We present a coarse-grained model of DNA-functionalized colloids that is computationally tractable. Importantly, the model parameters are solely based on experimental data. Using this highly simplified model, we can predict the phase behavior of DNA-functionalized nanocolloids without assuming pairwise additivity of the intercolloidal interactions. Our simulations show that, for nanocolloids, the assumption of pairwise additivity leads to substantial errors in the estimate of the free energy of the crystal phase. We compare our results with available experimental data and find that the simulations predict the correct structure of the solid phase and yield a very good estimate of the melting temperature. Current experimental estimates for the contour length and persistence length of single-stranded (ss) DNA sequences are subject to relatively large uncertainties. Using the best available estimates, we obtain predictions for the crystal lattice constants that are off by a few percent: this indicates that more accurate experimental data on ssDNA are needed to exploit the full power of our coarse-grained approach.

For biopolymers like cytoskeletal actin filaments and microtubules, assembly and disassembly are inherently dissipative processes. Molecular motors can affect the rates of subunit removal at filament ends. We introduce a driven lattice-gas model to study the effects of motor-induced depolymerization on the length of active biopolymers and find that increasing motor activity sharpens unimodal steady-state length distributions. Furthermore, for sufficiently fast moving motors, the relative width of the length distribution is determined only by the attachment rate of motors. Our results show how established molecular processes can be used to robustly regulate the size of cytoskeletal structures like mitotic spindles.

Length regulation of microtubules (MTs) is essential for many cellular processes. Molecular motors like kinesin-8, which move along MTs and also act as depolymerases, are known as key players in MT dynamics. However, the regulatory mechanisms of length control remain elusive. Here, we investigate a stochastic model accounting for the interplay between polymerization kinetics and motor-induced depolymerization. We determine the dependence of MT length and variance on rate constants and motor concentration. Moreover, our analyses reveal how collective phenomena lead to a well-defined MT length.

A complete geometric view is presented for the optimal unambiguous discrimination among $N>2$ pure states. A single intuitive picture contains all aspects of the problem: linear independence of the states, positivity of the detection operators, and a graphic method for finding and classifying the optimal solutions. The method is illustrated on the example of three states. We show that the problem depends on the phases of the complex inner products only through an invariant combination, the Berry phase $\varphi$, and present complete analytical results for $\varphi =0$ and $\varphi =\pi$. The optimal solution exhibits full permutational symmetry and is single valued for a large range of parameters. However, for $\varphi =0$ it can be bivalued: beyond a critical value of the parameters a second, less symmetric solution becomes optimal. The bifurcation is analogous to a second-order symmetry-breaking phase transition. We conclude with a discussion of the unambiguous discrimination of $N>3$ states.

Using the effective Lagrangian approach, we clarify general issues about Nambu-Goldstone bosons without Lorentz invariance. We show how to count their number and study their dispersion relations. Their number is less than the number of broken generators when some of them form canonically conjugate pairs. The pairing occurs when the generators have a nonzero expectation value of their commutator. For non-semi-simple algebras, central extensions are possible. The underlying geometry of the coset space in general is partially symplectic.

The observation of a new $b$ baryon via its strong decay into ${\Xi }_b^{-}{\pi }^{+}$ (plus charge conjugates) is reported. The measurement uses a data sample of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of $5.3{\mathrm{fb}}^{-1}$. The known ${\Xi }_b^{-}$ baryon is reconstructed via the decay chain ${\Xi }_b^{-}\to J/\psi {\Xi }^{-}\to {\mu }^{+}{\mu }^{-}{\Lambda }^0{\pi }^{-}$, with ${\Lambda }^0\to p{\pi }^{-}$. A peak is observed in the distribution of the difference between the mass of the ${\Xi }_b^{-}{\pi }^{+}$ system and the sum of the masses of the ${\Xi }_b^{-}$ and ${\pi }^{+}$, with a significance exceeding 5 standard deviations. The mass difference of the peak is $14.84\pm 0.74(\mathrm{stat})\pm 0.28(\mathrm{syst})\mathrm{MeV}$. The new state most likely corresponds to the $J^{\mathrm{P}}=3/2^{+}$ companion of the ${\Xi }_b$.

