Group-invariant soliton equations and bi-Hamiltonian geometric curve flows in Riemannian symmetric spaces

Universal bi-Hamiltonian hierarchies of group-invariant (multicomponent) soliton equations are derived from non-stretching geometric curve flows \map(t,x) in Riemannian symmetric spaces $M=G/H$, including compact semisimple Lie groups $M=K$ for $G=K\times K$, $H={\rm diag} G$. The derivation of these soliton hierarchies utilizes a moving parallel frame and connection 1-form along the curve flows, related to the Klein geometry of the Lie group $G\supset H$ where $H$ is the local frame structure group. The soliton equations arise in explicit form from the induced flow on the frame components of the principal normal vector N=\covder{x}\mapder{x} along each curve, and display invariance under the equivalence subgroup in $H$ that preserves the unit tangent vector T=\mapder{x} in the framing at any point $x$ on a curve. Their bi-Hamiltonian integrability structure is shown to be geometrically encoded in the Cartan structure equations for torsion and curvature of the parallel frame and its connection 1-form in the tangent space T_\map M of the curve flow. The hierarchies include group-invariant versions of sine-Gordon (SG) and modified Korteweg-de Vries (mKdV) soliton equations that are found to be universally given by curve flows describing non-stretching wave maps and mKdV analogs of non-stretching Schrodinger maps on $G/H$. These results provide a geometric interpretation and explicit bi-Hamiltonian formulation for many known multicomponent soliton equations. Moreover, all examples of group-invariant (multicomponent) soliton equations given by the present geometric framework can be constructed in an explicit fashion based on Cartan's classification of symmetric spaces.Comment: Published version, with a clarification to Theorem 4.5 and a correction to the Hamiltonian flow in Proposition 5.1

Relativistic Compact Objects in Isotropic Coordinates

We present a matrix method for obtaining new classes of exact solutions for Einstein's equations representing static perfect fluid spheres. By means of a matrix transformation, we reduce Einstein's equations to two independent Riccati type differential equations for which three classes of solutions are obtained. One class of the solutions corresponding to the linear barotropic type fluid with an equation of state $p=\gamma \rho$ is discussed in detail.Comment: 9 pages, no figures, accepted for publication in Pramana-Journal of Physic

Behaviour of Magnetic Tubes in Neutron Star's Interior

It is found from Maxwell's equations that the magnetic field lines are good analogues of relativistic strings. It is shown that the super-conducting current in the neutron star's interior causes local rotation of magnetic flux tubes carrying quantized flux.Comment: 6 pages, no figure

Dynamics and stability of the Godel universe

We use covariant techniques to describe the properties of the Godel universe and then consider its linear response to a variety of perturbations. Against matter aggregations, we find that the stability of the Godel model depends primarily upon the presence of gradients in the centrifugal energy, and secondarily on the equation of state of the fluid. The latter dictates the behaviour of the model when dealing with homogeneous perturbations. The vorticity of the perturbed Godel model is found to evolve as in almost-FRW spacetimes, with some additional directional effects due to shape distortions. We also consider gravitational-wave perturbations by investigating the evolution of the magnetic Weyl component. This tensor obeys a simple plane-wave equation, which argues for the neutral stability of the Godel model against linear gravity-wave distortions. The implications of the background rotation for scalar-field Godel cosmologies are also discussed.Comment: Revised version, to match paper published in Class. Quantum Gra

Strategies for conducting situated studies of technology use in hospitals

Ethnographic methods are widely used for understanding situated practices with technology. When authors present their data gathering methods, they almost invariably focus on the bare essentials. These enable the reader to comprehend what was done, but leave the impression that setting up and conducting the study was straightforward. Text books present generic advice, but rarely focus on specific study contexts. In this paper, we focus on lessons learnt by non-clinical researchers studying technology use in hospitals: gaining access; developing good relations with clinicians and patients; being outsiders in healthcare settings; and managing the cultural divide between technology human factors and clinical practice. Drawing on case studies across various hospital settings, we present a repertoire of ways of working with people and technologies in these settings. These include engaging clinicians and patients effectively, taking an iterative approach to data gathering and being responsive to the demands and opportunities provided by the situation. The main contribution of this paper is to make visible many of the lessons we have learnt in conducting technology studies in healthcare, using these lessons to present strategies that other researchers can take up

Cinema-going trajectories in the digital age

The activity of cinema-going constantly evolves and gradually integrates the use of digital data and platforms to become more engaging for the audiences. Combining methods from the fields of Human Computer Interaction and Film Studies, we conducted two workshops seeking to understand cinema audiences’ digital practices and explore how the contemporary cinema-going experience is shaped in the digital age. Our findings suggest that going to the movies constitutes a trajectory during which cinemagoers interact with multiple digital platforms. At the same time, depending on their choices, they construct unique digital identities that represent a set of online behaviours and rituals that cinemagoers adopt before, while and after cinema-going. To inform the design of new, engaging cinemagoing experiences, this research establishes a preliminary map of contemporary cinema-going including digital data and platforms. We then discuss how audiences perceive the potential improvement of the experience and how that would lead to the construction of digital identities

