Ergodic to Non-ergodic Behavior Transitions and Hysteresis in Ecosystem Models

A widely used concept in natural sciences is the ergodic principle stating that the temporal average state of system equals the average of single states of an ensemble of the system. Originally formulated by Boltzmann to describe the physics of an ideal gas, the ergodic principle was and still is applied in, for example, the assessment of developmental aspects of individuals, but also in the growth series concept of whole ecosystems. Hysteresis on the other hand describes the observable contrary of the ergodic principle, that is, that the current state of a system strictly depends on the individual temporal development steps, or that individual history is unequivocally important. This work will provide evidence for ergodic to non-ergodic transitions in the application of biogeochemical ecosystem models using the showcase of Congo Basin rainforests. Using a climate gradient from west to east, ergodic model behavior is shown for a virgin forest refuge, non-ergodic behavior for a current forest savannah mosaic and ergodic behavior again for large open savannahs. Additionally, the occurrence of hysteresis related to the prevailing initial vegetation will be demonstrated, whereby the non-ergodic phase along the climate gradient is shown to be more extensive if rainforest was the original vegetation, as opposed to rainforest establishing on non-forest sites. The combination of ergodic to non-ergodic transitions—sometimes referred to as catastrophic shifts in ecosystems—will be put into context with the changing distribution patterns of rainforest and savannah over the course of the Holocene

Common Factors Underlying the Five Facets of Mindfulness and Proposed Mechanisms: a Psychometric Study Among Meditators and Non-meditators

Objectives: This study investigated whether common factors underlie the established mindfulness facets, as assessed by the Five Facet Mindfulness Questionnaire (FFMQ) and some of the mechanisms, which have been previously proposed to explain the beneficial effects of mindfulness on mental health. Methods: Multigroup exploratory structural equation models (ESEM) were fitted to samples of non-meditators and meditators (total N = 3265) to (1) identify the number of factors that underlie the facets and mechanisms of mindfulness, (2) establish measurement invariance, and (3) conduct path analyses to determine the associations of extracted factors with psychological symptoms. Results: Five measurement-invariant common factors were found to underlie the mechanisms and facets of mindfulness. The FFMQ facets loaded distinctly, but none of them highest, on these common factors. The common factors represented different ways of focusing, dealing with distress, and relating towards one’s own thoughts, feelings, emotions, and body sensations. Three of the common factors appeared to specifically reflect meditation experience. The FFMQ facets accounted for less variance of depression, anxiety, somatization, and stress scores than marker scales of the five common factors, all of which derived from the proposed mechanisms. Conclusions: The common factors appear to be elements of the supporting mechanisms and psychological faculties of mindfulness. Their existence may explain the mutual interrelations between mechanisms and self-reported mindfulness but also suggests that self-reported mindfulness may not be factorially distinct from its assumed mechanisms. Longitudinal studies as well as behavioral data are needed to probe the generalizability and causality of these psychometric results

Probabilistic Spatial and Temporal Resilience Landscapes for the Congo Basin

Recent research by Hirota et al. (2011) introduced the concept of resilience landscapes for tropical forests and savannahs. Basically, the approach statistically relates the probability of current forest/savannah occurrence with the concept of tipping points, at which the ecosystem has no other choice except to switch from on stable state (e.g., forest) to its alternative stable state (e.g., savannah) or vice versa. This work will use a biogeochemical modelling approach to establish such probabilistic resilience landscapes for the Congo Basin rainforest biome. In a first step, the occurrence of tipping points will be related to climate features like annual precipitation, dry season length, occurrence of startiform non-precipitating cloud cover and the inter-annual variation in precipitation. In the second, spatial resilience landscapes for the Congo Basin will be provided using present climate conditions. Their relation to current forest/savannah distribution will be assessed and evident congruencies and discrepancies will be discussed. In a third step, the concept of temporal resilience landscapes will be developed along the patch-level life cycle dynamics of the Congo Basin rainforest biome. In a final step, the implications of results for ecosystem management decision will be assessed and possible implications on policy and land-use decisions will be presented

Legacies in Organizations.

