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Letteratura scientifica selezionata sul tema "Molecular clouds"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 26 ottobre 2024

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Articoli di riviste sul tema "Molecular clouds"

1

Sullivan, Colin H., L. M. Fissel, P. K. King, C.-Y. Chen, Z.-Y. Li e J. D. Soler. "Characterizing the magnetic fields of nearby molecular clouds using submillimeter polarization observations". Monthly Notices of the Royal Astronomical Society 503, n. 4 (16 marzo 2021): 5006–24. http://dx.doi.org/10.1093/mnras/stab596.

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ABSTRACT Of all the factors that influence star formation, magnetic fields are perhaps the least well understood. The goal of this paper is to characterize the 3D magnetic field properties of nearby molecular clouds through various methods of statistically analysing maps of polarized dust emission. Our study focuses on nine clouds, with data taken from the Planck Sky Survey as well as data from the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry observations of Vela C. We compare the distributions of polarization fraction (p), dispersion in polarization angles ($\mathcal {S}$), and hydrogen column density (NH) for each of our targeted clouds. To broaden the scope of our analysis, we compare the distributions of our clouds’ polarization observables with measurements from synthetic polarization maps generated from numerical simulations. We also use the distribution of polarization fraction measurements to estimate the inclination angle of each cloud’s cloud-scale magnetic field. We obtain a range of inclination angles associated with our clouds, varying from 16○ to 69○. We establish inverse correlations between p and both $\mathcal {S}$ and NH in almost every cloud, but we are unable to establish a statistically robust $\mathcal {S}$ versus NH trend. By comparing the results of these different statistical analysis techniques, we are able to propose a more comprehensive view of each cloud’s 3D magnetic field properties. These detailed cloud analyses will be useful in the continued studies of cloud-scale magnetic fields and the ways in which they affect star formation within these molecular clouds.

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2

Clube, S. V. M. "Molecular clouds: comet factories?" International Astronomical Union Colloquium 83 (1985): 19–30. http://dx.doi.org/10.1017/s0252921100083779.

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AbstractRecent discoveries seem to indicate a catastrophic history of terrestrial evolution, explicable in terms of Oort cloud disturbance by molecular clouds in the Galactic disc. The problem of Oort cloud replenishment thus assumes considerable significance and reasons are given for supposing comet exchange takes place during actual penetration of molecular clouds. The number density of comets in molecular clouds, thereby implied, seems to suggest primary condensations of ≤103km in a dense precursor state of spiral arms. If chemical and/or isotopic signatures of comets should indicate an extra-Solar System source, the theory of terrestrial catastrophism may place new constraints on our understanding of the origin of molecular clouds.

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3

Bot, Caroline, Mónica Rubio, François Boulanger, Marcus Albrecht, Frank Bertoldi, Alberto D. Bolatto e Adam K. Leroy. "Tracing the cold molecular gas reservoir through dust emission in the SMC". Proceedings of the International Astronomical Union 4, S256 (luglio 2008): 148–53. http://dx.doi.org/10.1017/s174392130802838x.

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AbstractThe amount of molecular gas is a key for understanding the future star formation in a galaxy. However, this quantity is difficult to infer as the cold H2 is almost impossible to observe and, especially at low metallicities, CO only traces part of the clouds, keeping large envelopes of H2 hidden from observations. In this context, millimeter dust emission tracing the cold and dense regions can be used as a tracer to unveil the total molecular gas masses. I present studies of a sample of giant molecular clouds in the Small Magellanic Cloud. These clouds have been observed in the millimeter and sub-millimeter continuum of dust emission: with SIMBA/SEST at 1.2 mm and the new LABOCA bolometer on APEX at 870 μm. Combining these with radio data for each cloud, the spectral energy distribution of dust emission are obtained and gas masses are inferred. The molecular cloud masses are found to be systematically larger than the virial masses deduced from CO emission. Therefore, the molecular gas mass in the SMC has been underestimated by CO observations, even through the dynamical masses. This result confirms what was previously observed by Bot et al. (2007). We discuss possible interpretations of the mass discrepancy observed: in the giant molecular clouds of the SMC, part of cloud's support against gravity could be given by a magnetic field. Alternatively, the inclusion of surface terms in the virial theorem for turbulent clouds could reproduce the observed results and the giant molecular clouds could be transient structures.

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4

Blitz, Leo. "Molecular Clouds at High z". Symposium - International Astronomical Union 144 (1991): 41–51. http://dx.doi.org/10.1017/s0074180900088896.

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The evidence for the existence of molecular clouds at large distances from the Galactic plane is reviewed. The molecular clouds at high Galactic latitudes are shown to be largely confined to the Galactic plane. There is evidence for one giant molecular cloud as much as four scale heights from the Galactic plane, but given the sample size from which the cloud is drawn, it is reasonable to suppose that it is part of the tail of the thin disk population. There is weak evidence that one star-forming molecular cloud may have originated in the Galactic halo. On the basis of kinematic evidence however, it is shown that there are three molecular clouds identified at high galactic latitude that, if not at high z, are likely to have resulted from interaction with gas in the halo. Understanding how these clouds have formed is likely to be an important key to understanding how the halo interacts with the disk gas.

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5

Wong, Tony, Annie Hughes, Jürgen Ott, Jorge L. Pineda e Erik Muller. "The Molecular Cloud Population of the Large Magellanic Cloud". Proceedings of the International Astronomical Union 8, S292 (agosto 2012): 71–74. http://dx.doi.org/10.1017/s1743921313000495.

