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1

Effect of arm exchange on the liquid-solid transition of dense suspensions of star polymers.  

PubMed

Star polymers with dynamic arm exchange are formed in water by self-assembly of amphiphilic diblock copolymers based on poly(ethylene oxide) end capped with a small hydrophobic block. The arm exchange was arrested in situ by photo-cross-linking of the core. The effect of dynamic arm exchange on the osmotic compressibility and viscosity was investigated systematically as a function of the concentration and temperature. The discontinuous liquid-solid transition reported for dense polymeric micelle suspensions was found to be preserved after dynamic arm exchange was arrested in situ. The effect of cross-linking and aggregation number on the liquid-solid transition was investigated. PMID:24015766

Puaud, Fanny; Nicolai, Taco; Benyahia, Lazhar; Nicol, Erwan

2013-10-10

2

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

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

3

Polydisperse star polymer solutions  

PubMed

We analyze the effect of polydispersity in the arm number on the effective interactions, structural correlations, and phase behavior of star polymers in a good solvent. The effective interaction potential between two star polymers with different arm numbers is derived using scaling theory. The resulting expression is tested against monomer-resolved molecular dynamics simulations. We find that the theoretical pair potential is in agreement with the simulation data in a much wider polydispersity range than other proposed potentials. We then use this pair potential as an input in a many-body theory to investigate polydispersity effects on the structural correlations and the phase diagram of dense star polymer solutions. In particular, we find that a polydispersity of 10%, which is typical in experimental samples, does not significantly alter previous findings for the phase diagram of monodisperse solutions. PMID:11102050

von Ferber C; Jusufi; Watzlawek; Likos; Lowen

2000-11-01

4

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

5

Dense Gas Processing of Polymers  

Microsoft Academic Search

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

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

2010-01-01

6

Multiarm star polymers dynamics  

NASA Astrophysics Data System (ADS)

Multiarm star polymers, consisting of a high number of linear homopolymer arms joined covalently to a central core, represent model soft 'hybrid' spheres encompassing both polymeric (arm) and colloidal (core) character. Due to this topology, the single star has a nonuniform monomer density distribution. In nondilute solutions, a liquid-like ordering occurs as a consequence of the enhanced osmotic pressure that outbalances the entropic stretching of the arms; this type of order persists in the melt as well, due to 'macromolecular excluded volume' effects. The resulting rich dynamic response, which is presented in this review, exhibits signatures of both polymeric and colloidal behaviour. In solution, concentration and number density fluctuations relax via cooperative diffusion, self-diffusion and structural relaxation. In the melt, the viscoelastic terminal relaxation involves arm relaxation (independent of arm number) and structural rearrangements of the stars (strongly dependent on arm number and size). The identification of the relaxation mechanisms in such complex soft spheres provides the necessary ingredients for the molecular design and control of novel composite materials combining properties of polymers and colloids.

Vlassopoulos, Dimitris; Fytas, George; Pakula, Tadeusz; Roovers, Jacques

2001-10-01

7

Multiarm Star Polymers as Model Soft Colloids  

NASA Astrophysics Data System (ADS)

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

Vlassopoulos, Dimitris

2010-03-01

8

Evolution of the binary population in young dense star clusters  

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

9

Solvable critical dense polymers on the cylinder  

NASA Astrophysics Data System (ADS)

A lattice model of critical dense polymers is solved exactly on a cylinder with finite circumference. The model is the first member {\\cal LM}(1,2) of the Yang-Baxter integrable series of logarithmic minimal models. The cylinder topology allows for non-contractible loops with fugacity ? 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 = - (J3 - 12J)/16 = (-1)F with eigenvalues R=(-1)^{\\ell /2} . This is reminiscent of supersymmetry with a pair of defects interpreted as a fermion. The number of defects \\ell thus separates the theory into Ramond (\\ell /2 even), Neveu-Schwarz (\\ell /2 odd) and \\mathbb {Z}_4 (\\ell odd) sectors. For the case of loop fugacity ? = 2, the inversion identity is solved exactly sector by sector for the eigenvalues in finite geometry. The eigenvalues are classified according to the physical combinatorics of the patterns of zeros in the complex spectral-parameter plane. This yields selection rules for the physically relevant solutions to the inversion identity. The finite-size corrections are obtained from Euler-Maclaurin formula. In the scaling limit, we obtain the conformal partition functions as sesquilinear forms and confirm the central charge c = - 2 and conformal weights \\Delta,\\bar {\\Delta }=\\Delta_t=(t^2-1)/8 . Here t=\\ell /2 and t=2r-s\\in \\mathbb {N} in the \\ell even sectors with Kac labels r = 1, 2, 3,...;s = 1, 2 while t\\in \\mathbb {Z}-\\frac 12 in the \\ell odd sectors. Strikingly, the \\ell /2 odd sectors exhibit a {\\cal 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.

Pearce, Paul A.; Rasmussen, Jørgen; Villani, Simon P.

2010-02-01

10

Dense Quark Matter in Compact Stars  

NASA Astrophysics Data System (ADS)

According to quantum chromodynamics (QCD), matter at ultra-high densities will take the form of a color-superconducting quark liquid, in which there is a condensate of Cooper pairs of quarks near the Fermi surface. I present a review of the physics of color superconductivity, and discuss possible signatures by which it might be detected in compact stars. I give a detailed discussion of the effects of color superconductivity on the mass-radius relationship of compact stars, showing that one would have to fix the bag constant by other measurements in order to see the effects of color superconductivity. An additional parameter in the quark matter equation of state connected with perturbative corrections allows quark matter to imitate nuclear matter over the relevant density range, so that hybrid stars can show a mass-radius relationship very similar to that of nuclear matter, and their masses can reach 1.9 M?.

Alford, M. G.

2004-04-01

11

Formation and evolution of black holes in dense star clusters  

NASA Astrophysics Data System (ADS)

Using supercomputer simulations combining stellar dynamics and stellar evolution, we have studied various problems related to the existence of black holes in dense star clusters. We consider both stellar and intermediate-mass black holes, and we focus on massive, dense star clusters, such as old globular clusters and young, so called "super star clusters." The first problem concerns the formation of intermediate-mass black holes in young clusters through the runaway collision instability. A promising mechanism to form intermediate-mass black holes (IMBHs) is runaway mergers in dense star clusters, where main-sequence stars collide re- peatedly and form a very massive star (VMS), which then collapses to a black hole (BH). Here 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 to model systems with N as high as 10^6 stars. Our Monte Carlo code includes an explicittreatment 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 (tcc). Although for smaller degrees of primordial mass segregation this decrease in tcc 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 tcc. Finally, flatter IMFs generally increase the average mass in the whole cluster, which increases tcc. For the range of IMFs investigated in this thesis, this increase in tcc is to some degree balanced by stellar collisions, which accelerate core collapse. Thus there is no significant change in tcc for the somewhat flatter global IMFs observed in very young massive clusters The second and third problems concern stellar-mass black holes in star clusters. First, we perform a systematic study of how black hole remnants form and evolve in young star clusters (ages ˜ 10 - 100 Myr). Using our Monte Carlo code for stellar dynamics, we model realistic star clusters with N ? 5 x 105 stars and significant binary fractions (up to 50%) with self-consistent treatments of stellar dynamics and stellar evolution. We compute the formation rates and charac- teristic properties of single and binary BHs for various representative ages, cluster parameters, and metallicities. Because of dynamical interactions and supernova (SN) kicks, more single BHs end up retained in clusters compared to BHs in binaries. We also find that the ejection of BHs from a cluster is a strong function of initial density. In low-density clusters (where dynamical effects are negligible), it is mainly SN kicks that eject BHs from the cluster, whereas in high-density clusters (initial central density rhoc(0) ˜ 105 M ? pc-3 in our models) the BH ejection rate is enhanced significantly by dynamics. Dynamical interactions of binary systems in dense clusters also modify the orbital period and eccentricity distributions while also increasing the probability of a BH having a more massive companion. As a last project, we re-examine the dynamical evolution of stellar BHs in old globular clusters, focusing especially on the related issues of energy equipartition and appearance of the Spitzer instability. It is expected from simple statistical mechanics arguments that dense star clusters evolve over many relaxations times towards a state of energy equipartition. We show in this last part of my thesis that this is not always true, using Monte Carlo simulations with realistic N and varying different initial parameters.

Goswami, Sanghamitra

12

THE FORMATION OF YOUNG DENSE STAR CLUSTERS THROUGH MERGERS  

SciTech Connect

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

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

2012-07-01

13

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

14

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

15

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

16

A proof of selection rules for critical dense polymers  

NASA Astrophysics Data System (ADS)

Among the lattice loop models defined by Pearce et al (2006 J. Stat. Mech. P11017), the model corresponding to critical dense polymers (? = 0) is the only one for which an inversion relation for the transfer matrix DN(u) was found by Pearce and Rasmussen (2007 J. Stat. Mech. P02015). From this result, they identified the set of possible eigenvalues for DN(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 TLN(?) algebra between the loop model link representation and that of the XXZ model for ? = -(q + q-1).

Morin-Duchesne, Alexi

2011-12-01

17

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

18

Well-behaved relativistic charged super-dense star models  

NASA Astrophysics Data System (ADS)

A new class of charged super-dense star models is obtained by using an electric intensity, which involves a parameter, K. The metric describing the model shares its metric potential g 44 with that of Durgapal's fourth solution (J. Phys. A, Math. Gen. 15:2637, 1982). The pressure-free surface is kept at the density ? b =2×1014 g/cm3 and joins smoothly with the Reissner-Nordstrom solution. The charge analogues are well-behaved for a wide range, 0? K?59, with the optimum value of X=0.264 i.e. the pressure, density, pressure-density ratio and velocity of sound are monotonically decreasing and the electric intensity is monotonically increasing in nature for the given range of the parameter K. The maximum mass and the corresponding radius occupied by the neutral solution are 4.22 M ? and 20 km, respectively for X=0.264. For the charged solution, the maximum mass and radius are defined by the expressions M?(0.0059 K+4.22) M ? and r b ?-0.021464 K+20 km respectively.

Faruqi, Shahab; Pant, Neeraj

2012-10-01

19

Interfacial Micellar Structures from Novel Amphiphilic Star Polymers  

SciTech Connect

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

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

2010-11-10

20

Stellar Collisions and Blue Straggler Stars in Dense Globular Clusters  

NASA Astrophysics Data System (ADS)

Blue Stragglers (BS) are stars that are brighter and bluer than the main-sequence (MS) turn-off in its neighborhood. Observations have revealed BSs in open, and globular clusters (GC) and even in the field. They are created either via physical collisions involving at least one MS star, or via mass transfer in a binary from a more evolved star to a MS star. Both processes are dependent on the environment and its dynamical history. Hence, understanding the dominant formation channel, and the typical formation ages of present-day BSs are interesting but they are not accessible via observations alone. We create over hundred detailed star-by-star N-body models of star clusters with properties typical of the Galactic GCs including all relevant physics. We identify the blue straggler stars. These models can be directly compared with the observed clusters. Our models reproduce all observed correlations between the number of BSs and a number of dynamically important cluster properties. We find that binary-mediated collisions dominate BS production in typical Galactic GCs. We further find that the present day BSs could have formed many billion years ago.

Chatterjee, Sourav; Rasio, F. A.; Sills, A.; Glebbeek, E.

2013-06-01

21

ATCA Imaging of Dense Gas in Star-Forming Environments  

NASA Astrophysics Data System (ADS)

The HCN (J=1-0) line is the primary indicator of dense (105 cm-3) molecular gas for extragalactic studies. However, the reliability of HCN as a tracer of dense gas mass has been questioned, given the possibility of abundance variations or mid-IR pumping. Alternatively, HCO+ has been proposed as a superior tracer of dense gas, although it may be enhanced along with ionized carbon in the presence of strong radiation fields. To investigate the variation in the HCN/HCO+ ratio across different environments, we have performed high-resolution simultaneous imaging in HCN and HCO+ of a circumnuclear starburst lacking nuclear activity (NGC 7552) and an HII region within the Large Magellanic Cloud (N113) using the upgraded Australia Telescope Compact Array. Variations in the HCN/HCO+ ratio as a function of spatial scale and IR emission brightness are discussed. This research was supported by an ARC/CSIRO Linkage Grant and the U. of Illinois.

Wong, Tony H.; Ott, J.; Ryder, S. D.; Kohno, K.; Buta, R.; Dahlem, M.; Whiteoak, J. B.; Chin, Y.; Cunningham, M. R.

2006-12-01

22

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

23

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

24

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

25

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

26

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

NASA Technical Reports Server (NTRS)

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

Myers, Philip C.

2002-01-01

27

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

28

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

29

Stellar Collisions and Blue Straggler Stars in Dense Globular Clusters  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

30

Mechanical properties of a fully dense polymer derived ceramic made by a novel pressure casting process  

Microsoft Academic Search

A new process has been developed for obtaining fully dense samples of silicon carbonitride (SiCN) from polymers. The process consists of two simple steps: cross-linking the liquid organic precursor under pressure, followed by controlled pyrolysis. Net shape processing is possible by casting the liquid into a mold before polymerization. The entire process is completed below 1000 °C. Basic mechanical properties

Sandeep R Shah; Rishi Raj

2002-01-01

31

Nature of Stress on the Atomic Level in Dense Polymer Systems  

Microsoft Academic Search

Stress in dense polymer systems is classically viewed as being molecular in character and is based on the entropic spring concept. A description on the atomic level has been developed on the basis of extensive computer simulations. An important new concept is the intrinsic monomer stress (IMS), the individual monomer contribution to the macroscopic stress referred to a local moving

Jianping Gao; Jerome H. Weiner

1994-01-01

32

The Neutron Star Mass-Radius Relation and the Equation of State of Dense Matter  

NASA Astrophysics Data System (ADS)

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

Steiner, Andrew W.; Lattimer, James M.; Brown, Edward F.

2013-03-01

33

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

SciTech Connect

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

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

2013-03-01

34

Extending the Mbh-? diagram with dense nuclear star clusters  

NASA Astrophysics Data System (ADS)

Four new nuclear star cluster masses, Mnc, plus seven upper limits, are provided for galaxies with previously determined black hole masses, Mbh. Together with a sample of 64 galaxies with direct Mbh measurements, 13 of which additionally now have Mnc measurements rather than only upper limits, plus an additional 29 dwarf galaxies with available Mnc measurements and velocity dispersions ?, an ? diagram is constructed. Given that major dry galaxy merger events preserve the Mbh/L ratio, and given that L??5 for luminous galaxies, it is first noted that the observation Mbh??5 is consistent with expectations. For the fainter elliptical galaxies it is known that L??2, and assuming a constant Mnc/L ratio, the expectation that Mnc??2 is in broad agreement with our new observational result that Mnc??1.57 ± 0.24. This exponent is however in contrast to the value of ˜4 which has been reported previously and interpreted in terms of a regulating feedback mechanism from stellar winds. Finally, it is predicted that host galaxies fainter than MB˜-20.5 mag (i.e. those not formed in dry merger events) which follow the relation Mbh??5, and are thus not 'pseudo-bulges', should not have a constant Mbh/Mhost ratio but instead have ?. It is argued that the previous near-linear ? and ? relations have been biased by the sample selection of luminous galaxies, and as such should not be used to constrain the co-evolution of supermassive black holes in galaxies other than those luminous few built by major dry merger events.

Graham, Alister W.

2012-05-01

35

Irreversible polymer adsorption from semidilute and moderately dense solutions  

NASA Astrophysics Data System (ADS)

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

Zajac, Richard; Chakrabarti, Amitabha

1995-12-01

36

The linear rheological responses of dense branched brush polymers with different side chain lengths and structures  

NASA Astrophysics Data System (ADS)

We examined the linear rheological responses of three kinds of dense and regular branched brush polymers. Brush polymers with different degree of polymerization were synthesized from the ?-Norbornenyl macromolecule (as main chain) with linear, three combined short arms, and dendronized brush structures. The master curves for these brush polymers were obtained by time temperature superposition (TTS) of the dynamic moduli from the glassy plateau region to the terminal flow region. The glassy modulus and rubbery modulus for these brush polymers were greatly influenced by the side chain properties. Two different relaxation processes can be observed for those samples with the higher molecular weight, slightly entangled, side chains. The dilution effect of the side chain which is related to the side chain volume fraction doesn't follows theoretical expectations.

Hu, Miao; McKenna, Gregory; Xia, Yan; Daeffler, Chris; Boydston, Andrew; Grubbs, Robert; Kornfield, Julia

2011-03-01

37

Nature of stress on the atomic level in dense polymer systems.  

PubMed

Stress in dense polymer systems is classically viewed as being molecular in character and is based on the entropic spring concept. A description on the atomic level has been developed on the basis of extensive computer simulations. An important new concept is the intrinsic monomer stress (IMS), the individual monomer contribution to the macroscopic stress referred to a local moving coordinate system in which the backbone bonds attached to that monomer are fixed. The IMS is time-independent and, for a given polymer system at fixed density, has the same value in the equilibrium melt, with the melt undergoing stress relaxation, and in the deformed cross-linked system. PMID:17730395

Gao, J; Weiner, J H

1994-11-01

38

Pair-instability supernovae via collision runaway in young dense star clusters  

NASA Astrophysics Data System (ADS)

Stars with helium cores between ˜64 and 133 M? are theoretically predicted to die as pair-instability supernovae. This requires very massive progenitors, which are theoretically prohibited for Pop II/I stars within the Galactic stellar mass limit due to mass-loss via line-driven winds. However, the runaway collision of stars in a dense, young star cluster could create a merged star with sufficient mass to end its life as a pair-instability supernova, even with enhanced mass-loss at non-zero metallicity. We show that the predicted rate from this mechanism is consistent with the inferred volumetric rate of roughly ˜2 × 10-9 Mpc-3 yr-1 of the two observed pair-instability supernovae, SN 2007bi and PTF 10nmn, neither of which has metal-free host galaxies. Contrary to prior literature, only pair-instability supernovae at low redshifts z < 2 will be observable with the Large Synoptic Survey Telescope. We estimate that the telescope will observe ˜102 such events per year that originate from the collisional runaway mergers in clusters.

Pan, Tony; Loeb, Abraham; Kasen, Daniel

2012-07-01

39

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

NASA Astrophysics Data System (ADS)

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

Kumar, Jitendra; Gupta, Y. K.

2013-06-01

40

Phase behavior of athermal colloid-star polymer mixtures  

NASA Astrophysics Data System (ADS)

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

Mahynski, Nathan A.; Panagiotopoulos, Athanassios Z.

2013-07-01

41

Comparing different coarse-grained potentials for star polymers.  

PubMed

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

Menichetti, Roberto; Pelissetto, Andrea

2013-03-28

42

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

43

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

44

High performance gene delivery polymeric vector: nano-structured cationic star polymers (star vectors).  

PubMed

Nano-structured hyperbranched cationic star polymers, called star vectors, were molecularly designed for a novel gene delivery non-viral vector. The linear and 3, 4 or 6 branched water-soluble cationic polymers, which had same molecular weight of ca. 18,000, were synthesized by iniferter (initiator-transfer agent-terminator)-based photo-living-radical polymerization of 3-(N,N-dimethylamino)propyl acrylamide, initiated from respective multi-dithiocarbamate-derivatized benzenes as an iniferter. All polymers produced polyion complexes 'polyplexes' by mixing with pDNA (pGL3-control plasmid), in which the particle size was ca. 250 nm in diameter [the charge ratio < 2/1 (vevtor/pDNA)] and ca. 150 nm (the charge ratio > 2.5/1), and the zeta-potential was ca. +10 mV (the charge ratio > 1/1). When COS-1 cells were incubated with the polyplexes 12 h after preparation under the charge ratio of 5/1, higher gene expression was obtained as an increase in branching, with a little cytotoxicity. The relative gene expression to the linear polymer was about 2, 5, and 10 times in 3-, 4-, and 6-branched polymers, respectively. The precise change in branching of polymers enabled the control of the gene transfer activity. PMID:16305408

Nakayama, Yasuhide; Masuda, Takeshi; Nagaishi, Makoto; Hayashi, Michiko; Ohira, Moto; Harada-Shiba, Mariko

2005-01-01

45

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

46

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

47

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

PubMed

Protein-polymer conjugates exhibit superior properties to unmodified proteins, generating a high demand for these materials in the fields of medicine, biotechnology, and nanotechnology. Multimeric conjugates are predicted to surpass the activity of monomeric conjugates. Herein, we report a straightforward method to synthesize multimeric polymer-conjugates. Four armed poly(N-isopropylacrylamide) (pNIPAAm) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of a tetra-functionalized trithiocarbonate chain transfer agent (CTA). The polymer molecular weight, architecture and polydispersity index (PDI) were verified by gel permeation chromatography (GPC), dynamic light scattering gel permeation chromatography (DLS-GPC), and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This approach afforded well-defined polymers (PDI's < 1.06) and the ability to target various molecular weights. Maleimide functional groups were introduced at the chain ends by heating the polymers in the presence of a furan-protected azo-initiator. This allowed for site-specific conjugation of V131C T4 lysozyme to the polymers to generate multimeric protein-polymer conjugates. MALDI-TOF mass spectrometry, electrospray ionization gas-phase electrophoretic-mobility macromolecule analysis (ESI-GEMMA), gel electrophoresis, and liquid chromatography tandem mass spectrometry (LC-MS/MS) of the trypsin digests demonstrated that multimeric protein-polymer conjugates had formed. This simple strategy provides ready access to star protein-polymer conjugates for application in the fields of drug discovery, drug delivery, and nanotechnology. PMID:21544227

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

2009-11-10

48

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm  

NASA Astrophysics Data System (ADS)

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-?m thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (<0.2 nm) and high side-lobe suppression (<-30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (<0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.

Sato, Atsushi; Scepanovic, Miodrag; Kostuk, Raymond K.

