26,537 research outputs found
Flight investigation of insect contamination and its alleviation
An investigation of leading edge contamination by insects was conducted with a JetStar airplane instrumented to detect transition on the outboard leading edge flap and equipped with a system to spray the leading edge in flight. The results of airline type flights with the JetStar indicated that insects can contaminate the leading edge during takeoff and climbout. The results also showed that the insects collected on the leading edges at 180 knots did not erode at cruise conditions for a laminar flow control airplane and caused premature transition of the laminar boundary layer. None of the superslick and hydrophobic surfaces tested showed any significant advantages in alleviating the insect contamination problem. While there may be other solutions to the insect contamination problem, the results of these tests with a spray system showed that a continouous water spray while encountering the insects is effective in preventing insect contamination of the leading edges
Clearcutting in Appalachia: Impacts on Stream Water Quality in an Appalachian Watershed
Clearcutting forests has the potential to impact the water quality of high water headwater streams. In this study, we measured the effect of forest clearcut events on parameters of stream water quality within Michaux State Forest. The watershed of two streams included 2.1% and 11.6% of the total catchment in clearcuts, while the other 4 watersheds had no clearcuts. We measured pH, electrical conductivity, total suspended solids, and nitrate (ppm) and phosphate (ppm) concentrations from six different tributary streams. Mann-Whitney U tests maintain no statistical difference observed between pH (U= 4.00, p= 1.00), temperature (U=1.00, p=0.165), electrical conductivity (U=2.00, p=0.355), suspended solids (U=2.00, p=0.325), nitrate concentration (U=2.00, p=0.264), or phosphate concentration (U=2.00, p=0.340). However, post-hoc analysis confirms stream 6 as an upper outlier for electrical conductivity (EC= 86.8 uS). This may be due to this site’s proximity to a busy road. These results suggest that there is no significant impact of clearcutting on stream water quality in Michaux State Forest. However, further repetition of this experiment would be necessary to make this conclusion statistically robust
S-Net for multi-memory multicores
Copyright ACM, 2010. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Proceedings of the 5th ACM SIGPLAN Workshop on Declarative Aspects of Multicore Programming: http://doi.acm.org/10.1145/1708046.1708054S-Net is a declarative coordination language and component technology aimed at modern multi-core/many-core architectures and systems-on-chip. It builds on the concept of stream processing to structure dynamically evolving networks of communicating asynchronous components. Components themselves are implemented using a conventional language suitable for the application domain. This two-level software architecture maintains a familiar sequential development environment for large parts of an application and offers a high-level declarative approach to component coordination. In this paper we present a conservative language extension for the placement of components and component networks in a multi-memory environment, i.e. architectures that associate individual compute cores or groups thereof with private memories. We describe a novel distributed runtime system layer that complements our existing multithreaded runtime system for shared memory multicores. Particular emphasis is put on efficient management of data communication. Last not least, we present preliminary experimental data
On the soft X-ray spectrum of cooling flows
Strong evidence for cooling flows has been found in low resolution X-ray
imaging and spectra of many clusters of galaxies. However high resolution X-ray
spectra of several clusters from the Reflection Grating Spectrometer (RGS) on
XMM-Newton now show a soft X-ray spectrum inconsistent with a simple cooling
flow. The main problem is a lack of the emission lines expected from gas
cooling below 1--2 keV. Lines from gas at about 2--3 keV are observed, even in
a high temperature cluster such as A 1835, indicating that gas is cooling down
to about 2--3 keV, but is not found at lower temperatures. Here we discuss
several solutions to the problem; heating, mixing, differential absorption and
inhomogeneous metallicity. Continuous or sporadic heating creates further
problems, including the targetting of the heat at the cooler gas and also the
high total energy required. So far there is no clear observational evidence for
widespread heating, or shocks, in cluster cores, except in radio lobes which
occupy only part of the volume. The implied ages of cooling flows are short, at
about 1 Gyr. Mixing. or absorption, of the cooling gas are other possibilities.
