Opaque Region Research Articles

Low-mass star formation in the dense interior of Barnard 18

view Abstract Citations (23) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Low-mass star formation in the dense interior of Barnard 18. Myers, P. C. Abstract CO observations, visible obscuration, and near-IR estimates of extinction in Barnard 18 indicate that the relatively dense visibly opaque region (with an H2 density of 3000 per cu cm) is associated with a less dense nearly transparent region (with an H2 density of 700 per cu cm) of greater spatial extent (2 pc x 5 pc). A two-component model and measurements of stellar extinction indicate that the dense inner gas has nine known stars, a star formation efficiency of 2%, and a star space density of 8 per cu pc, while the less dense gas has eight known stars, a star formation efficiency of 1%, and a star space density of 0.9 per cu pc. Therefore, these young (300,000 years) low-mass stars are preferentially located in the dense inner gas. Calculations of escape speed and estimates of stellar speed indicate that most of the stars are probably gravitationally bound by the cloud. Publication: The Astrophysical Journal Pub Date: June 1982 DOI: 10.1086/160018 Bibcode: 1982ApJ...257..620M Keywords: Carbon Monoxide; Interstellar Matter; Molecular Clouds; Nebulae; Star Formation; Stellar Interiors; Stellar Structure; Gas Density; Gravitational Effects; Near Infrared Radiation; Star Distribution; Stellar Mass Ejection; Stellar Models; Stellar Occultation; Astrophysics full text sources ADS | data products SIMBAD (15)

Formation of protostars in collapsing, rotating, turbulent clouds

view Abstract Citations (26) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Formation of protostars in collapsing, rotating, turbulent clouds Regev, O. ; Shaviv, G. Abstract Collapse and star formation processes in rotating turbulent interstellar gas clouds have been studied. For this purpose numerical collapse calculations have been performed for a number of representative cases. These calculations have been carried out by a two-dimensional hydrodynamical computer code, which solves the equations of hydrodynamics explicitly, coupled to the Poisson equation. The computer code has been written especially for this work and has been thoroughly tested. The calculations in this work have been performed with an effort to obtain physically reliable results (by repeating the same calculations with different numerical spatial resolutions). A physical mechanism for angular momentum transport by turbulent viscosity has been proposed and incorporated in new collapse calculations. The main results can be summarized as follows: 1. When there is no physical mechanism for angular momentum transport, the result of the collapse is a ringlike structure. If the rotation is fast enough, a quasi-static mild ringlike structure inside a flattened configuration forms. In the case of slower rotation a deep collapse with a ring ensues. The ring collapses onto itself, and its density grows up to the point where it becomes opaque. This result supports the findings of Bodenheimer and Tscharnuter. 2. The turbulent viscosity affects the nature of the collapse. The results of collapse calculations with turbulent viscosity are radically different from the respective "nonviscous" calculations. The angular momentum transport interferes with the ring formation and enables the formation of a central dense and opaque region. This region is surrounded by a flat disk. 3. For the two cases studied, the mass of the central object is a major fraction (30%) of the total mass of the system. 4. The exact form of the central object and its ultimate fate depend on the parameters, especially β (β ≡ rotational energy/gravitational energy) and Re (turbulent Reynolds number). 5. The present calculations cannot predict the future evolution of the central object because they have an insufficient spatial resolution at the center and the isothermal approximation breaks down. However, it seems likely that the collapse with turbulent viscosity leads to the formation of a central protostar surrounded by a disk (proto-planetary nebula) when the rotation is slow enough and the turbulence efficient. When the rotation is fast or the turbulent transport less efficient, the central opaque object is very flat. This raises the possibility of multiple system formation (e.g., binary). 6. The importance of this work lies in the fact that a new theoretical model is proposed, in which a central protostar forms as a result of the collapse of a protostellar rotating cloud. Publication: The Astrophysical Journal Pub Date: May 1981 DOI: 10.1086/158871 Bibcode: 1981ApJ...245..934R Keywords: Gravitational Collapse; Interstellar Gas; Protostars; Stellar Evolution; Stellar Rotation; Turbulent Diffusion; Angular Momentum; Boundary Value Problems; Equations Of Motion; Hydrodynamic Equations; Nebulae; Rotating Fluids; Stellar Models; Transport Properties; Astrophysics full text sources ADS |