In this Letter, we propose an original and novel experimental method to characterize both the onset and morphology of Taylor-Couette instability occurring in a non-Newtonian cylindrical Couette flow. Using synchrotron-based rheological small angle x-ray scattering experiments, we jointly investigate the shear-thinning behavior of natural swelling clays suspensions and the associated anisotropy developing in such media. Combined with a linear stability analysis for power law fluids, a destabilizing effect is shown both numerically and experimentally and the vortices morphology is found to be dependent on the fluid index. Still, the strong destabilizing effect and large vortex size can not be assigned to shear-thinning only, which clearly evidences the impact of medium anisotropy on Taylor-Couette instability.

We calculate the nonlinear optical response of graphene in strong magnetic and optical fields, using a quantum-mechanical density-matrix formalism. We show that graphene in a magnetic field possesses a giant mid- or far-infrared optical nonlinearity, perhaps the highest among known materials. The high nonlinearity originates from unique electronic properties and selection rules near the Dirac point. As a result, even one monolayer of graphene gives rise to an appreciable nonlinear frequency conversion efficiency for incident infrared radiation.

The random-phase approximation (RPA) is a promising approximation to the exchange-correlation energy of density functional theory, since it contains the van der Waals (vdW) interaction and yields a potential with the correct band gap. However, its calculation is computationally very demanding. We apply a range-separation concept to RPA and demonstrate how it drastically speeds up the calculations without loss of accuracy. The scheme is then successfully applied to a layered system subjected to weak vdW attraction and is used to address the controversy of the self-diffusion in silicon. We calculate the formation and migration energies of self-interstitials and vacancies taking into account atomic relaxations. The obtained activation energies deviate significantly from the earlier calculations and challenge some of the experimental interpretations: the diffusion of vacancies and interstitials has almost the same activation energy.

A logarithmic oscillator (in short, log-oscillator) behaves like an ideal thermostat because of its infinite heat capacity: When it weakly couples to another system, time averages of the system observables agree with ensemble averages from a Gibbs distribution with a temperature $T$ that is given by the strength of the logarithmic potential. The resulting equations of motion are Hamiltonian and may be implemented not only in a computer but also with real-world experiments, e.g., with cold atoms.

Optical solitons or solitonlike states shed light to blueshifted frequencies through a resonant emission process. We predict a mechanism by which a second propagating mode is generated. This mode, called negative resonant radiation, originates from the coupling of the soliton mode to the negative-frequency branch of the dispersion relation. Measurements in both bulk media and photonic-crystal fibers confirm our predictions.

The room-temperature longitudinal piezoresistance of $n$-type and $p$-type crystalline silicon along selected crystal axes is investigated under uniaxial compressive stresses up to 3 GPa. While the conductance ($G$) of $n$-type silicon eventually saturates at $\approx 45\%$ of its zero-stress value ($G_0$) in accordance with the charge transfer model, in $p$-type material $G/G_0$ increases above a predicted limit of $\approx 4.5$ without any significant saturation, even at 3 GPa. Calculation of $G/G_0$ using ab initio density functional theory reveals that neither $G$ nor the mobility, when properly averaged over the hole distribution, saturate at stresses lower than 3 GPa. The lack of saturation has important consequences for strained-silicon technologies.

Many swimming microorganisms governed by low Reynolds number hydrodynamics utilize flagellar undulations for self-propulsion. Most of the existing theoretical models assume that the shape kinematics is directly controlled, while in reality, eukaryotes actuate internal bending moments along their flagellum. Under this control, the shape is dynamically evolving and periodic gaits may become unstable. This Letter addresses the problem by revisiting Purcell’s three-link swimmer model where joint torques are controlled, and the geometric symmetries underlying the dynamics of the swimmer are analyzed. It is found that one has to break the front-back symmetry of the swimmer’s structure and/or actuation profile in order to induce stable shape kinematics. The results may explain why most of the flagellated eukaryotes swim with their head forward.

We study fluid flow at the interfaces between elastic solids with randomly rough, self-affine surfaces. We show by numerical simulation that elastic deformation lowers the relative contact area at which contact patches percolate in comparison to traditional approaches to seals. Elastic deformation also suppresses leakage through contacts even far away from the percolation threshold. Reliable estimates for leakage can be obtained by combining Persson’s contact mechanics theory with a slightly modified version of Bruggeman’s effective-medium solution of the Reynolds equation.

