No abstract

The effect of damping on the response of elastic and inelastic single-degree-of-freedom systems was studied by nonlinear response-history analysis using earthquake histories that matched on average a 2000 NEHRP spectrum on a stiff soil site for a region of high seismic risk. New displacement reduction factors for levels of damping greater than 5% of critical are presented. New equations to relate inelastic and elastic displacements in the short-period range, for levels of damping greater than 5% of critical, are presented. The technical basis for reducing the minimum design base shear in damped buildings by a maximum of 25%, from that required for the corresponding undamped building, is derived based on comparable levels of damage in both the damped and undamped buildings.

The 2000 NEHRP Provisions include simplified methods of analysis of inelastic buildings equipped with linear viscous, nonlinear viscous, and hysteretic damping devices. These methods are based in part on the data presented in the paper. Nonlinear response-history analysis was used to validate the methods. The derivation of the 2000 NEHRP simplified methods for calculating the maximum acceleration and maximum velocity in damped framing systems are presented. These simplified methods produce exact or conservative estimates of peak displacement and peak acceleration, and reasonable estimates of peak velocities. The estimated velocities are within 25% of the average values obtained from response-history analysis for a broad range of periods and damping ratios. Velocity correction factors are provided to calculate peak velocity given the pseudo-velocity.

Facial skin resurfacing using the carbon dioxide laser has become an increasingly popular procedure. Improvements in carbon dioxide laser technology have made the procedure simpler and more reliable. However, difficulties in the postoperative period can lead to patient morbidity and physician anxiety. Common problems such as prolonged erythema, hyperpigmentation, acne, milia, dermatitis, and infection can be controlled or avoided with proper postoperative care. Less common sequela such as hypertrophic scarring and prolonged healing are often a results of errors committed in the postoperative period. The authors have performed laser resurfacing in almost 2100 patients in the last 4 years. Changes in the postoperative regimen to include no pretreatment, use of semipermeable dressings, antiviral and antibacterial prophylaxis, and early treatment with sunscreens and bleaching agents have made for a smoother recovery with more predictable results.