Halothermal circulation

Abstract: Mars is a relatively small, desert planet with only a thin atmosphere at present. These basic properties are all directly reflected in its global circulation, which is fundamentally similar to that on Earth in many ways, but very different in other ways. The investigation of the global circulation of the Martian atmosphere has a surprisingly long history, as a result of the basic terrestrial similarities and the very early spacecraft missions to Mars. The virtual explosion in spacecraft observations during the last two decades has made the global atmospheric circulation of Mars by far the best characterized and understood atmospheric circulation in the Solar System, other than that of Earth. By comparison with Earth our knowledge of the global atmospheric circulation of Mars remains quite limited: there are extremely few direct wind observations, very few surface pressure observations, and the local time coverage of the global observations is very limited. Our knowledge of the planetary boundary layer (which can be extremely deep by comparison to Earth) on Mars is limited at present. It is only with the aid of extensive numerical modeling that our fundamental understanding of the global circulation of the Martian atmosphere has been fleshed out. Data assimilation efforts for Mars are still at a relatively early stage but these certainly have great potential for the future – if observations of the global atmosphere continue to be obtained.

Abstract: kill0 one lwledge, physiology offers at present an extraordinary contrast: In field a mass of exact, quanti tative knowledge; in the closely rela ted and equally important department, nothing but conceptions so vague that in practice we scarcely realize that definite quantities exist. In the one a technique, widely used both in laboratory and clinic, to determine exactly the activity of the functions concerned; in the other no accepted method of measurement and, therefore, no estimate of alteration of function more definite than a “considerable increase” or a “slight decrease.” The extent of our knowledge, or rather of our control of these fields, is determined by the effectiveness of the available methods of measurement. The two fields referred to are those in which the beginnings were made respectively by Lavoisier and by Harvey. Suppose that these two pioneers could come back to survey the development and application of their ideas. Lavoisier would find his main conception fully developed and in active practical use. Every physiological laboratory and every first rate hospital now has apparatus for the determination of basal metabolism, for measurement of the respiratory exchange and the energy expenditure by indirect calorimetry. He would recognize at once such apparatus and methods as the realization of his own plans. Very different and very disappointing for Harvey would be the contrast in present conditions in respect to the circulation. He would recognize the immense importance of the measurement of arterial pressure and of the .evidence that comes from the electrocardiogram, but his interest in these phases of his field would be rather impersonal. We may well imagine him as saying: “Three hundred years have passed since I showed that the blood circulates; twice the length of time that has elapsed since Lavoisier showed that oxygen is consumed. But now when I ask how many ounces or (as you say now) liters of blood are pumped by th .e heart each minute in this patient, or that athlete, or yonder school child, or exactly how the blood stream varies in rest and exercise, you physiologists cannot answer?