2,345 research outputs found
Statistical properties of high performance cesium standards
The intermediate term frequency stability of a group of new high-performance cesium beam tubes at the U.S. Naval Observatory were analyzed from two viewpoints: (1) by comparison of the high-performance standards to the MEAN(USNO) time scale and (2) by intercomparisons among the standards themselves. For sampling times up to 5 days, the frequency stability of the high-performance units shows significant improvement over older commercial cesium beam standards
Home range and habitat use by Kemp's Ridley turtles in West-Central Florida
The Kemp's ridley turtle (Lepidochelys kempii) is an endangered species whose recovery depends in part on
the identification and protection of required habitats. We used radio and sonic telemetry on subadult Kemp's ridley
turtles to investigate home-range size and habitat use in the coastal waters of west-central Florida from 1994 to
1996. We tracked 9 turtles during May-August up to 70 days after release and fou.ld they occupied 5-30 km2 foraging
ranges. Compositional analyses indicated that turtles used rock outcroppings in their foraging ranges at a
significantly higher proportion than expected. based on availability within the study area. Additionally. turtles used
live bottom (e.g .• sessile invertebrates) and green macroalgae habitats significantly more than seagrass habitat. Similar
studies are needed through'mt the Kemp's ridley turtles' range to investigate regional and stage-specific differences
in habitat use. which can then be used to conserve important foraging areas
Friedmann Equation for Brans Dicke Cosmology
In the context of Brans-Dicke scalar tensor theory of gravitation, the
cosmological Friedmann equation which relates the expansion rate of the
universe to the various fractions of energy density is analyzed rigorously. It
is shown that Brans-Dicke scalar tensor theory of gravitation brings a
negligible correction to the matter density component of Friedmann equation.
Besides, in addition to and in standard
Einstein cosmology, another density parameter, , is
expected by the theory. This implies that if is found to
be nonzero, data will favor this model instead of the standard Einstein
cosmological model with cosmological constant and will enable more accurate
predictions for the rate of change of Newtonian gravitational constant in the
future.Comment: minor reference change
Unbiased contaminant removal for 3D galaxy power spectrum measurements
Citation: Kalus, B., Percival, W. J., Bacon, D. J., & Samushia, L. (2016). Unbiased contaminant removal for 3D galaxy power spectrum measurements. Monthly Notices of the Royal Astronomical Society, 463(1), 467-476. doi:10.1093/mnras/stw2008We assess and develop techniques to remove contaminants when calculating the 3D galaxy power spectrum. We separate the process into three separate stages: (i) removing the contaminant signal, (ii) estimating the uncontaminated cosmological power spectrum and (iii) debiasing the resulting estimates. For (i), we show that removing the best-fitting contaminant (mode subtraction) and setting the contaminated components of the covariance to be infinite (mode deprojection) are mathematically equivalent. For (ii), performing a quadratic maximum likelihood (QML) estimate after mode deprojection gives an optimal unbiased solution, although it requires the manipulation of large matrices (N-mode being the total number of modes), which is unfeasible for recent 3D galaxy surveys. Measuring a binned average of the modes for (ii) as proposed by Feldman, Kaiser & Peacock (FKP) is faster and simpler, but is sub-optimal and gives rise to a biased solution. We present a method to debias the resulting FKP measurements that does not require any large matrix calculations. We argue that the sub-optimality of the FKP estimator compared with the QML estimator, caused by contaminants, is less severe than that commonly ignored due to the survey window
Efficient Power Spectrum Estimation for High Resolution CMB Maps
Estimation of the angular power spectrum of the Cosmic Microwave Background
(CMB) on a small patch of sky is usually plagued by serious spectral leakage,
specially when the map has a hard edge. Even on a full sky map, point source
masks can alias power from large scales to small scales producing excess
variance at high multipoles. We describe a new fast, simple and local method
for estimation of power spectra on small patches of the sky that minimizes
spectral leakage and reduces the variance of the spectral estimate. For
example, when compared with the standard uniform sampling approach on a 8
degree X 8 degree patch of the sky with 2% area masked due to point sources,
