We simulate the sorting of a mixture of two types of biological cells using a modified version of the large-Q Potts model with differential adhesivity. We find long-distance cell movement leading to sorting with a logarithmic increase in the length scale of homogeneous clusters. Sorted clusters then round. We find two successive phases: A rapid boundary-driven creation of a low-cohesivity cell monolayer around the aggregate, and a slower boundary-independent internal rearrangement.

We show that if a change of spatial topology is mediated by a spacetime with an everywhere-non-singular metric of Lorentzian signature which admits a spinor structure, then the Kervaire semicharacteristic of the boundary plus the kink number of the Lorentzian metric on the boundary must vanish modulo 2. The kink number is a measure of how many times the light cone tips over on the boundary. It vanishes if the boundary is everywhere spacelike. This result gives a generalization of a previous selection rule: The number of wormholes plus the number of kinks created during a topology change is conserved modulo 2.

The results of an experiment searching for the difference Δg in the free-fall acceleration of aluminum and copper, in vacuum, obtained on the Earth in a differential Galileo type measurement are reported. Within the sensitivity of the measurement, Δg/g=7.2×${10}^{\mathrm{-}10}$; no g universality violation has been observed.

We present an analysis of 800-GeV proton-induced Drell-Yan production data from isoscalar targets ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and C, and from W, which has a large neutron excess. The ratio of cross sections per nucleon, R-${\mathrm{\sigma }}_{\mathrm{W}}$/${\mathrm{\sigma }}_{\mathrm{IS}}$, is sensitive to the difference between the d¯(x) and u¯(x) structure functions of the proton. We find that R is close to unity in the range 0.04≤x≤0.27, allowing upper limits to be set on the d¯-u¯ asymmetry. Additionally, the shape of the differential cross section ${\mathit{m}}^3$ ${\mathit{d}}^2$σ/${\mathit{dx}}_{\mathit{F}}$ dm for ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ at ${\mathit{x}}_{\mathit{F}}$≊0 shows no evidence of an asymmetric sea in the proton. We examine the implications of these data for various models of the violation of the Gottfried sum rule in deep-inelastic lepton scattering.

We report results of an experiment to search for a resonance enhancement of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ scattering cross section in a metallic Li target utilizing an energy-tunable monoenergetic positron beam. Within statistical uncertainties (0.27%) no evidence has been observed for deviations from Bhabha scattering over the entire invariant-mass region 1560 keV/${\mathit{c}}^2$<${\mathit{M}}_{\mathit{X}}^0$<1860 keV/${\mathit{c}}^2$ that can be associated with the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ sum-peak energies in GSI heavy-ion experiments. Under the assumptions that the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ channel dominates, we deduce lower limits on lifetimes τ>3.3×${10}^{\mathrm{-}13}$ sec (J=0) and τ>8.2×${10}^{\mathrm{-}13}$ sec (J=1), at 90% C.L.

The search for s-channel production of light neutral particles coupled to ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ has been extended by more than 3 orders of magnitude in lifetime beyond the region which is accessible to elastic ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ scattering. The whole mass range 1500≲${\mathit{M}}_{\mathit{X}}^0$≲1860 keV/${\mathit{c}}^2$ suggested by the observation of anomalous ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ pairs in heavy-ion collisions has been investigated. These measurements find no evidence for ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ states within lifetime ranges (90% C.L.) of 1.4×${10}^{\mathrm{-}12}$≲τ≲4×${10}^{\mathrm{-}10}$ sec (J=0) and 1.4×${10}^{\mathrm{-}12}$≲τ≲6×${10}^{\mathrm{-}10}$ sec (J=1), assuming that the state does not break up by interacting within the target.

Lifetimes of states in two ΔI=1 bands in ${}_{}{}^{198}{}_{}{}^{}\mathrm{Pb}$ have been measured using the Doppler-shift attenuation method. The in-band reduced transition probabilities are ∼1–2 Weisskopf units assuming magnetic dipole transitions. The measured lifetimes in conjunction with the partial level scheme support an oblate collective interpretation for these structures.

We demonstrate a new cooling technique which is used to cool sodium atoms in one dimension to an effective temperature of 100 nK, less than 1/10 of the single photon recoil temperature ${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathrm{rec}}$=(ħk${)}^2$/2M.

Observations of a new dynamical process, absorption of two optical photons during a binary collision, have been made. Measurements on magnesium-rare-gas collisions display a rich phenomenology associated with the collisions, the relative linear polarization directions of the exciting light beams, and their separate detunings from atomic Mg 3s ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$→3p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$→5s ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ stepwise resonance. Polarization spectra for Mg-Ne and Mg-Ar fractional collisions are reported, and are seen to contain information on short-range collision dynamics and on evolution of alignment produced in the process.

The autoresonance in nonlinear three-wave interactions is discussed. The phenomenon is characteristic of inhomogenous (or time-dependent) media in the presence of nonlinear wave-vector (frequency) shifts and leads to a persistent and efficient redistribution of the wave action fluxes (action densities) via a continuing spatial (temporal) self-adjustment of the nonlinear resonance relation. Conditions for the autoresonance are found and the phenomenon is illustrated by numerical examples.

