Science.gov

Sample records for dense star polymer

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

    DOEpatents

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

    1995-02-28

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

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

    DOEpatents

    Hedstrand, David M.; Tomalia, Donald A.

    1995-01-01

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

  3. Cooling of dense stars

    NASA Technical Reports Server (NTRS)

    Tsuruta, S.

    1972-01-01

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

  4. Multiarm Star Polymers as Model Soft Colloids

    NASA Astrophysics Data System (ADS)

    Vlassopoulos, Dimitris

    2010-03-01

    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).

  5. Bottle-brush polymers as an intermediate between star and cylindrical polymers

    NASA Astrophysics Data System (ADS)

    Denesyuk, N. A.

    2003-09-01

    We present a theoretical study of a single bottle-brush molecule, which consists of multiarmed polymer stars grafted densely onto a stiff backbone. Mean-field approximation and a variational approach are used to calculate the dominant trajectories of the grafted chains, the shape of the molecule, and the segment density distribution around the backbone. All these properties are calculated for an arbitrary relationship between the size of the backbone and that of a grafted star. Hence cylindrical comb copolymer brushes and spherically symmetric polymer stars are considered as the limiting cases of the present problem.

  6. Probing dense matter in neutron stars with axial w modes

    SciTech Connect

    Chatterjee, Debarati; Bandyopadhyay, Debades

    2009-07-15

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

  7. Nanoparticle diffusion in dense polymer melts

    NASA Astrophysics Data System (ADS)

    Kalathi, Jagannathan T.; Kumar, Sanat K.; Grest, Gary S.

    2013-03-01

    The diffusion of nanoparticles in melts and solutions of polymers facilitates understanding of the viscoelastic behavior of the respective polymers and their composites. It also plays a vital role in determining the equilibrium structure and morphology of polymer nanocomposites and hence, their mechanical properties. In this work, we present the diffusion coefficients of non-sticky smooth spherical particles of different sizes (1-10 ?) in an athermal mixture of particles and polymers of different chain lengths (N = 20 to 400) using molecular dynamics simulations. The diffusion of nanoparticles of size comparable to the polymer segment size (?) is independent of chain length and hence, nanoparticles apparently feel only the local viscosity, as predicted by scaling theories. When the nanoparticle becomes larger than a segment (or alternately the correlation length in the melt), then, the diffusion coefficient decreases. This is due to the fact that the mobility of the particles is retarded either by a chain section of size equivalent to the particle size or by entanglement mesh size depending on the nanoparticle size. We also elucidate the role of chain entanglements on diffusion of nanoparticles.

  8. Dense Matter in the Crust of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Yao, C. C.; Cheng, K. S.

    1996-05-01

    With the relativistic extended Thomas-Fermi method, we study the dense matter in the inner crust of neutron stars based on the Zimanyi & Moszkowski (1990, ZM) model in the relativistic mean field theory. We also compare these results with those based on the Boguta & Bodmer (1977, BB) model with a resent satisfactory parameter set.

  9. Physical hydrogels of associative star polymers

    SciTech Connect

    Zhou, G.; Smid, J.

    1993-12-31

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

  10. Velocity Gradients in Star-forming Dense Cores

    NASA Astrophysics Data System (ADS)

    Luhong

    2015-01-01

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

  11. Formation and evolution of black holes in dense star clusters

    NASA Astrophysics Data System (ADS)

    Goswami, Sanghamitra

    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.

  12. Dense molecular gas tracers in high mass star formation regions

    NASA Astrophysics Data System (ADS)

    Ma, Hong-Jun; Gao, Yu; Wu, Jing-Wen

    2016-02-01

    We report the FCRAO observations that mapped HCN (1–0), CS (2–1), HNC (1–0) and HCO+ (1–0) in ten high-mass star forming cores associated with water masers. We present velocity integrated intensity maps of the four lines for these dense cores, compare their line profiles, and derive physical properties of these cores. We find that these four tracers identify areas with similar properties in these massive dense cores, and in most cases, the emissions of HCN and HCO+ are stronger than those of HNC and CS. We also use the line ratios of HCO+/HCN, HNC/HCN and HNC/HCO+ as the diagnostics to explore the environment of these high-mass star forming regions, and find that most of the cores agree with the model that photodominated regions dominate the radiation field, except for W44, for which the radiation field is similar to an X-ray dominated region.

  13. Dense molecular gas tracers in high mass star formation regions

    NASA Astrophysics Data System (ADS)

    Ma, Hong-Jun; Gao, Yu; Wu, Jing-Wen

    2016-02-01

    We report the FCRAO observations that mapped HCN (10), CS (21), HNC (10) and HCO+ (10) in ten high-mass star forming cores associated with water masers. We present velocity integrated intensity maps of the four lines for these dense cores, compare their line profiles, and derive physical properties of these cores. We find that these four tracers identify areas with similar properties in these massive dense cores, and in most cases, the emissions of HCN and HCO+ are stronger than those of HNC and CS. We also use the line ratios of HCO+/HCN, HNC/HCN and HNC/HCO+ as the diagnostics to explore the environment of these high-mass star forming regions, and find that most of the cores agree with the model that photodominated regions dominate the radiation field, except for W44, for which the radiation field is similar to an X-ray dominated region.

  14. THE FORMATION OF YOUNG DENSE STAR CLUSTERS THROUGH MERGERS

    SciTech Connect

    Fujii, M. S.; Portegies Zwart, S. F.; Saitoh, T. R.

    2012-07-01

    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.

  15. Lattice cluster theory for dense, thin polymer films

    SciTech Connect

    Freed, Karl F.

    2015-04-07

    While the application of the lattice cluster theory (LCT) to study the miscibility of polymer blends has greatly expanded our understanding of the monomer scale molecular details influencing miscibility, the corresponding theory for inhomogeneous systems has not yet emerged because of considerable technical difficulties and much greater complexity. Here, we present a general formulation enabling the extension of the LCT to describe the thermodynamic properties of dense, thin polymer films using a high dimension, high temperature expansion. Whereas the leading order of the LCT for bulk polymer systems is essentially simple Flory-Huggins theory, the highly non-trivial leading order inhomogeneous LCT (ILCT) for a film with L layers already involves the numerical solution of 3(L − 1) coupled, highly nonlinear equations for the various density profiles in the film. The new theory incorporates the essential “transport” constraints of Helfand and focuses on the strict imposition of excluded volume constraints, appropriate to dense polymer systems, rather than the maintenance of chain connectivity as appropriate for lower densities and as implemented in self-consistent theories of polymer adsorption at interfaces. The ILCT is illustrated by presenting examples of the computed profiles of the density, the parallel and perpendicular bonds, and the chain ends for free standing and supported films as a function of average film density, chain length, temperature, interaction with support, and chain stiffness. The results generally agree with expected general trends.

  16. Massive Star Formation: Characterising Infall and Outflow in dense cores.

    NASA Astrophysics Data System (ADS)

    Akhter, Shaila; Cunningham, Maria; Harvey-Smith, Lisa; Jones, Paul Andrew; Purcell, Cormac; Walsh, Andrew John

    2015-08-01

    Massive stars are some of the most important objects in the Universe, shaping the evolution of galaxies, creating chemical elements, and hence shaping the evolution of the Universe. However, the processes by which they form, and how they shape their environment during their birth processes, are not well understood. We are using NH3 data from the "The H2O Southern Galactic Plane Survey" (HOPS) to define the positions of dense cores/clumps of gas in the southern Galactic plane that are likely to form stars. Due to its effective critical density, NH3 can detect massive star forming regions effectively compared to other tracers. We did a comparative study with different methods for finding clumps and found Fellwalker as the best. We found ~ 10% of the star forming clumps with multiple components and ~ 90% clumps with single component along the line of sight. Then, using data from the "The Millimetre Astronomy Legacy Team 90 GHz" (MALT90) survey, we search for the presence of infall and outflow associated with these cores. We will subsequently use the "3D Molecular Line Radiative Transfer Code" (MOLLIE) to constrain properties of the infall and outflow, such as velocity and mass flow. The aim of the project is to determine how common infall and outflow are in star forming cores, hence providing valuable constraints on the timescales and physical process involved in massive star formation.

  17. Surface wave excitations and backflow effect over dense polymer brushes.

    PubMed

    Biagi, Sofia; Rovigatti, Lorenzo; Sciortino, Francesco; Misbah, Chaouqi

    2016-01-01

    Polymer brushes are being increasingly used to tailor surface physicochemistry for diverse applications such as wetting, adhesion of biological objects, implantable devices and much more. Here we perform Dissipative Particle Dynamics simulations to study the behaviour of dense polymer brushes under flow in a slit-pore channel. We discover that the system displays flow inversion at the brush interface for several disconnected ranges of the imposed flow. We associate such phenomenon to collective polymer dynamics: a wave propagating on the brush surface. The relation between the wavelength, the amplitude and the propagation speed of the flow-generated wave is consistent with the solution of the Stokes equations when an imposed traveling wave is assumed as the boundary condition (the famous Taylor's swimmer). PMID:26975329

  18. Surface wave excitations and backflow effect over dense polymer brushes

    PubMed Central

    Biagi, Sofia; Rovigatti, Lorenzo; Sciortino, Francesco; Misbah, Chaouqi

    2016-01-01

    Polymer brushes are being increasingly used to tailor surface physicochemistry for diverse applications such as wetting, adhesion of biological objects, implantable devices and much more. Here we perform Dissipative Particle Dynamics simulations to study the behaviour of dense polymer brushes under flow in a slit-pore channel. We discover that the system displays flow inversion at the brush interface for several disconnected ranges of the imposed flow. We associate such phenomenon to collective polymer dynamics: a wave propagating on the brush surface. The relation between the wavelength, the amplitude and the propagation speed of the flow-generated wave is consistent with the solution of the Stokes equations when an imposed traveling wave is assumed as the boundary condition (the famous Taylor’s swimmer). PMID:26975329

  19. Cellular uptake of densely packed polymer coatings on gold nanoparticles.

    PubMed

    Liang, Mingtao; Lin, I-Chun; Whittaker, Michael R; Minchin, Rodney F; Monteiro, Michael J; Toth, Istvan

    2010-01-26

    A variety of functional polymer chains prepared by RAFT were directly grafted onto 5, 10, and 20 nm gold nanoparticles (AuNPs). The polymer shell coating the AuNPs was densely packed because of the strong binding between the trithioester groups on the polymer chain-ends and gold. It was found that due to the densely packed nature of the shell the polymer chains were significantly stretched compared to their usual Gaussian coil conformation in water. This was even evident for polymer chains where ionic repulsion between neighboring chains should be significant. Therefore, with such high grafting densities the surface properties and size of the hybrid nanoparticles should be the only contributing factors in cellular uptake in epithelial Caco-2 cells. This study has provided valuable insight into the effects of charge and size of NPs for the application of NPs in the delivery of therapeutic agents across the intestine. Our results showed that the negatively charged AuNPs were taken up by the cells with greater efficiency than the neutral AuNPs, most probably due to binding with membrane proteins. The positively charged AuNPs as expected gave the greatest uptake efficiency. Interestingly, the uptake for PNIPAM-AuNPs (hydrophobic coating at 37 degrees C) increased from approximately 2% efficiency after a 30 min incubation to 8% after 2 h, and was much greater than the negative or neutral AuNPs. We believe that this was due to the interplay between the hydrophobic nature of the NPs and their increased size. PMID:19947583

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  1. Method for forming a uniformly dense polymer foam body

    SciTech Connect

    Whinnery, Jr., Leroy

    2002-01-01

    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.

  2. Hydrophilic polymer composites synthesized by electrospinning under dense carbon dioxide

    NASA Astrophysics Data System (ADS)

    Wahyudiono, Okamoto, Koichi; Machmudah, Siti; Kanda, Hideki; Goto, Motonobu

    2015-12-01

    Electrospinning technique is feasible in some applications, it has attracted more attention in recent years. Various polymers have been successfully electrospun into ultrafine fibers in solvent solution and some in melt form. In this work, polyvinylpyrrolidone (PVP) as a hydrophilic polymer would be synthesized by electrospinning under dense carbon dioxide (CO2). The experiments were performed at 40 °C and ˜ 5 MPa. During the electrospinning process, the applied voltage was 10-17 kV and the distance of nozzle and collector was 8 cm. The concentration of PVP solution as a major component was 4 wt%. The results showed that the fibers surface morphology from PVP which blended with poly L-lactide acid (PLLA) were smooth with hollow core fibers at 5 MPa. At the same conditions, PVP-carbon nanotube was also successfully generated into electrospun fiber products with diameter ˜ 2 μm.

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

    SciTech Connect

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

    2010-12-10

    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.

  4. Self-Diffusion of Symmetric Star Polymers

    NASA Astrophysics Data System (ADS)

    Frischknecht, Amalie; Milner, Scott T.

    2000-03-01

    We use a recent theory of arm retraction in star polymers, which successfully describes their distinctive rheology, to calculate the self-diffusion constant of symmetric stars. Star polymers can only take a diffusive step when an arm fully retracts to the center. Due to the wide separation of relaxation times along the star arms, star polymers obey dynamic dilution, in which the effective entanglement network dilutes as portions of the star arms relax. This implies a picture of self-diffusion in which the junction point hops a distance of order the dilated tube diameter ad associated with the diluted network, rather than a distance of order the original ``skinny'' tube diameter a0 defined by the entanglement molecular weight. The difference is substantial, since ad scales with arm length N as a_0N^2/7. However, comparing our results to self-diffusion data of Bartels et. al.,(C. R. Bartels, B. Crist, Jr., L. J. Fetters, and W. W. Graessley, Macromolecules 19), 785, 1986. we find that the data is more consistent with diffusive hops of a length scale a0 rather than a_d.

  5. Collapse of Telechelic Star Polymers to Watermelon Structures

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

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

  6. Stellar-Mass Black Holes in Dense Star Clusters

    NASA Astrophysics Data System (ADS)

    Morscher, Meagan; Rasio, F.

    2012-05-01

    Globular Clusters with core-collapse times longer that the lifetime of the most massive stars can are thought to produce many stellar-mass black holes (BH) and retain most of them initially. The dynamical evolution of stellar BHs in clusters is important for studies of merging BH-BH binaries, which will be detectable by future gravitational wave observatories. Since BHs are among the most massive objects in a cluster, they tend to sink to the center through two-body relaxation, forming a dense core in which BH-BH binaries can be formed, destroyed, and ejected. The fate of BHs in clusters, however, is still highly uncertain. Only recently have dynamics codes become powerful enough to simulate clusters with realistic N, full stellar mass spectra, and significant numbers of primordial binaries. Using a Monte Carlo method, we model realistic star clusters with stellar-mass BHs. We discuss the evolution of BH populations within clusters, as well as the implications for gravitational wave astronomy.

  7. Modular invariant partition function of critical dense polymers

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  8. Barrier crossing by a star polymer.

    PubMed

    Debnath, Ananya; Sebastian, K L

    2007-11-01

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

  9. Dense gas tracers and star formation laws: Multi-transition CS survey in nearby active star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyu; Gao, Yu; Henkel, Christian; Zhao, Yinghe; Wang, JunZhi; Menten, Karl M.

    2015-08-01

    Recent studies on star formation indicate that stars, especially massive stars, are predominantly formed in dense molecular cores. We have performed a survey of multiple transitions of CS (from J=1-0 to 7-6), and HCN/HCO+ J=4-3 in nearby star-forming galaxies, including normal spirals, starburst, and ULIRGs. We find linear correlations between the luminosities of LIR and L'gas for all dense gas tracers across eight magnitudes of IR luminosity (LIR from 104 Lsun to 1012 Lsun), on scales from entire galaxies to Galactic dense cores. Irrespective of the critical density of a specific transition, dense molecular gas is universally related in a linear way to star forming activities for self-gravitationally bound gas systems.

  10. Motions and Initial Conditions in Star-Forming Dense Cores

    NASA Technical Reports Server (NTRS)

    Myers, Philip C.

    2001-01-01

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

  11. Polymer quantum effects on compact stars models

    NASA Astrophysics Data System (ADS)

    Chacn-Acosta, Guillermo; Hernandez-Hernandez, Hctor H.

    2015-03-01

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

  12. Connecting the Dense Gas and Young Stars in the CARMA Large Area Star Formation Survey

    NASA Astrophysics Data System (ADS)

    Mundy, Lee G.; Storm, Shaye; Looney, Leslie; Lee, Katherine I.; Fernandez Lopez, Manuel; Ostriker, Eve C.; Chen, Che-Yu; CLASSy Team

    2016-01-01

    The CARMA Large Area Star Formation Survey (CLASSy) imaged the dense gas structure and kinematics in five, roughly 1 pc scale regions in the Serpens and Perseus clouds with 7" angular resolution. The spatial distribution and Class of the young stellar population (YSOs) is available for these regions from the Spitzer c2d and Gould Belt surveys, with added sources from the Herschel 70 micron images. Together, these datasets allow us to compare, for the first time at similar spatial resolutions, the distributions of the dense gas and YSOs over regions containing up to 90 identified YSOs. This enables a detailed look at the separation between YSOs and the nearest dense gas peak and a measure of overall relationship between the YSO and dense gas distributions. We find that most Class 0 YSOs are forming in the highest column density regions: leaves in the dendrogram analysis utilized by CLASSy. In Serpens and Perseus, we find that 29% and 38%, respectively, of the leaves have identified embedded YSOs. Class 1 sources are less confined to leaf locations; Class II sources are distributed throughout regions, mostly away from hierarchical peaks. This trend could be due to a modest (0.1 km/sec) velocity difference between YSOs and their natal cores, or due to the YSOs consuming or dispersing their natal cores.

  13. Influence of Molecular Solvation on the Conformation of Star Polymers

    SciTech Connect

    Li, Xin; Porcar, L.; Sanchez-Diaz, Luis E; Do, Changwoo; Liu, Yun; Smith, Gregory Scott; Hong, Kunlun; Chen, Wei-Ren

    2014-01-01

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

  14. Dynamical eigenmodes of star and tadpole polymers

    NASA Astrophysics Data System (ADS)

    Keesman, Rick; Barkema, Gerard T.; Panja, Debabrata

    2013-02-01

    The dynamics of phantom bead-spring chains with the topology of a symmetric star with f arms and tadpoles (f = 3, a special case) is studied, in the overdamped limit. In the simplified case where the hydrodynamic radius of the central monomer is f times as heavy as the other beads, we determine their dynamical eigenmodes exactly, along the lines of the Rouse modes for linear bead-spring chains. These eigenmodes allow full analytical calculations of virtually any dynamical quantity. As examples we determine the radius of gyration, the mean square displacement of a tagged monomer, and, for star polymers, the autocorrelation function of the vector that spans from the center of the star to a bead on one of the arms.

  15. Interfacial Micellar Structures from Novel Amphiphilic Star Polymers

    SciTech Connect

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

    2010-11-10

    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.

  16. Star Formation and Dense Gas in Galaxy Mergers from the VIXENS Survey

    NASA Astrophysics Data System (ADS)

    Heiderman, Amanda L.; VIXENS Team

    2016-01-01

    We present our λ= 3 mm IRAM and NRO single dish line survey for a sample of 15 interacting galaxies in the VIRUS-P Investigation of the eXtreme ENvironments of Starbursts (VIXENS) survey. Our sample of merging galaxies range from early to late interaction stages (close pairs to merger remnants, respectively). A variety of molecular lines are detected including dense gas tracers HCN, HCO+, HNC, CS, CN (and others) as well as 12CO and 13CO. We compare the dense gas fractions with 12CO and 13CO as well as star formation efficiencies defined by infrared-to-dense gas tracer luminosity ratio and discuss trends with interaction stage. We also investigate relations between star formation and dense gas content in our merger sample and compare them to non-interacting star forming galaxies and Galactic star forming regions in the Milky Way.

  17. Flow-induced translocation of star polymers through a nanopore.

    PubMed

    Ding, Mingming; Duan, Xiaozheng; Shi, Tongfei

    2016-03-01

    We study the flow-induced translocation of the star polymers through a nanopore using a hybrid simulation method that incorporates a lattice-Boltzmann approach for the fluid into a molecular dynamics model for the polymer. Our simulation demonstrates the existence of an optimal forward arm number of the star polymers captured by the nanopore, and illustrates its significance in determining the critical velocity flux of the star polymer translocation through the nanopore. Importantly, we find that the critical velocity flux of the star polymers is independent of the arm polymerization degree, but exhibits a linear dependence on the arm number. Based on previous scaling arguments and our simulation results, we conclude a linear dependence of the critical velocity flux on the arm number of the star polymers, which can successfully describe the dynamics of the star polymer translocation. Our simulation results rationalize the experimental results for the dependence of the critical velocity flux on the arm polymerization degree and the arm number of the star polymers, which provide new insights for the characterization and the purification of the star polymers. PMID:26879130

  18. Dense cores in dark clouds - Young embedded stars at 2 micrometers

    NASA Technical Reports Server (NTRS)

    Benson, P. J.; Myers, P. C.; Wright, E. L.

    1984-01-01

    Twenty-five visually opaque regions which contain strong sources of NH3 (1,1) line emission (dense cores) have been surveyed for evidence of associated stars at two microns. Five such stars have been found, of which three - in B5, L1489, and L1582 - are optically invisible and probably embedded in their associated cores. The stars in B5 and L1489 have 2-100 micron spectra and luminosity similar to those of HL Tau, a very young T Tauri star. These stars probably formed in the cores where they are now seen. These results tend to confirm earlier suggestions that low-mass stars form in dense cores.

  19. Scattering from Star Polymers including Excluded Volume Effects

    SciTech Connect

    Li, Xin; Do, Changwoo; Liu, Yun; Sanchez-Diaz, Luis E; Hong, Kunlun; Smith, Greg; Chen, Wei-Ren

    2014-01-01

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

  20. Properties of Dense Matter in Neutron Stars and Supernovae

    SciTech Connect

    Shen, H.; Wang, Y. N.; Wen, W.

    2010-08-12

    We study the equation of state (EOS) of nuclear matter at finite temperature density with various proton fractions for use in supernova simulations. The properties of nuclear matter with both uniform and non-uniform distributions are studied consistently. We also discuss the EOS of neutron star matter at zero temperature in a wide density range including hyperons antikaons quarks. The EOS of neutron star matter could be softened by incorporating these new degrees of freedom.

  1. Compatibility of Medical-Grade Polymers with Dense CO2

    PubMed Central

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

    2009-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Myers, Philip C.

    2003-01-01

    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.

  3. Main chain decomposable star shaped polymer for EUV resist

    NASA Astrophysics Data System (ADS)

    Iwashita, Jun; Mimura, Takeyoshi; Hirayama, Taku; Iwai, Takeshi

    2009-03-01

    The Extreme Ultra Violet lithography (EUVL) is expected to be the most promising semiconductor fabrication technology for 22 nm node and beyond. Kozawa and his colleagues have documented that non-constant acid diffusion coefficient have a significant impact on the latent image quality of 22 nm patterns. We prepared a novel main chain decomposable star shaped polymer (STAR polymer) to examine the concept. STAR polymer consists of a core unit and several arm units which connect to the core unit as shown in Fig.1. The arm units are partially protected poly (p-hydroxystyrene) (PHS) base linear polymer. The core unit that attached on the arm units employs easily acid cleavable group. The adoption of living anion polymerization for the arm units of the STAR polymer makes the controlled polymerization of one monomer unit possible. Based on this material design concept, the protecting group on the arm unit is de-protected by the acid generated during exposure and continues its reaction at the Post Exposure Bake (PEB) step and the acid will also cleave the bonding of the core unit which would then result in a lower molecular weight polymer of lower Tg. The concept of the novel polymer, which is the decomposition of the core and protecting group of arm units of the STAR polymer, was confirmed with a gel-permeation-chromatography (GPC) study. The thermal property of the exposed and unexposed area was also investigated through a thermal flow method. The Tg decrease of the exposed area was observed with the STAR polymer, regardless of increase in Tg of the linear polymer. General lithographic performance on EUV exposure for STAR polymer was also discussed.

  4. Superfluid ultra-dense deuterium D(-1) on polymer surfaces: Structure and density changes at a polymer-metal boundary

    NASA Astrophysics Data System (ADS)

    Olofson, Frans; Holmlid, Leif

    2012-06-01

    Ultra-dense deuterium D(-1) with D-D bond distance 2.3 pm is the first ultra-dense material studied. It is a superfluid quantum material and may also be superconductive. Its interaction with metal and polymer surfaces is of immediate interest. D(-1) exists on organic polymer surfaces like (poly(methyl methacrylate)) PMMA even at a distance of a few millimeter from a metal in contact with the polymer. The density of D(-1) decreases from the metal surface to the open polymer surface, and is to some extent replaced by D(1) on the polymer surface. At low surface density of D(-1), the long chain-clusters appear to lie parallel the surface, while at large densities the clusters stand vertical to the surface. Various polymers give different structures of D(-1), for example fewer non-superfluid clusters D4 are observed on fluorocarbon surfaces relative to hydrogen containing polymers. Isotope exchange reactions in four-atom clusters are probably observed between deuterium in D(-1) and protium atoms in the hydrogenated polymer surface.

  5. Variations in the Star Formation Efficiency of the Dense Molecular Gas across the Disks of Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Usero, Antonio; Leroy, Adam K.; Walter, Fabian; Schruba, Andreas; García-Burillo, Santiago; Sandstrom, Karin; Bigiel, Frank; Brinks, Elias; Kramer, Carsten; Rosolowsky, Erik; Schuster, Karl-Friedrich; de Blok, W. J. G.

    2015-10-01

    We present a new survey of HCN(1-0) emission, a tracer of dense molecular gas, focused on the little-explored regime of normal star-forming galaxy disks. Combining HCN, CO, and infrared (IR) emission, we investigate the role of dense gas in star formation, finding systematic variations in both the apparent dense gas fraction (traced by the HCN-to-CO ratio) and the apparent star formation efficiency of dense gas (traced by the IR-to-HCN ratio). The latter may be unexpected, given the recent popularity of gas density threshold models to explain star formation scaling relations. Our survey used the IRAM 30 m telescope to observe HCN(1-0), CO(1-0), and several other emission lines across 29 nearby disk galaxies whose CO(2-1) emission has previously been mapped by the HERACLES survey. We detected HCN in 48 out of 62 observed positions. Because our observations achieve a typical resolution of ˜1.5 kpc and span a range of galaxies and galactocentric radii (56% lie at {r}{gal}\\gt 1 kpc), we are able to investigate the properties of the dense gas as a function of local conditions in a galaxy disk. We focus on how the ratios IR-to-CO, HCN-to-CO, and IR-to-HCN (observational cognates of the star formation efficiency, dense gas fraction, and dense gas star formation efficiency) depend on the stellar surface density, {{{Σ }}}{star}, and the molecular-to-atomic gas ratio, {{{Σ }}}{mol}/{{{Σ }}}{atom}. The HCN-to-CO ratio is low, often ˜1/30, and correlates tightly with both the molecular-to-atomic ratio and the stellar mass surface density across a range of 2.1 dex (factor of ≈125) in both parameters. Thus for the assumption of fixed CO-to-H2 and HCN-to-dense gas conversion factors, the dense gas fraction depends strongly on location in the disk, being higher in the high surface density, highly molecular parts of galaxies. At the same time, the IR-to-HCN ratio (closely related to the star formation efficiency of dense molecular gas) decreases systematically with these same parameters and is ˜6-8 times lower near galaxy centers than in the outer regions of the galaxy disks. For fixed conversion factors, these results are incompatible with a simple model in which star formation depends only on the amount of gas mass above some density threshold. Moreover, only a very specific set of environment-dependent conversion factors can render our observations compatible with such a model. Whole cloud models, such as the theory of turbulence regulated star formation, do a better job of matching our observations. We explore one such model in which variations in the Mach number drive many of the trends within galaxy disks, while density contrasts drive the differences between disk and merging galaxies. Based on observations with the IRAM 30 m telescope. IRAM is supported by CNRS/INSU (France), the MPG (Germany), and the IGN (Spain).

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

    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.

  7. Collision--induced absorption in dense atmospheres of cool stars

    SciTech Connect

    Borysow, Aleksandra; Joergensen, Uffe Graae

    1999-04-01

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

  8. Entropy-induced separation of star polymers in porous media

    SciTech Connect

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

    2006-09-15

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

  9. STELLAR COLLISIONS AND BLUE STRAGGLER STARS IN DENSE GLOBULAR CLUSTERS

    SciTech Connect

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

    2013-11-10

    Blue straggler stars (BSSs) are abundantly observed in all Galactic globular clusters (GGCs) where data exist. However, observations alone cannot reveal the relative importance of various formation channels or the typical formation times for this well-studied population of anomalous stars. Using a state-of-the-art Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ∼10{sup 3} M{sub ☉} pc{sup –3}, the dominant formation channel is stellar collisions, while for lower density clusters, mass transfer in binaries provides a significant contribution (up to 60% in our models). The majority of these collisions are binary-mediated, occurring during three-body and four-body interactions. As a result, a strong correlation between the specific frequency of BSSs and the binary fraction in a cluster can be seen in our models. We find that the number of BSSs in the core shows only a weak correlation with the collision rate estimator Γ 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.

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

    SciTech Connect

    Ladd, E. F.; Wong, T.; Bourke, T. L.; Thompson, K. L.

    2011-12-20

    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.

  11. Are superluminous supernovae and long GRBs the products of dynamical processes in young dense star clusters?

    SciTech Connect

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

    2013-12-20

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  13. The rate and latency of star formation in dense, massive clumps in the Milky Way

    NASA Astrophysics Data System (ADS)

    Heyer, M.; Gutermuth, R.; Urquhart, J. S.; Csengeri, T.; Wienen, M.; Leurini, S.; Menten, K.; Wyrowski, F.

    2016-04-01

    Context. Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. Aims: We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. Methods: A sample of 24 μm-based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps, f∗, that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 μm dust continuum emission and NH3 line emission. Results: Linear correlations are identified between the star formation rate surface density, ΣSFR, and the quantities ΣH2/τff and ΣH2/τcross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 μm saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2 M⊙) stars with emergent 24 μm fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified. Full Tables 2-4 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/588/A29

  14. Deposition of zwitterionic polymer brushes in a dense gas medium.

    PubMed

    Puniredd, Sreenivasa Reddy; Jayaraman, Sundaramurthy; Gandhimathi, Chinnasamy; Ramakrishna, Seeram; Venugopal, Jayarama Reddy; Yeo, Tin Wei; Guo, Shifeng; Quintana, Robert; Jańczewski, Dominik; Srinivasan, M P

    2015-06-15

    Poly(sulfobetaine methacrylate) (PSBMA) films known for their resistance to nonspecific protein adsorption, cell/bacterial adhesion and biofilm formation were produced by surface initiated polymerization on a silicon surface via a batch reaction system in CO2 expanded liquid (CO2-EL) medium. Atom transfer radical polymerization (ATRP) was carried out using 2,2'-bipyridyl as ligand and CuBr as a catalyst in water/methanol mixture with trichloro[4-(chloromethyl)phenyl]silane (CMPS) used as the initiating species. The films were grown in the CO2-EL environment at a range of conditions and thickness up to 10nm. In contrast to films produced by conventional solvent systems at atmospheric pressure, the polymer films grown by the CO2-EL process showed uniform thickness and pin-hole free topography. Most importantly, the CO2-EL processed PSBMA films showed no trace of copper (used as the catalyst), thus obviating the need for post-deposition processing and avoiding adverse effects of the metal leaching during service. Finally, PSBMA films from both the conventional and CO2-EL processes were exposed to Human mesenchymal stem cells (hMSCs) and the results showed that, while in both the cases the cell proliferation rate was inhibited by the charged polymeric brush surface, the CO2-EL-processed brush exhibited inhibition to a larger extent due to the reduced occurrence of pinholes. The process can be easily exploited effectively when carrying out surface initiated polymerization on non-flat topographies, such as in trenches and nanostructured features with high aspect ratios. PMID:25728486

  15. Wavelength selective polymer network formation of end-functional star polymers.

    PubMed

    Kaupp, Michael; Hiltebrandt, Kai; Trouillet, Vanessa; Mueller, Patrick; Quick, Alexander S; Wegener, Martin; Barner-Kowollik, Christopher

    2016-01-21

    A wavelength selective technique for light-induced network formation based on two photo-active moieties, namely ortho-methylbenzaldehyde and tetrazole is introduced. The network forming species are photo-reactive star polymers generated via reversible activation fragmentation chain transfer (RAFT) polymerization, allowing the network to be based on almost any vinylic monomer. Direct laser writing (DLW) allows to form any complex three-dimensional structure based on the photo-reactive star polymers. PMID:26687371

  16. Field-theoretical approach to a dense polymer with an ideal binary mixture of clustering centers

    NASA Astrophysics Data System (ADS)

    Fantoni, Riccardo; Mller-Nedebock, Kristian K.

    2011-07-01

    We propose a field-theoretical approach to a polymer system immersed in an ideal mixture of clustering centers. The system contains several species of these clustering centers with different functionality, each of which connects a fixed number segments of the chain to each other. The field theory is solved using the saddle point approximation and evaluated for dense polymer melts using the random phase approximation. We find a short-ranged effective intersegment interaction with strength dependent on the average segment density and discuss the structure factor within this approximation. We also determine the fractions of linkers of the different functionalities.

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

    NASA Astrophysics Data System (ADS)

    Rubio, M.; Paron, S.; Dubner, G.

    2009-10-01

    Context: The 30 Doradus region in the Large Magellanic Cloud is one of the most outstanding star-forming regions of the Local Group and a primary target for studying star formation in an environment of low metallicity. Aims: To obtain a more complete picture of the cool gas that has not yet been consumed or dispersed, we searched for line emission from molecular clouds that could be associated with molecular hydrogen emission detected in the region. Methods: We obtained a high sensitivity 12CO J = 2-1 map with the 15-m SEST telescope, complemented by pointed observations of 13CO J = 2-1 and CS J=2-1. Results: We report the discovery of a dense molecular cloud towards an embedded young massive star at 20 ( 5 pc, at the distance of 50 kpc) northwest of R136, the compact massive central stellar cluster powering 30 Doradus in the LMC, which could be triggering star formation in the surrounding molecular clouds. We derived a molecular mass of ?104 M?, a linear radius of 3 pc, as an upper limit, and a mean density of ?103 cm-3 for the cloud. The detection of the CS J = 2-1 emission line indicates higher densities, 106 cm-3. The dense molecular cloud is associated with molecular 2.12 ?m H{2} emission. We suggest that the observed molecular gas could be the remains of dense molecular material surviving the action of strong UV fields and winds in which the young massive star has formed. The observations were made with the Swedish-ESO Submillimeter Telescope, SEST, which was operated jointly by the Swedish National Facility for Radioastronomy and ESO.

  18. Tacticity control in the synthesis of poly(lactic acid) polymer stars with dipentaerythritol cores.

    PubMed

    Shaver, Michael P; Cameron, Donald J A

    2010-12-13

    The synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is presented. Dipentaerythritol cores support six poly(lactic acid) (PLA) arms. Lewis acidic tin and aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. The analysis of these polymers by NMR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Preliminary decomposition studies suggest that the biodegradation profile of a polymer star may also be tuned by stereochemical control. This is the first systematic altering of tacticity in PLA polymer stars, showing that polymer tacticity can have a great impact on star properties. PMID:21033736

  19. Amylose-Based Cationic Star Polymers for siRNA Delivery

    PubMed Central

    Nishimura, Tomoki; Umezaki, Kaori; Mukai, Sada-atsu; Sawada, Shin-ichi; Akiyoshi, Kazunari

    2015-01-01

    A new siRNA delivery system using a cationic glyco-star polymer is described. Spermine-modified 8-arm amylose star polymer (with a degree of polymerization of approximately 60 per arm) was synthesized by chemoenzymatic methods. The cationic star polymer effectively bound to siRNA and formed spherical complexes with an average hydrodynamic diameter of 230?nm. The cationic 8-arm star polymer complexes showed superior cellular uptake characteristics and higher gene silencing effects than a cationic 1-arm polymer. These results suggest that amylose-based star polymers are a promising nanoplatform for glycobiomaterials. PMID:26539548

  20. Monte Carlo simulation of dense polymer melts using event chain algorithms

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    We propose an efficient Monte Carlo algorithm for the off-lattice simulation of dense hard sphere polymer melts using cluster moves, called event chains, which allow for a rejection-free treatment of the excluded volume. Event chains also allow for an efficient preparation of initial configurations in polymer melts. We parallelize the event chain Monte Carlo algorithm to further increase simulation speeds and suggest additional local topology-changing moves ("swap" moves) to accelerate equilibration. By comparison with other Monte Carlo and molecular dynamics simulations, we verify that the event chain algorithm reproduces the correct equilibrium behavior of polymer chains in the melt. By comparing intrapolymer diffusion time scales, we show that event chain Monte Carlo algorithms can achieve simulation speeds comparable to optimized molecular dynamics simulations. The event chain Monte Carlo algorithm exhibits Rouse dynamics on short time scales. In the absence of swap moves, we find reptation dynamics on intermediate time scales for long chains.

  1. Phase separation in star-linear polymer mixtures

    NASA Astrophysics Data System (ADS)

    Camargo, Manuel; Likos, Christos N.

    2009-05-01

    We study mixtures of star polymers and linear chains in good solvent conditions. We consider the effect of the addition of small chains on the equilibrium structure as well as on the phase behavior of low- and intermediate-functionality star solutions. By using a recently introduced effective cross interaction between stars and chains [C. Mayer and C. N. Likos, Macromolecules 40, 1196 (2007)], we solve the two-component Ornstein-Zernike equation, finding evidence for cluster formation, which is accompanied by a spinodal instability at moderate chain concentrations. The binodal lines are numerically calculated and the dependence of the observed phenomena on functionality, size, and concentrations is rationalized by considering the attractive contribution, which is displayed by the effective, chain-modified star-star interaction potential.

  2. Turbulence in star formation: Tracing the velocity fields of dense cores

    NASA Astrophysics Data System (ADS)

    Volgenau, Nikolaus H.

    2004-09-01

    The theory of star formation that has developed over the past several decades supposes that dense cores are quiescent and isolated from energetic events. However, observations of star-forming regions show that cores develop in active environments. Thus, although the "standard" theory is quantitatively rigorous, it can only explain a fraction of real star-forming events. The point of departure for this work is the hypothesis that turbulence is a fundamental component of the star formation process. In a turbulent star formation theory, the effects of random gas motions extend from molecular cloud scales down to scales of thousands or hundreds of AU. Dense cores form rapidly at the collision interfaces of turbulent flows and evolve according to the specific physical conditions at those interfaces. Star formation is dynamic and interactive, rather than quasi-static and isolated. This work presents evidence for turbulent motions in dense cores. The evidence comes from observations of cores in the Perseus cloud made with the BIMA interferometer and the FCRAO 14 m antenna. The cores were mapped in C 18 O J 1 [arrow right] 0 emission with resolutions of ~44, 10, 5, and 3 arc-seconds. The higher angular resolutions correspond to physical scales within the characteristic core radius (~0.1 pc) identified in previous studies. In general, the range of velocities traced by the C 18 O, as well as the complexity of the fields, increases with resolution. No core resembles a quiescent condensation undergoing simple systematic rotation. The cores are analyzed by applying a gridding technique developed by Ostriker, Stone, & Gammie (2001) to quantify the properties of model clouds. Spectra taken through the datacubes over a wide range of sizes are used to construct correlations between line widths and spatial scale, which show a broad range of line widths even at the smallest measurable scales. The narrowest lines must have a turbulent component at least as great as the thermal component, and for nearly all lines, the turbulent component makes the dominant contribution. A statistical analysis of the variations in line properties as a function of spatial separation across a core shows that the means and variances of the central velocity ([Special characters omitted.] ) and line width ([Special characters omitted.] ) difference distributions exhibit properties characteristic of a hierarchy of turbulent gas motions (Miesch & Bally 1994). The high resolution BIMA data reveal that these turbulent motions persist on sub-core scales.

