10,888 research outputs found
Temperature-stabilized, triggerable microelectronic astable multivibrator starts reliably
Multiple chip custom block, MIC construction is used to fabricate an ultracompact, low-power astable multivibrator. The design provides a multivibrator that free runs, eliminating lockup, is triggerable, pulling into synchronization with an external signal source, and permits design flexibility for controlling the frequency variations with temperature
Rightsizing LISA
The LISA science requirements and conceptual design have been fairly stable
for over a decade. In the interest of reducing costs, the LISA Project at NASA
has looked for simplifications of the architecture, at downsizing of
subsystems, and at descopes of the entire mission. This is a natural activity
of the formulation phase, and one that is particularly timely in the current
NASA budgetary context. There is, and will continue to be, enormous pressure
for cost reduction from both ESA and NASA, reviewers and the broader research
community. Here, the rationale for the baseline architecture is reviewed, and
recent efforts to find simplifications and other reductions that might lead to
savings are reported. A few possible simplifications have been found in the
LISA baseline architecture. In the interest of exploring cost sensitivity, one
moderate and one aggressive descope have been evaluated; the cost savings are
modest and the loss of science is not.Comment: To be published in Classical and Quantum Gravity; Proceedings of the
Seventh International LISA Symposium, Barcelona, Spain, 16-20 Jun. 2008; 10
pages, 1 figure, 3 table
Confirmation of the Copernican principle at Gpc radial scale and above from the kinetic Sunyaev Zel'dovich effect power spectrum
The Copernican principle, a cornerstone of modern cosmology, remains largely
unproven at Gpc radial scale and above. Here we will show that, violations of
this type will inevitably cause a first order anisotropic kinetic Sunyaev
Zel'dovich (kSZ) effect. If large scale radial inhomogeneities have amplitude
large enough to explain the "dark energy" phenomena, the induced kSZ power
spectrum will be much larger than the ACT/SPT upper limit. This single test
confirms the Copernican principle and rules out the adiabatic void model as a
viable alternative to dark energy.Comment: 4 pages, 2 figures. v2: updated with ACT result. v3: updated with SPT
result. Expanded discussions. Accepted to PR
Cold + Hot Dark Matter and the Cosmic Microwave Background
We examine the cosmic microwave background power spectrum for adiabatic
models with a massive neutrino component. We present the results of a detailed
numerical evolution of cold + hot dark matter (CHDM) models and compare with
the standard cold dark matter (CDM) spectrum. The difference is of order
for for currently popular CHDM models. With
semi-analytic approximations, we also discuss the relevant physics involved.
Finally we remark on the ability of future experiments to differentiate between
these models. An all-sky experiment with a beam size smaller than 30 arcminutes
can distinguish between CHDM and CDM if other cosmological parameters are
known. Even allowing other parameters to vary, it may be possible to
distinguish CDM from CHDM.Comment: Compressed uuencoded postscript, 26 pages including figures. Color
version available at http://www-astro-theory.fnal.gov
Perturbations from cosmic strings in cold dark matter
A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed
Perturbations from strings don't look like strings!
A systematic analysis is challenging popular ideas about perturbation from cosmic strings. One way in which the picture has changed is reviewed. It is concluded that, while the scaling properties of cosmic strings figure significantly in the analysis, care must be taken when thinking in terms of single time snapshots. The process of seeding density perturbations is not fundamentally localized in time, and this fact can wash out many of the details which appear in a single snapshot
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