Development of a portable precision landing system

A portable, tactical approach guidance (PTAG) system, based on a novel, X-band, precision approach concept, was developed and flight tested as a part of NASA's Rotorcraft All-Weather Operations Research Program. The system is based on state-of-the-art X-band technology and digital processing techniques. The PTAG airborne hardware consists of an X-band receiver and a small microprocessor installed in conjunction with the aircraft instrument landing system (ILS) receiver. The microprocessor analyzes the X-band, PTAG pulses and outputs ILS compatible localizer and glide slope signals. The ground stations are inexpensive, portable units, each weighing less than 85 lb, including battery, that can be quickly deployed at a landing site. Results from the flight test program show that PTAG has a significant potential for providing tactical aircraft with low cost, portable, precision instrument approach capability

Realistic Earth escape strategies for solar sailing

With growing interest in solar sailing comes the requirement to provide a basis for future detailed planetary escape mission analysis by drawing together prior work, clarifying and explaining previously anomalies. Previously unexplained seasonal variations in sail escape times from Earth orbit are explained analytically and corroborated within a numerical trajectory model. Blended-sail control algorithms, explicitly independent of time, which providenear-optimal escape trajectories and maintain a safe minimum altitude and which are suitable as a potential autonomous onboard controller, are then presented. These algorithms are investigated from a range of initial conditions and are shown to maintain the optimality previously demonstrated by the use of a single-energy gain control law but without the risk of planetary collision. Finally, it is shown that the minimum sail characteristic acceleration required for escape from a polar orbit without traversing the Earth shadow cone increases exponentially as initial altitude is decreased

Ground-state of two-dimensional finite electron systems in the Quantum Hall regime

We study electronic structures of quasi-two-dimensional finite electron systems in high magnetic fields. The solutions in the fractional quantum Hall regime are interpreted as quantum liquids of electrons and off-electron vortices. The ground states are classified according to the number of vortices inside the electron droplet. The theory predicts observable effects due to vortex formation in the chemical potentials and magnetization of electron droplets. We compare the transitions in the theory to those found in electron transport experiments on a quantum dot device and find significant correspondence.Comment: 4 pages, 4 figures (3 in colour), revised in response to referees' comments, to appear in Phys. Rev. let

The association between prior appendicectomy and/ or tonsillectomy in females and subsequent pregnancy rate: A cohort study

OBJECTIVE: To study pregnancy rates after appendectomy and/or tonsillectomy. DESIGN: Population-based cohort study using the United Kingdom (U.K.) primary health care–based Clinical Practice Research Datalink (CPRD). SETTING: Not applicable. PATIENT(S): Female patients who underwent appendectomy, tonsillectomy, or both from 1987 to 2012 and appropriate comparators. INTERVENTION(S): Timed follow-up until first pregnancy after surgery. The association between prior surgery and subsequent pregnancy was determined with the use of Cox regression models. MAIN OUTCOMES AND MEASURE(S): Pregnancy rate and time to first pregnancy after surgery. RESULT(S): The analyses included 54,675 appendectomy-only patients, 112,607 tonsillectomy-only patients, 10,340 patients who had both appendectomy and tonsillectomy, and 355,244 comparators matched for exact age and practice from the rest of female patients in the database. There were 29,732 (54.4%), 60,078 (53.4%), and 6,169 (59.7%) pregnancies in the appendectomy-only, tonsillectomy-only, and both appendectomy tonsillectomy cohorts, respectively versus 155,079 (43.7%) in the comparator cohort during a mean follow-up of 14.7 ± 9.7 years. Adjusted hazard ratios (HRs) for subsequent birth rates were 1.34 (95% confidence interval [CI] 1.32–1.35), 1.49 (95% CI 1.48–1.51), and 1.43 (95% CI 1.39–1.47), respectively. Time to pregnancy was shortest after both appendectomy and tonsillectomy followed by appendectomy only and then tonsillectomy only compared with the rest of the population. CONCLUSIONS(S): Appendectomy and/or tonsillectomy was associated with increased subsequent pregnancy rates and shorter time to pregnancy. The effect of the surgical procedures on the pregnancy outcome was cumulative

Development and flight test of a helicopter, X-band, portable precision landing system concept

A beacon landing system (BLS) is being developed and flight tested as a part of NASA's Rotorcraft All-Weather Operations Research Program. The system is based on state-of-of-the-art X-band radar technology and digital processing techniques. The bLS airborne hardware consists of an X-band receiver and a small micropreocessor, installed in conjunction wht the aircraft instrument landing system (ILS) receiver. The microprocessor analyzes the X-band, BLS pulses and outputs ILS-compatible localizer and glide slope signals. Range information is obtained using an on-board weather/mapping radar in conjunction with the BLS. The ground station is an inexpensive, portable unit; it weighs less than 70 lb and can be quickly deployed at a landing site. Results from the flight-test program show that the BLS has a significant potential for providing rotorcaraft with low-cost, precision instrument approach capability in remote areas

Magnetic Anisotropy in Quantum Hall Ferromagnets

We show that the sign of magnetic anisotropy energy in quantum Hall ferromagnets is determined by a competition between electrostatic and exchange energies. Easy-axis ferromagnets tend to occur when Landau levels whose states have similar spatial profiles cross. We report measurements of integer QHE evolution with magnetic-field tilt. Reentrant behavior observed for the $\nu = 4$ QHE at high tilt angles is attributed to easy-axis anisotropy. This interpretation is supported by a detailed calculation of the magnetic anisotropy energy.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let

Effective QCD Partition Function in Sectors with Non-Zero Topological Charge and Itzykson-Zuber Type Integral

It was conjectured by Jackson et.al. that the finite volume effective partition function of QCD with the topological charge $M-N$ coincides with the Itzyskon-Zuber type integral for $M\times N$ rectangular matrices. In the present article we give a proof of this conjecture, in which the original Itzykson-Zuber integral is utilized.Comment: 7pages, LaTeX2