The asymmetric profile of the H76 alpha line emission from MWC349

MWC349 is an emission-line star found by Merrill, Humason and Burwell (1932). Braes, Habing and Schoenmaker (1972) discovered that it is a strong radio source. The radio emission originates in a massive ionized wind that is expanding with a velocity of about 50 km s(-1). Its continuum spectrum fits well a nu(0.6) power law from the cm wavelengths to the far-IR. Radio recombination line emission from the envelope of MWC349 was first detected by Altenhoff, Strittmatter and Wendker (1981). We have obtained good signal-to-noise ratio, Very Large Array observations of the H76 alpha radio recombination line from the ionized wind of MWC349. Our data reveal that the profile is markedly asymmetric, with a steep rise on the blue side. This asymmetry could be due to non-LTE effects in the formation and transfer of the line or to intrinsic asymmetries in the envelope. Our analysis suggests that most probably the peculiar profile is caused by a non-LTE enhancement of the line emission from the side of the envelope nearer to the observer. This asymmetry has the opposite sense than that observed in optical and IR recombination lines, where a different effect (absorption of the stellar continuum by the gas in the wind between the star and the observer) is known to be dominant, leading to the classic P Cygni profile. We propose that the profiles of the radio recombination lines from ionized stellar winds will have this characteristic shape, while optical and IR recombination lines are characterized by P Cygni-like profiles. Unfortunately, at present the detection of radio recombination lines from ionized stellar winds is only feasible for MWC349 and a few other objects

Dimensões humanas do uso e cobertura das terras na Amazônia: uma contribuição do LBA.

O entendimento das mudanças em paisagens amazônicas depende de documentação das alterações na cobertura da terra. Este artigo parte de resultados do Experimento de Larga Escala de Biosfera Atmosfera na Amazônia (LBA) relativos ao tema para focalizar um estudo transversal que analisa as dimensões sociais e biofísicas dessas transformações

A heterogeneidade das mudanças de uso e cobertura das terras na Amazônia: em busca de um mapa da estrada.

As mudanças de uso e cobertura das terras, a consequente fragmentação de paisagens naturais e seus potenciais impactos nas mudanças globais, ciclos biogeoquímicos, dinâmicas regionais e biodiversidade têm se tornado temas centrais em Ciências da Terra (Vitousek et al., 1997; National Research Council, 1998; Lambin et al., 1999; Moran et al., 2001), modernos métodos para o estudo de relações espaciais (Turner et al. 1995; Forman, 1997) e diversas aplicações no planejamento e monitoramento de territórios têm contribuído para uma leitura diferenciada sobre a dominação humana em espaços terrestres (GOIodland et al., 1993; Daily et al., 2000). As ciências sociais acompanham essas tendências e catalisam a atividade científica para abordagens mais integradoras (Liverman et al., 1998; Lubchenco, 1998; Berkes & Folke, 2000; Fox et al., 2002). Por sua abrangência geográfica e relevância socioambiental, o processo mais importante de fragmentação da paisagem em nível regional, e com possíveis consequências globais, e o desmatamento de florestas tropicais, em particular da Amazônia (Lambin, 1997; Williams, 2003)..

A method for determining landing runway length for a STOL aircraft

Based on data obtained from flight tests of the augmentor wing jet STOL research aircraft, a method is proposed for determining the length of the landing runway for powered-lift STOL aircraft. The suggested method determines runway landing length by summing three segments: the touchdown-dispersion distance, the transition distance from touchdown to application of brakes, and the stopping distance after brakes are applied. It is shown how the landing field length can be reduced either through improved autoland system design or by providing the pilot with appropriate information to allow him to identify a "low probability" long or short landing and to execute a go-around. The proposed method appears to determine a safe runway landing length for the STOL application and offers the potential for reducing runway length if great emphasis is placed on a short-runway capability. FAR Parts 25 and 121 appear conservative and suitable for the situation where no great emphasis is placed on reducing the runway length requirement

Integration of vegetation inventory data and thematic mapper image for Amazonian successional and mature forest classification.

Successional and mature forest classification is often difficult in moist tropical regions. This paper explores vegetation stand structures of successional and mature forests and their spectral characteristics. Canonical discriminant analysis (CDA) was used to identify important stand parameters for secondary succession and mature forest classification. Correlation coefficient was used to analyze different stand parameter relationships and associated TM spectral signatures. Transformed divergence was used to analyze the separability of succession stages and mature forest based on the resultant images from CDA and principal component analysis (PCA), respectively. This study indicates that five vegetation categories, i.e., initial succession, intermediate succession, advanced succession, small biomass mature forest, and large biomass mature forest, can be istinguished based on vegetation stand features using field measurements, but some of them are difficult to be classified using TM data. Tree diameter at breast height, tree height, aboveground biomass, and ratio of tree biomass to total aboveground biomass are the best stand parameters distinguishing vegetation classes. Bands TM 4 and TM 5 are best for distinguishing vegetation classes. The transformation using CDA improved separability of vegetation classes, but not using PCA. Two successional stages and one mature forest class are suitable in this study area

What Can the Organization of the Brain’s Default Mode Network Tell us About Self-Knowledge?

Understanding ourselves has been a fundamental topic for psychologists and philosophers alike. In this paper we review the evidence linking specific brain structures to self-reflection. The brain regions most associated with self-reflection are the posterior cingulate and medial prefrontal (mPFC) cortices, together known as the cortical midline structures (CMSs). We review evidence arguing that self-reflection is special in memory, while noting that these brain regions are often engaged when we think about others in our social worlds. Based on the CMSs’ patterns of connectivity and activity, we speculate about three possible interpretations of their role in supporting self-reflection that are somewhat overlapping, and not intended to be mutually exclusive. First, self may be a powerful, but ordinary case for a cognitive system specialized for thinking about people. Second, mPFC may serve as a processing “hub,” binding together information from all sensory modalities with internally generated information. Third, mPFC may serve as a cortical director of thought, helping to guide moment-by-moment conscious processing. Suggestions are made for future research avenues aimed at testing such possibilities

VLBI study of water maser emission in the Seyfert 2 galaxy NGC5793. I: Imaging blueshifted emission and the parsec-scale jet

We present the first result of VLBI observations of the blueshifted water maser emission from the type 2 Seyfert galaxy NGC5793, which we combine with new and previous VLBI observations of continuum emission at 1.7, 5.0, 8.4, 15, and 22 GHz. Maser emission was detected earlier in single-dish observations and found to have both red- and blueshifted features relative to the systemic velocity. We could image only the blueshifted emission, which is located 3.6 pc southwest of the 22 GHz continuum peak. The blueshifted emission was found to originate in two clusters that are separated by 0.7 milliarcsecond (0.16 pc). No compact continuum emission was found within 3.6 pc of the maser spot. A compact continuum source showing a marginally inverted spectrum between 1.7 and 5.0 GHz was found 4.2 pc southwest of the maser position. The spectral turnover might be due to synchrotron self-absorption caused by a shock in the jet owing to collision with dense gas, or it might be due to free-free absorption in an ionized screen possibly the inner part of a disk, foreground to the jet. The water maser may be part of a maser disk. If so, it would be rotating in the opposite sense to the highly inclined galactic disk observed in CO emission. We estimate a binding mass within 1 pc of the presumed nucleus to be on the order of 10^7 Msun. Alternatively, the maser emission could result from the amplification of a radio jet by foreground circumnuclear molecular gas. In this case, the high blueshift of the maser emission might mean that the masing region is moving outward away from the molecular gas surrounding an active nucleus.Comment: 20 pages, 6 figures, to appear in ApJ, Oct. 200