2003-02-01

49

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

PubMed

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

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

2013-05-13

50

Radiation-driven winds of hot luminous stars XVI. Expanding atmospheres of massive and very massive stars and the evolution of dense stellar clusters  

NASA Astrophysics Data System (ADS)

Context. Starbursts play an essential role in the evolution of galaxies. In these environments, massive stars, with their short lifetimes, are of particular importance. The stellar winds of massive stars significantly influence not only on their surroundings, but the associated mass loss also profoundly affects the evolution of the stars themselves. The evolution of the dense cores of massive starburst clusters is also affected by dynamical processes induced by N-body interactions, in addition to the evolution of each star, and the formation of very massive stars with masses up to several thousand solar masses may be decisive for the evolution of the cluster. The interpretation of the corresponding observations relies mainly on the theoretical modeling of such starbursts, which is a major challenge. Aims: The primary objective is to introduce an advanced diagnostic method of O-type stellar atmospheres with winds, including an assessment of the accuracy of the determinations of abundances, stellar and wind parameters. Moreover, observational results are interpreted in the framework of our stationary, one-dimensional theory of line driven winds. Possible effects caused by non-homogeneous time dependent structures are also discussed. Methods: We combine consistent models of expanding atmospheres with stellar evolutionary calculations of massive and very massive (up to several 1000 solar masses) single stars with regard to the evolution of dense stellar clusters. Essential in this context are accurate dynamic parameters of the winds of very massive stars. Because the atmospheric mass outflow has substantial influence on the radiation field and the atomic occupation numbers, and the radiation field and the occupation numbers in turn directly influence the radiative acceleration and thus the strength and velocity of the outflow, the determination of the hydrodynamic structures requires a highly consistent treatment of the statistical equilibrium and the hydrodynamic and radiative processes in the expanding atmospheres. Results: We present computed mass loss rates, terminal wind velocities, and spectral energy distributions of massive and very massive stars of different metallicities, calculated from atmospheric models with an improved level of consistency. These computations have important implications for (i) the primordial chemical enrichment of Population III very massive stars; (ii) the age determination of globular clusters; and (iii) the formation of intermediate mass black holes in dense stellar clusters with respect to the importance of stellar wind mass loss for the evolution of their progenitor stars. Conclusions: Stellar evolutionary calculations, using the mass loss rates of very massive stars obtained in the present paper, show that very massive stars with a low metallicity lose only a very small amount of their mass; thus it is unlikely that very massive population III stars cause a significant helium enrichment of the interstellar medium. Solar-metallicity stars have higher mass-loss rates, but these are not so high to exclude very massive stars of solar metallicity, formed by dynamical processes in dense clusters, from ending their life massive enough to form intermediate-mass black holes.

Pauldrach, A. W. A.; Vanbeveren, D.; Hoffmann, T. L.

2012-02-01

51

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

NASA Astrophysics Data System (ADS)

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

Gomez, Lizabeth

52

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

NASA Astrophysics Data System (ADS)

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

Kudo, Takuya; Ishigure, Takaaki

2014-03-01

53

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

54

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.

Nardai, Michael M.; Zifferer, Gerhard

2013-01-01

55

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

56

Versatile and efficient functionalisation of multiallylic dendronised polymers: can dense packing be reached?  

PubMed

Surface modification of a multiallylic dendronised polymer was performed using hydrosilylation, hydroboration or radical addition of thiols to cover the polymer with various functional moieties; surface congestion is expected to occur when bulky groups are grafted. PMID:18389127

Moingeon, Firmin; Roeser, Jérôme; Masson, Patrick; Arnaud, Françoise; Méry, Stéphane

2008-03-21

57

Constraints on R-mode Amplitudes in LMXB Neutron Stars: Probing the Phases of Ultra-dense Matter  

NASA Astrophysics Data System (ADS)

The phases of ultra-dense neutron star (NS) matter can be probed with X-ray observations that constrain the evolution of the dynamic properties of NSs, such as their spin period and temperature. While their bulk properties, such as mass and radius, depend on the equation of state (EOS) of dense matter, the dynamic properties of NSs also depend on the low energy degrees of freedom, because they are affected by the transport and thermodynamic properties of dense matter such as neutrino emissivity, viscosity and heat capacity. As different phases of dense matter have very different low energy degrees of freedom, the dynamic properties of NSs can efficiently discriminate between them. The r-mode oscillations of NSs can be potentially powerful probes of ultra-dense NS matter, because they couple the low energy degrees of freedom of dense matter to macroscopic dynamic observables, such as the spin period. Here we present upper limits on the amplitude of r-mode oscillations, and their gravitational-radiation-induced spin-down rates, in LMXB neutron stars under the assumption that the quiescent NS luminosity is powered by dissipation from a steady-state r-mode. We calculated results for NS models constructed with the APR EOS for masses of 1.4, 2 and 2.21 $M_{sun}$. For the lower mass NS models (1.4 and 2 $M_{sun}$) we find dimensionless r-mode amplitudes in the range from about $1\\times 10^{-8}$ to $1.5\\times 10^{-6}$. At these amplitudes less than 2% of the observed, quiescent spin-down rates in these sources can be due to gravitational radiation from unstable r-modes. Our highest mass model (2.21 $M_{sun}$) can support enhanced, direct URCA neutrino emission in the core and thus can have higher r-mode amplitudes. Indeed, the inferred r-mode spin-down rates at these higher amplitudes are inconsistent with the observed spin-down rates for some of the LMXB sources, such as IGR J00291+5934 and XTE J1751-305. This can be used to put an upper limit on the masses of these sources if they are made of normal nuclear matter, or it could be used to probe the existence of exotic matter in these sources if the NS mass in these systems were known.

Mahmoodifar, Simin; Strohmayer, T. E.

2013-04-01

58

Uniform PEO star polymers synthesized in water via free radical polymerization or atom transfer radical polymerization.  

PubMed

Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross-linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple "arm-first" method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross-linked by divinylbenzene (DVB) using 2,2'-azoisobutyronitrile (AIBN). Uniform star polymers (Mw/Mn < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross-linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP. PMID:21432973

Li, Wenwen; Matyjaszewski, Krzysztof

2011-01-01

59

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

Microsoft Academic Search

An equation of state (EOS) of neutron star matter, describing both the neutron star crust and the liquid core, is calculated. It is based on the effective nuclear interaction SLy of the Skyrme type, which is particularly suitable for the application to the calculation of the properties of very neutron rich matter (Chabanat et al. 1997, 1998). The structure of

F. Douchin; P. Haensel

2001-01-01

60

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

61

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

62

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

Microsoft Academic Search

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

P. Haensel

2003-01-01

63

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

SciTech Connect

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

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

2010-07-27

64

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

NASA Astrophysics Data System (ADS)

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

Chen, Han-Wen

2001-12-01

65

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

NASA Astrophysics Data System (ADS)

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

Douchin, F.; Haensel, P.

2001-12-01

66

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

NASA Astrophysics Data System (ADS)

Equilibrium configurations of cold neutron stars near the minimum mass are studied, using the recent equation of state SLy, which describes in a unified, physically consistent manner, both the solid crust and the liquid core of neutron stars. Results are compared with those obtained using an older FPS equation of state of cold catalyzed matter. The value of Mmin =~ 0.09 Msun depends very weakly on the equation of state of cold catalyzed matter: it is 0.094 Msun for the SLy model, and 0.088 Msun for the FPS one. Central density at Mmin is significantly lower than the normal nuclear density: for the SLy equation of state we get central density 1.7x 1014 g cm-3, to be compared with 2.3x 1014 g cm-3 obtained for the FPS one. Even at Mmin, neutron stars have a small liquid core of radius of about 4 km, containing some 2-3% of the stellar mass. Neutron stars with 0.09 Msunstars is studied. Rotation increases the value of Mmin; at rotation period of 10 ms the minimum mass of neutron stars increases to 0.13 Msun, and corresponds to the mass-shedding (Keplerian) configuration. In the case of the shortest observed rotation period of radio pulsars 1.56 ms, minimum mass of uniformly rotating cold neutron stars corresponds to the mass-shedding limit, and is found at 0.61 Msun for the SLy EOS and 0.54 Msun for the FPS EOS.

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

2002-04-01

67

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

PubMed

A luminous X-ray source is associated with MGG 11--a cluster of young stars approximately 200 pc 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 (350 M(o)), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800-3,000 M(o) which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11. PMID:15085124

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

2004-04-15

68

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

PubMed

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

Drumheller, P D; Hubbell, J A

1995-02-01

69

Stars  

NASA Astrophysics Data System (ADS)

We will begin our study with a more or less superficial inspection of the "forest" of stars that we see in the skies. The first thing we notice is that, as sources of light, they are much weaker than the Sun. Second, their apparent colors vary; from a bluish-white in most of them to a reddish-yellow, which is rarer. There is also a third aspect, though it is not very obvious to the naked eye: most of the stars group themselves in small families of two, three or more members. A good example is the Alpha Centauri, the closest star to us, which, in fact, is a triple system of stars. Another is the group of 7 stars that make up the Pleiades, which will be discussed later on. In fact, almost half of the stars are double systems with only two members, called binary stars. Most of these double stars, though together, are separated by several astronomical units (one astronomical unit, AU, is the distance from Earth to the sun: see Chapter 1), and revolve around each other over periods of several years. And yet the revolutions of some binary stars, separated by much smaller distances, occur in only a few hours! These stars are so close to each other that they can share enveloping material. Often this exchange occurs in a somewhat violent manner. Local explosions may occur, expelling matter away from the system. In other binary systems, where one of the components is a very compact, dense star, companion material flows more calmly, making up a light disk around the compact star.

Capelato, Hugo Vicente

1999-01-01

70

Synthesis of functional core, star polymers via RAFT polymerization for drug delivery applications.  

PubMed

Poly(oligoethylene glycol) methyl ether acrylate was polymerized via reversible addition fragmentation transfer polymerization (RAFT), and then chain extended in the presence of both a cross-linker and vinyl benzaldehyde (VBA), yielding monodisperse star polymers. The presence of aldehyde groups in the core was exploited to attach doxorubicin. The drug loading was controlled by the amount of VBA incorporated (until 28 wt% in drug). The doxorubicin release was studied at pH = 5.5 and 7.4; conditions representative of endosomal and extra cellular environments. In vitro studies revealed that the doxorubicin-conjugated star polymers had a level of cytotoxicity comparable to that found for free doxorubicin. Confocal microscopy and flow cytometry studies confirmed efficient cell uptake of the star polymers. PMID:22495770

Liu, Jinna; Duong, Hien; Whittaker, Michael R; Davis, Thomas P; Boyer, Cyrille

2012-05-14

71

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

SciTech Connect

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 {sup 3}P{sub 2} channel. We find that the critical temperature for this superfluid transition is {approx_equal}0.5x10{sup 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.

Page, Dany [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Mexico D.F. 04510 (Mexico); Prakash, Madappa [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701-2979 (United States); Lattimer, James M. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Steiner, Andrew W. [Joint Institute for Nuclear Astrophysics, National Superconducting Cyclotron Laboratory and, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States)

2011-02-25

72

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

73

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

74

A Unified Equation for the Reaction Rate in Dense Matter Stars  

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

75

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

SciTech Connect

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

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

2009-06-15

76

Open clusters in dense fields: the importance of field-star decontamination for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37  

Microsoft Academic Search

Star clusters projected on to dense stellar fields in general require field-star (FS) decontamination to confirm their nature and derive intrinsic photometric and structural fundamental parameters. This work focuses on the open clusters (OCs) or candidates NGC5715, Lyngå4, Lyngå9, Trumpler23, Trumpler26 and Czernik37 which are projected within and , against crowded bulge and\\/or disc fields. To tackle these difficult objects

C. Bonatto; E. Bica

2007-01-01

77

Polymer-mediated spatial organization of nanoparticles in dense melts: Transferability and an effective one-component approach.  

PubMed

We study two problems in the framework of the integral equation theory of polymer-mediated spatial organization of nanoparticles in dense melts motivated by multiscale simulation and many body physics issues. How nonspherical nanoparticle shape modifies polymer-induced interactions under dilute nanoparticle conditions is investigated over a range of primary particle sizes and interfacial cohesion strengths. Nonuniversal consequences of nonspherical shape are found for the pair-correlation function on local scales and some qualitative differences on larger scales due primarily to intraparticle connectivity constraints. For a large enough nanoparticle site diameter, the potentials of mean force (PMF) for all shapes studied (sphere, rod, disk, compact tetrahedral cluster) exhibit linear scaling with the size ratio of nanoparticle to polymer monomer site diameter and quite good "transferability." The ability of a simple effective one-component approach, based on the dilute nanoparticle PMF as an effective pair-decomposable potential, to describe interparticle structure at nonzero volume fractions is also studied. Although not generally quantitatively accurate due to neglect of many body correlation effects, especially at high nanoparticle loadings and near contact separations, the simple approach captures rather well many aspects of the real space structure. The errors incurred depend systematically on whether interfacial cohesion strength results in contact aggregation, steric stabilization, or bridging. For the filler collective static structure factor, many body effects are weakest for local cage scale correlations and grow significantly at smaller wavevectors under depletion or bridging conditions. PMID:20950039

Chakrabarti, Rajarshi; Schweizer, Kenneth S

2010-10-14

78

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

79

Open clusters in dense fields: the importance of field-star decontamination for NGC5715, Lynga4, Lynga9, Trumpler23, Trumpler26 and Czernik37  

Microsoft Academic Search

Star clusters projected onto dense stellar fields require field star\\u000adecontamination to confirm their nature and derive intrinsic photometric and\\u000astructural fundamental parameters. The present work focusses on the OCs or\\u000acandidates NGC5715, Lynga4,9, Trumpler23,26 and Czernik37 which are projected\\u000aagainst crowded bulge and\\/or disc fields. We develop a CMD field star\\u000adecontamination algorithm based on 2MASS data, and respective

Charles Bonatto; Eduardo Bica

2007-01-01

80

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

Microsoft Academic Search

Surface tension of symmetric 4 and 11 arm polystyrenes have been measured for a series of different molecular weights. We observe that entropic effects contribute significantly to the variation of surface tension as a function of molecular weight. Minnikanti and Archer have developed an expression that relates the surface tension of a symmetric star polymer with its molecular weight. To

Zhenyu Qian; Venkatachala Minnikanti; Lynden Archer; Bryan Sauer

2007-01-01

81

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

82

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

83

A single-component inimer containing cross-linkable ultrathin polymer coating for dense polymer brush growth.  

PubMed

We have developed a highly versatile universal approach to grow polymer brushes from a variety of substrates with high grafting density by using a single-component system. We describe a random copolymer which consists of an inimer, p-(2-bromoisobutyloylmethyl)styrene (BiBMS), copolymerized with glycidyl methacrylate (GMA) synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Thermal cross-linking created a mat that was stable during long exposure in organic solvent even with sonication or during Soxhlet extraction. The absolute bromine density was determined via X-ray photoelectron spectroscopy (XPS) to be 1.86 ± 0.12 Br atoms/nm(3). The ratio of experimental density to calculated absolute initiator density suggests that ~25% of the bromine is lost during cross-linking. Surface-initiated ATRP (SI-ATRP) was used to grow PMMA brushes on the substrate with sacrificial initiator in solution. The brushes were characterized by ellipsometry, XPS, and atomic force microscopy (AFM) to determine thickness, composition, and homogeneity. By correlating the molecular weight of polymer grown in solution with the brush layer thickness, a high grafting density of 0.80 ± 0.06 chains/nm(2) was calculated. By synthesizing the copolymer before cross-linking on the substrate, this single-component approach avoids any issues with blend miscibility as might be present for a multicomponent curable mixture, while resulting in high chain density on a range of substrates. PMID:23425347

Sweat, Daniel P; Kim, Myungwoong; Yu, Xiang; Gopalan, Padma

2013-03-19

84

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

Microsoft Academic Search

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

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

1994-01-01

85

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

SciTech Connect

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

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

1991-01-01

86

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.; Borro, M. de Val; 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

87

Nonequilibrium polymer chains induced by conformational transitions in densely interfacial layers  

NASA Astrophysics Data System (ADS)

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

Zhu, Peng-Wei

2012-09-01

88

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

Microsoft Academic Search

\\u000a Star polymers and cylindrical polymer brushes (CPBs), i.e. polymers possessing side groups densely grafted from a linear main\\u000a chain, have attracted considerable experimental and theoretical interest over the past decade, owing to their peculiar solution\\u000a and bulk properties. We have used the grafting-from approach via ATRP to synthesize well-defined star polymers and core—shell\\u000a CPBs with homopolymer and block copolymer side

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

2009-01-01

89

Neutron star properties with unified equations of state of dense matter  

NASA Astrophysics Data System (ADS)

Aims: In this paper, we study the global properties of neutron stars (NSs), as predicted by the Brussels-Montreal equations of state (EoSs). These EoSs, which provide a unified description of all regions of a NS, are based on the generalised Skyrme functionals BSk19, BSk20, and BSk21 that were simultaneously fitted to almost all the nuclear mass data and constrained to reproduce various properties of infinite nuclear matter, as obtained from microscopic calculations. Methods: We solved Einstein's equations of general relativity for both non-rotating and rigidly rotating NSs using these unified EoSs. Results: The NS properties thus obtained are compared with various astrophysical observations. We find that only the stiffest EoS, based on the functional BSk21, is compatible with all the constraints inferred from these observations. Tables of the equations of state 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/559/A128

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

2013-11-01

90

Extensive Study of Interaction Force Between Spherical Colloids and Star Polymers  

NASA Astrophysics Data System (ADS)

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

Himmi, Mustapha; Mohammadi, Laila

2012-07-01

91

The Small Blue Straggler Star Population in the Dense Galactic Globular Cluster NGC 6752  

NASA Astrophysics Data System (ADS)

We used high-resolution Hubble Space Telescope (HST)-WFPC2 and wide-field ground-based observations to construct a catalog of blue straggler stars (BSSs) that spans the entire radial extent of the globular cluster NGC 6752. The BSS sample is the most extensive ever obtained for this cluster. Although NGC 6752 is a high-density cluster with a large binary population, we found that its BSS content is surprisingly low: the specific number of BSSs is among the lowest ever measured in a cluster. The BSS distribution is highly peaked in the cluster center, shows a rapid decrease at intermediate radii, and rises again at larger distances. This distribution closely resembles those observed in M3 and 47 Tuc by Ferraro and coworkers. To date, BSS surveys covering the central regions with HST and the outer regions with wide-field CCD ground-based observations have been performed for only these three clusters. Despite the different dynamical properties, a bimodal radial distribution has been found in each. A detailed comparison of observed BSS luminosity and temperature distributions with theoretical models reveals a population of luminous, hot BSSs that is not easily interpreted. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. Also based on Wide Field Imager observations collected at the European Southern Observatory, La Silla, Chile, within the observing program 62.L-0354 and 64.L-0439.

Sabbi, E.; Ferraro, F. R.; Sills, A.; Rood, R. T.

2004-12-01

92

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

PubMed

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

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

2014-07-23

93

Dense neutron star matter  

NASA Astrophysics Data System (ADS)

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

Stone, J. R.

2014-05-01

94

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

95

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

96

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

PubMed

We use time-resolved rheology to elucidate the slow dynamics and aging in highly concentrated suspensions of multiarm star polymers. The linear and nonlinear rheological properties exhibit a terminal regime corresponding to a well-defined maximal relaxation time. Terminal relaxation is driven by arm relaxation which speeds up the escape of stars from their cages. The fact that the system fully relaxes and flows at long times has important consequences. The yield stress only exists in the limited range of frequencies or shear rates where solid-like behavior is observed. Aging is controlled by the total time elapsed after flow cessation and not by the time elapsed from flow cessation to the beginning of the measurement as in other glassy materials. Our results, which demonstrate the importance of particle architecture with respect to glassy dynamics, should be generic for long hairy particles. PMID:21797359

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

2011-06-01

97

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

98

Synthesis and characterization of AB 2 -type star polymers via combination of ATRP and click chemistry  

Microsoft Academic Search

Homo\\/miktoarm star polymers were successfully synthesized via combination of the “arm-first” and “coupling-onto” strategies.\\u000a Firstly, the multifunctional coupling agent (core), 2, 4, 6-tris(3-ethynylphenyl)-1,3,5-triazine-2,4,6-triamine (TPTTA), was\\u000a synthesized. Secondly, the linear polystyrene-Cl (PS-Cl) and poly(2-(dimethylamino)ethyl methacrylate)-Br (PDMAEMA-Br) were\\u000a prepared by atom transfer radical polymerization (ATRP) method. Then, the linear PS-Cl and PDMAEMA-Br chains were modified\\u000a by a nucleophilic substitution reaction with sodium

Weidong Zhang; Wei Zhang; Zhengbiao Zhang; Jian Zhu; Qinmin Pan; Xiulin Zhu

2009-01-01

99

Brownian Dynamics Study on the Dynamics of Asymmetric and Symmetric Star-Branched Polymers in Dilute Solutions  

NASA Astrophysics Data System (ADS)

It has been known that the dynamical behavior of branched polymers can significantly be different from linear polymers even in dilute solutions. The goal of this investigation is to understand detailed configuration and stretching dynamics of polymers with complex branching topologies in dilute solutions under various flows. In particular, we are interested in the transient stress response and conformational hysteresis of star-branched polymers in shear and extensional flows. Using Brownian dynamics simulations of bead-spring models, systems such as dilute solutions of Y-branched and star-branched polymers under flows are investigated. Studies on polymers with asymmetric arms reveal that the initial transient response is governed by both the number of arms and the shortest arm, whereas the stress response at intermediate strains becomes dominated by the longest arm. The results obtained from stress-conformation hysteresis simulations indicate that rapid extension followed by retarded relaxation of short arms in star-branched molecules. Finally, excluded-volume interactions are incorporated through the Lennard-Jones potential, and are applied to the study of the dynamics of branched polymers under confinement.

