Shock-wave properties of glass with implications for failure kinetics

New, previously unpublished shock wave data on soda-lime glass are presented. These data are examined in light of recent experimental evidence for failure wave behavior in brittle solids. An underlying physical basis for failure waves is explored in terms of inelastic deformation kinetics processes

The role of dynamic experimentation for computation analysis

In this paper a brief description of dynamic techniques commonly available for determining material property studies is presented. For many impact applications, the material generally experiences a complex loading path. In most cases, the initial loading conditions can be represented by the shock commonly referred to as the Hugoniot state. Subsequent loading or release structure, i.e., off-Hugoniot states would however be dependent on the physical processes dominating the material behavior. The credibility of the material model is tested by the accuracy of predictions of off-Hugoniot states. Experimental techniques commonly used to determine off-Hugoniot states are discussed in this survey

Shock-wave properties of soda-lime glass

Planar impact experiments and wave profile measurements provided single and double shock equation of state data to 30 GPa. Both compression wave wave profile structure and release wave data were used to infer time-dependent strength and equation of state properties for soda-lime glass

Survey of the hypervelocity impact technology and applications.

HVIS 2005 was a clear success. The Symposium brought together nearly two hundred active researchers and students from thirteen countries around the world. The 84 papers presented at HVIS 2005 constitute an ''update'' on current research and the state-of-the-art of hypervelocity science. Combined with the over 7000 pages of technical papers from the eight previous Symposia, beginning in 1986, all published in the International Journal of Impact Engineering, the papers from HVIS 2005 add to the growing body of knowledge and the progressing state-of-the-art of hypervelocity science. It is encouraging to report that even with the limited funding resources compared to two decades ago, creativity and ingenuity in hypervelocity science are alive and well. There is considerable overlap in different disciplines that allows researchers to leverage. Experimentally, higher velocities are now available in the laboratory and are ideally suited for space applications that can be tied to both civilian (NASA) and DoD military applications. Computationally, there is considerable advancement both in computer and modeling technologies. Higher computing speeds and techniques such as parallel processing allow system level type applications to be addressed directly today, much in contrast to the situation only a few years ago. Needless to say, both experimentally and computationally, the ultimate utility will depend on the curiosity and the probing questions that will be incumbent upon the individual researcher. It is quite satisfying that over two dozen students attended the symposium. Hopefully this is indicative of a good pool of future researchers that will be needed both in the government and civilian industries. It is also gratifying to note that novel thrust areas exploring different and new material phenomenology relevant to hypervelocity impact, but a number of other applications as well, are being pursued. In conclusion, considerable progress is still being made that is beneficial for continuous development of hypervelocity impact technology and applications even with the relatively limited resources that are being directed in this field

Shock response of dry sand.

The dynamic compaction of sand was investigated experimentally and computationally to stresses of 1.8 GPa. Experiments have been performed in the powder's partial compaction regime at impact velocities of approximately 0.25, 0.5, and 0.75 km/s. The experiments utilized multiple velocity interferometry probes on the rear surface of a stepped target for an accurate measurement of shock velocity, and an impedance matching technique was used to deduce the shock Hugoniot state. Wave profiles were further examined for estimates of reshock states. Experimental results were used to fit parameters to the P-Lambda model for porous materials. For simple 1-D simulations, the P-Lambda model seems to capture some of the physics behind the compaction process very well, typically predicting the Hugoniot state to within 3%

ALEGRA -- code validation: Experiments and simulations

In this study, the authors are providing an experimental test bed for validating features of the ALEGRA code over a broad range of strain rates with overlapping diagnostics that encompass the multiple responses. A unique feature of the Arbitrary Lagrangian Eulerian Grid for Research Applications (ALEGRA) code is that it allows simultaneous computational treatment, within one code, of a wide range of strain-rates varying from hydrodynamic to structural conditions. This range encompasses strain rates characteristic of shock-wave propagation (10{sup 7}/s) and those characteristic of structural response (10{sup 2}/s). Most previous code validation experimental studies, however, have been restricted to simulating or investigating a single strain-rate regime. What is new and different in this investigation is that the authors have performed well-instrumented experiments which capture features relevant to both hydrodynamic and structural response in a single experiment. Aluminum was chosen for use in this study because it is a well characterized material--its EOS and constitutive material properties are well defined over a wide range of loading rates. The current experiments span strain rate regimes of over 10{sup 7}/s to less than 10{sup 2}/s in a single experiment. The input conditions are extremely well defined. Velocity interferometers are used to record the high strain-rate response, while low strain rate data were collected using strain gauges

Which executive functioning deficits are associated with AD/HD, ODD/CD and comorbid AD/HD+ODD/CD?

