Dynamics of fingering convection II: The formation of thermohaline staircases

Regions of the ocean's thermocline unstable to salt fingering are often observed to host thermohaline staircases, stacks of deep well-mixed convective layers separated by thin stably-stratified interfaces. Decades after their discovery, however, their origin remains controversial. In this paper we use 3D direct numerical simulations to shed light on the problem. We study the evolution of an analogous double-diffusive system, starting from an initial statistically homogeneous fingering state and find that it spontaneously transforms into a layered state. By analysing our results in the light of the mean-field theory developed in Paper I, a clear picture of the sequence of events resulting in the staircase formation emerges. A collective instability of homogeneous fingering convection first excites a field of gravity waves, with a well-defined vertical wavelength. However, the waves saturate early through regular but localized breaking events, and are not directly responsible for the formation of the staircase. Meanwhile, slower-growing, horizontally invariant but vertically quasi-periodic gamma-modes are also excited and grow according to the gamma-instability mechanism. Our results suggest that the nonlinear interaction between these various mean-field modes of instability leads to the selection of one particular gamma-mode as the staircase progenitor. Upon reaching a critical amplitude, this progenitor overturns into a fully-formed staircase. We conclude by extending the results of our simulations to real oceanic parameter values, and find that the progenitor gamma-mode is expected to grow on a timescale of a few hours, and leads to the formation of a thermohaline staircase in about one day with an initial spacing of the order of one to two metres.Comment: 18 pages, 9 figures, associated mpeg file at http://earth.uni-muenster.de/~stellma/movie_small.mp4, submitted to JF

Career transitions : creating rainbows

v, 77 leaves ; 29 cm. --The past four years have marked a period of tremendous growth in my life. The events that have initiated my career transition are presented through the use of metaphor. 111 During the course of the metaphors I moved from being a single person to not single, being a child of a nuclear family to being a child of divorce and a fatherless daughter, and from being a regular classroom teacher to being a teacher in a non-traditional assignment. The purpose of this project is to present the events, to describe their impact, and to compare my story to current career transition theory. Specifically, the project addresses the question: what have I learned about myself and the nature of transitions as a result of the events of the past three years. The last stage of the career transition process is marked by a beginning. I am a work-in-progress. The metaphor included in the last chapter represents my new direction

What is “inspiration porn” on social media and how does it effect [sic] deaf people and communities?

As a deaf person situated firmly in hearing culture, I face ableism and audism on a regular basis. I wanted to explore the ableist dynamics and desire to represent deafness and hearing devices in an audio centric way, and how this ultimately impacts all of society not just those who are deaf. This led to the topic of Inspiration Porn, which is the objectification of disabled people portrayed as ‘overcoming’ their disability and I wanted to look at this concept in the context of deaf Inspiration Porn on social media. The case study clips selected for textual analyses were both posted on Facebook and I use them as discussion points within the questionnaires and interviews. I used Grounded Theory to analyse the qualitative data collected on the lived experiences of Deaf, deaf and hearing participants. By combining all these data sets with a review of key historical events and contemporary views of deafness in the digital era, I was able to find the roots of many issues and why they have persisted. The result of this study was that the overall impact on society was profoundly negative and social media in this context does not improve how deafness is viewed. Recommended areas for further research are included to build upon this study with a view to include a wider diversity of deaf people or specific communities and how they interact with Inspiration Porn content

KIC 9533489: a genuine γ Doradus – δ Scuti Kepler hybrid pulsator with transit events

