3,202 research outputs found
Calculation of the Autocorrelation Function of the Stochastic Single Machine Infinite Bus System
Critical slowing down (CSD) is the phenomenon in which a system recovers more
slowly from small perturbations. CSD, as evidenced by increasing signal
variance and autocorrelation, has been observed in many dynamical systems
approaching a critical transition, and thus can be a useful signal of proximity
to transition. In this paper, we derive autocorrelation functions for the state
variables of a stochastic single machine infinite bus system (SMIB). The
results show that both autocorrelation and variance increase as this system
approaches a saddle-node bifurcation. The autocorrelation functions help to
explain why CSD can be used as an indicator of proximity to criticality in
power systems revealing, for example, how nonlinearity in the SMIB system
causes these signs to appear.Comment: Accepted for publication/presentation in Proc. North American Power
Symposium, 201
Effect of spin on electron motion in a random magnetic field
We consider properties of a two-dimensional electron system in a random
magnetic field. It is assumed that the magnetic field not only influences
orbital electron motion but also acts on the electron spin. For calculations,
we suggest a new trick replacing the initial Hamiltonian by a Dirac
Hamiltonian. This allows us to do easily a perturbation theory and derive a
supermatrix sigma model, which takes a form of the conventional sigma model
with the unitary symmetry. Using this sigma model we calculate several
correlation functions including a spin-spin correlation function. As compared
to the model without spin, we get different expressions for the single-particle
lifetime and the transport time. The diffusion constant turns out to be 2 times
smaller than the one for spinless particles.Comment: 7 pages, revtex, result of the spin correlation function corrected,
Appendix adde
Sorting and separation of microparticles by surface properties using liquid crystal-enabled electro-osmosis
Sorting and separation of microparticles is a challenging problem of
interdisciplinary nature. Existing technologies can differentiate
microparticles by their bulk properties, such as size, density, electric
polarizability, etc. The next level of challenge is to separate particles that
show identical bulk properties and differ only in subtle surface features, such
as functionalization with ligands. In this work, we propose a technique to sort
and separate particles and fluid droplets that differ in surface properties. As
a dispersive medium, we use a nematic liquid crystal (LC) rather than an
isotropic fluid, which allows us to amplify the difference in surface
properties through distinct perturbations of LC order around the dispersed
particles. The particles are placed in a LC cell with spatially distorted
molecular orientation subject to an alternating current electric field. The
gradients of the molecular orientation perform two functions. First, elastic
interactions between these pre-imposed gradients and distortions around the
particles separate the particles with different surface properties in space.
Second, these pre-imposed patterns create electro-osmotic flows powered by the
electric field that transport the sorted particles to different locations thus
separating them. The demonstrated unique sorting and separation capability
opens opportunities in lab-on-a-chip, cell sorting and bio-sensing
applications
New records of Praethecacineta halacari (Schulz) (Suctorea: Ciliophora) from Taiwan, Tanzania and Canada
The present study reports on a range extension of the suctorian species Praethecacineta halacari to the region of He-Ping-Dao,
north-east of Taiwan (West Pacific Ocean), Matemwe, the east coast of Unguja, Zanzibar, Tanzania (West Indian Ocean) and
Nova Scotia, Canada (West Atlantic Ocean). Praethecacineta halacari is reported here for the first time from Taiwan, Tanzania
and Canada. Earlier records include the Caspian Sea, Western Australia, Brazil, India, and various coastal sites in Europe
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