Quantum slow relaxation and metastability due to dynamical constraints

One of the general mechanisms that give rise to the slow cooperative relaxation characteristic of classical glasses is the presence of kinetic constraints in the dynamics. Here we show that dynamical constraints can similarly lead to slow thermalisation and metastability in translationally invariant quantum many-body systems. We illustrate this general idea by considering two simple models: (i) a one-dimensional quantum analogue to classical constrained lattice gases where excitation hopping is constrained by the state of neighbouring sites, mimicking excluded-volume interactions of dense fluids; and (ii) fully packed quantum dimers on the square lattice. Both models have a Rokhsar–Kivelson (RK) point at which kinetic and potential energy constants are equal. To one side of the RK point, where kinetic energy dominates, thermalisation is fast. To the other, where potential energy dominates, thermalisation is slow; memory of initial conditions persists for long times, and separation of timescales leads to pronounced metastability before eventual thermalisation. Furthermore, in analogy with what occurs in the relaxation of classical glasses, the slow-thermalisation regime displays dynamical heterogeneity as manifested by spatially segregated growth of entanglement

Out of the darkness: A History of Huntington's Disease in Australia

Huntington’s disease (HD) is a genetic neurological condition which has a profound influence on the families it affects. The symptoms of the disease are challenging – in addition, social forces strongly influence the way the disease is experienced. It has been a deeply stigmatised condition, and its presence was often kept secret. In this dissertation, I have explored both social and medical aspects of the history of HD, primarily in Australia, building on the work of two scholars, Peter Harper (UK) and Alice Wexler (US). By tracing the histories of HD families, I discovered that HD has been part of the fabric of life in Australia since the convict era, and that some families with the disease were well-respected in their communities, in contrast to narratives which have presented the stigma as inevitable. Wexler has previously shown that in the US, the degree of stigma faced by HD families has varied over time, and my research found this to be also true of the disease in Australia. The earliest descriptions of the disease in the US were mostly made by physicians familiar with HD families. My research revealed a similar story - two physicians who published on HD both grew up in an area of Tasmania with relatively high rates of the disease. The impact of eugenic thinking in the stigmatization of HD in the US, Germany and the UK was noted more than 20 years ago, though its impact in other countries has remained unexplored. Eugenics as a formal movement was not successful in Australia, however eugenic ideas formed part of the social discourse. I show through medical journal articles, items in the popular press and educational organisations how those with hereditary diseases were labeled as “unfit”, promoting stigma which contributed to it being hidden. Finally I describe how the disease began to emerge from “the closet” in the early 1970s, with families and researchers forging a new collaboration to search for treatments, support families and reduce stigma

Sanov and central limit theorems for output statistics of quantum Markov chains

In this paper, we consider the statistics of repeated measurements on the output of a quantum Markov chain. We establish a large deviations result analogous to Sanov’s theorem for the multi-site empirical measure associated to finite sequences of consecutive outcomes of a classical stochastic process. Our result relies on the construction of an extended quantum transition operator (which keeps track of previous outcomes) in terms of which we compute moment generating functions, and whose spectral radius is related to the large deviations rate function. As a corollary to this, we obtain a central limit theorem for the empirical measure. Such higher level statistics may be used to uncover critical behaviour such as dynamical phase transitions, which are not captured by lower level statistics such as the sample mean. As a step in this direction, we give an example of a finite system whose level-1 (empirical mean) rate function is independent of a model parameter while the level-2 (empirical measure) rate is not

Physics-guided neural networks for feedforward control with input-to-state-stability guarantees

