Toward a dynamical systems analysis of neuromodulation

This work presents some first steps toward a more thorough understanding of the control systems employed in evolutionary robotics. In order to choose an appropriate architecture or to construct an effective novel control system we need insights into what makes control systems successful, robust, evolvable, etc. Here we present analysis intended to shed light on this type of question as it applies to a novel class of artificial neural networks that include a neuromodulatory mechanism: GasNets. We begin by instantiating a particular GasNet subcircuit responsible for tuneable pattern generation and thought to underpin the attractive property of “temporal adaptivity”. Rather than work within the GasNet formalism, we develop an extension of the well-known FitzHugh-Nagumo equations. The continuous nature of our model allows us to conduct a thorough dynamical systems analysis and to draw parallels between this subcircuit and beating/bursting phenomena reported in the neuroscience literature. We then proceed to explore the effects of different types of parameter modulation on the system dynamics. We conclude that while there are key differences between the gain modulation used in the GasNet and alternative schemes (including threshold modulation of more traditional synaptic input), both approaches are able to produce tuneable pattern generation. While it appears, at least in this study, that the GasNet’s gain modulation may not be crucial to pattern generation , we go on to suggest some possible advantages it could confer

The High-zz Universe Confronts Warm Dark Matter: Galaxy Counts, Reionization and the Nature of Dark Matter

We use $N$-body simulations to show that high-redshift galaxy counts provide an interesting constraint on the nature of dark matter, specifically Warm Dark Matter (WDM), owing to the lack of early structure formation these models. Our simulations include three WDM models with thermal-production masses of 0.8 keV, 1.3 keV, and 2.6 keV, as well as CDM. Assuming a relationship between dark halo mass and galaxy luminosity that is set by the observed luminosity function at bright magnitudes, we find that 0.8 keV WDM is disfavored by direct galaxy counts in the Hubble Ultra Deep Field at $>\!\!10\sigma$. Similarly, 1.3 keV WDM is statistically inconsistent at $2.2\sigma$. Future observations with JWST (and possibly HST via the Frontier Fields) could rule out $1.3$ keV WDM at high significance, and may be sensitive to WDM masses greater than 2.6 keV. We also examine the ability of galaxies in these WDM models to reionize the universe, and find that 0.8 keV and 1.3 keV WDM produce optical depths to the Cosmic Microwave Background (CMB) that are inconsistent at 68% C.L. with current Planck results, even with extremely high ionizing radiation escape fractions, and 2.6 keV WDM requires an optimistic escape fraction to yield an optical depth consistent with Planck data. Although CMB optical depth calculations are model dependent, we find a strong challenge for stellar processes alone to reionize the universe in a 0.8 keV and 1.3 keV WDM cosmology

Evidence-Based Policing and Crime Reduction

There have been calls for research evidence to be drawn into police practice. We examine evidence-based practice in the policing and crime reduction agenda, drawing on the experience of implementing problem-oriented policing in the UK and beyond. We suggest that that the development of such an agenda has been hampered by certain factors. Evidence is not routinely used by police officers (or partnerships) developing strategies to deal with crime problems who prefer to deliver traditional (law enforcement) responses. There is a limited knowledge base on which practitioners can draw in developing responses to crime problems, and the nature of evidence about what is effective is contested amongst academics. Whilst welcoming the moves to incorporate evidence in policing, we caution against excessive optimism about what can be achieved and make some recommendations for those engaged in developing evidence-based practice

