Electron transfer in alkali-molecule collisions to gas phase thymine and uracil yielding ${\mathrm{H}}^{-}$ formation is selectively controlled in the energy range between 5.3 and 66.1 eV. By tuning the collision energy, electron transfer from the alkali to partly deuterated thymine, methylated thymine at the ${\mathrm{N}}_1$ and methylated uracil at the ${\mathrm{N}}_3$ positions, ${\mathrm{H}}^{-}$ loss proceeds not only through the breaking of the (C–H) against (N–H) bonds but also through ${\mathrm{N}}_1$ against ${\mathrm{N}}_3$ sites. Such selectivity, as far as bond and site are concerned, is here reported for the first time by electron transfer induced dissociation experiments in alkali-molecule collisions.

The squeezing of soft solids, the constrained growth of biological tissues, and the swelling of soft elastic solids such as gels can generate large compressive stresses at their surfaces. This causes the otherwise smooth surface of such a solid to become unstable when its stress exceeds a critical value. Previous analyses of the surface instability have assumed two-dimensional plane-strain conditions, but in experiments isotropic stresses often lead to complex three-dimensional sulcification patterns. Here we show how such diverse morphologies arise by numerically modeling the lateral compression of a rigidly clamped elastic layer. For incompressible solids, close to the instability threshold, sulci appear as $\mathsf{I}$-shaped lines aligned orthogonally with their neighbors; at higher compressions they are $\mathsf{Y}$-shaped and prefer a hexagonal arrangement. In contrast, highly compressible solids when squeezed show only one sulcified phase characterized by a hexagonal sulcus network.

The “textbook” phonon mean free path of heat carrying phonons in silicon at room temperature is $\sim 40\mathrm{nm}$. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range $\sim 1–10\mu \mathrm{m}$. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.

We study the fractionalization of an electron tunneling into a strongly interacting electronic one-dimensional ring. As a complement to transport measurements in quantum wires connected to leads, we propose noninvasive measures involving the magnetic field profile around the ring to probe this fractionalization. In particular, we show that the magnetic field squared produced by the electron and the power that it would induce in a detector exhibit anisotropic profiles that depend on the degree of fractionalization. We contrast true fractionalization with two other scenarios which could mimic it—quantum superposition and classical probabilistic electron insertion. We show that the proposed field-dependent measures and those of the persistent current can distinguish between these three scenarios.

Microscopic structural instabilities of ${\mathrm{EuTiO}}_3$ single crystals were investigated by synchrotron x-ray diffraction. Antiferrodistortive (AFD) oxygen octahedron rotational order was observed alongside Ti derived antiferroelectric distortions. The competition between the two instabilities is reconciled through a cooperatively modulated structure allowing both to coexist. The combination of electric and magnetic fields increases the population of the modulated AFD order, illustrating how the origin of the large magnetoelectric coupling derives from the dynamic equilibrium between AFD and polar instabilities.

By analysis and simulation, we demonstrate two methods for achieving complete orientational alignment of a set of identical asymmetric colloidal objects dispersed randomly in a fluid. Sedimentation or electrophoresis in a constant field can lead to partial alignment, in which the objects rotate about a common body axis, but the phases of rotation for these objects are random. We show that this phase disorder can be removed by two forms of programed forcing. First, simply alternating the forcing between two directions reduces the statistical entropy of the orientation arbitrarily. Second, the addition of a small rotating component to the applied field in analogy to magnetic resonance can lead to phase locking of the objects’ orientation. We identify conditions for alignment of a broad class of generic objects and discuss practical limitations.

We study the time scales associated with diffusion processes that take place on multiplex networks, i.e., on a set of networks linked through interconnected layers. To this end, we propose the construction of a supra-Laplacian matrix, which consists of a dimensional lifting of the Laplacian matrix of each layer of the multiplex network. We use perturbative analysis to reveal analytically the structure of eigenvectors and eigenvalues of the complete network in terms of the spectral properties of the individual layers. The spectrum of the supra-Laplacian allows us to understand the physics of diffusionlike processes on top of multiplex networks.

