The Experts below are selected from a list of 24 Experts worldwide ranked by ideXlab platform
H. Zinnecker - One of the best experts on this subject based on the ideXlab platform.
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The X-ray view of the central part of IC 1396.
Astronomy and Astrophysics, 1997Co-Authors: Norbert S. Schulz, T. W. Berghoefer, H. ZinneckerAbstract:The galactic HII region IC 1396 contains one of the youngest known open star clusters Trumpler 37, Tr 37. Its very core hosts the Multiple O-star System HD 206267, which in many respects is similar to the Orion Trapezium. So far X-ray emission has been observed only from HD 206267 with the Einstein observatory. Soft X-ray observations with the ROSAT PSPCrevealedX-rayemissionfromanareaof30'radiusaround the center of globule IC 1396A, which was resolved into 85 discreteSources.Someoftheemissionstillremainsunresolved. MostofthedetectedX-raySources,exceptHD206267,arevery weak, which causes the measured luminosity function to be cut off at log Lx < 30:3(erg s 1 ). X-ray Sources are located not onlyinTr37butarealsoscatteredaroundthemolecularglobule IC 1396A. From the distribution of Sources, their apparently hard spectra, and a steep luminosity function we argue that this sample contains a large number of previously unknown low- mass PMS stars. The X-ray Source centered on HD 206267 appeared extended indicating a Multiple Source System at the verycenterofTr37.ThetotalX-rayluminosityofthetrapezium HD 206267 does compare with the X-ray luminosity of single O-type stars. We set an upper limit of log(Lx/Lbol) to -6.90 and brieflydiscussthisresultinthecontextofcollidingandeclipsing wind models in early type binaries.
Michael J. White - One of the best experts on this subject based on the ideXlab platform.
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A new fast field program for a Multiple‐Source System
Journal of the Acoustical Society of America, 1994Co-Authors: Michael J. WhiteAbstract:A new fast field program (FFP) has been developed for numerical computation of sound pressure from a phased Multiple‐Source or Multiple‐receiver System in a layered medium. The new FFP is based on a far‐field approximation. Using the stationary phase method, the twofold integral for sound pressure in the far field is reduced to a onefold integral. The onefold integral makes the new FFP very efficient and more practical than computation performed individually for each Source. A criterion for validity of the far‐field approximation is also given. The sound pressure of several phased‐array Systems in a layered medium has been computed. Numerical results from the new FFP are compared with some well‐known results. The agreement is excellent.
Gonzalo R. Arce - One of the best experts on this subject based on the ideXlab platform.
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Coded aperture optimization for compressive X-ray tomosynthesis.
Optics express, 2015Co-Authors: Angela P. Cuadros, Christopher Peitsch, Henry Arguello, Gonzalo R. ArceAbstract:Radiation dose is a concern in X-ray tomographic imaging; coded aperture compressive X-ray tomosynthesis is an approach used to reduce radiation. It places a coded aperture in front of an X-ray Source in order to obtain 2D patterned projections of a three-dimensional object onto a detector plane. By using different coded apertures in a Multiple Source System, Multiplexed projections can be obtained instead of sequential projections as in conventional tomosynthesis Systems. Compressed sensing (CS) reconstruction algorithms are then used to recover the three-dimensional data cube. An optimization approach to design the structure of the coded apertures in a Multiple Source compressive X-ray tomosynthesis imaging System is presented. A uniform energy criteria on the voxels and detector elements is used so that the object is uniformly sensed and the elements of the detector plane uniformly sense the information. Simulations and experimental results for optimized coded apertures are shown, and their performance is compared to the use of random coded apertures.
Norbert S. Schulz - One of the best experts on this subject based on the ideXlab platform.
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The X-ray view of the central part of IC 1396.
Astronomy and Astrophysics, 1997Co-Authors: Norbert S. Schulz, T. W. Berghoefer, H. ZinneckerAbstract:The galactic HII region IC 1396 contains one of the youngest known open star clusters Trumpler 37, Tr 37. Its very core hosts the Multiple O-star System HD 206267, which in many respects is similar to the Orion Trapezium. So far X-ray emission has been observed only from HD 206267 with the Einstein observatory. Soft X-ray observations with the ROSAT PSPCrevealedX-rayemissionfromanareaof30'radiusaround the center of globule IC 1396A, which was resolved into 85 discreteSources.Someoftheemissionstillremainsunresolved. MostofthedetectedX-raySources,exceptHD206267,arevery weak, which causes the measured luminosity function to be cut off at log Lx < 30:3(erg s 1 ). X-ray Sources are located not onlyinTr37butarealsoscatteredaroundthemolecularglobule IC 1396A. From the distribution of Sources, their apparently hard spectra, and a steep luminosity function we argue that this sample contains a large number of previously unknown low- mass PMS stars. The X-ray Source centered on HD 206267 appeared extended indicating a Multiple Source System at the verycenterofTr37.ThetotalX-rayluminosityofthetrapezium HD 206267 does compare with the X-ray luminosity of single O-type stars. We set an upper limit of log(Lx/Lbol) to -6.90 and brieflydiscussthisresultinthecontextofcollidingandeclipsing wind models in early type binaries.
Asher Laufer - One of the best experts on this subject based on the ideXlab platform.
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Numerical analysis of flow and transport from a Multiple‐Source System in a partially saturated heterogeneous soil under cropped conditions
Water Resources Research, 2006Co-Authors: David Russo, Jacob Zaidel, Aldo Fiori, Asher LauferAbstract:[1] Field-scale solute transport in a three-dimensional, heterogeneous, variably saturated soil, originating from Multiple planar Sources (MS) is analyzed and compared with its counterpart originating from a single planar Source (SS). The case under consideration is a citrus grove planted on a Hamra Red Mediterranean soil (Rhodoxeralf) in the central part of the coastal region of Israel, with a distinct rainy period during the winter and irrigations during the rest of the year. Results of the analyses show that for both the MS and the SS cases, solute transport during the irrigation season is characterized by a restricted downward movement and spread and by a considerable increase in concentration, while the opposite situation occurs during the rain season. In addition, results of the analyses suggest that as compared with the SS case, the MS case is characterized by a larger uncertainty in the concentration point values, by a slower solute convection and a smaller longitudinal solute spread, by a larger transverse solute spread, and by larger skewness and uncertainty in the solute breakthrough curve (BTC). Regarding the solute sampling design problem, our findings suggest that for both cases a pair of sampling points located in the horizontal plane of the field may be sufficient in order to provide relatively accurate estimates of characteristics of the transport (i.e., displacement and spread of the solute plume in the direction of the mean flow and mean solute BTC) for the entire spatially heterogeneous domain. To achieve these desirable results, in the MS case the first sampling point must be located within the wetted area in the vicinity of one of the planar Sources, while in the SS case these results are independent of the location of the first sampling point. For both cases, however, an effort to quantify the uncertainty in the mean solute BTC requires few additional sampling points.