Polarized, stored beams are becoming a more and more important tool in nuclear and high-energy physics. In order to measure the beam polarization in a storage ring the polarization vector of the stored beam has to aim, revolution for revolution, over a period of seconds to minutes, into the same, so-called ‘‘stable’’ direction. In this paper measurements at the Indiana University Cooler Ring are described in which for the first time in a storage ring, oscillations around this stable direction have been measured. The existence and the dynamics of such oscillations are, for instance, important for a new proposed technique for polarizing stored hadron beams.

Electrically coupled light-emitting diodes have been configured to demonstrate multiple light beams with correlated sub-shot-noise intensity fluctuations. Photocurrent covariance measurements of the two light beams from a pair of series-connected diodes show a positive correlation, similar to that observed with nonlinear crystal down-converters. Shunt-connected diodes are shown to generate negatively correlated light beams.

A beam of 3.6-MeV electrons has been used to study the generation of radiation in the far infrared (FIR) by the Smith-Purcell mechanism. The dependence of wavelength on angle of emission, over angles from 56° to 150° and wavelengths from 350 to 1860 μm, is in excellent agreement with the Smith-Purcell dispersion relation. Comparison of the yield with that from a 5000-K source suggests that the spontaneous Smith-Purcell effect offers an easily tunable alternative to the synchrotron as a coherent FIR source, and that it could also form the basis of an inexpensive, compact free-electron laser.

The properties of ion-acoustic waves in a plasma are investigated by analytically solving the electron Fokker-Planck (FP) and cold-ion fluid equations for arbitrary electron-ion (e-i) collision strength. This is achieved by developing a reduced form of the FP equation with a generalized collision frequency. It is demonstrated that the effective wave damping can be treated as a combination of collisional and collisionless mechanisms. Contrary to several previous reports, weak e-i collisions are shown to increase the damping rate above the collisionless electron Landau limit.

Scanning tunneling microscope images of ${\mathrm{Ta}}_2$${\mathrm{NiSe}}_7$ taken at 77 and 4.2 K show a complex electronic rearrangment occurring below the charge-density-wave (CDW) onset temperature of 52.5 K. A large energy gap of 41.0±3.0 meV is observed and a CDW amplitude modulation of wavelength ∼2${\mathit{b}}_0$ is detected. The electronic transfer between chains appears to drive the CDW formation.

Substrate disorder effects on the scaling properties of growing crystalline surfaces in solidification or epitaxial deposition processes are investigated. Within the harmonic approach there is a phase transition into a low-temperature (low-noise) superrough phase with a continuously varying dynamic exponent z>2 and a nonlinear response. In the presence of the Kardar-Parisi-Zhang nonlinearity the disorder causes the lattice effects to decay on large scales with an intermediate crossover behavior. The mobility of the rough surface has a complex dependence on the temperature and the other physical parameters.

Lubrication is documented on a microscopic scale with a friction force microscopy: A reduction in friction is observed for Langmuir-Blodgett film-covered surfaces, compared to the bare substrates. Film defects not detected in the AFM topographic mode are clearly recorded in the friction force mode. With applied forces over 10 nN, the initial stages of wear are observed. Small islands of bilayer height are moved in the entirety, conserving the normal orientation of the aliphatic chains. This collective motion of molecules allows the shear strength of the films to be determined. The observed ability of the molecules to remain in the ordered state illustrates one of the fundamental origins of boundary lubrication.

We observe a new wetting layer growth mechanism at the liquid/vapor surface of the critical mixture acetone+hexadecane. After spinodal decomposition of the bulk liquid, a metastable surface state forms. This metastable state is consistent with critical adsorption and persists until a wetting film or droplets of the lower phase are nucleated at the surface. Film growth occurs for ΔT=${\mathit{T}}_{\mathit{c}}$-T<0.1 °C while droplet growth occurs for ΔT>0.1 °C. The droplet nucleation time is consistent with classical nucleation theory provided the droplet line tension, scrL, is included in the surface free energy. We determine that scrL∼${\mathit{t}}^{0.83}$ close to ${\mathit{T}}_{\mathit{c}}$ where t is the reduced temperature.

Recently, Mester et al. have made measurements of the cooling effect of a superfluid He film on a composite bolometer. In interpreting their results they suggest that the main thermal resistance is caused by an insufficient generation of excitations, which can cause evaporation, in the He film. In this Letter we suggest an alternative explanation which accounts for their measurements in considerable detail. The main thermal resistance is found to be between the Ge and sapphire, and we conclude that the Kapitza conductance to a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film is the same as that to bulk liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$.

We study theoretically the equilibrium behavior of the lamellar phase of an A-B diblock copolymer melt. Each lamellar layer is an A-B,B-A repeat unit and n such layers are confined between, and parallel to, two identical flat plates. We find that the configurations with a half-odd-integer number of layers occur only when the difference between the two polymer-plate surface tensions is small, and then only below some critical plate separation. We calculate the discontinuity in the pressure at the transition point between two different values of n.