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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

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

DOEpatents

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

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

1995-01-01

3

Anomalous structure factor of dense star polymer solutions  

E-print Network

The core-core structure factor of dense star polymer solutions in a good solvent is shown theoretically to exhibit an unusual behaviour above the overlap concentration. Unlike usual liquids, these solutions display a structure factor whose first peak decreases by increasing density while the second peak grows. The scenario repeats itself with the subsequent peaks as the density is further enhanced. For low enough arm numbers $f$ ($f \\leq 32$), various different considerations lead to the conclusion that the system remains fluid at all concentrations.

M. Watzlawek; H. Loewen; C. N. Likos

1998-06-22

4

Cooling of dense stars  

NASA Technical Reports Server (NTRS)

Some recent work on thermal properties of dense stars is described. It is now generally believed that pulsars are rotating, magnetic neutron stars (Gold, 1968). Moreover, theoretical considerations and some observational evidence (such as the speed-ups of the Crab and Vela pulsars) suggest the presence of superfluids in neutron stars. In the earlier cooling calculations the effect of magnetic fields and superfluidity was not taken into account. In the recent work, emphasis was placed on the effect of these new factors, which were expected to reduce cooling rates significantly. The new outcome may prove valuable for the understanding of pulsar and X-ray star problems.

Tsuruta, S.

1974-01-01

5

Polydisperse star polymer solutions  

E-print Network

We analyze the effect of polydispersity in the arm number on the effective interactions, structural correlations and the phase behavior of star polymers in a good solvent. The effective interaction potential between two star polymers with different arm numbers is derived using scaling theory. The resulting expression is tested against monomer-resolved molecular dynamics simulations. We find that the theoretical pair potential is in agreement with the simulation data in a much wider polydispersity range than other proposed potentials. We then use this pair potential as an input in a many-body theory to investigate polydispersity effects on the structural correlations and the phase diagram of dense star polymer solutions. In particular we find that a polydispersity of 10%, which is typical in experimental samples, does not significantly alter previous findings for the phase diagram of monodisperse solutions.

Christian von Ferber; Arben Jusufi; Martin Watzlawek; Christos N. Likos; Hartmut Lowen

2000-07-31

6

STAR FORMATION IN DENSE CLUSTERS  

SciTech Connect

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

Myers, Philip C., E-mail: pmyers@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2011-12-10

7

Hydrodynamic stellar interactions in dense star clusters  

NASA Technical Reports Server (NTRS)

Highly detailed HST observations of globular-cluster cores and galactic nuclei motivate new theoretical studies of the violent dynamical processes which govern the evolution of these very dense stellar systems. These processes include close stellar encounters and direct physical collisions between stars. Such hydrodynamic stellar interactions are thought to explain the large populations of blue stragglers, millisecond pulsars, X-ray binaries, and other peculiar sources observed in globular clusters. Three-dimensional hydrodynamics techniques now make it possible to perform realistic numerical simulations of these interactions. The results, when combined with those of N-body simulations of stellar dynamics, should provide for the first time a realistic description of dense star clusters. Here I review briefly current theoretical work on hydrodynamic stellar interactions, emphasizing its relevance to recent observations.

Rasio, Frederic A.

1993-01-01

8

Cold Dense Baryonic Matter and Compact Stars  

NASA Astrophysics Data System (ADS)

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

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

9

White Dwarf Sequences in Dense Star Clusters  

E-print Network

We use the results of realistic N-body simulations to investigate the appearance of the white dwarf population in dense star clusters. We show that the presence of a substantial binary population in a star cluster, and the interaction of this population with the cluster environment, has serious consequences for the morphology of the observed white dwarf sequence and the derived white dwarf cooling age of the cluster. We find that over time the dynamical evolution of the cluster -- mass-segregation, stellar interactions and tidal stripping -- hampers the use of white dwarfs as tracers of the initial mass function, and also leads to a significant enhancement of the white dwarf mass fraction. Future observations of star clusters should be conducted slightly interior to the half-mass radius of the cluster in order to best obtain information about the cluster age and initial mass function from the white dwarf luminosity function. The evolution of binary stars and the cluster environment must necessarily be accounted for when studying the white dwarf populations of dynamically evolved star clusters.

Jarrod R. Hurley; Michael M. Shara

2003-02-06

10

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

11

Polydisperse star polymer solutions C. von Ferber, A. Jusufi, M. Watzlawek,* C. N. Likos, and H. Lowen  

E-print Network

Polydisperse star polymer solutions C. von Ferber, A. Jusufi, M. Watzlawek,* C. N. Likos, and H. Lo and the phase diagram of dense star polymer solutions. In particular, we find that a polydispersity of 10 number on the effective interactions, structural correla- tions, and phase behavior of star polymers

Likos, Christos N.

12

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

E-print Network

HBT 28-Jun-2005 Formation of Planets in Dense Star Clusters Henry Throop Southwest Research September 23, 2005 #12;HBT 28-Jun-2005 Where Do Most Stars Form? · Stars form by the collapse of molecular = Giant Molecular Clouds) #12;HBT 28-Jun-2005 Case I: Star Formation in Open Clusters Small clouds: e

Throop, Henry

13

Bondi-Hoyle Accretion in Dense Star Clusters: Implications for Stars, Disks, and Planets  

E-print Network

Bondi-Hoyle Accretion in Dense Star Clusters: Implications for Stars, Disks, and Planets Draft the Bondi-Hoyle accretion of gas from a GMC onto young star- disk systems in a cluster. This post stars and removed from the cluster, or when low-mass stars are ejected from the cluster. We perform N

Throop, Henry

14

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

15

Dense hadronic matter in neutron stars  

E-print Network

The existence of stars with masses up to $2 M_{\\odot}$ and the hints of the existence of stars with radii smaller than $\\sim 11$ km seem to require, at the same time, a stiff and a soft hadronic equation of state at large densities. We argue that these two apparently contradicting constraints are actually an indication of the existence of two families of compact stars: hadronic stars which could be very compact and quark stars which could be very massive. In this respect, a crucial role is played, in the hadronic equation of state, by the delta isobars whose early appearance shifts to large densities the formation of hyperons. We also discuss how recent experimental information on the symmetry energy of nuclear matter at saturation indicate, indirectly, an early appearance of delta isobars in neutron star matter.

Giuseppe Pagliara; Alessandro Drago; Andrea Lavagno; Daniele Pigato

2014-04-24

16

Probing dense matter in neutron stars with axial w modes  

SciTech Connect

We study the problem of extracting information about composition and equation of state of dense matter in neutron star interior using axial w modes. We determine complex frequencies of axial w modes for a set of equations of state involving hyperons as well as Bose-Einstein condensates of antikaons adopting the continued fraction method. Hyperons and antikaon condensates result in softer equations of state leading to higher frequencies and lower damping times of first axial w modes than those of the nuclear matter case. The presence of condensates may lead to the appearance of a new stable branch of superdense stars beyond the neutron star branch called the third family. The existence of the same mass compact stars in both branches is known as neutron star twins. Further investigation of twins reveals that first axial w-mode frequencies of superdense stars in the third family are higher than those of the corresponding twins in the neutron star branch.

Chatterjee, Debarati; Bandyopadhyay, Debades [Theory Division and Centre for Astroparticle Physics, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064 (India)

2009-07-15

17

Tagged chain diffusion equation and effective friction tensor in dense polymer solutions  

E-print Network

Tagged chain diffusion equation and effective friction tensor in dense polymer solutions Grzegorz dynamics of dense polymer solutions and derive an effective diffusion equation for a tagged probe chain The dynamics of polymer melts and concentrated solu- tions is qualitatively different from that of simple

Szamel, Grzegorz

18

Two-dimensional polymeric liquids and polymer stars: learning from conflicting theories  

NASA Astrophysics Data System (ADS)

We discuss systems for which two carefully derived, yet conflicting, theories coexisted. Dense polymers in two dimensions and star-shaped polymers in the ?-regime are considered. In both cases the two proposed theories are in a sense exact, but turn out to satisfy different crossing rules (for the 2d polymer) or to correspond to different orders of limits. Finally, both theories prove very useful, albeit for different subclasses of physical systems.

Johner, A.; Thalmann, F.; Baschnagel, J.; Meyer, H.; Obukhov, S.; Wittmer, J. P.

2014-04-01

19

Method for forming a uniformly dense polymer foam body  

SciTech Connect

A method for providing a uniformly dense polymer foam body having a density between about 0.013 .sup.g /.sub.cm.sup..sub.3 to about 0.5 .sup.g /.sub.cm.sup..sub.3 is disclosed. The method utilizes a thermally expandable polymer microballoon material wherein some of the microballoons are unexpanded and some are only partially expanded. It is shown that by mixing the two types of materials in appropriate ratios to achieve the desired bulk final density, filling a mold with this mixture so as to displace all or essentially all of the internal volume of the mold, heating the mold for a predetermined interval at a temperature above about 130.degree. C., and then cooling the mold to a temperature below 80.degree. C. the molded part achieves a bulk density which varies by less then about .+-.6% everywhere throughout the part volume.

Whinnery, Jr., Leroy (Danville, CA)

2002-01-01

20

Ferromagnetism of dense matter and magnetic properties of neutron stars  

E-print Network

Possible consequences of ferromagnetic transition in dense matter suggested recently by Kutschera and W{\\'o}jcik, for the magnetic properties of neutron stars, are studied. Specific model of dense matter, in which a small admixture of protons is completely polarized due to their interaction with neutrons, is considered. Magnetic field of neutron stars with a ferromagnetic core is calculated within the framework of general relativity. Two types of boundary conditions at the ferromagnetic core edge are considered, corresponding to normal and superconducting liquid envelope, respectively. Numerical results for the neutron star magnetic dipole moment are confronted with pulsar timing. To be consistent with observations, ferromagnetic cores surrounded by a non-superconducting envelope, should consist of weakly ordered ferromagnetic domains. If domains are highly ordered, ferromagnetic core should be screened by a superconducting envelope.

P. Haensel; S. Bonazzola

1996-05-24

21

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

22

Velocity Gradients in Star-forming Dense Cores  

NASA Astrophysics Data System (ADS)

Initial conditions of a star-forming core, such as its mass, rotation rates and angular momentum, are vital to the study of star formation. The current study sought to reevaluate relationships between the velocity gradients of dense cores and their size. 7 regions: L1448, IC348, B5, L1445 in the Perseus Molecular Cloud and OphB, OphC, OphF in the Ophiuchus Molecular Cloud were studied using ammonia maps obtained by the Green Bank Telescope (GBT). Using a dendrogram technique on the velocity cubes paired with maps of ammonia integrated intensity, we subdivided regions into substructures. By fitting a solid-body-rotation model to each of the sub-regions, we derived sub-regions' velocity gradients. With higher resolution data, the current study showed the existence of previously overlooked substructures and filaments. While looking at velocity gradients of substructures, we found that substructures inside previously well defined dense cores exhibit rotations different from that of the overall core, and that the substructures themselves might be the true dense cores. By comparing the rotation rates of substructures to their size, we also found that velocity gradients of substructures dramatically increase at the size of <0.2 parsecs. The newly discovered radius of 0.2 parsecs matches up with the previously identified radius of coherence and provides new insight to defining the boundaries of star-forming dense cores.

Luhong

2015-01-01

23

Dense cloud formation and star formation in a barred galaxy  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

24

Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State  

E-print Network

With central densities way above the density of atomic nuclei, neutron stars contain matter in one of the densest forms found in the universe. Depending of the density reached in the cores of neutron stars, they may contain stable phases of exotic matter found nowhere else in space. This article gives a brief overview of the phases of ultra-dense matter predicted to exist deep inside neutron stars and discusses the equation of state associated with such matter.

Fridolin Weber; Matthew Meixner; Rodrigo P. Negreiros; Manuel Malheiro

2006-06-05

25

Modular invariant partition function of critical dense polymers  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

26

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.

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

2014-10-01

27

Multiscale Structure, Interfacial Cohesion, Adsorbed Layers, and Thermodynamics in Dense Polymer-Nanoparticle Mixtures  

NASA Astrophysics Data System (ADS)

We establish the existence and size of adsorbed polymer layers in miscible dense nanocomposites and their consequences on microstructure and the bulk modulus. Using contrast-matching small-angle neutron scattering to characterize all partial collective structure factors of polymers, particles, and their interface, we demonstrate qualitative failure of the random phase approximation, accuracy of the polymer reference site interaction model theory, ability to deduce the adsorbed polymer layer thickness, and high sensitivity of the nanocomposite bulk modulus to interfacial cohesion.

Kim, So Youn; Schweizer, Kenneth S.; Zukoski, Charles F.

2011-11-01

28

Barrier crossing by a star polymer.  

PubMed

We analyze the dynamics of a star polymer of F arms trapped in a double well potential. Initially the molecule is confined to one of the minima and can cross over the barrier to the other side. We use the continuum version of the Rouse-Ham model and calculate the rate of crossing using the multidimensional approach due to Langer [Ann. Phys. (N.Y.) 54, 258 (1969)]. Finding the transition state for the process is shown to be equivalent to the solution of Newton's equations for F independent particles, moving in an inverted potential. For each star polymer, there is a critical barrier top curvature, below which the star crosses over in coiled conformation. The value of the critical curvature is determined by the first Rouse mode of the star. If the curvature is greater than this critical value, the saddle point for the crossing is a stretched conformation of the star. For the coiled transition state, the activation energy is proportional to the total arm length of the star. For the stretched transition state, as one increases the length of an arm of the star, the activation energy at first increases and then decreases. This results from the fact that in the stretched state, only one arm of the polymer is stretched across the top of the barrier, while others need not be. We calculate the rate by expanding the energy around the saddle up to second order in the fluctuations. As we use the continuum model, there are infinite modes for the polymer and, consequently, the prefactor has infinite products. We show that these infinite products can be reduced to a simple expression, and evaluated easily. However, the rate diverges near NTc due to the multifurcation, which results in more than one unstable mode. The cure for this divergence is to keep terms up to fourth order in the expansion of energy for these modes. Performing this, we have calculated the rate as a function of the length of the star. It is found that the rate has a nonmonotonic dependence on the length, suggesting that longer stars may actually cross over the barrier faster. PMID:18233677

Debnath, Ananya; Sebastian, K L

2007-11-01

29

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. Sánchez-Diáz; Changwoo Do; Yun Liu; Tae-Hwan Kim; Gregory S. Smith; William A. Hamilton; Kunlun Hong; Wei-Ren Chen

2014-04-24

30

Polymer quantum effects on compact stars models  

E-print Network

In this work we study a completely degenerated fermion gas at zero temperature within a semiclassical approximation for the Hamiltonian arising in polymer quantum mechanics. Polymer quantum systems are quantum mechanical models quantized in a similar way as in loop quantum gravity that allow the study of the discreteness of space and other features of the loop quantization in a simplified way. We obtain the polymer modified thermodynamical properties noticing that the corresponding Fermi energy is exactly the same as if one directly polymerizes the momentum $p_F$. We also obtain the corresponding expansion of thermodynamical variables for small values of the polymer length scale $\\lambda$. With this results we study a simple model of a compact object where the gravitational collapse is supported by electron degeneracy pressure. We find polymer corrections to the mass of the star. When compared with typical measurements of the mass of white dwarfs we obtain a bound on the polymer length of $\\lambda^2\\lesssim 10^{-26}m^2$.

Guillermo Chacon-Acosta; Hector Hernandez-Hernandez

2014-08-05

31

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

32

Star Formation in the Taurus Filament L 1495: From Dense Cores to Stars  

NASA Astrophysics Data System (ADS)

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 line = 17 M sun pc-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 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 ? = 1.2 ± 0.2, a form commonly observed in star-forming regions. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC).

Schmalzl, Markus; Kainulainen, Jouni; Quanz, Sascha P.; Alves, João; Goodman, Alyssa A.; Henning, Thomas; Launhardt, Ralf; Pineda, Jaime E.; Román-Zúñiga, Carlos G.

2010-12-01

33

Analysis of Anionic Polymer Dispersant Behavior in Dense Silicon Nitride and Carbide Suspensions Using an AFM  

Microsoft Academic Search

The paper focuses on the interaction mechanism caused by anionic polymer dispersants in dense silicon nitride and silicon carbide suspensions. An atomic force microscope (AFM) was used to determine the relationship between the macroscopic suspension viscosity and the microscopic structure adsorbing of a polymer dispersant at the solid\\/liquid interface. The surface interactions within the suspensions were analyzed under various dispersant

M. Nojiri; S. Matsui; H. Hasegawa; T. Ono; Y. Fukuda; M. Tsukada; H. Kamiya

2001-01-01

34

Shift of Optical Absorbance with Pressure in Star Polymers  

NASA Astrophysics Data System (ADS)

The optical absorbance dependence on pressure is studied for star polymers dispersed (less than 1% wt./wt.) in either polymethylmethacrylate or polycarbonate. The star polymer is composed of a hyperbranched core and ?-conjugated polymer arms. The optical absorbance red shifts with increasing pressure and is expected to be due to increase in the conjugation length. The sensitivity on pressure is greater with the star polymers than for a pure linear polymer of the conjugated arm. The proposed enhancement mechanism is a non-uniform distribution of strain in analogy with the impact toughening of a matrix material by multidimensional additives.

Ferguson, John; Long, Barry

2006-03-01

35

Multiscale structure, interfacial cohesion, adsorbed layers, and thermodynamics in dense polymer-nanoparticle mixtures.  

PubMed

We establish the existence and size of adsorbed polymer layers in miscible dense nanocomposites and their consequences on microstructure and the bulk modulus. Using contrast-matching small-angle neutron scattering to characterize all partial collective structure factors of polymers, particles, and their interface, we demonstrate qualitative failure of the random phase approximation, accuracy of the polymer reference site interaction model theory, ability to deduce the adsorbed polymer layer thickness, and high sensitivity of the nanocomposite bulk modulus to interfacial cohesion. PMID:22182034

Kim, So Youn; Schweizer, Kenneth S; Zukoski, Charles F

2011-11-25

36

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. Sánchez-Diáz; Kunlun Hong; Gregory S. Smith; Wei-Ren Chen

2014-04-28

37

Engineering A polymer brush is a dense monolayer of highly  

E-print Network

for enhanced pulmonary drug delivery. Seminar Interfacial and Performance Properties of Polymer Brush and their ability to stabilize those interfaces. The emulsification performance of such particles, including-scale forces and structures that govern the macroscopic performance properties of complex fluids and colloidal

38

Neutrinos from Protoneutron Stars: A Probe of Hot and Dense matter  

E-print Network

Neutrino processes in dense matter play a key role in the dynamics, deleptonization and early cooling of hot protoneutron stars formed in the gravitational collapse of massive stars. Here we calculate neutrino mean free paths from neutrino-hyperon interactions in dense matter containing hyperons. Significant contributions to the neutrino opacity arise from scattering and absorption reactions involving the sigma minus particle. The estimates given here emphasise the need for (a) opacities which incoparate many-body effects in a multi-component mixture, and (b) new calculations of thermal and leptonic evolution of protoneutron stars with neutrino transport and equations of state with strangeness-rich matter.

Sanjay Reddy; Madappa Prakash

1995-08-03

39

Entropy-induced separation of star polymers in porous media  

SciTech Connect

We present a quantitative picture of the separation of star polymers in a solution where part of the volume is influenced by a porous medium. To this end, we study the impact of long-range-correlated quenched disorder on the entropy and scaling properties of f-arm star polymers in a good solvent. We assume that the disorder is correlated on the polymer length scale with a power-law decay of the pair correlation function g(r){approx}r{sup -a}. Applying the field-theoretical renormalization group approach we show in a double expansion in {epsilon}=4-d and {delta}=4-a that there is a range of correlation strengths {delta} for which the disorder changes the scaling behavior of star polymers. In a second approach we calculate for fixed space dimension d=3 and different values of the correlation parameter a the corresponding scaling exponents {gamma}{sub f} that govern entropic effects. We find that {gamma}{sub f}-1, the deviation of {gamma}{sub f} from its mean field value is amplified by the disorder once we increase {delta} beyond a threshold. The consequences for a solution of diluted chain and star polymers of equal molecular weight inside a porous medium are that star polymers exert a higher osmotic pressure than chain polymers and in general higher branched star polymers are expelled more strongly from the correlated porous medium. Surprisingly, polymer chains will prefer a stronger correlated medium to a less or uncorrelated medium of the same density while the opposite is the case for star polymers.

Blavats'ka, V. [Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 79011 Lviv (Ukraine); Institut fuer Theoretische Physik, Universitaet Leipzig, D-04109 Leipzig (Germany); Ferber, C. von [Theoretische Polymerphysik, Universitaet Freiburg, D-79104 Freiburg (Germany); Complex Systems Research Center, Jagiellonian University, 31007 Cracow (Poland); Holovatch, Yu. [Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 79011 Lviv (Ukraine); Institut fuer Theoretische Physik, Johannes Kepler Universitaet Linz, 4040, Linz (Austria); Ivan Franko National University of Lviv, 79005 Lviv (Ukraine)

2006-09-15

40

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

Microsoft Academic Search

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

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

2003-01-01

41

Observations of young low-mass stars in dense cores  

NASA Technical Reports Server (NTRS)

In this period the first maps were made during two flights of the Kuipper Airborne Observatory (KAO) in January 1986. One of these shows extended emission at 100 and 160 microns from the dense core B35 containing the IRAS point source 05417+0907. The 160 micron emission has approximately the same extent as the NH3 (1,1) line emission at 1.4 cm, indicating close correspondence between the warm dust and the dense gas. The 160 micron map shows a previously unknown secondary maximum about 90 arcsec north of the IRAS source.

Myers, Philip C.

1987-01-01

42

Osmotic shrinkage in star/linear polymer mixtures.  

PubMed

Multiarm star polymers were used as model grafted colloidal particles with long hairs, to study their size variation due to osmotic forces arising from added linear homopolymers of smaller size. This is the origin of the depletion phenomenon that has been exploited in the past as a means to melt soft colloidal glasses by adding linear chains and analyzed using dynamic light scattering experiments and an effective interactions analysis yielding the depletion potential. Shrinkage is a generic phenomenon for hairy particles, which affects macroscopic properties and state transitions at high concentrations. In this work we present a small-angle neutron scattering study of star/linear polymer mixtures with different size ratios (varying the linear polymer molar mass) and confirm the depletion picture, i.e., osmotic star shrinkage. Moreover, we find that as the linear/star polymer size ratio increases for the same effective linear volume fraction (c/c* with c* the overlapping concentration), the star shrinkage is reduced whereas the onset of shrinkage appears to take place at higher linear polymer volume fractions. A theoretical description of the force balance on a star polymer in solution, accounting for the classic Flory contributions, i.e. elastic and excluded volume, as well as the osmotic force due to the linear chains, accurately predicts the experimental findings of reduced star size as a function of linear polymer concentration. This is done in a parameter-free fashion, in which the size of the cavity created by the star, and from which the chains are excluded, is related to the radius of the former from first principles. PMID:20596881

Wilk, A; Huissmann, S; Stiakakis, E; Kohlbrecher, J; Vlassopoulos, D; Likos, C N; Meier, G; Dhont, J K G; Petekidis, G; Vavrin, R

2010-06-01

43

Life and Death of Young Dense Star Clusters near the Galactic Center  

E-print Network

We discuss the structural change and degree of mass segregation of young dense star clusters within about 100pc of the Galactic center. In our calculations, which are performed with GRAPE-6, the equations of motion of all stars and binaries are calculated accurately but the external potential of the Galaxy is solved (semi)analytically. The simulations are preformed to model the Arches star cluster. We find that star clusters with are less strongly perturbed by the tidal field and dynamical friction are much stronger affected by mass segregation; resulting in a significant pile-up of massive stars in the cluster center. At an age of about 3.5Myr more than 90 per cent of the stars more massive than ~10Msun are concentrated within the half-mass radius of the surviving cluster. Star clusters which are strongly perturbed by the tidal field of the parent Galaxy are much less affected by mass segregation.

Simon Portegies Zwart; Stephen McMillan; Holger Baumgardt

2004-03-05

44

Phase separation in star polymer-colloid mixtures  

E-print Network

We examine the demixing transition in star polymer-colloid mixtures for star arm numbers f=2,6,16,32 and different star-colloid size ratios. Theoretically, we solve the thermodynamically self-consistent Rogers-Young integral equations for binary mixtures using three effective pair potentials obtained from direct molecular computer simulations. The numerical results show a spinodal instability. The demixing binodals are approximately calculated, and found to be consistent with experimental observations.

J. Dzubiella; A. Jusufi; C. N. Likos; C. von Ferber; H. Lowen; J. Stellbrink; J. Allgaier; D. Richter; A. B. Schofield; P. A. Smith; W. C. K. Poon; P. N. Pusey

2000-10-12

45

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

46

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 addition–fragmentation chain-transfer (RAFT) polymerization, we prepared star polymers comprising 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 high-performance liquid chromatography (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

2013-01-01

47

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

48

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

49

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 Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ?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

50

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

51

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

SciTech Connect

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; Hagi, Keisuke; Ogiwara, Naoki [Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); Horike, Satoshi, E-mail: horike@sbchem.kyoto-u.ac.jp, E-mail: kitagawa@icems.kyoto-u.ac.jp [Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Tassel, Cedric [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); The Hakubi Center for Advanced Research, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501 (Japan); Kageyama, Hiroshi [Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); Higo, Yuji [Japan Synchrotron Radiation Research Institute, Hyogo 679-5198 (Japan); Kitagawa, Susumu, E-mail: horike@sbchem.kyoto-u.ac.jp, E-mail: kitagawa@icems.kyoto-u.ac.jp [Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501 (Japan)

2014-12-01

52

A novel geometric embedding algorithm for efficiently generating dense polymer structures  

NASA Astrophysics Data System (ADS)

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

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

2001-06-01

53

Parallelized event chain algorithm for dense hard sphere and polymer systems  

NASA Astrophysics Data System (ADS)

We combine parallelization and cluster Monte Carlo for hard sphere systems and present a parallelized event chain algorithm for the hard disk system in two dimensions. For parallelization we use a spatial partitioning approach into simulation cells. We find that it is crucial for correctness to ensure detailed balance on the level of Monte Carlo sweeps by drawing the starting sphere of event chains within each simulation cell with replacement. We analyze the performance gains for the parallelized event chain and find a criterion for an optimal degree of parallelization. Because of the cluster nature of event chain moves massive parallelization will not be optimal. Finally, we discuss first applications of the event chain algorithm to dense polymer systems, i.e., bundle-forming solutions of attractive semiflexible polymers.

Kampmann, Tobias A.; Boltz, Horst-Holger; Kierfeld, Jan

2015-01-01

54

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

55

Effective interaction parameter of linear/star polymer blends and comparison with that of linear/linear and star/star blends  

E-print Network

Effective interaction parameter of linear/star polymer blends and comparison with that of linear/linear and star/star blends P. E. Theodorakis and A. Avgeropoulos Department of Materials Science and Engineering a detailed study of the microscopic parameters, which control the miscibility in binary linear/star polymer

Theodorakis, Panagiotis E.

56

A novel parallel-rotation algorithm for atomistic Monte Carlo simulation of dense polymer systems  

NASA Astrophysics Data System (ADS)

We develop and test a new elementary Monte Carlo move for use in the off-lattice simulation of polymer systems. This novel Parallel-Rotation algorithm (ParRot) permits moving very efficiently torsion angles that are deeply inside long chains in melts. The parallel-rotation move is extremely simple and is also demonstrated to be computationally efficient and appropriate for Monte Carlo simulation. The ParRot move does not affect the orientation of those parts of the chain outside the moving unit. The move consists of a concerted rotation around four adjacent skeletal bonds. No assumption is made concerning the backbone geometry other than that bond lengths and bond angles are held constant during the elementary move. Properly weighted sampling techniques are needed for ensuring detailed balance because the new move involves a correlated change in four degrees of freedom along the chain backbone. The ParRot move is supplemented with the classical Metropolis Monte Carlo, the Continuum-Configurational-Bias, and Reptation techniques in an isothermal-isobaric Monte Carlo simulation of melts of short and long chains. Comparisons are made with the capabilities of other Monte Carlo techniques to move the torsion angles in the middle of the chains. We demonstrate that ParRot constitutes a highly promising Monte Carlo move for the treatment of long polymer chains in the off-lattice simulation of realistic models of dense polymer systems.

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

2001-06-01

57

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

NASA Astrophysics Data System (ADS)

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

Ohishi, Yukie; Sorai, Kazuo; Habe, Asao

2012-08-01

58

Polymers of complex topologies: rosette vs. star-like structures  

E-print Network

Multiple loop formation in polymer macromolecules is an important feature of the chromatin organization and DNA compactification in the nuclei. We analyze the size and shape characteristics of complex polymer structures, containing in general $f_1$ loops (petals) and $f_2$ linear chains (branches). Within the frames of continuous model of Gaussian macromolecule, we apply the path integration method and obtain the estimates for gyration radius $R_g$ and asphericity $\\hat{A}$ of typical conformation as functions of parameters $f_1$, $f_2$. In particular, our results qualitatively reveal the extent of anisotropy of star-like topologies as compared to the rosette structures of the same total molecular weight.

Viktoria Blavatska; Ralf Metzler

2014-12-08

59

Phase behavior of athermal colloid-star polymer mixtures.  

PubMed

We investigate the depletion-induced phase behavior of athermal colloid-star polymer mixtures on a fine lattice using grand canonical Monte Carlo simulations in the "protein limit," that is, where polymer dimensions exceed those of the colloid. We consider the influence of the star's functionality, f, the macroscopic size ratio, qr = 2Rg, s??c, where Rg, s is the radius of gyration of the star and ?c is the colloid diameter, and the microscopic size ratio, d = ?m??c, where ?m is the diameter of a Kuhn segment. Recent theoretical predictions concerning the qualitative interplay of qr and f in determining the phase stability of these mixtures [D. Marzi, C. N. Likos, and B. Capone, J. Chem. Phys. 137, 014902 (2012)] in the limit of large f are mostly corroborated by our results which span a much lower range of functionalities. Our results suggest a direct connection between the phase behavior and the scaling regimes of single star structure in the classical Daoud-Cotton (DC) description [M. Daoud and J. P. Cotton, J. Phys. 43, 531-538 (1982)]. Using this formalism, we define a "low" functionality limit through scaling arguments, for which our model provides a mapping of the phase behavior of colloidal mixtures with star polymers (f > 2) to linear chains (f = 2). Furthermore, our simulations suggest that as qr increases, both the critical monomer and colloid densities tend to a constant, finite value for all f; thus, we do not find the prediction by Marzi and co-workers of an upper limit to immiscibility (infinite critical densities) in terms of qr to be accurate for the stars we have investigated. PMID:23862965

Mahynski, Nathan A; Panagiotopoulos, Athanassios Z

2013-07-14

60

Thermodynamic instabilities in dense asymmetric nuclear matter and in compact stars  

NASA Astrophysics Data System (ADS)

We investigate the presence of thermodynamic instabilities in compressed asymmetric baryonic matter, reachable in high energy heavy ion collisions, and in the cold ?-stable compact stars. To this end we study the relativistic nuclear equation of state with the inclusion of ?-isobars and require the global conservation of baryon and electric charge numbers. Similarly to the low density nuclear liquid-gas phase transition, we show that a phase transition can occur in dense asymmetric nuclear matter and it is characterized by both mechanical instability (fluctuations on the baryon density) and by chemical-diffusive instability (fluctuations on the electric charge concentration). Such thermodynamic instabilities can imply a very different electric charge fraction Z/A in the coexisting phases during the phase transition and favoring an early formation of ?- particles with relevant phenomenological consequences in the physics of the protoneutron stars and compact stars. Finally, we discuss the possible co-existence of very compact and very massive compact stars in terms of two separate families: compact hadronic stars and very massive quark stars.

