6,866 research outputs found
Results of TC-1 boost pump icing tests in the space power facility
A series of tests were conducted in the space power facility to investigate the failure of the Centaur oxidizer boost pump during the Titan/Centaur proof flight February 11, 1974. The three basic objectives of the tests were: (1) demonstrate if an evaporative freezing type failure mechanism could have prevented the pump from operating, (2) determine if steam from the exhaust of one of the attitude control engine could have entered a pump seal cavity and caused the failure, and (3) obtain data on the heating effects of the exhaust plume from a hydrogen peroxide attitude control engine
Localized exciton-polariton modes in dye-doped nanospheres: a quantum approach
We model a dye-doped polymeric nanosphere as an ensemble of quantum emitters
and use it to investigate the localized exciton-polaritons supported by such a
nanosphere. By determining the time evolution of the density matrix of the
collective system, we explore how an incident laser field may cause transient
optical field enhancement close to the surface of such nanoparticles. Our
results provide further evidence that excitonic materials can be used to good
effect in nanophotonics.Comment: 16 pages, 4 figure
Power computation for the triboelectric nanogenerator
We consider, from a mathematical perspective, the power generated by a
contact-mode triboelectric nanogenerator, an energy harvesting device that has
been well studied recently. We encapsulate the behaviour of the device in a
differential equation, which although linear and of first order, has periodic
coefficients, leading to some interesting mathematical problems. In studying
these, we derive approximate forms for the mean power generated and the current
waveforms, and describe a procedure for computing the Fourier coefficients for
the current, enabling us to show how the power is distributed over the
harmonics. Comparisons with accurate numerics validate our analysis
Resummation of perturbation series and reducibility for Bryuno skew-product flows
We consider skew-product systems on T^d x SL(2,R) for Bryuno base flows close
to constant coefficients, depending on a parameter, in any dimension d, and we
prove reducibility for a large measure set of values of the parameter. The
proof is based on a resummation procedure of the formal power series for the
conjugation, and uses techniques of renormalisation group in quantum field
theory.Comment: 30 pages, 12 figure
The Field White Dwarf Mass Distribution
We revisit the properties and astrophysical implications of the field white
dwarf mass distribution in preparation of Gaia applications. Our study is based
on the two samples with the best established completeness and most precise
atmospheric parameters, the volume-complete survey within 20 pc and the Sloan
Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of
the observed mass distributions with Monte Carlo simulations, but find that it
is difficult to constrain independently the initial mass function (IMF), the
initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the
variation of the Galactic disk vertical scale height as a function of stellar
age, and binary evolution. Each of these input ingredients has a moderate
effect on the predicted mass distributions, and we must also take into account
biases owing to unidentified faint objects (20 pc sample), as well as unknown
masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS
sample). Nevertheless, we find that fixed standard assumptions for the above
parameters result in predicted mean masses that are in good qualitative
agreement with the observed values. It suggests that derived masses for both
studied samples are consistent with our current knowledge of stellar and
Galactic evolution. Our simulations overpredict by 40-50% the number of massive
white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a
Salpeter IMF when we account for all biases. Furthermore, we find no evidence
of a population of double white dwarf mergers in the observed mass
distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA
Enhancing Natural-Hazard Exposure Modeling Using Natural Language Processing: a Case-Study for Maltese Planning Applications
The algorithmic processing of written language for tools such as predictive text, sentiment analysis, and translation services has become commonplace. The segment of computer science concerned with the interpretation of human language, NLP (Natural Language Processing), is a versatile and fast-developing field. In this paper, NLP is deployed unconventionally to gather insights into a building's multi-hazard exposure characteristics consistent with the GED4ALL attributes. NLP is used in this study to "read" the contents of digitally-submitted planning applications made on the Maltese archipelago. Maltese architects/engineers submit a concise but detailed description of the proposed works on any given site as part of a planning process. It is suggested that valuable insights exist within this description that can assist in classifying buildings within the bounds of the GED4ALL taxonomy. NLP can be used to layer additional, building-by-building information onto existing exposure models based on more conventional data. Although the results of this study are preliminary, NLP may prove a valuable tool for enhancing exposure modeling for multi-hazard risk quantification and management
Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments
We present measurements, using two complementary methods, of the breakdown of
atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark
states are rendered weakly absorbing due to fine-structure mixing during Rb-He
collisions. The effect substantially increases the photon demand for optical
pumping of dense vapors
Discovery of a red quasar with recurrent activity
We report a new double-double radio quasar, DDRQ, J07464526 which exhibits
two cycles of episodic activity. From radio continuum observations at 607 MHz
using the GMRT and 1400 MHz from the FIRST survey we confirm its episodic
nature. We examine the SDSS optical spectrum and estimate the black hole mass
to be (8.20.3)10M from its observed MgII emission
line, and the Eddington ratio to be 0.03. The black hole mass is significantly
smaller than for the other reported DDRQ, J0935+0204, while the Eddington
ratios are comparable. The SDSS spectrum is significantly red continuum
dominated suggesting that it is highly obscured with
mag. This high obscuration further indicates the
existence of a large quantity of dust and gas along the line of sight, which
may have a key role in triggering the recurrent jet activity in such objects.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Ap
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