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

1995-02-28

2

Thermal vitrification of dense suspensions of multi-arm star polymers: A Molecular Dynamics Study  

NASA Astrophysics Data System (ADS)

Dense suspensions of multi-arm star polymers are known to exhibit `liquid-like' ordering due to their similarities with colloidal particles. Experimental studies reported a counter-intuitive solidification of these suspensions upon increase of the temperature in marginal solvents( M. Kapnistos, D. Vlassopoulos, G. Fytas, K. Mortensen, G. Fleischer, J. Roovers, Phys. Rev. Lett. 85), 4072 (2000).. Our work investigates by MD simulations the temperature induced changes in colloidal superstructure and star dynamics under marginal solvent conditions. Multi-arm star polymers are modeled as soft spheres interacting via a soft, long ranged potential, derived from polymer physics principles. Simulations show a transition towards a ``glassy'' state at a temperature very close to the one reported experimentally. The features of the transition are consistent with those of ideal glass transitions, as described by ideal Mode Coupling Theory^2 M. Kapnistos, D. Vlassopoulos, G. Fytas, K. Mortensen, G. Fleischer, J. Roovers, Phys. Rev. Lett. 85, 4072 (2000). ^2 W.Gotze, Condensed Matter Physics, 1, No. 4(16), 1-32, (1998).

Bitsanis, Ioannis A.; Rissanou, Anastassia; Vlassopoulos, Dimitrios

2004-03-01

3

Phases of Dense Matter in Neutron Stars  

E-print Network

After a brief history of neutron stars and supernovae recent developments are discussed. Based on modern nucleon-nucleon potentials more reliable equations of state for dense nuclear matter have been constructed. Furthermore, phase transitions such as pion, kaon and hyperon condensation, superfluidity and quark matter can occur in cores of neutron stars. Specifically, the nuclear to quark matter phase transition and its mixed phases with intriguing structures is treated. Rotating neutron stars with and without phase transitions are discussed and compared to observed masses, radii and glitches. The observations of possible heavy $\\sim 2M_\\odot$ neutron stars in X-ray binaries and QPO's require relatively stiff equation of states and restricts strong phase transitions to occur at very high nuclear densities only.

H. Heiselberg

1999-10-12

4

Star polymers in correlated disorder  

E-print Network

We analyze the impact of a porous medium (structural disorder) on the scaling of the partition function of a star polymer immersed in a good solvent. We show that corresponding scaling exponents change if the disorder is long-range-correlated and calculate the exponents in the new universality class. A notable finding is that star and chain polymers react in qualitatively different manner on the presence of disorder: the corresponding scaling exponents increase for chains and decrease for stars. We discuss the physical consequences of this difference.

V. Blavats'ka; C. von Ferber; Yu. Holovatch

2007-11-23

5

HBT 28-Jun-2005 Formation of Planets in Dense Star  

E-print Network

-studied example · Distance ~ 450 pc, diameter ~ few pc, N ~ 10,000+ stars in last 10 Myr #12;HBT 28-Jun-2005 Life Cycle of Giant Molecular Clouds (GMCs) · Star formation is inefficient: 90% of gas remains not in starsHBT 28-Jun-2005 Formation of Planets in Dense Star Clusters Henry Throop Southwest Research

Throop, Henry

6

Star polymer unimicelles on graphene oxide flakes.  

PubMed

We report the interfacial assembly of amphiphilic heteroarm star copolymers (PSnP2VPn and PSn(P2VP-b-PtBA)n (n = 28 arms)) on graphene oxide flakes at the air-water interface. Adsorption, spreading, and ordering of star polymer micelles on the surface of the basal plane and edge of monolayer graphene oxide sheets were investigated on a Langmuir trough. This interface-mediated assembly resulted in micelle-decorated graphene oxide sheets with uniform spacing and organized morphology. We found that the surface activity of solvated graphene oxide sheets enables star polymer surfactants to subsequently adsorb on the presuspended graphene oxide sheets, thereby producing a bilayer complex. The positively charged heterocyclic pyridine-containing star polymers exhibited strong affinity onto the basal plane and edge of graphene oxide, leading to a well-organized and long-range ordered discrete micelle assembly. The preferred binding can be related to the increased conformational entropy due to the reduction of interarm repulsion. The extent of coverage was tuned by controlling assembly parameters such as concentration and solvent polarity. The polymer micelles on the basal plane remained incompressible under lateral compression in contrast to ones on the water surface due to strongly repulsive confined arms on the polar surface of graphene oxide and a preventive barrier in the form of the sheet edges. The densely packed biphasic tile-like morphology was evident, suggesting the high interfacial stability and mechanically stiff nature of graphene oxide sheets decorated with star polymer micelles. This noncovalent assembly represents a facile route for the control and fabrication of graphene oxide-inclusive ultrathin hybrid films applicable for layered nanocomposites. PMID:23883114

Choi, Ikjun; Kulkarni, Dhaval D; Xu, Weinan; Tsitsilianis, Constantinos; Tsukruk, Vladimir V

2013-08-01

7

Photoluminescence of Conjugated Star Polymers  

NASA Astrophysics Data System (ADS)

Higher dimensionality "star" polymers provide new properties beyond those found in their linear analogs. They have been used to improving electronic properties for nonlinear optics through exciton transfer and molecular antenna structures for example (M. Kawa, J. M. J. Frechet, Chem. Mater. 10, 286 (1998).). We report on photoluminescence properties of star polymers with a hyperbranched core (both hyperbranched phenlyene and hyperbranched triphenylamine) and polyhexylthiophene arms. The arm is a conjugated oligomer of polythiophene that has been investigated extensively for metallic like conductivity when doped as well as utilized in field effect transistors in its undoped form (A. Tsumara, H. Koezuka, T. Ando, Appl. Phys. Lett. 49, 1210 (1986).). The cores are respectively, a nonconjugated polymer in the case of hyperbranched phenlyene and a conjugated polymer in the case of hyperbranched triphenylamine. The photoluminesce spectrum (?_max at 575 nm) is identical for both star polymers with the two electronically different hyperbranched cores and for linear polythiophene alone. We conclude the wave functions of the core and arms do not strongly interact to form states different from their individual states and excitons formed on the hyperbranched cores migrate to the lower bandgap polythiophene before recombining.

Ferguson, J. B.; Prigodin, N. V.; Epstein, A. J.; Wang, F.

2000-10-01

8

Tight and loose shapes in flat entangled dense polymers  

E-print Network

We investigate the effects of topological constraints (entanglements) on two dimensional polymer loops in the dense phase, and at the collapse transition (Theta point). Previous studies have shown that in the dilute phase the entangled region becomes tight, and is thus localised on a small portion of the polymer. We find that the entropic force favouring tightness is considerably weaker in dense polymers. While the simple figure-eight structure, created by a single crossing in the polymer loop, localises weakly, the trefoil knot and all other prime knots are loosely spread out over the entire chain. In both the dense and Theta conditions, the uncontracted knot configuration is the most likely shape within a scaling analysis. By contrast, a strongly localised figure-eight is the most likely shape for dilute prime knots. Our findings are compared to recent simulations.

Andreas Hanke; Ralf Metzler; Paul G. Dommersnes; Yacov Kantor; Mehran Kardar

2003-07-24

9

Pulsar-irradiated stars in dense globular clusters  

NASA Technical Reports Server (NTRS)

We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

Tavani, Marco

1992-01-01

10

URCA Processes in Dense Matter and Neutron Star Cooling  

NASA Astrophysics Data System (ADS)

Urca-processes were introduced into astrophysics by Gamow and Schoenberg in 1941. Neutrino cooling resulting from urca-processes plays an important role at the latest stages of evolution of massive stars. Recent work on neutrino emissivity of dense matter shows that neutrino cooling via urca-processes could determine the thermal evolution of young neutron stars and depends dramatically on the composition of the neutron star core. In particular, if a neutron star contains a central core in which the direct urca-process is operative, the cooling timescale shortens by many orders of magnitude.

Haensel, Pawe?

1995-11-01

11

Physical hydrogels of associative star polymers  

SciTech Connect

Amphiphilic star polymers consisting of a hydrophobic core and hydrophilic arms end-capped with hydrophobic moieties exhibit associative properties in aqueous solution. Using large hydrophobic aliphatic tri- or tetraisocyanates derived from m-TMI, a series of well-defined stars with three or four polyethylene oxide arms and nonylphenoxy end groups were synthesized and characterized. When dissolved in water, separation into a dilute and concentrated phase occurs. The polymer concentration remains constant in each phase, their volume fractions being proportional to the total polymer concentration. The gel phase resembles an amphiphilic hydrogel with a strong affinity for hydrophobic compounds. Brookfield viscosity measurements also confirm the associative properties of the star polymers.

Zhou, G.; Smid, J. [State Univ. of New York, Syracuse, NY (United States)

1993-12-31

12

Slow Star Formation in Dense Gas: Evidence and Implications  

E-print Network

It has been known for more than 30 years that star formation in giant molecular clouds (GMCs) is slow, in the sense that only ~1% of the gas forms stars every free-fall time. This result is entirely independent of any particular model of molecular cloud lifetime or evolution. Here we survey observational data on higher density objects in the interstellar medium, including infrared dark clouds and dense molecular clumps, to determine if these objects form stars slowly like GMCs, or rapidly, converting a significant fraction of their mass into stars in one free-fall time. We find no evidence for a transition from slow to rapid star formation in structures covering three orders of magnitude in density. This has important implications for models of star formation, since competing models make differing predictions for the characteristic density at which star formation should transition from slow to rapid. The data are inconsistent with models that predict that star clusters form rapidly and in free-fall collapse. Magnetic- and turbulence-regulated star formation models can reproduce the observations qualitatively, and the turbulence-regulated star formation model of Krumholz & McKee quantitatively reproduces the infrared-HCN luminosity correlation recently reported by Gao & Solomon. Slow star formation also implies that the process of star cluster formation cannot be one of global collapse, but must instead proceed over many free-fall times. This suggests that turbulence in star-forming clumps must be driven, and that the competitive accretion mechanism does not operate in typical cluster-forming molecular clumps.

Mark R. Krumholz; Jonathan C. Tan

2006-06-12

13

Interfacial Micellar Structures from Novel Amphiphilic Star Polymers  

E-print Network

Interfacial Micellar Structures from Novel Amphiphilic Star Polymers Kirsten L. Genson, Joshua: August 4, 2004 An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic amphiphilicity and suggests a profound influence of star molecular architecture on the self

Vakni, David

14

THE FORMATION OF YOUNG DENSE STAR CLUSTERS THROUGH MERGERS  

SciTech Connect

Young star clusters such as NGC 3603 and Westerlund 1 and 2 in the Milky Way and R136 in the Large Magellanic Cloud are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of N-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters.

Fujii, M. S.; Portegies Zwart, S. F. [Leiden Observatory, Leiden University, NL-2300RA Leiden (Netherlands); Saitoh, T. R. [Interactive Research Center of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551 (Japan)

2012-07-01

15

Superlattice Formation on Star Polymer Solutions  

PubMed

Polyisoprene (PI) stars (arm number f = 4 approximately 237) were prepared by coupling of PI monoanions with tetrachlorosilane or by cross-linking PI anions with divinylbenzene. The structural ordering of such stars was investigated through small-angle X-ray scattering. PI stars (f > ca. 90) formed a body-centered cubic (bcc) structure near the overlap threshold. This structure changed to a mixed lattice of bcc and face-centered cubic structures with increasing polymer concentration. PMID:9268558

Ishizu; Ono; Uchida

1997-08-01

16

Polymer Film Surface Fluctuation Dynamics in the Limit of Very Dense Branching  

NASA Astrophysics Data System (ADS)

The surface height fluctuations of melt films of densely branched comb polystyrenes of thicknesses greater than 55nm and at temperatures more than 23 C above the Tg,bulk can be rationalized using the hydrodynamic continuum theory (HCT) known to describe melts of unentangled linear and cyclic chains. Film viscosities (?XPCS) for three combs inferred from fits of the HCT to X-ray Photon Correlation Spectroscopy (XPCS) data are the same as bulk viscosities (?bulk) measured with rheometry. For the comb most like a star polymer and the comb closest to showing bulk entanglement behavior, ?XPCS is greater than ?bulk. However, the values of ?XPCS-?bulk are much smaller than those seen for less densely branched polystyrenes. We conjecture that the smaller magnitude of ?XPCS-?bulk for the densely grafted combs is due to a lack of interpenetration of the side chains when branching is very dense. While data of relaxation time versus T for cyclic chains virtually collapse to a single curve when Tg,bulk is accounted for, that is not the case for combs. Tg,bulk and specific chain architecture both play important roles in determining the surface fluctuations. Acknowledgements: NSF CBET 0730692, CBET-0731319, DURIP W911NF-09-1-0122.

Foster, Mark; Liu, Boxi; Narayanan, Suresh; Wu, David T.

2013-03-01

17

Star polymers rupture induced by constant forces  

NASA Astrophysics Data System (ADS)

In this work, we study the breakage process of an unknotted three-arm star-shaped polymer when it is pulled from its free ends by a constant force. The star polymer configuration is described through an array of monomers coupled by anharmonic bonds, while the rupture process is tracked in three-dimensional space by means of Langevin Molecular Dynamics simulations. The interaction between monomers is described by a Morse potential, while a Weeks-Chandler-Anderson energetic contribution accounts for the excluded volume interaction. We explore the effect of the molecular architecture on the distributions of rupture times over a broad interval of pulling forces and star configurations. It was found that the rupture time distribution of the individual star arms is strongly affected by the star configuration imposed by the pulling forces and the length of the arms. We also observed that for large pulling forces the rupture time distributions resemble the dominant features observed for linear polymer chains. The model introduced here provides the basic ingredients to describe the effects of tensile forces on stress-induced degradation of branched macromolecules and polymer networks.

Garca, N. A.; Febbo, M.; Vega, D. A.; Milchev, A.

2014-10-01

18

Star polymers rupture induced by constant forces.  

PubMed

In this work, we study the breakage process of an unknotted three-arm star-shaped polymer when it is pulled from its free ends by a constant force. The star polymer configuration is described through an array of monomers coupled by anharmonic bonds, while the rupture process is tracked in three-dimensional space by means of Langevin Molecular Dynamics simulations. The interaction between monomers is described by a Morse potential, while a Weeks-Chandler-Anderson energetic contribution accounts for the excluded volume interaction. We explore the effect of the molecular architecture on the distributions of rupture times over a broad interval of pulling forces and star configurations. It was found that the rupture time distribution of the individual star arms is strongly affected by the star configuration imposed by the pulling forces and the length of the arms. We also observed that for large pulling forces the rupture time distributions resemble the dominant features observed for linear polymer chains. The model introduced here provides the basic ingredients to describe the effects of tensile forces on stress-induced degradation of branched macromolecules and polymer networks. PMID:25362341

Garca, N A; Febbo, M; Vega, D A; Milchev, A

2014-10-28

19

Connecting Dense Gas Tracers of Star Formation in our Galaxy to High-z Star Formation  

E-print Network

Observations have revealed prodigious amounts of star formation in starburst galaxies as traced by dust and molecular emission, even at large redshifts. Recent work shows that for both nearby spiral galaxies and distant starbursts, the global star formation rate, as indicated by the infrared luminosity, has a tight and almost linear correlation with the amount of dense gas as traced by the luminosity of HCN. Our surveys of Galactic dense cores in HCN 1-0 emission show that this correlation continues to a much smaller scale, with nearly the same ratio of infrared luminosity to HCN luminosity found over 7-8 orders of magnitude in L_IR, with a lower cutoff around 10^{4.5} L_sun of infrared luminosity. The linear correlation suggests that we may understand distant star formation in terms of the known properties of local star-forming regions. Both the correlation and the luminosity cutoff can be explained if the basic unit of star formation in galaxies is a dense core, similar to those studied in our Galaxy.

Jingwen Wu; Neal J. Evans II; Yu Gao; Philip M. Solomon; Yancy L. Shirley; Paul A. Vanden Bout

2005-11-15

20

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

21

Influence of Molecular Solvation on the Conformation of Star Polymers  

E-print Network

We have used neutron scattering to investigate the influence of concentration on the conformation of a star polymer. By varying the contrast between the solvent and isotopically labeled stars, we obtain the distributions of polymer and solvent within a star polymer from analysis of scattering data. A correlation between the local desolvation and the inward folding of star branches is discovered. From the perspective of thermodynamics, we find an analogy between the mechanism of polymer localization driven by solvent depletion and that of the hydrophobic collapse of polymers in solutions.

Li, Xin; Snchez-Diz, Luis E; Do, Changwoo; Liu, Yun; Kim, Tae-Hwan; Smith, Gregory S; Hamilton, William A; Hong, Kunlun; Chen, Wei-Ren

2014-01-01

22

Influence of Molecular Solvation on the Conformation of Star Polymers  

E-print Network

We have used neutron scattering to investigate the influence of concentration on the conformation of a star polymer. By varying the contrast between the solvent and isotopically labeled stars, we obtain the distributions of polymer and solvent within a star polymer from analysis of scattering data. A correlation between the local desolvation and the inward folding of star branches is discovered. From the perspective of thermodynamics, we find an analogy between the mechanism of polymer localization driven by solvent depletion and that of the hydrophobic collapse of polymers in solutions.

Xin Li; Lionel Porcar; Luis E. Snchez-Diz; Changwoo Do; Yun Liu; Tae-Hwan Kim; Gregory S. Smith; William A. Hamilton; Kunlun Hong; Wei-Ren Chen

2014-04-24

23

Motions and Initial Conditions in Star-Forming Dense Cores  

NASA Technical Reports Server (NTRS)

Under this grant in the past year we have pursued spectral-line observations of star-forming regions over size scales from 0.01 pc to 0.5 pc. Our main goal has been to measure the systematic and turbulent motions of condensing and collapsing gas. In this area, our results include (1) in 67 starless dense cores, some 19 show clear evidence of spatially extended inward motions, with typical line-of-sight inward speed 0.05-0.09 km s(sup -1) and with typical plane-of-the-sky extent 0.1-0.3 pc, (2) In some 40 nearby regions with embedded groups and clusters, we see extended infall asymmetry in lines of CS and HCO(+) clearly in 4 regions and less clearly in 4 others, (3) Using finer resolution (15 arcsec or 0.01-0.02 pc) and lines tracing higher density, we see spatial concentration of infall asymmetry near the protostars in NGC 1333 IRS 4A and B, L483, and L1251B, and with still finer resolution (2 arcsec or 0.003 pc or 600 AU) we detect inverse P Cyg profiles, indicating absorption of continuum emission from the protostellar envelope by infalling gas in NGC 1333 IRS 4A and 4B. Further, at high resolution we identify regions of stellar mass and low turbulence ("kernels") which are good candidates to become the next generation of stars in embedded clusters. In addition we have completed a survey for the OH Zeeman effect in absorption against nearby H II regions, indicating that the large-scale magnetic field may be nearly critical if it typically threads a flattened structure. We have also developed a model of spatially extended infall motions based on dissipation of turbulence in a magnetized, selfgravitating layer. In the following we describe some of these results in more detail.

Myers, Philip C.

2001-01-01

24

Interfacial Micellar Structures from Novel Amphiphilic Star Polymers  

SciTech Connect

An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic/hydrophilic arms of polystyrene (PS) and poly(acrylic acid) (PAA) connected to a well-defined rigid aromatic core was studied at the air-water and the air-solid interfaces. At the air-water interface, the molecules spontaneously form pancakelike micellar aggregates which measure up to several microns in diameter and 5 nm in thickness. Upon reduction of the surface area per molecule to 7 nm2, the two-dimensional micelles merged into a dense monolayer. We suggest that confined phase separation of dissimilar polymer arms occurred upon their segregation on the opposite sides of the rigid disklike aromatic core, forcing the rigid cores to adopt a face-on orientation with respect to the interface. Upon transfer onto solid supports the PS chains face the air-film interface making it completely hydrophobic, and the PAA chains were found to collapse and form a thin flattened underlayer. This study points toward new strategies to create large 2D microstructures with facial amphiphilicity and suggests a profound influence of star molecular architecture on the self-assembly of amphiphiles at the air-water interface.

Genson, Kirsten L.; Hoffman, Joshua; Teng, Jing; Zubarev, Eugene R.; Vaknin, David; Tsukruk, Vladimir V. (Iowa State)

2010-11-10

25

Scattering from Star Polymers including Excluded Volume Effects  

E-print Network

In this work we present a new model for the form factor of a star polymer consisting of self-avoiding branches. This new model incorporates excluded volume effects and is derived from the two point correlation function for a star polymer.. We compare this model to small angle neutron scattering (SANS) measurements from polystyrene (PS) stars immersed in a good solvent, tetrahydrofuran (THF). It is shown that this model provides a good description of the scattering signature originating from the excluded volume effect and it explicitly elucidates the connection between the global conformation of a star polymer and the local stiffness of its constituent branch.

Li, Xin; Liu, Yun; Snchez-Diz, Luis E; Hong, Kunlun; Smith, Gregory S; Chen, Wei-Ren

2014-01-01

26

Scattering from Star Polymers including Excluded Volume Effects  

E-print Network

In this work we present a new model for the form factor of a star polymer consisting of self-avoiding branches. This new model incorporates excluded volume effects and is derived from the two point correlation function for a star polymer.. We compare this model to small angle neutron scattering (SANS) measurements from polystyrene (PS) stars immersed in a good solvent, tetrahydrofuran (THF). It is shown that this model provides a good description of the scattering signature originating from the excluded volume effect and it explicitly elucidates the connection between the global conformation of a star polymer and the local stiffness of its constituent branch.

Xin Li; Changwoo Do; Yun Liu; Luis E. Snchez-Diz; Kunlun Hong; Gregory S. Smith; Wei-Ren Chen

2014-04-24

27

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. PMID:19756235

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

2009-01-01

28

The formation and evolution of very massive stars in dense stellar systems  

E-print Network

The early evolution of dense stellar systems is governed by massive single star and binary evolution. Core collapse of dense massive star clusters can lead to the formation of very massive objects through stellar collisions ($M\\geq$ 1000 \\msun). Stellar wind mass loss determines the evolution and final fate of these objects, and decides upon whether they form black holes (with stellar or intermediate mass) or explode as pair instability supernovae, leaving no remnant. We present a computationaly inexpensive evolutionary scheme for very massive stars that can readily be implemented in an N-body code. Using our new N-body code 'Youngbody' which includes a detailed treatment of massive stars as well as this new scheme for very massive stars, we discuss the formation of intermediate mass and stellar mass black holes in young starburst regions. A more detailed account of these results can be found in Belkus et al. 2007.

H. Belkus; J. Van Bever; D. Vanbeveren

2007-10-09

29

Rheology of blends of dense star-like polystyrene soft nanospheres  

NASA Astrophysics Data System (ADS)

Highly branched polymeric materials exhibit significantly different rheological behavior compared to linear polymers, suggesting that controlled branch density can have technological benefits. We have synthesized a dense star polystyrene molecule, (PSnano) with 50 arms, Ma= 5,000 g/mol. Using rheo-optics and triple-detection GPC, we have shown that these materials act as soft nanospheres, with a size of 8 nm. We are studying the effect of the nanospheres on the blending behavior of miscible polystyrene/ poly (vinyl methyl ether) (PS/PVME) blends with the help of dynamic stress-optical measurements. In PSnano/PVME blends, at higher PSnano wt. fractions,the interparticle distance between PSnano is smaller than radius of gyration of PVME. Therefore we expect to see the conformational changes in PVME chains induced by PSnano and compare it with linear PS (L-PS)/PVME blends. However the rheo-optics data suggests that the relaxation dynamics of PVME is not significantly altered by PSnano whereas for L-PS/PVME blends the relaxation dynamics of PVME is slowed down by L-PS. DSC results show a single transition suggesting miscibility. Our results suggest that, the segments of PS near the periphery of PSnano may be miscible, but the segments at the core would be immiscible, resulting in a molecularly dispersed blend, rather than a segmentaly miscible L-PS/PVME blend.

Kulkarni, Ajay; Kannan, R. M.

2006-03-01

30

Microstructure of dense colloid polymer suspensions and gels  

NASA Astrophysics Data System (ADS)

A systematic experimental study of polymer-induced changes of the collective structure of model hard-sphere nanocolloids in the fluid and gel states has been carried out using ultra-small-angle x-ray scattering. The focus is on small, non-adsorbing polymer depletants where a direct transition from the homogeneous fluid phase to a nonequilibrium gel state occurs with increasing polymer additions. As the polymer concentration is increased in the homogeneous fluid phase, the low angle concentration fluctuations monotonically increase, the characteristic interparticle separation decreases and tends to saturate, and the intensity of the cage order peak varies in a non-monotonic manner. These equilibrium structural changes depend in a systematic fashion on colloid volume fraction and polymer-colloid size asymmetry, and are in near quantitative agreement with the parameter-free polymer reference interaction site model theory calculations. By combining the accurate equilibrium theory with experimental observations, the loss of ergodicity and nonequilibrium structure formation in the gel state can be deduced. Abrupt departures between theory and experiment on the ~2-3 particle diameter and greater length scales are observed as the gel boundary is traversed. The liquid-like local cage structure is arrested. Intermediate scale fluctuations are suppressed suggesting the formation of small, compact clusters. Large amplitude, Porod-like fluctuations emerge on large length scales due to quenched heterogeneities which are analysed using a random two-phase composite model. By combining the results of all the scattering experiments and theoretical calculations a qualitative real space picture of the gel microstructure is constructed, and its mechanical consequences are qualitatively discussed.

Shah, S. A.; Chen, Y.-L.; Ramakrishnan, S.; Schweizer, K. S.; Zukoski, C. F.

2003-07-01

31

Interactions Between Forming Stars and Dense Gas in a Small Low Mass Cluster  

NASA Astrophysics Data System (ADS)

We present observations of dense gas and outflow activity in the Cederblad 110 region of the Chamaleleon I Dark Cloud. The region contains eight 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 (?_YSO 150 pc^-2). The analysis of our N2H+ (J=1-0) maps indicates the presence of 15 solar masses of dense (n 10^5 cm^-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. Smaller column densities of more stable dense gas are found toward the region's Class I sources. Little or no dense gas is colocated with the Class II and III sources in the region. The outflow from the Class I source IRS 4 is interacting with the dense core associated with MMS 1. The molecular component of the outflow appears to be deflected by the densest part of the core, after which it plows through some of the lower column density portions of the core. The working surface at the head of the outflow lobe can be seen in the enhanced velocity dispersion of the dense gas. The Class III source IRS 2 may also be influencing the dense gas in the region. A dust temperature gradient across the core is consistent with warming from the 3.4 Lo source, 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, Edwin F.; Wong, T.; Bourke, T. L.; Thompson, K. L.

2011-05-01

32

Structure, Motion, and Evolution of Star-Forming Dense Cores  

NASA Technical Reports Server (NTRS)

We have pursued spectral-line observations of star-forming regions over size scales from 0.01 pc to 0.5 pc. Our main goal has been to measure the systematic and turbulent motions of condensing and collapsing gas.

Myers, Philip C.

2003-01-01

33

Exploring the Physics of Dense Matter with Neutron Star Transients  

SciTech Connect

Many accreting neutron stars do so intermittently; that is, the accretion ceases for long quiescent intervals. During the accretion outburst, reactions are induced in the crust by the continual accumulation of matter. These reactions heat the crust out of thermal equilibrium with the core, and when accretion stops and the system goes into quiescence, the thermal relaxation of the crust is detectable. This contribution gives a summary of recent theoretical and observational work interpreting the cooling lightcurves of these quasi-persistent transients. In particular, the lightcurves can constrain the core temperature of the neutron star, the thermal conductivity and heat capacity of the inner crust, and the distribution of heat sources in the outer crust.

Brown, Edward F. [Dept. Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320 (United States)

2009-05-07

34

Slow Star Formation in Dense Gas: Evidence and Implications  

Microsoft Academic Search

It has been known for more than 30 years that star formation in giant\\u000amolecular clouds (GMCs) is slow, in the sense that only ~1% of the gas forms\\u000astars every free-fall time. This result is entirely independent of any\\u000aparticular model of molecular cloud lifetime or evolution. Here we survey\\u000aobservational data on higher density objects in the interstellar

Mark R. Krumholz; Jonathan C. Tan

2006-01-01

35

Structure, Motion, and Evolution of Star-Forming Dense Cores  

NASA Technical Reports Server (NTRS)

Under this grant in the past year we have pursued spectral-line observations of star-forming regions over size scales from 0.01 pc to 0.5 pc. Our main goal has been to measure the systematic and turbulent motions of condensing and collapsing gas. The following summary is excerpted from our recent application for a new three-year grant, submitted in June, 2002.

Myers, Philip C.

2002-01-01

36

Dense baryonic matter: constraints from recent neutron star observations  

E-print Network

Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of two-solar-mass neutron stars rules out many soft equations of state with prominent "exotic" compositions. The present work reviews the conditions required for the pressure as a function of baryon density in order to satisfy these new constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless additional strongly repulsive correlations, e.g. through vector current interactions between quarks, are introduced. The extent to which strangeness can accumulate in the equation of state is also discussed.

Thomas Hell; Wolfram Weise

2014-02-17

37

Dense baryonic matter: constraints from recent neutron star observations  

E-print Network

Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of two-solar-mass neutron stars rules out many soft equations of state with prominent "exotic" compositions. The present work reviews the conditions required for the pressure as a function of baryon density in order to satisfy these new constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless addition...

Hell, Thomas

2014-01-01

38

Dense baryonic matter: Constraints from recent neutron star observations  

NASA Astrophysics Data System (ADS)

Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of 2M? neutron stars rules out many soft equations of state with prominent "exotic" compositions. The present work reviews the conditions required for the pressure as a function of baryon density to satisfy these constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov-Nambu-Jona-Lasinio model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless additional strongly repulsive correlations, e.g., through vector current interactions between quarks, are introduced. The extent to which strangeness can accumulate in the equation of state is also discussed.

Hell, Thomas; Weise, Wolfram

2014-10-01

39

Interactions between Forming Stars and Dense Gas in the Small Low-mass Cluster Cederblad 110  

NASA Astrophysics Data System (ADS)

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 (?YSO ~ 150 pc-2). The analysis of our N2H+ (J = 1?0) maps indicates the presence of 13 3 solar masses of dense (n ~ 105 cm-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?0) line of 12CO, 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.; Wong, T.; Bourke, T. L.; Thompson, K. L.

2011-12-01

40

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

41

Are Superluminous Supernovae and Long GRBs the Products of Dynamical Processes in Young Dense Star Clusters?  

NASA Astrophysics Data System (ADS)

Superluminous supernovae (SLSNe) occur almost exclusively in small galaxies (Small/Large Magellanic Cloud (SMC/LMC)-like or smaller), and the few SLSNe observed in larger star-forming galaxies always occur close to the nuclei of their hosts. Another type of peculiar and highly energetic supernovae are the broad-line Type Ic SNe (SN Ic-BL) that are associated with long-duration gamma-ray bursts (LGRBs). Also these have a strong preference for occurring in small (SMC/LMC-like or smaller) star-forming galaxies, and in these galaxies LGRBs always occur in the brightest spots. Studies of nearby star-forming galaxies that are similar to the hosts of LGRBs show that these brightest spots are giant H II regions produced by massive dense young star clusters with many hundreds of O- and Wolf-Rayet-type stars. Such dense young clusters are also found in abundance within a few hundred parsecs from the nucleus of larger galaxies like our own. We argue that the SLSNe and the SNe Ic-BL/LGRBs are exclusive products of two types of dynamical interactions in dense young star clusters. In our model the high angular momentum of the collapsing stellar cores required for the engines of an SN Ic-BL results from the post-main-sequence mergers of dynamically produced cluster binaries with almost equal-mass components. The merger produces a critically rotating single helium star with sufficient angular momentum to produce an LGRB; the observed "metal aversion" of LGRBs is a natural consequence of the model. We argue that, on the other hand, SLSNe could be the products of runaway multiple collisions in dense clusters, and we present (and quantize) plausible scenarios of how the different types of SLSNe can be produced.

van den Heuvel, E. P. J.; Portegies Zwart, S. F.

2013-12-01

42

STELLAR COLLISIONS AND BLUE STRAGGLER STARS IN DENSE GLOBULAR CLUSTERS  

SciTech Connect

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 Hnon-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 ?10{sup 3} M{sub ?} pc{sup 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 [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Rasio, Frederic A. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Sills, Alison [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1 (Canada); Glebbeek, Evert, E-mail: s.chatterjee@astro.ufl.edu [Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen (Netherlands)

2013-11-10

43

Star-shaped polymers for DNA sequencing by capillary electrophoresis.  

PubMed

The separation and sequencing of DNA are the main objectives of the Human Genome Project, and this project has also been very useful for gene analysis and disease diagnosis. Capillary electrophoresis (CE) is one of the most common techniques for the separation and analysis of DNA. DNA separations are usually achieved using capillary gel electrophoresis (CGE) mode, in which polymer gel is packed into the capillary. Compared with a traditional CGE matrix, a hydrophilic polymer matrix, which can be adsorb by the capillary wall has numerous advantages, including stability, reproducibility and ease of automation. Various water-soluble additives, such as linear poly(acrylamide) (PAA) and poly(N,N-dimethylacrylamide) (PDMA), have been employed as media. In this study, different star-shaped PDMA polymers were designed and synthesized to achieve lower polymer solution viscosity. DNA separations with these polymers avoid the disadvantages of high viscosity and long separation time while maintaining high resolution (10 bp between 271 bp and 281 bp). The influences of the polymer concentration and structure on DNA separation were also determined in this study; higher polymer concentration yielded better separation performance, and star-like polymers were superior to linear polymers. This work indicates that modification of the polymer structure is a potential strategy for optimizing DNA separation. PMID:21481881

Gao, Fan; Tie, Cai; Zhang, Xin-Xiang; Niu, Zhiqiang; He, Xiaojin; Ma, Yuguo

2011-05-20

44

Effectively delivering a unique hsp90 inhibitor using star polymers  

PubMed Central

We report the synthesis of a novel heat shock protein 90 (hsp90) inhibitor conjugated to a star polymer. Using reversible additionfragmentation chain-transfer (RAFT) polymerization, we prepared star polymers comprised of PEG attached to a predesigned functional core. The stars were cross-linked using disulfide linkers, and a tagged version of our hsp90 inhibitor was conjugated to the polymer core to generate nanoparticles (14 nM). Dynamic light scattering showed that the nanoparticles were stable in cell growth media for 5 days, and HPLC analysis of compound-release at 3 different pH values showed that release was pH dependent. Cell cytotoxicity studies and confocal microscopy verify that our hsp90 inhibitor was delivered to cells using this nanoparticle delivery system. Further, delivery of our hsp90 inhibitor using star polymer induces apoptosis by a caspase 3-dependent pathway. These studies show that we can deliver our hsp90 inhibitor effectively using star polymers, and induce apoptosis by the same pathway as the parent compound. PMID:24379910

Kim, Seong Jong; Ramsey, Deborah M.; Boyer, Cyrille; Davis, Thomas P.; McAlpine, Shelli R.

2013-01-01

45

On the source of dense outflows from T Tauri stars - III. Winds driven from the star-disc shear layer  

Microsoft Academic Search

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (Te~= 80 000 K) and dense (ne~= 1010 cm-3) component associated with the large-scale jet. This hot component is formed very close to the base of the jet providing fundamental information on the jet formation mechanism. In this series, we have investigated whether this component

Ana I. Gmez de Castro; Brigitta von Rekowski

2011-01-01

46

THE NEUTRON STAR MASS-RADIUS RELATION AND THE EQUATION OF STATE OF DENSE MATTER  

SciTech Connect

The equation of state (EOS) of dense matter has been a long-sought goal of nuclear physics. EOSs generate unique mass versus radius (M-R) relations for neutron stars, the ultra-dense remnants of stellar evolution. In this work, we determine the neutron star mass-radius relation and, based on recent observations of both transiently accreting and bursting sources, we show that the radius of a 1.4 solar mass neutron star lies between 10.4 and 12.9 km, independent of assumptions about the composition of the core. We show, for the first time, that these constraints remain valid upon removal from our sample of the most extreme transient sources or of the entire set of bursting sources; our constraints also apply even if deconfined quark matter exists in the neutron star core. Our results significantly constrain the dense matter EOS and are furthermore consistent with constraints from both heavy-ion collisions and theoretical studies of neutron matter. We predict a relatively weak dependence of the symmetry energy on the density and a value for the neutron skin thickness of lead which is less than 0.20 fm, results that are testable in forthcoming experiments.

Steiner, Andrew W.; Brown, Edward F. [Joint Institute for Nuclear Astrophysics, National Superconducting Cyclotron Laboratory, and the Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Lattimer, James M., E-mail: steiner3@uw.edu, E-mail: ebrown@pa.msu.edu, E-mail: james.lattimer@stonybrook.edu [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States)

2013-03-01

47

Pressure-induced amorphization of a dense coordination polymer and its impact on proton conductivity  

NASA Astrophysics Data System (ADS)

The proton conductivity of a dense coordination polymer (CP) was investigated under high-pressure conditions. Impedance measurements under high pressures revealed that the proton conductivity of the CP decreased more than 1000-fold at pressures of 3-7 GPa and that the activation energy for proton conduction almost doubled compared with that at ambient pressure. A synchrotron X-ray study under high pressure identified the amorphization process of the CP during compression, which rationally explains the decrease in conductivity and increase in activation energy. This phenomenon is categorized as reversible pressure-induced amorphization of a dense CP and is regarded as a demonstration of the coupling of the mechanical and electrical properties of a CP.

Umeyama, Daiki; Horike, Satoshi; Tassel, Cedric; Kageyama, Hiroshi; Higo, Yuji; Hagi, Keisuke; Ogiwara, Naoki; Kitagawa, Susumu

2014-12-01

48

Ordered structures of small numbers of nanorods induced by semiflexible star polymers  

NASA Astrophysics Data System (ADS)

The ordered structures of nanorods (NRs) in the semiflexible star polymer/NR mixtures are explored by employing molecular dynamics simulation. The structures of small numbers of NRs can be well controlled by varying the stiffness of semiflexible star polymers. At a moderate binding energy between star polymers and NRs, four completely different structures of small numbers of NRs are observed, including that the side-to-side hexagonal aggregation structures of NRs for flexible star polymers, the partly parallel aggregation structures of NRs and the end-to-end contact parallel aggregation structures of NRs for semiflexible star polymers, and the partial dispersion of NRs for rigid star polymers. Helical conformations of semiflexible star polymers binding with NRs are responsible for the formation of the end-to-end contact parallel aggregation structures for small numbers of NRs. This investigation may provide a possible pathway to develop ``smart'' medium to construct novel materials with high performance.

Zhang, Dong; He, Lilin; Zhang, Linxi

2014-09-01

49

Dynamical Modeling of Dense Star Clusters with a Parallel Monte Carlo Code  

NASA Astrophysics Data System (ADS)

We will investigate the dynamical evolution of dense star clusters, such as globular clusters in the Milky Way and other galaxies, using numerical simulations on parallel supercomputers. Our new parallel Monte Carlo code allows us to model clusters with realistic numbers of stars (N ~ 10^5 - 10^6), both single and in binaries, and with accurate treatments of all dynamical and stellar evolution processes. Even a small initial binary fraction (e.g., 10% of stars in binaries) can play a key role in supporting a cluster against gravothermal collapse for many relaxation times. Inelastic encounters between binaries and single stars or other binaries provide a very significant energy source for the cluster. These dynamical interactions also lead to the production of large numbers of important sources containing, e.g., neutron stars and black holes in bright X-ray binaries, or millisecond radio pulsars. Our new parallel code is based on Henon's Monte Carlo algorithm for computing the dynamical evolution of dense stellar systems in the Fokker-Planck approximation. This new code allows us to calculate accurately the entire evolution of even the largest globular clusters (e.g., 47 Tuc) in typically just a few hours of computing time, allowing us to explore and understand the complex dynamical and stellar processes at play over the full range of relevant physical parameters. The results of this investigation will provide a solid theoretical framework for the interpretation of data from many current and future NASA missions such as HST, Chandra, Fermi, Spitzer, and JWST. Such a framework is currently lacking because of the severe computational limits of other methods like direct N-body integrations.

Rasio, Frederic

50

Stability of the $?$-equilibrated dense matter and core-crust transition in neutron stars  

E-print Network

The stability of the $\\beta$-equilibrated dense nuclear matter is analyzed with respect to the thermodynamic stability conditions. Based on the density dependent M3Y effective nucleon-nucleon interaction, the effects of the nuclear incompressibility on the proton fraction in neutron stars and the location of the inner edge of their crusts and core-crust transition density and pressure are investigated. The high-density behavior of symmetric and asymmetric nuclear matter satisfies the constraints from the observed flow data of heavy-ion collisions. The neutron star properties studied using $\\beta$-equilibrated neutron star matter obtained from this effective interaction for a pure hadronic model agree with the recent observations of the massive compact stars. The density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of neutron stars are determined to be $\\rho_t=$ 0.0938 fm$^{-3}$, P$_t=$ 0.5006 MeV fm$^{-3}$ and x$_{p(t)}=$ 0.0308, respectively.

Debasis Atta; D. N. Basu

2014-06-20

51

The Green Bank Telescope Maps the Dense, Star-forming Gas in the Nearby Starburst Galaxy M82  

NASA Astrophysics Data System (ADS)

Observations of the Milky Way and nearby galaxies show that dense molecular gas correlates with recent star formation, suggesting that the formation of this gas phase may help regulate star formation. A key test of this idea requires wide-area, high-resolution maps of dense molecular gas in galaxies to explore how local physical conditions drive dense gas formation, but these observations have been limited because of the faintness of dense gas tracers like HCN and HCO+. Here we demonstrate the power of the Robert C. Byrd Green Bank Telescope (GBT)the largest single-dish millimeter radio telescopefor mapping dense gas in galaxies by presenting the most sensitive maps yet of HCN and HCO+ in the starburst galaxy M82. The HCN and HCO+ in the disk of this galaxy correlates with both recent star formation and more diffuse molecular gas and shows kinematics consistent with a rotating torus. The HCO+ emission extending to the north and south of the disk is coincident with the outflow previously identified in CO and traces the eastern edge of the hot outflowing gas. The central starburst region has a higher ratio of star formation to dense gas than the outer regions, pointing to the starburst as a key driver of this relationship. These results establish that the GBT can efficiently map the dense molecular gas at 90 GHz in nearby galaxies, a capability that will increase further with the 16 element feed array under construction.

