342 research outputs found
Coherent manipulation of spin wave vector for polarization of photons in an atomic ensemble
We experimentally demonstrate the manipulation of two-orthogonal components
of a spin wave in an atomic ensemble. Based on Raman two-photon transition and
Larmor spin precession induced by magnetic field pulses, the coherent rotations
between the two components of the spin wave is controllably achieved.
Successively, the two manipulated spin-wave components are mapped into two
orthogonal polarized optical emissions, respectively. By measuring Ramsey
fringes of the retrieved optical signals, the \pi/2-pulse fidelity of ~96% is
obtained. The presented manipulation scheme can be used to build an arbitrary
rotation for qubit operations in quantum information processing based on atomic
ensembles
Scenario Generation for Cooling, Heating, and Power Loads Using Generative Moment Matching Networks
Scenario generations of cooling, heating, and power loads are of great
significance for the economic operation and stability analysis of integrated
energy systems. In this paper, a novel deep generative network is proposed to
model cooling, heating, and power load curves based on a generative moment
matching networks (GMMN) where an auto-encoder transforms high-dimensional load
curves into low-dimensional latent variables and the maximum mean discrepancy
represents the similarity metrics between the generated samples and the real
samples. After training the model, the new scenarios are generated by feeding
Gaussian noises to the scenario generator of the GMMN. Unlike the explicit
density models, the proposed GMMN does not need to artificially assume the
probability distribution of the load curves, which leads to stronger
universality. The simulation results show that the GMMN not only fits the
probability distribution of multi-class load curves well, but also accurately
captures the shape (e.g., large peaks, fast ramps, and fluctuation),
frequency-domain characteristics, and temporal-spatial correlations of cooling,
heating, and power loads. Furthermore, the energy consumption of generated
samples closely resembles that of real samples.Comment: This paper has been accepted by CSEE Journal of Power and Energy
System
A Review of Graph Neural Networks and Their Applications in Power Systems
Deep neural networks have revolutionized many machine learning tasks in power
systems, ranging from pattern recognition to signal processing. The data in
these tasks is typically represented in Euclidean domains. Nevertheless, there
is an increasing number of applications in power systems, where data are
collected from non-Euclidean domains and represented as graph-structured data
with high dimensional features and interdependency among nodes. The complexity
of graph-structured data has brought significant challenges to the existing
deep neural networks defined in Euclidean domains. Recently, many publications
generalizing deep neural networks for graph-structured data in power systems
have emerged. In this paper, a comprehensive overview of graph neural networks
(GNNs) in power systems is proposed. Specifically, several classical paradigms
of GNNs structures (e.g., graph convolutional networks) are summarized, and key
applications in power systems, such as fault scenario application, time series
prediction, power flow calculation, and data generation are reviewed in detail.
Furthermore, main issues and some research trends about the applications of
GNNs in power systems are discussed
Quantum Interference of Stored Coherent Spin-wave Excitations in a Two-channel Memory
Quantum memories are essential elements in long-distance quantum networks and
quantum computation. Significant advances have been achieved in demonstrating
relative long-lived single-channel memory at single-photon level in cold atomic
media. However, the qubit memory corresponding to store two-channel spin-wave
excitations (SWEs) still faces challenges, including the limitations resulting
from Larmor procession, fluctuating ambient magnetic field, and
manipulation/measurement of the relative phase between the two channels. Here,
we demonstrate a two-channel memory scheme in an ideal tripod atomic system, in
which the total readout signal exhibits either constructive or destructive
interference when the two-channel SWEs are retrieved by two reading beams with
a controllable relative phase. Experimental result indicates quantum coherence
between the stored SWEs. Based on such phase-sensitive storage/retrieval
scheme, measurements of the relative phase between the two SWEs and Rabi
oscillation, as well as elimination of the collapse and revival of the readout
signal, are experimentally demonstrated
Epidemiological and virological characteristics of pandemic influenza A (H1N1) 2009 in school outbreaks in China
Background: During the 2009 pandemic influenza H1N1 (2009) virus (pH1N1) outbreak, school students were at an
increased risk of infection by the pH1N1 virus. However, the estimation of the attack rate showed significant variability.
Methods: Two school outbreaks were investigated in this study. A questionnaire was designed to collect information by
interview. Throat samples were collected from all the subjects in this study 6 times and sero samples 3 times to confirm the
infection and to determine viral shedding. Data analysis was performed using the software STATA 9.0.
Findings: The attack rate of the pH1N1 outbreak was 58.3% for the primary school, and 52.9% for the middle school. The
asymptomatic infection rates of the two schools were 35.8% and 37.6% respectively. Peak virus shedding occurred on the
day of ARI symptoms onset, followed by a steady decrease over subsequent days (p = 0.026). No difference was found either
in viral shedding or HI titer between the symptomatic and the asymptomatic infectious groups.
Conclusions: School children were found to be at a high risk of infection by the novel virus. This may be because of a
heightened risk of transmission owing to increased mixing at boarding school, or a lack of immunity owing to socioeconomic
status. We conclude that asymptomatically infectious cases may play an important role in transmission of the
pH1N1 virus
The Emerging of Hydrovoltaic Materials as a Future Technology: A Case Study for China
Water contains tremendous energy in various forms, but very little of this energy has yet been harvested. Nanostructured materials can generate electricity by water-nanomaterial interaction, a phenomenon referred to as hydrovoltaic effect, which potentially extends the technical capability of water energy harvesting. In this chapter, starting by describing the fundamental principle of hydrovoltaic effect, including water-carbon interactions and fundamental mechanisms of harvesting water energy with nanostructured materials, experimental advances in generating electricity from water flows, waves, natural evaporation, and moisture are then reviewed. We further discuss potential applications of hydrovoltaic technologies, analyze main challenges in improving the energy conversion efficiency and scaling up the output power, and suggest prospects for developments of the emerging technology, especially in China
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