High resolution microwave and infrared spectra of ${\mathrm{H}\mathrm{e}}_N\mathrm{\text{−}}{\mathrm{N}}_2\mathrm{O}$ clusters were studied in the range $N=3$ to 12. The apparent cluster moments of inertia increase from $N=3$ to 6, but then decrease, showing oscillatory behavior for $N=7$ to 12. This provides direct experimental evidence for the decoupling of helium atoms from the rotation of the dopant molecule in this size regime, signaling the transition from a molecular complex to a quantum solvated system and directly exploring the microscopic evolution of “molecular superfluidity.”

It is shown that laminar thermal convection can drive a chain reaction of DNA replication. The convection is triggered by a constant horizontal temperature gradient, moving molecules along stationary paths between hot and cold regions. This implements the temperature cycling for the classical polymerase chain reaction (PCR). The amplification is shown to be exponential and reaches 100 000-fold gains within 25 min. Besides direct applications, the mechanism might have implications for the molecular evolution of life.

Within the inherent structure thermodynamic formalism introduced by Stillinger and Weber [F. H. Stillinger and T. A. Weber, Phys. Rev. A 25, 978 (1982)], we address the basic question of the physics of the liquid-liquid transition and of density maxima observed in some complex liquids such as water by identifying, for the first time, the statistical properties of the potential energy landscape responsible for these anomalies. We also provide evidence of the connection between density anomalies and the liquid-liquid critical point. Within the simple (and physically transparent) model discussed, density anomalies do imply the existence of a liquid-liquid transition.

We propose a phenomenological model where the gravitational interaction between dark matter and baryons is suppressed on small, subgalactic scales. We describe the gravitational force by adding a Yukawa contribution to the standard Newtonian potential and show that this interaction scheme is effectively suggested by the available observations of the inner rotation curves of small mass galaxies. Besides helping in interpreting the cuspy profile of dark matter halos observed in $N$-body simulations, this potential regulates the quantity of baryons within halos of different masses.

We demonstrate theoretically that the shot noise produced by a tunnel barrier in a two-channel conductor violates a Bell inequality. The nonlocality is shown to originate from entangled electron-hole pairs created by tunneling events—without requiring electron-electron interactions. The degree of entanglement (concurrence) equals $2(T_1{T}_2{)}^{1/2}(T_1+T_2{)}^{-1}$, with $T_1,T_2\ll 1$ the transmission eigenvalues. A pair of edge channels in the quantum Hall effect is proposed as an experimental realization.

The local structure of simple liquids is significantly different from that of corresponding crystalline systems. Signatures of fivefold local ordering have been previously found, but current knowledge is limited to pair distribution, leaving considerable uncertainty in the determination of the geometrical structure. New x-ray absorption experimental results on liquid and undercooled liquid copper, interpreted using an advanced data-analysis method based on multiple-scattering simulations, are shown to contain direct information on triplet correlations making feasible a reliable determination of the bond-angle distribution and fraction of nearly icosahedral configurations in liquids.

A new technique is described for the isochoric heating (i.e., heating at constant volume) of matter to high energy-density plasma states () on a picosecond time scale (). An intense, collimated, ultrashort-pulse beam of protons—generated by a high-intensity laser pulse—is used to isochorically heat a solid density material to a temperature of several eV. The duration of heating is shorter than the time scale for significant hydrodynamic expansion to occur; hence the material is heated to a solid density warm dense plasma state. Using spherically shaped laser targets, a focused proton beam is produced and used to heat a smaller volume to over 20 eV. The technique described of ultrafast proton heating provides a unique method for creating isochorically heated high-energy density plasma states.

We present the results of experiments on impact craters formed by dropping a steel ball vertically into a container of small glass beads. As the energy of impact increases, we observe a progression of crater morphologies analogous to that seen in craters on the moon. We find that both the diameter and the depth of the craters are proportional to the $1/4$ power of the energy. The ratio of crater diameter to rim-to-floor depth is constant for low-energy impacts, but increases at higher energy, similar to what is observed for lunar craters.

We observe the formation of an intense optical wave packet fully localized in all dimensions, i.e., both longitudinally (in time) and in the transverse plane, with an extension of a few tens of fsec and microns, respectively. Our measurements show that the self-trapped wave is an X-shaped light bullet spontaneously generated from a standard laser wave packet via the nonlinear material response (i.e., second-harmonic generation), which extend the soliton concept to a new realm, where the main hump coexists with conical tails which reflect the symmetry of linear dispersion relationship.

While the form factors and parton distributions provide separately the shape of the proton in coordinate and momentum spaces, a more powerful imaging of the proton structure can be obtained through phase-space distributions. Here we introduce the Wigner-type quark and gluon distributions which depict a full-3D proton at every fixed light-cone momentum, like what is seen through momentum (“color”) filters. After appropriate phase-space reductions, the Wigner distributions are related to the generalized parton distributions (GPDs) and transverse-momentum dependent parton distributions, which are measurable in high-energy experiments. The new interpretation of GPDs provides a classical way to visualize the orbital motion of the quarks, which is known to be the key to the spin and magnetic moment of the proton.

Using a catalog of seismicity for Southern California, we measure how the number of triggered earthquakes increases with the earthquake magnitude. The trade-off between this relation and the distribution of earthquake magnitudes controls the relative role of small compared to large earthquakes. We show that seismicity triggering is driven by the smallest earthquakes, which trigger fewer events than larger earthquakes, but which are much more numerous. We propose that the nontrivial scaling of the number of triggered earthquakes emerges from the fractal spatial distribution of seismicity.

