Simple Escape Research Articles

Self-organization of collective escape in pigeon flocks.

Bird flocks under predation demonstrate complex patterns of collective escape. These patterns may emerge by self-organization from local interactions among group-members. Computational models have been shown to be valuable for identifying what behavioral rules may govern such interactions among individuals during collective motion. However, our knowledge of such rules for collective escape is limited by the lack of quantitative data on bird flocks under predation in the field. In the present study, we analyze the first GPS trajectories of pigeons in airborne flocks attacked by a robotic falcon in order to build a species-specific model of collective escape. We use our model to examine a recently identified distance-dependent pattern of collective behavior: the closer the prey is to the predator, the higher the frequency with which flock members turn away from it. We first extract from the empirical data of pigeon flocks the characteristics of their shape and internal structure (bearing angle and distance to nearest neighbors). Combining these with information on their coordination from the literature, we build an agent-based model adjusted to pigeons' collective escape. We show that the pattern of turning away from the predator with increased frequency when the predator is closer arises without prey prioritizing escape when the predator is near. Instead, it emerges through self-organization from a behavioral rule to avoid the predator independently of their distance to it. During this self-organization process, we show how flock members increase their consensus over which direction to escape and turn collectively as the predator gets closer. Our results suggest that coordination among flock members, combined with simple escape rules, reduces the cognitive costs of tracking the predator while flocking. Such escape rules that are independent of the distance to the predator can now be investigated in other species. Our study showcases the important role of computational models in the interpretation of empirical findings of collective behavior.

A Simple Escape from Moral Twin Earth

This paper offers a simple response to the Moral Twin Earth (MTE) objection to naturalist moral realism (NMR). NMR typically relies on an externalist metasemantics such as a causal theory of reference. The MTE objection is that such a theory predicts that terms like ‘good’ and ‘right’ have a different reference in certain twin communities where it’s intuitively clear that the twins are talking about the same thing when using ‘good’. I argue that Boyd’s causal regulation theory, the original target of the MTE objection, was never vulnerable to this objection. The theory contains an epistemic constraint on reference which implies that either the property that causally regulates uses of ‘good’ isn’t different for the twin communities or, in scenarios where the reference is different, the communities diverge in ways where it’s not intuitively clear that ‘good’ has the same reference for them.

Reducedinsulin signaling maintains electrical transmission in a neural circuit in aging flies.

Lowered insulin/insulin-like growth factor (IGF) signaling (IIS) can extend healthy lifespan in worms, flies, and mice, but it can also have adverse effects (the “insulin paradox”). Chronic, moderately lowered IIS rescues age-related decline in neurotransmission through the Drosophila giant fiber system (GFS), a simple escape response neuronal circuit, by increasing targeting of the gap junctional protein innexin shaking-B to gap junctions (GJs). Endosomal recycling of GJs was also stimulated in cultured human cells when IIS was reduced. Furthermore, increasing the activity of the recycling small guanosine triphosphatases (GTPases) Rab4 or Rab11 was sufficient to maintain GJs upon elevated IIS in cultured human cells and in flies, and to rescue age-related loss of GJs and of GFS function. Lowered IIS thus elevates endosomal recycling of GJs in neurons and other cell types, pointing to a cellular mechanism for therapeutic intervention into aging-related neuronal disorders.

