7,678 research outputs found
Dynamical mechanism of anticipating synchronization in excitable systems
We analyze the phenomenon of anticipating synchronization of two excitable
systems with unidirectional delayed coupling which are subject to the same
external forcing. We demonstrate for different paradigms of excitable system
that, due to the coupling, the excitability threshold for the slave system is
always lower than that for the master. As a consequence the two systems respond
to a common external forcing with different response times. This allows to
explain in a simple way the mechanism behind the phenomenon of anticipating
synchronization.Comment: 4 pages including 7 figures. Submitted for publicatio
16α,17α-Epoxy-5α-hydroxy-6β-nitrooxy-20-oxopregnan-3β-yl acetate
The title steroid, C23H33NO8, is a pregnane derivative obtained regio-, stereo- and chemoselectively from the ring opening of the corresponding 5α,6α;16α,17α-diepoxide with bismuth(III) nitrate. There are two symmetry-independent molecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. All rings are trans-fused. The conformations of the six-membered rings are close to chair forms, while the five-membered ring adopts an envelope conformation. The molecules are held together by an extensive O—H⋯O hydrogen-bonding network of chains runnning along the a axis
BiFeO3/La0.7Sr0.3MnO3 heterostructures deposited on Spark Plasma Sintered LaAlO3 Substrates
Multiferroic BiFeO3 (BFO) / La0.7Sr0.3MnO3 heterostructured thin films were
grown by pulsed laser deposition on polished spark plasma sintered LaAlO3 (LAO)
polycrystalline substrates. Both polycrystalline LAO substrates and BFO films
were locally characterized using electron backscattering diffraction (EBSD),
which confirmed the high-quality local epitaxial growth on each substrate
grain. Piezoforce microscopy was used to image and switch the piezo-domains,
and the results are consistent with the relative orientation of the
ferroelectric variants with the surface normal. This high-throughput synthesis
process opens the routes towards wide survey of electronic properties as a
function of crystalline orientation in complex oxide thin film synthesis.Comment: 10 pages, 4 figures, Submitted to Applied Physics Letter
6β-Acetamido-5α-hydroxycholestan-3β-yl acetate
The title steroid, C31H53NO4, was prepared from the corresponding 5α,6α-epoxycholestane. The conformation of the six-membered rings is close to a chair form, while the five-membered ring adopts a twist conformation. The hydroxyl and acetamide groups are in axial positions. The nucleophilic species bound to the steroid nucleus at position 6 by the β-face, whereas the hydroxyl group at position 5 has α-orientation. All rings are trans-fused. The crystal packing shows that the molecules related by twofold symmetry exist as O—H⋯O hydrogen-bonded dimers
Highlights of Natural Products in Prostate Cancer Drug Discovery
The remarkable impact of natural products (NPs) in the quest for new agents and new directions in medicinal discovery is well established. The exploration of Nature as a source of novel active agents that may serve as leads and scaffolds for drugs targeting a myriad of diseases and the use of synthetic organic chemistry to modify them have been a driving force for drug discovery. Worldwide, prostate cancer (PC) is the second leading cause of death after lung cancer on both USA and Australia, and the third after lung and colo-rectal cancers in Europe
Microanalysis Characterization of Bioactive Protein-Bound Polysaccharides Produced by Amanita Ponderosa Cultures
Different compounds of edible mushrooms are responsible for their bioactivity. The ability to
synthesize polysaccharides, namely protein–polysaccharide (PPS) complexes, is related to the antioxidant
capacity of these compounds and present great interest in preventing a number of diseases, including cancer,
cardiovascular and auto-immune diseases, and accelerated aging. Amanita ponderosa are wild edible mushrooms
that grow in Mediterranean “montado” areas [Portuguese name given to cork oak (Quercus suber) and holm oak
(Quercus ilex) forests]. The aim of this study was to evaluate the production of PPS complexes obtained from
A. ponderosa cultures using a new microanalytical approach to quickly and easily monitor the production process.
Microanalysis using Fourier-transform infrared using attenuated total reflection and Raman spectroscopy of PPS
samples showed spectra compatible with identification of this type of compound in culture extracts. PPS separated
by size-exclusion chromatography showed seven main complexes. Molecular weights of the main PPS complexes
isolated from cultures ranged between 1.5 and 20 kDa and did not present toxicity against Artemia salina,
demonstrating the potential of A. ponderosa as a source of biologically active compounds with nutraceutical value.
Application of this microanalytical approach to monitoring the production of PPS compounds can be successfully
applied in biotechnological processes
Non-Markovian Stochastic Resonance: three state model of ion channel gating
Stochastic Resonance in single voltage-dependent ion channels is investigated
within a three state non-Markovian modeling of the ion channel conformational
dynamics. In contrast to a two-state description one assumes the presence of an
additional closed state for the ion channel which mimics the manifold of
voltage-independent closed subconformations (inactivated ``state''). The
conformational transition into the open state occurs through a domain of
voltage-dependent closed subconformations (closed ``state''). At distinct
variance with a standard two-state or also three-state Markovian approach, the
inactivated state is characterized by a broad, non-exponential probability
distribution of corresponding residence times. The linear response to a
periodic voltage signal is determined for arbitrary distributions of the
channel's recovery times. Analytical results are obtained for the spectral
amplification of the applied signal and the corresponding signal-to-noise
ratio. Alternatively, these results are also derived by use of a corresponding
two-state non-Markovian theory which is based on driven integral renewal
equations [I. Goychuk and P. Hanggi, Phys. Rev. E 69, 021104 (2004)]. The
non-Markovian features of stochastic resonance are studied for a power law
distribution of the residence time-intervals in the inactivated state which
exhibits a large variance. A comparison with the case of bi-exponentially
distributed residence times possessing the same mean value, i.e. a simplest
non-Markovian two-state description, is also presented
Second order Raman spectroscopy of the wurtzite form of GaN
We report on Raman scattering by phonon pairs in GaN films grown on sapphire substrates by plasma‐enhanced molecular beam epitaxy. The first order data are consistent with results obtained from GaN bulk crystals of the wurtzite structure. The A1 and the much weaker E2 symmetry components of the second order scattering have been identified. Two‐phonon spectra are dominated by contributions due to longitudinal optical phonons. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70248/2/JAPIAU-77-11-6042-1.pd
- …