The decay parameters of ${\Lambda }^0\to p+{\pi }^{-}$ have been determined to be $\alpha =+0.65\mathrm{}\pm 0.02$, $\beta =-0.10\mathrm{}\pm 0.07$, $\gamma =+0.75\mathrm{}\pm 0.02$. Under time-reversal invariance, $\frac{\beta }{\alpha }=-tan({\delta }_s-{\delta }_p)$, where ${\delta }_s$ and ${\delta }_p$ are appropriate pion-nucleon scattering phase shifts; from this experiment $\frac{\beta }{\alpha }=-0.16\mathrm{}\pm 0.10=-tan(9\mathrm{}°\pm 5.5°)$ in good agreement with the known value of $({\delta }_s-{\delta }_p)=6.5\mathrm{}°\pm 1.5°$.

Using finite-energy sum rules we predict important features of the Regge structure of $\rho$ poles from low-energy $\pi N$ data. The combined effect of $N^{*}$ resonances in generating (via the sum rules) properties of the exchanged $\rho$ poles is discussed, thus starting a new type of bootstrap calculation.

Ambiguities arising in some applications of current algebra are overcome by employing the algebra of currents to calculate the subtraction constant in a once-subtracted dispersion relation. The new approach is applied to $K\to 2\pi$ decay and yields corrections to the usual current-algebra method of about 10%. The branching ratio $\frac{(K^{+}\to {\pi }^{+}+{\pi }^0)}{({K_1}^0\to {\pi }^{+}+{\pi }^{-})}$ is also computed and agrees well with experiment.

The intensity of triplet-exciton annihilation luminescence in anthracene crystals at room temperature increases in weak magnetic fields up to a maximum increase of 5% at 350 Oe. For stronger fields the intensity decreases, finally leveling off at 80% of the zero-field value for $H\gtrsim 5$ kOe. Sharp dips are found in the high-field intensity for field orientations at which a particular kind of level crossing occurs for pairs of triplet excitons. These effects result solely from field-induced changes in the rate constant for triplet-triplet annihilation.

The density of ${\mathrm{He}}^4$ has been measured along five isotherms near the critical point. Using a modified form of the power-law expression $|P-P_c|\propto {|\rho -{\rho }_c|}^{\delta }$ for the critical isotherm, we find $3.8<~\delta <~4.1$. Assuming that the specific heat follows a relation $C_v\propto {|T-T_c|}^{-{\alpha }^{\prime }}$ and that the density of the coexistence curve behaves as $|\rho -{\rho }_c|\propto {(T_c-T)}^{\beta }$, previous measurements for ${\alpha }^{\prime }$ and $\beta$ allow us to test Griffith's inequality $\beta (\delta +1)+{\alpha }^{\prime }>~2$. We obtain a maximum value for $\beta (\delta +1)+{\alpha }^{\prime }$ of 1.9.

Persistent-current methods are used to obtain critical-velocity data for flow of superfluid helium through filter materials with uniform pore size. For the smallest pore size investigated, 0.2μ, evidence is seen for a small depression (7.5×${10}^{-4\mathrm{}}$°K) of the transition temperature. The critical velocity for this pore size is found to vary linearly with the superfluid density as the transition temperature is approached.

Along the $\lambda$ line in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures, the specific heat at constant chemical potential presumably becomes infinite. It is suggested that the $\lambda$ transition changes over to a first-order transition at a point at which the specific heat at constant composition becomes infinite. Possible reasons for such a change are discussed. The thermodynamic relationships are introduced through analogy with a system in which the variables are pressure and volume rather than chemical potential and composition.

Calculations of a two-stream instability have been made by following the motion of the phase-space boundaries of an incompressible and constant-density phase-space fluid. Because of the condensation of holes, which to a good approximation act as gravitational particles, large-scale nonlinear pulses develop.

From the strain-induced change of the reflectance, the change of ${\epsilon }_2$ is derived. The measurements are used to identify electronic transitions and to evaluate three deformation potentials. Two of the deformation potentials are compared with the result of a theoretical model.

We evaluate the contribution to the tunnel conductance due to inelastic tunneling processes whereby the tunneling electron excites continuum modes in the barrier. For acoustical dispersion relations ${\omega }_{\overrightarrow{\mathrm{p}}}=v_{s}p+{\omega }_0$ of the continuum modes, the coherent inelastic contribution is usually proportional to ${\mathrm{}\left(\right|eV|-\hslash {\omega }_0)}^2\theta \mathrm{}\left(\right|eV|-\hslash {\omega }_0)\theta (\hslash {\omega }_{\mathrm{D}}-|\mathrm{eV}\left|\right)$, in which ${\omega }_{\mathrm{D}}=v_s{p}_{max}+{\omega }_0$. Comparison with experimental data suggests that certain zero-bias minima may be attributed to phonon excitation via inelastic tunneling.