The impact of celestial pole offset modelling on VLBI UT1 Intensive results

Very Long Baseline Interferometry (VLBI) Intensive sessions are scheduled to provide operational Universal Time (UT1) determinations with low latency. UT1 estimates obtained from these observations heavily depend on the model of the celestial pole motion used during data processing. However, even the most accurate precession-nutation model, IAU 2000/2006, is not accurate enough to realize the full potential of VLBI observations. To achieve the highest possible accuracy in UT1 estimates, a celestial pole offset (CPO), which is the difference between the actual and modelled precession-nutation angles, should be applied. Three CPO models are currently available for users. In this paper, these models have been tested and the differences between UT1 estimates obtained with those models are investigated. It has been shown that neglecting CPO modelling during VLBI UT1 Intensive processing causes systematic errors in UT1 series of up to 20 microarcseconds. It has been also found that using different CPO models causes the differences in UT1 estimates reaching 10 microarcseconds. Obtained results are applicable to the satellite data processing as well.Comment: 8 pp., accepted for publication in Journal of Geodes

Analysis of the Accuracy of Prediction of the Celestial Pole Motion

VLBI observations carried out by global networks provide the most accurate values of the precession-nutation angles determining the position of the celestial pole; as a rule, these results become available two to four weeks after the observations. Therefore, numerous applications, such as satellite navigation systems, operational determination of Universal Time, and space navigation, use predictions of the coordinates of the celestial pole. In connection with this, the accuracy of predictions of the precession- nutation angles based on observational data obtained over the last three years is analyzed for the first time, using three empiric nutation models---namely, those developed at the US Naval Observatory, the Paris Observatory, and the Pulkovo Observatory. This analysis shows that the last model has the best of accuracy in predicting the coordinates of the celestial pole. The rms error for a one-month prediction proposed by this model is below 100 microarcsecond.Comment: 13 p

The influence of Galactic aberration on precession parameters determined from VLBI observations

The influence of proper motions of sources due to Galactic aberration on precession models based on VLBI data is determined. Comparisons of the linear trends in the coordinates of the celestial pole obtained with and without taking into account Galactic aberration indicate that this effect can reach 20 $\mu$as per century, which is important for modern precession models. It is also shown that correcting for Galactic aberration influences the derived parameters of low-frequency nutation terms. It is therefore necessary to correct for Galactic aberration in the reduction of modern astrometric observations

Coherent States for Generalized Laguerre Functions

We explicitly construct a Hamiltonian whose exact eigenfunctions are the generalized Laguerre functions. Moreover, we present the related raising and lowering operators. We investigate the corresponding coherent states by adopting the Gazeau-Klauder approach, where resolution of unity and overlapping properties are examined. Coherent states are found to be similar to those found for a particle trapped in a P\"oschl-Teller potential of the trigonometric type. Some comparisons with Barut-Girardello and Klauder-Perelomov methods are noticed.Comment: 12 pages, clarifications and references added, misprints correcte

An Unconditional Exact Test For Small Samples Matched Binary Pairs

When investigators have N pairs of binary data, a common test for an increased rate of response is McNemar\u27s test. However, McNemar\u27s is an approximate, conditional test. An exact, unconditional test exists, but requires restrictive assumptions. Critical values and power tables are presented for an exact, unconditional test free of these assumptions

Extraterritorial Application of United States Commodity and Securities Laws to Market Transactions in an Age of Intercontinental Trading Links

The recently operational trading link between the Chicago Mercantile Exchange ( CME ) and the Singapore International Monetary Exchange ( SIMEX ) is one of the most significant developments to occur in the securities industry in recent memory. While the initial phase of this intermarket, intercontinental link involves only the trading of Eurodollar, Deutsche mark, and Japanese yen futures contracts, the prospects for the trading of additional contracts, and the further expansion of trading hours, ultimately to round-the-clock trading, appear favorable. The internationalization of both foreign and domestic futures markets is clearly the order of the day. A trading link connecting the futures exchanges of two separate nations, however, represents a new and truly experimental phenomenon, one which has prompted concern among regulators and members of the investment community inasmuch as the once abstract regulatory and jurisdictional issues raised by an international trading link have now presented themselves as realities for the first time

Extraterritorial Application of United States Commodity and Securities Laws to Market Transactions in an Age of Intercontinental Trading Links

The recently operational trading link between the Chicago Mercantile Exchange ( CME ) and the Singapore International Monetary Exchange ( SIMEX ) is one of the most significant developments to occur in the securities industry in recent memory. While the initial phase of this intermarket, intercontinental link involves only the trading of Eurodollar, Deutsche mark, and Japanese yen futures contracts, the prospects for the trading of additional contracts, and the further expansion of trading hours, ultimately to round-the-clock trading, appear favorable. The internationalization of both foreign and domestic futures markets is clearly the order of the day. A trading link connecting the futures exchanges of two separate nations, however, represents a new and truly experimental phenomenon, one which has prompted concern among regulators and members of the investment community inasmuch as the once abstract regulatory and jurisdictional issues raised by an international trading link have now presented themselves as realities for the first time

Supersymmetry and a Time-Dependent Landau System

A general technique is outlined for investigating supersymmetry properties of a charged spin-\half quantum particle in time-varying electromagnetic fields. The case of a time-varying uniform magnetic induction is examined and shown to provide a physical realization of a supersymmetric quantum-mechanical system. Group-theoretic methods are used to factorize the relevant Schr\"odinger equations and obtain eigensolutions. The supercoherent states for this system are constructed.Comment: 47 pages, submitted to Phys. Rev. A, LaTeX, IUHET 243 and LA-UR-93-20

Recognizing Graph Theoretic Properties with Polynomial Ideals

Many hard combinatorial problems can be modeled by a system of polynomial equations. N. Alon coined the term polynomial method to describe the use of nonlinear polynomials when solving combinatorial problems. We continue the exploration of the polynomial method and show how the algorithmic theory of polynomial ideals can be used to detect k-colorability, unique Hamiltonicity, and automorphism rigidity of graphs. Our techniques are diverse and involve Nullstellensatz certificates, linear algebra over finite fields, Groebner bases, toric algebra, convex programming, and real algebraic geometry.Comment: 20 pages, 3 figure