Kepley, Amanda A.; Leroy, Adam K.; Frayer, David; Usero, Antonio; Marvil, Josh; Walter, Fabian

2014-01-01

52

Merging Timescales and Merger Rates of Star Clusters in Dense Star Cluster Complexes  

NASA Astrophysics Data System (ADS)

Interacting galaxies like the famous Antennae (NGC 4038/4039) or Stephan's Quintet (HCG 92) show considerable star forming activity in their tidal arms. High resolution images (e.g. from HST-observations) indicate that these regions consist of up to hundreds of massive stellar clusters or tidal dwarf galaxies (TDG). In this paper we want to investigate the future fate of these clusters of massive star clusters (in this work called super-clusters). We simulate compact super-clusters in the tidal field of a host-galaxy and investigate the influence of orbital and internal parameters on the rate and timescale of the merging process. We show that it is possible that such configurations merge and build a dwarf galaxy, which could be an important mechanism of how long-lived dwarf satellite galaxies form. A detailed study of the merger object will appear in a follow-up paper.

Fellhauer, M.; Baumgardt, H.; Kroupa, P.; Spurzem, R.

2002-02-01

53

Discovery of a dense molecular cloud towards a young massive embedded star in 30 Doradus  

E-print Network

The 30 Doradus region in the Large Magellanic Cloud is one of the most outstanding star forming regions of the Local Group and a primary target to study star formation in an environment of low metallicity. In order to obtain a more complete picture of the not yet consumed or dispersed cool gas, we searched for line emission from molecular clouds that could be associated with molecular hydrogen emission detected in the region. We obtained a high sensitivity 12CO J=2-1 map with the 15-m SEST telescope, complemented by pointed observations of 13CO J=2-1 and CS J=2-1. We report the discovery of a dense molecular cloud towards an embedded young massive star at ~ 20" (~5 pc, at the distance of 50 kpc) northwest of R136, the compact massive central stellar cluster powering 30 Doradus in the LMC, that could be triggering star formation in the surrounding molecular clouds. We derived a molecular mass of $\\lesssim 10^4$ \\msol, a linear radius of 3 pc, as an upper limit, and a mean density of $\\gtrsim 10^{3}$ cm$^{-3}$ ...

Rubio, M; Dubner, G

2009-01-01

54

Dense gas without star formation: The kpc-sized molecular disk in 3C326 N  

E-print Network

We report the discovery of a 3 kpc disk of few 10^9 Ms of dense, warm H_2 in the nearby radio galaxy 3C326 N, which shows no signs of on-going or recent star formation and falls a factor 60 below the Schmidt-Kennicutt law. VLT/SINFONI imaging spectroscopy shows broad (FWHM \\sim 500 km/s) ro-vibrational H_2 lines across all of the disk, with irregular profiles and line ratios consistent with shocks. The ratio of turbulent and gravitational energy suggests that the gas is highly turbulent and not gravitationally bound. In absence of the driving by the jet, short turbulent dissipation times suggest the gas should collapse rapidly and form stars, at odds with the recent star-formation history. Motivated by hydrodynamic models of rapid H_2 formation boosted by turbulent compression, we propose that the molecules formed from diffuse atomic gas in the turbulent jet cocoon. Since the gas is not self-gravitating, it cannot form molecular clouds or stars while the jet is active, and is likely to disperse and become ato...

Nesvadba, Nicole; Lehnert, Matt; Guillard, Pierre; Salome, Philippe

2011-01-01

55

THE AGE, STELLAR CONTENT, AND STAR FORMATION TIMESCALE OF THE B59 DENSE CORE  

SciTech Connect

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{sub sun}) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the {rho} 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{sup +4.1}{sub -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 {approx}6%. While the {approx}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.; Muench, A. A.; Forbrich, J.; Ascenso, J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Roman-Zuniga, C. [Centro Astronomico Hispano Aleman/CSIC-IAA, Granada 18006 (Spain)

2010-10-20

56

On the source of dense outflows from T Tauri stars - III. Winds driven from the star-disc shear layer  

NASA Astrophysics Data System (ADS)

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (Te? 80 000 K) and dense (ne? 1010 cm-3) component associated with the large-scale jet. This hot component is formed very close to the base of the jet providing fundamental information on the jet formation mechanism. In this series, we have investigated whether this component can be formed in disc winds, either cool or warm. To conclude the series, jet launching from the interface between the magnetic rotor (the star) and the disc is studied. Synthetic profiles are calculated from numerical simulations of outflow launching by star-disc interaction. Profiles are calculated for several possible configurations of the stellar field: dipolar (with surface strengths B* of 1, 2 and 5 kG) or dynamo fed. Also two types of discs, passive or subjected to an ??-dynamo, are considered. These profiles have been used to define the locus of the various models in the observational diagram: dispersion versus centroid, for the profiles of the Si III] line. Bulk motions produce an increasing broadening of the profile as the lever arm launching the jet becomes more efficient; predicted profiles are however sensitive to the disc inclination. Models are compared with observations of the Si III] lines obtained with the Hubble Space Telescope. In addition, it is shown that the non-stationary nature of star-disc winds produce a flickering of the profile during quiescence with variations in the line flux of about 10 per cent. At outburst, accretion signatures appear in the profiles together with an enhancement of the wind, producing the correlation between accretion and outflow as reported from RU Lup, AA Tau and RW Aur observations.

Gmez de Castro, Ana I.; von Rekowski, Brigitta

2011-02-01

57

Temporal scaling analysis: Viscoelastic properties of star polymers  

NASA Astrophysics Data System (ADS)

A generalized temporal scaling ansatz for the frequency dependence of the loss and storage moduli and for the shear dependence of the viscosity is tested against studies on entangled solutions of star polymers in good and theta solvents. At lower frequencies or shear rates, the ansatz calls for an exponential or stretched-exponential form [e.g., G0 exp(-???)] for G''(?)/? and G'(?)/?2, and correspondingly in ? for ?(?). At higher frequencies, the ansatz indicates that each of these quantities has a power-law dependence on its primary variable. The predicted forms are in excellent agreement with literature data on solutions of poly-?-methylstyrene, polybutadiene, polystyrene, and polyisoprene stars. A power-law correlation ?~G02/3 is observed between the zero-frequency, zero-shear modulus G0 and the low-frequency or low-shear decay constant ? of the stretched exponential, the same power-law line describing both star and linear polymers in good solvents.

Phillies, George D. J.

1999-11-01

58

Properties of hadron matter. II - Dense baryon matter and neutron stars.  

NASA Technical Reports Server (NTRS)

In this article we have provided certain details of a nuclear-matter computation, based on the Brueckner-Bethe-Goldstone theory of nuclear reaction, which leads to an equation of state for matter in the density region of 10 to 500 trillion g/cu cm. We also explore the possibilities that at very high baryon densities or for very short baryon separations, the net baryon-baryon interaction may be negligible so that the results of dynamical models, like the statistical bootstrap model and the dual-resonance model, may be applicable to the study of dense baryon matter. Several plausible equations of state are constructed, and their effect on the limiting mass of the neutron star is examined.

Leung, Y. C.; Wang, C. G.

1971-01-01

59

Supernova 2002ic: the collapse of a stripped-envelope, massive star in a dense medium ?  

E-print Network

We revisit the case of SN2002ic that recently revived the debate about the progenitors of SNeIa after the claim of the unprecedented presence of hydrogen lines over a diluted SNIa spectrum. As an alternative to the previous interpretation, we suggest that SN2002ic actually was a type Ic SN, the core collapse of a massive star which lost its hydrogen and helium envelope. In this scenario the observed interaction with a dense circumstellar material (CSM) is the predictable consequence of the intense mass-loss of the progenitor and/or of the presence of a gas rich environment. With this view we establish a link between energetic SNeIc and highly interacting SNeIIn and add some credits to the proposed association of some SNeIIn to GRBs.

S. Benetti; E. Cappellaro; M. Turatto; S. Taubenberger; A. Harutyunyan; S. Valenti

2006-11-03

60

FORMATION OF DENSE MOLECULAR GAS AND STARS AT THE CIRCUMNUCLEAR STARBURST RING IN THE BARRED GALAXY NGC 7552  

SciTech Connect

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 [Department of Astronomical Science, Graduate University for Advanced Studies, Shonan Village, Hayama, Kanagawa 240-0193 (Japan); Lim, Jeremy [Department of Physics, University of Hong Kong, Pokfulam (Hong Kong); Matsushita, Satoki [Academia Sinica, Institute of Astronomy and Astrophysics (ASIAA), P.O. Box 23-141, Taipei 10617, Taiwan (China); Wong, Tony [Department of Astronomy, University of Illinois, 1002 W. Green Street, Urbana, IL 61801 (United States); Ryder, Stuart, E-mail: pan.h.a@nao.ac.jp [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia)

2013-05-01

61

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. PMID:21544227

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

2011-01-01

62

CLUSTERED STAR FORMATION IN MAGNETIC CLOUDS: PROPERTIES OF DENSE CORES FORMED IN OUTFLOW-DRIVEN TURBULENCE  

SciTech Connect

We investigate the physical properties of dense cores formed in turbulent, magnetized, parsec-scale clumps of molecular clouds, using three-dimensional numerical simulations that include protostellar outflow feedback. The dense cores are identified in the simulated density data cube through a clumpfind algorithm. We find that the core velocity dispersion does not show any clear dependence on the core size, in contrast to Larson's linewidth-size relation, but consistent with recent observations. In the absence of a magnetic field, the majority of the cores have supersonic velocity dispersions. A moderately strong magnetic field reduces the dispersion to a subsonic or at most transonic value typically. Most of the cores are out of virial equilibrium, with the external pressure dominating the self-gravity. The implication is that the core evolution is largely controlled by the outflow-driven turbulence. Even an initially weak magnetic field can retard star formation significantly, because the field is amplified by the outflow-driven turbulence to an equipartition strength, with the distorted field component dominating the uniform one. In contrast, for a moderately strong field, the uniform component remains dominant. Such a difference in the magnetic structure is evident in our simulated polarization maps of dust thermal emission; it provides a handle on the field strength. Recent polarization measurements show that the field lines in cluster-forming clumps are spatially well ordered. It is indicative of a moderately strong, dynamically important field which, in combination with outflow feedback, can keep the rate of star formation in embedded clusters at the observationally inferred, relatively slow rate of several percent per free-fall time.

Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Li Zhiyun, E-mail: fumitaka.nakamura@nao.ac.jp, E-mail: zl4h@virginia.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States)

2011-10-10

63

Synthesis of Star Polymer Architectures with Site-Isolated Chromophore Cores  

E-print Network

the synthesis of star polymers with site-isolated chromophores obtained by nitroxide- mediated polymerization-dimensional structures such as microgels,1­6 star polymers,2­9 micelles,10,11 and dendrimers8,12,13 have been explored and synthetic ease of preparation. Among synthetic methods based on living free radical polymerizations,14

Harth, Eva M.

64

Ammonia capture in porous organic polymers densely functionalized with Brnsted acid groups.  

PubMed

The elimination of specific environmental and industrial contaminants, which are hazardous at only part per million to part per billion concentrations, poses a significant technological challenge. Adsorptive materials designed for such processes must be engendered with an exceptionally high enthalpy of adsorption for the analyte of interest. Rather than relying on a single strong interaction, the use of multiple chemical interactions is an emerging strategy for achieving this requisite physical parameter. Herein, we describe an efficient, catalytic synthesis of diamondoid porous organic polymers densely functionalized with carboxylic acids. Physical parameters such as pore size distribution, application of these materials to low-pressure ammonia adsorption, and comparison with analogous materials featuring functional groups of varying acidity are presented. In particular, BPP-5, which features a multiply interpenetrated structure dominated by <6 pores, is shown to exhibit an uptake of 17.7 mmol/g at 1 bar, the highest capacity yet demonstrated for a readily recyclable material. A complementary framework, BPP-7, features slightly larger pore sizes, and the resulting improvement in uptake kinetics allows for efficient adsorption at low pressure (3.15 mmol/g at 480 ppm). Overall, the data strongly suggest that the spatial arrangement of acidic sites allows for cooperative behavior, which leads to enhanced NH3 adsorption. PMID:24456083

Van Humbeck, Jeffrey F; McDonald, Thomas M; Jing, Xiaofei; Wiers, Brian M; Zhu, Guangshan; Long, Jeffrey R

2014-02-12

65

From Gas to Stars in Energetic Environments: Dense Gas Clumps in the 30 Doradus Region within the Large Magellanic Cloud  

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 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO+ emission in the filament and signatures of recent star formation activity including H2O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward the massive compact star cluster R136 in the southwest. We present detailed comparisons of clump properties (masses, linewidths, and sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, and N44). Our analysis shows that the 30Dor-10 clumps have similar masses but wider linewidths and similar HCN/HCO+ (1-0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well shielded against the intense ionizing field that is present in the 30Doradus region.

Anderson, Crystal N.; Meier, David S.; Ott, Jrgen; Hughes, Annie; Wong, Tony; Henkel, Christian; Chen, Rosie; Indebetouw, Remy; Looney, Leslie; Muller, Erik; Pineda, Jorge L.; Seale, Jonathan

2014-09-01

66

On the onset of runaway stellar collisions in dense star clusters I. Dynamics of the first collision  

E-print Network

We study the circumstances under which first collisions occur in young and dense star clusters. The initial conditions for our direct $N$-body simulations are chosen such that the clusters experience core collapse within a few million years, before the most massive stars have left the main-sequence. It turns out that the first collision is typically driven by the most massive stars in the cluster. Upon arrival in the cluster core, by dynamical friction, massive stars tend to form binaries. The enhanced cross section of the binary compared to a single star causes other stars to engage the binary. A collision between one of the binary components and the incoming third star is then mediated by the encounters between the binary and other cluster members. Due to the geometry of the binary-single star engagement the relative velocity at the moment of impact is substantially different than in a two-body encounter. This may have profound consequences for the further evolution of the collision product.

E. Gaburov; A. Gualandris; S. Portegies Zwart

2007-07-03

67

On the source of dense outflows from T Tauri Stars. and III. Winds driven from the star-disc shear layer  

Microsoft Academic Search

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that\\u000athere is a hot (Te ~ 80,000 K) and dense (ne ~ 1e10 cm-3) component associated\\u000awith the large scale jet. This hot component is formed very close to the base\\u000aof the jet providing fundamental information on the jet formation mechanism. In\\u000athis series, we have investigated whether

Ana I. Gomez de Castro; Brigitta von Rekowski

2010-01-01

68

Dense Gas and Star Formation Along the Major Axis of M33 (HERM33ES)  

NASA Astrophysics Data System (ADS)

Using the IRAM 30m telescope we observed and detected HCN and HCO^+ 1-0 towards 6 positions along the major axis of the nearby spiral galaxy M33, at radial distances of up to 3.4 kpc. M33, viewed at an intermediate inclination from a distance of 840 kpc, is an ideal source to study these molecules in an environment not affected by an active galactic nucleus (AGN). Unlike the Galaxy, which is seen edge-on, M33's inclination of 56 degrees allows to determine precise positions and velocities inside its large scale disk. Furthermore, at this distance M33 is still near enough that individual giant molecular clouds (GMCs) can be resolved by the 28" beam of the IRAM 30m at the frequencies of HCN and HCO^+, which translates to 114 pc spatial resolution. HCN, HCO^+, and 13CO were observed at an RMS level of about 0.7 mK at 2 km/s resolution. Additionally, the frequencies of the isotopmeres of HCN and HCO^+, HNC and HOC^+ also fall within the bandwidth of our observation setup. By stacking all observed spectra, paying the price of losing the positional information, we could lower the baseline RMS even further to 0.27 mK and detected HNC and HOC^+ as well as CCH at a very low level of ? 3 ?. Having high critical densities they trace the dense gas and thus also star formation (SF). HCN shows a tight correlation with SF that holds for galactic GMCs to the nuclear environment of distant star-burst (SB) galaxies as has been shown by Gao & Solomon 2004 and Wu et al. 2005. Furthermore, the ratio of HCO^+ to HCN is a popular tool in extra-galactic astronomy to investigate the predominant radiation mechanism (X-Ray - AGN , UV - SB) in galactic nuclei. Interestingly, we find HCN-to-HCO^+ ratios in the range of 0.7-2.8. This includes typical values found towards AGN and SB dominated galactic nuclei suggesting that on local scale this interpretation does not hold, since M33 is neither dominated by intense X-ray radiation nor by the influence of a nearby AGN. These observations are embedded in the Herschel open key time project HERM33ES that targets the major axis of M33 to observe the major FIR gas cooling lines, e.g. CII and OI. In the scope of this project a huge data set of complementary observations has been obtained that give a wealth of information on the regions we studied in HCN and HCO^+.

Buchbender, C.; Kramer, C.; Rosolowsky, E.

2011-05-01

69

SN 2006jc: A Wolf-Rayet Star Exploding in a Dense He-Rich Circumstellar Medium  

E-print Network

We present optical photometry and spectra of the peculiar Type Ib supernova (SN) 2006jc. Strong and relatively narrow He I emission lines indicate the progenitor star exploded inside a dense circumstellar medium (CSM) rich in He. An exceptionally blue apparent continuum persists from our first spectrum obtained 15 days after discovery through our last spectrum ~1 month later. Based on the presence of isolated Fe II emission lines, we interpret the blue "continuum" as blended, perhaps fluorescent, Fe emission. One or two of the reddest He I line profiles in our spectra are double peaked, suggesting that the CSM has an aspherical geometry. The He I lines that are superposed on the blue continuum show P-Cygni profiles, while the redder He I lines do not, implying that the blue continuum also originates from an asymmetric mass distribution. The He-rich CSM, aspherical geometry, and line velocities indicate that the progenitor star was a WNE Wolf-Rayet (WR) star. A recent (2 years before the SN), coincident, luminous outburst similar to those seen in luminous blue variables (LBVs) is the leading candidate for the dense CSM. Such an eruption associated with a WR star has not been seen before, indicating that the progenitor star may have recently transitioned from the LBV phase. We also present unpublished spectral and photometric data on SN 2002ao which, along with SN 1999cq, is very similar to SN 2006jc. We propose that these three objects may represent a new and distinct class of SNe arising from WR progenitors surrounded by a dense CSM.

Ryan J. Foley; Nathan Smith; Mohan Ganeshalingam; Weidong Li; Ryan Chornock; Alexei V. Filippenko

2006-12-27

70

MOLECULAR AND ATOMIC LINE SURVEYS OF GALAXIES. I. THE DENSE, STAR-FORMING GAS PHASE AS A BEACON  

SciTech Connect

We predict the space density of molecular gas reservoirs in the universe and place a lower limit on the number counts of carbon monoxide (CO), hydrogen cyanide (HCN) molecular, and [C II] atomic emission lines in blind redshift surveys in the submillimeter-centimeter spectral regime. Our model uses (1) recently available HCN spectral line energy distributions (SLEDs) of local luminous infrared galaxies (LIRGs, L{sub IR} > 10{sup 11} L{sub Sun }), (2) a value for {epsilon}{sub *} = SFR/M{sub dense}(H{sub 2}) provided by new developments in the study of star formation feedback on the interstellar medium, and (3) a model for the evolution of the infrared luminosity density. Minimal 'emergent' CO SLEDs from the dense gas reservoirs expected in all star-forming systems in the universe are then computed from the HCN SLEDs since warm, HCN-bright gas will necessarily be CO-bright, with the dense star-forming gas phase setting an obvious minimum to the total molecular gas mass of any star-forming galaxy. We include [C II] as the most important of the far-infrared cooling lines. Optimal blind surveys with the Atacama Large Millimeter Array (ALMA) could potentially detect very distant (z {approx} 10-12) [C II] emitters in the {>=}ULIRG galaxy class at a rate of {approx}0.1-1 hr{sup -1} (although this prediction is strongly dependent on the star formation and enrichment history at this early epoch), whereas the (high-frequency) Square Kilometer Array will be capable of blindly detecting z > 3 low-J CO emitters at a rate of {approx}40-70 hr{sup -1}. The [C II] line holds special promise for detecting metal-poor systems with extensive reservoirs of CO-dark molecular gas where detection rates with ALMA can reach up to 2-7 hr{sup -1} in Bands 4-6.

Geach, James E. [Department of Physics, McGill University, 3600 rue University, Montreal, Quebec H3A 2T8 (Canada); Papadopoulos, Padelis P., E-mail: jimgeach@physics.mcgill.ca, E-mail: padelis@mpifr-bonn.mpg.de [Max Planck Institute for Radioastronomy, Auf dem Huegel 69, D-53121 Bonn (Germany)

2012-10-01

71

Examining the Initial Conditions of Star Formation Through Dense Gas Kinematics  

NASA Astrophysics Data System (ADS)

Simulations of star forming molecular clouds give the ability to compare realities and expectations, providing a look at the relative importance of different physical processes. We obtained five sample cores from a global, turbulent, molecular cloud simulation and six perspectives for each core, giving us a total of thirty datacubes. The purpose of this analysis was to compare kinematic simulations of dense gas in protostellar cores to both single-dish and interferometer observations. To accomplish this, we convolved the simulation data with a single-dish beam corresponding to the IRAM 30m, and used synthetic interferometer observations corresponding to the CARMA array in D configuration. We then constructed moment maps for each perspective and derived velocity gradients across the Moment 1 maps and average line widths across the Moment 2 maps. Velocity gradients gave bulk motion in the envelope, and line widths gave velocity distribution along the line of sight. These values were then compared to observations of existing protostellar cores taken with the aforementioned telescopes using the Kolmogorov-Smirnov (KS) statistical test to find the probability that the simulation and observation samples came from the same parent distribution. In general, we had low probabilities that our null hypothesis was false, indicating that it was likely that, for both single-dish and interferometer, the simulations and observations were not describing the same kinematics. We conclude that the difference between the simulation and observations was due to differing initial conditions in the molecular clouds in which they formed, which gives insight into performing more accurate simulations in the future. In particular, the extreme broadness of line widths for the single-dish simulations indicates an excess of supersonic turbulence driving strong infall in the cores. Also, although we wanted to interpret velocity gradients as rotation, they did not really seem to trace rotation.

Mead, Adrian T.; Tobin, J. J.; Smith, R.

2014-01-01

72

Phase transition of a single star polymer: a Wang-Landau sampling study  

E-print Network

Star polymer is a typical nonlinear macromolecule possessing special thermodynamic behaviors for the existence of a jointing point. The thermodynamic transitions of a single star polymer are systematically studied with bond fluctuation model using Wang-Landau sampling technique. A new analysis method applying the shape factor is proposed to determine coil-globule (CG) and liquid-crystal (LC) transitions, which shows higher efficiency and precision than canonical specific heat function. It is found that the LC transition of star polymer at lower temperature obeys the identical scaling law as linear polymer. With the increase of the arm density of star polymer, however, the CG transition point, corresponding to {\\theta} temperature, shifts towards the LC transition and the reason comes from the high density arms of star polymer, which requires the lower temperature for attracting force to overcome the volume excluding effects of chain. This work clearly demonstrates that the distinction of linear and star polymers in structures only affects CG transition and has no influence on LC transition.

Zilu Wang; Xuehao He

2011-04-18

73

From Gas to Stars in Energetic Environments: Dense Gas Clumps in the 30 Doradus Region Within the Large Magellanic Cloud  

E-print Network

We present parsec scale interferometric maps of HCN(1-0) and HCO$^{+}$(1-0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via the varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO$^{+}$ emission in the filament and signatures of recent star formation activity including H$_{2}$O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward t...

Anderson, Crystal N; Ott, Jrgen; Hughes, Annie; Wong, Tony; Henkel, Christian; Chen, Rosie; Indebetouw, Remy; Looney, Leslie; Muller, Erik; Pineda, Jorge L; Seale, Jonathan

2014-01-01

74

Shielding effects in polymer-polymer reactions. V. Concentration dependence of contact formation between star-branched and linear chains?  

PubMed Central

By use of the Dissipative Particle Dynamics (DPD) simulation technique mixtures of star-branched (arm number F=4) and linear chains in athermal (good) solvent are analyzed regarding probabilities for intermolecular contacts of various reactive sites within different polymer coils. The accompanying sterical hindrances are described in the framework of shielding factors in order to investigate reactions and side reactions in radical polymerization and other techniques that involve polymerpolymer coupling. The shielding factors are studied as a function of total concentration from high dilution up to the bulk for different chain lengths of star-shaped and linear chains. Results indicate that their concentration dependence can be described by a power law for systems above the overlap concentration, whereas the chain length dependence vanishes when extrapolating to infinite chain lengths in that concentration range. Also the influence of the ratio of star chains and linear chains is studied for various concentrations. PMID:23874002

Nardai, Michael M.; Zifferer, Gerhard

2013-01-01

75

Phase behavior of rigid, amphiphilic star polymers Christian Koch,*a  

E-print Network

Phase behavior of rigid, amphiphilic star polymers Christian Koch,*a Athanassios Z. Panagiotopoulos,b Federica Lo Versoc and Christos N. Likosa We determine the phase behavior of rigid, amphiphilic diblock polymers that feature amphiphilicity and high rigidity are a manifestation of the character of these hybrid

Likos, Christos N.

76

THE GALACTIC CENTER CLOUD G0.253+0.016: A MASSIVE DENSE CLOUD WITH LOW STAR FORMATION POTENTIAL  

SciTech Connect

We present the first interferometric molecular line and dust emission maps for the Galactic Center (GC) cloud G0.253+0.016, observed using CARMA and the SMA. This cloud is very dense, and concentrates a mass exceeding the Orion Molecular Cloud Complex (2 Multiplication-Sign 10{sup 5} M{sub Sun }) into a radius of only 3 pc, but it is essentially starless. G0.253+0.016 therefore violates ''star formation laws'' presently used to explain trends in galactic and extragalactic star formation by a factor {approx}45. Our observations show a lack of dense cores of significant mass and density, thus explaining the low star formation activity. Instead, cores with low densities and line widths {approx}< 1 km s{sup -1}-probably the narrowest lines reported for the GC region to date-are found. Evolution over several 10{sup 5} yr is needed before more massive cores, and possibly an Arches-like stellar cluster, could form. Given the disruptive dynamics of the GC region, and the potentially unbound nature of G0.253+0.016, it is not clear that this evolution will happen.

Kauffmann, Jens; Pillai, Thushara [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Zhang Qizhou, E-mail: jens.kauffmann@astro.caltech.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS78, Cambridge, MA 02138 (United States)

2013-03-10

77

A Class of Super Dense Stars Models Using Charged Analogues of Hajj-Boutros Type Relativistic Fluid Solutions  

NASA Astrophysics Data System (ADS)

We present a spherically symmetric solution of the general relativistic field equations in isotropic coordinates for perfect charged fluid, compatible with a super dense star modeling. The solution is well behaved for all the values of Schwarzschild parameter u lying in the range 0 < u < 0.1727 for the maximum value of charge parameter K = 0.08163. The maximum mass of the fluid distribution is calculated by using stellar surface density as ? b = 4.68881014g cm-3. Corresponding to K = 0.08 and u max = 0.1732, the resulting well behaved solution has a maximum mass M = 0.9324M ? and radius R = 8.00 and by assuming ? b = 21014g cm-3 the solution results a stellar configuration with maximum mass M = 1.43M ? and radius R b = 12.25 km. The maximum mass is found increasing with increasing K up to 0.08. The well behaved class of relativistic stellar models obtained in this work might has astrophysical significance in the study of internal structure of compact star such as neutron star or self-bound strange quark star like Her X-1.

Pant, Neeraj; Pradhan, N.; Murad, Mohammad Hassan

2014-07-01

78

A Class of Super Dense Stars Models Using Charged Analogues of Hajj-Boutros Type Relativistic Fluid Solutions  

NASA Astrophysics Data System (ADS)

We present a spherically symmetric solution of the general relativistic field equations in isotropic coordinates for perfect charged fluid, compatible with a super dense star modeling. The solution is well behaved for all the values of Schwarzschild parameter u lying in the range 0 < u < 0.1727 for the maximum value of charge parameter K = 0.08163. The maximum mass of the fluid distribution is calculated by using stellar surface density as ? b = 4.68881014g cm-3. Corresponding to K = 0.08 and u max = 0.1732, the resulting well behaved solution has a maximum mass M = 0.9324 M ? and radius R = 8.00 and by assuming ? b = 21014g cm-3 the solution results a stellar configuration with maximum mass M = 1.43 M ? and radius R b = 12.25 km. The maximum mass is found increasing with increasing K up to 0.08. The well behaved class of relativistic stellar models obtained in this work might has astrophysical significance in the study of internal structure of compact star such as neutron star or self-bound strange quark star like Her X-1.

Pant, Neeraj; Pradhan, N.; Murad, Mohammad Hassan

2014-11-01

79

Deuterium chemistry of dense gas in the vicinity of low-mass and massive star forming regions  

E-print Network

The standard interstellar ratio of deuterium to hydrogen (D/H) atoms is $\\sim 1.5 \\times 10^{-5}$. However, the deuterium fractionation is in fact found to be enhanced, to different degrees, in cold, dark cores, hot cores around massive star forming regions, lukewarm cores, and warm cores ({\\it hereafter}, hot corinos) around low-mass star forming regions. In this paper, we investigate the overall differences in the deuterium chemistry between hot cores and hot corinos. We have modelled the chemistry of dense gas around low-mass and massive star forming regions using a gas-grain chemical model. We investigate the influence of varying the core density, the depletion efficiency of gaseous species on to dust grains, the collapse mode and the final mass of the protostar on the chemical evolution of star forming regions. We find that the deuterium chemistry is, in general, most sensitive to variations of the depletion efficiency on to grain surfaces, in agreement with observations. In addition, the results showed ...

Awad, Zainab; Bayet, Estelle; Caselli, Paola

2014-01-01

80

HUBBLE UNCOVERS MYSTERY OBJECTS IN THE DENSE CORE OF A NEARBY STAR CLUSTER  

NASA Technical Reports Server (NTRS)

Piercing the heart of a glittering swarm of stars, NASA's sharp-eyed Hubble Space Telescope unveils the central region of the globular cluster M22, a 12- to 14-billion-year-old grouping of stars in the constellation Sagittarius. The telescope's view of the cluster's core measures 3.3 light-years across. The stars near the cluster's core are 100,000 times more numerous than those in the Sun's neighborhood. Buried in the glow of starlight are about six 'mystery objects,' which astronomers estimate are no larger than one quarter the mass of the giant planet Jupiter, the solar system's heftiest planet. The mystery objects are too far and dim for Hubble to see directly. Instead, the orbiting observatory detected these unseen celestial bodies by looking for their gravitational effects on the light from far distant stars. In this case, the stars are far beyond the cluster in the galactic bulge, about 30,000 light-years from Earth at the center of the Milky Way Galaxy. M22 is 8,500 light-years away. The invisible objects betrayed their presence by bending the starlight gravitationally and amplifying it, a phenomenon known as microlensing. From February 22 to June 15, 1999, Hubble's Wide Field and Planetary Camera 2 looked through this central region and monitored 83,000 stars. During that time the orbiting observatory recorded six unexpectedly brief microlensing events. In each case a background star jumped in brightness for less than 20 hours before dropping back to normal. These transitory spikes in brightness mean that the object passing in front of the star must have been much smaller than a normal star. Hubble also detected one clear microlensing event. In that observation a star appeared about 10 times brighter over an 18-day span before returning to normal. Astronomers traced the leap in brightness to a dwarf star in the cluster floating in front of the background star. The inset photo shows the entire globular cluster of about 10 million stars. M22 is about 60 light-years wide. The image was taken in June 1995 by the Burrell Schmidt telescope at the Case Western Reserve University's Warner and Swasey Observatory on Kitt Peak in Arizona. This release is issued jointly by NASA and ESA. Credits for Hubble image: NASA, Kailash Sahu, Stefano Casertano, Mario Livio, Ron Gilliland (Space Telescope Science Institute), Nino Panagia (European Space Agency/Space Telescope Science Institute), Michael Albrow and Mike Potter (Space Telescope Science Institute) Credits for ground-based image: Nigel A.Sharp, REU program/AURA/NOAO/NSF

2002-01-01

81

Application of binary interaction theory to linear and nonlinear rheology of star-branched polymers  

NASA Astrophysics Data System (ADS)

The binary interaction (BI) theory recently developed by David W. Mead, Ronald G. Larson, and Masao Doi (1998) is based on two fundamental postulates strongly supported by experimental data: (1)stress-optic rule, (2)binary interaction principle. The BI theory is general and in principle applies to all entangled flexible polymers regardless of molecular architecture. Three parameters are required in the BI theory to establish the length and time scales for the system: the plateau modulus, the entanglement molecular weight, and the Rouse relaxation time scale. This thesis focuses on the first application of the BI theory to polymers with long-chain branches (LCB): star polymers. A mathematically simplified star model is derived analytically by performing a boundary layer analysis on the full BI model, resulting in an entanglement flux balance between star tip fluctuational penetration inward and convective constraint release (CCR)/convection outward from the star core. The simplified BI star theory for small deformations is compared with the well-established Ball-McLeish model. Juxtaposition of both simulations shows essentially quantitative equivalence. The empirical Cox-Merz viscosity rule for star-branched polymers is analytically derived from the simplified BI star model. The underlying physical basis of the validity of the Cox-Merz relationship for fast, nonlinear flows is a direct consequence of the combined effect of CCR and convection. Simulations from the simplified BI star model agree well with experimental dynamic moduli and flow curves of melts/concentrated solutions of various polymer species from literature data with no adjustable parameters. Flow curve crossover phenomena and subsequent merger reported for matched star and linear polymers are quantitatively predicted by the BI theory. The flow curve crossover of a matched set of star and linear polymers represents a transition of material response from Brownian-motion- governed linear viscoelasticity to CCR/convection- dominated nonlinear rheology. The merger of star and linear flow curves at high shear rates further supports the hypothesis that the high-deformation-rate portion of the shear flow curve is independent of molecular weight, molecular weight distribution, and molecular architecture.

Chen, Han-Wen

2001-12-01

82

QMC and the nature of dense matter: written in the stars?  

SciTech Connect

We discuss the recent progress in calculating the properties of 'hybrid stars'(stellar objects similar to neutron stars, classified by the incorporation of non-nucleonic degrees of freedom, including but not limited to hyperons and/or a quark-matter core) using the octet-baryon Quark-Meson Coupling (QMC) model. The version of QMC used is a recent improvement which includes the in-medium modification of the quark-quark hyperfine interaction.

Carroll, J. D. [Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, SA 5005 (Australia)

2010-07-27

83

GRAVITATIONAL CONUNDRUM? DYNAMICAL MASS SEGREGATION VERSUS DISRUPTION OF BINARY STARS IN DENSE STELLAR SYSTEMS  

SciTech Connect

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 {approx}> 2{sigma} level of significance (>3{sigma} 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 {sub Sun }) 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; Kouwenhoven, M. B. N. [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China)] [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai; Hu, Yi; Wicker, James E., E-mail: grijs@pku.edu.cn [National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

2013-03-01

84

Dynamic effective elastic modulus of polymer matrix composites with dense piezoelectric nano-fibers considering surface/interface effect  

NASA Astrophysics Data System (ADS)

Based on effective field method, the dynamic effective elastic modulus of polymer matrix composites embedded with dense piezoelectric nano-fibers is obtained, and the interacting effect of piezoelectric surfaces/interfaces around the nano-fibers is considered. The multiple scattering effects of harmonic anti-plane shear waves between the piezoelectric nano-fibers with surface/interface are averaged by effective field method. To analyze the interacting results among the random nano-fibers, the problem of two typical piezoelectric nano-fibers is introduced by employing the addition theorem of Bessel functions. Through numerical calculations, the influence of the distance between the randomly distributed piezoelectric nano-fibers under different surface/interface parameters is analyzed. The effect of piezoelectric property of surface/interface on the effective shear modulus under different volume fractions is also examined. Comparison with the simplified cases is given to validate this dynamic electro-elastic model.

Fang, XueQian; Huang, MingJuan; Zhu, ZiTao; Liu, JinXi; Feng, WenJie

2014-07-01

85

A new relativistic model of hybrid star with interactive quark matter and dense baryonic matter  

E-print Network

We propose a relativistic model of hybrid star admitting conformal symmetry considering quark matter and baryonic matter as two different fluids. We define interaction equations between the normal baryonic matter and the quark matter and study the physical situations for repulsive, attractive and zero interaction between the constituent matters. From the interaction equations we find out the value of the equation of state (EOS) parameter for normal baryonic matter which is found to be consistent with the value obtained from the Walecka model for nucleonic matter at high density. The measured value of the Bag constant is used to explore the space time geometry inside the star. The theoretical mass-radius values are compared with the available observational data of the compact objects. From the nature of the match with the observational data, we predict the nature of interaction that must be present inside the hybrid stars

Chakraborty, Koushik; Mallick, Arkopriya

2014-01-01

86

A new relativistic model of hybrid star with interactive quark matter and dense baryonic matter  

E-print Network

We propose a relativistic model of hybrid star admitting conformal symmetry considering quark matter and baryonic matter as two different fluids. We define interaction equations between the normal baryonic matter and the quark matter and study the physical situations for repulsive, attractive and zero interaction between the constituent matters. From the interaction equations we find out the value of the equation of state (EOS) parameter for normal baryonic matter which is found to be consistent with the value obtained from the Walecka model for nucleonic matter at high density. The measured value of the Bag constant is used to explore the space time geometry inside the star. The theoretical mass-radius values are compared with the available observational data of the compact objects. From the nature of the match with the observational data, we predict the nature of interaction that must be present inside the hybrid stars

Koushik Chakraborty; Farook Rahaman; Arkopriya Mallick

2014-10-08

87

Rearrangement of the Fermi Surface of Dense Neutron Matter and Direct Urca Cooling of Neutron Stars  

E-print Network

It is proposed that a rearrangement of single-particle degrees of freedom may occur in a portion of the quantum fluid interior of a neutron star. Such a rearrangement is associated with the pronounced softening of the spin-isospin collective mode which, under increasing density, leads to pion condensation. Arguments and estimates based on fundamental relations of many-body theory show that one realization of this phenomenon could produce very rapid cooling of the star via a direct nucelon Urca process displaying a $T^5$ dependence on temperature.

D. N. Voskresensky; V. A. Khodel; M. V. Zverev; J. W. Clark

2000-03-13

88

Zero sound in neutron stars with dense quark matter under strong magnetic fields  

SciTech Connect

We study a neutron star with a quark matter core under extremely strong magnetic fields. We investigate the possibility of an Urca process as a mechanism for the cooling of such a star. We found that apart from very particular cases, the Urca process cannot occur. We also study the stability of zero sound modes under the same conditions. We derive limits for the coupling constant of an effective theory, in order the zero sound to be undamped. We show that zero sound modes can help kinematically to facilitate a cooling process. Our conclusions hold for unpaired quark matter and not superconducting.

Kouvaris, Chris [Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen O (Denmark)

2009-06-15

89

On the source of dense outflows from T Tauri Stars. and III. Winds driven from the star-disc shear layer  

E-print Network

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (Te ~ 80,000 K) and dense (ne ~ 1e10 cm-3) component associated with the large scale jet. This hot component is formed very close to the base of the jet providing fundamental information on the jet formation mechanism. In this series, we have investigated whether this component can be formed in disc winds, either cool or warm. To conclude the series, jet launching from the interface between the magnetic rotor (the star) and the disc is studied. Synthetic profiles are calculated from numerical simulations of outflow launching by star-disc interaction. Profiles are calculated for several possible configurations of the stellar field: dipolar (with surface strengths, B of 1, 2 and 5 kG) or dynamo fed. Also two types of discs, passive or subjected to an alpha/Omega-dynamo, are considered. These profiles have been used to define the locus of the various models in the observational diagram: dispersion versus centroid, for the ...

de Castro, Ana I Gomez

2010-01-01

90

Nanoparticle (star polymer) delivery of nitric oxide effectively negates Pseudomonas aeruginosa biofilm formation.  

PubMed

Biofilms are increasingly recognized as playing a major role in human infectious diseases, as they can form on both living tissues and abiotic surfaces, with serious implications for applications that rely on prolonged exposure to the body such as implantable biomedical devices or catheters. Therefore, there is an urgent need to develop improved therapeutics to effectively eradicate unwanted biofilms. Recently, the biological signaling molecule nitric oxide (NO) was identified as a key regulator of dispersal events in biofilms. In this paper, we report a new class of core cross-linked star polymers designed to store and release nitric oxide, in a controlled way, for the dispersion of biofilms. First, core cross-linked star polymers were prepared by reversible addition-fragmentation chain transfer polymerization (RAFT) via an arm first approach. Poly(oligoethylene methoxy acrylate) chains were synthesized by RAFT polymerization, and then chain extended in the presence of 2-vinyl-4,4-dimethyl-5-oxazolone monomer (VDM) with N,N-methylenebis(acrylamide) employed as a cross-linker to yield functional core cross-linked star polymers. Spermine was successfully attached to the star core by reaction with VDM. Finally, the secondary amine groups were reacted with NO gas to yield NO-core cross-linked star polymers. The core cross-linked star polymers were found to release NO in a controlled, slow delivery in bacterial cultures showing great efficacy in preventing both cell attachment and biofilm formation in Pseudomonas aeruginosa over time via a nontoxic mechanism, confining bacterial growth to the suspended liquid. PMID:24915286

Duong, Hien T T; Jung, Kenward; Kutty, Samuel K; Agustina, Sri; Adnan, Nik Nik M; Basuki, Johan S; Kumar, Naresh; Davis, Thomas P; Barraud, Nicolas; Boyer, Cyrille

2014-07-14

91

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

E-print Network

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 ~ 10^19 [G], which suggests that the quantum anomaly can be a microscopic origin of the magnetars (highly magnetized neutron stars).

