Готові списки джерел за темами / Dwards form

Добірка наукової літератури з теми "Dwards form"

Автор: Grafiati

Опубліковано: 30 травня 2022

Оновлено: 31 травня 2022

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Статті в журналах з теми "Dwards form"

Jackson, R. A., S. Kaviraj, G. Martin, J. E. G. Devriendt, A. Slyz, J. Silk, Y. Dubois, et al. "Dark matter-deficient dwarf galaxies form via tidal stripping of dark matter in interactions with massive companions." Monthly Notices of the Royal Astronomical Society 502, no. 2 (January 15, 2021): 1785–96. http://dx.doi.org/10.1093/mnras/stab093.

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ABSTRACT In the standard ΛCDM (Lambda cold dark matter) paradigm, dwarf galaxies are expected to be dark matter-rich, as baryonic feedback is thought to quickly drive gas out of their shallow potential wells and quench star formation at early epochs. Recent observations of local dwarfs with extremely low dark matter content appear to contradict this picture, potentially bringing the validity of the standard model into question. We use NewHorizon, a high-resolution cosmological simulation, to demonstrate that sustained stripping of dark matter, in tidal interactions between a massive galaxy and a dwarf satellite, naturally produces dwarfs that are dark matter-deficient, even though their initial dark matter fractions are normal. The process of dark matter stripping is responsible for the large scatter in the halo-to-stellar mass relation in the dwarf regime. The degree of stripping is driven by the closeness of the orbit of the dwarf around its massive companion and, in extreme cases, produces dwarfs with halo-to-stellar mass ratios as low as unity, consistent with the findings of recent observational studies. ∼30 per cent of dwarfs show some deviation from normal dark matter fractions due to dark matter stripping, with 10 per cent showing high levels of dark matter deficiency (Mhalo/M⋆ < 10). Given their close orbits, a significant fraction of dark matter-deficient dwarfs merge with their massive companions (e.g. ∼70 per cent merge over time-scales of ∼3.5 Gyr), with the dark matter-deficient population being constantly replenished by new interactions between dwarfs and massive companions. The creation of these galaxies is therefore a natural by-product of galaxy evolution and their existence is not in tension with the standard paradigm.

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Chandra, Vedant, Hsiang-Chih Hwang, Nadia L. Zakamska, and Tamás Budavári. "Computational tools for the spectroscopic analysis of white dwarfs." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 25, 2020): 2688–98. http://dx.doi.org/10.1093/mnras/staa2165.

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ABSTRACT The spectroscopic features of white dwarfs are formed in the thin upper layer of their stellar photosphere. These features carry information about the white dwarf’s surface temperature, surface gravity, and chemical composition (hereafter ‘labels’). Existing methods to determine these labels rely on complex ab-initio theoretical models, which are not always publicly available. Here, we present two techniques to determine atmospheric labels from white dwarf spectra: a generative fitting pipeline that interpolates theoretical spectra with artificial neural networks and a random forest regression model using parameters derived from absorption line features. We test and compare our methods using a large catalogue of white dwarfs from the Sloan Digital Sky Survey (SDSS), achieving the same accuracy and negligible bias as compared to previous studies. We package our techniques into an open-source python module ‘wdtools’ that provides a computationally inexpensive way to determine stellar labels from white dwarf spectra observed from any facility. We will actively develop and update our tool as more theoretical models become publicly available. We discuss applications of our tool in its present form to identify interesting outlier white dwarf systems including those with magnetic fields, helium-rich atmospheres, and double-degenerate binaries.

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Martín, Eduardo L., Mike Connelley, Dan Potter, and Hervé Bouy. "Brown Dwarf Companions to Solar-Type Stars and other Brown Dwarfs." Symposium - International Astronomical Union 213 (2004): 111–14. http://dx.doi.org/10.1017/s007418090019309x.

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We report on our ongoing imaging efforts to detect brown dwarfs orbiting solar-type stars and other brown dwarfs. We study the properties of brown dwarf companions as a function of primary mass. Our results indicate that the frequency of brown dwarf companions around solar-type stars for separations larger than about 40 AU is non-negligible. The frequency of brown dwarf binaries is about 20%. There is a dearth of brown dwarf binaries with separations larger than ∼20 AU. We propose that brown dwarf systems are a scaled down version of stellar systems, which probably form via triggered collapse of small molecular cores.

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Allard, France, Tristan Guillot, Hans-Günter Ludwig, Peter H. Hauschildt, Andreas Schweitzer, David R. Alexander, and Jason W. Ferguson. "Model Atmospheres and Spectra: The Role of Dust." Symposium - International Astronomical Union 211 (2003): 325–32. http://dx.doi.org/10.1017/s0074180900210875.

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Brown dwarf atmospheres form molecules, then high temperature condensates (corundum, titanates, silicates, and iron compounds), and then low temperature condensates (ices) as they cool down over time. These produce large opacities which govern entirely their spectral energy distribution. Just as it is important to know molecular opacities (TiO, H2O, CH4, etc.) with accuracy, it is imperative to understand the interplay of processes (e.g. condensation, sedimentation, coagulation, convection) that determines the radial and size distribution of grains. Limiting case models have shown that young, hot brown (L) dwarfs form dust mostly in equilibrium, while at much cooler stages (late T dwarfs) all high temperature condensates have sedimented out of their photospheres. But this process is gradual and all intermediate classes of brown dwarfs can partly be understood in terms of partial sedimentation of dust. With new models accounting for these processes, we describe the effects they may have upon brown dwarf spectral properties.

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Nomoto, K., and M. Hashimoto. "White Dwarf Models of Supernovae and Cataclysmic Variables." International Astronomical Union Colloquium 93 (1987): 395–411. http://dx.doi.org/10.1017/s0252921100105135.

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AbstractIf the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae and observations. We describe various types of evolution of accreting white dwarfs as a function of binary parameters (i.e, composition, mass, and age of the white dwarf, its companion star, and mass accretion rate), and discuss the conditions for the precursors of exploding or collapsing white dwarfs, and their relevance to cataclysmic variables. Particular attention is given to helium star cataclysmics which might be the precursors of some Type I supernovae or ultrashort period X-ray binaries. Finally we present new evolutionary calculations using the updated nuclear reaction rates for the formation of O+Ne+Mg white dwarfs, and discuss the composition structure and their relevance to the model for neon novae.