Lavagno, A.; Drago, A.; Pagliara, G.; Pigato, D.

2014-07-01

61

Star Cluster Ecology: VII The evolution of young dense star clusters containing primordial binaries  

E-print Network

We study the first 100Myr of the evolution of isolated star clusters initially containing 144179 stars, including 13107 (10%) primordial hard binaries. Our calculations include the effects of both stellar and binary evolution. Gravitational interactions among the stars are computed by direct N-body integration using high precision GRAPE-6 hardware. The evolution of the core radii and central concentrations of our simulated clusters are compared with the observed sample of young (about 100Myr) star clusters in the large Magellanic cloud. Even though our simulations start with a rich population of primordial binaries, core collapse during the early phase of the cluster evolution is not prevented. Throughout the simulations, the fraction of binaries remains roughly constant (about 10%). Due to the effects of mass segregation the mass function of intermediate-mass main-sequence stars becomes as flat as $\\alpha=-1.8$ in the central part of the cluster (where the initial Salpeter mass function had $\\alpha=-2.35$). About 6--12% of the neutron stars were retained in our simulations; the fraction of retained black holes is 40--70%. In each simulation about three neutron stars become members of close binaries with a main-sequence companion. Such a binary will eventually become an x-ray binary, when the main-sequence star starts to fill its Roche lobe. Black holes are found more frequently in binaries; in each simulated cluster we find about 11 potential x-ray binaries containing a black hole. Abstract abbreviated....

Simon Portegies Zwart; Steve McMillan; Jun Makino

2006-09-27

62

Star-like polymer click-functionalized with small capping molecules: an initial investigation into  

E-print Network

Star-like polymer click-functionalized with small capping molecules: an initial investigation,b Timothy Bunning,c Timothy White*c and Zhiqun Lin*a A novel class of polymer, star-like poly). The star-like architecture was composed of 21 separate arms connected to a high-functionality b

Lin, Zhiqun

63

Probing dense matter in compact star cores with radio pulsar data  

NASA Astrophysics Data System (ADS)

Astrophysical observations of compact stars provide, in addition to collider experiments, the other big source of information on matter under extreme conditions. The largest and most precise data set about neutron stars is the timing data of radio pulsars. We show how this unique data can be used to learn about the ultra-dense matter in the compact star interior. The method relies on astro-seismology based on special global oscillation modes (r-modes) that emit gravitational waves. They would prohibit pulsars from spinning with their observed high frequencies, unless the damping of these modes, determined by the microscopic properties of matter, can prevent this. We show that for each form of matter there is a distinct region in a frequency/spindown-rate diagram where r-modes can be present. We find that stars containing ungapped quark matter are consistent with both the observed radio and X-ray data, whereas, even when taking into account the considerable uncertainties, neutron star models with standard viscous damping are inconsistent with both data sets and additional damping mechanisms would be required.

Alford, Mark G.; Schwenzer, Kai

2014-11-01

64

Measuring the neutron star radius to constrain the dense-matter equation of state.  

NASA Astrophysics Data System (ADS)

A physical understanding of the behaviour of cold ultra-dense matter - at and above nuclear density - can only be achieved by the study of neutron stars, and the thermal emission from quiescent low-mass X-ray binaries inside globular clusters have proven very useful for that purpose. The recent ~2M? mass measurements suggest that strange quark matter and hyperons/kaons condensate equations of states (EoS) are disfavoured, in favour of hadronic "normal matter" EoSs. Over much of the neutron star mass-radius parameter space, "normal matter" EoSs produce lines of quasi-constant radii (within the measurement uncertainties, of about 10%). We present a simultaneous spectral analysis of several globular cluster quiescent low-mass X-ray binaries where we require the radius to be the same among all neutron stars analyzed. The Markov-Chain Monte-Carlo method and the Bayesian approach developed in this analysis permits including uncertainties in the distance, in the hydrogen column density, and possible contributions to the spectra due to un-modelled spectrally hard components. Our results suggest a neutron star radius much smaller than previously reported, with a value RNS = 9.1±1.4 km, at 90% confidence, using conservative assumptions, which suggests that neutron star matter is best described by the softest "normal matter" equations of state.

Guillot, Sebastien; Servillat, Mathieu; Webb, Natalie; Rutledge, Robert E.

2014-08-01

65

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

E-print Network

In this work, we consider a semi-dilute solution of identical star-polymers, made of attached flexible long polymer chains of the same polymerization degree N. We first compute the effective pair-potential between star-polymers. Such a potential results from the excluded volume forces between monomers. We show that this potential is logarithmic, below some known characteristic distance, ?, depending on the number of attached chains per star-polymer, f, and volume fraction of polymers, ?0 . Beyond ?, the potential fails exponentially. Second, we investigate the structure and thermodynamics of these star-polymers. To this end, we use the integral equation method with the hybridized-mean spherical approximation. The numerical resolution of this equation gives the structure factor of the star-polymers, for various particle densities. Finally, the standard relationships between thermodynamics and structure enable us to deduce three physical quantities, namely the isotherm compressibility, pressure and internal energy, as functions of density.

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

2007-03-21

66

On the relative motions of dense cores and envelopes in star-forming molecular clouds  

NASA Astrophysics Data System (ADS)

Hydrodynamical simulations of star formation indicate that the motions of protostars through their natal molecular clouds may be crucial in determining the properties of stars through competitive accretion and dynamical interactions. Walsh, Myers & Burton recently investigated whether such motions might be observable in the earliest stages of star formation by measuring the relative shifts of line-centre velocities of low- and high-density tracers of low-mass star-forming cores. They found very small (~0.1kms-1) relative motions. In this paper, we analyse the hydrodynamical simulation of Bate, Bonnell & Bromm and find that it also gives small relative velocities between high-density cores and low-density envelopes, despite the fact that competitive accretion and dynamical interactions occur between protostars in the simulation. Thus, the simulation is consistent with the observations in this respect. However, we also find some differences between the simulation and the observations. Overall, we find that the high-density gas has a higher velocity dispersion than that observed by Walsh et al. We explore this by examining the dependence of the gas velocity dispersion on density and its evolution with time during the simulation. We find that early in the simulation the gas velocity dispersion decreases monotonically with increasing density, while later in the simulation, when the dense cores have formed multiple objects, the velocity dispersion of the high-density gas increases. Thus, the simulation is in best agreement with the observations early on, before many objects have formed in each dense core.

Ayliffe, Ben A.; Langdon, James C.; Cohl, Howard S.; Bate, Matthew R.

2007-02-01

67

The neutron star radius and the dense-matter equation of state  

NASA Astrophysics Data System (ADS)

A physical understanding of the behaviour of cold ultra-dense matter - at and above nuclear density - can only be achieved by the study of neutron stars, and the thermal emission from quiescent low-mass X-ray binaries inside globular clusters have proven very useful for that purpose. The recent 1.97±0.04 Msun measurement for the radio pulsar PSR 1614-2230 suggests that strange quark matter and hyperons/kaons condensate equations of states (EoS) are disfavoured, in favour of hadronic "normal matter" EoSs. Over much of the neutron star mass-radius parameter space, "normal matter" EoSs produce lines of quasi-constant radii (within the measurement uncertainties, of about 10%). We present a simultaneous spectral analysis of several globular cluster quiescent low-mass X-ray binaries where we require the radius to be the same among all neutron stars analyzed. The Markov-Chain Monte-Carlo method and the Bayesian approach developed in this analysis permits including uncertainties in the distance, in the hydrogen column density, and possible contributions to the spectra due to un-modelled spectrally hard components. Our results suggest a neutron star radius much smaller than previously reported, with a value Rns = 9.1±1.4 km, at 90% confidence, using conservative assumptions, which suggests that neutron start matter is best described by the softest "normal matter" equations of state.

Guillot, Sebastien; Servillat, M.; Webb, N.; Rutledge, R. E.

2014-01-01

68

Utilization of star-shaped polymer architecture in the creation of high-density polymer brush coatings for the prevention of platelet and bacteria adhesion.  

PubMed

We demonstrate utilization of star-shaped polymers as high-density polymer brush coatings and their effectiveness to inhibit the adhesion of platelets and bacteria. Star polymers consisting of poly(2-hydroxyethyl methacrylate) (PHEMA) and/or poly(methyl methacrylate) (PMMA), were synthesized using living radical polymerization with a ruthenium catalyst. The polymer coatings were prepared by simple drop casting of the polymer solution onto poly(ethylene terephthalate) (PET) surfaces and then dried. Among the star polymers prepared in this study, the PHEMA star polymer (star-PHEMA) and the PHEMA/PMMA (mol. ratio of 71/29) heteroarm star polymer (star-H71M29) coatings showed the highest percentage of inhibition against platelet adhesion (78-88% relative to noncoated PET surface) and Escherichia coli (94-97%). These coatings also showed anti-adhesion activity against platelets after incubation in Dulbecco's phosphate buffered saline or surfactant solution for 7 days. In addition, the PMMA component of the star polymers increased the scratch resistance of the coating. These results indicate that the star-polymer architecture provides high polymer chain density on PET surfaces to prevent adhesion of platelets and bacteria, as well as coating stability and physical durability to prevent exposure of bare PET surfaces. The star polymers provide a simple and effective approach to preparing anti-adhesion polymer coatings on biomedical materials against the adhesion of platelets and bacteria. PMID:25485105

Totani, Masayasu; Ando, Tsuyoshi; Terada, Kayo; Terashima, Takaya; Kim, Ill Yong; Ohtsuki, Chikara; Xi, Chuanwu; Kuroda, Kenichi; Tanihara, Masao

2014-09-01

69

Inter-channel crosstalk in densely aligned multimode polymer parallel optical waveguides  

NASA Astrophysics Data System (ADS)

We theoretically estimate the inter-channel crosstalk in densely aligned multimode polymer parallel optical waveguides using a beam propagation method, and compare the results of graded-index (GI)-core waveguides with those of conventional step-index (SI)-core counterpart. In particular, we simulate the crosstalk in bridged core waveguides. Here, the bridged core is sometimes observed in the waveguides fabricated using the imprinting method. The inter-channel crosstalk in SI-core waveguide increases from -25 dB to -4 dB with increasing the bridge thickness. Contrastingly, the worst crosstalk in a GI-core is as low as -15 dB despite the bridged structure as long as the bridge of the core is not included in the index distribution of the GI-core core, namely SI bridged core. In addition, the crosstalk in the GI-core decreases when the multiple cores aligned in parallel have a different structure (core size, refractive index, etc.), because the difference in the core structure makes changes in the distribution of propagation constants, resulting in decreasing the mode coupling efficiency between the two cores. Hence, the worst crosstalk in the GI-core waveguide with a slightly different core structure is as low as -19 dB despite the bridged structure. Thus, the imprinting method should be utilized for GI-core waveguides: the inter-channel crosstalk is un-problematic even if a residual layer remains.

Kudo, Takuya; Ishigure, Takaaki

2014-03-01

70

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

PubMed

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

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

2013-03-15

71

Role of hydrophilicity and length of diblock arms for determining star polymer physical properties.  

PubMed

We present a molecular simulation study of star polymers consisting of 16 diblock copolymer arms bound to a small adamantane core by varying both arm length and the outer hydrophilic block when attached to the same hydrophobic block of poly-?-valerolactone. Here we consider two biocompatible star polymers in which the hydrophilic block is composed of polyethylene glycol (PEG) or polymethyloxazoline (POXA) in addition to a polycarbonate-based polymer with a pendant hydrophilic group (PC1). We find that the different hydrophilic blocks of the star polymers show qualitatively different trends in their interactions with aqueous solvent, orientational time correlation functions, and orientational correlation between pairs of monomers of their polymeric arms in solution, in which we find that the PEG polymers are more thermosensitive compared with the POXA and PC1 star polymers over the physiological temperature range we have investigated. PMID:25254622

Felberg, Lisa E; Brookes, David H; Head-Gordon, Teresa; Rice, Julia E; Swope, William C

2015-01-22

72

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

73

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

74

Star Polymers and the Failure of Time-Temperature Superposition Alex J. Levine* and Scott T. Milner  

E-print Network

Star Polymers and the Failure of Time-Temperature Superposition Alex J. Levine* and Scott T. Milner; Revised Manuscript Received August 27, 1998 ABSTRACT: We model the arm of a star polymer as an anchored. For melts of star polymers, however, the assumption of thermorheological simplicity can lead

Levine, Alex J.

75

Critical dense polymers with Robin boundary conditions, half-integer Kac labels and Z4 fermions  

NASA Astrophysics Data System (ADS)

For general Temperley-Lieb loop models, including the logarithmic minimal models 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 LM (1 , 2) of the family of logarithmic minimal models and has loop fugacity ? = 0 and central charge c = - 2. Specialising to 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 finitised characters related to spaces of coinvariants of Z4 fermions. In the continuum scaling limit, the Robin boundary conditions are associated with irreducible Virasoro Verma modules with conformal weights ? r , s -1/2 =1/32 (L2 - 4) where L = 2 s - 1 - 4 r, r ? Z, s ? N. These conformal weights 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.

Pearce, Paul A.; Rasmussen, Jørgen; Tipunin, Ilya Yu.

2014-12-01

76

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, Jürgen; Hughes, Annie; Wong, Tony; Henkel, Christian; Chen, Rosie; Indebetouw, Remy; Looney, Leslie; Muller, Erik; Pineda, Jorge L.; Seale, Jonathan

2014-09-01

77

Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature.  

PubMed

Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties. PMID:25638003

Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F

2015-01-28

78

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

NASA Astrophysics Data System (ADS)

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

Schweizer, Ken

2012-02-01

79

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.

80

Synthesis and properties of star-comb polymers and their doxorubicin conjugates.  

PubMed

We describe a six-step synthesis to water-soluble doxorubicin (DOX)-loaded biodegradable PEGylated star-comb polymers with favorable pharmaceutical properties by atom transfer radical polymerization (ATRP) starting with a commercially available tripentaerythritol carrying eight reactive sites. The low polydispersity polymers degrade in a stepwise manner into lower molecular weight (MW) fragments by 15 days at 37 °C at either pH 5.0 or pH 7.4. The half-life of the star-comb polymers in blood is dependent upon the molecular weight; the 44 kDa star-comb has a t(1/2, ?) of 30.5 ± 2.1 h, which is not significantly changed (28.6 ± 2.7 h) when 6.6 wt % of DOX is attached to it via a pH-sensitive hydrazone linker. The star-comb polymers have low accumulation in organs but a high accumulation in C26 flank tumors implanted in Balb/C mice. The hydrodynamic diameter of polymer-DOX conjugates measured by dynamic light scattering increases from 8 to 35 to 41 nm as the loading is increased from 6.6 to 8.4 to 10.2 wt %. Although there is no significant difference in the t(1/2, ?) or in the accumulation of polymer-DOX in C-26 tumors, the uptake of polymer in the spleen is significantly higher for polymers with DOX loadings greater than 6.6 wt %. Polymer accumulation in other vital organs is independent of the DOX loading. The facile synthesis, biodegradability, long circulation time, and high tumor accumulation of the attached drug suggests that the water-soluble star-comb polymers have promise in therapeutic applications. PMID:21375296

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

2011-04-20

81

Unconventional ordering behavior of semi-flexible polymers in dense brushes under compression  

E-print Network

Using a coarse-grained bead-spring model for semi-flexible macromolecules forming a polymer brush, structure and dynamics of the polymers is investigated, varying chain stiffness and grafting density. The anchoring condition for the grafted chains is chosen such that their first bonds are oriented along the normal to the substrate plane. Compression of such a semi-flexible brush by a planar piston is observed to be a two-stage process: for small compressions the chains contract by "buckling" deformation whereas for larger compression the chains exhibit a collective (almost uniform) bending deformation. Thus, the stiff polymer brush undergoes a 2-nd order phase transition of collective bond reorientation. The pressure, required to keep the stiff brush at a given degree of compression, is thereby significantly smaller than for an otherwise identical brush made of entirely flexible polymer chains! While both the brush height and the chain linear dimension in the z-direction perpendicular to the substrate increase monotonically with increasing chain stiffness, lateral (xy) chain linear dimensions exhibit a maximum at intermediate chain stiffness. Increasing the grafting density leads to a strong decrease of these lateral dimensions, compatible with an exponential decay. Also the recovery kinetics after removal of the compressing piston is studied, and found to follow a power-law / exponential decay with time. A simple mean-field theoretical consideration, accounting for the buckling/bending behavior of semi-flexible polymer brushes under compression, is suggested.

Andrey Milchev; Kurt Binder

2014-01-27

82

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

2015-01-01

83

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

84

The Initial Conditions of Clustered Star Formation. I. NH3 Observations of Dense Cores in Ophiuchus  

NASA Astrophysics Data System (ADS)

We present combined interferometer and single dish telescope data of NH3 (J, K) = (1,1) and (2,2) emission toward the clustered star forming Ophiuchus B, C, and F Cores at high spatial resolution (~1200 AU) using the Australia Telescope Compact Array, the Very Large Array, and the Green Bank Telescope. While the large-scale features of the NH3 (1,1) integrated intensity appear similar to 850 ?m continuum emission maps of the Cores, on 15'' (1800 AU) scales we find significant discrepancies between the dense gas tracers in Oph B, but good correspondence in Oph C and F. Using the CLUMPFIND structure identifying algorithm, we identify 15 NH3 clumps in Oph B, and three each in Oph C and F. Only five of the Oph B NH3 clumps are coincident within 30'' (3600 AU) of a submillimeter clump. We find v LSR varies little across any of the cores, and additionally varies by only ~1.5 km s-1 between them. The observed NH3 line widths within the Oph B and F Cores are generally large and often mildly supersonic, while Oph C is characterized by narrow line widths which decrease to nearly thermal values. We find several regions of localized narrow line emission (?v lsim 0.4 km s-1), some of which are associated with NH3 clumps. We derive the kinetic temperatures of the gas, and find they are remarkably constant across Oph B and F, with a warmer mean value (TK = 15 K) than typically found in isolated regions and consistent with previous results in clustered regions. Oph C, however, has a mean TK = 12 K, decreasing to a minimum TK = 9.4 K toward the submillimeter continuum peak, similar to previous studies of isolated starless clumps. There is no significant difference in temperature toward protostars embedded in the Cores. NH3 column densities, N(NH3), and abundances, X(NH3), are similar to previous work in other nearby molecular clouds. We find evidence for a decrease in X(NH3) with increasing N(H2) in Oph B2 and C, suggesting the NH3 emission may not be tracing well the densest core gas.

Friesen, R. K.; Di Francesco, J.; Shirley, Y. L.; Myers, P. C.

2009-06-01

85

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

86

Shock compression of dense polymer and foam systems using molecular dynamics and DFT  

NASA Astrophysics Data System (ADS)

Organic polymers and nanocomposites are increasingly being subjected to extreme environments. Molecular scale modeling of these materials offers insight into failure mechanisms and response. Classical molecular dynamics (MD) and density functional theory (DFT) MD simulations of the principal shock Hugoniot will be presented for two hydrocarbon polymers, polyethylene (PE) and poly(4-methyl-1-pentene) (PMP). We studied two reactive and two non-reactive classical MD interaction potentials. We will show the exp-6 interaction of Borodin et al. has much better agreement with experiment than OPLS. Futher, that ReaxFF displayed decidedly better agreement than AIREBO. DFT were in excellent agreement with experiment. NEMD studies of low-density foam materials will be discussed. Qualitative response will be characterized. Quantitative comparison will be made with experiment.

Lane, J. Matthew D.; Grest, Gary S.; Thompson, Aidan P.; Cochrane, Kyle R.; Desjarlais, Michael P.; Mattsson, Thomas R.

2011-06-01

87

A novel parallel-rotation algorithm for atomistic Monte Carlo simulation of dense polymer systems  

Microsoft Academic Search

We develop and test a new elementary Monte Carlo move for use in the off-lattice simulation of polymer systems. This novel Parallel-Rotation algorithm (ParRot) permits moving very efficiently torsion angles that are deeply inside long chains in melts. The parallel-rotation move is extremely simple and is also demonstrated to be computationally efficient and appropriate for Monte Carlo simulation. The ParRot

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

2001-01-01

88

Nonequilibrium polymer chains induced by conformational transitions in densely interfacial layers  

NASA Astrophysics Data System (ADS)

Nonequilibrium poly(N-isopropylacrylamide) (PNIPAM) chains are generated by temperature-induced conformational transitions in the densely interfacial PNIPAM layer at high adsorbed amounts in aqueous solution. The interleaving chains relax in a spatially heterogeneous space of adsorbed layer which is filled with the domains via the hydrogen bonding and hydrophobic interactions. The relaxation dynamics of interleaving chains is changed from the weekly stretched exponential behaviour at the lower adsorbed amount to the strongly stretched exponential behaviour at the higher adsorbed amount. The kinetic constraints for the relaxation dynamics depend on the segment density of the adsorbed layer which is controlled by the temperature. The stretched exponential relaxation is related to an ensemble of relaxations confined in the domains with different physical origins for the heterogeneous dynamics. The range of energy barriers for the relaxation is estimated from the stretched exponent based on the random first order transition theory.

Zhu, Peng-Wei

2012-09-01

89

Nonequilibrium polymer chains induced by conformational transitions in densely interfacial layers.  

PubMed

Nonequilibrium poly(N-isopropylacrylamide) (PNIPAM) chains are generated by temperature-induced conformational transitions in the densely interfacial PNIPAM layer at high adsorbed amounts in aqueous solution. The interleaving chains relax in a spatially heterogeneous space of adsorbed layer which is filled with the domains via the hydrogen bonding and hydrophobic interactions. The relaxation dynamics of interleaving chains is changed from the weekly stretched exponential behaviour at the lower adsorbed amount to the strongly stretched exponential behaviour at the higher adsorbed amount. The kinetic constraints for the relaxation dynamics depend on the segment density of the adsorbed layer which is controlled by the temperature. The stretched exponential relaxation is related to an ensemble of relaxations confined in the domains with different physical origins for the heterogeneous dynamics. The range of energy barriers for the relaxation is estimated from the stretched exponent based on the random first order transition theory. PMID:22979886

Zhu, Peng-Wei

2012-09-14

90

Lymphatic trafficking kinetics and near-infrared imaging using star polymer architectures with controlled anionic character  

PubMed Central

Targeted lymphatic delivery of nanoparticles for drug delivery and imaging is primarily dependent on size and charge. Prior studies have observed increased lymphatic uptake and retentions of over 48 hrs for negatively charged particles compared to neutral and positively charged particles. We have developed new polymeric materials that extend retention over a more pharmaceutically relevant 7-day period. We used whole body fluorescence imaging to observe in mice the lymphatic trafficking of a series of anionic star poly-(6-O-methacryloyl-D-galactose) polymer-NIR dye (IR820) conjugates. The anionic charge of polymers was increased by modifying galactose moieties in the star polymers with succinic anhydride. Increasing anionic nature was associated with enhanced lymphatic uptake up to a zeta potential of ca. -40 mV; further negative charge did not affect lymphatic uptake. Compared to the 20% acid-conjugate, the 40 to 90% acid-star-polymer conjugates exhibited a 2.5- to 3.5-fold increase in lymphatic uptake in both the popliteal and iliac nodes. The polymer conjugates exhibited node half-lives of 2 to 20 hrs in the popliteal nodes and 19 to 114 hrs in the deeper iliac nodes. These polymer conjugates can deliver drugs or imaging agents with rapid lymphatic uptake and prolonged deep-nodal retention; thus they may provide a useful vehicle for sustained intralymphatic drug delivery with low toxicity. PMID:22546180

Bagby, Taryn R.; Cai, Shuang; Duan, Shaofeng; Yang, Qiuhong; Thati, Sharadvi; Berkland, Cory; Aires, Daniel J.; Forrest, M. Laird

2015-01-01

91

Predicting water sorption and volume swelling in dense polymer systems via computer simulation.  

PubMed

Atomistic model structures of amorphous polyamide 6 (PA-6) and of an adhesive system consisting of the diglycidyl ether of bisphenol A (DGEBA) as epoxy resin and isophorone diamine (IPD) as a curing agent are generated. For the adhesive, we use a new approach for the generation of the cross-linked polymer networks. It takes into account the chemical reaction kinetics of the curing reaction and, therefore, results in more realistic network structures. On the basis of the corresponding model structures, the equilibrium water content and the swelling ratio of amorphous PA-6 and of the DGEBA+IPD networks are calculated via computer simulation for different thermodynamic conditions. A hybrid method is used combining the molecular dynamics technique with an accelerated test particle insertion method. The results are in reasonable agreement with experiments and, in the case of the PA-6 system, with results obtained via other computer simulation methods. PMID:21141921

Hörstermann, Henning; Hentschke, Reinhard; Amkreutz, Marc; Hoffmann, Michael; Wirts-Rütters, Martin

2010-12-30

92

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

93

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

NASA Astrophysics Data System (ADS)

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

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

2009-06-01

94

On the Origin of the Dense Frequency Spectra of Space Observed Intermediate Mass Pulsating Stars  

NASA Astrophysics Data System (ADS)

Several hypotheses have been advanced to explain the wealthy spectra of space observed intermediate mass pulsating stars. Among which we can find the rotational splitting, stochastic excitation or detection of coloured noise due to superficial granulation. An overview of the problem requires a coherent analysis of a large number of stars looking for correlations between the observed frequency spectra and the position on the HR diagram.

Pascual-Granado, J.; Grigahcène, A.; Díaz-Fraile, D.; Gruberbauer, M.; Garrido, R.; Amado, P.; Suárez, J. C.

95

Asymmetric poly(ethylene glycol) star polymers with a cholic acid core and their aggregation properties.  

PubMed

Poly(ethylene glycol) (PEG) arms are grafted onto a cholic acid core via anionic polymerization, yielding star-shaped polymers with a unique asymmetric structure with facial amphiphilicity. Well-defined cholic acid-PEG(4) stars (polydispersity index, ca. 1.05) with tunable molar masses (ca. 1000-13,000) were obtained and characterized by the use of size exclusion chromatography, MALDI-TOF mass spectrometry, NMR spectroscopy, and thermal analysis. The asymmetric star polymers were found to aggregate differently from cholic acid salt. The critical aggregation concentrations of the star polymers were determined by surface tension measurements, and spherical aggregates of the polymers with different PEG chain lengths were observed by transmission electron microscopy using the freeze-fracture etching technique. The elongated aggregates formed by the sodium salt of cholic acid were also observed. The hydrodynamic diameters of the aggregates were also measured using dynamic light scattering technique. The formation of aggregates makes them interesting systems as potential drug carriers. PMID:19281151

Luo, Juntao; Giguère, Guillaume; Zhu, X X

2009-04-13

96

From Filamentary Networks to Dense Cores in Molecular Clouds: Toward a New Paradigm for Star Formation  

NASA Astrophysics Data System (ADS)

Recent studies of the nearest star-forming clouds of the Galaxy at submillimeter wavelengths with the Herschel Space Observatory have provided us with unprecedented images of the initial and boundary conditions of the star-formation process. The Herschel results emphasize the role of interstellar filaments in the star-formation process and connect remarkably well with nearly a decade’s worth of numerical simulations and theory that have consistently shown that the interstellar medium (ISM) should be highly filamentary on all scales, and star formation is intimately related to self-gravitating filaments. In this review, we trace how the apparent complexity of cloud structure and star formation is governed by relatively simple universal processes — from filamentary clumps to galactic scales. We emphasize two crucial and complementary aspects: (1) the key observational results obtained with Herschel over the past three years, along with relevant new results obtained from the ground on the kinematics of interstellar structures; and (2) the key existing theoretical models and the many numerical simulations of interstellar cloud structure and star formation. We then synthesize a comprehensive physical picture that arises from the confrontation of these observations and simulations.

André, P.; Di Francesco, J.; Ward-Thompson, D.; Inutsuka, S.-I.; Pudritz, R. E.; Pineda, J. E.

97

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

98

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

99

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

100

Phase transitions in dense matter and the maximum mass of neutron stars  

NASA Astrophysics Data System (ADS)

Context. The recent precise measurement of the mass of pulsar PSR J1614-2230, as well as observational indications of even more massive neutron stars, has revived the question of the composition of matter at the high densities prevailing inside neutron-star cores. Aims: We study the impact on the maximum possible neutron-star mass of an "exotic" core consisting of non-nucleonic matter. For this purpose, we study the occurrence of a first-order phase transition in nucleonic matter. Methods: Given the current lack of knowledge of non-nucleonic matter, we consider the stiffest possible equation of state subject only to the constraints of causality and thermodynamic stability. The case of a hadron-quark phase transition is discussed separately. The purely nucleonic matter is described using a set of unified equations of state that have been recently developed to permit a consistent treatment of both homogeneous and inhomogeneous phases. We then compute the mass-radius relation of cold nonaccreting neutron stars with and without exotic cores from the Tolman-Oppenheimer-Volkoff equations. Results: We find that even if there is a significant softening of the equation of state associated with the actual transition to an exotic phase, there can still be a stiffening at higher densities closer to the center of the star that is sufficient to increase the maximum possible mass. However, with quarks the maximum neutron-star mass is always reduced by assuming that the sound speed is limited by c/?3 as suggested by QCD calculations. In particular, by invoking such a phase transition, it becomes possible to support PSR J1614-2230 with a nucleonic equation of state that is soft enough to be compatible with the kaon and pion production in heavy-ion collisions.

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

2013-05-01

101

Star cluster formation in turbulent, magnetized dense clumps with radiative and outflow feedback  

NASA Astrophysics Data System (ADS)

We present three ORION simulations of star cluster formation in a 1000 M?, turbulent molecular cloud clump, including the effects of radiative transfer, protostellar outflows, and magnetic fields. Our simulations all use self-consistent turbulent initial conditions and vary the mean mass-to-flux ratio relative to the critical value over ?? = 2, ?? = 10, and ?? = ? to gauge the influence of magnetic fields on star cluster formation. We find, in good agreement with previous studies, that magnetic fields corresponding to ?? = 2 lower the star formation rate by a factor of ?2.4 and reduce the amount of fragmentation by a factor of ?2 relative to the zero-field case. We also find that the field increases the characteristic sink particle mass, again by a factor of ?2.4. The magnetic field also increases the degree of clustering in our simulations, such that the maximum stellar densities in the ?? = 2 case are higher than the others by again a factor of ?2. This clustering tends to encourage the formation of multiple systems, which are more common in the rad-MHD runs than the rad-hydro run. The companion frequency in our simulations is consistent with observations of multiplicity in Class I sources, particularly for the ?? = 2 case. Finally, we find evidence of primordial mass segregation in our simulations reminiscent of that observed in star clusters like the Orion Nebula Cluster.

Myers, Andrew T.; Klein, Richard I.; Krumholz, Mark R.; McKee, Christopher F.

