Radar imaging mechanism of marine sand waves at very low grazing angle illumination

The investigations carried out between 2002-2004 during several field experiments within the Op-erational radar and optical mapping in monitoring hydrodynamic, morphodynamic and environ-mental parameters for coastal management project (OROMA) aimed to improve the effectiveness of new monitoring technologies such as shipborne imaging radars in coastal waters. The coastal monitoring radar of the GKSS Research Centre, Geesthacht, Germany, is based on a Kelvin Hughes RSR 1000 X-band (9.42 GHz) VV polarized river radar and was mounted on board the research vessel Ludwig Prandtl during the experiments in the Lister Tief, a tidal inlet of the German Bight in the North Sea. The important progress realized in this investigation is the availability of calibrated X-band radar data. Another central point of the study is to demonstrate the applicability of the quasi-specular scattering theory in combination with the weak hydrodynamic interaction the-ory for the radar imaging mechanism of the sea bed. It is shown that specular point scattering con-tributes significantly to the normalized radar cross section (NRCS) modulation due to marine sand waves. According to the theory quasi-specular scattering can be applied for wind speeds Uw ≤ 8 m s-1. Measured and simulated NRCS modulations caused by flood and ebb tide oriented marine sand waves have been compared and agree fairly wel

Influence of Ibuprofen on Phospholipid Membranes

Basic understanding of biological membranes is of paramount importance as these membranes comprise the very building blocks of life itself. Cells depend in their function on a range of properties of the membrane, which are important for the stability and function of the cell, information and nutrient transport, waste disposal and finally the admission of drugs into the cell and also the deflection of bacteria and viruses. We have investigated the influence of ibuprofen on the structure and dynamics of L-alpha-phosphatidylcholine (SoyPC) membranes by means of grazing incidence small-angle neutron scattering (GISANS), neutron reflectometry and grazing incidence neutron spin echo spectroscopy (GINSES). From the results of these experiments we were able to determine that ibuprofen induces a two-step structuring behavior in the SoyPC films, where the structure evolves from the purely lamellar phase for pure SoyPC over a superposition of two hexagonal phases to a purely hexago- nal phase at high concentrations. Additionally, introduction of ibuprofen stiffens the membranes. This behavior may be instrumental in explaining the toxic behavior of ibuprofen in long-term application.Comment: -Improved indexing in Fig. 4e) -changed concentrations to mol% -improved arguments, however conclusions stay unchange

Traceable GISAXS measurements for pitch determination of a 25 nm self-assembled polymer grating

The feature sizes of only a few nanometers in modern nanotechnology and next-generation microelectronics continually increase the demand for suitable nanometrology tools. Grazing incidence small-angle X-ray scattering (GISAXS) is a versatile technique to measure lateral and vertical sizes in the nm-range, but the traceability of the obtained parameters, which is a prerequisite for any metrological measurement, has not been demonstrated so far. In this work, the first traceable GISAXS measurements, demonstrated with a self-assembled block copolymer grating structure with a nominal pitch of 25 nm, are reported. The different uncertainty contributions to the obtained pitch value of 24.83(9) nm are discussed individually. The main uncertainty contribution results from the sample-detector distance and the pixel size measurement, whereas the intrinsic asymmetry of the scattering features is of minor relevance for the investigated grating structure. The uncertainty analysis provides a basis for the evaluation of the uncertainty of GISAXS data in a more general context, for example in numerical data modeling.Comment: 9 pages, 6 figures; submitted to Journal of Applied Crystallograph

Streaking and splashing: design of a grazing incidence x-ray streak camera and time-resolved measurements of the structure of water

The performance of cesium iodide photocathodes has been characterized for use with grazing incidence soft x-rays. The total electron yield and pulsed quantum efficiency has been measured in a reflection geometry as a function of photon energy (100 eV to 1 keV), angle of incidence, and the electric field between the anode and photocathode. The total electron yield and pulsed quantum efficiency increase as the x-ray penetration depth approaches the secondary electron escape depth Unit quantum efficiency in a grazing incidence geometry is demonstrated. A weak electnc-field dependence is observed for the total yield measurements, while no significant dependence is found for the pulsed quantum efficiency. The effect of the pulse height distribution on the detective quantum efficiency is discussed Theoretical predictions agree accurately with expenment. Demonstrated unit quantum efficiency in a reflection geometry motivated the development of a grazing incidence x-ray streak camera for the Ultrafast X-ray Science beamline, under construction at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA Design considerations particular to synchrotron radiation sources are discussed. An analytical model and particle simulation for a camera incorporating magnetostatic imaging and meander sweep plates is presented. The camera is characterised with the third harmonic from a titanium-sapphire based laser system, 70 ps intrinsic and 150 fs “sliced” x-ray photon pulses from a synchrotron bend magnet source. A grazing incidence x-ray streak camera with an instrument temporal response of 6 ps is demonstrated. Dynamical changes in the structure factor of liquid water are measured using time-resolved x-ray diffraction techniques with 100 ps resolution. On short time scales, before the system has had time to expand following femtosecond optical excitation, temperatureinduced changes associated with rearrangements of the hydrogen-bonded structure at constant volume are observed. Transient changes in the pair correlation function associated with isochonc heating effects are extracted and interpreted in terms of a decrease in the local tetrahedral ordering in the liquid

