It is proposed that the randomly diluted elastic network of Hooke's-law central-force springs in two dimensions may have a hitherto unrecognized splay-rigid phase in which the bulk and shear moduli vanish but the Frank elastic constant, $K$, is nonzero. Exponents for the associated splay-rigidity percolation and torsional resistance are estimated by series-expansion techniques. These exponents are related to that for $K$ through the node-link picture.

The specific heat of amorphous Ge films evaporated at room temperature shows a strong magnetic field dependence at very low temperatures (0.07 K < T < 1.5 K). This effect is quantitatively attributed to magnetic excitations arising from localized unpaired electronic states (dangling bonds). It is shown that other kinds of excitations, e.g., tunneling states known from other amorphous solids, do not contribute measurably to the specific heat.

We report the first observation of a pressure-induced breakdown of a magnetically ordering ${\mathrm{Eu}}^{2+}$ ($J=\frac{7}{2}$) state to a nonmagnetic intermediate-valent state in antiferromagnetically ordered Eu(${\mathrm{Pd}}_{0.8}$${\mathrm{Au}}_{0.2}$)${}_2{}^{}{}_{}{}^{}\mathrm{Si}_2^{}{}_{}{}^{}$. The experimental results allow us to determine the limits of the range of the Eu mean valence of $2.0<~\overline{v}<~2.2$ at 4.2 K, over which magnetic order and intermediate valence can coexist.

We present a unified scheme that, by combining molecular dynamics and density-functional theory, profoundly extends the range of both concepts. Our approach extends molecular dynamics beyond the usual pair-potential approximation, thereby making possible the simulation of both covalently bonded and metallic systems. In addition it permits the application of density-functional theory to much larger systems than previously feasible. The new technique is demonstrated by the calculation of some static and dynamic properties of crystalline silicon within a self-consistent pseudopotential framework.

A new approach to the Monte Carlo simulation of electron transport is presented. The Monte Carlo technique is regarded as a stochastic evaluation of the Green's function expressed as a Feynman path integral. By a proper weighting of the randomly generated trajectories, conventional Monte Carlo simulations can be used to obtain the correct quantum solution. This technique is applied to silicon dioxide by employment of the scattering rates obtained from the Dyson equation, thus extending the validity of the solution beyond the quasiclassical and perturbation approximations.

Sound propagation in the heavy-fermion superconductor U${\mathrm{Be}}_{13}$ is studied at frequencies from 0.9 to 2.4 GHz and temperatures from 0.01 to 100 K. A peak in the acoustic attenuation is observed below the superconducting transition of 0.9 K, instead of the rapid drop expected for a BCS superconductor. Absorption into a collective mode of a nonsinglet, anisotropic superconductor is proposed.

The envelope function of a surface state in Ag(111) has been determined with a new experimental approach on the concept that spatially varying physical quantities near the surface can be probed in real space with the use of samples with tailored atomic configurations. Samples of Ag(111) with one near-surface atomic layer replaced by a closely matched Au atomic layer were fabricated by molecular-beam epitaxy.

We have measured the $\frac{1}{f}$ noise in polycrystalline films of Al, Al-Si(1%), and Al-Cu(4%) in the temperature range of 300 to 600 K. The temperature dependence indicated activation energies of 0.69, 0.80, and 0.89 eV, respectively. These energies are similar to the activation energies found for Al diffusion along grain boundaries for films of the same size and composition measured in the same temperature range. Measurements of samples with identical compositions but differing widths and thicknesses revealed significant departures from the usual inverse volume dependence of the $\frac{1}{f}$ noise.

Hyperfine interaction parameters near clean and Ag-covered Fe(110) surfaces could be measured for the first time, for the first and the second monolayer separately, by means of in situ conversion-electron Mössbauer spectroscopy of oligatomic Fe(110) films on W(110) with monolayer ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ probes. Quadrupole splitting deviates strongly from zero in the topmost monolayer only, indicating the reduced symmetry; it can be used to measure first- to second-layer self-diffusion. Magnetic hyperfine fields provide information on magnetic order near the surface with monolayer resolution.

We present specific-heat measurements as a function of field (3-6 T) and temperature (0.35-1.7 K) of a single crystal of the organic conductor tetramethyltetraselenafulvalenium perchlorate [${\mathrm{}\left(\mathrm{TMTSF}\right)\mathrm{}}_2$Cl${\mathrm{O}}_4$]. The small electronic contribution, 40 nJ/K, shows clearly above a temperature-dependent threshold field, a series of jumps and peaks. The phase diagram deduced from this magnetocalorimetric investigation exhibits in the threshold region indications of a partial reentrance of the normal metal in between semimetallic regions.

