A complete Late Weichselian and Holocene record of aeolian coversands, drift sands and soils forced by climate change and human impact, Ossendrecht, The Netherlands

A stacked aeolian sequence with intercalated soils is presented from the southern Netherlands, which fully covers the Late Weichselian and Holocene periods. An integrated sedimentological (sedimentary structures, grain size), palynological (pollen) and dating approach (radiocarbon, optically stimulated luminescence (OSL)) was applied to unravel climatic and human forcing factors. The dating results of soils and sediments are compatible, and no large hiatuses between the radiocarbon-dated top of the soils and OSL-dated overlying sands were observed. It is argued that the peaty top of wet-type podzols can be used for reliable radiocarbon dating. This study reveals more phases than previously known of landscape stability (Usselo Soil and two podzol soils) and instability (Younger Coversand I and II, two drift-sand units) that are related to Late Weichselian climate change and Holocene human occupation. Regional aeolian deposition in source-bordering (river) dunes (Younger Coversand II) took place in the second part of the Younger Dryas, after 12.3 ka cal. BP, implying a delayed response to Younger Dryas cooling, vegetation cover decline and river pattern change of the Scheldt. The onset of podzolisation and development of ericaceous vegetation occurred prior to the introduction of Neolithic farming, which is earlier than previously assumed. Early podzolisation was followed by a short phase of local drift-sand deposition, at c.5500 cal. BP, that possibly relates to agriculture. Strong human impact on the landscape by deforestation and agriculture resulted in a second phase of widespread drift-sand deposition covering the younger podzol soil after AD 1000

Synchronous collaborative information retrieval: techniques and evaluation

Synchronous Collaborative Information Retrieval refers to systems that support multiple users searching together at the same time in order to satisfy a shared information need. To date most SCIR systems have focussed on providing various awareness tools in order to enable collaborating users to coordinate the search task. However, requiring users to both search and coordinate the group activity may prove too demanding. On the other hand without effective coordination policies the group search may not be effective. In this paper we propose and evaluate novel system-mediated techniques for coordinating a group search. These techniques allow for an effective division of labour across the group whereby each group member can explore a subset of the search space.We also propose and evaluate techniques to support automated sharing of knowledge across searchers in SCIR, through novel collaborative and complementary relevance feedback techniques. In order to evaluate these techniques, we propose a framework for SCIR evaluation based on simulations. To populate these simulations we extract data from TREC interactive search logs. This work represent the first simulations of SCIR to date and the first such use of this TREC data

Theory of traces

AbstractThe theory of traces, originated by A. Mazurkiewicz in 1977, is an attempt to provide a mathematical description of the behavior of concurrent systems. Its aim is to reconcile the sequential nature of observations of the system behavior on the one hand and the nonsequential nature of causality between the actions of the system on the other hand.One can see the theory of traces to be rooted in formal string language theory with the notion of partial commutativity playing the central role. Alternatively one can see the theory of traces to be rooted in the theory of labeled acyclic directed graphs (or even in the theory of labeled partial orders).This paper attempts to present a major portion of the theory of traces in a unified way. However, it is not a survey in the sense that a number of new notions are introduced and a number of new results are proved. Although traditionally most of the development in the theory of traces follows the string-language-theoretic line, we try to demonstrate to the reader that the graph-theoretic point of view may be more appropriate.The paper essentially consists of two parts. The first one (Sections 1 through 4) is concerned with the basic theory of traces. The second one (Section 5) presents applications of the theory of traces to the theory of the behavior of concurrent systems, where the basic system model we have chosen is the condition/event system introduced by C.A. Petri