Online Safety Nets: How Perceived Isolation Motivates Network Closure.

The feeling of being alone – and drive to vanquish that feeling – represents a common interest among theorists in communication, psychology, and sociology. Despite extensive literatures on isolation, exclusion, rejection, and loneliness, less is known about how these feelings reverberate through personal networks. Concurrently, the ascent of mobile and social technologies has generated a range of communicative possibilities that complicate our understanding of how people respond to moments of social isolation. Indeed, evolving network theories suggest that these media affordances have the potential to steer communication toward certain people and away from others. In this dissertation, I attempt to interlace this dual theoretical backdrop, integrating classic theories on the experience of social isolation with recent theories on the social implications of online affordances. I argue that perceived isolation is likely to drive people toward network closure, or what Kadushin (2012) refers to as “network safety”. I also argue that this thrust is more likely to occur in online networks that are defined by availability and awareness, such as Facebook. In order to substantiate these claims, this dissertation encompasses studies measuring online network outcomes in combination with three different versions of perceived isolation: induced exclusion (Study 1), exclusion reactivity (Study 2), and rejection sensitivity (Study 3). Altogether, the combined results indicate that feelings of isolation can shift social attention and preference toward trusted ties and core circles. Over time, these patterns suggest that people who experience more frequent and intense feelings of isolation may choose to fortify close relationships and closed communities, rather than embrace weak ties and open networks. To conclude, I contextualize the findings within other models of perceived isolation, and propose an extra component for the observed network dynamics. Expanding on this phenomenon, I theorize how certain cognitive states may operate as network switches, changing personal network motivations in a dynamic manner. With the emergence of increased availability and awareness, individuals have increased capacity to choose, and thus shift, their personal network patterns during daily life. Consequently, I call for new research on the cognitive mechanisms that underlie social network motivations, perceptions, and choices.PhDCommunication StudiesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133276/1/joebayer_1.pd

New magnetostatic modes in small nonellipsoidal magnetic particles

Magnetostatic normal modes are investigated here in elongated rods. The dipolar field resulting from the dipole-dipole interactions is calculated numerically in points of the axis connecting opposite rod face centers (\emph{central axis}) by collecting individual contributions to this field coming from each of the atomic planes perpendicular to the central axis. The applied magnetic field is assumed to be oriented along the central axis, and the magnetization to be uniform throughout the sample. The \emph{frequency} spectrum of magnetostatic waves propagating in the direction of the applied field is found numerically by solving the Landau-Lifshith equation of motion with the spatially \emph{nonhomogeneous} dipolar field taken into account; the mode amplitude \emph{profiles} are depicted as well. While energetically highest modes have \emph{bulk-extended} character, the modes forming the lower part of the spectrum are localized in the subsurface region (\emph{bulk-dead modes}). Between these two mode types, magnetostatic modes of a new type (\emph{comb modes}) are found to occur, characterized by two clearly discernible regions: a zone of fast amplitude oscillations inside the rod, and narrow slow-oscillation regions at the borders. Absorbing virtually no energy from an applied alternating field, comb modes will have no significant contribution to the magnetic noise.Comment: 16 pages, 6 figures, conferences paper: Physics of Magnetism'05, Poznan, Polan

Weak error rates for option pricing under linear rough volatility

In quantitative finance, modeling the volatility structure of underlying assets is vital to pricing options. Rough stochastic volatility models, such as the rough Bergomi model [Bayer, Friz, Gatheral, Quantitative Finance 16(6), 887-904, 2016], seek to fit observed market data based on the observation that the log-realized variance behaves like a fractional Brownian motion with small Hurst parameter, $H < 1/2$, over reasonable timescales. Both time series of asset prices and option-derived price data indicate that $H$ often takes values close to $0.1$ or less, i.e., rougher than Brownian motion. This change improves the fit to both option prices and time series of underlying asset prices while maintaining parsimoniousness. However, the non-Markovian nature of the driving fractional Brownian motion in rough volatility models poses severe challenges for theoretical and numerical analyses and for computational practice. While the explicit Euler method is known to converge to the solution of the rough Bergomi and similar models, its strong rate of convergence is only $H$. We prove rate $H + 1/2$ for the weak convergence of the Euler method for the rough Stein-Stein model, which treats the volatility as a linear function of the driving fractional Brownian motion, and, surprisingly, we prove rate one for the case of quadratic payoff functions. Our proof uses Talay-Tubaro expansions and an affine Markovian representation of the underlying and is further supported by numerical experiments. These convergence results provide a first step toward deriving weak rates for the rough Bergomi model, which treats the volatility as a nonlinear function of the driving fractional Brownian motion.Comment: 28 pages, 4 figure

