Non-Fourier heat transport in metal-dielectric core-shell nanoparticles under ultrafast laser pulse excitation

Relaxation dynamics of embedded metal nanoparticles after ultrafast laser pulse excitation is driven by thermal phenomena of different origins the accurate description of which is crucial for interpreting experimental results: hot electron gas generation, electron-phonon coupling, heat transfer to the particle environment and heat propagation in the latter. Regardingthis last mechanism, it is well known that heat transport in nanoscale structures and/or at ultrashort timescales may deviate from the predictions of the Fourier law. In these cases heat transport may rather be described by the Boltzmann transport equation. We present a numerical model allowing us to determine the electron and lattice temperature dynamics in a spherical gold nanoparticle core under subpicosecond pulsed excitation, as well as that of the surrounding shell dielectric medium. For this, we have used the electron-phonon coupling equation in the particle with a source term linked with the laser pulse absorption, and the ballistic-diffusive equations for heat conduction in the host medium. Either thermalizing or adiabatic boundary conditions have been considered at the shell external surface. Our results show that the heat transfer rate from the particle to the matrix can be significantly smaller than the prediction of Fourier's law. Consequently, the particle temperature rise is larger and its cooling dynamics might be slower than that obtained by using Fourier's law. This difference is attributed to the nonlocal and nonequilibrium heat conduction in the vicinity of the core nanoparticle. These results are expected to be of great importance for analyzing pump-probe experiments performed on single nanoparticles or nanocomposite media

Off-resonance field enhancement by spherical nanoshells

We study light scattering by spherical nanoshells consistent of metal/dielectric composites. We consider two geometries of metallic nanoshell with dielectric core, and dielectric coated metallic nanoparticle. We demonstrate that for both geometries the local field enhancement takes place out of resonance regions ("dark states"), which, nevertheless, can be understood in terms of the Fano resonance. At optimal conditions the light is stronger enhanced inside the dielectric material. By using nonlinear dielectric materials it will lead to a variety nonlinear phenomena applicable for photonics applications

Anisotropic Decay Dynamics of Photoexcited Aligned Carbon Nanotube Bundles

We have performed polarization-dependent ultrafast pump-probe spectroscopy of a film of aligned single-walled carbon nanotube bundles. By taking into account imperfect nanotube alignment as well as anisotropic absorption cross sections, we quantitatively determined distinctly different photo-bleaching dynamics for polarizations parallel and perpendicular to the tube axis. For perpendicular polarization, we observe a slow (1.0-1.5 ps) relaxation process, previously unobserved in randomly-oriented nanotube bundles. We attribute this slower dynamics to the excitation and relaxation of surface plasmons in the radial direction of the nanotube bundles.Comment: 4 pages, 3 figure

On-command enhancement of single molecule fluorescence using a gold nanoparticle as an optical nano-antenna

We investigate the coupling of a single molecule to a single spherical gold nanoparticle acting as a nano-antenna. Using scanning probe technology, we position the particle in front of the molecule with nanometer accuracy and measure a strong enhancement of more than 20 times in the fluorescence intensity simultaneous to a 20-fold shortening of the excited state lifetime. Direct comparison with three-dimensional calculations allow us to decipher the contributions of the excitation enhancement, spontaneous emission modification, and quenching. Furthermore, we provide direct evidence for the role of the particle plasmon resonance in the modification of the molecular emission.Comment: 5 pages, 4 figures. submitted to Phys.Rev.Lett. 12/04/200

Luminescence Decay and the Absorption Cross-Section of Individual Single-Walled Carbon Nanotubes

The absorption cross section of highly luminescent individual single-walled carbon nanotubes is determined using time-resolved and cw luminescence spectroscopy. A mean value of 1x10-17 cm2 per carbon atom is obtained for (6,5) tubes excited at their second optical transition, and corroborated by single tube photothermal absorption measurements. Biexponential luminescence decays are systematically observed, with short and long lifetimes around 45 and 250 ps. This behavior is attributed to the band edge exciton fine structure with a dark level lying a few meV below a bright one

