Quasi-steady stages in the process of premixed flame acceleration in narrow channels

The present paper addresses the phenomenon of spontaneous acceleration of a pre-mixed flame front propagating in micro-channels, with subsequent deflagration-to-detonation transition. It has recently been shown experimentally [M. Wu, M. Burke, S. Son, and R. Yetter, Proc. Combust. Inst. 31, 2429 (2007)], computationally [D. Valiev, V. Bychkov, V. Akkerman, and L.-E. Eriksson, Phys. Rev. E 80, 036317 (2009)], and analytically [V. Bychkov, V. Akkerman, D. Valiev, and C. K. Law, Phys. Rev. E 81, 026309 (2010)] that the flame acceleration undergoes different stages, from an initial exponential regime to quasi-steady fast deflagration with saturated velocity. The present work focuses on the final saturation stages in the process of flame acceleration, when the flame propagates with supersonic velocity with respect to the channel walls. It is shown that an intermediate stage may occur during acceleration with quasi-steady velocity, noticeably below the Chapman-Jouguet deflagration speed. The intermediate stage is followed by additional flame acceleration and subsequent saturation to the Chapman-Jouguet deflagration regime. We elucidate the intermediate stage by the joint effect of gas pre-compression ahead of the flame front and the hydraulic resistance. The additional acceleration is related to viscous heating at the channel walls, being of key importance at the final stages. The possibility of explosion triggering is also demonstrated

The effect of COVID-19 on transplant function and development of CLAD in lung transplant patients:A multicenter experience

Background : Concerns have been raised on the impact of coronavirus disease (COVID-19) on lung transplant (LTx) patients. The aim of this study was to evaluate the transplant function pre- and post-COVID-19 in LTx patients. Methods : Data were retrospectively collected from LTx patients with confirmed COVID-19 from all 3 Dutch transplant centers, between February 2020 and September 2021. Spirometry results were collected pre-COVID-19, 3- and 6-months post infection. Results : Seventy-four LTx patients were included. Forty-two (57%) patients were admitted, 19 (26%) to the intensive care unit (ICU). The in-hospital mortality was 20%. Twelve out of 19 ICU patients died (63%), a further 3 died on general wards. Patients with available spirometry (78% at 3 months, 65% at 6 months) showed a significant decline in mean forced expiratory volume in 1 second (FEV1) (ΔFEV1 138 ± 39 ml, p = 0.001), and forced vital capacity (FVC) (ΔFVC 233 ±74 ml, p = 0.000) 3 months post infection. Lung function improved slightly from 3 to 6 months after COVID-19 (ΔFEV1 24 ± 38 ml; ΔFVC 100 ± 46 ml), but remained significantly lower than pre-COVID-19 values (ΔFEV1 86 ml ± 36 ml, p = 0.021; ΔFVC 117 ± 35 ml, p = 0.012). FEV1/FVC was > 0.70. Conclusions: In LTx patients COVID-19 results in high mortality in hospitalized patients. Lung function declined 3 months after infection and gradually improved at 6 months, but remained significantly lower compared to pre-COVID-19 values. The more significant decline in FVC than in FEV1 and FEV1/FVC > 70%, suggested a more restrictive pattern

Correction: Protocol of the Healthy Brain Study:An accessible resource for understanding the human brain and how it dynamically and individually operates in its bio-social context

[This corrects the article DOI: 10.1371/journal.pone.0260952.]

Efficient measurement and calculation of MR diffusion Anisotropy images using the platonic variance method

The Platonic variance method produces MR diffusion anisotropy (DA) images with a minimum amount of computational effort. It can be programmed in a self-contained MR sequence, thus eliminating the need for postprocessing on a separate workstation. The method uses gradient acquisition schemes, based on Platonic solids: the "icosahedric" scheme (N = 6), the "dodecahedric" scheme (N = 10), and combinations thereof. For these schemes the average of the diffusion tensor eigenvalues equals the average of the measured apparent diffusion coefficients (ADCs), and the variance of the eigenvalues equals 5/2 times the variance of the diffusion coefficients. This results in compact expressions for anisotropy measures, directly in terms of the acquired images, i.e., without calculating the eigenvalues or even the tensor elements. The resulting anisotropy images were shown to be identical to the ones traditionally derived. It is expected that this method will considerably promote the routine use of DA imaging. (C) 2003 Wiley-Liss, In