2014-04-01

102

Structural Arrest in Dense Star-Polymer Solutions F. Sciortino,1  

E-print Network

. Zaccarelli,1 F. Lo Verso,2 L. Reatto,2 K. A. Dawson,3 and C. N. Likos4 1 Dipartimento di Fisica and INFM-00185 Rome, Italy 2 Istituto Nazionale di Fisica della Materia and Dipartimento di Fisica, Universita

Sciortino, Francesco

103

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

104

Decoding the Viscoelastic Response of Polydisperse Star/Linear Polymer Blends  

NASA Astrophysics Data System (ADS)

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

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

2008-07-01

105

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 ${\\cal LM}(p,p')$ 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 ${\\cal LM}(1,2)$ of the family of logarithmic minimal models and has loop fugacity $\\beta=0$ and central charge $c=-2$. Specializing to ${\\cal LM}(1,2)$ 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 $\\Delta_{r,s-\\frac{1}{2}}=\\frac{1}{32}(L^2-4)$ where $L=2s-1-4r$, $r\\in\\mathbb{Z}$, $s\\in\\mathbb{N}$. These conformal weights 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

2014-10-28

106

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

Microsoft Academic Search

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

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

2004-01-01

107

Conformational properties of complex polymers: rosette versus star-like structures  

E-print Network

Multiple loop formation in polymer macromolecules is an important feature of the chromatin organization and DNA compactification in the nuclei. We analyze the size and shape characteristics of complex polymer structures, containing in general $f_1$ loops (petals) and $f_2$ linear chains (branches). Within the frames of continuous model of Gaussian macromolecule, we apply the path integration method and obtain the estimates for gyration radius $R_g$ and asphericity $\\hat{A}$ of typical conformation as functions of parameters $f_1$, $f_2$. In particular, our results qualitatively reveal the extent of anisotropy of star-like topologies as compared to the rosette structures of the same total molecular weight.

Viktoria Blavatska; Ralf Metzler

2015-01-19

108

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; Boissé, P; Cabrit, S; Lesaffre, P; Gerin, M; Forêts, G Pineau des

2014-01-01

109

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

E-print Network

?? In this work, multi-layered thin film materials comprised of cobalt ferrite (CoFe2O4) magnetic nanoparticles and polystyrene amine-functionalized (PS-NH2) star polymers have been prepared on… (more)

Shah, Shimul

2011-01-01

110

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

PubMed

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

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

2013-06-01

111

Influence of entropic configurational effects on the surface tension of symmetric star polymers  

NASA Astrophysics Data System (ADS)

Surface tension of symmetric 4 and 11 arm polystyrenes have been measured for a series of different molecular weights. We observe that entropic effects contribute significantly to the variation of surface tension as a function of molecular weight. Minnikanti and Archer have developed an expression that relates the surface tension of a symmetric star polymer with its molecular weight. To determine the dependence of surface tension on the reciprocal of molecular weight, the number of arms and dimensionless attraction of the ends and branched point towards the surface play a significant role. We estimated the entropic attraction of the ends and joints from independent self consistent field simulations of a polymer on a lattice. The predicted variations in surface tensions due to entropic reasons were found to constitute a large part of the experimentally observed surface tension variation with molecular weights for 4 and 11 arm stars.

Qian, Zhenyu; Minnikanti, Venkatachala; Archer, Lynden; Sauer, Bryan

2007-03-01

112

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

SciTech Connect

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

Glendening, N.K.

1989-06-01

113

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 für 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 Católica 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.

Jordán, Andrés; Brahm, Rafael; Bakos, G. Á.; 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.; de Val-Borro, M.; Buchhave, L.; Csák, B.; Henning, T.; Schmidt, B.; Tan, T. G.; Noyes, R. W.; Béky, B.; Butler, R. P.; Shectman, S.; Crane, J.; Thompson, I.; Williams, A.; Martin, R.; Contreras, C.; Lázár, J.; Papp, I.; Sári, P.

2014-08-01

114

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

Pitkänen, Leena; Striegel, André M

2014-11-21

115

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.; López-Sepulcre, A.; Gusdorf, A.; Csengeri, T.; Anderl, S.

2014-10-01

116

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 UV–vis spectroscopy and even the naked eye. PMID:25298793

Fleischmann, Carolin; Wöhlk, Hendrik

2014-01-01

117

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

118

Star-like supramolecular polymers fabricated by a Keplerate cluster with cationic terminated polymers and their self-assembly into vesicles.  

PubMed

The electrostatic combination of a Keplerate cluster, [Mo(132)O(372)(CH(3)COO)(30)(H(2)O)(72)](42-) with cationic terminated poly(styrene) yields polyoxometalate-based supramolecular star polymers, which can further self-assemble into vesicular aggregates in CHCl(3)-MeOH mixed solvent. PMID:22683742

Zhang, Qian; He, Lipeng; Wang, Hui; Zhang, Cheng; Liu, Weisheng; Bu, Weifeng

2012-07-18

119

Telechelic star polymers as self-assembling units from the molecular to the macroscopic scale.  

PubMed

By means of multiscale molecular simulations, we show that telechelic-star polymers are a simple, robust, and tunable system, which hierarchically self-assembles into soft-patchy particles and mechanically stabilizes selected, open crystalline structures. The self-aggregating patchy behavior can be fully controlled by the number of arms per star and by the fraction of attractive monomeric units at the free ends of the arms. Such self-assembled soft-patchy particles while forming, upon augmenting density, gel-like percolating networks, preserve properties as particle size, number, and arrangement of patches per particle. In particular, we demonstrate that the flexibility inherent in the soft-patchy particles brings forward a novel mechanism that leads to the mechanical stability of diamond and simple cubic crystals over a wide range of densities, and for molecular sizes ranging from about 10 nm up to the micrometer scale. PMID:23368272

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

2012-12-01

120

Dense neutron star matter  

SciTech Connect

The microscopic composition and properties of matter at super-saturation densities have been a subject of intense investigation for decades. The scarcity of experimental and observational data has lead to the necessary reliance on theoretical models. However, there remains great uncertainty in these models, which, of necessity, have to go beyond the over-simple assumption that high-density matter consists only of nucleons and leptons. Heavy strange baryons, mesons and quark matter in different forms and phases have to be included to fulfill basic requirements of fundamental laws of physics.

Stone, J. R. [Department of Physics, Oxford University, Parks Road, OX1 3PU Oxford, UK and Department of Physics and Astronomy, University of Tennessee, Knoxville TN 37996 (United States)

2014-05-02

121

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

NASA Astrophysics Data System (ADS)

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

Randisi, Ferdinando; Pelissetto, Andrea

2013-10-01

122

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

Sánchez-Monge, Á.; Beltrán, 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

123

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

124

Polymers.  

ERIC Educational Resources Information Center

Presents an open-ended experiment which has students exploring polymer chemistry and reverse osmosis. This activity involves construction of a polymer membrane, use of it in a simple osmosis experiment, and application of its principles in solving a science-technology-society problem. (ML)

Tucker, David C.

1986-01-01

125

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

PubMed

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

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

2013-03-26

126

Charged-current weak interaction processes in hot and dense matter and its impact on the spectra of neutrinos emitted from protoneutron star cooling.  

PubMed

We perform three-flavor Boltzmann neutrino transport radiation hydrodynamics simulations covering a period of 3 s after the formation of a protoneutron star in a core-collapse supernova explosion. Our results show that a treatment of charged-current neutrino interactions in hot and dense matter as suggested by Reddy et al. [Phys. Rev. D 58, 013009 (1998)] has a strong impact on the luminosities and spectra of the emitted neutrinos. When compared with simulations that neglect mean-field effects on the neutrino opacities, we find that the luminosities of all neutrino flavors are reduced while the spectral differences between electron neutrinos and antineutrinos are increased. Their magnitude depends on the equation of state and in particular on the symmetry energy at subnuclear densities. These modifications reduce the proton-to-nucleon ratio of the outflow, increasing slightly their entropy. They are expected to have a substantial impact on nucleosynthesis in neutrino-driven winds, even though they do not result in conditions that favor an r process. Contrary to previous findings, our results show that the spectra of electron neutrinos remain substantially different from those of other (anti)neutrino flavors during the entire deleptonization phase of the protoneutron star. The obtained luminosity and spectral changes are also expected to have important consequences for neutrino flavor oscillations and neutrino detection on Earth. PMID:23368446

Martínez-Pinedo, G; Fischer, T; Lohs, A; Huther, L

2012-12-21

127

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

SciTech Connect

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

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

2012-08-10

128

A poly(L-lysine)-based hydrophilic star block co-polymer as a protein nanocarrier with facile encapsulation and pH-responsive release.  

PubMed

A hydrophilic star block co-polymer was synthesized, characterized, and evaluated as a protein nanocarrier. The star block co-polymer was composed of a hyperbranched polyethylenimine (PEI) core, a poly(L-lysine) (PLL) inner shell, and a poly(ethylene glycol) (PEG) outer shell. The model protein insulin can be rapidly and efficiently encapsulated by the synthesized polymer in aqueous phosphate buffer at physiological pH. Complexation between PEI-PLL-b-PEG and insulin was investigated using native polyacrylamide gel electrophoresis. The uptake of enhanced green fluorescent protein into Ad293 cells mediated by PEI-PLL-b-PEG was also investigated. The encapsulated insulin demonstrated sustained release at physiological pH and showed accelerated release when the pH was decreased. The insulin released from the star block co-polymer retained its chemical integrity and immunogenicity. PMID:22373818

Yan, Yunsong; Wei, Daixu; Li, Jiayan; Zheng, Jinhong; Shi, Ganggang; Luo, Wenhong; Pan, Ying; Wang, Jinzhi; Zhang, Lumian; He, Xiaoying; Liu, Daojun

2012-07-01

129

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

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.

131

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

132

WASP-5b: a dense, very-hot Jupiter transiting a 12th-mag Southern-hemisphere star  

E-print Network

We report the discovery of WASP-5b, a Jupiter-mass planet orbiting a 12th-mag G-type star in the Southern hemisphere. The 1.6-d orbital period places WASP-5b in the class of very-hot Jupiters and leads to a predicted equilibrium temperature of 1750 K. WASP-5b is the densest of any known Jovian-mass planet, being a factor seven denser than TrES-4, which is subject to similar stellar insolation, and a factor three denser than WASP-4b, which has a similar orbital period. We present transit photometry and radial-velocity measurements of WASP-5 (= USNO-B1 0487-0799749), from which we derive the mass, radius and density of the planet: M_P = 1.58 +0.13 -0.08 M_J, R_P = 1.090 +0.094 -0.058 R_J and Rho_P = 1.22 +0.19 -0.24 Rho_J. The orbital period is P = 1.6284296 +0.0000048 -0.0000037 d and the mid-transit epoch is T_C (HJD) = 2454375.62466 +0.00026 -0.00025.

D. R. Anderson; M. Gillon; C. Hellier; P. F. L. Maxted; F. Pepe; D. Queloz; D. M. Wilson; A. Collier Cameron; B. Smalley; T. A. Lister; S. J. Bentley; A. Blecha; D. J. Christian; B. Enoch; L. Hebb; K. Horne; J. Irwin; Y. C. Joshi; S. R. Kane; M. Marmier; M. Mayor; N. R. Parley; D. L. Pollacco; F. Pont; R. Ryans; D. Ségransan; I. Skillen; R. A. Street; S. Udry; R. G. West; P. J. Wheatley

2008-02-22

133

ALMA Observations of Warm Dense Gas in NGC 1614—Breaking of the Star Formation Law in the Central Kiloparsec  

NASA Astrophysics Data System (ADS)

We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 ?m dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1{\\prime \\prime }= 329 pc). The CO emission is well resolved by the ALMA beam (0.''26 × 0.''20) into a circumnuclear ring, with an integrated flux of f CO(6-5) = 898 (± 153) Jy km s-1, which is 63(± 12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc < r < 350 pc from the nucleus, looks clumpy and includes seven unresolved (or marginally resolved) knots with median velocity dispersion of ~40 km s-1. These knots are associated with strong star formation regions with ?SFR ~ 100 M ? yr-1 kpc-2 and ? Gas˜ 104 {M}_? pc-2. The non-detections of the nucleus in both the CO (6-5) line emission and the 435 ?m continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between ?Gas and ?SFR, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of ~100 pc. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Xu, C. K.; Cao, C.; Lu, N.; Gao, Y.; Diaz-Santos, T.; Herrero-Illana, R.; Meijerink, R.; Privon, G.; Zhao, Y.-H.; Evans, A. S.; König, 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.

2015-01-01

134

Well-defined star-shaped conjugated macroelectrolytes as efficient electron-collecting interlayer for inverted polymer solar cells.  

PubMed

A star-shaped monodisperse conjugated macroelectrolyte grafted with cationic side chains, TrNBr, was designed, synthesized, and utilized as efficient electron-collecting cathode interlayers for inverted polymer solar cells. A neutral one composed of identical star-shaped conjugated backbone, TrOH, was also investigated for comparison. The surface properties and the function as interfacial layers on modulating the work function of bottom electrode (indium tin oxide) were systematically studied. Both interfacial electron-selective materials show strongly thickness-dependent performance for inverted polymer solar cells, and the best performance could be achieved via optimizing the thickness with 2.4 nm of TrNBr and 8.7 nm of TrOH. Parallel investigations of optimized TrNBr and TrOH interlayer in inverted architecture with active blend layer of poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:ICBA) demonstrated a remarkable power conversion efficiency (PCE) enhancement (PCE of 4.88% for TrNBr and 4.74% for TrOH) in comparison with those of conventional noninverted devices using Ca/Al cathodes (3.94%) and inverted devices with sol-gel ZnO buffer layer (4.21%). In addition, the inverted devices using the TrNBr and TrOH interlayer exhibited improved device stability in contrast to conventional noninverted devices using Ca/Al cathodes. PMID:25496704

Xu, Weidong; Kan, Zhipeng; Ye, Tengling; Zhao, Li; Lai, Wen-Yong; Xia, Ruidong; Lanzani, Guglielmo; Keivanidis, Panagiotis E; Huang, Wei

2015-01-14

135

Rheology of associative polymer solutions  

Microsoft Academic Search

Investigations of the rheological properties of associative polymer solutions that appeared over the last 5years are reviewed. Attention is focused on synthetic polymers containing relatively small solvophobic blocks that associate into dense spherical domains. We distinguish between polymers that contain a single associative group; so-called telechelic polymers that contain two associative groups; and polymers that contain many associative groups.

Christophe Chassenieux; Taco Nicolai; Lazhar Benyahia

2011-01-01

136

Nanoparticles based on star polymers as theranostic vectors: endosomal-triggered drug release combined with MRI sensitivity.  

PubMed

Dual-functional star polymers (diameters 15 nm) are synthesized producing nanoparticles with excellent colloidal stability in both water and serum. The nanoparticles are built with aldehyde groups in the core and activated esters in the arms. The different reactivity of the two functional groups to sequentially react with different amino compounds is exploited; doxorubicin (DOX) and 1-(5-amino-3-aza-2-oxypentyl)-4,7,10-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane (DO3A-tBu-NH2 )-a chelating agent effective for the complexation of Gadolinium ions (Gd). The activated ester group is employed to attach the DO3A chelating agent, while the aldehyde groups are exploited for DOX conjugation, providing a controlled release mechanism for DOX in acidic environments. DOX/Gd-loaded nanoparticles are rapidly taken up by MCF-7 breast cancer cells, subsequently releasing DOX as demonstrated using in vitro fluorescence lifetime imaging microscopy (FLIM). Endosomal, DOX release is observed, using a phasor plot representation of the fluorescence lifetime data, showing an increase of native DOX with time. The MRI properties of the stars are assessed and the relaxivity of Gd loaded in stars is three times higher than conventional organic Gd/DO3A complexes. The DOX/Gd-conjugated nanoparticles yield a similar IC50 to native DOX for breast cancer cell lines, confirming that DOX integrity is conserved during nanoparticle attachment and release. PMID:24985790

Li, Yang; Duong, Hien T T; Laurent, Sophie; MacMillan, Alexandre; Whan, Renee Megan; Elst, Luce Vander; Muller, Robert N; Hu, Jinming; Lowe, Andrew; Boyer, Cyrille; Davis, Thomas P

2015-01-01

137

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

PubMed Central

Biomaterials play pivotal roles in engineering tissue regeneration and repair. To regenerate irregular shaped defects, injectable cell carriers are desirable. Here, we report the development of self-assembled nanofibrous hollow microspheres from star-shaped biodegradable polymers as an injectable cell carrier for tissue regeneration. The nanofibrous hollow microspheres were shown to efficiently accommodate cells and enhance cartilage regeneration over control microspheres. The nanofibrous hollow microspheres also supported a significantly larger amount and higher quality cartilage regeneration over the chondrocytes alone group in an ectopic implantation model. In a critical-size rabbit osteochondral defect repair model, the nanofibrous hollow microspheres/chondrocytes group achieved substantially better cartilage repair and integration compared to the chondrocytes alone group that simulates the clinically available autologous chondrocyte implantation (ACI) procedure. These results indicate that the nanofibrous hollow microspheres are an excellent cell carrier for cartilage regeneration and are worthy of further investigation towards the aimed clinical application. PMID:21499313

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

2011-01-01

138

Effects of amphiphilic star-shaped poly(ethylene glycol) polymers with a cholic acid core on human red blood cell aggregation  

PubMed Central

Elevated red blood cell (RBC) aggregation increases low-shear blood viscosity and is closely related to several pathophysiological diseases such as atherosclerosis, thrombosis, diabetes, hypertension, cancer, and hereditary chronic hemolytic conditions. Non-ionic linear polymers such as poly(ethylene glycol) (PEG) and Pluronic F68 have shown inhibitory effects against RBC aggregation. However, hypersensitivity reactions in some individuals, attributed to a diblock component of Pluronic F68, have been reported. Therefore, we investigated the use of an amphiphilic star-shaped PEG polymer based on a cholic acid core as a substitute for Pluronics to reduce RBC aggregation. Cholic acid is a natural bile acid produced in the human liver and therefore should assure biocompatibility. Cholic acid based PEG polymers, termed CA(PEG)4, were synthesized by anionic polymerization. Size exclusion chromatography indicated narrow mass distributions and hydrodynamic radii less than 2 nm were calculated. The effects of CA(PEG)4 on human RBC aggregation and blood viscosity were investigated and compared to linear PEGs by light transmission aggregometry. Results showed optimal reduction of RBC aggregation for molar masses between 10–16 kDa of star-shaped CA(PEG)4 polymers. Cholic acid based PEG polymers affect the rheology of erythrocytes and may find applications as alternatives to linear PEG or Pluronics to improve blood fluidity. PMID:23262308

Janvier, Florence; Zhu, Julian X. X.; Armstrong, Jonathan; Meiselman, Herbert J.; Cloutier, Guy

2013-01-01

139

Mechanisms of the self-organization of star-shaped polymers with a varied structure of branching center based on fullerene C{sub 60} in solutions  

SciTech Connect

The self-organization of star-shaped polymers in toluene has been studied by small-angle neutron scattering. Polystyrene stars with a mono-C{sub 60} branching center are ordered into globular clusters ({approx}1700 nm in diameter), whereas stars with a double (C{sub 60}-C{sub 60}) center are ordered into anisotropic structures (superchains), which are linked (depending on the concentration) into triads (chain clusters {approx}2500 nm in diameter). On the contrary, heteroarm polystyrene and poly-2-vinylpyridine stars with a C{sub 60} center are weakly associated into dimers. Moderately polar stars with arms composed of polystyrene and diblock copolymer (poly-2-vinylpyridine-poly-tret-butyl methacrylate) form short chains composed of four macromolecules, while stars of higher polarity based on polystyrene and poly-tret-butyl methacrylate form clusters containing {approx}12 macromolecules {approx}50 nm in diameter. Thus, by varying the structure of the center and the arm polarity, one can control the modes of star structuring.

Lebedev, V. T., E-mail: vlebedev@pnpi.spb.ru [Russian Academy of Sciences, St. Petersburg Nuclear Physics Institute (Russian Federation); Toeroek, Gy. [Research Institute for Solid State Physics and Optics (Hungary); Vinogradova, L. V. [Russian Academy of Sciences, Institute of Macromolecular Compounds (Russian Federation)

2011-12-15

140

Effects of capillary pressure and use of polymer solutions on dense, non-aqueous-phase liquid retention and mobilization in a rough-walled fracture  

SciTech Connect

In this laboratory study, perchloroethylene (PCE) was permitted to migrate through a horizontal rough-walled limestone fracture under controlled conditions to assess fracture retention capacity. Retention of immiscible-phase PCE in the absence of an applied wetting-phase hydraulic gradient varied between 11% and 26% of the fracture volume. A portion of this residual could be removed through water flooding; however, even at the maximum applied hydraulic gradient of 1.0, residual PCE remained in the fracture. The observed correlation of reduced residual saturation with capillary number (N[sub c]) demonstrated that this rough-walled fracture exhibited behavior similar to that of a porous medium under water-flooding conditions. For a given hydraulic gradient, polymer-enhanced floods (using xanthan gum) were not as successful as conventional water flooding at removing residual from the fracture. The traditional form of the capillary number became an increasingly poor predictor of mobilization behavior as the viscosity of the displacing phase was increased. Incorporation of ([mu][sub w]/[mu][sub nw])[sup [minus]0.5] into the traditional capillary number provided a more appropriate dimensionless group with which to correlate residual PCE saturation in the fracture as [mu][sub w] increased.

Longino, B.L.; Kueper, B.H. (Queen's Univ., Kingston, Ontario (Canada). Dept. of Civil Engineering)

1999-07-15

141

Scale-free center-of-mass displacement correlations in dense polymer solutions and melts without topological constraints and momentum conservation: A bond-fluctuation model study  

E-print Network

By Monte Carlo simulations of a variant of the bond-fluctuation model without topological constraints we examine the center-of-mass (COM) dynamics of polymer melts in $d=3$ dimensions. Our analysis focuses on the COM displacement correlation function $\\CN(t) \\approx \\partial_t^2 \\MSDcmN(t)/2$, measuring the curvature of the COM mean-square displacement $\\MSDcmN(t)$. We demonstrate that $\\CN(t) \\approx -(\\RN/\\TN)^2 (\\rhostar/\\rho) \\ f(x=t/\\TN)$ with $N$ being the chain length ($16 \\le N \\le 8192$), $\\RN\\sim N^{1/2}$ the typical chain size, $\\TN\\sim N^2$ the longest chain relaxation time, $\\rho$ the monomer density, $\\rhostar \\approx N/\\RN^d$ the self-density and $f(x)$ a universal function decaying asymptotically as $f(x) \\sim x^{-\\omega}$ with $\\omega = (d+2) \\times \\alpha$ where $\\alpha = 1/4$ for $x \\ll 1$ and $\\alpha = 1/2$ for $x \\gg 1$. We argue that the algebraic decay $N \\CN(t) \\sim - t^{-5/4}$ for $t \\ll \\TN$ results from an interplay of chain connectivity and melt incompressibility giving rise to the correlated motion of chains and subchains.

Joachim P. Wittmer; Patrycia Poli?ska; Anna Cavallo; Hendrik Meyer; Jean Farago; Albert Johner; Jörg Baschnagel

2011-02-24

142

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

NASA Astrophysics Data System (ADS)

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 stars orbiting the black hole at distances of a few to a few tens of milli parsecs.

Schödel, R.; Feldmeier, A.; Neumayer, N.; Meyer, L.; Yelda, S.

2014-12-01

143

On the Evolution of the Dense Core Mass Function  

E-print Network

The mass distributions of dense cores in star-forming regions are measured to have a shape similar to the initial mass function of stars. This has been generally interpreted to mean that the constituent cores will form individual stars or stellar systems at a nearly constant star formation efficiency. This article presents a series of numerical experiments evolving distributions of dense cores into stars to quantify the effects of stellar multiplicity, global core fragmentation, and a varying star formation efficiency. We find that the different evolutionary schemes have an overall small effect on the shape of the resultant distribution of stars. Our results imply that at the current level of observational accuracy the comparison between the mass functions of dense cores and stars alone is insufficient to discern between different evolutionary models. Observations over a wide range of mass scales including the high or low-mass tails of these distributions have the largest potential for discerning between different core evolutionary schemes.

Jonathan J. Swift; Jonathan P. Williams

2008-02-14

144

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...

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

2014-01-01

145

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

146

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

147

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

148

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

SciTech Connect

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

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

2011-11-20

149

Dynamics of microemulsions bridged with hydrophobically end-capped star polymers studied by neutron spin-echo.  

PubMed

The mesoscopic dynamical properties of oil-in-water microemulsions (MEs) bridged with telechelic polymers of different number of arms and with different lengths of hydrophobic stickers were studied with neutron spin-echo (NSE) probing the dynamics in the size range of individual ME droplets. These results then were compared to those of dynamicic light scattering (DLS) which allow to investigate the dynamics on a much larger length scale. Studies were performed as a function of the polymer concentration, number of polymer arms, and length of the hydrophobic end-group. In general it is observed that the polymer bridging has a rather small influence on the local dynamics, despite the fact that the polymer addition leads to an increase of viscosity by several orders of magnitude. In contrast to results from rheology and DLS, where the dynamics on much larger length and time scales are observed, NSE shows that the linear polymer is more efficient in arresting the motion of individual ME droplets. This finding can be explained by a simple simulation, merely by the fact that the interconnection of droplets becomes more efficient with a decreasing number of arms. This means that the dynamics observed on the short and on the longer length scale depend in an opposite way on the number of arms and hydrophobic stickers. PMID:25669409

Hoffmann, I; de Molina, Paula Malo; Farago, B; Falus, P; Herfurth, Christoph; Laschewsky, André; Gradzielski, M

2014-01-21

150

Organogelation behavior and thermal properties of supramolecular polymer network composed of carboxy- and pyridyl-terminated 4-arm star-shaped ?-caprolactone oligomers.  

PubMed

Carboxy-terminated 4-arm star-shaped ?-caprolactone oligomers (Tetra-SA-CLO, Tetra-PA-CLO, and Tetra-TCPA-CLO) were synthesized by the reactions of hydroxy-terminated 4-arm star-shaped ?-caprolactone oligomers (Tetra-OH-CLO) having the degree of polymerization per one oligocaprolactone chain, n=3 and 5 with succinic anhydride, phthalic anhydride, and 2,3,4,5-tetrachlorophthalic anhydride, respectively. As a pyridyl-terminated analog, nicotinate-functionalized 4-arm star-shaped ?-caprolactone oligomer (Tetra-NA-CLO) was synthesized by the esterification reaction of Tetra-OH-CLO with nicotinic acid. All mixtures of the carboxy- and pyridyl-terminated analogs became thermoreversible organogels in N,N-dimethylformamide and nitromethane at around 15°C. The (1)H NMR and FT-IR analyses of the mixtures revealed the formation of hydrogen-bonded polymer network. The glass transition and cold crystallization temperatures of the mixtures were higher than the values estimated from those of the single components. PMID:23684230

Nakamura, Taro; Chu, Xiaoyun; Shimasaki, Toshiaki; Shibata, Mitsuhiro

2013-08-15

151

Choosing Nutrient Dense Foods  

MedlinePLUS Videos and Cool Tools

... eat. Are they primarily nutrient-dense, like these, [ photos of melon, red bell pepper, oatmeal ] or are they mostly calorie dense, like these? [ photos of butter crackers, bacon, coffee cake ] Some older ...

152

White Dwarf Stars  

Microsoft Academic Search

A white dwarf is a very dense star: The earth-sized remains of a Sun-like star that has burned all of its nuclear fuel. Although it's unable to carry out the workaday activities of a living star, a white dwarf is still an interesting object to astronomers. For one thing, white dwarfs experience \\

Steven Kawaler; Michael Dahlstrom

2000-01-01

153

Star formation Simon Goodwin  

E-print Network

Star formation Simon Goodwin Dept Physics & Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, UK. s.goodwin@sheffield.ac.uk 1 Abstract Stars are one of the most important consituents of the Universe, and understanding their formation is crucial to many areas of astrophysics. Stars form from dense

Crowther, Paul

154

Probing Cold Dense Nuclear Matter  

E-print Network

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

R. Subedi; R. Shneor; P. Monaghan; B. D. Anderson; K. Aniol; J. Annand; J. Arrington; H. Benaoum; F. Benmokhtar; W. Bertozzi; W. Boeglin; J. -P. Chen; Seonho Choi; E. Cisbani; B. Craver; S. Frullani; F. Garibaldi; S. Gilad; R. Gilman; O. Glamazdin; J. -O. Hansen; D. W. Higinbotham; T. Holmstrom; H. Ibrahim; R. Igarashi; C. W. de Jager; E. Jans; X. Jiang; L. Kaufman; A. Kelleher; A. Kolarkar; G. Kumbartzki; J. J. LeRose; R. Lindgren; N. Liyanage; D. J. Margaziotis; P. Markowitz; S. Marrone; M. Mazouz; D. Meekins; R. Michaels; B. Moffit; C. F. Perdrisat; E. Piasetzky; M. Potokar; V. Punjabi; Y. Qiang; J. Reinhold; G. Ron; G. Rosner; A. Saha; B. Sawatzky; A. Shahinyan; S. Širca; K. Slifer; P. Solvignon; V. Sulkosky; G. Urciuoli; E. Voutier; J. W. Watson; L. B. Weinstein; B. Wojtsekhowski; S. Wood; X. -C. Zheng; L. Zhu

2009-08-11

155

Probing Cold Dense Nuclear Matter  

E-print Network

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

Subedi, R; Monaghan, P; Anderson, B D; Aniol, K; Annand, J; Arrington, J; Benaoum, H; Benmokhtar, F; Bertozzi, W; Boeglin, W; Chen, J -P; Choi, Seonho; Cisbani, E; Craver, B; Frullani, S; Garibaldi, F; Gilad, S; Gilman, R; Glamazdin, O; Hansen, J -O; Higinbotham, D W; Holmstrom, T; Ibrahim, H; Igarashi, R; De Jager, C W; Jans, E; Jiang, X; Kaufman, L; Kelleher, A; Kolarkar, A; Kumbartzki, G; LeRose, J J; Lindgren, R; Liyanage, N; Margaziotis, D J; Markowitz, P; Marrone, S; Mazouz, M; Meekins, D; Michaels, R; Moffit, B; Perdrisat, C F; Piasetzky, E; Potokar, M; Punjabi, V; Qiang, Y; Reinhold, J; Ron, G; Rosner, G; Saha, A; Sawatzky, B; Shahinyan, A; Širca, S; Slifer, K; Solvignon, P; Sulkosky, V; Urciuoli, G; Voutier, E; Watson, J W; Weinstein, L B; Wojtsekhowski, B; Wood, S; Zheng, X -C; Zhu, L; 10.1126/science.1156675

2009-01-01

156

Probing Cold Dense Nuclear Matter  

SciTech Connect

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

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

2008-06-01

157

Probing cold dense nuclear matter.  

SciTech Connect

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

Subedi, R.; Monaghan, P.; Shneor, R.; Anderson, B. D.; Aniol, K.; Arrington, J.; Physics; Kent State Univ.; Tel Aviv Univ.; California State Univ. Los Angeles

2008-06-13

158

Photoenhanced gene transfection by a star-shaped polymer consisting of a porphyrin core and poly(L-lysine) dendron arms.  