Minoru Eto; Koji Hashimoto; Tetsuo Hatsuda

2012-09-21

92

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

93

An arm-first approach to cleavable mikto-arm star polymers by RAFT polymerization.  

PubMed

Redox-cleavable mikto-arm star polymers are prepared by an "arm-first" approach involving copolymerization of a dimethacrylate mediated by a mixture of macroRAFT agents. Thus, RAFT copolymerization of the monomers BMA, DMAEMA, and OEGMA, with the disulfide dimethacrylate cross-linker (DSDMA), bis(2-methacryloyl)oxyethyl disulfide, mediated by a 1:1:1 mixture of three macroRAFT agents with markedly different properties [hydrophilic, poly[oligo(ethylene glycol) methacrylate]-P(OEGMA)8-9 ; cationizable, poly[2-(dimethylamino)ethyl methacrylate]-P(DMAEMA); hydrophobic, poly(n-butyl methacrylate)-P(BMA)] provides low dispersity mikto-arm star polymers. Good control (? < 1.3) is observed for the target P(DMAEMA)/P(OEGMA)/P(BMA) (3:3:1) mikto-arm star, a double hydrophilic P(DMAEMA)/P(OEGMA) (3:3) mikto-arm star and a hydrophobic P(BMA) homo-arm star. However, ? for the target mikto-arm stars increases with an increase in either the ratio [DSDMA]:[total macroRAFT] or the fraction of hydrophobic P(BMA) macroRAFT agent. The quaternized mikto-arm star in dilute aqueous solution shows a monomodal particle size distribution and an average size of ?145 nm. PMID:24504709

Wei, Xiaohu; Moad, Graeme; Muir, Benjamin W; Rizzardo, Ezio; Rosselgong, Julien; Yang, Wantai; Thang, San H

2014-04-01

94

Dense molecular globulettes and the dust arc towards the runaway O star AE Aur (HD 34078)  

E-print Network

Some runaway stars are known to display IR arc-like structures around them, resulting from their interaction with surrounding interstellar material. The properties of these features as well as the processes involved in their formation are still poorly understood. We aim at understanding the physical mechanisms that shapes the dust arc observed near the runaway O star AEAur (HD34078). We obtained and analyzed a high spatial resolution map of the CO(1-0) emission that is centered on HD34078, and that combines data from both the IRAM interferometer and 30m single-dish antenna. The line of sight towards HD34078 intersects the outer part of one of the detected globulettes, which accounts for both the properties of diffuse UV light observed in the field and the numerous molecular absorption lines detected in HD34078's spectra, including those from highly excited H2 . Their modeled distance from the star is compatible with the fact that they lie on the 3D paraboloid which fits the arc detected in the 24 {\\mu}m Spitz...

Gratier, P; Boiss, P; Cabrit, S; Lesaffre, P; Gerin, M; Forts, G Pineau des

2014-01-01

95

Synthesis and characterization of dendritic star-shaped zwitterionic polymers as novel anticancer drug delivery carriers.  

PubMed

In this work, a novel dendritic star-shaped zwitterionic polymer, polyamidoamine-graft-poly[3-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate] (PAMAM-g-PDMAPS), was synthesized. PAMAM dendrimers (generation 2, G2) were firstly prepared and then converted into the PAMAM-Br macroinitiator with 2-bromoisobutyryl bromide for ATRP. Finally, ATRP of zwitterionic DMAPS was carried out to obtain the dendritic star-shaped polymers PAMAM-g-PDMAPS with different PDMAPS chain lengths. Fourier transform-infrared spectroscopy, (1)H?NMR, dynamic laser light scattering (DLS), and TEM were used to characterize the polymers. Encapsulation of adriamycin (ADR) by PAMAM-g-PDMAPS nanoparticles and ADR release behavior from ADR-loaded PAMAM-g-PDMAPS nanoparticles were investigated in detail. PAMAM-g-PDMAPS polymers, even starting from low-generation PAMAM core (G2), were found to show high loading efficiency for ADR because ADR existed not only within G2 PAMAM cores but also in PDMAPS layers. The release profile of ADR from ADR-loaded PAMAM-g-PDMAPS nanoparticles was pH-sensitive and could be controlled by the length of PDMAPS chains. Cell viability studies indicated that ADR-loaded PAMAM-g-PDMAPS could effectively restrain the growth of HepG2 cells and even kill them, whereas PAMAM-g-PDMAPS exhibited nontoxicity. All these results demonstrated that dendritic star-shaped zwitterionic polymers PAMAM-g-PDMAPS are attractive candidates as anticancer drug delivery carriers. PMID:25025700

Li, Lina; Wang, Yan; Ji, Feng; Wen, Yan; Li, Junjie; Yang, Boguang; Yao, Fanglian

2014-10-01

96

Multiple glass transitions in star polymer mixtures: Insights from theory and simulations  

E-print Network

The glass transition in binary mixtures of star polymers is studied by mode coupling theory and extensive molecular dynamics computer simulations. In particular, we have explored vitrification in the parameter space of size asymmetry $\\delta$ and concentration $\\rho_2$ of the small star polymers at fixed concentration of the large ones. Depending on the choice of parameters, three different glassy states are identified: a single glass of big polymers at low $\\delta$ and low $\\rho_2$, a double glass at high $\\delta$ and low $\\rho_2$, and a novel double glass at high $\\rho_2$ and high $\\delta$ which is characterized by a strong localization of the small particles. At low $\\delta$ and high $\\rho_2$ there is a competition between vitrification and phase separation. Centered in the $(\\delta, \\rho_2)$-plane, a liquid lake shows up revealing reentrant glass formation. We compare the behavior of the dynamical density correlators with the predictions of the theory and find remarkable agreement between the two.

Christian Mayer; Francesco Sciortino; Christos N. Likos; Piero Tartaglia; Hartmut Loewen; Emanuela Zaccarelli

2008-11-10

97

HATS-4b: A Dense Hot-Jupiter Transiting a Super Metal-Rich G Star  

E-print Network

We report the discovery by the HATSouth survey of HATS-4b, an extrasolar planet transiting a V=13.46 mag G star. HATS-4b has a period of P = 2.5167 d, mass of Mp = 1.32 Mj, radius of Rp = 1.02 Rj and density of rho_p = 1.55 +- 0.16 g/cm^3 ~ 1.24 rhoj. The host star has a mass of 1.00 Msun, a radius of 0.92 Rsun and a very high metallicity [Fe/H]= 0.43 +- 0.08. HATS-4b is among the densest known planets with masses between 1-2 Mj and is thus likely to have a significant content of heavy elements of the order of 75 Mearth. In this paper we present the data reduction, radial velocity measurement and stellar classification techniques adopted by the HATSouth survey for the CORALIE spectrograph. We also detail a technique to estimate simultaneously vsini and macroturbulence using high resolution spectra.

Jordn, A; Bakos, G ; Bayliss, D; Penev, K; Hartman, J D; Zhou, G; Mancini, L; Mohler-Fischer, M; Ciceri, S; Sato, B; Csubry, Z; Rabus, M; Suc, V; Espinoza, N; Bhatti, W; Borro, M de Val; Buchhave, L; Csk, B; Henning, T; Schmidt, B; Tan, T G; Noyes, R W; Bky, B; Butler, R P; Shectman, S; Crane, J; Thompson, I; Williams, A; Martin, R; Contreras, C; Lzr, J; Papp, I; Sri, P

2014-01-01

98

SiO excitation from dense shocks in the earliest stages of massive star formation  

E-print Network

Molecular outflows are a direct consequence of accretion, and therefore they represent one of the best tracers of accretion processes in the still poorly understood early phases of high-mass star formation. Previous studies suggested that the SiO abundance decreases with the evolution of a massive young stellar object probably because of a decay of jet activity, as witnessed in low-mass star-forming regions. We investigate the SiO excitation conditions and its abundance in outflows from a sample of massive young stellar objects through observations of the SiO(8-7) and CO(4-3) lines with the APEX telescope. Through a non-LTE analysis, we find that the excitation conditions of SiO increase with the velocity of the emitting gas. We also compute the SiO abundance through the SiO and CO integrated intensities at high velocities. For the sources in our sample we find no significant variation of the SiO abundance with evolution for a bolometric luminosity-to-mass ratio of between 4 and 50 $L_\\odot/M_\\odot$. We also ...

Leurini, S; Lpez-Sepulcre, A; Gusdorf, A; Csengeri, T; Anderl, S

2014-01-01

99

Dense molecular globulettes and the dust arc toward the runaway O star AE Aurigae (HD 34078)  

NASA Astrophysics Data System (ADS)

Context. Some runaway stars are known to display IR arc-like structures around them, resulting from their interaction with surrounding interstellar material. The properties of these features as well as the processes involved in their formation are still poorly understood. Aims.We aim to understand the physical mechanisms that shape the dust arc observed near the runaway O-star AE Aur (HD 34078). Methods.We obtained and analyzed a high spatial resolution (4.4'') map of the 12CO(1-0) emission that is centered on HD 34078, and that combines data from both the IRAM interferometer and 30 m single-dish antenna. Results: One third of the 30 m flux mainly originates from two small (no larger than 5'' 10'' or 0.013 0.026 pc), and bright (1 and 3 K peak temperatures) CO globulettes. The line of sight toward HD 34078 intersects the outer part of one of the globulettes, which accounts for both the properties of diffuse UV light observed in the field and the numerous molecular absorption lines detected in HD 34078's spectra, including those from highly excited H2. Their modeled distance from the star(0.2 pc) is compatible with the fact that they lie on the 3D paraboloid, which fits the arc detected in the 24 ?m Spitzer image. Four other compact CO globulettes are detected in the mapped area, all lying close to the rim of this paraboloid. These globulettes have a high density and linewidth, and are strongly pressure-confined or transient. Conclusions: The presence of molecular globulettes at such a close distance from an O star is unexpected, and probably related to the high proper motion of HD 34078. Indeed, the good spatial correlation between the CO globulettes and the IR arc suggests that they result from the interaction of the radiation and wind emitted by HD 34078 with the ambient gas. However, the details of this interaction remain unclear. A wind mass-loss rate significantly larger than the value inferred from UV lines is favored by the large IR arc size, but does not easily explain the low velocity of the CO globulettes. The effect of radiation pressure on dust grains also meets several issues in explaining the observations. Further observational and theoretical work is needed to fully elucidate the processes shaping the gas and dust in bow shocks around runaway O stars. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).PdeB map in FITS format is only available at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A71

Gratier, P.; Pety, J.; Boiss, P.; Cabrit, S.; Lesaffre, P.; Gerin, M.; Pineau des Forts, G.

2014-10-01

100

HATS-4b: A Dense Hot Jupiter Transiting a Super Metal-rich G star  

NASA Astrophysics Data System (ADS)

We report the discovery by the HATSouth survey of HATS-4b, an extrasolar planet transiting a V = 13.46 mag G star. HATS-4b has a period of P ? 2.5167 days, mass of Mp ? 1.32 M Jup, radius of Rp ? 1.02 R Jup, and density of ? p = 1.55 0.16 g cm-3 ?1.24 ?Jup. The host star has a mass of 1.00 M ?, a radius of 0.92 R ?, and a very high metallicity [Fe/H]=0.43 0.08. HATS-4b is among the densest known planets with masses between 1 and 2 M J and is thus likely to have a significant content of heavy elements of the order of 75 M ?. In this paper we present the data reduction, radial velocity measurements, and stellar classification techniques adopted by the HATSouth survey for the CORALIE spectrograph. We also detail a technique for simultaneously estimating vsin i and macroturbulence using high resolution spectra. The HATSouth network is operated by a collaboration consisting of Princeton University (PU), the Max Planck Institut fr Astronomie (MPIA), and the Australian National University (ANU). The station at Las Campanas Observatory (LCO) of the Carnegie Institution is operated by PU in conjunction with collaborators at the Pontificia Universidad Catlica de Chile, the station at the High Energy Spectroscopic Survey site is operated in conjunction with MPIA, and the station at Siding Spring Observatory (SSO) is operated jointly with ANU. This paper includes data gathered with the 6.5 m Magellan Telescopes located at LCO, Chile. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and on observations made with the MPG/ESO 2.2 m Telescope at the ESO Observatory in La Silla. This paper uses observations obtained with facilities of the Las Cumbres Observatory Global Telescope.

Jordn, Andrs; Brahm, Rafael; Bakos, G. .; Bayliss, D.; Penev, K.; Hartman, J. D.; Zhou, G.; Mancini, L.; Mohler-Fischer, M.; Ciceri, S.; Sato, B.; Csubry, Z.; Rabus, M.; Suc, V.; Espinoza, N.; Bhatti, W.; Borro, M. de Val; Buchhave, L.; Csk, B.; Henning, T.; Schmidt, B.; Tan, T. G.; Noyes, R. W.; Bky, B.; Butler, R. P.; Shectman, S.; Crane, J.; Thompson, I.; Williams, A.; Martin, R.; Contreras, C.; Lzr, J.; Papp, I.; Sri, P.

2014-08-01

101

CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1  

NASA Astrophysics Data System (ADS)

We present details of the CARMA Large Area Star Formation Survey (CLASSy), while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that spectrally imaged N2H+, HCO+, and HCN (J = 1 ? 0 transitions) across over 800 square arcminutes of the Perseus and Serpens Molecular Clouds. The observations have angular resolution near 7'' and spectral resolution near 0.16 km s-1. We imaged ~150 square arcminutes of Barnard 1, focusing on the main core, and the B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with morphology similar to cool dust in the region, while HCO+ and HCN trace several molecular outflows from a collection of protostars in the main core. We identify a range of kinematic complexity, with N2H+ velocity dispersions ranging from ~0.05 to 0.50 km s-1 across the field. Simultaneous continuum mapping at 3 mm reveals six compact object detections, three of which are new detections. A new, non-binary dendrogram algorithm is used to analyze dense gas structures in the N2H+ position-position-velocity (PPV) cube. The projected sizes of dendrogram-identified structures range from about 0.01 to 0.34 pc. Size-linewidth relations using those structures show that non-thermal line-of-sight velocity dispersion varies weakly with projected size, while rms variation in the centroid velocity rises steeply with projected size. Comparing these relations, we propose that all dense gas structures in Barnard 1 have comparable depths into the sky, around 0.1-0.2 pc this suggests that overdense, parsec-scale regions within molecular clouds are better described as flattened structures rather than spherical collections of gas. Science-ready PPV cubes for Barnard 1 molecular emission are available for download.

Storm, Shaye; Mundy, Lee G.; Fernndez-Lpez, Manuel; Lee, Katherine I.; Looney, Leslie W.; Teuben, Peter; Rosolowsky, Erik; Arce, Hctor G.; Ostriker, Eve C.; Segura-Cox, Dominique M.; Pound, Marc W.; Salter, Demerese M.; Volgenau, Nikolaus H.; Shirley, Yancy L.; Chen, Che-Yu; Gong, Hao; Plunkett, Adele L.; Tobin, John J.; Kwon, Woojin; Isella, Andrea; Kauffmann, Jens; Tassis, Konstantinos; Crutcher, Richard M.; Gammie, Charles F.; Testi, Leonardo

2014-10-01

102

Fluorous microgel star polymers: selective recognition and separation of polyfluorinated surfactants and compounds in water.  

PubMed

Immiscible with either hydrophobic or hydrophilic solvents, polyfluorinated compounds (PFCs) are generally "fluorous", some of which have widely been employed as surfactants and water/oil repellents. Given the prevailing concern about the environmental pollution and the biocontamination by PFCs, their efficient removal and recycle from industrial wastewater and products are critically required. This paper demonstrates that fluorous-core star polymers consisting of a polyfluorinated microgel core and hydrophilic PEG-functionalized arms efficiently and selectively capture PFCs in water into the cores by fluorous interaction. For example, with over 10?000 fluorine atoms in the core and approximately 100 hydrophilic arms, the fluorous stars remove perfluorooctanoic acid (PFOA) and related PFCs in water from 10 ppm to as low as a parts per billion (ppb) level, or an over 98% removal. Dually functionalized microgel-core star polymers with perfluorinated alkanes and additional amino (or ammonium) groups cooperatively recognize PFOA or its ammonium salt and, in addition, release the guests upon external stimuli. The "smart" performance shows that the fluorous-core star polymers are promising PFC separation, recovery, and recycle materials for water purification toward sustainable society. PMID:25300369

Koda, Yuta; Terashima, Takaya; Sawamoto, Mitsuo

2014-11-01

103

SiO excitation from dense shocks in the earliest stages of massive star formation  

NASA Astrophysics Data System (ADS)

Molecular outflows are a direct consequence of accretion, and therefore they represent one of the best tracers of accretion processes in the still poorly understood early phases of high-mass star formation. Previous studies suggested that the SiO abundance decreases with the evolution of a massive young stellar object probably because of a decay of jet activity, as witnessed in low-mass star-forming regions. We investigate the SiO excitation conditions and its abundance in outflows from a sample of massive young stellar objects through observations of the SiO(8-7) and CO(4-3) lines with the APEX telescope. Through a non-local thermodynamic equilibrium analysis, we find that the excitation conditions of SiO increase with the velocity of the emitting gas. We also compute the SiO abundance through the SiO and CO integrated intensities at high velocities. For the sources in our sample we find no significant variation of the SiO abundance with evolution for a bolometric luminosity-to-mass ratio of between 4 and 50 L?/M?. We also find a weak increase of the SiO(8-7) luminosity with the bolometric luminosity-to-mass ratio. We speculate that this might be explained with an increase of density in the gas traced by SiO. We find that the densities constrained by the SiO observations require the use of shock models that include grain-grain processing. For the first time, such models are compared and found to be compatible with SiO observations. A pre-shock density of 105cm-3 is globally inferred from these comparisons. Shocks with a velocity higher than 25 km s-1 are invoked for the objects in our sample where the SiO is observed with a corresponding velocity dispersion. Our comparison of shock models with observations suggests that sputtering of silicon-bearing material (corresponding to less than 10% of the total silicon abundance) from the grain mantles is occurring. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme ID 089.C-0203.Appendix A is available in electronic form at http://www.aanda.orgAPEX data (spectra) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/570/A49 侯賢

Leurini, S.; Codella, C.; Lpez-Sepulcre, A.; Gusdorf, A.; Csengeri, T.; Anderl, S.

2014-10-01

104

CARMA Large Area Star Formation Survey: Structure and Kinematics of Dense Gas in Serpens Main  

E-print Network

We present observations of N2H+(1-0), HCO+(1-0), and HCN(1-0) toward the Serpens Main molecular cloud from the CARMA Large Area Star Formation Survey (CLASSy). We mapped 150 square arcminutes of Serpens Main with an angular resolution of 7 arcsecs. The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. The majority of gas in the two subclusters has subsonic to sonic velocity dispersions. We applied a dendrogram technique with N2H+(1-0) to study the gas structures; the SE subcluster has a higher degree of hierarchy than the NW subcluster. Combining the dendrogram and line fitting analyses reveals two distinct relations: a flat relation between nonthermal velocity dispersion and size, and a positive correlation between variation in velocity centroids and size. The two relations imply a characteristic depth of 0.15 pc for the cloud. Furthermore, we have identified s...

Lee, Katherine I; Storm, Shaye; Looney, Leslie W; Mundy, Lee G; Segura-Cox, Dominique; Teuben, Peter; Rosolowsky, Erik; Arce, Hector G; Ostriker, Eve C; Shirley, Yancy L; Kwon, Woojin; Kauffmann, Jens; Tobin, John J; Plunkett, Adele L; Pound, Marc W; Salter, Demerese M; Volgenau, N H; Chen, Che-Yu; Tassis, Konstantinos; Isella, Andrea; Crutcher, Richard M; Gammie, Charles F; Testi, Leonardo

2014-01-01

105

CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1  

E-print Network

We present details of the CARMA Large Area Star Formation Survey (CLASSy), while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that spectrally imaged N2H+, HCO+, and HCN (J=1-0 transitions) across over 800 square arcminutes of the Perseus and Serpens Molecular Clouds. The observations have angular resolution near 7" and spectral resolution near 0.16 km/s. We imaged ~150 square arcminutes of Barnard 1, focusing on the main core, and the B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with morphology similar to cool dust in the region, while HCO+ and HCN trace several molecular outflows from a collection of protostars in the main core. We identify a range of kinematic complexity, with N2H+ velocity dispersions ranging from ~0.05-0.50 km/s across the field. Simultaneous continuum mapping at 3 mm reveals six compact object detections, three of which are new detections. A new non-binary dendrogram algorithm is used to analyze dense gas structures in the N2H+ position...

Storm, S; Fernndez-Lpez, M; Lee, K I; Looney, L W; Teuben, P J; Rosolowsky, E; Arce, H G; Ostriker, E C; Segura-Cox, D; Pound, M W; Salter, D M; Volgenau, N H; Shirley, Y L; Chen, C; Gong, H; Plunkett, A L; Tobin, J J; Kwon, W; Isella, A; Kauffmann, J; Tassis, K; Crutcher, R M; Gammie, C F; Testi, L

2014-01-01

106

Arm-cleavable microgel star polymers: a versatile strategy for direct core analysis and functionalization.  

PubMed

Arm-cleavable microgel star polymers were developed, where the arm chains can readily be cleaved by acidolysis after the synthesis, allowing isolation of the core, direct analysis of its structure, and also the creation of functional nanometer-sized microgels. The key is to employ a macroinitiator (PEG-acetal-Cl) that carries an acetal linkage between a poly(ethylene glycol) arm chain and a chloride initiating site. From this, star polymers were synthesized via the linking reaction with a divinyl monomer and a ruthenium catalyst in living radical polymerization. The arms were subsequently cleaved by acidolysis of the acetal linker to give soluble microgels (cores free from arms). Full characterization revealed that the microgel cores are spherical, nano-sized (<20 nm), and of relatively low density. Amphiphilic, water-soluble, and thermosensitive arm-free microgels can be obtained by additionally employing functional methacrylate upon arm linking. PMID:25003826

Terashima, Takaya; Nishioka, Saki; Koda, Yuta; Takenaka, Mikihito; Sawamoto, Mitsuo

2014-07-23

107

Planet-Satellite Nanostructures Made To Order by RAFT Star Polymers.  

PubMed

The investigation and application of complex nanostructures requires the hierarchical arrangement of distinct domains on a small scale. Herein, we report a method to prepare planet-satellite arrangements using RAFT polymers. Our approach is based on star polymers decorated with trithiocarbonate groups on their outer periphery that attach to gold surfaces and thus provide the polymer with the ability to connect (larger) gold nanoparticle planets with (smaller) gold nanoparticle satellites. By adjusting the molecular weight of the polymeric linker, nanostructures with tailored planet-satellite distances, as evidenced by transmission electron microscopy, are obtained. This strategy offers a straightforward way to prepare gold nanoparticle scaffolds with multiple reactive functionalities at defined distances from the central core. PMID:25138594

Rossner, Christian; Vana, Philipp

2014-11-10

108

Critical dense polymers with Robin boundary conditions, half-integer Kac labels and $\\mathbb{Z}_4$ fermions  

E-print Network

For general Temperley-Lieb loop models, including the logarithmic minimal models $\\mathcal{LM}(p,p')$ with $p,p'$ coprime integers, we construct an infinite family of Robin boundary conditions on the strip as linear combinations of Neumann and Dirichlet boundary conditions. These boundary conditions are Yang-Baxter integrable and allow loop segments to terminate on the boundary. Algebraically, the Robin boundary conditions are described by the one-boundary Temperley-Lieb algebra. Solvable critical dense polymers is the first member $\\mathcal{LM}(1,2)$ of the family of logarithmic minimal models and has loop fugacity $\\beta=0$ and central charge $c=-2$. Specializing to $\\mathcal{LM}(1,2)$ with our Robin boundary conditions, we solve the model exactly on strips of arbitrary finite size $N$ and extract the finite-size conformal corrections using an Euler-Maclaurin formula. The key to the solution is an inversion identity satisfied by the commuting double row transfer matrices. This inversion identity is established directly in the Temperley-Lieb algebra. We classify the eigenvalues of the double row transfer matrices using the physical combinatorics of the patterns of zeros in the complex spectral parameter plane and obtain finitized characters related to spaces of coinvariants of $\\mathbb{Z}_4$ fermions. In the continuum scaling limit, the Robin boundary conditions are associated with irreducible Virasoro Verma modules with conformal weights $\\Delta_{r,s-1/2}=(L^2-4)/32$ where $L=2s-1-4r$, $r\\in\\mathbb{Z}$, $s\\in\\mathbb{N}$. These conformal weights coincide with those of the $L$-leg operators and populate a Kac table with half-integer Kac labels. Fusion of the corresponding modules with the generators of the Kac fusion algebra is examined and general fusion rules are proposed.

Paul A. Pearce; Jorgen Rasmussen; Ilya Yu. Tipunin

2014-05-03

109

AF4/MALS/QELS/DRI characterization of regular star polymers and their "span analogs".  

PubMed

Asymmetric flow field-flow fractionation (AF4) coupled with multi-angle static and quasi-elastic light scattering and differential refractive index detectors, was employed for the separation and characterization of regular star-shaped polystyrenes and their linear and span analogs in tetrahydrofuran. Stars with different arm lengths were separated from each other by employing a binary slope cross-flow gradient. Cross-flow optimization enabled fast separation of polystyrenes in two- and three-component blends. Macromolecular parameters were obtained by using light-scattering and refractive index detection, and properties of polystyrenes with different molecular architectures were compared. To our knowledge, this is the first report on the separation of star polymers by AF4. Novel characterization approaches for stars are important from both applied and fundamental standpoints, as these macromolecules are valued for their tribological, drug delivery, catalytic and coating capabilities, and also serve as model compounds for the structured study of long-chain branching and its effects in polymers. PMID:25221791

Pitknen, Leena; Striegel, Andr M

2014-10-15

110

End group functionalization of poly(ethylene glycol) with phenolphthalein: towards star-shaped polymers based on supramolecular interactions  

PubMed Central

Summary The synthesis of a new phenolphthalein azide derivative, which can be easily utilized in polymer analogous reactions, is presented. The subsequent cycloaddition reaction with propargyl-functionalized methoxypoly(ethylene glycol) yielded polymers bearing phenolphthalein as the covalently attached end group. In presence of per-?-cyclodextrin-dipentaerythritol, the formation of stable inclusion complexes was observed, representing an interesting approach towards the formation of star shaped polymers. The decolorization of a basic polymer solution caused by the complexation was of great advantage since this behavior enabled following the complex formation by UVvis spectroscopy and even the naked eye. PMID:25298793

Fleischmann, Carolin; Wohlk, Hendrik

2014-01-01

111

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

2013-01-01

112

The Herschel view of massive star formation in G035.39-00.33: dense and cold filament of W48 undergoing a mini-starburst  

NASA Astrophysics Data System (ADS)

The filament IRDC G035.39-00.33 in the W48 molecular complex is one of the darkest infrared clouds observed by Spitzer. It has been observed by the PACS (70 and 160 ?m) and SPIRE (250, 350, and 500 ?m) cameras of the Herschel Space Observatory as part of the W48 molecular cloud complex in the framework of the HOBYS key programme. The observations reveal a sample of 28 compact sources (deconvolved FWHM sizes < 0.3 pc) complete down to ~5 M? in G035.39-00.33 and its surroundings. Among them, 13 compact sources are massive dense cores with masses >20 M?. The cloud characteristics we derive from the analysis of their spectral energy distributions are masses of 20-50 M?, sizes of 0.1-0.2 pc, and average densities of 2-20 105 cm-3, which make these massive dense cores excellent candidates to form intermediate- to high-mass stars. Most of the massive dense cores are located inside the G035.39-00.33 ridge and host IR-quiet high-mass protostars. The large number of protostars found in this filament suggests that we are witnessing a mini-burst of star formation with an efficiency of ~15% and a rate density of ~40 M? yr-1kpc-2 within ~8 pc2, a large area covering the full ridge. Part of the extended SiO emission observed towards G035.39-00.33 is not associated with obvious protostars and may originate from low-velocity shocks within converging flows, as advocated by previous studies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. See http://herschel.esac.esa.int/Figures 9-11 are available in electronic form at http://www.aanda.org

Nguyen Luong, Q.; Motte, F.; Hennemann, M.; Hill, T.; Rygl, K. L. J.; Schneider, N.; Bontemps, S.; Men'shchikov, A.; Andr, Ph.; Peretto, N.; Anderson, L. D.; Arzoumanian, D.; Deharveng, L.; Didelon, P.; di Francesco, J.; Griffin, M. J.; Kirk, J. M.; Knyves, V.; Martin, P. G.; Maury, A.; Minier, V.; Molinari, S.; Pestalozzi, M.; Pezzuto, S.; Reid, M.; Roussel, H.; Sauvage, M.; Schuller, F.; Testi, L.; Ward-Thompson, D.; White, G. J.; Zavagno, A.

2011-11-01

113

Tailoring the efficacy of nimodipine drug delivery using nanocarriers based on A2B miktoarm star polymers.  

PubMed

We report a nanocarrier based on A(2)B type miktoarm polymers (A=polyethylene glycol (PEG); B=polycaprolactone (PCL)) for nimodipine (NIM), a hydrophobic drug with very poor aqueous solubility that is commonly prescribed for the prevention and treatment of delayed ischemic neurological disorders. The A(2)B star polymers were constructed on a core with orthogonal functionalities that facilitated the performance of "click" chemistry followed by ring-opening polymerization. These star polymers assemble into spherical micelles into which NIM can be easily loaded by the co-solvent evaporation method. The micelles obtained from the star polymer PEG775(2)-PCL5800 showed NIM encapsulation efficiency of up to 78 wt% at a feed weight ratio of 5.0%. The loading efficiency of the micelles was dependent on the length of the PCL arm in the A(2)B miktoarm polymers. Aqueous solubility of NIM was increased by approximately 200 fold via micellar encapsulation. The in vitro release of NIM from the micelles was found to occur at a much slower rate than from its solution. Lipopolysaccharide induced nitric oxide production in N9 microglia cells was reduced in the presence of micelle-encapsulated NIM, as well as in the presence of micelles alone. The treatment of microglia with micelle-encapsulated NIM reduced the release of TNF-alpha, a pro-inflammatory cytokine. These results suggest that NIM-loaded miktoarm micelles could be useful in the treatment of neuroinflammation. PMID:20691471

Soliman, Ghareb M; Sharma, Rishi; Choi, Angela O; Varshney, Sunil K; Winnik, Franoise M; Kakkar, Ashok K; Maysinger, Dusica

2010-11-01

114

Synthesis of oligo(thiophene)-coated star-shaped ROMP polymers: unique emission properties by the precise integration of functionality.  

PubMed

A facile synthesis of oligo(thiophene)-modified (coated) "soluble" star (ball)-shaped polymers has been achieved via sequential living ring-opening metathesis polymerization (ROMP) of norbornene and a cross-linking reagent using Mo(CHCMe(2)Ph)(N-2,6-(i)Pr(2)C(6)H(3))(O(t)Bu)(2) as the initiator and oligo(thiophene) carboxaldehydes for termination. The resultant star-shaped ROMP polymers containing ter- and tetrathiophene moieties exhibit unique emission properties due to an integration of the ROMP polymers (arranged functionalities): the blue emission was tuned to the white emission upon addition of 2-[2-[(E)-4-(dimethylamino)styryl]-6-methyl-4H-pyran-4-ylidene]malononitrile. PMID:22494263

Takamizu, Kenji; Nomura, Kotohiro

2012-05-01

115

A necklace of dense cores in the high-mass star forming region G35.20-0.74 N: ALMA observations  

NASA Astrophysics Data System (ADS)

Context. The formation process of high-mass stars (with masses >8 M?) is still poorly understood, and represents a challenge from both the theoretical and observational points of view. The advent of the Atacama Large Millimeter Array (ALMA) is expected to provide observational evidence to better constrain the theoretical scenarios. Aims: The present study aims at characterizing the high-mass star forming region G35.20-0.74 N, which is found associated with at least one massive outflow and contains multiple dense cores, one of them recently found associated with a Keplerian rotating disk. Methods: We used the radio-interferometer ALMA to observe the G35.20-0.74 N region in the submillimeter continuum and line emission at 350 GHz. The observed frequency range covers tracers of dense gas (e.g., H13CO+, C17O), molecular outflows (e.g., SiO), and hot cores (e.g., CH3CN, CH3OH). These observations were complemented with infrared and centimeter data. Results: The ALMA 870 ?m continuum emission map reveals an elongated dust structure (~0.15 pc long and ~0.013 pc wide; full width at half maximum) perpendicular to the large-scale molecular outflow detected in the region, and fragmented into a number of cores with masses ~1-10 M? and sizes ~1600 AU (spatial resolution ~960 AU). The cores appear regularly spaced with a separation of ~0.023 pc. The emission of dense gas tracers such as H13CO+ or C17O is extended and coincident with the dust elongated structure. The three strongest dust cores show emission of complex organic molecules characteristic of hot cores, with temperatures around 200 K, and relative abundances 0.2-2 10-8 for CH3CN and 0.6-5 10-6 for CH3OH. The two cores with highest mass (cores A and B) show coherent velocity fields, with gradients almost aligned with the dust elongated structure. Those velocity gradients are consistent with Keplerian disks rotating about central masses of 4-18 M?. Perpendicular to the velocity gradients we have identified a large-scale precessing jet/outflow associated with core B, and hints of an east-west jet/outflow associated with core A. Conclusions: The elongated dust structure in G35.20-0.74 N is fragmented into a number of dense cores that may form high-mass stars. Based on the velocity field of the dense gas, the orientation of the magnetic field, and the regularly spaced fragmentation, we interpret this elongated structure as the densest part of a 1D filament fragmenting and forming high-mass stars. Appendix is available in electronic form at http://www.aanda.orgReduced FITS files (cube and continum) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/569/A11

Snchez-Monge, .; Beltrn, M. T.; Cesaroni, R.; Etoka, S.; Galli, D.; Kumar, M. S. N.; Moscadelli, L.; Stanke, T.; van der Tak, F. F. S.; Vig, S.; Walmsley, C. M.; Wang, K.-S.; Zinnecker, H.; Elia, D.; Molinari, S.; Schisano, E.

2014-09-01

116

Miktoarm star polymer based multifunctional traceable nanocarriers for efficient delivery of poorly water soluble pharmacological agents.  

PubMed

A versatile methodology to develop an inherently fluorescent and thus traceable multifunctional nanodelivery platform based on miktoarm polymers is reported. Miktoarm stars containing covalently linked tetraiodofluorescein dye, polyethylene glycol, and polycaprolactone self-assemble into micelles, and integrate multiple functions including fluorescent tags for imaging, a hydrophobic core for drug incorporation, and a hydrophilic corona for micelle stabilization. Curcumin, a pleiotropic but very poorly water-soluble drug, is loaded into these micelles with an efficiency of 25-60?wt%. It leads to a 25?000-fold increase in its aqueous solubility, and a sustained release over a period of 7 d. These micelles are rapidly internalized into murine J774A.1 macrophages, and accumulated into discrete cellular compartments, whereas the free and physically encapsulated dye is diffused in the cytoplasm. Curcumin-loaded micelles reduce lipopolysaccharide-induced nitric oxide release. The studies establish miktoarm star based nanocarriers as highly efficient in tracking their fate and expanding the scope of pharmacological agents with limited utility in experimental medicine. PMID:24903981

Soliman, Ghareb M; Redon, Rocio; Sharma, Anjali; Meja, Diana; Maysinger, Dusica; Kakkar, Ashok

2014-09-01

117

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. PMID:17915935

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

2008-01-01

118

Compatibilization of polystyrene/poly(dimethylsiloxane) blends using star polymers containing a gamma-cyclodextrin core and polystyrene arms  

NASA Astrophysics Data System (ADS)

Star polymers containing a gamma-cyclodextrin (CD) core and polystyrene (PS) arms (CD-star) were successfully synthesized by atom transfer radical polymerization. These stars are the first of their kind containing a gamma-CD core. CD-stars made with twelve PS arms proved to be soluble in typical PS solvents. Control over CD-star arm length was achieved, as shown by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) analysis. Rapidly stirred blends of polydimethylsiloxane (PDMS) and PS prepared in chloroform with and without CD-star formed an emulsion. Adding CD-star to these turbid solutions resulted in clearing, whereas control solutions without CD-star remained turbid. Post-stirring, these clear solutions demonstrated excellent temporal stability illustrating their successful compatibilization. Characterization of these clear solutions by 2D-NMR revealed that CD-stars were threaded onto PDMS. This complexation formed a hybrid slip-ring copolymer with PDMS as the backbone and CD-star PS arms effectively acting as the grafts. Solution characterization via capillary viscometery, dynamic light scattering, and GPC showed traits similar to traditional graft copolymers. Films were made from the blended solutions by spin or solution casting. Spun-cast films prepared from compatibilized solutions exhibited homogeneous nanophase morphology, whereas non-compatibilized solutions displayed heterogeneous microphase morphology. Atomic force microscopy and scanning electron microscopy analyses of these films revealed PDMS phase domains measuring 50nm or less. However, solution cast films with subsequent compression molding showed macroscopic phase segregation for samples with or without CD-star. Significant loss of PDMS was observed during processing. Compositional analysis conducted by 1H-NMR revealed 80% PDMS retention for films with CD-star, whereas only 20% retention was observed for films without CD-star. This larger PDMS retention for samples with CD-star results from the anchoring of PDMS chains which threaded through CD-stars. Differential scanning calorimetry and dynamic mechanical analysis characterization point to partial compatibilization, as determined from the glass-transition temperatures of the homopolymers shifting toward each other. Solution-cast film characterization by thermal gravimetric analysis confirmed the PDMS thermal degradation decreased with increased CD-star complexation.

Busche, Bradley James

119

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

120

EARLY STAR-FORMING PROCESSES IN DENSE MOLECULAR CLOUD L328; IDENTIFICATION OF L328-IRS AS A PROTO-BROWN DWARF  

SciTech Connect

This paper presents the results of millimeter to sub-millimeter observations of CO, HCN, N{sub 2}H{sup +}, and HCO{sup +} 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 {sup 13}CO and N{sub 2}H{sup +} 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{sup 7} M{sub ?} yr{sup 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{sub ?}) 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 [Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon (Korea, Republic of); Saito, Masao; Kurono, Yasutaka [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Myers, Philip C., E-mail: cwl@kasi.re.kr [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-11-01

121

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

122

Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time  

E-print Network

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 (T_Ice ~ 150-170 K) during formation for a time comparable to the planet formation timescale. The protoplanetary disks 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 disks. 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 characteris...

Thompson, Todd A

2012-01-01

123

ALMA Observations of Warm Dense Gas in NGC 1614 --- Breaking of Star Formation Law in the Central kpc  

E-print Network

We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435um dust continuum emission in the central kpc of NGC 1614, a local luminous infrared galaxy (LIRG) at a distance of 67.8 Mpc (1 arcsec = 329 pc). The CO emission is well resolved by the ALMA beam (0".26 x 0".20) into a circum-nuclear ring, with an integrated flux of f_{CO(6-5)} = 898 (+-153) Jy km/s, which is 63(+-12)% of the total CO(6-5) flux measured by Herschel. The molecular ring, located between 100pc < r < 350pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of 40 km/s. These knots are associated with strong star formation regions with \\Sigma_{SFR} 100 M_\\sun/yr/kpc^{2} and \\Sigma_{Gas} 1.0E4 M_\\sun/pc^{2}. The non-detections of the nucleus in both the CO (6-5) line emission and the 435um continuum rule out, with relatively high confidence, a Compton-thick AGN in NGC 1614. Comparisons with radio continuum emission show a strong deviation fro...

Xu, C K; Lu, N; Gao, Y; Diaz-Santos, T; Herrero-Illana, R; Meijerink, R; Privon, G; Zhao, Y -H; Evans, A S; Knig, S; Mazzarella, J M; Aalto, S; Appleton, P; Armus, L; Charmandaris, V; Chu, J; Haan, S; Inami, H; Murphy, E J; Sanders, D B; Schulz, B; van der Werf, P

2014-01-01

124

Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length  

PubMed Central

Summary Due to the low solubility of poly(glycolic acid) (PGA), its use is generally limited to the synthesis of random copolyesters with other hydroxy acids, such as lactic acid, or to applications that permit direct processing from the polymer melt. Insolubility is generally observed for PGA when the degree of polymerization exceeds 20. Here we present a strategy that allows the preparation of PGA-based multi-arm structures which significantly exceed the molecular weight of processable oligomeric linear PGA (<1000 g/mol). This was achieved by the use of a multifunctional hyperbranched polyglycerol (PG) macroinitiator and the tin(II)-2-ethylhexanoate catalyzed ring-opening polymerization of glycolide in the melt. With this strategy it is possible to combine high molecular weight with good molecular weight control (up to 16,000 g/mol, PDI = 1.41.7), resulting in PGA multi-arm star block copolymers containing more than 90 wt % GA. The successful linkage of PGA arms and PG core via this core first/grafting from strategy was confirmed by detailed NMR and SEC characterization. Various PG/glycolide ratios were employed to vary the length of the PGA arms. Besides fluorinated solvents, the materials were soluble in DMF and DMSO up to an average arm length of 12 glycolic acid units. Reduction in the T g and the melting temperature compared to the homopolymer PGA should lead to simplified processing conditions. The findings contribute to broadening the range of biomedical applications of PGA. PMID:20703381

Wolf, Florian K; Fischer, Anna M

2010-01-01

125

"Brush-first" method for the parallel synthesis of photocleavable, nitroxide-labeled poly(ethylene glycol) star polymers.  

