326 research outputs found
Benjamin F. Husten and Emory D. Heberling adjusting the first NBS Atomic Clock circa 1949
No full textBenjamin F. Husten (left) and Emory D. Heberling (right) of the National Bureau of Standards Central Radio Propagation Laboratory, Microwave Standards section, are shown making adjustments to the amplifier and power supply circuits of NBS's first atomic clock, an ammonia molecule clock developed by NBS from 1948-1949. The amount of equipment shown is larger than needed for the clock alone since some of the instruments are for measurements and performance tests. The circuits essential to the operation of this atomic clock could be condensed into one of the two cabinet racks. Circa 1949.
This image is part of the Atomic Clock collection. The Atomic Clock collection is comprised of images documenting the development of the atomic clocks at the National Bureau of Standards (NBS). The NBS atomic clock program sought to provide a spectroscopic standard capable of being used as a new atomic standard of time and frequency to replace the mean solar day and so change the arbitrary units of time to atomic ones
Retention of Latex Colloids on Calcite as a Function of Surface Roughness and Topography
No full textAdhesion of colloidal particles to mineral and rock surfaces is important for environmental and technological processes. Surface topography variations of mineral and rock surfaces at the submicrometer scale may play a significant role in colloid retention in the environment. Here, we present colloid deposition data on calcite as a function of submicrometer surface roughness based on surface data over a field of view of several square millimeters, sufficient to trace the pattern of common inhomogeneities on mineral surfaces. A freshly cleaved calcite crystal was reacted to produce a well-defined etch pit density of similar to 3.4 +/- 1.2 to 8.3 +/- 1.6 [10(-3) mu m(-2)] and etch pit depth ranging from similar to 4 to 50 nm. This surface was exposed at the point of zero charge (PZC) of calcite to a colloidal suspension. We used a bimodal particle size distribution of nonfunctionalized polystyrene latex spheres with average diameters of 499 and 903 nm. Vertical scanning interferometry (VSI) was applied to quantify calcite surface topography variations its well as the retention of latex colloids. For both particle sizes, the experiments showed a positive correlation between the surface roughness (Rq) and the number of adsorbed particles. Etch pits were preferred sites for colloidal deposition in contrast to surface steps. The majority of adsorbed particles were trapped at etch pit walls compared to etch pit bottoms. Increasing pit density (D) and depth (d) resulted in an increase of colloidal retention. Deposition of smaller particles exceeded that of the larger-sized fraction of the bimodal system investigated here. Our results show that colloidal deposition at rough mineral and rock surfaces is an important geochemical process. The results about surface roughness dependent particle adsorption will foster the understanding and predictability of colloidal retention for a multitude of natural and technical processes
Genotypic analysis of CCMV clones.
No full text(A) Drop in sequencing read coverage indicates that a large proportion of viral genomes within the parental CCMV Heberling pool have a deletion event between IRS1 and US10. (B) Whole genome sequencing revealed variations in genomic sequences of selected CCMV BAC clones and the parental CCMV Heberling. Positions of missense, frameshift, deletion and insertion mutations for BAC clones are plotted in the grey tracks of the Circos plot. Intra-strain variations of the CCMV Heberling isolate are plotted in the green track; the frequency of each variation is indicated. Outer tracks: CCMV ORFs (red) and genomic regions. (C) The individual BAC clones were compared with the CCMV Heberling reference sequence for the absolute counts of single nucleotide variations (SNVs). White stacked bars indicate number of variations detected based on the alignment to the reference genome sequence of Heberling (NC_003521.1) but found in the re-sequenced parental CCMV virus stock pool. Colored bars indicate de novo variations in each clone that are neither detected in the original reference sequence nor the parental CCMV virus stock. CCMV BAC-177 showed the lowest number of SNVs and contained no frameshift mutations. (D) Similarly, the BAC clones were analyzed for the spectrum of transition and transversion mutations.</p
Deposition of Latex Colloids at Rough Mineral Surfaces: An Analogue Study Using Nanopatterned Surfaces
