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Recent progress in the determination of both masses and radii of neutron stars is starting to place stringent constraints on the dense matter equation of state. In particular, new theoretical developments together with improved statistical tools seem to favor stellar radii that are significantly smaller than those predicted by models using purely nucleonic equations of state. Given that the underlying equation of state must also account for the observation of 2M☉ neutron stars, theoretical approaches to the study of the dense matter equation of state are facing serious challenges. In response to this challenge, we compute the underlying equation of state associated with an assumed mass-radius template similar to the "common radius" assumption used in recent studies. Once such a mass-radius template is adopted, the equation of state follows directly from the implementation of Lindblom's algorithm; assumptions on the nature or composition of the dense stellar core are not required. By analyzing mass-radius profiles with a maximum mass consistent with observation and common radii in the 8-11 km range, a lower limit on the stellar radius of a 1.4M☉ neutron star of RNS ≳ 10.7 km is required to prevent the equation of state from violating causality. [ABSTRACT FROM AUTHOR]

We propose a dynamic model for a system consisting of self-propelled agents in which the influence of an agent on another agent is weighted by geographical distance. A parameter a is introduced to adjust the influence: The smaller value of a means that the closer neighbors have a stronger influence on the moving direction. We find that there exists an optimal value of a leading to the highest degree of direction consensus. The value of optimal α increases as the system size increases, while it decreases as the absolute velocity, the sensing radius, and the noise amplitude increase. [ABSTRACT FROM AUTHOR]

A weakly nonlinear approach is used to investigate interfacial pattern formation in a lifting Hele-Shaw cell containing a yield stress fluid surrounded by a fluid of negligible viscosity. By considering the onset of nonlinear effects and the regime in which viscous effects dominate over yield stress, we study how the system responds to changes in two controlling dimensionless parameters: (i) the geometric aspect ratio (ratio of the initially circular radius of the fluid-fluid interface to the initial Hele-Shaw cell plate spacing), and (ii) a yield stress parameter (relative measure of yield stress to viscous forces). Within this context, we discuss how these key factors influence interface stability and finger competition dynamics during early linear and intermediate stages of pattern evolution. [ABSTRACT FROM AUTHOR]

Within the framework of the Lifshitz-Slyozov-Wagner theory of Ostwald ripening, the amount of volume of the second (solid) phase in a liquid solution that is newly formed by recrystallization is investigated. It is shown that in the late stage, the portion of the newly generated volume formed within an interval from time t0 to t is a certain function of t/t0 and an explicit expression of this volume is given. To achieve this, we introduce the notion of the return radius r(t,t0), which is the unique radius of a particle at time t0 such that this particle has--after growing and shrinking--the same radius at time t. We derive a formula for the return radius, which later on is used to obtain the newly formed volume. Moreover, formulas for the growth rate of the return radius and the recrystallized material at time t0 are derived. [ABSTRACT FROM AUTHOR]

We investigate the impact fragmentation of spherical solid bodies made of heterogeneous brittle materials by means of a discrete element model. Computer simulations are carried out for four different system sizes varying the impact velocity in a broad range. We perform a finite size scaling analysis to determine the critical exponents of the damage-fragmentation phase transition and deduce scaling relations in terms of radius R and impact velocity v0. The scaling analysis demonstrates that the exponent of the power law distributed fragment mass does not depend on the impact velocity; the apparent change of the exponent predicted by recent simulations can be attributed to the shifting cutoff and to the existence of unbreakable discrete units. Our calculations reveal that the characteristic time scale of the breakup process has a power law dependence on the impact speed and on the distance from the critical speed in the damaged and fragmented states, respectively. The total amount of damage is found to have a similar behavior, which is substantially different from the logarithmic dependence on the impact velocity observed in two dimensions. [ABSTRACT FROM AUTHOR]