PubMed

We describe the parallel, one-pot synthesis of core-photocleavable, poly(norbornene)-co-poly(ethylene glycol) (PEG) brush-arm star polymers (BASPs) via a route that combines the "graft-through" and "arm-first" methodologies for brush polymer and star polymer synthesis, respectively. In this method, ring-opening metathesis polymerization of a norbornene-PEG macromonomer generates small living brush initiators. Transfer of various amounts of this brush initiator to vials containing a photocleavable bis-norbornene cross-linker yielded a series of water-soluble BASPs with low polydispersities and molecular weights that increased geometrically as a function of the amount of bis-norbornene added. The BASP cores were cleaved upon exposure to UV light; the extent of photo-disassembly depended on the amount of cross-linker. EPR spectroscopy of nitroxide-labeled BASPs was used to probe differences between the BASP core and surface environments. We expect that BASPs will find applications as easy-to-synthesize, stimuli-responsive core-shell nanostructures. PMID:22953714

Liu, Jenny; Burts, Alan O; Li, Yongjun; Zhukhovitskiy, Aleksandr V; Ottaviani, M Francesca; Turro, Nicholas J; Johnson, Jeremiah A

2012-10-01

126

Telechelic star polymers as self-assembling units from the molecular to the macroscopic scaleBarbara Capone  

E-print Network

By means of multiscale molecular simulations, we show that telechelic-star polymers are a simple, robust and tunable system, which hierarchically self-assembles first into soft-patchy particles and then into targeted 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 and stable ordered structures, 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 stabilisation 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.

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

2012-09-24

127

Self-organized honeycomb morphology of star-polymer polystyrene films  

Microsoft Academic Search

AN important challenge in the preparation of porous polymer membranes for technological applications is to control both the size distribution and the relative positions of the pores. We have found a way to generate polymer films with an essentially monodisperse pore size, in which the pores are organized spontaneously into periodic hexagonal arrays. The films, which are 10-30 um thick,

Gilles Widawski; Michel Rawiso; Bernard Franois

1994-01-01

128

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

129

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

130

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

131

Single-chain nanoparticles vs. star, hyperbranched and dendrimeric polymers: effect of the nanoscopic architecture on the flow properties of diluted solutions.  

PubMed

The flow properties of dilute solutions of linear, star, hyperbranched and dendrimeric polymers have been the subject of numerous studies. However, no systematic analysis has been carried out for the case of single-chain nanoparticles (SCNPs) of different nature, which are unimolecular soft nano-objects consisting of individual polymer chains collapsed to a certain degree by means of intramolecular bonding. On the basis of the fractal nature of SCNPs and experimental data of the hydrodynamic radius, a simple predictive power-law between the intrinsic viscosity and molecular weight is proposed. Furthermore, a comparison is made between the intrinsic viscosities of SCNPs and of low-functionality stars, hyperbranched and dendrimeric polymers of the same chemical nature and molecular weight. As a consequence of their complex nanoscopic architecture, the intrinsic viscosities of SCNPs are systematically smaller than those of linear chains and low-functionality stars. When compared with hyperbranched and dendrimeric polymers, a complex behaviour is found, this being highly dependent on the molecular weight and amount of X-linkers of SCNPs. PMID:25343377

Perez-Baena, Irma; Moreno, Angel J; Colmenero, Juan; Pomposo, Jos A

2014-12-21

132

Anti-tumor drug delivery system based on cyclodextrin-containing pH-responsive star polymer: In vitro and in vivo evaluation.  

PubMed

A cyclodextrin-containing pH-responsive star polymer, with cyclodextrin polymer and pH-sensitive poly(2-(dimethylamino)ethyl methacrylate) as the core and poly(ethylene glycol) as the arm, was evaluated as drug carriers in vitro and in vivo. Doxorubicin (DOX) was successfully loaded into the star polymer to form nanoparticles (DOX-NPs) via host-guest interaction. The physicochemical properties such as drug loading content, size, morphology, stability and physical state of DOX-NPs were characterized in detail by (1)H NMR, DLS, SEM and DSC. Uniform and stable DOX-NPs with high encapsulation efficiency of 77.1% were obtained, and they also exhibited sustainable and controllable release of DOX in vitro. The cellular uptake of DOX-NPs was in concentration-, time- and cell type-dependent manners, and the cytotoxicity of DOX-NPs was significantly high toward HeLa and HepG2 cancer cells. Furthermore, in vivo anti-tumor experiment on BALB/c mice bearing cervical tumor showed that DOX-NPs could effectively suppress the growth of tumor without significant side effect. These findings suggest that the cyclodextrin-containing pH-responsive star polymer has a promising potential in developing novel drug delivery system for cancer therapy. PMID:25149124

Xiong, Qingqing; Zhang, Mingming; Zhang, Zhibao; Shen, Wei; Liu, Lingrong; Zhang, Qiqing

2014-10-20

133

Illuminating Dense Quark Matter  

E-print Network

We imagine shining light on a lump of cold dense quark matter, in the CFL phase and therefore a transparent insulator. We calculate the angles of reflection and refraction, and the intensity of the reflected and refracted light. Although the only potentially observable context for this phenomenon (reflection of light from and refraction of light through an illuminated quark star) is unlikely to be realized, our calculation casts new light on the old idea that confinement makes the QCD vacuum behave as if filled with a condensate of color-magnetic monopoles.

Cristina Manuel; Krishna Rajagopal

2001-07-19

134

Dense Gas Tracers and Star Formation Laws in Active Galaxies: APEX Survey of HCN J=4-3, HCO+ J=4-3, and CS J=7-6  

E-print Network

We report HCN J=4-3, HCO+ J=4-3, and CS J=7-6 observations in 20 nearby star-forming galaxies with the Acatama Pathfinder EXperiment 12-m telescope. Combined with 4 HCN, 3 HCO+, and 4 CS detections in literature, we probe the empirical link between the luminosity of molecular gas (L_gas) and that of infrared emission (L_IR), up to the highest gas densities (10^6 - 10^8 cm-3) that have been probed so far. For nearby galaxies with large radii, we measure the IR luminosity within the submm beam-size (14"-18") to match the molecular emission. We find linear slopes for L_CS76-L_IR and L_HCN43-L_IR, and a slightly super-linear slope for L_HCO+43-L_IR. The correlation of L_CS76-L_IR even extends over eight orders of luminosity magnitude down to Galactic dense cores, with a fit of log(L_IR)=1.00(\\pm 0.01) \\times log(L_CS76) + 4.03(\\pm 0.04). Such linear correlations appear to hold for all densities >10^4 cm-3, and indicate that star formation rate is not related to free-fall time scale for dense molecular gas.

Zhang, Zhi-Yu; Henkel, Christian; Zhao, Yinghe; Wang, Junzhi; Menten, Karl M; Guesten, Rolf

2014-01-01

135

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

136

Hypernuclear Physics for Neutron Stars  

E-print Network

The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon-nucleon and hyperon-hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Non-mesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.

Jurgen Schaffner-Bielich

2008-01-24

137

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

138

Brush-first synthesis of core-photodegradable miktoarm star polymers via ROMP: towards photoresponsive self-assemblies.  

PubMed

This report describes the synthesis of miktoarm brush-arm star polymers (BASPs) from branched and linear norbornene-terminated macromonomers (MMs) via the brush-first ring-opening metathesis polymerization (ROMP) method. First, a polystyrene (PS)-branch-poly(lactic acid) (PLA) MM is synthesized via a combination of atom transfer radical polymerization (ATRP), tin(II)-mediated ring opening polymerization, and copper-catalyzed azide-alkyne cycloaddition reactions. Graft-through ROMP of this MM followed by in situ cross-linking with a photo-cleavable bis-norbornene derivative provided nanoscopic BASPs with photodegradable cores and a precise 1:1 PS:PLA arm composition. Three-miktoarm BASPs are prepared in an analogous manner via copolymerization of the same PS-branch-PLA MM with a poly(ethylene glycol) (PEG) MM prior to cross-linking. Intramolecular phase segregation of these miktoarm BASPs is characterized by transmission electron microscopy (TEM); a UV-induced structural rearrangement from three-faced Janus particles to micelles is observed. PMID:24265215

Burts, Alan O; Gao, Angela X; Johnson, Jeremiah A

2014-01-01

139

Neutron Stars  

NASA Technical Reports Server (NTRS)

Neutron stars were discovered almost 40 years ago, and yet many of their most fundamental properties remain mysteries. There have been many attempts to measure the mass and radius of a neutron star and thereby constrain the equation of state of the dense nuclear matter at their cores. These have been complicated by unknown parameters such as the source distance and burning fractions. A clean, straightforward way to access the neutron star parameters is with high-resolution spectroscopy. I will present the results of searches for gravitationally red-shifted absorption lines from the neutron star atmosphere using XMM-Newton and Chandra.

Cottam, J.

2007-01-01

140

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.

2013-12-01

141

XVI. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content  

Microsoft Academic Search

We announce the discovery of the transiting planet CoRoT-13b. Ground based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing Keck data. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter masses, 0.9 Jupiter

J. Cabrera; H. Bruntt; M. Ollivier; R. F. D iaz; S. Aigrain; R. Alonso; J.-M. Almenara; M. Auvergne; A. Baglin; P. Barge; A. S. Bonomo; P. Bord; F. Bouchy; L. Carone; S. Carpano; M. Deleuil; H. J. Deeg; R. Dvorak; A. Erikson; S. Ferraz-Mello; M. Fridlund; D. Gandolfi; J.-C. Gazzano; M. Gillon; E. W. Guenther; T. Guillot; A. Hatzes; M. Havel; G. Hebrard; L. Jorda; A. L eger; A. Llebaria; H. Lammer; C. Lovis; T. Mazeh; C. Moutou; D. Queloz; H. Rauer; D. Rouan; A. Santerne; J. Schneider; B. Tingley; R. Titz-Weider; G. Wuchterl

2010-01-01

142

The nuclear cluster of the Milky Way: Our primary testbed for the interaction of a dense star cluster with a massive black hole  

E-print Network

This article intends to provide a concise overview, from an observational point-of-view, of the current state of our knowledge of the most relevant properties of the Milky Way's nuclear star cluster (MWNSC). The MWNSC appears to be a typical specimen of nuclear star clusters, which are found at the centers of the majority of all types of galaxies. Nuclear clusters represent the densest and most massive stellar systems in the present-day Universe and frequently coexist with central massive black holes. They are therefore of prime interest for studying stellar dynamics and the MWNSC is the only one that allows us to obtain data on milli-parsec scales. After discussing the main observational constraints, we start with a description of the overall structure and kinematics of the MWNSC, then focus on a comparison to extragalactic systems, summarize the properties of the young, massive stars in the immediate environment of the Milky Way's central black hole, Sagittarius\\,A*, and finally focus on the dynamics of sta...

Schdel, R; Neumayer, N; Meyer, L; Yelda, S

2014-01-01

143

The Dense Gas in M82  

NASA Astrophysics Data System (ADS)

Galactic winds are responsible of carrying energy and matter from the inner regions of galaxies to the outer regions, even reaching the intergalactic medium. This process removes gas from the inner regions, the available material to form stars. How and in which amount these winds remove gas from galaxies plays an important role in galaxy evolution. To study this effect we have obtained 3 mm maps of dense gas (n_{{crit}}>10^{4} cm^{-3}) in the central region of the starburst galaxy M82. We detect line emission from the dense molecular gas tracers HCN, HCO^{+}, HNC, CS, HC_{3}N and C_{6}H. Our maps reveal a considerable amount of HCO^{+} emission extending above and bellow the central star-forming disk, indicating that the dense gas is entangled in the outflow. The mass of molecular Hydrogen outside the central starburst is M_{{out}}? 3 1 10^{6} M_{odot}, while in the central starburst is M_{{disk}}? 8 2 10^{6} M_{odot}. These maps also show variations of the amount of dense gas over the starburst disk, revealing that the gas is more concentrated towards the center of the starburst and less towards the edges. It is the average amount of dense gas what drives the observed star formation law between dense gas and star formation rate on galactic scales.

Salas, P.; Galaz, G.; Salter, D.; Bolatto, A.; Herrera-Camus, R.

2014-10-01

144

Atomic Transport/ Dense Metallic  

E-print Network

Atomic Transport/ Dense Metallic Hydrogen Separation Systems #12;Participants -- Atomic Transport contaminants + partial pressure #12;Technology Options ­ Atomic Transport/Dense Metallic Systems Pd alloy intensification Membrane plus reactor #12;Barrier Categories-- Atomic Transport/Dense Metallic Systems Membrane

145

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

146

A computational and experimental study of the linear and nonlinear response of a star polymer melt with a moderate number of unentangled arms.  

PubMed

We present from simulations and experiments results on the linear and nonlinear rheology of a moderate functionality, low molecular weight unentangled polystyrene (PS) star melt. The PS samples were anionically synthesized and close to monodisperse while their moderate functionality ensures that they do not display a pronounced core effect. We employ a highly coarse-grained model known as Responsive Particle Dynamics where each star polymer is approximated as a point particle. The eliminated degrees of freedom are used in the definition of an appropriate free energy as well as describing the transient pair-wise potential between particles that accounts for the viscoelastic response. First we reproduce very satisfactorily the experimental moduli using simulation. We then consider the nonlinear response of the same polymer melts by implementing a start-up shear protocol for a wide range of shear rates. As in experiments, we observe the development of a stress overshoot with increasing shear rate followed by a steady-state shear stress. We also recover the shear-thinning nature of the melt, although we slightly overestimate the extent of shear-thinning with simulations. In addition, we study relaxations upon the removal of shear where we find encouraging agreement between experiments and simulations, a finding that corroborates our agreement for the linear rheology. PMID:25240372

Fitzgerald, Barry W; Lentzakis, Helen; Sakellariou, Georgios; Vlassopoulos, Dimitris; Briels, Wim J

2014-09-21

147

A computational and experimental study of the linear and nonlinear response of a star polymer melt with a moderate number of unentangled arms  

NASA Astrophysics Data System (ADS)

We present from simulations and experiments results on the linear and nonlinear rheology of a moderate functionality, low molecular weight unentangled polystyrene (PS) star melt. The PS samples were anionically synthesized and close to monodisperse while their moderate functionality ensures that they do not display a pronounced core effect. We employ a highly coarse-grained model known as Responsive Particle Dynamics where each star polymer is approximated as a point particle. The eliminated degrees of freedom are used in the definition of an appropriate free energy as well as describing the transient pair-wise potential between particles that accounts for the viscoelastic response. First we reproduce very satisfactorily the experimental moduli using simulation. We then consider the nonlinear response of the same polymer melts by implementing a start-up shear protocol for a wide range of shear rates. As in experiments, we observe the development of a stress overshoot with increasing shear rate followed by a steady-state shear stress. We also recover the shear-thinning nature of the melt, although we slightly overestimate the extent of shear-thinning with simulations. In addition, we study relaxations upon the removal of shear where we find encouraging agreement between experiments and simulations, a finding that corroborates our agreement for the linear rheology.

Fitzgerald, Barry W.; Lentzakis, Helen; Sakellariou, Georgios; Vlassopoulos, Dimitris; Briels, Wim J.

2014-09-01

148

Infrared Stars: The interaction between stars and interstellar clouds produces "infrared stars" of two different kinds.  

PubMed

Our 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 clouds that may be planetary systems in an early stage of formation. PMID:17792840

Johnson, H L

1967-08-11

149

Neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars are laboratories for dense matter and gravitational physics. Observations of neutron stars from sources such as radio pulsars, low-mass X-ray binaries, X-ray bursts and thermally-emitting neutron stars are setting bounds to neutron star masses, radii, rotation rates, temperatures and ages. Mass measurements constrain the equation of state at the highest densities and set firm bounds to the highest possible density of cold matter. Radii constrain the equation of state in the vicinity of the nuclear saturation density and yield information about the density dependence of the nuclear symmetry energy. Laboratory measurements and theoretical studies of pure neutron matter are in remarkable agreement with observational bounds.

Lattimer, James M.

2014-05-01

150

Triggered Star Formation by Massive Stars  

E-print Network

We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the Lambda Ori region, Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars and Herbig Ae/Be stars tend to line up between luminous O stars and bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively younger they are. Our positional and chronological study lends support to the validity of the radiation-driven implosion mechanism, where the Lyman continuum photons from a luminous O star create expanding ionization fronts to evaporate and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive pressure then causes dense clumps to collapse, prompting the formation of low-mass stars on the cloud surface (i.e., the bright rim) and intermediate-mass stars somewhat deeper in the cloud. These stars are a signpost of current star formation; no young stars are seen leading the ionization fronts further into the cloud. Young stars in bright-rimmed or comet-shaped clouds are likely to have been formed by triggering, which would result in an age spread of several megayears between the member stars or star groups formed in the sequence.

Hsu-Tai Lee; W. P. Chen

2005-09-13

151

Runaway Merger in a Dense Stellar Cluster as a Progenitor of Gamma-ray Burst  

Microsoft Academic Search

Dynamical simulations of dense star clusters in starburst galaxy M82 have revealed that massive stars sunk into the center of the cluster and merged with each other to form a supermassive star with the mass exceeding few thousand solar mass (Portegies Zwart et al 2004). The gravitational core collapse of such supermassive star is a good candidate of gamma-ray bust:

T. Ebisuzaki; J. Makino; R. Yamazaki; H. Baumgardt; T. Matsubayashi; K. Makishima

2004-01-01

152

Neutron Star Collision  

NSDL National Science Digital Library

Systems of orbiting neutron stars are born when the cores of two old stars collapse in supernova explosions. Neutron stars have the mass of our Sun but are the size of a city, so dense that boundaries between atoms disappear. Einsteins theory of general relativity predicts that the orbit shrinks from ripples of space-time called gravitational waves. After about 1 billion simulation years, the two neutron stars closely circle each other at 60,000 revolutions per minute. The stars finally merge in a few milliseconds, sending out a burst of gravitational waves.

Bock, Dave; Shalf, John; Swesty, Doug; Calder, Alan; Wang, Ed

1999-01-21

153

Dense Stellar Cores in Merger Remnants  

E-print Network

We use numerical models which include star formation to analyze the mass profiles of remnants formed by mergers of disk galaxies. During a merger, dissipation in gas and ensuing star formation leave behind a dense stellar core in the remnant. Rather than joining smoothly onto a de Vaucouleurs profile, the starburst population leads to a sharp break in the surface density profile at a few percent the effective radius. While our results are preliminary, the lack of such signatures in most elliptical galaxies suggests that mergers of gas-rich disk galaxies may not have contributed greatly to the population of present-day ellipticals.

Chris Mihos; Lars Hernquist

1994-09-29

154

Pycnonuclear reactions in dense stellar matter  

NASA Astrophysics Data System (ADS)

We discuss pycnonuclear burning of highly exotic atomic nuclei in deep crusts of neutron stars, at densities up to 1013 g cm-3. As an application, we consider pycnonuclear burning of matter accreted on a neutron star in a soft X-ray transient (SXT, a compact binary containing a neutron star and a low-mass companion). The energy released in this burning, while the matter sinks into the stellar crust under the weight of newly accreted material, is sufficient to warm up the star and initiate neutrino emission in its core. The surface thermal radiation of the star in quiescent states becomes dependent on the poorly known equation of state (EOS) of supranuclear matter in the stellar core, which gives a method to explore this EOS. Four qualitatively different model EOSs are tested against observations of SXTs. They imply different levels of the enhancement of neutrino emission in massive neutron stars by 1) the direct Urca process in nucleon/hyperon matter; 2) pion condensates; 3) kaon condensates; 4) Cooper pairing of neutrons in nucleon matter with the forbidden direct Urca process. A low level of the thermal quiescent emission of two SXTs, SAX J1808.4-3658 and Cen X-4, contradicts model 4). Observations of SXTs test the same physics of dense matter as observations of thermal radiation from cooling isolated neutron stars, but the data on SXTs are currently more conclusive.

Yakovlev, D. G.; Levenfish, K. P.; Gnedin, O. Y.

2005-09-01

155

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

156

Enhanced conductivity of novel star branched liquid crystalline copolymer based on poly(ethylene oxide) for solid polymer electrolytes  

NASA Astrophysics Data System (ADS)

Novel star branched amphiphilic liquid crystalline (LC) copolymers, namely, 4-Arm poly(ethylene oxide)-co-x-[(4-cyano-4?-biphenyl)oxy]alkyl methacrylate (TPEO-MAxLC-?) (x = 6, ? = 20, 30; x = 9, ? = 10, 19) containing cyanobiphenyl mesogenic pendants (MAxLC) are prepared by atom-transfer radical polymerization (ATRP). The effects of structural variations on the properties, and the relationship between morphology and the ionic conductivity of the copolymer electrolytes are studied. The strong assembly of cyanobiphenyl mesogens induces the copolymers with enantiotropic mesophase, even after doped with LiClO4. And lamellar structures are also achieved by cooperative assembly of hydrophobic mesogen-containing polymethacrylate groups and the hydrophilic TPEO nanoscale aggregation, especially after LC thermal annealing. The ionic conductivity has been improved greatly by incorporation of the cyanobiphenyl mesogens. This is because the mesogens not only favor the ordered morphology to provide the efficient ion transportation pathway, but also suppress TPEO crystallization to offer the movement of TPEO chains. Among all of the electrolyte films, TPEO-MA9LC-19 shows the best ion conductivity of 2.24 10-5 S cm-1 at 25 C and even reaches to 5.39 10-5 S cm-1 after annealed at LC states.

Tong, Yongfen; Chen, Lie; Chen, Yiwang; He, Xiaohui

2012-10-01

157

Polymers containing fullerene or carbon nanotube structures  

Microsoft Academic Search

This review deals with recent progress in studies of polymeric covalent and noncovalent modifications of fullerenes (mainly C60) and carbon nanotubes (CNTs), and their applications. By using functional polymers to react with fullerenes, or synthesizing polymers in the presence of fullerenes, various kinds of polymeric fullerenes can be prepared: side-chain polymers, main-chain polymers, dendritic fullerenes, star-shaped polymers, fullerene end-capped polymers,

Changchun Wang; Zhi-Xin Guo; Shoukuan Fu; Wei Wu; Daoben Zhu

2004-01-01

158

From nuclear matter to Neutron Stars  

E-print Network

Neutron stars are the most dense objects in the observable Universe and conventionally one uses nuclear theory to obtain the equation of state (EOS) of dense hadronic matter and the global properties of these stars. In this work, we review various aspects of nuclear matter within an effective Chiral model and interlink fundamental quantities both from nuclear saturation as well as vacuum properties and correlate it with the star properties.

T. K. Jha

2009-02-02

159

Simulating Dense Matter  

E-print Network

I review the Sign Problem hindering lattice QCD simulations of dense baryonic matter, focussing where possible on its physical relevance. The possibility of avoiding the Sign Problem via a duality transformation is also briefly considered. Finally, I review evidence for deconfinement at non-zero quark density in recent simulations of Two Color QCD.

Simon Hands

2007-03-19

160

New Ferro Powder for Selective Laser Sintering of Dense Parts  

Microsoft Academic Search

The paper describes a new powder composition specially developed for selective laser sintering (SLS). The aim is to obtain a ferro powder that can be sintered without need for a (sacrificial) polymer binder and that results in quasi dense parts that do not need any post-processing like furnace sintering, infiltration or HIP. The powder is a mixture of different types

J. P. Kruth; L. Froyen; M. Rombouts; J. Van Vaerenbergh; P. Mercells

2003-01-01

161

The Neutron Star Laboratory  

Microsoft Academic Search

Neutron stars provide a rich and unique cosmic laboratory for studying fundamental questions in physics and astrophysics, including the effects of superstrong magnetic fields, nuclear deflagration and detonation in dense matter, neutron superfluidity and proton superconductivity, the properties of the nuclear force at high densities, the expected transition to quark matter, and gravitational physics in the strong-field regime. X- and

Frederick K. Lamb

1998-01-01

162

Fluctuation studies in STAR  

E-print Network

Study of event by event fluctuations of thermodynamic quantities offer us more insight about the hot and dense matter created in the relativistic heavy ion collisions. In this review the recent results on these studies carried out by the STAR collaboration are presented.

Supriya Das

2006-10-30

163

Cationic star-shaped polymer as an siRNA carrier for reducing MMP-9 expression in skin fibroblast cells and promoting wound healing in diabetic rats  

PubMed Central

Background Excessive expression of matrix metalloproteinase-9 (MMP-9) is deleterious to the cutaneous wound-healing process in the context of diabetes. The aim of the present study was to explore whether a cationic star-shaped polymer consisting of ?-cyclodextrin (?-CD) core and poly(amidoamine) dendron arms (?-CD-[D3]7) could be used as the gene carrier of small interfering RNA (siRNA) to reduce MMP-9 expression for enhanced diabetic wound healing. Methods The cytotoxicity of ?-CD-(D3)7 was investigated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (MMT) method in the rat CRL1213 skin fibroblast cell line. The transfection efficiency of ?-CD-(D3)7/MMP-9-small interfering RNA (siRNA) complexes was determined by confocal microscopy and flow cytometry. Quantitative real time (RT) polymerase chain reaction was performed to measure the gene expression of MMP-9 after the transfection by ?-CD-(D3)7/MMP-9-siRNA complexes. The ?-CD-(D3)7/MMP-9-siRNA complexes were injected on the wounds of streptozocin-induced diabetic rats. Wound closure was measured on days 4 and 7 post-wounding. Results ?-CD-(D3)7 exhibited low cytotoxicity in fibroblast cells, and easily formed the complexes with MMP-9-siRNA. The ?-CD-(D3)7/MMP-9-siRNA complexes were readily taken up by fibroblast cells, resulting in the downregulation of MMP-9 gene expression (P<0.01). Animal experiments revealed that the treatment by ?-CD-(D3)7/MMP-9-siRNA complexes enhanced wound closure in diabetic rats on day 7 post-wounding (P<0.05). Conclusion ?-CD-(D3)7 may be used as an efficient carrier for the delivery of MMP-9-siRNA to reduce MMP-9 expression in skin fibroblast cells and promote wound healing in diabetic rats. PMID:25075185

Li, Na; Luo, Heng-Cong; Yang, Chuan; Deng, Jun-Jie; Ren, Meng; Xie, Xiao-Ying; Lin, Diao-Zhu; Yan, Li; Zhang, Li-Ming

2014-01-01

164

Neutrino emission processes in dense high-temperature plasmas  

Microsoft Academic Search

The neutrino emission processes in dense high temperature plasmas are reviewed. The neutrino emission processes are key factors which decide the evolution of stars. Stellar evolution proceeds through the balance between the energy generation due to thermonuclear reactions and the energy loss due to neutrino emission processes. Recent developments in the study of the four major neutrino emission processes are

Naoki Itoh

1993-01-01

165

Dynamics of black holes in dense stellar systems  

Microsoft Academic Search

We develop physical models to describe the dynamics of N black holes inside dense stellar systems. For N = 1, we show that the force on a single massive black hole consists of two independent parts: the slowly varying influence of the aggregate stellar system, and a rapidly fluctuating stochastic force arising from discrete encounters with individual stars. Detailed properties

Pinaki Chatterjee

2004-01-01

166

Transiting exoplanets from the CoRoT space mission . XIII. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content  

Microsoft Academic Search

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing HIRES spectra from the Keck telescope. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter

Juan Cabrera; Hans Bruntt; M. Ollivier; R. F. Daz; Szilard Csizmadia; Suzanne Aigrain; Roi Alonso; J.-M. Almenara; Michel Auvergne; Annie Baglin; P. Barge; A. S. Bonomo; P. Bord; F. Bouchy; L. Carone; S. Carpano; M. Deleuil; H. J. Deeg; R. Dvorak; A. Erikson; S. Ferraz-Mello; M. Fridlund; D. Gandolfi; J.-C. Gazzano; M. Gillon; E. W. Guenther; T. Guillot; A. Hatzes; M. Havel; G. Hbrard; L. Jorda; A. Lger; A. Llebaria; H. Lammer; C. Lovis; T. Mazeh; C. Moutou; A. Ofir; P. von Paris; M. Ptzold; D. Queloz; H. Rauer; D. Rouan; A. Santerne; J. Schneider; B. Tingley; R. Titz-Weider; G. Wuchterl

2010-01-01

167

Chaotic Star Birth  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset

Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives.

The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region.

The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333.

In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.

2005-01-01

168

Dense Stellar Systems as Laboratories for Fundamental Physics  

E-print Network

Galactic nuclei and globular clusters act as laboratories in which nature experiments with normal stars, neutron stars and black holes, through collisions and through the formation of bound states, in the form of binaries. The main difference with the usual Earth-based laboratories is that we cannot control the experiments. Instead, we have no choice but to create virtual laboratories on Earth, in order to simulate all the relevant physics in large-scale computational experiments. This implies a realistic treatment of stellar dynamics, stellar evolution, and stellar hydrodynamics. Each of these three fields has its own legacy codes, workhorses that are routinely used to simulate star clusters, stars, and stellar collisions, respectively. I outline the main steps that need to be taken in order to embed and where needed transform these legacy codes in order to produce a far more modular and robust environment for modeling dense stellar systems. The time is right to do so: within a few years computers will reach the required speed, in the Petaflops range, to follow a star cluster with a million stars for ten billion years, while resolving the internal binary and multiple star motions. By that time simulation software will be the main bottleneck in our ability to analyze dense stellar systems. Only through full-scale simulations will we be able to critically test our understanding of the `microphysics' of stellar collisions and their aftermath, in a direct comparison with observations.

Piet Hut

2006-01-11

169

Dense stellar systems as laboratories for fundamental physics  

NASA Astrophysics Data System (ADS)

Galactic nuclei and globular clusters act as laboratories in which nature experiments with normal stars, neutron stars and black holes, through collisions and through the formation of bound states, in the form of binaries. The main difference with the usual Earth-based laboratories is that we cannot control the experiments. Instead, we have no choice but to create virtual laboratories on Earth, in order to simulate all the relevant physics in large-scale computational experiments. This implies a realistic treatment of stellar dynamics, stellar evolution, and stellar hydrodynamics. Each of these three fields has its own legacy codes, workhorses that are routinely used to simulate star clusters, stars, and stellar collisions, respectively. I outline the main steps that need to be taken in order to embed and where needed transform these legacy codes in order to produce a far more modular and robust environment for modeling dense stellar systems. The time is right to do so: within a few years computers will reach the required speed, in the Petaflops range, to follow a star cluster with a million stars for 10 billion years, while resolving the internal binary and multiple star motions. By that time simulation software will be the main bottleneck in our ability to analyze dense stellar systems. Only through full-scale simulations will we be able to critically test our understanding of the 'microphysics' of stellar collisions and their aftermath, in a direct comparison with observations.

Hut, Piet

2010-03-01

170

Dense molecular thermodynamics  

SciTech Connect

We are examining the thermodynamics of dense molecular fluids from the theoretical view. Our interests range from modeling single-species, spherically symmetric, atomic systems, through adding the complication of nonspherical molecular potentials, to mixing various molecular species with the inclusion of chemistry. We discuss what has been accomplished and evaluate the directions to be taken in attacking the unsolved problems. The various theoretical approaches, both analytic and numerical, are presented. We finish with a discussion of the recent advance in treating nonspherical molecular potentials with effective spherical potentials in the calculation of thermodynamics.

Johnson, J.D.; Shaw, M.S.; Holian, B.L.

1983-01-01

171

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

172

Microporous polymer films and methods of their production  

DOEpatents

A process is described for producing thin microporous polymeric films for a variety of uses. The process utilizes a dense gas (liquefied gas or supercritical fluid) selected to combine with a solvent-containing polymeric film so that the solvent is dissolved in the dense gas, the polymer is substantially insoluble in the dense gas, and two phases are formed. A microporous film is obtained by removal of a dense gas-solvent phase. 9 figs.

Aubert, J.H.

1995-06-06

173

An overview (introductory notes on dense stellar systems)  

NASA Astrophysics Data System (ADS)

An Overview on Dense Stellar Systems is given - relevant time scales for young massive or old globular star clusters are reviewed and compared to the different conditions in dense galactic nuclei possibly with one or more massive black holes. It is discussed how our physical knowledge depends on the advancement of computing and simulation techniques and the underlying physical methods. Different methods such as direct N-body gaseous or Fokker-Planck models are discussed and compared and recent theoretical developments are highlighted.

Spurzem, Rainer

2005-01-01

174

Geometrical Optics of Dense Aerosols  

SciTech Connect

Assembling a free-standing, sharp-edged slab of homogeneous material that is much denser than gas, but much more rare ed than a solid, is an outstanding technological challenge. The solution may lie in focusing a dense aerosol to assume this geometry. However, whereas the geometrical optics of dilute aerosols is a well-developed fi eld, the dense aerosol limit is mostly unexplored. Yet controlling the geometrical optics of dense aerosols is necessary in preparing such a material slab. Focusing dense aerosols is shown here to be possible, but the nite particle density reduces the eff ective Stokes number of the flow, a critical result for controlled focusing. __________________________________________________

Hay, Michael J.; Valeo, Ernest J.; Fisch, Nathaniel J.

2013-04-24

175

Cooling of neutron stars  

NASA Technical Reports Server (NTRS)

It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.

Pethick, C. J.

1992-01-01

176

Neutron stars - thermal emitters  

E-print Network

Confronting theoretical models with observations of thermal radiation emitted by neutron stars is one of the most important ways to understand the properties of both, superdense matter in the interiors of the neutron stars and dense magnetized plasmas in their outer layers. Here we review the theory of thermal emission from the surface layers of strongly magnetized neutron stars, and the main properties of the observational data. In particular, we focus on the nearby sources for which a clear thermal component has been detected, without being contaminated by other emission processes (magnetosphere, accretion, nebulae). We also discuss the applications of the modern theoretical models of the formation of spectra of strongly magnetized neutron stars to the observed thermally emitting objects.

Potekhin, A Y; Pons, J A

2014-01-01

177

Stellar Dynamics of Dense Stellar Systems  

E-print Network

Stellar dynamics is almost unreasonably well suited for an implementation in terms of special-purpose hardware. Unlike the case of molecular dynamics, stellar dynamics deals exclusively with a long-range force, gravity, which leads to a computational cost scaling as the square of the number of stars involved. While special tricks can lead to a reduction of this cost from $\\sim N^2$ to $\\sim N\\log N$ in the case of very large particle numbers, such tricks are not suitable for all areas within stellar dynamics. When a stellar system is close to equilibrium, and has a very high density, it still pays to compute all interactions on a star by star basis, even for $N=10^5$. Any $cN\\log N$ approach would either gloss over the subtle net effects of near-canceling interactions, driving the evolution of such a system, or would carry a prohibitively large coefficient $c$. This paper presents a brief introduction to the stellar dynamics of dense stellar systems, aimed at researchers using special purpose computers in other branches of physics.

Piet Hut

1998-04-08

178

Mechanics of large-strain deformation of particle-modified polymers  

E-print Network

Over the past several decades, engineering polymers have become increasingly prevalent in the manufacture of virtually all types of products. Polymers are substantially less dense than metals, easy to machine, and readily ...

Parsons, Ethan M. (Ethan Moore), 1972-

2006-01-01

179

Particle Physics From Stars  

Microsoft Academic Search

Low-mass particles, such as neutrinos, axions, other Nambu-Goldstone bosons, and gravitons, are produced in the hot and dense interior of stars. Therefore, astrophysical arguments constrain the properties of these particles in ways that are often complementary to cosmological arguments and to laboratory experiments. This review provides an update on the most important stellar-evolution limits and discusses them in the context

Georg G. Raffelt

1999-01-01

180

The State and Evolution of Isolated Dense Molecular Cores  

NASA Astrophysics Data System (ADS)

This work presents studies of nearby (< 500 pc) dense molecular cloud cores, the sites of low-mass star formation. The sample includes starless and protostellar cores and allows to compare their properties in a homogenous manner. All of the projects presented here are related to an extensive dust thermal continuum emission imaging survey at 1.2 mm wavelength that probes the mass distribution of dense cores. Many of them are also related to the Spitzer Legacy Project "From Molecular Cores to Planet Forming Disks" (c2d) that stimulated the dust emission survey and provided a general framework for my thesis. The main body of this work discusses the dust emission survey and the properties and nature of an unusually faint (< 0.1 L_sun ) source that is apparently embedded in one of the dense cores surveyed. The data from the dust emission survey is used to study the physical state and evolution of starless cores, "normal" protostars, and of the recently discovered Very Low Luminosity Objects (VeLLOs). This is the first study probing VeLLO dense core properties homogeneously for a larger sample of sources. Given that this survey covers both starless and protostellar cores, it is well suited to perform comparative studies. The aim is to understand how the mass distribution in dense cores controls the presence or absence of active star formation. As part of this effort I infer conditions that are necessary (but not sufficient) for active star formation to be possible. These can be understood as a consequence of the quasistatic evolution of a dense core, but do not conclusively imply the latter. Most VeLLO cores fulfil these conditions, questioning the notion that some VeLLOs form in cores that are not sufficiently evolved to form stars. I suggest a revision of the criteria used to identify "evolved" cores. Class 0 and class I protostars covered by my survey cannot be uniquely discriminated, suggesting also a revision of criteria used to assign infrared classes. Furthermore, I report the discovery of L1148-IRS, a candidate Very Low Luminosity Object (VeLLO; L < 0.1 L_sun ) in the nearby (325 pc) L1148 dense core. The global spectral energy distribution, the morphology of nebulosity detected near 1 μm wavelength, the inferred density profile of the dense core, and the tentative detection of inward motions towards L1148-IRS are consistent with the source being an embedded protostar. It is unlikely that L1148-IRS is a galaxy by chance projected onto the L1148 dense core. I do, however, not detect hallmarks of active star formation like molecular outflows or clear bipolar nebulosity proving a protostellar nature of L1148-IRS. This is consistent with our present view of VeLLOs. If L1148-IRS is a VeLLO, then it is a very interesting one. Its present mass would be substellar, and its immediate envelope has a mass of only about 0.15 M_sun . Thus, L1148-IRS would be the first protostar to definitely have a significantly sub-solar final mass. The collapse of the natal dense core could not be understood in the framework of quasistatically evolving cores. This would make L1148 the first dense core in which non-quasistatic evolution plays a significant role.

Kauffmann, Jens

2007-06-01

181

The Massive Star Population of Cygnus OB2: Constraining the Formation of Massive Stars  

NASA Astrophysics Data System (ADS)

It is often stated that all stars form in clusters or that massive stars can only form in dense star clusters. The existence of low density massive OB associations containing as many massive stars as dense star clusters therefore raises a number of important questions. Do all stars form in clusters and massive OB associations are simply the expanded remnants of massive star clusters forced apart due to gas expulsion? Are there multiple modes of star formation, clustered and distribution, and if so does the massive star population vary between these? How can a theory of massive star formation explain the existence of stars up to 100 solar masses in both dense massive star clusters and diffuse OB associations? Our nearest massive OB association, Cygnus OB2, is an ideal environment to address these questions. It is home to over 60 O-type stars and hundreds of OB stars but at only 1.4 kpc it can be studied in great detail. I will present results form a photometric and spectroscopic study of the massive star population that reveals evidence of spatially-correlated age spreads that suggests multiple stellar populations along the line of sight. I will also present results from a 3-dimensional kinematical survey combining radial velocities and proper motions for 3000 members of the association that provides new insights into how the region formed. The observations reveal considerable dynamical substructure that argues against the formation of the region as a single massive cluster and instead argues for a hierarchical model of star formation. The implications of these results for theories of the formation of massive stars and star clusters will be discussed.

Wright, N.

2013-06-01

182

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

183

Coordination polymers  

Microsoft Academic Search

This paper is a review of the metal complex forming coordination polymers. A polymermetal complex is composed of synthetic polymer and metal ions bound to the polymer ligand by a coordinate bond. A polymer ligand contains anchoring sites like nitrogen, oxygen or sulphur obtained either by the polymerization of monomer possessing the coordinating site or by a chemical reaction between

T. Kaliyappan; P. Kannan

2000-01-01

184

Diffusion and Coulomb separation of ions in dense matter.  

PubMed

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. PMID:24182248

Beznogov, M V; Yakovlev, D G

2013-10-18

185

Nucleation of strange matter in dense stellar cores  

SciTech Connect

We investigate the nucleation of strange quark matter inside hot, dense nuclear matter. Applying Zel'dovich's kinetic theory of nucleation we find a lower limit of the temperature {ital T} for strange-matter bubbles to appear, which happens to be satisfied inside the Kelvin-Helmholtz cooling era of a compact star life but not much after it. Our bounds thus suggest that a prompt conversion could be achieved, giving support to earlier expectations for nonstandard type-II supernova scenarios.

Horvath, J.E. (Instituto Astronomico e Geofisico, Universidade de Sao Paulo, Avenida M. Stefano 4200, Agua Funda (04301) Sao Paulo, Sao Paulo (Brazil)); Benvenuto, O.G. (Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N (1900) La Plata (Argentina)); Vucetich, H. (Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 49 y 115, C.C.67 (1900) La Plata (Argentina))

1992-05-15

186

Extreme Horizontal Branch Stars  

E-print Network

A review is presented on the properties, origin and evolutionary links of hot subluminous stars which are generally believed to be extreme Horizontal Branch stars or closely related objects. Amongst the field stars a large fraction of sdBs are found to reside in close binaries. The companions are predominantly white dwarfs, or low mass main sequence stars. Systems with sufficiently massive WD companions may qualify as SN Ia progenitors. Recently evidence has been found that the masses of some unseen companions might exceed the Chandrasekhar mass, hence they must be neutron stars or black holes. Even a planet has recently been detected orbiting the pulsating sdB star V391 Peg. Quite to the opposite, in globular clusters, only very few sdB binaries are found indicating that the dominant sdB formation processes is different in a dense environment. Binary population synthesis models identify three formation channels, (i) stable Roche lobe overflow, (ii) one or two common envelope ejection phases and (iii) the merger of two helium white dwarfs. The latter channel may explain the properties of the He-enriched sdO stars because their binary fraction is lower than that of the sdBs by a factor of ten or more. Pulsating subluminous B (sdB) stars play an important role for asteroseismology as this technique has already led to mass determinations for a handful of stars. A unique hyper-velocity sdO star moving so fast that it is unbound to the Galaxy has probably been ejected by the super-massive black hole in the Galactic centre. (abridged)

Ulrich Heber

2008-04-03

187

Nucleosynthesis in Hot and Dense Media  

E-print Network

We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe 0.045 % is higher than the corresponding contribution to helium abundance of a heating universe 0.031% due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic function of temperature, before and after the nucleosynthesis. However, this quadratic behavior was not the same before the decoupling temperature due to weak interactions; so the nucleosynthesis did not even start before the universe had cooled down to the neutrino decoupling temperatures and QED became a dominant theory. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions depend on the ratio between temperature and chemical potential and not the chemical potential or temperature only. It has been noticed that temperature plays a role of regulating parameter in an extremely dense systems.

