835 research outputs found
Effects Of Stress On Electron Emission From Nanostructured Carbon Materials
The electron field emission from a graphite like amorphous carbon film was investigated. Threshold fields as low as 8 V/Îœm were observed at an assisting energy of 400eV. The field emission characteristics of the films were explained in terms of the high sp2 concentration, and the high intrinsic compressive stress modifying the electronic band structure of the film/graphitic nanostructures.21417101714McKenzie, D.R., Muller, D., Pailthope, B.A., (1991) Phys. Rev. Lett., 67, p. 773Schwan, J., Ulrich, S., Theel, T., Roth, H., Ehrhardt, H., Becker, P., Silva, S.R.P., (1997) J. Appl. Phys., 82, p. 6024Lifshitz, Y., Kasi, S.R., Rabalais, J.W., Eckstein, W., (1990) Phys. Rev. B, 41, p. 10468Robertson, J., (1993) Diamond Relat. Mater., 2, p. 984Lacerda, R.G., Hammer, P., Lepienski, C.M., Alvarez, F., Marques, F.C., (2001) J. Vac. Sci. Technol. A, 19, p. 971Bhattacharyya, S., Subramanyam, S.V., (1997) Appl. Phys. Lett., 71, p. 632Kilic, C., Mehrez, H., Ciraci, S., (1998) Phys. Rev. B, 58, p. 7872Uher, C., Hockey, R.L., Ben-Jacob, E., (1987) Phys. Rev. B, 35, p. 4483Satyanarayana, B.S., Hart, A., Milne, W.I., Robertson, J., (1997) Appl. Phys. Lett., 71, p. 1430Carey, J.D., Forrest, R.D., Silva, S.R.P., (2001) Appl. Phys. Lett., 78, p. 2339Illie, A., Ferrari, C., Yagi, T., Robertson, J., (2000) Appl. Phys. Lett., 76, p. 2627De Lima M.M., Jr., Lacerda, R.G., Vilcarromero, J., Marques, F.C., (1999) J. Appl. Phys., 86, p. 4936Hoffman, R.W., (1966) Physics of Thin Films, 3, pp. 211-273. , edited by G. Hass and R. E. Thun (Academic, New YorkCarey, J.D., Silva, S.R.P., (2001) Appl. Phys. Lett., 78, p. 347Hammer, P., Victoria, N.M., Alvarez, F., (2000) J. Vac. Sci. Technol. A, 18, p. 2277Lifshitz, Y., Lempert, G.D., Grossman, E., Avigal, L., Uzan-Saguy, C., Kalish, R., Khlik, J., Rabalais, J.W., (1995) Diamond Relat. Mater., 4, p. 318Fallon, P.J., Veerasamy, V.S., Davis, C.A., Robertson, J., Amaratunga, G.A.J., Milne, W.I., Koskinen, J., (1993) Phys. Rev. B, 48, p. 4777Ahuja, R., Auluck, S., Trygg, J., Wills, J.M., Eriksson, O., Johansson, B., (1995) Phys. Rev. B, 51, p. 4813Reynolds, W.N., Goggin, P.R., (1960) Philos. Mag., 5, p. 1049Lynch, R.W., Drickamer, H.G., (1966) J. Chem. Phys., 44, p. 181Chaumet, P.C., Dufour, J.P., (1998) J. Electrost., 43, p. 145Hryd, R., Charlier, A., McRae, E., (1997) Phys. Rev. B, 55, p. 682
The transfer of fibres in the carding machine
The problem of understanding the transfer of fibres between carding-machine surfaces is addressed by considering the movement of a single fibre in an airflow. The structure of the aerodynamic flow field predicts how and when fibres migrate between the different process surfaces. In the case of a revolving-flats carding machine the theory predicts a âstrongâ aerodynamic mechanism between taker-in and cylinder and a âweakâ mechanism between cylinder and removal cylinder resulting in effective transfer in the first case and a more limited transfer in the second
Dissipation in Dynamics of a Moving Contact Line
The dynamics of the deformations of a moving contact line is studied assuming
two different dissipation mechanisms. It is shown that the characteristic
relaxation time for a deformation of wavelength of a contact line
moving with velocity is given as . The velocity
dependence of is shown to drastically depend on the dissipation
mechanism: we find for the case when the dynamics is governed
by microscopic jumps of single molecules at the tip (Blake mechanism), and
when viscous hydrodynamic losses inside the moving
liquid wedge dominate (de Gennes mechanism). We thus suggest that the debated
dominant dissipation mechanism can be experimentally determined using
relaxation measurements similar to the Ondarcuhu-Veyssie experiment [T.
