. We present a scenario relating the observed X-ray and radio
emission.Comment: 7 pages, 6 figures, accepted for publication in A&
Engaging the articulators enhances perception of concordant visible speech movements
PURPOSE
This study aimed to test whether (and how) somatosensory feedback signals from the vocal tract affect concurrent unimodal visual speech perception.
METHOD
Participants discriminated pairs of silent visual utterances of vowels under 3 experimental conditions: (a) normal (baseline) and while holding either (b) a bite block or (c) a lip tube in their mouths. To test the specificity of somatosensory-visual interactions during perception, we assessed discrimination of vowel contrasts optically distinguished based on their mandibular (English /ɛ/-/æ/) or labial (English /u/-French /u/) postures. In addition, we assessed perception of each contrast using dynamically articulating videos and static (single-frame) images of each gesture (at vowel midpoint).
RESULTS
Engaging the jaw selectively facilitated perception of the dynamic gestures optically distinct in terms of jaw height, whereas engaging the lips selectively facilitated perception of the dynamic gestures optically distinct in terms of their degree of lip compression and protrusion. Thus, participants perceived visible speech movements in relation to the configuration and shape of their own vocal tract (and possibly their ability to produce covert vowel production-like movements). In contrast, engaging the articulators had no effect when the speaking faces did not move, suggesting that the somatosensory inputs affected perception of time-varying kinematic information rather than changes in target (movement end point) mouth shapes.
CONCLUSIONS
These findings suggest that orofacial somatosensory inputs associated with speech production prime premotor and somatosensory brain regions involved in the sensorimotor control of speech, thereby facilitating perception of concordant visible speech movements.
SUPPLEMENTAL MATERIAL
https://doi.org/10.23641/asha.9911846R01 DC002852 - NIDCD NIH HHSAccepted manuscrip
The evolution of the X-ray emission of HH 2 - Investigating heating and cooling processes
Young stellar objects often drive powerful bipolar outflows which evolve on
time scales of a few years. An increasing number of these outflows has been
detected in X-rays implying the existence of million degree plasma almost
co-spatial with the lower temperature gas observed in the optical and near-IR.
The details of the heating and cooling processes of the X-ray emitting part of
these so-called Herbig-Haro objects are still ambiguous, e.g., whether the
cooling is dominated by expansion, radiation or thermal conduction.
We present a second epoch Chandra observation of the first X-ray detected
Herbig-Haro object (HH 2) and derive the proper-motion of the X-ray emitting
plasma and its cooling history. We argue that the most likely explanation for
the constancy of the X-ray luminosity, the alignment with the optical emission
and the proper-motion is that the cooling is dominated by radiative losses
leading to cooling times exceeding a decade. We explain that a strong shock
caused by fast material ramming into slower gas in front of it about ten years
ago can explain the X-ray emission while being compatible with the available
multi-wavelength data of HH 2.Comment: 5 pages with 4 figures; accepted for publication by Astronomy and
Astrophysic
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