4,033 research outputs found
Axial segregation behaviour of a reacting biomass particle in fluidized bed reactors: experimental results and model validation
Axial segregation behaviour of a single biomass particle in a lab-scale bubbling fluidized bed has been investigated from both experimental and modelling perspectives. Experiments were conducted using beech wood particles of different sizes, ranging from 8 to 12 mm under either oxidizing or inert conditions. The fluidized bed reactor was operated at temperatures and fluidization velocity ratios, U/Umf, in the range of 500–650 °C and 1–2, respectively. A one-dimensional model has been developed to predict the axial location of the particle over time, taking into account both dynamic and thermal conversion mechanisms. X-ray imaging techniques allowed to identify endogenous bubbles released during devolatilization and carry out direct measurements of their size. This information was used to propose an expression for the lift force acting on the fuel particle. The model showed very accurate predictions and the segregation behaviour of the fuel particle appeared to be independent of the nature of the fluidizing medium
The conceptual and practical ethical dilemmas of using health discussion board posts as research data.
Increasing numbers of people living with a long-term health condition are putting personal health information online, including on discussion boards. Many discussion boards contain material of potential use to researchers; however, it is unclear how this information can and should be used by researchers. To date there has been no evaluation of the views of those individuals sharing health information online regarding the use of their shared information for research purposes
Financial Transaction Tax: Small is Beautiful
The case for taxing financial transactions merely to raise more revenues from the financial sector is not particularly strong. Better alternatives to tax the financial sector are likely to be available. However, a tax on financial transactions could be justified in order to limit socially
undesirable transactions when more direct means of doing so are unavailable for political or
practical reasons. Some financial transactions are indeed likely to do more harm than good,
especially when they contribute to the systemic risk of the financial system. However, such a
financial transaction tax should be very small, much smaller than the negative externalities in
question, because it is a blunt instrument that also drives out socially useful transactions.
There is a case for taxing over-the-counter derivative transactions at a somewhat higher rate
than exchange-based derivative transactions. More targeted remedies to drive out socially
undesirable transactions should be sought in parallel, which would allow, after their
implementation, to reduce or even phase out financialtransaction taxes
Reconstructing generalized ghost condensate model with dynamical dark energy parametrizations and observational datasets
Observations of high-redshift supernovae indicate that the universe is
accelerating at the present stage, and we refer to the cause for this cosmic
acceleration as ``dark energy''. In particular, the analysis of current data of
type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic
microwave background (CMB) anisotropy implies that, with some possibility, the
equation-of-state parameter of dark energy may cross the cosmological-constant
boundary () during the recent evolution stage. The model of ``quintom''
has been proposed to describe this crossing behavior for dark energy. As
a single-real-scalar-field model of dark energy, the generalized ghost
condensate model provides us with a successful mechanism for realizing the
quintom-like behavior. In this paper, we reconstruct the generalized ghost
condensate model in the light of three forms of parametrization for dynamical
dark energy, with the best-fit results of up-to-date observational data.Comment: 8 pages, 3 figures; references added; accepted for publication in
Mod. Phys. Lett.
Holographic dark matter and dark energy with second order invariants
One of the main goals of modern cosmology remains to summon up a self
consistent policy, able to explain, in the framework of the Einstein's theory,
the cosmic speed up and the presence of Dark Matter in the Universe.
Accordingly to the Holographic principle, which postulates the existence of a
minimal size of a physical region, we argue, in this paper, that if this size
exists for the Universe and it is accrued from the independent geometrical
second order invariants, it would be possible to ensure a surprising source for
Dark Matter and a viable candidate for explaining the late acceleration of the
Universe. Along the work, we develop low redshift tests, such as Supernovae Ia
and kinematical analysis complied by the use of Cosmography and we compare the
outcomes with higher redshift tests, such as CMB peak and anisotropy of the
cosmic power spectrum. All the results indicate that the models presented here
can be interpreted as unified models that are capable to describe both the dark
matter and the dark energy.Comment: 12 figures, revtex styl
Keck Planet Imager and Characterizer (KPIC): status update
Here we report on the status of the The Keck Planet Imager and Characterizer (KPIC), which is an on-going series of upgrades to the W.M. Keck II adaptive optics system and instrument suite focused on exoplanet imaging and spectroscopic characterization. The KPIC infrared pyramid wavefront sensor and fiber injection unit to high-resolution infrared spectrograph NIRSPEC have been assembled, integrated and are under-going tests at the University of Hawaii before installation at the Summit in the Fall of 2018
Hubble Space Telescope Observations of the Planetary Nebula K648 in the Globular Cluster M15
We have obtained observations of the planetary nebula K648 in the Galactic
globular cluster M15 with the Hubble Space Telescope's WFPC2 camera, covering
an interval of 7 days. The frames provide both time-sampled broad-band
photometry of the central star and high-resolution images of the nebula in the
light of H-alpha, [OIII], and [NII]. In the deep narrow-band images, K648 is a
fairly typical double-shelled elliptical, but with a bright arc at one end of
the major axis that is especially prominent in [NII]; this feature is probably
a collection of FLIERs. The nebula is surrounded by a faint, smooth elliptical
halo, which appears undisturbed by any interaction with the interstellar
medium. Adopting Teff = 40,000 +- 3,000 K based upon published spectral-line
analyses, and employing our new broad-band optical flux data along with the
known cluster distance, we find log L/L_sun = 3.78 +- 0.08 for the K648 central
star. Theoretical post-asymptotic-giant-branch evolutionary tracks imply a mass
of 0.60 +- 0.02 M_sun for this luminosity, which is significantly higher than
the mean mass of white dwarfs in globular clusters and the halo field (0.50 +-
0.02). The K648 central star exhibits no significant photometric variability in
our data; thus we find no direct evidence of a close binary companion. We
suggest that the progenitor of K648 experienced mass augmentation in a
close-binary merger, allowing it to evolve to a remnant of higher mass than
those of the single stars in the cluster.Comment: Accepted for publication in The Astronomical Journal (23 pages,
includes 3 figures, one color image
First version of the fiber injection unit for the Keck Planet Imager and Characterizer
Coupling a high-contrast imaging instrument to a high-resolution spectrograph has the potential to enable the most detailed characterization of exoplanet atmospheres, including spin measurements and Doppler mapping. The high-contrast imaging system serves as a spatial filter to separate the light from the star and the planet while the high-resolution spectrograph acts as a spectral filter, which differentiates between features in the stellar and planetary spectra. The Keck Planet Imager and Characterizer (KPIC) located downstream from the current W. M. Keck II adaptive optics (AO) system will contain a fiber injection unit (FIU) combining a high-contrast imaging system and a fiber feed to Keck’s high resolution infrared spectrograph NIRSPEC. Resolved thermal emission from known young giant exoplanets will be injected into a single-mode fiber linked to NIRSPEC, thereby allowing the spectral characterization of their atmospheres. Moreover, the resolution of NIRSPEC (R = 37,500 after upgrade) is high enough to enable spin measurements and Doppler imaging of atmospheric weather phenomenon. The module was integrated at Caltech and shipped to Hawaii at the beginning of 2018 and is currently undergoing characterization. Its transfer to Keck is planned in September and first on-sky tests sometime in December
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