460 research outputs found
Observational evidence for stochastic biasing
We show that the galaxy density in the Las Campanas Redshift Survey (LCRS)
cannot be perfectly correlated with the underlying mass distribution since
various galaxy subpopulations are not perfectly correlated with each other,
even taking shot noise into account. This rules out the hypothesis of simple
linear biasing, and suggests that the recently proposed stochastic biasing
framework is necessary for modeling actual data.Comment: 4 pages, with 2 figures included. Minor revisions to match accepted
ApJL version. Links and color fig at
http://www.sns.ias.edu/~max/r_frames.html or from [email protected]
Field dependence of non-reciprocal magnons in chiral MnSi
Spin waves in chiral magnetic materials are strongly influenced by the
Dzyaloshinskii-Moriya interaction resulting in intriguing phenomena like
non-reciprocal magnon propagation and magnetochiral dichroism. Here, we study
the non-reciprocal magnon spectrum of the archetypical chiral magnet MnSi and
its evolution as a function of magnetic field covering the field-polarized and
conical helix phase. Using inelastic neutron scattering, the magnon energies
and their spectral weights are determined quantitatively after deconvolution
with the instrumental resolution. In the field-polarized phase the imaginary
part of the dynamical susceptibility is shown to
be asymmetric with respect to wavevectors longitudinal to the applied
magnetic field , which is a hallmark of chiral magnetism. In the
helimagnetic phase, becomes increasingly
symmetric with decreasing due to the formation of helimagnon bands
and the activation of additional spinflip and non-spinflip scattering channels.
The neutron spectra are in excellent quantitative agreement with the low-energy
theory of cubic chiral magnets with a single fitting parameter being the
damping rate of spin waves.Comment: Paper: 10 pages, 5 figures Supplement: 8 pages, 11 figure
Isometries and the double copy
In the standard derivation of the Kerr-Schild double copy, the geodicity of
the Kerr-Schild vector and the stationarity of the spacetime are presented as
assumptions that are necessary for the single copy to satisfy Maxwell's
equations. However, it is well known that the vacuum Einstein equations imply
that the Kerr-Schild vector is geodesic and shear-free, and that the spacetime
possesses a distinguished vector field that is simultaneously a Killing vector
of the full spacetime and the flat background, but need not be timelike with
respect to the background metric. We show that the gauge field obtained by
contracting this distinguished Killing vector with the Kerr-Schild graviton
solves the vacuum Maxwell equations, and that this definition of the
Kerr-Schild double copy implies the Weyl double copy when the spacetime is
Petrov type D. When the Killing vector is taken to be timelike with respect to
the background metric, we recover the familiar Kerr-Schild double copy, but the
prescription is well defined for any vacuum Kerr-Schild spacetime and we
present new examples where the Killing vector is null or spacelike. While most
examples of physical interest are type D, vacuum Kerr-Schild spacetimes are
generically of Petrov type II. We present a straightforward example of such a
spacetime and study its double copy structure. Our results apply to real
Lorentzian spacetimes as well as complex spacetimes and real spacetimes with
Kleinian signature, and provide a simple correspondence between real and
self-dual vacuum Kerr-Schild spacetimes. This correspondence allows us to study
the double copy structure of a self-dual analog of the Kerr spacetime. We
provide evidence that this spacetime may be diffeomorphic to the self-dual
Taub-NUT solution.Comment: 28 pages; Matches version to appear in JHE
Internet Industry: A Perspective Review through Internet of Things and Internet of Everything
The objective of this article is to concisely explore the Internet industry through a new perspective and concept of Internet of Things (IoT) and Internet of Everything (IoE). Within this article, a brief description and development of Internet industry are presented; following with competitive strategy within the Internet industry; then value chain and the use of applications in the Internet industry. Followed by effects and benefits; and challenges, legal and ethical issues of IoT and IoE. Finally, a Concise Concluding Statement for Thoughts is stated
Rest-Frame Optical Spectra of Three Strongly Lensed Galaxies at z~2
We present Keck II NIRSPEC rest-frame optical spectra for three recently
discovered lensed galaxies: the Cosmic Horseshoe (z = 2.38), the Clone (z =
2.00), and SDSS J090122.37+181432.3 (z = 2.26). The boost in signal-to-noise
ratio (S/N) from gravitational lensing provides an unusually detailed view of
the physical conditions in these objects. A full complement of high S/N
rest-frame optical emission lines is measured, spanning from rest-frame 3600 to
6800AA, including robust detections of fainter lines such as H-gamma,
[SII]6717,6732, and in one instance [NeII]3869. SDSS J090122.37+181432.3 shows
evidence for AGN activity, and therefore we focus our analysis on star-forming
regions in the Cosmic Horseshoe and the Clone. For these two objects, we
estimate a wide range of physical properties, including star-formation rate
(SFR), metallicity, dynamical mass, and dust extinction. In all respects, the
lensed objects appear fairly typical of UV-selected star-forming galaxies at
z~2. The Clone occupies a position on the emission-line diagnostic diagram of
[OIII]/H-beta vs. [NII]/H-alpha that is offset from the locations of z~0
galaxies. Our new NIRSPEC measurements may provide quantitative insights into