Conservation Laws and Electromagnetic Interactions

Aside from energy, light carries linear and angular momenta that can be transferred to matter. The interaction between light and matter is governed by conservation laws that can manifest themselves as mechanical effects acting on both matter and light waves. This interaction permits remote, precise, and noninvasive manipulation and sensing at microscopic levels. In this dissertation, we demonstrated for the first time a complete set of opto-mechanical effects that are based on nonconservative forces and act at the interface between dielectric media. Without structuring the light field, forward action is provided by the conventional radiation pressure while a backward movement can be achieved through the natural enhancement of linear momentum. If the symmetry of scattered field is broken, a side motion can also be induced due to the transformation between spin and orbital angular momenta. In experiments, these opto-mechanical effects can be significantly amplified by the long-range hydrodynamic interactions that provide an efficient recycling of energy. These unusual opto-mechanical effects open new possibilities for efficient manipulation of colloidal microparticles without having to rely on intricate structuring or shaping of light beams. Optically-controlled transport of matter is sought after in diverse applications in biology, colloidal physics, chemistry, condensed matter and others. Another consequence of light-matter interaction is the modification of the optical field itself, which can manifest, for instance, as detectable shifts of the centroids of optical beams during reflection and refraction. The spin-Hall effect of light (SHEL) is one type of such beam shifts that is due to the spin-orbit transformation governed by the conservation of angular momentum. We have shown that this effect can be amplified by the structural anisotropy of random nanocomposite materials

Surface wave, internal wave, and source motion effects on matched field processing in a shallow water waveguide

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1989Given well known environmental conditions, matched field processing has been shown to be a promising signal processing technique for the localization of acoustic sources. However, when environmental data are incomplete or inaccurate, a 'mismatch' occurs between the measured field and model field which can lead to a severe degradation of the localization estimator. We investigate the possible mismatch effects of surface and internal waves on matched field processing in a shallow water waveguide. We utilize a modified ray theory, based on the work of Tindle, to calculate the acoustic pressure field. This allows us to simply incorporate range dependent environmental conditions as well as to generalize our work to deeper waveguides. In general, the conventional (Bartlett) matched field beamformer does not provide sufficient resolution to unambiguously locate a source, even in a perfectly matched environment. The maximum likelihood method (MLM) matched field beamformer has much better resolution but is extremely susceptible to mismatch. The mismatch due to surface roughness can result in a large reduction of the estimator peak. Part, but not all, of the peak can be regained by 1)using a model which includes incomplete reflection at the surface based on actual sea surface statistics and 2) short time averaging of the measured signal, with times on the order of the period of the surface waves. Mismatch due to internal waves can also result in a large degradation of the estimator. Averaging over the same time period as surface waves provides little improvement and leads one to surmise that internal waves may be a limiting constraint on matched field processing. Finally, we combine the surface and internal wave fields with a slowly moving source. This example highlights the necessity for the development of a beamformer which has a broader mainlobe while maintaining adequate sidelobe suppression, and we address this issue by looking at two such beamformers

Radar imaging mechanism of marine sand waves at very low grazing angle illumination caused by unique hydrodynamic interactions

