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1

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

DOEpatents

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

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

1995-01-01

2

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

DOEpatents

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

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

1995-02-28

3

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

E-print Network

Structural Arrest in Dense Star-Polymer Solutions G. Foffi,1 F. Sciortino,1 P. Tartaglia,1 E of disordered arrested states in star-polymer solutions. DOI: 10.1103/PhysRevLett.90.238301 PACS numbers: 83. Especially at high functionalities, the solutions display a gelation transition, i.e., a dynamical arrest

Sciortino, Francesco

4

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

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

5

Solvable Critical Dense Polymers  

E-print Network

A lattice model of critical dense polymers is solved exactly for finite strips. The model is the first member of the principal series of the recently introduced logarithmic minimal models. The key to the solution is a functional equation in the form of an inversion identity satisfied by the commuting double-row transfer matrices. This is established directly in the planar Temperley-Lieb algebra and holds independently of the space of link states on which the transfer matrices act. Different sectors are obtained by acting on link states with s-1 defects where s=1,2,3,... is an extended Kac label. The bulk and boundary free energies and finite-size corrections are obtained from the Euler-Maclaurin formula. The eigenvalues of the transfer matrix are classified by the physical combinatorics of the patterns of zeros in the complex spectral-parameter plane. This yields a selection rule for the physically relevant solutions to the inversion identity and explicit finitized characters for the associated quasi-rational representations. In particular, in the scaling limit, we confirm the central charge c=-2 and conformal weights Delta_s=((2-s)^2-1)/8 for s=1,2,3,.... We also discuss a diagrammatic implementation of fusion and show with examples how indecomposable representations arise. We examine the structure of these representations and present a conjecture for the general fusion rules within our framework.

Paul A. Pearce; Jorgen Rasmussen

2007-02-06

6

Cooling of dense stars  

NASA Technical Reports Server (NTRS)

Cooling rates were calculated for neutron stars of about one solar mass and 10 km radius, with magnetic fields from zero to about 10 to the 14th power gauss, for extreme cases of maximum and zero superfluidity. The results show that most pulsars are so cold that thermal ionization of surface atoms would be negligible. Nucleon superfluidity and crystallization of heavy nuclei were treated quantitatively, and more realistic hadron star models were chosen. Cooling rates were calculated for a stable hyperon star near the maximum mass limit, a medium weight neutron star, and a light neutron star with neutron-rich heavy nuclei near the minimum mass limit. Results show that cooling rates are a sensitive function of density. The Crab and Vela pulsars are considered, as well as cooling of a massive white dwarf star.

Tsuruta, S.

1972-01-01

7

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

8

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

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

Solvable Critical Dense Polymers on the Cylinder  

E-print Network

A lattice model of critical dense polymers is solved exactly on a cylinder with finite circumference. The model is the first member LM(1,2) of the Yang-Baxter integrable series of logarithmic minimal models. The cylinder topology allows for non-contractible loops with fugacity alpha that wind around the cylinder or for an arbitrary number ell of defects that propagate along the full length of the cylinder. Using an enlarged periodic Temperley-Lieb algebra, we set up commuting transfer matrices acting on states whose links are considered distinct with respect to connectivity around the front or back of the cylinder. These transfer matrices satisfy a functional equation in the form of an inversion identity. For even N, this involves a non-diagonalizable braid operator J and an involution R=-(J^3-12J)/16=(-1)^{F} with eigenvalues R=(-1)^{ell/2}. The number of defects ell separates the theory into sectors. For the case of loop fugacity alpha=2, the inversion identity is solved exactly for the eigenvalues in finite geometry. The eigenvalues are classified by the physical combinatorics of the patterns of zeros in the complex spectral-parameter plane yielding selection rules. The finite-size corrections are obtained from Euler-Maclaurin formulas. In the scaling limit, we obtain the conformal partition functions and confirm the central charge c=-2 and conformal weights Delta_t=(t^2-1)/8. Here t=ell/2 and t=2r-s in the ell even sectors with Kac labels r=1,2,3,...; s=1,2 while t is half-integer in the ell odd sectors. Strikingly, the ell/2 odd sectors exhibit a W-extended symmetry but the ell/2 even sectors do not. Moreover, the naive trace summing over all ell even sectors does not yield a modular invariant.

Paul A. Pearce; Jorgen Rasmussen; Simon P. Villani

2010-02-26

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

Photoluminescence of Conjugated Star Polymers  

NASA Astrophysics Data System (ADS)

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

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

2000-10-01

14

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

15

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

16

Dense brushes of stiff polymers or filaments in fluid flow  

NASA Astrophysics Data System (ADS)

Dense filamentous brush-like structures are present in many biological interfacial systems (e.g., glycocalyx layer in blood vessels) to control their surface properties. Such structures can regulate the softness of a surface and modify fluid flow. In this letter, we propose a theoretical model which predicts quantitatively flow-induced deformation of a dense brush of stiff polymers or filaments, whose persistence length is larger or comparable to their contour length. The model is validated by detailed mesoscopic simulations and characterizes different contributions to brush deformation including hydrodynamic friction due to flow and steric excluded-volume interactions between grafted filaments. This theoretical model can be used to describe the effect of a stiff-polymer brush on fluid flow and to aid in the quantification of experiments.

Römer, F.; Fedosov, D. A.

2015-03-01

17

The Baxter Q Operator of Critical Dense Polymers  

E-print Network

We consider critical dense polymers ${\\cal L}_{1,2}$, corresponding to a logarithmic conformal field theory with central charge $c=-2$. An elegant decomposition of the Baxter $Q$ operator is obtained in terms of a finite number of lattice integrals of motion. All local, non local and dual non local involutive charges are introduced directly on the lattice and their continuum limit is found to agree with the expressions predicted by conformal field theory. A highly non trivial operator $\\Psi(\

Alessandro Nigro

2009-09-07

18

On the Relativistic Collapse of Dense Star Clusters  

E-print Network

We investigate the fate of a relativistic star cluster with a dense core which is undergoing a gravothermal catastrophe and is far from thermodynamic equilibrium. Nonlinear cooperative contributions are included in the standard transport equations for the last stage of evolution of a highly dense core of stellar remnants. We find that the core redshift does not necessarily increase without limit as the core becomes increasingly dense, preventing collapse to a black hole. In particular, the redshift can remain less than the critical value for relativistic collapse, resulting in a stable, massive dark core with a Newtonian mantle and halo.

J. W. Moffat

1997-05-30

19

Relativistic modelling of stable anisotropic super-dense star  

E-print Network

In the present article we have obtained new set of exact solutions of Einstein field equations for anisotropic fluid spheres by using the Herrera et al.[1] algorithm. The anisotropic fluid spheres so obtained join continuously to Schwarzschild exterior solution across the pressure free boundary.It is observed that most of the new anisotropic solutions are well behaved and utilized to construct the super-dense star models such as neutron star and pulsars.

Maurya, S K; Jasim, M K

2015-01-01

20

Simulation of dense amorphous polymers by generating representative atomistic models  

NASA Astrophysics Data System (ADS)

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

Curcó, David; Alemán, Carlos

2003-08-01

21

Growth of a dense polymer brush layer from solution  

NASA Astrophysics Data System (ADS)

The chemical grafting of alkanethiol-terminated poly(ethylene glycol) to a gold substrate from dimethylformamide solution was monitored by in situ ellipsometry for several molar concentrations. In the initial stage a layer of mushroom-like moieties forms and, on a much longer time scale, is followed by conformational conversion (and further adsorption) to a dense brush of stretched polymers. A statistical mechanical theory is presented that allows for a nonuniform grafting density and conformational conversion. It accounts fully for all observed details.

Himmelhaus, M.; Bastuck, T.; Tokumitsu, S.; Grunze, M.; Livadaru, L.; Kreuzer, H. J.

2003-11-01

22

Method for forming a uniformly dense polymer foam body  

DOEpatents

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

23

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

24

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

25

Polymer absorption in dense polymer brushes vs. polymer adsorption on the brush-solvent interface  

NASA Astrophysics Data System (ADS)

Molecular-dynamics simulations of a coarse-grained model of a dense brush of flexible polymers (of type A) interacting with a long flexible macromolecule (of type B) are presented, considering the case of an attractive AB interaction, while effective interactions between AA and BB pairs of monomers are repulsive. Varying the strength \\varepsilon_{AB} of the attraction between unlike monomers, an adsorption transition at some critical value \\varepsilon^c_{AB} is found, where the B-chain is bound to the brush-solvent interface, similar to the adsorption on a planar solid substrate. However, when \\varepsilon_{AB} is much higher than \\varepsilon^c_{AB} , the long macromolecule is gradually “sucked in” the brush, developing many pieces that are locally stretched in the z-direction perpendicular to the substrate, in order to fit between the brush chains. The resulting hairpin-like structures of the absorbed chain shows up via oscillatory decay of the bond vector autocorrelation function. Chain relaxation is only possible via reptation.

Milchev, Andrey; Binder, Kurt

2014-06-01

26

A Proof of Selection Rules for Critical Dense Polymers  

E-print Network

Among the lattice loop models defined by Pearce, Rasmussen and Zuber (2006), the model corresponding to critical dense polymers ($\\beta = 0$) is the only one for which an inversion relation for the transfer matrix $D_N(u)$ was found by Pearce and Rasmussen (2007). From this result, they identified the set of possible eigenvalues for $D_N(u)$ and gave a conjecture for the degeneracies of its relevant eigenvalues in the link representation, in the sector with $d$ defects. In this paper, we set out to prove this conjecture, using the homomorphism of the $TL_N (\\beta)$ algebra between the loop model link representation and that of the XXZ model for $\\beta = -(q+q^{-1})$.

Alexi Morin-Duchesne

2011-09-29

27

Modular invariant partition function of critical dense polymers  

E-print Network

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 Omega and Omega^{-1}. In this enlarged algebra, the non-contractible loop fugacity is alpha and the contractible loop fugacity is beta. 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 Tr_d (with a fixed number of defects d) and Chebyshev polynomials of the first kind. For critical dense polymers, where beta=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 alpha=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.

Alexi Morin-Duchesne; Paul A. Pearce; Jorgen Rasmussen

2013-05-28

28

Star polymers rupture induced by constant forces.  

PubMed

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

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

2014-10-28

29

Polymer quantum effects on compact stars models  

NASA Astrophysics Data System (ADS)

In this work we study a completely degenerate Fermi gas at zero temperature by a semiclassical approximation for a Hamiltonian that arises in polymer quantum mechanics. Polymer quantum systems are quantum mechanical models quantized in a similar way as in loop quantum gravity, allowing 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 for this system by noticing that the corresponding Fermi energy is exactly the same as if one directly polymerizes the momentum pF. We also obtain the expansion of the corresponding thermodynamical variables in terms of small values of the polymer length scale ?. We apply these results to study a simple model of a compact one-dimensional star where the gravitational collapse is supported by electron degeneracy pressure. As a consequence, polymer corrections to the mass of the object are found. By using bounds for the polymer length found in Bose-Einstein condensates experiments we compute the modification in the mass of the compact object due to polymer effects of order 10-8. This result is similar to the other order found by different approaches such as generalized uncertainty principle (GUP), and that certainly is within the error reported in typical measurements of white dwarf masses.

Chacón-Acosta, Guillermo; Hernandez-Hernandez, Héctor H.

2015-03-01

30

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

31

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

32

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

33

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

34

Molecular dynamics of spherical nanoparticles in dense polymer melts.  

PubMed

By performing molecular dynamics simulations, we investigate the structural and dynamical properties of polymer melts containing probe spherical nanoparticles. Generally speaking, the behavior of these polymer nanocomposites is strongly affected by the interaction strength established between the nanoparticles and the chain monomers and by the nanoparticle sizes. We highlight that this dependence is not always evident and some intriguing properties, such as the heterogeneous dynamics of both polymer chains and nanoparticles and their nonGaussian behavior at short and long timescales, are not particularly influenced by the degree of attraction between nanoparticles and polymer for the range of interactions we study (up to 6 kBT). We find the existence of weakly ordered interdigitated structures with sequential arrangements of particles and polymer chains, which separate each other and hence inhibit the formation of nanoparticle clusters. This is especially evident with big nanoparticles, being less prone to aggregate than small ones, even when their interaction with the polymer chain is as low as 0.5 kBT. Moreover, by integrating the stress-tensor autocorrelation functions, we estimate the shear viscosity and determine its dependence on the strength of the polymer-nanoparticle interactions and on the nanoparticle size. By acting as plasticizers, small nanoparticles decrease the viscosity, especially at low-to-moderate interactions with the polymer. By contrast, big nanoparticles that establish strongly attractive interactions with the polymer chains behave as thickening agents and significantly increase the viscosity. This complex and perhaps still scantily understood balance between the geometry of nanoparticles and their interaction with the polymer is key to predict and fully control the macroscopic response of nanocomposite materials and hence suitably tailor their mechanical properties. PMID:24620825

Patti, Alessandro

2014-04-01

35

Coarse grain forces in star polymer melts.  

PubMed

An analysis is presented of forces acting on the centers of mass of three-armed star polymers in the molten state. The arms consist of 35 Kremer-Grest beads, which is slightly larger than needed for one entanglement mass. For a given configuration of the centers of mass, instantaneous forces fluctuate wildly around averages which are two orders of magnitude smaller than their root mean square deviations. Average forces are well described by an implicit many-body potential, while pair models fail completely. The fluctuating forces are modelled by means of dynamical variables quantifying the degree of mixing of the various polymer pairs. All functions and parameters in a coarse grain model based on these concepts are obtained from the underlying small scale simulation. The coarse model reproduces both the diffusion coefficient and the shear relaxation modulus. Ways to improve the model suggest themselves on the basis of our findings. PMID:25158294

Liu, L; den Otter, W K; Briels, W J

2014-10-21

36

Motions and Initial Conditions in Star-Forming Dense Cores  

NASA Technical Reports Server (NTRS)

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

Myers, Philip C.

2001-01-01

37

Monte Carlo Simulation of Dense Polymer Melts Using Event Chain Algorithms  

E-print Network

We propose an efficient Monte Carlo scheme for the simulation of dense hard sphere polymer melts using cluster moves, called event chains, which allow for a rejection-free treatment of the excluded volume. Our implementation of this algorithm produces the correct ideal behavior of polymer chains in the dense melt in equilibrium. Moreover, the event chain Monte Carlo algorithm captures the inter- and intrapolymer diffusion, i.e., essential features of the polymer dynamics in melts correctly. Event chains also allow for an efficient preparation of initial configurations in the dense limit. We parallelize the event chain Monte Carlo algorithm and suggest additional local topology-changing moves ("swap" moves) to further increase simulation speeds in melts. We show that these event chain Monte Carlo algorithms achieve simulation speeds comparable to optimized molecular dynamics simulations.

Tobias Alexander Kampmann; Horst-Holger Boltz; Jan Kierfeld

2015-02-23

38

Exact multileg correlation functions for the dense phase of branching polymers in two E. V. Ivashkevich1,2  

E-print Network

Exact multileg correlation functions for the dense phase of branching polymers in two dimensions E boundary conditions and exactly calculate correlation functions of k polymer chains that connect two polymers spanning trees 5,6 ; de Gennes 7 explained how the par- tition function of dilute polymers can

39

Compatibility of Medical-Grade Polymers with Dense CO2  

PubMed Central

This study reports the effect of exposure to liquid carbon dioxide on the mechanical properties of selected medical polymers. The tensile strengths and moduli of fourteen polymers are reported. Materials were exposed to liquid CO2, or CO2 + trace amounts of aqueous H2O2, at 6.5 MPa and ambient temperature. Carbon dioxide uptake, swelling, and distortion were observed for the more amorphous polymers while polymers with higher crystallinity showed little effect from CO2 exposure. Changes in tensile strength were not statistically significant for most plastics, and most indicated good tolerance to liquid CO2. These results are relevant to evaluating the potential of liquid CO2-based sterilization technology. PMID:19756235

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

2009-01-01

40

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

41

Compatibilization of polymer blends with star polymers containing a gamma-cyclodextrin core and polystyrene arms  

NASA Astrophysics Data System (ADS)

Cyclodextrins (CDs) are cyclic starch molecules having a hollow central cavity which can be threaded by a polymer to form an inclusion compound. This characteristic is exploited in a new type of compatibilizer: a star polymer with a gamma-CD (g-CD) core and polystyrene (PS) arms (CD-star). The mechanism of compatibilization involves threading of the CD core by a second polymer and solubilization of the threading polymer into a PS matrix by the PS star arms. In principle, the same CD-star polymer can be used to compatibilize blends of several different polymers with PS, provided that the second polymer is able to thread the CD core. We have taken the first step toward demonstrating the generality of this approach by producing compatibilized blends of PS with poly(dimethyl siloxane) (PDMS) or poly(methyl methacrylate) (PMMA) using the same CD-star polymer. Thin spun-cast films of these blends exhibit a nanoscale level of mixing, while spun-cast films of the same blends without CD-star exhibit large-scale phase separation. The number of CD-star molecules that must be threaded onto the polymer chain to achieve compatibilization is larger for PMMA than for PDMS.

Balik, C. M.; Tonelli, A. E.; Libert, Ryan

2012-02-01

42

Coarse graining of star-polymer colloid nanocomposites Daniela Marzi, Christos N. Likos, and Barbara Capone  

E-print Network

Coarse graining of star-polymer ­ colloid nanocomposites Daniela Marzi, Christos N. Likos OF CHEMICAL PHYSICS 137, 014902 (2012) Coarse graining of star-polymer ­ colloid nanocomposites Daniela Marzi mixtures of self-avoiding multiarm star polymers with hard colloids that are smaller than the star polymer

Likos, Christos N.

43

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

44

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

45

Hydrodynamic screening of star polymers in shear flow.  

PubMed

The mutual effects of the conformations of a star polymer in simple shear flow and the deformation of the solvent flow field are investigated by a hybrid mesoscale simulation technique. We characterize the flow field near the star polymer as a function of its functionality (arm number) f . A strong screening of the imposed flow is found inside the star polymer, which increases with increasing f . To elucidate the importance of hydrodynamic screening, we compare results for hydrodynamic and random solvents. The dependence of the polymer orientation angle on the Weissenberg number shows a power law behavior with super-universal exponent --independent of hydrodynamic and excluded-volume interactions. In contrast, the polymer rotation frequency changes qualitatively when hydrodynamic interactions are switched on. PMID:17712520

Ripoll, M; Winkler, R G; Gompper, G

2007-08-01

46

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

E-print Network

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

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

2007-10-09

47

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

48

Strange stars: how dense can their crust be?  

NASA Astrophysics Data System (ADS)

The strong electric field at the surface of a strange star is discussed, and a self-consistent model is proposed to calculate its capability of supporting a "normal" nuclear material crust. We find that the electric field is already not able to support the crust even when the bottom density of the crust is still considerably lower than the neutron drip point, which means that it is not the neutron drip effect that limits the maximum crust density of a strange star. The maximum crust density is probably only about 8.3x10^10^g/cm^3^, so that a typical strange star (1.4Msun_) can not have a crust more massive than ~3.4x10^-6^Msun_. Considerable limitations are also presented for strange dwarfs.

Huang, Y. F.; Lu, T.

1997-09-01

49

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

SciTech Connect

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

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

2011-12-20

50

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

51

Temperature-induced crystallization in concentrated suspensions of multiarm star polymers: a molecular dynamics study.  

PubMed

In this work, we study temperature-induced crystallization in dense suspensions of multiarm star polymers. This is a continuation of a previous study, which identified and studied the emergence of "glassy" amorphous states, in accordance with experimental observations. We performed molecular dynamics simulations on two types of star polymers: 128-arm stars and 64-arm stars dissolved in n-decane in the temperature range of 20-60 degrees C. These supramolecules are modeled as "soft spheres" interacting via a theoretically developed potential of mean field. Both systems attain a crystalline structure with the characteristics of a face-centered-cubic (fcc) crystal beyond a certain temperature. Kinetics is sensitive on initial configuration. Interestingly, kinetic trapping in "temporary" energy wells leads to highly crystalline structures, yet less ordered than their genuine equilibrium fcc structure. This complication illustrates the difficulty in reaching the equilibrium state, which is crystalline at high temperatures. A structural analysis of the final conformations is presented. The effect of size dispersity and star functionality of soft spheres on microstructure is also examined. Both factors influence crystallization and their effect is quantified by our study. PMID:16460210

Rissanou, Anastassia N; Yiannourakou, Marianna; Economou, Ioannis G; Bitsanis, Ioannis A

2006-01-28

52

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

53

Collision--induced absorption in dense atmospheres of cool stars  

SciTech Connect

In the atmosphere of the Sun the major interaction between the matter and the radiation is through light absorption by ions (predominantly the negative ion of hydrogen atoms), neutral atoms and a small amount of polar molecules. The majority of stars in the universe are, however, cooler and denser than our Sun, and for a large fraction of these, the above absorption processes are very weak. Here, collision-induced absorption (CIA) becomes the dominant opacity source. The radiation is absorbed during very short mutual passages ('collisions') of two non-polar molecules (and/or atoms), while their electric charge distributions are temporarily distorted which gives rise to a transient dipole moment. We present here a review of the present-day knowledge about the impact of collision-induced absorption processes on the structure and the spectrum of such stars.