why high-redshift objects display such properties. From the [SII] line ratio,
high electron densities (~1000 cm^(-3)) are inferred compared to local
galaxies, and [OIII]/[OII] line ratios indicate higher ionization parameters
compared to the local population. Building on previous similar results at z~2,
these measurements provide further evidence (at high S/N) that star-forming
regions are significantly different in high-redshift galaxies, compared to
their local counterparts (abridged).Comment: 16 pages, 8 figures. Accepted for publication in the Astrophysical
Journa
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Learning Companion to Bending the Curve: Climate Change Solutions
The Learning Companion to Bending the Curve: Climate Change Solutions can help all readers gain the most from this book. This resource includes questions for review and discussion which help connect ideas, understand key concepts, and to increase the ability of readers at all levels to effectively discuss and explain climate change solutions.The Learning Companion provides review questions that can be used to assess familiarity with key concepts, ensuring all readers are ready to apply what they’ve learned. These questions can also help instructors identify areas of learning that may require additional explanation. The Learning Companion also provides questions for discussion which can help facilitate both classroom and public discourse, and expanding each reader’s learning about climate change solutionsWe recognize the importance of public communication and education to help promote a broad culture of climate action. Using the questions in the Learning Companion can help you take action, and to collaborate with others as a learning community, focused on climate change solutions
KL Estimation of the Power Spectrum Parameters from the Angular Distribution of Galaxies in Early SDSS Data
We present measurements of parameters of the 3-dimensional power spectrum of
galaxy clustering from 222 square degrees of early imaging data in the Sloan
Digital Sky Survey. The projected galaxy distribution on the sky is expanded
over a set of Karhunen-Loeve eigenfunctions, which optimize the signal-to-noise
ratio in our analysis. A maximum likelihood analysis is used to estimate
parameters that set the shape and amplitude of the 3-dimensional power
spectrum. Our best estimates are Gamma=0.188 +/- 0.04 and sigma_8L = 0.915 +/-
0.06 (statistical errors only), for a flat Universe with a cosmological
constant. We demonstrate that our measurements contain signal from scales at or
beyond the peak of the 3D power spectrum. We discuss how the results scale with
systematic uncertainties, like the radial selection function. We find that the
central values satisfy the analytically estimated scaling relation. We have
also explored the effects of evolutionary corrections, various truncations of
the KL basis, seeing, sample size and limiting magnitude. We find that the
impact of most of these uncertainties stay within the 2-sigma uncertainties of
our fiducial result.Comment: Fig 1 postscript problem correcte
IGVC drive by wire project: Critical design report
Investigate and develop a Drive-By-Wire (DBW) system, its computer interface, and user interface for a Polaris Gem e2. The vehicle is planned to participate in the IGVC 2023 autonomous vehicle competition. The DBW system includes automatic control of brakes, throttle, steering, and potentially other components, such as lights. The final solution included hydraulic autonomous brakes, a cabled emergency brake, and numerous custom controller boards. The boards interface via a research CAN bus, include hardware based ESTOP handling, and a interface with the vehicle through a system of relays designed to fully disconnect the boards during manual control
The Angular Correlation Function of Galaxies from Early SDSS Data
The Sloan Digital Sky Survey is one of the first multicolor photometric and
spectroscopic surveys designed to measure the statistical properties of
galaxies within the local Universe. In this Letter we present some of the
initial results on the angular 2-point correlation function measured from the
early SDSS galaxy data. The form of the correlation function, over the
magnitude interval 18<r*<22, is shown to be consistent with results from
existing wide-field, photographic-based surveys and narrower CCD galaxy
surveys. On scales between 1 arcminute and 1 degree the correlation function is
well described by a power-law with an exponent of ~ -0.7. The amplitude of the
correlation function, within this angular interval, decreases with fainter
magnitudes in good agreement with analyses from existing galaxy surveys. There
is a characteristic break in the correlation function on scales of
approximately 1-2 degrees. On small scales, < 1', the SDSS correlation function
does not appear to be consistent with the power-law form fitted to the 1'<
theta <0.5 deg data. With a data set that is less than 2% of the full SDSS
survey area, we have obtained high precision measurements of the power-law
angular correlation function on angular scales 1' < theta < 1 deg, which are
robust to systematic uncertainties. Because of the limited area and the highly
correlated nature of the error covariance matrix, these initial results do not
yet provide a definitive characterization of departures from the power-law form
at smaller and larger angles. In the near future, however, the area of the SDSS
imaging survey will be sufficient to allow detailed analysis of the small and
large scale regimes, measurements of higher-order correlations, and studies of
angular clustering as a function of redshift and galaxy type
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