Performance of Young Children on ‘‘Traveling Salesperson’’ Navigation Tasks Presented on a Touch Screen

Background

The traveling salesperson problem (TSP) refers to a task in which one finds the shortest path when traveling through multiple spatially distributed points. Little is known about the developmental course of the strategies used to solve TSPs. The present study examined young children''s performance and route selection strategies in one-way TSPs using a city-block metric. A touch screen-based navigation task was applied.

Methodology/Principal Findings

Children (39–70 months) and adults (21–35 years) made serial responses on a touch screen to move a picture of a dog (the target) to two or three identical pictures of a bone (the goals). For all the versions of the tasks, significant improvement in measures of performance was observed from younger to older participants. In TSPs in which a specific route selection strategy such as the nearest-neighbor strategy minimized the total traveling distance, older participants used that strategy more frequently than younger ones. By contrast, in TSPs in which multiple strategies equally led to the minimal traveling distance, children tended to use strategies different from those used by adults, such as traveling straight to the farthest goal first.

Conclusions/Significance

The results primarily suggest development of efficient route selection strategies that can optimize total numbers of movements and/or solution time. Unlike adults, children sometimes prioritized other strategies such as traveling straight ahead until being forced to change directions. This may reflect the fact that children were either less attentive to the task or less efficient at perceiving the overall shape of the problem and/or the relative distance from the starting location to each goal.     

The flagella of ‘Candidatus Liberibacter asiaticus’ and its movement in planta

Citrus huanglongbing (HLB) is the most devastating citrus disease worldwide. ‘Candidatus Liberibacter asiaticus’ (Las) is the most prevalent HLB causal agent that is yet to be cultured. Here, we analysed the flagellar genes of Las and Rhizobiaceae and observed two characteristics unique to the flagellar proteins of Las: (i) a shorter primary structure of the rod capping protein FlgJ than other Rhizobiaceae bacteria and (ii) Las contains only one flagellin-encoding gene flaA (CLIBASIA_02090), whereas other Rhizobiaceae species carry at least three flagellin-encoding genes. Only flgJ_Atu but not flgJ_Las restored the swimming motility of Agrobacterium tumefaciens flgJ mutant. Pull-down assays demonstrated that FlgJ_Las interacts with FlgB but not with FliE. Ectopic expression of flaA_Las in A. tumefaciens mutants restored the swimming motility of ∆flaA mutant and ∆flaAD mutant, but not that of the null mutant ∆flaABCD. No flagellum was observed for Las in citrus and dodder. The expression of flagellar genes was higher in psyllids than in planta. In addition, western blotting using flagellin-specific antibody indicates that Las expresses flagellin protein in psyllids, but not in planta. The flagellar features of Las in planta suggest that Las movement in the phloem is not mediated by flagella. We also characterized the movement of Las after psyllid transmission into young flush. Our data support a model that Las remains inside young flush after psyllid transmission and before the flush matures. The delayed movement of Las out of young flush after psyllid transmission provides opportunities for targeted treatment of young flush for HLB control.     

The ‘requirement of total evidence’ and its role in phylogenetic systematics

The question of whether or not to partition data for the purposes of inferring phylogenetic hypotheses remains controversial. Opinions have been especially divided since Kluge's (1989, Systematic Zoology 38, 7–25) claim that data partitioning violates the requirement of total evidence (RTE). Unfortunately, advocacy for or against the RTE has not been based on accurate portrayals of the requirement. The RTE is a basic maxim for non-deductive inference, stipulating that evidence must be considered if it has relevance to an inference. Evidence is relevant if it has a positive or negative effect on a given conclusion. In the case of ℈partitioned’ phylogenetic inferences, the RTE is violated, and the basis for rational belief in any conclusion is compromised, unless it is shown that the partitions are evidentially irrelevant to one another. The goal of phylogenetic systematics is to hypothesize past causal conditions to account for observed shared similarities among two or more species. Such inferences are non-deductive, necessitating consideration of the RTE. Some phylogeneticists claim the parsimony criterion as justification for the RTE. There is no relation between the two – parsimony is a relation between a hypothesis and causal question(s). Parsimony does not dictate the content of premises prior to an inference. ℈Taxonomic congruence,’ ℈supertrees,’ and ℈conditional combination’ methods violate the RTE. Taxonomic congruence and supertree methods also fail to achieve the intended goal of phylogenetic inference, such that ℈consensus trees’ and ℈supertrees’ lack an empirical basis. ℈Conditional combination’ is problematic because hypotheses derived from partitioned data cannot be compared – a causal hypothesis inferred to account for a set of effects only has relevance to those effects, not any comparative relevance to other causal hypotheses. A similar problem arises in the comparisons of hypotheses derived from different causal theories.     

