135 research outputs found
Fingerprinting Sources of the Sediments Deposited in the Riparian Zone of the Ruxi Tributary Channel of the Three Gorges Reservoir (China)
The riparian zone of the Three Gorges Reservoir serves as a critical transitional zone located between the aquatic and surrounding terrestrial environments. The periodic anti-seasonal alternation of wet and dry periods results in an intensive exchange of substance within the riparian zone. The discrimination of the sources of the sediments deposited within the riparian zone is of fundamental importance for the evaluation of the soil pollution and associated environmental impacts and for the protection of the water quality in the reservoir. In this study, a composite fingerprinting technique has been applied to apportion the sediment sources for the riparian zone with different elevations, ranging between 145—155, 155–165, and 165–175 m in a typical tributary channel. From a sediment perspective, the sediments suspended from the Yangtze mainstream represent the primary sources of the riparian deposits. From a contamination perspective, the sediment input from the Ruxi tributary channel represents an important source of pollution for the riparian environment. More effective sediment and sediment-associated contaminant control plans are needed to reduce the potential environmental problems of the riparian zone
Measurement-efficient quantum Krylov subspace diagonalisation
The Krylov subspace methods, being one category of the most important
classical numerical methods for linear algebra problems, their quantum
generalisation can be much more powerful. However, quantum Krylov subspace
algorithms are prone to errors due to inevitable statistical fluctuations in
quantum measurements. To address this problem, we develop a general theoretical
framework to analyse the statistical error and measurement cost. Based on the
framework, we propose a quantum algorithm to construct the Hamiltonian-power
Krylov subspace that can minimise the measurement cost. In our algorithm, the
product of power and Gaussian functions of the Hamiltonian is expressed as an
integral of the real-time evolution, such that it can be evaluated on a quantum
computer. We compare our algorithm with other established quantum Krylov
subspace algorithms in solving two prominent examples. It is shown that the
measurement number in our algorithm is typically to times
smaller than other algorithms. Such an improvement can be attributed to the
reduced cost of composing projectors onto the ground state. These results show
that our algorithm is exceptionally robust to statistical fluctuations and
promising for practical applications.Comment: 18 pages, 5 figure
Physical-layer key distribution using synchronous complex dynamics of DBR semiconductor lasers
Common-signal-induced synchronization of semiconductor lasers with optical
feedback inspired a promising physical key distribution with
information-theoretic security and potential in high rate. A significant
challenge is the requirement to shorten the synchronization recovery time for
increasing key rate without sacrificing operation parameter space for security.
Here, open-loop synchronization of wavelength-tunable multi-section distributed
Bragg reflector (DBR) lasers is proposed as a solution for physical-layer key
distribution. Experiments show that the synchronization is sensitive to two
operation parameters, i.e., currents of grating section and phase section.
Furthermore, fast wavelength-shift keying synchronization can be achieved by
direct modulation on one of the two currents. The synchronization recovery time
is shortened by one order of magnitude compared to close-loop synchronization.
An experimental implementation is demonstrated with a final key rate of 5.98
Mbit/s over 160 km optical fiber distance. It is thus believed that
fast-tunable multi-section semiconductor lasers opens a new avenue of high-rate
physical-layer key distribution using laser synchronization.Comment: 13 pages, 5 figure
3D simulations of positive streamers in air in a strong external magnetic field
We study how external magnetic fields from 0 to 40 T influence positive
streamers in atmospheric air, using 3D PIC-MCC (particle-in-cell, Monte Carlo
collision) simulations. When a magnetic field B is applied perpendicular to the
background field E, the streamers tend to branch quite symmetrically in the
plane spanned by E and B. With a stronger magnetic field the branching angle
increases, and for the 40 T case the branches grow almost parallel to the
magnetic field. We also observe a deviation in the -ExB direction, which is
related to the ExB drift of electrons. Both with a perpendicular and with a
parallel magnetic field, the streamer radius decreases with the magnetic field
strength
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