Here, we show that the ponderomotive force associated with laser speckles can scatter electrons in a laser-produced plasma in a manner similar to Coulomb scattering. Analytic expressions for the ...effective collision rates are given. The electron-speckle collisions become important at high laser intensity or during filamentation, affecting both long- and short-pulse laser intensity regimes. As an example, we find that the effective collision rate in the laser-overlap region of hohlraums on the National Ignition Facility is expected to exceed the Coulomb collision rate by 1 order of magnitude, leading to a fundamental change to the electron transport properties. At the high intensities characteristic of short-pulse laser-plasma interactions (I ≳ 1017 W cm–2), the scattering is strong enough to cause the direct absorption of laser energy, generating hot electrons with energy scaling as E ≈ 1.44 (I/1018 W cm–2)1/2 MeV , close to experimentally observed results.
Magnetic field generated by the Biermann battery is thought to be one of the principal mechanisms behind the inhibition of heat flow in laser-plasma interactions, and is predicted to grow ...exponentially in some contexts due to the thermomagnetic instability Tidman and Shanny, Phys. Fluids 17, 1207 (1974)PFLDAS0031-917110.1063/1.1694866. In contrast to these predictions, however, we have conducted Vlasov-Fokker-Planck simulations of magnetic field dynamics under a range of classically unstable laser-fusion conditions, and find field generation to be strongly suppressed, preventing magnetization of the transport, and stabilizing instability. By deriving new scaling laws, we show that this stabilization is a consequence of (i) heavy suppression of the Biermann battery under nonlocal conditions; (ii) rapid convection of magnetic field by the heat flow; and (iii) comparatively short field length scales. Our results indicate that classical models substantially overestimate the importance of magnetic fields generated by the Biermann battery, and the susceptibility of laser-fusion plasmas to the thermomagnetic instability.
Acromegaly Dineen, R; Stewart, P M; Sherlock, M
QJM : An International Journal of Medicine,
2017-Jul-01, 20170701, Letnik:
110, Številka:
7
Journal Article
Recenzirano
Acromegaly is a rare, chronic, progressive disease characterized by an excess secretion of growth hormone (GH) and increased circulating insulin-like growth factor 1 (IGF-1) concentrations. It is ...caused by a pituitary adenoma in the vast majority of cases. The clinical diagnosis, based on symptoms related to GH excess, is often delayed due to the insidious nature of the disease. Consequently, patients often have established systemic complications at diagnosis with increased morbidity and premature mortality. Serum IGF-1 measurement is recommended as the initial screen for patients with suspected acromegaly. The gold standard diagnostic test remains the oral glucose tolerance test with concomitant GH measurement. Therapy for acromegaly is targeted at decreasing GH and IGF-1 levels, ameliorating patients' symptoms and decreasing any local compressive effects of the pituitary adenoma. The therapeutic options for acromegaly include surgery, medical therapies (such as dopamine agonists, somatostatin receptor agonists and the GH receptor antagonist pegvisomant) and radiotherapy. A multidisciplinary approach is recommended with often a requirement for combined treatment modalities. With disease control, associated morbidity and mortality can be reduced. The recently published evidence-based guidelines by the Endocrine society addressed important clinical issues regarding the evaluation and management of acromegaly. This review discusses advances in our understanding of the pathophysiology of acromegaly, diagnosis of various forms of the disease and focuses on current treatment modalities, and on future pharmacological therapies for patients with acromegaly.
Diabetes in Patients With Acromegaly Hannon, A. M.; Thompson, C. J.; Sherlock, M.
