33 research outputs found
Why It Takes So Long to Connect to a WiFi Access Point
Today's WiFi networks deliver a large fraction of traffic. However, the
performance and quality of WiFi networks are still far from satisfactory. Among
many popular quality metrics (throughput, latency), the probability of
successfully connecting to WiFi APs and the time cost of the WiFi connection
set-up process are the two of the most critical metrics that affect WiFi users'
experience. To understand the WiFi connection set-up process in real-world
settings, we carry out measurement studies on million mobile users from
representative cities associating with million APs in billion WiFi
sessions, collected from a mobile "WiFi Manager" App that tops the Android/iOS
App market. To the best of our knowledge, we are the first to do such large
scale study on: how large the WiFi connection set-up time cost is, what factors
affect the WiFi connection set-up process, and what can be done to reduce the
WiFi connection set-up time cost. Based on the measurement analysis, we develop
a machine learning based AP selection strategy that can significantly improve
WiFi connection set-up performance, against the conventional strategy purely
based on signal strength, by reducing the connection set-up failures from
to and reducing time costs of the connection set-up
processes by more than times.Comment: 11pages, conferenc
Beyond Sharing: Conflict-Aware Multivariate Time Series Anomaly Detection
Massive key performance indicators (KPIs) are monitored as multivariate time
series data (MTS) to ensure the reliability of the software applications and
service system. Accurately detecting the abnormality of MTS is very critical
for subsequent fault elimination. The scarcity of anomalies and manual labeling
has led to the development of various self-supervised MTS anomaly detection
(AD) methods, which optimize an overall objective/loss encompassing all
metrics' regression objectives/losses. However, our empirical study uncovers
the prevalence of conflicts among metrics' regression objectives, causing MTS
models to grapple with different losses. This critical aspect significantly
impacts detection performance but has been overlooked in existing approaches.
To address this problem, by mimicking the design of multi-gate
mixture-of-experts (MMoE), we introduce CAD, a Conflict-aware multivariate KPI
Anomaly Detection algorithm. CAD offers an exclusive structure for each metric
to mitigate potential conflicts while fostering inter-metric promotions. Upon
thorough investigation, we find that the poor performance of vanilla MMoE
mainly comes from the input-output misalignment settings of MTS formulation and
convergence issues arising from expansive tasks. To address these challenges,
we propose a straightforward yet effective task-oriented metric selection and
p&s (personalized and shared) gating mechanism, which establishes CAD as the
first practicable multi-task learning (MTL) based MTS AD model. Evaluations on
multiple public datasets reveal that CAD obtains an average F1-score of 0.943
across three public datasets, notably outperforming state-of-the-art methods.
Our code is accessible at https://github.com/dawnvince/MTS_CAD.Comment: 11 pages, ESEC/FSE industry track 202
Effects of Pressure and Doping on Ruddlesden-Popper phases Lan+1NinO3n+1
Recently the discovery of superconductivity with a critical temperature Tc up
to 80 K in Ruddlesden-Popper phases Lan+1NinO3n+1 (n = 2) under pressure has
garnered considerable attention. Up to now, the superconductivity was only
observed in La3Ni2O7 single crystal grown with the optical-image floating zone
furnace under oxygen pressure. It remains to be understood the effect of
chemical doping on superconducting La3Ni2O7 as well as other Ruddlesden-Popper
phases. Here, we systematically investigate the effect of external pressure and
chemical doping on polycrystalline Ruddlesden-Popper phases. Our results
demonstrate the application of pressure and doping effectively tunes the
transport properties of Ruddlesden-Popper phases. We find pressure-induced
superconductivity up to 86 K in La3Ni2O7 polycrystalline sample, while no
signatures of superconductivity are observed in La2NiO4 and La4Ni3O10 systems
under high pressure up to 50 GPa. Our study sheds light on the exploration of
high-Tc superconductivity in nickelates.Comment: 21 papes, 8 figures and 1 tabl
Effect of physical and chemical pressure on the superconductivity of caged-type quasiskutterudite Lu5Rh6Sn18
Lu5Rh6Sn18 is one of the caged-type quasiskutterudite superconductors with
superconducting transition temperature Tc = 4.12 K. Here, we investigate the
effect of pressure on the superconductivity in Lu5Rh6Sn18 by combining high
pressure electrical transport, synchrotron x-ray diffraction (XRD) and chemical
doping. Application of high pressure can enhance both the metallicity and the
superconducting transition temperature in Lu5Rh6Sn18. Tc is found to show a
continuous increase reaching up to 5.50 K at 11.4 GPa. Our high pressure
synchrotron XRD measurements demonstrate the stability of the pristine crystal
structure up to 12.0 GPa. In contrast, Tc is suppressed after the substitution
of La ions in Lu sites, inducing negative chemical pressure. Our study provides
valuable insights into the improvement of superconductivity in caged compounds.Comment: 9 pages, 8 figure