The investigations carried out between 2002 and 2004 during six field experiments within the Operational Radar and Optical Mapping in monitoring hydrodynamic, morphodynamic and environmental parameters for coastal management (OROMA) project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters. The coastal monitoring radar of the GKSS Research Center, Geesthacht, Germany, is based on a Kelvin Hughes RSR 1000 X band (9.42 GHz) vertical (VV) polarized river radar and was mounted on board the research vessel Ludwig Prandtl during the experiments in the Lister Tief, a tidal inlet of the German Bight in the North Sea. The important progress realized in this investigation is the availability of calibrated X band radar data. Another central point of the study is to demonstrate the applicability of the quasi-specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed. Radar data have been taken at very low grazing angles ≤2.6° of flood and ebb tide–oriented sand wave signatures at the sea surface during ebb tidal current phases. Current speeds perpendicular to the sand wave crest ≤0.6 m s−1 have been measured at wind speeds ≤4.5 m s−1 and water depths ≤25 m. The difference between the maximum measured and simulated normalized radar cross section (NRCS) modulation of the ebb tide–oriented sand wave is 27%. For the flood tide–oriented sand wave, a difference of 21% has been calculated. The difference between the minimum measured and simulated NRCS modulation of the ebb tide–oriented sand wave is 10%, and for the flood tide–oriented sand wave, a value of 43% has been derived. Phases of measured and simulated NRCS modulations correspond to asymmetric sand wave slopes. The results of the simulated NRCS modulation show the qualitative trend but do not always quantitatively match the measured NRCS modulation profiles because the quasi-specular scattering theory at very low grazing angle is a first-order theory

Investigating the Liquid State of Carbon

Carbon materials have a many contemporary applications and new carbon allotropes are being discovered. However, while graphite and diamond are well understood, very little is known about the liquid state of carbon due to the high temperatures (above 5,000 K) and pressures (above 10 MPa) required for its formation. Initial studies used electrical heating to determine the melting point of graphite and the resistivity of liquid carbon. More recent studies used non-thermal laser melting to generate a metastable liquid that was studied with visible reflectivity and X-ray spectroscopies. Shock waves have also been used to transiently generate liquid carbon. Theoretical calculations of liquid carbon initially suggested the possibility of a liquid-liquid phase transition, but later ab initio quantum mechanical simulations showed only a continuous change in liquid coordination as its density increased. In this dissertation, extreme-UV (EUV) reflectivity and chirped coherent anti-Stokes Raman spectroscopy (c-CARS) were used to study non-thermally melted liquid carbon. Femtosecond laser pulses at 250 nm with a fluence of 0.45 J/cm2 (3.5 x 1012 W/cm2 intensity) were used to generate liquid carbon from an amorphous carbon substrate and the time evolution of EUV reflectivity was probed. EUV wavelengths from 20 to 42 nm were used with both s and p polarizations. The reflectivity decreased at all wavelengths probed as the material expanded and ablated. For wavelengths below 32 nm, the reflectivity decay time was less than ~2 ps. This time constant describes the lattice dynamics after melting, while above 32 nm, the reflectivity is also sensitive to the hot electron plasma generated by the melting pulse. From these results and equations for the behavior of a shock wave in a material, the electron temperature of the melted material was found to be 0.30 ± 0.6 eV. The reflectivity at two different polarizations was also used to calculate the complex refractive index of the material as it evolved over time. C-CARS spectra were obtained for highly ordered pyrolytic graphite (HOPG) and glassy carbon using CARS pump wavelengths of 400 nm and 800 nm. These spectra showed strong G peak resonance (1580 cm-1), corresponding to the relative vibrations of sp2 carbons in the material. The D peak (~1350 cm-1) resonance seen in Raman scattering of disordered graphite films was not observed in the CARS spectra. As this mode occurs when the excited electron scatters from a defect or phonon, it could be that the stimulated Stokes emission that occurs during the CARS process prevents such scattering. The sample was melted with an 800 nm, 90 fs laser pulse with fluences from 0.40 to 0.85 J/cm2 (intensities of 4.4 x 1012 to 9.4 x 1012 W/cm2). Delay times of less than 500 fs and as long as 100 ps all showed no broadening or shifting of the G peak, as would be expected for damaging and disordering of the material; only an intensity change is seen as the material ablates. Microscope images show permanent damage to the substrate and the fluences and times studied were comparable to those used in published reflectivity studies of liquid carbon. To advance the study of liquid carbon, a soft X-ray second harmonic generation (SHG) technique was developed and explored. X-ray absorption provides element-specific information on the electronic structure of a material that is sensitive to the environment around the element. Combining this with the interface specificity of SHG, provides a useful technique for studying solid-solid interfaces that are difficult to study otherwise. Our first soft X-ray SHG experiments on graphite films showed that the technique was indeed highly interface specific. The technique was also sensitive to resonance amplification when the input photons were at or above the carbon K-edge. A second experiment compared the boron/vacuum interface to a buried boron/carbon (Parylene-N) interface. The technique was sensitive to interface effects, showing larger SHG intensity at the boron K-edge for the boron/Parylene-N interface compared to the boron/vacuum interface. Ab initio quantum simulations were used to calculate the soft X-ray SHG spectra of these systems, verifying the interface sensitivity of the technique