Evaluation of LANDSAT-D Orbit Determination Using a Filter/Smoother (PREFER)

Simulated range and range rate data for five tracking stations were first generated using batch least squares orbit determination (GTDS). Then GTDS was used (in the differential correction mode) to produce a nominal trajectory which was input to PREFER. The GTDS differential correction (DC) run was made using models which differed from those used to produce the simulated data. These model differences were chosen to be fairly realistic approximations to the errors in the models actually used for operational orbit determination. Several different simulation runs were made with different types of model errors in order to determine the sensitivity to these errors. The nominal trajectory and the simulated measurement data were input to PREFER to produce a smoothed ephemeris file. Numerous runs of PREFER were made in which parameters describing the statistics of the model errors were varied. The likelihood function computed by the Kalman filter determined the ""best'' choice of input parameters. There was strong negative correlation between the likelihood function and the errors in the smoothed ephemeris

Pion Charge Exchange on Deuterium

We investigate quantum corrections to a classical intranuclear cascade simulation of pion single charge exchange on the deuteron. In order to separate various effects the orders of scattering need to be distinguished and, to that end, we develop signals for each order of scattering corresponding to quasi-free conditions. Quantum corrections are evaluated for double scattering and are found to be large. Global agreement with the data is good.Comment: 30 pages, 12 figure

Geomagnetic modeling by optimal recursive filtering

The results of a preliminary study to determine the feasibility of using Kalman filter techniques for geomagnetic field modeling are given. Specifically, five separate field models were computed using observatory annual means, satellite, survey and airborne data for the years 1950 to 1976. Each of the individual field models used approximately five years of data. These five models were combined using a recursive information filter (a Kalman filter written in terms of information matrices rather than covariance matrices.) The resulting estimate of the geomagnetic field and its secular variation was propogated four years past the data to the time of the MAGSAT data. The accuracy with which this field model matched the MAGSAT data was evaluated by comparisons with predictions from other pre-MAGSAT field models. The field estimate obtained by recursive estimation was found to be superior to all other models

Stable Kalman filters for processing clock measurement data

Kalman filters have been used for some time to process clock measurement data. Due to instabilities in the standard Kalman filter algorithms, the results have been unreliable and difficult to obtain. During the past several years, stable forms of the Kalman filter have been developed, implemented, and used in many diverse applications. These algorithms, while algebraically equivalent to the standard Kalman filter, exhibit excellent numerical properties. Two of these stable algorithms, the Upper triangular-Diagonal (UD) filter and the Square Root Information Filter (SRIF), have been implemented to replace the standard Kalman filter used to process data from the Deep Space Network (DSN) hydrogen maser clocks. The data are time offsets between the clocks in the DSN, the timescale at the National Institute of Standards and Technology (NIST), and two geographically intermediate clocks. The measurements are made by using the GPS navigation satellites in mutual view between clocks. The filter programs allow the user to easily modify the clock models, the GPS satellite dependent biases, and the random noise levels in order to compare different modeling assumptions. The results of this study show the usefulness of such software for processing clock data. The UD filter is indeed a stable, efficient, and flexible method for obtaining optimal estimates of clock offsets, offset rates, and drift rates. A brief overview of the UD filter is also given

User's Guide for the Precision Recursive Estimator for Ephemeris Refinement (PREFER)

PREFER is a recursive orbit determination program which is used to refine the ephemerides produced by a batch least squares program (e.g., GTDS). It is intended to be used primarily with GTDS and, thus, is compatible with some of the GTDS input/output files

Covariance analysis of the airborne laser ranging system

The requirements and limitations of employing an airborne laser ranging system for detecting crustal shifts of the Earth within centimeters over a region of approximately 200 by 400 km are presented. The system consists of an aircraft which flies over a grid of ground deployed retroreflectors, making six passes over the grid at two different altitudes. The retroreflector baseline errors are assumed to result from measurement noise, a priori errors on the aircraft and retroreflector positions, tropospheric refraction, and sensor biases

The 2008 HMDA data: the mortgage market during a turbulent year

The data that mortgage lending institutions reported for 2008 under the Home Mortgage Disclosure Act of 1975 (HMDA) reflect the ongoing difficulties in the housing and mortgage markets. This article presents a number of key findings from a review of the 2008 HMDA data. In particular, it documents a reduction in lending activity that was experienced by all groups of borrowers, highlights the Federal Housing Administration's greatly expanded role in the mortgage market, and examines how atypical changes in the interest rate environment affected the incidence of reported higher-priced lending in 2008 relative to earlier years.Mortgages ; Home Mortgage Disclosure Act

Estimation of Kalman filter model parameters from an ensemble of tests

A methodology for estimating initial mean and covariance parameters in a Kalman filter model from an ensemble of nonidentical tests is presented. In addition, the problem of estimating time constants and process noise levels is addressed. Practical problems such as developing and validating inertial instrument error models from laboratory test data or developing error models of individual phases of a test are generally considered

It's OK not to be OK: Shared Reflections from two PhD Parents in a Time of Pandemic

Adopting an intersectional feminist lens, we explore our identities as single and co‐parents thrust into the new reality of the UK COVID‐19 lockdown. As two PhD students, we present shared reflections on our intersectional and divergent experiences of parenting and our attempts to protect our work and families during a pandemic. We reflect on the social constructions of ‘masculinities’ and ‘emphasized femininities’ as complicated influence on our roles as parents. Finally, we highlight the importance of time and self‐care as ways of managing our shared realities during this uncertain period. Through sharing reflections, we became closer friends in mutual appreciation and solidarity as we learned about each other’s struggles and vulnerabilities

The Boltzmann factor, DNA melting, and Brownian ratchets: Topics in an introductory physics sequence for biology and premedical students

Three, interrelated biologically-relevant examples of biased random walks are presented: (1) A model for DNA melting, modelled as DNA unzipping, which provides a way to illustrate the role of the Boltzmann factor in a venue well-known to biology and pre-medical students; (2) the activity of helicase motor proteins in unzipping double-stranded DNA, for example, at the replication fork, which is an example of a Brownian ratchet; (3) force generation by actin polymerization, which is another Brownian ratchet, and for which the force and actin-concentration dependence of the velocity of actin polymerization is determined