The Role of the Goal in Solving Hard Computational Problems: Do People Really Optimize?

The role that the mental, or internal, representation plays when people are solving hard computational problems has largely been overlooked to date, despite the reality that this internal representation drives problem solving. In this work we investigate how performance on versions of two hard computational problems differs based on what internal representations can be generated. Our findings suggest that problem solving performance depends not only on the objective difficulty of the problem, and of course the particular problem instance at hand, but also on how feasible it is to encode the goal of the given problem. A further implication of these findings is that previous human performance studies using NP-hard problems may have, surprisingly, underestimated human performance on instances of problems of this class. We suggest ways to meaningfully frame human performance results on instances of computationally hard problems in terms of these problems’ computational complexity, and present a novel framework for interpreting results on problems of this type. The framework takes into account the limitations of the human cognitive system, in particular as it applies to the generation of internal representations of problems of this class

Human Performance on Hard Non-Euclidean Graph Problems: Vertex Cover

Recent studies on a computationally hard visual optimization problem, the Traveling Salesperson Problem (TSP), indicate that humans are capable of finding close to optimal solutions in near-linear time. The current study is a preliminary step in investigating human performance on another hard problem, the Minimum Vertex Cover Problem, in which solvers attempt to find a smallest set of vertices that ensures that every edge in an undirected graph is incident with at least one of the selected vertices. We identify appropriate measures of performance, examine features of problem instances that impact performance, and describe strategies typically employed by participants to solve instances of the Vertex Cover problem

Characterization of commercial synthetic resins by pyrolysis-gas chromatography/mass spectrometry : application to modern art and conservation

To characterize a set of synthetic resins, a methodology by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been developed. The studied reference materials were commercial versions of a wide range of synthetic resins. For each polymer, the pyrolytic and chromatographic conditions were optimized to adequately resolve the fragment mixture in a short time. The proposed analytical method does not require previous treatment of the sample, and due to its high sensitivity, only a small sample quantity in the microgram range can be used. The pyrolysis temperature was found to have little effect on the obtained pyrograms. The summarized data set for the individual polymer materials, especially the characteristic fragments with a structure close to the monomeric unit, was useful to identify commercial synthetic resins. These materials were used in the art and conservation field, as binding media, paint additives, painting varnishes, coatings, or consolidants. Two case studies are introduced where direct Py-GC/MS and thermally assisted hydrolysis and methylation GC/MS were applied on art objects: first, a modern gluing material of a medieval reverse glass painting, and the second example, the binding medium of a painting by Georg Baselitz (“Senta”, 1992/1993) from the Sammlung Moderne Kunst at the Pinakothek der Moderne, MunichVersió editoria

The Teachers’ Role in Behavioral Problems of Pupils With EBD in Special Education:Teacher–Child Relationships Versus Structure

This longitudinal study examined bidirectional associations between special education pupils’ teacher–child relationship characteristics (quality, satisfaction, and conflict), classroom structure, and behavioral problems (externalizing and attention-hyperactivity). A secondary goal was to investigate the extent to which severity of behavioral problems moderated the prospective associations. Participants were 586 pupils (86% boys) in Grades 4 to 6 (Mage time 1 = 10.82 years, SD = 0.86) from 13 special education schools in the Netherlands and their teachers. Findings indicated that primarily teacher–child conflict was related to increased externalizing problems. More classroom structure was related to decreased attention-hyperactivity problems, but higher teacher–child relationship quality was linked to increases in attention-hyperactivity problems. Moreover, both types of problems were related to increases in conflict. Severity of behavior problems did not moderate these associations. Although findings were not consistent in both school years, they suggested that particularly reducing conflict and instilling more classroom structure were the most effective strategies in reducing behavioral problems. Furthermore, disrupting negative transactional associations between conflict and externalizing behavior is important to reduce externalizing behavior.</p

Investigation of amphibian mortality events in wildlife reveals an on-going ranavirus epidemic in the North of the Netherlands

