4,223 research outputs found
Particle-stabilized oscillating diver: a self-assembled responsive capsule
We report the experimental discovery of a self-assembled capsule, with
density set by interfacial glass beads and an internal bubble, that
automatically performs regular oscillations up and down a vial in response to a
temperature gradient. Similar composites featuring interfacial particles and
multiple internal compartments could be the solution to a variety of
application challenges.Comment: 7 pages, 3 figure
Detection of Far-Infrared Water Vapor, Hydroxyl, and Carbon Monoxide Emissions from the Supernova Remnant 3C 391
We report the detection of shock-excited far-infrared emission of H2O, OH,
and CO from the supernova remnant 3C 391, using the ISO Long-Wavelength
Spectrometer. This is the first detection of thermal H2O and OH emission from a
supernova remnant. For two other remnants, W~28 and W~44, CO emission was
detected but OH was only detected in absorption. The observed H2O and OH
emission lines arise from levels within ~400 K of the ground state, consistent
with collisional excitation in warm, dense gas created after the passage of the
shock front through the dense clumps in the pre-shock cloud. The post-shock gas
we observe has a density ~2x10^5 cm^{-3} and temperature 100-1000 K, and the
relative abundances of CO:OH:H2O in the emitting region are 100:1:7 for a
temperature of 200 K. The presence of a significant column of warm H2O suggests
that the chemistry has been significantly changed by the shock. The existence
of significant column densities of both OH and H2O, which is at odds with
models for non-dissociative shocks into dense gas, could be due to
photodissociation of H2O or a mix of fast and slow shocks through regions with
different pre-shock density.Comment: AASTeX manuscript and 4 postscript figure
A New Look At Carbon Abundances In Planetary Nebulae. III. DDDM1, IC 3568, IC4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009
This paper is the third in a series reporting on a study of carbon abundances
in a carefully chosen sample of planetary nebulae representing a large range in
progenitor mass and metallicity. We make use of the IUE Final Archive database
containing consistently-reduced spectra to measure line strengths of C III]
1909 along with numerous other UV lines for the planetary nebulae DDDM1, IC
3568, IC 4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009. We combine the IUE
data with line strengths from optical spectra obtained specifically to match
the IUE slit positions as closely as possible, to determine values for the
abundance ratios He/H, O/H, C/O, N/O, and Ne/O. The ratio of C III] 1909/C II
4267 is found to be effective for merging UV and optical spectra when He II
1640/4686 is unavailable. Our abundance determination method includes a 5-level
program whose results are fine-tuned by corrections derived from detailed
photoionization models constrained by the same set of emission lines. All
objects appear to have subsolar levels of O/H, and all but one show N/O levels
above solar. In addition, the seven planetary nebulae span a broad range in C/O
values. We infer that many of our objects are matter bounded, and thus the
standard ionization correction factor for N/O may be inappropriate for these
PNe. Finally, we estimate C/O using both collisionally-excited and
recombination lines associated with C+2 and find the well established result
that abundances from recombination lines usually exceed those from
collisionally-excited lines by several times.Comment: 36 pages, 7 tables, 2 figures, latex. Tables and figures supplied as
two separate postscript files. Accepted for publication in Ap
Spin-Correlation Coefficients and Phase-Shift Analysis for p+He Elastic Scattering
Angular Distributions for the target spin-dependent observables A,
A, and A have been measured using polarized proton beams at
several energies between 2 and 6 MeV and a spin-exchange optical pumping
polarized He target. These measurements have been included in a global
phase-shift analysis following that of George and Knutson, who reported two
best-fit phase-shift solutions to the previous global p+He elastic
scattering database below 12 MeV. These new measurements, along with
measurements of cross-section and beam-analyzing power made over a similar
energy range by Fisher \textit{et al.}, allowed a single, unique solution to be
obtained. The new measurements and phase-shifts are compared with theoretical
calculations using realistic nucleon-nucleon potential models.Comment: Submitted to Phys. Rev.