PubMed

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

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

2013-09-01

159

Dibaryons in neutron stars  

NASA Technical Reports Server (NTRS)

The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.

Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.

1991-01-01

160

Neutrinos from Protoneutron Stars  

E-print Network

We study the diffusive transport of neutrinos in a newly born neutron star to explore its sensitivity to dense matter properties. Energy and lepton number which are trapped during the catastrophic implosion diffuse out on the time scale of a few tens of seconds. Results for different dense matter models are presented.

S. Reddy; J. Pons; M. Prakash; J. M. Lattimer

1998-02-24

161

Evolution of Randall-Sundrum Black Holes in Dense Media  

E-print Network

In the framework of Randall-Sundrum model, we discuss the evolution of microscopic black holes created by cosmic particles hitting a neutron or a strange star. We set up the general equations of evolution for the black hole mass and momentum in a dense medium, and discuss the possibility of collapse due to the black hole's growth inside the star.

Veronique Van Elewyck

2003-05-14

162

Are energy dense diets also nutrient dense?  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

163

Atomic Transport/ Dense Metallic  

E-print Network

contaminants + partial pressure #12;Technology Options ­ Atomic Transport/Dense Metallic Systems Pd alloy membranes Free standing foils Physical composites Chemical composites Pd coated metals Process/Dense Metallic Systems Module Construction Lack of economical, large-scale manufacturing methods Lack of sealing

164

Triggered Star Formation by Massive Stars  

NASA Astrophysics Data System (ADS)

We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the ? 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.

Lee, Hsu-Tai; Chen, W. P.

2007-03-01

165

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

2009-02-03

166

Ice, Dust and Extinction in Dense Clouds  

NASA Astrophysics Data System (ADS)

We present the results of our ongoing study of ice evolution, dust properties and extinction in dense cores, dense clouds with varying levels of star formation activity, and young stellar objects (Chiar et al. 2007, 2011; Boogert et al. 2008, 2011). Our studies are based on 5 to 25 micron spectra from Spitzer's Infrared Spectrometer, 2 to 4 micron spectra from ground-based facilities (IRTF-SpeX, VLT-ISAAC, Keck-NIRSPEC), and 2 to 24 micron photometry from Spitzer and 2MASS. For the dense core and clouds, we use background field stars to probe the dense cloud environments. We used the K-band spectra, in conjunction with stellar photosphere models, to accurately classify the spectral type of the field stars, helping to better quantify the extinction curve across the full spectral range. For quiescent clouds as probed by field stars, we find that the extinction between 13 and 25 micron is 50% less than that at 2.2 micron. In addition to the continuum extinction that is well-fitted by our empirically derived extinction curve, we also analyzed the ice and dust features for each line of sight. The H2O-ice column is determined from the 3 micron band (where observed) and, where there is a high enough dust column, absorption features centered at 6.0 and 6.85 micron are observed. The 6.0 and 6.85 micron features likely have several carriers in addition to H2O-ice: CH3OH, NH4+, HCOOH, H2CO and NH3. These ice features show no signs of thermal or energetic processing of the ice species, unlike many YSO environments. The 3.53 and 9.7 micron stretching modes of CH3OH-ice are also detected in a few lines of sight. These are the first detections of CH3OH-ice in dense clouds unassociated with YSO environments. For our large sample, we have also substantiated the result by Chiar et al. (2007) that the ratio of the 9.7 micron silicate absorption to the near-IR color excess is smaller in dense clouds compared to the diffuse interstellar medium.

Chiar, J.; Boogert, A.; Knez, C.; Tielens, X.

2011-05-01

167

Relaxation dynamics of branched polymers  

NASA Astrophysics Data System (ADS)

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

Ghosh, Arnav

168

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.

Dave Bock

1999-01-21

169

Dense gases for extraction and refining  

SciTech Connect

Procedures for extracting or refining sensitive substances using dense gases have been developed for numerous purposes. Applications have been tested on the laboratory or pilot plant scales and shown to be mostly economical. Uses as varied as the non-aggressive extraction of spice, extraction of polymers, refining of spent oil, pyrolysis/extraction of wood and liquefaction of coal show the extremely wide range of application. The book reviews the present state of development and features examples of application of this new technique.

Stahl, E.; Quirin, K.W.; Gerard, D.

1987-01-01

170

Polymer films  

DOEpatents

A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

Granick, Steve (Champaign, IL); Sukhishvili, Svetlana A. (Maplewood, NJ)

2008-12-30

171

Quark Stars: Features and Findings  

E-print Network

Under extreme conditions of temperature and/or density, quarks and gluons are expected to undergo a deconfinement phase transition. While this is an ephemeral phenomenon at the ultra-relativistic heavy-ion collider (BNL-RHIC), quark matter may exist naturally in the dense interior of neutron stars. Herein, we present an appraisal of the possible phase structure of dense quark matter inside neutron stars, and the likelihood of its existence given the current status of neutron star observations. We conclude that quark matter inside neutron stars cannot be dismissed as a possibility, although recent observational evidence rules out most soft equations of state.

Prashanth Jaikumar

2007-01-25

172

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

173

The ? Orionis Star Forming Region  

NASA Astrophysics Data System (ADS)

Around the O8 star ? Orionis is a highly evolved star-forming region, comprising recently formed stars from 0.2 M?Mar to 24 M?Mar and dark clouds actively forming stars, all within a 30-pc radius ring of dust and neutral and molecular hydrogen. The spatial and age distributions of the stars show that originally star formation occurred in an elongated giant molecular cloud, with the most massive stars forming in a dense central core. A supernova is suggested as the mechanism that terminated star formation in that core and formed the surrounding ring. Star formation continues in remnant dark clouds distant from the original core. The local initial mass functions differ significantly across the region, although the global IMF is field-like. Interestingly, the lack of H? emission in stars near ? Ori indicates that the environment of the massive stars was not conducive for the survival of accretion disks.

Mathieu, R. D.

2008-12-01

174

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

175

Microporous polymer films and methods of their production  

DOEpatents

A process for producing thin microporous polymeric films for a variety of uses. The process utilizes a dense gas (liquified 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.

Aubert, James H. (Albuquerque, NM)

1995-01-01

176

Bondi-Hoyle Accretion in Star Clusters: Implications for Stars, Disks, and Planets  

E-print Network

Bondi-Hoyle Accretion in Star Clusters: Implications for Stars, Disks, and Planets Henry Throop of forming star clusters may occasionally pass through associated dense molecular gas and experience Bondi. N-body simulations of stars orbiting in three young model clusters containing comparable initial

Throop, Henry

177

Star and planet formation in young stellar clusters Die meisten Sterne in unserer Milchstrae wer-  

E-print Network

Star and planet formation in young stellar clusters Die meisten Sterne in unserer MilchstraÃ?e wer such as Orion demonstrated that most of the young stars there are found in dense aggregates or clusters around binary stars and in dense clusters will evolve quite differently to those around single stars

178

Polyelectrolyte Stars and Cylindrical Brushes Made by ATRP: New Building Blocks in Nanotechnology  

NASA Astrophysics Data System (ADS)

Star polymers and cylindrical polymer brushes (CPBs), i.e. polymers possessing side groups densely grafted from a linear main chain, have attracted considerable experimental and theoretical interest over the past decade, owing to their peculiar solution and bulk properties. We have used the grafting-from approach via ATRP to synthesize well-defined star polymers and core—shell CPBs with homopolymer and block copolymer side chains. The diblock copolymer side chains may include combinations of soft-hard, hydrophilic-hydrophobic and crystalline-amorphous block segments. In particular, we have been interested in polyelectrolyte blocks; then the polymers resemble intramolecular spherical and cylindrical micelles, respectively. Star polymers of poly(acrylic acid) (PAA) and poly(N,N-dimethylaminoethyl methacrylate) (DMAEMA) were made using sugar- or silsesquioxane-based ATRP initiators. Their LCST and UCST phase behaviour depends on pH, counterion charge, temperature, and light. PDMAEMA CPBs react in a similar way, and on addition of trivalent counterions they even form helical structures. We have also synthesized hybrid nanowires of semiconducting CdS and CdSe or nanomagnets of ?-Fe2O3 inside the PAA core of CPBs. Here, we present novel water-soluble and biocompatible silica nanowires based on CPBs. They have a core consisting of a silsesquioxane network of crosslinked poly(3-acryloylpropyl trimethoxysilane) (PAPTS) and a shell of poly(oligoe-thyleneglycol methacrylate) (POEGMA). Sequential ATRP of APTS and OEGMA initiated by a polyinitiator backbone (DP = 3,200) was carried out in benzene. Due to the cylindrical shape of the brushes the functional TMS moieties were arranged into a 1D manner and then crosslinked via alkaline condensation, rendering the rigid core—shell hybrid CPBs. Finally, uniform silica nanowires were achieved by the simultaneous removal of the hybrid CPB template via pyrolysis. The length as well as the diameter of silica nanowires are well-defined.

Plamper, Felix; Xu, Youyong; Yuan, Jiayin; Ballauff, Matthias; Müller, Axel H. E.

179

Effect of polymer electrode morphology on performance of a lithium/polypyrrole battery  

E-print Network

membrane is used as a template in which to electrochemically polymerize pyrrole, then the membrane is dissolved, leaving the polymer in a fibrillar form. Conventionally, the polymer is electrochemically polymerized as a dense polymer film on a smooth Pt... disk electrode. Previous work has shown that when the polymer is electrochemically polymerized in fibrillar form, charge transport rates are faster and charge capacities are greater than for dense, conventionally grown films containing the same...

Nicholson, Marjorie Anne

2012-06-07

180

Star Formation in the Orion Nebula Cluster  

Microsoft Academic Search

We study the record of star formation activity within the dense cluster associated with the Orion Nebula. The bolometric luminosity function of 900 visible members is well matched by a simplified theoretical model for cluster formation. This model assumes that stars are produced at a constant rate and distributed according to the field-star initial mass function. Our best-fit age for

Francesco Palla; Steven W. Stahler

1999-01-01

181

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

182

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

2006-12-08

183

Dense Molecular Gas in Centaurus A  

NASA Astrophysics Data System (ADS)

Centaurus A (NGC 5128) is the closest radio galaxy, and its molecular interstellar medium has been studied extensively in recent years. However, these studies used mostly molecular lines tracing low to medium density gas (see e.g. Eckart et al. 1990. Wild et al. 1997). The amount and distribution of the dense component remained largely unknown. We present spectra of the HCN(1-0) emission - which traces dense (n(H2) > 104 cm-3) molecular gas - at the center and along the prominent dust lane at offset positions +/- 60" and +/- 100", as well as single CS(2-1) and CS(3-2) spectra, observed with the SEST on La Silla, Chile. At the central position, the integrated intensity ratio I(HCN)/I(CO) peaks at 0.064, and decreases to somewhat equal to 0.02 to 0.04 in the dust lane. Based on the line luminosity ratio L(HCN)/L(CO) we estimate that there is a significant amount of dense gas in Centaurus A. The fraction of dense molecular gas as well as the star formation efficiency LFIR/LCO towards the center of Cen A is comparable to ultra-luminous infrared galaxies, and falls in between the values for ULIRGs and normal galaxies for positions in the dust lane. Details will be published in Wild & Eckart (A&A, in prep.). Eckart et al. 1990, ApJ 363, 451 Rydbeck et al. 1993, Astr.Ap. (Letters) 270, L13. Wild, W., Eckart, A. & Wiklind, T. 1997, Astr.Ap. 322, 419.

Wild, Wolfgang; Eckart, Andreas

1999-10-01

184

Tracing the Dense Molecular Gas in the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

We report findings from the Magellanic Mopra Assessment (MAGMA) Dense Gas Survey of the Large Magellanic Cloud (LMC), which comprises spectra of HCO+(1-0), HCN(1-0), and HNC(1-0) toward 48 giant molecular clouds (GMCs) distributed across the LMC. 12CO(1-0) and 13CO(1-0) data from the MAGMA survey were also included. These molecules trace dense gas and hence are the ingredients of future star formation. We investigate possible correlations between the dense gas tracers and various physical and dynamical properties across the LMC. No correlation between the dense gas fraction (CO/HCN) and the position of the parent GMC is observed in the LMC. We compare our 12CO data in these clouds to the 70 micron flux at those locations and find that our results are not consistent with the Kennicutt-Schmidt Law. However we do find that star formation rate is linearly correlated with the dense gas as traced by HCN. This further validates the usefulness of HCN to trace the dense gas in the molecular clouds. The analogous correlation using HCO+ is found to be more complex. It appears that HCO+ may saturate below a certain amount of star formation, hinting at an additional diffuse component in HCO+. We find that the HCO+/HCN line ratio is greater than 2 in the clouds studied here, whereas previous studies of this ratio in other galaxies typically report HCO+/HCN roughly 1. This provides additional evidence for enhanced HCO+.

Levy, Rebecca C.; Ott, Juergen; Meier, David S.; Hughes, Annie

2015-01-01

185

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

186

Quantum-Dense Metrology  

E-print Network

Quantum metrology utilizes entanglement for improving the sensitivity of measurements. Up to now the focus has been on the measurement of just one out of two non-commuting observables. Here we demonstrate a laser interferometer that provides information about two non-commuting observables, with uncertainties below that of the meter's quantum ground state. Our experiment is a proof-of-principle of quantum dense metrology, and uses the additional information to distinguish between the actual phase signal and a parasitic signal due to scattered and frequency shifted photons. Our approach can be readily applied to improve squeezed-light enhanced gravitational-wave detectors at non-quantum noise limited detection frequencies in terms of a sub shot-noise veto-channel.

Sebastian Steinlechner; Jöran Bauchrowitz; Melanie Meinders; Helge Müller-Ebhardt; Karsten Danzmann; Roman Schnabel

2012-11-15

187

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

188

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

189

Microgravity Polymers  

NASA Technical Reports Server (NTRS)

A one-day, interactive workshop considering the effects of gravity on polymer materials science was held in Cleveland, Ohio, on May 9, 1985. Selected programmatic and technical issues were reviewed to introduce the field to workshop participants. Parallel discussions were conducted in three disciplinary working groups: polymer chemistry, polymer physics, and polymer engineering. This proceedings presents summaries of the workshop discussions and conclusions.

1986-01-01

190

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.

191

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

192

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

193

The viscoelastic properties of linear-star blends  

E-print Network

In order to understand the nature of polydispersity and characterize the effect of branching architecture, the model blend of linear and star polymer, which is the simplest branched polymer, is contrived. In this blend system, chain dynamics...

Lee, Jung Hun

2000-01-01

194

Dense Hypervelocity Plasma Jets  

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

195

Densely Cratered Region  

NASA Technical Reports Server (NTRS)

One of Mariner 10's two TV cameras took this picture (FDS 166614) of a densely cratered region of Mercury at 12:39 p.m. PDT, September 21, 1974, 80 minutes prior to the spacecraft's second close encounter with the planet. Taken from a range of about 76,000 kilometers (47,000 miles) the picture shows a scarp, or cliff, two kilometers (7500 feet) above the surrounding area and is part of a larger system of faults which extends for hundreds of kilometers. Mariner 10, which mapped about one-quarter of Mercury's surface last March, is the first spacecraft to return to its target planet.

The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.

Image Credit: NASA/JPL/Northwestern University

1974-01-01

196

Ammonia and HC7N Emission in Starless Dense Cores  

NASA Astrophysics Data System (ADS)

Dense cores represent the transition between the turbulent, diffuse ISM and protostars. Thus, understanding dense cores' chemical and physical properties provides valuable information about the early stages of low mass star formation. We present an analysis of 13 starless dense cores in the Taurus Molecular Cloud using new data taken with the Green Bank Telescope. Our observations consist of ammonia (NH3) (1,1) and (2,2) and HC7N (J=21-20) emission. We present new detections of HC7N (a carbon chain bearing species) in four cores and confirm detection in two cores. We also present temperature and velocity gradient maps. These results are the foundation of a more complete survey and illustrate an important relationship between ammonia and the carbon chain bearing species HC7N.

Candelaria, Tierra M.; Scott Schnee, Kathryn Devine, John Carpenter, Paola Caselli, Mario Tafalla, Youngmin Seo, Yancy Shirley, James Di Francesco, John Tobin, Shadi Chitsazzadeh, Sarah Sadavoy, Alyssa Goodman, Luca Ricci,; Shigehisa Takakuwa

2015-01-01

197

Noncontractible loops in the dense O (n ) loop model on the cylinder  

NASA Astrophysics Data System (ADS)

A lattice model of critical dense polymers O (n ) is considered for finite cylinder geometry. Due to the presence of noncontractible loops with a fixed fugacity ? , the model at n =0 is a generalization of the critical dense polymers solved by Pearce, Rasmussen, and Villani. We found the free energy for any height N and circumference L of the cylinder. The density ? of noncontractible loops is obtained for N ?? and large L . The results are compared with those found for the anisotropic quantum chain with twisted boundary conditions. Using the latter method, we derived ? for any O (n ) model and an arbitrary fugacity.

Alcaraz, F. C.; Brankov, J. G.; Priezzhev, V. B.; Rittenberg, V.; Rogozhnikov, A. M.

2014-11-01

198

Kaon condensation in dense stellar matter  

SciTech Connect

This article combines two talks given by the authors and is based on Works done in collaboration with G.E. Brown and D.P. Min on kaon condensation in dense baryonic medium treated in chiral perturbation theory using heavy-baryon formalism. It contains, in addition to what was recently published, astrophysical backgrounds for kaon condensation discussed by Brown and Bethe, a discussion on a renormalization-group analysis to meson condensation worked out together with H.K. Lee and S.J. Sin, and the recent results of K.M. Westerberg in the bound-state approach to the Skyrme model. Negatively charged kaons are predicted to condense at a critical density 2 {approx_lt} {rho}/{rho}o {approx_lt} 4, in the range to allow the intriguing new phenomena predicted by Brown and Bethe to take place in compact star matter.

Lee, Chang-Hwan [Seoul National Univ. (Korea, Republic of); Rho, M. [CEA Centre d`Etudes Nucleaires de Saclay, 91 - Gif-sur-Yvette (France). Service de Physique Theorique]|[Washington Univ., Seattle, WA (United States). Inst. for Nuclear Theory

1995-03-01

199

Diffusive currents and Coulomb separation of ions in dense matter  

NASA Astrophysics Data System (ADS)

We derive diffusive currents in strongly coupled Coulomb ion mixtures in dense stellar matter. Coulomb coupling in the presence of gravity and electric fields, induced by gravity owing to plasma polarization, creates a specific diffusion current which separates ions with the same A/Z (mass to charge number ratios) but different Z. This Coulomb separation can be important in white dwarfs and neutron stars.

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

2014-12-01

200

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

201

The theory of polymer solutions at intermediate concentration  

Microsoft Academic Search

It is argued that polymer solutions can be classified into three broad types which may be characterized in terms of N the total number of (micro) molecules, n the number of polymer chains, l the effective length of a micromolecule, v the excluded volume per micromolecule and V the total volume. The types are: (i) dense solutions in which V\\/N

S F Edwards

1966-01-01

202

Tailormade Polymers  

NASA Astrophysics Data System (ADS)

The national Symposium of the Division of Macromolecular Chemistry of the GDCh (Gesellschaft Deutscher Chemiker) in March 2000 was held in Merseburg with a topic of Tailormade Polymers. The scientific program was divided in two parts: contemporary activities in polymer synthesis and the tailoring of polymer properties by suitable modification steps. An excellent insight into contemporary activities in polymer synthesis, modification and characterization was given. A selection of the contributions is presented in this volume.

Cherdron, Harald; Sandner, Barbara; Schenk, H. U.; Voit, Brigitte; Meisel, I.; Kniep, C. S.; Spiegel, S.

2001-05-01

203

Piezoelectric Polymers  

NASA Technical Reports Server (NTRS)

The purpose of this review is to detail the current theoretical understanding of the origin of piezoelectric and ferroelectric phenomena in polymers; to present the state-of-the-art in piezoelectric polymers and emerging material systems that exhibit promising properties; and to discuss key characterization methods, fundamental modeling approaches, and applications of piezoelectric polymers. Piezoelectric polymers have been known to exist for more than forty years, but in recent years they have gained notoriety as a valuable class of smart materials.

Harrison, J. S.; Ounaies, Z.; Bushnell, Dennis M. (Technical Monitor)

2001-01-01

204

Star-shaped polymers of bio-inspired algae core and poly(acrylamide) and poly(acrylic acid) as arms in dissolution of silica/silicate.  

PubMed

Silica, in natural waters (due to weathering of rocks) decreases system performance in water processing industry due to scaling. In view of that, the present work involves the synthesis of novel green star shaped additives of algae core (a bio-inspired material as diatom maintains silicic acid equilibrium in sea water) as silica polymerization inhibitors. Star shaped materials with bio-inspired core and poly(acrylamide) [poly(AAm)] and poly(acrylic acid) [poly(AAc)] arms were synthesized by economical green approach. The proficiency was evaluated in 'mini lab' scale for the synthesized APAAm (Algae-g-poly(AAm)) and APAAc (Algae-g-poly(AAc)) dendrimers (star shaped) in colloidal silica mitigation/inhibition at 35 °C and 55 °C. Synthesized dendrimers were equally proficient in silica inhibition at 12 h and maintains ?450 ppm soluble silica. However, APAAm dendrimers of generation 0 confirmed better results (?300 ppm) in contrast to APAAc dendrimers in silica inhibition at 55 °C. Additionally, dendrimers also worked as a nucleator for heterogeneous polymerization to inhibit silica homo-polymerization. APAAm dendrimer test set showed no silica deposit for more than 10 days of inhibition. EDX characterization results support nucleator mechanism with Si content of 6.97%-10.98% by weight in silica deposits (SiO2-APAAm dendrimer composites). PMID:24681378

Chauhan, Kalpana; Patiyal, Priyanka; Chauhan, Ghanshyam S; Sharma, Praveen

2014-06-01

205

Color superconductivity and dense quark matter  

E-print Network

The properties of cold and dense quark matter have been the subject of extensive investigation, especially in the last decade. Unfortunately, we still lack of a complete understanding of the properties of matter in these conditions. One possibility is that quark matter is in a color superconducting phase which is characterized by the formation of a diquark condensate. We review some of the basic concepts of color superconductivity and some of the aspects of this phase of matter which are relevant for compact stars. Since quarks have color, flavor as well as spin degrees of freedom many different color superconducting phases can be realized. At asymptotic densities QCD predicts that the color flavor locked phase is favored. At lower densities where the QCD coupling constant is large, perturbative methods cannot be applied and one has to rely on some effective model, eventually trying to constrain such a model with experimental observations. The picture is complicated by the requirement that matter in the interior of compact stars is in weak equilibrium and neutral. These conditions and the (possible) large value of the strange quark mass conspire to separate the Fermi momenta of quarks with different flavors, rendering homogenous superconducting phases unstable. One of the aims of this presentation is to introduce non-experts in the field to some of the basic ideas of color superconductivity and to some of its open problems.

Massimo Mannarelli

2008-12-15

206

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

207

Dense coordination network capable of selective CO2 capture from C1 and C2 hydrocarbons.  

PubMed

We elucidated the specific adsorption property of CO(2) for a densely interpenetrated coordination polymer which was a nonporous structure and observed gas separation properties of CO(2) over CH(4), C(2)H(4), and C(2)H(6), studied under both equilibrium and kinetic conditions of gases at ambient temperature and pressure. PMID:22667323

Horike, Satoshi; Kishida, Keisuke; Watanabe, Yoshihiro; Inubushi, Yasutaka; Umeyama, Daiki; Sugimoto, Masayuki; Fukushima, Tomohiro; Inukai, Munehiro; Kitagawa, Susumu

2012-06-20

208

NANOINDENTATION CHARACTERIZATION OF VINYLESTER GLASS-FIBER COMPOSITES SUBMITTED TO DENSE UV-RADIATION EXPOSURE  

E-print Network

1 NANOINDENTATION CHARACTERIZATION OF VINYLESTER GLASS-FIBER COMPOSITES SUBMITTED TO DENSE UV resins, glass fibers and their composites has shown significant losses in their mechanical properties of polymer matrix composites in building and construction has become increasingly attractive, though some

Paris-Sud XI, Université de

209

Extreme horizontal branch stars  

NASA Astrophysics Data System (ADS)

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. They exist both in the disk and halo populations (globular clusters) of the Galaxy. Amongst the field stars a large fraction of sdBs are found to reside in close binaries. The companions are predominantly white dwarfs, but also low mass main sequence stars are quite common. Systems with sufficiently massive white dwarf companions may qualify as Supernova 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 amongst 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 subluminous O stars, the hotter sisters of the sdB stars, because their binary fraction is lower than that of the sdBs by a factor of ten or more. The rivaling ''late hot flasher'' scenario is also discussed. 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.

Heber, U.

210

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

211

Could Dense Quark Matter be a Source of Super High Energy Cosmic Rays?  

E-print Network

We propose that the dense quark matter could be a source of the high-energy secondary hadrons. These particles can be created from hadronization of the parton(s), which possess the energy of grouped partons from coherent interactions as a result of their collective behav- ior in high dense medium. The medium might be formed in the centre of some massive stars, and it could be a source of the super high-energy cosmic rays. In this work we consider some experimental results as an evidence on collective phenomenon, that can lead to coherent interactions in high dense medium and production of the high-energy secondary hadrons.

Mais Suleymanov

2011-10-10

212

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

213

The physics of neutron stars.  

PubMed

Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics, and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near 10(10) kelvin, opaqueness to neutrinos, and magnetic fields in excess of 10(13) Gauss. Here, we describe the formation, structure, internal composition, and evolution of neutron stars. Observations that include studies of pulsars in binary systems, thermal emission from isolated neutron stars, glitches from pulsars, and quasi-periodic oscillations from accreting neutron stars provide information about neutron star masses, radii, temperatures, ages, and internal compositions. PMID:15105490

Lattimer, J M; Prakash, M

2004-04-23

214

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.

David Teegarden

2004-01-01

215

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

216

The dense gas mass fraction in the W51 cloud and its protoclusters  

NASA Astrophysics Data System (ADS)

Context. The density structure of molecular clouds determines how they will evolve. Aims: We map the velocity-resolved density structure of the most vigorously star-forming molecular cloud in the Galactic disk, the W51 giant molecular cloud. Methods: We present new 2 cm and 6 cm maps of H2CO, radio recombination lines, and the radio continuum in the W51 star forming complex acquired with Arecibo and the Green Bank Telescope at ~ 50? resolution. We use H2CO absorption to determine the relative line-of-sight positions of molecular and ionized gas. We measure gas densities using the H2CO densitometer, including continuous measurements of the dense gas mass fraction (DGMF) over the range 104cm-3dense gas mass fraction has been measured over a range of densities with a single data set. Results: The DGMF in W51 A is high, f ? 70% above n> 104cm-3, while it is low, f< 20%, in W51 B. We did not detect any H2CO emission throughout the W51 GMC; all gas dense enough to emit under normal conditions is in front of bright continuum sources and therefore is seen in absorption instead. Conclusions: (1) The dense gas fraction in the W51 A and B clouds shows that W51 A will continue to form stars vigorously, while star formation has mostly ended in W51 B. The lack of dense, star-forming gas around W51 C indicates that collect-and-collapse is not acting or is inefficient in W51. (2) Ongoing high-mass star formation is correlated with n ? 1 × 105cm-3 gas. Gas with n> 104cm-3 is weakly correlated with low and moderate mass star formation, but does not strongly correlate with high-mass star formation. (3) The nondetection of H2CO emission implies that the emission detected in other galaxies, e.g. Arp 220, comes from high-density gas that is not directly affiliated with already-formed massive stars. Either the non-star-forming ISM of these galaxies is very dense, implying the star formation density threshold is higher, or H ii regions have their emission suppressed. The data set has been made public at http://dx.doi.org/10.7910/DVN/26818Appendices are available in electronic form at http://www.aanda.org

Ginsburg, Adam; Bally, John; Battersby, Cara; Youngblood, Allison; Darling, Jeremy; Rosolowsky, Erik; Arce, Héctor; Lebrón Santos, Mayra E.

2015-01-01

217

Polymers All Around You!  

ERIC Educational Resources Information Center

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

Gertz, Susan

218

Spontaneous polarization in dense hydrogen  

Microsoft Academic Search

More than six decades have passed since Wigner and Huntington proposed that hydrogen might form a solid metallic phase at high density with characteristics similar to the alkali metals. This possibility has been investigated using the diamond-anvil cell to compress the crystalline state of molecular hydrogen, but there is still no definitive evidence for a dense, low-temperature metallic state. Below

B. Edwards; N. W. Ashcroft

1997-01-01

219

Filamentary Dense Gas Clump Structures in the Galactic Center  

NASA Astrophysics Data System (ADS)

The Galactic Center is a violent place where large amounts of gas and dust follow trajectories that lead to frequent cloud-cloud collisions. The gas is funneled from the disk along self-intersecting x1 orbits toward the inner, orthogonal x2 orbits. We present interferometric ATCA data which is sensitive to the cold, clumpy structure of the dense gas. The data are insensitive to the large-scale, extended, warmer gas envelopes that otherwise dominate Galactic Center gas maps. We use NH3 as a gas tracer and we show that a large fraction of gas clump locations seem to be aligned. Some of the gas likely follows the 100pc dust ring, but other structures may be due to re-alignment due to the mechanical impact of massive star clusters. We also show the relation of large scale magnetic field structures to the dense gas clumps. In particular we find an anti-correlation of the thin thermal and non-thermal radio continuum filaments with the dense gas clumps which indicates that large scale magnetic fields only have limited influence on the formation and alignment of dense gas filaments.

Ott, Juergen

2015-01-01

220

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.

221

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

SciTech Connect

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

Weber, F.; Glendenning, N.K.

1992-11-02

222

H-cluster stars  

E-print Network

The study of dense matter at ultra-high density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. It is well known that the state of cold matter at supra-nuclear density depends on the non-perturbative nature of quantum chromo-dynamics (QCD) and is essential for modeling pulsars. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other there. That might render quarks grouped in clusters, although the hypothetical quark-clusters in cold dense matter has not been confirmed due to the lack of both theoretical and experimental evidence. Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we are therefore considering here a possible kind of quark-clusters, H-clusters, that could emerge inside compact stars during their initial cooling, as the dominant components inside (the degree of freedom could then be H-clusters there).Taking into account the in-medium stiffening effect, we find that at baryon densities of compact stars $H$-cluster matter could be more stable than nuclear matter. We also find that for the H-cluster matter with lattice structure, the equation of state could be so stiff that it would seem to be "superluminal" in most dense region. However, the real sound speed for H-cluster matter is in fact hard to calculate, so at this stage we do not put constraints on our model from the usual requirment of causality.