Borysow, Aleksandra; Joergensen, Uffe Graae [Niels Bohr Institute, for Astronomy, Physics and Geophysics, University Observatory, Juliane Maries vej 30, DK-2100 Copenhagen (Denmark)

1999-04-01

54

Dynamical evolution of dense star clusters in galactic nuclei  

NASA Astrophysics Data System (ADS)

By means of direct numerical N-body modeling, we investigate the orbital evolution of an initially thin, central mass dominated stellar disk. We include the perturbative gravitational influence of an extended spherically symmetric star cluster and the mutual gravitational interaction of the stars within the disk. Our results show that the two-body relaxation of the disk leads to significant changes of its radial density profile. In particular, the disk naturally evolves, for a variety of initial configurations, a similar broken power-law surface density profile. Hence, it appears that the single power-law surface density profile ?R -2 suggested by various authors to describe the young stellar disk observed in the Sgr A* region does not match theoretical expectations.

Haas, Jaroslav; Šubr, Ladislav

2014-05-01

55

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

56

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

57

Fluctuation spectrum of membranes with anchored linear and star polymers  

NASA Astrophysics Data System (ADS)

The effect of linear homopolymers, diblock copolymers, and star polymers anchored to a membrane on the membrane’s fluctuation spectrum is investigated for low grafting densities. Due to the nonlocality of the polymer-membrane interaction, the effective bending rigidity ?eff(q) of the composite membrane is found to depend strongly on the wave vector q of the membrane undulations. Analytical calculations for ideal linear chains and simulations for ideal and self-avoiding linear chains as well as for star polymers are presented. The analytical calculations are based on the Green’s function approach of Bickel and Marques [Eur. Phys. J. E 9, 349 (2002)]; for the simulations the Monte Carlo method is used. The functional form of ?eff(q) differs for end-grafted chains and diblock copolymers. In general, the polymer effect is most pronounced for undulations on length scales larger than or comparable to the polymer size, and decreases rapidly for smaller undulation wavelengths. Anchored linear chains always increase ? ; anchored star polymers may increase as well as decrease ? , depending on whether they are anchored symmetrically or asymmetrically to the membrane.

Auth, Thorsten; Gompper, Gerhard

2005-09-01

58

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

59

INVESTIGATION OF THE STRUCTURE AND THERMODYNAMICS OF STAR-POLYMERS IN SEMI-  

E-print Network

INVESTIGATION OF THE STRUCTURE AND THERMODYNAMICS OF STAR-POLYMERS IN SEMI- DILUTE SOLUTION F : Clothed colloids ­ Star-polymers ­ Semi-dilute solutions ­ Effective pair- potential ­ Structure - Thermodynamics. Abstract : In this work, we consider a semi-dilute solution of identical star-polymers, made

Boyer, Edmond

60

Silver–Polymer Composite Stars: Synthesis and Applications  

PubMed Central

Colloidal “silver stars” were synthesized upon poly(lactic-co-glycolic) acid nanosphere templates via a facile two-step silver reduction method. Myriad dendrimer-like Ag star morphologies were synthesized by varying the amount of poly(vinyl alcohol) and trisodium citrate used during silver reduction. Scanning electron microscopy studies revealed that star-shaped silver–polymer composites possessing nanoscopic, fractal morphologies with diameters ranging from 500 nm to 7 ?m were produced. These composites have broad applications from antibacterial agents to catalysis; two such applications were tested here. Surface-enhanced Raman spectroscopy (SERS) studies showed multiple hot spots of SERS activity within a single star. Electrochemical catalysis experiments demonstrated the feasibility of using the silver stars instead of platinum for the oxygen reduction reaction in alkaline fuel cells. PMID:21660240

Homan, Kimberly A.; Chen, Jeffrey; Schiano, Adriane; Mohamed, Mona; Willets, Katherine A.; Murugesan, Sankaran; Stevenson, Keith J.

2011-01-01

61

Phase behavior of athermal colloid-star polymer mixtures  

NASA Astrophysics Data System (ADS)

We investigate the depletion-induced phase behavior of athermal colloid-star polymer mixtures on a fine lattice using grand canonical Monte Carlo simulations in the "protein limit," that is, where polymer dimensions exceed those of the colloid. We consider the influence of the star's functionality, f, the macroscopic size ratio, qr = 2Rg, s/?c, where Rg, s is the radius of gyration of the star and ?c is the colloid diameter, and the microscopic size ratio, d = ?m/?c, where ?m is the diameter of a Kuhn segment. Recent theoretical predictions concerning the qualitative interplay of qr and f in determining the phase stability of these mixtures [D. Marzi, C. N. Likos, and B. Capone, J. Chem. Phys. 137, 014902 (2012)], 10.1063/1.4730751 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)], 10.1051/jphys:01982004303053100. Using this formalism, we define a "low" functionality limit through scaling arguments, for which our model provides a mapping of the phase behavior of colloidal mixtures with star polymers (f > 2) to linear chains (f = 2). Furthermore, our simulations suggest that as qr increases, both the critical monomer and colloid densities tend to a constant, finite value for all f; thus, we do not find the prediction by Marzi and co-workers of an upper limit to immiscibility (infinite critical densities) in terms of qr to be accurate for the stars we have investigated.

Mahynski, Nathan A.; Panagiotopoulos, Athanassios Z.

2013-07-01

62

Comparing different coarse-grained potentials for star polymers  

NASA Astrophysics Data System (ADS)

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

Menichetti, Roberto; Pelissetto, Andrea

2013-03-01

63

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

64

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

65

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

E-print Network

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

Debasis Atta; D. N. Basu

2014-07-08

66

Probing dense matter in compact star cores with radio pulsar data  

E-print Network

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 prevent 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.

Mark G. Alford; Kai Schwenzer

2014-08-13

67

Force between unlike star-polymers versus the solvent quality  

NASA Astrophysics Data System (ADS)

We re-examine here the computation of the effective force between two star-polymers A and B of different chemical nature, which are immersed in a common solvent. This force originates from the excluded-volume interactions and chemical segregation. We assume that the solvent quality may be different for the two unlike star-polymers, that is the solvent can be 1) a good solvent for A and B, 2) a good solvent for A and a Theta -solvent for B, or 3) a Theta -solvent for the two polymers. The purpose is a quantitative study of the effect of the solvent quality on the effective force, which is a function of the center-to-center distance. Calculations are achieved using the renormalization theory applied to the Edwards continuous model. We first show that, when the mutual interactions are present, the effective force decays as the inverse of distance, but with a universal amplitude depending on the solvent quality. Second, we demonstrate the existence of three kinds of forces related to situations 1), 2) and 3) described above, and give the third-order ? -expansions (? =4-d, 4 is the critical dimension) of the corresponding amplitudes. These series can be resummed using the Borel-Leroy techniques to obtain the best three-dimensional values for the expected force amplitudes. Finally, this work must be regarded as a natural extension of a published one which dealt with the same problem, but where the solvent was assumed to be good for the two unlike star-polymers.

Benzouine, F.; Benhamou, M.; Himmi, M.

2004-04-01

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

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

70

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

SciTech Connect

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

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

2013-05-01

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

Screening Corrections to the Electron Capture Rates in Dense Stars by the Relativistically Degenerate Electron Liquid  

NASA Astrophysics Data System (ADS)

We calculate the screening corrections to the electron capture rates in dense stars by the relativistically degenerate electron liquid. In order to calculate the screening corrections we adopt the linear response theory, which is widely used in the field of solid-state physics and liquid-metal physics. In particular, we use the longitudinal dielectric function for the relativistically degenerate electron liquid derived by Jancovici. We calculate the screening potential at the position of the nucleus. By using this screening potential one can calculate the screening corrections to the electron capture rates. We present accurate analytic fitting formulae which summarize our numerical results. These fitting formulae will facilitate the application of the present results. The screening corrections to the electron capture rates are typically a few percent.

Itoh, Naoki; Tomizawa, Nami; Tamamura, Masaya; Wanajo, Shinya; Nozawa, Satoshi

2002-11-01

73

Screening Corrections to the Electron Capture Rates in Dense Stars by the Relativistically Degenerate Electron Liquid  

E-print Network

We calculate the screening corrections to the electron capture rates in dense stars by the relativistically degenerate electron liquid. In order to calculate the screening corrections we adopt the linear response theory which is widely used in the field of solid state physics and liquid metal physics. In particular, we use the longitudinal dielectric function for the relativistically degenerate electron liquid derived by Jancovici. We calculate the screening potential at the position of the nucleus. By using this screening potential one can calculate the screening corrections to the electron capture rates. We will present accurate analytic fitting formulae which summarize our numerical results. These fitting formulae will facilitate the application of the present results. The screening corrections to the electron capture rates are typically a few percent.

Itoh, N; Tamamura, M; Wanajo, S; Nozawa, S; Itoh, Naoki; Tomizawa, Nami; Tamamura, Masaya; Wanajo, Shinya; Nozawa, Satoshi

2002-01-01

74

Screening Corrections to the Electron Capture Rates in Dense Stars by the Relativistically Degenerate Electron Liquid  

E-print Network

We calculate the screening corrections to the electron capture rates in dense stars by the relativistically degenerate electron liquid. In order to calculate the screening corrections we adopt the linear response theory which is widely used in the field of solid state physics and liquid metal physics. In particular, we use the longitudinal dielectric function for the relativistically degenerate electron liquid derived by Jancovici. We calculate the screening potential at the position of the nucleus. By using this screening potential one can calculate the screening corrections to the electron capture rates. We will present accurate analytic fitting formulae which summarize our numerical results. These fitting formulae will facilitate the application of the present results. The screening corrections to the electron capture rates are typically a few percent.

Naoki Itoh; Nami Tomizawa; Masaya Tamamura; Shinya Wanajo; Satoshi Nozawa

2007-08-02

75

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

E-print Network

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

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

2006-11-03

76

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

77

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

78

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

79

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.

80

Aliphatic polyester polymer stars: synthesis, properties and applications in biomedicine and nanotechnology.  

PubMed

A critical review: the ring-opening polymerization of cyclic esters provides access to an array of biodegradable, bioassimilable and renewable polymeric materials. Building these aliphatic polyester polymers into larger macromolecular frameworks provides further control over polymer characteristics and opens up unique applications. Polymer stars, where multiple arms radiate from a single core molecule, have found particular utility in the areas of drug delivery and nanotechnology. A challenge in this field is in understanding the impact of altering synthetic variables on polymer properties. We review the synthesis and characterization of aliphatic polyester polymer stars, focusing on polymers originating from lactide, ?-caprolactone, glycolide, ?-butyrolactone and trimethylene carbonate monomers and their copolymers including coverage of polyester miktoarm star copolymers. These macromolecular materials are further categorized by core molecules, catalysts employed, self-assembly and degradation properties and the resulting fields of application (262 references). PMID:21082079

Cameron, Donald J A; Shaver, Michael P

2011-03-01

81

Control of Chemical, Thermal, and Gas Transport Properties in Dense Phosphazene Polymer Membranes.  

SciTech Connect

Polyphosphazenes are hybrid polymers having organic pendant groups attached to an inorganic backbone. Phosphazene polymers can be tailored to specific applications through the attachment of a variety of different pendant groups to the phosphazene backbone. Applications for which these polymers have proven useful include solid polymer electrolytes for batteries and fuel cells, as well as, membranes for gas and liquid separations. In past work, phosphazene polymers have been synthesized using mixtures of pendant groups with differing chemical affinities. Specific ratios of hydrophobic and hydrophilic pendant groups were placed on the phosphazene backbone with a goal of demonstrating control of solubility, and therefore chemical selectivity. In this work, a series of phosphazene homo-polymers were synthesized having varying amounts of hydrophobic and hydrophilic character on each individual pendant group. Polymers were synthesized having a hydrophilic portion next to the polymer backbone and the hydrophobic portion on the terminal end of the pendant group. The effects of these combined hydrophobic/hydrophilic pendant groups on polymer morphology and gas transport properties are presented. The following data will be addressed: thermal characterization, pure gas permeability on seven gases (Ar, H2, O2, N2, CO2, and CH4 ), and ideal selectivity for the gas pairs: O2/N2, H2/CO2, CO2/H2, CO2/CH4 and CO2/N2.

Christopher J. Orme; Frederick F. Stewart; Mark L. Stone; Mason K. Harrup; Thomas A. Luther; Eric S. Peterson

2005-10-01

82

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

83

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

PubMed Central

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

Nardai, Michael M.; Zifferer, Gerhard

2013-01-01

84

The effect of electron gas polarization on thermonuclear reaction rates in dense stars  

E-print Network

In dense stars the nuclear reaction rates are influenced by screening effects arising from both ions and electrons. In this paper we calculate the enhancement factors due to electron polarization in the high-density, degenerate and relativistic regime, for non-resonant nuclear reaction rates. In an earlier analysis, Sahrling had proposed the possibility that the polarized electrons would lower the reaction rate instead of enhancing it. This analysis was based on Monte Carlo simulations with only one choice of density, temperature and charge. Here we extend the analysis to a wider range of densities, temperatures and charges and calculate analytical expressions for the enhancement factors. We concentrate on carbon and oxygen ions and show that at very high-densities, high-order quantum effects will be important and act to reduce the zeroth order, classical value for the enhancement factor. We show that in any case, the total electron contribution remains weak, namely an enhancement in the reaction of about a factor 2, contrarily to what had been claimed by some authors in previous calculations. We examine the astrophysical implications of these results on the final stages of massive white dwarfs, near the carbon-ignition curve.

Mikael Sahrling; Gilles Chabrier

1998-01-29

85

"Brush-First" Method for the Parallel Synthesis of Photocleavable, Nitroxide-Labeled Poly(ethylene glycol) Star Polymers  

E-print Network

(ethylene glycol) Star Polymers Jenny Liu,,# Alan O. Burts,,# Yongjun Li, Aleksandr V. Zhukhovitskiy, M. Francesca-pot synthesis of core-photocleavable, poly(norbornene)-co-poly(ethylene gly- col) (PEG) brush-arm star polymers (BASPs) via a route that combines the "graft-through" and "arm-first" methodologies for brush polymer

Turro, Nicholas J.

86

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

87

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

88

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.

89

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

90

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

PubMed

Using a coarse-grained bead-spring model for semi-flexible macromolecules which form a polymer brush, the structure and dynamics of the polymers were investigated, varying the chain stiffness and the grafting density. The anchoring conditions for the grafted chains were chosen such that their first bonds were oriented along the normal to the substrate plane. The compression of such a semi-flexible brush by a planar piston was observed to be a two-stage process: for a small compression the chains were shown to contract by "buckling" deformation whereas for a larger compression the chains exhibited a collective (almost uniform) bending deformation. Thus, the stiff polymer brush underwent a 2nd order phase transition of collective bond reorientation. The pressure, required to keep the stiff brush at a given degree of compression, was thereby significantly smaller than for an otherwise identical brush made of entirely flexible polymer chains! While both the brush height and the chain linear dimensions in the z-direction perpendicular to the substrate increased monotonically with an increase in the chain stiffness, the lateral (xy) chain linear dimensions exhibited a maximum at an intermediate chain stiffness. Increasing the grafting density led to a strong decrease of these lateral dimensions which is compatible with an exponential decay. Also the recovery kinetics after removal of the compressing piston were studied, and were 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 was suggested. PMID:24700280

Milchev, Andrey; Binder, Kurt

2014-06-01

91

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

NASA Astrophysics Data System (ADS)

Star polymers, as an important class of nonlinear macromolecules, process special thermodynamic properties for the existence of a common connecting point. The thermodynamic transitions of a single star polymer are systematically studied with the bond fluctuation model using Wang-Landau sampling techniques. A new analysis method employing the shape factor is proposed to locate the coil-globule (CG) and liquid-crystal (LC) transitions, which shows a higher efficiency and accuracy than the canonical specific heat function. The LC transition temperature is found to obey the identical scaling law as the linear polymers. However, the CG transition temperature shifts towards the LC transition with the increasing of the arm number. The reason is that for the star polymer a lower temperature is needed for the attractive force to overcome the excluded volume effect of the polymer chain because of its high arm density. This work clearly proves the structural distinction of the linear and star polymers can only affect the CG transition while has no influence on the LC transition.

Wang, Zilu; He, Xuehao

2011-09-01

92

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

93

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

94

White polymer light-emitting diodes based on star-shaped polymers with an orange dendritic phosphorescent core.  

PubMed

A series of new star-shaped polymers with a triphenylamine-based iridium(III) dendritic complex as the orange-emitting core and poly(9,9-dihexylfluorene) (PFH) chains as the blue-emitting arms is developed towards white polymer light-emitting diodes (WPLEDs). By fine-tuning the content of the orange phosphor, partial energy transfer and charge trapping from the blue backbone to the orange core is realized to achieve white light emission. Single-layer WPLEDs with the configuration of ITO (indium-tin oxide)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer/CsF/Al exhibit a maximum current efficiency of 1.69 cd A(-1) and CIE coordinates of (0.35, 0.33), which is very close to the pure white-light point of (0.33, 0.33). To the best of our knowledge, this is the first report on star-shaped white-emitting single polymers that simultaneously consist of fluorescent and phosphorescent species. PMID:25363235

Zhu, Minrong; Li, Yanhu; Cao, Xiaosong; Jiang, Bei; Wu, Hongbin; Qin, Jingui; Cao, Yong; Yang, Chuluo

2014-12-01

95

How big are supermassive black holes formed from the collapse of dense star clusters?  

Microsoft Academic Search

If a star cluster becomes sufficiently relativistic in its center, it is unstable to catastrophic collapse to a black hole. In general, the final state consists of a central massive black hole surrounded by a halo of orbiting stars. The authors present a method for estimating how much mass goes into the black hole and how much is left in

Christopher S. Kochanek; Stuart L. Shapiro; Saul A. Teukolsky

1987-01-01

96

Pair correlation function in a dense plasma and pycnonuclear reactions in stars  

Microsoft Academic Search

The short-range behavior of the pair correlation function in a dense onecomponent plasma (jellium) is investigated. As an intermediate step, the short-range behavior of the classical pair correlation function is obtained. Actually, although the temperature and the density are assumed to be such that the thermodynamic properties are almost classical, quantum mechanics (tunnel effect) always dominates the pair correlation function

B. Jancovici

1977-01-01

97

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

98

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

99

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

E-print Network

-functionalized capping agent (i.e., CNBP) with structural similarity to low molar mass liquid crystal, 4-cyano-40Star-like polymer click-functionalized with small capping molecules: an initial investigation(tert-butyl acrylate) (PtBA) capped with 4-isocyano-40 -(prop-2-yn-1- yloxy)biphenyl (CNBP), with a well-defined size

Lin, Zhiqun

100

Beyond the mean-potential approximation in the calculation of thermonuclear reaction rates in dense stars  

NASA Astrophysics Data System (ADS)

In dense matter the thermonuclear reaction rate is significantly affected by neighbouring ions to a reacting pair. The rigorous theory of Alastuey & Jancovici shows that, if small quantum-mechanical effects associated with the neighbouring ions are neglected, the correct way to estimate thermonuclear reaction rates in dense matter is first to calculate the rate for a fixed configuration of neighbours to the fusing pair, and then to thermally average over positions of the neighbours. The standard assumption made in most calculations of rates is that the processes of thermodynamic averaging and the evaluation of the tunneling amplitude may be reversed. This is equivalent to assuming that the fusing pair of ions move in the average potential produced by the other ions. We make quantitative estimates of the reaction rate for a simple, physically motivated, three-dimensional model, and show that under some circumstances the standard approximation can give reaction rates that are too high by a factor 2.

Sahrling, M.

1994-03-01

101

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

E-print Network

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

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

2008-11-10

102

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

103

Stars, dendrimers and hyperbranched polymers: Towards understanding structure-property relationships for single molecule constructs  

SciTech Connect

New families of tetrahedral core molecules for synthesizing star and hyperbranched polymers are based on new adamantane derivatives. Four-arm structures have been obtained that are capable of chain extension and thermal conversion to highly crosslinked materials. Hyperbranched and star polymers containing siloxysilane repeat units have also been made through polyaddition hydrosilation reactions with star nodes and A-B monomers or A-B{sub 3} monomers. Terminal functionalization has been demonstrated for a variety of reactive and interactive groups that offer possibilities for use in artificial blood and interfacial microreactors. Combination of rigid tetrahedral cores with start or hyperbranched arms should make available new families of materials for composite synthesis, fiber interphase, formation and impact modification.

Mathias, L.J.; Reichert, V.R.; Carothers, T.W.; Bozen, R.M. [Univ. of Southern Mississippi, Hattiesburg, MS (United States)

1993-12-31

104

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

105

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

106

Rapid cooling of the neutron star in Cassiopeia A triggered by neutron superfluidity in dense matter.  

PubMed

We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the (3)P(2) channel. We find that the critical temperature for this superfluid transition is ?0.5×10(9) K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star. PMID:21405561

Page, Dany; Prakash, Madappa; Lattimer, James M; Steiner, Andrew W

2011-02-25

107

Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter  

E-print Network

We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the 3P2 channel. We find that the critical temperature for this superfluid transition is ~0.5x10^9 K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star.

Dany Page; Madappa Prakash; James M. Lattimer; Andrew W. Steiner

2011-01-19

108

Hyaluronic acid conjugated ?-cyclodextrin-oligoethylenimine star polymer for CD44-targeted gene delivery.  