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Damasco, OP, ID Godwin, MK Smith, and SW Adkins. "Gibberellic acid detection of dwarf offtypes in micropropagated Cavendish bananas." Australian Journal of Experimental Agriculture 36, no. 2 (1996): 237. http://dx.doi.org/10.1071/ea9960237.

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Detection of dwarf offtypes produced by micropropagation of Cavendish bananas (Musa spp.) cultivars New Guinea Cavendish and Williams was achieved by spraying gibberellic acid (GA3) solution (289 pmol/L) onto deflasked plants and measuring various plantlet responses. The most useful identification criterion was elongation of the sheath of the first leaf to form after GA3 application. Elongation of this structure was about 2-fold greater in normal plants than observed in dwarfs. Similar measurements taken earlier during in vitro culture or later during plant establishment in soil were not as useful in discriminating between normals and dwarfs as the measurements made at deflasking. The similar GA3-induced elongation response of the dwarf offtype and that of the naturally occurring dwarf cultivar Dwarf Parfitt suggests that the mechanism for dwarfism could be the same in the 2 cases.

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Nelson, A. H., and P. R. Williams. "Numerical Simulation of the Dwarf Companions of Giant Galaxies." Proceedings of the International Astronomical Union 3, S244 (June 2007): 226–30. http://dx.doi.org/10.1017/s1743921307014020.

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AbstractWe report simulations of the formation of a giant disc galaxy from cosmological initial conditions. Two sets of initial conditions are used, initially smooth density for both gas and stars, representing the Warm dark Matter scenario, and an initially fluctuating density representing the standard spectrum for the Cold dark Matter scenario. For the WDM initial conditions, the galaxy has a population of long lived dwarf satellites at z = 0, with orbits close to a plane coincident with that of the giant galaxy disc. The detailed properties of these dwarfs mimic closely the observed properties of Local Group dwarfs with respect to mass, and kinematics. However they do not have individual dark matter halos, but orbit in the nearly spherical dark matter halo of the giant galaxy. The reason for this is that the initial population of dwarf dark matter haloes, which form during the initial collapse phase, all merge into the halo of the giant galaxy within a few to several Gyears, while the long lived dwarfs form as a secondary population by gravitational collapse of high angular momentum gas in the outer reaches of the giants proto-galactic disc. Due to their late formation and their more distant orbits, they survive until the present epoch as individual dwarf galaxies at radii 20-50kpc from the giants centre. For CDM initial conditions there are many more dwarf satellites at z = 0, some of which form early on as gas condensations in DM sub-halos, and survive with these individual DM halos till z = 0 due to their being sufficiently well bound to avoid merging with the main galaxy. However even in this case some second generation satellites form as initially gas only objects, just as for the smooth initial conditions of WDM.

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Tremmel, M., A. C. Wright, A. M. Brooks, F. Munshi, D. Nagai, and T. R. Quinn. "The formation of ultradiffuse galaxies in the RomulusC galaxy cluster simulation." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 13, 2020): 2786–810. http://dx.doi.org/10.1093/mnras/staa2015.

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ABSTRACT We study the origins of 122 ultradiffuse galaxies (UDGs) in the Romulus c zoom-in cosmological simulation of a galaxy cluster (M200 = 1.15 × 1014 M⊙), one of the only such simulations capable of resolving the evolution and structure of dwarf galaxies (M⋆ < 109 M⊙). We find broad agreement with observed cluster UDGs and predict that they are not separate from the overall cluster dwarf population. UDGs in cluster environments form primarily from dwarf galaxies that experienced early cluster in-fall and subsequent quenching due to ram pressure. The ensuing dimming of these dwarf galaxies due to passive stellar evolution results in a population of very low surface brightness galaxies that are otherwise typical dwarfs. UDGs and non-UDGs alike are affected by tidal interactions with the cluster potential. Tidal stripping of dark matter, as well as mass-loss from stellar evolution, results in the adiabatic expansion of stars, particularly in the lowest mass dwarfs. High-mass dwarf galaxies show signatures of tidal heating while low-mass dwarfs that survive until z = 0 typically have not experienced such impulsive interactions. There is little difference between UDGs and non-UDGs in terms of their dark matter haloes, stellar morphology, colours, and location within the cluster. In most respects cluster UDG and non-UDGs alike are similar to isolated dwarf galaxies, except for the fact that they are typically quenched.

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Kilic, Mukremin, P. Bergeron, Simon Blouin, and A. Bédard. "The most massive white dwarfs in the solar neighbourhood." Monthly Notices of the Royal Astronomical Society 503, no. 4 (March 16, 2021): 5397–408. http://dx.doi.org/10.1093/mnras/stab767.

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ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

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Whelan, Emma T., Thomas P. Ray, Francesca Bacciotti, Sofia Randich, Ray Jayawardhana, Antonella Natta, Leonardo Testi, and Subu Mohanty. "Outflow activity in brown dwarfs." Proceedings of the International Astronomical Union 3, S243 (May 2007): 357–64. http://dx.doi.org/10.1017/s1743921307009714.

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AbstractWhile numerous studies have been aimed at understanding the properties of young brown dwarfs relatively little exploration of their potential as drivers of outflows has occurred. Forbidden emission lines are important probes of outflows from young stellar objects, as they trace the shocks which form as an outflow interacts with the ambient medium of its driving source. While forbidden emission was identified in the spectra of young brown dwarfs, indicating the presence of outflows, these lines were weak and confined to the brown dwarf continuum position. Hence their origin in an outflow could not be confirmed. Our approach to this problem, is to analyse the forbidden line regions of brown dwarfs using spectro-astrometry. Spectro-astrometry is a novel technique which allows the user to recover spatial information from a spectrum beyond the limitations of the seeing of the observation. Using this technique we have found two brown dwarf outflows to date. In this chapter we outline this technique, describe our results for the brown dwarfs ρ-Oph 102 and 2MASS1207-3932 and discuss our future plans.

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Більше джерел

Дисертації з теми "Dwards form"

Талмач, Дмитро Павлович. "Детерміновані методи відображення повідомлення в точку еліптичної кривої, заданої у різних формах". Bachelor's thesis, КПІ ім. Ігоря Сікорського, 2021. https://ela.kpi.ua/handle/123456789/44276.