The densest binary sphere packings in the &agr;-x plane of small to large sphere radius ratio &agr; and small sphere relative concentration x have historically been very difficult to determine. Previous research had led to the prediction that these packings were composed of a few known "alloy" phases including, for example, the AlB2 (hexagonal &ohgr;), HgBr2, and AuTe2 structures, and to XYn structures composed of close-packed large spheres with small spheres (in a number ratio of n to 1) in the interstices, e.g., the NaCl packing for n = 1. However, utilizing an implementation of the Torquato-Jiao sphere-packing algorithm [Torquato and Jiao, Phys. Rev. E 82, 061302 (2010)], we have discovered that many more structures appear in the densest packings. For example, while all previously known densest structures were composed of spheres in small to large number ratios of one to one, two to one, and very recently three to one, we have identified densest structures with number ratios of seven to three and five to two. In a recent work [Hopkins et al., Phys. Rev. Lett. 107, 125501 (2011)], we summarized these findings. In this work, we present the structures of the densest-known packings and provide details about their characteristics. Our findings demonstrate that a broad array of different densest mechanically stable structures consisting of only two types of components can form without any consideration of attractive or anisotropic interactions. In addition, the structures that we have identified may correspond to currently unidentified stable phases of certain binary atomic and molecular systems, particularly at high temperatures and pressures. [ABSTRACT FROM AUTHOR]

The article discusses a study which measured the radius of the localized electron emission sites on multiwalled carbon nanotubes (MWNTs) with caps closed by a fullerene-like structure. The study also determined the distance between the emission sites and the radius of the total emission area including all spots. Its concluded that electron emission from a capped nanotube occurs from localized states present at the cap of a nanotube.

This paper revisits one of the puzzling behaviors in a developable cone (d-cone), the shape obtained by pushing a thin sheet into a circular container of radius R by a distance η. The mean curvature was reported to vanish at the rim where the d-cone is supported. We investigate the ratio of the two principal curvatures versus sheet thickness h over a wider dynamic range than was used previously, holding R and ij fixed. Instead of tending toward 1 as suggested by previous work, the ratio scales as (h/R)l/3. Thus the mean curvature does not vanish for very thin sheets as previously claimed. Moreover, we find that the normalized rim profile of radial curvature in a d-cone is identical to that in a "c-cone" which is made by pushing a regular cone into a circular container. In both c-cones and d-cones, the ratio of the principal curvatures at the rim scales as (R/h)5/2 F/(YR2), where F is the pushing force and Y is the Young's modulus. Scaling arguments and analytical solutions confirm the numerical results. [ABSTRACT FROM AUTHOR]

The interplay of geometrical and topological entanglement in semiflexible knotted polymer rings confined inside a spherical cavity is investigated by using advanced numerical methods. By using stringent and robust algorithms for locating knots, we characterize how the knot length lk depends on the ring contour length Lc. and the radius of the confining sphere Rc. In the no- and strong-confinement cases, we observe weak knot localization and complete knot delocalization, respectively. We show that the complex interplay of lk, Lc, and Rc that seamlessly bridges these two limits can be encompassed by a simple scaling argument based on deflection theory. The same argument is used to rationalize the multiscale character of the entanglement that emerges with increasing confinement. [ABSTRACT FROM AUTHOR]

Unexpected formation of regular high-Q whispering gallery modes in a deformed microdisk where the radius is of the order of the vacuum wavelength is explained in terms of partial barriers in phase space. Using a semiclassical approach to determine the action flux of the partial barriers, we successfully predict spectral ranges in which the high-Q modes can exist. Our analysis enables optimization of emission directionality and the Q factor of deformed ultrasmall microcavities. [ABSTRACT FROM AUTHOR]

We report the results of a computation of the full next-to-leading order QCD corrections to the production of two bb pairs at the LHC. This calculation at the patton level provides predictions for well separated b jets. The results show that the next-to-leading order corrections lead to an enhancement of the cross section for the central scale choice by roughly 50% with respect to the leading order result. The theoretical uncertainty estimated by variation of the renormalization and factorization scales is strongly reduced by the inclusion of next-to-leading order corrections. [ABSTRACT FROM AUTHOR]

