Direct Inversion of Digital 3D Fraunhofer Holography Maps

The Differential Fourier Holography (DFH) gives an exact mathematical solution of the inverse problem of diffraction in the Fraunhofer regime. After the first publication [1] the Differential Fourier Holography was successfully applied in many experiments to obtain amplitude and phase information about two-dimensional (2D) images. In this article we demonstrate numerically the possibility to apply the DFH also for investigation of unknown 3D Objects. The first simulation is made for a double-spiral structure plus a line as a reference object

Energy and land use in the Pamir-Alai Mountains

In a comparative study of energy resources and energy consumption patterns in the Pamir-Alai Mountains of Kyrgyzstan and Tajikistan, the relations between energy consumption, land use, and livelihoods were investigated. An approach that presents energy flow through an ecosystem was developed, in particular to highlight ecosystem services and the scope of action for human interventions in the energy-land management nexus. Qualitative data were collected during a field study in October 2009 through household interviews and group discussions. Based on the relationship between energy supply and ecosystem services, typical village profiles depicting the flows of energy and financial assets are presented that illustrate the relation between energy resources, land use, and livelihood assets. The household interviews reflect situations in the different villages and allow a distinction to be made between the energy consumption patterns of poor and wealthier families. This case study in the Pamir-Alai Mountains emphasizes that a reappraisal of energy as a central focus within mountain ecosystems and their services to the population is necessary for both ecosystem preservation and poverty reduction

Spin-Forster transfer in optically excited quantum dots

The mechanisms of energy and spin transfer in quantum dot pairs coupled via the Coulomb interaction are studied. Exciton transfer can be resonant or phonon-assisted. In both cases, the transfer rates strongly depend on the resonance conditions. The spin selection rules in the transfer process come from the exchange and spin-orbit interactions. The character of energy dissipation in spin transfer is different than that in the traditional spin currents. The spin-dependent photon cross-correlation functions reflect the exciton transfer process. In addition, a mathematical method to calculate F\"orster transfer in crystalline nanostructures beyond the dipole-dipole approximation is described.Comment: 22 pages, 10 figures, Phys. Rev. B, in pres

Ion-ion dynamic structure factor, acoustic modes and equation of state of two-temperature warm dense aluminum

The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasi-equilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasi-equilibrium situations. Analyzing the van Hove function, we find that ion-ion correlations vanish in a time significantly smaller than the electron-ion relaxation time so that dynamical properties have a physical meaning for the quasi-equilibrium state. A significant increase in the speed of sound is predicted from the modification of the dispersion relation of the ion acoustic mode as the electron temperature is increased. The two-temperature equation of state including the free energy, internal energy and pressure is also presented

Current-voltage correlations in interferometers

We investigate correlations of current at contacts and voltage fluctuations at voltage probes coupled to interferometers. The results are compared with correlations of current and occupation number fluctuations at dephasing probes. We use a quantum Langevin approach for the average quantities and their fluctuations. For higher order correlations we develop a stochastic path integral approach and find the generating functions of voltage or occupation number fluctuations. We also derive a generating function for the joint distribution of voltage or occupation number at the probe and current fluctuations at a terminal of a conductor. For energy independent scattering we found earlier that the generating function of current cumulants in interferometers with a one-channel dephasing or voltage probe are identical. Nevertheless, the distribution function for voltage and the distribution function for occupation number fluctuations differ, the latter being broader than that of former in all examples considered here.Comment: 23 pages, 10 figures, minor changes, additional appendix, added reference

Capability of Cherenkov Telescopes to Observe Ultra-fast Optical Flares

The large optical reflector (~ 100 m^2) of a H.E.S.S. Cherenkov telescope was used to search for very fast optical transients of astrophysical origin. 43 hours of observations targeting stellar-mass black holes and neutron stars were obtained using a dedicated photometer with microsecond time resolution. The photometer consists of seven photomultiplier tube pixels: a central one to monitor the target and a surrounding ring of six pixels to veto background events. The light curves of all pixels were recorded continuously and were searched offline with a matched-filtering technique for flares with a duration of 2 us to 100 ms. As expected, many unresolved (500 us) background events originating in the earth's atmosphere were detected. In the time range 3 to 500 us the measurement is essentially background-free, with only eight events detected in 43 h; five from lightning and three presumably from a piece of space debris. The detection of flashes of brightness ~ 0.1 Jy and only 20 us duration from the space debris shows the potential of this setup to find rare optical flares on timescales of tens of microseconds. This timescale corresponds to the light crossing time of stellar-mass black holes and neutron stars.Comment: Accepted for publication in Astroparticle Physics, 8 pages, 9 figures, 1 tabl

