Architecture As Gateway: A Cultural Center in Annapolis, Maryland

I contend that a gateway can be created to link the two polar conditions without necessarily creating a physical passageway from one condition to the other, but by creating a link between past and present; A link between humanity and nature; a link between ignorance and understanding

Experimental evidence for tipping points in social convention

Theoretical models of critical mass have shown how minority groups can initiate social change dynamics in the emergence of new social conventions. Here we study an artificial system of social conventions in which human subjects interact to establish a new coordination equilibrium. The findings provide direct empirical demonstration of the existence of a tipping point in the dynamics of changing social conventions. When minority groups reached the critical mass –that is, the critical group size for initiating social change –they were consistently able to overturn the established behavior. The size of the required critical mass is expected to vary based on theoretically identifiable features of a social setting. Our results show that the theoretically predicted dynamics of critical mass do in fact emerge as expected within an empirical system of social coordination

A Multi Level Multi Domain Method for Particle In Cell Plasma Simulations

A novel adaptive technique for electromagnetic Particle In Cell (PIC) plasma simulations is presented here. Two main issues are identified in designing adaptive techniques for PIC simulation: first, the choice of the size of the particle shape function in progressively refined grids, with the need to avoid the exertion of self-forces on particles, and, second, the necessity to comply with the strict stability constraints of the explicit PIC algorithm. The adaptive implementation presented responds to these demands with the introduction of a Multi Level Multi Domain (MLMD) system (where a cloud of self-similar domains is fully simulated with both fields and particles) and the use of an Implicit Moment PIC method as baseline algorithm for the adaptive evolution. Information is exchanged between the levels with the projection of the field information from the refined to the coarser levels and the interpolation of the boundary conditions for the refined levels from the coarser level fields. Particles are bound to their level of origin and are prevented from transitioning to coarser levels, but are repopulated at the refined grid boundaries with a splitting technique. The presented algorithm is tested against a series of simulation challenges

Hydraulics and heat transfer in the IFMIF liquid lithium target: CFD calculations

CFD (Computational fluid dynamics) calculation turns out to be a good approximation to the real behavior of the lithium (Li) flow of the target of the international fusion materials irradiation facility (IFMIF). A three-dimensional (3D) modelling of the IFMIF design Li target assembly, made with the CFD commercial code ANSYS-FLUENT has been carried out. The simulation by a structural mesh is focused on the thermal-hydraulic analysis inside the Li jet flow. For, this purpose, the two deuteron beams energy deposition profile is modelled as an energy source term inside the volume of liquid affected. Turbulence is estimated using the RNG k– model, and a surface-tracking technique applied to a fixed Eulerian mesh called volume of fluid (VOF) is used to determine the position of the free surface. Calculations varying the jet velocity from a range of 10–20 m/s, show that maximum calculated temperatures are still below the lithium's boiling point, due to the increase of the pressure induced by centrifugal forc

An Unsplit Godunov Method for Ideal MHD via Constrained Transport in Three Dimensions

We present a single step, second-order accurate Godunov scheme for ideal MHD which is an extension of the method described by Gardiner & Stone (2005) to three dimensions. This algorithm combines the corner transport upwind (CTU) method of Colella for multidimensional integration, and the constrained transport (CT) algorithm for preserving the divergence-free constraint on the magnetic field. We describe the calculation of the PPM interface states for 3D ideal MHD which must include multidimensional ``MHD source terms'' and naturally respect the balance implicit in these terms by the ${\bf\nabla\cdot B}=0$ condition. We compare two different forms for the CTU integration algorithm which require either 6- or 12-solutions of the Riemann problem per cell per time-step, and present a detailed description of the 6-solve algorithm. Finally, we present solutions for test problems to demonstrate the accuracy and robustness of the algorithm.Comment: Extended version of the paper accepted for publication in JC

Respiratory Health of 985 Children Exposed to the World Trade Center Disaster: Report on World Trade Center Health Registry Wave 2 Follow-up, 2007–2008

