4,638 research outputs found
Results from the Wilkinson Microwave Anisotropy Probe
The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of
temperature and polarization over the entire sky in five microwave frequency
bands. These full-sky maps were used to obtain measurements of temperature and
polarization anisotropy of the cosmic microwave background with the
unprecedented accuracy and precision. The analysis of two-point correlation
functions of temperature and polarization data gives determinations of the
fundamental cosmological parameters such as the age and composition of the
universe, as well as the key parameters describing the physics of inflation,
which is further constrained by three-point correlation functions. WMAP
observations alone reduced the flat cold dark matter (CDM)
cosmological model (six) parameter volume by a factor of >68,000 compared with
pre-WMAP measurements. The WMAP observations (sometimes in combination with
other astrophysical probes) convincingly show the existence of non-baryonic
dark matter, the cosmic neutrino background, flatness of spatial geometry of
the universe, a deviation from a scale-invariant spectrum of initial scalar
fluctuations, and that the current universe is undergoing an accelerated
expansion. The WMAP observations provide the strongest ever support for
inflation; namely, the structures we see in the universe originate from quantum
fluctuations generated during inflation.Comment: 26 pages, 9 figures, invited review for Special Section "CMB
Cosmology" of Progress of Theoretical and Experimental Physics (PTEP). (v2)
New ns-r figure added. Accepted for publicatio
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Texas Business Review, July 1977
College Enrollment Shifts Anticipate Current Job Market; San Antonio: A Military, Trade and Service Center; The High Price of HousingBureau of Business Researc
Astrophysical Observations: Lensing and Eclipsing Einstein's Theories
Albert Einstein postulated the equivalence of energy and mass, developed the
theory of special relativity, explained the photoelectric effect, and described
Brownian motion in five papers, all published in 1905, 100 years ago. With
these papers, Einstein provided the framework for understanding modern
astrophysical phenomena. Conversely, astrophysical observations provide one of
the most effective means for testing Einstein's theories. Here, I review
astrophysical advances precipitated by Einstein's insights, including
gravitational redshifts, gravitational lensing, gravitational waves, the
Lense-Thirring effect, and modern cosmology. A complete understanding of
cosmology, from the earliest moments to the ultimate fate of the universe, will
require developments in physics beyond Einstein, to a unified theory of gravity
and quantum physics.Comment: 6 pages, 4 figures (resol. Reduced to 85 dpi
Vector Reflectometry in a Beam Waveguide
We present a one-port calibration technique for characterization of beam
waveguide components with a vector network analyzer. This technique involves
using a set of known delays to separate the responses of the instrument and the
device under test. We demonstrate this technique by measuring the reflected
performance of a millimeter-wave variable-delay polarization modulator
Producing Mega-pixel CMB Maps from Differential Radiometer Data
A major goal of cosmology is to obtain sensitive, high resolution maps of the
Cosmic Microwave Background (CMB) anisotropy. Such maps, as would be produced
by the recently proposed Microwave Anisotropy Probe (MAP), will contain a
wealth of primary information about conditions in the early universe. To
mitigate systematic effects when observing the microwave background, it is
desirable for the raw data to be collected in differential form: as a set of
temperature differences between points in the sky. However, the production of
large (mega-pixel) maps from a set of temperature differences is a potentially
severe computational challenge. We present a new technique for producing maps
from differential radiometer data that has a computational cost that grows in
the slowest possible way with increasing angular resolution and number of map
pixels. The required central processor (CPU) time is proportional to the number
of differential data points and the required random access memory (RAM) is
proportional to the number of map pixels. We test our technique, and
demonstrate its feasibility, by simulating one year of a space-borne anisotropy
mission.Comment: 8 pages Latex with 3 Postscript figures embedded using eps
The Submillimeter Polarization Spectrum of M17
We present 450 {\mu}m polarimetric observations of the M17 molecular cloud
obtained with the SHARP polarimeter at the Caltech Submillimeter Observatory.
Across the observed region, the magnetic field orientation is consistent with
previous submillimeter and far-infrared polarization measurements. Our
observations are centered on a region of the molecular cloud that has been
compressed by stellar winds from a cluster of OB stars. We have compared these
new data with previous 350 {\mu}m polarimetry and find an anti-correlation
between the 450 to 350 {\mu}m polarization magnitude ratio and the ratio of 21
cm to 450 {\mu}m intensity. The polarization ratio is lower near the east end
of the studied region where the cloud is exposed to stellar winds and
radiation. At the west end of the region, the polarization ratio is higher. We
interpret the varying polarization spectrum as evidence supporting the
radiative alignment torque (RAT) model for grain alignment, implying higher
alignment efficiency in the region that is exposed to a higher anisotropic
radiation field.Comment: 24 pages, 10 figure
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