362 research outputs found
Kraichnan-Leith-Batchelor similarity theory and two-dimensional inverse cascades
No full textWe study the scaling properties and Kraichnan-Leith-Batchelor (KLB) theory of forced inverse cascades in generalized two-dimensional (2D) fluids (-turbulence models) simulated at resolution . We consider (surface quasigeostrophic flow), (2D vorticity dynamics) and . The forcing scale is well-resolved, a direct cascade is present and there is no large-scale dissipation. Coherent vortices spanning a range of sizes, most larger than the forcing scale, are present for both and . The active scalar field for contains comparatively few and small vortices. The energy spectral slopes in the inverse cascade are steeper than the KLB prediction in all three systems. Since we stop the simulations well before the cascades have reached the domain scale, vortex formation and spectral steepening are not due to condensation effects; nor are they caused by large-scale dissipation, which is absent. One- and two-point pdfs, hyperflatness factors and structure functions indicate that the inverse cascades are intermittent and non-Gaussian over much of the inertial range for and , while the inverse cascade is much closer to Gaussian and non-intermittent. For the steep spectrum is close to that associated with enstrophy equipartition. Continuous wavelet analysis shows approximate KLB scaling () and () in the interstitial regions between the coherent vortices. Our results demonstrate that coherent vortex formation ( and ) and non-realizability () cause 2D inverse cascades to deviate from the KLB predictions, but that the flow between the vortices exhibits KLB scaling and non-intermittent statistics for and . The results will appear in \cite{BurgessEA2015}, which has been accepted to the \emph{Journal of Fluid Mechanics}
Astrocytic tumors: diffuse astrocytoma, anaplastic astrocytoma, glioblastoma, and gliomatosis cerebri
No full textThe works of Mr. Congreve : in two volumes; to which is prefixed The Life of the author.
No full textv.1. The life of the author. The old batchelor. The double dealer. Love for love. -- v.2. The mourning bride. The way of the world. The judgment of Paris. Semele. Poems on several occasions.Mode of access: Internet
Turbulent super-diffusion as a ballistic cascade
No full textSince the pioneering work of Richardson in 1926, later refined by Batchelor and Obukhov in 1950, it is predicted that the rate of separation of pairs of fluid elements in turbulent flows with initial separation at inertial scales, grows ballistically first (Batchelor regime), before undergoing a transition towards a super-diffusive regime where the mean-square separation grows as (Richardson regime). Richardson empirically interpreted this super-diffusive regime in terms of a non-Fickian process with a scale dependent diffusion coefficient (the celebrated Richardson's ``4/3rd'' law). However, the actual physical mechanism at the origin of such a scale dependent diffusion coefficient remains unclear. The present work proposes a simple physical phenomenology for the Richardson super-diffusivity in turbulence based on a scale dependent \emph{ballistic} scenario rather than a scale dependent \emph{diffusive} scenario. It is shown that this phenomenology elucidates several aspects of turbulent dispersion: (i) it gives a simple physical explanation of the origin of the super diffusive Richardson regime as an iterative cascade of scale-dependent ballistic separations, (ii) it simply relates the Richardson constant to the Kolmogorov constant (and eventually to a ballistic persistence parameter), (iii) it gives a simple physical interpretation of the non-Fickian scale-dependent diffusivity coefficient as originally proposed by Richardson and (iv) a further extension of the phenomenology, taking into account higher order corrections to the local ballisitic motion, gives a robust interpretation of the assymetry between forward and backward dispersion, with an explicit connection to the energy flux accross scales
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Recent Advances in Treatment of Primary Central Nervous System Lymphoma
No full textOpinion statement Therapeutic options are limited in primary central nervous system lymphoma (PCNSL) with no uniform consensus on optimal management and few published, randomized trials. High-dose methotrexate in combination with other chemotherapeutic agents forms the mainstay of treatment. There hasn’t been much progress beyond high-dose methotrexate in this disease, and although results from trials using high-dose chemotherapy and autologous stem-cell transplant seem promising, these need to be further validated. Moreover, the role of whole brain radiation in the upfront setting remains to be determined. However, international efforts in this direction are underway, with ongoing randomized trials in newly diagnosed PCNSL, more research on the molecular pathogenesis and biomarkers, and the use of novel agents in salvage therapy. There also is emphasis on quality of life parameters and neurocognitive status. Future treatment options should optimize high-efficacy rates while minimizing the risk of neurotoxicity.Version of Recor
Non-local dispersion and the reassessment of Richardson's t<sup>3</sup>-scaling law
No full textThe Richardson-scaling law states that the mean square separation of a fluid particle pair grows according to twithin the inertial range and at intermediate times. The theories predicting this scaling regime assume that the pair separation is within the inertial range and that the dispersion is local, which means that only eddies at the scale of the separation contribute. These assumptions ignore the structural organization of the turbulent flow into large-scale shear layers, where the intense small-scale motions are bounded by the large-scale energetic motions. Therefore, the large scales contribute to the velocity difference across the small-scale structures. It is shown that, indeed, the pair dispersion inside these layers is highly non-local and approaches Taylor dispersion in a way that is fundamentally different from the Richardson-scaling law. Also, the layer's contribution to the overall mean square separation remains significant as the Reynolds number increases. This calls into question the validity of the theoretical assumptions. Moreover, a literature survey reveals that, so far, tscaling is not observed for initial separations within the inertial range. We propose that the intermediate pair dispersion regime is a transition region that connects the initial Batchelor- with the final Taylor-dispersion regime. Such a simple interpretation is shown to be consistent with observations and is able to explain why tscaling is found only for one specific initial separation outside the inertial range. Moreover, the model incorporates the observed non-local contribution to the dispersion, because it requires only small-time-scale properties and large-scale properties. Fluid Mechanic
Diagnosis and management of primary central nervous system lymphoma
No full textPrimary central nervous system lymphoma (PCNSL) is a rare and aggressive extranodal non-Hodgkin lymphoma (NHL) that is confined to the brain, eyes, spinal cord, or leptomeninges without systemic involvement. The overall prognosis, diagnosis, and management of PCNSL differ from those for other types of NHL. Prompt diagnosis and initiation of treatment are vital for improving clinical outcomes. PCNSL is responsive to radiation therapy; however, whole-brain radiotherapy (WBRT) inadequately controls the disease when it is used alone, and its delayed neurotoxicity causes neurocognitive impairment, especially in elderly patients. High-dose methotrexate (HD-MTX)-based induction chemotherapy with or without autologous stem cell transplantation (ASCT) or reduced-dose WBRT leads to durable disease control and less neurotoxicity. The optimal treatment has yet to be defined; however, HD-MTX-based induction chemotherapy is considered standard for newly diagnosed PCNSL. Ongoing randomized trials are addressing the roles of rituximab and consolidative treatment with ASCT or reduced-dose WBRT. Despite high tumor response rates with the initial treatment, many patients relapse with a very poor prognosis. The optimal treatment for refractory or relapsed PCNSL is poorly defined. The choice of salvage treatment depends on a patient's age, previous treatment and response, performance status, and comorbidities at the time of relapse. This review provides an overview of the clinical features, diagnosis, pathology, and management of PCNSL in immunocompetent patients, and it focuses on recent advances in treatment. Cancer 2017;123:4314-24. © 2017 American Cancer Society
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