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AbstractWe have mapped an extensive sample of molecular clouds in the Large Magellanic Cloud (LMC) at 11 pc resolution in the CO(1-0) line as part of the Magellanic Mopra Assessment (MAGMA). We identify clouds as regions of connected CO emission and determine their sizes, line widths, and fluxes. We find that GMCs are not preferentially located in regions of high Hi line width or velocity gradient, and that there is no clear Hi column density threshold for CO detection. The luminosity function of CO clouds is steeper than dN/dL ∝ L−2, suggesting a substantial fraction of mass in low-mass clouds. The correlation between size and linewidth, while apparent for the largest emission structures, breaks down when those structures are decomposed into smaller structures. The virial parameter (the ratio of a cloud's kinetic to gravitational energy) shows a wide range of values and exhibits no clear trends with the likelihood of hosting young stellar object (YSO) candidates, suggesting that this parameter is a poor reflection of the evolutionary state of a cloud. More massive GMCs are more likely to harbor a YSO candidate, and more luminous YSOs are more likely to be coincident with detectable CO emission, confirming GMCs as the principal sites of massive star formation.

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6

Körtgen, Bastian. "The turbulence driving parameter of molecular clouds in disc galaxies". Monthly Notices of the Royal Astronomical Society 497, n. 1 (24 luglio 2020): 1263–74. http://dx.doi.org/10.1093/mnras/staa2028.

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ABSTRACT Supersonic turbulence plays a pivotal role during the formation of molecular clouds and stars in galaxies. However, little is known about how the fraction of compressive and solenoidal modes in the velocity field evolves over time and how it depends on properties of the molecular cloud or the galactic environment. In this work, we carry out magnetohydrodynamical simulations of disc galaxies and study the time evolution of the turbulence driving parameter for an ensemble of clouds. We find that the time-averaged turbulence driving parameter is insensitive to the position of the cloud within the galaxy. The ensemble-averaged driving parameter is found to be rather compressive with b ∼ 0.5–0.7, indicating almost time-independent global star formation properties. However, each individual cloud shows a highly fluctuating driving parameter, which would strongly affect the cloud’s star formation rate. We find that the mode of turbulence driving can rapidly change within only a few Myr, both from solenoidal to compressive and vice versa. We attribute these changes to cloud collisions and to tidal interactions with clouds or overdensities in the environment. Last, we find no significant differences in the average driving parameter between hydrodynamic and initially strongly magnetized galaxies. However, the magnetic field tends to reduce the overall fluctuation of the driving parameter. The average driving and its uncertainty are seen to be in agreement with recent constraints on the turbulence driving mode for solar neighbourhood clouds.

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7

Li, Pak Shing, e Richard I. Klein. "Magnetized interstellar molecular clouds – II. The large-scale structure and dynamics of filamentary molecular clouds". Monthly Notices of the Royal Astronomical Society 485, n. 4 (27 marzo 2019): 4509–28. http://dx.doi.org/10.1093/mnras/stz653.

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Abstract We perform ideal magnetohydrodynamics high-resolution adaptive mesh refinement simulations with driven turbulence and self-gravity and find that long filamentary molecular clouds are formed at the converging locations of large-scale turbulence flows and the filaments are bounded by gravity. The magnetic field helps shape and reinforce the long filamentary structures. The main filamentary cloud has a length of ∼4.4 pc. Instead of a monolithic cylindrical structure, the main cloud is shown to be a collection of fibre/web-like substructures similar to filamentary clouds such as L1495. Unless the line-of-sight is close to the mean field direction, the large-scale magnetic field and striations in the simulation are found roughly perpendicular to the long axis of the main cloud, similar to L1495. This provides strong support for a large-scale moderately strong magnetic field surrounding L1495. We find that the projection effect from observations can lead to incorrect interpretations of the true three-dimensional physical shape, size, and velocity structure of the clouds. Helical magnetic field structures found around filamentary clouds that are interpreted from Zeeman observations can be explained by a simple bending of the magnetic field that pierces through the cloud. We demonstrate that two dark clouds form a T-shaped configuration that is strikingly similar to the infrared dark cloud SDC13, leading to the interpretation that SDC13 results from a collision of two long filamentary clouds. We show that a moderately strong magnetic field (${{\cal M}_{\rm A}}\sim 1$) is crucial for maintaining a long and slender filamentary cloud for a long period of time ∼0.5 Myr.

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8

Braine, J., E. Rosolowsky, P. Gratier, E. Corbelli e K. F. Schuster. "Properties and rotation of molecular clouds in M 33". Astronomy & Astrophysics 612 (aprile 2018): A51. http://dx.doi.org/10.1051/0004-6361/201732405.

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The sample of 566 molecular clouds identified in the CO(2–1) IRAM survey covering the disk of M 33 is explored in detail. The clouds were found using CPROPS and were subsequently catalogued in terms of their star-forming properties as non-star-forming (A), with embedded star formation (B), or with exposed star formation (C, e.g., presence of Hα emission). We find that the size-linewidth relation among the M 33 clouds is quite weak but, when comparing with clouds in other nearby galaxies, the linewidth scales with average metallicity. The linewidth and particularly the line brightness decrease with galactocentric distance. The large number of clouds makes it possible to calculate well-sampled cloud mass spectra and mass spectra of subsamples. As noted earlier, but considerably better defined here, the mass spectrum steepens (i.e., higher fraction of small clouds) with galactocentric distance. A new finding is that the mass spectrum of A clouds is much steeper than that of the star-forming clouds. Further dividing the sample, this difference is strong at both large and small galactocentric distances and the A vs. C difference is a stronger effect than the inner vs. outer disk difference in mass spectra. Velocity gradients are identified in the clouds using standard techniques. The gradients are weak and are dominated by prograde rotation; the effect is stronger for the high signal-to-noise clouds. A discussion of the uncertainties is presented. The angular momenta are low but compatible with at least some simulations. Finally, the cloud velocity gradients are compared with the gradient of disk rotation. The cloud and galactic gradients are similar; the cloud rotation periods are much longer than cloud lifetimes and comparable to the galactic rotation period. The rotational kinetic energy is 1–2% of the gravitational potential energy and the cloud edge velocity is well below the escape velocity, such that cloud-scale rotation probably has little influence on the evolution of molecular clouds.

