39,869 research outputs found
Continuously observing a dynamically decoupled spin-1 quantum gas
We continuously observe dynamical decoupling in a spin-1 quantum gas using a
weak optical measurement of spin precession. Continuous dynamical decoupling
aims to dramatically modify the character and energy spectrum of spin states to
render them insensitive to parasitic fluctuations. Continuous observation
measures this new spectrum in a single-preparation of the quantum gas. The
measured time-series contains seven tones, which spectrogram analysis parses as
splittings, coherences, and coupling strengths between the decoupled states in
real-time. With this we locate a regime where a transition between two states
is decoupled from magnetic field instabilities up to fourth order,
complementary to the parallel work at higher fields by Trypogeorgos et al.
(arXiv:1706.07876). The decoupled microscale quantum gas offers magnetic
sensitivity in a tunable band, persistent over many milliseconds: the length
scales, frequencies, and durations relevant to many applications, including
sensing biomagnetic phenomena such as neural spike trains.Comment: 5+ pages, 4 figures, 1 table; revised citation of Trypogeorgos et al.
(2017
Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics
We consider thermodynamic and dynamic phase transitions in plaquette spin
models of glasses. The thermodynamic transitions involve coupled (annealed)
replicas of the model. We map these coupled-replica systems to a single replica
in a magnetic field, which allows us to analyse the resulting phase transitions
in detail. For the triangular plaquette model (TPM), we find for the
coupled-replica system a phase transition between high- and low-overlap phases,
occuring at a coupling eps*(T), which vanishes in the low-temperature limit.
Using computational path sampling techniques, we show that a single TPM also
displays space-time transitions between active and inactive dynamical phases.
These first-order dynamical transitions occur at a critical counting field
s_c(T)>=0 that appears to vanish at zero temperature, in a manner reminiscent
of the thermodynamic overlap transition. In order to extend the ideas to three
dimensions we introduce the square pyramid model which also displays both
overlap and activity transitions. We discuss a possible common origin of these
various phase transitions, based on long-lived (metastable) glassy states.Comment: 12 pages, 9 fig
Scalar Field as Dark Matter in the Universe
We investigate the hypothesis that the scalar field is the dark matter and
the dark energy in the Cosmos, wich comprises about 95% of the matter of the
Universe. We show that this hypothesis explains quite well the recent
observations on type Ia supernovae.Comment: 4 pages REVTeX, 1 eps figure. Minor changes. To appear in Classical
and Quantum Gravit
A versatile high resolution objective for imaging quantum gases
We present a high resolution objective lens made entirely from catalog
singlets that has a numerical aperture of 0.36. It corrects for aberrations
introduced by a glass window and has a long working distance of 35mm, making it
suitable for imaging objects within a vacuum system. This offers simple high
resolution imaging for many in the quantum gas community. The objective
achieves a resolution of 1.3{\mu}m at the design wavelength of 780nm, and a
diffraction-limited field of view of 360{\mu}m when imaging through a 5mm
window. Images of a resolution target and a pinhole show quantitative agreement
with the simulated lens performance. The objective is suitable for
diffraction-limited imaging on the D2 line of all the alkalis by changing only
the aperture diameter, retaining numerical apertures above 0.32. The design
corrects for window thicknesses of up to 15mm if the singlet spacings are
modified
Inlet spillage drag tests and numerical flow-field analysis at subsonic and transonic speeds of a 1/8-scale, two-dimensional, external-compression, variable-geometry, supersonic inlet configuration
Accurate spillage drag and pressure data are presented for a realistic supersonic inlet configuration. Results are compared with predictions from a finite-differencing, inviscid analysis computer procedure. The analytical technique shows good promise for the evaluation of inlet drag, but necessary refinements were identified. A detailed description of the analytical procedure is contained in the Appendix
Data curation standards and the messy world of social science occupational information resources
Occupational information resources – data about the characteristics of different occupational positions – play a unique role in social science research. They are of relevance across diverse research disciplines and in numerous disparate contexts. They are also very widely available, typically freely downloadable from research-oriented academic web-pages. But they are also one of the most uncoordinated types of information resource that social scientists routinely come across. In this paper we describe issues in curating occupational information resources during the GEODE research project (Grid Enabled Occupational Data Environment, http:/www.geode.stir.ac.uk). This project attempts to develop long-term standards for the distribution of occupational information resources, by providing a standardised framework electronic depository for occupational information resources, and by providing a data-indexing service, premised upon eScience middleware, which collates occupational information resources and makes them readily accessible to non-specialist social scientists
Data curation standards and social science occupational information resources
Occupational information resources - data about the characteristics of different occupational positions - are widely used in the social sciences, across a range of disciplines and international contexts. They are available in many formats, most often constituting small electronic files that are made freely downloadable from academic web-pages. However there are several challenges associated with how occupational information resources are distributed to, and exploited by, social researchers. In this paper we describe features of occupational information resources, and indicate the role digital curation can play in exploiting them. We report upon the strategies used in the GEODE research project (Grid Enabled Occupational Data Environment, http://www.geode.stir.ac.uk). This project attempts to develop long-term standards for the distribution of occupational information resources, by providing a standardized framework-based electronic depository for occupational information resources, and by providing a data indexing service, based on e-Science middleware, which collates occupational information resources and makes them readily accessible to non-specialist social scientists
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