Theory of the critical state of low-dimensional spin glass

We analyse the critical region of finite-($d$)-dimensional Ising spin glass, in particular the limit of $d$ closely above the lower critical dimension $d_\ell$. At criticality the thermally active degrees of freedom are surfaces (of width zero) enclosing clusters of spins that may reverse with respect to their environment. The surfaces are organised in finite interacting structures. These may be called {\em protodroplets}\/, since in the off-critical limit they reduce to the Fisher and Huse droplets. This picture provides an explanation for the phenomenon of critical chaos discovered earlier. It also implies that the spin-spin and energy-energy correlation functions are multifractal and we present scaling laws that describe them. Several of our results should be verifiable in Monte Carlo studies at finite temperature in $d=3$.Comment: RevTeX, 33 pages + 1 PostScript figure (uuencoded). Uses german.sty and an input file def.tex, joined. Three additional figures may be requested from the author

On the utility of dreaming: a general model for how learning in artificial agents can benefit from data hallucination

We consider the benefits of dream mechanisms – that is, the ability to simulate new experiences based on past ones – in a machine learning context. Specifically, we are interested in learning for artificial agents that act in the world, and operationalize “dreaming” as a mechanism by which such an agent can use its own model of the learning environment to generate new hypotheses and training data. We first show that it is not necessarily a given that such a data-hallucination process is useful, since it can easily lead to a training set dominated by spurious imagined data until an ill-defined convergence point is reached. We then analyse a notably successful implementation of a machine learning-based dreaming mechanism by Ha and Schmidhuber (Ha, D., & Schmidhuber, J. (2018). World models. arXiv e-prints, arXiv:1803.10122). On that basis, we then develop a general framework by which an agent can generate simulated data to learn from in a manner that is beneficial to the agent. This, we argue, then forms a general method for an operationalized dream-like mechanism. We finish by demonstrating the general conditions under which such mechanisms can be useful in machine learning, wherein the implicit simulator inference and extrapolation involved in dreaming act without reinforcing inference error even when inference is incomplete

Fallas del estado, violencia y comercio: rutas comerciales peligrosas en Colombia

