Real Space Visualization of Thermomagnetic Irreversibility within Supercooling and Superheating Spinodals in Mn1.85Co0.15SbMn_{1.85}Co_{0.15}Sb using Scanning Hall Probe Microscopy

Phase coexistence across disorder-broadened and magnetic-field-induced first order antiferromagnetic to ferrimagnetic transition in polycrystalline $Mn_{1.85}Co_{0.15}Sb$ has been studied mesoscopically by Scanning Hall Probe Microscope at 120K and up to 5 Tesla magnetic fields. We have observed hysteresis with varying magnetic field and the evolution of coexisting antiferromagnetic and ferrimagnetic state on mesoscopic length scale. These studies show that the magnetic state of the system at low field depends on the path followed to reach 120 K. The low field magnetic states are mesoscopically different for virgin and second field increasing cycle when 120 K is reached by warming from 5K, but are the same within measurement accuracy when the measuring temperature of 120K is reached from 300K by cooling

Interview with Arnold O. Beckman

Interview in two sessions, 1978, with Arnold O. Beckman--alumnus, faculty member, and trustee of Caltech and founder of Beckman Instruments (now Beckman Coulter, Inc.)--begins with his recollections of his early interest in chemistry. He attends University High School at Illinois State Normal University. Brief stint in the Marine Corps near end of World War I. After the war, he continues his education at the University of Illinois in Urbana, where he studies with C. S. Marvel, Gerhard Dietrichson, and Richard Chace Tolman. B.S. (chemical engineering) 1922, M.S. (physical chemistry) 1923. Follows Tolman to Caltech; does his graduate work with Roscoe Dickinson. Recollections of Arthur Amos Noyes and the Chemistry Division. Leaves Caltech in 1924 before receiving his PhD, works for Walter Shewhart at Bell Laboratories on West Street in Manhattan. Noyes prompts him to return to his graduate studies; he does so in the fall of 1926; joins Caltech faculty after receiving PhD in 1928. His consultant work and development of the pH meter. Development and production of the Helipot (helical potentiometer) and the quartz (Model DU) spectrophotometer. Establishes National Technical Laboratories while still a member of the Caltech faculty; leaves Caltech in 1939 to become its president (name changed to Beckman Instruments in 1950). Use of Helipots and spectrophotometers in World War II. In 1953, he returns to Caltech as a member of the Board of Trustees (chairman 1964-1974). Comments on Linus Pauling controversy; on changes in American work ethic prompting moving of plants overseas; on admission of women to Caltech. Founds Lincoln Club of Orange County, 1962. His interest in behavioral biology and creation of Caltech's Beckman Laboratories of Behavioral Biology. Recalls his involvement in air-pollution abatement in Los Angeles in the late 1940s and early 1950s and the work of Arie Haagen-Smit

The structure, energy, and electronic states of vacancies in Ge nanocrystals

The atomic structure, energy of formation, and electronic states of vacancies in H-passivated Ge nanocrystals are studied by density functional theory (DFT) methods. The competition between quantum self-purification and the free surface relaxations is investigated. The free surfaces of crystals smaller than 2 nm distort the Jahn-Teller relaxation and enhance the reconstruction bonds. This increases the energy splitting of the quantum states and reduces the energy of formation to as low as 1 eV per defect in the smallest nanocrystals. In crystals larger than 2 nm the observed symmetry of the Jahn-Teller distortion matches the symmetry expected for bulk Ge crystals. Near the nanocrystal's surface the vacancy is found to have an energy of formation no larger than 0.5 to 1.4 eV per defect, but a vacancy more than 0.7 nm inside the surface has an energy of formation that is the same as in bulk Ge. No evidence of the self-purification effect is observed; the dominant effect is the free surface relaxations, which allow for the enhanced reconstruction. From the evidence in this paper, it is predicted that for moderate sized Ge nanocrystals a vacancy inside the crystal will behave bulk-like and not interact strongly with the surface, except when it is within 0.7 nm of the surface.Comment: In Press at Phys. Rev.

