4,319 research outputs found
Prompt Gamma Activation Analysis (PGAA): Technique of choice for nondestructive bulk analysis of returned comet samples
Prompt gamma activation analysis (PGAA) is a well-developed analytical technique. The technique involves irradiation of samples in an external neutron beam from a nuclear reactor, with simultaneous counting of gamma rays produced in the sample by neutron capture. Capture of neutrons leads to excited nuclei which decay immediately with the emission of energetic gamma rays to the ground state. PGAA has several advantages over other techniques for the analysis of cometary materials: (1) It is nondestructive; (2) It can be used to determine abundances of a wide variety of elements, including most major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Co, Ni), volatiles (H, C, N, F, Cl, S), and some trace elements (those with high neutron capture cross sections, including B, Cd, Nd, Sm, and Gd); and (3) It is a true bulk analysis technique. Recent developments should improve the technique's sensitivity and accuracy considerably
Magnetic field tuning of coplanar waveguide resonators
We describe measurements on microwave coplanar resonators designed for
quantum bit experiments. Resonators have been patterned onto sapphire and
silicon substrates, and quality factors in excess of a million have been
observed. The resonant frequency shows a high sensitivity to magnetic field
applied perpendicular to the plane of the film, with a quadratic dependence for
the fundamental, second and third harmonics. Frequency shift of hundreds of
linewidths can be obtained.Comment: Accepted for publication in AP
On the properties of superconducting planar resonators at mK temperatures
Planar superconducting resonators are now being increasingly used at mK
temperatures in a number of novel applications. They are also interesting
devices in their own right since they allow us to probe the properties of both
the superconductor and its environment. We have experimentally investigated
three types of niobium resonators - including a lumped element design -
fabricated on sapphire and SiO_2/Si substrates. They all exhibit a non-trivial
temperature dependence of their centre frequency and quality factor. Our
results shed new light on the interaction between the electromagnetic waves in
the resonator and two-level fluctuators in the substrate.Comment: V2 includes some minor corrections/changes. Submitted to PR
Circuit QED with a Flux Qubit Strongly Coupled to a Coplanar Transmission Line Resonator
We propose a scheme for circuit quantum electrodynamics with a
superconducting flux-qubit coupled to a high-Q coplanar resonator. Assuming
realistic circuit parameters we predict that it is possible to reach the strong
coupling regime. Routes to metrological applications, such as single photon
generation and quantum non-demolition measurements are discussed.Comment: 8 pages, 5 figure
Spatial Variability of Soil Erosion and Soil Quality on Hillslopes in the Chinese Loess Plateau
Soil erosion rates and soil quality indicators were measured along two hillslope transects in the Loess Plateau near Yan'an, China. The objectives were to: (a) quantify spatial patterns and controlling processes of soil redistribution due to water and tillage erosion, and (b) correlate soil quality parameters with soil redistribution along the hillslope transects for different land use management systems. Water erosion data were derived from 137Cs measurements and tillage erosion from the simulation of a Mass Balance Model along the hillslope transects.
Soil quality measurements, i.e. soil organic matter, bulk density and available nutrients were made at the same sampling locations as the 137Cs measurements. Results were compared at the individual site locations and along the hillslope transect through statistical and applied time series analysis. The results showed that soil loss due to water erosion and soil deposition from tillage are the dominant soil redistribution processes in range of 23-40 m, and soil deposition by water erosion and soil loss by tillage are dominant processes occurring in range of more than 80 m within the cultivated landscape. However, land use change associated with vegetation cover can significantly change both the magnitudes and scale of these spatial patterns within the hillslope landscapes. There is a strong interaction between the spatial patterns of soil erosion processes and soil quality. It was concluded that soil loss by water erosion and deposition by tillage are the main cause for the occurrence of significant scale dependency of spatial variability of soil quality along hillslope transects
Sharing the Burden of Collective Security in the European Union. Research Note
This article compares European Union (EU) burden-sharing in security governance distinguishing between assurance, prevention, protection, and compellence policies. We employ joint-product models and examine the variation in the level of publicness, the asymmetry of the distribution of costs and benefits, and aggregation technologies in each policy domain. Joint-product models predict equal burden sharing for protection and assurance because of their respective weakest-link and summation aggregation technologies with symmetric costs. Prevention is also characterized by the technology of summation, but asymmetry of costs implies uneven burden-sharing. Uneven burden-sharing is predicted for compellence because it has the largest asymmetry of costs and a best-shot aggregation technology. Evaluating burden-sharing relative to a country?s ability to contribute, Kendall tau-tests examine the rank-correlation between security burden and the capacity of EU member states. These tests show that the smaller EU members disproportionately shoulder the costs of assurance and protection; wealthier EU members carry a somewhat disproportionate burden in the provision of prevention, and larger EU members in the provision of compellence. When analyzing contributions relative to expected benefits, asymmetric marginal costs can largely explain uneven burden-sharing. The main conclusion is that the aggregated burden of collective security governance in the EU is shared quite evenly
Implications of new measurements of O-16 + p + C-12,13, N-14,15 for the abundances of C, N isotopes at the cosmic ray source
The fragmentation of a 225 MeV/n O-16 beam was investigated at the Bevalac. Preliminary cross sections for mass = 13, 14, 15 fragments are used to constrain the nuclear excitation functions employed in galactic propagation calculations. Comparison to cosmic ray isotonic data at low energies shows that in the cosmic ray source C-13/C approximately 2% and N-14/0=3-6%. No source abundance of N-15 is required with the current experimental results
Kappa-symmetric non-abelian Born-Infeld actions in three dimensions
A superembedding construction of general non-abelian Born-Infeld actions in
three dimensions is described. These actions have rigid target space and local
worldvolume supersymmetry(i.e. kappa symmetry). The standard abelian
Born-Infeld gauge multiplet is augmented with an additional worldvolume SU(N)
gauge supermultiplet. It is shown how to construct single-trace actions and in
particular a kappa-supersymmetric extension of the symmetrised trace action.Comment: 14 page
Topological twisted sigma model with H-flux revisited
In this paper we revisit the topological twisted sigma model with H-flux. We
explicitly expand and then twist the worldsheet Lagrangian for bi-Hermitian
geometry. we show that the resulting action consists of a BRST exact term and
pullback terms, which only depend on one of the two generalized complex
structures and the B-field. We then discuss the topological feature of the
model.Comment: 16 pages. Appendix adde
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