125,295 research outputs found
RFI mitigation with phase-only adaptive beamforming
Connected radio interferometers are sometimes used in the tied-array mode:
signals from antenna elements are coherently added and the sum signal applied
to a VLBI backend or pulsar processing machine. Usually there is no
computer-controlled amplitude weighting in the existing radio interferometer
facilities. Radio frequency interference (RFI) mitigation with phase-only
adaptive beamforming is proposed for this mode of observation. Small phase
perturbations are introduced in each of the antenna's signal. The values of
these perturbations are optimized in such a way that the signal from a radio
source of interest is preserved and RFI signals suppressed. An evolutionary
programming algorithm is used for this task. Computer simulations, made for
both one-dimensional and two-dimensional array set-ups, show considerable
suppression of RFI and acceptable changes to the main array beam in the radio
source direction.Comment: 7 pages, 11 figure
Memory-Efficient Adaptive Optimization
Adaptive gradient-based optimizers such as Adagrad and Adam are crucial for
achieving state-of-the-art performance in machine translation and language
modeling. However, these methods maintain second-order statistics for each
parameter, thus introducing significant memory overheads that restrict the size
of the model being used as well as the number of examples in a mini-batch. We
describe an effective and flexible adaptive optimization method with greatly
reduced memory overhead. Our method retains the benefits of per-parameter
adaptivity while allowing significantly larger models and batch sizes. We give
convergence guarantees for our method, and demonstrate its effectiveness in
training very large translation and language models with up to 2-fold speedups
compared to the state-of-the-art
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