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The programme to design plasma scenarios for the Spherical Tokamak for Energy Production (STEP), a reactor concept aiming at net electricity production, seeks to exploit the inherent advantages of the spherical tokamak (ST) while making conservative assumptions about plasma performance. This approach is motivated by the large gap between present-day STs and future burning plasmas based on this concept. It is concluded that plasma exhaust in such a device is most likely to be manageable in a double null (DN) configuration, and that high core performance is favoured by positive triangularity (PT) plasmas with an elevated central safety factor. Based on a full technical and physics assessment of external heating and current drive (CD) systems, it was decided that the external CD is provided most effectively by microwaves. Operation with active resistive wall mode (RWM) stabilization as well as high elongation is needed for the most compact solution. The gap between existing devices and STEP is most pronounced in the area of core transport, owing to high normalized plasma pressure in the latter which changes qualitatively the nature of the turbulence controlling transport. Plugging this gap will require dedicated experiments, particularly on high-performance STs, and the development of reduced models that faithfully represent turbulent transport at high normalized pressure. Plasma scenarios in STEP will also need to be such that edge localized modes (ELMs) either do not occur or are small enough to be compatible with material lifetime limits. The high current needed for a power plant-relevant plasma leads to the unavoidable generation of high runaway electron beam current during a disruption, where novel mitigation techniques may be needed. This article is part of the theme issue 'Delivering Fusion Energy – The Spherical Tokamak for Energy Production (STEP)'. [ABSTRACT FROM AUTHOR]

Porphyromonas gingivalis is a key pathobiont in periodontitis. Its long fimbriae consist of a single anchor (FimB), a varying number of stalk (FimA), and three accessory (tip‐related) proteins (FimC, FimD, and FimE). Based on 133 strains/genomes available, it was our aim to investigate the diversity within FimA and FimB and explain the variety of long fimbriae (super‐)structures. Combining the new forward primer fimAnewF with the established fimAunivR, we were able to amplify and sequence fimA including its leader region covering all genotypes and serotypes for phylogenetic analysis. We designed two primer pairs sensing the presence of an internal stop codon in fimB with an impact on fimbrial length. Finally, we examined fimbrial secondary structures by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The phylogeny of fimA/FimA revealed two new subtypes (IIa and IIb) with specific changes in functional domains and thus adding to the current classification scheme (I, Ib, and II‐V). Regarding evolution, we confirm that Porphyromonas gulae fimA‐type A is closely related to human P. gingivalis strains of cluster Ib and might be its ancestor genotype. A fimB internal stop codon is rare and was found in ATCC 33277 only. Comparing P. gingivalis TEM/SEM pictures of type I ATCC 33277 with type V OMI622 revealed a broad spectrum of fimbrial structures including bundling, cell–cell knotting, and brick–wall formation. In conclusion, FimA forms more distinct subtypes than previously known. The bundling of long fimbriae, a mechanism known from EPEC/EHEC and Salmonella, is proposed and supported by TEM/SEM pictures for the first time here. The role and variations of terminal accessory FimC‐E in superstructure formation and/or (co‐) adhesion should be investigated more closely next. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations of supercooled polymer melts are reported for long chains. This is the first simulation study at melt densities where the formation of chain-folded structures resembling the lamellae of polymer crystals is observed. Crystallization and subsequent melting temperatures are related linearly to the inverse lamellar thickness. Analysis of the single chain conformations in the crystal shows that most chains reenter the same lamella by tight backfolds. Simulations are performed with a mesoscopic bead-spring model including a specific angle bending potential. They demonstrate that chain stiffness alone, without an attractive inter-particle potential, is a sufficient driving force for the formation of chain-folded lamellae. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have constructed an apparatus containing a linear ion trap and a high-finesse optical cavity in the ultraviolet spectral range. In our construction, we have avoided all organic materials inside the ultrahigh vacuum chamber. We show that, unlike previously reported, the optical cavity does not degrade in performance over a time scale of 9 months. [ABSTRACT FROM AUTHOR]

