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.

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions. In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first time a double-twist molecular orientation in a helical crystal has been observed.

Bohr's correspondence principle, i.e., the expectation that the semiclassical approximation works better for states with greater quantum numbers, is shown to break down in all quantum systems in which the asymptotic interaction between the fragments behaves as ${-C}_n/r^n$ with $n>\mathrm{}2\mathrm{}$.

Experiments are performed to demonstrate the generation and propagation of acoustic solitary waves in an air-filled tube with a periodic array of Helmholtz resonators connected axially. The purpose is to verify the theoretical findings made so far that nonlinear acoustic waves do not evolve into a shock but into a solitary wave propagating steadily without any change of its smooth profile. To identify the solitary wave, the temporal pressure profile is compared directly with the theoretical profile of the solitary wave. Also checked are the relation between the peak sound pressure of the solitary wave and its half-value width in time, and the relation between the peak sound pressure and the deviation of propagation speed from sound speed. The experimental results show good quantitative agreement with the theory.

We present an analytical theory of susceptibility induced nuclear spin dephasing in the capillary network of myocardium. Using a strong collision approach, equations are obtained for the relaxation rate of the free induction and the spin echo decay. Simulation and experimental data are well predicted by the theory. Since paramagnetic deoxyhemoglobin as the origin of nuclear spin dephasing has a higher tissue concentration in myocardium supplied by a stenotic, i.e., significantly narrowed, coronary artery, spin dephasing might serve as a diagnostic tool. Our approach can be modified for capillary networks in other tissues than myocardium and may be applied in material science.

We report observations of a new quasistatic nonequilibrium phenomenon in the density of electronic states (DOS) of a superconductor. Tunneling measurements of the DOS of ultrathin Al films, at the spin paramagnetically limited parallel magnetic field transition, reveal a strongly hysteretic DOS spectrum. We show that the hysteresis can be characterized as a quasistatic state memory effect in which the state of a film (normal or superconducting) is determined by its state prior to entering the hysteretic region. We also show that state memory can lead to the onset of superconductivity with increasing temperature, i.e., reentrance.

With the aim of constraining the structural properties of neutron stars and the equation of state of dense matter, we study sudden spin-ups, glitches, occurring in the Vela pulsar and in six other pulsars. We present evidence that glitches represent a self-regulating instability for which the star prepares over a waiting time. The angular momentum requirements of glitches in Vela indicate that $\ge 1.4\%$ of the star's moment of inertia drives these events. If glitches originate in the liquid of the inner crust, Vela's “radiation radius” $R_{\infty }$ must exceed $\simeq 12\mathrm{km}$ for a mass of ${1.4M}_{\odot }$. Observational tests of whether other neutron stars obey this constraint will be possible in the near future.

We demonstrate that local transformations on a composite quantum system can be enhanced in the presence of certain entangled states. These extra states act much like catalysts in a chemical reaction: they allow otherwise impossible local transformations to be realized, without being consumed in any way. In particular, we show that this effect can considerably improve the efficiency of entanglement concentration procedures for finite states.

The number density and orientation of molecules at the surface of a total-internal-reflection-ring minicavity are probed with extremely high sensitivity in a novel realization of the cavity ring-down optical absorption experiment. The modes of the ultralow-loss cavity, which are excited by photon tunneling, have long lifetimes that are sensitive to the presence of absorbing species in the evanescent field near a cavity facet. The total-internal-reflection-ring cavity extends cavity ring-down spectroscopy to surfaces and condensed matter, permitting a wide range of novel fundamental studies and applications. Routine single molecule detection may ultimately be feasible.

We use the method of adiabatic following to prepare a single molecule in its fluorescing excited state. Spontaneous emission from this state gives rise to a single photon. With our current experimental conditions, up to $74\%$ of the sweeps lead to the emission of a single photon. Since the adiabatic passage is done on command, the molecule performs as a high rate source of triggered photons. The experimental results are in quantitative agreement with quantum Monte Carlo simulations.

Transmission metallic gratings with very narrow and deep enough slits can exhibit transmission resonances for wavelengths larger than the period of the grating. By using a transfer matrix formalism and a quasianalytical model based on a modal expansion, we show that there are two possible ways of transferring light from the upper surface to the lower one: by the excitation of coupled surface plasmon polaritons on both surfaces of the metallic grating or by the coupling of incident plane waves with waveguide resonances located in the slits. Both mechanisms can lead to almost perfect transmittance for those particular resonances.