Double power series method for approximating cosmological perturbations

We introduce a double power series method for finding approximate analytical solutions for systems of differential equations commonly found in cosmological perturbation theory. The method was set out, in a non-cosmological context, by Feshchenko, Shkil' and Nikolenko (FSN) in 1966, and is applicable to cases where perturbations are on sub-horizon scales. The FSN method is essentially an extension of the well known Wentzel-Kramers-Brillouin (WKB) method for finding approximate analytical solutions for ordinary differential equations. The FSN method we use is applicable well beyond perturbation theory to solve systems of ordinary differential equations, linear in the derivatives, that also depend on a small parameter, which here we take to be related to the inverse wave-number. We use the FSN method to find new approximate oscillating solutions in linear order cosmological perturbation theory for a flat radiation-matter universe. Together with this model's well known growing and decaying M\'esz\'aros solutions, these oscillating modes provide a complete set of sub-horizon approximations for the metric potential, radiation and matter perturbations. Comparison with numerical solutions of the perturbation equations shows that our approximations can be made accurate to within a typical error of 1%, or better. We also set out a heuristic method for error estimation. A Mathematica notebook which implements the double power series method is made available online.Comment: 22 pages, 10 figures, 2 tables. Mathematica notebook available from Github at https://github.com/AndrewWren/Double-power-series.gi

Variation in early life maternal care predicts later long range frontal cortex synapse development in mice.

Empirical and theoretical work suggests that early postnatal experience may inform later developing synaptic connectivity to adapt the brain to its environment. We hypothesized that early maternal experience may program the development of synaptic density on long range frontal cortex projections. To test this idea, we used maternal separation (MS) to generate environmental variability and examined how MS affected 1) maternal care and 2) synapse density on virally-labeled long range axons of offspring reared in MS or control conditions. We found that MS and variation in maternal care predicted bouton density on dorsal frontal cortex axons that terminated in the basolateral amygdala (BLA) and dorsomedial striatum (DMS) with more, fragmented care associated with higher density. The effects of maternal care on these distinct axonal projections of the frontal cortex were manifest at different ages. Maternal care measures were correlated with frontal cortex → BLA bouton density at mid-adolescence postnatal (P) day 35 and frontal cortex → DMS bouton density in adulthood (P85). Meanwhile, we found no evidence that MS or maternal care affected bouton density on ascending orbitofrontal cortex (OFC) or BLA axons that terminated in the dorsal frontal cortices. Our data show that variation in early experience can alter development in a circuit-specific and age-dependent manner that may be relevant to understanding the effects of early life adversity

Early maternal separation impacts cognitive flexibility at the age of first independence in mice.

Early life adversity is associated with increased risk for mental and physical health problems, including substance abuse. Changes in neural development caused by early life insults could cause or complicate these conditions. Maternal separation (MS) is a model of early adversity for rodents. Clear effects of MS have been shown on behavioral flexibility in rats, but studies of effects of MS on cognition in mice have been mixed. We hypothesized that previous studies focused on adult mice may have overlooked a developmental transition point when juvenile mice exhibit greater flexibility in reversal learning. Here, using a 4-choice reversal learning task we find that early MS leads to decreased flexibility in post-weaning juvenile mice, but no significant effects in adults. In a further study of voluntary ethanol consumption, we found that adult mice that had experienced MS showed greater cumulative 20% ethanol consumption in an intermittent access paradigm compared to controls. Our data confirm that the MS paradigm can reduce cognitive flexibility in mice and may enhance risk for substance abuse. We discuss possible interpretations of these data as stress-related impairment or adaptive earlier maturation in response to an adverse environment

Siren City: Sound and Source Music in Classic American Noir, by Robert Miklitsch

Unsettlingly ambiguous, oft-times nonlinear narratives; dialogue-driven actions announcing acts of violence among a barrage of stark, angular shadows; isolating metropolises, beautiful and scheming women, and their ensuing battles against all odds—if not to rise above, then to survive until sunrise: whether in unison or discord, these elements both inscribe and orchestrate the very measures through which a unique body of films (and their literary antecedents) are interpreted. It is hardly surprising, then, that American film noir retains a popularity today wholly reminiscent of that in its heyday, well over half a century ago

