Feasibility Study of Short Takeoff and Landing Urban Air Mobility Vehicles Using Geometric Programming

Electric Short Takeoff and Landing (eSTOL) vehicles are proposed as a path towards implementing an Urban Air Mobility (UAM) network that reduces critical vehicle certification risks and offers advantages in vehicle performance compared to the widely proposed Electric Vertical Takeoff and Landing (eVTOL) aircraft. An overview is given of the system constraints and key enabling technologies that must be incorporated into the design of the vehicle. The tradeoffs between vehicle performance and runway length are investigated using geometric programming, a robust optimization framework. Runway lengths as short as 100-300 ft are shown to be feasible, depending on the level of technology and the desired cruise speed. The tradeoffs between runway length and the potential to build new infrastructure in urban centers are investigated using Boston as a representative case study. The placement of some runways up to 600ft is shown to be possible in the urban center, with a significant increase in the number of potential locations for runways shorter than 300ft. Key challenges and risks to implementation are discussed

Guarding the Town Walls: Mechanisms and Motives for Restricting Multifamily Housing in Massachusetts

Local governments frequently restrict multifamily housing through a variety of zoning tools, which may reduce the ability of low-income households to afford housing in desirable locations. In this article, I use a new and unusually rich data set on zoning in Massachusetts to test several hypotheses about why municipalities restrict multifamily housing. Under regulations adopted in the 1940s and 1950s, communities with more existing multifamily housing or governed by a city council zoned more leniently for multifamily housing. Beginning in the 1970s, the use of special permits increased and smaller, more affluent communities were more restrictive. Copyright 2008 American Real Estate and Urban Economics Association

Ankle-Brachial Index and cardiovascular events in atrial fibrillation: The ARAPACIS study

Atrial fibrillation (AF) patients are at high risk for thrombotic and vascular events related to their cardiac arrhythmia and underlying systemic atherosclerosis. Ankle-Brachial Index (ABI) is a non-invasive tool in evaluating systemic atherosclerosis, useful in predicting cardiovascular events in general population; no data are available in AF patients. ARAPACIS is a prospective multicentre observational study performed by the Italian Society of Internal Medicine, analysing association between low ABI (≤ 0.90) and vascular events in NVAF out- or in-patients, enrolled in 136 Italian centres. A total of 2,027 non-valvular AF (NVAF) patients aged > 18 years from both sexes followed for a median time of 34.7 (interquartile range: 22.0–36.0) months, yielding a total of 4,614 patient-years of observation. Mean age was 73 ± 10 years old with 55% male patients. A total of 176 patients (8.7%) experienced a vascular event, with a cumulative incidence of 3.81%/patient-year. ABI≤ 0.90 was more prevalent in patients with a vascular event compared with patients free of vascular events (32.2 vs 20.2%, p< 0.05). On Cox proportional hazard analysis, ABI≤ 0.90 was an independent predictor of vascular events (hazard ratio (HR): 1.394, 95% confidence interval (CI): 1.042–1.866; p=0.02), vascular death (HR: 2.047, 95% CI: 1.255–3.338; p=0.004) and MI (HR: 2.709, 95% CI: 1.485–5.083; p=0.001). This latter association was also confirmed after excluding patients with previous MI (HR: 2.901, 95% CI: 1.408–5.990, p=0.004). No association was observed between low ABI and stroke/transient ischaemic attack (p=0.91). In conclusion, low ABI is useful to predict MI and vascular death in NVAF patients and may independently facilitate cardiovascular risk assessment in NVAF patients