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

2011-07-05

223

Star-Spangled Ghibli: Star Voices in the American Versions of Hayao Miyazaki's Films  

Microsoft Academic Search

This article offers an examination of the use of American stars in re-voicing a set of Japanese animated texts. The author argues that a new industrial, contextual and textual understanding of stardom is required to penetrate the dense network of meanings attached to star voices in animation. Furthermore, she utilizes a mixed textual and contextual approach to several of Studio

Rayna Denison

2008-01-01

224

Chemical composition of gas and grains in dense interstellar clouds  

NASA Astrophysics Data System (ADS)

It is shown that dense, molecular interstellar clouds contain most of their carbon, magnesium and heavier elements in the form of grains, as silicates, silicon carbide, graphite and ices. Most hydrogen and noble gases are in the gaseous phase, with oxygen and nitrogen being probably distributed between gas and grains. It is suggested that grains form in the expanding atmospheres of cool stars, then survive in the denser parts of the diffuse medium. Ice mantles grow from molecules in the gas phase in the interior of dense clouds and seem to be destroyed outside them, perhaps due to the effect of UV radiation. It is noted that grain mantles are potential sources of complex organic molecules in the early solar system.

Lequeux, J.

1982-05-01

225

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

226

Dense matter in neutron stars and their envelopes  

E-print Network

.A.Kirzhnits (1964): Tc ~ 1010 K, ~ 1013 ­ 1015 g/cc. Neutrino emission. H.-Y.Chiu & E.E.Salpeter (1964); J.N.Bahcall & R.A.Wolf (1965). Cooling. R.Stabler (1960, PhD); Chiu (1964); Chiu & Salpeter (1964); D

227

Limits of dense graph sequences  

Microsoft Academic Search

We show that if a sequence of dense graphs Gn has the property that for every fixed graph F, the density of copies of F in Gn tends to a limit, then there is a natural “limit object,” namely a symmetric measurable function W:[0,1]2?[0,1]. This limit object determines all the limits of subgraph densities. Conversely, every such function arises as

László Lovász; Balázs Szegedy

2006-01-01

228

Polymer nanolithography  

NASA Astrophysics Data System (ADS)

Nanolithography involves making patterns of materials with at least one dimension less than 100 nanometers. Surprisingly, writable CDs can provide polymer nanostructures for pennies a piece. Building on work previously done in the Drain lab, with an inherited home-built oven press, this research will explore the relationships between polymer chemical reactivity, polymer printing, and material surface energies. In addition, a relatively inexpensive entry point into high school and undergraduate education in nanolithography is presented. The ability to pattern cheaply at the nanoscale and microscale is necessary and attractive for many technologies towards biosensors, organic light emitting diodes, identification tags, layered devices, and transistors.

Vance, Jennifer M.

229

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

230

Nonlinear electrostatic excitations in magnetized dense plasmas with nonrelativistic and ultra-relativistic degenerate electrons  

SciTech Connect

Linear and nonlinear electrostatic waves in magnetized dense electron-ion plasmas are studied with nonrelativistic and ultra-relativistic degenerate and singly, doubly charged helium (He{sup +}, He{sup ++}) and hydrogen (H{sup +}) ions, respectively. The dispersion relation of electrostatic waves in magnetized dense plasmas is obtained under both the energy limits of degenerate electrons. Using reductive perturbation method, the Zakharov-Kuznetsov equation for nonlinear propagation of electrostatic solitons in magnetized dense plasmas is derived for both nonrelativistic and ultra-relativistic degenerate electrons. It is found that variations in plasma density, magnetic field intensity, different mass, and charge number of ions play significant role in the formation of electrostatic solitons in magnetized dense plasmas. The numerical plots are also presented for illustration using the parameters of dense astrophysical plasma situations such as white dwarfs and neutron stars exist in the literature. The present investigation is important for understanding the electrostatic waves propagation in the outer periphery of compact stars which mostly consists of hydrogen and helium ions with degenerate electrons in dense magnetized plasmas.

Mahmood, S.; Sadiq, Safeer; Haque, Q. [Theoretical Physics Division (TPD), PINSTECH, P.O. Nilore, Islamabad 44000 (Pakistan)] [Theoretical Physics Division (TPD), PINSTECH, P.O. Nilore, Islamabad 44000 (Pakistan)

2013-12-15

231

Nonlinear electrostatic excitations in magnetized dense plasmas with nonrelativistic and ultra-relativistic degenerate electrons  

NASA Astrophysics Data System (ADS)

Linear and nonlinear electrostatic waves in magnetized dense electron-ion plasmas are studied with nonrelativistic and ultra-relativistic degenerate and singly, doubly charged helium (He+, He++) and hydrogen (H+) ions, respectively. The dispersion relation of electrostatic waves in magnetized dense plasmas is obtained under both the energy limits of degenerate electrons. Using reductive perturbation method, the Zakharov-Kuznetsov equation for nonlinear propagation of electrostatic solitons in magnetized dense plasmas is derived for both nonrelativistic and ultra-relativistic degenerate electrons. It is found that variations in plasma density, magnetic field intensity, different mass, and charge number of ions play significant role in the formation of electrostatic solitons in magnetized dense plasmas. The numerical plots are also presented for illustration using the parameters of dense astrophysical plasma situations such as white dwarfs and neutron stars exist in the literature. The present investigation is important for understanding the electrostatic waves propagation in the outer periphery of compact stars which mostly consists of hydrogen and helium ions with degenerate electrons in dense magnetized plasmas.

Mahmood, S.; Sadiq, Safeer; Haque, Q.

2013-12-01

232

Dense periodic packings of tori.  

PubMed

Dense packings of nonoverlapping bodies in three-dimensional Euclidean space R(3) 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 in R(3), which are multiply connected nonconvex bodies of genus 1, as well as horn and spindle tori. Specifically, 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, Phys. Rev. E 86, 011102 (2012)]. We find that the horn tori as well as certain spindle and ring tori can achieve a packing density not only higher than that of spheres (i.e., ?/sqrt[18] = 0.7404...) but also higher than the densest known ellipsoid packings (i.e., 0.7707...). In addition, we study dense packings of clusters of pair-linked ring tori (i.e., Hopf links), which can possess much higher densities than corresponding packings consisting of unlinked tori. PMID:25353448

Gabbrielli, Ruggero; Jiao, Yang; Torquato, Salvatore

2014-02-01

233

Dense periodic packings of tori  

NASA Astrophysics Data System (ADS)

Dense packings of nonoverlapping bodies in three-dimensional Euclidean space R3 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 in R3, which are multiply connected nonconvex bodies of genus 1, as well as horn and spindle tori. Specifically, we analytically construct a family of dense periodic packings of unlinked tori guided by the organizing principles originally devised for simply connected solid bodies [22 Torquato and Jiao, Phys. Rev. E 86, 011102 (2012), 10.1103/PhysRevE.86.011102]. We find that the horn tori as well as certain spindle and ring tori can achieve a packing density not only higher than that of spheres (i.e., ? /?18 =0.7404...) but also higher than the densest known ellipsoid packings (i.e., 0.7707...). In addition, we study dense packings of clusters of pair-linked ring tori (i.e., Hopf links), which can possess much higher densities than corresponding packings consisting of unlinked tori.

Gabbrielli, Ruggero; Jiao, Yang; Torquato, Salvatore

2014-02-01

234

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

Microsoft Academic Search

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

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

2005-01-01

235

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

236

Dynamical evolution of star-forming regions  

NASA Astrophysics Data System (ADS)

We model the dynamical evolution of star-forming regions with a wide range of initial properties. We follow the evolution of the regions' substructure using the Q-parameter, we search for dynamical mass segregation using the ?MSR technique, and we also quantify the evolution of local density around stars as a function of mass using the ?LDR method. The amount of dynamical mass segregation measured by ?MSR is generally only significant for subvirial and virialized, substructured regions - which usually evolve to form bound clusters. The ?LDR method shows that massive stars attain higher local densities than the median value in all regions, even those that are supervirial and evolve to form (unbound) associations. We also introduce the Q - ? _LDR plot, which describes the evolution of spatial structure as a function of mass-weighted local density in a star-forming region. Initially dense (>1000 stars pc-2), bound regions always have Q > 1, ? _LDR > 2 after 5 Myr, whereas dense unbound regions always have Q < 1, ? _LDR > 2 after 5 Myr. Less dense regions (<100 stars pc-2) do not usually exhibit ?LDR > 2 values, and if relatively high local density around massive stars arises purely from dynamics, then the Q - ? _LDR plot can be used to estimate the initial density of a star-forming region.

Parker, Richard J.; Wright, Nicholas J.; Goodwin, Simon P.; Meyer, Michael R.

2014-02-01

237

A nonlinear model for magnetoacoustic waves in dense dissipative plasmas with degenerate electrons  

SciTech Connect

The properties of nonlinear fast magnetoacoustic waves in dense dissipative plasmas with degenerate electrons are studied theoretically in the framework of the Zabolotskaya-Khokhlov (ZK) equation for small but finite amplitude excitations. Shock-like solutions of the ZK equation are obtained and are applied to parameters relevant to white dwarf stars.

Masood, W. [COMSATS Institute of Information Technology, Islamabad (Pakistan); National Centre for Physics (NCP), Shahdra Valley Road, Islamabad (Pakistan); Jahangir, R.; Siddiq, M. [National Centre for Physics (NCP), Shahdra Valley Road, Islamabad (Pakistan); Eliasson, B. [SUPA, Physics Department, University of Strathclyde, Glasgow (United Kingdom)

2014-10-15

238

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

239

Organometallic Polymers.  

ERIC Educational Resources Information Center

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

Carraher, Charles E., Jr.

1981-01-01

240

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

SciTech Connect

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

Weber, F.; Glendenning, N.K.

1992-11-02

241

Self and Tracer Diffusion of Polymers in Solution  

E-print Network

The literature on self- and tracer- diffusion of polymers in solution, and on tracer diffusion of probe polymers through solutions of matrix polymers, is reviewed. I show via systematic reanalysis that the entirety of the published literature has its concentration c and matrix M and probe P molecular weight dependences described by a single functional form, namely the stretched exponential in c, P, and M. Correlations of the scaling prefactor and exponents with polymer molecular weight, concentration, and size are examined. Scaling parameters for the diffusion of star polymers do not differ substantially from scaling parameters for the diffusion of linear chains of equal size.

George D. J. Phillies

2004-03-03

242

Degenerate stars. XII - Recognition of hot nondegenerates  

NASA Astrophysics Data System (ADS)

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

Greenstein, J. L.

1980-12-01

243

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

244

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

2007-11-13

245

The origin of OB runaway stars.  

PubMed

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

Fujii, Michiko S; Portegies Zwart, Simon

2011-12-01

246

Stellar Wind Disruption by an Orbiting Neutron Star  

NSDL National Science Digital Library

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

Alan McConnell

1990-07-10

247

Dense arrays of uniform submicron pores in silicon and their applications.  

PubMed

We report a versatile particle-based route to dense arrays of parallel submicron pores with high aspect ratio in silicon and explore the application of these arrays in sensors, optics, and polymer micropatterning. Polystyrene (PS) spheres are convectively assembled on gold-coated silicon wafers and sputter-etched, resulting in well-defined gold disc arrays with excellent long-range order. The gold discs act as catalysts in metal-assisted chemical etching, yielding uniform pores with straight walls, flat bottoms, and high aspect ratio. The resulting pore arrays can be used as robust antireflective surfaces, in biosensing applications, and as templates for polymer replica molding. PMID:25493543

Brodoceanu, Daniel; Elnathan, Roey; Prieto-Simón, Beatriz; Delalat, Bahman; Guinan, Taryn; Kroner, Elmar; Voelcker, Nicolas H; Kraus, Tobias

2015-01-21

248

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

SciTech Connect

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

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

1996-04-01

249

Low-temperature cracking of polymer-modified asphalt  

Microsoft Academic Search

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

U. Isacsson; H. Zeng

1998-01-01

250

Chemical modeling of interstellar molecules in dense cores  

NASA Astrophysics Data System (ADS)

There are billions of stars in our galaxy, the Milky Way Galaxy. In between the stars is where the so-called "interstellar medium" locates. The majority of the mass of interstellar medium is clumped into interstellar clouds, in which cold and hot dense cores exist. Despite of the extremely low densities and low temperatures of the dense cores, over one hundred molecules have been found in these sources. This makes the field of astrochemistry vivid. Chemical modeling plays very important roles to understand the mechanism of formation and destruction of interstellar molecules. In this thesis, chemical kinetics models of different types were applied: in Chapter 4, pure gas phase models were used for seven newly detected or confirmed molecules by the Green Bank Telescope; in Chapter 5, the potential reason of non-detection of O 2 was explored; in Chapter 6, the mysterious behavior of CHNO and CHNS isomers were studied by gas-grain models. In addition, effects of varying rate coefficients to the models are also discussed in Chapter 3 and 7.

Quan, Donghui

251

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

252

Accreting neutron stars, black holes, and degenerate dwarf stars  

NASA Astrophysics Data System (ADS)

During the past 8 years, extended temporal and broadband spectroscopic studies carried out by X-ray astronomical satellites have led to the identification of specific compact X-ray sources as accreting neutron stars, black holes, and degenerate dwarf stars in close binary systems. Such sources provide a unique opportunity to study matter under extreme conditions not accessible in the terrestrial laboratory. Quantitative theoretical models have been developed which demonstrate that detailed studies of these sources will lead to a greatly increased understanding of dense and superdense hadron matter, hadron superfluidity, high-temperature plasma in superstrong magnetic fields, and physical processes in strong gravitational fields. Through a combination of theory and observation such studies will make possible the determination of the mass, radius, magnetic field, and structure of neutron stars and degenerate dwarf stars and the identification of further candidate black holes, and will contribute appreciably to our understanding of the physics of accretion by compact astronomical objects.

Pines, D.

1980-02-01

253

Antimocrobial Polymer  

DOEpatents

A polymeric composition having antimicrobial properties and a process for rendering the surface of a substrate antimicrobial are disclosed. The composition comprises a crosslinked chemical combination of (i) a polymer having amino group-containing side chains along a backbone forming the polymer, (ii) an antimicrobial agent selected from quaternary ammonium compounds, gentian violet compounds, substituted or unsubstituted phenols, biguanide compounds, iodine compounds, and mixtures thereof, and (iii) a crosslinking agent containing functional groups capable of reacting with the amino groups. In one embodiment, the polymer is a polyamide formed from a maleic anhydride or maleic acid ester monomer and alkylamines thereby producing a polyamide having amino substituted alkyl chains on one side of the polyamide backbone; the crosslinking agent is a phosphine having the general formula (A)3P wherein A is hydroxyalkyl; and the antimicrobial agent is chlorhexidine, dimethylchlorophenol, cetyl pyridinium chloride, gentian violet, triclosan, thymol, iodine, and mixtures thereof.

McDonald, William F. (Utica, OH); Huang, Zhi-Heng (Walnut Creek, CA); Wright, Stacy C. (Columbus, GA)

2005-09-06

254

Swift heavy ion modification of polymers  

Microsoft Academic Search

We have studied the effects of dense electronic excitations on vinyl linear polymers, by performing swift heavy ion, SHI, irradiations. We used different ion beams, from C to Pb, provided by the GANIL accelerator at energies of a few MeV\\/u. We mainly studied the physico-chemical modifications induced in polyethylene (PE), but the role of chemical substitutions has also been investigated

E. Balanzat; N. Betz; S. Bouffard

1995-01-01

255

Stars in the Tarantula Nebula  

NASA Technical Reports Server (NTRS)

In the most active starburst region in the local universe lies a cluster of brilliant, massive stars, known to astronomers as Hodge 301. Hodge 301, seen in the lower right hand corner of this image, lives inside the Tarantula Nebula in our galactic neighbor, the Large Magellanic Cloud. This star cluster is not the brightest, or youngest, or most populous star cluster in the Tarantula Nebula, that honor goes to the spectacular R136. In fact, Hodge 301 is almost 10 times older than the young cluster R136. But age has its advantages; many of the stars in Hodge 301 are so old that they have exploded as supernovae. These exploded stars are blasting material out into the surrounding region at speeds of almost 200 miles per second. This high speed ejecta are plowing into the surrounding Tarantula Nebula, shocking and compressing the gas into a multitude of sheets and filaments, seen in the upper left portion of the picture. Hodge 301 contains three red supergiants - stars that are close to the end of their evolution and are about to go supernova, exploding and sending more shocks into the Tarantula. Also present near the center of the image are small, dense gas globules and dust columns where new stars are being formed today, as part of the overall ongoing star formation throughout the Tarantula region.

1999-01-01

256

The performance of dense medium processes  

SciTech Connect

Dense medium washing in baths and cyclones is widely carried out in South Africa. The paper shows the reason for the preferred use of dense medium processes rather than gravity concentrators such as jigs. The factors leading to efficient separation in baths are listed and an indication given of the extent to which these factors may be controlled and embodied in the deployment of baths and dense medium cyclones in the planning stages of a plant.

Horsfall, D.W. [Univ. of Witwatersrand, Johannesburg (South Africa). Dept. of Metallurgy & Materials Engineering

1993-12-31

257

From Nuclei to Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Reddy, Sanjay

2007-10-01

258

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

259

Deterministic and unambiguous dense coding  

SciTech Connect

Optimal dense coding using a partially-entangled pure state of Schmidt rank D and a noiseless quantum channel of dimension D is studied both in the deterministic case where at most L{sub d} messages can be transmitted with perfect fidelity, and in the unambiguous case where when the protocol succeeds (probability {tau}{sub x}) Bob knows for sure that Alice sent message x, and when it fails (probability 1-{tau}{sub x}) he knows it has failed. Alice is allowed any single-shot (one use) encoding procedure, and Bob any single-shot measurement. For D{<=}D a bound is obtained for L{sub d} in terms of the largest Schmidt coefficient of the entangled state, and is compared with published results by Mozes et al. [Phys. Rev. A71, 012311 (2005)]. For D>D it is shown that L{sub d} is strictly less than D{sup 2} unless D is an integer multiple of D, in which case uniform (maximal) entanglement is not needed to achieve the optimal protocol. The unambiguous case is studied for D{<=}D, assuming {tau}{sub x}>0 for a set of DD messages, and a bound is obtained for the average <1/{tau}>. A bound on the average <{tau}> requires an additional assumption of encoding by isometries (unitaries when D=D) that are orthogonal for different messages. Both bounds are saturated when {tau}{sub x} is a constant independent of x, by a protocol based on one-shot entanglement concentration. For D>D it is shown that (at least) D{sup 2} messages can be sent unambiguously. Whether unitary (isometric) encoding suffices for optimal protocols remains a major unanswered question, both for our work and for previous studies of dense coding using partially-entangled states, including noisy (mixed) states.

Wu Shengjun [Physics Department, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Hefei National Laboratory for Physical Science at the Microscale, University of Science and Technology of China (China); Cohen, Scott M. [Physics Department, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Physics Department, Duquesne University, Pittsburgh, Pennsylvania 15282 (United States); Sun Yuqing; Griffiths, Robert B. [Physics Department, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

2006-04-15

260

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

261

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

262

Equation of state of dense matter for core-collapse supernovae, compact objects and neutrino bursts  

SciTech Connect

This paper reviews the recent progress in the research of equation of state of dense matter for supernova simulations. The equation of state plays an important role to clarify the mechanism of core-collapse supernovae, the formation of compact objects and the properties of supernova neutrinos. We describe the problems of explosion mechanism in current supernova simulations, putting emphasis on the equation of state. We discuss also the topics on the birth of neutron stars (or black holes) and the associated neutrino bursts, which reflect the properties of dense matter.

Sumiyoshi, Kohsuke

2008-05-21

263

Rheological characterization in shear of a model dumbbell polymer concentrated solution  

Microsoft Academic Search

We investigate the linear and non-linear rheological behavior in shear of a concentrated solution of “dumbbell” polystyrene\\u000a with long linear backbone and dense short brushes at both ends and compare it with corresponding linear polymers. This type\\u000a of dumbbells has never been rheologically characterized before. In linear viscoelasticity, the dumbbell polymers show significant\\u000a differences with conventional linear polymers. In particular,

Florian J. Stadler; Merina Rajan; Uday S. Agarwal; Chen-Yang Liu; K. E. George; Piet J. Lemstra; Christian Bailly

264

The Birth, Evolution and Death of Star Clusters  

Microsoft Academic Search

A dense-enough gas-accumulation evolves, over a few Myr of intensifying star formation, to an embedded cluster. If it contains a sufficient amount of mass, O stars form and explosively expel the remaining gas, whereas poorer clusters reduce their embryonic gas content more gradually. The sudden expulsion of gas unbinds most of a rich cluster, but a significant fraction of it

P. Kroupa

2001-01-01

265

The Star Clustering Algorithm for Static and Dynamic Information Organization  

Microsoft Academic Search

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

Javed A. Aslam; Ekaterina Pelekhov; Daniela Rus

2004-01-01

266

The dense gas mass fraction in the W51 cloud and its protoclusters  

E-print Network

We present new 2 cm and 6 cm maps of H2CO, radio recombination lines, and the radio continuum in the W51 star forming complex acquired with Arecibo and the Green Bank Telescope at ~50" resolution. We use H2CO absorption to determine the relative line-of-sight positions of molecular and ionized gas. We measure gas densities using the H2CO densitometer, including continuous measurements of the dense gas mass fraction (DGMF) over the range 10^4 cm^-3 ~70% above n>10^4 cm^-3, while it is low, f 10^4 cm-3 is weakly correlated with low and moderate mass star formation, but does not strongly correlate with high-mass star formation. (3) The nondetection of H2CO emission implies that the emission detected in other galaxies, e.g. Arp 220, comes from high-density gas that is not directly affiliated with already-formed massive stars. Either the non-star-forming ISM of these galaxies is very dense, implying the star formation density threshold is higher, or H ii regions have their emission suppressed.

Ginsburg, Adam; Battersby, Cara; Youngblood, Allison; Darling, Jeremy; Rosolowsky, Erik; Arce, Hector; Santos, Mayra E Lebrón

2014-01-01

267

Nanostructuring Titania by Embossing with Polymer Molds Made from Anodic  

E-print Network

Nanostructuring Titania by Embossing with Polymer Molds Made from Anodic Alumina Templates Chiatzun(methyl methacrylate) (PMMA) molds to make thin films of titania that have dense arrays of 35-65 nm diameter pores, whose features are 1 order of magnitude smaller than those previously demonstrated for sol-gel molding

McGehee, Michael

268

Boundary effect of deterministic dense coding  

SciTech Connect

We present a rigorous proof of an interesting boundary effect of deterministic dense coding first observed by S. Mozes, J. Oppenheim, and B. Reznik [Phys. Rev. A 71, 012311 (2005)]. Namely, it is shown that d{sup 2}-1 cannot be the maximal alphabet size of any isometric deterministic dense coding schemes utilizing d-level partial entanglement.

Ji Zhengfeng; Feng Yuan; Duan Runyao; Ying Mingsheng [State Key Laboratory of Intelligent Technology and Systems, Department of Computer Science and Technology, Tsinghua University, Beijing 100084 (China)

2006-03-15

269

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

270

Interaction effects in optically dense materials  

Microsoft Academic Search

The properties of optically dense materials are influenced by interactions between elementary optical excitations (oscillators). Since such interactions are absent in the dilute limit, the resulting properties are unique to optically dense materials. While linear optical experiments can probe these effects, for example the Lorentz-Lorenz resonance shift, they are often more apparent in nonlinear experiments that are sensitive to coherence.

Steven T. Cundiff; Justin M. Shacklette; Virginia O. Lorenz

2001-01-01

271

Molecular cloud evolution and star formation  

NASA Technical Reports Server (NTRS)

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

Silk, J.

1985-01-01

272

Novel Phases at High Density and their Roles in the Structure and Evolution of Neutron Stars  

E-print Network

We present a pedagogic discussion on the role of novel phases of dense baryonic matter in ``neutron'' stars. Qualitative aspects of the physics that drives phase transitions and some of its astrophysical consequences are discussed. Observable aspects of neutron star structure and early evolution of the newly born neutron star are discussed in some detail.

Sanjay Reddy

2002-11-14

273

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

274

Method of Preparing Polymers with Low Melt Viscosity  

NASA Technical Reports Server (NTRS)

This invention is an improvement in standard polymerizations procedures, i.e., addition-type and step-growth type polymerizations, wherein monomers are reacted to form a growing polymer chain. The improvement includes employing an effective amount of a trifunctional monomer (such as a trifunctional amine anhydride, or phenol) in the polymerization procedure to form a mixture of polymeric materials consisting of branced polymers, star-shaped polymers, and linear polymers. This mixture of polymeric materials has a lower melt temperature and a lower melt viscosity than corresponding linear polymeric materials of equivalent molecular weight.

Jensen, Brian J. (Inventor)

2001-01-01

275

Polymers with spatial or topological constraints: theoretical and computational results  

E-print Network

In this review we provide an organized summary of the theoretical and computational results which are available for polymers subject to spatial or topological constraints. Because of the interdisciplinary character of the topic, we provide an accessible, non-specialist introduction to the main topological concepts, polymer models, and theoretical/computational methods used to investigate dense and entangled polymer systems. The main body of our review deals with: (i) the effect that spatial confinement has on the equilibrium topological entanglement of one or more polymer chains and (ii) the metric and entropic properties of polymer chains with fixed topological state. These problems have important technological applications and implications for the life-sciences. Both aspects, especially the latter, are amply covered. A number of selected open problems are finally highlighted.

Cristian Micheletti; Davide Marenduzzo; Enzo Orlandini

2011-03-22

276

Fundamental vibrational mode in a highly inhomogeneous star  

E-print Network

The eigenfrequency problem of fundamental vibrational mode in a highly inhomogeneous star, modeled by self-gravitating mass of viscous liquid with singular density at the center, is considered in juxtaposition with that for Kelvin fundamental mode in the liquid star model with uniform density. Particular attention is given to the difference between spectral equations for the frequency and lifetime of f-mode in the singular and homogeneous star models. The newly obtained results are discussed in the context of theoretical asteroseismology of pre-white dwarf stars and stellar cocoons -- spherical gas-dust clouds with dense star-forming core at the center.

S. I. Bastrukov; H. -K. Chang; E. -H. Wu; I. V. Molodtsova

2008-11-17

277

The Ecology of Black Holes in Star Clusters  

E-print Network

In this lecture we investigate the formation and evolution of black holes in star clusters. The star clusters under consideration are generally rich, containing more than 10^4 stars, and with a density exceeding 10^4 stars/pc^3. Among these are young dense clusters (YoDeCs), globular cluster and the nuclei of galaxies. We will also address the the possible evolutionary link between stellar mass black holes, via intermediate mass black holes to supermassive black holes, mainly focus on the ecology of star clusters.

Simon Portegies Zwart

2004-06-24

278

Dielectric Actuation of Polymers  

E-print Network

cross-linked polymer networks II. Swelling, The Journal ofswelling ratio is determined by the chemical crosslinking density of the polymer andinto the polymer network. Overall, the swelling ratio with

Niu, Xiaofan

2013-01-01

279

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

280

Shrinking polymer lasers  

NASA Astrophysics Data System (ADS)

Semiconducting polymers are a rapidly advancing class of optoelectronic materials. They give efficient light emission under optical or electrical stimulation, and offer promise as compact, lightweight and simple to fabricate lasers. The development of such active polymer components complements developments in polymer fibre and planar lightwave circuits opening new directions in polymer integrated optics. In this article progress towards making compact practical polymer lasers is described. The potential for polymer lasers to operate in the space radiation environment is also discussed.

Samuel, I. D. W.; Vasdekis, A. E.; Tsiminis, G.; Turnbull, G. A.; Taylor, E. W.

2007-09-01

281

New ion conducting systems based on star branched block copolymer  

Microsoft Academic Search

A new proton-conducting polymer based on sulfonated hydrogenated poly(styrene–butadiene) star block copolymer (HPBSE–SH) has been synthesized and characterized. The free acid samples and their blends with the non-sulfonated polymer (HPBSE) and Polypropylene (PP) were studied. The effect of sulfonation on polymer structure was studied using FTIR. Dynamic mechanical analysis and differential scanning calorimetry have been used for microstructure characterization. Glass

A Mokrini; J. L Acosta

2001-01-01

282

Interpretations of Polymer-Polymer Miscibility.  

ERIC Educational Resources Information Center

Discusses various aspects of polymeric mixtures, mixtures of structurally different homopolymers, copolymers, terpolymers, and the like. Defines concepts of polymer-polymer miscibility from practical and theoretical viewpoints, and ways of predicting such miscibility. (JN)

Olabisi, Olagoke

1981-01-01

283

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

284

Two-dimensional dense gas dynamics  

Microsoft Academic Search

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

Brady Polk Brown

1997-01-01

285

Quark Matter in Neutron Stars: An apercu  

E-print Network

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this brief review article, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.

Prashanth Jaikumar; Sanjay Reddy; Andrew W. Steiner

2006-08-16

286

From Commodity Polymers to Functional Polymers  

PubMed Central

Functional polymers bear specified chemical groups, and have specified physical, chemical, biological, pharmacological, or other uses. To adjust the properties while keeping material usage low, a method for direct synthesis of functional polymers is indispensable. Here we show that various functional polymers can be synthesized by in situ cross-linked polymerization/copolymerization. We demonstrate that the polymers synthesized by the facile method using different functional monomers own outstanding pH-sensitivity and pH-reversibility, antifouling property, antibacterial, and anticoagulant property. Our study opens a route for the functionalization of commodity polymers, which lead to important advances in polymeric materials applications. PMID:24710333

Xiang, Tao; Wang, Ling-Ren; Ma, Lang; Han, Zhi-Yuan; Wang, Rui; Cheng, Chong; Xia, Yi; Qin, Hui; Zhao, Chang-Sheng

2014-01-01

287

Scattering from Polymers  

Microsoft Academic Search

Knowledge and understanding from scattering provides a scientific basis of control of polymer properties. This understanding has fueled technological advances in synthetic polymers that have revolutionized our daily lives. This issue of Polymer Reviews focuses on recent advances in scattering instrumentation, data analysis and modeling, and its application to the structure-property characterization of polymers. We highlight research directions where the

Yvonne A. Akpalu

2010-01-01

288

Ultraviolet Spectroscopy of Young Compact Regions in Dense Molecular Clouds  

NASA Astrophysics Data System (ADS)

It is proposed to use the IUE short wavelength, low resolution spectrograph for a period of five observing shifts to observe at least 16 of 21 compact nebulae, associated with active sites of recent and current star formation. There is ample evidence from a variety of data (optical, IR, MM and radio) to suggest that these nebulae have recently emerged from a dense ( ^nH 2 = 10^4 - 10^5 cm^-3 ) condensation on the near edge of their parent molecular cloud: All are closer than 3 kpc and exhibit luminosities at least as great as a BOIV star. Hence, each should be detectable within 60 min integration with the short wavelength camera. The objectives are (1) to determine physical characteristics, (2) to search for strong, highly ionized, spectral lines for future high resolution observations to study stellar wind molecular cloud interactions, (3) to obtain crude C and Si abundances, (4) to refine extinction estimates and (5) to resolve conflicts between sets of data at other wavelengths regarding the nature of certain sources.

Blair, G. N.