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

Interobserver Variability in Hysterosalpingography Interpretation: Radiologists vs Gynecologists

Ceyda Karadag,1 Cemil Gurses,2 Adnan Kabaalioglu,3 Bengi Gurses,3 İsmail Güzelmansur,4 Turgay Daplan,4 Arzu Turan,5 Hakan Artas,6 Sadan Tutus,7 Safak Olgan,8 İlknur Col Madendag,7 Ahmet Demir,9 Sezcan Mumusoglu,10 Yunus Aydin,11 Emre Goksan Pabuccu12 1Department of Obstetrics and Gynecology, Antalya City Hospital, Antalya, Turkey; 2Department of Radiology, University of Health Sciences Antalya Training and Research Hospital, Antalya, Turkey; 3Department of Radiology, Koç University Faculty of Medicine, Istanbul, Turkey; 4Department of Radiology, Hatay State Hospital, Hatay, Turkey; 5Department of Radiology, Acıbadem Bodrum Hospital, Bodrum, Turkey; 6Department of Radiology, Firat University Faculty of Medicine, Elazig, Turkey; 7Department of Radiology, University of Health Sciences Kayseri Training and Research Hospital, Kayseri, Turkey; 8Department of Obstetrics and Gynecology, Memorial Antalya Hospital, Antalya, Turkey; 9Department of Radiology, University of Health Sciences Tepecik Training and Research Hospital, Izmir, Turkey; 10Department of Obstetrics and Gynecology, Hacettepe University Faculty of Medicine, Ankara, Turkey; 11Department of IVF, Private Health Hospital, Denizli, Turkey; 12Department of Obstetrics and Gynecology, Ufuk University Faculty of Medicine, Ankara, TurkeyCorrespondence: Ceyda Karadag, Department of Obstetrics and Gynecology, Antalya City Hospital, Dumlupınar Bulvarı, Antalya, 07070, Turkey, Tel +905345942264, Email [email protected]: To evaluate interobserver variability in the interpretation of hysterosalpingography (HSG) examinations among radiologists, gynecologists, and between the two specialties, highlighting areas of diagnostic agreement and discrepancy.Materials and Methods: In this prospective, multicenter study, 12 specialists (6 radiologists and 6 gynecologists) independently reviewed HSG images from 100 patients, evaluating 10 predefined diagnostic categories and overall image quality. Fleiss’ kappa (κ) was used to assess interobserver agreement within and between groups.Results: Interobserver agreement ranged from poor to moderate across most diagnostic categories. The highest agreement was observed for tubal occlusion (κ = 0.508 radiologists vs gynecologists; κ = 0.536 among radiologists; κ = 0.460 among gynecologists), followed by uterine anomalies and hydrosalpinx. Poor agreement was noted for subjective parameters such as image quality and additional findings (κ values < 0.1), with some negative kappa scores indicating agreement below chance.Conclusion: Significant interobserver variability exists in HSG interpretation, particularly between radiologists and gynecologists. Structured findings yielded higher agreement, while subjective assessments showed poor reproducibility. These findings underscore the need for standardized reporting guidelines, interdisciplinary collaboration, and the potential integration of AI-assisted interpretation to enhance diagnostic consistency and improve patient outcomes.Keywords: hysterosalpingography, interobserver variability, radiologists, gynecologists, infertility, diagnostic imaging, Fleiss’ kappa, standardization, artificial intelligenc

Cholesterol efflux promoting function of high-density lipoproteins in calcific aortic valve stenosis

Background and aims: Cholesterol efflux capacity is a functional property of high-density lipoproteins (HDL) reflecting the efficiency of the atheroprotective reverse cholesterol transport process in humans. Its relationship with calcific aortic valve stenosis (CAVS) has not been fully assessed yet. Methods: We evaluated HDL-CEC in a patient population with varying degrees of aortic valvular calcific disease, assessed using echocardiography and cardiac computed tomography. Measurement of biomarkers that reflect osteogenic and tissue remodeling, along with dietary and gut microbiota-derived metabolites were performed. Results: Patients with moderate-severe CAVS had significantly lower HDL-CEC compared to both control and aortic sclerosis subjects (mean: 6.09%, 7.32% and 7.26%, respectively). HDL-CEC displayed negative correlations with peak aortic jet velocity and aortic valve calcium score, indexes of CAVS severity (ρ = -0.298, p = 0.002 and ρ = -0.358, p = 0.005, respectively). In multivariable regression model, HDL-CEC had independent association with aortic valve calcium score (B: -0.053, SE: 0.014, p < 0.001), GFR (B: -0.034, SE: 0.012, p = 0.007), as well as with levels of total cholesterol (B: 0.018, SE: 0.005, p = 0.002). Conclusion: These results indicate an impairment of HDL-CEC in moderate-severe CAVS and may contribute to identify potential novel targets for CAVS management