Academic literature on the topic 'Sabra shell model'

Abstract. Substorm-associated radar auroral surges (SARAS) are a short lived (15–90 minutes) and spatially localised (~5° of latitude) perturbation of the plasma convection pattern observed within the auroral E-region. The understanding of such phenomena has important ramifications for the investigation of the larger scale plasma convection and ultimately the coupling of the solar wind, magnetosphere and ionosphere system. A statistical investigation is undertaken of SARAS, observed by the Sweden And Britain Radar Experiment (SABRE), in order to provide a more extensive examination of the local time occurrence and propagation characteristics of the events. The statistical analysis has determined a local time occurrence of observations between 1420 MLT and 2200 MLT with a maximum occurrence centred around 1700 MLT. The propagation velocity of the SARAS feature through the SABRE field of view was found to be predominately L-shell aligned with a velocity centred around 1750 m s–1 and within the range 500 m s–1 and 3500 m s–1. This comprehensive examination of the SARAS provides the opportunity to discuss, qualitatively, a possible generation mechanism for SARAS based on a proposed model for the production of a similar phenomenon referred to as sub-auroral ion drifts (SAIDs). The results of the comparison suggests that SARAS may result from a similar geophysical mechanism to that which produces SAID events, but probably occurs at a different time in the evolution of the event.Key words. Substorms · Auroral surges · Plasma con-vection · Sub-auroral ion drifts

Abstract Glioblastoma (GBM) is the most common malignant primary brain tumor in adults. Despite an aggressive standard of care that includes maximally safe surgical resection, chemo-radiotherapy, median overall survival remains stagnant at 15 months. However, immunotherapeutic strategies have provided an exciting avenue of exploration to meet clinical need. Chimeric antigen receptor T-cell (CAR-T) therapy has shown promising results in liquid malignancies, but clinical trials in GBM targeting various tumor antigens have not shown durable clinical benefit. While this may be attributable to various tumor-intrinsic immune evasion strategies characteristic of GBM, little work has assessed whether the issue is due to the quality of the CAR-T treatment itself. Currently, CAR-Ts for clinical studies are manufactured in an autologous setting wherein T-cells are extracted from patients, engineered ex-vivo, and subsequently re-infused back. However, peripheral T-cells taken from untreated GBM patients have demonstrated qualitative and functional deficits, which may contribute to suboptimal treatment outcomes. Thus, we aimed to establish whether CAR-Ts generated from GBM patients would show reduced efficacy in comparison to healthy donors using our previously validated CD133 CAR-T. In this work, we show that in-spite of no inherent phenotypic differences, patient derived CAR-Ts shows pre-treatment exhaustion and upon preclinical evaluation using an orthotopic xenograft model of human GBM reduced survival advantage in autologous, patient-derived CD133-targeting CAR-T cell products was observed as compared to the controls. Transcriptomic analysis highlighted a decreased panel-wide enrichment in genes related to T cell and lymphocyte activation, lower prevalence of T cells (including Th1 and CD8+) and higher prevalence of exhausted CD8+ cells in T-cells products derived from GBM donors as compared to healthy donors. To overcome the functional and logistical considerations of autologous therapy, we additionally aimed to generate an “off-the-shelf” allogeneic CD133 CAR-T. Using CRISPR gene editing technology, we generated TCR-knockout CAR-T cells with comparable pre-clinical efficacy to our autologous models. In conclusion, this work highlights the need to reassess autologous CAR-T therapy for GBM and considers allogeneic approaches as promising alternatives. By addressing the inherent deficits in patient-derived CAR-Ts, allogeneic CD133 CAR-Ts may offer a more effective and logistically feasible therapeutic option for treating GBM. Citation Format: Muhammad Vaseem Shaikh, Sabra K. Salim, Jeffrey Wei, William T. Maich, Alisha A. Anand, Oliver Young Tang, Minomi K. Subapanditha, Yujin Suk, Manoj Singh, Zahra Alizada, Benjamin Brakel, Vassil Dimitrov, Zoya Tabunshchyk, Kevin Brown, Parvez Vora, Zev Binder, Chitra Venugopal, Jason Moffat, Sheila K. Singh. Generation of allogeneic CAR-T circumvents functional deficits in patient-derived autologous product for glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5241.

Shell models are simplified models of hydrodynamic turbulence, retaining only some essential features of the original equations, such as the non-linearity, symmetries and quadratic invariants. Yet, they were shown to reproduce the most salient properties of developed turbulence, in particular universal statistics and multi-scaling. We set up the functional renormalisation group (FRG) formalism to study generic shell models. In particular, we formulate an inverse RG flow, which consists in integrating out fluctuation modes from the large scales (small wavenumbers) to the small scales (large wavenumbers), which is physically grounded and has long been advocated in the context of turbulence. Focusing on the Sabra shell model, we study the effect of both a large-scale forcing, and a power-law forcing exerted at all scales. We show that these two types of forcing yield different fixed points, and thus correspond to distinct universality classes, characterised by different scaling exponents. We find that the power-law forcing leads to dimensional (K41-like) scaling, while the large-scale forcing entails anomalous scaling.

