71 research outputs found
Preliminary navigation accuracy analysis for the TDRSS Onboard Navigation System (TONS) experiment on EP/EUVE
A Tracking and Data Relay Satellite System (TDRSS) Onboard Navigation System (TONS) is currently being developed by NASA to provide a high accuracy autonomous navigation capability for users of TDRSS and its successor, the Advanced TDRSS (ATDRSS). The fully autonomous user onboard navigation system will support orbit determination, time determination, and frequency determination, based on observation of a continuously available, unscheduled navigation beacon signal. A TONS experiment will be performed in conjunction with the Explorer Platform (EP) Extreme Ultraviolet Explorer (EUVE) mission to flight quality TONS Block 1. An overview is presented of TONS and a preliminary analysis of the navigation accuracy anticipated for the TONS experiment. Descriptions of the TONS experiment and the associated navigation objectives, as well as a description of the onboard navigation algorithms, are provided. The accuracy of the selected algorithms is evaluated based on the processing of realistic simulated TDRSS one way forward link Doppler measurements. The analysis process is discussed and the associated navigation accuracy results are presented
Collisional stability of a three-component degenerate Fermi gas
We report on the creation of a degenerate Fermi gas consisting of a balanced
mixture of atoms in three different hyperfine states of Li. This new system
consists of three distinguishable Fermions with different and tunable
interparticle scattering lengths , and . We are able
to prepare samples containing atoms in each state at a
temperature of about nK, which corresponds to . We
investigated the collisional stability of the gas for magnetic fields between 0
and 600 G and found a prominent loss feature at 130 G. From lifetime
measurements we determined three-body loss coefficients, which vary over nearly
three orders of magnitude
Atom-Dimer Scattering in a Three-Component Fermi Gas
Ultracold gases of three distinguishable particles with large scattering
lengths are expected to show rich few-body physics related to the Efimov
effect. We have created three different mixtures of ultracold 6Li atoms and
weakly bound 6Li2 dimers consisting of atoms in three different hyperfine
states and studied their inelastic decay via atom-dimer collisions. We have
found resonant enhancement of the decay due to the crossing of Efimov-like
trimer states with the atom-dimer continuum in one mixture as well as minima of
the decay in another mixture, which we interpret as a suppression of exchange
reactions of the type |12>+|3> -> |23>+|1>. Such a suppression is caused by
interference between different decay paths and demonstrates the possiblity to
use Efimov physics to control the rate constants for molecular exchange
reactions in the ultracold regime.Comment: 5 pages, 3 figure
A Universal Trimer in a Three-Component Fermi Gas
We show that the recently measured magnetic field dependence of three-body
loss in a three-component mixture of ultracold Li atoms [1,2] can be
explained by the presence of a universal trimer state. Previous work suggested
a universal trimer state as a probable explanation, yet failed to get good
agreement between theory and experiment over the whole range of magnetic
fields. For our description we adapt the theory of Braaten and Hammer [3] for
three identical bosons to the case of three distinguishable fermions by
combining the three scattering lengths and between
the three components to an effective interaction parameter . We show that
taking into account a magnetic field variation of the lifetime of the trimer
state is essential to obtain a complete understanding of the observed decay
rates.Comment: 5 pages, 3 figure
Deterministic Preparation of a Tunable Few-Fermion System
Systems consisting of few interacting fermions are the building blocks of
matter with atoms and nuclei being the most prominent examples. We have created
an artificial few-body quantum system with complete control over the system's
quantum state using ultracold fermionic atoms in an optical dipole trap. We
deterministically prepare ground state systems consisting of one to ten
particles with fidelities of ~ 90%. We can tune the inter-particle interactions
to arbitrary values using a Feshbach resonance and have observed the
interaction-induced energy shift for a pair of repulsively interacting atoms.
