There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

I. the origin of species by means of natural selection

Artificial Neural Networks (ANNs) are being used increasingly to predict and forecast water resources variables. In this paper, the steps that should be followed in the development of such models are outlined. These include the choice of performance criteria, the division and pre-processing of the available data, the determination of appropriate model inputs and network architecture, optimisation of the connection weights (training) and model validation. The options available to modellers at each of these steps are discussed and the issues that should be considered are highlighted. A review of 43 papers dealing with the use of neural network models for the prediction and forecasting of water resources variables is undertaken in terms of the modelling process adopted. In all but two of the papers reviewed, feedforward networks are used. The vast majority of these networks are trained using the backpropagation algorithm. Issues in relation to the optimal division of the available data, data pre-processing and the choice of appropriate model inputs are seldom considered. In addition, the process of choosing appropriate stopping criteria and optimising network geometry and internal network parameters is generally described poorly or carried out inadequately. All of the above factors can result in non-optimal model performance and an inability to draw meaningful comparisons between different models. Future research efforts should be directed towards the development of guidelines which assist with the development of ANN models and the choice of when ANNs should be used in preference to alternative approaches, the assessment of methods for extracting the knowledge that is contained in the connection weights of trained ANNs and the incorporation of uncertainty into ANN models.

Neural networks for the prediction and forecasting of water resources variables: a review of modelling issues and applications

We explore the effect of dimensionality on the nearest neighbor problem. We show that under a broad set of conditions (much broader than independent and identically distributed dimensions), as dimensionality increases, the distance to the nearest data point approaches the distance to the farthest data point. To provide a practical perspective, we present empirical results on both real and synthetic data sets that demonstrate that this effect can occur for as few as 10-15 dimensions. These results should not be interpreted to mean that high-dimensional indexing is never meaningful; we illustrate this point by identifying some high-dimensional workloads for which this effect does not occur. However, our results do emphasize that the methodology used almost universally in the database literature to evaluate high-dimensional indexing techniques is flawed, and should be modified. In particular, most such techniques proposed in the literature are not evaluated versus simple linear scan, and are evaluated over workloads for which nearest neighbor is not meaningful. Often, even the reported experiments, when analyzed carefully, show that linear scan would outperform the techniques being proposed on the workloads studied in high (10-15) dimensionality!.

When is nearest neighbor meaningful

The World Wide Web can be considered as a large distributed information system that provides access to shared data objects. As one of the most popular applications currently running on the Internet, the World Wide Web is of an exponential growth in size, which results in network congestion and server overloading. Web caching has been recognized as one of the effective schemes to alleviate the service bottleneck and reduce the network traffic, thereby minimize the user access latency. In this paper, we first describe the elements of a Web caching system and its desirable properties. Then, we survey the state-of-art techniques which have been used in Web caching systems. Finally, we discuss the research frontier in Web caching.

/pdf/a-survey-of-web-caching-schemes-for-the-internet-jf7e8c3wv1.pdf

A survey of web caching schemes for the Internet

http://directory.umm.ac.id/Data%20Elmu/jurnal/A/Agriculture,%20Ecosystems%20and%20Environment/Vol78.Issue3.May2000/1508.pdf

An international cooperative programme indicates the widespread occurrence of ozone injury on crops

Artificial neural networks (ANNs) are used to model the interactions that occur between ozone pollution, climatic conditions, and the sensitivity of crops and other plants to ozone A number of generic methods for analysis and modeling are presented These methods are applicable to the modeling and analysis of any data where an effect (in this case damage to plants) is caused by a number of variables that have a nonlinear influence Multilayer perceptron ANNs are used to model data from a number of sources and analysis of the trained optimized models determines the accuracy of the model's predictions The models are sufficiently general and accurate to be employed as decision support systems by United Nations Economic Commission for Europe (UNECE) in determining the critical acceptable levels of ozone in Europe Comparison is made of the accuracy of predictions for a number of modeling approaches It is shown that the ANN approach is more accurate than other methods and that the use of principal components analysis on the inputs can improve the model The validation of the models relies on more than simply an error measure on the test data The relative importance of the causal agents in the model is established in the first instance by summing absolute weight values This indicates whether the model is consistent with domain knowledge The application of a range of conditions to the model then allows predictions to be made about the nonlinear influences of the individual principal inputs and of combinations of two inputs viewed as a three-dimensional graph Equations are synthesized from the ANN to represent the model in an explicit mathematical form Models are formed with essential parameters and other inputs are added as necessary, in order of decreasing priority, until an acceptable error level is reached Secondary indicators substituting for primary indicators with which they are strongly correlated can be removed From the synthesized equations both known and novel aspects of the process modeled can be identified Known effects validate the model Novel effects form the basis of hypotheses which can then be tested