Анализ деятельности предприятия нефтегазового комплекса в современных условиях

Выпускная квалификационная работа 80 страниц, 4 рисунка, 18 таблиц, … источников, … приложений. Ключевые слова: нефтехимия, предприятие, экономическая деятельность, анализ, конкурентоспособность. Объект исследования: ООО «Томскнефтехим». Цель работы – рассмотреть и проанализировать нефтехимический рынок в современных условиях. В процессе исследования проводилось рассмотрение российского предприятия нефтехимического производства. В результате исследования было проанализировано предприятие нефтехимической деятельности на примере предприятия ООО «Томскнефтехим». Степень внедрения: в рамках данного предприятия. Область применения: экономическая. Экономическая эффективность/значимость работы проявляет себя в дополнении к существующей теоретической базе, посвященной вопросам деятельности предприятия в современных условиях.Final qualifying work 80 pages, 4 figures, 18 tables, sources ... ... applications. Tags: petrochemistry, enterprise, economic activity, the analysis of competitiveness. The object of study: OOO "Tomskneftekhim". Purpose - to consider and analyze the petrochemical market in modern conditions. The study was conducted to examine the Russian enterprises of petrochemical production. The study analyzed the petrochemical activity on the example of the company OOO "Tomskneftekhim". Degree of implementation: within the enterprise. Scope: economic. Cost-effectiveness / value of the work manifests itself in addition to the existing theoretical base, devoted to activity of the enterprise in modern conditions

Extracción de bases de reglas simples y lingüísticamente interpretables

Comunicación presentada al "XIII ESTYLF'06" celebrado en Ciudad Real del 20 al 22 de Septiembre de 2006.Este artículo presenta una técnica basada en la lógica difusa para extraer bases de reglas a partir de datos numéricos. Permite obtener bases de reglas interpretables lingüísticamente a la vez que simples en cuanto a número de reglas, sencillez en las partes antecedentes y consecuentes y facilidad de implementación hardware/software. Los pasos más significativos de esta técnica son los siguientes: (1) extracción de la base de reglas empleando particiones granulares de las variables del problema, (2) ajuste de las funciones de pertenencia para las variables de salida y posterior simplificación, (3) simplificación tabular de la base de reglas y (4) simplificación de las funciones de pertenencia para las variables de entrada. La técnica puede aplicarse de forma automática mediante las herramientas de CAD integradas en el entorno Xfuzzy 3. Se incluye un ejemplo de aplicación en robótica móvil para ilustrar las ventajas de la técnica propuesta.Peer reviewe

Optical microscopy via spectral modifications of a nano-antenna

The existing optical microscopes form an image by collecting photons emitted from an object. Here we report on the experimental realization of microscopy without the need for direct optical communication with the sample. To achieve this, we have scanned a single gold nanoparticle acting as a nano-antenna in the near field of a sample and have studied the modification of its intrinsic radiative properties by monitoring its plasmon spectrum.Comment: 6 pages, 4 figures (color

Light propagation in nanorod arrays

We study propagation of TM- and TE-polarized light in two-dimensional arrays of silver nanorods of various diameters in a gelatin background. We calculate the transmittance, reflectance and absorption of arranged and disordered nanorod arrays and compare the exact numerical results with the predictions of the Maxwell-Garnett effective-medium theory. We show that interactions between nanorods, multipole contributions and formations of photonic gaps affect strongly the transmittance spectra that cannot be accounted for in terms of the conventional effective-medium theory. We also demonstrate and explain the degradation of the transmittance in arrays with randomly located rods as well as weak influence of their fluctuating diameter. For TM modes we outline the importance of skin-effect, which causes the full reflection of the incoming light. We then illustrate the possibility of using periodic arrays of nanorods as high-quality polarizers.Comment: 6 pages, 7 figure