En este documento se investiga el efecto de la violencia armada doméstica provocada por la inestabilidad política sobre las fricciones de la distancia en la movilidad de carga. Además, el efecto de esas fricciones sobre el acceso diferencial de las regiones a los mercados globales. Se concluye que el sistema de transporte colombiano se ve obstaculizado por deficiencias en la infraestructura e instituciones de transporte terrestre y por entornos políticos fragmentados. El análisis a nivel micro de los registros de exportaciones hacia Estados Unidos corrobora que el envío de carga de exportación desde las regiones del interior se redirige para evitar exposiciones a la violencia armada doméstica a pesar de las amplias distancias de envío marítimo y terrestre existentes. Aprovechamos las trayectorias del transporte de carga desde las regiones colombianas y los patrones espaciales de los conflictos armados violentos para ver cómo los entornos geopolíticos inestables son perjudiciales para la movilidad del transporte de carga y la apertura del mercado. A través de un modelo de elección discreta se muestra que el flujo de envío se ve frenado por el desvío debido a la violencia armada doméstica y que las regiones del interior tienen acceso restringido al mercado global. La percepción de riesgo y comportamiento de redireccionamiento se considera heterogénea entre los envíos y está condicionada a las características del envío, como el tipo de mercancía, el tamaño y el valor del flete. Los resultados resaltan que el conseguir la estabilidad política puede ayudar a mejorar la movilidad de carga y el desarrollo económico orientado a la exportación en el Sur globalWe investigate the effect of domestic armed violence brought about by political instability on the geography of distance frictions in freight mobility and the resulting differential access of regions to global markets. The Colombian transportation system has been found to be impeded by deficiencies in landside transport infrastructure and institutions, and by fragmented political environments. The micro-level analysis of U.S.-bounded export shipping records corroborates that export freight shipping from inland regions is re-routed to avoid exposures to domestic armed violence despite greatly extended landside and maritime shipping distances. We exploit the trajectories of freight shipping from Colombian regions and spatial patterns of violent armed conflicts to see how unstable geopolitical environments are detrimental to freight shipping mobility and market openness. The discrete choice model shows that the shipping flow is greatly curbed by the extended re-routing due to domestic armed violence and that inland regions have restricted access to the global market. The perception of risk and re-routing behavior is found heterogeneous across shipments and conditional to shipment characteristics, such as commodity type, freight value and shipper sizes. The results highlight that political stability must be accommodated for improved freight mobility and export-oriented economic development in the global South.Fallas del estado, violencia y comercio: Rutas comerciales peligrosas en Colombia Enfoque En este artículo se investiga cómo el efecto la violencia armada, que surge en medio de entornos geopolíticos inestables, es perjudicial para la movilidad de carga y el acceso de las regiones a las cadenas globales de logística de mercancías. Nuestro análisis se centra en el caso de Colombia en 2006-2007, por ser un periodo que estuvo muy permeado por la violencia y delincuencia, en muchas de las rutas principales de transporte al interior del país. El objetivo es determinar cómo la inseguridad durante este período de tiempo actuó como un impedimento para el movimiento del transporte marítimo de carga en el comercio internacional, actuando como otros de sus determinantes, tales como los factores arancelarios y no arancelarios. De esta manera, se propone la hipótesis de que los encargados de la logística del transporte buscarían reducir su exposición a conflictos armados domésticos a lo largo de las rutas, desplazándose a puertos más lejanos, a los que se pueda acceder de manera más segura, pese a tener que opotar por distancias de envío más extendidas. Para este efecto, este trabajo explota la existencia de registros de embarque proveniente de las bases de datos de Port Import Export Reporting Services y los datos georreferenciados de conflictos armados nacionales de Uppsala Conflict Data Program. Contribución La visión tradicional en la literatura comercial se ha concentrado en cómo el efecto de los aranceles, las cuotas, el acceso al mar, las fronteras internacionales o la calidad de la infraestructura logística limitan las actividades de exportación y el comercio internacional. Nuestra principal contribución a la discusión está relacionada con los efectos que puede tener la inseguridad como otro impedimento importante para el cruce de fronteras de mercancías. Específicamente, calculamos las equivalencias en distancia del riesgo observado de conflictos armados internos para medir el costo del cambio de ruta y evaluamos hasta qué punto estos restringen el acceso a los mercados globales. Conclusiones Encontramos evidencia sobre Colombia, centrados en el período 2006-2007, de que el riesgo de violencia a lo largo de las rutas de transporte marítimo terrestre resulta en una geografía de la movilidad de carga alterada, con rutas de envío más riesgosas a los puertos que se evitan, en favor de otras opciones más seguras. Los transportistas cambiarían una ruta más corta, pero más riesgosa, por una ruta más segura a puertos ubicados más lejos del origen del envío. Además, estarían dispuestos a tomar la ruta de envío terrestre a puertos donde haya mayor seguridad, incluso en el caso en que el segmento marítimo de la distancia de envío, asociada al puerto de entrada de los Estados Unidos, sea más extenso. Nuestro estudio plantea que la falta de control de la violencia armada a lo largo de las rutas comerciales impide extensamente el transporte de carga, aumenta el costo de hacer negocios y limita en gran medida el acceso al mercado global, lo que podría desalentar las actividades económicas orientadas a la exportación. Frase destacada: Nuestro estudio plantea que la falta de control de la violencia armada a lo largo de las rutas comerciales impide extensamente el transporte de carga, aumenta el costo de hacer negocios y limita el acceso al mercado global, lo que podría desalentar las actividades económicas orientadas a la exportación

Implementing Affordable Socially Assistive Pet Robots in Care Homes Before and During the COVID-19 Pandemic: Stratified Cluster Randomized Controlled Trial and Mixed Methods Study.

BACKGROUND: Robot pets may assist in the challenges of supporting an aging population with growing dementia prevalence. Prior work has focused on the impacts of the robot seal Paro on older adult well-being, but recent studies have suggested the good acceptability and implementation feasibility of more affordable devices (Joy for All [JfA] cats and dogs). OBJECTIVE: We aimed to address the limited effectiveness research on JfA devices. METHODS: We conducted an 8-month, stratified, cluster randomized controlled trial in 8 care homes in Cornwall, United Kingdom. Over 4 months, 4 care homes each received 2 JfA devices (1 cat and 1 dog; intervention group), and 4 homes received care as usual (control group). Psychometrics were collected before and after the intervention to compare the change from baseline to follow-up between the groups. In the final 4 months, all 8 care homes received devices, but only qualitative data were collected owing to COVID-19 and reduced capacity. The primary outcome was neuropsychiatric symptoms (Neuropsychiatric Inventory [NPI] Nursing Home version). Care provider burden was a secondary outcome (occupational disruptiveness NPI subscale), alongside the Challenging Behavior scale, the Holden communication scale, the Campaign to End Loneliness questionnaire, and medication use. Qualitative data were collected through care staff observation calendars and end-of-study interviews to understand use, experience, and impact. We also collected demographic data and assessed dementia severity. In total, 253 residents had robot interaction opportunities, and 83 were consented for direct data collection. RESULTS: There was a significant difference in the total change from baseline to follow-up between the intervention and control groups for NPI (P<.001) and occupational disruptiveness (P=.03). Neuropsychiatric symptoms increased in the control group and decreased in the intervention group. No significant difference was seen for communication issues or challenging behavior. For NPI subdomains, there were significant differences from baseline to follow-up in delusions (P=.03), depression (P=.01), anxiety (P=.001), elation (P=.02), and apathy (P=.009), all of which decreased in the intervention group and increased slightly in the control group. The summative impact results suggested that most residents (46/54, 85%) who interacted with robots experienced a positive impact. Those who interacted had significantly higher dementia severity scores (P=.001). The qualitative results suggested good adoption, acceptability, and suitability for subjectively lonely individuals and lack of a novelty effect through sustained use, and demonstrated that the reasons for use were entertainment, anxiety, and agitation. CONCLUSIONS: Affordable robot pets hold potential for improving the well-being of care home residents and people with dementia, including reducing neuropsychiatric symptoms and occupational disruptiveness. This work suggests no novelty effect and contributes toward understanding robot pet suitability. Moreover, interactions were more common among residents with more moderate/severe dementia and those subjectively lonely. TRIAL REGISTRATION: ClinicalTrials.gov NCT04168463; https://www.clinicaltrials.gov/ct2/show/NCT0416846