  3. The Physics of Mergers: Theoretical and Statistical Techniques Applied to Stellar Mergers in Dense Star Clusters

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan

    2011-08-01

    (abridged) This thesis presents theoretical and statistical techniques broadly related to systems of dynamically-interacting particles composed of several different types of populations. They are applied to observations of dense star clusters (SCs) in order to study gravitational interactions between stars. We present a new analytic method of quantifying the frequency of encounters involving single, binary and triple stars. With this technique, we have shown that dynamical encounters involving triple stars occur commonly in at least some SCs, and that they are likely to be an important dynamical channel for stellar mergers to occur. We have also used our techniques to analyze observational data for a large sample of SCs taken from the ACS Survey for Globular Clusters. The results of this analysis are as follows: (1) We have compiled a homogeneous catalogue of stellar populations for every cluster in our sample, including main-sequence (MS), red giant branch, horizontal branch and blue straggler (BS) stars. (2) With this catalogue, we have quantified the effects of the cluster dynamics in determining the relative sizes and spatial distributions of these stellar populations. (3) These results are particularly interesting for BSs since they provide compelling evidence that they are descended from binary stars. (4) Our analysis of the MS populations is consistent with a remarkably universal initial stellar mass function in old massive SCs in the Milky Way. This is a new result with important implications for our understanding of star formation in the early Universe and, more generally, the history of our Galaxy. Finally, we describe how our techniques are ideally suited for application to a number of other outstanding puzzles of modern astrophysics, including chemical reactions in the interstellar medium and mergers between galaxies in galaxy clusters.

  4. THE GREEN BANK TELESCOPE MAPS THE DENSE, STAR-FORMING GAS IN THE NEARBY STARBURST GALAXY M82

    SciTech Connect

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  6. Confinement and partitioning of a single polymer chain in a dense array of nanoposts.

    PubMed

    Joo, Heesun; Kim, Jun Soo

    2015-11-14

    We present a Brownian dynamics simulation study on the confinement and partitioning of a single, flexible polymer chain in a dense array of nanoposts with different sizes and separations, especially, when the volume of an interstitial space formed among four nanoposts is less than the volume of the polymer chain. As the interstitial volume decreases by either increasing the nanopost diameter or decreasing the separation between nanoposts, the chain conformation becomes elongated in the direction parallel to the nanoposts. Interestingly, however, the degree of chain elongation varies in a non-monotonic fashion as the interstitial volume decreases while keeping the passage width between two nanoposts constant at a small value. We calculate the free energy of chain partitioning over several interstitial spaces from the partitioning probability, and find that the non-monotonic dependence of the chain elongation results from an interplay between the confinement-driven chain elongation along the direction parallel to the nanoposts and the chain spreading perpendicular to the nanoposts by partitioning chain segments over several interstitial spaces. These results present the possibility of utilizing a dense array of nanoposts as a template to control polymer conformations. PMID:26350540

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

    SciTech Connect

    Umeyama, Daiki; Hagi, Keisuke; Ogiwara, Naoki; Horike, Satoshi E-mail: kitagawa@icems.kyoto-u.ac.jp; Tassel, Cedric; Kageyama, Hiroshi; Higo, Yuji; Kitagawa, Susumu E-mail: kitagawa@icems.kyoto-u.ac.jp

    2014-12-01

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

  8. The Dynamical Evolution of Stellar-Mass Black Holes in Dense Star Clusters

    NASA Astrophysics Data System (ADS)

    Morscher, Maggie

    Globular clusters are gravitationally bound systems containing up to millions of stars, and are found ubiquitously in massive galaxies, including the Milky Way. With densities as high as a million stars per cubic parsec, they are one of the few places in the Universe where stars interact with one another. They therefore provide us with a unique laboratory for studying how gravitational interactions can facilitate the formation of exotic systems, such as X-ray binaries containing black holes, and merging double black hole binaries, which are produced much less efficiently in isolation. While telescopes can provide us with a snapshot of what these dense clusters look like at present, we must rely on detailed numerical simulations to learn about their evolution. These simulations are quite challenging, however, since dense star clusters are described by a complicated set of physical processes occurring on many different length and time scales, including stellar and binary evolution, weak gravitational scattering encounters, strong resonant binary interactions, and tidal stripping by the host galaxy. Until very recently, it was not possible to model the evolution of systems with millions of stars, the actual number contained in the largest clusters, including all the relevant physics required describe these systems accurately. The Northwestern Group's Henon Monte Carlo code, CMC, which has been in development for over a decade, is a powerful tool that can be used to construct detailed evolutionary models of large star clusters. With its recent parallelization, CMC is now capable of addressing a particularly interesting unsolved problem in astrophysics: the dynamical evolution of stellar black holes in dense star clusters. Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters may have formed hundreds to thousands of stellar-mass black holes, the remnants of stars with initial masses from 20 - 100 Solar masses. Birth kicks from supernova explosions may eject some black holes from their birth clusters, but most should be retained initially. Using our Monte Carlo code, we have investigated the long-term dynamical evolution of globular clusters containing large numbers of stellar black holes. Our study is the first to explore in detail the dynamics of BHs in clusters through a large number of realistic simulations covering a wide range of initial conditions (cluster masses from 105 -- 106 Solar masses, as well as variation in other key parameters, such as the virial radius, central concentration, and metallicity), that also includes all the required physics. In almost all of our models we find that significant numbers of black holes (up to about a 1000) are retained all the way to the present. This is in contrast to previous theoretical expectations that most black holes should be ejected dynamically within a few Gyr. The main reason for this difference is that core collapse driven by black holes (through the Spitzer "mass segregation instability'') is easily reverted through three-body processes, and involves only a small number of the most massive black holes, while lower-mass black holes remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar black holes does not lead to a long-term physical separation of most black holes into a dynamically decoupled inner core, as often assumed previously; this is one of the most important results of this dissertation. Combined with the recent detections of several black hole X-ray binary candidates in Galactic globular clusters, our results suggest that stellar black holes could still be present in large numbers in many globular clusters today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.

  9. Peptidomimetic Star Polymers for Targeting Biological Ion Channels.

    PubMed

    Chen, Rong; Lu, Derong; Xie, Zili; Feng, Jing; Jia, Zhongfan; Ho, Junming; Coote, Michelle L; Wu, Yingliang; Monteiro, Michael J; Chung, Shin-Ho

    2016-01-01

    Four end-functionalized star polymers that could attenuate the flow of ionic currents across biological ion channels were first de novo designed computationally, then synthesized and tested experimentally on mammalian K+ channels. The 4-arm ethylene glycol conjugate star polymers with lysine or a tripeptide attached to the end of each arm were specifically designed to mimic the action of scorpion toxins on K+ channels. Molecular dynamics simulations showed that the lysine side chain of the polymers physically occludes the pore of Kv1.3, a target for immuno-suppression therapy. Two of the compounds tested were potent inhibitors of Kv1.3. The dissociation constants of these two compounds were computed to be 0.1 μM and 0.7 μM, respectively, within 3-fold to the values derived from subsequent experiments. These results demonstrate the power of computational methods in molecular design and the potential of star polymers as a new infinitely modifiable platform for ion channel drug discovery. PMID:27007701

  10. Hydrodynamic correlations and diffusion coefficient of star polymers in solution.

    PubMed

    Singh, Sunil P; Huang, Chien-Cheng; Westphal, Elmar; Gompper, Gerhard; Winkler, Roland G

    2014-08-28

    The center-of-mass dynamics of star polymers in dilute solution is analyzed by hybrid mesoscale simulations. The fluid is modeled by the multiparticle collision dynamics approach, a particle-based hydrodynamic simulation technique, which is combined with molecular dynamics simulations for the polymers. Star polymers of various functionalities are considered. We determine the center-of-mass velocity correlation functions, the corresponding mean square displacements, and diffusion coefficients. The velocity correlation functions exhibit a functionality-dependent and structure-specific intermediate time regime, with a slow decay. It is followed by the long-time tail t(-3/2), which is solely determined by the fluid. Infinite-system-size diffusion coefficients are determined from the velocity correlation function by a combination of simulation and analytical results, as well as from the center-of-mass mean square displacement for various systems sizes and extrapolation. In terms of the hydrodynamic radius, the star polymer hydrodynamic diffusion coefficient exhibits the same universal system-size dependence as a spherical colloid. The functionality dependence of the ratio of hydrodynamic radii and the radii of gyration agrees well with experimental predictions. PMID:25173039

  11. Peptidomimetic Star Polymers for Targeting Biological Ion Channels

    PubMed Central

    Chen, Rong; Lu, Derong; Xie, Zili; Feng, Jing; Jia, Zhongfan; Ho, Junming; Coote, Michelle L.; Wu, Yingliang; Monteiro, Michael J.; Chung, Shin-Ho

    2016-01-01

    Four end-functionalized star polymers that could attenuate the flow of ionic currents across biological ion channels were first de novo designed computationally, then synthesized and tested experimentally on mammalian K+ channels. The 4-arm ethylene glycol conjugate star polymers with lysine or a tripeptide attached to the end of each arm were specifically designed to mimic the action of scorpion toxins on K+ channels. Molecular dynamics simulations showed that the lysine side chain of the polymers physically occludes the pore of Kv1.3, a target for immuno-suppression therapy. Two of the compounds tested were potent inhibitors of Kv1.3. The dissociation constants of these two compounds were computed to be 0.1 μM and 0.7 μM, respectively, within 3-fold to the values derived from subsequent experiments. These results demonstrate the power of computational methods in molecular design and the potential of star polymers as a new infinitely modifiable platform for ion channel drug discovery. PMID:27007701

  12. A novel geometric embedding algorithm for efficiently generating dense polymer structures

    NASA Astrophysics Data System (ADS)

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

    2001-06-01

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

  13. Parallelized event chain algorithm for dense hard sphere and polymer systems

    SciTech Connect

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

    2015-01-15

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

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

    NASA Astrophysics Data System (ADS)

    Covey, K. R.; Lada, C. J.; Romn-Ziga, C.; Muench, A. A.; Forbrich, J.; Ascenso, J.

    2010-10-01

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

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

    SciTech Connect

    Covey, K. R.; Lada, C. J.; Muench, A. A.; Forbrich, J.; Ascenso, J.; Roman-Zuniga, C.

    2010-10-20

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

  16. Star/linear polymer topology transformation facilitated by mechanical linking of polymer chains.

    PubMed

    Aoki, Daisuke; Uchida, Satoshi; Takata, Toshikazu

    2015-06-01

    Topology transformation of a star polymer to a linear polymer is demonstrated for the first time. A three-armed star polymer possessing a mechanical linking of two polymer chains was synthesized by the living ring-opening polymerization of ?-valerolactone initiated by a pseudo[2]rotaxane having three hydroxy groups as the initiator sites on the wheel component and at both axle termini. The polymerization was followed by the propagation end-capping reaction with a bulky isocyanate not only to prevent the wheel component deslippage but also to introduce the urethane moiety at the axle terminal. The resulting rotaxane-linked star polymer with a fixed rotaxane linkage based on the ammonium/crown ether interaction was subjected to N-acetylation of the ammonium moiety, which liberated the components from the interaction to move the wheel component to the urethane terminal as the interaction site, eventually affording the linear polymer. The physical property change caused by the present topology transformation was confirmed by the hydrodynamic volume and viscosity. PMID:25892579

  17. Dense Gas Fraction and Star-formation Efficiency Variations in the Antennae Galaxies

    NASA Astrophysics Data System (ADS)

    Bigiel, F.; Leroy, A. K.; Blitz, L.; Bolatto, A. D.; da Cunha, E.; Rosolowsky, E.; Sandstrom, K.; Usero, A.

    2015-12-01

    We use the Combined Array for Research in Millimeter-wave Astronomy (CARMA) millimeter interferometer to map the Antennae Galaxies (NGC 4038/39), tracing the bulk of the molecular gas via the 12CO(1-0) line and denser molecular gas via the high density transitions HCN(1-0), HCO+(1-0), CS(2-1), and HNC(1-0). We detect bright emission from all tracers in both the two nuclei and three locales in the overlap region between the two nuclei. These three overlap region peaks correspond to previously identified "supergiant molecular clouds." We combine the CARMA data with Herschel infrared (IR) data to compare observational indicators of the star formation efficiency (star formation rate/H2 ? IR/CO), dense gas fraction (HCN/CO), and dense gas star formation efficiency (IR/HCN). Regions within the Antennae show ratios consistent with those seen for entire galaxies, but these ratios vary by up to a factor of six within the galaxy. The five detected regions vary strongly in both their integrated intensities and these ratios. The northern nucleus is the brightest region in millimeter-wave line emission, while the overlap region is the brightest part of the system in the IR. We combine the CARMA and Herschel data with ALMA CO data to report line ratio patterns for each bright point. CO shows a declining spectral line energy distribution, consistent with previous studies. HCO+ (1-0) emission is stronger than HCN (1-0) emission, perhaps indicating either more gas at moderate densities or higher optical depth than is commonly seen in more advanced mergers.

  18. Structure and rheology of star polymers in confined geometries: a mesoscopic simulation study.

    PubMed

    Zheng, Feiwo; Goujon, Florent; Mendonça, Ana C F; Malfreyt, Patrice; Tildesley, Dominic J

    2015-11-28

    Mesoscopic simulations of star polymer melts adsorbed onto solid surfaces are performed using the dissipative particle dynamics (DPD) method. A set of parameters is developed to study the low functionality star polymers under shear. The use of a new bond-angle potential between the arms of the star creates more rigid chains and discriminates between different functionalities at equilibrium, but still allows the polymers to deform appropriately under shear. The rheology of the polymer melts is studied by calculating the kinetic friction and viscosity and there is good agreement with experimental properties of these systems. The study is completed with predictive simulations of star polymer solutions in an athermal solvent. PMID:26435466

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

    NASA Astrophysics Data System (ADS)

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

    2001-06-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1971-01-01

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

  1. Spatially Resolved Dense Molecular Gas and Star Formation Rate in M51

    NASA Astrophysics Data System (ADS)

    Chen, Hao; Gao, Yu; Braine, Jonathan; Gu, Qiusheng

    2015-09-01

    We present the spatially resolved observations of HCN J = 1-0 emission in the nearby spiral galaxy M51 using the IRAM 30 m telescope. The HCN map covers an extent of 4\\prime 5\\prime , which is, so far, the largest in M51 with a spatial resolution of 28\\prime\\prime . There is a correlation between infrared emission (an indication of star formation rate (SFR)) and HCN (1-0) emission (a dense gas tracer) on a kiloparsec scale in M51, a natural extension of the proportionality between the SFR and the dense gas mass established globally in galaxies. Within M51, the relation appears to be sub-linear (with a slope of 0.74 0.16) as {L}{IR} rises less quickly than {L}{HCN}. We attribute this to a difference between center and outer disk such that the central regions have stronger HCN (1-0) emission per unit star formation. The IR-HCN correlation in M51 is further compared with global ones from the Milky Way to high-z galaxies and bridges the gap between giant molecular clouds and galaxies. Like the centers of nearby galaxies, the {L}{IR}/{L}{HCN} ratio measured in M51 (particularly in the central regions) is slightly lower than what is measured globally in galaxies, yet is still within the scatter. This implies that though the {L}{IR}/{L}{HCN} ratio varies as a function of physical environment in the different positions of M51, IR, and HCN indeed show a linear correlation over 10 orders of magnitude.

  2. First-Passage Time in Entangled Star Polymers Melts

    NASA Astrophysics Data System (ADS)

    Cao, Jing; Zhu, Jian; Wang, Zuowei; Likhtman, Alexei

    2015-03-01

    For a single star polymer in a melt of extremely long linear chains, the stress of star polymer relaxes by arm-retraction in which the star arms explore new configurations by withdrawing along their tubes and stretching out towards a new direction. Pearson and Helfand proposed that the arm in the tube can be represented as a harmonic spring with an applied thermal tension such that the arm-end feels an entropic force if it fluctuates away from its equilibrium position. We have investigated the first-passage(FP) time of the destruction of tube segments by representing the arm as a one-dimensional Rouse chain. In contrast, we found that the disengagement of a tube segment is getting faster with more Rouse modes added in, which means the FP problem has to be modelled by a multi-dimensional Kramer's problem. We found a new way of solving the multi-dimensional FP problem by projecting the problem along the most probable trajectory termed ``minimal action trajectory'' and correcting it by entropy term. In addition, we performed direct and forward-flux simulations of Rouse chains of different lengths. A good agreement between the analytical calculations and simulations was achieved for both discrete and continuous Rouse chains.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  4. From gas to stars in energetic environments: dense gas clumps in the 30 Doradus region within the Large Magellanic Cloud

    SciTech Connect

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

    2014-09-20

    We present parsec-scale interferometric maps of HCN(1-0) and HCO{sup +}(1-0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO{sup +} emission in the filament and signatures of recent star formation activity including H{sub 2}O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward the massive compact star cluster R136 in the southwest. We present detailed comparisons of clump properties (masses, linewidths, and sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, and N44). Our analysis shows that the 30Dor-10 clumps have similar masses but wider linewidths and similar HCN/HCO{sup +} (1-0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well shielded against the intense ionizing field that is present in the 30 Doradus region.

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

    PubMed Central

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

    2014-01-01

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

  6. Thermodynamic instabilities in warm and dense asymmetric nuclear matter and in compact stars

    NASA Astrophysics Data System (ADS)

    Lavagno, A.; Gervino, G.; Pigato, D.

    2016-01-01

    We investigate the possible thermodynamic instability in a warm and dense nuclear medium where a phase transition from nucleonic matter to resonance-dominated Δ-matter can take place. Such a phase transition is characterized by both mechanical instability (fluctuations on the baryon density) and by chemical-diffusive instability (fluctuations on the isospin concentration) in asymmetric nuclear matter. Similarly to the liquid-gas phase transition, the nucleonic and the Δ-matter phase have a different isospin density in the mixed phase. In the liquid-gas phase transition, the process of producing a larger neutron excess in the gas phase is referred to as isospin fractionation. A similar effects can occur in the nucleon- Δmatter phase transition due essentially to a Δ- excess in the Δ-matter phase in asymmetric nuclear matter. In this context we also discuss the relevance of Δ-isobar degrees of freedom in the bulk properties and in the maximum mass of compact stars.

  7. SANS structural characterization of fullerenol-derived star polymers in solutions

    NASA Astrophysics Data System (ADS)

    Jeng, U.-S.; Lin, T.-L.; Wang, L. Y.; Chiang, L. Y.; Ho, D. L.; Han, C. C.

    We have studied the chain conformations of fullerenol-derived star polymers in two organic solvents using small-angle neutron scattering (SANS). The SANS results indicate that the six poly(urethane-ether) arms, chemically bonded on the fullerenol of the C60-based star polymer, have a Gaussian chain conformation in toluene. However, these arms exhibit a pronounced excluded-volume effect in dimethylformamide solutions. We use a scattering model, with the polydispersity of the polymer taken into account, and a fractal model to extract the radius of gyration Rg values and the persistence lengths of the C60-star polymers in these two organic solutions.

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

    PubMed

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

    2015-01-22

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  10. Dense Molecular Gas and Star Formation in High Redshift Quasars: HCN Observations of IRAS F10214+4724

    NASA Astrophysics Data System (ADS)

    Solomon, P. M.; Vanden Bout, P. A.; Maddalena, R.

    2004-05-01

    We report observations of strong HCN (1-0) emission from the z = 2.2 infrared-luminous quasar IRAS F10214+4724 using the Green Bank Telescope (GBT). HCN emission associated with the cores of giant molecular clouds is a signpost of dense, star-forming molecular gas. HCN has a critical density for excitation of n ? 105 cm-3 , 300 times higher than that of CO. An important question is whether the far-infrared luminosity from high redshift quasars is due to the active galactic nucleus (AGN) or a huge starburst occurring in a disk around the AGN. After allowing for magnification by an intervening lens, the HCN line luminosity and mass of dense molecular gas is higher in F10214+4724 than in local ultra-luminous infrared galaxies (ULIRGs) like Arp 220, strongly supporting a star formation origin for the 1013 L? of far-infrared luminosity. The ratio of far infrared to line luminosities, L(FIR)/L(HCN), indicates that the star formation rate per solar mass of dense gas is similar to that of local ULIRGs and only slightly higher than that of normal spiral galaxies. A very large fraction of all molecular gas in this galaxy is dense gas. This is the essential condition for a starburst. A starburst of this magnitude is a major event in the formation of a galaxy and may be responsible for forming the galactic bulge. We will present a detailed comparison of the dense gas in F10214+4724 with that in local universe galaxies and in the Cloverleaf, another high redshift quasar with HCN emission. These observations demonstrate the power of the GBT for the detection of broad , weak spectral lines.

  11. The Dense Filamentary Giant Molecular Cloud G23.0-0.4: Birthplace of Ongoing Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Su, Yang; Zhang, Shaobo; Shao, Xiangjun; Yang, Ji

    2015-10-01

    We present observations of 1.5 square degree maps of the 12CO, 13CO, and C18O (J = 1 - 0) emission toward the complex region of the supernova remnant (SNR) W41 and SNR G22.7-0.2. A massive (˜ 5× {10}5 {M}⊙ ), large (˜84 × 15 pc), and dense (˜103 cm-3) giant molecular cloud (GMC), G23.0-0.4 with {V}{LSR} ˜ 77 km s-1, is found to be adjacent to the two SNRs. The GMC displays a filamentary structure approximately along the Galactic plane. The filamentary structure of the dense molecular gas, traced by C18O (J = 1 - 0) emission, is also coincident well with the distribution of the dust-continuum emission in the direction. Two dense massive MC clumps, two 6.7 GHz methanol masers, and one H ii/SNR complex, associated with the 77 km s-1 GMC G23.0-0.4, are aligned along the filamentary structure, indicating the star-forming activity within the GMC. These sources have periodic projected spacing of 0.°18-0.°26 along the giant filament, which is consistent with the theoretical predictions of 0.°22. This indicates that the turbulence seems to dominate the fragmentation process of the dense gaseous filament on a large scale. The established 4.4 kpc distance of the GMC and the long dense filament traced by C18O emission, together with the rich massive star-formation groups in the nearby region, suggest that G23.0-0.4 is probably located at the near side of the Scutum-Centaurus arm in the first quadrant. Considering the large scale and the elongation structure along the Galactic plane, we speculate that the dense filamentary GMC is related to the spiral density wave of the Milky Way.

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

    SciTech Connect

    Daligault, J.; Gupta, S. E-mail: guptasanjib@lanl.go

    2009-09-20

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

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

    SciTech Connect

    Geach, James E.; Papadopoulos, Padelis P. E-mail: padelis@mpifr-bonn.mpg.de

    2012-10-01

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

  14. Star Forming Dense Cloud Cores in the TeV -ray SNR RX J1713.7-3946

    SciTech Connect

    Sano, H.; Sato, J.; Yamamoto, H.; Hayakawa, T.; Torii, K.; Moribe, N.; Kawamura, A.; Okuda, T.; Mizuno, N.; Onishi, T.; Maezawa, H.; Inoue, T.; Inutsuka, S.; Tanaka, T.; Mizuno, A.; Ogawa, H.; Stutzki, J.; Bertoldi, F.; Anderl, S.; Bronfman, L.; Koo, B.C.

    2010-10-27

    RX J1713.7-3946 is one of the TeV {gamma}-ray supernova remnants (SNRs) emitting synchrotron X rays. The SNR is associated with molecular gas located at {approx}1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C and D, in the SNR in the {sup 12}CO(J=2-1) and {sup 13}CO(J=2-1) transitions at angular resolution of 90 degrees. The most intense core in {sup 13}CO, peak C, was also mapped in the {sup 12}CO(J=4-3) transition at angular resolution of 38 degrees. Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source and has a steep gradient with a r{sup -2.2 {+-} 0.4} variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X rays are physically associated with the molecular gas (Fukui et al. 2003). We present a scenario where the densest molecular core, peak C, survived against the blast wave and is now embedded within the SNR. Numerical simulations of the shock-cloud interaction indicate that a dense clump can indeed survive shock erosion, since shock propagation speed is stalled in the dense clump. Additionally, the shock-cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to the enhanced synchrotron X rays around dense cores.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    For general Temperley-Lieb loop models, including the logarithmic minimal models LM (p ,p‧) with p ,p‧ coprime integers, we construct an infinite family of Robin boundary conditions on the strip as linear combinations of Neumann and Dirichlet boundary conditions. These boundary conditions are Yang-Baxter integrable and allow loop segments to terminate on the boundary. Algebraically, the Robin boundary conditions are described by the one-boundary Temperley-Lieb algebra. Solvable critical dense polymers is the first member LM (1 , 2) of the family of logarithmic minimal models and has loop fugacity β = 0 and central charge c = - 2. Specialising to LM (1 , 2) with our Robin boundary conditions, we solve the model exactly on strips of arbitrary finite size N and extract the finite-size conformal corrections using an Euler-Maclaurin formula. The key to the solution is an inversion identity satisfied by the commuting double row transfer matrices. This inversion identity is established directly in the Temperley-Lieb algebra. We classify the eigenvalues of the double row transfer matrices using the physical combinatorics of the patterns of zeros in the complex spectral parameter plane and obtain finitised characters related to spaces of coinvariants of Z4 fermions. In the continuum scaling limit, the Robin boundary conditions are associated with irreducible Virasoro Verma modules with conformal weights Δ r , s -1/2 =1/32 (L2 - 4) where L = 2 s - 1 - 4 r, r ∈ Z, s ∈ N. These conformal weights populate a Kac table with half-integer Kac labels. Fusion of the corresponding modules with the generators of the Kac fusion algebra is examined and general fusion rules are proposed.

  16. Structure analysis of adsorbed star-like polymers with GISAS and SFM

    NASA Astrophysics Data System (ADS)

    Wolkenhauer, M.; Mller-Buschbaum, P.; Wunnicke, O.; Stamm, M.; Roovers, J.; von Krosigk, G.; Cubitt, R.

    The lateral structures of dried adsorbed binary mixtures of star polymers were investigated. Blends of protonated and deuterated polybutadiene stars were prepared from cyclohexane solutions and adsorbed onto silicon substrates. The number of arms and the molecular weight of the arms was varied. With grazing incidence small angle scattering techniques (GISAS) and scanning force microscopy (SFM), different dominant in-plane length scales were determined. The morphology of these structures is dominated by blob-like structures created from single stars or agglomerates of star polymers.

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

    SciTech Connect

    Kauffmann, Jens; Pillai, Thushara; Zhang Qizhou

    2013-03-10

    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.

  18. Determination of the interaction parameter and topological scaling features of symmetric star polymers in dilute solution

    NASA Astrophysics Data System (ADS)

    Rai, Durgesh K.; Beaucage, Gregory; Ratkanthwar, Kedar; Beaucage, Peter; Ramachandran, Ramnath; Hadjichristidis, Nikos

    2015-07-01

    Star polymers provide model architectures to understand the dynamic and rheological effects of chain confinement for a range of complex topological structures like branched polymers, colloids, and micelles. It is important to describe the structure of such macromolecular topologies using small-angle neutron and x-ray scattering to facilitate understanding of their structure-property relationships. Modeling of scattering from linear, Gaussian polymers, such as in the melt, has applied the random phase approximation using the Debye polymer scattering function. The Flory-Huggins interaction parameter can be obtained using neutron scattering by this method. Gaussian scaling no longer applies for more complicated chain topologies or when chains are in good solvents. For symmetric star polymers, chain scaling can differ from ? =0.5 (df=2 ) due to excluded volume, steric interaction between arms, and enhanced density due to branching. Further, correlation between arms in a symmetric star leads to an interference term in the scattering function first described by Benoit for Gaussian chains. In this work, a scattering function is derived which accounts for interarm correlations in symmetric star polymers as well as the polymer-solvent interaction parameter for chains of arbitrary scaling dimension using a hybrid Unified scattering function. The approach is demonstrated for linear, four-arm and eight-arm polyisoprene stars in deuterated p -xylene.

  19. Determination of the interaction parameter and topological scaling features of symmetric star polymers in dilute solution.

    PubMed

    Rai, Durgesh K; Beaucage, Gregory; Ratkanthwar, Kedar; Beaucage, Peter; Ramachandran, Ramnath; Hadjichristidis, Nikos

    2015-07-01

    Star polymers provide model architectures to understand the dynamic and rheological effects of chain confinement for a range of complex topological structures like branched polymers, colloids, and micelles. It is important to describe the structure of such macromolecular topologies using small-angle neutron and x-ray scattering to facilitate understanding of their structure-property relationships. Modeling of scattering from linear, Gaussian polymers, such as in the melt, has applied the random phase approximation using the Debye polymer scattering function. The Flory-Huggins interaction parameter can be obtained using neutron scattering by this method. Gaussian scaling no longer applies for more complicated chain topologies or when chains are in good solvents. For symmetric star polymers, chain scaling can differ from ν=0.5(d(f)=2) due to excluded volume, steric interaction between arms, and enhanced density due to branching. Further, correlation between arms in a symmetric star leads to an interference term in the scattering function first described by Benoit for Gaussian chains. In this work, a scattering function is derived which accounts for interarm correlations in symmetric star polymers as well as the polymer-solvent interaction parameter for chains of arbitrary scaling dimension using a hybrid Unified scattering function. The approach is demonstrated for linear, four-arm and eight-arm polyisoprene stars in deuterated p-xylene. PMID:26274195

  20. Open boundary molecular dynamics of sheared star-polymer melts.

    PubMed

    Sablić, Jurij; Praprotnik, Matej; Delgado-Buscalioni, Rafael

    2016-02-17

    Open boundary molecular dynamics (OBMD) simulations of a sheared star polymer melt under isothermal conditions are performed to study the rheology and molecular structure of the melt under a fixed normal load. Comparison is made with the standard molecular dynamics (MD) in periodic (closed) boxes at a fixed shear rate (using the SLLOD dynamics). The OBMD system exchanges mass and momentum with adjacent reservoirs (buffers) where the external pressure tensor is imposed. Insertion of molecules in the buffers is made feasible by implementing there a low resolution model (blob-molecules with soft effective interactions) and then using the adaptive resolution scheme (AdResS) to connect with the bulk MD. Straining with increasing shear stress induces melt expansion and a significantly different redistribution of pressure compared with the closed case. In the open sample, the shear viscosity is also a bit lowered but more stable against the viscous heating. At a given Weissenberg number, molecular deformations and material properties (recoverable shear strain and normal stress ratio) are found to be similar in both setups. We also study the modelling effect of normal and tangential friction between monomers implemented in a dissipative particle dynamics (DPD) thermostat. Interestingly, the tangential friction substantially enhances the elastic response of the melt due to a reduction of the kinetic stress viscous contribution. PMID:26820315

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

    NASA Astrophysics Data System (ADS)

    Mahmoodifar, Simin; Strohmayer, T. E.

    2013-04-01

    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.

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

    SciTech Connect

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

    2005-10-01

    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.

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

    NASA Technical Reports Server (NTRS)

    2002-01-01

    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

  4. Into the polymer brush regime through the "grafting-to" method: densely polymer-grafted rodlike viruses with an unusual nematic liquid crystal behavior.

    PubMed

    Zan, Tingting; Wu, Fengchi; Pei, Xiaodong; Jia, Shaoyi; Zhang, Ran; Wu, Songhai; Niu, Zhongwei; Zhang, Zhenkun

    2016-01-21

    The current work reports an intriguing discovery of how the force exerted on protein complexes like filamentous viruses by the strong interchain repulsion of polymer brushes can induce subtle changes of the constituent subunits at the molecular scale. Such changes transform into the macroscopic rearrangement of the chiral ordering of the rodlike virus in three dimensions. For this, a straightforward "grafting-to" PEGylation method has been developed to densely graft a filamentous virus with poly(ethylene glycol) (PEG). The grafting density is so high that PEG is in the polymer brush regime, resulting in straight and thick rodlike particles with a thin viral backbone. Scission of the densely PEGylated viruses into fragments was observed due to the steric repulsion of the PEG brush, as facilitated by adsorption onto a mica surface. The high grafting density of PEG endows the virus with an isotropic-nematic (I-N) liquid crystal (LC) phase transition that is independent of the ionic strength and the densely PEGylated viruses enter into the nematic LC phase at much lower virus concentrations. Most importantly, while the intact virus and the one grafted with PEG of low grafting density can form a chiral nematic LC phase, the densely PEGylated viruses only form a pure nematic LC phase. This can be traced back to the secondary to tertiary structural change of the major coat protein of the virus, driven by the steric repulsion of the PEG brush. Quantitative parameters characterising the conformation of the grafted PEG derived from the grafting density or the I-N LC transition are elegantly consistent with the theoretical prediction. PMID:26531814

  5. Targeted Gene Delivery to Macrophages by Biodegradable Star-Shaped Polymers.

    PubMed

    Zhang, Yajie; Wang, Yafeng; Zhang, Chi; Wang, Jin; Pan, Dejing; Liu, Jianghuai; Feng, Fude

    2016-02-17

    In this report, two biodegradable star-shaped polyasparamide derivatives and four analogues modified with either mannose or folic acid moiety for preferential targeting of a difficult-to-transfect immune cell type, i.e., macrophage, have been synthesized. Each of the prepared star polymers complexes with plasmid DNA to form nanosized particles featuring a core-shell-like morphology. Mannose or folate functionalized star polymers can greatly improve the transfection performance on a macrophage cell line RAW 264.7. As a result, a combination of targeting ligand modification and topological structures of gene carriers is a promising strategy for immune cells-based gene therapy. PMID:26420603

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

    SciTech Connect

    Carroll, J. D.

    2010-07-27

    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.

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

    NASA Astrophysics Data System (ADS)

    Schweizer, Ken

    2012-02-01

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

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

    PubMed

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

    2004-04-15

    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

  9. A Unified Equation for the Reaction Rate in Dense Matter Stars

    SciTech Connect

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

    2007-10-26

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

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

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Rajarshi; Schweizer, Kenneth S.

    2010-10-01

    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.

  11. The Dense Matter Equation of State from Neutron Star Radius and Mass Measurements

    NASA Astrophysics Data System (ADS)

    Özel, Feryal; Psaltis, Dimitrios; Güver, Tolga; Baym, Gordon; Heinke, Craig; Guillot, Sebastien

    2016-03-01

    We present a comprehensive study of spectroscopic radius measurements of twelve neutron stars obtained during thermonuclear bursts or in quiescence. We incorporate, for the first time, a large number of systematic uncertainties in the measurement of the apparent angular sizes, Eddington fluxes, and distances, in the composition of the interstellar medium, and in the flux calibration of X-ray detectors. We also take into account the results of recent theoretical calculations of rotational effects on neutron star radii, of atmospheric effects on surface spectra, and of relativistic corrections to the Eddington critical flux. We employ Bayesian statistical frameworks to obtain neutron star radii from the spectroscopic measurements as well as to infer the equation of state from the radius measurements. Combining these with the results of experiments in the vicinity of nuclear saturation density and the observations of ∼ 2 {M}ȯ neutron stars, we place strong and quantitative constraints on the properties of the equation of state between ≈ 2{--}8 times the nuclear saturation density. We find that around M=1.5{M}ȯ , the preferred equation of state predicts radii between 10.1 and 11.1 km. When interpreting the pressure constraints in the context of high density equations of state based on interacting nucleons, our results suggest a relatively weak contribution of the three-body interaction potential.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  13. Toward complex network droplets - a computational study of bicontinuous network regions in star polymer droplets

    NASA Astrophysics Data System (ADS)

    Marson, Ryan; Glotzer, Sharon

    2015-03-01

    The complexity and functionality of network phases in soft matter systems offer a wealth of possible technological applications ranging from photonics to medicine. Through Dissipative Particle Dynamics (DPD) simulations, with explicit solvent, of over 1 million particles we demonstrate control of nano- and micro- scale ordering in star polymer droplets. By tuning the building block geometry and interactions between star polymer components we produce a droplet phase diagram. In particular we highlight regions of the structure that contain phase separated bicontinuous network domains. This system demonstrates the possibility of functional droplets composed of complex networks, with a hierarchy of scales that can be tuned for specific applications.

  14. Synthesis and characterization of novel acid-sensitive tert-butyl methacrylate and isobutyl methacrylate containing star-shaped polymers

    NASA Astrophysics Data System (ADS)

    Long, Timothy E.; Kilian, Lars; Wang, Zhen-He; Esker, Alan R.

    2001-10-01

    Star-shaped polymers containing poly(isobutyl methacrylate) (iBMA) and poly(tert-butyl methacrylate) (t-BMA) arms coupled to a 2,5-dimethyl-2,5-hexanediol dimethacrylate (DHDMA) core were synthesized using arm-first living anionic polymerization. Gel permeation chromatography (GPC) indicated that coupling efficiencies were high and coupled products exhibited a monomodal molecular weight distribution. The star-shaped polymer number--average molecular weights were 8-10 times higher than the precursor arm molecular weights. The ratio of coupling reagent to living chain end concentration controlled the molecular weight of the star-shaped polymer and the number of coupled arms. The molecular weight distributions of the star-shaped polymers ranged from 1.5-2.0. Due to the labile tertiary- butyl esters contained in the DHDMA cores, these star-shaped polymers were readily hydrolyzed in the presence of acid catalysts. For example, poly(iBMA) star-shaped polymers were hydrolytically stable at 25 degree(s)C and hydrolyzed readily at 65 degree(s)C in the presence of hydrochloric acid. In addition, the poly(t-BMA) containing star--shaped polymers degraded under similar conditions. The degradation process for the iBMA and t-BMA containing star-shaped polymers was confirmed using 1H NMR spectroscopy, and poly(iBMA)-block- poly(methacrylic acid) and poly(methacrylic acid) were obtained, respectively.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  16. Constraining the Dense Matter Equation of State with ATHENA-WFI observations of Neutron Stars in Quiescent LMXBs

    NASA Astrophysics Data System (ADS)

    Guillot, Sebastien; Oezel, F.