Samina S. Masood

2014-05-06

188

The evolution of very massive stars  

E-print Network

Core collapse of dense massive star clusters is unavoidable and this leads to the formation of massive objects, with a mass up to 1000 $\\msun$ and even larger. When these objects become stars, stellar wind mass loss determines their evolution and final fate, and decides upon whether they form black holes (with normal mass or with intermediate mass) or explode as a pair instability supernova. In the present paper, we discuss the evolution of very massive stars and we present a convenient evolution recipe that can be implemented in a gravitational N-body code to study the dynamics of dense massive clusters.

H. Belkus; J. Van Bever; D. Vanbeveren

2007-01-11

189

Shocks in Dense Clouds in the Vela Supernova Remnant: FUSE  

NASA Technical Reports Server (NTRS)

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; Sonneborn, George (Technical Monitor)

2002-01-01

190

Field OB Stars that Formed In Situ  

NASA Astrophysics Data System (ADS)

We present 14 of the most compelling candidates for field OB star formation found to date, identified from our RIOTS4 field star survey of the SMC. These massive stars are all centrally situated within dense, symmetric HII regions, with no evidence of bow shocks. Their radial velocities are within 10 km s^{-1} of bulk HI components. All objects are at least 28 pc from other OB stars, and 9 show the presence of small companions. The evidence is strongly inconsisent with any of these stars being runaways, implying that they formed in relative, if not pure, isolation.

Oey, M. S.; Lamb, J. B.; Kushner, C. T.; Pellegrini, E. W.; Graus, A. S.

2013-06-01

191

ROSAT survey of emission from Be stars  

NASA Technical Reports Server (NTRS)

ROSAT pointed observations of bright, classical Be stars have demonstrated that detection of soft x-rays at a level expected for normal B stars of comparable T(sub eff) and luminosity is anti-correlated with the presence of episodes of enhanced mass ejection and formation of a dense, moderately ionized equatorial circumstellar disk. At epochs of lower than average disk column density, x-ray flaring has been detected in 2 Be stars, lambda Eri and pi Aqr.

Grady, Carol

1993-01-01

192

DENSE GAS DISPERSION MODEL (DEGADIS)  

EPA Science Inventory

The Dense Gas Dispersion Model (DEGADIS) is a mathematical dispersion model that can be used to model the transport of toxic chemical releases into the atmosphere. Its range of applicability includes continuous, instantaneous, finite duration, and time- variant releases; negative...

193

Metal-polymer composites comprising nanostructures and applications thereof  

DOEpatents

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

194

Metal-polymer composites comprising nanostructures and applications thereof  

DOEpatents

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

195

Complexity and neutron stars structure  

E-print Network

We apply the statistical measure of complexity introduced by Lopez-Ruiz, Mancini and Calbet to neutron stars structure. Neutron stars is a classical example where the gravitational field and quantum behavior are combined and produce a macroscopic dense object. Actually, we continue the recent application of Sanudo and Pacheco to white dwarfs structure. We concentrate our study on the connection between complexity and neutron star properties, like maximum mass and the corresponding radius, applying a specific set of realistic equation of states. Moreover, the effect of the strength of the gravitational field on the neutron star structure and consequently on the complexity measure is also investigated. It is seen that neutron stars, consistent with astronomical observations so far, are ordered systems (low complexity), which cannot grow in complexity as their mass increases. This is a result of the interplay of gravity, the short-range nuclear force and the very short-range weak interaction.

K. Ch. Chatzisavvas; V. P. Psonis; C. P. Panos; Ch. C. Moustakidis

2009-05-27

196

Toward Understanding Massive Star Formation  

E-print Network

Although fundamental for astrophysics, the processes that produce massive stars are not well understood. Large distances, high extinction, and short timescales of critical evolutionary phases make observations of these processes challenging. Lacking good observational guidance, theoretical models have remained controversial. This review offers a basic description of the collapse of a massive molecular core and a critical discussion of the three competing concepts of massive star formation: - monolithic collapse in isolated cores - competitive accretion in a protocluster environment - stellar collisions and mergers in very dense systems We also review the observed outflows, multiplicity, and clustering properties of massive stars, the upper initial mass function and the upper mass limit. We conclude that high-mass star formation is not merely a scaled-up version of low-mass star formation with higher accretion rates, but partly a mechanism of its own, primarily owing to the role of stellar mass and radiation pressure in controlling the dynamics.

Hans Zinnecker; Harold W. Yorke

2007-07-09

197

Polymers Presentation  

NSDL National Science Digital Library

This 15 page PowerPoint contains the presentation for the polymers module from Nano-Link. This lesson requires a background in eight grade science. Various details of polymers are discussed including molecular structures, cross-linked polymers, and ringed polymers. Lastly, an activity to explore cross-linked polymers is included. Visitors must complete a quick and free registration to access the materials.

2014-09-10

198

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

199

Spiral arm triggering of star formation  

E-print Network

We present numerical simulations of the passage of clumpy gas through a galactic spiral shock, the subsequent formation of giant molecular clouds (GMCs) and the triggering of star formation. The spiral shock forms dense clouds while dissipating kinetic energy, producing regions that are locally gravitationally bound and collapse to form stars. In addition to triggering the star formation process, the clumpy gas passing through the shock naturally generates the observed velocity dispersion size relation of molecular clouds. In this scenario, the internal motions of GMCs need not be turbulent in nature. The coupling of the clouds' internal kinematics to their externally triggered formation removes the need for the clouds to be self-gravitating. Globally unbound molecular clouds provides a simple explanation of the low efficiency of star formation. While dense regions in the shock become bound and collapse to form stars, the majority of the gas disperses as it leaves the spiral arm.

Ian A. Bonnell

2006-11-07

200

Dense periodic packings of tori  

E-print Network

Dense packings of nonoverlapping bodies in three-dimensional Euclidean space are useful models of the structure of a variety of many-particle systems that arise in the physical and biological sciences. Here we investigate the packing behavior of congruent ring tori, which are multiply connected nonconvex bodies of genus 1, as well as horn and spindle tori. We analytically construct a family of dense periodic packings of unlinked tori guided by the organizing principles originally devised for simply connected solid bodies [Torquato and Jiao, PRE 86, 011102 (2012)]. We find that the horn tori as well as certain spindle and ring tori can achieve a packing density higher than the densest known packing of both sphere and ellipsoids. In addition, we study dense packings of cluster of pair-linked ring tori (i.e., Hopf links).

Ruggero Gabbrielli; Yang Jiao; Salvatore Torquato

2014-02-26

201

Cyclodextrin Inclusion Polymers Forming Hydrogels  

NASA Astrophysics Data System (ADS)

This chapter reviews the advances in the developments of supramolecular hydrogels based on the polypseudorotaxanes and polyrotaxanes formed by inclusion complexes of cyclodextrins threading onto polymer chains. Both physical and chemical supramolecular hydrogels of many different types are discussed with respect to their preparation, structure, property, and gelation mechanism. A large number of physical supramolecular hydrogels were formed induced by self-assembly of densely packed cyclodextrin rings threaded on polymer or copolymer chains acting as physical crosslinking points. The thermo-reversible and thixotropic properties of these physical supramolecular hydrogels have inspired their applications as injectable drug delivery systems. Chemical supramolecular hydrogels synthesized from polypseudorotaxanes and polyrotaxanes were based on the chemical crosslinking of either the cyclodextrin molecules or the included polymer chains. The chemical supramolecular hydrogels were often made biodegradable through incorporation of hydrolyzable threading polymers, end caps, or crosslinkers, for their potential applications as biomaterials.

Li, Jun

202

Phi Meson in Dense Matter  

E-print Network

. It has been shown in Ref. [16] that the decreasing phi meson mass in dense matter enhances its production in heavy-ion collisions and may account for the large gita ratio measured in the CERN experiments [17]. If we take the strangeness content.... It has been shown in Ref. [16] that the decreasing phi meson mass in dense matter enhances its production in heavy-ion collisions and may account for the large gita ratio measured in the CERN experiments [17]. If we take the strangeness content...

Ko, Che Ming; Levai, P.; Qiu, X. J.; Li, C. T.

1992-01-01

203

Modeling Dense Stellar Systems: Background  

E-print Network

I provide some background about recent efforts made in modeling dense stellar systems, within the context of the MODEST initiative. During the last four years, we have seen more than fifteen MODEST workshops, with an attendance between twenty and a hundred participants, and topics ranging from very specialized discussions to rather general overviews.

Piet Hut

2006-10-07

204

Method for dense packing discovery.  

PubMed

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. PMID:21230619

Kallus, Yoav; Elser, Veit; Gravel, Simon

2010-11-01

205

Star formation in the "Gulf of Mexico"  

NASA Astrophysics Data System (ADS)

We present an optical/infrared study of the dense molecular cloud, L935, dubbed "The Gulf of Mexico", which separates the North America and the Pelican nebulae, and we demonstrate that this area is a very active star forming region. A wide-field imaging study with interference filters has revealed 35 new Herbig-Haro objects in the Gulf of Mexico. A grism survey has identified 41 H? emission-line stars, 30 of them new. A small cluster of partly embedded pre-main sequence stars is located around the known LkH? 185-189 group of stars, which includes the recently erupting FUor HBC 722.

Armond, T.; Reipurth, B.; Bally, J.; Aspin, C.

2011-04-01

206

Neutron star matter in an effective model  

E-print Network

We study the equation of state (EOS) for dense matter in the core of the compact star with hyperons and calculate the star structure in an effective model in the mean field approach. With varying incompressibility and effective nucleon mass, we analyse the resulting EOS with hyperons in beta equilibrium and its underlying effect on the gross properties of the compact star sequences. The results obtained in our analysis are compared with predictions of other theoretical models and observations. The maximum mass of the compact star lies in the range $1.21-1.96 ~M_{\\odot}$ for the different EOS obtained, in the model.

T. K. Jha; P. K. Raina; P. K. Panda; S. K. Patra

2006-08-04

207

Dynamics of Dense Cores in the Perseus Molecular Cloud  

E-print Network

We survey the kinematics of over one hundred and fifty candidate (and potentially star-forming) dense cores in the Perseus molecular cloud with pointed N2H+(1-0) and simultaneous C18O(2-1) observations. Our detection rate of N2H+ is 62%, rising to 84% for JCMT SCUBA-selected targets. In agreement with previous observations, we find that the dense N2H+ targets tend to display nearly thermal linewidths, particularly those which appear to be starless (using Spitzer data), indicating turbulent support on the small scales of molecular clouds is minimal. For those N2H+ targets which have an associated SCUBA dense core, we find their internal motions are more than sufficient to provide support against the gravitational force on the cores. Comparison of the N2H+ integrated intensity and SCUBA flux reveals fractional N2H+ abundances between 10^-10 and 10^-9. We demonstrate that the relative motion of the dense N2H+ gas and the surrounding C18O gas is less than the sound speed in the vast majority of cases (~90%). The point-to-point motions we observe within larger extinction regions appear to be insufficient to provide support against gravity, although we sparsely sample these regions.

Helen Kirk; Doug Johnstone; Mario Tafalla

2007-07-18

208

Synthesis, patterning and applications of star-shaped poly(ethylene glycol) biofunctionalized surfaces.  

PubMed

Poly(ethylene) glycol (PEG) is an excellent material to modify surfaces to resist non-specific protein adsorption. Linear PEG has been extensively studied both theoretically and experimentally and it has been found that resistance of PEG-coated surfaces to protein adsorption depends mainly on the molecular weight of the polymer and the surface grafting density. End-functionalized star-shaped PEGs allow for interpolymer crosslinking to form a dense layer. An excellent example of such a system consists of a 6-arm PEG/PPG (4 : 1) star polymer functionalized with isocyanate using IPDI. The end functionalization may be further biofunctionalized to recognize specific biomolecules such as streptavidin, His-tagged proteins, amino-terminated oligonucleotides and cell receptors. This functionalization may be patterned into specific geometries using stamping techniques or randomly distributed by statistical reaction of the end group with the biofunctional molecule in solution. The surface preparation uses simple spin-, dip- or spray-coating and produces smooth layers with low background fluorescence. These properties, together with the advantageous chemical properties of PEG, render the surfaces ideal for immobilizing proteins on surfaces with detection limits down to the single molecule level. Proteins immobilized on such surfaces are able to maintain their folded, functional form and are able to completely refold if temporarily exposed to denaturing conditions. Immobilized enzyme molecules were able to perform their function with the same activity as the enzyme in solution. Future directions of using surfaces coated with such crosslinked star polymers in highly sensitive and robust biotechnology applications will be discussed. PMID:17533455

Heyes, Colin D; Groll, Jrgen; Mller, Martin; Nienhaus, G Ulrich

2007-06-01

209

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 32

Eason, Oliver

210

Dense gas in high-latitude molecular clouds  

NASA Technical Reports Server (NTRS)

The nearby molecular clouds MBM 7, 12, 30, 32, 40, 41, and 55 were surveyed for tracers of dense gas, including the (1-0), (2-1), and (3-2) rotational lines of CS and the (1-0) lines of HCO(+) and HCN. MBM 7 and MBM 12 contain dense cores, while the other clouds contain little or no traces of dense gas. Comparison of the emission from dense gas tracers to that of (13)CO reveals that the former are more compact in angular size as well as line width. An extensive CS(2-1) survey of part of MBM 12 reveals that the emission is characterized by clumps on approximately 3 min scales as well as extended emission. Observations of the CS(1-0) and (3-2) lines using telescopes with matched beam sizes reveal that the volume density must be at least approximately 10(exp 4.5)/cc within the (3-2) emitting regions, which are approximately 0.03 pc in radius. Electron excitation of the CS rotational levels is ruled out (in the cores) by comparing the (3-2)/(1-0) line ratios with models including H2 and electron collisions. The volume density in the cores is substantially larger than in the portions of the cloud traced by CO emission. The density increases into the cores as r(exp -2), suggesting dynamical collapse. The masses of the cores are close to the virial mass, suggesting they are dynamically bound. The cores in MBM 7 and MBM 12 are thus likely to form stars; they are the nearest sites of star formation.

Reach, William T.; Pound, Marc W.; Wilner, David J.; Lee, Youngung

1995-01-01

211

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

212

Dilatons for dense hadronic matter  

NASA Astrophysics Data System (ADS)

The idea that the explicit breaking of scale invariance by the trace anomaly of QCD can be rephrased as a spontaneous breaking has been recently exploited to capture the low-energy strong interaction dynamics of dense (and also hot) matter in terms of two dilaton fields, the soft (?) and the hard (?) fields, in the frame work of the hidden local gauge symmetry. In the Freund-Nambu model, the spontaneous symmetry breaking of scale symmetry is induced by an explicitly breaking term, while the spontaneous symmetry breaking is possible in the flat potential model which is scale symmetric. We discuss the interplay of the soft and hard dilatons using the spontaneously broken scale symmetry schemes and uncover a novel structure of dense matter hitherto unexplored.

Lee, Hyun Kyu; Rho, Mannque

2010-11-01

213

Radiative properties of dense nanofluids.  

PubMed

The radiative properties of dense nanofluids are investigated. For nanofluids, scattering and absorbing of electromagnetic waves by nanoparticles, as well as light absorption by the matrix/fluid in which the nanoparticles are suspended, should be considered. We compare five models for predicting apparent radiative properties of nanoparticulate media and evaluate their applicability. Using spectral absorption and scattering coefficients predicted by different models, we compute the apparent transmittance of a nanofluid layer, including multiple reflecting interfaces bounding the layer, and compare the model predictions with experimental results from the literature. Finally, we propose a new method to calculate the spectral radiative properties of dense nanofluids that shows quantitatively good agreement with the experimental results. PMID:22945164

Wei, Wei; Fedorov, Andrei G; Luo, Zhongyang; Ni, Mingjiang

2012-09-01

214

Observational characteristics of dense cores with deeply embedded young protostars  

E-print Network

Class 0 objects, which are thought to be the youngest protostars, are identified in terms of NIR or radio emission and/or the presence of molecular outflows. We present combined hydrodynamic and radiative transfer simulations of the collapse of a star-forming molecular core, which suggest two criteria for identifying dense cores with deeply embedded very young protostars that may not be observable in the NIR or radio with current telescopes. We find that cores with protostars are relatively warm (T>15K) with their SEDs peaking at wavelengths <170 micron, and they tend to appear circular.

D. Stamatellos; A. P. Whitworth; S. P. Goodwin

2005-11-03

215

Astrophysical and laboratory constraints for the dense matter equation of state  

SciTech Connect

New measurements of neutron star masses and radii have lead to powerful constraints on the dense matter equation of state. In the vicinity of the nuclear saturation density, the symmetry energy is the least well understood aspect of the nuclear force. Independent constraints from a variety of nuclear experiments are now able to refine the parameters of the symmetry energy.

Lattimer, James M. [Dept. of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)

2012-11-12

216

The Cooling of Compact Stars  

E-print Network

The cooling of a compact star depends very sensitively on the state of dense matter at supranuclear densities, which essentially controls the neutrino emission, as well as on the structure of the stellar outer layers which control the photon emission. Open issues concern the hyperon population, the presence of meson condensates, superfluidity and superconductivity, and the transition of confined hadronic matter to quark matter. This paper describes these issues and presents cooling calculations based on a broad collection of equations of state for neutron star matter and strange matter. These results are tested against the body of observed cooling data.

Dany Page; Ulrich Geppert; Fridolin Weber

2005-08-01

217

Dense molecular cloud cores as a source of micrometer-sized grains in galaxies  

NASA Astrophysics Data System (ADS)

Coreshine in dense molecular cloud cores (dense cores) is interpreted as evidence for micrometer-sized grains (referred to as very large grains, VLGs). VLGs may have a significant influence on the total dust amount and the extinction curve. We estimate the total abundance of VLGs in the Galaxy, assuming that dense cores are the site of VLG formation. We find that the VLG abundance relative to the total dust mass is roughly ?VLG~0.01(1-?)/?((fVLG/0.5)(tshat/108 year), where ? is the star formation efficiency in dense cores, ?SF is the timescale of gas consumption by star formation, fVLG is the fraction of dust mass eventually coagulated into VLGs in dense cores, and tshat is the lifetime of VLGs (determined by shattering). Adopting their typical values for the Galaxy, we obtain ?VLG~0.02-0.09. This abundance is well below the value detected in the heliosphere by Ulysses and Galileo, which means that local enhancement of VLG abundance in the solar neighborhood is required if the VLGs originate from dense cores. We also show that the effects of VLGs on the extinction curve are negligible even with the upper value of the above range, ?VLG~0.09. If we adopt an extreme value, ?VLG~0.5, close to that inferred from the above spacecraft data, the extinction curve is still in the range of the variation in Galactic extinction curves, but is not typical of the diffuse ISM.

Hirashita, Hiroyuki; Asano, Ryosuke S.; Nozawa, Takaya; Li, Zhi-Yun; Liu, Ming-Chang

2014-10-01

218

Probing the neutron star interior with glitches  

NASA Astrophysics Data System (ADS)

With the aim of constraining the structural properties of neutron stars and the equation of state of dense matter, we study sudden spin-ups, glitches, occurring in the Vela pulsar and in six other pulsars. We present evidence that glitches represent a self-regulating instability for which the star prepares over a waiting time. The angular momentum requirements of glitches in Vela indicate that at least 1.4% of the star's moment of inertia drives these events. If glitches originate in the liquid of the inner crust, Vela's `radiation radius' $R_\\infty$ must exceed ~12 km for a mass of 1.4 solar masses. The isolated neutron star RX J18563-3754 is a promising candidate for a definitive radius measurement, and offers to further our understanding of dense matter and the origin of glitches.

Link, Bennett; Epstein, Richard I.; Lattimer, James M.

219

Constructing Dense Graphs with Unique Hamiltonian Cycles  

ERIC Educational Resources Information Center

It is not difficult to construct dense graphs containing Hamiltonian cycles, but it is difficult to generate dense graphs that are guaranteed to contain a unique Hamiltonian cycle. This article presents an algorithm for generating arbitrarily large simple graphs containing "unique" Hamiltonian cycles. These graphs can be turned into dense graphs

Lynch, Mark A. M.

2012-01-01

220

Dense Water Overflow Off Continental Shelves  

Microsoft Academic Search

This paper presents a world-wide inventory of confirmed events of dense water cas- cades over the shelf break, provides synergetic analysis of observational data, com- pares and contrasts the identified cases. The data were used to check theoretical mod- els of cascading and infer the parameters of dense plume evolution. The study is fo- cused on mesoscale plumes of dense

G. I. Shapiro; V. V. Ivanov; J. M. Huthnance; D. L. Aleinik

2002-01-01

221

Embedded Star Formation in the Eagle Nebula  

E-print Network

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 microns. 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 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.

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

2002-01-17

222

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

223

A quest for super dense aluminium  

NASA Astrophysics Data System (ADS)

The extreme pressure phase diagram of materials is important not only for understanding the interiors of planets or stars, but also for the fundamental understanding of the relation between crystal structure and electronic structure. Structural transitions induced by extreme pressure are governed by the deformation of valence electron charge density which bears the brunt of increasing compression while the relative volume occupied by the nearly incompressible ionic core electrons increases. At extreme pressures common materials are expected to transform into new dense phases with extremely compact atomic arrangements that may also have unusual physical properties. In this report, we present new experiments carried out on aluminium. A simple system like Al is not only important as a benchmark for theory, but can also be used as a standard for pressures in the TPa range and beyond which are targeted at new dynamic compression facilities such as the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in the US or Laser Mgajoule (LMJ) in Bordeaux in France. For aluminium, first principle calculations have consistently predicted a phase transition sequence from fcc to hcp and hcp to bcc in a pressure range below 0.5 TPa [Tambe et al., Phys. Rev. B 77, 172102, 2008]. The hcp phase was identified at 217 GPa in a recent experiment [Akahama et al., Phys. Rev. Lett. 96, 45505, 2006] but the detection of the predicted bcc phase has been hampered by the difficulty of routine static high pressure experiments beyond 350 GPa. Here, we report on the overcoming of this obstacle and the detection of all the structural phase transitions predicted in Al by achieving a pressure in excess of 500 GPa in the static regime in a diamond-anvil cell. In particular, using X-ray diffraction at the high-pressure beamline ID27 at the European Synchrotron Radiation Facility (ESRF), we find a bcc super-dense phase of aluminium at a pressure of 380 GPa. In this report, we provide detailed information on this phase transition as well as details on how to achieve controlled static experiments in the range 3 to 5 Mbar.

Fiquet, G.; Narayana, C.; Bellin, C.; Shukla, A.; Esteve, I.; Mezouar, N.

2013-12-01

224

Internal structure of dense electrodeposits  

NASA Astrophysics Data System (ADS)

We report experimental investigations of the structure of dense patterns obtained during electrochemical deposition of copper in thin cells. The deposit correlation function reveals the periodic structuration of the patterns but shows that the primary spacing is not steady during the growth and that moreover it is not simply related to the diffusion length. Another measurable quantity is the occupancy ratio of the fingers in the cell. Its variation as a function of the experimental parameters is interpreted from specific properties of electrochemical growth. The results are discussed with respect to the well-known behavior of cellular solidification fronts.

Lger, Christophe; Elezgaray, Juan; Argoul, Franoise

2000-05-01

225

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

226

Thermal Spray Formation of Polymer Coatings  

NASA Technical Reports Server (NTRS)

This innovation forms a sprayable polymer film using powdered precursor materials and an in-process heating method. This device directly applies a powdered polymer onto a substrate to form an adherent, mechanically-sound, and thickness-regulated film. The process can be used to lay down both fully dense and porous, e.g., foam, coatings. This system is field-deployable and includes power distribution, heater controls, polymer constituent material bins, flow controls, material transportation functions, and a thermal spray apparatus. The only thing required for operation in the field is a power source. Because this method does not require solvents, it does not release the toxic, volatile organic compounds of previous methods. Also, the sprayed polymer material is not degraded because this method does not use hot combustion gas or hot plasma gas. This keeps the polymer from becoming rough, porous, or poorly bonded.

Coquill, Scott; Galbraith, Stephen L.; Tuss. Darren L.; Ivosevic, Milan

2008-01-01

227

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

228

Polymer carpets.  

PubMed

The fabrication of defined polymer objects of reduced dimensions such as polymer-coated nanoparticles (zero-dimensional (0D)), cylindrical brushes (1D), and polymer membranes (2D), is currently the subject of intense research. In particular, ultrathin polymer membranes with high aspect ratios are being discussed as novel materials for miniaturized sensors because they would provide extraordinary sensitivity and dynamic range when sufficient mechanical stability can be combined with flexibility and chemical functionality. Unlike current approaches that rely on crosslinking of polymer layers for stabilization, this report presents the preparation of a new class of polymer material, so-called "polymer carpets," a freestanding polymer brush grown by surface-initiated polymerization on a crosslinked 1-nm-thick monolayer. The solid-supported, as well as freestanding, polymer carpets are found to be mechanically robust and to react instantaneously and reversibly to external stimuli by buckling. The carpet mechanics and the dramatic changes of the film properties (optical, wetting) upon chemical stimuli are investigated in detail as they allow the development of completely new integrated micro-/nanotechnology devices. PMID:20635346

Amin, Ihsan; Steenackers, Marin; Zhang, Ning; Beyer, Andr; Zhang, Xianghui; Pirzer, Tobias; Hugel, Thorsten; Jordan, Rainer; Glzhuser, Armin

2010-08-01

229

Nuclear fusion in dense matter: Reaction rate and carbon burning  

E-print Network

In this paper we analyze the nuclear fusion rate between 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 which covers all cases. The parameters of this formula can be varied, taking into account current theoretical uncertainties in the reaction rate. The results are illustrated for the example of the ^{12}C+^{12}C fusion reaction. This reaction is very important for the understanding of nuclear burning in evolved stars, in exploding white dwarfs producing type Ia supernovae, 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 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 > 10^9 g/cc.

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

2005-06-16

230

A Fokker-Planck study of dense rotating stellar clusters  

NASA Astrophysics Data System (ADS)

The dynamical evolution of dense stellar systems is simulated using a two-dimensional Fokker-Planck method, with the goal of providing a model for the formation of supermassive stars which could serve as seed objects for the supermassive black holes of quasars. This work follows and expands on earlier one-dimensional studies of spherical clusters of main-sequence stars. The two-dimensional approach allows for the study of rotating systems, as would be expected due to cosmological tidal torquing; other physical effects included are collisional mergers of individual stars and a bulk stellar bar perturbation in the system's gravitational potential. The 3 Myr main-sequence lifetime for large stars provides an upper limit on the allowed simulation times. Two general classes of initial systems are studied: Plummer spheres, which represent stellar clusters, and "gamma = 0" spheres, which model galactic spheroids. At the initial densities of the modeled systems, mass segregation and runaway stellar collisions alone are insufficient to induce core collapse within the main-sequence lifetime limit, if no bar perturbation is included. However, core collapse is not a requirement for the formation of a massive object: the choice of stellar initial mass function (IMF) is found to play a crucial role. When using an IMF similar to that observed for dense stellar clusters (weighted towards high masses but with a high-mass cutoff of Mmax?150M? ) the simulations presented here show, in all cases, that the stellar system forms massive (250M?) objects by collisional mergers of lower-mass stars; in almost all such cases the presence of a stellar bar allows for sufficient additional outward transport of angular momentum that a core-collapse state is reached with corresponding further increase in the rate of formation of massive objects. In contrast, simulations using an IMF similar to that observed for field stars in general (which is weighted more towards lower masses) produce no massive objects, and reach core collapse only for initial models which represent the highest-density galactic spheriods. Possible extensions of the work presented here include continuing to track stellar populations after they evolve off the main sequence, and allowing for a (possibly changing) nonspherical component to the overall system potential.

Girash, John Andrew

231

TESTING 24 {mu}m AND INFRARED LUMINOSITY AS STAR FORMATION TRACERS FOR GALACTIC STAR-FORMING REGIONS  

SciTech Connect

We have tested some relations for star formation rates used in extragalactic studies for regions within the Galaxy. In nearby molecular clouds, where the initial mass function is not fully sampled, the dust emission at 24 {mu}m greatly underestimates star formation rates (by a factor of 100 on average) when compared to star formation rates determined from counting young stellar objects. The total infrared emission does no better. In contrast, the total far-infrared method agrees within a factor of two on average with star formation rates based on radio continuum emission for massive, dense clumps that are forming enough massive stars to have L{sub TIR} exceed 10{sup 4.5} L{sub Sun }. The total infrared and 24 {mu}m also agree well with each other for both nearby, low-mass star-forming regions and the massive, dense clump regions.

Vutisalchavakul, Nalin; Evans, Neal J. II [University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400 Austin, TX 78712-1205 (United States)

2013-03-10

232

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

233

Study of exciton transfer in dense quantum dot nanocomposites  

NASA Astrophysics Data System (ADS)

Nanocomposites of colloidal quantum dots (QDs) integrated into conjugated polymers (CPs) are key to hybrid optoelectronics, where engineering the excitonic interactions at the nanoscale is crucial. For such excitonic operation, it was believed that exciton diffusion is essential to realize nonradiative energy transfer from CPs to QDs. In this study, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites of dense QDs, where exciton transfer can be as efficient as 80% without requiring the assistance of exciton diffusion. This is enabled by uniform dispersion of QDs at high density (up to ~70 wt%) in the nanocomposite while avoiding phase segregation. Theoretical modeling supports the experimental observation of weakly temperature dependent nonradiative energy transfer dynamics. This new finding provides the ability to design hybrid light-emitting diodes that show an order of magnitude enhanced external quantum efficiencies.Nanocomposites of colloidal quantum dots (QDs) integrated into conjugated polymers (CPs) are key to hybrid optoelectronics, where engineering the excitonic interactions at the nanoscale is crucial. For such excitonic operation, it was believed that exciton diffusion is essential to realize nonradiative energy transfer from CPs to QDs. In this study, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites of dense QDs, where exciton transfer can be as efficient as 80% without requiring the assistance of exciton diffusion. This is enabled by uniform dispersion of QDs at high density (up to ~70 wt%) in the nanocomposite while avoiding phase segregation. Theoretical modeling supports the experimental observation of weakly temperature dependent nonradiative energy transfer dynamics. This new finding provides the ability to design hybrid light-emitting diodes that show an order of magnitude enhanced external quantum efficiencies. Electronic supplementary information (ESI) available: Information about the functionalized polymer structure, TEM of the QDs, XPS analysis of the nanocomposites, derivation of the energy transfer models and temperature dependent steady state PLs. See DOI: 10.1039/c4nr03456b

Guzelturk, Burak; Hernandez-Martinez, Pedro Ludwig; Sharma, Vijay Kumar; Coskun, Yasemin; Ibrahimova, Vusala; Tuncel, Donus; Govorov, Alexander O.; Sun, Xiao Wei; Xiong, Qihua; Demir, Hilmi Volkan

2014-09-01

234

New Signposts of Star Cluster Formation  

NASA Astrophysics Data System (ADS)

The unbiased CHaMP survey of massive, dense molecular clumps in the southern Milky Way gives properties of clouds which represent the vast majority of star formation in the Galactic disk. Most of these clumps, while massive, are less dense and have lower star formation activity than more popularly-studied areas, suggesting a relatively long-lived, qui- escent phase of clump evolution before the onset of vigorous massive star formation disperses the clump, e.g. HCO + line emission is strongly correlated with associated Br? emission from embedded young clusters. The HCO+ is also strongly correlated with a number of other molecular tracers, including 13CO and HCN. In contrast, H_2 and N_2H+ emission are neither correlated with each other nor with HCO + or Br?, but the HCO+/N_2 H+ ratio is correlated with Br?/L_bol , and so indicates a clumps progress in forming massive stars or clusters from a colder, earlier, less active state. Therefore, many dense gas tracers dont really trace dense gas alone, but rather a combination of excitation and density, and should be interpreted with caution in the extragalactic context.

Barnes, P.; Ryder, S.

2014-09-01

235

Color Ferromagnetic Quark Matter in Neutron Stars  

E-print Network

We show that color ferromagnetic phase of quark matter is energetically more favored than color superconducting phases in neutron stars. Namely, increasing baryon density in neutron stars transforms nuclear matter into the quark matter of the color ferromagnetic phase. Further increase of the density makes the quark matter take the color superconducting phases. We find that a critical mass of the neutron star with such an internal structure is about $1.6M_{\\odot}$. We stress that analysis of gluon dynamics is crucial for exploring dense quark matter.

Aiichi Iwazaki; Osamu Morimatsu; Tetsuo Nishikawa; Munehisa Ohtani

2005-07-13

236

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

237

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

238

Polymers Guide  

NSDL National Science Digital Library

This 21 page document contains an instructor guide for the polymers module from Nano-Link. The activity requires a background in eight grade science. The document includes background information on polymers, a hands-on learning activity, questions to check understanding, links to multimedia resources, and further readings. Visitors must complete a quick and free registration to access the materials.

2014-09-09

239

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

240

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

241

Electroluminescent polymers  

Microsoft Academic Search

Electroluminescent polymers are reviewed in terms of synthesis and relationships between structure and light emission properties.The main concepts, problems and ideas related to the subject as a whole and to each class of electroluminescence (EL) polymer, have been systematically addressed. The elements of device architecture were considered, such as electrode characteristics and transport layers. The main mechanisms for light emission

Leni Akcelrud

2003-01-01

242

Viscoelastic behavior of dense microemulsions  

NASA Astrophysics Data System (ADS)

We have performed extensive measurements of shear viscosity, ultrasonic absorption, and sound velocity in a ternary system consisting of water-decane-sodium di(2-ethylhexyl)sulfo- succinate(AOT), in the one-phase region where it forms a water-in-oil microemulsion. We observe a rapid increase of the static shear viscosity in the dense microemulsion region. Correspondingly the sound absorption shows unambiguous evidence of a viscoelastic behavior. The absorption data for various volume fractions and temperatures can be reduced to a universal curve by scaling both the absorption and the frequency by the measured static shear viscosity. The sound absorption can be interpreted as coming from the high-frequency tail of the viscoelastic relaxation, describable by a Cole-Cole relaxation formula with unusually small elastic moduli.

Cametti, C.; Codastefano, P.; D'arrigo, G.; Tartaglia, P.; Rouch, J.; Chen, S. H.

1990-09-01

243

Optimal super dense coding over memory channels  

E-print Network

We study the super dense coding capacity in the presence of quantum channels with correlated noise. We investigate both the cases of unitary and non-unitary encoding. Pauli channels for arbitrary dimensions are treated explicitly. The super dense coding capacity for some special channels and resource states is derived for unitary encoding. We also provide an example of a memory channel where non-unitary encoding leads to an improvement in the super dense coding capacity.

Zahra Shadman; Hermann Kampermann; Chiara Macchiavello; Dagmar Bru

2011-07-18

244

Crystallization of dense neutron matter  

NASA Technical Reports Server (NTRS)

The equation of state for cold neutron matter at high density is studied in the t-matrix formulation, and it is shown that energetically it is convenient to have neutrons in a crystalline configuration rather than in a liquid state for values of the density exceeding 1600 Tg/cu cm. The study of the mechanical properties indicates that the system is stable against shearing stresses. A solid core in the deep interior of heavy neutron stars appears to offer the most plausible explanation of speed-ups observed in the Vela pulsar.

Canuto, V.; Chitre, S. M.

1974-01-01

245

Organization of polymers at interfaces  

NASA Astrophysics Data System (ADS)

We consider a set of ``simple'' polymer chains (linear, flexible, neutral, homogeneous) in the presence of a flat solid-liquid interface, where the surface is attractive and the chains adsorb reversibly. We show that the scaling approach recently proposed by Aubouy, Guiselin, and Raphal (AGR) [Macromolecules 29, 7261 (1996)] to describe polymer layers theoretically is able to explain the major features of these interfaces: (i) The polymer chains build an interfacial layer with a well-defined structure. (ii) There is preferential adsorption of the longest chains in the dilute regime. (iii) There is preferential adsorption of the shortest chains in the concentrated regime. (iv) Ultrathin polymer films dewet surfaces that thick films would wet. We can thus (a) identify a single physical process responsible for all these different behaviors, namely: the competition between the entropy of the set of loops (which favors the ``dense states'' of the layer) and the repulsive loop-loop interactions (which favors the ``dilute states'' of the layer), and (b) show that the AGR approach may provide the basis of a powerful and wide-ranging theory of polymers at interfaces.

Aubouy, Miguel

1997-09-01

246

The Quark-Meson Coupling model as a description of dense matter  

SciTech Connect

Quantum Hadrodynamics provides a useful framework for investigating dense matter, yet it breaks down easily when strangeness carrying baryons are introduced into the calculations, as the baryon effective masses become negative due to large meson field potentials. The Quark-Meson Coupling model overcomes this issue by incorporating the quark structure of the nucleon, thus allowing for a feedback between the the nuclei and the interaction with the meson fields. With the inclusion of this feature, QMC provides a successful description of finite nuclei and nuclear matter. We present the latest parameterization of QMC and discuss the predictions for dense nuclear matter and 'neutron' stars.

Carroll, J. D. [Centre for the Subatomic Structure of Matter (CSSM), Department of Physics, University of Adelaide, SA 5005 (Australia)

2011-10-24

247

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

248

Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, arent doing much of anything. In this video, Jonathans 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

249

Dynamic structure factors of a dense mixture  

E-print Network

We compute the dynamic structure factors of a dense binary liquid mixture. These describe dynamics on molecular length scales, where structural relaxation is important. We find that the presence of a few large particles in a dense fluid of small particles slows down the dynamics considerably. We also observe a deep narrowing of the spectrum for a disordered mixture composed of a nearly equal packing of the two species. In contrast, a few small particles diffuse easily in the background of a dense fluid of large particles. We expect our results to describe neutron scattering from a dense mixture.

Supurna Sinha

2005-05-22

250

Dense Molecular Clumps Associated with the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5  

NASA Astrophysics Data System (ADS)

We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. 12CO (J = 3-2, 1-0) and 13CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H2)) of the clumps are distributed from low to high density (103-105 cm3) and their kinetic temperatures (T kin) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of H?, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H2) and T kin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

Fujii, Kosuke; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Kawamura, Akiko; Muller, Erik; Dawson, Joanne; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie E.; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Ezawa, Hajime; Fukui, Yasuo

2014-12-01

251

Modelling the spectral energy distribution of ULIRGs II: The energetic environment and the dense interstellar medium  

E-print Network

We fit the near-infrared to radio spectral energy distributions of 30 luminous and ultra-luminous infrared galaxies with pure starburst models or models that include both starburst and AGN components to determine important physical parameters for this population of objects. In particular we constrain the optical depth towards the luminosity source, the star formation rate, the star formation efficiency and the AGN fraction. We find that although about half of our sample have best-fit models that include an AGN component, only 30% have an AGN which accounts for more than 10% of the infrared luminosity, whereas all have an energetically dominant starburst. Our derived AGN fractions are generally in good agreement other measurements based in the mid-infrared line ratios measured by Spitzer IRS, but lower than those derived from PAH equivalent widths or the mid-infrared spectral slope. Our models determine the mass of dense molecular gas via the extinction required to reproduce the SED. Assuming that this mass is that traced by HCN, we reproduce the observed linear relation between HCN and infrared luminosities found by Gao & Solomon. We also find that the star formation efficiency, defined as the current star formation rate per unit of dense molecular gas mass, is enhanced in the ULIRGs phase. If the evolution of ULIRGs includes a phase in which an AGN contributes an important fraction to the infrared luminosity, this phase should last an order of magnitude less time than the starburst phase. Because the mass of dense molecular gas which we derive is consistent with observations of the HCN molecule,it should be possible to estimate the mass of dense, star-forming molecular gas in such objects when molecular line data are not available.

O. Vega; M. S. Clemens; A. Bressan; G. L. Granato; L. Silva; P. Panuzzo; --

2007-12-07

252

Determining the star formation efficiency in shock-induced star-forming regions  

NASA Astrophysics Data System (ADS)

The passage of a ionization front trough a dense molecular cloud can trigger star formation in the region. The efficiency of the mechanism of star formation is found to be on the order of a few percents in some giant molecular clouds, but very little is known about the star formation efficiency and lifetimes of shock-induced star-forming regions. We propose to observe the cometary cloud Lynds 1622, where star formation has been likely induced by the interaction of the cloud with the Ori OB1 Association ionization front. Our aim is to determine the efficiency of star formation in this cloud through the robust determination of the stellar census of the region.

Lopez-Santiago, Javier

2013-10-01

253

Scintillating Stars  

NSDL National Science Digital Library

Often, a bright planet that is visible over the horizon will be mistaken for a star. Some believe they can tell the difference between a star and a planet because stars twinkle, or scintillate , and planets do not. In actuality however, both will twinkle because any light that passes through our atmosphere, whether it be reflected from a planet or generated by a star, will be interfered with by the atmospheric elements. This month's column sheds light on this "scintillating" subject and engages students in a research activity that revolves around the question: Is Pluto a planet?

