A New Class of non-Hermitian Quantum Hamiltonians with PT Symmetry

In a remarkable development Bender and coworkers have shown that it is possible to formulate quantum mechanics consistently even if the Hamiltonian and other observables are not Hermitian. Their formulation, dubbed PT quantum mechanics, replaces hermiticity by another set of requirements, notably that the Hamiltonian should be invariant under the discrete symmetry PT, where P denotes parity and T denotes time reversal. All prior work has focused on the case that time reversal is even (T^2 = 1). We generalize the formalism to the case of odd time reversal (T^2 = -1). We discover an analogue of Kramer's theorem for PT quantum mechanics, present a prototypical example of a PT quantum system with odd time reversal, and discuss potential applications of the formalism. Odd time reversal symmetry applies to fermionic systems including quarks and leptons and a plethora of models in nuclear, atomic and condensed matter physics. PT quantum mechanics makes it possible to enlarge the set of possible Hamiltonians that physicists could deploy to describe fundamental physics beyond the standard model or for the effective description of condensed matter phenomena.Comment: Replaced submitted version with accepted version; to appear in Phys Rev

Analysis of SIR epidemic models with sociological phenomenon

We propose two SIR models which incorporate sociological behavior of groups of individuals. It is these differences in behaviors which impose different infection rates on the individual susceptible populations, rather than biological differences. We compute the basic reproduction number for each model, as well as analyze the sensitivity of $R_0$ to changes in sociological parameter values

Composition-differentiation operators on the Dirichlet space

We investigate composition-differentiation operators acting on the Dirichlet space of the unit disk. Specifically, we determine characterizations for bounded, compact, and Hilbert-Schmidt composition-differentiation operators. In addition, for particular classes of inducing maps, we derive an adjoint formula, compute the norm, and identify the spectrum

Among-site variability in the stochastic dynamics of East African coral reefs

Coral reefs are dynamic systems whose composition is highly influenced by unpredictable biotic and abiotic factors. Understanding the spatial scale at which long-term predictions of reef composition can be made will be crucial for guiding conservation efforts. Using a 22-year time series of benthic composition data from 20 reefs on the Kenyan and Tanzanian coast, we studied the long-term behaviour of Bayesian vector autoregressive state-space models for reef dynamics, incorporating among-site variability. We estimate that if there were no among-site variability, the total long-term variability would be approximately one third of its current value. Thus among-site variability contributes more to long-term variability in reef composition than does temporal variability. Individual sites are more predictable than previously thought, and predictions based on current snapshots are informative about long-term properties. Our approach allowed us to identify a subset of possible climate refugia sites with high conservation value, where the long-term probability of coral cover <= 0.1 was very low. Analytical results show that this probability is most strongly influenced by among-site variability and by interactions among benthic components within sites. These findings suggest that conservation initiatives might be successful at the site scale as well as the regional scale.Comment: 97 pages, 49 figure

Deep-Learning for Classification of Colorectal Polyps on Whole-Slide Images

Histopathological characterization of colorectal polyps is an important principle for determining the risk of colorectal cancer and future rates of surveillance for patients. This characterization is time-intensive, requires years of specialized training, and suffers from significant inter-observer and intra-observer variability. In this work, we built an automatic image-understanding method that can accurately classify different types of colorectal polyps in whole-slide histology images to help pathologists with histopathological characterization and diagnosis of colorectal polyps. The proposed image-understanding method is based on deep-learning techniques, which rely on numerous levels of abstraction for data representation and have shown state-of-the-art results for various image analysis tasks. Our image-understanding method covers all five polyp types (hyperplastic polyp, sessile serrated polyp, traditional serrated adenoma, tubular adenoma, and tubulovillous/villous adenoma) that are included in the US multi-society task force guidelines for colorectal cancer risk assessment and surveillance, and encompasses the most common occurrences of colorectal polyps. Our evaluation on 239 independent test samples shows our proposed method can identify the types of colorectal polyps in whole-slide images with a high efficacy (accuracy: 93.0%, precision: 89.7%, recall: 88.3%, F1 score: 88.8%). The presented method in this paper can reduce the cognitive burden on pathologists and improve their accuracy and efficiency in histopathological characterization of colorectal polyps, and in subsequent risk assessment and follow-up recommendations

Analysis of SIR Epidemic Models with Sociological Phenomenon

We propose two SIR models which incorporate sociological behavior of groups of individuals. It is these differences in behaviors which impose different infection rates on the individual susceptible populations, rather than biological differences. We compute the basic reproduction number for each model, as well as analyze the sensitivity of R0 to changes in sociological parameter values

Editorial: perception and cognition: interactions in the ageing brain

Healthy ageing can lead to declines in both perceptual and cognitive functions. Many of the studies in this Topic demonstrate such age-related declines, but also identify links between them. Encouragingly, these links suggest that improving perception could benefit cognition. In addition, while compensatory cognitive strategies were mainly unsuccessful in improving perception, cognitive training was effective under certain condition

Good Catch! Using Interdisciplinary Teams and Team Reflexivity to Improve Patient Safety

Interdisciplinary teams play an important role implementing innovations that facilitate the quality and safety of patient care. This article examined the role of reflexivity in team innovation implementation and its association with an objective patient safety outcome, inpatient fall rates (a fall is an unintended downward displacement of a patient’s body to the ground or other object). In this study, we implemented, supported, and evaluated interdisciplinary teams intended to decrease fall risk in 16 small rural hospitals. These hospitals were part of a collaborative that sought to increase knowledge and facilitate reflexivity about fall event reporting and fall risk reduction structures and processes. We assessed team reflexivity at the start and at the end of the 2-year intervention and innovation implementation at the end of the intervention. The 16 hospitals reported objective fall event data and patient days throughout the project, which we used to calculate comparative rates for assisted, unassisted, and injurious falls. The results suggest that teams benefited from the intervention, increasing reflexivity from the start of the project to the end, which was related to innovation implementation and decreases in fall rates. Theoretical and practical applications of the results are discussed

Group and Organizational Safety Norms Set the Stage for Good Post-Fall Huddles

We explored group and organizational safety norms as antecedents to meeting leader behaviors and achievement of desired outcomes in a special after-action review case—a post-fall huddle. A longitudinal survey design was used to investigate the relationship between organizational/group safety norms, huddle leader behavior, and huddle meeting effectiveness. The sample included health care workers in critical access hospitals (N = 206) who completed a baseline safety norm assessment and an assessment of post-fall huddle experiences 3 to 6 months later. Findings indicate that organizational and group safety norms relate to perceived huddle meeting effectiveness through appropriate huddle leader behavior in a partial mediated framework. In contrast to previous research showing after-action reviews predicting group and organizational safety norms, the longitudinal study presented here suggests that group and organizational safety norms set the stage for the enactment of post-fall huddles in an effective manner