Exact two-dimensionalization of low-magnetic-Reynolds-number flows subject to a strong magnetic field

We investigate the behavior of flows, including turbulent flows, driven by a horizontal body-force and subject to a vertical magnetic field, with the following question in mind: for very strong applied magnetic field, is the flow mostly two-dimensional, with remaining weak three-dimensional fluctuations, or does it become exactly 2D, with no dependence along the vertical? We first focus on the quasi-static approximation, i.e. the asymptotic limit of vanishing magnetic Reynolds number Rm << 1: we prove that the flow becomes exactly 2D asymptotically in time, regardless of the initial condition and provided the interaction parameter N is larger than a threshold value. We call this property "absolute two-dimensionalization": the attractor of the system is necessarily a (possibly turbulent) 2D flow. We then consider the full-magnetohydrodynamic equations and we prove that, for low enough Rm and large enough N, the flow becomes exactly two-dimensional in the long-time limit provided the initial vertically-dependent perturbations are infinitesimal. We call this phenomenon "linear two-dimensionalization": the (possibly turbulent) 2D flow is an attractor of the dynamics, but it is not necessarily the only attractor of the system. Some 3D attractors may also exist and be attained for strong enough initial 3D perturbations. These results shed some light on the existence of a dissipation anomaly for magnetohydrodynamic flows subject to a strong external magnetic field.Comment: Journal of Fluid Mechanics, in pres

Refraction of swell by surface currents

Using recordings of swell from pitch-and-roll buoys, we have reproduced the classic observations of long-range surface wave propagation originally made by Munk et al. (1963) using a triangular array of bottom pressure measurements. In the modern data, the direction of the incoming swell fluctuates by about $\pm 10^\circ$ on a time scale of one hour. But if the incoming direction is averaged over the duration of an event then, in contrast with the observations by Munk et al. (1963), the sources inferred by great-circle backtracking are most often in good agreement with the location of large storms on weather maps of the Southern Ocean. However there are a few puzzling failures of great-circle backtracking e.g., in one case, the direct great-circle route is blocked by the Tuamoto Islands and the inferred source falls on New Zealand. Mirages like this occur more frequently in the bottom-pressure observations of Munk et al. (1963), where several inferred sources fell on the Antarctic continent. Using spherical ray tracing we investigate the hypothesis that the refraction of waves by surface currents produces the mirages. With reconstructions of surface currents inferred from satellite altimetry, we show that mesoscale vorticity significantly deflects swell away from great-circle propagation so that the source and receiver are connected by a bundle of many rays, none of which precisely follow a great circle. The $\pm 10^\circ$ directional fluctuations at the receiver result from the arrival of wave packets that have travelled along the different rays within this multipath. The occasional failure of great-circle backtracking, and the associated mirages, probably results from partial topographic obstruction of the multipath, which biases the directional average at the receiver.Comment: Journal of Marine Research, in pres

The experience of ICU nurses working on the frontline during the COVID-19 pandemic

The impact that COVID-19 is having on the worldwide population has been made clear by the emerging literature on the ongoing COVID-19 pandemic, which links it to a broader idea of collective trauma. However, its implications on the healthcare system are particularly significant, considering that the National Health System was already in decline before the pandemic due to persistent underfunding and, as a result, a shortage of staff. Literature on previous pandemics and more recent literature on the COVID-19 outbreak have both drawn attention to the considerable hardships that pandemics impose on frontline workers. Questions about the experience of ICU nurses working on the frontline during the COVID-19 outbreak arise in light of this multi-layered context. This question is being investigated in the current study adopting a hermeneutic phenomenological approach in order to explore participants' relationships to the world and their lived experiences related to this specific phenomenon. Semi-structured interviews were conducted with six senior registered nurses who worked on the frontline as ICU nurses from the start of the pandemic in March 2020 to July 2020. Interviews were transcribed and analysed using Interpretative Phenomenological Analysis (IPA). Four Group Experiential Themes have emerged from the data: ““SURREAL” INSIDE AND OUTSIDE HOSPITALS”, “DOING (VERSUS BEING): THE ADAPTATION TO THE COVID REALITY”, “BYSTANDER: DISAPPOINTMENT WITH THE GOVERNMENT AND THE PUBLIC” and “EMOTIONAL DETACHMENT AS COPING SRATEGY”. As per the methodological underpinning, emphasis has been placed on reflexive awareness. The study seeks to contribute to a new perspective on the topic, integrating literature from Counselling Psychology, Social Justice, and the Power-Threat Meaning Framework (Johnstone & Boyle, 2020)

A study of the personality characteristics, interests, and abilities of Boston University freshman women students in residence in relation to their choice of professional school or college

