271 research outputs found
High purity H2 by sorption-enhanced chemical looping reforming of waste cooking oil in a packed bed reactor.
High purity hydrogen (>95%) was produced at 600 degrees C and 1 atm by steam reforming of waste cooking oil at a molar steam to carbon ratio of 4 using chemical looping, a process that features redox cycles of a Ni catalyst with the in-situ carbonation/calcination of a CO(2) sorbent (dolomite) in a packed bed reactor under alternated feedstreams of fuel-steam and air. The fuel and steam conversion were higher with the sorbent present than without it. Initially, the dolomite carbonation was very efficient (100%), and 98% purity hydrogen was produced, but the carbonation decreased to around 56% with a purity of 95% respectively in the following cycles. Reduction of the nickel catalyst occurred alongside steam reforming, water gas shift and carbonation, with H(2) produced continuously under fuel-steam feeds. Catalyst and CO(2)-sorbent regeneration was observed, and long periods of autothermal operation within each cycle were demonstrated
Explicit tracking of uncertainty increases the power of quantitative rule-of-thumb reasoning in cell biology
"Back-of-the-envelope" or "rule-of-thumb" calculations involving rough
estimates of quantities play a central scientific role in developing intuition
about the structure and behaviour of physical systems, for example in so-called
`Fermi problems' in the physical sciences. Such calculations can be used to
powerfully and quantitatively reason about biological systems, particularly at
the interface between physics and biology. However, substantial uncertainties
are often associated with values in cell biology, and performing calculations
without taking this uncertainty into account may limit the extent to which
results can be interpreted for a given problem. We present a means to
facilitate such calculations where uncertainties are explicitly tracked through
the line of reasoning, and introduce a `probabilistic calculator' called
Caladis, a web tool freely available at www.caladis.org, designed to perform
this tracking. This approach allows users to perform more statistically robust
calculations in cell biology despite having uncertain values, and to identify
which quantities need to be measured more precisely in order to make confident
statements, facilitating efficient experimental design. We illustrate the use
of our tool for tracking uncertainty in several example biological
calculations, showing that the results yield powerful and interpretable
statistics on the quantities of interest. We also demonstrate that the outcomes
of calculations may differ from point estimates when uncertainty is accurately
tracked. An integral link between Caladis and the Bionumbers repository of
biological quantities further facilitates the straightforward location,
selection, and use of a wealth of experimental data in cell biological
calculations.Comment: 8 pages, 3 figure
Hydrogen production by sorption-enhanced steam reforming of glycerol
Catalytic steam reforming of glycerol for H(2) production has been evaluated experimentally in a continuous flow fixed-bed reactor. The experiments were carried out under atmospheric pressure within a temperature range of 400-700 degrees C. A commercial Ni-based catalyst and a dolomite sorbent were used for the steam reforming reactions and in situ CO(2) removal. The product gases were measured by on-line gas analysers. The results show that H(2) productivity is greatly increased with increasing temperature and the formation of methane by-product becomes negligible above 500 degrees C. The results suggest an optimal temperature of approximately 500 degrees C for the glycerol steam reforming with in situ CO(2) removal using calcined dolomite as the sorbent, at which the CO(2) breakthrough time is longest and the H(2) purity is highest. The shrinking core model and the 1D-diffusion model describe well the CO(2) removal under the conditions of this work
The IDV source J1128+5925, a new candidate for annual modulation?