The direct tensor solution and higher-order acquisition schemes for generalized diffusion tensor imaging

Both in diffusion tensor imaging (DTI) and in generalized diffusion tensor imaging (GDTI) the relation between the diffusion tensor and the measured apparent diffusion coefficients is given by a tensorial equation, which needs to be inverted in order to solve the diffusion tensor. The traditional way to do this does not preserve the tensorial structure of the equation, which we consider a weakness in the method. For a physically correct measurement procedure, the condition number of the acquisition scheme, which is a determinant of the noise behavior, needs to be rotationally invariant. The method which traditionally is used to find such schemes, however, is cumbersome and mathematically unsatisfactory. This is considered a second weakness, closely connected to the first. In this paper we present an alternative inversion of the diffusion tensor equation, which does preserve the tensor form, for arbitrary order, and which is named the direct tensor solution (DTS). The DTS is derived under the assumption that the apparent diffusion coefficient in any direction is known, i.e. in the infinite acquisition scheme. Whenever the DTS is valid for a given finite acquisition scheme and for a given order, the condition number is rotationally invariant. The DTS provides a compact, algebraic procedure to check this rotational invariance. We also present a method to construct acquisition schemes, for which the DTS is valid for the measurement of higher-order diffusion tensors. Furthermore, the DTS leads to other mathematical insights, such as tensorial relationships between diffusion tensors of different orders, and a more general understanding of the Platonic Variance Method, which we published befor

From Gaucher's disease to metabolic radiology: translational radiological research and clinical practice

Imaging has an increasing role in the management of patients with inborn errors of metabolism. This role is related to expensive enzyme replacement therapy that requires a surrogate biomarker, such as magnetic resonance imaging. This review paper raises the issue of the potential for metabolic radiology to become a subspecialt

Changes in sub-calcaneal fat pad composition and their association with dynamic plantar foot pressure in people with diabetic neuropathy

Background: Diabetic foot disease is associated with physiological and biomechanical abnormalities in the foot that increase risk for ulceration. The objective was to assess MRI changes in the composition of sub-calcaneal fat pad tissue and its association with plantar pressure during walking. Methods: Fourteen people with diabetes and peripheral neuropathy and five age-matched healthy controls underwent T1-weighted sagittal plane spin-echo Dixon MRI of the rearfoot. Dixon Chemical Shift Imaging was used to create fat-only and water-only images from which the fat signal fraction in a defined ROI of the sub-calcaneal fat pad was calculated. Barefoot plantar pressure distribution during walking was assessed and associated with fat pad outcomes. Findings: Mean ± SD fat signal fraction was significantly lower in the neuropathic subjects than in the healthy controls (0.55 ± 0.11 vs. 0.72 ± 0.03, p < 0.005), and was explained by a lowering in fat signal (R2 0.87), more than an increase in water signal (R2 0.32). Mean ± SD peak pressure at the heel was 391 ± 119 kPa for the neuropathic subjects and 325 ± 53 kPa for the healthy controls (non-significantly different). Fat signal fraction and peak pressure were significantly inversely correlated (r = −0.59, p < 0.01). Interpretation: Dixon chemical shift MRI showed a reduced fat signal fraction in sub-calcaneal fat pad tissue in people with diabetic neuropathy. Both neuropathic and non-neuropathic factors may be attributed to this outcome. Fat pad function also seems to be compromised, as indicated by an associated increase in peak plantar pressures. This may increase risk for foot ulceration

The Rayleigh-Taylor instability in inertial fusion, astrophysical plasma and flames

Previous results are reviewed and new results are presented on the Rayleigh-Taylor instability in inertial confined fusion, flames and supernovae including gravitational and thermonuclear explosion mechanisms. The instability couples micro-scale plasma effects to large-scale hydrodynamic phenomena. In inertial fusion the instability reduces target compression. In supernovae the instability produces large-scale convection, which determines the fate of the star. The instability is often accompanied by mass flux through the unstable interface, which may have either a stabilizing or a destabilizing influence. Destabilization happens due to the Darrieus-Landau instability of a deflagration front. Still, it is unclear whether the instabilities lead to well-organized large-scale structures (bubbles) or to relatively isotropic turbulence (mixing layer