A tree partitioning dynamic policy for OVSF codes assignment in wideband CDMA

This paper proposes some novel techniques to accommodate users with different rate requirements in a wideband code-division multiple-access system employing orthogonal variable spreading factor codes. Two simple static code assignment strategies are first considered, and an improvement based on multicode assignment. Then the new idea of tree partitioning is introduced and used to devise a dynamic code reassignment algorithm. The behavior of these different techniques is experimentally investigated, in terms of call blocking probability and number of required reassignments. The tree partitioning method exhibits very good performances.     

HiPoLDS: A Hierarchical Security Policy Language for Distributed Systems

Expressing security policies to govern distributed systems is a complex and error-prone task. Policies are hard to understand, often expressed with unfriendly syntax, making it difficult for security administrators and for business analysts to create intelligible specifications. We introduce the Hierarchical Policy Language for Distributed Systems (HiPoLDS), which has been designed to enable the specification of security policies in distributed systems in a concise, readable, and extensible way. HiPoLDS design focuses on decentralized execution environments under the control of multiple stakeholders. It represents policy enforcement through the use of distributed reference monitors, which control the flow of information between services. HiPoLDS allows the definition of both abstract and concrete policies, expressing respectively high-level properties required and concrete implementation details to be ultimately introduced into the service implementation.     

On Prize-collecting Tours and the Asymmetric Travelling Salesman Problem

We consider a variant of the Travelling Salesman Problem which is to determine a tour visiting each vertex in the graph at most at one time; if a vertex is left unrouted a given penalty has to be paid. The objective function is to find a balance between these penalties and the cost of the tour. We call this problem the Profitable Tour Problem(PTP). If, in addition, each vertex is associated with a prize and there is a knapsack constraint which guarantees that a sufficiently large prize is collected, we have the well-known Prize-collecting Travelling Salesman Problem (PCTSP). In this paper we summarize the main results presented in the literature, then we give lower bounds for the asymmetric version of PTP and PCTSP. Moreover, we show, through computational experiments, that large size instances of the asymmetric PTP can be solved exactly.     

Lost at sea: genetic,oceanographic and meteorological evidence for storm-forced dispersal

For many species, there is broad-scale dispersal of juvenile stages and/or long-distance migration of individuals and hence the processes that drive these various wide-ranging movements have important life-history consequences. Sea turtles are one of these paradigmatic long-distance travellers, with hatchlings thought to be dispersed by ocean currents and adults often shuttling between distant breeding and foraging grounds. Here, we use multi-disciplinary oceanographic, atmospheric and genetic mixed stock analyses to show that juvenile turtles are encountered ‘downstream’ at sites predicted by currents. However, in some cases, unusual occurrences of juveniles are more readily explained by storm events and we show that juvenile turtles may be displaced thousands of kilometres from their expected dispersal based on prevailing ocean currents. As such, storms may be a route by which unexpected areas are encountered by juveniles which may in turn shape adult migrations. Increased stormy weather predicted under climate change scenarios suggests an increasing role of storms in dispersal of sea turtles and other marine groups with life-stages near the ocean surface.     

Aqueous and Solvent‐Free Uncatalyzed Three‐Component Vinylogous Mukaiyama–Mannich Reactions of Pyrrole‐Based Silyl Dienolates

A catalyst‐free, environmentally benign three‐component vinylogous Mukaiyama–Mannich reaction of pyrrole‐based silyl dienolates is presented, which works effectively in both aqueous and solvent‐free environments. Both lipophilic and hydrophilic aldehyde candidates are suitable substrates, allowing access to a rich repertoire of unsaturated vicinal aminolactam structures with virtually complete γ‐site selectivity and moderate to good anti‐diastereoselectivity. The utility of this technology is highlighted by protecting group‐free synthesis of densely hydroxylated, sugar‐related lactam frameworks. The role of water as an indispensable H‐bonding reaction propeller is demonstrated.     

An overview of solid–liquid separation of residues from coal liquefaction processes

Direct coal liquefaction process typically produces mixed oils (60%) and gases (15%). The remainder is a high‐boiling viscous residue that contains oils, asphaltenes, unreacted coal, mineral matter and potentially valuable liquefaction catalyst. Effective separation of the components of the residue stream is important to the economic and environmental performance of the process. Solid–liquid separation technologies, such as filtration, hydrocyclones, centrifugation, critical solvent deashing and distillation have been reviewed in relation to their use in coal liquefaction processes. Individual operations used have not been completely satisfactory, and a better overall result is obtained when they are used in combination. © 2012 Canadian Society for Chemical Engineering