Multifrequency spin resonance in diamond

Magnetic resonance techniques provide a powerful tool for controlling spin systems, with applications ranging from quantum information processing to medical imaging. Nevertheless, the behavior of a spin system under strong excitation remains a rich dynamical problem. In this paper, we examine spin resonance of the nitrogen-vacancy center in diamond under conditions outside the regime where the usual rotating wave approximation applies, focusing on effects of multifrequency excitation and excitation with orientation parallel to the spin quantization axis. Strong-field phenomena such as multiphoton transitions and coherent destruction of tunneling are observed in the spectra and analyzed via numerical and analytic theory. In addition to illustrating the response of a spin system to strong multifrequency excitation, these observations may inform techniques for manipulating electron-nuclear spin quantum registers

Reimaginging Learning: A Big Bet on the Future of American Education

Today's young people are the most diverse, connected generation in history and have incredible aspirations for themselves. Educators all over the country are reimagining learning to better meet this generation's needs, rethinking classrooms and schools so they work better for students. It's an exciting time for innovation in education.At the same time, big bets are an increasingly popular concept in philanthropy. Several articles and papers in the last year have encouraged donors to consider them as a way of creating meaningful change, including in education. Big bets are usually defined as large grants to a specific issue or an individual organization.We're proposing something different.We've been working with partners across the country who are pursuing a common vision: reimagining learning with a broad set of outcomes in mind, so that every student finishes high school with an abundance of choices and the freedom to pursue them. Philanthropists have an opportunity to make a big bet on this shared vision.Most schools weren't designed with this vision in mind. But right now, all over the country, teams of educators are working to change this. They are partnering with families to create schools that speak to their hopes and honor their strengths. These schools prioritize rigorous academics and help students develop critical thinking skills, set important goals and create plans to reach them, and develop the mindsets and habits they need to take charge of their futures.Through deep engagement with our partners, we've thought concretely about how these ideas might spread and where existing momentum and early evidence might shine a light on a path forward. In September 2015, with our partners Summit Public Schools and Transcend, we released a paper entitled Dissatisfied Yet Optimistic (DYO), which made the case for reimagining learning. This new companion piece explores what it might take to strengthen and accelerate the momentum created by the early pioneers who are designing schools consistent with the ideas in DYO.What follows is a big idea for how $4 billion in philanthropy over 10 years could dramatically improve the performance of our schools by focusing on this emerging vision for how schools could produce much better and broader outcomes for students

Stirring by swimming bodies

We consider the stirring of an inviscid fluid caused by the locomotion of bodies through it. The swimmers are approximated by non-interacting cylinders or spheres moving steadily along straight lines. We find the displacement of fluid particles caused by the nearby passage of a swimmer as a function of an impact parameter. We use this to compute the effective diffusion coefficient from the random walk of a fluid particle under the influence of a distribution of swimming bodies. We compare with the results of simulations. For typical sizes, densities and swimming velocities of schools of krill, the effective diffusivity in this model is five times the thermal diffusivity. However, we estimate that viscosity increases this value by two orders of magnitude.Comment: 5 pages, 5 figures. PDFLaTeX with RevTeX 4 macros. Final versio

Parametric Analysis Using the Finite Element Method to Investigate Prosthetic Interface Stresses for Persons with Trans-tibial Amputation

A finite element (FE) model of the below-knee residual limb and prosthetic socket was created to investigate the effects of parameter variations on the interface stress distribution during static stance. This model was based upon geometric approximations of anthropometric residual limb geometry. The model was not specific to an individual with amputation, but could be scaled to approximate the limb of a particular subject. Parametric analyses were conducted to investigate the effects of prosthetic socket design and residual limb geometry on the residual limb/prosthetic socket interface stresses. Behavioral trends were illustrated via sensitivity analysis. The results of the parametric analyses indicate that the residual limb/prosthetic socket interface stresses are affected by variations in both prosthetic design and residual limb geometry. Specifically, the analyses indicate : 1) the residual limb/prosthetic liner interface pressures are relatively insensitive to the socket stiffness ; 2) the stiffness of the prosthetic liner influences the interface stress distribution for both the unrectified and patellar-tendon-bearing (PTB) rectified models-- the external load state appears to influence the interface pressure distribution, while the prosthetic socket rectification appears to influence the interface shear stress distribution ; 3) the interface pressures are - very sensitive to the prosthetic rectification ; 4) the shape and relative bulk of soft tissue may significantly influence the interface pressure distribution ; 5) the interface pressure distribution is also influenced by the residual limb length; and 6) the stiffness/compliance of the residual limb soft tissues may significantly alter the interface pressure distribution