PubMed

A new CD44-targeted gene delivery system, the star-shaped cationic polymer containing a ?-cyclodextrin (?-CD) core and multiple branched oligoethylenimine (OEI) arms with conjugated oligomer of hyaluronic acid (HA), was synthesized by reductive amination between ?-CD-OEI star polymer and HA, and was characterized for pDNA condensation and nanoparticle formation, followed by evaluation for targeted gene delivery of luciferase reporter gene and wild type p53 gene in CD44-positive and CD44-negative cell lines. The ?-CD-OEI-HA polymer contained 6 arms of OEI (600Da) and a short HA segment. It could fully condense pDNA to form nanoparticles with sizes ranging from 100 to 200nm at N/P ratios of 8 or higher. The conjugation of HA reduced cytotoxicity of ?-CD-OEI-HA/pDNA polyplexes. It was found that CD44 receptor was highly expressed and localized at the membrane of MDA-MB-231 breast cancer cell line, while no CD44 was found at the membrane of MCF-7 epithelial cell line. Compared with PEI (25kDa) and ?-CD-OEI star polymers, ?-CD-OEI-HA demonstrated significant increased gene transfection efficiency in MDA-MB-231 cells, while such effect was absent in MCF-7 cells. The targeted delivery of wild type p53 gene by ?-CD-OEI-HA in MDA-MB-231 cells resulted in an increased cell cycle arrest at sub-G1 phase. PMID:25681725

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

2015-04-10

109

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

110

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

111

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

NASA Astrophysics Data System (ADS)

Multiple loop formation in polymer macromolecules is an important feature of the chromatin organization and DNA compactification in the nuclei. We analyse the size and shape characteristics of complex polymer structures, containing in general f1 loops (petals) and f2 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 Rg and asphericity \\hat{A} of typical conformation as functions of parameters f1, f2. 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.

Blavatska, V.; Metzler, R.

2015-04-01

112

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

113

Selective-broadcast optical passive star comer design for dense WDM networks  

Microsoft Academic Search

A technique is described for design and implementation of an integrated selective-broadcast passive optical star couplers that uses a space-varying refractive index slab. The coupler offers the potential for inexpensive implementation of various routing schemes. It is possible to incorporate a network traffic routing matrix in the design fabric of this bandwidth-selective coupler. The matrix may resemble any desired physical

Mohsen Kavehrad; Mahmoud Tabiani

1991-01-01

114

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

115

FORMATION OF MASSIVE BLACK HOLES IN DENSE STAR CLUSTERS. II. INITIAL MASS FUNCTION AND PRIMORDIAL MASS SEGREGATION  

SciTech Connect

A promising mechanism to form intermediate-mass black holes is the runaway merger in dense star clusters, where main-sequence stars collide and form a very massive star (VMS), which then collapses to a black hole (BH). In this paper, we study the effects of primordial mass segregation and the importance of the stellar initial mass function (IMF) on the runaway growth of VMSs using a dynamical Monte Carlo code for N-body systems with N as high as 10{sup 6} stars. Our code now includes an explicit treatment of all stellar collisions. We place special emphasis on the possibility of top-heavy IMFs, as observed in some very young massive clusters. We find that both primordial mass segregation and the shape of the IMF affect the rate of core collapse of star clusters and thus the time of the runaway. When we include primordial mass segregation, we generally see a decrease in core-collapse time (t{sub cc}). Although for smaller degrees of primordial mass segregation this decrease in t{sub cc} is mostly due to the change in the density profile of the cluster, for highly mass-segregated (primordial) clusters, it is the increase in the average mass in the core which reduces the central relaxation time decreasing t{sub cc}. The final mass of the VMS formed is always close to {approx}10{sup -3} of the total cluster mass, in agreement with previous studies and is reminiscent of the observed correlation between the central BH mass and the bulge mass of the galaxies. As the degree of primordial mass segregation is increased, the mass of the VMS increases at most by a factor of three. Flatter IMFs generally increase the average mass in the whole cluster, which increases t{sub cc}. For the range of IMFs investigated in this paper, this increase in t{sub cc} is to some degree balanced by stellar collisions, which accelerate core collapse. Thus, there is no significant change in t{sub cc} for the somewhat flatter global IMFs observed in very young massive clusters.

Goswami, Sanghamitra; Umbreit, Stefan; Rasio, Frederic A. [Department of Physics and Astronomy, Dearborn Observatory, Northwestern University, Evanston, IL 60208 (United States); Bierbaum, Matt [Department of Physics, Clark Hall, Cornell University, Ithaca, NY 14853 (United States)

2012-06-10

116

Amphiphilic networks based on cross-linked star polymers: a small-angle neutron scattering study.  

PubMed

Four different polymer model networks of identical molecular architecture based on cross-linked stars (CLSs) were investigated by small-angle neutron scattering (SANS). One of the model networks was a hydrophilic homopolymer CLS of 2-(dimethylamino)ethyl methacrylate (DMAEMA), and the other three were amphiphilic copolymer CLS co-networks of DMAEMA and hydrophobic methyl methacrylate (MMA): one based on a star with random copolymer arms and the other two based on heteroarm star copolymers. For the homopolymer and random copolymer star networks, the scattering curves show shoulders at low values of the scattering vector, indicating very small compacted domains with radii of 1.0-1.3 nm, with the random copolymer star co-network having somewhat larger domains. For the heteroarm star co-networks, pronounced peak maxima are observed because of a much higher degree of microphase structuring than for the other two co-networks. The scattering patterns are described by the presence of well-defined hydrophobic domains with radii of 7.1 and 10.3 nm in the two heteroarm star co-networks, respectively, thereby proving pronounced microphase separation in these systems. PMID:17824716

Vamvakaki, Maria; Patrickios, Costas S; Lindner, Peter; Gradzielski, Michael

2007-10-01

117

Synthesis and characterization of four-armed star mesogen-jacketed liquid crystal polymer  

Microsoft Academic Search

The synthesis of four-armed star mesogen-jacketed liquid crystal polymer was achieved by atom transfer radical polymerization in chlorobenzene solution using pentaerythritol terakis(2-bromoisobutyrate) (PT-Br) as an initiator and CuBr\\/sparteine complex as a catalyst. The results show that the number average molecular weigh is creased linearly vs. monomer conversion, and that the polydispersities were quite narrow (<1.19), which is the character of

Xingzhu Wang; Hailiang Zhang; Guanqun Zhong; Xiayu Wang

2004-01-01

118

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

E-print Network

with EDAC activation and HOBt·H 2 O as the catalyst. A cooled solution (0 °C) of the sugar-acid-star polymer 3 (60% acid) (75 mg) in 20 ml dry DMF, EDAC (28.1 mg, 0.147 mmol) and HOBt·H 2 O (22.5 mg, 0.147 mmol) were combined. After five minutes, 4 (65 mg...

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

2012-04-22

119

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

120

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

NASA Astrophysics Data System (ADS)

We present observations of N2H+ (J = 1 ? 0), HCO+ (J = 1 ? 0), and HCN (J = 1 ? 0) toward the Serpens Main molecular cloud from the CARMA Large Area Star Formation Survey (CLASSy). We mapped 150 arcmin2 of Serpens Main with an angular resolution of ~7''. The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. The majority of gas in the two subclusters has subsonic to sonic velocity dispersions. We applied a dendrogram technique with N2H+(1-0) to study the gas structures; the SE subcluster has a higher degree of hierarchy than the NW subcluster. Combining the dendrogram and line fitting analyses reveals two distinct relations: a flat relation between nonthermal velocity dispersion and size, and a positive correlation between variation in velocity centroids and size. The two relations imply a characteristic depth of 0.15 pc for the cloud. Furthermore, we have identified six filaments in the SE subcluster. These filaments have lengths of ~0.2 pc and widths of ~0.03 pc, which is smaller than a characteristic width of 0.1 pc suggested by Herschel observations. The filaments can be classified into two types based on their properties. The first type, located in the northeast of the SE subcluster, has larger velocity gradients, smaller masses, and nearly critical mass-per-unit-length ratios. The other type, located in the southwest of the SE subcluster, has the opposite properties. Several YSOs are formed along two filaments which have supercritical mass per unit length ratios, while filaments with nearly critical mass-per-unit-length ratios are not associated with YSOs, suggesting that stars are formed on gravitationally unstable filaments.

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

2014-12-01

121

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

122

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

123

Equilibrium properties of highly asymmetric star-polymer mixtures Christian Mayer, Christos N. Likos, and Hartmut Lwen  

E-print Network

Equilibrium properties of highly asymmetric star-polymer mixtures Christian Mayer, Christos N effective interaction potentials to study the equilibrium structure and phase behavior of highly asymmetric with a small number of arms and a small size on a concentrated solution of large stars with a high

Likos, Christos N.

124

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

125

Faint disks around classical T Tauri stars: Small but dense enough to form planets  

NASA Astrophysics Data System (ADS)

Context. Most Class II sources (of nearby star-forming regions) are surrounded by disks with weak millimeter continuum emission. These "faint" disks may hold clues to the disk dissipation mechanism. However, the physical properties of protoplanetary disks have been directly constrained by imaging only the brightest sources. Aims: We attempt to determine the characteristics of such faint disks around classical T Tauri stars and to explore the link between disk faintness and the proposed disk dispersal mechanisms (accretion, viscous spreading, photo-evaporation, planetary system formation). Methods: We performed high angular resolution (0.3'') imaging of a small sample of disks (9 sources) with low 1.3 mm continuum flux (mostly <30 mJy) with the IRAM Plateau de Bure interferometer and simultaneously searched for 13CO (or CO) J = 2-1 line emission. Using a simple parametric disk model, we determined characteristic sizes for the disks in dust and gas, and we constrained surface densities in the central 50 AU. Results: All disks are much smaller than the bright disks imaged so far, both in continuum and 13CO lines (5 detections). In continuum, half of the disks are very small, with characteristic radii less than 10 AU, but still have high surface density values. Small sizes appear to be the main cause of the low disk luminosity. Direct evidence for grain growth is found for the three disks that are sufficiently resolved. Low continuum opacity is attested in only two systems, but we cannot firmly distinguish between a low gas surface density and a lower dust emissivity resulting from grain growth. Finally, we report a tentative discovery of a ~20 AU radius cavity in DS Tau, which with the (unresolved) "transition" disk of CX Tau, brings the proportion of "transitional" disks to a similar value to that of brighter sources. The existence of cavities cannot by itself explain their observed low mm flux. Conclusions: This study highlights a category of very compact dust disks that still exhibit high surface densities, which may represent up to 25% of the whole disk population. While its origin is unclear with the current data alone, it may be related to the compact planetary systems found by the Kepler mission. Based on observations carried out with the IRAM Plateau de Bure interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Appendices A and B are available in electronic form at http://www.aanda.org

Piétu, V.; Guilloteau, S.; Di Folco, E.; Dutrey, A.; Boehler, Y.

2014-04-01

126

Analysis of Star-Branched Polymers with Triple Detection (Refractive Index, Viscometry, Light Scattering) Gel Permeation Chromatography  

Microsoft Academic Search

This paper deals with the characterization of star-branched model copolymers. The polymer branches are composed of PMMA\\/PtBuA di-block copolymers of poly(methyl methacrylate) and poly(tert-butylacrylate) with well-controlled chemical composition and structure (very low polydispersity). When these copolymer branches are chemically coupled, they produce star-branched copolymers with various numbers of branches. Number-average molecular weights Mn of stars and branches were used to

James Lesec; Michele Millequant

1996-01-01

127

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

128

STAR-FORMING DENSE CLOUD CORES IN THE TeV GAMMA-RAY SNR RX J1713.7-3946  

SciTech Connect

RX J1713.7-3946 is one of the TeV {gamma}-ray supernova remnants (SNRs) emitting synchrotron X-rays. The SNR is associated with molecular gas located at {approx}1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C, and D, in the SNR in the {sup 12}CO(J = 2-1) and {sup 13}CO(J = 2-1) transitions at an angular resolution of 90''. The most intense core in {sup 13}CO, peak C, was also mapped in the {sup 12}CO(J = 4-3) transition at an angular resolution of 38''. Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source, and has a steep gradient with a r {sup -2.2{+-}0.4} variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X-rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X-rays are physically associated with the molecular gas. We present a scenario where the densest molecular core, peak C, survived the blast wave and is now embedded within the SNR. Numerical simulations of the shock-cloud interaction indicate that a dense clump can indeed survive shock erosion, since the shock propagation speed is stalled in the dense clump. Additionally, the shock-cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to enhanced synchrotron X-rays around dense cores.

Sano, H.; Sato, J.; Horachi, H.; Moribe, N.; Yamamoto, H.; Hayakawa, T.; Torii, K.; Kawamura, A.; Okuda, T.; Mizuno, N.; Onishi, T.; Inutsuka, S.; Matsumoto, H. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8602 (Japan); Maezawa, H.; Mizuno, A. [Solar-terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Inoue, T. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tanaka, T. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 382 Via Pueblo Mall, MC 4060, Stanford, CA 94305 (United States); Ogawa, H. [Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan); Stutzki, J. [KOSMA, I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Straesse 77, 50937 Koeln (Germany); Bertoldi, F., E-mail: sano@a.phys.nagoya-u.ac.j [Argelander-Institut fuer Astronomie, Auf dem Huegel 71, 53121 Bonn (Germany)

2010-11-20

129

Effective shielding of triplet energy transfer to conjugated polymer by its dense side chains from phosphor dopant for highly efficient electrophosphorescence.  

PubMed

To examine the quenching of a triplet exciton by low triplet energy (E(T)) polymer hosts with different chain configurations for high E(T) phosphor guests, the quenching rate constant measurements were carried out and analyzed by the standard Stern-Volmer equation. We found that an effective shielding of triplet energy transfer from a high E(T) phosphor guest to a low E(T) polymer host is possible upon introducing dense side chains to the polymer to block direct contact from the guest such that the possibility of Dexter energy transfer between them is reduced to a minimum. Together with energy level matching to allow charge trapping on the guest, high device efficiency can be achieved. The extent of shielding for the systems of phenylene-based conjugated structures from iridium complexes follows the sequence di-substituted (octoxyl chain) in the para position (dC8OPPP) is greater than monosubstituted (mC8OPPP) and the PPPs with longer side chains are much higher than a phenylene tetramer (P4) with two short methyl groups. Further, capping the dialkoxyl-susbstituents with a carbazole (Cz) moiety (CzPPP) provides enhanced extent of shielding. Excellent device efficiency of 30 cd/A (8.25%) for a green electrophosphorescent device can be achieved with CzPPP as a host, which is higher than that of dC8OPPP as host (15 cd/A). The efficiency is higher than those of high E(T) conjugated polymers, poly(3,6-carbazole) derivatives, as hosts (23 cd/A). This observation suggests a new route for molecular design of electroluminescent polymers as a host for a phosphorescent dopant. PMID:18336021

Huang, Szu-Po; Jen, Tzu-Hao; Chen, Yen-Chun; Hsiao, An-En; Yin, Shu-Hui; Chen, Hsiang-Yun; Chen, Show-An

2008-04-01

130

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

131

Probing the neutron star interior and the Equation of State of cold dense matter with the SKA  

E-print Network

With an average density higher than the nuclear density, neutron stars (NS) provide a unique test-ground for nuclear physics, quantum chromodynamics (QCD), and nuclear superfluidity. Determination of the fundamental interactions that govern matter under such extreme conditions is one of the major unsolved problems of modern physics, and -- since it is impossible to replicate these conditions on Earth -- a major scientific motivation for SKA. The most stringent observational constraints come from measurements of NS bulk properties: each model for the microscopic behaviour of matter predicts a specific density-pressure relation (its `Equation of state', EOS). This generates a unique mass-radius relation which predicts a characteristic radius for a large range of masses and a maximum mass above which NS collapse to black holes. It also uniquely predicts other bulk quantities, like maximum spin frequency and moment of inertia. The SKA, in Phase 1 and particularly in Phase 2 will, thanks to the exquisite timing precision enabled by its raw sensitivity, and surveys that dramatically increase the number of sources: 1) Provide many more precise NS mass measurements (high mass NS measurements are particularly important for ruling out EOS models); 2) Allow the measurement of the NS moment of inertia in highly relativistic binaries such as the Double Pulsar; 3) Greatly increase the number of fast-spinning NS, with the potential discovery of spin frequencies above those allowed by some EOS models; 4) Improve our knowledge of new classes of binary pulsars such as black widows and redbacks (which may be massive as a class) through sensitive broad-band radio observations; and 5) Improve our understanding of dense matter superfluidity and the state of matter in the interior through the study of rotational glitches, provided that an ad-hoc campaign is developed.

Anna Watts; Renxin Xu; Cristobal Espinoza; Nils Andersson; John Antoniadis; Danai Antonopoulou; Sarah Buchner; Shi Dai; Paul Demorest; Paulo Freire; Jason Hessels; Jerome Margueron; Micaela Oertel; Alessandro Patruno; Andrea Possenti; Scott Ransom; Ingrid Stairs; Ben Stappers

2014-12-30

132

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

133

Emerging synthetic strategies for core cross-linked star (CCS) polymers and applications as interfacial stabilizers: bridging linear polymers and nanoparticles.  

PubMed

Core cross-linked star (CCS) polymers become increasingly important in polymer science and are evaluated in many value-added applications. However, limitations exist to varied degrees for different synthetic methods. It is clear that improvement in synthetic efficiency is fundamental in driving this field moving even further. Here, the most recent advances are highlighted in synthetic strategies, including cross-linking with cross-linkers of low solubility, polymerization-induced self-assembly in aqueous-based heterogeneous media, and cross-linking via dynamic covalent bonds. The understanding of CCS polymers is also further refined to advocate their role as an intermediate between linear polymers and polymeric nanoparticles, and their use as interfacial stabilizers is rationalized within this context. PMID:24038784

Chen, Qijing; Cao, Xueteng; Xu, Yuanyuan; An, Zesheng

2013-10-01

134

Tailoring the efficacy of nimodipine drug delivery using nanocarriers based on A 2B miktoarm star polymers  

Microsoft Academic Search

We report a nanocarrier based on A2B type miktoarm polymers (A=polyethylene glycol (PEG); B=polycaprolactone (PCL)) for nimodipine (NIM), a hydrophobic drug with very poor aqueous solubility that is commonly prescribed for the prevention and treatment of delayed ischemic neurological disorders. The A2B star polymers were constructed on a core with orthogonal functionalities that facilitated the performance of “click” chemistry followed

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

2010-01-01

135

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

NASA Astrophysics Data System (ADS)

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

Yamada, Shinji

2012-11-01

136

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

137

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

138

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

139

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

140

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

141

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

142

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

143

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.

144

Dense or porous packing? Two-dimensional self-assembly of star-shaped mono-, bi-, and terpyridine derivatives.  

PubMed

The self-assembly behavior of five star-shaped pyridyl-functionalized 1,3,5-triethynylbenzenes was studied at the interface between an organic solvent and the basal plane of graphite by scanning tunneling microscopy. The mono- and bipyridine derivatives self-assemble in closely packed 2D crystals, whereas the derivative with the more bulky terpyridines crystallizes with porous packing. DFT calculations of a monopyridine derivative on graphene, support the proposed molecular model. The calculations also reveal the formation of hydrogen bonds between the nitrogen atoms and a hydrogen atom of the neighboring central unit, as a small nonzero tunneling current was calculated within this region. The title compounds provide a versatile model system to investigate the role of multivalent steric interactions and hydrogen bonding in molecular monolayers. PMID:25652664

Trawny, Daniel; Schlexer, Philomena; Steenbergen, Krista; Rabe, Jürgen P; Paulus, Beate; Reissig, Hans-Ulrich

2015-04-01

145

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

146

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

E-print Network

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

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

2012-09-24

147

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

148

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

E-print Network

I show that the temperature of nuclear star clusters, starburst clusters in M82, compact high-z galaxies, and some globular clusters of the Galaxy likely exceeded the ice line temperature (T_Ice ~ 150-170 K) during formation for a time comparable to the planet formation timescale. The protoplanetary disks within these systems will thus not have an ice line, decreasing the total material available for building protoplanetary embryos, inhibiting the formation of gas- and ice-giants if they form by core accretion, and prohibiting habitability. Planet formation by gravitational instability is similarly suppressed because Toomre's Q > 1 in all but the most massive disks. I discuss these results in the context of the observed lack of planets in 47 Tuc. I predict that a similar search for planets in the globular cluster NGC 6366 ([Fe/H] = -0.82) should yield detections, whereas (counterintuitively) the relatively metal-rich globular clusters NGC 6440, 6441, and 6388 should be devoid of giant planets. The characteris...

Thompson, Todd A

2012-01-01

149

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

150

Strong electroactive biodegradable shape memory polymer networks based on star-shaped polylactide and aniline trimer for bone tissue engineering.  

PubMed

Preparation of functional shape memory polymer (SMP) for tissue engineering remains a challenge. Here the synthesis of strong electroactive shape memory polymer (ESMP) networks based on star-shaped polylactide (PLA) and aniline trimer (AT) is reported. Six-armed PLAs with various chain lengths were chemically cross-linked to synthesize SMP. After addition of an electroactive AT segment into the SMP, ESMP was obtained. The polymers were characterized by (1)H NMR, GPC, FT-IR, CV, DSC, DMA, tensile test, and degradation test. The SMP and ESMP exhibited strong mechanical properties (modulus higher than GPa) and excellent shape memory performance: short recovery time (several seconds), high recovery ratio (over 94%), and high fixity ratio (almost 100%). Moreover, cyclic voltammetry test confirmed the electroactivity of the ESMP. The ESMP significantly enhanced the proliferation of C2C12 cells compared to SMP and linear PLA (control). In addition, the ESMP greatly improved the osteogenic differentiation of C2C12 myoblast cells compared to PH10 and PLA in terms of ALP enzyme activity, immunofluorescence staining, and relative gene expression by quantitative real-time polymerase chain reaction (qRT-PCR). These intelligent SMPs and electroactive SMP with strong mechanical properties, tunable degradability, good electroactivity, biocompatibility, and enhanced osteogenic differentiation of C2C12 cells show great potential for bone regeneration. PMID:25742188

Xie, Meihua; Wang, Ling; Ge, Juan; Guo, Baolin; Ma, Peter X

2015-04-01

151

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

152

Constitutive equations for the flow behavior of entangled polymeric systems: Application to star polymers  

NASA Astrophysics Data System (ADS)

A semimicroscopic derivation is presented of equations of motion for the density and the flow velocity of concentrated systems of entangled polymers. The essential ingredient is the transient force that results from perturbations of overlapping polymers due to flow. A Smoluchowski equation is derived that includes these transient forces. From this, an equation of motion for the polymer number density is obtained, in which body forces couple the evolution of the polymer density to the local velocity field. Using a semimicroscopic Ansatz for the dynamics of the number of entanglements between overlapping polymers, and for the perturbations of the pair-correlation function due to flow, body forces are calculated for nonuniform systems where the density as well as the shear rate varies with position. Explicit expressions are derived for the shear viscosity and normal forces, as well as for nonlocal contributions to the body force, such as the shear-curvature viscosity. A contribution to the equation of motion for the density is found that describes mass transport due to spatial variation of the shear rate. The two coupled equations of motion for the density and flow velocity predict flow instabilities that will be discussed in more detail in a forthcoming publication.