    2015-09-01

    The study of neutron star quiescent low-mass X-ray binaries (qLMXBs) will address one of the main science goals of the Athena x-ray observatory. The study of the soft X-ray thermal emission from the neutron star surface in qLMXBs is a crucial tool to place constrains on the dense matter equation of state. I will briefly review this method, its strength and current weaknesses and limitations, as well as the current constraints on the equation of state from qLMXBs. The superior sensitivity of Athena will permit the acquisition of unprecedentedly high signal-to-noise spectra from these sources. It has been demonstrated that a single qLMXB, even with high S/N, will not place useful constraints on the EoS. However, a combination of qLMXBs spectra has shown promises of obtaining tight constraints on the equation of state. I will discuss the expected prospects for observations of qLMXBs inside globular clusters -- those that Athena will be able to resolve. I will also present the constraints on the equation of state that Athena will be able to obtain from these qLMXBs and from a population of qLMXBs in the field of the Galaxy, with distance measurements provided by Gaia.

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

    SciTech Connect

    Goswami, Sanghamitra; Umbreit, Stefan; Rasio, Frederic A.; Bierbaum, Matt

    2012-06-10

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

  18. HATS-4b: A dense hot Jupiter transiting a super metal-rich G star

    SciTech Connect

    Jordán, Andrés; Brahm, Rafael; Rabus, M.; Suc, V.; Espinoza, N.; Bakos, G. Á.; Penev, K.; Hartman, J. D.; Csubry, Z.; Bhatti, W.; De Val Borro, M.; Bayliss, D.; Zhou, G.; Mancini, L.; Mohler-Fischer, M.; Ciceri, S.; Csák, B.; Henning, T.; Sato, B.; Buchhave, L.; and others

    2014-08-01

    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 M{sub p} ≈ 1.32 M {sub Jup}, radius of R{sub p} ≈ 1.02 R {sub Jup}, and density of ρ {sub p} = 1.55 ± 0.16 g cm{sup –3} ≈1.24 ρ{sub Jup}. The host star has a mass of 1.00 M {sub ☉}, a radius of 0.92 R {sub ☉}, 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 {sub J} and is thus likely to have a significant content of heavy elements of the order of 75 M {sub ⊕}. 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.

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

    PubMed

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

    2014-07-14

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

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

    PubMed

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

    2014-04-01

    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

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

    PubMed

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

    2014-12-01

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

  2. CARMA LARGE AREA STAR FORMATION SURVEY: STRUCTURE AND KINEMATICS OF DENSE GAS IN SERPENS MAIN

    SciTech Connect

    Lee, Katherine I.; Storm, Shaye; Mundy, Lee G.; Teuben, Peter; Pound, Marc W.; Salter, Demerese M.; Chen, Che-Yu; Fernndez-Lpez, Manuel; Looney, Leslie W.; Segura-Cox, Dominique; Rosolowsky, Erik; Arce, Hctor G.; Plunkett, Adele L.; Ostriker, Eve C.; Shirley, Yancy L.; Kwon, Woojin; Kauffmann, Jens; Tobin, John J.; Volgenau, N. H.; Tassis, Konstantinos; and others

    2014-12-20

    We present observations of N{sub 2}H{sup +} (J = 1 ? 0), HCO{sup +} (J = 1 ? 0), and HCN (J = 1 ? 0) toward the Serpens Main molecular cloud from the CARMA Large Area Star Formation Survey (CLASSy). We mapped 150 arcmin{sup 2} of Serpens Main with an angular resolution of ?7''. The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. The majority of gas in the two subclusters has subsonic to sonic velocity dispersions. We applied a dendrogram technique with N{sub 2}H{sup +}(1-0) to study the gas structures; the SE subcluster has a higher degree of hierarchy than the NW subcluster. Combining the dendrogram and line fitting analyses reveals two distinct relations: a flat relation between nonthermal velocity dispersion and size, and a positive correlation between variation in velocity centroids and size. The two relations imply a characteristic depth of 0.15 pc for the cloud. Furthermore, we have identified six filaments in the SE subcluster. These filaments have lengths of ?0.2 pc and widths of ?0.03 pc, which is smaller than a characteristic width of 0.1 pc suggested by Herschel observations. The filaments can be classified into two types based on their properties. The first type, located in the northeast of the SE subcluster, has larger velocity gradients, smaller masses, and nearly critical mass-per-unit-length ratios. The other type, located in the southwest of the SE subcluster, has the opposite properties. Several YSOs are formed along two filaments which have supercritical mass per unit length ratios, while filaments with nearly critical mass-per-unit-length ratios are not associated with YSOs, suggesting that stars are formed on gravitationally unstable filaments.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

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

    PubMed

    Koda, Yuta; Terashima, Takaya; Sawamoto, Mitsuo

    2014-11-01

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

  6. Electrochemical Interrogation of G3-Poly(propylene thiophenoimine) Dendritic Star Polymer in Phenanthrene Sensing

    PubMed Central

    Makelane, Hlamulo R.; Tovide, Oluwakemi; Sunday, Christopher E.; Waryo, Tesfaye; Iwuoha, Emmanuel I.

    2015-01-01

    A novel dendritic star-copolymer, generation 3 poly(propylene thiophenoimine) (G3PPT)-co-poly(3-hexylthiophene) (P3HT) star co-polymer on gold electrode (i.e., Au|G3PPT-co-P3HT) was used as a sensor system for the determination of phenanthrene (PHE). The G3PPT-co-P3HT star co-polymer was synthesized via in situ electrochemical co-polymerization of generation 3 poly (propylene thiophenoimine) and poly (3-hexylthiophene) on gold electrode. 1HNMR spectroscopy was used to determine the regioregularity of the polymer composites, whereas Fourier transform infrared spectroscopy and scanning electron microscopy were used to study their structural and morphological properties. Au|G3PPT-co-P3HT in the absence of PHE, exhibited reversible electrochemistry attributable to the oligo (thiophene) ‘pendants’ of the dendrimer. PHE produced an increase in the voltammetric signals (anodic currents) due to its oxidation on the dendritic material to produce catalytic current, thereby suggesting the suitability of the Au|G3PPT-co-P3HT electrode as a PHE sensor. The electrocatalysis of PHE was made possible by the rigid and planar oligo-P3HT species (formed upon the oxidation of the oligo (thiophene) pendants of the star-copolymer), which allowed the efficient capture (binding) and detection (electrocatalytic oxidation) of PHE molecules. PMID:26404296

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

    NASA Astrophysics Data System (ADS)

    Blavatska, V.; Metzler, R.

    2015-04-01

    Multiple loop formation in polymer macromolecules is an important feature of the chromatin organization and DNA compactification in the nuclei. We analyse the size and shape characteristics of complex polymer structures, containing in general f1 loops (petals) and f2 linear chains (branches). Within the frames of continuous model of Gaussian macromolecule, we apply the path integration method and obtain the estimates for gyration radius Rg and asphericity \\hat{A} of typical conformation as functions of parameters f1, f2. In particular, our results qualitatively reveal the extent of anisotropy of star-like topologies as compared to the rosette structures of the same total molecular weight.

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

    PubMed Central

    Li, Xianfeng; Latour, Robert A.

    2009-01-01

    A systematic procedure has been developed to construct a relaxed dense-phase atomistic structure of a complex amorphous polymer. The numerical procedure consists of (1) coarse graining the atomistic model of the polymer into a mesoscopic model based on an iterative algorithm for potential inversion from distribution functions of the atomistic model, (2) relaxation of the coarse grained chain using a molecular dynamics scheme, and (3) recovery of the atomistic structure by reverse mapping based on the superposition of atomistic counterparts on the corresponding coarse grained coordinates. These methods are demonstrated by their application to construct a relaxed, dense-phase model of poly(DTB succinate), which is an amorphous tyrosine-derived biodegradable polymer that is being developed for biomedical applications. Both static and dynamic properties from the coarse-grained and atomistic simulations are analyzed and compared. The coarse-grained model, which contains the essential features of the DTB succinate structure, successfully described both local and global structural properties of the atomistic chain. The effective speedup compared to the corresponding atomistic simulation is substantially above 102, thus enabling simulation times to reach well into the characteristic experimental regime. The computational approach for reversibly bridging between coarse-grained and atomistic models provides an efficient method to produce relaxed dense-phase all-atom molecular models of complex amorphous polymers that can subsequently be used to study and predict the atomistic-level behavior of the polymer under different environmental conditions in order to optimally design polymers for targeted applications. PMID:20161121

  9. CARMA Large Area Star Formation Survey: project overview with analysis of dense gas structure and kinematics in Barnard 1

    SciTech Connect

    Storm, Shaye; Mundy, Lee G.; Lee, Katherine I.; Teuben, Peter; Pound, Marc W.; Salter, Demerese M.; Chen, Che-Yu; Gong, Hao; Fernández-López, Manuel; Looney, Leslie W.; Segura-Cox, Dominique M.; Rosolowsky, Erik; Arce, Héctor G.; Plunkett, Adele L.; Ostriker, Eve C.; Volgenau, Nikolaus H.; Shirley, Yancy L.; Tobin, John J.; Kwon, Woojin; Isella, Andrea; and others

    2014-10-20

    We present details of the CARMA Large Area Star Formation Survey (CLASSy), while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that spectrally imaged N{sub 2}H{sup +}, HCO{sup +}, and HCN (J = 1 → 0 transitions) across over 800 square arcminutes of the Perseus and Serpens Molecular Clouds. The observations have angular resolution near 7'' and spectral resolution near 0.16 km s{sup –1}. We imaged ∼150 square arcminutes of Barnard 1, focusing on the main core, and the B1 Ridge and clumps to its southwest. N{sub 2}H{sup +} shows the strongest emission, with morphology similar to cool dust in the region, while HCO{sup +} and HCN trace several molecular outflows from a collection of protostars in the main core. We identify a range of kinematic complexity, with N{sub 2}H{sup +} velocity dispersions ranging from ∼0.05 to 0.50 km s{sup –1} across the field. Simultaneous continuum mapping at 3 mm reveals six compact object detections, three of which are new detections. A new, non-binary dendrogram algorithm is used to analyze dense gas structures in the N{sub 2}H{sup +} position-position-velocity (PPV) cube. The projected sizes of dendrogram-identified structures range from about 0.01 to 0.34 pc. Size-linewidth relations using those structures show that non-thermal line-of-sight velocity dispersion varies weakly with projected size, while rms variation in the centroid velocity rises steeply with projected size. Comparing these relations, we propose that all dense gas structures in Barnard 1 have comparable depths into the sky, around 0.1-0.2 pc; this suggests that overdense, parsec-scale regions within molecular clouds are better described as flattened structures rather than spherical collections of gas. Science-ready PPV cubes for Barnard 1 molecular emission are available for download.

  10. A Small-angle Study of the Solution Properties of Dendrimer-like Star Polymers

    SciTech Connect

    Pople, John A.

    2001-03-22

    The solution properties of poly(e-caprolactone) dendritic polymers are investigated by small angle neutron scattering (SANS) techniques. Comparisons of the scattering function in the intermediate region of the SANS patterns with molecular dynamic simulations indicate that the dendritic polymers are relatively extended in their conformation. We report a decay exponent, which scales as l/{nu}, of -1.2, which suggests a conformation more extended than star polymers, approaching the case of sea urchins. Guinier plots of SANS patterns yield radius of gyration measurements R{sub g} {approx} 30{angstrom}, which increase with generation number. Modeling the scattering profiles according to a ''blob'' model yields values of the random walk persistence length <{xi}{sub E}> {approx} 10{angstrom}, which decreases with increasing polymerization generation.

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

    SciTech Connect

    Pople, John A.

    1999-03-01

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

  12. Dense neutron star matter

    SciTech Connect

    Stone, J. R.

    2014-05-02

    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.

  13. Coarse-graining and phase behavior of model star polymer-colloid mixtures in solvents of varying quality.

    PubMed

    Nikoubashman, Arash; Mahynski, Nathan A; Capone, Barbara; Panagiotopoulos, Athanassios Z; Likos, Christos N

    2015-12-28

    We study the effective interactions and phase behavior of star polymer-colloid mixtures through theory and Monte Carlo simulations. We extend previous theoretical approaches for calculating the effective star-colloid pair potential to take into account attractive contributions, which become significant at worsening solvent conditions. In order to assess the validity of our simulation and theory, we compute the effective interactions via virtual move parallel tempering Monte Carlo simulations using a microscopic bead-spring model for the star polymer and achieve excellent agreement. Finally, we perform grand canonical Monte Carlo simulations of the coarse-grained systems to study the effect of solvent quality on the phase behavior. PMID:26723593

  14. Coarse-graining and phase behavior of model star polymer-colloid mixtures in solvents of varying quality

    NASA Astrophysics Data System (ADS)

    Nikoubashman, Arash; Mahynski, Nathan A.; Capone, Barbara; Panagiotopoulos, Athanassios Z.; Likos, Christos N.

    2015-12-01

    We study the effective interactions and phase behavior of star polymer-colloid mixtures through theory and Monte Carlo simulations. We extend previous theoretical approaches for calculating the effective star-colloid pair potential to take into account attractive contributions, which become significant at worsening solvent conditions. In order to assess the validity of our simulation and theory, we compute the effective interactions via virtual move parallel tempering Monte Carlo simulations using a microscopic bead-spring model for the star polymer and achieve excellent agreement. Finally, we perform grand canonical Monte Carlo simulations of the coarse-grained systems to study the effect of solvent quality on the phase behavior.

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

    PubMed

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

    2015-04-10

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

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

    PubMed Central

    Fleischmann, Carolin; Whlk, Hendrik

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    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.

  18. Modulating Antimicrobial Activity and Mammalian Cell Biocompatibility with Glucosamine-Functionalized Star Polymers.

    PubMed

    Wong, Edgar H H; Khin, Mya Mya; Ravikumar, Vikashini; Si, Zhangyong; Rice, Scott A; Chan-Park, Mary B

    2016-03-14

    The development of novel reagents and antibiotics for combating multidrug resistance bacteria has received significant attention in recent years. In this study, new antimicrobial star polymers (14-26 nm in diameter) that consist of mixtures of polylysine and glycopolymer arms were developed and were shown to possess antimicrobial efficacy toward Gram positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) (with MIC values as low as 16 μg mL(-1)) while being non-hemolytic (HC50 > 10 000 μg mL(-1)) and exhibit excellent mammalian cell biocompatibility. Structure function analysis indicated that the antimicrobial activity and mammalian cell biocompatibility of the star nanoparticles could be optimized by modifying the molar ratio of polylysine to glycopolymers arms. The technology described herein thus represents an innovative approach that could be used to fight deadly infectious diseases. PMID:26859230

  19. Electrophoretic mobility of linear and star-branched DNA in semidilute polymer solutions.

    PubMed

    Saha, Sourav; Heuer, Daniel M; Archer, Lynden A

    2006-08-01

    Electrophoresis of large linear T2 (162 kbp) and 3-arm star-branched (N(Arm) = 48.5 kbp) DNA in linear polyacrylamide (LPA) solutions above the overlap concentration c* has been investigated using a fluorescence visualization technique that allows both the conformation and mobility mu of the DNA to be determined. LPA solutions of moderate polydispersity index (PI approximately 1.7-2.1) and variable polymer molecular weight Mw (0.59-2.05 MDa) are used as the sieving media. In unentangled semidilute solutions (c* < c < c(e)), we find that the conformational dynamics of linear and star-branched DNA in electric fields are strikingly different; the former migrating in predominantly U- or I-shaped conformations, depending on electric field strength E, and the latter migrating in a squid-like profile with the star-arms outstretched in the direction opposite to E and dragging the branch point through the sieving medium. Despite these visual differences, mu for linear and star-branched DNA of comparable size are found to be nearly identical in semidilute, unentangled LPA solutions. For LPA concentrations above the entanglement threshold (c > c(e)), the conformation of migrating linear and star-shaped DNA manifest only subtle changes from their unentangled solution features, but mu for the stars decreases strongly with increasing LPA concentration and molecular weight, while mu for linear DNA becomes nearly independent of c and Mw. These findings are discussed in the context of current theories for electrophoresis of large polyelectrolytes. PMID:16850503

  20. Simulation of dilute solutions of linear and star-branched polymers by dissipative particle dynamics.

    PubMed

    Nardai, M M; Zifferer, G

    2009-09-28

    A most promising off-lattice technique in order to simulate not only static but in addition dynamic behavior of linear and star-branched chains is the dissipative particle dynamics (DPD) method. In this model the atomistic representation of polymer molecules is replaced by a (coarse-grained) equivalent chain consisting of beads which are repulsive for each other in order to mimic the excluded volume effect (successive beads in addition are linked by springs). Likewise solvent molecules are combined to beads which in turn are repulsive for each other as well as for the polymer segments. The system is relaxed by molecular dynamics solving Newton's laws under the influence of short ranged conservative forces (i.e., repulsion between nonbonded beads and a proper balance of repulsion and attraction between bonded segments) and dissipative forces due to friction between particles, the latter representing the thermostat in conjunction with proper random forces. A variation of the strength of the repulsion between different types of beads allows the simulation of any desired thermodynamic situation. Static and dynamic properties of isolated linear and star-branched chains embedded in athermal, exothermal, and endothermal solvent are presented and theta conditions are examined. The generally accepted scaling concept for athermal systems is fairly well reproduced by linear and star-branched DPD chains and theta conditions appear for a unique parameter independent of functionality as in the case of Monte Carlo simulations. Furthermore, the correspondence between DPD and Monte Carlo data referring to the shape of chains and stars is fairly well, too. For dilute solutions the Zimm behavior is expected for dynamic properties which is indeed realized in DPD systems. PMID:19791917

  1. Efficient and robust star polymer catalysts for living radical polymerization: cooperative activation in microgel-core reactors.

    PubMed

    Terashima, Takaya; Nomura, Akihisa; Ouchi, Makoto; Sawamoto, Mitsuo

    2012-05-14

    Multifunctional microgel-core star polymers with ruthenium catalysts are designed as catalyst-bearing nanoreactors to improve activity, controllability, and functionality tolerance in living radical polymerization. Multifunctional ligands are efficiently incorporated into the core of star polymers by sequential tandem procedures: 1) ruthenium-catalyzed living radical polymerization, 2) in situ core hydrogenation, and 3) core-ruthenium removal. Typically, the star polymer ligands comprising multiple phosphines and amines within the core cooperatively enclose a ruthenium complex (>100 per core). As a result, the in-core pseudo hetero P,N-chelation of the ruthenium complexes not only showed high activity for methyl methacrylate but also high tolerance to unprotected methacrylic acid. PMID:22528733

  2. Alcohol-soluble Star-shaped Oligofluorenes as Interlayer for High Performance Polymer Solar Cells

    PubMed Central

    Zou, Yang; He, Zhicai; Zhao, Baofeng; Liu, Yuan; Yang, Chuluo; Wu, Hongbin; Cao, Yong

    2015-01-01

    Two star-shaped oligofluorenes with hexakis(fluoren-2-yl)benzene as core are designed and sythesized for interfacial materials in polymer solar cell. Diethanolamino groups are attached to the side chain of fluorene units for T0-OH and T1-OH to enable the alcohol solubility, and additional hydrophobic n-hexyl chains are also grafted on the increased fluorene arms for T1-OH. In conventional device with PCDTBT/PC71BM as active layer, a 50% enhanced PCE is obtained by incorporating T0-OH and T1-OH as the interlayer compared with device without interlayer. By optimizing the active material with PTB7 and with the inverted device structure, a maximum PCE of 9.30% is achieved, which is among the highest efficiencies for PTB7 based polymer solar cells. The work function of modified electrode, the surface morphology and the suraface properties are systematically studied. By modifying the structures of the star-shaped molecules, a balance between the hydrophobic and hydrophilic property is finely tuned, and thus facilitate the interlayer for high performance of PSCs. PMID:26612688

  3. Alcohol-soluble Star-shaped Oligofluorenes as Interlayer for High Performance Polymer Solar Cells

    NASA Astrophysics Data System (ADS)

    Zou, Yang; He, Zhicai; Zhao, Baofeng; Liu, Yuan; Yang, Chuluo; Wu, Hongbin; Cao, Yong

    2015-11-01

    Two star-shaped oligofluorenes with hexakis(fluoren-2-yl)benzene as core are designed and sythesized for interfacial materials in polymer solar cell. Diethanolamino groups are attached to the side chain of fluorene units for T0-OH and T1-OH to enable the alcohol solubility, and additional hydrophobic n-hexyl chains are also grafted on the increased fluorene arms for T1-OH. In conventional device with PCDTBT/PC71BM as active layer, a 50% enhanced PCE is obtained by incorporating T0-OH and T1-OH as the interlayer compared with device without interlayer. By optimizing the active material with PTB7 and with the inverted device structure, a maximum PCE of 9.30% is achieved, which is among the highest efficiencies for PTB7 based polymer solar cells. The work function of modified electrode, the surface morphology and the suraface properties are systematically studied. By modifying the structures of the star-shaped molecules, a balance between the hydrophobic and hydrophilic property is finely tuned, and thus facilitate the interlayer for high performance of PSCs.

  4. ALMA Resolves the Properties of Star-forming Regions in a Dense Gas Disk at z 3

    NASA Astrophysics Data System (ADS)

    Swinbank, A. M.; Dye, S.; Nightingale, J. W.; Furlanetto, C.; Smail, Ian; Cooray, A.; Dannerbauer, H.; Dunne, L.; Eales, S.; Gavazzi, R.; Hunter, T.; Ivison, R. J.; Negrello, M.; Oteo-Gomez, I.; Smit, R.; van der Werf, P.; Vlahakis, C.

    2015-06-01

    We exploit long baseline ALMA submillimeter observations of the lensed star-forming galaxy SDP 81 at z = 3.042 to investigate the properties of the interstellar medium (ISM) on scales of 50-100 pc. The kinematics of the 12CO gas within this system are well described by a rotationally supported disk with an inclination-corrected rotation speed, {{v}rot} = 320 20 km s-1, and a dynamical mass of {{M}dyn} = (3.5 1.0) 1010 {{M}? } within a radius of 1.5 kpc. The disk is gas-rich and unstable, with a Toomre parameter, Q = 0.30 0.10, and so into star-forming regions with Jeans length {{L}J} 130 pc. We identify five star-forming regions within the ISM on these scales and show that their scaling relations between luminosity, line widths, and sizes are significantly offset from those typical of molecular clouds in local galaxies (Larsons relations). These offsets are likely to be caused by the high external hydrostatic pressure for the ISM, {{P}tot}/{{k}B} 40-20+30 107 K cm-3, which is 104 higher than the typical ISM pressure in the Milky Way. The physical conditions of the star-forming ISM and giant molecular clouds appear to be similar to those found in the densest environments in the local universe, such as those in the Galactic center.

  5. Probing star formation in the dense environments of z ˜ 1 lensing haloes aligned with dusty star-forming galaxies detected with the South Pole Telescope

    NASA Astrophysics Data System (ADS)

    Welikala, N.; Béthermin, M.; Guery, D.; Strandet, M.; Aird, K. A.; Aravena, M.; Ashby, M. L. N.; Bothwell, M.; Beelen, A.; Bleem, L. E.; de Breuck, C.; Brodwin, M.; Carlstrom, J. E.; Chapman, S. C.; Crawford, T. M.; Dole, H.; Doré, O.; Everett, W.; Flores-Cacho, I.; Gonzalez, A. H.; González-Nuevo, J.; Greve, T. R.; Gullberg, B.; Hezaveh, Y. D.; Holder, G. P.; Holzapfel, W. L.; Keisler, R.; Lagache, G.; Ma, J.; Malkan, M.; Marrone, D. P.; Mocanu, L. M.; Montier, L.; Murphy, E. J.; Nesvadba, N. P. H.; Omont, A.; Pointecouteau, E.; Puget, J. L.; Reichardt, C. L.; Rotermund, K. M.; Scott, D.; Serra, P.; Spilker, J. S.; Stalder, B.; Stark, A. A.; Story, K.; Vanderlinde, K.; Vieira, J. D.; Weiß, A.

    2016-01-01

    We probe star formation in the environments of massive (˜1013 M⊙) dark matter haloes at redshifts of z ˜ 1. This star formation is linked to a submillimetre clustering signal which we detect in maps of the Planck High Frequency Instrument that are stacked at the positions of a sample of high redshift (z > 2) strongly lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope (SPT) 2500 deg2 survey. The clustering signal has submillimetre colours which are consistent with the mean redshift of the foreground lensing haloes (z ˜ 1). We report a mean excess of star formation rate (SFR) compared to the field, of (2700 ± 700) M⊙ yr-1 from all galaxies contributing to this clustering signal within a radius of 3.5 arcmin from the SPT DSFGs. The magnitude of the Planck excess is in broad agreement with predictions of a current model of the cosmic infrared background. The model predicts that 80 per cent of the excess emission measured by Planck originates from galaxies lying in the neighbouring haloes of the lensing halo. Using Herschel maps of the same fields, we find a clear excess, relative to the field, of individual sources which contribute to the Planck excess. The mean excess SFR compared to the field is measured to be (370 ± 40) M⊙ yr-1 per resolved, clustered source. Our findings suggest that the environments around these massive z ˜ 1 lensing haloes host intense star formation out to about 2 Mpc. The flux enhancement due to clustering should also be considered when measuring flux densities of galaxies in Planck data.

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

    SciTech Connect

    Garofali, Kristen; Converse, Joseph M.; Chandar, Rupali; Rangelov, Blagoy

    2012-08-10

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

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

    PubMed

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

    2012-12-21

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

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

    NASA Astrophysics Data System (ADS)

    Busche, Bradley James

    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.

  9. X-ray emission from dense plasma in classical T Tauri stars: hydrodynamic modeling of the accretion shock

    NASA Astrophysics Data System (ADS)

    Sacco, G. G.; Argiroffi, C.; Orlando, S.; Maggio, A.; Peres, G.; Reale, F.

    2008-11-01

    Context: High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at temperature T 2-3 106 K and density n_e 1011-1013 cm-3, which are unobserved in non-accreting stars. Stationary models suggest that this emission is due to shock-heated accreting material, but do not allow us to analyze the stability of the material and its position in the stellar atmosphere. Aims: We investigate the dynamics and stability of shock-heated accreting material in classical T Tauri stars and the role of the stellar chromosphere in determining the position and thickness of the shocked region. Methods: We perform one-dimensional hydrodynamic simulations of the impact of an accretion flow on the chromosphere of a CTTS, including the effects of gravity, radiative losses from optically thin plasma, thermal conduction and a well tested detailed model of the stellar chromosphere. We present the results of a simulation based on the parameters of the CTTS MP Mus. Results: We find that the accretion shock generates an hot slab of material above the chromosphere with a maximum thickness of 1.8 109 cm, density n_e 1011-1012 cm-3, temperature T 3 106 K, and uniform pressure equal to the ram pressure of the accretion flow (~450 dyn cm-2). The base of the shocked region penetrates the chromosphere and remains at a position at which the ram pressure is equal to the thermal pressure. The system evolves with quasi-periodic instabilities of the material in the slab leading to cyclic disappearance and re-formation of the slab. For an accretion rate of ~10-10~M? yr-1, the shocked region emits a time-averaged X-ray luminosity of L_X? 7 1029 erg s-1, which is comparable with the X-ray luminosity observed in CTTSs of identical mass. Furthermore, the X-ray spectrum synthesized from the simulation reproduces in detail all the main features of the O VIII and O VII lines of the star MP Mus.

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

    SciTech Connect

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

    2013-11-01

    This paper presents the results of millimeter to sub-millimeter observations of CO, HCN, N{sub 2}H{sup +}, and HCO{sup +} lines in the dense molecular cloud L328, which harbors L328-IRS, a Very Low Luminosity Object (VeLLO). Our analysis of the line width finds that {sup 13}CO and N{sub 2}H{sup +} lines are broadened right over the smallest sub-core S2 where L328-IRS is located, while they are significantly narrower in other regions of L328. Thus, L328-IRS has a direct association with the sub-core. CO observations show a bipolar outflow from this VeLLO with an extent of ?0.08 pc. The outflow momentum flux and efficiency are much less than those of low-mass protostars. The most likely mass accretion rate (?3.6 10{sup 7} M{sub ?} yr{sup 1}) inferred from the analysis of the CO outflow is an order of magnitude smaller than the canonical value for a protostar. If the main accretion lasts during the typical Class 0 period of a protostar, L328-IRS will accrete the mass of a brown dwarf, but not that of a star. Given that its envelope mass is small (?0.09 M{sub ?}) and 100% star formation rate is unlikely, we suggest that L328-IRS is likely a proto-brown dwarf. Inward motions are found in global scale in the L328 cloud and its sub-cores with a typical infall speed found in starless cores. L328 is found to be fairly well isolated from other nearby clouds and seems to be forming three sub-cores simultaneously through a gravitational fragmentation process. Altogether, these all leave L328-IRS as the best example supporting the idea that a brown dwarf forms like a normal star.

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

    PubMed

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

    2015-04-01

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

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

    SciTech Connect

    Wagg, Jeff; Pope, Alexandra; Alberts, Stacey; Armus, Lee; Desai, Vandana; Brodwin, Mark; Bussmann, Robert S.; Dey, Arjun; Jannuzi, Buell; Le Floc'h, Emeric; Melbourne, Jason; Stern, Daniel

    2012-06-20

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

  13. CO J = 2-1 Line Emission in Cluster Galaxies at z ~ 1: Fueling Star Formation in Dense Environments

    NASA Astrophysics Data System (ADS)

    Wagg, Jeff; Pope, Alexandra; Alberts, Stacey; Armus, Lee; Brodwin, Mark; Bussmann, Robert S.; Desai, Vandana; Dey, Arjun; Jannuzi, Buell; Le Floc'h, Emeric; Melbourne, Jason; Stern, Daniel

    2012-06-01

    We present observations of CO J = 2-1 line emission in infrared-luminous cluster galaxies at z ~ 1 using the IRAM Plateau de Bure Interferometer. Our two primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie within 2 Mpc of the centers of two massive (>1014 M ?) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3? upper limits to the CO J = 2-1 line luminosities, L'CO < 6.08 109 and <6.63 109 K km s-1 pc2. Assuming a CO-to-H2 conversion factor derived for ultraluminous infrared galaxies in the local universe, this translates to limits on the cold molecular gas mass of M_H_2 < 4.86 \\times 10^{9} \\,M_{\\odot } and M_H_2 < 5.30 \\times 10^{9} \\,M_{\\odot }. Both DOGs exhibit mid-infrared continuum emission that follows a power law, suggesting that an active galactic nucleus (AGN) contributes to the dust heating. As such, estimates of the star formation efficiencies in these DOGs are uncertain. A third cluster member with an infrared luminosity, L IR < 7.4 1011 L ?, is serendipitously detected in CO J = 2-1 line emission in the field of one of the DOGs located roughly two virial radii away from the cluster center. The optical spectrum of this object suggests that it is likely an obscured AGN, and the measured CO line luminosity is L'CO = (1.94 0.35) 1010 K km s-1 pc2, which leads to an estimated cold molecular gas mass M_H_2 = (1.55 +/- 0.28)\\times 10^{10}\\,M_{\\odot }. A significant reservoir of molecular gas in a z ~ 1 galaxy located away from the cluster center demonstrates that the fuel can exist to drive an increase in star formation and AGN activity at the outskirts of high-redshift clusters. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  14. The Pharmacokinetics and Biodistribution of a 64 kDa PolyPEG Star Polymer After Subcutaneous and Pulmonary Administration to Rats.

    PubMed

    Khor, Song Yang; Hu, Jinming; McLeod, Victoria M; Quinn, John F; Porter, Christopher J H; Whittaker, Michael R; Kaminskas, Lisa M; Davis, Thomas P

    2016-01-01

    PolyPEG star polymers have potential utility as cost-effective polymeric drug delivery vehicles, and as such, it is important to develop an understanding of their biopharmaceutical behavior. Moreover, although a number of studies have evaluated the utility of PolyPEG stars in vitro, investigation of these novel materials in vivo has been limited. Herein, we evaluated the pharmacokinetics of a 64 kDa tritiated PEG-based star polymer after subcutaneous and pulmonary administration in rats. After subcutaneous administration, the star polymer showed near complete bioavailability (∼80%) and a similar organ biodistribution profile to the polymer after intravenous administration. After intratracheal instillation to the lungs, the star polymer showed limited bioavailability (∼3%), and most of the administered radiolabel was recovered in lung tissue and feces after 6 d. The data reported here suggest that star polymers display similar pharmaceutical behavior to PEGylated dendrimers after subcutaneous and inhaled delivery and may therefore be used as similar, but more cost-effective drug delivery vehicles. PMID:26852861

  15. Cyclodextrin-based star polymers as a versatile platform for nanochemotherapeutics: Enhanced entrapment and uptake of idarubicin.

    PubMed

    Nafee, N; Hirosue, M; Loretz, B; Wenz, G; Lehr, C-M

    2015-05-01

    A series of cyclodextrin-based star polymers were synthesized using β-cyclodextrin (CD) as hydrophilic core, methyl methacrylate (MMA) and tert-butyl acrylate (tBA) as hydrophobic arms. Star polymers, either homopolymers or random/block copolymers, showed narrow molecular weight distributions. Grafting hydrophobic arms created CD-based nanoparticles (CD-NPs) in the size range (130-200nm) with narrow PdI <0.15 and slightly negative ζ-potential. Particle surface could be modified with chitosan to impart a positive surface charge. Colloidal stability of CD-NPs was a function of pH as revealed by the pH-titration curves. CD-NPs were used as carrier for the chemotherapeutic drug idarubicin (encapsulation efficiency, EE ∼40%) ensuring prolonged release profile (∼80% after 48h). For cell-based studies, coumarin-6 was encapsulated as a fluorescent marker (EE ∼75%). Uptake studies carried out on A549 and Caco-2 cell lines proved the uptake of coumarin-loaded NPs as a function of time and preferential localization in the cytoplasm. Uptake kinetics revealed no saturation or plateau over 6h. Chitosan-modified NPs showed significantly improved, concentration-dependent cellular uptake. Meanwhile, CD-NPs were non-cytotoxic on both cell lines over the concentration range (0.25-3mg/ml) as studied by MTT and LDH assays. In conclusion, CD star polymers can be considered a versatile platform for a new class of biocompatible nanochemotherapy. PMID:25819363

  16. Molecular Differentiated Initiator Reactivity in the Synthesis of Poly(caprolactone)-Based Hydrophobic Homopolymer and Amphiphilic Core Corona Star Polymers.

    PubMed

    Deng, Eileen; Nguyen, Nam T; Hild, Frédéric; Hamilton, Ian E; Dimitrakis, Georgios; Kingman, Samuel W; Lau, Phei-Li; Irvine, Derek J

    2015-01-01

    Macromolecules that possess three-dimensional, branched molecular structures are of great interest because they exhibit significantly differentiated application performance compared to conventional linear (straight chain) polymers. This paper reports the synthesis of 3- and 4-arm star branched polymers via ring opening polymerisation (ROP) utilising multi-functional hydroxyl initiators and Sn(Oct)2 as precatalyst. The structures produced include mono-functional hydrophobic and multi-functional amphiphilic core corona stars. The characteristics of the synthetic process were shown to be principally dependent upon the physical/dielectric properties of the initiators used. ROP's using initiators that were more available to become directly involved with the Sn(Oct)₂ in the "in-situ" formation of the true catalytic species were observed to require shorter reaction times. Use of microwave heating (MWH) in homopolymer star synthesis reduced reaction times compared to conventional heating (CH) equivalents, this was attributed to an increased rate of "in-situ" catalyst formation. However, in amphiphilic core corona star formation, the MWH polymerisations exhibited slower propagation rates than CH equivalents. This was attributed to macro-structuring within the reaction medium, which reduced the potential for reaction. It was concluded that CH experiments were less affected by this macro-structuring because it was disrupted by the thermal currents/gradients caused by the conductive/convective heating mechanisms. These gradients are much reduced/absent with MWH because it selectively heats specific species simultaneously throughout the entire volume of the reaction medium. These partitioning problems were overcome by introducing additional quantities of the species that had been determined to selectively heat. PMID:26569198

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

    PubMed

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

    2015-01-14

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

  18. Polymers.

    ERIC Educational Resources Information Center

    Tucker, David C.

    1986-01-01

    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)

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

    PubMed

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  1. Doxorubicin-loaded aromatic imine-contained amphiphilic branched star polymer micelles: synthesis, self-assembly, and drug delivery

    PubMed Central

    Qiu, Liang; Hong, Chun-Yan; Pan, Cai-Yuan

    2015-01-01

    Redox-and pH-sensitive branched star polymers (BSPs), BP(DMAEMA-co-MAEBA-co-DTDMA)(PMAIGP)ns, have been successively prepared by two steps of reversible additionfragmentation chain transfer (RAFT) polymerization. The first step is RAFT polymerization of 2-(N,N-dimethylaminoethyl)methacrylate (DMAEMA) and p-(methacryloxyethoxy) benzaldehyde (MAEBA) in the presence of divinyl monomer, 2,2?-dithiodiethoxyl dimethacrylate (DTDMA). The resultant branched polymers were used as a macro-RAFT agent in the subsequent RAFT polymerization. After hydrolysis of the BSPs to form BP(DMAEMA-co-MAEBA-co-DTDMA)(PMAGP)ns (BSP-H), the anticancer drug doxorubicin (DOX) was covalently linked to branched polymer chains by reaction of primary amine of DOX and aldehyde groups in the polymer chains. Their compositions, structures, molecular weights, and molecular weight distributions were respectively characterized by nuclear magnetic resonance spectra and gel permeation chromatography measurements. The DOX-loaded micelles were fabricated by self-assembly of DOX-containing BSPs in water, which were characterized by transmission electron microscopy and dynamic light scattering. Aromatic imine linkage is stable in neutral water, but is acid-labile; controlled release of DOX from the BSP-H-DOX micelles was realized at pH values of 5 and 6, and at higher acidic solution, fast release of DOX was observed. In vitro cytotoxicity experiment results revealed low cytotoxicity of the BSPs and release of DOX from micelles in HepG2 and HeLa cells. Confocal laser fluorescence microscopy observations showed that DOX-loaded micelles have specific interaction with HepG2 cells. Thus, this type of BSP micelle is an efficient drug delivery system. PMID:26056444

  2. Customizing wormlike mesoscale structures via self-assembly of amphiphilic star polymers.

    PubMed

    Koch, Christian; Panagiotopoulos, Athanassios Z; Lo Verso, Federica; Likos, Christos N

    2015-05-14

    We examine the phase behavior of end-functionalized diblock copolymer stars by means of Grand Canonical Monte Carlo simulations. We focus on solutions of diblock copolymer stars with a solvophobic outer block shorter than the solvophilic inner block, which are expected to nucleate microphase aggregates. By tuning the temperature and rigidity of the molecules, we target specific mesoscale structures, which can act as powerful rheology modifiers. In particular, we control the hierarchical self-assembly of single micelles in a "pearl-necklace" fashion, which eventually merge into elongated, wormlike supermicelles. PMID:25790108

  3. 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)

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

    2011-03-01

    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.

  4. 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

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

    2011-12-15

    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.

