Preserving Film Preservation in the Digital Era

This paper explores the current controversies surrounding film preservation in the digital era. Questions address the benefits of new technologies and the potential sacrifices to a film\u27s authenticity and designation as a valued historical, social, and cultural artifact. Issues examined include film\u27s frail format, archives\u27s financial and storage limitations, the concept of the original film, and how current digitization methods affect each of these areas. This paper addresses the recent restorations of two particular films—Fritz Lang\u27s Metropolis (1927) and Alfred Hitchcock\u27s Vertigo (1958)—and concludes that digital technologies are not stable enough to replace traditional preservation methods, but they can greatly increase exposure to lesser-known films and support the general preservation of film

Laying a Solid Foundation: Strategies for Effective Program Replication

With limited funds available for social investment, policymakers and philanthropists are naturally interested in supporting programs with the greatest chance of effectiveness and the ability to benefit the largest number of people. When a program rises to the fore with strong, proven results, it makes sense to ask whether that success can be reproduced in new settings.Program replication is premised on the understanding that many social problems are common across diverse communities -- and that it is far more cost-effective to systematically replicate an effective solution to these problems than to continually reinvent the wheel. When done well, replication of strong social programs has the potential to make a positive difference not just for individual participants, but indeed for entire communities, cities and the nation as a whole.Yet despite general agreement among policymakers and philanthropists about the value of replication, successful efforts to bring social programs to scale have been limited, and rarely is replication advanced through systematic public policy initiatives. More often, replication is the result of a particular social entrepreneur's tireless ambition, ability to raise funds and marketing savvy. The failure to spread social program successes more widely and methodically results from a lack of knowledge about the science and practice of replication and from the limited development of systems -- at local, state or federal levels -- to support replication.Fortunately, there seems to be growing awareness of the need to invest in such systems. For example, the 2009 Serve America Act included authorization for a new Social Innovation Fund that would "strengthen the infrastructure to identify, invest in, replicate and expand" proven initiatives. The Obama administration recently requested that Congress appropriate $50 million to this fund, with a focus on "find(ing) the most effective programs out there and then provid(ing) the capital needed to replicate their success in communities around the country."But more than financial capital is required to ensure that when a program is replicated, it will continue to achieve strong results. Over the past 15 years, Public/ Private Ventures (P/PV) has taken a deliberate approach to advancing the science and practice of program replication. Through our work with a wide range of funders and initiatives, including the well-regarded Nurse-Family Partnership, which has now spread to more than 350 communities nationwide, we have accumulated compelling evidence about specific strategies that can help ensure a successful replication. We have come to understand that programs approach replication at different stages in their development -- from fledgling individual efforts that have quickly blossomed and attracted a good deal of interest and support to more mature programs that have slowly expanded their reach and refined their approach over many years. There are rarer cases in which programs have rigorous research in hand proving their effectiveness, multiple sites in successful operation and willing funders prepared to support large-scale replication.Regardless of where a promising program may be in its development, our experience points to a number of important lessons and insights about the replication process, which can inform hard decisions about whether, when and how to expand a program's reach and total impact. In the interest of expanding programs that work, funders sometimes neglect the structures and processes that must be in place to support successful replication. These structures should be seen as the "connective tissue" between a program that seeks to expand and the provision of funding for that program's broad replication.This report represents a synthesis of P/PV's 30 years of designing, testing and replicating a variety of social programs and explains the key structures that should be in place before wide-scale replication is considered. It is designed to serve as a guide for policymakers, practitioners and philanthropists interested in a systematic approach to successful replication

Extracting the Mott gap from energy measurements in trapped atomic gases

We show that the measure of the so-called {\it release-energy}, which is an experimentally accessible quantity, makes it possible to assess the value of the Mott gap in the presence of the confinement potential that is unavoidable in the actual experimental setup. Indeed, the curve of the release-energy as a function of the total number of particles shows kinks that are directly related to the existence of excitation gaps. Calculations are presented within the Gutzwiller approach, but the final results go beyond this simple approximation and represent a genuine feature of the real system. In the case of harmonic confinement, the Mott gaps may be renormalized with respect to the uniform case. On the other hand, in the case of the recently proposed off-diagonal confinement, our results show an almost perfect agreement with the homogeneous case.Comment: 4 pages and 5 figure

Nagaoka ferromagnetism in the two-dimensional infinite-U Hubbard model

We present different numerical calculations based on variational quantum Monte Carlo simulations supporting a ferromagnetic ground-state for finite and small hole densities in the two-dimensional infinite-$U$ Hubbard model. Moreover, by studying the energies of different total spin sectors, these calculations strongly suggest that the paramagnetic phase is unstable against a phase with a partial polarization for large hole densities $\delta \sim 0.40$ with evidence for a second-order transition to the paramagnetic large doping phase.Comment: 4 page