Chaos in a Two-Dimensional Ising Spin Glass

We study chaos in a two dimensional Ising spin glass by finite temperature Monte Carlo simulations. We are able to detect chaos with respect to temperature changes as well as chaos with respect to changing the bonds, and find that the chaos exponents for these two cases are equal. Our value for the exponent appears to be consistent with that obtained in studies at zero temperature.Comment: 4 pages, LaTeX, 4 postscript figures included. The analysis of the data is now done somewhat differently. The results are consistent with the chaos exponent found at zero temperature. Additional papers of PY can be obtained on-line at http://schubert.ucsc.edu/pete

Finite Temperature and Dynamical Properties of the Random Transverse-Field Ising Spin Chain

We study numerically the paramagnetic phase of the spin-1/2 random transverse-field Ising chain, using a mapping to non-interacting fermions. We extend our earlier work, Phys. Rev. 53, 8486 (1996), to finite temperatures and to dynamical properties. Our results are consistent with the idea that there are ``Griffiths-McCoy'' singularities in the paramagnetic phase described by a continuously varying exponent $z(\delta)$, where $\delta$ measures the deviation from criticality. There are some discrepancies between the values of $z(\delta)$ obtained from different quantities, but this may be due to corrections to scaling. The average on-site time dependent correlation function decays with a power law in the paramagnetic phase, namely $\tau^{-1/z(\delta)}$, where $\tau$ is imaginary time. However, the typical value decays with a stretched exponential behavior, $\exp(-c\tau^{1/\mu})$, where $\mu$ may be related to $z(\delta)$. We also obtain results for the full probability distribution of time dependent correlation functions at different points in the paramagnetic phase.Comment: 10 pages, 14 postscript files included. The discussion of the typical time dependent correlation function has been greatly expanded. Other papers of APY are available on-line at http://schubert.ucsc.edu/pete

Griffiths-McCoy singularities in the transverse field Ising model on the randomly diluted square lattice

The site-diluted transverse field Ising model in two dimensions is studied with Quantum-Monte-Carlo simulations. Its phase diagram is determined in the transverse field (Gamma) and temperature (T) plane for various (fixed) concentrations (p). The nature of the quantum Griffiths phase at zero temperature is investigated by calculating the distribution of the local zero-frequency susceptibility. It is pointed out that the nature of the Griffiths phase is different for small and large Gamma.Comment: 21 LaTeX (JPSJ macros included), 12 eps-figures include

Temporal convolutional autoencoder for unsupervised anomaly detection in time series

Algorithms and the Foundations of Software technolog

Numerical Study of Spin and Chiral Order in a Two-Dimensional XY Spin Glass

The two dimensional XY spin glass is studied numerically by a finite size scaling method at T=0 in the vortex representation which allows us to compute the exact (in principle) spin and chiral domain wall energies. We confirm earlier predictions that there is no glass phase at any finite T. Our results strongly support the conjecture that both spin and chiral order have the same correlation length exponent $\nu \approx 2.70$. We obtain preliminary results in 3d.Comment: 4 pages, 2 figures, revte

Critical Behavior and Griffiths-McCoy Singularities in the Two-Dimensional Random Quantum Ising Ferromagnet

We study the quantum phase transition in the two-dimensional random Ising model in a transverse field by Monte Carlo simulations. We find results similar to those known analytically in one-dimension. At the critical point, the dynamical exponent is infinite and the typical correlation function decays with a stretched exponential dependence on distance. Away from the critical point there are Griffiths-McCoy singularities, characterized by a single, continuously varying exponent, z', which diverges at the critical point, as in one-dimension. Consequently, the zero temperature susceptibility diverges for a RANGE of parameters about the transition.Comment: 4 pages RevTeX, 3 eps-figures include