Lak Joo, Yong

2005-03-01

100

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

PubMed

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

Randisi, Ferdinando; Pelissetto, Andrea

2013-10-21

101

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

NASA Astrophysics Data System (ADS)

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

Randisi, Ferdinando; Pelissetto, Andrea

2013-10-01

102

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

NASA Astrophysics Data System (ADS)

We report HCN J = 4 ? 3, HCO+ J = 4 ? 3, and CS J = 7 ? 6 observations in 20 nearby star-forming galaxies with the Atacama Pathfinder EXperiment 12 m telescope. Combined with four HCN, three HCO+, and four CS detections from the literature, we probe the empirical link between the luminosity of molecular gas (L^{\\prime }_gas) and that of infrared emission (L IR), up to the highest gas densities (~106 cm-3) that have been probed so far. For nearby galaxies with large radii, we measure the IR luminosity within the submillimeter beam size (14''-18'') to match the molecular emission. We find linear slopes for L^{\\prime }_{CS\\, J=7{--}6}-L IR and L^{\\prime }_{HCN\\, J=4{--}3}-L IR, and a slightly super-linear slope for L^{\\prime }_{HCO^+\\, J=4{--}3}-L IR. The correlation of L^{\\prime }_{CS\\, J=7{--}6}-L IR even extends over eight orders of luminosity magnitude down to Galactic dense cores, with a fit of log(L IR) =1.00(± 0.01) ×log(L^{\\prime }_{CS\\, J=7{--}6}) + 4.03(± 0.04). Such linear correlations appear to hold for all densities >104 cm-3, and indicate that star formation rate is not related to the free-fall timescale for dense molecular gas.

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

2014-04-01

103

Dense astrophysical plasmas.  

PubMed

Degenerate bodies composed primarily of dense hydrogen and helium plasmas range from giant planets to the so far hypothetical brown dwarfs. More massive objects begin their lives as nondegenerate stars and may end as white dwarfs, composed primarily of carbon and oxygen, or as neutron stars, with solid crusts of iron or heavier elements and cores of neutron matter. The physical properties of dense plasmas that are necessary to construct theoretical models of such degenerate stars include the equation of state, transport properties, and nuclear reaction rates. PMID:17740936

VAN Horn, H M

1991-04-19

104

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

105

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

106

On the Dynamical Formation of Very Young, X-Ray Emitting Black Hole Binaries in Dense Star Clusters  

NASA Astrophysics Data System (ADS)

We recently discovered a population of very young (? <~ 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 (~6000 M ?) 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; Converse, Joseph M.; Chandar, Rupali; Rangelov, Blagoy

2012-08-01

107

Charged-Current Weak Interaction Processes in Hot and Dense Matter and its Impact on the Spectra of Neutrinos Emitted from Protoneutron Star Cooling  

NASA Astrophysics Data System (ADS)

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)PRVDAQ0556-2821] 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.

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

2012-12-01

108

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

109

Star Formation  

NASA Astrophysics Data System (ADS)

Stars are one of the most important constituents of the Universe, and understanding their formation is crucial to many areas of astrophysics. Stars form from dense molecular gas, and they tend not to form in isolation. Stars often form in binary and multiple systems, and these systems tend to form in clusters with 102-105 members. Stars also form with a wide range of masses, from substellar brown dwarfs with masses < 0. 1 M ? to massive stars > 100 M ?, and wherever stars form the distribution of their masses seems always to be the same. This chapter will review our current understanding of star formation from cold gas to young star clusters.

Goodwin, Simon

110

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

PubMed

A novel non-viral gene transfection method in which DNA complexes were kept in contact with a deposition surface (deposition transfection) was developed. We designed a novel aqueous thermoresponsive adsorbent material for DNA deposition, which was a star-shaped copolymer with 4-branched chains. Each chain is comprised of a cationic poly(N,N-dimethylaminopropyl acrylamide) (PDMAPAAm) block (Mn: ca. 3000 g x mol(-1)), which formed an inner domain for DNA binding and a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) block (Mn: ca. 6000 g x mol(-1)), which formed an outer domain for surface adsorption. Complex formation between the copolymer and the luciferase-encoding plasmid DNA occurred immediately upon simple mixing in an aqueous medium; polyplexes approximately 100 nm in size were formed. Because the lower critical solution temperature of the polyplexes was approximately 35 degrees C, they could deposit on the substrate by precipitation from an aqueous solution upon warming, which was confirmed by quartz crystal microbalance (QCM) method and water contact angle measurement. When COS-1 cells were cultured on the polyplex-deposited substrate in a culture medium, the luciferase activity observed was higher than that observed on a DNA-coated substrate with or without the cationic polymer before and after complete adhesion and by conventional solution transfection using the polyplexes. The activity was enhanced with an increase in the charge ratio (surfactant/pDNA) with permissible cellular cytotoxicity. PMID:17881077

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

2007-11-20

111

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

PubMed

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

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

2011-03-01

112

Self-organized honeycomb morphology of star-polymer polystyrene films  

Microsoft Academic Search

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

Gilles Widawski; Michel Rawiso; Bernard François

1994-01-01

113

Star-shaped MePEGn polymers as H+ conducting electrolytes.  

PubMed

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

Sun, Chengjun; Ritchie, Jason E

2011-07-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

115

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

116

Relaxation dynamics of branched polymers  

Microsoft Academic Search

The Rouse model for star polymers was successfully derived by solving the differential equations governing the net force acting on each bead in a star polymer chain. As opposed to a linear polymer, where we have N unique roots for N beads, in the case of star polymers, there are only 2 Na+1 unique roots and all odd unique roots

Arnav Ghosh

2007-01-01

117

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

Microsoft Academic Search

The binary interaction (BI) theory recently developed by David W. Mead, Ronald G. Larson, and Masao Doi (1998) is based on two fundamental postulates strongly supported by experimental data: (1)stress-optic rule, (2)binary interaction principle. The BI theory is general and in principle applies to all entangled flexible polymers regardless of molecular architecture. Three parameters are required in the BI theory

Han-Wen Chen

2001-01-01

118

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

Microsoft Academic Search

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

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

2007-01-01

119

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

120

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

121

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

PubMed Central

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

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

2013-01-01

122

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

123

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

124

Astrochemistry of Dense Protostellar and Protoplanetary Environments  

Microsoft Academic Search

Dense molecular clouds contain a remarkably rich chemistry, as revealed by combined submillimeter and infrared observations. Simple and complex (organic) gases, polycyclic aromatic hydrocarbons, ices and silicates have been unambiguously detected in both low- and high-mass star forming regions. During star- and planet formation, these molecules undergo large abundance changes, with most of the heavy species frozen out as icy

Ewine F. van Dishoeck

2009-01-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

126

A z = 2.5 protocluster associated with the radio galaxy MRC 2104-242: star formation and differing mass functions in dense environments  

NASA Astrophysics Data System (ADS)

We present results from a narrow-band survey of the field around the high-redshift radio galaxy MRC 2104-242. We have selected H? emitters in a 7 arcmin2 field and compared the measured number density with that of a field sample at similar redshift. We find that MRC 2104-242 lies in an overdensity of galaxies that is 8.0 ± 0.8 times the average density of a blank field, suggesting it resides in a large-scale structure that may eventually collapse to form a massive cluster. We find that there is more dust obscured star formation in the protocluster galaxies than in similarly selected control field galaxies and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average we do not find a difference between the star formation rate (SFR)-mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ˜ 2.5 is governed predominantly by galaxy mass and not the host environment. We also find that the stellar mass distribution of the protocluster galaxies is skewed towards higher masses and there is a significant lack of galaxies at M < 1010 M? within our small field of view. Based on the level of overdensity we expect to find ˜22 star-forming galaxies below 1010 M? in the protocluster and do not detect any. This lack of low-mass galaxies affects the level of overdensity which we detect. If we only consider high-mass (M > 1010.5 M?) galaxies, the density of the protocluster field increases to ˜55 times the control field density.

Cooke, E. A.; Hatch, N. A.; Muldrew, S. I.; Rigby, E. E.; Kurk, J. D.

2014-06-01

127

Suprathermal viscosity of dense matter  

SciTech Connect

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

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

2010-12-22

128

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

SciTech Connect

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

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

2011-11-20

129

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

SciTech Connect

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

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

2010-05-01

130

Ionization compression impact on dense gas distribution and star formation. Probability density functions around H II regions as seen by Herschel  

NASA Astrophysics Data System (ADS)

Aims: Ionization feedback should impact the probability distribution function (PDF) of the column density of cold dust around the ionized gas. We aim to quantify this effect and discuss its potential link to the core and initial mass function (CMF/IMF). Methods: We used Herschel column density maps of several regions observed within the HOBYS key program in a systematic way: M 16, the Rosette and Vela C molecular clouds, and the RCW 120 H ii region. We computed the PDFs in concentric disks around the main ionizing sources, determined their properties, and discuss the effect of ionization pressure on the distribution of the column density. Results: We fitted the column density PDFs of all clouds with two lognormal distributions, since they present a "double-peak" or an enlarged shape in the PDF. Our interpretation is that the lowest part of the column density distribution describes the turbulent molecular gas, while the second peak corresponds to a compression zone induced by the expansion of the ionized gas into the turbulent molecular cloud. Such a double peak is not visible for all clouds associated with ionization fronts, but it depends on the relative importance of ionization pressure and turbulent ram pressure. A power-law tail is present for higher column densities, which are generally ascribed to the effect of gravity. The condensations at the edge of the ionized gas have a steep compressed radial profile, sometimes recognizable in the flattening of the power-law tail. This could lead to an unambiguous criterion that is able to disentangle triggered star formation from pre-existing star formation. Conclusions: In the context of the gravo-turbulent scenario for the origin of the CMF/IMF, the double-peaked or enlarged shape of the PDF may affect the formation of objects at both the low-mass and the high-mass ends of the CMF/IMF. In particular, a broader PDF is required by the gravo-turbulent scenario to fit the IMF properly with a reasonable initial Mach number for the molecular cloud. Since other physical processes (e.g., the equation of state and the variations among the core properties) have already been said to broaden the PDF, the relative importance of the different effects remains an open question. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Tremblin, P.; Schneider, N.; Minier, V.; Didelon, P.; Hill, T.; Anderson, L. D.; Motte, F.; Zavagno, A.; André, Ph.; Arzoumanian, D.; Audit, E.; Benedettini, M.; Bontemps, S.; Csengeri, T.; Di Francesco, J.; Giannini, T.; Hennemann, M.; Nguyen Luong, Q.; Marston, A. P.; Peretto, N.; Rivera-Ingraham, A.; Russeil, D.; Rygl, K. L. J.; Spinoglio, L.; White, G. J.

2014-04-01

131

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

Microsoft Academic Search

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

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

2011-01-01

132

Neutron stars  

NASA Astrophysics Data System (ADS)

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

Lattimer, James M.

2014-05-01

133

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

SciTech Connect

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

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

1999-07-15

134

Astrochemistry of Dense Protostellar and Protoplanetary Environments  

Microsoft Academic Search

Dense molecular clouds contain a remarkably rich chemistry, as revealed by combined submillimeter and infrared observations.\\u000a Simple and complex (organic) gases, polycyclic aromatic hydrocarbons, ices and silicates have been unambiguously detected\\u000a in both low- and high-mass star forming regions. During star- and planet formation, these molecules undergo large abundance\\u000a changes, with most of the heavy species frozen out as icy

Ewine F. van Dishoeck

135

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

NASA Astrophysics Data System (ADS)

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

2014-01-01

136

Probing cold dense nuclear matter.  

PubMed

The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars. PMID:18511658

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

2008-06-13

137

Neutron Star Collision  

NSDL National Science Digital Library

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

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

1999-01-21

138

Neutron star cooling  

Microsoft Academic Search

The impact of nuclear physics theories on cooling of isolated neutron stars\\u000ais analyzed. Physical properties of neutron star matter important for cooling\\u000aare reviewed such as composition, the equation of state, superfluidity of\\u000avarious baryon species, neutrino emission mechanisms. Theoretical results are\\u000acompared with observations of thermal radiation from neutron stars. Current\\u000aconstraints on theoretical models of dense matter,

D. G. Yakovlev; O. Y. Gnedin; M. E. Gusakov; A. D. Kaminker; K. P. Levenfish; A. Y. Potekhin

2005-01-01

139

Tension in Highly Branched Polymers  

NASA Astrophysics Data System (ADS)

We propose a systematic method of designing branched macromolecules capable of building up high tension in their covalent bonds, which can be controlled by changing solvent quality. This tension is achieved exclusively due to intramolecular interactions by focusing lower tensions from its numerous branches to a particular section of the designed molecule. The simplest molecular architecture, which allows this tension amplification, is a so-called pom-pom macromolecule consisting of a relatively short linear spacer and two z-arm stars at its ends. Tension developed in the stars due to crowding of their branches is amplified by a factor of z and focused to the spacer. There are other highly branched macromolecules, such as molecular brushes - comb polymers with high density of side branches, that have similar focusing and amplification properties. In addition molecular brushes transmit tension along their backbone. Adsorption or grafting of these branched molecules on a substrate results in further increase in tension as compared to molecules in solution. Molecular architectures similar to pom-pom and molecular brushes with a high tension amplification parts can be used in numerous sensor applications. Unique conformations of molecular brushes in a pre-wetting layer allow direct visualization by atomic force microscope. Detailed images of individual molecules spreading along the surface enable critical evaluation of theories of chain dynamics in polymer monolayer. Strong spreading of densely branched macromolecules on a planar substrate can lead to high tension in the molecular backbone sufficient to break covalent bonds.

Rubinstein, Michael

2012-02-01

140

Dense topological spaces and dense continuity  

NASA Astrophysics Data System (ADS)

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

Aldwoah, Khaled A.

2013-09-01

141

Microwave-assisted synthesis, characterization and ammonia sensing properties of polymer-capped star-shaped zinc oxide nanostructures  

Microsoft Academic Search

Zinc oxide nanostructures were prepared by microwave-irradiation technique in the presence of polyvinyl pyrrolidone as a shape\\u000a modifier. The synthesized nanostructures were analyzed using scanning and transmission electron microscopy, selected-area\\u000a electron diffraction, X-ray diffraction, and Fourier transform infrared spectroscopy (FT-IR). Characterization techniques\\u000a revealed the formation of crystalline ZnO with a star-like shaped morphology, having the crystal structure of wurtzite. The

T. Krishnakumar; R. Jayaprakash; D. Sathya Raj; N. Pinna; V. N. Singh; A. R. Phani; G. Neri

142

The ? Orionis Star Forming Region  

NASA Astrophysics Data System (ADS)

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

Mathieu, R. D.

2008-12-01

143

Physics of dense matter; International Conference, Paris, France, September 17-21, 1979, Proceedings  

NASA Astrophysics Data System (ADS)

Several problems of interest in astrophysics are examined: the conditions under which stellar matter becomes a highly correlated plasma, the chemical composition of dense matter, and the physics of dense astrophysical objects (white dwarfs, neutron stars, supernovae, etc.). Particular consideration is given to superfluidity in neutron stars, the condensed matter physics of planetary interiors, and the nonexplosive collapse of a white dwarf.

1980-03-01

144

Dense stellar cores in merger remnants  

NASA Technical Reports Server (NTRS)

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

Mihos, J. Christopher; Hernquist, Lars

1994-01-01

145

The Physics of Neutron Stars  

Microsoft Academic Search

Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics, and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near

J. M. Lattimer; M. Prakash

2004-01-01

146

Star Formation in the Orion Nebula Cluster  

Microsoft Academic Search

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

Francesco Palla; Steven W. Stahler

1999-01-01

147

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

SciTech Connect

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

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

2009-12-01

148

Polymers containing fullerene or carbon nanotube structures  

Microsoft Academic Search

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

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

2004-01-01

149

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

150

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.

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

151

Polymer Modified Concrete Study.  

National Technical Information Service (NTIS)

The Federal Highway Administration has approved the use of three (3) polymer-modifiers in concrete as alternates to low slump dense concrete (LSDC). These products are: Dow SM Modifier 'A', Thermoflex 8002 and Arco-Dylex 1186. The Department introduced th...

S. M. Law M. Rasoulian

1980-01-01

152

Relaxation dynamics of branched polymers  

NASA Astrophysics Data System (ADS)

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

Ghosh, Arnav

153

Infrared and Submilllimeter Studies of Dense Cores  

NASA Astrophysics Data System (ADS)

Dense Cores are the birthplace of stars, and so understanding their structure and evolution is key to understanding star formation. Information on the density, temperature, and motions within cores are needed to describe these properties, and are obtained through continuum and line observations at far infrared and submm/mm wavelengths. Recent observations of dust emission with Herschel and molecular line observations with single-dish telescopes and interferometers provide the wavelength coverage and resolution to finally map core properties without appealing to spherical simplifications. Although large scale Herschel observations reveal numerous filaments in molecular clouds which are well described by cylindrical geometries, cores are still modeled as spherical entities. A few examples of other core geometries exist in the literature, and the wealth of new data on cloud filaments demand that non-spherical models receive more attention in future studies. This talk will examine the evidence for non-spherical cores and their connection to the filaments from which they form.

Bourke, Tyler L.

2014-07-01

154

Global star formation in the L1630 molecular cloud  

NASA Technical Reports Server (NTRS)

The first systematic and coordinated surveys for both dense gas and young stellar objects within a single molecular cloud, the L1630 molecular cloud are compared. It is found that (1) star formation in the L1630 molecular cloud occurs almost exclusively within the dense gas; (2) star formation does not occur uniformly throughout the dense gas and is strongly favored in a few very massive dense cores, where efficient conversion of molecular gas into stars has resulted in the production of rich stellar clusters; and (3) high gas densities and high gas mass may be necessary but not sufficient conditions for the formation of star clusters since two of the five most massive dense cores in the cloud have very low levels of star formation activity.

Lada, Elizabeth A.

1992-01-01

155

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

NASA Astrophysics Data System (ADS)

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing HIRES spectra from the Keck telescope. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter masses, 0.9 Jupiter radii, and a density of 2.34 g cm-3. It orbits a G0V star with T_eff = 5 945 K, M* = 1.09 M?, R_* = 1.01 R?, solar metallicity, a lithium content of + 1.45 dex, and an estimated age of between 0.12 and 3.15 Gyr. The lithium abundance of the star is consistent with its effective temperature, activity level, and age range derived from the stellar analysis. The density of the planet is extreme for its mass, implies that heavy elements are present with a mass of between about 140 and 300 {M}?. The CoRoT space mission, launched on December 27th 2006, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain. Part of the observations were obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations made with HARPS spectrograph on the 3.6-m European Organisation for Astronomical Research in the Southern Hemisphere telescope at La Silla Observatory, Chile (ESO program 184.C-0639). Based on observations made with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. Part of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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

2010-11-01

156

The Relationship Between Dense Cores, Filaments, and YSOs in the Perseus and Serpens Molecular Clouds  

NASA Astrophysics Data System (ADS)

The CARMA Large Area Star Formation Survey (CLASSy) provides a broad overview of the molecular emission from dense gas distribution in a total of five regions in the Perseus and Serpens Molecular Clouds with 7" angular resolution. These regions span a wide range of star formation activity, allowing a detailed comparison of the dense gas, dust, and young stellar object distributions on the scales from thousands of AU to 1-2 parsecs. This poster will specifically looks at the relationship between dense cores, filaments, and YSO's in these regions.

Mundy, Lee G.; Storm, Shaye

2014-07-01

157

Dense molecular thermodynamics  

SciTech Connect

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

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

1983-01-01

158

Unified EOS for neutron stars  

NASA Astrophysics Data System (ADS)

The equation of state (EOS) of dense matter is a crucial input for the neutron-star structure calculations. This Fortran code can obtain a "unified EOS" in the many-body calculations based on a single effective nuclear Hamiltonian, and is valid in all regions of the neutron star interior. For unified EOSs, the transitions between the outer crust and the inner crust and between the inner crust and the core are obtained as a result of many-body calculations.

Chamel, Nicolas; Potekhin, Alexander

2014-03-01

159

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

NASA Astrophysics Data System (ADS)

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

Wright, N.

2013-06-01

160

Quantum-dense metrology  

NASA Astrophysics Data System (ADS)

Quantum metrology utilizes entanglement to improve the sensitivity of measurements. To date, the focus has been on the measurement of a single observable. Its orthogonal observable, however, may contain additional information, the knowledge of which can be used to further improve the measurement result beyond what is possible with state-of-the-art quantum metrology. Here we demonstrate a laser interferometer that provides information about two non-commuting observables, with uncertainties below the meter's quantum ground state. Our experiment is a proof of principle of what we call `quantum-dense metrology', referring to its increased measurement information and its analogy to quantum-dense coding in quantum information science. We propose to use the additional information to discriminate between the actual science signal and parasitic signals originating from scattered photons. Our approach can be readily applied to improve squeezed-light enhanced gravitational-wave detectors at non-quantum noise-limited detection frequencies by providing a sub-shot-noise veto trigger against stray-light-induced signals.

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

2013-08-01

161

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

162

Dense Molecular Gas in Centaurus A  

NASA Astrophysics Data System (ADS)

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

Wild, Wolfgang; Eckart, Andreas

1999-10-01

163

H-cluster stars  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

164

Geometrical optics of dense aerosols: forming dense plasma slabs.  

PubMed

Assembling a freestanding, sharp-edged slab of homogeneous material that is much denser than gas, but much more rarefied 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 field, 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 finite particle density reduces the effective Stokes number of the flow, a critical result for controlled focusing. PMID:24237567

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

2013-11-01

165

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

166

Microporous polymer films and methods of their production  

DOEpatents

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

Aubert, J.H.

1995-06-06

167

Polymer Concretes.  

National Technical Information Service (NTIS)

A review of the uses of polmers in concretes was carried out, including: polymer concretes such as impregnated composites, premixed polymer concretes and polymer bound aggregates; concretes which have solid, water soluble or dispersed polymers added to th...

