We propose a new computer-simulation technique, based on the Widom test-particle method, to calculate the chemical potentials of components in a polymeric system. The technique is based on the insertion of test segments onto a polymer and is applicable for any chain length at gas and liquidlike densities. We perform sample calculations on homopolymers and show that the proposed technique allows for the enumeration of their thermodynamic behavior in the subcritical and supercritical temperature ranges.

An atomic interferometer based on a Young’s-type double-slit arrangement has been demonstrated. A supersonic beam of metastable helium atoms passes through a 2-μm-wide slit in a thin gold foil. This transversely coherent beam impinges on a second microfabricated transmission structure, consisting of two 1-μm-wide slits at a lateral distance of 8 μm. This double slit defines two possible paths on which the atoms can reach the detector slit. The good visibility of the observed fringes should make it possible to measure differential phase shifts in the interferometer of 1/3 rad in less than 10 min.

We have demonstrated an interferometer for atoms. A three-grating geometry is used, in which the interfering beams are distinctly separated in both position and momentum. We used a highly collimated beam of sodium atoms with a de Broglie wavelength of 16 pm and high-quality 0.4-μm-period free-standing gratings which we fabricated using a novel method. The interference signal is 70 counts/s, which allows us to determine the phase to 0.1 rad in 1 min. Applications of atom interferometers are briefly discussed.

We calculate the spectrum and high-energy ν background flux from photomeson production in active galactic nuclei (AGN), using the recent UV and x-ray observations to define the photon fields and an accretion-disk shock-acceleration model for producing high-energy particles. Collectively, AGN produce the dominant isotropic ν background between ${10}^4$ and ${10}^{10}$ GeV, detectable with current instruments. AGN ν’s should produce a sphere of stellar disruption which may explain the ‘‘broad-line region’’ seen in AGN.

We show that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11–15%. The proton concentration, which is determined by the poorly known symmetry energy of matter above nuclear density, exceeds the critical value in many current calculations. If it occurs, the direct URCA process enhances neutrino emission and neutron star cooling rates by a large factor compared to any process considered previously.

In a class of models with global SU(n) family symmetry, the possibility naturally exists that n-1 generations have light neutrinos and the remaining generation has a medium-heavy neutrino, of the order of the charged-lepton mass or the quark mass, as a consequence of an incomplete action of the seesaw mechanism. We discuss as applications two possibilities: (i) The heavy neutrino is identified with the neutral particle of mass 17 keV suggested by Simpson from β-decay experiments, and (ii) there may exist a fourth generation and the associated neutrino has a heavy mass, probably of the order of a hundred GeV.

${\mathit{E}}_6$ string models for which (i) ${\mathrm{E}}_6$ breaks to [SU(3)${]}^3$ at the Planck scale, (ii) [SU(3)${]}^3$ breaks to SU(3)×SU(2)×U(1) at an intermediate scale ${\mathit{M}}_{\mathit{I}}$ triggered by a (mass${)}^2$ ${\mathit{m}}^2$<0 where ≲1 TeV, and (iii) the model possesses a matter-parity invariance lead to the new-physics signals of μ→eγ and τ→μγ decays which may be accessible experimentally. The outgoing lepton is nearly 100% right handed and the τ→μγ branching ratio about ${10}^5$ times larger than the μ→eγ. Possible ways of detecting these decays are discussed.

Experimental results obtained at the CERN Super Proton Synchrotron on the structure-function ratio ${\mathit{F}}_2^{\mathit{n}}$/${\mathit{F}}_2^{\mathit{p}}$ in the kinematic range 0.004<x<0.8 and 0.4<${\mathit{Q}}^2$<190 ${\mathrm{GeV}}^2$, together with the structure function ${\mathit{F}}_2^{\mathit{d}}$ determined from a fit to published data, are used to derive the difference ${\mathit{F}}_2^{\mathit{p}}$(x)-${\mathit{F}}_2^{\mathit{n}}$(x). The value of the Gottfried sum F(${\mathit{F}}_2^{\mathit{p}}$-${\mathit{F}}_2^{\mathit{n}}$)dx/x=0.240±0.016 is below the quark-parton-model expectation of 1/3.

To search for spontaneous conversion of muonium to antimuonium with very low background, a new signature was implemented that required the coincident detection of the decay products of the antimuonium atom, the energetic ${\mathit{e}}^{\mathrm{-}}$ and the atomic ${\mathit{e}}^{+}$. No conversion events were seen, which sets an improved upper limit of 6.5×${10}^{\mathrm{-}7}$ (90% C.L.) on the conversion probability. The corresponding limit on the coupling constant, using a V-A form for the conversion Hamiltonian, is ${\mathit{G}}_{\mathit{M}\mathit{M}\mathrm{¯}}$<0.16${\mathit{G}}_{\mathit{F}}$ (90% C.L.), where ${\mathit{G}}_{\mathit{F}}$ is the Fermi coupling constant.