We have studied the Ostwald ripening of three-dimensional islands on a homogeneous surface with an original off-lattice kinetic Monte Carlo algorithm. In this algorithm, adatom trajectories are highly simplified, while still ensuring that the adatom fluxes between islands are exactly described. From the simulations, we obtained the evolution of the island size distribution over a large time range. The simulations obtained are compared with the results of numerical integration of rate equations derived from a mean-field approximation. Both results indicate that the equilibrium radius of the islands follows a power-law behavior in the limit of a very dilute phase, with an exponent close to 1/4. A general, excellent agreement is obtained, showing the validity of our approach, whereas the validity of the mean-field approximation is discussed for a very small mean island size, or for a large fraction of the surface covered by the islands. [ABSTRACT FROM AUTHOR]

The induced current density, corresponding to the massless Dirac equation in (2+1) dimensions in a magnetic flux tube of small radius is considered. This problem is important for graphene. In the case, when an electron can not penetrate the region of nonzero magnetic field, this current is the odd periodical function of the magnetic flux. If the region inside the magnetic tube is not forbidden for penetration of electron, the induced current is not a periodical function of the magnetic flux. However in the limit R → 0, where R is the radius of magnetic flux tube, this function has the universal form which is independent of the magnetic field distribution inside the magnetic tube at fixed value of the magnetic flux. [ABSTRACT FROM AUTHOR]

Structural modification of vitreous SiO2 by Au ion irradiation is investigated over an energy regime (∼0.3-15 MeV) in which the decrease of the nuclear energy loß with increasing energy is compensated by the increase of the electronic energy loß, leading to a nearly constant total energy loß of ∼4 keV/nm. The radii of damaged zones resulting from the ion impact, deduced from changes in infrared bands as a function of ion fluence, decrease from 4.9 nm at 0.3 MeV to 2.5 and 2.6 nm at 9.8 and 14.8 MeV, respectively. Based on previous data where vitreous SiO2 was irradiated with much higher energy Au ions, the damage zone radius increases from 2.4 nm at 22.7 MeV to 5.4 nm at 168 MeV, and a U-shaped dependence on energy is observed is observed in the energy region from 0.3 to 168 MeV. The current results demonstrate that large damage radii at low and high ion energy can be explained by the elastic or inelastic thermal spike model, respectively. In the transition regime where both nuclear and electronic energy loss are significant, a unified thermal spike model consisting of a coherent synergy of the elastic collision spike model with the inelastic thermal spike model is suggested to interpret and describe the radius evolution from the nuclear to the electronic energy regime. [ABSTRACT FROM AUTHOR]

The nuclear root-mean-square charge radius of 54 Ni was determined with collinear laser spectroscopy to be R (54 Ni) = 3.737 (3) fm. In conjunction with the known radius of the mirror nucleus 54 Fe, the difference of the charge radii was extracted as R ch = 0.049 (4) fm. Based on the correlation between R ch and the slope of the symmetry energy at nuclear saturation density (L), we deduced 21 = L = 88 MeV. The present result is consistent with the L from the binary neutron star merger GW170817, favoring a soft neutron matter EOS, and barely consistent with the PREX-2 result within 1 s error bands. Our result indicates the neutron-skin thickness of 48 Ca as 0.15-0.21 fm. [ABSTRACT FROM AUTHOR]

The nonlocalized cluster model provides a new perspective on nuclear cluster effects and has been applied successfully to study cluster structures in various bound states and quasibound states (i.e., long-lived resonant states). In this work, we extend the application scope of the nonlocalized cluster model further to resonant and scattering states. Following the R-matrix theory, the configuration space is divided into the interior and exterior regions by a large channel radius such that the nuclear forces and the antisymmetrization effects become negligible between clusters in the exterior region. In the interior region, the picture of nonlocalized clustering is realized mathematically by adopting the Brink-Tohsaki-Horiuchi-Schuck-Röpke wave functions as the bases to construct the interior wave functions. The Bloch-Schrödinger equation is used to match the interior wave functions continuously with the asymptotic boundary conditions of the resonant and scattering states at the channel radius, which leads eventually to solutions of the problem. As a first test of the formalism, the low-lying resonant states of 8Be and the phase shifts of the α+α elastic scattering are studied. The numerical results agree well with the experimental data, which shows the validity of the theoretical framework. [ABSTRACT FROM AUTHOR]