Riddle, Bob

2003-02-01

254

On the Formation of Massive Stars  

E-print Network

We present a model for the formation of massive ($M > 10 M_\\odot$) stars through accretion-induced collisions in the cores of embedded dense stellar clusters. This model circumvents the problem of accreting onto a star whose luminosity is sufficient to reverse the infall of gas. Instead, the central core of the cluster accretes from the surrounding gas, thereby decreasing its radius until collisions between individual components become significant. These components are, in general, intermediate-mass stars that have formed through accretion onto low-mass protostars. Once a sufficiently massive star has formed to expel the remaining gas, the cluster expands in accordance with this loss of mass, halting further collisions. This process implies a critical stellar density for the formation of massive stars, and a high rate of binaries formed by tidal capture.

Ian A. Bonnell; Matthew R. Bate; Hans Zinnecker

1998-02-26

255

Complex Nanoscopic Objects from Well-defined Polymers that Contain Functional Units  

E-print Network

of macromonomers through covalent bond formation and self-assembly of block copolymers via non-covalent interactions are two typical strategies to afford nanoscopic structures. Molecular brush polymers are composed of densely-grafted side chains along a polymeric...

Li, Ang 1982-

2012-08-29

256

Cyanoacetylene in IC 342: An Evolving Dense Gas Component with Starburst Age  

NASA Astrophysics Data System (ADS)

We present the first images of the J = 5-4 and J = 16-15 lines of the dense gas tracer, cyanoacetylene, HC3N, 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. HC3N(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 HC3N 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. HC3N excitation temperatures are consistent with those determined from C18O; the gas is dense 104 - 105 cm-3 and cool, Tk < 40 K. So as to not violate limits on the total H2 mass determined from C18O, at least two dense components are required to model IC 342's giant molecular clouds. These observations suggest that HC3N(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. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Meier, David S.; Turner, Jean L.; Schinnerer, Eva

2011-07-01

257

Entropic force of polymers on a cone tip  

E-print Network

We consider polymers attached to the tip of a cone, and the resulting force due to entropy loss on approaching a plate (or another cone). At separations shorter than the polymer radius of gyration R_g, the only relevant length scale is the tip-plate (or tip-tip) separation h, and the entropic force is given by F=A kT/h. The universal amplitude A can be related to (geometry dependent) correlation exponents of long polymers. We compute A for phantom polymers, and for self-avoiding (including star) polymers by epsilon-expansion, as well as by numerical simulations in 3 dimensions.

Mohammad F. Maghrebi; Yacov Kantor; Mehran Kardar

2011-09-26

258

Branched Polymers  

E-print Network

Building on and from the work of Brydges and Imbrie, we give an elementary calculation of the volume of the space of branched polymers of order $n$ in the plane and in 3-space. Our development reveals some more general identities, and allows exact random sampling. In particular we show that a random 3-dimensional branched polymer of order $n$ has diameter of order $\\sqrt{n}$.

Richard Kenyon; Peter Winkler

2007-09-14

259

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

260

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

261

Field theoretic simulations of polymer nanocomposites  

SciTech Connect

Polymer field theory has emerged as a powerful tool for describing the equilibrium phase behavior of complex polymer formulations, particularly when one is interested in the thermodynamics of dense polymer melts and solutions where the polymer chains can be accurately described using Gaussian models. However, there are many systems of interest where polymer field theory cannot be applied in such a straightforward manner, such as polymer nanocomposites. Current approaches for incorporating nanoparticles have been restricted to the mean-field level and often require approximations where it is unclear how to improve their accuracy. In this paper, we present a unified framework that enables the description of polymer nanocomposites using a field theoretic approach. This method enables straightforward simulations of the fully fluctuating field theory for polymer formulations containing spherical or anisotropic nanoparticles. We demonstrate our approach captures the correlations between particle positions, present results for spherical and cylindrical nanoparticles, and we explore the effect of the numerical parameters on the performance of our approach.

Koski, Jason; Chao, Huikuan; Riggleman, Robert A., E-mail: rrig@seas.upenn.edu [Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)

2013-12-28

262

Compton scattering measurements from dense plasmas  

Microsoft Academic Search

Compton scattering techniques have been developed for accurate measurements of densities and temperatures in dense plasmas. One future challenge is the application of this technique to characterize compressed matter on the National Ignition Facility where hydrogen and beryllium will approach extremely dense states of matter of up to 1000 g\\/cc. In this regime, the density, compressibility, and capsule fuel adiabat

S. H. Glenzer; P. Neumayer; T. Dppner; O. L. Landen; R. W. Lee; R. J. Wallace; S. Weber; H. J. Lee; A. L. Kritcher; R. Falcone; S. P. Regan; H. Sawada; D. D. Meyerhofer; G. Gregori; C. Fortmann; V. Schwarz; R. Redmer

2008-01-01

263

DNA: structure, dense phases, charges, interactions  

E-print Network

DNA: structure, dense phases, charges, interactions #12;Outline 1. DNA: structure, charges, dense phases 2. Counterion and DNA condensation 3. ES DNA-DNA interactions 4. DNA toroidal structures 5. Interactions of real DNA helices 6. DNA-DNA ES recognition 7. DNA melting in aggregates 8. Azimuthal

Potsdam, Universität

264

MOdelling DEnse STellar systems A personal survey  

E-print Network

Lund MOdelling DEnse STellar systems A personal survey Douglas Heggie University of Edinburgh, UK d;Lund 0. Introduction to Dense Stellar Systems 47 Tuc M67 The Galactic centre #12;Lund The MODEST Arena Models of Stellar Systems by a New Integration Procedure." #12;Lund Effects of tides inside a cluster

Heggie, Douglas

265

Boundary effect of deterministic dense coding  

E-print Network

We present a rigorous proof of an interesting boundary effect of deterministic dense coding first observed by Mozes et al. [Phys. Rev. A 71, 012311 (2005)]. Namely, it is shown that $d^2-1$ cannot be the maximal alphabet size of any isometric deterministic dense coding schemes utilizing $d$-level partial entanglement.

Zhengfeng Ji; Yuan Feng; Runyao Duan; Mingsheng Ying

2006-01-20

266

On the Approximability of Dense Steiner Problems  

E-print Network

On the Approximability of Dense Steiner Problems M. Hauptmann #3; February 15, 2008 Abstract The #15;-Dense Steiner Tree Problem was de#12;ned by Karpinski and Zelikovsky [11] who proved of various Steiner Tree problems. In particular, we give polynomial time approximation schemes for the #15

Eckmiller, Rolf

267

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

268

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

269

VLA observations of dwarf M flare stars and magnetic stars  

NASA Astrophysics Data System (ADS)

The VLA has been used to search for 6 cm emission from 16 nearby dwarf M stars, leading to the detection of only one of them - Gliese 735. The dwarf M flare stars AD Leonis and YZ Canis Minoris were also monitored at 6 cm and 20 cm wavelength in order to study variability. Successive oppositely circularly polarized bursts were detected from AD Leo at 6 cm, suggesting the presence of magnetic fields of both magnetic polarities. An impulsive 20-cm burst from YZ CMi preceded slowly varying 6-cm emission. The VLA was also used, unsuccessfully, to search for 6-cm emission from 13 magnetic Ap stars, all of which exhibit kG magnetic fields. Although the Ap magnetic stars have strong dipolar magnetic fields, the failure to detect gyroresonant radiation suggests that these stars do not have hot, dense coronae. The quiescent microwave emission from GL 735 is probably due to nonthermal radiation, since unusually high (H = 50 kG or greater) surface magnetic fields are inferred under the assumption that the 6-cm radiation is the gyroresonant radiation of thermal electrons.

Willson, R. F.; Lang, K. R.; Foster, P.

1988-06-01

270

VLA observations of dwarf M flare stars and magnetic stars  

NASA Technical Reports Server (NTRS)

The VLA has been used to search for 6 cm emission from 16 nearby dwarf M stars, leading to the detection of only one of them - Gliese 735. The dwarf M flare stars AD Leonis and YZ Canis Minoris were also monitored at 6 cm and 20 cm wavelength in order to study variability. Successive oppositely circularly polarized bursts were detected from AD Leo at 6 cm, suggesting the presence of magnetic fields of both magnetic polarities. An impulsive 20-cm burst from YZ CMi preceded slowly varying 6-cm emission. The VLA was also used, unsuccessfully, to search for 6-cm emission from 13 magnetic Ap stars, all of which exhibit kG magnetic fields. Although the Ap magnetic stars have strong dipolar magnetic fields, the failure to detect gyroresonant radiation suggests that these stars do not have hot, dense coronae. The quiescent microwave emission from GL 735 is probably due to nonthermal radiation, since unusually high (H = 50 kG or greater) surface magnetic fields are inferred under the assumption that the 6-cm radiation is the gyroresonant radiation of thermal electrons.

Willson, R. F.; Lang, K. R.; Foster, P.

1988-01-01

271

On quantum advantage in dense coding  

E-print Network

The quantum advantage of dense coding is studied, considering general encoding quantum operations. Particular attention is devoted to the case of many senders, and it is shown that restrictions on the possible operations on the senders' side may make some quantum state useless for dense-coding. It is shown, e.g., that some states are useful for dense coding if the senders can communicate classically (but not quantumly), yet they cannot be used for dense coding, if classical communication is not allowed. These no-go results are actually independent of the particular quantification of the quantum advantage, being valid for any reasonable choice. It is further shown that the quantum advantage of dense coding satisfies a monogamy relation with the so-called entanglement of purification.

M. Horodecki; M. Piani

2007-01-18

272

Universe: Birth, Life, and Death of Stars  

NSDL National Science Digital Library

This Science Object is the third of five Science Objects in the Universe SciPack. It explores the life cycle of stars and the variables that determine eventual characteristics of stars. The formation of a star begins with an immense cloud, containing molecules of the lightest elements, collapses under the influence of gravity. The molecules in the cloud heat (up as the cloud becomes more dense) until light elements consistently fuse into heavier ones, producing large amounts of energy. Eventually, the most massive of stars explode, producing new clouds that contain heavier elements. These new clouds of material set the stage for the formation of other stars and planets, in a cycle that repeatedly continues even today. The speed of this process and ultimate fate of a star depends primarily on its initial mass. Stars can differ from each other in size, temperature, and age, but they all behave according to the same physical principles. Learning Outcomes:� Recount key aspects of the stellar life cycle. � Recognize the variables and conditions that would be needed to make predictions about the life cycle of a star, including the prominent role of initial mass. � Determine whether a reasonable prediction can be made, given certain knowns and unknowns.� Explain how the elements that compose our planet and solar system (and the rest of the universe) were formed.� Explain where the energy released by our Sun and other stars comes from.

National Science Teachers Association (NSTA)

2006-11-01

273

Two-dimensional dense gas dynamics  

NASA Astrophysics Data System (ADS)

Certain polyatomic fluids with large molecular weights referred to as dense gases exhibit unusual thermodynamic and flow properties in the region of the thermodynamic critical point. A computer program developed to solve two-dimensional flow fields is used to analyze non- classical dense gas phenomena in the single-phase gas region. A two-step, flux-limited, total variation diminishing scheme solves the time-dependent Euler equations for supersonic steady flow fields and mixed subsonic and supersonic transient flow fields. Two non- ideal gas models are incorporated into the numerical scheme in order to simulate dense gas effects. The van der Waals model, which is the simplest gas model that will show dense gas behavior, is employed to economically demonstrate qualitative trends in dense gas flows. The more complex Martin-Hou model is incorporated for cases where quantitative accuracy becomes more important. Simulated flows over simple geometries such as wedges, arcs, ramps, and steps using both the van der Waals gas model and the perfect gas model demonstrate significant differences in wave field configurations between dense gases and ideal gases. Results are also computed using the Martin-Hou equation of state which is more conservative in predicting dense gas effects than the van der Waals model. In addition to exploring the basic nature of dense gas flows for simple geometries, the utilization of dense gas properties to improve the efficiency of organic Rankine- cycle engines is investigated. Simulations of supersonic dense gas flows through impulse turbine cascades demonstrate improvements in flow quality through the cascades by reducing losses due to shock waves.

Brown, Brady Polk

274

An Observational Perspective of Low-Mass Dense Cores I: Internal Physical and Chemical Properties  

E-print Network

Low-mass dense cores represent the state of molecular gas associated with the earliest phases of low-mass star formation. Such cores are called "protostellar" or "starless," depending on whether they do or do not contain compact sources of luminosity. In this chapter, the first half of the review of low-mass dense cores, we describe the numerous inferences made about the nature of starless cores as a result of recent observations, since these reveal the initial conditions of star formation. We focus on the identification of isolated starless cores and their internal physical and chemical properties, including morphologies, densities, temperatures, kinematics, and molecular abundances. These objects display a wide range of properties since they are each at different points on evolutionary paths from ambient molecular cloud material to cold, contracting, and centrally concentrated configurations with significant molecular depletions and, in rare cases, enhancements.

J. Di Francesco; N. J. Evans II; P. Caselli; P. C. Myers; Y. Shirley; A. Aikawa; M. Tafalla

2006-02-17

275

Gravothermal Star Clusters - Theory and Computer Modelling  

NASA Astrophysics Data System (ADS)

In the George Darwin lecture, delivered to the British Royal Astronomical Society in 1960 by Viktor A. Ambartsumian he wrote on the evolution of stellar systems that it can be described by the "dynamic evolution of a gravitating gas" complemented by "a statistical description of the changes in the physical states of stars". This talk will show how this physical concept has inspired theoretical modeling of star clusters in the following decades up to the present day. The application of principles of thermodynamics shows, as Ambartsumian argued in his 1960 lecture, that there is no stable state of equilibrium of a gravitating star cluster. The trend to local thermodynamic equilibrium is always disturbed by escaping stars (Ambartsumian), as well as by gravothermal and gravogyro instabilities, as it was detected later. Here the state-of-the-art of modeling the evolution of dense stellar systems based on principles of thermodynamics and statistical mechanics (Fokker-Planck approximation) will be reviewed. Recent progress including rotation and internal correlations (primordial binaries) is presented. The models have also very successfully been used to study dense star clusters around massive black holes in galactic nuclei and even (in a few cases) relativistic supermassive dense objects in centres of galaxies (here again briefly touching one of the many research fields of V.A. Ambartsumian). For the modern present time of high-speed supercomputing, where we are tackling direct N-body simulations of star clusters, we will show that such direct modeling supports and proves the concept of the statistical models based on the Fokker-Planck theory, and that both theoretical concepts and direct computer simulations are necessary to support each other and make scientific progress in the study of star cluster evolution.

Spurzem, Rainer

2010-11-01

276

Self-regulated star formation in galaxies via momentum input from massive stars  

NASA Astrophysics Data System (ADS)

Feedback from massive stars is believed to play a critical role in shaping the galaxy mass function, the structure of the interstellar medium (ISM) and the low efficiency of star formation, but the exact form of the feedback is uncertain. In this paper, the first in a series, we present and test a novel numerical implementation of stellar feedback resulting from momentum imparted to the ISM by radiation, supernovae and stellar winds. We employ a realistic cooling function, and find that a large fraction of the gas cools to ?100 K, so that the ISM becomes highly inhomogeneous. Despite this, our simulated galaxies reach an approximate steady state, in which gas gravitationally collapses to form giant 'molecular' clouds (GMCs), dense clumps and stars; subsequently, stellar feedback disperses the GMCs, repopulating the diffuse ISM. This collapse and dispersal cycle is seen in models of Small Magellanic Cloud (SMC)-like dwarfs, the Milky Way and z 2 clumpy disc analogues. The simulated global star formation efficiencies are consistent with the observed Kennicutt-Schmidt relation. Moreover, the star formation rates are nearly independent of the numerically imposed high-density star formation efficiency, density threshold and density scaling. This is a consequence of the fact that, in our simulations, star formation is regulated by stellar feedback limiting the amount of very dense gas available for forming stars. In contrast, in simulations without stellar feedback, i.e. under the action of only gravity and gravitationally induced turbulence, the ISM experiences runaway collapse to very high densities. In these simulations without feedback, the global star formation rates exceed observed galactic star formation rates by 1-2 orders of magnitude, demonstrating that stellar feedback is crucial to the regulation of star formation in galaxies.

Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

2011-10-01

277

Star block-copolymers: enzyme-inspired catalysts for oxidation of alcohols in water.  

PubMed

A number of fluorous amphiphilic star block-copolymers containing a tris(benzyltriazolylmethyl)amine motif have been prepared. These polymers assembled into well-defined nanostructures in water, and their mode of assembly could be controlled by changing the composition of the polymer. The polymers were used for enzyme-inspired catalysis of alcohol oxidation. PMID:24912078

Mugemana, Clment; Chen, Ba-Tian; Bukhryakov, Konstantin V; Rodionov, Valentin

2014-07-25

278

Neutrino Processes in Neutron Stars  

NASA Astrophysics Data System (ADS)

The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called standard and non-standard cooling scenarios are replaced by one general nuclear medium cooling scenario which relates slow and rapid neutron star coolings to the star masses (interior densities). The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Greens function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Greens functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong interaction effects can be included within the Greens function formalism. Softening of the pion mode with an baryon density increase is explicitly incorporated. We show examples of inconsistencies in calculations without inclusion of medium effects. Then we demonstrate calculations of different reaction rates in non-superfluid nuclear matter with taking into account medium effects. Many new reaction channels are open up in the medium and should be analyzed. Part IV: We discuss the neutrino production reactions in superfluid nuclear systems. The reaction rates of processes associated with the pair breaking and formation are calculated. Special attention is focused on the gauge invariance and the exact fulfillment of the Ward identities for the vector current. Finally we present comparison of calculations of neutron star cooling performed within nuclear medium cooling scenario with the available data.

Kolomeitsev, E. E.; Voskresensky, D. N.

2010-10-01

279

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

280

Explicit flavor symmetry breaking and holographic compact stars  

E-print Network

We study the effects of flavor symmetry breaking on holographic dense matter and compact stars in the D4/D6 model. To this end, two light flavors and one intermediate mass flavor are considered. For two light quarks, we investigate how the strong isospin violation affects the properties of holographic dense matter and compact stars. We observe that quark-antiquark condensates are flavor dependent and show interesting behavior near the transition from dense matter with only one flavor to matter with two flavors. An intermediate mass quark is introduced to investigate the role of the third flavor. The mass-radius relations of holographic compact stars with three flavors show that the mass-radius curve changes drastically at a transition density from which the third flavor begins to appear in the matter.

Youngman Kim; Chang-Hwan Lee; Ik Jae Shin; Mew-Bing Wan

2014-04-14

281

Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation  

E-print Network

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems tha...

Peters, Thomas; Mac Low, Mordecai-Mark; Banerjee, Robi

2010-01-01

282

Origin of Warm High-Velocity Dense Gas in ULIRGs  

E-print Network

Possible origins of the molecular absorption discovered in some ULIRGs are investigated, based on a 3-D hydrodynamic model of star-forming interstellar gas in a galactic central region. The blue-shifted, warm ($\\sim 200-300$ K), dense ($>10^6$ cm$^{-3}$) molecular gas suggested by CO absorption in IRAS 08752+3915 could be caused by the innermost region of the inhomogeneous inter-stellar medium (ISM) around a supermassive black hole. The infrequent observations of the dense gas with absorption in ULIRGs and Seyfert 2 galaxies could simply suggest that the high-density regions occupy only a very small volume fraction of the obscuring material. This is naturally expected if the inhomogeneous structure of the ISM is caused by non-linear development of instabilities. The model predicts a turbulent velocity field in the obscuring material, therefore blue- and red-shifted gases should be observable with nearly the same probability for the large enough statistical samples.

Keiichi Wada

2007-06-19

283

Dense and Warm Molecular Gas between Double Nuclei of the Luminous Infrared Galaxy NGC 6240  

E-print Network

High spatial resolution observations of the 12CO(1-0), HCN(1-0), HCO+(1-0), and 13CO(1-0) molecular lines toward the luminous infrared merger NGC 6240 have been performed using the Nobeyama Millimeter Array and the RAINBOW Interferometer. All of the observed molecular emission lines are concentrated in the region between the double nuclei of the galaxy. However, the distributions of both HCN and HCO+ emissions are more compact compared with that of 12CO, and they are not coincident with the star-forming regions. The HCN/12CO line intensity ratio is 0.25; this suggests that most of the molecular gas between the double nuclei is dense. A comparison of the observed high HCN/13CO intensity ratio, 5.9, with large velocity gradient calculations suggests that the molecular gas is dense [n(H_2)=10^{4-6} cm^-3] and warm (T_kin>50 K). The observed structure in NGC 6240 may be explained by time evolution of the molecular gas and star formation, which was induced by an almost head-on collision or very close encounter of the two galactic nuclei accompanied with the dense gas and star-forming regions.

K. Nakanishi; S. K. Okumura; K. Kohno; R. Kawabe; T. Nakagawa

2005-07-07

284

Dense module enumeration in biological networks.  

PubMed

Automatic discovery of functional complexes from protein interaction data is a rewarding but challenging problem. While previous approaches use approximations to extract dense modules, our approach exactly solves the problem of dense module enumeration. Furthermore, constraints from additional information sources such as gene expression and phenotype data can be integrated, so we can systematically detect dense modules with interesting profiles. Given a weighted protein interaction network, our method discovers all protein sets that satisfy a user-defined minimum density threshold. We employ a reverse search strategy, which allows us to exploit the density criterion in an efficient way. PMID:23192536

Tsuda, Koji; Georgii, Elisabeth

2013-01-01

285

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

286

Mixed-ionic and electronic conductivity in polymers  

SciTech Connect

The aim in this portion of the research is to prepare new electroactive films with high ion mobility, and to characterize the transport properties of these materials. The classic conducting polymers, polyacetylene, polythiophene, and polypyrrole have dense structures that prevent rapid redox switching because of the low diffusivity of ions. The objective is to modify the last two polymers with pendant polyethers, which should greatly improve ion transport.

Ratner, M.A.; Shriver, D.F.

1991-01-01

287

Star fruit  

Microsoft Academic Search

The carambola or star fruit belongs to the Oxalidaceae family, species Averrhoa carambola. Slices cut in cross-section have the form of a star (Figure 1). It is believed to have originated in Ceylon and the Moluccas\\u000a but it has been cultivated in southeast Asia and Malaysia for many centuries. It is commonly grown in some provinces in southern\\u000a China, in

Miguel M. Neto; Ruither O. Carolino; Norberto P. Lopes; Norberto Garcia-Cairasco

288

Entropic phase separation in polymer-microemulsion networks.  

PubMed

We study theoretically a model system of a transient network of microemulsion droplets connected by telechelic polymers and explain recent experimental findings. Despite the absence of any specific interactions between either the droplets or polymer chains, we predict that as the number of polymers per drop is increased, the system undergoes a first-order phase separation into a dense, highly connected phase, in equilibrium with dilute droplets, decorated by polymer loops. The phase transition is purely entropic and is driven by the interplay between the translational entropy of the drops and the configurational entropy of the polymer connections between them. Because it is dominated by entropic effects, the phase behavior of the system is extremely robust and is independent of the detailed properties of either polymers or drops. PMID:12906554

Zilman, A; Kieffer, J; Molino, F; Porte, G; Safran, S A

2003-07-01

289

Galaxy Evolution Explorer Spies Band of Stars  

NASA Technical Reports Server (NTRS)

The Galaxy Evolution Explorer's ultraviolet eyes have captured a globular star cluster, called NGC 362, in our own Milky Way galaxy. In this new image, the cluster appears next to stars from a more distant neighboring galaxy, known as the Small Magellanic Cloud.

Globular clusters are densely packed bunches of old stars scattered in galaxies throughout the universe. NGC 362, located 30,000 light-years away, can be spotted as the dense collection of mostly yellow-tinted stars surrounding a large white-yellow spot toward the top-right of this image. The white spot is actually the core of the cluster, which is made up of stars so closely packed together that the Galaxy Evolution Explorer cannot see them individually.

The light blue dots surrounding the cluster core are called extreme horizontal branch stars. These stars used to be very similar to our sun and are nearing the end of their lives. They are very hot, with temperatures reaching up to about four times that of the surface of our sun (25,000 Kelvin or 45,500 degrees Fahrenheit).

A star like our sun spends most of its life fusing hydrogen atoms in its core into helium. When the star runs out of hydrogen in its core, its outer envelope will expand. The star then becomes a red giant, which burns hydrogen in a shell surrounding its inner core. Throughout its life as a red giant, the star loses a lot of mass, then begins to burn helium at its core. Some stars will have lost so much mass at the end of this process, up to 85 percent of their envelopes, that most of the envelope is gone. What is left is a very hot ultraviolet-bright core, or extreme horizontal branch star.

Blue dots scattered throughout the image are hot, young stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way located approximately 200,000 light-years away. The stars in this galaxy are much brighter intrinsically than extreme horizontal branch stars, but they appear just as bright because they are farther away. The blue stars in the Small Magellanic Cloud are only about a few tens of millions of years old, much younger than the approximately 10-million-year-old stars in NGC 362.

Because NGC 362 sits on the northern edge of the Small Magellanic Cloud galaxy, the blue stars are denser toward the south, or bottom, of the image.

Some of the yellow spots in this image are stars in the Milky Way galaxy that are along this line of sight. Astronomers believe that some of the other spots, particularly those closer to NGC 362, might actually be a relatively ultraviolet-dim family of stars called 'blue stragglers.' These stars are formed from collisions or close encounters between two closely orbiting stars in a globular cluster.

This image is a false-color composite, where light detected by the Galaxy Evolution Explorer's far-ultraviolet detector is colored blue, and light from the telescope's near-ultraviolet detector is red.

2007-01-01

290

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

291

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

292

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

293

Complementary Heating of Densely Packaged Microcircuits.  

National Technical Information Service (NTIS)

Some microcircuits dissipate as much as equivalent circuits using discrete transistors and resistors. Dense packaging and the resultant complementary heating therefore create reliability problems similar to those experienced with discrete components. (Aut...

H. F. Dean

1967-01-01

294

Dynamics and evolution of dense stellar systems  

E-print Network

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 ...

Fregeau, John M. (John Michael), 1977-

2004-01-01

295

Star-Like Micelles with Star-Like Interactions: A quantitative Evaluation of Structure Factor and Phase Diagram  

E-print Network

PEP-PEO block copolymer micelles offer the possibility to investigate phase behaviour and interactions of star polymers (ultra-soft colloids). A star-like architecture is achieved by an extremely asymmetric block ratio (1:20). Micellar functionality f can be smoothly varied by changing solvent composition (interfacial tension). Structure factors obtained by SANS can be quantitatively described in terms of an effective potential developed for star polymers. The experimental phase diagram reproduces to a high level of accuracy the predicted liquid/solid transition. Whereas for intermediate f a bcc phase is observed, for high f the formation of a fcc phase is preempted by glass formation.

M. Laurati; J. Stellbrink; R. Lund; L. Willner; D. Richter; E. Zaccarelli

2005-05-04

296

Hyperon and nuclear symmetry energy in the neutron star  

E-print Network

In this work, masses and radii of neutron stars are considered to investigate the effect of nuclear symmetry energy to the astrophysical observables. A relativistic mean field model with density-dependent meson-baryon coupling constants is employed in describing the equation of state of dense nuclear matter, and the density dependencies of the symmetry energies are quoted from the recent phenomenological formulae obtained from the heavy ion data at subnuclear saturation densities. Since hyperons can take part in the $\\beta$-equilibrium of the dense matter inside neutron stars, we include hyperons in our estimation and their roles are discussed in combination with that of the nuclear symmetry energy.

Chung-Yeol Ryu; Chang Ho Hyun; Chang-Hwan Lee

2011-08-30

297

Hyperons and nuclear symmetry energy in neutron star matter  

NASA Astrophysics Data System (ADS)

In this work, masses and radii of neutron stars are considered to investigate the effect of nuclear symmetry energy on astrophysical observables. A relativistic mean-field model with density-dependent meson-baryon coupling constants is employed in describing the equation of state of dense nuclear matter, and the density dependencies of the symmetry energies are quoted from the recent phenomenological formulas obtained from heavy-ion data at subnuclear saturation densities. Since hyperons can take part in the ?-equilibrium of the dense matter inside neutron stars, we include hyperons in our estimation and their roles are discussed in combination with that of the nuclear symmetry energy.

Ryu, Chung-Yeol; Hyun, Chang Ho; Lee, Chang-Hwan

2011-09-01

298

Dynamical theory of dense groups of galaxies  

NASA Technical Reports Server (NTRS)

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.

1990-01-01

299

Dissociation energy of molecules in dense gases  

NASA Technical Reports Server (NTRS)

A general approach is presented for calculating the reduction of the dissociation energy of diatomic molecules immersed in a dense (n = less than 10 exp 22/cu cm) gas of molecules and atoms. The dissociation energy of a molecule in a dense gas differs from that of the molecule in vacuum because the intermolecular forces change the intramolecular dynamics of the molecule, and, consequently, the energy of the molecular bond.

Kunc, J. A.

1992-01-01

300

Gravitational Condensate Stars  

NASA Astrophysics Data System (ADS)

The issue of the final state of the gravitational collapse will be addressed. Ishall present physical arguments to the effect that the remnant of the gravitationalcollapse of super-massive stars is a cold and dark super-dense object which isthermodynamically and dynamically stable: a Gravitational Condensate Star orQuasi Black Hole (QBH). A QBH is characterized by a huge, but not an infinite,surface redshift. This surface redshift depends universally on the total mass of aQBH and the proper thickness of a thin shell of an exotic matter described bythe Zel'dovich equation of state p = c2 . The velocity of sound in a thin shell isequal to the velocity of light. Hence, this thin shell replaces the event horizon of amathematical black hole ( = 0). Inside a thin shell the zero entropy gravitationalcondensate characterized by the cosmological equation of state p = -c2 resides.A QBH is described by a new static and spherically symmetric solution of Ein-stein's equations supplemented with the proper boundary conditions based on mi-crophysics considerations. The new solution has no singularities and no eventhorizons. Its entropy is maximized under small fluctuations and is given by thestandard hydrodynamic entropy of the thin shell which is proportional to the to-tal mass instead of the Bekenstein-Hawking entropy which is proportional to thesquare of the total mass. This resolves the paradox of an excessively high en-tropy of black holes as compared to their progenitors. The formation of such acold gravitational condensate stellar remnant very likely would require a violentcollapse process with an explosive output of energy. Some observational conse-quences of the formation of gravitational condensate stars will be described.

Mazur, P.; Mottola, E.

301

Ferroelectric polymers  

Microsoft Academic Search

In the early 1970s it became clear that the polymer polyvinylidene fluoride is ferroelectric. There have been extensive studies of its properties and of the properties of copolymers of vinylidene fluoride with tri- or tetra-fluoroethylene. This work has led to a fairly complete understanding of the ferroelectric and related properties of these materials. The emphasis in this review is on

R. G. Kepler; R. A. Anderson

1992-01-01

302

Polymer solutions  

DOEpatents

There is provided a method of making a polymer solution comprising polymerizing one or more monomer in a solvent, wherein said monomer comprises one or more ethylenically unsaturated monomer that is a multi-functional Michael donor, and wherein said solvent comprises 40% or more by weight, based on the weight of said solvent, one or more multi-functional Michael donor.

Krawczyk, Gerhard Erich (Bremen, DE); Miller, Kevin Michael (West Dundee, IL)

2011-07-26

303

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

304

STAR FORMATION RATES IN MOLECULAR CLOUDS AND THE NATURE OF THE EXTRAGALACTIC SCALING RELATIONS  

SciTech Connect

In this paper, we investigate scaling relations between star formation rates and molecular gas masses for both local Galactic clouds and a sample of external galaxies. We specifically consider relations between the star formation rates and measurements of dense, as well as total, molecular gas masses. We argue that there is a fundamental empirical scaling relation that directly connects the local star formation process with that operating globally within galaxies. Specifically, the total star formation rate in a molecular cloud or galaxy is linearly proportional to the mass of dense gas within the cloud or galaxy. This simple relation, first documented in previous studies, holds over a span of mass covering nearly nine orders of magnitude and indicates that the rate of star formation is directly controlled by the amount of dense molecular gas that can be assembled within a star formation complex. We further show that the star formation rates and total molecular masses, characterizing both local clouds and galaxies, are correlated over similarly large scales of mass and can be described by a family of linear star formation scaling laws, parameterized by f{sub DG}, the fraction of dense gas contained within the clouds or galaxies. That is, the underlying star formation scaling law is always linear for clouds and galaxies with the same dense gas fraction. These considerations provide a single unified framework for understanding the relation between the standard (nonlinear) extragalactic Schmidt-Kennicutt scaling law, that is typically derived from CO observations of the gas, and the linear star formation scaling law derived from HCN observations of the dense gas.

Lada, Charles J.; Forbrich, Jan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Lombardi, Marco [Department of Physics, University of Milan, via Celoria 16, I-20133 Milan (Italy); Alves, Joao F., E-mail: clada@cfa.harvard.edu, E-mail: jforbrich@cfa.harvard.edu, E-mail: marco.lombardi@gmail.com, E-mail: joao.alves@univie.ac.at [Institute for Astronomy, University of Vienna, Tuerkenschanzstrasse 17, A-1180 Vienna (Austria)

2012-02-01

305

Chemical Differentiation of CS and N2H+ in Dense Starless Cores  

NASA Astrophysics Data System (ADS)

CS molecule as an important tracer for studying inward motions in dense cores is known to be adsorbed onto dusts in cold (T~10K) dense cores, resulting in its significant depletion in the central region of the cores which may hamper a proper study of kinematics stage of star formation. However, the chemical behavior of this molecule still seems under questions because of a paucity of the cases showing the CS depletion in dense cores. In this study we choose five evolved dense starless cores, L1544, L1552, L1689B, L694-2 and L1197, to investigate how depletion of CS molecule is significant and how the molecule differentiates depending on the evolutional status of the dense cores, by using a rare isotopomer C34S. We performed mapping observations in C34S(J=2-1) and N2H+(J=1-0) with Nobeyama 45-m telescope. We compared the intensity maps of two molecular lines with 850?m continuum data as a reference of the density distribution of the dense cores, finding that CS molecules are centrally depleted in all of our targets and seen as semi-ring-like holes in its distribution, while N2H+ shows a central peak distribution as the one in dust continuum. This is also seen in the abundance radial profiles of two molecules for all of our targets where the CS abundance decreases toward the core center while the N2H+ keeps abundant constantly. Our data confirm the claim that CS molecule generally depletes out in the central region in starless cores, while N2H+ keeps abundant as they get evolved. The quantitative analysis on CS depletion in the dense cores, for example, the size of CS depletion area and radial (or gas density) dependence of CS depletion, is presented in the conference.

Kim, Shinyoung; Lee, Chang Won

2014-07-01

306

Externally fed star formation: a numerical study  

NASA Astrophysics Data System (ADS)

We investigate, through a series of numerical calculations, the evolution of dense cores that are accreting external gas up to and beyond the point of star formation. Our model clouds are spherical, unmagnetized configurations with fixed outer boundaries, across which gas enters subsonically. When we start with any near-equilibrium state, we find that the cloud's internal velocity also remains subsonic for an extended period, in agreement with observations. However, the velocity becomes supersonic shortly before the star forms. Consequently, the accretion rate building up the protostar is much greater than the benchmark value c_s^3/G, where cs is the sound speed in the dense core. This accretion spike would generate a higher luminosity than those seen in even the most embedded young stars. Moreover, we find that the region of supersonic infall surrounding the protostar races out to engulf much of the cloud, again in violation of the observations, which show infall to be spatially confined. Similar problematic results have been obtained by all other hydrodynamic simulations to date, regardless of the specific infall geometry or boundary conditions adopted. Low-mass star formation is evidently a quasi-static process, in which cloud gas moves inward subsonically until the birth of the star itself. We speculate that magnetic tension in the cloud's deep interior helps restrain the infall prior to this event.

Mohammadpour, Motahareh; Stahler, Steven W.

2013-08-01

307

The Orion Star-Forming Region  

E-print Network

General properties of the Orion star-forming region are discussed, with a focus on the dense Orion Nebula Cluster (ONC). This cluster contains between 2500 and 4500 objects located within a few parsecs of the eponymous Trapezium stars. Its members are aged <1 to a few Myr and encompass the full spectrum of stellar masses <50 Msun, as well as brown dwarfs detected with masses as low as <0.02 Msun (20 Mjup) thusfar. Recent results from optical, near-infrared, and x-ray studies of the stellar/sub-stellar population associated with this cluster are summarized.

Lynne A. Hillenbrand; John M. Carpenter; Eric D. Feigelson

2000-10-31

308

The pair potential of colloidal stars  

E-print Network

We report on the construction of colloidal stars: 1 micrometer polystyrene beads grafted with a dense brush of 1 micrometer long and 10 nm wide semi-flexible filamentous viruses. The pair interaction potentials of colloidal stars are measured using an experimental implementation of umbrella sampling, a technique originally developed in computer simulations in order to probe rare events. The influence of ionic strength and grafting density on the interaction is measured. Good agreements are found between the measured interactions and theoretical predictions based upon the osmotic pressure of counterions.

F. Huang; K. Addas; A. Ward; N. T. Flynn; E. Velasco; M. F. Hagan; Z. Dogic; S. Fraden

2008-10-08

309

Bipolar thiols as coupling agent for the grafting of conducting polymers  

NASA Astrophysics Data System (ADS)

The deposition of conducting polymers onto metallic substrates (Pt,Ti) is performed after a chemical pretreatment of the surface substrate using aliphatic (CH3-(CH2)n-SH n=0 to 10) and bipolar thiols (?-(CH2)nSH, n=0,1,2,3). The pretreatment impedes the metal oxidation and improves the polymer film adhesion with aromatic thiols. Moreover, this procedure leads to dense, longer conjugated polymers with fewer defects.

Lang, P.; Mekhalif, Z.; Garnier, F.; Regis, A.

1996-01-01

310

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

311

The friendly stars  

NASA Astrophysics Data System (ADS)

Describes prominent stars such as Vega, Arcturus, and Antares and means of identifying them, discusses the constellations in which they are located, and explains star names, stellar light, distances between stars, and types of stars.

Martin, Martha Evans

312

Energy Star  

E-print Network

ENERGY STAR ENERGY TARGETS ESL-KT-12-10-08 CATEE 2012: Clean Air Through Energy Efficiency Conference, Galveston, TX, October 9-11, 2012 POP QUIZ!!!! What is EUI?? Energy Use Intensity Do you know the EUI and any of the buildings you designed... Efficiency Conference, Galveston, TX, October 9-11, 2012 The CFLs in an ENERGY STAR qualified light fixture only need to be changed once every 8 years on average, compared with an annual ladder-climb for incandescent light bulbs. 6 CONSIDERING TIME...

Reihl, K.; Tullos, A.

2012-01-01

313

Dynamical Interactions in Dense Stellar Clusters  

E-print Network

This chapter reviews the dynamical processes in young stellar clusters. The accretion of gas by individual stars affects the dynamics of the cluster, and the masses of the stars. Dynamical mass segregation cannot explain the degree of mass segregation observed in clusters such as the Trapezium Cluster in Orion, implying that the location of the massive stars is an indication of where they formed. This can, however, be explained by the competitive accretion model. If most, if not all, stars form in binary systems, then the high proportion of pre-main sequence binary systems can evolve in clusters to the smaller proportion of Galactic field stars through binary-binary and binary-single interactions. These models make definite predictions for the distribution of binary properties. The early evolution of a cluster sensitively depends on the primordial binary star proportion. Close encounters between stars with circum-stellar discs have drastic effects on the discs and on the stellar orbits. The discs are truncated at radii comparable to the encounter peri-astron, limiting their lifetimes and affecting their potential for planet formation. If the gas represents a significant fraction of the total cluster mass, its removal on dynamical time-scales can unbind the cluster allowing the stars to escape and populate the field. (shortened)

Ian Bonnell; Pavel Kroupa

1998-02-24

314

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

315

Advanced Polymer  

NASA Technical Reports Server (NTRS)

In the mid-1980's, Langley developed a polyimide sulfone, combining desirable properties of two classes of polymers. Composites and other products made from polyimide sulfone can be used with solvents and corrosive fluids, are light weight, low cost and can be easily fabricated for a wide range of industrial uses. High Technology Systems, Inc. obtained a license for the polymer and was awarded a Small Business Innovation Research (SBIR) contract for development in a powder form. Although its principal use is as a matrix resin for composites, the material can also be used as a high temperature structural adhesive for aircraft structures and as a coating for protection from heat and radiation for electronic components.

1992-01-01

316

Neutron star moment-of-inertia in the extended Zimanyi-Moszkowski model  

E-print Network

Neutron star moment-of-inertia in the extended Zimanyi-Moszkowski model K. Miyazaki E-mail: miyazakiro@rio.odn.ne.jp Abstract We revisit the extended Zimanyi-Moszkowski (EZM) model of dense neutron observations of neutron stars (NSs) in RX J1856-3754 [2] and EXO 0748-676 [3] favor a sti¤ EOS. We are however

317

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; Rck, Lisa M; Hger, Sigurd

2012-08-20

318

Periodic Polymers  

NASA Astrophysics Data System (ADS)

Periodic polymers can be made by self assembly, directed self assembly and by photolithography. Such materials provide a versatile platform for 1, 2 and 3D periodic nano-micro scale composites with either dielectric or impedance contrast or both, and these can serve for example, as photonic and or phononic crystals for electromagnetic and elastic waves as well as mechanical frames/trusses. Compared to electromagnetic waves, elastic waves are both less complex (longitudinal modes in fluids) and more complex (longitudinal, transverse in-plane and transverse out-of-plane modes in solids). Engineering of the dispersion relation between wave frequency w and wave vector, k enables the opening of band gaps in the density of modes and detailed shaping of w(k). Band gaps can be opened by Bragg scattering, anti-crossing of bands and discrete shape resonances. Current interest is in our group focuses using design - modeling, fabrication and measurement of polymer-based periodic materials for applications as tunable optics and control of phonon flow. Several examples will be described including the design of structures for multispectral band gaps for elastic waves to alter the phonon density of states, the creation of block polymer and bicontinuous metal-carbon nanoframes for structures that are robust against ballistic projectiles and quasi-crystalline solid/fluid structures that can steer shock waves.

