13 research outputs found
High Pressure Hugoniot Measurements Using Converging Shocks
Plate impact experiments are a powerful tool in equation of state development, but are inherently limited by the range of impact velocities accessible to the gun. In an effort to dramatically increase the range of pressures which can be studied with available impact velocities, a new experimental technique is being developed. The possibility of using converging shock waves to produce a high pressure Mach reflection is examined. The technique proposed uses a composite target simply consisting of two concentric cylinders, with the only requirement being the initial shock speed in the outer cylinder is greater than that in the inner cylinder. Conically converging shocks will be generated at the interface due to the impedance mismatch and axisymmetric geometry of the composite target. Upon convergence, an irregular reflection must occur, at which point the conical analog of a Mach reflection develops. Once the Mach reflection reaches a steady state, the high pressure state in the Mach disk can be measured using velocity interferometry and impedance matching techniques. Experimental results on a copper inner cylinder are in good agreement with numerical simulations and data in the literature
Microstructure and Mechanical Properties of Precipitation Hardened Aluminum Under High Rate Deformation
A Cross-Lagged Model of the Development of ADHD Inattention Symptoms and Rapid Naming Speed
Long-term neurocognitive effects of methylphenidate in patients with attention deficit hyperactivity disorder, even at drug-free status
<p>Abstract</p> <p>Background</p> <p>Methylphenidate (MPH), a psycho-stimulant, is the most widely administered drug for the pharmacological management of patients with attention deficit hyperactivity disorder (ADHD). This study attempts to determine whether sustainable improvements occur in neurocognitive function among ADHD patients following 12-month treatment with MPH, at drug-free status. Whether age groups, gender or ADHD subtypes differ in neurocognitive performance during MPH treatment is also examined.</p> <p>Methods</p> <p>Study participants consisted of 103 ADHD patients (mean age: 9.1 ± 1.9 years old) who were drug naïve or drug free for at least 6 months. The patients were prescribed oral short-acting MPH at each dose range of 0.3–1.0 mg/kg daily. During 12 months of the study, the patients underwent the test of variables of attention (TOVA) at the baseline, month 6 and month12. Patients were instructed to not intake MPH for one week before the second and the third TOVA.</p> <p>Results</p> <p>Seventy five patients completed the study. Results of this study indicated that although commission errors and response sensitivity (d’) significantly improved during MPH treatment for 12 months, omission errors, response time, response time variability and ADHD score did not. While younger ADHD patients (<9 y/o) performed better in response time, response time variability, d’ and ADHD score than older ones (≥9 y/o), the latter more significantly improved in response time than the former during 12 months of treatment. Additionally, boys improved more than girls in omission error and d’. Moreover, although ADHD subtypes significantly differed in ADHD score during the treatment, MPH treatment and ADHD subtypes did not interact with each other for all TOVA indices.</p> <p>Conclusions</p> <p>ADHD patients significantly improved in impulsivity and perceptual sensitivity, determined as TOVA, during MPH treatment for 12 months. Age and gender, yet not ADHD subtypes, appear to influence the MPH treatment effects in some indices of TOVA. A future study containing a comparison group is suggested to confirm whether the neurocognitive improvements are attributed to long-term effects of MPH or natural maturation of patients.</p