  5. Drug-loaded pseudo-block copolymer micelles with a multi-armed star polymer as the micellar exterior

    NASA Astrophysics Data System (ADS)

    Xie, Chen; Zhang, Peng; Zhang, Zhengkui; Yang, Chenchen; Zhang, Jialiang; Wu, Wei; Jiang, Xiqun

    2015-07-01

    Supramolecular constructed pseudo block copolymer micelles based on β-cyclodextrin terminated 4 and 7 armed star poly(N-vinylpyrrolidone) and adamantane terminated linear poly(ε-caprolactone) were prepared. The size, morphology, stability and protein adsorption were experimentally examined. The micelles with 7 armed PVP chains as the micellar exterior showed the lowest amount of protein adsorption and the best stability in media. When cabazitaxel, a new taxane, was loaded into the micelles, 14.4% drug loading content and 85% encapsulation efficacy were achieved. In vitro cytotoxicity studies demonstrated that the cabazitaxel-loaded micelles show significant cytotoxicity against drug-resistant A2780/T cell lines. Biodistribution studies showed that the micelles can almost double the content of cargo in tumor sites compared with the free cargo. In vivo antitumor activity examinations indicated that cabazitaxel-loaded micelles show superior antitumor activity over free paclitaxel and free cabazitaxel.Supramolecular constructed pseudo block copolymer micelles based on β-cyclodextrin terminated 4 and 7 armed star poly(N-vinylpyrrolidone) and adamantane terminated linear poly(ε-caprolactone) were prepared. The size, morphology, stability and protein adsorption were experimentally examined. The micelles with 7 armed PVP chains as the micellar exterior showed the lowest amount of protein adsorption and the best stability in media. When cabazitaxel, a new taxane, was loaded into the micelles, 14.4% drug loading content and 85% encapsulation efficacy were achieved. In vitro cytotoxicity studies demonstrated that the cabazitaxel-loaded micelles show significant cytotoxicity against drug-resistant A2780/T cell lines. Biodistribution studies showed that the micelles can almost double the content of cargo in tumor sites compared with the free cargo. In vivo antitumor activity examinations indicated that cabazitaxel-loaded micelles show superior antitumor activity over free paclitaxel and free cabazitaxel. Electronic supplementary information (ESI) available: Synthetic procedures, tables and figures for the synthesized polymers. See DOI: 10.1039/c5nr02861b

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  7. Looped star polymers show conformational transition from spherical to flat toroidal shapes.

    PubMed

    Reiss, Pascal; Fritsche, Miriam; Heermann, Dieter W

    2011-11-01

    Inspired by the topological organization of the circular Escherichia coli chromosome, which is compacted by separate domains, we study a polymer architecture consisting of a central ring to which either looped or linear side chains are grafted. A shape change from a spherical to a toroidal organization takes place as soon as the inner ring becomes large enough for the attached arms to fit within its circumference. Building up a torus, the system flattens, depending on the effective bending rigidity of the chain induced by entropic repulsion of the attached loops and, to a lesser extent, linear arms. Our results suggest that the natural formation of a toroidal structure with a decreased amount of writhe induced by a specific underlying topology could be one driving force, among others, that nature exploits to ensure proper packaging of the genetic material within a rod-shaped, bacterial envelope. PMID:22181447

  8. 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)

    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

    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.

  9. Neutron Stars

    NASA Technical Reports Server (NTRS)

    Cottam, J.

    2007-01-01

    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.

  10. Improving hydrophilicity and protein resistance of poly(vinylidene fluoride) membranes by blending with amphiphilic hyperbranched-star polymer.

    PubMed

    Zhao, Yong-Hong; Zhu, Bao-Ku; Kong, Li; Xu, You-Yi

    2007-05-01

    To endow hydrophobic poly(vinylidene fluoride) (PVDF) membranes with reliable hydrophilicity and protein resistance, an amphiphilic hyperbranched-star polymer (HPE-g-MPEG) with about 12 hydrophilic arms in each molecule was synthesized by grafting methoxy poly(ethylene glycol) (MPEG) to the hyperbranched polyester (HPE) molecule using terephthaloyl chloride (TPC) as the coupling agent and blended with PVDF to fabricate porous membranes via phase inversion process. The chemical composition changes of the membrane surface were confirmed by X-ray photoelectron spectroscopy (XPS), and the membrane morphologies were measured by scanning electron microscopy (SEM). Water contact angle, static protein adsorption, and filtration experiments were used to evaluate the hydrophilicity and anti-fouling properties of the membranes. It was found that MPEG segments of HPE-g-MPEG enriched at the membrane surface substantially, while the water contact angle decreased as low as 49 degrees for the membrane with a HPE-g-MPEG/PVDF ratio of 3/10. More importantly, the water contact angle of the blend membrane changed little after being leached continuously in water at 60 degrees C for 30 days, indicating a quite stable presence of HPE-g-MPEG in the blend membranes. Furthermore, the blend membranes showed lower static protein adsorption, higher water and protein solution fluxes, and better water flux recovery after cleaning than the pure PVDF membrane. PMID:17408299

  11. DENSE GAS TRACERS AND STAR FORMATION LAWS IN ACTIVE GALAXIES: APEX SURVEY OF HCN J = 4 → 3, HCO{sup +} J = 4 → 3, AND CS J = 7 → 6

    SciTech Connect

    Zhang, Zhi-Yu; Gao, Yu; Zhao, Yinghe; Wang, Junzhi

    2014-04-01

    We report HCN J = 4 → 3, HCO{sup +} 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{sup +}, and four CS detections from the literature, we probe the empirical link between the luminosity of molecular gas (L{sub gas}{sup ′}) and that of infrared emission (L {sub IR}), up to the highest gas densities (∼10{sup 6} cm{sup –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{sub CS} {sub J=7--6}{sup ′}-L {sub IR} and L{sub HCN} {sub J=4--3}{sup ′}-L {sub IR}, and a slightly super-linear slope for L{sub HCO{sup +}} {sub J=4--3}{sup ′}-L {sub IR}. The correlation of L{sub CS} {sub J=7--6}{sup ′}-L {sub IR} even extends over eight orders of luminosity magnitude down to Galactic dense cores, with a fit of log(L {sub IR}) =1.00(± 0.01) ×log(L{sub CS} {sub J=7--6}{sup ′}) + 4.03(± 0.04). Such linear correlations appear to hold for all densities >10{sup 4} cm{sup –3}, and indicate that star formation rate is not related to the free-fall timescale for dense molecular gas.

  12. Understanding the thermosensitivity of POEGA-based star polymers: LCST-type transition in water vs. UCST-type transition in ethanol.

    PubMed

    Hou, Lei; Chen, Qijing; An, Zesheng; Wu, Peiyi

    2016-02-17

    The lower critical solution temperature (LCST) transition in water and the upper critical solution temperature (UCST) transition in ethanol of poly(oligo(ethylene glycol) acrylate) (POEGA)-based core cross-linked star (CCS) polymers have been investigated and compared by employing turbidity, dynamic light scattering (DLS), (1)H NMR and FTIR measurements. Macroscopic phase transitions in water and in ethanol were observed to occur when passing through the transition temperature, as revealed by DLS and turbidity measurements. Analysis by IR indicated that the interactions between the polymer chains and solvent molecules in water are stronger than those in ethanol such that the CCS polymer arm chains in water adopt more extended conformations. Moreover, hydrophobic interaction among the aliphatic groups plays a predominant role in the LCST-type transition in water whereas weak solvation of the polymer chains results in the UCST-type transition in ethanol. Additionally, the LCST-type transition in water was observed to be much more abrupt and complete than the UCST-type transition in ethanol, as suggested by (1)H NMR and IR at the molecular level. Finally, an abnormal "forced hydration" phenomenon was observed during the LCST transition upon heating. This study provides a detailed understanding of the subtle distinctions between the thermal transitions of CCS polymers in two commonly used solvents, which may be useful to guide future materials design for a wide range of applications. PMID:26822827

  13. 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

    Swinbank, A. M.; Smail, Ian; Papadopoulos, P. P.; Cox, P.; Krips, M.; Neri, R.; Ivison, R. J.; Thomson, A. P.; Richard, J.; Ebeling, H.

    2011-11-20

    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.

  14. 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)

    Tremblin, P.; Schneider, N.; Minier, V.; Didelon, P.; Hill, T.; Anderson, L. D.; Motte, F.; Zavagno, A.; Andr, 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

    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.

  15. Asymmetric AB3 Miktoarm Star Polymers: Synthesis, Self-Assembly, and Study of Micelle Stability Using AF4 for Efficient Drug Delivery.

    PubMed

    Moquin, Alexandre; Sharma, Anjali; Cui, Yiming; Lau, Anthony; Maysinger, Dusica; Kakkar, Ashok

    2015-12-01

    A simple and versatile methodology, which employs a combination of ring-opening polymerization and alkyne-azide click chemistry to synthesize amphiphilic AB3 miktoarm stars, is reported. Their aqueous self-assembly behavior was studied using dynamic light scattering, fluorescence, and asymmetrical flow field-flow fractionation (AF4 ). AB3 miktoarm stars form micelles which incorporate curcumin with high efficiency, and significantly reduce the viability of glioblastoma cells in spheroids. We demonstrate that AF4 is an effective technique to determine the size distribution of self-assembled structures exposed to a biological medium. The ease, with which asymmetric AB3 miktoarm polymers are constructed, provides a platform that can be widely employed to deliver a variety of lipophilic drugs. PMID:26259625

  16. ALMA OBSERVATIONS OF WARM DENSE GAS IN NGC 1614—BREAKING OF THE STAR FORMATION LAW IN THE CENTRAL KILOPARSEC

    SciTech Connect

    Xu, C. K.; Cao, C.; Lu, N.; Diaz-Santos, T.; Zhao, Y.-H.; Mazzarella, J. M.; Appleton, P.; Armus, L.; Murphy, E. J.; Gao, Y.; Herrero-Illana, R.; Privon, G.; Evans, A. S.; König, S.; Aalto, S.; Charmandaris, V.; Chu, J.; Haan, S.; Inami, H.; and others

    2015-01-20

    We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 μm dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1{sup ′′}=329 pc). The CO emission is well resolved by the ALMA beam (0.''26 × 0.''20) into a circumnuclear ring, with an integrated flux of f {sub CO(6-5)} = 898 (± 153) Jy km s{sup –1}, which is 63(± 12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pcstar formation regions with Σ{sub SFR} ∼ 100 M {sub ☉} yr{sup –1} kpc{sup –2} and Σ{sub Gas}∼10{sup 4} M{sub ⊙} pc{sup −2}. The non-detections of the nucleus in both the CO (6-5) line emission and the 435 μm continuum rule out, with relatively high confidence, a Compton-thick active galactic nucleus in NGC 1614. Comparisons with radio continuum emission show a strong deviation from an expected local correlation between Σ{sub Gas} and Σ{sub SFR}, indicating a breakdown of the Kennicutt-Schmidt law on the linear scale of ∼100 pc.

  17. 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

    Longino, B.L.; Kueper, B.H. . Dept. of Civil Engineering)

    1999-07-15

    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.

  18. Magnetic Phases in Dense Quark Matter

    SciTech Connect

    Incera, Vivian de la

    2007-10-26

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  20. Dual effective organic/inorganic hybrid star-shaped polymer coatings on ultrafiltration membrane for bio- and oil-fouling resistance.

    PubMed

    Kim, Dong-Gyun; Kang, Hyo; Han, Sungsoo; Lee, Jong-Chan

    2012-11-01

    Amphiphilic organic/inorganic hybrid star-shaped polymers (SPP) were prepared by atom transfer radical polymerization (ATRP) using poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 3-(3,5,7,9,11,13,15-heptacyclohexyl-pentacyclo[9.5.1.1,?.1?,?.1?,]-octasiloxane-1-yl)propyl methacrylate (MA-POSS) as monomers and octakis(2-bromo-2-methylpropionoxypropyldimethylsiloxy)-octasilsesquioxane (OBPS) as an initiator. Star-shaped polymers (SPM) having PEGMA and methyl methacrylate (MMA) moieties were also prepared for comparative purposes. Polysulfone (PSf) ultrafiltration membranes coated with the SPP showed higher bio- and oil-fouling resistance and flux-recovery ability than the bare PSf membrane. Moreover, the SPP-coated membranes exhibited better antifouling properties than the SPM-coated membrane when they were used for oil/water emulsion filtration. The dual effective antifouling properties of the SPP were ascribed to the simultaneous enrichment of hydrophilic PEG and hydrophobic POSS moieties on the membrane surfaces resulting in the decrease in interactions with proteins and the increase in repellence to oils. PMID:23054388

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  2. Dibaryons in neutron stars

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    SciTech Connect

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

    2014-01-21

    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.

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

    PubMed

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

    2014-01-21

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

  5. Probing Cold Dense Nuclear Matter

    SciTech Connect

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

    2008-06-01

    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.

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

    PubMed

    Wagner, Victoria E; Bryers, James D

    2003-07-01

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

  7. Uniformly dense polymeric foam body

    DOEpatents

    Whinnery, Jr., Leroy

    2003-07-15

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

  8. Are energy dense diets also nutrient dense?

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  9. Atoms in dense plasmas

    SciTech Connect

    More, R.M.

    1986-01-01

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

  10. Dense stellar cores in merger remnants

    NASA Technical Reports Server (NTRS)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    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.

  11. The Galactic Dense Gas Distribution and Properties

    NASA Astrophysics Data System (ADS)

    Glenn, Jason

    2015-08-01

    As the nearest spiral galaxy, the Milky Way provides a foundation for understanding galactic astrophysics. However, our position within the Galactic plane makes it challenging to decipher the detailed disk structure. The Galactic distribution of dense gas is relatively poorly known; thus, it is difficult to assess models of galaxy evolution by comparison to the Milky Way. Furthermore, fundamental aspects of star formation remain unknown, such as why the stellar and star cluster initial mass functions appear to be ubiquitous.Sub/millimeter dust continuum surveys, coupled with molecular gas surveys, are revealing the 3D distribution and properties of dense, star-forming gas throughout the disk. Here we report on the use of BGPS and Hi-GAL. BGPS is a 1.1 mm survey of the 1st Galactic quadrant and some lines of sight in the 2nd quadrant, totalling 200 deg2. We developed a technique using the Galactic rotation curve to derive distance probability density functions (DPDFs) to molecular cloud structures identified with continuum surveys. DPDFs combine vLSR measures from dense gas tracers and 13CO with distance discriminators, such as 8 μm extinction, HI self absorption, and (l, b, vLSR) associations with objects of known distances. Typical uncertainties are σdist ≤ 1 kpc for 1,710 BGPS objects with well-constrained distances.From DPDFs we derived the dense gas distribution and the dense gas mass function. We find evidence for dense gas in and between putative spiral arms. A log-normal distribution describes the mass function, which ranges from cores to clouds, but is primarily comprised of clumps. High-mass power laws do not fit the entire data set well, although power-law behavior emerges for sources nearer than 6.5 kpc (α = 2.0±0.1) and for objects between 2 kpc and 10 kpc (α = 1.9±0.1). The power law indices are generally between those of GMC and the stellar IMF. We have begun to apply this approach to the Hi-GAL (70 - 500 μm). With coverage of the entire plane and senstivity to detect dense molecular gas througout the entire disk, Hi-GAL enables a comprehensive dense gas map for comparison to galaxy formation and evolution models, other galaxies, and ISM models.

  12. Drug-loaded pseudo-block copolymer micelles with a multi-armed star polymer as the micellar exterior.

    PubMed

    Xie, Chen; Zhang, Peng; Zhang, Zhengkui; Yang, Chenchen; Zhang, Jialiang; Wu, Wei; Jiang, Xiqun

    2015-08-01

    Supramolecular constructed pseudo block copolymer micelles based on ?-cyclodextrin terminated 4 and 7 armed star poly(N-vinylpyrrolidone) and adamantane terminated linear poly(?-caprolactone) were prepared. The size, morphology, stability and protein adsorption were experimentally examined. The micelles with 7 armed PVP chains as the micellar exterior showed the lowest amount of protein adsorption and the best stability in media. When cabazitaxel, a new taxane, was loaded into the micelles, 14.4% drug loading content and 85% encapsulation efficacy were achieved. In vitro cytotoxicity studies demonstrated that the cabazitaxel-loaded micelles show significant cytotoxicity against drug-resistant A2780/T cell lines. Biodistribution studies showed that the micelles can almost double the content of cargo in tumor sites compared with the free cargo. In vivo antitumor activity examinations indicated that cabazitaxel-loaded micelles show superior antitumor activity over free paclitaxel and free cabazitaxel. PMID:26144838

  13. Quark stars : features and findings.

    SciTech Connect

    Jaikumar, P.; Physics

    2007-01-01

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

  14. The Dense Gas Fraction in Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Imara, Nia

    2016-01-01

    Stars form in the densest regions of molecular clouds, which are known to have varying levels of star formation activity. But the origin of the so-called dense-gas fraction - the amount of dense gas in a molecular cloud above a certain critical threshold - is unclear. In this study, we compare the dense gas fractions of two molecular clouds with very different rates of star formation: the Rosette and Maddalena. Using far-infrared Herschel observations, we find that ~4% of the molecular mass in the Rosette is contained in gas with extinction AV > 7.3 mag [N(H2) > 6.9 x 1021 cm-2], while Maddalena has only ~0.7% of its gas above this threshold. Although Maddalena is the more massive cloud, it has fewer young stellar objects (YSOs). In fact, the two clouds follow a power-law relationship described by Lada et al. (2010), in which the number of YSOs, N(YSO), increase as a function of mass above 7.3 mag, M0, according to N(YSO) ~ (M0)0.96.

  15. Quantum dense key distribution

    SciTech Connect

    Degiovanni, I.P.; Ruo Berchera, I.; Castelletto, S.; Rastello, M.L.; Bovino, F.A.; Colla, A.M.; Castagnoli, G.

    2004-03-01

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

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

    SciTech Connect

    Shinnaga, Hiroko; Phillips, Thomas G.; Furuya, Ray S.; Kitamura, Yoshimi E-mail: tgp@submm.caltech.ed E-mail: kitamura@isas.jaxa.j

    2009-12-01

    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.

  17. Polymersomes via Self-Assembly of Amphiphilic β-Cyclodextrin-Centered Triarm Star Polymers for Enhanced Oral Bioavailability of Water-Soluble Chemotherapeutics.

    PubMed

    Hu, Mengying; Shen, Yurun; Zhang, Lu; Qiu, Liyan

    2016-03-14

    To date, improving oral bioavailability of water-soluble drugs with poor membrane permeability is still challenging. An example of this includes doxorubicin hydrochloride (DOX·HCl), a widely used chemotherapeutic. We therefore developed a novel DOX·HCl-loaded polymersome (Ps-DOX·HCl) self-assembled by amphiphilic β-cyclodextrin-centered triarm star polymer (mPEG(2k)-PLA(3k))3-CD with the considerable drug loading capability. Using Madin-Darby canine kidney (MDCK) cells trans-well models, it was found that the cellular uptake and absorptive transport of DOX·HCl was significantly increased and the efflux was attenuated when delivered through polymersomes than free drugs. This phenomenon was further verified in mechanistic studies, which was attributed to the change in membrane transport pathway from paracellular route (free DOX·HCl) to active transcellular transport (drug-loaded polymersomes). Moreover, in vivo pharmacokinetic studies in mice demonstrated a significant increase in the oral bioavailability of Ps-DOX·HCl compared with free DOX·HCl (7.32-fold), as well as extended half-life (8.22-fold). This resulted in a substantial anticancer efficacy against mouse sarcoma 180 (S180) tumor in vivo. The cardiotoxicity, which is intrinsically induced by DOX·HCl, and toxicity toward gastrointestinal tissues were avoided according to histological studies. These findings indicate that (mPEG(2k)-PLA(3k))3-CD copolymer displays great potential as a vehicle for the effective oral delivery of water-soluble drugs with low permeability. PMID:26840277

  18. Planetary systems in star clusters

    NASA Astrophysics Data System (ADS)

    Cai, Maxwell Xu; Spurzem, Rainer; Kouwenhoven, M. B. N.

    2016-02-01

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

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

    PubMed

    Chen, Qijing; Deng, Xiaoyong; An, Zesheng

    2014-06-01

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

  20. Observational Studies of the Formation and Evolution of Dense Cores

    NASA Astrophysics Data System (ADS)

    Tafalla, Mario

    2015-08-01

    Dense cores are the simplest star-forming sites. They represent the end point of the fragmentation hierarchy that characterizes molecular clouds, and they likely control the efficiency of star formation via their relatively low numbers. Recent continuum observations of entire molecular clouds show that dense cores often lie along large-scale filamentary structures, suggesting that the cores form by some type of fragmentation process in a close-to-cylindrical geometry. To understand the exact formation mechanism of cores, additional kinematic information is needed, and this requires observations made using molecular-line tracers of both the dense cores and their surrounding cloud material. In this talk, I will present some of the most recent efforts to clarify the kinematic structure of core-forming regions, like those in the nearby Taurus molecular cloud. These observations show that the filamentary structures seen in clouds are often more complex than suggested by the maps of continuum emission, and that consist of multiple fiber-like components having different velocities and sonic internal motions. These components likely arise from turbulent fragmentation of the large scale flows that generate the filamentary structures. While not all these fiber-like components further fragment to form dense cores, a small group does so, likely by gravitational instability, and produces characteristic chain-like groups of dense cores that further evolve toward star formation.

  1. Chaotic Star Birth

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [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.

  2. 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

    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

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

  3. Infrared and Submilllimeter Studies of Dense Cores

    NASA Astrophysics Data System (ADS)

    Bourke, Tyler L.

    2014-07-01

    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.

  4. Introduction to neutron stars

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2015-02-01

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

  5. Introduction to neutron stars

    SciTech Connect

    Lattimer, James M.

    2015-02-24

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

  6. Dense molecular thermodynamics

    SciTech Connect

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

    1983-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

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

  8. Kaons in dense half-Skyrmion matter

    SciTech Connect

    Park, Byung-Yoon; Kim, Joon-Il; Rho, Mannque

    2010-03-15

    Dense hadronic matter at low temperatures is expected to be in a crystalline state and at high density to make a transition to a chirally restored but color-confined state, which is a novel phase hitherto unexplored. This phase transition is predicted in both skyrmion matter in four dimensions and instanton matter in five dimensions, the former in the form of half-skyrmions and the latter in the form of half-instantons or dyons. We predict that when K{sup -}'s are embedded in this half-skyrmion or half-instanton (dyonic) matter, which may be reached not far past the normal density, there arises an enhanced attraction from both the soft dilaton field figuring for the trace anomaly of QCD and the Wess-Zumino term. This attraction may have relevance for a possible strong binding of antikaons in dense nuclear matter and for kaon condensation in neutron-star matter. Such kaon property in the half-skyrmion phase is highly nonperturbative and may not be accessible by low-order chiral perturbation theory. Relevance of the half-skyrmion or dyonic matter to compact stars is discussed.

  9. DENSE MEDIUM CYCLONE OPTIMIZATON

    SciTech Connect

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

    2005-06-30

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

  10. Geometrical optics of dense aerosols: forming dense plasma slabs.

    PubMed

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

    2013-11-01

    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

  11. Dense Molecular Gas in Centaurus A

    NASA Astrophysics Data System (ADS)

    Wild, Wolfgang; Eckart, Andreas

    1999-10-01

    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.

  12. Cooling of neutron stars

    NASA Technical Reports Server (NTRS)

    Pethick, C. J.

    1992-01-01

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

  13. Geometrical Optics of Dense Aerosols

    SciTech Connect

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

    2013-04-24

    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. __________________________________________________

  14. Weakly dissipative solitons in dense relativistic-degenerate plasma

    NASA Astrophysics Data System (ADS)

    Ahmad, Saeed; Ata-ur-Rahman; Khan, S. A.

    2015-07-01

    We investigate the features of weakly nonlinear waves in a collisional dense plasma consisting of ultra-relativistic degenerate electrons and non-relativistic degenerate ions. In weak dissipation limit, the dynamics of low frequency nonlinear ion (solitary) wave is described by solving a damped Korteweg-deVries equation. The analytical and numerical analysis shows the existence of weakly dissipative solitons evolving with time. The characteristics of soliton evolution with plasma number density and slow ion-neutral collision rate are discussed with some detail. The relevance of the study with degenerate plasmas in ultra-dense astrophysical objects, particularly white dwarf stars is also pointed out.

  15. Young Stars in IC 2118

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Rebull, Luisa; Daou, Doris; Maranto, Tony; Roelofsen, Theresa; Sepulveda, Babs; Weehler, Cynthia

    2005-02-01

    IC 2118, the Witch Head Nebula (~210 parsecs), is region forming stars located near the supergiant star Rigel in the constellation Orion. Kun et al. (2004, A&A, 418, 89) have determined that IC 2118 is on the near side of the Orion-Eridanus Super Bubble and that stellar winds from the Orion OB1 association may be triggering new star formation in the nebula. We propose using IRAC and MIPS to reexamine a small dense region of this nebula where Kun et al. have spectroscopically identified three 2MASS sources as T Tauri stars embedded in the cloud. Previous all-sky surveys, including both IRAS and 2MASS, have included this region, but not to the resolution that Spitzer can provide, and there are few studies of this particular region in the literature. Our team proposes to use IRAC and MIPS observations to (1) investigate star formation, (2) look for likely cluster member stars with infrared excesses, and characterize this young star population by obtaining their colors and therefore estimates of masses and ages, (3) study the distribution of stars, their relationship to the ISM, and the possibilities of triggered star formation, (4) compare the young star population, distribution, and age to other similar sites of star formation, e.g., IC 1396 and (5) produce a dramatic image of the interstellar medium in the region surrounding IC 2118. Since this region is in the Orion constellation near the bright star Rigel, it provides additional appeal to students and the general public.

  16. Novel polymers and method of preparing same

    NASA Technical Reports Server (NTRS)

    Hirshfield, S. M. (Inventor)

    1973-01-01

    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.

  17. Transparent dense sodium

    SciTech Connect

    Ma, Y.; Eremets, M.; Oganov, A.R.; Xie, Y.; Trojan, I.; Medvedev, S.; Lyakhov, A.O.; Valle, M.; Prakapenka, V.

    2009-04-27

    Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behaviour. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals such as lithium and sodium, leading in turn to structurally complex phases and superconductivity with a high critical temperature. But the most intriguing prediction- that the seemingly simple metals Li and Na will transform under pressure into insulating states, owing to pairing of alkali atoms - has yet to be experimentally confirmed. Here we report experimental observations of a pressure-induced transformation of Na into an optically transparent phase at {approx}200 GPa (corresponding to {approx}5.0-fold compression). Experimental and computational data identify the new phase as a wide bandgap dielectric with a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to p-d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.

  18. Masers in star forming regions

    NASA Astrophysics Data System (ADS)

    Bartkiewicz, Anna; van Langevelde, Huib Jan

    2012-07-01

    Maser emission plays an important role as a tool in star formation studies. It is widely used for deriving kinematics, as well as the physical conditions of different structures, hidden in the dense environment very close to the young stars, for example associated with the onset of jets and outflows. We will summarize here the recent observational and theoretical progress on this topic since the last maser symposium: the IAU Symposium 242 in Alice Springs.

  19. Dynamical and Radiation Processes in Star and Planet Formation

    NASA Astrophysics Data System (ADS)

    Bally, J.

    Most stars are born in dense environments where radiation fields and dynamical interactions with sibling stars may profoundly influence the ultimate outcome of star formation. I review how radiation fields photo-evaporate cloud cores and circumstellar disks. I also comment on the role of gravitational interactions with sibling stars. These processes may be fundamental for determining the initial mass function of stars and pose hazards to planet formation.

  20. The physics of neutron stars.

    PubMed

    Lattimer, J M; Prakash, M

    2004-04-23

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

  1. Compactness of Neutron Stars.

    PubMed

    Chen, Wei-Chia; Piekarewicz, J

    2015-10-16

    Recent progress in the determination of both masses and radii of neutron stars is starting to place stringent constraints on the dense matter equation of state. In particular, new theoretical developments together with improved statistical tools seem to favor stellar radii that are significantly smaller than those predicted by models using purely nucleonic equations of state. Given that the underlying equation of state must also account for the observation of 2M⊙ neutron stars, theoretical approaches to the study of the dense matter equation of state are facing serious challenges. In response to this challenge, we compute the underlying equation of state associated with an assumed mass-radius template similar to the "common radius" assumption used in recent studies. Once such a mass-radius template is adopted, the equation of state follows directly from the implementation of Lindblom's algorithm; assumptions on the nature or composition of the dense stellar core are not required. By analyzing mass-radius profiles with a maximum mass consistent with observation and common radii in the 8-11 km range, a lower limit on the stellar radius of a 1.4M⊙ neutron star of RNS≳10.7  km is required to prevent the equation of state from violating causality. PMID:26550859

  2. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2008-12-30

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

  3. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2004-05-25

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

  4. Kaon condensation in dense stellar matter

    SciTech Connect

    Lee, Chang-Hwan; Rho, M. |

    1995-03-01

    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.

  5. Ammonia and HC7N Emission in Starless Dense Cores

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  6. Ammonia and HC7 N Emission in Dense Cores

    NASA Astrophysics Data System (ADS)

    Candelaria, Tierra; Schnee, Scott; Devine, Katie; NRAO Team; The College of Idaho Team

    2015-04-01

    Dense cores represent the transition between the turbulent, diffuse ISM and protostars. Thus, understanding dense cores' chemical and physical properties provides valuable information about the early stages of low mass star formation. We present an analysis of 13 starless dense cores in the Taurus Molecular Cloud using new data taken with the Green Bank Telescope. Our observations consist of ammonia (NH3) (1,1) and (2,2) and HC7 N (J =21-20) emission. We present new detections of HC7 N (a carbon chain bearing species) in four cores and confirm detection in two cores. We also present temperature and velocity gradient maps. These results are the foundation of a more complete survey and illustrate an important relationship between ammonia and the carbon chain bearing species HC7 N.

  7. Diffusion and Coulomb separation of ions in dense matter.

    PubMed

    Beznogov, M V; Yakovlev, D G

    2013-10-18

    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

  8. Nucleation of strange matter in dense stellar cores

    SciTech Connect

    Horvath, J.E. Sao Paulo, Sao Paulo ); Benvenuto, O.G. La Plata ); Vucetich, H. La Plata )

    1992-05-15

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

  9. Nonlinear nanostructures in dense quantum plasmas

    SciTech Connect

    Shukla, P. K.; Eliasson, B.

    2009-10-08

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

  10. ROSAT survey of emission from Be stars

    NASA Technical Reports Server (NTRS)

    Grady, Carol

    1993-01-01

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

  11. Communication: When does a branched polymer become a particle?

    NASA Astrophysics Data System (ADS)

    Chremos, Alexandros; Douglas, Jack F.

    2015-09-01

    Polymer melts with topologically distinct molecular structures, namely, linear chain, ring, and star polymers, are investigated by molecular dynamics simulation. In particular, we determine the mean polymer size and shape, and glass transition temperature for each molecular topology. Both in terms of structure and dynamics, unknotted ring polymers behave similarly to star polymers with f ≈ 5-6 star arms, close to a configurational transition point between anisotropic chains to spherically symmetric particle-like structures. These counter-intuitive findings raise fundamental questions regarding the importance of free chain-ends and chain topology in the packing and dynamics of polymeric materials.

  12. The early evolution of stars

    NASA Technical Reports Server (NTRS)

    Strom, Stephen E.

    1995-01-01

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

  13. Neutron Star Physics and EOS

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2016-02-01

    Neutron stars are important because measurement of their masses and radii will determine the dense matter equation of state. They will constrain the nuclear matter symmetry energy, which controls the neutron star matter pressure and the interior composition, and will influence the interpretation of nuclear experiments. Astrophysical observations include pulsar timing, X-ray bursts, quiescent low-mass X-ray binaries, pulse profiles from millisecond pulsars, neutrino observations from gravitational collapse supernovae,and gravitational radiation from compact object mergers. These observations will also constrain the neutron star interior, including the properties of superfluidity there, and determine the existence of a possible QCD phase transition.

  14. The Green Bank Telescope Maps the Dense Molecular Gas in the Starburst Galaxy M82

    NASA Astrophysics Data System (ADS)

    Kepley, Amanda A.; Leroy, A. K.; Frayer, D. T.; Usero, A.; Marvil, J.; Walter, F.

    2014-01-01

    In both the Milky Way and nearby galaxies, the presence of dense molecular gas is correlated with recent star formation, suggesting that the formation of this gas may represent a key regulating step in the star formation process. Testing this idea requires wide-area, high-resolution maps of dense molecular gas in galaxies to explore how local physical conditions drive dense gas formation. Until now, these observations have been limited by the faintness of dense gas tracers like HCN and HCO+, but new instruments like the 4mm receiver on Robert C. Byrd Green Bank Telescope (GBT) -- the largest single-dish millimeter telescope -- are poised to change this picture. We present GBT maps of the dense gas tracers HCN and HCO+ in the prototypical nearby starburst galaxy M82. The HCN and HCO+ in the disk of M82 correlates both with recent star formation and the diffuse molecular gas and shows kinematics consistent with a rotating torus. HCO+ emission is also associated with the outflow of molecular gas previously identified in CO. These observations mark the first time that dense molecular gas like HCO+ has been associated with an outflow in a nearby galaxy and suggests that the outflow of dense molecular gas from the center of galaxies like M82 may regulate the star formation globally. Finally, the CO-to-HCN and CO-to-HCO+ line ratios reveal that there is more dense gas at the center of M82, pointing to the starburst as a key driver of this relationship. These results establish that the GBT can efficiently map the dense molecular gas at 90 GHz in nearby galaxies; this capability will increase further with the 16-element feed array currently being built for the GBT.

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

    SciTech Connect

    Weber, F.; Glendenning, N.K.

    1992-11-02

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

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

    PubMed

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

    2014-06-01

    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 35C and 55C. Synthesized dendrimers were equally proficient in silica inhibition at 12h and maintains ?450ppm soluble silica. However, APAAm dendrimers of generation 0 confirmed better results (?300ppm) in contrast to APAAc dendrimers in silica inhibition at 55C. 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

  17. DENSE GAS DISPERSION MODEL (DEGADIS)

    EPA Science Inventory

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

  18. Dense molecular gas in starburst galaxies: Warmer than expected?

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

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

    SciTech Connect

    Weber, F.; Glendenning, N.K.

    1992-11-02

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

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

    SciTech Connect

    Shinnaga, Hiroko; Phillips, Thomas G.; Novak, Giles; Vaillancourt, John E.; Machida, Masahiro N.; Kataoka, Akimasa; Tomisaka, Kohji; Davidson, Jacqueline; Houde, Martin; Dowell, C. Darren; Leeuw, Lerothodi

    2012-05-10

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  2. Young Massive Star Clusters

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  3. Strange stars

    NASA Technical Reports Server (NTRS)

    Alcock, Charles; Farhi, Edward; Olinto, Angela

    1986-01-01

    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.

  4. Search for dense cores in the Musca filamentary cloud

    NASA Astrophysics Data System (ADS)

    Tachihara, Kengo; Yonekura, Yoshinori; Miyamoto, Izumi; Niwa, Takahiro; Oasa, Yumiko; Itoh, Yoichi; Takeda, Masao

    2008-04-01

    We propose to search for dense (n(H_2) 10^5 cm^{-3}) and compact cores embedded in C^{18}O cores that we identified in the last season. In this remarkably filamentary cloud, we will investigate the star-formation activities under the influence of magnetic field and turbulence through physical properties of the dense cores. In our previous statistical studies, cloud cores with smaller linewidth tend to be gravitationally bound and more evolved. The C^{18}O result shows it the Musca cloud has typically small linewidth, namely little turbulence, while star formation is not as active as for the Taurus and Chamaeleon I clouds. The complex velocity and morphological structures indicate that the cloud has been gravitationally fragmented into even denser cores. Optically thin high density tracers of H^{13}CO^{+} and N_{2}H^{+} lines will be used for the dense core census and their linewwidth estimation, while optically thick HCO^{+} line will reveal indications of gravitational collapse, if exist.

  5. Stars and Star Myths.

    ERIC Educational Resources Information Center

    Eason, Oliver

    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

  6. Stars and Star Myths.

    ERIC Educational Resources Information Center

    Eason, Oliver

    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…

  7. Be Stars

    NASA Astrophysics Data System (ADS)

    Peters, G.; Murdin, P.

    2000-11-01

    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...

  8. The origin of OB runaway stars.

    PubMed

    Fujii, Michiko S; Portegies Zwart, Simon

    2011-12-01

    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

  9. Neutron star matter in an effective model

    SciTech Connect

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

    2006-11-15

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

  10. Method for dense packing discovery.

    PubMed

    Kallus, Yoav; Elser, Veit; Gravel, Simon

    2010-11-01

    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 ϕ=128/219≈0.5845 and with a similar structure to the densest-known tetrahedron packing. PMID:21230619

  11. Metal-polymer composites comprising nanostructures and applications thereof

    DOEpatents

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

    2012-04-03

    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.

  12. Metal-polymer composites comprising nanostructures and applications thereof

    DOEpatents

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

    2011-08-02

    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.

  13. Fast pulsars, variational bound, other facets of compact stars

    SciTech Connect

    Glendenning, N.K.

    1991-05-01

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

  14. Microgravity Polymers

    NASA Technical Reports Server (NTRS)

    1986-01-01

    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.

  15. The chemistry of dense interstellar clouds

    NASA Technical Reports Server (NTRS)

    Irvine, W. M.

    1991-01-01

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

  16. Sleuthing the Isolated Compact Stars

    NASA Astrophysics Data System (ADS)

    Drake, J. J.

    2004-08-01

    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.

  17. Hybrid Stars and Coronal Evolution

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  18. Neutron StarsThermal Emitters

    NASA Astrophysics Data System (ADS)

    Potekhin, Alexander Y.; De Luca, Andrea; Pons, Jos A.

    2015-10-01

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

  19. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  20. Dense gas in high-latitude molecular clouds

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  1. Fusion reactions in multicomponent dense matter

    SciTech Connect

    Yakovlev, D. G.; Gasques, L. R.; Afanasjev, A. V.; Beard, M.; Wiescher, M.

    2006-09-15

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

  2. Boundary Preserving Dense Local Regions.

    PubMed

    Kim, Jaechul; Grauman, Kristen

    2015-05-01

    We propose a dense local region detector to extract features suitable for image matching and object recognition tasks. Whereas traditional local interest operators rely on repeatable structures that often cross object boundaries (e.g., corners, scale-space blobs), our sampling strategy is driven by segmentation, and thus preserves object boundaries and shape. At the same time, whereas existing region-based representations are sensitive to segmentation parameters and object deformations, our novel approach to robustly sample dense sites and determine their connectivity offers better repeatability. In extensive experiments, we find that the proposed region detector provides significantly better repeatability and localization accuracy for object matching compared to an array of existing feature detectors. In addition, we show our regions lead to excellent results on two benchmark tasks that require good feature matching: weakly supervised foreground discovery and nearest neighbor-based object recognition. PMID:26353319

  3. Dense, finely, grained composite materials

    DOEpatents

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

    1990-01-01

    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.

  4. Cyclodextrin Inclusion Polymers Forming Hydrogels

    NASA Astrophysics Data System (ADS)

    Li, Jun

    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.