Briels, W. J.; Vlassopoulos, D.; Kang, Kyongok; Dhont, Jan K. G.

2011-03-01

153

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

154

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

PubMed

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

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

2014-12-21

155

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

PubMed

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

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

2014-10-20

156

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

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

157

Investigations of the structure and conformations of star-shaped polymers with fullerene branching centers: Polystyrenes with different structures and functionalities of the C60 centers in toluene  

NASA Astrophysics Data System (ADS)

The structure of regular star-shaped polystyrenes in deuterated toluene with single (C60) and double (C60-C60) branching centers and different numbers of arms ( f = 6, 12, 22) has been investigated using small-angle neutron scattering. For functionalities f = 6 and 12, the thermodynamic rigidity and sizes of arms are larger than the corresponding characteristics of the linear polystyrene precursor; however, for f = 22, the situation reverses: the flexibility increases, the arms are compressed, and the radius of gyration of the stars decreases. The stars transform into dense spherical aggregates, the behavior of which is inconsistent with the Benoit and Daoud-Cotton theories for structures with a high functionality and Gaussian arms. This is explained by the competition between the structuring effect of the fullerene branching center on the solvent and by the reverse effect of the arms playing the role of defects in an ordered layer of the solvent around the fullerene.

Lebedev, V. T.; Török, Gy.; Vinogradova, L. V.

2014-01-01

158

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

159

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

PubMed

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

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

2014-01-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

161

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

162

Controlled insulin release from glucose-sensitive self-assembled multilayer films based on 21-arm star polymer  

Microsoft Academic Search

A glucose-sensitive multilayer film was fabricated by the layer-by-layer (LbL) assembly method with positively charged 21-arm poly[2-(dimethylamino)ethyl methacrylate] (star PDMAEMA) and negatively charged insulin and glucose oxidase (GOD) in the form of {(Star PDMAEMA\\/Insulin)4 + (Star PDMAEMA\\/GOD)4 + Star PDMAEMA}. The multilayer film shows an on-off regulation of insulin release in response to stepwise glucose challenge in vitro. It is found that the unique

Xingyu Chen; Wei Wu; Zhizhang Guo; Jianyu Xin; Jianshu Li

2011-01-01

163

The Properties of Dense Molecular Gas in the Milky Way and Galaxies  

E-print Network

We review the evidence for a constant star formation rate per unit mass in dense molecular gas in the Milky Way and the extragalactic correlations of L_IR with L' from observations of dense molecular gas. We discuss the connection between the constant SFR/M interpretation in dense gas and the global Schmidt-Kennicutt star formation law.

Yancy L. Shirley; Jingwen Wu; R. Shane Bussmann; Al Wootten

2007-11-28

164

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

165

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

166

The Spitzer c2d Survey of Nearby Dense Cores: III: Low Mass Star Formation in a Small Group, L1251B  

E-print Network

We present a comprehensive study of a low-mass star-forming region,L1251B, at wavelengths from the near-infrared to the millimeter. L1251B, where only one protostar, IRAS 22376+7455, was known previously, is confirmed to be a small group of protostars based on observations with the Spitzer Space Telescope. The most luminous source of L1251B is located 5" north of the IRAS position. A near-infrared bipolar nebula, which is not associated with the brightest object and is located at the southeast corner of L1251B, has been detected in the IRAC bands. OVRO and SMA interferometric observations indicate that the brightest source and the bipolar nebula source in the IRAC bands are deeply embedded disk sources.Submillimeter continuum observations with single-dish telescopes and the SMA interferometric observations suggest two possible prestellar objects with very high column densities. Outside of the small group, many young stellar object candidates have been detected over a larger region of 12' x 12'. Extended emission to the east of L1251B has been detected at 850 micron; this "east core" may be a site for future star formation since no point source has been detected with IRAC or MIPS. This region is therefore a possible example of low-mass cluster formation, where a small group of pre- and protostellar objects (L1251B) is currently forming, alongside a large starless core (the east core).

Jeong-Eun Lee; James Di Francesco; Shih-Ping Lai; Tyler L. Bourke; Neal J. Evans II; Bill Spiesman; Philip C. Myers; Lori E. Allen; Timothy Y. Brooke; Alicia Porras; Zahed Wahhaj

2006-05-18

167

Uniformly dense polymeric foam body  

DOEpatents

A method for providing a uniformly dense polymer foam body having a density between about 0.013 g/cm.sup.3 to about 0.5 g/cm.sup.3 is disclosed. The method utilizes a thermally expandable polymer microsphere material wherein some of the microspheres 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

2003-07-15

168

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

169

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

SciTech Connect

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.

Hoffmann, I., E-mail: ingo.hoffmann@tu-berlin.de [Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin (Germany); Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9 (France); Malo de Molina, Paula; Gradzielski, M., E-mail: michael.gradzielski@tu-berlin.de [Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 124, Sekr. TC 7, D-10623 Berlin (Germany); Farago, B.; Falus, P. [Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9 (France)] [Institut Max von Laue-Paul Langevin (ILL), F-38042 Grenoble Cedex 9 (France); Herfurth, Christoph; Laschewsky, André [Fraunhofer Institut für Angewandte Polymerforschung IAP, Geiselbergstraße 69, 14476 Potsdam-Golm (Germany)] [Fraunhofer Institut für Angewandte Polymerforschung IAP, Geiselbergstraße 69, 14476 Potsdam-Golm (Germany)

2014-01-21

170

The viscoelastic properties of linear-star blends  

E-print Network

for 2'lo and 5 lo linear-star blends. . 14 4. Entanglement densities of star polymer. 16 CHAPTER I INTRODUCTION Due to the polydispersity and random branching structure of commercial polymers like LDPE, the rheology of branched polymer has been... polymer like star polymer, the branching point of nonlinear polymer makes a significant effect on the chain dynamics. For example, branched polymer like LDPE or HDPE can exhibit ether an enhancement or a reduction of the zero shear viscosity relative...

Lee, Jung Hun

2000-01-01

171

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

172

CoRoT 101186644: A transiting low-mass dense M-dwarf on an eccentric 20.7-day period orbit around a late F-star. Discovered in the CoRoT lightcurves  

NASA Astrophysics Data System (ADS)

We present the study of the CoRoT transiting planet candidate 101186644, also named LRc01_E1_4780. Analysis of the CoRoT lightcurve and the HARPS spectroscopic follow-up observations of this faint (mV = 16) candidate revealed an eclipsing binary composed of a late F-type primary (Teff = 6090 ± 200 K) and a low-mass, dense late M-dwarf secondary on an eccentric (e = 0.4) orbit with a period of ~20.7 days. The M-dwarf has a mass of 0.096 ± 0.011 M?, and a radius of 0.104-0.006+0.026 R?, which possibly makes it the smallest and densest late M-dwarf reported so far. Unlike the claim that theoretical models predict radii that are 5-15% smaller than measured for low-mass stars, this one seems to have a radius that is consistent and might even be below the radius predicted by theoretical models. Based on observations made with the 1-m telescope at the Wise Observatory, Israel, the Swiss 1.2-m Leonhard Euler telescope at La Silla Observatory, Chile, the IAC-80 telescope at the Observatory del Teide, Canarias, Spain, and the 3.6-m telescope at La Silla Observatory (ESO), Chile (program 184.C-0639).

Tal-Or, L.; Mazeh, T.; Alonso, R.; Bouchy, F.; Cabrera, J.; Deeg, H. J.; Deleuil, M.; Faigler, S.; Fridlund, M.; Hébrard, G.; Moutou, C.; Santerne, A.; Tingley, B.

2013-05-01

173

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

174

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

175

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 ...

176

Thermoresponsive micellization and micellar stability of poly(N-isopropylacrylamide)-b-DNA diblock and miktoarm star polymers.  

PubMed

Linear and miktoarm star-shaped diblock copolymers consisting of single-stranded DNA and poly(N-isopropylacrylamide) (PNIPAAm) with various compositions were synthesized via atom transfer radical polymerization and click chemistry. The temperature-responsive phase transition behavior, micellization, was systematically examined using UV-vis spectrometry, high-sensitivity differential scanning calorimetry, dynamic light scattering, and small-angle X-ray scattering. The lower critical solution temperature (LCST) increased, and its enthalpy decreased with decreasing PNIPAAm content. The copolymers self-assembled into well-defined nanoparticles having a core composed of PNIPAAm and a coronal layer of DNA above LCST. The particle size and micellar aggregation number of copolymer chains depended on the macromolecular composition and chain architecture. On the other hand, regardless of their factors, the surface area occupied by one DNA strand was found to be almost unchanged. The hybridization of DNA on the nanoparticles with fully complementary one induced the aggregation of the particles in a non-cross-linking configuration. The nanoparticle composed of miktoarm star copolymer showed a quicker DNA-hybridization response in this non-cross-linking aggregation compared with the case of a linear analogue. PMID:23013374

Pan, Pengju; Fujita, Masahiro; Ooi, Wei-Yang; Sudesh, Kumar; Takarada, Tohru; Goto, Atsushi; Maeda, Mizuo

2012-10-01

177

Atomic Transport/ Dense Metallic  

E-print Network

Matzakos, Andreas N. Medlin, Will Mettes, Jacques Morreale, Bryan O'Brien, Kevin Rubenstein, Leon intensification Membrane plus reactor #12;Barrier Categories-- Atomic Transport/Dense Metallic Systems Membrane

178

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

179

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

180

Warm Extended Dense Gas at the Heart of a Cold Collapsing Dense Core  

NASA Astrophysics Data System (ADS)

In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (~30-70 K), extended (radius of ~2400 AU), dense (a few times 105 cm-3) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, "warm-in-cold core stage (WICCS)," i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitute a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar outflow.

Shinnaga, Hiroko; Phillips, Thomas G.; Furuya, Ray S.; Kitamura, Yoshimi

2009-12-01

181

Primordial polymer perturbations  

E-print Network

We study the generation of primordial fluctuations in pure de Sitter inflation where the quantum scalar field dynamics are governed by polymer (not Schrodinger) quantization. This quantization scheme is related to, but distinct from, the structures employed in Loop Quantum Gravity; and it modifies standard results above a polymer energy scale $M_{\\star}$. We recover the scale invariant Harrison Zel'dovich spectrum for modes that have wavelengths bigger than $M_{\\star}^{-1}$ at the start of inflation. The primordial spectrum for modes with initial wavelengths smaller than $M_{\\star}^{-1}$ exhibits oscillations superimposed on the standard result. The amplitude of these oscillations is proportional to the ratio of the inflationary Hubble parameter $H$ to the polymer energy scale. For reasonable choices of $M_{\\star}$, we find that polymer effects are likely unobservable in CMB angular power spectra due to cosmic variance uncertainty, but future probes of baryon acoustic oscillations may be able to directly constrain the ratio $H/M_{\\star}$.

Sanjeev S. Seahra; Iain A. Brown; Golam Mortuza Hossain; Viqar Husain

2012-09-25

182

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; Sukhishvili, Svetlana A.

2004-05-25

183

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

184

Positivity and Dense Matter  

E-print Network

We elaborate on previous results concerning the positivity of the Euclidean path integral measure for low-energy modes in dense fermionic matter. We show that the sign problem usually associated with fermions is absent if one considers only low-energy degrees of freedom. We describe a method for simulating dense QCD on the lattice and give a proof using rigorous inequalities that the color-flavor locked (CFL) phase is the true vacuum of three flavor, massless QCD. We also discuss applications to electronic systems in condensed matter, such as generalized Hubbard models.

Deog Ki Hong; Stephen D. H. Hsu

2003-07-04

185

pH-induced inversion of water-in-oil emulsions to oil-in-water high internal phase emulsions (HIPEs) using core cross-linked star (CCS) polymer as interfacial stabilizer.  

PubMed

A pH-responsive core cross-linked star (CCS) polymer containing poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) arms was used as an interfacial stabilizer for emulsions containing toluene (80 v%) and water (20 v%). In the pH range of 12.1-9.3, ordinary water-in-oil emulsions were formed. Intermediate multiple emulsions of oil-in-water-in-oil and water-in-oil-in-water were formed at pH 8.6 and 7.5, respectively. Further lowering the pH resulted in the formation of gelled high internal phase emulsions of oil-in-water type in the pH range of 6.4-0.6. The emulsion behavior was correlated with interfacial tension, conductivity and configuration of the CCS polymer at different pH. PMID:24700484

Chen, Qijing; Deng, Xiaoyong; An, Zesheng

2014-06-01

186

Novel polymers and method of preparing same  

NASA Technical Reports Server (NTRS)

Polymers are prepared with terminal functional groups by reacting a compound selected from the group consisting of lithium p-lithiophenoxide and tetrabutylammonium p-lithiophenoxide as an initiator with material such as butadiene. The resulting functionally terminated new polymers are then capable of reacting with coupling agents to form star polymers.

Hirshfield, S. M. (inventor)

1973-01-01

187

Mechanics of large-strain deformation of particle-modified polymers  

E-print Network

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

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

2006-01-01

188

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

189

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

PubMed Central

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

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

2014-01-01

190

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.

191

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

192

From nuclear matter to Neutron Stars  

E-print Network

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

T. K. Jha

2009-02-02

193

Modelling Eclipsing Binaries with Dense Spot Coverage  

NASA Astrophysics Data System (ADS)

To synthesise images of stellar photospheres with high spot filling factors, we model an extrapolated solar size distribution of spots on an immaculate SV Cam. These models of starspot coverage show that the primary star is peppered with a large number of subresolution spots. Using these model starspot distributions we generate a photometric lightcurve, which is then used as input to an maximum-entropy eclipse mapping code, that is based on chi-squared minimisation. I solve for the system parameters to show the effect of dense spot coverage on the derived system parameters, and show that surface brightness distributions reconstructed from these lightcurves have distinctive spots on the primary star at its quadrature points. It is concluded that two-spot modelling or chi-squared minimisation techniques are more susceptible to spurious structures being generated by systematic errors, arising from incorrect assumptions about photospheric surface brightness, than simple Fourier analysis of the light-curves.

Jeffers, S. V.

2006-08-01

194

Massive binary stars and the kinematics of Young Massive Clusters   

E-print Network

Located in the Large Magellanic Cloud, R136 is a rare example of a nearby young and dense massive star cluster in which individual stars can be resolved. Often suggested as a globular cluster in formation, its study is ...

Henault-Brunet, Vincent; Brunet, Vincent

2013-11-28

195

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

196

The sun, our star  

Microsoft Academic Search

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

R. W. Noyes

1982-01-01

197

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

198

Exotica in rotating compact stars  

E-print Network

The determination of mass and radius of a single neutron star EXO 0748-676 has been reported recently. Also, the estimate of radius from the measurement of moment of inertia of pulsar A in double pulsar system PSR J0737-3039 would be possible in near future. Here we construct models of static and uniformly rotating neutron stars involving exotic matter and compare our theoretical calculations with the recent findings from observations to probe dense matter in neutron stars.

Debarati Chatterjee; Sarmistha Banik; Debades Bandyopadhyay

2005-06-25

199

Planetary Systems in Star Clusters  

E-print Network

In the solar neighborhood, where the typical relaxation timescale is larger than the cosmic age, at least 10\\% to 15\\% of Sun-like stars have planetary systems with Jupiter-mass planets. In contrast, dense star clusters, charactered by frequent close encounters, have been found to host very few planets. We carry out numerical simulations with different initial conditions to investigate the dynamical stability of planetary systems in star cluster environments.

Cai, Maxwell Xu; Kouwenhoven, M B N

2015-01-01

200

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

201

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

202

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

203

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

204

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.

205

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

206

Dense Probabilistic Encryption Josh Benaloh  

E-print Network

Dense Probabilistic Encryption Josh Benaloh Clarkson University Abstract This paper describes a method of dense probabilistic encryption. Previous probabilistic encryption methods require large numbers of random bits and produce large amounts of ciphertext for the encryption of each bit of plaintext

Bernstein, Phil

207

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

208

Fluid Mechanics in Disks Around Young Stars  

Microsoft Academic Search

This article reviews hydrodynamic and magnetohydrodynamic processes in disks around young stars, encompassing the epochs of molecular-cloud turbulence, dense core collapse, disk formation, disk evolution, and planetesimal formation.

Karim Shariff

2009-01-01

209

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

PubMed

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. PMID:25493770

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

2014-11-01

210

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

211

A COMPLETE Survey for Dense Clumps in Perseus  

NASA Astrophysics Data System (ADS)

As part of the COMPLETE Survey of Star Forming Regions we have recently completed new high-sensitivity 12CO and 13CO maps of Perseus, covering an area of almost 4 square degrees, and containing 150,000 individual spectra in each map. We have used the Clumpfind algorithm on the 13CO map to search for dense molecular condensations. We compare the results of using the 2d and 3d versions of the code, and show, as expected, that the 3d version is able to reveal clumps which are missed by the 2d version. Finally, we present a list of all the dense clumps in the known star-forming regions NGC1333 and IC348.

Borkin, M.; Ridge, N.; Schnee, S.; Goodman, A.; Pineda, J.

2004-12-01

212

Positivity and Fermionic Dense Matter  

E-print Network

Euclidean dense matter generically suffers from the fermion sign problem. However, we argue that the sign problem is absent if one considers only low-energy degrees of freedom. Specifically, the low energy effective theory of dense QCD has positive Euclidean path integral measure, which allows one to establish rigorous inequalities showing that the color-flavor locked (CFL) phase is the true vacuum of three flavor, massless QCD. We then describe a method for simulating dense QCD on the lattice. We also discuss applications to electronic systems in condensed matter, such as generalized Hubbard models.

Deog Ki Hong; Stephen D. H. Hsu

2003-09-16

213

Post-Newtonian Dynamics in Dense Stellar Systems  

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

214

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

215

Coordination polymers  

Microsoft Academic Search

1.The properties of the beryllium-containing internal-complex polymer derived from bis-p-acetoacetylphenyl ether were investigated.2.The polymer is stable to heat: appreciable decomposition sets in only after long heating above 280°. The rate and extent of the degradation of the polymer at high temperatures are higher in air than in nitrogen. The internal-complex polymer undergoes no substantial change in properties as a result

M. G. Vinogradov; S. V. Vinogradova; Yu. A. Davidovich; V. V. Korshak

1963-01-01

216

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

217

Equation of state for dense nucleon matter  

NASA Astrophysics Data System (ADS)

We report microscopic calculations of the equation of state for dense nuclear and neutron matter. The calculations are performed for five Hamiltonians: the Argonne v14 and Urbana v14 two-nucleon potentials, both alone and with the Urbana VII three-nucleon potential, and the density-dependent Urbana v14 plus three-nucleon interaction model of Lagaris, Friedman, and Pandharipande. The beta-stable equation of state and neutron star structure are also calculated for three of the models. The models with the three-nucleon potential bracket the density-dependent model and are significantly stiffer than those with an unmodified two-nucleon potential only. The Argonne v14 plus Urbana VII Hamiltonian produces a softening in the neutron matter equation of state localized around twice nuclear matter density which may indicate a neutral pion condensate.

Wiringa, R. B.; Fiks, V.; Fabrocini, A.

1988-08-01

218

Kaon condensation in dense stellar matter  

E-print Network

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\\lsim \\rho/\\rho_0\\lsim 4, in the range to allow the intriguing new phenomena predicted by Brown and Bethe to take place in compact star matter.

Lee, C H; Lee, Chang Hwan; Rho, Mannque

1995-01-01

219

Diffusion and Coulomb separation of ions in dense matter.  

PubMed

We analyze diffusion equations in strongly coupled Coulomb mixtures of ions in dense stellar matter. Strong coupling of ions in the presence of gravitational forces and electric fields (induced by plasma polarization in the presence of gravity) produces a specific diffusion current which can separate ions with the same A/Z (mass to charge number) ratios but different Z. This Coulomb separation of ions can be important for the evolution of white dwarfs and neutron stars. PMID:24182248

Beznogov, M V; Yakovlev, D G

2013-10-18

220

Placing stars within cosmological simulations  

E-print Network

I investigate the process of converting gas into stars within the framework of a standard cosmological model. By examining the set of objects grown in a combined N-body plus smoothed particle hydrodynamics simulation with those obtained in similar models where some of the cold, dense gas was replaced by collisionless ``star'' particles I show that it is possible to make this substitution without affecting the subsequent gas cooling rate. With even the most basic star forming criteria the masses of isolated objects are nearly identical to the mass of cold, dense gas found within the same objects in a non-star forming run. No evidence is found to support the contention that converting gas into stars might affect the amount of cold gas obtained in a simulation by retarding the cooling rate within those objects where stars have already formed. In practice, because cold gas can be reheated by shocks but stars remain as such whatever happens the masses of the largest objects found in the star forming runs are generally higher than those in the standard run. Finally, I demonstrate that an excellent match to the observed star formation rate can be achieved with even a very basic star formation prescription.