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Данна робота присвячена розробцi детермiнованих полiномiальних алгоритмiв кодування бiтових векторiв в точки елiптичних кривих представлених у рiзних формах. У роботi приводяться основнi необхiднi для розумiння викладок вiдомостi про елiптичнi кривi, особливо кривi в формi Едвардса. Далi детально розглядається проблема кодування елементiв поля, над яким визначена крива, у множину точок кривої для використання у криптографiчних протоколах, в основi яких лежить хешування або задача iнкапсуляцiї ключа. У останньому роздiлi презентуються новi алгоритми, наводиться їх порiвняльний аналiз.
The work is devoted to constructing deterministic polynomial algorithm for encoding sequences of bits into points of Elliptic Curves represented in different forms. The work presents basic information related to the topic of Elliptic Curves, especially in the Edwards form, that is necessary for understanding further mathematical calculations. Next, the problem of encoding underlying field elements, over which the curve is defined, into points of the curve for using this encoding in cryptographic protocols, which are based on hashing or key encapsulation schemes, is considered in more detail. In the last section new algorithms are presented and compared.

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Voss, Björn. "White dwarfs in the SPY and HQS surveys an analysis of a large set of white dwarf spectra and a search for variable ZZ Ceti white dwarfs /." [S.l.] : [s.n.], 2006. http://e-diss.uni-kiel.de/diss_1796/d1796.pdf.

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Gomes, Joana. "Searching for benchmark systems containing ultra-cool dwarfs and white dwarfs." Thesis, University of Hertfordshire, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.630036.

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I here present my search for benchmark systems with main sequence stars widely separated from ultracool dwarfs or white dwarfs. Different near-infrared and optical surveys have been used to create samples of L dwarf candidates from colour cuts and by exploring the faintest limits of available surveys. I started by using the Two Micron All Sky Survey, and then expanded my method in order to include sources from the UKIRT Infrared Deep Sky Survey, which has not yet been fully explored for L dwarfs. In order to search for wide main sequence star companions I have used stars from Hipparcos, Gliese and PPMXL. I then applied a set of selection rules based on photometry and proper motion to find these systems. This search led to the discovery of two new benchmark systems with genuine L dwarfs, that have been spectroscopically confirmed. A large sample of potentially new systems still awaits a complete analysis, and we thus expect more exciting discoveries to stem from the method utilized. A method to identify new late-T and Y dwarfs from the Wide-field Infrared Survey was also been developed, with the aim of using the surveys maximum sensitive limits. The technique relies on objects only detected in the W2-band and through a series of rejection methods 158 sources are retrieved with signal-to-noises ranging from 8-10. I have performed aperture photometry and measured proper motions for a set of candidates that were observed during the follow-up campaign. I then present a new sample of potentially white dwarfs with common proper motions main sequence star companions. The white dwarfs are retrieved from SuperCOSMOS whereas stellar companions are from Tycho. I present spectra for 39 WD candidates and for 6 stars. Temperatures and surface gravities are estimated for the white dwarf objects, whilst main sequence stars abundances are obtained from the fitting of synthetic spectra to the observations. Finally I discuss the implications of these findings and what future work can be done with these benchmark systems.

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Deshpande, Rohit. "Search for gas giants around late-M dwarfs." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4640.

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The absolute radial and rotational velocities of our targets were also calculated. Values of rotational velocities indicate that M dwarfs are, in general, slow rotators. Using our result and that from literature, we extended our study of rotational velocities to L dwarfs. Our observations show an increase in rotational velocities from late M to L dwarfs. We also find that the mean periods of M dwarfs are less than 10 hours. In order to improve our precision in measuring relative radial velocity (RV), we employed the use of deconvolution method. With this method we were able to ameliorate relative RV precision from 300 m/s to 200 m/s. This was a substantial improvement in our ability to detect gas-giant planets. However none of the 15 dwarfs we monitored indicate a presence of companions. This null result was then used to compute the upper limit to the binary frequency and close-in Jupiter mass planetary frequency. We find the binary frequency to be 11% while the planetary frequency was 1.20%.; We carried out a near-infrared radial velocity search for Jupiter-mass planets around 36 late M dwarfs. This survey was the first of its kind undertaken to monitor radial velocity variability of these faint dwarfs. For this unique survey we employed the 10-m Keck II on Mauna Kea in Hawaii. With a resolution of 20,000 on the near-infrared spectrograph, NIRSPEC, we monitored these stars over four epochs in 2007. In addition to the measurement of relative radial velocity we established physical properties of these stars. The physical properties of M dwarfs we determined included the identification of neutral atomic lines, the measurement of pseudo-equivalent widths, masses, surface gravity, effective temperature, absolute radial velocities, rotational velocities and rotation periods. The identification of neutral atomic lines was carried out using the Vienna Atomic line Database. We were able to confirm these lines that were previously identified. We also found that some of the lines observed in the K-type stars, such as Mg I though weak, still persist in late M dwarfs. Using the measurement of pseudo-equivalent widths (p-EW) of 13 neutral atomic lines, we have established relations between p-EW and spectral type. Such relations serve as a tool in determining the spectral type of an unknown dwarf star by means of measuring its p-EW. We employed the mass-luminosity relation to compute the masses of M dwarfs. Our calculations indicate these dwarfs to be in the range of 0.1 to 0.07 solar masses. This suggests that some of the late M dwarfs appear to be in the Brown dwarf regime. Assuming their radii of 0.1 solar radii, we calculated their surface gravity. The mean surface gravity is, log g = 5.38. Finally their effective temperature was determined by using the spectral-type temperature relationship. Our calculations show effective temperatures in the range of 3000 to 2300 K. Comparison of these values with models in literature show a good agreement.
ID: 029094443; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 224-246).
Ph.D.
Doctorate
Department of Physics
Sciences

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Day-Jones, A. C. "Searching for brown dwarf companions." Thesis, University of Hertfordshire, 2009. http://hdl.handle.net/2299/3475.

