A Worst-Case Approximate Analysis of Peak Age-of-Information Via Robust Queueing Approach

A new timeliness metric, called Age-of-Information (AoI), has recently attracted a lot of research interests for real-time applications with information updates. It has been extensively studied for various queueing models based on the probabilistic approaches, where the analyses heavily depend on the properties of specific distributions (e.g., the memoryless property of the exponential distribution or the i.i.d. assumption). In this work, we take an alternative new approach, the robust queueing approach, to analyze the Peak Age-of-Information (PAoI). Specifically, we first model the uncertainty in the stochastic arrival and service processes using uncertainty sets. This enables us to approximate the expected PAoI performance for very general arrival and service processes, including those exhibiting heavy-tailed behaviors or correlations, where traditional probabilistic approaches cannot be applied. We then derive a new bound on the PAoI in the single-source single-server setting. Furthermore, we generalize our analysis to two-source single-server systems with symmetric arrivals, which involves new challenges (e.g., the service times of the updates from two sources are coupled in one single uncertainty set). Finally, through numerical experiments, we show that our new bounds provide a good approximation for the expected PAoI. Compared to some well-known bounds in the literature (e.g., one based on Kingman's bound under the i.i.d. assumption) that tends to be inaccurate under light load, our new approximation is accurate under both light and high loads, both of which are critical scenarios for the AoI performance.Comment: Published in IEEE INFOCOM 202

Turbulent Flow Overtopping a Dam - A CFD Modeling Study

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Primary synovial sarcoma of the heart

Primary synovial sarcoma of the heart is very rare, accounting for 5% of cardiac malignancies. Of the few cases reported in the literature to date, nearly all have had a very poor outcome. We present a further case. This uncommon malignancy has no specific symptoms during its development, which results in delayed diagnosis. Echocardiography, chest computed tomography, and magnetic resonance imaging can provide effective information about this tumor. With the identification of the characteristic and diagnostic chromosomal abnormality t(X; 18), this malignancy will become increasingly recognized. Synovial sarcoma of the heart requires surgical intervention to improve the prognosis. Adjuvant and/or genetic therapy pre- or postoperation can help prolong life. Chemotherapy is usually recommended as it may benefit the patients. The key to treatment in the future is to find new therapeutic agents. Further elucidation of the effects of this chromosomal abnormality may lead to better-directed therapies in future. (Cardiol J 2011; 18, 2: 128-133

Infrared Optical Path Adjustment Method for Common-path Optical Coherence Tomography

A new, common-path, in-axis concentric beam-splitting Michelson interferometer is demonstrated for optical coherence tomography (OCT), which can be used to perform high resolution cross-sectional in vivo and in situ imaging of biological tissues. a piece of glass tube with its inner diameter smaller than the beamwidth of the collimated light is used to split the light into a reference and sample beam. in order to obtain the optimal spectral interferogram of this OCT system, an infrared optical path adjustment method was introduced in this paper. © (2012) Trans Tech Publications, Switzerland

Magneto-Induced Topological Phase Transition in Inverted InAs/GaSb Bilayers

We report a magneto-induced topological phase transition in inverted InAs/GaSb bilayers from a quantum spin Hall insulator to a normal insulator. We utilize a dual-gated Corbino device in which the degree of band inversion, or equivalently the electron and hole densities, can be continuously tuned. We observe a topological phase transition around the magnetic field where a band crossing occurs, that is accompanied by a bulk-gap closure characterized by a bulk conductance peak (BCP). In another set of experiments, we study the transition under a tilted magnetic field (tilt angle $\theta$). We observe the characteristic magneto-conductance around BCP as a function of $\theta$, which dramatically depends on the density of the bilayers. In a relatively deep-inversion (hence a higher density) regime, where the electron-hole hybridization dominates the excitonic interaction, the BCP grows with $\theta$. On the contrary, in a shallowly-inverted (a lower density) regime, where the excitonic interaction dominates the hybridization, the BCP is suppressed indicating a smooth crossover without a gap closure. This suggests the existence of a low-density, correlated insulator with spontaneous symmetry breaking near the critical point. Our highly controllable electron-hole system offers an ideal platform to study interacting topological states as proposed by recent theories.Comment: 15+15 pages, 4+9 figure

Waiting but not Aging: Optimizing Information Freshness Under the Pull Model

The Age-of-Information is an important metric for investigating the timeliness performance in information-update systems. In this paper, we study the AoI minimization problem under a new Pull model with replication schemes, where a user proactively sends a replicated request to multiple servers to "pull" the information of interest. Interestingly, we find that under this new Pull model, replication schemes capture a novel tradeoff between different values of the AoI across the servers (due to the random updating processes) and different response times across the servers, which can be exploited to minimize the expected AoI at the user's side. Specifically, assuming Poisson updating process for the servers and exponentially distributed response time, we derive a closed-form formula for computing the expected AoI and obtain the optimal number of responses to wait for to minimize the expected AoI. Then, we extend our analysis to the setting where the user aims to maximize the AoI-based utility, which represents the user's satisfaction level with respect to freshness of the received information. Furthermore, we consider a more realistic scenario where the user has no prior knowledge of the system. In this case, we reformulate the utility maximization problem as a stochastic Multi-Armed Bandit problem with side observations and leverage a special linear structure of side observations to design learning algorithms with improved performance guarantees. Finally, we conduct extensive simulations to elucidate our theoretical results and compare the performance of different algorithms. Our findings reveal that under the Pull model, waiting does not necessarily lead to aging; waiting for more than one response can often significantly reduce the AoI and improve the AoI-based utility in most scenarios.Comment: 15 pages. arXiv admin note: substantial text overlap with arXiv:1704.0484

Influence of sympathetic inrush on voltage dips caused by transformer energisation

Energising a transformer with other adjacent transformers in service may induce sympathetic inrush that could lead to long duration voltage dips. This study addresses this issue through analysing voltage dip events observed on a 400/132 kV grid when energisations of several generator step-up transformers were performed. With the help of a number of field measurements of voltage dips involving sympathetic inrush, a detailed network model in alternative transients program/electromagnetic transients program has been developed and validated. Based on the network model, comprehensive simulation studies have been performed. In addition, because of the nature of multiple controlling parameters, sensitivity assessment has been carried out to identify the key influential parameters. It is found that the sympathetic inrush, although does not affect voltage dip magnitude, can prolong voltage dip duration by 143% under the worst energisation condition. The sympathetic inrush occurring in substation transformers gives rise to a network-wide sympathetic interaction, resulting in further prolonged voltage dips on the 132 kV grid. Finally, it is proven that application of static var compensator is able to speed up the voltage dip recovery. © The Institution of Engineering and Technology 2013