In-depth analysis of the Naming Game dynamics: the homogeneous mixing case

Language emergence and evolution has recently gained growing attention through multi-agent models and mathematical frameworks to study their behavior. Here we investigate further the Naming Game, a model able to account for the emergence of a shared vocabulary of form-meaning associations through social/cultural learning. Due to the simplicity of both the structure of the agents and their interaction rules, the dynamics of this model can be analyzed in great detail using numerical simulations and analytical arguments. This paper first reviews some existing results and then presents a new overall understanding.Comment: 30 pages, 19 figures (few in reduced definition). In press in IJMP

Characteristics and Hardships Associated With Bank Account Ownership Among Refund to Savings Participants

Having a bank account is one important way for households to securely accumulate savings, build credit, and earn interest on assets. Nationally, 7.7% of households are unbanked—lacking both a checking and a savings account. One proposed step toward financial inclusion is to encourage unbanked households to open accounts and deposit refunds into savings at tax time, when many low-income households receive the year’s largest lump sum of cash. This brief utilizes data from the 2013 Refund to Savings study to summarize differences between banked and unbanked households. The findings show that unbanked status is a marker for other financial disadvantages, including having more unsecured debt and fewer assets. However, many who were unbanked at the time of the first survey were banked by the 6-month follow-up survey. Also, about a third of unbanked households expressed interest in opening a new account at tax time. Policies and products should facilitate account opening and retention of low-income households in the banking system

Hofstadter butterflies of carbon nanotubes: Pseudofractality of the magnetoelectronic spectrum

The electronic spectrum of a two-dimensional square lattice in a perpendicular magnetic field has become known as the Hofstadter butterfly [Hofstadter, Phys. Rev. B 14, 2239 (1976).]. We have calculated quasi-one-dimensional analogs of the Hofstadter butterfly for carbon nanotubes (CNTs). For the case of single-wall CNTs, it is straightforward to implement magnetic fields parallel to the tube axis by means of zone folding in the graphene reciprocal lattice. We have also studied perpendicular magnetic fields which, in contrast to the parallel case, lead to a much richer, pseudofractal spectrum. Moreover, we have investigated magnetic fields piercing double-wall CNTs and found strong signatures of interwall interaction in the resulting Hofstadter butterfly spectrum, which can be understood with the help of a minimal model. Ubiquitous to all perpendicular magnetic field spectra is the presence of cusp catastrophes at specific values of energy and magnetic field. Resolving the density of states along the tube circumference allows recognition of the snake states already predicted for nonuniform magnetic fields in the two-dimensional electron gas. An analytic model of the magnetic spectrum of electrons on a cylindrical surface is used to explain some of the results.Comment: 14 pages, 12 figures update to published versio

The Role of Health Insurance in the Financial Lives of Low- and Moderate-Income Households

Health insurance is an important resource for enabling access to and use of medical care, and is associated with reduced risk for mortality and poor health outcomes. Health insurance also protects households from incurring major medical expenses and unmanageable levels of medical debt. About a quarter of a sample of low- and moderate-income (LMI) tax filers have no health insurance, compared to 10% of all individuals in the United States. As of 2014, the proportion of filers without insurance was 11 percentage points higher in states that had not expanded Medicaid through the Affordable Care Act (ACA) than it was in expansion states. Lack of insurance is associated with lower income and assets, and higher unsecured debt, as well as greater likelihood of experiencing financial difficulties and material hardship. Despite progress in expanding health insurance coverage under the ACA, additional efforts are needed, including effort to further expand Medicaid and high-risk insurance pools, strengthen charity care policies and practices, and forgive medical debt

The Role of Choice Architecture in Promoting Saving at Tax Time: Evidence From a Large-Scale Field Experiment

This paper presents the findings of a large-scale field experiment (N = 646,16) from the Refund to Savings Initiative. The experiment tested a choice architecture and persuasive messaging intervention that increased saving among low-moderate income (LMI) consumers by approximately 50% during tax refund time. Two follow-up experiments parsed components of the intervention. The first follow-up experiment (N = 569) tested the messaging and choice architecture interventions separately, finding that each can increase savings. a final follow-up experiment (N = 554) tested individual elements of the choice architecture intervention, demonstrating that mere mention of savings within choice options was not sufficient to increase saving, however, heavy emphasis of savings and making saving “frictionless” within choice options both effectively increased saving intentions. The final experiment also demonstrated that the choice architecture effect operates similarly for both LMI and non-LMI consumers

