Sarah Iams - Academia.edu (original) (raw)

Papers by Sarah Iams

Research paper thumbnail of Assessing the robustness of spatial pattern sequences in a dryland vegetation model

Proceedings. Mathematical, physical, and engineering sciences / the Royal Society, 2016

A particular sequence of patterns, 'gaps→labyrinth→spots', occurs with decreasing precipi... more A particular sequence of patterns, 'gaps→labyrinth→spots', occurs with decreasing precipitation in previously reported numerical simulations of partial differential equation dryland vegetation models. These observations have led to the suggestion that this sequence of patterns can serve as an early indicator of desertification in some ecosystems. Because parameter values in the vegetation models can take on a range of plausible values, it is important to investigate whether the pattern sequence prediction is robust to variation. For a particular model, we find that a quantity calculated via bifurcation-theoretic analysis appears to serve as a proxy for the pattern sequences that occur in numerical simulations across a range of parameter values. We find in further analysis that the quantity takes on values consistent with the standard sequence in an ecologically relevant limit of the model parameter values. This suggests that the standard sequence is a robust prediction of th...

Research paper thumbnail of Reacting flow computations with reduced chemical mechanisms

Research paper thumbnail of Flight Stability of Mosquitos: A Reduced Model

SIAM Journal on Applied Mathematics, 2014

Research paper thumbnail of Stochastic equilibrium: Concepts and computations for Lindley processes

International Journal of Economic Theory, 2010

... Sarah Iams 1 ,; Mukul Majumdar 2. ... Denote the distribution function representing π* by F*.... more ... Sarah Iams 1 ,; Mukul Majumdar 2. ... Denote the distribution function representing π* by F*. Typically, an explicit computation or analytical specification of F* is difficult (see Examples 1 and 2 below for the Lindley process that we explore in Sections 2 and 3, and Goswami (2004). ...

Research paper thumbnail of Loading a Dipole Trap from a Magneto-optically Trapped ^87Rb Cloud

We have used a high numerical aperature optical system (NA=.30) to create a focused beam dipole t... more We have used a high numerical aperature optical system (NA=.30) to create a focused beam dipole trap with a 100 W, 10.6 mum CO2 laser. This produces a beam waist of 20 mum which affords a tightly confining trap even at low powers. We will discuss overlapping the trap with our rubidium MOT cloud to maximize the number of atoms

Research paper thumbnail of Optimal perturbation growth and bypass transition in mixing layers

Hyperbolic mixing layers are strongly unstable to the normal-mode Kelvin-Helmholtz instability (K... more Hyperbolic mixing layers are strongly unstable to the normal-mode Kelvin-Helmholtz instability (KHI). At finite amplitude, KHI billows are unstable to the hyperbolic instability, which becomes streamwise-aligned braid-centred rib vortices that trigger turbulence transition. However, the underlying linear operator is non-normal, and so there may be transient non-normal-mode perturbations. We use numerically-calculated power iteration of the linear Navier-Stokes operator and its

Research paper thumbnail of On weakly mixing and doubly ergodic nonsingular actions

Colloquium Mathematicum, 2005

We study weak mixing and double ergodicity for nonsingular actions of locally compact Polish abel... more We study weak mixing and double ergodicity for nonsingular actions of locally compact Polish abelian groups. We show that if T is a nonsingular action of G, T is weakly mixing if and only if for all cocompact subgroups A of G the action of T restricted to A is weakly mixing. We show that a doubly ergodic nonsingular action is weakly mixing and construct an infinite measure-preserving flow that is weakly mixing but not doubly ergodic. We also construct an infinite measure-preserving flow whose cartesian square is ergodic.

Research paper thumbnail of Transient Growth on the Homogenous Mixing Layer

IUTAM Bookseries, 2009

We compute the three-dimensional (3D) optimal perturbations of an homogeneous mixing layer. We co... more We compute the three-dimensional (3D) optimal perturbations of an homogeneous mixing layer. We consider as a base state both the hyperbolic tangent (tanh) velocity profile and the developing two-dimensional (2D) Kelvin-Helmholtz (KH) billow. For short enough times, ...

