The MiniBooNE experiment at Fermilab reports results from an analysis of ${\overline{\nu }}_e$ appearance data from $11.27\times {10}^{20}$ protons on target in the antineutrino mode, an increase of approximately a factor of 2 over the previously reported results. An event excess of $78.4\pm 28.5$ events ($2.8\sigma$) is observed in the energy range $200<E_{\nu }^{\mathrm{QE}}<1250\mathrm{MeV}$. If interpreted in a two-neutrino oscillation model, ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$, the best oscillation fit to the excess has a probability of 66% while the background-only fit has a ${\chi }^2$ probability of 0.5% relative to the best fit. The data are consistent with antineutrino oscillations in the $0.01<\Delta m^2<1.0{\mathrm{eV}}^2$ range and have some overlap with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector. All of the major backgrounds are constrained by in situ event measurements so nonoscillation explanations would need to invoke new anomalous background processes. The neutrino mode running also shows an excess at low energy of $162.0\pm 47.8$ events ($3.4\sigma$) but the energy distribution of the excess is marginally compatible with a simple two neutrino oscillation formalism. Expanded models with several sterile neutrinos can reduce the incompatibility by allowing for $CP$ violating effects between neutrino and antineutrino oscillations.

The charge transfer reaction ${\mathrm{Ar}}^{+}+{\mathrm{N}}_2\to \mathrm{Ar}+{\mathrm{N}}_2^{+}$ has been investigated in a crossed-beam experiment in combination with three-dimensional velocity map imaging. Angular-differential state-to-state cross sections were determined as a function of the collision energy. We found that scattering into the first excited vibrational level dominates as expected, but only for scattering in the forward direction. Higher vibrational excitations up to $v^{\prime }=6$ have been observed for larger scattering angles. For decreasing collision energy, scattering into higher scattering angles becomes increasingly important for all kinematically allowed quantum states. Our detailed measurements indicate that a quantitative agreement between experiment and theory for this basic ion-molecule reaction now comes within reach.

Thermal or chaotic light sources emit radiation characterized by a slightly enhanced probability of emitting photons in bunches, described by a zero-delay second-order correlation function $g^{(2)}(0)=2$. Here we explore photon-coincidence counting statistics of thermal cavities in the ultrastrong coupling regime, where the atom-cavity coupling rate becomes comparable to the cavity resonance frequency. We find that, depending on the system temperature and coupling rate, thermal photons escaping the cavity can display very different statistical behaviors, characterized by second-order correlation functions approaching zero or greatly exceeding two.

We demonstrate unconditional quantum-noise suppression in a collective spin system via feedback control based on quantum nondemolition measurement. We perform shot-noise limited collective spin measurements on an ensemble of $3.7\times {10}^5$ laser-cooled ${}^{171}\mathrm{Yb}$ atoms in their spin-$1/2$ ground states. Correlation between two sequential quantum nondemolition measurements indicates $-{0.80}_{-0.12}^{+0.11}\mathrm{dB}$ quantum-noise suppression in a conditional manner. Our feedback control successfully converts the conditional quantum-noise suppression into the unconditional one without significant loss of the noise reduction level.

We report on a theoretical and experimental study of the optical coupling between a whispering-gallery type resonator and a waveguide lying on different planes. In contrast to the usual in-plane geometry, the present vertical one is characterized by an oscillatory behavior of the effective coupling as a function of the vertical gap. This behavior manifests itself as oscillations in both the resonance peak waveguide transmission and the mode quality factor. An analytical description based on coupled-mode theory and a two-port beam-splitter model of the waveguide-resonator vertical coupling is developed for arbitrary phase-matching conditions and is successfully used to interpret the experimental observations.

Using particle-in-cell simulations, we examine hot electron generation from electron plasma waves excited by stimulated Raman scattering and rescattering in the kinetic regime where the wave number times the Debye length ($k{\lambda }_D$) is $\gtrsim 0.3$ for backscatter. We find that for laser and plasma conditions of possible relevance to experiments at the National Ignition Facility, anomalously energetic electrons can be produced through the interaction of a discrete spectrum of plasma waves generated from stimulated Raman scattering (back and forward scatter), rescatter, and the Langmuir decay of the rescatter-generated plasma waves. Electrons are bootstrapped in energy as they propagate into plasma waves with progressively higher phase velocities.

Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low-terahertz region. A helically corrugated interaction region was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5 A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88–102.5 GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell numerical simulations.

We have experimentally observed the emergence of spontaneous antiferromagnetic spatial order in a sodium spinor Bose-Einstein condensate that was quenched through a magnetic phase transition. For negative values of the quadratic Zeeman shift, a gas initially prepared in the $F=1$, $m_F=0$ state collapsed into a dynamically evolving superposition of all three spin projections, $m_F=0$, $\pm 1$. The quench gave rise to rich, nonequilibrium behavior where both nematic and magnetic spin waves were generated. We characterized the spatiotemporal evolution through two particle correlations between atoms in each pair of spin states. These revealed dramatic differences between the dynamics of the spin correlations and those of the spin populations.

We show that phase separation must occur in a mixture of fermions with repulsive interaction if their mass difference is sufficiently large. This phenomenon is highly dimension dependent. Consequently, the density profiles of phase separated 3D mixtures are very different from those in 1D. Noting that the ferromagnetic transition of a spin-$1/2$ repulsive Fermi gas is the equal mass limit of the phase separation in mixtures, we show from the Bethe ansatz solution that a ferromagnetic transition will take place in the scattering states when the interaction passes through the strongly repulsive regime and becomes attractive.

The structural and dynamical properties of amorphous and liquid ${\mathrm{As}}_x{\mathrm{Se}}_{1-x}$ ($0.2<x<0.4$) are studied by first principles molecular dynamics. Within the above range of compositions, thresholds and anomalies are found in the behavior of reciprocal space properties that can be correlated to the experimental location of the so-called Boolchand intermediate phase in these glassy networks. These findings are associated with diffusion anomalies for the parent liquid phase, thereby linking structural and dynamical atomic-scale fingerprints for the onset of rigidity within the network, while also providing a much more complex picture than the one derived from mean-field approaches of stiffness transitions.

The energy landscapes of electrostatically charged particles embedded on constant mean curvature surfaces are analyzed for a wide range of system size, curvature, and interaction potentials. The surfaces are taken to be rigid, and the basin-hopping method is used to locate the putative global minimum structures. The defect motifs favored by potential energy agree with experimental observations for colloidal systems: extended defects (scars and pleats) for weakly positive and negative Gaussian curvatures, and isolated defects for strongly negative Gaussian curvatures. Near the phase boundary between these regimes, the two motifs are in strong competition, as evidenced from the appearance of distinct funnels in the potential energy landscape. We also report a novel defect motif consisting of pentagon pairs.

Silicon and germanium transform from diamond to $\beta$-tin structure under compression, but upon decompression they turn into metastable BC8 Si and ST12 Ge phases, respectively, instead of returning to the lowest-enthalpy diamond structure. Here we explore by first-principles calculations the atomistic mechanism underlying this intriguing phenomenon. We identify a body-centered tetragonal structure in $I{4}_1/a$ ($C_{4h}^6$) symmetry as a precursory state of the BC8 Si phase formed via a double cell bond-rotation mechanism with a low kinetic barrier. Kinetics also play a central role in selecting the decompression pathway in Ge via a trinary cell bond-twisting reconstruction process toward the ST12 Ge phase. In both cases, transformation back to energetically more favorable diamond structure is inhibited by the higher enthalpy barrier. These results explain experimental findings and highlight the kinetic origin of the divergent decompression pathways in Si and Ge.

A spin-density-wave (SDW) for $(\mathrm{TMTSF}){}_2\mathrm{PF}_6$ has been reported to appear below $T_{\mathrm{SDW}}$ ($\simeq 12\mathrm{K}$), with a subphase transition at $T^{*}$ ($\simeq 4\mathrm{K}$). To determine the structure of the subphase, we synthesized $(\mathrm{TMTSF}){}_2\mathrm{PF}_6$, in which one side of the central carbon bond in each TMTSF molecule was replaced by ${}^{13}\mathrm{C}$, and utilized this compound in ${}^{13}\mathrm{C}$ nuclear magnetic resonance measurements. Below $T_{\mathrm{SDW}}$, the spectrum became broad and $T_1^{-1}$ decreased, in agreement with previous results. Below $T^{*}$, fine structures emerged in the center of the spectrum and $T_1^{-1}$ decreased exponentially. These phenomena were attributed to the emergence of commensurability at $T^{*}$.

