Future Supernovae observations as a probe of dark energy

We study the potential impact of improved future supernovae data on our understanding of the dark energy problem. We carefully examine the relative utility of different fitting functions that can be used to parameterize the dark energy models, and provide concrete reasons why a particular choice (based on a parameterization of the equation of state) is better in almost all cases. We discuss the details of a representative sample of dark energy models and show how future supernova observations could distinguish among these. As a specific example, we consider the proposed ``SNAP'' satellite which is planned to observe around 2000 supernovae. We show how a SNAP-class data set taken alone would be a powerful discriminator among a family of models that would be approximated by a constant equation of state for the most recent epoch of cosmic expansion. We show how this family includes most of the dark energy models proposed so far. We then show how an independent measurement of $\Omega_{\rm m}$ can allow SNAP to probe the evolution of the equation of state as well, allowing further discrimination among a larger class of proposed dark energy models. We study the impact of the satellite design parameters on this method to distinguish the models and compare SNAP to alternative measurements. We establish that if we exploit the full precision of SNAP it provides a very powerful probe.Comment: 29 pages, 22 figures; replaced to match version accepted for publication in PRD, section V shortend and merged into section VI; brief discussion on non-flat cosmologies adde

On the electric conductivity of highly ordered monolayers of monodisperse metal nanoparticles

Monolayers of colloidally synthesized cobalt-platinum nanoparticles of different diameters characterized by TEM (transmission electron microscopy) were deposited on structured silicon oxide substrates and characterized by SEM (scanning electron microscopy), GISAXS (grazing incidence x-ray scattering), and electric transport measurements. The highly ordered nanoparticle films show a thermally activated electron hopping between spatially adjacent particles at room temperature and Coulomb blockade at low temperatures. We present a novel approach to experimentally determine the particles charging energies giving values of 6.7-25.4 meV dependent on the particles size and independent of the interparticle distance. These observations are supported by FEM (finite element method) calculations showing the self-capacitance to be the determining value which only depends on the permittivity constant of the surrounding space and the particles radius.Comment: 6 pages, 5 figure

Superposition of induced polarization signals measured on pyrite–sand mixtures

Induced polarization (IP) is a common method in ore exploration. IP spectra measured over a wide frequency range can be used to characterize material properties of ores, slags and other residual material from mines and processing facilities. Previous studies have shown that IP parameters are sensitive to type, content or grain size of electronically conductive or semi-conductive minerals. Up to now, a variety of experiments has been performed on sand mixtures with fractions of ore minerals. Most experiments consider only a single fraction with a fixed grain size. We continue a series of experiments that have been done with sand–pyrite mixtures. The presented study compares IP spectra recorded for samples either with a single grain radius fraction (E-samples) or with two different grain radii fractions (Z-samples). The spectra are fitted to Pelton models. A Debye decomposition that provides a relaxation time distribution (RTD) is applied to the complex conductivity spectra. The RTD indicates separated maxima only if the ratio of mean grain radii is larger than a factor five. The resolution of the phase spectra and the spectra of imaginary part of conductivity is lower. Even though the volumetric pyrite content is equal in each fraction, the phase spectra and RTD of the Z-samples indicate much higher signals for the pyrite fraction with smaller grain radius. The same observation is made for the chargeability that shows larger values for decreasing grain radii. This finding contradicts existing theories that consider the chargeability as a suitable proxy of the volumetric content of ore minerals. We explain the observed effect by an interaction between neighbouring pyrite particles. The conductivity of the mixtures of the E-samples increases with decreasing grain radius of the pyrite fraction. This effect is attributed to dissolution effects on the surface of the pyrite particles during the sample preparation. We find that the additive superposition of the phase spectra of two E-samples is in good agreement with the measured phase spectra of the Z-samples (measured superposition) containing the two corresponding pyrite fractions. The agreement is slightly worse for the spectra of imaginary part of conductivity, where the measured superposition overestimates the mathematical superposition. The experimental results of our study motivate a further improvement of existing mechanistic models

Anisotropy of permeability, P-wave velocity and electrical resistivity of Upper Cretaceous carbonate samples from Tushka Area, Western Desert, Egypt

Petrophysical properties (such as porosity, permeability, grain density, bulk density, electrical resistivity, and P-wave velocity), as well as the anisotropy of the permeability, seismic velocity (P-wave velocity) and electrical resistivity were characterized in 42 carbonates (limestone) rock samples, collected from shallow wells (seven wells encountered the Upper Cretaceous carbonate rocks with variation in thickness, where well 1 encountered 50 ft thick Nubian sandstone, which decreased to about 30 ft thickness in well 7) from Tushka area, Egypt. The petrographic investigation of the studied carbonate rock samples shows three microfacies associations: Facies1 (MFA-1) is mainly an oolitic, low dolomitic and low glauconitic, fossil-rich packstone with a tendency towards floatstone or rudstone, Facies 2 (MFA-2) is mainly a glauconite rich, low dolomitic floatstone with some tendencies towards rudstone and Facies3 (MFA-3) is mainly a sparry calcite-cemented, low dolomitic rudstone rich in glauconite and iron minerals. The MFA-2 with the lowest average density and highest average porosity is characterized by a strong anisotropy of both permeability and electrical resistivity. The values of the anisotropy ratio of seismic velocity (P-wave velocity) are close to one for all facies, this means that no anisotropy can be detected in the seismic velocity. A comparison between the coefficients of anisotropy reveals that the anisotropy of electrical resistivity and permeability are related to each other

