Exponential Decay of Correlations for Strongly Coupled Toom Probabilistic Cellular Automata

We investigate the low-noise regime of a large class of probabilistic cellular automata, including the North-East-Center model of Toom. They are defined as stochastic perturbations of cellular automata belonging to the category of monotonic binary tessellations and possessing a property of erosion. We prove, for a set of initial conditions, exponential convergence of the induced processes toward an extremal invariant measure with a highly predominant spin value. We also show that this invariant measure presents exponential decay of correlations in space and in time and is therefore strongly mixing.Comment: 21 pages, 0 figure, revised version including a generalization to a larger class of models, structure of the arguments unchanged, minor changes suggested by reviewers, added reference

Involvement of BMP-2, TGF-ß2 and TGF-ß3 Signaling in Initial and Early Stages of Heterotopic Ossification in a rat Experimental Model

This study focused on the localization and expression of bone morphogenetic protein 2 (BMP-2) and different  isoforms of transforming growth factor s (TGF-s1, TGF-s2 and TGF-s3) in the initial and early stages  of heterotopic ossification (HO) employing an animal model mimicking the situation after total hip arthroplasty  (THA). Bone growth was induced in rats using s-tricalcium phosphate implants immersed either in  osteoinductive rhBMP-2 solution or in saline and implanted at the site where the HO is usually expected  to develop after THA. Implants were removed at 3 or 21 days after the operation and handled according to  stereology principles. mRNA expression and protein staining of growth factors in different types of tissues  was determined by in situ hybridization and immunohistochemistry, respectively. After three days, TGF-s3 content in the undifferentiated mesenchymal-like cells in the rhBMP-2 treated  implants was, as assessed by immunohistochemistry, 49.6% higher compared to the saline treated group  (p=0.024). This was also supported by in situ hybridization of mRNA of TGF-s3, which showed stronger  expression in rhBMP-2 treated group. Immunohistochemical investigation showed that after 21 days the  connective tissue in the rhBMP-2 treated implants contained more TGF-s1, TGF-s2 and TGF-s3, compared  to BMP-2 and osteoblasts contained significantly (27.2%) more TGF-s3 compared to TGF-s1 (p=0.045). In  the formed HO the proportion of the TGF-s2 and TGF-s3 producing bone tissue was increased by 32.1% and  47.8% respectively, compared to the TGF-s1 producing bone tissue (p=0.007 and p=0.006) and although  this difference was not so clear at mRNA level, this suggests that TGF-s2 and TGF-s3 signaling seem to play  an important role during initial and early stages of HO formation.

Multicomponent dynamical systems: SRB measures and phase transitions

We discuss a notion of phase transitions in multicomponent systems and clarify relations between deterministic chaotic and stochastic models of this type of systems. Connections between various definitions of SRB measures are considered as well.Comment: 13 pages, LaTeX 2

COVID-19 presenting as stroke

© 2020 Elsevier Inc. Objective: Acute stroke remains a medical emergency even during the COVID-19 pandemic. Most patients with COVID-19 infection present with constitutional and respiratory symptoms; while others present with atypical gastrointestinal, cardiovascular, or neurological manifestations. Here we present a series of four patients with COVID-19 that presented with acute stroke. Methods: We searched the hospital databases for patients that presented with acute stroke and concomitant features of suspected COVID-19 infection. All patients who had radiographic evidence of stroke and PCR-confirmed COVID-19 infection were included in the study. Patients admitted to the hospital with PCR- confirmed COVID-19 disease whose hospital course was complicated with acute stroke while inpatient were excluded from the study. Retrospective patient data were obtained from electronic medical records. Informed consent was obtained. Results: We identified four patients who presented with radiographic confirmation of acute stroke and PCR-confirmed SARS-CoV-2 infection. We elucidate the clinical characteristics, imaging findings, and the clinical course. Conclusions: Timely assessment and hyperacute treatment is the key to minimize mortality and morbidity of patients with acute stroke. Stroke teams should be wary of the fact that COVID-19 patients can present with cerebrovascular accidents and should dawn appropriate personal protective equipment in every suspected patient. Further studies are urgently needed to improve current understandings of neurological pathology in the setting of COVID-19 infection

