33,800 research outputs found
Pressure regulating system Patent
Pressure regulating system with high pressure fluid source, adapted to maintain constant downstream pressur
Polarimetry from the Ground Up
Ground-based solar polarimetry has made great progress over the last decade.
Nevertheless, polarimetry is still an afterthought in most telescope and
instrument designs, and most polarimeters are designed based on experience and
rules of thumb rather than using more formal systems engineering approaches as
is common in standard optical design efforts. Here we present the first steps
in creating a set of systems engineering approaches to the design of
polarimeters that makes sure that the final telescope-instrument-polarimeter
system is more than the sum of its parts.Comment: To appear in proceedings of the Solar Polarization Workshop
Economic method for measuring ultra-low flow rates of fluids
Capillary tube flowmeter measures ultra-low flows of very corrosive fluids /such as chlorine trifluoride and liquid fluorine/ and other liquids with reasonable accuracy. Flowmeter utilizes differential pressure transducer and operates on the principle that for laminar flow in the tube, pressure drop is proportional to flow rate
Recurrence spectrum in smooth dynamical systems
We prove that for conformal expanding maps the return time does have constant
multifractal spectrum. This is the counterpart of the result by Feng and Wu in
the symbolic setting
Arc-Length Continuation and Multigrid Techniques for Nonlinear Elliptic Eigenvalue Problems
We investigate multi-grid methods for solving linear systems arising from arc-length continuation techniques applied to nonlinear elliptic eigenvalue problems. We find that the usual multi-grid methods diverge in the neighborhood of singular points of the solution branches. As a result, the continuation method is unable to continue past a limit point in the Bratu problem. This divergence is analyzed and a modified multi-grid algorithm has been devised based on this analysis. In principle, this new multi-grid algorithm converges for elliptic systems, arbitrarily close to singularity and has been used successfully in conjunction with arc-length continuation procedures on the model problem. In the worst situation, both the storage and the computational work are only about a factor of two more than the unmodified multi-grid methods
Scalable photonic quantum computation through cavity-assisted interaction
We propose a scheme for scalable photonic quantum computation based on cavity
assisted interaction between single-photon pulses. The prototypical quantum
controlled phase-flip gate between the single-photon pulses is achieved by
successively reflecting them from an optical cavity with a single-trapped atom.
Our proposed protocol is shown to be robust to practical nose and experimental
imperfections in current cavity-QED setups.Comment: 5 pages, 2 figure
Experimental evidence for kin-biased helping in a cooperatively breeding vertebrate
The widespread belief that kin selection is necessary for the evolution of cooperative breeding in vertebrates has recently been questioned. These doubts have primarily arisen because of the paucity of unequivocal evidence for kin preferences in cooperative behaviour. Using the cooperative breeding system of long-tailed tits (Aegithalos caudatus) in which kin and non-kin breed within each social unit and helpers are failed breeders, we investigated whether helpers preferentially direct their care towards kin following breeding failure. First, using observational data, we show that not all failed breeders actually become helpers, but that those that do help usually do so at the nest of a close relative. Second, we confirm the importance of kinship for helping in this species by conducting a choice experiment. We show that potential helpers do not become helpers in the absence of close kin and, when given a choice between helping equidistant broods belonging to kin and non-kin within the same social unit, virtually all helped at the nest of kin. This study provides strong evidence that kinship plays an essential role in the maintenance of cooperative breeding in this species
Momentum-resolved electron-phonon interaction in lead determined by neutron resonance spin-echo spectroscopy
Neutron resonance spin-echo spectroscopy was used to monitor the temperature
evolution of the linewidths of transverse acoustic phonons in lead across the
superconducting transition temperature, , over an extended range of the
Brillouin zone. For phonons with energies below the superconducting energy gap,
a linewidth reduction of maximum amplitude eV was observed below
. The electron-phonon contribution to the phonon lifetime extracted from
these data is in satisfactory overall agreement with {\it ab-initio}
lattice-dynamical calculations, but significant deviations are found
Polarization properties of real aluminum mirrors; I. Influence of the aluminum oxide layer
In polarimetry it is important to characterize the polarization properties of
the instrument itself to disentangle real astrophysical signals from
instrumental effects. This article deals with the accurate measurement and
modeling of the polarization properties of real aluminum mirrors, as used in
astronomical telescopes. Main goals are the characterization of the aluminum
oxide layer thickness at different times after evaporation and its influence on
the polarization properties of the mirror. The full polarization properties of
an aluminum mirror are measured with Mueller matrix ellipsometry at different
incidence angles and wavelengths. The best fit of theoretical Mueller matrices
to all measurements simultaneously is obtained by taking into account a model
of bulk aluminum with a thin aluminum oxide film on top of it. Full Mueller
matrix measurements of a mirror are obtained with an absolute accuracy of ~1%
after calibration. The determined layer thicknesses indicate logarithmic growth
in the first few hours after evaporation, but it remains stable at a value of
4.12+/-0.08 nm on the long term. Although the aluminum oxide layer is
established to be thin, it is necessary to consider it to accurately describe
the mirror's polarization properties.Comment: accepted for publication in PAS
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