| 1. |
- Gevorgian, Spartak, 1948, et al.
(författare)
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Optical electromagnetic wave generator
- 2003
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- Microwaves are generated by heterodyning the outputs of two or more optical lasers which have differing central frequencies to produce beat frequencies in the microwave range. One of the beat frequencies is used to modulate the output of at least one of the lasers so as to produce sidebands which differ from the central frequency by an integral number of the sideband frequency. Each laser is connected to one of the other lasers by a weak optical link to optically injection lock the laser to the sideband of the other laser
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| 2. |
- Gevorgian, Spartak, 1948, et al.
(författare)
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Optical electromagnetic wave generator
- 2001
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Microwaves are generated by heterodyning the outputs of two or more optical lasers which have differing central frequencies to produce beat frequencies in the microwave range. One of the beat frequencies is used to modulate the output of at least one of the lasers so as to produce sidebands which differ from the central frequency by an integral number of the sideband frequency. Each laser is connected to one of the other lasers by a weak optical link to optically injection lock the laser to the sideband of the other laser
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| 3. |
- Bellomo, Nicola, 1943, et al.
(författare)
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The generalized-kinetics-based equilibrium distribution function for composite particles
- 2003
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Ingår i: Comptes Rendus - Mecanique. - : Elsevier Science B.V., Amsterdam.. - 1631-0721 .- 1873-7234. ; 331:7, s. 461-467
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Tidskriftsartikel (refereegranskat)abstract
- This work is devoted to the equilibrium distribution function for a fluid of mutually non-interacting identical composite point particles in three-dimensional physical space. The distribution function is derived within the generalized-kinetics (GK) vision from the proposed probabilistic model based on quantum-mechanical bosons and fermions. The first GK advantage is that the derivation does not involve any assumption on the interpolation between bosons and fermions whereas the resulting function provides this interpolation. The second GK advantage is that composons, the particles described with the GK-based distribution function, are considerably less schematic and more consistent physically than quons. Composons correspond to a specific case of Isakov's general q-commutation relation involving an infinite number of the q-coefficients. Connection of the composon concept to previous results in the literature is pointed out. A few directions for future research on the topic are formulated. The results of the work can be used in the composite-particle fluid problems where the Maxwell–Boltzmann description is not valid, for instance, in dense populations of not too massive point-like particles of a complex, composite nature at not too high temperatures. FRENCH: Ce travail s'intéresse à la fonction de distribution d'équilibre pour un fluide mutuellement non agissant, composé de particules points dans un espace de dimension trois. La fonction de distribution provient, d'un point de vue de CG, d'un modèle probabiliste issu de la mécanique quantique des fermions et des bosons. Le premier avantage de CG est que la dérivation ne nécessite aucune hypothèse sur l'interpolation entre les bosons et les fermions alors que la fonction résultante fournit cette interpolation. Le second est que les composons, les particules décrites par ce procédé sont considérablement moins schématiques et plus consistantes, physiquement, que les quons. Les composons correspondent à un cas particulier de la relation générale de q-commutation d'Isakov, pour un nombre infini de q-coefficients. Les résultats antérieurs liés au concept de composon sont signalés et quelques directions de recherches futures sont proposées. Les résultats de ce travail peuvent servir pour l'étude de fluides composés, où la description Maxwell–Boltzmann n'est pas valable, par exemple, pour une dense population de particules, pas trop lourdes et a des températures pas trop élevées, et d'une comoposition de nature complexe.
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| 4. |
- Borejdo, J., et al.
(författare)
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Application of surface plasmon coupled emission to study of muscle
- 2006
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 91:7, s. 2626-2635
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Tidskriftsartikel (refereegranskat)abstract
- Muscle contraction results from interactions between actin and myosin cross-bridges. Dynamics of this interaction may be quite different in contracting muscle than in vitro because of the molecular crowding. In addition, each cross-bridge of contracting muscle is in a different stage of its mechanochemical cycle, and so temporal measurements are time averages. To avoid complications related to crowding and averaging, it is necessary to follow time behavior of a single cross-bridge in muscle. To be able to do so, it is necessary to collect data from an extremely small volume (an attoliter, 10 -18 liter). We report here on a novel microscopic application of surface plasmon-coupled emission (SPCE), which provides such a volume in a live sample. Muscle is fluorescently labeled and placed on a coverslip coated with a thin layer of noble metal. The laser beam is incident at a surface plasmon resonance (SPR) angle, at which it penetrates the metal layer and illuminates muscle by evanescent wave. The volume from which fluorescence emanates is a product of two near-field factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited fluorophores to the surface plasmons. The fluorescence is quenched at the metal interface (up to ∼10 nm), which further limits the thickness of the fluorescent volume to ∼50 nm. The fluorescence is detected through a confocal aperture, which limits the lateral dimensions of the detection volume to ∼200 nm. The resulting volume is ∼2 × 10-18 liter. The method is particularly sensitive to rotational motions because of the strong dependence of the plasmon coupling on the orientation of excited transition dipole. We show that by using a high-numerical-aperture objective (1.65) and high-refractive-index coverslips coated with gold, it is possible to follow rotational motion of 12 actin molecules in muscle with millisecond time resolution. © 2006 by the Biophysical Society.
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| 5. |
- Borejdo, J., et al.
