Publications
Collective dynamics and atom loss in bright-soliton matter waves
Motivated by recent experiments, we model the dynamics of bright solitons formed by cold gases in quasi-1D traps. A dynamical variational Ansatz captures the far-from-equilibrium excitations of these solitons. Due to a separation of scales, the radial and axial modes decouple, allowing for closed-form approximations for the dynamics. We explore how soliton dynamics influence atom loss and find that the time-averaged loss is largely insensitive to the degree of excitation.
Enhancement of spin transparency by interfacial alloying
We report that atomic-layer alloying (intermixing) at a Pt/Co interface can increase, by approximately 30%, rather than degrade the interfacial spin transparency, and thereby strengthen the efficiency of the dampinglike spin-orbit torque arising from the spin Hall effect in the Pt. At the same time, this interfacial alloying substantially reduces fieldlike spin-orbit torque.
Online storage ring optimization using dimension-reduction and genetic algorithms
Particle storage rings are a rich application domain for online optimization algorithms. The Cornell Electron Storage Ring (CESR) has hundreds of independently powered magnets, making it a high-dimensional test-problem for algorithmic tuning. We investigate algorithms that restrict the search space to a small number of linear combinations of parameters ("knobs") which contain most of the effect on our chosen objective (the vertical emittance), thus enabling efficient tuning.
A re-examination of the fundamental parameters approach to calibration of the Curiosity rover alpha particle X-ray spectrometer
In terrestrial instruments for X-ray emission analysis (e.g. X-ray fluorescence, electron microprobe) the angle of excitation and the angle of characteristic X-ray emission by samples are typically well-defined. This is not the case for the Mars rovers’ alpha particle X-ray spectrometers, necessitating use of “effective” angles in any fundamental parameters approach to spectrum fitting and derivation of element concentrations.
Audio cues enhance mirroring of arm motion when visual cues are scarce
Swing in a crew boat, a good jazz riff, a fluid conversation: these tasks require extracting sensory information about how others flow in order to mimic and respond. To determine what factors influence coordination, we build an environment to manipulate incoming sensory information by combining virtual reality and motion capture. We study how people mirror the motion of a human avatar’s arm as we occlude the avatar. We efficiently map the transition from successful mirroring to failure using Gaussian process regression.
Density Wave Probes Cuprate Quantum Phase Transition
In cuprates, the strong correlations in proximity to the antiferromagnetic Mott insulating state give rise to an array of unconventional phenomena beyond high-temperature superconductivity. Developing a complete description of the ground-state evolution is crucial to decoding the complex phase diagram. Here we use the structure of broken translational symmetry, namely, d-form factor charge modulations in (Bi,Pb)2(Sr,La)2CuO6+δ as a probe of the ground-state reorganization that occurs at the transition from truncated Fermi arcs to a large Fermi surface.
Experimental 3D coherent diffractive imaging from photon-sparse random projections
The routine atomic resolution structure determination of single particles is expected to have profound implications for probing structure-function relationships in systems ranging from energy-storage materials to biological molecules. Extremely bright ultrashort-pulse X-ray sources - X-ray free-electron lasers (XFELs) - provide X-rays that can be used to probe ensembles of nearly identical nanoscale particles.
Ice formation and solvent nanoconfinement in protein crystals
Ice formation within protein crystals is a major obstacle to the cryocrystallographic study of protein structure, and has limited studies of how the structural ensemble of a protein evolves with temperature in the biophysically interesting range from ∼260K to the protein-solvent glass transition near 200K. Using protein crystals with solvent cavities as large as ∼70Å, time-resolved X-ray diffraction was used to study the response of protein and internal solvent during rapid cooling.
Operationalizing the AAPT Learning Goals for the Lab
Calls for reform to instructional labs mean many instructors and departments are facing the daunting task of identifying goals for their introductory lab courses. Fortunately, the American Association of Physics Teachers (AAPT) released a set of recommendations for learning goals for the lab to support lab redevelopment. Here we outline the process we have undergone to identify a set of learning goals for the labs that operationalize those provided by the AAPT.
Practical considerations for high-speed X-ray pixel array detectors and X-ray sensing materials
Advances in synchrotron light sources are creating new opportunities for scientific discovery by producing intense, low-emittance pulses of X-ray illumination. Detectors play a critical link in the experimental process because they are the tools of observation, charged with providing quantitative records of events that are the product of experiments. The capabilities of X-ray imaging detectors often limit the experimental possibilities, and dedicated development is needed to meet source capabilities.