289

Theory of interparticle correlations in dense, high-temperature plasmas. I - General formalism. II Correlation functions. III - Thermodynamic functions. IV Stopping power  

Microsoft Academic Search

A clarification of the basic properties of the high-density materials encountered in the inertially-confined-fusion experiments and in the interior of the main-sequence stars requires a theoretical study of the interparticle correlations in dense, high-temperature plasmas. The present paper represents the first in a series of papers which is concerned with a systematic study of multiparticle correlation effects in the dense,

Setsuo Ichimaru; Shinichi Mitake; Shigenori Tanaka; X.-Z. Yan

1985-01-01

290

Stationary Star  

NSDL National Science Digital Library

This is an activity about star movement due to the Earth's rotation. Learners will utilize the Sky Tonight online program to find the star that appears stationary in our night sky. They will then draw conclusions about the Earthâs rotation based on the position changes of certain stars. This activity requires the use of a computer with Internet access. This activity is Sky Tonight Activity 2 in a larger resource, Space Update.

291

Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, aren’t doing much of anything. In this video, Jonathan’s 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.

2012-07-28

292

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

293

Lucky Star  

NSDL National Science Digital Library

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

2008-01-01

294

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

295

Solid State Chemistry in Dense Clouds Along Quiescent Lines of Sight  

NASA Astrophysics Data System (ADS)

We propose 5.3-21.8 um spectroscopic observations of background field stars along sight-lines through dense interstellar clouds, with little or no star formation activity, to assess the early chemistry of molecular cloud dust. Dense clouds produce molecules and ices critical to star and planet formation. The formation of organic compounds in these ices is one of the first steps towards the complex molecular materials needed for life. Infrared spectroscopy provides a powerful tool for the study of the composition and evolution of interstellar ices. The most diagnostic features of solid-state materials occur in the mid-infrared. To date, mid-IR absorption studies have primarily been towards embedded protostars where the ice may well have been processed either thermally or by FUV photons from the star. Such sightlines demonstrate a preponderance of simple molecules (H2O, CH3OH, CO, CO2, and NH3) and energetically processed species (X- CN) in the surrounding ices, revealing that protostars strongly influence their circumstellar environments. Lines of sight to these objects are unlikely to be representative of dense cloud materials as a whole. A more complete understanding of the composition of dense clouds and their chemical dynamics requires that we also probe lines of sight through the general quiescent cloud medium. We will obtain low resolution IRS spectra (including 6.0 um H2O, 6.85 um NH4+/CH3OH, 7.6 um CH4, and 15.2 um CO2 band), plus high resolution IRS spectra for selected high AV sources, to study detailed band profiles. We will correlate band strengths with Av to determine the abundances and densities required for the ice components to appear, and study the chemical changes in molecular clouds as a function of temperature and density. These observations will provide a snapshot of the chemical state of a molecular cloud prior to the formation of stars, and a general baseline for studies of dust chemistry in regions of star formation.

Pendleton, Yvonne; Allamandola, Louis; Bernstein, Max; Boogert, Adwin; Chiar, Jean; Ennico, Kim; Greene, Thomas; Keane, Jacqueline; Lada, Charles; Mason, Rachel; Roellig, Thomas; Sandford, Scott; Tielens, Alexander; Tokunaga, Alan

2004-09-01

296

Gamma-ray bursts from extinct neutron stars  

NASA Technical Reports Server (NTRS)

The paper concentrates on disks around old extinct pulsars, that can produce gamma-ray bursts owing to viscous evolution of the disk bringing it into the near vicinity of the neutron star, with runaway ionization of the disk and simultaneous precipitation of this plasma onto the neutron star. An old extinct pulsar is modeled as a magnetized neutron star circled by a ring of cold dense matter with an orbital period approximately equal to the rotational period of the neutron star. The numerical estimates produced are found to be consistent with the observed properties of gamma-ray bursters.

Michel, F. C.

1990-01-01

297

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

298

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

299

Coalescence preference in densely packed microbubbles.  

PubMed

A bubble merged from two parent bubbles with different size tends to be placed closer to the larger parent. This phenomenon is known as the coalescence preference. Here we demonstrate that the coalescence preference can be blocked inside a densely packed cluster of bubbles. We utilized high-speed high-resolution X-ray microscopy to clearly visualize individual coalescence events inside densely packed microbubbles with a local packing fraction of ~40%. The surface energy release theory predicts an exponent of 5 in a relation between the relative coalescence position and the parent size ratio, whereas our observation for coalescence in densely packed microbubbles shows a different exponent of 2. We believe that this result would be important to understand the reality of coalescence dynamics in a variety of packing situations of soft matter. PMID:25583640

Kim, Yeseul; Lim, Su Jin; Gim, Bopil; Weon, Byung Mook

2015-01-01

300

The Landscape of Dense Image Matching Algorithms  

E-print Network

Both improvements in camera technology and the rise of new matching approaches triggered the development of suitable software tools for image based 3D reconstruction by research groups and vendors of photogrammetric software. Based on dense pixel-wise matching, the photogrammetric generation of dense 3D point clouds and Digital Surface Models from highly overlapping aerial images has become feasible. In order to evaluate the quality of these matching algorithms in terms of accuracy and reliability, the European Spatial Data Research Organisation (EuroSDR) started a benchmark on image based DSM generation in February 2013. This test is based on two representative image blocks, which were processed by different groups with different software systems. The results provided from the different groups give a profound insight to the landscape of dense matching algorithms and are used within the paper to evaluate the potential of image based photogrammetric data collection.

Norbert Haala

301

Warm dense matter through classical molecular dynamics  

NASA Astrophysics Data System (ADS)

A classical Molecular Dynamics code has been developed to simulate dense plasmas i.e. neutral systems of interacting ions and electrons. Our goal is to design a tool that relies on a reduced set of microscopic mechanisms in order to obtain solutions of complex time dependent N-body problems and to allow an efficient description of the plasma states between classical high temperature systems to strongly coupled plasmas. Our present objective is an attempt to explore the behavior of such a classical approach for typical conditions of warm dense matter. We calculate the dynamic structure factor in warm dense beryllium by means of our molecular dynamics simulations. The results are then compared with those obtained within the framework of the random phase approximation (RPA).

Calisti, A.; Ferri, S.; Marciante, M.; Talin, B.

2014-12-01

302

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.; Döppner, T.; Lee, H. J.; Glenzer, S. H.; Redmer, R.

2012-05-01

303

Coalescence preference in densely packed microbubbles  

PubMed Central

A bubble merged from two parent bubbles with different size tends to be placed closer to the larger parent. This phenomenon is known as the coalescence preference. Here we demonstrate that the coalescence preference can be blocked inside a densely packed cluster of bubbles. We utilized high-speed high-resolution X-ray microscopy to clearly visualize individual coalescence events inside densely packed microbubbles with a local packing fraction of ~40%. The surface energy release theory predicts an exponent of 5 in a relation between the relative coalescence position and the parent size ratio, whereas our observation for coalescence in densely packed microbubbles shows a different exponent of 2. We believe that this result would be important to understand the reality of coalescence dynamics in a variety of packing situations of soft matter. PMID:25583640

Kim, Yeseul; Lim, Su Jin; Gim, Bopil; Weon, Byung Mook

2015-01-01

304

Fabrication and Characterization of Dense Zirconia and Zirconia-Silica Ceramic Nanofibers  

PubMed Central

The objective of this study was to prepare dense zirconia-yttria (ZY), zirconia-silica (ZS) and zirconia-yttria-silica (ZYS) nanofibers as reinforcing elements for dental composites. Zirconium (IV) propoxide, yttrium nitrate hexahydrate, and tetraethyl orthosilicate (TEOS) were used as precursors for the preparation of zirconia, yttria, and silica sols. A small amount (1–1.5 wt%) of polyethylene oxide (PEO) was used as a carry polymer. The sols were preheated at 70 °C before electrospinning and their viscosity was measured with a viscometer at different heating time. The gel point was determined by viscosity–time (?–t) curve. The ZY, ZS and ZYS gel nanofibers were prepared using a special reactive electrospinning device under the conditions near the gel point. The as-prepared gel nanofibers had diameters between 200 and 400 nm. Dense (nonporous) ceramic nanofibers of zirconia-yttria (96/4), zirconia-silica (80/20) and zirconia-yttria-silica (76.8/3.2/20) with diameter of 100–300 nm were obtained by subsequent calcinations at different temperatures. The gel and ceramic nanofibers obtained were characterized by scanning electron microscope (SEM), high-resolution field-emission scanning electron microscope (FE-SEM), thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), Fourier transform infrared spectrometer (FT-IR), and X-ray diffraction (XRD). SEM micrograph revealed that ceramic ZY nanofibers had grained structure, while ceramic ZS and ZYS nanofibers had smooth surfaces, both showing no visible porosity under FE-SEM. Complete removal of the polymer PEO was confirmed by TGA/DSC and FT-IR. The formation of tetragonal phase of zirconia and amorphous silica was proved by XRD. In conclusion, dense zirconia-based ceramic nanofibers can be fabricated using the new reactive sol–gel electrospinning technology with minimum organic polymer additives. PMID:21133090

Guo, Guangqing; Fan, Yuwei

2011-01-01

305

Global star formation in the L1630 molecular cloud  

NASA Technical Reports Server (NTRS)

This paper presents the preliminary results of a study of star formation in the L1630 molecular cloud. An unbiased well sampled systematic CS (2 to 1) survey for density condensations and a 2.2-micron survey for embedded infrared sources in L1630 have been completed. These surveys have provided a complete census of the dense cores and young stellar objects within this molecular cloud. As a result, four embedded stellar clusters have been identified in this cloud. These clusters are located near the most massive CS cores implying that the most active sites of star formation are located within the most massive dense cores.

Lada, Elizabeth A.

1990-01-01

306

Multicomponent polymer materials  

SciTech Connect

Interpenetrating polymer networks are discussed, taking into account interpenetrating polymer networks based on polybutadiene and polystyrene, polyurethane-polysiloxane simultaneous interpenetrating polymer networks, extraction studies and morphology of physical-chemical interpenetrating polymer networks based on block polymer and polystyrene, twoand three-component interpenetrating polymer networks, and poly(acrylourethane)-polyepoxide semiinterpenetrating networks formed by electron-beam curing. Other topics studied are related to the characterization of polymer blends, the characterization of block copolymers, the mechanical behavior, and rheology and applications. Attention is given to a new silicone flame-retardant system for thermoplastics, recent developments in interpenetrating polymer networks and related materials, miscibility in random copolymer blends, crystallization and melting in compatible polymer blends, and fatigue in rubber-modified epoxies and other polyblends.

Paul, D.R.; Sperling, L.H.

1986-01-01

307

The Onset of Cluster Formation around Intermediate Mass Stars  

E-print Network

Abstract. We present the results of a recent near-infrared survey of the fields surrounding a large sample of intermediate-mass pre-main-sequence (Herbig Ae/Be) stars. While late-type Be and Ae stars are never associated with conspicuous groups of young lower mass stars, early-type Be stars are usually found within rich clusters. This finding has been tested against possible biases due to different mass sensitivity of the observations or dynamical dissipation of the clusters around older stars. Our results suggest that massive stars are preferentially produced in dense stellar clusters, possibly by dynamical interaction rather than by standard gas accretion as in the case of lower mass stars. The possibility that the observed correlation between maximum stellar mass and cluster richness could be the results of random sampling the cluster size spectrum and the stellar IMF is also discussed. Future observational tests capable of discriminating between these two competitive models are outlined. 1.

Leonardo Testi; Francesco Palla; Antonella Natta

2000-01-01

308

Alternative screening for dense breasts: MRI.  

PubMed

OBJECTIVE. The purpose of this article is to review the use of MRI in breast density measurement and breast cancer risk estimation and to discuss the role of MRI as an alternative screening to mammography for screening women with dense breasts. CONCLUSION. The potential of MRI for screening women with dense breasts remains controversial because of the paucity of clinical evidence, the possibility of overdiagnosis, and the cost-effectiveness of the technique in this population. Although methods of MRI measurement require standardization and automation, future addition of MRI density to risk models may positively impact their value. PMID:25615774

O'Flynn, Elizabeth A M; Ledger, Araminta E W; deSouza, Nandita M

2015-02-01

309

Star Life  

NSDL National Science Digital Library

Visitors to this site can follow the life cycle of a star, beginning with its formation from matter exploded outward by the Big Bang, followed by its expansion into a red giant as nuclear "fuel" is consumed, and ending with its "death" in a supernova, after which it becomes a neutron star or black hole.

310

Star formation and extinct radioactivities  

NASA Technical Reports Server (NTRS)

An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

Cameron, A. G. W.

1984-01-01

311

Star formation and extinct radioactivities  

SciTech Connect

An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system. 36 references.

Cameron, A.G.W.

1984-11-01

312

Dense-gas chromatography of nonvolatile substances of high molecular weight.  

PubMed

Working at pressures of up to 2000 atmospheres, more than ten times higher than in previous gas chromatography, we used the solvent power of dense gases to enable migration of chromatographic substances of molecular weights as high as 400,000. Carotenoids, corticol steroids, sterols, nucleosides, amino acids, carbohydrates, and several polymers have been caused to migrate, separated, and detected in NH(3) and CO(2) carrier gases at temperatures of 140 degrees and 40 degrees C, just above the respective critical points. Previously such compounds either defied separation by gas chromatography or had to be chromatographed as their more volatile derivatives. PMID:5634909

McLaren, L; Myers, M N; Giddings, J C

1968-01-12

313

Star Cluster Buzzing With Pulsars  

NASA Astrophysics Data System (ADS)

A dense globular star cluster near the center of our Milky Way Galaxy holds a buzzing beehive of rapidly-spinning millisecond pulsars, according to astronomers who discovered 21 new pulsars in the cluster using the National Science Foundation's 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. The cluster, called Terzan 5, now holds the record for pulsars, with 24, including three known before the GBT observations. Pulsar Diagram Pulsar Diagram: Click on image for more detail. "We hit the jackpot when we looked at this cluster," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, VA. "Not only does this cluster have a lot of pulsars -- and we still expect to find more in it -- but the pulsars in it are very interesting. They include at least 13 in binary systems, two of which are eclipsing, and the four fastest-rotating pulsars known in any globular cluster, with the fastest two rotating nearly 600 times per second, roughly as fast as a household blender," Ransom added. Ransom and his colleagues reported their findings to the American Astronomical Society's meeting in San Diego, CA, and in the online journal Science Express. The star cluster's numerous pulsars are expected to yield a bonanza of new information about not only the pulsars themselves, but also about the dense stellar environment in which they reside and probably even about nuclear physics, according to the scientists. For example, preliminary measurements indicate that two of the pulsars are more massive than some theoretical models would allow. "All these exotic pulsars will keep us busy for years to come," said Jason Hessels, a Ph.D student at McGill University in Montreal. Globular clusters are dense agglomerations of up to millions of stars, all of which formed at about the same time. Pulsars are spinning, superdense neutron stars that whirl "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is left after a massive star explodes as a supernova at the end of its life. The pulsars in Terzan 5 are the product of a complex history. The stars in the cluster formed about 10 billion years ago, the astronomers say. Some of the most massive stars in the cluster exploded and left the neutron stars as their remnants after only a few million years. Normally, these neutron stars would no longer be seen as swiftly-rotating pulsars: their spin would have slowed because of the "drag" of their intense magnetic fields until the "lighthouse" effect is no longer observable. The Green Bank Telescope The Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF (Click on image for GBT gallery) However, the dense concentration of stars in the cluster gave new life to the pulsars. In the core of a globular cluster, as many as a million stars may be packed into a volume that would fit easily between the Sun and our nearest neighbor star. In such close quarters, stars can pass near enough to form new binary pairs, split apart such pairs, and binary systems even can trade partners, like an elaborate cosmic square dance. When a neutron star pairs up with a "normal" companion star, its strong gravitational pull can draw material off the companion onto the neutron star. This also transfers some of the companion's spin, or angular momentum, to the neutron star, thereby "recycling" the neutron star into a rapidly-rotating millisecond pulsar. In Terzan 5, all the pulsars discovered are rotating rapidly as a result of this process. Astronomers previously had discovered three pulsars in Terzan 5, some 28,000 light-years distant in the constellation Sagittarius, but suspected there were more. On July 17, 2004, Ransom and his colleagues used the GBT, and, in a 6-hour observation, found 14 new pulsars, the most ever found in a single observation. "This was possible because of the great sensitivity of the GBT and the new capabilities of our backend processor," said Ingrid Stairs, a professor at the Univer

2005-01-01

314

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

315

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

316

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

317

The onset of cluster formation around Herbig Ae/Be stars  

E-print Network

The large body of near infrared observations presented in Testi et al. (1997; 1998) are analysed with the aim of characterizing the young stellar clusters surrounding Herbig Ae/Be stars. The results confirm the tendency of early Be stars to be surrounded by dense clusters of lower mass "companions", while Ae stars are never found to be associated with conspicuous groups. The transition between the different environments appears to occur smoothly from Ae to Be stars without a sharp threshold. No correlation of the richness of the stellar groups detected is found with the galactic position or the age of the central Herbig Ae/Be star. The stellar volume densities estimated for the groups surrounding pre-main-sequence stars of intermediate mass show the transition from the low density aggregates of T Tauri stars and the dense clusters around massive stars. Only the most massive stars (10-20Msun) are found to be associated with dense (10^3 pc^-3) stellar clusters. This is exactly the mass regime at which the conventional accretion scenario for isolated star formation faces theoretical problems. Thus our findings strongly supports the idea that the formation of high-mass stars is influenced by dynamical interaction in a young cluster environment.

L. Testi; F. Palla; A. Natta

1998-11-13

318

Hadronic matter and rapidly rotating compact stars  

SciTech Connect

In part one of this paper the authors review the present status of neutron star matter calculations, and introduce a representative collection of realistic nuclear equations of state which are derived for different assumptions about the physical behavior of dense matter (baryon populations, pion condensation, possible transition of baryon matter to quark matter). Part two deals with the theoretical determination of the minimum possible rotational periods of neutron stars, performed in the framework of general relativity, whose knowledge serves to distinguish between pulsars that can be understood as rotating neutron stars and those that cannot. Likely candidates for the latter are hypothetical strange stars. Their properties are discussed in the third part of this contribution.

Weber, F.; Kettner, C. [Univ. of Munich (Germany). Inst. for Theoretical Physics; Glendenning, N.K. [Lawrence Berkeley Lab., CA (United States). Nuclear Science Div.

1994-03-01

319

AC conductivity of warm dense aluminum  

Microsoft Academic Search

Summary form only given, as follows. The AC conductivity of aluminum in the warm dense matter regime of several electron-volts and solid density is of particular interest because of its proximity to the predicted region of conductivity minimum. In this paper, we will describe the first determination of AC conductivity of a well defined, single plasma state using measured values

T. Ao; A. Ng; K. Widmann; M. E. Foord; D. F. Price; P. T. Springer

2002-01-01

320

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

321

Dense flows of cohesive granular materials  

Microsoft Academic Search

Using molecular dynamic simulations, we investigate the characteristics of dense flows of model cohesive grains. We describe their rheological behaviour and its origin at the scale of the grains and of their organization. Homogeneous plane shear flows give access to the constitutive law of cohesive grains which can be expressed by a simple friction law similar to the case of

Pierre G. Rognon

2008-01-01

322

Robert Collins Tracking in Dense Crowds  

E-print Network

Penn State Robert Collins VLPR 2012 Tracking in Dense Crowds Goal: Track targets in high typical crowd behavior to provide better motion priors. #12;Penn State Robert Collins VLPR 2012 Point realistic interactions Crowd Flow Social Force Models #12;Penn State Robert Collins VLPR 2012 Crowd Flow

Collins, Robert T.

323

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

324

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

325

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

326

Dense Spray Cooled DC-DC Converter  

Microsoft Academic Search

Advances in system packaging are driving densities to unprecedented levels. The increasing densities are creating significant thermal management challenges. In addition, the military is operating under conditions that are pushing operating temperatures to much higher levels. This combination of events is pushing the military to adopt more aggressive liquid-cooling technologies. The authors have demonstrated a dense DC-DC power converter for

Tahir Cader; Ben Tolman; C. Kabrell; D. Olsen

2006-01-01

327

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. Gondré-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

328

Performance Evaluation of Dense Gas Dispersion Models  

Microsoft Academic Search

This paper summarizes the results of a study to evaluate the performance of seven dense gas dispersion models using data from three field experiments. Two models (DEGADIS and SLAB) are in the public domain and the other five (AIRTOX, CHARM, FOCUS, SAFEMODE, and TRACE) are proprietary. The field data used are the Desert Tortoise pressurized ammonia releases, Burro liquefied natural

Jawad S. Touma; William M. Cox; Harold Thistle; James G. Zapert

1995-01-01

329

Propagating systems of dense linear integer constraints  

E-print Network

possibly to do reduced cost variable fixing). 1 #12;Alternatively one can also use linear programmingPropagating systems of dense linear integer constraints Thibaut Feydy and Peter J. Stuckey March 31 it is common to build stronger propagators from systems of linear equations. This, as far as we are aware

Stuckey, Peter J.

330

Oxygen ion-conducting dense ceramic  

Microsoft Academic Search

Preparation, structure, and properties of mixed metal oxide compositions and their uses are described. Mixed metal oxide compositions of the invention have stratified crystalline structure identifiable by means of powder X-ray diffraction patterns. In the form of dense ceramic membranes, the present compositions demonstrate an ability to separate oxygen selectively from a gaseous mixture containing oxygen and one or more

Uthamalingam Balachandran; Mark S. Kleefisch; Thaddeus P. Kobylinski; Sherry L. Morissette; Shiyou Pei

1998-01-01

331

Screening for dense breasts: digital breast tomosynthesis.  

PubMed

OBJECTIVE. Digital breast tomosynthesis (DBT) is a recent imaging technology that was developed to address the limitations of conventional 2D mammography. The limitations of standard mammography are well known and include reduced sensitivity in dense breasts. Clinical research studies of DBT and the implementation of DBT have revealed that DBT has potential benefits for evaluating patients with dense breasts. This article will discuss the benefits and limitations of DBT as a screening alternative for women with dense breasts. CONCLUSION. Studies to date have revealed that the use of DBT reduces recall rates and increases cancer detection rates. This has been demonstrated with the use of DBT for both screening and diagnostic purposes, as well as with imaging dense breasts. DBT has the ability to reduce breast tissue overlap, thus potentially revealing lesions that would otherwise have been missed. The limitations of DBT include longer interpretation times, higher costs, and increased radiation dose. These limitations present challenges that radiologists must consider before DBT implementation. PMID:25615747

Destounis, Stamatia V; Morgan, Renee; Arieno, Andrea

2015-02-01

332

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

333

The Milky Way as a Star Formation Engine  

E-print Network

The cycling of material from the interstellar medium (ISM) into stars and the return of stellar ejecta into the ISM is the engine that drives the ``galactic ecology'' in normal spirals, a cornerstone in the formation and evolution of galaxies through cosmic time. Major observational and theoretical challenges need to be addressed in determining the processes responsible for converting the low-density ISM into dense molecular clouds, forming dense filaments and clumps, fragmenting them into stars, OB associations and bound clusters, and characterizing the feedback that limits the rate and efficiency of star formation. This formidable task can be now effectively attacked thanks to the combination of new global-scale surveys of the Milky Way Galactic Plane from infrared to radio wavelengths, offering the possibility of bridging the gap between local and extragalactic star formation studies. The Herschel, Spitzer and WISE mid to far infrared continuum surveys, complemented by analogue surveys from ground-based fa...

Molinari, Sergio; Glover, Simon; Moore, Toby; Noriega-Crespo, Alberto; Plume, René; Testi, Leonardo; Vázquez-Semadeni, Enrique; Zavagno, Annie; Bernard, Jean-Philippe; Martin, Peter

2014-01-01

334

Exploding star  

NASA Astrophysics Data System (ADS)

Three astronomers report that the star Eta Carinae, 100 times more massive than the sun, is nearing its life expectancy and will explode sometime in the next 10,000 years. Until now, astronomers have been unable to discern whether the star was in the process of being born, was a middle-aged star with an unusual outflow of material, or an aged star about to explode.The huge star is coming to the end of what is considered a normal lifetime—about 2 million years—for a star of its size, according to Kris Davidson at the University of Minnesota, Nolan R. Walborn (presently at the Goddard Space Flight Center) of Cerro Tololo Inter-American Observatory, and Theodore R. Gull at Goddard. When Eta Carinae explodes, the astronomers report, it could emit more light than all the hundreds of billions of other stars in the galaxy for weeks. The expected explosion, or supernova, could produce a bright point of light that would be visible in broad daylight, they add.

335

Introduction to Polymer Chemistry.  

ERIC Educational Resources Information Center

Reviews the physical and chemical properties of polymers and the two major methods of polymer synthesis: addition (chain, chain-growth, or chain-reaction), and condensation (step-growth or step-reaction) polymerization. (JN)

Harris, Frank W.

1981-01-01

336

Mechanical Properties of Polymers.  

ERIC Educational Resources Information Center

Mechanical properties (stress-strain relationships) of polymers are reviewed, taking into account both time and temperature factors. Topics include modulus-temperature behavior of polymers, time dependence, time-temperature correspondence, and mechanical models. (JN)

Aklonis, J. J.

1981-01-01

337

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

338

Distances to dense cores that contain very low luminosity objects  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

339

Magnetic Fields and Galactic Star Formation Rates  

NASA Astrophysics Data System (ADS)

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 giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to ? 0.5 pc. Including an empirically motivated prescription for star formation from dense gas ({{n}H}\\gt {{10}5} c{{m}-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 ?G. However, our chosen kiloparsec-scale region, extracted from a global galaxy simulation, happens to contain a starbursting cloud complex that is only modestly affected by these magnetic fields and likely requires internal star formation feedback to regulate its SFR.

Van Loo, Sven; Tan, Jonathan C.; Falle, Sam A. E. G.

2015-02-01

340

Super-massive stars: Radiative transfer  

NASA Astrophysics Data System (ADS)

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

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

341

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

342

Quantum network dense coding via continuous-variable graph states  

NASA Astrophysics Data System (ADS)

We present a dense coding network based on continuous-variable graph state along with its corresponding protocol. A scheme to distill bipartite entanglement between two arbitrary modes in a graph state is provided in order to realize the dense coding network. We also analyze the capacity of network dense coding and provide a method to calculate its maximum mutual information. As an application, we analyze the performance of dense coding in a square lattice graph state network. The result showed that the mutual information of the dense coding is not largely affected by the complexity of the network. We conclude that the performance of dense coding network is very optimistic.

Zhang, Jiahao; He, Guangqiang

2014-08-01

343

Dendritic Polyurea Polymers.  

PubMed

Dendritic polymers, subsuming dendrimers as well as hyperbranched or highly branched polymers are well established in the field of polymer chemistry. This review article focuses on urea based dendritic polymers and summarizes their synthetic routes through both isocyanate and isocyanate-free processes. Furthermore, this article highlights applications where dendritic polyureas show their specific chemical and physical potential. For these purposes scientific publications as well as patent literature are investigated to generate a comprehensive overview on this topic. PMID:25475145

Tuerp, David; Bruchmann, Bernd

2014-12-01

344

The Birth, Evolution and Death of Star Clusters  

Microsoft Academic Search

A dense-enough gas-accumulation evolves, over a few Myr of intensifying star\\u000aformation, to an embedded cluster. If it contains a sufficient amount of mass,\\u000aO stars form and explosively expel the remaining gas, whereas poorer clusters\\u000areduce their embryonic gas content more gradually. The sudden expulsion of gas\\u000aunbinds most of a rich cluster, but a significant fraction of it

Pavel Kroupa

2000-01-01

345

Polymer modified asphalt binders  

Microsoft Academic Search

This paper is a review of research that has been conducted on polymer modified binders over the last three decades. Polymer modification of asphalt binders has increasingly become the norm in designing optimally performing pavements, particularly in the United States, Canada, Europe and Australia. Specific polymers that have been used include rubber, SBR, SBS and Elvaloy®. Specifications have been designed

Yetkin Yildirim

2007-01-01

346

orbit their host star at distances closer than Mercury's orbit around the Sun (Fig. 1) --is  

E-print Network

orbit their host star at distances closer than Mercury's orbit around the Sun (Fig. 1 since the discovery7 in 2006 of three Neptune-mass planets on compact orbits around star HD69830 by the gravitational tug of an orbiting planet. The most dense multi- planet configurations have been observed

Schnaufer, Achim

347

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

PubMed

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

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

2012-08-20

348

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

SciTech Connect

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. [Department of Physics, Jahangirnagar University, Savar (Bangladesh)] [Department of Physics, Jahangirnagar University, Savar (Bangladesh); Zobaer, M. S. [Department of Applied Science, Bangladesh University of Textiles, Tejgaon (Bangladesh)] [Department of Applied Science, Bangladesh University of Textiles, Tejgaon (Bangladesh)

2014-02-15

349

Image restoration of R136 - The dense core of NGC 2070  

NASA Technical Reports Server (NTRS)

We present results from the application of a new seeing deconvolution technique to images of the dense core of NGC 2070 = 30 Doradus (the controversial object R136a). We utilize a new maximum entropy algorithm capable of restoring images to very high resolution, even to subpixel accuracy. Images of the object in different colors, as well as comparisons with previous speckle results, have been used to check the validity of the results. Our images of R136 have an angular resolution approaching 0.2 arcsec, better than any direct images of this object published to date, and corroborate evidence that R136a is a dense star cluster core, rather than a single ultraluminous object.

Weir, N.; Djorgovski, S.; Meylan, G.

1991-01-01

350

Numerical study of ion acoustic shock waves in dense quantum plasma  

SciTech Connect

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.; Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-e-Azam University, Islamabad 45320 (Pakistan)] [Theoretical Plasma Physics Group, Department of Physics, Quaid-e-Azam University, Islamabad 45320 (Pakistan); Ali, S.; Mukhtar, Q., E-mail: qaisarm@ncp.edu.pk [National Center for Physics, Quaid-e-Azam University Campus, Shahdra Valley Road, Islamabad 44000 (Pakistan)

2014-03-15

351

Classifying stars  

NSDL National Science Digital Library

You will be able to describe the H-R diagram and explain how astronomers use it. The most important characteristics for classifying stars are: a) Color b) Temperature c) Size d) Composition e) Brightness The classification scheme that we currently use is the H-R diagram which is in the Earth Science Reference Tables (ESRT). The H-R diagram groups stars by surface temperature compared to their luminosity. 1)Today you will be reading a short tutorial ...

B, Mr.

2007-11-10

352

Tycho's Star  

NASA Astrophysics Data System (ADS)

A supernova remnant in Cassiopeia, 7.7° north of ? Cas, which suddenly appeared as a brilliant naked-eye star in November 1572 and reached a maximum apparent magnitude of -3.5. Until its disappearance 16 months later, it was extensively studied by the Danish astronomer Tycho Brahe (1546-1601), who described its early appearance as follows: `Initially, the new star was brighter than any other fixe...

Murdin, P.

2000-11-01

353

STARS no star on Kauai  

SciTech Connect

The island of Kuai, home to the Pacific Missile Range Facility, is preparing for the first of a series of Star Wars rocket launches expected to begin early this year. The Strategic Defense Initiative plans 40 launches of the Stategic Target System (STARS) over a 10-year period. The focus of the tests appears to be weapons and sensors designed to combat multiple-warhead ICBMs, which will be banned under the START II Treaty that was signed in January. The focus of this article is to express the dubious value of testing the STARS at a time when their application will not be an anticipated problem.

Jones, M.