Influence of transport and ocean ice extent on biogenic aerosol sulfur in the Arctic atmosphere

The recent decline in sea ice cover in the Arctic Ocean could affect the regional radiative forcing via changes in sea ice-atmosphere exchange of dimethyl sulfide (DMS) and biogenic aerosols formed from its atmospheric oxidation, such as methanesulfonic acid (MSA). This study examines relationships between changes in total sea ice extent north of 70 degrees N and atmospheric MSA measurement at Alert, Nunavut, during 1980-2009; at Barrow, Alaska, during 1997-2008; and at Ny-Alesund, Svalbard, for 1991-2004. During the 1980-1989 and 1990-1997 periods, summer (July-August) and June MSA concentrations at Alert decreased. In general, MSA concentrations increased at all locations since 2000 with respect to 1990 values, specifically during June and summer at Alert and in summer at Barrow and Ny-Alesund. Our results show variability in MSA at all sites is related to changes in the source strengths of DMS, possibly linked to changes in sea ice extent as well as to changes in atmospheric transport patterns. Since 2000, a late spring increase in atmospheric MSA at the three sites coincides with the northward migration of the marginal ice edge zone where high DMS emissions from ocean to atmosphere have previously been reported. Significant negative correlations are found between sea ice extent and MSA concentrations at the three sites during the spring and June. These results suggest that a decrease in seasonal ice cover influencing other mechanisms of DMS production could lead to higher atmospheric MSA concentrations

Stochastic theory of non-equilibrium wetting

We study a Langevin equation describing non-equilibrium depinning and wetting transitions. Attention is focused on short-ranged attractive substrate-interface potentials. We confirm the existence of first order depinning transitions, in the temperature-chemical potential diagram, and a tricritical point beyond which the transition becomes a non-equilibrium complete wetting transition. The coexistence of pinned and depinned interfaces occurs over a finite area, in line with other non-equilibrium systems that exhibit first order transitions. In addition, we find two types of phase coexistence, one of which is characterized by spatio-temporal intermittency (STI). A finite size analysis of the depinning time is used to characterize the different coexisting regimes. Finally, a stationary distribution of characteristic triangles or facets was shown to be responsible for the structure of the STI phase.Comment: To appear in Europhys. Lett. // 3 figure

Impact of Using Unedited CT-Based DIR-Propagated Autocontours on Online ART for Pancreatic SBRT

PURPOSE: To determine the dosimetric impact of using unedited autocontours in daily plan adaptation of patients with locally advanced pancreatic cancer (LAPC) treated with stereotactic body radiotherapy using tumor tracking. MATERIALS AND METHODS: The study included 98 daily CT scans of 35 LAPC patients. All scans were manually contoured (MAN), and included the PTV and main organs-at-risk (OAR): stomach, duodenum and bowel. Precision and MIM deformable image registration (DIR) methods followed by contour propagation were used to generate autocontour sets on the daily CT scans. Autocontours remained unedited, and were compared to MAN on the whole organs and at 3, 1 and 0.5 cm from the PTV. Manual and autocontoured OAR were used to generate daily plans using the VOLO™ optimizer, and were compared to non-adapted plans. Resulting planned doses were compared based on PTV coverage and OAR dose-constraints. RESULTS: Overall, both algorithms reported a high agreement between unclipped MAN and autocontours, but showed worse results when being evaluated on the clipped structures at 1 cm and 0.5 cm from the PTV. Replanning with unedited autocontours resulted in better OAR sparing than non-adapted plans for 95% and 84% plans optimized using Precision and MIM autocontours, respectively, and obeyed OAR constraints in 64% and 56% of replans. CONCLUSION: For the majority of fractions, manual correction of autocontours could be avoided or be limited to the region closest to the PTV. This practice could further reduce the overall timings of adaptive radiotherapy workflows for patients with LAPC