No full textDeposition of latex colloids on a structured silicon surface was investigated. The surface with well-defined roughness and topography pattern served as an analogue for rough mineral surfaces with half-pores in the submicrometer size. The silicon topography consists of a regular pit pattern (pit diameter = 400 nm, pit spacing = 400 nm, pit depth = 100 nm). Effects of hydrodynamics and colloidal interactions in transport and deposition dynamics of a colloidal suspension were investigated in a parallel plate flow chamber. The experiments were conducted at pH similar to 5.5 under both favorable and unfavorable adsorption conditions using carboxylate functionalized colloids to study the impact of surface topography on particle retention. Vertical scanning interferometry (VSI) was applied for both surface topography characterization and the quantification of colloidal retention over large fields of view. The influence of particle diameter variation (d = 0.3-2 mu m) on retention of monodisperse as well as polydisperse suspensions was studied as a function of flow velocity. Despite electrostatically unfavorable conditions, at all flow velocities, an increased retention of colloids was observed at the rough surface compared to a smooth surface without surface pattern. The impact of surface roughness on retention was found to be more significant for smaller colloids (d = 0.3, 0.43 vs. 1, 2 mu m). From smooth to rough surfaces, the deposition rate of 0.3 and 0.43 mu m colloids increased by a factor of similar to 2.7 compared to a factor of 1.2 or 1.8 for 1 and 2 mu m colloids, respectively. For a substrate herein, with constant surface topography, the ratio between substrate roughness and radius of colloid, Rq/r(c), determined the deposition efficiency. As Rq/r(c), increased, particle-substrate overall DLVO interaction energy decreased. Larger colloids (1 and 2 mu m) beyond a critical velocity (7 X 10(-5) and 3 X 10(-6) m/s) (when drag force exceeds adhesion force) tend to detach from the surface irrespective of the impact of roughness. For polydisperse solutions, an increase in the polydispersity and flow velocity resulted in a reduction of colloid deposition efficiency due to the resulting enhanced double-layer repulsion. Quantification of surface topography variations of two endmembers of natural grain surfaces showed that half-pore depths and roughness of sedimentary quartz grains are mainly in the micrometer range. Grains with diagenetically formed quartz overgrowths, however, show surface roughness mainly in the submicrometer range. Thus, surface topography features applied in the here presented analogue study and resulting variation in particle retention can serve as quantitative analogue for particle reactions in diagenetically altered quartz sands and sandstones. The reported impact of particle polydispersity can have an important application for quantitative prediction of retention of varying types of minerals, such as different clay minerals in the environment under prevailing unfavorable conditions
THE EFFECT OF THE NUMBER OF CHOICE SETS ON RESPONSES IN A STATED CHOICE SURVEY
No full textAn important issue for the stated choice method is the effect of the number of choice sets on responses. Based on a study of this issue in a mailed survey, results indicate that the number of choice sets does not affect survey response rates or item non-response rates.Research Methods/ Statistical Methods,
Restoration of deleted US regions and floxing of BAC cassette.
No full text(A) Schematic overview of US2-US6 and US8-US13 regions that were restored by BAC mutagenesis in CCMV BAC-177. Region IRS1 to US1 was not reinstated. LoxP sites were inserted at both ends of the BAC cassette to remove prokaryotic sequences by Cre recombinase expression during virus reconstitution. The final CCMV-BAC construct was named BAC-Phan9. Whole genome sequencing verified the integrity of BAC-Phan9. Coverage of DNA sequencing and positions of minor sequence variations in the US and TR regions are plotted. Sanger sequencing of DNA from reconstituted virus confirms the expected Cre-mediated recombination outcome at the US6-US7 region. (B) One-step growth curves of CCMV BAC-177, BAC-Phan9 and CCMV Heberling were analyzed in human fibroblasts. Means (center of the error bar) and standard errors of the mean of n = 3 are depicted. (C) Cells infected with either CCMV Heberling or BAC-Phan9 were analyzed for protein expression by mass spectrometry. The observed differences at 6 and 24 hpi are depicted as volcano plots. Proteins enriched in BAC-Phan9 infection and proteins orginitating from the US2-US10 region are labeled in blue, proteins enriched in Heberling infection in red. (D) Flow cytometry analysis of MHC-I surface expression during infection with CCMV BAC-Phan9, HCMV Merlin (upper row) and CCMV Heberling (lower row).</p
ISAR Tomography for Full-Polarimetric 3-D Radar Cross-Section Measurements
No full textS.2853-2858Radar cross-section (RCS) images are valuable for understanding the 3-D target scattering center distribution of objects. However, 3-D RCS imaging requires more complex measurement systems and much more data points compared to conventional 2-D methods. A reduction of measurement effort can be achieved by using a tomographic technique based on amplitude-phase-spectrum estimation, scale-invariant feature transform image registration, and constant false alarm rate detection. Besides an amplitude spectrum, the proposed method also obtains the phase spectrum of the scattering center distribution, which allows the application of polarimetric decompositions. The generation of full-polarimetric 3-D images is demonstrated based on measurement data obtained in a compact antenna test range. Since all relevant scattering mechanisms can be identified, the approach proved to be useful for an advanced understanding of the scattering mechanisms occuring at radar targets.67Nr.4, Pt.
