836 research outputs found
A Search for Scalar Chameleons with ADMX
Scalar fields with a "chameleon" property, in which the effective particle
mass is a function of its local environment, are common to many theories beyond
the standard model and could be responsible for dark energy. If these fields
couple weakly to the photon, they could be detectable through the "afterglow"
effect of photon-chameleon-photon transitions. The ADMX experiment was used in
the first chameleon search with a microwave cavity to set a new limit on scalar
chameleon-photon coupling excluding values between 2*10^9 and 5*10^14 for
effective chameleon masses between 1.9510 and 1.9525 micro-eV.Comment: 4 pages, 3 figure
Studies of the motion and decay of axion walls bounded by strings
We discuss the appearance at the QCD phase transition, and the subsequent
decay, of axion walls bounded by strings in N=1 axion models. We argue on
intuitive grounds that the main decay mechanism is into barely relativistic
axions. We present numerical simulations of the decay process. In these
simulations, the decay happens immediately, in a time scale of order the light
travel time, and the average energy of the radiated axions is for . is found to increase
approximately linearly with . Extrapolation of this behaviour
yields in axion models of interest. We find that the
contribution to the cosmological energy density of axions from wall decay is of
the same order of magnitude as that from vacuum realignment, with however large
uncertainties. The velocity dispersion of axions from wall decay is found to be
larger, by a factor or so, than that of axions from vacuum realignment
and string decay. We discuss the implications of this for the formation and
evolution of axion miniclusters and for the direct detection of axion dark
matter on Earth. Finally we discuss the cosmology of axion models with in
which the domain wall problem is solved by introducing a small U(1)
breaking interaction. We find that in this case the walls decay into
gravitational waves.Comment: 37 pages, 10 figures, a minor mistake was corrected, several
references and comments were adde
Counterfeit Detection and Prevention in Additive Manufacturing Based on Unique Identification of Optical Fingerprints of Printed Structures
Printed Electronics (PE) based on additive manufacturing has a rapidly growing market. Due to large feature sizes and reduced complexity of PE applications compared to silicon counterparts, they are more prone to counterfeiting. Common solutions to detect counterfeiting insert watermarks or extract unique fingerprints based on (irreproducible) process variations of valid components. Commonly, such fingerprints have been extracted through electrical methods, similar to those of physically unclonable functions (PUFs). Hence, they introduce overhead to the production resulting in additional costs. While such costs may be negligible for application domains targeted by silicon-based technologies, they are detrimental to the ultra-low-cost PE applications. In this paper, we propose an optical unique identification, by extracting fingerprints from the optically visible variations of printed inks in the PE components. The images can be obtained from optical cameras, such as cell phones, thanks to large feature sizes of PE, by trusted parties, such as an end user wanting to verify the authenticity of a particular product. Since this approach does not require any additional circuitry, the fingerprint production cost consists of merely acquisition, processing and saving an image of the circuit components, matching the requirements of ultra-low-cost applications of PE. To further decrease the storage costs for the unique fingerprints, we utilize image downscaling resulting in a compression rate between 83– 188× , while preserving the reliability and uniqueness of the fingerprints. The proposed fingerprint extraction methodology is applied to four datasets and the results show that the optical variation printed inks is suitable to prevent counterfeiting in PE
A SQUID-based microwave cavity search for dark-matter axions
Axions in the micro eV mass range are a plausible cold dark matter candidate
and may be detected by their conversion into microwave photons in a resonant
cavity immersed in a static magnetic field. The first result from such an axion
search using a superconducting first-stage amplifier (SQUID) is reported. The
SQUID amplifier, replacing a conventional GaAs field-effect transistor
amplifier, successfully reached axion-photon coupling sensitivity in the band
set by present axion models and sets the stage for a definitive axion search
utilizing near quantum-limited SQUID amplifiers.Comment: 4 pages, 5 figures, submitted to PR
Charged current cross section for massive cosmological neutrinos impinging on radioactive nuclei
We discuss the cross section formula both for massless and massive neutrinos
on stable and radioactive nuclei. The latter could be of interest for the
detection of cosmological neutrinos whose observation is one of the main
challenges of modern cosmology. We analyze the signal to background ratio as a
function of the ratio of the neutrino mass over the detector resolution and
show that an energy resolution less than 0.5 eV would be required for sub-eV
neutrino masses, independently of the gravitational neutrino clustering.
Finally we mention the non-resonant character of neutrino capture on
radioactive nuclei.Comment: 5 pages, 2 figure
Move of a large but delicate apparatus on a trailer with air-ride suspension
When valuable delicate goods are shipped by truck, attention must be paid to
vibrations that may cause damage. We present a case study of moving an
extremely delicate 6230-kg superconducting magnet, immersed in liquid nitrogen,
from Livermore, CA to Seattle, WA showing the steps of fatigue analysis of the
load, a test move, and acceleration monitoring of the final move to ensure a
successful damage-free transport
Prospect for relic neutrino searches
Unlike the relic photons, relic neutrinos have not so far been observed. The
Cosmic Neutrino Background (CB) is the oldest relic from the Big Bang,
produced a few seconds after the Bang itself. Due to their impact in cosmology,
relic neutrinos may be revealed indireclty in the near future through
cosmological observations. In this talk we concentrate on other proposals, made
in the last 30 years, to try to detect the CB directly, either in
laboratory searches (through tiny accelerations they produce on macroscopic
targets) or through astrophysical observations (looking for absorption dips in
the flux of Ultra-High Energy neutrinos, due to the annihilation of these
neutrinos with relic neutrinos at the Z-resonance). We concentrate mainly on
the first of these two possibilities.Comment: Talk given at the Nobel Symposium on Neutrino Physics, Enkoping,
Sweden, Augus 19-24, 2004; 16 page
Enhanced magnetocaloric effect in frustrated magnets
The magnetothermodynamics of strongly frustrated classical Heisenberg
antiferromagnets on kagome, garnet, and pyrochlore lattices is examined. The
field induced adiabatic temperature change (dT/dH)_S is significantly larger
for such systems compared to ordinary non-frustrated magnets and also exceeds
the cooling rate of an ideal paramagnet in a wide range of fields. An
enhancement of the magnetocaloric effect is related to presence of a
macroscopic number of soft modes in frustrated magnets below the saturation
field. Theoretical predictions are confirmed with extensive Monte Carlo
simulations.Comment: 7 page
Scaling Property of the global string in the radiation dominated universe
We investigate the evolution of the global string network in the radiation
dominated universe by use of numerical simulations in 3+1 dimensions. We find
that the global string network settles down to the scaling regime where the
energy density of global strings, , is given by with the string tension per unit length and the scaling parameter,
, irrespective of the cosmic time. We also find that the
loop distribution function can be fitted with that predicted by the so-called
one scale model. Concretely, the number density, , of the loop with
the length, , is given by
where and is related with the Nambu-Goldstone(NG)
boson radiation power from global strings, , as with
. Therefore, the loop production function also scales and
the typical scale of produced loops is nearly the horizon distance. Thus, the
evolution of the global string network in the radiation dominated universe can
be well described by the one scale model in contrast with that of the local
string network.Comment: 18 pages, 9 figures, to appear in Phys. Rev.
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