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We consider several language-theoretic aspects of various notions of unique decipherability (or unique factorization) in formal languages. Given a language L at some position within the Chomsky hierarchy, we investigate the language of words UD (L) in L ⁎ that have unique factorization over L. We also consider similar notions for weaker forms of unique decipherability, such as numerically decipherable words ND (L) , multiset decipherable words MSD (L) and set decipherable words SD (L). Although these notions of unique factorization have been considered before, it appears that the languages of words having these properties have not been positioned in the Chomsky hierarchy up until now. We show that UD (L) , ND (L) , MSD (L) and SD (L) need not be context-free if L is context-free. In fact ND (L) and MSD (L) need not be context-free even if L is finite, although UD (L) and SD (L) are regular in this case. We show that if L is context-sensitive, then so are UD (L) , ND (L) , MSD (L) and SD (L). We also prove that the membership problem (resp., emptiness problem) for these classes is PSPACE-complete (resp., undecidable). We finally determine upper and lower bounds on the length of the shortest word of L ⁎ not having the various forms of unique decipherability into elements of L. [ABSTRACT FROM AUTHOR]

This paper demonstrates the application of marine radar and a newly developed waterline mapping technique to the continued surveillance and monitoring of inter- and intra-annual intertidal morphological change, thus capturing new detail on coastal system behaviours. Marine radar data from 2006 to 2009 are used to create a sequence of waterline elevation surveys that show clear morphological evolution of two different sites in the Dee estuary, UK. An estimate of volumetric change was made at two locations: West Hoyle sandbank and the NW Wirral beach. Both sites exhibited a similar cyclic pattern of volumetric change, with lowest volumes in autumn and winter, respectively. The average beach elevations above Admiralty Chart Datum clearly reflect the observed change in sediment volume, with reduced elevations in winter and increased elevations in summer, suggesting a trend of high-energy storm waves in autumn and winter that remove sediment and simultaneously moderate the vertical dimension of bedforms in the intertidal area. Data at this temporal and spatial scale are not easily obtainable by other current remote sensing techniques. The use of marine radar as a tool for quantifying coastal change over seasonal and event timescales in complex hydrodynamic settings is illustrated. Specifically, its unique application to monitoring areas with dynamic morphology or that is vulnerable to erosion and/or degradation by storm events is exemplified. [ABSTRACT FROM AUTHOR]

We study variants of a recently introduced hybrid system model, called a Hierarchical Piecewise Constant Derivative (HPCD). These variants (loosely called Restricted HPCDs) form a class of natural models with similarities to many other well known hybrid system models in the literature such as Stopwatch Automata, Rectangular Automata and PCDs. We study the complexity of reachability and mortality problems for variants of RHPCDs and show a variety of results, depending upon the allowed powers. These models form a useful tool for the study of the complexity of such problems for hybrid systems, due to their connections with existing models. We show that the reachability problem and the mortality problem are co-NP-hard for bounded 3-dimensional RHPCDs (3-RHPCDs). Reachability is shown to be in PSPACE, even for n -dimensional RHPCDs. We show that for an unbounded 3-RHPCD, the reachability and mortality problems become undecidable. For a nondeterministic variant of 2-RHPCDs, the reachability problem is shown to be PSPACE-complete. [ABSTRACT FROM AUTHOR]

Mapping the morphology of intertidal areas is a logistically challenging, time consuming and expensive task due to their large expanse and difficulties associated with access. A technique is presented here that uses standard marine navigational radar operating at X-band frequency. The method uses a series of time-exposure radar images over the course of a two-week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images, thereby building up a morphological map of the target intertidal area. This “Temporal Waterline” method is applied to a dataset acquired from Hilbre Island at the mouth of the Dee Estuary, UK, spanning March 2006 to January 2007. The radar gathered data with a radial range of 4 km and the resulting elevation maps describe the intertidal regions of that area. The results are compared with airborne LiDAR data surveyed over the same area and within the radar survey time period. The residual differences show good agreement across large areas of beach and sandbanks, with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water. This paper presents the theoretical framework of the method and demonstrates its stability and accuracy. The Temporal Waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines. [ABSTRACT FROM AUTHOR]

Abstract: We study decidability and complexity questions related to a continuous analogue of the Skolem-Pisot problem concerning the zeros and nonnegativity of a linear recurrent sequence. In particular, we show that the continuous version of the nonnegativity problem is NP-hard in general and we show that the presence of a zero is decidable for several subcases, including instances of depth two or less, although the decidability in general is left open. The problems may also be stated as reachability problems related to real zeros of exponential polynomials or solutions to initial value problems of linear differential equations, which are interesting problems in their own right. [ABSTRACT FROM AUTHOR]

Abstract: This project examined relationships among two dimensions of the “Big Five” personality factor theory (Costa & McCrae, 1992) and the conflict resolution styles of competing, collaborating, accommodating, and avoiding (Thomas & Kilmann, 1974). Some 288 students at Colorado State University participated. The Big Five personality measures of agreeableness (A) and extraversion (E) were significant predictors of all four conflict resolution style scores. These findings show that contemporary personality measures are significant predictors of conflict resolution styles. The findings suggest that personality measures may be helpful predictors of conflict resolution style preference in mediation and negotiation situations. [Copyright &y& Elsevier]

Abstract: In this paper we consider several reachability problems such as vector reachability, membership in matrix semigroups and reachability problems in piecewise linear maps. Since all of these questions are undecidable in general, we work on lowering the bounds for undecidability. In particular, we show an elementary proof of undecidability of the reachability problem for a set of 5 two-dimensional affine transformations. Then, using a modified version of a standard technique, we also prove that the vector reachability problem is undecidable for two (rational) matrices in dimension 11. The above result can be used to show that the system of piecewise linear functions of dimension 12 with only two intervals has an undecidable set-to-point reachability problem. We also show that the “zero in the upper right corner” problem is undecidable for two integral matrices of dimension 18 lowering the bound from 23. [Copyright &y& Elsevier]

