25,721 research outputs found
NOSS/ALDCS analysis and system requirements definition
The results of system analyses and implementation studies of an advanced location and data collection system (ALDCS) , proposed for inclusion on the National Oceanic Satellite System (NOSS) spacecraft are reported. The system applies Doppler processing and radiofrequency interferometer position location technqiues both alone and in combination. Aspects analyzed include: the constraints imposed by random access to the system by platforms, the RF link parameters, geometric concepts of position and velocity estimation by the two techniques considered, and the effects of electrical measurement errors, spacecraft attitude errors, and geometric parameters on estimation accuracy. Hardware techniques and trade-offs for interferometric phase measurement, ambiguity resolution and calibration are considered. A combined Doppler-interferometer ALDCS intended to fulfill the NOSS data validation and oceanic research support mission is also described
Analysis of Meteorological Satellite location and data collection system concepts
A satellite system that employs a spaceborne RF interferometer to determine the location and velocity of data collection platforms attached to meteorological balloons is proposed. This meteorological advanced location and data collection system (MALDCS) is intended to fly aboard a low polar orbiting satellite. The flight instrument configuration includes antennas supported on long deployable booms. The platform location and velocity estimation errors introduced by the dynamic and thermal behavior of the antenna booms and the effects of the presence of the booms on the performance of the spacecraft's attitude control system, and the control system design considerations critical to stable operations are examined. The physical parameters of the Astromast type of deployable boom were used in the dynamic and thermal boom analysis, and the TIROS N system was assumed for the attitude control analysis. Velocity estimation error versus boom length was determined. There was an optimum, minimum error, antenna separation distance. A description of the proposed MALDCS system and a discussion of ambiguity resolution are included
Birman-Schwinger and the number of Andreev states in BCS superconductors
The number of bound states due to inhomogeneities in a BCS superconductor is
usually established either by variational means or via exact solutions of
particularly simple, symmetric perturbations. Here we propose estimating the
number of sub-gap states using the Birman-Schwinger principle. We show how to
obtain upper bounds on the number of sub-gap states for small normal regions
and derive a suitable Cwikel-Lieb-Rozenblum inequality. We also estimate the
number of such states for large normal regions using high dimensional
generalizations of the Szego theorem. The method works equally well for local
inhomogeneities of the order parameter and for external potentials.Comment: Final version to appear in Phys Rev
Multiparticle Schrodinger operators with point interactions in the plane
We study a system of N bosons in the plane interacting with delta function
potentials. After a coupling constant renormalization we show that the
Hamiltonian defines a self-adjoint operator and obtain a lower bound for the
energy. The same results hold if one includes a regular inter-particle
potential.Comment: 17 pages, Late
Dipoles in Graphene Have Infinitely Many Bound States
We show that in graphene charge distributions with non-vanishing dipole
moment have infinitely many bound states. The corresponding eigenvalues
accumulate at the edges of the gap faster than any power
Adiabatically switched-on electrical bias in continuous systems, and the Landauer-Buttiker formula
Consider a three dimensional system which looks like a cross-connected pipe
system, i.e. a small sample coupled to a finite number of leads. We investigate
the current running through this system, in the linear response regime, when we
adiabatically turn on an electrical bias between leads. The main technical tool
is the use of a finite volume regularization, which allows us to define the
current coming out of a lead as the time derivative of its charge. We finally
prove that in virtually all physically interesting situations, the conductivity
tensor is given by a Landauer-B{\"u}ttiker type formula.Comment: 20 pages, submitte
Simplicity of extremal eigenvalues of the Klein-Gordon equation
We consider the spectral problem associated with the Klein-Gordon equation
for unbounded electric potentials. If the spectrum of this problem is contained
in two disjoint real intervals and the two inner boundary points are
eigenvalues, we show that these extremal eigenvalues are simple and possess
strictly positive eigenfunctions. Examples of electric potentials satisfying
these assumptions are given
Temporal Ordering in Quantum Mechanics
We examine the measurability of the temporal ordering of two events, as well
as event coincidences. In classical mechanics, a measurement of the
order-of-arrival of two particles is shown to be equivalent to a measurement
involving only one particle (in higher dimensions). In quantum mechanics, we
find that diffraction effects introduce a minimum inaccuracy to which the
temporal order-of-arrival can be determined unambiguously. The minimum
inaccuracy of the measurement is given by dt=1/E where E is the total kinetic
energy of the two particles. Similar restrictions apply to the case of
coincidence measurements. We show that these limitations are much weaker than
limitations on measuring the time-of-arrival of a particle to a fixed location.Comment: New section added, arguing that order-of-arrival can be measured more
accurately than time-of-arrival. To appear in Journal of Physics
Volatile metal deposits on lunar soils: Relation to volcanism
Parallel leaching and volatilization experiments conducted on lunar samples and similar experiments on sphalerite do not supply the information needed to resolve the question of the chemical nature of pb 204, Zn, Bi and Tl deposits on lunar soil surfaces. It is proposed that in Apollo 17 mare and terra soils and fractions of pb 204, Zn and Tl that are insoluble under mild, hot pH 5HNO3, leaching conditions and involatile at 600 C were originally surface deposits which became immobilized by migration into the silicate substrate or by chemisorption. Only Bi is predominantly indigenous. The implication is also that the soils over their respective times of evolution were exposed to heavy metal vapors or that an episodic exposure occurred after they had evolved. A sequence of events is proposed to account for orange 74220 and black 74001 glasses by lava fountaining and for soil 74241 as tephra from an explosive volcanic eruption
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