“August on Sourdough”: An Archival View of Gary Snyder’s Intercultural Poetics

“August on Sourdough”An Archival View of Gary Snyder’s Intercultural Poetics Andrew Hageman (bio) A Glimpse into Literary Production Archived in the Gary Snyder Papers at the University of California, Davis, are five distinct drafts of the poem eventually published under the title “August on Sourdough: A Visit from Dick Brewer” in Gary Snyder’s 1967 collection, The Back Country. The various reworkings of this poem provide a fascinating view into the poet’s process of creative production, but they also provide new insights that intervene in scholarly critiques of Snyder’s intercultural poetic innovations. For one thing, the set of drafts underscores the poem’s participation in the Chinese poetic genre of hermits being visited by old friends and/or new acquaintances. Snyder, however, transforms the genre into an intercultural version, and one specifically of the Pacific Rim, by blending twentieth-century US form and content with the Chinese tradition. In particular, the different drafts show Snyder exploring different concepts and representations of subjectivity. In addition to the generic insight, the drafts also reveal that Snyder initially wrote the poem to fit exactly into a seven-syllable traditional Chinese poetic form. Only over the course of subsequent drafts did Snyder reshape the visual layout of the lines on the page to fit into the switchback or zigzag appearance that is widely recognized as a signature of his poetics. To see this dual technique of rigorous calculation and design, followed by a formal shift that retains yet transforms the underlying framework, creates a dissonance that calls us to reread Snyder’s intercultural poetics. Collectively, these insights intervene in Snyder criticism in two key ways. First, Snyder and his poetry have long been haunted by challenges that arise with intercultural approaches to art. Leslie [End Page 135] Marmon Silko and Geary Hobson among others have accused Snyder of appropriating Native American cultural traditions, and Ling Chung has posed similar questions regarding Chinese cultural heritage.1 I argue that these and other lingering accusations of cultural exploitation can begin to be reframed in light of the intercultural dynamics made visible through this set of drafts. Such reframing connects to the second intervention this essay is waging. The sophisticated exploration of subjectivity revealed through these drafts advances our understanding of Snyder’s contribution to ecological poetics and thought. The intercultural approach Snyder forges perturbs conventional notions of human subjectivity, not by proposing a simple escape hatch through which to slip out of the self, but through the arduous work toward dissolving self. Unlike those Western deployments of Buddhist ideals and practices that seem to offer a readymade and simple solution to social and ecological crises in the West, Snyder’s intercultural poetics confront the horizons of our ability to think through the self, to empathize with others, and to think ecological thoughts. By perturbing subjectivity through his particular intercultural poetics in the mid-1960s, Snyder was at the vanguard of aesthetic approaches to perceiving and representing the overlapping contours of ecology and globalization as a means to transcend the destructive aspects of the increasing planetary interconnectedness. Generic Tradition of Visiting a Hermit Robert Hass has remarked that “August on Sourdough” “belongs to a tradition of poems of leave-taking in China and Japan” (109). Hass is correct, but it is useful to define this intercultural poetic relationship with still finer precision. Thematically, Snyder’s text resonates with a Chinese generic tradition prevalent among Tang and Song Dynasty poetry. Each poem in this tradition narrates either a brief meeting between a hermit in reclusion and a friend from the social world or the friend visiting the hermit’s abode but finding him gone. Beyond mere leave-taking and the distance across which relationships endure and grow, poems of the visiting-a-hermit genre tend to meditate on the vicissitudes of the hermit’s life, being drawn at turns toward the eremitic world and the social, revealing a renewed commitment to the meditative and [End Page 136] contemplative work facilitated by reclusion in the mountains but never completely removed from the social, historical world. Such hermits do not endeavor to remove themselves from the world and worldly things entirely. Refining Hass’s generic classification...

Jumping behavior of the springtail Folsomia candida as a novel soil quality indicator in metal-contaminated soils

This study validates that the jumping ability of the springtail Folsomia candida may be used to evaluate the soil quality of Cu and Ni polluted sites. The jumping ability of the springtail F. candida exposed to metal-contaminated soil was evaluated by observing the frequency, distance, and direction of jumping. The jumping assay was performed using individuals that survived a chronic soil test, in which jumping was induced by chemical stress (methyl alcohol). The chronic soil test generated expected adverse effects on springtail reproduction and survival rates. In the jumping assay, the control group exhibited high jumping frequency and variable escape maneuvers. In contrast, the exposed group exhibited a significant decrease in jumping ability (with some individuals being unable to jump) and performed very simple escape maneuvers. The toxicity indicator values of the jumping assay were comparable to reproduction data, and were more sensitive compared to survival data. To the best of our knowledge, this is the first study to assess the jumping ability of F. candida on metal-contaminated soils. The evaluation of jumping activity may represent a viable field screening technique for soil quality.

