Han T.,CSIRO |
Best A.I.,UK National Oceanography Center |
Sothcott J.,UK National Oceanography Center |
North L.J.,UK National Oceanography Center |
Journal of Applied Geophysics | Year: 2015
The improved interpretation of marine controlled source electromagnetic (CSEM) data requires knowledge of the inter-relationships between reservoir parameters and low frequency electrical resistivity. Hence, the electrical resistivities of 67 brine (35. g/l) saturated sandstone samples with a range of petrophysical properties (porosity from 2% to 29%, permeability from 0.0001. mD to 997.49. mD and volumetric clay content from 0 to 28%) were measured in the laboratory at a frequency of 2. Hz using a four-electrode circumferential resistivity method with an accuracy of ±. 2%. The results show that sandstones with porosity higher than 9% and volumetric clay content up to 22% behave like clean sandstones and follow Archie's law for a brine concentration of 35. g/l. By contrast, at this brine salinity, sandstones with porosity less than 9% and volumetric clay content above 10% behave like shaly sandstones with non-negligible grain surface conductivity. A negative, linear correlation was found between electrical resistivity and hydraulic permeability on a logarithmic scale. We also found good agreement between our experimental results and a clay pore blocking model based on pore-filling and load-bearing clay in a sand/clay mixture, variable (non-clay) cement fraction and a shaly sandstone resistivity model. The model results indicate a general transition in shaly sandstones from clay-controlled resistivity to sand-controlled resistivity at about 9% porosity. At such high brine concentrations, no discernible clay conduction effect was observed above 9% porosity. © 2014 Elsevier B.V. Source
Karasik M.,U.S. Navy |
Weaver J.L.,U.S. Navy |
Aglitskiy Y.,Leidos Inc. |
Oh J.,RSI |
Obenschain S.P.,U.S. Navy
Physical Review Letters | Year: 2015
Imprinting of laser nonuniformity is a limiting factor in direct-drive inertial confinement fusion experiments, particularly when available laser smoothing is limited. A thin (∼400Å) high-Z metal coating is found to substantially suppress laser imprint for planar targets driven by pulse shapes and intensities relevant to implosions on the National Ignition Facility while retaining low adiabat target acceleration. A hybrid of indirect and direct drive, this configuration results in initial ablation by x rays from the heated high-Z layer, creating a large standoff for perturbation smoothing. © 2015 American Physical Society. Source
Agency: National Science Foundation | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2006
This Small Business Innovative Research Phase I project will develop a highly sensitive optical sensor system for use in high-throughput screening applications. The heart of the proposed sensor system is a periodic dielectric waveguide in which resonant leaky modes are excited by an incident optical wave. Attachment of biomolecular layers on the sensor surface yields spectral shifts that are measured to identify the binding event with high sensitivity and specificity without fluorescent tags. Both major polarization states have independent resonant peaks to accurately sense a biomaterial binding event. This feature enables the capability to distinguish between average thickness changes and average density changes occurring at the sensor surface. High resolution (from narrow, well defined resonance peaks) and high sensitivities permit a high probability of accurately detecting an event. The new class of bio- and chemical sensors proposed will provide benefits to society due to their utility in drug development, genomics, environmental monitoring, and homeland security. The fact that they operate without chemical tags permits observation and study of unperturbed biochemical processes in real-time, and no foreign substance are introduced. This will result in a deeper understanding of chemical and bio-chemical molecular processes and may lead to significant advances in drug and chemical development.