The language of self, power, meaning: Japanese literature and the cultural boundaries of ideology

To understand the idioms used in representing literary selfhood as enactments and rhetorical assertions is to observe their contextual construction within shifting fields of power and meaning inseparable from the specific and discernible situations, culturally specific conventions affecting their narration, in short, the specificity of historical moment. In the Japanese context, identity is clearly not the unified essence implied by the Cartesian premise, but it can be the presentation or performance of a spatiotemporal locatedness of contradiction and disunity, a nexus wherein multiple discourses temporarily coincide in remarkable and discernible ways we apprehend in the abstracted self. But it is not enough that we as readers celebrate in the particularity of these performance as expressions of what is often dismissed as "local knowledge." Rather, we must question what social institutions--be they alien or indigenous--these performances address. What conventions did they oppose? What apparatus of power does the dialectic of the gaze set itself in opposition? For only by questioning the strategies that erected the facade of boundedness in general and one in particular that created the illusions of insulating the self from the play of power relations in specific works of fictional self-representation can we hope to force a larger reconsideration of selves and their pathways to emergence. In many ways, my task as a member of a particular reading audience has been and will always be to visualize the overall impact of cultural forces on patterns of fictional self-representation and to accept that identity is negotiated, open, shifting, ambiguous, the result of culturally available meanings and the open-ended, power-laden enactments of these meanings in everyday situations

Development and evaluation of a thermochemistry concept inventory for college-level general chemistry

The research presented in this dissertation culminated in a 10-item Thermochemistry Concept Inventory (TCI). The development of the TCI can be divided into two main phases: qualitative studies and quantitative studies. Both phases focused on the primary stakeholders of the TCI, college–level general chemistry instructors and students. Each phase was designed to collect evidence for the validity of the interpretations and uses of TCI testing data. A central use of TCI testing data is to identify student conceptual misunderstandings, which are represented as incorrect options of multiple– choice TCI items. Therefore, quantitative and qualitative studies focused heavily on collecting evidence at the item–level, where important interpretations may be made by TCI users. Qualitative studies included student interviews (N = 28) and online expert surveys (N = 30). Think-aloud student interviews (N = 12) were used to identify conceptual misunderstandings used by students. Novice response process validity interviews (N = 16) helped provide information on how students interpreted and answered TCI items and were the basis of item revisions. Practicing general chemistry instructors (N = 18), or experts, defined boundaries of thermochemistry content included on the TCI. Once TCI items were in the later stages of development, an online version of the TCI was used in expert response process validity survey (N = 12), to provide expert feedback on item content, format and consensus of the correct answer for each item. Quantitative studies included three phases: beta testing of TCI items (N = 280), pilot testing of the a 12-item TCI (N = 485), and a large data collection using a 10-item TCI (N = 1331). In addition to traditional classical test theory analysis, Rasch model analysis was also used for evaluation of testing data at the test and item level. The TCI was administered in both formative assessment (beta and pilot testing) and summative assessment (large data collection), with items performing well in both. One item, item K, did not have acceptable psychometric properties when the TCI was used as a quiz (summative assessment), but was retained in the final version of the TCI based on the acceptable psychometric properties displayed in pilot testing (formative assessment)

Finite-element modelling of mechanobiological factors influencing sesamoid tissue morphology in the patellar tendon of an ostrich

The appearance and shape of sesamoid bones within a tendon or ligament wrapping around a joint are understood to be influenced by both genetic and epigenetic factors. Ostriches (Struthio camelus) possess two sesamoid patellae (kneecaps), one of which (the distal patella) is unique to their lineage, making them a good model for investigating sesamoid tissue development and evolution. Here we used finite-element modelling to test the hypothesis that specific mechanical cues in the ostrich patellar tendon favour the formation of multiple patellae. Using three-dimensional models that allow application of loading conditions in which all muscles, or only distal or only proximal muscles to be activated, we found that there were multiple regions within the tendon where transformation from soft tissue to fibrocartilage was favourable and therefore a potential for multiple patellae based solely upon mechanical stimuli. While more studies are needed to better understand universal mechanobiological principles as well as full developmental processes, our findings suggest that a tissue differentiation algorithm using shear strain and compressive strain as inputs may be a roughly effective predictor of the tissue differentiation required for sesamoid development