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9

Yan, Qing-Zeng, Ji Yang, Yang Su, Yan Sun, Xin Zhou, Ye Xu, Hongchi Wang, Shaobo Zhang e Zhiwei Chen. "Dependence of Molecular Cloud Samples on Angular Resolution, Sensitivity, and Algorithms". Astronomical Journal 164, n. 2 (18 luglio 2022): 55. http://dx.doi.org/10.3847/1538-3881/ac77ea.

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Abstract In this work, we investigate the observational and algorithmic effects on molecular cloud samples identified from position–position–velocity (PPV) space. By smoothing and cutting off the high quality data of the Milky Way Imaging Scroll Painting (MWISP) survey, we extract various molecular cloud samples from those altered data with the DBSCAN (density-based spatial clustering of applications with noise) algorithm. Those molecular cloud samples are subsequently used to gauge the significance of sensitivity, angular/velocity resolution, and DBSCAN parameters. Two additional surveys, the FCRAO Outer Galaxy Survey and the CfA-Chile 1.2 m complete CO (CfA-Chile) survey, are used to verify the MWISP results. We found that molecular cloud catalogs are not unique and that the catalog boundary and therefore the sample size show strong variation with angular resolution and sensitivity. At low angular resolution (large beam sizes), molecular clouds merge together in PPV space, while a low sensitivity (high cutoffs) misses small faint molecular clouds and takes bright parts of large molecular clouds as single ones. At high angular resolution and sensitivity, giant molecular clouds (GMCs) are resolved into individual clouds, and their diffuse components are also revealed. Consequently, GMCs are more appropriately interpreted as clusters or aggregates of molecular clouds, i.e., GMCs represent molecular cloud samples themselves.

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10

Duarte-Cabral, A., D. Colombo, J. S. Urquhart, A. Ginsburg, D. Russeil, F. Schuller, L. D. Anderson et al. "The SEDIGISM survey: molecular clouds in the inner Galaxy". Monthly Notices of the Royal Astronomical Society 500, n. 3 (11 settembre 2020): 3027–49. http://dx.doi.org/10.1093/mnras/staa2480.

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ABSTRACT We use the 13CO (2–1) emission from the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) high-resolution spectral-line survey of the inner Galaxy, to extract the molecular cloud population with a large dynamic range in spatial scales, using the Spectral Clustering for Interstellar Molecular Emission Segmentation (scimes) algorithm. This work compiles a cloud catalogue with a total of 10 663 molecular clouds, 10 300 of which we were able to assign distances and compute physical properties. We study some of the global properties of clouds using a science sample, consisting of 6664 well-resolved sources and for which the distance estimates are reliable. In particular, we compare the scaling relations retrieved from SEDIGISM to those of other surveys, and we explore the properties of clouds with and without high-mass star formation. Our results suggest that there is no single global property of a cloud that determines its ability to form massive stars, although we find combined trends of increasing mass, size, surface density, and velocity dispersion for the sub-sample of clouds with ongoing high-mass star formation. We then isolate the most extreme clouds in the SEDIGISM sample (i.e. clouds in the tails of the distributions) to look at their overall Galactic distribution, in search for hints of environmental effects. We find that, for most properties, the Galactic distribution of the most extreme clouds is only marginally different to that of the global cloud population. The Galactic distribution of the largest clouds, the turbulent clouds and the high-mass star-forming clouds are those that deviate most significantly from the global cloud population. We also find that the least dynamically active clouds (with low velocity dispersion or low virial parameter) are situated further afield, mostly in the least populated areas. However, we suspect that part of these trends may be affected by some observational biases (such as completeness and survey limitations), and thus require further follow up work in order to be confirmed.

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Più fonti

Tesi sul tema "Molecular clouds"

1

Beletsky, Yuri. "Extragalactic molecular clouds and chemistry of diffuse interstellar clouds". Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-105670.

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2

Vichetti, Rafael Mário [UNESP]. "Síntese dos isótopos do monóxido de carbono no meio interestelar". Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/91889.