The Role of Stress Resistance in Cell Transplantation Efficacy for Muscle Regeneration

Despite the regenerative capacity of skeletal muscle, chronic myopathy and muscle trauma present significant clinical problems with limited therapeutic options. Myogenic cell therapies are being actively investigated to mitigate muscle degeneration that otherwise progresses to fibrosis and long-term loss of function. The rationale for this strategy is based on augmenting the native myogenic progenitor or stem cell reserve, populated by satellite cells, by transplanting myogenic cells into the injured muscle. However, engraftment efficiency in myogenic cell transplantation is impaired by rapid cell death, which represents a precipitous loss of cell viability within 48hrs of injection, therefore severely limiting engraftment and tissue regeneration. Upon transplantation, cells experience a host response of rapid inflammation; an environment of oxidative and inflammatory stress that may cause a dramatic loss in cell viability. This effect may determine the regeneration capacity irrespective of the cell's multilineage differentiation potential. Our lab has isolated and characterized multiple populations of myogenic progenitors from murine and human skeletal muscle, including the muscle derived stem cell (MDSC) isolated by a modified preplate technique. In our studies of MDSCs, we observed an increase in post-transplantation survival and skeletal muscle regeneration capacity over that of early preplate myoblasts. Furthermore, a strong correlation of improved survival and regeneration with inflammatory and oxidative stress resistance emerged. In this dissertation, we examined the role stress resistance and survival during myogenic differentiation of MDSCs. By treating the transplanted cells with a membrane permeable reactive oxygen species scavenger, XJB-5-131, prior to transplantation, the survival and myogenic differentiation capacity under stress conditions was significantly improved. Furthermore, we isolated a novel sub-population of muscle derived cells with elevated stress resistance from murine and human skeletal muscle by their enhanced aldehyde dehydrogenase activity. ALDHlo and ALDHhi cells were characterized in terms of their myogenic potential and stress tolerance in vitro and muscle regeneration capacity in vivo. These studies are aimed at understanding the importance of survival and stress tolerance of transplanted cells in skeletal muscle cell therapy and how this tolerance modifies the efficacy of cell therapy

Development of the Precerebellar Nuclei in the Rat: 11. The Intramural Olivary Migratory Stream and the Neurogenetic Organization of the Inferior Olive

ABSTRACT Sequential thymidine radiograms from rats labeled on days E l 3 and E14, and killed at daily intervals thereafter, were analyzed to trace the migratory route and settling pattern of neurons of the inferior olive. Longsurvival thymidine radiograms from perinatal rats injected on day El4 were used to subdivide the inferior olivary complex on the basis of neurogentic criteria. The inferior olivary neurons originate on days E l 3 and El4 in the primary precerebellar neuroepithelium. The olivary neurons labeled on day El4 (the late generated components) translocate into the inferior olivary premigratory zone on day E15. On day El6 these cells join the olivary migratory stream, which follows an intramural circumferential path between the gray and white matters of the medulla. By day El7 the olivary migratory stream is reduced to a small band near the corpus of the inferior olive, which has been settled by this time by neurons generated on day E13. As a result, the unlabeled cells are situated on day El7 dorsomedially and the labeled cells ventrolaterally. The regional segregation of neurons forming subdivisions of the inferior olive begins on day E18, and by day E l 9 the major subdivisions are all recognizable. In thymidine radiograms from perinatal rats injected on day E14, four neurogenetic components can be distinguished in the inferior olive, those composed: (1) of unlabeled cells (generated on day E13), (2) of predominantly unlabeled cells, (3) of predominantly labeled cells (generated on day E14), and (4) of labeled cells. By combining these neurogenetic differences with the morphological features of the inferior olivary complex, we propose a modification of the currently accepted classification. The four major divisions of the inferior olive are the successively produced posterodorsal olive, anterolateral (principal) olive, posteroventral olive, and anteroventral olive. The location and configuration of these divisions are illustrated in relation to the traditional classification both in the coronal and the sagittal plane. Key words: cell migration, neurogenesis, thymidine autoradiography According to His (1891), the neurons of the human infe-olive. He inferred that the two were interconnected by a rior olive originate in the rhombic lip (Rautenlippe) and helleres Mittelstiick (a lighter midportion; His, 1891) consistmigrate ventromedially during the second and third months ing of bands of migrating cells. The brief descriptions by of embryonic life by way of the olivary stream (Olivenstrei-His and single illustration (His, 1891