THE SERIAL OBSERVATION OF EMBRYOGENESIS IN A CARROT CELL SUSPENSION CULTURE

SUMMARYSerial observations were made of the early stages of somatic embryogenesis in a cell suspension culture of carrot (Daucus carota L. cv. ‘Kurodagosun’) using a series of cell clusters which divided synchronously. Three phases were recognized in each of which the rate of cell division was different: the first phase (0 to 3 days) during which cells divided slowly, the second phase (3 to 4 days) during which cells divided very rapidly in the determined locus of the cell cluster, leading to the formation of globular embryos, and the third phase (4 to 6 days) during which cell division occurred at a slower rate than the second phase. Three regions were distinguishable in the cell clusters at the end of the second phase: a transparent region destined to develop into the shoot, an opaque region destined to develop into the root and another opaque region which had ceased to grow, suggesting that the determination of differentiation had already occurred by the end of the second phase. The rapid cell division which occurred in the second phase is considered to be a characteristic event in embryogenesis.

Sulfur oxidation in selected human cortical cataracts and nuclear cataracts

The water soluble protein, the water insoluble non-membrane protein, and the membrane fraction were isolated from both the cortex and nucleus of nuclear and cortical cataracts. Measurements of cysteine and methionine oxidation in these fractions indicated that sulfur oxidation occurs in the transparent as well as the opaque region of the lenses. Cysteic acid is found only in the opaque region. In the nucleus of nuclear cataracts, extrinsic and cytoplasmic polypeptides are found covalently linked by disulfide bonds to the intrinsic membrane. In the cortex of cortical cataracts, there is no intrinsic membrane involvement. However, a high molecular weight disulfide linked aggregate can be isolated from the cortex of cortical cataracts. This aggregate appears to contain the same extrinsic and cytoplasmic proteins as are found covalently attached to the membrane of the nuclear cataracts.

Piezobirefringence analysis in an opaque region

We report a new method to analyze the piezobirefringence coefficient in an opaque region in which the stress-induced changes in both the real ($\ensuremath{\Delta}{\ensuremath{\epsilon}}_{1}$) and imaginary part ($\ensuremath{\Delta}{\ensuremath{\epsilon}}_{2}$) of the dielectric constant are properly taken into account. New coefficients, which determine the fractional contributions of $\ensuremath{\Delta}{\ensuremath{\epsilon}}_{1}$ and $\ensuremath{\Delta}{\ensuremath{\epsilon}}_{2}$ to the piezobirefringence coefficient, have been derived from an analytical point of view. The experimental data on Si and ZnSe reported recently have been analyzed by using the present result. Good agreement between the experiment and calculation has been found. The present method provides a guiding principle for analyzing the piezobirefringence coefficient in an opaque region.

An asymptotic limit to optical pumping in an opaque region

An asymptotic limit to the optical pumping of low-lying levels of an ion or molecule in an optically thick medium has been found. The net rate of optical pumping approaches zero when optical depth is sufficiently large, even though individual line intensities generally increase as the optical depth increases. The optical pumping rate nears zero because the lines approach a detailed balance resulting from proton conservation; this detailed balance occurs for any geometry, line profiles or redistribution processes. An intermediate domain of large optical depths (the pumping-dominated limit) in which level populations are identical to those in an optically thin region is also found. Results of this optical pumping study may be applied to the excitation of atomic fine-structure levels in H II regions and quasars.

Linewidth measurement with an optical microscope: the effect of operating conditions on the image profile

A theoretical model of the optical microscope based on the theory of partial coherence is used to predict the image profiles of lines on IC photomasks and assess factors contributing to measurement errors for different conditions of microscope operation. A comparison of experimental and theoretical image profiles is given, showing good agreement with theory for a 0.9 N.A. and linewidths as small as 0.5 microm. The primary sources of differences appear to be edge quality and accuracy of focus. The theory indicates that for well-corrected microscope optical systems, spectrally filtered to eliminate longitudinal chromatic aberration and chromatic difference of magnification, accurate determinations of linewidth may be made from the image profile using a threshold of 25% of maximum intensity (corrected for finite background transmittance in the opaque region). The correspondence between the edge location and the 25% threshold appears to be nearly invariant with small amounts of defocus and spherical aberration as well as variation in the numerical aperture of the condenser.

