Hiroshi Terashima

A front-tracking/ghost-fluid method for fluid interfaces in compressible flows

A front-tracking/ghost-fluid method is introduced for simulations of fluid interfaces in compressible flows. The new method captures fluid interfaces using explicit front-tracking and defines interface conditions with the ghost-fluid method. Several examples of multiphase flow simulations, including a shock-bubble interaction, the Richtmyer-Meshkov instability, the Rayleigh-Taylor instability, the collapse of an air bubble in water and the breakup of a water drop in air, using the Euler or the Navier-Stokes equations, are performed in order to demonstrate the accuracy and capability of the new method. The computational results are compared with experiments and earlier computational studies. The results show that the new method can simulate interface dynamics accurately, including the effect of surface tension. Results for compressible gas-water systems show that the new method can be used for simulations of fluid interface with large density differences.

Early onset epileptic encephalopathy caused by de novo SCN8A mutations.

De novo SCN8A mutations have been reported in patients with epileptic encephalopathy. Herein we report seven patients with de novo heterozygous SCN8A mutations, which were found in our comprehensive genetic analysis (target capture or whole‐exome sequencing) for early onset epileptic encephalopathies (EOEEs).

Approach for simulating gas-liquid-like flows under supercritical pressures using a high-order central differencing scheme

This study proposes an approach for simulations of cryogenic fluid mixing under supercritical pressures using high-order schemes. In this approach, we introduce a pressure evolution equation and consistently construct numerical diffusion terms to maintain the velocity and pressure equilibriums at fluid interfaces. The interfaces with high density and temperature ratio are successfully captured without the generation of spurious oscillations, while a high-order central differencing scheme resolves the flow fields. The present method preserves the mass and momentum conservation properties, while the poor energy conservation property is recognized. The one-dimensional single and multi-species interface advection and two-dimensional cryogenic jet mixing problems demonstrate the superiority and robustness of the present method over a conventional fully conservative method.

Numerical (error) issues on compressible multicomponent flows using a high-order differencing scheme: Weighted compact nonlinear scheme

A weighted compact nonlinear scheme (WCNS) is applied to numerical simulations of compressible multicomponent flows, and four different implementations (fully or quasi-conservative forms and conservative or primitive variables interpolations) are examined in order to investigate numerical oscillation generated in each implementation. The results show that the different types of numerical oscillation in pressure field are generated when fully conservative form or interpolation of conservative variables is selected, while quasi-conservative form generally has poor mass conservation property. The WCNS implementation with quasi-conservative form and interpolation of primitive variables can suppress these oscillations similar to previous finite volume WENO scheme, despite the present scheme is finite difference formulation and computationally cheaper for multi-dimensional problems. Series of analysis conducted in this study show that the numerical oscillation due to fully conservative form is generated only in initial flow fields, while the numerical oscillation due to interpolation of conservative variables exists during the computations, which leads to significant spurious numerical oscillations near interfaces of different component of fluids. The error due to fully conservative form can be greatly reduced by smoothing interface, while the numerical oscillation due to interpolation of conservative variables cannot be significantly reduced. The primitive variable interpolation is, therefore, considered to be better choice for compressible multicomponent flows in the framework of WCNS. Meanwhile better choice of fully or quasi-conservative form depends on a situation because the error due to fully conservative form can be suppressed by smoothed interface and because quasi-conservative form eliminates all the numerical oscillation but has poor mass conservation.

High-Resolution Numerical Method for Supercritical Flows with Large Density Variations

is introduced with the aim of simulating jet mixing under supercritical pressure environments. The nonlinear localized artificial diffusivity provides the stability to capture different types of discontinuity, such as shock wave, contact surface, and material interface, whereas the high-order compact difference scheme resolves broadband scales in the rest of the domain. The present method is tested on several one-dimensional discontinuity-related problems under super/transcritical conditions and a comparatively more illustrative two-dimensional lowtemperature planar jet problem under a supercritical pressure condition. The localized artificial diffusivity, especially artificial thermal conductivity for temperature gradients, effectively suppresses numerical wiggles near the interfaces. The effects of the artificial thermal conductivity on numerical stability and accuracy are examined. Comparisons between the present method and a conventional low-order scheme demonstrate the superior performance of the present method for resolving a wide range of flow scales while successfully capturing large density/temperature variations at interfaces.

Nationwide survey of Cockayne syndrome in Japan: Incidence, clinical course and prognosis

In the first nationwide survey of Cockayne syndrome (CS) in Japan, the incidence of CS was estimated to be 2.77 per million births (95%CI: 2.19–3.11) and the prevalence was approximately 1 in 2 500 000. A total of 47 CS patients (24 surviving and 23 deceased) were identified. Based on clinical course, these 47 patients were classified into CS type 1 (n = 41; 21 surviving, 20 deceased), CS type 2 (n = 2; all deceased), CS type 3 (n = 3; all surviving), and CS/xeroderma pigmentosum type D (n = 1, deceased). In the 41 CS type 1 patients, seven findings (i.e. failure to thrive; photosensitivity; deafness; characteristic facial appearance of CS [sunken eyes]; foot joint contracture; intellectual disability; and basal ganglia calcification on computed tomography [CT]) were observed in >90% of patients. Of these, failure to thrive, photosensitivity, and intellectual disability (language delays) developed before 2 or 3 years of age, whereas deafness, sunken eyes, and basal ganglia calcification on CT occurred later. Features such as bodyweight and height stagnation, language delay, abnormal nutritional pathways (tube feeding), and renal failure were more prominent in the 20 deceased CS type 1 patients than in the 21 surviving CS type 1 patients. Of the 20 deceased CS type 1 patients, nine developed severe renal failure during the terminal stages of their condition. The present findings suggest that the clinical course of CS includes a diverse range of symptoms, but each type has characteristic symptoms. In addition, the management of renal failure and nutrition are very important for ensuring good quality of life throughout the long‐term course of CS.