Topological materials, including topological insulators, magnets with Skyrmions and ferroelectrics with topological vortices, have recently attracted phenomenal attention in the materials science community. Complex patterns of ferroelectric domains in hexagonal ${\mathrm{REMnO}}_3$ (RE: rare earths) turn out to be associated with the macroscopic emergence of $Z_2\times Z_3$ symmetry. The results of our depth profiling of crystals with a self-poling tendency near surfaces reveal that the partial dislocation (i.e., wall-wall) interaction, not the interaction between vortices and antivortices, is primarily responsible for topological condensation through the macroscopic breaking of the $Z_2$ symmetry.

Elastin is an intriguing extracellular matrix protein present in all connective tissues of vertebrates, rendering essential elasticity to connective tissues subjected to repeated physiological stresses. Using piezoresponse force microscopy, we show that the polarity of aortic elastin is switchable by an electrical field, which may be associated with the recently discovered biological ferroelectricity in the aorta. More interestingly, it is discovered that the switching in aortic elastin is largely suppressed by glucose treatment, which appears to freeze the internal asymmetric polar structures of elastin, making it much harder to switch, or suppressing the switching completely. Such loss of ferroelectricity could have important physiological and pathological implications from aging to arteriosclerosis that are closely related to glycation of elastin.

We provide conclusive evidence of nonmonotonic mechanical behavior in the extension of long-chain branched polymer melts. While nonmonotonic behavior is known to occur for solids, for the case of polymeric melts, this phenomenon is in direct contrast with current theoretical models. We rule out the possibility of the overshoot being an experimental artifact by confirming the existence of steady flow after a maximum in the ratio of stress to strain rate versus strain under both constant stress and constant strain-rate kinematics. This observation indicates the omission of important physics from current models for these industrially important materials, whose processing properties depend on extreme molecular extension.

We study the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids in a dynamic magnetic field. The sedimented ribbon assembles due to time averaged dipolar interactions between the beads. The time dependence of the dipolar interactions together with hydrodynamic interactions cause a twisted ribbon conformation. Domain walls of high twist connect domains of nearly constant orientation and negligible twist and travel through the ribbon. The particular form of the domain walls can be controlled via the frequency and the eccentricity of the modulation. The flux of twist walls—a true ribbon property absent in slender bodies—provides the thrust onto the surrounding liquid that propels this biomimetic flagellum into the opposite direction. The propulsion efficiency increases with frequency and ceases abruptly at a critical frequency where the conformation changes discontinuously to a flat standing ribbon conformation.

Face-to-face interaction networks describe social interactions in human gatherings, and are the substrate for processes such as epidemic spreading and gossip propagation. The bursty nature of human behavior characterizes many aspects of empirical data, such as the distribution of conversation lengths, of conversations per person, or of interconversation times. Despite several recent attempts, a general theoretical understanding of the global picture emerging from data is still lacking. Here we present a simple model that reproduces quantitatively most of the relevant features of empirical face-to-face interaction networks. The model describes agents that perform a random walk in a two-dimensional space and are characterized by an attractiveness whose effect is to slow down the motion of people around them. The proposed framework sheds light on the dynamics of human interactions and can improve the modeling of dynamical processes taking place on the ensuing dynamical social networks.

We show that the dynamics of a driven quantum system weakly coupled to the environment can exhibit two distinct regimes. While the relaxation basis is usually determined by the $\mathrm{\text{system}}+\mathrm{\text{drive}}$ Hamiltonian (system-governed dynamics), we find that under certain conditions it is determined by specific features of the environment, such as, the form of the coupling operator (environment-governed dynamics). We provide an effective coupling parameter describing the transition between the two regimes and discuss how to observe the transition in a superconducting charge pump.

Comprehensive and high-accuracy $\overrightarrow{n}\mathrm{\text{−}}{}^3\mathrm{He}$ elastic scattering analyzing power $A_y(\theta )$ angular distributions were obtained at five incident neutron energies between 1.60 and 5.54 MeV. The data are compared to rigorous four-nucleon calculations using high-precision nucleon-nucleon potential models; three-nucleon force effects are found to be very small. The agreement between data and calculations is fair at the lower energies and becomes less satisfactory with increasing neutron energy. Comparison to $p\mathrm{\text{−}}{}^3\mathrm{He}$ scattering over the same energy range exhibits unexpectedly large isospin effects.