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1

Small cell foams containing a modified dense star polymer or dendrimer as a nucleating agent  

DOEpatents

A small cell foam having a modified dense star polymer or dendrimer is described. This modified dense star polymer or dendrimer has a highly branched interior of one monomeric composition and an exterior structure of a different monomeric composition capable of providing a hydrophobic outer shell and a particle diameter of from about 5 to about 1,000 nm with a matrix polymer.

Hedstrand, David M. (Midland, MI); Tomalia, Donald A. (Midland, MI)

1995-01-01

2

Small cell foams containing a modified dense star polymer or dendrimer as a nucleating agent  

DOEpatents

A small cell foam having a modified dense star polymer or dendrimer is described. This modified dense star polymer or dendrimer has a highly branched interior of one monomeric composition and an exterior structure of a different monomeric composition capable of providing a hydrophobic outer shell and a particle diameter of from about 5 to about 1,000 nm with a matrix polymer.

Hedstrand, D.M.; Tomalia, D.A.

1995-02-28

3

Star Formation in Dense Clusters  

NASA Astrophysics Data System (ADS)

A model of core-clump accretion with equally likely stopping describes star formation in the dense parts of clusters, where models of isolated collapsing cores may not apply. Each core accretes at a constant rate onto its protostar, while the surrounding clump gas accretes as a power of protostar mass. Short accretion flows resemble Shu accretion and make low-mass stars. Long flows resemble reduced Bondi accretion and make massive stars. Accretion stops due to environmental processes of dynamical ejection, gravitational competition, and gas dispersal by stellar feedback, independent of initial core structure. The model matches the field star initial mass function (IMF) from 0.01 to more than 10 solar masses. The core accretion rate and the mean accretion duration set the peak of the IMF, independent of the local Jeans mass. Massive protostars require the longest accretion durations, up to 0.5 Myr. The maximum protostar luminosity in a cluster indicates the mass and age of its oldest protostar. The distribution of protostar luminosities matches those in active star-forming regions if protostars have a constant birthrate but not if their births are coeval. For constant birthrate, the ratio of young stellar objects to protostars indicates the star-forming age of a cluster, typically ~1 Myr. The protostar accretion luminosity is typically less than its steady spherical value by a factor of ~2, consistent with models of episodic disk accretion.

Myers, Philip C.

2011-12-01

4

Dense Gas Processing of Polymers  

Microsoft Academic Search

There is a growing global awareness about environmental pollution, and many sanctions and sustainable practices have been implemented. In particular, the use of volatile organic compounds (VOCs) is a practice that is being limited and minimized world-wide. These VOCs are not only damaging to the environment, but are also an occupational hazard. The polymer processing industry is known to use

R. B. Yoganathan; R. Mammucari; N. R. Foster

2010-01-01

5

Cold Dense Baryonic Matter and Compact Stars  

NASA Astrophysics Data System (ADS)

Probing dense hadronic matter is thus far an uncharted field of physics. Here we give a brief summary of the highlights of what has been so far accomplished and what will be done in the years ahead by the World Class University III Project at Hanyang University in the endeavor to unravel and elucidate the multifacet of the cold dense baryonic matter existing in the interior of the densest visible stable object in the universe, i.e. neutron stars, strangeness stars and/or quark stars, from a modest and simplified starting point of an effective field theory modeled on the premise of QCD as well as from a gravity dual approach of hQCD. The core of the matter of our research is the possible origin of the ~ 99% of the proton mass that is to be accounted for and how the "vacuum" can be tweaked so that the source of the mass generation can be uncovered by measurements made in terrestrial as well as space laboratories. Some of the issues treated in the program concern what can be done — both theoretically and experimentally — in anticipation of what's to come for basic physics research in Korea.

Lee, Hyun Kyu; Rho, Mannque; Sin, Sang-Jin

6

GRAPE-6 Simulations of Dense Star Clusters  

NASA Astrophysics Data System (ADS)

We report on recent results from a long-term program of N-body simulations of dense star cluster evolution which is being done with GRAPE-6 systems at Indiana University and Purdue University Calumet. We have been simulating cases of star cluster evolution with a particular focus on the dynamical evolution of hard binary populations of varying size. Initial models with a range of mass spectra, both with and without primordial binary populations, are being investigated to points well beyond core collapse. Our goal is to better understand the evoultion of compact binary populations in collapsed-core globular clusters. Observations of collapsed-core clusters with HST and Chandra have revealed populations of hard, X-ray binaries well outside the cluster core. Our work is focused on understanding the diffusion of these dynamically hardened binaries to regions in the cluster halo and the robustness of this process in models with mass spectra versus single-mass models.

Slavin, Shawn D.; Maxwell, J. E.; Cohn, H. N.; Lugger, P. M.

2007-12-01

7

Adsorption of star polymers  

NASA Astrophysics Data System (ADS)

The adsorption of star polymers on a flat solid surface is analyzed by means of scalling arguments based on the Daoud-Cotton blob model. For the adsorption of a single star, consisting of f arms comprising each N monomers, we distinguish three regimes determined by the adsorption energy of a monomer at the surface, ? kT. 1) Strong adsorption characterized by the full adsorption of all arms occurs for ? > (f/N)^{3/5}. 2) A “Sombrero” like structure comprising f_ads fully adsorbed arms and f{-}f_ads free arms is obtained for (f/N)^{3/5}> ? > f^{9/20}/N^{3/5}. 3) Weakly adsorbed stars retain, essentially, the structure of a free star. This regime occurs for ? < f^{9/20}/N^{3/5}. The weakly adsorbed structure may also exist as a metastable state if ? > f^{9/5}/N^{3/5}. Nous étudions l'adsorption de polymères en étoile sur une surface solide en utilisant une approche de lois d'échelles basée sur le modèle de blobs de Daoud et Cotton. Pour une étoile formée de f bras contenant chacun N monomères, nous distinguons trois régimes suivant la valeur de l'énergie d'adsorption d'un monomère sur la surface ? kT. 1) L'adsorption forte caractérisée par une adsorption complète de tous les bras se produit lorsque ? > (f/N)^{3/5}. 2) Une structure en “sombrero” avec f_ads bras adsorbés et f{-}f_ads bras libres est obtenue si f^{9/20}/N^{3/5}? < (f/N)^{3/5}. 3) Les étoiles faiblement adsorbées gardent une structure très similaire à celle des étoiles libres en solution. Ce régime existe si ? < f^{9/20}/N^{3/5}. La structure correspondant aux étoiles faiblement adsorbées peut aussi exister comme un état métastable si ? > f^{9/5}/N^{3/5}.

Halperin, A.; Joanny, J. F.

1991-06-01

8

Poly(ethylene glycol) Star Polymer Hydrogels  

Microsoft Academic Search

Poly(ethylene glycol) (PEG) star polymer hydrogels were prepared by Á-irradiation of aqueous solutions of star PEG polymers. The swelling behavior of these gels in deionized water at 37 °C indicated that the gels prepared from PEG star polymers with a small number of long arms swelled to a greater extent than those prepared from PEG star polymers with a large

Kelley Britton Keys; Fotios M. Andreopoulos; Nikolaos A. Peppas

1998-01-01

9

Evolution of Dense Gas with Starburst Age: When Star Formation Versus Dense Gas Relations Break Down  

Microsoft Academic Search

Dense gas correlates well with star formation on kpc scales. On smaller scales, motions of individual clouds become comparable to the 100 Myr ages of starbursts. One then expects the star formation rate vs. dense gas relations to break down on giant molecular cloud scales. We exploit this to study the evolutionary history of nuclear starburst in the nearby spiral,

David S. Meier; J. L. Turner; E. Schinnerer

2011-01-01

10

Dense Gas-Star Systems: Evolution of Supermassive Stars  

NASA Astrophysics Data System (ADS)

In the 60s and 70s super-massive central objects (from now onwards SMOs) were thought to be the main source of active galactic nuclei (AGNs) characteristics (luminosities of L ?1012 Lodot). The release of gravitational binding energy by the accretion of material on to an SMO in the range of 107 - 109 Modot has been suggested to be the primary powerhouse (Lynden-Bell 1969). That rather exotic idea in early time has become common sense nowadays. Not only our own galaxy harbours a few million-solar mass black hole (Genzel 2001) but also many of other non-active galaxies show kinematic and gas-dynamic evidence of these objects (Magorrian et al. 1998) The concept of central super-massive stars (SMSs henceforth) (cal M ? 5 × 104 Modot, where cal M is the mass of the SMS) embedded in dense stellar systems was suggested as a possible explanation for high- energy emissions phenomena occurring in AGNs and quasars (Vilkoviski 1976, Hara 1978), such as X-ray emissions (Bahcall and Ostriker, 1975). SMSs and super-massive black holes (SMBHs) are two possibilities to explain the nature of SMOs, and SMSs may be an intermediate step towards the formation of SMBHs (Rees 1984). In this paper we give the equations that describe the dynamics of such a dense star-gas system which are the basis for the code that will be used in a prochain future to simulate this scenario. We also briefly draw the mathematical fundamentals of the code.

Amaro-Seoane, P.; Spurzem, R.

11

Multiarm Star Polymers as Model Soft Colloids  

NASA Astrophysics Data System (ADS)

Over the last decade, star polymers emerged as a useful model colloids that interpolate between polymers and hard sphere colloids. Together with microgels, they represent two benchmark soft colloidal systems, their internal structure being the key difference. Indeed, in the case of stars with open structure, the arms can interpenetrate in dense suspensions. The latter feature, that can be probed experimentally, is responsible for a number of interesting structural and dynamic properties of star polymers that set them apart from microgels. In this talk we present the basic properties of star polymers and focus on their extraordinary behavior in the highly concentrated regime, which is typically glassy. Our rheological and scattering experiments demonstrate unique features of the star glasses. Here we discuss two major ones: (i) Aging after pre-shear (the so-called rejuvenation) proceeds via a two-step process, associated with a fast arm engagement and a slow cooperative (cage) rearrangement. Remarkably, at extremely long times a steady state is observed and the terminal time in these systems can be experimentally accessible (and hence tailored at molecular level), as a consequence of the arms fluctuations. (ii) Multiple glassy states can be obtained when mixing stars with polymers or with other stars. Simultaneous theoretical and simulations work suggests that the softness is at the core of this unexpected behavior where depletion gives rise to glass melting and eventually re-entrant glasses are formed. Construction of a state diagram suggests kinetic pathways for tailoring the flow of soft colloids. These examples outline the importance of particle architecture on colloidal properties. Stars are a representative of a large class of hairy particles. The parallel important developments in mode coupling theory and its verses provide much needed predictive tools and rationalization for a number of phenomena such as those discussed here, as well as the complex rheological response. A wide range of applications in this exciting, fast growing field appear to emerge. Parts of this work reflect collaboration with M. Cloitre (ESPCI), B. Erwin (FORTH/ESPCI), C. N. Likos (Duesseldorf), G. Petekidis (FORTH), F. Sciortino (Rome), E. Stiakakis (FORTH), and E. Zaccarelli (Rome). Synthesis of particles by N. Hadjichristidis (Athens), M. Gauthier (Waterloo) and J. Roovers (NRC).

Vlassopoulos, Dimitris

2010-03-01

12

Physics of dense matter, neutron stars, and supernova  

SciTech Connect

Nuclear and astrophysical evidence on the equation of state of dense matter is examined. The role of hyperonization of matter in the development of proto-neutron stars is briefly discussed. 7 refs., 4 figs.

Glendenning, N.K.

1989-02-01

13

Evolution of the binary population in young dense star clusters  

NASA Astrophysics Data System (ADS)

Context. Field stars are not always single stars, but can often be found in bound double systems. Since binary frequencies in the birth places of stars, young embedded clusters, are sometimes even higher than on average the question arises of how binary stars form in young dense star clusters and how their properties evolve to those observed in the field population. Aims: We assess, the influence of stellar dynamical interactions on the primordial binary population in young dense cluster environments. Methods: We perform numerical N-body simulations of the Orion nebula cluster like star cluster models including primordial binary populations using the simulation code nbody6++. Results: We find two remarkable results that have yet not been reported: The first is that the evolution of the binary frequency in young dense star clusters is independent predictably of its initial value. The time evolution of the normalized number of binary systems has a fundamental shape. The second main result is that the mass of the primary star is of vital importance to the evolution of the binary. The more massive a primary star, the lower the probability that the binary is destroyed by gravitational interactions. This results in a higher binary frequency for stars more massive than 2 M? compared to the binary frequency of lower mass stars. The observed increase in the binary frequency with primary mass is therefore most likely not due to differences in the formation process but can be entirely explained as a dynamical effect. Conclusions: Our results allow us to draw conclusions about the past and the future number of binary systems in young dense star clusters and demonstrate that the present field stellar population has been influenced significantly by its natal environments.

Kaczmarek, T.; Olczak, C.; Pfalzner, S.

2011-04-01

14

Dense quark matter in compact stars  

NASA Astrophysics Data System (ADS)

The densest predicted state of matter is colour superconducting quark matter, in which quarks near the Fermi surface form a condensate of Cooper pairs. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is an ongoing enterprise. Using a bag model of quark matter, I will discuss the effects of colour superconductivity on the mass-radius relationship of compact stars, showing that colour superconducting quark matter will occur in compact stars at values of the bag constant where ordinary quark matter would not be allowed. The resultant 'hybrid' stars with colour superconducting quark matter interior and nuclear matter surface have masses in the range 1.3-1.6 Modot and radii 8-11 km.

Alford, M.

2004-01-01

15

Star-Forming Galaxies in Dense Environments  

NASA Astrophysics Data System (ADS)

We report on preliminary results from an ongoing study of star-forming galaxies in the Virgo Cluster with the aim of understanding the role played by the environment on their evolution. First, the chemical evolution of nine spiral galaxies located in the inner parts of the cluster has been studied using chemical abundances recomputed for a sample of HII regions. Second, long-slit optical spectroscopy has been obtained for 22 blue dwarf galaxies selected across the Virgo central field. This sample is a subset of a larger list of dwarf galaxies for which deep H? imaging has been collected. Chemical abundances have been derived for the sample using either a direct estimation of the electron temperature or empirical calibrations. Abundance results correlate with blue and near infrared magnitude, total HI mass and color.

Vílchez, José M.; Iglesias-Píramo, Jorge

2002-07-01

16

Dense circumstellar nebulae in wide binary central stars  

NASA Astrophysics Data System (ADS)

Detection of close binary central stars with periods of less than a day is now well-tested and routinely possible via photometric monitoring. For wide binary central stars with periods of weeks to years detection techniques are still in their infancy. Radial velocity monitoring programs are yet to be applied to very large samples and the method suffers from large systematic errors as well as intrinsic wind variability. One alternative we are exploring is the detection of dense circumstellar nebulae residing around a wide companion. The archetype of this class is EGB6 as revealed by HST imaging (Bond 2009). Here we present spectroscopic evidence for other EGB6-like central stars and discuss their relationship to symbiotic stars. A probable 12.5-day irradiated binary is also presented to demonstrate the limits of the photometric monitoring technique.

Miszalski, B.; Acker, A.; Parker, Q. A.; Boffin, H. M. J.; Frew, D. J.; Mikolajewska, J.; Moffat, A. F. J.; Napiwotzki, R.

17

Functional dendrimers, hyperbranched and star polymers  

Microsoft Academic Search

Over the past decade, a number of excellent reviews on hyperbranched polymers and dendrimers have been published covering the topics from details to highlights and perspectives. The purpose of the present article is to review the synthesis, properties, and functionality of dendrimers, hyperbranched polymer, and star polymers with emphasis on functional aspects.

K. Inoue

2000-01-01

18

Dense cloud formation and star formation in a barred galaxy  

NASA Astrophysics Data System (ADS)

We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2MASS data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40 Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than 104 M? (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholz & McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The star formation efficiency in the bar region is ˜60 per cent of the spiral arm region. This trend is consistent with observations of barred galaxies.

Nimori, M.; Habe, A.; Sorai, K.; Watanabe, Y.; Hirota, A.; Namekata, D.

2013-03-01

19

Scaling model for symmetric star polymers  

Microsoft Academic Search

Neutron scattering data from symmetric star polymers with six poly (urethane-ether) arms, chemically bonded to a C-60 molecule are fitted using a new scaling model and scattering function. The new scaling function can describe both good solvent and theta solvent conditions as well as resolve deviations in chain conformation due to steric interactions between star arms. The scaling model quantifies

Ram Ramachandran; Durgesh K. Rai; Gregory Beaucage

2010-01-01

20

Environments of star formation - Relationship between molecular clouds, dense cores and young stars  

Microsoft Academic Search

In this chapter, the star-forming properties of three molecular cloud complexes, Taurus-Auriga, Ophiuchus and Orion, are discussed. In particular, recent observational knowledge of the distribution and properties of dense molecular gas and young stellar objects within each complex is reviewed. Studies of the two nearest molecular cloud complexes, Taurus and Ophiuchus, have shown that at least two modes or environments

Elizabeth A. Lada; Karen M. Strom; Philip C. Myers

1993-01-01

21

STAR FORMATION IN THE TAURUS FILAMENT L 1495: FROM DENSE CORES TO STARS  

SciTech Connect

We present a study of dense structures in the L 1495 filament in the Taurus Molecular Cloud and examine its star-forming properties. In particular, we construct a dust extinction map of the filament using deep near-infrared observations, exposing its small-scale structure in unprecedented detail. The filament shows highly fragmented substructures and a high mass-per-length value of M{sub line} = 17 M{sub sun} pc{sup -1}, reflecting star-forming potential in all parts of it. However, a part of the filament, namely B 211, is remarkably devoid of young stellar objects. We argue that in this region the initial filament collapse and fragmentation is still taking place and star formation is yet to occur. In the star-forming part of the filament, we identify 39 cores with masses from 0.4 to 10 M{sub sun} and preferred separations in agreement with the local Jeans length. Most of these cores exceed the Bonnor-Ebert critical mass, and are therefore likely to collapse and form stars. The dense core mass function follows a power law with exponent {Gamma} = 1.2 {+-} 0.2, a form commonly observed in star-forming regions.

Schmalzl, Markus; Kainulainen, Jouni; Henning, Thomas; Launhardt, Ralf [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Quanz, Sascha P. [Institute for Astronomy-Swiss Federal Institute of Technology (ETH), Wolfgang-Pauli-Strasse 27, 8093 Zurich (Switzerland); Alves, Joao [University of Vienna, Tuerkenschanzstrasse 17, 1180 Vienna (Austria); Goodman, Alyssa A.; Pineda, Jaime E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138 (United States); Roman-Zuniga, Carlos G., E-mail: schmalzl@mpia.d [Centro Astronomico Hispano Aleman/Instituto de Astrofisica de AndalucIa (IAA-CSIC), Glorieta de la Astronomia, S/N, Granada 18008 (Spain)

2010-12-10

22

Collapse of Telechelic Star Polymers to Watermelon Structures  

NASA Astrophysics Data System (ADS)

Conformational properties of star-shaped polymer aggregates that carry attractive end groups, called telechelic star polymers, are investigated by simulation and analytical variational theory. We focus on the case of low telechelic star polymer functionalities, f?5, a condition which allows aggregation of all attractive monomers on one site. We establish the functionality- and polymerization-number dependence of the transition temperature from the “star burst” to the “watermelon” macroparticle structure. Extensions to telechelic stars featuring partially collapsed configurations are also discussed.

Verso, Federica Lo; Likos, Christos N.; Mayer, Christian; Löwen, Hartmut

2006-05-01

23

Simulation of dense amorphous polymers by generating representative atomistic models  

NASA Astrophysics Data System (ADS)

A method for generating atomistic models of dense amorphous polymers is presented. The generated models can be used as starting structures of Monte Carlo and molecular dynamics simulations, but also are suitable for the direct evaluation physical properties. The method is organized in a two-step procedure. First, structures are generated using an algorithm that minimizes the torsional strain. After this, an iterative algorithm is applied to relax the nonbonding interactions. In order to check the performance of the method we examined structure-dependent properties for three polymeric systems: polyethyelene (?=0.85 g/cm3), poly(L,D-lactic) acid (?=1.25 g/cm3), and polyglycolic acid (?=1.50 g/cm3). The method successfully generated representative packings for such dense systems using minimum computational resources.

Curcó, David; Alemán, Carlos

2003-08-01

24

Scaling model for symmetric star polymers  

NASA Astrophysics Data System (ADS)

Neutron scattering data from symmetric star polymers with six poly (urethane-ether) arms, chemically bonded to a C-60 molecule are fitted using a new scaling model and scattering function. The new scaling function can describe both good solvent and theta solvent conditions as well as resolve deviations in chain conformation due to steric interactions between star arms. The scaling model quantifies the distinction between invariant topological features for this star polymer and chain tortuosity which changes with goodness of solvent and steric interaction. Beaucage G, Phys. Rev. E 70 031401 (2004).; Ramachandran R, et al. Macromolecules 41 9802-9806 (2008).; Ramachandran R, et al. Macromolecules, 42 4746-4750 (2009); Rai DK et al. Europhys. Lett., (Submitted 10/2009).

Ramachandran, Ram; Rai, Durgesh K.; Beaucage, Gregory

2010-03-01

25

Modular invariant partition function of critical dense polymers  

NASA Astrophysics Data System (ADS)

A lattice model of critical dense polymers is solved exactly for arbitrary system size on the torus. More generally, an infinite family of lattice loop models is studied on the torus and related to the corresponding Fortuin-Kasteleyn random cluster models. Starting with a cylinder, the commuting periodic single-row transfer matrices are built from the periodic Temperley-Lieb algebra extended by the shift operators ?±1. In this enlarged algebra, the non-contractible loop fugacity is ? and the contractible loop fugacity is ?. The torus is formed by gluing the top and bottom of the cylinder. This gives rise to a variety of non-contractible loops winding around the torus. Because of their nonlocal nature, the standard matrix trace does not produce the proper geometric torus. Instead, we introduce a modified matrix trace for this purpose. This is achieved by using a representation of the enlarged periodic Temperley-Lieb algebra with a parameter v that keeps track of the winding of defects on the cylinder. The transfer matrix representatives and their eigenvalues thus depend on v. The modified trace is constructed as a linear functional on planar connectivity diagrams in terms of matrix traces Trd (with a fixed number of defects d) and Chebyshev polynomials of the first kind. For critical dense polymers, where ?=0, the transfer matrix eigenvalues are obtained by solving a functional equation in the form of an inversion identity. The solution depends on d and is subject to selection rules which we prove. Simplifications occur if all non-contractible loop fugacities are set to ?=2 in which case the traces are evaluated at v=1. In the continuum scaling limit, the corresponding conformal torus partition function obtained from finite-size corrections agrees with the known modular invariant partition function of symplectic fermions.

Morin-Duchesne, Alexi; Pearce, Paul A.; Rasmussen, Jørgen

2013-09-01

26

Structure and dynamics of dense polymer chains in 2D  

NASA Astrophysics Data System (ADS)

Self-avoiding polymers in two-dimensional melts are known to adopt compact and segregated configurations. Compactness does obviously not imply Gaussian chain statistics nor does segregation of chains impose disk-like shapes minimizing the average perimeter length of the chains. Using scaling arguments and molecular dynamics simulations with chain length up to 2048 we show that the chain perimeters are highly irregular and characterized by a fractal line dimension 5/4. This result may be verified experimentally from the power-law scaling of the intrachain form factor in the intermediate wavevector regime in agreement with a generalized Porod law for a compact object of fractal border [1]. The dynamics of dense polymer chains exhibits two interesting features: the incompressibility induces long range correlations in the displacement auto-correlations and a relaxation channel due to friction at the fractal contours of compact sub-segments leads to relaxation faster than a Rouse model would predict [2].[4pt] [1] H. Meyer et al Phys. Rev. E 79 050802(R) (2009); J. Chem. Phys. (2010)[0pt] [2] J. Wittmer et al. Phys. Rev. Lett 105 (2010) 037802.

Meyer, Hendrik; Wittmer, Joachim P.; Johner, Albert; Baschnagel, Jorg

2011-03-01

27

Instanton effects in the equation of state for dense neutron star matter  

Microsoft Academic Search

Vacuum fluctuation effects in quantum chromodynamics due to instantons were studied in dense neutron state matter. In the density region of interest to neutron star cores, a density dependence of approximately (n syb B)(-1\\/3) was found.

C. G. Kaellman

1979-01-01

28

Instanton Effects in the Equation of State for Dense Neutron Star Matter.  

National Technical Information Service (NTIS)

Vacuum fluctuation effects in quantum chromodynamics due to instantons were studied in dense neutron state matter. In the density region of interest to neutron star cores, a density dependence of approximately (n syb B)(-1/3) was found.

C. G. Kaellman

1979-01-01

29

Star cluster ecology - VII. The evolution of young dense star clusters containing primordial binaries  

NASA Astrophysics Data System (ADS)

We study the first ~100 Myr of the evolution of isolated star clusters initially containing 144179 stars, including 13107 (10 per cent) primordial hard binaries. Our calculations include the effects of both stellar and binary evolution. Gravitational interactions among the stars are computed by direct N-body integration using high-precision GRAPE-6 hardware. The evolution of the core radii and central concentrations of our simulated clusters are compared with the observed sample of young (<~100Myr) star clusters in the large Magellanic Cloud. Even though our simulations start with a rich population of primordial binaries, core collapse during the early phase of the cluster evolution is not prevented. Throughout the simulations, the fraction of binaries remains roughly constant (~10 per cent). Due to the effects of mass segregation the mass function of intermediate-mass main-sequence stars becomes as flat as ? = -1.8 in the central part of the cluster (where the initial Salpeter mass function had ? = -2.35). About 6-12 per cent of the neutron stars were retained in our simulations; the fraction of retained black holes is 40-70 per cent. In each simulation about three neutron stars become members of close binaries with a main-sequence companion. Such a binary will eventually become an X-ray binary, when the main-sequence star starts to fill its Roche lobe. Black holes are found more frequently in binaries; in each simulated cluster we find ~11 potential X-ray binaries containing a black hole. Binaries consisting of two white dwarfs are quite common, but few (20-30) are sufficiently close that they will merge within a Hubble time due to the emission of gravitational radiation. Clusters with shorter relaxation times tend to produce fewer merging white dwarf binaries. The white dwarf binaries that do merge are all sufficiently massive to produce a Type Ia supernova. The densest cluster produces about twice as many blue stragglers as a field population containing the same number of binaries, and these blue stragglers are more massive, bluer and brighter than in less dense clusters.

Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Makino, Junichiro

2007-01-01

30

Equation of state of dense matter and maximum rotation frequency of neutron stars  

Microsoft Academic Search

Maximum rotation frequency of uniformly rotating neutron star models, determined by the mass shedding condition, {OMEGA}_max_, has been calculated using a high precision numerical method, for a large set of equations of state of dense matter. The values of {OMEGA}_max_ for the subset of equations of state, which are causal within neutron star models, are fitted, within a few percent,

P. Haensel; M. Salgado; S. Bonazzola

1995-01-01

31

Formation of Massive Black Holes in Dense Star Clusters. I. Mass Segregation and Core Collapse  

Microsoft Academic Search

We study the early dynamical evolution of young, dense star clusters using\\u000aMonte Carlo simulations for systems with up to N~10^7 stars. Rapid mass\\u000asegregation of massive main-sequence stars and the development of the Spitzer\\u000ainstability can drive these systems to core collapse in a small fraction of the\\u000ainitial half-mass relaxation time. If the core collapse time is less

M. Atakan Gurkan; Marc Freitag; Frederic A. Rasio

2003-01-01

32

Core cross-linked star polymers via controlled radical polymerisation  

Microsoft Academic Search

Star polymers are comprised of multiple arms or branches radiating from a central point or core and have been of huge scientific interest since they were first prepared sixty years ago, as a result of their unique physical properties. Star polymers are not just an academic curiosity, but are currently employed or under investigation in a wide range of industries

Anton Blencowe; Jing Fung Tan; Tor Kit Goh; Greg G. Qiao

2009-01-01

33

Effective interactions between star polymers and colloidal particles  

Microsoft Academic Search

Using monomer-resolved molecular dynamics simulations and theoretical arguments based on the radial dependence of the osmotic pressure in the interior of a star, we systematically investigate the effective interactions between hard, colloidal particles and star polymers in a good solvent. The relevant parameters are the size ratio q between the stars and the colloids, as well as the number of

A. Jusufi; J. Dzubiella; C. N. Likos; C. von Ferber; H. Löwen

2001-01-01

34

Interaction force between incompatible star-polymers in dilute solution  

Microsoft Academic Search

:   We consider a low-density assembly of spherical colloids, such that each is clothed by L end-grafted chemically incompatible polymer chains either of types A or B. These are assumed to be dissolved in a good common solvent. We assume that colloids are of small size to be considered as\\u000a star-polymers. Two adjacent star-polymers A and B interact through a

M. Benhamou; F. Benzouine

2001-01-01

35

From nondegenerate conducting polymers to dense matter in the massive Gross-Neveu model  

Microsoft Academic Search

Using results from the theory of nondegenerate conducting polymers like cis-polyacetylene, we generalize our previous work on dense baryonic matter and the soliton crystal in the massless Gross-Neveu model to finite bare fermion mass. In the large N limit, the exact crystal ground state can be constructed analytically, in close analogy to the bipolaron lattice in polymers. These findings are

Michael Thies; Konrad Urlichs

2005-01-01

36

Influence of additive content of anionic polymer dispersant on dense alumina suspension viscosity  

Microsoft Academic Search

This paper reports on a new method to analyze the adsorbed structure of an anionic polymer dispersant on an alumina powder surface in dense suspension with different additive content by using an atomic force microscope (AFM). Anionic polymer dispersants were adsorbed on both the polished surface of a thin piece of sintered alumina and the surface of alumina powders in

Yoshiyuki Fukuda; Tsunetaka Togahi; Yoshio Suzuki; Makio Naito; Hidehiro Kamiya

2001-01-01

37

Collision-induced absorption in dense atmospheres of cool stars  

Microsoft Academic Search

In the atmosphere of the Sun the major interaction between the matter and the radiation is through light absorption by ions (predominantly the negative ion of hydrogen atoms), neutral atoms and a small amount of polar molecules. The majority of stars in the universe are, however, cooler and denser than our Sun, and for a large fraction of these, the

Aleksandra Borysow

1999-01-01

38

Unified description of dense matter in neutron stars and magnetars  

NASA Astrophysics Data System (ADS)

We have recently developed a set of equations of state based on the nuclear energy density functional theory providing a unified description of the different regions constituting the interior of neutron stars and magnetars. The nuclear functionals, which were constructed from generalized Skyrme effective nucleon-nucleon interactions, yield not only an excellent fit to essentially all experimental atomic mass data but were also constrained to reproduce the neutron-matter equation of state as obtained from realistic many-body calculations.

Chamel, N.; Pavlov, R. L.; Mihailov, L. M.; Velchev, Ch. J.; Stoyanov, Zh. K.; Mutafchieva, Y. D.; Ivanovich, M. D.; Fantina, A. F.; Pearson, J. M.; Goriely, S.

2013-03-01

39

INTERACTIONS BETWEEN FORMING STARS AND DENSE GAS IN THE SMALL LOW-MASS CLUSTER CEDERBLAD 110  

SciTech Connect

We present observations of dense gas and outflow activity in the Cederblad 110 region of the Chamaeleon I dark cloud complex. The region contains nine forming low-mass stars in evolutionary stages ranging from Class 0 to Class II/III crowded into a 0.2 pc region with high surface density ({Sigma}{sub YSO} {approx} 150 pc{sup -2}). The analysis of our N{sub 2}H{sup +} (J = 1{yields}0) maps indicates the presence of 13 {+-} 3 solar masses of dense (n {approx} 10{sup 5} cm{sup -3}) gas in this region, much of which is unstable against gravitational collapse. The most unstable material is located near the Class 0 source MMS-1, which is almost certainly actively accreting material from its dense core. Smaller column densities of more stable dense gas are found toward the region's Class I sources, IRS 4, 11, and 6. Little or no dense gas is colocated with the Class II and III sources in the region. The outflow from IRS 4 is interacting with the dense core associated with MMS-1. The molecular component of the outflow, measured in the (J = 1{yields}0) line of {sup 12}CO, appears to be deflected by the densest part of the core, after which it appears to plow through some of the lower column density portions of the core. The working surface between the head of the outflow lobe and the dense core material can be seen in the enhanced velocity dispersion of the dense gas. IRS 2, the Class III source that produces the optical reflection nebula that gives the Cederblad 110 region its name, may also be influencing the dense gas in the region. A dust temperature gradient across the MMS-1 dense core is consistent with warming from IRS 2, and a sharp gradient in dense gas column density may be caused by winds from this source. Taken together, our data indicate that this region has been producing several young stars in the recent past, and that sources which began forming first are interacting with the remaining dense gas in the region, thereby influencing current and future star formation activity.

Ladd, E. F. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Wong, T. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Thompson, K. L., E-mail: ladd@bucknell.edu [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States)

2011-12-20

40

Exact effective force between star-polymers in a -solvent  

Microsoft Academic Search

We re-examine here the computation of the effective force between two star-polymers of respective numbers of branches f 1 and f 2, immersed in a common $\\\\Theta$ -solvent. Such a force originates essentially from the repulsive three-body interactions. To achieve this, we take advantage of some established results using renormalization theory for three-dimensional star-polymers, or conformal invariance for two-dimensional ones.

M. Benhamou; M. Himmi; F. Benzouine; A. Bettachy; A. Derouiche

2004-01-01

41

Force between unlike star-polymers versus the solvent quality  

Microsoft Academic Search

We re-examine here the computation of the effective force between two star-polymers A and B of different chemical nature, which are immersed in a common solvent. This force originates from the excluded-volume interactions and chemical segregation. We assume that the solvent quality may be different for the two unlike star-polymers, that is the solvent can be 1) a good solvent

F. Benzouine; M. Benhamou; M. Himmi

2004-01-01

42

Stellar Collisions and Blue Straggler Stars in Dense Globular Clusters  

NASA Astrophysics Data System (ADS)

Blue straggler stars (BSSs) are abundantly observed in all Galactic globular clusters (GGCs) where data exist. However, observations alone cannot reveal the relative importance of various formation channels or the typical formation times for this well-studied population of anomalous stars. Using a state-of-the-art Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ~103 M ? pc–3, the dominant formation channel is stellar collisions, while for lower density clusters, mass transfer in binaries provides a significant contribution (up to 60% in our models). The majority of these collisions are binary-mediated, occurring during three-body and four-body interactions. As a result, a strong correlation between the specific frequency of BSSs and the binary fraction in a cluster can be seen in our models. We find that the number of BSSs in the core shows only a weak correlation with the collision rate estimator ? traditionally used by observers, in agreement with the latest Hubble Space Telescope Advanced Camera for Surveys data. Using an idealized "full mixing" prescription for collision products, our models indicate that the BSSs observed today may have formed several Gyr ago. However, denser clusters tend to have younger (~1 Gyr) BSSs.

Chatterjee, Sourav; Rasio, Frederic A.; Sills, Alison; Glebbeek, Evert

2013-11-01

43

From Gas to Stars in Energetic Environments: Dense Gas Clumps in the 30 Doradus Region  

NASA Astrophysics Data System (ADS)

We present parsec-scale interferometric maps of HCN(1-0) and HCO+(1-0) emission from dense gas in the star-forming region 30Dor10, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud, is characterized by a very intense ionizing radiation field and sub-solar metallicity, both of which are expected to affect molecular cloud structure. We detect 13 clumps of dense molecular gas, some of which are aligned in a filamentary structure. Our analysis of the clump properties shows that they have similar mass but slightly wider linewidths than clumps detected in other LMC star-forming regions.

Anderson, C. N.; Meier, D. S.; Ott, J.; Hughes, A.; Wong, T.

2013-03-01

44

Compatibility of Medical-Grade Polymers with Dense CO2  

PubMed Central

This study reports the effect of exposure to liquid carbon dioxide on the mechanical properties of selected medical polymers. The tensile strengths and moduli of fourteen polymers are reported. Materials were exposed to liquid CO2, or CO2 + trace amounts of aqueous H2O2, at 6.5 MPa and ambient temperature. Carbon dioxide uptake, swelling, and distortion were observed for the more amorphous polymers while polymers with higher crystallinity showed little effect from CO2 exposure. Changes in tensile strength were not statistically significant for most plastics, and most indicated good tolerance to liquid CO2. These results are relevant to evaluating the potential of liquid CO2-based sterilization technology.

Jimenez, A; Thompson, G L; Matthews, M A; Davis, T A; Crocker, K; Lyons, J S; Trapotsis, A

2009-01-01

45

Neutrinos from Protoneutron Stars: Probing Hot and Dense Matter  

NASA Astrophysics Data System (ADS)

In this work, we elucidate the role of microphysics in the macrophysical evolution of a newly-born neutron star, termed a protoneutron star (PNS). The roles of strong and weak interactions, particularly their interdependence through the equation of state (EOS) and neutrino opacities, during the early neutrino emission phase is investigated. We calculate charged and neutral current weak interaction rates that determine the neutrino opacities inside a PNS. We establish an efficient formalism for calculating the mean free paths for interacting, nucleonic matter at arbitrary degeneracy. First, strong interaction corrections are incorporated through in-medium single particle energies, using both potential and field-theoretical models. Second, strong and electromagnetic correlations are calculated using the Random Phase Approximation and are found to substantially modify the neutrino mean free path. In matter containing hyperons, neutral current tree-level neutrino-hyperon couplings were computed for the first time. Together with known charged current couplings, these couplings were employed to calculate neutrino opacities in hyperonic matter. Simulations of the evolution of a PNS were performed using different EOS models, including those with hyperons, to predict the corresponding neutrino luminosities. Hyperons considerably soften the EOS and increase the specific heat of matter during the late stages of deleptonization. Relative to nucleons-only case, the central density and the neutrino opacities during the cooling phase are significantly larger. This, however, results in only a marginal increase in the neutrino diffusion time due to feedbacks from the larger specific heat of hyperonic matter. Significant differences between EOS models with and without hyperons are manifest in the emergent neutrino luminosities only for those cases in which the PNS mass is close to the maximum mass. These differences are enhanced only at late times; the early emission is fairly insensitive to the high density EOS. The possible subsidence of the PNS into a black hole that could accompany deleptonization is also studied. In matter with hyperons, the EOS softens during deleptonization and eventually becomes hydrostatically unstable for masses larger than the maximum mass of the cold catalyzed neutron star. This metastable phase, which is absent in nucleonic matter, could last for a few minutes.

Reddy, Sanjay K.

46

Rheology of core cross-linked star polymers  

Microsoft Academic Search

The rheological characterization for a set of structurally diverse core cross-linked star (CCS) polymers is presented. The influence of arm molecular weight (Mw(arm)) and CCS polymer molecular weight (Mw(CCSP)) on the steady- and dynamic-shear properties determined by plate rheometry will be discussed. Both these parameters dramatically affect the CCS polymer solution properties and determine its “molecular softness”; a key feature

Tor Kit Goh; Kristopher D. Coventry; Anton Blencowe; Greg G. Qiao

2008-01-01

47

The Melt Rheology of Bimodal Blends of Star Polymers  

NASA Astrophysics Data System (ADS)

Experiments on solution-cast blends of two anionically synthesised monodisperse star-shaped polyisoprene molecules of widely different molecular weight exhibit very rich rheological behaviour. The time-dependent moduli are exponentially dependent on the relative volume fraction of each species. Our works aim to model these new features by extending existing tube model theories for monodisperse melts of star polymers to blends of two monodisperse star polymers with two different molecular weight, keeping the same chemistry. We treat the tube model with constraint release for star polymers in both an approximate (Ball-McLeish) and then a more exact level (McLeish-Milner). The latter, with its treatment of non-activated breathing modes, is able to account quantitatively for the huge range of blend rheologies.

Blottiere, B.; McLeish, T. C. B.; Young, R.; Hakiki, A.; Milner, S. T.

1998-03-01

48

Apparent hydrodynamic thickness of densely grafted polymer layers in a theta solvent  

Microsoft Academic Search

We study the drainage of a near-theta solvent through densely grafted polymer layers and compare to recent notions that these layers display little permeabil- ity to solvent flow at surface separations less than a ''hydrodynamic thickness.'' The solvent is trans-decalin (a near-theta solvent at the experimental temperature of 247C). The polymer is polystyrene (PS) end-attached to two opposed mica surfaces

Yoon-Kyoung Cho; Ali Dhinojwala; Steve Granick

1997-01-01

49

A class of regular and well behaved relativistic super-dense star models  

NASA Astrophysics Data System (ADS)

We obtain a new class of charged super-dense star models after prescribing particular forms of the metric potential g 44 and electric intensity. The metric describing the superdense stars joins smoothly with the Reissner-Nordstrom metric at the pressure free boundary. The interior of the stars possess there energy density, pressure, pressure-density ratio and velocity of sound to be monotonically decreasing towards the pressure free interface. In view of the surface density 2×1014 g/cm3, the heaviest star occupies a mass 5.6996 M ? with its radius 17.0960 km. The red shift at the centre and boundary are found to be 3.5120 and 1.1268 respectively. In absence of the charge we are left behind with the regular and well behaved fifth model of Durgapal (J. Phys. A 15:2637, 1982).

Gupta, Y. K.; Maurya, Sunil Kumar

2011-03-01

50

From Gas to Stars in Energetic Environments: Dense Gas Clumps in the 30 Doradus Region  

NASA Astrophysics Data System (ADS)

We present interferometric mapping of dense molecular gas tracers toward the giant molecular clouds (GMCs) of the star forming region 30Dor10, located in the Large Magellanic Cloud (LMC) conducted with the Australia Telescope Compact Array (ATCA). The LMC is the nearest major galaxy to the Milky Way and it contains the most intense star forming region in the Local Group. The large number of OB stars in 30 Doradus create a very intense ionizing photon field, that in combination with the sub-solar metallicity of the LMC, may mimic the conditions present in young starburst galaxies of the early Universe. HCN(1-0) and HCO^+(1-0) transitions, tracers for dense, ultimately star forming molecular clumps are mapped at parsec scale resolution. We show the first detection of several resolved clumps in 30Dor10, with some of these clumps possibly tracing a molecular filament. We present detailed comparisons of clump structure (masses, linewidths, sizes) in 30Dor10 to those in other star forming regions of the LMC. These observations also reveal low HCN/HCO^+line ratios in 30Dor10 compared to some of the other LMC GMCs.

Anderson, Crystal; Meier, David S.; Ott, Juergen; Hughes, Annie; Wong, Tony

2012-10-01

51

Densely spaced FDM coherent star network with optical signals confined to equally spaced frequencies  

Microsoft Academic Search

The results obtained with a fiber-optical star network using densely spaced frequency-division-multiplexing (FDM) and heterodyne detection techniques are discussed. The system consists of three optical sources transmitting around 1.28 ?m, frequency-shift keying (FSK) modulated at 45 Mb\\/s and spaced by 300 MHz. A 4×4 optical coupler combines the three optical signals. The FDM signals, received from one of the four

J. Stone; K. J. Pollock; P. J. Fitzgerald; B. L. Kasper; L. W. Stulz

1988-01-01

52

Formation of Dense Gas and Stars near the End of the Galactic Bar  

NASA Astrophysics Data System (ADS)

We carried out H13CO+ (J = 1-0) observations of a molecular cloud containing a massive star-forming region, G23.44-0.18, using the Nobeyama 45-m radio telescope. We identified three clumps, named Clumps A, B, and C, on the periphery of the HII region in the cloud. The most massive clump, Clump A, has a radius of 0.74±0.20 pc and a mass of 1100+800-640 M?. Both Clumps B and C, however, have much smaller size and mass than Clump A. These three clumps seem not to be virialized. We also found four sub-clumps in Clump A. These sub-clumps may be affected by the strong outflow penetrating Clump A. The star-formation efficiency (SFE) of the entire cloud is ˜0.4%, which is typical for galactic star-forming clouds. The SFE of Clump A is 25+14-11%. This value is higher than other embedded cluster-forming clumps, which implies that stars, including massive ones, are formed efficiently and actively in Clump A. The dense gas fraction estimated from H13CO+ (J = 1-0) and 13 CO (J = 1-0) of the cloud are lower than those of other star-forming regions. The results mean that this star-forming region is young, and suggest that the formation of dense gas and stars in the cloud has just begun. Comparing the dynamical age of the HII region with the fragmentation timescale for the collect and collapse process, molecular gas is accumulating through expansion of the HII region in Clumps B and C. Since there are massive young stellar objects (YSOs) in Clump A, we suggest that this clump has already become denser than the other regions in the cloud due to converging flow, or some external factors, such as an old bubble and cloud-cloud interaction.

Ohishi, Yukie; Sorai, Kazuo; Habe, Asao

2012-08-01

53

Irreversible polymer adsorption from semidilute and moderately dense solutions  

NASA Astrophysics Data System (ADS)

We present results from a Monte Carlo study of polymer adsorption from solution at a solid-liquid interface, in the limit of infinitely large adsorption energy. We study the kinetics of adsorbed layer formation for both the cases of end-functionalized chains and homopolymers. In the former case, the adsorbed layer is found to be in the ``brush'' regime described by Milner, Witten, and Cates [Macromolecules 21, 2610 (1988)], and its growth is consistent with the formation of an activation barrier, as predicted by Ligoure and Leibler [J. Phys. (Paris) 51, 1313 (1990)]. In the latter case, the resulting ``pancake'' layer is analyzed in terms of loop, train, and tail distributions. The results are compared with recent scaling arguments proposed by Guiselin [Europhys. Lett. 17, 225 (1992)]. (c) 1995 The American Physical Society

Zajac, Richard; Chakrabarti, Amitabha

1995-12-01

54

Diffusional behaviour of entangled star polymers  

Microsoft Academic Search

The dynamic properties of concentrated solutions and melts of linear polymers are reasonably well understood in terms of the reptation concept, whereby molecules are constrained to curvilinear motion within `tubes' formed by entanglements with their neighbours1-3. Understanding of dynamics of entangled nonlinear polymers, however, is still rather limited. Reptation in such cases is expected to be strongly suppressed, but there

Jacob Klein; Dianne Fletcher; Lewis J. Fetters

1983-01-01

55

From nondegenerate conducting polymers to dense matter in the massive Gross-Neveu model  

SciTech Connect

Using results from the theory of nondegenerate conducting polymers like cis-polyacetylene, we generalize our previous work on dense baryonic matter and the soliton crystal in the massless Gross-Neveu model to finite bare fermion mass. In the large N limit, the exact crystal ground state can be constructed analytically, in close analogy to the bipolaron lattice in polymers. These findings are contrasted to the standard scenario with homogeneous phases only and a first order phase transition at a critical chemical potential.

Thies, Michael; Urlichs, Konrad [Institut fuer Theoretische Physik III, Universitaet Erlangen-Nuernberg, D-91058 Erlangen (Germany)

2005-11-15

56

A novel geometric embedding algorithm for efficiently generating dense polymer structures  

Microsoft Academic Search

A new algorithm for generating starting polymer structures for molecular simulations (e.g., MD) in dense phase is presented. The algorithm yields structures that fulfill to a large extent rotational isomeric state (RIS) probabilities and avoid atomic overlap. The heuristic search bases on the new parallel-rotation (ParRot) technique. We tested the performance of the algorithm on two polymeric systems: Atomistic polyethylene

M. Müller; J. Nievergelt; S. Santos; U. W. Suter

2001-01-01

57

A class of new solutions of generalized charged analogues of Buchdahl's type super-dense star  

NASA Astrophysics Data System (ADS)

The present paper reports a class of new solutions of charged fluid spheres expressed by a space time with its hypersurfaces t=const. as spheroid for the case 0< K<1 with surface density 2×1014 gm/cm3. When the Buchdahl's type fluid spheres are electrified with generalized charged intensity and it is utilized to construct a super-dense star and found that star satisfies all reality conditions except the casual condition for 0< K?0.05. The maximum mass occupied and the corresponding radius have been obtained 8.130871 M ? and 24.60916 km respectively. Further, the redshift at the centre and on the surface are noted by z 0=0.933729 and z a =0.383808 respectively.

Kumar, Jitendra; Gupta, Y. K.

2013-06-01

58

The Age, Stellar Content, and Star Formation Timescale of the B59 Dense Core  

NASA Astrophysics Data System (ADS)

We have investigated the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Using the SpeX spectrograph on the NASA Infrared Telescope Facility, we obtained moderate resolution, near-infrared (NIR) spectra for 20 candidate young stellar objects (YSOs) in B59 and a representative sample of NIR and mid-IR bright sources distributed throughout the Pipe. Measuring luminosity and temperature sensitive features in these spectra, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. To measure B59's age, we place its candidate YSOs in the Hertzsprung-Russell diagram and compare their location to YSOs in several well-studied star-forming regions, as well as predictions of pre-main-sequence (PMS) evolutionary models. We find that B59 is composed of late-type (K4-M6) low-mass (0.9-0.1 M sun) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the ? Oph, Taurus, and Chameleon star-forming regions. Deriving absolute age estimates from PMS models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6 ± 0.8 Myr. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6+4.1 -2.6 Myr. We also find that the relative age orderings implied by PMS evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependences. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggests that the B59 dense core has been stable against global collapse for roughly six dynamical timescales and is actively forming stars with a star formation efficiency per dynamical time of ~6%. While the ~150% uncertainties associated with our age measurement propagate directly into these derived star formation timescales, the maximum likelihood values nonetheless agree well with recent star formation simulations that incorporate various forms of support against collapse, such as subcritical magnetic fields, outflows, and radiative feedback from protostellar heating.

Covey, K. R.; Lada, C. J.; Román-Zúñiga, C.; Muench, A. A.; Forbrich, J.; Ascenso, J.

