819 research outputs found
Modified permittivity observed in bulk Gallium Arsenide and Gallium Phosphide samples at 50 K using the Whispering Gallery mode method
Whispering Gallery modes in bulk cylindrical Gallium Arsenide and Gallium
Phosphide samples have been examined both in darkness and under white light at
50 K. In both samples we observed change in permittivity under light and dark
conditions. This results from a change in the polarization state of the
semiconductor, which is consistent with a free electron-hole
creation/recombination process. The permittivity of the semiconductor is
modified by free photocarriers in the surface layers of the sample which is the
region sampled by Whispering Gallery modes.Comment: 8 pages, 3 figure
Cryogenic sapphire oscillator with exceptionally high long-term frequency stability
We report on the development of a sapphire cryogenic microwave resonator
oscillator long-term fractional frequency stability of 2x10^-17Sqrt[\tau] for
integration times \tau>10^3 s and negative drift of about 2.2x10^-15/day. The
short-term frequency instability of the oscillator is highly reproducible and
also state-of-the-art: 5.6x10^-16 for an integration time of \tau ~ 20 s.Comment: Accepted for publication in Applied Physics Letter
Direct Terrestrial Test of Lorentz Symmetry in Electrodynamics to 10
Lorentz symmetry is a foundational property of modern physics, underlying the
standard model of particles and general relativity. It is anticipated that
these two theories are low energy approximations of a single theory that is
unified and consistent at the Planck scale. Many unifying proposals allow
Lorentz symmetry to be broken, with observable effects appearing at
Planck-suppressed levels; thus precision tests of Lorentz invariance are needed
to assess and guide theoretical efforts. Here, we use ultra-stable oscillator
frequency sources to perform a modern Michelson-Morley experiment and make the
most precise direct terrestrial test to date of Lorentz symmetry for the
photon, constraining Lorentz violating orientation-dependent relative frequency
changes / to 9.210.7 (95 confidence
interval). This order of magnitude improvement over previous Michelson-Morley
experiments allows us to set comprehensive simultaneous bounds on nine boost
and rotation anisotropies of the speed of light, finding no significant
violations of Lorentz symmetry.Comment: 20 pages, 13 figure
Optimum design of a high-Q room-temperature Whispering-Gallery-mode x-band sapphire resonator
A process for optimal design of a room temperature Whispering Gallery mode sapphire resonator has been developed. In particular, design rules were determined to enable choice of the optimum azimuthal mode number and resonator radius for a given resonance frequency. The coupling probe design was investigated and it was found that straight antenna probes aligned radially and positioned in the mid-plane of the resonator gave the highest unloaded Q-factors due to minimized probe losses. We noted that when coupling through this technique (as compared with a perpendicular-positioned probe) the mode standing wave pattern would lock to some asymmetry in the crystal resonator itself and not to the probe. This was confirmed by noting that the coupling could be altered over a significant range by mere rotation of the resonator. Following these optimal design rules we were able to measure the Q-factors of quasi-TE and quasi-TM modes with high precision in four cylindrical sapphire resonators at room temperature. The highest attainable Q-factor was (2.1 +/- 0.1) x 10^5 at 9 GHz in a quasi-TM mode.John G. Hartnett, Michael E. Tobar, Eugene N. Ivanov and Andre N. Luite
Test of Lorentz Invariance in Electrodynamics Using Rotating Cryogenic Sapphire Microwave Oscillators
We present the first results from a rotating Michelson-Morley experiment that
uses two orthogonally orientated cryogenic sapphire resonator-oscillators
operating in whispering gallery modes near 10 GHz. The experiment is used to
test for violations of Lorentz Invariance in the frame-work of the photon
sector of the Standard Model Extension (SME), as well as the isotropy term of
the Robertson-Mansouri-Sexl (RMS) framework. In the SME we set a new bound on
the previously unmeasured component of
, and set more stringent bounds by up to a factor of 7
on seven other components. In the RMS a more stringent bound of
on the isotropy parameter, is set, which is more than a factor of 7 improvement. More detailed
description of the experiment and calculations can be found in: hep-ph/0506200Comment: Final published version, 4 pages, references adde
Mad Is Required for Wingless Signaling in Wing Development and Segment Patterning in Drosophila
A key question in developmental biology is how growth factor signals are integrated to generate pattern. In this study we investigated the integration of the Drosophila BMP and Wingless/GSK3 signaling pathways via phosphorylations of the transcription factor Mad. Wingless was found to regulate the phosphorylation of Mad by GSK3 in vivo. In epistatic experiments, the effects of Wingless on wing disc molecular markers (senseless, distalless and vestigial) were suppressed by depletion of Mad with RNAi. Wingless overexpression phenotypes, such as formation of ectopic wing margins, were induced by Mad GSK3 phosphorylation-resistant mutant protein. Unexpectedly, we found that Mad phosphorylation by GSK3 and MAPK occurred in segmental patterns. Mad depletion or overexpression produced Wingless-like embryonic segmentation phenotypes. In Xenopus embryos, segmental border formation was disrupted by Smad8 depletion. The results show that Mad is required for Wingless signaling and for the integration of gradients of positional information
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Constraining the mass of dark photons and axion-like particles through black-hole superradiance
Large-scale periodicity in the distribution of QSO absorption-line systems
The spatial-temporal distribution of absorption-line systems (ALSs) observed
in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is
investigated on the base of our updated catalog of absorption systems. We
consider so called metallic systems including basically lines of heavy
elements. The sample of the data displays regular variations (with amplitudes ~
15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution,
where eta is a dimensionless line-of-sight comoving distance, relatively to
smoother dependences. The eta-distribution reveals the periodicity with period
Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic
scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20)
h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a
spatial interpretation of the results treating the pattern obtained as a trace
of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in
Astrophysics & Space Scienc
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