Abstract Background A major goal of evolutionary developmental biology is to discover general models and mechanisms that create the phenotypes of organisms. However, universal models of such fundamental growth and form are rare, presumably due to the limited number of physical laws and biological processes that influence growth. One such model is the logarithmic spiral, which has been purported to explain the growth of biological structures such as teeth, claws, horns, and beaks. However, the logarithmic spiral only describes the path of the structure through space, and cannot generate these shapes. Results Here we show a new universal model based on a power law between the radius of the structure and its length, which generates a shape called a ‘power cone’. We describe the underlying ‘power cascade’ model that explains the extreme diversity of tooth shapes in vertebrates, including humans, mammoths, sabre-toothed cats, tyrannosaurs and giant megalodon sharks. This model can be used to predict the age of mammals with ever-growing teeth, including elephants and rodents. We view this as the third general model of tooth development, along with the patterning cascade model for cusp number and spacing, and the inhibitory cascade model that predicts relative tooth size. Beyond the dentition, this new model also describes the growth of claws, horns, antlers and beaks of vertebrates, as well as the fangs and shells of invertebrates, and thorns and prickles of plants. Conclusions The power cone is generated when the radial power growth rate is unequal to the length power growth rate. The power cascade model operates independently of the logarithmic spiral and is present throughout diverse biological systems. The power cascade provides a mechanistic basis for the generation of these pointed structures across the tree of life.

Dans cette thèse nous nous intéressons à deux modèles simplifiés décrivant des écoulements turbulents. Dans ces deux modèles, la turbulence est caractérisée par l'invariance d'échelle et des propriétés statistiques universelles, comme observé pour la turbulence hydrodynamique réelle. Ce type de comportement est très familier en physique: il s'agit d'un système critique. Dans cette thèse, nous utilisons un outil très répandu pour l'étude de la criticalité: le groupe de renormalisation fonctionnel (FRG). Le premier modèle, nommé modèle de Sabra, décrit les interactions effectives entre un nombre discret de modes de vitesse d'un fluide turbulent. Cette description schématique conserve beacoup de propriétés essentielles de la turbulence. En particulier, le champ de vitesse est multi-fractal. La façon dont la dynamique engendre cette multi-fractalité est encore mal comprise d'un point de vue théorique. Dans cette thèse, nous formulons un flot de renormalisation inverse, c'est-à-dire intégrant les plus grandes échelles d'abord. Grâce à cette méthode, nous trouvons un point fixe du flot de renormalisation ayant une invariance d'échelle anormale, et relativement proche de la valeur attendue pour certaines observables. Nous montrons que ce point fixe diffère de celui obtenu lorsque toutes les échelles sont forcées, par un forçage avec un spectre en loi de puissance, qui correspond au point fixe du RG obtenu en théorie de perturbation. Le second modèle étudié est l'équation de Burgers, qui décrit la dynamique d'un fluide en l'absence de pression. Nous nous intéressons à l'effet d'un bruit conservatif sur le champ de vitesse. Nous prouvons l'existence d'un régime d'invariance d'échelle avec un exposant critique dynamique z=1 en utilisant une fermeture exacte de l'équation de flot de renormalisation. Cette fermeture est permise par l'existence de certaines symétries de l'équation de Burgers. Ce nouveau régime d'invariance d'échelle avait été observé auparavant dans des solutions numériques de l'équation de Burgers. Nous apportons dans cette thèse une preuve théorique de son existence, et calculons les propriétés universelles associées
In this thesis, we focus on two simplified models describing turbulent flows. In these two models, the turbulent state exhibits scale-invariance and universal statistical properties resembling those of true hydrodynamical turbulence. This type of behaviour is very familiar in physics: it corresponds to a critical system. In this work, we use a widely used tool in the study of criticality: the functional renormalisation group (FRG). The first model, named the Sabra shell model, describes effective interactions among a discrete number of velocity modes of a turbulent fluid. This schematic description captures many essential properties of turbulent flows. In particular, the velocity field is multifractal. The way in which the dynamics generates this multifractality is still poorly understood from a theoretical perspective. In this thesis, we formulate a reverse renormalisation flow, meaning that we integrate out the largest scales first. Using this method, we find a fixed point of the renormalisation flow with anomalous scale invariance, relatively close to the expected value for certain observables. We show that it is clearly distinct from the fixed point obtained when all scales are forced, through a forcing with a power-law spectrum, which corresponds to the fixed point of the RG obtained in perturbation theory. The second model studied is the Burgers equation, which describes the dynamics of a fluid in the absence of pressure. We focus on the effect of a conservative noise on the velocity field. We prove the existence of a scale invariant regime with a critical dynamical exponent z=1 using an exact closure of the renormalisation flow equation. This closure relies on the existence of certain symmetries of the Burgers equation. Indications of the existence of this new scaling regime were previously found in numerical solutions of the Burgers equation. We provide in this thesis a theoretical proof of its existence and calculate the associated universal properties

The transfer of energy in turbulent flows occurs as a product of breaking of smaller and smaller eddies, this implies that in a spectral formulation, the transfer occurs from small wavenumbers to large wavenumbers. In order to observe the energy cascading, dissipation scales must be reached, which depend on the Reynolds number, this makes direct simulations of the Navier-Stokes equation impractical. Reduced models were investigated in recent years, such as shell models. Shell models are built by mimicking the spectral model respecting the mechanisms that are preserved, such as energy conservation, scaling and symmetries. In this paper, we will use the Sabra shell model for the study of the energy cascading in turbulent flows and we will show numerically that the energy dissipation is approximately −1/3 which is in agreement with the K41 theory.