506 research outputs found
Fluid Flow Velocity Measurement in Active Wells Using Using Fiber Optic Distributed Acoustic Sensors
Real time monitoring of the behaviour of fluids along the whole length of fluid filled well pipes is important to the oil and gas industry as it enables well operators to maximize oil and gas production and optimize the quality of oil and gas produced, whilst reducing the cost. Flow speed measurement is one of the key approaches in fluid flow monitoring in wells. In this paper, three methods are designed, developed and demonstrated to estimate the speed and direction of flow at a range of depths in real world oil, gas and water wells using acoustic data set from distributed acoustic sensors that attached to the wells. The developed methods are based on a new combination of several techniques from signal processing, machine learning and physics. The Terabyte size acoustic dataset are recorded from each well as a two-dimensional function of both distance along the pipeline and time. The aim of the developed methods is estimating flow speed at each point along over 3000 meters pipelines and increasing the accurately and efficiently of the flow speed calculation compared to the existing method. The methods developed in this paper are computationally inexpensive, which make them suitable for real time well monitoring
Swift observation of Segue 1: constraints on sterile neutrino parameters in the darkest galaxy
Some extensions of standard particle physics postulate that dark matter may
be partially composed of weakly interacting sterile neutrino particles that
have so far eluded detection. We use a short (~5 ks) archival X-ray observation
of Segue 1 obtained with the X-ray Telescope (XRT) onboard the Swift satellite
to exclude the presence of sterile neutrinos in the 1.6 - 14 keV mass range
down to a flux limit of 6 x 10^{-12} erg cm-2 s-1 within 67 pc of its centre.
With an estimated mass-to-light ratio of ~3400 Msun/Lsun, Segue 1 is the
darkest ultrafaint dwarf galaxy currently measured. Spectral analysis of the
Swift XRT data fails to find any non-instrumental spectral feature possibly
connected with the radiative decay of a dark matter particle. Accordingly, we
establish upper bounds on the sterile neutrino parameter space based on the
non-detection of emission lines in the spectrum. The present work provides the
most sensitive X-ray search for sterile neutrinos in a region with the highest
dark matter density yet measured.Comment: 5 pages, 3 figures. Accepted in MNRAS Letter
A Keck/DEIMOS spectroscopic survey of faint Galactic satellites: searching for the least massive dwarf galaxies
[abridged] We present the results of a spectroscopic survey of the recently
discovered faint Milky Way satellites Boo, UMaI, UMaII and Wil1. Using the
DEIMOS spectrograph on Keck, we have obtained samples that contain from 15 to
85 probable members of these satellites for which we derive radial velocities
precise to a few km/s down to i~21-22. About half of these stars are observed
with a high enough S/N to estimate their metallicity to within \pm0.2 dex. From
this dataset, we show that UMaII is the only object that does not show a clear
radial velocity peak. However, the measured systemic radial velocity
(v_r=115\pm5 km/s) is in good agreement with recent simulations in which this
object is the progenitor of the recently discovered Orphan Stream. The three
other satellites show velocity dispersions that make them highly dark-matter
dominated systems. In particular the Willman 1 object is not a globular cluster
given its metallicity scatter over -2.0<[Fe/H]<-1.0 and is therefore almost
certainly a dwarf galaxy or dwarf galaxy remnant. We measure a radial velocity
dispersion of only 4.3_{-1.3}^{+2.3} km/s around a systemic velocity of
-12.3\pm2.3 km/s which implies a mass-to-light ratio of ~700 and a total mass
of ~5x10^5 Msun for this satellite, making it the least massive satellite
galaxy known to date. Such a low mass could mean that the 10^7 Msun limit that
had until now never been crossed for Milky Way and Andromeda satellite galaxies
may only be an observational limit and that fainter, less massive systems exist
within the Local Group. However, more modeling and an extended search for
potential extra-tidal stars are required to rule out the possibility that these
systems have not been significantly heated by tidal interaction.Comment: 24 pages, 11 figures, MNRAS accepte
The Least Luminous Galaxy: Spectroscopy of the Milky Way Satellite Segue 1
We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low luminosity (M_V
= -1.5) Milky Way satellite companion. While the combined size and luminosity
of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we
present spectroscopic evidence that this object is a dark matter-dominated
dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean
heliocentric recession velocity of 206 +/- 1.3 kms. We measure an internal
velocity dispersion of 4.3+/-1.2 kms. Under the assumption that these stars are
in dynamical equilibrium, we infer a total mass of 4.5^{+4.7}_{-2.5} x 10^5
Msun in the case where mass-follow-light; using a two-component maximum
likelihood model, we determine a similar mass within the stellar radius of 50
pc. This implies a mass-to-light ratio of ln(M/L_V) = 7.2^{+1.1}_{-1.2} or
M/L_V = 1320^{+2680}_{-940}. The error distribution of the mass-to-light ratio
is nearly log-normal, thus Segue 1 is dark matter-dominated at a high
significance. Using spectral synthesis modeling, we derive a metallicity for
the single red giant branch star in our sample of [Fe/H]=-3.3 +/- 0.2 dex.