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In this thesis I present the search for ultracool dwarf companions to main sequence stars, subgiants and white dwarfs. The ultracool dwarfs identified here are benchmark objects, with known ages and distances. The online data archives, the two micron all sky survey (2MASS) and SuperCOSMOS were searched for ultracool companions to white dwarfs, where one M9 1 companion to a DA white dwarf is spectroscopically confirmed as the widest separated system of its kind known to date. The age of the M9 1 is constrained to a minium age of 1.94Gyrs, based on the estimated age of the white dwarf from a spectroscopically derived Teff and log g and an initial-final mass relation. This search was extended using the next generation surveys, the sloan digital sky survey (SDSS) and the UK infrared deep sky survey (UKIDSS), where potential white dwarf + ultracool dwarf binary systems from this search are presented. A handful of these candidate systems were followed-up with second epoch near infrared (NIR) imaging. A new white dwarf with a spectroscopic M4 companion and a possible wide tertiary ultracool component is here confirmed. Also undertaken was a pilot imaging survey in the NIR, to search for ultracool companions to subgiants in the southern hemisphere using the Anglo-Australian telescope. The candidates from that search, as well as the subsequent follow-up of systems through second epoch NIR/optical imaging and methane imaging are presented. No systems are confirmed from the current data but a number of good candidates remain to be followed-up and look encouraging. A search for widely separated ultracool objects selected from 2MASS as companions to Hipparcos main-sequence stars was also undertaken. 16 candidate systems were revealed, five of which had been previously identified and two new L0 2 companions are here confirmed, as companions to the F5V spectroscopic system HD120005 and the M dwarf GD 605. The properties of HD120005C were calculated using the DUSTY and COND models from the Lyon group, and the age of the systems were inferred from the primary members. For GD 605B no age constraint could be placed due to the lack of information available about the primary, but HD120005C has an estimated age of 2-4Gyr. In the final part of this thesis I investigate correlations with NIR broadband colours (J - H, H - K and J - K) with respect to properties, Teff , log g and [Fe/H] for the benchmark ultracool dwarfs, both confirmed from the searches undertaken in this work and those available from the literature. This resulted in an observed correlation with NIR colour and Teff, which is presented here. I find no correlation however with NIR colours and log g or [Fe/H], due in part to a lack of suitable benchmarks. I show that despite the current lack of good benchmark objects, this work has the potential to allow UCD properties to be measured from observable characteristics, and suggest that expanding this study should reveal many more benchmarks where true correlation between properties and observables can be better investigated.

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Kuzmychov, Oleksii [Verfasser], and Svetlana [Akademischer Betreuer] Berdyugina. "Spectropolarimetric approach for measuring magnetic fields on brown dwarfs." Freiburg : Universität, 2015. http://d-nb.info/1122742681/34.

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Edstam, Louise. "Ranking line-depth ratios for determining relative star temperatures in dwarfs." Thesis, Uppsala universitet, Observationell astrofysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-202315.

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The central line-depths of absorption lines depend upon stellar temperature. By dividing the central line-depth of such a line with a central line-depth independent of temperature, a thermometer of relative star temperatures is obtained in the form of a line-depth ratio (LDR), once it is related to an effective temperature scale. Such thermometers are known to give precise results which is why the method is pursued. The purpose of this work is to rank LDRs according to a set of criteria to find the most suitable ratio to measure temperature. This is done based on a set of LDRs measured for a large sample of dwarf stars with known effective temperature, atmospheric pressure and chemical composition. Numerous LDRs are eliminated because their temperature dependence are limited to a short temperature interval. Further LDRs are eliminated due to dependence on the atmospheric pressure and chemical composition of the LDR. The remaining LDRs are ranked based on the strength of temperature dependence, the fit of the representative polynomial to the data points and the number of data points available. The best ranked LDR provides a temperature resolution smaller than 10 K over a temperature interval of 4500-6250 K, assuming an uncertainty in LDR of 0.01.

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Rowell, Nicholas. "The luminosity function for white dwarfs in the SuperCOSMOS Sky Survey." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/25139.

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I present a magnitude and proper motion limited catalogue of ~ 10,000 white dwarf candidates, obtained from the SuperCOSMOS Sky Survey by means of reduced proper motion selection. This catalogue extends to R ~ 19.75 and μ ~ 0".05 yr⁻¹, and covers more than three quarters of the sky. Spectroscopic follow-up observations have been obtained for a subsample of objects, and are used to assess the reliability of the selection procedure and contamination of the final catalogue. Photometric parallaxes provide distance estimates accurate to ~ 50%. This catalogue is used to measure the luminosity function (LF) for white dwarfs in the Solar neighbourhood over the range 4 ≤ Mbol ≤ 18. A new technique is devised to separate the LFs for disk and spheroid stars, which allows all stars to contribute to the LF even at tangential velocities where the populations overlap. The disk LF shows a sharp decline at Mbol = 15.75, in agreement with other studies, and extends over a magnitude fainter than previously determined. The spheroid LF has a sharp peak at Mbol = 15.75, then levels out and shows no sign of a drop off at faint magnitudes, as expected for a considerably older population. By simulating white dwarf LFs for stellar populations with a range of star formation histories, I measure the age of the local disk and spheroid. The disk age of 9.13⁺⁰ ⁶⁶₋₀.₆₇ Gyr agrees with that measured in similar studies, and with the basic picture of galaxy formation in a cosmological context. No reliable solution is found for the spheroid age. By integrating the LFs, I investigate the local mass density of spheroid white dwarfs, with particular reference to their contribution to the baryonic dark matter content of the Galaxy. I also place an upper limit on their contribution to the possible MACHO population and the microlensing events observed towards the LMC.

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Hendler, Nathanial P., Gijs D. Mulders, Ilaria Pascucci, Aaron Greenwood, Inga Kamp, Thomas Henning, Francois Menard, William R. F. Dent, and Neal J. II Evans. "Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624452.

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The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O I] 63 mu m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O I] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O I] 63 mu m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA-to establish if and how disk radii scale with stellar mass-should be pursued further.

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Hepburn, Ian David. "Development of linear InSb array instrumentation and the search for brown dwarfs." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46816.

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Книги з теми "Dwards form"

East, Jacqueline. Snow White and the seven dwarfs. New York, NY: Parragon Books Ltd, 2013.

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Snow White and the Seven Dwarfs (Favourite Tales). Ladybird Books, 1993.

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Bohn, James, and Jeff Kurtti. Music in Disney's Animated Features. University Press of Mississippi, 2017. http://dx.doi.org/10.14325/mississippi/9781496812148.001.0001.