With this work, quantum simulation of strongly correlated fewbody systems has
become possible. In addition, these microscopic quantum systems can be used as
building blocks for scalable quantum information processing.Comment: 8 pages, 6 figure
Density profiles and density oscillations of an interacting three-component normal Fermi gas
We use a semiclassical approximation to investigate density variations and
dipole oscillations of an interacting three-component normal Fermi gas in a
harmonic trap. We consider both attractive and repulsive interactions between
different pairs of fermions and study the effect of population imbalance on
densities. We find that the density profiles significantly deviate from those
of non-interacting profiles and extremely sensitive to interactions and
population imbalance. Unlike for a two-component Fermi system, we find density
imbalance even for balanced populations. For some range of parameters, one
component completely repels from the trap center giving rise a donut shape
density profile. Further, we find that the in-phase dipole oscillation
frequency is consistent with Kohn's theorem and other two dipole mode
frequencies are strongly effected by the interactions and the number of atoms
in the harmonic trap.Comment: Total seven pages with five figures. Published versio
Efimov Trimers near the Zero-crossing of a Feshbach Resonance
Near a Feshbach resonance, the two-body scattering length can assume any
value. When it approaches zero, the next-order term given by the effective
range is known to diverge. We consider the question of whether this divergence
(and the vanishing of the scattering length) is accompanied by an anomalous
solution of the three-boson Schr\"odinger equation similar to the one found at
infinite scattering length by Efimov. Within a simple zero-range model, we find
no such solutions, and conclude that higher-order terms do not support Efimov
physics.Comment: 8 pages, no figures, final versio
Nuclear Alpha-Particle Condensates
The -particle condensate in nuclei is a novel state described by a
product state of 's, all with their c.o.m. in the lowest 0S orbit. We
demonstrate that a typical -particle condensate is the Hoyle state
( MeV, state in C), which plays a crucial role for
the synthesis of C in the universe. The influence of antisymmentrization
in the Hoyle state on the bosonic character of the particle is
discussed in detail. It is shown to be weak. The bosonic aspects in the Hoyle
state, therefore, are predominant. It is conjectured that -particle
condensate states also exist in heavier nuclei, like O,
Ne, etc. For instance the state of O at MeV
is identified from a theoretical analysis as being a strong candidate of a
condensate. The calculated small width (34 keV) of ,
consistent with data, lends credit to the existence of heavier Hoyle-analogue
states. In non-self-conjugated nuclei such as B and C, we discuss
candidates for the product states of clusters, composed of 's,
triton's, and neutrons etc. The relationship of -particle condensation
in finite nuclei to quartetting in symmetric nuclear matter is investigated
with the help of an in-medium modified four-nucleon equation. A nonlinear order
parameter equation for quartet condensation is derived and solved for
particle condensation in infinite nuclear matter. The strong qualitative
difference with the pairing case is pointed out.Comment: 71 pages, 41 figures, review article, to be published in "Cluster in
Nuclei (Lecture Notes in Physics) - Vol.2 -", ed. by C. Beck,
(Springer-Verlag, Berlin, 2011
Image Mission Attitude Support Experiences
The spin-stabilized Imager for Magnetopause to Aurora Global Exploration (IMAGE) is the National Aeronautics and Space Administration's (NASA's) first Medium-class Explorer Mission (MIDEX). IMAGE was launched into a highly elliptical polar orbit on March 25, 2000 from Vandenberg Air Force Base, California, aboard a Boeing Delta II 7326 launch vehicle. This paper presents some of the observations of the flight dynamics analyses during the launch and in-orbit checkout period through May 18, 2000. Three new algorithms - one algebraic and two differential correction - for computing the parameters of the coning motion of a spacecraft are described and evaluated using in-flight data from the autonomous star tracker (AST) on IMAGE. Other attitude aspects highlighted include support for active damping consequent upon the failure of the passive nutation damper, performance evaluation of the AST, evaluation of the Sun sensor and magnetometer using AST data, and magnetometer calibration
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