We give an extended review of recent numerical and analytical studies on semiflexible chains near surfaces undertaken at Institut Charles Sadron (sometimes in collaboration) with a focus on static properties. The statistical physics of thin confined layers, strict two-dimensional (2D) layers and adsorption layers (both at equilibrium with the dilute bath and from irreversible chemisorption) are discussed for the well-known worm-like-chain (WLC) model. There is mounting evidence that biofilaments (except stable d-DNA) are not fully described by the WLC model. A number of augmented models, like the (super) helical WLC model, the polymorphic model of microtubules (MT) and a model with (strongly) nonlinear flexural elasticity are presented, and some aspects of their surface behavior are analyzed. In many cases, we use approaches different from those in our previous work, give additional results and try to adopt a more general point of view with the hope to shed some light on this complex field. [ABSTRACT FROM AUTHOR]

We present the realization of a combined trapped-ion and optical cavity system, in which a single Yb+ ion is confined by a micron-scale ion trap inside a 230 μam-1ong optical fiber cavity. We characterize the spatial ion-cavity coupling and measure the ion-cavity coupling strength using a cavity-stimulated A transition. Owing to the small mode volume of the fiber resonator, the coherent coupling strength between the ion and a single photon exceeds the natural decay rate of the dipole moment. This system can be integrated into ion-photon quantum networks and is a step towards cavity quantum electrodynamics based quantum information processing with trapped ions. [ABSTRACT FROM AUTHOR]

This paper studies the rheology of weakly entangled polymer melts and films in the glassy domain and near the rubbery domain using two different methods: molecular dynamics (MD) and finite element (FE) simulations. In a first step, the uniaxial mechanical behavior of a bulk polymer sample is studied by means of particle-based MD simulations. The results are in good agreement with experimental data, and mechanical properties may be computed from the simulations. This uniaxial mechanical behavior is then implemented in FE simulations using an elasto-viscoelasto-viscoplastic constitutive law in a continuum mechanics (CM) approach. In a second step, the mechanical response of a polymer film during an indentation test is modeled with the MD method and with the FE simulations using the same constitutive law. Good agreement is found between the MD and CM results. This work provides evidence in favor of using MD simulations to investigate the local physics of contact mechanics, since the volume elements studied are representative and thus contain enough information about the microstructure of the polymer model, while surface phenomena (adhesion and surface tension) are naturally included in the MD approach. [ABSTRACT FROM AUTHOR]

Virtual reality (VR) is a potent educational tool with untapped potential in medical training. However, its integration into medical schools faces challenges such as cybersickness and hesitancy among medical students and professionals. Notably, there has been no systematic assessment of the acceptance of medical educational VR applications by both students and educators. In our single-center study, we enrolled 133 medical students and 14 medical educators. Following a practical demonstration of the established VR anatomy application, Sharecare YOU VR, participants completed a self-reporting survey based on the Technology Acceptance Model (TAM), exploring user acceptance of information technologies and focusing on perceived usefulness (PU), perceived ease of use (PEU), and attitude toward using (ATU). We also sought insights into potential future applications of VR in medical education. Our findings indicate a high level of acceptance among medical students and educators upon structured exposure to VR with significantly positive responses for all three TAM variables (PU, PEU, and ATU). Intriguingly, hands-on experience influenced acceptance. Students envisioned VR's benefits in anatomy, surgery, emergency medicine, and communication skill training with patients. Both students and educators believed that VR could enhance traditional approaches and complement the existing curriculum, anticipating improved preparedness for medical students through VR training applications. In conclusion, our results demonstrate the receptivity of both students and educators to immersive technologies, including VR, in medical education. Importantly, the data suggest that the adoption of VR in this field would be welcomed rather than resisted, potentially enhancing students' self-efficacy and enriching the medical school curriculum. [ABSTRACT FROM AUTHOR]

