30,646 research outputs found
Inferring telescope polarization properties through spectral lines without linear polarization
We present a technique to determine the polarization properties of a
telescope through observations of spectral lines that have no intrinsic linear
polarization signals. For such spectral lines, any observed linear polarization
must be induced by the telescope optics. We apply the technique to observations
taken with the SPINOR at the DST and demonstrate that we can retrieve the
characteristic polarization properties of the DST at three wavelengths of 459,
526, and 615 nm. We determine the amount of crosstalk between the intensity
Stokes I and the linear and circular polarization states Stokes Q, U, and V,
and between Stokes V and Stokes Q and U. We fit a set of parameters that
describe the polarization properties of the DST to the observed crosstalk
values. The values for the ratio of reflectivities X and the retardance tau
match those derived with the telescope calibration unit within the error bars.
Residual crosstalk after applying a correction for the telescope polarization
stays at a level of 3-10%. We find that it is possible to derive the parameters
that describe the polarization properties of a telescope from observations of
spectral lines without intrinsic linear polarization signal. Such spectral
lines have a dense coverage (about 50 nm separation) in the visible part of the
spectrum (400-615 nm), but none were found at longer wavelengths. Using
spectral lines without intrinsic linear polarization is a promising tool for
the polarimetric calibration of current or future solar telescopes such as
DKIST.Comment: 22 pages, 24 figures, accepted for publication in A&
Counting statistics and detector properties of quantum point contacts
Quantum detector properties of the quantum point contact (QPC) are analyzed
for arbitrary electron transparency and coupling strength to the measured
system and are shown to be determined by the electron counting statistics.
Conditions of the quantum-limited operation of the QPC detector which prevent
information loss through the scattering time and scattering phases are found
for arbitrary coupling. We show that the phase information can be restored and
used for the quantum-limited detection by inclusion of the QPC detector in the
electronic Mach-Zehnder interferometer.Comment: 4 pages, 2 figures, published versio
Beneficial and Harmful Agile Practices for Product Quality
There is the widespread belief that Agile neglects the product quality. This
lack of understanding how Agile processes assure the quality of the product
prevents especially companies from regulated domains from an adoption of Agile.
This work aims to identify which Agile Practices contribute towards product
quality. Hence, data from a survey study is analyzed to identify Ag-ile
Practices which are beneficial or harmful for the quality of the product. From
49 practices that were used in the survey so far, 36 were perceived to have a
positive impact on product quality, while four practices were rated as being
harmful. The results enrich understanding of how product quality can be
achieved in Agile, and support selection of practices to improve quality
Effective action approach to the Leggett's mode in two-band superconductors
We investigate a collective excitation (Leggett's mode) corresponding to
small fluctuations of the relative phase of two condensates in two-band
superconductor using the effective ``phase only'' action. We consider the
possibility of observing Leggett's mode in MgB superconductor and conclude
that for the known at present values of the two-band model parameters for
MgB Leggett's mode arises above the two-particle threshold.Comment: 9 pages, RevTeX4; final version published in EPJ
Dynamic Characteristics of Woodframe Buildings
The dynamic properties of wood shearwall buildings were evaluated, such as modal frequencies, damping and mode shapes of the structures. Through analysis of recorded earthquake response and by forced vibration testing, a database of periods and damping ratios of woodframe buildings was developed. Modal identification was performed on strong-motion records obtained from five buildings, and forced vibration tests were performed on a two-story house and a three-story apartment building, among others. A regression analysis is performed on the database to obtain a period formula specific for woodframe buildings. It should be noted that all test results, including the seismic data, are at small drift ratios (less than 0.1%), and the periods would be significantly longer for stronger shaking of these structures. Despite these low amplitudes, the equivalent viscous dampings for the fundamental modes were usually more than 10% of critical during earthquake shaking
Filamentary Diffusion of Cosmic Rays on Small Scales
We investigate the diffusion of cosmic rays (CR) close to their sources.
Propagating individual CRs in purely isotropic turbulent magnetic fields with
maximal scale of spatial variations Lmax, we find that CRs diffuse
anisotropically at distances r <~ Lmax from their sources. As a result, the CR
densities around the sources are strongly irregular and show filamentary
structures. We determine the transition time t* to standard diffusion as t* ~
10^4 yr (Lmax/150 pc)^b (E/PeV)^(-g) (Brms/4 muG)^g, with b ~ 2 and g =
0.25-0.5 for a turbulent field with Kolmogorov power spectrum. We calculate the
photon emission due to CR interactions with gas and the resulting irregular
source images.Comment: 5 pages (2 columns), 4 figures. Published in Physical Review Letter
Sensitivity of Building Loss Estimates to Major Uncertain Variables
This paper examines the question of which sources of uncertainty most strongly affect the repair cost of a building in a future earthquake. Uncertainties examined here include spectral acceleration, ground-motion details, mass, damping, structural force-deformation behavior, building-component fragility, contractor costs, and the contractor's overhead and profit. We measure the variation (or swing) of the repair cost when each basic input variable except one is taken at its median value, and the remaining variable is taken at its 10th and at its 90th percentile. We perform this study using a 1960s highrise nonductile reinforced-concrete moment-frame building. Repair costs are estimated using the assembly-based vulnerability (ABV) method. We find that the top three contributors to uncertainty are assembly capacity (the structural response at which a component exceeds some damage state), shaking intensity (measured here in terms of damped elastic spectral acceleration, Sa), and details of the ground motion with a given Sa
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