Thomas, Edwin

2013-03-01

319

A Study of Dense, Glassy Flows: Dense Pahoehoe Lava Flows From Kilauea Volcano, Hawaii  

Microsoft Academic Search

Thi s research project reviews existing literature and U. S. Geological Survey field reports for specific references to dense, glassy lava flows and includes a petrographic study of dense, glassy lava samples. The study will help us better understand the dynamics of lava flows and possibly lead to improving our ability to predict future lava flow hazards.

Laura L. Sage

2000-01-01

320

Star Power  

ScienceCinema

The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

None

2014-11-18

321

STAR Highlights  

E-print Network

We report selected results from STAR collaboration at RHIC, focusing on jet-hadron and jet-like correlations, quarkonium suppression and collectivity, di-electron spectrum in both p+p and Au+Au, and higher moments of net-protons as well as azimuthal anisotropy from RHIC Beam Energy Scan program.

Hiroshi Masui; for the STAR Collaboration

2011-06-29

322

Star Power  

NSDL National Science Digital Library

In this activity, learners create a star show and discover how they can prevent light pollution. Using simple materials, learners first design constellation boxes. Next, learners use their constellation boxes and desk lamps to explore how city lights impact the visibility of constellations. Finally, learners design shields to reduce light pollution and increase the visibility of constellations.

Television, Twin C.

2010-01-01

323

Dynamic structure factor in warm dense beryllium  

NASA Astrophysics Data System (ADS)

We calculate the dynamic structure factor (DSF) in warm dense beryllium by means of ab initio molecular dynamics simulations. The dynamic conductivity is derived from the Kubo-Greenwood formula, and a Drude-like behaviour is observed. The corresponding dielectric function is used to determine the DSF. Since the ab initio approach is so far only applicable for wavenumbers k = 0, the k-dependence of the dielectric function is modelled via the Mermin ansatz. We present the results for the dielectric function and DSF of warm dense beryllium and compare these with perturbative treatments such as the Born-Mermin approximation. We found considerable differences between the results of these approaches; this underlines the need for a first-principles determination of the DSF of warm dense matter.

Plagemann, K.-U.; Sperling, P.; Thiele, R.; Desjarlais, M. P.; Fortmann, C.; Dppner, T.; Lee, H. J.; Glenzer, S. H.; Redmer, R.

2012-05-01

324

Turbulence modulation and dense-spray structure  

NASA Astrophysics Data System (ADS)

A theoretical and experimental study of phenomena related to dense sprays is described. Two aspects of dense sprays are being considered: effects of turbulence modulation, which is the direct effect of particle (drop) motion on the turbulence properties of multiphase flows; and the structure and mixing properties of the dense-spray region of pressure atomized sprays. Turbulence modulation is being studied by considering spherical monodisperse glass particles falling in a stagnant water bath, where effects of turbulence modulation are responsible for the entire turbulence field. Measurements involve phase velocities and temporal and spatial correlations and spectra of the continuous phase velocities using a two-point phase-discriminating laser Doppler anemometer. Flow properties are being analyzed using stochastic methods: assuming linear superposition of randomly arriving particle wakes (Poisson statistics) for liquid phase properties; and random-walk calculations based on statistical time-series methods for particle properties.

Parthasarathy, R. N.; Ruff, G. A.; Faeth, G. M.

1988-08-01

325

Limiting Accretion onto Massive Stars by Fragmentation-induced Starvation  

NASA Astrophysics Data System (ADS)

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform and analyze simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive-mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

Peters, Thomas; Klessen, Ralf S.; Mac Low, Mordecai-Mark; Banerjee, Robi

2010-12-01

326

Pion stability in a hot dense media  

E-print Network

Pions may remain stable under certain conditions in a dense media at zero temperature in the normal phase (non pion superfluid state). The stability condition is achieved when the in-media pion width vanishes. However, thermal fluctuations will change this stable regime. For low temperature pions will remain in a metastable state. Here we discuss the different possible scenarios for leptonic pion decays at finite temperature, taking into account all the different chemical potentials involved. The neutrino emission due to pions in a hot-dense media is calculated, as well as the coolig rate of a pion-lepton gas.

M. Loewe; C. Villavicencio

2011-07-19

327

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

328

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 (?v~Rai), 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

329

Spectroscopy: Star Light, Star Bright  

NSDL National Science Digital Library

This is a student reading about the different types of spectra: continuous, absorption, and emission. Learners will read about the differences between each and see graphical representations of each. This activity is from the Stanford Solar Center's All About the Sun: Sun and Stars activity guide for Grades 5-8 and can also accompany the Stanford Solar Center's Build Your Own Spectroscope activity.

330

Molecular Composition and Chemistry of Isolated Dense Cores  

NASA Astrophysics Data System (ADS)

The composition of molecular clouds and the envelopes and disks surrounding low mass protostars within them is still poorly known. There is little doubt that a large fraction of the molecules is frozen on grains, but the abundance of several crucial species (e.g. NH3, CH3OH, ions) in the ices is still highly uncertain. In addition, prominent spectral features discovered decades ago are still not securely identified (e.g. the 6.85 micron absorption band). Gas phase and grain surface chemistry play pivotal roles in molecule formation, but numerous other processes could have significant impacts as well: shocks, thermal heating, irradiation of ices by ultraviolet photons and cosmic rays. Complex species could be formed this way, profoundly influencing cloud, disk, and planetary/cometary chemistry. We propose to obtain Spitzer/IRS spectra of an unprecedented sample of sight-lines tracing dense isolated cores. These cores physically differ from the large, cluster-forming molecular clouds (Ophiuchus, Perseus) that are commonly studied: they are less turbulent, colder, less dense, and likely longer lived. These IRS spectra of isolated cores will thus provide unique information on the ice formation and destruction mechanisms. For example, the longer survival time of ices in these cores might promote the energetic formation of more complex species. Variations in the 6.85 um absorption band may elucidate its carrier. The CO2 band will reflect variations in H and O chemistry as well as thermal history. In an unbiased sample of 66 isolated cores imaged with IRAC/MIPS by the "c2d" Legacy program, we found 30 mostly new protostars. Toward the same cores we selected 33 highly extincted background stars as well, tracing the quiescent cloud medium against which the (processed?) ices around protostars can be contrasted. With this unique source sample it is possible to address the most fundamental questions in astrochemistry: what is the composition of the interstellar medium and how are complex molecules formed?

Boogert, Adwin; Blake, Geoff; Brooke, Tim; Huard, Tracy; Jorgensen, Jes; Myers, Phil; van Dishoeck, Ewine

2005-06-01

331

A simple feature of yielding behavior of highly dense suspensions of soft micro-hydrogel particles.  

PubMed

The highly dense suspensions of soft micro-hydrogels with a narrow size distribution (typically ?eff > 0.9 where ?eff is the apparent volume fraction of the particle), which form a regular lattice structure, exhibit a simple feature in the yielding behavior: the yield strain ?c [ca. 2.5% and ca. 4.8% for poly(N-isopropylmethacrylamide) (PNIPMA) and poly(N-isopropylacrylamide) (PNIPA) hydrogel particles, respectively] is nearly insensitive to the cross-link concentration (cx), particle diameter (Dh), and particle concentration (c) in the limited c range examined here, and ?c is almost constant in a wide range of equilibrium shear moduli over two orders of magnitude. In addition, no appreciable difference in ?c is observed in the dense pastes with crystalline and glassy structures which are formed by mono- and bidisperse microgels, respectively. This is in contrast to a finite difference in ?c for the crystal and glass formed by the hard sphere reported by Koumakis et al. [Soft Matter, 4, 2008 (2008)]. Furthermore, the highly dense suspensions of NIPA core-NIPMA shell microgels are similar in ?c to those of NIPMA microgels. These results indicate that ?c for the highly dense suspensions of soft micro-hydrogels depends primarily on the kind of constituent polymer near the particle surface. The yield strain ?c is expected to be governed by short-range interactions such as adhesion and friction. PMID:25346296

Urayama, Kenji; Saeki, Taku; Cong, Shen; Uratani, Shota; Takigawa, Toshikazu; Murai, Masaki; Suzuki, Daisuke

2014-12-21

332

Gluon Vortices and Induced Magnetic Field in Compact Stars  

SciTech Connect

The natural candidates for the realization of color superconductivity are the extremely dense cores of compact stars, many of which have very large magnetic fields, especially the so called magnetars. In this paper we discuss how a color superconducting core can serve to generate and enhance the stellar magnetic field without appealing to a magnetohydrodynamic dynamo mechanism.

Ferrer, Efrain J. [Department of Physics, Western Illinois University, Macomb, IL 61455 (United States)

2007-10-26

333

Star formation and the ages of stars  

NASA Astrophysics Data System (ADS)

In this contribution we illustrate how the knowledge of the ages of stars is important to constrain star formation processes. We focus on two specific cases: star formation around the supermassive black hole at the center of the Galaxy and triggered star formation on the borders of Hii regions.

Martins, F.

2014-11-01

334

The evolution of massive stars: a selection of facts and questions  

E-print Network

In the present paper we discuss a selection of facts and questions related to observations and evolutionary calculations of massive single stars and massive stars in interacting binaries. We focus on the surface chemical abundances, the role of stellar winds, the early Be-stars, the high mass X-ray binaries, the effects of rotation on stellar evolution. Finally, we present an unconventionally formed object scenario (a UFO-scenario) of WR binaries in dense stellar environments.

Dany Vanbeveren

2004-10-01

335

A submillimeter continuum study of massive star formation in NGC 7538 and M17  

Microsoft Academic Search

I have used sensitive submillimeter continuum images to probe the earliest stages of massive star formation in NGC 7538 and M17, two of the nearest massive star-forming regions. I have located almost 200 cold, dense, potentially star-forming clumps: 77 in NGC 7538 and 121 in M17. Using images at two wavelengths, 850 and 450 mm, I have estimated the mean

Michael A. Reid

2005-01-01

336

The role of low-mass star clusters in massive star formation. The Orion Case  

NASA Astrophysics Data System (ADS)

To distinguish between the different theories proposed to explain massive star formation, it is crucial to establish the distribution, the extinction, and the density of low-mass stars in massive star-forming regions. We analyze deep X-ray observations of the Orion massive star-forming region using the Chandra Orion Ultradeep Project (COUP) catalog. We studied the stellar distribution as a function of extinction, with cells of 0.03 pc x 0.03 pc, the typical size of protostellar cores. We derived stellar density maps and calculated cluster stellar densities. We found that low-mass stars cluster toward the three massive star-forming regions: the Trapezium Cluster (TC), the Orion Hot Core (OHC), and OMC1-S. We derived low-mass stellar densities of 10^5 stars pc^-3 in the TC and OMC1-S, and of 10^6 stars pc^-3 in the OHC. The close association between the low-mass star clusters with massive star cradles supports the role of these clusters in the formation of massive stars. The X-ray observations show for the first time in the TC that low-mass stars with intermediate extinction are clustered toward the position of the most massive star, which is surrounded by a ring of non-extincted low-mass stars. This "envelope-core" structure is also supported by infrared and optical observations. Our analysis suggests that at least two basic ingredients are needed in massive star formation: the presence of dense gas and a cluster of low-mass stars. The scenario that better explains our findings assumes high fragmentation in the parental core, accretion at subcore scales that forms a low-mass stellar cluster, and subsequent competitive accretion. Finally, although coalescence does not seem a common mechanism for building up massive stars, we show that a single stellar merger may have occurred in the evolution of the OHC cluster, favored by the presence of disks, binaries, and gas accretion.

Rivilla, M. V.; Martin-Pintado, J.; Jimenez-Serra, I.; Rodriguez-Franco, A.

2013-06-01

337

Unexplained Brightening of Unusual Star  

NASA Astrophysics Data System (ADS)

Recent observations with the Hubble Space Telescope (HST) have documented an unexpected and rapid, seven-fold brightening of an unusual double star at the centre of the impressive 47 Tucanae globular cluster in the southern sky. This is the first HST observation of such a rare phenomenon. The astronomers [1] who are involved in this observational program find that this event cannot be explained by any of the common processes known to occur in such stars. The cores of globular clusters Globular clusters are like huge swarms of stars, containing about one million suns, which move around in their common gravitational field. Most galaxies contain globular clusters; around 150 are known within the confines of our Galaxy, the Milky Way. Globular clusters change with time. In particular, at some stage in the life of a globular cluster, its central region will contract whereby the stars there move closer to each other. This phenomenon is referred to as core collapse [2]. Observations with the Hubble Space Telescope (HST) have revealed enormous central densities of the order of 30,000 stars per cubic light-year in clusters with fully collapsed cores; this is to be compared with the stellar density in the solar neighborhood of only 0.003 stars per cubic light-year [3]. Binary stars in globular clusters Binary (i.e., double) stars play an important role in the evolution of globular clusters: they can delay, halt, or even reverse the process of core collapse. In this dense stellar environment, close encounters between passing stars and binaries are relatively frequent. Such events may leave the binary stars more tightly bound, and at the same time speed up the motion of the stars involved, thereby counteracting the contraction of the core. The same close stellar encounters may also produce a diverse progeny of exotic objects. The centers of globular clusters contain blue stragglers (stars that ``look'' younger than they really are), millisecond pulsars (rapidly rotating, very compact objects), both high- and low-luminosity X-ray sources , and cataclysmic variables (double stars whose light `flickers'). The kinds and numbers of these objects in cluster cores constrain the complex and as yet incompletely understood formation channels, most of which involve encounters with binaries. Many of the above exotic objects are strong emitters of ultraviolet light. The globular cluster 47 Tucanae 47 Tucanae is an impressive globular cluster that is visible with the naked eye from the southern hemisphere. It is one of the closest (distance 15,000 lightyears) and heaviest (total mass about 1 million solar masses) in our Galaxy. It contains about 1 million stars and the member stars have been intensively studied for decades. The observed structure of 47 Tucanae indicates that it is now approaching its ultimate fate during a core collapse phase. There are five known low-luminosity X-ray sources in the core of this cluster, eleven millisecond pulsars, many blue stragglers, and a centrally concentrated population of eclipsing binary stars. The observations support the idea that the population of primordial binaries in this cluster has been heavily modified by stellar encounters. The HST observations In late 1996, the group of astronomers obtained time to observe the central area of 47 Tucanae with the Hubble Space Telescope and the second Wide Field and Planetary Camera (WFPC2). During a period of more than 4 hours, a total of 15 CCD exposures were obtained through an ultraviolet filter (transmission near 3000 A), showing the thousands of individual stars in this densely populated region. Caption to ESO PR Photo 03/97 [GIF, 57k] When inspecting this material, it immediately became clear that one of the stars had undergone a substantial brightening in the course of these observations. In fact, its brightness increased by as much as 2.1 magnitudes, that is a factor of seven, in less than one hour; see the photos that accompany this Press Release. By the end of the observations, it had become the brightest star in the core of the cluster. Caption to ESO

1997-01-01

338

Metal-polymer and polymer-polymer interfaces: Application to conjugated polymer electronic devices  

Microsoft Academic Search

The study of metal-polymer and polymer-polymer interfaces is applied to conjugated polymer electronic devices. Conjugated polymers are a class of organic materials which have metallic or semiconducting properties which are being investigated as alternatives to traditional semiconducting materials. When conjugated polymers are used in devices, the interfaces are found to be critical to device performance. X-ray photoelectron spectroscopy (XPS) and

Julie Anne Osladil Smallfield

2002-01-01

339

Magnetic Fields and Galactic Star Formation Rates  

E-print Network

The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of molecular clouds within a kiloparsec patch of a disk galaxy. Including an empirically motivated prescription for star formation from dense gas ($n_{\\rm{H}}>10^5\\:{\\rm{cm}^{-3}}$) at an efficiency of 2\\% per local free fall time, we derive the amount of suppression of star formation by magnetic fields compared to the nonmagnetized case. We find GMC fragmentation, dense clump formation and SFR can be significantly affected by the inclusion of magnetic fields, especially in our strongest investigated $B$-field case of $80\\:{\\rm{\\mu}}$G. However, our chosen kpc scale region, extracted from a global galaxy simulation, happens to contain a starbu...

Van Loo, Sven; Falle, Sam A E G

2014-01-01

340

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

341

Technology Trends in Dense WDM Demultiplexers  

Microsoft Academic Search

Demultiplexers are a key component in dense WDM systems. The performance of these devices helps determine the overall system capacity. A variety of technologies have been developed to implement WDMs. This article reviews the various device technologies and their key characteristics.

Bruce Nyman; Mark Farries; Calvin Si

2001-01-01

342

A method for dense packing discovery  

E-print Network

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 \\textit{de novo} (from-scratch) searches for dense packings becomes crucial. In this paper, we use the \\textit{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 improvements in the densest-known tetrahedron packing which are reported in [arXiv:0910.5226]. 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 (the first such numerical evidence for their optimality in some of these dimensions). For non-spherical particles, we report a new dense packing of regular four-dimensional simplices with density $\\phi=128/219\\approx0.5845$ and with a similar structure to the densest known tetrahedron packing.

Yoav Kallus; Veit Elser; Simon Gravel

2010-03-17

343

Preparation of a dense, polycrystalline ceramic structure  

DOEpatents

Ceramic nanopowder was sealed inside a metal container under a vacuum. The sealed evacuated container was forced through a severe deformation channel at an elevated temperature below the melting point of the ceramic nanopowder. The result was a dense nanocrystalline ceramic structure inside the metal container.

Cooley, Jason (Los Alamos, NM); Chen, Ching-Fong (Los Alamos, NM); Alexander, David (Los Alamos, NM)

2010-12-07

344

DENSE NONAQUEOUS PHASE LIQUIDS -- A WORKSHOP SUMMARY  

EPA Science Inventory

site characterization, and, therefore, DNAPL remediation, can be expected. Dense nonaqueous phase liquids (DNAPLs) in the subsurface are long-term sources of ground-water contamination, and may persist for centuries before dissolving completely in adjacent ground water. In respo...

345

Chiral thermodynamics of dense hadronic matter  

SciTech Connect

We discuss phases of hot and dense hadronic matter using chiral Lagrangians. A two-flavored parity doublet model constrained by the nuclear matter ground state predicts chiral symmetry restoration. The model thermodynamics is shown within the mean-field approximation. A field-theoretical constraint on possible phases from the anomaly matching is also discussed.

Sasaki, C., E-mail: sasaki@fias.uni-frankfurt.de [Frankfurt Institute for Advanced Studies (Germany)

2012-05-15

346

Electrical conductivity of dense metal plasmas  

Microsoft Academic Search

The composition of dense metal plasmas is calculated considering higher ionization stages of the atoms. A system of coupled mass action laws is solved self-consistently taking into account medium corrections which lead to pressure ionization at high densities. The electrical conductivity is calculated within linear response theory. The interactions between the various species are treated on T matrix level. The

Ronald Redmer

1999-01-01

347

Robust dense registration of partial nonrigid shapes.  

PubMed

This paper presents a complete and robust solution for dense registration of partial nonrigid shapes. Its novel contributions are founded upon the newly proposed heat kernel coordinates (HKCs) that can accurately position points on the shape, and the priority-vicinity search that ensures geometric compatibility during the registration. HKCs index points by computing heat kernels from multiple sources, and their magnitudes serve as priorities of queuing points in registration. We start with shape features as the sources of heat kernels via feature detection and matching. Following the priority order of HKCs, the dense registration is progressively propagated from feature sources to all points. Our method has a superior indexing ability that can produce dense correspondences with fewer flips. The diffusion nature of HKCs, which can be interpreted as a random walk on a manifold, makes our method robust to noise and small holes avoiding surface surgery and repair. Our method searches correspondence only in a small vicinity of registered points, which significantly improves the time performance. Through comprehensive experiments, our new method has demonstrated its technical soundness and robustness by generating highly compatible dense correspondences. PMID:22025752

Hou, Tingbo; Qin, Hong

2012-08-01

348

Mechanizing the expert dense linear algebra developer  

Microsoft Academic Search

The efforts of an expert to parallelize and optimize a dense linear algebra algorithm for distributed-memory targets are largely mechanical and repetitive. We demonstrate that these efforts can be encoded and automatically applied to obviate the manual implementation of many algorithms in high-performance code.

Bryan Marker; Andy Terrel; Jack Poulson; Don Batory; Robert van de Geijn

2012-01-01

349

Benchmarking GPUs to tune dense linear algebra  

Microsoft Academic Search

We present performance results for dense linear algebra using recent NVIDIA GPUs. Our matrix-matrix multiply routine (GEMM) runs up to 60% faster than the vendor's implementa- tion and approaches the peak of hardware capabilities. Our LU, QR and Cholesky factorizations achieve up to 80-90% of the peak GEMM rate. Our parallel LU running on two GPUs achieves up to ~540

Vasily Volkov; James Demmel

2008-01-01

350

Dense-Core Secretory Granule Biogenesis  

NSDL National Science Digital Library

The dense-core secretory granule is a key organelle for secretion of hormones and neuropeptides in endocrine cells and neurons, in response to stimulation. Cholesterol and granins are critical for the assembly of these organelles at the trans-Golgi network, and their biogenesis is regulated quantitatively by posttranscriptional and posttranslational mechanisms.

Taeyoon Kim (National Institutes of Health Section on Cellular Neurobiology, National Institute of Child Health and Human Development); Marjorie C. Gondr©-Lewis (National Institutes of Health Section on Cellular Neurobiology, National Institute of Child Health and Human Development); Irina Arnaoutova (National Institutes of Health Section on Cellular Neurobiology, National Institute of Child Health and Human Development); Y. Peng Loh (National Institutes of Health Section on Cellular Neurobiology, National Institute of Child Health and Human Development)

2006-04-01

351

Detecting Dominant Motions in Dense Crowds  

Microsoft Academic Search

We discuss the problem of detecting dominant motions in dense crowds, a challenging and societally important problem. First, we survey the general literature of computer vision algorithms that deal with crowds of people, including model- and feature-based approaches to segmentation and tracking as well as algorithms that analyze general motion trends. Second, we present a system for automatically identifying dominant

Anil M. Cheriyadat; Richard J. Radke

2008-01-01

352

The Southern California Dense GPS Geodetic Array  

NASA Technical Reports Server (NTRS)

The Southern California Earthquake Center is coordinating a effort by scientists at the Jet Propulsion Laboratory, the U.S. Geological Survey, and various academic institutions to establish a dense 250 station, continuously recording GPS geodetic array in southern California for measuring crustal deformation associated with slip on the numerous faults that underlie the major metropolitan areas of southern california.

Webb, F.

1994-01-01

353

Multilayer Structure of Dense Anodic Alumina Films  

NASA Astrophysics Data System (ADS)

Dependences of the chemical etching of dense anodic alumina films with the simultaneous recording of a steady-state electrode potential and the film thickness are discussed. The film was determined to have up to 6 characteristic layers differing in the thickness and in the chemical dissolution rate. The procedure proposed is an express method to study characteristic layers throughout the oxide film thickness.

Sokol, V.; Yakovtseva, V.; Balucani, M.

2013-05-01

354

Modeling mass loss from B(e) stars  

NASA Technical Reports Server (NTRS)

It was suggested by Zickgraf et al. (1986) that the outer atmospheres of some B(e) stars have a two-component structure: a fast, radiation-driven wind from the pole, and a dense, slow outflow from the equator. Poe et al. (1989) developed this theory to explain the momentum problem associated with WR stars. This paper uses the multiforce wind theory of Poe et al. to model the B(e) outflow phenomenon. Two general questions are investigated: (1) whether B(e) stars can be rotating near critical speed, and if so, (2) what constraints can be placed on the parameters that determine the two-component flow structure.

Cassinelli, J. P.; Schulte-Ladbeck, R. E.; Abbott, M.; Poe, C. H.

1989-01-01

355

On the maximum mass of hyperonic neutron stars  

E-print Network

Chiral Lagrangian and quark-meson coupling models of hyperon matter are used to estimate the maximum mass of neutron stars. Our relativistic calculations include, for the first time, both Hartree and Fock contributions in a consistent manner. Being related to the underlying quark structure of baryons, these models are considered to be good candidates for describing the dense core of neutron stars. Taking account of the known experimental constraints at saturation density, the equations of state deduced from these relativistic approaches cannot sustain a neutron star with a mass larger than 1.6-1.66 $M_\\odot$.

Elisabeth Massot; Jrme Margueron; G. Chanfray

2012-01-13

356

Christmas star.  

NASA Astrophysics Data System (ADS)

There are continuous attempts to identify the legendary Christmas Star with a real astronomical event accompanying the birth of Jesus from Nazareth. Unfortunately, the date of birth is difficult to establish on the basis of historical records with better accuracy than a few years. During that period a number of peculiar astronomical events were observed and it seem to be impossible to identify the right one unambiguously.

Bia?a, J.

357

The effects of dense cluster environments on galaxies and intracluster dust  

NASA Astrophysics Data System (ADS)

Dense cluster environment influences the properties of galaxies and their evolution. In order to understand this environmental effect and how it evolves with time, we study the infrared (IR) properties of galaxies in three rich clusters. The IR luminosities provide us with extinction-free measurements of the star formation rates (SFRs) of these cluster galaxies. We find a strong evolution in the IR luminosity function (LF) of two z ~ 0.8 clusters when compared to two local clusters. The evolution rate of the IR LF found in these clusters is consistent with the evolution in field IR LFs. The similar evolution rate found in very different environments favors some internal mechanism, e.g., the gradual consumption of the gas fuel in galaxies, as being responsible for much of the star formation evolution. The mass-normalized integrated SFRs within 0.5 R 200 of these clusters also shows an evolution trend, 0( (1 + z ) 5 . But this evolution has large scatter and may be affected by the mass selection effect of the sample. In the dense cluster core regions ( r < 0.3 Mpc), we find evidence for enhanced SFR suppression. A substantial fraction of members in MS 1054-03 ( z ~ 0.8) are still forming stars actively. This cannot be explained by the scenario where the cluster is only passively accreting star-forming galaxies from the surrounding field, after which their star formation is quenched quickly. We also study the extended IR emission from the intracluster dust (ICD) in A2029. We only find weak signals at 24 and 7 0 mm and obtain upper limits for the ICD emission.

Bai, Lei

358

Planck stars  

E-print Network

A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density --not by size-- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

Rovelli, Carlo

2014-01-01

359

Planck stars  

E-print Network

A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density ---not by size--- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. We consider arguments for $n=1/3$ and for $n=1$. There is no causality violation or faster-than-light propagation. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

Carlo Rovelli; Francesca Vidotto

2014-01-25

360

The Formation of Massive Binary Stars  

E-print Network

The formation of massive stars in close binary systems is complicated due to their high radiation pressure, the crowded environment and the expected minimum separation for fragmentation being many times greater than the orbital separation. I discuss how massive star formation can be understood as being due to competitive accretion in stellar clusters. Massive binary systems are then formed due to accretion onto wider low-mass systems. The combination of accretion and dynamical interactions with other stars in the cluster then result in producing a close binary system. Tidal and 3-body captures in dense stellar cores can also play a role in forming massive binary systems while stellar mergers of such close binary systems due to interactions may play an important role in overcoming the radiation pressure.

Ian A. Bonnell

2005-01-13

361

Polymer microphotonics  

NASA Astrophysics Data System (ADS)

We report on a polymer-based planar lightwave circuit platform that enables high levels of integration. The materials used represent the state of the art in optical polymers, and include properties such as ultra-low loss (0.1 dB/cm in single-mode waveguides at 1550 nm), widely tunable refractive index contrast (0-35%), and large thermo-optic coefficient (-3.210-4/C). The large index contrast values enable compact photonic microcircuits. The circuits are produced photolithographically, and can have a variety of inorganic materials integrated in them (e.g., by insertion in slots or by flip-chip mounting), resulting in a platform that can support functions that span the range of the building blocks needed in optical circuitry, while using the highest-performance material for each function. In this manuscript, we focus on the polymeric microcircuits, which provide interconnects, static routing elements such as couplers, taps, and multi/demultiplexers, as well as thermo-optically dynamic elements such as tunable couplers, switches, variable optical attenuators, and tunable notch filters. We demonstrate complex-functionality polymeric photonic microcircuits based on this technology, including fully reconfigurable optical add/drop multiplexing subsystems on a chip that perform channel switching, power monitoring, load balancing, and wavelength shuffling.

Eldada, Louay A.

2003-10-01

362

Rejecting Proposed Dense Matter Equations of State with Quiescent Low-mass X-Ray Binaries  

NASA Astrophysics Data System (ADS)

Neutrons stars are unique laboratories for discriminating between the various proposed equations of state of matter at and above nuclear density. One sub-class of neutron starsthose inside quiescent low-mass X-ray binaries (qLMXBs)produce a thermal surface emission from which the neutron star radius (R NS) can be measured, using the widely accepted observational scenario for qLMXBs, assuming unmagnetized H atmospheres. In a combined spectral analysis, this work first reproduces a previously published measurement of the R NS, assumed to be the same for all neutron stars, using a slightly expanded data set. The radius measured is {R_NS}=9.4+/- 1.2{ km}. On the basis of spectral analysis alone, this measured value is not affected by imposing an assumption of causality in the core. However, the assumptions underlying this R NS measurement would be falsified by the observation of any neutron star with a mass >2.6 M ?, since radii <11{ km} would be rejected if causality is assumed, which would exclude most of the R NS parameter space obtained in this analysis. Finally, this work directly tests a selection of dense matter equations of state: WFF1, AP4, MPA1, PAL1, MS0, and three versions of equations of state produced through chiral effective theory. Two of those, MS0 and PAL1, are rejected at the 99% confidence level, accounting for all quantifiable uncertainties, while the other cannot be excluded at >99% certainty.

Guillot, Sebastien; Rutledge, Robert E.

2014-11-01

363

Polymer-mediated entropic forces between scale-free objects  

E-print Network

The number of configurations of a polymer is reduced in the presence of a barrier or an obstacle. The resulting loss of entropy adds a repulsive component to other forces generated by interaction potentials. When the obstructions are scale invariant shapes (such as cones, wedges, lines or planes) the only relevant length scales are the polymer size R_0 and characteristic separations, severely constraining the functional form of entropic forces. Specifically, we consider a polymer (single strand or star) attached to the tip of a cone, at a separation h from a surface (or another cone). At close proximity, such that h<polymer correlations in the presence of obstacles. We use analytical, numerical and epsilon-expansion techniques to compute the exponent \\eta for a polymer attached to the tip of the cone (with or without an additional plate or cone) for ideal and self-avoiding polymers. The entropic force is of the order of 0.1 pN at 0.1 micron for a single polymer, and can be increased for a star polymer.

Mohammad F. Maghrebi; Yacov Kantor; Mehran Kardar

2012-08-28

364

Dynamics of black holes in dense stellar systems  

NASA Astrophysics Data System (ADS)

We develop physical models to describe the dynamics of N black holes inside dense stellar systems. For N = 1, we show that the force on a single massive black hole consists of two independent parts: the slowly varying influence of the aggregate stellar system, and a rapidly fluctuating stochastic force arising from discrete encounters with individual stars. Detailed properties of the resulting Brownian wandering of the black hole are calculated, and it is shown that in equilibrium, the position and velocity of the black hole are distributed as independent Gaussians. The results are applied to derive a lower limit on the mass of the black hole Sgr A* at the center of our Galaxy. We also consider whether in the stationary state the black hole achieves a state of equipartition of kinetic energy with the surrounding stars, and show that in certain cases, deviation from equipartition can be large. For N = 2, we study the case of massive binary black holes in spherically symmetric bulges of galaxies, and investigate whether the Brownian motion of a binary's center of mass can allow its continued interaction with stellar orbits, and to keep hardening to the point of coalescence by the emission of gravitational radiation. We find that a considerable fraction of binaries in galaxies can by this means coalesce within a Hubble time. The predictions of the above models are confirmed by N-body simulations. We examine the interactions of N ? 2 stellar-mass black holes in globular clusters with a population of primordial stellar binaries. We find that close encounters between them result in the rapid exchange of the stellar members of the binaries with black holes. Repeated encounters between the black hole binaries and single black holes then result in the ejection of almost all the black holes from the cluster in a fraction of the age of the Universe. This may explain why no accreting black holes in X-ray binaries have been seen in globular clusters.

Chatterjee, Pinaki

2004-07-01

365

An Overview of STAR Experimental Results  

E-print Network

With large acceptance and excellent particle identification, STAR is one of the best mid-rapidity collider experiments for studying high-energy nuclear collisions. The STAR experiment provides full information on initial conditions, properties of the hot and dense medium as well as the properties at freeze-out. In Au+Au collisions at $\\sqrt{s_{NN}} = 200$ GeV, STAR's focus is on the nature of the sQGP produced at RHIC. In order to explore the properties of the QCD phase diagram, since 2010, the experiment has collected sizable data sets of Au+Au collisions at the lower collision energy region where the net-baryon density is large. At the 2014 Quark Matter Conference, the STAR experiment made 16 presentations that cover physics topics including {\\it collective dynamics}, {\\it electromagnetic probes}, {\\it heavy flavor}, {\\it initial state physics}, {\\it jets}, {\\it QCD phase diagram}, {\\it thermodynamics and hadron chemistry}, and {\\it future experimental facilities, upgrades, and instrumentation} [1-16]. In this overview we will highlight a few results from the STAR experiment, especially those from the recent measurements of the RHIC beam energy scan program. At the end, instead of a summary, we will discuss STAR's near future physics programs at RHIC.

N. Xu

2014-08-15

366

Shock waves and double layers in electron degenerate dense plasma with viscous ion fluids  

NASA Astrophysics Data System (ADS)

The properties of ion-acoustic shock waves and double layers propagating in a viscous degenerate dense plasma (containing inertial viscous ion fluid, non-relativistic and ultra-relativistic degenerate electron fluid, and negatively charged stationary heavy element) is investigated. A new nonlinear equation (viz. Gardner equation with additional dissipative term) is derived by the reductive perturbation method. The properties of the ion-acoustic shock waves and double layers are examined by the analysis of the shock and double layer solutions of this new equation (we would like to call it "M-Z equation"). It is found that the properties of these shock and double layer structures obtained from this analysis are significantly different from those obtained from the analysis of standard Gardner or Burgers' equation. The implications of our results to dense plasmas in astrophysical objects (e.g., non-rotating white dwarf stars) are briefly discussed.

Mamun, A. A.; Zobaer, M. S.

2014-02-01

367

Numerical study of ion acoustic shock waves in dense quantum plasma  

NASA Astrophysics Data System (ADS)

Two fluid quantum hydrodynamic equations are solved numerically to investigate the propagation characteristics of ion acoustic shock waves in an unmagnetized dense quantum plasma, whose constituents are the electrons and ions. For this purpose, we employ the standard finite difference Lax Wendroff and relaxation methods, to examine the quantum effects on the profiles of shock potential, the electron/ion number densities, and velocity even for quantum parameter at H = 2. The effects of the latter vanish in a weakly non-linear limit while obeying the KdV theory. It is shown that the evolution of the wave depends sensitively on the plasma density and the quantum parameter. Numerical results reveal that the kinks or oscillations are pronounced for large values of quantum parameter, especially at H = 2. Our results should be important to understand the shock wave excitations in dense quantum plasmas, white dwarfs, neutron stars, etc.

Hanif, M.; Ali, S.; Mukhtar, Q.; Mirza, Arshad M.

2014-03-01

368

Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs  

E-print Network

Aims: Hydrogen deficient white dwarfs are characterized by very dense, fluid-like atmospheres of complex physics and chemistry that are still poorly understood. The incomplete description of these atmospheres by the models results in serious problems with the description of spectra of these stars and subsequent difficulties in derivation of their surface parameters. Here, we address the problem of infrared (IR) opacities in the atmospheres of cool white dwarfs by direct $ab$ $initio$ simulations of IR absorption of dense helium. Methods: We applied state-of-the-art density functional theory-based quantum molecular dynamics simulations to obtain the time evolution of the induced dipole moment. The IR absorption coefficients were obtained by the Fourier transform of the dipole moment time autocorrelation function. Results: We found that a dipole moment is induced due to three- and more-body simultaneous collisions between helium atoms in highly compressed helium. This results in a significant IR absorption that...

Kowalski, Piotr M

2014-01-01

369

When Stars Collide  

E-print Network

When two stars collide and merge they form a new star that can stand out against the background population in a starcluster as a blue straggler. In so called collision runaways many stars can merge and may form a very massive star that eventually forms an intermediate mass blackhole. We have performed detailed evolution calculations of merger remnants from collisions between main sequence stars, both for lower mass stars and higher mass stars. These stars can be significantly brighter than ordinary stars of the same mass due to their increased helium abundance. Simplified treatments ignoring this effect give incorrect predictions for the collision product lifetime and evolution in the Hertzsprung-Russell diagram.

E. Glebbeek; O. R. Pols

2007-10-09

370

Pair diffusion, hydrodynamic interactions, and available volume in dense fluids  

PubMed Central

We calculate the pair diffusion coefficient D(r) as a function of the distance r between two hard sphere particles in a dense monodisperse fluid. The distance-dependent pair diffusion coefficient describes the hydrodynamic interactions between particles in a fluid that are central to theories of polymer and colloid dynamics. We determine D(r) from the propagators (Green's functions) of particle pairs obtained from molecular dynamics simulations. At distances exceeding ?3 molecular diameters, the calculated pair diffusion coefficients are in excellent agreement with predictions from exact macroscopic hydrodynamic theory for large Brownian particles suspended in a solvent bath, as well as the Oseen approximation. However, the asymptotic 1/r distance dependence of D(r) associated with hydrodynamic effects emerges only after the pair distance dynamics has been followed for relatively long times, indicating non-negligible memory effects in the pair diffusion at short times. Deviations of the calculated D(r) from the hydrodynamic models at short distances r reflect the underlying many-body fluid structure, and are found to be correlated to differences in the local available volume. The procedure used here to determine the pair diffusion coefficients can also be used for single-particle diffusion in confinement with spherical symmetry. PMID:22830686

Mittal, Jeetain; Hummer, Gerhard

2012-01-01

371

The Warm And Dense Gas In Embedded Low-mass Protostars  

NASA Astrophysics Data System (ADS)

The central regions of embedded low-mass protostars is characterized by warm (T? K) and dense (10^6 cm-3) gas. Although short (10^5 years), these stages are critical for the subsequent evolution of the system. The total mass of the system and the initial conditions for (massive) planet formation are determined. Outflows, disks and envelopes all exist on scales of a few hundred to thousand AU, but except for a few cases, the physical structure has mainly been constrained on scales of a few thousand AU through observations of the cold, quiescent gas and dust. We present recent observations of observations using newly commisioned array receivers HARP-B on the JCMT and CHAMP+ on APEX of rotational emission lines of CO, HCO+ and their isotopologues ranging in frequency from 230 to 900 GHz for to probe the warm and dense gas, both close to the star and within the immedeate surroundings of the protostellar system. Observations were supplemented with continuum data ranging from the near-IR to radio. Special emphasis was put on the results obtained by the c2d program carried out on Spitzer. A large number of sources was observed, ranging from luminous, deeply embedded sources to weak sources where most of the envelope has accreted onto the central star/disk system. Initial results show that the amount of warm and dense gas is not necessarily related. Warm gas seems to be more present at more evolved sources, even at low luminosities, while dense gas is more present in the massive envelopes surrounding the deeply embedded Class 0 protostars. It is also shown that the warm (T 100 K) gas is mostly quiescent and not related to outflow activity. It is likely that the gas is thermally heated.

Van Kempen, Tim; van Dishoeck, E. F.; Hogerheijde, M. R.; Joergensen, J. K.; Guesten, R.; Schilke, P.

2008-03-01

372

Equation of state of neutron star matter, limiting, rotational periods of fast pulsars, and the properties of strange stars  

SciTech Connect

In this paper the following items will be treated: The present status of dense nuclear matter calculations and constraints on the behavior of the associated equation of state at high densities from data on rapidly rotating pulsars. Recent finding of the likely existence of a mixed phase of baryons and quarks forming a coulomb lattice in the dense cores of neutron stars. Review of important findings of recently performed calculations of rapidly rotating compact stars. These are constructed in the framework of general relativity theory for a representative collection of realistic nuclear equations of state. Establish the minimum-possible rotational periods of gravitationally bound neutron stars and self-bound strange stars. Its knowledge is of fundamental importance for the decision between pulsars that can be understood as rotating neutron stars and those that cannot (signature of hypothetical self-bound matter of which strange stars are the likely stellar candidates. Investigate the properties of sequences of strange stars. Specifically, we 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. [Technische Univ. Muenchen, Garching (Germany). Inst. fuer Theoretische Physik]|[Lawrence Berkeley Lab., CA (United States); Glendenning, N.K. [Lawrence Berkeley Lab., CA (United States)

1993-10-25

373

The Initial Conditions for Star Formation in Clusters  

NASA Astrophysics Data System (ADS)

A fundamental problem in astrophysics is how do stars form in clusters of 100 or more, in a region of size 1 pc, in a time of 1 Myr, with a mass distribution following the IMF. Stars form within dense gas cores, and recent work suggests the initial conditions provided by those cores are a key to the problem. We have recently mapped the distribution of dense gas in 5 nearby cluster forming regions via N2H+ 1-0 observations with Mopra, to determine their physical state. Here we propose to measure the kinetic temperature of the cores identified in the maps, through observations of the (1,1) and (2,2) lines of NH3, to determine whether thermal or non-thermal motions dominate, and whether they are bound and so likely to form new stars.

