NMR Characterization of Sulphur Substitution Effects in the K(x)Fe(2-y)Se(2-z)S(z) high Tc Superconductor

We present an NMR study of the effect of S substitution in the high Tc superconductor K(x)Fe(2-y)Se(2-z)S(z) in a temperature range up to 250 K. We present NMR Knight shift and nuclear spin-lattice relaxation rate 1/T1 data, and compare our results to that of the non-substituted system K(x)Fe(2-y)Se(2).Comment: Typos fixed, figure replace

To synchronize or not to synchronize, that is the question: finite-size scaling and fluctuation effects in the Kuramoto model

The entrainment transition of coupled random frequency oscillators presents a long-standing problem in nonlinear physics. The onset of entrainment in populations of large but finite size exhibits strong sensitivity to fluctuations in the oscillator density at the synchronizing frequency. This is the source for the unusual values assumed by the correlation size exponent $\nu'$. Locally coupled oscillators on a $d$-dimensional lattice exhibit two types of frequency entrainment: symmetry-breaking at $d > 4$, and aggregation of compact synchronized domains in three and four dimensions. Various critical properties of the transition are well captured by finite-size scaling relations with simple yet unconventional exponent values.Comment: 9 pages, 1 figure, to appear in a special issue of JSTAT dedicated to Statphys2

Criteria of efficiency for conformal prediction

We study optimal conformity measures for various criteria of efficiency of classification in an idealised setting. This leads to an important class of criteria of efficiency that we call probabilistic; it turns out that the most standard criteria of efficiency used in literature on conformal prediction are not probabilistic unless the problem of classification is binary. We consider both unconditional and label-conditional conformal prediction.Comment: 31 page

77Se NMR Investigation of the K(x)Fe(2-y)Se(2) High Tc Superconductor (Tc=33K)

We report a comprehensive 77Se NMR study of the structural, magnetic, and superconducting properties of a single crystalline sample of the newly discovered FeSe-based high temperature superconductor K(x)Fe(2-y)Se(2) (Tc=33K) in a broad temperature range up to 290 K. We will compare our results with those reported for FeSe (Tc=9K) and FeAs-based high Tc systems.Comment: Final versio

Soliton with a Pion Field in the Global Color Symmetry Model

We calculate the property of the global color symmetry model soliton with the pion field being included explicitly. The calculated results indicate that the pion field provides a strong attraction so that the eigen-energy of a quark and the mass of a soliton reduce drastically, in contrast to those with only the sigma field.Comment: 15 pages, 2 figure

Collisionless Magnetic Reconnection via Alfven Eigenmodes

We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfven eigenmodes' generation and dissipation. Alfven eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh^2 potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n=1 mode. The prediction of the n=1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields

Steady-State Analysis of Load Balancing with Coxian-22 Distributed Service Times

This paper studies load balancing for many-server ($N$ servers) systems. Each server has a buffer of size $b-1,$ and can have at most one job in service and $b-1$ jobs in the buffer. The service time of a job follows the Coxian-2 distribution. We focus on steady-state performance of load balancing policies in the heavy traffic regime such that the normalized load of system is $\lambda = 1 - N^{-\alpha}$ for $0<\alpha<0.5.$ We identify a set of policies that achieve asymptotic zero waiting. The set of policies include several classical policies such as join-the-shortest-queue (JSQ), join-the-idle-queue (JIQ), idle-one-first (I1F) and power-of-$d$-choices (Po$d$) with $d=O(N^\alpha\log N)$. The proof of the main result is based on Stein's method and state space collapse. A key technical contribution of this paper is the iterative state space collapse approach that leads to a simple generator approximation when applying Stein's method

Linear and nonlinear capacitive coupling of electro-opto-mechanical photonic crystal cavities

We fabricate and characterize a microscale silicon electro-opto-mechanical system whose mechanical motion is coupled capacitively to an electrical circuit and optically via radiation pressure to a photonic crystal cavity. To achieve large electromechanical interaction strength, we implement an inverse shadow mask fabrication scheme which obtains capacitor gaps as small as 30 nm while maintaining a silicon surface quality necessary for minimizing optical loss. Using the sensitive optical read-out of the photonic crystal cavity, we characterize the linear and nonlinear capacitive coupling to the fundamental 63 MHz in-plane flexural motion of the structure, showing that the large electromechanical coupling in such devices may be suitable for realizing efficient microwave-to-optical signal conversion.Comment: 8 papers, 4 figure

Reconciling magnetoelectric response and time-reversal symmetry in non-magnetic Z2\mathbb{Z}_2 topological insulators

A delicate tension complicates the relationship between the topological magnetoelectric effect in three-dimensional $\mathbb{Z}_2$ topological insulators (TIs) and time-reversal symmetry (TRS). TRS underlies a particular $\mathbb{Z}_2$ topological classification of the electronic ground state of a bulk insulator and the associated quantization of the magnetoelectric coefficient calculated using linear response theory, but according to standard symmetry arguments simultaneously forbids any physically meaningful magnetoelectric response. This tension between theories of magnetoelectric response in bulk and finite-sized materials originates from the distinct approaches required to introduce notions of polarization and orbital magnetization in those fundamentally different environments. In this work we argue for a modified interpretation of the bulk linear response calculations in non-magnetic TIs that is more plainly consistent with TRS, and use this interpretation to discuss the effect's observation - still absent over a decade after its prediction. Our analysis is reinforced by microscopic bulk and thin film calculations carried out using a simplified but still realistic model for the well established V$_2$VI$_3$ (V $=$ (Sb,Bi) and VI $=$ (Se,Te)) family of non-magnetic $\mathbb{Z}_2$ TIs. We conclude that the topological magnetoelectric effect in non-magnetic $\mathbb{Z}_2$ TIs is activated by magnetic surface dopants, and that the charge density response to magnetic fields and the orbital magnetization response to electric fields in a given sample are controlled in part by the configuration of those dopants.Comment: 30 pages, 5 figure