Thesis (Ed.M.)--Boston Universit

Spacelab Data Processing Facility (SLDPF) quality assurance expert systems development

The Spacelab Data Processing Facility (SLDPF) is an integral part of the Space Shuttle data network for missions that involve attached scientific payloads. Expert system prototypes were developed to aid in the performance of the quality assurance function of the Spacelab and/or Attached Shuttle Payloads processed telemetry data. The Spacelab Input Processing System (SIPS) and the Spacelab Output Processing System (SOPS), two expert systems, were developed to determine their feasibility and potential in the quality assurance of processed telemetry data. The capabilities and performance of these systems are discussed

Food Demand Projections Using Full Demand Systems

Disaggregated food demand projections for developing countries, although essential for improved development planning and effective policy making, are rare. Moreover food demand projection models are usually based on aggregated, national-level data. In this article, under conditions of weak separability and multistage budgeting decisions, a structural model capable fo generating regional-level food demand projections for a disaggregated set of commodities is developed and estimated using data from an Indonesian expenditure survey. Regional food demand projections in Indonesia obtain under a scenario assuming constant real prices are then combines into national-level estimates.

Regional unemployment and productivity in Europe

We analyze the relationship between regional unemployment and labour productivity in Europe, basing our empirical analysis on the predictions of a Neary-type General Oligopolistic Equilibrium trade model with efficiency-wages. Using semiparametric and dynamic panel data estimators and controlling for other factors, we give evidence of a nonlinear relationship between productivity and regional unemployment in Europe: with a level of productivity smaller than a certain threshold, this relationship is negative, while no relation occurs in the case of higher productivity regions. This evidence proves an important role of a wage-floor (induced by efficiency wages and exacerbated by institutional factors) under which the productivity gap cannot be compensated by a wage gap

Destabilizing Taylor-Couette flow with suction

We consider the effect of radial fluid injection and suction on Taylor-Couette flow. Injection at the outer cylinder and suction at the inner cylinder generally results in a linearly unstable steady spiralling flow, even for cylindrical shears that are linearly stable in the absence of a radial flux. We study nonlinear aspects of the unstable motions with the energy stability method. Our results, though specialized, may have implications for drag reduction by suction, accretion in astrophysical disks, and perhaps even in the flow in the earth's polar vortex.Comment: 34 pages, 9 figure

Semaphorin 4D Promotes Skeletal Metastasis in Breast Cancer.

Bone density is controlled by interactions between osteoclasts, which resorb bone, and osteoblasts, which deposit it. The semaphorins and their receptors, the plexins, originally shown to function in the immune system and to provide chemotactic cues for axon guidance, are now known to play a role in this process as well. Emerging data have identified Semaphorin 4D (Sema4D) as a product of osteoclasts acting through its receptor Plexin-B1 on osteoblasts to inhibit their function, tipping the balance of bone homeostasis in favor of resorption. Breast cancers and other epithelial malignancies overexpress Sema4D, so we theorized that tumor cells could be exploiting this pathway to establish lytic skeletal metastases. Here, we use measurements of osteoblast and osteoclast differentiation and function in vitro and a mouse model of skeletal metastasis to demonstrate that both soluble Sema4D and protein produced by the breast cancer cell line MDA-MB-231 inhibits differentiation of MC3T3 cells, an osteoblast cell line, and their ability to form mineralized tissues, while Sema4D-mediated induction of IL-8 and LIX/CXCL5, the murine homologue of IL-8, increases osteoclast numbers and activity. We also observe a decrease in the number of bone metastases in mice injected with MDA-MB-231 cells when Sema4D is silenced by RNA interference. These results are significant because treatments directed at suppression of skeletal metastases in bone-homing malignancies usually work by arresting bone remodeling, potentially leading to skeletal fragility, a significant problem in patient management. Targeting Sema4D in these cancers would not affect bone remodeling and therefore could elicit an improved therapeutic result without the debilitating side effects

Economic Equity and the Food Stamp Program

The Thrifty Food Plan (TFP) is used to estimate the household food cost used for determining benefits for participants in the food stamp program. Dietary norms and requirements for macro and micronutrients are reflected in the TFP. Because the TFP is important in calculating benefit levels for FSP participants, it has received broad attention in policy debate. The present analysis shows that household food costs quite similar to those from the TFP can be calculated directly from available USDA Nationwide Food Consumption Survey data. The method developed and applied is simpler and more specialized to household by size and composition than the TFP. Also, it does not use dietary requirements. The new approach has a sound foundation in economics and could result in a more equitable distribution of food stamp program benefits