Large increases in the upper critical field $B_{C2}(0)$ are reported in bulk superconductors that demonstrate another novel property for nanocrystalline materials. Disordered nanocrystalline ${\mathrm{P}\mathrm{b}\mathrm{M}\mathrm{o}}_6{\mathrm{S}}_8$ superconductors were fabricated by mechanical milling and hot isostatic pressing. Conventional ${\mathrm{P}\mathrm{b}\mathrm{M}\mathrm{o}}_6{\mathrm{S}}_8$ has $B_{C2}(0)\sim 50\mathrm{T}$. The nanocrystalline materials have higher resistivity (${\rho }_N$) and $B_{C2}(0)\sim 100\mathrm{T}$. The disorder produced in these nanocrystalline materials is significantly different from that produced by doping because it increases ${\rho }_N$ and, hence, $B_{C2}(0)$ without significantly reducing the electronic density of states or superconducting transition temperature ($T_C$). Furthermore, the disorder reduces the electron mean-free path to $\sim 1\mathrm{n}\mathrm{m}$ which is more than an order of magnitude smaller than the grain size and necessary to achieve the unprecedented increase in $B_{C2}(0)$.

It is known empirically that multivalent ions generate attractions between like-charged polyelectrolytes, with different valence requirements for different systems. How multivalent must an ion be before it can condense a given polyelectrolyte? Using charge-tunable $M13$ virus rods and a family of artificial homologous “dumbbell” divalent ions of different sizes, we have constructed a multivalent ion-polyelectrolyte phase diagram, and find an experimentally motivated general criterion for like-charged attraction based on the ion valence, ion size, and the Gouy-Chapman length.

Based on the idea that the hardness of covalent crystal is intrinsic and equivalent to the sum of the resistance to the indenter of each bond per unit area, a semiempirical method for the evaluation of hardness of multicomponent crystals is presented. Applied to $\beta \mathrm{\text{−}}{\mathrm{B}\mathrm{C}}_2\mathrm{N}$ crystal, the predicted value of hardness is in good agreement with the experimental value. It is found that bond density or electronic density, bond length, and degree of covalent bonding are three determinative factors for the hardness of a polar covalent crystal. Our method offers the advantage of applicability to a broad class of materials and initializes a link between macroscopic property and electronic structure from first principles calculation.

The vibrational modes in three-dimensional ordered arrays of unembedded ${\mathrm{S}\mathrm{i}\mathrm{O}}_2$ nanospheres have been studied by Brillouin light scattering. Multiple distinct Brillouin peaks are observed whose frequencies are found to be inversely proportional to the diameter ($\approx 200–340\mathrm{n}\mathrm{m}$) of the nanospheres, in agreement with Lamb’s theory. This is the first Brillouin observation of acoustic mode quantization in a nanoparticle arising from spatial confinement. The distinct spectral peaks measured afford an unambiguous assignment of seven surface and inner acoustic modes. Interestingly, the relative intensities and polarization dependence of the Brillouin spectrum do not agree with the predictions made for Raman scattering.

Two-dimensional hydrodynamic simulations of stellar core collapse are presented which for the first time were performed by solving the Boltzmann equation for the neutrino transport including a state-of-the-art description of neutrino interactions. Stellar rotation is also taken into account. Although convection develops below the neutrinosphere and in the neutrino-heated region behind the supernova shock, the models do not explode. This suggests missing physics, possibly with respect to the nuclear equation of state and weak interactions in the subnuclear regime. However, it might also indicate a fundamental problem with the neutrino-driven explosion mechanism.

In this work we propose a ratchet effect which provides a general means of performing clocked logic operations on discrete particles, such as single electrons or vortices. The states are propagated through the device by the use of an applied ac drive. We numerically demonstrate that a complete logic architecture is realizable using this ratchet. We consider specific nanostructured superconducting geometries using superconducting materials under an applied magnetic field, with the positions of the individual vortices in samples acting as the logic states. These devices can be used as the building blocks for an alternative microelectronic architecture.

The tangential motion at the contact of two solid objects is studied. It consists of a sliding and a spinning degree of freedom (no rolling). We show that the friction force and torque are inherently coupled. As a simple test system, a sliding and spinning disk on a horizontal flat surface is considered. We calculate, and also measure, how the disk slows down and find that it always stops its sliding and spinning motion at the same moment. We discuss the impact of this coupling between friction force and torque on the physics of granular materials.

We show how a carefully chosen combination of strong linearly and circularly polarized laser fields can bind two same-sign charges, not only suppressing their Coulomb repulsion in all three spatial dimensions, but also creating an effective attraction. As an example, we show how a molecule ${\mathrm{H}\mathrm{D}}^{2+}$ stripped of both electrons can be kept bound by the laser fields.

Quantum interference of one- and two-photon excitation of unbiased semiconductors yields ballistic currents of carriers. The magnitudes and directions of the currents and the spin orientations of the carriers are controlled by the polarization and relative phase of the exciting femtosecond laser fields. We provide direct experimental evidence for the spin polarization of the optically injected spin currents by detecting a phase-dependent spatial shift of the circularly polarized photoluminescence in cubic ZnSe.