Escape Decision-Making Based on Intuition and Deliberation under Simple and Complex Judgment and Decision Conditions

The purpose of the present study was to explore and compare the effects of intuition and deliberation in escape decision-making under emergency conditions. We adopted Dijksterhuis et al.’s (2006) Unconscious Thinking Theory (UTT) to explain the effects of intuition and deliberation under emergency. We also attempted to extend the use of UTT in emergency situations. According to Dijksterhuis et al. (2006), whether unconscious thought or conscious thought would yield better decisions depends on the complexity of the situation. However, we have noticed that for Dijksterhuis et al., the complexity of the situation only meant the complexity of judgment rather than the decision task, and the situation was limited to daily decision-making. In the present study, we further differentiated the complexity of decision conditions into the complexities of judgment references and decision tasks based on UTT, and attempted to examine the effects of intuition and deliberation when the complexities of judgment references and the decision tasks were both different under emergency. Dijksterhuis et al. (2006) demonstrated that conscious thought was better in making the best choice among simple conditions, whereas unconscious thought was better in making the best choice among complex conditions. Although unconscious thought is not the same as intuition, they are both unconscious processing. The difference is that intuition appears immediately, but unconscious thought needs time. Deliberation could be same as conscious thought. So it is comparable between unconscious and conscious thought, and intuition and deliberation. Accordingly, our main hypotheses were established based on UTT. Hypothesis one was that the effect of deliberation was better than that of intuition under simple judgment reference and simple decision task condition. Hypothesis two was that the effect of intuition was better than that of deliberation under complex judgment reference and complex decision task conditions. The study consisted of two main experiments and two preliminary experiments. We recruited 85 and 87 participants for experiments 1 and 2 respectively. A 2 (mode of thought: intuition and deliberation) × 2 (complexity of judgment reference: simple and complex) between-group design was adopted. The dependent variable for experiment 1 was simple escape decision task which was shown directly (simple style), and the dependent variable for experiment 2 was complex escape decision task, which was presented indirectly (complex style). The main findings were: (1) There were no significant differences in escape decision-making between intuition and deliberation under simple judgment reference and simple decision task condition, as well as under complex judgment reference and simple decision task condition. (2) Deliberation was better in making good decisions than intuition under simple judgment reference and complex decision task condition. (3) Intuition was better in making good decisions than deliberation under complex judgment reference and complex decision task condition. In conclusion: UTT was not supported in simple escape decision task condition, but it was supported in complex escape decision task condition. In other words, whether the UTT is able to or not to explain the effects of intuition and deliberation in emergency setting depends on what the decision task is.

