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Time-frequency representation of earthquake accelerograms and inelastic structural response records using the adaptive chirplet decomposition and empirical mode decomposition
In this paper, the adaptive chirplet decomposition combined with the Wigner-Ville transform and the empirical mode decomposition combined with the Hilbert transform are employed to process various non-stationary signals (strong ground motions and structural responses). The efficacy of these two adaptive techniques for capturing the temporal evolution of the frequency content of specific seismic signals is assessed. In this respect, two near-field and two far-field seismic accelerograms are analyzed. Further, a similar analysis is performed for records pertaining to the response of a 20-story steel frame benchmark building excited by one of the four accelerograms scaled by appropriate factors to simulate undamaged and severely damaged conditions for the structure. It is shown that the derived joint time–frequency representations of the response time histories capture quite effectively the influence of non-linearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event; in this context, tracing the mean instantaneous frequency of records of critical structural responses is adopted.
The study suggests, overall, that the aforementioned techniques are quite viable tools for detecting and monitoring damage to constructed facilities exposed to seismic excitations
Baryon resonances from a novel fat-link fermion action
We present first results for masses of positive and negative parity excited
baryons in lattice QCD using an O(a^2) improved gluon action and a Fat Link
Irrelevant Clover (FLIC) fermion action in which only the irrelevant operators
are constructed with fat links. The results are in agreement with earlier
calculations of N^* resonances using improved actions and exhibit a clear mass
splitting between the nucleon and its chiral partner, even for the Wilson
fermion action. The results also indicate a splitting between the lowest J^P =
1/2^- states for the two standard nucleon interpolating fields.Comment: 5 pages, 3 figures, talk given by W.Melnitchouk at LHP 2001 workshop,
Cairns, Australi
Effect of pre-straining and bake hardening on the microstructure and mechanical properties of CMnSi trip steels
The effects of pre-straining and bake hardening on the mechanical behaviour and microstructural changes were studied in two CMnSi TRansformation-Induced Plasticity (TRIP) steels with different microstructures after intercritical annealing. The TRIP steels before and after pre-straining and bake hardening were characterised by X-ray diffraction, optical microscopy, transmission electron microscopy, three dimensional atom probe and tensile tests. Both steels exhibited discontinuous yielding behaviour and a significant strength increase with some reduction in ductility after pre-straining and bake hardening treatment. The following main microstructural changes are responsible for the observed mechanical behaviours: a decrease in the volume fraction of retained austenite, an increase in the dislocation density and the formation of cell substructure in the polygonal ferrite, higher localized dislocation density in the polygonal ferrite regions adjacent to martensite or retained austenite, and the precipitation of fine iron carbides in bainite and martensite. The mechanism for the observed yield point phenomenon in both steels after treatment was analysed.<br /
Gain reversal studies in photorefractive waveguides
We report on low-loss photorefractive BaTiO3 H+ implanted waveguides exhibiting reversal of two-beam-coupling gain direction, caused by induced colour centres. The anomalous two-beam-coupling gain has been investigated as a function of the input beam ratio
A Brief History, Status, and Perspective of Modified Oligonucleotides for Chemotherapeutic Applications
The advent of rapid and efficient methods of oligonucleotide synthesis has allowed the design of modified oligonucleotides that are complementary to specific nucleotide sequences in mRNA targets. Such modified oligonucleotides can be used to disrupt the flow of genetic information from transcribed mRNAs to proteins. This antisense strategy has been used to develop therapeutic oligonucleotides against cancer and various infectious diseases in humans. This overview reports recent advances in the application of oligonucleotides as drug candidates, describes the relationship between oligonucleotide modifications and their therapeutic profiles, and provides general guidelines for enhancing oligonucleotide drug properties.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143788/1/cpnc0401.pd
Plasticity and learning in a network of coupled phase oscillators
A generalized Kuramoto model of coupled phase oscillators with slowly varying
coupling matrix is studied. The dynamics of the coupling coefficients is driven
by the phase difference of pairs of oscillators in such a way that the coupling
strengthens for synchronized oscillators and weakens for non-synchronized
pairs. The system possesses a family of stable solutions corresponding to
synchronized clusters of different sizes. A particular cluster can be formed by
applying external driving at a given frequency to a group of oscillators. Once
established, the synchronized state is robust against noise and small
variations in natural frequencies. The phase differences between oscillators
within the synchronized cluster can be used for information storage and
retrieval.Comment: 10 page
Novel fat-link fermion actions
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link
clover fermion action in which only the irrelevant operators of the fermion
action are constructed using smeared links. The simulations are performed on a
16^3 X 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with
n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat Link
Irrelevant Clover (FLIC) action provides scaling which is superior to
mean-field improvement, and offers advantages over nonperturbative O(a)
improvement.Comment: 5 pages, 2 figures, talk given by J.Zanotti at LHP 2001 workshop,
Cairns, Australi
Resonant inelastic x-ray scattering (RIXS) spectra of magnesium diboride
Using the tight-binding linear muffin-tin orbitals method, the soft x-ray
fluorescence K-emission spectra of boron in MgB_2, excited close to the
absorption edge, are estimated. In the calculations the angle of incidence
between the direction of the incoming photon and the hexagonal axis of the
specimen is 60 degrees and 75 degrees. Comparison with experiment is possible
in the former case where good agreement is found. Furthermore, another resonant
feature below the Fermi energy is predicted for the larger angle. This feature
can be related to the excitations to the antibonding B pi-band in the
neighbourhood of the L-H line in the Brillouin zone.Comment: 4 pages with 4 figure
Far-infrared photo-conductivity of electrons in an array of nano-structured antidots
We present far-infrared (FIR) photo-conductivity measurements for a
two-dimensional electron gas in an array of nano-structured antidots. We
detect, resistively and spectrally resolved, both the magnetoplasmon and the
edge-magnetoplasmon modes. Temperature-dependent measurements demonstrates that
both modes contribute to the photo resistance by heating the electron gas via
resonant absorption of the FIR radiation. Influences of spin effect and phonon
bands on the collective excitations in the antidot lattice are observed.Comment: 5 pages, 3 figure
Nodal Quasiparticle Dispersion in Strongly Correlated d-wave Superconductors
We analyze the effects of a momentum-dependent self-energy on the
photoemission momentum distribution curve (MDC) lineshape, dispersion and
linewidth. We illustrate this general analysis by a detailed examination of
nodal quasiparticles in high Tc cuprates. We use variational results for the
nodal quasiparticle weight Z (which varies rapidly with hole doping x) and the
low energy Fermi velocity (which is independent of x), to show that
the high energy MDC dispersion , so that it is much
larger than the bare (band structure) velocity and also increases strongly with
underdoping. We also present arguments for why the low energy Fermi velocity
and the high energy dispersion are independent of the bare band structure at
small x. All of these results are in good agreement with earlier and recent
photoemission data [Zhou et al, Nature 423, 398 (2003)].Comment: 4 pages, 3 eps fig
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