1975-01-01

168

Dense Deposit Disease  

PubMed Central

Dense deposit disease (DDD) is an orphan disease that primarily affects children and young adults without sexual predilection. Studies of its pathophysiology have shown conclusively that it is caused by fluid-phase dysregulation of the alternative pathway of complement, however the role played by genetics and autoantibodies like C3 nephritic factors must be more thoroughly defined if we are to make an impact in the clinical management of this disease. There are currently no mechanism-directed therapies to offer affected patients, half of whom progress to end stage renal failure disease within 10 years of diagnosis. Transplant recipients face the dim prospect of disease recurrence in their allografts, half of which ultimately fail. More detailed genetic and complement studies of DDD patients may make it possible to identify protective factors prognostic for naïve kidney and transplant survival, or conversely risk factors associated with progression to renal failure and allograft loss. The pathophysiology of DDD suggests that a number of different treatments warrant consideration. As advances are made in these areas, there will be a need to increase healthcare provider awareness of DDD by making resources available to clinicians to optimize care for DDD patients.

Smith, Richard J.H; Harris, Claire L.; Pickering, Matthew C.

2011-01-01

169

Densely Cratered Region  

NASA Technical Reports Server (NTRS)

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

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

Image Credit: NASA/JPL/Northwestern University

1974-01-01

170

Dense Hypervelocity Plasma Jets  

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

171

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

172

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

173

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

174

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

175

Strange stars  

Microsoft Academic Search

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

Charles Alcock; Edward Farhi; Angela Olinto

1986-01-01

176

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

177

Modeling the Formation and Evolution of Dense Stellar Systems  

NASA Astrophysics Data System (ADS)

Dense stellar systems -- star forming regions, young star clusters, globular clusters, and galactic nuclei -- are complex environments in which many physical processes compete to control the overall dynamics and long-term evolution. Of particular interest is the interplay between radiation, gas dynamics, stellar dynamics, and stellar and binary physics in determining the fates of these systems. However, modeling the combined effects of all these processes places stringent demands on both simulation software and computer hardware. As part of an ongoing effort to understand cluster formation and evolution, I will describe the Astrophysical MUltiphysics Software Environment (AMUSE), a general-purpose framework for combining multiple high-performance simulation modules within a homogeneous software interface. I will present some applications of AMUSE to simulations of various stages of cluster evolution, including hierarchical assembly, radiative feedback from massive stars and the ejection of residual gas, and the longer-term dynamics of the system.

McMillan, Stephen L. W.

2014-05-01

178

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

179

Star formation in the "Gulf of Mexico"  

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

180

Be Stars  

NASA Astrophysics Data System (ADS)

A Be star (pronounced `bee-ee' star) is a non-supergiant B-type star whose spectrum displays or has displayed one or more Balmer lines in emission and Be is the notation for the spectral classification of such a star (see also CLASSIFICATION OF STELLAR SPECTRA). `Classical' Be stars are believed to have acquired the circumstellar (CS) material that produces the Balmer emission through ejection of...

Peters, G.; Murdin, P.

2000-11-01

181

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

182

The Milky Way nuclear star cluster beyond 1 pc  

NASA Astrophysics Data System (ADS)

Within the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster, forming a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ˜75% of nearby galaxies. It is, however, not fully understood how nuclear clusters form. Because the Milky Way nuclear star cluster is at a distance of only 8 kpc, we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster a reference object for understanding the structure and assembly history of all nuclear star clusters.

Feldmeier, A.; Neumayer, N.; Seth, A.; de Zeeuw, P. T.; Schödel, R.; Lützgendorf, N.; Kissler-Patig, M.; Nishiyama, S.; Walcher, C. J.

2014-05-01

183

Stellar Wind Disruption by an Orbiting Neutron Star  

NSDL National Science Digital Library

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

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

1990-07-10

184

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

185

Models of Collapsing Clouds and Star-Forming Regions as Analogs of the Solar Nebula  

Microsoft Academic Search

Stars form inside gas and dust condensations within molecular clouds called dense cores. These objects are observed throughout our Galaxy but particular attention is devoted to nearby (<200pc) dense coresideal targets to carry out detailed studies with available telescopes. About one half of nearby dense cores are starless and a small (~ 5%) fraction is thought to be on the

Paola Caselli

2005-01-01

186

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

187

CN Zeeman Mapping of Magnetic Fields in Dense Molecular Cores  

NASA Astrophysics Data System (ADS)

The many possible roles of magnetic fields in star formation remain unclear, requiring observations of magnetic fields at all stages and conditions to further our understanding. Zeeman observations provide the only direct measurement of magnetic field strengths in molecular clouds and cores, and maps provide information about field structure. Of the Zeeman-sensitive species, CN offers the best opportunity to sample the higher density gas in molecular cores and their envelopes. Earlier single-dish CN Zeeman N=1-0 measurements were with 23" resolution; needed next are higher angular resolution CN Zeeman maps in order to explore magnetic field strengths and morphologies in dense cores and their envelopes. Here I report CARMA Zeeman-effect mapping of the N=2-1 CN transitions with ~3" resolution toward W3OH and DR21OH, both high-mass star formation regions that have previous single-dish Zeeman detections at 23” resolution. Toward W3OH the line-of-sight field strength reaches 4 mG (4 times higher than the single-dish result) with clear spatial structure. The analysis of DR21OH results will be completed by the meeting and presented also. These are the first interferometric CN Zeeman observations and detections of dense molecular cores. I discuss the implications for the role of magnetic fields in the formation and evolution of dense cores and the possibilities for future ALMA Zeeman work.

Crutcher, Richard

2014-07-01

188

Metal-polymer composites comprising nanostructures and applications thereof  

DOEpatents

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

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

2011-08-02

189

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

190

STAR Publications  

Cancer.gov

STAR Publications The following citations are of reports that have been published in the scientific literature concerning the Study of Tamoxifen and Raloxifene (STAR). The citations are listed in reverse chronological order.

191

Naked dense bodies provoke depression.  

PubMed

At presynaptic active zones (AZs), the frequently observed tethering of synaptic vesicles to an electron-dense cytomatrix represents a process of largely unknown functional significance. Here, we identified a hypomorphic allele, brpnude, lacking merely the last 1% of the C-terminal amino acids (17 of 1740) of the active zone protein Bruchpilot. In brpnude, electron-dense bodies were properly shaped, though entirely bare of synaptic vesicles. While basal glutamate release was unchanged, paired-pulse and sustained stimulation provoked depression. Furthermore, rapid recovery following sustained release was slowed. Our results causally link, with intramolecular precision, the tethering of vesicles at the AZ cytomatrix to synaptic depression. PMID:20980589

Hallermann, Stefan; Kittel, Robert J; Wichmann, Carolin; Weyhersmüller, Annika; Fouquet, Wernher; Mertel, Sara; Owald, David; Eimer, Stefan; Depner, Harald; Schwärzel, Martin; Sigrist, Stephan J; Heckmann, Manfred

2010-10-27

192

Development of polymer films by the coalescence of polymer particles in powdered and aqueous polymer-modified mortars  

SciTech Connect

This paper evaluates and compares the coalescence of polymer particles (continuous polymer films formation) in powdered polymer-modified mortars (PPMMs) and aqueous polymer-modified mortars (APMMs). Polymer-modified mortars (PMMs) using various redispersible polymer powders (powdered cement modifiers) and polymer dispersions (aqueous cement modifiers) were prepared by varying the polymer-cement ratio (P/C) and were tested for the characterization of polymer films using a scanning electron microscope (SEM) after curing for 28 days. It is concluded from the test results that mortar constituents of unmodified mortar (UMM) are loosely joined with each other due to the absence of polymer films, thus having a structure with comparatively lower mechanical and durability characteristics. By contrast, mortar constituents in PPMMs and APMMs are compactly joined with each other due to the presence of interweaving polymer films, thereby forming a monolithic structure with improved mechanical and durability characteristics. However, the results make obvious the poor coalescence of polymer particles or development of inferior quality polymers films in PPMMs as compared to that observed in APMMs. Moreover, PPMMs show less uniform distribution of polymer films as compared to that in APMMs. Different powdered cement modifiers have different film-forming capabilities. However, such difference is hardly recognized in aqueous cement modifiers. The polymer films in PPMMs and APMMs may acquire different structures. They may appear as mesh-like, thread-like, rugged, dense or fibrous with fine or rough surfaces. Development of coherent polymer films is not well pronounced at a P/C of 5% in PPMMs, whereas sometimes coherent polymer films are observed at a P/C of 5% in APMMs. At a P/C of 10% or more, fully developed, coherent polymer films are observed in both PPMMs and APMMs.

Afridi, M.U.K.; Ohama, Y.; Demura, K.; Iqbal, M.Z

2003-11-01

193

The Loss-Cone Problem in Dense Nuclei Revisited  

NASA Astrophysics Data System (ADS)

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

Amaro-Seoane, Pau; Spurzem, Rainer

194

STAR System.  

ERIC Educational Resources Information Center

The STAR System is a developmental guidance approach to be used with elementary school children in the 5th or 6th grades. Two basic purposes underlie STAR: to increase learning potential and to enhance personal growth and development. STAR refers to 4 basic skills: sensory, thinking, adapting, and revising. Major components of the 4 skills are:…

Doverspike, James E.

195

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

NSDL National Science Digital Library

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

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

1990-07-10

196

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

197

Advanced Polymers  

Microsoft Academic Search

Polymer science gains its power from the infinite versatility of synthetic polymers. Not only the bulk materials but also their basic constituents, polymer molecules, are tailor-made. The polymer molecule is built from smaller molecular units known as monomers, repeated hundreds or thousands of times in a chainlike structure. The choice of monomers and the way they are assembled shape the

Eric Baer

1986-01-01

198

The Diversity of Neutron Stars  

NASA Astrophysics Data System (ADS)

Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the >1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby, isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population---distances, ages, and magnetic fields---the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 1e6 year-old cooling neutron stars with magnetic fields above 1e13 Gauss. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication of central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

Kaplan, David L.

2004-12-01

199

Method for dense packing discovery  

NASA Astrophysics Data System (ADS)

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

Kallus, Yoav; Elser, Veit; Gravel, Simon

2010-11-01

200

Galaxy collisions in dense groups  

Microsoft Academic Search

Examination of a sample of 18 dense groups of galaxies reveals that the size of the largest galaxy in each group is correlated with the mean intergalactic separation. This limitation of galaxy sizes and its dependence on the group's velocity dispersion can be roughly understood in terms of a simple theory of tidal stripping. The observed galaxy sizes are consistent

P. Hickson; D. O. Richstone; E. L. Turner

1977-01-01

201

Relativistic Processes and the Internal Structure of Neutron Stars  

SciTech Connect

Models for the internal composition of Dense Compact Stars are reviewed as well as macroscopic properties derived by observations of relativistic processes. Modeling of pure neutron matter Neutron Stars is presented and crust properties are studied by means of a two fluid model.

Alvarez-Castillo, D. E.; Kubis, S. [Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Krakow (Poland)

2011-10-14

202

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

203

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

204

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

205

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

206

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

207

Methanol masers and massive star formation  

Microsoft Academic Search

It has been established that massive stars form in dense clusters, when large molecular clouds collapse. However, the high obscuration and small spatial scales make it difficult to investigate the earliest stage of high mass stellar evolution. Therefore methanol masers are of special interests as they are closely associated with high mass protostars and offer high spatial resolution. We present

Anna Bartkiewicz; Marian Szymczak; Huib Jan van Langevelde

2007-01-01

208

Energy Emission from a Neutron Star  

Microsoft Academic Search

ALTHOUGH there are still many problems concerning the supernovae, there is little doubt that a very dense stellar core has to be left behind after the explosion (at least in some cases). During the contraction of this core, inverse beta reactions take place and transform most of the nuclei and electrons into neutrons. If the mass of the neutron star

F. Pacini

1967-01-01

209

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

210

Superfluidity in dense nuclear matter  

NASA Astrophysics Data System (ADS)

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

Zuo, W.; Lombardo, U.

2009-08-01

211

Radiative properties of dense nanofluids.  

PubMed

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

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

2012-09-01

212

Stationary countable dense random sets  

Microsoft Academic Search

We study the probability theory of countable dense random subsets of (uncountably\\u000ainfinite) Polish spaces. It is shown that if such a set is stationary with respect to\\u000aa transitive (locally compact) group of symmetries then any event which concerns the\\u000arandom set itself (rather than accidental details of its construction) must have\\u000aprobability zero or one. Indeed the result

Wilfrid S. Kendall

2000-01-01

213

Deterministic and unambiguous dense coding  

Microsoft Academic Search

Optimal dense coding using a partially-entangled pure state of Schmidt rank\\u000a$\\\\bar D$ and a noiseless quantum channel of dimension $D$ is studied both in\\u000athe deterministic case where at most $L_d$ messages can be transmitted with\\u000aperfect fidelity, and in the unambiguous case where when the protocol succeeds\\u000a(probability $\\\\tau_x$) Bob knows for sure that Alice sent message $x$,

Shengjun Wu; Scott M. Cohen; Yuqing Sun; Robert B. Griffiths

2006-01-01

214

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

215

Dense periodic packings of tori  

NASA Astrophysics Data System (ADS)

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

Gabbrielli, Ruggero; Jiao, Yang; Torquato, Salvatore

2014-02-01

216

Dense water formation around islands  

NASA Astrophysics Data System (ADS)

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

Spall, Michael A.

2013-05-01

217

Neutron Stars as Physics Laboratories  

NASA Astrophysics Data System (ADS)

X-ray timing and spectrophotometry of accretion-powered neutron stars have been used to determine or constrain many of the intrinsic properties of these stars, including their masses, radii, magnetic fields, spin frequencies, and internal structure. These measurements have important implications for the evolution of ordinary and neutron stars in binary systems, the supernova process in massive stars, accretion-induced collapse of white dwarfs and neutron stars, and the properties of extremely dense matter. High-speed X-ray spectrophotometry has also revealed a variety of phenomena, such as pulse-frequency variations, QPOs, aperiodic X-ray variability, and systematic X-ray brightness and spectral changes that provide valuable information about the structure and dynamics of accretion flows, the interaction of such flows with the magnetic fields and surfaces of neutron stars, and hydrodynamics in the presence of intense radiation and very strong magnetic fields. The X-ray Timing Explorer will have a unique combination of large-area detectors, 2--200 keV energy response, all-sky monitors, microsecond time resolution, sophisticated onboard data processing, high telemetry rates, and unprecedented maneuverability and is expected to produce major advances in these areas of physics and astrophysics. Some of the possible advances will be described.

Lamb, F. K.

1994-12-01

218

Stationary Star  

NSDL National Science Digital Library

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

219

Structure and Thermodynamics of Model Polymer Nanocomposites  

NASA Astrophysics Data System (ADS)

The polymer reference interaction site model (PRISM) theory is employed to study the structure and thermodynamic properties of dense binary mixtures of chain polymers and spherical particles or fillers. A wide range of particle volume fraction, filler diameter, polymer degree of polymerization, and strength of the polymer-particle local cohesive attractions are investigated. The addition of particles results in reorganization of the polymer collective structure on the local cage (amorphous halo), radius of gyration and filler diameter length scales. Microphase like scattering peaks emerge at low wavevectors in both athermal and attractive mixtures which provide insight to the molecular aspects of bound polymer layer formation and steric stabilization of particles. Softening of the bulk modulus is found with the addition of particles which may have implications for filler-induced modification of the glass transition.

Hooper, Justin B.; Schweizer, Kenneth S.

2004-03-01

220

Lateral Instability of Nanoimprinted Polymer Patterns during Thermal Annealing  

Microsoft Academic Search

Nanoimprint Lithography (NIL) is a promising candidate for next generation lithography. Dense polymer patterns with relatively high aspect ratios can be created using NIL. Upon thermal annealing, the as-imprinted polymer patterns will smooth out due to the surface energy and sometimes residual stress within the patterns. Both effects will predominately drive the pattern decay vertically. Here, we present that under

Yifu Ding; Kyle Alvine; Hyunwook Ro; Manish Kulkarni; Jack Douglas; Christopher Soles

2009-01-01

221

Genetics Home Reference: Dense deposit disease  

MedlinePLUS

... II to refer to dense deposit disease. How common is dense deposit disease? Dense deposit disease is very rare, affecting 2 ... the condition? Why are some genetic conditions more common in particular ethnic groups? ... bacteria ; diabetes ; diabetes mellitus ; end-stage renal ...

222

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

223

Organosilane Polymers.  

National Technical Information Service (NTIS)

Purified dialkyldichlorosilane monomers were reacted with alkali metals in organic solvent solutions to form linear diorganosilane homopolymers and copolymers. The organosilane polymers were characterized by spectrometric and thermal analysis. Polymer sol...

J. P. Wesson T. C. Williams

1976-01-01

224

Statistical comparison of clouds and star clusters  

NASA Astrophysics Data System (ADS)

The extent to which the projected distribution of stars in a cluster is due to a large-scale radial gradient, and the extent to which it is due to fractal substructure, can be quantified - statistically - using the measure ?. Here ? is the normalized mean edge length of its minimum spanning tree (i.e. the shortest network of edges connecting all stars in the cluster) and ? is the correlation length (i.e. the normalized mean separation between all pairs of stars). We show how ? can be indirectly applied to grey-scale images by decomposing the image into a distribution of points from which ? and ? can be calculated. This provides a powerful technique for comparing the distribution of dense gas in a molecular cloud with the distribution of the stars that condense out of it. We illustrate the application of this technique by comparing ? values from simulated clouds and star clusters.

Lomax, O.; Whitworth, A. P.; Cartwright, A.

2011-03-01

225

Neutron stars as dark matter probes  

SciTech Connect

We examine whether the accretion of dark matter onto neutron stars could ever have any visible external effects. Captured dark matter which subsequently annihilates will heat the neutron stars, although it seems the effect will be too small to heat close neutron stars at an observable rate while those at the galactic center are obscured by dust. Nonannihilating dark matter would accumulate at the center of the neutron star. In a very dense region of dark matter such as that which may be found at the center of the galaxy, a neutron star might accrete enough to cause it to collapse within a period of time less than the age of the Universe. We calculate what value of the stable dark matter-nucleon cross section would cause this to occur for a large range of masses.

Lavallaz, Arnaud de; Fairbairn, Malcolm [Physics, King's College London, Strand, London WC2R 2LS (United Kingdom)

2010-06-15

226

Circumstellar Material Around Evolved Massive Stars  

NASA Astrophysics Data System (ADS)

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 environments.

Smith, Nathan

2011-01-01

227

Zoetic polymers  

Microsoft Academic Search

Conditions mediating the formation of biological polymers in situ are reviewed, and terminology suggested to differentiate polymers found in living cells from synthetic materials and polymers derived from biological sources that are modified or studied in a way that obscures their biological function. Methods currently used to characterize the mechanical properties of biopolymer networks in cells are briefly discussed.

Ralph Nossal

2004-01-01

228

Discovery of dense absorbing clouds in Cygnus X-2  

NASA Astrophysics Data System (ADS)

We report results of several day-long observation of Cygnus X-2 using Chandra and XMM-Newton. The source displayed extensive dipping events in the lightcurve often seen before in the source and causing an additional track in the hardness-intensity Z-track diagram. For the first time we are able to investigate these events using both high efficiency CCD continuum spectra and highly-resolved grating data. In the XMM PN instrument, the dips are 30% deep and resemble those in the low mass X-ray binary dip sources. However, remarkably, in the Chandra HEG and MEG no absorption or edge features can be seen corresponding to expected increases of column density in excess of the interstellar column. Non-dip and dip PN spectra are fitted well with a model containing point-like blackbody emission which we associate with the neutron star plus Comptonized emission of the ADC which must be extended. Dipping can be explained without absorption of the blackbody emission, but by covering 40% of the extended ADC emission by dense absorber. In the covered fraction almost no flux remains and so no significant additional optical depths appear in the neutral K edges in the grating spectra. The dipping appears not to be explicable by absorption in the outer disk, but requires large, dense blobs of absorber that do not overlap the neutron star in the line-of-sight. The nature of these blobs is unknown.

Balucinska-Church, Monika; Schulz, Norbert S.; Church, Michael; Wilms, Joern; Hanke, Manfred

229

Star Images, Star Performances (College Course File).  

ERIC Educational Resources Information Center

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

Butler, Jeremy G.

1990-01-01

230

Formation and structure of amorphous carbon char from polymer materials  

NASA Astrophysics Data System (ADS)

Amorphous carbonaceous char produced from burning polymer solids has insulating properties that make it valuable in thermal protection and fire-retardant systems. A pyrolytic molecular dynamics simulation method is devised to study the transformation of the local microstructure from virgin polymer to a dense, disordered char. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated char structure. Mechanisms of the char formation process and the morphology of the resulting structures are elucidated.

Lawson, John W.; Srivastava, Deepak

2008-04-01

231

Dilepton Measurements at STAR  

NASA Astrophysics Data System (ADS)

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

Geurts, Frank; STAR Collaboration

2013-08-01

232

Dilatons in Dense Baryonic Matter  

NASA Astrophysics Data System (ADS)

We discuss the role of dilaton, which is supposed to be representing a special feature of scale symmetry of QCD, trace anomaly, in dense baryonic matter. The idea that the scale symmetry breaking of QCD is responsible for the spontaneous breaking of chiral symmetry is presented along the similar spirit of Freund-Nambu model. The incorporation of dilaton field in the hidden local symmetric parity doublet model is briefly sketched with the possible role of dilaton at high density baryonic matter, the emergence of linear sigma model in dilaton limit.

Lee, Hyun Kyu; Rho, Mannque

233

Lattice dynamics of dense lithium.  