  5. Interaction of fast magnetoacoustic solitons in dense plasmas

    NASA Astrophysics Data System (ADS)

    Jahangir, R.; Masood, W.; Siddiq, M.; Batool, Nazia; Saleem, Khalid

    2015-09-01

    One dimensional propagation of fast magnetoacoustic solitary waves in dense plasmas with degenerate electrons is investigated in this paper in the small amplitude limit. In this regard, Korteweg deVries equation is derived and discussed using the plasma parameters that are typically found in white dwarf stars. The interaction of fast magnetoacoustic solitons is explored by using the Hirota bilinear formalism, which admits multi soliton solutions. It is observed that the values of the propagation vectors determine the interaction of solitary waves. It is further noted that the amplitude of the respective solitary waves remain unchanged after the interaction; however, they do experience a phase shift.

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

    SciTech Connect

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

    2014-10-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    SciTech Connect

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

    2013-12-15

    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.

  9. Constructing Dense Graphs with Unique Hamiltonian Cycles

    ERIC Educational Resources Information Center

    Lynch, Mark A. M.

    2012-01-01

    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…

  10. Constructing Dense Graphs with Unique Hamiltonian Cycles

    ERIC Educational Resources Information Center

    Lynch, Mark A. M.

    2012-01-01

    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

  11. Massive star birth: A crossroads of Astrophysics

    NASA Astrophysics Data System (ADS)

    Cesaroni, R.; Felli, M.; Churchwell, E.; Walmsley, M.

    Massive stars, those with between 10 and 100 times the mass of the Sun, are among the rarest stars of all. They live fast and die young, but during their short lives produce the most dramatic effects on the surrounding interstellar medium in terms of dynamics, ionization, and chemical enrichment. Until a few decades ago massive star birth was literally shrouded in mystery, since these stars are born deep inside dense clouds of swirling dust and gas that obscures our view. At IAU S227, more than 200 of the world's leading astronomers presented a cornucopia of new results concerning the birth and infancy of massive stars. These proceedings show the achievements reached in this field, due to observations in the radio at mm and sub-mm wavelengths and in the infrared, and to theoretical models that simulate what happens in the cradle of a massive star.

  12. Polymers in Confined Geometry

    NASA Astrophysics Data System (ADS)

    Brochard-Wyart, Francoise

    2008-03-01

    Thanks to P. G. de Genne's famous ``n = 0'' theorem (relating the configuration of a polymer chain to a magnetic phase transition with an order parameter of n = 0 component), the swelling exponent ? (R=N^?a) was calculated in terms of space dimension d and fitted the qualitative Flory calculation. Using scaling laws, or the ``blob'' picture, it became possible to derive the conformation of a chain confined in a tube or a slit. The dynamics of confined polymers followed immediately. The new feature was the screening of the hydrodynamic interactions in confined geometry leading to Rouse-like behaviour. In a third step, de Gennes focused on the forced penetration of polymers (linear, branched, stars, neutral or charged) in narrow tubes, when they are submitted to a flow (or an electrical field for DNA). From all these calculations, the conclusion was that the threshold velocity (or field) corresponds to the penetration of the first blob. Afterwards, the friction force increases linearly with the penetrated length, whereas the confinement force remains constant. In the last few years, with his collaboration we studied the penetration of DNA in ``soft'' tubes. We predicted a transition from extended to globular DNA observed experimentally. We also showed that semi flexible polymer chains, like DNA, are ideal in 3d, but swollen effects are more pronounced in confined geometries. We will also discuss experiments inspired by his work on confined polymers, in the last thirty years.

  13. Constraining the Fraction of Dense Gas in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Mills, Elisabeth A.; Ginsburg, Adam; Barnes, Jonathan; Morris, Mark; Wiesenfeld, Laurent; Faure, Alexandre

    2016-01-01

    The central 500 parsecs of the Milky Way-- the Central Molecular Zone or CMZ-- is one of the most extreme environments for molecular gas in our Galaxy. Recent studies have suggested that the star formation relations in this region are anomalous, with less star formation per unit dense (n > 10^4 cm^-3) gas than is seen elsewhere in the universe. While this would be an exciting result indicating that star formation may proceed differently as a function of environment, it must be verified that it is not an effect of either undercounting the amount of star formation, or overestimating the bulk gas density in this region. CMZ gas densities in particular have not been revisited in several decades, and have only been measured accurately for a small handful of clouds in this region. We address this deficiency by presenting updated gas densities for a sample of 10 of the most massive molecular clouds in the CMZ. We use the Robert C. Byrd Green Bank Telescope, MOPRA, and APEX to measure lines of HC3N from J = 3-2 to J=30-29, and then perform radiative transfer analysis to constrain gas densities. We find that typical gas densities are somewhat lower than previously indicated, and present the first constraints on the fraction of gas with n >10^5 cm^-3 for multiple clouds in this region.

  14. Piezoelectric Polymers

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  15. A quest for super dense aluminium

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  16. Nuclear fusion in dense matter: Reaction rate and carbon burning

    SciTech Connect

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

    2005-08-01

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

  17. Discovery of dense absorbing clouds in Cygnus X-2

    NASA Astrophysics Data System (ADS)

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

    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.

  18. Temperature Relaxation in Dense Plasmas

    NASA Astrophysics Data System (ADS)

    Daughton, William

    2000-10-01

    For strongly coupled dense plasmas, where the potential energy exceeds the mean thermal energy, much of traditional plasma physics breaks down and a clear separation between atomic and plasma physics is no longer possible. In these difficult regimes, there are a variety of reasons to question the validity of Spitzer-type relaxation rates and transport coefficients. In particular, the problem of temperature relaxation between ions and electrons is of fundamental importance for these regimes. In this work, the energy exchange rate is calculated using a modified Ziman approach, a technique which has been used extensively to compute the electrical resistivity in liquid metals and dense plasmas. The necessary correlation functions and interaction potentials are computed using a simplified density functional theory. The theoretical description amounts to a self-consistent coupling between Thomas-Fermi-Dirac theory to describe the electrons and the hypernetted chain theory to describe strong ion correlations. Comparisons are made with the Spitzer coefficient over an interesting range of parameters.

  19. Conjugated polymers: Watching polymers dance

    NASA Astrophysics Data System (ADS)

    Rothberg, Lewis

    2011-06-01

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

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

    SciTech Connect

    Vutisalchavakul, Nalin; Evans, Neal J. II

    2013-03-10

    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.

  1. Dynamics and evolution of dense stellar systems

    NASA Astrophysics Data System (ADS)

    Fregeau, John M.

    2004-10-01

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

  2. Hypernuclei and the hyperon problem in neutron stars

    NASA Astrophysics Data System (ADS)

    Bedaque, Paulo F.; Steiner, Andrew W.

    2015-08-01

    The likely presence of Λ baryons in dense hadronic matter tends to soften the equation of state to an extent that the observed heaviest neutron stars are difficult to explain. We analyze this "hyperon problem" with a phenomenological approach. First, we review what can be learned about the interaction of Λ particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on nonstrange dense matter, including its uncertainties, to conclude that the interaction between Λ 's and dense matter has to become repulsive at densities below three times the nuclear saturation density.

  3. DYNAMICAL CAPTURE BINARY NEUTRON STAR MERGERS

    SciTech Connect

    East, William E.; Pretorius, Frans

    2012-11-20

    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.

  4. Star Mapper

    NASA Technical Reports Server (NTRS)

    1983-01-01

    A COSMIC (Computer Software Management and Information Center) program known as Skymap Star Catalog and Data Base provides a very accurate star map. The data assists Perkin Elmer Corporation in designing an optical system of proper size and field of view, and confirms the design integrity of star sensors which are very accurate and represent a major advance in optical technology. Perkin Elmer is the prime contractor for the optical telescope assembly of NASA's space telescope.

  5. Conformational properties of bottle-brush polymers

    NASA Astrophysics Data System (ADS)

    Denesyuk, N. A.

    2003-05-01

    General and renormalized perturbation theories are used to study the conformational properties of a bottle-brush molecule, composed of multiarmed polymer stars grafted regularly onto a flexible backbone. The end-to-end distances of the backbone and of an arm of the middle star are calculated within the first order of perturbation theory. For the high grafting densities of stars, the calculated expressions are generalized with the help of the scaling arguments to give the equivalent power laws. According to these laws, the molecule may adopt a sequence of three different conformations (star-rod-coil) as the length of the backbone grows.

  6. The chemistry of transient dense cores

    NASA Astrophysics Data System (ADS)

    Garrod, R. T.; Williams, D. A.; Hartquist, T. W.; Rawlings, J. M. C.; Viti, S.

    2005-01-01

    We investigate the chemistry of a transient density fluctuation, with properties similar to those of a dense core within a molecular cloud. We run a multipoint chemical code through a core's condensation from a diffuse medium to its eventual dispersion, over a period of ~1 Myr. We find a significant enhancement of the chemical composition of the core material on its return to diffuse conditions, whilst the expansion of the core as it disperses moves this material out to large distances from the core centre. This process transports molecular species formed in the high-density regions out into the diffuse medium. Chemical enrichment of the cloud as a whole also occurs, as other cores of various sizes, life-spans and separations evolve throughout. Enrichment is strongly affected by freeze-out on to dust grains, which takes place in high-density, high visual extinction regions. As the core disperses after reaching its peak density and the visual extinction drops below a critical value, grain mantles are evaporated back into the gas phase, initiating more chemistry. The influence of the sizes, masses and cycle periods of cores will be large both for the level of chemical enrichment of a dark cloud and ultimately for the low-mass star formation rate. We also consider the case of a self-gravitating core, by holding its peak density conditions for a further 0.4 Myr. We find that the differences are generally small, and the resultant column densities do not provide definitive criteria for detection of this condition. However, increases in fractional abundances due to reinjection of mantle-borne species may provide a criterion for a negative detection.

  7. The use of azide-alkyne click chemistry in recent syntheses and applications of polytriazole-based nanostructured polymers

    NASA Astrophysics Data System (ADS)

    Shi, Yi; Cao, Xiaosong; Gao, Haifeng

    2016-02-01

    The rapid development of efficient organic click coupling reactions has significantly facilitated the construction of synthetic polymers with sophisticated branched nanostructures. This Feature Article summarizes the recent progress in the application of efficient copper-catalyzed and copper-free azide-alkyne cycloaddition (CuAAC and CuFAAC) reactions in the syntheses of dendrimers, hyperbranched polymers, star polymers, graft polymers, molecular brushes, and cyclic graft polymers. Literature reports on the interesting properties and functions of these polytriazole-based nanostructured polymers are also discussed to illustrate their potential applications as self-healing polymers, adhesives, polymer catalysts, opto-electronic polymer materials and polymer carriers for drug and imaging molecules.

  8. Formation and structure of amorphous carbon char from polymer materials

    NASA Astrophysics Data System (ADS)

    Lawson, John W.; Srivastava, Deepak

    2008-04-01

    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.

  9. DPIS for warm dense matter

    SciTech Connect

    Kondo, K.; Kanesue, T.; Horioka, K.; Okamura, M.

    2010-05-23

    Warm Dense Matter (WDM) offers an challenging problem because WDM, which is beyond ideal plasma, is in a low temperature and high density state with partially degenerate electrons and coupled ions. WDM is a common state of matter in astrophysical objects such as cores of giant planets and white dwarfs. The WDM studies require large energy deposition into a small target volume in a shorter time than the hydrodynamical time and need uniformity across the full thickness of the target. Since moderate energy ion beams ({approx} 0.3 MeV/u) can be useful tool for WDM physics, we propose WDM generation using Direct Plasma Injection Scheme (DPIS). In the DPIS, laser ion source is connected to the Radio Frequency Quadrupole (RFQ) linear accelerator directly without the beam transport line. DPIS with a realistic final focus and a linear accelerator can produce WDM.

  10. Extended thermodynamics of dense gases

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  11. Ultra-dense nanowire arrays

    NASA Astrophysics Data System (ADS)

    Johnston-Halperin, Ezekiel; Green, J. E.; Wang, D. W.; Deionno, E.; Choi, J. W.; Luo, Y.; Boukai, A.; Bunimovich, Y.; Sheriff, B. A.; Heath, J. R.

    2006-03-01

    The development of the superlattice nanowire pattern transfer (SNAP) technique has allowed for the fabrication of highly ordered arrays of hundreds of nanowires (both metallic and semiconducting) at pitches down to 16 nm and aspect ratios up to 10^6. Applications of these nanowire arrays range from bridging length scales via binary-tree demultiplexing [1], to the development of ultra-dense arrays of molecular switch tunnel junctions ( 1 TBit/in^2), to the integration of complementary logic arrays within a crossbar architecture. In addition, at the narrowest pitches the periodicity of the SNAP array is only a few tens of atoms, allowing access to length scales compatible with coherent electronic transport and opening the door to fundamental studies. These topics will be discussed within the context of the flexibility of the SNAP fabrication technique and its wide applicability to a number of both basic and applied challenges in nanoscience/nanotechnology. [1] Science, 310, 465 (2005).

  12. Chandra Reveals Nest of Tight Binaries in Dense Cluster

    NASA Astrophysics Data System (ADS)

    2001-05-01

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

  13. Deterministic and unambiguous dense coding

    SciTech Connect

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

    2006-04-15

    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.

  14. Microwave Continuum Emission and Dense Gas Tracers in NGC 3627: Combining Jansky VLA and ALMA Observations

    NASA Astrophysics Data System (ADS)

    Murphy, Eric J.; Dong, Dillon; Leroy, Adam K.; Momjian, Emmanuel; Condon, James J.; Helou, George; Meier, David S.; Ott, Jrgen; Schinnerer, Eva; Turner, Jean L.

    2015-11-01

    We present Karl G. Jansky Very Large Array Ka band (33 GHz) and Atacama Large Millimeter Array (ALMA) Band 3 (94.5 GHz) continuum images covering the nucleus and two extranuclear star-forming regions within the nearby galaxy NGC 3627 (M 66), observed as part of the Star Formation in Radio Survey. Both images achieve an angular resolution of ?2?, allowing us to map radio spectral indices and estimate thermal radio fractions at a linear resolution of ?90 pc. The thermal fraction at 33 GHz reaches unity at and around the peaks of each H ii region; the spectral index between 33 and 94.5 GHz additionally becomes both increasingly negative and positive away from the H ii region peaks, indicating an increase of non-thermal emission from diffusing cosmic-ray electrons and the possible presence of cold dust, respectively. While the ALMA observations were optimized for collecting continuum data, they also detected line emission from the J=1\\to 0 transitions of HCN and HCO+. The peaks of dense molecular gas traced by these two spectral lines are spatially offset from the peaks of the continuum emission for both extranuclear star-forming regions, indicating that our data reach an angular resolution at which one can spatially distinguish sites of recent star formation from the sites of future star formation. Finally, we find trends of decreasing dense gas fraction and velocity dispersion with increasing star formation efficiency among the regions observed, indicating that the dynamical state of the dense gas, rather than its abundance, plays a more significant role in the star formation process.

  15. Water in dense molecular clouds

    NASA Technical Reports Server (NTRS)

    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

    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.

  16. Crystallization of dense neutron matter

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Chitre, S. M.

    1974-01-01

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

  17. The Proportion of Stars with Planets

    NASA Astrophysics Data System (ADS)

    Woolfson, M. M.

    2016-02-01

    Estimates of the proportion of Sun-like stars with accompanying planets vary widely; the best present estimate is that it is about 0.34. The capture theory of planet formation involves an interaction between a condensed star and either a diffuse protostar or a high-density region in a dense embedded cluster. The protostar, or dense region, is tidally stretched into a filament that is gravitationally unstable and breaks up into a string of protoplanetary blobs, which subsequently collapse to form planets, some of which are captured by the star. A computational model, in which the passage of collapsing protostars, with initial radii 1000, 1500 and 2000 au, through a dense embedded cluster are followed, is used to estimate the proportion of protostars that would be disrupted to give planets, in environments with star number-densities in the range 5000-25,000 pc-3. It is concluded from the results that the capture theory might explain the presently-estimated proportion of stars with exoplanet companions, although other possible ways of producing exoplanets are not excluded.

  18. The performance of dense medium processes

    SciTech Connect

    Horsfall, D.W.

    1993-12-31

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

  19. Low-mass star and planet formation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1989-01-01

    Low-mass star and planet formation is reviewed through a brief comparison of the results of cosmogonical models with observations ranging from studies of star-forming regions to searches for planetary companions to low-mass stars. Five key phases are described, starting from the dense, interstellar cloud cores that form low-mass stars, through the protostellar collapse and fragmentation phase, to the formation of a protostellar object accreting gas from the surrounding protostellar disk and cloud envelope. Descriptions are given for the phase where planets are formed in the protostellar disk, and the dissipation of the bulk of the protostellar disk and the appearance of an optically visible, premain-sequence star.

  20. Radio stars.

    PubMed

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars. PMID:17836594

  1. Star dust.

    PubMed

    Ney, E P

    1977-02-11

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

  2. Polymer adsorption

    NASA Astrophysics Data System (ADS)

    Joanny, Jean-Francois

    2008-03-01

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

  3. Star Images, Star Performances (College Course File).

    ERIC Educational Resources Information Center

    Butler, Jeremy G.

    1990-01-01

    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)

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  5. Dense molecular clumps associated with the Large Magellanic Cloud supergiant shells LMC 4 and LMC 5

    SciTech Connect

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

    2014-12-01

    We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. {sup 12}CO (J = 3-2, 1-0) and {sup 13}CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H{sub 2})) of the clumps are distributed from low to high density (10{sup 3}-10{sup 5} cm{sup 3}) and their kinetic temperatures (T {sub kin}) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of H?, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H{sub 2}) and T {sub kin}, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

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

    SciTech Connect

    Carroll, J. D.

    2011-10-24

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

  7. Coupled modes in magnetized dense plasma with relativistic-degenerate electrons

    SciTech Connect

    Khan, S. A.

    2012-01-15

    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.

  8. Infrared Two-Color Diagrams for AGB Stars, Post-AGB Stars, and Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Suh, Kyung-Won

    2015-08-01

    We present various infrared two-color diagrams (2CDs) for asymptotic giant branch (AGB) stars, post-AGB stars, and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use catalogs from the available literature for the sample of 4903 AGB stars (3373 O-rich; 1168 C-rich; 362 S-type), 660 post-AGB stars (326 post-AGB; 334 pre-PN), and 1510 PNe in our Galaxy. For each object in the catalog, we cross-identify the IRAS, AKARI, Midcourse Space Experiment, and 2MASS counterparts. The IR 2CDs can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. To find possible evolutionary tracks from AGB stars to PNe on the 2CDs, we investigate spectral evolution of post-AGB stars by making simple but reasonable assumptions on the evolution of the central star and dust shell. We perform radiative transfer model calculations for the detached dust shells around evolving central stars in the post-AGB phase. We find that the theoretical dust shell model tracks using dust opacity functions of amorphous silicate and amorphous carbon roughly coincide with the densely populated observed points of AGB stars, post-AGB stars, and PNe on various IR 2CDs. Even though some discrepancies are inevitable, the end points of the theoretical post-AGB model tracks generally converge in the region of the observed points of PNe on most 2CDs.

  9. Polymer Electrolytes

    NASA Astrophysics Data System (ADS)

    Hallinan, Daniel T.; Balsara, Nitash P.

    2013-07-01

    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.

  10. Polymer Chemistry

    NASA Technical Reports Server (NTRS)

    Williams, Martha; Roberson, Luke; Caraccio, Anne

    2010-01-01

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

  11. Ferroelectric polymers

    SciTech Connect

    Lovinger, A.J.

    1983-06-10

    Piezoelectricity and pyroelectricity, traditionally encountered in certain single crystals and ceramics, have now also been documented in a number of polymers. Recently, one such polymer - poly(vinylidene fluoride) - and some of its copolymers have been shown to be ferroelectric as well. The extraordinary molecular and supermolecular structural requirements for ferroelectric behavior in polymers are discussed in detail, with particular emphasis on poly(vinylidene fluoride). Piezoelectric, pyroelectric, and ferroelectric properties are also briefly reviewed, as are some promising applications of such polymers. 8 figures, 1 table.

  12. Thermal Spray Formation of Polymer Coatings

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  13. Aggregation in dense particulate systems

    NASA Astrophysics Data System (ADS)

    Fry, Dan James

    The aim of this work is to bridge the gap between two extreme limits of aggregating systems: the dilute limit and percolation. We present a broad description of aggregation for particulate systems that start out in a dilute state and, because of their fractal nature, evolve to a dense state. This work is a simulation study that uses an off lattice monte carlo algorithm to model the cluster-cluster aggregation process. We have studied the aggregation kinetics, aggregate structure, and aggregate shape as the system evolves for diffusion-limited, ballistic-limited, and reaction-limited aggregation classes. These results are complemented by simulations of site percolation, the Hierarchial model, and particle-cluster aggregation. Irreversible aggregation kinetics at early times when dilute are in agreement with the mean-field Smoluchowski equation. Since the aggregates are fractal in structure, they increasingly occupy the physical volume and the system becomes increasingly dense. This crowding between aggregates modifies the aggregation kernel functionality by modifying the kernel homogeneity constant. Remarkably, this new and evolving kernel homogeneity, folds back into the mean-field Smoluchowski equation, retaining the meanfield description despite the crowding. At low occupied cluster volume fraction, aggregate shape is self-preserving, with one characteristic axis approximately three times longer than the other two in three dimensions (3d). Once the system has evolved to an occupied cluster volume fraction roughly equal to the site percolation threshold, two things happen. First, a new aggregate structure develops, marked by a crossover length scale. Aggregates retain their dilute-limit structure across length scales less than the crossover length. However, at larger length scales, the aggregates resemble the backbone structure of site percolation. Second, aggregate shape anisotropy begins to decrease, until at the gel point it reaches a value consistent with site percolation clusters. Monte carlo results of aggregation with random bond fragmentation are in agreement with the mean-field predictions for liquid drops. However, because random bond breaking can happen over any length scale of the cluster, we find that the structural crossover length is washed out.

  14. Percolation in dense storage arrays

    NASA Astrophysics Data System (ADS)

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

    2002-11-01

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

  15. Filter-Dense Multicolor Microscopy.

    PubMed

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

    2015-01-01

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

  16. Polymers & People

    ERIC Educational Resources Information Center

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

    2004-01-01

    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

  17. Polymers & People

    ERIC Educational Resources Information Center

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

    2004-01-01

    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…

  18. Polymers All Around You!

    ERIC Educational Resources Information Center

    Gertz, Susan

    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

  19. Star Cluster Buzzing With Pulsars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    A dense globular star cluster near the center of our Milky Way Galaxy holds a buzzing beehive of rapidly-spinning millisecond pulsars, according to astronomers who discovered 21 new pulsars in the cluster using the National Science Foundation's 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. The cluster, called Terzan 5, now holds the record for pulsars, with 24, including three known before the GBT observations. Pulsar Diagram Pulsar Diagram: Click on image for more detail. "We hit the jackpot when we looked at this cluster," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, VA. "Not only does this cluster have a lot of pulsars -- and we still expect to find more in it -- but the pulsars in it are very interesting. They include at least 13 in binary systems, two of which are eclipsing, and the four fastest-rotating pulsars known in any globular cluster, with the fastest two rotating nearly 600 times per second, roughly as fast as a household blender," Ransom added. Ransom and his colleagues reported their findings to the American Astronomical Society's meeting in San Diego, CA, and in the online journal Science Express. The star cluster's numerous pulsars are expected to yield a bonanza of new information about not only the pulsars themselves, but also about the dense stellar environment in which they reside and probably even about nuclear physics, according to the scientists. For example, preliminary measurements indicate that two of the pulsars are more massive than some theoretical models would allow. "All these exotic pulsars will keep us busy for years to come," said Jason Hessels, a Ph.D student at McGill University in Montreal. Globular clusters are dense agglomerations of up to millions of stars, all of which formed at about the same time. Pulsars are spinning, superdense neutron stars that whirl "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is left after a massive star explodes as a supernova at the end of its life. The pulsars in Terzan 5 are the product of a complex history. The stars in the cluster formed about 10 billion years ago, the astronomers say. Some of the most massive stars in the cluster exploded and left the neutron stars as their remnants after only a few million years. Normally, these neutron stars would no longer be seen as swiftly-rotating pulsars: their spin would have slowed because of the "drag" of their intense magnetic fields until the "lighthouse" effect is no longer observable. The Green Bank Telescope The Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF (Click on image for GBT gallery) However, the dense concentration of stars in the cluster gave new life to the pulsars. In the core of a globular cluster, as many as a million stars may be packed into a volume that would fit easily between the Sun and our nearest neighbor star. In such close quarters, stars can pass near enough to form new binary pairs, split apart such pairs, and binary systems even can trade partners, like an elaborate cosmic square dance. When a neutron star pairs up with a "normal" companion star, its strong gravitational pull can draw material off the companion onto the neutron star. This also transfers some of the companion's spin, or angular momentum, to the neutron star, thereby "recycling" the neutron star into a rapidly-rotating millisecond pulsar. In Terzan 5, all the pulsars discovered are rotating rapidly as a result of this process. Astronomers previously had discovered three pulsars in Terzan 5, some 28,000 light-years distant in the constellation Sagittarius, but suspected there were more. On July 17, 2004, Ransom and his colleagues used the GBT, and, in a 6-hour observation, found 14 new pulsars, the most ever found in a single observation. "This was possible because of the great sensitivity of the GBT and the new capabilities of our backend processor," said Ingrid Stairs, a professor at the University of British Columbia in Vancouver. The processor, named, appropriately, the Pulsar Spigot, was built in a collaboration between the NRAO and the California Institute of Technology. The processor, which generates almost 100 GigaBytes of data per hour, allowed the astronomers to gather and analyze radio waves over a wide range of frequencies (1650-2250 MegaHertz), adding to the sensitivity of their system. Eight more observations between July and November of 2004 discovered seven additional pulsars in Terzan 5. In addition, the astronomers' data show evidence for several more pulsars that still need to be confirmed. Future studies of the pulsars in Terzan 5 will help scientists understand the nature of the cluster and the complex interactions of the stars at its dense core. Also, several of the pulsars offer a rich yield of new scientific information. The scientists suspect that one pulsar, which shows strange eclipses of its radio emission, has recently traded its original binary companion for another, and two others have white-dwarf companions that they believe may have been produced by the collision of a neutron star and a red-giant star. Subtle effects seen in these two systems can be explained by Einstein's general relativistic theory of gravity, and indicate that the neutron stars are more massive than some theories allow. The material in a neutron star is as dense as that in an atomic nucleus, so that fact has implications for nuclear physics as well as astrophysics. "Finding all these pulsars has been extremely exciting, but the excitement really has just begun," Ransom said. "Now we can start to use them as a rich and valuable cosmic laboratory," he added. In addition to Ransom, Hessels and Stairs, the research team included Paulo Freire of Arecibo Observatory in Puerto Rico, Fernando Camilo of Columbia University, Victoria Kaspi of McGill University, and David Kaplan of the Massachusetts Institute of Technology. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The pulsar research also was supported by the Canada Foundation for Innovation, Science and Engineering Research Canada, the Quebec Foundation for Research on Nature and Technology, the Canadian Institute for Advanced Research, Canada Research Chairs Program, and the National Science Foundation.

  20. Gravothermal Star Clusters - Theory and Computer Modelling

    NASA Astrophysics Data System (ADS)

    Spurzem, Rainer

    2010-11-01

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

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

    SciTech Connect

    Kujawski, W.; Waczynski, M.; Lasota, M.

    1996-04-01

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

  2. Photometric detection of high proper motions in dense stellar fields using difference image analysis

    NASA Astrophysics Data System (ADS)

    Eyer, L.; Wo?niak, P. R.

    2001-10-01

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

  3. Neutrino Processes in Neutron Stars

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  4. Gel trapping of dense colloids.

    PubMed

    Laxton, Peter B; Berg, John C

    2005-05-01

    Phase density differences in sols, foams, or emulsions often lead to sedimentation or creaming, causing problems for materials where spatial uniformity over extended periods of time is essential. The problem may be addressed through the use of rheology modifiers in the continuous phase. Weak polymer gels have found use for this purpose in the food industry where they appear to be capable of trapping dispersoid particles in a three-dimensional matrix while displaying water-like viscosities at low shear. Attempts to predict sedimentation stability in terms of particle properties (size, shape, density difference) and gel yield stress have led to qualitative success for suspensions of large particles. The effect of particle size, however, in particular the case in which colloidal dimensions are approached, has not been investigated. The present work seeks to determine useful stability criteria for colloidal dispersions in terms of readily accessible viscoelastic descriptors. Results are reported for systems consisting of 12 microm poly(methyl methacrylate) (PMMA) spheres dispersed in aqueous gellan gum. Monovalent salt concentration is varied to control rheological properties, and sedimentation/centrifugation experiments are performed to determine dispersion stability. Necessary conditions for stability consist of a minimum yield stress together with a value of tan delta less than unity. PMID:15797408

  5. Star Formation in IC 348

    NASA Astrophysics Data System (ADS)

    Herbst, W.

    2008-12-01

    A review of work on the small, compact, nearby young cluster IC 348 is given. This region is particularly important because it is well surveyed at a variety of wavelengths and intermediate in nature between dense clusters and loose associations. Its earliest type star is B5 and it contains a few hundred stellar members as well as some brown dwarfs, protostars, Herbig-Haro objects and starless sub-mm cores. The total mass of its components is 90 M_?, most of which is in the form of pre-main sequence stars. Perhaps the biggest challenge to work on the cluster is the relatively high and variable extinction (A_v=3D1-7 mag). Studies to date have provided particularly valuable insights into the initial mass function, disk lifetimes, stellar rotation properties, X-ray properties, outflows and substructure of the cluster. Results on the stellar component include the following: 1) the initial mass function matches that for field stars in the stellar and brown dwarf regimes, 2) the fraction of stars with disks is probably normal for the cluster's age, 3) the rotation properties match those of the Orion Nebula Cluster and are significantly different, in the sense of slower rotation, than NGC 2264, 4) the X-ray properties of the stars appear normal for T Tauri stars. There is a ridge of high extinction that lies 10 arcmin (0.9 pc in projection) to the southwest of IC 348 and contains about a dozen Class 0 and I protostars as well as some Herbig Haro objects and sub-mm cores. This region, which also contains the "Flying Ghost Nebula" and the well-studied object HH 211, clearly signals that star formation in this part of the Perseus dark clouds is not yet finished. An extensive kinematical study involving both proper motions and radial velocities for the 400 members of the cluster would be most desirable.

  6. ON THE FORMATION OF GLYCOLALDEHYDE IN DENSE MOLECULAR CORES

    SciTech Connect

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

    2012-05-01

    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 CH{sub 3}OH + 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, H{sub 3}CO + HCO.

  7. Nearby regions of massive star formation

    NASA Astrophysics Data System (ADS)

    Bally, John; Cunningham, Nathaniel; Moeckel, Nickolas; Smith, Nathan

    Observations of the nearest regions of massive star formation such as Orion are reviewed. Early-type stars in the local OB associations, as well as their superbubbles and supershells provide a fossil record of massive star birth in the Solar vicinity over about the last 40 Myr. This record shows that most massive stars are born from dense, high-pressure, hot cores which spawn transient clusters that dissipate into the field soon after formation. A large fraction (15 to 30%) of massive stars are high-velocity runaways moving at more than 20 km s^{-1}. High-mass stars have a larger companion fraction than their lower-mass siblings. The Orion star forming complex contains the nearest site of on-going massive star formation. Studies of the Orion Nebula and the dense molecular cloud core located immediately behind the HII region provide our sharpest view of massive star birth. This region has formed a hierarchy of clusters within clusters. The Trapezium, OMC-1S, and OMC-1 regions represent three closely spaced sub-clusters within the more extended Orion Nebula Cluster. The oldest of these sub-clusters, which consists of the Trapezium stars, has completely emerged from its natal core. The OMC-1S and OMC-1 regions, are still highly embedded and forming clusters of additional moderate and high mass stars. Over a dozen YSOs embedded in OMC-1S are driving jets and outflows, many of which are injecting energy and momentum into the Orion Nebula. Recent proper motion measurements indicate that the Becklin-Neugebauer object is a high-velocity star moving away from the OMC1 core with a velocity of 30 km s^{-1}, making it the youngest high-velocity star known. Source I may be moving in the opposite direction with a velocity of about 12 km s^{-1}. The projected separation between source I and BN was less than few hundred AU about 500 years ago. The spectacular bipolar molecular outflow and system of shock-excited H_2 fingers emerging from OMC-1 has a dynamical age of about 1100 years. It is possible that a dynamical i nteraction between three or more stars in OMC-1 led to the formation of this eruptive outflow.

  8. Three body dynamics in dense gravitational systems

    NASA Astrophysics Data System (ADS)

    Moody, Kenneth

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

  9. Galaxy Evolution Explorer Spies Band of Stars

    NASA Technical Reports Server (NTRS)

    2007-01-01

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

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

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

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

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

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

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

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

  10. Polymer nanolithography

    NASA Astrophysics Data System (ADS)

    Vance, Jennifer M.

    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.

  11. Atomic Transitions in Dense Plasmas

    NASA Astrophysics Data System (ADS)

    Murillo, Michael Sean

    Motivation for the study of hot, dense ( ~solid density) plasmas has historically been in connection with stellar interiors. In recent years, however, there has been a growing interest in such plasmas due to their relevance to short wavelength (EUV and x-ray) lasers, inertial confinement fusion, and optical harmonic generation. In constrast to the stellar plasmas, these laboratory plasmas are typically composed of high-z elements and are not in thermal equilibrium. Descriptions of nonthermal plasma experiments must necessarily involve the consideration of the various atomic processes and the rates at which they occur. Traditionally, the rates of collisional atomic processes are calculated by considering a binary collision picture. For example, a single electron may be taken to collisionally excite an ion. A cross section may be defined for this process and, multiplying by a flux, the rate may be obtained. In a high density plasma this binary picture clearly breaks down as the electrons no longer act independently of each other. The cross section is ill-defined in this regime and another approach is needed to obtain rates. In this thesis an approach based on computing rates without recourse to a cross section is presented. In this approach, binary collisions are replaced by stochastic density fluctuations. It is then these density fluctuations which drive transitions in the ions. Furthermore, the oscillator strengths for the transitions are computed in screened Coulomb potentials which reflect the average polarization of the plasma near the ion. Numerical computations are presented for the collisional ionization rate. The effects of screening in the plasma -ion interaction are investigated for He^+ ions in a plasma near solid density. It is shown that dynamic screening plays an important role in this process. Then, density effects in the oscillator strength are explored for both He^+ and Ar^{+17}. Approximations which introduce a nonorthogonality between the initial and final states is shown to introduce a nonnegligible error. Changes in the bound state energy levels are included in the calculation as well and are shown to dramatically increase the ionization rate over the low density result. Finally, a calculation is presented in which the final state wavefunctions are found exactly within a (density-dependent) screened Coulomb potential.

  12. Star formation and extinct radioactivities

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.

    1984-01-01

    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.

  13. Organic molecules in the gas phase of dense interstellar clouds

    NASA Technical Reports Server (NTRS)

    Irvine, W. M.

    1995-01-01

    Since a previous Committee on Space Research (COSPAR) review on this subject, the number of molecular species identified by astronomers in dense interstellar clouds or in the envelopes expelled by evolved stars has grown from about eighty to approximately one hundred. Recent detections in stellar envelopes include the radical CP, the second phosphorus-containing astronomical molecule; SiN, the first astronomical molecule with a Si-N bond; and the HCCN radical. In the dense interstellar clouds recent detections or verifications of previous possible identifications include the H3O(+) ion, which is a critical intermediary in the production of H2O and O2; the CCO radical, which is isoelectronic with HCCN; the SO(+) ion, which appears to be diagnostic of shock chemistry; two new isomers of cyanoacetylene, HCCNC and CCCNH; and the two cumulenes H2C3 and H2C4. Some recent work is also described on the mapping of interstellar clouds in multiple molecular transitions in order to separate variations in chemical abundance from gradients in physical parameters.

  14. ENHANCED DENSE GAS FRACTION IN ULTRALUMINOUS INFRARED GALAXIES

    SciTech Connect

    Juneau, S.; Shirley, Y. L.; Bussmann, R. S.; Narayanan, D. T.; Moustakas, J.; Kennicutt, R. C.; Vanden Bout, P. A. E-mail: yshirley@as.arizona.ed E-mail: dnarayanan@cfa.harvard.ed E-mail: robk@ast.cam.ac.u

    2009-12-20

    We present a detailed analysis of the relation between infrared luminosity and molecular line luminosity, for a variety of molecular transitions, using a sample of 34 nearby galaxies spanning a broad range of infrared luminosities (10{sup 10} L{sub sun} < L{sub IR} < 10{sup 12.5} L{sub sun}). We show that the power-law index of the relation is sensitive to the critical density of the molecular gas tracer used, and that the dominant driver in observed molecular line ratios in galaxies is the gas density. As most nearby ultraluminous infrared galaxies (ULIRGs) exhibit strong signatures of active galactic nuclei (AGNs) in their center, we revisit previous claims questioning the reliability of HCN as a probe of the dense gas responsible for star formation in the presence of AGNs. We find that the enhanced HCN(1-0)/CO(1-0) luminosity ratio observed in ULIRGs can be successfully reproduced using numerical models with fixed chemical abundances and without AGN-induced chemistry effects. We extend this analysis to a total of 10 molecular line ratios by combining the following transitions: CO(1-0), HCO{sup +}(1-0), HCO{sup +}(3-2), HCN(1-0), and HCN(3-2). Our results suggest that AGNs reside in systems with higher dense gas fraction, and that chemistry or other effects associated with their hard radiation field may not dominate (NGC 1068 is one exception). Galaxy merger could be the underlying cause of increased dense gas fraction, and the evolutionary stage of such mergers may be another determinant of the HCN/CO luminosity ratio.

  15. The JCMT Gould Belt Survey: A First Look at Dense Cores in Orion B

    NASA Astrophysics Data System (ADS)

    Kirk, H.; Di Francesco, J.; Johnstone, D.; Duarte-Cabral, A.; Sadavoy, S.; Hatchell, J.; Mottram, J. C.; Buckle, J.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Jenness, T.; Nutter, D.; Pattle, K.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Hogerheijde, M. R.; Ward-Thompson, D.; Bastien, P.; Bresnahan, D.; Butner, H.; Chen, M.; Chrysostomou, A.; Coude, S.; Davis, C. J.; Drabek-Maunder, E.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Kirk, J. M.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Mowat, C.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

    2016-02-01

    We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 μm map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 μm peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found in previous dense core analyses, with a Salpeter-like slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1–2 × 1023 cm‑2, most of the mass is found within dense cores, while at lower cloud column densities, below 1 × 1023 cm‑2, this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (<8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.

  16. Theory of spots on chemically peculiar stars

    NASA Astrophysics Data System (ADS)

    Shulyak, D.

