120,954 research outputs found
Sequences, modular forms and cellular integrals
It is well-known that the Ap\'ery sequences which arise in the irrationality
proofs for and satisfy many intriguing arithmetic
properties and are related to the th Fourier coefficients of modular forms.
In this paper, we prove that the connection to modular forms persists for
sequences associated to Brown's cellular integrals and state a general
conjecture concerning supercongruences.Comment: 26 pages, to appear in Mathematical Proceedings of the Cambridge
Philosophical Societ
An analytical and experimental assessment of flexible road ironwork support structures
This paper describes work undertaken to investigate the mechanical performance of road ironwork installations in highways, concentrating on the chamber construction. The principal aim was to provide the background research which would allow improved designs to be developed to reduce the incidence of failures through improvements to the structural continuity between the installation and the surrounding pavement. In doing this, recycled polymeric construction materials (Jig Brix) were studied with a view to including them in future designs and specifications. This paper concentrates on the Finite Element (FE) analysis of traditional (masonry) and flexible road ironwork structures incorporating Jig Brix. The global and local buckling capacity of the Jig Brix elements was investigated and results compared well with laboratory measurements. FE models have also been developed for full-scale traditional (masonry) and flexible installations in a surrounding flexible (asphalt) pavement structure. Predictions of response to wheel loading were compared with full-scale laboratory measurements. Good agreement was achieved with the traditional (masonry) construction but poorer agreement for the flexible construction. Predictions from the FE model indicated that the use of flexible elements significantly reduces the tensile horizontal strain on the surface of the surrounding asphaltic material which is likely to reduce the incidence of surface cracking
Lessons Learned about Change Capital in the Arts: Reflections on a four-year evaluation of Nonprofit Finance Fund's Leading for the Future initiative
This report takes stock of a four-year evaluation of Leading for the Future: Innovative Support for Artistic Excellence (LFF), an experimental 1 million in change capital, drawn down according to individual plans for change, and an additional 225,000 were awarded to organizations that made the most progress on their change efforts, for the purpose of advancing ongoing change efforts or seeding new plans.1 The 10 grantees invested LFF change capital in a wide variety of "business model transformations" ranging from building technologies with the potential to attract new donors and audiences, to experimenting with different models for touring, to investing in marketing and development capacities.NFF has previously published a series of working papers, case studies and video highlights from the LFF initiative, exploring the concepts of capital and financial reporting for capital, and documenting the 10 grantees' experiences.2 We will avoid citing the accomplishments and challenges of specific grantees in this report, and focus instead on program level issues and ideas that might be helpful to future investors of change capital. Indeed, the LFF initiative has played out against the backdrop of a national dialogue about capitalization in the nonprofit arts sector, both learning from, and contributing to, a good deal of productive thinking about capital.While the LFF initiative involved large grants, much was learned that might be of value to funders with more modest resources who are interested in exploring the role of capital in the artistic and financial health of the sector
Solving the electrical control of magnetic coercive field paradox
The ability to tune magnetic properties of solids via electric voltages instead of external magnetic fields is a physics curiosity of great scientific and technological importance. Today, there is strong published experimental evidence of electrical control of magnetic coercive fields in composite multiferroic solids. Unfortunately, the literature indicates highly contradictory results. In some studies, an applied voltage increases the magnetic coercive field and in other studies the applied voltage decreases the coercive field of composite multiferroics. Here, we provide an elegant explanation to this paradox and we demonstrate why all reported results are in fact correct. It is shown that for a given polarity of the applied voltage, the magnetic coercive field depends on the sign of two tensor components of the multiferroic solid: magnetostrictive and piezoelectric coefficient. For a negative applied voltage, the magnetic coercive field decreases when the two material parameters have the same sign and increases when they have opposite signs, respectively. The effect of the material parameters is reversed when the same multiferroic solid is subjected to a positive applied voltage
Reversal Modes of Simulated Iron Nanopillars in an Obliquely Oriented Field
Stochastic micromagnetic simulations are employed to study switching in
three-dimensional magnetic nanopillars exposed to highly misaligned fields. The
switching appears to proceed through two different decay modes, characterized
by very different average lifetimes and different average values of the
transverse magnetization components.Comment: 3 pages, 4 figure
The Structural Estimation of Principal-Agent Models by Least Squares: Evidence from Land Tenancy in Madagascar
We develop a method to structurally estimate principal-agent models by ordinary least squares (OLS). We set up a general principal-agent model which explicitly incorporates the wealth levels of each party and the opportunity cost to the agent of entering the contract. This yields an optimal contract that is linearized by way of an Nth order Taylor approximation. This in turn imposes N(3N-1)/2 restrictions on the parameters and yields an empirical test of the canonical principal-agent model. In the application, we consider the case where N = 2 and apply our method to a sample of land tenancy contracts in rural Madagascar. Empirical tests lead to consistent failure to reject the hypotheses derived from our structural model, which lends support to our structural method as well as to the canonical principal-agent model.Principal-Agent Models, Contract Theory, Structural Estimations, Risk and Uncertainty, C12, C13, D86, O12, Q12,
Molecular dynamics simulations of reflection and adhesion behavior in Lennard-Jones cluster deposition
We conduct molecular dynamics simulations of the collision of atomic clusters
with a weakly-attractive surface. We focus on an intermediate regime, between
soft-landing and fragmentation, where the cluster undergoes deformation on
impact but remains largely intact, and will either adhere to the surface (and
possibly slide), or be reflected. We find that the outcome of the collision is
determined by the Weber number, We i.e. the ratio of the kinetic energy to the
adhesion energy, with a transition between adhesion and reflection occurring as
We passes through unity. We also identify two distinct collision regimes: in
one regime the collision is largely elastic and deformation of the cluster is
relatively small but in the second regime the deformation is large and the
adhesion energy starts to depend on the kinetic energy. If the transition
between these two regimes occurs at a similar kinetic energy to that of the
transition between reflection and adhesion, then we find that the probability
of adhesion for a cluster can be bimodal. In addition we investigate the
effects of the angle of incidence on adhesion and reflection. Finally we
compare our findings both with recent experimental results and with macroscopic
theories of particle collisions.Comment: 18 pages, 13 figure
Tunable magnetization damping in transition metal ternary alloys
We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be
enhanced sufficiently to reduce post-switching magnetization precession to an
acceptable level by alloying with the transition metal osmium (Os). The damping
increases monotonically upon raising the Os-concentration in Py, at least up to
9% of Os. Other effects of alloying with Os are suppression of magnetization
and enhancement of in-plane anisotropy. Magnetization damping also increases
significantly upon alloying with the five other transition metals included in
this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly
as with Os.Comment: 4 pages, submitted to Appl. Phys. Let
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