395 research outputs found
Frequency Response Functions for Nonlinear Rational Models.
A recursive algorithm which maps a general class of nonlinear rational model, defined as the ratio of two polynomial functions, into the frequency domain is derived using the harmonic expansion method. The new algorithm provides, for the first time, a direct analytic map from the time domain rational model parameters to the higher order frequency response functions. Complex nonlinear time domain behaviours can be analysed and interpreted in the frequency domain and simulated examples are included to illustrate the concepts involved
High frequency variations of Helicobacter pylori isolates in individual hosts in a Chinese population
SummaryBackgroundColonization of individual hosts by multiple Helicobacter pylori genotypes may be one reason why this infection is persistent and difficult to eradicate.MethodsIn order to study the diversity of H. pylori in individuals, a modified randomly amplified polymorphic DNA (RAPD) method was applied using primary culture isolates instead of passaged cultures.ResultsThe results showed that variations in H. pylori were prevalent among individuals in the Chinese population, and the incidence of multiple colonization was 99.1% (115/116), significantly higher than in other reports. Moreover, the number of RAPD genotypes was found to be significantly associated with the process of disease development (p<0.05). Indeed, a trend for a higher number of RAPD genotypes within a single host (up to five genotypes) was observed as the disease developed or became more serious. After subculturing for three generations in our experiment, some genotypes present in the primary cultures were lost. The different genotypes in one patient may have originated from a single ancestral strain, as determined by analysis of six H. pylori housekeeping gene alleles, most of which were shown to be identical.ConclusionsThese results suggest that investigating isolates of the primary culture will better reflect the H. pylori diversity in individuals. Also, they indicate that continuous variation of one strain in the gastric microenvironment may be the main cause of H. pylori diversity in individuals in the Chinese population
X-Ray Diffuse Scattering Study on Ionic-Pair Displacement Correlations in Relaxor Lead Magnesium Niobate
Ionic-pair equal-time displacement correlations in relaxor lead magnesium
niobate, , have been investigated at room
temperature in terms of an x-ray diffuse scattering technique. Functions of the
distinct correlations have been determined quantitatively. The results show the
significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O,
and O-O' pairs. Their spatial distribution forms an ellipse or a sphere with
the radii of 30-80. This observation of local structure in the system
proves precursory presence of the polar microregions in the paraelectric state
which leads to the dielectric dispersion.Comment: 11 pages, 3 figure
The effect of substrate clamping on the paraelectric to antiferroelectric phase transition in Nd-doped BiFeO₃ thin films
Thin films were deposited on Pt/Ti/SiO₂/Si substrates using pulsed laser deposition from a target with a composition (Bi₀.₈₂₅Nd₀.₁₇₅Fe₀.₉₇Ti₀.₀₃O₃) with 5 mol% excess Bi₂O₃ within the antiferroelectric (AFE) region of the NdFeO₃-BiFeO₃ phase diagram. However, Raman spectroscopy and transmission electron microscopy (TEM) revealed that films consisted of a mosaic microstructure in which (AFE), ferroelectric (FE) and paraelectric (PE) phases coexisted. Variation in the spatial distribution of Nd is typically greater in bulk ceramics than in thin films and therefore, the absence of single phase AFE cannot be attributed to local changes in composition. Instead, it is proposed that clamping due to mismatch in thermal expansion coefficient with the substrate suppresses the large volume change associated with the PE-FE and PE-AFE transition in bulk and its absence in the thin film prevents an avalanche-like transition throughout grains, which in bulk sustains single phase AFE, irrespective of local deviations in the Nd concentration
Further Investigation on the Real Rate Effect of Dynamic Tensile Strength for Concrete-Like Materials
Scaling of anisotropy flows in intermediate energy heavy ion collisions
Anisotropic flows (, and ) of light nuclear clusters are
studied by a nucleonic transport model in intermediate energy heavy ion
collisions. The number-of-nucleon scalings of the directed flow () and
elliptic flow () are demonstrated for light nuclear clusters. Moreover,
the ratios of of nuclear clusters show a constant value of 1/2
regardless of the transverse momentum. The above phenomena can be understood by
the coalescence mechanism in nucleonic level and are worthy to be explored in
experiments.Comment: Invited talk at "IX International Conference on Nucleus-Nucleus
Collisions", Rio de Janeiro, Aug 28- Sept 1, 2006; to appear on the
proceeding issue in Nuclear Physics
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV
By analyzing the data sets of 17.3 pb taken at GeV
and 6.5 pb taken at GeV with the BESII detector at the
BEPC collider, we have measured the observed cross sections for 12 exclusive
light hadron final states produced in annihilation at the two energy
points. We have also set the upper limits on the observed cross sections and
the branching fractions for decay to these final states at 90%
C.L.Comment: 8 pages, 5 figur
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