2010-10-01

59

Interaction Force Between Polydisperse Star Polymers in a ?-SOLVENT  

NASA Astrophysics Data System (ADS)

We consider a dilute solution of very small spherical particles clothed each by f end-grafted flexible polymer chains, we regard as star-polymers, and immersed in a ?-solvent. The presence of a ?-solvent induces an effective force between adjacent star-polymers. We are interested in the investigation of the polydispersity effects on this interaction force. This work is a natural extension of that where we have considered the same system but in the presence of a good solvent. Consequently we use the same theoretical approach to determine the structure of our system, and particularly the extension of polydisperse star-polymer in a ?-solvent. We assume that the lengths of the f grafted chains are randomly distributed, with a distribution ˜ {S}(n). The latter is the number of chains having more than n monomers and which generally is related to the probability to have a grafted chain of n monomers. To make explicit calculation of the expected force, F?(h), as a function of the interparticle-distance h we choose the particular form for the distribution ˜ {S}(n) used in the good solvent case. This distribution is a power law in the n-variable that is, ˜ {S}(n)\\cong f n1-? , if n < N, and ˜ {S}(n) = 0, if n > N. Here, 1 ? ? < 2 is the polydispersity exponent and N is the polymerization degree of the longest grafted chain. To obtain the force expression, we use some method developed by Witten and Pincus for monodisperse star-polymers in a good solvent. We show that the computation of the force depends on the polymerization degree N compared with the typical number Nc f1/(?-1).

Himmi, M.; Mohammadi, L.

60

Phase behavior of athermal colloid-star polymer mixtures  

NASA Astrophysics Data System (ADS)

We investigate the depletion-induced phase behavior of athermal colloid-star polymer mixtures on a fine lattice using grand canonical Monte Carlo simulations in the ``protein limit,'' that is, where polymer dimensions exceed those of the colloid. We consider the influence of the star's functionality, f, the macroscopic size ratio, qr = 2Rg, s/?c, where Rg, s is the radius of gyration of the star and ?c is the colloid diameter, and the microscopic size ratio, d = ?m/?c, where ?m is the diameter of a Kuhn segment. Recent theoretical predictions concerning the qualitative interplay of qr and f in determining the phase stability of these mixtures [D. Marzi, C. N. Likos, and B. Capone, J. Chem. Phys. 137, 014902 (2012)] in the limit of large f are mostly corroborated by our results which span a much lower range of functionalities. Our results suggest a direct connection between the phase behavior and the scaling regimes of single star structure in the classical Daoud-Cotton (DC) description [M. Daoud and J. P. Cotton, J. Phys. 43, 531-538 (1982)]. Using this formalism, we define a ``low'' functionality limit through scaling arguments, for which our model provides a mapping of the phase behavior of colloidal mixtures with star polymers (f > 2) to linear chains (f = 2). Furthermore, our simulations suggest that as qr increases, both the critical monomer and colloid densities tend to a constant, finite value for all f; thus, we do not find the prediction by Marzi and co-workers of an upper limit to immiscibility (infinite critical densities) in terms of qr to be accurate for the stars we have investigated.

Mahynski, Nathan A.; Panagiotopoulos, Athanassios Z.

2013-07-01

61

Elemental compositions of hyper-metal-poor stars formed in dust-enriched dense shells of population III supernova remnants  

NASA Astrophysics Data System (ADS)

We describe the evolution of dust within Population III supernova remnants (SNRs) and investigate the chemical compositions of the dust piled up in their dense shells. We show that the resulting abundance patterns of the major elements in the dense shells are in good agreement with that observed for a Galactic halo star, SDSS J102915+172927. This allows us to propose that SDSS J102915+172927 might be the second-generation star formed in the dust-enriched dense shell of a Population III SNR. We conclude that the segregation of dust from the metal-rich ejecta gas can be an important process in determining the abundance patterns of primitive low-mass stars.

Nozawa, Takaya; Kozasa, Takashi; Nomoto, Ken'ichi; Maeda, Keiichi; Tominaga, Nozomu; Umeda, Hideyuki; Habe, Asao

2012-09-01

62

Comparing different coarse-grained potentials for star polymers.  

PubMed

We compare different coarse-grained single-blob models for star polymers. We find that phenomenological models inspired by the Daoud-Cotton theory reproduce quite poorly the thermodynamics of these systems, even if the potential is assumed to be density dependent, as done in the analysis of experimental results. Using the numerically determined coarse-grained potential, we also determine the minimum value f(c) of the functionality of the star polymer for which a fluid-solid transition occurs. By applying the Hansen-Verlet criterion we find 35 < f(c) ? 40. This result is confirmed by an analysis that uses the modified (reference) hypernetted chain method and is qualitatively consistent with previous work. PMID:23556746

Menichetti, Roberto; Pelissetto, Andrea

2013-03-28

63

Comparing different coarse-grained potentials for star polymers  

NASA Astrophysics Data System (ADS)

We compare different coarse-grained single-blob models for star polymers. We find that phenomenological models inspired by the Daoud-Cotton theory reproduce quite poorly the thermodynamics of these systems, even if the potential is assumed to be density dependent, as done in the analysis of experimental results. Using the numerically determined coarse-grained potential, we also determine the minimum value fc of the functionality of the star polymer for which a fluid-solid transition occurs. By applying the Hansen-Verlet criterion we find 35 < fc <~ 40. This result is confirmed by an analysis that uses the modified (reference) hypernetted chain method and is qualitatively consistent with previous work.

Menichetti, Roberto; Pelissetto, Andrea

2013-03-01

64

Penicillin V-conjugated PEG-PAMAM star polymers  

Microsoft Academic Search

Starburst ® PAMAM dendrimers are potential carriers for drug delivery due to their unique structure. Drug-delivery scaffolds were designed and built up based on the polyethylene glycol- polyamidoamine (PEG-PAMAM) star polymer. Penicillin V was used as a model carboxylic group containing drug to conjugate with full- and half-generation PAMAM dendrimers. G2.5 PAMAM (with 32 carboxylic groups on the surface) dendrimers

Hu Yang; Stephanie T. Lopina

2003-01-01

65

Efficient and versatile synthesis of star polymers in water and their use as emulsifiers.  

PubMed

Core cross-linked star polymers of low polydispersity were efficiently prepared in high yield by RAFT-mediated emulsion and dispersion polymerizations in water at high solid content. These star polymers were demonstrated to be effective emulsifiers, and the emulsion was successfully used as template to fabricate polymer particles. PMID:22037974

Qiu, Qian; Liu, Guangyao; An, Zesheng

2011-10-31

66

A novel geometric embedding algorithm for efficiently generating dense polymer structures  

NASA Astrophysics Data System (ADS)

A new algorithm for generating starting polymer structures for molecular simulations (e.g., MD) in dense phase is presented. The algorithm yields structures that fulfill to a large extent rotational isomeric state (RIS) probabilities and avoid atomic overlap. The heuristic search bases on the new parallel-rotation (ParRot) technique. We tested the performance of the algorithm on two polymeric systems: Atomistic polyethylene and polystyrene. The algorithm permits to tackle the problem of packing chains into large boxes of size up to 50 Å in a couple of hours on common workstations. Moreover, our packing algorithm is applicable for general polymer systems. The algorithm requires CPU effort scaling with a power 2.8 in the chain length, and with a power 1.5 in the number of chains.

Müller, M.; Nievergelt, J.; Santos, S.; Suter, U. W.

2001-06-01

67

DNA ligase-mediated translation of DNA into densely functionalized nucleic acid polymers.  

PubMed

We developed a method to translate DNA sequences into densely functionalized nucleic acids by using T4 DNA ligase to mediate the DNA-templated polymerization of 5'-phosphorylated trinucleotides containing a wide variety of appended functional groups. This polymerization proceeds sequence specifically along a DNA template and can generate polymers of at least 50 building blocks (150 nucleotides) in length with remarkable efficiency. The resulting single-stranded highly modified nucleic acid is a suitable template for primer extension using deep vent (exo-) DNA polymerase, thereby enabling the regeneration of template DNA. We integrated these capabilities to perform iterated cycles of in vitro translation, selection, and template regeneration on libraries of modified nucleic acid polymers. PMID:23256841

Hili, Ryan; Niu, Jia; Liu, David R

2012-12-26

68

DNA Ligase-Mediated Translation of DNA Into Densely Functionalized Nucleic Acid Polymers  

PubMed Central

We developed a method to translate DNA sequences into densely functionalized nucleic acids by using T4 DNA ligase to mediate the DNA-templated polymerization of 5?-phosphorylated trinucleotides containing a wide variety of appended functional groups. This polymerization proceeds sequence specifically along a DNA template and can generate polymers of at least 50 building blocks (150 nucleotides) in length with remarkable efficiency. The resulting single-stranded highly modified nucleic acid is a suitable template for primer extension using deep vent (exo-) DNA polymerase, thereby enabling the regeneration of template DNA. We integrated these capabilities to perform iterated cycles of in vitro translation, selection, and template regeneration on libraries of modified nucleic acid polymers.

2012-01-01

69

Properties of dense cores in clustered massive star-forming regions at high angular resolution  

NASA Astrophysics Data System (ADS)

We aim at characterizing dense cores in the clustered environments associated with intermediate-/high-mass star-forming regions. For this, we present a uniform analysis of Very Large Array NH3 (1,1) and (2,2) observations towards a sample of 15 intermediate-/high-mass star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities of the total sample are ˜0.06 pc and ˜1015 cm-2, respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, ˜1.0 km s-1 and 16 K, than linewidths and temperatures of protostellar (˜1.8 km s-1 and 21 K), and perturbed starless (˜1.4 km s-1 and 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of intermediate-/high-mass stars are still significantly larger than the typical linewidths and rotational temperatures measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions (spatial scales ˜0.05 pc) the correlations previously found with single-dish telescopes (spatial scales ? 0.1 pc) between the linewidth and the rotational temperature of the cores, as well as between the rotational temperature and the linewidth with respect to the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-gravitating, turbulent, virialized hierarchy of structures from clumps (˜0.1-10 pc) to cores (˜0.05 pc). A closer inspection of the dynamical state taking into account external pressure effects reveals that relatively strong magnetic field support may be needed to stabilize the cores, or that they are unstable and thus on the verge of collapse.

Sánchez-Monge, Álvaro; Palau, Aina; Fontani, Francesco; Busquet, Gemma; Juárez, Carmen; Estalella, Robert; Tan, Jonathan C.; Sepúlveda, Inma; Ho, Paul T. P.; Zhang, Qizhou; Kurtz, Stan

2013-07-01

70

Formation of Dense Molecular Gas and Stars at the Circumnuclear Starburst Ring in the Barred Galaxy NGC 7552  

NASA Astrophysics Data System (ADS)

We present millimeter molecular line complemented by optical observations, along with a reanalysis of archival centimeter H I and continuum data, to infer the global dynamics and determine where dense molecular gas and massive stars preferentially form in the circumnuclear starburst ring of the barred-spiral galaxy NGC 7552. We find diffuse molecular gas in a pair of dust lanes each running along the large-scale galactic bar, as well as in the circumnuclear starburst ring. We do not detect dense molecular gas in the dust lanes, but find such gas concentrated in two knots where the dust lanes make contact with the circumnuclear starburst ring. When convolved to the same angular resolution as the images in dense gas, the radio continuum emission of the circumnuclear starburst ring also exhibits two knots, each lying downstream of an adjacent knot in dense gas. The results agree qualitatively with the idea that massive stars form from dense gas at the contact points, where diffuse gas is channeled into the ring along the dust lanes, and later explode as supernovae downstream of the contact points. Based on the inferred rotation curve, however, the propagation time between the respective pairs of dense gas and centimeter continuum knots is about an order of magnitude shorter than the lifetimes of OB stars. We discuss possible reasons for this discrepancy, and conclude that either the initial mass function is top-heavy or massive stars in the ring do not form exclusively at the contact points where dense molecular gas is concentrated.

Pan, Hsi-An; Lim, Jeremy; Matsushita, Satoki; Wong, Tony; Ryder, Stuart

2013-05-01

71

Functional star polymers with a cholic acid core and their thermosensitive properties.  

PubMed

Star polymers derived from cholic acid with poly(allyl glycidyl ether) arms have been prepared via anionic polymerization, yielding polymers with well-defined molecular weight and low polydispersity. The double bonds of the allyl groups on the polymer are used to introduce either amine or carboxylic acid groups to obtain amphiphilic polymers with cationic and anionic groups, respectively. The polymers can aggregate in water above a certain critical concentration, which was found to vary with the arm length of the star polymers. The star polymers bearing amino groups showed interesting thermosensitivity, which also depends on the pH of the media. A simple acetylation of the amine groups can sharpen the transition and vary the cloud point from 15 to 48 degrees C, depending on the degree of acetylation. Such polymers offer useful alternatives to the existing thermosensitive polymers. PMID:19994878

Giguère, Guillaume; Zhu, X X

2010-01-11

72

Stable emulsions with thermally responsive microstructure and rheology using poly(ethylene oxide) star polymers as emulsifiers.  

PubMed

Poly(ethylene oxide) star polymers (PEO stars) were prepared by atom transfer radical polymerization of 2000 molecular weight PEO methacrylate macromonomer with divinylbenzene as a crosslinking co-monomer. With an average of 460 arms per star, these PEO stars had a 12 nm radius of gyration that is consistent with a dense polymer core surrounded by an extended PEO corona. The PEO stars were extremely efficient emulsifiers, stabilizing cyclohexane-in-water or xylene-in-water emulsions against coalescence for several months at aqueous phase concentrations as low as 0.008 wt% or 0.01 wt%, respectively. Consistent with their emulsifying performance, PEO star adsorption decreased interfacial tension by approximately 22 mN/m and imparted significant dilatational elasticity to the xylene/water interface. PEO stars were thermally responsive, displaying a cloud point upon heating in water that was tuned by addition of kosmotropic electrolytes, and they in turn produced xylene-in-water emulsions that were thermally responsive in terms of the dispersion state of the emulsion droplets and the emulsion rheology. Emulsions prepared at room temperature mainly had non-flocculated droplets. Heating such an emulsion above the cloud point temperature triggered droplet flocculation, but not coalescence, that in turn was associated with increased viscous and elastic moduli of the emulsion measured after cooling back to room temperature. Emulsions that initially were homogenized above the cloud point temperature and then cooled showed neither droplet flocculation nor rheological thickening relative to emulsions that were prepared and held at room temperature. A mechanism based on the bridging behavior of PEO stars adsorbed at the droplet/water interface is postulated to explain this thermal response of the emulsion microstructure. PMID:23266031

Saigal, Trishna; Yoshikawa, Alex; Kloss, Dennis; Kato, Masanari; Golas, Patricia Lynn; Matyjaszewski, Krzysztof; Tilton, Robert D

2012-12-03

73

Stress relaxation of polymer networks containing low concentrations of dangling chains and star shaped polymers  

NASA Astrophysics Data System (ADS)

We analyze the influence of low concentrations of star and dangling polymer chains on the stress relaxation process of model polymer networks. Model PDMS networks with well defined structure were obtained by the hydrosylilation reaction, based on the addition of hydrogen silanes from a trifunctional cross- linker to end vinyl groups of ?- ? polydimethylsiloxane chains. Rheological characterization was carried out in a rotational rheometer by dynamic and stress relaxation tests. Viscoelastic properties of the networks depend strongly on the molecular weight of the stars or pendant chains. It was found that a modified Pearson-Helfand model provides a very good fit to the behavior of these networks. This model incorporates the effect of higher Rouse modes on the arm retraction [Milner and McLeish, Macromolecules, 1997] and the potential for arm retraction originally proposed by Doi and Kuzuu.

Vega, Daniel A.; Gómez, Leopoldo R.

2005-03-01

74

Synthesis of Maleimide-End Functionalized Star Polymers and Multimeric Protein-Polymer Conjugates  

PubMed Central

Protein-polymer conjugates exhibit superior properties to unmodified proteins, generating a high demand for these materials in the fields of medicine, biotechnology, and nanotechnology. Multimeric conjugates are predicted to surpass the activity of monomeric conjugates. Herein, we report a straightforward method to synthesize multimeric polymer-conjugates. Four armed poly(N-isopropylacrylamide) (pNIPAAm) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of a tetra-functionalized trithiocarbonate chain transfer agent (CTA). The polymer molecular weight, architecture and polydispersity index (PDI) were verified by gel permeation chromatography (GPC), dynamic light scattering gel permeation chromatography (DLS-GPC), and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This approach afforded well-defined polymers (PDI's < 1.06) and the ability to target various molecular weights. Maleimide functional groups were introduced at the chain ends by heating the polymers in the presence of a furan-protected azo-initiator. This allowed for site-specific conjugation of V131C T4 lysozyme to the polymers to generate multimeric protein-polymer conjugates. MALDI-TOF mass spectrometry, electrospray ionization gas-phase electrophoretic-mobility macromolecule analysis (ESI-GEMMA), gel electrophoresis, and liquid chromatography tandem mass spectrometry (LC-MS/MS) of the trypsin digests demonstrated that multimeric protein-polymer conjugates had formed. This simple strategy provides ready access to star protein-polymer conjugates for application in the fields of drug discovery, drug delivery, and nanotechnology.

Tao, Lei; Kaddis, Catherine S.; Loo, Rachel R. Ogorzalek; Grover, Gregory N.; Loo, Joseph A.; Maynard, Heather D.

2011-01-01

75

From Gas to Stars in Energetic Environments: Dense Gas Clumps and PDRs in the 30 Doradus Region  

NASA Astrophysics Data System (ADS)

We present interferometric mapping of dense molecular gas toward the giant molecular clouds (GMCs) of the star forming region 30Dor10, located in the Large Magellanic Cloud (LMC) conducted with the Australia Telescope Compact Array (ATCA). The LMC is the nearest major galaxy to the Milky Way and it contains the most intense star forming region in the Local Group. The large number of OB stars in 30 Doradus create a very intense ionizing photon field, that in combination with the sub-solar metallicity of the LMC, may mimic the conditions present in young starburst galaxies of the early Universe. HCN(1-0) and HCO^{+}(1-0) transitions, tracers for dense, ultimately star forming molecular clumps are mapped at parsec scale resolution. We show the first detection of several resolved clumps in 30Dor10, with some of these clumps possibly tracing a molecular filament. We present detailed comparisons of clump structure (masses, linewidths, sizes) in 30Dor10 to those in other star forming regions of the LMC. These results suggest 30Dor10 is more turbulent, and possibly that the dense cores don't follow the entire GMC velocity field, as might be expected if it is a distinct filament. These observations reveal low HCN/HCO^{+}line ratios in 30Dor10 compared to some of the other LMC GMCs. We also discuss followup photon-dominated region (PDR) chemical tracers toward selected dense cores associated with the starburst. Also, we show new deep ^{12}CO(1-0) field observations of the entire 30Doradus region observed with Mopra. This work is supported by the National Science Foundation grant AST-1009620

Anderson, Crystal N.; Meier, D. S.; Ott, J.; Wong, T. H.; Hughes, A.

2013-01-01

76

Star polymers with a cationic core prepared by ATRP for cellular nucleic acids delivery.  

PubMed

Poly(ethylene glycol) (PEG)-based star polymers with a cationic core were prepared by atom transfer radical polymerization (ATRP) for in vitro nucleic acid (NA) delivery. The star polymers were synthesized by ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA). Star polymers were characterized by gel permeation chromatography, zeta potential, and dynamic light scattering. These star polymers were combined with either plasmid DNA (pDNA) or short interfering RNA (siRNA) duplexes to form polyplexes for intracellular delivery. These polyplexes with either siRNA or pDNA were highly effective in NA delivery, particularly at relatively low star polymer weight or molar ratios, highlighting the importance of NA release in efficient delivery systems. PMID:23560989

Cho, Hong Y; Averick, Saadyah E; Paredes, Eduardo; Wegner, Katarzyna; Averick, Amram; Jurga, Stefan; Das, Subha R; Matyjaszewski, Krzysztof

2013-04-18

77

Does a hadron-quark phase transition in dense matter preclude the existence of massive neutron stars?  

NASA Astrophysics Data System (ADS)

We study the impact of a hadron-quark phase transition on the maximum neutron-star mass. The hadronic part of the equation of state relies on the most up-to-date Skyrme nuclear energy density functionals, fitted to essentially all experimental nuclear mass data and constrained to reproduce the properties of infinite nuclear matter as obtained from microscopic calculations using realistic forces. We show that the softening of the dense matter equation of state due to the phase transition is not necessarily incompatible with the existence of massive neutron stars like PSR J1614-2230.

Chamel, N.; Fantina, A. F.; Pearson, J. M.; Goriely, S.

2013-03-01

78

New conformational search method based on local torsional deformations for cyclic molecules, loops in proteins, and dense polymer systems  

SciTech Connect

We propose a conformational search method, based on {ital local} torsional deformations (LTD) for locating the low energy structures of cyclic peptides, loops in proteins or dense polymer systems. LTD is applied preliminarily to cycloundecane modeled by the MM2 force field, and is found to be more efficient than other techniques. {copyright} {ital 1996 American Institute of Physics.}

Baysal, C.; Meirovitch, H. [Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306-4052 (United States)

1996-11-01

79

Investigation of the structure and thermodynamics of star-polymers in semi-dilute solution  

Microsoft Academic Search

In this work, we consider a semi-dilute solution of identical star-polymers, made of attached flexible long polymer chains of the same polymerization degree N. We first compute the effective pair-potential between star-polymers. Such a potential results from the excluded volume forces between monomers. We show that this potential is logarithmic, below some known characteristic distance, ?, depending on the number

F. Benzouine; M. Yassine; A. Derouiche; A. Bettachy; M. Benhamou

2007-01-01

80

Unusual microscopic dynamics in melts of star-like polymer grafted nanoparticles and their binary mixtures  

NASA Astrophysics Data System (ADS)

Star polymers have attracted wide attention due to their fascinating structural, dynamical and rheological behavior including observation of multiple glassy states in concentrated solutions [1]. We have shown recently [2] that the microscopic dynamics in melts of a novel type of star-like polymers created by grafting of linear polymer chains on nanoparticle surfaces shows an unusual dynamical arrest in the case of low number, f, of grafted chains as opposed to that predicted and observed so far for both melts and solutions of star polymers. Here we extend our studies further to include similar star polymers with large range of f and their binary mixtures. Remarkably we find that the structural relaxation times of the star polymers becomes smaller with increasing arm number upto a certain value above which the relaxation time increases with f. Further, in binary mixtures of star polymers of two different sizes the relaxation time decreases dramatically with very low added small star fraction but shows dynamical arrest at significantly higher fraction of smaller stars. Reference: 1. C. Mayer et al Nature Materials 7, 780 (2008); 2. A. K. Kandar et al, J Chem Phys 130, 121102 (2009)

Basu, Jaydeep; Srivastava, S.; C, Sivasurender; Kandar, A.; C, Sarika; Narayanan, S.; Sandy, A.

2010-03-01

81

Statistical Mechanical Theory of Phase Separation and Structure in Dense Polymer-Particle Mixtures  

NASA Astrophysics Data System (ADS)

Microscopic liquid state theory has been applied to investigate phase separation and structure of dense mixtures of hard spherical particles and flexible polymer chains in the presence of interfacial attractive interactions. The entire range of filler loading, from the dilute particle regime to the colloid science relevant case of ultra-high particle volume fraction with dilute polymer additives, has been studied for the first time. Many body effects can result in large quantitative, or even qualitative, changes of spinodal demixing boundaries compared to a low order virial treatment. In the temperature-particle volume fraction representation both upper and lower critical temperatures are present, separated by a miscibility window. Entropic effects dominate for weak interfacial attractions (high temperature) resulting in depletion phase separation with a critical point at roughly 10% filler loading. At relatively high interfacial cohesion (low temperature) a network bridging transition occurs characterized by a highly asymmetric spinodal boundary which depends sensitively on attraction spatial range. Deep contact or bridging minima in the particle potential of mean force can occur, which raises the possibility that kinetic gelation or aggregation pre-empts equilibrium phase separation. The evolution of the real space correlations and scattering structure factors as phase separation is approached has been studied in detail.

Hall, Lisa; Schweizer, Ken

2008-03-01

82

ELECTRON-ION SCATTERING IN DENSE MULTI-COMPONENT PLASMAS: APPLICATION TO THE OUTER CRUST OF AN ACCRETING NEUTRON STAR  

SciTech Connect

The thermal conductivity of a dense multi-component plasma (MCP) is critical to the modeling of accreting neutron stars. To this end, we perform large-scale molecular dynamics simulations to calculate the static structure factor of the dense MCP in the neutron star crust from near the photosphere-ocean boundary to the vicinity of the neutron drip point. The structure factors are used to validate a microscopic linear mixing rule that is valid for arbitrarily complex plasmas over a wide range of Coulomb couplings. The microscopic mixing rule in turn implies and validates the linear mixing rule (LMR) for the equation of state properties and also the LMR for the electrical and thermal conductivities of dense MCPs. To make our result as useful as possible, for the specific cases of electrical and thermal conductivities, we provide a simple analytic fit that is valid for arbitrarily complex MCPs over a wide range of Coulomb couplings. We compute the thermal conductivity for a representative compositional profile of the outer crust of an accreting neutron star in which hundreds of nuclear species can be present. We utilize our results to re-examine the so-called impurity parameter formalism as used to characterize impure plasmas.

Daligault, J.; Gupta, S., E-mail: daligaul@lanl.go, E-mail: guptasanjib@lanl.go [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2009-09-20

83

Investigation of star polymer nanoshells for use in diagnostic imaging and photothermal cancer therapy applications  

NASA Astrophysics Data System (ADS)

Gold nanoshells can be designed to possess high light scattering and strong absorption of near-infrared light. Thus, they have the potential to be used in biological applications as contrast agents for diagnostic imaging as well as for thermal ablation of tumor cells in future cancer treatments. In this study, gold nanoshells with dye-loaded star polymer cores were investigated. Uniform near-infrared gold nanoshells with 100 nm diameters were successfully generated using different batches of star polymer templates and were characterized by UV-visible spectroscopy and scanning electron microscopy. The star polymers used were block copolymer structures with a hydrophobic polystyrene (PS) core and a hydrophilic poly(N,N-dimethylaminoethylmethracrylate) (DMAEMA) outer shell. Within this work, a general procedure was established in order to achieve a desired gold nanoshell size regardless of the star polymer batch used, since the synthesis process conditions can cause star polymers to vary in size as well in the number and length of amino-functionalized arms. Control of the gold nanoshell diameter was optimized after an in-depth analysis of the synthesis parameters that affected the formation and final size of the dye-loaded star polymer gold nanoshells. The main parameters examined were pH of the gold seeds used to nucleate the templates and the ratio of star polymer to gold hydroxide used during the growth of the outer gold shell.

Gomez, Lizabeth

84

Amphiphilic heteroarm star polymer synthesized by RAFT dispersion polymerization in water/ethanol solution.  

PubMed

Well-defined amphiphilic heteroarm core cross-linked star (CCS) polymer was efficiently synthesized by RAFT-mediated arm-first strategy in dispersion polymerization, and its direct self-assembly in water was demonstrated. PMID:22711229

Shi, Xiaofang; Zhou, Wei; Qiu, Qian; An, Zesheng

2012-06-19

85

Exact effective force between star-polymers in a mth{Theta}-solvent  

Microsoft Academic Search

We re-examine here the computation of the effective force between two star-polymers of respective numbers of branches f1 and f_2, immersed in a common Theta -solvent. Such a force originates essentially from the repulsive three-body interactions. To achieve this, we take advantage of some established results using renormalization theory for three-dimensional star-polymers, or conformal invariance for two-dimensional ones. We first

M. Benhamou; M. Himmi; F. Benzouine; A. Bettachy; A. Derouiche

2004-01-01

86

Templating of inorganic nanoparticles by PAMAM\\/PEG dendrimer–star polymers  

Microsoft Academic Search

Poly(amidoamine) (PAMAM) dendrimers with amine endgroups (PAMAM–NH2) are converted to starlike copolymers by grafting of monofunctional poly(ethylene glycol) (PEG) ‘arms’ onto the dendrimer endgroups. Generation 4, 7, and 10 dendrimers are converted to 60-arm, 235-arm, and 750-arm PAMAM\\/PEG stars, respectively. The dendrimer–stars are studied as polymer templates for stabilization of gold and cadmium sulfide nanoparticles of 1–6nm diameter. PAMAM\\/PEG star

Ronald C Hedden; Barry J Bauer; A Paul Smith; Franziska Gröhn; Eric Amis

2002-01-01

87

Neutron star interiors and the equation of state of ultra-dense matter  

SciTech Connect

There has been much recent progress in our understanding of quark matter, culminating in the discovery that if such matter exists in the cores of neutron stars it ought to be in a color superconducting state. This paper explores the impact of superconducting quark matter on the properties (e.g., masses, radii, surface gravity, photon emission) of compact stars.

Weber, F.; Negreiros, R.; Rosenfield, P. [Dept. of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182 (United States); Torres i Cuadrat, Andreu [Physics Department, Universitat Autonoma de Barcelona (Spain)

2007-02-27

88

The Unsolved Problem of Star Formation: Dusty Dense Cores and the Origin of Stellar Masses  

Microsoft Academic Search

The development of a predictive theory of star formation is one of the prime goals of modern astrophysics. The problem of star formation is a very complex one and its solution depends critically on empirical data. In this contribution, I review some of the progress that has been achieved in identifying and measuring the fundamental boundary and initial conditions that

Charles J. Lada

2009-01-01

89

Equation of state of dense matter and the minimum mass of cold neutron stars  

Microsoft Academic Search

Equilibrium configurations of cold neutron stars near the minimum mass are studied, using the recent equation of state SLy, which describes in a unified, physically consistent manner, both the solid crust and the liquid core of neutron stars. Results are compared with those obtained using an older FPS equation of state of cold catalyzed matter. The value of Mmin =~

P. Haensel; J. L. Zdunik; F. Douchin

2002-01-01

90

Synthesis and Properties of Star-Comb Polymers and Their Doxorubicin Conjugates  

PubMed Central

We describe a six step synthesis to water soluble doxorubicin (DOX)-loaded biodegradable PEGylated star-comb polymers with favorable pharmaceutical properties by atom transfer radical polymerization (ATRP) starting with a commercially available tripentaerythritol carrying eight reactive sites. The low polydispersity polymers degrade in a stepwise manner into lower molecular weight (MW) fragments by 15 days at 37 °C at either pH 5.0 or pH 7.4. The half-life of the star-comb polymers in blood is dependent upon the molecular weight; the 44 kDa star-comb has a t1/2, ? of 30.5 ± 2.1 h, which is not significantly changed (28.6 ±2.7 h) when 6.6 wt% of DOX is attached to it via a pH-sensitive hydrazone linker. The star-comb polymers have low accumulation in organs but a high accumulation in C26 flank tumors implanted in Balb/C mice. The hydrodynamic diameter of polymer-DOX conjugates measured by dynamic light scattering increases from 8 to 35 to 41 nm as the loading is increased from 6.6 to 8.4 to 10.2 wt%. Although there is no significant difference in the t1/2, ? or in the accumulation of polymer-DOX in C-26 tumors, the uptake of polymer in the spleen is significantly higher for polymers with DOX loadings greater than 6.6 wt%. Polymer accumulation in other vital organs is independent of the DOX loading. The facile synthesis, biodegradability, long circulation time and high tumor accumulation of the attached drug suggests that the water-soluble star-comb polymers have promise in therapeutic applications.

Chen, Bo; van der Poll, Derek G.; Jerger, Katherine; Floyd, William C.; Frechet, Jean M. J.; Szoka, Francis C.

2011-01-01

91

Sterilization effects on starPEG coated polymer surfaces: characterization and cell viability  

Microsoft Academic Search

Sterilization is frequently an issue for polymeric biomaterials including hydrogels, where autoclaving needs to be discarded,\\u000a and ?-irradiation and low temperature hydrogen peroxide gas plasma sterilization are already important alternatives. Coatings\\u000a based on poly(ethylene glycol) are a well-known strategy to reduce unspecific protein interactions on biomaterial surfaces.\\u000a Dense, ultrathin coatings of isocyanate terminated star-shaped poly(ethylene glycol) (starPEG) molecules have proven

Júlia Lleixà Calvet; Dirk Grafahrend; Doris Klee; Martin Möller

2008-01-01

92

The Unsolved Problem of Star Formation: Dusty Dense Cores and the Origin of Stellar Masses  

Microsoft Academic Search

The development of a predictive theory of star formation is one of the prime goals of modern astrophysics. The problem of\\u000a star formation is a very complex one and its solution depends critically on empirical data. In this contribution, I review\\u000a some of the progress that has been achieved in identifying and measuring the fundamental boundary and initial conditions that

Charles J. Lada

93

Equation of State of Dense Matter and Maximum Mass of Neutron Stars  

Microsoft Academic Search

Theoretical models of the equation of state (EOS) of neutron-star matter (starting with the crust and ending at the densest region of the stellar core) are reviewed. Apart from a broad set of baryonic EOSs, strange quark matter, and even more exotic (abnormal and Q-matter) EOSs are considered. Results of calculations of M_max for non-rotating neutron stars and exotic compact

P. Haensel

2003-01-01

94

A unified equation of state of dense matter and neutron star structure  

NASA Astrophysics Data System (ADS)

An equation of state (EOS) of neutron star matter, describing both the neutron star crust and the liquid core, is calculated. It is based on the effective nuclear interaction SLy of the Skyrme type, which is particularly suitable for the application to the calculation of the properties of very neutron rich matter (Chabanat et al. 1997, 1998). The structure of the crust, and its EOS, is calculated in the T=0 approximation, and under the assumption of the ground state composition. The crust-core transition is a very weakly first-order phase transition, with relative density jump of about one percent. The EOS of the liquid core is calculated assuming (minimal) npemu composition. Parameters of static neutron stars are calculated and compared with existing observational data on neutron stars. The minimum and maximum masses of static neutron stars are 0.094 Msun and 2.05 Msun, respectively. Effects of rotation on the minimum and the maximum mass of neutron stars are briefly discussed.

Douchin, F.; Haensel, P.

2001-12-01

95

Gravitational Conundrum? Dynamical Mass Segregation versus Disruption of Binary Stars in Dense Stellar Systems  

NASA Astrophysics Data System (ADS)

Upon their formation, dynamically cool (collapsing) star clusters will, within only a few million years, achieve stellar mass segregation for stars down to a few solar masses, simply because of gravitational two-body encounters. Since binary systems are, on average, more massive than single stars, one would expect them to also rapidly mass segregate dynamically. Contrary to these expectations and based on high-resolution Hubble Space Telescope observations, we show that the compact, 15-30 Myr old Large Magellanic Cloud cluster NGC 1818 exhibits tantalizing hints at the >~ 2? level of significance (>3? if we assume a power-law secondary-to-primary mass-ratio distribution) of an increasing fraction of F-star binary systems (with combined masses of 1.3-1.6 M ?) with increasing distance from the cluster center, specifically between the inner 10''-20'' (approximately equivalent to the cluster's core and half-mass radii) and the outer 60''-80''. If confirmed, then this will offer support for the theoretically predicted but thus far unobserved dynamical disruption processes of the significant population of "soft" binary systems—with relatively low binding energies compared to the kinetic energy of their stellar members—in star clusters, which we have access to here by virtue of the cluster's unique combination of youth and high stellar density.

de Grijs, Richard; Li, Chengyuan; Zheng, Yong; Deng, Licai; Hu, Yi; Kouwenhoven, M. B. N.; Wicker, James E.

2013-03-01

96

A new class of charged analogues of Vaidya-Tikekar type super-dense star  

NASA Astrophysics Data System (ADS)

First ever closed form solution for charged fluid sphere expressed by a space time with its hypersurfaces t= constant as spheroid is obtained for the case 0< K<1. The same is utilized to construct a superdense star with surface density 2×1014 gm/cm3. The star is seen to satisfy the reality and causality conditions for 0< K?0.045 and possesses maximum mass and radius to be 0.065216 M ? and 1.137496 km respectively. Moreover the interior of the star satisfy strong energy condition. However in the absence of the causality condition, the reality conditions are valid for a wider range 0< K?0.13. The maximum mass and radius for the later case are 1.296798 M ? and 2.6107 km respectively for the strong energy condition, while the said parameters for the weak energy condition read as 1.546269 M ? and 2.590062 km respectively.

Gupta, Y. K.; Pratibha; Kumar, Jitendra

2011-05-01

97

A class of well behaved charged analogues of Vaidya-Tikekar type super-dense star  

NASA Astrophysics Data System (ADS)

In the present article a model of well behaved charged superdense star with surface density 2×1014 gm/cm3 is constructed by considering a static spherically symmetric metric with t=const hypersurfaces as hyperboloid. So far well behaved model described by such metric could not be obtained. Maximum mass of the star is found to be 0.343457 M ? and the corresponding radius is 9.57459 km. The red shift at the centre and on the surface are given as 0.068887 and 0.031726 respectively.

Gupta, Y. K.; Kumar, Jitendra

2011-08-01

98

A Unified Equation for the Reaction Rate in Dense Matter Stars  

SciTech Connect

We analyze thermonuclear and pycnonuclear reaction rates in multi-component dense stellar plasma. First we describe calculations of the astrophysical S-factor at low energies using the Sao Paulo potential on the basis of the barrier penetration model. Then we present a simple phenomenological expression for a reaction rate. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature.

Gasques, L. R. [Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200 (Australia); Wiescher, M. [Department of Physics and The Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States); Yakovlev, D. G. [Ioffe Physico-Technical Institute, Poliekhnicheskaya 26, 194021 Saint-Petersburg (Russian Federation)

2007-10-26

99

A Unified Equation for the Reaction Rate in Dense Matter Stars  

NASA Astrophysics Data System (ADS)

We analyze thermonuclear and pycnonuclear reaction rates in multi-component dense stellar plasma. First we describe calculations of the astrophysical S-factor at low energies using the Sa~o Paulo potential on the basis of the barrier penetration model. Then we present a simple phenomenological expression for a reaction rate. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature.

Gasques, L. R.; Wiescher, M.; Yakovlev, D. G.

2007-10-01

100

Densely crosslinked polymer networks of poly(ethylene glycol) in trimethylolpropane triacrylate for cell-adhesion-resistant surfaces.  

PubMed

Densely crosslinked semi-interpenetrating polymer networks (semi-IPNs) of poly(ethylene glycol) (PEG) were synthesized by photopolymerizing a melt of PEG of various molecular weights and end-group functionalities in neat trimethylolpropane triacrylate (TMPTA). Increasing the molecular weight of PEG in the matrix from 1000 to 100,000 g/mol reduced the advancing and receding contact angles, contact angle hysteresis, and adsorption of human fibrinogen and bovine serum albumin. Crosslinked TMPTA homonetworks supported human fibroblast adhesion in vitro, whereas the resistance to cell adhesion of the semi-IPNs depended upon PEG molecular weight: Lower molecular weight PEG reduced the number of adherent cells; higher molecular weight PEG further reduced and eliminated cell adhesion, as did networks containing acrylate-functionalized PEG. A polymer system incorporated with PEG throughout a hydrophobic, densely crosslinked matrix, rather than as a blend or surface treatment, may be particularly useful for limiting biologic interactions when bulk material properties must be independent of the solvent environment and where surface abrasion may occur. PMID:7738068

Drumheller, P D; Hubbell, J A

1995-02-01

101

Folic acid conjugated amino acid-based star polymers for active targeting of cancer cells.  

PubMed

Amino acid-based core cross-linked star (CCS) polymers (poly(L-lysine)(arm)poly(L-cystine)(core)) with peripheral allyl functionalities were synthesized by sequential ring-opening polymerization (ROP) of amino acid N-carboxyanhydrides (NCAs) via the arm-first approach, using N-(trimethylsilyl)allylamine as the initiator. Subsequent functionalization with a poly(ethylene glycol) (PEG)-folic acid conjugate via thiol-ene click chemistry afforded poly(PEG-b-L-lysine)(arm)poly(L-cystine)(core) stars with outer PEG coronas decorated with folic acid targeting moieties. Similarly, a control was prepared without folic acid, using just PEG. A fluorophore was used to track both star polymers incubated with breast cancer cells (MDA-MB-231) in vitro. Confocal microscopy and flow cytometry revealed that the stars could be internalized into the cells, and higher cell internalization was observed when folic acid moieties were present. Cytotoxicity studies indicate that both stars are nontoxic to MDA-MB-231 cells at concentrations of up to 50 ?g/mL. These results make this amino acid-based star polymer an attractive candidate in targeted drug delivery applications including chemotherapy. PMID:21854075

Sulistio, Adrian; Lowenthal, Justin; Blencowe, Anton; Bongiovanni, Marie N; Ong, Lydia; Gras, Sally L; Zhang, Xiaoqing; Qiao, Greg G

2011-09-02

102

Formation of massive black holes through runaway collisions in dense young star clusters  

Microsoft Academic Search

A luminous X-ray source is associated with MGG 11-a cluster of young stars ~200pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained by invoking a black hole with a mass of at least 350 solar masses (350Msolar), which is intermediate between stellar-mass and supermassive black holes. A nearby

Simon F. Portegies Zwart; Holger Baumgardt; Piet Hut; Junichiro Makino; Stephen L. W. McMillan

2004-01-01

103

On the Mass of Dense Star Clusters in Starburst Galaxies from SpectroPhotometry  

Microsoft Academic Search

The mass of unresolved young star clusters derived from spectro-photometric\\u000adata may well be off by a factor of 2 or more once the migration of massive\\u000astars driven by mass segregation is accounted for. We quantify this effect for\\u000aa large set of cluster parameters, including variations in the stellar IMF, the\\u000aintrinsic cluster mass, and mean mass density.

J.-J. Fleck; C. M. Boily; A. Lancon; S. Deiters

2006-01-01

104

Ferromagnetic neutron stars: Axial anomaly, dense neutron matter, and pionic wall  

NASA Astrophysics Data System (ADS)

We show that a chiral nonlinear sigma model coupled to degenerate neutrons exhibits a ferromagnetic phase at high density. The magnetization is due to the axial anomaly acting on the parallel layers of neutral pion domain walls spontaneously formed at high density. The emergent magnetic field would reach the QCD scale ˜1019[G], which suggests that the quantum anomaly can be a microscopic origin of the magnetars (highly magnetized neutron stars).

Eto, Minoru; Hashimoto, Koji; Hatsuda, Tetsuo

2013-10-01

105

On the mass of dense star clusters in starburst galaxies from spectrophotometry  

NASA Astrophysics Data System (ADS)

The mass of unresolved young star clusters derived from spectrophotometric data may well be off by a factor of 2 or more once the migration of massive stars driven by mass segregation is accounted for. We quantify this effect for a large set of cluster parameters, including variations in the stellar initial mass function (IMF), the intrinsic cluster mass, and mean mass density. Gas-dynamical models coupled with the Cambridge stellar evolution tracks allow us to derive a scheme to recover the real cluster mass given measured half-light radius, one-dimensional velocity dispersion and age. We monitor the evolution with time of the ratio of real to apparent mass through the parameter ?. When we compute ? for rich star clusters, we find non-monotonic evolution in time when the IMF stretches beyond a critical cut-off mass of 25.5Msolar. We also monitor the rise of colour gradients between the inner and outer volume of clusters: we find trends in time of the stellar IMF power indices overlapping well with those derived for the Large Magellanic Cloud cluster NGC 1818 at an age of 30Myr. We argue that the core region of massive Antennae clusters should have suffered from much segregation despite their low ages. We apply these results to a cluster mass function, and find that the peak of the mass distribution would appear to observers shifted to lower masses by as much as 0.2dex. The star formation rate derived for the cluster population is then underestimated by from 20 to 50 per cent.

Fleck, J.-J.; Boily, C. M.; Lançon, A.; Deiters, S.

2006-07-01

106

Star polymers composed entirely of amino acid building blocks: a route towards stereospecific, biodegradable and hierarchically functionalized stars.  

PubMed

Highly functionalized water soluble core cross-linked star (CCS) polymers having degradable cores and hierarchical functionalities spanning from the peripheral groups along the arms to the core have been synthesized entirely from amino acid building blocks. The core-isolated moieties were shown to undergo further reactions, such as click chemistry, as well as being capable of encapsulating water-insoluble drugs. PMID:21152645

Sulistio, Adrian; Widjaya, Adrian; Blencowe, Anton; Zhang, Xiaoqing; Qiao, Greg

2010-12-13

107

CHaMP@Spitzer: The Formation and Early Evolution of Star Clusters in a Large Unbiased Sample of Dense Gas Clumps  

NASA Astrophysics Data System (ADS)

The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, and panchromatic survey of the formation and early evolution of stars and star clusters covering 20 by 6 deg. of the Galactic Plane. The survey is based on a complete sample of ~300 dense (HCO+ J=1-0 emitting) gas clumps, selected by a recursive mapping of the peaks of 12CO, 13CO, and C18O emission, and then mapped by the Mopra radio telescope in a multitude of molecular transitions. Thus, for the first time we have a full census of the dense gas structures in a large volume of the Milky Way. The goal of this proposal is to use Warm Spitzer to characterize the star formation activity in this entire sample, probing the complete range of dense gas environments. We can resolve the formation of individual stars, but at the same time the full dataset will give us a measure of the global star formation activity of a large portion of the Milky Way, and the range of star formation efficiencies exhibited by molecular clouds. In particular, Spitzer data will: 1. Yield a complete census of any Young Stellar Objects in each clump down to about a solar mass, including their spatial distributions. 2. Combined with other infrared data, allow systematic measurements of the properties of any embedded clusters, including luminosity and mass functions, broad-band spectral classification, protostellar and disk fractions, outflow indicators, and how these vary with cluster mass and density. 3. Combined with mm data, permit a detailed comparison of the embedded stellar populations with their natal dense gas to derive star formation efficiencies and feedback effects.

Barnes, Peter; Lada, Elizabeth; Smith, Nathan; Tan, Jonathan; Romita, Krista; O'Dougherty, Stefan; Ma, Bo; Ryder, Stuart; Hopkins, Andrew

2011-05-01

108

Multiscale structure, interfacial cohesion, adsorbed layers, miscibility and properties in dense polymer-particle mixtures  

NASA Astrophysics Data System (ADS)

A major goal in polymer nanocomposite research is to understand and predict how the chemical and physical nature of individual polymers and nanoparticles, and thermodynamic state (temperature, composition, solvent dilution, filler loading), determine bulk assembly, miscibility and properties. Microscopic PRISM theory provides a route to this goal for equilibrium disordered mixtures. A major prediction is that by manipulating the net polymer-particle interfacial attraction, miscibility is realizable via the formation of thin thermodynamically stable adsorbed layers, which, however, are destroyed by entropic depletion and bridging attraction effects if interface cohesion is too weak or strong, respectively. This and related issues are quantitatively explored for miscible mixtures of hydrocarbon polymers, silica nanospheres, and solvent using x-ray scattering, neutron scattering and rheology. Under melt conditions, quantitative agreement between theory and silica scattering experiments is achieved under both steric stabilization and weak depletion conditions. Using contrast matching neutron scattering to characterize the collective structure factors of polymers, particles and their interface, the existence and size of adsorbed polymer layers, and their consequences on microstructure, is determined. Failure of the incompressible RPA, accuracy of PRISM theory, the nm thickness of adsorbed layers, and qualitative sensitivity of the bulk modulus to interfacial cohesion and particle size are demonstrated for concentrated PEO-silica-ethanol nanocomposites. Temperature-dependent complexity is discovered when water is the solvent, and nonequilibrium effects emerge for adsorbing entangled polymers that strongly impact structure. By varying polymer chemistry, the effect of polymer-particle attraction on the intrinsic viscosity is explored with striking non-classical effects observed. This work was performed in collaboration with S.Y.Kim, L.M.Hall, C.Zukoski and B.Anderson.

Schweizer, Ken

2012-02-01

109

Sterilization effects on starPEG coated polymer surfaces: characterization and cell viability.  

PubMed

Sterilization is frequently an issue for polymeric biomaterials including hydrogels, where autoclaving needs to be discarded, and gamma-irradiation and low temperature hydrogen peroxide gas plasma sterilization are already important alternatives. Coatings based on poly(ethylene glycol) are a well-known strategy to reduce unspecific protein interactions on biomaterial surfaces. Dense, ultrathin coatings of isocyanate terminated star-shaped poly(ethylene glycol) (starPEG) molecules have proven to be resistant to unspecific adsorption of proteins and enable direct biofunctionalization. The effectivity and stability of the starPEG coatings on poly(vinylidene fluoride) (PVDF) were studied after gamma-irradiation (normed dosis 25 kGy) and plasma sterilization (Sterrad 100S). The selected surface properties determined were: surface composition (X-ray photoelectron spectroscopy, XPS), wettability (sessile drop contact angle) and protein adsorption by fluorescence microscopy (Avidin-TexasRed, Bovine Serum Albumin-Rhodamin). Preliminary cell experiments with the cell line L929 were performed prior and after sterilization to investigate the cell repellence of the starPEG coatings as well as cell viability and specific cell adhesion on GRGDS-modified coatings. The starPEG coating undergoes a slight oxidation due to plasma and gamma-sterilization; this represents a minor variation confirmed by XPS and contact angle results. The non-sterilized starPEG and the plasma-sterilized coatings are protein repellent, however the protein adsorption on starPEG coated substrates is much stronger after gamma-sterilization for both avidin and bovine serum albumin. The cell experiments indicate that the starPEG coatings are appliable homogeneously by incubation and are non-cell adherent. Moreover, after both sterilization processes the starPEG coatings remain cell repellent and the GRGDS-modified coatings presented vital cells. Thus we conclude that the plasma sterilization is more convenient for the starPEG coatings and GRGDS-modified starPEG coatings. PMID:18228118

Lleixà Calvet, Júlia; Grafahrend, Dirk; Klee, Doris; Möller, Martin

2008-01-29

110

Neutron stars, fast pulsars, supernovae and the equation of state of dense matter  

SciTech Connect

We discuss the prospects for obtaining constraints on the equation of state from astrophysical sources. Neutron star masses although few are known at present, provide a very direct constraint in as much as the connection to the equation of state involves only the assumption that Einstein's general theory of relativity is correct at the macroscopic scale. If the millisecond pulses briefly observed in the remnant of SN1987A can be attributed to uniform rotation of a pulsar, then a very severe constraint is placed on the equation of state. The theory again is very secure. The precise nature of the constraint is not yet understood, but it appears that the equation of state must be neither too soft nor stiff, and it may be that there is information not only on the stiffness of the equation of state but on its shape. Supernovae simulations involve such a plethora of physical processes including those involved in the evolution of the precollapse configuration, not all of them known or understood, that they provide no constraint at the present time. Not even the broad category of mechanism for the explosion is agreed upon (prompt shock, delayed shock, or nuclear explosion). In connection with very fast pulsars, we include some speculations on pure quark matter stars, and on possible scenarios for understanding the disappearance of the fast pulsar in SN1987A. 47 refs., 16 figs., 1 tab.

