Daily Earth rotation determinations from IRIS very long baseline interferometry
Classical optical determinations of Earth rotation (UT1) require several weeks of observations to achieve an accuracy of ∼1.5 ms of time, whereas modern techniques have demonstrated an accuracy of 0.7–0.9 ms on timescales of 1–5 days l,2. Here we have probed the limits of the accuracy and time resolution of very long baseline inteferometry (VLBI) determinations of UT1 by conducting a series of 1-h observing sessions using only one baseline. Comparison of the results from the 1-h sessions with corresponding determinations from 24-h multi-baseline sessions establishes that the accuracy of the 1-h determinations is close to 0.1 ms of time. These observations were scheduled as part of the project MERIT (monitor earth rotation and intercompare techniques of observation and analysis3) intensive observing campaign.
The Earth's Angular Momentum Budget on Subseasonal Time Scales
Irregular length of day (LOD) fluctuations on time scales of less than a few years are largely produced by atmospheric torques on the underlying planet. Significant coherence is found between the respective time series of LOD and atmospheric angular momentum (AAM) determinations at periods down to 8 days, with lack of coherence at shorter periods caused by the declining signal-to-measurement noise ratios of both data types. Refinements to the currently accepted model of tidal Earth rotation variations are required, incorporating in particular the nonequilibrium effect of the oceans. The remaining discrepancies between LOD and AAM in the 100- to 10-day period range may be due to either a common error in the AAM data sets from different meteorological centers, or another component of the angular momentum budget.
Nonsingular multidimensional cosmologies with Lobachevsky spatial sections
Examples of nonsingular cosmological models are presented on the basis of exact solutions to multidimensional gravity equations. These examples involve pure imaginary scalar fields, or, in other terms, “phantom” fields with an unusual sign of the kinetic term in the Lagrangian. We show that, with such fields, hyperbolic nonsingular models with a cosmological bounce (unlike spherical and spatially flat models) emerge without special relations among the integration constants, i.e., without fine tuning. In such models, the extra-dimension scale factors as well as scalar fields evolve smoothly between different finite asymptotic values. Examples of theories which create phantom scalar fields are obtained from string-inspired multidimensional field models and from theories of gravity in integrable Weyl space-times.