We investigate the upper bound on angular momentum transport in Taylor-Couette flow theoretically and numerically by a one-dimensional background field method. The flow is bounded between a rotating inner cylinder of radius Ri and a fixed outer cylinder of radius Ro. A variational problem is formulated and solved by a pseudo-time-stepping method up to a Taylor number Ta = 109. The angular momentum transport, characterized by a Nusselt number Nu, is bounded by Nu ≤ cTa1/2, where the prefactor c depends on the radius ratio η = Ri / Ro. Three typical radius ratios are investigatedi.e., η = 0.5, 0.714, and 0.909, and the corresponding prefactors c = 0.0049, 0.0075, and 0.0086 are found to improve (lower) the rigorous upper bounds by Doering and Constantin [C. Doering and P. Constantin, Phys. Rev. Lett. 69, 1648 (1992)] and Constantin [P. Constantin, SIAM Rev. 36, 73 (1994)] by at least one order of magnitude. Furthermore, we show, via an inductive bifurcation analysis, that considering a three-dimensional background velocity field is unable to lower the bound. [ABSTRACT FROM AUTHOR]

We study a model for the evolution of an axially symmetric bubble of inviscid fluid in a homogeneous porous medium otherwise saturated with a viscous fluid. The model is a moving boundary problem that is a higher-dimensional analog of Hele-Shaw flow. Here we are concerned with the development of pinch-off singularities characterized by a blowup of the interface curvature and the bubble subsequently breaking up into two; these singularities do not occur in the corresponding two-dimensional Hele-Shaw problem. By applying a numerical scheme based on the level set method, we show that solutions to our problem can undergo pinch-off in various geometries. A similarity analysis suggests that the minimum radius behaves as a power law in time with exponent α=1/3 just before and after pinch-off has occurred, regardless of the initial conditions; our numerical results support this prediction. Further, we apply our numerical scheme to simulate the time-dependent development and translation of axially symmetric Saffman-Taylor fingers and Taylor-Saffman bubbles in a cylindrical tube, highlighting key similarities and differences with the well-studied two-dimensional cases. [ABSTRACT FROM AUTHOR]

Using a Bayesian approach, we combine measurements of neutron star macroscopic observables obtained by astrophysical and gravitational observations to derive joint constraints on the equation of state (EOS) of matter at supranuclear density. In our analysis, we use two sets of data: (i) the masses and tidal deformabilities measured in the binary neutron star event GW170817, detected by LIGO and Virgo, and (ii) the masses and stellar radii measured from observations of nuclear bursts in accreting low-mass x-ray binaries. Using a phenomenological parametrization of the equation of state, we compute the posterior probability distributions of the EOS parameters, using which we infer the posterior distribution for the radius and the mass of the two neutron stars of GW170817. The constraints we set on the radii are tighter than previous bounds. [ABSTRACT FROM AUTHOR]

The influence of magic numbers on nuclear radii is investigated via the Hartree-Fock-Bogolyubov calculations and available experimental data. With the ls potential including additional density dependence suggested from the chiral effective-field theory, kinks are universally predicted at the jj-closed magic numbers and antikinks (i.e., inverted kinks) are newly predicted at the ls-closed magic numbers, both in the charge radii and in the matter radii along the isotopic and isotonic chains where nuclei stay spherical. These results seem consistent with the kinks of the charge radii observed in Ca, Sn, and Pb and the antikink in Ca. The kinks and the antikinks could be a peculiar indicator for magic numbers, discriminating jj closure and ls closure. [ABSTRACT FROM AUTHOR]

