The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

Accounting for International War: The State of the Discipline

In studies of war it is important to observe that the processes leading to so frequent an event as conflict are not necessarily those that lead to so infrequent an event as war. Also, many models fail to recognize that a phenomenon irregularly distributed in time and space, such as war, cannot be explained on the basis of relatively invariant phenomena. Much research on periodicity in the occurrence of war has yielded little result, suggesting that the direction should now be to focus on such variables as diffusion and contagion. Structural variables, such as bipolarity, show contradictory results with some clear inter-century differences. Bipolarity, some results suggest, might have different effects on different social entities. A considerable number of studies analysing dyadic variables show a clear connection between equal capabilities among contending nations and escalation of conflict into war. Finally, research into national attributes often points to strength and geographical location as important variables. In general, the article concludes, there is room for modest optimism, as research into the question of war is no longer moving in non-cumulative circles. Systematic research is producing results and there is even a discernible tendency of convergence, in spite of a great diversity in theoretical orientations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69148/2/10.1177_002234338101800101.pd

Motor dysphasia A comparative study

SIGLEAvailable from British Library Document Supply Centre-DSC:D191542 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Heavy schistosomiasis associated with poor short-term memory and slower reaction times in Tanzanian schoolchildren.

Cross-sectional studies of the relationship between helminth infection and cognitive function can be informative in ways that treatment studies cannot. However, interpretation of results of many previous studies has been complicated by the failure to control for many potentially confounding variables. We gave Tanzanian schoolchildren aged 9-14 a battery of 11 cognitive and three educational tests and assessed their level of helminth infection. We also took measurements of an extensive range of potentially confounding or mediating factors such as socioeconomic and educational factors, anthropometric and other biomedical measures. A total of 272 children were moderately or heavily infected with Schistosoma haematobium, hookworm or both helminth species and 117 were uninfected with either species. Multiple regression analyses, controlling for all confounding and mediating variables, revealed that children with a heavy S. haematobium infection had significantly lower scores than uninfected children on two tests of verbal short-term memory and two reaction time tasks. In one of these tests the effect was greatest for children with poor nutritional status. There was no association between infection and educational achievement, nor between moderate infection with either species of helminth and performance on the cognitive tests. We conclude that children with heavy worm burdens and poor nutritional status are most likely to suffer cognitive impairment, and the domains of verbal short- term memory and speed of information processing are those most likely to be affecte

Interaction between phonological and grammatical processing in single word production in Kiswahili

Grammatical priming of picture naming was investigated in Kiswahili, which has a complex grammatical noun class system (a system like grammatical gender), with up to 15 noun classes that have obligatory agreements on adjectives, verbs, pronouns and other parts of speech. Participants heard a grammatically agreeing (concordant), nonagreeing (discordant) or neutral prime before seeing a picture of a common object and being asked to name the object. Priming was found, with naming following concordant primes being faster than naming following the neutral prime ('say'). However, more interestingly, effects were found such that where two noun classes share a prefix, the grammatical prime from each of these two noun classes also primed words that have the same prefix but are not in the same noun class, and hence for which the prime was not grammatical. It is concluded that the prime appears to be facilitating the phonological form of the prefix rather than the syntacto-semantic group of words that are known as a noun class, and that the phonological form associated with a grammatical entity may be more significant in its processing than has previously been supposed

Maternal depression is the predominant persistent risk for child cognitive and social-emotional problems from early childhood to pre-adolescence:A longitudinal cohort study

Rationale Brain development occurs rapidly during early childhood and continues throughout middle childhood. Early and later windows of opportunity exist to alter developmental trajectories. Few studies in low- and middle-income countries have examined the importance of the timing of exposure to risks for poor pre-adolescent cognitive and social-emotional outcomes. Methods We assessed 359 children who participated in two follow-up studies of the Supplementation with Multiple Micronutrients Intervention Trial conducted in Indonesia in 2001–2004: at 3.5 years in 2006 and 9–12 years in 2012–2014. Using structural equation models, we examined indicators of early childhood (3.5 y) and pre-adolescent (9–12 y) exposure to risks (child height-for-age z-score [HAZ], hemoglobin [Hb], maternal depressive symptoms [MDS], home environment [HOME]), with two developmental outcomes: cognitive ability and social-emotional problems. We characterized patterns of change by calculating residuals of indicators measured earlier (3.5 y) predicting the same indicators measured later (9–12 y), for example, the residual of 3.5 y MDS predicting 9–12 y MDS (rMDS). Results Three early risk indicators (HOME, Hb, and MDS) were indirectly associated with pre-adolescent cognitive scores through early cognitive scores (HOME: 0.15, [95% CI 0.09, 0.21]; Hb: 0.08 [0.04, 0.12], MDS: −0.07 [-0.12, −0.02]). Pre-adolescent cognitive scores were also associated with change in MDS (rMDS: −0.13 [-0.23, −0.02]) and Hb (rHb: 0.10 [0.00, 0.20]) during middle childhood. For pre-adolescent social-emotional problems, both early childhood MDS (0.31 [0.19, 0.44]) and change in MDS during middle childhood (rMDS: 0.48 [0.37, 0.60]) showed strong direct associations with this outcome. Conclusions Our findings confirm those of previous studies that prevention of risk exposures during early childhood is likely to support long-term child development. It also adds evidence to a previously scarce literature for the middle childhood period. Prevention of maternal depressive symptoms and child anemia during middle childhood should be assessed for effectiveness to support child development

Articulating novel words: children's oromotor skills predict non-word repetition abilities

Purpose: Pronouncing a novel word for the first time requires the transformation of a newly encoded speech signal into a series of coordinated, exquisitely timed oromotor movements. Individual differences in children's ability to repeat novel nonwords are associated with vocabulary development and later literacy. Nonword repetition (NWR) is often used to test clinical populations. While phonological/auditory memory contributions to learning and pronouncing nonwords have been extensively studied, much less is known about the contribution of children's oromotor skills to this process. Method: Two independent cohorts of children (7–13 years, N = 40, and 6.9–7.7 years, N = 37) were tested on a battery of linguistic and non-linguistic tests, including NWR and oromotor tasks. Results: In both cohorts, individual differences in oromotor control were a significant contributor to NWR abilities; moreover, in an omnibus analysis including experimental and standardized tasks, oromotor control predicted the most unique variance in NWR. Conclusions: Results indicate that nonlinguistic oromotor skills contribute to children's NWR ability, and suggest that important aspects of language learning and consequent language deficits may be rooted in the ability to perform complex sensorimotor transformations

Constructing tests of cognitive abilities for schooled and unschooled children.

It is frequently necessary to assess children with little or no schooling to determine their level of cognitive functioning, especially in developing countries. It is not possible, however, to assume that assessments will hold equal validity for children with and without the experience of schooling. The authors, therefore, set out to create a battery of tests suitable for both schooled and unschooled children. They assessed 973 schooled and 645 unschooled children in rural coastal Kenya using culturally adapted cognitive tests. Significant effects of age and schooling were found on all tests. On some tests (verbal knowledge, speeded figure matching, and pattern copying), unschooled children did not improve as much with age as schooled children. The effects of length of exposure to schooling and of age were greater than that of initial enrollment in school. The authors conclude that it is possible to assess unschooled children, but test batteries must be carefully constructed and standardized