Passive Monitoring Techniques Research Articles

Combining active and passive network measurements to build scalable monitoring systems on the grid

Because the network provides the wires that connect a grid, understanding the performance provided by a network is crucial to achieving satisfactory performance from many grid applications. Monitoring the network to predict its performance for applications is an effective solution, but the costs and scalability challenges of actively injecting measurement traffic, as well as the information access and accuracy challenges of using passively collected measurements, complicate the problem of developing a monitoring solution for a global grid. This paper is a preliminary report on the Wren project, which is focused on developing scalable solutions for network performance monitoring. By combining active and passive monitoring techniques, Wren is able to reduce the need for invasive measurements of the network without sacrificing measurement accuracy on either the WAN or LAN levels. Specifically, we present topology-based steering, which dramatically reduces the number of measurements taken for a system by using passively acquired topology and utilization to select the bottleneck links that require active bandwidth probing. Furthermore, by using passive measurements while an application is running and active measurements when none is running, we preserve our ability to offer accurate, timely predictions of network performance, while eliminating additional invasive measurements.

Indoor-outdoor relationship of SO2 concentrations in a rural and an urban community of Alberta

Passive monitoring techniques were used to measure 7-day average concentrations of SO2 in indoor–outdoor air in two Alberta communities, Boyle (population 860) and Sherwood Park (population 42 000). Sampling occurred during a 5-week period in late fall, a time of year when SO2 is less reactive in the outdoor environment. Outdoor levels of SO2 at 12 homes in Boyle (median 4.3 µg/m3, range 3.7–5.6 µg/m3) were two times lower than those at 13 homes in Sherwood Park (median 9.9 µg/m3, range 8.2–13 µg/m3). Slightly higher indoor SO2 levels were measured in Sherwood Park homes (median 1.4 µg/m3, range 0.9–5.2 µg/m3) than in Boyle homes (median 0.5 µg/m3, range 0.2–2.3 µg/m3). These results are consistent with the characteristics of the two communities involved in this study. Sherwood Park has many more SO2-related emission sources than in Boyle (i.e., increased vehicle traffic and industrial emissions). Indoor and outdoor SO2 levels measured in both communities were [Formula: see text]13 µg/m3. These levels are considered low compared with benchmark levels intended for protection of people: 365 µg/m3 averaged over 24 h (short-term exposure) or 80 µg/m3 averaged over 1 year (long-term exposure). The median indoor–outdoor SO2 concentration ratio was 0.13 for both communities.Key words: air quality, indoor, outdoor, passive monitoring, sulphur dioxide.

Recent advances in seismic monitoring technology at Canadian mines

We provide an overview of the current status of seismic monitoring instrumentation employed in Canadian underground mines. Based on several case studies, we outline how passive seismic monitoring techniques are being used to evaluate fractures and stress conditions associated with ore extraction at depth. It is shown that induced microseismicity allows for the remote monitoring of active fractures, delineating modes of failure with advancing excavation fronts, and identifying variations in principal stress orientations during sequential stages of mining. Advances into the characterization of excavation zone of influence through deformation state analysis and the use of seismic hazard analysis to evaluate the potential for ground instability are also discussed.

Passive radon monitoring techniques with and without electret collection

The processes of passive sampling and electret collection are discussed. Two types of passive sampling chamber have been developed in our laboratory: a passive sampling chamber with electret collection (PSCE) used for environmental radon concentration monitoring and radon flux rate measurement; and a passive sampling chamber with and without electret collection (PSCP) used as a personal radon dosemeter and area radon monitor. The lower limits of detection for radon concentration monitoring are 3.0 T-1, 2.0*102 T-1 and 3.8*103 T-1 Bq m-3 for PSCE and PSCP with and without electret collection, respectively, where T is the sampling period in hours. The lower limit of detection for radon flux rate measurement with PSCE is 2.0*10-4 T-2 Bq m-2 s-1. The characteristics of the passive sampling monitoring techniques and some monitoring results are described.

Operator exposure from closed system loading and application of alachlor herbicide.

Biological monitoring (urine) and passive monitoring (patch) techniques were used to estimate total body dose in sixteen operators of closed system transfers of the emulsifiable concentrate (EC) and the micro-encapsulated (MT) formulations of alachlor herbicide from prepackaged bulk containers. Four of the operators were also monitored during the subsequent soil incorporation applications. The dermal deposition was very low and, more importantly, the analysis of 12-hour composites of urine collected for five days, revealed undetectable (<5 ppb) concentrations of alachlor metabolites in every sample from 12 of 16 operators. The mean normalized absorbed dose of alachlor was 4.1×10−7 mg/kg bw/lb applied for EC tank fill plus application, zero (undetected) for EC tank fill only, and 1.1×10−7 mg/kg bw/lb applied for MT tank fill only. These results demonstrate that operators wearing normal clothing plus protective clothing as recommended on the product label, will experience negligible exposure while using well designed closed transfer systems. The urine samples in this study were analyzed by a new method which utilizes base-pressure hydrolysis to convert the alachlor metabolites to the anilines which are separated by high pressure liquid chromatography (HPLC) and detected by an electrochemical detector.

Indications for Electrophysiologic Studies

The indications for invasive electrophysiologic evaluation of patients with arrhythmia problems have broadened considerably in the last decade. The major advantage of electrophysiologic studies over other forms of arrhythmia evaluation, particularly passive monitoring techniques, is the ability to detect the arrhythmia by provocative stimulation techniques, eliminating the need for serendipitous recording of a sporadic event. Once the arrhythmia can be reproducibly induced, its electrophysiologic characteristics may be studied and the effect of drugs and/or pacemakers in preventing or terminating the arrhythmia can be determined. Furthermore, if these therapeutic modalities are unsuccessful, electrophysiologic mapping procedures can be performed to determine the feasibility of surgical therapy of the arrhythmia and can help to guide the surgical approach and maximize success. Electrophysiologic evaluation is not without its limitations. It is applicable only to arrhythmias that can be reproducibly induced by programmed ventricular stimulation, and it has the potential for significant complications, including vascular complications of catheterization plus potential morbidity from the induction of life-threatening arrhythmias. Therefore, electrophysiologic evaluation should not be applied haphazardly to any patient with arrhythmia-related symptoms or even documented asymptomatic arrhythmias. Still, in the hands of experienced personnel and in the appropriate setting, electrophysiologic studies have become a valuable tool in the evaluation and therapy of patients with significant and often life-threatening arrhythmias.