Transformation Optics Approach to Plasmon-Exciton Strong Coupling in Nanocavities

We investigate the conditions yielding plasmon-exciton strong coupling at the single emitter level in the gap between two metal nanoparticles. A quasi-analytical transformation optics approach is developed that makes possible a thorough exploration of this hybrid system incorporating the full richness of its plasmonic spectrum. This allows us to reveal that by placing the emitter away from the cavity center, its coupling to multipolar dark modes of both even and odd parity increases remarkably. This way, reversible dynamics in the population of the quantum emitter takes place in feasible implementations of this archetypal nanocavity.Comment: 5 pages, 4 figure

A New Algorithm for the Evaluation of the Elastic Forces in the Absolute Nodal Coordinate Formulation

The use of the Absolute Nodal Coordinate Formulation (ANCF) to model flexible multibody systems leads to a system of equations in which the mass matrix is constant. Among other advantages of the ANCF, as the simplicity of the formulation of joint constraint, the constancy of the mass matrix is specially useful since it implies that the mass matrix is calculated once before the analysis and stored as a invariant quantity. On the other hand, the evaluation of the elastic forces has been considered as a difficult task since they result in large nonlinear functions. Both linear and nonlinear formulations based on either Continuum Mechanics or Timoshenko/Euler-Bernoulli approaches have been supposed to lead to the same level of complexity of the elastic force function. The evaluation of the elastic forces when using a nonlinear Continuum Mechanics approach requires, as presented in the literature, the integration over the volume of the element. However, it can be shown that this integration can be avoided for every evaluation since there is a closed form of the elastic force function that can be obtained before the simulation. Finite elements based on ANCF have such a large number of nodal coordinate (24 and 48 for three-dimensional beams and plates, respectively) that the search for a closed form of the elastic force function becomes difficult and costly. This paper presents a set of constant matrices that are integrated in advance (before simulation) and allows the evaluation of the elastic forces without the integration over the volume of the element suggested in the literature. In addition, the amount of data that has to be stored in order to evaluate the function is reduced. These constant matrices together with the mass matrix complete the set of invariants of the ANCF that allows an acceleration of simulations. Numerical simulations comparing CPU time and number of arithmetic operations carried out when these invariant matrices are used with those carried out when they are not used, support the convenience of their use.Ministerio de Ciencia y Tecnología DPI2000-056

Experimental estimation of the residual fatigue life of in-service wind turbine bolts

This study presents an experimental methodology aimed at estimating the residual fatigue life of in-service wind turbine bolts. The main objective is to assess the residual life of the bolts to plan their replacement and to avoid unexpected breakages of wind turbine blade connections. To develop the methodology, M16 bolts of quality 10.9 with controlled predamage were used, simulating in-service operating conditions. The fatigue tests were carried out taking care to place the nut at the point on the bolt that produces the highest damage at the same point where the predamage was performed. In addition, the influence of a possible angular positioning error on the residual fatigue life has been investigated. The residual fatigue life is estimated from the difference in fatigue life of new bolt tests and the fatigue life of predamaged bolt tests, simulating service conditions. Special care has been taken to guarantee that the most damaged zone of the bolt in service is also in the position that produces the highest damage during tests. An experimental procedure for determining the fatigue life of a new bolt from tests conducted on a bolt under the same operating conditions was developed. The developed methodology has been applied to M20 bolts belonging to real turbines in service

The Possible White Dwarf-Neutron Star Connection

The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and E. Garcia-Berro (Dordrecht: Kluwer

EFFECT OF SEASON ON SERUM COPPER AND ZINC CONCENTRATIONS IN CROSSBRED GOATS HAVING DIFFERENT REPRODUCTIVE STATUS UNDER SEMIARID RANGELAND CONDITIONS IN SOUTHERN MEXICO STATE

