11,803 research outputs found
The Carina Nebula and Gum 31 molecular complex: II. The distribution of the atomic gas revealed in unprecedented detail
We report high spatial resolution observations of the HI 21cm line in the
Carina Nebula and the Gum 31 region obtained with the Australia Telescope
Compact Array. The observations covered 12 deg centred on , achieving an angular resolution of 35
arcseconds. The HI map revealed complex filamentary structures across a wide
range of velocities. Several "bubbles" are clearly identified in the Carina
Nebula Complex, produced by the impact of the massive star clusters located in
this region. An HI absorption profile obtained towards the strong extragalactic
radio source PMN J1032--5917 showed the distribution of the cold component of
the atomic gas along the Galactic disk, with the Sagittarius-Carina and Perseus
spiral arms clearly distinguishable. Preliminary calculations of the optical
depth and spin temperatures of the cold atomic gas show that the HI line is
opaque ( 2) at several velocities in the Sagittarius-Carina
spiral arm. The spin temperature is K in the regions with the highest
optical depth, although this value might be lower for the saturated components.
The atomic mass budget of Gum 31 is of the total gas mass. HI self
absorption features have molecular counterparts and good spatial correlation
with the regions of cold dust as traced by the infrared maps. We suggest that
in Gum 31 regions of cold temperature and high density are where the atomic to
molecular gas phase transition is likely to be occurring.Comment: 20 pages, 1 table, 16 Figures, Accepted for Publication in the
Monthly Notices of the Royal Astronomical Society Journa
Parallel symbolic state-space exploration is difficult, but what is the alternative?
State-space exploration is an essential step in many modeling and analysis
problems. Its goal is to find the states reachable from the initial state of a
discrete-state model described. The state space can used to answer important
questions, e.g., "Is there a dead state?" and "Can N become negative?", or as a
starting point for sophisticated investigations expressed in temporal logic.
Unfortunately, the state space is often so large that ordinary explicit data
structures and sequential algorithms cannot cope, prompting the exploration of
(1) parallel approaches using multiple processors, from simple workstation
networks to shared-memory supercomputers, to satisfy large memory and runtime
requirements and (2) symbolic approaches using decision diagrams to encode the
large structured sets and relations manipulated during state-space generation.
Both approaches have merits and limitations. Parallel explicit state-space
generation is challenging, but almost linear speedup can be achieved; however,
the analysis is ultimately limited by the memory and processors available.
Symbolic methods are a heuristic that can efficiently encode many, but not all,
functions over a structured and exponentially large domain; here the pitfalls
are subtler: their performance varies widely depending on the class of decision
diagram chosen, the state variable order, and obscure algorithmic parameters.
As symbolic approaches are often much more efficient than explicit ones for
many practical models, we argue for the need to parallelize symbolic
state-space generation algorithms, so that we can realize the advantage of both
approaches. This is a challenging endeavor, as the most efficient symbolic
algorithm, Saturation, is inherently sequential. We conclude by discussing
challenges, efforts, and promising directions toward this goal
Automated Quantitative Description of Spiral Galaxy Arm-Segment Structure
We describe a system for the automatic quantification of structure in spiral
galaxies. This enables translation of sky survey images into data needed to
help address fundamental astrophysical questions such as the origin of spiral
structure---a phenomenon that has eluded theoretical description despite 150
years of study (Sellwood 2010). The difficulty of automated measurement is
underscored by the fact that, to date, only manual efforts (such as the citizen
science project Galaxy Zoo) have been able to extract information about large
samples of spiral galaxies. An automated approach will be needed to eliminate
measurement subjectivity and handle the otherwise-overwhelming image quantities
(up to billions of images) from near-future surveys. Our approach automatically
describes spiral galaxy structure as a set of arcs, precisely describing spiral
arm segment arrangement while retaining the flexibility needed to accommodate
the observed wide variety of spiral galaxy structure. The largest existing
quantitative measurements were manually-guided and encompassed fewer than 100
galaxies, while we have already applied our method to more than 29,000
galaxies. Our output matches previous information, both quantitatively over
small existing samples, and qualitatively against human classifications from
Galaxy Zoo.Comment: 9 pages;4 figures; 2 tables; accepted to CVPR (Computer Vision and
Pattern Recognition), June 2012, Providence, Rhode Island, June 16-21, 201
A new approach to the inverse problem for current mapping in thin-film superconductors
A novel mathematical approach has been developed to complete the inversion of
the Biot-Savart law in one- and two-dimensional cases from measurements of the
perpendicular component of the magnetic field using the well-developed
Magneto-Optical Imaging technique. Our approach, especially in the 2D case, is
provided in great detail to allow a straightforward implementation as opposed
to those found in the literature. Our new approach also refines our previous
results for the 1D case [Johansen et al., Phys. Rev. B 54, 16264 (1996)], and
streamlines the method developed by Jooss et al. [Physica C 299, 215 (1998)]
deemed as the most accurate if compared to that of Roth et al. [J. Appl. Phys.