Multivitamins in Prevention of Cardiovascular Disease

CARDIOVASCULAR DISEASE (CVD) IS THE MAJOR CAUSE of death and disability globally and affects more than 50% of men and 40% of women during their lifetimes. Despite remarkable scientific advances, in 2008 CVD accounted for 1 of every 3 deaths in the United States and for health care costs estimated at close to $300 billion. The major risk factors for CVD are well known but remain ubiquitous in populations. For example, about one-third of US adults ( 75 million) have hypertension; more than 20% smoke; more than one-third ( 78 million) are obese; 8% ( 18 million) have diagnosed diabetes, with similar rates of undiagnosed diabetes and an additional 35% with prediabetes; 15% have high cholesterol levels; and, in the 2009-2010 NHANES survey, 46.5% (102.5 million) had at least 1 major risk factor among uncontrolled blood pressure, high cholesterol levels, and current smoking. These risk factors are also major contributors to other chronic diseases such as cancer, depression, arthritis, kidney disease, and cognitive decline. Strategies to prevent the development of these risk factors, which are largely related to lifestyle habits, and effective therapies to lower risk factor levels when these are present, can lead to substantial reductions in the burden of CVD. The sources of unfavorable lifestyle habits are largely known, and therapies that can effectively and safely lower levels of risk factors have been identified and extensively tested. Yet the apparently simple task of implementing this knowledge grounded in decades of sound research continues to remain extremely challenging and seems at times insurmountable. Thus, even though CVD mortality rates have declined greatly in the United States and other developed countries, the disease burden remains high, and the progress that has been made is threatened by increasing rates of obesity, physical inactivity, and diabetes. Furthermore, urbanization, profound lifestyle changes, and a decline in competing risks for premature death have resulted in substantial increases in CVD in developing countries. Numerous factors account for the current failure to achieve optimal results in CVD prevention, including (1) low adoption and adherence to healthy lifestyles and to proven, inexpensive, and safe pharmacological therapies, even when prescribed using sound evidence and to persons at highest risk; (2) the complexity of implementing meaningful lifestyle intervention programs, which require not only behavioral interventions to modify individual lifestyles but also changes in health policy, the environment, and cultural attitudes; and (3) the cost and affordability of implementing meaningful lifestyle modification programs and of using proven drugs when necessary. Many individuals and societies as a whole resort to the use of vitamins and other dietary supplements as a simple and miraculous escape from the difficult and complex task of implementing effective prevention strategies. Most required vitamins and micronutrients can generally be derived from a healthy, well-balanced diet. In addition, many food products are already fortified with folic acid, vitamin D, calcium, fluoride, and other micronutrients, which may be needed in higher amounts by some individuals or may not be readily available to others (eg, infants, pregnant women, postmenopausal women with low exposure to sunlight, or those living in poverty). However, despite the lack of solid evidence for benefit from the widespread use of vitamins and dietary supplements, more than half of US adults take at least 1 dietary supplement (about 10% take 5 such supplements), and these numbers continue to increase; 32% of the US population used at least 1 dietary supplement in the 1970s, 42% in 19881994, and 53% in 2003-2006. Moreover, such dietary supplements are used more frequently by healthier, more educated and affluent people—those at lowest risk for dietary deficiencies. Multivitamins/multiminerals are by far the most frequently used dietary supplement; 30% of the US population used them in 1988-1994 and 39% in 2003-2006. Regulations governing the approval and marketing of dietary supplements remain less strict than those for prescription or even over-the counter drugs and do not mandate conclusive proof of benefit or safety based on large randomized controlled clinical trials (RCTs). This has allowed for claims of benefit in preventing or curing an amazingly diverse and

Animal escapology I: theoretical issues and emerging trends in escape trajectories.

Escape responses are used by many animal species as their main defence against predator attacks. Escape success is determined by a number of variables; important are the directionality (the percentage of responses directed away from the threat) and the escape trajectories (ETs) measured relative to the threat. Although logic would suggest that animals should always turn away from a predator, work on various species shows that these away responses occur only approximately 50-90% of the time. A small proportion of towards responses may introduce some unpredictability and may be an adaptive feature of the escape system. Similar issues apply to ETs. Theoretically, an optimal ET can be modelled on the geometry of predator-prey encounters. However, unpredictability (and hence high variability) in trajectories may be necessary for preventing predators from learning a simple escape pattern. This review discusses the emerging trends in escape trajectories, as well as the modulating key factors, such as the surroundings and body design. The main ET patterns identified are: (1) high ET variability within a limited angular sector (mainly 90-180 deg away from the threat; this variability is in some cases based on multiple peaks of ETs), (2) ETs that allow sensory tracking of the threat and (3) ETs towards a shelter. These characteristic features are observed across various taxa and, therefore, their expression may be mainly related to taxon-independent animal design features and to the environmental context in which prey live - for example whether the immediate surroundings of the prey provide potential refuges.