F. R. Pearce

1998-03-11

221

Introduction to neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

Lattimer, James M.

2015-02-01

222

Nonlinear nanostructures in dense quantum plasmas  

SciTech Connect

Dense quantum plasmas are ubiquitous in compact astrophysical objects (e.g. the interior of white dwarf stars, in magnetars, etc.), in semiconductors and micro-mechanical systems, as well as in the next generation intense laser-solid density plasma interaction experiments. In contrast to classical plasmas, one encounters extremely high plasma density and low temperature in dense quantum plasmas. In the latter, the electrons and positrons obey the Fermi-Dirac statistics, and there are new forces associated with i) quantum statistical electron and positron pressures, ii) electron and positron tunneling through the Bohm potential, and iii) electron and positron spin-1/2. Inclusion of these quantum forces gives rise to very high-frequency plasma waves (e.g. in the x-ray regime) at nanoscales. Our objective here is to present nonlinear equations that depict the localization of electron plasma waves in the form of a quantum electron hole and quantum vortex, as well as the trapping of intense electromagnetic waves into a quantum electron hole. Our simulation results reveal that these nonlinear nanostructures are quite robust. Hence, they can be explored for the purpose of transferring localized electrostatic and electromagnetic energies over nanoscales.

Shukla, P. K.; Eliasson, B. [Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2009-10-08

223

Simulations of Polymer Translocation  

NASA Astrophysics Data System (ADS)

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

Vocks, H.

2008-07-01

224

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

225

Shocks in Dense Clouds in the Vela Supernova Remnant: FUSE  

NASA Technical Reports Server (NTRS)

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

Nichols, Joy; Sonneborn, George (Technical Monitor)

2002-01-01

226

Patternable conjugated polymers for organic solar cells  

NASA Astrophysics Data System (ADS)

Photocrosslinking is known as a suitable method for patterning organic semiconductors in organic light emitting diodes. We extend this concept to the field of organic solar cells using conjugated polymers bearing sidechains with photocrosslinkable oxetane units. By UV irradiation in the presence of a photo acid generator the oxetane groups polymerize, leading to the formation of a densely crosslinked, and thus insoluble, network of a low-bandgap polymer. In this paper we present the synthesis of two novel photocrosslinkable low-bandgap polymers PFDTBTOx and PCDTBTOx and discuss several strategies for the fabrication of organic solar cells taking advantage of the novel crosslinkable materials.

Strohriegl, Peter; Knauer, Philipp; Saller, Christina; Scheler, Esther

2013-10-01

227

SMA and VLA Observations of Dense Cores at Different Evolutionary Phases in Filamentary IRDCs  

NASA Astrophysics Data System (ADS)

Infrared dark clouds (IRDCs) are recognized as nurseries of high-mass stars in the Galaxy given that they are massive, dense, and cold. High angular resolution millimeter/sub-millimeter observations are necessary to penetrate the dense gas and resolve the embedded cores in these clouds. With the SMA, we selected four dense molecular clumps probably at quite different evolutionary phases in the IRDC G28.53-0.25, and obtained their dust emission and molecular spectral lines. We identified six dense cores. Those at very early phases exhibit few spectral lines, while those that are more evolved exhibit complex organic molecular lines as well as signature of outflows. Both types of cores are massive enough (a few tens of solar mass) to form high-mass (>8 Msun) stars. VLA ammonia spectral lines were also obtained, to constrain optical depth, temperature, and gas kinematics. Furthermore, we selected four filamentary IRDCs from our VLA ammonia survey of high-mass star forming regions, and conducted a mini survey with the SMA in order to study the relation between filaments and high-mass star formation. We found star forming cores in the intersection of filaments, as well as cores embedded in filaments that show little star formation signatures.

Lu, Xing; Zhang, Qizhou

2014-07-01

228

Cooling of neutron stars  

NASA Technical Reports Server (NTRS)

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

Pethick, C. J.

1992-01-01

229

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

2008-12-26

230

Diffuse interstellar band formation in dense clouds  

NASA Technical Reports Server (NTRS)

Data are presented which show that the strengths of the diffuse interstellar bands at 4430, 5780, and 5797 A tend to be deficient with respect to color excess in the lines of sight to stars lying behind dense interstellar clouds. In addition, diffuse-band data for ten stars in the well-studied rho Ophiuchi cloud complex are presented, and systematic variations of band strengths with optical depth are discussed. It is found that the band strength per grain in the line of sight apparently decreases with increasing grain size, taking the ratio of total-to-selective absorption and the wavelength of maximum polarization as indicators of the latter. It is concluded that diffuse-band formation probably takes place most efficiently in the outer regions of interstellar clouds. This may be consistent with a diffuse-band origin in small grains which are coated by mantles in cloud interiors; or in some molecule or molecules which are most abundant in the outer portions of interstellar clouds.

Snow, T. P., Jr.; Cohen, J. G.

1974-01-01

231

Thermal Spray Formation of Polymer Coatings  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

232

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

233

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

234

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

235

Polymer Chemistry  

NASA Technical Reports Server (NTRS)

This viewgraph presentation describes new technologies in polymer and material chemistry that benefits NASA programs and missions. The topics include: 1) What are Polymers?; 2) History of Polymer Chemistry; 3) Composites/Materials Development at KSC; 4) Why Wiring; 5) Next Generation Wiring Materials; 6) Wire System Materials and Integration; 7) Self-Healing Wire Repair; 8) Smart Wiring Summary; 9) Fire and Polymers; 10) Aerogel Technology; 11) Aerogel Composites; 12) Aerogels for Oil Remediation; 13) KSC's Solution; 14) Chemochromic Hydrogen Sensors; 15) STS-130 and 131 Operations; 16) HyperPigment; 17) Antimicrobial Materials; 18) Conductive Inks Formulations for Multiple Applications; and 19) Testing and Processing Equipment.

Williams, Martha; Roberson, Luke; Caraccio, Anne

2010-01-01

236

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

237

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

238

Polymers Guide  

NSDL National Science Digital Library

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

239

Polymers & People  

ERIC Educational Resources Information Center

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

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

2004-01-01

240

Phi Meson in Dense Matter  

E-print Network

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

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

1992-01-01

241

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

242

Dynamics of Dense Cores in the Perseus Molecular Cloud  

E-print Network

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

Helen Kirk; Doug Johnstone; Mario Tafalla

2007-07-18

243

The early evolution of stars  

NASA Technical Reports Server (NTRS)

This review outlines the observational properties of young stellar objects as they evolve from their birth within dense rotating molecular cores to fully-formed pre-main sequence stars. Current work suggests that most of the mass which ultimately comprises a fully-formed star is transferred from a flattened infalling envelope (of size approximately several thousand AU) through a circumstellar accretion disk to the stellar surface. We summarize current estimates for the duration of the envelope infall and disk accretion phases and discuss the implication of these timescales for the formation of stars of different mass and of planetary systems.

Strom, Stephen E.

1995-01-01

244

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

2013-03-20

245

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

246

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

PubMed

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

Heyes, Colin D; Groll, Jürgen; Möller, Martin; Nienhaus, G Ulrich

2007-06-01

247

The Physics of Star Formation  

E-print Network

Our current understanding of the physical processes of star formation is reviewed, with emphasis on processes occurring in molecular clouds like those observed nearby. The dense cores of these clouds are predicted to undergo gravitational collapse characterized by the runaway growth of a central density peak that evolves toward a singularity. As long as collapse can occur, rotation and magnetic fields do not change this qualitative behavior. The result is that a very small embryonic star or protostar forms and grows by accretion at a rate that is initially high but declines with time as the surrounding envelope is depleted. Rotation causes some of the remaining matter to form a disk around the protostar, but accretion from protostellar disks is not well understood and may be variable. Most, and possibly all, stars form in binary or multiple systems in which gravitational interactions can play a role in redistributing angular momentum and driving episodes of disk accretion. Variable accretion may account for some peculiarities of young stars such as flareups and jet production, and protostellar interactions in forming systems of stars will also have important implications for planet formation. The most massive stars form in the densest environments by processes that are not yet well understood but may include violent interactions and mergers. The formation of the most massive stars may have similarities to the formation and growth of massive black holes in very dense environments.

Richard B. Larson

2003-08-17

248

The chemistry of dense interstellar clouds  

NASA Technical Reports Server (NTRS)

The basic theme of this program is the study of molecular complexity and evolution in interstellar and circumstellar clouds incorporating the biogenic elements. Recent results include the identification of a new astronomical carbon-chain molecule, C4Si. This species was detected in the envelope expelled from the evolved star IRC+10216 in observations at the Nobeyama Radio Observatory in Japan. C4Si is the carrier of six unidentified lines which had previously been observed. This detection reveals the existence of a new series of carbon-chain molecules, C sub n Si (n equals 1, 2, 4). Such molecules may well be formed from the reaction of Si(+) with acetylene and acetylene derivatives. Other recent research has concentrated on the chemical composition of the cold, dark interstellar clouds, the nearest dense molecular clouds to the solar system. Such regions have very low kinetic temperatures, on the order of 10 K, and are known to be formation sites for solar-type stars. We have recently identified for the first time in such regions the species of H2S, NO, HCOOH (formic acid). The H2S abundance appears to exceed that predicted by gas-phase models of ion-molecule chemistry, perhaps suggesting the importance of synthesis on grain surfaces. Additional observations in dark clouds have studied the ratio of ortho- to para-thioformaldehyde. Since this ratio is expected to be unaffected by both radiative and ordinary collisional processes in the cloud, it may well reflect the formation conditions for this molecule. The ratio is observed to depart from that expected under conditions of chemical equilibrium at formation, perhaps reflecting efficient interchange between cold dust grains in the gas phase.

Irvine, W. M.

1991-01-01

249

Nuclear fusion in dense plasmas  

Microsoft Academic Search

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

Setsuo Ichimaru

1993-01-01

250

Dense, finely, grained composite materials  

DOEpatents

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

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

1990-01-01

251

Viscoelastic behavior of dense microemulsions  

Microsoft Academic Search

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

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

1990-01-01

252

Dense matter in neutron stars and their envelopes  

E-print Network

exploded on July 4, 1054 (according to Chinese chronicles). Discovered in 1731 by amateur astronomer John.B.Zeldovich (1961) ­ maximally stiff EOS model. Superfluidity. BCS: J.Bardeen, L.N.Cooper, & J.R.Schrieffer (1957

253

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

254

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

255

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

256

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

257

Observational characteristics of dense cores with deeply embedded young protostars  

E-print Network

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

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

2005-11-03

258

Branched Polymers  

E-print Network

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

Richard Kenyon; Peter Winkler

2007-09-14

259

Polymer Synthesis  

NSDL National Science Digital Library

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

David Teegarden

2004-01-01

260

Spiral arm triggering of star formation  

E-print Network

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

Ian A. Bonnell

2006-11-07

261

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

262

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

263

Astrophysical and laboratory constraints for the dense matter equation of state  

SciTech Connect

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

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

2012-11-12

264

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

NASA Astrophysics Data System (ADS)

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.; Jahangir, R.; Eliasson, B.; Siddiq, M.

2014-10-01

265

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

266

Photometric detection of high proper motions in dense stellar fields using Difference Image Analysis  

E-print Network

The Difference Image Analysis (DIA) of the images obtained by the Optical Gravitational Lensing Experiment (OGLE-II) revealed a peculiar artifact in the sample of stars proposed as variable by Wozniak (2000) in one of the Galactic bulge fields: the occurrence of pairs of candidate variables showing anti-correlated light curves monotonic over a period of 3 years. This effect can be understood, quantified and related to the stellar proper motions. DIA photometry supplemented with a simple model offers an effective and easy way to detect high proper motion stars (HPM stars) in very dense stellar fields, where conventional astrometric searches are extremely inefficient.

Wozniak, P R

2001-01-01

267

Photometric detection of high proper motions in dense stellar fields using Difference Image Analysis  

E-print Network

The Difference Image Analysis (DIA) of the images obtained by the Optical Gravitational Lensing Experiment (OGLE-II) revealed a peculiar artifact in the sample of stars proposed as variable by Wozniak (2000) in one of the Galactic bulge fields: the occurrence of pairs of candidate variables showing anti-correlated light curves monotonic over a period of 3 years. This effect can be understood, quantified and related to the stellar proper motions. DIA photometry supplemented with a simple model offers an effective and easy way to detect high proper motion stars (HPM stars) in very dense stellar fields, where conventional astrometric searches are extremely inefficient.

L. Eyer; P. R. Wozniak

2001-02-02

268

Star clusters  

Microsoft Academic Search

Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which

M. Gieles

2006-01-01

269

Pair Interaction between End-Grafted Polymers onto Spherical Surfaces: A Monte Carlo Study  

E-print Network

follows the same scaling relationship found in the star polymer systems approximation. I. Introduction particles has been found to be a useful and nondestructive way to probe and size systems ranging from blood a star-shaped polymer. Witten and Pincus23 (to be referred as WP) derived an expression for the effective

Toral, Raúl

270

A quest for super dense aluminium  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

271

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

272

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

273

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

274

Young Massive Star Clusters  

NASA Astrophysics Data System (ADS)

Young massive clusters (YMCs) are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few YMCs that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. YMCs are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in YMCs, although their older cousins, the globular clusters, are unusually rich in stellar exotica. In this review, we focus on star clusters younger than ˜100 Myr, more than a few current crossing times old, and more massive than ˜104M?; the size of the cluster and its environment are considered less relevant as distinguishing parameters. We describe the global properties of the currently known young massive star clusters in the Local Group and beyond, and discuss the state of the art in observations and dynamical modeling of these systems. In order to make this review readable by observers, theorists, and computational astrophysicists, we also review the cross-disciplinary terminology.

Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gieles, Mark

2010-09-01

275

Polymer inflation  

E-print Network

We consider the semi-classical dynamics of a free massive scalar field in a homogeneous and isotropic cosmological spacetime. The scalar field is quantized using the polymer quantization method assuming that it is described by a gaussian coherent state. For quadratic potentials, the semi-classical equations of motion yield a universe that has an early "polymer inflation" phase which is generic and almost exactly de Sitter, followed by a epoch of slow-roll inflation. We compute polymer corrections to the slow roll formalism, and discuss the probability of inflation in this model using a physical Hamiltonian arising from time gauge fixing. We also show how in this model, it is possible to obtain a significant amount of slow-roll inflation from sub-Planckain initial data, hence circumventing some of the criticisms of standard scenarios. These results show the extent to which a quantum gravity motivated quantization method affects early universe dynamics.

Syed Moeez Hassan; Viqar Husain; Sanjeev S. Seahra

2015-03-05

276

Polymer inflation  

E-print Network

We consider the semi-classical dynamics of a free massive scalar field in a homogeneous and isotropic cosmological spacetime. The scalar field is quantized using the polymer quantization method assuming that it is described by a gaussian coherent state. For quadratic potentials, the semi-classical equations of motion yield a universe that has an early "polymer inflation" phase which is generic and almost exactly de Sitter, followed by a epoch of slow-roll inflation. We compute polymer corrections to the slow roll formalism, and discuss the probability of inflation in this model using a physical Hamiltonian arising from time gauge fixing. These results show the extent to which a quantum gravity motivated quantization method affects early universe dynamics.

Hassan, Syed Moeez; Seahra, Sanjeev S

2014-01-01

277

Polymer inflation  

NASA Astrophysics Data System (ADS)

We consider the semiclassical dynamics of a free massive scalar field in a homogeneous and isotropic cosmological spacetime. The scalar field is quantized using the polymer quantization method assuming that it is described by a Gaussian coherent state. For quadratic potentials, the semiclassical equations of motion yield a universe that has an early "polymer inflation" phase which is generic and almost exactly de Sitter, followed by an epoch of slow-roll inflation. We compute polymer corrections to the slow-roll formalism, and discuss the probability of inflation in this model using a physical Hamiltonian arising from time gauge fixing. We also show how in this model, it is possible to obtain a significant amount of slow-roll inflation from sub-Planckian initial data, hence circumventing some of the criticisms of standard scenarios. These results show the extent to which a quantum gravity motivated quantization method affects early universe dynamics.

Hassan, Syed Moeez; Husain, Viqar; Seahra, Sanjeev S.

2015-03-01

278

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

279

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

280

Nuclear fusion in dense matter: Reaction rate and carbon burning  

SciTech Connect

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

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

2005-08-01

281

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

282

Glue Polymer  

NSDL National Science Digital Library

What is a polymer, and what are some of its properties? This material is part of a series of hands-on science activities designed to arouse student interest. In this discovery activity students use white glue, water, and borax to make a vinyl polymer and study its properties. The activity includes a description, a list of science process skills and complex reasoning strategies being used, and a compilation of applicable K-12 national science education standards. Also provided are content topics, a list of necessary supplies, instructions, and presentation techniques. The content of the activity is explained, and assessment suggestions are provided.

Mid-continent Research for Education and Learning (McREL)

2004-01-01

283

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

284

Influence of polymer structure on plasma-polymer interactions in resist materials  

NASA Astrophysics Data System (ADS)

The controlled patterning of polymer resists by plasma plays an essential role in the fabrication of integrated circuits and nanostructures. As the dimensions of patterned structures continue to decrease, we require an atomistic understanding underlying the morphological changes that occur during plasma-polymer interactions. In this work, we investigated how plasma surface modifications and the initial polymer structure influenced plasma etch behavior and morphological changes in polymer resists. Using a prototypical argon discharge, we observed polymer modification by ions and vacuum ultraviolet (VUV) radiation from the plasma. A thin, highly dense modified layer was formed at the polymer surface due to ion bombardment. The thickness and physical properties of this ion-damaged layer was independent of polymer structure for the systems examined here. A relationship was observed that strongly suggests that buckling caused by ion-damaged layer formation on a polymer is the origin of roughness that develops during plasma etching. Our results indicate that with knowledge of the mechanical properties of the ion-damaged layer and the polymer being processed, plasma-induced surface roughness can be predicted and the surface morphology calculated. Examining a wide variety of polymer structures, the polymer poly(4-vinylpyridine) (P4VP) was observed to produce extremely smooth surfaces during high-ion energy plasma etching. Our data suggest that VUV crosslinking of P4VP below the ion-damaged layer may prevent wrinkling. We also studied another form of resists, silicon-containing polymers that form a SiO2 etch barrier layer during O2 plasma processing. In this study, we examined whether assisting SiO2 layer formation by adding Si-O bonds to the polymer structure would improve O2 etch behavior and reduce polymer surface roughness. Our results showed that while adding Si-O bonds decreased etch rates and silicon volatilization during O2 plasma exposure, the surface roughness became worse. Enhanced roughening was linked to the decrease in glass transition temperature and elastic modulus as Si-O bonds were added to the polymer structure. For polymers used as resists it is required that the mechanical properties of the ion-damaged layer and the polymer be taken into account to understand their roughening behavior.

Bruce, Robert Lawson

285

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

286

Polymer Blends  

Microsoft Academic Search

The concept of appropriately combining two or more different polymers to obtain a new material system with the desirable features of its constituents is not new. Over the years, numerous systems based on the chemical combination of different monomers through random, block, and graft copolymerization methods have been developed with this goal in mind. For similar reasons, the coatings and

D. R. Paul; J. W. Barlow

1980-01-01

287

Antimicrobial polymers.  

PubMed

Better health is basic requirement of human being, but the rapid growth of harmful pathogens and their serious health effects pose a significant challenge to modern science. Infections by pathogenic microorganisms are of great concern in many fields such as medical devices, drugs, hospital surfaces/furniture, dental restoration, surgery equipment, health care products, and hygienic applications (e.g., water purification systems, textiles, food packaging and storage, major or domestic appliances etc.) Antimicrobial polymers are the materials having the capability to kill/inhibit the growth of microbes on their surface or surrounding environment. Recently, they gained considerable interest for both academic research and industry and were found to be better than their small molecular counterparts in terms of enhanced efficacy, reduced toxicity, minimized environmental problems, resistance, and prolonged lifetime. Hence, efforts have focused on the development of antimicrobial polymers with all desired characters for optimum activity. In this Review, an overview of different antimicrobial polymers, their mechanism of action, factors affecting antimicrobial activity, and application in various fields are given. Recent advances and the current clinical status of these polymers are also discussed. PMID:25408272

Jain, Anjali; Duvvuri, L Sailaja; Farah, Shady; Beyth, Nurit; Domb, Abraham J; Khan, Wahid

2014-12-01

288

Hybrid Stars and Coronal Evolution  

NASA Technical Reports Server (NTRS)

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, TrA (K2 11-111). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars.

Mushotzky, Richard (Technical Monitor); Dupree, Andrea K.

2004-01-01

289

Sleuthing the Isolated Compact Stars  

NASA Astrophysics Data System (ADS)

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

Drake, J. J.

2004-08-01

290

Modeling the extended atmospheres of WN stars  

NASA Astrophysics Data System (ADS)

A detailed study of WN stars with particular reference to HD 50896 is initiated. Using radiative transfer calculations in the comoving frame, the author examines the behavior of the He II, He I, and H departure coefficients in a dense extended atmosphere. The models indicate that in HD 50896 (WN5) the helium ionization decreases strongly with radius, so that helium is predominantly singly ionized in the radio emitting region. This will necessitate the revision of mass loss rates for Wolf-Rayet (W-R) stars similar to HD 50896, which have been derived from radio data. It is shown that a star with a small core (2.5 R_sun;) and a dense stellar wind (M? 5×10-5M_sun;yr-1) can explain the observed energy distribution of W-R stars similar to HD 50896.

Hillier, D. J.