Context Several hundred candidate hybrid pulsators of type A–F have been identified from space-based observations. Their large number allows both statistical analyses and detailed investigations of individual stars. This offers the opportunity to study the full interior of the genuine hybrids, in which both low-radial-order p- and high-order g-modes are self-excited at the same time. However, a few other physical processes can also be responsible for the observed hybrid nature, related to binarity or to surface inhomogeneities. The finding that most δ Scuti stars also show long-period light variations represents a real challenge for theory. Aims We aim at determining the pulsation frequencies of KIC 9533489, to search for regular patterns and spacings among them, and to investigate the stability of the frequencies and the amplitudes. An additional goal is to study the serendipitously detected transit events: is KIC 9533489 the host star? What are the limitations on the physical parameters of the involved bodies? Methods Fourier analysis of all the available Kepler light curves. Investigation of the frequency and period spacings. Determination of the stellar physical parameters from spectroscopic observations. Modelling of the transit events. Results The Fourier analysis of the Kepler light curves revealed 55 significant frequencies clustered into two groups, which are separated by a gap between 15 and 27 d −1. The light variations are dominated by the beating of two dominant frequencies located at around 4 d −1 . The amplitudes of these two frequencies show a monotonic long-term trend. The frequency spacing analysis revealed two possibilities: the pulsator is either a highly inclined moderate rotator (v ≈ 70 km s −1 , i > 70 ◦ ) or a fast rotator (v ≈ 200 km s −1 ) with i ≈ 20 ◦ . The transit analysis disclosed that the transit events, which occur with a ≈ 197 d period may be caused by a 1.6 R_Jup body orbiting a fainter star, which would be spatially coincident with KIC 9533489

A Genealogy of Neoliberal and Anti-neoliberal Resilience in the Ecuadorian Pacific coast

Resilience appears to be everywhere, morphing and seducing global discourses, national governmental practices, and scholarship. Inasmuch as hegemonic discourses and national governments promote resilience through both disaster reduction and sustainable development policies, critical resilience scholars have emphasized resilience as a neoliberal security technique. By reinforcing resilience as a governmental practice embedded in neoliberal rationale, theory and practice are neglecting other areas to contextualize resilience. My dissertation traces a genealogy of neoliberal and anti-neoliberal State interventions underpinned by resilience thinking, organizing coastal rural lives in Ecuador. My dissertation shows, no matter the Ecuadorian governments’ rationale, both genuflected to global hegemonic discourses on resilience that justify government intervention to secure the population’s future. My analysis also reveals that both governmental rationales promoting resilience implemented similar techniques: legal framework adaptations, decentralizing processes, technocratic planning, and participatory management. After I captured resilience practices morphing through neoliberal and anti-neoliberal governance, a comprehensive ethnographic account also discloses unintended outcomes threatening the beach ecosystem. Ecosystems are a critical foundation of the socio-ecological relationship; however, profound changes in the beach ecosystem are now a consequence of the neoliberal and anti-neoliberal governmental emphasis on protecting the population and tourist infrastructure. More importantly, this research untangles resilience precepts underlying the neoliberal and anti-neoliberal problematization of nature to justify governmental intervention in coastal management. My particular critique of resilience does not replicate academic emphasis on catastrophic events. Hegemonic frameworks underrepresent the slow, local, and small emergencies by emphasizing acute and sudden events. However, resilience theory admits that continuous processes can also change the nature of a complex system. Thus, I focus on slow emergencies, those not regular, not acute emergencies, which also demand collective political or ethical response. My dissertation captures the constructive role of slow emergencies, frequently missed in disaster resilience analysis, to argue that resilience is a political process among nature, population, and governmental security techniques. The politics of resilience captures the social and cultural dimension of nature; then, nature emerges as an object of political struggles within complex, socio-ecological indeterminacy

1-Safe Petri nets and special cube complexes: equivalence and applications

Nielsen, Plotkin, and Winskel (1981) proved that every 1-safe Petri net $N$ unfolds into an event structure $\mathcal{E}_N$. By a result of Thiagarajan (1996 and 2002), these unfoldings are exactly the trace regular event structures. Thiagarajan (1996 and 2002) conjectured that regular event structures correspond exactly to trace regular event structures. In a recent paper (Chalopin and Chepoi, 2017, 2018), we disproved this conjecture, based on the striking bijection between domains of event structures, median graphs, and CAT(0) cube complexes. On the other hand, in Chalopin and Chepoi (2018) we proved that Thiagarajan's conjecture is true for regular event structures whose domains are principal filters of universal covers of (virtually) finite special cube complexes. In the current paper, we prove the converse: to any finite 1-safe Petri net $N$ one can associate a finite special cube complex ${X}_N$ such that the domain of the event structure $\mathcal{E}_N$ (obtained as the unfolding of $N$) is a principal filter of the universal cover $\widetilde{X}_N$ of $X_N$. This establishes a bijection between 1-safe Petri nets and finite special cube complexes and provides a combinatorial characterization of trace regular event structures. Using this bijection and techniques from graph theory and geometry (MSO theory of graphs, bounded treewidth, and bounded hyperbolicity) we disprove yet another conjecture by Thiagarajan (from the paper with S. Yang from 2014) that the monadic second order logic of a 1-safe Petri net is decidable if and only if its unfolding is grid-free. Our counterexample is the trace regular event structure $\mathcal{\dot E}_Z$ which arises from a virtually special square complex $\dot Z$. The domain of $\mathcal{\dot E}_Z$ is grid-free (because it is hyperbolic), but the MSO theory of the event structure $\mathcal{\dot E}_Z$ is undecidable

Can God Promise Us a New Past? A Response to Lebens and Goldschmidt

Samuel Lebens and Tyron Goldschmidt provided original theodicies, which suggest that at one time God will change the past, either by erasing/substituting the sins of humans or erasing the whole entirety of evils. Both theodicies imply the idea that God can completely change the past without leaving any traces. In this paper, I argue that Lebens’ and Goldschmidt’s preferred model, which they call the scene-changing theory, is problematic. First, its complex metaphysical foundation could be replaced with presentism (roughly, the view in the ontology of time that only present things exist) without losing any substantial heuristics. Second, their theory either implies a controversial theory of truthmaking under presentistic and hyper-presentistic ontology or implies controversial views on the counting of events under presentistic and hyper-presentistic ontology. Thirdly, I will argue that any theory of elimination/substitution of evils of the past implies that there are unnecessary evils, which is inconsistent with God’s goodness

Episodic memory, the cotemporality problem, and common sense

Direct realists about episodic memory claim that a rememberer has direct contact with a past event. But how is it possible to be acquainted with an event that ceased to exist? That’s the so-called cotemporality problem. The standard solution, proposed by Sven Bernecker, is to distinguish between the occurrence of an event and the existence of an event: an event ceases to occur without ceasing to exist. That’s the eternalist solution for the cotemporality problem. Nevertheless, some philosophers of memory claim that the adoption of an eternalist metaphysics of time would be too high a metaphysical price to be paid to hold direct realist intuitions about memory. Although I agree with these critics, I will try to show two things. First, that this kind of “common sense argument” is far from decisive. Second, that Bernecker’s proposal remains the best solution to the cotemporality problem

A counterexample to Thiagarajan's conjecture on regular event structures

We provide a counterexample to a conjecture by Thiagarajan (1996 and 2002) that regular event structures correspond exactly to event structures obtained as unfoldings of finite 1-safe Petri nets. The same counterexample is used to disprove a closely related conjecture by Badouel, Darondeau, and Raoult (1999) that domains of regular event structures with bounded $\natural$-cliques are recognizable by finite trace automata. Event structures, trace automata, and Petri nets are fundamental models in concurrency theory. There exist nice interpretations of these structures as combinatorial and geometric objects. Namely, from a graph theoretical point of view, the domains of prime event structures correspond exactly to median graphs; from a geometric point of view, these domains are in bijection with CAT(0) cube complexes. A necessary condition for both conjectures to be true is that domains of regular event structures (with bounded $\natural$-cliques) admit a regular nice labeling. To disprove these conjectures, we describe a regular event domain (with bounded $\natural$-cliques) that does not admit a regular nice labeling. Our counterexample is derived from an example by Wise (1996 and 2007) of a nonpositively curved square complex whose universal cover is a CAT(0) square complex containing a particular plane with an aperiodic tiling. We prove that other counterexamples to Thiagarajan's conjecture arise from aperiodic 4-way deterministic tile sets of Kari and Papasoglu (1999) and Lukkarila (2009). On the positive side, using breakthrough results by Agol (2013) and Haglund and Wise (2008, 2012) from geometric group theory, we prove that Thiagarajan's conjecture is true for regular event structures whose domains occur as principal filters of hyperbolic CAT(0) cube complexes which are universal covers of finite nonpositively curved cube complexes