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Abstract-We have developed a Web-based program for quickly estimating the regional environmental consequences of a comet or asteroid impact on Earth (www.lpl.arizona.edu/ impacteffects). This paper details the observations, assumptions and equations upon which the program is based. It describes our approach to quantifying the principal impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The program requires six inputs: impactor diameter, impactor density, impact velocity before atmospheric entry, impact angle, the distance from the impact at which the environmental effects are to be calculated, and the target type (sedimentary rock, crystalline rock, or a water layer above rock). The program includes novel algorithms for estimating the fate of the impactor during atmospheric traverse, the thermal radiation emitted by the impact-generated vapor plume (fireball), and the intensity of seismic shaking. The program also approximates various dimensions of the impact crater and ejecta deposit, as well as estimating the severity of the air blast in both crater-forming and airburst impacts. We illustrate the utility of our program by examining the predicted environmental consequences across the United States of hypothetical impact scenarios occurring in Los Angeles. We find that the most wide-reaching environmental consequence is seismic shaking: both ejecta deposit thickness and air-blast pressure decay much more rapidly with distance than with seismic ground motion. Close to the impact site the most devastating effect is from thermal radiation; however, the curvature of the Earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon.

Among patients with osteoporosis who were at high risk for fracture, bone mineral density increased more in patients receiving teriparatide than in those receiving alendronate. (ClinicalTrials.gov number, NCT00051558 [ClinicalTrials.gov].).

We studied the acquisition of bone mineral in 45 healthy prepubertal and pubertal girls and related changes in bone mass to age, body mass, pubertal status, calcium intake, and exercise. A subgroup of 12 girls was followed longitudinally. Bone mineral content (BMC) of the lumbar spine, whole body, and femoral neck was measured by dual energy x-ray absorptiometry and that at the midradius by single photon absorptiometry. For comparison, spine and whole body mineral contents were also measured by dual photon absorptiometry. Bone mass was expressed in conventional terms of BMC and area density (BMD). However, we show that BMD fails to account for differences in bone thickness. Since bone size increases during adolescence, we present a new expression, bone mineral apparent density (BMAD), which is BMC normalized to a derived bone reference volume. This term minimizes the effect of bone geometry and allows comparisons of mineral status among bones of similar shape but different size. BMC increased with age at all sites. These increases were most rapid in the early teens and plateaued after 16 yr of age. When bone mineral values at all sites were regressed against age, height, weight, or pubertal stage, consistent relationships emerged, in which BMC was most strongly correlated, BMD was correlated to an intermediate degree, and BMAD correlated only modestly or without significance. Dietary calcium and exercise level did not correlate significantly with bone mass. From these relationships, we attribute 50% of the pubertal increase in spine mineral and 99% of the change in whole body mineral to bone expansion rather than to an increase in bone mineral per unit volume. In multiple regressions, pubertal stage most consistently predicted mineral status. This study emphasizes the importance of pubertal development and body size as determinants of bone acquisition in girls. BMAD may prove to be particularly useful in studies of bone acquisition during periods of rapid skeletal growth.

Osteopenia is a frequent complication of anorexia nervosa (AN). To determine whether the deficit in bone mineral changes during the course of this illness, we studied 15 adolescent patients prospectively for 12-16 months using dual photon absorptiometry of the spine and whole body. At follow-up, mean weight, height, and body mass index (BMI) had increased significantly, although 6 girls had further weight loss or minimal gain (less than 1.2 kg). Spontaneous menses occurred in 2 girls, and 3 others were given estrogen replacement. Bone mineral density of the lumbar spine did not change significantly (mean +/- SD, 0.836 +/- 0.137 vs. 0.855 +/- 0.096 g/cm2), while whole body bone mineral density increased (0.710 +/- 0.118 vs. 0.773 +/- 0.105; P less than 0.05). Despite gains in bone mineral, 8 patients had osteopenia of the spine and/or whole body. Changes in weight, height, and BMI were significant predictors of change in bone mineral density. Increased bone mass occurred with weight gain before return of menses; conversely, weight loss was associated with further decreases in bone density. In 1 patient who failed to gain weight, estrogen therapy resulted in increased spinal, but not whole body, bone mineral. We also studied a second group of 9 women who had recovered from AN during adolescence. All 9 had normal whole body bone mineral for age, but 3 had osteopenia of the lumbar spine. We conclude that osteopenia in adolescents with AN reflects bone loss, perhaps combined with decreased bone accretion. Weight rehabilitation results in increased bone mineral before the return of menses. Estrogen may have an independent effect on bone mass. The persistence of osteopenia after recovery indicates that deficits in bone mineral acquired during adolescence may not be completely reversible.

Bone densitometry using dual-photon absorptiometry (DPA) or dual-energy x-ray absorptiometry (DXA) has become a standard method for assessing bone mineral content in the spine and other skeletal regions. A projected areal density, referred to as bone mineral density (BMD,g/cm2), is normally calculated to assess regional bone density and strength. We demonstrate that this measure can be misleading when used to compare bones of different sizes due to inherent biases caused by bone thickness differences. For example, assuming that volumetric bone density remains constant and bony linear dimensions are proportional to height, a 20% increase in height would result in a 20% increase in both the thickness and the BMD of any bone. We describe new analysis methods to reduce the confounding effect of bone size, and we introduce a parameter, bone mineral apparent density (BMAD, g/cm3), that better reflects bone apparent density. Using this parameter, we calculate a quantity that serves as an index of bone strength (IBS, g2/cm4) for whole vertebral bodies. These analyses were applied to lumbar spine (L2-4) DXA measurements in a population of women 17-40 years old and appear to offer advantages to conventional techniques.