We implemented a coarse-graining procedure to construct mesoscopic models of complex molecules. The final aim is to obtain better results on properties depending on slow modes of the molecules. Therefore the number of particles considered in molecular dynamics simulations is reduced while conserving as many properties of the original substance as possible. We address the problem of finding nonbonded interaction parameters which reproduce structural properties from experiment or atomistic simulations. The approach consists of optimizing automatically nonbonded parameters using the simplex algorithm to fit structural properties like the radial distribution function as target functions. Moreover, any mix of structural and thermodynamic properties can be included in the target function. Different spherically symmetric inter-particle potentials are discussed. Besides demonstrating the method for Lennard-Jones liquids, it is applied to several more complex molecular liquids such as diphenyl carbonate, tetrahydrofurane, and monomers of poly(isoprene). © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Neutron scattering and extensive molecular dynamics simulations of an all atom C100H202 system were performed to address the short-time dynamics leading to center-of-mass self-diffusion. The simulated dynamics are in excellent agreement with resolution resolved time-of-flight quasielastic neutron scattering. The anomalous subdiffusive center-of-mass motion could be modeled by explicitly accounting for viscoelastic hydrodynamic interactions. A model-free analysis of the local reorientations of the molecular backbone revealed three relaxation processes: While two relaxations characterize local bond rotation and global molecular reorientation, the third component on intermediate times could be attributed to transient flowlike motions of atoms on different molecules. The existence of these collective motions, which are clearly visualized in this Letter, strongly contribute to the chain relaxations in molecular liquids. [ABSTRACT FROM AUTHOR]

Abstract: We developed a multiscale scheme using molecular dynamics (MD) and finite element (FE) methods for evaluating the effective thermal conductivity of graphene epoxy nanocomposites. The proposed hierarchical multiscale approach includes three different scales. First, we used MD simulations for the investigation of thermal conduction in graphene epoxy assembly at atomic scale. Our results suggest that thermal conductivity of single layer graphene decline by around 30% in epoxy matrix for two different hardener chemicals. Using MD, we also calculated thermal boundary conductance (TBC) between crosslinked epoxy and graphene sheet. In the next step, using the results obtained by the MD method, we developed FE based representative volume elements (RVE) of the nanocomposite in order to evaluate the thermal conductivity at the microscale. Finally, nanocomposite effective thermal conductivity was obtained using FE homogenization of an ensemble of microscale RVEs. The validity of the proposed approach was confirmed by comparing predicted results with experimental results in the literature. [Copyright &y& Elsevier]

The reptation mechanism, introduced by de Gennes and Edwards, where a polymer diffuses along a fluffy tube, defined by the constraints imposed by its surroundings, convincingly describes the relaxation of long polymers in concentrated solutions and melts. We propose that the scale for the tube diameter is set by local chain segregation, which we study analytically. We show that the concept of local segregation is especially operational for confined geometries, where segregation extends over mesoscopic domains, drastically reducing binary contacts, and provide an estimate of the entanglement length. Our predictions are quantitatively supported by extensive molecular dynamics simulations on systems consisting of long, entangled chains. [ABSTRACT FROM AUTHOR]

The Mega Amp Spherical Tokamak (MAST) program and a major upgrade are aimed at using MASTs capabilities and parameter ranges to address specific issues for ITER physics, help find solutions for DEMO (in particular plasma exhaust), and develop a credible physics basis for possible ST-based Component Test Facilities/Fusion Nuclear Science Facilities. MAST also provides an attractive access point for scientists and engineers joining fusion. The general approach is to combine experiments, theory, and modeling intimately to help create usable predictive models for future devices. Physics results include edge-localized mode (ELM) mitigation with the flexible resonant magnetic perturbation coils (up to n=6), where smaller, more frequent ELMs are generated, challenging conventional 2-D stability theory. Gyrokinetic theory and models are combined with experiments in the areas of pedestal stability, pellet fueling optimization, and impurity transport. Fast particle stability and confinement are used to optimize scenarios and neutral beam geometry. Exhaust modeling includes turbulence processes that enhance cross-field transport to help ease the power handling. The first major phase of the upgrade program is well under way, to increase the toroidal field and the transformer flux swing and especially implement the flexible exhaust physics platform by means of 17 new poloidal field coils and a closed pumpable divertor. Changes in the neutral beam systems (off-axis as well as on-axis) and new diagnostics especially of the divertor complete the present upgrade scope. [ABSTRACT FROM PUBLISHER]