An inequality relating averages of generalized correlations to averages of generalized susceptibilities for Gaussian field distributions is presented. This inequality is applied to random-field systems to prove under the assumption of a continuous transition the (tree level) decoupling of the quenched two-point function. By assumption of only a power-law divergence, a lower bound for $\eta$ is obtained. It rules out the possibility that some recent experimental and numerical results reflect equilibrium properties near a continuous transition.

It is shown that it is possible to calculate the ammonia synthesis rate in a catalytic reactor at industrial conditions (150-300 atm, 375-500°C) starting from measurements of the properties of the reactants on well-defined single-crystal surfaces under ultrahigh-vacuum conditions. A generalized form of Fowler and Guggenheim's statistical mechanical treatment of adsorption is used in conjunction with the reaction scheme proposed by Ertl et al. The calculation contains no adjustable parameters and reproduces experimental data over a broad range of conditions.

Ionization of hydrogen atoms with principal quantum number $n=32\mathrm{}$, 40, and 51-74 by a 9.92-GHz electric field $\mathrm{F}\mathrm{}\left(t\right)=\hat{z}{F}_{0}cos\omega t$ was studied with a superimposed static electric field ${\overline{F}}_s=0, 2, 5, \mathrm{and} 8$ V/cm. The measured field strengths $F_0\mathrm{}(10\%)\mathrm{}$ at which 10% of the atoms were ionized are in excellent agreement with classical calculations in both one and two spatial dimensions. Covering finer detail as well as gross structure of the $n$ dependence of $F_0\mathrm{}(10\%)\mathrm{}$, the agreement supports the application of classical dynamics to the analysis of this strongly perturbed quantum system.

An interface attracted by weaker bonds to a wall can be depinned by quenched impurities in the bulk as well as by thermal fluctuations. Exact calculations in two dimensions indicate that the depinning transition with randomness is characterized by a discontinuous specific heat and a quadratic divergence of the localization length. Numerical simulations indicate delocalization by randomness in cases where there is no analogous depinning by thermal fluctuations, e.g., as in an interface bound to a strip of weak bonds in the bulk, or for two attracting interfaces.

We study the European Muon Collaboration effect within the conventional nuclear theory using the free-nucleon structure function. It is shown that qualitative agreement with the experiment can be obtained by taking into account the momentum (Fermi motion) and the energy distributions of nucleons in nuclei.

We study the effective three-dimensional SU(3) spin model with nonzero chemical potential. This model describes the strong-coupling, large-fermion-mass limit of QCD at finite temperature and baryon density. The results obtained with a complex Langevin algorithm are encouraging for a future simulation of QCD with nonzero chemical potential. The Langevin simulations converge even for large values of the chemical potential, and excellent agreement with exact solutions in the extreme strong-coupling ($\beta =0\mathrm{}$) limit has been found.

We show that QED fluctuations for present metal-oxide-semiconductor field-effect transistor microcircuit devices are substantial and thus cannot be ignored. For example, the Casimir energy of a gate-region capacitor is typically $\frac{1}{10}$ of the electrostatic energy. Measurement of their electronic transport properties is suggested as a tool to learn about some nonperturbative aspects of QED which cannot be reached via high-energy or atomic physics.

The success of the Fritzsch mass-matrix Ansatz in reproducing the observed pattern of the Kobayashi-Maskawa mixings can be explained by having the mass matrices of the charge $\frac{2}{3}$ and $-\frac{1}{3}$ quarks closely proportional to each other. Thus except for light quarks, the ratio of these two masses in each generation should be the same. Extending this to the fourth generation and using the electroweak $\rho$-parameter constraint we expect that the fourth charged lepton and the seventh (down type) and the eighth (up type) quarks, if they exist, are likely to have masses around 25, 60, and 450 GeV, respectively.

We present a new way to solve the strong $\mathrm{CP}$ problem in models with a spontaneously broken $\mathrm{CP}$ invariance. It is simpler than existing non-Peccei-Quinn approaches. It predicts the existence of light (i.e., weak scale) colored Higgs bosons which could be seen in colliders.

Perturbative QCD predictions are given for the $e^{+}{e}^{-}$ pair production of vector and pseudoscalar hadrons which are bound states of heavy quarks. A striking result is the prediction of an exact zero above threshold for the production of helicity-zero hadron pairs.