The diffusion of growing or evaporating two-dimensional clusters is investigated. At equilibrium, it is well known that the mean square displacement (MSD) of the cluster center of mass is linear in time. In nonequilibrium conditions, we find that the MSD exhibits a nonlinear time dependence, leading to three regimes: (i) during curvature-driven evaporation, the MSD shows a square-root singularity close to the collapse time; (ii) in slow growth or evaporation, the dynamics is in the Edwards-Wilkinson universality class, and the MSD shows a logarithmic behavior; (iii) far from equilibrium, the dynamics belongs to the Kardar-Parisi-Zhang universality class and the MSD shows a power-law behavior with a characteristic exponent $1/3$. These results agree with kinetic Monte Carlo simulations, and can be generalized to other universality classes.

We report ac susceptibility and continuous wave and pulsed EPR experiments performed on ${\mathrm{GdW}}_{10}$ and ${\mathrm{GdW}}_{30}$ polyoxometalate clusters, in which a ${\mathrm{Gd}}^{3+}$ ion is coordinated to different polyoxometalate moieties. Despite the isotropic character of gadolinium as a free ion, these molecules show slow magnetic relaxation at very low temperatures, characteristic of single molecule magnets. For $T\lesssim 200\mathrm{mK}$, the spin-lattice relaxation becomes dominated by pure quantum tunneling events, with rates that agree quantitatively with those predicted by the Prokof’ev and Stamp model [Phys. Rev. Lett. 80, 5794 (1998)]. The sign of the magnetic anisotropy, the energy level splittings, and the tunneling rates strongly depend on the molecular structure. We argue that ${\mathrm{GdW}}_{30}$ molecules are also promising spin qubits with a coherence figure of merit $Q_{\mathrm{M}}\gtrsim 50$.

We analyze the optomechanicslike properties of a Bose-Einstein condensate (BEC) trapped inside an optical resonator and driven by both a classical and a quantized light field. We find that this system exhibits the nature of role reversal between the matter-wave field and the quantized light field. As a result, the matter-wave field now plays the role of the quantized light field, and the quantized light field behaves like a movable mirror, in contrast to the familiar situation in BEC-based cavity optomechanics [Brennecke et al., Science 322, 235 (2008); Murch et al., Nature Phys. 4, 561 (2008)]. We demonstrate that this system can lead to the creation of a variety of nonclassical matter-wave fields, in particular, cat states, and discuss several possible protocols to measure their Wigner function.

The electron shakeoff probability of ${}^6\mathrm{Li}^{2+}$ ions resulting from the ${\beta }^{-}$ decay of ${}^6\mathrm{He}^{+}$ ions has been measured with high precision using a specially designed recoil ion spectrometer. This is the first measurement of a pure electron shakeoff following nuclear $\beta$ decay, not affected by multielectron processes such as Auger cascades. In this ideal textbook case for the application of the sudden approximation, the experimental ionization probability was found to be $P_{\mathrm{so}}^{\exp }=0.02339(36)$ in perfect agreement with simple quantum mechanical calculations.

We present a systematic Raman study of unconventionally stacked double-layer graphene, and find that the spectrum strongly depends on the relative rotation angle between layers. Rotation-dependent trends in the position, width and intensity of graphene 2D and G peaks are experimentally established and accounted for theoretically. Our theoretical analysis reveals that changes in electronic band structure due to the interlayer interaction, such as rotational-angle dependent Van Hove singularities, are responsible for the observed spectral features. Our combined experimental and theoretical study provides a deeper understanding of the electronic band structure of rotated double-layer graphene, and leads to a practical way to identify and analyze rotation angles of misoriented double-layer graphene.

Granular materials have been studied for decades, driven by industrial and technological applications. These very simple systems, composed of agglomerations of mesoscopic particles, are characterized, in specific regimes, by a large number of metastable states and an extreme sensitivity (e.g., in sound transmission) to the arrangement of grains; they are not substantially affected by thermal phenomena, but can be controlled by mechanical solicitations. Laser emission from shaken granular matter is so far unexplored. Here we provide experimental evidence that laser emission can be affected and controlled by the status of the motion of the granular material; we also find that competitive random lasers can be observed. We hence demonstrate the potentialities of gravity-affected moving disordered materials for optical applications, and open the road to a variety of novel interdisciplinary investigations, involving modern statistical mechanics and disordered photonics.