Effect of Glucose on the Lactoferrin’s Conformation and its Effect on MC 3T3-E1 Cell Proliferation

The objective of this research was to investigate the influence of glucose on bovine lactoferrin’s (LF) conformation, thermodynamic stability and osteoblastic cell proliferation. The conformation and thermodynamic stability of LF was detected by spectroscopic and differential scanning calorimetry (DSC). The osteoblastic cell proliferation of LF at physiological concentrations (100 μg/ml) was measured by BrdU incorporation. The binding constant between glucose and LF is KSV = 5 × 10⁻³, and Tyr residues of LF were located in a more hydrophobic environment, while Trp residues were located in a more hydrophilic environment. LF with glucose had increased α-helix and β-sheet contents by 6 and 14 %, respectively. It showed a two-step denaturation of LF. There was a gradual changs in the denaturation temperature and the calorimetric enthalpies (ΔHcal) with a growing concentration of glucose. It has also revealed that glucose dose dependently reduced the ability of LF to increase MC 3T3-E1 cell proliferation. Increasing the binding with glucose, LF might cause to change its native state, which reduced the stimulation activity of osteoblasts cell proliferation.     

Aboriginal ‘Difference’ and ‘Autonomy’ Then and Now: Four Decades of Change in a Western Desert Society

In just a few decades, Aboriginal people living near Australia's Western Desert fringe have experienced an extraordinarily intense trajectory of change: from a highly autonomous nomadic existence, through ‘first contacts’, the pastoral and mission frontiers, the devastating impacts of alcohol and of Western lifestyle diseases, the outstation movement, resource exploration and mining, a long but largely successful struggle for native title, and much else. In this paper, notions of ‘difference’ and ‘autonomy’ are used to explore these transformations. The situation among the Mardu is here linked to the gulf between government policies and lived Aboriginal experience. If the self‐management thrust of 1970s policies achieved partial restoration of Aboriginal autonomy, recent Federal Government policies are intent on intervention to reduce difference and claw back some of that autonomy. Their determination to force Aboriginal people out of their ‘dysfunctional’ ‘cultural museums’ (homeland settlements) and into greater economic engagement ignores the crucial underpinnings of security and identity among remote Aborigines. The retention of difference, albeit at considerable social cost and entrenched disadvantage, is still strongly preferred by Mardu to the kinds of engagement with the dominant society that not only assault their sense of self but also threaten to overwhelm whatever autonomy remains to them.     

The midpoint of sleep on working days: A measure for chronodisruption and its association to individuals’ well-being