The effect of season (rainy: RS, and dry: DS) and reproductive status on copper (Cu) and zinc (Zn) concentrations in blood serum of crossbred goats (BW= 36.01 ± 1.59 kg) were studied under semiarid rangeland conditions in Southern Mexico State. Blood samples from 80 crossbred goats were taken each season (RS and DS). The goats were clustered into 10 different groups considering their reproductive status. Concentrations of Cu and Zn in serum were assayed using atomic absorption. Data were analyzed using a general linear model procedure for a completely randomized design and differences among means were examined using a Tukey test. Blood serum concentrations of Cu and Zn were affected by reproductive status and season (P<0.001). In relation to the season, Cu and Zn serum levels were lower in RS than DS (P<0.05). Overall, kidded goats had the highest values (P<0.01) for Cu than other animals in both seasons (RS or DS). Anestrous goats had the lowest concentrations (P<0.01) for Zn during RS, while all goats at their second or more kidding, rearing single or twins, showed the highest concentrations of Zn (P<0.001) in this season. Adult goats in Southern Mexico State showed a deficiency of Cu and Zn, especially during RS. As such, mineral supplements should be provided with respect to these elements in feeding systems for goats under semiarid rangeland conditions in order to evaluate their impact on health and reproduction

Calibration of semi-analytic models of galaxy formation using Particle Swarm Optimization

We present a fast and accurate method to select an optimal set of parameters in semi-analytic models of galaxy formation and evolution (SAMs). Our approach compares the results of a model against a set of observables applying a stochastic technique called Particle Swarm Optimization (PSO), a self-learning algorithm for localizing regions of maximum likelihood in multidimensional spaces that outperforms traditional sampling methods in terms of computational cost. We apply the PSO technique to the SAG semi-analytic model combined with merger trees extracted from a standard $\Lambda$CDM N-body simulation. The calibration is performed using a combination of observed galaxy properties as constraints, including the local stellar mass function and the black hole to bulge mass relation. We test the ability of the PSO algorithm to find the best set of free parameters of the model by comparing the results with those obtained using a MCMC exploration. Both methods find the same maximum likelihood region, however the PSO method requires one order of magnitude less evaluations. This new approach allows a fast estimation of the best-fitting parameter set in multidimensional spaces, providing a practical tool to test the consequences of including other astrophysical processes in SAMs.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in ApJ. Comments are welcom

Effective interactions of colloids on nematic films

The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied theoretically for large separations $d$. The elastic interaction is repulsive and of quadrupolar type, varying as $d^{-5}$. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to $d^{-5}$ as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying capillary attractions. However, their strength turns out to be too small to be of importance for the recently observed pattern formation of colloidal droplets on nematic films.Comment: 13 pages, accepted by EPJ

Spoofing GPS Receiver Clock Offset of Phasor Measurement Units

We demonstrate the feasibility of a spoofing attack on the GPS receiver of a phasor measurement unit (PMU). We formulate the attack as an optimization problem where the objective is to maximize the difference between the time offset of the PMU’s receiver clock before and after the attack. Since the PMU uses this clock offset to compute a time stamp for its measurements, an error in the receiver clock offset introduces a proportional phase error in the voltage or current phase measurements provided by the PMU, with a phase-wrap of 2pi (in practice, the computed maximum receiver clock offset error is never large enough to induce a phase error that requires a phase-wrap of 2pi) . The decision variables in the optimization problem are the satellites’ ephemerides, pseudoranges, and the receiver coordinates. The constraints are cast such that the receiver and satellite positions computed from the solution of the optimization problem will be close to their pre-attack values to avoid detection. We show that the spoofing attack is feasible for any number of visible satellites. Simulation results, in which four and seven satellites are spoofed, are presented to illustrate the effect of the attack on the phase measurement provided by a PMU.Department of Energy and Department of Homeland Security / DE-OE0000097Ope

Collective decision-making on triadic graphs

Many real-world networks exhibit community structures and non-trivial clustering associated with the occurrence of a considerable number of triangular subgraphs known as triadic motifs. Triads are a set of distinct triangles that do not share an edge with any other triangle in the network. Network motifs are subgraphs that occur significantly more often compared to random topologies. Two prominent examples, the feedforward loop and the feedback loop, occur in various real-world networks such as gene-regulatory networks, food webs or neuronal networks. However, as triangular connections are also prevalent in communication topologies of complex collective systems, it is worthwhile investigating the influence of triadic motifs on the collective decision-making dynamics. To this end, we generate networks called Triadic Graphs (TGs) exclusively from distinct triadic motifs. We then apply TGs as underlying topologies of systems with collective dynamics inspired from locust marching bands. We demonstrate that the motif type constituting the networks can have a paramount influence on group decision-making that cannot be explained solely in terms of the degree distribution. We find that, in contrast to the feedback loop, when the feedforward loop is the dominant subgraph, the resulting network is hierarchical and inhibits coherent behavior