Two aspects of the irreversible measurement transformation are explored. The first is the range of allowed values for the joint uncertainty of two operators having no common eigenvector. The second is the constraint on states and operations following from the requirement that the uncertainty resolved by completing a measurement shall be always finite.

We use the duality between the Abelian Higgs model and pure U(1) lattice gauge theory to estimate the ratio $\sqrt{2}\kappa =\frac{\lambda }{\xi }$ of penetration depth and coherence length at the tricritical point to be $\sqrt{2}\kappa \approx 0.93$, thus placing the tricritical point slightly on the type-I side of the borderline between type-I and type-II superconductivity in four dimensions.

The wavelength of the pionic $4f-3d$ transition in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ has been measured with a curved-crystal spectrometer. The new value of the pion-electron mass ratio is deduced to be $\frac{m_{{\pi }^{-}}}{m_{e^{-}}}=273.126\mathrm{}77\left(71\right)\mathrm{}$. The consequence of this value for the rest mass of the muon neutrino is discussed.

It is argued that neither spin observables in electron-deuteron scattering nor form factors can serve as an unambiguous testing ground of predictions of perturbative QCD in the momentum-transfer region of a few GeV/c. The calculations based on nucleon and $\Delta$-isobar degrees of freedom give results similar to those of perturbative QCD. The influence of $\Delta$ isobars on the short-range behavior of the nucleon components of the deuteron wave function is stressed.

A new analysis of inclusive quasielastic electron-scattering data for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is presented. Integrated momentum distributions are derived from the data for the first time and the $Q^2$ dependence is shown to exhibit a slight deviation from the perfect scaling. If this is interpreted as a change in the nucleon radius, a result for the ratio of the nucleon radius in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ to the free-nucleon radius of 1.025 ± 0.011 is obtained, corresponding to an upper limit of 3.6% for the radius increase.

We report the first observation of electron-ejection asymmetries due to molecular orientation following $K$-shell photoexcitation in a free molecule. The angular distributions of electrons emitted by the decay of $K$-shell vacancies were measured in the vicinity of the ${\pi }^{*}$ discrete and the ${\sigma }^{*}$ shape resonance of CO. We see a sharp drop of the angular distribution asymmetry parameter to $\beta =-1\mathrm{}$ at the ${\pi }^{*}$ resonance as predicted by theory, but no comparable effect across the ${\sigma }^{*}$ shape resonance. The results are discussed with respect to the intrinsic anisotropy of the $K$-shell vacancies.

A long-range ion-atom potential is for the first time measured directly by electric-field-induced dissociation of selectively laser-excited $\mathrm{O}_2^{}{}_{}{}^{+}$ ions in a fast beam. The laser excitation spectrum reflects the molecular properties at "normal" internuclear distances of 1-2 Å while the threshold field required to dissociate the excited molecule determines the ${\mathrm{O}}^{+}{}_{-}{}^{}{}_{}{}^{}\mathrm{O}$ potential in the range 10-20 Å.

We find that thermal-energy muonium atoms are emitted from a clean hot tungsten foil in which positive muons are stopping near the surface. The temperature dependence of the thermal-muonium signal yields a surprisingly low activation energy of 0.66(4) eV, suggesting that we are observing the thermionic emission of muonium from the solid. The total muonium yield at 2300 K is about 0.04 per stopped muon of 23 MeV/c initial muon momentum. A number of new experiments should be possible using this unique source of thermal muonium in vacuum.

The structure of the $n=30\mathrm{}$, $M=0\mathrm{}$ manifold of lithium has been investigated experimentally in the presence of weak parallel electric and magnetic fields. The main properties of the spectra and their evolution with increasing field strengths are interpreted from the analysis of the approximate integral of motion obtained for hydrogen. The lithium spectra exhibit additional alterations which are typical of the short-range core effects.

Recent experiments have confirmed that coherent effects in the multiple scattering of light affect the angular dependence of the intensity reflected by disordered media. By considering the constructive interferences between time-reversed paths of light in a semi-infinite medium, we analyze the experimental line shape of the albedo within the diffusion approximation and explain the observed effects of polarization.

We report the first coherent excitation of phonon polaritons in a centrosymmetric crystal. Energy dispersion and linewidth of the $A_{\mathrm{u}}$ upper-branch bulk polaritons in Ti${\mathrm{O}}_2$ were determined by optical four-wave mixing.

Long-range icosahedral orientational order in an Al + 12-at.%-Mn alloy is confirmed by direct observation in field-ion microscopy. In addition, a considerable amount of local disorder and a large number of defects or antiphase boundaries are found.

A unified picture is obtained for the solid-on-solid interface in two dimensions constrained either by an external field or by finiteness of the system size. From the direct correlation function, intrinsic parts are separated which persist in the limit of vanishing external field, agree with $C_{\mathrm{cond}}$, a new direct correlation function based on conditional probabilities, and have the same new longitudinal correlation length ${\xi }_{\mathrm{}\left|\right|\mathrm{}}$ as in other cases of large systems in zero field.

Sharp charge-density-wave satellites in potassium have been located at (0.995, 0.975, 0.015). They are smaller than the {110} reflections by ∼ ${10}^5$, and each is surrounded by a prolate ellipsoidal cloud of diffuse phason scattering having its major axis along a line through the point (1,1,0).

We have induced nonlinear conduction and current oscillations in the charge-density-wave state of $o-\mathrm{Ta}{\mathrm{S}}_3$ in an open-circuit ($I=0\mathrm{}$) configuration using a temperature gradient to generate thermal voltages exceeding a threshold. The above features are associated with a current carried by the condensate which is compensated by a normal current in the opposite direction. Our experiments provide the first clear observation of decoupled motion of the condensed and uncondensed electrons in solids with a charge-density-wave ground state.

We report detailed measurements on the weak-localization corrections in well-defined and -characterized arrays of quasi one-dimensional normal-metal rings. The Bohm-Aharonov oscillations are very well resolved. Measurements on sets of samples of varying ring size and geometry determine the distinct effects of these parameters and allow an unambiguous, quantitative comparison to the weak localization theory for ring geometries.

The technique of polarization-dependent near-edge x-ray absorption is applid to an interface by taking advantage of core-level and Auger energy shifts for interface atoms. For epitaxial Ca${\mathrm{F}}_2$/Si(111) several unoccupied Ca- and F-derived interface states are found. The orientation of the corresponding orbitals is determined from the polarization dependence. The Ca atoms at the interface are found to be in the 1 + oxidation state.

We study the variation of the permeability in the vicinity of the sol-gel transition observed during free-radical copolymerization of acrylamide and bisacrylamide at low concentrations. The main difficulty of the experiment arises from the low values of the elastic moduli which can lead to deformation effects; these have been carefully analyzed. For the first time, the exponent $\nu$ and the prefactor ${\xi }_{\theta }$ of the correlation length have been determined experimentally. We find that $\nu$ is equal to 0.9 ± 0.1 independently of the concentration while ${\xi }_{\theta }$ decreases as the concentration is increased.

We show that a class of deterministic lattice gases with discrete Boolean elements simulates the Navier-Stokes equation, and can be used to design simple, massively parallel computing machines.

The graviton propagator in a de Sitter background is found to be divergent. We show that as a consequence of this divergence, de Sitter space is not a solution of the equations of motion of the complete theory. If we start from de Sitter space as a classical ground state, quantum corrections change it into flat Minkowski space.