There is consistent evidence suggesting a relationship between individuals’ sleep–wake rhythms and well-being. The indiscriminate demands from daily working routines, which do not respect this individual physiological rhythm, might be mediating this phenomenon. The aim of the present study was to evaluate the relationship between the characteristics of sleep routines during working days and psychological well-being. This was a cross-sectional study on 825 individuals from rural communities from southern Brazil. The study protocol included a questionnaire on demographic characteristics, working routines, health complaints, and habits; the Munich Chronotype Questionnaire for sleep–wake rhythm and; the WHO-Five well-being index. Since sex has been shown to affect sleep circadian rhythm and well-being, analysis was performed on men and women separately. In the proposed hierarchical regression models, different factors contributed to well-being according to sex. Among men, sleep–wake and work-related variables did not predict well-being scores. Among women, later midpoints of sleep on working days (B?=??1.243, SE B?=?0.315, β?=??0.220), working more days per week (B?=??1.507, SE B?=?0.494, β?=?0.150), having longer working journeys (B?=??0.293, SE B?=?0.105, β?=??0.166), earlier working journey midpoints (B?=?0.465, SE B?=?0.222, β?=?0.115), and being exposed to less sunlight (B?=?0.140, SE B?=?0.064, β?=?0.103) predicted worse well-being. For the subgroup of women with days free from work, we have found a correlation between later midpoints of sleep during the week with worse well-being (Pearson’s r?=??0.159, p?=?0.045) while the same relationship was not significantly observed with the midpoint of sleep on non-working days (Pearson’s r?=??0.153, p?=?0.054). Considering WHO-Five as categorical, based on proposed clinical cut-offs, among women working 7-d/week, those with worst well-being (WHO-Five?<?13) had the latest midpoint of sleep (F?=?4.514, p?=?0.012). Thus, the midpoint of sleep on working days represents the interaction between individuals’ sleep–wake behavior and working routines. It plays an important role as a stress factor and may be a useful alternative variable related to chronodisruption.     

Genetic and biochemical studies on perchloroethylene ‘in vitro’ and ‘in vivo’

Perchloroethylene (PCE) was tested in a diploid strain (D7) of the yeast Saccharomyces cerevisiae in suspension tests with and without a mammalian microsomal activation system (S9) and ‘in vivo’ by the intrasanguineous host-mediated assay. In addition, enzyme alteration studies were performed in mice non-pretreated or pretreated with phenobarbital + β-naphthoflavone. PCE did not induce any genetic effect either ‘in vitro’ or ‘in vivo’. In the suspension test, PCE was more toxic without metabolic activation and less toxic with mammalian microsomal activation. The enzymatic determinations showed an increase of the aminopyrine demethylase activity and of the level of cytochrome P-450.     

The economic approach to ‘theory of mind’

Theory of mind (ToM) is a great evolutionary achievement. It is a special intelligence that can assess not only one''s own desires and beliefs, but also those of others. Whether it is uniquely human or not is controversial, but it is clear that humans are, at least, significantly better at ToM than any other animal. Economists and game theorists have developed sophisticated and powerful models of ToM and we provide a detailed summary of this here. This economic ToM entails a hierarchy of beliefs. I know my preferences, and I have beliefs (a probabilistic distribution) about your preferences, beliefs about your beliefs about my preferences, and so on. We then contrast this economic ToM with the theoretical approaches of neuroscience and with empirical data in general. Although this economic view provides a benchmark and makes useful suggestions about empirical tendencies, it does not always generate a close fit with the data. This provides an opportunity for a synergistic interdisciplinary production of a falsifiable theory of bounded rationality. In particular, a ToM that is founded on evolutionary biology might well be sufficiently structured to have predictive power, while remaining quite general. We sketch two papers that represent preliminary steps in this direction.     

The ‘greenhouse effect’ and UK agriculture

Book Review

The greenhouse effect and UK agricultureR.M. Bennett (Ed.), Reading: Centre for Agricultural Strategy, 1989. 144 pages, paperback. £15.00. ISBN 0-7049-0988-X     

‘Hemiepiphyte’: a confusing term and its history

Background and Scope

Over more than 120 years of scientific study since Schimper''s seminal work, the recognized categories of structurally dependent plants have changed several times. Currently, ignoring parasitic mistletoes, it is usual to distinguish four functional groups: (1) true epiphytes; (2) primary hemiepiphytes; (3) secondary hemiepiphytes; and (4) climbing plants, i.e. lianas and vines. In this Viewpoint, it is argued that the term secondary hemiepiphytes (SHs) is misleading, that its definition is hard to impossible to apply in the field and, possibly causally related to this conceptual problem, that the use of this category in field studies is inconsistent, which now hampers interpretation and generalization.