PHYLOGENETIC RELATIONSHIPS OFCAULERPA(CHLOROPHYTA) BASED ON COMPARATIVE CHLOROPLAST ULTRASTRUCTURE1,2

SUMMARYThe ultrastructure of chloroplasts from 28 of the 73 species ofCaulerpaLamouroux (Chlorophyta, Caulerpales) has been studied to aid in interpreting phylogenetic relationships among the 12 recognized sections. Variations of systematic value include pyrenoid occurrence and fine structure, thylakoid architecture and amount of photosynthate storage. Comparisons of field and culture specimens indicate these characters are consistent. Chloroplast thylakoids are grouped into bands, with the distribution of bands differing among species. In the most common arrangement, bands are evenly distributed throughout the chloroplast. A few species show lateral displacement of bands whereas others have a majority of bands arranged at one end of the chloroplast. Starch is stored cither as one or two large grains (> 1 μm diam.) or numerous small grains (< 0.5 μm diam.). Electron‐transparent regions are common in other species in which chloroplasts rarely store starch. Simple, embedded pyrenoids are present in several species of section Sedoideae. An opaque region occurs in chloroplasts ofC. elongatawhich may represent an intermediate stage in the evolutionary loss of the pyrenoid. It is suggested that the chloroplast ofCaulerpaevolved, from a large, complex, pyrenoid‐containing organelle housing both photosynthetic and amylogenic functions, to a small, structurally simpler one, specialized for photosynthesis alone. A phylogeny of the 12 sections ofCaulerpais constructed, based on chloroplast evolution which agrees with an earlier morphology‐based hypothesis on the origin and evolution ofCaulerpa.

PHYLOGENETIC RELATIONSHIPS OF CAULERPA (CHLOROPHYTA) BASED ON COMPARATIVE CHLOROPLAST ULTRASTRUCTURE1,2

The ultrastructure of chloroplasts from 28 of the 73 species of Caulerpa Lamouroux (Chlorophyta, Caulerpales) has been studied to aid in interpreting phylogenetic relationships among the 12 recognized sections. Variations of systematic value include pyrenoid occurrence and fine structure, thylakoid architecture and amount of photosynthate storage. Comparisons of field and culture specimens indicate these characters are consistent. Chloroplast thylakoids are grouped into bands, with the distribution of bands differing among species. In the most common arrangement, bands are evenly distributed throughout the chloroplast. A few species show lateral displacement of bands whereas others have a majority of bands arranged at one end of the chloroplast. Starch is stored cither as one or two large grains (> 1 μm diam.) or numerous small grains (< 0.5 μm diam.). Electron‐transparent regions are common in other species in which chloroplasts rarely store starch. Simple, embedded pyrenoids are present in several species of section Sedoideae. An opaque region occurs in chloroplasts of C. elongata which may represent an intermediate stage in the evolutionary loss of the pyrenoid. It is suggested that the chloroplast of Caulerpa evolved, from a large, complex, pyrenoid‐containing organelle housing both photosynthetic and amylogenic functions, to a small, structurally simpler one, specialized for photosynthesis alone. A phylogeny of the 12 sections of Caulerpa is constructed, based on chloroplast evolution which agrees with an earlier morphology‐based hypothesis on the origin and evolution of Caulerpa.

Genetic inhibition of mesenchymal cell death and the development of form and skeletal pattern in the limbs oftalpid3(ta3) mutant chick embryos

ABSTRACTVital staining reveals that in homozygous (ta3/ta3) talpid3 embryos, the areas of mesen-chymal cell death which occur regularly in normal limb development are absent or reduced.The necrotic locus in the central mesenchyme (the ‘opaque patch’) which in the normal chick limb reaches maximum development at stages 24 and 25 is absent or much reduced in talpid3 fore-and hindlimb-buds. Autoradiographic studies, following application of a 2 h pulse of 40 μCi of35SO4 to the vitelline circulation, show that normal tibia and fibula incorporate 35SO4 into chondroitin sulphate at stage 24 and more strongly at stage 26 during the process of chondrogenesis. The mesenchyme in the opaque patch region of normal limbs ceases to incorporate 35SO4 into chondroitin sulphate at stage 24. Talpid3 mesenchyme cells in the equivalent position at stages 24 and 26 continue to incorporate 35SO4, remain viable and become chondrogenic. It is suggested that absence or reduction of this central necrotic locus in talpid3 is causally related to the fusion of radius/ulna and (in some cases) of tibia/fibula characteristic of the later stages (28–35) of talpid3 limb development. This evidence supports the hypothesis that cell death in the opaque patch plays a morphogenetic role in separation of radius/ulna and tibia/fibula.The digital plate of stage 32 normal limbs is characterized by massive necrosis of the interdigital tissue. In talpid3 forelimbs of stages 30–35 interdigital necrosis is absent, and there is no regression of the tissue between the digits (‘soft tissue syndactyly’). In talpid3 hindlimbs of stage 30–35 interdigital necrosis is either absent or much reduced, and there is little or no erosion of the soft tissue between the digits. This evidence supports the hypothesis that the morphogenetic role of interdigital cell death is in causing separation of the digits through shaping and remodelling the contours of the digital plate.