Too Big to Fail in the Local Group

We compare the dynamical masses of dwarf galaxies in the Local Group (LG) to the predicted masses of halos in the ELVIS suite of $\Lambda$CDM simulations, a sample of 48 Galaxy-size hosts, 24 of which are in paired configuration similar to the LG. We enumerate unaccounted-for dense halos ($V_\mathrm{max} \gtrsim 25$ km s$^{-1}$) in these volumes that at some point in their histories were massive enough to have formed stars in the presence of an ionizing background ($V_\mathrm{peak} > 30$ km s$^{-1}$). Within 300 kpc of the Milky Way, the number of unaccounted-for massive halos ranges from 2 - 25 over our full sample. Moreover, this "too big to fail" count grows as we extend our comparison to the outer regions of the Local Group: within 1.2 Mpc of either giant we find that there are 12-40 unaccounted-for massive halos. This count excludes volumes within 300 kpc of both the MW and M31, and thus should be largely unaffected by any baryonically-induced environmental processes. According to abundance matching -- specifically abundance matching that reproduces the Local Group stellar mass function -- all of these missing massive systems should have been quite bright, with $M_\star > 10^6M_\odot$. Finally, we use the predicted density structure of outer LG dark matter halos together with observed dwarf galaxy masses to derive an $M_\star-V_\mathrm{max}$ relation for LG galaxies that are outside the virial regions of either giant. We find that there is no obvious trend in the relation over three orders of magnitude in stellar mass (a "common mass" relation), from $M_\star \sim 10^8 - 10^5 M_\odot$, in drastic conflict with the tight relation expected for halos that are unaffected by reionization. Solutions to the too big to fail problem that rely on ram pressure stripping, tidal effects, or statistical flukes appear less likely in the face of these results.Comment: 16 pages, 14 figures, 2 tables, submitted to MNRA

Running with BICEP2: Implications for Small-Scale Problems in CDM

The BICEP2 results, when interpreted as a gravitational wave signal and combined with other CMB data, suggest a roll-off in power towards small scales in the primordial matter power spectrum. Among the simplest possibilities is a running of the spectral index. Here we show that the preferred level of running alleviates small-scale issues within the $\Lambda$CDM model, more so even than viable WDM models. We use cosmological zoom-in simulations of a Milky Way-size halo along with full-box simulations to compare predictions among four separate cosmologies: a BICEP2-inspired running index model ($\alpha_s$ = -0.024), two fixed-tilt $\Lambda$CDM models motivated by Planck, and a 2.6 keV thermal WDM model. We find that the running BICEP2 model reduces the central densities of large dwarf-size halos ($V_\mathrm{max}$ ~ 30 - 80 km s$^{-1}$) and alleviates the too-big-to-fail problem significantly compared to our adopted Planck and WDM cases. Further, the BICEP2 model suppresses the count of small subhalos by ~50% relative to Planck models, and yields a significantly lower "boost" factor for dark matter annihilation signals. Our findings highlight the need to understand the shape of the primordial power spectrum in order to correctly interpret small-scale data.Comment: 10 pages, 8 figures, 2 tables, published in MNRA

Occupation Dynamics of Trap States in an a-Si:H Thin-Film Transistor

We calculate the dynamical behavior of a-Si:H thin-film transistors with an emphasis on the occupation dynamics of trap states. The appropriate rate equation for the occupation function of trap states is included. We show the relations of filling the trap states with the switch-on time and of emptying the trap charges with the switch-off time. The occupation functions in both cases are non-Fermi distribution. The quasi-equilibrium approximation underestimates those two time constants. Thus, transit time theory cannot describe the speeds of transistors made from disordered materials

#SocialWorkAdvocacy

What separates social work from other fields of human services is the underlying need to work toward equality and social justice for every population. This is often accomplished by working on behalf of those who are oppressed, marginalized, or disenfranchised. For that reason, it can be argued that advocacy is at the foundation of social work practice (Belluomini, 2014). The growth of social media and availability of low-cost and user-friendly innovations have changed the way people engage in advocacy. Social media has become an emerging tool for electronic advocacy. In the 21st century, social workers have engaged in electronic advocacy using new tools to address ongoing client issues and policy outcomes. There is a need for social work to heed the call to explore new forms of innovation to engage in advocacy. This article explores the practical usage of technological innovations as tools for engagement in electronic social work advocacy