Conclusions

Categories will frequently fail to capture gradual biological variation, but terms and concepts should be as unambiguous as possible to facilitate productive communication. A detailed analysis of the conceptual problems associated with the term SH and its application in scientific studies clearly shows that this goal is not fulfilled in this case. Consequently, the use of SH should be abandoned. An alternative scheme to categorize structurally dependent flora is suggested.     

A comment on ‘colonialism and ethnicity’

Self‐reported incidence of racial discrimination was investigated among four Asian‐American groups to explore their magnitude and the ways of coping with the discrimination episodes. The samples showed that among the two modes of coping ‐ problem‐focused or emotion‐focused coping ‐ a majority of Asian Americans has utilized the latter. Reasons of adopting these coping strategies were further explored for their determinants. Intergroup differences in ethnicity, education, gender and cultural values were found to exert influences on the ways of coping with racial discrimination among Asian Americans.     

Forty Years of ‘The Strategy’: Levins on Model Building and Idealization

This paper is an interpretation and defense of Richard Levins’ “The Strategy of Model Building in Population Biology,” which has been extremely influential among biologists since its publication 40 years ago. In this article, Levins confronted some of the deepest philosophical issues surrounding modeling and theory construction. By way of interpretation, I discuss each of Levins’ major philosophical themes: the problem of complexity, the brute-force approach, the existence and consequence of tradeoffs, and robustness analysis. I argue that Levins’ article is concerned, at its core, with justifying the use of multiple, idealized models in population biology.

Effect of Dietary Selenium and Vitamin E on Ganders’ Response to Semen Collection and Ejaculate Characteristics

Compared to other domestic bird species, geese exhibit the lowest reproductive efficiency (poor semen quality, low egg production, and poor fertility and hatchability rates). From an economic perspective, it is a necessity of improve these reproductive traits. Studies have demonstrated that the essential trace element—selenium—plays key roles in testicular development and the maintenance of spermatogenesis. The aim of the present study was to determine the effect of feed supplementation with organic selenium and vitamin E on ganders’ response to manual semen collection and semen quality. Sixteen 3-year-old White Koluda ganders were randomly divided into two groups. The control group was provided commercial feed while the experimental group was provided with the same commercial feed supplemented with selenium (0.3 mg/kg) and vitamin E (100 mg/kg). The response of individual ganders from both groups to manual semen collection and the quality of the semen collected were evaluated. The supplements increased (P?≤?0.05) the frequency and decreased the time interval of a complete ejaculatory response of the ganders to manual semen collections (82.7 % supplement vs. 73.5 % control). Males from the supplemented group had significantly higher (P?≤?0.01; P?≤?0.05) ejaculate volumes, sperm concentrations, and percentages of viable sperm and lower percentages of immature sperm (spermatids). Lipids peroxidation, expressed in terms of the malondialdehyde concentration, was lower (P?≤?0.01) in semen of the supplemented group (0.172 nmol/50?×?10⁶) as compared to the controls (0.320 nmol/50?×?10⁶). Moreover, the duration of the reproductive period of the ganders in the experimental group was 1 week longer. The results show that supplemental dietary selenium and vitamin E improved both the ganders’ response to manual semen collection and semen quality. We conclude that such feed supplementation could lead to greater economic benefits through increased reproductive efficiency within the goose production industry.     

Three reasons to re-evaluate fungal diversity ‘on Earth and in the ocean’

Attempts to assess fungal global species richness are confounded by several problems: uncertainty about the number of described species, incomplete fungal inventories even at a high taxonomic level, high diversity of unknown, often small and elusive taxa, high levels of morphological conservation, and incomplete knowledge of their ecological and biogeographical distributions. The two main bases for estimating total fungal diversity are (1) the number of described species and their taxonomic structure, and (2) extrapolating species-area relationships. We argue that knowledge of fungal taxonomy and environmental sampling of fungi are both too incomplete for either approach to be reliable. However, it is likely that the true number of fungal species on the planet is a seven-digit number, and may even be an order of magnitude higher.