Nonequilibrium stationary states of thermodynamic systems dissipate a positive amount of energy per unit of time. If we consider transformations of such states that are realized by letting the driving depend on time, the amount of energy dissipated in an unbounded time window then becomes infinite. Following the general proposal by Oono and Paniconi and using results of the macroscopic fluctuation theory, we give a natural definition of a renormalized work performed along any given transformation. We then show that the renormalized work satisfies a Clausius inequality and prove that equality is achieved for very slow transformations, that is, in the quasistatic limit. We finally connect the renormalized work to the quasipotential of the macroscopic fluctuation theory, which gives the probability of fluctuations in the stationary nonequilibrium ensemble.

The effect of a stochastic background of cosmological perturbations on the luminosity-redshift relation is computed to second order through a recently proposed covariant and gauge-invariant light-cone averaging procedure. The resulting expressions are free from both ultraviolet and infrared divergences, implying that such perturbations cannot mimic a sizable fraction of dark energy. Different averages are estimated and depend on the particular function of the luminosity distance being averaged. The energy flux being minimally affected by perturbations at large $z$ is proposed as the best choice for precision estimates of dark-energy parameters. Nonetheless, its irreducible (stochastic) variance induces statistical errors on ${\Omega }_{\Lambda }(z)$ typically lying in the few-percent range.

A search for the rare decays $B_s^0\to {\mu }^{+}{\mu }^{-}$ and $B^0\to {\mu }^{+}{\mu }^{-}$ is performed with data collected in 2011 and 2012 with the LHCb experiment at the Large Hadron Collider. The data samples comprise $1.1{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=8\mathrm{TeV}$ and $1.0{\mathrm{fb}}^{-1}$ at $\sqrt{s}=7\mathrm{TeV}$. We observe an excess of $B_s^0\to {\mu }^{+}{\mu }^{-}$ candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is $5.3\times {10}^{-4}$ corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of $\mathcal{B}(B_s^0\to {\mu }^{+}{\mu }^{-})=({3.2}_{-1.2}^{+1.5})\times {10}^{-9}$, where the statistical uncertainty is 95% of the total uncertainty. This result is in agreement with the standard model expectation. The observed number of $B^0\to {\mu }^{+}{\mu }^{-}$ candidates is consistent with the background expectation, giving an upper limit of $\mathcal{B}(B^0\to {\mu }^{+}{\mu }^{-})<9.4\times {10}^{-10}$ at 95% confidence level.

Cracks in drying colloidal dispersions are typically modeled by elastic fracture mechanics, which assumes that all strains are linear, elastic, and reversible. We tested this assumption in films of a hard latex, by intermittently blocking evaporation over a drying film, thereby relieving the film stress. Here we show that although the deformation around a crack tip has some features of brittle fracture, only 20%–30% of the crack opening is relieved when it is unloaded. Atomic force micrographs of crack tips also show evidence of plastic deformation, such as microcracks and particle rearrangement. Finally, we present a simple scaling argument showing that the yield stress of a drying colloidal film is generally comparable to its maximum capillary pressure, and thus that the plastic strain around a crack will normally be significant. This also suggests that a film’s fracture toughness may be increased by decreasing the interparticle adhesion.

The effect of target material on fast-electron transport is investigated using a high-intensity (0.7 ps, ${10}^{20}\mathrm{W}/{\mathrm{cm}}^2$) laser pulse irradiated on multilayered solid Al targets with embedded transport (Au, Mo, Al) and tracer (Cu) layers, backed with millimeter-thick carbon foils to minimize refluxing. We consistently observed a more collimated electron beam (36% average reduction in fast-electron induced Cu $K\alpha$ spot size) using a high- or mid-$Z$ (Au or Mo) layer compared to Al. All targets showed a similar electron flux level in the central spot of the beam. Two-dimensional collisional particle-in-cell simulations showed formation of strong self-generated resistive magnetic fields in targets with a high-$Z$ transport layer that suppressed the fast-electron beam divergence; the consequent magnetic channels guided the fast electrons to a smaller spot, in good agreement with experiments. These findings indicate that fast-electron transport can be controlled by self-generated resistive magnetic fields and may have important implications to fast ignition.