1993-04-01

354

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

355

Monte Carlo Simulations of Dense Galactic Nuclei  

E-print Network

We have developed a new numerical code to simulate the joint evolution of a massive black hole (MBH) and a surrounding stellar cluster at the center of a galaxy. The physics treated in the simulations include: 2-body relaxation, stellar collisions (using a large set of "SPH" hydrodynamical simulations) and tidal disruption of stars by the MBH. In particular, we investigate the rates of star disruptive events that provide the MBH with gas to accrete.

Marc Freitag; Willy Benz

2001-01-11

356

Nanoporous polymer electrolyte  

DOEpatents

A nanoporous polymer electrolyte and methods for making the polymer electrolyte are disclosed. The polymer electrolyte comprises a crosslinked self-assembly of a polymerizable salt surfactant, wherein the crosslinked self-assembly includes nanopores and wherein the crosslinked self-assembly has a conductivity of at least 1.0.times.10.sup.-6 S/cm at 25.degree. C. The method of making a polymer electrolyte comprises providing a polymerizable salt surfactant. The method further comprises crosslinking the polymerizable salt surfactant to form a nanoporous polymer electrolyte.

Elliott, Brian (Wheat Ridge, CO); Nguyen, Vinh (Wheat Ridge, CO)

2012-04-24

357

Many-electron effects on dynamic processes in dense matter  

SciTech Connect

Large scale calculations quantum mechanical calculations of dynamic processes in dense helium suggest that quasi-molecular effects may play an important role in determining the transport properties of dense plasma. 7 refs., 3 figs.

Younger, S.M.

1989-01-01

358

Stellar Rotation: A Probe of Initial Star-Forming Conditions  

NASA Astrophysics Data System (ADS)

Projected rotational velocities (vsini) have been measured for B stars in the rich, dense h and chi Persei double cluster along with 7 young (1-7 Myr age) clusters of intermediate density, and compared with the distribution of rotational velocities for a sample of field stars having similar ages. In comparison with stars populating the field (and presumably formed in low density environments), the observed rotation speeds among stars formed in denser cluster environments are consistently higher. Moreover, the cluster population lacks the large cohort of slow (vsini < 50 km/sec) stars found among field B stars. We argue that both the higher rotation rates and the pattern of rotation speeds that differentiate B stars in clusters from their field analogs were likely imprinted during the star formation process rather than a result of angular momentum evolution. We suggest that these differences may reflect the effects of the higher accretion rates that theory suggests are characteristic of regions that give birth to dense clusters, namely, (1) higher initial rotation speeds; and (2) higher initial radii along the stellar birth line, resulting in greater spin-up between the birth line and the ZAMS.

Strom, Stephen; Wolff, Sidney

2005-07-01

359

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

360

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

361

Observations of Plasmons in Warm Dense Matter  

SciTech Connect

We present the first collective x-ray scattering measurements of plasmons in solid-density plasmas. The forward scattering spectra of a laser-produced narrow-band x-ray line from isochorically heated beryllium show that the plasmon frequency is a sensitive measure of the electron density. Dynamic structure calculations that include collisions and detailed balance match the measured plasmon spectrum indicating that this technique will enable new applications to determine the equation of state and compressibility of dense matter.

Glenzer, S H; Landen, O L; Neumayer, P; Lee, R W; Widmann, K; Pollaine, S W; Wallace, R J; Gregori, G; Holl, A; Bornath, T; Thiele, R; Schwarz, V; Kraeft, W; Redmer, R

2006-09-05

362

Oxygen ion-conducting dense ceramic  

DOEpatents

Preparation, structure, and properties of mixed metal oxide compositions and their uses are described. Mixed metal oxide compositions of the invention have stratified crystalline structure identifiable by means of powder X-ray diffraction patterns. In the form of dense ceramic membranes, the present compositions demonstrate an ability to separate oxygen selectively from a gaseous mixture containing oxygen and one or more other volatile components by means of ionic conductivities.

Balachandran, Uthamalingam (Hinsdale, IL); Kleefisch, Mark S. (Plainfield, IL); Kobylinski, Thaddeus P. (Prospect, PA); Morissette, Sherry L. (Las Cruces, NM); Pei, Shiyou (Naperville, IL)

1998-01-01

363

Confined magnetic monopoles in dense QCD  

NASA Astrophysics Data System (ADS)

Non-Abelian strings exist in the color-flavor locked phase of dense QCD. We show that kinks appearing in the world-sheet theory on these strings, in the form of the kink-antikink bound pairs, are the magnetic monopoles—descendants of the ’t Hooft-Polyakov monopoles surviving in such a special form in dense QCD. Our consideration is heavily based on analogies and inspiration coming from certain supersymmetric non-Abelian theories. This is the first ever analytic demonstration that objects unambiguously identifiable as the magnetic monopoles are native to non-Abelian Yang-Mills theories (albeit our analysis extends only to the phase of the monopole confinement and has nothing to say about their condensation). Technically, our demonstration becomes possible due to the fact that low-energy dynamics of the non-Abelian strings in dense QCD is that of the orientational zero modes. It is described by an effective two-dimensional CP(2) model on the string world sheet. The kinks in this model representing confined magnetic monopoles are in a highly quantum regime.

Gorsky, A.; Shifman, M.; Yung, A.

2011-04-01

364

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

365

Spin light of electron in dense neutrino fluxes  

E-print Network

An electron motion in a dense neutrino flux is investigated. The Dirac equation exact solutions for the electron energy and wave function in this external environment are obtained. On this basis we predict the existence of an electromagnetic radiation that can be emitted by electrons in dense neutrino fluxes. We term this phenomenon "the spin light of electron in dense neutrino flux" ($SLe_{\

Ilya Balantsev; Alexander Studenikin

2014-05-18

366

DISPERSION OF DENSE GAS RELEASES IN A WIND TUNNEL  

EPA Science Inventory

The paper documents two dense gas projects undertaken at the US EPA Fluid Modeling Facility. The study investigated the basic nature of the transport and dispersion of a dense gas plume in a simulated neutral atmospheric boundary layer. The two dense gas releases were CO2 and SF6...

367

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. Årthun; R. B. Ingvaldsen; L. H. Smedsrud; C. Schrum

2011-01-01

368

ON THIN, VERY THIN, AND SLIM DENSE Gary Gruenhage  

E-print Network

ON THIN, VERY THIN, AND SLIM DENSE SETS Gary Gruenhage£ Department of Mathematics and Statistics-mail: zpiotr@math.ysu.edu August 30 Abstract The notions of thin and very thin dense subsets of a product space): Primary 54B10; Secondary: 54A25; 03E75; 54C08. Key words: dense set; thin set; very thin set; irresolvable

Gruenhage, Gary

369

Vortices and Other Topological Solitons in Dense Quark Matter  

E-print Network

In this review, we discuss various properties of topological solitons in dense QCD matter, with a particular emphasis on the CFL phase exhibiting superfluidity and superconductivity, and their phenomenological implications in terms of the effective field theories such as the Ginzburg-Landau theory, the chiral Lagrangian, or the Bogoliubov--de Gennes equation. The most fundamental topological excitations are non-Abelian vortices, which are 1/3 quantized superfluid vortices and color magnetic flux tubes. They are created at a phase transition or a rotation such compact stars. The intervortex-interaction is repulsive and consequently a vortex lattice is formed. Bosonic and fermionic zero-energy modes are trapped in the vortex core and propagate along it as gapless excitations. The former consists of translational zero modes (a Kelvin mode) with a quadratic dispersion and CP(2) Nambu-Goldstone gapless modes with a linear dispersion, while the latter is the triplet Majorana fermion zero modes. The low-energy effec...

Eto, Minoru; Nitta, Muneto; Yasui, Shigehiro

2013-01-01

370

ICES IN THE QUIESCENT IC 5146 DENSE CLOUD  

SciTech Connect

This paper presents spectra in the 2 to 20 {mu}m range of quiescent cloud material located in the IC 5146 cloud complex. The spectra were obtained with NASA's Infrared Telescope Facility SpeX instrument and the Spitzer Space Telescope's Infrared Spectrometer. We use these spectra to investigate dust and ice absorption features in pristine regions of the cloud that are unaltered by embedded stars. We find that the H{sub 2}O-ice threshold extinction is 4.03 {+-} 0.05 mag. Once foreground extinction is taken into account, however, the threshold drops to 3.2 mag, equivalent to that found for the Taurus dark cloud, generally assumed to be the touchstone quiescent cloud against which all other dense cloud and embedded young stellar object observations are compared. Substructure in the trough of the silicate band for two sources is attributed to CH{sub 3}OH and NH{sub 3} in the ices, present at the {approx}2% and {approx}5% levels, respectively, relative to H{sub 2}O-ice. The correlation of the silicate feature with the E(J - K) color excess is found to follow a much shallower slope relative to lines of sight that probe diffuse clouds, supporting the previous results by Chiar et al.

Chiar, J. E. [SETI Institute, Carl Sagan Center, 189 Bernardo Avenue, Mountain View, CA 94035 (United States); Pendleton, Y. J.; Allamandola, L. J.; Ennico, K.; Greene, T. P.; Roellig, T. L.; Sandford, S. A. [NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035 (United States); Boogert, A. C. A. [IPAC, NASA Herschel Science Center, Mail Code 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Geballe, T. R.; Mason, R. E. [Gemini Observatory, Northern Operations Center, 670 North A'ohoku Place, Hilo, HI 96720 (United States); Keane, J. V. [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Lada, C. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tielens, A. G. G. M. [Leiden Observatory, P.O. Box 9513, 2300 RA Leiden (Netherlands); Werner, M. W. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Whittet, D. C. B. [New York Center for Astrobiology, Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Decin, L. [Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); Eriksson, K., E-mail: jchiar@seti.org [Department of Physics and Astronomy, Uppsala University, Box 515, 751 20 Uppsala (Sweden)

2011-04-10

371

Neutrino diffusion and mass ejection in protoneutron stars  

SciTech Connect

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

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

2010-11-15

372

The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems  

NASA Astrophysics Data System (ADS)

In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of 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.

Belkus, H.; van Bever, J.; Vanbeveren, D.

373

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

374

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

375

Constraints on the equation of state of cold dense matter from nuclear physics and astrophysics  

NASA Astrophysics Data System (ADS)

The Brussels-Montreal equations of state of cold dense nuclear matter that have been recently developed are tested against various constraints coming from both nuclear physics and astrophysics. The nuclear physics constraints include the analysis of nuclear flow and kaon production in heavy-ion collision experiments, as well as recent microscopic many-body calculations of infinite homogeneous neutron matter. Astrophysical observations, especially recent neutron-star mass measurements, provide valuable constraints on the high-density part of the equation of state that is not accessible in laboratory experiments.

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

2014-03-01

376

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

377

The Evolution of Massive Stars: a Selection of Facts and Questions  

NASA Astrophysics Data System (ADS)

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 and the effects of rotation on stellar evolution. Finally, we present an unconventionally formed object scenario (UFO-scenario) of WR binaries in dense stellar environments.

Vanbeveren, D.

378

Fabrication of polymer photonic crystal superprism structures using polydimethylsiloxane soft molds  

E-print Network

Fabrication of polymer photonic crystal superprism structures using polydimethylsiloxane soft molds photonic crystal superprism structures using elastomeric polydimethylsiloxane templates. Dense two-dimensional photonic crystal superprism structures with feature sizes of 150­500 nm and aspect ratios of up to 1

Jiang, Wei

379

LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION  

SciTech Connect

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.; Banerjee, Robi [Institut fuer Theoretische Astrophysik, Zentrum fuer Astronomie der Universitaet Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Low, Mordecai-Mark Mac, E-mail: thomas.peters@ita.uni-heidelberg.d [Department of Astrophysics, American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024-5192 (United States)

2010-12-10

380

Massive Star Evolution in Different Environments  

E-print Network

We review the properties of massive star evolution in different environments, where the major environmental factor is metallicity. Comparisons between evolutionary models and observations of massive OB, WR stars and related objects are presented. We also review several observations asking for future improvements of stellar models and theoretical developments in this respect. We summarize evolutionary scenarios for the most massive stars and try to clarify recent questions regarding their evolutionary status as core-H or core-He burning objects. Another environmental effect, which might affect stellar evolution is a cluster environment with a high stellar density. As test cases of massive star evolution in dense clusters we summarize recent work on the densest known resolved young clusters: R136, NGC 3603, and the three Galactic Center star clusters (the central cluster, Quintuplet and "Arches" cluster). For the central cluster we present new comparisons between stellar parameters of emission line stars derived by Najarro et al. (1994, 1997), and appropriate evolutionary models. From their parameters we argue that most of these stars can be regarded as WNL stars, and do hence not necessarily represent a peculiar class. We suggest that some apparent differences with well known WR stars can be understood in terms of their core burning stage and/or other changes due to a high metallicity. Based on our present knowledge we conclude that in young clusters with central stellar densities up to rho_c ~ 10.**(5-6) Msun/pc**3 no compelling evidence for a secondary effect influencing the evolution of massive stars has yet been found.

Daniel Schaerer

1998-08-27

381

Polymer brush under flow as an anchored microswimmer  

E-print Network

Polymer brushes are increasingly used to tailor surface physicochemistry for various applications such as wetting, adhesion of biological objects, implantable devices, etc. We perform Dissipative Particle Dynamics simulations to study the behavior of dense polymer brushes under flow in a slit-pore channel. We discover that the system displays flow inversion at the brush interface for several disconnected ranges of the imposed flow. We associate such phenomenon to collective polymer dynamics: a wave propagating on the brush surface. The relation between the wavelength, the amplitude and the propagation speed of the flow-generated wave is consistent with the solution of the Stokes equations when an imposed traveling wave is assumed as boundary condition (the famous Taylor's swimmer).

Biagi, Sofia; Sciortino, Francesco; Misbah, Chaouqi

2015-01-01

382

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

383

Elastic properties of polycrystalline dense matter  

E-print Network

Elastic properties of the solid regions of neutron star crusts and white dwarfs play an important role in theories of stellar oscillations. Matter in compact stars is presumably polycrystalline and, since the elastic properties of single crystals of such matter are very anisotropic, it is necessary to relate elastic properties of the polycrystal to those of a single crystal. We calculate the effective shear modulus of polycrystalline matter with randomly oriented crystallites using a self-consistent theory that has been very successful in applications to terrestrial materials and show that previous calculations overestimate the shear modulus by approximately 28%.

Kobyakov, D

2015-01-01

384

High Performance Polymers  

NASA Technical Reports Server (NTRS)

This report summarizes results from research on high performance polymers. The research areas proposed in this report include: 1) Effort to improve the synthesis and to understand and replicate the dielectric behavior of 6HC17-PEK; 2) Continue preparation and evaluation of flexible, low dielectric silicon- and fluorine- containing polymers with improved toughness; and 3) Synthesis and characterization of high performance polymers containing the spirodilactam moiety.

Venumbaka, Sreenivasulu R.; Cassidy, Patrick E.

2003-01-01

385

Grain Growth and Silicates in Dense Clouds  

NASA Technical Reports Server (NTRS)

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 di&se 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 5 146, 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).

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

2006-01-01

386

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

387

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.

Twin Cities Public Television

2010-01-01

388

Brittle Star  

USGS Multimedia Gallery

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

389

Star Power  

SciTech Connect

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

2014-10-17

390

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

391

Electrical and thermal conductivities in dense plasmas  

SciTech Connect

Expressions for the electrical and thermal conductivities in dense plasmas are derived combining the Chester-Thellung-Kubo-Greenwood approach and the Kramers approximation. The infrared divergence is removed assuming a Drude-like behaviour. An analytical expression is obtained for the Lorenz number that interpolates between the cold solid-state and the hot plasma phases. An expression for the electrical resistivity is proposed using the Ziman-Evans formula, from which the thermal conductivity can be deduced using the analytical expression for the Lorenz number. The present method can be used to estimate electrical and thermal conductivities of mixtures. Comparisons with experiment and quantum molecular dynamics simulations are done.

Faussurier, G., E-mail: gerald.faussurier@cea.fr; Blancard, C.; Combis, P.; Videau, L. [CEA, DAM, DIF, F-91297 Arpajon (France)

2014-09-15

392

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

2006-11-10

393

Approximation of Dense-n -Subgraph and  

E-print Network

Zhang December 1999 Abstract We consider the DENSE- n 2 -SUBGRAPH problem, i.e., determine a block S #26; V to minimize 1 2 X (i;j)2E;i2S;j2V nS w ij such that bn #20; jSj #20; (1 b)n, where n = jV j) subject to n X j=1 x j = 0 or e T x = 0 x 2 j = 1; j = 1; : : : ; n; where e 2 R n is the column vector

Ye, Yinyu

394

Approximation of Dense-n -Subgraph and  

E-print Network

Zhang November 1999 (Modi#12;ed December 1999) Abstract We consider the DENSE- n 2 -SUBGRAPH problem, i.e S #26; V to minimize 1 2 X (i;j)2E;i2S;j2V nS w ij such that bn #20; jSj #20; (1 b)n, where n = jV j) subject to n X j=1 x j = 0 or e T x = 0 x 2 j = 1; j = 1; : : : ; n; where e 2 R n is the column vector

Ye, Yinyu

395

Electrical and thermal conductivities in dense plasmas  

NASA Astrophysics Data System (ADS)

Expressions for the electrical and thermal conductivities in dense plasmas are derived combining the Chester-Thellung-Kubo-Greenwood approach and the Kramers approximation. The infrared divergence is removed assuming a Drude-like behaviour. An analytical expression is obtained for the Lorenz number that interpolates between the cold solid-state and the hot plasma phases. An expression for the electrical resistivity is proposed using the Ziman-Evans formula, from which the thermal conductivity can be deduced using the analytical expression for the Lorenz number. The present method can be used to estimate electrical and thermal conductivities of mixtures. Comparisons with experiment and quantum molecular dynamics simulations are done.

Faussurier, G.; Blancard, C.; Combis, P.; Videau, L.

2014-09-01

396

An electron conductivity model for dense plasmas  

NASA Astrophysics Data System (ADS)

An electron conductivity model for dense plasmas is described which gives a consistent and complete set of transport coefficients including not only electrical conductivity and thermal conductivity, but also thermoelectric power, and Hall, Nernst, Ettinghausen, and Leduc-Righi coefficients. The model is useful for simulating plasma experiments with strong magnetic fields. The coefficients apply over a wide range of plasma temperature and density and are expressed in a computationally simple form. Different formulas are used for the electron relaxation time in plasma, liquid, and solid phases. Comparisons with recent calculations and available experimental measurement show the model gives results which are sufficiently accurate for many practical applications.

Lee, Y. T.; More, R. M.

1984-05-01

397

Resolving ultrafast heating of dense cryogenic hydrogen.  

PubMed

We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ?300??fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ?0.9??ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory. PMID:24679300

Zastrau, U; Sperling, P; Harmand, M; Becker, A; Bornath, T; Bredow, R; Dziarzhytski, S; Fennel, T; Fletcher, L B; Förster, E; Göde, S; Gregori, G; Hilbert, V; Hochhaus, D; Holst, B; Laarmann, T; Lee, H J; Ma, T; Mithen, J P; Mitzner, R; Murphy, C D; Nakatsutsumi, M; Neumayer, P; Przystawik, A; Roling, S; Schulz, M; Siemer, B; Skruszewicz, S; Tiggesbäumker, J; Toleikis, S; Tschentscher, T; White, T; Wöstmann, M; Zacharias, H; Döppner, T; Glenzer, S H; Redmer, R

2014-03-14

398

Gravity-driven dense granular flows  

SciTech Connect

The authors report and analyze the results of numerical studies of dense granular flows in two and three dimensions, using both linear damped springs and Hertzian force laws between particles. Chute flow generically produces a constant density profile that satisfies scaling relations suggestive of a Bagnold grain inertia regime. The type for force law has little impact on the behavior of the system. Failure is not initiated at the surface, consistent with the absence of surface flows and different principal stress directions at vs. below the surface.

ERTAS,DENIZ; GREST,GARY S.; HALSEY,THOMAS C.; DEVINE,DOV; SILBERT,LEONARDO E.

2000-03-29

399

Predictive aging of polymers  

NASA Technical Reports Server (NTRS)

A method of predicting aging of polymers operates by heating a polymer in the outdoors to an elevated temperature until a change of property is induced. The test is conducted at a plurality of temperatures to establish a linear Arrhenius plot which is extrapolated to predict the induction period for failure of the polymer at ambient temperature. An Outdoor Photo Thermal Aging Reactor (OPTAR) is also described including a heatable platen for receiving a sheet of polymer, means to heat the platen and switching means such as a photoelectric switch for turning off the heater during dark periods.

Cuddihy, Edward F. (Inventor); Willis, Paul B. (Inventor)

1990-01-01

400

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

401

Dense Molecular Gas and H2O Maser Emission in Galaxies  

NASA Astrophysics Data System (ADS)

Extragalactic H2O masers have been found in dense gas circumstance in off-nuclear star formation regions or within parsecs of Active Galactic Nuclei (AGNs). HCN molecular (one of the best dense gas tracers) emission has been detected in more than 60 galaxies. For HCN-detected galaxy sample, the relation of maser and gas emission was investigated here to identify physical observable properties that differentiate maser and non-maser galaxies. Our analysis results show that there is no significant difference on the infrared and gas emission between maser galaxies and galaxies without maser detection. For maser host HCN-galaxies, maser luminosity is found to be correlated to CO luminosity (a proxy of the total molecular gas) and HCN luminosity, i.e., kilomasers ( L_{H2O} < 10 L ?) with low maser luminosity having low gas emission luminosity, with respect to megamasers ( L_{H2O} > 10 L ?). For normalized maser and HCN luminosity (for removing distance effect), the correlation is still apparent. However, for normalized maser and CO luminosity, the correlation disappeared completely. Thus one proposition that the amount of dense molecular gas should be a good tracer of H2O maser emission can be made.

Huang, F.; Zhang, J. S.; Li, R. M.; Li, H. K.

2014-11-01

402

A Complete Census of Dense Cores in Chamaeleon I: Results from an ALMA Cycle 1 Survey  

NASA Astrophysics Data System (ADS)

Stars form from the gravitational collapse of dense molecular cloud cores, yet many details relating to the onset of collapse and fragmentation into multiple systems remain unknown. I will present the results of an ALMA cycle 1 survey of all known dense cores (starless and protostellar) in the Chamaeleon I molecular cloud complex (d~170pc). The goals of this survey are to provide a complete census of protostars, including those too young, too low in luminosity, and/or too deeply embedded to detect in previous infrared and (sub)millimeter surveys, and to characterize when and how dense cores fragment into multiple systems. With these results we will report new detections of protostellar multiplicity and provide updated constraints on the fraction of starless cores that are truly starless, the lifetime of the first hydrostatic core phase, and the relative durations of the starless and protostellar core populations. We will also report a lack of detections among the starless cores and discuss implications of these results.

Dunham, Michael; Schnee, Scott; Pineda, Jaime E.; Offner, Stella; Price, Daniel; Arce, Hector G.; Di Francesco, James; Johnstone, Doug I.; Bourke, Tyler L.; Tobin, John J.; Chen, Xuepeng

2015-01-01

403

Monolayers and multilayers of conjugated polymers as nanosized electronic components.  

PubMed

Conjugated polymers (CPs) are interesting materials for preparing devices based on nanoscopic molecular architectures because they exhibit electrical, electronic, magnetic, and optical properties similar to those of metals or semiconductors while maintaining the flexibility and ease of processing of polymers. The production of well-defined mono- and multilayers of CPs on electrodes with nanometer-scale, one-dimensional resolution remains, however, an important challenge. In this Account, we describe the preparation and conductive properties of nanometer-sized CP molecular structures formed on electrode surfaces--namely, self-assembled monolayer (SAM), brush-type, and self-assembled multilayer CPs--and in combination with gold nanoparticles (AuNPs). We have electrochemically polymerized SAMs of carboxyalkyl-functionalized terthiophenes aligned either perpendicular or parallel to the electrode surface. Anodic coupling of various pyrrole- and thiophene-based monomers in solution with the oligothiophene-based SAMs produced brush-like films. Microcontact printing of these SAMs produced patterns that, after heterocoupling, exhibited large height enhancements, as measured using atomic force microscopy (AFM). We have employed layer-by-layer self-assembly of water-soluble polythiophene-based polyelectrolytes to form self-assembled multilayers. The combination of isostructural polycationic and polyanionic polythiophenes produced layers of chains aligned parallel to the substrate plane. These stable, robust, and dense layers formed with high regularity on the preformed monolayers, with minimal interchain penetration. Infrared reflection/adsorption spectroscopy and X-ray diffraction analyses revealed unprecedented degrees of order. Deposition of soluble polypyrroles produced molecular layers that, when analyzed using a gold-coated AFM tip, formed gold-polymer-gold junctions that were either ohmic or rectifying, depending of the layer sequence. We also describe the electronic conduction of model alpha,omega-capped sexithiophenes featuring a range of electron donor/acceptor units and lengths of additional conjugation. The sexithiophene cores exhibit redox-type conductivity, developing at the neutral/cation and cation/dication levels with values depending the nature of the substitution and the redox system. Extending the conjugation beyond the sexithiophene frame introduces further oxidation processes displaying enhanced conductivity. Finally, we discuss the ability of CP-based monolayers to coordinate AuNPs. Although thiophene- and pyrrole-based oligomers aggregate toluene-soluble AuNPs, alkyl substitution inhibits the aggregation process through steric restraint. Consequently, we investigated the interactions between AuNPs and polypyrrole or polythiophene monolayers, including those formed from star-shaped molecules. The hindered aggregation provided by alkyl substituents allowed us to adsorb thiol-functionalized oligothiophenes and oligopyrroles directly onto preformed AuNPs. Novel materials incorporating AuNPs of the same size but bearing different conjugated ends or bridges have great promise for applications in electrocatalysis, electroanalysis, and organic electronics. PMID:18570441

Zotti, Gianni; Vercelli, Barbara; Berlin, Anna

2008-09-01

404

An overview of STAR experimental results  

NASA Astrophysics Data System (ADS)

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 ?{sNN} = 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 collective dynamics, electromagnetic probes, heavy-flavor, initial state physics, jets, QCD phase diagram, thermodynamics and hadron chemistry, and future experimental facilities, upgrades, and instrumentation[1]. 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.

Xu, Nu

2014-11-01

405

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

406

STAR heavy flavor tracker  

NASA Astrophysics Data System (ADS)

Hadrons containing heavy quarks are a clean probe of the early dynamic evolution of the dense and hot medium created in high-energy nuclear collisions. To explore heavy quark production at RHIC, the Heavy Flavor Tracker (HFT) for the STAR experiment was built and installed in time for RHIC Run 14. The HFT consists of four layers of silicon detectors. The two outermost layers are silicon strip detectors and the two innermost layers are made from state-of-the-art ultra-thin CMOS Monolithic Active Pixel Sensors (MAPS). This is the first application of a CMOS MAPS detector in a collider experiment. The use of thin pixel sensors plus the use of carbon fiber supporting material limits the material budget to be only 0.4% radiation length per pixel detector layer, enabling the reconstruction of low pT heavy flavor hadrons. The status and performance of the HFT in the RHIC 200 GeV Au + Au run in 2014 are reported. Very good detector efficiency, hit residuals and track resolution (DCAs) were observed in the cosmic ray data and in the Au + Au data.

Qiu, Hao

2014-11-01

407

The sun, our star  

NASA Astrophysics Data System (ADS)

Observational data, analytical models, and instrumentation used to study the sun and its evolution are detailed, and attention is given to techniques for converting solar energy to useful power on earth. The star ignited when the mutual gravitational attractions of dust and vapor in a primordial cloud in the Galaxy caused an in-rush of accelerating particles which eventually became dense enough to ignite. The heat grew until inward rushing matter was balanced by outward moving radiative forces. The planets formed from similar debris, and solar radiation is suggested to have triggered the chemical reactions giving rise to life on earth. Visual, spectroscopic, coronagraphic, and UV observations of the sun from the ground and from spacecraft, particularly Skylab, are described, together with features of the solar surface, magnetic field, sunspots, and coronal loops. Models for the processes that occur in the solar interior are explored, as are the causes of solar flares. Attention is given to solar cells, heliostat arrays, wind turbines, and water turbines as means to convert, either directly or indirectly, the earth-bound solar energy to electrical and thermal power. Finally, the life cycle of the sun, about 9 billion yr in duration, is summarized, noting the current status of midlife.

Noyes, R. W.

408

The conductivity of dense molecular gas  

E-print Network

We evaluate the conductivity tensor for molecular gas at densities ranging from 10^4 to 10^15 cm^-3 for a variety of grain models. The Hall contribution to the conductivity has generally been neglected in treatments of the dynamics of molecular gas. We find that it is not important if only 0.1 micron grains are considered, but for a Mathis-Rumpl-Nordsieck grain-size distribution (with or without PAHs) it becomes important for densities between 10^7 and 10^11 cm^-3. If PAHs are included, this range is reduced to 10^9 -- 10^10 cm^-3. The consequences for the magnetic field evolution and dynamics of dense molecular gas are profound. To illustrate this, we consider the propagation of Alfven waves under these conditions. A linear analysis yields a dispersion relation valid for frequencies below the neutral collision frequencies of the charged species. The dispersion relation shows that there is a pair of circularly polarised modes with distinct propagation speeds and damping rates. We note that the gravitational collapse of dense cloud cores may be substantially modified by the Hall term.

Mark Wardle; Cindy Ng

1998-10-28

409

Ion Beam Driven Warm Dense Matter Experiments  

NASA Astrophysics Data System (ADS)

We report plans and experimental results in ion beam-driven warm dense matter (WDM) experiments. Initial experiments use a 0.3 MeV K+ beam from the NDCX-I accelerator. The WDM conditions are to be achieved by longitudinal and transverse neutralized drift compression to provide a hot spot on the target with a 1-mm beam spot size, and 2-ns pulse length. As a technique for heating matter to high energy density, intense ion beams can deliver precise and uniform beam energy deposition, in a relatively large sample size, and can heat any solid-phase target material. The range of the beams in solid targets is less than 1 micron, which can be lengthened by using reduced density porous targets. We have developed a WDM target chamber and target diagnostics including a fast multi-channel optical pyrometer, optical streak camera, VISAR, and high-speed gated cameras. Initial experiments will explore measurement of temperature and other target parameters. Experiments are planned in areas such as dense electronegative targets, porous target homogenization and two-phase equation of state.

Bieniosek, F. M.; Henestroza, E.; Leitner, M. A.; Lidia, S. M.; Logan, B. G.; More, R. M.; Ni, P. A.; Seidl, P. A.; Waldron, W. L.; Barnard, J. J.

2008-11-01

410

Dynamics of Kr in dense clathrate hydrates.  

SciTech Connect

The dynamics of Kr atoms as guests in dense clathrate hydrate structures are investigated using site specific {sup 83}Kr nuclear resonant inelastic x-ray scattering (NRIXS) spectroscopy in combination with molecular dynamics simulations. The dense structure H hydrate and filled-ice structures are studied at high pressures in a diamond anvil high-pressure cell. The dynamics of Kr in the structure H clathrate hydrate quench recovered at 77 K is also investigated. The Kr phonon density of states obtained from the experimental NRIXS data are compared with molecular dynamics simulations. The temperature and pressure dependence of the phonon spectra provide details of the Kr dynamics in the clathrate hydrate cages. Comparison with the dynamics of Kr atoms in the low-pressure structure II obtained previously was made. The Lamb-Mossbauer factor obtained from NRIXS experiments and molecular dynamics calculations are in excellent agreement and are shown to yield unique information on the strength and temperature dependence of guest-host interactions.

