A steady-state, fully noninductive plasma current has been sustained for the first time in a tokamak using electron cyclotron current drive only. In this discharge, 123 kA of current have been sustained for the entire gyrotron pulse duration of 2 s. Careful distribution across the plasma minor radius of the power deposited from three 0.5-MW gyrotrons was essential for reaching steady-state conditions. With central current drive, up to 153 kA of current have been fully replaced transiently for 100 ms. The noninductive scenario is confirmed by the ability to recharge the Ohmic transformer. The dependence of the current drive efficiency on the minor radius is also demonstrated.

Novel implementation of the Fourier imaging technique on conduction electron spins in the one-dimensional organic conductors $(\mathrm{FA}{)}_2{\mathrm{PF}}_6$ (FA: fluoranthene) is reported. Two-dimensional spatial imaging of resolution $30\mu {\mathrm{m}}^2$ is combined with the pulsed-gradient spin-echo technique, to derive maps revealing the local properties of the electron spin density and mobility. The maps generally show pronounced inhomogeneity of both density and mobility on the scale of $\sim 30–300\mu \mathrm{m}$. Highly mobile regions were identified to exist, and the mobility in these was quantitatively evaluated by a basic theoretical model of restricted diffusion.

A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- $(7\times 7)$ surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few Å of the surface.

Scanning tunneling microscopy was used to study molecular order in monolayer organic films formed by solution-phase growth from thermotropic liquid crystal solvents. The films develop macroscopically uniaxial alignment, with adlayer orientation controlled by an external magnetic field through interactions mediated by the liquid crystal. Results are presented for two films deposited from nematic and smectic- $A$ solvents, along with a discussion of the alignment mechanism.

The faceting of monocrystals of the lyotropic cubic liquid crystals in equilibrium with a humid atmosphere is observed. Experiments reveal the presence of more than 60 different types of facets on the surface of a spherical crystal of radius $R=1\mathrm{}\mathrm{mm}$. The devil's staircase type of faceting has been predicted theoretically when the interaction between steps on the crystal surface is repulsive.

Modern data are showing increasing evidence that the Universe is accelerating. So far, all attempts to account for the acceleration have required some fundamental dimensionless quantities to be extremely small. We show how a class of scalar field models (which may emerge naturally from superstring theory) can account for acceleration which starts in the present epoch with all the potential parameters $O\left(1\right)$ in Planck units.

Making use of self-assembly techniques, we realize nanoscopic semiconductor quantum rings in which the electronic states are in the true quantum limit. We employ two complementary spectroscopic techniques to investigate both the ground states and the excitations of these rings. Applying a magnetic field perpendicular to the plane of the rings, we find that, when approximately one flux quantum threads the interior of each ring, a change in the ground state from angular momentum $\ell =0\mathrm{}$ to $\ell =-1\mathrm{}$ takes place. This ground state transition is revealed both by a drastic modification of the excitation spectrum and by a change in the magnetic-field dispersion of the single-electron charging energy.

Reversible conductance transitions are demonstrated on the molecular scale in a complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine, by application of local electric field pulses. Both macroscopic and local current-voltage (I/V) measurements show similar electrical bistability behavior. The mechanism of the electrical bistability is discussed.

We experimentally demonstrate resonant coupling between photons and excitons in microcavities which can efficiently generate enormous single-pass optical gains approaching 100. This new parametric phenomenon appears as a sharp angular resonance of the incoming pump beam, at which the moving excitonic polaritons undergo very large changes in momentum. Ultrafast stimulated scattering is clearly identified from the exponential dependence on pump intensity. This device utilizes boson amplification induced by stimulated energy relaxation.

A streak camera with high spatial and temporal resolution was used for imaging the dynamics of the violent collapse in single-bubble sonoluminescence. The high pressure in the last phase of the bubble collapse leads to the emission of a shock wave, which is launched with a shock velocity of almost 4000 m/s. The shock amplitude decays much faster than $\sim 1/r$. From the strongly nonlinear propagation the pressure in the vicinity of the bubble can be calculated to be in the range of 40–60 kbar.