Embryonic Development of the Rat Cerebellum. 11. Translocation and Regional Distribution of the Deep Neurons

ABSTRACT In thymidine radiograms and plastic-embedded sections, the migration of cerebellar deep neurons was traced from their germinal source to their final settling sites. The route proved to be roundabout and three developmental events could be distinguished during the process. First, between days El4 and E16, transversely oriented cells of the nuclear transitory zone move in an arc from the ventrolateral neuroepithelium of the lateral cerebellar primordium in a medial direction. Second, between days El6 and E18, the cells of the rostral component of the nuclear transitory zone assume a longitudinal orientation. We postulated that this is the period of axonogenesis, the longitudinally oriented cells issuing efferents that join the superior cerebellar peduncle ipsilaterally and the transversely oriented cells (representing the neurons of the caudal fastigial nucleus) sending decussating fibers to the uncinate fasciculus (the hook bundle of Russell). Third, between days E l 8 and E21, the earlier-produced superficial cells of the nuclear transitory zone and the later-produced deep cells of the cortical transitory zone (the young Purkinje cells) exchange positions. The descent of the deep neurons is in the direction of the fibers of the inferior cerebellar peduncle, which becomes distributed throughout the cerebellum on day E17. The ascent of the Purkinje cells is in the direction of the external germinal layer, which begins to spread from caudal to rostral on day E17. The three deep nuclei, the lateral (dentate), interpositus, and medial (fastigial), can be distinguished before their descent into the depth of the cerebellum, and by day E22 a small-celled and a large-celled subdivision is identifiable in each nucleus

Who Likes to be Reachable? Availability Preferences, Weak Ties, and Bridging Social Capital

In this paper, we investigate how individual differences in availability preferences are related to (1) self-reported quality of interaction with strong and weak ties and (2) perceptions of bridging social capital. We employed experience sampling methods and collected data over the course of two weeks—combined with surveys at baseline and endpoint, from a random sample of college students (N = 154). We show that individuals who prefer to be more available to others report more rewarding interactions with weak ties. Furthermore, we demonstrate how the quality of weak tie interactions mediates a positive relationship between availability preferences and bridging social capital. We conclude by discussing the relationships between availability, interaction quality, and bridging social capital. We propose availability preferences as a key construct to be considered in future research

Metabolic changes associated with adaptive resistance to daptomycin in Streptococcus mitis-oralis

