The Little-Hopfield model on a Random Graph

We study the Hopfield model on a random graph in scaling regimes where the average number of connections per neuron is a finite number and where the spin dynamics is governed by a synchronous execution of the microscopic update rule (Little-Hopfield model).We solve this model within replica symmetry and by using bifurcation analysis we prove that the spin-glass/paramagnetic and the retrieval/paramagnetictransition lines of our phase diagram are identical to those of sequential dynamics.The first-order retrieval/spin-glass transition line follows by direct evaluation of our observables using population dynamics. Within the accuracy of numerical precision and for sufficiently small values of the connectivity parameter we find that this line coincides with the corresponding sequential one. Comparison with simulation experiments shows excellent agreement.Comment: 14 pages, 4 figure

On the conditions for the existence of Perfect Learning and power law in learning from stochastic examples by Ising perceptrons

In a previous letter, we studied learning from stochastic examples by perceptrons with Ising weights in the framework of statistical mechanics. Under the one-step replica symmetry breaking ansatz, the behaviours of learning curves were classified according to some local property of the rules by which examples were drawn. Further, the conditions for the existence of the Perfect Learning together with other behaviors of the learning curves were given. In this paper, we give the detailed derivation about these results and further argument about the Perfect Learning together with extensive numerical calculations.Comment: 28 pages, 43 figures. Submitted to J. Phys.

Fixed Points of Hopfield Type Neural Networks

The set of the fixed points of the Hopfield type network is under investigation. The connection matrix of the network is constructed according to the Hebb rule from the set of memorized patterns which are treated as distorted copies of the standard-vector. It is found that the dependence of the set of the fixed points on the value of the distortion parameter can be described analytically. The obtained results are interpreted in the terms of neural networks and the Ising model.Comment: RevTEX, 19 pages, 2 Postscript figures, the full version of the earler brief report (cond-mat/9901251

Violent extremism and terrorism online in 2021: The year in review

The 2021 Year in Review treats developments in the violent extremist and terrorist online scene(s) in the 12-month period from 1 December 2020 to 30 November 2021. It accomplishes this by surveying, describing, and integrating the findings of relevant articles and reports produced by academics, think tanks, civil society, and governmental organisations; high quality media coverage; and the first-hand experience and primary research of the authors. The March 2019 Christchurch attacks, a series of subsequent attacks in the United States, Germany, and elsewhere, events online and offline around the US Presidential election, and a general uptick in ‘real world’ and extreme right online activity globally during the Covid-19 pandemic have all put violent extreme right (online) activity firmly centre stage however, which is reproduced in the structuring of the present report. This does not necessarily mean that the threat from violent jihadism is diminished, but rather reflects the reason behind the increased focus by a range of relevant actors on the risks posed by unfettered online violent extreme right activit

Near-Infrared Spectroscopy of Molecular Filaments in the Reflection Nebula NGC 7023

We present near-infrared spectroscopy of fluorescent molecular hydrogen (H_2) emission from molecular filaments in the reflection nebula NGC 7023. We derive the relative column densities of H_2 rotational-vibrational states from the measured line emission and compare these results with several model photodissociation regions covering a range of densities, incident UV-fields, and excitation mechanisms. Our best-fit models for one filament suggest, but do not require, either a combination of different densities, suggesting clumps of 10^6 cm^{-3} in a 10^4 - 10^5 cm^{-3} filament, or a combination of fluorescent excitation and thermally-excited gas, perhaps due to a shock from a bipolar outflow. We derive densities and UV fields for these molecular filaments that are in agreement with previous determinations.Comment: ApJ accepted, 26 pages including 5 embedded figures, uses AASTEX. Also available at http://www-astronomy.mps.ohio-state.edu/~martini/pubs.htm

A prospective audit of bed utilisation and delays in care across London

Background A prospective bed utilisation census of acute London hospitals using an established Day of Care Survey (DoCS), which quantified adult patients not meeting criteria for in-hospital care. Methods Twenty-three hospitals were surveyed over two weeks in October/November 2017 using supervised trained hospital staff. Pairs of staff visited wards, reviewed all patients and identified those not meeting inpatient care criteria, recording reasons for delay. Patient demographics, length of stay (LOS), ward specialty and delay reasons were collected. Results Overall – In total, 8,656 in-patients were studied (overall occupancy 96%, range 82-117%): 800 definite discharges were excluded, leaving 7,856 patients for analysis; seven hospitals had ≥100% occupancy; 1,919/7,856 patients (24%, range 12–43%) did not meet criteria; 56% of patients were over 70 years; five hospitals had higher number of patients 14 days; 13 hospitals had greater/equal number of patients in ≤14 days LOS. For delayed patients in ≤14 days group, most were within seven days of admission (627 ≤7days, 393 8-14 days). In total 34% (range 11-54%) of delays were related to acute hospital reasons (AHR) and 61% (range 46-83%) to wider system reasons (WSR). Eight common themes accounted for 67% of recorded reasons and were equally split between AHR and WSR. Conclusion Data showed high occupancy levels with insufficient discharges. This study suggests policies selecting age and/or LOS alone as cut offs to tackle delays in care may miss a large proportion of patients requiring more timely interventions. Adopting a proactive thematic approach to improvement using the top eight delay reasons provides an obvious opportunity to reduce delays while noting the inter site variation. All metrics analysed emphasized the need for informed local data to help support local change