PubMed

We report low-frequency high-resolution Raman spectroscopy and ab-initio calculations on dense lithium from 40 to 200 GPa at low temperatures. Our experimental results reveal rich first-order Raman activity in the metallic and semiconducting phases of lithium. The computed Raman frequencies are in excellent agreement with the measurements. Free energy calculations provide a quantitative description and physical explanation of the experimental phase diagram only when vibrational effect are correctly treated. The study underlines the importance of zero-point energy in determining the phase stability of compressed lithium. PMID:22400938

Gorelli, F A; Elatresh, S F; Guillaume, C L; Marqués, M; Ackland, G J; Santoro, M; Bonev, S A; Gregoryanz, E

2012-02-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

235

The Properties of the Dense Gas in the Nuclei of Spiral Galaxies  

NASA Astrophysics Data System (ADS)

The properties of the star-forming clouds in galactic nuclei are largely unknown, and no clear explanation exists for the origin and evolution of starburst galaxies-galaxies with unusually high star formation rates. My goal is to determine the relation between the interstellar cloud properties in galaxies and their star formation activity by estimating the gas densities in starburst galaxies and comparing them to those of normal galaxies and the Milky Way. I perform three programs: observing the emission from dense gas in galaxies, wide-field mapping of the Milky Way, and millimeter-wave interferometry of starburst galaxies. In starburst galaxies, I map the millimeter- and submillimeter-wave emission from molecules that require high densities for excitation, such as hydrogen cyanide and carbon monosulfide. This emission is closely tied to star forming regions. I find that the densest clouds lie within several hundred parsecs of starburst nuclei, and the star formation efficiency of a galaxy is correlated with its average gas density. Unfortunately, the spatial resolution of most observations of galaxies is poor, but comparing different sources properly requires examining them on similar spatial scales. Therefore, to compare the gas properties of starburst galaxies and the Milky Way, I utilize innovations at millimeter-wave telescopes to map the large-scale emission from dense gas in the Milky Way. I find that dense gas comprises a higher fraction of the molecular mass in starburst galaxies than in the Milky Way. Further, the density derived from the averaged spectra of the Milky Way equals the mean density found from modeling each map position. Therefore, analyses of this type probe the average gas properties in galaxies. Finally, I use millimeter-wave interferometry to examine dense gas in starburst galaxies on the spatial scales of individual cloud complexes. I find that dense clouds in starburst galaxies are associated with star-forming regions, and some clouds may contain 20-100 times the number of massive stars as the most luminous star-forming regions in the Milky Way. I also find large-scale gradients in chemical abundances and gas densities.

Paglione, Timothy A. D.

1997-01-01

236

VLA observations of dwarf M flare stars and magnetic stars  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

237

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

238

Dense Quark Matter in Nature  

NASA Astrophysics Data System (ADS)

According to quantum chromodynamics (QCD), matter at ultra-high densities will take the form of a color-superconducting quark liquid, in which there is a condensate of Cooper pairs of quarks near the Fermi surface. I present a review of the physics of color superconductivity. I give particular attention to the recently proposed gapless CFL (gCFL) phase, which has unusual properties such as quasiquarks with a near-quadratic dispersion relation, and which may well be the favored phase of quark matter in the density range relevant to compact stars. I also discuss the effects of color superconductivity on the mass-radius relationship of compact stars, showing that one would have to fix the bag constant by other measurements in order to see the effects of color superconductivity. An additional parameter in the quark matter equation of state connected with perturbative corrections allows quark matter to imitate nuclear matter over the relevant density range, so that hybrid stars can show a mass-radius relationship very similar to that of nuclear matter, and their masses can reach 1.9 M?.

Alford, M.

239

Object recognition in dense clutter.  

PubMed

Observers in recognition experiments invariably view objects against a blank background, whereas observers of real scenes sometimes view objects against dense clutter. In this study, we examined whether an object's background affects the information used for recognition. Our stimuli consisted of color photographs of everyday objects. The photographs were organized either as a sparse array, as is typical of a visual search experiment, or as high density clutter, such as might be found in a toy chest, a handbag, or a kitchen drawer. The observer's task was to locate an animal, vehicle, or food target in the stimulus. We varied the information in the stimuli by convolving them with a low-pass filter (blur) or a high-pass filter (edge) or converting them to grayscale. In two experiments, we found that the blur and edge manipulations produced a modest decrement in performance with the sparse arrangement but a severe decrement in performance with the clutter arrangement. These results indicate that the information used for recognition depends on the object's background. Thus, models of recognition that have been developed for isolated objects may not generalize to objects in dense clutter. PMID:17153187

Bravo, Mary J; Farid, Hany

2006-08-01

240

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

241

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

242

The Structure, Kinematics, and Evolution of Massive Star and Cluster Forming Regions  

NASA Astrophysics Data System (ADS)

The light from massive stars dominates our picture of the universe around us, yet our understanding of the conditions under which massive stars and stellar clusters form and how they evolve is far from complete. I report on the physical properties of dense molecular gas clumps in our Galaxy, derived from Herschel, Spitzer, and the EVLA, and the transformation of these clumps into massive stars and stellar clusters. I present the structure, properties, and dynamics of a massive star-forming Infrared Dark Cloud embedded within a Massive Molecular Filament at high-resolution using NH3 on the EVLA and then expand this to a global view of massive star formation using Herschel and Spitzer. I derive temperatures and column densities from Herschel data using a unique method that separates the dense clumps from the diffuse ISM. Comparing these temperatures and densities with star formation tracers reveals that warmer, more diffuse gas traces active star formation while colder, denser gas remains in a pre- or embedded star-forming phase. I estimate the duration of evolutionary phases of massive star forming clumps from the fraction of Herschel sources exhibiting each star formation tracer. I will discuss the search for pre-cursors to stellar clusters in the Milky Way and what recent results of global dense gas kinematics in star-forming filaments tells us about the mode and duration of star formation in a clustered environment.

Battersby, Cara

2013-01-01

243

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

NASA Astrophysics Data System (ADS)

We present the first images of the J = 5-4 and J = 16-15 lines of the dense gas tracer, cyanoacetylene, HC3N, in an external galaxy. The central 200 pc of the nearby star-forming spiral galaxy, IC 342, was mapped using the Very Large Array and the Plateau de Bure Interferometer. HC3N(5-4) line emission is found across the nuclear mini-spiral, but is very weak toward the starburst site, the location of the strongest mid-IR and radio emission. The J = 16-15 and 10-9 lines are also faint near the large H II region complex, but are brighter relative to the 5-4 line, consistent with higher excitation. The brightest HC3N emission is located in the northern arm of the nuclear mini-spiral, 100 pc away from the radio/IR source to the southwest of the nucleus. This location appears less affected by ultraviolet radiation and may represent a more embedded, earlier stage of star formation. HC3N excitation temperatures are consistent with those determined from C18O; the gas is dense 104 - 105 cm-3 and cool, Tk < 40 K. So as to not violate limits on the total H2 mass determined from C18O, at least two dense components are required to model IC 342's giant molecular clouds. These observations suggest that HC3N(5-4) is an excellent probe of the dense, quiescent gas in galaxies. The high excitation combined with faint emission toward the dense molecular gas at the starburst indicates that it currently lacks large masses of very dense gas. We propose a scenario where the starburst is being caught in the act of dispersing or destroying its dense gas in the presence of the large H II region. This explains the high star formation efficiency seen in the dense component. The little remaining dense gas appears to be in pressure equilibrium with the starburst H II region. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

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

2011-07-01

244

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.

245

Deterministic and unambiguous dense coding  

SciTech Connect

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

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

2006-04-15

246

Water in dense molecular clouds  

NASA Technical Reports Server (NTRS)

The G.P. Kuiper Airborne Observatory (KAO) was used to make initial observations of the half-millimeter ground-state transition of water in seven giant molecular clouds and in two late-type stars. No significant detections were made, and the resulting upper limits are significantly below those expected from other, indirect observations and from several theoretical models. The implied interstellar H2O/CO abundance is less than 0.003 in the cores of three giant molecular clouds. This value is less than expected from cloud chemistry models and also than estimates based on HDO and H3O(+) observations.

Wannier, P. G.; Kuiper, T. B. H.; Frerking, M. A.; Gulkis, S.; Pickett, H. M.; Wilson, W. J.; Pagani, L.; Lecacheux, A.; Encrenaz, P.

1991-01-01

247

Disposable polymer \\  

Microsoft Academic Search

The recent development of an innovative disposable polymer smart lab-on-a-chip, which includes smart passive microfluidics, embedded on-chip power sources, and integrated biosensor array, has opened a new era for the point-of-care testing in clinical diagnostics. Several challenging issues in the development of the disposable polymer smart lab-on-a-chip have been explored and addressed in this work. A new disposable polymer \\

Chong H. Ahn

2005-01-01

248

Polymer Electrolytes  

NASA Astrophysics Data System (ADS)

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

Hallinan, Daniel T.; Balsara, Nitash P.

2013-07-01

249

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

250

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

251

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

PubMed

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

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

2014-06-24

252

Symbiotic stars  

NASA Technical Reports Server (NTRS)

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

253

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

254

Global star formation in the L1630 molecular cloud  

NASA Technical Reports Server (NTRS)

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

Lada, Elizabeth A.

1990-01-01

255

Barrier Polymers  

Microsoft Academic Search

The general theory of permeation of a gas or liquid through a polymer matrix [1] states that permeation is the product of a diffusion term and a solubility constant of the permeant in the polymer matrix, both of which are often independent of each other. The process of permeation through a polymeric barrier involves four steps: absorption of the permeating

M. Salame; S. Steingiser

1977-01-01

256

Disordered polymers  

Microsoft Academic Search

A single polymer macromolecule is considered with disorder types such as branches, knots, and heterogeneous sequences of chemical units. In all cases, simple theoretical approaches are employed to gain useful physical insights. For branched polymers, a simple Flory-type theory is described by means of which the difference between the universality classes for molecules with quenched and annealed branches is demonstrated.

Aleksandr Yu Grosberg

1997-01-01

257

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

258

Antimocrobial Polymer  

Microsoft Academic Search

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

William F. McDonald; Zhi-Heng Huang; Stacy C. Wright

2005-01-01

259

Antimicrobial Polymer  

Microsoft Academic Search

A polymeric composition having antimicrobial properties and a process for rendering the surface of a substrate antimicrobial are disclosed. The polymeric 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 metals, metal alloys, metal salts, metal complexes and mixtures thereof, and (iii)

William F. McDonald; Stacy C. Wright; Andrew C. Taylor

2004-01-01

260

Dense gas around bipolar outflow sources  

Microsoft Academic Search

Stars begin their lives deeply embedded in clouds of gas and dust, and in order to become visible, they have to disperse their obscuring environment. How this transition from embedded object to visible star occurs is not yet well understood, although it is often assumed that a strong wind from the star, in the form of a bipolar outflow, clears

Mario Tafalla

1993-01-01

261

Ultrastable nanostructured polymer glasses.  

PubMed

Owing to the kinetic nature of the glass transition, the ability to significantly alter the properties of amorphous solids by the typical routes to the vitreous state is restricted. For instance, an order of magnitude change in the cooling rate merely modifies the value of the glass transition temperature (T(g)) by a few degrees. Here we show that matrix-assisted pulsed laser evaporation (MAPLE) can be used to form ultrastable and nanostructured glassy polymer films which, relative to the standard poly(methyl methacrylate) glass formed on cooling at standard rates, are 40% less dense, have a 40 K higher T(g), and exhibit a two orders of magnitude enhancement in kinetic stability at high temperatures. The unique set of properties of MAPLE-deposited glasses may make them attractive in technologies where weight and stability are central design issues. PMID:22306770

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

2012-04-01

262

Robotic aided dense medium target fabrication  

Microsoft Academic Search

A method for fabricating dense medium targets with known distributions and scatterer locations has been developed. The technique involves the use of a robot for accurate scatterer positioning. Performing measurements on these targets will give a better understanding of dense medium scattering mechanisms

R. L. Porco; J. W. Bredow; B. L. Huff

1994-01-01

263

Video compression with dense motion fields  

Microsoft Academic Search

We propose a motion-compensated video coding system employing dense motion fields. The dense motion field is calculated at the transmitter, and the motion information is efficiently encoded and transmitted along with the residual frame. The motion estimation is performed by existing techniques in the literature, while we focus on the coding of the motion field and the displaced frame difference

Soo-Chul Han; Christine I. Podilchuk

2001-01-01

264

Boundary effect of deterministic dense coding  

NASA Astrophysics Data System (ADS)

We present a rigorous proof of an interesting boundary effect of deterministic dense coding first observed by S. Mozes, J. Oppenheim, and B. Reznik [Phys. Rev. A 71, 012311 (2005)]. Namely, it is shown that d2-1 cannot be the maximal alphabet size of any isometric deterministic dense coding schemes utilizing d -level partial entanglement.

Ji, Zhengfeng; Feng, Yuan; Duan, Runyao; Ying, Mingsheng

2006-03-01

265

Spatial patterns in dense algal blooms  

Microsoft Academic Search

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

Peter J. S. Franks

1997-01-01

266

Entropic force of polymers on a cone tip  

NASA Astrophysics Data System (ADS)

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

Maghrebi, Mohammad F.; Kantor, Yacov; Kardar, Mehran

2011-12-01

267

Externally fed star formation: a numerical study  

NASA Astrophysics Data System (ADS)

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

Mohammadpour, Motahareh; Stahler, Steven W.

2013-08-01

268

Structure and Thermodynamics of Branched Polymer Melts and Blends  

Microsoft Academic Search

Liquid state theory is employed to study the conformation, intermolecular correlations, thermodynamics and phase behavior of star and comb polymer melts and binary blends of linear and branched macromolecules. Nonideal conformational changes in one-component melts is predicted and its influence on cohesive energy is determined. Binary blends of chemically identical linear and branched polymers are studied at the level of

R. Patil; K. S. Schweizer; T. M. Chang

2002-01-01

269

Chameleon stars  

SciTech Connect

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

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

2011-10-15

270

On the Formation of Glycolaldehyde in Dense Molecular Cores  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

271

Free volume and water vapor permeability of dense segmented polyurethane membrane  

Microsoft Academic Search

This paper presented micro-structure, free volume and water vapor permeability of dense segmented polyurethane (SPU) membrane. Wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques were employed to investigate the micro-structure. Free volume was measured by positron annihilation life spectroscopy (PALS). WAXD and DSC results indicated microcrystalline structure presents in the polymer membrane. Percent

S. Mondal; J. L. Hu; Z. Yong

2006-01-01

272

HNCO in massive galactic dense cores  

NASA Astrophysics Data System (ADS)

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

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

2000-09-01

273

Brittle Star  

USGS Multimedia Gallery

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

2010-04-15

274

Polymer nanolithography  

NASA Astrophysics Data System (ADS)

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

Vance, Jennifer M.

275

On the massive star-forming capacity of molecular clouds  

NASA Technical Reports Server (NTRS)

Assuming that photoionization is the self-limiting process for continued star formation, we estimate the maximum number of massive (OB) stars that can form within a molecular cloud. The most efficient cloud destruction mechanism in the early stages of H II region evolution is the evaporation of the cloud by stars located near the cloud boundary. The maximum number of OB stars is of order 1 per 10(exp 4) solar mass of average molecular gas, or 10 per 10(exp 4) solar mass of dense molecular gas. The resulting star-forming efficiencies within cloud complexes range from 2% to 16% depending on both the location of the stars in the cloud and the details of the initial mass function, with an overall value of about 5% for average molecular gas.

Franco, Jose; Shore, Steven N.; Tenorio-Tagle, Guillermo

1994-01-01

276

Unraveling the Origins of Nearby Young Stars  

NASA Astrophysics Data System (ADS)

A systematic search for close conjunctions and clusterings in the past of nearby stars younger than the Pleiades is undertaken, which may reveal the time, location, and mechanism of formation of these often isolated, disconnected from clusters and star-forming regions, objects. The sample under investigation includes 101 T Tauri, post-TT, and main-sequence stars and stellar systems with signs of youth, culled from the literature. Their Galactic orbits are traced back in time and near approaches are evaluated in time, distance, and relative velocity. Numerous clustering events are detected, providing clues to the origin of very young, isolated stars. Each star's orbit is also matched with those of nearby young open clusters, OB and TT associations and star-forming molecular clouds, including the Ophiuchus, Lupus, Corona Australis, and Chamaeleon regions. Ejection of young stars from open clusters is ruled out for nearly all investigated objects, but the nearest OB associations in Scorpius-Centaurus, and especially, the dense clouds in Ophiuchus and Corona Australis have likely played a major role in the generation of the local streams (TWA, Beta Pic, and Tucana-Horologium) that happen to be close to the Sun today. The core of the Tucana-Horologium association probably originated from the vicinity of the Upper Scorpius association 28 Myr ago. A few proposed members of the AB Dor moving group were in conjunction with the coeval Cepheus OB6 association 38 Myr ago.

Makarov, Valeri V.

2007-03-01

277

Field theoretic simulations of polymer nanocomposites  

NASA Astrophysics Data System (ADS)

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.

2013-12-01

278

Molecular dynamics for dense matter  

NASA Astrophysics Data System (ADS)

We review a molecular dynamics method for nucleon many-body systems called quantum molecular dynamics (QMD), and our studies using this method. These studies address the structure and the dynamics of nuclear matter relevant to neutron star crusts, supernova cores, and heavy-ion collisions. A key advantage of QMD is that we can study dynamical processes of nucleon many-body systems without any assumptions about the nuclear structure. First, we focus on the inhomogeneous structures of low-density nuclear matter consisting not only of spherical nuclei but also of nuclear "pasta", i.e., rod-like and slab-like nuclei. We show that pasta phases can appear in the ground and equilibrium states of nuclear matter without assuming nuclear shape. Next, we show our simulation of compression of nuclear matter which corresponds to the collapsing stage of supernovae. With the increase in density, a crystalline solid of spherical nuclei changes to a triangular lattice of rods by connecting neighboring nuclei. Finally, we discuss fragment formation in expanding nuclear matter. Our results suggest that a generally accepted scenario based on the liquid-gas phase transition is not plausible at lower temperatures.

Maruyama, Toshiki; Watanabe, Gentaro; Chiba, Satoshi

2012-08-01

279

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

280

Massive Star Formation in the Galactic Center as Revealed by Spitzer\\/IRAC Observations  

Microsoft Academic Search

We investigate massive star formation in the central 280x210 pc of the Galaxy as revealed by Spitzer Space Telescope\\/IRAC observations (Stolovy et al., this conference). The region contains three known extremely dense clusters of massive hot young stars which ionize the unusual thermal filaments that are seen at radio wavelengths and in PAH emission in the IRAC images. We will

A. S. Cotera; S. Stolovy; S. Ramirez; J. Karr; R. G. Arendt; D. Gezari; H. Moseley; C. Law; F. Yusef-Zadeh; K. Sellgren; H. A. Smith; R. Smith

2005-01-01

281

LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION  

SciTech Connect

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

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

2010-12-10

282

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

283

Spectroscopy: Star Light, Star Bright  

NSDL National Science Digital Library

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

284

Converting neutron stars into strange stars  

NASA Technical Reports Server (NTRS)

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

Olinto, A. V.

1991-01-01

285

Comparison of star and linear ArF resists  

NASA Astrophysics Data System (ADS)

Linear and star-shaped ArF photoresists were prepared and preliminary lithographic comparison was performed using electron-beam exposure. An oligo-initiator based on saccharose forms the core of the star shaped photoresist from which three standard ArF photoresist monomers, ?-gamma butyrolactone methacrylate (GBLMA), methyl adamantyl methacrylate (MAMA) and hydroxyl adamantyl methacrylate (HAMA) were polymerized. Conditions were adjusted to obtain a low polydispersity, 6 kg/mol star polymer with a degree of polymerization of approximately five mers per arm. For comparison, a linear photoresist control was prepared using the same scheme. The star resist architecture was found to improve roughness without reducing sensitivity or resolution.

Forman, Drew C.; Wieberger, Florian; Gröschel, Andre; Müller, Axel H. E.; Schmidt, Hans-Werner; Ober, Christopher K.

2010-03-01

286

Fabrication of Dense Fine Grained Ceramic Materials.  

National Technical Information Service (NTIS)

High pressure hot pressing was used to prepare dense, crack free billets of boron carbide, silicon carbide, titanium carbide and titanium nitride. These materials were fabricated from high purity powders without the additions of densification promoters. F...

D. Kalish E. V. Clougherty J. Ryan

1966-01-01

287

Complementary Heating of Densely Packaged Microcircuits.  

National Technical Information Service (NTIS)

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

H. F. Dean

1967-01-01

288

Transport Properties of Dense Laser Plasmas.  

National Technical Information Service (NTIS)

Generalized kinetic equations are used to investigate transport properties of dense plasmas in strong laser fields. Quantum statistical expressions are derived for, e.g., the collision frequency to account for nonlinear field phenomena as well as strong c...

D. Kremp M. Schlanges P. Hilse T. Bornath

2003-01-01

289

Supported Dense Ceramic Membranes for Oxygen Separation.  

National Technical Information Service (NTIS)

This report describes results from the first contract year of a research project whose overall objective is to explore the fundamental and practical issues confronting the successful development of thick-film dense ceramic membrane technology for oxygen s...

T. L. Ward

2000-01-01

290

Dense feature maps for detection of calcifications.  

National Technical Information Service (NTIS)

We present initial results on the use of dense feature maps classified by binary decision trees for the detection of clusters of calcification. This extends prior work which used the same technique to detect speculated lesions in mammograms. To determine ...

W. P. Kegelmeyer M. C. Allmen

1994-01-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

292

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

293

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

294

Extinction with 2MASS: star counts and reddening toward the North America and the Pelican Nebulae  

NASA Astrophysics Data System (ADS)

We propose a general method to map the extinction in dense molecular clouds using 2MASS near-infrared data. It is based on the simultaneous utilization of star count and color analysis. These two techniques provide independent estimations of the extinction and each method reacts differently to foreground star contamination and to star clustering. We take advantage of the specificities of both methods to build a large scale extinction map of the North America-Pelican nebulae complex. With Ks star counts and H-Ks color analysis the visual extinction is mapped up to 35 mag and nine star clusters are identified in the area.

