Current reversal with type-I intermittency in deterministic inertia ratchets

The intermittency is investigated when the current reversal occurs in a deterministic inertia ratchet system. To determine which type the intermittency belongs to, we obtain the return map of velocities of particle using stroboscopic recording, and numerically calculate the distribution of average laminar length ${}$. The distribution follows the scaling law of ${} \propto {\epsilon}^{-1/2}$, the characteristic relation of type-I intermittency.Comment: 4 pages, 7 figure

Energetic Ion Moments and Polytropic Index in Saturn’s Magnetosphere using Cassini/MIMI Measurements: A Simple Model Based on κ‐Distribution Functions

Moments of the charged particle distribution function provide a compact way of studying the transport, acceleration, and interactions of plasma and energetic particles in the magnetosphere. We employ κ‐distributions to describe the energy spectra of H+ and O+, based on >20 keV measurements by the three detectors of Cassini’s Magnetospheric Imaging Instrument, covering the time period from DOY 183/2004 to 016/2016, 5 < L < 20. From the analytical spectra we calculate the equatorial distributions of energetic ion moments inside Saturn’s magnetosphere and then focus on the distributions of the characteristic energy (Ec=IE/In), temperature, and κ‐index of these ions. A semiempirical model is utilized to simulate the equatorial ion moments in both local time and L‐shell, allowing the derivation of the polytropic index (Γ) for both H+ and O+. Primary results are as follows: (a) The ∼9 < L < 20 region corresponds to a local equatorial acceleration region, where subadiabatic transport of H+ (Γ∼1.25) and quasi‐isothermal behavior of O+ (Γ∼0.95) dominate the ion energetics; (b) energetic ions are heavily depleted in the inner magnetospheric regions, and their behavior appears to be quasi‐isothermal (Γ<1); (c) the (quasi‐) periodic energetic ion injections in the outer parts of Saturn’s magnetosphere (especially beyond 17–18 RS) produce durable signatures in the energetic ion moments; (d) the plasma sheet does not seem to have a ground thermodynamic state, but the extended neutral gas distribution at Saturn provides an effective cooling mechanism that does not allow the plasma sheet to behave adiabatically.Key PointsDerivation of energetic ion moments, κ‐index, characteristic energy, temperature, and polytropic index in Saturn’s magnetospherePresentation of a semiempirical analytical model for the 20 keV energetic ion Pressure, density, and temperatureThe neutral gas at Saturn provides an effective cooling mechanism and does not allow the plasma sheet to behave adiabaticallyPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146558/1/jgra54546.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146558/2/jgra54546_am.pd

Molecular motor that never steps backwards

We investigate the dynamics of a classical particle in a one-dimensional two-wave potential composed of two periodic potentials, that are time-independent and of the same amplitude and periodicity. One of the periodic potentials is externally driven and performs a translational motion with respect to the other. It is shown that if one of the potentials is of the ratchet type, translation of the potential in a given direction leads to motion of the particle in the same direction, whereas translation in the opposite direction leaves the particle localized at its original location. Moreover, even if the translation is random, but still has a finite velocity, an efficient directed transport of the particle occurs.Comment: 4 pages, 5 figures, Phys. Rev. Lett. (in print

Multiple current reversals in forced inhomogeneous ratchets

Transport properties of overdamped Brownian paricles in a rocked thermal ratchet with space dependent friction coefficient is studied. By tuning the parameters, the direction of current exhibit multiple reversals, both as a function of the thermal noise strength as well as the amplitude of rocking force. Current reversals also occur under deterministic conditions and exhibits intriguing structure. All these features arise due to mutual interplay between potential asymmetry,noise, driving frequency and inhomogeneous friction.Comment: 6 figure