By using effective chiral Lagrangians with a suitable incorporation of the scaling property of QCD, we establish the approximate in-medium scaling law, ${\mathit{m}}_{\mathrm{\sigma }}^{\mathrm{*}}$/${\mathit{m}}_{\mathrm{\sigma }}$≊${\mathit{m}}_{\mathrm{N}}^{\mathrm{*}}$/${\mathit{m}}_{\mathrm{N}}$ ≊${\mathit{m}}_{\mathrm{\rho }}^{\mathrm{*}}$/${\mathit{m}}_{\mathrm{\rho }}$≊${\mathit{m}}_{\mathrm{\omega }}^{\mathrm{*}}$/${\mathit{m}}_{\mathrm{\omega }}$≊${\mathit{f}}_{\mathrm{\pi }}^{\mathrm{*}}$/${\mathit{f}}_{\mathrm{\pi }}$. This has a highly nontrivial implication for nuclear processes at and above nuclear-matter density. Some concrete cases are cited in this paper.

This paper reports for the first time continuous-wave, high-resolution, all-optical triple resonance spectroscopy. Using this technique, one can overcome the spin forbiddeness nature of a singlet-triplet transition and consequently unperturbed triplet rovibronic levels can be reached from a singlet ground state. This technique also facilitates state-selective population transfer to highly excited vibrational levels, both in the ground state and in excited states.

We report the results of a complex Kohn variational calculation of the low-energy electron scattering from ethylene, ${\mathrm{C}}_2$${\mathrm{H}}_4$. Our calculations are the first to confirm the existence of the Ramsauer-Townsend effect in a molecule which possesses a permanent quadrupole moment and suggest that such minima may be found in electron-scattering cross sections for many nonpolar molecules. The calculations also reveal a low-energy shape resonance in ${}_{}{}^2{}_{}{}^{}$${\mathit{B}}_{2\mathit{g}}$ symmetry at 1.83 eV, in excellent agreement with both beam and swarm measurements.

Numerical solution of two-dimensional incompressible hydrodynamics shows that states of a near-minimal ratio of enstrophy to energy can be attained in times short compared with the flow decay time, confirming the simplest turbulent selective decay conjecture, and suggesting that coherent vortex structures do not terminate nonlinear processes. After all possible vortex mergers occur, the vorticity attains a particlelike character, suggested by the late-time similarity of the streamlines to Ewald potential contours.

Freely evolving two-dimensional turbulence is dominated by coherent vortices. The density of these vortices decays in time as ρ∼${\mathit{t}}^{\mathrm{-}\xi }$ with ξ≊0.75. A new scaling theory is proposed which expresses all statistical properties in terms of ξ. Thus the average circulation of the vortices increases as ${\mathit{t}}^{\xi /2\mathrm{}}$ and their average radius as ${\mathit{t}}^{\xi /4\mathrm{}}$. The total energy is constant, the enstrophy decreases as ${\mathit{t}}^{\mathrm{-}\xi /2\mathrm{}}$, and the vorticity kurtosis increases as ${\mathit{t}}^{\xi /2\mathrm{}}$. These results are supported both by numerical simulations of the fluid equations and by solutions of a modified point-vortex model.

We present the first measurements of an instability in Taylor-Sedov blast waves propagating through a uniform gas. The instability occurred in a gas whose adiabatic index was low. Amplitude perturbations grew as a power of time. Our observations are compared to theory.

It is demonstrated both experimentally and theoretically that broken translational and vertical symmetries of a horizontal convection layer heated from below can lead to a qualitatively new effect, namely the onset of time-dependent convection. In particular, the behavior of a non-Boussinesq fluid in a layer with sinusoidal variation of the horizontal boundaries is studied near onset.

The evolution of the spectral bandwidth in free-electron-laser (FEL) oscillators is studied and found to be different for different saturation characteristics: For weakly saturated FELs in storage rings, the limiting bandwidth is given by that derived in the supermode theory; for linac-based FELs, where the gain reduction due to the high-intensity effect is significant, it is determined by the Fourier transform of the electron pulse length; for the case of a dc beam, it is given by a Schawlow-Townes formula, but the approach to the limit is very slow.

The self-organized critical state exhibited by a sandpile model is shown to correspond to motion on an attractor characterized by an invariant distribution of the conserved variable. The largest Lyapunov exponent is equal to zero. Yet over time scales of the order of the linear size of the system, the model displays intermittent chaos. The divergence of local histories is found to exhibit intermittency in both time and space.

We report the results of an experimental study of the effect of a dilute silica network on critical phenomena in a binary mixture of 2,6-lutidine and water. Light-scattering measurements of this sytem show that its structure does not differ significantly from that of the gel, but that the scattered intensity increases dramatically as the two-base region is approached. We interpret these results in terms of a layer of lutidine-rich fluid adsorbed in the silica surface and the resulting changes in concentration of the nonadsorbed fluid.

Ultrathin films of simple nonpolar molecular fluids (3–8 segmental dimensions thick) show a strikingly long relaxation time in response to oscillatory shear when confined between mica plates at 27 °C. When the shear rate exceeds this inverse time, the effective viscosity decays as an apparent power law in the shear rate, implying considerable distortion of the dynamic structure. The relaxation time is orders of magnitude longer than the Brownian relaxation time in the bulk state and may reflect collective motions induced by confinement.