1987-04-01

291

SUPER STAR CLUSTERS VERSUS OB ASSOCIATIONS  

SciTech Connect

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

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

2010-12-01

292

Super Star Clusters Versus OB Associations  

NASA Astrophysics Data System (ADS)

Super star clusters (M ecl > 105 M sun) are the largest stellar nurseries in our local Universe, containing hundreds of thousands to millions of young stars within a few light years. Many of these systems are found in external galaxies, especially in pairs of interacting galaxies, and in some dwarf galaxies, but relatively few in disk galaxies like our own Milky Way. We show that a possible explanation for this difference is the presence of shear in normal spiral galaxies which impedes the formation of the very large and dense super star clusters but prefers the formation of loose OB associations possibly with a less massive cluster at the center. In contrast, in interacting galaxies and in dwarf galaxies, regions can collapse without having a large-scale sense of rotation. This lack of rotational support allows the giant clouds of gas and stars to concentrate into a single, dense, and gravitationally bound system.

Weidner, Carsten; Bonnell, Ian A.; Zinnecker, Hans

2010-12-01

293

Dense Inclined Flows of Spheres  

NASA Astrophysics Data System (ADS)

We operate in the context of a slightly modified hydrodynamic theory for frictionless spheres and consider deep, dense flows down a bumpy incline. The modification is the introduction of a length other than the diameter in the expression for the rate of collisional dissipation. The idea is that the first influence of the formation of particle chains is felt by the rate of dissipation. The chain length is determined by a simple algebraic balance between the creation and destruction of chains. The resulting theory is used together with the boundary conditions at a bumpy base and a free surface to determine the profiles of volume fraction, mean velocity, and fluctuation energy for steady, fully-developed flows of identical spheres. The profiles exhibit the features seen in numerical simulations. The integration of the energy balance through the depth of the flow result in an improvement of a velocity scaling often employed in the interpretation of physical experiments.

Jenkins, James

2006-11-01

294

Barred disks in dense environments  

NASA Astrophysics Data System (ADS)

We investigate the properties of bright barred and unbarred disks in the Abell 901/902 cluster system at z˜ 0.165 with the STAGES HST ACS survey. We find that the global optical bar fraction in the clusters is ˜ 30% regardless of the method of disk selection. Within a given absolute magnitude bin, the bar fraction increases for galaxies with no significant bulge component. Within each morphological type bin, the bar fraction increases for brighter galaxies. We find no strong trend for the bar fraction with local density within the cluster between the core and virial radius. We discuss the implications of our results for the evolution of bars and disks in dense environments.

Marinova, I.; Jogee, S.; Heiderman, A.; Barazza, F. D.; Gray, M. E.; Barden, M.; Wolf, C.; Peng, C. Y.; Bacon, D.; Balogh, M.; Bell, E. F.; Böhm, A.; Caldwell, J. A. R.; Häußler, B.; Heymans, C.; Jahnke, K.; van Kampen, E.; Lane, K.; McIntosh, D. H.; Meisenheimer, K.; Sánchez, S. F.; Somerville, R.; Taylor, A.; Wisotzki, L.; Zheng, X.

295

Star Formation Through Cosmic Time  

NASA Astrophysics Data System (ADS)

I will review the literature on the star formation history of the Universe, from the first stars up to the current day. The first (population III) stars appear to be responsible for the re-ionization of the Universe, and for seeding the inter-galactic medium with heavy elements, facilitating the formation of subsequent generations. There are now many lines of evidence from sub-mm galaxies, deep surveys, and from steep-spectrum radio sources to suggest that the collapse of massive galaxies and the formation of central massive black holes occurred surprisingly early in time. These objects enjoyed galaxy-wide starbursts, were very rapidly enriched in heavy elements, and rapidly became very dusty. Relativistic jets from the active nuclei seem to have provided an important means of terminate the initial burst of star formation in these massive galaxies, though possibly accompanied by large amounts of not so quiescent shock-induced star formation. Subsequently, the massive galaxies have evolved passively (or nearly so, modulo a merger or two) to form the ellipticals and cD galaxies well distinguished by their color (`red and dead') in the SDSS data. In less dense environments, star formation proceeded more slowly through disk galaxies. With time only smaller and smaller fragments having high rates of specific star formation, until today only the dwarf irregular galaxies have high gas to star ratios. This process is frequently referred to as `down-sizing'.

Dopita, Michael A.

2007-05-01

296

Polymers Pushing Polymers: Polymer Mixtures in Thermodynamic Equilibrium with a Pore  

E-print Network

Polymers Pushing Polymers: Polymer Mixtures in Thermodynamic Equilibrium with a Pore R. Podgornik, 1000 Ljubljana, Slovenia Polymer Science and Engineering Department, University of Massachusetts, Amherst, Massachusetts 01003, United States ABSTRACT: We investigate polymer partitioning from polymer

Podgornik, Rudolf

297

POLYMER PROGRAM SEMINAR "Nanomanufacturing with Polymers"  

E-print Network

POLYMER PROGRAM SEMINAR "Nanomanufacturing with Polymers" Prof. Joey Mead University Lowell has developed a suite of processes to enable the nanomanufacturing of polymer based products of properties (e.g. biocompatibility, polarity, and modulus). Polymer materials can be used as substrates

Alpay, S. Pamir

298

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

299

Coupled modes in magnetized dense plasma with relativistic-degenerate electrons  

SciTech Connect

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

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

2012-01-15

300

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

301

Observed instabilities in OB and Wolf-Rayet stars  

Microsoft Academic Search

A wealth of recent observations confirms that the fast, dense winds of OB and Wolf-Rayet (WR) stars are highly structured, with the structures resulting from the inherently unstable nature of a radiatively-driven wind, as well as being triggered from the underlying photosphere. This review mainly addresses variability patterns observed in the winds and photospheric regions of presumably single stars. Schematically

Sergey V. Marchenko

2003-01-01

302

Strange stars  

NASA Technical Reports Server (NTRS)

Strange matter, a form of quark matter that is postulated to be absolute stable, may be the true ground stage of the hadrons. If this hypothesis is correct, neutron stars may convert to 'strange stars'. The mass-radius relation for strange stars is very different from that of neutron stars; there is no minimum mass, and for mass of 1 solar mass or less, mass is proportional to the cube of the radius. For masses between 1 solar mass and 2 solar masses, the radii of strange stars are about 10 km, as for neutron stars. Strange stars may have an exposed quark surface, which is capable of radiating at rates greatly exceeding the Eddington limit, but has a low emissivity for X-ray photons. The stars may have a thin crust with the same composition as the preneutron drip outer layer of a conventional neutron star crust. Strange stars cool efficiently via neutrino emission.

Alcock, Charles; Farhi, Edward; Olinto, Angela

1986-01-01

303

Insights from Simulations of Star Formation  

E-print Network

Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar disks often form from the gas being accreted by the forming stars, and accretion from these disks may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many processes of star formation, and detailed numerical simulations are needed to advance our understanding of the subject.

Richard B. Larson

2007-02-07

304

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

305

Stars and Star Myths.  

ERIC Educational Resources Information Center

Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

Eason, Oliver

306

Boundary effect of deterministic dense coding  

E-print Network

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

Zhengfeng Ji; Yuan Feng; Runyao Duan; Mingsheng Ying

2006-01-20

307

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

308

Crystallization of dense neutron matter  

NASA Technical Reports Server (NTRS)

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

Canuto, V.; Chitre, S. M.

1974-01-01

309

Phthalocyanine polymers  

NASA Technical Reports Server (NTRS)

A method of forming 4,4',4'',4''' -tetraamino phthalocyanines involves reducing 4,4',4'',4''' -tetranitro phthalocyanines, polymerizing the metal tetraamino phthalocyanines with a tetracarboxylic dianhydride (preferably aromatic) or copolymerizing with a tetracarboxylic dianhydride and a diamine (preferably also aromatic) to produce amic acids which are then dehydrocyclized to imides. Thermally and oxidatively stable polymers result which form tough, flexible films, varnishes, adhesives, and fibers.

Achar, B. N.; Fohlen, G. M.; Parker, J. A. (inventors)

1985-01-01

310

On quantum advantage in dense coding  

E-print Network

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

M. Horodecki; M. Piani

2009-09-11

311

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

312

Stress Relaxation in Entangled Melts of Unlinked Ring Polymers  

NASA Astrophysics Data System (ADS)

Stress relaxation in unlinked ring polymer melts poses an important challenge to our theoretical understanding of entangled polymer dynamics. Recent experiments on entangled unlinked ring melts show power-law stress relaxation with no hint of a rubbery plateau, usually the hallmark of entangled polymers. Here we present a theory for stress relaxation in rings analogous to the successful approach for star polymers. We augment our theory with mesoscale Monte Carlo dynamics simulations of equivalent “lattice animal” configurations. We find a stress relaxation function G(t)˜t-? with ??1/2 consistent with experiment, emerging ultimately from the disparate relaxation times of more- and less-central portions of ring conformations.

Milner, Scott T.; Newhall, Jillian D.

2010-11-01

313

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

314

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

NSDL National Science Digital Library

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

Alan McConnell

1990-07-10

315

Embedded Star Formation in the Eagle Nebula  

E-print Network

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

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

2002-01-17

316

New Signposts of Star Cluster Formation  

NASA Astrophysics Data System (ADS)

The unbiased CHaMP survey of massive, dense molecular clumps in the southern Milky Way gives properties of clouds which represent the vast majority of star formation in the Galactic disk. Most of these clumps, while massive, are less dense and have lower star formation activity than more popularly-studied areas, suggesting a relatively long-lived, qui- escent phase of clump evolution before the onset of vigorous massive star formation disperses the clump, e.g. HCO + line emission is strongly correlated with associated Br? emission from embedded young clusters. The HCO+ is also strongly correlated with a number of other molecular tracers, including 13CO and HCN. In contrast, H_2 and N_2H+ emission are neither correlated with each other nor with HCO + or Br?, but the HCO+/N_2 H+ ratio is correlated with Br?/L_bol , and so indicates a clump’s progress in forming massive stars or clusters from a colder, earlier, less active state. Therefore, many “dense gas” tracers don’t really trace dense gas alone, but rather a combination of excitation and density, and should be interpreted with caution in the extragalactic context.

Barnes, P.; Ryder, S.

2014-09-01

317

Filter-Dense Multicolor Microscopy  

PubMed Central

Immunofluorescence microscopy is a unique method to reveal the spatial location of proteins in tissues and cells. By combining antibodies that are labeled with different fluorochromes, the location of several proteins can simultaneously be visualized in one sample. However, because of the risk of bleed-through signals between fluorochromes, standard multicolor microscopy is restricted to a maximum of four fluorescence channels, including one for nuclei staining. This is not always enough to address common scientific questions. In particular, the use of a rapidly increasing number of marker proteins to classify functionally distinct cell populations and diseased tissues emphasizes the need for more complex multistainings. Hence, multicolor microscopy should ideally offer more channels to meet the current needs in biomedical science. Here we present an enhanced multi-fluorescence setup, which we call Filter-Dense Multicolor Microscopy (FDMM). FDMM is based on condensed filter sets that are more specific for each fluorochrome and allow a more economic use of the light spectrum. FDMM allows at least six independent fluorescence channels and can be applied to any standard fluorescence microscope without changing any operative procedures for the user. In the present study, we demonstrate an FDMM setup of six channels that includes the most commonly used fluorochromes for histology. We show that the FDMM setup is specific and robust, and we apply the technique on typical biological questions that require more than four fluorescence microscope channels. PMID:25739088

Kijani, Siavash; Yrlid, Ulf; Heyden, Maria; Levin, Malin; Borén, Jan; Fogelstrand, Per

2015-01-01

318

Percolation in dense storage arrays  

NASA Astrophysics Data System (ADS)

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

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

2002-11-01

319

Polymer Energy Rechargeable System Battery Being Developed  

NASA Technical Reports Server (NTRS)

Long description. Illustrations of discotic liquid crystals, rod-coil polymers, lithium-ion conducting channel dilithium phthalocyanine (Li2Pc) from top and side, novel star polyethylene oxide structures, composite polyethylene oxide materials (showing polyethylene oxide + lithium salt, carbon atoms and oxygen atoms), homopolyrotaxanes, and diblock copolymers In fiscal year 2000, NASA established a program to develop the next generation, lithium-based, polymer electrolyte batteries for aerospace applications. The goal of this program, known as Polymer Energy Rechargeable Systems (PERS), is to develop a space-qualified, advanced battery system embodying polymer electrolyte and lithium-based electrode technologies and to establish world-class domestic manufacturing capabilities for advanced batteries with improved performance characteristics that address NASA s future aerospace battery requirements.

Manzo, Michelle A.

2003-01-01

320

Observations show that most, if not all, massive stars form in clusters. This combination of massive stars and clusters has led to the suggestions that massive stars form by  

E-print Network

Spectrometer (NICMOS) on Hubble Space Telescope (HST). These stars, which are still embedded in dense envelopes Janet P. Simpson1,2 , Michael G. Burton3 , Sean W. J. Colgan1 , Angela S. Cotera2 , Edwin F. Erickson1

Schneider, Glenn

321

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

322

Polymer Electronics: Power from Polymers  

SciTech Connect

We review polymer-based electronics and photovoltaics to provide the reader with a sense of how the field has developed, where we stand at present, and what possibilities are looming in the future. Expertise in areas ranging from synthesis to morphology to device design was sought to achieve this end. While these reviews cannot be exhaustive, they do provide a snapshot of the field at present and give some sense of where the key impediments are.

Venkataraman, D.; Russell, Thomas P.

2012-01-01

323

Initial Conditions for Massive Star Birth -- Infrared Dark Clouds  

E-print Network

We summarize the properties of Infrared Dark Clouds, massive, dense, and cool aggregations of interstellar gas and dust that are found througout the Galaxy in projection against the strong mid-infrared background. We describe their distribution and give an overview of their physical properties and chemistry. These objects appear to be the progenitors of high-mass stars and star clusters, but seem to be largely devoid of star formation, which however is taking place in localized spots.

K. M. Menten; T. Pillai; F. Wyrowski

2005-08-02

324

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

325

DYNAMICAL CAPTURE BINARY NEUTRON STAR MERGERS  

SciTech Connect

We study dynamical capture binary neutron star mergers as may arise in dense stellar regions such as globular clusters. Using general-relativistic hydrodynamics, we find that these mergers can result in the prompt collapse to a black hole or in the formation of a hypermassive neutron star, depending not only on the neutron star equation of state but also on impact parameter. We also find that these mergers can produce accretion disks of up to a tenth of a solar mass and unbound ejected material of up to a few percent of a solar mass. We comment on the gravitational radiation and electromagnetic transients that these sources may produce.

East, William E.; Pretorius, Frans [Department of Physics, Princeton University, Princeton, NJ 08544 (United States)

2012-11-20

326

Color Ferromagnetic Quark Matter in Neutron Stars  

E-print Network

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

Aiichi Iwazaki; Osamu Morimatsu; Tetsuo Nishikawa; Munehisa Ohtani

2005-12-16

327

Young stars and clouds in Camelopardalis  

E-print Network

Star formation in the Local spiral arm in the direction of the Galactic longitudes 132--158 deg is reviewed. Recent star-forming activity in this Milky Way direction is evidenced by the presence here of the Cam OB1 association and dense dust and molecular clouds containing H$\\alpha$ emission stars, young irregular variables and infrared stellar objects. The clouds of the Local arm concentrate in two layers at 150-300 pc and at about 900 pc from the Sun. The Perseus arm objects in this direction are at a distance of about 2 kpc.

V. Straizys; V. Laugalys

2008-11-18

328

Dense Correspondence Estimation for Image Interpolation  

E-print Network

We evaluate the current state-of-the-art in dense correspondence estimation fortheuseinmulti-imageinterpolationalgorithms. Theevaluationiscarried out on three real-world scenes and one synthetic scene, each featuring varying challenges for dense correspondence estimation. The primary focus of our study is on the perceptual quality of the interpolation sequences created from the estimated flow fields. Perceptual plausibility is assessed by means of a psychophysical userstudy. Our results show that current state-of-theart in dense correspondence estimation does not produce visually plausible interpolations. 2

Christian Linz; Prof Dr; Ing Marcus Magnor

2010-01-01

329

Temperature dependence of modified CNO nuclear reaction rates in dense stellar plasmas  

Microsoft Academic Search

We study the dependence of the CNO nuclear reaction rates on temperature, in the range of 107–108K, the typical range of temperature evolution from a Sun-like star towards a white dwarf. We show that the temperature dependence of the CNO nuclear reaction rates is strongly affected by the presence of non-extensive statistical effects in the dense stellar core. A very

F. Ferro; A. Lavagno; P. Quarati

2004-01-01

330

Molecular Composition and Chemistry of Isolated Dense Cores  

NASA Astrophysics Data System (ADS)

The composition of molecular clouds and the envelopes and disks surrounding low mass protostars within them is still poorly known. There is little doubt that a large fraction of the molecules is frozen on grains, but the abundance of several crucial species (e.g. ammonia, methanol, ions) in the ices is still uncertain. In addition, prominent spectral features discovered decades ago are still not securely identified (e.g. the 6.85-micron absorption band). Gas phase and grain surface chemistry play pivotal roles in molecule formation, but numerous other processes could have significant impacts as well: shocks, thermal heating, irradiation of ices by ultraviolet photons and cosmic rays. Complex species could be formed this way, profoundly influencing cloud, disk and planetary/cometary chemistry. We have obtained Spitzer/IRS spectra of an unprecedented sample of sight-lines tracing 25 dense isolated cores. These cores physically differ from the large, cluster-forming molecular clouds (e.g. Ophiuchus, Perseus) that are commonly studied: they are less turbulent, colder, less dense, and likely longer lived. These IRS spectra of isolated cores thus provide unique information on ice formation and destruction mechanisms. Toward the same cores, we observed 33 highly extincted background stars as well, tracing the quiescent cloud medium against which the ices around protostars can be contrasted.

Cook, Amanda; Boogert, A.

2009-01-01

331

Hybrid Stars  

E-print Network

Recently there have been important developments in the determination of neutron star masses which put severe constraints on the composition and equation of state (EOS) of the neutron star matter. Here we study the effect of quark and nuclear matter mixed phase on mass radius relationship of neutron stars employing recent models from two classes of EOS's and discuss their implications.

Ashok Goyal

2003-03-21

332

Circumpolar Stars  

Microsoft Academic Search

Stars that never set as seen from a particular location. The requirement for this to happen is that the star's polar distance is less than the observer's latitude---thus from a location in latitude 52° North, stars of NPD less than 52° (i.e. with declinations of between 0° and +38°) are circumpolar and will be seen to circle around the north

P. Murdin

2000-01-01

333

Polymer Spheulites  

NASA Astrophysics Data System (ADS)

The growth and/or structural features that determine lamellar shape in polymer spherulites and therefore their structure and properties have been debated for many years. The spectacular twisting of lamellae in optically banded spherulites has been explained by the existence of unbalanced stresses in opposite fold surfaces of the lamellae. This mechanical origin implying the folds explains also the demonstrated absence of correlation between lamellar twist sense and molecular chirality of chiral polymers. Unbalanced surface stresses may also generate spherulites made of scrolled lamellae, with the scroll axis radial. This original morphology was first observed in spherulites of poly(vinylidene fluoride) in its ? phase. It arises from a chemical disparity of folds formed on opposite fold surfaces, the volumes of which differ by 10å*3. Similar chemical disparities have been suggested to explain the formation of highly unusual scrolled single crystals of polyamide 66 obtained from solution under specific annealing and crystallization conditions. Related thermal histories lead to the formation, in the bulk, of unusual optically negative spherulites of polyamide 66 that were first observed in the 1940s. These still poorly understood negative spherulites may well display a similar scrolled lamellar morphology. The analysis of unbalanced surface stresses requires to evaluate the interplay and mutual impact of crystal and fold structures. The stresses associated with different fold structures are locally small perturbations but are cumulative and are exerted on thin, flexible lamellae. The latter non-planar morphologies reveal these stresses and help reach sub-moleculr insights on the fold structures.

Lotz, Bernard

2013-03-01

334

Recombination Lines of Embedded Star Clusters  

E-print Network

Aims. We are trying to probe conditions in the youngest super star clusters, those still embedded in dense obscuring clouds. Methods. The hydrogen recombination lines in the radio and infrared can be observed through the obscuration, as the optical and UV lines cannot, and give us the kinematics of the ionized gas. Results. The line profiles of the clusters resemble superpositions of the lines of many very young ultra-compact or hyper-compact HII regions. This can be explained if each OB star is individually embedded in dense material which it is accreting, even as it ionizes. Conclusions. We speculate on what this implies for the status and evolutionary state of cluster stars.

S. C. Beck

2008-08-13

335

Dense transmit and receive phased arrays  

E-print Network

A dense antenna array architecture is developed to ease the circuit requirements of the radio frequency (RF) front-end in beamforming applications. In the architecture, antennas are spaced more closely than required by the ...

Yeang, Chen-Pang

336

Dynamics and evolution of dense stellar systems  

E-print Network

The research presented in this thesis comprises a theoretical study of several aspects relating to the dynamics and evolution of dense stellar systems such as globular clusters. First, I present the results of a study of ...

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

2004-01-01

337

Genetics Home Reference: Dense deposit disease  

MedlinePLUS

... example, the disorder can occur with acquired partial lipodystrophy, a condition characterized by a lack of fatty ( ... occur with dense deposit disease, including acquired partial lipodystrophy and a buildup of drusen in the retina. ...

338

Capillary flow of dense colloidal suspensions   

E-print Network

The purpose of this thesis is to study the flow of dense colloidal suspensions into micronsized capillaries at the particle level. Understanding the flow of complex fluids in terms of their constituents (colloids, ...