INTEGRA reports on a new technical note produced by Analytik Jena (www.analytik-jena.de/en.html) that compares the performance of the INTEGRA VOYAGER adjustable tip spacing multichannel pipette with a manual single channel pipette for performing real-time PCR experiments. As reaction components for real-time PCR experiments come in a range of different labware formats, scientists traditionally have used single channel pipettes to prepare the reaction mixes. Unfortunately preparing and transferring samples one by one is not only error prone but also very time consuming. In this technical note the authors compare the results from using an 8-channel VOYAGER pipette and a conventional single channel pipette to prepare eight samples of extracted human gDNA in twelve replicates for real-time PCR. Real-Time amplification of the SRY-gene was performed by using innuMIX qPCR MasterMix SyGreen and qTOWER3 system. In undertaking these experiments, Analytik Jena researchers found that the unique electronically adjustable tip facility on the VOYAGER not only generated time savings of up to 80% from minimizing the number of required manual handling steps but also improved pipetting reproducibility and reduced pipetting errors. The pipettes feature motorized tip spacing, enabling parallel transfer of multiple samples between labware of different sizes. Tip spacing can be changed by the simple push of a button, no manual adjustments or two handed operations are needed. This not only boosts your pipetting productivity, but also reduces the risk of developing a repetitive strain injury (RSI). The VOYAGER variable tip spacing pipettes are available in 4, 6, 8 and 12 channel versions and expand anywhere from 4.5 mm to 32.5 mm. This provides access to a wide range of labware formats such as microplates, tube racks or gel boxes. This makes the VOYAGER pipette an ideal companion for a wide variety of Genomic, Proteomic and Cell Culture applications.
The Rosetta spacecraft arrived at comet 67P/Churyumov–Gerasimenko on 6 August 2014 after a ten year cruise. The final approach manoeuvre was performed at a distance of 100 km from the nucleus. After drifting along with the comet at that distance, the orbit was successfully lowered to 30 km in September 2014 and to 10 km in November 2014. The goals of the Rosetta Radio Science Investigation experiment (RSI)6 are to determine the mass of the nucleus, its bulk density and its gravity field in order to constrain the internal structure of the nucleus. At distances of 100 km and 30 km, the nucleus still appears as a point mass expressed as GM (gravitational constant G times body mass M). It was previously thought that higher moments of the gravity field could only be determined if the spacecraft’s orbit about the nucleus were to be lowered to a distance of 10 km or closer7. In fact, the higher moments of the gravity field were already sensed and determined at distances below 30 km, a fact which is solely explained by the odd shape of the nucleus. RSI uses the two-way coherent radio link between the ground station antennas of the ESA’s European Space Tracking Network (ESTRACK) and NASA’s Deep Space Network (DSN) and the spacecraft. The Doppler shifts of the two radio carrier signals at the X-band (8.4 GHz) and the S-band (2.3 GHz) are examined for changes caused by the perturbing gravitational force of the nucleus acting on the spacecraft. The comet’s attracting force changes the trajectory and velocity of the spacecraft, imposing an additional Doppler shift onto the carrier frequencies. The additional Doppler shift can be extracted by predicting and subtracting the unperturbed Doppler shift, assuming that the comet nucleus is not there. This procedure has been successfully applied to spacecraft fly-bys at planetary bodies in the past8, 9, 10. Our team developed a software package to process radio tracking fly-by data, which was successfully applied to the fly-bys of Mars Express at Phobos11, 12 and the Rosetta fly-by at asteroid Lutetia13 (see the Methods). More than three months’ worth of spacecraft radio tracking data between 100 km and 10 km have been processed and solutions of the gravity field generated by the analysis are presented here. Using different initial guesses based on pre-arrival high- and low-mass estimates, consistent solutions of the point mass that are insensitive to the initial guesses are obtained with an average GM = (666.2 ± 0.2) m3 s−2 or M = (9,982 ± 3) × 109 kg for distances larger than 30 km. The mass of the nucleus is by far the smallest mass ever determined using this technique for a body of the Solar System. The errors of GM and M and all other errors given later are one standard deviation (1σ). Images from the OSIRIS camera14 onboard Rosetta were used to determine the bilobate shape and the volume of the nucleus. Two shape models separately derived by the Laboratoire d'Astrophysique de Marseille (LAM) and by DLR Berlin-Adlershof (DLR) give volume estimates of (18.8 ± 0.3) km3 and (18.7 ± 0.4) km3, respectively. These two estimates agree very well within their error bars and are more precise, but are substantially smaller by about 10% than the volume value published earlier14. The resulting weighted average volume and bulk density are thus (18.7 ± 0.2) km3 and (533 ± 6) kg m−3, respectively. This bulk density value, about half the density of water ice, implies that the nucleus is