Glendening, N.K.

1989-06-01

111

Thermal emission from old neutron stars: constraints on dense-matter and gravitational physics  

NASA Astrophysics Data System (ADS)

The equilibrium composition of neutron star matter is achieved through weak interactions direct and inverse beta decays which proceed on relatively long time scales If the density of a matter element is perturbed it will relax to the new chemical equilibrium through non-equilibrium reactions which produce entropy that is partly released through neutrino emission while a similar fraction heats the matter and is eventually radiated as thermal photons Reisenegger 1995 We examined two possible causes of such density perturbations begin enumerate item the reduction in centrifugal force caused by spin-down particularly in millisecond pulsars leading to rotochemical heating Fern a ndez Reisenegger 2005 and item a hypothetical time-variation of the gravitational constant as predicted by some theories of gravity and current cosmological models gravitochemical heating Jofr e 2005 end enumerate If only slow weak interactions modified Urca reactions are allowed in the neutron star rotochemical heating can account for the observed ultraviolet emission from the closest millisecond pulsar PSR J0437-4715 Kargaltsev et al 2004 which also provides a constraint on vert dG dt vert of the same order as the best available in the literature For slower classical pulsars beyond their initial cooling epoch detectable thermal emission due to rotochemical heating is also possible if their initial rotation rate was fast enough to build up a substantial chemical imbalance This

Reisenegger, A.; Fernández, R.; Jofré, P.

112

Far-infrared and submillimeter-wavelength observations of star-forming dense cores. I. Spectra  

SciTech Connect

Far-infrared and submillimeter photometry of 10 low-mass star formation regions containing embedded IRAS sources is presented. These new observations define the peak of the spectral energy distributions of these objects and provide more precise estimates of their bolometric luminosities. Two new sources, L1527 and L483, are among the reddest known low-mass objects, with spectral energy distribution peaks at 100-200 microns and extremely steep IRAS slopes. These cold sources have spectra which are similar to blackbodies of 30-40 K but have significant excess emission on the Wien side. Models of the spectral energy distributions using a spherically symmetric core structure indicate that these sources have visual extinctions greater than 1000 mag. However, models with these large extinctions predict too little near-infrared emission. A nonspherically symmetric distribution of circumstellar material may play a role in the generation of the extra near-infrared emission. 64 refs.

Ladd, E.F.; Adams, F.C.; Fuller, G.A.; Casey, S.; Davidson, J.A. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA) Yerkes Observatory, Williams Bay, WI (USA) NASA, Ames Research Center, Moffett Field, CA (USA))

1991-01-01

113

Model for the shear viscosity of suspensions of star polymers and other soft particles  

NASA Astrophysics Data System (ADS)

We propose a model to describe the concentration dependence of the viscosity of soft particles. We incorporate in a very simple way the softness of the particles into expressions originally developed for rigid spheres. This is done by introducing a concentration-dependent critical packing, which is the packing at which the suspension looses fluidity. The resultant expression reproduces with high accuracy the experimental results for suspensions of star polymers in good solvents. The model allows to explain a weak increase of the viscosity observed in the case of diblock copolymer stars suggesting that the reason for this peculiar behavior is mainly a consequence of the softness of the particles. In the semi-dilute regime, suspensions of star polymers are modeled using the Daoud-Cotton picture to complete the description in the whole concentration regime.

Mendoza, Carlos

2013-03-01

114

A systematic procedure to build a relaxed dense-phase atomistic representation of a complex amorphous polymer using a coarse-grained modeling approach  

PubMed Central

A systematic procedure has been developed to construct a relaxed dense-phase atomistic structure of a complex amorphous polymer. The numerical procedure consists of (1) coarse graining the atomistic model of the polymer into a mesoscopic model based on an iterative algorithm for potential inversion from distribution functions of the atomistic model, (2) relaxation of the coarse grained chain using a molecular dynamics scheme, and (3) recovery of the atomistic structure by reverse mapping based on the superposition of atomistic counterparts on the corresponding coarse grained coordinates. These methods are demonstrated by their application to construct a relaxed, dense-phase model of poly(DTB succinate), which is an amorphous tyrosine-derived biodegradable polymer that is being developed for biomedical applications. Both static and dynamic properties from the coarse-grained and atomistic simulations are analyzed and compared. The coarse-grained model, which contains the essential features of the DTB succinate structure, successfully described both local and global structural properties of the atomistic chain. The effective speedup compared to the corresponding atomistic simulation is substantially above 102, thus enabling simulation times to reach well into the characteristic experimental regime. The computational approach for reversibly bridging between coarse-grained and atomistic models provides an efficient method to produce relaxed dense-phase all-atom molecular models of complex amorphous polymers that can subsequently be used to study and predict the atomistic-level behavior of the polymer under different environmental conditions in order to optimally design polymers for targeted applications.

Li, Xianfeng; Latour, Robert A.

2009-01-01

115

A new model with non-spherical interactions for dense polymer systems  

NASA Astrophysics Data System (ADS)

We introduce a new general model for the simulation of dense macromolecular systems. It consists of basic ellipsoidally shaped units stringed together to form chains, including branched and side chains. The ellipsoidally shaped unit can vary in its principal axes, allowing for flexible modeling of a chain. The variation in the main principal axis is used for the intramolecular potential of the bond type. Intramolecular units interact through a harmonic bond-angle potential and the intermolecular interaction is modelled by a confocally decreasing Lennard-Jones potential. We present the model for the special case of a polycarbonate and indicate the generalization to other cases.

Zimmer, Klaus M.; Heermann, Dieter W.

1995-04-01

116

Dense polymer film and membrane formation via the dry-cast process part I. Model development  

Microsoft Academic Search

The dry-cast membrane-formation process is a major phase-inversion technique by which asymmetric membranes are manufactured. In this paper a fully predictive model which incorporates coupled heat and mass transfer is developed to describe the evaporation of both solvent and nonsolvent from an ini- tially homogeneous polymer\\/solvent\\/nonsolvent system. This unsteady-state, one-dimensional, coupled heat- and mass-transport model allows for local film shrinkage

Saeed S. Shojaie; William B. Krantz; Alan R. Greenberg

1994-01-01

117

Extensive Study of Interaction Force Between Spherical Colloids and Star Polymers  

NASA Astrophysics Data System (ADS)

We consider a system consisting of very small colloidal particles clothed each by f end-grafted flexible polymer chains we regarded as star polymers, and hard spherical colloidal particles in a good solvent. Our main objective is to determine the expression of the interaction force between a spherical colloid and a star polymer as a function of distance between them. We limit ourselves to the case where the star polymer is smaller than the colloid. In the first part, the system is dissolved in a melt of short linear chains of polymerization degree Pf* =? {P}) and (2) small-grafting density (f < f*). For (f > f*), we show that the expression of the expected force coincides exactly with that of the case of a small molecular weight solvent. For (f < f*), we show that there is a change in behavior. In the second part, we assume that the lengths of the f grafted chains were randomly distributed and there is talk of a polydisperse star polymer. We show that the computation of the expected force depends on the relative values of the polymerization degree of longest grafted chain, N, when it is compared to the typical one Nc f1/(?-1). Here ? is the polydispersity exponent. We distinguish two regimes depending on whether N < Nc or N > Nc. For the regime with N < Nc, and comparing the expression of the force obtained for the monodisperse case, we can say that the polydispersity of grafted chains induce a drastic change of the force expression. For the regime with N > Nc, we found the existence of two distance-ranges. For small distances, the effective force expression is identical to that relative to the above case (N < Nc). But for high distances, the effective force expression is similar to the monodisperse case.

Himmi, Mustapha; Mohammadi, Laila

2012-07-01

118

Synthesis and properties of polymeric cation conductors and amphiphilic star polymers  

SciTech Connect

Polymeric alkali ion conductors consisting of a comblike polysiloxane with oligo-oxyethylene side chains and pendant sulfonate groups were synthesized by the quantitative hydrosilylation of an allyl methoxy-polyethylene glycol and allyl glycidyl ether with polyhydrogenmethyl-siloxane, followed by the sulfonation of the epoxy group. The addition of Si-H is chiefly to the B-vinyl carbon and the sulfonation reaction is quantitative. DSC and conductivity measurements show that these materials are essentially amorphous and their cation conducting behavior can be interpreted by a VTF type equation. Due to the tightness of the alkali sulfonate ion pairs the conductivity of these polymers is low compared to that of dual polymer electrolytes containing LiClO{sub 4} or LiCF{sub 3}SO{sub 3} salt. However, conductivities of up to 10{sup {minus}5} S cm{sup {minus}1} at 25{degrees}C can be achieved by adding cation chelating ligands such as tetraethylene glycol. The effect of cation, temperature, ion content, glass transition temperature, and additives on the conductivity of these materials is discussed. Well-defined multifunctional isocyantes are obtained in high purity and quantitative yield by hydrosilylation of m-isopropenyl-{alpha}, {alpha}-dimethylbenzyl isocyanate (m-TMI) with cyclic and acyclic hydrogen-methylsiloxanes. The products were exclusively result from {beta}-addition of Si-H to the double bond in m-TMI. The polyisocyanates were reacted with methoxypolyethylene glycols (MPEG) and with nonlphenoxypolyethylene glycols (NPPEG) to yield amphiphilic star polymers with a precise number of arms. Amphiphilic star homopolmers made from MPEG form micelles in water. Star polymers with NPPEG arms in aqueous solutions separate into two phases of constant composition, the condensed phase being an associative network resembling a hydrogel. Surface tension, viscosities, cloud points, salt binding and solubilities were determined and compared with linear or star polymers.

Zho, Guangbin

1992-12-31

119

Decoding the Viscoelastic Response of Polydisperse Star/Linear Polymer Blends  

NASA Astrophysics Data System (ADS)

It is well known that polydispersity and branching have important and, at the same time, hardly predictable effects on the rheological and processing properties of industrial polymers. In the literature, many studies have been undertaken in order to predict the rheology of polydisperse linear polymers and monodisperse, well-defined, branched polymers. Industrial polymers are usually, simultaneously polydisperse and branched, exhibiting a much more complex viscoelastic behaviour. When polydispersity and branching are both present, many different relaxation processes are indeed active and sometimes coupled. In order to understand the viscoelastic behaviour of such a class of complex materials, we investigated the rheology of several blends of polydisperse linear and stars polymers with the help of a coarse grained-tube model. A series of polydisperse star/linear polybutadiene blends characterized by different composition and arm average molecular weight was prepared. Linear ``parent'' polymers were synthesized via anionic polymerization. A coupling agent was introduced in a second stage in order to obtain the blends. In order to characterize the composition of the blends, light scattering data were performed for determining their molar mass distributions (MMD). Then, using an adequate statistical approach, MMD were divided into different categories of architectures. We obtained a full set of linear and non-linear rheological data. Then, we extended our tube-based model to predict their linear viscoelasticity. This requires several modifications of the initial model in order to deal with a very large number of different particles and star molecules having arms of different lengths. The non-linear rheological response was analyzed with special attention to the time-strain separability at short and long times, whereas the response to uniaxial extension was also investigated.

Balacca, L.; van Ruymbeke, E.; Coppola, S.; Righi, S.; Vlassopoulos, D.

2008-07-01

120

Bis-ureidodeazapterin (Bis-DeAP) as a general route to supramolecular star polymers  

Microsoft Academic Search

Supramolecular recognition unit Bis-DeAP, 1, containing two high affinity hydrogen-bonding acceptor–acceptor–donor–donor (AADD) arrays was designed to self-assemble into cyclic assemblies. It was prepared through a highly scalable synthesis and was further functionalized with 2-bromo-2-methylpropanoyl bromide and used to initiate the polymerization of methylmethacrylate (MMA). Bis-DeAP–PMMA polymers quantitatively self-assembled into star polymers in toluene. In DMF Bis-DeAP–PMMA forms a mixture of

Eric M. Todd; Steven C. Zimmerman

2008-01-01

121

Effective delivery of siRNA into cancer cells and tumors using well-defined biodegradable cationic star polymers.  

PubMed

Cancer is one of the most common causes of death worldwide. Two types of cancer that have high mortality rates are pancreatic and lung cancer. Despite improvements in treatment strategies, resistance to chemotherapy and the presence of metastases are common. Therefore, novel therapies which target and silence genes involved in regulating these processes are required. Short-interfering RNA (siRNA) holds great promise as a therapeutic to silence disease-causing genes. However, siRNA requires a delivery vehicle to enter the cell to allow it to silence its target gene. Herein, we report on the design and synthesis of cationic star polymers as novel delivery vehicles for siRNA to silence genes in pancreatic and lung cancer cells. Dimethylaminoethyl methacrylate (DMAEMA) was polymerized via reversible addition-fragmentation transfer polymerization (RAFT) and then chain extended in the presence of both cross-linkers N,N-bis(acryloyl)cistamine and DMAEMA, yielding biodegradable well-defined star polymers. The star polymers were characterized by transmission electron microscopy, dynamic light scattering, ? potential, and gel permeation chromatography. Importantly, the star polymers were able to self-assemble with siRNA and form small uniform nanoparticle complexes. Moreover, the ratios of star polymer required to complex siRNA were nontoxic in both pancreatic and lung cancer cells. Treatment with star polymer-siRNA complexes resulted in uptake of siRNA into both cell lines and a significant decrease in target gene mRNA and protein levels. In addition, delivery of clinically relevant amounts of siRNA complexed to the star polymer were able to silence target gene expression by 50% in an in vivo tumor setting. Collectively, these results provide the first evidence of well-defined small cationic star polymers to deliver active siRNA to both pancreatic and lung cancer cells and may be a valuable tool to inhibit key genes involved in promoting chemotherapy drug resistance and metastases. PMID:23611705

Boyer, Cyrille; Teo, Joann; Phillips, Phoebe; Erlich, Rafael B; Sagnella, Sharon; Sharbeen, George; Dwarte, Tanya; Duong, Hien T T; Goldstein, David; Davis, Thomas P; Kavallaris, Maria; McCarroll, Joshua

2013-05-06

122

Synthesis of well-defined star-branched polymers by stepwise iterative methodology using living anionic polymerization  

Microsoft Academic Search

This article reviews the synthesis of regular and asymmetric star-branched polymers with well-defined structures by methodologies using living anionic polymerization, especially focusing on the synthetic approaches accessible for precisely controlled architectures of star-branched polymers concerning molecular weight, molecular weight distribution, arm number, and composition. The reason for selecting living anionic polymerization from many living\\/controlled polymerization systems so far developed is

Tomoya Higashihara; Mayumi Hayashi; Akira Hirao

2011-01-01

123

Six Isomers of Dendrimer-like Star Polymers: Design and Synthesis  

SciTech Connect

The control of polymer properties through the synthesis of complex macromolecular architectures is central to many areas of research and advanced technological applications. properties of novel materials are altered mainly through modification of their constitution. Examples of constitutional changes include the use of different monomers, variable molecular weights, block structures, grafted branching and so on. Living polymerization techniques has facilitated the preparation of these structures. The use of new multifunctional initiators has enhanced the availability of for example star polymers, which are believed to have smaller hydrodynamic volume and lower melt viscosity than their linear counterparts. Dendrimers and hyperbranched polymers are other classes of macromolecules which have received a lot of attention due to their unique architectures.

Pople, John A.

1999-03-01

124

Intravaginal gene silencing using biodegradable polymer nanoparticles densely loaded with small-interfering RNA  

PubMed Central

Vaginal instillation of small-interfering RNA (siRNA) using liposomes has led to silencing of endogenous genes in the genital tract and protected against challenge from infectious disease. Although siRNA lipoplexes are easily formulated, several of the most effective transfection agents available commercially may be toxic to the mucosal epithelia and none are able to provide controlled or sustained release. Here, we demonstrate an alternate approach, using nanoparticles composed entirely of FDA-approved materials. To render these materials effective for gene silencing we developed novel approaches to load them with high amounts of siRNA. A single dose of siRNA-loaded nanoparticles to the mouse female reproductive tract caused efficient and sustained gene silencing. Knockdown of gene expression was observed proximal (in the vaginal lumen) and distal (in the uterine horns) to the site of topical delivery. In addition, nanoparticles penetrated deep into the epithelial tissue. This is the first report demonstrating that biodegradable polymer nanoparticles are effective delivery vehicles for siRNA in the vaginal mucosa.

Woodrow, Kim A.; Cu, Yen; Booth, Carmen J.; Saucier-Sawyer, Jennifer K.; Wood, Monica J.; Saltzman, W. Mark

2009-01-01

125

Structural investigation of star polymers in solution by small angle neutron scattering  

SciTech Connect

Using small angle neutron scattering, the authors investigated the conformation of star polymers with functionalities ranging from f = 8 to f = 128 in a good solvent. The stars were made anionic polymerization of isoprene or butadiene using multifunctional chlorosilane linking agents. Single star form factors at zero concentration were determined by extrapolating low concentration data to [phi] = 0. Conformations at finite concentrations were obtained by the zero average contrast method. In general the star form factors are well described in terms of the Daoud-Cotton scaling model. This concerns the molecular weight, functionality, and concentration dependence of R[sub G] as well as the shape of the form factor. In particular the step height between the low Q and asymptotic power law regime was found to follow an f[sup 3/2] law. Furthermore, with increasing functionality the star form factors were found to tend toward spherelike behavior, bearing evidence for a secondary maximum at the position of the third oscillation of the corresponding sphere form factor.

Willner, L.; Jucknischke, O.; Richter, D. (Inst. fuer Festkoerperforschung, Juelich (Germany)) (and others)

1994-07-04

126

Effect of molecular architecture on the self-diffusion of polymers in aqueous systems: A comparison of linear, star, and dendritic poly(ethylene glycol)s  

Microsoft Academic Search

Star polymers with a hydrophobic cholane core and four poly(ethylene glycol) (PEG) arms, CA(EGn)4, have been synthesized by anionic polymerization. Pulsed-gradient spin-echo NMR spectroscopy was used to study the diffusion behavior of the star polymers, ranging from 1000 to 10,000g\\/mol, in aqueous solutions and gels of poly(vinyl alcohol) (PVA) at 23°C. The star polymers have a lower self-diffusion coefficient than

Y. J. Wang; H. Therien-Aubin; W. E. Baille; J. T. Luo; X. X. Zhu

2010-01-01

127

Conditions leading to the formation of polymer thin layers with densely dispersed organic dyes using the vapor transportation method with vacuum technique  

NASA Astrophysics Data System (ADS)

The "vapor transportation method" with vacuum technique, developed previsouly in our laboratory, was used to form polymer thin layers with densely dispersed photochromic dyes on polystyrene (PS), poly(methyl methacrylate) (PMMA), and polymcarbonate (PC) substrates. The organic photochrmoic dye cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethane (CMTE) was used, and the rate of formation of the CMTE-conatining layer was as follows: PS > PC > PMMA. These observations are important for application of the present method to the formation of organic memory media for optical recording etc. These results also indicate that the formation rate is dependent on not only the chemical composition and the structure of the polymer substrate, but also on the treatment temperature. Optical density measurements of the CMTE-dispersed thin polymer films showed maximum values near the glass transition temperature (g) with increases in temperature of film formation. The Tg values of CMTE-dispersed polymers decreased rapidly after CMTE-dispersal into the polymer matrices, indicating that Tg values of the polymers are important parameters for investigation of the mechanism of formation of CMTE-dispersed layers on polymer substrates using the present method.

Mizokuro, Toshiko; Mochizuki, Hiroyuki; Yamamoto, Noritaka; Tanaka, Norio; Horiuchi, Shin; Tanigaki, Nobutaka; Hiraga, Takashi

2003-07-01

128

Exact effective force between star-polymers in a Theta-solvent.  

PubMed

We re-examine here the computation of the effective force between two star-polymers of respective numbers of branches f(1) and f(2), immersed in a common Theta-solvent. Such a force originates essentially from the repulsive three-body interactions. To achieve this, we take advantage of some established results using renormalization theory for three-dimensional star-polymers, or conformal invariance for two-dimensional ones. We first show that, in dimension d = 3, the force, F(r), decreases with the center-to-center distance r as F(r)/kappa BT congruent with Af1f2 x [r ln (R2/r2]-1 (rpolymer chain at the Theta-point, an exponential decay of the force is expected. PMID:15170534

Benhamou, M; Himmi, M; Benzouine, F; Bettachy, A; Derouiche, A

2004-04-01

129

Aging and stiction dynamics in confined films of a star polymer melt.  

PubMed

The stiction properties of a star polyisoprene (PIP) melt (having 22 arms and an arm molecular weight of around 5000, M(w) ? 110,000) confined between mica surfaces were investigated using the surface forces apparatus. Stop-start experiments were carried out and the stiction spike was measured as a function of surface stopping (aging) time t and applied pressure P; the time constants of the phase transitions in the stiction dynamics (freezing on stopping and melting on starting) were obtained from the force relaxation behaviors. The results were compared with those of a confined linear-PIP melt (M(w) ? 48,000) and other confined fluid systems; the effect of star architecture on the phase transitions in confinement during aging is discussed. Estimation of the molecular size gives that the confined star-PIP films consist of three molecular layers; a non-adsorbed layer sandwiched between two layers adsorbed on opposed mica surfaces. There are (at least) four time constants in the freezing transition of the confined star-PIP melt; fast (?(1)) and slow (?(2)) time constants for lateral force relaxation on stopping, critical aging time for freezing (?(f)), and the logarithmic increase of the spike height against t. The three time constants on stopping, ?(1), ?(2), and ?(f), increase with the increase of P (decrease of the thickness D). As regards the melting transition on starting, spike force decay was fitted by a single exponential function and one time constant was obtained, which is insensitive to P (D). Comparison of the time constants between freezing and melting, and also with the results of linear-PIP reveals that the stiction dynamics of the star-PIP system involves the relaxation and rearrangement of segmental-level and whole molecular motions. Lateral force relaxation on stopping is governed by the individual and cooperative rearrangements of local PIP segments and chain ends of the star, which do not directly lead to the freezing of the system. Instead, geometrical rearrangements of the soft star-PIP spheres into dense packing between surfaces (analogous to the concept of a colloidal glass transition) are the major mechanism of the freezing transition (stiction) after aging. Interdigitation of PIP segments/chain ends between neighboring star molecules also contributes to the spike growth along with aging, and the melting transition on starting. PMID:23181327

Yamada, Shinji

2012-11-21

130

Compatibilization of polystyrene and poly(dimethyl siloxane) with a star polymer having a ?tcyclodextrin core and polystyrene arms  

NASA Astrophysics Data System (ADS)

Cyclodextrins (CDs) are cyclic starch molecules having a hollow central cavity which can be threaded by a polymer to form an inclusion compound. This characteristic is exploited in a new type of compatibilizer: a star polymer with a ?tCD core and polystyrene (PS) arms. Atom transfer radical polymerization is used to grow and control the size of the PS arms from brominated initiator sites on ?tCD. Solutions and thin films of PS and poly(dimethyl siloxane) (PDMS) are compatibilized by this CD-star. The mechanism of compatibilization involves threading of the CD core by PDMS and solubilization of the resulting ``slip-ring graft copolymer'' via the PS star arms. Compatibilization of PS/PDMS in chloroform is visually observed when the initially turbid suspensions become clear solutions after addition of CD-star. Thin films spin-cast from these solutions exhibit a high degree of homogeneity and a nanoscale level of mixing. The solutions are characterized with NMR, dynamic light scattering and intrinsic viscosity measurements, and the thin films are characterized with optical and atomic force microscopy. Many different polymers are capable of threading the CD core, thus the same CD-star molecule could be used to compatibilize several different threading polymers with the same matrix polymer.

Balik, C. M.; Tonelli, A. E.; Busche, Brad

2010-03-01

131

Synthesis of biocompatible PEG-Based star polymers with cationic and degradable core for siRNA delivery.  

PubMed

Star polymers with poly(ethylene glycol) (PEG) arms and a degradable cationic core were synthesized by the atom transfer radical copolymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate macromonomer (PEGMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a disulfide dimethacrylate (cross-linker, SS) via an "arm-first" approach. The star polymers had a diameter ~15 nm and were degraded under redox conditions by glutathione treatment into individual polymeric chains due to cleavage of the disulfide cross-linker, as confirmed by dynamic light scattering. The star polymers were cultured with mouse calvarial preosteoblast-like cells, embryonic day 1, subclone 4 (MC3T3-E1.4) to determine biocompatibility. Data suggest star polymers were biocompatible, with ? 80% cell viability after 48 h of incubation even at high concentration (800 ?g/mL). Zeta potential values varied with N/P ratio confirming complexation with siRNA. Successful cellular uptake of the star polymers in MC3T3-E1.4 cells was observed by confocal microscopy and flow cytometry after 24 h of incubation. PMID:21894897

Cho, Hong Y; Srinivasan, Abiraman; Hong, Joanna; Hsu, Eric; Liu, Shiguang; Shrivats, Arun; Kwak, Dan; Bohaty, Andrew K; Paik, Hyun-Jong; Hollinger, Jeffrey O; Matyjaszewski, Krzysztof

2011-09-06

132

Supramolecular star polymers. Increased molecular weight with decreased polydispersity through self-assembly.  

PubMed

A ditopic structure containing two heterocyclic DeAP units and programmed to self-assemble is used as an initiation unit for the synthesis of polylactide and polystyrene. The resultant polymers self-assemble into higher molecular weight structures with a lower molecular weight distribution. The largest discrete nanoscale polymeric assembly is proposed to be a hexameric star with a molecular weight of ca. 92.7 kDa. All polymeric assemblies generally exhibit PDI values of 1.3 to 1.5, which are lower than the PDI value of the corresponding polymeric arms. A hexameric assembly is stabilized by 30 hydrogen bonds, including six AADD.DDAA contacts. The hexameric star is formed under conditions that are at least partially controlled by kinetics. PMID:17983229

Todd, Eric M; Zimmerman, Steven C

2007-11-06

133

Unique slow dynamics and aging phenomena in soft glassy suspensions of multiarm star polymers  

NASA Astrophysics Data System (ADS)

We use time-resolved rheology to elucidate the slow dynamics and aging in highly concentrated suspensions of multiarm star polymers. The linear and nonlinear rheological properties exhibit a terminal regime corresponding to a well-defined maximal relaxation time. Terminal relaxation is driven by arm relaxation which speeds up the escape of stars from their cages. The fact that the system fully relaxes and flows at long times has important consequences. The yield stress only exists in the limited range of frequencies or shear rates where solid-like behavior is observed. Aging is controlled by the total time elapsed after flow cessation and not by the time elapsed from flow cessation to the beginning of the measurement as in other glassy materials. Our results, which demonstrate the importance of particle architecture with respect to glassy dynamics, should be generic for long hairy particles.

Erwin, Brian M.; Vlassopoulos, Dimitris; Gauthier, Mario; Cloitre, Michel

2011-06-01

134

Telechelic Star Polymers as Self-Assembling Units from the Molecular to the Macroscopic Scale  

NASA Astrophysics Data System (ADS)

By means of multiscale molecular simulations, we show that telechelic-star polymers are a simple, robust, and tunable system, which hierarchically self-assembles into soft-patchy particles and mechanically stabilizes selected, open crystalline structures. The self-aggregating patchy behavior can be fully controlled by the number of arms per star and by the fraction of attractive monomeric units at the free ends of the arms. Such self-assembled soft-patchy particles while forming, upon augmenting density, gel-like percolating networks, preserve properties as particle size, number, and arrangement of patches per particle. In particular, we demonstrate that the flexibility inherent in the soft-patchy particles brings forward a novel mechanism that leads to the mechanical stability of diamond and simple cubic crystals over a wide range of densities, and for molecular sizes ranging from about 10 nm up to the micrometer scale.

Capone, Barbara; Coluzza, Ivan; LoVerso, Federica; Likos, Christos N.; Blaak, Ronald

2012-12-01

135

Synthesis of ABC-type miktoarm star polymers by “click” chemistry, ATRP and ROP  

Microsoft Academic Search

ABC-type miktoarm star polymers, poly(ethylene oxide)-block-polystyrene-block-poly (?-caprolactone)s (PEO-b-PS-b-PCL) were synthesized via combination of “click” chemistry, atom-transfer radical polymerization (ATRP) and ring opening polymerization (ROP). Azide ended PEO arms, PEO–N3, and a trifunctional molecule, propargyl 2-hydroxylmethyl-2-(?-bromoisobutyraloxymethyl)-propionate (PHBP), were prepared first, respectively. A “click” reaction of PEO–N3 and PHBP generated a PEO macroinitiator, PEO–(Br)(OH) with two functionalities, one is hydroxyl group and

Guohua Deng; Deyun Ma; Zizhen Xu

2007-01-01

136

High-functionality star-branched macromolecules: Polymer size and virial coefficients.  

PubMed

We perform high-statistics Monte Carlo simulations of a lattice model to compute the radius of gyration Rg, the center-to-end distance, the monomer distribution, and the second and third virial coefficients of star polymers for a wide range of functionalities f, 6 ? f ? 120. We consider systems with a large number L of monomers per arm (100 ? L ? 1000 for f ? 40 and 100 ? L ? 400 for f = 80, 120), which allows us to determine accurately all quantities in the scaling regime. Results are extrapolated to determine the behavior of the different quantities in the limit f ? ?. Structural results are finally compared with the predictions of the Daoud-Cotton model. It turns out that the blob picture of a star polymer is essentially correct up to the corona radius Rc, which depends on f and which varies from 0.7Rg for f = 6 to 1.0Rg for f = 40. The outer region (r > Rc), in which the monomer distribution decays exponentially, shrinks as f increases, but it does not disappear in the scaling regime even in the limit f ? ?. We also consider the Daoud-Cotton scaling relation Rg (2)?f(1-?)L(2?), which is found to hold only for f ? 100. PMID:24160541

Randisi, Ferdinando; Pelissetto, Andrea

2013-10-21

137

High-functionality star-branched macromolecules: Polymer size and virial coefficients  

NASA Astrophysics Data System (ADS)

We perform high-statistics Monte Carlo simulations of a lattice model to compute the radius of gyration Rg, the center-to-end distance, the monomer distribution, and the second and third virial coefficients of star polymers for a wide range of functionalities f, 6 <= f <= 120. We consider systems with a large number L of monomers per arm (100 <~ L <~ 1000 for f <= 40 and 100 <~ L <~ 400 for f = 80, 120), which allows us to determine accurately all quantities in the scaling regime. Results are extrapolated to determine the behavior of the different quantities in the limit f --> ?. Structural results are finally compared with the predictions of the Daoud-Cotton model. It turns out that the blob picture of a star polymer is essentially correct up to the corona radius Rc, which depends on f and which varies from 0.7Rg for f = 6 to 1.0Rg for f = 40. The outer region (r > Rc), in which the monomer distribution decays exponentially, shrinks as f increases, but it does not disappear in the scaling regime even in the limit f --> ?. We also consider the Daoud-Cotton scaling relation Rg2~f1-?L2?, which is found to hold only for f >> 100.

Randisi, Ferdinando; Pelissetto, Andrea

2013-10-01

138

Particles without a Box: Brush-first Synthesis of Photodegradable PEG Star Polymers under Ambient Conditions.  

PubMed

Convenient methods for the rapid, parallel synthesis of diversely functionalized nanoparticles will enable discovery of novel formulations for drug delivery, biological imaging, and supported catalysis. In this report, we demonstrate parallel synthesis of brush-arm star polymer (BASP) nanoparticles by the "brush-first" method. In this method, a norbornene-terminated poly(ethylene glycol) (PEG) macromonomer (PEG-MM) is first polymerized via ring-opening metathesis polymerization (ROMP) to generate a living brush macroinitiator. Aliquots of this initiator stock solution are added to vials that contain varied amounts of a photodegradable bis-norbornene crosslinker. Exposure to crosslinker initiates a series of kinetically-controlled brush+brush and star+star coupling reactions that ultimately yields BASPs with cores comprised of the crosslinker and coronas comprised of PEG. The final BASP size depends on the amount of crosslinker added. We carry out the synthesis of three BASPs on the benchtop with no special precautions to remove air and moisture. The samples are characterized by gel permeation chromatography (GPC); results agreed closely with our previous report that utilized inert (glovebox) conditions. Key practical features, advantages, and potential disadvantages of the brush-first method are discussed. PMID:24145552

Liu, Jenny; Gao, Angela Xiaodi; Johnson, Jeremiah A

2013-10-10

139

Transfer hydrogenation of ketones catalyzed by PEG-armed ruthenium-microgel star polymers: microgel-core reaction space for active, versatile and recyclable catalysis  

Microsoft Academic Search

Poly(ethylene glycol) (PEG)-armed Ru(II)-bearing microgel-core star polymer catalysts were used for the transfer hydrogenation of ketones. The star catalysts (Ru(II)-PEG Star) were one-pot synthesized by ruthenium-catalyzed living radical polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and a sequential linking reaction with ethylene glycol dimethacrylate (1) and diphenylphosphinostyrene (2). The polymers efficiently and homogeneously reduced acetophenone into 1-phenylethanol in 2-propanol

Takaya Terashima; Makoto Ouchi; Tsuyoshi Ando; Mitsuo Sawamoto

2011-01-01

140

Conformational and Structural Properties of High Functionality Dendrimer-like Star Polymers Synthesized from Living Polymerization Techniques  

SciTech Connect

The design, synthesis and solution properties of dendritic-linear hybrid macromolecules is described. The synthetic strategy employs living ring-opening polymerization in combination with selective and quantitative organic transformations for the preparation of new molecular architectures similar to classical star polymers and dendrimers. The polymers were constructed from high molecular weight poly(e-caprolactone) initiated from the surface hydroxyl groups of dendrimers derived from bis(hydroxymethyl) propionic acid (bis-MPA) in the presence of stannous 2-ethyl hexanoate (Sn(Oct)2). In this way, star and hyperstar poly(e-caprolactones) were elaborated depending on the generation of dendrimer employed. The ROP from these hydroxy groups was found to be a facile process leading to controlled molecular weight, low dispersity products (Mw/Mn) < 1.15. In addition to the use of dendrimers as building blocks to star polymers, functional dendrons derived from bis-MPA were attached to chain ends of the star polymers, yielding structures that closely resemble that of the most advanced dendrimers. Measurements of the solution properties (hydrodynamic volume vs. molecular weight) on the dendritic-linear hybrids show a deviation from linearity, with a lower than expected hydrodynamic volume, analogous to the solution properties of dendrimers of high generation number. The onset of the deviation begins with the polymers initiated from the second generation dendrimer of bis-MPA and becomes more exaggerated with the higher generations. It was found that polymerization amplifies the nonlinear solution behavior of dendrimers. Small angle neutron scattering (SANS) measurements revealed that the radius of gyration scaled with arm functionality (f) as f 2/3, in accordance with the Daoud-Cotton model for many arm star polymer.

Pople, John A.

2001-03-22

141

An AZTEC\\/ASTE 1.1mm Survey Of The Young, Dense, Nearby Star-forming Region, Serpens South  

Microsoft Academic Search

The Serpens South embedded cluster, recently discovered by the Spitzer Gould Belt Legacy Survey, stands out among over 100 clusters and groups surveyed by Spitzer as the densest (>430 pc-2) and youngest (77% Class I protostars) clustered star forming region known within the nearest 400 pc. In order to better characterize the primordial structure of the cluster's natal cloud, we

Robert A. Gutermuth; T. Bourke; B. Matthews; M. Dunham; L. Allen; P. Myers; J. Jorgensen; G. Wilson; M. Yun; D. Hughes; I. Aretxaga; K. Ryohei; K. Kotaro; K. Scott; J. Austermann

2010-01-01

142

Insight into Polymer De-wetting: A Neutron Reflectivity Study of Three-Arm Polystyrene Stars in Polystyrene Thin films  

NASA Astrophysics Data System (ADS)

While polymeric coatings are ubiquitous, de-wetting remains a challenge. As both enthalpic and entropic contributions often affect the de-wetting process, small changes either compositional or in processing conditions are sufficient to impact the stability of thin films. We have recently shown that blending small amounts of three-arm polystyrene (PS) star polymers are sufficient to inhibit de-wetting of thin polystyrene thin films. The role of the three-arm star has been investigated using neutron reflectometry. We have followed the distribution of the three-arm PS stars in a thin film of d-PS as function of time as the temperature was raised above Tg of the PS. Films of d-PS/h-three-arm star PS were cast from toluene and the polymer profiles were determined as a function of time as the temperature was varied. The result show a clear migration of the three-arm stars to both interfaces, enhancing the number of chain ends at the interface. As the molecular weights of the star arm increases, it migrates slower to the interface.

Etampawala, Thusitha; Pangpaiboon, Nampueng; Perahia, Dvora; Halbert, Candice; Browning, Jim; Traiphol, Nisanart; Traiphol, Rakchart

2013-03-01

143

An Exact Solution to the First-Passage Time in Low-Functionality Star Polymer Melts  

NASA Astrophysics Data System (ADS)

We present an extension to the Milner and McLeish (MM) theory for stress relaxation in star polymer melts. In the MM model [Macromolecules, 30, 2159 (1997)] the dynamic and relaxation moduli were determined through an approximation to the first-passage time (FPT). In this work we calculate exactly the FPT, which is related to the time required for each arm to escape from its original tube, and determine the range of applicability of the MM approximations, as well as different viscoelastic properties: the terminal relaxation time, the steady-state recoverable compliance, and the zero-shear viscosity, among others. In addition, we show that several viscoelastic properties obtained through our exact expression for the FPT compare very well with experimental data.

Vega, Daniel A.; Sebastian, John M.; Russel, William B.; Register, Richard A.

2001-03-01

144

Resonantly enhanced off-specular X-ray scattering from polymer/polymer interfaces(small star, filled).  

PubMed

We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion. PMID:16025193

Hu, Xuesong; Jiao, Xuesong; Narayanan, Suresh; Jiang, Zhang; K Sinha, Sunil; Lurio, L B; Lal, Jyotsana

2005-07-18

145

Peptide-Functionalized Poly(ethylene glycol) Star Polymers: DNA Delivery Vehicles with Multivalent Molecular Architecture  

PubMed Central

Exploring the development of nonviral nucleic acid delivery vectors with progressive, specific, and novel designs in molecular architecture is a fundamental way to investigate how aspects of chemical and physical structure impact the transfection process. In this study, macromolecules comprised of a four-arm star poly(ethylene glycol) and termini modified with one of five different heparin binding peptides have been investigated for their ability to bind, compact, and deliver DNA to mammalian cells in vitro. These new delivery vectors combine a PEG-derived stabilizing moiety with peptides that exhibit unique cell-surface binding ability in a molecular architecture that permits multivalent presentation of the cationic peptides. Five peptide sequences of varying heparin binding affinity were studied; each was found to sufficiently bind heparin for biological application. Additionally, the macromolecules were able to bind and compact DNA into particles of proper size for endocytosis. In biological studies, the PEG-star peptides displayed a range of toxicity and transfection efficiency dependent on the peptide identity. The vectors equipped with peptides of highest heparin binding affinity were found to bind DNA tightly, increase levels of cellular internalization, and display the most promising transfection qualities. Our results suggest heparin binding peptides with specific sequences hold more potential than nonspecific cationic polymers to optimize transfection efficiency while maintaining cell viability. Furthermore, the built-in multivalency of these macromolecules may allow simultaneous binding of both DNA at the core of the polyplex and heparan sulfate on the surface of the cell. This scheme may facilitate a bridging transport mechanism, tethering DNA to the surface of the cell and subsequently ushering therapeutic nucleic acids into the cell. This multivalent star shape is therefore a promising architectural feature that may be exploited in the design of future polycationic gene delivery vectors.

Fichter, Katye M.; Zhang, Le; Kiick, Kristi L.; Reineke, Theresa M.

2008-01-01

146

Folic acid modified cationic ?-cyclodextrin-oligoethylenimine star polymer with bioreducible disulfide linker for efficient targeted gene delivery.  

PubMed

For an efficient folate-targeted delivery, while the interaction between the folate on the carriers and the folate receptor (FR) on the cells is necessary, the recovering and recycling of FR to maintain a high density level of FR on the cellular membrane is also important. Herein, we demonstrate a design and synthesis of a new star-shaped cationic polymer containing a ?-cyclodextrin (?-CD) core and multiple oligoethylenimine (OEI) arms with folic acid (FA) linked by a bioreducible disulfide bond for efficient targeted gene delivery. The newly synthesized cationic polymer, named ?-CD-OEI-SS-FA, could be cleaved efficiently, and FA was readily released under reductive condition similar to intracellular environment. The ?-CD-OEI-SS-FA polymer was well-characterized and studied in terms of its gene delivery properties in FR-positive KB cells and FR-negative A549 cells under various conditions, in comparison with cationic polymers such as high molecular weight branched polyethylenimine (PEI), ?-CD-OEI star-shaped cationic polymer, ?-CD-OEI-FA polymer where FA was directed linked to the star polymer without disulfide linker. Our data have demonstrated that the new ?-CD-OEI-SS-FA gene carrier had low cytotoxicity and possessed capacity to target and deliver DNA to specific tumor cells that overexpress FRs, as well as functions to recover and recycle FRs onto cellular membranes to facilitate continuous FR-mediated endocytosis to achieve very high levels of gene expression. This study has expanded the strategy of FA-targeted delivery by combining the smart FR-recycling function to achieve the significant enhancement of gene expression. The new FA-targeted and bioreducible carrier may be a promising efficient gene delivery system for potential cancer gene therapy. PMID:23323627

Zhao, Feng; Yin, Hui; Zhang, Zhongxing; Li, Jun

2013-01-16

147

Dense molecular cocoons in the massive protocluster W3 IRS5: a test case for models of massive star formation  

NASA Astrophysics Data System (ADS)

Context. Two competing models describe the formation of massive stars in objects like the Orion Trapezium. In the turbulent core accretion model, the resulting stellar masses are directly related to the mass distribution of the cloud condensations. In the competitive accretion model, the gravitational potential of the protocluster captures gas from the surrounding cloud for which the individual cluster members compete. Aims: With high resolution submillimeter observations of the structure, kinematics, and chemistry of the proto-Trapezium cluster W3 IRS5, we aim to determine which mode of star formation dominates. Methods: We present 354 GHz Submillimeter Array observations at resolutions of 1?-3? (1800-5400 AU) of W3 IRS5. The dust continuum traces the compact source structure and masses of the individual cores, while molecular lines of CS, SO, SO2, HCN, H2CS, HNCO, and CH3OH (and isotopologues) reveal the gas kinematics, density, and temperature. Results: The observations show five emission peaks (SMM1-5). SMM1 and SMM2 contain massive embedded stars (~20 M?); SMM3-5 are starless or contain low-mass stars (<8 M?). The inferred densities are high, ?107 cm-3, but the core masses are small, 0.2-0.6 M?. The detected molecular emission reveals four different chemical zones. Abundant (X ~ few 10-7 to 10-6) SO and SO2 are associated with SMM1 and SMM2, indicating active sulfur chemistry. A low abundance (5 × 10-8) of CH3OH concentrated on SMM3/4 suggest the presence of a hot core that is only just turning on, possibly by external feedback from SMM1/2. The gas kinematics are complex with contributions from a near pole-on outflow traced by CS, SO, and HCN; rotation in SO2, and a jet in vibrationally excited HCN. Conclusions: The proto-Trapezium cluster W3 IRS5 is an ideal test case to discriminate between models of massive star formation. Either the massive stars accrete locally from their local cores; in this case the small core masses imply that W3 IRS5 is at the very end stages (1000 yr) of infall and accretion, or the stars are accreting from the global collapse of a massive, cluster forming core. We find that the observed masses, densities and line widths observed toward W3 IRS 5 and the surrounding cluster forming core are consistent with the competitive accretion of gas at rates of ? ~ 10-4M? yr-1 by the massive young forming stars. Future mapping of the gas kinematics from large to small scales will determine whether large-scale gas inflow occurs and how the cluster members compete to accrete this material.

Wang, K.-S.; Bourke, T. L.; Hogerheijde, M. R.; van der Tak, F. F. S.; Benz, A. O.; Megeath, S. T.; Wilson, T. L.

2013-10-01

148

ON THE DYNAMICAL FORMATION OF VERY YOUNG, X-RAY EMITTING BLACK HOLE BINARIES IN DENSE STAR CLUSTERS  

SciTech Connect

We recently discovered a population of very young ({tau} {approx}< 6-8 Myr), X-ray emitting black hole binaries (BHBs) in the nearby starburst galaxy NGC 4449. These BHBs are located within or near to very young star clusters, indicating that they form within the clusters, but that some fraction are dynamically ejected. Here we present results from a suite of N-body simulations of N = 16,384 ({approx}6000 M{sub Sun }) star clusters, similar to the masses of BHB hosts in NGC 4449, through the first 10 Myr of their lives. Our goal is to determine whether dynamical interactions are responsible for the observed population of BHBs in NGC 4449. Our simulations span a wide range of initial size and density profiles, both with and without primordial mass segregation, testing both realistic initial conditions and extreme ones. We find that clusters without primordial mass segregation only dynamically produce BHBs within 10 Myr when they are extremely compact and centrally concentrated. Preliminary results that include primordial binaries support this conclusion. The introduction of strong primordial mass segregation, however, greatly increases the rapidity with which the binaries form, although these are still not tight enough that they will emit X-rays. We conclude that X-ray emitting BHBs are unlikely to form dynamically in clusters of this mass under realistic conditions. Instead, they probably originate from binaries that contain two massive stars with small orbital separations, which are present from the cluster's birth.

Garofali, Kristen [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Converse, Joseph M.; Chandar, Rupali; Rangelov, Blagoy, E-mail: garofal4@msu.edu [Department of Physics and Astronomy, University of Toledo, 2801 W Bancroft Street, Toledo, OH 43606 (United States)

2012-08-10

149

Polyisobutylene-based mikto-arm star polymers synthesized via quasiliving cationic polymerization and atom transfer radical polymerization  

NASA Astrophysics Data System (ADS)

This research pertains to the synthesis of mikto-arm star polymers created via quasiliving cationic polymerization (QCP) and atom transfer radical polymerization (ATRP). The first part of this work focuses on the synthesis of cationic initiators that contain latent functionalities for initiation of ATRP polymerizations. In the second part of this work, well-defined copolymers of polyisobutylene (PIB) and polystyrene (PS) were created by cationic polymerization. After transformation of the initiating site, poly(tert-butyl acrylate) (PtBA) was synthesized via ATRP. This block was later hydrolyzed to form poly(acrylic acid) (PAA), which serves as a hydrophilic segment of the material. The polymers had narrow PDIs and target polymer compositions. However, molecular weights were higher than expected when low molecular weight polymers were targeted. This is attributed to a complexation between the Lewis acid, titanium tetrachloride (TiCl4), and the carbonyl group in the initiators.

Breland, Lesli Krystin

150

Early Star-forming Processes in Dense Molecular Cloud L328; Identification of L328-IRS as a Proto-brown Dwarf  

NASA Astrophysics Data System (ADS)

This paper presents the results of millimeter to sub-millimeter observations of CO, HCN, N2H+, and HCO+ lines in the dense molecular cloud L328, which harbors L328-IRS, a Very Low Luminosity Object (VeLLO). Our analysis of the line width finds that 13CO and N2H+ lines are broadened right over the smallest sub-core S2 where L328-IRS is located, while they are significantly narrower in other regions of L328. Thus, L328-IRS has a direct association with the sub-core. CO observations show a bipolar outflow from this VeLLO with an extent of ~0.08 pc. The outflow momentum flux and efficiency are much less than those of low-mass protostars. The most likely mass accretion rate (~3.6 × 10–7 M ? yr–1) inferred from the analysis of the CO outflow is an order of magnitude smaller than the canonical value for a protostar. If the main accretion lasts during the typical Class 0 period of a protostar, L328-IRS will accrete the mass of a brown dwarf, but not that of a star. Given that its envelope mass is small (~0.09 M ?) and 100% star formation rate is unlikely, we suggest that L328-IRS is likely a proto-brown dwarf. Inward motions are found in global scale in the L328 cloud and its sub-cores with a typical infall speed found in starless cores. L328 is found to be fairly well isolated from other nearby clouds and seems to be forming three sub-cores simultaneously through a gravitational fragmentation process. Altogether, these all leave L328-IRS as the best example supporting the idea that a brown dwarf forms like a normal star.

Lee, Chang Won; Kim, Mi-Ryang; Kim, Gwanjeong; Saito, Masao; Myers, Philip C.; Kurono, Yasutaka

2013-11-01

151

Gas giants in hot water: inhibiting giant planet formation and planet habitability in dense star clusters through cosmic time  

NASA Astrophysics Data System (ADS)

I show that the temperature of nuclear star clusters, starburst clusters in M82, compact high-z galaxies and some globular clusters of the Galaxy likely exceeded the ice-line temperature (TIce ? 150-170 K) during formation for a time comparable to the planet formation time-scale. The protoplanetary discs within these systems will thus, not have an ice line, decreasing the total material available for building protoplanetary embryos, inhibiting the formation of gas- and ice-giants if they form by core accretion, and prohibiting habitability. Planet formation by gravitational instability is similarly suppressed because Toomre's Q > 1 in all but the most massive discs. I show that cluster irradiation can in many cases dominate the thermodynamics and structure of passive and active protoplanetary discs for semi-major axes larger than ˜1-5 au. I discuss these results in the context of the observed lack of planets in 47 Tuc. I predict that a similar search for planets in the globular cluster NGC 6366 ([Fe/H] = -0.82) should yield detections, whereas (counterintuitively) the relatively metal-rich globular clusters NGC 6440, 6441 and 6388 should be devoid of giant planets. The characteristic stellar surface density above which TIce is exceeded in star clusters is ˜ 6 × 103 M? pc- 2 f- 1/2dg, MW, where fdg, MW is the dust-to-gas ratio of the embedding material, normalized to the Milky Way value. Simple estimates suggest that ˜5-50 per cent of the stars in the universe formed in an environment exceeding this surface density. Future microlensing planet searches that directly distinguish between the bulge and disc planet populations of the Galaxy and M31 can test these predictions. Caveats and uncertainties are detailed.