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Music in Disney’s Animated Features: Snow White and the Seven Dwarfs to The Jungle Book investigates how music functions in Disney Animated films. The book identifies several techniques used in a number of Disney animated movies. In addition it also presents a history of music in Disney animated films, as well as biographical information on several of the Studios’ seminal composers. The popularity and critical acclaim of Disney animated features is built as much on music as it is on animation. From Steamboat Willie through Bambi, music is the organizing element of Disney’s animation. Songs that establish character and aid in narrative form the backbone of the Studios’ animated features from Snow White and the Seven Dwarfs through The Jungle Book and beyond. In the course of their early animated features the Studios’ composers developed a number of techniques and models that have been used throughout their oeuvre. Instrumental instances of a given film’s songs are used to comment on various character’s thoughts, as well as on the plot and action. Songs featured in Disney films are often transitioned into or out of using rhymed, metered dialog, functioning in much the same way as recitative in opera. The book also explores the use of theme and variation technique, leitmotif, theatrical conventions, and song archetypes.

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Braude, S. Ya, and V. M. Kontorovich. Radio Waves Tell About the Universe. PH “Akademperiodyka”, 2005. http://dx.doi.org/10.15407/akademperiodyka.005.279.

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The book tells about the achievements of modern radio astronomy. Data on radio galaxies, quasars, pulsars, space masers, and other space objects emitting radio waves are presented in a popular form. The ways of evolution of stars, supernovae and radio eruptions of their remains, the formation of white dwarfs and neutron stars, the phenomena in the centers of galaxies and the fusion of galaxies responsible for the formation of radio galaxies and quasars are considered. The radio radiation of the Sun and planets is discussed. A modern view of the evolution of the universe, the origin of the relic radiation left over from the Great Eruption, and its anisotropy is presented. A separate chapter is devoted to the description of radio telescopes.

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Saha, Prasenjit, and Paul A. Taylor. Gravity versus Pressure. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198816461.003.0005.

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Formally, the title of this chapter is a statement of the equation of hydrostatic equilibrium. A large number of stellar objects exist in the balance between gravity and pressure, with the large ‘zoo’ of observed types being due to the various physical phenomena providing the latter. This chapter is devoted to various applications of that equilibrium. Some cases can be solved exactly, such as spheres of solid rock or ice; some cases can only be solved in detail numerically, notably degenerate white dwarfs up to the Chandrasekhar mass limit. For other cases, analytical approximations such as a version of the virial theorem are helpful in understanding underlying structure and behaviour.

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Schrijver, Karel. Aged Stars and Disrupted Exosystems. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198799894.003.0008.

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Several chapters in this book illustrate the long, complex paths that the scientific community takes to uncover the workings of the Universe. This chapter focuses on the chemical analysis of stars by spectrographically unravelling their light into its constituent colors that, in retrospect, revealed the first evidence of planetary systems, although that remained unrecognized for a long time. A century ago astronomers discovered that many burned-out stars, no longer working as fusion reactors, had unexpected chemicals in their atmospheres. Now these are recognized as evaporated fragments of planetary-system bodies that came too close to the dead star and were eventually pulled into it. With aged stars first clearing their neighborhood by swelling into giants, how can it be that fragments of planetary-system bodies end up in a continuing stream of material crashing into the resulting white dwarfs, ongoing even as they are observed many millions of years after that occurred?

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Matthews, Philippa C. Cestodes (tapeworms). Edited by Philippa C. Matthews. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780198737773.003.0013.

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This chapter consists of short notes, diagrams, maps, and tables to summarize human cestode (‘tapeworm’) infections, starting with a classification of relevant organisms. The chapter then goes on to cover dwarf tapeworm, fish tapeworm, beef/pork tapeworm, and hydatid disease. For ease of reference, each topic is broken down into sections, including classification, epidemiology, microbiology, pathophysiology, clinical syndromes, diagnosis, treatment, and prevention.

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Lee, Sherry D. Modernist Opera’s Stigmatized Subjects. Edited by Blake Howe, Stephanie Jensen-Moulton, Neil Lerner, and Joseph Straus. Oxford University Press, 2016. http://dx.doi.org/10.1093/oxfordhb/9780199331444.013.12.

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While nineteenth-century opera saw its share of damaged and acutely afflicted bodies, and its music more frequently aestheticized suffering than it either objectified or sympathized with it, the early twentieth century saw a shift in emphasis with regard to the staged and musical representation of subjects stigmatized by congenital or permanent physical disabilities. This essay considers the ways in which the musicodramatic framework for interpretation, spectatorship, and identification in modernist opera (including depictions by Strauss, Schreker, and Zemlinsky of dwarves and hunchbacks) is subtly reconfigured according to shifting modernist aesthetic and sociocultural contexts, such that the visual and sonic signification of physical disability is conceptualized as a kind of metaphor for damaged subjectivity or personhood—a status not infrequently understood as encapsulating the broader fate of the modern self.

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Schrijver, Karel. One of Ten Billion Earths. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198799894.001.0001.

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Illustrated with breathtaking images of the Solar System and of the Universe around it, this book explores how the discoveries within the Solar System and of distant exoplanets come together to aid understanding of the habitability of Earth, and how this guides the search for exoplanets that could support life. The author recounts how, within two decades of the discovery of the first planets outside the Solar System in the 1990s, scientists concluded that planets are so common that most stars are orbited by them. The twelve chapters highlight what we have learned about exoplanets and how the lives of exoplanets and their stars are inextricably interwoven. Stars are the seeds around which planetary systems form. Stars provide their planets with light and warmth for as long as they shine. At the end of their lives, stars expel massive amounts of newly forged elements into deep space. That ejected material is incorporated into subsequent generations of planets. How do we learn about these distant worlds? What does the exploration of other planets tell us about the history of Earth? Can we find out what the distant future may have in store for us? What do we know about exoworlds and starbirth, and where do migrating hot Jupiters, polluted white dwarfs, and free-roaming nomad planets fit in? What does all that have to do with the habitability of Earth and the possibility of finding extraterrestrial life? And how did the globe-spanning network of the sciences begin to answer all these questions?

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Mee, Nicholas. The Cosmic Mystery Tour. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198831860.001.0001.