Short time-scale radio variations of compact extragalactic radio sources,
known as IntraDay Variability, can be explained in at least some sources by a
source-extrinsic effect, in which the variations are interpreted as
scintillation of radio waves caused by the turbulent ISM of the Milky Way. One
of the most convincing observational arguments in favour of propagation-induced
variability is the so called annual modulation of the characteristic
variability time-scale, which is due to the orbital motion of the Earth. Data
for the recently discovered and highly variable IDV source J1128+5925 are
presented. We study the frequency and time dependence of the IDV in this
compact quasar. We measure the characteristic variability time-scale of the IDV
throughout the year, and analyze whether the observed changes in the
variability time-scale are consistent with annual modulation. We monitored the
flux density variability of J1128+5925 with dense time sampling between 2.7 and
10.45GHz with the 100m Effelsberg radio telescope of the MPIfR and with the 25m
Urumqi radio telescope. From ten observing sessions, we determine the
variability characteristics and time-scales. The observed pronounced changes of
the variability time-scale of J1128+5925 are modelled with an anisotropic
annual modulation model. The observed frequency dependence of the variation is
in good agreement with the prediction from interstellar scintillation. Adopting
a simple model for the annual modulation model and using also the frequency
dependence of the IDV, we derive a lower limit to the distance of the
scattering screen and an upper limit to the scintillating source size. The
latter is found to be consistent with the measured core size from VLBI.Comment: 15 pages, 9 figures Accepted for publication in Astronomy and
Astrophysic
The stationary phase point method for transitional scattering: diffractive radio scintillation for pulsar
The stationary phase point (SPP) method in one-dimensional case is introduced
to treat the diffractive scintillation. From weak scattering, where the SPP
number N=1, to strong scattering (N1), via transitional scattering regime
(N2,3), we find that the modulation index of intensity experiences the
monotonically increasing from 0 to 1 with the scattering strength,
characterized by the ratio of Fresnel scale \rf to diffractive scale
\rdiff.Comment: Hanas Meeting paper, appear in ChJAA, 2006, 6, Su
Interstellar Scintillation of the Polarized Flux Density in Quasar, PKS 0405-385
The remarkable rapid variations in radio flux density and polarization of the
quasar PKS 0405-385 observed in 1996 are subject to a correlation analysis,
from which characteristic time scales and amplitudes are derived. The
variations are interpreted as interstellar scintillations. The cm wavelength
observations are in the weak scintillation regime for which models for the
various auto- and cross-correlations of the Stokes parameters are derived and
fitted to the observations. These are well modelled by interstellar
scintillation (ISS) of a 30 by 22 micro-as source, with about 180 degree
rotation of the polarization angle along its long dimension. This success in
explaining the remarkable intra-day variations (IDV)in polarization confirms
that ISS gives rise to the IDV in this quasar. However, the fit requires the
scintillations to be occurring much closer to the Earth than expected according
to the standard model for the ionized interstellar medium (IISM). Scattering at
distances in the range 3-30 parsec are required to explain the observations.
The associated source model has a peak brightness temperature near 2.0
10^{13}K, which is about twenty-five times smaller than previously derived for
this source. This reduces the implied Doppler factor in the relativistic jet,
presumed responsible to 10-20, high but just compatible with cm wavelength VLBI
estimates for the Doppler factors in Active Galactic Nuclei (AGNs).Comment: 43 pages 15 figures, accepted for ApJ Dec 200
Fungi, Myxomycetes, Ceratiomyxales, Liceales, Trichiales, Stemonitales, Physarales.
v. 1, pt. 1 (1945
First Results from MASIV: The Micro-Arcsecond Scintillation-Induced Variability Survey
We are undertaking a large-scale, Micro-Arcsecond Scintillation-Induced
Variability (MASIV) survey of the northern sky, Dec > 0 deg, at 4.9 GHz with
the VLA. Our objective is to construct a sample of 100 to 150 scintillating
extragalactic sources with which to examine both the microarcsecond structure
and the parent populations of these sources, and to probe the turbulent
interstellar medium responsible for the scintillation. We report on our first
epoch of observations which revealed variability on timescales ranging from
hours to days in 85 of 710 compact flat-spectrum sources. The number of highly
variable sources, those with RMS flux density variations greater than 4% of the
mean, increases with decreasing source flux density but rapid, large amplitude
variables such as J1819+3845 are very rare. When compared with a model for the
scintillation due to irregularities in a 500 pc thick electron layer, our
preliminary results indicate maximum brightness temperatures ~10E+12 K, similar
to those obtained from VLBI surveys even though interstellar scintillation is
not subject to the same angular resolution limit.Comment: 18 pages, 5 figures. To appear in the Astronomical Journa
On the influence of the Sun on the rapid variability of compact extragalactic sources
Starting from December 2004, a program for the monitoring of intraday
variable sources at a frequency of 5 GHz was performed at the Urumqi
Observatory. The analysis of the variability characteristics of the
flat-spectrum radio source AO 0235+164 revealed the existence of an annual
cycle in the variability amplitude. This appears to correlate with the solar
elongation of the source. A thorough analysis of the results of the MASIV IDV
survey --- which provides the variability characteristics of a large sample of
compact radio sources --- confirms that there is a small but detectable
component of the observed fractional modulation which increases with decreasing
solar elongation. We discuss the hypothesis that the phenomenon is related to
interplanetary scintillation.Comment: 10 pages, 12 figures and 2 tables. Accepted for publication in
Astronomy and Astrophysic
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