Experiment for Development of Simple Escape Countermeasures for Frogs Falling into Concrete Canals

Experiment for Development of Simple Escape Countermeasures for Frogs Falling into Concrete Canals

Fractal art using variations on escape time algorithms in the complex plane

The creation of fractal art is easily accomplished through the use of widely-available software, and little mathematical knowledge is required for its use. But such an approach is inherently limiting and obscures many possible avenues of investigation. This paper explores the use of orbit traps together with a simple escape time algorithm for creating fractal art based on nontrivial complex-valued functions. The purpose is to promote a more direct hands-on approach to exploring fractal artistic expressions. The article includes a gallery of images illustrating the visual effects of function, colour palette, and orbit trap choices, and concludes with suggestions for further experimentation.

Locating Paradise in the Post-Civil Rights Era: Toni Morrison and Critical Race Theory

Locating Paradise in the Post–Civil Rights Era:Toni Morrison and Critical Race Theory Richard L. Schur (bio) Home is not a little thing. Toni Morrison, Paradise This article attempts to "locate" Toni Morrison's Paradisein the post-civil rights era by identifying its place within contemporary discussions about African American culture and the civil rights movement's legacy. Paradise is but one instance of an ongoing conversation among critical race theorists about the possibility of social, cultural, and legal reform. In the twenty-eight-year period between the publication of The Bluest Eye (1970) and Paradise (1998), the civil rights movement declined as a contemporary social force. By the early 1980s, critical race theory emerged and began "uncover[ing] the ongoing dynamics of racialized power, and its embeddedness in practices and values which have been shorn of any explicit, formal manifestation of racism" (Crenshaw et al. xxix). The 1990s brought groundbreaking books that developed critical race theory and blurred disciplinary boundaries to demonstrate how discursive spheres have been racialized, gendered, classed, and sexed (Bell, Delgado, Guinier, hooks and West, and Williams). Due to its engagement with critical race theory, Morrison's novel translates paradise from a universalized concept that transcends race, class, nation, and gender toward a smaller, more local, and more "manageable" version. Paradise exemplifies and contributes to these new discourses on race and otherness by narrating the complementary histories of an all-black town (named Ruby) in rural Oklahoma and the nearby [End Page 276] convent that became a refuge for young women. The stories ultimately come together at the conclusion of the civil rights movement when the men of Ruby attack the "Convent Women" to drive them off and/or kill them. Through these interwoven stories, Morrison describes how the idealization of whiteness haunts the Convent and Ruby (spaces seemingly free from racism and white people), and how racial identity is always gendered and gender identity always raced.1 By situating the novel in the late 1960s and early 1970s, Morrison captures the shift from the civil rights movement to the post-civil rights era, in which the realities of racial integration and gender equality, as putative paradises, were first being examined. Morrison insists that there can be no simple escape from the effects of race, racism, gender, and sexism without some sort of decolonization. In Paradise, Morrison portrays how African Americans have houses, but not homes. Haven, this group's first settlement, and then Ruby fail to live up to their names because racist and sexist ideologies do not respect the borders established by the townspeople. These communities based on a utopian ideal are not homes because the racial ideologies that the inhabitants of Ruby sought to escape follow them within their hearts and minds. As in much of Morrison's work, racist ideologies transform "domestic" sites into racialized spaces due to the racism and sexism built into their foundations. Paradise thus testifies to the difficulties of building a real home within the racialized soil of the United States. In her nonfiction writings, Morrison has explored how an unspoken African American presence haunts American literature [End Page 277] ("Unspeakable Things" 210, 212). Thus the very foundation of Morrison's fiction, the discipline of literature, is marked by racialization. These racializations come to shape how scholars and students understand literary texts, including her own. Morrison has argued that "[f]or the most part, the literature of the United States has taken as its concern the architecture of a new white man" (Playing in the Dark 14-15). Her interrogation of literature's foundations suggests that perhaps other disciplinary tools, methods, and concerns may be useful in uncovering the effects of literature. To do justice to Paradise, students of Morrison must not use the tools of the literary tradition to limit the meaning of her work. While at work on Paradise, Morrison stated in a speech that "[i]n the novel I am now writing, I am trying first to enunciate and then eclipse the racial gaze altogether" ("Home" 9). In that same speech, she characterized her entire oeuvre as seeking a way "to convert a racist house into a race-specific yet nonracist home" ("Home...

