Transport of K in PVC matrix membranes containing valinomycin

We report impedance measurements on PVC matrix membranes which contain KBPh₄ with varying proportions of valinomycin. In agreement with our earlier measurements the value of the bulk membrane resistance (R_b) is much larger in the presence of valinomycin, indicating that the mobility of K⁺ is greatly reduced by the valinomycin. R_b shows a linear variation with valinomycin/K⁺ ratio between 0 and 1, but it is invariant at higher valinomycin/K⁺ ratios. Thus there is no evidence for a special transport mechanism for K⁺ in these membranes.     

A market-based approach to managing the risk of peer-to-peer transactions

Market-based principles can be used to manage the risk of distributed peer-to-peer transactions. This is demonstrated by Ptrim, a system that builds a transaction default market on top of a main transaction processing system, within which peers offer to underwrite the transaction risk for a slight increase in the transaction cost. The insurance cost, determined through market-based mechanisms, is a way of identifying untrustworthy peers and perilous transactions. The risk of the transactions is contained, and at the same time members of the peer-to-peer network capitalise on their market knowledge by profiting as transaction insurers. We evaluated the approach through trials with the deployed Ptrim prototype, as well as composite experiments involving real online transaction data and real subjects participating in the transaction default market. We examine the efficacy of our approach both from a theoretical and an experimental perspective. Our findings suggest that the Ptrim market layer functions in an efficient manner, and is able to support the transaction processing system through the insurance offers it produces, thus acting as an effective means of reducing the risk of peer-to-peer transactions. In our conclusions we discuss how a system like Ptrim assimilates properties of real world markets, and its potential exposure and possible countermeasures to events such as those witnessed in the recent global financial turmoil.     

Hiding message delivery latency using Direct-to-Cache-Transfer techniques in message passing environments

Communication overhead is the key obstacle to reaching hardware performance limits. The majority is associated with software overhead, a significant portion of which is attributed to message copying. To reduce this copying overhead, we have devised techniques that do not require to copy a received message in order for it to be bound to its final destination. Rather, a late-binding mechanism, which involves address translation and a dedicated cache, facilitates fast access to received messages by the consuming process/thread.We have introduced two policies namely Direct to Cache Transfer (DTCT) and lazy DTCT that determine whether a message after it is bound needs to be transferred into the data cache. We have studied the proposed methods in simulation and have shown their effectiveness in reducing access times to message payloads by the consuming process.     

SDriver: Location-specific signatures prevent SQL injection attacks

SQL injection attacks involve the construction of application input data that will result in the execution of malicious SQL statements. Many web applications are prone to SQL injection attacks. This paper proposes a novel methodology of preventing this kind of attacks by placing a secure database driver between the application and its underlying relational database management system. To detect an attack, the driver uses stripped-down SQL queries and stack traces to create SQL statement signatures that are then used to distinguish between injected and legitimate queries. The driver depends neither on the application nor on the RDBMS and can be easily retrofitted to any system. We have developed a tool, SDriver, that implements our technique and used it on several web applications with positive results.     

Resource allocation on computational grids using a utility model and the knapsack problem

This work introduces a utility model (UM) for resource allocation on computational grids and formulates the allocation problem as a variant of the 0–1 multichoice multidimensional knapsack problem. The notion of task-option utility is introduced, and it is used to effect allocation policies. We present a variety of allocation policies, which are expressed as functions of metrics that are both intrinsic and external to the task and resources. An external user-defined credit-value metric is shown to allow users to intervene in the allocation of urgent or low priority tasks. The strategies are evaluated in simulation against random workloads as well as those drawn from real systems. We measure the sensitivity of the UM-derived schedules to variations in the allocation policies and their corresponding utility functions. The UM allocation strategy is shown to optimally allocate resources congruent with the chosen policies.     

Job Security

Some consider unmaintainable code a tool that provides job security. At the low level, you can obtain such code through incorrect or inconsistent formatting, naming, and commenting. Complex and gratuitous coupling, lack of assertions, and failure to use a language's type system can further complicate the picture. At a higher level, deep and wide class hierarchies, lack of cohesion, and unhelpful package relationships can hinder maintainability. Finally, at the development process level, lack of version control, subpar build-and-release procedures, a lacking testing infrastructure, and the hiring of mediocre developers will hammer the last nails into a project's maintainability coffin.     

Search Algorithms for Subdatatype-Based Multimedia Retrieval

Recently, researchers have mainly been interested only in the search for data content that are globally similar to the query and not in the search for inside data items. This paper presents an algorithm, called a generalized virtual node (GVN) algorithm, to search for data items where parts (subdatatype) are similar to the incoming query. We call this subdatatype-based multimedia retrieval. Each multimedia datatype, such as image and audio is represented in this paper as a k-dimensional signal in the spatio-temporal domain. A k-dimensional signal is transformed into characteristic features and these features are stored in a hierarchical multidimensional structure, called the k-tree. Each node on the k-tree contains partial content corresponding to the spatial and/or temporal positions in the data. The k-tree structure allows us to build a unified retrieval model for any types of multimedia data. It also eliminates unnecessary comparisons of cross-media querying. The experimental results of the use of the new GVN algorithm for subaudio and subimage retrievals show that it takes much less retrieval times than other earlier algorithms such as brute-force and the partial-matching algorithm, while the accuracy is acceptable.