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Free-space optical communication can allow high-bandwidth data links that are hard to detect, intercept, or jam. This makes them attractive for many applications. However, these links also require very accurate pointing, and their availability is affected by weather. These challenges have limited the deployment of free-space optical systems. The U.S. Naval Research Laboratory has, for the last 15 years, engaged in research into atmospheric propagation and photonic components with a goal of characterizing and overcoming these limitations. In addition several demonstrations of free-space optical links in real-world Navy applications have been conducted. This paper reviews this work and the principles guiding it.

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All work presented in this case report was completed at The Ohio State University Hospitals.Accepted for publication 24th October, 1992. Substance abuse among pregnant women is becoming more prevalent. Random urine toxicology studies have demonstrated illicit drug use in 10-25% of patients, l This population is at increased risk for increased perinatal morbidity and mortality.Cocaine use, in particular, can present numerous problems. 2 It is particularly concerning because, in comparison with previous drug epidemics, more women of childbeating age appear to be affected by cocaine use) In a recent study, 11.8% of newborns tested positive for cocaine. 4 Adverse outcomes associated with cocaine use include statistically significant increased incidences of low birth weight infants, prematurity, abruptio placentae, placenta previae and perinatal death) Apart from the increased demands on the obstetrician and perinatologist, CAN J ANAESTH 1993 / 40:2 / pp 160-4

The northern distribution of the pawpaw (Asimina triloba) is reviewed in terms of the likelihood that Iroquois populations were directly responsible for its extension into southern Ontario and western New York, a proposition advanced by Keener and Kuhns (1997). Their argument is flawed by ignoring or misrepresenting other probable means of dispersal and by coloring or selecting evidence to strengthen their case. It is concluded that natural dispersal by a variety of medium to large mammals is an adequate explanation, and there is insufficient reason to believe that Iroquois trade or warfare was a significant or even viable mechanism for the widespread growth of Asimina in the Carolinian biotic province of southern Ontario and western New York.

Quantum key distribution (QKD) can be used to produce a cryptographic key whose security is guaranteed by quantum mechanics. The range of fiber-based QKD links is limited, by loss, to a few hundred kilometers, and cannot be used between mobile platforms. Free space QKD can, in principle, overcome these limitations. In practice, very narrow beam divergences must be used, requiring highly accurate pointing of the transmitting terminal to the receiver. This makes deployment very difficult. Here we describe the experimental implementation of a new type of free space QKD link, using modulating retro-reflectors (MRR). The MRR-QKD link eases the pointing requirements by more than three orders of magnitude, from microradians to degrees, while maintaining the narrow beam divergence necessary for long-range communication links. The system uses new, high extinction surface-normal multiple quantum well modulators with a modulation rate of 100 MHz. A laboratory-based BB84 QKD link using multiple quantum well MRRs is demonstrated, link budgets for possible applications are discussed, and security issues are considered.

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