Attosecond nanoplasmonic streaking of localized fields near metal nanospheres

Collective electron dynamics in plasmonic nanosystems can unfold on timescales in the attosec- ond regime and the direct measurements of plasmonic near-field oscillations is highly desirable. We report on numerical studies on the application of attosecond nanoplasmonic streaking spectroscopy to the measurement of collective electron dynamics in isolated Au nanospheres. The plasmonic field oscillations are induced by a few-cycle NIR driving field and are mapped by the energy of photoemitted electrons using a synchronized, time-delayed attosecond XUV pulse. By a detailed analysis of the amplitudes and phase shifts, we identify the different regimes of nanoplasmonic streaking and study the dependence on particle size, XUV photoelectron energy and emission position. The simulations indicate that the near-fields around the nanoparticles can be spatio-temporally reconstructed and may give detailed insight into the build-up and decay of collective electron motion.Comment: Revised versio

On the Experimental Estimation of Surface Enhanced Raman Scattering (SERS) Cross Sections by Vibrational Pumping

We present an in-depth analysis of the experimental estimation of cross sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented.Comment: To be submitted to J. Phys. Chem.

Surface plasmon lifetime in metal nanoshells

The lifetime of localized surface plasmon plays an important role in many aspects of plasmonics and its applications. In small metal nanostructures, the dominant mechanism restricting plasmon lifetime is size-dependent Landau damping. We performed quantum-mechanical calculations of Landau damping for the bright surface plasmon mode in a metal nanoshell. In contrast to the conventional model based on the electron surface scattering, we found that the damping rate decreases as the nanoshell thickness is reduced. The origin of this behavior is traced to the spatial distribution of plasmon local field inside the metal shell. We also found that, due to interference of electron scattering amplitudes from nanoshell's two metal surfaces, the damping rate exhibits pronounced quantum beats with changing shell thickness.Comment: 9 pages, 4 Figure

Is it possible to formulate least action principle for dissipative systems?

A longstanding open question in classical mechanics is to formulate the least action principle for dissipative systems. In this work, we give a general formulation of this principle by considering a whole conservative system including the damped moving body and its environment receiving the dissipated energy. This composite system has the conservative Hamiltonian $H=K_1+V_1+H_2$ where $K_1$ is the kinetic energy of the moving body, $V_1$ its potential energy and $H_2$ the energy of the environment. The Lagrangian can be derived by using the usual Legendre transformation $L=2K_1+2K_2-H$ where $K_2$ is the total kinetic energy of the environment. An equivalent expression of this Lagrangian is $L=K_1-V_1-E_d$ where $E_d$ is the energy dissipated by the friction from the moving body into the environment from the beginning of the motion. The usual variation calculus of least action leads to the correct equation of the damped motion. We also show that this general formulation is a natural consequence of the virtual work principle.Comment: 11 pages, no figur

Functional equivalence of stem cell and stem cell-derived extracellular vesicle transplantation to repair the irradiated brain.

Cranial radiotherapy, although beneficial for the treatment of brain tumors, inevitably leads to normal tissue damage that can induce unintended neurocognitive complications that are progressive and debilitating. Ionizing radiation exposure has also been shown to compromise the structural integrity of mature neurons throughout the brain, an effect believed to be at least in part responsible for the deterioration of cognitive health. Past work has shown that cranially transplanted human neural stem cells (hNSCs) or their extracellular vesicles (EVs) afforded long-term beneficial effects on many of these cognitive decrements. To provide additional insight into the potential neuroprotective mechanisms of cell-based regenerative strategies, we have analyzed hippocampal neurons for changes in structural integrity and synaptic remodeling after unilateral and bilateral transplantation of hNSCs or EVs derived from those same cells. Interestingly, hNSCs and EVs similarly afforded protection to host neurons, ameliorating the impact of irradiation on dendritic complexity and spine density for neurons present in both the ipsilateral and contralateral hippocampi 1 month following irradiation and transplantation. These morphometric improvements were accompanied by increased levels of glial cell-derived growth factor and significant attenuation of radiation-induced increases in postsynaptic density protein 95 and activated microglia were found ipsi- and contra-lateral to the transplantation sites of the irradiated hippocampus treated with hNSCs or hNSC-derived EVs. These findings document potent far-reaching neuroprotective effects mediated by grafted stem cells or EVs adjacent and distal to the site of transplantation and support their potential as therapeutic agents to counteract the adverse effects of cranial irradiation

Dual-tip-enhanced ultrafast CARS nanoscopy

Coherent anti-Stokes Raman scattering (CARS) and, in particular, femtosecond adaptive spectroscopic techniques (FAST CARS) have been successfully used for molecular spectroscopy and microscopic imaging. Recent progress in ultrafast nanooptics provides flexibility in generation and control of optical near fields, and holds promise to extend CARS techniques to the nanoscale. In this theoretical study, we demonstrate ultrafast subwavelentgh control of coherent Raman spectra of molecules in the vicinity of a plasmonic nanostructure excited by ultrashort laser pulses. The simulated nanostructure design provides localized excitation sources for CARS by focusing incident laser pulses into subwavelength hot spots via two self-similar nanolens antennas connected by a waveguide. Hot-spot-selective dual-tip-enhanced CARS (2TECARS) nanospectra of DNA nucleobases are obtained by simulating optimized pump, Stokes and probe near fields using tips, laser polarization- and pulse-shaping. This technique may be used to explore ultrafast energy and electron transfer dynamics in real space with nanometre resolution and to develop novel approaches to DNA sequencing.Comment: 11 pages, 6 figure

Informal Action—Adjudication—Rule Making: Some Recent Developments in Federal Administrative Law

Direct energy consumption of ICT hardware is only “half the story.” In order to get the “whole story,” energy consumption during the entire life cycle has to be taken into account. This chapter is a first step toward a more comprehensive picture, showing the “grey energy” (i.e., the overall energy requirements) as well as the releases (into air, water, and soil) during the entire life cycle of exemplary ICT hardware devices by applying the life cycle assessment method. The examples calculated show that a focus on direct energy consumption alone fails to take account of relevant parts of the total energy consumption of ICT hardware as well as the relevance of the production phase. As a general tendency, the production phase is more and more important the smaller (and the more energy-efficient) the devices are. When in use, a tablet computer is much more energy-efficient than a desktop computer system with its various components, so its production phase has a much greater relative importance. Accordingly, the impacts due to data transfer when using Internet services are also increasingly relevant the smaller the end-user device is, reaching up to more than 90 % of the overall impact when using a tablet computer.QC 20140825</p