Electron microscopic studies on the outer layers of Staphylococcus aureus using a lytic enzyme from Falvobacterium.

The structure of the outer layers (cell wall and membrane) of Staphylococcus aureus was studied by electron microscope using a bacteriolytic enzyme from Flavobacterium sp. called the L-11 enzyme. Comparative studies on the morphology of bacteria before and after treatment with this enzyme and cell wall and membrane fractions obtained from bacteria after the enzyme treatment led to the following conclusions. (1) The cell wall of S. aureus is composed of morphologically distinct two layers which are both susceptible to the L-11 enzyme. (2) Between the cell wall and membrane, there is an electron opaque region which could not be stained using any of the methods tested. (3) Before treatment of bacteria with the enzyme the cell membrane could not be seen clearly. However, after enzyme treatment the membrane was clearly seen. (4) The infolding of the inner layer of the cell wall, forming a structure like a mesosome, was liberated by extensive enzyme treatment.

Infrared Spectral Emittance and Optical Properties of Yttrium Vanadate

The infrared spectral emittance $E$ of single scrystals of YV${\mathrm{O}}_{4}$ has been examined near 4.2 and 77\ifmmode^\circ\else\textdegree\fi{}K in the wavelength range 4-125 \ensuremath{\mu}m. Of the expected seven active transverse optical modes at k\ensuremath{\sim}0, six have been observed and assigned to their symmetry species based on their polarization with respect to the crystalline axes. The observed frequencies of the transverse optic ${E}_{u}$ modes were 196, 261, and 788 ${\mathrm{cm}}^{\ensuremath{-}1}$; and for ${A}_{2u}$ modes, 310, 455, and 803 ${\mathrm{cm}}^{\ensuremath{-}1}$. The relation between emittance and reflectance, $E=1\ensuremath{-}R$ in the opaque region of lattice vibrations, permits one to determine the reflectance $R$. By least-square-fitting the reflectance data to an independent set of damped harmonic oscillators, infrared dispersion parameters were determined for the ${E}_{u}$ vibrations.

Streak Interferometry

A modification of the Mach-Zehnder interferometer is described which permits streak interferometry of transient axisymmetric flows. Examples are shown of interferograms taken of flows produced by exploding fine metallic wires. Prominent features of the interferograms include (1) clearly defined shock waves, (2) a narrow, transparent, flow region behind the strong shock where fringes may be seen, (3) an opaque region presumed to be caused by the dispersed metal, and (4) luminous regions associated with the second shock wave and electronic excitation of the material near the axis of symmetry.

The Abbe Theory of Microscopic Vision and the Gibbs Phenomenon

An elementary discussion of the Abbe theory of microscopic vision is given, suitable for teaching purposes. The effect of the phases in the back focal plane of the objective is briefly outlined. The consequence of limiting the aperture of the system in this plane is shown to be an image marred by diffraction. The relationship to Fourier's theorem having been indicated, the Gibbs phenomenon is next described. A standard formula for the finite sum of a Fourier series is taken and adapted to the case of imaging a suitable grating with a microscope objective limited by a slit aperture. If the grating slits are very narrow compared with the opaque region separating them, the image of each is shown to be marred by a set of fringes, due to the Gibbs phenomenon, exactly equivalent to the diffraction fringes from the single slit in the microscope objective.

Histoplasma Capsulatum: Its Cultivation on the Chorio-Allantoic Membrane of the Developing Chick and Resultant Lesions 1

Summary 1. The chorio-allantoic membrane of the developing chick was successfully inoculated with a seven year old culture of Histoplasma capsulatum. 2. Eggs were incubated 12 days and observed 6 days after inoculation. 3. The macroscopic appearance of the lesion showed a thickened, yellowish-gray plaque with a peripheral opaque region. 4. Microscopically, there was a marked reaction in the ectoderm, mesoderm, and the underlying entoderm. 5. The cellular response consisted of the appearance of large numbers of fibroblasts, monocytes, leucocytes, red blood cells with a marked eosinophilia. 6. The organism showed a conversion into yeastlike cells analogous to the formation of arthrospores and oidia. 7. The ascus-like cells, stalagmospores or aleuriospores became converted into many yeastlike cells which seemed to indicate that they are most likely ascus-like structures, probably of a degenerate nature.