    2014-09-01

    Surface inhomogeneities are found in many stars. In active sun-like stars and cool giants temperature spots similar to that found in the Sun are recovered from the inversion of spectroscopic data. M-dwarfs also show highly inhomogeneous surface structures in polarized light and photometric variability that are believed to be connected with cool regions on their surface, too. Supergiants have highly inhomogeneous atmospheres because large convective cells, and therefore bright and dark regions, have sizes comparable to the size of stars themselves. Hot luminous stars can have dense clamps in their atmospheres caused by an interaction of fast stellar wind, rotation, and the magnetic fields. Finally, a special class of main-sequence B-F stars, called chemically peculiar stars, have spots of abundance origin. Spots in these stars can look bright or dark depending on wavelength of observation. Modern interferometry is capable of reaching a very high angular resolution that will make it possible to study starspots in very detail. In this review we will focus on starspots in general and abundance spots in chemically peculiar stars in particular, as well as possible application of interferometry to study them.

  17. Hunting for Shooting Stars in 30 Doradus

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  18. Gravitational Condensate Stars

    NASA Astrophysics Data System (ADS)

    Mazur, P.; Mottola, E.

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

  19. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Lige (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99-2 in the LMC. PR Photo 09c/03: Nebula near the hot binary star BAT99-49 in the LMC. PR Photo 09d/03: The N44C Nebula in the LMC. Four unique images of highly excited nebulae in the Magellanic Clouds ESO PR Photo 09a/03 ESO PR Photo 09a/03 [Preview - JPEG: 400 x 472 pix - 74k [Normal - JPEG: 800 x 943 pix - 720k] [Full-Res - JPEG: 1200 x 1414 pix - 1.2M] ESO PR Photo 09b/03 ESO PR Photo 09b/03 [Preview - JPEG: 400 x 466 pix - 70k [Normal - JPEG: 800 x 931 pix - 928k] [Full-Res - JPEG: 1200 x 1397 pix - 1.8M] ESO PR Photo 09c/03 ESO PR Photo 09c/03 [Preview - JPEG: 400 x 469 pix - 74k [Normal - JPEG: 800 x 937 pix - 1.1M] [Full-Res - JPEG: 1200 x 1405 pix - 2.2M] ESO PR Photo 09d/03 ESO PR Photo 09d/03 [Preview - JPEG: 400 x 473 pix - 28k [Normal - JPEG: 800 x 945 pix - 368k] [Full-Res - JPEG: 1200 x 1418 pix - 600k] Captions: PR Photo 09a/03 is a reproduction of a "near-true" three-colour composite image of the highly excited nebula around the hot double star AB7 in the Small Magellanic Cloud (SMC), obtained in January 2002 with the FORS1 multi-mode instrument at the 8.2-m VLT MELIPAL telescope at the Paranal Observatory (Chile). It is based on three exposures through narrow-band optical (interference) filters that isolate the light from specific atoms and ions. In this rendering, the blue colour represents the light from singly ionized Helium (He II; wavelength 468.6 nm; exposure time 30 min), green corresponds to doubly ionized oxygen ([O III]; 495.7 + 500.7 nm; 5 min) and red to hydrogen atoms (H; H-alpha line at 656.2 nm; 5 min). Of these three ions, He II is the tracer of high excitation, i.e. the bluest areas of the nebula are the hottest. The sky field measures 400 x 400 arcsec2; the original pixel size on the 2k x 2k CCD is 0.23 arcsec. North is up and east to the left. Before combination, the CCD frames were flat-fielded and cleaned of cosmic-rays. Moreover, the stars in the blue (He II) image were removed in order to provide a clearer view of the surrounding nebular emission. The reproduced brightness is proportional to the square-root of the actual intensity; this increases the "dynamical range" of the image, i.e. it shows better areas of very different brightness. PR Photo 09b/03 is a similar reproduction of the sky area with the nebula near the Wolf-Rayet (WR) star BAT99-2 in the LMC. The filters are the same, but the exposure times were 60, 5 and 5 min for the blue, green and red exposures, respectively. PR Photo 09c/03 shows, in the same way, the nebula around the hot double star BAT99-49 in the LMC. The filters are the same, but the exposure times were 45, 5 and 5 min for the blue, green and red exposures, respectively. Finally, PR Photo 09d/03 shows the N44C nebula in the LMC, photographed through the same optical filters with exposure times of 20, 5 and 5 min for the blue, green and red exposures, respectively. The sky field measures 208 x 208 arcsec2. The above collection of impressive VLT colour photos is unique. They show some of the highest excitation nebulae in the Magellanic Clouds (MCs), two satellite galaxies of our own Milky Way. They may be enjoyed for their beauty alone. However, each of them also carries a message about the depicted objects, their properties and evolutionary state. In fact, they represent the spectacular and visible result of a dedicated research programme begun by an international team of astronomers from Belgium and the United States of America [1], and aimed at unravelling the secrets of unsually hot nebulae. What makes them shine? From where come the enormous energies needed to make these nebulae glow in the light of ionized helium atoms? Emission nebulae Nebulae are huge clouds of gas and dust, the cosmic material from which stars and planets form, cf. the Appendix. Many of them emit their own light, and are then called emission nebulae. Astronomers distinguish between Planetary Nebulae (PNe), Supernova Remnants (SNRs) and "normal" emission nebulae or "HII regions" (pronounced "Eitch-two"). PNe result from the death of comparatively light stars, similar to our Sun, while SNRs originate from the explosive death of heavier stars. The collision between the surrounding interstellar matter and that ejected by the dying star, accompanied by the intense radiation from the hot stellar remnant (white dwarf, neutron star) excites the gas and makes it shine brightly. But the radiation of young hot stars embedded in an interstellar cloud is also able to heat the surrounding gas, resulting in the apparition of another type of emission nebula, that shines mostly in the light of ionized hydrogen (H) atoms. Such nebulae are therefore often referred to as "HII regions". The well-known Orion Nebula is an outstanding example of that type of nebula, cf. ESO PR Photos 03a-c/01. Highly excited nebulae The hotter the central object of an emission nebula, whether a white dwarf, a neutron star or just a young star, the hotter and more excited will be the surrounding nebula. The word "excitation" refers to the degree of ionization of the nebular gas. The more energetic the impinging particles and radiation, the more electrons will be lost and higher is the degree of excitation. Only in the most excited nebulae is there enough ultraviolet energy to completely ionize the helium atoms. When these ions subsequently capture an electron, this process gives rise to the characteristic radiation of single ionized helium (HeII). A particularly useful way to trace the very highest excitation areas is thus to map the distribution of HeII by means of imaging or spectroscopic observations that are sensitive to the radiation from these helium ions, for example at a particular wavelength in blue light (468.6 nm). It is common to detect the presence of HeII in Planetary Nebulae around extremely hot white dwarf stars, but not in "normal" HII regions. However, a few otherwise seemingly normal HII regions reveal the characteristics of high excitation. One of them is located in our own Milky Way galaxy, another has been found in the nearby galaxy IC 1613, and five others are situated in the Magellanic Clouds. Astronomers have also detected the presence of HeII ions in a number of remote galaxies undergoing a phase of intense star formation ("starburst galaxies") and in the vicinity of ultraluminous X-ray sources in very distant galaxies. What is going on in those remote objects in the early Universe? Do we see the action of young and very hot stars or is something unknown going on? What can the existence of those hot nebulae in young galaxies tell about the evolution of our own Milky Way? Searching for the energy source We would like to know, but those distant nebulae are unfortunately too faint to be studied in any reasonable detail, even by means of the largest available telescopes. The only way forward is therefore to look closer at the nearest ones in the hope that they will provide clues about the processes leading to the observed high excitation and thus help to better understand their cousins in those distant galaxies. There appears to be three possible answers to the basic question about the nature of the energetic sources that heat these strange emission nebulae: * very fast particles: if there is in the area a fast-moving gas (more than 100 km/s), the shock created by the impact of this material is able to heat the ambient interstellar medium sufficiently to produce a HeII nebula. * ultraviolet emission from massive stars: according to the most recent model calculations, even the most massive O-type stars do not emit enough ultraviolet light to ionize a sufficient number of helium atoms in the surrounding nebula to produce a detectable HeII nebula. However, some of the hottest stars of the so-called Wolf-Rayet (W-R) type (that are the evolved descendants of O-stars) may produce enough high energy emission to completely ionize the helium atoms in their surroundings. * intense X-ray emission: close binary stars in which one component is a "compact" object (a white dwarf, a neutron star, or a black hole) and the other an "ordinary" star can produce an intense X-ray emission. This happens because the compact object is so dense and massive that it siphons off matter from its companion star - astronomers refer to this as an accretion process, sometimes also called "stellar cannibalism". When the "stolen" matter approaches the compact object, it gradually heats up and may reach temperatures of millions of degrees. It then emits X-rays. At the same time, ultraviolet radiation is also emitted, which may produce high excitation regions in the surrounding nebula. This scenario can also explain the association of HeII nebulae with ultraluminous X-ray sources in other galaxies. VLT observations of highly excited nebulae in the MCs Observations of a number of highly excited nebulae in the Magellanic Clouds were carried out by a team composed of Belgian and American astronomers [1] in January 2002, by means of the FORS1 multi-mode instrument at the 8.2-m VLT MELIPAL telescope. Detailed images were obtained through various special optical filters - they bring into light the complex structure of these nebulae and reveal for the first time the exact morphology of the high excitation zones. Some of exposures have been combined to produce the colour photos shown in PR Photos 09a-d/03. Here, the blue colour traces the exceptional HeII emission, whilst the red and green correspond to the more common nebular emissions from atomic hydrogen and doubly-ionized oxygen, respectively. All four nebulae shown were found to be associated with very hot stars. They carry rather prosaic names: BAT99-2 and BAT99-49, AB7 and N44C Star #2 [2]. The first three of these objects contain some of the highly evolved massive stars, of the so-called Wolf-Rayet (WR) type, while the fourth is an mid-age massive star, of type O. Massive stars, with masses more than 20 times that of the Sun, are very bright (100,000 to 10 million times brighter than the Sun), very blue and very hot, with surface temperatures of a few tens of thousands of degrees. Another property of these exceptional stars is their very strong stellar winds: they continuously eject energetic particles - like the "solar wind" from the Sun - but some 10 to 1000 million times more intensely than our star! These powerful winds exert an enormous pressure on the surrounding interstellar material and forcefully shape those clouds into "bubbles". These photos have now provided the astronomers with sufficient information to understand exactly what is going on in three of those unusual nebulae - while one case still remains ambiguous. The nebulae around BAT99-2, BAT99-49 and AB7 BAT99-2 (cf. PR Photo 09b/03) is one of the hottest WR-stars known in the Large Magellanic Cloud (LMC). Before this star reached this phase of its short life, the strong stellar wind from its progenitor O-type star swept the interstellar medium and created a "bubble", much like a snowplough pushes aside the snow on a road. Part of this "bubble" can still be seen as a large half-ring to the south of the star. When the star did become a WR, the increasingly intense stellar wind impacted on the material previously ejected from the star. This created a new bubble, now visible as a small arc-like structure to the north-west of the star. We are appparently witnessing an ongoing merger of these two bubbles. With its strong ultraviolet (UV) radiation, BAT99-2 is strongly heating its immediate surroundings, in particular the above mentioned arc-like feature that, due to the resulting high excitation, is seen as a violet-pink region in the colour image. The entire field is very complex - the presence of a supernova remnant (SNR) is revealed by a few faint red filaments rather close to the high excitation nebula, to the north-west of the arc-like structure. AB7 (PR Photo 09a/03) and BAT99-49 (PR Photo 09c/03) are both binary stars, consisting of one WR-star and a companion O-type star. Like in the case of BAT99-2, the strong UV-radiation from their WR-star has created HeII nebulae around them, well visible in the photos by their blue colour. AB7 is particularly remarkable: the associated huge nebula and HeII region indicate that this star is one of the, if not THE, hottest WR-star known so far, with a surface temperature in excess of 120,000 degrees! Just outside this nebula, a small network of green filaments is visible - they are the remains of another supernova explosion. The new VLT images, complemented with VLT spectra, demonstrate that these stars are indeed the source of the observed ionization. These very first maps of the HeII emission unveil the as yet undiscovered complex structure of those highly excited nebulae. Moreover, the new observations provide the first accurate determination of the true ionizing power of these exceptional stars. They allow a direct measurement of the otherwise unobservable intensity of the far-UV emission of WR stars. The new observations have clearly identified the ultraviolet emission of very massive stars as the energy source in these three nebulae. Using the latest theoretical models to interpret these unique data, the Belgian astronomers and their American collaborator were also able to show that all of these stars are hotter than 90,000 degrees! The N44C nebula The fourth photo, PR Photo 09d/03, shows the very peculiar nebula N44C in the LMC. There is a beautiful (blue) HeII nebula near the two central stars. It is very different from the larger, "normal" HII region that is delimited by the light from atomic hydrogen (red) and doubly-ionized oxygen (green): this hot central region of N44C rather appears to "enshroud" the stars like a veil. There is a mystery, though. With a temperature of "only" a few tens of thousand degrees, even the hottest of the two stars, an O-type star (the upper one), cannot possibly be responsible for this inner high excitation nebula [3]. Moreover, no fast motions have so far been detected in the vicinity. Some astronomers have suggested that N44C is a "fossil X-ray nebula". What does that mean ? It may well be that this O-type star is not alone, but actually possesses a compact companion. The X-ray emission from such a binary may not be constant. During their orbital motion, the two stars can move away from each other, and the larger separation may cause the X-ray emission to stop (because of the cessation of accretion of matter onto the compact object). In this case, the observed high excitation nebula could still persist for a short period of time as a "fossil" of the previous X-ray ionized nebula. Later, that part of the nebula would then gradually disappear. However, to the astonishment of the astronomers, the present VLT observations show little or no variation in the HeII emission. Thus the above described "fossil X-ray nebula" explanation does not appear to be completely adequate and the cause of the high excitation in N44C remains a challenge to astronomers. "You can't win them all", says Yal Naz. "We were able to fully understand three nebulae, but we must now look more closely at N44C. I would not be surprised, if we will be able to solve this riddle by means of additional VLT observations." More information The information contained in this press release is based on two research articles to be published in the European research journal "Astronomy & Astrophysics", one of which is available at the preprint website at the Institut d'Astrophysique et de Gophysique de Lige (Belgium). Notes [1]: The team consists of Yal Naz, Grgor Rauw, Jean Manfroid and Jean-Marie Vreux (Lige Institute, Belgium), and You-Hua Chu (University of Illinois, USA). [2]: The names of these stars refer to the research papers in which they were first decribed. BAT99-2 and BAT99-49 are nos. 2 and 49 in the list published by Breysacher, Azzopardi and Testor (A&AS, 137, 117, 1999), AB7 is star no. 7 in the list by Azzopardi and Breysacher (A&A, 75, 120, 1979) and N44C Star #2 is included in a paper by Stasinska, Testor and Heydari-Malayeri (A&A, 170, L4, 1986). [3]: Consequently, contrary to what was possible in the other three nebulae, the observed extent of that nebula does not allow measuring the temperature of the hot O-type star. Contact Yal Naz Institut d'Astrophysique et de Gophysique Lige, Belgium Phone: +32 4 366 97 20 email: naze@astro.ulg.ac.be Appendix: Different types of nebulae   Nebulae are huge clouds of gas and dust, the cosmic material from which stars and planets form. Most of them belong to five main categories, each representing a different physical state. Two of these do not shine by their own light, but three others do. Dark nebulae and reflection nebulae If the gas does not emit visible light by itself, astronomers talk about dark nebulae or reflection nebulae. The former block the light from objects behind them, and they are therefore seen as dark regions in the sky - famous examples are the Barnard 68 "globule" (cf. ESO ESO PR 01/01 and ESO PR Photos 29a-c/99) and the "Horsehead Nebula" (ESO PR Photos 02a-b/02). Contrarily, reflection nebulae appear as bright areas in the sky because their dust particles reflect the light emitted by nearby stars. A good example is the nebulae surrounding some of the brightest stars in the "Pleiades" stellar cluster or in the southern Chamaeleon I area, cf. ESO PR Photo 17c/99. Emission nebulae Other nebulae emit visible light of their own. Astronomers distinguish between Planetary Nebulae (PNs), Supernova Remnants (SNRs) and "normal" emission nebulae or "HII regions" (pronounced "Eitch-two"). When stars die, they eject copious amounts of matter into neighbouring space. These ejecta collide with and heat the surrounding interstellar matter. This is sometimes accompanied by intense radiation from the hot stellar remnant at the centre. These processes excite the interstellar gas (and the ejecta) so that they shine brightly. In the case of lighter stars like the Sun, the remnant object is a hot "white dwarf", a star barely larger than the Earth and the surrounding nebula is called a "Planetary Nebula (PN)". This historical term refers to the planet-like appearance of such a nebula in a small telescope. A fine example is the "Dumbbell Nebula", photographed by the VLT in 1998, cf. ESO PR Photos 38a-b/98. On the other hand, heavier stars explode violently - such dramatic events are seen as supernovae - and leave behind a exceedingly hot and dense, rotating "neutron star" of diameter 10-20 km (or, in the case of the heaviest stars, presumably a "black hole") as well as a surrounding nebula, the supernova remnant (SNR). A famous example is the "Crab Nebula" from the supernova that exploded in the year 1054, cf. ESO PR Photos 40f-i/99. Finally, the radiation of young hot stars embedded in an interstellar cloud is also able to heat the surrounding gas, resulting in the apparition of an emission nebula, that shines mostly in the light of ionized hydrogen (H) atoms. Such nebulae are therefore often referred to as "HII regions". The well-known Orion Nebula is an outstanding example of that type of nebula, cf. ESO PR Photos 03a-c/01.

  20. Hadronic matter and rapidly rotating compact stars

    SciTech Connect

    Weber, F.; Kettner, C.; Glendenning, N.K.

    1994-03-01

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

  1. Semiconducting polymers

    NASA Astrophysics Data System (ADS)

    Hermann, A. M.

    A review is presented of the electrical properties of those polymers whose conductivities occupy the middle ground between polymeric insulators and polymeric superconductors. Attention is confined to polymers in which conduction occurs through electronic, rather than ionic, transport. Four classes of semiconductors are discussed: (1) highly-conjugated polymers, including those formed by pyrolysis; (2) polymeric charge-transfer complexes and radical-ion salts; (3) organometallic polymeric semiconductors; and (4) composite polymer systems containing carbon or other highly conducting media. The possible applications discussed include cathodes in solid-state metal/halogen primary batteries, cathodes in lithium/poly-p-phenylene or polyacetylene secondary batteries, conductive coatings and epoxies, and chemical sensing agents. Other applications are Peltier cooling devices, pressure transducers, photovoltaic devices, infrared radiation detectors, and switches and resistors.

  2. Organometallic Polymers.

    ERIC Educational Resources Information Center

    Carraher, Charles E., Jr.

    1981-01-01

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

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

    SciTech Connect

    Kirk, Helen; Johnstone, Doug; Pineda, Jaime E.; Goodman, Alyssa

    2010-11-01

    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}.

  4. Polymers All Around You!

    ERIC Educational Resources Information Center

    Gertz, Susan

    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…

  5. Neutrino Propagation in Dense Magnetized Matter

    NASA Astrophysics Data System (ADS)

    Arbuzova, E. V.; Lobanov, A. E.; Murchikova, E. M.

    2009-01-01

    We obtained a complete system of solutions of the Dirac-Pauli equation for a massive neutrino interacting with dense matter and strong electromagnetic field. We demonstrated that these solutions can describe precession of the neutrino spin.

  6. Genetics Home Reference: Dense deposit disease

    MedlinePLUS

    ... diabetes mellitus. Autoimmune diseases occur when the immune system malfunctions and attacks the body's tissues and organs. Where can I find information about diagnosis or management of dense deposit disease? These resources address the ...

  7. Dynamical theory of dense groups of galaxies

    NASA Technical Reports Server (NTRS)

    Mamon, Gary A.

    1990-01-01

    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.

  8. Field theoretic simulations of polymer nanocomposites

    SciTech Connect

    Koski, Jason; Chao, Huikuan; Riggleman, Robert A.

    2013-12-28

    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.

  9. Field theoretic simulations of polymer nanocomposites.

    PubMed

    Koski, Jason; Chao, Huikuan; Riggleman, Robert A

    2013-12-28

    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. PMID:24387400

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

    SciTech Connect

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

    2010-01-15

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

  11. Chameleon stars

    SciTech Connect

    Dzhunushaliev, Vladimir; Folomeev, Vladimir; Singleton, Douglas

    2011-10-15

    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.

  12. Externally fed star formation: a numerical study

    NASA Astrophysics Data System (ADS)

    Mohammadpour, Motahareh; Stahler, Steven W.

    2013-08-01

    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.

  13. Magnetic fields and galactic star formation rates

    SciTech Connect

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

    2015-02-10

    The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to ≃0.5 pc. Including an empirically motivated prescription for star formation from dense gas (n{sub H}>10{sup 5} cm{sup −3}) at an efficiency of 2% per local free-fall time, we derive the amount of suppression of star formation by magnetic fields compared to the nonmagnetized case. We find GMC fragmentation, dense clump formation, and SFR can be significantly affected by the inclusion of magnetic fields, especially in our strongest investigated B-field case of 80 μG. However, our chosen kiloparsec-scale region, extracted from a global galaxy simulation, happens to contain a starbursting cloud complex that is only modestly affected by these magnetic fields and likely requires internal star formation feedback to regulate its SFR.

  14. The Transition from Diffuse to Dense Gas in Herschel Dust Emission Maps

    NASA Astrophysics Data System (ADS)

    Goldsmith, Paul

    Dense cores in dark clouds are the sites where young stars form. These regions manifest as relatively small (<0.1pc) pockets of cold and dense gas. If we wish to understand the star formation process, we have to understand the physical conditions in dense cores. This has been a main aim of star formation research in the past decade. Today, we do indeed possess a good knowledge of the density and velocity structure of cores, as well as their chemical evolution and physical lifetime. However, we do not understand well how dense cores form out of the diffuse gas clouds surrounding them. It is crucial that we constrain the relationship between dense cores and their environment: if we only understand dense cores, we may be able to understand how individual stars form --- but we would not know how the star forming dense cores themselves come into existence. We therefore propose to obtain data sets that reveal both dense cores and the clouds containing them in the same map. Based on these maps, we will study how dense cores form out of their natal clouds. Since cores form stars, this knowledge is crucial for the development of a complete theoretical and observational understanding of the formation of stars and their planets, as envisioned in NASA's Strategic Science Plan. Fortunately, existing archival data allow to derive exactly the sort of maps we need for our analysis. Here, we describe a program that exclusively builds on PACS and SPIRE dust emission imaging data from the NASA-supported Herschel mission. The degree-sized wide-field Herschel maps of the nearby (<260pc) Polaris Flare and Aquila Rift clouds are ideal for our work. They permit to resolve dense cores (<0.1pc), while the maps also reveal large-scale cloud structure (5pc and larger). We will generate column density maps from these dust emission maps and then run a tree-based hierarchical multi-scale structure analysis on them. Only this procedure permits to exploit the full potential of the maps: we will characterize cloud structure over a vast range of spatial scales. This work has many advantages over previous studies, where information about dense cores and their environment was pieced together using a variety of methods an instruments. Now, the Herschel maps permit for the first time to characterize both molecular clouds and their cores in one shot in a single data set. We use these data to answer a variety of simple yet very important questions. First, we study whether dense cores have sharp boundaries. If such boundaries exist, they would indicate that dense cores have an individual identity well-separate from the near-fractal cloud structure on larger spatial scales. Second, we will --- in very approximate sense --- derive global density gradients for molecular clouds from radii <0.1pc to 5pc and larger. These "synoptic" density gradients provide a useful quantitative description of the relation between cloud material at very different spatial scales. Also, these measurements can be compared to synoptic density gradients derived in the same fashion for theoretical cloud models. Third, we study how dense cores are nested into the "clumps" forming molecular clouds, i.e., we study whether the most massive dense cores in a cloud (<0.1pc) reside in the most massive regions identified on lager spatial scale (1pc and larger). This will show how the properties of dense cores are influenced by their environment. Our study will derive unique constraints to cloud structure. But our small sample forbids to make strong statements. This pilot study does thus prepare future larger efforts. Our entire project builds on data reduction and analysis methods which our team has used in the past. This guarantees a swift completion of the project with predictable efficiency. We present pilot studies that demonstrate that the data and analysis methods are suited to tackle the science goals. This project is thus guaranteed to return significant results.

  15. Why neutron stars have three hairs

    NASA Astrophysics Data System (ADS)

    Stein, Leo; Yagi, Kent; Pappas, George; Yunes, Nicolas; Apostolatos, Theocharis

    2015-04-01

    Neutron stars have recently been found to enjoy a certain `baldness' in their multipolar structure which is independent of the equation of state (EoS) of dense nuclear matter. This is reminiscent of the black hole no-hair relations, and in stark contrast to regular stars. Why is this? Is it because realistic EoSs are sufficiently similar, or because GR effects are especially important, or because the nuclear matter is `cold'? We explore the physics behind these and more hypotheses, and give a convincing explanation for the true origin of the three-hair relations.

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

    SciTech Connect

    Lada, Charles J.; Forbrich, Jan; Lombardi, Marco; Alves, Joao F. E-mail: jforbrich@cfa.harvard.edu E-mail: joao.alves@univie.ac.at

    2012-02-01

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

  17. Forming equatorial rings around dying stars

    NASA Astrophysics Data System (ADS)

    Akashi, Muhammad; Sabach, Efrat; Yogev, Ohad; Soker, Noam

    2015-10-01

    We suggest that clumpy dense outflowing equatorial rings around evolved giant stars, such as in supernova 1987A and the Necklace planetary nebula, are formed by bipolar jets that compress gas towards the equatorial plane. The jets are launched from an accretion disc around a stellar companion. Using the FLASH hydrodynamics numerical code we perform 3D numerical simulations, and show that bipolar jets expanding into a dense spherical shell can compress gas towards the equatorial plane and lead to the formation of an expanding equatorial ring. Rayleigh-Taylor instabilities in the interaction region break the ring to clumps. Under the assumption that the same ring formation mechanism operates in massive stars and in planetary nebulae, we find this mechanism to be more promising for ring formation than mass-loss through the second Lagrangian point. The jets account also for the presence of a bipolar nebula accompanying many of the rings.

  18. Redox-cleavable star cationic PDMAEMA by arm-first approach of ATRP as a nonviral vector for gene delivery.

    PubMed

    Dai, Fengying; Sun, Peng; Liu, Yongjie; Liu, Wenguang

    2010-01-01

    In this work, we synthesized a star cationic polymer(s-PDMAEMA) consisting of cleavable poly[N,N-bis(acryloyl) cystamine](PBAC) crosslinked core and poly(N,N-dimethyl-ethylamine methacrylate) (PDMAEMA) arms by atomic transfer radical polymerization using one-pot "arm first" method. The s-PDMAEMA that was degradable in a mimic intracellular redox environment was more efficient in condensing DNA. It was shown that s-PDMAEMA achieved higher gene transfection levels relative to their linear precursors and s-PDMAEMA200 with longer and more arms exhibited superior transfection efficiencies and lower cytotoxicity compared to PEI25K. The buffer capacities were examined by acid-base titration; the pH-dependent morphological evolution and enzyme stability of PDMAEMA/DNA complexes were investigated by atomic force microscopy (AFM) and time-resolved fluorescence spectroscopy, respectively. The results indicated that the star polymers exhibited a stronger buffering ability than their linear precursors due to the increased inner osmotic pressure. By decreasing the pH from 7.4 to 5.0, the linear PDMEMA/DNA complexes became more compact; in contrast, s-PDMAEMA200/DNA complex adopted a loose morphology due to the steric barrier of inter-arms and outward extension of positively charged arms. Analysis of the fluorescence life times of free and intercalated ethidium bromide unveiled more effective protection of DNA afforded by s-PDMAEMA. The effect of medium pH on the star PDMAEMA system was smaller owing to the ability of densely tertiary amino groups along multiple arms to absorb more protons, which was favorable for endosomolytic escape of complexes. PMID:19796806

  19. Dense molecular gas in ultraluminous and high redshift galaxies.

    NASA Astrophysics Data System (ADS)

    Radford, S. J. E.

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

  20. Star Power

    SciTech Connect

    2014-10-17

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

  1. Star Power

    ScienceCinema

    None

    2014-11-18

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

  2. 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. ...

  3. Variational Theory of Hot Dense Matter

    ERIC Educational Resources Information Center

    Mukherjee, Abhishek

    2009-01-01

    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

  4. Variational Theory of Hot Dense Matter

    ERIC Educational Resources Information Center

    Mukherjee, Abhishek

    2009-01-01

    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…

  5. Color Superconductivity in Compact Stars

    NASA Astrophysics Data System (ADS)

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

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

  6. Antimicrobial Polymer

    DOEpatents

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

    2004-09-28

    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.

  7. Antimocrobial Polymer

    DOEpatents

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

    2005-09-06

    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.

  8. Turbidity study of polymer-polymer interaction

    NASA Astrophysics Data System (ADS)

    Schwartz, Jacob; Lu, Xihua; Hu, Zhibing

    2000-10-01

    The interaction between hydroxypropyl cellulose (HPC)polymer chains and poly(acrylic acid) (PAA) polymer chains has been studied using turbidity techniques. The lower critical solution temperature of the polymer mixture has been measured as a function of polymer concentration and polymer molecular weight. The phase behavior of the polymer mixture has been discussed in terms of hydrogen bonding between HPC and PAA. Studies in this area may lead to technological advances in controlled drug delivery and bioadhesives.

  9. Star Formation Laws, Rates, and Thresholds in Galaxies

    NASA Astrophysics Data System (ADS)

    Di Francesco, James

    2015-08-01

    It has been long recognized that stars form out of gas within the interstellar mediums of galaxies. Though earlier treatments focused on the relationship between star formation and the surface densities of available molecular gas in disks (e.g., the Kennicutt-Schmidt law), more recently the relevance of dense molecular gas within galaxies has become better appreciated. In this short review talk, I will provide an overview of how this shift in thinking in the last few years has occurred through observations. For example, strong correlations have been seen between the luminosities of HCN 1-0 (tracing dense gas) and infrared emission (tracing young stars) over nearly ten orders of magnitude. Also, the number of young stellar objects in nearby clouds seems to be related to the amount of mass in a cloud above a column density 'threshold' of Av ? 6 (surface density ? 120 Msun/pc2). Indeed, recent far-infrared/submillimetre continuum data of nearby molecular clouds from Herschel have shown strong links between star formation and filamentary structures in clouds above a critical mass per unit length of ~16 Msun/pc (Av ? 8), providing a possible origin of the observed 'threshold.' Also, the current star formation rate in a dense molecular cloud clump, as traced by the local number of Class 0 objects, appears to be highly correlated with the relative fraction of high column density material in the clump. Prospects for future exploration of star-formation thresholds will also be discussed.

  10. Mixed-ionic and electronic conductivity in polymers

    SciTech Connect

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

    1991-01-01

    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.

  11. From Gas to Stars Over Cosmic Time

    NASA Astrophysics Data System (ADS)

    Mac Low, Mordecai-Mark

    2013-01-01

    The formation of stars from gas drives the evolution of galaxies. Yet, this remains one of the hardest processes to understand when trying to connect observations of modern and high-redshift stellar and galactic populations to models of large scale structure formation. The star formation rate at redshifts z>2 now appears to drop off rather more quickly than was thought even five years ago. Theoretical models have tended to overpredict the star formation rate at these high redshifts substantially, primarily due to overcooling. Overcooling in models of galaxies typically occurs because of unphysical radiative cooling caused by insufficient numerical resolution of interfaces between hot, rarefied and cold, dense gas. As a result, insufficient turbulence is driven by stellar feedback in these model galaxies. Such turbulence has the net effect of inhibiting star formation, despite its ability to intermittently promote star formation by compression. Radiation pressure appears less likely to be a dominant driver of the turbulence than has been argued because Rayleigh-Taylor instability tends to release photons before many scatterings have occurred, but supernovae and magnetorotational instabilities remain viable driving mechanisms. Gravity alone cannot be the main driver, because otherwise well-resolved models without feedback would accurately predict star formation rates. Understanding ionization heating and radiation pressure from the most massive stars requires much higher resolution models (sub-parsec scale) than resolving supernova feedback. Star formation rate surface density correlates well with observed molecular gas surface density, as well as with other tracers of high density material. Correlation does not, however, necessarily imply causation. In this case, it appears that both molecule formation and star formation occur as a consequence of gravitational collapse, with molecules typically playing an important but not an essential role in cooling. The basic concept that gravitational instability drives star formation appears to remain a true guide through the thickets of complexity surrounding this topic. I acknowledge funding from NSF grant AST11-09395.

  12. Characterising molecular gas in nearby star forming galaxies

    NASA Astrophysics Data System (ADS)

    Kelly, George; Viti, Serena; Garcia-Burillo, Santiago

    2015-08-01

    Regions of very dense, star-forming gas in the interstellar medium are necessary to maintain star formation activity in hostile conditions. Star-forming regions in these environments are able to resist winds and radiative forces from newly formed stars longer than gas in the surrounding ISM. Subject to a proper interpretation, observations of molecules can be used for many purposes: tracing the reservoir or leftover of the star formation process; tracing the process of star formation itself; and determining the galaxy energetics through influence of newly-formed stars or an AGN on their environments. We map the distribution of several tracer molecules over three nearby galaxies. We begin by mapping two starburst galaxies with single dish observations of the dense gas tracer CS. The formation of CS is modelled under different conditions with results fed into a molecular line radiative transfer model. From this we can obtain the physical conditions of the regions of the ISM where there is a high rate of star-formation, as well as compare how the conditions vary away from the galactic centre. Moving on from here, we use ALMA to map NGC 1068. Observations of several molecules across the AGN and starburst regions are used to determine conditions and processes with a spatial resolution of less than 35 parsecs.

  13. Numerical study of the properties of compact stars

    NASA Astrophysics Data System (ADS)

    Negreiros, Rodrigo Picanco

    2009-10-01

    Compact stars are formed in catastrophic astrophysical events such as supernova explosions and binary stellar collisions. These objects permanently harbor compressed ultra-dense nuclear matter in their interiors. This key feature, together with the ongoing progress in observational astrophysics, make compact stars superb astrophysical laboratories for a wide range of intriguing physicals studies. Several such studies are performed in this thesis. The first activity concerns the widely unknown nuclear equation of state and the core composition of compact stars. Particular attention is paid to the possible presence of hyperons in the cores of neutron stars as well as to stars made of unconfined up, down and strange quarks (strange quark stars). The effects of ultra-strong electric fields on the surfaces of the latter is explored. The second activity aims at investigating the structure and stability of rapidly rotating compact stars. Special attention is paid to the maximal stable rotational frequencies of rotating compact stars. The third activity focuses on the thermal evolution of compact stars, driven by neutrino emission from their cores and by photon emission from the surfaces. It is show that the thermal behavior depends very strongly on the stellar core composition. Moreover, it is found that the thermal evolution of neutron stars is significantly different to that of strange quark stars. The studies performed in this thesis are key for our understanding of the thermal evolution of isolated rotating neutron stars, anomalous X-ray pulsars and soft gamma repeaters, and provide most valuable information about the phase diagram of isospin-asymmetric ultra-dense nuclear matter which can not be probed in high-energy collision experiments.

  14. Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

    SciTech Connect

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

    2010-08-25

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

  15. LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION

    SciTech Connect

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

    2010-12-10

    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.

  16. Converting neutron stars into strange stars

    NASA Technical Reports Server (NTRS)

    Olinto, A. V.

    1991-01-01

    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.

  17. Coalescence preference in densely packed microbubbles

    DOE PAGESBeta

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

    2015-01-13

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

  18. Coalescence preference in densely packed microbubbles

    SciTech Connect

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

    2015-01-13

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

  19. Dynamic structure factor in warm dense beryllium

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  20. Pressure in electronically excited warm dense metals

    NASA Astrophysics Data System (ADS)

    Stegailov, Vladimir; Zhilyaev, Petr

    2015-06-01

    Non-equilibrium two-temperature warm dense metals consist of the ion subsystem that is subjected to structural transitions and involved in the mass transfer, and the electron subsystem that in various pulsed experiments absorbs energy and then evolves together with ions to equilibrium. Definition of pressure in such non-equilibrium systems causes certain controversy. In this work we make an attempt to clarify this definition that is vital for proper description of the whole relaxation process. Using the density functional theory we analyze on examples of Al and Au electronic pressure components in warm dense metals. Appealing to the Fermi gas model we elucidate a way to find a number of free delocalized electrons in warm dense metals. First results has been published in. This work is supported by the Russian Science Foundation grant No. 14-19-01487.

  1. Coalescence preference in densely packed microbubbles

    PubMed Central

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

    2015-01-01

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

  2. Roughness coefficients for densely vegetated flood plains

    USGS Publications Warehouse

    Arcement, G.J.; Schneider, V.R.

    1987-01-01

    Although much research has been done on Manning 's roughness coefficients for stream channels, very little has been done on the selection of roughness values for densely vegetated flood plains. In this report four method for determining roughness coefficients for flood plains are examined and evaluated. Field data were collected at 13 sites on wide, densely vegetated flood plains where verified n values were known. The ' vegetation density ' of representative sample areas was measured at each site for use in determining roughness coefficients. The vegetation density method, proved to be useful in determining n values for wide, densely wooded plains. By measuring the area occupied by tree trunks and vegetation in a representative sample area, the vegetation density can be determined. Using the vegetation density in an equation developed from Manning 's formula, the Manning 's n can be determined for the representative sample area. (USGS)

  3. Hybrid Stars

    SciTech Connect

    Menezes, D.P.; Providencia, C.

    2004-12-02

    In the present paper we calculate the properties of hybrid stars, namely, its gravitational, baryonic masses and central energy densities by solving the Tolman-Volkoff-Oppenheimer equations, which were derived from Einstein's equations for compact stellar objects. In order to obtain these properties, an adequate equation of state (EOS) is necessary. Hybrid stars are formed when a phase transition to a deconfined phase is thermodinamically possible. In this work we have used the non-linear Walecka model for the hadron matter and the MIT Bag (unpaired quark phase) and the Nambu-Jona-Lasinio (NJL) models for the quark matter in order to build the appropriate equations of state for the mixed phase constituted by hadrons and quarks in {beta}-equilibrium.

  4. Christmas star.

    NASA Astrophysics Data System (ADS)

    Biała, J.

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

  5. Characterizing star cluster formation with WISE: 652 newly found star clusters and candidates

    NASA Astrophysics Data System (ADS)

    Camargo, D.; Bica, E.; Bonatto, C.

    2016-01-01

    We report the discovery of 652 star clusters, stellar groups and candidates in the Milky Way with Wide-field Infrared Survey Explorer (WISE). Most of the objects are projected close to Galactic plane and are embedded clusters. The present sample complements a similar study (Paper I) which provided 437 star clusters and alike. We find evidence that star formation processes span a wide range of sizes, from populous dense clusters to small compact embedded ones, sparse stellar groups or in relative isolation. The present list indicates multiple stellar generations during the embedded phase, with giant molecular clouds collapsing into several clumps composing an embedded cluster aggregate. We investigate the field star decontaminated colour-magnitude diagrams and radial density profiles of nine cluster candidates in the list, and derive their parameters, confirming them as embedded clusters.

