773 research outputs found
Family Versus Public Solidarity: Theory and Experiment
We present an overlapping generations model with two families who can guarantee old age support either by intra-family transfers from child to parent or via a tax-financed public pension system encompassing both families.We derive the individually and family-specific optimal decisions and present some more behavioristic hypotheses.Our experimental observations allow conclusions on (1) whether raising taxes crowds out voluntary transfers, (2) how income distributions influence family and public solidarity, and (3) whether participants prefer more to less public solidarity.voting;pensions;families;overlapping generations
Family Versus Public Solidarity:Theory and Experiment
We present an overlapping generations model with two families who can guarantee old age support either by intra-family transfers from child to parent or via a tax-financed public pension system encompassing both families.We derive the individually and family-specific optimal decisions and present some more behavioristic hypotheses.Our experimental observations allow conclusions on (1) whether raising taxes crowds out voluntary transfers, (2) how income distributions influence family and public solidarity, and (3) whether participants prefer more to less public solidarity.
Design and implementation of sparse aperture imaging systems
In order to better understand the technological difficulties involved in designing and building a sparse aperture array, the challenge of building a white light Golay-3 telescope was undertaken. The MIT Adaptive Reconnaissance Golay-3 Optical Satellite (ARGOS) project exploits wide-angle Fizeau interferometer technology with an emphasis on modularity in the optics and spacecraft subsystems. Unique design procedures encompassing the nature of coherent wavefront sensing, control and combining as well as various system engineering aspects to achieve cost effectiveness, are developed. To demonstrate a complete spacecraft in a 1-g environment, the ARGOS system is mounted on a frictionless air-bearing, and has the ability to track fast orbiting satellites like the ISS or the planets. Wavefront sensing techniques are explored to mitigate initial misalignment and to feed back real-time aberrations into the optical control loop. This paper presents the results and the lessons learned from the conceive, design and implementation phases of ARGOS. A preliminary assess-ment shows that the beam combining problem is the most challenging aspect of sparse optical arrays. The need for optical control is paramount due to tight beam combining tolerances. The wavefront sensing/control requirements appear to be a major technology and cost driver
The Molecular Line Opacity of MgH in Cool Stellar Atmospheres
A new, complete, theoretical rotational and vibrational line list for the A-X
electronic transition in MgH is presented. The list includes transition
energies and oscillator strengths for all possible allowed transitions and was
computed using the best available theoretical potential energies and dipole
transition moment function with the former adjusted to account for experimental
data. The A-X line list, as well as new line lists for the B'-X and the X-X
(pure rovibrational) transitions, were included in comprehensive stellar
atmosphere models for M, L, and T dwarfs and solar-type stars. The resulting
spectra, when compared to models lacking MgH, show that MgH provides
significant opacity in the visible between 4400 and 5600 Angstrom. Further,
comparison of the spectra obtained with the current line list to spectra
obtained using the line list constructed by Kurucz (1993) show that the Kurucz
list significantly overestimates the opacity due to MgH particularly for the
bands near 5150 and 4800 Angstrom with the discrepancy increasing with
decreasing effective temperature.Comment: 10 pages, 4 figures, 3 table
ARGOS testbed: study of multidisciplinary challenges of future spaceborne interferometric arrays
Future spaceborne interferometric arrays must meet stringent optical performance and tolerance requirements while exhibiting modularity and acceptable manufacture and integration cost levels. The Massachusetts Institute of Technology (MIT) Adaptive Reconnaissance Golay-3 Optical Satellite (ARGOS) is a wide-angle Fizeau interferometer spacecraft testbed designed to address these research challenges. Designing a space-based stellar interferometer, which requires tight tolerances on pointing and alignment for its apertures, presents unique multidisciplinary challenges in the areas of structural dynamics, controls, and multiaperture phasing active optics. In meeting these challenges, emphasis is placed on modularity in spacecraft subsystems and optics as a means of enabling expandability and upgradeability. A rigorous theory of beam-combining errors for sparse optical arrays is derived and flown down to the design of various subsystems. A detailed elaboration on the optics system and control system is presented based on the performance requirements and beam-combining error tolerances. The space environment is simulated by floating ARGOS on a frictionless air-bearing that enables it to track both fast and slow moving targets