The increasing demand on precision and throughput within high-precision mechatronics industries requires a new generation of feedforward controllers with higher accuracy than existing, physics-based feedforward controllers. As neural networks are universal approximators, they can in principle yield feedforward controllers with a higher accuracy, but suffer from bad extrapolation outside the training data set, which makes them unsafe for implementation in industry. Motivated by this, we develop a novel physics-guided neural network (PGNN) architecture that structurally merges a physics-based layer and a black-box neural layer in a single model. The parameters of the two layers are simultaneously identified, while a novel regularization cost function is used to prevent competition among layers and to preserve consistency of the physics-based parameters. Moreover, in order to ensure stability of PGNN feedforward controllers, we develop sufficient conditions for analyzing or imposing (during training) input-to-state stability of PGNNs, based on novel, less conservative Lipschitz bounds for neural networks. The developed PGNN feedforward control framework is validated on a real-life, high-precision industrial linear motor used in lithography machines, where it reaches a factor 2 improvement with respect to physics-based mass–friction feedforward and it significantly outperforms alternative neural network based feedforward controllers

Sphingosine 1-phosphate receptor 5 mediates the immune quiescence of the human brain endothelial barrier

BACKGROUND: The sphingosine 1-phosphate (S1P) receptor modulator FTY720P (Gilenya®) potently reduces relapse rate and lesion activity in the neuroinflammatory disorder multiple sclerosis. Although most of its efficacy has been shown to be related to immunosuppression through the induction of lymphopenia, it has been suggested that a number of its beneficial effects are related to altered endothelial and blood–brain barrier (BBB) functionality. However, to date it remains unknown whether brain endothelial S1P receptors are involved in the maintenance of the function of the BBB thereby mediating immune quiescence of the brain. Here we demonstrate that the brain endothelial receptor S1P(5) largely contributes to the maintenance of brain endothelial barrier function. METHODS: We analyzed the expression of S1P(5) in human post-mortem tissues using immunohistochemistry. The function of S1P(5) at the BBB was assessed in cultured human brain endothelial cells (ECs) using agonists and lentivirus-mediated knockdown of S1P(5). Subsequent analyses of different aspects of the brain EC barrier included the formation of a tight barrier, the expression of BBB proteins and markers of inflammation and monocyte transmigration. RESULTS: We show that activation of S1P(5) on cultured human brain ECs by a selective agonist elicits enhanced barrier integrity and reduced transendothelial migration of monocytes in vitro. These results were corroborated by genetically silencing S1P(5) in brain ECs. Interestingly, functional studies with these cells revealed that S1P(5) strongly contributes to brain EC barrier function and underlies the expression of specific BBB endothelial characteristics such as tight junctions and permeability. In addition, S1P(5) maintains the immunoquiescent state of brain ECs with low expression levels of leukocyte adhesion molecules and inflammatory chemokines and cytokines through lowering the activation of the transcription factor NFκB. CONCLUSION: Our findings demonstrate that S1P(5) in brain ECs contributes to optimal barrier formation and maintenance of immune quiescence of the barrier endothelium

Coalition unionism : exploring how and when coalitions contribute to union renewal in Sydney, Toronto and Chicago

Item does not contain fulltextWe have previously identified eight novel autoantibody targets in the cerebrospinal fluid of multiple sclerosis (MS) patients, including sperm-associated Ag 16 (SPAG16). In the current study, we further investigated the autoantibody response against SPAG16-a protein with unknown function in the CNS-and its expression in MS pathology. Using isoelectric focusing, we detected SPAG16-specific oligoclonal bands in the cerebrospinal fluid of 5 of 23 MS patients (22%). Analysis of the anti-SPAG16 Ab reactivity in the plasma of a total of 531 donors using ELISA demonstrated significantly elevated anti-SPAG16 Ab levels (p = 0.002) in 32 of 153 MS patients (21%) compared with all other control groups with 95% specificity for the disease. To investigate the pathologic relevance of anti-SPAG16 Abs in vivo, anti-SPAG16 Abs were injected in mice with experimental autoimmune encephalomyelitis, resulting in a significant disease exacerbation. Finally, we demonstrated a consistent upregulation of SPAG16 in MS brain and experimental autoimmune encephalomyelitis spinal cord lesions, more specifically in reactive astrocytes. We conclude that SPAG16 is a novel autoantibody target in a subgroup of MS patients and in combination with other diagnostic criteria, elevated levels of anti-SPAG16 Abs could be used as a biomarker for diagnosis. Furthermore, the pathologic relevance of anti-SPAG16 Abs was shown in vivo