Cambresy, L.; Beichman, C. A.; Jarrett, T. H.; Cutri, R. M.

2001-05-01

295

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

296

Electron scattering in hot-dense plasmas  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

297

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

NASA Astrophysics Data System (ADS)

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

Vanbeveren, D.

298

Mixed-ionic and electronic conductivity in polymers  

SciTech Connect

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

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

1991-01-01

299

Features of nucleosynthesis in binary stars  

NASA Astrophysics Data System (ADS)

Chemical anomalies observed in some binary stars are analyzed. These anomalies are caused by: (1) nuclear processes in their cores; (2) diffusive and convective mixing of material between neighboring layers with nuclear heating; and, (3) ejection of matter from the surface into interstellar space. The effect of merging of the components of multiple stars in dense star-dust complexes on the evolution of the chemical composition is examined. It is shown that the neutrino yield from these complexes can increase. The estimated neutrino fluxes from the Orion nebula complex and the nucleus of the galaxy can be as high as 5?105 and 104 cm-2s-1, respectively, at the earth.

Leushin, V. V.

2013-06-01

300

In situ diffusion measurements during RBS analysis of polymers coated with aluminium  

Microsoft Academic Search

Using metal plasma immersion ion implantation and deposition (MePIIID), it is possible to form dense metallic layers with excellent adhesion properties at low temperatures, for example on polymers. Rutherford backscattering spectroscopy is one method to determine the thickness of the layer and the interface: albeit, the polymer is destroyed by the high energy ions and gaseous products can diffuse out.

S. Mändl; B. Stritzker; B. Rauschenbach

2002-01-01

301

Tethered polymer chains: surface chemistry and their impact on colloidal and surface properties  

Microsoft Academic Search

In this review the grafting of polymer chains to solid supports or interfaces and the subsequent impact on colloidal properties is examined. We start by examining theoretical models for densely grafted polymers (brushes), experimental techniques for their preparation and the properties of the ensuing structures. Our aim is to present a broad overview of the state of the art in

E. P. K. Currie; W. Norde; M. A. Cohen Stuart

2003-01-01

302

Polymers Technical Activities, 1996.  

National Technical Information Service (NTIS)

Technical activities for the Polymers Division, 854, for the 1996 fiscal year are described. The report is organized by programs: Electronic Packaging and Interconnections, Polymer Blends and Processing, Polymer Composites, Polymer Characterization, Denta...

B. M. Fanconi L. E. Smith

1996-01-01

303

Study of Stellar Clusters Containing Massive Stars  

NASA Astrophysics Data System (ADS)

Most stars form in clusters, but the percentage of stars born in dense stellar systems is currently matter of controversy and depends very much on the own definition of cluster. The cluster definition and hence the morphologies of individual clusters appear to vary significantly from region to region, as well as with age, which suggests that either, star formation in clusters is not universal and may depend on the local environment, or that all clusters form with the same morphology but early dynamical evolution quickly modifies the structure of the phase space distribution. In addition, young populated clusters containing massive stars are excellent labs for the study of the formation of the massive stellar component of the Galactic disk. Three main scenarios have been proposed for the formation of high-mass stars (M > 7-8 M_{?}): a) monolithic collapse of proto-stellar nuclei; b) competitive accretion inside the proto-cluster molecular cloud; and c) coalescence of proto-stellar nuclei and low-mass stars in very dense atmospheres. Both scientific questions: a) cluster formation and b) formation of high mass stars in clusters are intimately connected via the structural description of the phase space distribution of cluster stars and their Mass Function (MF). Models of static clusters with different initial spatial and kinematic distributions show how the spatial distribution dynamically evolves with time, allowing a characterization of their dynamical state from snapshots of their spatial distribution. Four are the main variables (and their distribution with mass and position) needed for a reliable characterization of the cluster dynamical state: a) Mass segregation parameter; b) Mapping of surface density for different ranges of masses; c) Q morphological parameter based on the minimum spanning tree graph and its variation with mass and cluster age, and d) MF of the cluster members. Two years ago, the Stellar System Group of IAA has begun an observational programme of stellar clusters containing massive stars, whose main objective is to answer the two scientific questions. In order to perform this study we need to measure the main physical variables of the cluster, determine cluster membership and mass and age of cluster members. The obtaining of this is best carried out through determination of the Spectral Energy Distribution (SED) of stars in the field, from multiband UBVRIH? + JHKs photometry. In this conference, we want to present some results for clusters currently under study.

Costado, Teresa; Alfaro, E. J.; Delgado, A. J.; Djupvik, A. A.; Maíz Apellániz, J.

2013-06-01

304

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

305

Antimicrobial Polymer  

DOEpatents

A polymeric composition having antimicrobial properties and a process for rendering the surface of a substrate antimicrobial are disclosed. The polymeric 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 metals, metal alloys, metal salts, metal complexes and mixtures thereof, and (iii) a crosslinking agent containing functional groups capable of reacting with the amino groups. In one example 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).sub.3 P wherein A is hydroxyalkyl; and the metallic antimicrobial agent is selected from chelated silver ions, silver metal, chelated copper ions, copper metal, chelated zinc ions, zinc metal and mixtures thereof.

McDonald, William F. (Utica, OH); Wright, Stacy C. (Flint, MI); Taylor, Andrew C. (Ann Arbor, MI)

2004-09-28

306

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

307

The sun, our star  

NASA Astrophysics Data System (ADS)

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

Noyes, R. W.

308

Glue Polymer  

NSDL National Science Digital Library

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

Mid-continent Research for Education and Learning (McREL); Jacobs, Steve

2004-01-01

309

HUBBLE CAPTURES THE HEART OF STAR BIRTH  

NASA Technical Reports Server (NTRS)

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

2002-01-01

310

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

SciTech Connect

In this paper the following items will be treated: The present status of dense nuclear matter calculations and constraints on the behavior of the associated equation of state at high densities from data on rapidly rotating pulsars. Recent finding of the likely existence of a mixed phase of baryons and quarks forming a coulomb lattice in the dense cores of neutron stars. Review of important findings of recently performed calculations of rapidly rotating compact stars. These are constructed in the framework of general relativity theory for a representative collection of realistic nuclear equations of state. Establish the minimum-possible rotational periods of gravitationally bound neutron stars and self-bound strange stars. Its knowledge is of fundamental importance for the decision between pulsars that can be understood as rotating neutron stars and those that cannot (signature of hypothetical self-bound matter of which strange stars are the likely stellar candidates. Investigate the properties of sequences of strange stars. Specifically, we answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

Weber, F. [Technische Univ. Muenchen, Garching (Germany). Inst. fuer Theoretische Physik]|[Lawrence Berkeley Lab., CA (United States); Glendenning, N.K. [Lawrence Berkeley Lab., CA (United States)

1993-10-25

311

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

312

Data Characterization Using Artificial-Star Tests: Performance Evaluation  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

313

Coarse-grained simulations of moderately entangled star polyethylene melts  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

314

DB Pulsating Stars  

NASA Astrophysics Data System (ADS)

Pulsating WHITE DWARF stars with nearly pure helium atmospheres exist in a narrow temperature range near 25 000 K. At this writing, there are eight of these stars known. Collectively, they go by two names: the V777 Her stars, named after the VARIABLE STAR designation of the first known star in the class, and the more informative name, the DBV stars. The name DBV follows the standard convention fo...

Winget, D.; Murdin, P.

2000-11-01

315

The role of low-mass star clusters in forming the massive stars in DR 21  

NASA Astrophysics Data System (ADS)

We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing optical and infrared (IR) surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMS low-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three main stellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. The cross-correlated X-ray/IR sample exhibits a radial `Spokes-like' stellar filamentary structure that extends from the DR 21 core towards the northeast. The near-IR data reveal a centrally peaked structure for the extinction, which exhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to the cluster centre. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of a stellar age segregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed. The results are consistent with the scenario where an elongated overall potential well created by the full low-mass stellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller scale local potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for the gas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellar collision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale and highly energetic outflow arising from this region.

Rivilla, V. M.; Jiménez-Serra, I.; Martín-Pintado, J.; Sanz-Forcada, J.

2014-01-01

316

Electroconductive Polymers.  

PubMed

Polymers of a new type with an unusual combination of properties have been synthesized. They are of high molecular weight, they are soluble in organic solvents, and they can be cast as films. Their electrical conduction is electronic in the solid state and can be controlled up to a conductivity of 10(-2) ohm(-1) cm(-1). PMID:17832400

Lupinski, J H; Kopple, K D

1964-11-20

317

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) [Bremen, DE; Miller, Kevin Michael (West Dundee, IL) [West Dundee, IL

2011-07-26

318

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

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

Molecular Geometry Fluctuation Model for the Mobility of Conjugated Polymers  

SciTech Connect

We present a model to describe electrical transport in dense films of conjugated polymers. The essential physical features of the model are as follows: (i) thermal fluctuations in the molecular geometry of the polymer modify the energy levels of localized electronic states in the material, and (ii) the primary restoring force for these fluctuations is steric, which leads to spatial correlation in the energies of the localized electronic states. The model describes the electric field dependence of the mobility and explains the carrier density dependences of mobility observed in polymer diodes and field effect transistors. (c) 2000 The American Physical Society.

Yu, Z. G.; Smith, D. L.; Saxena, A.; Martin, R. L.; Bishop, A. R.

2000-01-24

321

Formation and structure of amorphous carbon char from polymer materials  

NASA Astrophysics Data System (ADS)

Amorphous carbonaceous char produced from burning polymer solids has insulating properties that makes it valuable for aerospace thermal protection systems as well as for fire retardants. A pyrolytic molecular dynamics simulation method is devised to study the transformation of the local microstructure from virgin polymer to a dense, disordered char. Release of polymer hydrogen is found to be critical to allow the system to collapse into a highly coordinated structure. Mechanisms of the char formation process and the morphology of the resulting structure are elucidated.

Lawson, John; Srivastava, Deepak

2008-03-01

322

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

323

Instabilities of a dense suspension jet  

NASA Astrophysics Data System (ADS)

We present experimental results on the behaviour of a dense suspension jet falling in a large volume of clear liquid. The jet is driven by gravity from a cylindrical reservoir full of a packed suspension. Different regimes are observed, depending on the Reynolds number of the jet, computed with the velocity of the suspension at the outlet of the reservoir. For viscous regimes, a striking feature is the formation of droplets of dense suspension which may be also unstable during their fall. For inertial regimes (large Reynolds number), dispersion of the particles occurs.

Nicolas, Maxime

2000-11-01

324

HOBYS Observations of Ridges and Filaments, and the Evolution of Massive Dense Cores  

NASA Astrophysics Data System (ADS)

Herschel large-scale observations of close-by massive star-forming regions obtained by HOBYS provide an unbiased view on the detailed cloud structure and its population of massive dense cores - excellent candidates for high-mass star precursors. Structures like the DR21 ridge, the most massive cloud structure in Cygnus X, could be formed by the merging of filaments or flows: several connected sub-filaments are resolved with Herschel. The sub-filaments are gravitationally unstable and form cores and protostars which may become low-mass members of the forming OB star cluster(s). They show decreasing dust temperature towards the ridge, indicating the pile-up of material to high densities which cools down to a minimum of 14 K towards the Northern part. The present mass in the sub-filaments is a factor of three lower than the ridge mass, so they represent remnant flows. However, their link to the clumps around DR21 and DR21(OH) suggests that these flows have been important to build-up massive clumps inside the ridge. Extrapolating, we would expect the assembly of massive clumps towards the Northern part of the DR21 ridge where the most massive subfilaments connect, in continuation of the evolutionary sequence of star formation along the ridge from South to North. We also use the large coverage of Cygnus X obtained by HOBYS (7,000 pc2) to establish an extensive sample of compact, cold, and dense cores in the region and constrain their luminosities, dust temperatures, and envelope masses. An evolutionary diagram and simple evolutionary tracks show that the sample provides the statistics to study the formation of stars with mass up to 20 M?.

Hennemann, Martin; Motte, Frédérique; Schneider, Nicola

325

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

NASA Astrophysics Data System (ADS)

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

Rivilla, V. M.; Martín-Pintado, J.; Jiménez-Serra, I.; Rodríguez-Franco, A.

2013-06-01

326

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

327

Star Search  

NSDL National Science Digital Library

In this online activity, learners can test their skills at finding constellations in the northern hemisphere's night sky. Learners can choose during which season to look, and then look for four constellations in that season. The simulation shows a simple representation of the night sky with key stars highlighted. Use this as a practice before going outside or just to give learners an idea of the difficulties involved in identifying constellations. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.

Science, American A.

2009-01-01

328

Image restoration of R136 - The dense core of NGC 2070  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

329

O stars and Wolf-Rayet stars  

NASA Technical Reports Server (NTRS)

Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (editor); Thomas, Richard (editor)

1988-01-01

330

Highly charged ions in hot, dense plasmas.  

National Technical Information Service (NTIS)

Highly-charged ions play a critical role in hot, dense plasmas. They affect the energy balance and hydrodynamic evolution of transient plasmas. The radiation emitted by highly charged ions may be used in several practical applications, such as inertial co...

A. L. Osterheld R. S. Walling B. K. F. Young W. H. Goldstein G. Shimkaveg

1992-01-01

331

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

332

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

333

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...

334

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

335

Dense LU Factorization on Multicore Supercomputer Nodes.  

National Technical Information Service (NTIS)

Dense LU factorization is a prominent benchmark used to rank the performance of supercomputers. Many implementations use block-cyclic distributions of matrix blocks onto a two-dimensional process grid. The process grid dimensions drive a trade-off between...

A. Arya J. Lifflander L. Kale P. Miller R. Venkataraman T. Jones

2013-01-01

336

Dense molecular gas in nearby galaxies  

NASA Astrophysics Data System (ADS)

We present the first observational evidence that the dense molecular gas, traced by HCN emission, is not confined to the inner ~1 kpc nuclear region in galaxies, although the highest concentrations of dense molecular gas are in the center. A significant fraction of dense molecular gas is distributed in the inner disks of galaxies outside the central starburst regions, and can be detected to radii as large as a few kpc, perhaps to diameters of D25/4. The starburst cores in galaxy centers usually have the highest fraction of dense molecular gas with surface brightness ratio (SBR = IHCN/ICO) ~0.1, comparable to those of ultraluminous IR galaxies, whereas this SBR ratio generally falls off in the galaxy inner disks at larger radii to a very low SBR ~0.01-0.03. However, some galaxies (IC 342 and NGC 6946) have pretty high SBR across over the inner disks we observed (3'-4' ~3-7 kpc in diameter), yet do not show apparent strong nuclear starburst core (or the size scale of nuclear starburst region is much smaller than our observed beam resolution). We suggest that the SBR and the global LHCN/LCO luminosity ratio (averaged SBR) may be a good indicator of starburst in galaxies and its relation with the galactic radius together with the distribution of the HCN emission may reveal the size scale of the nuclear starburst core or the scale of global starburst region in the centers of galaxies.

Gao, Y.; Solomon, P. M.

337

Dense Surface Models of the Human Face  

Microsoft Academic Search

Abstract This thesis describes and evaluates Dense Surface Models (DSMs), a new technique for building point distribution models of surfaces, from raw input data. DSMs can be used on data from a wide range of surface acquisition systems without preprocessing since they do not require that the surfaces be closed or even locally manifold, and can cope well with holes

Tim J. Hutton

2004-01-01

338

Molecule formation in cool, dense interstellar clouds  

Microsoft Academic Search

A discussion is given of the general processes and considerations that arise in attempting to understand molecular reactions in cool, dense interstellar clouds. Basic elements of the gas phase, 'ion-molecule' scheme are given explicitly before surveying topics in which there is considerable current activity. These topics include: (1) refined comparisons of prediction and observation for species of 'intermediate' complexity, (2)

W. D. Watson

1980-01-01

339

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

340

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

2010-12-07

341

Dense ceramic membranes for methane conversion.  

National Technical Information Service (NTIS)

This report focuses on a mechanism for oxygen transport through mixed- oxide conductors as used in dense ceramic membrane reactors for the partial oxidation of methane to syngas (CO and H(sub 2)). The in-situ separation of O(sub 2) from air by the membran...

U. Balachandran R. L. Mieville B. Ma C. A. Udovich

1996-01-01

342

Recent Developments in Dense Numerical Linear Algebra  

Microsoft Academic Search

We survey recent developments in dense numerical linear algebra, coveringlinear systems, least squares problems and eigenproblems. Topicsconsidered include the design and analysis of block, partitioned and parallelalgorithms, condition number estimation, componentwise error analysis,and the computation of practical error bounds. Frequent referenceis made to LAPACK, the state of the art package of Fortran software designedto solve linear algebra problems efficiently and

Nicholas J. Higham

2000-01-01

343

Chiral thermodynamics of dense hadronic matter  

SciTech Connect

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

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

2012-05-15

344

Neutrino physics in hot and dense media  

SciTech Connect

Neutrino dispersion in hot and dense media is calculated for ranges of temperature and chemical potential [ital T], [mu][much lt][ital T][sub QCD] (200 MeV) for energies [ital q][sup 2][much lt][ital m][sub [ital Z

Masood, S.S. (Department of Physics, Quaid-i-Azam University, Islamabad (Pakistan))

1993-10-01

345

Advanced Polymer  

NASA Technical Reports Server (NTRS)

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

1992-01-01

346

Emulsion Polymers  

NASA Astrophysics Data System (ADS)

The symposium "Emulsion Polymers" was held at the 217th American Chemical Society (ACS) Meeting in Anaheim, CA in March 1999. Topic areas presented included novel concepts in emulsion and miniemulsion homo- and copolymerization, the role of polymeric stabilizers in emulsion polymerization, particle morphology and film formation, and applications of latex systems. The papers in this volume of Macromolecular Symposia cover a broad range of topics characteristic of the symposium.

El-Aasser, Mohamed S.; Smith, Carrington D.; Meisel, I.; Spiegel, S.; Kniep, C. S.

2000-08-01

347

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

348

THE DEPENDENCE OF STAR FORMATION EFFICIENCY ON GAS SURFACE DENSITY  

SciTech Connect

Studies by Lada et al. and Heiderman et al. have suggested that star formation mostly occurs above a threshold in gas surface density {Sigma} of {Sigma}{sub c} {approx} 120 M{sub Sun} pc{sup -2} (A{sub K} {approx} 0.8). Heiderman et al. infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area {Sigma}{sub SFR} with increasing {Sigma}, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of {Sigma}{sub SFR}, approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of {Sigma}{sub SFR} versus {Sigma} in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A {approx} {Sigma}{sup -3} for low-mass regions and A {approx} {Sigma}{sup -1} for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada et al. similarly does not demand a particular threshold for star formation and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse.

Burkert, Andreas [University Observatory Munich, Scheinerstrasse 1, D-81679 Munich (Germany); Hartmann, Lee, E-mail: burkert@usm.lmu.de, E-mail: lhartm@umich.edu [Department of Astronomy, University of Michigan, 830 Dennison, 500 Church St., Ann Arbor, MI 48109-1042 (United States)

2013-08-10

349

The Dependence of Star Formation Efficiency on Gas Surface Density  

NASA Astrophysics Data System (ADS)

Studies by Lada et al. and Heiderman et al. have suggested that star formation mostly occurs above a threshold in gas surface density ? of ? c ~ 120 M ? pc-2 (AK ~ 0.8). Heiderman et al. infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area ?SFR with increasing ?, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of ?SFR, approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of ?SFR versus ? in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A ~ ?-3 for low-mass regions and A ~ ?-1 for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada et al. similarly does not demand a particular threshold for star formation and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse.

Burkert, Andreas; Hartmann, Lee

2013-08-01

350

Lifestyles of the Stars.  

ERIC Educational Resources Information Center

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

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

351

StarHeads  

NSDL National Science Digital Library

StarHeads, the last product of the Star*s Family is now available at the Centre de Donnees astronomiques de Strasbourg (CDS). StarHeads gives access to about 400 individual pages of astronomers and space scientists, and this figure is rapidly growing. Forms based browser is required.

352

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

NASA Astrophysics Data System (ADS)

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

Storm, Shaye; Mundy, Lee

2014-07-01

353

The Warm And Dense Gas In Embedded Low-mass Protostars  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

354

Surveying the Dense Gas in Barnard 1 and NGC 1333 from Cloud to Core Scales  

NASA Astrophysics Data System (ADS)

The CARMA Large Area Star formation Survey (CLASSy) is mapping molecular emission across large areas of the nearby Perseus and Serpens Molecular Clouds. With an angular resolution of 7 arcsec, CLASSy probes dense gas on scales from a few thousand AU to parsecs with CARMA-23 and single-dish observations. The resulting maps of N2H+, HCN, and HCO+ J=1-0 trace the kinematics and structure of the high-density gas in regions covering a wide range of intrinsic star formation activity. This poster presents an overview of three completed CLASSy fields, NGC 1333, Barnard 1, and Serpens Main, and then focuses on the dendrogram analysis that CLASSy is using to characterize the emission structure. We have chosen a dendrogram analysis over traditional clump finding because dendrograms better encode the hierarchical nature of cloud structure and better facilitate analysis of cloud properties across the range of size scales probed by CLASSy. We present a new dendrogram methodology that allows for non-binary mergers of kernels, which results in a gas hierarchy that is more true to limitations of the S/N in the data. The resulting trees from Barnard 1 and NGC 1333 are used to derive physical parameters of the identified gas structures, and to probe the kinematic relationship between gas structures at different spatial scales and evolutionary stages. We derive a flat relation between mean internal turbulence and structure size for the dense gas in both regions, but find a difference between the magnitude of the internal turbulence in regions with and without protostars; the dense gas in the B1 main core and NGC 1333 are characterized by mostly transonic to supersonic turbulence, while the B1 filaments and clumps southwest of the main core have mostly subsonic turbulence. These initial results, along with upcoming work analyzing the completed CLASSy observations, will be used to test current theories for star formation in turbulent molecular clouds.