Operational improvements of long-term predicted ephemerides of the Tracking and Data Relay Satellites (TDRSs)

Tracking and Data Relay Satellite (TDRS) orbit determination and prediction are supported by the Flight Dynamics Facility (FDF) of the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). TDRS System (TDRSS)-user satellites require predicted TDRS ephemerides that are up to 10 weeks in length. Previously, long-term ephemerides generated by the FDF included predictions from the White Sands Complex (WSC), which plans and executes TDRS maneuvers. TDRSs typically have monthly stationkeeping maneuvers, and predicted postmaneuver state vectors are received from WSC up to a month in advance. This paper presents the results of an analysis performed in the FDF to investigate more accurate and economical long-term ephemerides for the TDRSs. As a result of this analysis, two new methods for generating long-term TDRS ephemeris predictions have been implemented by the FDF. The Center-of-Box (COB) method models a TDRS as fixed at the center of its stationkeeping box. Using this method, long-term ephemeris updates are made semiannually instead of weekly. The impulse method is used to model more maneuvers. The impulse method yields better short-term accuracy than the COB method, especially for larger stationkeeping boxes. The accuracy of the impulse method depends primarily on the accuracy of maneuver date forecasting

Semicausal operations are semilocalizable

We prove a conjecture by DiVincenzo, which in the terminology of Preskill et al. [quant-ph/0102043] states that ``semicausal operations are semilocalizable''. That is, we show that any operation on the combined system of Alice and Bob, which does not allow Bob to send messages to Alice, can be represented as an operation by Alice, transmitting a quantum particle to Bob, and a local operation by Bob. The proof is based on the uniqueness of the Stinespring representation for a completely positive map. We sketch some of the problems in transferring these concepts to the context of relativistic quantum field theory.Comment: 4 pages, 1 figure, revte

Production and quality assurance automation in the Goddard Space Flight Center Flight Dynamics Facility

The Flight Dynamics Facility (FDF) at the NASA Goddard Space Flight Center (GSFC) generates numerous products for NASA-supported spacecraft, including the Tracking and Data Relay Satellites (TDRS's), the Hubble Space Telescope (HST), the Extreme Ultraviolet Explorer (EUVE), and the space shuttle. These products include orbit determination data, acquisition data, event scheduling data, and attitude data. In most cases, product generation involves repetitive execution of many programs. The increasing number of missions supported by the FDF has necessitated the use of automated systems to schedule, execute, and quality assure these products. This automation allows the delivery of accurate products in a timely and cost-efficient manner. To be effective, these systems must automate as many repetitive operations as possible and must be flexible enough to meet changing support requirements. The FDF Orbit Determination Task (ODT) has implemented several systems that automate product generation and quality assurance (QA). These systems include the Orbit Production Automation System (OPAS), the New Enhanced Operations Log (NEOLOG), and the Quality Assurance Automation Software (QA Tool). Implementation of these systems has resulted in a significant reduction in required manpower, elimination of shift work and most weekend support, and improved support quality, while incurring minimal development cost. This paper will present an overview of the concepts used and experiences gained from the implementation of these automation systems

The kinematics of the quadrupolar nebula M1-75 and the identification of its central star

The link between the shaping of bipolar planetary nebulae and their central stars is still poorly understood. The kinematics and shaping of the multipolar nebula M 1-75 are hereby investigated, and the location and nature of its central star are briefly discussed. Fabry-Perot data from GHaFAS on the WHT sampling the Doppler shift of the [N II] 658.3 nm line are used to study the dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model. Multi-wavelength images and spectra from the WFC and IDS on the INT, and from ACAM on the WHT, allowed us to constrain the parameters of the central star. The two pairs of lobes, angularly separated by ~22 degrees, were ejected simultaneously approx. ~3500-5000 years ago, at the adopted distance range from 3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point symmetry. The shaping of the nebula could be explained by wind interaction in a system consisting of a post-AGB star surrounded by a disc warped by radiative instabilities. This requires the system to be a close binary or a single star which engulfed a planet as it died. On the other hand, we present broad- and narrow-band images and a low S/N optical spectrum of the highly-reddened, previously unnoticed star which is likely the nebular progenitor. Its estimated V-I colour allows us to derive a rough estimate of the parameters and nature of the central star.Comment: 8 pages, 6 figures, accepted for publication in Astronomy & Astrophysic