127,846 research outputs found
Study of advanced radial outflow turbine for solar steam Rankine engines
The performance characteristics of various steam Rankine engine configurations for solar electric power generation were investigated. A radial outflow steam turbine was investigated to determine: (1) a method for predicting performance from experimental data; (2) the flexibility of a single design with regard to power output and pressure ratio; and (3) the effect of varying the number of turbine stages. All turbine designs were restricted to be compatible with commercially available gearboxes and generators. A study of several operating methods and control schemes for the steam Rankine engine shows that from an efficiency and control simplicity standpoint, the best approach is to hold turbine inlet temperature constant, vary turbine inlet pressure to match load, and allow condenser temperature to float maintaining constant heat rejection load
Combined high vacuum/high frequency fatigue tester
Apparatus permits application of significantly greater number of cycles or equivalent number of cycles in shorter time than conventional fatigue test machines. Environment eliminates problems associated with high temperature oxidation and with sensitivity of refractory alloy behavior to atmospheric contamination
Conditioning of pulses from aerosol-particle detectors
Pulse-conditioner translates pulses generated by aerosol-particle detectors to a form acceptable by commercially available pulse height analyzers designed for nuclear-energy spectroscopy
Automated weighing by sequential inference in dynamic environments
We demonstrate sequential mass inference of a suspended bag of milk powder
from simulated measurements of the vertical force component at the pivot while
the bag is being filled. We compare the predictions of various sequential
inference methods both with and without a physics model to capture the system
dynamics. We find that non-augmented and augmented-state unscented Kalman
filters (UKFs) in conjunction with a physics model of a pendulum of varying
mass and length provide rapid and accurate predictions of the milk powder mass
as a function of time. The UKFs outperform the other method tested - a particle
filter. Moreover, inference methods which incorporate a physics model
outperform equivalent algorithms which do not.Comment: 5 pages, 7 figures. Copyright IEEE (2015
Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants
We aim to investigate mass loss and luminosity in a large sample of evolved
stars in several Local Group galaxies with a variety of metalliticies and
star-formation histories: the Small and Large Magellanic Cloud, and the Fornax,
Carina, and Sculptor dwarf spheroidal galaxies. Dust radiative transfer models
are presented for 225 carbon stars and 171 oxygen-rich evolved stars for which
spectra from the Infrared Spectrograph on Spitzer are available. The spectra
are complemented with available optical and infrared photometry to construct
spectral energy distributions. A minimization procedure was used to determine
luminosity and mass-loss rate (MLR). Pulsation periods were derived for a large
fraction of the sample based on a re-analysis of existing data. New deep K-band
photometry from the VMC survey and multi-epoch data from IRAC and
AllWISE/NEOWISE have allowed us to derive pulsation periods longer than 1000
days for some of the most heavily obscured and reddened objects. We derive
(dust) MLRs and luminosities for the entire sample. The estimated MLRs can
differ significantly from estimates for the same objects in the literature due
to differences in adopted optical constants (up to factors of several) and
details in the radiative transfer modelling. Updated parameters for the
super-AGB candidate MSX SMC 055 (IRAS 00483-7347) are presented. Its current
mass is estimated to be 8.5 +- 1.6 \msol, suggesting an initial mass well above
8~\msol. Using synthetic photometry, we present and discuss colour-colour and
colour-magnitude diagrams which can be expected from the James Webb Space
Telescope.Comment: A&A accepted. The full version (100 pages, 12 MB) with complete
tables and all figures of the appendices is available at
http://homepage.oma.be/marting/articlesgroen.htm
Electronic Hong-Ou-Mandel interferometry in two-dimensional topological insulators
The edge states of a two-dimensional topological insulator are characterized
by their helicity, a very remarkable property which is related to the
time-reversal symmetry and the topology of the underlying system. We
theoretically investigate a Hong-Ou-Mandel like setup as a tool to probe it.
Collisions of two electrons with the same spin show a Pauli dip, analogous to
the one obtained in the integer quantum Hall case. Moreover, the collisions
between electrons of opposite spin also lead to a dip, known as
dip, which is a direct consequence of the constraints imposed
by time-reversal symmetry. In contrast to the integer quantum Hall case, the
visibility of these dips is reduced by the presence of the additional edge
channels, and crucially depends on the properties of the quantum point contact.
As a unique feature of this system, we show the possibility of three-electron
interference, which leads to a total suppression of the noise independently of
the point contact configuration. This is assured by the peculiar interplay
between Fermi statistics and topology. This work intends to extend the domain
of applicability of electron quantum optics.Comment: 12 pages, 7 figure
On the Disalignment of Interstellar Grains
Several mechanisms have been proposed to explain the alignment of grains with
the interstellar magnetic field, including paramagnetic dissipation, radiative
torques, and supersonic gas-grain streaming. These must compete with
disaligning processes, including randomly directed torques arising from
collisions with gas atoms. I describe a novel disalignment mechanism for grains
that have a time-varying electric dipole moment and that drift across the
magnetic field. Depending on the drift speed, this mechanism may yield a much
shorter disalignment timescale than that associated with random gas atom
impacts. For suprathermally rotating grains, the new disaligning process may be
more potent for carbonaceous dust than for silicate dust. This could result in
efficient alignment for silicate grains but poor alignment for carbonaceous
grains.Comment: 19 pages, 3 figures, submitted to Ap
Numerical residual perturbation solution applied to an earth satellite including luni-solar effects
Mathematical model and computer program for numerical solution of earth orbit differential equations of motio
Experimental constraints on the polarizabilities of the 6s^2 1S0 and 6s6p 3P0 states of Yb
We utilize accurate experimental data available in the literature to yield
bounds on the polarizabilities of the ground and first excited states of atomic
Yb. For the 6s^2 1S0 ground state, we find the polarizability alpha to be
constrained to 134.4<alpha<144.2 in atomic units, while for the 6s6p 3P0
excited state we find 280.1<alpha<289.9. The uncertainty in each of these
values is 1.0. These constraints provide a valuable check for ab initio and
semi-empirical methods used to compute polarizabilities and other related
properties in Yb.Comment: 7 pages, 1 figur
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