Modeling complex environmental data

Experimental studies of the T cell requirement for rejection of class I major histocompatibility complex (MHC)-disparate grafts have generated controversy over both the autonomy of CD8+ T cells and the mechanism whereby CD4+ T cells are able to independently mediate rejection. In this study of rejection of RT1Aa class I MHC-disparate rat cardiac and skin allografts by high-responder PVG RT1u recipients, we show that elimination of CD8+ T cells [by anti-CD8 monoclonal antibody (mAb) administration in vivo] fails to prolong graft survival, whereas partial depletion of CD4+ T cells (by anti-CD4 mAb treatment) markedly delays rejection of class I-disparate heart grafts, and marginally prolongs survival of skin grafts. Anti-CD4-treated PVG-RT1u athymic nude rats reconstituted with CD8+ T cells failed to reject class I-disparate skin grafts for several weeks and eventual rejection correlated with re-emergence of a small number of donor derived CD4+ T cells. Conversely, anti-CD8-treated nude rats reconstituted with CD4+ T cells alone rapidly rejected class I-disparate skin grafts. Passive transfer of anti-class I immune serum to anti-CD4-treated euthymic recipients promptly restored their ability to specifically reject a class I-disparate heart graft. Similarly, passive transfer of immune serum to PVG-RT1u nude rats bearing skin allografts caused destruction of class I-disparate but not third-party grafts. These results demonstrate that CD4+ T cells are both necessary and sufficient to cause rejection of class I-disparate heart and skin grafts in this model and that CD4+ T cell-dependent alloantibody plays a decisive role in effecting rejection.

CD4+ T cell-mediated rejection of major histocompatibility complex class I-disparate grafts: a role for alloantibody"

In this paper we describe some of the practical issues involved in designing, building and deploying a sensor network for oceanographic monitoring The paper explains some of the design decisions and their consequences, and some of the lessons learned from a first sensor network trial at sea

/pdf/real-world-issues-in-deploying-a-wireless-sensor-network-for-11yl7riuct.pdf

Real World Issues in Deploying a Wireless Sensor Network for Oceanography.

A method of operating an ad hoc network comprising a plurality of devices ( 11 - 16 ). Each device includes communication means for communicating with other ones of the plurality of devices when they are in range. The method involves storing on each device one or more nodal policies ( 1 - 6 ) which specify rules for determining how a device should behave in response to various prevailing circumstances and controlling each device to operate in accordance with one or more of the stored nodal policies. Additionally, each device stores a fitness parameter and adjusts the value of the fitness parameter in dependence upon the level of activity of the device (in particular, activity which is consistent with its stored policies). Additionally, each device monitors the value of its stored fitness parameter and the activity of its communication means and transmits ( 46, 48, 49 ), to other ones of the devices which are in range ( 13, 15, 16 ) one ore more of its stored nodal policies ( 5 ) in the event that its fitness parameter exceeds a threshold of value and its communication means is not required for other purposes.

Chris Roadknight

Papers

An international cooperative programme indicates the widespread occurrence of ozone injury on crops

Modeling complex environmental data

CD4+ T cell-mediated rejection of major histocompatibility complex class I-disparate grafts: a role for alloantibody"

Real World Issues in Deploying a Wireless Sensor Network for Oceanography.

Ad Hoc Network