Bicycles efficiency

Reflectors appear to provide a significant margin of added safety at a relatively small monetary coat and loss in bicycle efficiency. In view of the Commission s careful balancing of the relevant factors, we do not find this standard to be irrational. [559 F.2d at 798.]... 

Laurion, U.S. Pat. No. 3,847,443, discloses an oma-mental wheel element which is designed to fit between the spokes, inside a wheel. Strazis, U.S. Pat. No. 4,682,821, discloses a semi-rigid, tension attached bicycle wheel cover assembly intended to improve the aero-dynamic efficiency of bicycle wheels. Monte, U.S. Pat. 

The classic method for controlling stereochemistry is to perform reactions on cyclic substrates. A rather lengthy but nonetheless efficient example in the prostaglandin field uses bicyclic structures for this purpose. Bisacetic acid derivative S is available in five steps from Diels-Alder reaction of trans-piperylene and maleic anhydride followed by side-chain homologation. Bromolactonization locks the molecule as bicyclic intermediate Esterification, reductive dehalogen-... 

Commute 3 miles by walking, bicycling, or mass fransif. 40 miles in an energy-efficient automobile. If there are high-occupancy vehicle lanes, will make effort to carpool. 60 miles in a 14 mpg sports utility vehicle, and a disdain for mass transit, carpooling and high-occupancy vehicle lanes. 

Bicycling is a simple, affordable, and energy-efficient means of transportation. Of all human-powered locomotion, it is the fastest and least energy-demanding. 

The bicycle has stunning efficiency advantages over other vehicles for several reasons ... 

The light weight and mechanical efficiency not only allow the bicycle to be powered by a nonathlet-ic human, but it can be walked over extreme terrain, or laden ivith heavy cargo, or picked up and carried. These options make the bicycle more versatile than any other vehicle, and allow a bicycle user door-to-door, on-dcinand transport. 

The bicycle s energy efficiency superiority extends beyond hninali loconiotion and beyond all other forms of transportation. By com ertmg food into the energy equivalent of gasoline, the kilocalories of food energy needed by a human to pedal a bicycle is only a fraction of that needed to propel planes, trains, and automobiles (see Table 1). 

The bicycle s advantages as the world s most mechanically efficient means of transportation are clouded by the limitations of the human engine. To put it in power output terms, the human body can produce sustained power only at modest levels. For most people, 100 watts would be too much, and for an elite athlete, 400 watts is the approximate ceiling. (The athlete may manage a brief burst of 1.1 kilowatts.)... 

The human engine cannot match this power output, yet the mechanical efficiency of the bicycle helps tremendously because a vei y small amount of horsepower can generate great speed. For example, 0.4 horsepower (298 watts) of output can result in 25 niph (40 kph) speeds or better. One set of calculations shows that if a cyclist rode on level ground, with no rolling resistance, and aided by a 25 mph tailwind, it would require only around 0.2 horsepower (150 watts) to sustain a 25 mph pace. 

If not for the need to climb steep hills, bicycling at a 15 mph (24 kph) clip would never be a strenuous exercise. It takes approximately 82 watts, or 0.11 horsepower, on an efficient bicycle, to ride 15 mph on flat ground. But ground is seldom flat. That same 82 watts achieves only 8 mph climbing a barely discernible two percent grade. A five percent grade slows one down to just over 4 mph. Most riders don t want to slow down that much, so they work harder to maintain some speed. On descents, they work less hard, while going still faster. 

These bikes could be a wonderful transportation option, combining the efficiency, quiet and nonpollution of a bicycle with the ease of riding a small motorcycle. For these reasons, electric-assist bikes sell at the rate of over 200,000 per year in Japan. But in the United States, these bikes run up against a cultural barrier. Bicycle enthusiasts, who are less likely to object to their four-figure price tags, do not want a motor and do not want a bike that weighs 60 pounds. Others do not want to be seen riding to work. So U.S. sales have been poor. 

For a situation where large torques are involved, such as a bicycle drive, a chain linkage is superior to a belt. A person putting all his or her weight on a pedal probably would make most belt systems slip. Another advantage of a chain over a belt is that a chain is more efficient, mainly because it does not require any ambient tension. The return side of a chain drive has only enongh tension to snpport itself. Furthermore, the chain links are equipped with rollers, which can rotate as they contact the teeth, reducing the frictional forces and wear. 

In 1980, a Merck group disclosed the results of a model study which amply demonstrated the efficiency with which the strained bicyclic ring system of thienamycin can be constructed by the carbene insertion cyclization strategy.12 Armed with this important precedent, Merck s process division developed and reported, in the same year, an alternative route to carbene precursor 4.13 Although this alternative approach suffers from the fact that it provides key intermediate 4, and ultimately thienamycin, in racemic form, it is very practical and is amenable to commercial scale production. The details of this interesting route are presented in Schemes 4-6. 

The hydrogeh atom bound to the amide nitrogen in 15 is rather acidic and it can be easily removed as a proton in the presence of some competent base. Naturally, such an event would afford a delocalized anion, a nucleophilic species, which could attack the proximal epoxide at position 16 in an intramolecular fashion to give the desired azabicyclo[3.2.1]octanol framework. In the event, when a solution of 15 in benzene is treated with sodium hydride at 100 °C, the processes just outlined do in fact take place and intermediate 14 is obtained after hydrolytic cleavage of the trifluoroacetyl group with potassium hydroxide. The formation of azabi-cyclo[3.2.1]octanol 14 in an overall yield of 43% from enone 16 underscores the efficiency of Overman s route to this heavily functionalized bicycle. 

A careful assessment of the constitution of compound 10 led to the development of a rather efficient strategy featuring the Diels-Alder reaction (see Scheme 3). Although the unassisted intermole-cular reaction between 3-hydroxy-2-pyrone (16)23 and a,/ -unsatu-rated ester 17 is unacceptable in terms of both regioselectivity and chemical yield, compounds 16 and 17 combine smoothly in refluxing benzene and in the presence of phenylboronic acid to give fused bicyclic lactone 12 (61% yield) after workup with 2,2-... 

A central focus in modem organic synthesis has been the development of highly efficient catalytic processes for the syntheses of natural and unnatural compounds of medicinal interest or intermediates useful for functional materials. A particularly attractive approach is to apply transition metal catalysed cyclisation reactions for the transformation of simple starting materials into monocyclic, bicyclic and polycyclic scaffolds that can be further elaborated into specific targets. 

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