165,242 research outputs found
The Cosmochemistry of Protostellar Matter
The different processes that can affect the chemical composition
of matter as it evolves from quiescent molecular clouds into
protostellar regions is discussed. Millimeter observations of
molecules at high angular resolution in cold, dark clouds such
as TMC-1 and L134N reveal large chemical gradients on scales
of a few tenths of a pc, which are not well understood.
Further, the abundances of the dominant oxygen- (H_2O, O_2,
O), and nitrogen-bearing (N_2, N) species are ill determined,
both observationally and theoretically, and little is known about
some important carbon-bearing molecules such as CH_4, CO_2 and
C_2H_2 . Observations of the distribution of molecular material in
disks surrounding newly-formed low-mass stars such as IRAS
16293 -2422 are just starting to become available, and reveal
a complex chemistry on scales of 500-10,000 AU. Remarkable
similarities are found with the chemistry observed in the highmass
star forming region Orion/KL, despite a factor of 1000
difference in stellar luminosity. A brief comparison with the
chemical composition comets is made
Local continuity laws on the phase space of Einstein equations with sources
Local continuity equations involving background fields and variantions of the
fields, are obtained for a restricted class of solutions of the
Einstein-Maxwell and Einstein-Weyl theories using a new approach based on the
concept of the adjoint of a differential operator. Such covariant conservation
laws are generated by means of decoupled equations and their adjoints in such a
way that the corresponding covariantly conserved currents possess some
gauge-invariant properties and are expressed in terms of Debye potentials.
These continuity laws lead to both a covariant description of bilinear forms on
the phase space and the existence of conserved quantities. Differences and
similarities with other approaches and extensions of our results are discussed.Comment: LaTeX, 13 page
Attitude determination and calibration using a recursive maximum likelihood-based adaptive Kalman filter
An adaptive Kalman filter design that utilizes recursive maximum likelihood parameter identification is discussed. At the center of this design is the Kalman filter itself, which has the responsibility for attitude determination. At the same time, the identification algorithm is continually identifying the system parameters. The approach is applicable to nonlinear, as well as linear systems. This adaptive Kalman filter design has much potential for real time implementation, especially considering the fast clock speeds, cache memory and internal RAM available today. The recursive maximum likelihood algorithm is discussed in detail, with special attention directed towards its unique matrix formulation. The procedure for using the algorithm is described along with comments on how this algorithm interacts with the Kalman filter
Active multilayer mirrors for reflectance tuning at extreme ultraviolet (EUV) wavelengths
We propose an active multilayer mirror structure for EUV wavelengths
which can be adjusted to compensate for reflectance changes. The multilayer structure tunes the reflectance via an integrated piezoelectric layer that can change its dimension due to an externally applied voltage. Here, we present design and optimization of the mirror structure for maximum reflectance tuning. In addition, we present preliminary results showing that the deposition of piezoelectric thin films with the requisite layer smoothness and crystal structure are possible. Finally, polarization switching of the smoothest piezoelectric film is presented
Formalization of the fundamental group in untyped set theory using auto2
We present a new framework for formalizing mathematics in untyped set theory
using auto2. Using this framework, we formalize in Isabelle/FOL the entire
chain of development from the axioms of set theory to the definition of the
fundamental group for an arbitrary topological space. The auto2 prover is used
as the sole automation tool, and enables succinct proof scripts throughout the
project.Comment: 17 pages, accepted for ITP 201
- …