Theoretical study of even denominator fractions in graphene: Fermi sea versus paired states of composite fermions

The physics of the state at even denominator fractional fillings of Landau levels depends on the Coulomb pseudopotentials, and produces, in different GaAs Landau levels, a composite fermion Fermi sea, a stripe phase, or, possibly, a paired composite fermion state. We consider here even denominator fractions in graphene, which has different pseudopotentials as well as a possible four fold degeneracy of each Landau level. We test various composite fermion Fermi sea wave functions (fully polarized, SU(2) singlet, SU(4) singlet) as well as the paired composite fermion states in the n=0 and $n=1$ Landau levels and predict that (i) the paired states are not favorable, (ii) CF Fermi seas occur in both Landau levels, and (iii) an SU(4) singlet composite fermion Fermi sea is stabilized in the appropriate limit. The results from detailed microscopic calculations are generally consistent with the predictions of the mean field model of composite fermions

Tracking the Tracker from its Passive Sonar ML-PDA Estimates

Target motion analysis with wideband passive sonar has received much attention. Maximum likelihood probabilistic data-association (ML-PDA) represents an asymptotically efficient estimator for deterministic target motion, and is especially well-suited for low-observable targets; the results presented here apply to situations with higher signal to noise ratio as well, including of course the situation of a deterministic target observed via clean measurements without false alarms or missed detections. Here we study the inverse problem, namely, how to identify the observing platform (following a two-leg motion model) from the results of the target estimation process, i.e. the estimated target state and the Fisher information matrix, quantities we assume an eavesdropper might intercept. We tackle the problem and we present observability properties, with supporting simulation results.Comment: To appear in IEEE Transactions on Aerospace and Electronic System

Magnetic field-tuned Aharonov-Bohm oscillations and evidence for non-Abelian anyons at v=5/2

We show that the resistance of the v=5/2 quantum Hall state, confined to an interferometer, oscillates with magnetic field consistent with an Ising-type non-Abelian state. In three quantum Hall interferometers of different sizes, resistance oscillations at v=7/3 and integer filling factors have the magnetic field period expected if the number of quasiparticles contained within the interferometer changes so as to keep the area and the total charge within the interferometer constant. Under these conditions, an Abelian state such as the (3,3,1) state would show oscillations with the same period as at an integer quantum Hall state. However, in an Ising-type non-Abelian state there would be a rapid oscillation associated with the "even-odd effect" and a slower one associated with the accumulated Abelian phase due to both the Aharonov-Bohm effect and the Abelian part of the quasiparticle braiding statistics. Our measurements at v=5/2 are consistent with the latter.Comment: 10 pages, 8 figures, includes Supplemental Material

3D Printing and Occupational Therapy: The Process of 3D Printing Adaptive Devices

Three-dimensional (3D) printing has been used in the healthcare field in order to create devices that improve the lives of patients. In occupational therapy, this technology is being used to create splints and adaptive devices that allow patients to heal and better perform tasks in their everyday life. Some of the benefits of 3D printing is that allows devices to be created faster and cheaper than traditional treatment methods. The purpose of this project was to determine how feasible it would be to buy a 3D printer and use it to print open-source assistive devices that could be used by potential clients. This project describes the start to finish process of using the FlashForge Finder printer to print twelve different devices, including writing aids, typing aids, bottle openers, and key turners. The cost analysis of the project reveals that each device costs under one dollar to print and only takes up to a few hours. The results of this study show that an entry-level printer is fairly easy to use and can be a beneficial tool for an occupational therapist. Some of the limitations of this project included a small print area and the ability to only print using one material

Measurement of filling factor 5/2 quasiparticle interference: observation of charge e/4 and e/2 period oscillations

A standing problem in low dimensional electron systems is the nature of the 5/2 fractional quantum Hall state: its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be employed to manipulate and measure quantum Hall edge excitations. Here we use a small area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharanov-Bohm effect are observed for integer and fractional quantum Hall states (filling factors 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these as charge calibrations, at 5/2 filling factor and at lowest temperatures periodic transmission through the device consistent with quasiparticle charge e/4 is observed. The principal finding of this work is that in addtion to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference, this presence of an effective e/2 period may empirically reflect an e/2 quasiparticle charge, or may reflect multiple passes of the e/4 quasiparticle around the interferometer. These results are discussed within a picture of e/4 quasiparticle excitations potentially possessing non-Abelian statistics. These studies demonstrate the capacity to perform interferometry on 5/2 excitations and reveal properties important for understanding this state and its excitations.Comment: version 3 contains additional data beyond version 2, 26 pages, 8 figures PNAS 081259910

Beyond the Fermi Liquid Paradigm: Hidden Fermi Liquids

An intense investigation of possible non-Fermi liquid states of matter has been inspired by two of the most intriguing phenomena discovered in the past quarter century, namely high temperature superconductivity and the fractional quantum Hall effect. Despite enormous conceptual strides, these two fields have developed largely along separate paths. Two widely employed theories are the resonating valence bond theory for high temperature superconductivity and the composite fermion theory for the fractional quantum Hall effect. The goal of this "perspective" article is to note that they subscribe to a common underlying paradigm: they both connect these exotic quantum liquids to certain ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation yields numerous nontrivial experimental consequences, exposing these theories to rigorous and definitive tests.Comment: perspective articl

"Willingness to Pay for Electric Vehicles and their Attributes"

This article presents a stated preference study of electric vehicle choice using data from a national survey. We used a choice experiment wherein 3029 respondents were asked to choose between their preferred gasoline vehicle and two electric versions of that preferred vehicle. We estimated a latent class random utility model and used the results to estimate the willingness to pay for five electric vehicle attributes: driving range, charging time, fuel cost saving, pollution reduction, and performance. Driving range, fuel cost savings, and charging time led in importance to respondents. Individuals were willing to pay (wtp) from $35 to$75 for a mile of added driving range, with incremental wtp per mile decreasing at higher distances. They were willing to pay from $425 to$3250 per hour reduction in charging time (for a 50 mile charge). Respondents capitalized about 5 years of fuel saving into the purchase price of an electric vehicle. We simulated our model over a range of electric vehicle configurations and found that people with the highest values for electric vehicles were willing to pay a premium above their wtp for a gasoline vehicle that ranged from $6000 to$16,000 for electric vehicles with the most desirable attributes. At the same time, our results suggest that battery cost must drop significantly before electric vehicles will find a mass market without subsidy.Electric Vehicles, Stated Preference, Discrete Choice