Characteristic MRI features of chronic inflammatory demyelinating polyradiculoneuropathy

We present characteristic magnetic resonance imaging (MRI) features in a pediatric female patient with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Muscle weakness developed at 8 years old and fluctuated during the clinical course over 7 years. Electrophysiological studies showed a demyelination pattern with moderately delayed nerve conduction velocity, as well as dispersion phenomenon. MRI showed marked changes in thickening of the spinal nerve roots and their peripheral nerves in the lumber and brachial plexuses, as well as in the bilateral trigeminal nerves. It is suggested that these MRI features are characteristic and strongly supportive of the diagnosis of CIDP with a prolonged clinical course.

Chemical Kinetics of Hypergolic Ignition in N2H4/N2O4-NO2 Gas Mixtures

A detailed chemical kinetic mechanism for hypergolic ignition of N2H4 in a N2O4-NO2 gas mixture has been constructed. In this mechanism, the hypergolic ignition is mainly caused by the sequential reactions of H atom abstraction from N2Hm by NO2:  N2Hm+NO2=N2Hm−1+HONO/HNO2(m=4∼1). Although the first step of the H atom abstraction (m=4) is endothermic, consecutive abstraction reactions for m=3, 2, and 1 are exothermic, and especially heat release by the reaction of N2H+NO2=N2+HONO(m=1) is large because of N2 production. Temperature rise caused by the heat release accelerates the endothermic initiation reaction (m=4). This thermal feedback is responsible for the hypergolic ignition at low temperatures. Because no experimental and theoretical information is available on these reactions, rate coefficients were evaluated on the basis of transition state theory, unimolecular rate theory, and master equation analysis with quantum chemical calculations of potential energy curves. In addition, reactions of N2H4 wit...

Missense mutations in sodium channel SCN1A and SCN2A predispose children to encephalopathy with severe febrile seizures.

OBJECTIVE Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a childhood encephalopathy following severe febrile seizures. The pathogenesis of AESD is considered to be fever-induced seizure susceptibility and excitotoxicity, which may be caused by sodium channel dysfunction in some cases. Here we studied whether mutations in genes encoding sodium channels, SCN1A and SCN2A, predispose children to AESD. METHODS We recruited 92 AESD patients in a nationwide survey of acute encephalopathy in Japan from 2008 to 2011. We collected their genomic DNA samples, and sequenced the entire coding region of SCN1A and SCN2A. RESULTS Five out of 92 patients (5.4%) had missense mutations either in SCN1A or SCN2A. After a preceding infection with fever, all the patients showed status epilepticus at the onset. Hemiconvulsion-hemiplegia was recognized in three patients during the acute/subacute phase. One patient had taken theophylline for the treatment of bronchial asthma just before the onset of AESD. Familial history was not remarkable except one patient with a SCN1A mutation (G1647S) whose mother had a similar episode of AESD in her childhood. A different substitution (G1674R) at the same amino acid position, as well as two other SCN1A mutations found in this study, had previously been reported in Dravet syndrome. Another SCN1A mutation (R1575C) had been detected in other types of acute encephahlitis/encephalopathy. One patient had SCN2A mutation, F328V, which had previously been reported in Dravet syndrome. Another SCN2A mutation, I172V, was novel. None of the patients were diagnosed with Dravet syndrome or genetic (generalized) epilepsy with febrile seizure plus in the following-up period. CONCLUSIONS Mutations in SCN1A and SCN2A are a predisposing factor of AESD. Altered channel activity caused by these mutations may provoke seizures and excitotoxic brain damage.

Acute myeloid leukemia-associated DNMT3A p.Arg882His mutation in a patient with Tatton-Brown–Rahman overgrowth syndrome as a constitutional mutation

DNA methylation plays a critical role in both embryonic development and tumorigenesis and is mediated through various DNA methyltransferases. Constitutional mutations in the de novo DNA methyltransferase DNMT3A cause a recently identified Tatton‐Brown–Rahman overgrowth syndrome (TBRS). Somatically acquired mutations in DNMT3A are causally associated with acute myeloid leukemia (AML), and p.Arg882His represents the most prevalent hotspot. So far, no patients with TBRS have been reported to have subsequently developed AML. Here, we report a live birth and the survival of a female with the TBRS phenotype who had a heterozygous constitutional DNMT3A mutation at the AML somatic mutation hotspot p.Arg882His in her DNA from peripheral blood and buccal tissue. Her characteristic features at birth included hypotonia, narrow palpebral fissures, ventricular septal defect, umbilical hernia, sacral cyst, Chiari type I anomaly. At the age of 6 years, she exhibited overgrowth (> 3 SD) and round face and intellectual disability. This report represents the first documentation of the same variant (DNMT3A p.Arg882His) as both the constitutional mutation associated with TBRS and the somatic mutation hotspot of AML. The observation neither confirms nor denies the notion that mutations responsible for TBRS and those for AML might share the same mode of action. Larger data sets are required to determine whether TBRS patients with constitutional DNMT3A mutations are at an increased risk for AML.