3,778 research outputs found
Effect of nonlinear filters on detrended fluctuation analysis
We investigate how various linear and nonlinear transformations affect the
scaling properties of a signal, using the detrended fluctuation analysis (DFA).
Specifically, we study the effect of three types of transforms: linear,
nonlinear polynomial and logarithmic filters. We compare the scaling properties
of signals before and after the transform. We find that linear filters do not
change the correlation properties, while the effect of nonlinear polynomial and
logarithmic filters strongly depends on (a) the strength of correlations in the
original signal, (b) the power of the polynomial filter and (c) the offset in
the logarithmic filter. We further investigate the correlation properties of
three analytic functions: exponential, logarithmic, and power-law. While these
three functions have in general different correlation properties, we find that
there is a broad range of variable values, common for all three functions,
where they exhibit identical scaling behavior. We further note that the scaling
behavior of a class of other functions can be reduced to these three typical
cases. We systematically test the performance of the DFA method in accurately
estimating long-range power-law correlations in the output signals for
different parameter values in the three types of filters, and the three
analytic functions we consider.Comment: 12 pages, 7 figure
Performance of two transferred modules in the Lagunera Region: Water relations
Water policy / Performance / Privatization / Irrigation systems / Operations / Maintenance / Irrigation efficiency / Water users' associations / Water rights / Water allocation / Water supply / Water distribution
A transient outward current in a mammalian central neurone blocked by 4-aminopyridine
It is becoming increasingly clear that nerve cells in the mammalian central nervous system (CNS) have a very complex electroresponsiveness. They exhibit not only time- and voltage-dependent Na+ and K+ conductances, analogous to those in the squid giant axon1, but also a variety of other conductances that have a significant role in the control of cell excitability. Of the outward currents, there are, in addition to the delayed rectifier, the Ca2+-activated K+ current2,3 which underlies the long-lasting spike afterhyperpolarization, and the M current4, a non-inactivating K+ current evoked by membrane depolarization and blocked by muscarinic, cholinergic agonists. We demonstrate here the existence in a mammalian central neurone (hip-pocampal CA3 pyramidal cells) of yet another outward current, which is transient and may be carried by K+ ions. Further, the experiments show that this current is substantially reduced by the convulsant 4-aminopyridine (4-AP)5, resulting in a marked increase in cell excitability
The Magnetic Electron Ion Spectrometer (MagEIS) Instruments Aboard the Radiation Belt Storm Probes (RBSP) Spacecraft
This paper describes the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the RBSP spacecraft from an instrumentation and engineering point of view. There are four magnetic spectrometers aboard each of the two spacecraft, one low-energy unit (20–240 keV), two medium-energy units (80–1200 keV), and a high-energy unit (800–4800 keV). The high unit also contains a proton telescope (55 keV–20 MeV). The magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulse-height analysis is used to determine if the energy of the incident electron is appropriate for the electron momentum selected by the magnet. Thus each event is a two-parameter analysis, an approach leading to a greatly reduced background. The physics of these instruments are described in detail followed by the engineering implementation. The data outputs are described, and examples of the calibration results and early flight data presented
Optical response of supported gold nanodisks
It is shown that the ellipsometric spectra of short range ordered
planar arrays of gold nanodisks supported on glass substrates can be
described by modeling the nanostructured arrays as uniaxial homogeneous
layers with dielectric functions of the Lorentz type. However, appreciable
deviations from experimental data are observed in calculated spectra of
irradiance measurements. A qualitative and quantitative description of all
measured spectra is obtained with a uniaxial effective medium dielectric
function in which the nanodisks are modeled as oblate spheroids. Dynamic
depolarization factors in the long-wavelength approximation and interaction
with the substrate are considered. Similar results are obtained calculating the
optical spectra using the island-film theory. Nevertheless, a small in-plane
anisotropy and quadrupolar coupling effects reveal a very complex optical
response of the nanostructured arrays
Typicality vs. probability in trajectory-based formulations of quantum mechanics
Bohmian mechanics represents the universe as a set of paths with a
probability measure defined on it. The way in which a mathematical model of
this kind can explain the observed phenomena of the universe is examined in
general. It is shown that the explanation does not make use of the full
probability measure, but rather of a suitable set function deriving from it,
which defines relative typicality between single-time cylinder sets. Such a set
function can also be derived directly from the standard quantum formalism,
without the need of an underlying probability measure. The key concept for this
derivation is the {\it quantum typicality rule}, which can be considered as a
generalization of the Born rule. The result is a new formulation of quantum
mechanics, in which particles follow definite trajectories, but which is only
based on the standard formalism of quantum mechanics.Comment: 24 pages, no figures. To appear in Foundation of Physic
Electronic structure calculations for PrFe4P12 filled skutterudite using Extended Huckel tight-binding method
To get insight into the electronic properties of PrFe4P12 skutterudite, band
electronic structure calculations, Total and Projected Density of States,
Crystal Orbital Overlap Population and Mulliken Population Analysis were
performed. The energy bands yield a semi metallic behavior with a direct gap
(at gamma) of 0.02 eV. Total and Projected Density of States provided
information of the contribution from each orbital of each atom to the total
Density of States. Moreover, the bonding strength between some atoms within the
unit cell was obtained. Mulliken Population analysis suggests ionic behavior
for this compound
Feeding Ecology of the Blackwing Searobin Prionotus rubio (Jordan, 1886) Over the Western Continental Shelf off Alvarado, Veracruz, Mexico
Seasonal changes of food habits of the blackwing searobin Prionotus rubio were studied over the continental shelf off Alvarado, Veracruz, Mexico, from Sept. 1994 to Aug. 1995. A total of 234 stomachs (182 with identifiable food) were analyzed. Brown shrimp Farfantopenaeus aztecus, blue crab Portunus spinicarpus, and rock shrimp Sicyonia dorsalis were the main dietary items. Low values of prey diversity and dietary breadth suggest the main prey were always relatively abundant over the western continental shelf of the Gulf of Mexico. We concluded the blackwing searobin is part of a trophic guild of demersal marine fish that impact mainly on epibenthic invertebrates
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