Within some organizations, certain individuals seem to “live on” after they are gone. We often refer to these individuals as having a legacy, or a representation that endures in the collective memory of the group after their departure. In this dissertation, I examine the role of legacies in organizations, providing a deeper understanding of the selection mechanisms that determine who gets remembered in an organization’s collective memory, the mnemonics or memory aids that contribute to their endurance, and the important role they play in the life of the organization. I accomplish this goal through a qualitative study of two organizations in the early stages of merging together. My findings suggest that the selection mechanisms governing who gets remembered reflect evolutionary pressures facing the organization as a for-profit entity and as a community of members. Thus legacies are greatly influenced by one’s impact on the trajectory of the organization as well as one’s impact on relationships within the organizational community. My findings also suggest that these legacies endure in three domains within organizations: 1) cognitive space, in the form of first and second-hand memories, 2) social space in the form of communicative acts, and 3) material space in the form of material artifacts. Individual memories supply the content of legacies, and material artifacts give the legacy physical form, but the legacy is granted social life through communicative acts. As communicative acts die off, so does the social life of the legacy. My findings also suggest that legacies influence social identity processes in organizations, giving clarity to the organizational identity, providing continuity to the organizational identity, enhancing the stability of the organizational identity, and enhancing the attractiveness of the organizational identity. Finally, my findings suggest that certain legacies become institutionalized as they come to embody the identity of the organization, infusing the legacy with moral power, and enabling the legacy to have an enduring influence on the attitudes and behaviors of current members. As a whole, this study illuminates the importance of collective memory processes for organizational studies and opens new avenues for the study of organizational memory, identity and culture.PhDBusiness AdministrationUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99997/1/jsbednar_1.pd

Modeling the Emergence of Whisker Direction Maps in Rat Barrel Cortex

Based on measuring responses to rat whiskers as they are mechanically stimulated, one recent study suggests that barrel-related areas in layer 2/3 rat primary somatosensory cortex (S1) contain a pinwheel map of whisker motion directions. Because this map is reminiscent of topographic organization for visual direction in primary visual cortex (V1) of higher mammals, we asked whether the S1 pinwheels could be explained by an input-driven developmental process as is often suggested for V1. We developed a computational model to capture how whisker stimuli are conveyed to supragranular S1, and simulate lateral cortical interactions using an established self-organizing algorithm. Inputs to the model each represent the deflection of a subset of 25 whiskers as they are contacted by a moving stimulus object. The subset of deflected whiskers corresponds with the shape of the stimulus, and the deflection direction corresponds with the movement direction of the stimulus. If these two features of the inputs are correlated during the training of the model, a somatotopically aligned map of direction emerges for each whisker in S1. Predictions of the model that are immediately testable include (1) that somatotopic pinwheel maps of whisker direction exist in adult layer 2/3 barrel cortex for every large whisker on the rat's face, even peripheral whiskers; and (2) in the adult, neurons with similar directional tuning are interconnected by a network of horizontal connections, spanning distances of many whisker representations. We also propose specific experiments for testing the predictions of the model by manipulating patterns of whisker inputs experienced during early development. The results suggest that similar intracortical mechanisms guide the development of primate V1 and rat S1

Mechanical response of plectonemic DNA: an analytical solution

We consider an elastic rod model for twisted DNA in the plectonemic regime. The molecule is treated as an impenetrable tube with an effective, adjustable radius. The model is solved analytically and we derive formulas for the contact pressure, twisting moment and geometrical parameters of the supercoiled region. We apply our model to magnetic tweezer experiments of a DNA molecule subjected to a tensile force and a torque, and extract mechanical and geometrical quantities from the linear part of the experimental response curve. These reconstructed values are derived in a self-contained manner, and are found to be consistent with those available in the literature.Comment: 14 pages, 4 figure