Caging and mosaic lengthscales in plaquette spin models of glasses

We consider two systems of Ising spins with plaquette interactions. They are simple models of glasses which have dual representations as kinetically constrained systems. These models allow an explicit analysis using the mosaic, or entropic droplet, approach of the random first-order transition theory of the glass transition. We show that the low temperature states of these systems resemble glassy mosaic states, despite the fact that excitations are localized and that there are no static singularities. By means of finite size thermodynamics we study a generalised caging effect whereby the system is frozen on short lengthscales, but free at larger lengthscales. We find that the freezing lengthscales obtained from statics coincide with those relevant to dynamic correlations, as expected in the mosaic view. The simple nucleation arguments of the mosaic approach, however, do not give the correct relation between freezing lengths and relaxation times, as they do not capture the transition states for relaxation. We discuss how these results make a connection between the mosaic and the dynamic facilitation views of glass formers.Comment: 14 pages, 14 figs, some typos correcte

Static and dynamic lengthscales in a simple glassy plaquette model

We study static and dynamic spatial correlations in a two-dimensional spin model with four-body plaquette interactions and standard Glauber dynamics by means of analytic arguments and Monte Carlo simulations. We study in detail the dynamical behaviour which becomes glassy at low temperatures due to the emergence of effective kinetic constraints in a dual representation where spins are mapped to plaquette variables. We study the interplay between non-trivial static correlations of the spins and the dynamic `four-point' correlations usually studied in the context of supercooled liquids. We show that slow dynamics is spatially heterogeneous due to the presence of diverging lengthscales and scaling, as is also found in kinetically constrained models. This analogy is illustrated by a comparative study of a froth model where the kinetic constraints are imposed.Comment: 12 pages, 13 figs; published versio

Metastable states and space-time phase transitions in a spin-glass model

We study large deviations of the dynamical activity in the random orthogonal model (ROM). This is a fully connected spin-glass model with one-step replica symmetry breaking behaviour, consistent with the random first-order transition scenario for structural glasses. We show that this model displays dynamical (space-time) phase-transitions between active and inactive phases, as demonstrated by singularities in large deviation functions. We argue that such transitions are generic in systems with long-lived metastable states.Comment: 4.1 pages, 4 fig

Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics

We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyse the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occuring at a coupling eps*(T), which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays space-time transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field s_c(T)>=0 that appears to vanish at zero temperature, in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions we introduce the square pyramid model which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states.Comment: 12 pages, 9 fig

Observations of atmospheric water vapor with the SAGE 2 instrument

The Stratospheric Aerosol and Gas Experiment 2 (SAGE 2) is discussed. The SAGE 2 instrument was a multichannel spectrometer that inferred the vertical distribution of water vapor, aerosols, nitrogen dioxide, and ozone by measuring the extinction of solar radiation at spacecraft sunrise/sunset. At altitudes above 20 km, the SAGE 2 and LIMS (Limb Infrared Monitor of the Stratosphere) data are in close agreement. The discrepancies below this altitude may be attributed to differences in the instruments' field of view and time of data acquisition

Duality symmetries and effective dynamics in disordered hopping models

We identify a duality transformation in one-dimensional hopping models that relates propagators in general disordered potentials linked by an up-down inversion of the energy landscape. This significantly generalises previous results for a duality between trap and barrier models. We use the resulting insights into the symmetries of these models to develop a real-space renormalisation scheme that can be implemented computationally and allows rather accurate prediction of propagation in these models. We also discuss the relation of this renormalisation scheme to earlier analytical treatments.Comment: 29 pages, 7 figs. Final version, some extra context and references adde

Variability of Temperature and Salinity in the Middle Atlantic Bight and Gulf of Maine

Monitoring of the waters of the Middle Atlantic Bight and Gulf of Maine has been conducted by the MARMAP Ships of Opportunity Program since the early 1970's. Presented in this atlas are portrayals of the temporal and spatial patterns of surface and bottom temperature and surface salinity for these areas during the period 1978-1990. These patterns are shown in the form of time-space diagrams for single-year and multiyear (base period) time frames. Each base period figure shows thirteen-year (1978-1990) mean conditions, sample variance in the form of standard deviations of the measured values, and data locations. Each single-year figure displays annual conditions, sampling locations, and departures of annual conditions from the thirteen-year means, expressed as algebraic anomalies and standardized anomalies. (PDF file contains 112 pages.

Prevalence and Antimicrobial Susceptibility of Methicillin-resistant Staphylococcus aureus in Pregnant Women and Their Newborns in Las Vegas, Nevada

Colonization and infection by resistant strains of Staphylococcus aureus are being reported in epidemic proportions. The goal of this study was to determine the local prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization in pregnant women in southern Nevada and how it correlates with colonization and infection of their neonates. Signed consent was obtained, and a brief questionnaire was administered by the medical staff to each pregnant woman to collect demographic data and pertinent medical, family and social history. Nasal and vaginal specimens were obtained from pregnant women at ≥35 weeks gestation, and nasal and umbilicus specimens were obtained from their newborns. Specimens were cultured onto two selective media for S. aureus and MRSA. Potential MRSA isolates were further evaluated for susceptibility to antibiotics. Specimens from 307 pregnant women and 174 neonates were collected, resulting in 172 mother-neonate paired specimens. A total of 278 questionnaires were received from study participants. MRSA prevalence in pregnant women was 1.0% and 0.3% for nasal and vaginal specimens, respectively. The MRSA prevalence in neonates was 0% and 0.6% for nasal and umbilical specimens, respectively. Four different antimicrobial susceptibility profiles were observed among the MRSA isolates. The results did not show transmission of MRSA from pregnant women to their newborns, or infections of newborns with MRSA. It is expected that the results of this study will inform future decisions on surveillance, treatment and prevention of MRSA infections in Nevada