Finally, we discuss the prospects for detecting gamma-rays from annihilation of
dark matter particles and show that Segue 1 is the most promising satellite for
indirect dark matter detection. We conclude that Segue 1 is the least luminous
of the ultra-faint galaxies recently discovered around the Milky Way, and is
thus the least luminous known galaxy.Comment: 12 pages, 6 figures, ApJ accepte
Hubble Space Telescope Imaging of the Ultra-Compact High Velocity Cloud AGC 226067: A stripped remnant in the Virgo Cluster
We analyze the optical counterpart to the ultra-compact high velocity cloud
AGC 226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS)
on the Hubble Space Telescope. The color magnitude diagram of the main body of
AGC 226067 reveals an exclusively young stellar population, with an age of
7--50 Myr, and is consistent with a metallicity of [Fe/H]0.3 as
previous work has measured via HII region spectroscopy. Additionally, the color
magnitude diagram is consistent with a distance of 17 Mpc,
suggesting an association with the Virgo cluster. A secondary stellar system
located 1.6' (8 kpc) away in projection has a similar stellar
population. The lack of an old red giant branch (5 Gyr) is contrasted
with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw
J122147+132853), and the total diffuse light from AGC~226067 is consistent with
the luminosity function of the resolved 7--50 Myr stellar population. The
main body of AGC~226067 has a =11.30.3, or
=5.41.310 given the stellar population.
We searched 20 deg of imaging data adjacent to AGC~226067 in the Virgo
Cluster, and found two similar stellar systems dominated by a blue stellar
population, far from any massive galaxy counterpart -- if this population has
similar star formation properties as AGC~226067, it implies 0.1
yr in Virgo intracluster star formation. Given its unusual
stellar population, AGC~226067 is likely a stripped remnant and is plausibly
the result of compressed gas from the ram pressure stripped M86 subgroup
(350 kpc away in projection) as it falls into the Virgo Cluster.Comment: 9 pages, 4 figures, 1 table. Accepted by the Astrophysical Journa
High-Velocity Clouds in the Nearby Spiral Galaxy M 83
We present deep HI 21-cm and optical observations of the face-on spiral
galaxy M 83 obtained as part of a project to search for high-velocity clouds
(HVCs) in nearby galaxies. Anomalous-velocity neutral gas is detected toward M
83, with 5.6x10^7 Msolar of HI contained in a disk rotating 40-50 km/s more
slowly in projection than the bulk of the gas. We interpret this as a
vertically extended thick disk of neutral material, containing 5.5% of the
total HI within the central 8 kpc. Using an automated source detection
algorithm to search for small-scale HI emission features, we find eight
distinct, anomalous-velocity HI clouds with masses ranging from 7x10^5 to
1.5x10^7 Msolar and velocities differing by up to 200 km/s compared to the HI
disk. Large on-disk structures are coincident with the optical spiral arms,
while unresolved off-disk clouds contain no diffuse optical emission down to a
limit of 27 r' mag per square arcsec. The diversity of the thick HI disk and
larger clouds suggests the influence of multiple formation mechanisms, with a
galactic fountain responsible for the slowly-rotating disk and on-disk discrete
clouds, and tidal effects responsible for off-disk cloud production. The mass
and kinetic energy of the HI clouds are consistent with the mass exchange rate
predicted by the galactic fountain model. If the HVC population in M 83 is
similar to that in our own Galaxy, then the Galactic HVCs must be distributed
within a radius of less than 25 kpc.Comment: 30 pages, 23 figures; accepted for publication in ApJ. Some figures
have been altered to reduce their siz
The targeted delivery of multicomponent cargos to cancer cells by nanoporous particle-supported lipid bilayers.
Encapsulation of drugs within nanocarriers that selectively target malignant cells promises to mitigate side effects of conventional chemotherapy and to enable delivery of the unique drug combinations needed for personalized medicine. To realize this potential, however, targeted nanocarriers must simultaneously overcome multiple challenges, including specificity, stability and a high capacity for disparate cargos. Here we report porous nanoparticle-supported lipid bilayers (protocells) that synergistically combine properties of liposomes and nanoporous particles. Protocells modified with a targeting peptide that binds to human hepatocellular carcinoma exhibit a 10,000-fold greater affinity for human hepatocellular carcinoma than for hepatocytes, endothelial cells or immune cells. Furthermore, protocells can be loaded with combinations of therapeutic (drugs, small interfering RNA and toxins) and diagnostic (quantum dots) agents and modified to promote endosomal escape and nuclear accumulation of selected cargos. The enormous capacity of the high-surface-area nanoporous core combined with the enhanced targeting efficacy enabled by the fluid supported lipid bilayer enable a single protocell loaded with a drug cocktail to kill a drug-resistant human hepatocellular carcinoma cell, representing a 10(6)-fold improvement over comparable liposomes
A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
We report five Local Volume dwarf galaxies (two of which are presented here
for the first time) uncovered during a comprehensive archival search for
optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC
population of HI clouds are thought to be candidate gas-rich, low mass halos at
the edge of the Local Group and beyond, but no comprehensive search for stellar
counterparts to these systems has been presented. Careful visual inspection of
all publicly available optical and ultraviolet imaging at the position of the
UCHVCs revealed six blue, diffuse counterparts with a morphology consistent
with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all
six candidate dwarf counterparts show that five have an H-derived
velocity consistent with the coincident HI cloud, confirming their association,
the sixth diffuse counterpart is likely a background object. The size and
luminosity of the UCHVC dwarfs is consistent with other known Local Volume
dwarf irregular galaxies. The gas fraction () of the five
dwarfs are generally consistent with that of dwarf irregular galaxies in the
Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC
HVC274.68+74.70123) has a very high 40. Despite the
heterogenous nature of our search, we demonstrate that the current dwarf
companions to UCHVCs are at the edge of detectability due to their low surface
brightness, and that deeper searches are likely to find more stellar systems.
If more sensitive searches do not reveal further stellar counterparts to
UCHVCs, then the dearth of such systems around the Local Group may be in
conflict with CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte
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