Experiments have been performed which study the relaxation of a nuclear spin system by paramagnetic impurities under conditions which inhibit spin diffusion. When spin diffusion is effectively absent, the magnetization is found ultimately to approach its equilibrium value as $\exp [-{\left(\frac{t}{{\tau }_1}\right)}^{\frac{1}{2}}]$. An expression is obtained describing the relaxation of such a diffusionless spin system valid for all times and in agreement with experiment. Under suitable conditions higher order spin diffusion effects are also observed.

The behavior of the ${\mathrm{Al}}^{27}$ NMR structures in ruby has been investigated under dynamic nuclear polarization (the solid-state effect) achieved by applying microwave pumping power at the center of a ${\mathrm{Cr}}^{3+}$ ESR line. Experimental results were found to be qualitatively consistent with the theoretical predictions. It is demonstrated that this type of investigation enables one to determine the sign of the quadrupole coupling constant.

We present experimental verification of the parametric enhancement of thermal fluctuations, the power balance, and the parametric threshold.

The integral equations for the calculation of the ground-state energy of the repulsive delta-function interaction problem in one dimension for $N$ particles are reduced to a system of algebraic equations by using the method of moments. We obtain explicit results in a limiting case.

The free energy of an assembly of slightly nonspherical molecules with a hard core is expressed as the sum of the free energy of a system of equivalent hard spheres plus correction terms related to eccentricity. An estimate of these terms is made for ellipsoidal molecules.

Experimental and theoretical evidence of resonant and nonresonant mode coupling of cyclotron harmonic plasma waves is presented.

A method of calculating the transport coefficients of a degenerate Fermi system is described and compared with previous approaches. Applications to dilute mixtures of ${\mathrm{He}}^3$ in liquid ${\mathrm{He}}^4$ and to nearly ferromagnetic Fermi liquids are given.

The phonon-dispersion curves in silicon are calculated from a microscopic model by a dielectric screening theory. The part of the dynamical matrix arising from the diagonal part of the inverse dielectric-function matrix is calculated just as in metals; the off-diagonal part is approximated by interactions of ions and bonds treated as point charges in Phillips's bond-charge model.

It is shown that certain nonlinearities associated with the energy dependence of the carrier-momentum relaxation time in semiconductors make contributions to the optically mixed output, which may be larger than the ones considered by earlier workers.

A standard spin-echo technique has been employed to determine the electronic phase-memory time of radiation-produced $E_1^{}{}_{}{}^{\prime }$ centers in crystalline quartz at 4.2, 77, and 300°K. The phase-memory time was found to be independent of temperature.

A polaron mass of $11m_e$ was measured by cyclotron resonance of photocarriers induced in semiconducting rare-earth-doped Cd${\mathrm{F}}_2$ between 1 and 4.5°K. A sharp transition at 178 ${\mathrm{cm}}^{-1\mathrm{}}$ is interpreted in terms of transitions between states of a polaron trapped by a rare-earth ion.

The bulk nature of the magnetization of Cr${\mathrm{Be}}_{12}$ is verified and the paramagnetic Curie temperature of about 50°K confirmed by conventional high-field NMR in the ferromagnetic as well as in the paramagnetic state. The equality of the hyperfine constants in the ferromagnetic and paramagnetic states suggests true ferromagnetic ordering. Significant magnetization density on the Be sites is inferred.

We present a modification of the two-dimensional Ising model which incorporates random impurities. The specific heat of this model is infinitely differentiable even at the critical temperature where it possesses an essential singularity. We find this specific heat to be in perfect quantitative agreement with the smooth peak recently observed by van der Hoeven, Teaney, and Moruzzi for $T\gtrsim T_c$ in the specific heat of EuS.

Proton spin flip in excitation of the first $2^{+}$ state in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ has been determined at 29.7 and 40.0 MeV by measuring the correlation between inelastically scattered protons and gamma rays emitted normal to the scattering plane. The data are well described by the distorted-wave Born-approximation collective model when the deformed spin-dependent potential has the full Thomas form.

A new resonance method is discussed which is suited for the investigations of hyperfine interactions of excited nuclear states with lifetimes longer than 1 μsec. A first experiment was performed on a 4-μsec state of ${}_{}{}^{69}{}_{}{}^{}\mathrm{Ge}$. The $g$ factor was determined as $g=-0.222\mathrm{}\pm 0.001$.

We report a numerical analysis of the electromagnetic wave equation with a saturable, intensity-dependent, refractive index. The solutions show the dynamical self-focusing of an intense optical beam through the focus. The transverse intensity profile develops a complex ringed structure, the central maximum of which has many of the properties of the small-scale filaments observed experimentally.

The ratio ${\left|{\eta }_{00}\right|}^2$ of the rate of decay $K_2^{}{}_{}{}^0\to 2{\pi }^0$ to the decay rate $K_1^{}{}_{}{}^0\to 2{\pi }^0$ has been measured to be ${\left|{\eta }_{00}\right|}^2=(-2\mathrm{}\pm 7)\times {10}^{-6\mathrm{}}$.

We report results of an investigation of elementary particle creation in expanding universes.

It is shown, by means of factorization, that the daughter Regge trajectories implied by analyticity in unequal-mass scattering amplitudes constitute a single Lorentz pole when they couple to an equal-mass channel. At zero energy the equal-mass elastic amplitude has the form $\mathrm{const}\times D_{-\alpha \mathrm{}\left(0\right)-2\mathrm{}}^{}{}_{}{}^1\mathrm{}(-z)\mathrm{}$.

On the basis of recent precise data on the earth's magnetic field, a new upper bound on the mass of the photon is obtained using a method that was originally proposed by Schrödinger. The limit is 1.15 × ${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$≡2.3 × ${10}^{-15\mathrm{}}$ eV≡4.0 × ${10}^{-48\mathrm{}}$ g, which is four orders of magnitude better than the best laboratory measurement, that of Plimpton and Lawton.