Spatial and non-spatial visual discrimination learning in zebrafish ( Danio rerio )

Zebrafish (Danio rerio) provide an excellent model for assessment of molecular processes of neurodevelopment. To determine the functional importance of molecular events during neurodevelopment, we have developed methods for assessing learning in zebrafish in a three-chambered fish tank. In the first study, simple escape response was assessed. Zebrafish tested with a moving net learned to escape to another chamber more rapidly over the six sessions of training than the fish with the still net which did not learn. Upon reversal of the contingencies, the fish switched to the inactive net rapidly learned to suppress the escape response and fish formerly in the inactive net condition learned to avoid the moving net. In the second study, spatial discrimination learning was assessed. Zebrafish were trained on a right-left position discrimination to avoid the active net. Zebrafish showed significant improvement in escape responses over six sessions of training with three trials per session. In the third study, red-blue non-spatial discrimination learning was assessed. There was a significant improvement over the first six training sessions. With the reversal of contingencies, there was a significant decline of performance. With continued training, the fish again significantly improved avoidance. These studies found an effective motivational stimulus and procedure for studying escape behavior in zebrafish; a procedure whereby zebrafish would learn both spatial and non-spatial discrimination. These methods are being developed to help determine the functional importance of molecular events during zebrafish neurodevelopment.

With J for TeX

Last summer I asked the Jforum for advice regarding the conversion of J text to a format suitable for placing J expressions and session logs into TeX word processing documents. There were a couple dozen follow-up posts to the Jforum and I received many private e-mail messages. There have been independent threads regarding TeX in comp.lang.apl too. I was quite surprised by the high level of interest and impressed by the number of sophisticated comments. I also enjoyed a few good laughs. This note offers some remarks on the Jforum discussion, what I eventually did, what the alternatives were, and what I might have done if I could have foreseen the future. While the core computation was simple escape sequence substitution, there also were subtle contexts for modifications when lines end and when box drawing characters appear. J's adverb facility helped with those situations and the use of J-defined function keys made the J to TeX conversion much easier.

Late Oligocene–Recent stress evolution in rift basins of northern and central Thailand: implications for escape tectonics

The Tertiary rift basins of Thailand are known through sub-surface seismic and borehole data collected for hydrocarbon and coal exploration, outcrops in open-cast coal mines, and a few natural outcrops. These data provide mixed perspectives on how the basins evolved, some providing data on ages and structural geometries, others palaeostress data. In general, the region evolved under approximately E–W extension, although the extension direction probably changed periodically within basins. Extension was episodically interrupted by inversion events associated with sub-horizontal NW–SE to NE–SW σ 1 direction. There is no evidence to suggest that the string of rift basins running from N. Thailand and Laos into the Gulf of Thailand evolved in a similar way. On the contrary, the evolution of each basin seems different, although certain regional trends along the rift system are apparent as follows: (1) Oligocene–Lower Miocene extension is widespread in the region. (2) In central and northern Thailand Middle Miocene extension is also important, and extension persisted into the Upper Miocene–Pliocene. (3) In the extreme south of the area (W. Natuna basin, Penyu basin, Malay basin) extension ceased in the earliest Miocene. (4) In the northern Gulf of Thailand extension ceased in the Middle Miocene. (5) Thermal subsidence is greatest (up to 4km) in the south (Malay, Pattani, W. Natuna and Penyu basins) and least in northern Thailand (a few tens to hundreds of metres). (6) Inversion in the southern Gulf of Thailand was intense and occurred during the Lower and Middle Miocene. In the northern Gulf of Thailand inversion is very mild and occurred during the Lower and Middle Miocene. Onshore inversion is patchy during the Miocene, but is strongest in the northwestern rift basins (particularly the Li basin). The most widespread inversion event that affects the north occurred during the Plio-Pleistocene. It might be associated with the change from left to right lateral motion on the Red River Fault. The relationship between strike-slip faults and rift basins in terms of timing of extensional and inversion events, and palaeostress orientation and evolution is more complex than can be explained by simple escape tectonic models.

