EXPERIMENTS carried out using a split Hopkinson torsional bar have shown that only one shear band develops in specimens of hot rolled steel which break during testing. We observed, however, that in specimens which were not deformed to failure, several fine shear bands appeared. We believe that these formed during the loading cycle before the appearance of the final shear band and were not due to the effect of unloading. So we developed a numerical model to study the evolution of shear banding from several finite amplitude disturbances (FADs) in both temperature and strain rate. This numerical model reveals the detailed processes by which the FADs evolve into a fully developed shear band and suggests that beyond instability, the so-called shear banding process consists of two stages : inhomogeneous shearing and true shear-banding. The latter is characterized by the collapse of the stress and an abrupt increase of the local shear strain rate. NARROW shear bands occur quite frequently in a variety of materials under dynamic loading and are usually termed adiabatic shear bands (ROGERS, 1979). The basic mechanism for them was proposed by ZENER and HOLLOMON (1944) as the thermoplastic instability of material during dynamic loading, caused by thermal softening (due to heat generated by plastic deformation) being stronger than strain hardening, strain rate hardening and other hardening mechanisms. In analytical studies, the maximum shear load criterion (CuLvER, 1973: STAKER, 1980) was developed to determine the susceptibility of materials to adiabatic shear banding and a one-dimensional model for simple shear was developed to study the process of dynamic shear. Using this model, instability as well as localization analyses have been carried out (CLIFTON et al., 1984; BAI, 1982: FRESSENGEAS and MOLINARI, 1987; BAI et al., 1986; MOLINAR! and CLIFTON, 1987). Computing codes have also been written to demonstrate various features of adiabatic shear banding (WADA and NAKAMURE, 1978~ DREW and FLAHERTY, 1984; WRIGHT and WALTER, 1987; BATRA, 1987 ; KWON and BATRA, 1988). Although theoretical studies provide some operational rules to predict the onset of shear banding, they do not reveal the whole process. Perhaps the most difficult aspect of adiabatic shear banding is its nonlinearity and transient nature and only small progress on this issue has been made in recent years. NOTATIONExperimentally, the split Hopkinson torsional bar is one of the most commonly used instruments to investigate the behaviour of materials under dynamic torsional loading (CoSTIN et al., 1979). Recently, a high-speed infrared radiation detection system and a photographic technique have been used to study the process of shear banding (HARTLEY et al., 1987: MARCHAND and DUFFY, 1988). By using these techniques, MARCHAND and DUFFY (1988) discovered that the process of shear banding consists of three stages : (i) a homogeneous strain state, (ii) an inhomogeneous strain state and (iii) a severe localization stage. In the third stage, severe local...
Enterovirus A71 (EV-A71) and many members of the Picornaviridae family are neurotropic pathogens of global concern. These viruses are primarily transmitted through the fecal-oral route, and thus suitable animal models of oral infection are needed to investigate viral pathogenesis. An animal model of oral infection was developed using transgenic mice expressing human SCARB2 (hSCARB2 Tg), murine-adapted EV-A71/MP4 virus, and EV-A71/MP4 virus with an engineered nanoluciferase gene that allows imaging of viral replication and spread in infected mice. Next-generation sequencing of EV-A71 genomes in the tissues and organs of infected mice was also performed. Oral inoculation of EV-A71/MP4 or nanoluciferase-carrying MP4 virus stably induced neurological symptoms and death in infected 21-day-old weaned mice. In vivo bioluminescence imaging of infected mice and tissue immunostaining of viral antigens indicated that orally-inoculated virus can spread to the central nervous system and other tissues. Next-generating sequencing further identified diverse mutations in viral genomes that can potentially contribute to viral pathogenesis. This study presents an EV-A71 oral infection murine model that efficiently infects weaned mice and allows tracking of viral spread, features that can facilitate research into viral pathogenesis and neuroinvasion via the natural route of infection. Importance Enterovirus A71 (EV-A71), a positive-strand RNA virus of the Picornaviridae , poses a persistent global public health problem. EV-A71 is primarily transmitted through the fecal-oral route, and thus suitable animal models of oral infection are needed to investigate viral pathogenesis. We present an animal model of EV-A71 infection that enables the natural route of oral infection in weaned and non-immunocompromised 21-day-old hSCARB2 transgenic mice. Our results demonstrate that severe disease and death could be stably induced and viral invasion of the CNS could be replicated in this model, similar to severe real-world EV-A71 infections. We also developed a nanoluciferase-containing EV-A71 virus that can be used with this animal model to track viral spread after oral infection in real-time. Such a model offers several advantages over existing animal models, and can facilitate future research into viral spread, tissue tropism, and viral pathogenesis, all pressing issues that remain unaddressed for EV-A71 infections.
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