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Made available in DSpace on 2014-06-11T19:25:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-12-21Bitstream added on 2014-06-13T19:53:20Z : No. of bitstreams: 1 vichietti_rm_me_rcla.pdf: 842604 bytes, checksum: 731ca276a75c1b92840e57bd7497b5e1 (MD5)
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De acordo com os resultados observacionais de condensações de nuvens moleculares escuras, grandes variações na razão 13CO/C18O são observadas quando se comparam os resultados obtidos nas condensações situadas dentro da mesma nuvem, bem como de nuvem para nuvem. O valor médio dessa razão na condensação principal de Ophiuchus é inferior a 5. Por outro lado, o valor encontrado nas condensações que estão situadas ao norte de Oph é maior que 10. Grandes diferenças também são encontradas quando se comparam os resultados observacionais de diferentes nuvens escuras, tais como Ophiuchus e Taurus, onde são observados também um decréscimo da razão C18O/C17O com o aumento da densidade. Os processos químicos e físicos que governam essas variações ainda não estão claros. Nesse sentido, o objetivo da presente proposta é analisar a influência do colapso gravitacional de condensações de nuvens moleculares escuras na síntese das moléculas CO, C17O, C18O, 13CO, 13C17O e 13C18O. Tal análise é feita com base em comparações entre modelos que consideram diferentes condições entre si, tais como, tamanho da cadeia química, velocidade de colapso, densidade inicial e processos de congelamento de espécies químicas na superfície de grãos de poeira. Os resultados obtidos mostram que o tamanho da cadeia química tem influência nas razões 13CO/C18O e C18O/C17O, mas não tanto quanto a densidade inicial e a velocidade do colapso. Além disso, o congelamento das espécies químicas nos grãos é mais significativo nos estágios mais avançados da evolução da condensação. Os modelos de condensações escuras que sofrem colapso gravitacional lento e em queda livre reproduzem satisfatoriamente as razões 13CO/C18O e C18O/C17O observadas, o que permite concluir que o colapso gravitacional pode ter um importante efeito nas referidas razões.
According to the observational results of dark molecular clouds condensations, large variations in the ratio 13CO/C18O are observed when comparing the results obtained in the condensations located within the same cloud and cloud to cloud. The average value of this ratio in the main condensation of Ophiuchus is below 5. On the other hand, the value found in the condensations that are located north of Oph is larger than 10. Large differences are also found when comparing the observational results of different dark clouds such as Ophiuchus and Taurus, in which are also found a decrease of the C18O/C17O ratio with increasing density. The chemical and physical processes that govern these variations are still unclear. In this sense, the objective of this proposal is to analyze the influence of the gravitational collapse of centrally condensed clumps of dense molecular gas in the synthesis of the CO, C17O, C18O, 13CO, 13C17O and 13C18O molecules. This analysis is based on comparisons among models that consider different condition, such as, chemical chain, initial density, speed of collapse and freezing processes of the chemical species on the surface of dust grains. The results show that the size of the chemical chain has influence on the 13CO/C18O and C18O/C17O ratios, but they are not as important as the initial density and the speed of the collapse. Furthermore, the freezing of chemical species on the grains occurs at later times of the collapse. The models of a gravitational free-fall collapsing core and of slowly contracting core with higher initial density are consistent with observations. These results indicate that the gravitational collapse of molecular cores can have an important effect in the 13CO/C18O and C18O/C17O ratios.

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3

Brown, Ian David. "The velocity of molecular clouds". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293612.

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4

Bretherton, Derek. "Star formation in molecular clouds". Thesis, Liverpool John Moores University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402927.

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Rowles, Jonathan Henry. "The structure of molecular clouds". Thesis, University of Kent, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.544095.

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6

Richardson, Kevin John. "Submillimetre molecular line observations and modelling of molecular clouds". Thesis, Queen Mary, University of London, 1985. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1705.

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Submillimetre molecular line observations of molecular clouds in our galaxy are presented, and the data analysed using various alternative cloud models. A critical review is given of the methods commonly used to interpret molecular line data, including both theoretical considerations and issues relating to calibration and comparability of results obtained with different telescopes. A detailed comparison is made between results predicted from large velocity gradient (LVG) models, including the generalisation to non-monotonic velocity flows, and those given by "microturbulent" clouds. An LVG model is employed in an investigation of conditions in the molecular outflows frequently found in star formation regions, for which observations in the CO J=3-2 rotational transition at 345 GHz are presented. These are combined with lower frequency data from the literature to derive various properties of the outflows for a sample of 13 sources. The most important result is that local H2 densities exist in the outflows which are higher, typically by an order of magnitude, than previously derived average values obtained using only lower frequency data. Observations are presented of the S255 and DR21 clouds in the transitions CO J=2-1, CO J=3-2, CS J=7-6, HCN J=4-3, HCO+ J=4-3 and -3- H13CO+ J=4-3 and are supplemented by continuum data at 350 s. n and (for DR21) at 20 pm. It is shown that, although some features of the data can be understood in terms of an LVG model, there is compelling evidence for fragmentation of the clouds on length scales much smaller than the cloud sizes. The data are used to constrain the local H2 densities and relative molecular abundances in the clumpy cloud cores, and compared with lower frequency results from the literature. The implications of these results for the star formation environment are discussed, and an assessment made of possible strategies for their further investigation.

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7

McElroy, Daniel. "Grain surface chemistry in molecular clouds". Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602462.

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This work ia a study of chemistry in molecular clouds. I begin by describing the improvements made to gas phase chemical reaction data in the recent release of the UMIST database for astrochemistry (Rate 12). Improvements to the reaction network include the addition of anions, new reaction rate coefficient and branching rate measurements across all reactions types and newly calculated photodissociation and photoionisation rates.

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8

Morisawa, Yusuke. "Spectroscopic study of some chemically significant molecules in molecular clouds". 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/144599.

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9

García, Fuentes Pablo Fernando. "Giant Molecular Clouds in the Southern Milky Way". Tesis, Universidad de Chile, 2007. http://www.repositorio.uchile.cl/handle/2250/104575.

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10

Dobbs, Clare Louise. "The formation of molecular clouds in spiral galaxies /". St Andrews, 2007. http://hdl.handle.net/10023/214.

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Più fonti

Libri sul tema "Molecular clouds"

1

Serra, Guy, a cura di. Nearby Molecular Clouds. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/3-540-15991-6.

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2

Herrmann, Franz. Atomic oxygen in molecular clouds. Garching bei München: Max-Planck-Institut für extraterrestrische Physik, 1993.

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3

A, James R., Millar T. J e University of Manchester. Astronomy Dept., a cura di. Molecular clouds: The proceedings of a conference at the Department ofAstronomy, University of Manchester, 26-30 March 1990. Cambridge (England): Cambridge Univerversity Press, 1991.

