8,013 research outputs found
Fast autotuning of a hydrogen maser by cavity Q modulation
A new fast autotuner for the hydrogen maser was implemented. By modulating the cavity, a phase shift in the maser output signal is induced which is proportional to the cavity tuning error. The phase shift is detected and fed back to a varactor tuner to stabilize the cavity against long-term drifts. Also, a PIN-diode cavity modulator which gives no incidental frequency shift over a very wide range of operation was developed. Modulated at over 200 Hz, it allows variations in maser cavity frequency to be compensated with a loop gain greater than 1000. Compensation of incidental amplitude modulation of the output was demonstrated
Operational parameters for the superconducting cavity maser
Tests of the superconducting cavity maser (SCM) ultra-stable frequency source have been made for the first time using a hydrogen maser for a frequency reference. In addition to characterizing the frequency stability, the sensitivity of the output frequency to several crucial parameters was determined for various operating conditions. Based on this determination, the refrigeration and thermal control systems of the SCM were modified. Subsequent tests showed substantially improved performance, especially at the longest averaging times
Versatile compact atomic source for high resolution dual atom interferometry
We present a compact Rb atomic source for high precision dual atom
interferometers. The source is based on a double-stage magneto-optical trap
(MOT) design, consisting of a 2-dimensional (2D)-MOT for efficient loading of a
3D-MOT. The accumulated atoms are precisely launched in a horizontal moving
molasses. Our setup generates a high atomic flux ( atoms/s) with
precise and flexibly tunable atomic trajectories as required for high
resolution Sagnac atom interferometry. We characterize the performance of the
source with respect to the relevant parameters of the launched atoms, i.e.
temperature, absolute velocity and pointing, by utilizing time-of-flight
techniques and velocity selective Raman transitions.Comment: uses revtex4, 9 pages, 12 figures, submitted to Phys. Rev.
Hot new directions for quasi-Monte Carlo research in step with applications
This article provides an overview of some interfaces between the theory of
quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC
theoretical settings: first order QMC methods in the unit cube and in
, and higher order QMC methods in the unit cube. One important
feature is that their error bounds can be independent of the dimension
under appropriate conditions on the function spaces. Another important feature
is that good parameters for these QMC methods can be obtained by fast efficient
algorithms even when is large. We outline three different applications and
explain how they can tap into the different QMC theory. We also discuss three
cost saving strategies that can be combined with QMC in these applications.
Many of these recent QMC theory and methods are developed not in isolation, but
in close connection with applications
Quasi-Monte Carlo sparse grid Galerkin finite element methods for linear elasticity equations with uncertainties
We explore a linear inhomogeneous elasticity equation with random Lam\'e
parameters. The latter are parameterized by a countably infinite number of
terms in separated expansions. The main aim of this work is to estimate
expected values (considered as an infinite dimensional integral on the
parametric space corresponding to the random coefficients) of linear
functionals acting on the solution of the elasticity equation. To achieve this,
the expansions of the random parameters are truncated, a high-order quasi-Monte
Carlo (QMC) is combined with a sparse grid approach to approximate the high
dimensional integral, and a Galerkin finite element method (FEM) is introduced
to approximate the solution of the elasticity equation over the physical
domain. The error estimates from (1) truncating the infinite expansion, (2) the
Galerkin FEM, and (3) the QMC sparse grid quadrature rule are all studied. For
this purpose, we show certain required regularity properties of the continuous
solution with respect to both the parametric and physical variables. To achieve
our theoretical regularity and convergence results, some reasonable assumptions
on the expansions of the random coefficients are imposed. Finally, some
numerical results are delivered
A Study of the Water Cherenkov Calorimeter
The novel idea of water Cherenkov calorimeter made of water tanks as the next
generation neutrino detector for nu factories and nu beams is investigated. A
water tank prototype with a dimension of 1*1*13m^3 is constructed, its
performance is studied and compared with a GEANT4 based Monte Carlo simulation.
By using measured parameters of the water tank, including the light collection
efficiency, attenuation length, angular dependent response etc, a detailed
Monte Carlo simulation demonstrates that the detector performance is excellent
for identifying neutrino charged current events while rejecting neutral current
and wrong-flavor backgrounds.Comment: 19 pages, 14 figures, submitted to NI
Sympathetic Cooling of Mixed Species Two-Ion Crystals for Precision Spectroscopy
Sympathetic cooling of trapped ions has become an indispensable tool for
quantum information processing and precision spectroscopy. In the simplest
situation a single Doppler-cooled ion sympathetically cools another ion which
typically has a different mass. We analytically investigate the effect of the
mass ratio of such an ion crystal on the achievable temperature limit in the
presence of external heating. As an example, we show that cooling of a single
Al+ with Be+, Mg+ and Ca+ ions provides similar results for heating rates
typically observed in ion traps, whereas cooling ions with a larger mass
perform worse. Furthermore, we present numerical simulation results of the
rethermalisation dynamics after a background gas collision for the Al+/Ca+
crystal for different cooling laser configurations.Comment: Made Graphics black & white print compatible, clarified abstract and
summar
Cosmological implications of a light dilaton
Supersymmetric Peccei-Quinn symmetry and string theory predict a complex
scalar field comprising a dilaton and an axion. These fields are massless at
high energies, but it is known since long that the axion is stabilized in an
instanton dominated vacuum. Instantons and axions together also provide a
mechanism to stabilize a dilaton, thus accounting for a dilaton as a possible
cold dark matter component accompanying the axion. We briefly review the
prospects of this scenario and point out further implications.Comment: LaTeX, 9 pages incl. 1 figure, reference adde
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