our estimator halves the errorbars at l=2000 and achieves a more than fourfold
reduction in errorbars at l=3500. Thus, a properly analyzed experiment will
have errorbars at l=3500 equivalent to those of an experiment analyzed with the
now standard technique with ~ 16-25 times the integration time.Comment: 22 pages, 15 figures; The TaperMaster package used in this paper will
be made available in the near future at
http://www.astro.princeton.edu/~sudeep/codes/tapermaster/tapermaster.htm
Coherent Line Removal: Filtering out harmonically related line interference from experimental data, with application to gravitational wave detectors
We describe a new technique for removing troublesome interference from
external coherent signals present in the gravitational wave spectrum. The
method works when the interference is present in many harmonics, as long as
they remain coherent with one another. The method can remove interference even
when the frequency changes. We apply the method to the data produced by the
Glasgow laser interferometer in 1996 and the entire series of wide lines
corresponding to the electricity supply frequency and its harmonics are
removed, leaving the spectrum clean enough to detect possible signals
previously masked by them. We also study the effects of the line removal on the
statistics of the noise in the time domain. We find that this technique seems
to reduce the level of non-Gaussian noise present in the interferometer and
therefore, it can raise the sensitivity and duty cycle of the detectors.Comment: 14 pages, 8 figures, Revtex, psfig. To appear in Phys. Rev.
From Heisenberg matrix mechanics to EBK quantization: theory and first applications
Despite the seminal connection between classical multiply-periodic motion and
Heisenberg matrix mechanics and the massive amount of work done on the
associated problem of semiclassical (EBK) quantization of bound states, we show
that there are, nevertheless, a number of previously unexploited aspects of
this relationship that bear on the quantum-classical correspondence. In
particular, we emphasize a quantum variational principle that implies the
classical variational principle for invariant tori. We also expose the more
indirect connection between commutation relations and quantization of action
variables. With the help of several standard models with one or two degrees of
freedom, we then illustrate how the methods of Heisenberg matrix mechanics
described in this paper may be used to obtain quantum solutions with a modest
increase in effort compared to semiclassical calculations. We also describe and
apply a method for obtaining leading quantum corrections to EBK results.
Finally, we suggest several new or modified applications of EBK quantization.Comment: 37 pages including 3 poscript figures, submitted to Phys. Rev.
Space-like Separation in a Bell Test assuming Gravitationally Induced Collapses
We report on a Bell experiment with space-like separation assuming that the
measurement time is related to gravity-induced state reduction. Two energy-time
entangled photons are sent through optical fibers and directed into unbalanced
interferometers at two receiving stations separated by 18 km. At each station,
the detection of a photon triggers the displacement of a macroscopic mass. The
timing ensures space-like separation from the moment a photon enters its
interferometer until the mass has moved. 2-photon interference fringes with a
visibility of up to 90.5% are obtained, leading to a violation of Bell
inequality
First-order thermal correction to the quadratic response tensor and rate for second harmonic plasma emission
Three-wave interactions in plasmas are described, in the framework of kinetic
theory, by the quadratic response tensor (QRT). The cold-plasma QRT is a common
approximation for interactions between three fast waves. Here, the first-order
thermal correction (FOTC) to the cold-plasma QRT is derived for interactions
between three fast waves in a warm unmagnetized collisionless plasma, whose
particles have an arbitrary isotropic distribution function. The FOTC to the
cold-plasma QRT is shown to depend on the second moment of the distribution
function, the phase speeds of the waves, and the interaction geometry. Previous
calculations of the rate for second harmonic plasma emission (via Langmuir-wave
coalescence) assume the cold-plasma QRT. The FOTC to the cold-plasma QRT is
used here to calculate the FOTC to the second harmonic emission rate, and its
importance is assessed in various physical situations. The FOTC significantly
increases the rate when the ratio of the Langmuir phase speed to the electron
thermal speed is less than about 3.Comment: 11 pages, 2 figures, submitted to Physics of Plasma
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