A brief method for conducting a negative-reinforcement assessment

A brief negative-reinforcement assessment was conducted with developmentally disabled children with severe destructive behavior. Five children were trained to engage in a simple escape response (e.g., a hand clap). Then each child was presented with a variety of stimuli or tasks that ranged on a scale from preferred to nonpreferred, based on parent ranking. The participant received a brief break from the stimuli or task, contingent on each escape response. For one child, an avoidance contingency was also implemented in which he could engage in the response to avoid the presentation of stimuli. Results showed that for each child, several stimuli were identified that may serve as effective negative reinforcers. Results also indicated that the procedure did not elicit any negative side effects for four children and low rates of destructive behavior for the fifth child. For one child, the results of the negative-reinforcement assessment were used to develop an effective treatment for destructive behavior. Additional applications of the reinforcement assessment to treatment interventions is discussed, as well as limitations to the procedure.

FexviiSoft X‐Ray Lines: Theory and Data Comparisons

Fe XVII soft X-ray spectral emission lines are examined using data from the Flat Crystal Spectrometer (FCS) on the Solar Maximum Mission satellite. Results are compared with theoretical calculations and with other recent observational results. Disparate findings from different studies on the inferred opacity of the bright resonance line at 15.01 A and on its center-to-limb behavior are reviewed. Present limitations on the use of resonance scattering to infer coronal plasma densities and absolute elemental abundances are discussed. An analysis is made of the temperature-insensitive ratio of the 15.01 A line of Fe XVII to the optically thin 16.78 A line. This analysis shows that approximately half of the photons expected in the 15.01 A line are missing from the bright emission cores of quiescent active regions on the solar disk; the missing fraction increases at most by 50% near the solar limb. If the missing flux has been resonantly scattered out of the line of sight, then the equivalent optical depth at line center of the 15.01 A line is τ0~2 on the disk, based on a simple escape probability treatment for a slab geometry. This suggests that the effects of resonance scattering for other FCS lines, with the possible exception of the O VIII doublet at 18.97 A, should be negligible for quiescent active region conditions. This is consistent with the lack of systematic center-to-limb dependence found previously for FCS lines other than Fe XVII at 15.01 A. Yohkoh Soft X-ray Telescope measurements of the expected lines of sight for active regions as a function of location on the solar disk, and resonance scattering results from other soft X-ray active region data sets all support a trend of increased opacity at the limb compared to disk center.

Within population genetic differentiation in traits affecting clonal growth: Festuca rubra in a mountain grassland

Abstract Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within‐population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonoše Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber.Highly significant variation among clones was found in almost all parameters. In the common garden, the clones differed in tussock growth (mean tillering rate), architecture (mean shoot angle, mean tussock density) and proportion of flowering shoots. In the growth chamber, both the aboveground parameters and parameters of the rhizome system were strongly affected by red/far red ratio; among‐clone variation was also almost always significant. The genotype × environment interaction was significant for tillering rate and rhizome architecture. The structure of the rhizome system (which is the major component of clonal spread in space) is a complex result of several components whose inter‐clone variations differ: (i) genetically determined mean rhizome system size, (ii) overall plasticity in rhizome system size (with no significant genetic variation in plasticity), and (iii) genetically determined plasticity in rhizome architecture. Because of the variation in plasticity in rhizome architecture, some c lones seemed to possess the ability to exploit a favourable habitat patch by producing short branches when there; whereas the remaining clones appeared to possess only a simple escape mechanism from unfavourable patches.Environmental variation in the light levels in the studied grassland is fine grained; horizontal growth rates of F. rubra are sufficient to make genets experience different patches in their lifetime. The high variation in both genotype means and plasticities is likely to be due to selection early in genet life in an environment which is heterogeneous at a fine scale.

