1,150 research outputs found
On the Value of Online Learning for Radar Waveform Selection
This paper attempts to characterize the kinds of physical scenarios in which
an online learning-based cognitive radar is expected to reliably outperform a
fixed rule-based waveform selection strategy, as well as the converse. We seek
general insights through an examination of two decision-making scenarios,
namely dynamic spectrum access and multiple-target tracking. The radar scene is
characterized by inducing a state-space model and examining the structure of
its underlying Markov state transition matrix, in terms of entropy rate and
diagonality. It is found that entropy rate is a strong predictor of online
learning-based waveform selection, while diagonality is a better predictor of
fixed rule-based waveform selection. We show that these measures can be used to
predict first and second-order stochastic dominance relationships, which can
allow system designers to make use of simple decision rules instead of more
cumbersome learning approaches under certain conditions. We validate our
findings through numerical results for each application and provide guidelines
for future implementations.Comment: 15 pages, 15 figures. Final version to appear in IEEE Transaction on
Radar Systems. arXiv admin note: substantial text overlap with
arXiv:2212.0059
Timely Target Tracking in Cognitive Radar Networks
We consider a scenario where a fusion center must decide which updates to
receive during each update period in a communication-limited cognitive radar
network. When each radar node in the network only is able to obtain noisy state
measurements for a subset of the targets, the fusion center may not receive
updates on every target during each update period. The solution for the
selection problem at the fusion center is not well suited for sequential
learning frameworks. We derive an Age of Information-inspired track sensitive
metric to inform node selection in such a network and compare it against
less-informed techniques.Comment: 6 pages, 6 figure
Experimental Analysis of Reinforcement Learning Techniques for Spectrum Sharing Radar
In this work, we first describe a framework for the application of
Reinforcement Learning (RL) control to a radar system that operates in a
congested spectral setting. We then compare the utility of several RL
algorithms through a discussion of experiments performed on Commercial
off-the-shelf (COTS) hardware. Each RL technique is evaluated in terms of
convergence, radar detection performance achieved in a congested spectral
environment, and the ability to share 100MHz spectrum with an uncooperative
communications system. We examine policy iteration, which solves an environment
posed as a Markov Decision Process (MDP) by directly solving for a stochastic
mapping between environmental states and radar waveforms, as well as Deep RL
techniques, which utilize a form of Q-Learning to approximate a parameterized
function that is used by the radar to select optimal actions. We show that RL
techniques are beneficial over a Sense-and-Avoid (SAA) scheme and discuss the
conditions under which each approach is most effective.Comment: Accepted for publication at IEEE Intl. Radar Conference, Washington
DC, Apr. 2020. This is the author's version of the wor
Feed-Forward Inhibition of Androgen Receptor Activity by Glucocorticoid Action in Human Adipocytes
SummaryWe compared transcriptomes of terminally differentiated mouse 3T3-L1 and human adipocytes to identify cell-specific differences. Gene expression and high content analysis (HCA) data identified the androgen receptor (AR) as both expressed and functional, exclusively during early human adipocyte differentiation. The AR agonist dihydrotestosterone (DHT) inhibited human adipocyte maturation by downregulation of adipocyte marker genes, but not in 3T3-L1. It is interesting that AR induction corresponded with dexamethasone activation of the glucocorticoid receptor (GR); however, when exposed to the differentiation cocktail required for adipocyte maturation, AR adopted an antagonist conformation and was transcriptionally repressed. To further explore effectors within the cocktail, we applied an image-based support vector machine (SVM) classification scheme to show that adipocyte differentiation components inhibit AR action. The results demonstrate human adipocyte differentiation, via GR activation, upregulates AR but also inhibits AR transcriptional activity
Channel estimation method with improved performance for the UMTS-TDD mode
Channel estimation is an essential building block for UTRA-TDD high performance receivers. Once the performance of the channel estimator algorithm proposed by 3GPP is highly dependent on the time spreading between consecutive multi-path components, a Successive Multi-path channel Estimation Technique (SMET) that improves the time resolution is proposed in this paper. A SMET based maximum likelihood approach for vectorial channel estimation, to include the estimation of the direction-of-arrival, is also proposed. This algorithm solves efficiently the complex problem of DOA estimation of multiple users in a multi path propagation environment even when the number of required DOA's exceeds the number of antenna array elements. Another property of the proposed algorithm is its ability to resolve signals from different users arriving from the same direction. This is due to processing in both time and space dimensions. The performance of these algorithms is assessed by resorting to simulations in multi-path environments using the UMTS-TDD specifications, and also by comparing the rms estimation errors against the Crámer-Rao Bound. The effect of imperfect channel estimation on the performance of RAKE and Hard-Decision Parallel Interference Canceller receivers is also analysed. The results show that a good performance can be achieved with SMET, from low to high values of Eb/n0
Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS
The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured
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