37,887 research outputs found
What can earth tide measurements tell us about ocean tides or earth structure?
Current experimental problems in Earth tides are reviewed using comparisons of tidal gravity and tilt measurements in Europe with loading calculations are examples. The limitations of present day instrumentation and installation techniques are shown as well as some of the ways in which they can be improved. Many of the geophysical and oceanographic investigations that are possible with Earth tide measurements are discussed with emphasis on the percentage accuracies required in the measurements in order to obtain new information about Earth or its oceans
Aircraft and satellite measurement of ocean wave directional spectra using scanning-beam microwave radars
A microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described. The technique, which employs short-pulse, noncoherent radars in a conical scan mode near vertical incidence, is shown to be suitable for both aircraft and satellite application, the technique was validated at 10 km aircraft altitude, where we have found excellent agreement between buoy and radar-inferred absolute wave height spectra
Radiocarbon dates from the Oxford AMS system: archaeometry datelist 35
This is the 35th list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst some of the sites included here are the latest series of determinations from the key sites of Abydos, El Mirón, Ban Chiang, Grotte de Pigeons (Taforalt), Alepotrypa and Oberkassel, as well as others dating to the Palaeolithic, Mesolithic and later periods. Comments on the significance of the results are provided by the submitters of the material
On a generalization of Jacobi's elliptic functions and the Double Sine-Gordon kink chain
A generalization of Jacobi's elliptic functions is introduced as inversions
of hyperelliptic integrals. We discuss the special properties of these
functions, present addition theorems and give a list of indefinite integrals.
As a physical application we show that periodic kink solutions (kink chains) of
the double sine-Gordon model can be described in a canonical form in terms of
generalized Jacobi functions.Comment: 18 pages, 9 figures, 3 table
Elasticity Theory and Shape Transitions of Viral Shells
Recently, continuum elasticity theory has been applied to explain the shape
transition of icosahedral viral capsids - single-protein-thick crystalline
shells - from spherical to buckled/faceted as their radius increases through a
critical value determined by the competition between stretching and bending
energies of a closed 2D elastic network. In the present work we generalize this
approach to capsids with non-icosahedral symmetries, e.g., spherocylindrical
and conical shells. One key new physical ingredient is the role played by
nonzero spontaneous curvature. Another is associated with the special way in
which the energy of the twelve topologically-required five-fold sites depends
on the background local curvature of the shell in which they are embedded.
Systematic evaluation of these contributions leads to a shape phase diagram in
which transitions are observed from icosahedral to spherocylindrical capsids as
a function of the ratio of stretching to bending energies and of the
spontaneous curvature of the 2D protein network. We find that the transition
from icosahedral to spherocylindrical symmetry is continuous or weakly
first-order near the onset of buckling, leading to extensive shape degeneracy.
These results are discussed in the context of experimentally observed
variations in the shapes of a variety of viral capsids.Comment: 53 pages, 17 figure
X-Ray Microanalysis of Ca and K in Corn Bran and Oat Hulls
Oat hulls and dry-milled corn bran were loaded with calcium or potassium and made into either sectioned bulk specimens of intact tissue embedded in resin or into non-sectioned bulk specimens made from powdered-compressed tissue formed into disks without resin. Regression lines of X-ray count versus mineral concentration were similar for both Ca and K. X-ray count versus mineral concentration relationships were similar for intact oat hulls and powdered-compressed specimens of either oat hulls or corn bran. However, the relationship for intact corn bran embedded in resin was significantly different. While the reason for this difference is not known, the result emphasizes the importance of using a proper calibration matrix to relate mineral concentration in biological material with X-ray count values. The standard error in slope of the regression lines, 0.07 and 0.08 for corn bran and oat hull, respectively, embedded in aged epoxy resin suggest that X-ray counts from these specimens allow one to estimate Ca or K concentration with a standard deviation of ± 10%. X-ray counts of Ca, K, and Cl in specimens embedded in epoxy resin decreased to stable values approximately four weeks after the resin was cured
Anomalous temperature evolution of the internal magnetic field distribution in the charge-ordered triangular antiferromagnet AgNiO2
Zero-field muon-spin relaxation measurements of the frustrated triangular
quantum magnet AgNiO2 are consistent with a model of charge disproportionation
that has been advanced to explain the structural and magnetic properties of
this compound. Below an ordering temperature of T_N=19.9(2) K we observe six
distinct muon precession frequencies, due to the magnetic order, which can be
accounted for with a model describing the probable muon sites. The precession
frequencies show an unusual temperature evolution which is suggestive of the
separate evolution of two opposing magnetic sublattices.Comment: 4 pages, 3 figure
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