Subsonic near-surface P-velocity and low S-velocity observations using propagator inversion

Detailed knowledge of near-surface P- and S-wave velocities is important for processing and interpreting multicomponent land seismic data because (1) the entire wavefield passes through and is influenced by the near-surface soil conditions, (2) both source repeatability and receiver coupling also depend on these conditions, and (3) near-surface P- and S-wave velocities are required for wavefield decomposition and demultiple methods. However, it is often difficult to measure these velocities with conventional techniques because sensitivity to shallow-wave velocities is low and because of the presence of sharp velocity contrasts or gradients close to the earth's free surface. We demonstrate that these near-surface P- and S-wave velocities can be obtained using a propagator inversion. This approach requires data recorded by at least one multicomponent geophone at the surface and an additional multicomponent geophone at depth. The propagator between them then contains all information on the medium parameters governing wave propagation between the geophones at the surface and at depth. Hence, inverting the propagator gives local estimates for these parameters. This technique has been applied to data acquired in Zeist, the Netherlands. The near-surface sediments at this site are unconsolidated sands with a thin vegetation soil on top, and the sediments considered are located above the groundwater table. A buried geophone was positioned 1.05 m beneath receivers on the surface. Propagator inversion yielded low near-surface velocities, namely, 270 ± 15 m/s for the compressional-wave velocity, which is well below the sound velocity in air, and 150 ± 9 m/s for the shear velocity. Existing methods designed for imaging deeper structures cannot resolve these shallow material properties. Furthermore, velocities usually increase rapidly with depth close to the earth's surface because of increasing confining pressure. We suspect that for this reason, subsonic near-surface P-wave velocities are not commonly observed

Monitoring the Dutch Phytophtora infestans population for virulence against new R-genes

New possibilities offered by marker assisted breeding and GMO breeding have sparked renewed international efforts to breed for durable potato late blight resistance. Phytophthora infestans is however known for its adaptability, a trait confirmed by recent discoveries on the structure of the P. infestans genome. One of the possibilities to enhance the durability of newly introduced host resistance is to monitor the pathogen population for virulence to new R genes, prior to - and after their introduction. The late blight control strategy should be adapted accordingly. The Dutch P. infestans population was monitored during the growing seasons 2006 – 2008. P. infestans isolates were collected from blighted production fields and from bait fields in which R gene containing potato clones were grown without fungicide protection. A selection of the P. infestans isolates collected were characterized for virulence to a range of new R genes using a detached leaf bio-assay. Virulence for all single R genes tested was found. When we focus on R genes Rpi-blb1 and Rpi-blb2, no virulence was found in 2006. One Rpi-blb1 virulent isolate was found in 2007. Another 2007 isolate was found to be virulent to Rpi-blb2. Depending on the genetic background in which Rpi-blb1 was placed 13 or 21 isolates were virulent in 2008. Depending on the genetic background in which Rpi-blb2 was placed 4 or 11 isolates were virulent in 2008. One isolate was found to infect the stacked Rpi-blb1 and Rpi-blb2 resistance genes in a detached leaf assay. From these findings it is recommended that monitoring systems should be part of future potato late blight control strategies. The resulting information on the dynamics of virulence within the local P. infestans population can then be used to enhance the durability of newly introduced host resistanc

Surface-consistent amplitude corrections for single or multicomponent sources and receivers using reciprocity and waveform inversion

In land seismics, near-surface conditions often vary within surveys, resulting in differences in source strength and signature. Furthermore, discrepancies between closely spaced recordings are also commonly observed. Processing and interpretation of recorded data require that data are corrected for these source and receiver perturbations in the early stages of processing. However, existing surface-consistent deconvolution techniques are applicable to primary reflection data only, and therefore require that ground roll and multiples are suppressed prior to the application. This is usually performed with multichannel filter operations. The performance of these filter operations, however, rapidly deteriorates in presence of acquisition-related amplitude and phase perturbations. We propose an alternative approach to compensate for acquisition-related amplitude perturbations, which has the advantage of being purely a pre-processing step. It has the following characteristics: (i) it can be applied to complete recordings, hence does not require the isolation of primary reflections in the data, (ii) no assumptions are imposed on the subsurface and (iii) it is applicable to multicomponent data. The procedure is based on reciprocity of the medium response, so that differences between normal and reciprocal traces can be attributed to source and receiver perturbations. The application of reciprocity requires symmetric data acquisition, that is, identical source and receiver patterns, identical locations, and the source orientations have to be identical to the receiver components. Besides reciprocity, additional constraints are required to determine the lateral source and receiver amplitude variations fully. We use criteria based on minimizing total energy differences between adjacent common source and common receiver gathers, and in common offset panels of the medium response. Synthetic tests demonstrate that acquisition-related amplitude differences can be significantly reduced using this method

Topologically non-trivial quantum layers

Given a complete non-compact surface embedded in R^3, we consider the Dirichlet Laplacian in a layer of constant width about the surface. Using an intrinsic approach to the layer geometry, we generalise the spectral results of an original paper by Duclos et al. to the situation when the surface does not possess poles. This enables us to consider topologically more complicated layers and state new spectral results. In particular, we are interested in layers built over surfaces with handles or several cylindrically symmetric ends. We also discuss more general regions obtained by compact deformations of certain layers.Comment: 15 pages, 6 figure

Possible explanations for different surface quality in laser cutting with 1 micron and 10 microns beams

In laser　cutting　of　thick　steel　sheets,　quality　difference　is　observed　between　cut　surfaces　obtained　with 1 micron and 10 micron laser beams. This paper investigates physical mechanisms for this interesting and important problem of the wavelength dependence. First, striation generation process is described, based on a 3D structure of melt flow on a kerf front, which was revealed for the first time by our recent experimental observations. Two fundamental processes are suggested to explain the difference in the cut surface quality: destabilization of the melt flow in the central part of the kerf front and downward displacement of discrete melt accumulations along the side parts of the front. Then each of the processes is analyzed using a simplified analytical model. The results show that in both processes, different angular dependence of the absorptivity of the laser beam can result in the quality difference. Finally we propose use of radial polarization to improve the quality with the 1 micron wavelength

Modulation of systemic cytokine levels by implantation of alginate encapsulated cells

The availability of cell lines that are transfected with IL-4, IL-5 and IFN-γ cytokine genes permits the prolonged in vivo delivery of functional cytokines in relatively large doses for the modulation of specific immune responses. Oft

Interference Fragmentation in SIDIS, pp and e+e−

This review highlights some recent developments in the measurement of the transverse-spin–dependent Interference Fragmentation Functions and di-hadron correlations in semi-inclusive deep inelastic scattering and proton-proton scattering. The latter measurements can be used to extract transversity using measurements of the fragmentation function in e+e− annihilation. Di-hadron correlations have been measured in pp at PHENIX and lepton-proton and lepton-deuteron scattering at HERMES and COMPASS. The Interference Fragmentation Function has recently been measured at the Belle experiment. The emphasis of this article will be the Belle and PHENIX results, as these results are not presented in other contributions to this volume