Theory and simulations of rigid polyelectrolytes

We present theoretical and numerical studies on stiff, linear polyelectrolytes within the framework of the cell model. We first review analytical results obtained on a mean-field Poisson-Boltzmann level, and then use molecular dynamics simulations to show, under which circumstances these fail quantitatively and qualitatively. For the hexagonally packed nematic phase of the polyelectrolytes we compute the osmotic coefficient as a function of density. In the presence of multivalent counterions it can become negative, leading to effective attractions. We show that this results from a reduced contribution of the virial part to the pressure. We compute the osmotic coefficient and ionic distribution functions from Poisson-Boltzmann theory with and without a recently proposed correlation correction, and also simulation results for the case of poly(para-phenylene) and compare it to recently obtained experimental data on this stiff polyelectrolyte. We also investigate ion-ion correlations in the strong coupling regime, and compare them to predictions of the recently advocated Wigner crystal theories.Comment: 32 pages, 15 figures, proceedings of the ASTATPHYS-MEX-2001, to be published in Mol. Phy

Structure and star formation in galaxies out to z=3: evidence for surface density dependent evolution and upsizing

We present an analysis of galaxies in the CDF-South. We find a tight relation to z=3 between color and size at a given mass, with red galaxies being small, and blue galaxies being large. We show that the relation is driven by stellar surface density or inferred velocity dispersion: galaxies with high surface density are red and have low specific star formation rates, and galaxies with low surface density are blue and have high specific star formation rates. Surface density and inferred velocity dispersion are better correlated with specific star formation rate and color than stellar mass. Hence stellar mass by itself is not a good predictor of the star formation history of galaxies. In general, galaxies at a given surface density have higher specific star formation rates at higher redshift. Specifically, galaxies with a surface density of 1-3 10^9 Msun/kpc^2 are "red and dead" at low redshift, approximately 50% are forming stars at z=1, and almost all are forming stars by z=2. This provides direct additional evidence for the late evolution of galaxies onto the red sequence. The sizes of galaxies at a given mass evolve like 1/(1+z)^(0.59 +- 0.10). Hence galaxies undergo significant upsizing in their history. The size evolution is fastest for the highest mass galaxies, and quiescent galaxies. The persistence of the structural relations from z=0 to z=2.5, and the upsizing of galaxies imply that a relation analogous to the Hubble sequence exists out to z=2.5, and possibly beyond. The star forming galaxies at z >= 1.5 are quite different from star forming galaxies at z=0, as they have likely very high gas fractions, and star formation time scales comparable to the orbital time.Comment: 20 pages, accepted for publication in ApJ, 2008, 68

Optical properties of coupled metal-semiconductor and metal-molecule nanocrystal complexes: the role of multipole effects

We investigate theoretically the effects of interaction between an optical dipole (semiconductor quantum dot or molecule) and metal nanoparticles. The calculated absorption spectra of hybrid structures demonstrate strong effects of interference coming from the exciton-plasmon coupling. In particular, the absorption spectra acquire characteristic asymmetric lineshapes and strong anti-resonances. We present here an exact solution of the problem beyond the dipole approximation and find that the multipole treatment of the interaction is crucial for the understanding of strongly-interacting exciton-plasmon nano-systems. Interestingly, the visibility of the exciton resonance becomes greatly enhanced for small inter-particle distances due to the interference phenomenon, multipole effects, and electromagnetic enhancement. We find that the destructive interference is particularly strong. Using our exact theory, we show that the interference effects can be observed experimentally even in the exciting systems at room temperature.Comment: 9 page