65, 361 (1989)]. We also verify and streamline the iterative technique, which
was developed following Laviano et al. [Supercond. Sci. Technol. 16, 71 (2002)]
to account for in-plane magnetic fields caused by the bending of the applied
magnetic field due to the demagnetising effect. After testing on
magneto-optical images of a high quality YBa2Cu3O7 superconducting thin film,
we show that the procedure employed is effective
COSMOSOMAS Observations of the CMB and Galactic Foregrounds at 11 GHz: Evidence for anomalous microwave emission at high Galactic Latitude
We present observations with the new 11 GHz radiometer of the COSMOSOMAS
experiment at the Teide Observatory (Tenerife). The sky region between 0 deg <=
RA <= 360 deg and 26 deg <= DEC 49 deg (ca. 6500 square degrees) was observed
with an angular resolution of 0.9 deg. Two orthogonal independent channels in
the receiving system measured total power signals from linear polarizations
with a 2 GHz bandwidth. Maps with an average sensitivity of 50 microK per beam
have been obtained for each channel. At high Galactic latitude (|b|>30deg) the
11 GHz data are found to contain the expected cosmic microwave background as
well as extragalactic radiosources, galactic synchrotron and free-free
emission, and a dust-correlated component which is very likely of galactic
origin. At the angular scales allowed by the window function of the experiment,
the dust-correlated component presents an amplitude \Delta T aprox. 9-13 microK
while the CMB signal is of order 27 microK. The spectral behaviour of the
dust-correlated signal is examined in the light of previous COSMOSOMAS data at
13-17 GHz and WMAP data at 22-94 GHz in the same sky region. We detect a
flattening in the spectral index of this signal below 20 GHz which rules out
synchrotron radiation as being responsible for the emission. This anomalous
dust emission can be described by a combination of free-free emission and
spinning dust models with a flux density peaking around 20 GHz.Comment: 17 pages, 10 tables, 20 figures. Details on the COSMOSOMAS experiment
can be found at http://www.iac.es/project/cmb/cosmosomas
Asynchronous nuclear division cycles in multinucleated cells
Synchronous mitosis is common in multinucleated cells. We analyzed a unique asynchronous nuclear division cycle in a multinucleated filamentous fungus, Ashbya gossypii. Nuclear pedigree analysis and observation of GFP-labeled spindle pole bodies demonstrated that neighboring nuclei in A. gossypii cells are in different cell cycle stages despite close physical proximity. Neighboring nuclei did not differ significantly in their patterns of cyclin protein localization such that both G1 and mitotic cyclins were present regardless of cell cycle stage, suggesting that the complete destruction of cyclins is not occurring in this system. Indeed, the expression of mitotic cyclin lacking NH(2)-terminal destruction box sequences did not block cell cycle progression. Cells lacking AgSic1p, a predicted cyclin-dependent kinase (CDK) inhibitor, however, showed aberrant multipolar spindles and fragmented nuclei that are indicative of flawed mitoses. We hypothesize that the continuous cytoplasm in these cells promoted the evolution of a nuclear division cycle in which CDK inhibitors primarily control CDK activity rather than oscillating mitotic cyclin proteins
Application of Thermoresponsive Polymer and Microfluidics to the Development of a Velocity-Dependent Cell-Sorting Microdevice
3rd Place, Denman Undergraduate Research ForumLow-cost velocity dependent cell sorting in 2D is a currently nonexistent technology for cancer research. The development of such a device would enable further research on the treatment of various deleterious cancers, such as Glioblastoma Multiforme (GBM), which metastasize based off the high motility of a single cell. Here we present a low-cost device capable of sorting these cells. Separation would enable development of highly specific therapeutic agents to limit cancer metastasis in patients. This device consists of microfluidics channels situated under microtextured Polydimethylsiloxane (PDMS) coated with the thermoresponsive polymer Poly(N-isopropylacrylamide) (PNIPAM). Cells are seeded on one end of the device and orient themselves parallel to the striations patterned into the PDMS; traveling further across the device over time. At a specific location (determined by velocity of target cells and time passed), low-temperature fluid can be passed through the microfluidic channel below which triggers a selective conformational change in the PNIPAM. This change shifts PNIPAM from nonpolar to polar, causing the polymer to release previously-adhered cells into solution in favor of binding to media. Establishing the PNIPAM layer capable of releasing cells while allowing them to adhere to microtextures on the PDMS involved a multi-step process. First, PDMS stamps are made of varying thickness, then they were placed in a plasma cleaner and exposed to Argon for 1,3, and 5 minutes at 30 Watts, 8-10 MHz, and ~1000microTorr. Then, samples were exposed to N-isopropylacrylamide (NIPAM) via immersion into a polymer solution and via dropping that solution onto samples and baked at 3 hours or 5 hours. Cell detachment analysis, goniometer experimentation, and SEM images showed that a 1 minute Argon gas exposure, with 1 minute of NIPAM immersion and a 3 hour bake yielded the most successful layer that lifted cells without inhibiting the PDMS microtexture. Future work involves optimizing the device to lift all cells exposed to the channel, as well as further corroborating its efficacy.A one-year embargo was granted for this item.Academic Major: Biomedical Engineerin
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