In the glassy state, all materials undergo a process of structural recovery as they age towards equilibrium. The resultant increase of relaxation times $t_{\alpha }$ is frequently described with a sublinear power of the wait time $t_w^{\mu }$ with an apparent aging exponent $\mu$. We show with molecular dynamics simulations of a Lennard-Jones glass former at various temperatures that the observed aging exponent can be strongly influenced by crossover effects from the freshly quenched state at short $t_w$ and into the equilibrated state at long $t_w$. The aging behavior on the molecular level is quantitatively reproduced by a coarse-grained continuous time random walk description over the entire range of temperatures and wait times. Our model glass always shows normal aging, $t_{\alpha }\sim t_w$, when the observation time window is no longer affected by crossover effects, in agreement with the well-known trap model of aging.

We investigate glassy dynamical properties of one-component three-dimensional system of particles interacting via pair repulsive potential by the molecular dynamic simulation in the wide region of densities. The glass state is superfragile and it has high glass-forming ability. The glass transition temperature $T_g$ has a pronounced minimum at densities where the frustration is maximal.

We present theoretical investigations that clarify elemental nitridation processes of corundum ${\mathrm{Al}}_2{\mathrm{O}}_3(0001)$ and ($1\overline{1}02$) surfaces. The calculations within the density functional theory framework reveal that the structures with substitutional N atoms beneath the surface are stabilized under nitridation conditions. We also find that the desorption of O atoms at the topmost layer induces outward diffusion of O atoms as well as inward diffusion of N atoms, leading to the transformation into AlN films. The kinetic Monte Carlo simulations in conjunction with density functional theory results indeed observe a dependence of these chemical and structural changes on temperature and pressure.

The dynamics of an exciton-polariton superfluid resonantly pumped in a semiconductor microcavity are investigated by mean-field theory. Modulational instability develops into crystalline order, and then, ordered and disordered states alternately form. It is found that the crystalline order at rest can coexist with superflow.

We study Coulomb drag in graphene near the Dirac point, focusing on the regime of interaction-dominated transport. We establish a novel, graphene-specific mechanism of Coulomb drag based on fast interlayer thermalization, inaccessible by standard perturbative approaches. Using the quantum kinetic equation framework, we derive a hydrodynamic description of transport in double-layer graphene in terms of electric and energy currents. In the clean limit the drag becomes temperature independent. In the presence of disorder the drag coefficient at the Dirac point remains nonzero due to higher-order scattering processes and interlayer disorder correlations. At low temperatures (diffusive regime) these contributions manifest themselves in the peak in the drag coefficient centered at the neutrality point with a magnitude that grows with lowering temperature.

The low-lying neutral excitation spectrum of the incompressible quantum Hall fluid at $\nu =5/2$ is investigated by inelastic light scattering. Gapped modes are observable only in a very narrow filling factor range centered at $5/2$ at energies that overlap estimates from transport activation gaps. The modes are interpreted as critical points in the wave-vector dispersion of excitations that preserve spin orientation. For very small changes $|\delta \nu |\lesssim 0.01$ the gapped modes disappear and a continuum of low-lying excitations takes over indicating the transition from an incompressible fluid at $5/2$ to a compressible state. Observations of spin wave modes indicate spin polarization of the $5/2$ and $2+1/3$ quantum Hall fluids.

High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide exhibit a simple, almost axial anisotropy and phase coherence times of the order of a millisecond at low temperatures. The anisotropy energy is tunable using an externally applied electric field. This can be used to control electrically the phase of spin superpositions and to drive spin transitions with resonant microwave electric fields.

A solid-state nanopore can electrophoretically capture a DNA molecule and pull it through in a folded configuration. The resulting ionic current signal indicates where along its length the DNA was captured. A statistical study using an 8-nm-wide nanopore reveals a strong bias favoring the capture of molecules near their ends. A theoretical model shows that bias to be a consequence of configurational entropy rather than a search by the polymer for an energetically favorable configuration. We also quantified the fluctuations and length dependence of the speed of simultaneously translocating polymer segments from our study of folded DNA configurations.