Isa, Lucio

2008-01-01

339

Atmospheric Erosion Caused by Stellar Coronal Plasma Flows on Terrestrial Exoplanets within Close-In Habitable Zones of Low Mass Stars  

Microsoft Academic Search

Since low mass M stars show a higher level of stellar activity compared to solar-like stars, and because of the closer orbital distance of their habitable zones compared to that of the Solar System, terrestrial exoplanets within M star habitable zones are expected to be much more strongly influenced by stellar winds and dense plasma ejected from the host star

H. Lammer; N. Terada; Yu. N. Kulikov; H. I. M. Lichtenegger; M. L. Khodachenko; T. Penz

2008-01-01

340

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

341

Heavy meson production in hot dense matter  

SciTech Connect

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

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

2010-12-28

342

Viscoelasticity and primitive path analysis of entangled polymer liquids: From f-actin to polyethylene  

E-print Network

We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on the primitive path analysis (PPA) of the microscopic topological state. Our results agree with experimentally measured plateau moduli for three different polymer classes over a wide rangeof reduced polymer densities: (i) semi-dilute theta solutions of synthetic polymers, (ii) the corresponding dense melts above the glass transition or crystallization temperature, and (iii) solutions of semi-flexible (bio)polymers such as f-actin or suspensions of rodlike viruses. Together these systems cover the entire range from loosely to tightly entangled polymers. In particular, we argue that the primitive path analysis renormalizes a loosely to a tightly entangled system and provide a new explanation of the successful Lin-Noolandi packing conjecture for polymer melts.

Nariya Uchida; Gary S. Grest; Ralf Everaers

2007-11-28

343

Viscoelasticity and primitive path analysis of entangled polymer liquids: From F-actin to polyethylene  

NASA Astrophysics Data System (ADS)

We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on the primitive path analysis of the microscopic topological state. Our results agree with experimentally measured plateau moduli for three different polymer classes over a wide range of reduced polymer densities: (i) semidilute theta solutions of synthetic polymers, (ii) the corresponding dense melts above the glass transition or crystallization temperature, and (iii) solutions of semiflexible (bio)polymers such as F-actin or suspensions of rodlike viruses. Together, these systems cover the entire range from loosely to tightly entangled polymers. In particular, we argue that the primitive path analysis renormalizes a loosely to a tightly entangled system and provide a new explanation of the successful Lin-Noolandi packing conjecture for polymer melts.

Uchida, Nariya; Grest, Gary S.; Everaers, Ralf

2008-01-01

344

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

SciTech Connect

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

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

2010-11-01

345

Hadron star models. [neutron stars  

NASA Technical Reports Server (NTRS)

The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

Cohen, J. M.; Boerner, G.

1974-01-01

346

Chemical Differentiation of CS and N2H+ in Dense Starless Cores  

NASA Astrophysics Data System (ADS)

CS molecule as an important tracer for studying inward motions in dense cores is known to be adsorbed onto dusts in cold (T~10K) dense cores, resulting in its significant depletion in the central region of the cores which may hamper a proper study of kinematics stage of star formation. However, the chemical behavior of this molecule still seems under questions because of a paucity of the cases showing the CS depletion in dense cores. In this study we choose five ‘evolved’ dense starless cores, L1544, L1552, L1689B, L694-2 and L1197, to investigate how depletion of CS molecule is significant and how the molecule differentiates depending on the evolutional status of the dense cores, by using a rare isotopomer C34S. We performed mapping observations in C34S(J=2-1) and N2H+(J=1-0) with Nobeyama 45-m telescope. We compared the intensity maps of two molecular lines with 850?m continuum data as a reference of the density distribution of the dense cores, finding that CS molecules are centrally depleted in all of our targets and seen as ‘semi-ring-like’ holes in its distribution, while N2H+ shows a central peak distribution as the one in dust continuum. This is also seen in the abundance radial profiles of two molecules for all of our targets where the CS abundance decreases toward the core center while the N2H+ keeps abundant constantly. Our data confirm the claim that CS molecule generally depletes out in the central region in starless cores, while N2H+ keeps abundant as they get evolved. The quantitative analysis on CS depletion in the dense cores, for example, the size of CS depletion area and radial (or gas density) dependence of CS depletion, is presented in the conference.

Kim, Shinyoung; Lee, Chang Won

2014-07-01

347

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

NASA Astrophysics Data System (ADS)

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

Lopez-Santiago, Javier

2013-10-01

348

From Commodity Polymers to Functional Polymers  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

349

From commodity polymers to functional polymers.  

PubMed

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

350

Antioxidant Stabilisation of Polymers  

Microsoft Academic Search

Physicochemical aspects of the stabilisation of polymers are discussed. Attention is paid mainly to the aging and stabilisation of polymers under processing conditions. Topics considered are the kinetics and mechanism of the high-temperature oxidation of polymers, critical phenomena in the inhibited oxidation of polymers, the theory of synergism and antagonism among antioxidants, the reasons for differences in efficiency of antioxidants,

Yurii A Shlyapnikov

1981-01-01

351

Microstructured polymer optical fibre  

Microsoft Academic Search

The first microstructured polymer optical fibre is described. Both experimental and theoretical evidence is presented to establish that the fibre is effectively single moded at optical wavelengths. Polymer-based microstructured optical fibres offer key advantages over both conventional polymer optical fibres and glass microstructured fibres. The low-cost manufacturability and the chemical flexibility of the polymers provide great potential for applications in

Martijn van Eijkelenborg; Maryanne Large; Alexander Argyros; Joseph Zagari; Steven Manos; Nader A. Issa; Ian M. Bassett; Simon C. Fleming; Ross C. McPhedran; C. Martijn de Sterke; Nicolae A. P. Nicorovici

2001-01-01

352

On the Formation of Massive Stars  

E-print Network

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

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

1998-02-26

353

Circumstellar Material Around Evolved Massive Stars  

E-print Network

I review multiwavelength observations of material seen around different types of evolved massive stars (i.e. red supergiants, yellow hypergiants, luminous blue variables, B[e] supergiants, and Wolf-Rayet stars), concentrating on diagnostics of mass, composition, and kinetic energy in both local and distant examples. Circumstellar material has significant implications for the evolutionary state of the star, the role of episodic mass loss in stellar evolution, and the roles of binarity and rotation in shaping the ejecta. This mass loss determines the type of supernova that results via the stripping of the star's outer layers, but the circumstellar gas can also profoundly influence the immediate pre-supernova environment. Dense circumstellar material can actually change the type of supernova that is seen when it is illuminated by the supernova or heated by the blast wave. As such, unresolved circumstellar material illuminated by distant supernovae can provide a way to study mass loss in massive stars in distant ...

Smith, Nathan

2010-01-01

354

The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)  

E-print Network

We present the abundance analysis of 82 red giant branch stars in the dense, metal-poor globular cluster NGC 6093 (M 80), the largest sample of stars analyzed in this way for this cluster. From high resolution UVES spectra of 14 stars and intermediate resolution GIRAFFE spectra for the other stars we derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu. On our UVES metallicity scale the mean metal abundance of M 80 is [Fe/H]=-1.791+/-0.006+/-0.076 (+/-statistical +/-systematic error) with rms=0.023 (14 stars). M 80 shows star to star variations in proton-capture elements, and the extension of the Na-O anticorrelation perfectly fit the relations with (i) total cluster mass, (ii) horizontal branch morphology, and (iii) cluster concentration previously found by our group. The chemistry of multiple stellar populations in M 80 does not look extreme. The cluster is also a typical representative of halo globular clusters for what concerns the pattern o...

Carretta, E; Gratton, R G; D'Orazi, V; Lucatello, S; Sollima, A; Momany, Y; Catanzaro, G; Leone, F

2015-01-01

355

Explicit flavor symmetry breaking and holographic compact stars  

E-print Network

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

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

2014-11-03

356

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

PubMed

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

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

2014-12-21

357

Atomistic Simulation of Polymer Crystallization at Realistic Length Scales  

SciTech Connect

Understanding the dynamics of polymer crystallization during the induction period prior to crystal growth is a key goal in polymer physics. Here we present the first study of primary crystallization of polymer melts via molecular dynamics simulations at physically realistic (about 46 nm) length scales. Our results show that the crystallization mechanism involves a spinodal decomposition microphase separation caused by an increase in the average length of rigid trans segments along the polymer backbone during the induction period. Further, the characteristic length of the growing dense domains during the induction period is longer than predicted by classical nucleation theory. These results indicate a new 'coexistence period' in the crystallization, where nucleation and growth mechanisms coexist with a phase separation mechanism. Our results provide an atomistic verification of the fringed micelle model.

Gee, R H; Fried, L E

2005-01-28

358

Gravothermal Star Clusters - Theory and Computer Modelling  

NASA Astrophysics Data System (ADS)

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

Spurzem, Rainer

2010-11-01

359

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 Earth’s 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.

2012-08-03

360

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

361

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?

Bob Riddle

2003-02-01

362

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

363

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

364

Dense dust structures in cryogenic complex plasma  

NASA Astrophysics Data System (ADS)

In the previous researches of cryogenic complex (dusty) plasma [1] we observed experimentally complex plasma systems formed in cryogenic environments. Particularly it was revealed from the experiments that dust structures with high concentration of macroparticles can be formed. So-called super dense dusty plasma structures in which interparticle distance is comparable with particle size were also observed. Thus concentration of particles was close to concentration of background plasma. Similar formations had unusual properties (sphere-like form, free boundaries, etc.) and represent new object in dusty plasma researches. In the present work new results on experimental investigations of dense dust structures at cryogenic temperatures were presented. The experiments were made by means of recently developed techniques and cryogenic facilities (optical cryostat). Possible nature of the unusual properties of super dense dusty plasma structures was discussed.

Antipov, S. N.; Vasiliev, M. M.; Alyapyshev, M. M.; Petrov, O. F.; Fortov, V. E.

2014-05-01

365

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

366

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

367

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

368

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

369

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

370

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

371

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

372

Ab Initio Simulations of Dense Helium Plasmas  

SciTech Connect

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

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

2011-04-08

373

Dense gas flow in minimum length nozzles  

SciTech Connect

Recently, dense gases have been investigated for many engineering applications such as for turbomachinery and wind tunnels. Supersonic nozzle design can be complicated by nonclassical dense-gas behavior in the transonic flow regime. In this paper, a method of characteristics (MOC) is developed for two-dimensional (planar) and axisymmetric flow of a van der Waals gas. A minimum length nozzle design code is developed that employs the MOC procedure to generate an inviscid wall contour. The van der Waals results are compared to perfect gas results to show the real-gas effects on the flow properties and inviscid wall contours.

Aldo, A.C.; Argrow, B.M. [Univ. of Colorado, Boulder, CO (United States). Dept. of Aerospace Engineering Sciences

1995-06-01

374

Numerical simulations of dense collisional systems  

NASA Astrophysics Data System (ADS)

The present use of a local simulation method akin to that of Wisdom and Tremaine (1988) to examine the viscous stability characteristics of dense planetary rings confirms that the viscous instability of the standard elastic model of icy particles should not occur for systems of identical, meter-sized particles, but may indeed occur in dense systems composed of cm-sized ones. In the case of nonidentical particles, small particles become more easily unstable. The layered structure of Wisdom and Tremaine's simulation with self-gravity can be substantially modified if the vertical field is calculated self-consistently; in some cases, a flattening to the central plane may be virtually complete.

Salo, H.

1991-04-01

375

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

376

Isomeric Trisaryloxycyclotriphosphazene Polymer Precursors  

NASA Technical Reports Server (NTRS)

Substances useful for making heat-and fire-resistant polymers. Cyclotriphosphazene-based monomers and polymer precursors led to development of high-temperature materials. Cyclotriphosphazene-derived monomers, polymer precursors, and polymers becoming important from both industrial and scientific points of view. Presence of phosphazene moiety in cyclotriphosphazene-based monomers and polymer precursors expected to impact special properties in desired high-performance materials containing inorganic backbones for aerospace applications. Useful for obtaining heat-and fire-resistant polymers for composites, adhesives, molding powders, and coating laminates. Also used in structures (e.g. secondary structures in aircraft), in construction of spacecraft, and in electronics and computer industries.

St. Clair, Terry L.; Kumar, Devendra

1990-01-01

377

Hyperons and nuclear symmetry energy in neutron star matter  

SciTech Connect

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

Ryu, Chung-Yeol [Department of Physics, Hanyang University, Seoul 133-791 (Korea, Republic of); Hyun, Chang Ho [Department of Physics Education, Daegu University, Gyeongsan 712-714 (Korea, Republic of); Lee, Chang-Hwan [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of)

2011-09-15

378

Double stars  

Microsoft Academic Search

The work devoted to the identification of double and multiple stars for the Hipparcos input catalog is presented. Ground based observations, and photometric and astrometric aspects are included. The aim of the work is to improve the main stream of the data reduction. The tasks performed by the input catalog (INCA) double star working groups are reported. The contents of

J. Dommanget

1989-01-01

379

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.

380

Rogue Star  

NSDL National Science Digital Library

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

Douglas Hamilton

381

Superconducting Superfluids in Neutron Stars  

E-print Network

For treatment of the layers below the crust of a neutron star it is useful to employ a relativistic model involving three independently moving constituents, representing superfluid neutrons, superfluid protons, and degenerate negatively charged leptons. A Kalb Ramond type formulation is used here to develop such a model for the specific purpose of application at the semi macroscopic level characterised by lengthscales that are long compared with the separation between the highly localised and densely packed proton vortices of the Abrikosov type lattice that carries the main part of the magnetic flux, but that are short compared with the separation between the neutron vortices.

Brandon Carter

2000-10-05

382

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

383

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

384

Star dust.  

PubMed

Infrared astronomy has shown that certain classes of stars are abundant producers of refractory grains, which condense in their atmospheres and are blown into interstellar space by the radiation pressure of these stars. Metallic silicates of the kind that produce terrestrial planets are injected by the oxygen-rich stars and carbon and its refractories by carbon stars. Much of the interstellar dust may be produced by this mechanism. A number of "infrared stars" are completely surrounded by their own dust, and a few of these exhibit a unique morphology that suggests the formation of a planetary system or a stage in the evolution of a planetary nebula. Certain novae also condense grains, which are blown out in their shells. In our own solar system, comets are found to contain the same silicates that are present elsewhere in the galaxy, suggesting that these constituents were present in the primeval solar nebula. PMID:17732279

Ney, E P

1977-02-11

385

Star Journey  

NSDL National Science Digital Library

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

Carolyn Anderson

386

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

387

Dynamical Interactions in Dense Stellar Clusters  

E-print Network

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

Ian Bonnell; Pavel Kroupa

1998-02-24

388

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

389

Three body dynamics in dense gravitational systems  

Microsoft Academic Search

In this thesis, I have used several techniques to answer the following questions: How many black hole binaries will a cluster produce, and will they have the required properties to be seen by our gravitational wave detectors? How often does the crowded environment of star forming cluster allow the exchange of a planet between stars? To answer these questions, I

Kenneth Moody

2009-01-01

390

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

391

Large area synthesis of a nanoporous two-dimensional polymer at the air/water interface.  

PubMed

We present the synthesis of a two-dimensional polymer at the air/water interface and its nm-resolution imaging. Trigonal star, amphiphilic monomers bearing three anthraceno groups on a central triptycene core are confined at the air/water interface. Compression followed by photopolymerization on the interface provides the two-dimensional polymer. Analysis by scanning tunneling microscopy suggests that the polymer is periodic with ultrahigh pore density. PMID:25715659

Murray, Daniel J; Patterson, Dustin D; Payamyar, Payam; Bhola, Radha; Song, Wentao; Lackinger, Markus; Schlüter, A Dieter; King, Benjamin T

2015-03-18

392

Playing with Polymers.  

ERIC Educational Resources Information Center

Presents an activity that enables students to gain a better understanding of the importance of polymers. Students perform an experiment in which polymer chains of polyvinyl acetate form crosslinks. Includes background information and discussion questions. (DDR)

Chemecology, 1997

1997-01-01

393

Stiff Quantum Polymers  

E-print Network

At ultralow temperatures, polymers exhibit quantum behavior, which is calculated here for the moments and of the end-to-end distribution in the large-stiffness regime. The result should be measurable for polymers in wide optical traps.

H. Kleinert

2007-05-01

394

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

395

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

396

Polymer composites containing nanotubes  

NASA Technical Reports Server (NTRS)

The present invention relates to polymer composite materials containing carbon nanotubes, particularly to those containing singled-walled nanotubes. The invention provides a polymer composite comprising one or more base polymers, one or more functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers and carbon nanotubes. The invention also relates to functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers, particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having side chain functionalization, and more particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having olefin side chains and alkyl epoxy side chains. The invention further relates to methods of making polymer composites comprising carbon nanotubes.

Bley, Richard A. (Inventor)

2008-01-01

397

Are compact groups of galaxies physically dense?  

Microsoft Academic Search

The properties of the compact groups of galaxies cataloged by Hickson (1982) are compared to the output of over 1000 numerical simulations of small groups of galaxies. Rather than being dense physical systems or transient unbound cores of loose groups, it is argued that roughly half of the compact groups in Hickson's catalog are simply chance alignments of galaxies within

G. A. Mamon

1986-01-01

398

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

399

DENSE NONAQUEOUS PHASE LIQUIDS -- A WORKSHOP SUMMARY  

EPA Science Inventory

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

400

Dense high temperature ceramic oxide superconductors  

DOEpatents

Dense superconducting ceramic oxide articles of manufacture and methods for producing these articles are described. Generally these articles are produced by first processing these superconducting oxides by ceramic processing techniques to optimize materials properties, followed by reestablishing the superconducting state in a desired portion of the ceramic oxide composite.

Landingham, Richard L. (Livermore, CA)

1993-01-01

401

Dense high temperature ceramic oxide superconductors  

DOEpatents

Dense superconducting ceramic oxide articles of manufacture and methods for producing these articles are described. Generally these articles are produced by first processing these superconducting oxides by ceramic processing techniques to optimize materials properties, followed by reestablishing the superconducting state in a desired portion of the ceramic oxide composite.

Landingham, R.L.

1993-10-12

402

Accelerators for studies of Warm Dense Matter  

Microsoft Academic Search

We determine requirements on ion beam accelerators needed for the study of warm dense matter physics using ion beams to isochorically heat matter to temperatures of order 1 to 10 eV and at 1 to 100 per cent solid density. We estimate the temperature uniformity of the heated foil, and explore the effects of ion beam velocity spread on the

John J. Barnard; Richard J. Briggs; Deborah A. Callahan; Ronald C. Davidson; Alex Friedman; Larry Grisham; Edward P. Lee; Richard W. Lee; B. Grant Logan; Jay N. Marx; David V. Rose; Andy M. Sessler; Max Tabak; Dale R. Welch; Jonathan S. Wurtele; Simon S. Yu

2004-01-01

403

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

404

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

405

Fitting smooth surfaces to dense polygon meshes  

Microsoft Academic Search

Recent progress in acquiring shape from range data permits the ac- quisition of seamless million-polygon meshes from physical mod- els. In this paper, we present an algorithm and system for con vert- ing dense irregular polygon meshes of arbitrary topology in to ten- sor product B-spline surface patches with accompanying displace- ment maps. This choice of representation yields a coarse

Venkat Krishnamurthy; Marc Levoy

1996-01-01

406

Dense Aluminum Plasma Equation of State Measurements  

NASA Astrophysics Data System (ADS)

Knowledge of the equation of state for any material is essential to a full understanding of its intrinsic and dynamic properties. Accurate experimental measurements of the equation of state for strongly coupled plasmas (? >= 1), relevant to astrophysical, geologic and ICF applications, have been extremely difficult. We present preliminary results on a novel method for off-Hugoniot measurements of the equation of state for dense plasmas (3 <= ? <= 16). A dense plasma jet is formed by expansion of a tamped exploding aluminum wire through an aperture. Up to 3.6 kJoules of energy is generated by a 300 kVolt, 100 kAmp, 4-stage Marx pulsed power device to create plasma densities of up to one-tenth solid and temperatures of a few eV from a 200 ?m diameter aluminum wire. Density and temperature profiles of the dense aluminum plasma are determined using laser-produced temporally- and spatially-resolved x-ray backlighters and optical streak records. Simulations indicate that the use of a laser-generated shock wave in the dense plasma can provide megabar pressures at 10 eV temperatures with ion densities of up to 10 times the initial density. Future experiments will concentrate on the use of this laser-generated shock to determine the equation of state through accurate density and shock-speed measurements.

Workman, J.; Tierney, T.; Kyrala Benage, G., Jr.