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4

N, Mead Kathryn, University of Texas at Austin. Dept. of Astronomy, McDonald Observatory e United States. National Aeronautics and Space Administration, a cura di. Molecular clouds in the outer galaxy. Austin, Tex: University of Texas at Austin, Dept. of Astronomy and McDonald Observatory, 1986.

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5

United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch., a cura di. Molecular clouds in Orion and Monoceros. [Washington, DC]: National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1986.

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6

United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch., a cura di. Molecular clouds in the Carina arm. [Washington, DC]: National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1986.

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7

United States. National Aeronautics and Space Administration., a cura di. [Theory of grain alignment in molecular clouds]: [annual status report, 1 May 1992 - 28 Feb. 1993]. [Washington, DC: National Aeronautics and Space Administration, 1993.

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8

United States. National Aeronautics and Space Administration., a cura di. Theoretical studies in interstellar cloud chemistry: Final report. [Washington, DC: National Aeronautics and Space Administration, 1993.

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9

United States. National Aeronautics and Space Administration., a cura di. [Theory of grain alignment in molecular clouds]: [annual status report, 1 May 1992 - 28 Feb. 1993]. [Washington, DC: National Aeronautics and Space Administration, 1993.

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10

Handa, T. Thermal SiO and H13CO+ line observations of the dense molecular cloud G0.11-0.11 in the galactic center region. Nobeyama, Minamisaku, Nagano-ken, Japan: Nobeyama Radio Observatory of the National Astronomical Observatory, 2005.

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Più fonti

Capitoli di libri sul tema "Molecular clouds"

1

Blitz, Leo, e Jonathan P. Williams. "Molecular Clouds". In The Origin of Stars and Planetary Systems, 3–28. Dordrecht: Springer Netherlands, 1999. http://dx.doi.org/10.1007/978-94-011-4509-1_1.

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2

Carraro, Giovanni. "Molecular Clouds". In UNITEXT for Physics, 319–40. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-75293-4_15.

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3

Jaffe, D. T. "Warm Molecular Clouds". In Astrochemistry of Cosmic Phenomena, 311–15. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2761-5_68.

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4

Reitner, Joachim. "Cosmic Molecular Clouds". In Encyclopedia of Geobiology, 292–93. Dordrecht: Springer Netherlands, 2011. http://dx.doi.org/10.1007/978-1-4020-9212-1_243.

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5

Wilson, T. L., R. A. Gaume, K. J. Johnston e J. Schmid-Burgk. "Galactic Molecular Clouds". In ESO Astrophysics Symposia, 177–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-540-69999-6_25.

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6

Lebrun, F. "A synthetic view at large scale of local molecular clouds". In Nearby Molecular Clouds, 3–14. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/3-540-15991-6_67.

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7

de Vries, C. P. "Comparison of optical appearance and infrared emission of extended dust clouds". In Nearby Molecular Clouds, 20–24. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/3-540-15991-6_69.

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8

Boulanger, F., B. Baud e G. D. van Albada. "Correlation of high galactic latitude HI and FIR emission and warm dust in the neutral interstellar medium". In Nearby Molecular Clouds, 28–32. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/3-540-15991-6_71.

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9

Ungerer, V., N. Mauron, J. Brillet e Nguyen-Quang-Rieu. "C18—O and optical observations of the Taurus cloud in front of 3C 111". In Nearby Molecular Clouds, 68–71. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/3-540-15991-6_77.

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10

Beichman, C. A., J. P. Emerson, R. E. Jennings, S. Harris, B. Baud e E. T. Young. "IRAS observations of star formation in nearby molecular clouds". In Nearby Molecular Clouds, 95–103. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/3-540-15991-6_83.

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Atti di convegni sul tema "Molecular clouds"

1

Hamden, Erika T., David Schiminovich, Neal Turner, Blakesley Burkhart, Tom Haworth, Nicole Arulanantham, Haeun Chung et al. "Eos: a FUV spectroscopic mission to observe molecular hydrogen in molecular clouds". In Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray, a cura di Jan-Willem A. den Herder, Kazuhiro Nakazawa e Shouleh Nikzad, 11. SPIE, 2024. http://dx.doi.org/10.1117/12.3017644.

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2

Puy, Denis, e Monique Signore. "Primordial molecular clouds". In 3 K COSMOLOGY. ASCE, 1999. http://dx.doi.org/10.1063/1.59317.

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3

Phillips, Thomas G. "Millimeter and submillimeter wave astronomy". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.mh3.

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Abstract (sommario):

The interstellar medium consists of diffuse clouds and dense clouds containing atoms, molecules, and dust particles at temperatures ranging from 3 to several hundred kelvins. The dense cloud gas particles are mostly molecular and the species found vary from simple molecules such as H2, CO, CS, HCN, etc. to heavy types such as the cyanopolyynes. Molecules other than symmetric ones, such as H2, have dipole moments and can be observed through their rotational transitions which lie in the millimeter and submillimeter bands. The emission line strengths as seen by large ground radio telescopes are usually in the 0.1-10 K range in terms of equivalent blackbody emission. Therefore, sensitive heterodyne detectors are used where noise temperatures are only about ten times the quantum limit. The most sensitive types employ SIS detector elements, which can be used in conjunction with focal plane antenna structures such as bow-ties. Many studies have been carried out including molecule identification, temperature and density measurements, and studies of dynamics of gas clouds in our galaxy and other galaxies.