Thompson, Todd A.

2013-05-01

152

The Spitzer c2d Survey of Nearby Dense Cores. X. Star Formation in L673 and CB188  

NASA Astrophysics Data System (ADS)

L673 and CB188 are two low-mass clouds isolated from large star-forming regions that were observed as part of the Spitzer Legacy Project "From Molecular Clouds to Planet Forming disks" (c2d). We identified and characterized all the young stellar objects (YSOs) of these two regions and modeled their spectral energy distributions (SEDs) to examine whether their physical properties are consistent with values predicted from the theoretical models and with the YSO properties in the c2d survey of larger clouds. Overall, 30 YSO candidates were identified by the c2d photometric criteria, 27 in L673 and 3 in CB188. We confirm the YSO nature of 29 of them and remove a false Class III candidate in L673. We further present the discovery of two new YSO candidates, one Class 0 and another possible Class I candidate in L673, therefore bringing the total number of YSO candidates to 31. Multiple sites of star formation are present within L673, closely resembling other well-studied c2d clouds containing small groups such as B59 and L1251B, whereas CB188 seems to consist of only one isolated globule-like core. We measure a star formation efficiency (SFE) of 4.6%, which resembles the SFE of the larger c2d clouds. From the SED modeling of our YSO sample we obtain envelope masses for Class I and Flat spectrum sources of 0.01-1.0 M sun. The majority of Class II YSOs show disk accretion rates from 3.3 × 10-10 to 3 × 10-8 M sun yr-1 and disk masses that peak at 10-4 to 10-3 M sun. Finally, we examined the possibility of thermal fragmentation in L673 as the main star-forming process. We find that the mean density of the regions where significant YSO clustering occurs is of the order of ~105 cm-3 using 850 ?m observations and measure a Jeans Length that is greater than the near-neighbor YSO separations by approximately a factor of 3-4. We therefore suggest that other processes, such as turbulence and shock waves, may have had a significant effect on the cloud's filamentary structure and YSO clustering.

Tsitali, Anastasia E.; Bourke, Tyler L.; Peterson, Dawn E.; Myers, Philip C.; Dunham, Michael M.; Evans, Neal J., II; Huard, Tracy L.

2010-12-01

153

Star-forming regions of the Aquila rift cloud complex. I. NH3 tracers of dense molecular cores  

NASA Astrophysics Data System (ADS)

Aims: The physics of star formation is an important part of Galactic evolution. Most stars are formed in high-density environments (n > 104 cm-3) and emit lines of diverse molecular transitions. In the present part of our survey we search for ammonia emitters in the Aquila rift complex, which trace the densest regions of molecular clouds. Methods: From a CO survey carried out with the Delingha 14-m telescope we selected ~150 targets for observations in other molecular lines. Here we describe the mapping observations in the NH3(1, 1) and (2, 2) inversion lines of the first 49 sources performed with the Effelsberg 100-m telescope. Results: The NH3(1, 1) emission lines are detected in 12 and the (2, 2) in 7 sources. Among the newly discovered NH3 sources, our sample includes the following well-known clouds: the starless core L694-2, the Serpens cloud cluster B, the Serpens dark cloudL572, the filamentary dark cloud L673, the isolated protostellar source B335, and the complex star-forming region Serpens South. Angular sizes between 40'' and 80'' (~0.04-0.08 pc) are observed for compact starless cores but can be as large as 9' (~0.5 pc) for filamentary dark clouds. The measured kinetic temperatures of the clouds lie between 9 K and 18 K. From NH3 excitation temperatures of 3-8 K we determine H2 densities with typical values of ~ (0.4-4) × 104 cm-3. The masses of the mapped cores range between ~0.05 and ~ 0.5 M?. The relative ammonia abundance X = [NH3]/[H2] varies from 1 × 10-7 to 5 × 10-7 with the mean ? X ? = (2.7 ± 0.6) × 10-7 (estimated from spatially resolved cores assuming a filling factor of ? = 1). In two clouds, we observe kinematically split NH3 profiles separated by ~1 km s-1. The splitting is most likely due to bipolar molecular outflows, for one of which we determine an acceleration of V ? ? 0.03 km s-1 yr-1. A starless core with significant rotational energy is found to have a higher kinetic temperature than the other ones, which is probably caused by magnetic energy dissipation. Appendices and Table 2 are available in electronic form at http://www.aanda.org

Levshakov, S. A.; Henkel, C.; Reimers, D.; Wang, M.; Mao, R.; Wang, H.; Xu, Y.

2013-05-01

154

Formation of nanostructured magnetic films using layer-by-layer self-assembly of star polymers and magnetic nanoparticles  

Microsoft Academic Search

In this work, multi-layered thin film materials comprised of cobalt ferrite (CoFe2O4) magnetic nanoparticles and polystyrene amine-functionalized (PS-NH2) star polymers have been prepared on silicon dioxide surfaces by means of organometallic-driven layer-by-layer (LBL) self-assembly. The films formed were characterized using surface plasmon resonance (SPR) spectroscopy, which indicated the rapid formation (sub-second to second time frames) of reproducible molecular thin layers.

Shimul Shah

2011-01-01

155

CO J = 2-1 LINE EMISSION IN CLUSTER GALAXIES AT z {approx} 1: FUELING STAR FORMATION IN DENSE ENVIRONMENTS  

SciTech Connect

We present observations of CO J = 2-1 line emission in infrared-luminous cluster galaxies at z {approx} 1 using the IRAM Plateau de Bure Interferometer. Our two primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie within 2 Mpc of the centers of two massive (>10{sup 14} M{sub Sun }) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3{sigma} upper limits to the CO J = 2-1 line luminosities, L'{sub CO} < 6.08 Multiplication-Sign 10{sup 9} and <6.63 Multiplication-Sign 10{sup 9} K km s{sup -1} pc{sup 2}. Assuming a CO-to-H{sub 2} conversion factor derived for ultraluminous infrared galaxies in the local universe, this translates to limits on the cold molecular gas mass of M{sub H{sub 2}}< 4.86 Multiplication-Sign 10{sup 9} M{sub Sun} and M{sub H{sub 2}}< 5.30 Multiplication-Sign 10{sup 9} M{sub Sun }. Both DOGs exhibit mid-infrared continuum emission that follows a power law, suggesting that an active galactic nucleus (AGN) contributes to the dust heating. As such, estimates of the star formation efficiencies in these DOGs are uncertain. A third cluster member with an infrared luminosity, L{sub IR} < 7.4 Multiplication-Sign 10{sup 11} L{sub Sun }, is serendipitously detected in CO J = 2-1 line emission in the field of one of the DOGs located roughly two virial radii away from the cluster center. The optical spectrum of this object suggests that it is likely an obscured AGN, and the measured CO line luminosity is L'{sub CO} = (1.94 {+-} 0.35) Multiplication-Sign 10{sup 10} K km s{sup -1} pc{sup 2}, which leads to an estimated cold molecular gas mass M{sub H{sub 2}}= (1.55{+-}0.28) Multiplication-Sign 10{sup 10} M{sub Sun }. A significant reservoir of molecular gas in a z {approx} 1 galaxy located away from the cluster center demonstrates that the fuel can exist to drive an increase in star formation and AGN activity at the outskirts of high-redshift clusters.

Wagg, Jeff [European Southern Observatory, Casilla 19001, Santiago (Chile); Pope, Alexandra; Alberts, Stacey [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Armus, Lee; Desai, Vandana [Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125 (United States); Brodwin, Mark [Department of Physics, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Bussmann, Robert S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Dey, Arjun; Jannuzi, Buell [National Optical Astronomy Observatory, Tucson, AZ 85726-6732 (United States); Le Floc'h, Emeric [AIM, CNRS, Universite Paris Diderot, Bat. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex (France); Melbourne, Jason [California Institute of Technology, Pasadena, CA 91125 (United States); Stern, Daniel, E-mail: jwagg@eso.org [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2012-06-20

156

1,1-diphenyl ethylene-mediated radical polymerisation: a general non-metal-based technique for the synthesis of precise core cross-linked star polymers.  

PubMed

This communication details the successful synthesis of low polydispersity core cross-linked star (CCS) polymers via DPE-mediated polymerisation. We demonstrate the ability to produce poly(methyl methacrylate) and poly(acrylonitrile) CCS polymers that are currently inaccessible via the two most common non-metal-based controlled radical polymerisation techniques (NMP and RAFT polymerisations). PMID:21590907

Tan, Jing Fung; Blencowe, Anton; Goh, Tor Kit; Qiao, Greg G

2009-12-01

157

Controlled synthesis of star-shaped L-lactide polymers using new spirocyclic tin initiators.  

PubMed

The reaction between pentaerythritol ethoxylate compounds and dibutyltin oxide was developed as a route to synthesize two new spirocyclic tin initiators. The initiators were successfully synthesized and they were characterized by (1)H NMR and differential scanning calorimetry (DSC). The (1)H NMR spectra showed the characteristic signals for the methylene protons in the ether chains. Furthermore, the usefulness of the new initiators was examined in ring-opening polymerizations of L-lactide in chloroform at 60 degrees C. L-Lactide was polymerized at monomer-to-initiator ([M]/[I]) ratios between 20 and 500. The results indicated that the initiation was instantaneous and that the molecular weight distribution was very narrow, <1.13. The number average molecular weight could be controlled by the [M]/[I] ratio, and the yield was very high. (1)H NMR, size exclusion chromatography, and DSC were used to clarify the architecture. The expected results were obtained. The star-shaped polymers had a smaller hydrodynamic volume, and the melting point was lower than that obtained for the corresponding linear poly(L-lactide). PMID:12099811

Finne, Anna; Albertsson, Ann-Christine

158

Highly efficient synthesis of low polydispersity core cross-linked star polymers by Ru-catalyzed living radical polymerization.  

PubMed

The efficient formation of low polydispersity core cross-linked star (CCS) polymers via controlled/living radical polymerization (LRP) and the arm-first approach was found to be dependent on the mediating catalyst system. The Ru catalyst, Ru(Ind)Cl(PPh?)? Cat. 1, and tertiary amine co-catalyst were used to synthesize highly living poly(methyl methacrylate) (PMMA) macroinitiators, which were then linked together with ethylene glycol dimethacrylate (EGDMA) to form PMMA(arm)PEGDMA(core) CCS polymers. The quantitative and near-quantitative synthesis of CCS polymers were observed for low to moderate molecular weight macroinitiators (M(n) = ?8 and 20?kDa), respectively. Lower conversions were observed for high-molecular weight macroinitiators (M(n) ?? ?60?kDa). Overall, an improvement of between 10 and 20% was observed when comparing the Cat. 1 system to a conventional Cu-catalyzed system. This significant improvement in macroinitiator-to-star conversion is explained in the context of catalyst system selection and CCS polymer formation. PMID:21433199

Goh, Tor Kit; Yamashita, Satoshi; Satoh, Kotaro; Blencowe, Anton; Kamigaito, Masami; Qiao, Greg G

2011-01-07

159

Poly(ethylene oxide) star polymer adsorption at the silica/aqueous interface and displacement by linear poly(ethylene oxide).  

PubMed

Multiarm star copolymers with approximately 460 poly(ethylene oxide) (PEO) arms that have a degree of polymerization N = 45 were synthesized via atom transfer radical polymerization (ATRP) of PEO-methacrylate macromonomers in the presence of divinyl benzene cross-linkers. These are an example of molecular or nanoparticulate brushes that are of interest as steric stabilizers or boundary lubrication agents when adsorbed from solution to a solid/aqueous interface. We use ellipsometry to measure adsorption isotherms at the silica/aqueous interface for PEO star polymers and linear PEO chains having molecular weights comparable either to the star polymer or to the individual arms. The compactness of the PEO star polymers (molecular weight 1.2 × 10(6)) yields a saturation surface excess concentration that is approximately 3.5 times greater than that of the high molecular weight (1 × 10(6)) linear PEO. Adsorption of low molecular weight (6000) linear PEO was below the detection limit. Competitive adsorption experiments were conducted with ellipsometry, complemented by independent quartz crystal microbalance with dissipation (QCM-D) measurements. Linear PEO (high molecular weight) displaced preadsorbed PEO star polymers over the course of approximately 1.5 h, to form a mixed adsorbed layer having not only a significantly lower overall polymer surface excess concentration, but also a significantly greater amount of hydrodynamically entrapped water. Challenging a preadsorbed linear PEO (high molecular weight) layer with PEO star polymers produced no measurable change in the overall polymer surface excess concentration, but changes in the QCM-D energy dissipation and resonance frequency suggested that the introduction of PEO star polymers caused a slight swelling of the layer with a correspondingly small increase in entrapped water content. PMID:23448185

Saigal, Trishna; Riley, John K; Golas, Patricia Lynn; Bodvik, Rasmus; Claesson, Per M; Matyjaszewski, Krzysztof; Tilton, Robert D

2013-03-12

160

Infrared Stars. The Interaction between Stars and Interstellar Clouds Produces 'Infrared Stars' of Two Different Kinds.  

National Technical Information Service (NTIS)

Searches for very cool stars have revealed three kinds of objects: very cool Mira stars, perhaps cooler than any of this type previously known; extremely dense interstellar clouds, more dense than any known heretofore; and probably, cool circumstellar clo...

H. L. Johnson

1967-01-01

161

Stars  

NSDL National Science Digital Library

This section of the Windows to the Universe web site provides information and images about stars including star statistics, and a star gallery. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging web site that spans the Earth and Space sciences and includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

Johnson, Roberta

2000-07-01

162

Fluorescent core-shell star polymers based bioassays for ultrasensitive DNA detection by surface plasmon fluorescence spectroscopy.  

PubMed

Multilayers containing a perylene diimide labelled star polymers (FSP) donor adjacent to phosphorus dendrimer layer on a silver substrate were constructed by layer by layer (LBL) approach. Using Surface Plasmon Enhanced Fluorescence Spectroscopy (SPFS) technique, a time-resolved ultrasensitive and selective detection of DNA targets relying on enhanced optical fields associated with energy transfer (ET) were achieved under the excitation at 543 nm. The detection limit is about 8 orders of magnitude better than the achieved one under the excitation at 632 nm, which is ascribed to no energy transfer from the donor to the acceptor under the excitation at 632 nm, resulting in much weak detection signal in turn. PMID:21480427

Feng, Chuan Liang; Yin, Meizhen; Zhang, Di; Zhu, Shenmin; Caminade, Anne Marie; Majoral, Jean Pierre; Müllen, Klaus

2011-03-07

163

Compact Stars  

NASA Astrophysics Data System (ADS)

Neutron stars are the smallest denses stars known, with densities some 1014 times that of the Earth. They rotate with periods of fractions of a second, and their magnetic fields drive intense interstellar dynamos, lighting up entire nebulae. This text discusses the physics of these extreme objects. It includes the needed background in classical general relativity in nuclear and particle physics.

Glendenning, Norman K.

164

Star-shaped MePEGn polymers as H+ conducting electrolytes.  

PubMed

Proton conducting electrolytes composed of a mixture of MePEG(7)SO(3)H acid and a four-armed, PEG-based, star molecule were prepared. Four MePEG(n) (n = 3, 7, 12) arms were attached to a pentaerythritol or tetrakis(dimethylsilyl) orthosilicate core to form the star molecules. We have examined the structure of these star electrolytes to observe how the structure of an electrolyte affects the observed ionic conductivity. In terms of structural parameters, these star electrolytes showed large volume fractions of PEG, high fluidities, and large fractional free volumes, all of which predict larger ionic conductivities. Through a comparison of the conductivity and structural parameters in a variety of different star electrolytes, we have shown that each of these three structural parameters are important and can strongly affect the observed ionic conductivity. Walden plots indicated a large extent of ion-pairing in our star electrolytes and that MePEG(7)SO(3)H acid was a weak acid in our star electrolytes. PMID:21591699

Sun, Chengjun; Ritchie, Jason E

2011-06-10

165

Hierarchical self-assembly of telechelic star polymers: from soft patchy particles to gels and diamond crystals  

NASA Astrophysics Data System (ADS)

The design of self-assembling materials in the nanometer scale focuses on the fabrication of a class of organic and inorganic subcomponents that can be reliably produced on a large scale and tailored according to their vast applications for, e.g. electronics, therapeutic vectors and diagnostic imaging agent carriers, or photonics. In a recent publication (Capone et al 2012 Phys. Rev. Lett. 109 238301), diblock copolymer stars have been shown to be a novel system, which is able to hierarchically self-assemble first into soft patchy particles and thereafter into more complex structures, such as the diamond and cubic crystal. The self-aggregating single star patchy behavior is preserved from extremely low up to high densities. Its main control parameters are related to the architecture of the building blocks, which are the number of arms (functionality) and the fraction of attractive end-monomers. By employing a variety of computational and theoretical tools, ranging from the microscopic to the mesoscopic, coarse-grained level in a systematic fashion, we investigate the crossover between the formation of microstructure versus macroscopic phase separation, as well as the formation of gels and networks in these systems. We finally show that telechelic star polymers can be used as building blocks for the fabrication of open crystal structures, such as the diamond or the simple-cubic lattice, taking advantage of the strong correlation between single-particle patchiness and lattice coordination at finite densities.

Capone, Barbara; Coluzza, Ivan; Blaak, Ronald; Lo Verso, Federica; Likos, Christos N.

2013-09-01

166

Glaciations and dense interstellar clouds  

Microsoft Academic Search

The theory proposed by McCrea in which the ice ages are attributed to the interaction of the sun with dense interstellar clouds is examined. The lack of extensive absorption of soft X-ray background and the low column densities of molecular hydrogen derived from satellite observations of H2 absorption lines in selected stars rule out the existence of a dense molecular

BRIAN DENNISON; V. N. Mansfield

1976-01-01

167

Synthesis of miktoarm star (block) polymers based on a heterofunctional initiator via combination of ROP, ATRP and functional group transformation  

Microsoft Academic Search

Versatile miktoarm three-arm star polymers, (polystyrene)(poly?-caprolactone)2 ((PS)(PCL)2), (PS-b-poly(n-butyl acrylate))(PCL-b-PS-b-poly(n-butyl acrylate))2 ((PS-b-PnBA)(PCL-b-PS-b-PnBA)2) and (PtBA-b-PS)(PCL-b-PtBA-b-PS)2 were synthesized via combination of atom-transfer radical polymerization (ATRP), functional group transformation technique and ring opening polymerization (ROP) using 1,1-dihydroxymethyl-1-(2-bromoisobutyryloxy)methyl ethane (DHB) as a heterofunctional initiator. In the synthesis of (PS)(PCL)2 by combination of ROP of ?-caprolactone (?-CL) and ATRP, the implementation sequence, ROP followed by ATRP,

Guohua Deng; Liwei Zhang; Chaodong Liu; Lihong He; Yongming Chen

2005-01-01

168

Nanofibrous hollow microspheres self-assembled from star-shaped polymers as injectable cell carriers for knee repair  

PubMed Central

Biomaterials play pivotal roles in engineering tissue regeneration and repair. To regenerate irregular shaped defects, injectable cell carriers are desirable. Here, we report the development of self-assembled nanofibrous hollow microspheres from star-shaped biodegradable polymers as an injectable cell carrier for tissue regeneration. The nanofibrous hollow microspheres were shown to efficiently accommodate cells and enhance cartilage regeneration over control microspheres. The nanofibrous hollow microspheres also supported a significantly larger amount and higher quality cartilage regeneration over the chondrocytes alone group in an ectopic implantation model. In a critical-size rabbit osteochondral defect repair model, the nanofibrous hollow microspheres/chondrocytes group achieved substantially better cartilage repair and integration compared to the chondrocytes alone group that simulates the clinically available autologous chondrocyte implantation (ACI) procedure. These results indicate that the nanofibrous hollow microspheres are an excellent cell carrier for cartilage regeneration and are worthy of further investigation towards the aimed clinical application.

Liu, Xiaohua; Jin, Xiaobing; Ma, Peter X.

2011-01-01

169

Deposition transfection technology using a DNA complex with a thermoresponsive cationic star polymer  

Microsoft Academic Search

A novel non-viral gene transfection method in which DNA complexes were kept in contact with a deposition surface (deposition transfection) was developed. We designed a novel aqueous thermoresponsive adsorbent material for DNA deposition, which was a star-shaped copolymer with 4-branched chains. Each chain is comprised of a cationic poly(N,N-dimethylaminopropyl acrylamide) (PDMAPAAm) block (Mn: ca. 3000 g·mol?1), which formed an inner domain

Yue-Min Zhou; Ayaka Ishikawa; Ryohei Okahashi; Kingo Uchida; Yasushi Nemoto; Mitsuko Nakayama; Yasuhide Nakayama

2007-01-01

170

Properties of polystyrene/poly(dimethyl siloxane) blends partially compatibilized with star polymers containing a gamma-cyclodextrin core and polystyrene arms  

NASA Astrophysics Data System (ADS)

Cyclodextrins (CDs) are cyclic starch molecules having a hollow central cavity which can be threaded by a polymer to form an inclusion compound. This characteristic is exploited in a new type of compatibilizer: a star polymer with a gamma-CD (g-CD) core and polystyrene (PS) arms (CD-star). Spun-cast thin films of PS containing up 20 weight percent poly(dimethyl siloxane) (PDMS) are compatibilized by CD-star. The mechanism of compatibilization involves threading of the CD core by PDMS and solubilization of the resulting slip-ring graft copolymer via the PS star arms. Thin spun-cast films of these blends exhibit a a nanoscale level of mixing and remain well-mixed after annealing at 125 C for three days. In contrast, thicker solution-cast films of these blends exhibit larger-scale phase separation since the film solidification process occurs over a period of days rather than seconds. This allows some of the PDMS to de-thread from the CD-star and phase separate. However, DSC, DMA and PDMS leaching data show that PS and PDMS remain partially compatibilized in the solution-cast films.

Balik, C. Maurice; Busche, Brad J.; Tonelli, Alan E.

2011-03-01

171

13CO and C18O emission from a dense gas disc at z = 2.3: abundance variations, cosmic rays and the initial conditions for star formation  

NASA Astrophysics Data System (ADS)

We analyse the spectral line energy distributions of 13CO and C18O for the J = 1?0 up to J = 7?6 transitions in the gravitationally lensed ultraluminous infrared galaxy SMM J2135-0102 at z = 2.3. This is the first detection of 13CO and C18O in a high-redshift star-forming galaxy. These data comprise observations of six transitions taken with Plateau de Bure Interferometer and we combine these with ˜33 GHz Jansky Very Large Array data and our previous spatially resolved 12CO and continuum emission information to better constrain the properties of the interstellar medium (ISM) within this system. We study both the velocity-integrated and kinematically decomposed properties of the galaxy and coupled with a large velocity gradient (LVG) model we find that the star-forming regions in the system vary in their cold gas properties, in particular in their chemical abundance ratios. We find strong C18O emission both in the velocity-integrated emission and in the two kinematic components at the periphery of the system, where the C18O line flux is equivalent to or higher than the 13CO. We derive an average velocity-integrated flux ratio of 13CO/C18O ˜ 1 which suggests an abundance ratio of [13CO]/[C18O] which is at least seven times lower than that in the Milky Way. This is suggestive of enhanced C18O abundance, perhaps indicating star formation preferentially biased to high-mass stars. We estimate the relative contribution to the ISM heating from cosmic rays and UV of (30-3300) × 10-25 erg s-1 and 45 × 10-25 erg s-1 per H2 molecule respectively and find them to be comparable to the total cooling rate of (0.8-20) × 10-25 erg s-1 from the CO. However, our LVG models indicate high (>100 K) temperatures and densities (>103) cm-3 in the ISM which may suggest that cosmic rays play a more important role than UV heating in this system. If cosmic rays dominate the heating of the ISM, the increased temperature in the star-forming regions may favour the formation of massive stars and so explain the enhanced C18O abundance. This is a potentially important result for a system which may evolve into a local elliptical galaxy.

Danielson, A. L. R.; Swinbank, A. M.; Smail, Ian; Bayet, E.; van der Werf, Paul P.; Cox, P.; Edge, A. C.; Henkel, C.; Ivison, R. J.

2013-10-01

172

Nanofibrous hollow microspheres self-assembled from star-shaped polymers as injectable cell carriers for knee repair  

NASA Astrophysics Data System (ADS)

To repair complexly shaped tissue defects, an injectable cell carrier is desirable to achieve an accurate fit and to minimize surgical intervention. However, the injectable carriers available at present have limitations, and are not used clinically for cartilage regeneration. Here, we report nanofibrous hollow microspheres self-assembled from star-shaped biodegradable polymers as an injectable cell carrier. The nanofibrous hollow microspheres, integrating the extracellular-matrix-mimicking architecture with a highly porous injectable form, were shown to efficiently accommodate cells and enhance cartilage regeneration, compared with control microspheres. The nanofibrous hollow microspheres also supported a significantly larger amount of, and higher-quality, cartilage regeneration than the chondrocytes-alone group in an ectopic implantation model. In a critical-size rabbit osteochondral defect-repair model, the nanofibrous hollow microspheres/chondrocytes group achieved substantially better cartilage repair than the chondrocytes-alone group that simulates the clinically available autologous chondrocyte implantation procedure. These results indicate that the nanofibrous hollow microspheres are an excellent injectable cell carrier for cartilage regeneration.

Liu, Xiaohua; Jin, Xiaobing; Ma, Peter X.

2011-05-01

173

Polymers  

NSDL National Science Digital Library

This page contains two documents explaining ring and cross link polymers. The topic is covered at an advanced level in relation to nanotechnology and requires background knowledge in eight grade science. A powerpoint with illustrations and instructor guide (available as both a Microsoft Word Document and PDF) containing activities are included to aid in teaching this subject.

2012-10-16

174

Mid-infrared diagnostics of starburst galaxies: clumpy, dense structures in star-forming regions in the Antennae (NGC 4038\\/4039)  

Microsoft Academic Search

Recently, mid-infrared instruments have become available on several large\\u000aground-based telescopes, resulting in data sets with unprecedented spatial\\u000aresolution at these long wavelengths. In this paper we examine\\u000a'ground-based-only' diagnostics, which can be used in the study of star-forming\\u000aregions in starburst galaxies. By combining output from the stellar population\\u000asynthesis code Starburst 99 with the photoionization code Mappings, we

Leonie Snijders; Lisa J. Kewley; Paul P. van der Werf

2007-01-01

175

Suprathermal viscosity of dense matter  

SciTech Connect

Motivated by the existence of unstable modes of compact stars that eventually grow large, we study the bulk viscosity of dense matter, taking into account non-linear effects arising in the large amplitude regime, where the deviation {mu}{sub {Delta}} of the chemical potentials from chemical equilibrium fulfills {mu}{sub {Delta}} > or approx. T. We find that this supra-thermal bulk viscosity can provide a potential mechanism for saturating unstable modes in compact stars since the viscosity is strongly enhanced. Our study confirms previous results on strange quark matter and shows that the suprathermal enhancement is even stronger in the case of hadronic matter. We also comment on the competition of different weak channels and the presence of suprathermal effects in various color superconducting phases of dense quark matter.

Alford, Mark; Mahmoodifar, Simin; Schwenzer, Kai [Department of Physics, Washington University in St. Louis, Missouri, 63130 (United States)

2010-12-22

176

THE INTERSTELLAR MEDIUM IN DISTANT STAR-FORMING GALAXIES: TURBULENT PRESSURE, FRAGMENTATION, AND CLOUD SCALING RELATIONS IN A DENSE GAS DISK AT z = 2.3  

SciTech Connect

We have used the Institut de Radioastronomie Millimetrique (IRAM) Plateau de Bure Interferometer and the Expanded Very Large Array to obtain a high-resolution map of the CO(6-5) and CO(1-0) emission in the lensed, star-forming galaxy SMM J2135-0102 at z = 2.32. The kinematics of the gas are well described by a model of a rotationally supported disk with an inclination-corrected rotation speed, v{sub rot} = 320 {+-} 25 km s{sup -1}, a ratio of rotational-to-dispersion support of v/{sigma} = 3.5 {+-} 0.2, and a dynamical mass of (6.0 {+-} 0.5) Multiplication-Sign 10{sup 10} M{sub Sun} within a radius of 2.5 kpc. The disk has a Toomre parameter, Q = 0.50 {+-} 0.15, suggesting that the gas will rapidly fragment into massive clumps on scales of L{sub J} {approx} 400 pc. We identify star-forming regions on these scales and show that they are {approx}10 Multiplication-Sign denser than those in quiescent environments in local galaxies, and significantly offset from the local molecular cloud scaling relations (Larson's relations). The large offset compared to local molecular cloud line-width-size scaling relations implies that supersonic turbulence should remain dominant on scales {approx}100 Multiplication-Sign smaller than in the kinematically quiescent interstellar medium (ISM) of the Milky Way, while the molecular gas in SMM J2135 is expected to be {approx}50 Multiplication-Sign denser than that in the Milky Way on all scales. This is most likely due to the high external hydrostatic pressure we measure for the ISM, P{sub tot}/k{sub B} {approx} (2 {+-} 1) Multiplication-Sign 10{sup 7} K cm{sup -3}. In such highly turbulent ISM, the subsonic regions of gravitational collapse (and star formation) will be characterized by much higher critical densities, n{sub crit} > = 10{sup 8} cm{sup -3}, a factor {approx}>1000 Multiplication-Sign more than the quiescent ISM of the Milky Way.

Swinbank, A. M.; Smail, Ian [Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Papadopoulos, P. P. [Max Planck Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Cox, P.; Krips, M.; Neri, R. [Institut de Radioastronomie Millimetrique, 300 rue de la Piscine, Domaine Universitaire, F-38406 Saint Martin d'Heres (France); Ivison, R. J.; Thomson, A. P. [Institute for Astronomy, University of Edinburgh, Edinburgh EH9 3HJ (United Kingdom); Richard, J. [CRAL, Observatoire de Lyon, Universite de Lyon 1, 9 avenue Ch. Andre, F-69561 Saint-Genis Laval (France); Ebeling, H., E-mail: a.m.swinbank@dur.ac.uk [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2011-11-20

177

PHYSICAL PROPERTIES OF DENSE CORES IN THE {rho} OPHIUCHI MAIN CLOUD AND A SIGNIFICANT ROLE OF EXTERNAL PRESSURES IN CLUSTERED STAR FORMATION  

SciTech Connect

Using the archive data of the H{sup 13}CO{sup +} (J = 1-0) line emission taken with the Nobeyama 45 m radio telescope with a spatial resolution of {approx} 0.01 pc, we have identified 68 dense cores in the central dense region of the {rho} Ophiuchi main cloud. The H{sup 13}CO{sup +} data also indicate that the fractional abundance of H{sup 13}CO{sup +} relative to H{sub 2} is roughly inversely proportional to the square root of the H{sub 2} column density with a mean of 1.72 x 10{sup -11}. The mean radius, FWHM line width, and LTE mass of the identified cores are estimated to be 0.045 {+-} 0.011 pc, 0.49 {+-} 0.14 km s{sup -1}, and 3.4 {+-} 3.6 M{sub sun}, respectively. The majority of the identified cores have subsonic internal motions. The virial ratio, the ratio of the virial mass to the LTE mass, tends to decrease with increasing LTE mass and about 60% of the cores have virial ratios smaller than 2, indicating that these cores are not transient structures but self-gravitating. The detailed virial analysis suggests that the surface pressure often dominates over the self-gravity and thus plays a crucial role in regulating core formation and evolution. By comparing the {rho} Oph cores with those in the Orion A molecular cloud observed with the same telescope, we found that the statistical properties of the core physical quantities are similar between the two clouds if the effect of the different spatial resolutions is corrected. The line widths of the {rho} Oph cores appear to be nearly independent of the core radii over the range of 0.01-0.1 pc and deviate upward from the Heyer and Brunt relation. This may be evidence that turbulent motions are driven by protostellar outflows in the cluster environment.

Maruta, Hajime; Nishi, Ryoichi [Department of Physics, Niigata University, 8050 Ikarashi-2, Niigata 950-2181 (Japan); Nakamura, Fumitaka [Division of Theoretical Astrophysics, National Astronomical Observatory of Japan, Mitaka, Tokyo, 181-8588 (Japan); Ikeda, Norio; Kitamura, Yoshimi [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan)

2010-05-01

178

Magnetic Phases in Dense Quark Matter  

SciTech Connect

In this paper I discuss the magnetic phases of the three-flavor color superconductor. These phases can take place at different field strengths in a highly dense quark system. Given that the best natural candidates for the realization of color superconductivity are the extremely dense cores of neutron stars, which typically have very large magnetic fields, the magnetic phases here discussed could have implications for the physics of these compact objects.

Incera, Vivian de la [Department of Physics, Western Illinois University, Macomb, IL 61455 (United States)

2007-10-26

179

Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization  

Microsoft Academic Search

A series of thermo-responsive and water-soluble 4- and 8-arm star-branched poly(2-(2?-methoxyethoxy)ethyl methacrylate) (poly(1)) with well-defined structures were synthesized by living anionic polymerization of 1, followed by a linking reaction with a core compound substituted with either four or eight benzyl bromide moieties. Furthermore, two kinds of sequentially different 4-arm star block copolymers composed of poly(1)-block-poly ((2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate) (poly(4)) were also

Akira Hirao; Reiko Inushima; Takefumi Nakayama; Takumi Watanabe; Hee-Soo Yoo; Takashi Ishizone; Kenji Sugiyama; Toyoji Kakuchi; Stephane Carlotti; Alain Deffieux

2011-01-01

180

Learning about dense matter from gravitational waves  

NASA Astrophysics Data System (ADS)

Binary neutron stars are some of the most promising sources for gravitational-wave detections with Advanced LIGO. For any gravitational-wave source containing matter, the matter contributes to the spacetime dynamics, leaving an imprint on radiation from the system. I will discuss how we can understand and model this imprint, so that we can use it to constrain our understanding of the properties of dense matter, with a focus on the inspiral and merger of binary neutron stars.

Read, Jocelyn

2013-04-01

181

Initial Conditions for Star Formation  

Microsoft Academic Search

Recent studies have provided important information on the initial conditions for the formation of low mass stars. These studies, using submillimeter continuum and line observations, have identified objects in the earliest stages of star formation as cold, dense cores in which most molecules are frozen onto dust grains. We are placing constraints on different theories of star formation with these

N. J. Evans

2002-01-01

182

Star Formation in Spiral Arms  

Microsoft Academic Search

The origin and types of spiral arms are reviewed with an emphasis on the connections between these arms and star formation. Flocculent spiral arms are most likely the result of transient instabilities in the gas that promote dense cloud formation, star formation, and generate turbulence. Long irregular spiral arms are usually initiated by gravitational instabilities in the stars, with the

B. G. Elmegreen

2011-01-01

183

Monocyte/macrophage interactions with base and linear- and star-like PEG-modified PEG-poly(acrylic acid) co-polymers.  

PubMed

Poly(ethylene glycol):poly(acrylate) PEG-g-PA co-polymers were made that inhibited nonspecific protein and cellular adhesion. PEG-g-PA co-polymers were then covalently modified with either cell adhesion peptides or fragments of antibodies to monocyte/macrophage integrin receptors (anti-VLA4, anti-beta(1), anti-beta(2), and anti-CD64) known to enhance macrophage adhesion and, perhaps, modulate their activation. Peptides were either directly conjugated to the base material or linked by way of PEO-star tethers. Fragments of the antibody region containing the antigen-binding site (Fab' fragments) were coupled to other PEG-g-PA samples using the sulhydryl end groups on Fab' fragments to amine-bearing PEO stars. Macrophage adhesion rates, phagocytic response (oxidative burst), and cytokine expression were determined for each PEG-g-PA material. Luminol-enhanced chemiluminescence was used as a semiquantitative indication of monocyte-macrophage phagocytic activation (oxidative burst). Macrophage cytokine expression in response to control, base, and modified materials was determined by ELISAs for TNF-alpha, IL-1 beta, IL-6, and IL-8. Tissue culture poly(styrene) (TCPS)-mediated the greatest number of adherent monocyte/macrophage cells relative to PEG-g-PA materials. Both YRGDS and YEILDV peptides, whether directly or indirectly (via StarPEO) conjugated to PEG-g-PA, increased adhesion versus controls. Fab' fragments of all four antibodies also promoted enhanced adhesion versus controls. Fab'StarPEO materials presented two orders of magnitude fewer ligands per surface unit area than peptide star materials (10(8) vs. 10(10)), but were able to adhere similar numbers of cells. For surfaces presenting Fab'(VLA-4) or YEILDV, both of which may both bind to a cell's VLA-4 receptor, the Star:VLA4 surface showed a greater number of adherent monocyte/macrophages. This result suggests that the Fab' had a higher affinity to the cell receptor than a corresponding minimal peptide binding sequence. All materials exhibited low oxidative burst (luminescence counts per minute, LCPM) per cell DNA without the addition of exogenous stimuli (LCPM/DNA < 100). Directly conjugated peptide materials, poly(propylene) (PP), and TCPS showed the lowest levels of LCPM/DNA without the addition of exogenous stimulus (LCPM/DNA < 20). There was no correlation between LCPM/DNA ratios, with and without added LPS stimulus, versus the individual substrates. Monocyte/macrophages adherent to TCPS substrata showed the overall highest stimulatory potential in cytokine expression response to exogenous LPS, followed by PP > PEG-g-PA > StarPEO. Cells adherent to peptide-modified materials and Fab'-modified materials were overall less stimulated. The method of presenting the peptides (i.e., directly or via Star PEO) influenced the level of cytokine secreted by the adherent macrophage. PMID:12833432

Wagner, Victoria E; Bryers, James D

2003-07-01

184

Dense Photodissociation Regions (PDRs)  

NASA Astrophysics Data System (ADS)

All neutral atomic hydrogen gas and a large fraction of the molecular gas in the Milky Way Galaxy and external galaxies lie in PDRs, and PDRs are the origin of most of the nonstellar infrared (IR) and the millimeter CO emission from a galaxy. On the surfaces (A_v 1-3) of interstellar clouds, the absorption of far ultraviolet (FUV) photons (h_v 13.6 eV) by gas and dust grains leads to intense emission of [C II] 158 um, [O I] 63, 146 um, and H2 rovibrational transitions, as well as IR dust continuum and polycyclic aromatic hydrocarbon (PAH) emission features. Deeper in PDRs, CO rotational and [C I] 370, 609 um lines originate. The transition of H to H2 and C+ to CO occurs within PDRs. Theoretical models compared with observations diagnose such physical parameters as the density and temperature structure, the elemental abundances, and the FUV radiation field in PDRs. Applications include clouds next to H II regions, reflection nebulae, planetary nebulae, red giant outflows, circumstellar gas around young stars, diffuse clouds, the warm neutral medium (WNM), and molecular clouds in the interstellar radiation field: In summary, much of the interstellar medium in galaxies. This review focuses on dense PDRs in the Milky Way Galaxy. Theoretical PDR models help explain the observed correlation of the the CO J = 1-0 luminosity with the molecular mass and also suggest FUV-induced feedback mechanisms that may regulate star formation rates and the column density through giant molecular clouds.

Hollenbach, D. J.; Tielens, A. G. G. M.

185

Dense Gas in High-Latitude Molecular Clouds  

Microsoft Academic Search

To date, no star formation has been detected in the nearest molecular clouds. We are attempting to determine whether the clouds contain suitable sites for future star formation by searching them for concentrations of dense (n(H_2) > 10(4) cm(-3) ) gas. Molecules with large dipole moments (e.g. CS, HCN, and HCO(+) ) are most likely to trace dense gas because

W. T. Reach; M. W. Pound; D. J. Wilner

1993-01-01

186

Probing Cold Dense Nuclear Matter  

SciTech Connect

The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

Subedi, Ramesh; Shneor, R.; Monaghan, Peter; Anderson, Bryon; Aniol, Konrad; Annand, John; Arrington, John; Benaoum, Hachemi; Benmokhtar, Fatiha; Bertozzi, William; Boeglin, Werner; Chen, Jian-Ping; Choi, Seonho; Cisbani, Evaristo; Craver, Brandon; Frullani, Salvatore; Garibaldi, Franco; Gilad, Shalev; Gilman, Ronald; Glamazdin, Oleksandr; Hansen, Jens-Ole; Higinbotham, Douglas; Holmstrom, Timothy; Ibrahim, Hassan; Igarashi, Ryuichi; De Jager, Cornelis; Jans, Eddy; Jiang, Xiaodong; Kaufman, Lisa; Kelleher, Aidan; Kolarkar, Ameya; Kumbartzki, Gerfried; LeRose, John; Lindgren, Richard; Liyanage, Nilanga; Margaziotis, Demetrius; Markowitz, Pete; Marrone, Stefano; Mazouz, Malek; Meekins, David; Michaels, Robert; Moffit, Bryan; Perdrisat, Charles; Piasetzky, Eliazer; Potokar, Milan; Punjabi, Vina; Qiang, Yi; Reinhold, Joerg; Ron, Guy; Rosner, Guenther; Saha, Arunava; Sawatzky, Bradley; Shahinyan, Albert; Sirca, Simon; Slifer, Karl; Solvignon, Patricia; Sulkosky, Vince; Sulkosky, Vincent; Sulkosky, Vince; Sulkosky, Vincent; Urciuoli, Guido; Voutier, Eric; Watson, John; Weinstein, Lawrence; Wojtsekhowski, Bogdan; Wood, Stephen; Zheng, Xiaochao; Zhu, Lingyan

2008-06-01

187

Quantum Anomalies and Topological Currents in Dense Matter  

NASA Astrophysics Data System (ADS)

We derive an anomalous effective Lagrangian describing the interactions of light particles such as axions, photons and superfluid phonons in the dense matter background. This effective Lagrangian, among other things, imlies that some nontrivial persistent non dissipating currents and charge densities may be formed in the dense matter. We speculate that these effects may influence such phenomena as neutron star kicks, glitches, cooling rate...

Zhitnitsky, Ariel

188

Photoenhanced Gene Transfection by a Star-Shaped Polymer Consisting of a Porphyrin Core and Poly(L-lysine) Dendron Arms.  

PubMed

A star-shaped polymer (PP-PLLD) consisting of a porphyrin (PP) core and poly(L-lysine) dendron arms (PLLD) is synthesized by the click reaction, and its ability to deliver pEGFP is investigated in this paper. It is found that PP-PLLD has a good buffer capacity and can form compact complexes with pEGFP. In vitro assay indicates that PP-PLLD shows photoenhanced gene transfection efficiency. PP-PLLD consisting of only third generation PLLD shows a higher transfected cell number than PEI under a Xe lamp at the N/P ratio of 20, and meanwhile shows a neglectable cytotoxicity to HeLa cells. Therefore, PP-PLLD with suited irradiation is a promising nontoxic and photoinducible effective gene delivery strategy, which should be encouraged in gene therapy. PMID:23828851

Ma, Dong; Zhao, Yi; Zhou, Xiao-Yan; Lin, Qian-Ming; Zhang, Yi; Lin, Jian-Tao; Xue, Wei

2013-07-05

189

Dense topological spaces and dense continuity  

NASA Astrophysics Data System (ADS)

There are several attempts to generalize (or "widen") the concept of topological space. This paper uses equivalence relations to generalize the concept of topological space via the concept of equivalence relations. By the generalization, we can introduce from particular topology on a nonempty set X many new topologies, we call anyone of these new topologies a dense topology. In addition, we formulate some simple properties of dense topologies and study suitable generalizations of the concepts of limit points, closeness and continuity, as well as Jackson, Nörlund and Hahn dense topologies.

Aldwoah, Khaled A.

2013-09-01

190

Thermal conductivity of dense and porous yttria-stabilized zirconia  

Microsoft Academic Search

The thermal conductivity of dense and porous yttria-stabilized zirconia (YSZ) ceramics has been measured as a function of temperature in the range 25 to 1000 °C. The dense specimens were either single crystal (8 mol% YSZ) or sintered polycrystalline (3 mol% and 8 mol% YSZ). The porous specimens (3 mol% YSZ) were prepared using the “fugitive” polymer method, where different

K. W. Schlichting; N. P. Padture; P. G. Klemens

2001-01-01

191

Neutrino Propagation in Dense Hadronic Matter  

NASA Astrophysics Data System (ADS)

Neutrino propagation in protoneutron stars requires the knowledge of the composition as well as the dynamical response function of dense hadronic matter. Matter at very high densities is probably composed of other particles than nucleons and little is known on the Fermi liquid properties of hadronic multicomponent systems. We will discuss the effects that the presence of {Lambda } hyperons might have on the response and, in particular, on its influence on the thermodynamical stability of the system and the mean free path of neutrinos in dense matter.

Rios, A.; Polls, A.; Margueron, J.

2006-08-01

192

High-mass star formation in the Milky Way  

Microsoft Academic Search

Abstract Massive star formation takes place in the dense cores of molecular clouds where the stars may be obscured at optical wavelengths. An excellent signpost of a massive young stellar object is the presence of an ultra-compact HII region, which is a dense photo-ionised cocoon of gas surrounding the newly formed star. UC H II regions are char- acterised by

Joao Ciotta Neves

2006-01-01

193

Dense with Sense  

NASA Astrophysics Data System (ADS)

Displacement encoding with stimulated echoes (DENSE) with a low encoding strength phase-cycled meta-DENSE readout and a two fold SENSE acceleration (R = 2) is described. This combination reduces total breath-hold times for increased patient comfort during cardiac regional myocardial contractility studies. Images from phantoms, normal volunteers, and a patient are provided to demonstrate the SENSE-DENSE combination of methods. The overall breath-hold time is halved while preserving strain map quality.

Aletras, Anthony H.; Ingkanisorn, W. Patricia; Mancini, Christine; Arai, Andrew E.

2005-09-01

194

Are energy dense diets also nutrient dense?  

Technology Transfer Automated Retrieval System (TEKTRAN)

Some beverages are nutrient dense, but they are often excluded from nutrient density calculations. The purpose of this study was to assess whether the energy-nutrient association changed when beverages were included in these calculations. Applying a cross-sectional design, a 24-hour dietary recall ...

195

Atoms in dense plasmas  

SciTech Connect

Recent experiments with high-power pulsed lasers have strongly encouraged the development of improved theoretical understanding of highly charged ions in a dense plasma environment. This work examines the theory of dense plasmas with emphasis on general rules which govern matter at extreme high temperature and density. 106 refs., 23 figs.

More, R.M.

1986-01-01

196

Magnetism in Dense Quark Matter  

NASA Astrophysics Data System (ADS)

We review the mechanisms via which an external magnetic field can affect the ground state of cold and dense quark matter. In the absence of a magnetic field, at asymptotically high densities, cold quark matter is in the Color-Flavor-Locked (CFL) phase of color superconductivity characterized by three scales: the superconducting gap, the gluon Meissner mass, and the baryonic chemical potential. When an applied magnetic field becomes comparable with each of these scales, new phases and/or condensates may emerge. They include the magnetic CFL (MCFL) phase that becomes relevant for fields of the order of the gap scale; the paramagnetic CFL, important when the field is of the order of the Meissner mass, and a spin-one condensate associated to the magnetic moment of the Cooper pairs, significant at fields of the order of the chemical potential. We discuss the equation of state (EoS) of MCFL matter for a large range of field values and consider possible applications of the magnetic effects on dense quark matter to the astrophysics of compact stars.

Ferrer, Efrain J.; de la Incera, Vivian

197

Star Formation in Spiral Arms  

Microsoft Academic Search

The origin and types of spiral arms are reviewed with an emphasis on the\\u000aconnections between these arms and star formation. Flocculent spiral arms are\\u000amost likely the result of transient instabilities in the gas that promote dense\\u000acloud formation, star formation, and generate turbulence. Long irregular spiral\\u000aarms are usually initiated by gravitational instabilities in the stars, with\\u000athe

Bruce G. Elmegreen

2011-01-01

198

H3+ in dense and diffuse clouds.  

PubMed

Interstellar H3+ has been detected in dense as well as diffuse clouds using three 3.7 microns infrared spectral lines of the nu 2 fundamental band. Column densities of H3+ from (1.7-5.5) x 10(14) cm-2 have been measured in dense clouds in absorption against the infrared continua of the deeply embedded young stellar objects GL2136, W33A, MonR2 IRS 3, GL961E, and GL2591. Strong and broad H3+ absorptions have been detected in dense and diffuse clouds towards GC IRS 3 and GCS3-2 in the region of the galactic center. A large column density of H3+, comparable to that of a dense cloud, has been detected towards the visible star Cygnus OB2 No. 12, which has a line of sight that crosses mostly diffuse clouds. The H3+ chemistry of dense and diffuse clouds are discussed using a very simple model. Some future projects and problems are discussed. PMID:9809013

McCall, B J; Hinkle, K H; Geballe, T R; Oka, T

1998-01-01

199

Quantum dense key distribution  

SciTech Connect

This paper proposes a protocol for quantum dense key distribution. This protocol embeds the benefits of a quantum dense coding and a quantum key distribution and is able to generate shared secret keys four times more efficiently than the Bennet-Brassard 1984 protocol. We hereinafter prove the security of this scheme against individual eavesdropping attacks, and we present preliminary experimental results, showing its feasibility.

