Stochastic and Collective Properties of Nonlinear Oscillators

Two systems of nonlinear oscillators are considered: (a) a single periodically driven nonlinear oscillator interacting with a heat bath, which may operate in the regime of bistability or monostability, and (b) a one-dimensional chain of self-sustaining phase oscillators with nearest-neighbor interaction. For a single oscillator we analyze the scaling crossovers in the thermal activation barrier between the two stable states. The rate of metastable decay in nonequilibrium systems is expected to display scaling behavior: the logarithm of the decay rate should scale as a power of the distance to a bifurcation point where the metastable state disappears. We establish the range where different scaling behavior is displayed and show how the crossover between different types of scaling occurs. Using the instanton method, we map numerically the entire parameter range of bistability and find the regions where the scaling exponents are 1 or 3/2, depending on the damping. The exponent 3/2 is found to extend much further from the bifurcation then where it would be expected to hold as a result of an overdamped soft mode. Additionally, we uncover a new scaling behavior with exponent of ≈1.3 that extends beyond the close vicinity of the bifurcation point. We also study the pattern of fluctuational trajectories in the monostable regime. For nonequilibrium systems, fluctuational and relaxational trajectories are not simply related by time-reversibility, as is the case in thermal equilibrium. One of the consequences of this is the onset of singularities in the pattern of fluctuational trajectories, where most probable paths to neighboring states are far away from each other. This also creates nonsmoothness in the probability distribution of the system in its phase space. We discover that the pattern of optimal paths in equilibrium systems is fragile with respect to the driving strength F, and investigate how the singularities occur as the system is driven away from equilibrium. As the strength of the driving F approaches zero, the cusp of the spiral caustic system recedes to larger radius R and the angle of the cusp also decreases. The dependence of R on F displays two scaling laws with crossovers, where the scaling exponents depend on the damping. For the one-dimensional chain of nearest-neighbor coupled phase oscillators, we develop a renormalization group method to investigate synchronization clusters. We apply it numerically to Lorentzian distributions of intrinsic frequencies and couplings and investigate the statistics of the resultant cluster sizes and frequencies. We find that the distributions of sizes of frequency clusters are exponential, with a characteristic length. The dependence of this length upon parameters of these Lorentzian distributions develops an asymptotic power law with an exponent of 0.48 ± 0.02. The findings obtained with the renormalization group are compared with numerical simulations of the equations of motion of the chain, with an excellent agreement in all the aforementioned quantities.</p

Thermal Fluctuations of the Electric Field in the Presence of Carrier Drift

We consider a semiconductor in a non-equilibrium steady state, with a dc current. On top of the stationary carrier motion there are fluctuations. It is shown that the stationary motion of the carriers (i.e., their drift) can have a profound effect on the electromagnetic field fluctuations in the bulk of the sample as well as outside it, close to the surface (evanescent waves in the near field). The effect is particularly pronounced near the plasma frequency. This is because drift leads to a significant modification of the dispersion relation for the bulk and surface plasmons.Comment: Comments are welcom

The embodied typist: Bimanual actions are modulated by words’ implied motility and number of evoked limbs

The planning and execution of manual actions can be influenced by concomitant processing of manual action verbs. However, this phenomenon manifests in varied ways throughout the literature, ranging from facilitation to interference effects. Suggestively, stimuli across studies vary randomly in two potentially relevant variables: verb motility and effector quantity (i.e., the amount of movement and the number of hands implied by the word, respectively). Here we examine the role of these factors during keyboard typing, a strategic bimanual task validated in previous works. Forty-one participants read and typed high and low motility items from four categories: bimanual, unimanual, and non-manual action verbs, as well as minimally motoric verbs. Motor planning and execution were captured by first-letter lag (the lapse between word presentation and first keystroke) and whole-word lag (the lapse between the first and last keystroke). We found that verb motility modulated action planning and execution, both stages being delayed by high (relative to low) motility verbs. Effector quantity also influenced both stages, which were facilitated by bimanual verbs relative to unimanual verbs and non-manual verbs (this effect being confined to high motility items during action execution). Accordingly, motor-language coupling effects seem sensitive to words’ implied motility and number of evoked limbs. These findings refine our understanding of how semantics influences bodily movement.Fil: Rolán, Katia. Universidad de La Laguna; España. Universidad de Vigo; EspañaFil: Sánchez Borges, Iván. Universidad de La Laguna; EspañaFil: Kogan, Boris. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Humanidades. Departamento de Filosofía; Argentina. Centro de Neurociencias Cognitivas ; Rectorado ; Universidad de San Andres;Fil: García Marco, Enrique. Universidad de La Laguna; España. Universidad de Huelva; EspañaFil: Álvarez, Carlos J.. Universidad de La Laguna; EspañaFil: de Vega, Manuel. Universidad de La Laguna; EspañaFil: García, Adolfo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Centro de Neurociencias Cognitivas ; Rectorado ; Universidad de San Andres; . University of California; Estados Unidos. Universidad de Santiago de Chile; Chil

Photothermally controlled methotrexate release system using β-cyclodextrin and gold nanoparticles

The inclusion compound (IC) of cyclodextrin (CD) containing the antitumor drug Methotrexate (MTX) as a guest molecule was obtained to increase the solubility of MTX and decrease its inherent toxic effects in nonspecific cells. The IC was conjugated with gold nanoparticles (AuNPs), obtained by a chemical method, creating a ternary intelligent delivery system for MTX molecules, based on the plasmonic properties of the AuNPs. Irradiation of the ternary system, with a laser wavelength tunable with the corresponding surface plasmon of AuNPs, causes local energy dissipation, producing the controlled release of the guest from CD cavities. Finally, cell viability was evaluated using MTS assays for β-CD/MTX and AuNPs + β-CD/MTX samples, with and without irradiation, against HeLa tumor cells. The irradiated sample of the ternary system AuNPs + β-CD/MTX produced a diminution in cell viability attributed to the photothermal release of MTX

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate $\gamma$-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic Vision 2010; 25 p., 25 figs; see also www.grips-mission.e

Does student loan debt deter higher education participation? New evidence from England

Research among prospective UK undergraduates in 2002 found that some students, especially from low social classes, were deterred from applying to university because of fear of debt. This paper investigates whether this is still the case today in England despite the changing higher education landscape since 2002. The paper describes findings from a 2015 survey of prospective undergraduates and compares them with those from the 2002 study. We find that students’ attitudes to taking on student loan debt are more favorable in 2015 than in 2002. Debt averse attitudes remain much stronger among lower-class students than among upper-class students, and more so than in 2002. However, lower-class students did not have stronger debt averse attitudes than middle-class students. Debt averse attitudes seem more likely to deter planned higher education participation among lower-class students in 2015 than in 2002