Background. The World Trade Center (WTC) disaster of September 11, 2001, has been associated with early respiratory problems including asthma in workers, residents, and children. Studies on adults have documented persistence of longer term, 9/11-related respiratory symptoms. There are no comparable reports on children. Methods. We surveyed 985 children aged 5–17 years who enrolled in the WTC Health Registry in 2003–04, and who were re-surveyed in 2007–08. Health data were provided by parents in both surveys and focused on respiratory symptoms suggestive of reactive airway impairment (wheezing or the combination of cough and shortness of breath) in the preceding 12 months. At follow-up, adolescents aged 11–17 years completed separate surveys that screened for post-traumatic stress symptoms and behavior problems (Strengths and Difficulties Questionnaire, SDQ). Associations between respiratory symptoms in the prior 12 months with 9/11 exposures and behavioral outcomes were evaluated with univariate and multivariate methods. Results. Of the 985 children, 142 (14.4%) children reported respiratory symptoms in the prior 12 months; 105 (73.9%) children with respiratory symptoms had previously been diagnosed with asthma. Among children aged 5–10 years, respiratory symptoms were significantly elevated among African-Americans (adjusted odds ratio, (aOR) 3.8; 95% confidence interval (CI) 1.2–11.5) and those with household income below $75,000 (aOR 1.9; CI 1.0–3.7), and was more than twice as great in children with dust cloud exposure (aOR 2.2; CI 1.2–3.9). Among adolescents aged 11–17 years, respiratory symptoms were significantly associated with household income below$75,000 (aOR 2.4; CI 1.2–4.6), and with a borderline or abnormal SDQ score (aOR 2.7, 95% CI 1.4–5.2). Symptoms were reported more than twice as often by adolescents with vs. without dust cloud exposure (24.8% vs. 11.5%) but the adjusted odds ratio was not statistically significant (aOR 1.7; CI 0.9–3.2). Conclusions. Most Registry children exposed to the 9/11 disaster in New York City reported few respiratory problems. Respiratory symptoms were associated with 9/11 exposures in younger children and with behavioral difficulties in adolescents. Our findings support the need for continued surveillance of 9/11 affected children as they reach adolescence and young adulthood, and for awareness of both physical and behavioral difficulties by treating clinicians

Investigation of transition frequencies of two acoustically coupled bubbles using a direct numerical simulation technique

The theoretical results regarding the ``transition frequencies'' of two acoustically interacting bubbles have been verified numerically. The theory provided by Ida [Phys. Lett. A 297 (2002) 210] predicted the existence of three transition frequencies per bubble, each of which has the phase difference of $\pi /2$ between a bubble's pulsation and the external sound field, while previous theories predicted only two natural frequencies which cause such phase shifts. Namely, two of the three transition frequencies correspond to the natural frequencies, while the remaining does not. In a subsequent paper [M. Ida, Phys. Rev. E 67 (2003) 056617], it was shown theoretically that transition frequencies other than the natural frequencies may cause the sign reversal of the secondary Bjerknes force acting between pulsating bubbles. In the present study, we employ a direct numerical simulation technique that uses the compressible Navier-Stokes equations with a surface-tension term as the governing equations to investigate the transition frequencies of two coupled bubbles by observing their pulsation amplitudes and directions of translational motion, both of which change as the driving frequency changes. The numerical results reproduce the recent theoretical predictions, validating the existence of the transition frequencies not corresponding to the natural frequency.Comment: 18 pages, 8 figures, in pres

Second Order Accurate Schemes for Magnetohydrodynamics With Divergence-Free Reconstruction

In this paper we study the problem of divergence-free numerical MHD and show that the work done so far still has four key unresolved issues. We resolve those issues in this paper. The problem of reconstructing MHD flow variables with spatially second order accuracy is also studied. The other goal of this paper is to show that the same well-designed second order accurate schemes can be formulated for more complex geometries such as cylindrical and spherical geometry. Being able to do divergence-free reconstruction in those geometries also resolves the problem of doing AMR in those geometries. The resulting MHD scheme has been implemented in Balsara's RIEMANN framework for parallel, self-adaptive computational astrophysics. The present work also shows that divergence-free reconstruction and the divergence-free time-update can be done for numerical MHD on unstructured meshes. All the schemes designed here are shown to be second order accurate. Several stringent test problems are presented to show that the methods work, including problems involving high velocity flows in low plasma-b magnetospheric environments.Comment: 85 pages, 6 figure