Degiovanni, I.P.; Ruo Berchera, I.; Castelletto, S.; Rastello, M.L.; Bovino, F.A.; Colla, A.M.; Castagnoli, G. [Istituto Elettrotecnico Nazionale G. Ferraris, Strada delle Cacce 91, 10135 Torino (Italy); ELSAG SpA, Via Puccini 2, 16154, Genova (Italy)

2004-03-01

200

The Origins of High Latitude Runaway B stars  

NASA Astrophysics Data System (ADS)

We analyzed a sample of 28 high latitude runaway B stars more than 0.5 kpc from the galactic plane. This sample has several characteristics which distinguish it from disk field star samples including: a low incidence of binaries, lack of slow rotators, and no Be stars. A preponderance of the evidence indicates that our sample is dominated by stars that were ejected from dense star clusters and star forming regions by the Dynamic Ejection Scenario (DES, reference).

Martin, JC

2005-12-01

201

WARM EXTENDED DENSE GAS AT THE HEART OF A COLD COLLAPSING DENSE CORE  

SciTech Connect

In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (approx30-70 K), extended (radius of approx2400 AU), dense (a few times 10{sup 5} cm{sup -3}) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, 'warm-in-cold core stage (WICCS)', i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitute a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar outflow.

Shinnaga, Hiroko; Phillips, Thomas G. [California Institute of Technology Submillimeter Observatory (CSO), 111 Nowelo Street, Hilo, HI 96720 (United States); Furuya, Ray S. [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96720 (United States); Kitamura, Yoshimi, E-mail: shinnaga@submm.caltech.ed, E-mail: tgp@submm.caltech.ed, E-mail: rsf@subaru.naoj.or, E-mail: kitamura@isas.jaxa.j [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan)

2009-12-01

202

Efficient gene transfection in the neurotypic cells by star-shaped polymer consisting of ?-cyclodextrin core and poly(amidoamine) dendron arms.  

PubMed

In order to develop the effective vectors that had high gene transfection capability and low cytotoxicity in the neuronal cells, we tested the star-shaped polymer consisting of ?-cyclodextrin core and poly(amidoamine) (PAMAM) dendron arms [?-CD-(D3)7] as the vector to transfect the human neuroblastoma SH-SY5Y cells. The physicochemical properties of the ?-CD-(D3)7/plasmid DNA (pDNA) complexes were characterized by using gel electrophoresis, dynamic light scattering, transmission electron microscopy and zeta-potential experiments. Among the human neuroblastoma SH-SY5Y cells, ?-CD-(D3)7/pDNA complex demonstrated a lower toxicity compared to those of PAMAM (G=4, with an ethylenediamine core)/pDNA complex. When the N/P ratio was over 20, it was observed that PAMAM had a faster increment in toxicity compared to ?-CD-(D3)7. Fluorescent image, confocal microscopy image and flow cytometry showed that ?-CD-(D3)7/pDNA complexes had significantly higher transgene activity than that of PAMAM/pDNA complexes. For example, the transfection efficiency was 20% and 7.5% for ?-CD-(D3)7/pDNA and PAMAM/pDNA complexes, respectively. These results indicated that ?-CD-(D3)7 might be a promising candidate for neurotypic cells gene delivery with the characteristics of good biocompatibility, relatively high gene transfection capability and potential in vivo gene delivery ability. PMID:23544527

Liang, Bing; Deng, Jun Jie; Yuan, Fang; Yang, Ning; Li, Wei; Yin, Jian Rui; Pu, Shu Xiang; Xie, Long Chang; Gao, Cong; Zhang, Li Ming

2013-01-08

203

Imaging Dense Globular Clusters like M3 and M15  

Microsoft Academic Search

The objective of this study is to explore new photometric methods for amateur telescope observations of cluster variables and globular clusters using CCD photometry. Amateur telescope photometric observations of cluster variables in globular clusters are limited because of dense, crowded star fields. However, with improvements in CCD photometric methods, there are opportunities to observe cluster variables, such as RR Lyrae

Rodney Howe; Strikis Iakovos-Marios; Ido Bareket; Stouraitis Dimitrios

2010-01-01

204

Determination of the Equation of State of Dense Matter  

Microsoft Academic Search

Nuclear collisions can compress nuclear matter to densities achieved within neutron stars and within core-collapse supernovae. These dense states of matter exist momentarily before expanding. We analyzed the flow of matter to extract pressures in excess of 1034 pascals, the highest recorded under laboratory-controlled conditions. Using these analyses, we rule out strongly repulsive nuclear equations of state from relativistic mean

Pawel Danielewicz; Roy Lacey; William G. Lynch

2002-01-01

205

Dense Medium Cyclone Optimization.  

National Technical Information Service (NTIS)

Dense medium cyclones (DMCs) are known to be efficient, high-tonnage devices suitable for upgrading particles in the 50 to 0.5 mm size range. This versatile separator, which uses centrifugal forces to enhance the separation of fine particles that cannot b...

2005-01-01

206

Dense suprasellar epidermoid cyst  

Microsoft Academic Search

A case of a dense epidermoid cyst of the suprasellar cistern is presented. The clinical symptoms were headache radiating to the left eye and a quadrant anopsia on the left eye. The density of the epidermoid was 62 HU and no significant contrast enhancement occured after contrast application. The main feature which allows differentiation from other hyperdense suprasellar lesions seems

O. Schubiger; A. Valavanis; E. Gessaga

1983-01-01

207

Neutrino oscillations in neutron star matter  

NASA Astrophysics Data System (ADS)

Mazurek's (1979) hypothesis, that neutrino oscillations may be able to transfer leptonic, zero-point energy to baryons during the gravitational collapse of a massive star which ends in a stellar explosion, is discussed. Upon derivation of the characteristic lengths for neutrino oscillation propagation in vacuum and in extremely dense matter, it becomes evident that vacuum oscillations can be suppressed in dense matter and that they should therefore have no influence on the neutrino emission of neutron stars.

Haubold, H. J.

1982-03-01

208

Molecules in Dense Globules in Planetary Nebulae  

NASA Astrophysics Data System (ADS)

We have investigated the formation of molecules in a dense, neutral globule, such as those observed in the Helix nebula (NGC 7293). We find that H2 and CO can possess large abundances in cold gas throughout the bulk of the globule, in spite of the enhanced photon field provided by the central star. Emission from C2H and CN wili be detectable from individual globules if they are carbon-rich. The temperature in the boundary layer between a globule and the wind of the nebula's central star is estimated, and found to be too low for neutral-neutral reactions to cause most boundary-layer oxygen to be in OH and H20. Key words: ISM: globules - ISM: molecules - planetary nebulae: general - planetary nebulae: individual: Helix nebula.

Howe, D. A.; Hartquist, T. W.; Williams, D. A.

1994-12-01

209

Relaxation dynamics of branched polymers  

NASA Astrophysics Data System (ADS)

The Rouse model for star polymers was successfully derived by solving the differential equations governing the net force acting on each bead in a star polymer chain. As opposed to a linear polymer, where we have N unique roots for N beads, in the case of star polymers, there are only 2 Na+1 unique roots and all odd unique roots (except the last root corresponding to the branch point) starting with the first root have a multiplicity of f-1. The relaxation time of the pth unique Rouse mode of a star polymer varies as (2Na + 1)2/p2. Since alternate Rouse modes in a star polymer have a multiplicity of f-1, they add to the terminal modulus of the star polymers and the terminal modulus, G(tau) ends up being proportional to f-1 (besides being inversely proportional to N, which is also the case with linear polymers). A self-consistent theory for the relaxation of entangled star polymers was developed based on the work done by Colby and Rubinstein on linear blends. This theory considers the duality of relaxation dynamics (direct stress relaxation and indirect relaxation by release of constraints) and models the relaxation due to constraint release R(t) based on Dean's approach in solving the vibration frequencies of glassy chains with random spring constants. In our case, the mobilities of beads were considered to be random and based on the relative weight of the prefactor of a Maxwell function, a group of which was fitted to the stress relaxation function mu(t) of a star polymer (proposed and derived by Doi). The tube dilation model for star and comb polymers was investigated in detail and predictions compared to rheological data from polypropylene, polybutadiene and polystyrene comb polymers along with PEP star polymers. The relaxation time from the Tube Dilation Model was compared with the classical Tube Model and was shown to have an extra power dependence on the fraction of the comb backbone.

Ghosh, Arnav

210

Massive stars, disks, and clustered star formation  

NASA Astrophysics Data System (ADS)

The formation of an isolated massive star is inherently more complex than the relatively well-understood collapse of an isolated, low-mass star. The dense, clustered environment where massive stars are predominantly found further complicates the picture, and suggests that interactions with other stars may play an important role in the early life of these objects. In this thesis we present the results of numerical hydrodynamic experiments investigating interactions between a massive protostar and its lower-mass cluster siblings. We explore the impact of these interactions on the orientation of disks and outflows, which are potentially observable indications of encounters during the formation of a star. We show that these encounters efficiently form eccentric binary systems, and in clusters similar to Orion they occur frequently enough to contribute to the high multiplicity of massive stars. We suggest that the massive protostar in Cepheus A is currently undergoing a series of interactions, and present simulations tailored to that system. We also apply the numerical techniques used in the massive star investigations to a much lower-mass regime, the formation of planetary systems around Solar- mass stars. We perform a small number of illustrative planet-planet scattering experiments, which have been used to explain the eccentricity distribution of extrasolar planets. We add the complication of a remnant gas disk, and show that this feature has the potential to stabilize the system against strong encounters between planets. We present preliminary simulations of Bondi-Hoyle accretion onto a protoplanetary disk, and consider the impact of the flow on the disk properties as well as the impact of the disk on the accretion flow.

Moeckel, Nickolas Barry

211

Do Iron Stars Really Exist?  

NASA Astrophysics Data System (ADS)

Only two stars have been classified as Iron Stars: XX Oph and AS 325. This distinction is bestowed upon them as their optical spectra consist entirely of a forest of emission lines, most of which are due to the ionized metals of iron, chromium, and titanium. Over the years, XX Oph (Merrill's iron star) and AS 325 have received various classifications including spectral types from B to M and even thought to be binary stars. Using new optical and near-IR spectroscopy we have finally observed the stellar photospheres in these two objects. They appear to be evolved stars trapped in a dense region of the Rho Oph star forming region. Taking our multi-wavelength observations plus past work by others, we have developed a new model for what these two unique objects really are.

Peña, M. A.; Cool, R. J.; Howell, S. B.; Adamson, A.

2004-12-01

212

Dense neutron matter  

Microsoft Academic Search

Neutron star matter with densities exceeding that of the normal nuclear matter (about 0.17\\/f cu m) is discussed in the light of the recent developments in the understanding of the structure of the nucleon in terms of its basic constituents: quarks and gluons. Two different scenarios of phase transition - pion condensation followed by quark matter or percolation followed by

Mannque Rho

1980-01-01

213

H-cluster stars  

NASA Astrophysics Data System (ADS)

The study of dense matter at ultrahigh density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. It is well known that the state of cold matter at supranuclear density depends on the non-perturbative nature of quantum chromodynamics (QCD) and is essential for modelling pulsars. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other there. That might render quarks grouped in clusters, although the hypothetical quark clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we therefore consider here a possible kind of quark clusters, H-clusters, that could emerge inside compact stars during their initial cooling as the dominant components inside (the degree of freedom could then be H-clusters there). Taking into account the in-medium stiffening effect, we find that at baryon densities of compact stars H-cluster matter could be more stable than nuclear matter. We also find that for the H-cluster matter with lattice structure, the equation of state could be so stiff that it would seem to be `superluminal' in the most dense region. However, the real sound speed for H-cluster matter is in fact difficult to calculate, so at this stage we do not put constraints on our model from the usual requirement of causality. We study the stars composed of H-clusters, i.e. H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M? as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general understanding of different manifestations of compact stars, we expect further observational and experimental tests for the H-cluster stars in the future.

Lai, X. Y.; Gao, C. Y.; Xu, R. X.

2013-06-01

214

Neutron stars, strange stars, and the nuclear equation of state  

SciTech Connect

This article consists of three parts. In part one we review the present status of dense nuclear matter calculations, and introduce a representative collection of realistic nuclear equations of state which are derived for different assumptions about the physical behavior of dense matter (baryon population, pion condensation,.possible transition of baryon matter to quark matter). In part two we review recently performed non-rotating and rotating compact star calculations performed for these equations of state. The minimum stable rotational periods of compact stars, whose knowledge is of decisive importance for the interpretation of rapidly rotating pulsars, axe determined. For this purpose two different limits on stable rotation are studied: rotation at the general relativistic Kepler period (below which mass shedding at the star`s equator sets in), and, secondly, rotation at the gravitational radiation-reaction instability (at which emission of gravitational waves set in which slows the star down). Part three of this article deals with the properties of hypothetical strange stars. Specifically we investigate the amount of nuclear solid crust that can be carried by a rotating strange star, and answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

Weber, F.; Glendenning, N.K.

1992-11-02

215

DENSE MEDIUM CYCLONE OPTIMIZATON  

SciTech Connect

Dense medium cyclones (DMCs) are known to be efficient, high-tonnage devices suitable for upgrading particles in the 50 to 0.5 mm size range. This versatile separator, which uses centrifugal forces to enhance the separation of fine particles that cannot be upgraded in static dense medium separators, can be found in most modern coal plants and in a variety of mineral plants treating iron ore, dolomite, diamonds, potash and lead-zinc ores. Due to the high tonnage, a small increase in DMC efficiency can have a large impact on plant profitability. Unfortunately, the knowledge base required to properly design and operate DMCs has been seriously eroded during the past several decades. In an attempt to correct this problem, a set of engineering tools have been developed to allow producers to improve the efficiency of their DMC circuits. These tools include (1) low-cost density tracers that can be used by plant operators to rapidly assess DMC performance, (2) mathematical process models that can be used to predict the influence of changes in operating and design variables on DMC performance, and (3) an expert advisor system that provides plant operators with a user-friendly interface for evaluating, optimizing and trouble-shooting DMC circuits. The field data required to develop these tools was collected by conducting detailed sampling and evaluation programs at several industrial plant sites. These data were used to demonstrate the technical, economic and environmental benefits that can be realized through the application of these engineering tools.

Gerald H. Luttrell; Chris J. Barbee; Peter J. Bethell; Chris J. Wood

2005-06-30

216

APPLICATIONS OF ISOCYANATION FOR POLYMER SYSTEMS  

Microsoft Academic Search

Isocyanate is a highly unsaturated compound. It reacts readily with compounds containing active proton such as alcohol, phenol, acid, and amine through isocyanation. In this article, this very useful synthesis route is reviewed with regard to applications of isocyanation for the synthesis of polyurethanes, polyurethane ionomers, polyamides, polyimides, polyamide-imides, interpenetrating network polymers, polymers for membrane separation, comb- and star-polymers, functional

Jiang-Qing Pan; Wayne W. Y. Lau

2001-01-01

217

Post-Newtonian Dynamics in Dense Stellar Systems  

NASA Astrophysics Data System (ADS)

Dense stellar systems (star clusters and galactic nuclei) are some of the most promising sources of gravitational waves since black holes may form and grow in them. In the talk I will describe how relativistic dynamics is included in N-body simulations of such systems, and discuss examples how we model sources in different wavelength regimes, showing results from triple and binary black holes in galactic nuclei, and giving an outlook to projected work for star clusters. Also I'll explain how these theoretical activities are embedded into collaborative programs with gravitational wave observatories, such as the VESF (Virgo-EGO science collaboration) and the German LISA cooperation.

Spurzem, Rainer; Merritt, D.; Berczik, Peter; Berentzen, Ingo; Preto, Miguel; Downing, Jonathan

2007-08-01

218

Neutron stars, strange stars, and the nuclear equation of state  

SciTech Connect

This article consists of three parts. In part one we review the present status of dense nuclear matter calculations, and introduce a representative collection of realistic nuclear equations of state which are derived for different assumptions about the physical behavior of dense matter (baryon population, pion condensation,.possible transition of baryon matter to quark matter). In part two we review recently performed non-rotating and rotating compact star calculations performed for these equations of state. The minimum stable rotational periods of compact stars, whose knowledge is of decisive importance for the interpretation of rapidly rotating pulsars, axe determined. For this purpose two different limits on stable rotation are studied: rotation at the general relativistic Kepler period (below which mass shedding at the star's equator sets in), and, secondly, rotation at the gravitational radiation-reaction instability (at which emission of gravitational waves set in which slows the star down). Part three of this article deals with the properties of hypothetical strange stars. Specifically we investigate the amount of nuclear solid crust that can be carried by a rotating strange star, and answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

Weber, F.; Glendenning, N.K.

1992-11-02

219

Diffusion and Coulomb Separation of Ions in Dense Matter  

NASA Astrophysics Data System (ADS)

We analyze diffusion equations in strongly coupled Coulomb mixtures of ions in dense stellar matter. Strong coupling of ions in the presence of gravitational forces and electric fields (induced by plasma polarization in the presence of gravity) produces a specific diffusion current which can separate ions with the same A/Z (mass to charge number) ratios but different Z. This Coulomb separation of ions can be important for the evolution of white dwarfs and neutron stars.

Beznogov, M. V.; Yakovlev, D. G.

2013-10-01

220

Synthesis, Characterization, and Evaluation as Transfection Reagents of Double-Hydrophilic Star Copolymers:  Effect of Star Architecture  

Microsoft Academic Search

Five star polymers of the ionizable hydrophilic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the nonionic hydrophilic methoxy hexa(ethylene glycol) methacrylate (HEGMA) were prepared by group transfer polymerization (GTP) using ethylene glycol dimethacrylate (EGDMA) as coupling agent. In particular, four isomeric star copolymers, one heteroarm, two star block and one statistical star, with 90% mol DMAEMA and 10% mol HEGMA, plus one star

Theoni K. Georgiou; Maria Vamvakaki; Leonidas A. Phylactou; Costas S. Patrickios

2005-01-01

221

Extreme Stars  

Microsoft Academic Search

Over the past 200 years, our knowledge of stars has expanded enormously. From seeing myriad dots of different brightnesses, we haved moved on to measure their distances, temperatures, sizes, chemical compositions, and even ages, finding both young and ancient stars that dwarf our Sun and are dwarfed by it. Unique in its approach, Extreme Stars describes the lives of stars

James B. Kaler

2001-01-01

222

Shocks in Dense Clouds in the Vela Supernova Remnant: FUSE  

NASA Astrophysics Data System (ADS)

We have obtained 8 LWRS FUSE spectra to study a recently identified interaction of the Vela supernova remnant with a dense cloud region along its western edge. The goal is to quantify the temperature, ionization, density, and abundance characteristics associated with this shock/dense cloud interface by means of UV absorption line studies. Our detection of high-velocity absorption line C I at +90 to +130 km/s with IUE toward a narrow region interior to the Vela SNR strongly suggests the Vela supernova remnant is interacting with a dense ISM or molecular cloud. The shock/dense cloud interface is suggested by (1) the rarity of detection of high-velocity C I seen in IUE spectra, (2) its very limited spatial distribution in the remnant, and (3) a marked decrease in X-ray emission in the region immediately west of the position of these stars where one also finds a 100 micron emission ridge in IRAS images. We have investigated the shock physics and general properties of this interaction region through a focussed UV absorption line study using FUSE spectra. We have FUSE data on OVI absorption lines observed toward 8 stars behind the Vela supernova remnant (SNR). We compare the OVI observations with IUE observations of CIV absorption toward the same stars. Most of the stars, which are all B stars, have complex continua making the extraction of absorption lines difficult. Three of the stars, HD 72088, HD 72089 and HD 72350, however, are rapid rotators (v sin i less than 100 km/s) making the derivation of absorption column densities much easier. We have measured OVI and CIV column densities for the "main component" (i.e. the low velocity component) for these stars. In addition, by removing the H2 line at 1032.35A (121.6 km/s relative to OVI), we find high velocity components of OVI at approximately 150 km/s that we attribute to the shock in the Vela SNR. The column density ratios and magnitudes are compared to both steady shock models and results of hydrodynamical SNR modeling. We find that the models require the shock to be relatively slow (approximately 100 - 170 km/s) to match the FUSE data. We discuss the implications of our results for models of the evolution of the Vela SNR.

Nichols, Joy

2002-03-01

223

Dense Hypervelocity Plasma Jets  

NASA Astrophysics Data System (ADS)

We are developing high velocity dense plasma jets for fusion and HEDP applications. Traditional coaxial plasma accelerators suffer from the blow-by instability which limits the mass accelerated to high velocity. In the current design blow-by is delayed by a combination of electrode shaping and use of a tailored plasma armature created by injection of a high density plasma at a few eV generated by arrays of capillary discharges or sparkgaps. Experimental data will be presented for a complete 32 injector gun system built for driving rotation in the Maryland MCX experiment, including data on penetration of the plasma jet through a magnetic field. We present spectroscopic measurements of plasma velocity, temperature, and density, as well as total momentum measured using a ballistic pendulum. Measurements are in agreement with each other and with time of flight data from photodiodes and a multichannel PMT. Plasma density is above 10^15 cm-3, velocities range up to about 100 km/s. Preliminary results from a quadrature heterodyne HeNe interferometer are consistent with these results.

Case, Andrew; Witherspoon, F. Douglas; Messer, Sarah; Bomgardner, Richard; Phillips, Michael; van Doren, David; Elton, Raymond; Uzun-Kaymak, Ilker

2007-11-01

224

The origin of OB runaway stars.  

PubMed

About 20% of all massive stars in the Milky Way have unusually high velocities, the origin of which has puzzled astronomers for half a century. We argue that these velocities originate from strong gravitational interactions between single stars and binaries in the centers of star clusters. The ejecting binary forms naturally during the collapse of a young (?1 million years old) star cluster. This model replicates the key characteristics of OB runaways in our galaxy, and it explains the presence of runaway stars of ?100 solar masses (M(?)) around young star clusters, such as R136 and Westerlund 2. The high proportion and the distributions in mass and velocity of runaways in the Milky Way are reproduced if the majority of massive stars are born in dense and relatively low-mass (5000 to 10,000 M(?)) clusters. PMID:22096104

Fujii, Michiko S; Portegies Zwart, Simon

2011-11-17

225

Near-infrared and optical observations of IRAS sources in and near dense cores  

SciTech Connect

This paper reports observations of 34 IRAS sources associated with dense cores in dark clouds at wavelengths 0.4-20 microns. The stars near cores tend to be visible T Tauri stars, while stars in cores tend to have circumstellar extinction 30-90 mag and luminosity about one solar, similar to that of T Tauri stars. The typical highly obscured star is probably accompanied by a luminous structure of substellar temperature, such as a circumstellar disk. In Taurus-Auriga, stars in cores probably become visible T Tauri stars less than 100,000 yr after they become detectable by IRAS; i.e., after they attain luminosity greater than about 0.1 solar. This implies that they are extremely young and may still be accreting. 54 references.

Myers, P.C.; Mathieu, R.D.; Fuller, G.A.; Beichman, C.A.; Benson, P.J.

1987-08-01

226

Degenerate stars. XII - Recognition of hot nondegenerates  

NASA Astrophysics Data System (ADS)

Fifty-one newly observed degenerate stars and 14 nondegenerates include 13 faint red stars, most of which do not show any lines except DF, Gr 554. Hot subdwarfs and an X-ray source are discussed along with the problem of low-resolution spectroscopic classification of dense hot stars. The multichannel spectrum of the carbon-rich magnetic star LP 790-29 is examined by fitting the undisturbed parts of the spectrum to a black body of 7625 K by the least squares method; the Swan bands absorb 600 A of the spectrum assuming that the blocked radiation is redistributed in the observed region.

Greenstein, J. L.

1980-12-01

227

Preparation and gas transport properties of dense fluoroaniline copolymer membranes  

Microsoft Academic Search

The first evaluation of gas transport properties of dense polyfluoroaniline and fluoroaniline copolymer membranes was presented. First of all, a series of fluoroaniline copolymers containing different feeding ratio of ortho-fluoroaniline\\/aniline were prepared by oxidative copolymerizations in CaCl2\\/HCl medium. These polymers were amorphous and could afford flexible films in high molecular weight, obtained by casting from solution. The results for gas

Kuan-Yeh Huang; Chang-Lung Shiu; Yu-An Su; Chia-Chi Yang; Jui-Ming Yeh; Yen Wei; Kueir-Rarn Lee

2009-01-01

228

Fast pulsars, variational bound, other facets of compact stars  

SciTech Connect

We derive a limit on the rotation period of a gravitationally bound star that is analogous to Ruffini's mass limit for a neutron star. We discuss the impact of gravitational radiation-reaction instabilities. The condition that self-bound stars can rotate faster is derived. The present status of searches for fast pulsars is reviewed. The composition of neutron stars is discussed in the context of nuclear and hypernuclear constraints. The phase transition from hadron to quark phase in the interior of dense neutron stars is discussed properly accounting for the fact that this first order phase transition involves two conserved charges. Hybrid stars are then described. 28 refs., 13 figs.

Glendenning, N.K.

1991-05-01

229

Stellar Wind Disruption by an Orbiting Neutron Star  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

230

Stars and Star Myths.  

ERIC Educational Resources Information Center

|Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following…

Eason, Oliver

231

The Angular Momentum of Dense Clumps in Elephant Trunks  

NASA Astrophysics Data System (ADS)

The radiation from newly born massive stars photoionize and erode the parental molecular cloud, producing structures such as the so-called elephant trunks. At the head of an elephant trunk, the interaction of theshock (driven by the photo evaporation process) with previously existing density perturbations leads to the formation of dense clumps. Some of these clumps have enough mass to be auto-gravitating, and therefore can eventually form new stars. We carry out a 3D simulation of this process, and from the results we compute the angular momenta of these collapsing clumps. We show that the angular momenta of the clumps have preferential directions, which in principle indicate the directions in which jets will eventually be ejected from the star+accretion disk systems that will be formed.

Lora, Veronica; Raga, Alejandro C.; Esquivel, Alejandro

232

Sleuthing the Isolated Compact Stars  

NASA Astrophysics Data System (ADS)

In the early 1990's, isolated thermally-emitting neutron stars accreting from the interstellar medium were predicted to show up in their thousands in the ROSAT soft X-ray all-sky survey. The glut of sources would provide unprecedented opportunities for probing the equation of state of ultra-dense matter. Only seven objects have been firmly identified to date. The reasons for this discrepency are discussed and recent high resolution X-ray spectroscopic observations of these objects are described. Spectra of the brightest of the isolated neutron star candidates, RX J1856.5-3754, continue to present interpretational difficulties for current neutron star model atmospheres and alternative models are briefly discussed. RX J1856.5-3754 remains a valid quark star candidate.

Drake, J. J.

2004-08-01

233

MAGNETIC FIELD IN THE ISOLATED MASSIVE DENSE CLUMP IRAS 20126+4104  

SciTech Connect

We measured polarized dust emission at 350 {mu}m toward the high-mass star-forming massive dense clump IRAS 20126+4104 using the SHARC II Polarimeter, SHARP, at the Caltech Submillimeter Observatory. Most of the observed magnetic field vectors agree well with magnetic field vectors obtained from a numerical simulation for the case when the global magnetic field lines are inclined with respect to the rotation axis of the dense clump. The results of the numerical simulation show that rotation plays an important role on the evolution of the massive dense clump and its magnetic field. The direction of the cold CO 1-0 bipolar outflow is parallel to the observed magnetic field within the dense clump as well as the global magnetic field, as inferred from optical polarimetry data, indicating that the magnetic field also plays a critical role in an early stage of massive star formation. The large-scale Keplerian disk of the massive (proto)star rotates in an almost opposite sense to the clump's envelope. The observed magnetic field morphology and the counterrotating feature of the massive dense clump system provide hints to constrain the role of magnetic fields in the process of high-mass star formation.

Shinnaga, Hiroko; Phillips, Thomas G. [California Institute of Technology Submillimeter Observatory, 111 Nowelo Street, Hilo, HI 96720 (United States); Novak, Giles [Department of Physics and Astronomy, Northwestern University, 633 Clark Street Evanston, IL 60208 (United States); Vaillancourt, John E. [Stratospheric Observatory for Infrared Astronomy, Universities Space Research Association, NASA Ames Research Center, Moffet Field, CA 94035 (United States); Machida, Masahiro N. [Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan); Kataoka, Akimasa [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Tomisaka, Kohji [National Astronomical Observatory of Japan and Department of Astronomy, School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI), Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Davidson, Jacqueline; Houde, Martin [School of Physics, University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Perth (Australia); Dowell, C. Darren [Jet Propulsion Laboratory, California Institute of Technology, MS 169-506, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Leeuw, Lerothodi [SETI Institute, 515 North Whisman Avenue, Mountain View, CA 94043 (United States)

2012-05-10

234

Nuclear physics of dense matter.  

National Technical Information Service (NTIS)

Recent progress in applying nuclear physics to calculate properties of dense matter is reviewed. Topics considered include nuclei below neutron drip, the equation of state of matter at densities both below and above that of nuclear matter, the possibility...

C. J. Pethick D. G. Ravenhall

1991-01-01

235

Dispersal of dense protostellar material - NH3 hot cores and outflows in Sagittarius B2  

SciTech Connect

VLA observations of Sgr B2 in six ammonia transitions have uncovered two 200-K condensations with approximately 0.2 pc diameters associated with water maser sources which are similar to the Orion hot core but are more massive. Total NH3 mass of the northern source is 1000 times higher than in the Orion hot core. The hot core emission traces dense gas around newly formed massive stars, and is produced during a relatively brief stage after the star begins to heat the surrounding medium and before the dense gas is dispersed by outflow and the emergence of an expanding H II region. 36 references.

Vogel, S.N.; Genzel, R.; Palmer, P.

1987-05-01

236

Heavy mesons in dense matter  

SciTech Connect

Charmed mesons in dense matter are studied within a unitary coupled-channel approach which takes into account Pauli-blocking effects and meson self-energies in a self-consistent manner. We obtain the open-charm meson spectral functions in this dense medium, and discuss their implications on hidden charm and charm scalar resonances and on the formation of D-mesic nuclei.

Tolos, Laura [Theory Group. KVI. University of Groningen, Zernikelaan 25, 9747 AA Groningen (Netherlands); Instituto de Ciencias del Espacio (IEEC/CSIC), Campus Universitat Autonoma de Barcelona, Facultat de Ciencies, Torre C5, E-08193 Bellaterra, Barcelona (Spain); Gamermann, Daniel; Ramos, Angels [Departament d'Estructura i Constituents de la Materia, Universitat de Barcelona, Diagonal 647, 08028 Barcelona (Spain); Garcia-Recio, Carmen [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad de Granada, E-18071 Granada (Spain); Molina, Raquel; Nieves, Juan; Oset, Eulogio [Instituto de Fisica Corpuscular (centro mixto CSIC-UV), Institutos de Investigacion de Paterna, Aptdo. 22085, 46071, Valencia (Spain)

2011-05-23

237

Dense molecular gas in starburst galaxies: Warmer than expected?  

NASA Astrophysics Data System (ADS)

Star formation processes and their feedback play a crucial role in the evolution of almost every galaxy, locally as well as at high redshifts. The question whether or not the initial mass function (IMF) is universal, i.e. the same in all kinds of environments, is still subject to intense debate. A number of recent observations have been interpreted as evidence for a top-heavy IMF, spanning a variety of objects, from the center of our Galaxy to circumnuclear starburst regions and ultra-compact dwarf galaxies. Hydrodynamical simulations can reproduce such a top-heavy IMF if the raw material of star formation, the dense molecular gas, is assumed to have a kinetic temperature of ˜ 100 K. Such a molecular gas phase is not observed in the dense cores in the Galactic plane, but may be present in active environments like the cores of starburst galaxies or near AGN. Unfortunately, the kinetic temperature of the molecular gas in many external galaxies is not well constrained, because many of the most common extragalactic tracer molecules suffer from a degeneracy between the kinetic temperature and the gas density in a non-LTE line ratio analysis. We demonstrate the diagnostic power of a selected set of para-formaldehyde lines as tracers of the kinetic temperature as well as the gas density in external galaxies using our non-LTE radiative transfer model. With this new observational tool, we have engaged in characterizing the properties of the dense molecular gas phase in a number of nearby starburst galaxies and near AGN. Our first results suggest the existence of a dense molecular gas phase that is significantly warmer than the dust and much warmer than dense molecular gas found in the Milky Way disk.

Muhle, S.; Henkel, C.; de Maio, T.; Seaquist, E. R.

2011-05-01

238

Understanding the star-forming environment in stellar clusters  

NASA Astrophysics Data System (ADS)

The main goal of this thesis is to investigate the physical conditions of the star-forming environment in stellar clusters, especially for the formation of low-mass cluster members. Embedded, young, and intermediate-mass stellar clusters around Herbig Ae/Be stars are sampled. Mid- and near-infrared observations identifying young stars and millimeter interferometric observations probing dense molecular gas and dust continuum are presented. These observations are used to reveal the large-scale young stellar population around the vicinity where the sampled clusters form, probe the physical conditions of dense molecular clumps which are capable of forming individual low-mass cluster members, and examine the influence of the most massive star in the cluster on its siblings and natal cluster-forming cloud. This study shows that stars within the cluster tend to seem younger than those outside the cluster, suggesting a higher and continuous star-forming rate within the cluster than outside, or massive stars are initiated later than low-mass stars within the same cloud. A thorough investigation of young stars and dense gas toward the MWC 1080 cluster further suggests a domination of the most massive star in the cluster on both the natal cloud dispersal and its low-mass cluster members. As active outflows and winds from the Herbig Ae/Be stars increase the non-thermal motion in the cloud, low-mass cluster members are formed within denser and more turbulent cores, than isolated low-mass star-forming cores. In addition, the strong gas dispersal from the Herbig Ae/Be stars also helps the removal of the circumstellar material around nearby low-mass stars. This makes these low-mass cluster members appear older. In summary, this thesis provides the observational evidence showing how the most massive star in the cluster affects the formation and evolution of low-mass cluster members and the physical conditions of star formation in the cluster.

Wang, Shiya

239

Construction of polymer-protein bioconjugates with varying chain topologies: polymer molecular weight and steric hindrance effects.  

PubMed

We report on the fabrication of well-defined polymer-protein bioconjugates with varying chain architectures, including star polymers, star block copolymers, and heteroarm star copolymers through the specific noncovalent interaction between avidin and biotinylated synthetic polymer precursors. Homopolymer and diblock precursors site-specifically labeled with a single biotin moiety at the chain terminal, chain middle, or diblock junction point were synthesized by a combination of atom-transfer radical polymerization (ATRP) and click reactions. By taking advantage of molecular recognition between avidin and biotin moieties, supramolecular star polymers, star block copolymers, and heteroarm star copolymers were successfully fabricated. This specific binding process was also assessed by using the diffraction optic technology (DOT) technique. We further investigated the effects of polymer molecular weights, location of biotin functionality within the polymer chain, and polymer chain conformations, that is, steric hindrance effects, on the binding numbers of biotinylated polymer chains per avidin within the polymer-protein bioconjugates, which were determined by the standard avidin/2-(4-hydroxyazobenzene)benzoic acid (HABA) assay. The binding numbers vary in the range of 1.9-3.3, depending on the molecular weights, locations of biotin functionality within synthetic polymer precursors, and polymer chain conformations. PMID:21898840

Wan, Xuejuan; Zhang, Guoying; Ge, Zhishen; Narain, Ravin; Liu, Shiyong

2011-09-02

240

SUPER STAR CLUSTERS VERSUS OB ASSOCIATIONS  

SciTech Connect

Super star clusters (M{sub ecl} > 10{sup 5} M{sub sun}) are the largest stellar nurseries in our local Universe, containing hundreds of thousands to millions of young stars within a few light years. Many of these systems are found in external galaxies, especially in pairs of interacting galaxies, and in some dwarf galaxies, but relatively few in disk galaxies like our own Milky Way. We show that a possible explanation for this difference is the presence of shear in normal spiral galaxies which impedes the formation of the very large and dense super star clusters but prefers the formation of loose OB associations possibly with a less massive cluster at the center. In contrast, in interacting galaxies and in dwarf galaxies, regions can collapse without having a large-scale sense of rotation. This lack of rotational support allows the giant clouds of gas and stars to concentrate into a single, dense, and gravitationally bound system.

Weidner, Carsten; Bonnell, Ian A. [Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Zinnecker, Hans, E-mail: cw60@st-andrews.ac.u, E-mail: iab1@st-andrews.ac.u, E-mail: hzinnecker@aip.d [Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)

2010-12-01

241

High mass stars: starbursts  

NASA Astrophysics Data System (ADS)

Starbursts are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. Starbursts are bright at ultraviolet (UV) wavelengths, and after the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues: a) The determination of the initial mass function in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments. b) The modes of star formation: Starburst clusters are an important mode of star formation. c) The role of starbursts in AGN. d) The interaction between massive stars and the interstellar and intergalactic media. e) The contribution of starbursts to the reionization of the universe. Despite the very significant progress obtained over the past two decades of UV observations of starbursts, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. Thus, a new UV mission furnished with an intermediate spectral resolution long-slit spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.

González Delgado, R. M.

2006-08-01

242

Magnetosonic shock waves in dense astrophysical electron-positron-ion plasmas  

NASA Astrophysics Data System (ADS)

Multifluid quantum magnetohydrodynamic model (QMHD) is used to investigate small but finite amplitude magnetosonic shock waves in dense) electron-positron-ion (e-p-i) plasmas. The Korteweg-de Vries-Burgers (KdVB) equation is derived by using reductive perturbation method. It is noticed that variations in the positron density modify the profile of magnetosonic shocks in dense e-p-i plasmas significantly. The numerical results are also presented by taking into account the dense plasma parameters from published literature of astrophysical conditions, in compact stars.

Hussain, S.; Mahmood, S.; Pasqua, A.

2013-11-01

243

Polymer Energy Rechargeable System Battery Being Developed.  

National Technical Information Service (NTIS)

Long description. Illustrations of discotic liquid crystals, rod-coil polymers, lithium-ion conducting channel dilithium phthalocyanine (Li2Pc) from top and side, novel star polyethylene oxide structures, composite polyethylene oxide materials (showing po...

M. A. Manzo

2003-01-01

244

From Nuclei to Neutron Stars  

NASA Astrophysics Data System (ADS)

I will describe recent theoretical advances in nuclear structure and nuclear astrophysics that have been instrumental in unraveling the connections between nuclear physics and astrophysics. The role of nuclei, neutrino processes, and the states of matter at extreme density, in nucleosynthesis, supernova explosions and neutron star phenomena are not only known to be important, but we now understand specific correlations between the underlying nuclear physics and astrophysical observations. These developments are impacting and benefiting from both terrestrial nuclear experiments and astrophysical observations. I will discuss this interplay and explore how this synergy will help forge the path forward to develop a quantitative theory for dense systems, from nuclei to neutron stars. I highlight advances in describing strongly coupled many-body systems and discuss the emerging connections between nuclear structure, dense matter and cold-atom physics.

Reddy, Sanjay

2007-10-01

245

Jet-Induced Star Formation  

SciTech Connect

Jets from radio galaxies can have dramatic effects on the medium through which they propagate. We review observational evidence for jet-induced star formation in low ('FR-I') and high ('FR-II') luminosity radio galaxies, at low and high redshifts respectively. We then discuss numerical simulations which are aimed to explain a jet-induced starburst ('Minkowski's Object') in the nearby FR-I type radio galaxy NGC 541. We conclude that jets can induce star formation in moderately dense (10 cm{sup -3}), warm (10{sup 4} K) gas; that this may be more common in the dense environments of forming, active galaxies; and that this may provide a mechanism for 'positive' feedback from AGN in the galaxy formation process.

van Breugel, W; Fragile, C; Anninos, P; Murray, S

2003-12-16

246

Variable stars  

SciTech Connect

This book covers the following topics: pulsating variables; eruptive variables; eclipsing stars; supplement to the classification; the discovery of variable stars; the significance of variable stars for research on the structure of the galaxy and stellar evolution; and observational methods and organizations.

Hoffmeister, C.; Richter, G.; Wenzel, W.

1985-01-01

247

Stellar Wind Disruption by an Orbiting Neutron Star: Neutron Star Close-up  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. The large scale structure seen in the accretion wake is powered by the release of gravitational potential energy near the surface of the neutron star. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

248

Probing the interiors of accreting neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars in low mass X-ray binaries accrete hydrogen and helium from a low mass companion. The neutron star can be observed directly in X-rays during periods of quiescence, when accretion switches off, or during thermonuclear X-ray bursts which result from unstable thermonuclear burning of the accreted matter. Recent long term monitoring observations of these systems have revealed new types of long duration X-ray bursts resulting from unstable burning of thick helium or carbon layers. The properties of these long bursts are sensitive to the heat flux emerging from deep in the star, and therefore give a new way to probe neutron star cooling. I discuss the current constraints on the neutrino emissivity of the stellar core, and the dense matter interior, including the possibility that these stars are in fact strange stars.

Cumming, Andrew

2006-10-01

249

Molecular cloud evolution and star formation  

NASA Astrophysics Data System (ADS)

The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

Silk, J.

250

Nuclear Physics for Compact Stars  

SciTech Connect

A brief overview is given of the different lines of research developed under the INFN project 'Compact Stellar Objects and Dense Hadronic Matter' (acronym CT51). The emphasis of the project is on the structure of Neutron Stars (NS) and related objects. Starting from crust, the different Nuclear Physics problems are described which are encountered going inside a NS down to its inner core. The theoretical challenges and the observational inputs are discussed in some detail.

Baldo, M. [INFN, Sez. Catania, Via S. Sofia 64, 95123 Catania (Italy)

2009-05-04

251

The Circumstellar Environment of Embedded Massive Stars  

NASA Astrophysics Data System (ADS)

Millimeter and submillimeter wavelength images of massive star-forming regions are revealing the morphologies of the natal material and the complexity of circumstellar environments on size scales from parsecs to 100's of AU. Massive stars appear to be gregarious siblings with regions at different evolutionary stages located within parsecs of each other. Often, different evolutionary stages even co-exist within an overall extended core. Current observational goals include the characterization of an early evolutionary sequence for massive stars, determination if the basic accretion process for massive stars is similar to, or different from, that of low-mass stars, and understanding of the significance of triggered or induced modes of massive star formation. Observations are beginning to make significant progress in many of these areas. Works identifying and characterizing the earliest stages of massive stars are producing a list of candidate sources. More detailed studies of dense warm cores and dense hot cores are refining our understanding of the nature of these regions. Chemical studies of these cores are helping to probe the energetics. Continuuing work over the next few years should provide a good templete for massive star formation and an understanding of their role in cluster formation.

Mundy, Lee G.; et al.

252

What triggers star formation in galaxies?  

NASA Astrophysics Data System (ADS)

Processes that promote the formation of dense cold clouds in the interstellar media of galaxies are reviewed. Those that involve background stellar mass include two-fluid instabilities, spiral density wave shocking, and bar accretion. Young stellar pressures trigger gas accumulation on the periphery of cleared cavities, which often take the form of rings by the time new stars form. Stellar pressures also trigger star formation in bright-rim structures, directly squeezing the pre-existing clumps in nearby clouds and clearing out the lower density gas between them. Observations of these processes are common. How they fit into the empirical star formation laws, which relate the star formation rate primarily to the gas density, is unclear. Most likely, star formation follows directly from the formation of cold dense gas, whatever the origin of that gas. If the average pressure from the weight of the gas layer is large enough to produce a high molecular fraction in the ambient medium, then star formation should follow from a variety of processes that combine and lose their distinctive origins. Pressurized triggering might have more influence on the star formation rate in regions with low average molecular fraction. This implies, for example, that the arm/interarm ratio of star formation efficiency should be higher in the outer regions of galaxies than in the main disks.

Elmegreen, Bruce G.

2012-08-01

253

Surface segregation of conformationally asymmetric polymer blends  

NASA Astrophysics Data System (ADS)

We have generalized the Edwards’ method of collective description of dense polymer systems in terms of effective potentials to polymer blends in the presence of a surface. With this method we have studied conformationally asymmetric athermic polymer blends in the presence of a hard wall to the first order in effective potentials. For polymers with the same gyration radius Rg but different statistical segment lengths lA and lB the excess concentration of stiffer polymers at the surface is derived as ??A(z=0)˜(lB-2-lA-2)ln(Rg2/lc2) , where lc is a local length below of which the incompressibility of the polymer blend is violated. For polymer blends differing only in degrees of polymerization the shorter polymer enriches the wall.

Stepanow, Semjon; Fedorenko, Andrei A.

2006-03-01

254

Surface segregation of conformationally asymmetric polymer blends.  

PubMed

We have generalized the Edwards' method of collective description of dense polymer systems in terms of effective potentials to polymer blends in the presence of a surface. With this method we have studied conformationally asymmetric athermic polymer blends in the presence of a hard wall to the first order in effective potentials. For polymers with the same gyration radius Rg but different statistical segment lengths lA and lB the excess concentration of stiffer polymers at the surface is derived as delta rho A(z=0) approximately (lB-2 - lA-2)ln(R2g/l2c), where lc is a local length below of which the incompressibility of the polymer blend is violated. For polymer blends differing only in degrees of polymerization the shorter polymer enriches the wall. PMID:16605548

Stepanow, Semjon; Fedorenko, Andrei A

2006-03-02

255

The Star Clustering Algorithm for Static and Dynamic Information Organization  

Microsoft Academic Search

Abstract We present and analyze the o - line star algorithm for clustering static information systems and the on - line star algorithm for clustering dynamic information systems These algorithms organize a document collection into a number of clusters that is naturally induced by the collection via a computationally e cient cover by dense subgraphs We further show a lower

Javed A. Aslam; Ekaterina Pelekhov; Daniela Rus

2004-01-01

256

Compact Stars. Nuclear Physics, Particle Physics and General Relativity.  

NASA Astrophysics Data System (ADS)

Neutron stars are the smallest denses stars known, with densities some 1014 times that of the Earth. They rotate with periods of fractions of a second, and their magnetic fields drive intense interstellar dynamos, lighting up entire nebulae. This text discusses the physics of these extreme objects. It includes the needed background in classical general relativity in nuclear and particle physics.

Glendenning, Norman

257

Star formation activity in cores within infrared dark clouds  

Microsoft Academic Search

In this dissertation, I probe the star formation activity of cores within infrared dark clouds (IRDCs). IRDCs are identified as extinction features against the bright Galactic plane at infrared wavelengths. They are dense, cold, and massive, conditions expected for clouds that host the elusive earliest stages of high-mass star formation. A sample of 38 IRDCs was mapped in 1.2 mm

Edward T. Chambers

2010-01-01

258

Universal version of density-functional theory for polymers with complex architecture  

Microsoft Academic Search

We propose a density-functional theory for inhomogeneous polyatomic fluids with complex architecture by introducing a different representation for the polymers. This representation gives an efficient hierarchical algorithm to calculate the direct bonding connectivity integral for polymers with complex architecture, such as linear, star, branched, and dendritic structures. A comparison with the available simulated data for linear and star polymers confirms

Xiaofei Xu; Dapeng Cao; Xianren Zhang; Wenchuan Wang

2009-01-01

259

The contagion of star-formation: its origin  

NASA Astrophysics Data System (ADS)

Dense pockets of cold, molecular gas preclude the formation of stars. During their infancy and later phases of evolution, stars inject considerable energy into the interstellar medium by driving shocks either due to ionising radiation or powerful winds. Interstellar shock-waves sweep up dense shells of gas that usually propagate at supersonic velocities. It is proposed, in this paper, to examine the possibility of dense structure-formation and perchance, future stellar wombs, in a molecular cloud shocked by such a shell. Here I shall discuss results of a self-gravitating, 3-dimensional, high-resolution simulation using the smoothed particle hydrodynamics.

Anathpindika, S.

260

The Loss-Cone Problem in Dense Nuclei Revisited  

NASA Astrophysics Data System (ADS)

This is the start-up of a project revisiting the star-gas interactions in young, dense galactic nuclei. Here we present some semi-analytic results following ideas given originally by Frank & Rees (1976), Vil'koviski (1976), Hara (1978), Langbein et al. (1990), and references therein. The heating rate of an assumed supermassive central gas-star object due to loss-cone stars, plunging onto it on elongated orbits from outside is calculated taking into account a possible anisotropy of the surrounding stellar distribution. We discuss for a range of central masses the rate of stars on such loss-cone orbits and their heating effect. Here we assume a simplified model of a galactic nucleus consisting of a Plummer model with an embedded density cusp, using stellar point masses. We plan to extend this investigation to numerical studies, allowing a wider range of possible stellar distribution functions and to take into account gas production by stellar collisions and star formation. A more detailed understanding of that early evolutionary phase of galactic nuclei from basic principles is one of the key features presently missing for the link between cosmology and galaxy formation. References: Frank J., Rees M.J., 1976, MNRAS, 176, 633. Hara T., 1978, Prog. Theor. Phys., 60, 711. Langbein, T., Spurzem, R., Fricke, K.J, Yorke, H.W., 1990, A&A, 227, 333. Vil'koviski E., 1976, Sov. Astr. Lett., 1, 137.

Amaro-Seoane, Pau; Spurzem, Rainer

261

Dense detector for baryon decay  

SciTech Connect

Our studies indicate that the dense detector represents a potentially powerful means to search for baryon decay and to study this process, if it occurs. The detector has good angular resolution and particle identification properties for both showering and non-showering events. Its energy resolution is particularly good for muons, but pion, electron and photon energies can also be measured with resolutions of at least 25 percent (standard deviation). The dense detector has strong logistical advantages over other proposed schemes. These advantages imply not only a lower cost but also faster construction and higher reliability. A particular advantage is that the dense detector can be prototyped in order to optimize its characteristics prior to the construction of a large module. Subsequent modules can also be added easily, while the initial detector continues operation.

Courant, H.; Heller, K.; Marshak, M.L.; Peterson, E.A.; Ruddick, K.; Shupe, M.

