3,176 research outputs found
Greater China and the twenty-first century
On the occasion of this meeting of Chinese comparatists, and as a conclusion of the fifth annual meeting of the American Association of Comparative Literature, I wish to offer some fin de siècle meditations and reminiscences along with some prospects, if not prophecies, about the future that awaits us in the twenty-first century
Lethal Mutagenesis in Viruses and Bacteria
Here we study how mutations which change physical properties of cell proteins
(stability) impact population survival and growth. In our model the genotype is
presented as a set of N numbers, folding free energies of cells N proteins.
Mutations occur upon replications so that stabilities of some proteins in
daughter cells differ from those in parent cell by random amounts drawn from
experimental distribution of mutational effects on protein stability. The
genotype-phenotype relationship posits that unstable proteins confer lethal
phenotype to a cell and in addition the cells fitness (duplication rate) is
proportional to the concentration of its folded proteins. Simulations reveal
that lethal mutagenesis occurs at mutation rates close to 7 mutations per
genome per replications for RNA viruses and about half of that for DNA based
organisms, in accord with earlier predictions from analytical theory and
experiment. This number appears somewhat dependent on the number of genes in
the organisms and natural death rate. Further, our model reproduces the
distribution of stabilities of natural proteins in excellent agreement with
experiment. Our model predicts that species with high mutation rates, tend to
have less stable proteins compared to species with low mutation rate
Intelligent manipulation technique for multi-branch robotic systems
New analytical development in kinematics planning is reported. The INtelligent KInematics Planner (INKIP) consists of the kinematics spline theory and the adaptive logic annealing process. Also, a novel framework of robot learning mechanism is introduced. The FUzzy LOgic Self Organized Neural Networks (FULOSONN) integrates fuzzy logic in commands, control, searching, and reasoning, the embedded expert system for nominal robotics knowledge implementation, and the self organized neural networks for the dynamic knowledge evolutionary process. Progress on the mechanical construction of SRA Advanced Robotic System (SRAARS) and the real time robot vision system is also reported. A decision was made to incorporate the Local Area Network (LAN) technology in the overall communication system
Synchrotron x-ray Studies of Superlattice Ordering in Pb(Mg1/3Nb2/3)O3 Single Crystals Doped with PbTiO3
The temperature dependence of the superlattice reflections: a) F spots and b)
alpha spots in a lead magnesium niobate (PMN) single crystals containing 0% and
6% of PbTiO3 (PT) has been studied using synchrotron x-ray scattering
techniques. (No superlattice reflections were found in PMN doped with 32% PT).
Analysis of the temperature dependence of the alpha spots suggests the
existence of the correlated anti-parallel atomic displacements that form
nanoregions different from the chemical nanodomains. While the correlation
length is temperature independent, the magnitude of these displacements
increases on cooling below the freezing temperature Tf. Intensities of the
alpha spots above this temperature become indistinguishable from the
background. Our results show that value of Tf for each composition is very
close to the one obtained from a Vogel-Fulcher fit to the frequency dependence
of the dielectric constant maximum Tm. The relation of these correlated
anti-ferrodistortive fluctuations to polar ferroelectric nanodomains and
relaxor behavior needs further study.Comment: 10 pages, 7 figures, Conference-Fundamental Physics of Ferroelectrics
200
Energetics of Protein-DNA Interactions
Protein-DNA interactions are vital for many processes in living cells,
especially transcriptional regulation and DNA modification. To further our
understanding of these important processes on the microscopic level, it is
necessary that theoretical models describe the macromolecular interaction
energetics accurately. While several methods have been proposed, there has not
been a careful comparison of how well the different methods are able to predict
biologically important quantities such as the correct DNA binding sequence,
total binding free energy, and free energy changes caused by DNA mutation. In
addition to carrying out the comparison, we present two important theoretical
models developed initially in protein folding that have not yet been tried on
protein-DNA interactions. In the process, we find that the results of these
knowledge-based potentials show a strong dependence on the interaction distance
and the derivation method. Finally, we present a knowledge-based potential that
gives comparable or superior results to the best of the other methods,
including the molecular mechanics force field AMBER99
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