9 research outputs found
Search in the Universe of Big Networks and Data
Searching in the Internet for some object characterised by its attributes in
the form of data, such as a hotel in a certain city whose price is less than
something, is one of our most common activities when we access the Web. We
discuss this problem in a general setting, and compute the average amount of
time and the energy it takes to find an object in an infinitely large search
space. We consider the use of N search agents which act concurrently. Both the
case where the search agent knows which way it needs to go to find the object,
and the case where the search agent is perfectly ignorant and may even head
away from the object being sought. We show that under mild conditions regarding
the randomness of the search and the use of a time-out, the search agent will
always find the object despite the fact that the search space is infinite. We
obtain a formula for the average search time and the average energy expended by
N search agents acting concurrently and independently of each other. We see
that the time-out itself can be used to minimise the search time and the amount
of energy that is consumed to find an object. An approximate formula is derived
for the number of search agents that can help us guarantee that an object is
found in a given time, and we discuss how the competition between search agents
and other agents that try to hide the data object, can be used by opposing
parties to guarantee their own success.Comment: IEEE Network Magazine - Special Issue on Networking for Big Data,
July-August 201
Capacity Based Evacuation with Dynamic Exit Signs
Exit paths in buildings are designed to minimise evacuation time when the
building is at full capacity. We present an evacuation support system which
does this regardless of the number of evacuees. The core concept is to even-out
congestion in the building by diverting evacuees to less-congested paths in
order to make maximal usage of all accessible routes throughout the entire
evacuation process. The system issues a set of flow-optimal routes using a
capacity-constrained routing algorithm which anticipates evolutions in path
metrics using the concept of "future capacity reservation". In order to direct
evacuees in an intuitive manner whilst implementing the routing algorithm's
scheme, we use dynamic exit signs, i.e. whose pointing direction can be
controlled. To make this system practical and minimise reliance on sensors
during the evacuation, we use an evacuee mobility model and make several
assumptions on the characteristics of the evacuee flow. We validate this
concept using simulations, and show how the underpinning assumptions may limit
the system's performance, especially in low-headcount evacuations
G-Networks with Adders
Queueing networks are used to model the performance of the Internet, of manufacturing and job-shop systems, supply chains, and other networked systems in transportation or emergency management. Composed of service stations where customers receive service, and then move to another service station till they leave the network, queueing networks are based on probabilistic assumptions concerning service times and customer movement that represent the variability of system workloads. Subject to restrictive assumptions regarding external arrivals, Markovian movement of customers, and service time distributions, such networks can be solved efficiently with “product form solutions” that reduce the need for software simulators requiring lengthy computations. G-networks generalise these models to include the effect of “signals” that re-route customer traffic, or negative customers that reject service requests, and also have a convenient product form solution. This paper extends G-networks by including a new type of signal, that we call an “Adder”, which probabilistically changes the queue length at the service center that it visits, acting as a load regulator. We show that this generalisation of G-networks has a product form solution
Area-Based Results For Mine Detection
The cost and the closely related length of time spent in searching for mines or unexploded ordnance (UXO) may well be largely determined by the number of false alarms. False alarms can result in time consuming digging of soil or in additional multi-sensory tests in the minefield. In this paper, we consider two area-based methods for reducing false alarms. These are: a) the previously known `declaration\u27 technique and b) the new δ technique, which we introduce. We first derive expressions and lower bounds for false-alarm probabilities as a function of declaration area and discuss their impact on receiver operation characteristic (ROC) curves. Second, we exploit characteristics of the statistical distribution of sensory energy in the immediate neighborhood of targets and of false alarms from available calibrated data, to propose the δ technique, which significantly improves discrimination between targets and false alarms. The results are abundantly illustrated with statistical data and ROC curves using electromagnetic-induction sensor data made available through DARPA from measurements at various calibrated sites
Area-based results for mine detection
The cost and the closely related length of time spent in searching for mines or unexploded ordnance (UXO) may well be largely determined by the numher of false alarms. False alarms can result in time consuming digging of soil or in additional multisensory tests in the minefield. In this paper, we consider two area-based methods for reducing false alarms. These are: a) the previously known declaration\u27\u27 technique [8], [10] and b) the new delta technique, which we introduce. We first derive expressions and lower bounds for false-alarm probabilities as a function of declaration area and discuss their impact on receiver operation characteristic (ROC) curves. Second, we exploit characteristics of the statistical distribution of sensory energy in the immediate neighborhood of targets and of false alarms from available calibrated data, to propose the delta technique, which significantly improves discrimination between targets and false alarms. The results are abundantly illustrated with statistical data and ROC curves using electromagnetic-induction sensor data made available through DARPA [8] from measurements at various calibrated sites