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The Cosmic Mystery Tour is a brief account of modern physics and astronomy presented in a broad historical and cultural context. The book is attractively illustrated and aimed at the general reader. Part I explores the laws of physics including general relativity, the structure of matter, quantum mechanics and the Standard Model of particle physics. It discusses recent discoveries such as gravitational waves and the project to construct LISA, a space-based gravitational wave detector, as well as unresolved issues such as the nature of dark matter. Part II begins by considering cosmology, the study of the universe as a whole and how we arrived at the theory of the Big Bang and the expanding universe. It looks at the remarkable objects within the universe such as red giants, white dwarfs, neutron stars and black holes, and considers the expected discoveries from new telescopes such as the Extremely Large Telescope in Chile, and the Event Horizon Telescope, currently aiming to image the supermassive black hole at the galactic centre. Part III considers the possibility of finding extraterrestrial life, from the speculations of science fiction authors to the ongoing search for alien civilizations known as SETI. Recent developments are discussed: space probes to the satellites of Jupiter and Saturn; the discovery of planets in other star systems; the citizen science project SETI@Home; Breakthrough Starshot, the project to develop technologies to send spacecraft to the stars. It also discusses the Fermi paradox which argues that we might actually be alone in the cosmos

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Частини книг з теми "Dwards form"

Khalid, Ayesha, Goutam Paul, and Anupam Chattopadhyay. "Dwarfs of Cryptography." In Domain Specific High-Level Synthesis for Cryptographic Workloads, 23–49. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-10-1070-5_3.

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Shah, Syed Jawad Ahmad, Muhammad Bashir, and Naheed Manzoor. "A Review on Barley Yellow Dwarf Virus." In Crop Production for Agricultural Improvement, 747–82. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-4116-4_29.

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Sion, Edward M. "White Dwarf Mass Loss, Rotation, Individual Masses and the Identification of the White Dwarf Remnants of Upper Main Sequence Stars." In Angular Momentum and Mass Loss for Hot Stars, 307–29. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-2105-4_36.

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Held, Enrico V. "Dwarf Galaxies in the Local Group: The VLT Perspectivev." In Scientific Drivers for ESO Future VLT/VLTI Instrumentation, 178–83. Berlin, Heidelberg: Springer Berlin Heidelberg, 2002. http://dx.doi.org/10.1007/978-3-662-43215-0_27.

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López Coto, Rubén. "Nova and Dwarf Nova Observations with MAGIC." In Very-high-energy Gamma-ray Observations of Pulsar Wind Nebulae and Cataclysmic Variable Stars with MAGIC and Development of Trigger Systems for IACTs, 187–200. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-44751-3_10.

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Tretyakova, Iraida N., and Denis N. Shuvaev. "Somatic Embryogenesis in Siberian Dwarf Pine (Pinus pumila (Pall.) Regel)." In Step Wise Protocols for Somatic Embryogenesis of Important Woody Plants, 307–17. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-89483-6_23.

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Nawaz, S., S. H. Hanjra, and R. H. Qureshi. "Effect of feeding Atriplex amnicola on growth and carcass quality of dwarf goats." In Halophytes as a resource for livestock and for rehabilitation of degraded lands, 277–80. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0818-8_27.

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Perkinson, James W. "Water Spirituality Beyond the Basin: Detroit Dwarf, Celt Hound, Afro-Orisha." In Political Spirituality for a Century of Water Wars, 125–71. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-14998-7_5.

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Sekimoto, Hitoshi, Mitsuo Hoshi, Takao Yokota, and Takahito Nomura. "Zinc efficiency of dwarf Zea mays treated with a gibberellin-biosynthesis inhibitor." In Plant Nutrition for Sustainable Food Production and Environment, 263–64. Dordrecht: Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-009-0047-9_72.

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Ferrer, Alexis, Floyd M. Byers, Betzabé Sulbarán-de-Ferrer, Bruce E. Dale, and Cateryna Aiello. "Optimizing Ammonia Pressurization/Depressurization Processing Conditions to Enhance Enzymatic Susceptibility of Dwarf Elephant Grass." In Twenty-First Symposium on Biotechnology for Fuels and Chemicals, 163–79. Totowa, NJ: Humana Press, 2000. http://dx.doi.org/10.1007/978-1-4612-1392-5_12.

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Тези доповідей конференцій з теми "Dwards form"

Lux, H., J. I. Read, G. Lake, Victor P. Debattista, and C. C. Popescu. "Determining Orbits for the Milky Way’s Dwarfs." In HUNTING FOR THE DARK: THE HIDDEN SIDE OF GALAXY FORMATION. AIP, 2010. http://dx.doi.org/10.1063/1.3458551.

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Bischoff-Kim, A., Joyce Ann Guzik, and Paul A. Bradley. "Asteroseismological Analysis of Rich Pulsating White Dwarfs." In STELLAR PULSATION: CHALLENGES FOR THEORY AND OBSERVATION: Proceedings of the International Conference. AIP, 2009. http://dx.doi.org/10.1063/1.3246573.

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Manakul, Kittituch, Peerapon Siripongwutikorn, Simon See, and Tiranee Achalakul. "Modeling Dwarfs for Workload Characterization." In 2012 IEEE 18th International Conference on Parallel and Distributed Systems (ICPADS). IEEE, 2012. http://dx.doi.org/10.1109/icpads.2012.126.

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Castanheira, Barbara G., S. O. Kepler, Joyce Ann Guzik, and Paul A. Bradley. "Seismology of White Dwarfs: The ZZ Ceti Stars." In STELLAR PULSATION: CHALLENGES FOR THEORY AND OBSERVATION: Proceedings of the International Conference. AIP, 2009. http://dx.doi.org/10.1063/1.3246572.

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Sismanis, Yannis, Antonios Deligiannakis, Yannis Kotidis, and Nick Roussopoulos. "Hierarchical dwarfs for the rollup cube." In the 6th ACM international workshop. New York, New York, USA: ACM Press, 2003. http://dx.doi.org/10.1145/956060.956064.

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Montgomery, M. H., Joyce Ann Guzik, and Paul A. Bradley. "White Dwarf and Pre-White Dwarf Pulsations." In STELLAR PULSATION: CHALLENGES FOR THEORY AND OBSERVATION: Proceedings of the International Conference. AIP, 2009. http://dx.doi.org/10.1063/1.3246571.

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Lestrade, Jean-François. "Detectability of Debris Disks Around Red Dwarfs at Submillimeter Wavelengths." In THE SEARCH FOR OTHER WORLDS: Fourteenth Astrophysics Conference. AIP, 2004. http://dx.doi.org/10.1063/1.1774509.

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MATHEWS, G. J., and J. R. WILSON. "RELATIVISTIC INDUCED COMPRESSION OF NEUTRON STARS AND WHITE DWARFS." In Proceedings of the MG10 Meeting held at Brazilian Center for Research in Physics (CBPF). World Scientific Publishing Company, 2006. http://dx.doi.org/10.1142/9789812704030_0209.

