99 research outputs found
Verification of Gyrokinetic codes: theoretical background and applications
In fusion plasmas the strong magnetic field allows the fast gyro-motion to be
systematically removed from the description of the dynamics, resulting in a
considerable model simplification and gain of computational time. Nowadays, the
gyrokinetic (GK) codes play a major role in the understanding of the
development and the saturation of turbulence and in the prediction of the
subsequent transport. Naturally, these codes require thorough verification and
validation.
Here we present a new and generic theoretical framework and specific
numerical applications to test the faithfulness of the implemented models to
theory and to verify the domain of applicability of existing GK codes. For a
sound verification process, the underlying theoretical GK model and the
numerical scheme must be considered at the same time, which has rarely been
done and therefore makes this approach pioneering. At the analytical level, the
main novelty consists in using advanced mathematical tools such as variational
formulation of dynamics for systematization of basic GK code's equations to
access the limits of their applicability. The verification of numerical scheme
is proposed via the benchmark effort.
In this work, specific examples of code verification are presented for two GK
codes: the multi-species electromagnetic ORB5 (PIC) and the radially global
version of GENE (Eulerian). The proposed methodology can be applied to any
existing GK code. We establish a hierarchy of reduced GK Vlasov-Maxwell
equations implemented in the ORB5 and GENE codes using the Lagrangian
variational formulation. At the computational level, detailed verifications of
global electromagnetic test cases developed from the CYCLONE Base Case are
considered, including a parametric -scan covering the transition from
ITG to KBM and the spectral properties at the nominal value.Comment: 16 pages, 2 Figures, APS DPP 2016 invited pape
First principles gyrokinetic analysis of electromagnetic plasma instabilities
A two-fold analysis of electromagnetic core tokamak instabilities in the
framework of the gyrokinetic theory is presented. First principle theoretical
foundations of the gyrokinetic theory are used to explain and justify the
numerical results obtained with the global electromagnetic particle-in-cell
code Orb5 whose model is derived from the Lagrangian formalism. The energy
conservation law corresponding to the Orb5 model is derived from the Noether
theorem and implemented in the code as a diagnostics for energy balance and
conservation verification. An additional Noether theorem based diagnostics is
implemented in order to analyse destabilising mechanisms for the electrostatic
and the electromagnetic Ion Temperature Gradient (ITG) instabilities in the
core region of the tokamak. The transition towards the Kinetic Ballooning Modes
(KBM) at high electromagnetic is also investigated.Comment: 22 pages, 10 Figures, material form the ICPP conference 2018, invite
Mitigation of the cancellation problem in the gyrokinetic particle-in-cell simulations of global electromagnetic modes
Linear and nonlinear excitation of TAE modes by external electromagnetic perturbations using ORB5
The excitation of toroidicity induced Alfv{\'e}n eigenmodes (TAEs) using
prescribed external electromagnetic perturbations (hereafter ``antenna") acting
on a confined toroidal plasma as well as its nonlinear couplings to other modes
in the system is studied. The antenna is described by an electrostatic
potential resembling the target TAE mode structure along with its corresponding
parallel electromagnetic potential computed from Ohm's law. Numerically stable
long-time linear simulations are achieved by integrating the antenna within the
framework of a mixed representation and pullback scheme [A. Mishchenko, et al.,
Comput. Phys. Commun. \textbf{238} (2019) 194]. By decomposing the plasma
electromagnetic potential into symplectic and Hamiltonian parts and using Ohm's
law, the destabilizing contribution of the potential gradient parallel to the
magnetic field is canceled in the equations of motion. Besides evaluating the
frequencies as well as growth/damping rates of excited modes compared to
referenced TAEs, we study the interaction of antenna-driven modes with fast
particles and indicate their margins of instability. Furthermore, we show first
nonlinear simulations in the presence of a TAE-like antenna exciting other TAE
modes, as well as Global Alfv\'en Eigenmodes (GAE) having different toroidal
wave numbers from that of the antenna
In vitro evaluation of the precision of working casts for implant-supported restoration with multiple abutments
OBJECTIVE: The purpose of this study was to compare the accuracy of two working cast fabrication techniques using strain-gauge analysis. METHODS: Two working cast fabrication methods were evaluated. Based on a master model, 20 working casts were fabricated by means of an indirect impression technique using polyether after splinting the square transfer copings with acrylic resin. Specimens were assigned to 2 groups (n=10): Group A (GA): type IV dental stone was poured around the abutment analogs in the conventional way; Group B (GB), the dental stone was poured in two stages. Spacers were used over the abutment analogs (rubber tubes) and type IV dental stone was poured around the abutment analogs in the conventional way. After the stone had hardened completely, the spacers were removed and more stone was inserted in the spaces created. Six strain-gauges (Excel Ltd.), positioned in a cast bar, which was dimensionally accurate (perfect fit) to the master model, recorded the microstrains generated by each specimen. Data were analyzed statistically by the variance analysis (ANOVA) and Tukey's test (α= 5%). RESULTS: The microstrain values (µepsilon) were (mean±SD): GA: 263.7±109.07µepsilon, and GB: 193.73±78.83µepsilon. CONCLUSION: There was no statistical difference between the two methods studied
Binge eating disorders and psychotherapy: is it possible to systematize a psychodynamic formulation case?