Sources, sinks and transport of energetic electrons near Saturn’s main rings

The inner boundary of Saturn's electron radiation belts, near the planet's A‐ring (∼2.27 Rs), is studied using Cassini's Proximal orbit measurements. We find that variable convective flows transport energetic electrons to the A‐ring, which absorbs them instantaneously, forming the inner belt boundary. These flows are also responsible for a variable and longitudinally asymmetric boundary configuration. Pre‐noon, the boundary oscillates towards and away from the A‐ring with a two‐week period. Post‐noon, it maps persistently near the F‐ring (∼2.32 Rs) and coexists with localized MeV electron intensity enhancements (microbelts). We propose that the microbelts contain electrons in drift resonance with corotation, trapped in local‐time confined trajectories which result from the aforementioned convective flows. The microbelts' collocation with the F‐ring implies either a local, secondary electron production due to Galactic Cosmic Ray collisions with F‐ring dust, or an enhanced resonant electron trapping due to an electrodynamic interaction between the F‐ring and Saturn's magnetosphere

IL-4-secreting CD4+ T cells are crucial to the development of CD8+ T-cell responses against malaria liver stages.

CD4+ T cells are crucial to the development of CD8+ T cell responses against hepatocytes infected with malaria parasites. In the absence of CD4+ T cells, CD8+ T cells initiate a seemingly normal differentiation and proliferation during the first few days after immunization. However, this response fails to develop further and is reduced by more than 90%, compared to that observed in the presence of CD4+ T cells. We report here that interleukin-4 (IL-4) secreted by CD4+ T cells is essential to the full development of this CD8+ T cell response. This is the first demonstration that IL-4 is a mediator of CD4/CD8 cross-talk leading to the development of immunity against an infectious pathogen

Adding our leaves: A communityâ wide perspective on research directions in ecohydrology

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154539/1/hyp13693.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154539/2/hyp13693_am.pd

VectorBase: a data resource for invertebrate vector genomics

VectorBase (http://www.vectorbase.org) is an NIAID-funded Bioinformatic Resource Center focused on invertebrate vectors of human pathogens. VectorBase annotates and curates vector genomes providing a web accessible integrated resource for the research community. Currently, VectorBase contains genome information for three mosquito species: Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus, a body louse Pediculus humanus and a tick species Ixodes scapularis. Since our last report VectorBase has initiated a community annotation system, a microarray and gene expression repository and controlled vocabularies for anatomy and insecticide resistance. We have continued to develop both the software infrastructure and tools for interrogating the stored data

A model of force balance in Saturn's magnetodisc

We present calculations of magnetic potential associated with the perturbation of Saturn's magnetic field by a rotating, equatorially-situated disc of plasma. Such structures are central to the dynamics of the rapidly rotating magnetospheres of Saturn and Jupiter. They are `fed' internally by sources of plasma from moons such as Enceladus (Saturn) and Io (Jupiter). We use a scaled form of Euler potentials for the Jovian magnetodisc field (Caudal, 1986). In this formalism, the magnetic field is assumed to be azimuthally symmetric about the planet's axis of rotation, and plasma temperature is constant along a field line. We perturb the dipole potential by using simplified distributions of plasma pressure and angular velocity for both planets, based on observations by Cassini (Saturn) and Voyager (Jupiter). Our results quantify the degree of radial `stretching' exerted on the dipolar field lines through the plasma's rotational motion and pressure. A simplified version of the field model, the `homogeneous disc', can be used to easily estimate the distance of transition in the outer magnetosphere between pressure-dominated and centrifugally-dominated disc structure. We comment on the degree of equatorial confinement as represented by the scale height associated with disc ions of varying mass and temperature. For Saturn, we identify the principal forces which contribute to the magnetodisc current and make comparisons between the field structure predicted by the model and magnetic field measurements from Cassini. For Jupiter, we reproduce Caudal's original calculation in order to validate our model implementation. We also show that compared to Saturn, where plasma pressure gradient is, on average, weaker than centrifugal force, the outer plasmadisc of Jupiter is clearly a pressure-dominated structure.Comment: 24 pages, 15 figures, 2 tables; accepted for publication in MNRA

Synergies between interstellar dust and heliospheric science with an interstellar probe

We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavours, and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an interstellar probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute – through measuring dust – to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it ‘rolls’ into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions