Inter-frequency Bias Estimation for the GPS Monitor Station Network

The inter-frequency bias (IFB) is present in all dual frequency combinations of GPS pseudorange and carrier phase observables. It is caused by the path dependent signal delays in both the satellite and receiver. That delay can be directly measured for a space vehicle prior to launch, or for a ground based receiver prior to its being used in the field. However the bias is known to drift, and monitoring the delay estimate by direct measurement is time consuming for ground based receivers and impossible for deployed space vehicles. Hansen (2002) examined the observability of IFB through a global model of ionosphere total electron content (TEC). Variation in the receiver portion of the IFB can also be observed in receivers with antennae in a zero-baseline configuration. This is referred to as an inter-receiver bias (IRB). In this study a Kalman filter is formulated to observe IFBs and IRBs. Process noise is used to allow the filter to track changes in the IFBs and IRBs. The filter also implements constraints to reflect the fact that a given IRB is not linearly independent of the IFBs. Because the receivers are distributed on a global scale, the Kalman filter requires a globally observable phenomenon by which to tie the IFBs. In this case ionosphere delay provides such a phenomenon. The filter was applied to observations collected by GPS monitor stations that comprise the National Geospatial- Intelligence Agency Monitor Station Network (MSN). Each monitor station contains two geodetic quality receivers in a zero-baseline configuration and continuously collects GPS observations. The GPS observations collected by this network are used to produce both precise ephemeris and the broadcast ephemeris. GPS observations made through the network are incorporated into the GPS Master Control Station (MCS) Kalman filter of the Operational Control System (OCS) (Wiley, 2006). The Kalman filter in the OCS estimates the orbital parameters that are transmitted via the navigation message. If estimated effectively, knowledge of the receiver portion of the IFB can aid in achieving better ionosphere models. IFBs are made observable using a global ionosphere delay model. A ninth order spherical harmonic model derived by Y.C. Chao (1997) was used in this study for ionosphere delay. Chao used this spherical harmonic model to capture ionospheric variations that occurred over a smaller global region in his IFB estimation process. In this study a similar model was used but was verified using observations that span a global coverage. The receiver portion of the IFB is observed precisely using the IRB. In this study error terms were introduced into the Kalman filter design to realign the IRB estimates to the IFB estimates produced for each of the two receivers in a zero baseline configuration. For a nominal epoch of measurement, there were 198 noisy measurements used each epoch to generate twelve monitor station specific IRBs. The IRB estimates showed small, decimeter level dynamic variation over the period of a day. The quality of the IFB estimate directly affects the quality of the ionospheric model formed during the estimation process. Results verify that the filter is operating properly. The ionosphere model, though simple, demonstrates that the total electron content (TEC) peaks during local noon and is at a minimum during local night. IRB estimates are roughly constant over time and have a magnitude of less than 2.5 meters. Similar estimates are formed for the IFBs, however when processing one day of observations, the IFB estimates are less stable than those of the IRBs. Future effort will involve tuning the filter, and establishing criteria for its convergence

Accurate measurement of residual dipolar couplings in anisotropic phase

The determination of residual dipolar couplings (RDCs) by quantitative J spectroscopy methods such as Heteronuclear Single Quantum Correlation with Phase Encoded Coupling (HSQC-PEC) is prone to systematic errors that may be caused by differential attenuation during the conversion of orthogonal density operator components into observable terms. The attenuation may be caused by miscalibration of radio-frequency pulses and by relaxation effects. A simple method is presented that allows one to remove most of these systematic errors without losses in sensitivity or resolutio

Spin Dynamics of the LAGEOS Satellite in Support of a Measurement of the Earth's Gravitomagnetism

LAGEOS is an accurately-tracked, dense spherical satellite covered with 426 retroreflectors. The tracking accuracy is such as to yield a medium term (years to decades) inertial reference frame determined via relatively inexpensive observations. This frame is used as an adjunct to the more difficult and data intensive VLBI absolute frame measurements. There is a substantial secular precession of the satellite's line of nodes consistent with the classical, Newtonian precession due to the non-sphericity of the earth. Ciufolini has suggested the launch of an identical satellite (LAGEOS-3) into an orbit supplementary to that of LAGEOS-1: LAGEOS-3 would then experience an equal and opposite classical precession to that of LAGEOS-1. Besides providing a more accurate real-time measurement of the earth's length of day and polar wobble, this paired-satellite experiment would provide the first direct measurement of the general relativistic frame-dragging effect. Of the five dominant error sources in this experiment, the largest one involves surface forces on the satellite, and their consequent impact on the orbital nodal precession. The surface forces are a function of the spin dynamics of the satellite. Consequently, we undertake here a theoretical effort to model the spin ndynamics of LAGEOS. In this paper we present our preliminary results.Comment: 16 pages, RevTeX, LA-UR-94-1289. (Part I of II, postscript figures in Part II

Scimitar Cat (Homotherium serum Cope) from Southwestern Alberta, Canada

Skull and tooth fragments of Homotherium serum recently recovered from the Wallyâ s Beach site (DhPg-8) in southwestern Alberta provide the first indications that scimitar cat populated the area of the St. Mary Reservoir. AMS radiocarbon dating provides a 2 sigma range calibrated age of Cal BP 12 715 to 12 655. This is the fourth known occurrence of the species in Canada, the first outside of Yukon, and is currently the youngest precisely dated occurrence of the species in North America. Well-preserved dentition combined with the temporal and geographic context allows the sample to be identified as Homotherium serum. The specimen is significant as it represents an extension of the geographic and chronological range of the species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Calix[4]arenes Linked to Multiple Bidentate N-Donors: Potential Ligands for Synthetic Modeling of Multinuclear Metalloenzymes

A series of calix[4]arenes incorporating three or four bidentate diamines or pyridylamines attached at the “upper rim” were synthesized via practical protocols. Proof of structure was obtained in one instance by X-ray crystallography. These molecules are designed for general use as ligands for the preparation of multinuclear active site models of metalloenzymes

Design parameters for the bistable mechanism prototypes.

<p>Design parameters for the bistable mechanism prototypes.</p

Overlay of the PRBM on the bistable mechanism.

<p>Overlay of the PRBM on the bistable mechanism.</p