5,855 research outputs found
Stochastic Resonance: influence of a noise spectrum
Here, in order to study \textit{stochastic resonance} (SR) in a double-well
potential when the noise source has a spectral density of the form
with varying , we have extended a procedure, introduced
by Kaulakys et al (Phys. Rev. E \textbf{70}, 020101 (2004)). In order to have
an analytical understanding of the results, we have obtained an effective
Markovian approximation, that allows us to make a systematic study of the
effect of such kind of noises on the SR phenomenon. The comparison of numerical
and analytical results shows an excellent qualitative agreement indicating that
the effective Markovian approximation is able to correctly describe the general
trends.Comment: 11 pages, 6 figures, submitted to Euro.Phys.J.
Exact Phase Solutions of Nonlinear Oscillators on Two-dimensional Lattice
We present various exact solutions of a discrete complex Ginzburg-Landau
(CGL) equation on a plane lattice, which describe target patterns and spiral
patterns and derive their stability criteria. We also obtain similar solutions
to a system of van der Pol's oscillators.Comment: Latex 11 pages, 17 eps file
Renormalization group approach to vibrational energy transfer in protein
Renormalization group method is applied to the study of vibrational energy
transfer in protein molecule. An effective Lagrangian and associated equations
of motion to describe the resonant energy transfer are analyzed in terms of the
first-order perturbative renormalization group theory that has been developed
as a unified tool for global asymptotic analysis. After the elimination of
singular terms associated with the Fermi resonance, amplitude equations to
describe the slow dynamics of vibrational energy transfer are derived, which
recover the result obtained by a technique developed in nonlinear optics [S.J.
Lade, Y.S. Kivshar, Phys. Lett. A 372 (2008) 1077].Comment: 11 page
Antimicrobial activity of Xylopia aethiopica, Aframomum melegueta and Piper guineense ethanolic extracts and the potential of using Xylopia aethiopica to preserve fresh orange juice
Antimicrobial activity of ethanolic extracts of Xylopia aethiopica, Aframomum melegueta and Piper guineense fruits were assayed against fourteen (14) microorganisms commonly associated with foodpoisoning and/or food spoilage. The microorganisms were Bacillus subtilis IAM1069, Bacillus cereus IFO 13494, Staphylococcus aureus FDA 209p, Escherichia coli NRIC 1023, Salmonella typhimurium IFO12529, Lactobacillus plantarum IAM 1041, Pediococcus acidilactici-M, Leuconostoc mesenteroides- M, Lactobacillus casei TISTR390, Saccharomyces cerevisiae OC-2, Hansenula anomala IFO 0140 (p), Pichia memb.IFO 0128, Penicillium funiclosum NBRC 6345 and Candida species. All the plant extracts exhibited selective antimicrobial activities on the test organisms. X. aethiopica extract exhibited the highest antimicrobial activity on the organisms with a minimum inhibitory concentration (MIC) of 50 ppm on Bacillus species and S. aureus. S. cerevisiae (MIC = 300 ppm), P. funiclosum NBRC 6345 and L. mesenteroides (MIC = 500 ppm) were also susceptible to X. aethiopica fruit extract but the MIC values for the other tested microorganisms were higher than 1000 ppm. This was followed by A. melegueta fruit extract with MIC of 100 ppm for B. cereus and S. aureus. Although P. guineense fruit extract inhibited the growth of B. cereus and S. aureus (MIC = 300 ppm); and B. subtilis (MIC = 1000), the MIC for the other microorganisms were higher than 5000 ppm. On the whole, all the plant extracts exhibited the least antimicrobial activities on Lactobacilli and fungi species. X. aethiopica fruit extract was used to preserve fresh orange juice. The ability of 100 and 1000 ppm extract to preserve the orange juice was significantly greater (p<0.05) than 50 ppm. The microbial concentration in orange juice containing 100 ppm of X. aethiopica extract was 4 cfu/mL after 28 days of storage at room temperature.Keywords: Food spoilage, food poisoning, microorganisms, spices, ethanolic extract, natural preservatives, orange juiceAfrican Journal of Biotechnology Vol. 12(16), pp. 1993-199
RF amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance
The radio-frequency (RF) voltage amplification property of a tunnel
magnetoresistance device driven by an RF external-magnetic-field-induced
ferromagnetic resonance was studied. The proposed device consists of a magnetic
tunnel junction (MTJ) and an electrically isolated coplanar waveguide. The
input RF voltage applied to the waveguide can excite the resonant dynamics in
the free layer magnetization, leading to the generation of an output RF voltage
under a DC bias current. The dependences of the RF voltage gain on the static
external magnetic field strength and angle were systematically investigated.
The design principles for the enhancement of the gain factor are also
discussed.Comment: 12 pages, 3 figure
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