Dynamics and Interaction of Dark Solitons in Bose-Einstein Condensates

Abstract: In this thesis we experimentally observe the dynamics of dark solitons in elongated Bose-Einstein condensates (BEC) in the crossover regime between 1D and 3D. Dark solitons are dynamically stable in this regime. This allows the observation of the collisional and oscillational dynamics of two dark solitons in a harmonically confined BEC over several oscillation periods. We can detect the repulsive intersolitonic interaction as an increase of the oscillation frequency of the two solitons strongly depending on their mean distance. Thereby we give the first experimental evidence of the theoretically predicted repulsive interaction between the solitons. We compare our experimental findings to numerical simulations of the Gross-Pitaevskii equation and effective 1D equations. Additionally we develop a model in which the solitons are approximated by repulsively interacting classical particles. This model is based on a soliton interaction potential suggested by [Kiv1995] and can describe the essentials of the soliton dynamics. We observe well agreement between the soliton oscillation frequencies measured in the experiment, the numerical simulations and the results of the particle model. Besides we verify the theoretical prediction that the oscillation frequency of dark solitons in a harmonically confined BEC should be slower than the trap frequency

Synthesis of tripodal catecholates and their immobilization on zinc oxide nanoparticles

A common approach to generate tailored materials and nanoparticles (NPs) is the formation of molecular monolayers by chemisorption of bifunctional anchor molecules. This approach depends critically on the choice of a suitable anchor group. Recently, bifunctional catecholates, inspired by mussel-adhesive proteins (MAPs) and bacterial siderophores, have received considerable interest as anchor groups for biomedically relevant metal surfaces and nanoparticles. We report here the synthesis of new tripodal catecholates as multivalent anchor molecules for immobilization on metal surfaces and nanoparticles. The tripodal catecholates have been conjugated to various effector molecules such as PEG, a sulfobetaine and an adamantyl group. The potential of these conjugates has been demonstrated with the immobilization of tripodal catecholates on ZnO NPs. The results confirmed a high loading of tripodal PEG-catecholates on the particles and the formation of stable PEG layers in aqueous solution

Spectral induced polarization: frequency domain versus time domain laboratory data

Spectral information obtained from induced polarization (IP) measurements can be used in a variety of applications and is often gathered in frequency domain (FD) at the laboratory scale. In contrast, field IP measurements are mostly done in time domain (TD). Theoretically, the spectral content from both domains should be similar. In practice, they are often different, mainly due to instrumental restrictions as well as the limited time and frequency range ofmeasurements. Therefore, a possibility of transition between both domains, in particular for the comparison of laboratory FD IP data and field TD IP results, would be very favourable. To compare both domains, we conducted laboratory IP experiments in both TD and FD.We started with three numerical models and measurements at a test circuit, followed by several investigations for different wood and sandstone samples. Our results demonstrate that the differential polarizability (DP), which is calculated from the TD decay curves, can be compared very well with the phase of the complex electrical resistivity. Thus, DP can be used for a first visual comparison of FD and TD data, which also enables a fast discriminationbetween different samples. Furthermore, to compare both domains qualitatively, we calculated the relaxation time distribution (RTD) for all data. The results are mostly in agreement between both domains, however, depending on the TD data quality. It is striking that the DP and RTD results are in better agreement for higher data quality in TD. Nevertheless, we demonstrate that IP laboratory measurements can be carried out in both TD and FD with almost equivalentresults. The RTD enables a good comparability of FD IP laboratory data with TD IP field data

Classification of slag material by spectral induced polarization laboratory and field measurements

Historical slag dumps are of increasing interest due to economic, environmental or archaeological reasons. Geophysical investigations can help accessing the potential reuse of slag material to recover metallic raw material or for the estimation of the hazard potential of the buried slag material due to dissolution occurrence.In our study, we have investigated various slag material in the laboratory with the spectral induced polarization (SIP) method, obtained from different historical slag dumps, located in the Harz Mountains, Germany. We also present SIP results from field measurements at a historical slag dump where most of the slag samples reveal high amounts of iron, zinc, silica, and barium.Our results reveal a discrimination between three different slag grades (low, medium, high) by using the imaginary conductivity σ″ at a medium frequency (1–10 Hz) in both laboratory and field. Furthermore, additional information is obtained by a classification based on the spectral polarization behaviour and considering the field frequency range (0.1 Hz – 100 Hz). Five different types of spectra (ascending, descending, constant, maximum and minimum type) can be discriminated and recognized in the laboratory and in distinct areas of the slag dump. Even though a direct comparison between the laboratory and field results still needs to be proven, the buried slag material can be differentiated from the surrounding material by the polarization magnitude

Quantum dot attachment and morphology control by carbon nanotubes

Novel applications in nanotechnology rely on the design of tailored nano-architectures. For this purpose, carbon nanotubes and nanoparticles are intensively investigated. In this work we study the influence of non-functionalized carbon nanotubes on the synthesis of CdSe nanoparticles by means of organometallic colloidal routes. This new synthesis methodology does not only provide an effective path to attach nanoparticles non-covalently to carbon nanotubes but represents also a new way to control the shape of nanoparticles.Comment: 6 pages, 6 figure