The Core Conflictual Relationship Theme (CCRT) method establishes psychotherapeutic guidelines for a patient's relational patterns. The CCRT was used in the analysis of narratives coming from psychodynamic psychotherapy sessions (taped and transcribed) from a patient suffering from Binge Eating Episodes. The CCRT method made it possible to systematize the connection between psychological conflicts and symptoms, not always an easy task for psychiatrists and psychologists in training.O método Tema Central de Conflito nos Relacionamentos - CCRT sistematiza as inferências feitas por psicoterapeutas dos padrões de relacionamento de pacientes submetidos à psicoterapia. O CCRT foi utilizado na análise das narrativas de uma paciente com Compulsão Alimentar Periódica, submetida a sessões de psicoterapia (gravadas e transcritas). Com o método CCRT foi possível sistematizar a relação entre os conflitos psíquicos e o aparecimento de sintomas, uma tarefa nem sempre fácil para psiquiatras e psicólogos em formação.Universidade Federal de São Paulo (UNIFESP)Universidade de São Paulo Instituto de PsicologiaUniversidade de São Paulo Faculdade de Filosofia, Ciência e Letras de Ribeirão PretoUniversidade de São Paulo Faculdade de Medicina Hospital das ClínicasUNIFESPSciEL
Characterization of novel calcium hydroxide- mediated highly porous chitosan- calcium scaffolds for potential application in dentin tissue engineering
The aim of this study was to develop a highly porous calcium- containing chitosan scaffold suitable for dentin regeneration. A calcium hydroxide (Ca[OH]2) suspension was used to modulate the degree of porosity and chemical composition of chitosan scaffolds. The chitosan solution concentration and freezing protocol were adjusted to optimize the porous architecture using the phase- separation technique. Scanning electron microscopy/energy- dispersive spectroscopy demonstrated the fabrication of a highly porous calcium- linked chitosan scaffold (CH- Ca), with a well- organized and interconnected porous network. Scaffolds were cross- linked on glutaraldehyde (GA) vapor. Following a 28- day incubation in water, cross- linked CH scaffold had no changes on humid mass, and CH- Ca featured a controlled degradability profile since the significant humid mass loss was observed only after 21 (26.0%) and 28- days (42.2%). Fourier- transform infrared spectroscopy indicated the establishment of Schiff base on cross- linked scaffolds, along with calcium complexation for CH- Ca. Cross- linked CH- Ca scaffold featured a sustained Ca2+ release up to 21- days in a humid environment. This porous and stable architecture allowed for human dental pulp cells (HDPCs) to spread throughout the scaffold, with cells exhibiting a widely stretched cytoplasm; whereas, the cells seeded onto CH scaffold were organized in clusters. HDPCs seeded onto CH- Ca featured significantly higher ALP activity, and gene expressions for ALP, Col1, DMP- 1, and DSPP in comparison to CH, leading to a significant 3.5 times increase in calcium- rich matrix deposition. In sum, our findings suggest that CH- Ca scaffolds are attractive candidates for creating a highly porous and bioactive substrate for dentin tissue engineering.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155906/1/jbmb34586.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155906/2/jbmb34586_am.pd
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