The three most probable processes for pumping of the upper lasing level of the 441.6 nm Cd II line under hollow-cathode discharge conditions, namely Penning ionization, 'direct' and 'stepwise' electron excitation, have been analysed. Atomic ionization and excitation cross sections and the electron distribution function in the energy interval up to 300 eV have been calculated. Radial dependencies of pumping rates of laser transition for a cylindrical cathode cavity and an integral pumping rate have been determined versus the cadmium vapour and helium pressures. It has been shown that the contributions of Penning ionization and direct and stepwise excitations to the pumping rate are strongly dependent on the pressures of discharge components. Contributions of these processes are found to reach up to about 70, 30 and less than 1%, respectively, under optimal conditions for the laser discharge. The comparison of calculated radial pumping rate distributions with experimental data confirmed that the Penning ionization plays the dominant role.

MS. recezved 1 M a y 1947ABSTRACT. A scheme of measurements is discussed from which absolute determinations of sound field pressure can be made The relation between the scheme and the reciprocity method is discussed. I t is shown that the measurements also yield the axial pressure and " projection efficiency " of a transceiver, the " projection efficiency " being defined as the ratio of the actual axial intensity to the axial intensity as it would be if the transceiver converted the whole energy absorbed into sound by vibrating 2.3 a simple piston. I t is suggested, without proof, that the upper limit of the projection efficiency is unity, and the relation between-this quantity and the efficiency defined as the ratio of radiated acoustic power to consumed electrical power is shown to depend on a directivity coefficient and on the effective area of the radiator face. I t is pointed out that neither of these quantities is readily determinable and that therefore the conversion efficiency of the transceiver, and hence the acoustic power radiated, cannot be obtained.* Security reasons still prevent the publication of actual numerical data, but the principles involved are of general interest in acoustical work and it has been thought worth while to prepare the theoretical work for publication.

A highly sensitive technique for measuring high power laser-generated shock-wave velocities is described. Shock-wave velocities produced by pressures as low as 50 GPa were measured, while there is no limit to the pressure that can be measured on the high pressure side.

We propose two approaches for determining the native basins in off-lattice models of proteins. The first of them is based on exploring the saddle points on selected trajectories emerging from the native state. In the second approach, the basin size can be determined by monitoring random distortions in the shape of the protein around the native state. Both techniques yield similar results. As a byproduct, a simple method to determine the folding temperature is obtained.Chains of beads on cubic or square lattices, with some effective interactions between the beads, often serve as simple models of proteins (see for instance [1]). A more realistic modelling, however, requires considering off-lattice systems. Simple off-lattice heteropolymers have been discussed recently by Iori et al [2], Irback et al [3], Klimov and Thirumalai [4] and by the present authors [5]. The purpose in using such models is to understand the basic mechanism of folding to the native state. In lattice models, the native state is usually non-degenerate and it coincides with the ground state of the system. Delineating boundaries of the native basin in off-lattice systems, however, is difficult, especially when the number of degrees of freedom is large, yet it is essential for studies of almost all equilibrium and dynamical properties of proteins. For instance, stability of a protein is determined by estimating the equilibrium probability to stay in the native basin: the temperature at which this probability is 1 2 defines the folding temperature, T f . The native basin consists of the native state and its immediate neighbourhood, as shown schematically in figure 1, and it should not be confused with the whole folding funnel. The latter involves a much larger set of conformations which are linked kinetically to the native state.In most studies, such as in [3,4], the size of a basin is declared by adopting a reasonable but ad hoc cutoff bound. Systematic approaches, however, are needed and will be presented here. The task of delineating of the native basin is facilitated by introducing the concept of a distance between two conformations a and b, δ ab . The distance should be defined in a way that excludes effects of an overall translation or rotation. There are two definitions of δ ab , for a sequence of N monomers, that we shall use. The first one is [2, 6]:

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