765 research outputs found
Enabling interactive safety and performance trade-offs in early airframe systems design
Presented is a novel interactive framework for incorporating both safety and performance analyses in early systems architecture design, thus allowing the study of possible trade-offs. Traditionally, a systems architecture is first defined by the architects and then passed to experts, who manually create artefacts such as Fault Tree Analysis (FTA) for safety assessment, or computational workflows, for performance assessment. The downside of this manual approach is that if the architect modifies the systems architecture, most of the process needs to be repeated, which is tedious and time consuming. This limits the exploration of the design space, with the associated risk of missing better architectures. To overcome this limitation, the proposed framework automates parts of the safety and performance analysis in the context of the Requirement, Functional, Logical, and Physical (RFLP) systems engineering paradigm. Safety analysis is carried out by automatic creation of FTA models from the functional and logical flow views. Regarding performance analysis, computational workflows are first automatically created from the logical flow view, and then executed for a set of flight conditions over the range of the mission in order to determine the most demanding condition. Finally, performance characteristics of the subsystems, such as weights, power offtakes, ram drag etc. are evaluated at the most demanding flight condition, which enables the architect to compare architectures at aircraft level. The framework is illustrated with a representative example involving the design of an environmental control system of a civil aircraft, where the safety and performance trade-off is conducted for multiple ECS architectures
Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function
In this second paper in a series dedicated to developing efficient numerical
techniques for the deblurring Cosmic Microwave Background (CMB) maps, we
consider the case of asymmetric point spread functions (PSF). Although
conceptually this problem is not different from the symmetric case, there are
important differences from the computational point of view because it is no
longer possible to use some of the efficient numerical techniques that work
with symmetric PSFs. We present procedures that permit the use of efficient
techniques even when this condition is not met. In particular, two methods are
considered: a procedure based on a Kronecker approximation technique that can
be implemented with the numerical methods used with symmetric PSFs but that has
the limitation of requiring only mildly asymmetric PSFs. The second is a
variant of the classic Tikhonov technique that works even with very asymmetric
PSFs but that requires discarding the edges of the maps. We provide details for
efficient implementations of the algorithms. Their performance is tested on
simulated CMB maps.Comment: 9 pages, 13 Figure
Characterization and winemaking application of a novel pectin-degrading enzyme complex from Aspergillus sojae ATCC 20235
A novel pectin-degrading enzyme complex produced by Aspergillus sojae ATCC 20235 (PC-AS) using lowcost substrates was characterised in terms of its enzyme activities relevant in winemaking. This novel PC-AS was applied at the maceration/fermentation stage during the elaboration of 'Tempranillo' red wines to study its effect on colour development and the phenolic and amino acid wine composition. PC-AS polygalacturonase activity was the major enzyme activity detected and quantified under winemaking conditions (pH 3.5, 20 °C) and proved being stable and active in the presence of sulfur dioxide. Xylanase activity, albeit in lesser amounts, was also present in PC-AS, and neither pectinesterase, which produces methanol, nor β-glucosidase, which is detrimental to wine colour, were detected in PC-AS. This pectin-degrading complex promoted a faster colour extraction since maximum colour intensity of the enzyme treated wines was reached earlier compared to their controls.
After 6 months of storage under winery conditions, wines elaborated with PC-AS presented higher concentrations of caffeic acid, coumaric acid and aspartic acid (p Ë‚ 0.05), suggesting an improved extraction of grape cell components. In conclusion, the application of PCAS yielded results that showed that it can be used in red winemaking to shorten the maceration time needed to reach high CI values and to improve the extraction of some phenolics and other compounds that enhance the quality of the final product.Facultad de Ciencias ExactasCentro de InvestigaciĂłn y Desarrollo en Fermentaciones Industriale
Characterization and winemaking application of a novel pectin-degrading enzyme complex from Aspergillus sojae ATCC 20235
A novel pectin-degrading enzyme complex produced by Aspergillus sojae ATCC 20235 (PC-AS) using lowcost substrates was characterised in terms of its enzyme activities relevant in winemaking. This novel PC-AS was applied at the maceration/fermentation stage during the elaboration of 'Tempranillo' red wines to study its effect on colour development and the phenolic and amino acid wine composition. PC-AS polygalacturonase activity was the major enzyme activity detected and quantified under winemaking conditions (pH 3.5, 20 °C) and proved being stable and active in the presence of sulfur dioxide. Xylanase activity, albeit in lesser amounts, was also present in PC-AS, and neither pectinesterase, which produces methanol, nor β-glucosidase, which is detrimental to wine colour, were detected in PC-AS. This pectin-degrading complex promoted a faster colour extraction since maximum colour intensity of the enzyme treated wines was reached earlier compared to their controls.