  6. The similar emission-line spectra of the young star LkH-alpha 101 and the hypergiant MWC 300

    SciTech Connect

    Hamann, F.; Persson, S.E. )

    1989-12-01

    High-resolution spectra from 0.63 to 1.75 microns are presented, showing that the luminous young star LkH-alpha 101 and the post-main-sequence hypergiant MWC 300 have very similar emission-line properties. Tables are given of line measurements and identifications. It is found that, in spite of their different histories, these stars have similar conditions of density, temperature, kinematics, and possibly geometry in their line-emitting envelopes. The results support models of hypergiants and luminous young stars which both invoke dense equatorial disks and suggest that disk structures around some evolved hot young stars are created by dense equatorial winds. 74 refs.

  7. Relativistic simulations of eccentric binary neutron star mergers: One-arm spiral instability and effects of neutron star spin

    NASA Astrophysics Data System (ADS)

    East, William E.; Paschalidis, Vasileios; Pretorius, Frans; Shapiro, Stuart L.

    2016-01-01

    We perform general-relativistic hydrodynamical simulations of dynamical capture binary neutron star mergers, emphasizing the role played by the neutron star spin. Dynamical capture mergers may take place in globular clusters, as well as other dense stellar systems, where most neutron stars have large spins. We find significant variability in the merger outcome as a function of initial neutron star spin. For cases where the spin is aligned with the orbital angular momentum, the additional centrifugal support in the remnant hypermassive neutron star can prevent the prompt collapse to a black hole, while for antialigned cases the decreased total angular momentum can facilitate the collapse to a black hole. We show that even moderate spins can significantly increase the amount of ejected material, including the amount unbound with velocities greater than half the speed of light, leading to brighter electromagnetic signatures associated with kilonovae and interaction of the ejecta with the interstellar medium. Furthermore, we find that the initial neutron star spin can strongly affect the already rich phenomenology in the postmerger gravitational wave signatures that arise from the oscillation modes of the hypermassive neutron star. In several of our simulations, the resulting hypermassive neutron star develops the one-arm (m =1 ) spiral instability, the most pronounced cases being those with small but non-negligible neutron star spins. For long-lived hypermassive neutron stars, the presence of this instability leads to improved prospects for detecting these events through gravitational waves, and thus may give information about the neutron star equation of state.

  8. Polymer solutions

    DOEpatents

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

    2011-07-26

    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.

  9. An increasing presence: the lone star tick, Amblyomma americanum

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In June and July, 2006 and 2007, flagging with the purpose of collecting large numbers of lone star tick, Amblyomma americanum, nymphs revealed hyper-dense foci of host-seeking nymphs occupying areas =5 by 5 m. Nymphs were concentrated in one or two core areas within the 5 by 5 m. It is unlikely tha...

  10. Gluon Vortices and Induced Magnetic Field in Compact Stars

    SciTech Connect

    Ferrer, Efrain J.

    2007-10-26

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

  11. Method of Preparing Polymers with Low Melt Viscosity

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor)

    2001-01-01

    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.

  12. Stress Relaxation in Entangled Melts of Unlinked Ring Polymers

    NASA Astrophysics Data System (ADS)

    Milner, Scott T.; Newhall, Jillian D.

    2010-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Vanbeveren, D.

    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.

  14. Star ratings. Stars of wonder.

    PubMed

    Dawes, David

    2002-09-12

    Analysis of trusts that changed their star-rating over the past two years indicates that a change of chief executive was not a significant factor. The length of time in post and the experience of the chief executive were also insignificant. This has serious implications for the theory behind franchising and the evaluation of franchised trusts. Holding chief executives to account for the organisation's performance within their first 12 months is unlikely to be effective. PMID:12357738

  15. Dense high temperature ceramic oxide superconductors

    DOEpatents

    Landingham, Richard L. (Livermore, CA)

    1993-01-01

    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.

  16. Preparation of a dense, polycrystalline ceramic structure

    DOEpatents

    Cooley, Jason; Chen, Ching-Fong; Alexander, David

    2010-12-07

    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.

  17. Dense high temperature ceramic oxide superconductors

    DOEpatents

    Landingham, R.L.

    1993-10-12

    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.

  18. Improvements in accuracy of dense OPC models

    NASA Astrophysics Data System (ADS)

    Kallingal, Chidam; Oberschmidt, James; Viswanathan, Ramya; Abdo, Amr; Park, OSeo

    2008-10-01

    Performing model-based optical proximity correction (MBOPC) on layouts has become an integral part of patterning advanced integrated circuits. Earlier technologies used sparse OPC, the run times of which explode when the density of layouts increases. With the move to 45 nm technology node, this increase in run time has resulted in a shift to dense simulation OPC, which is pixel-based. The dense approach becomes more efficient at 45nm technology node and beyond. New OPC model forms can be used with the dense simulation OPC engine, providing the greater accuracy required by smaller technology nodes. Parameters in the optical model have to be optimized to achieve the required accuracy. Dense OPC uses a resist model with a different set of parameters than sparse OPC. The default search ranges used in the optimization of these resist parameters do not always result in the best accuracy. However, it is possible to improve the accuracy of the resist models by understanding the restrictions placed on the search ranges of the physical parameters during optimization. This paper will present results showing the correlation between accuracy of the models and some of these optical and resist parameters. The results will show that better optimization can improve the model fitness of features in both the calibration and verification set.

  19. 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...

  20. Chiral thermodynamics of dense hadronic matter

    SciTech Connect

    Sasaki, C.

    2012-05-15

    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.

  1. Detecting modified gravity in the stars

    NASA Astrophysics Data System (ADS)

    Sakstein, Jeremy; Jain, Bhuvnesh; Vikram, Vinu

    2014-07-01

    Modified theories of gravity have received a renewed interest due to their ability to account for the cosmic acceleration. In order to satisfy the solar system tests of gravity, these theories need to include a screening mechanism that hides the modifications on small scales. One popular and well-studied theory is chameleon gravity. Our own galaxy is necessarily screened, but less dense dwarf galaxies may be unscreened and their constituent stars can exhibit novel features. In particular, unscreened stars are brighter, hotter and more ephemeral than screened stars in our own galaxy. They also pulsate with a shorter period. In this paper, we exploit these new features to constrain chameleon gravity to level three orders of magnitude lower the previous measurements. These constraints are currently the strongest in the literature.

  2. The dense gas mass fraction of molecular clouds in the Milky Way

    SciTech Connect

    Battisti, Andrew J.; Heyer, Mark H. E-mail: heyer@astro.umass.edu

    2014-01-10

    The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using {sup 13}CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1 mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') {sup 13}CO J = 1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200 M {sub ?} pc{sup 2}, which are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin {sup 13}CO J = 1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11{sub ?0.06}{sup +0.12}. The high column density subregions comprise 0.07{sub ?0.05}{sup +0.13} of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4 km s{sup 1} for various flow configurations.

  3. Drama of HII regions: Clustered and Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Li, Jinzeng; YUAN, Jinghua; LIU, Hongli; Wu, Yuefang; Huang, Yafang

    2015-08-01

    Intense ultraviolet radiation from young massive stars ionizes ambient material leading to the formation of HII regions which have keen impact upon the birth of new stars in the vicinities. The strong radiation may be responsible for the dispersal of molecular clouds to hinder star formation, while the expansion of HII regions would collect neutral material to form dense layers which may be gravitationally unstable to collapse to give birth to new stars.In order to understand the star formation process under the influence of HII regions, we have carried out extensive investigations to well selected star-forming regions which all have been profoundly affected by existing massive O type stars. On the basis of multi-wavelength data from mid-infrared to millimeter collected using Spitzer, Herschel, and ground based radio telescope, the physical status of interstellar medium and star formation in these regions have been revealed. Clustered and sequential star formation have been detected toward well known HII regions, such as IC1396 and Sh-155. In a relatively large infrared dust bubble, active star formation is undergoing and the shell is still expanding. Socked features and signs of triggered star formation have been tentatively detected in a relatively small bubble. The dense cores in the Rosette Molecular Complex detected at 1.1 mm using SMA have been speculated to have a likely triggered origin according to their spatial distribution. Although some observational results have been obtained, more efforts are necessary to reach trustworthy conclusions. And more regions will be extensively explored based on multi-wavelength observations, especially the data collected using the Herschel Space Observatory.

  4. Studies of liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Clingman, Scott Richard

    1998-05-01

    Several series of liquid crystalline polymers comprised of various chain architectures have been designed, synthesized and characterized to examine the influence of chain architecture on polymer chain dynamics. Two liquid crystalline (LC) side-group poly(methacrylates) were synthesized, and their melt dynamics were compared with each other and a third, main- chain side-group combined LC polymer. A new route was employed to synthesize the side-group polymers, which were chosen to study the melt dynamics of LC polymers with different side-group packing. The main-chain side- group poly(malonate) had a similar side-group but possessed a more complex phase behavior. Side-group interdigitation appears to lead to much slower diffusion in the direction perpendicular to the smectic layer planes. The influence of branching on mesomorphic behavior and defect structure was examined by comparing two families of linear and 3-armed star oligomers based on different mesogens. The use of AB monomers allowed the synthesis of various molecular weight AB oligomers with exactly one functional group, which were then cyclotrimerized into single-branched, or 3-armed star systems. The presence of a branch point was found to have a drastic affect on the ability of the molecules to form mesophases, and for the mesophases to undergo defect annihilation. Three block copolymers were synthesized through the coupling of ? or /alpha,/omega end- functionalized LC poly(ethers) with monodisperse monocarboxylic acid-terminated poly(styrene) or poly(ethylene) homopolymers. This family of polydisperse block copolymers was examined in an effort to evaluate the synthetic route and to study the interaction between the two chemically different blocks. Finally, several series of semi-rigid main-chain polymers were prepared to examine the influence of side groups, hydrogen bonding, stiffness and mesogen choice on polymer properties. Based on the choice of mesogen, hydrogen bonding was found to either inhibit or promote mesomorphism. Increasing 'spacer' stiffness led to shorter chain lengths, decreased solubility and increased transition temperatures.

  5. Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Palous, J.; Ehlerov, S.

    2002-02-01

    The star formation triggered in dense walls of expanding shells is discussed. The fragmentation process is studied using the linear and non-linear perturbation theory. The influence of the energy input, the ISM distribution, and the speed of sound is examined analytically and by numerical simulations. We formulate the condition for the gravitational fragmentation of expanding shells: if the total surface density of the disc is higher than a certain critical value, shells are unstable. This value depends on the energy of the shell and the sound speed in the ISM. As an example the formation of OB associations near the Sun is discussed. We trace their orbits in the Milky Way to see where they have been born: 10-12 Myr ago progenitors of the Scorpius-Centaurus OB associations and the Orion OB association resided together within a sheet-like region elongated in the l = 20^o-200^o direction, showing that the local OB associations may be formed as fragments of an expanding supershell.

  6. STAR heavy flavor tracker

    NASA Astrophysics Data System (ADS)

    Qiu, Hao

    2014-11-01

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

  7. The sun, our star

    NASA Astrophysics Data System (ADS)

    Noyes, R. W.

    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.

  8. Polymer Energy Rechargeable System Battery Being Developed

    NASA Technical Reports Server (NTRS)

    Manzo, Michelle A.

    2003-01-01

    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.

  9. How Galactic Environment Regulates Star Formation

    NASA Astrophysics Data System (ADS)

    Meidt, Sharon E.

    2016-02-01

    In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.

  10. The SOFIA Massive (SOMA) Star Formation Survey

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan C.; De Buizer, James M.; Zhang, Yichen; Liu, Mengyao; Sandell, Göran H. L.; Staff, Jan E.; Beltrán, Maria T.; Shuping, Ralph

    2016-01-01

    Massive stars play leading roles in shaping the interstellar and intergalactic media, thus regulating star formation activity and the evolution of galaxies. The formation mechanism of massive stars remains much debated, with the central question being whether it is simply a scaled-up version of low-mass star formation from gas cores or involves more complex, chaotic accretion flows in the crowded centers of concurrently forming star clusters. Using the unique ~10 to 40 micron imaging capabilities of SOFIA-FORCAST, we are in the process of observing a large (>40) sample of high- and intermediate-mass protostars in a variety of Galactic environments. These observations probe warm dust that is often a signature of irradiated protostellar outflow cavities. Thus analysis of the resulting spectral energy distributions and multi-wavelength images and comparison with radiative transfer models provides powerful constraints on the geometry of dense accretion flows and lower density outflows around these protostars, and thus tests massive star formation theories. We summarize latest results from the SOMA survey and its impact on theoretical modeling.

  11. The Production of HMXBs in Star Clusters

    NASA Astrophysics Data System (ADS)

    Johns, Paula; Chandar, Rupali; Rangelov, Blagoy

    2016-01-01

    High-mass X-ray binaries (HMXBs), where a black hole or neutron star accretes material from a massive donor star, often dominate the high-energy output from nearby galaxies. Most massive stars, the progenitors of HMXBs, form in star clusters, and therefore it follows that there should be a link between the production of HMXBs and clusters. We use a catalog of HMXBs based on Chandra X-ray Observatory observations and a catalog of star clusters based on Hubble Space Telescope observations to study the production of HMXBs in star clusters in the Antennae, the closest pair of actively merging galaxies. We find the highest number of HMXBs associated with very young, ~3-6 Myr clusters, but also find clear evidence that they form in older stellar systems. We test whether HMXBs are more likely to form in the most massive or most dense clusters (at any age), or if their production is simply governed by statistics, i.e. whether more massive clusters produce a HMXB at the same rate as a grouping of less massive clusters that have the same total mass.

  12. Shaping the outflows of evolved stars

    NASA Astrophysics Data System (ADS)

    Mohamed, Shazrene

    2015-08-01

    Both hot and cool evolved stars, e.g., red (super)giants and Wolf-Rayet stars, lose copious amounts of mass, momentum and mechanical energy through powerful, dense stellar winds. The interaction of these outflows with their surroundings results in highly structured and complex circumstellar environments, often featuring knots, arcs, shells and spirals. Recent improvements in computational power and techniques have led to the development of detailed, multi-dimensional simulations that have given new insight into the origin of these structures, and better understanding of the physical mechanisms driving their formation. In this talk, I will discuss three of the main mechanisms that shape the outflows of evolved stars:- interaction with the interstellar medium (ISM), i.e., wind-ISM interactions- interaction with a stellar wind, either from a previous phase of evolution or the wind from a companion star, i.e., wind-wind interactions- and interaction with a companion star that has a weak or insignicant outflow (e.g., a compact companion such as a neutron star or black hole), i.e., wind-companion interactions.I will also highlight the broader implications and impact of these stellar wind interactions for other phenomena, e.g, for symbiotic and X-ray binaries, supernovae and Gamma-ray bursts.

  13. Theory of plasmon decay in dense plasmas and warm dense matters

    SciTech Connect

    Son, S.; Ku, S.; Moon, Sung Joon

    2010-11-15

    The prevalent Landau damping theory for classical plasmas does not fully explain the Langmuir wave decay in dense plasmas. A dielectric function theory adapted from the condensed matter physics is extended to be applicable for the dense plasmas and warm dense matters. This theory, accounting for the Umklapp process, predicts much higher decay rates than the Landau damping theory, which results in better agreement with the available experimental data obtained from the metals. The detailed calculations are presented for the following four cases: classical plasmas, Maxwellian plasmas, degenerate quantum plasmas, and partially degenerate plasmas.

  14. Chemical Dense Gas Modeling in Cities

    NASA Astrophysics Data System (ADS)

    Brown, M. J.; Williams, M. D.; Nelson, M. A.; Streit, G. E.

    2007-12-01

    Many industrial facilities have on-site storage of chemicals and are within a few kilometers of residential population. Chemicals are transported around the country via trains and trucks and often go through populated areas on their journey. Many of the chemicals, like chlorine and phosgene, are toxic and when released into the air are heavier-than-air dense gases that hug the ground and result in high airborne concentrations at breathing level. There is considerable concern about the vulnerability of these stored and transported chemicals to terrorist attack and the impact a release could have on highly-populated urban areas. There is the possibility that the impacts of a dense gas release within a city would be exacerbated since the buildings might act to trap the toxic cloud at street level and channel it over a large area down side streets. However, no one is quite sure what will happen for a release in cities since there is a dearth of experimental data. There are a number of fast-running dense gas models used in the air pollution and emergency response community, but there are none that account for the complex flow fields and turbulence generated by buildings. As part of this presentation, we will discuss current knowledge regarding dense gas releases around buildings and other obstacles. We will present information from wind tunnel and field experiments, as well as computational fluid dynamics modeling. We will also discuss new fast response modeling efforts which are trying to account for dense gas transport and dispersion in cities.

  15. Structure of random silicates: polymers, colloids, and porous solids

    SciTech Connect

    Schaefer, D.W.; Keefer, K.D.

    1985-01-01

    Small angle x-ray scattering and light scattering are used to characterize structures grown by random processes within the silica system. Dense colloids, rough colloids, and branched polymers are grown by polymerization in solution. Supermolecular structures are also studied, including gels, colloidal liquids, and aggregates.

  16. Binary stars.

    PubMed

    Paczynacuteski, B

    1984-07-20

    Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars. PMID:17749544

  17. Magnetic Fields and Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Zhang, Qizhou; Qiu, Keping; Girart, Josep M.; (Baobab Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Li, Zhi-Yun; Keto, Eric; Ho, Paul T. P.; Rao, Ramprasad; Lai, Shih-Ping; Ching, Tao-Chung; Frau, Pau; Chen, How-Huan; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain; Csengeri, Timea; Jurez, Carmen

    2014-09-01

    Massive stars (M > 8 M ?) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 ?m obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of lsim0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40 of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (lsim 103 AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  18. Magnetic fields and massive star formation

    SciTech Connect

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan; Qiu, Keping; Girart, Josep M.; Juárez, Carmen; Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping; Li, Zhi-Yun; Frau, Pau; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  19. Thermal properties of hot and dense matter with finite range interactions

    NASA Astrophysics Data System (ADS)

    Constantinou, Constantinos; Muccioli, Brian; Prakash, Madappa; Lattimer, James M.

    2015-08-01

    We explore the thermal properties of hot and dense matter using a model that reproduces the empirical properties of isospin symmetric and asymmetric bulk nuclear matter, optical-model fits to nucleon-nucleus scattering data, heavy-ion flow data in the energy range 0.5-2 GeV/A , and the largest well-measured neutron star mass of 2 M? . This model, which incorporates finite range interactions through a Yukawa-type finite range force, is contrasted with a conventional zero range Skyrme model. Both models predict nearly identical zero-temperature properties at all densities and proton fractions, including the neutron star maximum mass, but differ in their predictions for heavy-ion flow data. We contrast their predictions of thermal properties, including their specific heats, and provide analytical formulas for the strongly degenerate and nondegenerate limits. We find significant differences in the results of the two models for quantities that depend on the density derivatives of nucleon effective masses. We show that a constant value for the ratio of the thermal components of pressure and energy density expressed as ?th=1 +(Pth/?th) , often used in simulations of proto-neutron stars and merging compact object binaries, fails to adequately describe results of either nuclear model. The region of greatest discrepancy extends from subsaturation densities to a few times the saturation density of symmetric nuclear matter. Our results suggest alternate approximations for the thermal properties of dense matter that are more realistic.

  20. Advanced Polymer

    NASA Technical Reports Server (NTRS)

    1992-01-01

    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.

  1. Formation and structure of amorphous carbon char from polymer materials

    NASA Astrophysics Data System (ADS)

    Lawson, John; Srivastava, Deepak

    2008-03-01

    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.

  2. Aqueous phase deposition of dense tin oxide films with nano-structured surfaces

    SciTech Connect

    Masuda, Yoshitake Ohji, Tatsuki; Kato, Kazumi

    2014-06-01

    Dense tin oxide films were successfully fabricated in an aqueous solution. The pH of the solutions was controlled to pH 1.3 by addition of HCl. Precise control of solution condition and crystal growth allowed us to obtain dense tin oxide films. Concaveconvex surface of fluorine-doped tin oxide (FTO) substrates was entirely-covered with the continuous films. The films were about 65 nm in thickness and had nano-structured surfaces. Morphology of the films was strikingly different from our previous reported nano-sheet assembled structures. The films were not removed from the substrates by strong water flow or air blow to show strong adhesion strength. The aqueous solution process can be applied to surface coating of various materials such as nano/micro-structured surfaces, particles, fibers, polymers, metals or biomaterials. - Graphical abstract: Dense tin oxide films of 65 nm were successfully fabricated in an aqueous solution. They had nano-structured surfaces. Concave-convex substrates were entirely-covered with the continuous films. - Highlights: Dense tin oxide films of 65 nm were successfully fabricated in an aqueous solution. They had nano-structured surfaces. Concaveconvex substrates were entirely-covered with the continuous films.

  3. Phthalocyanine polymers

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    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.

  4. Eutactic star closest to a given star

    SciTech Connect

    Gomez, A.; Torres, M.; Aragon, J. L.

    2007-05-15

    A eutactic star is a set of M vectors in R{sup n} (M>n) that are projections of M orthogonal vectors in R{sup M}. Eutactic stars have remarkable properties that have been exploited in several fields such as crystallography, graph theory, wavelets, and quantum measurement theory. In this work we show that given an arbitrary star of vectors, there exists a closest eutactic star in the Frobenius norm. An algorithm for calculating this star is presented. Additionally, the distance between both stars provides a new measure of eutacticity.

  5. Periodic Polymers

    NASA Astrophysics Data System (ADS)

    Thomas, Edwin

    2013-03-01

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

  6. HUBBLE CAPTURES THE HEART OF STAR BIRTH

    NASA Technical Reports Server (NTRS)

    2002-01-01

    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.

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

    SciTech Connect

    Weber, F. |; Glendenning, N.K.

    1993-10-25

    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.

  8. Reentrant Stabilization of Grafted Nanoparticles in Polymer Solutions.

    PubMed

    Feng, Huanhuan; Bhmer, Marcel; Fokkink, Remco; Sprakel, Joris; Leermakers, Frans

    2015-10-01

    Polymer chains grafted onto nanoparticles may facilitate the dispersion of such particles in a polymer solution. We explore the optimal strategy for stabilizing polymer-grafted nanoparticles using self-consistent field theory and experiments. The best results are obtained for relatively low grafting densities and for chain lengths of the brush polymer NB larger than that of the freely floating polymers Nf. When Nf > NB, one finds a compatibilization gap and re-entrant stabilization: At both very low and very high polymer concentrations particles disperse in the polymer solution, while at intermediate concentrations the particles lose their colloidal stability. At low grafting densities the underlying surface is in contact with the solvent. Particles covered by a bidisperse brush can combine a low grafting outer region with full coverage of the surface by a densely grafted inner layer. Using classical colloid-chemical stabilization criteria the region in the phase diagram for which the particles are expected to mix with a concentrated polymer solution opens up. Now, also upon an increase in the length of the freely dispersed polymers, a re-entrant colloid-chemical stabilization is found for particles on the nanometer length scale: At both short and long polymer chains in solution the particles will not aggregate, whereas at intermediate lengths the colloidal stability is marginal. This multi re-entrant behavior is found from numerical self-consistent field calculations, and these predictions are consistent with corresponding experiments. PMID:26368593

  9. Ion acoustic solitons in dense magnetized plasmas with nonrelativistic and ultrarelativistic degenerate electrons and positrons

    SciTech Connect

    Sadiq, Safeer; Mahmood, S.; Haque, Q.; Ali, Munazza Zulfiqar

    2014-09-20

    The propagation of electrostatic waves in a dense magnetized electron-positron-ion (EPI) plasma with nonrelativistic and ultrarelativistic degenerate electrons and positrons is investigated. The linear dispersion relation is obtained for slow and fast electrostatic waves in the EPI plasma. The limiting cases for ion acoustic wave (slow) and ion cyclotron wave (fast) are also discussed. Using the reductive perturbation method, two-dimensional propagation of ion acoustic solitons is found for both the nonrelativistic and ultrarelativistic degenerate electrons and positrons. The effects of positron concentration, magnetic field, and mass of ions on ion acoustic solitons are shown in numerical plots. The proper form of Fermi temperature for nonrelativistic and ultrarelativistic degenerate electrons and positrons is employed, which has not been used in earlier published work. The present investigation is useful for the understanding of linear and nonlinear electrostatic wave propagation in the dense magnetized EPI plasma of compact stars. For illustration purposes, we have applied our results to a pulsar magnetosphere.

  10. Frontiers of dense plasma physics with intense ion and laser beams and accelerator technology

    NASA Astrophysics Data System (ADS)

    Hoffmann, D. H. H.; Blazevic, A.; Rosmej, O. N.; Spiller, P.; Tahir, N. A.; Weyrich, K.; Dafni, T.; Kuster, M.; Roth, M.; Udrea, S.; Varentsov, D.; Jacoby, J.; Zioutas, K.; Mintsev, V.; Fortov, V. E.; Sharkov, B. Yu; Maron, Y.

    2006-04-01

    Interaction phenomena of intense ion and laser radiation with matter have a large range of application in different fields of science, from basic research of plasma properties to application in energy science. The hot dense plasma of our neighbouring star the Sun provides a deep insight into the physics of fusion, the properties of matter at high energy density, and is moreover an excellent laboratory for astroparticle physics. As such the Sun's interior plasma can even be used to probe the existence of novel particles and dark matter candidates. We present an overview on recent results and developments of dense plasma physics addressed with heavy ion and laser beams combined with accelerator and nuclear physics technology.

  11. Fully nonlinear ion-sound waves in a dense Fermi magnetoplasma

    NASA Astrophysics Data System (ADS)

    Ali, S.; Moslem, W. M.; Shukla, P. K.; Kourakis, I.

    2007-07-01

    The nonlinear propagation of ion-sound waves in a collisionless dense electron-ion magnetoplasma is investigated. The inertialess electrons are assumed to follow a non-Boltzmann distribution due to the pressure for the Fermi plasma and the ions are described by the hydrodynamic (HD) equations. An energy balance-like equation involving a new Sagdeev-type pseudo-potential is derived in the presence of the quantum statistical effects. Numerical calculations reveal that the profiles of the Sagdeev-like potential and the ion-sound density excitations are significantly affected by the wave direction cosine and the Mach number. The present studies might be helpful to understand the excitation of nonlinear ion-sound waves in dense plasmas such as those in superdense white dwarfs and neutron stars as well as in intense laser-solid density plasma experiments.

  12. Numerical study of ion acoustic shock waves in dense quantum plasma

    SciTech Connect

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

    2014-03-15

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

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

    SciTech Connect

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

    2014-02-15

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

  14. Undercover Stars Among Exoplanet Candidates

    NASA Astrophysics Data System (ADS)

    2005-03-01

    Very Large Telescope Finds Planet-Sized Transiting Star Summary An international team of astronomers have accurately determined the radius and mass of the smallest core-burning star known until now. The observations were performed in March 2004 with the FLAMES multi-fibre spectrograph on the 8.2-m VLT Kueyen telescope at the ESO Paranal Observatory (Chile). They are part of a large programme aimed at measuring accurate radial velocities for sixty stars for which a temporary brightness "dip" has been detected during the OGLE survey. The astronomers find that the dip seen in the light curve of the star known as OGLE-TR-122 is caused by a very small stellar companion, eclipsing this solar-like star once every 7.3 days. This companion is 96 times heavier than planet Jupiter but only 16% larger. It is the first time that direct observations demonstrate that stars less massive than 1/10th of the solar mass are of nearly the same size as giant planets. This fact will obviously have to be taken into account during the current search for transiting exoplanets. In addition, the observations with the Very Large Telescope have led to the discovery of seven new eclipsing binaries, that harbour stars with masses below one-third the mass of the Sun, a real bonanza for the astronomers. PR Photo 06a/05: Brightness "Dip" and Velocity Variations of OGLE-TR-122. PR Photo 06b/05: Properties of Low-Mass Stars and Planets. PR Photo 06c/05: Comparison Between OGLE-TR-122b, Jupiter and the Sun. The OGLE Survey When a planet happens to pass in front of its parent star (as seen from the Earth), it blocks a small fraction of the star's light from our view [1]. These "planetary transits" are of great interest as they allow astronomers to measure in a unique way the mass and the radius of exoplanets. Several surveys are therefore underway which attempt to find these faint signatures of other worlds. One of these programmes is the OGLE survey which was originally devised to detect microlensing events by monitoring the brightness of a very large number of stars over extended time intervals. During the past years, it has also included a search for periodic, very shallow "dips" in the brightness of stars, caused by the regular transit of small orbiting objects (small stars, brown dwarfs [2] or Jupiter-size planets). The OGLE team has since announced 177 "planetary transit candidates" from their survey of several hundred thousand stars in three southern sky fields, one in the direction of the Galactic Centre, another within the Carina constellation and the third within the Centaurus/Musca constellations. The nature of the transiting object can however only be established by subsequent radial-velocity observations of the parent star. The size of the velocity variations (the amplitude) is directly related to the mass of the companion object and therefore allows discrimination between stars and planets as the cause of the observed brightness "dip". A Bonanza of Low-Mass Stars An international team of astronomers [3] has made use of the 8.2-m VLT Kueyen telescope for this work. Profiting from the multiplex capacity of the FLAMES/UVES facility that permits to obtain high-resolution spectra of up to 8 objects simultaneously, they have looked at 60 OGLE transit candidate stars, measuring their radial velocities with an accuracy of about 50 m/s [4]. This ambitious programme has so far resulted in the discovery of five new transiting exoplanets (see, e.g., ESO PR 11/04 for the announcement of two of those). Most of the other transit candidates identified by OGLE have turned out to be eclipsing binaries, that is, in most cases common, small and low-mass stars passing in front of a solar-like star. This additional wealth of data on small and light stars is a real bonanza for the astronomers. Constraining the Relation Between Mass and Radius Low-mass stars are exceptionally interesting objects, also because the physical conditions in their interiors have much in common with those of giant planets, like Jupiter in our solar system. Moreover, a determination of the sizes of the smallest stars provides indirect, crucial information about the behaviour of matter under extreme conditions [5]. Until recently, very few observations had been made and little was known about low-mass stars. At this moment, exact values of the radii are known only for four stars with masses less than one-third of the mass of the Sun (cf. ESO PR 22/02 for measurements made with the Very Large Telescope Interferometer) and none at all for masses below one-eighth of a solar mass. This situation is now changing dramatically. Indeed, observations with the Very Large Telescope have so far led to the discovery of seven new eclipsing binaries, that harbour stars with masses below one-third the mass of the Sun. This new set of observations thus almost triples the number of low-mass stars for which precise radii and masses are known. And even better - one of these stars now turns out to be the smallest known! Planet-Sized Stars ESO PR Photo 06a/05 ESO PR Photo 06a/05 Brightness "Dip" and Velocity Variations of OGLE-TR-122 [Preview - JPEG: 400 x 474 pix - 33k] [Normal - JPEG: 800 x 948 pix - 176k] Caption: The top panel of ESO PR Photo 06a/05 shows the brightness dip of OGLE-TR-122 as measured by OGLE. The signal from the star is reduced by 1.5% for a little more than 3 hours. This is the probable indication that an object passed in front of the star. The bottom panel presents the velocity variations of the star. They were determined with the FLAMES instrument on the VLT. The orbital solution fitting the data is also shown as the solid line. These measurements indicate the presence of a low-mass stellar companion to OGLE-TR-122. ESO PR Photo 06b/05 ESO PR Photo 06b/05 Properties of Low-Mass Stars and Planets [Preview - JPEG: 400 x 464 pix - 23k] [Normal - JPEG: 800 x 928 pix - 130k] Caption: ESO PR Photo 06b/05 illustrates the properties of low-mass stars and planets, expressed in solar units. The newly determined, precise values of the mass and radius of OGLE-TR-122b are indicated as the red dot. The blue symbols are values for low-mass stars, while the black symbols on the left represent exoplanets. Note that the "hot Jupiters" - exoplanets orbiting very close to their host star - are larger than OGLE-TR-122b. The various lines represent theoretical models from G. Chabrier, I. Baraffe and colleagues, showing a good agreement between theory and observations. The newly found stellar gnome is the companion of OGLE-TR-122, a rather remote star in the Milky Way galaxy, seen in the direction of the southern constellation Carina. The OGLE programme revealed that OGLE-TR-122 experiences a 1.5 per cent brightness dip once every 7 days 6 hours and 27 minutes, each time lasting just over 3 hours (about 188 min). The FLAMES/UVES measurements, made during 6 nights in March 2004, reveal radial velocity variations of this period with an amplitude of about 20 km/s. This is the clear signature of a very low-mass star, close to the Hydrogen-burning limit, orbiting OGLE-TR-122. This companion received the name OGLE-TR-122b. As Franois Bouchy of the Observatoire Astronomique Marseille Provence (France) explains: "Combined with the information collected by OGLE, our spectroscopic data now allow us to determine the nature of the more massive star in the system, which appears to be solar-like". This information can then be used to determine the mass and radius of the much smaller companion OGLE-TR-122b. Indeed, the depth (brightness decrease) of the transit gives a direct estimate of the ratio between the radii of the two stars, and the spectroscopic orbit provides a unique value of the mass of the companion, once the mass of the larger star is known. The astronomers find that OGLE-TR-122b weighs one-eleventh of the mass of the Sun and has a diameter that is only one-eighth of the solar one. Thus, although the star is still 96 times as massive as Jupiter, it is only 16% larger than this giant planet! A Dense Star "Imagine that you add 95 times its own mass to Jupiter and nevertheless end up with a star that is only slightly larger", suggests Claudio Melo from ESO and member of the team of astronomers who made the study. "The object just shrinks to make room for the additional matter, becoming more and more dense." The density of such a star is more than 50 times the density of the Sun. "This result shows the existence of stars that look strikingly like planets, even from close by", emphasizes Frederic Pont of the Geneva Observatory (Switzerland). "Isn't it strange to imagine that even if we were to receive images from a future space probe approaching such an object at close range, it wouldn't be easy to discern whether it is a star or a planet?" As all stars, OGLE-TR-122b produces indeed energy in its interior by means of nuclear reactions. However, because of its low mass, this internal energy production is very small, especially compared to the energy produced by its solar-like companion star. Not less striking is the fact that exoplanets which are orbiting very close to their host star, the so-called "hot Jupiters", have radii which may be larger than the newly found star. The radius of exoplanet HD209458b, for example, is about 30% larger than that of Jupiter. It is thus substantially larger than OGLE-TR-122b! Masqueraders ESO PR Photo 06c/05 ESO PR Photo 06c/05 Comparison Between OGLE-TR-122b, Jupiter and the Sun [Preview - JPEG: 400 x 598 pix - 30k] [Normal - JPEG: 800 x 1196 pix - 350k] [HiRes - JPEG: 5000 x 3344 pix - 2.2M] Caption: ESO PR Photo 06c/05 is a comparison between the newly found low-mass star OGLE-TR-122b and the Sun and Jupiter. OGLE-TR-122b, while still 96 times as massive as Jupiter, is only 16% larger than this giant planet. It weighs 1/11th the mass of the Sun and has 1/8th of its diameter. (credits: Sun image: SOHO/ESA; Jupiter: Cassini/NASA/JPL/University of Arizona/ESA) This discovery also has profound implications for the ongoing search for exoplanets. These observations clearly demonstrate that some stellar objects can produce precisely the same photometric signals (brightness changes) as transiting Jupiter-like planets [6]. What's more, the present study has shown that such stars are not rare. Stars like OGLE-TR-122b are thus masqueraders among giant exoplanets and the outermost care is required to differentiate them from their planetary cousins. Uncovering such small stars can only be done with follow-up high-resolution spectral measurements with the largest telescopes. There is more work ahead for the Very Large Telescope! More information The information contained in this press release is based on a research article to appear soon as a Letter to the Editor in the leading research journal "Astronomy & Astrophysics" ("A planet-sized transiting star around OGLE-TR-122" by F. Pont et al.). The paper is available in PDF format on the A&A website.

  15. A Review in Mixed Chemistry of Low Mass Evolved Stars

    NASA Astrophysics Data System (ADS)

    Guzman-Ramirez, L.

    2015-12-01

    During the late stages of their evolution, Sun-like stars bring the products of nuclear burning to the surface. Although there is a chemical dichotomy between oxygen-rich and carbon-rich evolved stars, the dredge-up itself has never been directly observed. In the last three decades, however, a few stars have been shown to display both carbon- and oxygen-rich material in their circumstellar envelopes. These phenomena is seen in both Galactic Disk and Bulge planetary nebulae. For the Galactic Disk objects the mixed chemistry phenomenon is best explained through a recent dredge-up of carbon produced by nucleosynthesis inside the star during the Asymptotic Giant Branch that changed the surface chemistry of the star. On the contrary, we conclude that the mixed chemistry phenomenon occurring in the Galactic Bulge planetary nebulae is best explained through hydrocarbon chemistry in an ultraviolet (UV)-irradiated, dense torus.

  16. Data Characterization Using Artificial-Star Tests: Performance Evaluation

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

    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.

  17. Star accretion onto supermassive black holes in axisymmetric galactic nuclei

    NASA Astrophysics Data System (ADS)

    Zhong, Shiyan; Berczik, Peter; Spurzem, Rainer

    2016-02-01

    Tidal Disruption (TD) of stars by supermassive central black holes from dense rotating star clusters is modeled by high-accuracy direct N-body simulation. We study the time evolution of the stellar tidal disruption rate and the origin of tidally disrupted stars. Compared with that in spherical systems, we found a higher TD rate in axisymmetric systems. The enhancement can be explained by an enlarged loss-cone in phase space which is raised from the fact that total angular momentum J is not conserved. As in the case of spherical systems, the distribution of the last apocenter distance of tidally accreted stars peaks at the classical critical radius. However, the angular distribution of the origin of the accreted stars reveals bimodal features. We show that the bimodal structure can be explained by the presence of two families of regular orbits, namely short axis tube and saucer orbits.

  18. IR Spectroscopy of PANHs in Dense Clouds

    NASA Astrophysics Data System (ADS)

    Allamandola, Louis; Mattioda, Andrew; Sandford, Scott

    2008-03-01

    Interstellar PAHs are likely to be frozen into ice mantles on dust grains in dense clouds. These PAHs will produce IR absorption bands, not emission features. A couple of very weak absorption features in ground based spectra of a few objects in dense clouds may be due to PAHs. It is now thought that aromatic molecules in which N atoms are substituted for a few of the C atoms in a PAH's hexagonal skeletal network (PANHs) may well be as abundant and ubiquitous throughout the interstellar medium as PAHs. Spaceborne observations in the 5 to 8 um region, the region in which PAH spectroscopy is rich, reveal unidentified new bands and significant variation from object to object. It is not possible to analyze these observations because lab spectra of PANHs and PAHs condensed in realistic interstellar ice analogs are lacking. This lab data is necessary to interpret observations because, in ice mantles, the surrounding molecules affect PANH and PAH IR band positions, widths, profiles, and intrinsic strengths. Further, PAHs (and PANHs?) are readily ionized in pure H2O ice, further altering the spectrum. This proposal starts to address this situation by studying the IR spectra of PANHs frozen in laboratory ice analogs that reflect the composition of the interstellar ices observed in dense clouds. Thanks to Spitzer Cycle-4 support, we are now measuring the spectra of PAHs in interstellar ice analogs to provide laboratory spectra that can be used to interpret IR observations. Here we propose to extend this work to PANHs. We will measure the spectra of these interstellar ice analogs containing PANHs before and after ionization and determine the band strengths of neutral and ionized PANHs in these ices. This will enable a quantitative assessment of the role that PANHs can play in the 5-8 um spectrum of dense clouds and address the following two fundamental questions associated with dense cloud spectroscopy and chemistry: 1- Can PANHs be detected in dense clouds? 2- Are PANH ions components of interstellar ice?

