12,060 research outputs found
Experimental comparison of icing cloud instruments
Icing cloud instruments were tested in the spray cloud Icing Research Tunnel (IRT) in order to determine their relative accuracy and their limitations over a broad range of conditions. It was found that the average of the readings from each of the liquid water content (LWC) instruments tested agreed closely with each other and with the IRT calibration; but all have a data scatter (+ or - one standard deviation) of about + or - 20 percent. The effect of this + or - 20 percent uncertainty is probably acceptable in aero-penalty and deicer experiments. Existing laser spectrometers proved to be too inaccurate for LWC measurements. The error due to water runoff was the same for all ice accretion LWC instruments. Any given laser spectrometer proved to be highly repeatable in its indications of volume median drop size (DVM), LWC and drop size distribution. However, there was a significant disagreement between different spectrometers of the same model, even after careful standard calibration and data analysis. The scatter about the mean of the DVM data from five Axial Scattering Spectrometer Probes was + or - 20 percent (+ or - one standard deviation) and the average was 20 percent higher than the old IRT calibration. The + or - 20 percent uncertainty in DVM can cause an unacceptable variation in the drag coefficient of an airfoil with ice; however, the variation in a deicer performance test may be acceptable
The Energy Dependence of the Aperiodic Variability for Cygnus X-1, GX 339-4, GRS 1758-258, & 1E 1740.7-2942
Using the data from the Rossi X-ray Timing Explorer (RXTE), we report the
different energy dependence of the variability of the four persistent hard
X-ray sources in the low-hard state: Cygnus X-1, GX 339-4, GRS 1758-258 and 1E
1740.7-2942. Cygnus X-1 is found to have a flatter power density spectrum (PDS)
shape at higher energies. The other three sources have energy independent PDS
shapes. The energy dependence of the overall variability (the integrated rms
amplitude) varies from source to source and from observation to observation.
1E~1740.7-2942, for example, has a variability generally increasing with energy
while GX 339-4 has a decreasing variability. A general trend is found in the
four sources that the integrated rms amplitude anti-correlates with the X-ray
flux. We compare these distinct energy dependent behaviors with several
emission models. None of the models can fully explain all the features that we
have found.Comment: 18 pages, 6 figures. Accepted for publication in Ap
Comparison of modern icing cloud instruments
Intercomparison tests with Particle Measuring Systems (PMS) were conducted. Cloud liquid water content (LWC) measurements were also taken with a Johnson and Williams (JW) hot-wire device and an icing rate device (Leigh IDS). Tests include varying cloud LWC (0.5 to 5 au gm), cloud median volume diameter (MVD) (15 to 26 microns), temperature (-29 to 20 C), and air speeds (50 to 285 mph). Comparisons were based upon evaluating probe estimates of cloud LWC and median volume diameter for given tunnel settings. Variations of plus or minus 10% and plus or minus 5% in LWC and MVD, respectively, were determined of spray clouds between test made at given tunnel settings (fixed LWC, MVD, and air speed) indicating cloud conditions were highly reproducible. Although LWC measurements from JW and Leigh devices were consistent with tunnel values, individual probe measurements either consistently over or underestimated tunnel values by factors ranging from about 0.2 to 2. Range amounted to a factor of 6 differences between LWC estimates of probes for given cloud conditions. For given cloud conditions, estimates of cloud MVD between probes were within plus or minus 3 microns and 93% of the test cases. Measurements overestimated tunnel values in the range between 10 to 20 microns. The need for improving currently used calibration procedures was indicated. Establishment of test facility (or facilities) such as an icing tunnel where instruments can be calibrated against known cloud standards would be a logical choice
Braided Hopf algebras obtained from coquasitriangular Hopf algebras
Let be a coquasitriangular Hopf algebra, not necessarily finite
dimensional. Following methods of Doi and Takeuchi, which parallel the
constructions of Radford in the case of finite dimensional quasitriangular Hopf
algebras, we define , a sub-Hopf algebra of , the finite dual of
. Using the generalized quantum double construction and the theory of Hopf
algebras with a projection, we associate to a braided Hopf algebra
structure in the category of Yetter-Drinfeld modules over .
