4,607 research outputs found
Go with the Flow, Average Holographic Universe
Gravity is a macroscopic manifestation of a microscopic quantum theory of
space-time, just as the theories of elasticity and hydrodynamics are the
macroscopic manifestation of the underlying quantum theory of atoms. The
connection of gravitation and thermodynamics is long and deep. The observation
that space-time has a temperature for accelerating observers and horizons is
direct evidence that there are underlying microscopic degrees of freedom. The
equipartition of energy, meaning of temperature, in these modes leads one to
anticipate that there is also an entropy associated. When this entropy is
maximized on a volume of space-time, then one retrieves the metric of
space-time (i.e. the equations of gravity, e.g. GR). Since the metric satisfies
the extremum in entropy on the volume, then the volume integral of the entropy
can readily be converted to surface integral, via Gauss's Theorem. This surface
integral is simply an integral of the macroscopic entropy flow producing the
mean entropy holographic principle. This approach also has the added value that
it naturally dispenses with the cosmological constant/vacuum energy problem in
gravity except perhaps for second order quantum effects on the mean surface
entropy.Comment: 14 page
Offset balancing in pseudo-correlation radiometers for CMB measurements
Radiometeric CMB measurements need to be highly stable and this stability is
best obtained with differential receivers. The residual 1/f noise in the
differential output is strongly dependent on the radiometer input offset which
can be cancelled using various balancing strategies. In this paper we discuss a
software method implemented in the Planck-LFI pseudo-correlation receivers
which uses a tunable "gain modulation factor, r, in the sky-load difference.
Numerical simulations and experimental data show how proper tuning of the
parameter r ensures a very stable differential output with knee frequencies of
the order of few mHz. Various approaches to calculate r using the radiometer
total power data are discussed with some examples relevant to Planck-LFI.
Although the paper focuses on pseudo-correlation receivers and the examples are
relative to Planck-LFI, the proposed method and its analysis is general and can
be applied to a large class of differential radiometric receivers.Comment: 12 pages, 8 figures, accepted for publication in A&A (updated version
with few editorial changes
The First Data from the MACHO Experiment
MAssive Compact Halo Objects such as brown dwarfs, Jupiters, and black holes
are prime candidates to comprise the dark halo of our galaxy. Paczynski noted
that objects (dubbed MACHOs) with masses in the range 10^{-6}M_\odot < M
\simlt 100 M_\odot. can be detected via gravitational microlensing of stars in
the Magellanic Clouds with the caveat that only about one in stars will
be lensed at any given time. Our group has recently begun a search for
microlensing using a refurbished 1.27 meter telescope at the Mount Stromlo
Observatory in Australia. Since the summer of 1992, we have been imaging up to
stars a night in the Large Magellanic Cloud using our large format
two-color pixel CCD camera. Here I report on our first results
based on an analysis of of these stars. Although this is not enough
data to make definitive statements about the nature of the dark matter, we are
able to conclude that the rate of variable star background events is not larger
than the expected MACHO signal.Comment: et. al., 7 pages, UCRL-JC-1111360
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