Storm, Shaye; Mundy, Lee; Teuben, Peter; Lee, Katherine; Fernandez-Lopez, Manuel; Looney, Leslie; Rosolowsky, Erik; Classy Collaboration

2013-07-01

355

Nanoporous organic polymer networks  

Microsoft Academic Search

Nanoporous organic polymer networks are a class of materials consisting solely of the lighter elements in the periodic table. These materials have potential uses in areas such as storage, separation, and catalysis. Here, we review the different classes of nanoporous polymer networks including covalent organic frameworks, hypercrosslinked polymers, conjugated microporous polymers, and polymers of intrinsic microporosity. The growing variety in

Robert Dawson; Andrew I. Cooper; Dave J. Adams

356

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

PubMed Central

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

Guo, Guangqing; Fan, Yuwei

2011-01-01

357

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

NSDL National Science Digital Library

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

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

1990-07-10

358

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

NSDL National Science Digital Library

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

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

1990-07-10

359

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

NSDL National Science Digital Library

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

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

1990-07-10

360

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

NSDL National Science Digital Library

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

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

1990-07-10

361

The Pillar in the Carina Nebula lithograph and In Search of...Star Birth activity  

NSDL National Science Digital Library

This Hubble Space Telescope image shows the tip of a huge pillar of star birth in a turbulent stellar nursery called the Carina Nebula. Nestled inside this dense structure are fledgling stars. They cannot be seen in this image because they are hidden by a wall of gas and dust. The accompanying classroom activity In Search ofâ¦Star Birth is designed for use as an introductory inquiry classroom activity. Students use the images and text on this lithograph to generate questions about star formation. They will conduct research to answer their questions. Students will create a presentation to demonstrate their understanding of the material, providing supporting evidence from their research.

Eisenhamer, Bonnie

2010-07-01

362

He 3-519 - A peculiar post-LBV, pre-WN star?  

NASA Technical Reports Server (NTRS)

We report IUE and ground-based data indicating that the star He 3-519 has a distance of roughly 8 kpc and an absolute bolometric magnitude of about -11, comparable to AG Car. Its luminosity, spectrum, and large, massive circumstellar shell indicate that this may be a post-LBV object which has not yet become a full-fledged WN star. One notable peculiarity of He 3-519 is its prominent Fe III (?) 3008 A emission; the reason why this feature is so bright in this star's dense envelope or wind, but not in other related stars, is not yet clear.

Davidson, Kris; Humphreys, Roberta M.; Hajian, Arsen; Terzian, Yervant

1993-01-01

363

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

SciTech Connect

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

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

2008-01-01

364

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

NASA Astrophysics Data System (ADS)

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

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

365

KEY ISSUES REVIEW: Insights from simulations of star formation  

NASA Astrophysics Data System (ADS)

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

Larson, Richard B.

2007-03-01

366

Global star formation in the L1630 molecular cloud  

NASA Astrophysics Data System (ADS)

The results of a study of dense cores and star formation in the L1630 (Orion B) molecular cloud are presented. Unbiased, well sampled, systematic surveys for density condensations and embedded infrared sources in the L1630 cloud were completed in an attempt to understand the relationship between dense cores and young stars. To identify the dense cores, L1630 was surveyed in the J=2-1 transition of CS using a 7-m telescope. Thirteen thousand positions were surveyed with 1 degree spacing to an rms noise level of 0.2 K. The total area covered was approximately 3.6 square degrees. Emission was detected over 10 percent of the area surveyed and this emission is not uniformly distributed throughout the cloud but is confined in 42 dense cores. A 2.2 micron survey of a significant portion of the L1630 cloud was carried out using an infrared array camera on a 1.3-m telescope. Three thousand 1 degree x 1 degree fields were surveyed, covering an area of approximately 0.8 square degrees. These regions included both areas containing CS emission and areas without CS emission. The completeness limit of this survey is estimated to be 13th magnitude at K (approximately 0.16 solar mass main sequence dwarf). As a result, four embedded infrared clusters were identified. These embedded clusters contain at least 58 percent but possibly as much as 96 percent of the total number of sources associated with this molecular cloud suggesting that the dominant mode of star formation in this region is in clusters. The CS and 2.2 micron surveys of L1630 provided the first census of dense cores and young stellar objects within a molecular cloud. A comparison of these surveys clearly shows that star formation in the region surveyed occurs exclusively in the dense gas. It is shown that the star formation in L1630 is a highly localized process both within the molecular cloud and within the dense gas.

Lada, Elizabeth Anne

367

ICES IN THE QUIESCENT IC 5146 DENSE CLOUD  

SciTech Connect

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

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

2011-04-10

368

Ices in the Quiescent IC 5146 Dense Cloud  

NASA Astrophysics Data System (ADS)

This paper presents spectra in the 2 to 20 ?m range of quiescent cloud material located in the IC 5146 cloud complex. The spectra were obtained with NASA's Infrared Telescope Facility SpeX instrument and the Spitzer Space Telescope's Infrared Spectrometer. We use these spectra to investigate dust and ice absorption features in pristine regions of the cloud that are unaltered by embedded stars. We find that the H2O-ice threshold extinction is 4.03 ± 0.05 mag. Once foreground extinction is taken into account, however, the threshold drops to 3.2 mag, equivalent to that found for the Taurus dark cloud, generally assumed to be the touchstone quiescent cloud against which all other dense cloud and embedded young stellar object observations are compared. Substructure in the trough of the silicate band for two sources is attributed to CH3OH and NH3 in the ices, present at the ~2% and ~5% levels, respectively, relative to H2O-ice. The correlation of the silicate feature with the E(J - K) color excess is found to follow a much shallower slope relative to lines of sight that probe diffuse clouds, supporting the previous results by Chiar et al.

Chiar, J. E.; Pendleton, Y. J.; Allamandola, L. J.; Boogert, A. C. A.; Ennico, K.; Greene, T. P.; Geballe, T. R.; Keane, J. V.; Lada, C. J.; Mason, R. E.; Roellig, T. L.; Sandford, S. A.; Tielens, A. G. G. M.; Werner, M. W.; Whittet, D. C. B.; Decin, L.; Eriksson, K.

2011-04-01

369

DR 21(OH): A Highly Fragmented, Magnetized, Turbulent Dense Core  

NASA Astrophysics Data System (ADS)

We present high angular resolution observations of the massive star-forming core DR21(OH) at 880 ?m using the Submillimeter Array (SMA). The dense core exhibits an overall velocity gradient in a Keplerian-like pattern, which breaks at the center of the core where SMA 6 and SMA 7 are located. The dust polarization shows a complex magnetic field, compatible with a toroidal configuration. This is in contrast with the large, parsec-scale filament that surrounds the core, where there is a smooth magnetic field. The total magnetic field strengths in the filament and in the core are 0.9 and 2.1 mG, respectively. We found evidence of magnetic field diffusion at the core scales, far beyond the expected value for ambipolar diffusion. It is possible that the diffusion arises from fast magnetic reconnection in the presence of turbulence. The dynamics of the DR 21(OH) core appear to be controlled energetically in equal parts by the magnetic field, magnetohydrodynamic turbulence, and the angular momentum. The effect of the angular momentum (this is a fast rotating core) is probably causing the observed toroidal field configuration. Yet, gravitation overwhelms all the forces, making this a clear supercritical core with a mass-to-flux ratio of ~= 6 times the critical value. However, simulations show that this is not enough for the high level of fragmentation observed at 1000 AU scales. Thus, rotation and outflow feedback are probably the main causes of the observed fragmentation.

Girart, J. M.; Frau, P.; Zhang, Q.; Koch, P. M.; Qiu, K.; Tang, Y.-W.; Lai, S.-P.; Ho, P. T. P.

2013-07-01

370

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

NASA Astrophysics Data System (ADS)

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

Mittal, Jeetain; Hummer, Gerhard

2012-07-01

371

Polymer-mediated entropic forces between scale-free objects  

NASA Astrophysics Data System (ADS)

The number of configurations of a polymer is reduced in the presence of a barrier or an obstacle. The resulting loss of entropy adds a repulsive component to other forces generated by interaction potentials. When the obstructions are scale invariant shapes (such as cones, wedges, lines, or planes) the only relevant length scales are the polymer size R0 and characteristic separations, severely constraining the functional form of entropic forces. Specifically, we consider a polymer (single strand or star) attached to the tip of a cone, at a separation h from a surface (or another cone). At close proximity, such that h?R0, separation is the only remaining relevant scale and the entropic force must take the form F=AkBT/h. The amplitude A is universal and can be related to exponents ? governing the anomalous scaling of polymer correlations in the presence of obstacles. We use analytical, numerical, and ?-expansion techniques to compute the exponent ? for a polymer attached to the tip of the cone (with or without an additional plate or cone) for ideal and self-avoiding polymers. The entropic force is of the order of 0.1 pN at 0.1 ?m for a single polymer and can be increased for a star polymer.

Maghrebi, Mohammad F.; Kantor, Yacov; Kardar, Mehran

2012-12-01

372

Structural relaxation of thin polymer films  

NASA Astrophysics Data System (ADS)

Time-dependent structural relaxations, physical aging, of films with thicknesses in the range of 50 nm to 2 microns, of star-shaped polystyrene (SPS) macromolecules are dependent on film thickness, H. In contrast to linear chain PS (LPS) where the aging rate, R, is independent of molecular weight, M, R is dependent on the functionality, f, and on the molecular weight per arm, Marm for SPS macromolecules. For example, the aging rates decreased 15 percent, for f of 8, and 40 percent, for f of 16, in comparison to that of linear chains, for a given film thickness. The aging rates, R, of the SPS macromolecules moreover are appreciably slower than their linear chain analogs, for a given H. The aging rates of the linear chain and star-shaped polymer films may be reconciled in terms of a model that accounts for changes in the local glass transition of the polymer films as a function of distance from an interface.

Frieberg, Bradley; Glynos, Emmanouil; Sakellariou, Georgios; Green, Peter

2013-03-01

373

Herschel's Star Gages  

NSDL National Science Digital Library

The EJS Herschel's Star Gages Model illustrates William Herschel's methods of "star gages" by which he attempted to map out the shape of our galaxy in 1785. Herschel's star gages (sic) relied on two important assumptions: that Herschel's telescope (his "large 20 foot" with an 18.5 inch aperture) could see to the ends of the galaxy, and that within the galactic system stars are distributed uniformly. If the first assumption holds then the stars seen in the telescope all lie within a conical region of space with the apex at the telescope and the base at the edge of the galaxy. If the second assumption holds then the number of stars seen in the telescope is proportional to the volume of this cone. Since the volume of the cone is proportional to the cube of its height, the distance to the galactic edge in any direction is proportional to the cube root of the number of stars seen in that direction. This simulation allows the user to use Herschel's method of star gages to map out the shape of an artificial "star system" for which Herschel's assumptions are valid. One window shows the view through a telescope, with a slider to change the telescopes direction (around a single fixed axis). Another window shows a 3D view of the star system, showing either all of the stars in the system or only those stars visible through the telescope. A third window shows a plot of the star gages. Plotting star gages for many different directions maps out a cross-section of the star system. An optional slider allows the user to decrease the distance to at which stars are no longer visible, and a menu allows the user to select a star system in which the stars are not distributed uniformly. These options let the user explore how violations of Herschel's two fundamental assumptions invalidate his star gage method.

Timberlake, Todd

2011-05-28

374

Siloxane-containing polymer matrices as coating materials  

Microsoft Academic Search

Coating materials based on siloxane-containing polymer matrices that had been modified with fluoropolymer or acrylic resins\\u000a and applied as organic components of hybrid systems were examined. The optimal recipes of the dispersion systems, applied\\u000a as polymer matrix precursors, were determined on the basis of factorial experiments, designed as 22 with additional ‘star’ experimental points to obtain greater accuracy in the

M. Zielecka; E. Bujnowska; K. Bajdor

2007-01-01

375

FEROS Finds a Strange Star  

NASA Astrophysics Data System (ADS)

New Spectrograph Explores the Skies from La Silla While a major effort is now spent on the Very Large Telescope and its advanced instruments at Paranal, ESO is also continuing to operate and upgrade the extensive research facilities at La Silla, its other observatory site. ESO PR Photo 03a/99 ESO PR Photo 03a/99 [Preview - JPEG: 800 x 1212 pix - 606k] [High-Res - JPEG: 1981 x 3000 pix - 3.6M] Caption to PR Photo 03a/99 : This photo shows the ESO 1.52-m telescope, installed since almost 30 years in its dome at the La Silla observatory in the southern Atacama desert. The new FEROS spectrograph is placed in an adjacent, thermally and humidity controlled room in the telescope building (where a classical coudé spectrograph was formerly located). The light is guided from the telescope to the spectrograph by 14-m long optical fibres. Within this programme, a new and powerful spectrograph, known as the Fibre-fed Extended Range Optical Spectrograph (FEROS) , has recently been built by a consortium of European institutes. It was commissioned in late 1998 at the ESO 1.52-m telescope by a small team of astronomers and engineers and has already produced the first, interesting scientific results. FEROS is able to record spectra of comparatively faint stars. For instance, it may be used to measure the chemical composition of stars similar to our Sun at distances of up to about 2,500 light-years, or to study motions in the atmospheres of supergiant stars in the Magellanic Clouds. These satellite galaxies to the Milky Way are more than 150,000 light-years away and can only be observed with telescopes located in the southern hemisphere. First FEROS observations uncover an unusual star ESO PR Photo 03b/99 ESO PR Photo 03b/99 [Preview - JPEG: 800 x 958 pix - 390k] [High-Res - JPEG: 3000 x 3594 pix - 1.7M] Caption to PR Photo 03b/99 : This diagramme shows the spectrum of the Lithium rich giant star S50 in the open stellar cluster Be21 , compared to that of a normal giant star ( S156 ) in the same cluster. The comparatively strong absorption line at the centre, at wavelength 6708 Å (671 nm), is caused by Lithium atoms (Li I) in the upper layers of the star's atmosphere. Lines from Iron (Fe I) and Calcium (Ca I) atoms are also present in this spectral region. While they are of about equal strength in the two stars, the Lithium line is not seen in the comparison spectrum of S156 . Stellar evolution theories do not predict the presence of Lithium in a giant star like S50 . Technical information: FEROS obtained two spectra (each of 90 min exposure) of S50 , both showing this strong Lithium line and thus proving that it cannot have been caused by an instrumental effect. These spectra also illustrate the great amount of information that may be obtained in each exposure with FEROS - the shown spectral interval is just 1/280 of the total range recorded. The (visual) magnitude of S50 is 15.6, i.e., about 7,000 times fainter than what can be seen with the unaided eye. During the first tests of FEROS at the 1.52-m telescope, spectra were obtained of many different stars. Some of these observational data could be used for scientific purposes and, in one case, led to the discovery of unusual properties of a giant star in a stellar cluster. Its spectrum shows an unexplained large amount of the cosmologically important, light element Lithium, cf. PR Photo 03b/99 . The star is thus an obvious object for further, even more detailed studies with ESO's Very Large Telescope (VLT). This giant star, designated as S50 , is a member of the open-type stellar cluster Be21 (less dense than globular clusters). This cluster is of special interest, since its stars contain few elements heavier than hydrogen and helium. It is located in the direction opposite to the Galactic Center and the distance has been measured as approximately 16,000 light-years. All of its stars were formed at the same time, about 2,000 - 2,500 million years ago; this corresponds to half of the age of the Solar System. The study of stars in this cluster provides important information about the chem

1999-02-01

376

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

Microsoft Academic Search

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

Julie Anne Osladil Smallfield

2002-01-01

377

Dense Deposit Disease and C3 Glomerulopathy  

PubMed Central

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

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

2013-01-01

378

Dense deposit disease and C3 glomerulopathy.  

PubMed

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

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

2013-11-01

379

Dense hadronic matter in holographic QCD  

NASA Astrophysics Data System (ADS)

We provide a method to study hadronic matter at finite density in the context of the Sakai-Sugimoto model. We introduce the baryon chemical potential through the external U(1) v gauge field in the induced (DBI plus CS) action on the D8-probe-brane, where baryons are skyrmions. Vector dominance is manifest at finite density. We derive the effect of the baryon density on the energy density, and on the dispersion relations of pions and vector mesons at large N c . The energy density asymptotes are constant at large density, suggesting that dense matter at large N c freezes, with the pion velocity dropping to zero. Holographic dense matter enforces exactly the tenets of vector dominance and efficiently screens vector mesons. At the freezing point, the ? — ?? coupling vanishes with a finite rho mass of about 20% its vacuum value.

Kim, Keun-Young; Sin, Sang-Jin; Zahed, Ismail

2013-10-01

380

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

NASA Astrophysics Data System (ADS)

We propose a density-functional theory for inhomogeneous polyatomic fluids with complex architecture by introducing a different representation for the polymers. This representation gives an efficient hierarchical algorithm to calculate the direct bonding connectivity integral for polymers with complex architecture, such as linear, star, branched, and dendritic structures. A comparison with the available simulated data for linear and star polymers confirms the accuracy of the present theory in reproducing the density profiles of the two types of polymer in the slits. By using the proposed algorithm, we also explore partitioning coefficients of polymers of different architectures in a slit, and find that the partitioning coefficients of branched, star, and dendrimer forms of 22-mers decrease to a minimum at extremely low packing fraction, and then increase monotonically with packing fraction. Moreover, it is found that it is more difficult for a linear polymer of 22-mers to enter the slit than for branched, star, and dendritic polymers. In addition, we also investigate the self-assembly of diblock copolymers with different tails in a slit. It is found that the linear copolymer self-assembles into a trilayer film structure, while copolymers with branched and dendritic tails self-assemble into a five-layer film structure. Interestingly, the copolymer with a star tail self-assembles into a trilayer film structure, and then the trilayer structure evolves into a five-layer structure with increase of the bulk packing fraction in the case studied.

Xu, Xiaofei; Cao, Dapeng; Zhang, Xianren; Wang, Wenchuan

2009-02-01

381

Dense Hypervelocity Plasma Jets for Fusion Applications  

Microsoft Academic Search

High velocity dense plasma jets are being developed for a variety of fusion applications, including refueling, disruption mitigation, High Energy Density Plasmas, magnetized target\\/magneto-inertial fusion, injection of angular momentum into centrifugally confined mirrors, and others. The technical goal is to accelerate plasma blobs of density >10^17 cm-3 and total mass >100 micrograms to velocities >200 km\\/s. The approach utilizes symmetrical

F. Douglas Witherspoon; Y. C. Francis Thio

2005-01-01

382

Dense point sets have sparse Delaunay triangulations  

Microsoft Academic Search

Abstract The spread of a finite set of points is the ratio between,the longest and shortest pairwise distances. We prove that the Delaunay triangulation of any set of n points in p,.s with spread A has complexity,O(AS}. This bound,is tight in the worst case for all A = O(v~). In particular, the Delaunay triangulation of any dense point set has

Jeff Erickson

2001-01-01

383

Controlled Simultaneous Teleportation and Dense Coding  

NASA Astrophysics Data System (ADS)

We propose a teleportation protocol and a dense coding protocol. In these protocols, one sender intends to send quantum states or classical bits to two receivers through two GHZ entanglement channels. The entanglement channels are locked by the sender and the communication process is supervised by a controller. In order to obtain the messages, the receivers need the controller's permission, and must collaborate to unlock the entanglement channels.

Situ, Haozhen

2013-11-01

384

Packing closed trails into dense graphs  

Microsoft Academic Search

It has been shown (Combin. Probab. Comput. 10 (2001) 463–499) that if n is odd and m1,…,mt are integers with mi?3 and ?i=1tmi=|E(Kn)| then Kn can be decomposed as an edge-disjoint union of closed trails of lengths m1,…,mt. Here we show that the corresponding result is also true for any sufficiently large and sufficiently dense even graph G.

Paul N. Balister

2003-01-01

385

Dense ceramic membranes for methane conversion  

Microsoft Academic Search

Dense ceramic membranes made from mixed oxygen-ionic and electronic conducting perovskite-related oxides allow separation of oxygen from an air supply at elevated temperatures (>700°C). By combining air separation and catalytic partial oxidation of methane to syngas into a ceramic membrane reactor, this technology is expected to significantly reduce the capital costs of conversion of natural gas to liquid added-value products.

Henny J. M. Bouwmeester

2003-01-01

386

Structures for dense, crack free thin films  

DOEpatents

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

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

2011-03-08

387

Structure and conditions in massive star forming giant molecular clouds  

NASA Astrophysics Data System (ADS)

Massive stars form in clusters within self-gravitating molecular clouds. The size scale of these clusters is sufficiently large that nonthermal, or turbulent, motions of the gas must be taken into account when considering their formation. Millimeter wavelengths radio observations of the gas and dust in these clouds reveal a complex, self-similar structure that reflects the turbulent nature of the gas. Differences are seen, however, towards dense bound cores in proto-clusters. Examination of the kinematics of gas around such cores suggests that dissipation of turbulence may be the first step in the star formation process. Newly formed stars, on the other hand, replenish turbulence through their winds and outflows. In this way, star formation may be self-regulated. Observations and simulations are beginning to demonstrate the key role that cloud turbulence plays in the formation and evolution of stellar groups.