highly porous. For reasonable dust material densities one can relate the porosity of the nucleus to the dust-to-ice ratio. The cometary dust particles may be extremely porous and fluffy objects, but the silicate material densities are likely to be around 3,000 kg m−3, as determined by the Stardust mission15. Organic carbonaceous particles may have material densities of 2,200 kg m−3. Assuming a ratio of 1:1 for both aggregates would account for an average global material density of 2,600 kg m−3, in accordance with earlier estimates16. Figure 1 shows the material density and the dust-to-ice mass ratio as a function of dust content by volume along curves of constant porosity computed from: where ρ is the dust material density, ρ is the observed average bulk density of 533 kg m−3, ρ = 940 kg m−3 is the density of amorphous water ice17, and f and f are the fractional contributions of the porosity and the dust to the total volume. The porosity must be greater than 45% for the observed bulk density (a lower limit for the case when f > 0). The 70% and 75% porosity curves in Fig. 1a require a dust volume of 14% and 16.5%, respectively, for the average dust material density of 2,600 kg m−3. These porosities yield average dust-to-ice mass ratios of 2.4 and 5.3, respectively, in Fig. 1b. The dust-to-ice mass ratio is 1.9 to 14 for the full range of credible dust material densities between 2,200 kg m−3 and 3,000 kg m−3. This means that a nucleus with 70% to 75% porosity can have up to fourteen times more dust than ice by mass, but can also have up to twice as much ice than dust by volume. The extremes are the 50% and 80% porosity curves. These porosity cases do not result in reasonable dust-to-ice mass ratios. The dust at the average dust material density would fill the remaining volume of 20% completely for the 80% porosity case. This would represent a highly porous dusty body with no ice. The 50% porosity case represents a porous icy body with an ice content 18 times higher than for dust by volume. Both cases are considered unrealistic. The GIADA instrument on Rosetta reports an inferred dust-to-ice mass ratio18 of 4 ± 1. Applying this value to the direct surface composition would constrain the surface porosity to 72% to 74%, well within the reasonable range of dust material densities. If the dust-to-ice mass ratio of 4 is correct18, then the nucleus of comet 67P/Churyumov–Gerasimenko appears to be a very porous, very dusty body with a dust content by volume about two times larger than the ice content by volume. With knowledge of the bulk parameters only, it is still not possible to distinguish clearly between micro- and macro-porosity, that is, between the inherent porosity of fluffy dust particles embedded in the ice matrix or the porosity that would result from large voids within the nucleus body originating from the formation of the nucleus. It has been argued that the micro-porosity of the dust material already accounts for most of the nucleus porosity16. The solution for the gravity field up to degree and order 2, considering all tracking data down to 10 km distance, is listed in Table 1. The tracking data between 10 km and 20 km (from November 2014) were only weakly perturbed by the outgassing with the increasing activity of the nucleus. This resulted in a larger error in the solution for GM compared to the solution for the point mass without appreciable outgassing perturbations (distances >30 km). Table 1 lists the gravity coefficients derived from the observations and the computed coefficients from both shape models assuming constant density. A similar approach was applied to recent studies12, 19. All coefficients in Table 1 are fully normalized and referenced to a radius of 2.65 km. The coefficients of degree and order 1 in Table 1 reflect the translation of the individual coordinate systems with respect to a common coordinate system with its origin in the centre of mass defined by the observed gravity field. The translation of the centre of mass of the shape models into the common coordinate system (see Extended Data Table 1) is of the order of the error of the axes of the shape models. Table 1 also directly compares the degree and order-2 coefficients from the RSI observation with those from the two shape models in a common coordinate system. A comparison of the observed and the theoretical gravity coefficients for a homogeneous nucleus in Table 1 reveals that all the C and the C values agree well within a 3σ standard variation. We therefore conclude that large voids within the nucleus (macro-porosity) can be excluded and that the interior of the nucleus is homogeneous on a global scale, which is in agreement with the CONSERT4 and OSIRIS observations20. The Rosetta CONSERT experiment, which studies the propagation of radio waves in the VHF-band (~100 MHz) between the Rosetta orbiter and the Philae lander through the nucleus, has concluded that at least the interior of the ‘head’ of the duck-shaped nucleus is homogeneous down to scales of 3 m and that the porosity is 75% to 85% (ref. 19). As stated above, we consider the lower-porosity value to be more likely because porosities larger than 75% unrealistically constrain the nucleus material to mostly dust with very little ice. The porosity of about 70% to 75% inferred from the mass and the bulk density must therefore be considered an inherent property of the nucleus material.