10,228 research outputs found
First Results from a 1.3 cm EVLA Survey of Massive Protostellar Objects: G35.03+0.35
We have performed a 1.3 centimeter survey of 24 massive young stellar objects
(MYSOs) using the Expanded Very Large Array (EVLA). The sources in the sample
exhibit a broad range of massive star formation signposts including Infrared
Dark Clouds (IRDCs), UCHII regions, and extended 4.5 micron emission in the
form of Extended Green Objects (EGOs). In this work, we present results for
G35.03+0.35 which exhibits all of these phenomena. We simultaneously image the
1.3 cm ammonia (1,1) through (6,6) inversion lines, four methanol transitions,
two H recombination lines, plus continuum at 0.05 pc resolution. We find three
areas of thermal ammonia emission, two within the EGO (designated the NE and SW
cores) and one toward an adjacent IRDC. The NE core contains an UCHII region
(CM1) and a candidate HCHII region (CM2). A region of non-thermal, likely
masing ammonia (3,3) and (6,6) emission is coincident with an arc of 44 GHz
methanol masers. We also detect two new 25 GHz Class I methanol masers. A
complementary Submillimeter Array 1.3 mm continuum image shows that the
distribution of dust emission is similar to the lower-lying ammonia lines, all
peaking to the NW of CM2, indicating the likely presence of an additional MYSO
in this protocluster. By modeling the ammonia and 1.3 mm continuum data, we
obtain gas temperatures of 20-220 K and masses of 20-130 solar. The diversity
of continuum emission properties and gas temperatures suggest that objects in a
range of evolutionary states exist concurrently in this protocluster.Comment: To appear in Astrophysical Journal Letters Special Issue on the EVLA.
16 pages, 3 figures. Includes the complete version of Figure 3, which was
unable to fit into the journal article due to the number of panel
The stochastic dynamics of nanoscale mechanical oscillators immersed in a viscous fluid
The stochastic response of nanoscale oscillators of arbitrary geometry
immersed in a viscous fluid is studied. Using the fluctuation-dissipation
theorem it is shown that deterministic calculations of the governing fluid and
solid equations can be used in a straightforward manner to directly calculate
the stochastic response that would be measured in experiment. We use this
approach to investigate the fluid coupled motion of single and multiple
cantilevers with experimentally motivated geometries.Comment: 5 pages, 5 figure
Government financial support for civil aircraft research, technology and development in four European countries and the United States
Data on the levels of government financial support for civil aircraft airframe and engine (CAAE) research and technology (R&T) in the United States and Europe (United Kingdom, West Germany, France and The Netherlands) and means of comparing these levels are provided. Data are presented for the years 1974-1977. European R&T expenditure data were obtained through visits to each of the four European countries, to the Washington office of the European Communities, and by a search of applicable literature. CAAE R&T expenditure data for the United States were obtained from NASA and Federal Aviation Administration (FAA)
Monte Carlo calculations of high energy nucleon meson cascades and applications to galactic cosmic ray transport
Results obtained using a recently developed calculational method for determining the nucleon-meson cascade induced in thick materials by high-energy nucleons and charged pions are presented. The calculational method uses the intranuclear-cascade-evaporation model to treat nonelastic collisions by particles with energies approximately or smaller than GeV and an extrapolation model at higher energies. The following configurations are considered: (1) 19.2-GeV/c protons incident on iron; (2) 30.3-GeV/c protons incident on iron; (3) solar and galactic protons incident on the moon, and (4) galactic protons incident on tissue. For the first three configurations, experimental results are available and comparisons between the experimental and calculated results are given
The Protocluster G18.67+0.03: A Test Case for Class I Methanol Masers as Evolutionary Indicators for Massive Star Formation
We present high angular resolution Submillimeter Array (SMA) and Karl G.
Jansky Very Large Array (VLA) observations of the massive protocluster
G18.67+0.03. Previously targeted in maser surveys of GLIMPSE Extended Green
Objects (EGOs), this cluster contains three Class I methanol maser sources,
providing a unique opportunity to test the proposed role of Class I masers as
evolutionary indicators for massive star formation. The millimeter observations
reveal bipolar molecular outflows, traced by 13CO(2-1) emission, associated
with all three Class I maser sources. Two of these sources (including the EGO)
are also associated with 6.7 GHz Class II methanol masers; the Class II masers
are coincident with millimeter continuum cores that exhibit hot core line
emission and drive active outflows, as indicated by the detection of SiO(5-4).