Quantum Phase Transition in Coupled Spin Ladders

The ground state of an array of coupled, spin-half, antiferromagnetic ladders is studied using spin-wave theory, exact diagonalization (up to 36 sites) and quantum Monte Carlo techniques (up to 256 sites). Our results clearly indicate the occurrence of a zero-temperature phase transition between a N\'eel ordered and a non-magnetic phase at a finite value of the inter-ladder coupling ($\alpha_c\simeq0.3$). This transition is marked by remarkable changes in the structure of the excitation spectrum.Comment: 4 pages, 6 postscript figures, to appear in Physical Review

Ground-state properties of the disordered Hubbard model in two dimensions

We study the interplay between electron correlation and disorder in the two-dimensional Hubbard model at half-filling by means of a variational wave function that can interpolate between Anderson and Mott insulators. We give a detailed description of our improved variational state and explain how the physics of the Anderson-Mott transition can be inferred from equal-time correlations functions, which can be easily computed within the variational Monte Carlo scheme. The ground-state phase diagram is worked out in both the paramagnetic and the magnetic sector. Whereas in the former a direct second-order Anderson-Mott transition is obtained, when magnetism is allowed variationally, we find evidence for the formation of local magnetic moments that order before the Mott transition. Although the localization length increases before the Mott transition, we have no evidence for the stabilization of a true metallic phase. The effect of a frustrating next-nearest-neighbor hopping $t^\prime$ is also studied in some detail. In particular, we show that $t^\prime$ has two primary effects. The first one is the narrowing of the stability region of the magnetic Anderson insulator, also leading to a first-order magnetic transition. The second and most important effect of a frustrating hopping term is the development of a ``glassy'' phase at strong couplings, where many paramagnetic states, with disordered local moments, may be stabilized.Comment: 13 pages and 16 figure

Polymer stress growth in viscoelastic fluids in oscillating extensional flows with applications to micro-organism locomotion

Simulations of undulatory swimming in viscoelastic fluids with large amplitude gaits show concentration of polymer elastic stress at the tips of the swimmers.We use a series of related theoretical investigations to probe the origin of these concentrated stresses. First the polymer stress is computed analytically at a given oscillating extensional stagnation point in a viscoelastic fluid. The analysis identifies a Deborah number (De) dependent Weissenberg number (Wi) transition below which the stress is linear in Wi, and above which the stress grows exponentially in Wi. Next, stress and velocity are found from numerical simulations in an oscillating 4-roll mill geometry. The stress from these simulations is compared with the theoretical calculation of stress in the decoupled (given flow) case, and similar stress behavior is observed. The flow around tips of a time-reversible flexing filament in a viscoelastic fluid is shown to exhibit an oscillating extension along particle trajectories, and the stress response exhibits similar transitions. However in the high amplitude, high De regime the stress feedback on the flow leads to non time-reversible particle trajectories that experience asymmetric stretching and compression, and the stress grows more significantly in this regime. These results help explain past observations of large stress concentration for large amplitude swimmers and non-monotonic dependence on De of swimming speeds

Projected wave function study of Z2 spin liquids on the kagome lattice for the spin-1/2 quantum Heisenberg antiferromagnet

Motivated by recent density-matrix renormalization group (DMRG) calculations [Yan, Huse, and White, Science 332, 1173 (2011)], which claimed that the ground state of the nearest-neighbor spin-1/2 Heisenberg antiferromagnet on the kagome lattice geometry is a fully gapped spin liquid with numerical signatures of Z2 gauge structure, and a further theoretical work [Lu, Ran, and Lee, Phys. Rev. B 83, 224413 (2011)], which gave a classification of all Schwinger-fermion mean-field fully symmetric Z2 spin liquids on the kagome lattice, we have thoroughly studied Gutzwiller-projected fermionic wave functions by using quantum variational Monte Carlo techniques, hence implementing exactly the constraint of one fermion per site. In particular, we investigated the energetics of all Z2 candidates (gapped and gapless) that lie in the neighborhood of the energetically competitive U(1) gapless spin liquids. By using a state-of-the-art optimization method, we were able to conclusively show that the U(1) Dirac state is remarkably stable with respect to all Z2 spin liquids in its neighborhood, and in particular for opening a gap toward the so-called Z2[0,{\pi}]{\beta} state, which was conjectured to describe the ground state obtained by the DMRG method. Finally, we also considered the addition of a small second nearest-neighbor exchange coupling of both antiferromagnetic and ferromagnetic type, and obtained similar results, namely, a U(1) Dirac spin-liquid ground state.Comment: 5 pages + supplementary material (2 pages), 3 figures, 1 Table: Final published version, selected as an Editor's suggestio