1997-11-01

407

THE SYMMETRY OF OPTIMALLY DENSE PACKINGS  

E-print Network

with packings of regular pentagons in the Euclidean plane, E 2 . First we recall that by a ``packing'' pTHE SYMMETRY OF OPTIMALLY DENSE PACKINGS by Charles Radin * Mathematics Department, University was the densest packings of simple bodies, for instance spheres or polyhedra, in Euclidean or hyperbolic spaces

408

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)

2006-04-01

409

Gravity-driven dense granular flows  

Microsoft Academic Search

Despite their importance in many areas of science and technology, the emergent physics of hard granular systems remain largely obscure, especially when the packing density approaches that of a jammed system. In particular, I will focus on the rheology of gravity-driven dense granular flows on an incline with a ``rough\\

Deniz Ertas

2002-01-01

410

Engineering fibrin polymers through engagement of alternative polymerization mechanisms  

PubMed Central

Fibrin is an attractive material for regenerative medicine applications. It not only forms a polymer but also contains cryptic matrikines that are released upon its activation/degradation and enhance the regenerative process. Despite this advantageous biology associated with fibrin, commercially available systems (e.g. TISSEEL) display limited regenerative capacity. This limitation is in part due to formulations that are optimized for tissue sealant applications and result in dense fibrous networks that limit cell infiltration. Recent evidence suggests that polymerization knob ‘B’ engagement of polymerization hole ‘b’ activates an alternative polymerization mechanism in fibrin, which may result in altered single fiber mechanical properties. We hypothesized that augmenting fibrin polymerization through the addition of PEGylated knob peptides with specificity to hole ‘b’ (AHRPYAAC-PEG) would result in distinct fibrin polymer architectures with grossly different physical properties. Polymerization dynamics, polymer architecture, diffusivity, viscoelasticity, and degradation dynamics were analyzed. Results indicate that specific engagement of hole ‘b’ with PEGylated knob ‘B’ conjugates during polymerization significantly enhances the porosity of and subsequent diffusivity through fibrin polymers. Paradoxically, these polymers also display increased viscoelastic properties and decreased susceptibility to degradation. As a result, fibrin polymer strength was significantly augmented without any adverse effects on angiogenesis within the modified polymers. PMID:22018389

Stabenfeldt, Sarah E.; Gourley, Merek; Krishnan, Laxminarayanan; Hoying, James B.; Barker, Thomas H.

2012-01-01

411

Formation of Globules, Pillars, and Dense Condensations Around H II Regions  

NASA Astrophysics Data System (ADS)

We present a new model for the formation of dense clumps and pillars around H II regions based on shocks curvature at the interface between a H II region and a molecular cloud. UV radiation leads to the formation of an ionization front and of a shock ahead. The gas is compressed between them forming a dense shell at the interface. This shell may be curved due to initial interface or density modulation caused by the turbulence of the molecular cloud. Low curvature leads to instabilities in the shell that form dense clumps while sufficiently curved shells collapse on itself to form pillars. When turbulence is high compared to the ionized-gas pressure, bubbles of cold gas have sufficient kinetic energy to penetrate into the H II region and detach themselves from the parent cloud, forming cometary globules. Using computational simulations, we show that these new models are extremely efficient to form dense clumps and stable and growing elongated structures, pillars, in which star formation might occur. The inclusion of turbulence in the model shows its importance in the formation of cometary globules. The code used for the simulation is the HERACLES code, that comprises hydrodynamics with various equation of state, radiative transfer, gravity, cooling and heating. We also present observational diagnostic of these new models based on the line-of-sight velocity profiles and probability density functions.

Tremblin, P.; Audit, E.

2013-04-01

412

Magnetic neutron stars in f( R) gravity  

NASA Astrophysics Data System (ADS)

Neutron stars with strong magnetic fields are considered in the framework of f( R) gravity. In order to describe dense matter in magnetic field, the model with baryon octet interacting through ???-fields is used. The hyperonization process results in softening the equation of state (EoS) and in decreasing the maximal mass. We investigate the effect of strong magnetic field in models involving quadratic and cubic corrections in the Ricci scalar R to the Hilbert-Einstein action. For large fields, the Mass-Radius relation differs considerably from that of General Relativity only for stars with masses close to the maximal one. Another interesting feature is the possible existence of more compact stable stars with extremely large magnetic fields (˜6×1018 G instead of ˜4×1018 G as in GR) in the central regions of the stars. Due to cubic terms, a significant increasing of the maximal mass is possible.

Astashenok, Artyom V.; Capozziello, Salvatore; Odintsov, Sergei D.

2015-02-01

413

Effect of Polymer Electrode Morphology on Performance of a Lithium/Polypyrrole Battery. M.S. Thesis  

NASA Technical Reports Server (NTRS)

A variety of conducting polymer batteries were described in the recent literature. In this work, a Li/Polypyrrole secondary battery is described. The effect of controlling the morphology of the polymer on enhancement of counterion diffusion in the polymer phase is explored. A method of preparing conducting polymers was developed which yields high surface area per unit volume of electrode material. A porous 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 fribrillar form, charge transport rates are faster and charge capacities are greater than for dense, conventionally grown films containing the same amount of polymer. The purpose is to expand previous work by further investigating the possibilities of the optimization of transport rates in polypyrrole films by controlling the morphology of the films. The utility of fibrillar polypyrrole as a cathode material in a lithium/polymer secondary battery is then assessed. The performance of the fibrillar battery is compared to the performance of an analogous battery which employed a conventionally grown polypyrrole film. The study includes a comparison of cyclic voltammetry, shape of charge/discharge curves, discharge time and voltage, cycle life, coulombic efficiencies, charge capacities, energy densities, and energy efficiencies.

Nicholson, Marjorie Anne

1991-01-01

414

Crust cooling of accretion-heated neutron stars  

NASA Astrophysics Data System (ADS)

We propose to continue our successful program to use the observed cooling of the crusts in accreting neutron star systems to probe the properties of ultra-dense matter. Those crusts are heated due to the accretion of matter onto neutron stars during the X-ray outburst and after the outbursts are over the crusts should cool down until they are in equilibrium with the core again. Following this cooling processes in several systems has already given us new insights in the structure of neutron stars (i.e., the crust but also the core and hence in ultra dense matter), but many uncertainties remain. Therefore it is needed to enlarge our sample of well studied sources to obtain better insights in the behavior of how neutron stars react to the accretion of matter.

Wijnands, Rudy

2014-09-01

415

Thermosetting Phthalocyanine Polymers  

NASA Technical Reports Server (NTRS)

Group of phthalocyanine polymers resist thermal degradation. Polymers expected semiconducting. Principal applications probably in molded or laminated parts that have to withstand high temperatures. Polymers made from either of two classes of monomer: Bisphthalonitriles with imide linkages or Bisphthalonitriles with ester-imide linkages.

Fohlen, G.; Parker, J.; Achar, B.

1985-01-01

416

Polymer Hydrogels: A Review  

Microsoft Academic Search

This review encompasses definitions, classification, main properties, and application of polymer hydrogels. Raw materials and preparation techniques of polymer hydrogels were described. The factors that affect absorption capacity and swelling properties of polymer hydrogels were reviewed. PHG materials are defined as a viscoelastic network structure, swellable and not soluble in water with high absorbent capacity, which may reach 1000 g\\/g of

Waham Ashaier Laftah; Shahrir Hashim; Akos N. Ibrahim

2011-01-01

417

Star Formation in a Crossing Time  

NASA Astrophysics Data System (ADS)

Observations suggest that star formation occurs in only one or two crossing times for a range of scales spanning a factor of ~1000. These observations include (1) measurements of embedded cluster ages in comparison with the cloud core dynamical times, (2) measurements of the age difference versus separation for clusters in the Large Magellanic Clouds in comparison with the crossing time versus size correlation for molecular clouds, (3) the hierarchical structure of embedded young clusters, and (4) the high fraction of dense clouds that contain star formation. Such a short overall timescale for star formation implies that sources of turbulent energy or internal feedback are not required to explain or extend cloud lifetimes and that star and protostar interactions cannot be important for the stellar initial mass function. Stars appear in a cloud as if they freeze out of the gas, preserving the turbulent-driven gas structure in their birth locations. The Galaxy-wide star formation rate avoids the Zuckerman-Evans catastrophe, which has long been a concern for molecular clouds that evolve this quickly, because the multifractal structure of interstellar gas ensures that only a small fraction of the mass is able to form stars. Star formation on large scales operates more slowly than on small scales, but in most cases the whole process is over in only a few dynamical times.

Elmegreen, Bruce G.

2000-02-01

418

Hunting for Shooting Stars in 30 Doradus  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

419

The pair potential of colloidal stars  

E-print Network

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

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

2008-12-06

420

Pair Potential of Charged Colloidal Stars  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

421

Dynamical Interactions in Dense Stellar Clusters  

E-print Network

This chapter reviews the dynamical processes in young stellar clusters. The accretion of gas by individual stars affects the dynamics of the cluster, and the masses of the stars. Dynamical mass segregation cannot explain the degree of mass segregation observed in clusters such as the Trapezium Cluster in Orion, implying that the location of the massive stars is an indication of where they formed. This can, however, be explained by the competitive accretion model. If most, if not all, stars form in binary systems, then the high proportion of pre-main sequence binary systems can evolve in clusters to the smaller proportion of Galactic field stars through binary-binary and binary-single interactions. These models make definite predictions for the distribution of binary properties. The early evolution of a cluster sensitively depends on the primordial binary star proportion. Close encounters between stars with circum-stellar discs have drastic effects on the discs and on the stellar orbits. The discs are truncate...

Bonnell, I A; Bonnell, Ian; Kroupa, Pavel

1998-01-01

422

Star Formation in Cluster Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of enhanced star formation in cluster dwarf galaxies by measuring the r- and u-band luminosity functions of several galaxy clusters using archival data from the Canada-France-Hawaii Telescope. Luminosity functions are created using various clustercentric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. An increase in the faint-end slope of the u-band luminosity function relative to the r-band indicates possible enhanced star formation. The location of the enhanced star formation from the cluster center may yield insights into what physical mechanisms are at work. In the cluster center, ram pressure from the ICM may; 1) compress the gas within a galaxy causing enhanced star formation, 2) remove the gas thus quenching star formation, or 3) compress and then remove the gas resulting in a burst of star formation followed by truncation. Alternatively, enhanced star formation near the edge of a cluster may signify galaxy-galaxy interactions as the dominant star formation mechanism as the ICM is generally less dense in this region.

Rude, Cody; Barkhouse, W.

2014-01-01

423

Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region  

NASA Astrophysics Data System (ADS)

Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ? several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular shells typical of luminous blue variable and late WN-type Wolf-Rayet stars.

Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

2011-11-01

424

Nanoparticle-polymer and polymer-polymer blend composite photovoltaics  

NASA Astrophysics Data System (ADS)

The main factors inhibiting higher conversion efficiencies in plain polymer layer sandwich photovoltaic devices are the low exciton dissociation efficiency and the low carrier mobilities in the polymer. We consider two different blend approaches for increasing these qualities. NiO (or LiNiO) hole transporting nanoparticles are blended into the photoactive polymer MEH-DOO-PPV in an attempt to increase hole mobility across the device. Improvements to device performance were not significant at these blend concentrations. Devices made using blends of hole and electron transporting polymers M3EH-PPV and CN-ether-PPV showed increased dissociation efficiency and gave power conversion efficiencies of up to 0.6% with stable electrodes.

Breeze, Alison J.; Schlesinger, Zack; Carter, Sue A.; Hoerhold, Hans-Heinrich; Tillmann, Hartwig; Ginley, David S.; Brock, Phillip J.

2001-02-01

425

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

426

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

427

Fire-safe polymers and polymer composites  

NASA Astrophysics Data System (ADS)

The intrinsic relationships between polymer structure, composition and fire behavior have been explored to develop new fire-safe polymeric materials. Different experimental techniques, especially three milligram-scale methods---pyrolysis-combustion flow calorimetry (PCFC), simultaneous thermal analysis (STA) and pyrolysis GC/MS---have been combined to fully characterize the thermal decomposition and flammability of polymers and polymer composites. Thermal stability, mass loss rate, char yield and properties of decomposition volatiles were found to be the most important parameters in determining polymer flammability. Most polymers decompose by either an unzipping or a random chain scission mechanism with an endothermic decomposition of 100--900 J/g. Aromatic or heteroaromatic rings, conjugated double or triple bonds and heteroatoms such as halogens, N, O, S, P and Si are the basic structural units for fire-resistant polymers. The flammability of polymers can also be successfully estimated by combining pyrolysis GC/MS results or chemical structures with TGA results. The thermal decomposition and flammability of two groups of inherently fire-resistant polymers---poly(hydroxyamide) (PHA) and its derivatives, and bisphenol C (BPC II) polyarylates---have been systematically studied. PHA and most of its derivatives have extremely low heat release rates and very high char yields upon combustion. PHA and its halogen derivatives can completely cyclize into quasi-polybenzoxazole (PBO) structures at low temperatures. However, the methoxy and phosphate derivatives show a very different behavior during decomposition and combustion. Molecular modeling shows that the formation of an enol intermediate is the rate-determining step in the thermal cyclization of PHA. BPC II-polyarylate is another extremely flame-resistant polymer. It can be used as an efficient flame-retardant agent in copolymers and blends. From PCFC results, the total heat of combustion of these copolymers or blends changes linearly with composition, but the change of maximum heat release rates also depends on the chemical structure of the components. The flammability of various polymers and polymer composites measured by PCFC, cone calorimeter ASTM E1354 and Ohio State University (OSU) calorimeter ASTM E906 were also compared. For pure polymers, there is a relatively good correlation between different methods. However, for polymer composites with inert fillers or flame-retardant additives, OSU and cone calorimetries are more suitable evaluation methods.

Zhang, Huiqing

428

Where is the Dust and Star Formation in Compact Groups of Galaxies?  

Microsoft Academic Search

Compact groups of galaxies provide a unique environment to study the mechanisms by which star formation occurs amid continuous gravitational encounters. These dense groups host a variety of modes of star formation, and they can provide insight into the role of gas in galaxy evolution. As part of a multi-wavelength effort to study compact groups of galaxies (spanning X-ray to

Kelsey Johnson; Jane Charlton; Sarah Gallagher; John Hibbard; Ann Hornschemeier

2004-01-01

429

Interior Solutions for Non-singular Gravity and the Dark Star alternative to Black Holes  

E-print Network

The general equations describing hydrostatic equilibrium are developed for Non-singular Gravity. A new type of astrophysical structure, a Super Dense Object (SDO) or "Dark Star", is shown to exist beyond Neutron star field strengths. These structures are intrinsically stable against gravitational collapse and represent the non-singular alternative to General Relativity's Black Holes.

Neil Cornish

1994-05-27

430

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

E-print Network

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

431

Low Mass Star Formation in Perseus: Large Field Mapping at 1mm with Bolocam  

Microsoft Academic Search

The earliest stages of low mass star formation, enshrouded in dense cores of dust and gas, are most easily studied at long wavelengths from the far-infrared to millimeter. SIRTF will provide unparalleled sensitivity in the 4-160 micron range, but coverage at longer wavelengths is necessary to developing a more complete picture of star formation in molecular clouds. As a complement

M. L. Enoch; A. I. Sargent; S. Golwala; J. Glenn; N. J. Evans II; K. E. Young

2003-01-01

432

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

433

Atomic Collision Processes in Dense Plasmas  

NASA Astrophysics Data System (ADS)

In the present work a detailed investigation of various atomic collision processes important to the determination of the structure and evolution of dense plasmas is presented. In volume 1 a study of general collisional processes in dense plasmas is given, while in volume 2 specific mechanisms by which energy is transferred among the constituents of a dense plasma is studied. Specifically, in chapter I, attention will be focused upon ion-ion recombination processes in dense plasmas, which involves the full set of multicomponent BBGKY equations appropriate for a three component gas composed of positive and negative ions, and neutral particles. This yields a set of coupled Boltzmann-type equations to be solved for the full phase-space evolution of the plasma, valid for arbitrary neutral gas density. In the limit of low (neutral) gas densities the theory in chapter I naturally tends to the exact quasi-equilibrium treatment of ion-ion recombination of Bates and Moffett, and Bates and Flannery. It also provides a firm basis for developing a fully general theory of recombination in dense plasmas subject to external electromagnetic fields as well as for dense plasmas with arbitrary ion densities. In chapter II symmetric resonance charge transfer processes Rg('+) + Rg (--->) Rg + Rg('+) for Rg = Ne, Ar, Kr, and Xe are studied via a quantal phase shift analysis. Accurate ab-initio and density functional potentials for the Rg(,2)('+), dimer are to be used, with the effects of spin-orbit coupling included, in order to compute elastic, charge-transfer, diffusion, and viscosity cross sections in the thermal energy region. In chapters III, IV of volume 2 the electron-impact excitation of excited hydrogen and helium atoms, respectively, are studied via the multichannel eikonal theory (MET) of Flannery and McCann. The MET is modified to account, asymptotically, for the strong dipole couplings present between the excited states of hydrogen and helium, thereby allowing accurate computation of differential and integral cross sections and the relevant orientation and alignment parameters.

Mansky, Edmund Jacob, II

434

Self-assembly of star micelle into vesicle in solvents of variable quality: the star micelle retains its core-shell nanostructure in the vesicle.  

PubMed

Intra- and intermolecular interactions of star polymers in dilute solutions are of fundamental importance for both theoretical interest and hierarchical self-assembly into functional nanostructures. Here, star micelles with a polystyrene corona and a small ionic core bearing platinum(II) complexes have been regarded as a model of star polymers to mimic their intra- and interstar interactions and self-assembled behaviors in solvents of weakening quality. In the chloroform/methanol mixture solvents, the star micelles can self-assemble to form vesicles, in which the star micelles shrink significantly and are homogeneously distributed on the vesicle surface. Unlike the morphological evolution of conventional amphiphiles from micellar to vesicular, during which the amphiphilic molecules are commonly reorganized, the star micelles still retain their core-shell nanostructures in the vesicles and the coronal chains of the star micelle between the ionic cores are fully interpenetrated. PMID:25634320

Liu, Nijuan; He, Qun; Bu, Weifeng

2015-03-01

435

Stars equilibrium  

NSDL National Science Digital Library

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

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

2003-01-01

436

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 ...

Mr. B

2007-11-10

437

Tycho's Star  

Microsoft Academic Search

A supernova remnant in Cassiopeia, 7.7° north of alpha 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

P. Murdin

2000-01-01

438

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

439

Dense packing crystal structures of physical tetrahedra  

E-print Network

We present a method for discovering dense packings of general convex hard particles and apply it to study the dense packing behavior of a one-parameter family of particles with tetrahedral symmetry representing a deformation of the ideal mathematical tetrahedron into a less ideal, physical, tetrahedron and all the way to the sphere. Thus, we also connect the two well studied problems of sphere packing and tetrahedron packing on a single axis. Our numerical results uncover a rich optimal-packing behavior, compared to that of other continuous families of particles previously studied. We present four structures as candidates for the optimal packing at different values of the parameter, providing an atlas of crystal structures which might be observed in systems of nano-particles with tetrahedral symmetry.

Yoav Kallus; Veit Elser

2010-11-17

440

Dense packing crystal structures of physical tetrahedra  

E-print Network

We present a method for discovering dense packings of general convex hard particles and apply it to study the dense packing behavior of a one-parameter family of particles with tetrahedral symmetry representing a deformation of the ideal mathematical tetrahedron into a less ideal, physical, tetrahedron and all the way to the sphere. Thus, we also connect the two well studied problems of sphere packing and tetrahedron packing on a single axis. Our numerical results uncover a rich optimal-packing behavior, compared to that of other continuous families of particles previously studied. We present four structures as candidates for the optimal packing at different values of the parameter, providing an atlas of crystal structures which might be observed in systems of nano-particles with tetrahedral symmetry.

Kallus, Yoav

2010-01-01

441

The dynamics of dense particle disks  

NASA Astrophysics Data System (ADS)

The authors investigate the mechanical equilibrium and collisional transport processes in differentially rotating dense particle disks in which the filling factor is not small, so that the ordinary Boltzmann kinetic theory is not accurate. The treatment is based on the Enskog theory of dense hard sphere gases, except that the spheres are inelastic. It is shown that the viscous instability which has been suggested as a source of the structure in Saturn's B ring does not arise in the authors' models. However, the ring may be subject to a phase transition similar to the liquid-solid transition seen in molecular dynamics simulations of elastic hard spheres; in this case the ring could have alternating zero-shear ("solid") and high-shear ("liquid") zones.

Araki, S.; Tremaine, S.

1986-01-01

442

Static dielectric properties of dense ionic fluids  

E-print Network

The static dielectric properties of dense ionic fluids, e.g., room temperature ionic liquids (RTILs) and inorganic fused salts, are investigated on different length scales by means of grandcanonical Monte Carlo simulations. A generally applicable scheme is developed which allows one to approximately decompose the electric susceptibility of dense ionic fluids into the orientation and the distortion polarization contribution. It is shown that at long range the well-known plasma-like perfect screening behavior occurs, which corresponds to a diverging distortion susceptibility, whereas at short range orientation polarization dominates, which coincides with that of a dipolar fluid of attached cation-anion pairs. This observation suggests that the recently debated interpretation of RTILs as dilute electrolyte solutions might not be simply a yes-no-question but it might depend on the considered length scale.

Zarubin, Grigory

2015-01-01

443

Static dielectric properties of dense ionic fluids  

E-print Network

The static dielectric properties of dense ionic fluids, e.g., room temperature ionic liquids (RTILs) and inorganic fused salts, are investigated on different length scales by means of grandcanonical Monte Carlo simulations. A generally applicable scheme is developed which allows one to approximately decompose the electric susceptibility of dense ionic fluids into the orientation and the distortion polarization contribution. It is shown that at long range the well-known plasma-like perfect screening behavior occurs, which corresponds to a diverging distortion susceptibility, whereas at short range orientation polarization dominates, which coincides with that of a dipolar fluid of attached cation-anion pairs. This observation suggests that the recently debated interpretation of RTILs as dilute electrolyte solutions might not be simply a yes-no-question but it might depend on the considered length scale.

Grigory Zarubin; Markus Bier

2015-03-06

444

Color Superconductivity in Compact Stars  

NASA Astrophysics Data System (ADS)

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

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

445

Droplet interaction of adiabatic dense sprays  

Microsoft Academic Search

The effect of the droplet interactions which arise in the interior of dense sprays is examined by considering the vaporization\\u000a of a single droplet in a confined region or “bubble”. In the present study the temporal variation of vaporization was determined\\u000a at two levels of approximation, such as “film analysis” and “quasi-steady analysis”. Thermodynamic analysis was used to determine\\u000a the

Suk Ho Lee; Hho-Jung Kim

1991-01-01