Massive Quiescent Cores in Orion. -- II. Core Mass Function

We have surveyed submillimeter continuum emission from relatively quiescent regions in the Orion molecular cloud to determine how the core mass function in a high mass star forming region compares to the stellar initial mass function. Such studies are important for understanding the evolution of cores to stars, and for comparison to formation processes in high and low mass star forming regions. We used the SHARC II camera on the Caltech Submillimeter Observatory telescope to obtain 350 \micron data having angular resolution of about 9 arcsec, which corresponds to 0.02 pc at the distance of Orion. Our analysis combining dust continuum and spectral line data defines a sample of 51 Orion molecular cores with masses ranging from 0.1 \Ms to 46 \Ms and a mean mass of 9.8 \Ms, which is one order of magnitude higher than the value found in typical low mass star forming regions, such as Taurus. The majority of these cores cannot be supported by thermal pressure or turbulence, and are probably supercritical.They are thus likely precursors of protostars. The core mass function for the Orion quiescent cores can be fitted by a power law with an index equal to -0.85$\pm$0.21. This is significantly flatter than the Salpeter initial mass function and is also flatter than the core mass function found in low and intermediate star forming regions. Thus, it is likely that environmental processes play a role in shaping the stellar IMF later in the evolution of dense cores and the formation of stars in such regions.Comment: 30 pages, 10 figures, accepted by Ap

Ultrastructural Characterization of SARS Coronavirus

Severe acute respiratory syndrome (SARS) was first described during a 2002–2003 global outbreak of severe pneumonia associated with human deaths and person-to-person disease transmission. The etiologic agent was initially identified as a coronavirus by thin-section electron microscopic examination of a virus isolate. Virions were spherical, 78 nm in mean diameter, and composed of a helical nucleocapsid within an envelope with surface projections. Herein, we show that infection with the SARS-associated coronavirus resulted in distinct ultrastructural features: double-membrane vesicles, nucleocapsid inclusions, and large granular areas of cytoplasm. These three structures and the coronavirus particles were shown to be positive for viral proteins and RNA by using ultrastructural immunogold and in situ hybridization assays. In addition, ultrastructural examination of a bronchiolar lavage specimen from a SARS patient showed numerous coronavirus-infected cells with features similar to those in infected culture cells. Electron microscopic studies were critical in identifying the etiologic agent of the SARS outbreak and in guiding subsequent laboratory and epidemiologic investigations

Egg Formation in Lepidoptera

Reproductive biology in the Twentieth Century produced comprehensive descriptions of the mechanisms of egg formation in most of the major orders of insects. While many general principles of ovarian development and physiology emerged, every order turned out to have a set of its own special motifs. Discovery of the lepidopteran motifs is summarized in this essay. The emphasis is on developmental mechanisms, beginning with the early growth and differentiation of female germ cells and ending, after many turns in morphogenesis, physiology and biosynthesis, with eggs that are filled with yolk and encased in chorions. Examples of uniquely lepidopteran traits include the cellular composition of ovarian follicles, the number of tubular ovarioles in which they mature, the functions of cell-to-cell junctional complexes in their maturation, their use of glycosaminoglycans to maintain intercellular patency during vitellogenesis, the role of proton and calcium pumps in their ion physiology, a separate postvitellogenic period of water and inorganic ion uptake, and the fine structure and protein composition of their chorions. Discovery of this combination of idiosyncracies was based on advances in the general concepts and techniques of cell and molecular biology and on insights borrowed from studies on other insects. The lepidopteran ovary in turn has contributed much to the understanding of egg formation in insects generally

The variation of productivity and its allocation along a tropical elevation gradient: a whole carbon budget perspective

Why do forest productivity and biomass decline with elevation? To address this question, research to date generally has focused on correlative approaches describing changes in woody growth and biomass with elevation. We present a novel, mechanistic approach to this question by quantifying the autotrophic carbon budget in 16 forest plots along a 3300 m elevation transect in Peru. Low growth rates at high elevations appear primarily driven by low gross primary productivity (GPP), with little shift in either carbon use efficiency (CUE) or allocation of net primary productivity (NPP) between wood, fine roots and canopy. The lack of trend in CUE implies that the proportion of photosynthate allocated to autotrophic respiration is not sensitive to temperature. Rather than a gradual linear decline in productivity, there is some limited but nonconclusive evidence of a sharp transition in NPP between submontane and montane forests, which may be caused by cloud immersion effects within the cloud forest zone. Leaf-level photosynthetic parameters do not decline with elevation, implying that nutrient limitation does not restrict photosynthesis at high elevations. Our data demonstrate the potential of whole carbon budget perspectives to provide a deeper understanding of controls on ecosystem functioning and carbon cycling