1981-01-01

262

Dust, Radiation Pressure, and Star Formation  

Microsoft Academic Search

Spitzer has shown that radiation can produce inverse square law ; attractive forces between absorbing interstellar grains. Whipple and Savedoff ; examined whether these forces could cause dust to flow through ambient gas and ; form dense clouds from which stars would form. Savedoff concluded that ; appreciable concentration of dust was not to be expected and that radiative ;

Martin Harwit

1962-01-01

263

A submillisecond pulsar and the equation of state of dense matter  

Microsoft Academic Search

If the submillisecond pulsar in the remnant of SN 1987A really is rotating stably with a period of 0.508 ms, its existence can be used to rule out nearly all 'realistic' equations of state for dense nuclear matter. A simple equation of state is presented here that yields, in the nonrotating case, maximally compact models of neutron stars, and it

P. Haensel; J. L. Zdunik

1989-01-01

264

Method for dense packing discovery  

NASA Astrophysics Data System (ADS)

The problem of packing a system of particles as densely as possible is foundational in the field of discrete geometry and is a powerful model in the material and biological sciences. As packing problems retreat from the reach of solution by analytic constructions, the importance of an efficient numerical method for conducting de novo (from-scratch) searches for dense packings becomes crucial. In this paper, we use the divide and concur framework to develop a general search method for the solution of periodic constraint problems, and we apply it to the discovery of dense periodic packings. An important feature of the method is the integration of the unit-cell parameters with the other packing variables in the definition of the configuration space. The method we present led to previously reported improvements in the densest-known tetrahedron packing. Here, we use the method to reproduce the densest-known lattice sphere packings and the best-known lattice kissing arrangements in up to 14 and 11 dimensions, respectively, providing numerical evidence for their optimality. For nonspherical particles, we report a dense packing of regular four-dimensional simplices with density ?=128/219?0.5845 and with a similar structure to the densest-known tetrahedron packing.

Kallus, Yoav; Elser, Veit; Gravel, Simon

2010-11-01

265

Metal-polymer composites comprising nanostructures and applications thereof  

SciTech Connect

Metal-polymer composites, and methods of making and use thereof, said composites comprising a thermally-cured dense polyaniline substrate; an acid dopant; and, metal nanostructure deposits wherein the deposits have a morphology dependent upon the acid dopant.

Wang, Hsing-Lin (Los Alamos, NM); Jeon, Sea Ho (Dracut, MA); Mack, Nathan H. (Los Alamos, NM)

2012-04-03

266

Metal-polymer composites comprising nanostructures and applications thereof  

SciTech Connect

Metal-polymer composites, and methods of making and use thereof, said composites comprising a thermally-cured dense polyaniline substrate; an acid dopant; and, metal nanostructure deposits wherein the deposits have a morphology dependent upon the acid dopant.

Wang, Hsing-Lin (Los Alamos, NM); Jeon, Sea Ho (Dracut, MA); Mack, Nathan H. (Los Alamos, NM)

2011-08-02

267

Symbiotic Stars  

NASA Astrophysics Data System (ADS)

During the production of the Henry Draper Catalog, Wilhemina Fleming identified several M-type stars with unusually strong hydrogen emission lines. Paul Merrill obtained higher quality spectra of these `stars with combination spectra' and found intense emission from He II or [O III] and [Ne III] in addition to H I. All of these stars varied by 0.5-1 mag on a timescale of several years. A few syst...

Kenyon, S.; Murdin, P.

2000-11-01

268

Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, arenât doing much of anything. In this video, Jonathanâs investigations reveal a slow-motion predator that hunts and attacks its prey. Traveling the world, Jonathan investigates sea stars from the tropics to the Antarctic and uses time-lapse photography to reveal an amazing complexity to the world of the sea star. Please see the accompanying study guide for educational objectives and discussion points.

Productions, Jonathan B.

2010-10-06

269

The dense stellar cores of giant H II regions.  

NASA Astrophysics Data System (ADS)

The authors explore the bright central diffuse objects of the closest visible giant H II regions 30 Dor (LMC) and NGC 3603 (Galaxy), with the aid of CCD imagery in 1arcsec seeing. Both cenral objects are interpreted as dense cluster cores composed of normal stars with masses ranging up to ?100 M_sun;. Each object appears to contain at least one close massive binary. Being significantly denser, the core of NGC 3603 seems to be dynamically more evolved than the core of 30 Dor.

Moffat, A. F. J.; Seggewiss, W.; Shara, M. M.

270

Lucky Star  

NSDL National Science Digital Library

Watch this video from Cyberchase and then play the Lucky Star game! The Lucky Star game show the will ask you math-related questions and give you four possible answers to choose from. Your goal is to answer the questions correctly and score as many points as you can. You can score points during two different rounds: the pick-a-star round and the lightning round. During the pick-a-star round you have as much time as you want to answer the questions. During the lightning round you have to think fast in order to earn the points. Good luck!

2008-01-01

271

Telechelic polymers by living and controlled\\/living polymerization methods  

Microsoft Academic Search

Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled\\/living polymerization methods; namely atom transfer radical polymerization, nitroxide

Mehmet Atilla Tasdelen; Muhammet U. Kahveci; Yusuf Yagci

2011-01-01

272

Fusion reactions in multicomponent dense matter  

SciTech Connect

We analyze thermonuclear and pycnonuclear fusion reactions in dense matter containing atomic nuclei of different types. We extend a phenomenological expression for the reaction rate, proposed recently by Gasques et al. [Phys. Rev. C 72, 025806 (2005)] for the one-component plasma of nuclei, to the multicomponent plasma. The expression contains several fit parameters which we adjust to reproduce the best microscopic calculations available in the literature. Furthermore, we show that pycnonuclear burning is drastically affected by an (unknown) structure of the multicomponent matter (a regular lattice, a uniform mix, etc.). We apply the results to study nuclear burning in a {sup 12}C-{sup 16}O mixture. In this context, we present new calculations of the astrophysical S factors for carbon-oxygen and oxygen-oxygen fusion reactions. We show that the presence of a C-O lattice can strongly suppress carbon ignition in white dwarf cores and neutron star crusts at densities {rho}(greater-or-similar sign)3x10{sup 9} g cm{sup -3} and temperatures T(less-or-similar sign)10{sup 8} K.

Yakovlev, D. G.; Gasques, L. R.; Afanasjev, A. V.; Beard, M.; Wiescher, M. [Ioffe Physico-Technical Institute, Poliekhnicheskaya 26, RU-194021 Saint Petersburg, Russia and Department of Physics and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Department of Physics and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Department of Physics and Astronomy, Mississippi State University, P.O. Drawer 5167, Mississippi 39762-5167 (United States); Department of Physics and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2006-09-15

273

Magnetar oscillations pose challenges for strange stars  

NASA Astrophysics Data System (ADS)

Compact relativistic stars allow us to study the nature of matter under extreme conditions, probing regions of parameter space that are otherwise inaccessible. Nuclear theory in this regime is not well constrained: one key issue is whether neutron stars are in fact composed primarily of strange quark matter. Distinguishing the two possibilities, however, has been difficult. The recent detection of seismic vibrations in the aftermath of giant flares from two magnetars (highly magnetized compact stars) is a major breakthrough. The oscillations excited seem likely to involve the stellar crust, the properties of which differ dramatically for strange stars. We show that the resulting mode frequencies cannot be reconciled with the observations for reasonable magnetar parameters. Ruling out strange star models would place a strong constraint on models of dense quark matter.

Watts, Anna L.; Reddy, Sanjay

2007-07-01

274

Infrared and optical imaging of newborn stars  

SciTech Connect

Deep optical and near-infrared imaging observations of five low- to intermediate-luminosity pre-main-sequence stars embedded within dense cores reveal an extended emission component. Four of the five stars were previously identified as outflow sources. Nebulosity is detected with the optical and J and H bandpasses for each source. The large measured polarization values (p = 10 to 70 percent) at H and K identify the nebulosity as scattered light. At K the intensity distribution is generally less extended than at J and H, and is characterized by an additional, unresolved component. The position of this point source likely identifies the location of the newborn star within the field. For all sources, the illuminating star is redder than its associated nebula. The observed correlation of cometary reflection nebulae with newborn stars undergoing mass outflow suggests that the low-opacity paths are cavities associated with energetic stellar winds. 35 refs.

Heyer, M.H.; Ladd, E.F.; Myers, P.C.; Campbell, B. (Carnegie Institution of Washington, Washington, DC (USA) Harvard Univ., Cambridge, MA (USA) Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA) New Mexico Univ., Albuquerque (USA))

1990-05-01

275

H? emitters in z˜ 2 protoclusters: evidence for faster evolution in dense environments  

NASA Astrophysics Data System (ADS)

This is a study of H? emitters in two dense galaxy protoclusters surrounding radio galaxies at z˜ 2. We show that the protocluster surrounding MRC 1138-262 contains 14 ± 2 times more H? candidates than the average field (9? significance), and the z= 2.35 radio galaxy 4C +10.48 is surrounded by 12 ± 2 times more emitters than the field (5?), so it is also likely to reside in a dense protocluster environment. We compared these H? emitters, situated in dense environments, to a control field sample selected from three separate fields forming a total area of 172 arcmin2. We constructed and compared H? and rest-frame R continuum luminosity functions of the emitters in both environments. The star formation density is on average 13 times greater in the protoclusters than the field at z˜ 2, so the total star formation rate within the central 1.5 Mpc of the protoclusters exceeds 3000 M? yr-1. However, we found no significant difference in the shape of the H? luminosity functions, implying that environment does not substantially affect the strength of the H? line from strongly star-forming galaxies. The protocluster emitters are typically 0.8 mag brighter in rest-frame R continuum than field emitters, implying they are twice as massive as their field counterparts at the same redshift. We also show the protocluster galaxies have lower specific star formation rates than field galaxies, meaning the emitters in the dense environments formed more of their stars earlier than the field galaxies. We conclude that galaxy growth in the early Universe was accelerated in dense environments, and that cluster galaxies differed from field galaxies even before the cluster had fully formed.

Hatch, N. A.; Kurk, J. D.; Pentericci, L.; Venemans, B. P.; Kuiper, E.; Miley, G. K.; Röttgering, H. J. A.

2011-08-01

276

Star Images, Star Performances (College Course File).  

ERIC Educational Resources Information Center

|Describes a course that focuses attention on the position of the actor, especially the star actor, in cinematic and television signification. Divides the course into three sections: "The Star System,""Stars as Images," and "Star Performance." (RS)|

Butler, Jeremy G.

1990-01-01

277

Superfluidity in dense nuclear matter  

SciTech Connect

We discuss the onset of superfluidity in neutron stars, where the model of nuclear matter is realized in a high-density and asymmetry state. In particular, we present the study of the effects of microscopic three-body forces on the proton pairing in the {sup 1}S{sub 0} channel and neutron pairing in {sup 3}PF{sub 1} channel for {beta}-stable neutron star matter. It is found that the main effects of three-body forces are to shrink the domain of existence of the {sup 1}S{sub 0} below the threshold of the direct URCA process and to stretch the density range of the {sup 3}PF{sub 1} pairing in a broad domain so to cover most part of the neutron-star core.

Zuo, W. [Chinese Academy of Science, Institute of Modern Physics (China); Lombardo, U., E-mail: lombardo@ct.infn.i [Universita di Catania, Dipartimento di Fisica e Astronomia (Italy)

2009-08-15

278

Rogue Star  

NSDL National Science Digital Library

This program calculates and depicts the effects of a rogue star coming through our solar system. Users adjust the date, the rogue star's mass, approach distance in astronomical units (AU) and flyby speed to run an animation of what would happen to the planets under the specified conditions.

Hamilton, Douglas

279

Star Journey  

NSDL National Science Digital Library

This National Geographic web-site contains information about the Hubble Space Telescope (HST) along with a star chart and facts about objects in the night sky. The HST section contains details about the building and structure of the HST, how it captures light, positioning the HST to targets, instruments used to record and measure infrared through UV wavelengths, how the HST is powered and communicates with the Earth. Star Attractions discusses properties of constellations, the Milky Way galaxy, other galaxies, star clusters and nebulae. This information is then put together on the National Geographic Star Chart. This chart contains maps of the heavens for the northern and southern hemispheres. The chart contains constellation names, location of stars and other objects, and links to HST images of various galaxies and objects on the chart with names and detailed descriptions. There is an image index to find HST images from the site, details about chart symbol meanings, and links for more information.

Anderson, Carolyn

280

Nuclear fusion in dense plasmas  

Microsoft Academic Search

The review begins by grouping the fundamental nuclear reactions into two classifications, namely, the usual binary processes and few-particle processes. In the few-particle processes, the possibility of electron-screened cold fusion is remarked. The special features of dense plasmas rest in the enhancement of reaction rates over these fundamental processes due to internuclear many-particle processes. The manyparticle processes arise from a

Setsuo Ichimaru

1993-01-01

281

Dense, finely, grained composite materials  

DOEpatents

Dense, finely grained composite materials comprising one or more ceramic phase or phase and one or more metallic and/or intermetallic phase or phases are produced by combustion synthesis. Spherical ceramic grains are homogeneously dispersed within the matrix. Methods are provided, which include the step of applying mechanical pressure during or immediately after ignition, by which the microstructures in the resulting composites can be controllably selected.

Dunmead, Stephen D. (Davis, CA); Holt, Joseph B. (San Jose, CA); Kingman, Donald D. (Danville, CA); Munir, Zuhair A. (Davis, CA)

1990-01-01

282

Dense, finely grained composite materials  

DOEpatents

Dense, finely grained composite materials comprising one or more ceramic phase or phase and one or more metallic and/or intermetallic phase or phases are produced by combustion synthesis. Spherical ceramic grains are homogeneously dispersed within the matrix. Methods are provided, which include the step of applying mechanical pressure during or immediately after ignition, by which the microstructures in the resulting composites can be controllably selected. 10 figs.

Dunmead, S.D.; Holt, J.B.; Kingman, D.D.; Munir, Z.A.

1988-10-21

283

Dilepton Measurements at STAR  

NASA Astrophysics Data System (ADS)

In the study of hot and dense nuclear matter, created in relativistic heavy-ion collisions, dilepton measurements play an essential role. Leptons, when compared to hadrons, have only little interaction with the strongly interacting system. Thus, dileptons provide ideal penetrating probes that allow the study of such a system throughout its space-time evolution. In the low mass range (Mll < 1.1 GeV/c2), the dominant source of dileptons originates from the decay of vector mesons which may see effects from chiral symmetry restoration. In the intermediate mass range (1.1 < Mll < 3.0 GeV/c2), the main contributions to the mass spectrum are expected to originate from the thermal radiation of a quark-gluon plasma as well as the decays of charm mesons. In the high mass range (Mll > 3.0 GeV/c2), dilepton measurements are expected to see contributions from primordial processes involving heavy quarks, and Drell-Yan production. With the introduction of the Time-of-Flight detector, the STAR detector has been able to perform large acceptance, high purity electron identification. In this contribution, we will present STAR's recent dielectron measurements in the low and intermediate mass range for RHIC beam energies ranging between 19.6 and 200 GeV. Compared to electrons, muon measurements have the advantage of reduced bremsstrahlung radiation in the surrounding detector materials. With the upcoming detector upgrades, specifically the muon detector (MTD), STAR will be able to include such measurements in its (di-)lepton studies. We will discuss the future dilepton program at STAR and the physics cases for these upgrades.

Geurts, Frank; STAR Collaboration

2013-08-01

284

Dense water formation around islands  

NASA Astrophysics Data System (ADS)

Basic constraints on the dense water formation rate and circulation resulting from cooling around an island are discussed. The domain under consideration consists of an island surrounded by a shelf, a continental slope, and a stratified ocean. Atmospheric cooling over the shelf forms a dense water that penetrates down the sloping bottom into the stratified basin. Strong azimuthal flows are generated over the sloping bottom as a result of thermal wind. Thermally direct and indirect mean overturning cells are also forced over the slope as a result of bands of convergent and divergent Reynolds stresses associated with the jets. The Coriolis force associated with the net mass flux into the downwelling region over the slope is balanced by these nonlinear terms, giving rise to a fundamentally different momentum budget than arises in semienclosed marginal seas subject to cooling. A similar momentum balance is found for cases with canyons and ridges around the island provided that the terms are considered in a coordinate system that follows the topography. Both eddy fluxes and the mean overturning cells are important for the radial heat flux, although the eddy fluxes typically dominate. The properties of the dense water formed over the shelf (temperature, diapycnal mass flux) are predicted well by application of baroclinic instability theory and simple heat and mass budgets. It is shown that each of these quantities depends only on a nondimensional number derived from environmental parameters such as the shelf depth, Coriolis parameter, offshore temperature field, and atmospheric forcing.

Spall, Michael A.

2013-05-01

285

Probing the Onset of Dust Coagulation in Dense Clouds  

NASA Astrophysics Data System (ADS)

Our previous Spitzer IRS observations have confirmed the striking break-down of the diffuse ISM linear correlation of the depth of the 9.7 mic silicate absorption feature (tau(9.7)) with near-IR color excess (E(J-Ks)) at high extinctions in dense clouds. In addition, the observed shape of the 9.7 mic band changes between dense clouds and the diffuse ISM. Theoretically, these variations have been attributed to the effect of grain growth by coagulation on the extinction properties of interstellar dust, but the conditions responsible for grain coagulation in dense clouds is not well understood. The new observations we propose here in combination with already existing deep IR extinction maps, provide us with a new and unique opportunity to directly probe the onset of dust coagulation and the change in the physical properties of the dust in the environment of a single nearby dense cloud: the Pipe Nebula. The goals of our proposal are: - We will measure the change in tau(9.7) as a function of near-IR extinction and density in dense cloud cores and the surrounding lower-density intercore material. - We will analyze the 9.7 mic profile shape, to observationally determine under what conditions deviations from the diffuse ISM feature become apparent. - We will establish, observationally, the interrelationship between the flattening of the tau(9.7)/E(J-Ks) relation and the change in shape of the silicate profile. Our lines of sight span a wide range of accurately determined (IR) extinctions (Av ~ 5 to 48 mag). We will accomplish our above goals by obtaining high S/N IRS observations of a well-chosen sample of background stars behind the Pipe Nebula and two of its most opaque dense cores. The source list ensures that the extinction range is well-sampled spatially and in terms of extinction value inside the cloud cores and the surrounding intercore material. In this way, we will be able to observe changes in the dust properties as they occur within a single dense cloud.

Chiar, Jean; Lada, Charles; Min, Michiel; Pendleton, Yvonne; Roman-Zuniga, Carlos; Tappe, Achim; Tielens, Alexander; Waters, Laurens; Whittet, Douglas; van Breemen, Johanna

2008-03-01

286

Nuclear fusion in dense matter: Reaction rate and carbon burning  

NASA Astrophysics Data System (ADS)

In this paper we analyze the nuclear fusion rates among equal nuclei for all five different nuclear burning regimes in dense matter (two thermonuclear regimes, two pycnonuclear ones, and the intermediate regime). The rate is determined by Coulomb barrier penetration in dense environments and by the astrophysical S factor at low energies. We evaluate previous studies of the Coulomb barrier problem and propose a simple phenomenological formula for the reaction rate that covers all cases. The parameters of this formula can be varied to take into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the 12C+12C fusion reaction. This reaction is important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovas, and in accreting neutron stars. The S factor at stellar energies depends on a reliable fit and extrapolation of the experimental data. We calculate the energy dependence of the S factor by using a recently developed parameter-free model for the nuclear interaction, taking into account the effects of the Pauli nonlocality. For illustration, we analyze the efficiency of carbon burning in a wide range of densities and temperatures of stellar matter with the emphasis on carbon ignition at densities ??109 g cm-3.

Gasques, L. R.; Afanasjev, A. V.; Aguilera, E. F.; Beard, M.; Chamon, L. C.; Ring, P.; Wiescher, M.; Yakovlev, D. G.

2005-08-01

287

A survey for dense cores in dark clouds  

SciTech Connect

A total of 149 dark cloud positions were surveyed for evidence of dense cores in the (J,K) = (1,1) rotating inversion line of NH3. Clouds with strong emission were mapped to determine the position of the core, and maps of 41 cores are presented. The spectrum of the peak emission is fitted by least-squares analysis to determine the optical depth, velocity, intrinsic line width, and excitation temperature. Statistical equilibrium analysis is used to determine the density of the core and the kinetic temperature when possible. Most of the dense cores have temperatures of 10-15 K, densities of 2000-20,000/cu cm, and intrinsic linewidths of 0.2-0.9 km/s. The core masses range from about 0.5 solar in L1517B to 760 solar in L1031B, and their sizes range from 0.06 to 0.9 pc. The cores are not generally spherically shaped, wtih aspect ratios ranging from 1.1 to 4 4. Cores with stars have broader lines than cores without stars. 74 refs.

Benson, P.J.; Myers, P.C. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA))

1989-09-01

288

Nuclear fusion in dense matter: Reaction rate and carbon burning  

SciTech Connect

In this paper we analyze the nuclear fusion rates among equal nuclei for all five different nuclear burning regimes in dense matter (two thermonuclear regimes, two pycnonuclear ones, and the intermediate regime). The rate is determined by Coulomb barrier penetration in dense environments and by the astrophysical S factor at low energies. We evaluate previous studies of the Coulomb barrier problem and propose a simple phenomenological formula for the reaction rate that covers all cases. The parameters of this formula can be varied to take into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the {sup 12}C+{sup 12}C fusion reaction. This reaction is important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovas, and in accreting neutron stars. The S factor at stellar energies depends on a reliable fit and extrapolation of the experimental data. We calculate the energy dependence of the S factor by using a recently developed parameter-free model for the nuclear interaction, taking into account the effects of the Pauli nonlocality. For illustration, we analyze the efficiency of carbon burning in a wide range of densities and temperatures of stellar matter with the emphasis on carbon ignition at densities {rho} > or approx. 10{sup 9} g cm{sup -3}.

Gasques, L.R.; Afanasjev, A.V.; Beard, M.; Wiescher, M. [Department of Physics and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Aguilera, E.F. [Departamento del Accelerador, Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, C.P. 11801, Destrito Federal (Mexico); Chamon, L.C. [Departamento de Fisica Nuclear, Instituto de Fisica da Universidade de Sao Paulo, Caixa Postal 66318, 05315-970, Sao Paulo, SP (Brazil); Ring, P. [Physik-Department, Technische Universitat Muenchen, D-85747, Garching (Germany); Yakovlev, D.G. [Ioffe Physical Technical Institute, Poliekhnicheskaya 26, RU-194021 St. Petersburg (Russian Federation)

2005-08-01

289

Shear viscosity in hybrid stars  

NASA Astrophysics Data System (ADS)

A study of the shear viscosity of hadrons and quarks in hybrid stars has been performed in the framework of the microscopic transport theory. The neutron-star structure has been determined employing the equation of state from the Brueckner theory with three-body force for the hadron phase, and the equation of state from the MIT bag model for the deconfined quark phase. The nucleon-nucleon cross sections in dense matter have been consistently calculated from the Brueckner G matrix, whereas for the quark-quark cross sections the perturbative QCD has been adopted. Despite that the quark contribution to the shear viscosity is quite small at low temperature, the transition to the deconfined phase makes the equation of state much softer with the result that the baryon viscosity turns out to be enhanced instead of reduced in hybrid stars. The damping time scale of r-modes due to the shear viscosity has been evaluated for several stable configurations of a hybrid star and compared with the neutron-star spin-down time scale induced by the emission gravitation radiation from the r-modes. The enhancement of the total viscosity makes the viscosity time scale comparable with the gravitation radiation one at low temperature.

Jaccarino, D.; Plumari, S.; Greco, V.; Lombardo, U.; Santra, A. B.

2012-05-01

290

COLLAPSE OF MASSIVE MAGNETIZED DENSE CORES USING RADIATION MAGNETOHYDRODYNAMICS: EARLY FRAGMENTATION INHIBITION  

SciTech Connect

We report the results of radiation-magnetohydrodynamics calculations in the context of high-mass star formation, using for the first time a self-consistent model for photon emission (i.e., via thermal emission and in radiative shocks) and with the high resolution necessary to properly resolve magnetic braking effects and radiative shocks on scales <100 AU. We investigate the combined effects of magnetic field, turbulence, and radiative transfer on the early phases of the collapse and the fragmentation of massive dense cores. We identify a new mechanism that inhibits initial fragmentation of massive dense cores where magnetic field and radiative transfer interplay. We show that this interplay becomes stronger as the magnetic field strength increases. Magnetic braking is transporting angular momentum outward and is lowering the rotational support and is thus increasing the infall velocity. This enhances the radiative feedback owing to the accretion shock on the first core. We speculate that highly magnetized massive dense cores are good candidates for isolated massive star formation while moderately magnetized massive dense cores are more appropriate forming OB associations or small star clusters.

Commercon, Benoit; Henning, Thomas [Max Planck Institut fur Astronomie, Konigsthul 17, 69117 Heidelberg (Germany); Hennebelle, Patrick, E-mail: benoit@mpia-hd.mpg.de [Laboratoire de radioastronomie, UMR 8112 du CNRS, Ecole normale superieure et Observatoire de Paris, 24 rue L'homond, 75231 Paris Cedex 05 (France)

2011-11-20

291

Type IIn superluminous supernovae from collision of supernova ejecta and dense circumstellar medium  

NASA Astrophysics Data System (ADS)

First stars are suggested to be dominated by massive stars. Some massive stars are now known to die as superluminous supernovae (SLSNe). Especially, Type IIn SLSNe show narrow emission lines which are believed to come from dense circumstellar medium (CSM) and the interaction between SN ejecta and dense CSM is presumed to be the reason for the high luminosity. Thanks to the deceleration of SN ejecta by dense CSM, the kinetic energy of SN ejecta is efficiently converted to thermal energy which is eventually emitted as radiation. We show the results of our LC modeling of Type IIn SLSNe performed by using a one-dimensional multigroup radiation hydrodynamics code STELLA. We show that the LCs of Type IIn SLSNe can be actually explained by the interaction between SN ejecta and dense CSM. In addition, we show that the spectra of Type IIn SLSNe tend to be bluer than other kinds of SNe because of the interaction and future NIR satellites like JWST or WISH can potentially detect Type IIn SLSNe appeared at z=10 or higher.

Moriya, T. J.; Blinnikov, S. I.; Tominaga, N.; Yoshida, N.; Tanaka, M.; Maeda, K.; Nomoto, K.

2012-09-01

292

Chandra Reveals Nest of Tight Binaries in Dense Cluster  

NASA Astrophysics Data System (ADS)

Scientists have gazed into an incredibly dense star cluster with NASA's Chandra X-ray Observatory and identified a surprising bonanza of binary stars, including a large number of rapidly rotating neutron stars. The discovery may help explain how one of the oldest structures in our Galaxy evolved over its lifetime. By combining Chandra, Hubble Space Telescope, and ground-based radio data, the researchers conducted an important survey of the binary systems that dominate the dynamics of 47 Tucanae, a globular cluster about 12 billion years old located in our Milky Way galaxy. Most of the binaries in 47 Tucanae are systems in which a normal, Sun-like companion orbits a collapsed star, either a white dwarf or a neutron star. White dwarf stars are dense, burnt-out remnants of stars like the Sun, while neutron stars are even denser remains of a more massive star. When matter from a nearby star falls onto either a white dwarf or a neutron star, as in the case with the binaries in 47 Tucanae, X-rays are produced. 47 Tuc This composite image shows relation of the Chandra image of 47 Tucanae to ground-based, optical observations. "This Chandra image provides the first complete census of compact binaries in the core of a globular cluster," said Josh Grindlay of the Harvard-Smithsonian Center for Astrophysics (CfA) and lead author of the report that appears in the May 18 issue of Science. "The relative number of neutron stars versus white dwarfs in these binaries tell us about the development of the first stars in the cluster, and the binaries themselves are key to the evolution of the entire cluster core." Many of the binaries in 47 Tucanae are exotic systems never before seen in such large quantities. Perhaps the most intriguing are the "millisecond pulsars", which contain neutron stars that are rotating extremely rapidly, between 100 to nearly 1000 times a second. "The Chandra data, in conjunction with radio observations, indicate that there are many more millisecond pulsars than we would expect based on the number of their likely progenitors we found," said co-author Peter Edmonds, also of the CfA. "While there is a general consensus on how some of the millisecond pulsars form, these new data suggest that there need to be other methods to create them." In addition to the millisecond pulsars, Chandra also detected other important populations of binary systems, including those with white dwarf stars and normal stars, and others where pairs of normal stars undergo large flares induced by their close proximity. The Chandra data also indicate an apparent absence of a central black hole. Stellar-sized mass black holes -- those about five to ten times as massive as the Sun -- have apparently not coalesced to the center of the star cluster. All or most stellar-sized black holes that formed over the lifetime of the cluster have likely been ejected by their slingshot encounters with binaries deep in the cluster core. "These results show that binary star systems are a source of gravitational energy which ejects stellar mass black holes and prevents the collapse of the cluster’s core to a more massive, central black hole," said the CfA's Craig Heinke. "In other words, binary systems - not black holes - are the dynamical heat engines that drive the evolution of globular clusters." Chandra observed 47 Tucanae on March 16-17, 2000, for a period of 74,000 seconds with the Advanced CCD Imaging Spectrometer (ACIS). The ACIS X-ray camera was developed for NASA by Penn State and the Massachusetts Institute of Technology. The High Energy Transmission Grating Spectrometer was built by MIT. NASA's Marshall Space Flight Center in Huntsville, AL, manages the Chandra program. TRW, Inc., Redondo Beach, California, is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, MA. Images associated with this release are available on the World Wide Web at: http://chandra.harvard.edu AND http://chandra.nasa.gov

2001-05-01

293

Environments of massive stars and the upper mass limit  

NASA Astrophysics Data System (ADS)

The locations of massive stars (>= 8M ?) within their host galaxies is reviewed. These range from distributed OB associations to dense star clusters within giant Hii regions. A comparison between massive stars and the environments of core-collapse supernovae and long duration Gamma Ray Bursts is made, both at low and high redshift. We also address the question of the upper stellar mass limit, since very massive stars (VMS, M init >> 100M ?) may produce exceptionally bright core-collapse supernovae or pair instability supernovae.

Crowther, Paul A.

2012-09-01

294

Stars equilibrium  

NSDL National Science Digital Library

What causes the fusion reaction in a star's core? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to processes inside a star. Students read about the equilibrium process in a star, in which outward gas pressure equals inward gravitational pressure. Then, an interactive lab activity offers students the opportunity to predict temperature, pressure, and gravity changes that occur during equilibrium. The chemical reactions of the fusion process are presented, and more specific detailed reactions are available in a pop-up box. Student practice quizzes about the equilibrium process and pressure and gravity interactions inside the star are included, as are answers. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)

2003-01-01

295

Dynamics and evolution of dense stellar systems  

NASA Astrophysics Data System (ADS)

The research presented in this thesis comprises a theoretical study of several aspects relating to the dynamics and evolution of dense stellar systems such as globular clusters. First, I present the results of a study of mass segregation in two-component star clusters, based on a large number of numerical N-body simulations using our Monte-Carlo code. Heavy objects, which could represent stellar remnants such as neutron stars or black holes, exhibit behavior that is in quantitative agreement with simple analytical arguments. Light objects, which could represent free-floating planets or brown dwarfs, are predominantly lost from the cluster, as expected from simple analytical arguments, but may remain in the halo in larger numbers than expected. Using a recent null detection of planetary-mass microlensing events in M22, I find an upper limit of ˜25% at the 63% confidence level for the current mass fraction of M22 in the form of very low-mass objects. Turning to more realistic clusters, I present a study of the evolution of clusters containing primordial binaries, based on an enhanced version of the Monte-Carlo code that treats binary interactions via cross sections and analytical prescriptions. All models exhibit a long-lived “binary burning” phase lasting many tens of relaxation times. The structural parameters of the models during this phase match well those of most observed Galactic globular clusters. At the end of this phase, clusters that have survived tidal disruption undergo deep core collapse, followed by gravothermal oscillations. The results clearly show that the presence of even a small fraction of binaries in a cluster is sufficient to support the core against collapse significantly beyond the normal core collapse time predicted without the presence of binaries. For tidally truncated systems, collapse is delayed sufficiently that the cluster will undergo complete tidal disruption before core collapse. Moving a step beyond analytical prescriptions, I incorporate into the Monte-Carlo code an exact treatment of binary-single interactions, and show that the results are in good agreement with those using analytical prescriptions. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.)

Fregeau, John M.

2004-10-01

296

Transport properties of dense matter  

Microsoft Academic Search

Using theoretical techniques that have proven useful in solid-state physics, Fermi-liquid theory, and the theory of liquid metals, the electron contribution to the electrical conductivity, the thermal conductivity, and the viscosity of neutron-star matter in the absence of magnetic fields is calculated for densities less than 2 by 10 to the 14th power g\\/cu cm (regions where there is solid

E. Flowers; N. Itoh

1976-01-01

297

Anomalous dynamics of polymer translocation  

NASA Astrophysics Data System (ADS)

We study the passage times of a translocating polymer of length N in three dimensions, while it passes through a narrow pore. We show that the behavior of the polymer stems from the polymer dynamics at the immediate vicinity of the pore --- in particular, the memory effects in the polymer chain tension imbalance across the pore. We take as a reaction coordinate the number s of the monomer residing in the pore. in the case of unbiased translocation, these memory effects cause the mobility of s to be anomalous diffusion for times up to the Rouse time N˜N^1+2? or Zimm time N˜N^3?, without or with hydrodynamics, respectively. Here, ? is the Flory exponent. Beyond this time, the dynamics becomes ordinary diffusion. As a consequence, the pore blockade time scales with length as ?d˜N^2+?. If a force of sufficient strength is pulling on one end, the pore blockade time scales as ?d˜N^2 in the absence of hydrodynamics. If a voltage is applied across the pore, which drives the charged polymer, the pore blockade time scales as ?d˜N^(1+2?)/(1+?) without, and ?d˜N^3?/(1+?) with hydrodynamics. In these cases, the pore blockade time decreases inversely with force and field strength, respectively. Our theoretical framework is substantiated with high-precision computer simulations. We will show that memory effects similar to those governing translocation, also play a role in the dynamics of dense polymer solutions and polymer melts.

Barkema, Gerard

2009-03-01

298

Hunting for Shooting Stars in 30 Doradus  

NASA Astrophysics Data System (ADS)

We are undertaking an ambitious proper motion survey of massive stars in the 30 Doradus region of the Large Magellanic Cloud using the unique capabilities of HST. We aim to derive the directions of motion of massive runaway stars, searching in particular for stars which have been ejected from the dense star cluster R136. These stars probe the dynamical processes in the core of the cluster. The core has been suggested as a formation site for very massive stars exceeding the canonical upper limit of the IMF. These are possible progenitors of intermediate-mass black holes. Furthermore, they provide insight about the origin of massive field stars, addressing open questions related to the poorly understood process of massive star formation. Some may originate from disrupted binary systems and bear the imprints of interaction with the original companion. They will end their life far away from their birth location as core collapse supernova or possibly even long gamma-ray bursts. Here we discuss the first epoch of observations, presenting a 16'x13' mosaic of the data, and initial results based on comparisons with archival data. SdM acknowledges the NASA Hubble Fellowship grant HST-HF-51270.01-A awarded by STScI, operated by AURA for NASA, contract NAS 5-26555.

de Mink, Selma E.; Lennon, D. J.; Sabbi, E.; Anderson, J.; Bedin, L. R.; Sohn, S.; van der Marel, R. P.; Walborn, N. R.; Bastian, N.; Bressert, E.; Crowther, P. A.; Evans, C. J.; Herrero, A.; Langer, N.; Sana, H.

2012-01-01

299

Coupled modes in magnetized dense plasma with relativistic-degenerate electrons  

SciTech Connect

Low frequency electrostatic and electromagnetic waves are investigated in ultra-dense quantum magnetoplasma with relativistic-degenerate electron and non-degenerate ion fluids. The dispersion relation is derived for mobile as well as immobile ions by employing hydrodynamic equations for such plasma under the influence of electromagnetic forces and pressure gradient of relativistic-degenerate Fermi gas of electrons. The result shows the coexistence of shear Alfven and ion modes with relativistically modified dispersive properties. The relevance of results to the dense degenerate plasmas of astrophysical origin (for instance, white dwarf stars) is pointed out with brief discussion on ultra-relativistic and non-relativistic limits.

Khan, S. A. [National Centre for Physics, Quaid-i-Azam University Campus, Islamabad 45320 (Pakistan)

2012-01-15

300

Neutron Stars and Quark Stars  

NASA Astrophysics Data System (ADS)

The tremendous densities reached in the centers of neutron stars provide a high pressure environment in which exciting particles processes are likely compete with each other and novel phases of matter may exist. The particle processes range from the generation of hyperons, to quark deconfinement, to the formation of kaon condensates and H-matter. Another striking possibility concerns the formation of absolutely stable strange quark matter. In the latter event all neutron stars could in fact be strange (quark matter) stars, which would be largely composed of pure quark matter possibly enveloped in a thin nuclear crust made up ordinary hadronic matter. This paper gives an overview of the properties of both classes of stars.

Weber, Fridolin

2004-08-01

301

Silicon Polymers.  

National Technical Information Service (NTIS)

Unsaturated carbosilane polymers have been prepared by anionic as well as metathesis polymerization of silacyclopent-3-enes. Of particular interest, is unsaturated carbosilane polymers with Si-H substitution have been prepared. These complementary functio...

W. P. Weber

1992-01-01

302

Piezoelectric Polymers.  

National Technical Information Service (NTIS)

The purpose of this review is to detail the current theoretical understanding of the origin of piezoelectric and ferroelectric phenomena in polymers; to present the state-of-the-art in piezoelectric polymers and emerging material systems that exhibit prom...

J. S. Harrison Z. Ounaies

2001-01-01

303

Discriminating strange star mergers from neutron star mergers by gravitational-wave measurements  

NASA Astrophysics Data System (ADS)

We perform three-dimensional relativistic hydrodynamical simulations of the coalescence of strange stars and explore the possibility to decide on the strange matter hypothesis by means of gravitational-wave measurements. Self-binding of strange quark matter and the generally more compact stars yield features that clearly distinguish strange star from neutron star mergers, e.g. hampering tidal disruption during the plunge of quark stars. Furthermore, instead of forming dilute halo structures around the remnant as in the case of neutron star mergers, the coalescence of strange stars results in a differentially rotating hypermassive object with a sharp surface layer surrounded by a geometrically thin, clumpy high-density strange quark matter disk. We also investigate the importance of including nonzero temperature equations of state in neutron star and strange star merger simulations. In both cases we find a crucial sensitivity of the dynamics and outcome of the coalescence to thermal effects, e.g. the outer remnant structure and the delay time of the dense remnant core to black hole collapse depend on the inclusion of nonzero temperature effects. For comparing and classifying the gravitational-wave signals, we use a number of characteristic quantities like the maximum frequency during inspiral or the dominant frequency of oscillations of the postmerger remnant. In general, these frequencies are higher for strange star mergers. Only for particular choices of the equation of state the frequencies of neutron star and strange star mergers are similar. In such cases additional features of the gravitational-wave luminosity spectrum like the ratio of energy emitted during the inspiral phase to the energy radiated away in the postmerger stage may help to discriminate coalescence events of the different types. If such characteristic quantities could be extracted from gravitational-wave signals, for instance with the upcoming gravitational-wave detectors, a decision on the strange matter hypothesis and the existence of strange stars should be possible.

Bauswein, A.; Oechslin, R.; Janka, H.-T.

2010-01-01

304

CYANOACETYLENE IN IC 342: AN EVOLVING DENSE GAS COMPONENT WITH STARBURST AGE  

SciTech Connect

We present the first images of the J = 5-4 and J = 16-15 lines of the dense gas tracer, cyanoacetylene, HC{sub 3}N, in an external galaxy. The central 200 pc of the nearby star-forming spiral galaxy, IC 342, was mapped using the Very Large Array and the Plateau de Bure Interferometer. HC{sub 3}N(5-4) line emission is found across the nuclear mini-spiral, but is very weak toward the starburst site, the location of the strongest mid-IR and radio emission. The J = 16-15 and 10-9 lines are also faint near the large H II region complex, but are brighter relative to the 5-4 line, consistent with higher excitation. The brightest HC{sub 3}N emission is located in the northern arm of the nuclear mini-spiral, 100 pc away from the radio/IR source to the southwest of the nucleus. This location appears less affected by ultraviolet radiation and may represent a more embedded, earlier stage of star formation. HC{sub 3}N excitation temperatures are consistent with those determined from C{sup 18}O; the gas is dense 10{sup 4} - 10{sup 5} cm{sup -3} and cool, T{sub k} < 40 K. So as to not violate limits on the total H{sub 2} mass determined from C{sup 18}O, at least two dense components are required to model IC 342's giant molecular clouds. These observations suggest that HC{sub 3}N(5-4) is an excellent probe of the dense, quiescent gas in galaxies. The high excitation combined with faint emission toward the dense molecular gas at the starburst indicates that it currently lacks large masses of very dense gas. We propose a scenario where the starburst is being caught in the act of dispersing or destroying its dense gas in the presence of the large H II region. This explains the high star formation efficiency seen in the dense component. The little remaining dense gas appears to be in pressure equilibrium with the starburst H II region.

Meier, David S. [New Mexico Institute of Mining and Technology, 802 Leroy Place, Socorro, NM 87801 (United States); Turner, Jean L. [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562 (United States); Schinnerer, Eva, E-mail: dmeier@nmt.edu, E-mail: turner@astro.ucla.edu, E-mail: schinner@mpia.de [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

2011-07-15

305

Simulations of Polymer Translocation  

NASA Astrophysics Data System (ADS)

Transport of molecules across membranes is an essential mechanism for life processes. These molecules are often long, and the pores in the membranes are too narrow for the molecules to pass through as a single unit. In such circumstances, the molecules have to squeeze -- i.e., translocate -- themselves through the pores. DNA, RNA and proteins are such naturally occuring long molecules in a variety of biological processes. Understandably, the process of translocation has been an active topic of current research: not only because it is a cornerstone of many biological processes, but also due to its relevance for practical applications. Translocation is a complicated process in living organisms -- the presence of chaperone molecules, pH, chemical potential gradients, and assisting molecular motors strongly influence its dynamics. Consequently, the translocation process has been empirically studied in great variety in biological literature. Study of translocation as a biophysical process is more recent. Herein, the polymer is simplified to a sequentially connected string of N monomers as it passes through a narrow pore on a membrane. The quantities of interest are the typical time scale for the polymer to leave a confining cell (the ``escape of a polymer from a vesicle'' time scale), and the typical time scale the polymer spends in the pore (the ``dwell'' time scale) as a function of N and other parameters like membrane thickness, membrane adsorption, electrochemical potential gradient, etc. Our research is focused on computer simulations of translocation. Since our main interest is in the scaling properties, we use a highly simplified description of the translocation process. The polymer is described as a self-avoiding walk on a lattice, and its dynamics consists of single-monomer jumps from one lattice site to another neighboring one. Since we have a very efficient program to simulate such polymer dynamics, which we decribe in Chapter 2, we can perform long simulations in which long polymers creep through tiny pores. In Chapter 3 we study pore blockage times for a translocating polymer of length N, driven by a field E across te pore. In three dimensions we find that the typical time the pore remains blocked during a translocation event scales as N^{1.37}/E We show that the scaling behavior stems from the polymer dynamics at the immediate vicinity of the pore -- in particular, the memory effects in the polymer chain tension imbalance across the pore. Chapter 4 studies the unbiased translocation of a polymer with length N, surrounded by equally long polymers, through a narrow pore in a membrane. We show that in dense polymeric systems a relaxation time exists that scales as N^{2.65}, much longer than the Rouse time N^2. If the polymers are well entangled, we find that the mean dwell times scales as N^{3.3}, while for shorter, less entangled polymers, we measure dwell times scaling as N^{2.7}. In Chapter 5 we study the translocation of an RNA molecule, pulled through a nanopore by an optical tweezer, as a method to determine its secondary structure. The resolution with which the elements of the secondary structure can be determined is limited by thermal fluctuations, ruling out single-nucleotide resolution under normal experimental conditions.

Vocks, H.

2008-07-01

306

Embedded Star Formation in the Eagle Nebula  

NASA Astrophysics Data System (ADS)

M16 (=NGC 6611), the Eagle Nebula, is a well-studied region of star formation and the source of a widely recognized Hubble Space Telescope (HST) image. High spatial resolution infrared observations with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) on HST reveal the detailed morphology of two embedded star formation regions that are heavily obscured at optical wavelengths. It is striking that only limited portions of the visually obscured areas are opaque at 2.2 ?m. Although the optical images imply substantial columns of material, the infrared images show only isolated clumps of dense gas and dust. Rather than being an active factory of star production, only a few regions are capable of sustaining current star formation. Most of the volume in the columns may be molecular gas and dust, protected by capstones of dense dust. Two active regions of star formation are located at the tips of the optical northern and central large ``elephant trunk'' features shown in the Wide Field Planetary Camera 2 (WFPC2) images. They are embedded in two capstones of infrared opaque material that contains and trails behind the sources. Although the presence of these sources was evident in previous observations at the same and longer wavelengths, the NICMOS images provide a high-resolution picture of their morphology. Two bright stars appear at the tip of the southern column and may be the result of recent star formation at the top of that column. These observations suggest that the epoch of star formation in M16 may be near its endpoint.

Thompson, Rodger I.; Smith, Bradford A.; Hester, J. Jeff

2002-05-01

307

New method to access hyperbranched polymers with uniform structure via one-pot polymerization of inimer in microemulsion.  

PubMed

A facile approach is presented for successful synthesis of hyperbranched polymers with high molecular weight and uniform structure by a one-pot polymerization of an inimer in a microemulsion. The segregated space in the microemulsion confined the inimer polymerization and particularly the polymer-polymer reaction within discrete nanoparticles. At the end of polymerization, each nanoparticle contained one hyperbranched polymer that had thousands of inimer units and low polydispersity. The hyperbranched polymers were used as multifunctional macroinitiators for synthesis of "hyper-star" polymers. When a degradable inimer was applied, the hyper-stars showed fast degradation into linear polymer chains with low molecular weight. PMID:22962851

Min, Ke; Gao, Haifeng

2012-09-13

308

Circumnuclear Rings: Probes of Star Formation and Galaxy Dynamics  

NASA Astrophysics Data System (ADS)

We propose to image the dense molecular gas associated with the star-forming circumnuclear ring (CNR) in the prototypical barred ringed galaxy NGC 1433, building on our successful observations of NGC 7552 in 2005. Our primary science goals include (1) comparing the locations of dense gas clouds with young UV-bright star clusters; (2) looking for an HCN enhancement relative to HCO+ in the nucleus, as has been reported in other Seyferts; and (3) deriving an inner rotation curve to test resonance ring theory. We request observations in H75 and H168 to produce a high-resolution image of the circumnuclear gas.

Wong, Tony; Dahlem, Michael; Ryder, Stuart; Kohno, Kotaro; Buta, Ron

2006-04-01

309

Conjugated polymers: Watching polymers dance  

NASA Astrophysics Data System (ADS)

Single-molecule spectroscopy allows fluctuations of conjugated polymer conformation to be monitored during solvent vapour annealing. Dramatic changes in fluorescence behaviour are observed and interpreted in terms of transformations between extended and collapsed polymer geometries.

Rothberg, Lewis

2011-06-01

310

Super-massive stars: Radiative transfer  

NASA Astrophysics Data System (ADS)

The concept of central super-massive stars (M ge 5 × 10^4 Modot, where M is the mass of the super-massive star) embedded in dense stellar systems was suggested as a possible explanation for high- energy emissions phenomena occurring in active galactic nuclei and quasars (Vilkoviski 1976; Hara 1978), such as X-ray emissions (Bahcall & Ostriker 1975). SMSs and super-massive black holes are two possibilities to explain the nature of super-massive central objects, and super-massive stars may be an intermediate step towards the formation of super-massive black holes (Rees 1984). Therefore it is important to study such a dense gas-star system in detail. We address here the implementation of radiative transfer in a model which was presented in former work (Amaro-Seoane & Spurzem 2001; Amaro-Seoane et al. 2002). In this sense, we extend here and improve the work done by Langbein et al. (1990) by describing the radiative transfer in super-massive stars using previous work on this subject (Castor 1972).

Amaro-Seoane, P.; Spurzem, R.; Just, A.

311

Transport in simple dense fluids  

SciTech Connect

A transport theory for Lennard-Jones (LJ) fluids is described. The underlying mean-field kinetic theory model the LJ potential by adding a hard-sphere core to the attractive tail of the LJ potential. The transport coefficients discussed here-shear viscosity, thermal conductivity, and self-diffusion coefficient-exhibit Enskog-like forms, but now the radial distribution function (rdf) bears explicit dependence on the LJ tail as well as on the hard-sphere core. The hard-sphere diameter is determined according to the well-known WCA method used in equilibrium statistical mechanics to mimic the LJ fluid. Hence the transport theory employs no adjustable parameters. Numerical results are compared to simulation and experimental results for many states, including saturated liquid, triple point, and dense gas. In general, a quantitatively accurate transport theory is obtained for the states considered. This represents improvement, both numerically and conceptually, over an earlier theory.

Karkheck, J.; Stell, G.; Xu, J.

1989-01-01

312

Dense inhibitory connectivity in neocortex.  