In these cases, the Class I masers are coincident with outflow lobes, and
appear as clear cases of excitation by active outflows. In contrast, the third
Class I source is associated with an ultracompact HII region, and not with
Class II masers. The lack of SiO emission suggests the 13CO outflow is a relic,
consistent with its longer dynamical timescale. Our data show that massive
young stellar objects associated only with Class I masers are not necessarily
young, and provide the first unambiguous evidence that Class I masers may be
excited by both young (hot core) and older (UC HII) MYSOs within the same
protocluster.Comment: Astrophysical Journal Letters, accepted. emulateapj, 7 pages
including 4 figures and 1 table. Figures compressed. v2: coauthor affiliation
updated, emulateapj versio
Taxation of forest land in South Missouri
This bulletin is a report on Department of Forestry Research Project 124, 'Timber Economics'--P. [2].Digitized 2007 AES.Includes bibliographical references (page 36)
Marketing farm woodlot products in Franklin, Osage, and Gasconade counties
Caption title.Includes bibliographical references
VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers
We present resolution Very Large Array (VLA) observations of four
CHOH - 25~GHz transitions (=3, 5, 8, 10) along with 1.3~cm
continuum toward 20 regions of active massive star formation containing
Extended Green Objects (EGOs), 14 of which we have previously studied with the
VLA in the Class~I 44~GHz and Class~II 6.7~GHz maser lines (Cyganowski et al.
2009). Sixteen regions are detected in at least one 25~GHz line (=5), with
13 of 16 exhibiting maser emission. In total, we report 34 new sites of
CHOH maser emission and ten new sites of thermal CHOH emission,
significantly increasing the number of 25~GHz Class I CHOH masers observed
at high angular resolution. We identify probable or likely maser counterparts
at 44~GHz for all 15 of the 25~GHz masers for which we have complementary data,
providing further evidence that these masers trace similar physical conditions
despite uncorrelated flux densities. The sites of thermal and maser emission of
CHOH are both predominantly associated with the 4.5 m emission from
the EGO, and the presence of thermal CHOH emission is accompanied by 1.3~cm
continuum emission in 9 out of 10 cases. Of the 19 regions that exhibit 1.3~cm
continuum emission, it is associated with the EGO in 16 cases (out of a total
of 20 sites), 13 of which are new detections at 1.3~cm. Twelve of the 1.3~cm
continuum sources are associated with 6.7~GHz maser emission and likely trace
deeply-embedded massive protostars
VLA Observations of the Infrared Dark Cloud G19.30+0.07
We present Very Large Array observations of ammonia (NH3) (1,1), (2,2), and
CCS (2_1-1_0) emission toward the Infrared Dark Cloud (IRDC) G19.30+0.07 at
~22GHz. The NH3 emission closely follows the 8 micron extinction. The NH3 (1,1)
and (2,2) lines provide diagnostics of the temperature and density structure
within the IRDC, with typical rotation temperatures of ~10 to 20K and NH3
column densities of ~10^15 cm^-2. The estimated total mass of G19.30+0.07 is
~1130 Msun. The cloud comprises four compact NH3 clumps of mass ~30 to 160
Msun. Two coincide with 24 micron emission, indicating heating by protostars,
and show evidence of outflow in the NH3 emission. We report a water maser
associated with a third clump; the fourth clump is apparently starless. A
non-detection of 8.4GHz emission suggests that the IRDC contains no bright HII
regions, and places a limit on the spectral type of an embedded ZAMS star to
early-B or later. From the NH3 emission we find G19.30+0.07 is composed of
three distinct velocity components, or "subclouds." One velocity component
contains the two 24 micron sources and the starless clump, another contains the
clump with the water maser, while the third velocity component is diffuse, with
no significant high-density peaks. The spatial distribution of NH3 and CCS
emission from G19.30+0.07 is highly anti-correlated, with the NH3 predominantly
in the high-density clumps, and the CCS tracing lower-density envelopes around
those clumps. This spatial distribution is consistent with theories of
evolution for chemically young low-mass cores, in which CCS has not yet been
processed to other species and/or depleted in high-density regions.Comment: 29 pages, 9 figures, accepted for publication by ApJ. Please contact
the authors for higher resolution versions of the figure
Fluctuation-dissipation ratios in the dynamics of self-assembly
We consider two seemingly very different self-assembly processes: formation
of viral capsids, and crystallization of sticky discs. At low temperatures,
assembly is ineffective, since there are many metastable disordered states,
which are a source of kinetic frustration. We use fluctuation-dissipation
ratios to extract information about the degree of this frustration. We show
that our analysis is a useful indicator of the long term fate of the system,
based on the early stages of assembly.Comment: 8 pages, 6 figure
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