Parameter Estimation via Conditional Expectation --- A Bayesian Inversion

When a mathematical or computational model is used to analyse some system, it is usual that some parameters resp.\ functions or fields in the model are not known, and hence uncertain. These parametric quantities are then identified by actual observations of the response of the real system. In a probabilistic setting, Bayes's theory is the proper mathematical background for this identification process. The possibility of being able to compute a conditional expectation turns out to be crucial for this purpose. We show how this theoretical background can be used in an actual numerical procedure, and shortly discuss various numerical approximations

Noisy quantum Monty Hall game

The influence of spontaneous emission channel and generalized Pauli channel on quantum Monty Hall Game is analysed. The scheme of Flittney and Abbott is reformulated using the formalism of density matrices. Optimal classical strategies for given quantum strategies are found. The whole presented scheme illustrates how quantum noise may change the odds of a zero-sum game.Comment: 10 pages, 3 figure

Minimally-intrusive frequent round trip time measurements using Synthetic Packet-Pairs

Accurate and frequent round trip time (RTT) measurements are important in testbeds and operational networks. Active measurement techniques inject probe packets that may modify the behaviour of the observed network and may produce misleading RTT estimates if the network handles probe packets differently to regular packets. Previous passive measurement techniques address these issues, but require precise time synchronisation or are limited to certain traffic types. We introduce Synthetic Packet-Pairs (SPP), a novel passive technique for RTT measurement. SPP provides frequently updated RTT measurements using any network traffic already present in the network without the need for time synchronisation. SPP accurately measures the RTT experienced by any application's traffic, even applications that do not exhibit symmetric client-server packet exchanges. We experimentally demonstrate the advantages of SPP

Transient Heat Analysis of a Carbon Composite Scramjet Combustion Chamber

A preliminary 2D transient analysis for a predicted trajectory in a representative scramjet flight path is presented. This model incorporates hypersonic convection and radiation heat transfer at the combustor walls and heat transfer to the fuel which is used as an endothermic heat sink. A heavy hydrocarbon fuel is selected due to the high density and energy release required for combustion, whilst still providing the necessary heat sink for cooling. In this process the fuel can be cracked to smaller carbon chained molecules for improved ignition and combustion. This analysis will be used in parallel with materials development to ensure appropriate composites are available in Australia for flight structures. The results show that for a postulated Mach 8 scramjet flight at 27km altitude that a combustor structure comprising of 1mm RCC, 1mm graphite foam insulation and a 3mm inconel fuel manifold the maximum temperatures reached are of the order of 1950K in the RCC. This falls within the temperature range allowed for the chosen materials to ensure that structural integrity is maintained. These results justify the further investigation into the use of composite materials and regenerative cooling with the aim of potentially using the analysis for the design of flight vehicles, including the upcoming HiFire series of experiments

Estimating IPv4 address space usage with capture-recapture

As of April 2013 almost 95% of the IPv4 address space has been allocated. Yet, the transition to IPv6 is still relatively slow. One reason could be existing “IPv4 reserves” – allocated but unused IPv4 addresses. Knowing how many addresses are actively used is important to predict a potential IPv4 address market, predict the IPv6 deployment time frame, and measure progressive exhaustion after the IPv4 space is fully allocated. Unfortunately, only a fraction of hosts respond to active probes, such as “ping”. We propose a capture-recapture method to estimate the actively used IPv4 addresses from multiple incomplete data sources, including “ping” censuses, network traces and server logs. We estimate that at least 950–1090 million IPv4 addresses are used, which is 36–41% of the publicly routed space. We analyse how the utilisation depends on various factors, such as region, country and allocation prefix length

Dynamics of the IP time to live field in internet traffic flows

The Time To Live (TTL) field present in the IP protocol header is used to limit the lifetime of packets in the network. Previous research has measured TTL for studying path lengths and dynamics in IP networks, and for detecting route changes. How the TTL varies over short timescales of subsequent packets of traffic flows has not yet been analysed. Such knowledge is needed for passively detecting route changes based on existing traffic in the network or traffic traces, and for designing mechanisms that modulate the TTL field such as IP traceback techniques and covert channels. In this paper we analyse small time scale TTL variation in Internet traffic flows based on a number of packet traces captured at different locations in the Internet

Client RTT and hop Count Distributions viewed from an Australian ‘Enemy Territory’ Server

Network game servers experience traffic caused by actual game players and by remote clients simply probing the game server’s current status. Game clients probe game servers for information such as the current map and number of current players on the server to enable players to fin d suitable games. The number of clients that probe a given server is orders of magnitudes higher than the number of eventual players. Network level round trip time (delay, or ‘la g’) between a client and server is a very important criterion for players when deciding which server to join. Often the round trip time is roughly proportional to hop count. In this paper we document and investigate the distributions of round trip time and hop count for game clients that only probe and clients that actually play on a public game server. We also examine the geographical distributions of both groups. Our data was gathered from a Wolfenstein Enemy Territory server operating in Melbourne, Australia, in late 2004

Economics of animal genetic resources use and conservation

Economic analysis can play an important role in the sustainable management of animal genetic resources (AnGR). The first report on The State of the World’s Animal Genetic Resources for Food and Agriculture (first SoW-AnGR) (FAO, 2007a) included a section on methods for economic evaluation 1 that provided an overview of the various types of value that can be distinguished (direct and indirect use values, option values, bequest values and existence values) and described potential methods and tools for assessing them. It also presented some examples of the use of these methods and tools and the findings obtained. This updated section provides an overview of recent developments in the economics of AnGR use and conservation. The revised title reflects the way in which this field of work has moved beyond just the development and testing of methods

The economics of managing crop diversity on-farm: Case studies from the genetic resources policy initiative

The purpose of this book is to assess a variety of economic issues as they relate to agro-biodiversity and show how addressing these issues can assist in agro-biodiversity policy-making. This is illustrated using empirical data from some of the countries (Ethiopia, Nepal and Zambia) which are part of the Genetic Resources Policy Initiative. The empirical chapters apply the relevant economic methods, including regression analysis, choice experiments, hedonic pricing, contingent valuation and farm business income analysis. The authors discuss the economics of managing crop diversity on-farm in the context of crop variety attribute preferences, farmers' perception of agro-biodiversity loss, and value addition and marketing of the products of traditional crop varieties. The case studies include detailed analysis of traditional varieties of groundnut, maize, rice, sorghum, and teff. The results are relevant not only to GRPI countries but also to other countries concerned with the sustainable utilization of these resources. Overall, the studies illustrate how genetic resources issues can be integrated into rural development interventions