Ondarcuhu and M. Veyssie, Nature {\bf 352}, 418 (1991)].Comment: REVTEX 8 pages, 9 PS figure
Roughening Transition in a Moving Contact Line
The dynamics of the deformations of a moving contact line on a disordered
substrate is formulated, taking into account both local and hydrodynamic
dissipation mechanisms. It is shown that both the coating transition in contact
lines receding at relatively high velocities, and the pinning transition for
slowly moving contact lines, can be understood in a unified framework as
roughening transitions in the contact line. We propose a phase diagram for the
system in which the phase boundaries corresponding to the coating transition
and the pinning transition meet at a junction point, and suggest that for
sufficiently strong disorder a receding contact line will leave a
Landau--Levich film immediately after depinning. This effect may be relevant to
a recent experimental observation in a liquid Helium contact line on a Cesium
substrate [C. Guthmann, R. Gombrowicz, V. Repain, and E. Rolley, Phys. Rev.
Lett. {\bf 80}, 2865 (1998)].Comment: 16 pages, 6 encapsulated figure
Spreading Dynamics of Polymer Nanodroplets
The spreading of polymer droplets is studied using molecular dynamics
simulations. To study the dynamics of both the precursor foot and the bulk
droplet, large drops of ~200,000 monomers are simulated using a bead-spring
model for polymers of chain length 10, 20, and 40 monomers per chain. We
compare spreading on flat and atomistic surfaces, chain length effects, and
different applications of the Langevin and dissipative particle dynamics
thermostats. We find diffusive behavior for the precursor foot and good
agreement with the molecular kinetic model of droplet spreading using both flat
and atomistic surfaces. Despite the large system size and long simulation time
relative to previous simulations, we find no evidence of hydrodynamic behavior
in the spreading droplet.Comment: Physical Review E 11 pages 10 figure
Discrete cilia modelling with singularity distributions
We discuss in detail techniques for modelling flows due to finite and infinite arrays of beating cilia. An efficient technique, based on concepts from previous âsingularity modelsâ is described, that is accurate in both near and far-fields. Cilia are modelled as curved slender ellipsoidal bodies by distributing Stokeslet and potential source dipole singularities along their centrelines, leading to an integral equation that can be solved using a simple and efficient discretisation. The computed velocity on the cilium surface is found to compare favourably with the boundary condition. We then present results for two topics of current interest in biology. 1) We present the first theoretical results showing the mechanism by which rotating embryonic nodal cilia produce a leftward flow by a âposterior tilt,â and track particle motion in an array of three simulated nodal cilia. We find that, contrary to recent suggestions, there is no continuous layer of negative fluid transport close to the ciliated boundary. The mean leftward particle transport is found to be just over 1 ÎŒm/s, within experimentally measured ranges. We also discuss the accuracy of models that represent the action of cilia by steady rotlet arrays, in particular, confirming the importance of image systems in the boundary in establishing the far-field fluid transport. Future modelling may lead to understanding of the mechanisms by which morphogen gradients or mechanosensing cilia convert a directional flow to asymmetric gene expression. 2) We develop a more complex and detailed model of flow patterns in the periciliary layer of the airway surface liquid. Our results confirm that shear flow of the mucous layer drives a significant volume of periciliary liquid in the direction of mucus transport even during the recovery stroke of the cilia. Finally, we discuss the advantages and disadvantages of the singularity technique and outline future theoretical and experimental developments required to apply this technique to various other biological problems, particularly in the reproductive system
Rings and bars: unmasking secular evolution of galaxies
Secular evolution gradually shapes galaxies by internal processes, in
contrast to early cosmological evolution which is more rapid. An important
driver of secular evolution is the flow of gas from the disk into the central
regions, often under the influence of a bar. In this paper, we review several
new observational results on bars and nuclear rings in galaxies. They show that
these components are intimately linked to each other, and to the properties of
their host galaxy. We briefly discuss how upcoming observations, e.g., imaging
from the Spitzer Survey of Stellar Structure in Galaxies (S4G), will lead to
significant further advances in this area of research.Comment: Invited review at "Galaxies and their Masks", celebrating Ken
Freeman's 70-th birthday, Sossusvlei, Namibia, April 2010. To be published by
Springer, New York, editors D.L. Block, K.C. Freeman, & I. Puerari; minor
change
Chemical Bonding in Solids
This chapter discusses the various classes of hydride compounds, with a special focus on saline and metallic hydrides as well as oxyhydrides. It includes the following topics: thermodynamic stability, crystal chemistry, synthesis, and physical properties. The chapter also highlights recent progress in understanding hydride ion mobility in alkaline earth hydrides. It further deals with hydride compounds and in particular those containing alkali, alkaline earth, and transition and rare earth metals. The saline hydrides, that is, AH and AeH2 (with A=Li, Na, K, Rb, and Cs; Ae=Mg, Ca, Sr, and Ba) are proper ionic materials, in which hydrogen is present as hydride anions, Hâ. Saline hydrides show many similarities with their halide analogues, especially concerning crystal and electronic structures and, perhaps to a lesser extent, physical attributes such as brittleness, hardness, and optical properties
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
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