301 research outputs found
Critical Dimension for Stable Self-gravitating Stars in AdS
We study the self-gravitating stars with a linear equation of state, , in AdS space, where is a constant parameter. There exists a critical
dimension, beyond which the stars are always stable with any central energy
density; below which there exists a maximal mass configuration for a certain
central energy density and when the central energy density continues to
increase, the configuration becomes unstable. We find that the critical
dimension depends on the parameter , it runs from to 10.1291 as
varies from to 1. The lowest integer dimension for a dynamically
stable self-gravitating configuration should be for any
rather than , the latter is the case of self-gravitating radiation
configurations in AdS space.Comment: Revtex, 11 pages with 7 eps figure
A critical dimension for the stability of perfect fluid spheres of radiation
An analysis of radiating perfect fluid models with asymptotically AdS
boundary conditions is presented. Such scenarios consist of a spherical gas of
radiation (a "star") localised near the centre of the spacetime due to the
confining nature of the AdS potential. We consider the variation of the total
mass of the star as a function of the central density, and observe that for
large enough dimensionality, the mass increases monotonically with the density.
However in the lower dimensional cases, oscillations appear, indicating that
the perfect fluid model of the star is becoming unrealistic. We find the
critical dimension separating these two regimes to be eleven.Comment: 18 pages, 5 figures; v2 reference and footnote added; v3 slight
reordering of content, new section added with further analysis; v4 Final
version - small changes, including a new title, accepted for publication in
CQ
Influence of multiwalled carbon nanotubes on the processing behavior of epoxy powder compositions and on the mechanical properties of their fiber reinforced composites
Β© 2015 Society of Plastics Engineers. This study reports the preparation of advanced carbon fiber composites with a nanocomposite matrix prepared by dispersing multiwall carbon nanotubes (CNTs) in a powder type epoxy oligomer with two different processing techniques (1) master batch dilution technique and (2) direct mixing (with the help of twin-screw extruder in both cases). The master batch technique shows a better efficiency for the dispersion of the CNTs aggregates. The rheological results demonstrate that the incorporation of the CNTs into the epoxy oligomer leads, as expected, to a marked increase in the viscosity and of the presence of a yield stress point that also depends on the processing technique adopted. Carbon fiber (CFRP) and glass fiber (GFRP) composite materials were produced by electrostatic spraying of the epoxy matrix formulations on the carbon and glass fabric, respectively, followed by calendering and mold pressing. The mechanical properties of the obtained epoxy/CNT-matrix composite materials, such as interlaminar fracture toughness, flexural strength, shear storage and loss moduli are discussed in terms of the processing techniques and fabric material. The incorporation of 1 wt% CNTs in the epoxy matrix results in a relevant increase of the fracture toughness, flexural strength and modulus of both CFRP and GFRP
ΠΠΎΠ½ΡΠΏΠ΅ΠΊΡ ΡΠΎΠ΄Π° Anopteris (Pteridophyta, Pteridaceae)
In the article a synopsis of the genus Anopteris (Prantl) Diels is given. The synopsis of Anopteris includes three species. For each species, the Latin name, basionym, nomenclatural citation, synonyms, information on locus classicus, type, habitat, and distribution are given. AnΒ original key for identification of the species of Anopteris is also prepared. The localities of occurrence of each species are precisely given.Β ΠΡΠΈΠ²Π΅Π΄Π΅Π½ ΠΊΠΎΠ½ΡΠΏΠ΅ΠΊΡ ΡΠΎΠ΄Π° Anopteris (Prantl) Diels. ΠΠΎΠ½ΡΠΏΠ΅ΠΊΡ Π²ΠΊΠ»ΡΡΠ°Π΅Ρ ΡΡΠΈ Π²ΠΈΠ΄Π°. ΠΠ»Ρ ΠΊΠ°ΠΆΠ΄ΠΎΠ³ΠΎ ΠΈΠ· Π½ΠΈΡ
ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡΡΡ Π»Π°ΡΠΈΠ½ΡΠΊΠΎΠ΅ Π½Π°Π·Π²Π°Π½ΠΈΠ΅, Π±Π°Π·ΠΈΠΎΠ½ΠΈΠΌ, Π½ΠΎΠΌΠ΅Π½ΠΊΠ»Π°ΡΡΡΠ½Π°Ρ ΡΠΈΡΠ°ΡΠ°, ΡΠΈΠ½ΠΎΠ½ΠΈΠΌΡ, ΠΎΡΠΊΡΠ΄Π° ΠΎΠΏΠΈΡΠ°Π½, ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΡ ΠΎ ΡΠΈΠΏΠ΅, Π΄Π°Π½Π½ΡΠ΅ ΠΎ ΠΌΠ΅ΡΡΠΎΠΎΠ±ΠΈΡΠ°Π½ΠΈΠΈ, ΡΠ°ΡΠΏΡΠΎΡΡΡΠ°Π½Π΅Π½ΠΈΠ΅ ΠΏΠΎ ΡΡΡΠ°Π½Π°ΠΌ Ρ ΡΠΈΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΠΌΠ΅ΡΡ ΡΠ±ΠΎΡΠ° ΠΈ ΠΎΠ±ΡΠ΅Π΅ ΡΠ°ΡΠΏΡΠΎΡΡΡΠ°Π½Π΅Π½ΠΈΠ΅. ΠΠ»Ρ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ Π²ΡΠ΅Ρ
Π²ΠΈΠ΄ΠΎΠ² ΡΠΎΠ΄Π° Anopteris ΡΠΎΡΡΠ°Π²Π»Π΅Π½ ΠΎΡΠΈΠ³ΠΈΠ½Π°Π»ΡΠ½ΡΠΉ ΠΊΠ»ΡΡ, ΡΠΊΠ°Π·Π°Π½Ρ ΠΏΠΎΠ΄ΡΠΎΠ±Π½ΡΠ΅ ΠΌΠ΅ΡΡΠ° ΠΏΡΠΎΠΈΠ·ΡΠ°ΡΡΠ°Π½ΠΈΡ.Β ΠΡΠΈΠ²Π΅Π΄Π΅Π½ ΠΊΠΎΠ½ΡΠΏΠ΅ΠΊΡ ΡΠΎΠ΄Π° Anopteris (Prantl) Diels. ΠΠΎΠ½ΡΠΏΠ΅ΠΊΡ Π²ΠΊΠ»ΡΡΠ°Π΅Ρ ΡΡΠΈ Π²ΠΈΠ΄Π°. ΠΠ»Ρ ΠΊΠ°ΠΆΠ΄ΠΎΠ³ΠΎ ΠΈΠ· Π½ΠΈΡ
ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡΡΡ Π»Π°ΡΠΈΠ½ΡΠΊΠΎΠ΅ Π½Π°Π·Π²Π°Π½ΠΈΠ΅, Π±Π°Π·ΠΈΠΎΠ½ΠΈΠΌ, Π½ΠΎΠΌΠ΅Π½ΠΊΠ»Π°ΡΡΡΠ½Π°Ρ ΡΠΈΡΠ°ΡΠ°, ΡΠΈΠ½ΠΎΠ½ΠΈΠΌΡ, ΠΎΡΠΊΡΠ΄Π° ΠΎΠΏΠΈΡΠ°Π½, ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΡ ΠΎ ΡΠΈΠΏΠ΅, Π΄Π°Π½Π½ΡΠ΅ ΠΎ ΠΌΠ΅ΡΡΠΎΠΎΠ±ΠΈΡΠ°Π½ΠΈΠΈ, ΡΠ°ΡΠΏΡΠΎΡΡΡΠ°Π½Π΅Π½ΠΈΠ΅ ΠΏΠΎ ΡΡΡΠ°Π½Π°ΠΌ Ρ ΡΠΈΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΠΌΠ΅ΡΡ ΡΠ±ΠΎΡΠ° ΠΈ ΠΎΠ±ΡΠ΅Π΅ ΡΠ°ΡΠΏΡΠΎΡΡΡΠ°Π½Π΅Π½ΠΈΠ΅. ΠΠ»Ρ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ Π²ΡΠ΅Ρ
Π²ΠΈΠ΄ΠΎΠ² ΡΠΎΠ΄Π° Anopteris ΡΠΎΡΡΠ°Π²Π»Π΅Π½ ΠΎΡΠΈΠ³ΠΈΠ½Π°Π»ΡΠ½ΡΠΉ ΠΊΠ»ΡΡ, ΡΠΊΠ°Π·Π°Π½Ρ ΠΏΠΎΠ΄ΡΠΎΠ±Π½ΡΠ΅ ΠΌΠ΅ΡΡΠ° ΠΏΡΠΎΠΈΠ·ΡΠ°ΡΡΠ°Π½ΠΈΡ.
Influence of multiwalled carbon nanotubes on the processing behavior of epoxy powder compositions and on the mechanical properties of their fiber reinforced composites
Β© 2015 Society of Plastics EngineersThis study reports the preparation of advanced carbon fiber composites with a nanocomposite matrix prepared by dispersing multiwall carbon nanotubes (CNTs) in a powder type epoxy oligomer with two different processing techniques (1) master batch dilution technique and (2) direct mixing (with the help of twin-screw extruder in both cases). The master batch technique shows a better efficiency for the dispersion of the CNTs aggregates. The rheological results demonstrate that the incorporation of the CNTs into the epoxy oligomer leads, as expected, to a marked increase in the viscosity and of the presence of a yield stress point that also depends on the processing technique adopted. Carbon fiber (CFRP) and glass fiber (GFRP) composite materials were produced by electrostatic spraying of the epoxy matrix formulations on the carbon and glass fabric, respectively, followed by calendering and mold pressing. The mechanical properties of the obtained epoxy/CNT-matrix composite materials, such as interlaminar fracture toughness, flexural strength, shear storage and loss moduli are discussed in terms of the processing techniques and fabric material. The incorporation of 1 wt% CNTs in the epoxy matrix results in a relevant increase of the fracture toughness, flexural strength and modulus of both CFRP and GFRP. POLYM. COMPOS., 37:2377β2383, 2016. Β© 2015 Society of Plastics Engineers
Thermodynamics of Large AdS Black Holes
We consider leading order quantum corrections to the geometry of large AdS
black holes in a spherical reduction of four-dimensional Einstein gravity with
negative cosmological constant. The Hawking temperature grows without bound
with increasing black hole mass, yet the semiclassical back-reaction on the
geometry is relatively mild, indicating that observers in free fall outside a
large AdS black hole never see thermal radiation at the Hawking temperature.
The positive specific heat of large AdS black holes is a statement about the
dual gauge theory rather than an observable property on the gravity side.
Implications for string thermodynamics with an AdS infrared regulator are
briefly discussed.Comment: 17 pages, 1 figure, v2. added reference
OPTIMIZATION OF CATALYST STRUCTURE FOR ASYMMETRIC ALLYLATION-TYPE REACTIONS OF FUNCTIONALIZED TRICHLOROSILANES WITH AROMATIC ALDEHYDES
The authors thank the Russian Science Foundation for Grant 18-73-10156-Π
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