Calibration of optimal execution of financial transactions in the presence of transient market impact

Trading large volumes of a financial asset in order driven markets requires the use of algorithmic execution dividing the volume in many transactions in order to minimize costs due to market impact. A proper design of an optimal execution strategy strongly depends on a careful modeling of market impact, i.e. how the price reacts to trades. In this paper we consider a recently introduced market impact model (Bouchaud et al., 2004), which has the property of describing both the volume and the temporal dependence of price change due to trading. We show how this model can be used to describe price impact also in aggregated trade time or in real time. We then solve analytically and calibrate with real data the optimal execution problem both for risk neutral and for risk averse investors and we derive an efficient frontier of optimal execution. When we include spread costs the problem must be solved numerically and we show that the introduction of such costs regularizes the solution.Comment: 31 pages, 8 figure

Sharp transition towards shared vocabularies in multi-agent systems

What processes can explain how very large populations are able to converge on the use of a particular word or grammatical construction without global coordination? Answering this question helps to understand why new language constructs usually propagate along an S-shaped curve with a rather sudden transition towards global agreement. It also helps to analyze and design new technologies that support or orchestrate self-organizing communication systems, such as recent social tagging systems for the web. The article introduces and studies a microscopic model of communicating autonomous agents performing language games without any central control. We show that the system undergoes a disorder/order transition, going trough a sharp symmetry breaking process to reach a shared set of conventions. Before the transition, the system builds up non-trivial scale-invariant correlations, for instance in the distribution of competing synonyms, which display a Zipf-like law. These correlations make the system ready for the transition towards shared conventions, which, observed on the time-scale of collective behaviors, becomes sharper and sharper with system size. This surprising result not only explains why human language can scale up to very large populations but also suggests ways to optimize artificial semiotic dynamics.Comment: 12 pages, 4 figure

Miniature Toroidal Radio Frequency Ion Trap Mass Analyzer

A miniature ion trap mass analyzer is reported. The described analyzer is a 1/5-scale version of a previously reported toroidal radio frequency (rf) ion trap mass analyzer. The toroidal ion trap operates with maximum rf trapping voltages about 1 kVp-p or less; however despite the reduced dimensions, it retains roughly the same ion trapping capacity as conventional 3D quadrupole ion traps. The curved geometry provides for a compact mass analyzer. Unit-mass resolved mass spectra for n-butylbenzene, xenon, and naphthalene are reported and preliminary sensitivity data are shown for naphthalene. The expected linear mass scale with rf amplitude scan is obtained when scanned using a conventional mass-selective instability scan mode combined with resonance ejection

Recombination rate and selection strength in HIV intra-patient evolution

The evolutionary dynamics of HIV during the chronic phase of infection is driven by the host immune response and by selective pressures exerted through drug treatment. To understand and model the evolution of HIV quantitatively, the parameters governing genetic diversification and the strength of selection need to be known. While mutation rates can be measured in single replication cycles, the relevant effective recombination rate depends on the probability of coinfection of a cell with more than one virus and can only be inferred from population data. However, most population genetic estimators for recombination rates assume absence of selection and are hence of limited applicability to HIV, since positive and purifying selection are important in HIV evolution. Here, we estimate the rate of recombination and the distribution of selection coefficients from time-resolved sequence data tracking the evolution of HIV within single patients. By examining temporal changes in the genetic composition of the population, we estimate the effective recombination to be r=1.4e-5 recombinations per site and generation. Furthermore, we provide evidence that selection coefficients of at least 15% of the observed non-synonymous polymorphisms exceed 0.8% per generation. These results provide a basis for a more detailed understanding of the evolution of HIV. A particularly interesting case is evolution in response to drug treatment, where recombination can facilitate the rapid acquisition of multiple resistance mutations. With the methods developed here, more precise and more detailed studies will be possible, as soon as data with higher time resolution and greater sample sizes is available.Comment: to appear in PLoS Computational Biolog