Background: Viridans group streptococci of the Streptococcus mitis-oralis subgroup are important endovascular pathogens. They can rapidly develop high-level and durable non-susceptibility to daptomycin both in vitro and in vivo upon exposure to daptomycin. Two consistent genetic adaptations associated with this phenotype (i.e., mutations in cdsA and pgsA) lead to the depletion of the phospholipids, phosphatidylglycerol and cardiolipin, from the bacterial membrane. Such alterations in phospholipid biosynthesis will modify carbon flow and change the bacterial metabolic status. To determine the metabolic differences between daptomycin-susceptible and non- susceptible bacteria, the physiology and metabolomes of S. mitis-oralis strains 351 (daptomycin-susceptible) and 351-D10 (daptomycin non-susceptible) were analyzed. S. mitis-oralis strain 351-D10 was made daptomycin non- susceptible through serial passage in the presence of daptomycin. Background: Viridans group streptococci of the Streptococcus mitis-oralis subgroup are important endovascular pathogens. They can rapidly develop high-level and durable non-susceptibility to daptomycin both in vitro and in vivo upon exposure to daptomycin. Two consistent genetic adaptations associated with this phenotype (i.e., mutations in cdsA and pgsA) lead to the depletion of the phospholipids, phosphatidylglycerol and cardiolipin, from the bacterial membrane. Such alterations in phospholipid biosynthesis will modify carbon flow and change the bacterial metabolic status. To determine the metabolic differences between daptomycin-susceptible and non- susceptible bacteria, the physiology and metabolomes of S. mitis-oralis strains 351 (daptomycin-susceptible) and 351-D10 (daptomycin non-susceptible) were analyzed. S. mitis-oralis strain 351-D10 was made daptomycin non- susceptible through serial passage in the presence of daptomycin. Conclusions: S. mitis-oralis metabolism is altered in daptomycin non-susceptible bacteria relative to the daptomycin susceptible parent strain. As demonstrated in Staphylococcus aureus, inhibiting the metabolic changes that facilitate the transition from a daptomycin susceptible state to a non-susceptible one, inhibits daptomycin non- susceptibility. By preventing these metabolic adaptations in S. mitis-oralis, it should be possible to deter the formation of daptomycin non-susceptibility

Non-invasive fractional flow reserve (FFRCT) in the evaluation of acute chest pain ? Concepts and first experiences

Objective: To evaluate 30 day rate of major adverse cardiac events (MACE) utilizing cCTA and FFRCT for evaluation of patients presenting to the Emergency Department (ED) with acute chest pain. Materials and methods: Patients between the ages of 18?95 years who underwent clinically indicated cCTA and FFRCT in the evaluation of acute chest pain in the emergency department were retrospectively evaluated for 30 day MACE, repeat presentation/admission for chest pain, revascularization, and additional testing. Results: A total of 59 patients underwent CCTA and subsequent FFRCT for the evaluation of acute chest pain in the ED over the enrollment period. 32 out of 59 patients (54 %) had negative FFRCT (>0.80) out of whom 18 patients (55 %) were discharged from the ED. Out of the 32 patients without functionally significant CAD by FFRCT, 32 patients (100 %) underwent no revascularization and 32 patients (100 %) had no MACE at the 30-day follow-up period. Conclusion: In this limited retrospective study, patients presenting to the ED with acute chest pain and with CCTA with subsequent FFRCT of >0.8 had no MACE at 30 days; however, for many of these patients results were not available at time of clinical decision making by the ED physician

\u3ci\u3eStaphylococcus aureus\u3c/i\u3e Metabolic Adaptations during the Transition from a Daptomycin Susceptibility Phenotype to a Daptomycin Nonsusceptibility Phenotype

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections. The success of S. aureus as a pathogen is due in part to its many virulence determinants and resistance to antimicrobials. In particular, methicillin-resistant S. aureus has emerged as a major cause of infections and led to increased use of the antibiotics vancomycin and daptomycin, which has increased the isolation of vancomycin-intermediate S. aureus and daptomycin-nonsusceptible S. aureus strains. The most common mechanism by which S. aureus acquires intermediate resistance to antibiotics is by adapting its physiology and metabolism to permit growth in the presence of these antibiotics, a process known as adaptive resistance. To better understand the physiological and metabolic changes associated with adaptive resistance, six daptomycin-susceptible and -nonsusceptible isogenic strain pairs were examined for changes in growth, competitive fitness, and metabolic alterations. Interestingly, daptomycin nonsusceptibility coincides with a slightly delayed transition to the postexponential growth phase and alterations in metabolism. Specifically, daptomycin-nonsusceptible strains have decreased tricarboxylic acid cycle activity, which correlates with increased synthesis of pyrimidines and purines and increased carbon flow to pathways associated with wall teichoic acid and peptidoglycan biosynthesis. Importantly, these data provided an opportunity to alter the daptomycin nonsusceptibility phenotype by manipulating bacterial metabolism, a first step in developing compounds that target metabolic pathways that can be used in combination with daptomycin to reduce treatment failures