Abstract: In this paper, we consider decidability questions that are related to the membership problem in matrix semigroups. In particular, we consider the membership of a given invertible diagonal matrix in a matrix semigroup and then a scalar matrix, which has a separate geometric interpretation. Both problems have been open for any dimensions and are shown to be undecidable in dimension 4 with integral matrices by a reduction of the Post Correspondence Problem (PCP). Although the idea of PCP reduction is standard for such problems, we suggest a new coding technique to cover the case of diagonal matrices. [Copyright &y& Elsevier]

The main objectives of the present study are to determine the time-dependent character of bedform dimensions and to assess the feasibility and reliability of dune-tracking techniques to estimate bedload transport in estuarine–marine conditions. A third additional aim is to evaluate the application of the Ribberink bedload transport formula for field conditions with a rippled bed. Field experiments were carried out on Spratt Sand, an intertidal shoal in the mouth of the Teign estuary, Devon, UK. In the framework of the COAST3D project, data of hydrodynamics, bedform development and sediment transport were collected over a period of a month. The presence of sediment on Spratt Sand turns out to be an important factor in the development of bedforms. As soon as sufficient sediment is available—a layer with a thickness of at least 0.20–0.30 m—ripples start to grow and develop into dunes. In general, an increase in bedform height is anticipated to result in an increase in bedload transport. However, the present study demonstrates that the development of dunes instead of ripples may lead to a reduction in migration rates, which, at the end, in reality causes a reduction in bedload transport. The presence of waves appears to be a critical factor to the applicability of the dune tracking technique. Dunes only start to migrate when wave orbital velocities exceed 0.3 m/s. Bedload transport by migrating dunes is generally in the order of 0–1.5 m2/s when orbital velocities remain below 0.7 m/s. Bedload transport increases by a factor 2 when wave orbital velocities reach values of 0.8–0.9 m/s. The increase in bedload transport is partly caused by the additional bed shear in the presence of waves. A second wave-generated mechanism is that stronger wave action reduces the effect of hiding which, under low wave–strong current conditions, suppresses sediment pick-up in the sand–gravel mixture.Application of the Ribberink bedload transport formula for conditions with a rippled bed and in case of unidirectional flows with superimposed oscillatory flows leads to a maximum difference between “measured” (dune-tracking) and computed bedload transport up to a factor 2. For low-energetic conditions, the difference is smaller and generally varies between 10% and 20%; for high-energetic conditions this figure amounts maximum 100%. [Copyright &y& Elsevier]

Highlights a survey on the attitudes of United States college students regarding two contrasting paradigms of the US Space Program. Scientific use of space compared to its commercial exploitation; Use of the pair-comparison method to validate survey results.

Abstract: Research in the area of driver anger and aggression has shown that several personality factors contribute to the growing problem. Pilot research indicated that drivers attribute human qualities such as a gender and name to their vehicles which suggested that this tendency to anthropomorphize the vehicle might predict aggressive driving tendencies. Two hundred four undergraduates completed personality inventories for both themselves and their vehicle along with several measures of driving anger and aggressive tendencies. Results suggest that driver and vehicle personalities were related but distinct, indicating that drivers were not just projecting their own personality onto the vehicle. Driver and vehicle personality scores were correlated with several indexes of aggressive driving tendencies. In some cases, vehicle personality predicted aggressive driving better than driver personality. However, initial decision of drivers to anthropomorphize did not relate to differences in aggressive driving tendencies. [Copyright &y& Elsevier]

We review past trading experiments and present 11 new experiments designed to show how the trading rate responds to alterations of the experimental procedure. In agreement with earlier studies, results show that if the trade decision is converted to one resembling a choice between goods the exchange asymmetry disappears, but otherwise the asymmetry is remarkably robust. Results also indicate that when trading is public herding can occur, which may have caused some of the more extreme examples of the exchange asymmetry, and that some of the lack of trade may result from preference indifference. Nevertheless, some form of status quo bias, which may consist of a combination of loss aversion, gain attraction, regret avoidance, and dislike of trading, and which may be enhanced by indifference between the goods offered, probably remains as an important influence on the trading rate. [ABSTRACT FROM AUTHOR]

Improved understanding and modelling of interactions between biological and physical processes has required progress in the understanding of sediment processes and their relationship to bedforms, hydrodynamics and benthic biology. Recently, simultaneous, co-located in situ measurements of suspended sediments, near-bed velocities and bed morphology have been made possible using new acoustic instruments, including a triple frequency acoustic backscatter system, (ABS); a uniaxial, and triple axis, coherent Doppler velocity profiler, (CDVP); a sand ripple imager (SRI); and a sand ripple profiler (SRP). Together these instruments measure the relevant hydrodynamic and sediment parameters necessary to investigate sediment processes in the bottom metre above the bed, with centimetric resolution. The range of data from such instruments is required to fully understand the related processes occurring near the seabed. The outcome of such measurements should improve our understanding of benthic processes in general. [Copyright &y& Elsevier]

Public judgments of the seriousness of environmental losses were found to be internally consistent for most respondents, and largely unaffected by attempts to manipulate responses by altering the mix of losses being judged. Both findings enhance confidence in the feasibility of developing reliable rankings of the seriousness of environmental losses to aid resource allocation and damage assessment. In addition, seriousness of loss was found to be sensitive to the cause of the loss, with human-caused environmental losses considered more serious than identical losses caused by natural events. This difference has important implications for assessment of environmental losses. [Copyright &y& Elsevier]