RESUMO
To reach even the nearest stars in a human lifetime requires a ship speed that is a substantial fraction of the speed of light. This means an enormous kinetic energy investment in the ship and suggests that maximizing the efficiency may be more important than minimizing the mass ratio. This paper develops the pertinent relativistic rocket equations and finds the conditions for high kinematic efficiency. Using the limiting efficiency of 100%, the minimum energy needed for one-way and for round trip voyages, and to explore all "good" suns out to a given distance, using pre-fueled rockets, is determined. Savings due to refueling the rocket (and reloading propellant) at the destination and in flight are both somewhat greater than 2:1.
Assuntos
Modelos Teóricos , Voo Espacial/instrumentação , Astronave/instrumentação , Matemática , Voo Espacial/economia , Astronave/economiaRESUMO
On Earth intelligent life evolved as a natural consequence of the events set in motion when the planet formed over 4 billion years ago. Since chemical evolution and solar-system formation appear to be occurring throughout the universe, we theorize that our universe may be rich with planets populated by intelligent beings who, like us, can search for evidence of other technological civilizations. Terrestrial civilization now has this capability. But if we do not begin the search soon, we'll lose the opportunity to do it from Earth as interfering signals of Earthly origin rapidly close the microwave window.
Assuntos
Astronomia , Comunicação , Exobiologia , Meio Ambiente Extraterreno , Micro-Ondas , Fenômenos Astronômicos , Planeta Terra , Origem da Vida , Sistema Solar , Fatores de Tempo , Estados Unidos , United States National Aeronautics and Space AdministrationRESUMO
NASA: The development of a multi-channel spectrum analyzer (MCSA) for the SETI program is described. The spectrum analyzer is designed for both all-sky surveys and targeted searches. The mechanisms of the MCSA are explained and a diagram is provided. Detection of continuous wave signals, pulses, and patterns is examined.^ieng
Assuntos
Astronomia/instrumentação , Comunicação , Exobiologia/instrumentação , Meio Ambiente Extraterreno , Processamento de Sinais Assistido por Computador , Algoritmos , Astronomia/métodos , Desenho de Equipamento , Espectrofotometria Infravermelho/instrumentação , Estados Unidos , United States National Aeronautics and Space AdministrationRESUMO
Placement of teeth according to accepted cephalometric criteria does not necessarily ensure that overlying soft tissue will drape in a harmonious manner. The purpose of this research was to investigate the influence of maxillary lip thickness and lip strain on the relationship between dental and integumental tissue changes in orthodontically treated patients. Data were derived from pretreatment and retention lateral cephalometric head films of forty Caucasian subjects with Class II, Division 1 malocclusions. All patients were treated with edgewise appliances. Percentile groups were created for males and females according to the magnitude of maxillary lip thickness and lip strain. It was found that there was significant correlation between osseous changes and soft-tissue changes in both males (r= 0.83, p less than 0.01) and females (r = 0.85, p less than 0.01). Strong correlations were found between osseous changes and soft-tissue changes in subjects with thin lips (males, r equal to 0.92, p less than 0.01; females, r = 0.98, p less than 0.01), whereas no significant correlations were found in subjects with thick lips. Significant correlations were found between incisor changes and vermillion border changes in males (r = 0.61, p less than 0.01) and females (r = 0.51, p less than 0.05). Correlations were strong between incisor changes and vermilion border changes in subjects with high lip strain (males, r equal 0.92, p less than 0.01; females, r = 0.82, p less than 0.05) but were significant in subjects with low lip strain.