Current Diabetes Reports,
02/2017, Letnik:
17, Številka:
2
Journal Article, Book Review
Recenzirano
Purpose of Review
Acromegaly is a clinical syndrome which results from growth hormone excess. Uncontrolled acromegaly is associated with cardiovascular mortality, due to an excess of risk factors ...including diabetes mellitus, hypertension and cardiomegaly. Diabetes mellitus is a frequent complication of acromegaly with a prevalence of 12–37%. This review will provide an overview of a number of aspects of diabetes mellitus and glucose intolerance in acromegaly including the following:
Epidemiology and pathophysiology of abnormalities of glucose homeostasis
The impact of different management options for acromegaly on glucose homeostasis
The management options for diabetes mellitus in patients with acromegaly
Recent Findings
Growth hormone and IGF-1 have complex effects on glucose metabolism. Insulin resistance, hyperinsulinaemia and increased gluconeogenesis combine to produce a metabolic milieu which leads to the development of diabetes in acromegaly. Treatment of acromegaly should ameliorate abnormalities of glucose metabolism, due to reversal of insulin resistance and a reduction in gluconeogenesis. Recent advances in medical therapy of acromegaly have varying impacts on glucose homeostasis. These adverse effects influence management choices in patients with acromegaly who also have diabetes mellitus or glucose intolerance.
Summary
The underlying mechanisms of disorders of glucose metabolism in patients with acromegaly are complex. The aim of treatment of acromegaly is normalisation of GH/IGF-1 with reduction of co-morbidities. The choice of therapy for acromegaly should consider the impact of therapy on several factors including glucose metabolism.
Nonlocal heat flux was measured in laser-produced coronal plasmas using a novel Thomson scattering technique. The measured heat flux was smaller than the classical values inferred from the measured ...plasma conditions in regions with large temperature gradients and agreed with classical values for weak gradients. Vlasov-Fokker-Planck simulations self-consistently calculated the electron distribution functions used to reproduce the measured Thomson scattering spectra and to determine the heat flux. Multigroup nonlocal simulations overestimated the measured heat flux.
A procedure for implementing Coulomb collisions into hybrid (particle-fluid) plasma models is outlined which is rapid in execution due to the use of approximate expressions for the collision ...integrals and conserves energy and momentum exactly. Particles undergo dynamic friction and diffusion in velocity-space at rates consistent with the velocity-dependent Fokker–Planck diffusion coefficients and there are no assumptions made about the shape or size of the particle distribution function. The method is tested against the analytical theory of test particle slowing in a background plasma and the thermal equilibration of a Maxwellian distribution.
Adrenocortical carcinoma (ACC) has an aggressive but variable clinical course. Prognostic stratification based on the European Network for the Study of Adrenal Tumours stage and Ki67 index is ...limited. We aimed to demonstrate the prognostic role of a points-based score (S-GRAS) in a large cohort of patients with ACC.
This is a multicentre, retrospective study on ACC patients who underwent adrenalectomy.
The S-GRAS score was calculated as a sum of the following points: tumour stage (1-2 = 0; 3 = 1; 4 = 2), grade (Ki67 index 0-9% = 0; 10-19% = 1; ≥20% = 2 points), resection status (R0 = 0; RX = 1; R1 = 2; R2 = 3), age (<50 years = 0; ≥50 years = 1), symptoms (no = 0; yes = 1), and categorised, generating four groups (0-1, 2-3, 4-5, and 6-9). Endpoints were progression-free survival (PFS) and disease-specific survival (DSS). The discriminative performance of S-GRAS and its components was tested by Harrell's Concordance index (C-index) and Royston-Sauerbrei's R2D statistic.
We included 942 ACC patients. The S-GRAS score showed superior prognostic performance for both PFS and DSS, with best discrimination obtained using the individual scores (0-9) (C-index = 0.73, R2D = 0.30, and C-index = 0.79, R2D = 0.45, respectively, all P < 0.01vs each component). The superiority of S-GRAS score remained when comparing patients treated or not with adjuvant mitotane (n = 481 vs 314). In particular, the risk of recurrence was significantly reduced as a result of adjuvant mitotane only in patients with S-GRAS 4-5.
The prognostic performance of S-GRAS is superior to tumour stage and Ki67 in operated ACC patients, independently from adjuvant mitotane. S-GRAS score provides a new important guide for personalised management of ACC (i.e. radiological surveillance and adjuvant treatment).
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