  19. Synthesis and supramolecular assembly of biomimetic polymers

    NASA Astrophysics Data System (ADS)

    Marciel, Amanda Brittany

    A grand challenge in materials chemistry is the synthesis of macromolecules and polymers with precise shapes and architectures. Polymer microstructure and architecture strongly affect the resulting functionality of advanced materials, yet understanding the static and dynamic properties of these complex macromolecules in bulk has been difficult due to their inherit polydispersity. Single molecule studies have provided a wealth of information on linear flexible and semi-flexible polymers in dilute solutions. However, few investigations have focused on industrially relevant complex topologies (e.g., star, comb, hyperbranched polymers) in industrially relevant solution conditions (e.g., semi-dilute, concentrated). Therefore, from this perspective there is a strong need to synthesize precision complex architectures for bulk studies as well as complex architectures compatible with current single molecule techniques to study static and dynamic polymer properties. In this way, we developed a hybrid synthetic strategy to produce branched polymer architectures based on chemically modified DNA. Overall, this approach enables control of backbone length and flexibility, as well as branch grafting density and chemical identity. We utilized a two-step scheme based on enzymatic incorporation of non-natural nucleotides containing bioorthogonal dibenzocyclooctyne (DBCO) functional groups along the main polymer backbone, followed by copper-free "click" chemistry to graft synthetic polymer branches or oligonucleotide branches to the DNA backbone, thereby allowing for the synthesis of a variety of polymer architectures, including three-arm stars, H-polymers, graft block copolymers, and comb polymers for materials assembly and single molecule studies. Bulk materials properties are also affected by industrial processing conditions that alter polymer morphology. Therefore, in an alternative strategy we developed a microfluidic-based approach to assemble highly aligned synthetic oligopeptides nanostructures using microscale extensional flows. This strategy enabled reproducible, reliable fabrication of aligned hierarchical constructs that do not form spontaneously in solution. In this way, fluidic-directed assembly of supramolecular structures allows for unprecedented manipulation at the nano- and mesoscale, which has the potential to provide rapid and efficient control of functional materials properties.

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

    PubMed Central

    Guo, Guangqing; Fan, Yuwei

    2011-01-01

    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 (η–t) curve. The ZY, ZS and ZYS gel nanofibers were prepared using a special reactive electrospinning device under the conditions near the gel point. The as-prepared gel nanofibers had diameters between 200 and 400 nm. Dense (nonporous) ceramic nanofibers of zirconia-yttria (96/4), zirconia-silica (80/20) and zirconia-yttria-silica (76.8/3.2/20) with diameter of 100–300 nm were obtained by subsequent calcinations at different temperatures. The gel and ceramic nanofibers obtained were characterized by scanning electron microscope (SEM), high-resolution field-emission scanning electron microscope (FE-SEM), thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), Fourier transform infrared spectrometer (FT-IR), and X-ray diffraction (XRD). SEM micrograph revealed that ceramic ZY nanofibers had grained structure, while ceramic ZS and ZYS nanofibers had smooth surfaces, both showing no visible porosity under FE-SEM. Complete removal of the polymer PEO was confirmed by TGA/DSC and FT-IR. The formation of tetragonal phase of zirconia and amorphous silica was proved by XRD. In conclusion, dense zirconia-based ceramic nanofibers can be fabricated using the new reactive sol–gel electrospinning technology with minimum organic polymer additives. PMID:21133090

  1. Polymer Electronics: Power from Polymers

    SciTech Connect

    Venkataraman, D.; Russell, Thomas P.

    2012-06-19

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

  2. Spitzer Digs Up Hidden Stars

    NASA Technical Reports Server (NTRS)

    2007-01-01

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

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

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

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

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

  3. Galaxies in most dense environments at z ~ 1.4

    NASA Astrophysics Data System (ADS)

    Strazzullo, V.

    2015-03-01

    The X-ray luminous system XMMU J2235-2557 at z~1.4 is among the most massive of the very distant galaxy clusters, and remains a unique laboratory to observe environment-biased galaxy evolution already 9 Gyr ago (Lidman et al. 2008, Rosati et al. 2009, Strazzullo et al. 2010). At a cosmic time when cluster cores start showing evidence of a still active galaxy population, star-forming (M>1010 M ⊙) galaxies in XMMU J2235-2557 are typically located beyond ~250kpc from the cluster center, with the cluster core already effectively quenched and dominated by massive galaxies on a tight red sequence, showing early-type spectral features and bulge-dominated morphologies. While masses and stellar populations of these red-sequence galaxies suggest that they have largely completed their formation, their size is found to be typically smaller that similarly massive early-type galaxies in the local Universe, in agreement with many high-redshift studies. This would leave room for later evolution, likely through non-secular processes, changing their structure to match their local counterparts. On the other hand, uncertainties and biases in the determination of masses and sizes, as well as in the local mass-size relation, and the possible effect of progenitor bias, still hamper a final conclusion on the actual relevance of size evolution for early-type galaxies in this dense high-redshift environment.

  4. ICES IN THE QUIESCENT IC 5146 DENSE CLOUD

    SciTech Connect

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

    2011-04-10

    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.

  5. The kinetic chemistry of dense interstellar clouds

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

  6. Dense Deposit Disease and C3 Glomerulopathy

    PubMed Central

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

    2013-01-01

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

  7. Cold dense plasma observed at the magnetopause

    NASA Astrophysics Data System (ADS)

    Simunek, Jiri; Safrankova, Jana; Nemecek, Zdenek; Granko, Galyna

    2013-04-01

    The Low-latitude boundary layer (LLBL) is generally formed by lobe reconnection during periods of the northward IMF orientation, thus it would be populated with accelerated magnetosheath plasma. However, quite often we can observe plasmaspheric plumes containing cold and dense ions of the ionospheric origin in the vicinity of the magnetopause. In situ observations by the Themis spacecraft during their "string-of-pearls" configuration provide us with the comprehensive data set for a detail analysis of the LLBL structure and sources of the LLBL plasma. The contribution deals with a detail analysis of the LLBL feeding with these populations and with the role of cold dense ions in the formation of magnetopause layers. We have found that the presence of the plume plasma influences the pressure balance at the magnetopause and thus the magnetopause can be found far away from its nominal location.

  8. STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2013-08-20

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

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

    NASA Astrophysics Data System (ADS)

    Storm, Shaye; Mundy, Lee

    2014-07-01

    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.

  10. Properties of holographic mesons on dense medium

    NASA Astrophysics Data System (ADS)

    Lee, Bum-Hoon; Park, Chanyong; Nam, Siyoung

    2015-05-01

    We study the energy dispersions of holographic light mesons and their decay constants on dense nuclear medium. As the spatial momenta of mesons along the boundary direction increase, both observables of the mesons not only increase but also split according to the isospin charges. The decay constant of the negative meson is more large than that of the positive meson of the same type due to the chemical potentials of the background nucleons.

  11. Structures for dense, crack free thin films

    DOEpatents

    Jacobson, Craig P.; Visco, Steven J.; De Jonghe, Lutgard C.

    2011-03-08

    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.

  12. Shear dispersion in dense granular flows

    SciTech Connect

    Christov, Ivan C.; Stone, Howard A.

    2014-04-18

    We formulate and solve a model problem of dispersion of dense granular materials in rapid shear flow down an incline. The effective dispersivity of the depth-averaged concentration of the dispersing powder is shown to vary as the Pclet number squared, as in classical TaylorAris dispersion of molecular solutes. An extension to generic shear profiles is presented, and possible applications to industrial and geological granular flows are noted.

  13. Oxygen ion-conducting dense ceramic

    DOEpatents

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

    1998-01-01

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

  14. Computer codes for dispersion of dense gas

    SciTech Connect

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

    1982-02-01

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

  15. Shear dispersion in dense granular flows

    DOE PAGESBeta

    Christov, Ivan C.; Stone, Howard A.

    2014-04-18

    We formulate and solve a model problem of dispersion of dense granular materials in rapid shear flow down an incline. The effective dispersivity of the depth-averaged concentration of the dispersing powder is shown to vary as the Péclet number squared, as in classical Taylor–Aris dispersion of molecular solutes. An extension to generic shear profiles is presented, and possible applications to industrial and geological granular flows are noted.

  16. Resistivity saturation in warm dense matter.

    PubMed

    Faussurier, Grald; Blancard, Christophe

    2015-01-01

    Electrical resistivity is shown to saturate in solid-density aluminum in the warm dense matter regime. Calculations are done using the average-atom model SCAALP and the finite-temperature Ziman-Evans formula for electrical resistivity. The mean free path is estimated using the Drude law. This mean free path is shown to present a minimum of the order of the interatomic spacing. PMID:25679721

  17. Resistivity saturation in warm dense matter

    NASA Astrophysics Data System (ADS)

    Faussurier, Grald; Blancard, Christophe

    2015-01-01

    Electrical resistivity is shown to saturate in solid-density aluminum in the warm dense matter regime. Calculations are done using the average-atom model SCAALP and the finite-temperature Ziman-Evans formula for electrical resistivity. The mean free path is estimated using the Drude law. This mean free path is shown to present a minimum of the order of the interatomic spacing.

  18. Electrical conductivity of an arbitrarily dense plasma

    SciTech Connect

    Rinker, G.

    1984-01-01

    This is the first of a series of papers concerning the electrical and thermal transport properties of dense plasmas. Temperatures and densities considered range from zero to 2/sup 13/ eV and 2/sup -13/ to 2/sup 13/ times compressed. In the present work we describe theoretical calculations of electrical conductivities using the t-matrix version of the Ziman theory with various self-consistent ionic potential models. The theoretical basis is described and illustrative results are given.

  19. Computational electromagnetics and parallel dense matrix computations

    SciTech Connect

    Forsman, K.; Kettunen, L.; Gropp, W.; Levine, D.

    1995-06-01

    We present computational results using CORAL, a parallel, three-dimensional, nonlinear magnetostatic code based on a volume integral equation formulation. A key feature of CORAL is the ability to solve, in parallel, the large, dense systems of linear equations that are inherent in the use of integral equation methods. Using the Chameleon and PSLES libraries ensures portability and access to the latest linear algebra solution technology.

  20. Computational electromagnetics and parallel dense matrix computations

    SciTech Connect

    Forsman, K.; Kettunen, L.; Gropp, W.

    1995-12-01

    We present computational results using CORAL, a parallel, three-dimensional, nonlinear magnetostatic code based on a volume integral equation formulation. A key feature of CORAL is the ability to solve, in parallel, the large, dense systems of linear equations that are inherent in the use of integral equation methods. Using the Chameleon and PSLES libraries ensures portability and access to the latest linear algebra solution technology.

  1. Gas dynamics in massive dense cores in Cygnus-X

    NASA Astrophysics Data System (ADS)

    Csengeri, T.; Bontemps, S.; Schneider, N.; Motte, F.; Dib, S.

    2011-03-01

    Context. The physical conditions in massive dense cores (MDCs) that form massive stars and clusters, are not well constrained. Few observations have been made to confront the theories. An extensive study has started of the most massive and youngest cores in the Cygnus-X molecular complex, whose first results have uncovered exceptional fragmentation properties in a sample of five cores where individual massive protostars have been recognized. Aims: We study the kinematic properties of dense gas surrounding massive protostars in these five cores to investigate whether turbulent support plays a major role in stabilizing the whole core against a rapid fragmentation into Jeans-mass objects. The observed kinematics could indicate a high level of dynamics suggesting that the cores are actually not in equilibrium and dynamical processes could be the main driver of the build up of the final stellar masses. Methods: We present IRAM 30m single-dish (H13CO+ and HCO+) data and IRAM Plateau de Bure Interferometer high angular-resolution observations of dense gas tracers (H13CO+ and H13CN) to reveal the kinematics of molecular gas on scales from 0.03 to 0.1 pc. Results: Using radiative transfer modeling, we show that the H13CO+ abundance drops within the envelopes of massive protostars and traces the bulk of material surrounding the protostars instead of their inner envelopes. H13CN shows a better correspondence with the peak of the continuum emission, possibly because of abundance anomalies and specific chemistry in the close vicinity of massive protostars. Analyzing the line-widths, we show that the observed line-dispersion of H13CO+ on the scale of MDCs is smaller than expected from the quasi-static, turbulent-core model. On large-scales, global organized bulk motions are identified for three of the MDCs. On small-scales, several spectral components are identified in all MDCs showing filamentary structures and intrinsic velocity gradients across the continuum peaks. The dynamics of these flows show diversity across the sample, which we link to the specific fragmentation properties of the MDCs. Altogether this is indicative of different initial conditions in CygX-N3 and -N63 compared to CygX-N12, -N48 and -N53, which may represent different evolutionary stages. Conclusions: No clear evidence is found of a turbulence-regulated, equilibrium scenario within the sample of MDCs. We propose a picture in which MDCs are not in equilibrium and their dynamics is governed by small-scale converging flows, which may initiate star-formation via their shears. We suggest that dynamical processes are linked to the formation of proto-clusters and high-mass protostars. The H13CO+ and H13CN data cubes obtained with the PdBI (associated with Fig. 4) are only available as FITS files at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A135

  2. Multishock Compression Properties of Warm Dense Argon.

    PubMed

    Zheng, Jun; Chen, Qifeng; Yunjun, Gu; Li, Zhiguo; Shen, Zhijun

    2015-01-01

    Warm dense argon was generated by a shock reverberation technique. The diagnostics of warm dense argon were performed by a multichannel optical pyrometer and a velocity interferometer system. The equations of state in the pressure-density range of 20-150?GPa and 1.9-5.3?g/cm(3) from the first- to fourth-shock compression were presented. The single-shock temperatures in the range of 17.2-23.4?kK were obtained from the spectral radiance. Experimental results indicates that multiple shock-compression ratio (?i?=??i/?0) is greatly enhanced from 3.3 to 8.8, where ?0 is the initial density of argon and ?i (i?=?1, 2, 3, 4) is the compressed density from first to fourth shock, respectively. For the relative compression ratio (?i'?=??i/?i-1), an interesting finding is that a turning point occurs at the second shocked states under the conditions of different experiments, and ?i' increases with pressure in lower density regime and reversely decreases with pressure in higher density regime. The evolution of the compression ratio is controlled by the excitation of internal degrees of freedom, which increase the compression, and by the interaction effects between particles that reduce it. A temperature-density plot shows that current multishock compression states of argon have distributed into warm dense regime. PMID:26515505

  3. Automated building extraction using dense elevation matrices

    NASA Astrophysics Data System (ADS)

    Bendett, A. A.; Rauhala, Urho A.; Pearson, James J.

    1997-02-01

    The identification and measurement of buildings in imagery is important to a number of applications including cartography, modeling and simulation, and weapon targeting. Extracting large numbers of buildings manually can be time- consuming and expensive, so the automation of the process is highly desirable. This paper describes and demonstrates such an automated process for extracting rectilinear buildings from stereo imagery. The first step is the generation of a dense elevation matrix registered to the imagery. In the examples shown, this was accomplished using global minimum residual matching (GMRM). GMRM automatically removes y- parallax from the stereo imagery and produces a dense matrix of x-parallax values which are proportional to the local elevation, and, of course, registered to the imagery. The second step is to form a joint probability distribution of the image gray levels and the corresponding height values from the elevation matrix. Based on the peaks of that distribution, the area of interest is segmented into feature and non-feature areas. The feature areas are further refined using length, width and height constraints to yield promising building hypotheses with their corresponding vertices. The gray shade image is used in the third step to verify the hypotheses and to determine precise edge locations corresponding to the approximate vertices and satisfying appropriate orthogonality constraints. Examples of successful application of this process to imagery are presented, and extensions involving the use of dense elevation matrices from other sources are possible.

  4. Multishock Compression Properties of Warm Dense Argon

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Chen, Qifeng; Yunjun, Gu; Li, Zhiguo; Shen, Zhijun

    2015-10-01

    Warm dense argon was generated by a shock reverberation technique. The diagnostics of warm dense argon were performed by a multichannel optical pyrometer and a velocity interferometer system. The equations of state in the pressure-density range of 20150?GPa and 1.95.3?g/cm3 from the first- to fourth-shock compression were presented. The single-shock temperatures in the range of 17.223.4?kK were obtained from the spectral radiance. Experimental results indicates that multiple shock-compression ratio (?i?=??i/?0) is greatly enhanced from 3.3 to 8.8, where ?0 is the initial density of argon and ?i (i?=?1, 2, 3, 4) is the compressed density from first to fourth shock, respectively. For the relative compression ratio (?i?=??i/?i-1), an interesting finding is that a turning point occurs at the second shocked states under the conditions of different experiments, and ?i increases with pressure in lower density regime and reversely decreases with pressure in higher density regime. The evolution of the compression ratio is controlled by the excitation of internal degrees of freedom, which increase the compression, and by the interaction effects between particles that reduce it. A temperature-density plot shows that current multishock compression states of argon have distributed into warm dense regime.

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

    NASA Astrophysics Data System (ADS)

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

    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.

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

    SciTech Connect

    Saumon, Didier; Fortney, Jonathan J; Glenzer, Siegfried H; Koenig, Michel; Brambrink, E; Militzer, Burkhard; Valencia, Diana

    2008-01-01

    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.

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

    PubMed

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

    2007-11-15

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

  8. Strange Stars : An interesting member of the compact object family

    SciTech Connect

    Bagchi, Manjari; Ray, Subharthi; Dey, Jishnu; Dey, Mira

    2008-01-10

    We have studied strange star properties both at zero temperature and at finite temperatures and searched signatures of strange stars in gamma-ray, x-ray and radio astronomy. We have a set of Equations of State (EoS) for strange quark matter (SQM) and solving the TOV equations, we get the structure of strange stars. The maximum mass for a strange star decreases with the increase of temperature, because at high temperatures, the EoS become softer. One important aspect of strange star is that, surface tension depends on the size and structure of the star and is significantly larger than the conventional values. Moment of inertia is another important parameter for compact stars as by comparing theoretical values with observed estimate, it is possible to constrain the dense matter Equation of State. We hope that this approach will help us to decide whether the members of the double pulsar system PSR J0737-3039 are neutron stars or strange stars.

  9. GPU-enabled particle-particle particle-tree scheme for simulating dense stellar cluster system

    NASA Astrophysics Data System (ADS)

    Iwasawa, Masaki; Portegies Zwart, Simon; Makino, Junichiro

    2015-07-01

    We describe the implementation and performance of the (Particle-Particle Particle-Tree) scheme for simulating dense stellar systems. In , the force experienced by a particle is split into short-range and long-range contributions. Short-range forces are evaluated by direct summation and integrated with the fourth order Hermite predictor-corrector method with the block timesteps. For long-range forces, we use a combination of the Barnes-Hut tree code and the leapfrog integrator. The tree part of our simulation environment is accelerated using graphical processing units (GPU), whereas the direct summation is carried out on the host CPU. Our code gives excellent performance and accuracy for star cluster simulations with a large number of particles even when the core size of the star cluster is small.

  10. O stars and Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  11. Interpretations of Polymer-Polymer Miscibility.

    ERIC Educational Resources Information Center

    Olabisi, Olagoke

    1981-01-01

    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)

  12. Effects of strong and electromagnetic correlations on neutrino interactions in dense matter

    SciTech Connect

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

    1999-05-01

    An extensive study of the effects of correlations on both charged and neutral current weak interaction rates in dense matter is performed. Both strong and electromagnetic correlations are considered. The propagation of particle-hole interactions in the medium plays an important role in determining the neutrino mean free paths. The effects due to Pauli blocking and density, spin, and isospin correlations in the medium significantly reduce the neutrino cross sections. As a result of the lack of experimental information at high density, these correlations are necessarily model dependent. For example, spin correlations in nonrelativistic models are found to lead to larger suppressions of neutrino cross sections compared to those of relativistic models. This is due to the tendency of the nonrelativistic models to develop spin instabilities. Notwithstanding the above caveats, and the differences between nonrelativistic and relativistic approaches such as the spin- and isospin-dependent interactions and the nucleon effective masses, suppressions of order 2{endash}3, relative to the case in which correlations are ignored, are obtained. Neutrino interactions in dense matter are especially important for supernova and early neutron star evolution calculations. The effects of correlations for protoneutron star evolution are calculated. Large effects on the internal thermodynamic properties of protoneutron stars, such as the temperature, are found. These translate into significant early enhancements in the emitted neutrino energies and fluxes, especially after a few seconds. At late times, beyond about 10 s, the emitted neutrino fluxes decrease more rapidly compared to simulations without the effects of correlations, due to the more rapid onset of neutrino transparency in the protoneutron star. {copyright} {ital 1999} {ital The American Physical Society}

  13. DISPERSION OF DENSE GAS RELEASES IN A WIND TUNNEL

    EPA Science Inventory

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

  14. Lifestyles of the Stars.

    ERIC Educational Resources Information Center

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

  15. Egyptian "Star Clocks"

    NASA Astrophysics Data System (ADS)

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  16. Extragalactic Star Clusters: the Resolved Star Approach

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  17. THE DEPENDENCE OF STAR FORMATION EFFICIENCY ON GAS SURFACE DENSITY

    SciTech Connect

    Burkert, Andreas; Hartmann, Lee E-mail: lhartm@umich.edu

    2013-08-10

    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.

  18. Linear viscoelasticity of branched polymer melts

    NASA Astrophysics Data System (ADS)

    Shanbhag, Sachin Ashok

    Standard analytical techniques like chromatography and spectrometry are not sensitive enough to resolve architectural details in branched polymer melts such as metallocene-catalyzed polyethylene to industrially acceptable levels. This has led to the belief that linear rheology, which is highly responsive to subtle differences in branching structure, can be employed as an analytical technique. A major difficulty hindering the application of rheology as an analytical tool has been the inability of the current analytical theory for branched polymers, which is based on the idea of "dynamic dilution", to describe the physics of branch point motion. We examine shortcomings of this theory, including the problem of branch point motion, using three case studies. We use a simulation model called the dual slip link model in which entanglements between chains are modeled as slip links that couple the dynamics of pairs of chains. First, in the late-time relaxation of symmetric stars we investigate the breakdown of the molecular picture implied by the "dynamic dilution" theory, by monitoring the dielectric and stress relaxation functions. We present a terminal relaxation model using the slip link model that offers a better description of the late-time dynamics. Next, we address the failure of the analytical theory to predict the anomalously slow viscoelastic response of asymmetric stars. We need to distinguish between the first-passage time and complete retraction time of the asymmetric arm in order to correctly set the timescale for the diffusion of the branch point. Although the slip link model fails for long arms, where it over-predicts the relaxation time, it points out that the timescale which sets the frequency of the branch point motion should be larger than the first-passage time of an arm. Finally, we study the effects of polydispersity on stars and H-polymers and find that the viscoelasticity of star polymers is insensitive to moderate amounts of poly-dispersity. However, H-polymers are extremely sensitive, especially to polydispersity in the arms. We submit that the relaxation of H-polymers is greatly accelerated if any one of the four arms is short. We suggest the experimental synthesis of asymmetric H-polymers in order to test this hypothesis.

  19. Spectroscopic survey of emission-line stars - I. B[e] stars

    NASA Astrophysics Data System (ADS)

    Aret, A.; Kraus, M.; Šlechta, M.

    2016-02-01

    Emission-line stars are typically surrounded by dense circumstellar material, often in form of rings or disc-like structures. Line emission from forbidden transitions trace a diversity of density and temperature regimes. Of particular interest are the forbidden lines of [O I] λλ6300, 6364 and [Ca II] λλ7291, 7324. They arise in complementary, high-density environments, such as the inner-disc regions around B[e] supergiants. To study physical conditions traced by these lines and to investigate how common they are, we initiated a survey of emission-line stars. Here, we focus on a sample of nine B[e] stars in different evolutionary phases. Emission of the [O I] lines is one of the characteristics of B[e] stars. We find that four of the objects display [Ca II] line emission: for the B[e] supergiants V1478 Cyg and 3 Pup, the kinematics obtained from the [O I] and [Ca II] line profiles agrees with a Keplerian rotating disc scenario; the forbidden lines of the compact planetary nebula OY Gem display no kinematical broadening beyond spectral resolution; the luminous blue variable candidate V1429 Aql shows no [O I] lines, but the profile of its [Ca II] lines suggests that the emission originates in its hot, ionized circumbinary disc. As none of the B[e] stars of lower mass displays [Ca II] line emission, we conclude that these lines are more likely observable in massive stars with dense discs, supporting and strengthening the suggestion that their appearance requires high-density environments.

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

    NASA Astrophysics Data System (ADS)

    Nicholson, Marjorie Anne

    1991-05-01

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

  1. Grain Growth and Silicates in Dense Clouds

    NASA Technical Reports Server (NTRS)

    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

    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).

  2. Multishock Compression Properties of Warm Dense Argon

    PubMed Central

    Zheng, Jun; Chen, Qifeng; Yunjun, Gu; Li, Zhiguo; Shen, Zhijun

    2015-01-01

    Warm dense argon was generated by a shock reverberation technique. The diagnostics of warm dense argon were performed by a multichannel optical pyrometer and a velocity interferometer system. The equations of state in the pressure-density range of 20–150 GPa and 1.9–5.3 g/cm3 from the first- to fourth-shock compression were presented. The single-shock temperatures in the range of 17.2–23.4 kK were obtained from the spectral radiance. Experimental results indicates that multiple shock-compression ratio (ηi = ρi/ρ0) is greatly enhanced from 3.3 to 8.8, where ρ0 is the initial density of argon and ρi (i = 1, 2, 3, 4) is the compressed density from first to fourth shock, respectively. For the relative compression ratio (ηi’ = ρi/ρi-1), an interesting finding is that a turning point occurs at the second shocked states under the conditions of different experiments, and ηi’ increases with pressure in lower density regime and reversely decreases with pressure in higher density regime. The evolution of the compression ratio is controlled by the excitation of internal degrees of freedom, which increase the compression, and by the interaction effects between particles that reduce it. A temperature-density plot shows that current multishock compression states of argon have distributed into warm dense regime. PMID:26515505

  3. Neutron Stars and NuSTAR

    NASA Astrophysics Data System (ADS)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses among all classes of neutron star binaries. Intrigued by this diversity - which points to diverse birth masses - we undertook a systematic survey to measure the masses of neutron stars in nine high-mass X-ray binaries. In this thesis, I present results from this ongoing project. While neutron stars formed the primary focus of my work, I also explored other topics in compact objects. Appendix A describes the discovery and complete characterization of a 1RXS J173006.4+033813, a polar cataclysmic variable. Appendix B describes the discovery of a diamond planet orbiting a millisecond pulsar, and our search for its optical counterpart.

  4. Phase boundary of hot dense fluid hydrogen

    NASA Astrophysics Data System (ADS)

    Ohta, Kenji; Ichimaru, Kota; Einaga, Mari; Kawaguchi, Sho; Shimizu, Katsuya; Matsuoka, Takahiro; Hirao, Naohisa; Ohishi, Yasuo

    2015-11-01

    We investigated the phase transformation of hot dense fluid hydrogen using static high-pressure laser-heating experiments in a laser-heated diamond anvil cell. The results show anomalies in the heating efficiency that are likely to be attributed to the phase transition from a diatomic to monoatomic fluid hydrogen (plasma phase transition) in the pressure range between 82 and 106?GPa. This study imposes tighter constraints on the location of the hydrogen plasma phase transition boundary and suggests higher critical point than that predicted by the theoretical calculations.

  5. Phase boundary of hot dense fluid hydrogen

    PubMed Central

    Ohta, Kenji; Ichimaru, Kota; Einaga, Mari; Kawaguchi, Sho; Shimizu, Katsuya; Matsuoka, Takahiro; Hirao, Naohisa; Ohishi, Yasuo

    2015-01-01

    We investigated the phase transformation of hot dense fluid hydrogen using static high-pressure laser-heating experiments in a laser-heated diamond anvil cell. The results show anomalies in the heating efficiency that are likely to be attributed to the phase transition from a diatomic to monoatomic fluid hydrogen (plasma phase transition) in the pressure range between 82 and 106 GPa. This study imposes tighter constraints on the location of the hydrogen plasma phase transition boundary and suggests higher critical point than that predicted by the theoretical calculations. PMID:26548442

  6. Dense optical-electrical interface module

    SciTech Connect

    Paul Chang

    2000-12-21

    The DOIM (Dense Optical-electrical Interface Modules) is a custom-designed optical data transmission module employed in the upgrade of Silicon Vertex Detector of CDF experiment at Fermilab. Each DOIM module consists of a transmitter (TX) converting electrical differential input signals to optical outputs, a middle segment of jacketed fiber ribbon cable, and a receiver (RX) which senses the light inputs and converts them back to electrical signals. The targeted operational frequency is 53 MHz, and higher rate is achievable. This article outlines the design goals, implementation methods, production test results, and radiation hardness tests of these modules.

  7. Phase boundary of hot dense fluid hydrogen.

    PubMed

    Ohta, Kenji; Ichimaru, Kota; Einaga, Mari; Kawaguchi, Sho; Shimizu, Katsuya; Matsuoka, Takahiro; Hirao, Naohisa; Ohishi, Yasuo

    2015-01-01

    We investigated the phase transformation of hot dense fluid hydrogen using static high-pressure laser-heating experiments in a laser-heated diamond anvil cell. The results show anomalies in the heating efficiency that are likely to be attributed to the phase transition from a diatomic to monoatomic fluid hydrogen (plasma phase transition) in the pressure range between 82 and 106?GPa. This study imposes tighter constraints on the location of the hydrogen plasma phase transition boundary and suggests higher critical point than that predicted by the theoretical calculations. PMID:26548442

  8. Ionization rate coefficients in warm dense plasmas.

    PubMed

    Aslanyan, V; Tallents, G J

    2015-06-01

    We recast the atomic processes in a warm, dense plasma using Fermi-Dirac statistics and compare them to the rates of the usual Maxwell-Boltzmann approach of many collisional-radiative models. Population calculations show insignificant differences to calculations assuming nondegenerate free electrons of plasmas at solid density close to local thermodynamic equilibrium, but show departures in average ionization in the presence of strong photoionization. For example, we show that electron degeneracy affects the evolution of plasmas created by ultraviolet free electron laser interaction with solid targets. PMID:26172807

  9. Molecular dynamics simulations of dense plasmas

    SciTech Connect

    Collins, L.A.; Kress, J.D.; Kwon, I.; Lynch, D.L.; Troullier, N.

    1993-12-31

    We have performed quantum molecular dynamics simulations of hot, dense plasmas of hydrogen over a range of temperatures(0.1-5eV) and densities(0.0625-5g/cc). We determine the forces quantum mechanically from density functional, extended Huckel, and tight binding techniques and move the nuclei according to the classical equations of motion. We determine pair-correlation functions, diffusion coefficients, and electrical conductivities. We find that many-body effects predominate in this regime. We begin to obtain agreement with the OCP and Thomas-Fermi models only at the higher temperatures and densities.

  10. Electrical Resistivity Measurements of Hot Dense Aluminum

    NASA Astrophysics Data System (ADS)

    Benage, J. F.; Shanahan, W. R.; Murillo, M. S.

    1999-10-01

    Electrical transport properties of dense aluminum are measured in the disordered liquidlike phase using a well-tamped, thermally equilibrated, exploding wire z pinch. Direct measurements of the electrical conductivity have been made using voltage and current measurements. Our measurements span the minimum conductivity regime, at higher densities than have been produced previously. We find that some Ziman-like theoretical predictions are in fair agreement with the data and one Ziman-like theoretical approach is in good agreement, in contrast to other experiments performed in similar regimes which indicate poor agreement with such theories.

  11. Electrical and thermal conductivities in dense plasmas

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  12. Electrical Resistivity Measurements of Hot Dense Aluminum

    SciTech Connect

    Benage, J.F.; Shanahan, W.R.; Murillo, M.S.

    1999-10-01

    Electrical transport properties of dense aluminum are measured in the disordered liquidlike phase using a well-tamped, thermally equilibrated, exploding wire {ital z} pinch. Direct measurements of the electrical conductivity have been made using voltage and current measurements. Our measurements span the minimum conductivity regime, at higher densities than have been produced previously. We find that some Ziman-like theoretical predictions are in fair agreement with the data and one Ziman-like theoretical approach is in good agreement, in contrast to other experiments performed in similar regimes which indicate poor agreement with such theories. {copyright} {ital 1999} {ital The American Physical Society }

  13. Efficient formalism for warm dense matter simulations

    NASA Astrophysics Data System (ADS)

    Cangi, Attila; Pribram-Jones, Aurora

    2015-10-01

    Simulation of warm dense matter requires computational methods that capture both quantum and classical behavior efficiently under high-temperature, high-density conditions. Currently, density functional theory molecular dynamics is used to model electrons and ions, but this method's computational cost skyrockets as temperatures and densities increase. We propose finite-temperature potential functional theory as an in-principle-exact alternative that suffers no such drawback. We derive an orbital-free free energy approximation through a coupling-constant formalism. Our density approximation and its associated free energy approximation demonstrate the method's accuracy and efficiency.

  14. Dense Electron-Positron Pair Plasma Expansion

    NASA Astrophysics Data System (ADS)

    Djebli, Mourad

    2015-10-01

    The expansion of an electron-positron plasma is studied based on quantum hydrodynamical equations for two fluids. The quasi-neutral expansion, depicted through the quantum screening distance, is investigated numerically when the annealing processes is very slow. It was found that the pair plasma behaves as a single fluid with a front expansion velocity that depends on the density and degenerate parameters. Faster expansion results from the existence of exchange-correlation potential, which is enhanced in high-density plasma. The present investigation may be useful in understanding the expansion of a dense plasma produced by the interaction between high-energy laser and solid targets.

  15. Electrical and thermal conductivities in dense plasmas

    SciTech Connect

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

    2014-09-15

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

  16. Polymer Spheulites

    NASA Astrophysics Data System (ADS)

    Lotz, Bernard

    2013-03-01

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

  17. The initial mass function of stars: evidence for uniformity in variable systems.

    PubMed

    Kroupa, Pavel

    2002-01-01

    The distribution of stellar masses that form in one star formation event in a given volume of space is called the initial mass function (IMF). The IMF has been estimated from low-mass brown dwarfs to very massive stars. Combining IMF estimates for different populations in which the stars can be observed individually unveils an extraordinary uniformity of the IMF. This general insight appears to hold for populations including present-day star formation in small molecular clouds, rich and dense massive star-clusters forming in giant clouds, through to ancient and metal-poor exotic stellar populations that may be dominated by dark matter. This apparent universality of the IMF is a challenge for star formation theory, because elementary considerations suggest that the IMF ought to systematically vary with star-forming conditions. PMID:11778039

  18. Properties of Neutron Stars in the Relativistic Mean-Field Theory

    NASA Astrophysics Data System (ADS)

    Cheng, K. S.; Dai, Z. G.; Yao, C. C.

    1996-06-01

    We study the properties of dense matter in neutron stars and calculate the structure of the stars based on the Zimanyi & Moszkowski (ZM) model in the relativistic mean-field theory. We also compare these results with those based on the Boguta & Bodmer (BB) model with a recent satisfactory parameter set. The two models satisfy the requirements from the observations of the masses of binary radio pulsars, the rotation frequencies of millisecond pulsars, the redshifts of the e+ annihilation lines of some ?-ray bursts if they are neutron stars, and the crustal moment of inertia of neutron stars deduced from the glitch events. Other observations may provide a way to discriminate between the two models. We suggest that the most important observational discriminant between these two models is found by observing the surface radiation of neutron stars, since the BB model leads to a large photon fraction of neutron star matter and rapid cooling of neutron stars, but the ZM model does not.

  19. Manipulating the backbone structure of semiconducting polymers

    NASA Astrophysics Data System (ADS)

    Luscombe, Christine

    2015-03-01

    Pi-Conjugated polymers are being used in the fabrication of a wide variety of organic electronic devices such as organic field-effect transistors (OFETs), organic photovoltaic (OPV) devices, and organic light-emitting diodes (OLEDs). The advances made in organic electronics have been driven by the syntheses of pi-conjugated polymers with increasingly complex structures but have heavily relied on an Edisonian approach. Despite these advances, there are many contradictory reports in the literature about our understanding of the performance of π-conjugated polymers in many applications. Our group has been studying and developing techniques to grow semiconducting polymers using a living polymerization method. This has allowed us to synthesize polymer architectures that we haven't been able to access till now including polythiophene brushes, star-shaped P3HT, as well as hyperbranched P3HT. It also allows us to accurately control the molecular weights of P3HT and produce materials with a narrow molecular weight distribution. In this presentation, our work towards creating brush polymers will be presented where a series of fully conjugated graft copolymers containing poly(3-hexylthiophene) (P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole donor-acceptor backbone were synthesized via a graft through Suzuki polymerization.

  20. Hydrogen cyanide polymers: from laboratory to space

    NASA Astrophysics Data System (ADS)

    Matthews, Clifford N.

    1995-02-01

    Hydrogen cyanide polymers - heterogeneous solids ranging in color from yellow to orange to red to black - may be among the organic macromolecules most readily formed within the solar system The non-volatile black crust of comet Halley for example, may consist largely of such polymers. It seems likely. too, that HCN polymers are a major constituent of the dark. CN bearing solids identified tentatively by IR spectra in the dust of some other comets. HCN polymerization could also account for some of the yellow-orange-red coloration of Jupiter and Saturn, and perhaps for the orange haze high in Titan's atmosphere. Studies of these polymers show that a yellow-brown powder can be extracted by water and further hydrolyzed to vield α-amino acids. Several instrumental methods used for the separation and identification of these intriguing materials. including pyrolysis mass spectrometry, Fourier transform IR photoacoustic spectroscopy and supercritical fluid extraction chromatography, reveal fragmentation patterns and chemical functionalities consistent with the presence of polymeric peptide precursors - polyamidines - in HCN polymers. Implications for prebiotic chemistry are profound. Primitive Earth may have been covered by HCN polymers and other organic products through bolide bombardment or terrestrial synthesis, producing a proteinaceous matrix able to bring about the molecular interactions leading to the emergence or life. Cyanide polymerization could also he a preferred pathway beyond Earth and the solar system, on planetary bodies and satellites around other stars and in the dusty molecular clouds of spiral galaxies.