PubMed

The connectivity diagram of neocortical circuits is still unknown, and there are conflicting data as to whether cortical neurons are wired specifically or not. To investigate the basic structure of cortical microcircuits, we use a two-photon photostimulation technique that enables the systematic mapping of synaptic connections with single-cell resolution. We map the inhibitory connectivity between upper layers somatostatin-positive GABAergic interneurons and pyramidal cells in mouse frontal cortex. Most, and sometimes all, inhibitory neurons are locally connected to every sampled pyramidal cell. This dense inhibitory connectivity is found at both young and mature developmental ages. Inhibitory innervation of neighboring pyramidal cells is similar, regardless of whether they are connected among themselves or not. We conclude that local inhibitory connectivity is promiscuous, does not form subnetworks, and can approach the theoretical limit of a completely connected synaptic matrix. PMID:21435562

Fino, Elodie; Yuste, Rafael

2011-03-24

313

Extended thermodynamics of dense gases  

NASA Astrophysics Data System (ADS)

We study extended thermodynamics of dense gases by adopting the system of field equations with a different hierarchy structure to that adopted in the previous works. It is the theory of 14 fields of mass density, velocity, temperature, viscous stress, dynamic pressure, and heat flux. As a result, most of the constitutive equations can be determined explicitly by the caloric and thermal equations of state. It is shown that the rarefied-gas limit of the theory is consistent with the kinetic theory of gases. We also analyze three physically important systems, that is, a gas with the virial equations of state, a hard-sphere system, and a van der Waals fluid, by using the general theory developed in the former part of the present work.

Arima, T.; Taniguchi, S.; Ruggeri, T.; Sugiyama, M.

2012-11-01

314

Chameleon stars  

SciTech Connect

We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.

Dzhunushaliev, Vladimir [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Folomeev, Vladimir [Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Singleton, Douglas [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Physics Department, CSU Fresno, Fresno, California 93740-8031 (United States)

2011-10-15

315

pH-sensitive micelles self-assembled from multi-arm star triblock co-polymers poly(?-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) for controlled anticancer drug delivery.  

PubMed

A series of amphiphilic 4- and 6-armed star triblock co-polymers poly(?-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4/6AS-PCL-b-PDEAEMA-b-PPEGMA) were developed by a combination of ring opening polymerization and continuous activators regenerated by electron transfer atom transfer radical polymerization. The critical micelle concentration values of the star co-polymers in aqueous solution were extremely low (2.2-4.0mgl(-1)), depending on the architecture of the co-polymers. The self-assembled blank and doxorubicin (DOX)-loaded three layer micelles were spherical in shape with an average size of 60-220nm determined by scanning electron microscopy and dynamic light scattering. The in vitro release behavior of DOX from the three layer micelles exhibited pH-dependent properties. The DOX release rate was significantly accelerated by decreasing the pH from 7.4 to 5.0, due to swelling of the micelles at lower pH values caused by the protonation of tertiary amine groups in DEAEMA in the middle layer of the micelles. The in vitro cytotoxicity of DOX-loaded micelles to HepG2 cells suggested that the 4/6AS-PCL-b-PDEAEMA-b-PPEGMA micelles could provide equivalent or even enhanced anticancer activity and bioavailability of DOX and thus a lower dosage is sufficient for the same therapeutic efficacy. The results demonstrate that the pH-sensitive multilayer micelles could have great potential application in delivering hydrophobic anticancer drugs for improved cancer therapy. PMID:23669619

Yang, You Qiang; Zhao, Bin; Li, Zhen Dong; Lin, Wen Jing; Zhang, Can Yang; Guo, Xin Dong; Wang, Ju Fang; Zhang, Li Juan

2013-05-10

316

Dense module enumeration in biological networks  

NASA Astrophysics Data System (ADS)

Analysis of large networks is a central topic in various research fields including biology, sociology, and web mining. Detection of dense modules (a.k.a. clusters) is an important step to analyze the networks. Though numerous methods have been proposed to this aim, they often lack mathematical rigorousness. Namely, there is no guarantee that all dense modules are detected. Here, we present a novel reverse-search-based method for enumerating all dense modules. Furthermore, constraints from additional data sources such as gene expression profiles or customer profiles can be integrated, so that we can systematically detect dense modules with interesting profiles. We report successful applications in human protein interaction network analyses.

Tsuda, Koji; Georgii, Elisabeth

2009-12-01

317

Effects of anisotropy on optimal dense coding  

NASA Astrophysics Data System (ADS)

Optimal dense coding with thermal entangled states of a two-qubit anisotropic XXZ model and a Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions is studied in this paper. The DM interaction is another kind of anisotropic antisymmetric exchange interaction. The effects of these two kinds of anisotropies on dense coding are studied in detail for both the antiferromagnetic and ferromagnetic cases. For the two models, I give the conditions that the parameters of the models have to satisfy for a valid dense coding. I also found that even though there is entanglement, it is unavailable for our optimal dense coding, which is the same as entanglement teleportation.

Zhang, Guo-Feng

2009-01-01

318

Attributes of a rotating neutron star with a hyperon core  

SciTech Connect

We study the effect of rotation on the global properties of a neutron star with a hyperon core in an effective chiral model with varying nucleon effective masses within a mean-field approach. The resulting gross properties of the rotating compact star sequences are then compared and analyzed with other theoretical predictions and observations from neutron stars. The maximum mass of the compact star predicted by the model lies in the range of (1.4-2.4)M{sub {center_dot}} at Kepler frequency {omega}{sub K}, which is consistent with recent observations of high mass stars, thereby reflecting the sensitivity of the underlying nucleon effective mass in the dense matter equation of state. We also discuss the implications of the experimental constraints from the flow data from heavy-ion collisions on the global properties of rotating neutron stars.

Jha, T. K.; Mishra, H.; Sreekanth, V. [Theoretical Physics Division, Physical Research Laboratory, Navrangpura, Ahmedabad, India-380 009 (India)

2008-04-15

319

Attributes of a rotating neutron star with a hyperon core  

NASA Astrophysics Data System (ADS)

We study the effect of rotation on the global properties of a neutron star with a hyperon core in an effective chiral model with varying nucleon effective masses within a mean-field approach. The resulting gross properties of the rotating compact star sequences are then compared and analyzed with other theoretical predictions and observations from neutron stars. The maximum mass of the compact star predicted by the model lies in the range of (1.4-2.4)M? at Kepler frequency ?K, which is consistent with recent observations of high mass stars, thereby reflecting the sensitivity of the underlying nucleon effective mass in the dense matter equation of state. We also discuss the implications of the experimental constraints from the flow data from heavy-ion collisions on the global properties of rotating neutron stars.

Jha, T. K.; Mishra, H.; Sreekanth, V.

2008-04-01

320

Beyond the Chandrasekhar limit: Structure and formation of compact stars  

Microsoft Academic Search

The concept of limiting mass, introduced by Chandrasekhar in case of white dwarfs, plays an important role in the formation\\u000a and stability of compact objects such as neutron stars and black holes. Like white dwarfs, neutron stars have their own mass\\u000a limit, and a compact configuration would progress from one family to the next, more dense one once a mass

Dipankar Bhattacharya

2011-01-01

321

Variable Stars  

NASA Astrophysics Data System (ADS)

It is a tradition to observe variable stars using small telescopes; actually, variable stars are the favorites of small telescopes. What it is needed is those telescopes to be well-equipped (to get good observations), and to be supplied with users (to be productive). The first can be easily achieved; the second, related to the poor job prospects, seems more difficult. Keeping in mind that there is no any Observatory, that could cover the whole sky and that an astronomical event can not be repeated, each individual observation, is very valuable. Especially that of variable stars, where the variability of their luminosity can be caused by many reasons, intrinsic or extrinsic. What is missing -from at least some of the small telescopes spread in whole Europe- is better organization. This means that, besides either some research projects of personal interest, or(/and) students training, some others -being parts of international programs- could also be carried out, focusing to specific objects and goals. The work carried out in the field of variable stars with the use of small telescopes in some European countries, will be presented.

Rovithis-Livaniou, Helen

322

Brittle Star  

USGS Multimedia Gallery

A tiny brittle star (the central disc is smaller than a dime) clings to the branches of a soft coral in a sample bucket brought into the shipboard laboratory from a submersible dive. This creature makes its home on the deep, dark ocean floor. ...

2010-04-15

323

Star quality.  

PubMed

Around 150 wards are participating in the voluntary Star Wards scheme to provide mental health inpatients with more activities with therapeutic value. Suggested activities range from a library, to horse riding Internet access and comedy. Service users are particularly keen to have more exercise, which can be a challenge in inpatient settings. PMID:17970387

Dent, Emma

2007-09-20

324

L43 - an example of interaction between molecular outflows and dense cores  

SciTech Connect

CCD images reveal the presence of a bay in the dark cloud L43, within which the very young star RNO 91 is situated. The bay is coincident with the blue lobe of the (C-12)O molecular outflow emission associated with RNO 91. It is suggested that the outflow originating at RNO 91 has blown through the dense core into lower density environs, revealing RNO and the outflow cavity in the process. 29 references.

Mathieu, R.D.; Myers, P.C.; Schild, R.E.; Benson, P.J.; Fuller, G.A.

1988-07-01

325

Color Superconductivity in Compact Stars  

NASA Astrophysics Data System (ADS)

After a brief review of the phenomena expected in cold dense quark matter, color superconductivity and color-flavor locking, we sketch some implications of recent developments in our understanding of cold dense quark matter for the physics of compact stars. We give a more detailed summary of our recent work on crystalline color superconductivity and the consequent realization that (some) pulsar glitches may originate in quark matter.We acknowledge helpful discussions with P. Bedaque, J. Berges, D. Blaschke, I. Bombaci, G. Carter, D. Chakrabarty, J. Madsen, C. Nayak, M. Prakash, D. Psaltis, S. Reddy, M. Ruderman, S.-J. Rey, T. Schäfer, A. Sedrakian, E. Shuryak, E. Shuster, D. Son, M. Stephanov, I. Wasserman, F. Weber and F. Wilczek. KR thanks the organizers of the ECT Workshop on Neutron Star Interiors for providing a stimulating environment within which many of the helpful discussions acknowledged above took place. This work is supported in part by the DOE under cooperative research agreement #DF-FC02-94ER40818. The work of JB was supported in part by an NDSEG Fellowship; that of KR was supported in part by a DOE OJI Award and by the A. P. Sloan Foundation.

Alford, Mark; Bowers, Jeffrey A.; Rajagopal, Krishna

326

The age of B59 and the Pipe Nebula: Implications for the Star Formation Timescale  

Microsoft Academic Search

The Pipe Nebula is a valuable new laboratory for studying the earliest stages of star formation. Containing only one small cluster (B59) of 20 young stars, until recently the Pipe had escaped detailed scrutiny despite its proximity ( 130 pc) and size ( 104 M_sun). Studies of dense cores in the Pipe (Rathborne et al. 2008, Muench et al. 2007,

Kevin R. Covey; C. Lada; A. Muench; C. Román-Zúñiga

2009-01-01

327

Impact of strange quark matter nuggets on pycnonuclear reaction rates in the crusts of neutron stars  

Microsoft Academic Search

This article presents an investigation into the pycnonuclear reaction rates in dense crustal matter of neutron stars contaminated with strange quark matter nuggets. The presence of such nuggets in the crustal matter of neutron stars would be a natural consequence if Witten's strange quark matter hypothesis is correct. The methodology presented in this article is a recreation of a recent

B. Golf; J. Hellmers; F. Weber

2009-01-01

328

Impact of strange quark matter nuggets on pycnonuclear reaction rates in the crusts of neutron stars  

Microsoft Academic Search

This paper presents an investigation into the pycnonuclear reaction rates in dense crustal matter of neutron stars contaminated with strange quark matter nuggets. The presence of such nuggets in the crustal matter of neutron stars would be a natural consequence if Witten's strange quark matter hypothesis is correct. The methodology presented in this paper is a recreation of a recent

Fridolin Weber; Barbara Golf; Joe Hellmers

2009-01-01

329

Surface Vibrations of Stratified Neutron Star in the Newtonian Limit of Gravity  

Microsoft Academic Search

From theoretical analysis of the radial distribution of bulk density in the neutron star interior it follows that a neutron star is a strongly stratified compact stellar object with a rather complicated layering structure: the density of outer layers (crust, neutron-rich nuclei, electrons) is much less than the density of the inner region of the stiff core (dense matter of

S. I. Bastrukov

1996-01-01

330

Triggered Collapse, Magnetic Fields, and Very Low Mass Star Formation (Invited Review)  

Microsoft Academic Search

Protostellar collapse calculations traditionally ignore the effects of nearby stars and of magnetic fields. Including these effects can help answer several questions, such as the origin of the Solar System and of free-floating planetary mass objects. Shock waves derived from massive stars can trigger the collapse of an otherwise stable dense cloud core, leading to the formation of single or

A. P. Boss

2003-01-01

331

Hierarchical self-assembly of polycyclic heteroaromatic stars into snowflake patterns.  

PubMed

Seeing stars: The two-dimensional patterns of the polycyclic heteroaromatic star molecules 1 on graphite vary with the side chain length. For n=12, frustrated self-assembly leads to hierarchically organized superstructures: up to 10 molecules form triangular aggregates which pack densely into hexagonal patterns with very large (15.5 nm) lattice constants. PMID:22821662

Jester, Stefan-S; Sigmund, Eva; Röck, Lisa M; Höger, Sigurd

2012-07-23

332

On the Formation of Glycolaldehyde in Dense Molecular Cores  

NASA Astrophysics Data System (ADS)

Glycolaldehyde is a simple monosaccharide sugar linked to prebiotic chemistry. Recently, it was detected in a molecular core in the star-forming region G31.41+0.31 at a reasonably high abundance. We investigate the formation of glycolaldehyde at 10 K to determine whether it can form efficiently under typical dense core conditions. Using an astrochemical model, we test five different reaction mechanisms that have been proposed in the astrophysical literature, finding that a gas-phase formation route is unlikely. Of the grain-surface formation routes, only two are efficient enough at very low temperatures to produce sufficient glycolaldehyde to match the observational estimates, with the mechanism culminating in CH3OH + HCO being favored. However, when we consider the feasibility of these mechanisms from a reaction chemistry perspective, the second grain-surface route looks more promising, H3CO + HCO.

Woods, Paul M.; Kelly, George; Viti, Serena; Slater, Ben; Brown, Wendy A.; Puletti, Fabrizio; Burke, Daren J.; Raza, Zamaan

2012-05-01

333

Spatial patterns in dense algal blooms  

Microsoft Academic Search

lntricatc and striking patterns are often created in dense algal blooms by the interaction of sinking, floating, or swllmming algae and local physical dynamics. The structure of these patterns can reveal a great deal about the processes underlying the pattern formation. Here I explore three common patterns in dense algal blooms: chaotic mixing, internal wave banding, and sharp fronts. For

Peter J. S. Franks

1997-01-01

334

Dense Photometric Stereo by Expectation Maximization  

Microsoft Academic Search

We formulate a robust method using Expectation Maximiza- tion (EM) to address the problem of dense photometric stereo. Previous approaches using Markov Random Fields (MRF) utilized a dense set of noisy photometric images for estimating an initial normal to encode the matching cost at each pixel, followed by normal refinement by consid- ering the neighborhood of the pixel. In this

Tai-pang Wu; Chi-keung Tang

2006-01-01

335

Nonlinear Interactions in Dense Quantum Plasmas  

Microsoft Academic Search

The purpose of this talk is to discuss some important collective processes in dense quantum plasmas, which are ubiquitous in micromechanical systems and ultrasmall electronic devices, in nanowires, in biophotonics, in intense laser-solid density plasma interaction experiments, as well as in astrophysical and cosmological environments. Tn dense quantum plasmas, which obey the Fermi-Dirac distributions, there are new pressure laws and

Padma Shukla

2007-01-01

336

Polymer adsorption  

NASA Astrophysics Data System (ADS)

The aim of this talk is to review Pierre-Gilles deGennes' work on polymer adsorption and the impact that it has now in our understanding of this problem. We will first present the self-consistent mean-field theory and its applications to adsorption and depletion. De Gennes most important contribution is probably the derivation of the self-similar power law density profile for adsorbed polymer layers that we will present next, emphasizing the differences between the tail sections and the loop sections of the adsorbed polymers. We will then discuss the kinetics of polymer adsorption and the penetration of a new polymer chain in an adsobed layer that DeGennes described very elegantly in analogy with a quantum tunneling problem. Finally, we will discuss the role of polymer adsorption for colloid stabilization.

Joanny, Jean-Francois

2008-03-01

337

Pervaporation properties of dense polyamide-6 membranes in separation of water-ethanol mixtures  

SciTech Connect

Several dense polyamide-6 membranes were prepared by casting 7 wt% and/or 10 wt% solutions of polymer in trifluoroethanol. The cast membranes were dried at different temperatures from 25 to 80{degrees}C. Sorption and pervaporation properties of PA-6 membranes in water-ethanol mixtures were obtained. The data obtained showed that water was preferentially sorbed into the membrane and transported through the membrane; however, the pervaporation selectivity factor {alpha}{sup PV} was close to unity at higher concentrations. The selectivity parameters in pervaporation were improved for membranes obtained from 10 wt% polymer and dried at higher temperatures.

Kujawski, W.; Waczynski, M.; Lasota, M. [Nicolaus Copernicus Univ., Torun (Poland)

1996-04-01

338

Percolation in dense storage arrays  

NASA Astrophysics Data System (ADS)

As computers and their accessories become smaller, cheaper, and faster the providers of news, retail sales, and other services we now take for granted on the Internet have met their increasing computing needs by putting more and more computers, hard disks, power supplies, and the data communications linking them to each other and to the rest of the wired world into ever smaller spaces. This has created a new and quite interesting percolation problem. It is no longer desirable to fix computers, storage or switchgear which fail in such a dense array. Attempts to repair things are all too likely to make problems worse. The alternative approach, letting units ``fail in place'', be removed from service and routed around, means that a data communications environment will evolve with an underlying regular structure but a very high density of missing pieces. Some of the properties of this kind of network can be described within the existing paradigm of site or bond percolation on lattices, but other important questions have not been explored. I will discuss 3D arrays of hundreds to thousands of storage servers (something which it is quite feasible to build in the next few years), and show that bandwidth, but not percolation fraction or shortest path lengths, is the critical factor affected by the ``fail in place'' disorder. Redundancy strategies traditionally employed in storage systems may have to be revised. Novel approaches to routing information among the servers have been developed to minimize the impact.

Kirkpatrick, Scott; Wilcke, Winfried W.; Garner, Robert B.; Huels, Harald

2002-11-01

339

Natural Polymers  

NSDL National Science Digital Library

Polymers that exist in nature, called biopolymers , include a large and diverse range of compounds. This chapter discusses the most important types of natural polymers--their chemical makeup, key properties, and where they are found. The focus will be more on the chemical and physical properties of natural polymers and less on their biological synthesis or physiological function. The references at the end of the chapter provide additional information.

Teegarden, David

2004-01-01

340

HNCO in massive galactic dense cores  

NASA Astrophysics Data System (ADS)

We surveyed 81 dense molecular cores associated with regions of massive star formation and Sgr A in the JK-1K-1 = 505-404 and 10010-909 lines of HNCO. Line emission was detected towards 57 objects. Selected subsamples were also observed in the 101-000, 404-303, 707-606, 15015-14014, 16016-15015 and 21021-20020 lines, covering a frequency range from 22 to 461 GHz. HNCO lines from the K-1 = 2,3 ladders were detected in several sources. Towards Orion-KL, K-1 = 5 transitions with upper state energies Eu/k ~ 1100 and 1300 K could be observed. Five HNCO cores were mapped. The sources remain spatially unresolved at 220 and 461 GHz (10010-909 and 21010-20020 transitions) with beam sizes of 24'' and 18\\arcsec, respectively. The detection of hyperfine structure in the 101-000 transition is consistent with optically thin emission under conditions of Local Thermodynamic Equilibrium (LTE). This is corroborated by a rotational diagram analysis of Orion-KL that indicates optically thin line emission also for transitions between higher excited states. At the same time a tentative detection of interstellar HN13CO (the 100,10-90,9 line at 220 GHz toward G 310.12-0.20) suggests optically thick emission from some rotational transitions. Typical HNCO abundances relative to H2 as derived from a population diagram analysis are ~ 10-9. The rotational temperatures reach ~ 500 K. The gas densities in regions of HNCO K-1=0 emission should be n>~ 106 cm-3 and in regions of K-1>0 emission about an order of magnitude higher even for radiative excitation. HNCO abundances are found to be enhanced in high-velocity gas. HNCO integrated line intensities correlate well with those of thermal SiO emission. This indicates a spatial coexistence of the two species and may hint at a common production mechanism, presumably based on shock chemistry. Based on the observations collected at the European Southern Observatory, La Silla, Chile and on observations with the Heinrich-Hertz-Telescope (HHT). The HHT is operated by the Submillimeter Telescope Observatory on behalf of Steward Observatory and the MPI für Radioastronomie. Tables 1, 2, 5, 6 are also available in electronic form and Tables 7-14 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Zinchenko, I.; Henkel, C.; Mao, R. Q.

2000-09-01

341

Properties of Dense and Cold QCD  

NASA Astrophysics Data System (ADS)

We study equilibrium and non-equilibrium aspects of the normal state of cold and dense QCD and QED. The exchange of dynamically screened magnetic gluons (photons) leads to infrared singularities in the fermion propagator for excitations near the Fermi surface and the breakdown of the Fermi liquid description. We implement a resummation of these infrared divergences via the Euclidean renormalization group to obtain the spectral density, dispersion relation, widths and wave function renormalization for single quasiparticles near the Fermi surface. We find that all feature scaling with anomalous dimensions:? p(k) ? |k - kF|1/{1-2?} ? (k) ? |k - kF|1/{1-2?} Zp(k) ? |k - kF|{2?}/{1-2?} with ? {?}/{6?} for QED, {?s}/{6?} {N2c-1}/{2Nc} for QCD with Nc colors and NF flavors. The discontinuity of the quasiparticle distribution at the Fermi surface vanishes. For k ? kF we find nk?{kF} = (sin[? ? ])/(2? ?) - {k-{kF}}/{? M(1-4? )} + O(k - kF)2 with M the dynamical screening scale of magnetic gluons (photons). The dynamical renormalization group is implemented to study non-equilibrium relaxation. The amplitude of single quasiparticle states with momentum near the Fermi surface falls off as |? k?{kF}(t)| ? |? k?{kF}(t0)|e-?(k) (t-{t0)}[t0/t]2? . Thus quasiparticle states with Fermi momentum have zero group velocity and relax with a power law with a coupling dependent anomalous dimension. If the core of neutron stars are composed of quark matter with a normal component, cooling by direct quark Urca processes may be modified by non-Fermi liquid corrections. We find that while the quasiparticle density of states is finite and non-zero at the Fermi surface, its frequency derivative diverges and results in non-Fermi liquid corrections to the specific heat of the normal, degenerate component of quark matter. We study these non-perturbative non-Fermi liquid corrections to the specific heat and the temperature dependence of the chemical potential and show that these lead to a reduction of the specific heat.

de Vega, H. J.

2003-04-01

342

Stars : the end of a star  

NSDL National Science Digital Library

What happens during the death of a star? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the final processes of stars. Here students read about low-mass, medium-mass, and massive stars. Low-mass stars produce white dwarfs. A pop-up window describes how white dwarfs form. Medium-mass stars produce neutron stars and supernova. Pop-up information explains the supernova process. Massive stars undergo carbon burning. An interactive lab activity presents students the opportunity to predict temperature, pressure, and gravity changes that occur during carbon fusion. In a final lab activity, students compare initial star size with the type of death that occurs. Activity questions about star death are provided for each star size and are recordable and printable. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)

2003-01-01

343

Polymer Electrolytes  

NASA Astrophysics Data System (ADS)

This review article covers applications in which polymer electrolytes are used: lithium batteries, fuel cells, and water desalination. The ideas of electrochemical potential, salt activity, and ion transport are presented in the context of these applications. Potential is defined, and we show how a cell potential measurement can be used to ascertain salt activity. The transport parameters needed to fully specify a binary electrolyte (salt + solvent) are presented. We define five fundamentally different types of homogeneous electrolytes: type I (classical liquid electrolytes), type II (gel electrolytes), type III (dry polymer electrolytes), type IV (dry single-ion-conducting polymer electrolytes), and type V (solvated single-ion-conducting polymer electrolytes). Typical values of transport parameters are provided for all types of electrolytes. Comparison among the values provides insight into the transport mechanisms occurring in polymer electrolytes. It is desirable to decouple the mechanical properties of polymer electrolyte membranes from the ionic conductivity. One way to accomplish this is through the development of microphase-separated polymers, wherein one of the microphases conducts ions while the other enhances the mechanical rigidity of the heterogeneous polymer electrolyte. We cover all three types of conducting polymer electrolyte phases (types III, IV, and V). We present a simple framework that relates the transport parameters of heterogeneous electrolytes to homogeneous analogs. We conclude by discussing electrochemical stability of electrolytes and the effects of water contamination because of their relevance to applications such as lithium ion batteries.

Hallinan, Daniel T.; Balsara, Nitash P.

2013-07-01

344

Star formation in the Eagle Nebula and NGC 6611  

NASA Astrophysics Data System (ADS)

M16, also known as the Eagle Nebula, is a prime example for the study of star formation under the hostile environment created by massive O-stars. A rich young stellar population (NGC6611) has been identified. The well-known elephant trunks are striking examples of the massive star feedback into the parent molecular cloud. The detection of several water maser sources as well as embedded IR objects points at current star formation. I will present an overview of our recent observations that aim at characterising not only the young pre-main-sequence (PMS) and their disc, but also the still embedded population. We have discovered a rich population of low-mass PMS stars concentrated around the massive stars and the first results show that the IMF in NGC6611 is consistent with the IMF in less extreme star forming regions. I am using VLT/ VIMOS spectroscopy to determine reddening, effective temperature and gravity for a sample of ~260 cluster candidates to test the validity of the photometric techniques. We have been awarded HST observations to extend the optical and near-IR survey down to brown dwarfs and planetary mass objects. Recent theoretical developments propose that the density in the molecular cloud and/or the UV radiation from O-stars may play an role in shaping the low-mass IMF, with the signs of such influence enhanced in the brown-dwarf regime. Our HST observations will help disentangle these two effects on the IMF. We have also conducted a deep survey of the central area of NGC 6611 in L-band to determine the fraction of low-mass stars with circumstellar discs. The K-L colours indicate that 58% of objects retain their circumstellar discs, implying that the O-stars might not significantly hasten disc dissipation. We are complementing our data on NGC6611 with Spitzer/IRAC data for the outer regions where crowding is less severe, allowing us to investigate disc properties like inner disc temperature and geometry. Star formation is still ongoing in the denser regions of the nebula. We are using VLT/VISIR imaging to identify young stars embedded in dense cores and clumps, and map the emission from the dust and ionised gas across these structures. This will allow us to assess the eroding effect of the NGC6611 massive stars on the molecular cloud and on star formation occurring within. massive stars on the molecular cloud and on star formation occurring within. Star formation is still ongoing in the denser regions of the nebula. I will be using VLT/VISIR imaging to identify young stars still embedded in dense cores and clumps, and map the emission from the dust and ionised gas across these structures. This will allow us to assess the eroding effect of the NGC6611 massive stars on the molecular cloud and on star formation occurring within. imply that the O-stars have little influence in hastening disc dissipation. We are complementing our data on NGC 6611 with Spitzer/IRAC data for the outer regions where crowding is less severe. This also allows us to investigate disc properties (e.g., inner disc temperature and geometry). Star formation is still ongoing in the denser regions of the nebula. I will be using VLT/VISIR imaging to identify young stars still embedded in dense cores and clumps, and map the emission from the dust and ionised gas across these structures. This will allow us to assess the eroding effect of the NGC6611 massive stars on the molecular cloud and on star formation occurring within.

Oliveira, J. M.; Jeffries, R. D.; van Loon, J. Th

345

Three body dynamics in dense gravitational systems  

NASA Astrophysics Data System (ADS)

In this thesis, I have used several techniques to answer the following questions: How many black hole binaries will a cluster produce, and will they have the required properties to be seen by our gravitational wave detectors? How often does the crowded environment of star forming cluster allow the exchange of a planet between stars? To answer these questions, I have studied three scenarios: the interaction of black holes in clusters, the effect of the Kozai mechanism on pulsars in clusters, and the effect of an exchanged planetary body on a planetary system. I have examined the interactions of a system of black holes in a globular cluster in which the black holes have different masses with a more realistic distribution. In my thesis, black hole masses are derived from population synthesis models and span a range of a few up to 50 or 80 [Special characters omitted.] depending on metallicity. My new calculations have reduced the efficiency of three-body interactions in ejecting the binary due to their non- equal masses. I also use timescales derived from earlier simulations of clusters (Sigurdsson 1995) to determine the end state of individual binaries interacting with single black holes. While N-body simulations of black hole systems such as in O'Leary et al. (2006) are less model dependent, my method can easily adapt to advances in the understanding of the processes that make black holes and rapidly produce results on rates of binary black hole mergers for gravitational wave observations and the possibilities of intermediate mass black hole seeds. Numerous black hole binaries are produced by clusters, they are hardened in the potential of the cluster, and the most massive black holes survive the interactions. Interactions with the other black holes preferentially produce binaries with higher eccentricities. I found that as many as one in seven binaries will coalesce within a Hubble time, and with the strength of signal that their higher mass gives they would rival galactic black hole binaries as a background source. I also found that the binaries are ejected from the cluster with, for the most part, a velocity just above the escape speed of the cluster which is a few tens of km/sec. These gravitational wave sources are thus constrained in their host galaxies as the galactic escape velocity is some hundreds of km/sec which only a very few binaries achieve in special cases. I studied the effect of the Kozai mechanism on two pulsars, one in the globular cluster M4, and the other J1903+0327. The M4 pulsar pulsar was found to have an unusually large orbital eccentricity, given that it is in a binary with a period of nearly 200 days. This unusual behavior led to the conclusion that a planet-like third body of much less than a solar mass was orbiting the binary. I used my own code to integrate the secular evolution equations with a broad set of initial conditions to determine the first detailed properties of the third body; namely that the mass of the planet is about that of Jupiter. The second pulsar J1903+0327 consists of a 2.15ms pulsar and a near solar mass companion in an e = 0.44 orbit. A preliminary study of this pulsar showed that the high eccentricity can be reproduced by my models, and there are three candidate clusters from which this pulsar could have originated. My third project was a study of the effect of a planet at 50 AU on the inner solar system. The origin of this planet is assumed to be from an exchange with another solar system in the early stages of the sun's life while it was still in the dense star forming region where it was born. Similar studies have been done with the exchange of stars among binaries by Malmberg et al. (2007b). The exchange once again allows the Kozai effect to bring about drastic change in the inner system. A planet is chosen as the outer object as, unlike a stellar companion, it would remain unseen by current radial velocity and direct observation methods, although it could be detected by upcoming astrometric missions. My study uses an outer body from the size of a super Earth to a

Moody, Kenneth

346

Death Star  

NSDL National Science Digital Library

Death Star, a program from the PBS NOVA series, probes the deep mysteries of gamma-ray bursts, the most powerful celestial explosions since the Big Bang. A description of what would happen to Earth if a gamma-ray burst occurred in our own galaxy, a celestial glossary, and a virtual tour of the electromagnetic spectrum are included. Additional websites and published works about space topics are given, and the accompanying video is available to order.

347

Symbiotic Stars  

NASA Astrophysics Data System (ADS)

Symbiotic stars are interacting binary systems composed of a white dwarf (WD) accreting at high rate from a cool giant companion, which frequently fills its Roche lobe. The WD usually is extremely hot and luminous, and able to ionize a sizeable fraction of the cool giant wind, because it is believed the WD undergoes stable hydrogen nuclear burning on its surface of the material accreted from the companion. This leads to consider symbiotic stars as good candidates for the yet-to-be-identified progenitors of type Ia supernovae. Symbiotic stars display the simultaneous presence of many different types of variability, induced by the cool giant, the accreting WD, the circumstellar dust and ionized gas, with time scales ranging from seconds to decades. The long orbital periods (typically a couple of years) and complex outburst patterns, lasting from a few years to a century, make observations from professionals almost impossible to carry out, and open great opportunities to amateur astronomers to contribute fundamental data to science.

Munari, U.

2012-06-01

348

Exceptional Stars  

NASA Astrophysics Data System (ADS)

As part of our Interdisciplinary Scientist effort (PI, Kulkarni) for the Space Interferometry Mission (SIM) we proposed an investigation with SIM of a number of exceptional stars. With SIM we plan to observe dozens of nearby white dwarfs and search for planets surviving the evolution away from the main sequence as well as (newly formed) planets formed in the circumbinary disks of post-AGB binaries or as a result of white dwarf mergers. We propose to measure the proper motion of a sample of X-ray binaries and Be star binaries with the view of understanding the originof high latitude objects and inferring natal kicks and pre-supernova orbits. We plan to observe several compact object binaries to determine the mass of the compact star. Of particular importance is the proposed observation of SS 433 (for which we propose to use the spectrometer on SIM to measure the proper motion of the emission line clumps embedded in the relativistic jets). Separately we are investigating the issue of frame tie between SIM and the ecliptic frame (by observing binary millisecond pulsars with SIM; the position of these objects is very well determined by pulsar timing) and the degree to which highly precise visibility amplitude measurements can be inverted to infer binary parameters.

Kulkarni, S. R.; Hansen, B.; van Kerkwijk, M.; Phinney, E. S.

2005-12-01

349

THE DYNAMICS OF DENSE CORES IN THE PERSEUS MOLECULAR CLOUD. II. THE RELATIONSHIP BETWEEN DENSE CORES AND THE CLOUD  

SciTech Connect

We utilize the extensive data sets available for the Perseus molecular cloud to analyze the relationship between the kinematics of small-scale dense cores and the larger structures in which they are embedded. The kinematic measures presented here can be used in conjunction with those discussed in our previous work as strong observational constraints that numerical simulations (or analytic models) of star formation should match. We find that dense cores have small motions with respect to the {sup 13}CO gas, about one third of the {sup 13}CO velocity dispersion along the same line of sight. Within each extinction region, the core-to-core velocity dispersion is about half of the total ({sup 13}CO) velocity dispersion seen in the region. Large-scale velocity gradients account for roughly half of the total velocity dispersion in each region, similar to what is predicted from large-scale turbulent modes following a power spectrum of P(k) {proportional_to} k {sup -4}.

Kirk, Helen; Johnstone, Doug [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Pineda, Jaime E.; Goodman, Alyssa, E-mail: hkirk@cfa.harvard.ed [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2010-11-01

350

Polymers All Around You!  

ERIC Educational Resources Information Center

Background information on natural polymers, synthetic polymers, and the properties of polymers is presented as an introduction to this curriculum guide. Details are provided on the use of polymer products in consumer goods, polymer recycling, polymer densities, the making of a polymer such as GLUEP, polyvinyl alcohol, dissolving plastics, polymers

Gertz, Susan

351

Ultrastable nanostructured polymer glasses  

NASA Astrophysics Data System (ADS)

Owing to the kinetic nature of the glass transition, the ability to significantly alter the properties of amorphous solids by the typical routes to the vitreous state is restricted. For instance, an order of magnitude change in the cooling rate merely modifies the value of the glass transition temperature (Tg) by a few degrees. Here we show that matrix-assisted pulsed laser evaporation (MAPLE) can be used to form ultrastable and nanostructured glassy polymer films which, relative to the standard poly(methyl methacrylate) glass formed on cooling at standard rates, are 40% less dense, have a 40?K higher Tg, and exhibit a two orders of magnitude enhancement in kinetic stability at high temperatures. The unique set of properties of MAPLE-deposited glasses may make them attractive in technologies where weight and stability are central design issues.

Guo, Yunlong; Morozov, Anatoli; Schneider, Dirk; Chung, Jae Woo; Zhang, Chuan; Waldmann, Maike; Yao, Nan; Fytas, George; Arnold, Craig B.; Priestley, Rodney D.

2012-04-01

352

Spherical polymer brushes under good solvent conditions: Molecular dynamics results compared to density functional theory  

Microsoft Academic Search

A coarse grained model for flexible polymers end-grafted to repulsive spherical nanoparticles is studied for various chain lengths and grafting densities under good solvent conditions by molecular dynamics methods and density functional theory. With increasing chain length, the monomer density profile exhibits a crossover to the star polymer limit. The distribution of polymer ends and the linear dimensions of individual

Federica Lo Verso; Sergei A. Egorov; Andrey Milchev; Kurt Binder

2010-01-01

353

The AP stars  

Microsoft Academic Search

Ap stars are stars with peculiar characteristics which made it difficult to assign them to the stellar types of the conventional classification scheme. Ap stars are frequently observed. Up to 10% Ap stars are found in the case of the concerned spectral types. Attention is given to the spectroscopic properties of the Ap stars, aspects of stellar spectrum and stellar

H. Muthsam

1977-01-01

354

Star formation in disks  

Microsoft Academic Search

It is noted that the principal characteristics of the stellar populations in galaxies depend on the history of star formation and the initial mass spectrum with which the stars are formed. Whereas there have been a number of attempts to model the history of star formation in galaxies using various quasi-theoretical descriptions of star formation, star formation remains poorly understood

R. B. Larson

1983-01-01

355

Polymer flooding  

Microsoft Academic Search

This book covers all aspects of polymer flooding, an enhanced oil recovery method using water soluble polymers to increase the viscosity of flood water, for the displacement of crude oil from porous reservoir rocks. Although this method is becoming increasingly important, there is very little literature available for the engineer wishing to embark on such a project. In the past,

Littmann

1988-01-01

356

Polymers & People  

ERIC Educational Resources Information Center

|Each Tuesday during the fall of 2002, teams of high school students from three South Carolina counties conducted a four-hour polymer institute for their peers. In less than two months, over 300 students visited the Charleston County Public Library in Charleston, South Carolina, to explore DNA, nylon, rubber, gluep, and other polymers. Teams of…

Lentz, Linda; Robinson, Thomas; Martin, Elizabeth; Miller, Mary; Ashburn, Norma

2004-01-01

357

Polymer Informatics  

NASA Astrophysics Data System (ADS)

Polymers are arguably the most important set of materials in common use. The increasing adoption of both combinatorial as well as high-throughput approaches, coupled with an increasing amount of interdisciplinarity, has wrought tremendous change in the field of polymer science. Yet the informatics tools required to support and further enhance these changes are almost completely absent. In the first part of the chapter, a critical analysis of the challenges facing modern polymer informatics is provided. It is argued, that most of the problems facing the field today are rooted in the current scholarly communication process and the way in which chemists and polymer scientists handle and publish data. Furthermore, the chapter reviews existing modes of representing and communicating polymer information and discusses the impact, which the emergence of semantic technologies will have on the way in which scientific and polymer data is published and transmitted. In the second part, a review of the use of informatics tools for the prediction of polymer properties and in silico design of polymers is offered.

Adams, Nico

358

Star-forming Substructure within Molecular Clouds  

NASA Astrophysics Data System (ADS)

Wide-field far-infrared/submillimeter continuum maps of molecular clouds by the Herschel Space Observatory GBS and HOBYS surveys are revealing the star-forming substructures that lead to star formation in dense gas. In particular, these maps have revealed the central role in clouds of filaments, likely formed through turbulent motions. These filaments appear to be non-isothermal and fragment into cores only when their column densities exceed a stability threshold. Organizations of filament networks suggest the relative role of turbulence and gravity can be traced in different parts of a cloud, and filament intersections may lead to larger amounts of mass flow that form the precursors of high-mass stars or clusters.

Di Francesco, James

2013-03-01

359

SUBMILLIMETER OBSERVATIONS OF DENSE CLUMPS IN THE INFRARED DARK CLOUD G049.40-00.01  

SciTech Connect

We obtained 350 and 850 {mu}m continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 {mu}m continuum map with an angular resolution of about 9.''6. We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M{sub Sun }. About 70% of the clumps are associated with bright 24 {mu}m emission sources, and they may contain protostars. The two most massive clumps show extended, enhanced 4.5 {mu}m emission indicating vigorous star-forming activity. The clump-size-mass distribution suggests that many of them are forming high-mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to H II regions.

Kang, Miju; Choi, Minho [Korea Astronomy and Space Science Institute, 776 Daedeokdaero, Yuseong, Daejeon 305-348 (Korea, Republic of); Bieging, John H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Rho, Jeonghee [SOFIA Science Center, USRA/NASA Ames Research Center, Moffet Field, CA 94035 (United States); Lee, Jeong-Eun [Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 446-701 (Korea, Republic of); Tsai, Chao-Wei, E-mail: mjkang@kasi.re.kr [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)

2011-12-20

360

Submillimeter Observations of Dense Clumps in the Infrared Dark Cloud G049.40-00.01  

NASA Astrophysics Data System (ADS)

We obtained 350 and 850 ?m continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 ?m continuum map with an angular resolution of about 9farcs6. We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M ?. About 70% of the clumps are associated with bright 24 ?m emission sources, and they may contain protostars. The two most massive clumps show extended, enhanced 4.5 ?m emission indicating vigorous star-forming activity. The clump-size-mass distribution suggests that many of them are forming high-mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to H II regions.

Kang, Miju; Choi, Minho; Bieging, John H.; Rho, Jeonghee; Lee, Jeong-Eun; Tsai, Chao-Wei

2011-12-01

361

Surface Photon Emissivity of Bare Strange Stars  

NASA Astrophysics Data System (ADS)

We consider the bremsstrahlung surface photon emissivity of strange quark stars, by systematically taking into account the effects of the multiple scatterings of highly relativistic quarks in a dense medium (the Landau-Pomeranchuk-Migdal effect). Because of interference between amplitudes of nearby interactions, the bremsstrahlung emissivity from a strange star surface is suppressed for frequencies smaller than a critical frequency. The range of the suppressed frequencies is a function of the quark matter density at the star's surface and of the QCD coupling constant. For temperatures much smaller than the Fermi energy of the quarks, the bremsstrahlung spectrum has the same temperature dependence as equilibrium blackbody radiation. Multiple collisions could reduce by an order of magnitude the intensity of the bremsstrahlung radiation. The effect of the thin electron layer at the surface of the quark star on the bremsstrahlung spectrum is also analyzed in detail. It is shown that absorption in the semidegenerate electron gas can also significantly reduce the intensity of the quark-quark bremsstrahlung radiation and, consequently, the surface radiation of the quark star. Hence, the combined effects of multiple collisions and absorption in the electron layer could make the soft photon surface radiation of quark stars 6 orders of magnitude smaller than equilibrium blackbody radiation.

Cheng, K. S.; Harko, T.

2003-10-01

362

Dense molecular gas in ultraluminous and high redshift galaxies.  

NASA Astrophysics Data System (ADS)

Molecular gas is the raw material for star formation and hence a crucial factor in galactic evolution. Ultraluminous infrared galaxies emit the bulk of their power in the far infrared, show disturbed morphologies indicative of recent mergers, and rival QSOs in their bolometric luminosities, but are more numerous in the local universe. Although they are as rich in molecular gas as the most gas rich normal spiral galaxies, they have elevated ratios of infrared luminosity to molecular mass that suggest they are undergoing bursts of very rapid and efficient star formation. A survey of HCN(1?0) emission from ten ultraluminous and normal galaxies shows that far infrared emission correlates better with the amount of dense, n(H2) > 104cm-3, molecular gas than with the total amount of molecular gas. The star formation efficiency appears to depend on the fraction of the molecular gas reservoir at high density. The galaxy IRAS 10214+4724 at z = 2.286 is perhaps the most luminous object in the universe. Observations of its CO (6?5), CO (4?3), and CO (3?2) lines indicate that this galaxy has as much molecular gas as the total mass of the Galaxy. The molecular gas in 10214+4724 is both warmer and denser than that in the Galaxy and the normal gas to dust ratio suggests the abundances are nearly solar. In the Milky Way, CO (6?5) is only observed in regions of high-mass star formation, so its presence in 10214+4724 implies the occurance of active star formation there. A map of the CO (3?2) emission with 2.3?resolution shows a small source slightly extended EW with a deconvolved size of (10×4)±4h-1kpc. The mass of molecular gas is comparable to the dynamical mass. This extraordinary primeval galaxy appears to have most of its mass in molecular gas and to be undergoing an extreme starburst that is generating metals with close to solar abundances.

Radford, S. J. E.

363

Neutrino diffusion and mass ejection in protoneutron stars  

SciTech Connect

We discuss the mass ejection mechanism induced by diffusion of neutrino during the early stage of the protoneutron star cooling. A dynamical calculation is employed in order to determine the amount of matter ejected and the remnant compact object mass. An equation of state considering hadronic and quark phases for the stellar dense matter was used to solve the whole time evolution of the system during the cooling phase. The initial neutrino population was obtained by considering beta equilibrium in the dense stellar matter with confined neutrinos, in the very early period of the deleptonic stage of the nascent pulsar. For specified initial configurations of the protoneutron star, we solve numerically the set of equations of motion together with neutrino diffusion through the dense stellar medium.

Almeida, L. G. [Universidade Federal do Acre-Campus Floresta, Estrada do Canela Fina, km 12, 69980-000, Cruzeiro do Sul, AC (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, 22290-180, Rio de Janeiro, RJ (Brazil); Rodrigues, H.; Portes, D. Jr. [Centro Federal de Educacao Tecnologica do Rio de Janeiro, Av. Maracana 249, 20271-110, Rio de Janeiro, RJ (Brazil); Duarte, S. B. [Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, 22290-180, Rio de Janeiro, RJ (Brazil)

2010-11-15

364

Collective Interactions between Neutrinos and Dense Plasmas.  

National Technical Information Service (NTIS)

A new interaction mechanism is described between neutrinos and dense plasmas. With the unification of the electromagnetic and weak forces, analogous processes should occur for intense neutrino fluxes as for photon fluxes. Intense EM waves excite parametri...

R. J. Bingham J. M. Dawson J. J. Su

1992-01-01

365

All teleportation and dense coding schemes  

Microsoft Academic Search

We establish a one-to-one correspondence between (1) quantum teleportation schemes, (2) dense coding schemes, (3) orthonormal bases of maximally entangled vectors, (4) orthonormal bases of unitary operators with respect to the Hilbert–Schmidt scalar product and (5) depolarizing operations, whose Kraus operators can be chosen to be unitary. The teleportation and dense coding schemes are assumed to be `tight' in the

R. F. Werner

2001-01-01

366

Electron scattering in hot-dense plasmas  

NASA Astrophysics Data System (ADS)

Hot-dense plasmas have direct industrial applications in inertial confinement fusion. We have used the convergent close-coupling (CCC) method to investigate electron scattering off hydrogen and helium atoms in a hot-dense weakly coupled (Debye) plasma. The Yukawa-type Debye-Hückel potential has been used to describe the plasma screening effects. Integrated excitation, total ionization and total cross sections have been calculated over a broad range of energies and various Debye lengths, D.

Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor

2012-11-01

367

Dynamical theory of dense groups of galaxies  

NASA Astrophysics Data System (ADS)

It is well known that galaxies associate in groups and clusters. Perhaps 40% of all galaxies are found in groups of 4 to 20 galaxies (e.g., Tully 1987). Although most groups appear to be so loose that the galaxy interactions within them ought to be insignificant, the apparently densest groups, known as compact groups appear so dense when seen in projection onto the plane of the sky that their members often overlap. These groups thus appear as dense as the cores of rich clusters. The most popular catalog of compact groups, compiled by Hickson (1982), includes isolation among its selection critera. Therefore, in comparison with the cores of rich clusters, Hickson's compact groups (HCGs) appear to be the densest isolated regions in the Universe (in galaxies per unit volume), and thus provide in principle a clean laboratory for studying the competition of very strong gravitational interactions. The $64,000 question here is then: Are compact groups really bound systems as dense as they appear? If dense groups indeed exist, then one expects that each of the dynamical processes leading to the interaction of their member galaxies should be greatly enhanced. This leads us to the questions: How stable are dense groups? How do they form? And the related question, fascinating to any theorist: What dynamical processes predominate in dense groups of galaxies? If HCGs are not bound dense systems, but instead 1D change alignments (Mamon 1986, 1987; Walke & Mamon 1989) or 3D transient cores (Rose 1979) within larger looser systems of galaxies, then the relevant question is: How frequent are chance configurations within loose groups? Here, the author answers these last four questions after comparing in some detail the methods used and the results obtained in the different studies of dense groups.

Mamon, Gary A.

1990-11-01

368

Heavy meson production in hot dense matter  

SciTech Connect

The properties of charmed mesons in dense matter are studied using a unitary coupled-channel approach in the nuclear medium which takes into account Pauli-blocking effects and meson self-energies in a self-consistent manner. We obtain the open-charm meson spectral functions in this dense nuclear environment, and discuss their implications on hidden charm and charm scalar resonances and on the formation of D-mesic nuclei at FAIR energies.

Tolos, Laura [Theory Group, KVI, University of Groningen, Zernikelaan 25, 9747 AA Groningen (Netherlands); Instituto de Ciencias del Espacio (IEEC/CSIC), Campus Universitat Autonoma de Barcelona, Facultat de Ciencies, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Gamermann, Daniel; Ramos, Angels [Departament d'Estructura i Constituents de la Materia, Universitat de Barcelona, Diagonal 647, 08028 Barcelona (Spain); Garcia-Recio, Carmen [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad de Granada, E-18071 Granada (Spain); Molina, Raquel; Nieves, Juan; Oset, Eulogio [Instituto de Fisica Corpuscular (centro mixto CSIC-UV), Institutos de Investigacion de Paterna, Aptdo. 22085, 46071, Valencia (Spain)

2010-12-28

369

Dense Photometric Stereo Using Tensorial Belief Propagation  

Microsoft Academic Search

Abstract We address the normal reconstruction problem by photometric stereo using a uniform and dense set of photometric images captured at flxed viewpoint. Our method,is robust to spurious noises caused by high- light and shadows and non-Lambertian re?ections. To simultaneously recover normal orientations and pre- serve discontinuities, we model the dense photometric stereo problem into two coupled Markov Random Fields

Kam-lun Tang; Chi-keung Tang; Tien-tsin Wong

2005-01-01

370

METHOD OF PRODUCING DENSE CONSOLIDATED METALLIC REGULUS  

DOEpatents

A methcd is presented for reducing dense metal compositions while simultaneously separating impurities from the reduced dense metal and casting the reduced parified dense metal, such as uranium, into well consolidated metal ingots. The reduction is accomplished by heating the dense metallic salt in the presence of a reducing agent, such as an alkali metal or alkaline earth metal in a bomb type reacting chamber, while applying centrifugal force on the reacting materials. Separation of the metal from the impurities is accomplished essentially by the incorporation of a constricted passageway at the vertex of a conical reacting chamber which is in direct communication with a collecting chamber. When a centrifugal force is applled to the molten metal and slag from the reduction in a direction collinear with the axis of the constricted passage, the dense molten metal is forced therethrough while the less dense slag is retained within the reaction chamber, resulting in a simultaneous separation of the reduced molten metal from the slag and a compacting of the reduced metal in a homogeneous mass.

