291 research outputs found
Approaching the Heisenberg limit in an atom laser
We present experimental and theoretical results showing the improved beam quality and reduced divergence
of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We
show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled
atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater
than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can
produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces
them, typically a factor of 1.3 above the Heisenberg limit
Investigation and comparison of multi-state and two-state atom laser output-couplers
We investigate the spatial structure and temporal dynamics created in a
Bose-Einstein condensate (BEC) by radio-frequency (RF) atom laser
output-couplers using a one-dimensional mean-field model. We compare the
behavior of a `pure' two-state atom laser to the multi-level systems
demonstrated in laboratories. In particular, we investigate the peak
homogeneous output flux, classical fluctuations in the beam and the onset of a
bound state which shuts down the atom laser output.Comment: 9 pages, 8 figure
80hk Momentum Separation with Bloch Oscillations in an Optically Guided Atom Interferometer
We demonstrate phase sensitivity in a horizontally guided,
acceleration-sensitive atom interferometer with a momentum separation of 80hk
between its arms. A fringe visibility of 7% is observed. Our coherent pulse
sequence accelerates the cold cloud in an optical waveguide, an inherently
scalable route to large momentum separation and high sensitivity. We maintain
coherence at high momentum separation due to both the transverse confinement
provided by the guide, and our use of optical delta-kick cooling on our
cold-atom cloud. We also construct a horizontal interferometric gradiometer to
measure the longitudinal curvature of our optical waveguide.Comment: 6 pages, 6 figure
Semiclassical limits to the linewidth of an atom laser
We investigate the linewidth of a quasi-continuous atom laser within a
semiclassical framework. In the high flux regime, the lasing mode can exhibit a
number of undesirable features such as density fluctuations. We show that the
output therefore has a complicated structure that can be somewhat simplified
using Raman outcoupling methods and energy-momentum selection rules. In the
weak outcoupling limit, we find that the linewidth of an atom laser is
instantaneously Fourier limited, but, due to the energy `chirp' associated with
the draining of a condensate, the long-term linewidth of an atom laser is
equivalent to the chemical potential of the condensate source. We show that
correctly sweeping the outcoupling frequency can recover the Fourier-limited
linewidth.Comment: 9 Figure
Genomic evaluations using data recorded on smallholder dairy farms in low- to middle-income countries
Breeding has increased genetic gain for dairy cattle in advanced economies but has had limited success in improving dairy cattle in low- to middle-income countries (LMIC). Genetic evaluations are a central component of delivering genetic gain, because they separate the genetic and environmental effects of animals' phenotypes. Genetic evaluations have been successful in advanced economies because of large data sets and strong genetic connectedness, provided by the widespread use of artificial insemination (AI) and accurate recording of pedigree information. In smallholder dairy production systems of many LMICs, the limited use of AI and small herd sizes results in a data structure with insufficient genetic connectedness between herds to facilitate genetic evaluations based on pedigree. Genomic information keeps track of shared haplotypes rather than shared relatives captured by pedigree records. Therefore, genomic information could capture âhiddenâ genetic relationships, that are not captured by pedigree information, to strengthen genetic connectedness in LMIC smallholder dairy data sets. This study's objective was to use simulation to quantify the power of genomic information to enable genetic evaluation using LMIC smallholder dairy data sets. The results from this study show that (1) genetic evaluations using genomic information were more accurate than those using pedigree information in populations with a high effective population size and weak genetic connectedness; and (2) genetic evaluations modeling herd as a random effect had higher or equal accuracy than those modeling herd as a fixed effect. This demonstrates the potential of genomic information to be an enabling technology in LMIC smallholder dairy production systems by facilitating genetic evaluations with in situ records collected from herds of â€4 cows. The establishment of routine genomic evaluations could allow the development of LMIC breeding programs comprising an informal set of nucleus animals distributed across many small herds within the target environment. These nucleus animals could be used for genetic evaluation, and the best animals could be disseminated to participating smallholder dairy farms. Together, this could increase the productivity, profitability, and sustainability of LMIC smallholder dairy production systems
The Reflux Disease Questionnaire: a measure for assessment of treatment response in clinical trials
© 2008 Shaw et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Removal of alleles by genome editing (RAGE) against deleterious load
Abstract Background In this paper, we simulate deleterious load in an animal breeding program, and compare the efficiency of genome editing and selection for decreasing it. Deleterious variants can be identified by bioinformatics screening methods that use sequence conservation and biological prior information about protein function. However, once deleterious variants have been identified, how can they be used in breeding? Results We simulated a closed animal breeding population that is subject to both natural selection against deleterious load and artificial selection for a quantitative trait representing the breeding goal. Deleterious load was polygenic and was due to either codominant or recessive variants. We compared strategies for removal of deleterious alleles by genome editing (RAGE) to selection against carriers. When deleterious variants were codominant, the best strategy for prioritizing variants was to prioritize low-frequency variants. When deleterious variants were recessive, the best strategy was to prioritize variants with an intermediate frequency. Selection against carriers was inefficient when variants were codominant, but comparable to editing one variant per sire when variants were recessive. Conclusions Genome editing of deleterious alleles reduces deleterious load, but requires the simultaneous editing of multiple deleterious variants in the same sire to be effective when deleterious variants are recessive. In the short term, selection against carriers is a possible alternative to genome editing when variants are recessive. Our results suggest that, in the future, there is the potential to use RAGE against deleterious load in animal breeding
Optically guided linear Mach-Zehnder atom interferometer
We demonstrate a horizontal, linearly guided Mach-Zehnder atom interferometer in an optical waveguide. Intended as a proof-of-principle experiment, the interferometer utilizes a Bose-Einstein condensate in the magnetically insensitive F=1,mF=0 state of 87Rb as an acceleration-sensitive test mass. We achieve a modest sensitivity to acceleration of Îa=7Ă10-4 m/s2. Our fringe visibility is as high as 38% in this optically guided atom interferometer. We observe a time of flight in the waveguide of over 0.5 s, demonstrating the utility of our optical guide for future sensors
Dynamics of Gas-Solids Fluidized Beds Through Pressure Fluctuations: A Brief Examination of Methods of Analysis
This paper revisits and critically examines a number of methods used for analysis of in-bed pressure signals recorded in gas-solid fluidized beds. The goal is to obtain information on the time scales of dominant phenomena present in the pressure time series of four fluidization regimes. It is demonstrated that the average cycle time represents an effective alternative to spectral analysis. In addition, we give evidence that the average cycle time yields equivalent information as some of the advanced methods of non-linear analysis (e.g. the Kolmogorov entropy). Finally, by using wavelets and wavelet packets, we show how to obtain an accurate time localization of the different frequency components present in the pressure signal
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