The ground-state energies and radii for 4He, 16O, and 40Ca are calculated with the unitary-model-operator approach (UMOA). In the present study, we employ similarity renormalization group (SRG) evolved nucleon-nucleon (NN) and three-nucleon (3N) interactions based on chiral effective field theory. This is the first UMOA calculation with both NN and 3N interactions. The calculated ground-state energies and radii are consistent with the recent ab initio results with the same interaction. We evaluate the expectation values of two- and three-body SRG evolved radius operators, in addition to those of the bare radius operator. With the aid of the higher-body evolution of the radius operator, it is seen that the calculated radii tend to be SRG resolution-scale independent. We find that the SRG evolution gives minor modifications for the radius operator. [ABSTRACT FROM AUTHOR]

We consider the process of chemical erosion of a porous medium infiltrated by a reactive fluid in a thin-front limit, in which the width of the reactive front is negligible with respect to the diffusive length. We show that in the radial geometry the advancing front becomes unstable only if the flow rate in the system is sufficiently high. The existence of such a stable region in parameter space is in contrast to the Saffman-Taylor instability in radial geometry, where for a given flow rate the front always eventually becomes unstable, after reaching a certain critical radius. We also examine the similarities between the reactive-infiltration instability and the similar instability in the heat transfer, which is driving the formation of star-like patterns on frozen lakes. [ABSTRACT FROM AUTHOR]

We investigate the statistical properties of adjacency relationships in a two-dimensional Vicsek model. We define adjacent edges for all particles at every time step by (a) Delaunay triangulation and (b) Euclidean distance, and obtain cumulative distributions P(τ) of lifetime τ of the edges. We find that the shape of P(τ) changes from an exponential to a power law depending on the interaction radius, which is a parameter of the Vicsek model. We discuss the emergence of the power-law distribution from the viewpoint of first passage time problem for a fractional Brownian motion. [ABSTRACT FROM AUTHOR]

The correlations of identical charged kaons were measured in p-Pb collisions at √sNN = 5.02 TeV by the ALICE experiment at the LHC. The femtoscopic invariant radii and correlation strengths were extracted from one-dimensional kaon correlation functions and were compared with those obtained in pp and Pb-Pb collisions at √s = 7 TeV and √sNN = 2.76 TeV, respectively. The presented results also complement the identical-pion femtoscopic data published by the ALICE collaboration. The extracted radii increase with increasing charged-particle multiplicity and decrease with increasing pair transverse momentum. At comparable multiplicities, the radii measured in p-Pb collisions are found to be close to those observed in pp collisions. The obtained femtoscopic parameters are reproduced by the EPOS 3 hadronic interaction model and disfavor models with large initial size or strong collective expansion at low multiplicities. [ABSTRACT FROM AUTHOR]

Hydrodynamic excitations corresponding to sound and shear modes in fluids are characterized by gapless dispersion relations. In the hydrodynamic gradient expansion, their frequencies are represented by power series in spatial momenta. We investigate the analytic structure and convergence properties of the hydrodynamic series by studying the associated spectral curve in the space of complexified frequency and complexified spatial momentum. For the strongly coupled N=4 supersymmetric Yang-Mills plasma, we use the holographic duality methods to demonstrate that the derivative expansions have finite nonzero radii of convergence. Obstruction to the convergence of hydrodynamic series arises from level crossings in the quasinormal spectrum at complex momenta. [ABSTRACT FROM AUTHOR]

The first laser spectroscopic determination of the change in the nuclear charge radius for a five-electron system is reported. This is achieved by combining high-accuracy ab initio mass-shift calculations and a high-accuracy measurement of the isotope shift in the 2s²2p ²P1/2→2s²3s ²S1/2 ground state transition in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes 10,11B and the results are used to extract their difference in the mean-square charge radius ⟨r²c⟩11-⟨r²c⟩10=-0.49(12) fm². The result is qualitatively explained by a possible cluster structure of the boron nuclei and quantitatively used to benchmark new ab initio nuclear structure calculations using the no-core shell model and Green's function Monte Carlo approaches. These results are the foundation for a laser spectroscopic determination of the charge radius of the proton-halo candidate 8B. [ABSTRACT FROM AUTHOR]