Magel, T.T.

1959-08-11

371

Physical properties of dense molecular gas in centres of Seyfert galaxies  

NASA Astrophysics Data System (ADS)

We present new ˜1 arcsec resolution data of the dense molecular gas in the central 50-100 pc of four nearby Seyfert galaxies. Plateau de Bure Interferometer (PdBI) observations of HCN and, in two of the four sources, simultaneously HCO+ allow us to carefully constrain the dynamical state of the dense gas surrounding the active galactic nuclei (AGN). The analysis of the kinematics shows large line widths of 100-200 km s-1 full width at half-maximum (FWHM) that can only partially arise from beam smearing of the velocity gradient. The observed morphological and kinematic parameters (dimensions, major axis position angle, red and blue channel separation, and integrated line width) are well reproduced by a thick disc, where the emitting dense gas has a large intrinsic dispersion (20-40 km s-1), implying that it exists at significant scale heights (25-30 per cent of the disc radius). To put the observed kinematics in the context of the starburst and AGN evolution, we estimate the Toomre Q parameter. We find this is always greater than the critical value, i.e. Q is above the limit such that the gas is stable against rapid star formation. This is supported by the lack of direct evidence, in these four Seyfert galaxies, for on-going star formation close around the AGN. Instead, any current star formation tends to be located in a circumnuclear ring. We conclude that the physical conditions are indeed not suited to star formation within the central ˜100 pc.

Sani, E.; Davies, R. I.; Sternberg, A.; Graciá-Carpio, J.; Hicks, E. K. S.; Krips, M.; Tacconi, L. J.; Genzel, R.; Vollmer, B.; Schinnerer, E.; García-Burillo, S.; Usero, A.; Orban de Xivry, G.

2012-08-01

372

Observing Star Formation: From the Interstellar Medium to Star-Forming Cores  

NASA Astrophysics Data System (ADS)

In the thirty years since the first mapping of molecular line emission from interstellar clouds, our ``picture" of the interstellar medium has evolved enormously. With only optical observations available, it was (correctly) hypothesized that new stars form from condensations of dense interstellar gas which appear optically as dark or bright nebulae. These early hypotheses often envisioned the overall collapse of whole clouds into stars, or fragmentation of entire clouds into ``Jeans mass"-size clumps. Thirty years of observing the clouds and the star-formation process which takes place within them has, alas, shown these hypotheses to be too simple. Radio-wavelength spectral-line mapping of interstellar gas, far-infrared and sub-millimeter continuum observations of thermal dust emission, and near-infrared and optical spectral and continuum observations of young stellar objects (YSO's) have revealed a detailed--yet nonetheless perplexing--view of the star-formation process. Molecular ``clouds" appear to be wispy, clumpy condensations of interstellar gas, with self-similar density and velocity structure on scales from hundreds of parsecs down to tenths of parsecs. Projected on density maxima in the gas distribution, one often finds point (or very compact) sources whose spectral colors are consistent with their being deeply embedded in dense gas. These sources are often the origin of powerful jets and outflows and are believed to be YSO's. The outflows, which can carry angular momentum away from a YSO, represent an important phase in the star-formation process. I will discuss the current observational ``picture" of star-forming molecular clouds, as well as some of the many theoretical models which have been proposed to explain cloud structure. Current theories and simulations include gravitational, magnetic and dynamical forces and seek to explain how these forces conspire to simultaneously regulate equilibrium, turbulent, and runaway (e.g. star-formation) processes observed in molecular clouds.

Goodman, Alyssa A.

1995-12-01

373

Variational Theory of Hot Dense Matter  

ERIC Educational Resources Information Center

|We develop a variational theory of hot nuclear matter in neutron stars and supernovae. It can also be used to study charged, hot nuclear matter which may be produced in heavy-ion collisions. This theory is a generalization of the variational theory of cold nuclear and neutron star matter based on realistic models of nuclear forces and pair…

Mukherjee, Abhishek

2009-01-01

374

Coarse-grained simulations of moderately entangled star polyethylene melts  

NASA Astrophysics Data System (ADS)

In this paper, a previous coarse-grain model [J. T. Padding and W. J. Briels, J. Chem. Phys. 117, 925 (2002)] to simulate melts of linear polymers has been adapted to simulate polymers with more complex hierarchies. Bond crossings between highly coarse-grained soft particles are prevented by applying an entanglement algorithm. We first test our method on a virtual branch point inside a linear chain to make sure it works effectively when linking two linear arms. Next, we apply our method to study the diffusive and rheological behaviors of a melt of three-armed stars. We find that the diffusive behavior of the three-armed star is very close to that of a linear polymer with the same molecular weight, while its rheological properties are close to those of a linear chain with molecular mass equal to that of the longest linear sub-chain in the star.

Liu, L.; Padding, J. T.; den Otter, W. K.; Briels, W. J.

2013-06-01

375

Polymers All Around You!  

ERIC Educational Resources Information Center

|Background information on natural polymers, synthetic polymers, and the properties of polymers is presented as an introduction to this curriculum guide. Details are provided on the use of polymer products in consumer goods, polymer recycling, polymer densities, the making of a polymer such as GLUEP, polyvinyl alcohol, dissolving plastics,…

Gertz, Susan

376

Microgravity Polymers.  

National Technical Information Service (NTIS)

A one-day, interactive workshop considering the effects of gravity on polymer materials science was held in Cleveland, Ohio, on May 9, 1985. Selected programmatic and technical issues were reviewed to introduce the field to workshop participants. Parallel...

1986-01-01

377

Organometallic Polymers.  

ERIC Educational Resources Information Center

Reactions utilized to incorporate a metal-containing moiety into a polymer chain (addition, condensation, and coordination) are considered, emphasizing that these reactions also apply to smaller molecules. (JN)

Carraher, Charles E., Jr.

1981-01-01

378

Polymer batteries  

NASA Astrophysics Data System (ADS)

This paper presents a state-of-the-art report on polymer battery development. The research and development activities related to materials of construction for battery components, i.e., anode, electrolyte, and cathode are reviewed. Major achievements have been accomplished in the last decade and the progress is very encouraging. Some potential problems have been identified and these problems may require significant development efforts before polymer batteries become a commercial reality.

Kumar, Binod; Marsh, Richard A.

1991-04-01

379

Polymer Synthesis  

NSDL National Science Digital Library

In the first four chapters, we have seen that many different kinds of polymers exist and that they have an extremely wide range of properties. Some are stiff, others are soluble, while still others are rubbery. There are plastics, and fibers, and adhesives, and foams. The structure and composition of the macromolecule dictate the ultimate properties. Structure and composition are determined when the macromolecule is synthesized. In this chapter we want to understand how monomers react together to form long polymer chains.

Teegarden, David

2004-01-01

380

Quark-Cluster Stars: Hints from the Surface  

NASA Astrophysics Data System (ADS)

The matter inside pulsar-like compact stars could be in a quark-cluster phase since in cold dense matter at a few nuclear densities (? 2 - 10?0), quarks could be coupled still very strongly and condensate in position space to form quark clusters. Quark-cluster stars are chromatically confined and could initially be bare, therefore the surface properties of quark-cluster stars would be quite different from that of conventional neutron stars. Some facts indicate that a bare and self-confined surface of pulsar-like compact stars might be necessary in order to naturally understand different observational manifestations. On one hand, as for explaining the drifting sub-pulse phenomena, the binding energy of particles on pulsar surface should be high enough to produce vacuum gaps, which indicates that pulsar's surface might be strongly self-confined. On the other hand, a bare surface of quark-cluster star can overcome the baryon contamination problem of ?-ray burst as well as promote a successful core-collapse supernova. What is more, the non-atomic thermal spectra of dead pulsars may indicate also a bare surface without atmosphere, and the hydro-cyclotron oscillation of the electron sea above the quark-cluster star surface could be responsible for those absorption features detected. These hints could reflect the property of compact star's surface and possibly the state of condensed matter inside, and then might finally result in identifying quark-cluster stars.

Dai, Shi; Xu, Renxin

2012-01-01

381

Polymer/Solvent and Polymer/Polymer Interaction Studies.  

National Technical Information Service (NTIS)

Polymer/polymer and polymer/solvent interaction information can be obtained from solution thermodyanmic studies. In this work, gas chromatography and piezoelectric sorption techniques were used to obtain experimental solution data. A brief review of exper...

J. C. Holste C. J. Glover D. T. Magnuson K. C. Dangayach T. A. Powell

1979-01-01

382

Distances to dense cores that contain very low luminosity objects  

NASA Astrophysics Data System (ADS)

Aims: We estimate the distances to dense molecular cores that harbour very low luminosity objects (VeLLOs) detected by the Spitzer Space Telescope and attempt to confirm their VeLLO nature. Methods: The cloud distances are estimated using a near-IR photometric method. We use a technique that performs a spectral classification of stars lying towards the fields containing the clouds as either main-sequence stars or giants. In this technique, the observed (J - H) and (H - Ks) colours are dereddened simultaneously using trial values of AV and a normal interstellar extinction law. The best fit of the dereddened colours to the intrinsic colours giving a minimum value of ?2 then yields the corresponding spectral type and AV for the star. The main-sequence stars, thus classified, are then utilized in an AV versus distance plot to bracket the cloud distances. The typical error in the estimation of distances to the clouds are found to be ~18%. Results: We estimate distances to seven cloud cores, IRAM 04191, L1521F, BHR 111, L328, L673-7, L1014, and L1148 using the above method. These clouds contain VeLLO candidates. The estimated distances to the cores are found to be 127 ± 25 pc (IRAM 04191), 136 ± 36 pc (L1521F), 355 ± 65 pc (BHR 111), 217 ± 30 pc (L328), 240 ± 45 pc (L673-7), 258 ± 50 pc (L1014), and 301 ± 55 pc (L1148). We re-evaluated the internal luminosities of the VeLLOs discovered in these seven clouds using the distances estimated from this work. Except for L1014 - IRS (Lint = 0.15 L?), all other VeLLO candidates are found to be consistent with the definition of a VeLLO (Lint ? 0.1 L?). In addition to the cores that harbour VeLLO candidates, we also obtained distances to the clouds L323, L675, L676, CB 188, L1122, L1152, L1155, L1157, and L1158, which are located in the directions of the above seven cores. Towards L1521F and L1148, we found evidence of multiple dust layers.

Maheswar, G.; Lee, C. W.; Dib, S.

2011-12-01

383

Polymer functionalization with manganites  

NASA Astrophysics Data System (ADS)

We investigated the transport properties of a series of composites made of La2/3Sr1/3MnO3 and different copolymers. The temperature dependence of the electrical resistance of the samples is strongly dependent on the nature of the polymers. We found four types of temperature dependences of the electrical resistance: i) simple current dependence of resistivity for poly(methyl-methacrylate-co-styrene) copolymers, ii) single peaked characteristics for poly(acryl amide-co-vinyl acetate), iii) multipeaked dependence found in poly(methyl-methacrylate-co-butadiene) and star type polysiloxane-gstyrene, and iv) current independent characteristics visible in the samples made with linear polysiloxane-based composites.

Sandu, V.; Popa, S.; Ivan, I.; Plapcianu, C.; Sandu, E.; Hurduc, N.; Nor, I.

2009-07-01

384

Synthesis of cationic polymer-grafted cellulose by aqueous ATRP  

Microsoft Academic Search

We describe the synthesis of cellulose fibers densely grafted with the cationic polymer poly[2-(methacryloyloxy)ethyl]-trimethylammoniumchloride (PMeDMA) through aqueous ATRP. The hydroxyl groups present on the cellulose surface were exploited to initiate the ATRP polymerization of MeDMA. We first grafted a bromide initiator, known to be an efficient initiator for ATRP, on the cellulose surface from which the polymer was then directly

O. Glaied; M. Dubé; B. Chabot; C. Daneault

2009-01-01

385

Low-temperature cracking of polymer-modified asphalt  

Microsoft Academic Search

A laboratory investigation was conducted to study different types of polymer-modified asphalt with regard to low temperature\\u000a behaviour. The thermal stress restrained specimen test (TSRST) was used to assess the disposition of asphalt mixtures to cracking\\u000a at low temperature. Five polymer modified bitumens and three mixture types (dense graded, stone mastic and porous asphalt)\\u000a were investigated. In addition, three different

U. Isacsson; H. Zeng

1998-01-01

386

Present-day star formation: Protostellar outflows and clustered star formation  

NASA Astrophysics Data System (ADS)

Stars form predominantly in clusters inside dense clumps of turbulent, magnetized molecular clouds. The typical size and mass of the cluster-forming clumps are ~ 1 pc and ~102-103Msolar, respectively. Here, we discuss some recent progress on theoretical and observational studies of clustered star formation in such parsec-scale clumps with emphasis on the role of protostellar outflow feedback. Recent simulations indicate that protostellar outflow feedback can maintain supersonic turbulence in a cluster-forming clump, and the clump can keep a virial equilibrium long after the initial turbulence has decayed away. In the clumps, star formation proceeds relatively slowly; it continues for at least several global free-fall times of the parent dense clump (tff ~ a few × 105 yr). The most massive star in the clump is formed at the bottom of the clump gravitational potential well at later times through the filamentary mass accretion streams that are broken up by the outflows from low-mass cluster members. Observations of molecular outflows in nearby cluster-forming clumps appear to support the outflow-regulated cluster formation model.

Nakamura, Fumitaka; Li, Zhi-Yun

2012-09-01

387

Controlled Architecture Polymers by Anionic Polymerization  

NASA Astrophysics Data System (ADS)

Anionic polymerization is the most important synthetic tool to produce model polymers and copolymers with complex macromolecular architectures. High vacuum techniques1 have to be used in order to avoid premature living chain termination or linking agent destruction. These techniques are very demanding in glass blowing practice, time consuming and usually lead to the synthesis of a few grams of model polymers. Nevertheless, these Â"limitationsÂ" are a small price to pay given the potential of anionic polymerization to generate true model polymeric materials. By using anionic polymerization and controlled chlorosilane chemistry a variety of macromolecular architectures have been created2. A few examples are the miktoarm stars ( AnB, AnBn), the á,ù-branched polymers ( AnBAn), and the comb-shaped polymers (A-g-B1or2) where A, B are polymeric chains with different molecular weight or chemistry and n, m: 2-8. Recent advances in anionic polymerization methodology led to the synthesis of well-defined cyclic co- and terpolymers3,4, as well as dendritic polymers5, multicomponent multiblock polymers6 and polymeric materials having as building blocks macromonomers7. References 1. N. Hadjichristidis, H. Iatrou, S. Pispas, M. Pitsikalis, J. Polym. Sci., Part A : Polym. Chem. 38, 3211 (2000). 2. N. Hadjichristidis, M. Pitsikalis, S. Pispas, H. Iatrou, Chem. Rev. 101, 3747 (2001). 3. H. Iatrou, N. Hadjichristidis, G. Meier H. Frielinghaus, and M. Monkenbusch, Macromolecules 35 5426 (2002) 4. D. Pantazis, D. Schulz, N. Hadjichristidis, J. Polym. Sci., Part A : Polym.Chem. 40, 1476 (2002) 5. I. Chalari, and N. Hadjichristidis, J. Polym. Sci., Part A: Polym. Chem. 40, 1519 (2002) 6. K. Takahashi, H. Hasegawa, T. Hashimoto, V. Bellas, H. Iatrou, N. Hadjichristidis, Macromolecules 35, 4859 (2002) 7. D. Pantazis, I. Chalari, N. Hadjichristidis, Macromolecules, submitted

Hadjichristidis, Nikos

2003-03-01

388

Electrochemical properties of composite polymer electrolyte applied to rechargeable lithium polymer battery  

Microsoft Academic Search

High-molecular-weight comb-shaped polyethers, poly(ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether-co-allyl glycidyl ether) (P(EO\\/EM\\/AGE)) and poly(ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether) (P(EO\\/EM)), were synthesized and used for the preparation of the all solid polymer electrolyte and the composite polymer electrolyte combined with a plasticizer Star-EO-OMe, pentaerythritol tetrakis(2-methoxyethyl ether), which shows low vapor pressure, respectively. Some electrochemical properties of the polymer electrolytes and performances of the

Yasuo Matoba; Shohei Matsui; Masato Tabuchi; Takaaki Sakai

2004-01-01

389

Nuclear Star-forming Ring of the Milky Way: Simulations  

NASA Astrophysics Data System (ADS)

We present hydrodynamic simulations of gas clouds in the central kpc region of the Milky Way that is modeled with a three-dimensional bar potential. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A ring of dense gas clouds forms as a result of X 1-X 2 orbit transfer, and our potential model results in a ring radius of ~200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star formation rate (SFR) in the CMZ, ~2 × 107 M sun and ~0.1 M sun yr-1. Star formation in our simulations takes place mostly in the outermost X 2 orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. Furthermore, from the relatively small size of the Milky Way's nuclear bulge, which is thought to be a result of sustained star formation in the CMZ, we infer that the Galactic inner bulge probably had a shallower density profile or stronger bar elongation in the past.

Kim, Sungsoo S.; Saitoh, Takayuki R.; Jeon, Myoungwon; Figer, Donald F.; Merritt, David; Wada, Keiichi

2011-07-01

390

Coherence in Dense Cores. II. The Transition to Coherence  

NASA Astrophysics Data System (ADS)

After studying how line width depends on spatial scale in low-mass star-forming regions, we propose that "dense cores" (Myers & Benson 1983) represent an inner scale of a self-similar process that characterizes larger scale molecular clouds. In the process of coming to this conclusion, we define four distinct types of line width-size relation ( Delta v~R^{ai}) , which have power-law slopes a1, a2, a3, and a4, as follows: Type 1--multitracer, multicloud intercomparison; Type 2--single-tracer, multicloud intercomparison; Type 3--multitracer study of a single cloud; and Type 4--single-tracer study of a single cloud. Type 1 studies (of which Larson 1981 is the seminal example) are compendia of Type 3 studies which illustrate the range of variation in the line width-size relation from one region to another. Using new measurements of the OH and C18O emission emanating from the environs of several of the dense cores studied in NH3 by Barranco & Goodman (1998; Paper I), we show that line width increases with size outside the cores with a4 ~ 0.2. On scales larger than those traced by C18O or OH, 12CO and 13CO observations indicate that a4 increases to ~0.5 (Heyer & Schloerb 1997). By contrast, within the half-power contour of the NH3 emission from the cores, line width is virtually constant, with a4 ~ 0. We interpret the correlation between increasing density and decreasing Type 4 power-law slope as a "transition to coherence." Our data indicate that the radius Rcoh at which the gas becomes coherent (i.e., a4 --> 0) is of order 0.1 pc in regions forming primarily low-mass stars. The value of the nonthermal line width at which "coherence" is established is always less than but still of order of the thermal line width of H2. Thus coherent cores are similar to, but not exactly the same as, isothermal balls of gas. Two other results bolster our proposal that a transition to coherence takes place at ~0.1 pc. First, the OH, C18O, and NH3 maps show that the dependence of column density on size is much steeper (N ~ R-0.9) inside Rcoh than outside of it (N ~ R-0.2), which implies that the volume filling factor of coherent cores is much larger than in their surroundings. Second, Larson (1995) has recently found a break in the power law characterizing the clustering of stars in Taurus at 0.04 pc, just inside of Rcoh. Larson and we interpret this break in slope as the point at which stellar clustering properties change from being determined by the (fractal) gas distribution (on scales greater than 0.04 pc) to being determined by fragmentation processes within coherent cores (on scales less than 0.04 pc). We speculate that the transition to coherence takes place when a dissipation threshold for the MHD turbulence that characterizes the larger scale medium is crossed at the critical inner scale Rcoh. We suggest that the most likely explanation for this threshold is the marked decline in the coupling of the magnetic field to gas motions due to a decreased ion/neutral ratio in dense, high filling factor gas.

Goodman, Alyssa A.; Barranco, Joseph A.; Wilner, David J.; Heyer, Mark H.

1998-09-01

391

Lifestyles of the Stars.  

ERIC Educational Resources Information Center

|Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)|

National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

392

Theories of star formation  

Microsoft Academic Search

A well defined theory of star formation does not yet exist. A serious deficiency therefore remains in current theories of the structure and evolution of stars. Since stars must be forming at the present phase of Galactic evolution, it is pertinent to investigate what conditions favour star formation. Observational evidence for the pre-main sequence phase of stellar evolution is entirely

D. McNally

1971-01-01

393

NRO M 33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC). II Dense Gas Formation  

NASA Astrophysics Data System (ADS)

We report the results of our observations of the 12 CO (J = 1-0) and 12 CO (J = 3-2) line emission of 74 major giant molecular clouds (GMCs) within the galactocentric distance of 5.1 kpc in the Local Group galaxy M 33. The observations have been conducted as part of the Nobeyama Radio Observatory M 33 All-disk survey of Giant Molecular Clouds project (NRO MAGiC). The spatial resolutions are 80 pc for 12 CO (J = 1-0) and 100 pc for 12 CO (J = 3-2). We detect 12 CO (J = 3-2) emission of 65 GMCs successfully. Furthermore, we find that the correlation between the surface density of the star formation rate, which is derived from a linear combination of H? and 24 ? m emissions, and the 12 CO (J = 3-2) integrated intensity still holds at this scale. This result shows that the star-forming activity is closely associated with warm and dense gases that are traced with the 12 CO (J = 3-2) line, even in the scale of GMCs. We also find that the GMCs with a high star-forming activity tend to show a high integrated intensity ratio (R3-2/1-0). Moreover, we also observe a mass-dependent trend of R3-2/1- 0 for the GMCs with a low star-forming activity. From these results, we speculate that the R3-2/1-0 values of the GMCs with a low star-forming activity mainly depend on the dense gas fraction and not on the temperature, and therefore, the dense gas fraction increases with the mass of GMCs, at least in the GMCs with a low star-forming activity.

Onodera, Sachiko; Kuno, Nario; Tosaki, Tomoka; Muraoka, Kazuyuki; Miura, Rie E.; Kohno, Kotaro; Nakanishi, Kouichiro; Sawada, Tsuyoshi; Komugi, Shinya; Kaneko, Hiroyuki; Hirota, Akihiko; Kawabe, Ryohei

2012-12-01

394

The Galactic Center massive black hole and nuclear star cluster  

NASA Astrophysics Data System (ADS)

The Galactic Center is an excellent laboratory for studying phenomena and physical processes that may be occurring in many other galactic nuclei. The center of our Milky Way is by far the closest galactic nucleus, and observations with exquisite resolution and sensitivity cover 18 orders of magnitude in energy of electromagnetic radiation. Theoretical simulations have become increasingly more powerful in explaining these measurements. This review summarizes the recent progress in observational and theoretical work on the central parsec, with a strong emphasis on the current empirical evidence for a central massive black hole and on the processes in the surrounding dense nuclear star cluster. Current evidence is presented, from the analysis of the orbits of more than two dozen stars and from the measurements of the size and motion of the central compact radio source, Sgr A* , that this radio source must be a massive black hole of about 4.4×106M? , beyond any reasonable doubt. What is known about the structure and evolution of the dense nuclear star cluster surrounding this black hole is reported, including the astounding fact that stars have been forming in the vicinity of Sgr A* recently, apparently with a top-heavy stellar-mass function. A dense concentration of fainter stars centered in the immediate vicinity of the massive black hole are discussed, three of which have orbital peri-bothroi of less than one light day. This “S-star cluster” appears to consist mainly of young early-type stars, in contrast to the predicted properties of an equilibrium “stellar cusp” around a black hole. This constitutes a remarkable and presently not fully understood “paradox of youth.” What is known about the emission properties of the accreting gas onto Sgr A* is also summarized and how this emission is beginning to delineate the physical properties in the hot accretion zone around the event horizon.

Genzel, Reinhard; Eisenhauer, Frank; Gillessen, Stefan

2010-10-01

395

A red Giant Star With a Strange Star as a Core  

NASA Astrophysics Data System (ADS)

The model of a red giant with the mass 5Modot, luminosity % 41740Lodot and the radius 980Rodot and with the strange quark as a core has been constructed. A comparison has been made with the object of Thorne-Zytkow that has analogous integral parameters. The difference in the inner structure is manifested just at the dense core. Convection does not stop up to the strange star, the matter over the core is withstood only due to the emission from the strange star. The lifetime of the red giants with the strange star turns out to be 500 times shorter than that of the Thorne-Zytkow's object, and is 10^5 year order.

Hajyan, G.; Vartanyan, Yu.; Grigoryan, A.

1998-12-01

396

J/? measurements in STAR Experiment at RHIC  

NASA Astrophysics Data System (ADS)

During the last decade STAR experiment has studied the hot and dense nuclear matter produced in heavy ion collisions at RHIC. The study of quarkonia, such as J/? meson, production provides the information about properties of this nuclear matter. It is predicted that due to the Debye screening the quarkonia production is suppressed when Quark Gluon Plasma (QGP) is presented. In order to understand the properties of hot and dense nuclear matter, it is necessary to study the production of quarkonia in hadron-hadron, hadron-ion, and ion-ion collisions separately to distinguish cold nuclear matter effect, such as gluon shadowing, from the suppression due to the formation of QGP. Moreover, the J/? hadron azimuthal correlations allow to extract the fraction of J/? that originates from B-mesons. This proceedings presents recent J/? measurements at mid-rapidity in p+p, and Au+Au collisions at = 200 GeV at STAR, the fraction of J/? originates from B-mesons, and J/? eliptic flow v2 as a function of transverse momentum in Au+Au collisions in = 200 GeV at STAR.

Hájková, Olga; Star Collaboration

2012-11-01

397

Supramolecular Star-Shaped Poly(ethylene glycol) Based on a [2?×?2] Grid-Like Metal Complex.  

PubMed

Supramolecular star-shaped polymers are a class of materials that are formed by self-assembly of polymeric precursors. The resulting structures combine the beneficial properties of conventional star-shaped polymers and (reversible) supramolecular interactions. We previously introduced [2?×?2] copper(I) grids of 3,6-di(2-pyridyl)-pyridazine (DPP) as structural motif to form the core of supramolecular star-shaped polymers. In the current work, this concept is expanded to star-shaped poly(ethylene glycol) (PEG) by end-functionalization of amine-functionalized PEG with DPP. The synthesis and characterization of PEG-DPP as well as the self-assembly into star-shaped supramolecular polymers upon copper(I) complexation are discussed in detail. PMID:21590976

Hoogenboom, Richard; Moore, Brian C; Schubert, Ulrich S

2010-03-04

398

Extragalactic Star Clusters: the Resolved Star Approach  

NASA Astrophysics Data System (ADS)

The physical processes leading to the dissolution of star clusters is a topic barely studied and still not understood. We started a pilot project to develop a new approach to directly detect and study the properties of stellar clusters while they are being destroyed. Our technique currently under development makes use of the exceptional spatial resolution and sensitivity of the ACS camera onboard HST to resolve individual stars in nearby galaxies. PSF stellar photometry and color-magnitude diagrams allows us to separate the most massive stars (more likely to be in clusters) from the star field background. While applying the method to the normal spiral galaxy NGC1313, we found that the method of studying star clusters through resolved stars in nearby galaxies is even more powerful than we first expected. The stellar maps obtained for NGC1313 show that a large fraction of early B-type stars contained in the galaxy are already part of the star field background rather that being in star clusters. Such stars live for 5 to 25 Myr. Since most stars form in clusters, the presence of such massive stars in the field means that they must have left their birthplace very rapidly. It also means that the processes involved in the dissolution of the clusters are extremely efficient. The only plausible explanation for so many young stars to be in the field background is the infant mortality of star clusters. We will present the latest results on the two galaxies NGC 1313 and IC 2475 and discuss the potential of the new approach for studying extragalactic stellar clusters.

Pellerin, Anne; Meyer, M. J.; Jason, H.; Calzetti, D.

2006-12-01

399

Dust condensation in dense interstellar clouds, and some related topics  

SciTech Connect

The hypothesis is proposed that dust grains form in dense interstellar clouds. If the composition of a molecular cloud is determined by gas-phase reactions and the density n approx. = 10/sup 5/ cm/sup -3/, active dust condensation can occur. After approx. = 10/sup 7/ yr the grains will have a relative abundance epsilon/sub d/ = n/sub d//napprox. = 10/sup -9/ and their radius will rapidly grow to r/sub d/approx. = 10/sup -6/ cm. Since densities napprox. = 10/sup 5/ cm/sup -3/ are possible only in the central parts of massive clouds, subsequent dispersal throughout the cloud of dust formed in the nuclear region, together with the growth of the grains by adhesion of new particles, will yield the values epsilon/sub d/approx. = 10/sup -12/, r/sub d/approx. = 10/sup -5/ cm typical of the interstellar medium. Several implications of the hypothesis are discussed. The dense nuclei of massive clouds, cooling as dust forms there, will contract rapidly, fragmenting and collapsing to produce star clusters. The formation of H/sub 2/ molecules on the grains will serve as a source of strong infrared radiation at lambdaapprox. = 300 ..mu... For a cloud of 10/sup 18/ cm radius the infrared luminosity will reach Lapprox. = 3.5 x 10/sup -7/ n/sup 2/ L/sub sun/. The far-infrared radiation observed in several clouds could originate in this way, and act as an indicator for discovery of condensing clouds. The present hypothesis can explain the depletion of several elements that we observe in the interstellar gas. The genetic association between gas and dust in the Galaxy and the characteristic distribution of dust in the spiral arms of galaxies now find a natural interpretation.

Kolesnik, I.G.

1978-09-01

400

Dense molecular gas in galactic nuclei  

NASA Astrophysics Data System (ADS)

The results of investigations of cool dense interstellar media are reviewed with particular attention given to observational data. Instrument technologies are described which allow the investigation of circumnuclear gas in the galaxies that are devoid of H I and inaccessible at optical wavelengths. Molecular mass estimates and correlations between nuclear and global galactic properties are described. CO observations are discussed in relation to strongly interacting nearby galaxies, and models of bars and rings are presented. Correlations between the kinematic, physical, and chemical properties of the dense gas and nuclear regions of the Galaxy are listed, and the molecular properties of distant ultraluminous galaxies are reviewed. It is shown that 10 percent of the galaxies measured in H I can be detected in CO, and it is recommended that many high-resolution CO maps be obtained in order to evaluate nuclear gas properties statistically. Other significant techniques are proposed to improve the study of dense molecular gas in galactic nuclei.

Henkel, C.; Baan, W. A.; Mauersberger, R.

1991-06-01

401

Stellar Wind Disruption by an Orbiting Neutron Star: Low X-Ray Luminosity  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. This simulation, in the reference frame of the neutron star, shows conditions of low X-ray luminosity. in which there is a small accretion radius, a slight asymmetry, and short timescales for variability. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

402

Tidal Streams in Massive X-ray Binary Systems: Neutron Star Close-up  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. In this simulation, the tidal distortion of the primary star and the resultant tidal stream is shown. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

403

Stellar Wind Disruption by an Orbiting Neutron Star: Moderate X-Ray Luminosity  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. This simulation, in the reference frame of the neutron star, shows conditions of low X-ray luminosity. in which there is a large accretion radius, significant asymmetry, and long timescales for variability. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

404

Stellar Wind Disruption by an Orbiting Neutron Star: High X-Ray Luminosity  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. This simulation, in the reference frame of the neutron star, shows conditions of high X-ray luminosity. in which there is a weak bowshock, no oscillation, and a large photoionization wake. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

405

Dust and young embedded stars in the Lagoon Nebula - a near-IR imaging survey.  

NASA Astrophysics Data System (ADS)

A large HII region, the Lagoon Nebula is one of the brightest sources of CO emission in the sky, containing at least two OB stars, and is surrounded by fairly warm (25-30 K) molecular gas and dust. It may be the site of ongoing star formation triggered by the OB stars. We have taken near infra-red broad band data (J,H and Ks) to hunt for deeply embedded young stars and to estimate the dust opacity in the dense gas, by comparing the near-IR extinction to the submillimeter continuum emission mapped with SCUBA. We present initial imaging and photometry over a 30 by 20 arcminute field.

Kenworthy, M. A.; Tothill, N. F. H.

2001-12-01

406

KEY ISSUES REVIEW: Insights from simulations of star formation  

NASA Astrophysics Data System (ADS)

Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar discs often form from the gas being accreted by the forming stars, and accretion from these discs may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many aspects of star formation, and detailed numerical simulations are needed to advance our understanding of the subject. 'The purpose of computing is insight, not numbers.' Richard W Hamming, in Numerical Methods for Scientists and Engineers (1962) 'There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.' William Shakespeare, in Hamlet, Prince of Denmark (1604)

Larson, Richard B.

2007-03-01

407

Physics of high temperature, dense plasmas  

NASA Astrophysics Data System (ADS)

The grant, 'The Physics of High Temperature, Dense Plasmas,' includes work on two projects in conjunction with the Advanced Concepts Branch of the Applied Physics Division at the Air Force Weapons Laboratory. The first is a relativistic electron beam-(REB) heated, dense plasma experiment using REB facilities at AFWL, and the second is soft X-ray instrumentation work pertinent to the SHIVA X-ray simulation facility. This report primarily details work in progress and results achieved in the REB-Plasma interaction experiments, since much of our effort during the period of this report have been directed at that project.

Woodall, D. M.

1981-03-01

408

All teleportation and dense coding schemes  

NASA Astrophysics Data System (ADS)

We establish a one-to-one correspondence between (1) quantum teleportation schemes, (2) dense coding schemes, (3) orthonormal bases of maximally entangled vectors, (4) orthonormal bases of unitary operators with respect to the Hilbert-Schmidt scalar product and (5) depolarizing operations, whose Kraus operators can be chosen to be unitary. The teleportation and dense coding schemes are assumed to be `tight' in the sense that all Hilbert spaces involved have the same finite dimension d, and the classical channel involved distinguishes d 2 signals. A general construction procedure for orthonormal bases of unitaries, involving Latin squares and complex Hadamard matrices is also presented.

Werner, R. F.

2001-09-01

409

Dense packing: surgical indications and technical considerations.  

PubMed

Dense packing is the philosophy of fitting more than 30 to 35 follicular unit grafts per square centimeter in one operation. The aim is to produce a more even, consistent, and natural looking flow of hair after just one procedure. Although desirable in principle, not all patients are suitable candidates nor is it possible to achieve in certain patients (eg, coarse or curly hair). Patients who have sufficient donor availability, reasonably stable hair loss, and high hair-to-skin color ratios are the ideal candidates. The authors highlight their philosophies and strategies for dense packing. PMID:24017984

Farjo, Bessam; Farjo, Nilofer

2013-08-01

410

Ab Initio Simulations of Dense Helium Plasmas  

SciTech Connect

We study the thermophysical properties of dense helium plasmas by using quantum molecular dynamics and orbital-free molecular dynamics simulations, where densities are considered from 400 to 800 g/cm{sup 3} and temperatures up to 800 eV. Results are presented for the equation of state. From the Kubo-Greenwood formula, we derive the electrical conductivity and electronic thermal conductivity. In particular, with the increase in temperature, we discuss the change in the Lorenz number, which indicates a transition from strong coupling and degenerate state to moderate coupling and partial degeneracy regime for dense helium.

Wang Cong [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); He Xiantu; Zhang Ping [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Center for Applied Physics and Technology, Peking University, Beijing 100871 (China)

2011-04-08

411

Exclusion principle for quantum dense coding  

NASA Astrophysics Data System (ADS)

We show that the classical capacity of a quantum state, as quantified by its ability to perform dense coding, respects an exclusion principle, for arbitrary pure or mixed three-party states in any dimension. This states that no two bipartite states which are reduced states of a common tripartite quantum state can have simultaneous quantum advantage in dense coding. The exclusion principle is robust against noise. Such a principle also holds for an arbitrary number of parties. This exclusion principle is independent of the content and distribution of entanglement in the multipartite state.

Prabhu, R.; Pati, Arun Kumar; Sen(De), Aditi; Sen, Ujjwal

2013-05-01

412

Formation of Globules, Pillars, and Dense Condensations Around H II Regions  

NASA Astrophysics Data System (ADS)

We present a new model for the formation of dense clumps and pillars around H II regions based on shocks curvature at the interface between a H II region and a molecular cloud. UV radiation leads to the formation of an ionization front and of a shock ahead. The gas is compressed between them forming a dense shell at the interface. This shell may be curved due to initial interface or density modulation caused by the turbulence of the molecular cloud. Low curvature leads to instabilities in the shell that form dense clumps while sufficiently curved shells collapse on itself to form pillars. When turbulence is high compared to the ionized-gas pressure, bubbles of cold gas have sufficient kinetic energy to penetrate into the H II region and detach themselves from the parent cloud, forming cometary globules. Using computational simulations, we show that these new models are extremely efficient to form dense clumps and stable and growing elongated structures, pillars, in which star formation might occur. The inclusion of turbulence in the model shows its importance in the formation of cometary globules. The code used for the simulation is the HERACLES code, that comprises hydrodynamics with various equation of state, radiative transfer, gravity, cooling and heating. We also present observational diagnostic of these new models based on the line-of-sight velocity profiles and probability density functions.

Tremblin, P.; Audit, E.

2013-04-01

413

The Life and Death of Dense Molecular Clumps Around Massive YSOs in the LMC  

NASA Astrophysics Data System (ADS)

We present observations of the dense molecular clumps toward active star formation regions N105, N113, N159, and N44 in the LMC. Observations were performed with the Australia Telescope Compact Array in the 3 mm transitions of HCO+ and HCN. The observations reveal that the molecular material is clumpy, with individual clump masses between 102 and 104 solar masses and radii of <1 pc to 2 pc. While many of the clumps are coincident with tracers of star formation, we find several to be devoid of any star formation signposts. The clumps with on-going star formation are on average 3-5 times more massive than those without, suggesting that the mass of the most massive star a clump forms may be determined by the mass of the natal clump. Moreover, we find a possible correlation between the mass of a clump and the projected distance between the clump's center and the forming star, suggesting that as a massive star forms, it becomes displaced from the clump's emission peak as it dissipates a significant fraction (>1/2) of the surrounding clump. We also find a number of YSOs within the imaged regions that are not associated with HCO+ or HCN emission; these YSOs have presumably destroyed their natal clumps to become evolutionarily older than those in clumps. The strength of the 10 micron silicate absorption feature seen in mid-IR spectra of YSOs is correlated with a source's association with a molecular clump; objects within clumps have deep silicate features, while those outside clumps have features that are weak or non-existent. This correlation suggests the silicate feature is formed by material on clump-sized scales. Using a large sample of LMC massive YSO spectra, we estimate that 60% of the YSOs detected in the LMC via their mid-IR emission are no longer located in molecular clumps.

Seale, Jonathan P.; Looney, L. W.; Wong, T.; Ott, J.

2011-01-01

414

Star Formation Triggering Mechanisms Revealed by Far-Ultraviolet, H? , and HI Images of Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

Far-Ultraviolet (FUV), H? , and HI observations of dwarf galaxies Holmberg II, IC2574, and Sextans A are used to investigate the means by which star formation propagates in galaxies lacking dominant global triggering mechanisms. The observations trace the interaction between sites of massive star formation and the neutral and ionized components of the surrounding interstellar medium (ISM) in these intrinsically simple systems. Both local and large scale triggering mechanisms related to massive star formation are seen suggesting that feedback from massive stars is a microscopic process operating in all galaxies to a certain degree. The data emphasizes the importance of local conditions in regulating star formation from evidence such as massive stars inside ionized shells, compact HII regions surrounding aging clusters, and stars formed in chains of progressing age. Surface brightness profiles show current activity correlates with the time averaged level of past star formation at a given radius demonstrating a reliance on local conditions. Normalized star formation rates show no dependence on global conditions in comparisons with global properties such as the gas fraction. Large scale triggering by HI shells is supported by observations of progenitor populations and secondary sites of star formation on the dense HI rims. Analysis of the energy available from massive stars inside HI shells indicates energy deposited into the ISM from supernovae and stellar winds is sufficient to account for the HI morphology. Ages of individual star forming regions are derived using B, H? , and FUV photometry and show both older, diffuse FUV regions and younger, compact HII regions. The distribution of ages is reconciled with the HI morphology showing a clear preference of young regions for areas of dense HI and old regions for HI voids. Global kinematical properties may also play a role in the star formation process since large scale feedback from massive stars is shown to operate in regions which lack differential shear and significant random motions in the neutral gas disk.

Stewart, S. G.

1998-12-01

415

Herschel's Star Gages  

NSDL National Science Digital Library

The EJS Herschel's Star Gages Model illustrates William Herschel's methods of "star gages" by which he attempted to map out the shape of our galaxy in 1785. Herschel's star gages (sic) relied on two important assumptions: that Herschel's telescope (his "large 20 foot" with an 18.5 inch aperture) could see to the ends of the galaxy, and that within the galactic system stars are distributed uniformly. If the first assumption holds then the stars seen in the telescope all lie within a conical region of space with the apex at the telescope and the base at the edge of the galaxy. If the second assumption holds then the number of stars seen in the telescope is proportional to the volume of this cone. Since the volume of the cone is proportional to the cube of its height, the distance to the galactic edge in any direction is proportional to the cube root of the number of stars seen in that direction. This simulation allows the user to use Herschel's method of star gages to map out the shape of an artificial "star system" for which Herschel's assumptions are valid. One window shows the view through a telescope, with a slider to change the telescopes direction (around a single fixed axis). Another window shows a 3D view of the star system, showing either all of the stars in the system or only those stars visible through the telescope. A third window shows a plot of the star gages. Plotting star gages for many different directions maps out a cross-section of the star system. An optional slider allows the user to decrease the distance to at which stars are no longer visible, and a menu allows the user to select a star system in which the stars are not distributed uniformly. These options let the user explore how violations of Herschel's two fundamental assumptions invalidate his star gage method.

Timberlake, Todd

2011-05-28

416

Glue Polymer  

NSDL National Science Digital Library

What is a polymer, and what are some of its properties? This material is part of a series of hands-on science activities designed to arouse student interest. In this discovery activity students use white glue, water, and borax to make a vinyl polymer and study its properties. The activity includes a description, a list of science process skills and complex reasoning strategies being used, and a compilation of applicable K-12 national science education standards. Also provided are content topics, a list of necessary supplies, instructions, and presentation techniques. The content of the activity is explained, and assessment suggestions are provided.

Mid-continent Research for Education and Learning (McREL); Jacobs, Steve

2004-01-01

417

Clumps and triggered star formation in ionized molecular clouds  

NASA Astrophysics Data System (ADS)

Infrared shells and bubbles are ubiquitous in the Galaxy and can generally be associated with H II regions formed around young, massive stars. In this paper, we use high-resolution 3D SPH simulations to explore the effect of a single O7 star emitting photons at 1049 s-1 and located at the centre of a molecular cloud with mass 104 M? and radius 6.4 pc; the internal structure of the cloud is characterized by its fractal dimension, D (with 2.0? D ? 2.8), and the variance of its (lognormal) density distribution, ? O^2 (with 0.36 ? ? O^2 ? 1.42). Our study focuses on the morphology of the swept-up cold gas and the distribution and statistics of the resulting star formation. If the fractal dimension is low, the border of the H II region is dominated by extended shell-like structures, and these break up into a small number of massive high-density clumps which then spawn star clusters; star formation occurs relatively quickly, and delivers somewhat higher stellar masses. Conversely, if the fractal dimension is high, the border of the H II region is dominated by a large number of pillars and cometary globules, which contain compact dense clumps and tend to spawn single stars or individual multiple systems; star formation occurs later, the stellar masses are somewhat lower, and the stars are more widely distributed.

Walch, S.; Whitworth, A. P.; Bisbas, T. G.; Wünsch, R.; Hubber, D. A.

2013-10-01

418

Isotropic stars in general relativity  

NASA Astrophysics Data System (ADS)

We present a general solution of the Einstein gravitational field equations for the static spherically symmetric gravitational interior space-time of an isotropic fluid sphere. The solution is obtained by transforming the pressure isotropy condition, a second order ordinary differential equation, into a Riccati type first order differential equation, and using a general integrability condition for the Riccati equation. This allows us to obtain an exact non-singular solution of the interior field equations for a fluid sphere, expressed in the form of infinite power series. The physical features of the solution are studied in detail numerically by cutting the infinite series expansions, and restricting our numerical analysis by taking into account only n=21 terms in the power series representations of the relevant astrophysical parameters. In the present model all physical quantities (density, pressure, speed of sound etc.) are finite at the center of the sphere. The physical behavior of the solution essentially depends on the equation of state of the dense matter at the center of the star. The stability properties of the model are also analyzed in detail for a number of central equations of state, and it is shown that it is stable with respect to the radial adiabatic perturbations. The astrophysical analysis indicates that this solution can be used as a realistic model for static general relativistic high density objects, like neutron stars.

Mak, M. K.; Harko, T.

2013-10-01

419

Preparing high-density polymer brushes by mechanically assisted polymer assembly (MAPA)  

NASA Astrophysics Data System (ADS)

We introduce a novel method of modifying the surface properties of materials. This technique, called MAPA (="mechanically assisted polymer assembly"), is based on: 1) chemically attaching polymerization initiators to the surface of an elastomeric network that has been previously stretched by a certain length, ?x, and 2) growing end-anchored macromolecules using surface initiated ("grafting from") atom transfer living radical polymerization. After the polymerization, the strain is removed from the substrate, which returns to its original size causing the grafted macromolecules to stretch away from the substrate and form a dense polymer brush. We demonstrate the feasibility of the MAPA method by preparing high-density polymer brushes of poly(acryl amide), PAAm. We show that, as expected, the grafting density of the PAAm brushes can be increased by increasing ?x. We demonstrate that polymer brushes with extremely high grafting densities can be successfully prepared by MAPA.

Wu, Tao; Efimenko, Kirill; Genzer, Jan

2001-03-01

420

H sub 2 O masers in star-forming regions  

SciTech Connect

A comprehensive model is presented for the powerful H2O masers observed in star-forming regions. The shocks are the result of interaction of dense, high-velocity clumps with dense shells or clumps in the ambient medium. The shocked material is a thin slab in physical space, but breaks up into a network of filaments in velocity space. These filaments are the individual H{sub 2}O maser features. The results of maser model calculations are presented which provide the maximum brightness temperatures that can be produced in single-temperature environments of any kind. 56 refs.

Elitzur, M.; Hollenbach, D.J.; Mckee, C.F. (Kentucky Univ., Lexington (USA) NASA, Ames Research Center, Moffett Field, CA (USA) California Univ., Berkeley (USA))

1989-11-01

421

Star Formation in Galaxies  

NASA Astrophysics Data System (ADS)

The process of star formation is at the core of the evolutionary cycle of galaxies, as newborn stars produce new chemical elements, dust, and light. The energetic output delivered first by stellar winds and then by supernovae a few Myr after a star formation episode may also directly impact on the evolution of galaxies and their interstellar medium (ISM), as well as having an effect on the intergalactic medium (IGM), through feedback and outflows.This chapter concerns star formation on galactic scales. First, the galactic processes that may affect large-scale star formation are presented. Second, the various methods to measure star formation rates are discussed (star formation tracers, timescales, calibrations, limits). Finally, the observational status concerning star formation in galaxies (its relation to other quantities and its evolution) is presented. The Schmidt Law (star formation rate-gas relationship) is amply discussed.

Boissier, Samuel

422

The gasdynamics of H II regions. IV - The champagne phase and the propagation of ionization fronts into dense clouds  

NASA Astrophysics Data System (ADS)

Numerical calculations of the gas dynamical evolution of H II regions undergoing the champagne phase are presented. The present calculations extend to times in the evolution when the champagne rarefaction wave influences the ionized gas that lies between the ionizing star and the ionization front moving into the dense cloud. The propagation of the ionization front is studied numerically as well as in an approximative semi-analytical way for various cases.

Bedijn, P. J.; Tenorio-Tagle, G.

1981-05-01

423

Deep Imagery of NGC 3603: Low-Mass Star Formation in the Closest Starburst Region  

NASA Astrophysics Data System (ADS)

This proposal aims at studying the intermediate and low-mass stellar population in NGC 3603, the most luminous visible starburst region in the Galaxy, which more than rivals the dense core R136 of 30 Dor in the 7 times more distant LMC. Although the massive star content of this very dense cluster is now fairly well known, our knowledge of the medium- and low -mass part {1.5 - 10 M_odot} of the IMF in NGC 3603, not to mention more distant starbursts, is marginal at best. We therefore propose to obtain deep WFPC2 images of NGC 3603 that will allow us to probe its stellar content and IMF down to V=22.5 {M_v = +3.5; M 1.5 M_odot}. Questions such as a possible low-mass cutoff, variation of the IMF slope as a function of radius, and differential star formation will be addressed. In particular, we want to know if violent star formation of the most massive stars {and the subsequent strong ionization field and wind kinetic energy they generate} has prevented, or delayed, the formation of less massive stars in the very core of the cluster. Because of its proximity, NGC 3603 is the only truly dense starburst where we can directly observe whether or not violent, massive star formation efficiently quenches the formation of lower mass stars.

Drissen, Laurent

1996-07-01

424

Solubility of Solids in Dense Gases.  

National Technical Information Service (NTIS)

The thermodynamics of solid-dense gas equilibria is discussed, and two techniques are described for calculating the solubility of a solid component in a gas at high pressure. The first one is based on the recent empirical equation of state of Redlich whic...