When a laser pulse of intensity ${10}^{19}\mathrm{W}{\mathrm{cm}}^{-2\mathrm{}}$ interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional $\gamma$-ray beam that can be used to carry out photonuclear reactions. The isotopes ${}^{11}\mathrm{C}$, ${}^{38}\mathrm{K}$, ${}^{62,64}\mathrm{Cu}$, ${}^{63}\mathrm{Zn}$, ${}^{106}\mathrm{Ag}$, ${}^{140}\mathrm{Pr}$, and ${}^{180}\mathrm{Ta}$ have been produced by $(\gamma ,n)$ reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in ${}^{238}\mathrm{U}$ has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the ${}^{11}\mathrm{C}$ and the ${}^{62}\mathrm{Cu}$ ${\beta }^{+}$ activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of $\sim {10}^{19}\mathrm{W}{\mathrm{cm}}^{-2\mathrm{}}$.

A new regime of laser-matter interactions in which the quiver motion of plasma electrons is fully relativistic, with energies extending well above the threshold for nuclear processes, is studied using a petawatt laser system. In solid target experiments with focused intensities exceeding ${10}^{20}\mathrm{W}/{\mathrm{cm}}^2$, high energy electron generation, hard bremsstrahlung, and nuclear phenomena have been observed. We report here a quantitative comparison of the high energy electrons and the bremsstrahlung spectrum, as measured by photonuclear reaction yields, including the photoinduced fission of ${}^{238}\mathrm{U}$.

We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide ( ${\mathrm{MoS}}_2$) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer ${\mathrm{MoS}}_2$ nanoparticles synthesized on Au(111), and establishes a new picture of the active edge sites of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in general.

Experimental observations of rotating spiral flame edges formed during near-limit combustion of a downward-facing, polymethylmethacrylate disk spinning in quiescent air are reported. These flames exhibit similarities to patterns commonly found in quiescent excitable media. The tail rotates rigidly while the tip executes a compound, meandering motion sometimes observed in Belousov-Zhabotinskii reactions. A model assuming a rigid-body rotation with a constant speed of propagation relative to the swirling gas flow generated by the spinning disk predicts the observed spiral shapes well.

We observe photochemical selectivity for $\mathrm{N}1s$ to ${\pi }^{*}$ excitations of chemisorbed ${\mathrm{N}}_2$. By narrow bandwidth synchrotron radiation we selectively excite one of the two atoms of the molecule. Photon stimulated desorption of neutral N atoms predominates for excitations of the N atom close to the surface, whereas excitation of the outer atom ejects predominantly ${\mathrm{N}}_2^0$ and small amounts of ${\mathrm{N}}^{+}$, demonstrating the predominant breaking of the inner or outer bond, respectively, of the ${\mathrm{N}}_2$ adsorbate. Analysis on the basis of previously obtained decay electron spectra after atom-selective excitation can explain the mechanism of localized bond breaking.

Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion.

We study the effect of the addition of long flexible polymers in stratified flows. A two-layer stratification is used, in which the lower layer is brought into motion and drives a two-dimensional turbulent flow in the upper layer through viscous friction. Upon polymer addition in either of the two layers the kinetic energy in the upper layer is reduced by roughly one-half: The polymer reduces the liquid-liquid friction that drives the flow in the upper layer. This drag reduction can be attributed to a change in the nonsteady viscous boundary layer. The main characteristics of the quasi-two-dimensional turbulence that results in the upper layer are found to remain unaffected by the addition of the polymer.

The high pressure evolution of silicon clathrates is studied at room temperature by x-ray diffraction up to 15 GPa. Remarkably, no transition towards the diamond structure is observed and the clathrate phase transforms directly into the $\beta$-tin metallic phase at 11 GPa. Further, the bulk modulus is found to be $90\pm 5\mathrm{GPa}$, that is, only $(8\pm 5)\%$ smaller than the one of the diamond phase. These results are in good agreement with ab initio calculations which predict further that carbon clathrates, if synthesized, should be less compressible than cubic BN.

The transmission of ultracold neutrons through natural Gd and isotopic enriched ${}^{157}\mathrm{Gd}$ samples has been measured. Absorption cross sections in the order of 100 Mb have been identified. Here one touches a region where fluctuations of the physical parameters influence the result and can cause a basic deviation from the exponential attenuation law and where a purely imaginary interaction potential exists within the sample.

Conventional wisdom states that Newton's force law implies only four noncompact dimensions. We demonstrate that this is not necessarily true in the presence of a nonfactorizable background geometry. The specific example we study is a single 3-brane embedded in five dimensions. We show that even without a gap in the Kaluza-Klein spectrum, four-dimensional Newtonian and general relativistic gravity is reproduced to more than adequate precision.