We explain the results of recent polarization measurements in the reaction ${\pi }^{-}p\to \eta n$ at intermediate energies by using a simple interference model. A possible determination of the ratio of $F$ to $D$ coupling of $N_{\gamma }\mathrm{}\left(2650\right)\mathrm{}$ is discussed and the conclusion drawn is unaffected in spite of the ambiguity regarding the sign of the $A_2$ residue associated with the spin-flip amplitude.

The $\mathrm{KNY}$ coupling constants are determined using a new procedure which includes a criterion for checking the self-consistency of the necessary extrapolation into the unphysical region.

New measurements of the continuum photoionization cross sections of xenon in the region 670-800 eV are reported which reveal, in the region of the $M_{\mathrm{IV}}$ and $M_{\mathrm{V}}$ edges, extreme nonhydrogenic behavior previously observed only at longer wavelengths.

A possible source of imcompleteness is pointed out in the most recent close-coupling calculations for the excitation cross sections of the $n=2\mathrm{}$ levels in hydrogen, some of the results of which disagree with experiment. We present a method which removes this difficulty by the implicit inclusion of all important effective polarization potential terms of order $\frac{\alpha }{{\mathcal{r}}^4}$.

A nonresonant Overhauser effect by photoexcited conduction electrons is obtained on ${\mathrm{Si}}^{29}$ nuclei in silicon at 77°K in two different ways: (a) Saturation of the electronic magnetization is achieved with unpolarized light by exciting an equal number of spins up and spins down. (b) Polarized electronic spins are produced by optical pumping with circularly polarized light; the nuclear magnetization obtained in 1 G by optically pumped electrons corresponds to the equilibrium value at 77°K in 28 kG.

Bubbles due to the zero-point motion of positronium atoms in liquid He, ${\mathrm{H}}_2$, Ne, and Ar have been observed and their sizes determined.

We report measurements of the specific heat of xenon near the critical point. Good accuracy and temperature resolution are achieved with a semiautomatic system permitting direct recording of the heat capacity. From analysis of the results allowing for the effects of gravity, we conclude a value for the exponent $\alpha$ of about 0.08, although a value between 0 and $\frac{1}{8}$ cannot be ruled out. A symmetric logarithm is not consistent with the results.

The magnetoresistance of dilute magnetic alloys is calculated for arbitrary magnetic fields and temperatures by $S$-matrix theory on the basis of the $s-d$ model. The results agree qualitatively with the experiments of Monod on Mn in Cu in the temperature range covered by him, but not with the results of Daybell and Steyert on Cr in Cu.

We report measurements of the "deformation effect" in the total cross section for neutrons on oriented ${\mathrm{Ho}}^{165}$ over the energy range 0.330-5.60 MeV. They are in good qualitative agreement with the prediction of a previous theoretical calculation, and the predicted inversion or sign change in the energy range 3-7 MeV is verified.

New measurements have been performed of the energies and natural linewidths of $2p-1s$ pionic x-ray transitions, as well as muonic transition energies, in ${\mathrm{Li}}^6$, ${\mathrm{Li}}^7$, ${\mathrm{Be}}^9$, ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, and ${\mathrm{C}}^{12}$. High-resolution Si(Li) and Ge(Li) spectrometers were used, resulting in a more precise determination than those previously reported of the transition energies and natural linewidths. Comparison of the measured complex energy shifts in the pionic transitions has been made with the theory of the Ericsons and good agreement found.

By solving the spectral-function sum rules consistently, the ratio $\frac{F_K}{F_{\pi }}$ is found to be unity to the first order of SU(3)-breaking effect.

Weinberg's first sum rule applied to the axial-vector currents is shown to split into two separately valid sum rules if the usual assumptions concerning SU(3) mixing are adopted. New relations among masses, coupling constants, and mixing angles are obtained in the meson-dominance approximation, e.g., $\frac{F_K}{F_{\pi }}=1\mathrm{}$, and the implications are discussed.

High-energy data on photoproduction of pions and $K$ mesons are fitted with a Regge-pole model involving conspiring trajectories.

Relations between possible $\Delta S=-\Delta Q$ decay rates of $K^0-{\overline{K}}^0$, $K^{+}$, ${\Sigma }^{+}$, and ${\Xi }^0$ are given. A connection between $\Delta S=-\Delta Q$ and $\Delta S=2\mathrm{}$ leptonic decays is also suggested.

We show to any order in $\alpha$ that the electromagnetic mass difference between the charged and the neutral pion is at most logarithmically divergent and derive a necessary and sufficient condition that the pion mass difference times the isovector form factor is finite to any order in $\alpha$. All results are valid whether or not perturbation theory makes sense.