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After photodissociation of carbon monoxide bound to myoglobin, the protein relaxes to the deoxy equilibrium structure in a quake-like motion. Investigation of the proteinquake and of related intramolecular equilibrium motions shows that states and motions have a hierarchical glasslike structure.The dynamic aspects of proteins have been studied extensively in recent years and a picture of ever increasing complexity has emerged. To bring some order into the complexity, we have introduced a model that classifies states and motions (1). In the present paper, we describe the model and its experimental basis in more detail. STATES, SUBSTATES, AND MOTIONSWe consider myoglobin (Mb), an oxygen storage protein, consisting of 153 amino acids, with molecular weight of 17,900 and approximate dimensions of2.5 x 4.4 x 4.4 nm (2). Embedded in the protein matrix is a heme group with a central iron atom, which binds small ligands such as dioxygen (02) or carbon monoxide (CO) reversibly. Thus, two states are involved in the function of Mb, deoxyMb and liganded Mb (e.g., MbCO). In the liganded state, the heme is planar and the iron has spin 0 and lies close to the mean heme plane. In the unliganded state, the heme group is domed, the iron has spin 2 and lies =0.5 A away from the mean heme plane, and the globin structure differs somewhat from the liganded one (3).A protein molecule in a particular state can assume a very large number of conformational substates (CS) (4-6). Different substates have the same overall structure, but they differ in details; they perform the same function, but with different rates. equilibrium (10). Return to equilibrium occurs through a proteinquake: the released strain energy is dissipated through waves [phonons (11) or solitons (12)1 and through the propagation of a deformation (2, 3). HIERARCHY OF SUBSTATESThe experiments described in the next section imply that the proteinquake released by photodissociation of MbCO propagates sequentially: Fig. 2, consequently is much more complex than we originally anticipated (4).The valley in the top diagram of Fig. 2a represents one state, say MbCO. MbCO can exist in a large number of conformational substates, CS1, separated by high barriers.Each valley in the first tier is structured into substates (CS2) with smaller barriers. The furcation continues through two more tiers, with decreasing barrier heights. The dynamic

The characteristics of many close, evolved binaries can be understood most easily if there exists some agency that can abstract angular momentum or mass, or both, from the precursor system. Close binaries may be defined as systems in which at least one of the components has filled or will fill its Roche lobe and attempt to transfer matter to its companion. If the time scale for mass transfer is considerably shorter than the time scale on which the accretor can adjust thermally to the proffered mass, the accreted layer will heat up, expand, and fill the Roche lobe of the accretor. The mass lost by the donor thereafter flows into a "common envelope" (CE) which encompasses both stars. The frictional interaction between this common envelope and the stellar cores produces drag forces that cause the cores to spiral in toward one another; some of the orbital energy helps drive matter from the CE into interstellar space. Examples of systems which are experiencing or have experienced this process include some planetary nebulae, cataclysmic variables, and close binary degenerate stars. Similar situations can arise if one of the components can support, of its own accord, a dense wind that flows out of the system; the drag luminosity produced by interaction between the companion and the wind may intensify the wind and contribute to mass loss from the donor. Systems undergoing this "wind-CE" process include novae and close binaries containing an OB star. Planetary nebulae with close binary central stars are actually ejected CEs, and precursors of many cataclysmic variables were once the central stars of planetary nebulae formed in a CE event. In this review, we ( 1 ) describe various initial configurations which will produce a CE, (2) discuss the physics of the CE event, (3) describe attempts to model the event quantitatively, and ( 4) apply what we have learned to describe, in several real situations, the transformations wrought by evolution through a CE phase.