Item does not contain fulltextThis study investigated (1) whether attention deficit/hyperactivity disorder (AD/HD) is associated with executive functioning (EF) deficits while controlling for oppositional defiant disorder/conduct disorder (ODD/CD), (2) whether ODD/CD is associated with EF deficits while controlling for AD/HD, and (3)~whether a combination of AD/HD and ODD/CD is associated with EF deficits (and the possibility that there is no association between EF deficits and AD/HD or ODD/CD in isolation). Subjects were 99~children ages 6–12 years. Three putative domains of EF were investigated using well-validated tests: verbal fluency, working memory, and planning. Independent of ODD/CD, AD/HD was associated with deficits in planning and working memory, but not in verbal fluency. Only teacher rated AD/HD, but not parent rated AD/HD, significantly contributed to the prediction of EF task performance. No EF deficits were associated with ODD/CD. The presence of comorbid AD/HD accounts for the EF deficits in children with comorbid AD/HD+ODD/CD. These results suggest that EF deficits are unique to AD/HD and support the model proposed by R. A. Barkley (1997).17 p

Advanced diagnostics for impact-flash spectroscopy on light-gas guns.

This study is best characterized as new technology development for implementing new sensors to investigate the optical characteristics of a rapidly expanding debris cloud resulting from hypervelocity impact regimes of 7 to 11 km/s. Our gas guns constitute a unique test bed that match operational conditions relevant to hypervelocity impact encountered in space engagements. We have demonstrated the use of (1) terahertz sensors, (2) silicon diodes for visible regimes, (3) germanium and InGaAs sensors for the near infrared regimes, and (4) the Sandia lightning detectors which are similar to the silicon diodes described in 2. The combination and complementary use of all these techniques has the strong potential of ''thermally'' characterizing the time dependent behavior of the radiating debris cloud. Complementary spectroscopic measurements provide temperature estimates of the impact generated debris by fitting its spectrum to a blackbody radiation function. This debris is time-dependent as its transport/expansion behavior is changing with time. The rapid expansion behavior of the debris cools the cloud rapidly, changing its thermal/temperature characteristics with time. A variety of sensors that span over a wide spectrum, varying from visible regime to THz frequencies, now gives us the potential to cover the impact over a broader temporal regime starting from high pressures (Mbar) high-temperatures (eV) to low pressures (mbar) low temperatures (less than room temperature) as the debris expands and cools

Clinical symptoms and performance on the continuous performance test in children with attention deficit hyperactivity disorder between subtypes: a natural follow-up study for 6 months

<p>Abstract</p> <p>Background</p> <p>The aims of this study were to determine the time course of improvements in attention deficit hyperactivity disorder (ADHD) clinical symptoms and neurocognitive function in a realistic clinical setting, and the differences in ADHD symptom improvement using different classifications of ADHD subtypes.</p> <p>Methods</p> <p>The Child Behavior Checklist (CBCL) was completed by parents of ADHD children at the initial visit. The computerized Continuous Performance Test (CPT), Swanson, Nolan, and Pelham, and Version IV Scale for ADHD (SNAP-IV), and ADHD Rating Scale (ADHD-RS) were performed at baseline, one month, three months, and six months later, respectively. Patient care including drug therapy was performed at the discretion of the psychiatrist. The ADHD patients were divided into DSM-IV subtypes (Inattentive, Hyperactive-impulsive and Combined type), and were additionally categorized into aggressive and non-aggressive subtypes by aggression scale in CBCL for comparisons.</p> <p>Results</p> <p>There were 50 ADHD patients with a mean age of 7.84 ± 1.64 years; 15 of them were inattentive type, 11 were hyperactive-impulsive type, and 24 were combined type. In addition, 28 of the ADHD patients were grouped into aggressive and 22 into non-aggressive subtypes. There were significant improvements in clinical symptoms of hyperactivity and inattention, and impulsivity performance in CPT during the 6-month treatment. The clinical hyperactive symptoms were significantly different between ADHD patients sub-grouping both by DSM-IV and aggression. Non-aggressive patients had significantly greater changes in distraction and impulsivity performances in CPT from baseline to month 6 than aggressive patients.</p> <p>Conclusions</p> <p>We found that ADHD symptoms, which included impulsive performances in CPT and clinical inattention and hyperactivity dimensions, had improved significantly over 6 months under pragmatic treatments. The non-aggressive ADHD patients might have a higher potential for improving in CPT performance than aggressive ones. However, it warrant further investigation whether the different classifications of ADHD patients could be valid for predicting the improvements in ADHD patients' clinical symptoms and neurocognitive performance.</p