α clustering in nuclei is considered with the quartet model (QM) where four valence nucleons (the quartet) move on the top of the core (daughter) nucleus. In the QM approach, it is assumed that the intrinsic wave function of the quartet is changed from the pure cluster configuration to the shell-model configuration when it crosses some critical radius and enters into the core nucleus. The QM approach could give not only the level scheme, the electromagnetic transition, and the nuclear radius but also the α -cluster formation probability. Numerical results are calculated for 20Ne, 44Ti, and 212Po, where a quartet moves on top of a double magic nucleus. Good agreement with experimental data and previous theoretical studies is obtained. The QM approach is a useful complement to the present phenomenological and microscopic models and could help deepen our understanding of α clustering across the nuclide chart. [ABSTRACT FROM AUTHOR]

I have compared matter radii for nuclei having the same neutron number but differing by one or two in proton number. The ratios reveal features that are less apparent in the actual matter radii. [ABSTRACT FROM AUTHOR]

We present benchmark calculations of Zemach moments and radii of 2,3H and 3,4He using various few-body methods. Zemach moments are required to interpret muonic atom data measured by the CREMA collaboration at the Paul Scherrer Institute. Conversely, radii extracted from spectroscopic measurements can be compared with ab initio computations, posing stringent constraints on the nuclear model. For a given few-body method, different numerical procedures can be applied to compute these quantities. A detailed analysis of the numerical uncertainties entering the total theoretical error is presented. Uncertainties from the few-body method and the calculational procedure are found to be smaller than the dependencies on the dynamical modeling and the single nucleon inputs, which are found to be ≲ 2%. When relativistic corrections and two-body currents are accounted for, the calculated moments and radii are in very good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

Background: There is significant current interest in knowing the value of the proton radius and also its proper definition. Purpose: Combine the disparate literatures of hydrogen spectroscopy and diverse modern parton distributions to understand the meaning of the proton radius in a manner consistent with the separate bodies of work. Methods: Use perturbation theory, light-front dynamics, and elementary techniques to find relativistically correct definitions of the proton radius and charge density. Results: It is found that the very same proton radius is accessed by measurements of hydrogen spectroscopy and elastic lepton scattering. The derivation of the mean-square radius as a moment of a spherically symmetric three-dimensional density is shown to be incorrect. A relativistically correct, two-dimensional charge density is related to the diverse modern literature of various parton distributions. Relativistically invariant moments thereof are derived in a new relativistic moment expansion, the RME. Conclusion: The equation rp2p =-6G'E(0) is the definition of the proton radius. [ABSTRACT FROM AUTHOR]

Nonlinear and low-frequency solitary waves are investigated in the framework of the one-dimensional Hall-magnetohydrodynamic model with finite Larmor effects and two different closure models for the pressures. For a double adiabatic pressure model, the organization of these localized structures in terms of the propagation angle with respect to the ambient magnetic field θ and the propagation velocity C is discussed. There are three types of regions in the θ-C plane that correspond to domains where either solitary waves cannot exist, are organized in branches, or have a continuous spectrum. A numerical method valid for the two latter cases, which rigorously proves the existence of the waves, is presented and used to locate many waves, including bright and dark structures. Some of them belong to parametric domains where solitary waves were not found in previous works. The stability of the structures has been investigated by performing a linear analysis of the background plasma state and by means of numerical simulations. They show that the cores of some waves can be robust, but, for the parameters considered in the analysis, the tails are unstable. The substitution of the double adiabatic model by evolution equations for the plasma pressures appears to suppress the instability in some cases and to allow the propagation of the solitary waves during long times. [ABSTRACT FROM AUTHOR]