X-ray spectroscopic diagnostics of mix in high growth factor spherical implosions

Rayleigh-Taylor (RT) instability of the pusher-fuel interface occurring upon acceleration and deceleration of the pusher is of major concern for current and future ICF experiments. One common diagnostic technique for measuring pusher-fuel mix in spherical implosion experiments involves placing spectroscopic dopants both in the capsule fuel region and the innermost region of the capsule wall adjacent to the fuel. As the degree of pusher-fuel mix is increased the pusher dopant x-ray emission increases relative to that of the fuel dopant. Spherical implosion experiments of this type using Ar and Ti dopants in the fuel and pusher, respectively, are being carried out on Nova. We first show that the Ti He-α Ar He-β line ratio shows promise as a mix diagnostic for high growth factor targets. We then discuss some of the important physical processes underlying Ar and Ti spectral line formation in these targets and discuss how these processes affect the calculation of simulated spectra. The importance of radiative transfer as well as high-density plasma phenomena such as continuum lowering and Stark broadening is demonstrated. The simulated spectra are also observed to be sensitive to assumptions regarding the treatment of electron thermal conduction in the mix region. Spectral postprocessing of 2-D hydrodynamic simulations using detailed line transfer methods has been carried out and implies that simple escape factor treatments must be tested carefully before they can be relied upon. Preliminary comparisons of experimental data with simulation are presented. It is shown that the computed spectra is sensitive to the laser energy and pusher temperature. These comparisons to data also imply that the inclusion of convective effects in computing the electron temperature profile through the mix region is necessary in order to satisfactorily model experimental spectra.

Die vreemdelíngskaptema in enkele romans van Karel Schoeman, ’n Bespreking van die tussenskap

The theme of alienation in the novels of Karel SchoemanThe state of alienation is one of the overriding themes in Karel Schoeman's oeuvre. This article, “The theme of alienation in the novels of Karel Schoeman”, deals with one of the manifestations of this theme, namely the dilemma of alienation. The world presented in Karel Schoeman's oeuvre is characterized by dichotomy, e.g. the known as opposed to the unknown - a phenomenon which causes uncertainty. This article examines the way in which an epistemological dichotomy is expressed as a kind of dilemma in the novels of Karel Schoeman. The dilemma is presented to discourage a simple escape by means of choice. In this position between alternative worlds or views, the Schoeman character faces limited options: to make a choice of sorts and win or risk sacrificing something of value; to accept this precarious position and confirm his life as one of passive silence; to conquer the impasse, e.g. by sidestepping the choice and creating an alternative world as in a dream or a work of art.

Lobe dynamics and the escape from a potential well

Periodically-forced nonlinear oscillators that permit escape from a potential well frequently possess unstable periodic orbits whose invariant manifolds are homoclinically tangled. The trellises formed by such overlapping manifolds separate the Poincaré plane into regions (calledlobes) whose fates at successive time periods are amenable to analysis. The lobe configurations observed in simple escape systems are discussed, together with their interrelation with the location of periodic orbits and other invariant sets. Three applications of this procedure are illustrated: (i) a numerical technique for localizing the non-wandering set; (ii) a demonstration that the existence of a saddle possessing aboundedhomoclinically tangled unstable manifold branch implies the existence of safe open regions in the global basin of attraction; (iii) the proposal of definitions of global integrity and escape times which may be used to relate safe basin erosion to the evolution of a homoclinic tangle.