After 6 months of storage under winery conditions, wines elaborated with PC-AS presented higher concentrations of caffeic acid, coumaric acid and aspartic acid (p Ë‚ 0.05), suggesting an improved extraction of grape cell components. In conclusion, the application of PCAS yielded results that showed that it can be used in red winemaking to shorten the maceration time needed to reach high CI values and to improve the extraction of some phenolics and other compounds that enhance the quality of the final product.Facultad de Ciencias ExactasCentro de InvestigaciĂłn y Desarrollo en Fermentaciones Industriale
The high-velocity clouds and the Magellanic Clouds
From an analysis of the sky and velocity distributions of the high-velocity
clouds (HVCs) we show that the majority of the HVCs has a common origin. We
conclude that the HVCs surround the Galaxy, forming a metacloud of 300 kpc in
size and with a mass of 3 10^9 M_sun, and that they are the product of a
powerful ``superwind'' (about 10^58 ergs), which occurred in the Magellanic
Clouds about 570 Myr ago as a consequence of the interaction of the Large and
Small Magellanic Clouds. The HVCs might be magnetic bubbles of semi-ionized
gas, blown from the Magellanic Clouds around 570 Myr ago, that circulate
largely through the halo of the Galaxy as a stream or flow of gas.Comment: 28 pages with 23 figure
The Evolution of Supernovae in Circumstellar Wind-Blown Bubbles I. Introduction and One-Dimensional Calculations
Mass loss from massive stars (\ga 8 \msun) can result in the formation of
circumstellar wind blown cavities surrounding the star, bordered by a thin,
dense, cold shell. When the star explodes as a core-collapse supernova (SN),
the resulting shock wave will interact with this modified medium around the
star, rather than the interstellar medium. In this work we first explore the
nature of the circumstellar medium around massive stars in various evolutionary
stages. This is followed by a study of the evolution of SNe within these
wind-blown bubbles. The evolution depends primarily on a single parameter
, the ratio of the mass of the dense shell to that of the ejected
material. We investigate the evolution for different values of this parameter.
We also plot approximate X-ray surface brightness plots from the simulations.
Our results show that in many cases the SN remnant spends a significant amount
of time within the bubble. The low density within the bubble can delay the
onset of the Sedov stage, and may end up reducing the amount of time spent in
the Sedov stage. The complicated density profile within the bubble makes it
difficult to infer the mass-loss properties of the pre-SN star by studying the
evolution of the resulting supernova remnant.Comment: 42 pages, 13 figures. Submitted to the Astrophysical Journal, Sept
200
Storm fronts over galaxy discs: Models of how waves generate extraplanar gas and its anomalous kinematics
The existence of partially ionized, diffuse gas and dust clouds at kiloparsec
scale distances above the central planes of edge-on, galaxy discs was an
unexpected discovery about 20 yrs ago. Subsequent observations showed that this
EDIG (extended or extraplanar diffuse interstellar gas) has rotation velocities
approximately 10-20% lower than those in the central plane, and have been hard
to account for. Here we present results of hydrodynamic models, with radiative
cooling and heating from star formation. We find that in models with star
formation generated stochastically across the disc an extraplanar gas layer is
generated as long as the star formation is sufficiently strong. However, this
gas rotates at nearly the same speed as the mid-plane gas. We then studied a
range of models with imposed spiral or bar waves in the disc. EDIG layers were
also generated in these models, but primarily over the wave regions, not over
the entire disc. Because of this partial coverage, the EDIG clouds move
radially, as well as vertically, with the result that observed kinematic
anomalies are reproduced. The implication is that the kinematic anomalies are
the result of three-dimensional motions when the cylindrical symmetry of the
disc is broken. Thus, the kinematic anomalies are the result of bars or strong
waves, and more face-on galaxies with such waves should have an asymmetric EDIG
component. The models also indicate that the EDIG can contain a significant
fraction of cool gas, and that some star formation can be triggered at
considerable heights above the disc midplane. We expect all of these effects to
be more prominent in young, forming discs, to play a role in rapidly smoothing
disc asymmetries, and in working to self-regulate disc structure.Comment: 30 pages, 9 figs., accepted for MNRAS with additional referee
correction
Radial Profiles of Star Formation in the Far Outer Regions of Galaxy Disks
Star formation in galaxies is triggered by a combination of processes,
including gravitational instabilities, spiral wave shocks, stellar compression,
and turbulence compression. Some of these persist in the far outer regions
where the column density is far below the threshold for instabilities, making
the outer disk cutoff somewhat gradual. We show that in a galaxy with a single
exponential gas profile the star formation rate can have a double exponential
with a shallow one in the inner part and a steep one in the outer part. Such
double exponentials have been observed recently in the broad-band intensity
profiles of spiral and dwarf Irregular galaxies. The break radius in our model
occurs slightly outside the threshold for instabilities provided the Mach
number for compressive motions remains of order unity to large radii. The ratio
of the break radius to the inner exponential scale length increases for higher
surface brightness disks because the unstable part extends further out. This is
also in agreement with observations. Galaxies with extended outer gas disks
that fall more slowly than a single exponential, such as 1/R, can have their
star formation rate scale approximately as a single exponential with radius,
even out to 10 disk scale lengths. Halpha profiles should drop much faster than
the star formation rate as a result of the rapidly decreasing ambient density.Comment: To appear in ApJ. Available from
ftp.lowell.edu/pub/dah/papers/sfouterdisks
The (Re-)Discovery of G350.1-0.3: A Young, Luminous Supernova Remnant and Its Neutron Star
We present an XMM-Newton observation of the long-overlooked radio source
G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma
with two components: a high-temperature (1.5 keV) region with a low ionization
time scale and enhanced abundances, plus a cooler (0.36 keV) component in
ionization equilibrium and with solar abundances. The X-ray spectrum and the
presence of non-thermal, polarized, radio emission together demonstrate that
G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival HI
and 12-CO data indicate a distance of 4.5 kpc. The diameter of the source then
implies an age of only ~900 years. The SNR's distorted appearance, small size
and the presence of 12-CO emission along the SNR's eastern edge all indicate
that the source is interacting with a complicated distribution of dense ambient
material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few
arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and
lack of any multi-wavelength counterpart suggest that this source is a neutron
star associated with G350.1-0.3, most likely a "central compact object", as
seen coincident with other young SNRs such as Cassiopeia A.Comment: 6 pages, uses emulateapj. One B/W figure, one color figure. Minor
text changes and update to Fig 2 following referee's report. ApJ Letters, in
pres
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