5,844 research outputs found
Experimental realization of plaquette resonating valence bond states with ultracold atoms in optical superlattices
The concept of valence bond resonance plays a fundamental role in the theory
of the chemical bond and is believed to lie at the heart of many-body quantum
physical phenomena. Here we show direct experimental evidence of a
time-resolved valence bond quantum resonance with ultracold bosonic atoms in an
optical lattice. By means of a superlattice structure we create a
three-dimensional array of independent four-site plaquettes, which we can fully
control and manipulate in parallel. Moreover, we show how small-scale plaquette
resonating valence bond states with s- and d-wave symmetry can be created and
characterized. We anticipate our findings to open the path towards the creation
and analysis of many-body RVB states in ultracold atomic gases.Comment: 7 page, 4 figures in main text, 3 figures in appendi
Nonthermal processes and neutrino emission from the black hole GRO J0422+32 in a bursting state
GRO J0422+32 is a member of the class of low-mass X-ray binaries (LMXBs). It
was discovered during an outburst in 1992. During the entire episode a
persistent power-law spectral component extending up to MeV was
observed, which suggests that nonthermal processes should have occurred in the
system. We study relativistic particle interactions and the neutrino production
in the corona of GRO J0422+32, and explain the behavior of GRO J0422+32 during
its recorded flaring phase. We have developed a magnetized corona model to fit
the spectrum of GRO J0422+32 during the low-hard state. We also estimate
neutrino emission and study the detectability of neutrinos with 1 km
detectors, such as IceCube. The short duration of the flares ( hours) and
an energy cutoff around a few TeV in the neutrino spectrum make neutrino
detection difficult. There are, however, many factors that can enhance neutrino
emission. The northern-sky coverage and full duty cycle of IceCube make it
possible to detect neutrino bursts from objects of this kind through
time-dependent analysis.Comment: 12 pages, 11 figures, accepted for publication in A&
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Register analysis and ESP pedagogy: Noun-phrase modification in a corpus of English for military navy submariners
© 2018 Elsevier Ltd Research in Maritime English (ME) has paid no attention to the range of texts and language to which Navy submariners are exposed during their training and professional careers. This research looked at Noun Phrase (NP)modification patterns in a longitudinal corpus of Submarine English (SE) professional texts in the Cartagena Military Submarine Corpus (CMSC). Using a combination of quantitative and qualitative analyses, we found that SE is characterised by heavy nominal premodification, low adjective premodification, low prepositional phrase postmodification and by the predominant use of appositive nouns in postmodifying slots. These distinctive features of SE call for a register-sensitive pedagogy that unpack these characteristics and present them in context. We argue that the contribution of corpus linguistics is essential to explore registers which, for different reasons, have not been addressed or described linguistically in the past. Similarly, we maintain that the examination and teaching of NPs is essential to understand current trends in professional writing and communication
Towards a quantum Hall effect for atoms using electric fields
An atomic analogue of Landau quantization based on the Aharonov-Casher (AC)
interaction is developed. The effect provides a first step towards an atomic
quantum Hall system using electric fields, which may be realized in a
Bose-Einstein condensate
Predicting Future Instance Segmentation by Forecasting Convolutional Features
Anticipating future events is an important prerequisite towards intelligent
behavior. Video forecasting has been studied as a proxy task towards this goal.
Recent work has shown that to predict semantic segmentation of future frames,
forecasting at the semantic level is more effective than forecasting RGB frames
and then segmenting these. In this paper we consider the more challenging
problem of future instance segmentation, which additionally segments out
individual objects. To deal with a varying number of output labels per image,
we develop a predictive model in the space of fixed-sized convolutional
features of the Mask R-CNN instance segmentation model. We apply the "detection
head'" of Mask R-CNN on the predicted features to produce the instance
segmentation of future frames. Experiments show that this approach
significantly improves over strong baselines based on optical flow and
repurposed instance segmentation architectures
Free expansion of lowest Landau level states of trapped atoms: a wavefunction microscope
We show that for any lowest-Landau-level state of a trapped, rotating,
interacting Bose gas, the particle distribution in coordinate space in a free
expansion (time of flight) experiment is related to that in the trap at the
time it is turned off by a simple rescaling and rotation. When the
lowest-Landau-level approximation is valid, interactions can be neglected
during the expansion, even when they play an essential role in the ground state
when the trap is present. The correlations in the density in a single snapshot
can be used to obtain information about the fluid, such as whether a transition
to a quantum Hall state has occurred.Comment: 5 pages, no figures. v2: discussion of neglect of interactions during
expansion improved, refs adde
Simulation of the soil water balance of wheat using daily weather forecast messages to estimate the reference evapotranspiration
Abstract. Aiming at developing real time water balance
modelling for irrigation scheduling, this study assesses the
accuracy of using the reference evapotranspiration (ETo) estimated
from daily weather forecast messages (ETo,WF) as
model input. A previous study applied to eight locations in
China (Cai et al., 2007) has shown the feasibility for estimating
ETo,WF with the FAO Penman-Monteith equation using
daily forecasts of maximum and minimum temperature,
cloudiness and wind speed. In this study, the global radiation
is estimated from the difference between the forecasted maximum
and minimum temperatures, the actual vapour pressure
is estimated from the forecasted minimum temperature
and the wind speed is obtained from converting the common
wind scales into wind speed. The present application
refers to a location in the North China Plain, Daxing, for the
wheat crop seasons of 2005–2006 and 2006–2007. Results
comparing ETo,WF with ETo computed with observed data
(ETo,obs) have shown favourable goodness of fitting indicators
and a RMSE of 0.77mmd−1. ETo was underestimated
in the first year and overestimated in the second. The water
balance model ISAREG was calibrated with data from
four treatments for the first season and validated with data of
five treatments in the second season using observed weather
data. The calibrated crop parameters were used in the simulations
of the same treatments using ETo,WF as model input.
Errors in predicting the soil water content are small, 0.010
and 0.012m3 m−3, respectively for the first and second year.
Other indicators also confirm the goodness of model predictions.
It could be concluded that using ETo computed from
daily weather forecast messages provides for accurate model
predictions and to use an irrigation scheduling model in real
tim
Numerical Simulation on Tunnel Splitting of Bose-Einstein Condensate in Multi-Well Potentials
The low-energy-level macroscopic wave functions of the Bose-Einstein
condensate(BEC) trapped in a symmetric double-well and a periodic potential are
obtained by solving the Gross-Pitaevskii equation numerically. The ground state
tunnel splitting is evaluated in terms of the even and odd wave functions
corresponding to the global ground and excited states respectively. We show
that the numerical result is in good agreement with the analytic level
splitting obtained by means of the periodic instanton method.Comment: 22 pages,7 figure
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