Specializing to , we obtain explicit formulas which endow
with a braided Hopf algebra structure within the category of
left Yetter-Drinfeld modules over .Comment: 43 pages, 1 figur
Far-Ultraviolet and Far-Infrared Bivariate Luminosity Function of Galaxies: Complex Relation between Stellar and Dust Emission
Far-ultraviolet (FUV) and far-infrared (FIR) luminosity functions (LFs) of
galaxies show a strong evolution from to , but the FIR LF
evolves much stronger than the FUV one. The FUV is dominantly radiated from
newly formed short-lived OB stars, while the FIR is emitted by dust grains
heated by the FUV radiation field. It is known that dust is always associated
with star formation activity. Thus, both FUV and FIR are tightly related to the
star formation in galaxies, but in a very complicated manner. In order to
disentangle the relation between FUV and FIR emissions, we estimate the UV-IR
bivariate LF (BLF) of galaxies with {\sl GALEX} and {\sl AKARI} All-Sky Survey
datasets. Recently we invented a new mathematical method to construct the BLF
with given marginals and prescribed correlation coefficient. This method makes
use of a tool from mathematical statistics, so called "copula". The copula
enables us to construct a bivariate distribution function from given marginal
distributions with prescribed correlation and/or dependence structure. With
this new formulation and FUV and FIR univariate LFs, we analyze various FUV and
FIR data with {\sl GALEX}, {\sl Spitzer}, and {\sl AKARI} to estimate the UV-IR
BLF. The obtained BLFs naturally explain the nonlinear complicated relation
between FUV and FIR emission from star-forming galaxies. Though the faint-end
of the BLF was not well constrained for high- samples, the estimated linear
correlation coefficient was found to be very high, and is remarkably
stable with redshifts (from 0.95 at to 0.85 at ). This implies
the evolution of the UV-IR BLF is mainly due to the different evolution of the
univariate LFs, and may not be controlled by the dependence structure.Comment: 10 pages, 7 figures, Earth, Planets and Space, in pres
Analysis of model Titan atmospheric components using ion mobility spectrometry
The Gas Chromatograph-Ion Mobility Spectrometer (GC-IMS) was proposed as an analytical technique for the analysis of Titan's atmosphere during the Cassini Mission. The IMS is an atmospheric pressure, chemical detector that produces an identifying spectrum of each chemical species measured. When the IMS is combined with a GC as a GC-IMS, the GC is used to separate the sample into its individual components, or perhaps small groups of components. The IMS is then used to detect, quantify, and identify each sample component. Conventional IMS detection and identification of sample components depends upon a source of energetic radiation, such as beta radiation, which ionizes the atmospheric pressure host gas. This primary ionization initiates a sequence of ion-molecule reactions leading to the formation of sufficiently energetic positive or negative ions, which in turn ionize most constituents in the sample. In conventional IMS, this reaction sequence is dominated by the water cluster ion. However, many of the light hydrocarbons expected in Titan's atmosphere cannot be analyzed by IMS using this mechanism at the concentrations expected. Research at NASA Ames and PCP Inc., has demonstrated IMS analysis of expected Titan atmospheric components, including saturated aliphatic hydrocarbons, using two alternate sample ionizations mechanisms. The sensitivity of the IMS to hydrocarbons such as propane and butane was increased by several orders of magnitude. Both ultra dry (waterless) IMS sample ionization and metastable ionization were successfully used to analyze a model Titan atmospheric gas mixture
Dusty Universe viewed by AKARI far infrared detector
We present the results of the analysis of multiwavelength Spectral Energy
Distributions (SEDs) of far-infrared galaxies detected in the AKARI Deep
Field-South (ADF--S) Survey. The analysis uses a carefully selected sample of
186 sources detected at the 90 m AKARI band, identified as galaxies with
cross-identification in public catalogues. For sources without known
spectroscopic redshifts, we estimate photometric redshifts after a test of two
independent methods: one based on using mainly the optical -- mid infrared
range, and one based on the whole range of ultraviolet -- far infrared data. We
observe a vast improvement in the estimation of photometric redshifts when far
infrared data are included, compared with an approach based mainly on the
optical -- mid infrared range. We discuss the physical properties of our
far-infrared-selected sample. We conclude that this sample consists mostly of
rich in dust and young stars nearby galaxies, and, furthermore, that almost 25%
of these sources are (Ultra)Luminous Infrared Galaxies. Average SEDs normalized
at 90 m for normal galaxies (138 sources), LIRGs (30 sources), and ULIRGs
(18 galaxies) a the significant shift in the peak wavelength of the dust
emission, and an increasing ratio between their bolometric and dust
luminosities which varies from 0.39 to 0.73.Comment: 8 pages, 7 figures, published in Earth, Planets and Spac
[Ultra] Luminous Infrared Galaxies selected at 90 m in the AKARI deep field: a study of AGN types contributing to their infrared emission
The aim of this work is to characterize physical properties of Ultra Luminous
Infrared Galaxies (ULIRGs) and Luminous Infrared Galaxies (LIRGs) detected in
the far-infrared (FIR) 90um band in the AKARI Deep Field-South (ADF-S) survey.