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4

Rice, Johnathan, e Steven Federman. "THE TRANSITION FROM DIFFUSE ATOMIC CLOUDS TO DENSE MOLECULAR CLOUDS". In 73rd International Symposium on Molecular Spectroscopy. Urbana, Illinois: University of Illinois at Urbana-Champaign, 2018. http://dx.doi.org/10.15278/isms.2018.rl08.

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5

Turner, B. E. "The nature of molecular clouds". In ASTROPHYSICAL IMPLICATIONS OF THE LABORATORY STUDY OF PRESOLAR MATERIALS. ASCE, 1997. http://dx.doi.org/10.1063/1.53334.

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6

Gredel, Roland. "Molecular abundances in translucent clouds". In The 50th international meeting of physical chemistry: Molecules and grains in space. AIP, 1994. http://dx.doi.org/10.1063/1.46571.

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7

Yuan, Chi, e Junhan You. "MOLECULAR CLOUDS AND STAR FORMATION". In Proceedings of the 7th Guo Shoujing Summer School on Astrophysics. WORLD SCIENTIFIC, 1995. http://dx.doi.org/10.1142/9789814533935.

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8

Chevalier, Roger A. "Supernova remnants in molecular clouds". In The eleventh astrophysics conference on young supernova remnants. AIP, 2001. http://dx.doi.org/10.1063/1.1377080.

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9

Krumholz, Mark R., Eduardo Telles, Renato Dupke e Daniela Lazzaro. "Star Formation in Molecular Clouds". In XV SPECIAL COURSES AT THE NATIONAL OBSERVATORY OF RIO DE JANEIRO. AIP, 2011. http://dx.doi.org/10.1063/1.3636038.

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Strong, Andy, Clive Dickinson e Eric Murphy. "Synchrotron emission from molecular clouds". In Cosmic Rays and the InterStellar Medium. Trieste, Italy: Sissa Medialab, 2015. http://dx.doi.org/10.22323/1.221.0036.

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Rapporti di organizzazioni sul tema "Molecular clouds"

1

Torres, D. High-Latitude Molecular Clouds as Gamma-Ray Sources for GLAST. Office of Scientific and Technical Information (OSTI), gennaio 2005. http://dx.doi.org/10.2172/839757.

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M, Padovani, Galli D., Liam Scarlett, Grassi T., U. Rehill, Mark Zammit, Bray I. e D. Fursa. Ultraviolet H2 luminescence in molecular clouds induced by cosmic rays. Office of Scientific and Technical Information (OSTI), ottobre 2023. http://dx.doi.org/10.2172/2377697.

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3

Digel, S. Small Molecular Clouds at High Latitudes as Gamma-Ray Sources for GLAST. Office of Scientific and Technical Information (OSTI), marzo 2005. http://dx.doi.org/10.2172/839933.

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4

Low, Mordecai-Mark Mac, Jayashree Toraskar, Jeffrey S. Oishi e Tom Abel. Dynamical Expansion of HII Regions From Ultracompact to Compact Sizes in Turbulent, Self-Gravitating Molecular Clouds. Office of Scientific and Technical Information (OSTI), maggio 2006. http://dx.doi.org/10.2172/882832.

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5

King, P. K. Gas Dynamics Near and Far: Observational Magnetohydrodynamics of Interstellar Molecular Clouds and X-Ray Ablation of Asteroids for the Earth's Defense. Office of Scientific and Technical Information (OSTI), giugno 2019. http://dx.doi.org/10.2172/1544929.

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6

Shomer, Ilan, Louise Wicker, Uzi Merin e William L. Kerr. Interactions of Cloud Proteins, Pectins and Pectinesterases in Flocculation of Citrus Cloud. United States Department of Agriculture, febbraio 2002. http://dx.doi.org/10.32747/2002.7580669.bard.

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The overall objective was to understand the cloud flocculation of citrus juice by characterization of the interactions between proteins and pectins, and to determine the role of PE isozymes in catalyzing this phenomenon. Specific objectives were to: 1. identify/characterize cloud-proteins in relation to their coagulable properties and affinity to pectins; 2. to determine structural changes of PME and other proteins induced by cation/pectin interactions; 3. localize cloud proteins, PME and bound protein/pectates in unheated and pasteurized juices; 4. to create "sensitized" pectins and determine their effect on clarification. The original objectives were not changed but the methods and approach were modified due to specific research requirements. Two i postulates were: 1. there is a specific interaction of cloud proteins with de-esterified regions of ! pectin and this contributes to cloud loss; 2. isozymes of pectin-methyl-esterase (PME) vary in efficiency to create sensitized pectins. The appearance of citrus fruit juice is an important quality factor and is determined by the color and turbidity that .are conferred by the suspended particles, i.e., by the cloud and its homogeneity. Under some circumstances the cloud tend to flocculate and the juice clarifies. The accepted approach to explain the clarification is based on pectin demethoxylation by PME that promotes formation of Ca-pectate. Therefore, the juice includes immediate heat-inactivation upon ~ squeezing. Protein coagulation also promotes cloud instability of citrus fruit extracts. However, the clarification mechanism is not fully understood. Information accumulated from several laboratories indicates that clarification is a more complex process than can be explained by a single mechanism. The increasing trend to consume natural-fresh juice emphasizing the importance of the knowledge to assure homogeneity of fresh juice. The research included complementary directions: Conditions that induce cloud-instability of natural- juice [IL]. Evaluate purification schemes of protein [USA]. Identifications of proteins, pectin and neutral sugars ([IL]; Structure of the cloud components using light and electron microscopy and immuno-labeling of PME, high-methoxyl-pectin (HMP) and low-methoxyl-pectin (LMP); Molecular weight of calcium sensitized pectins [US]; Evaluation of the products of PME activity [US]. Fractions and size distribution and cloud components [IL-US]. The optimal pH activity of PME is 7 and the flocculation pH of the cloud is 3-4. Thus, the c roles of PME, proteins and pectins in the cloud instability, were studied in pH ranges of 2- 7. The experiments led to establish firstly repeatable simulate conditions for cloud instability [IL]. Thermostable PME (TS-PE) known to induce cloud instability, but also thermolabile forms of PME (TL-PE) caused clarification, most likely due to the formation and dissolution of inactive :. PE-pectin complexes and displacement of a protective colloid from the cloud surface [US]. Furthermore, elimination of non-PME protein increases TS-PE activity, indicating that non-PME proteins moderate PME activity [US]. Other experiments Concomitantly with the study of the PME activity but promotes the association of cloud-proteins to pectin. Adjusting of the juice pH to f 7 retains the cloud stability and re-adjusting of the pH to 40% DE reacts to immuno-labeling in the cloud fragments, whereas