Signal recovery on the sphere from compressive and phaseless measurements
No full textIn this thesis, we investigate the possibility of reducing the number of measurements and using only their magnitudes to reconstruct spherical signals and their three-dimensional rotations. These problems appear, for instance, in spherical near-field (SNF) antenna measurements, where the number of samples to acquire a signal implies a long measurement time and occasionally unreliable phase information. We tailor the compressed sensing (CS) approach to reconstruct spherical signals from fewer measurements. Instead of considering fully random sensing matrices like in the typical CS, we restrict the randomness to follow certain structures derived from the properties of spherical harmonics and Wigner D-functions. In this setting, we provide a bound on the number of measurements required to allow stable and robust signal recovery as well as numerical evaluations to verify these results. Although we limit the randomness, applying random sampling on the sphere is still cumbersome since collecting samples requires the use of mechanical devices that move smoothly over the spherical surface, such as robots. Hence, a deterministic sampling pattern to construct sensing matrices is still desired in many applications and the notion of coherence is used to measure the sensing matrices’ quality. First, we show a class of commonly used deterministic sampling patterns on the sphere that produces the worst coherence sensing matrices and, thereby, is unsuitable for CS. Subsequently, we propose a sampling strategy on the sphere to construct low coherence deterministic sensing matrices from spherical harmonics and Wigner D-functions, and derive a coherence bound for both cases. Apart from dealing with compressive measurements, we also study signal recovery on the sphere from phase less measurements and identify some potential ambiguities under this setting. We analyse ambiguities which arise from the properties of complex and real spherical harmonics, as well as the ambiguity caused by the implementation of inappropriate sampling patterns. As a further contribution, numerical evaluations are conducted to compare several reconstruction algorithms as well as the effects of different sampling patterns on the sphere. Finally, these results are implemented using SNF data, where we numerically show that our proposed sampling pattern requires significantly less number of measurements to provide high-quality reconstructions of far-field patterns when compared to classical approaches
Structural incorporation of Neptunyl(V) into Calcite: Interfacial Reactions and Kinetics
No full textIn this experimental work the calcite-water interface is characterized by means of zetapotential and surface diffraction measurements. Based on the experimental results a new Basic Stern Surface Complexation model for calcite is developed.
Neptunyl(V) adsorption at the calcite surface and incorporation into the calcite structure is studied by batch type adsorption- and mixed flow reactor experiments. Adsorption and incorporation species of Neptunyl are investigated by EXAFS spectroscopy
Accurate and Efficient Computation of Antenna Measurements Via Spherical Wave Expansion
No full textS.8266-8269The estimation of measurement uncertainties is mandatory for every high-accuracy antenna measurement. However, a method to analyze the uncertainties of complete 3-D measurements caused by arbitrary test zone field imperfections in a precise and computationally efficient way is still missing. This gap in the uncertainty analysis is closed by simulating a measurement scenario via spherical wave expansion. Thereby, the actual measurement sequence is imitated by using the matrix-vector representation of an antenna measurement. The spherical mode coefficients of the antenna under test held by the vector are mathematically rotated step by step and repeatedly multiplied by the field within the test zone which is represented by the coefficients in the matrix. As the technique is applicable to far-field and near-field data, the evaluation of antenna measurements is considered in general, and the emulation of a measurement process is exemplary carried out for a compact antenna test range. Finally, the numerical results are compared to an implementation of the coupling equation demonstrating the usefulness and efficiency of the proposed algorithm.68Nr.1
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