A Framework for Orbital Performance Evaluation in Distributed Space Missions for Earth Observation
Distributed Space Missions (DSMs) are gaining momentum in their application to earth science missions owing to their unique ability to increase observation sampling in spatial, spectral and temporal dimensions simultaneously. DSM architectures have a large number of design variables and since they are expected to increase mission flexibility, scalability, evolvability and robustness, their design is a complex problem with many variables and objectives affecting performance. There are very few open-access tools available to explore the tradespace of variables which allow performance assessment and are easy to plug into science goals, and therefore select the most optimal design. This paper presents a software tool developed on the MATLAB engine interfacing with STK, for DSM orbit design and selection. It is capable of generating thousands of homogeneous constellation or formation flight architectures based on pre-defined design variable ranges and sizing those architectures in terms of predefined performance metrics. The metrics can be input into observing system simulation experiments, as available from the science teams, allowing dynamic coupling of science and engineering designs. Design variables include but are not restricted to constellation type, formation flight type, FOV of instrument, altitude and inclination of chief orbits, differential orbital elements, leader satellites, latitudes or regions of interest, planes and satellite numbers. Intermediate performance metrics include angular coverage, number of accesses, revisit coverage, access deterioration over time at every point of the Earth's grid. The orbit design process can be streamlined and variables more bounded along the way, owing to the availability of low fidelity and low complexity models such as corrected HCW equations up to high precision STK models with J2 and drag. The tool can thus help any scientist or program manager select pre-Phase A, Pareto optimal DSM designs for a variety of science goals without having to delve into the details of the engineering design process
ΠΠ΅ΡΠΎΠ΄ΠΈΠΊΠ° Π»ΠΎΠΊΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΠΈΠ·ΠΎΠ±ΡΠ°ΠΆΠ΅Π½ΠΈΡ Π»ΠΈΡΠ° Π΄Π»Ρ ΡΠΈΡΡΠ΅ΠΌ Π²ΠΈΠ΄Π΅ΠΎΠΊΠΎΠ½ΡΡΠΎΠ»Ρ Π½Π° ΠΎΡΠ½ΠΎΠ²Π΅ Π½Π΅ΠΉΡΠΎΠ½Π½ΠΎΠΉ ΡΠ΅ΡΠΈ
ΠΡΠ΅Π΄Π»Π°Π³Π°Π΅ΡΡΡ ΠΌΠ΅ΡΠΎΠ΄ ΠΈ Π°Π»Π³ΠΎΡΠΈΡΠΌ Π»ΠΎΠΊΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ Π»ΠΈΡΠ° ΡΠ΅Π»ΠΎΠ²Π΅ΠΊΠ° Π΄Π»Ρ Π°Π²ΡΠΎΠΌΠ°ΡΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Π½ΡΡ
ΡΠΈΡΡΠ΅ΠΌ ΡΠ°ΡΠΏΠΎΠ·Π½Π°Π²Π°Π½ΠΈΡ ΠΈ Π²ΠΈΠ΄Π΅ΠΎΠΊΠΎΠ½ΡΡΠΎΠ»Ρ Π½Π° Π±Π°Π·Π΅ ΡΠ²Π΅ΡΡΠΎΡΠ½ΡΡ
Π½Π΅ΠΉΡΠΎΠ½Π½ΡΡ
ΡΠ΅ΡΠ΅ΠΉ. ΠΡΠ΅ΠΈΠΌΡΡΠ΅ΡΡΠ²ΠΎ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ ΡΠ²ΡΡΡΠΎΡΠ½ΡΡ
Π½Π΅ΠΉΡΠΎΠ½Π½ΡΡ
ΡΠ΅ΡΠ΅ΠΉ Π² ΡΠΎΠΌ, ΡΡΠΎ ΠΎΠ½ΠΈ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΠ²Π°ΡΡ ΡΡΡΠΎΠΉΡΠΈΠ²ΠΎΡΡΡ ΠΊ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡΠΌ ΠΌΠ°ΡΡΡΠ°Π±Π°, ΡΠΌΠ΅ΡΠ΅Π½ΠΈΡΠΌ, ΠΏΠΎΠ²ΠΎΡΠΎΡΠ°ΠΌ, ΡΠΌΠ΅Π½Π΅ ΡΠ°ΠΊΡΡΡΠ° ΠΈ Π΄ΡΡΠ³ΠΈΠΌ ΠΈΡΠΊΠ°ΠΆΠ΅Π½ΠΈΡΠΌ Π²Ρ
ΠΎΠ΄Π½ΠΎΠ³ΠΎ ΠΈΠ·ΠΎΠ±ΡΠ°ΠΆΠ΅Π½ΠΈΡ. ΠΠ±ΠΎΡΠ½ΠΎΠ²ΡΠ²Π°Π΅ΡΡΡ ΡΠΎΠΏΠΎΠ»ΠΎΠ³ΠΈΡ ΠΈΡΠΏΠΎΠ»ΡΠ·ΡΠ΅ΠΌΠΎΠΉ Π½Π΅ΠΉΡΠΎΠ½Π½ΠΎΠΉ ΡΠ΅ΡΠΈ ΠΈ ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠ° Π΅Π΅ ΠΎΠ±ΡΡΠ΅Π½ΠΈΡ
The Molecular Continuum Opacity of MgH in Cool Stellar Atmospheres
The opacity due to photodissociation of 24MgH is investigated in the
atmospheres of cool stars. The lowest two electronic transitions A 2Pi -- X
2Sigma+ and B' 2Sigma+ -- X 2 Sigma+ are considered where the cross sections
for the latter were published previously (Weck, Stancil, & Kirby 2002) while
the former are presented in this work. Model atmospheres calculated with the
PHOENIX code are used to investigate the effect of the photodissociation
opacity on spectra of cool stars. The A -- X photodissociation cross sections
are obtained using a combination of ab initio and experimentally derived
potential curves and dipole transition moments. Partial cross sections have
been evaluated over the accessible wavelength range 1770-4560 Angstrom for all
rotational transitions from the vibrational levels v''=0-11. Assuming a
Boltzmann distribution of the rovibrational levels of the X 2Sigma+ state, LTE
photodissociation cross sections are presented for temperatures between 1000
and 5000 K. Shape resonances, arising from rotational predissociation of
quasi-bound levels of the A 2Pi state near threshold, characterize the LTE
photodissociation cross sections. A sum rule is proposed as a check on the
accuracy of the photodissociation calculations.Comment: 9 pages, 8 figure
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