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7

Bacharach, Eran, e Sagar Goyal. Generation of Avian Pneumovirus Modified Clones for the Development of Attenuated Vaccines. United States Department of Agriculture, novembre 2008. http://dx.doi.org/10.32747/2008.7696541.bard.

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Abstract (one page maximum, single spaced), include: List the original objectives, as defined in the approved proposal, and any revisions made at the beginning or during the course of project: The main goal described in our original proposal has been the development of a molecular infectious clone of the avian metapneumovirus subtype B (aMPV-B) and the modification of this clone to create mutated viruses for the development of attenuated vaccines. The Achievements and Appendix/Part I sections of this report describes the accomplishments in creating such a molecular clone. These sections also contain the results of a longitudinal study that we made in Israel, demonstrating the infiltration of field strains of aMPV into vaccinated flocks and emphasizing the need for the development of better vaccines. We also describe our unexpected findings regarding the ability of aMPV to establish persistent infection in cell cultures. Although this direction of research was not described in the original proposal we feel that it is highly important for the understanding of aMPV pathogenesis. For example, this direction has provided us with evidence showing that aMPV replication can augment influenza replication. Moreover, we observed that viruses that were produced from chronically-infected cells show reduced ciliostasis. Accordingly, we carried vaccination trials using such viruses. In the original grant proposal we also offered that the American lab will clone and express immunomodulators in the context of an aMPV -based replicon that the Israeli lab has generated. However, as we reported in our annual reports, further analysis of this replicon by the Israeli lab has revealed that the level of expression achieved by this vehicle is relatively poor; thus, the American lab has focused on sequencing the genomes of different aMPV-C isolates that differ in their virulence (including vaccine strains). Achievements and Appendix/Part II sections of this report include the summary of this effort. Background to the topic: The aMPVs belong to the paramyxoviridae family and cause mild to severe respiratory tract diseases mainly in turkeys and also in chickens. Four aMPV subgroups, A, B, C and D, have been characterized; in Israel aMPV-A and B are the common subtypes while in the USA type C is the prevalent one. Although vaccine strains do exist for aMPVs, they do not always provide full protection against virulent strains and the vaccines themselves may induce disease to some extent. Improved vaccines against aMPV are needed, to achieve better protection of the poultry industry against this pathogen. Major conclusions, solutions, achievements: We isolated aMPV-B from a diseased flock and accomplished the sequencing and cloning of its full-genome. In addition, we cloned the four genes encoding the viral replicase. These should serve as the platform for generation of modified aMPV-Bs from molecular clones. We also identified aMPVs that are attenuated in respect to their ciliostatic activity and accordingly showed the potential of such viruses as vaccine strains. For aMPV-C, the different mutations scattered along the genome of different isolates with varied virulence have been determined. Implications, both scientific and agricultural: The newly identified pattern of mutations in attenuated strains will allow better understanding of the pathogenicity of aMPV and the generation of aMPV molecular clones, together with isolation of strains with attenuated ciliostatic activity should generate improved vaccine strains Abstract (one page maximum, single spaced), include: List the original objectives, as defined in the approved proposal, and any revisions made at the beginning or during the course of project: The main goal described in our original proposal has been the development of a molecular infectious clone of the avian metapneumovirus subtype B (aMPV-B) and the modification of this clone to create mutated viruses for the development of attenuated vaccines. The Achievements and Appendix/Part I sections of this report describes the accomplishments in creating such a molecular clone. These sections also contain the results of a longitudinal study that we made in Israel, demonstrating the infiltration of field strains of aMPV into vaccinated flocks and emphasizing the need for the development of better vaccines. We also describe our unexpected findings regarding the ability of aMPV to establish persistent infection in cell cultures. Although this direction of research was not described in the original proposal we feel that it is highly important for the understanding of aMPV pathogenesis. For example, this direction has provided us with evidence showing that aMPV replication can augment influenza replication. Moreover, we observed that viruses that were produced from chronically-infected cells show reduced ciliostasis. Accordingly, we carried vaccination trials using such viruses. In the original grant proposal we also offered that the American lab will clone and express immunomodulators in the context of an aMPV -based replicon that the Israeli lab has generated. However, as we reported in our annual reports, further analysis of this replicon by the Israeli lab has revealed that the level of expression achieved by this vehicle is relatively poor; thus, the American lab has focused on sequencing the genomes of different aMPV-C isolates that differ in their virulence (including vaccine strains). Achievements and Appendix/Part II sections of this report include the summary of this effort. Background to the topic: The aMPVs belong to the paramyxoviridae family and cause mild to severe respiratory tract diseases mainly in turkeys and also in chickens. Four aMPV subgroups, A, B, C and D, have been characterized; in Israel aMPV-A and B are the common subtypes while in the USA type C is the prevalent one. Although vaccine strains do exist for aMPVs, they do not always provide full protection against virulent strains and the vaccines themselves may induce disease to some extent. Improved vaccines against aMPV are needed, to achieve better protection of the poultry industry against this pathogen. Major conclusions, solutions, achievements: We isolated aMPV-B from a diseased flock and accomplished the sequencing and cloning of its full-genome. In addition, we cloned the four genes encoding the viral replicase. These should serve as the platform for generation of modified aMPV-Bs from molecular clones. We also identified aMPVs that are attenuated in respect to their ciliostatic activity and accordingly showed the potential of such viruses as vaccine strains. For aMPV-C, the different mutations scattered along the genome of different isolates with varied virulence have been determined. Implications, both scientific and agricultural: The newly identified pattern of mutations in attenuated strains will allow better understanding of the pathogenicity of aMPV and the generation of aMPV molecular clones, together with isolation of strains with attenuated ciliostatic activity should generate improved vaccine strains.