Alternatively, if the metals in the intracluster medium are not uniformly
spread but are clumped, then little line emission is expected from the gas
cooling below 1 keV. The low metallicity part cools without line emission
whereas the strengths of the soft X-ray lines from the metal-rich gas depend on
the mass fraction of that gas and not on the abundance, since soft X-ray line
emission dominates the cooling function below 2 keV.Comment: 5 pages, with 2 figures, submitted to MNRA
Delineation of the boundaries of a buried pre-glacial valley with LANDSAT-1 data
The continuity of a narrow meandering strip of Udoll (prairie) soils running east and west for approximately 40 miles across north central Indiana in an area predominantly of Udalfs (timber soils) was detected from LANDSAT-1 data taken on June 9, 1973. This data was processed through a clustering procedure and classified with resulting increased definition of the boundaries among soils grouped according to nine categories and vegetation to two categories of reflectance. This dark stretch of prairie soil is believed to have formed in the heavy textured, poorly drained glacial debris which filled a major pre-glacial tributary of the Teays River System. Ready identification and location of the valley has significance to soil survey and land classification people as a guide to soil classification and land use and to geologists as a guide to location of a potentially economically significant aquifer
On the evolution of cooling cores in X-ray galaxy clusters
(Abridged) To define a framework for the formation and evolution of the
cooling cores in X-ray galaxy clusters, we study how the physical properties
change as function of the cosmic time in the inner regions of a 4 keV and 8 keV
galaxy cluster under the action of radiative cooling and gravity only. The
cooling radius, R_cool, defined as the radius at which the cooling time equals
the Universe age at given redshift, evolves from ~0.01 R200 at z>2, where the
structures begin their evolution, to ~0.05 R200 at z=0. The values measured at
0.01 R200 show an increase of about 15-20 per cent per Gyr in the gas density
and surface brightness and a decrease with a mean rate of 10 per cent per Gyr
in the gas temperature. The emission-weighted temperature diminishes by about
25 per cent and the bolometric X-ray luminosity rises by a factor ~2 after 10
Gyrs when all the cluster emission is considered in the computation. On the
contrary, when the core region within 0.15 R500 is excluded, the gas
temperature value does not change and the X-ray luminosity varies by 10-20 per
cent only. The cooling time and gas entropy radial profiles are well
represented by power-law functions. The behaviour of the inner slopes of the
gas temperature and density profiles are the most sensitive and unambiguous
tracers of an evolving cooling core. Their values after 10 Gyrs of radiative
losses, T_gas ~ r^0.4 and n_gas ~ r^(-1.2) for the hot (cool) object, are
remarkably in agreement with the observational constraints available for nearby
X-ray luminous cooling core clusters. Because our simulations do not consider
any AGN heating, they imply that the feedback process does not greatly alter
the gas density and temperature profiles as generated by radiative cooling
alone.Comment: 8 pages. MNRAS in pres
Extensions of the space trajectories error analysis programs
A generalized covariance analysis technique which permits the study of the sensitivity of linear estimation algorithms to errors in a priori statistics has been developed and programed. Several sample cases are presented to illustrate the use of this technique. Modifications to the Simulated Trajectories Error Analysis Program (STEAP) to enable targeting a multiprobe mission of the Planetary Explorer type are discussed. The logic for the mini-probe targeting is presented. Finally, the initial phases of the conversion of the Viking mission Lander Trajectory Reconstruction (LTR) program for use on Venus missions is discussed. An integrator instability problem is discussed and a solution proposed
Demonstration of efficient nonreciprocity in a microwave optomechanical circuit
The ability to engineer nonreciprocal interactions is an essential tool in
modern communication technology as well as a powerful resource for building
quantum networks. Aside from large reverse isolation, a nonreciprocal device
suitable for applications must also have high efficiency (low insertion loss)
and low output noise. Recent theoretical and experimental studies have shown
that nonreciprocal behavior can be achieved in optomechanical systems, but
performance in these last two attributes has been limited. Here we demonstrate
an efficient, frequency-converting microwave isolator based on the
optomechanical interactions between electromagnetic fields and a mechanically
compliant vacuum gap capacitor. We achieve simultaneous reverse isolation of
more than 20 dB and insertion loss less than 1.5 dB over a bandwidth of 5 kHz.
We characterize the nonreciprocal noise performance of the device, observing
that the residual thermal noise from the mechanical environments is routed
solely to the input of the isolator. Our measurements show quantitative
agreement with a general coupled-mode theory. Unlike conventional isolators and
circulators, these compact nonreciprocal devices do not require a static
magnetic field, and they allow for dynamic control of the direction of
isolation. With these advantages, similar devices could enable programmable,
high-efficiency connections between disparate nodes of quantum networks, even
efficiently bridging the microwave and optical domains.Comment: 9 pages, 6 figure
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