Williams, Jonathan

388

Parameters of rotating neutron stars with and without hyperons  

NASA Astrophysics Data System (ADS)

Context. The discovery of a 2 M? neutron star provided a robust constraint for the theory of exotic dense matter, bringing into question the existence of strange baryons in the interiors of neutron stars. Although many theories fail to reproduce this observational result, several equations of state containing hyperons are consistent with it. Aims: We study global properties of stars using equations of state containing hyperons, and compare them to those without hyperons to find similarities, differences, and limits that can be compared with the astrophysical observations. Methods: Rotating, axisymmetric, and stationary stellar configurations in general relativity are obtained, and their global parameters are studied. Results: Approximate formulæ describing the behavior of the maximum and minimum stellar mass, compactness, surface redshifts, and moments of inertia as functions of spin frequency are provided. We also study the thin disk accretion and compare the spin-up evolution of stars with different moments of inertia.

Bejger, M.

2013-04-01

389

Many-electron effects on dynamic processes in dense matter  

SciTech Connect

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

Younger, S.M.

1989-01-01

390

Stormy Clouds of Star Birth  

NASA Technical Reports Server (NTRS)

Hidden behind a shroud of dust in the constellation Cygnus is an exceptionally bright source of radio emission called DR21. Visible light images reveal no trace of what is happening in this region because of heavy dust obscuration. In fact, visible light is attenuated in DR21 by a factor of more than 10,000,000,000,000,000,000,000,000,000, 000,000,000,000 (ten thousand trillion heptillion).

New images from NASA's Spitzer Space Telescope allow us to peek behind the cosmic veil and pinpoint one of the most massive natal stars yet seen in our Milky Way galaxy. The never-before-seen star is 100,000 times as bright as the Sun. Also revealed for the first time is a powerful outflow of hot gas emanating from this star and bursting through a giant molecular cloud.

This image shows a 24-micron image mosaic, obtained with the Multiband Imaging Photometer aboard Spitzer (MIPS). This image maps the cooler infrared emission from interstellar dust found throughout the interstellar medium. The DR21 complex is clearly seen near the center of the strip, which covers about twice the area of the IRAC image.

Perhaps the most fascinating feature in this image is a long and shadowy linear filament extending towards the 10 o'clock position of DR21. This jet of cold and dense gas, nearly 50 light-years in extent, appears in silhouette against a warmer background. This filament is too long and massive to be a stellar jet and may have formed from a pre-existing molecular cloud core sculpted by DR21's strong winds. Regardless of its true nature, this jet and the numerous other arcs and wisps of cool dust signify the interstellar turbulence normally unseen by the human eye.

2004-01-01

391

Dense mode clustering in brain maps.  

PubMed

A mode-based clustering method is developed for identifying spatially dense clusters in brain maps. This type of clustering focuses on identifying clusters in brain maps independent of their shape or overall variance. This can be useful for both localization in terms of interpretation and for subsequent graphical analysis that might require more coherent or dense regions of interest as starting points. The method automatically does signal/noise sharpening through density mode seeking. We also discuss the problem of parameter selection with this method and propose a new method involving 2-parameter control surface, in which we show that the same cluster solution results from tradeoff of these 2 parameters (the local density k and the radius r of the spherical kernel). We benchmark the new dense mode clustering by using several artificially created data sets and brain imaging data sets from an event perception task by perturbing the data set with noise and measuring three kinds of deviation from the original cluster solution. We present benchmark results that demonstrate that the mode clustering method consistently outperforms the commonly used single-linkage clustering, k means method (centroid method) and Ward's method (variance method). PMID:17459639

Hanson, Stephen José; Rebecchi, Rebbechi; Hanson, Catherine; Halchenko, Yaroslav O

2007-11-01

392

Numerical modeling for dilute and dense sprays  

NASA Technical Reports Server (NTRS)

We have successfully implemented a numerical model for spray-combustion calculations. In this model, the governing gas-phase equations in Eulerian coordinate are solved by a time-marching multiple pressure correction procedure based on the operator-splitting technique. The droplet-phase equations in Lagrangian coordinate are solved by a stochastic discrete particle technique. In order to simplify the calculation procedure for the circulating droplets, the effective conductivity model is utilized. The k-epsilon models are utilized to characterize the time and length scales of the gas phase in conjunction with turbulent modulation by droplets and droplet dispersion by turbulence. This method entails random sampling of instantaneous gas flow properties and the stochastic process requires a large number of computational parcels to produce the satisfactory dispersion distributions even for rather dilute sprays. Two major improvements in spray combustion modelings were made. Firstly, we have developed a probability density function approach in multidimensional space to represent a specific computational particle. Secondly, we incorporate the Taylor Analogy Breakup (TAB) model for handling the dense spray effects. This breakup model is based on the reasonable assumption that atomization and drop breakup are indistinguishable processes within a dense spray near the nozzle exit. Accordingly, atomization is prescribed by injecting drops which have a characteristic size equal to the nozzle exit diameter. Example problems include the nearly homogeneous and inhomogeneous turbulent particle dispersion, and the non-evaporating, evaporating, and burning dense sprays. Comparison with experimental data will be discussed in detail.

Chen, C. P.; Kim, Y. M.; Shang, H. M.; Ziebarth, J. P.; Wang, T. S.

1992-01-01

393

Interpretations of Polymer-Polymer Miscibility.  

ERIC Educational Resources Information Center

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

Olabisi, Olagoke

1981-01-01

394

Wolf-Rayet stars  

NASA Technical Reports Server (NTRS)

The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.

Abbott, David C.; Conti, Peter S.

1987-01-01

395

MD Simulations of the Breaking Strain of Coulomb Crystals in Neutron Stars: Star mountains and gravitational waves  

NASA Astrophysics Data System (ADS)

Neutron stars --- collapses stars half again as massive as the sun but with a 10-kilometer radius --- have solid crusts made of dense coulomb crystals. We perform large-scale molecular dynamic simulations of the breaking strain (strength) of this crust including the effects of impurities, defects, and grain boundaries. We find neutron star crust to be the strongest material known, with a breaking stress 10 billion times stronger than steel [1]. This is because of the high density, high pressure, and the long-range nature of the coulomb interactions where each ion interacts with thousands of its neighbors. The crust can support massive mountains that, on a rapidly rotating neutron star, can radiate detectable gravitational waves. These oscillations of space and time, predicted by Einstein almost 100 years ago, should be detected in the next few years. [4pt] [1] C. J. Horowitz and Kai Kadau, Phys. Rev. Letters 102, 191102 (2009).

Horowitz, Charles; Hughto, Joe; Schneider, Andre; Berry, Don

2011-03-01

396

Dense water formation and circulation in the Barents Sea  

Microsoft Academic Search

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

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

2011-01-01

397

Spiral Shocks, Cooling, and the Origin of Star Formation Rates  

NASA Astrophysics Data System (ADS)

We have performed the first numerical simulations to resolve the star formation process on sub-parsec scales, whilst also following the dynamics of the interstellar medium (ISM) on galactic scales. The warm low density ISM gas flows into the spiral arms where orbit crowding produces the shock formation of dense clouds, held together temporarily by their external pressure. Cooling allows the gas to be compressed to sufficiently high densities that local regions collapse under their own gravity and form stars. The star formation rates follow a Schmidt-Kennicutt ? SFR ? ? gas 1.4 \\varSigma _{SFR} ? \\varSigma _{gas}^{1.4} type relation with the local surface density of gas while following a linear relation with the dense cold gas. Cooling is the primary driver of star formation and the star formation rates as it determines the amount of cold gas available for gravitational collapse.

Bonnell, Ian; Dobbs, Clare L.; Smith, Rowan J.

398

Are Double Periodic Variables Progenitors of Some Be Stars?  

NASA Astrophysics Data System (ADS)

The phenomenon of Double Periodic Variables is summarized, with special attention to their photometric and spectroscopic fingerprints. In all well-studied cases the orbital light curve can be modeled with a B-type star surrounded by a dense disk-like envelope and a cooler donor (spectral types B, A, F, G) filling its Roche lobe. The study of V393 Scorpii provides clues on the evolutionary stage of these variables, and suggests that a bi-polar wind is responsible for the long-cycle variability. It is argued that Double Periodic Variables could be progenitors of some Be stars.

Mennickent, R.

2012-12-01

399

Equation of state of nucleon matter and neutron star structure  

Microsoft Academic Search

Properties of dense nucleon matter and the structure of neutron stars are\\u000astudied using variational chain summation methods and the new Argonne v18\\u000atwo-nucleon interaction. The neutron star gravitational mass limit obtained\\u000awith this interaction is 1.67 M_{solar}. Boost corrections to the two-nucleon\\u000ainteraction, which give the leading relativistic effect of order (v\\/c)^2, as\\u000awell as three-nucleon interactions, are also

A. Akmal; V. R. Pandharipande; D. G. Ravenhall

1998-01-01

400

Magnetic Flux Expulsion in Star Formation  

NASA Astrophysics Data System (ADS)

Stars form in dense cores of magnetized molecular clouds. If the magnetic flux threading the cores is dragged into the stars, the stellar field would be orders of magnitude stronger than observed. This well-known "magnetic flux problem" demands that most of the core magnetic flux be decoupled from the matter that enters the star. We carry out the first exploration of what happens to the decoupled magnetic flux in three dimensions, using a magnetohydrodynamic (MHD) version of the ENZO adaptive mesh refinement code. The field-matter decoupling is achieved through a sink particle treatment, which is needed to follow the protostellar accretion phase of star formation. We find that the accumulation of the decoupled flux near the accreting protostar leads to a magnetic pressure buildup. The high pressure is released anisotropically along the path of least resistance. It drives a low-density expanding region in which the decoupled magnetic flux is expelled. This decoupling-enabled magnetic structure has never been seen before in three-dimensional MHD simulations of star formation. It generates a strong asymmetry in the protostellar accretion flow, potentially giving a kick to the star. In the presence of an initial core rotation, the structure presents an obstacle to the formation of a rotationally supported disk, in addition to magnetic braking, by acting as a rigid magnetic wall that prevents the rotating gas from completing a full orbit around the central object. We conclude that the decoupled magnetic flux from the stellar matter can strongly affect the protostellar collapse dynamics.

Zhao, Bo; Li, Zhi-Yun; Nakamura, Fumitaka; Krasnopolsky, Ruben; Shang, Hsien

2011-11-01

401

Star Formation in Galaxies  

NASA Technical Reports Server (NTRS)

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

1987-01-01

402

Open Star Clusters  

NSDL National Science Digital Library

This site offers information about the formation of star clusters, the pleiades, how to calculate star cluster distances, and much more. There are also some great images that techers can use on this website.

2005-02-11

403

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

404

From Commodity Polymers to Functional Polymers  

PubMed Central

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

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

2014-01-01

405

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

406

HUBBLE SPIES GIANT STAR CLUSTERS NEAR GALACTIC CENTER  

NASA Technical Reports Server (NTRS)

Penetrating 25,000 light-years of obscuring dust and myriad stars, NASA's Hubble Space Telescope has provided the clearest view yet of a pair of the largest young clusters of stars inside our Milky Way galaxy, located less than 100 light-years from the very center of the Galaxy. Having the equivalent mass greater than 10,000 stars like our sun, the monster clusters are ten times larger than typical young star clusters scattered throughout our Milky Way. Both clusters are destined to be ripped apart in just a few million years by gravitational tidal forces in the Galaxy's core. But in the brief time they are around, they shine more brightly than any other star cluster in the Galaxy. Arches cluster (left): The more compact Arches cluster is so dense, over 100,000 of its stars would fill a spherical region in space whose radius is the distance between the Sun and its nearest neighbor, the star Alpha Centauri, 4.3 light-years away. At least 150 of its stars are among the brightest ever seen in the Galaxy. Quintuplet cluster (right): This 4-million-year-old cluster is more dispersed than the Arches cluster. It has stars on the verge of blowing up as supernovae. It is the home of the brightest star seen in the Galaxy, called the Pistol star. Both pictures were taken in infrared light by Hubble's NICMOS camera in September 1997. The false colors correspond to infrared wavelengths. The galactic center stars are white, the red stars are enshrouded in dust or behind dust, and the blue stars are foreground stars between us and the Milky Way's center. The clusters are hidden from direct view behind black dust clouds in the constellation Sagittarius. If the clusters could be seen from Earth they would appear to the naked eye as a pair of third magnitude 'stars,' 1/6th of a full moon's diameter apart. Credit: Don Figer (Space Telescope Science Institute) and NASA

2002-01-01

407

Lithuim in Very Low-Mass Stars in the Pleiades  

NASA Astrophysics Data System (ADS)

High-resolution, Keck Telescope echelle observations from 630 nm to 850 nm of seven Pleiads with spectral types from M5 to M6.5 reveal rather rapid rotation, with an average v sin i ~ 52 km s(-1) , and chromospheric activity in H? emission. The activity in these stars is not any stronger than that of other Pleiades low-mass stars, despite the expected high contrast of H? with their cool photospheres and their rapid rotation. This shows that the ``levelling off'' of H? equivalent widths previously noted in low-mass stars in young clusters is not related to the conventional rotation-activity connection. None of the stars previously categorized as brown dwarf candidates have lithium signatures in their spectra. They are, therefore, very low-mass stars and not brown dwarfs. However, two stars, HHJ 339 and HHJ 430, 1 and 2 magnitudes above the Pleiades zero-age main sequence, do show absorption due to Li 1 at 670.8 nm and in the subordinate feature at 812.6 nm. These two stars are also rotating very rapidly. These facts strongly suggest that these stars are rather young. Their proper motions and radial velocities agree with those measured for the Pleiades as a whole. We discuss various explanations for these stars, none of which is completely satisfactory. In one scenario they represent very late star formation in the Pleiades cluster (implying a huge range in the ages of Pleiads). This seems unpalatable given the lack of matter dense enough to form stars in the Pleiades at present. Another possibility is that these stars formed in a nearby, more recent star formation site and drifted into the Pleiades. Although the cluster recently passed through a clump of young Taurus stars, we do not see how it could ``accrete'' two of them. In our most feasible explanation, we posit that a cloud which was a member of the ``Pleiades Supercluster'' recently formed stars, which are now scattered between us and the Pleiades. HHJ 339 and HHJ 430 could be members of this group whose motion has now brought them near the older open star cluster.

Oppenheimer, B. R.; Basri, G.; Nakajima, T.; Kulkarni, S. R.

1997-01-01

408

RCW 108: Massive Young Stars Trigger Stellar Birth  

NASA Technical Reports Server (NTRS)

RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars.

This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image.

The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193.

Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas clouds in RCW 108 to be compressed, leading to gravitational collapse and the formation of new stars.

2008-01-01

409

'Polaris, Mark Kummerfeldt's Star, and My Star.'  

ERIC Educational Resources Information Center

In most astronomy courses, descriptions of stars and constellations reveal the western European origins of the astronomers who named them. However, it is suggested that a study of non-western views be incorporated into astronomy curricula. Descriptions of various stars and constellations from different cultures and instructional strategies are…

McLure, John W.

1984-01-01

410

Southern Cool Stars Misclassified as Carbon Stars  

NASA Astrophysics Data System (ADS)

We report a list of 24 red stars classified as carbon stars by one author. Close examination of them on near-IR objective-prism plates reveals that they are of M type or earlier. Three are variable in the ASAS-3 Catalog.

MacConnell, D. J.

2006-01-01

411

A star tracking algorithm suitable for star sensor  

NASA Astrophysics Data System (ADS)

The sufficient attitude knowledge including location of recognized stars in star image can be obtained with Lost-in-Space case. In order to make use of the sufficient attitude knowledge, the star sensor may work in star tracking case. To achieve this, a star tracking algorithm is proposed in this paper. The previous location of recognized stars in star image may be used to obtain location of observed star in proper region of current star image with the star tracking algorithm. The simulations and real sky experiment results show that the star tracking algorithm proposed in this paper not only improves update rate of star sensor, but also avoids fault star pattern recognition. Finally, a star sensor featuring star tracking algorithm proposed in this paper was for on-orbit demonstration.

Li, Baohua; Zhang, Yingchun; Li, Huayi; Wang, Changhong

2007-03-01

412

Spectroscopy of be stars  

NASA Astrophysics Data System (ADS)

This chapter describes non supergiant B-type stars that show emission lines, called Be stars. The emission is caused by the presence of a circumstellar decretion disk. Many physical phenomena are thought to be involved in these stars, such as rapid rotation, pulsations and magnetic fields, and give rise to variations. Spectroscopy is used as a diagnostic tool to study Be stars, by professional astronomers as well as by amateurs.

Neiner, C.

2011-04-01

413

Chromospheres of Coronal Stars  

NASA Technical Reports Server (NTRS)

We summarize the main results obtained from the analysis of ultraviolet emission line profiles of coronal late-type stars observed with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. The excellent GHRS spectra provide new information on magnetohydrodynamic phenomena in the chromospheres and transition regions of these stars. One exciting new result is the discovery of broad components in the transition region lines of active stars that we believe provide evidence for microflare heating in these stars.

Linsky, Jeffrey L.; Wood, Brian E.

1996-01-01

414

“Enabling Technology” Polymers  

Microsoft Academic Search

An area of polymer science that is of current and growing industrial importance is where the polymer is the enabling technology that makes a component, system, or process work. Without the special polymer, the technology simply does not operate in a useful manner.The characteristics of this arena are very different from high volume commodity or engineering polymers. Performance is the

Joseph G. Wirth

1997-01-01

415

Influence of strange matter admixtures on macroscopic properties of neutron stars  

SciTech Connect

We used the equations of state (EoS) of dense nuclear matter to construct the macroscopic properties of neutron stars and test them using available observational results. The Dirac-Brueckner-Hartree-Fock mean field calculations approximated by their parameterized form are the basis of our calculations for the star interior. We calculated the central pressure, density, radius and mass both without and with allowance for hyperons, and compared these results with astronomical observations.

Urbanec, M.; Stuchlik, Z. [Institute of Physics, Silesian University, 74601 Opava (Czech Republic); Betak, E. [Institute of Physics, Silesian University, 74601 Opava (Czech Republic); Institute of Physics SAS, 84511 Bratislava (Slovakia)

2011-10-28

416

Relationship Between Dense Gas and Total Infrared Luminosity Along Spiral Arms in M51  

NASA Astrophysics Data System (ADS)

We investigate the relationship between the dense molecular gas tracer, HCN (J=1-0), luminosity and total infrared luminosity in nearby grand design spiral, M51. Previous work has shown a near linear correlation between the total infrared luminosity and HCN luminosity between Galactic dense cores and spirals and starburst galaxies. This relationship spans over seven orders of magnitude. Our aim is to test this relationship using intermediate points with HCN luminosities larger than galactic dense cores and smaller than that of total spiral and starburst galaxies. The linear correlation between HCN and total infrared luminosity continues to hold for gas along spiral arms in M51, suggesting that HCN is tracing the gas most relevant for star formation. The HCN emission was mapped using interferometric observations from the Owens Valley Radio Observatory and Combined Array for Research in Millimeter Astronomy. We compare the total recovered HCN emission to single dish maps taken with the Green Bank Telescope. Total infrared maps are made from Spitzer MIPS 24 micron and Hershel PACS 70micron and 160 micron maps.

Louie, Melissa N.; Koda, J.; Egusa, F.

2014-01-01

417

Supernova Star Maps  

NSDL National Science Digital Library

This fun astronomy activity allows learners to experience finding stars in the night sky that will eventually go supernova. This activity is perfect for a star party outdoors. The PDF contains step-by-step instructions, photos, presentation tips, ready-to-print star maps, and links to background information.

Pacific, Astronomical S.

2008-01-01

418

Star Field Simulator.  

National Technical Information Service (NTIS)

A Star Field Simulator has been developed to serve as a source of radiation for the ASTRO Star Tracker. The star tracker and simulator are components of a motion compensation test facility located at Marshall Space Flight Center in Huntsville, Alabama. Pr...

1985-01-01

419

Main Sequence Stars  

NSDL National Science Digital Library

This website from the Australian Telescope Outreach and Education Group provides a thorough introduction to the life and death of stars. The website uses text, diagrams, and images to help explain how stars evolve. Highlights include a discussion of stellar fusion reactions and also a straightforward calculation of the lifetime of a star.

2007-06-12

420

Life Cycles of Stars  

NSDL National Science Digital Library

This Powerpoint presentation inroduces younger students to the life cycles of stars. Topics include stellar nurseries, types of stars, supernovae, the fates of stars of either high or low mass, and the creation of heavier elements by continued fusion of successively heavier elements.

421

America's Star Libraries  

ERIC Educational Resources Information Center

"Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

Lyons, Ray; Lance, Keith Curry

2009-01-01

422

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

PubMed

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

Lego, Béatrice; François, Marion; Skene, W G; Giasson, Suzanne

2009-05-01

423

Grain Growth and Silicates in Dense Clouds  

NASA Technical Reports Server (NTRS)

Interstellar silicates are likely to be a part of all grains responsible for visual extinction (Av) in the diffuse interstellar medium (ISM) and dense clouds. A correlation between Av and the depth of the 9.7 micron silicate feature (measured as optical depth, tau(9.7)) is expected if the dust species are well 'mixed. In the di&se ISM, such a correlation is observed for lines of sight in the solar neighborhood. A previous study of the silicate absorption feature in the Taurus dark cloud showed a tendency for the correlation to break down at high Av (Whittet et al. 1988, MNRAS, 233,321), but the scatter was large. We have acquired Spitzer Infrared Spectrograph data of several lines of sight in the IC 5 146, Barnard 68, Chameleon I and Serpens dense clouds. Our data set spans an Av range between 2 and 35 magnitudes. All lines of sight show the 9.7 micron silicate feature. The Serpens data appear to follow the diffuse ISM correlation line whereas the data for the other clouds show a non-linear correlation between the depth of the silicate feature relative to Av, much like the trend observed in the Taurus data. In fact, it appears that for visual extinctions greater than about 10 mag, tau(9.7) begins to level off. This decrease in the growth of the depth of the 9.7 micron feature with increasing Av could indicate the effects of grain growth in dense clouds. In this poster, we explore the possibility that grain growth causes an increase in opacity (Av) without causing a corresponding increase in tau(9.7).

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

2006-01-01