| 1. |
- Samoc, Marek, et al.
(författare)
-
Nonlinear absorption and nonlinear refraction: Maximizing the merit factors
- 2012
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489012 ; 8258, s. Art. no. 82580V-
-
Konferensbidrag (refereegranskat)abstract
- Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications.
|
|
| 2. |
- Abramowicz, Marek A, 1945, et al.
(författare)
-
The perihelion of Mercury advance and the light bending calculated in (enhanced) Newton's theory
- 2014
-
Ingår i: General Relativity and Gravitation. - : Springer Science and Business Media LLC. - 0001-7701 .- 1572-9532. ; 46:1
-
Tidskriftsartikel (refereegranskat)abstract
- We show that results of a simple dynamical gedanken experiment interpreted according to standard Newton's gravitational theory, may reveal that threedimensional space is curved. The experiment may be used to reconstruct the curved geometry of space, i.e. its non-Euclidean metric 3gik. The perihelion of Mercury advance and the light bending calculated from the Poisson equation 3gik∇i∇kΦ = -4πGρ and the equation of motion Fi = mai in the curved geometry 3gik have the correct (observed) values. Independently, we also show that Newtonian gravity theory may be enhanced to incorporate the curvature of three dimensional space by adding an extra equation which links the Ricci scalar 3R with the density of matter ρ. Like in Einstein's general relativity, matter is the source of curvature. In the spherically symmetric (vacuum) case, the metric of space 3gik that follows from this extra equation agrees, to the expected accuracy, with the metric measured by the Newtonian gedanken experiment mentioned above. © 2013 The Author(s).
|
|
| 3. |
- Ciesielski, A., et al.
(författare)
-
Stability of radiation-pressure dominated disks: I. the dispersion relation for a delayed heating α-viscosity prescription
- 2012
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 538
-
Tidskriftsartikel (refereegranskat)abstract
- We derive and investigate the dispersion relation for accretion disks with retarded or advanced heating. We follow the α-prescription but allow for a time offset τ between heating and pressure perturbations, as well as for a diminished response of heating to pressure variations. We study in detail solutions of the dispersion relation for disks with radiation-pressure fraction, 1-β, and ξ, the ratio of viscous stress response to pressure perturbations. For τ < 0 (advanced heating) the number and sign of real solutions for the growth rate depend on the values of τ, and ξ: if the magnitude of τ is larger than a critical value (e.g., more than twice the thermal time,-τ > 2 τ th, for β = 0 and ξ = 1) two real solutions exist, which are both negative. These results imply that radiation-pressure dominated accretion disks may be stabilized when there is a time delay between stress fluctuations and fluctuations in heating. © 2012 ESO.
|
|
| 4. |
- Wielgus, M., et al.
(författare)
-
Cosmic background radiation in the vicinity of a Schwarzschild black hole: No classic firewall
- 2014
-
Ingår i: Physical Review D. - 1550-7998. ; 90:12
-
Tidskriftsartikel (refereegranskat)abstract
- The cosmic blackbody background radiation pervades the entire Universe, and so falls into every astrophysical black hole. The blueshift of the infalling photons, measured by a static observer, is infinite at the event horizon. This raises a question as to whether a "firewall" of high energy density may form just outside the horizon, or whether the effect can be attributed exclusively to a singular behavior of the static observer's frame at the horizon. In principle, the presence of such a firewall may alter the motion of the infalling matter, influence the black hole evolution, or even invalidate the vacuum Einstein field equation solution as a realistic approximation for black holes. In this paper we show by means of analytic calculations that all these effects indeed exist, but their magnitude is typically negligibly small, even though the matter stress tensor is divergent in the static frame at r = 2M. That is not surprising because of the divergent relation of that frame to a freely falling frame as r -> 2M; however, it represents a kind of classical analogue for the black hole complementarity principle that has been proposed for quantum effects near a black hole. What is perhaps more surprising is the divergence of the radiation stress tensor for massive particles moving on circular geodesic orbits for values of r approaching r = 3M. However such orbits will not occur for infalling matter in realistic accretion discs. RAMOWICZ MA, 1983, ASTROPHYSICS AND SPACE SCIENCE, V96, P431 RAMOWICZ MA, 1990, ASTROPHYSICAL JOURNAL, V361, P470
|
|