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8

Offner, S., M. Krumholz, R. Klein e C. McKee. The Kinematics of Molecular Cloud Cores in the Presence of Driven and Decaying Turbulence: Comparisons with Observations. Office of Scientific and Technical Information (OSTI), aprile 2008. http://dx.doi.org/10.2172/938508.

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9

Banai, Menachem, e Gary Splitter. Molecular Characterization and Function of Brucella Immunodominant Proteins. United States Department of Agriculture, luglio 1993. http://dx.doi.org/10.32747/1993.7568100.bard.

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The BARD project was a continuation of a previous BARD funded research project. It was aimed at characterization of the 12kDa immunodominant protein and subsequently the cloning and expression of the gene in E. coli. Additional immunodominant proteins were sought among genomic B. abortus expression library clones using T-lymphocyte proliferation assay as a screening method. The 12kDa protein was identified as the L7/L12 ribosomal protein demonstrating in the first time the role a structural protein may play in the development of the host's immunity against the organism. The gene was cloned from B. abortus (USA) and B. melitensis (Israel) showing identity of the oligonucleotide sequence between the two species. Further subcloning allowed expression of the protein in E. coli. While the native protein was shown to have DTH antigenicity its recombinant analog lacked this activity. In contrast the two proteins elicited lymphocyte proliferation in experimental murine brucellosis. CD4+ cells of the Th1 subset predominantly responded to this protein demonstrating the development of protective immunity (g-IFN, and IL-2) in the host. Similar results were obtained with bovine Brucella primed lymphocytes. UvrA, GroE1 and GroEs were additional Brucella immunodominant proteins that demonstrated MHC class II antigenicity. The role cytotoxic cells are playing in the clearance of brucella cells was shown using knock out mice defective either in their CD4+ or CD8+ cells. CD4+ defective mice were able to clear brucella as fast as did normal mice. In contrast mice which were defective in their CD8+ cells could not clear the organisms effectively proving the importance of this subtype cell line in development of protective immunity. The understanding of the host's immune response and the expansion of the panel of Brucella immunodominant proteins opened new avenues in vaccine design. It is now feasible to selectively use immunodominant proteins either as subunit vaccine to fortify immunity of older animals or as diagnostic reagents for the serological survaillance.

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Newton, Ronald, Joseph Riov e John Cairney. Isolation and Functional Analysis of Drought-Induced Genes in Pinus. United States Department of Agriculture, settembre 1993. http://dx.doi.org/10.32747/1993.7568752.bard.

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Drought is a common factor limiting timber production in the U.S. and Israel. Loblolly (Pinus taeda) and alleppo pine (Pinus halepensis) seedling survival is reduced when out planted, and growth and reproduction are often hindered by periodic droughts during later stages of tree development. Molecular and gene responses to drought stress have not been characterized. The objectives were to characterize drought-induced gene clones from these pines, to determine the effects of a growth regulator on drought tolerance, ABA levels, and drought-induced gene expression in alleppo pine, and to develop procedures for loblolly pine transformation. Nearly 20 cDNA clones influenced by gradual, prolonged drought stress have been isolated. Many of these have been shown to be induced by drought stress, whereas several others are down-regulated. These are the first drought-induced genes isolated from a pine species. Two genomic clones (lp5-1 and lp3-1) have been sequenced and characterized, and each has been found to be associated with a gene family. Clone lp5 appears to code for a cell wall protein, and clone lp3 codes for a nuclear protein. The former may be associated with changing the elastic properties of the cell wall, while the latter may be involved in signal transduction and/or protection from desiccation in the nucleus. Clone lp3 is similar to a drought-induced gene from tomato and is regulated by ABA. Several DNA sequences that are specific to induction during growth-retardation in alleppo pine by uniconazole have been identified. The active DNA species is now being identified. Promoters from genomic clones, lp3 and lp5, have been sequenced. Both are functional when fused with the gus reporter gene and transferred to other plant tissues as well as responding to a simulated drought stress. Through exodeletion analysis, it has been established that the promoter ABRE element of lp3 responds to ABA and that drought-induction of lp3 expression may also involve ABA. Stable tobacco transformants carrying either the lp5 or the lp3 promoter fused to a reporter gus gene have been obtained. The lp5lgus fusion was expressed at several stages of tobacco development and differentiation including the reproductive stage. There was no difference in phenotype between the transformants and the wild type. Embryogenesis procedures were developed for slash pine, but attempts to couple this process with gene transfer and plantlet transformation were not successful. Transformation of pine using Agrobacterium appears tractable, but molecular data supporting stable integration of the Agrobacterium-transferred gene are still inconclusive.

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