In the four years following the first detection of ranavirus (genus Ranavirus, family Iridoviridae) infection in Dutch wildlife in 2010, amphibian mortality events were investigated nationwide to detect, characterize and map ranaviruses in amphibians over time, and to establish the affected host species and the clinico-pathological presentation of the disease in these hosts. The ultimate goal was to obtain more insight into ranavirus disease emergence and ecological risk. In total 155 dead amphibians from 52 sites were submitted between 2011 and 2014, and examined using histopathology, immunohistochemistry, virus isolation and molecular genetic characterization. Ranavirus-associated amphibian mortality events occurred at 18 sites (35%), initially only in proximity of the 2010 index site. Specimens belonging to approximately half of the native amphibian species were infected, including the threatened Pelobates fuscus (spadefoot toad). Clustered massive outbreaks involving dead adult specimens and ranavirus genomic identity indicated that one common midwife toad virus (CMTV)-like ranavirus strain is emerging in provinces in the north of the Netherlands. Modelling based on the spatiotemporal pattern of spread showed a high probability that this emerging virus will continue to be detected at new sites (the discrete reproductive power of this outbreak is 0.35). Phylogenetically distinct CMTV-like ranaviruses were found in the south of the Netherlands more recently. In addition to showing that CMTV-like ranaviruses threaten wild amphibian populations not only in Spain but also in the Netherlands, the current spread and risk of establishment reiterate that understanding the underlying causes of CMTV-like ranavirus emergence requires international attention

The Teachers’ Role in Behavioral Problems of Pupils With EBD in Special Education:Teacher–Child Relationships Versus Structure

This longitudinal study examined bidirectional associations between special education pupils’ teacher–child relationship characteristics (quality, satisfaction, and conflict), classroom structure, and behavioral problems (externalizing and attention-hyperactivity). A secondary goal was to investigate the extent to which severity of behavioral problems moderated the prospective associations. Participants were 586 pupils (86% boys) in Grades 4 to 6 (Mage time 1 = 10.82 years, SD = 0.86) from 13 special education schools in the Netherlands and their teachers. Findings indicated that primarily teacher–child conflict was related to increased externalizing problems. More classroom structure was related to decreased attention-hyperactivity problems, but higher teacher–child relationship quality was linked to increases in attention-hyperactivity problems. Moreover, both types of problems were related to increases in conflict. Severity of behavior problems did not moderate these associations. Although findings were not consistent in both school years, they suggested that particularly reducing conflict and instilling more classroom structure were the most effective strategies in reducing behavioral problems. Furthermore, disrupting negative transactional associations between conflict and externalizing behavior is important to reduce externalizing behavior.</p

Subclinical salmonella infection in Danish finishing pig herds - the effect of salmonella contaminated feed

As part of the integrated salmonella programme in the pig production, feed produced in Danish feed mills is examined for salmonella after heat treatment. The results of the bacteriological examination have shown that the prevalence of salmonella in the finished feed products has been \u3c 0.1% (Annual Report on Zoonoses in Denmark, 1996). Since feed may be contaminated during transport, storage or in the feeding systems at the farms, and only the concentrate part of homemixed feed is being heat treated and examined, the actual occurrence of salmonella in the feed when fed to the pigs is unknown. The aim of this study was to determine the prevalence of salmonella in feed at the outlets in the pens, to establish whether certain feeding systems or types of feed were more likely to be contaminated and to assess the possible association between salmonella detected in feed and salmonella infection of pig herds

Signal Gain Due To A Polarization Coupling In An Algaas Channel Wave-Guide

We experimentally demonstrate signal gain for picosecond signals due to an orthogonally polarized pump beam in an AlGaAs channel waveguide at a wavelength of 1.55 mu m, below half the band gap. We show as much as 40% signal gain, or depletion, depending on the polarization states of the pump and the probe. The results are in good agreement with theory