7,711 research outputs found
A Lensed Arc in the Low Redshift Cluster Abell 2124
We report the discovery of an arc-like object 27" from the center of the cD
galaxy in the redshift cluster A2124. Observations with the Keck II
telescope reveal that the object is a background galaxy at ,
apparently lensed into an arc of length \sim 8 \farcs5 and total R magnitude
. The width of the arc is resolved; we estimate it to be
0\farcs6 after correcting for seeing. A lens model of the A2124 core mass
distribution consistent with the cluster galaxy velocity dispersion reproduces
the observed arc geometry and indicates a magnification factor \gta 9. With
this magnification, the strength of the [OII] \lambda 3727 line implies a
star-formation rate of SFR \sim 0.4 h^{-2}\msun yr^{-1}$. A2124 thus appears to
be the lowest redshift cluster known to exhibit strong lensing of a distant
background galaxy.Comment: 6 pages using emulateapj.sty; 4 Postscript figures; Figure 4 uses
color. Accepted for publication, but ApJ Letters' new policy of counting data
images makes the manuscript too long; will appear in main journal. This final
version has minor correction
Rectification in single molecular dimers with strong polaron effect
We study theoretically the transport properties of a molecular two level
system with large electron-vibron coupling in the Coulomb blockade regime. We
show that when the electron-vibron coupling induces polaron states, the
current-voltage characteristic becomes strongly asymmetric because, in one
current direction, one of the polaron state blocks the current through the
other. This situation occurs when the coupling between the polaron states is
smaller than the coupling to the leads. We discuss the relevance of our
calculation for experiments on C_140 molecules.Comment: 4 pages, 4 figure
A Definitive Optical Detection of a Supercluster at z = 0.91
We present the results from a multi-band optical imaging program which has
definitively confirmed the existence of a supercluster at z = 0.91. Two massive
clusters of galaxies, CL1604+4304 at z = 0.897 and CL1604+4321 at z = 0.924,
were originally observed in the high-redshift cluster survey of Oke, Postman &
Lubin (1998). They are separated by 4300 km/s in radial velocity and 17
arcminutes on the plane of the sky. Their physical and redshift proximity
suggested a promising supercluster candidate. Deep BRi imaging of the region
between the two clusters indicates a large population of red galaxies. This
population forms a tight, red sequence in the color--magnitude diagram at (R-i)
= 1.4. The characteristic color is identical to that of the
spectroscopically-confirmed early-type galaxies in the two member clusters. The
red galaxies are spread throughout the 5 Mpc region between CL1604+4304 and
CL1604+4321. Their spatial distribution delineates the entire large scale
structure with high concentrations at the cluster centers. In addition, we
detect a significant overdensity of red galaxies directly between CL1604+4304
and CL1604+4321 which is the signature of a third, rich cluster associated with
this system. The strong sequence of red galaxies and their spatial distribution
clearly indicate that we have discovered a supercluster at z = 0.91.Comment: Accepted for publication in Astrophysical Journal Letters. 13 pages,
including 5 figure
Alarm-Based Prescriptive Process Monitoring
Predictive process monitoring is concerned with the analysis of events
produced during the execution of a process in order to predict the future state
of ongoing cases thereof. Existing techniques in this field are able to
predict, at each step of a case, the likelihood that the case will end up in an
undesired outcome. These techniques, however, do not take into account what
process workers may do with the generated predictions in order to decrease the
likelihood of undesired outcomes. This paper proposes a framework for
prescriptive process monitoring, which extends predictive process monitoring
approaches with the concepts of alarms, interventions, compensations, and
mitigation effects. The framework incorporates a parameterized cost model to
assess the cost-benefit tradeoffs of applying prescriptive process monitoring
in a given setting. The paper also outlines an approach to optimize the
generation of alarms given a dataset and a set of cost model parameters. The
proposed approach is empirically evaluated using a range of real-life event
logs
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Surface Profiling of Natural Dust Devils
We present results from the first high-resolution near-surface profiles conducted on dust devil wind fields. These results are integrated with extensive geologic mapping to understand the factors that influence vortex generation and erosive efficacy
Evaluation of wind tunnel performance testings of an advanced 45 deg swept 8-bladed propeller at Mach numbers from 0.45 to 0.85
The increased emphasis of fuel conservation in the world and the rapid increase in the cost of jet fuel has stimulated a series of studies of both conventional and unconventional propulsion systems for commercial aircraft. The results of these studies indicate that a fuel saving of 15 to 30 percent may be realized by the use of an advanced high-speed turboprop (Prop-Fan) compared to aircraft equipped with high bypass turbofan engines of equivalent technology. The Prop-Fan propulsion system is being investigated as part of the NASA Aircraft Energy Efficient Program. This effort includes the wind tunnel testing of a series of 8 and 10-blade Prop-Fan models incorporate swept blades. Test results indicate efficiency levels near the goal of 80 percent at Mach 0.8 cruise and an altitude of 10.67 km (35,000 ft). Each successive swept model has shown improved efficiency relative to the straight blade model. The fourth model, with 45 deg swept blades reported herein, shows a net efficiency of 78.2 at the design point with a power loading of 301 kW/sq meter and a tip speed of 243.8 m/sec (800 ft/sec.)
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A close encounter with a terrestrial dust devil
We report on an extremely well characterised encounter with a terrestrial dust devil, and its comparison with martian dust devils
A Search for Distant Galactic Cepheids Toward l=60
We present results of a survey of a 6-square-degree region near l=60, b=0 to
search for distant Milky Way Cepheids. Few MW Cepheids are known at distances
>~ R_0, limiting large-scale MW disk models derived from Cepheid kinematics;
this work was designed to find a sample of distant Cepheids for use in such
models. The survey was conducted in the V and I bands over 8 epochs, to a
limiting I~=18, with a total of ~ 5 million photometric observations of ~ 1
million stars. We present a catalog of 578 high-amplitude variables discovered
in this field. Cepheid candidates were selected from this catalog on the basis
of variability and color change, and observed again the following season. We
confirm 10 of these candidates as Cepheids with periods from 4 to 8 days, most
at distances > 3 kpc. Many of the Cepheids are heavily reddened by intervening
dust, some with implied extinction A_V > 10 mag. With a future addition of
infrared photometry and radial velocities, these stars alone can provide a
constraint on R_0 to 8%, and in conjunction with other known Cepheids should
provide good estimates of the global disk potential ellipticity.Comment: 18 pages, 4 tables, 13 figures (LaTeX / AASTeX
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