Research paper thumbnail of Assessing the robustness of spatial pattern sequences in a dryland vegetation model

Proceedings. Mathematical, physical, and engineering sciences / the Royal Society, 2016

A particular sequence of patterns, 'gaps→labyrinth→spots', occurs with decreasing precipi... more A particular sequence of patterns, 'gaps→labyrinth→spots', occurs with decreasing precipitation in previously reported numerical simulations of partial differential equation dryland vegetation models. These observations have led to the suggestion that this sequence of patterns can serve as an early indicator of desertification in some ecosystems. Because parameter values in the vegetation models can take on a range of plausible values, it is important to investigate whether the pattern sequence prediction is robust to variation. For a particular model, we find that a quantity calculated via bifurcation-theoretic analysis appears to serve as a proxy for the pattern sequences that occur in numerical simulations across a range of parameter values. We find in further analysis that the quantity takes on values consistent with the standard sequence in an ecologically relevant limit of the model parameter values. This suggests that the standard sequence is a robust prediction of th...

Research paper thumbnail of Reacting flow computations with reduced chemical mechanisms

Research paper thumbnail of Flight Stability of Mosquitos: A Reduced Model

SIAM Journal on Applied Mathematics, 2014

Research paper thumbnail of Stochastic equilibrium: Concepts and computations for Lindley processes

International Journal of Economic Theory, 2010

... Sarah Iams 1 ,; Mukul Majumdar 2. ... Denote the distribution function representing π* by F*.... more ... Sarah Iams 1 ,; Mukul Majumdar 2. ... Denote the distribution function representing π* by F*. Typically, an explicit computation or analytical specification of F* is difficult (see Examples 1 and 2 below for the Lindley process that we explore in Sections 2 and 3, and Goswami (2004). ...

Research paper thumbnail of Loading a Dipole Trap from a Magneto-optically Trapped ^87Rb Cloud

We have used a high numerical aperature optical system (NA=.30) to create a focused beam dipole t... more We have used a high numerical aperature optical system (NA=.30) to create a focused beam dipole trap with a 100 W, 10.6 mum CO2 laser. This produces a beam waist of 20 mum which affords a tightly confining trap even at low powers. We will discuss overlapping the trap with our rubidium MOT cloud to maximize the number of atoms

Research paper thumbnail of Optimal perturbation growth and bypass transition in mixing layers

Hyperbolic mixing layers are strongly unstable to the normal-mode Kelvin-Helmholtz instability (K... more Hyperbolic mixing layers are strongly unstable to the normal-mode Kelvin-Helmholtz instability (KHI). At finite amplitude, KHI billows are unstable to the hyperbolic instability, which becomes streamwise-aligned braid-centred rib vortices that trigger turbulence transition. However, the underlying linear operator is non-normal, and so there may be transient non-normal-mode perturbations. We use numerically-calculated power iteration of the linear Navier-Stokes operator and its

Research paper thumbnail of On weakly mixing and doubly ergodic nonsingular actions

Colloquium Mathematicum, 2005

We study weak mixing and double ergodicity for nonsingular actions of locally compact Polish abel... more We study weak mixing and double ergodicity for nonsingular actions of locally compact Polish abelian groups. We show that if T is a nonsingular action of G, T is weakly mixing if and only if for all cocompact subgroups A of G the action of T restricted to A is weakly mixing. We show that a doubly ergodic nonsingular action is weakly mixing and construct an infinite measure-preserving flow that is weakly mixing but not doubly ergodic. We also construct an infinite measure-preserving flow whose cartesian square is ergodic.

Research paper thumbnail of Transient Growth on the Homogenous Mixing Layer

IUTAM Bookseries, 2009

We compute the three-dimensional (3D) optimal perturbations of an homogeneous mixing layer. We co... more We compute the three-dimensional (3D) optimal perturbations of an homogeneous mixing layer. We consider as a base state both the hyperbolic tangent (tanh) velocity profile and the developing two-dimensional (2D) Kelvin-Helmholtz (KH) billow. For short enough times, ...