46,478 research outputs found
Comment on "Limits on the Time Variation of the Electromagnetic Fine-Structure Constant in the Low Energy Limit from Absorption Lines in the Spectra of Distant Quasars"
In their Letter [Phys. Rev. Lett. 92, 121302 (2004)] (also [Astron.
Astrophys. 417, 853 (2004)]), Srianand et al. analysed optical spectra of
heavy-element species in 23 absorption systems along background quasar
sight-lines, reporting limits on relative variations in the fine-structure
constant: da/a=(-0.06+/-0.06) x 10^{-5}. Here we demonstrate basic flaws in
their analysis, using the same data and absorption profile fits, which led to
spurious values of da/a and significantly underestimated uncertainties. We
conclude that these data and fits offer no stringent test of previous evidence
for a varying alpha.
In their Reply (arXiv:0711.1742) to this Comment, Srianand et al. state or
argue several points regarding their original analysis and our new analysis. We
discuss these points here, dismissing all of them because they are demonstrably
incorrect or because they rely on a flawed application of simple statistical
arguments.Comment: 1+2 pages, 1 EPS figure. Page 1 accepted as PRL Comment on
arXiv:astro-ph/0402177 . Further details available in arXiv:astro-ph/0612407
. v2: Added critical discussion of Reply from Srianand et al.
(arXiv:0711.1742
Accurate laboratory ultraviolet wavelengths for quasar absorption-line constraints on varying fundamental constants
The most precise method of investigating possible space-time variations of
the fine-structure constant, using high-redshift quasar absorption lines, is
the many-multiplet (MM) method. For reliable results this method requires very
accurate relative laboratory wavelengths for a number of UV resonance
transitions from several different ionic species. For this purpose laboratory
wavelengths and wavenumbers of 23 UV lines from MgI, MgII, TiII, CrII, MnII,
FeII and ZnII have been measured using high-resolution Fourier Transform (FT)
spectrometry. The spectra of the different ions (except for one FeII line, one
MgI line and the TiII lines) are all measured simultaneously in the same FT
spectrometry recording by using a composite hollow cathode as a light source.
This decreases the relative uncertainties of all the wavelengths. In addition
to any measurement uncertainty, the wavelength uncertainty is determined by
that of the ArII calibration lines, by possible pressure shifts and by
illumination effects. The absolute wavenumbers have uncertainties of typically
0.001 to 0.002 cm^(-1) (0.06 to 0.1 mAA at 2500 AA), while the relative
wavenumbers for strong, symmetric lines in the same spectral recording have
uncertainties of 0.0005 cm^(-1) (0.03 mAA at 2500 AA) or better, depending
mostly on uncertainties in the line fitting procedure. This high relative
precision greatly reduces the potential for systematic effects in the MM
method, while the new TiII measurements now allow these transitions to be used
in MM analyses.Comment: Accepted for publication in MNRAS, 10 pages, 9 figure
Modelling and directionally encoding the acoustics of a room
Geometrical methods are often used to model the acoustic properties of a room, but are valid only for high frequencies. At low frequencies. diffraction and the effects of room modes cannot be neglected. A method for modelling the two-dimensional propagation of sound within an enclosed room is presented which encompasses both of these particular properties by making use of a digital waveguide model
Calling Bulls**t on the Lanham Act: The 2(a) Bar for Immoral, Scandalous, and Disparaging Marks
As the Lanham Act approaches the age of 65, it is a good time to take stock of its application to, and place within, the object and purpose of trademark law. Trademark law seeks to promote fair competition by reducing consumer search costs and preventing confusion in the minds of consumers as to the source of goods and services. However, Section 2(a) of the Lanham Act prevents registration of marks that are “immoral,” “scandalous,” “disparaging,” “deceptive,” or which “create a false association” with persons, institutions, beliefs, or national symbols. The 2(a) bar expands trademark law well beyond its basic goals. While a bar to registration for marks that are deceptive or create a false association is related to the overall object and purpose of trademark law, we argue that the bar to registration for marks that are immoral, scandalous, or disparaging is not, and that the 2(a) bar is — both in definition and application — ineffective, inconsistent, and vague, and that it should be removed from the Lanham Act
SSME Long-life Bearings
Hybrid hydrostatic/ball bearings for LH2 and LO2 service in turbopumps were studied as a means of improving speed and life capabilities. Four hybrid bearing configurations were designed with emphasis on achieving maximum stiffness and damping. Parallel load bearings were tested at steady-state and transient conditions with LH2 (externally fed) and LN2 (internally fed). The hydrostatic elements were tested with Freon 113 for empirical determination of dynamic characteristics. Tests using an eccentric journal for loading showed the externally and internally fed hydrostatic bearings to have significant separated coefficients of direct stiffness and damping. For the internally fed bearing, the strongly speed-dependent cross-coupling stiffness arising from fluid swirl, along with significant cross-coupling damping, resulted in low net effective stiffness and damping. The test method used can produce separated coefficients with a sufficiently elliptic journal orbit; otherwise, only net effective coefficients combining direct and cross-coupling terms can be determined. Testing with nonsynchronous excitation is recommended to avoid this restriction. Investigation of hard materials, including ceramics, is recommended as a means of eliminating the need for the rolling bearing for startup and shutdown support. The testing was performed in 1984 (LH2), 1985 (LN2) and 1985-86 (Freon)
Waveguide physical modeling of vocal tract acoustics: flexible formant bandwidth control from increased model dimensionality
Digital waveguide physical modeling is often used as an efficient representation of acoustical resonators such as the human vocal tract. Building on the basic one-dimensional (1-D) Kelly-Lochbaum tract model, various speech synthesis techniques demonstrate improvements to the wave scattering mechanisms in order to better approximate wave propagation in the complex vocal system. Some of these techniques are discussed in this paper, with particular reference to an alternative approach in the form of a two-dimensional waveguide mesh model. Emphasis is placed on its ability to produce vowel spectra similar to that which would be present in natural speech, and how it improves upon the 1-D model. Tract area function is accommodated as model width, rather than translated into acoustic impedance, and as such offers extra control as an additional bounding limit to the model. Results show that the two-dimensional (2-D) model introduces approximately linear control over formant bandwidths leading to attainable realistic values across a range of vowels. Similarly, the 2-D model allows for application of theoretical reflection values within the tract, which when applied to the 1-D model result in small formant bandwidths, and, hence, unnatural sounding synthesized vowels
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