Klug, D. D.; Tse, J. S.; Zhao, J. Y.; Sturhahn, W.; Alp, E. E.; Tulk, C. A. (X-Ray Science Division); (National Research Council of Canada); (Univ. of Saskatchewan); (ORNL)

2011-01-01

411

Compton scattering measurements from dense plasmas  

SciTech Connect

Compton scattering has 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 may be directly measured from the Compton scattered spectrum of a high-energy x-ray line source. Specifically, the scattered spectra directly reflect the electron velocity distribution. In non-degenerate plasmas, the width provides an accurate measure of the electron temperatures, while in partially Fermi degenerate systems that occur in laser-compressed matter it provides the Fermi energy and hence the electron density. Both of these regimes have been accessed in experiments at the Omega laser by employing isochorically heated solid-density beryllium and moderately compressed beryllium foil targets. In the latter experiment, compressions by a factor of 3 at pressures of 40 Mbar have been measured in excellent agreement with radiation hydrodynamic modeling.

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

2007-10-02

412

Nuclear quantum dynamics in dense hydrogen  

NASA Astrophysics Data System (ADS)

Nuclear dynamics in dense hydrogen, which is determined by the key physics of large-angle scattering or many-body collisions between particles, is crucial for the dynamics of planet's evolution and hydrodynamical processes in inertial confinement confusion. Here, using improved ab initio path-integral molecular dynamics simulations, we investigated the nuclear quantum dynamics regarding transport behaviors of dense hydrogen up to the temperatures of 1 eV. With the inclusion of nuclear quantum effects (NQEs), the ionic diffusions are largely higher than the classical treatment by the magnitude from 20% to 146% as the temperature is decreased from 1 eV to 0.3 eV at 10 g/cm3, meanwhile, electrical and thermal conductivities are significantly lowered. In particular, the ionic diffusion is found much larger than that without NQEs even when both the ionic distributions are the same at 1 eV. The significant quantum delocalization of ions introduces remarkably different scattering cross section between protons compared with classical particle treatments, which explains the large difference of transport properties induced by NQEs. The Stokes-Einstein relation, Wiedemann-Franz law, and isotope effects are re-examined, showing different behaviors in nuclear quantum dynamics.

Kang, Dongdong; Sun, Huayang; Dai, Jiayu; Chen, Wenbo; Zhao, Zengxiu; Hou, Yong; Zeng, Jiaolong; Yuan, Jianmin

2014-06-01

413

Nitrogen superfractionation in dense cloud cores  

E-print Network

We report new calculations of interstellar 15N fractionation. Previously, we have shown that large enhancements of 15N/14N can occur in cold, dense gas where CO is frozen out, but that the existence of an NH + N channel in the dissociative recombination of N2H+ severely curtails the fractionation. In the light of recent experimental evidence that this channel is in fact negligible, we have reassessed the 15N chemistry in dense cloud cores. We consider the effects of temperatures below 10 K, and of the presence of large amounts of atomic nitrogen. We also show how the temporal evolution of gas-phase isotope ratios is preserved as spatial heterogeneity in ammonia ice mantles, as monolayers deposited at different times have different isotopic compositions. We demonstrate that the upper layers of this ice may have 15N/14N ratios an order of magnitude larger than the underlying elemental value. Converting our ratios to delta-values, we obtain delta(15N) > 3,000 per mil in the uppermost layer, with values as high as 10,000 per mil in some models. We suggest that this material is the precursor to the 15N `hotspots' recently discovered in meteorites and IDPs

S. D. Rodgers; S. B. Charnley

2008-02-13

414

Solids flow rate measurement in dense slurries  

SciTech Connect

Accurate and rapid flow rate measurement of solids in dense slurries remains an unsolved technical problem, with important industrial applications in chemical processing plants and long-distance solids conveyance. In a hostile two-phase medium, such a measurement calls for two independent parameter determinations, both by non-intrusive means. Typically, dense slurries tend to flow in laminar, non-Newtonian mode, eliminating most conventional means that usually rely on calibration (which becomes more difficult and costly for high pressure and temperature media). These issues are reviewed, and specific solutions are recommended in this report. Detailed calculations that lead to improved measuring device designs are presented for both bulk density and average velocity measurements. Cross-correlation, chosen here for the latter task, has long been too inaccurate for practical applications. The cause and the cure of this deficiency are discussed using theory-supported modeling. Fluid Mechanics are used to develop the velocity profiles of laminar non-Newtonian flow in a rectangular duct. This geometry uniquely allows the design of highly accurate `capacitive` devices and also lends itself to gamma transmission densitometry on an absolute basis. An absolute readout, though of less accuracy, is also available from a capacitive densitometer and a pair of capacitive sensors yields signals suitable for cross-correlation velocity measurement.

Porges, K.G.; Doss, E.D.

1993-09-01

415

Dense Hadronic Matter and Finite Nuclei in AN Rmf Model with a Chiral Potential  

NASA Astrophysics Data System (ADS)

In constructing the dense matter equation of state (EOS), it is desired to respect both chiral symmetry and hypernuclear physics. In dense matter, strangeness is expected to play a decisive role and the partial restoration of chiral symmetry would modify the hadron properties. For chiral symmetry side, We have recently developed the chiral SU(2) symmetric RMF model with logarithmic sigma potential derived in the strong coupling limit (SCL) of the lattice QCD. In this SCL model, we can describe not only symmetric nuclear matter but also bulk properties of finite nuclei. We find that the EOS of symmetric matter is softened by the scalar meson with hidden strangeness, which couples with sigma meson through the determinant interaction. In this paper, we present this RMF model including chiral SU(3) potential and its results. We discuss the importance of hyperon in neutron star in this chiral SU(3) RMF model and show an effect to nuclear star maximum mass by introducing this potential. We also inquire the effect of meson-meson-baryon coupling which is corresponding to density dependent couplings.

Tsubakihara, K.; Ohnishi, A.

2010-09-01

416

A review of Monte Carlo simulations of polymers with PERM  

E-print Network

In this review, we describe applications of the pruned-enriched Rosenbluth method (PERM), a sequential Monte Carlo algorithm with resampling, to various problems in polymer physics. PERM produces samples according to any given prescribed weight distribution, by growing configurations step by step with controlled bias, and correcting "bad" configurations by "population control". The latter is implemented, in contrast to other population based algorithms like e.g. genetic algorithms, by depth-first recursion which avoids storing all members of the population at the same time in computer memory. The problems we discuss all concern single polymers (with one exception), but under various conditions: Homopolymers in good solvents and at the $\\Theta$ point, semi-stiff polymers, polymers in confining geometries, stretched polymers undergoing a forced globule-linear transition, star polymers, bottle brushes, lattice animals as a model for randomly branched polymers, DNA melting, and finally -- as the only system at low temperatures, lattice heteropolymers as simple models for protein folding. PERM is for some of these problems the method of choice, but it can also fail. We discuss how to recognize when a result is reliable, and we discuss also some types of bias that can be crucial in guiding the growth into the right directions.

Hsiao-Ping Hsu; Peter Grassberger

2011-07-06

417

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.

418

Data Characterization Using Artificial-Star Tests: Performance Evaluation  

NASA Astrophysics Data System (ADS)

Traditional artificial-star tests are widely applied to photometry in crowded stellar fields. However, to obtain reliable binary fractions (and their uncertainties) of remote, dense, and rich star clusters, one needs to recover huge numbers of artificial stars. Hence, this will consume much computation time for data reduction of the images to which the artificial stars must be added. In this article, we present a new method applicable to data sets characterized by stable, well-defined, point-spread functions, in which we add artificial stars to the retrieved-data catalog instead of to the raw images. Taking the young Large Magellanic Cloud cluster NGC 1818 as an example, we compare results from both methods and show that they are equivalent, while our new method saves significant computational time.

Hu, Yi; Deng, Licai; de Grijs, Richard; Liu, Qiang

2011-01-01

419

Converting neutron stars into strange stars  

NASA Technical Reports Server (NTRS)

If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

Olinto, A. V.

1991-01-01

420

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

421

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

422

Probing the Birth of Super Star Clusters: Implications for Massive Star Formation  

E-print Network

Super Star Clusters are one of the most extreme star forming environments in the universe, and the most massive and dense of these may be proto globular clusters. Like individual massive stars, the earliest stages of super star cluster evolution are deeply obscured, and therefore our knowledge about their birth environments is currently very incomplete. However, the study of natal super star clusters has become somewhat of a cottage industry in recent years, and the sample of such objects has been growing rapidly with high-quality long-wavelength data now available from a number of observatories. The natal super star clusters identified in thermal-infrared and radio observations represent the youngest stage of massive star cluster evolution yet observed. Their properties appear to be similar to those of ultracompact HII regions in the Milky Way, but scaled up in total mass and luminosity. I will overview what we think we know about these objects based on existing observations, discuss their relationship to ultracompact HII regions, present new models of their spectral energy distributions based on 3-D simulations, and outline some of the most significant gaps in our current understanding.

Kelsey E. Johnson

2005-07-22

423

Luminous Infrared Galaxies with the Submillimeter Array. III. The Dense Kiloparsec Molecular Concentrations of Arp 299  

NASA Astrophysics Data System (ADS)

We have used high-resolution (~2farcs3) observations of the local (D L = 46 Mpc) luminous infrared galaxy Arp 299 to map out the physical properties of the molecular gas that provides the fuel for its extreme star formation activity. The 12CO J = 3-2, 12CO J = 2-1, and 13CO J = 2-1 lines were observed with the Submillimeter Array, and the short spacings of the 12CO J = 2-1 and J = 3-2 observations have been recovered using the James Clerk Maxwell Telescope single dish observations. We use the radiative transfer code RADEX to estimate the physical properties (density, column density, and temperature) of the different regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694 and NGC 3690, are consistent with a wide range of gas components, from warm moderately dense gas with T kin > 30 K and n(H2) ~ 0.3-3 × 103 cm-3 to cold dense gas with T kin ~ 10-30 K and n(H2) > 3 × 103 cm-3. The overlap region is shown to have a better constrained solution with T kin ~ 10-50 K and n(H2) ~ 1-30 × 103 cm-3. We estimate the gas masses and star formation rates of each region in order to derive molecular gas depletion times. The depletion times of all regions (20-50 Myr) are found to be about two orders of magnitude lower than those of normal spiral galaxies. This rapid depletion time can probably be explained by a high fraction of dense gas on kiloparsec scales in Arp 299. We estimate the CO-to-H2 factor, ?co to be 0.4 ± 0.3(3 × 10-4/x CO) M? (K km s-1 pc2)-1 for the overlap region. This value agrees well with values determined previously for more advanced merger systems.

Sliwa, Kazimierz; Wilson, Christine D.; Petitpas, Glen R.; Armus, Lee; Juvela, Mika; Matsushita, Satoki; Peck, Alison B.; Yun, Min S.

2012-07-01

424

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

425

Imine Oligomers and Polymers  

Microsoft Academic Search

In the last few years, polymers with highly conjugated chains have attracted much attention because of their wide variety of applications in the field of electronics, opto?electronics, and photonics. Polyimines (PIs) (polymeric Schiff bases) is a class of polymer family, which has been less reviewed. In this paper, we focus on the synthesis methods of PIs by polycondensation, using diamines

Mircea Grigoras; Carmen Otilia Catanescu

2004-01-01

426

EDITORIAL: Electroactive polymer materials  

Microsoft Academic Search

Imitating nature's mechanisms offers enormous potential for the improvement of our lives and the tools we use. This field of the study and imitation of, and inspiration from, nature's methods, designs and processes is known as biomimetics. Artificial muscles, i.e. electroactive polymers (EAPs), are one of the emerging technologies enabling biomimetics. Polymers that can be stimulated to change shape or

Yoseph Bar-Cohen; Kwang J. Kim; Hyouk Ryeol Choi; John D. W. Madden

2007-01-01

427

Electroactive polymer materials  

Microsoft Academic Search

Imitating nature's mechanisms offers enormous potential for the improvement of our lives and the tools we use. This field of the study and imitation of, and inspiration from, nature's methods, designs and processes is known as biomimetics. Artificial muscles, i.e. electroactive polymers (EAPs), are one of the emerging technologies enabling biomimetics. Polymers that can be stimulated to change shape or

Yoseph Bar-Cohen; Kwang J Kim; Hyouk Ryeol Choi; John D W Madden

2007-01-01

428

Laser Nanostructuring of Polymers  

NASA Astrophysics Data System (ADS)

We discuss laser nanostructuring of polymer surfaces by means of interference and colloidal particle lens array approaches. We focus on laser swelling as a mechanism of surface structuring. 3D laser nanopolymerization, laser induced formation of metal nanoclusters within a polymer matrix as well as laser bubbling are also considered.

Bityurin, Nikita M.

429

Fluorocarbon associative polymers  

Microsoft Academic Search

Fluorocarbon associative polymers modified along the backbone or at the extremities by hydrophobic groups are reviewed with respect to their association and rheological properties in aqueous solutions. Above a threshold concentration corresponding to the formation of a reversible network structure, the solutions behave as physical gels. In this review, it is shown that the viscoelasticity of fluorocarbon associative polymer gels

Jean-François Berret; Damien Calvet; André Collet; Michel Viguier

2003-01-01

430

Shape Memory Polymer Research  

Microsoft Academic Search

The past several years have witnessed significant advances in the field of shape memory polymers (SMPs) with the elucidation of new compositions for property tuning, the discovery of new mechanisms for shape fixing and recovery, and the initiation of phenomenological modeling. We critically review research findings on new shape memory polymers along these lines, emphasizing exciting progress in the areas

Patrick T. Mather; Xiaofan Luo; Ingrid A. Rousseau

2009-01-01

431

Shape memory polymer nanocomposites  

Microsoft Academic Search

The paper describes the fabrication and characterization of composites with a shape memory polymer matrix and SiC nanoparticulate reinforcements. Composites based on a SMP matrix are active materials capable of recovering relatively large mechanical strains due to the application of heat. The composites were synthesized from a commercial shape memory polymer resin system and particulate SiC with an average diameter

Ken Gall; Martin L. Dunn; Yiping Liu; Dudley Finch; Mark Lake; Naseem A. Munshi

2002-01-01

432

Polymers Are Everywhere.  

ERIC Educational Resources Information Center

Describes the history of the human understanding of polymers from alchemy to modern times. Discusses renaissance chemistry, polymers in the nineteenth century, synthetic elastomers, thermoplastic elastomers, fibers, coatings, adhesives, derivatives of natural rubber, thermosets, step-reaction, and chain polymerization. (CW)

Seymour, Raymond B.

1988-01-01

433

Polymers that Conduct Electricity.  

ERIC Educational Resources Information Center

Although polymers are regarded as electrical insulators, it was discovered that they can be made to conduct electricity. This discovery has opened vast new practical and theoretical areas for exploration by physicists and chemists. Research studies with these conducting polymers and charge-transfer salts as well as possible applications are…

Edelson, Edward

1983-01-01

434

METAL COMPLEXING SILOXANE POLYMERS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Novel silicone polymers containing pendant phosphonate groups have been synthesized. A new silicone monomer, (CH3O)2CH3Si(CH2)3P=O(OCH2CH3)2 has been copolymerized with dimethyldimethoxysilane to form polymers capable of binding metal salts. The viscous liquids can complex a variety of metals, inc...

435

Evolution of a Neutron Star From its Birth to Old Age  

E-print Network

The main stages in the evolution of a neutron star, from its birth as a proto-neutron star, to its old age as a cold, catalyzed configuration, are described. A proto-neutron star is formed in the aftermath of a successful supernova explosion and its evolution is dominated by neutrino diffusion. Its neutrino signal is a valuable diagnostic of its internal structure and composition. During its transformation from a hot, lepton-rich to a cold, catalyzed remnant, the possibility exists that it can collapse into a black hole, which abruptly terminates neutrino emissions. The essential microphysics, reviewed herein, that controls its evolution are the equation of state of dense matter and its associated neutrino opacities. Several simulations of the proto-neutron star evolution, involving different assumptions about the composition of dense matter, are described. After its evolution into a nearly isothermal neutron star a hundred or so years after its birth, it may be observable through its thermal emission in X-rays during its life in the next million years. Its surface temperature will depend upon the rapidity of neutrino emission processes in its core, which depends on the composition of dense matter and whether or not its constituents exhibit superfluidity and superconductivity. Observations of thermal emission offer the best hope of a determination of the radius of a neutron star. The implications for the underlying dense matter equation of state of an accurate radius determination are explored.

M. Prakash; J. M. Lattimer; J. A. Pons; A. W. Steiner; S. Reddy

2000-12-06

436

Gas Permeation in Thin Glassy Polymer Films  

NASA Astrophysics Data System (ADS)

The development of asymmetric and composite membranes with very thin dense "skins" needed to achieve high gas fluxes enabled the commercial use of membranes for molecular level separations. It has been generally assumed that these thin skins, with thicknesses of the order of 100 nm, have the same permeation characteristics as films with thicknesses of 25 microns or more. Thick films are easily made in the laboratory and have been used extensively for measuring permeation characteristics to evaluate the potential of new polymers for membrane applications. There is now evidence that this assumption can be in very significant error, and use of thick film data to select membrane materials or predict performance should be done with caution. This presentation will summarize our work on preparing films of glassy polymers as thin as 20 nm and characterizing their behavior by gas permeation, ellipsometry and positron annihilation lifetime spectroscopy. Some of the most important polymers used commercially as gas separation membranes, i.e., Matrimid^ polyimide, polysulfone (PSF) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), have been made into well-defined thin films in our laboratories by spin casting techniques and their properties studied using the techniques we have developed. These thin films densify (or physically age) much faster than thicker films, and, as result, the permeability decreases, sometimes by several-fold over weeks or months for thin films. This means that the properties of these thin films can be very different from bulk films. The techniques, interpretations and implications of these observations will be discussed. In a broader sense, gas permeation measurements can be a powerful way of developing a better understanding of the effects of polymer chain confinement and/or surface mobility on the behavior of thin films.

Paul, Donald

2011-03-01

437

STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS  

SciTech Connect

Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 {mu}m, H{alpha}, and UV down to rates of 0.03 M{sub Sun} yr{sup -1}. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 {mu}m and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies.

Tyler, K. D.; Rieke, G. H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Bai, L. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street Room 101, Toronto, Ontario M5S 3H4 (Canada)

2013-08-20

438

Porous polymer media  

DOEpatents

Highly crosslinked monolithic porous polymer materials for chromatographic applications. By using solvent compositions that provide not only for polymerization of acrylate monomers in such a fashion that a porous polymer network is formed prior to phase separation but also for exchanging the polymerization solvent for a running buffer using electroosmotic flow, the need for high pressure purging is eliminated. The polymer materials have been shown to be an effective capillary electrochromatographic separations medium at lower field strengths than conventional polymer media. Further, because of their highly crosslinked nature these polymer materials are structurally stable in a wide range of organic and aqueous solvents and over a pH range of 2-12.

Shepodd, Timothy J. (Livermore, CA)

2002-01-01

439

Modeling semiflexible polymer networks  

E-print Network

Here, we provide an overview of theoretical approaches to semiflexible polymers and their networks. Such semiflexible polymers have large bending rigidities that can compete with the entropic tendency of a chain to crumple up into a random coil. Many studies on semiflexible polymers and their assemblies have been motivated by their importance in biology. Indeed, crosslinked networks of semiflexible polymers form a major structural component of tissue and living cells. Reconstituted networks of such biopolymers have emerged as a new class of biological soft matter systems with remarkable material properties, which have spurred many of the theoretical developments discussed here. Starting from the mechanics and dynamics of individual semiflexible polymers, we review the physics of semiflexible bundles, entangled solutions and disordered cross-linked networks. Finally, we discuss recent developments on marginally stable fibrous networks, which exhibit critical behavior similar to other marginal systems such as jammed soft matter.

Chase P. Broedersz; Fred. C. MacKintosh

2014-04-16

440

Rapid Polymer Sequencer  

NASA Technical Reports Server (NTRS)

Method and system for rapid and accurate determination of each of a sequence of unknown polymer components, such as nucleic acid components. A self-assembling monolayer of a selected substance is optionally provided on an interior surface of a pipette tip, and the interior surface is immersed in a selected liquid. A selected electrical field is impressed in a longitudinal or transverse direction at the tip, a polymer sequence is passed through the tip, and a change in an electrical current signal is measured as each polymer component passes through the tip. Each measured change in electrical current signals is compared with a database of reference signals, with each reference signal identified with a polymer component, to identify the unknown polymer component. The tip preferably has a pore inner diameter of no more than about 40 nm and is prepared by heating and pulling a very small section of a glass tubing.

Stolc, Viktor (Inventor); Brock, Mathew W. (Inventor)

2011-01-01

441

Addressing Unsolved Mysteries of Polymer Viscoelasticity  

NASA Astrophysics Data System (ADS)

By using coarse-grained bead-spring and entanglement tube models, much progress has been made over the past 50 years in understanding and modeling the dynamics and rheology of polymers, both in dilute solution state and in entangled solutions and melts. However, several major issues have remained unresolved, and these are now being addressed using microscopic simulations resolved at the level of the monomer. In the dilute solution state, the dynamics can be described by a coarse-grained bead-spring model, with each spring representing around 100 backbone bonds, even at frequencies high enough that one expects to see modes of relaxation associated with local motions of smaller numbers of bonds. The apparent absence of these local modes has remained a mystery, but microscopic simulations now indicate that these modes are slowed down by torsional barriers to the extent that they are coincident with much longer ranged spring-like modes. Other mysteries of dilute solution rheology include extension-thinning behavior observed at very high extension rates, an apparent lack of complete stretching of polymers in fast extensional flows as measured by light scattering experiments, and the unusual molecular weight dependence of polymer scission in fast flows. In entangled solutions, it is still not entirely clear how, or even if, the rheology can be mapped onto that of a "dynamically equivalent" melt, and, if so, what the scaling laws are for choosing the appropriate renormalized monomer size and renormalized time and modulus scales. It is also not yet clear to what extent "dynamic dilution" can be used to simplify and organize constraint release effects in the relaxation of monodisperse and polydisperse linear and long-chain branched polymers. For multiply-branched polymers, the motion of the branch point is critical in determining the rate of relaxation of the molecule, and theories for this motion have not been adequately tested. As with dilute solutions, simulations resolved at the level of the monomer are now helping to settle these issues. For example, molecular dynamics simulations of branched polymers show that ideas of hierarchical relaxation, introduced by McLeish and coworkers, appear to be valid. Similar simulations indicate that the effective "tube diameter" increases gradually starting at times as short as the "equilibration time" at which the polymer first "feels" the presence of the tube, and that this slow increase in effective tube diameter can help explain some anomalies in the relaxation of asymmetric star branched polymers.

Larson, Ronald G.

2008-02-01

442

Vortices and Other Topological Solitons in Dense Quark Matter  

E-print Network

In this review, we discuss various properties of topological solitons in dense QCD matter, with a particular emphasis on the CFL phase exhibiting superfluidity and superconductivity, and their phenomenological implications in terms of the effective field theories such as the Ginzburg-Landau theory, the chiral Lagrangian, or the Bogoliubov--de Gennes equation. The most fundamental topological excitations are non-Abelian vortices, which are 1/3 quantized superfluid vortices and color magnetic flux tubes. They are created at a phase transition or a rotation such compact stars. The intervortex-interaction is repulsive and consequently a vortex lattice is formed. Bosonic and fermionic zero-energy modes are trapped in the vortex core and propagate along it as gapless excitations. The former consists of translational zero modes (a Kelvin mode) with a quadratic dispersion and CP(2) Nambu-Goldstone gapless modes with a linear dispersion, while the latter is the triplet Majorana fermion zero modes. The low-energy effective theory of the bosonic zero modes is a non-relativistic free complex scalar field and a CP(2) model in 1+1 dimensions. The effects of strange quark mass, electromagnetic interactions and non-perturbative quantum corrections are taken into account. Colorful boojums at the CFL interface, quantum color magnetic monopole confined by vortices, which supports the notion of quark-hadron duality, and Yang-Mills instantons inside a vortex as lumps are discussed. The interactions between a vortex and quasi-particles such as phonons, gluons, mesons, and photons are studied. A vortex lattice is shown to behave as a cosmic polarizer. Non-Abelian vortices are shown to behave as a novel kind of non-Abelian anyons. For the chiral symmetry breaking, we discuss fractional and integer axial domain walls, Abelian and non-Abelian axial vortices, axial wall-vortex composites, and Skyrmions.

Minoru Eto; Yuji Hirono; Muneto Nitta; Shigehiro Yasui

2014-02-02

443

In vitro mineralization of dense collagen substrates: a biomimetic approach toward the development of bone-graft materials.  

PubMed

Bone is an organic-inorganic composite which has hierarchical structuring that leads to high strength and toughness. The nanostructure of bone consists of nanocrystals of hydroxyapatite embedded and aligned within the interstices of collagen fibrils. This unique nanostructure leads to exceptional properties, both mechanical and biological, making it difficult to emulate bone properties without having a bone-like nanostructured material. A primary goal of our group's work is to use biomimetic processing techniques that lead to bone-like structures. In our prior studies, we demonstrated that intrafibrillar mineralization of porous collagen sponges, leading to a bone-like nanostructure, can be achieved using a polymer-induced liquid precursor (PILP) mineralization process. The objective of this study was to investigate the use of this polymer-directed crystallization process to mineralize dense collagen substrates. To examine collagen scaffolds that truly represent the dense-packed matrix of bone, manatee bone was demineralized to isolate its collagen matrix, consisting of a dense, lamellar osteonal microstructure. This biogenic collagen scaffold was then remineralized using polyaspartate to direct the mineralization process through an amorphous precursor pathway. The various conditions investigated included polymer molecular weight, substrate dimension and mineralization time. Mineral penetration depths of up to 100 ?ms were achieved using this PILP process, compared to no penetration with only surface precipitates observed for the conventional crystallization process. Electron microscopy, wide-angle X-ray diffraction and thermal analysis were used to characterize the resulting hydroxyapatite/collagen composites. These studies demonstrate that the original interpenetrating bone nanostructure and osteonal microstructure could be recovered in a biogenic matrix using the PILP process. PMID:21550424

Thula, Taili T; Rodriguez, Douglas E; Lee, Myong Hwa; Pendi, Laura; Podschun, Jacob; Gower, Laurie B

2011-08-01

444

Dense Cores in Galaxies Out to z = 2.5 in SDSS, UltraVISTA, and the Five 3D-HST/CANDELS Fields  

NASA Astrophysics Data System (ADS)

The dense interiors of massive galaxies are among the most intriguing environments in the universe. In this paper,we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass >3 × 1010 M ? inside r = 1 kpc out to z = 2.5, using the 3D-HST survey and data at low redshift. Remarkably, the number density of galaxies with dense cores appears to have decreased from z = 2.5 to the present. This decrease is probably mostly due to stellar mass loss and the resulting adiabatic expansion, with some contribution from merging. We infer that dense cores were mostly formed at z > 2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3 from z = 2.5 to z = 0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z = 2.5 to ~15% at z = 0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the universe is a strong function of redshift. The stars in cores with M 1 kpc > 3 × 1010 M ? make up ~0.1% of the stellar mass density of the universe today but 10%-20% at z ~ 2, depending on their initial mass function. The formation of these cores required the conversion of ~1011 M ? of gas into stars within ~1 kpc, while preventing significant star formation at larger radii.

van Dokkum, Pieter G.; Bezanson, Rachel; van der Wel, Arjen; Nelson, Erica June; Momcheva, Ivelina; Skelton, Rosalind E.; Whitaker, Katherine E.; Brammer, Gabriel; Conroy, Charlie; Förster Schreiber, Natascha M.; Fumagalli, Mattia; Kriek, Mariska; Labbé, Ivo; Leja, Joel; Marchesini, Danilo; Muzzin, Adam; Oesch, Pascal; Wuyts, Stijn

2014-08-01

445

Proton-conducting polymer electrolyte membranes based on hydrocarbon polymers  

Microsoft Academic Search

This paper presents an overview of the synthesis, chemical and electrochemical properties, and polymer electrolyte fuel cell applications of new proton-conducting polymer electrolyte membranes based on hydrocarbon polymers. Due to their chemical stability, high degree of proton conductivity, and remarkable mechanical properties, perfluorinated polymer electrolytes such as Nafion®, Aciplex®, Flemion®, and Dow membranes are some of the most promising electrolyte

M Rikukawa; K Sanui

2000-01-01

446

Dense annular flows of granular media  

NASA Astrophysics Data System (ADS)

Dense granular flows constitute an important topic for geophysics and process engineering. To describe them, a rheology based on the coaxiality between the stress and strain tensors with a Mohr-Coulomb yield criterion has been proposed. We propose here an analytic study of flows in an annular cell, with this rheology. This geometry is relevant for a series of powder rheometers or mixing devices, but the discussion is focused on the split-bottom geometry, for which the internal flow has been investigated by NMR technique. In this case, the full resolution of the velocity and stress fields allow to localize the shear deformations. The theoretical results obtained for the latter are compared with the torque measurements by Dijksman et al. [Phys. Rev. E, 82 (2010) 060301].

de Ryck, Alain; Louisnard, Olivier

2013-06-01

447

Nonlinear extraordinary wave in dense plasma  

NASA Astrophysics Data System (ADS)

Conditions for the propagation of a slow extraordinary wave in dense magnetized plasma are found. A solution to the set of relativistic hydrodynamic equations and Maxwell's equations under the plasma resonance conditions, when the phase velocity of the nonlinear wave is equal to the speed of light, is obtained. The deviation of the wave frequency from the resonance frequency is accompanied by nonlinear longitudinal-transverse oscillations. It is shown that, in this case, the solution to the set of self-consistent equations obtained by averaging the initial equations over the period of high-frequency oscillations has the form of an envelope soliton. The possibility of excitation of a nonlinear wave in plasma by an external electromagnetic pulse is confirmed by numerical simulations.

Krasovitskiy, V. B.; Turikov, V. A.

2013-10-01

448

Dense flows of cohesive granular materials  

NASA Astrophysics Data System (ADS)

Using molecular dynamic simulations, we investigate the characteristics of dense flows of model cohesive grains. We describe their rheological behaviour and its origin at the scale of the grains and of their organization. Homogeneous plane shear flows give access to the constitutive law of cohesive grains which can be expressed by a simple friction law similar to the case of cohesionless grains, but intergranular cohesive forces strongly enhance the resistance to the shear. Then we show the consequence on flows down a slope: a plugged region develops at the free surface where the cohesion intensity is the strongest. Moreover, we measure various indicators of the microstructure within flows which evidence the aggregation of grains owing to cohesion and we analyse the properties of the contact network (force distributions and anisotropy). This provides new insights into the interplay between the local contact law, the microstructure and the macroscopic behavior of cohesive grains. Movies are available with the online version of the paper.

Rognon, Pierre G.; Roux, Jean-No?L.; Naa?M, Mohamed; Chevoir, Fran?Ois

449