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Barstow, Martin A. "Soft X-ray, EUV and far-UV studies of hot white dwarfs." In SMALL MISSIONS FOR ENERGETIC ASTROPHYSICS. ASCE, 1999. http://dx.doi.org/10.1063/1.1302216.

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Bovill, Mia S., Massimo Ricotti, Daniel J. Whalen, Volker Bromm, and Naoki Yoshida. "The Ultra-Faint Dwarfs as Fossils of the First Galaxies." In THE FIRST STARS AND GALAXIES: CHALLENGES FOR THE NEXT DECADE. AIP, 2010. http://dx.doi.org/10.1063/1.3518863.

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Звіти організацій з теми "Dwards form"

McMillan, S. S., S. M. Ammons, and D. Pham. Towards the Best Parallaxes and a Limit on the Giant Planet Occurrence Rate for Nearby T Brown Dwarfs. Office of Scientific and Technical Information (OSTI), August 2017. http://dx.doi.org/10.2172/1643755.

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Winget, Donald E., Michael H. Montgomery, Thomas A. Gomez, Ross E. Falcon, and Marc Andre Schaeuble. White Dwarf Photospheres in the Laboratory: A Testbed for Fundamental Atomic Processes. Office of Scientific and Technical Information (OSTI), February 2018. http://dx.doi.org/10.2172/1421934.

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Zilberman, Mark. Shouldn’t Doppler 'De-boosting' be accounted for in calculations of intrinsic luminosity of Standard Candles? Intellectual Archive, September 2021. http://dx.doi.org/10.32370/iaj.2569.

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"Doppler boosting / de-boosting" is a well-known relativistic effect that alters the apparent luminosity of approaching/receding radiation sources. "Doppler boosting" alters the apparent luminosity of approaching light sources to appear brighter, while "Doppler de-boosting" alters the apparent luminosity of receding light sources to appear fainter. While "Doppler boosting / de-boosting" has been successfully accounted for and observed in relativistic jets of AGN, double white dwarfs, in search of exoplanets and stars in binary systems it was ignored in the establishment of Standard Candles for cosmological distances. A Standard Candle adjustment appears necessary for "Doppler de-boosting" for high Z, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of "Doppler de-boosting" but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)^(α-3) and for Type Ia supernova as ℳ(Z) = L/Lo=(Z+1)^(-2). These formulas are obtained within the framework of Special Relativity and may require adjustments within the General Relativity framework.

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Chen, Pictiaw, Yoav Sarig, F. Grosz, Amnon Erez, and Hanoch Pasternak. Engineering Systems for Production and Harvest of Fruit Grown in High Density Dwarf-Tree Orchards. United States Department of Agriculture, October 1985. http://dx.doi.org/10.32747/1985.7566570.bard.

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Drlica-Wagner, Alex. Searching for dwarf spheroidal galaxies and other galactic dark matter substructures with the Fermi large area telescope. Office of Scientific and Technical Information (OSTI), August 2013. http://dx.doi.org/10.2172/1245111.

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Nicholson, Ralph, Reuven Reuveni, and Moshe Shimoni. Biochemical Markers for Disease Resistance in Corn. United States Department of Agriculture, May 1996. http://dx.doi.org/10.32747/1996.7613037.bard.

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The objective was to screen maize lines for their ability to express resistance based on biochemical traits. Cultivars were screened for retention of the hydroxamic acid DIMBOA and the synthesis of phenols (based on anthocyanin production) as markers for resistance. Lines were selected and inoculated with fungal pathogens (Exserohilum turcicum, Puccinia sorghi, Cochliobolus heterostraphus, Colletotricum graminicola.), and the Maize Dwarf Mosaic and Johnson Grass Mosaic viruses. Lines were screened in the field and greenhouse. Results showed that lines selected for augmented phenol synthesis do exhibit heightened levels of resistance to fungal pathogens. Isolation of mRNA followed by northern analyses for expression of A1 (dihydroflavanol reductase) and peroxidase confirmed that genes for these enzymes were turned on in response to inoculation of lines predicted to exhibit resistance. Peroxidase and b-1,3-glucanase were assayed in breeding lines having or lacking the se gene. A specific ionically-bound peroxidase isozyme and a b-1,3-glucanase isozyme were revealed in lines having the se gene. Data suggest that peroxidase and b-1,3-glucanase isozymes, may be considered as markers to identify resistance to E. turcicum in maize genotypes with the se gene.

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Cohen, Yuval, Christopher A. Cullis, and Uri Lavi. Molecular Analyses of Soma-clonal Variation in Date Palm and Banana for Early Identification and Control of Off-types Generation. United States Department of Agriculture, October 2010. http://dx.doi.org/10.32747/2010.7592124.bard.

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Date palm (Phoenix dactylifera L.) is the major fruit tree grown in arid areas in the Middle East and North Africa. In the last century, dates were introduced to new regions including the USA. Date palms are traditionally propagated through offshoots. Expansion of modern date palm groves led to the development of Tissue Culture propagation methods that generate a large number of homogenous plants, have no seasonal effect on plant source and provide tools to fight the expansion of date pests and diseases. The disadvantage of this procedure is the occurrence of off-type trees which differ from the original cultivar. In the present project we focused on two of the most common date palm off-types: (1) trees with reduced fruit setting, in which most of the flowers turn into three-carpel parthenocarpic fruits. In a severe form, multi-carpel flowers and fruitlets (with up to six or eight carpels instead of the normal three-carpel flowers) are also formed. (2) dwarf trees, having fewer and shorter leaves, very short trunk and are not bearing fruits at their expected age, compared to the normal trees. Similar off-types occur in other crop species propagated by tissue culture, like banana (mainly dwarf plants) or oil palm (with a common 'Mantled' phenotype with reduced fruit setting and occurrence of supernumerary carpels). Some off-types can only be detected several years after planting in the fields. Therefore, efficient methods for prevention of the generation of off-types, as well as methods for their detection and early removal, are required for date palms, as well as for other tissue culture propagated crops. This research is aimed at the understanding of the mechanisms by which off-types are generated, and developing markers for their early identification. Several molecular and genomic approaches were applied. Using Methylation Sensitive AFLP and bisulfite sequencing, we detected changes in DNA methylation patterns occurring in off-types. We isolated and compared the sequence and expression of candidate genes, genes related to vegetative growth and dwarfism and genes related to flower development. While no sequence variation were detected, changes in gene expression, associated with the severity of the "fruit set" phenotype were detected in two genes - PdDEF (Ortholog of rice SPW1, and AP3 B type MADS box gene), and PdDIF (a defensin gene, highly homologous to the oil palm gene EGAD). We applied transcriptomic analyses, using high throughput sequencing, to identify genes differentially expressed in the "palm heart" (the apical meristem and the region of embryonic leaves) of dwarf vs. normal trees. Among the differentially expressed genes we identified genes related to hormonal biosynthesis, perception and regulation, genes related to cell expansion, and genes related to DNA methylation. Using Representation Difference Analyses, we detected changes in the genomes of off-type trees, mainly chloroplast-derived sequences that were incorporated in the nuclear genome and sequences of transposable elements. Sequences previously identified as differing between normal and off-type trees of oil palms or banana, successfully identified variation among date palm off-types, suggesting that these represent highly labile regions of monocot genomes. The data indicate that the date palm genome, similarly to genomes of other monocot crops as oil palm and banana, is quite unstable when cells pass through a cycle of tissue culture and regeneration. Changes in DNA sequences, translocation of DNA fragments and alteration of methylation patterns occur. Consequently, patterns of gene expression are changed, resulting in abnormal phenotypes. The data can be useful for future development of tools for early identification of off-type as well as for better understanding the phenomenon of somaclonal variation during propagation in vitro.