(författare)
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Fluorescence correlation spectroscopy in surface plasmon coupled emission microscope
- 2006
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Ingår i: Optics Express. - 1094-4087. ; 14:17, s. 7878-7888
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Tidskriftsartikel (refereegranskat)abstract
- Study of dynamics of single molecules by Fluorescence Correlation Spectroscopy (PCS) requires that the rate of photon detection per molecule be high, that the background be low, and that there be a large change in fluorescent signal associated with change in a position of a molecule. PCS applied to microscopic Surface Plasmon Coupled Emission (SPCE) suggests a powerful method to meet those requirements. In this method, the observational volume is made shallow by placing a sample on a thin metal film and illuminating it with the laser beam at Surface Plasmon Resonance (SPR) angle through high numerical aperture objective. The illuminating light excites surface plasmons in the metal film that produce an evanescent wave on the aqueous side of the interface. The thickness of the detection volume is a product of evanescent wave penetration depth and distance-dependent fluorescence coupling to surface plasmons. It is further reduced by a metal quenching of excited fluorophores at a close proximity (below 10 nm) to a surface. The fluorescent light is emitted through the metal film only at an SPCE angle. Objective collects emitted light, and a confocal aperture inserted in its conjugate image plane reduces lateral dimensions of the detection volume to a fraction of a micrometer. By using diffusion of fluorescent microspheres, we show that SPCE-FCS is an efficient method to measure molecular diffusion and that on gold surface the height of the detection volume is ∼35 nm.
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| 6. |
- Borejdo, J., et al.
(författare)
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Reduction of photobleaching and photodamage in single molecule detection: observing single actin monomer in skeletal myofibrils
- 2008
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Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1560-2281 .- 1083-3668. ; 13:3, s. 10-
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in detector technology make it possible to achieve single molecule detection (SMD) in a cell. SMD avoids complications associated with averaging signals from large assemblies and with diluting and disorganizing proteins. However, it requires that cells be illuminated with an intense laser beam, which causes photobleaching and cell damage. To reduce these effects, we study cells on coverslips coated with silver nanoparticle monolayers (NML). Muscle is used as an example. Actin is labeled with a low concentration of fluorescent phalloidin to assure that less than a single molecule in a sarcomere is fluorescent. On a glass substrate, the fluorescence of actin decays in a step-wise fashion, establishing a single molecule detection regime. Single molecules of actin in living muscle are visualized for the first time. NML coating decreases the fluorescence lifetime 17 times and enhances intensity ten times. As a result, fluorescence of muscle bleaches four to five times slower than on glass. Monolayers decrease photobleaching because they shorten the fluorescence lifetime, thus decreasing the time that a fluorophore spends in the excited state when it is vulnerable to oxygen attack. They decrease damage to cells because they enhance the electric field near the fluorophore, making it possible to illuminate samples with weaker light.
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| 7. |
- Calander, Nils, 1953
(författare)
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Focused optical beams obtained at planar structures by an imaginary shift in position
- 2007
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Ingår i: Journal of the Optical Society of America A: Optics and Image Science, and Vision. - 1084-7529 .- 1520-8532. ; 24:9, s. 2513-2515
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Tidskriftsartikel (refereegranskat)abstract
- A theory for focused optical beams at planar structures is described. It is an extension of a previous theory based on summation of plane waves. The focused beam is obtained by an imaginary shift in the position vector of the plane waves. It is well suited for calculations of electromagnetic fields at planar surface plasmon resonance structures excited by a focused optical beam.
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| 8. |
- Calander, Nils, 1953, et al.
(författare)
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Interference of surface plasmon resonances causes enhanced depolarized light scattering from metal nanoparticles
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 434:4-6, s. 326-330
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Tidskriftsartikel (refereegranskat)abstract
- We show that the strongly depolarized light scattering from noble metal particles is a result of interference of two surface plasmon resonances on the same particle. The maximum depolarization occurs between two resonances. Under favorable conditions the anisotropy of the scattering light can be much lower than what is possible for dielectric particles. This explanation is discussed in relation to earlier published experimental measurements. Comparison of experimental results with theoretical calculations provides information on the shape distribution of metallic particles in the suspension. (c) 2006 Elsevier B.V. All rights reserved.
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| 9. |
- Calander, Nils, 1953
(författare)
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Molecular detection and analysis by using surface plasmon resonances
- 2006
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Ingår i: Current Analytical Chemistry. - : Bentham Science Publishers Ltd.. - 1573-4110. ; 2:2, s. 203-211
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Tidskriftsartikel (refereegranskat)abstract
- The surface plasmon resonance technique for molecular detection and analysis is reviewed, for example for monitoring binding of molecules to surfaces and for enhancing Raman spectroscopy. The possibility of modifying the emission and radiative decay rates of fluorophores by surface plasmon resonance is reviewed. Specifically, it concerns surface plasmon-coupled directional emission at planar structures.
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| 10. |
- Calander, Nils, 1953
(författare)
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Propensity of a circadian clock to adjust to the 24 h day-night light cycle and its sensitivity to molecular noise
- 2006
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Ingår i: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 241:4, s. 716-724
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Tidskriftsartikel (refereegranskat)abstract
- The circadian clock of Drosophila melanogaster and its tendency to adjust to the day-night light cycle is simulated by deterministic and stochastic methods. The robustness of the locking to the light-cycle with respect to molecular noise is studied. It is found that within the model studied, the molecular noise in the stochastic simulation erases the finer injection-locking structures, stronger injection signals are needed and the locking has the character of prolonged locked time intervals with cycle slips in between. The simulations are compared to a simple injection-locking model with noise that seems to describe the overall behavior well. © 2006 Elsevier Ltd. All rights reserved.
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