Bourke, Tyler; Jorgensen, Jes; di Francesco, James; Myers, Phil; Caselli, Paola; Hedden, Abigail

2009-04-01

374

The Initial Conditions for Star Formation in Clusters: Temperature  

NASA Astrophysics Data System (ADS)

A fundamental problem in astrophysics is how do stars form in clusters of 100 or more, in a region of size 1 pc, in a time of 1 Myr, with a mass distribution following the IMF. Stars form within dense gas cores, and recent work suggests the initial conditions provided by those cores are a key to the problem. We have recently mapped the distribution of dense gas in 5 nearby cluster forming regions via N2H+ 1-0 observations with Mopra, to determine their physical state. Here we propose to measure the kinetic temperature of the cores identified in the N2H+ map, through mapping observations of the (1,1) and (2,2) lines of ammonia, to determine whether thermal or non-thermal motions dominate, and whether they are bound and so likely to form new stars.

Bourke, Tyler; Friesen, Rachel; Mader, Stacy; Myers, Phil; Hedden, Abigail

2010-10-01

375

Large Area, High Resolution N2H+ studies of dense gas in the Perseus and Serpens Molecular Clouds  

NASA Astrophysics Data System (ADS)

Star formation in molecular clouds occurs over a wide range of spatial scales and physical densities. Understanding the origin of dense cores thus requires linking the structure and kinematics of gas and dust from cloud to core scales. The CARMA Large Area Star Formation Survey (CLASSy) is a CARMA Key Project that spectrally imaged five diverse regions of the Perseus and Serpens Molecular Clouds in N2H+ (J=1-0), totaling over 800 square arcminutes. The observations have 7 angular resolution (~0.01 pc spatial resolution) to probe dense gas down to core scales, and use combined interferometric and single-dish data to fully recover line emission up to parsec scales. CLASSy observations are complete, and this talk will focus on three science results. First, the dense gas in regions with existing star formation has complex hierarchical structure. We present a non-binary dendrogram analysis for all regions and show that dense gas hierarchy correlates with star formation activity. Second, well-resolved velocity information for each dendrogram-identified structure allows a new way of looking at linewidth-size relations in clouds. Specifically, we find that non-thermal line-of-sight velocity dispersion varies weakly with structure size, while rms variation in the centroid velocity increases strongly with structure size. We argue that the typical line-of-sight depth of a cloud can be estimated from these relations, and that our regions have depths that are several times less than their extent on the plane of the sky. This finding is consistent with numerical simulations of molecular cloud turbulence that show that high-density sheets are a generic result. Third, N2H+ is a good tracer of cold, dense gas in filaments; we resolve multiple beams across many filaments, some of which are narrower than 0.1 pc. The centroid velocity fields of several filaments show gradients perpendicular to their major axis, which is a common feature in filaments formed from numerical simulations of planar converging, turbulent flows. All of these initial results imply that over-dense, sheet-like regions in molecular clouds fragment into filaments, and build up hierarchical structures on the pathway to forming dense cores.

Storm, Shaye; Mundy, Lee

2014-07-01

376

Warm-Dense Molecular Gas in the ISM of Starbursts, LIRGs and ULIRGs  

E-print Network

The role of star formation in luminous and ultraluminous infrared galaxies is a hotly debated issue: while it is clear that starbursts play a large role in powering the IR luminosity in these galaxies, the relative importance of possible enshrouded AGNs is unknown. It is therefore important to better understand the role of star forming gas in contributing to the infrared luminosity in IR-bright galaxies. The J=3 level of 12CO lies 33K above ground and has a critical density of ~1.5 X 10^4 cm^-3. The 12CO(J=3-2) line serves as an effective tracer for warm-dense molecular gas heated by active star formation. Here we report on 12CO (J=3-2) observations of 17 starburst spirals, LIRGs and ULIRGs which we obtained with the Heinrich Hertz Submillimeter Telescope on Mt. Graham, Arizona. Our main results are the following: 1. We find a nearly linear relation between the infrared luminosity and warm-dense molecular gas such that the infrared luminosity increases as the warm-dense molecular gas to the power 0.92; We interpret this to be roughly consistent with the recent results of Gao & Solomon (2004a,b). 2. We find L_IR/M_H2 ratios ranging from ~10 to ~128 L_sun/M_sun using a standard CO-H2 conversion factor of 3 X 10^20 cm^-2 (K km s^-1)^-1. If this conversion factor is ~an order of magnitude less, as suggested in a recent statistical survey (Yao et al. 2003), then 2-3 of our objects may have significant contributions to the L_IR by dust-enshrouded AGNs.

Desika Narayanan; Christopher K. Walker; Christopher E. Groppi

2005-04-19

377

HUBBLE CAPTURES THE HEART OF STAR BIRTH  

NASA Technical Reports Server (NTRS)

NASA Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) has captured a flurry of star birth near the heart of the barred spiral galaxy NGC 1808. On the left are two images, one superimposed over the other. The black-and-white picture is a ground-based view of the entire galaxy. The color inset image, taken with the Hubble telescope's Wide Field and Planetary Camera 2 (WFPC2), provides a close-up view of the galaxy's center, the hotbed of vigorous star formation. The ground-based image shows that the galaxy has an unusual, warped shape. Most spiral galaxies are flat disks, but this one has curls of dust and gas at its outer spiral arms (upper right-hand corner and lower left-hand corner). This peculiar shape is evidence that NGC 1808 may have had a close interaction with another nearby galaxy, NGC 1792, which is not in the picture Such an interaction could have hurled gas towards the nucleus of NGC 1808, triggering the exceptionally high rate of star birth seen in the WFPC2 inset image. The WFPC2 inset picture is a composite of images using colored filters that isolate red and infrared light as well as light from glowing hydrogen. The red and infrared light (seen as yellow) highlight older stars, while hydrogen (seen as blue) reveals areas of star birth. Colors were assigned to this false-color image to emphasize the vigorous star formation taking place around the galaxy's center. NGC 1808 is called a barred spiral galaxy because of the straight lines of star formation on both sides of the bright nucleus. This star formation may have been triggered by the rotation of the bar, or by matter which is streaming along the bar towards the central region (and feeding the star burst). Filaments of dust are being ejected from the core into a faint halo of stars surrounding the galaxy's disk (towards the upper left corner) by massive stars that have exploded as supernovae in the star burst region. The portion of the galaxy seen in this 'wide-field' image is about 35,000 light-years across. The right-hand image, taken by WFPC2, provides a closer look at the flurry of star birth at the galaxy's core. The star clusters (blue) can be seen (and many more are likely obscured) amid thick lanes of gas and dust. This image shows that stars are often born in compact clusters within star bursts, and that dense gas and dust heavily obscures the star burst region. The brightest knot of star birth seen here is probably a giant cluster of stars, about 100 light-years in diameter, at the very center of the galaxy. The other star clusters are about 10 to 50 light-years in diameter. The entire star burst region shown here is about 3,000 light-years across. This galaxy is about 40 million light-years away in the southern constellation Columba. The observation was taken Aug. 14, 1997, and was the last of 13 Hubble Space Telescope amateur programs. Credits: Jim Flood, an amateur astronomer affiliated with Sperry Observatory at Union College in New Jersey, and Max Mutchler, a member of the Space Telescope Science Institute staff who volunteered to work with Jim.

2002-01-01

378

Polymer-Sensitized Solar Cells Using Polythiophene Derivatives with Directly Attached Carboxylic Acid Groups  

NASA Astrophysics Data System (ADS)

Polythiophene derivatives with carboxylic acid groups directly attached to the thiophene rings were synthesized for polymer-sensitized solar cells (PSSCs). The polymer layer densely and uniformly covering the surface of the TiO2 particle in the photoanode of the PSSCs allows excitons to diffuse to the polymer/TiO2 interface efficiently. The PSSCs yielded a maximum incident photon-to-current conversion efficiency of about 80% at 480 nm and the open-circuit voltage (VOC) values but also short-circuit current density (JSC) values increased with decreasing hydrolysis ratio of the polymer.

Akitsu, Kenta; Kubo, Takaya; Uchida, Satoshi; Segawa, Hiroshi; Otani, Naoki; Tomura, Misayo; Tamura, Takayuki; Matsumura, Mitsunobu

2012-10-01

379

Nanoparticles of well-defined 4-arm stars made using nanoreactors in water.  

PubMed

In this work, the use of a nanoreactor is demonstrated to rapidly prepare monodisperse polymer nanoparticles in water-based dispersion consisting of 4-arm star polymer via the R-group RAFT approach. It is shown that by heating a nanoparticle assembler above its lower critical solution temperature (LCST), stabilized nanoparticles are formed that act as a template for the 4-arm star RAFT-mediated polymerization of styrene. Monodisperse nanoparticles of size (between 40 and 90 nm) containing monodisperse polymer of desired molecular weight (30-95 k) are obtained with little star-star coupling due to compartmentalization. The nanoreactor technique allows independent control over the size and molecular weight with a 4-arm star topology. PMID:24288277

Sebakhy, Khaled O; Gavrilov, Mikhail; Valade, David; Jia, Zhongfan; Monteiro, Michael J

2014-01-01

380

Chemistry and Radiative Transfer of Water in Cold, Dense Clouds  

E-print Network

The Herschel Space Observatory's recent detections of water vapor in the cold, dense cloud L1544 allow a direct comparison between observations and chemical models for oxygen species in conditions just before star formation. We explain a chemical model for gas phase water, simplified for the limited number of reactions or processes that are active in extreme cold ($water is removed from the gas phase by freezing onto grains and by photodissociation. Water is formed as ice on the surface of dust grains from O and OH and released into the gas phase by photodesorption. The reactions are fast enough with respect to the slow dynamical evolution of L1544 that the gas phase water is in equilibrium for the local conditions thoughout the cloud. We explain the paradoxical radiative transfer of the H$_2$O ($1_{10}-1_{01}$) line. Despite discouragingly high optical depth caused by the large Einstein A coefficient, the subcritical excitation in the cold, rarefied H$_2$ causes the line brightnes...

Keto, Eric; Caselli, Paola

2014-01-01

381

Intelligent manufacturing of polymers  

Microsoft Academic Search

Integrated multivariable process control can have a significant strategic impact on polymer plant operability and economics. Polymer manufacturers face increasing pressures for production cost reductions and more stringent polymer quality requirements. The main goals in operating a polymer reactor (e.g. high yield, better product quality and safe operation) are very difficult, if not impossible, to achieve without efficient and reliable

C. Kiparissides; J. Morris

1996-01-01

382

Study of iso/dense bias of BARCs and gap-fill materials on via wafers  

NASA Astrophysics Data System (ADS)

The topography of a back-end wafer contains high-aspect vias that are unevenly distributed on a wafer with pitches ranging from 1:1 dense to isolated. The difference in via density causes thickness bias across the wafer, which causes the shift of resist depth of focus and critical dimension swing. The bottom anti-reflective coating (BARC) topography is formed basically after spin coating and reshaped through thermal reflowing when the coating is baked at high temperature to cure the film. In this paper, we discuss the thicknesess at isolated and dense via patterned areas in the spin-coating process and the baking process. Spin coating is a method commonly used to cast BARC and gap-fill materials on silicon wafers. The first stage of spin coating is the deposition of the coating liquid onto the wafer. The second stage is when the substrate is accelerated up to its final, desired rotation speed. The third stage is when the substrate is spinning at a constant rate and fluid viscous forces dominate the fluid thinning behavior. The fourth stage is when the substrate is spinning at a constant rate and solvent evaporation dominates the coating thinning behavior. Viscous flow and solvent evaporation occur throughout all stages. After spin coating, high-temperature baking cures the film and makes it insoluble in organic solvents that are used in the next spin-coating step. However, this step also gives the polymer a chance to undergo thermal flow because the bake temperature is much higher than the polymer's glass transition temperature (T g). A chemical reaction occurs at the same time to form a polymer network that stops the thermal flow. The study of how far material can flow before the gel point of the polymer has been reached is presented in this paper. The calculation of the material transformation due to solvent evaporation and polymer rheometry is based on dynamic and kinetic effects. The work described in this paper showed how the parameters related to material properties and to the chemical reaction of crosslinking affected iso/dense bias. This work gives us guidance regarding what kind of materials and process conditions are good for planarization.

Huang, Runhui

2006-03-01

383

Hopping conductivity in dense hydrogen fluid  

NASA Astrophysics Data System (ADS)

A transition from semiconducting behavior to conductivities typical for simple metals was observed in dense hydrogen fluid at 1.4 Mbar and 3000 K in multiple shock-compression experiments [S. T. Weir, A. C. Mitchell, and W. J. Nellis, Phys. Rev. Lett. 76, 1860 (1996)]. Various mechanisms such as band gap closure, self-doping, or thermally activated transport have been proposed to explain this nonmetal-to-metal transition. We perform an exploratory calculation of the hopping conductivity in dense hydrogen fluid which is considered as a partially dissociated system of H atoms and H2 molecules. It is shown that hopping processes between H atoms play an important role in this nonmetal-to-metal transition.

Redmer, Ronald; Rpke, Gerd; Kuhlbrodt, Sandra; Reinholz, Heidi

2001-06-01

384

The kinetic chemistry of dense interstellar clouds  

NASA Technical Reports Server (NTRS)

A model of the time-dependent chemistry of dense interstellar clouds is formulated to study the dominant chemical processes in carbon and oxygen isotope fractionation, the formation of nitrogen-containing molecules, and the evolution of product molecules as a function of cloud density and temperature. The abundances of the dominant isotopes of the carbon- and oxygen-bearing molecules are calculated. The chemical abundances are found to be quite sensitive to electron concentration since the electron concentration determines the ratio of H3(+) to He(+), and the electron density is strongly influenced by the metals abundance. For typical metal abundances and for H2 cloud density not less than 10,000 molecules/cu cm, nearly all carbon exists as CO at late cloud ages. At high cloud density, many aspects of the chemistry are strongly time dependent. Finally, model calculations agree well with abundances deduced from observations of molecular line emission in cold dense clouds.

Graedel, T. E.; Langer, W. D.; Frerking, M. A.

1982-01-01

385

Dense Deposit Disease and C3 Glomerulopathy  

PubMed Central

Summary C3 glomerulopathy refers to those renal lesions characterized histologically by predominant C3 accumulation within the glomerulus, and pathogenetically by aberrant regulation of the alternative pathway of complement. Dense deposit disease is distinguished from other forms of C3 glomerulopathy by its characteristic appearance on electron microscopy. The extent to which dense deposit disease also differs from other forms of C3 glomerulopathy in terms of clinical features, natural history, and outcomes of treatment including renal transplantation is less clear. We discuss the pathophysiology of C3 glomerulopathy, with evidence for alternative pathway dysregulation obtained from affected individuals and complement factor H (Cfh)-deficient animal models. Recent linkage studies in familial C3 glomerulopathy have shown genomic rearrangements in the Cfh-related genes, for which the novel pathophysiologic concept of Cfh deregulation has been proposed. PMID:24161036

Barbour, Thomas D.; Pickering, Matthew C.; Terence Cook, H.

2013-01-01

386

Dense silica coatings on ceramic powder particles  

SciTech Connect

Dense silica coatings on the surface of inorganic powders particles are prepared by the hydrolysis of tetraethoxysilane (TEOS) in alcoholic suspensions. In a first reaction step, the TEOS is pre-hydrolysed in acidic solution and afterwards, a suspension of powder particles in this reaction solution is treated with ammonia which results in a dense silica coating of typically 10 - 100 nm thickness. Different luminescent powders which are used in the manufacture of cathode-ray tubes or fluorescent lamps have been coated by this procedure. The silica coating forms a transparent layer and the suspension properties of the coated powders are determined by the silica layer. The silica coating also protects sulfidic luminescent powders from being attacked by oxidizing agents like dichromate ions which are used in the suspension formulations for TV tube fabrication.

Opitz, J.F.A.; Mayr, W. [Philips GmbH Forschungslaboratorien, Aachen (Germany)

1995-09-01

387

The effects of stellar dynamics on the evolution of young dense stellar systems  

E-print Network

In the present paper we report on first results of a project in Brussels where we study the effects of stellar dynamics on the evolution of young dense stellar systems using the 3 decades expertise in massive star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass loss formalism on the formation of intermediate mass black holes.

H. Belkus; J. Van Bever; D. Vanbeveren

2004-10-21

388

Neutrino scattering from hydrodynamic modes in hot and dense neutron matter  

E-print Network

We calculate the scattering rate of low energy neutrinos in hot and dense neutron matter encountered in neutrons stars and supernova in the hydrodynamic regime. We find that the Brillouin peak, associated with the sound mode, and the Rayleigh peak, associated with the thermal diffusion mode, dominate the dynamic structure factor. Although the total scattering cross section is constrained by the compressibility sum rule, the differential cross-section calculated using the hydrodynamic response function differs from results obtained in approximate treatments often used in astrophysics such as random phase approximations (RPA). We identified these differences and discuss its implications for neutrino transport in supernova.

Gang Shen; Sanjay Reddy

2013-11-24

389

Neutrino scattering from hydrodynamic modes in hot and dense neutron matter  

NASA Astrophysics Data System (ADS)

We calculate the scattering rate of low-energy neutrinos in hot and dense neutron matter encountered in neutrons stars and supernovae in the hydrodynamic regime. We find that the Brillouin peak, associated with the sound mode, and the Rayleigh peak, associated with the thermal diffusion mode, dominate the dynamic structure factor. Although the total scattering cross section is constrained by the compressibility sum rule, the differential cross section calculated using the hydrodynamic response function differs from results obtained in approximate treatments often used in astrophysics such as random phase approximations. We identified these differences and discuss their implications for neutrino transport in supernovae.

Shen, Gang; Reddy, Sanjay

2014-03-01

390

Frontier of the physics of dense plasmas and planetary interiors: experiments, theory, applications  

SciTech Connect

Recent developments of dynamic x-ray characterization experiments of dense matter are reviewed, with particular emphasis on conditions relevant to interiors of terrestrial and gas giant planets. These studies include characterization of compressed states of matter in light elements by x-ray scattering and imaging of shocked iron by radiography. Several applications of this work are examined. These include the structure of massive 'super-Earth' terrestrial planets around other stars, the 40 known extrasolar gas giants with measured masses and radii, and Jupiter itself, which serves as the benchmark for giant planets.

Saumon, Didier [Los Alamos National Laboratory; Fortney, Jonathan J [UC SANTA CRUZ; Glenzer, Siegfried H [LLNL; Koenig, Michel [LULI (FRANCE); Brambrink, E [LULI(FRANCE); Militzer, Burkhard [UC BERKELEY; Valencia, Diana [HARVARD U

2008-01-01

391

Dense gas dispersion modeling for aqueous releases  

E-print Network

friends while attending Texas AEcM University. Special appreciation is given to my family for their unconditional support and love. TABLE OF CONTENTS ABSTRACT. . . Page DEDICATION. ACKNOWLEDGEMENTS. VI TABLE OF CONTENTS. VI I LIST OF FIGURES.... . LIST OF TABLES. IX XI CHAPTER I INTRODUCTION. II BACKGROUND. . II-1, Historical Background. II-2. Development of a Dense-Gas Cloud. II-3. Thermodynamics of Gas Dispersion. III NON-IDEAL THERMODYNAMICS . . IV MODEL IMPLEMENTATION. . 18 22 26...

Lara, Armando

2012-06-07

392

Structures for dense, crack free thin films  

DOEpatents

The process described herein provides a simple and cost effective method for making crack free, high density thin ceramic film. The steps involve depositing a layer of a ceramic material on a porous or dense substrate. The deposited layer is compacted and then the resultant laminate is sintered to achieve a higher density than would have been possible without the pre-firing compaction step.

Jacobson, Craig P. (Lafayette, CA); Visco, Steven J. (Berkeley, CA); De Jonghe, Lutgard C. (Lafayette, CA)

2011-03-08

393

Computer codes for dispersion of dense gas  

SciTech Connect

Two models for describing the behavior of dense gases have been adapted for specific applications at the Savannah River Plant (SRP) and have been programmed on the IBM computer. One of the models has been used to predict the effect of a ruptured H/sub 2/S storage tank at the 400 Area. The other model has been used to simulate the effect of an unignited release of H/sub 2/S from the 400-Area flare tower.

Weber, A.H.; Watts, J.R.

1982-02-01

394

Cloud and Star Formation in Disk Galaxy Models with Feedback  

E-print Network

We include feedback in global hydrodynamic simulations in order to study the star formation properties, and gas structure and dynamics, in models of galactic disks. We extend previous models by implementing feedback in gravitationally bound clouds: momentum is injected at a rate proportional to the star formation rate. This mechanical energy disperses cloud gas back into the surrounding ISM, truncating star formation in a given cloud, and raising the overall level of ambient turbulence. Propagating star formation can however occur as expanding shells collide, enhancing the density and triggering new cloud and star formation. By controlling the momentum injection per massive star and the specific star formation rate in dense gas, we find that the negative effects of high turbulence outweigh the positive ones, and in net feedback reduces the fraction of dense gas and thus the overall star formation rate. The properties of the large clouds that form are not, however, very sensitive to feedback, with cutoff masses of a few million solar masses, similar to observations. We find a relationship between the star formation rate surface density and the gas surface density with a power law index ~2 for our models with the largest dynamic range, consistent with theoretical expectations for our model of disk flaring. We point out that the value of the "Kennicutt-Schmidt" index depends on the thickness of the disk. With our simple feedback prescription (a single combined star formation event per cloud), we find that global spiral patterns are not sustained; less correlated feedback and smaller scale turbulence appear to be necessary for spiral patterns to persist.

Rahul Shetty; Eve C. Ostriker

2008-05-26

395

Avoiding Communication in Dense Linear Algebra Grey Ballard  

E-print Network

Avoiding Communication in Dense Linear Algebra Grey Ballard Electrical Engineering and Computer on servers or to redistribute to lists, requires prior specific permission. #12;Avoiding Communication #12;Avoiding Communication in Dense Linear Algebra Copyright 2013 by Grey Malone Ballard #12

California at Berkeley, University of

396

Photoabsorption in Hot Dense Plasmas W. R. Johnson  

E-print Network

Photoabsorption in Hot Dense Plasmas W. R. Johnson Department of Physics ­ 225 Nieuwland Science version of the time-dependent local-density approxi- mation designed to study photoabsorption in hot dense

Johnson, Walter R.

397

Star formation - An overview  

NASA Technical Reports Server (NTRS)

Methods for studying star formation are reviewed. Stellar clusters and associations, as well as field stars, provide a fossil record of the star formation process. Regions of current star formation provide a series of snapshots of different epochs of star formation. A simplified picture of individual star formation as it was envisioned in the late 1970s is contrasted with the results of recent observations, in particular the outflow phenomenon.

Evans, N. J., II

1985-01-01

398

Spitzer Digs Up Hidden Stars  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] 3-Panel Version Figure 1 [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Visible Light Figure 2 Infrared (IRAC) Figure 3 Combined Figure 4

Two rambunctious young stars are destroying their natal dust cloud with powerful jets of radiation, in an infrared image from NASA's Spitzer Space Telescope.

The stars are located approximately 600 light-years away in a cosmic cloud called BHR 71. In visible light (left panel), BHR 71 is just a large black structure. The burst of yellow light toward the bottom of the cloud is the only indication that stars might be forming inside. In infrared light (center panel), the baby stars are shown as the bright yellow smudges toward the center. Both of these yellow spots have wisps of green shooting out of them. The green wisps reveal the beginning of a jet. Like a rainbow, the jet begins as green, then transitions to orange, and red toward the end. The combined visible-light and infrared composite (right panel) shows that a young star's powerful jet is responsible for the rupture at the bottom of the dense cloud in the visible-light image. Astronomers know this because burst of light in the visible-light image overlaps exactly with a jet spouting-out of the left star, in the infrared image.

The jets' changing colors reveal a cooling effect, and may suggest that the young stars are spouting out radiation in regular bursts. The green tints at the beginning of the jet reveal really hot hydrogen gas, the orange shows warm gas, and the reddish wisps at the end represent the coolest gas. The fact that gas toward the beginning of the jet is hotter than gas near the middle suggests that the stars must give off regular bursts of energy -- and the material closest to the star is being heated by shockwaves from a recent stellar outburst. Meanwhile, the tints of orange reveal gas that is currently being heated by shockwaves from a previous stellar outburst. By the time these shockwaves reach the end of the jet, they have slowed down so significantly that the gas is only heated a little, and looks red. The combination of views also brings out some striking details that evaded visible-light detection. For example, the yellow dots scattered throughout the image are actually young stars forming inside BHR 71. Spitzer also uncovered another young star with jets, located to the right of the powerful jet seen in the visible-light image. Spitzer can see details that visible-light telescopes don't, because its infrared instruments are sensitive to 'heat.'

The infrared image is made up of data from Spitzer's infrared array camera. Blue shows infrared light at 3.6 microns, green is light at 4.5 microns, and red is light at 8.0 microns.

2007-01-01

399

A runaway collision in a young star cluster as the origin of the brightest supernova.  

PubMed

Supernova SN 2006gy in the galaxy NGC 1260 is the most luminous recorded. Its progenitor might have been a very massive (>100 Mo, where is the mass of the Sun) star, but that interpretation is incompatible with hydrogen in the spectrum of the supernova; stars >40 Moare believed to have shed their hydrogen envelopes several hundred thousand years before the explosion. Alternatively, the progenitor might have arisen from the merger of two massive stars. Here we show that the collision frequency of massive stars in a dense and young cluster (of the kind to be expected near the centre of a galaxy) is sufficient to provide a reasonable chance that SN 2006gy resulted from such a bombardment. If this is the correct explanation, then we predict that when the supernova fades (in a year or so) a dense cluster of massive stars will become visible at the site of the explosion. PMID:18004377

Portegies Zwart, Simon F; van den Heuvel, Edward P J

2007-11-15

400

Stresa, Italy, 25-27 April 2007 STUDIES OF POLYMER DEFORMATION AND RECOVERY IN HOT EMBOSSING  

E-print Network

Stresa, Italy, 25-27 April 2007 STUDIES OF POLYMER DEFORMATION AND RECOVERY IN HOT EMBOSSING X. C focuses on the microstructure formation, polymer deformation and recovery in micro hot embossing, Singapore 639798 * E-mail (X.C. Shan): xcshan@simtech.A-star.edu.sg ABSTRACT In large area micro hot

Paris-Sud XI, Université de

401

Dynamical evolution of rotating dense stellar systems with embedded black holes  

E-print Network

Evolution of self-gravitating rotating dense stellar systems (e.g. globular clusters, galactic nuclei) with embedded black holes is investigated. The interaction between the black hole and stellar component in differential rotating flattened systems is followed. The interplay between velocity diffusion due to relaxation and black hole star accretion is investigated together with cluster rotation using 2D+1 Fokker-Planck numerical methods. The models can reproduce the Bahcall-Wolf solution $f \\propto E^{1/4}$ ($n \\propto r^{-7/4}$) inside the zone of influence of the black hole. Gravo-gyro and gravothermal instabilities conduce the system to a faster evolution leading to shorter collapse times with respect to the non-rotating systems. Angular momentum transport and star accretion support the development of central rotation in relaxation time scales. We explore system dissolution due to mass-loss in the presence of an external tidal field (e.g. globular clusters in galaxies).

J. Fiestas; R. Spurzem

2008-10-21

402

Polymer brush covalently attached to OH-functionalized mica surface via surface-initiated ATRP: control of grafting density and polymer chain length.  

PubMed

The controlled grafting density of poly(tert-butyl acrylate) was studied on OH-activated mica substrates via surface-initiated atom-transfer radical polymerization (ATRP). By properly adjusting parameters such as the immobilization reaction time and the concentration of an ATRP initiator, a wide range of initiator surface coverages and hence polymer densities on mica were possible. The covalently immobilized initiator successfully promoted the polymerization of tert-butyl acrylate on mica surfaces. The resulting polymer layer thickness was measured by AFM using a step-height method. Linear relationships of the polymer thickness with respect to the molecular weight of the free polymer and with respect to the monomer conversion were observed, suggesting that ATRP is well controlled and relatively densely end-grafted layers were obtained. The polymer grafting density controlled by adjusting the initiator surface coverage was confirmed by the polymer layer swelling capacity and film thickness measurements. PMID:19256467

Lego, Batrice; Franois, Marion; Skene, W G; Giasson, Suzanne

2009-05-01

403

Chromosomal "Fingerprints" of Prior Exposure to Densely Ionizing Radiation  

E-print Network

COMMENTARY Chromosomal "Fingerprints" of Prior Exposure to Densely Ionizing Radiation D. J. Brenner. Chromosomal "Fingerprints" of Prior Exposure to Densely Ionizing Radiation. Radiat. Res. 140,134-142 (1994 interest in finding a detectable biological "fingerprint" preferentially produced by densely ionizing

Brenner, David Jonathan

404

Dense water formation and circulation in the Barents Sea  

Microsoft Academic Search

Dense water masses from Arctic shelf seas are an important part of the Arctic thermohaline system. We present previously unpublished observations from shallow banks in the Barents Sea, which reveal large interannual variability in dense water temperature and salinity. To examine the formation and circulation of dense water, and the processes governing interannual variability, a regional coupled ice-ocean model is

M. rthun; R. B. Ingvaldsen; L. H. Smedsrud; C. Schrum

2011-01-01

405

Optimal dense coding with arbitrary pure entangled states  

E-print Network

We examine dense coding with an arbitrary pure entangled state sharing between the sender and the receiver. Upper bounds on the average success probability in approximate dense coding and on the probability of conclusive results in unambiguous dense coding are derived. We also construct the optimal protocol which saturates the upper bound in each case.

Yuan Feng; Runyao Duan; Zhengfeng Ji

2006-04-20

406

Brownian motion of black holes in stellar systems with non-Maxwellian distribution of the field stars  

Microsoft Academic Search

A massive black hole at the center of a dense stellar system, such as a globular cluster or a galactic nucleus, is subject to a random walk due gravitational encounters with nearby stars. It behaves as a Brownian particle, since it is much more massive than the surrounding stars and moves much more slowly than they do. If the distribution

Isabel Tamara Pedron; Carlos H. Coimbra-Arajo

2007-01-01

407

On stars and Steiner stars Adrian Dumitrescu  

E-print Network

On stars and Steiner stars Adrian Dumitrescu Csaba D. T´oth Guangwu Xu§ March 9, 2009 Abstract A Steiner star for a set P of n points in Rd connects an arbitrary point in Rd to all points of P, while a star connects one of the points in P to the remaining n - 1 points of P. All connections are realized

Dumitrescu, Adrian

408

The role of low-mass star clusters in massive star formation. The Orion case  

NASA Astrophysics Data System (ADS)

Context. Different theories have been proposed to explain the formation of massive stars: two are based on accretion processes (monolithic core accretion and competitive accretion), and another on coalescence of low- and intermediate-mass stars. To distinguish between these theories, it is crucial to establish the distribution, the extinction, and the density of young low-mass stars in massive star-forming regions. X-ray observations can penetrate the very obscured cradles of massive stars, directly sampling the distribution of the population of pre-main sequence (PMS) low-mass stars in these regions. Aims: Our aim is to analyze deep X-ray observations of the Orion massive star-forming region using the Chandra Orion Ultradeep Project (COUP) catalog, to reveal the distribution of the population and clustering of PMS low-mass stars, and to study their possible role in massive star formation. Methods: We studied the distribution of PMS low-mass stars with X-ray emission in Orion as a function of extinction with two different methods: a spatial gridding and a close-neigbors method with cells of ~0.03 0.03 pc2, the typical size of protostellar cores. We derived density maps of the stellar population and calculated cluster stellar densities. Results: Consistent with previous studies, we found that PMS low-mass stars cluster toward the three massive star-forming regions: the Trapezium cluster (TC), the Orion hot core (OHC), and the OMC1-S region. We derived PMS low-mass stellar densities of 105 stars pc-3 in the TC and OMC1-S, and of 106 stars pc-3 in the OHC. The close association between the low-mass star clusters with massive star cradles supports the role of these clusters in the formation of massive stars. The X-ray observations show for the first time in the TC that low-mass stars with intermediate extinction are clustered toward the position of the most massive star ?1 Ori C, which is surrounded by a ring of non-extincted PMS low-mass stars. This "envelope-core" structure is also supported by infrared and optical observations. Our analysis suggests that at least two basic ingredients are needed in massive star formation: the presence of dense gas and a cluster of low-mass stars. The scenario that better explains our findings assumes high fragmentation in the parental core, accretion at subcore scales that forms a low-mass stellar cluster, and subsequent competitive accretion. Finally, although coalescence does not seem a common mechanism for building up massive stars, we show that a single stellar merger may have occurred in the evolution of the OHC cluster, favored by the presence of disks, binaries, and gas accretion.

Rivilla, V. M.; Martn-Pintado, J.; Jimnez-Serra, I.; Rodrguez-Franco, A.

2013-06-01

409

Local mobility of polymer chains with specific interactions  

NASA Astrophysics Data System (ADS)

The local mobility of polymer chains depends on single-chain properties as well as the local environment of the chain segments. Recent experiments on polymer blends have shown that hydrogen bonding has a large effect on the segmental relaxation of the polymers in the blend; cf. Ref. [1]. In earlier work, we developed a simple lattice model for poly (ethylene oxide) (PEO) in aqueous solutions that accounts for entropic and enthalpic effects of specific interactions. We applied it to the Soret effect of PEO in ethanol/water mixtures and found qualitative agreement between theory and experimental data. In this work, we consider a lattice model for dense polymeric systems with specific interactions and present first results for the effect of hydrogen bonding on the mobility of chain segments. [1] S. H. Zhang, X. Jin, P. C. Painter, and J. Runt, Polymer 45, 3993 (2004).

Luettmer-Strathmann, Jutta

2005-03-01

410

Transport properties of dense matter. II  

Microsoft Academic Search

Exact solutions for the transport coefficients of a multicomponent system of several interacting Fermi liquids are given in the low temperature limit. The transport coefficients are found by solving a set of coupled Boltzmann transport equations. These solutions for the transport coefficients are used to evaluate the thermal conductivity and viscosity of neutron star matter in the density regime where

E. Flowers; N. Itoh

1979-01-01

411

Star forming filaments in warm dark models  

E-print Network

We performed a hydrodynamical cosmological simulation of the formation of a Milky Way-like galaxy in a warm dark matter (WDM) cosmology. Smooth and dense filaments, several co-moving mega parsec long, form generically above z 2 in this model. Atomic line cooling allows gas in the centres of these filaments to cool to the base of the cooling function, resulting in a very striking pattern of extended Lyman-limit systems (LLSs). Observations of the correlation function of LLSs might hence provide useful limits on the nature of the dark matter. We argue that the self-shielding of filaments may lead to a thermal instability resulting in star formation. We implement a sub-grid model for this, and find that filaments rather than haloes dominate star formation until z 6. Reionisation decreases the gas density in filaments, and the more usual star formation in haloes dominates below z 6, although star formation in filaments continues until z=2. Fifteen per cent of the stars of the z=0 galaxy formed in filaments. At hi...

Gao, Liang; Springel, Volker

2014-01-01

412

Constraints on the dense matter EOS from the measurements of PSR J0737-3039A moment of inertia and PSR J0751+1807 mass  

E-print Network

The moment of inertia of the pulsar A in the neutron star binary J0737-3039 will soon be measurable through detailed measurements of the periastron advance. We present the calculation of the moment of inertia of neutron stars with the masses of the components of the binary J0737-3039 for a broad range of equations of state of dense matter and discuss the implications of such measurement for constraining the equation of state. An observational determination of the moment of inertia of the pulsar A in J0737-3039 with the accuracy of 10% shall narrow down considerably the range of viable equations of state. We also show that limits on maximal mass of a neutron star provide a complementary set of constraints on the properties of dense nuclear matter.

M. Bejger; T. Bulik; P. Haensel

2005-08-03

413

Grain Growth and Silicates in Dense Clouds  

NASA Astrophysics Data System (ADS)

Interstellar silicates are likely to be a part of all grains responsible for visual extinction (Av) in the diffuse interstellar medium (ISM) and dense clouds. A correlation between Av and the depth of the 9.7 micron silicate feature (measured as optical depth, tau(9.7)) is expected if the dust species are well mixed. In the diffuse ISM, such a correlation is observed for lines of sight in the solar neighborhood. A previous study of the silicate absorption feature in the Taurus dark cloud showed a tendency for the correlation to break down at high Av (Whittet et al. 1988, MNRAS, 233, 321), but the scatter was large.We have acquired Spitzer Infrared Spectrograph data of several lines of sight in the IC 5146, Barnard 68, Chameleon I and Serpens dense clouds. Our data set spans an Av range between 2 and 35 magnitudes. All lines of sight show the 9.7 micron silicate feature. The Serpens data appear to follow the diffuse ISM correlation line whereas the data for the other clouds show a non-linear correlation between the depth of the silicate feature relative to Av, much like the trend observed in the Taurus data. In fact, it appears that for visual extinctions greater than about 10 mag, tau(9.7) begins to level off. This decrease in the growth of the depth of the 9.7 micron feature with increasing Av could indicate the effects of grain growth in dense clouds. In this poster, we explore the possibility that grain growth causes an increase in opacity (Av) without causing a corresponding increase in tau(9.7).

Pendleton, Yvonne J.; Chiar, J. E.; Ennico, K.; Boogert, A.; Greene, T.; Knez, C.; Lada, C.; Roellig, T.; Tielens, A.; Werner, M.; Whittet, D.

2006-06-01

414

Impact-activated solidification of dense suspensions  

NASA Astrophysics Data System (ADS)

Shear-thickening, non-Newtonian fluids have typically been investigated under steady-state conditions. This approach has produced two pictures for suspension response to imposed forcing. In the weak shear-thickening picture, the response is typically attributed to the hydrodynamic interactions giving rise to hydroclusters, small groups of particles interacting through lubrication forces. At the other end of the spectrum, in the discontinuous shear-thickening regime, the response can be seen as a system-wide jamming that is ultimately limited in strength by the system boundaries. While these steady-state pictures have proven extremely useful, some of the most interesting phenomena associated with dense suspensions is transient and local in character. A prototypical example is the extraordinarily large impact resistance of dense suspensions such as cornstarch and water. When poked lightly these materials respond like a fluid, but when punched or kicked they seem to temporarily ``solidify'' and provide enormous resistance to the motion of the impacting object. Using an array of experimental techniques, including high-speed video, embedded force and acceleration sensing, and x-ray imaging, we are able to investigate the dynamic details this process as it unfolds. We find that an impacting object drives the rapid growth of a jammed, solid-like region directly below the impact site. Being coupled to the surrounding fluid by grain-mediated lubrication forces, this creates substantial peripheral flow and ultimately leads to the sudden extraction of the impactor's momentum. With a simple jamming picture to describe the solidification and an added mass model to explain the force on the rod, we are able to predict the forces on the impactor quantitatively. These findings highlight the importance of the non-equilibrium character of dense suspensions near jamming and might serve as a bridge between the weak and discontinuous shear-thickening pictures.

Waitukaitis, Scott

2013-03-01

415

Lipid-absorbing Polymers  

NASA Technical Reports Server (NTRS)

The removal of bile acids and cholesterol by polymeric absorption is discussed in terms of micelle-polymer interaction. The results obtained with a polymer composed of 75 parts PEO and 25 parts PB plus curing ingredients show an absorption of 305 to 309%, based on original polymer weight. Particle size effects on absorption rate are analyzed. It is concluded that crosslinked polyethylene oxide polymers will absorb water, crosslinked polybutadiene polymers will absorb lipids; neither polymer will absorb appreciable amounts of lipids from micellar solutions of lipids in water.

Marsh, H. E., Jr.; Wallace, C. J.

1973-01-01

416

Laser Sheet Dropsizing of dense sprays  

NASA Astrophysics Data System (ADS)

A new technique has been developed that produces instantaneous or time-averaged two-dimensional images of Sauter Mean Diameter from a spray. Laser Sheet Dropsizing (LSD) combines elastic and inelastic light scattered from a laser sheet. Compared with Phase Doppler Anemometry (PDA), the new technique offers advantages in increased spatial and temporal resolution and more rapid spray characterisation. Moreover, the technique can also be applied to dense sprays. Successful implementation requires careful calibration, particularly of the effect of dye concentration on the dropsize dependence of the inelastic scattered light.

Le Gal, P.; Farrugia, N.; Greenhalgh, D. A.

1999-02-01

417

Spin light of electron in dense matter  

E-print Network

We derive the modified Dirac equation for an electron undergos an influence of the standard model interaction with the nuclear matter. The exact solutions for this equation and the electron energy spectrum in matter are obtained. This establishes a rather powerful method for investigation of different processes that can appear when electrons propagate in background matter. On this basis we study in detail the spin light of electron in nuclear matter, a new type of electromagnetic radiation which can be emitted by an electron moving in dense matter.

Alexander Grigoriev; Sergey Shinkevich; Alexander Studenikin; Alexei Ternov; Ilya Trofimov

2006-11-09

418

Molecular dissociation in hot, dense hydrogen  

Microsoft Academic Search

We present a path-integral Monte Carlo study of dissociation in dense hydrogen (1.75{ital r}{sub {ital s}}2.2, with {ital r}{sub {ital s}} the Wigner sphere radius). As the temperature is lowered from 10⁵ to 5000 K, a molecular hydrogen gas forms spontaneously from a neutral system of protons and electrons. At high density, {ital r}{sub {ital s}}>2.0, thermally activated dissociation is

W. R. Magro; D. M. Ceperley; C. Pierleoni; B. Bernu

1996-01-01

419

Ballistic Impact of Dense Particle Suspensions  

E-print Network

The ballistic impact of various dense particle suspensions is of interest for the development of superior materials for personal protective equipment. The dynamic response of the fluids under impact of a fragment simulating projectile at various incident velocities was examined for this purpose. High-speed fluid dynamic videos of these ballistic impacts were used to analyze the effects of various suspension parameters on the response of the fluids. It was found experimentally that the shear thickening behaviour of the suspensions dominated the response at low incident velocities, but the results converge based on density at higher impact velocities.

Marr, Bradley J; Higgins, Andrew J; Frost, David L; Ouellet, Simon

2011-01-01

420