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Grafi, Gideon, and Brian Larkins. Endoreduplication in Maize Endosperm: An Approach for Increasing Crop Productivity. United States Department of Agriculture, September 2000. http://dx.doi.org/10.32747/2000.7575285.bard.

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The focus of this research project is to investigate the role of endoreduplication in maize endosperm development and the extent to which this process contributes to high levels of starch and storage protein synthesis. Although endoreduplication has been widely observed in many cells and tissues, especially those with high levels of metabolic activity, the molecular mechanisms through which the cell cycle is altered to produce consecutive cycles of S-phase without an intervening M-phase are unknown. Our previous research has shown that changes in the expression of several cell cycle regulatory genes coincide with the onset of endoreduplication. During this process, there is a sharp reduction in the activity of the mitotic cyclin-dependent kinase (CDK) and activation of the S-phase CDK. It appears the M-phase CDK is stable, but its activity is blocked by a proteinaceous inhibitor. Coincidentally, the S-phase checkpoint protein, retinoblastoma (ZmRb), becomes phosphorylated, presumably releasing an E2F-type transcriptional regulator which promotes the expression of genes responsible for DNA synthesis. To investigate the role of these cell cycle proteins in endoreduplication, we have created transgenic maize plants that express various genes in an endosperm-specific manner using a storage protein (g-zein) promoter. During the first year of the grant, we constructed point mutations of the maize M-phase kinase, p34cdc2. One alteration replaced aspartic acid at position 146 with asparagine (p3630-CdcD146N), while another changed threonine 161 to alanine (p3630-CdcT161A). These mutations abolish the activity of the CDK. We hypothesized that expression of the mutant forms of p34cdc2 in endoreduplicating endosperm, compared to a control p34cdc2, would lead to extra cycles of DNA synthesis. We also fused the gene encoding the regulatory subunit of the M- phase kinase, cyclin B, under the g-zein promoter. Normally, cyclin B is expected to be destroyed prior to the onset of endoreduplication. By producing high levels of this protein in developing endosperm, we hypothesized that the M-phase would be extended, potentially reducing the number of cycles of endoreduplication. Finally, we genetically engineered the wheat dwarf virus RepA protein for endosperm-specific expression. RepA binds to the maize retinoblastoma protein and presumably releases E2F-like transcription factors that activate DNA synthesis. We anticipated that inactivation of ZmRb by RepA would lead to additional cycles of DNA synthesis.

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Savaldi-Goldstein, Sigal, and Todd C. Mockler. Precise Mapping of Growth Hormone Effects by Cell-Specific Gene Activation Response. United States Department of Agriculture, December 2012. http://dx.doi.org/10.32747/2012.7699849.bard.

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Plant yield largely depends on a complex interplay and feedback mechanisms of distinct hormonal pathways. Over the past decade great progress has been made in elucidating the global molecular mechanisms by which each hormone is produced and perceived. However, our knowledge of how interactions between hormonal pathways are spatially and temporally regulated remains rudimentary. For example, we have demonstrated that although the BR receptor BRI1 is widely expressed, the perception of BRs in epidermal cells is sufficient to control whole-organ growth. Supported by additional recent works, it is apparent that hormones are acting in selected cells of the plant body to regulate organ growth, and furthermore, that local cell-cell communication is an important mechanism. In this proposal our goals were to identify the global profile of translated genes in response to BR stimulation and depletion in specific tissues in Arabidopsis; determine the spatio-temporal dependency of BR response on auxin transport and signaling and construct an interactive public website that will provide an integrated analysis of the data set. Our technology incorporated cell-specific polysome isolation and sequencing using the Solexa technology. In the first aim, we generated and confirmed the specificity of novel transgenic lines expressing tagged ribosomal protein in various cell types in the Arabidopsis primary root. We next crossed these lines to lines with targeted expression of BRI1 in the bri1 background. All lines were treated with BRs for two time points. The RNA-seq of their corresponding immunopurified polysomal RNA is nearly completed and the bioinformatic analysis of the data set will be completed this year. Followed, we will construct an interactive public website (our third aim). In the second aim we started revealing how spatio-temporalBR activity impinges on auxin transport in the Arabidopsis primary root. We discovered the unexpected role of BRs in controlling the expression of specific auxin efflux carriers, post-transcriptionally (Hacham et al, 2012). We also showed that this regulation depends on the specific expression of BRI1 in the epidermis. This complex and long term effect of BRs on auxin transport led us to focus on high resolution analysis of the BR signaling per se. Taking together, our ongoing collaboration and synergistic expertise (hormone action and plant development (IL) and whole-genome scale data analysis (US)) enabled the establishment of a powerful system that will tell us how distinct cell types respond to local and systemic BR signal. BR research is of special agriculture importance since BR application and BR genetic modification have been shown to significantly increase crop yield and to play an important role in plant thermotolerance. Hence, our integrated dataset is valuable for improving crop traits without unwanted impairment of unrelated pathways, for example, establishing semi-dwarf stature to allow increased yield in high planting density, inducing erect leaves for better light capture and consequent biomass increase and plant resistance to abiotic stresses.

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