A Markov Chain based method for generating long-range dependence
This paper describes a model for generating time series which exhibit the
statistical phenomenon known as long-range dependence (LRD). A Markov Modulated
Process based upon an infinite Markov chain is described. The work described is
motivated by applications in telecommunications where LRD is a known property
of time-series measured on the internet. The process can generate a time series
exhibiting LRD with known parameters and is particularly suitable for modelling
internet traffic since the time series is in terms of ones and zeros which can
be interpreted as data packets and inter-packet gaps. The method is extremely
simple computationally and analytically and could prove more tractable than
other methods described in the literatureComment: 8 pages, 2 figure
A Compendium of Far-Infrared Line and Continuum Emission for 227 Galaxies Observed by the Infrared Space Observatory
Far-infrared line and continuum fluxes are presented for a sample of 227
galaxies observed with the Long Wavelength Spectrometer on the Infrared Space
Observatory. The galaxy sample includes normal star-forming systems,
starbursts, and active galactic nuclei covering a wide range of colors and
morphologies. The dataset spans some 1300 line fluxes, 600 line upper limits,
and 800 continuum fluxes. Several fine structure emission lines are detected
that arise in either photodissociation or HII regions: [OIII]52um, [NIII]57um,
[OI]63um, [OIII]88um, [NII]122um, [OI]145um, and [CII]158um. Molecular lines
such as OH at 53um, 79um, 84um, 119um, and 163um, and H2O at 58um, 66um, 75um,
101um, and 108um are also detected in some galaxies. In addition to those lines
emitted by the target galaxies, serendipitous detections of Milky Way
[CII]158um and an unidentified line near 74um in NGC1068 are also reported.
Finally, continuum fluxes at 52um, 57um, 63um, 88um, 122um, 145um, 158um, and
170um are derived for a subset of galaxies in which the far-infrared emission
is contained within the ~75" ISO LWS beam. The statistics of this large
database of continuum and line fluxes, including trends in line ratios with the
far-infrared color and infrared-to-optical ratio, are explored.Comment: Accepted for publication in the Astrophysical Journal Supplement
Serie
ISO LWS Spectroscopy of M82: A Unified Evolutionary Model
We present the first complete far-infrared spectrum (43 to 197 um) of M82,
the brightest infrared galaxy in the sky, taken with the Long Wavelength
Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine
structure emission lines, [OI] 63 and 145 um, [OIII] 52 and 88 um, [NII] 122
um, [NIII] 57 um and [CII] 158 um, and fit their ratios to a combination
starburst and photo-dissociation region (PDR) model. The best fit is obtained
with HII regions with n = 250 cm^{-3} and an ionization parameter of 10^{-3.5}
and PDRs with n = 10^{3.3} cm^{-3} and a far-ultraviolet flux of G_o =
10^{2.8}. We applied both continuous and instantaneous starburst models, with
our best fit being a 3-5 Myr old instantaneous burst model with a 100 M_o
cut-off. We also detected the ground state rotational line of OH in absorption
at 119.4 um. No excited level OH transitions are apparent, indicating that the
OH is almost entirely in its ground state with a column density ~ 4x10^{14}
cm^{-2}. The spectral energy distribution over the LWS wavelength range is well
fit with a 48 K dust temperature and an optical depth, tau_{Dust} proportional
to lambda^{-1}.Comment: 23 pages, 4 figures, accepted by ApJ, Feb. 1, 199
Studies of a Lacustrine-Volcanic Mars Analog Field Site with Mars-2020-like Instruments
On the upcoming Marsâ2020 rover two remote sensing instruments, MastcamâZ and SuperCam, and two microscopic proximity science instruments, SHERLOC and PIXL, will collect compositional (mineralogy, chemistry, and organics) data essential for paleoenvironmental reconstruction. The synergies between and limitations of these instruments were evaluated via study of a Mars analog field site in the Mojave Desert, using instruments approximating the data that will be returned by Marsâ2020. A ground truth dataset was generated for comparison to validate the results. The site consists of a succession of clayârich mudstones of lacustrine origin, interbedded tuffs, a carbonateâsilica travertine deposit, and gypsiferous mudstone strata. The major geological units were mapped successfully using simulated Marsâ2020 data. Simulated MastcamâZ data identified unit boundaries and Feâbearing weathering products. Simulated SuperCam passive shortwave infrared and green Raman data were essential in identifying major mineralogical composition and changes in lacustrine facies at distance; this was possible even with spectrally downsampled passive IR data. LIBS and simulated PIXL data discriminated and mapped major element chemistry. Simulated PIXL revealed mmâscale zones enriched in zirconium, of interest for age dating. SHERLOCâlike data mapped sulfate and carbonate at subâmm scale; silicates were identified with increased laser pulses/spot or by averaging of hundreds of spectra. Fluorescence scans detected and mapped varied classes of organics in all samples, characterized further with followâon spatially targeted deepâUV Raman spectra. Development of dedicated organics spectral libraries is needed to aid interpretation. Given these observations, the important units in the outcrop would be sampled and cached for sample return
- âŠ