11,209 research outputs found
Measurement of absorption with a p-u sound intensity probe in an impedance tube
An alternative method of measuring the normal-incidence sound absorption of a sample of material in an impedance tube is examined. The method is based on measurement of the sound pressure and the normal component of the particle velocity using a "p-u" sound intensity probe. This technique is compared with the traditional, well-established "transfer function method" based on two pressure microphones. The results suggest that the new method can be as accurate as the established method, but whereas the influence of transducer mismatch on the transfer function method can be eliminated using a simple "sensor-switching technique," the method based on a p-u intensity probe relies on accurate calibration of the probe
On the universality of compact polymers
Fully packed loop models on the square and the honeycomb lattice constitute
new classes of critical behaviour, distinct from those of the low-temperature
O(n) model. A simple symmetry argument suggests that such compact phases are
only possible when the underlying lattice is bipartite. Motivated by the hope
of identifying further compact universality classes we therefore study the
fully packed loop model on the square-octagon lattice. Surprisingly, this model
is only critical for loop weights n < 1.88, and its scaling limit coincides
with the dense phase of the O(n) model. For n=2 it is exactly equivalent to the
selfdual 9-state Potts model. These analytical predictions are confirmed by
numerical transfer matrix results. Our conclusions extend to a large class of
bipartite decorated lattices.Comment: 13 pages including 4 figure
Expression of an expansin carbohydrate-binding module affects xylem and phloem formation
Expansins are believed to be involved in disrupting the non-covalent adhesion of cellulose to matrix polysaccharides, thereby promoting wall creep. We have targeted a putative potato expansin (EXPA)carbohydrate-binding module (CBM) to the cell walls of tobacco plants. Histological examinations and electron microscopy indicated that 30% of the xylem cells of the transgenic stems with high expressionof the expansin CBM are wider (radial surface area) than those of the controls. Similarly, 37% of the xylem cells of the stems of the high expressers have thinner cell walls than those of the controls. Therewere no such phenotypes in the low and none expressers, as well as in the control plants. The transgenic tobacco plants expressing the potato expansin CBM did not exhibit marked change in plant morphology. Analysis of cellulose content in the stem cell walls was similar between the high expresser of the transgene and the control plants. Nonetheless, our results taken together demonstrate that expansin CBM alone can bring about changes in the plant cell walls
Finite average lengths in critical loop models
A relation between the average length of loops and their free energy is
obtained for a variety of O(n)-type models on two-dimensional lattices, by
extending to finite temperatures a calculation due to Kast. We show that the
(number) averaged loop length L stays finite for all non-zero fugacities n, and
in particular it does not diverge upon entering the critical regime n -> 2+.
Fully packed loop (FPL) models with n=2 seem to obey the simple relation L = 3
L_min, where L_min is the smallest loop length allowed by the underlying
lattice. We demonstrate this analytically for the FPL model on the honeycomb
lattice and for the 4-state Potts model on the square lattice, and based on
numerical estimates obtained from a transfer matrix method we conjecture that
this is also true for the two-flavour FPL model on the square lattice. We
present in addition numerical results for the average loop length on the three
critical branches (compact, dense and dilute) of the O(n) model on the
honeycomb lattice, and discuss the limit n -> 0. Contact is made with the
predictions for the distribution of loop lengths obtained by conformal
invariance methods.Comment: 20 pages of LaTeX including 3 figure
Inelastic Scattering in Metal-H2-Metal Junctions
We present first-principles calculations of the dI/dV characteristics of an
H2 molecule sandwiched between Au and Pt electrodes in the presence of
electron-phonon interactions. The conductance is found to decrease by a few
percentage at threshold voltages corresponding to the excitation energy of
longitudinal vibrations of the H2 molecule. In the case of Pt electrodes, the
transverse vibrations can mediate transport through otherwise non-transmitting
Pt -channels leading to an increase in the differential conductance even
though the hydrogen junction is characterized predominately by a single almost
fully open transport channel. In the case of Au, the transverse modes do not
affect the dI/dV because the Au d-states are too far below the Fermi level. A
simple explanation of the first-principles results is given using scattering
theory. Finally, we compare and discuss our results in relation to experimental
data.Comment: Accepted in Phys. Rev.
Taenia solium Cysticercosis, Irian Jaya, Indonesia
Centers for Disease Control and Prevention, Toni, Wandra ; Akira, Ito ; Hiroshi, Yamasaki ; Thomas, Suroso ; Sri S. Margono, Emerging Infectious Diseases, 9(7), 2003, 884-885.
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Bayesian Error Estimation in Density Functional Theory
We present a practical scheme for performing error estimates for Density
Functional Theory calculations. The approach which is based on ideas from
Bayesian statistics involves creating an ensemble of exchange-correlation
functionals by comparing with an experimental database of binding energies for
molecules and solids. Fluctuations within the ensemble can then be used to
estimate errors relative to experiment on calculated quantities like binding
energies, bond lengths, and vibrational frequencies. It is demonstrated that
the error bars on energy differences may vary by orders of magnitude for
different systems in good agreement with existing experience.Comment: 5 pages, 3 figure
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