The evolving scholarly record

This report presents a framework to help organize and drive discussions about the evolving scholarly record. The framework provides a high-level view of the categories of material the scholarly record potentially encompasses, as well as the key stakeholder roles associated with the creation, management, and use of the scholarly record. Key highlights: A confluence of trends is accelerating changes to the scholarly record\u27s content and stakeholder roles. Scholarly outcomes are contextualized by materials generated in the process and aftermath of scholarly inquiry. The research process generates materials covering methods employed, evidence used, and formative discussion. The research aftermath generates materials covering discussion, revision, and reuse of scholarly outcomes. The scholarly record is evolving to have greater emphasis on collecting and curating context of scholarly inquiry. The scholarly record’s stakeholder ecosystem encompasses four key roles: create, fix, collect, and use. The stakeholder ecosystem supports thinking about how roles are reconfigured as the scholarly record evolves. The ways and means of scholarly inquiry are experiencing fundamental change, with consequences for scholarly communication and ultimately, the scholarly record. The boundaries of the scholarly record are both expanding and blurring, driven by changes in research practices, as well as changing perceptions of the long-term value of certain forms of scholarly materials. Understanding the nature, scope, and evolutionary trends of the scholarly record is an important concern in many quarters—for libraries, for publishers, for funders, and of course for scholars themselves. Many issues are intrinsic to the scholarly record, such as preservation, citation, replicability, provenance, and data curation. The conceptualization of the scholarly record and its stakeholder ecosystem provided in the report can serve as a common point of reference in discussions within and across domains, and help cultivate the shared understanding and collaborative relationships needed to identify, collect, and make accessible the wide range of materials the scholarly record is evolving to include

Generic, Geometric Finite Element Analysis of the Transtibial Residual Limb and Prosthetic Socket

Finite element analysis was used to investigate the stress distribution between the residual limb and prosthetic socket of persons with transtibial amputation (TTA). The purpose of this study was to develop a tool to provide a quantitative estimate of prosthetic interface pressures to improve our understanding of residual limb/prosthetic socket biomechanics and prosthetic fit. FE models of the residual limb and prosthetic socket were created. In contrast to previous FE models of the prosthetic socket/residual limb system, these models were not based on the geometry of a particular individual, but instead were based on a generic, geometric approximation of the residual limb. These models could then be scaled for the limbs of specific individuals. The material properties of the bulk soft tissues of the residual limb were based upon local in vivo indentor studies. Significant effort was devoted toward the validation of these generic, geometric FE models; prosthetic interface pressures estimated via the FE model were compared to experimentally determined interface pressures for several persons with TTA in a variety of socket designs and static load/alignment states. The FE normal stresses were of the same order of magnitude as the measured stresses (0-200 kPa); however, significant differences in the stress distribution were observed. Although the generic, geometric FE models do not appear to accurately predict the stress distribution for specific subjects, the models have practical applications in comparative stress distribution studies

A prospectus for a theory of variable variability

It is proposed that the kind of stellar variability exhibited by the Sun in its magnetic activity cycle should be considered as a prototype of a class of stellar variability. The signature includes long 'periods' (compared to that of the radial fundamental model), erratic behavior, and intermittency. As other phenomena in the same variability class we nominate the liminosity fluctuations of ZZ Ceti stars and the solar 160 m oscillation. We discuss the possibility that analogous physical mechanisms are at work in all these cases, namely instabilities driven in a thin layer. These instabilities should be favorable to grave modes (in angle) and should arise in conditions that may allow more than one kind of instability to occur at once. The interaction of these competing instabilities produces complicated temporal variations. Given suitable idealizations, it is shown how to begin to compute solutions of small, but finite, amplitude

Lagrangian coherent structures in nonlinear dynamos

Turbulence and chaos play a fundamental role in stellar convective zones through the transportof particles, energy and momentum, and in fast dynamos, through the stretching, twisting and folding of magnetic flux tubes. A particularly revealing way to describe turbulent motions is through the analysis of Lagrangian coherent structures (LCS), which are material lines or surfaces that act as transport barriers in the fluid. We report the detection of Lagrangian coherent structures in helical MHD dynamo simulations with scale separation. In an ABC--flow, two dynamo regimes, a propagating coherent mean--field regime and an intermittent regime, are identified as the magnetic diffusivity is varied. The sharp contrast between the chaotic tangle of attracting and repelling LCS in both regimes permits a unique analysis of the impact of the magnetic field on the velocity field. In a second example, LCS reveal the link between the level of chaotic mixing of the velocity field and the saturation of a large--scale dynamo when the magnetic field exceeds the equipartition value