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A modification to the rate-dependent damage and failure model developed by Addessio and Johnson [J. Appl. Phys. 74, 1640 (1993)] for ductile materials under high-rate loading is presented. In the current formulation the equilibrium stress, which is used to calculate the plastic strain rate and damage in the material, is defined as the orthogonal projection of the final stress onto an equilibrium yield surface, instead of being a projection of the trial stress onto the yield surface as is done in the original formulation. The modification makes the current formulation fully consistent with the viscoplasticity theory. An implicit algorithm is also presented for the modified model and numerical results of copper under uniaxial strain loading are given to show the features of the model and the algorithm. Comparisons with the results of the original formulation are also presented. [ABSTRACT FROM AUTHOR]

An implicit numerical algorithm has been developed for a rate-dependent model for damage and failure of ductile materials under high-rate dynamic loading [F. L. Addessio and J. N. Johnson, J. Appl. Phys. 74, 1640 (1993)]. Over each time step, the algorithm first implicitly determines the equilibrium state on a Gurson surface, and then calculates the final state by solving viscous relaxation equations, also implicitly. Numerical examples are given to demonstrate the key features of the algorithm. Compared to the explicit algorithm used previously, the current algorithm allows significantly larger time steps that can be used in the analysis. As the viscosity of the material vanishes, the results of the rate-dependent model are shown here to converge to that of the corresponding rate-independent model, a result not achieved with the explicit algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a study of anisotropic damage and cracking in a hot isostatically pressed assembly of titanium alloy encapsulated AD-995 ceramic under ballistic impact using the statistical crack mechanics approach. Anisotropy of crack growth in the ceramic is illustrated numerically by examining the growth in crack sizes along three orientations. Comparisons with the experimental measurements of the predicted backsurface profile and the damage (cracking) in the ceramic suggest that the model predictions are consistent with the experimental data. Numerical simulation also indicates that a prestress of roughly 2 kbar (200 MPa) compensates for about 1% of initial porosity in the ceramic. A comparison is made to the Rajendran–Grove ceramic model in EPIC which assumes an isotropic crack distribution. [ABSTRACT FROM AUTHOR]

A thermodynamic approach is used to develop a framework for modeling uranium-niobium alloys under the conditions of high-strain rate. Using this framework, a three-dimensional phenomenological model, which includes nonlinear elasticity (equation of state), phase transformation, crystal reorientation, rate-dependent plasticity, and porosity growth, is presented. An implicit numerical technique is used to solve the evolution equations for the material state. Comparisons are made between the model and data for low-strain rate loading and unloading as well as heating and cooling experiments. Comparisons of the model and data also are made for low- and high-strain-rate uniaxial stress and uniaxial strain experiments. A uranium-6 wt % niobium alloy is used in comparisons of the model and experiment. [ABSTRACT FROM AUTHOR]

Antiepilepsirine (AES) is one of the derivatives of a Chinese folk prescription. It is a new antiepileptic drug (AED) synthesized in cooperation by Chinese medical and pharmaceutical workers. Pharmacological experiments on animal models prove that its antiepileptic action is marked, but there has been little evaluation of its clinical effects. We used the double-blind placebo-controlled crossover study which is generally acceptable as a proper method for new drug study. This study covered 58 epileptic children treated with classical AEDs and observed 6.5 months. Every patient took AES and placebo for 3 months each by random crossover on the basis of add-on therapy. The blood levels of AES and other antiepileptic drugs were determined regularly. The results show that there are no significant differences in clinical effects between AES and placebo in pediatric epilepsies as a whole, but AES is effective in tonic-clonic seizures (P less than 0.05), the most common type of seizure in the series. There are no significant differences in AED blood levels between the AES effective and ineffective groups. AES has no effect on the blood levels of other AEDs. AES is very safe, children given large doses (10 mg/kg/day) demonstrate no serious side-effects. It is suggested that there is potential improvement in patient psychological and cognitive status. This article also discusses the evaluation of new drugs for clinical effects, subject sampling, the criteria for efficacy evaluation and relationship between animal information and human outcome. The AES chemical structure is different from other well-known AEDs, this is a unique advantage.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraventricular injection of iron causes seizures and lipid peroxidation in brain tissue. To determine the effects of iron-induced lipid peroxidation on GABA uptake and release, synaptosomal fraction was prepared from 30-day-old iron-treated and control Wistar rats. Our data demonstrated that GABA release was more severely damaged than GABA uptake by lipid peroxidation. This imbalance between release and uptake may reduce GABA inhibition, which could contribute to the neurochemical pathogenesis of iron-induced seizures.

A kindling-like effect was produced by exposing 30-day-old rats to repeated hyperthermia-induced seizures. Naive audiogenic seizure (AGS)-susceptible rats (P77PMC) were easier to be kindled than AGS-resistant rats (Wistar). This hyperthermic kindling model may be used to study the outcome and mechanisms of human febrile seizures. The mechanisms underlying hyperthermic kindling remain to be investigated.

A new audiogenic seizure (AGS)-susceptible strain of rats (P77PMC) was evaluated as a possible model of human febrile seizures. The long-term effects of experimental febrile seizures were observed. All 30-day-old rat pups exhibited clonic seizures during exposure to an ambient temperature of 45 +/- 0.5 degree C. The mean latency from the beginning of the hyperthermic stimulus to the onset of convulsion was 16.9 +/- 2.2 min. The rats survived this hyperthermic seizure, developed a resistance to acoustic stimulations, but were more susceptible at the age of 50 to 60 days to kainate-induced limbic seizures than controls. The results of this study imply that febrile seizures of developing P77PMC rats can change later seizure susceptibility, and there may be some correlation between febrile convulsion and temporal lobe epilepsy.

A new animal model for epilepsy was successfully produced by microinjection of cobaltous chloride into the lateral cerebral ventricle of the rat. The median convulsive dose (CD50) and the median lethal dose (LD50) of CoCl2 was 0.45 microM/10 microliters (0.27-0.77 microM/10 microliters) and 1.07 microM/10 microliters (0.73-1.57 microM/10 microliters), respectively. The behavioral changes, electrocorticogram (ECoG), and the action of 5 classical anticonvulsants were studied using this new model. Seizures induced by cobaltous chloride are clinically similar to those produced by systemic administration of kainic acid and amygdala kindling. These are characterized by staring spells, wet dog shakes, mild convulsive movements, and stereotyped convulsions. ECoG findings demonstrated a unique epileptic burst during the wet dog shakes. Generalized epileptiform discharges were seen during typical seizures. The burst of spikes first occurred in the opposite temporal and frontal regions; and then became generalized. Among the 5 anticonvulsants studied, phenobarbital (30 mg/kg) and nitrazepam (3 mg/kg) completely antagonized the seizures; carbamazepine showed a moderate effect; and phenytoin as well as sodium valproate showed little effect. It is postulated that the seizures induced by cobaltous chloride may originate in the limbic system; and that cobalt ions are responsible for the seizure-inducing action. The mechanism remains to be investigated.