In particular, we want to estimate the AGN contribution to the [U]LIRGs'
infrared emission and which types of AGNs are related to their activity. We
examined 69 galaxies at z>0.05 detected at 90um by the AKARI satellite in the
ADF-S, with optical counterparts and spectral coverage from the ultraviolet to
the FIR. We used two independent spectral energy distribution fitting codes:
one fitting the SED from FIR to FUV (CIGALE) and gray-body + power spectrum fit
for the infrared part of the spectra (CMCIRSED) in order to identify a
subsample of [U]LIRGs, and to estimate their properties. Based on the CIGALE
SED fitting, we have found that [U]LIRGs selected at the 90um AKARI band
compose ~56% of our sample (we found 17 ULIRGs and 22 LIRGs, spanning over the
redshift range 0.06<z<1.23). Their physical parameters, such as stellar mass,
star formation rate (SFR), and specific SFR are consistent with the ones found
for other samples selected at IR wavelengths. We have detected a significant
AGN contribution to the MIR luminosity for 63% of LIRGs and ULIRGs. Our LIRGs
contain Type 1, Type 2, and intermediate types of AGN, whereas for ULIRGs, a
majority (more than 50%) of AGN emission originates from Type 2 AGNs. The
temperature--luminosity and temperature--mass relations for the dust component
of ADF--S LIRGs and ULIRGs indicate that these relations are shaped by the dust
mass and not by the increased dust heating. We conclude that LIRGs contain Type
1, Type 2, and intermediate types of AGNs, with an AGN contribution to the MIR
emission at the median level of 13+/-3%, whereas the majority of ULIRGs contain
Type 2 AGNs, with a median AGN fraction equal to 19+/-8%.Comment: 24 pages, 21 figures, accepted for publication in Astronomy &
Astrophysic
Niobium based intermetallics as a source of high-current/high-magnetic field superconductors
The article is focused on low temperature intermetallic A15 superconducting
wires development for Nuclear Magnetic Resonance, NMR, and Nuclear Magnetic
Imaging, MRI, magnets and also on cryogen-free magnets. There are many other
applications which would benefit from new development such as future Large
Hadron Collider to be built from A15 intermetallic conductors. This paper
highlights the current status of development of the niobium based
intermetallics with special attention to Nb 3 (Al 1-x, Ge x). Discussion is
focused on the materials science aspects of conductor manufacture, such as
b-phase (A15) formation, with particular emphasis on the maximisation of the
superconducting parameters, such as critical current density, Jc, critical
temperature, Tc, and upper critical field, Hc2 . Many successful manufacturing
techniques of the potential niobium-aluminide intermetallic superconducting
conductors, such as solid-state processing, liquid-solid processing, rapid
heating/cooling processes, are described, compared and assessed. Special
emphasis has been laid on conditions under which the Jc (B) peak effect occurs
in some of the Nb3(Al,Ge) wires. A novel electrodeoxidizing method developed in
Cambridge whereby the alloys and intermetallics are produced cheaply making all
superconducting electromagnetic devices, using low cost LTCs, more cost
effective is presented.This new technique has potential to revolutionise the
existing superconducting industry enabling reduction of cost orders of
magnitude.Comment: Paper presented at EUCAS'01 conference, Copenhagen, 26-30 August 200
Information criteria for efficient quantum state estimation
Recently several more efficient versions of quantum state tomography have
been proposed, with the purpose of making tomography feasible even for
many-qubit states. The number of state parameters to be estimated is reduced by
tentatively introducing certain simplifying assumptions on the form of the
quantum state, and subsequently using the data to rigorously verify these
assumptions. The simplifying assumptions considered so far were (i) the state
can be well approximated to be of low rank, or (ii) the state can be well
approximated as a matrix product state. We add one more method in that same
spirit: we allow in principle any model for the state, using any (small) number
of parameters (which can, e.g., be chosen to have a clear physical meaning),
and the data are used to verify the model. The proof that this method is valid
cannot be as strict as in above-mentioned cases, but is based on
well-established statistical methods that go under the name of "information
criteria." We exploit here, in particular, the Akaike Information Criterion
(AIC). We illustrate the method by simulating experiments on (noisy) Dicke
states
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